The interaction of water with solid surfaces: Fundamental aspects

The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Aqueous HF etching of silicon surfaces results in the removal of the surface oxide and leaves behind silicon surfaces terminated by atomic hydrogen. The effect of varying the solution pH on the surface structure is studied by measuring the SiH stretch vibrations with infrared absorption spectroscopy. Basic solutions ( pH=9–10) produce ideally terminated Si(111) surfaces with silicon monohydride ( 3/4 SiH) oriented normal to the surface. The surface is found to be very homogeneous with low defect density (<0.5%) and narrow vibrational linewidth (0.95 cm−1 ).

Ideal hydrogen termination of the Si (111) surface

Interaction of hydrogen with solid surfaces

Working memory is the process of maintaining an active representation of information so that it is available for use. In monkeys, a prefrontal cortical region important for spatial working memory lies in and around the principal sulcus, but in humans the location, and even the existence, of a region for spatial working memory is in dispute. By using functional magnetic resonance imaging in humans, an area in the superior frontal sulcus was identified that is specialized for spatial working memory. This area is located more superiorly and posteriorly in the human than in the monkey brain, which may explain why it was not recognized previously.

https://science.sciencemag.org/content/sci/279/5355/1347.full.pdf

An Area Specialized for Spatial Working Memory in Human Frontal Cortex

The adsorbed states of ethylene on the Si(100)c(4×2), Si(100)(2×1), and the Si(100) 9° vicinal surfaces have been studied using high resolution electron energy loss spectroscopy (EELS) and low‐energy electron diffraction (LEED). Ethylene is nondissociatively chemisorbed on the Si(100) surface in the wide temperature range between 77 and ∼600 K, and is rehybridized to have a near sp3 hybridization state. The adsorbed structure is proposed in which ethylene is di‐σ bonded to two adjacent Si atoms of the dimer at the Si(100) surface. The thermal decomposition of chemisorbed ethylene and the influence of steps on the adsorbed states of ethylene are discussed.

The adsorbed states of ethylene on Si(100)c(4×2), Si(100)(2×1), and vicinal Si(100) 9°: Electron energy loss spectroscopy and low‐energy electron diffraction studies

The adsorption and thermal decomposition of acetylene on Si(100) and vicinal Si(100)9

High resolution electron energy loss spectroscopy (vibrational and electronic excitations) and monochromatic low‐energy electron diffraction (LEED) have been applied to the study of atomic‐hydrogen adsorption on the Si(111) (7×7) surface at ∼300 K. Adsorbed states of hydrogen are differentiated by taking the vibrational loss spectra of the Si(111) surface exposed to various amounts of hydrogen and of the same surface subsequently heated to high temperatures. The existence of four adsorbed states is proposed. Hydrogen adsorption is considered to proceed as follows. In the very early stage (fractional hydrogen coverage θ≲0.3), the SiH species are produced by the covalent bond formation of hydrogen atoms with the dangling bonds of the Si(111) surface atoms. Then, the Si–Si bond breaking and the desorption of SiH4 and, possibly, SiH3 occur, and the corrosion‐induced SiH (with the bond axes parallel to and away from the surface‐normal direction), SiH2, and SiH3 species are also produced. The hydrogen coverage is saturated at θ∼1.5, where the amount of the SiH2 and SiH3 species formed is estimated to be <1/4 of that of the total SiH species. The electronic transition associated with the SiH species is observed at 9.1 eV for low hydrogen exposure, which is shifted to lower energy by the increase in the exposure. Corrosion‐induced surface roughening is reflected in the high background and in the degradation of the 1/7 order beam intensities of LEED angular profiles. Patch formation of the SiH, SiH2, and SiH3 species is evident from the slow decay of the 1/7 order beam intensities.

Reactions of atomic hydrogen with the Si(111) (7×7) surface by high resolution electron energy loss spectroscopy

High-resolution vibrational electron-energy-loss spectroscopy has been used to study the interaction of ${\mathrm{NH}}_{3}$ with the Si(100)-(2\ifmmode\times\else\texttimes\fi{}1) surface. ${\mathrm{NH}}_{3}$ is decomposed on the Si(100) surface at 300 K to form the ${\mathrm{SiNH}}_{2}$ and SiH species. It is proposed that the amino (${\mathrm{NH}}_{2}$) species is bonded to the dangling bond of the Si(100) surface atom. Changes in the adsorbed state of both species under heat treatment are discussed.

Electron-energy-loss spectra of the Si(100)-(2×1) surface exposed to NH 3

The adsorbed state of ethylene on Pd(110) at 90 K and its thermal decomposition in the temperature region between 90 and 600 K have been studied by the use of high resolution electron energy loss spectroscopy (EELS), low‐energy electron diffraction (LEED), and thermal desorption spectroscopy (TDS). At 90 K, ethylene is π bonded to the Pd(110) surface and is adsorbed almost disorderedly. The c(2×2)‐C2H4 patches are formed near the saturation coverage (which corresponds to 0.58 C2H4 molecule per surface Pd atom). By heating the C2H4‐saturated Pd(110) surface to 260 K, some C2H4 admolecules are desorbed intact and the remaining admolecules rearrange their adsorbed sites to form the c(2×2)‐C2H4 structure. At above 300 K, almost all the C2H4 admolecules are dehydrogenated, and the ethynyl (CCH) species, H adatoms and unstable dehydrogenated species [possibly, vinyl (CHCH2) species] are formed; the C2H4 desorption occurs by the recombination of H adatoms and dehydrogenated species. The remaining H adatoms are d...

Chemisorption and thermal decomposition of ethylene on Pd(110): Electron energy loss spectroscopy, low‐energy electron diffraction, and thermal desorption spectroscopy studies

M. Onchi

Papers

The adsorbed states of ethylene on Si(100)c(4×2), Si(100)(2×1), and vicinal Si(100) 9°: Electron energy loss spectroscopy and low‐energy electron diffraction studies

The adsorption and thermal decomposition of acetylene on Si(100) and vicinal Si(100)9

Reactions of atomic hydrogen with the Si(111) (7×7) surface by high resolution electron energy loss spectroscopy

Electron-energy-loss spectra of the Si(100)-(2×1) surface exposed to NH 3

Chemisorption and thermal decomposition of ethylene on Pd(110): Electron energy loss spectroscopy, low‐energy electron diffraction, and thermal desorption spectroscopy studies