Relaxation Techniques

Relax Your Mind

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Creep and Stress Relaxation

This is especially important for microstructures subjected to thermal loading and or operated at elevated temperatures. When one or more of the layers consists of a metal or polymer film, creep and stress relaxation in the film can significantly influence deformation and compromise device performance, and so their effects must be carefully considered. For example, Miller et al. 35.41 designed and fabricated microrelay switch arrays for RF communications applications using prestressed gold polysilicon bimaterial beams as electrostatically actuatable switches. They observed a change in the switch shape and position over time and attributed it to stress relaxation in the gold. Vickers-Kirby et al. 35.42 report that creep in gold and nickel cantilever beams leads to voltage drops in micromachined tunneling accelerometers over time. Creep and stress relaxation phenomena have been investigated in some detail for thin film on thick substrate systems, motivated primarily by microelectronics...

Hydrodynamic Lubrication and Relaxation

In the classical theories of tribology by da Vinci, Amon-ton, and Coulomb, not much attention was given to the dependence of kinetic friction on the sliding velocity. This clearly changed in the 19th century during the first industrial revolution, at which time lubricants became increasingly important, for instance, in ball and journal bearings. It was Petrov 29.4 , Tower 29.5 , and Reynolds 29.6 who established that the liquid viscous shear properties determine the frictional kinetics. Reynolds 29.6 combined the pressure-gradient determined Poisseuille flow with the bearing surface induced Couette flow assuming, based on Petrov's law 29.4 , a no-slip condition at the interface between lubricant and solid. This led to the widely used linear relationship between friction and velocity. Reynolds' hydrodynamic theory of lubrication can be applied to steady state sliding at constant relative velocity and to transient decay sliding (sliding is stopped from an initial velocity v and a...

Piezo Relaxation and Hysteresis

The last important benefit from low-temperature operation of SPMs is that artifacts given by the response of the piezoelectric scanners are substantially reduced. After applying a voltage ramp to one electrode of a piezoelectric scanner, its immediate initial deflection, I0, is followed by a much slower relaxation, Al, with a logarithmic time dependence. This effect, known as piezo relaxation or creep , diminishes substantially at low temperatures, typically by a factor of ten or more. As a consequence, piezo nonlinearities and piezo hysteresis decrease accordingly. Additional information is given by Hug et al. 14.13 .

Determination of Creep Stress Relaxation and Other Attributes to Local Plasticity

In order to determine the rate sensitivity of hardness (stress) by indentation tests, various approaches can be used, for example, indentation creep, rate change, or load relaxation experiments 148, 196 . In an indentation load relaxation experiment, the indenter is pushed into the specimen surface until a predetermined load is reached then the depth is held fixed, allowing the load to relax as elastic displacement due to the specimen and load-train is gradually traded for plastic penetration. In the indentation creep experiment, the indenter is pushed into the specimen surface at a fixed rate of displacement until a predetermined load is reached then the load is held constant, allowing the penetration depth to increase with time while the penetration is monitored. In an indentation creep test, the load slightly decreases as the projected area increases during the test, in contrast to a tensile creep test with a constant load, where the stress gradually increases with decreasing...

Magnetic Relaxation In Ferrofluids

Ferromagnetic particles suspended in a liquid carrier are generally referred to as ferroflu-ids 19 . The dynamic behavior of these ferrofluids is governed by two very different magnetization relaxation pathways. Either the magnetization can change within each magnetic particle (Neel relaxation) or the whole particle can rotate in the liquid (Brow-nian relaxation). We will first discuss each mechanism individually and then turn to systems with size dispersions, where both relaxation mechanisms can be present simultaneously. 4.3.1 Internal Magnetic Relaxation In the following we will neglect magnetic interactions between magnetic particles, which may arise from dipolar coupling. This assumption is nontrivial, but in the case of biologically functionalized magnetic nanoparticles, the ligand coating helps to separate the individual particles independent of their concentration. The important parameter for assessing the importance of interactions is the ratio of interaction to thermal...

Experimental Techniques of Nanocomposite Characterization

The interphase (polymer-filler) interactions in composites are examined using various techniques. Mainly, the viscoelastic properties (temperature, strain, or frequency dependence) are the perfect tool to detect the interaction between phases by DMA. Determination of the chain immobilization evidenced by a new relaxation process occurring at a higher temperature is the simplest approach. Moreover, the nonlinear behavior of composites manifests itself by a decrease in modulus at a low strain amplitude - the so-called Payne effect 36 - and is assumed to reflect the dynamics of polymer at the interface 37, 38 , thus characterizing the polymer-filler interaction. In addition, other relaxation methods like DES, thermally stimulated depolarization currents (TSDC), or the NMR relaxation techniques are applied to follow the polymer chain dynamics and to investigate the interaction. In addition, swelling experiments are used to evaluate the interaction by assuming that the swelling of the...

And Viscoelastic Behavior

An additional capability of nanoindentation is to measure the viscoelastic properties of polymers. In order to do so, flat-end cylindrical indenters are normally used. The contact area being constant during penetration, the pressure distribution for a determined depth under the indenter can be considered almost constant if low loads are used. Basic equations of flat punch nanoindentation on polymers are presented by Cheng et al. 175 . The standard three-element viscoelastic material indented by an axisymmetric flat-ended indenter was investigated theoretically. The solutions of the equations of viscoelastic deformation were derived for the standard viscoelastic material for compressible as well as incompressible solids. They analyzed both the flat-punch creep test and the load-relaxation test, providing a fundamental basis for probing the elastic and viscous properties of coatings with nanoindentation tests.

Heat Transfer to the Support

The last step in the energy relaxation is the heat transfer between the nanoparticles and the support (host matrix, substrate). A single electronic cluster-substrate interaction process happens in the femtosecond time scale, as reported by Reihl and co-workers 74 . Photoemission spectra of silver particles on a graphite surface reveal distinct deviations in the Fermi-level onset from the step-like shape typical for metals. These deviation could be explained by using a simple model that takes into account the finite lifetime of the photohole remaining on the metal cluster during the photoemission process and the cluster-substrate.

STM and molecular reorientations

By molecular reorientation have been obtained 15 , much higher frequencies are to be probed here, and it is a very long way to it from the technique currently available. Suggestions to study possible orientational order-disorder transitions, where the critical slowing down may lead to rather slow relaxation times 16 , may appear to be more realistic.

Structure and Mechanical Properties

High- and low-density polyethylene (HDPE and LDPE), iso-tactic and atactic polypropylene (iPP and aPP), and polymer blends were investigated regarding the friction coefficient and the elastic modulus via SFM. Structural changes and the mechanical property changes around the glass transition temperature have been monitored during temperature runs. The enhanced ordering of the backbone correlates to the increased surface modulus. Additionally, the elastic modulus, the time-dependent relaxation process, and the friction properties were measured as a function of pressure. Loads between 1 and 1000 nN were applied. At low pressure the deformation of the polymer is elastic. With increasing pressure there is a phase transition to a plastic behavior attributed to a polymer alignment effect. Friction properties were investigated concerning the contact pressure and contact area, revealing an increased elastic modulus with increased density and crystallinity and a linear increase with contact...

Application to Real Surfaces

Changes in solid surfaces occur either during the formation of a new phase as in vapor deposition, molecular beam epitaxis, chemical vapor deposition and metal electrodeposition, or during a phase disappearance as is the case of metallic corrosion and material erosion. Similar changes occur in roughness relaxation, a process which plays a relevant role in establishing, for instance, the lifetime of solid catalysts.

Cryogenic Conditions and Dynamics

At least one kind of chemical processes still remains active at cryogenic temperatures, indeed nearly as active as at room temperature the processes involving movements of charges only, electrons or holes. Because electrons are very light particles, tunnelling dominates the first steps of charge transfer within small molecules, and often dominates transfer between neighboring molecules as well. In other words, cryogenic conditions will give a good first approximation of the electronic structure of biomolecules, that is, of the spatial distribution of relevant electronic wavefunctions, and of the relaxation pathways and intermediate states between different redox states. Spectroscopy at cryogenic conditions is facilitated by the improved spectral resolution and by the longer relaxation times of all other processes, that is, those involving molecular rearrangements. Low-temperature studies therefore form a reliable basis for the discussion of electronic properties in physiological...

Structural Properties

Interactions between the positively charged protein and the negatively charged silica oxide groups. Instead, salts other than KCl induced a concentration-dependent increase in the a-helical content, and the ion effect was in accordance with the Hofmeister series, suggesting an important role of the unusual water structure in the gel pores on the conformation of encapsulated apo-myoglobin. The spectroscopic and kinetic heterogeneity of sol-gel encapsulated carbonmonoxy (CO)-myoglobin was investigated by resonance Raman and absorption spectroscopy 76 . The authors compared the visible Raman spectra and CO rebinding kinetics after photodissociation of myoglobin encapsulated in the deoxy or liganded state. Differences in the resonance Raman frequency of the iron-proximal histidine stretching mode were attributed to different positions of the F helix, which in turn account for differences in CO rebinding. The CO binding-induced conformational changes were reported to be qualitatively...

G1t JfTjexpf txdlnx

The relaxation time distribution, x A(x), is obtained by performing the inverse Laplace transform (ILT) with the aid of a constrained regularization algorithm (REPES). The mean diffusion coefficient (D) is calculated from the second moments of the peaks as DC (l- r Q 2, where Q - (4 voA,) sin( 9 2) is the magnitude of the scattering vector and r 1 x is the relaxation rate. Here is the scattering angle, no the refractive index of pure solvent and X the wavelength of the incident light.

