Long-range structures on the dihydride Si(001) surface

From several large supercell MD simulations with an empirical tight-binding method, we have found the long-range structure on the dihydride Si(001) surface. This structure can be viewed as the well-known canted phase with domain walls. The formation energy of a single domain wall on the surface is estimated to be 1.3–1.5 eV.     

True atomic resolution imaging of surface structure and surface charge on the GaAs(110)

We demonstrated a novel method to detect the van der Waals and the electrostatic force interactions simultaneously on an atomic scale, which is based on frequency modulation detection method. For the first time, the surface structure and the surface charge at atomic-scale point defects on the GaAs(110) surface have been simultaneously resolved with true atomic resolution under ultra-high vacuum condition. From the bias voltage dependence of the image contrast, we can verify that the sign of the atomically resolved surface charge at the point defect was positive.     

Adsorption sites of Ge adatoms on stepped Si(110) surface

We have investigated the possible adsorption sites of Ge adatoms on stepped Si(110) surface by total electronic energy calculations using the empirical tight-binding method. It has been found that Ge adatoms prefer to bond to the Si atoms at or near the step. In the case of more than one adatom the minimum total electronic energy configuration corresponds to the maximum number of saturated Si atoms.     

Submonolayer structures of Ce adsorbed on Mo(110) surface

The surface structure of Ce adsorbed on a Mo(110) surface was studied by reflection high energy electron diffraction. Five kinds of surface structures were found with different deposition coverages in the submonolayer region. These structures have a common feature that Ce atoms possess a periodicity with double spacing at the atomic rows in the Mo[ 10] direction. Observed at 1 ML of Ce coverage was a surface structure related to a deformed fcc Ce(111) plane.     

Anisotropic interaction of Ag-induced missing dimer vacancies on Si(001) surfaces

Ag-induced missing dimer vacancies on Si(001)2 × 1 surfaces are shown to form vacancy lines when the vacancy concentration is larger than ∼10%. The formation of the vacancy lines is driven by the short-range attractive interaction between the vacancies in adjacent dimer rows and the long-range repulsive interaction between them in the same dimer row. The form and magnitudes of the interactions are derived from the thermally-excited wandering of the vacancy lines.     

Leaky pseudo surface wave on the water–Si(110) interface

The present letter demonstrates that a leaky pseudo surface wave (LPSW) should exist on the interface of water and a cubic crystal silicon (110) plane. The phase velocity distribution of the LPSW on the above interface has been theoretically predicted by the reflection coefficient analysis and experimentally measured by using acoustic spectro-microscopy (ASM). The measured phase velocity distribution of the LPSW is in good agreement with the predicted one.     

Dopant-pair structures segregated on a hydrogen-terminated Si(100) surface

Novel atomic structures on a H-terminated Si(100)-(2x1)-H surface were found using scanning tunneling microscopy (STM). The structures are distinguishable only from Si dimers in empty-state STM images. They were observed on arsenic- and phosphorus-doped substrates, but not on boron-doped substrates. Surface density of these structures was found to be proportional to the dopant density in the substrate. First-principles calculations clarify that they are consisting of dopant pairs that are segregated from the bulk material. Hydrogen atoms attached to the dopant pair are found to flip between two positions on the surface due to a quantum effect.     

Sulfur dioxide adsorption and reaction with atomic oxygen on the Ag(110) surface

The adsorption of SO₂ on Ag(110) and the reaction of SO₂ with oxygen adatoms have been studied under ultrahigh vacuum conditions using low energy electron diffraction, temperature programmed reaction spectroscopy and photoelectron spectroscopy. Below 300 K, SO₂ adsorbs molecularly giving p(1×2) and c(4×2) LEED patterns at coverages of one half and three quarter monolayers. respectively. At intermediate coverages, streaked diffraction patterns, similar to those reported for noble gas and alkali metal adsorption on the (110) face of face-centered cubic metals were observed, indicating adsorption out of registry with the surface. A feature at low binding energy in the ultraviolet photoemission spectrum appeared which was assigned to a weak chemisorption bond to the surface via the sulfur, analogous to bonding observed in SO₂-amine charge transfer complexes and in transition metal complexes. SO₂ exhibited three binding states on Ag(110) with binding energies of 41, 53 and 64 kJ mol^?1; no decomposition on clean Ag(110) was observed. On oxygen pretreated Ag(110), SO₂ reacted with oxygen adatoms to form SO_3(a), as determined by X-ray photoelectron spectroscopy. Reacting preadsorbed atomic oxygen in a p(2 × 1) structure with SO₂ resulted in a c(6 × 2) pattern for SO_3(a). The adsorbed SO_3(a) decomposed and disproportionated upon heating to 500 K to yield SO_2(g), SO_4(a) and subsurface oxygen.     

