Ge surface

Sample Atomic ratio (Si Ge) Surface area (m"g- ) Pore volume (cm g ) Pore size (nm) d-spacing° (nm) Energy gap (eV)... 

The surface states play an important role in the STM experiments. On Si and Ge surfaces, near the Fermi level, the surface states usually dominate the surface charge density, which are what STM is probing. The tips are usually made of d band metals, W, Pt, and Ir. Surface states have a strong presence on the tips and often dominate tunneling current. 

In the case ofn-Ge(lll) substrates, surface states affect electrochemical deposition of Pb [319]. At high cathodic potentials, the deposition occurs by instantaneous nucleation and diffusion-controlled three-dimensional growth of lead clusters. Comparing H- and OH-terminated n-Ge(lll) surfaces, the nucleation is more inhibited at n-Ge(lll)-OH, which can be explained by the different densities of Ge surface free radicals, being nucleation sites. In this case, nucleation site density is about 1 order of magnitude lower than that for n-Ge(lll)-H. 

For a semiconductor like Ge, the pattern of electronic interaction between the surface and an adsorbate is more complex than that for a metal. Semiconductors possess a forbidden gap between the filled band (valence band) and the conduction band. Fig. 6a shows the energy levels for a semiconductor where Er represents the energy of the top of the valence band, Ec the bottom of the conduction band, and Ey is the Fermi energy level. The clean Ge surface is characterized by the presence of unfilled orbitals which trap electrons from the bulk, and the free bonds give rise to a space-charge layer S and hence a substantial dipole moment. Furthermore, an appreciable field is produced inside the semiconductor, as distinct from a metal, and positive charges may be distributed over several hundred A. 

Germanium surface passivation by chloride termination inhibits oxide formation and maintains a well-ordered surface. The chloride-terminated surface can also be used as a reactive precursor for wet organic functionalization. For example, Cullen et al. [105] first demonstrated the reaction of a chloride-terminated Ge(lll) surface with ethyl Grignard as a means of ethylation for use in surface stabilization. The chlorination was performed by a mixture of Cl2 and HC1 gas with N2 above atmospheric pressures [105]. Although this resulted in approximately a one-to-one ratio of adsorbed chlorine atoms with Ge surface atoms, the high pressures resulted in severe etching of the substrate [105]. 

The wet chemical functionalization of Ge surfaces has not been as well studied as that of Si surfaces [13,20], despite the fact that the first report on Ge functionalization was made by more than 40 years ago [105]. Three methods of wet chemical functionalization have been reported on Ge surfaces to date (a) Grignard reactions on chloride-terminated surfaces, (b) hydrogermylation reactions on... 

Because of the similarity between the structures of the Ge(100)-2 x 1 and Si(100)-2x1 surfaces, cycloaddition products like those observed on Si(100)-2 x 1 are also expected to form at the Ge surface. Indeed, studying butadiene, Teplyakov et al. [240] showed that a similar Diels-Alder product formed on the surface of Ge(100)-2 x 1. Studies of alkenes have also revealed the formation of [2 + 2] cycloaddition products on germanium. For example, cyclopentene has been shown to form the [2 + 2] cycloaddition product on both surfaces [224,296,297]. In further studies of several other dienes and alkenes (including ethylene [298-303], acetylene [304-306], and cyclohexadiene [307]), cycloaddition products were found for Ge(100)-2 x 1 similar to those observed for Si(100)-2 x 1. 

Boonstra, A. H. and Van Ruler, J. Adsorption of various gases on clean and oxidized Ge surfaces. Surface Science 4, 141-149 (1966). 

The filtered preparation of gum arabic contained 13 pg/mg protein (dry wt). When a 0.01% (w v) aqueous solution, at pH 6.5, was exposed to a Ge IRE, no polysaccharide was observed to adsorb from a flowing solution at the aqueous/solid interface, as the characteristic C-0 stretching bands of gum arabic were not visible in the water-subtracted spectra. The protein (1.3%) associated with gum arabic demonstrated a high affinity for the Ge surface, adsorbing from a flowing solution at a concentration of 1.3 ppm, while polysaccharide, present at a concentration of 100 ppm, did not adsorb on the IRE. Distinct Amide I and Amide II bands of this adsorbed protein are visible in the water subtracted spectra. At the end of 4 hr, the 1549 cm 1 band intensity was 0.9 mAU. Rinsing with Milli-Q water (pH 6.5) did not affect the Amide II band intensity, indicating that the protein was firmly adsorbed to the Ge surface. 

At a gum arabic concentration of 0.1% (w v), protein and a small amount of polysaccharide were detected at the Ge surface as shown in Figure 5. The Amide II band intensity increased slowly and steadily throughout the initial 4-hr period, as shown in Figure 6. The Amide II band intensity peaked at approximately 11 mAU however, protein adsorption did not stop before the water rinse was initiated. Polysaccharide adsorbed rapidly onto the IRE... 

At a gum arabic concentration of 1.0% (w v), polysaccharide was detected at the Ge surface within the first minute of exposure to the flowing solution as shown in the first spectrum (T 0 min) in Figure 7. The intensities of both the protein and polysaccharide bands then rose rapidly in a 15-min period of time as shown in Figure 6. The 1070 cm 1 polysaccharide band plateaued at 14.7 mAU after 30 min whereas the Amide II band stabilized at 12.5 mAU after approximately 2 hr. The intensity of the 1070 cm 1 polysaccharide band dropped rapidly when Milli-Q water was pumped through the flow cell. A 90% decrease in the 1070 cm 1 band intensity occurred over the 4-hr rinse period. The final intensity of this band was not significantly different from the intensity observed when gum arabic was adsorbed onto germanium at a concentration that was 10 times less. The protein was more firmly bound to the IRE surface as indicated by the Amide II band intensity which dropped less than 10% during the rinse period. Only 15% less protein remained firmly attached to the Ge IRE when it was adsorbed from a gum arabic solution concentration of 0.1% as compared to 1%. Experiments to study adsorption of proteins and polysaccharides on copper and nickel are not yet complete, but appear to show similar trends. 