Nonadiabatic Behavior of a System and Interfacial Electron Transfer

However, in the case of adsorbents on surfaces, the situation is not so simple. Because the number of electrons involved is infinite in the substrate, simple partition into the electronic degree of freedom and the nuclear degree of freedom is questionable. In particular, on a metal surface, the adsorbed molecules experience strong friction against nuclear motion. The vibrationally excited states of the adsorbents are quickly quenched because of coupling with the conducting electrons 151 . A similar friction is observed in the photoinduced desorption process from a metal surface as well 152 . The conducting electrons have a continuous energy spectrum, and thus, they dissipate the vibrational energy efficiently by creating electron hole pairs 153 . In general, the number of electrons in an adsorbent or embedded cluster system is not necessarily an integer. Head-Gordon et al. theoretically analyzed the vibrational relaxation of CO Cu(100) 154 using molecular dynamics with electronic...

Spin Injection Processes and Devices

Spin transport in metal-, metal-insulator, and semiconductor heterostructures holds promise for the next generation of high-speed low-power electronic devices 3,4,100-107 . Amongst important spintronic effects already used in practice one can indicate a giant magnetoresistance (MR) in magnetic multilayers 108 and tunnel magnetoresistance (TMR) in FM-insulator-FM (FM-I-FM) structures 109-115 . Another promising effect is domain wall switching in giant magnetoresistance (GMR) nanopillars directly by the flow of current through them 116-120 . Injection of spin-polarized electrons into semiconductors is of particular interest because of relatively large spin relaxation time ( 1 nsec in semiconductors, 1 msec in organics) 4 during which the electron can travel over macroscopic distances without losing polarization, or stay in a quantum dot well. This also opens up possibilities, albeit speculative ones, for quantum information processing using spins in semiconductors.

Recognition of Redox Active Species

The host-binding ability of b-CD immobilized on gold nanoparticles was further verified using compound 17 as guest probe in a 1H NMR study. 18 The displacement and broadening of the ferrocene proton resonance in the presence of PSH-b-CD-Au were attributed to the formation of the inclusion complexes on the nanoparti-cle surfaces, as they were similar to those observed upon the addition of free b-CD to solutions of ferrocene derivatives. The substantial line broadening must have resulted also from the association of the ferrocene guest to the massive nanoparticles, and was probably related to chemical exchange (free ferrocene going to bound ferrocene and back), as well as to relaxation effects in the bound state. Note that when the ferrocene guest was bound to a CD cavity, it became a part of a rather large supramolecular assembly.

Nanoelectronics and Sensors

Recent experiments have shown that the electronic conductivity of semiconducting SWNTs is extremely sensitive to certain gas molecules even in miniscule (parts per million) amounts 128,129 . These have led to applications in chemical and gas sensors with fast response time and ultra-high sensitivity. The sensing mechanism involves detecting conductance change of the CNTs induced by charge transfer from gas molecules adsorbed on CNT surfaces. The initial experiments and simulation-based investigations focused on NO2, NH3, and O2 as adsorbing gases. The changes in the electronic band structures and change transfer, using ab-initio DFT-based approaches, due to adsorption of these gases have been computed 130,131 . For example, each NO2 gas molecule adsorbed on the nanotube surface induces a small amount (about 0.1 e) of electron transfer so that the CNT becomes a p-type doped semiconductor, and conductivity changes significantly 131 . A similar amount of charge transfer for chemisorption...

Magnetic Resonance Imaging MRI the Basics

Objects to be imaged are exposed to a strong magnetic field and a well-defined radio frequency pulse. The external magnetic field (B0) serves to loosely align protons either with (lower energy level) or against (high energy level) the field, the difference between the two energy levels being proportional to B0. Once the protons are separated into these two populations, a short multi-wavelength burst (or pulse) of radio frequency energy is applied. Any particular proton will absorb only the frequency that matches its particular energy (the Larmor frequency). This resonance absorption is followed by the excitation of protons from the low to high energy level and of equivalent protons moving from high to low energy levels. After the radio frequency pulse, protons rapidly return to their original equilibrium energy levels. This process is called relaxation and involves the release of absorbed energy. Once equilibrium is again established, another pulse can be applied. Data is collected by...

Nanoparticle Contrast Agents

Paramagnetic metals used for enhanced MRI contrast (gadolinium, Gd, iron, Fe, chromium, Cr, and manganese, Mn) have permanent magnetic fields, though the magnetic moments of individual domains are unaligned 10.94 . Upon exposure to an external magnetic field, individual domain moments become aligned, generating a strong local field (up to 104 gauss 10.95 ). Paramagnetic metal ions interact with water molecules, causing an enhanced relaxation of the water molecules via tumbling of the water-metal complex, dramatically decreasing the T1 value for the water molecules and enhancing the proton signal 10.94 . Contrast enhancement by paramagnetics is thus due to the indirect effect the contrast agent has on water and its magnetic resonance properties.

Spin Injection into Organic Materials

The main reason for long spin-diffusion length compared to the usual mean free path is a long spin relaxation time Ts in semiconductors. This is a result of relatively small SO coupling that causes spin relaxation. Since the SO coupling scales as a fourth power of the atomic charge Z, it is very tempting to try carbon-based (Z 6) organic materials. There the spin relaxation time is huge, Ts 10 3 sec. Unfortunately, the mobility is usually very bad, 1 cm2 V sec in the best case like penthacene, so the spin-diffusion length Ls is limited. Still, it has been found that in organic materials Ls 100 nm 149 , so this research is promising. Spin valves with organic materials have also been demonstrated 150 . There may be interesting developments in the organic spintronics.

Sensing Applications Utilizing Rotational Brownian Motion

Rotational Brownian motion for the signal transduction of biochemical binding events. In one of the earliest measurements, the random rotational motion of a wire in a liquid was detected by light reflected from a mirror attached to the wire 9 . Obviously, the detection of rotational Brownian motion for spherical particles is more complicated and requires an anisotropy to break the spherical symmetry. Examples of symmetry-breaking are permanent electric dipole moments, whose motion can be detected with inelastic light scattering 10 , or anisotropic optical properties, which leave a distinct signature of the rotational motion in dynamical light-scattering experiments 11 . Clearly, a permanent magnetic moment will also break the spherical symmetry its use for the detection of rotational Brownian motion is discussed in Section 4.3.2. An alternative approach for the detection of Brownian relaxation is nuclear magnetic resonance, since the relaxation time for nuclear spins is modified by...

Structure and interaction with light

The most striking effects are observed in surface-enhanced Raman scattering (SERS) 26 , but other effects such as second-harmonic generation 27 and photocurrents 28 are also strongly affected by surface roughness. The most effective metal for this kind of investigations is silver, whose surface is normally roughened by an oxidation-reduction cycle (ORC). In-situ STM was of assistance in showing that surface roughness is stabilized at far negative potentials, but decays rapidly at potentials positive to the point of zero charge as shown in Fig. 6 29 . In turn, this relaxation in roughness is responsible for an irreversible quenching of the photoelectrochemical response of the electrode 30 .

Polymer Layered Silicates

The good potential of SSNMR in the study of both polymers 57 and clays 64 gave an impulse in experimenting the NMR characterization for the determination of the structure of clay methyl methacrylate copolymer nanocomposites 65 . They prepared interlayer complexes of several MMA 2-(N-methyl-N,N-diethylammonium iodide) ethyl acrylate (MDEA) copolymers with two different clays, bentonite and hectorite, using two different preparations. These complexes were studied by means of solid-state 13C NMR. Given the relatively high content of paramagnetic centres in bentonite, which is 50 times more paramagnetic than hectorite, the SPE MAS and CP MAS spectra of the different nanocomposites with bentonite show differences according to the proximity of the different copolymer moieties to the clay surface. The dynamics of the organic molecules in the organic interlayers were investigated by NMR relaxation time measurements. The paramagnetism of the clay, when relevant, strongly influences the...

Selfassembly At The Gassolid Interface

For the next situation, where the intermolecular forces are smaller than the solid surface-building unit interaction, the building units that are adsorbed onto the solid surface have little tendency to be reorganized following their force balance. In this case, instead of assembly of building units, surface reconstruction by possible surface instability and a coarsening process often results in the formation of a periodic nanoscale surface pattern (Soukiassian and Enriquez, 2004). This can be understood as the self-assembled aggregate that is driven by the force balance among the forces originated on from the solid surfaces. This process is often triggered by an external perturbation such as sputtering or annealing (Deak et al., 2006). Surface relaxation is the case in the rearrangement of the uppermost atoms in a direction perpendicular to the surface. Since it is also a process toward the force balance between the atoms that are rearranged and those beneath the surface, it can also...

Atomically Resolved Imaging of a Ni0001 Surface

In the past, extensive theoretical studies on the short-range magnetic interaction between a ferromagnetic tip and a ferromagnetic sample have been performed by a simple calculation 13.80 , a tight-binding approximation 13.81 , and first-principles calculations 13.82 . In the calculations performed by Nakamura et al. 13.82 , three-atomic-layer Fe(001) films, which are separated by a vacuum gap, are used as a model for the tip and sample. The exchange force (Fex) is defined as the difference of the forces (Fp, Fap) in each spin configuration (parallel P, anti-parallel AP) of the tip and sample. The tip-sample distance dependency of the exchange force demonstrates that the amplitude of the exchange force is on the order of 10-10 N or above and is large enough to be detected by NC-AFM. Also, the site dependency of the exchange force indicates that the discrimination of the exchange force enables the direct imaging of the magnetic moments on an atomic scale. Recently, the interaction...