Long-range surface reconstruction: Si(110)-(16 x 2)

A variety of reconstruction models is studied for the Si(110)-(16 x 2) surface using first-principles calculations. Assuming appropriate rebonding of edge atoms and surface chains buckled in antiphase, we show that steps along the [112] direction yielding a trench indeed lower the surface energy. We explain the long-range surface reconstruction and develop a geometry model based on steps, adatoms, tetramers, and interstitials. The model is able to explain the stripes of paired pentagons seen obviously in empty-state scanning tunneling microscopy images.     

Comments on the structures observed for atomic adsorption on (110) surfaces of face-centred cubic metals

The hybridisation model for face-centred cubic metals, proposed by Altmann, Coulson and Hume-Rothery, is used for analysing some aspects of the surface structures reported by LEED crystallography for S adsorbed on the (110) surfaces of nickel and rhodium, and for O adsorbed on the (110) surfaces of nickel and iridium. The main objectives are to rationalise the different adsorption sites adopted by S and O, and to assess the measured bond lengths. For the latter, use is made of a bond length-bond order relationship given by Pauling.     

Change of the surface induced optical anisotropy of the clean Si(110) surface by oxidation

Normal incidence ellipsometry has been used to measure the change in the complex anisotropic reflectance ratio γ upon oxidation of the clean Si(110)16 × 2 surface. The spectroscopic change in the amplitude of γ (tan(Ψ)) shows a broad maximum of height 1.4 × 10⁻³ in the high energy region above 2.5 eV. No phase shift difference for the reflectance coefficients belonging to the surface principal optical axes has been measured. A Kramers-Kronig transformation of the amplitude ratio showed that a change in the phase is not expected. The change in tan(Ψ) indicates that the change in reflection upon oxidation in the optical region ismainly in the ( 10) direction.     

Mechanisms for oxygen adsorption on the Si(110) surface studied by Auger electron spectroscopy

Oxygen adsorption on the Si(110) surface has been studied by Auger electron spectroscopy. For a clean annealed surface chemisorption occurs, with an initial sticking probability of ～6 × 10^?3. In this case the oxygen o_kll signal saturates and no formation of SiO₂ can be detected from an analysis of the Si L_2,3VV lineshape. With electron impact on the surface during oxygen exposure much larger quantities are adsorbed with the formation of an SiO₂ surface layer. This increased reactivity towards oxygen is due to either a direct effect of the electron beam or to a combined action of the beam with residual CO during oxygen inlet, which creates reactive carbon centers on the surface. Thus in the presence of an electron beam on the surface separate exosures to CO showed adsorption of C and O. For this surface subsequent exposure in the absence of the electron beam resulted in additional oxygen adsorption and formation of SiO₂. No adsorption of CO could be detected without electron impact. The changes in surface chemistry with adsorption are detectable from the Si L_2,3VV Auger spectrum. Assignments can be made of two main features in the spectra, relating to surface and bulk contributions to the density of states in the valence band.     

Type of the second hole subband on the Si(110) surface: Spin splitting anisotropy

Magnetoresistance measurements have been performed for the cases of one and two occupied size-quantization hole subbands in silicon field-effect transistors prepared on the Si (110) surface. In both cases, Shubnikov-de Haas oscillations exhibit very weak sensitivity to the in-plane component of the magnetic field. This indicates that both lowest subbands are formed by heavy holes. This conclusion disagrees with the wide-spread opinion that the second subband is the ground subband of light holes in the system under consideration.     

An STM study of desorption-induced thallium structures on the Si(111) surface

The scanning tunneling microscopy is used to study morphology of a Tl adlayer in various stages of Tl desorption from the Si(111) surface. Transition from the Si(111)/(1 × 1)-Tl structure through the (√3 × √3)R30° mosaic phase to domains of metastable Si reconstructions is observed. Silicon substitutional atoms are found to be intrinsic to the (√3 × √3)R30° structure. The temperature dependence of the amount of residual Tl atoms on the surface is successfully fitted by a model using the first order desorption. The same desorption energy of (2.1 ± 0.3) eV and frequency prefactor 5 × 10^14 ± 2 s^? 1 during all stages of the desorption are sufficient for the fitting. It is concluded that bonding of Tl in both (1 × 1) and (√3 × √3) configurations is of the same nature.