Info

Fig. 4. In-situ STM image of an Ag(100) -c(2 x 2) Pb domain together with bare substrate in the system Ag(100)/5 x 10"3 M Pb(C104)2 + 10"2 M HC104 at T= 298 K. AE= 175 mV, 7t = 5 nA, Pt-Ir tip.

2D Me overlayers formed at low AE are observed to act as precursors for subsequent 3D Me phase formation in the OPD range [11,13,15-18].

Fig. 5. In-situ STM image of a compressed 2D hep Pbads overlayer showing a higher-order superstructure with moiré pattern in the system Au(l 11)/5 x 10"3 M Pb(C104)2 + 10"2 M HCIO4 at AE = 0 mV and T = 298 K, /, = 40 nA, Pt-Ir tip.

Fig. 5. In-situ STM image of a compressed 2D hep Pbads overlayer showing a higher-order superstructure with moiré pattern in the system Au(l 11)/5 x 10"3 M Pb(C104)2 + 10"2 M HCIO4 at AE = 0 mV and T = 298 K, /, = 40 nA, Pt-Ir tip.

Tabel 1. Epitaxy of 2D and 3D Me Phases

System 2D Meads overlayer 3D Me phase

Ag(100) [110] || 2D hep Pb [110] Ag(100) [110] ||Pb(lll) [110]

Ag(l 11) [110] || 2D hep Pb [110] R 4.5° Ag(l 11) [110] || Pb(l 11) [110]R 4.5°

Fig. 6. In-situ STM image of a first-order phase transformation of a condensed 2D Pb overlayer into an expanded one on Au(100) during anodic polarization in the system Au(100)5xl0"3 M Pb2+ + 0.01 M HC104 at T = 298 K. (a) cyclic voltammogram I dE/dt | = 10 mVs"1, (b) in-situ STM image, 7, = 40 nA, Pt-Ir tip, ■ Au(100) - c(3a/2 x V2) R 45° Pb, 0bare Au(100) substrate, ■ Au(100) - hep 2D Pb overlayer.

Fig. 6. In-situ STM image of a first-order phase transformation of a condensed 2D Pb overlayer into an expanded one on Au(100) during anodic polarization in the system Au(100)5xl0"3 M Pb2+ + 0.01 M HC104 at T = 298 K. (a) cyclic voltammogram I dE/dt | = 10 mVs"1, (b) in-situ STM image, 7, = 40 nA, Pt-Ir tip, ■ Au(100) - c(3a/2 x V2) R 45° Pb, 0bare Au(100) substrate, ■ Au(100) - hep 2D Pb overlayer.

This means, that the epitaxy of 2D Me overlayer is reflected in the epitaxy of 3D Me crystallites, as summarized in Table 1 [11,18]. The structural and energetic properties of 2D Me overlayers are found to determine the nucleation and growth kinetics of 3D Me phases [11, 15, 18],

3 Preparative Nanoelectrochemistry

Local structuring and modification of solid-state surfaces by electrodeposition of metals are of great practical importance. However, the realization of these processes requires an exact knowledge of UPD and OPD of Me at an atomic level. At present, first attempts have been started to develop appropriate polarization routines for a defined nanostructuring or nanomodification of solid-state surfaces (metals, semiconductors, superconductor films) using in-situ STM and AFM.

For example, 3D Ag crystallites cathodically deposited on HC)PG(0001) decorate preferentially monatomic steps and other surface imperfections at relatively low |r)|, as shown in Fig. 7. In the OPD range -35 mV < r| < -10 mV, the number of atoms in critical Ag clusters is found to be Ncnt = 4. Ag clusters can be deposited on flat terraces only at much higher |r|| or by special polarization routines as demonstrated in Fig. 8 [11,14].

Investigations of local Me deposition on Si(100) in the OPD range are more difficult due to the band gap of the semiconductor, which influences the process itself as well as the tunneling conditions for in-situ STM [18],

Fig. 7. In-situ STM images of a stepped HOPG (0001) surface in the system HOPG(0001)/10"2 M AgC104 + 1 M HCIO4 at T= 298 K. Left image: bare substrate surface at AE = 100 mV. Right image: after Ag deposition at ri = -125 mV. /, = 5 nA, Pt-Ir tip.

Fig. 8. In-situ STM images in the system HC>PG(0001)/10"2 M AgC104 + 1 M HC104 at T = 298 K. Left image: bare substrate surface. Right image: Ag clusters locally deposited on a flat substrate terasse applying tip-positive 6 V bias with 0.1 ms duration. 7t = 5 nA; Pt-Ir tip.

Fig. 8. In-situ STM images in the system HC>PG(0001)/10"2 M AgC104 + 1 M HC104 at T = 298 K. Left image: bare substrate surface. Right image: Ag clusters locally deposited on a flat substrate terasse applying tip-positive 6 V bias with 0.1 ms duration. 7t = 5 nA; Pt-Ir tip.

0 0

Post a comment