Observing Condensed Phase Movement

The switching behavior of amphiphilic, bistable 2 rotaxanes has also been confirmed by studying74 the redox-controlled switching behavior in solution, polymer gels, SAMs, and MSTJs. The switching cycles can be detected by a number of experimental observations in the cyclic voltammogram (CV) studied, providing information which can be used to understand switching behavior across different environments. The first oxidation potential of the GSCC corresponds to the one-electron oxidation of TTF to TTF+ and occurs at +490 mV, while the same oxidation of TTF to TTF+ in the MSCC is +310 mV (potentials referenced to an Ag AgCl electrode).72,73 Knowing that relaxation of the MSCC back to the GSCC is temperature-dependant, thermal activation parameters may be quantified by time- and temperature-dependent CV measurements. The ratio of MSCC to GSCC is dependent on the structural features of the particular bistable molecules, whereas changes in kinetic parameters (lifetime and decay) are more...

Laser Beam Crystallization

The primary interaction between laser light and semiconductors is based on excitation of electrons and phonons 131 . The dominating interaction mechanisms depend on the laser parameters and the particular type of semiconductor, its microstructure (amorphous crystalline), doping, etc. The interaction mechanisms may be thermal or non-thermal depending on the relative size of the thermal relaxation time and the time for structural rearrangements of material atoms or molecules. In most cases of semiconductor processing, the excitation energy is rapidly dissipated into heat (thermal laser processing previously mentioned). In spite of the thermal character, laser-driven processes may be quite different from those initiated by a conventional heat source. The laser-induced temperature rise can be localized in space and time. Temperature changes of more than 104 K can be induced in a small volume at a heat rating of 1015 K s. For example, heat flow calculations have been performed for a-Si H...

Films Grown by an Unfocused Beam

In thick films only damped bulk acoustic phonons with a typical wavelength Xph of the order of 170 nm have been detected. This indicates that for a length d Xph the film bulk can be modeled as a continuum 196 with approximate translational invariance and effective elastic constants, although structural disorder at smaller scales scatters the phonons significantly. The presence of a rather strong central peak in the spectra could be ascribed to nonpropagating (overdamped) or confined vibrational excitations, probably connected with different characteristic correlation lengths less than d. The most damped bulk acoustic phonons could be coupled to the confined modes by a relaxation mechanism. The surface phonons could be almost overdamped if not already replaced by surface fractons or by localized cluster modes 211 . Instead in thinner films, notwithstanding the high degree of surface roughness, which increases with film thickness, intense surface peaks can be detected up to a critical...

Fnewredg f Af fId f Afred

Where and blue are the individual single-phase collision operators for the two phases. They have the conventional form of the single-step Bhatnagher-Gross-Krook relaxation 32 according to with the characteristic relaxation times tred and tblue, and the equilibrium distributions fred'eq(x, t) and blue,eq(i, t). One should note that the viscosity of each fluid phase can be individually selected by choosing the desired relaxation times for that phase, since the corresponding operators account for collisions with particles of the same type only. The particle velocity equilibrium distribution for each individual phase, fred,eq(x, t), fblue'eq(x, t), depends (in all multi-phase flow lattice models) on the local macroscopic variables pertaining to that phase, i.e. (x, t), p (x, t) and u (x, t). The equilibrium distributions can, hence, be written as

Scaling Down of Mechanical Processing Techniques

Another aspect is the sharpness of the edges. In the nanometer range, no sharp edge is ideal. In the ultimate case, the radius of curvature is the radius of an atom. Macro-scopically sharp edges often appear from an ultramicroscopic point of view as mountain ranges of material, and even the sharpness revealed by light microscopy can contain hidden areas with sizes of several atom diameters. Therefore, edge quality should be described by incorporating the radius of curvature and the distribution of the radii if necessary. The sharpness of edges depends on mechanical and chemical stress and especially on the mobility of particles in the material itself. Because of attempts of the atoms and molecules situated on the surface to increase the number of interactions with other particles in order to achieve minimal energy, all materials show a tendency towards rounding edges. Surface energies and mechanical relaxation processes influence the geometries of nanostructures 1 . At solid-liquid...

Interfacial Interaction

In a recent report on grafted nano-SiO2 particle-filled PP composites studied by atomic force microscopy (AFM) 192 , it was shown that PP molecules are able to immigrate into the nanoparticle agglomerates in the molten state of PP (Fig. 30). An interdiffusion and entanglement between the molecules of the grafting polymers and the matrix can thus take place outside and inside the nanoparticle agglomerates. Moreover, Shumsky et al. 193 measured the viscoelas-tic behavior of the nanocomposites employed in 107 in the molten state. Drastic changes in the pattern and broadening of the relaxation times spectra to longer relaxation times for the composites were attributed to the onset of plastic yielding of a spatial network of the filler particles grafted with macromolecular chains, preceding the macroscopic melt flow. The results of this study can be regarded as experimental evidence for a shear-resistant, stiff spatial structure of filler particles coated with a polymer boundary layer in...


What we mean by walk in this Markovian dynamics, is going from one state of the system to another by some stochastic process. If this walk is done correctly, meaning any state is within reach (Ergodicity), and provided the walk is continued long enough, then after reaching some relaxation time, one reaches the equilibrium state and can perform the needed statistics. The relaxation time is the time required for a system to recover a specified condition after a disturbance. In stochastic processes, it is a measure of the rate at which a disequilibrium distribution decays toward an equilibrium distribution. It should be mentioned that there is no simple way of finding the relaxation time in advance. The easiest way is to let the system evolve once, then from the time series of different physical quantities, estimate the relaxation time.

Heat Conductivity of Carbon Nanotubes

With vz being the group velocity and t being the relaxation time of the individual phonon state. It is evident that phonons with a high band velocity or a long free path, respectively, contribute the most to heat conductivity. Therefore, carbon nanotubes along their axis feature the highest heat conductivity ever measured for any material. The value at right angles to the tubular axis, on the other hand, is only about a hundredth of Kzz. Multiwalled carbon nanotubes and bundles of single -walled species should thus be expected to possess about the same heat conductivity like their single components, whereas samples with an unordered arrangement of individual tubes should show lower values due to intertubular coupling. These assumptions have been confirmed by experimental results. Heat conductivities of up to 3000Wm-1K-1 have been measured for single MWNT, whereas for mats of SWNT, they only range from 35 to 200 W m-1 K-1 depending on the degree of parallelism. The temperature...

Phonon Confinement in Quantum Dots

Quantum dots (QDs) fabricated by precipitation methods are usually embedded in an amorphous matrix, like glass or organic polymers, to stabilize them from aggregation. Theoretical investigations predict that among the optical phonons TO, LO an infinite series of surface optical modes (SO) exist in the nanocrystallite. Because of the eigenfrequency mismatch between the dots and the amorphous matrix the lattice vibrations cannot penetrate into the matrix the phonon wavefunctions are confined within the dots. In the Raman scattering process, this spatial confinement results in a relaxation of the momentum conservation, which increases with decreasing crystallite radius. This leads to an enhancement of transition probability between the vibrational states and therefore to a shortening of the lifetime of the excited state. Finally, this shortening of the lifetime results in a size-dependent increase of the homogeneous linewidth. The relaxation can be observed in the Raman spectra as a...

Theory of the trNOESY Experiment

In which P , L , and PL are the molar concentrations of the protein, the ligand, and the complex, respectively and kon and koff are the association and dissociation constants, respectively. In the trNOE experiment, the exchange of the ligand between the free and bound states alters the relaxation dynamics of the ligand more significantly than of the protein. Under equilibrium conditions, the binding constant, KD, is the ratio of koff to kon. The exchange rate that is relevant to the NMR experiments, kex, depends on the relative populations of the protein and ligand as well as the binding constant and is defined as in which Tm is the mixing time, and the elements of the matrix V(Tm) are the measured peak volumes of the crosspeaks in the trNOESY spectrum, which are described in terms of the exchange-relaxation matrix r. The exchange rates (kex) as well as the self- (py) and cross-relaxation (Gy) rates of the various proton pairs are included in r. When the exchange is fast relative to...

Strain Effects in Nanostructures Due to Lattice Mismatch in Multi Quantum Wells

Arrangements of dislocations are formed 143 and total relaxation by the formation of arrays of misfit dislocations takes place. For thicknesses beyond 600 nm the wavenum-ber gradually approaches the value of the stress-free LO phonon. The appearance of misfit dislocations and stacking faults leads to a strong decrease of the lattice quality. Therefore, for the growth of a high-quality layer it is necessary to keep the layer thicknesses below the critical thickness. The strains in these layers lead to changes in the vibrational properties, which can be estimated by Raman spectroscopy. By these experiments the dependence of the strain on the layer thickness can be evaluated in one and the same sample 22, 145 . In ZnTe ZnSe superlattices with a lattice mismatch of about 7 and thicknesses of 0.5-5.0 nm the superlattice is not destroyed by diffusion of Se or Te even for very small layer thicknesses. The Raman spectra of these samples show an asymmetrical LO phonon peak with increasing...

