GaAs surface

Fig. 11. SFM pictures of etched GaAs surface obtained by using (a) the MWCNT probe and (b) standard silicon nitride probe [36],...

Loo, Y. L. et al. 2002. High-resolution transfer printing on GaAs surfaces using alkane dithiol monolayers. J. Vac. Sci. Technol. B 20 2853-2856. 

Pd (15), and Au (15). Once again, STM s unique contribution in these applications arises from the small areas (ca. 2-4 A ) that are involved in the measurement process. These capabilities have enabled the mapping of the spatial distribution of electronic states. For example, cation and anion sites on GaAs surfaces have been discriminated (Stroscio, J.A. Feenstra, R.M. Newns, D.M. ... 

Figure 6. Scanning electron micrograph (SEM) of n-GaAs surface electrochemically etched with a scanning electrochemical and tunneling microscope (SETM). Etching was accomplished in Aq. 5 mU NaOH, 1 mM EDTA. Photoelectric current - 0.7 /iA, Scan rate - 0.1 /tm/sec, bias voltage — 4 V. Tip was moved in an "L" pattern. Reproduced with permission of Ref. 89. Copyright 1987 The Electrochemical Society Inc.

Reaction (7.3.16) enriches the GaAs surface with elemental arsenic, resulting in a negative shift in the onset potential as well as an increase in the photocurrent density, which in turn promotes H2 photogeneration [118,119]. The stability of elemental arsenic on a GaAs surface depends on the electrolyte pH, as well as the applied potential. At veiy low pH and a potential of -0.45 V, arsenic is oxidized to stable AS2O3 [120] ... 

Snell s law of refraction may be solved graphically using slowness surfaces. It may be expressed as the requirement that the tangential component of the k-vector be conserved across a refracting interface. This is illustrated for waves in water incident on an (001) GaAs surface in Fig. 11.3. The slowness surfaces... 

Lunt, S. R., Ryba, G. N., Santangelo, P. G. and Lewis, N. S. Chemical studies of the passivation of GaAs surface recombination using sulfides and thiols. Journal of Applied Physics 70, 7449 (1991). 

Shaporenko, A., Adlkofer, K., Johansson, L. S. O., Tanaka, M. and Zharnikov, M. Functionalization of GaAs surfaces with aromatic self-assembled monolayers A synchrotron-based spectroscopic study. Langmuir 19, 4992 (2003). 

Is the intervalley scattering time on a GaAs surface faster or slower than that in bulk GaAs ... 

The presence of arsenic at the interface implies that surface states within the band gap will be introduced (see Fig. 1). We associate the high surface recombination velocity with the presence of arsenic. The formation of elemental As on the GaAs surface explains the difference in behavior of InP and of GaAs. In InP the thermodynamically stable phase that results from oxidation of the surface is colorless InP04 which straddles the band gap. In GaAs it is Ga203 and small band gap As. 

Figure 3. Decay of the band gap luminescence in the same n-GaAs crystal (a) with GaAlAs windows on both sides (b) with a GaAlAs window on one side and an air-exposed GaAs surface on the other (c) same as (b) after chemisorption of Ru3 on the GaAs surface. For details, see Ref. 33.

It is notable that once strongly chemisorbed Ru3+ has been adsorbed on an n-GaAs surface, Bi3+ causes little deterioration in cell performance. This suggests that the two ions react with the same chemical species or "site" on the GaAs surface. 

While desorption is operative to some extent at most Semico nductor/electrolyte interfaces, in some cases surface passivation can occur. Here charge transfer across the interface is used to establish covalent bonds with electrolyte species, which results in changes in surface composition. This is typified by the well-known oxide film growth on n-GaP and n-GaAs surfaces in aqueous solutions. In these cases, however, the passivation process can be competed with effectively by the use of high concentrations of other redox species such as the polychalcogenides. 

Fig. 51. A sequence of SFM images acquired during the formation of GaAs nanoparticles on a GaAs surface. The SFM tip was used to push the particles to their final positions in the line. Reproduced from [468]...

The conductivity of a generic semiconductor film is likely to be modulated by absorption of a polar species on the film surface. For example, a group at the Weiz-mann Institute has examined GaAs surfaces and found that porphyrin receptors linked to it will attract nitrogen oxide NO, and the binding of NO caused a change in resistance [5]. Other embodiments of GaAs sensors were found to be sensitive to ions in solution [25]. 

Figure 3. The scheme of photoelectrochemical cell for hydrogen storage (a) and Auger-spectrum of GaAs surface modified by Pt (b).

As seen in Fig. 3a, impurities on the surface (C, N, O) accompanies Pt deposition. The value of inter-planes distance for 200, d = 0.203 nm was established under investigations of Pt films with TEM. Thus the lattice constant for Pt on GaAs surface is a = 2 d = 0.406 nm. This value is higher as compared with that given in literature, 0.392 nm [7]. The larger value in our case may be explained by impurities likely implanted in the Pt lattice or by the interaction of Pt with GaAs surface. The Pt particles with average dimension 5 10 nm were obtained with our technique [8],... 

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