Info

Particle (Quantum) Nature of Matter: Photons, Electrons, Atoms, Molecules

The granular nature of matter is the fundamental limit to making anything arbitrarily small. No transistor smaller than an atom, about 0.1 nm, is possible. That chemical matter is composed of atoms is well known! In practice, of course, there are all sorts of limits on assembling small things to an engineering specification. At present there is hardly any systematic approach to making arbitrarily designed devices or machines whose parts are much smaller than a millimeter! A notable exception is the photolithographic technology of the semiconductor electronics industry which make very complex electronic circuits with internal elements on a much smaller scale, down to about 100 nm. However, this approach is essentially limited to forming two-dimensional planar structures.

It is not hard to manufacture Avogadro's number of H20 molecules, which are individually less than one nm in size. One can react appropriate masses of hydrogen and oxygen, and the H20 molecules will "self-assemble" (but stand back!). But to assemble even 1000 of those H20 molecules (below 0°C) in the form, e.g., of the letters "IBM", is presently impossible. Perhaps this will not always be so.

The most surprising early recognition of the granularity of nature was forced by the discovery that light is composed of particles, called photons, whose precise energy is hv. Here h is Planck's constant, 6.6 x 10~34 J-s, and v is the light frequency in Hz. The value of the fundamental constant h was established by quantitative fits to the measurements of the classically anomalous wavelength distribution of light intensity emitted by a body in equilibrium at a temperature T, the so-called "black body spectrum" [1].

The energy of a particle of light in terms of its wavelength, X, is

A convenient approach to calculating E, in eV, giving X in nm, involves remembering that the product he = 1240 eV - nm.

Later, it was found that electrons are emitted in a particular discrete manner from a metal surface illuminated by light of wavelength X=cjv. The maximum kinetic energy of the photoelectrons, K, was measured to be

0 0

Post a comment