Oxidation at Open Sidewalls

Etching of quantum wires and dots out of 2d-grown quantum well structures (mesas), which is the topic of this section, inherently creates new interfaces at the sidewalls of those dots and wires. The cleanliness of the side faces is crucial for the optical properties of these systems. The increased surface recombination rate at the sidewalls creates dead layers. The process technology applied for the etching process as well as exposure of the sidewalls to air ambient crucially affects the properties of the dead layers 175-177 . Additionally, oxide layers are expected to affect the sidewall strain relaxation of a strained active layer in very small structures (

NMR Experimental Setup

One common modification is the insertion of a relaxation filter to suppress extraneous protein signals, which may interfere with the detection of the ligand signal. This can be achieved by the T1p (or R2) filter. This filter can be introduced either prior to or after the first 90 pulse. If introduced prior to the first pulse, the filter needs to be flanked by additional 90 pulses or windowless multiple pulse sequences such as DIPSI (39) need to be used, so that the magnetization is along the Z-axis after the filter is employed. If the filter is introduced after the first 90 pulse, as in the original experiment proposed by Scherf and Anglister (40), care must be taken to acquire the first t1 point to avoid the need for large phase corrections in the indirect dimension.

Direct Writing of Structures by a Particle Beam

In analogy with structure fabrication with neutral atomic beams, cluster beams also allow additive structure generation. Clusters arriving on a solid surface create layer dements with shapes determined by their relaxation behavior, their energy and the surface temperature2).

Improving Human Performance

A method to assess performance readiness could be used as a predictor of performance success, especially if it were noninvasive, reliable, and not time-consuming. If stress or other factors have produced decreased sensory gating, then remedial actions could be instituted to restore sensory gating to acceptable levels, e.g., coping strategies, relaxation techniques, pharmacotherapy. It should be noted that this technique also may be useful in detecting slowly developing (as a result of cumulative stress) chronic sensory gating deficits that could arise from clinical depression or anxiety disorder, in which case remedial actions may require psychopharmacological intervention with, for example, anxiolytics or antidepressants.

The Mechanism of Surface Induced Mechanical Energy Dissipation

When a periodic macroscopic stress is applied to a (imperfect) material, the chemical bonds surrounding the defects will be stressed, usually anisotropically. If the stress puts the defects in a non-equilibrium configuration, the defects will relax to their ground state configuration with a finite relaxation time, t*. If this relaxation time is much faster or much slower than the vibrational period (i.e., if relaxation is

Magnetic Characterization of Electrospun Nanofibers

The magnetic response of magnetic nanoparticles to an oscillating magnetic field provides unique information about the particles' magnetization dynamics (see Figure 21.13). This response can be modeled mathematically using the relaxation equation where M is the magnetization of the suspension, x , the initial susceptibility, H, the applied magnetic field, and t, the magnetic relaxation time. If we consider an oscillating magnetic field H defined as H H0 cos(Qt), the magnetization response becomes M x'H0 cos(Qt) + x''H0 sin(Qt), where Q is the field frequency. ' and are known as the real and imaginary components of the complex or dynamic susceptibility, and are defined by The magnetic relaxation time, T, is dependent on the mechanism by which particles respond to a change in an external magnetic field. Two possibilities are rotational Brownian motion and Neel relaxation. The first mechanism is related to particle rotation along with its magnetic moment and the second is due to the...

Further Spectroscopic Properties

NMR-Spectroscopy of Nanodiamond NMR-spectroscopic examinations of nanodiamond turned out quite complicated. Most of all the in parts extremely long spin relaxation times t lead to long measuring times. For high-grade diamonds of gem quality, t may amount up to 3 days due to their low density of defects For synthetic diamonds bearing several defects like nitrogen vacancy centers, the relaxation times are still observed to be about 1 s. For an explanation, one has to consider the low frequency of isotope 13C and the associated weak dipole-dipole interactions between these nuclei as well as the long distance between the - 3C-spins and the nearest unpaired electron. For nanoscale diamond particles, on the other hand, rather short relaxation times of ca. 140 ms are observed as there is an efficient spin-lattice relaxation channel the nuclear spins may couple to unpaired localized electrons resulting from the existence of unsaturated bonding sites.

Magnetic Nanoparticles As Biosensors

When multivalent magnetic nanoparticles bind to multivalent targets in solution they form stable nanoassemblies, and associated with nanoassembly formation is an increase in R2 relaxivity and decrease in the spin-spin relaxation time (T2) of surrounding water molecules 23 , see Figure 8.3. Nanoassemblies can be disassembled and returned to their original dispersed state by a number of methods (heat, enzyme cleavage, disulfide bond reduction). Thus nanoparticles switch between a dispersed and nanoassembled states and are termed magnetic relaxation switches (MRSW). MRSW are unique as a biosensor system because they do not employ a biomolecule immobilized on a solid phase, and because they use radiofrequency radiation at the Larmour precession frequency of water protons rather than light. Therefore they are homogeneous type assays (no separation of bound and free), and can be performed in media that absorb, scatter or fluoresce when they interact with

TAkffkoldX t ffkeqX t Sfk31

Where t 1, t2, ,tk are the relaxation parameters for the 1, 2, , k individual flows (i.e. they do not account for interactions among dissimilar particle types). The index stands for the n base vectors of the respective lattice type. The index f refers to the different fluid phases (running from f 1 to f k). The equilibrium distributions for the individual phases are in the model of Shan and co-workers 42-45 formulated in the same way as outlined above for the chromodynamic model, equation (24). where Sf is the interaction source term for phase f in the direction of the lattice vector e and Ff is the total effective interparticle force vector acting on the f th component associated with the pseudo-potential of the pairwise interaction between different particle types. Interactions between identical particle types are considered by the single-phase one-step relaxation terms, as in all Bhatnagher-Gross-Krook versions of the lattice Boltzmann model.

Example One Local Mechanical Spectroscopy of Polymers

Fig. 21.2 (a) Local mechanical spectroscopy spectra as a function of temperature of a technical PVC The vibration amplitude is displayed as a thin line and the phase lag as a thick line. Four temperature domains can be distinguished From left to right, a small vibration amplitude decrease is associated with a first phase lag peak (1), in the next domain, vibration amplitude increases (2), then a large decrease of vibration amplitude is associated with a large phase lag peak (3) and finally phase lag increases slowly (4). (b) DSC measurements of the same sample. For clarity, the temperature domains observed on Fig. 21.5a have been reported. The graph displays the first (dashed line) and the second (solid line) heating. The glass transition can easily be recognized around 340 K (labeled A), slightly below the temperature range of domain 3. An irreversible endothermic relaxation takes place in the same temperature range (only visible on the first run). A reversible endothermic event...

Nonlinear Material Behavior

So far we have discussed in some detail the linear ther-moelastic response of multilayer films and to a lesser degree, the effects of geometric nonlinearity. An additional complication is material nonlinearity. It can arise in numerous forms including plasticity, creep, stress relaxation, and evolution of the material microstructure (densification, grain growth, defect annihilation, etc.) during thermomechanical loading. In this section we briefly discuss nonlinear material behavior of multilayer films, focusing on the phenomena most relevant for the realization of reliable devices. The discussion in this section is concerned primarily with multilayer films where one of the films is a metal.

In GeSi Heteroepitaxy

In Ge Si heteroepitaxy, most of the step-decoration research has been focused on growth using vicinal Si(001) substrates and primarily on multilayer structures 10, 41 . For sub-monolayer deposition of Ge, agglomeration at atomic steps has been demonstrated 260 and attributed to step-flow growth, lower step energy for Ge, and enhanced relaxation of Ge-Si lattice mismatch at steps 10 . Deposition of SiGe Si multilayers on vicinal Si(001) results in self-organized arrays of self-assembled SiGe nanowires 261 , the process driven by local strain relaxation 135, 262-264 . The nanowire-like structures within each SiGe layer are formed by thickness undulations within the 5-nm-thick layer with about 100 nm periodicity (Fig. 20) 261 . The facets of these wires are defined by Si and SiGe step bunches thus the structural confinement of the individual wires can be improved by using templates with stronger bunching, such as Si(113) 261, 265 . The width and periodicity of these structures (intrinsic...

Local Equilibrium Description

As already pointed out in the previous section, we want to analyze what kind of constitutive equations follow from the deviation from thermal equilibrium if we apply a relaxation time approximation. Therefore, we introduce the picture of local equilibrium. This means that at least locally in position space a thermodynamic equilibrium distribution f 0( k, x, t ) exists to which f (k, x, t) relaxes. Let us assume that the equilibrium distribution is given by a Fermi distribution The distribution function that locally deviates from its equilibrium value is given by f (k, x, t) f0 (k, x, t) + bf (k, x, t). Once we have bf (k, x, t) it is possible to calculate all the current densities introduced in 6.1.4 as moments of bf (k, x, t). We insert the expansion of the distribution function into the BTE (6.2) with the scattering term given by a relaxation time approximation (6.23) and obtain

Nuclear Magnetic Resonance Imaging MRI

Among the substances in the human body that are important for MRI construction, namely H1, P31, and Na23, the first one (H1) gives by far the strongest signal since it is present in almost all tissues and organs. When nuclei of elements with a weak external spin are placed in a strong homogenous magnetic field, they align themselves with the direction of the field. When a force is applied on the spinning atomic nuclei by a radio frequency at the so-called Larmor frequency, perpendicular to the direction of the magnetic field, the nuclei are tilted away from the aligned equilibrium direction and will perform a precession around the direction of the magnetic field. During this displacement from the equilibrium orientation the nuclei absorb energy. As soon as the radio frequency or excitation is removed, the nuclei will reorientate in the direction of the homogeneous field. The time constant describing the return movement of a group of nuclei to the field direction, or longitudinal...