Adsorption of the enzymes subtilisin BPN and lysozyme onto model hydrophilic and hydrophobic surfaces was examined using adsorption isotherm experiments, infrared reflection-absorption spectroscopy (IRRAS), and attenuated total reflectance (ATR) infrared (IR) spectroscopy. For both lysozyme and BPN, most of the enzyme adsorbed onto the model surface within ten seconds. Nearly an order-of-magnitude more BPN adsorbed on the hydrophobic Ge surface than the hydrophilic one, while lysozyme adsorbed somewhat more strongly to the hydrophilic Ge surface. No changes in secondary structure were noted for either enzyme. The appearance of carboxylate bands in some of the adsorbed BPN spectra suggests hydrolysis of amide bonds has occurred. 

The Pt(l 11) surface alloyed by a small amount of Ge is a nice alloy substrate for studying the origin of the desorption activity in UV laser-induced desorption [87]. This surface alloy is prepared by repeated cycles of deposition of a few ML Ge and subsequent annealing to 1100°C until a constant Ge Auger electron signal was obtained. The total amount of Ge contained in several surface layers of this alloy is 0.1 ML and the Ge coverage in the top layer is 0.04 ML due to a 5 x 5 structure observed by STM [88]. Fukutani et al. call this surface the Pt(l 1 1)-Ge surface alloy. 

When ArF excimer laser irradiates the Pt( 111 )-Ge surface alloy saturated by NO or CO at 80 K, desorbed NO molecules are detected by the REMPI method, while no CO desorption is observed [87]. Only a little modification of the Pt(l 1 1) surface brings such a remarkable change of the desorption activity. TDS of NO from the alloy at various NO coverages is shown in Fig. 29. Every spectrum has a prominent peak at 220 K, and NO is saturated at 0.2 L exposure in contrast with Pt(l 1 1), on which NO is saturated at 2 L exposure and saturation coverage is 0.75 ML. 

Figure 30 Rotational energy distribution of NO (v = 0) desorbed from the Pt(l 1 1)-Ge surface alloy at 90 K at 193 nm. Filled circle Q = 1/2, open circle Q = 3/2 [60].

Finally, we would like to make a scenario of the desorption activity for NO and CO desorption from Pt(l 1 1) and Pt(l 1 1)-Ge surface alloy. This scenario will be extended to a general concept of desorption in the DIET process of simple molecules from metal surfaces. The lifetime and the critical residence time in the intermediate excited state followed by desorption are important keys for solving what is the origin of the desorption activity in the DIET process from metal surfaces. The excited molecules are not desorbed, if the residence time in the excited state is shorter than the critical residence... 

The rotational temperature obtained from a linear relation in the Boltzmann plot of the rotational energy distribution is an index of the lifetime in the intermediate excited state and decreases with decreasing lifetime. The rotational temperature of CO desorbed from Pt(l 1 1) is very low as compared with that of NO desorption, i.e. the lifetime of the excited CO is supposed to be much shorter than that of NO. In the case of CO desorption from Pt(l 11), however, the lifetime is not obtained from the rotational energy distribution, since desorbed molecules are detected by the (2 + 1 )REMPI method in the experiment [ 12] and then the single rotational states are not resolved. On the other hand, the rotational temperature of NO desorbed from Pt(l 1 1)-Ge surface alloy is lower than that from Pt(l 1 1). Then, it is speculated that the lifetime of the excited CO on the alloy is shorter than that on Pt( 111) and the residence time of the excited CO on the alloy is too short to be desorbed. As a consequence, the excited CO molecules are recaptured in the relaxation without desorption. However, it has not been understood why the lifetime of the excited CO molecule (or the excited CO-Pt complex) on Pt( 1 1 1) is shorter than that of the excited NO molecule (complex) on Pt(l 11), and further on the Pt-Ge alloy as compared with Pt(l 1 1). 

Positive charges either trapped or formed because of adsorption on Ge surfaces produce... 

Given the very high level of technological infrastructure that already exists for these elemental semiconductors because of microelectronics applications, it is not surprising that both these materials were examined early on in the evolution of the field of photoelectrolysis of water. As mentioned in an introductory paragraph, cathodic reduction of the Ge surface is accompanied by H2 evolution.58,559 However, we are not aware of studies under irradiation of Ge electrodes from a HER or OER perspective. The extreme instability of this semiconductor in aqueous media coupled with its low band gap (Eg = 0.66 eV) make it rather unattractive for water photosplitting applications. 

For the dissociative adsorption of hydrogen on the Ge surface, the equation analogous to (10-84) is... 

Ortyl TT, Peck GE. Surface charge of titanium dioxide and its effect on dye adsorption and aqueous suspension stability. Drug Dev Ind Pharm 1991 17 2245-2268. 

Metallic Li deposited on Si and Ge surfaces is heated in a closed tube in a He atmosphere at 450-1000°CL The Li-diffused layer is n-type. The doping layer consists of Li2Si -I- Si, especially above the eutectic temperature of 650°C. The dimorphic silicide, Li4Si, may also be formed, depending on the composition of the Li-Si compound. ... 

The doping of Ge with Li is also carried out by spreading solutions of LiAlH4 and LiOH spread on the Ge surface. 

---