Homo and block copolymers coalesced from their cyclodextrininclusion compounds

When poly(ethylene terephthalate) (PET) was coalesced from its IC formed with y-CD, it was observed to be significantly reorganized with respect to the as-received and solution and melt processed (normal) samples.21, 32 For example, coalesced PET was found to have an FTIR spectrum that was distinct from those of normal PET samples, with much improved resolution. DSC observations of coalesced PET repeatedly evidence high-temperature crystallization, with resulting high crystalline contents, upon cooling rapidly from the melt, which is uncharacteristic of PETs that are generally slow to crystallize and can easily be quenched into a totally amorphous material. Furthermore, repeated DSC heating scans of coalesced PET fail to reveal a macroscopic glass-transition, and this was confirmed on a microscopic scale by measurement of temperature-dependent solid-state 13C-NMR-observed 1H spin-lattice relaxation times, T1p(1H).32

Ux t T fjedx t fbusx tCi

The evolution of the particle populations follow, for the k different fluid components at each lattice node, a form of the lattice Boltzmann equation with different relaxation and interparticle interaction properties, as outlined above for the chromodynamic model, according to

Thermomechanical Fatigue

It is also important to understand the development of damage and its effect on deformation during cyclic thermomechanical loading. To date, only very limited attention has been directed toward this issue. Zhang and Dunn 35.33 showed that if gold polysilicon multilayers were cycled (Fig. 35.20) to an elevated temperature and then cooled to room temperature, they followed the thermoelastic path on subsequent cycling to a temperature below the maximum reached during the initial thermal cycle. Presumably over this range of temperature and time, the gold microstructure has been stabilized by the first cycle, and the polysilicon microstructure is not changing. This was confirmed for only a few, perhaps ten, cycles. Gall et al. 35.48 have shown that for thousands of cycles, though, a gradual shift of the thermoelastic curve downward is observed, possibly due to creep and stress relaxation in the gold, although the thermoelastic slope is maintained.

Magnetic Hyperthermia

The heating of magnetic oxide particles with low electrical conductivity in an external alternating magnetic field is mainly due to either loss processes during the reversal of coupled spins within the particles or due to frictional losses if the particles rotate in an environment of appropriate viscosity. Inductive heating of magnetic oxide particles (i.e., via eddy currents) is negligible due to the low electrical conductivity 223 . Hysteresis losses dominate when thermal energy is too low to facilitate reorientation. On the other hand, since the energy barriers decrease with a decreasing particle volume, thermal fluctuations facilitate the magnetisation reversal of small particles. Thus, relaxational losses dominate at the nanoparticle level when thermal energy can overcome the magnetic anisotropy barrier. Relaxational losses can be divided in Neel losses due to reorientation of the magnetic moment in a particle, and Brownian losses due to reorientation of the magnetic particle...

Optical birefringence and infrared activation

The polarised monofilament images and double refractive index measured for lsv fibres melt-spun at lower take-up speed did not exhibit significant variation in birefringence. The observed dark spots along the core of lsv monofilaments would manifest the presence of isotropic type crystal formed through melt nucleating (Buchko et al., 1999). Nucleation of the isotropic crystal is attributed to lower cooling rate associated with lower spin speed and hence more favourable chain relaxation process. A similar crystal feature was also exhibited by the hsv PPEZ, PPG3, PPG5 and PPB3 which comprised a predominantly intercalated layered-silicate structure. However, this feature is not seen for the highly exfoliated hsv PPEX and neat PP fibres, which displayed an intense core brightening associated with enhanced molecular chain conformation. This is confirmed by their considerably higher refractive index plots shown in Fig. 19.7. The absence of isotropic crystal in the exfoliated The enhanced...

Paramagnetic Contrast Agents

Bloch first described the use of a paramagnetic salt, ferric nitrate, to enhance the relaxation rates of water protons 123 . Later on, Lauterbur et al. were first to show the feasibility, exploiting paramagnetic agents for tissue discrimination on the basis of differential water proton relaxation times 124 . Since this pioneering work, many studies have been carried out on the use and development of paramagnetic contrast agents.

Structure and Microstructure

La1-xCaxMnO3 14 , where the bottom part of the film, close to the substrate, is perfectly coherent with the substrate, suggesting an important strain, while the upper part shows a domain structure. The perfect epitaxy between the film and the substrate can also be viewed on the cross-section of Pr05Ca05MnO3 deposited on SrTiO3 (Fig. 5). This film is grown in the 010 -direction, that is, 2aP, perpendicular to the substrate plane. The cross section along the 110 -direction of the substrate clearly shows the perfect coherence of the interface since the 100 - or 001 -directions of the film match the 110 -direction of the substrate. The lattice parameter length in this direction is aP T2. No dislocation has been detected, whatever the film zone, ruling out definitely such a structural mechanism for explaining the relaxation. A detailed examination allows a mechanism of smooth variation to be proposed. The images indeed show very local variations of the contrast. They appear as pointlike...

Photosensitivity Mechanisms in Functionalized Hybrimers

(laser dye, second-order nonlinear chromophores, reverse saturable absorbers, photochromic molecules, etc) into the siloxane matrix to form doped xerogels with specific optical properties. Thus, the optically functionalized hybrimers exposed to UV light are another type of photosensitive hybrimers for photofabrication of optical micro-structures. It is well known that a high birefringence ( 0.01) can be created in materials containing azobenzene chromophores via the photo-excitation of azobenzene groups by polarized light. The mechanism involves successive trans-cis photo-isomerization and thermal cis-trans relaxation, whose process is illustrated in Fig. 13.21 44, 45 . This leads to the alignment of azo groups in a direction perpendicular to the polarization of the incident light. The azobenzene incorporated into polymers, chemically bonded or not, often called azo-polymers, have been investigated for potential technological applications due to their interesting photosensitivity to...

Selected Area Electron Diffraction

Electrodeposited thin film having (110) texture. This grain of about 400 nm extension in a plane perpendicular to its fivefold axis exhibits secondary twin boundaries in two of the tetrahedral units. Accordingly, in the diffractogram a slight splitting of related spots of 111 and 222 type can be seen, which indicates an inhomogeneous relaxation of elastic strains due to the space filling gap. For the sake of clarity, no assignment of spots has been added to the SAED pattern, but two circles are drawn enclosing the innermost spots of 111 and 200 type. From this rather complex electron diffraction pattern, it can be clearly seen that not one single crystal, but a grain consisting of five subunits in well-defined orientation relationship are transmitted by the electron beam. Likewise, diffraction patterns from regions of 1 nm size of multiply twinned Au nanoparticles obtained by means of a microdiffraction equipment operated in the scanning transmission mode 396 confirm the particle...

Stability Of The Model Of The Nanofiber

Two different nanofibers of C100H202 were studied. One system (f36) contained 36 independent parent chains, and the other system (f72) contained 72 independent parent chains, both in boxes in which LX was initially 5.25 nm. The simulation protocol for collapse of the fiber consisted of a cycle of increasing Lx by 0.25 nm, followed by relaxation for 105 Monte Carlo steps at a temperature of 509K. This cycle was continued until collapse was observed. The smaller system with 36 independent parent chains collapsed to droplets when Lx reached 10 nm. The larger system, with 72 independent parent chains, did not collapse even when Lx exceeded the length of the fully extended chain, which is 12.5 nm.

Applications of Nanocrystalline Superplasticity

It has also been shown that nanocrystalline ceramics can be used for direct bonding of ceramic materials to each other. Superplasticity allows the mating surfaces to adapt better to surface asperities. The superplastic ceramic may also be in the form of an interlayer as in the case of metals. This interlayer may also be used to accommodate stresses in thermally mismatched structures as in metal-ceram joints and metal-ceram coating systems. When the compound is heated, a superplastic interlayer or coating could accommodate larger thermal mismatch strains than conventional interlayers or coatings without cracking by the processes of superplastic flow and stress relaxation 438 .

Electroninduced Xray Spectroscopy

Electron-induced X-ray spectroscopy is a method for the determination of the atomic composition of a thin layer. Through the impact of energetic electron beams on a target, the electrons are slowed down by interactions with the target atoms. The deceleration of the charged particles induces the emission of electromagnetic radiation. With increasing kinetic energy of the electrons, the emission edge of this radiation shifts to a shorter wavelength range. As a result of the typical electron energies of around lOkeV, the spectrum starts in the medium X-ray and extends through the UV to the visible range. Individual sharp emission bands are overlaid around this broad continuum of Bremsstrahlung radiation. They originate through the direct interactions of the beam electrons with electrons of the inner shells of the target atom. With sufficient energy transfer, the shell electrons leave the solid and a relaxation process occurs that includes the movement of electrons of the outer shells...

Targeted Nanoparticles And Imaging Of Cancer

Although treatment of cancer with targeted nanoparticles is an important goal, more accurate imaging of cancer is needed to allow for the optimal treatment for each patient. Towards that end, a considerable amount of research is underway with various imaging techniques to establish more accurate determination of the presence and extent of cancer growth and metastases. Because magnetic resonance imaging (MRI) is a widely used imaging technique, much work is currently being done to develop targeted imaging agents for MRI. Some of these involve paramagnetic and superparamagnetic iron oxides due to their ability to affect water relaxation times Tj and T2. Gasco and collaborators have prepared solid lipid nanoparticles containing Endorem, superparamagnetic iron oxide nanopar-ticles (Guebert and Advanced Magnetics), using either a multiple emulsion technique or an oil in water emulsion technique.76 Although the loading rates achieved were less than 1 wt iron, it was possible to detect and...

Microstructure Of Bulk Nanocrystalline Substances

The microstructure of submicrocrystalline substances, which are synthesized using severe plastic deformation, differs from the microstructure of compacted nanocrystalline substances. The main feature of the structure of submicrocrystalline substances is the presence of randomly misoriented non-equilibrium grain boundaries. Unannealed submicrocrystalline metals and alloys are characterized by extinction contours along grain boundaries, which point to large elastic stresses. Annealing eliminates dislocations from grains, extinction contours vanish, and a stripe contrast, which is typical of the equilibrium state, appears. The relaxation of interfaces is accompanied by growth of grains during annealing.

Nanotube Reinforced Polymer

Matrix crack and demonstrates excellent bonding between nanotubes and matrix material. Viscoelastic properties have also been investigated, with some evidence that well-dispersed nanotubes impact the mobility of the polymer chains themselves, causing changes in glass transition temperature and relaxation characteristics,343,344 a feature not observed in polymers with a micron-sized reinforcing phase. Limited work on electrical properties shows that percolation can be reached with nanotube volume fractions of less than 1 ,333 leading to dramatic changes in electrical response of the polymer. This enables applications such as polymer coatings with electrostatic discharge capability.345

Nanostructures as Optical Sensors

Fluorescent nanoparticles are an interesting alternative as markers for the detection of molecular binding events. For diameters in the lower nanometer range (2-5 nm), molecules labeled with these particles are still able to react highly specifically, because of the low strength of non-specific interactions. The particle diameter controls the fluorescence wavelength. Choice of particle size and material allows a broad optical range between the UV and the NIR to be addressed. Applicable materials are, e. g., the compound semiconductors CdSe, InP, ZnS, CdS and InAs 128 129 . In addition to these inorganic particles, organic nanoparticles are also applicable. Therefore, fluorescence dyes are incorporated into polymer particles that are surface-functionalized. Thus a well-defined and relatively rigid chemical environment is provided for the organic fluorophores, in order to enhance the relaxation behavior and the stability of the quantum yield. By the use of different dyes, a multichannel...

Protein Cooperativity Historical View

This concept was supported by several allies including Wei (1974) who suggested dipole coupling among membrane proteins to explain nerve functions. McClare's general model of resonant dipole coupling was greeted by skepticism, however. Highly respected biochemist Gregorio Weber (1974) raised two objections. He noted that at least some of the emitted energy following molecular excitation is emitted in 10-12 seconds, too short to be utilized by biomolecules. The second objection referred to the transfer of quantum vibrational energy through the surrounding medium. The process of dipole-dipole coupling involves a similarity of the energies emitted and received, and requires that the interacting oscillators be surrounded by a medium transparent to the wavelength of the transferred energy quantum. Water surrounds every biomolecule and provides a medium which appeared to be opaque to the infrared energy McClare described. Weber implied any emitted energy would be dissipated as heat to the...

Conclusions and Outlook

The use of an aqueous sol-gel method, involving a freshly formed tungstic acid precursor combined with a structure-directing agent belonging to the group of polyhydroxylated organic compounds, allows the fabrication of mesoporous WO3 films of considerable thicknesses, which are able to absorb a large portion of the incident light with energies close to the bandgap of the semiconductor. Such nanostructures, consisting of several tens of stacked WO3 nanoparticles permeated by an electrolyte, form a large number of Schottky (semiconductor electrolyte) nano-junctions interpenetrating the whole film. A configuration of this kind allows the relaxation of the usual constraint concerning the lifetime of the minority charge carriers, provided the hole diffusion length will actually be larger than the size of the n-type semiconductor nanoparticles in contact with the electrolyte. The implication for a material such as WO3 is that the distance between the site where e h + pairs are generated and...

Structures that Assist Measurement

Electron-induced X-ray spectroscopy is a method for the determination of the atomic composition of a thin layer. Through the impact of energetic electron beams on a target, the electrons are slowed down by interactions with the target atoms. The deceleration of the charged particles induces the emission of electromagnetic radiation. With increasing kinetic energy of the electrons, the emission edge of this radiation shifts to a shorter wavelength range. As a result of the typical electron energies of around 10 keV, the spectrum starts in the medium X-ray and extends through the UV to the visible range. Individual sharp emission bands are overlaid around this broad continuum of Bremsstrahlung radiation. They originate through the direct interactions of the beam electrons with electrons of the inner shells of the target atom. With sufficient energy transfer, the shell electrons leave the solid and a relaxation process occurs that includes the movement of electrons of the outer shells...

Experimental Techniques to Characterize the Microstructure Development

NMR has been an ever-present and key technique in the characterization of binders, from the post-war period with Pakes's article Pake, 1948 showing proton NMR spectra of gypsum, until today where dynamic NMR methods deliver new outstanding results on cement paste porosity. The recent progresses made in cement field were reviewed in the following articles Nestle, 2007 & Skibsted, 2008 . Two-dimensional NMR relaxometry provides unique information on exchange of water between the silicate surface and the capillary pores McDonald 2005 & 2007 . Proton relaxation at the surface of hydrate is a probe (and non-invasive) for the determination of specific surface area of these hydrates and its evolution during the hydration Zajac, 2007 . It also enables to study the pore size distribution over time. For instance, the fractal character of cement paste was clearly demonstrated with the power-law followed by the pore size distribution Plassais, 2005 . New NMR techniques are certainly a...

Single Particle Tracking

In single-chromophore tracking, instead of the scattered illumination light, Stokes shifted fluorescence is used to detect a label (Figure 6.2). Typically, an area of 1030 im diameter is illuminated by collimated laser light (intensity 1 kWcm-1). The excitation light is absorbed by the chromophore that enters the first electronically excited state. After fast relaxation (the Stokes or solvent shift) and after an exponential residence time (the fluorescence lifetime) the emitted red-shifted fluorescence light is detected by a camera. The two characteristic properties of fluorescence with respect to the excitation, red shifted and delayed, can be exploited to efficiently block the excitation light by dichroic mirrors and spectral filters, and also by employing time criteria, that is, pulsed laser sources and time-gated detection. For these reasons, fluorescence has the potential of being a background-free technique. In reality, however, autofluorescence from intracellular fluorescent...

Analysis of the Fluorescence Intensity Transients

Using this threshold-method, off-time histograms (Pofi(t) ) were constructed. Examples of three different concentrations are shown in Figure 7.7A-C. The logarithmic-linear scale emphasizes the nonexponential relaxation pattern. The histograms could be fitted best with a stretched exponential function, also known as the Kohlrausch-WilliamsWatts (KWW)-function shown in Equation (7.1) (Lindsey and Patterson 1980). This KWW-function is often used to describe heterogeneous systems showing a continuous distribution of the investigated parameter rather than a discrete set of exponentials. where 0 a 1 is a so-called width or stretch parameter that may be interpreted either as a measure of the nonexponential character of Poff(t), or as a measure of the width of the underlying distribution of relaxation times. When a is close to one, the deviation from monoexponential decay is minimal and consequently, the decay may be approximated by a sum of a few exponential terms. A value a close to zero...

Electron Beam Lithography

More important for the dimensions of the interaction volumes is a second effect after the ionization of target atoms, an electronic relaxation occurs by transfer of electrons from the outer shells to the free places of the inner shells and an energy emission as radiation. Owing to the large differences in energy, X-ray radiation is generated. This radiation is readily absorbed by the adjacent material. However, the expansion distance is much larger than the diameter of the electron beam. Under the influence of direct electronic excitation and the secondary effect of the X-rays, an excitation volume element develops in the target material around the impact area of the electron beam, which extends to a larger penetration depth and is therefore pear-shaped (Fig. 72). Because X-rays induce ionization and therefore chemical reactions, the resist solubility in this volume changes. The lithographic resolution of electron beam lithography is mainly determined by the dimensions of this...

Design of CSH Nucleation and Growth

The beauty of this model exists firstly in its simplicity since it utilizes only five parameters3 that are directly connected with physical measures and secondly in its capacity to give precious information on C-S-H development in various systems Garrault, 2001 & Nicoleau, 2004 & 2010 . Further aggregation around the first nuclei cause cluster growth on the grain surface which coalesce when they are big enough. This coalescence can be observed by NMR relaxation Zajac, 2007 since the lateral surface of growing clusters disappears. After a certain time, C-S-H particles cover the whole surface of the cement grains and at this point kinetics become limited by a diffusion process of reactants through the newly formed C-S-H layer. Hydration is roughly summarized in Fig. 7 by the succession of three steps the primary nucleation occurring during the induction period, the expansion of

Superparamagnetic Contrast Agents

Superparamagnetic nanoparticles represent an alternative class of NMR contrast agents that are usually referred to as T2 or T2* contrast agents, as opposed to T1 agents such as paramagnetic chelates ( 135 and references therein). The change in relaxation time produced by magnetic particles is a contribution of several complex mechanisms. The size and the composition of these particles represent the essential parameters. The particles possess very large magnetic moments in the presence of a static magnetic field, and dipolar interactions between the superparamagnetic cores and surrounding solvent protons result in decreasing both longitudinal and transverse relaxation times. prepared from hybrid Fe nanoparticles (12 nm) synthesized by continuous laser pyrolysis of Fe(CO)5 vapors 144 , The feasibility of these dispersions to be used as MRI contrast agents has been analyzed in terms of chemical structure, magnetic properties, 'H NMR relaxation times and biokinetics. The results showed a...

Hall Petch Strengthening Mechanism

Extrapolation of the Hall-Petch relationship to nanostruc-tured materials should show a much higher hardness than that of coarse-grained materials having the same composition. However, limitations should be taken into account 199 since (1) hardness cannot increase indefinitely, (2) relaxation processes in grain boundaries can decrease hardness, and (3) in nanometer-sized grains the Hall-Petch strengthening is not valid for nanograins less than 2 nm 333 . Regarding nanolayered composites, the Hall-Petch strengthening is not as applicable 334 when the bilayer repeat period approaches a few nanometers in size.

The Assemblies of NiC and NiO Particle Systems

Nanoparticles Pxrd

Fig. 3 shows the magnetization vs. field plots (M vs. H hysteresis loops) at 300 K (Fig. 3A) and 2 K (Fig. 3B) for the assemblies of Ni(C) nanoparticles. Figure 3A indicates a rapid increase with increasing applied magnetic field without saturation because of the superpar-amagnetic relaxation and the noncollinear moment of the surface spins in the smaller particle assembly. 20 Hysteresis is absent with a little remanence and coer-civity (HC), which suggests the presence of a long-range magnetic dipole-dipole interaction among the assemblies of superparamagnetic Ni(C) particles. With decreasing temperature, the magnetization of the samples increases and exhibits a symmetric hysteresis loop under both ZFC and FC at 2K, indicating a transition from superparamagnetic to ferromagnetic behavior. Specifically, the temperature dependence of

Localizing Nanoparticle Concentrations

Magnetic resonance imaging has been shown to be very well suited for diagnostic cancer imaging as a result of the exceptional anatomical resolution of this modality 29,30 . The basis of molecular MRI is generally based on the assumption that antibodies, peptides, or other targeting molecules, tagged with a magnetic contrast agent, binds to the target and produces a local magnetic field perturbation that results in an increased proton relaxation rate that is detectable by magnetic resonance techniques. Magnetic nanoparticles are a form of magnetic contrast agent in MRI. Para- and superparamagnetic agents such as Gd(III) and various forms of iron oxide in both molecular and nanoparticle form have been used in a broad range of MRI applications to enhance image contrast. This approach is only limited by the inherent sensitivity of MRI, and the specific pulse sequence chosen, to the presence and distribution of the magnetic contrast agent 25,26,31,32 .

Structural And Chemical Properties Of Micro And Mesoporous Materials

Chemical Properties Gold

Acid base sites generated by substitution in crystalline materials are generally more stable than sites in mesopo-rous materials with amorphous walls, because the latter material does not face constraints in the relaxation of bonds. 34,35 In contrast to the crystalline materials, mesoporous materials have pores generated by the condensation of (X-ray amorphous) oxides 36 around medium and high molecular weight surfactants. 37 After forming a coherent structure, the surfactants are removed and the regular void structure with pore diameters between 20 and 100 nm remains. The large pores possess many hydroxyl groups, 38 which are well suitable for anchoring functional groups or metal-organic com-plexes. 39 The most prominent members of the family are the MCM41S-type materials (e.g., MCM-41, MCM-48) with hexagonally or cubic structures 40 and materials such as SBA15 synthesized using non-ionic tri-block copolymers. 41,42 For postsynthetic modifications these materials are frequently used...

Controlling the GMI Effect

The effect of ac frequency on the GMI was studied by Knobel et al. 77 and Ovari et al. 78 , and they found the GMI generally increases with frequency. However, depending upon the types of ferromagnetic glasses and annealing conditions, the GMI decreases when the frequency is beyond 1-200 MHz due to the domain wall damping that causes permeability relaxation at very high frequencies 66 . The amplitudes of the dc bias and ac currents and the internal stress of the ferromagnetic glass have also been found to influence the sensitivity of the GMI

Sources of Warpage in Microchannel Arrays

Several sources have been identified for causing warpage within microchannel arrays. As shown above, one source of microchannel warpage can be the application of bonding pressure on regions of external laminae adjacent to microchannel regions. Another noted source of warpage can come directly from warpage in the raw shimstock, foil or film. Out of the box, even annealed, cold-rolled shimstock can have flatnesses greater than 50 pm on a 50 pm thick foil (Wattanutchariya and Paul 2004). Consequently, flattening procedures are generally required for precision microchannel array fabrication prior to the patterning step. Unannealed metal foils are particularly susceptible to warpage during the bonding cycle due to the relaxation of residual stresses built up in the foils during cold rolling or electrodeposition (in the case of electroplated foils). Perhaps the greatest source of warpage can come from sideloads on the foils either due to friction between laminae, friction between external...

Spectroscopic Characterization

Cages are bound to protons, there are small differences of relaxation time and of the nuclear Overhauser effect. This makes it possible to quantitatively count the number of carbon atoms of 13C-NMR spectra. Unfortunately, there are some difficulties in obtaining satisfactory 13C-NMR spectra low solubility of dimers, long relaxation time, as well as the concentration of resonances of fullerene cage atoms in a small domain. For these reasons, many 13C-NMR experiments on dimers required a long acquisition time, relaxation reagent, and a relatively high field NMR. It is not uncommon in this field to have routine spectra acquired for a few days. A typical example of the structure determined by 13 C-NMR is 14 76 . The 13C-NMR spectrum shown in Figure 6 was measured under the following conditions instrument JEOL LNM270 (1H 270 MHz), solvent 1-chloronaphthalene with 20 v v 1-methylnaphthalene-d10, relaxation reagent Cr(acac)3 10 mM, flip angle 90 , pulse repetition time 10.000 s (acquisition...

The Cohesive Energy Density Of Polymer Liquids

It has long been understood that the surface tension is a direct manifestation of the cohesive forces that hold liquids together. Correlations between the CED and the surface tensions of small molecule liquids have been demonstrated.3 However, in the case of polymer liquids, accurate surface tension data have not been available until recently.4 The measurment of the thermodynamic properties of polymer liquids is difficult due to the fact that the temperature domain of the liquid state is frequently high enough for degradation reactions to occur which detract from a accurate measurement of many thermodynamic properties. PVT data for polymer liquids have also only recently become available due to the need for special dilatometers for the measurement of viscoelastic liquids5 The above mentioned stability problem necessitates a rapid measurement of the surface tension. This rules out conventional methods due to the long relaxation times associated with...

The Many Body Sutton and Chen SC Long Range Potentials

Where e is a parameter with the dimensions of energy, a is a parameter with the dimensions of length and is normally taken to be the equilibrium lattice constant, m and n are positive integers with n m. The power-law form of the potential terms was adopted so as to construct a unified model that can combine the short-range interactions, afforded by the N-body second term in Eq. (22) and useful for the description of surface relaxation phenomena, with a van der Waals tail that gives a better description of the interactions at the long range. For a particular FCC elemental metal, the potential in Eq. (22) is completely specified by the values of m and n, since the equilibrium lattice condition fixes the value of c. The values of the potential parameters, computed for a cut-off radius of 10 lattice constants, are listed in Table 3.

Partially Soluble Bicomponent Fibers

One of the approaches to producing I S fibers is the spunbonding process. The structure and properties of spunbonded fibers and fabrics are determined by processing conditions such as extrusion temperature, melt throughput, quench air temperature, and drawing conditions, and by the material properties of the polymers used. The melting temperature, melting viscosity, initial structure, glass transition temperature, solidification point, and many other parameters of fiber-forming polymers play an important role in the final fiber structure and properties. When I S fibers are produced via the spunbonding, the number of islands, polymer composition, and materials used as the islands and sea also play an important role in the final fiber properties. At the stage of the selection of polymers for islands or sea, their spinnability in the I S bico-configuration has to be accounted for. The most profound effect on the spinnability of the two polymers in the bico-configuration is their...

Microstructural Characterization

Figure 1 shows the DSC curves of the as-prepared amorphous alloy (Fe73 5Cu1Nb3Si175B5, trademark Finemet), as well as of that of alloy previously annealed for 1 hour at 703 K and 763 K, respectively 36 . For the as-prepared alloy, the calorimetric signal shows some relaxation before the exothermic nanocrystallization process, as well as with the Curie temperature of the amorphous phase (Tqmc 595 K). When the sample has been annealed at 703 K, relaxation is no longer apparent in the calorimetric signal, the Curie temperature is shifted about 15 K, to higher values, and the nanocrystallization process is slightly advanced in temperature (2 K). On further increasing the annealing temperature, the calorimetric signal shows no clear changes in the Curie temperature of the annealed sample with respect to annealing at 703 K. However, a clear shift of the nanocrystallization onset toward higher temperatures (40 K) can be observed, as well as a significant decrease of its area 36 ....

Nanodiamond Properties

Very few theoretical studies of single nanodiamonds properties have been performed. Halicioglu 36 relaxed spherical nanometric diamond slabs with Brenner potentials. The so-formed structures exhibit inward relaxation from the top surface layers, the interatomic distance between neighboring atoms decreasing from the center of the cluster to the surface. They also noticed significant variations in relative cohesive energy with respect to bulk diamond. Recently, an ab initio molecular dynamics simulation, a parameter-free technique that solves quantum mechanical equations with great accuracy, was used to simulate the structure and to compute the electronic and optical properties of nanodiamonds. 23 Contrary to classical treatment, the quantum simulation of nanodiamonds yields an expansion of the cluster volume with respect to bulk diamonds. That tensile stress is at the opposite of what is observed in Si or Ge nanoparticles. The surface reconstruction of nanodiamonds has been shown to...

Quantum Structure Nanofabrication Using Strain Induced Self Assembly

Which the lattice constants are equal. When a critical thickness is exceeded, a significant strain in the layer leads to the breakdown of this ordered structure and the spontaneous formation of randomly distributed islets of regular shape and similar size (usually 30 nmin diameter). This mode of growth is usually referred to as the Stranski-Krastanow mode. The quantum dot size, separation, and height depend on the deposition parameters (i. e., total deposited material, growth rate, and temperature) and material combinations. As can be seen, this is a very convenient method to grow perfect crystalline nanostructures over a large area without any lithography and etching. One major drawback of this technique is the randomness of the quantum dot distribution. It should be mentioned that this technique can also be used to fabricate quantum wires by strain relaxation bunching at the step edges.

Ceramic Nanofibers For Clean Energy Sources Excitonic Solar Cells

There are at least nine fundamental processes that can control the final energy conversion efficiency in an excitonic solar cell (Figure 4b). The fundamental processes occur in KSCs arc (i) photon absorption which is determined by the wavelength window where the harvester absorbs, intensity of solar radiation at that window, and absorption cross-section of the dye (T) (2) radiative recombination determined by the carrier life time and the probability for radiative recombination in the excited state (Trcr) (3) exciton diffusion and its diffusion length (VDI) which controlled by the exciton diffusion coefficient (t KD) and exciton life time (4) interfacial electron transfer and its rate (T)CT) (5) interfacial charge recombination determined by the rate at the interface (T)l(1i) and (6) the exciton relaxation (T)f11n) through which the exciton lose its energy due to relaxation (7) electron transport through the electrode with drift (Ve), (8) the phonon relaxation (r pUN) through which an...

Soft XRay and Electron Spectroscopies

Silicte Melt Structure Flow

XES requires a high-flux excitation source and thus is best performed with high-brilliance synchrotron radiation from a third-generation synchrotron light source. For XES, the tunability of the excitation source is very important to optimize photoionization cross-sections. This is particularly true in the soft X-ray regime, since the competing relaxation process (i.e., Auger electron emission) is substantially faster and thus overwhelmingly dominant. Consequently, XES is a photon-hungry experiment, requiring high-flux excitation, as well as efficient detection. In order to extract detailed information about the electronic structure, however, this detection also needs to be performed with high-energy resolution (i.e., on the scale of a few tenths of an eV), which in turn calls for highly sophisticated soft X-ray spectrometers 19 22 .

Levels of Anesthesia Consciousness

Codidos Barra

With the widespread advent of diethyl ether, anesthesia became somewhat standardized and it became useful to delineate stages in the continuum from the awake state through anesthesia to respiratory paralysis, cardiovascular collapse, and death. In 1847 John Snow published his pioneer monograph, On the Inhalation of the Vapour of Ether in which he described five empirical levels through which an anesthetized patient progressed from consciousness to respiratory paralysis. Surgery could be performed in stage three characterized by analgesia (pain relief) and amnesia (lack of memory storage), or in stage four characterized by muscular relaxation and regular, automatic breathing. Snow's scheme was expanded in 1920 by Arthur Guedel who published codified stages and signs of anesthesia, later detailed in his 1937 monograph, On Inhalation Anesthesia A Fundamental Guide. Guedel predicated his stages on obvious physical signs involving muscle tone, respiratory patterns, and eye signs. He...

Tensile stress positive a

Stresses in thin films cause wafer curvature, as shown in Figure 7.12. Imagine a free film attached to a massive wafer and forcefit to the wafer size. Next, imagine, stress relaxation through the wafer curvature. A film under tensile stress will result in a concave shape, while a compressively stressed film will end up with a convex profile.

SPMNPs Used as Magnetic Contrast Agents in MRI

MRI works by the dual application of an external magnetic field Bo (up to 2 T) and a transverse (i.e., transverse to Bo) radio frequency (RF) pulse on protons which are present in large amounts in biological tissues (e.g., in water molecules, membrane lipids, proteins, etc.). Each proton has a tiny magnetic moment that can be aligned by applying an external magnetic field. The external magnetic field first applies and aligns a magnetic moment of each proton. The RF pulse is then directed to the region of interest, and the protons absorb energy from the pulse and spin in a direction different than the direction of the external field. The RF pulse then will be turned off, the protons now begin to return to their original alignment with the external magnetic field and release excess stored energy through a process called relaxation. When this happens, a signal will be given off and the MRI system can detect this signal and process it to transform it into images of the tissue area of...

Interatomic Potentials for Metallic Systems

(b) The prediction of the unrelaxed vacancy formation energy gives values around the cohesive energy which is completely incorrect for metals. The relaxation energy for metals is quite small and the experimental data suggest that the vacancy formation energy for metals is about one third of the cohesive energy. (c) The interatomic distance between the first and second atomic layers within an unreconstructed surface structure (bulk cross section) is predicted to be expanded by pairwise potentials. This is in contrast with the experimental data which suggest a contraction of the open surface lattice spacing, i.e. pair potentials fail to predict an inward relaxation of the metallic surfaces.

Dissipation Of Energy 31 Internal Thermalization

As pointed out above, Drude and radiation damping are the dominant mechanisms for the decay of the collective excitation in a metallic nanoparticle with sizes 10 nm. In the case of Drude damping, the energy is primarily transferred into one or several quasiparticle pairs (electron-hole pairs). The next step of the energy relaxation corresponds to an internal thermalization of the electron gas. The excited electronic states tend to a Fermi-Dirac distribution with a well-defined temperature which depends on the laser pulse intensity. It has to be noted, however, that the expression thermalization time has never been deeply discussed so far, for example, the question of what fraction of electrons

EpoxyPOSS Networks

Ether - poly(oxypropylene)diamine D230 (Jeffamine) resulted in broadening of the glass transition, increase in Tg, and slowing down of the chain relaxation in the glassy state. However, in the case of the monofunctional POSS, phase separation usually occurs due to incompatibility of the inorganic framework and organic matrix resulting in POSS aggregation. The phase separation in the POSS-polymer nanocomposites can be controlled by the type of POSS organic substituents and by covalent bonding to the polymer. The prereaction of the monofunctional epoxy-POSS with diamine 126 or of amino-POSS with a die-poxide monomer 127 partly suppresses POSS aggregation in the organic medium, and facilitates formation of a more homogeneous network. Moreover, the use of small curing agents such as dicyandiamide can avoid macrophase separation 127 .


The impact of ultrafast excitation and relaxation of the conduction band electrons of metallic nanoparticles has been reviewed. The attention is confined to metallic nanoparticles with sizes larger than 100 A, for example, the metal is still considered as a three-dimensional system. Quantum size effects due to the discrete nature of the electronic states 6 do not show up, and do not play a role in the energy dissipation processes. However, the size of the nanoparticles is smaller than the wavelength of light, as well as the optical penetration depth. Hence, all atoms in the particle can be collectively excited. This in turn influences the excitation (optical properties) and relaxation (electrodynamic properties) process.

Growth Models

Growth models developed for phase growth far from equilibrium comprise a flux of arriving particles which is much faster than the mass transport processes along the growing surface, such as surface diffusion and other surface-tension-like relaxation processes. Then, the stochastic arrival of depositing particles is film-growth-determining. These models can be described as discrete (atomistic) models by using molecular dynamics and Monte Carlo calculations or by continuous motion equations. Among the simplest discrete models the random deposition model, the random deposition with surface relaxation model, the ballistic deposition model and the Eden model can be considered 5, 6 . A reasonable explanation of this type of growth is provided by continuum models in which the growth of the solid film implies a competition between a roughening and a smoothening contribution. Roughening is caused by the stochastic arrival of depositing particles through a white noise of arriving particles,...

Concluding Remarks

Progress is also expected in local measurements of mechanical properties. There are a number of different approaches (force modulation, oscillatory shearing, nanoin-dentation, etc.), which are applied for this purpose. These techniques provide semiquantitative data in a relatively narrow frequency range, mostly around resonant frequencies of the piezoactuators or probes. Although such measurements are extremely important they should be extended to a broader frequency range over several decades of frequencies where molecular motion and relaxation of macromolecules take place. Such studies of polymer viscoelastic behavior have become important not only for macroscopic samples but also for functional plastic and rubbery-like structures and elements with dimensions in the millimeter and micron range. Measurements at those scales should be performed with AFM related techniques. The demand for such studies will further increase with development of nanotechnology.

Relaxation Audio Sounds Dusk At The Oasis

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