Leed studies of vicinal surfaces of silicon

Clean silicon surfaces inclined at small angles to (111), (100) and (110) planes were investigated by LEED. Surfaces oriented at low angles to the (111) plane contain steps with edges towards [2̄11] or [21̄1̄]. Steps with edges towards [2̄11] have a height of two interplanar distances d₁₁₁ at low temperatures. At 800°C the reversible reconstruction of this step array into the steps of monolayer height takes place. Steps with edges towards [21̄1̄] can be seen at low temperatures only. They are of monolayer height and disappear at annealing in vacuum. Surfaces oriented at low angles to the (100) plane contain steps with (100) terraces and have a height of about two interplanar distances d₁₀₀. Surfaces at low angles to (110) planes are facetted and contain facets of the (47 35 7) type. The information about surface self-diffusion of silicon may be obtained using the kinetic data of structural reconstructions on surfaces close to (111) at different temperatures.     

Grafting of 1-alkynes to hydrogen-terminated (100)silicon surfaces

Hydrogen-terminated, atomically flat, 1×1 (un)reconstructed, (100)-oriented, silicon surfaces have been functionalized with 1-octyne and then studied via X-ray photoelectron spectroscopy. The C 1s signal shows that the addition of the hydrocarbon chain occurs through the formation of environmentally stable Si-C bonds, in agreement with hydrosilation as the major grafting route. PACS 82.65.+r; 68.39.-p; 73.20.-r; 79.60.Jv     

Leed measurements of Fe epitaxially grown on Cu(100)

Iron was epitaxially grown on a Cu(100) surface. Low energy electron diffraction (LEED) intensity versus energy curves were recorded for 1 and 10 layers of iron on Cu(100) at room temperature. A full dynamical analysis was performed using the renormalized forward scattering perturbation method. The surface Debye temperatures were determined to be 233 K for 1 ML Fe and 380 K for 10 layers of Fe. The value obtained for fcc iron was 550 K. A multiple relaxation approach was employed in analyzing the experimental data. The estimated interlayer spacings for the first and second layers were 1.78±0.02 Å (first) and 1.81±0.02 Å (second) for 1 ML Fe, and 1.81±0.02 Å (first) and 1.78±0.02 Å (second) for 10 layers of Fe on Cu(100). Auger electron spectroscopy was used to determine the thickness of the Fe films, and the LEED measurements indicate approximately a layer-by-layer growth until about 17 layers at room temperature. At higher temperatures there is evidence of iron diffusion or copper surface segregation.     

Theoretical study of oxygen chemisorption on (111) and (100) silicon surfaces

The chemisorption of atomic oxygen on (111) and (100) silicon surfaces has been studied by the MNDO method using a cluster approach. The results show that, for both surfaces, chemisorption occurs preferentially on bridge positions, but chemisorption on top positions can play a significant role especially for the (111) surface.     

An alternative model of the reconstructed (100) surfaces of gold,platinum and iridium

Gold, platinum and iridium (100) clean surfaces are reconstructed, the widely accepted model of the reconstruction is that the top layer is a slightly compressed hexagonal (111) plane. The aim of this paper is to show that there is an alternative model to explain the reconstruction that requires very little displacement of the surface atoms. No proof can be given of either model, but both of them should be used in LEED intensity calculations.     

Leed debye-waller analysis of vibrational hybridization for p(2 × 2)-O/Pd(100)

The temperature dependence of the 75 eV specular LEED beam intensity was measured between ～100–300°C and ~50–200°C for clean p(1 × 1) and quarter-monolayer O-covered p(2 × 2) Pd(100), respectively. The experiments were performed in a near-normal-incidence geometry to increase sensitivity to vibrations perpendicular to the surface, which include the high-energy, HRELS-active O-stretch mode. The measurements indicate that the effective meansquare displacements were ～40% larger for the clean surface than for the bulk, in qualitative agreement with expectation, and were increased another 20% for the O-chemisorption structure. This observed increase in the Debye—Waller effect upon chemisorption is interpreted to suggest hybridization between the substrate phonon continuum and the high-energy, O-stretch modes. As a result of the hybridization oxygen would have a vibrational component within the substrate continuum that would dominate the magnitude of the oxygen mean-square displacements. A bulk impurity model due to Mannheim is invoked for numerical simulation of such hybridization effects and to serve as an analogy with the surface problem. It is shown that this analogy can be extended to describe resonant modes on a clean surface, and the force-constant increases necessary to create local modes at step defects, in agreement with more realistic treatments. It is shown also that vibrational hybridization can significantly influence the choice of the appropriate adsorbate Debye temperature — an important contrast parameter — that enters into dynamical LEED calculations.     

On the interaction of halogen atoms with (111) and (100) surfaces of silicon

The chemisorption of F, Cl, Br, and I atoms on the (111) and (100) surfaces of silicon has been studied by the MNDO method and using clusters of Si atoms to simulate the substrate. In the case of the adducts F-Si₄H₉ and Cl-Si₄H₉ the MNDO results are in close agreement with previous ab-initio ones concerning both the equilibrium distances and the chemisorption energies. For all the cases considered, the binding energy decreases in the order F>Cl>Br>I. The most stabel adduct is always obtained upon chemisorption at the bridge position on the (100) surface. Chemisorption at on-top positions leads to slightly less stabel adducts and is nearly isoenergetic on (100) and (111) surfaces. All the results are essentially insensitive to the dimensions of the clusters used to simulate the substrate.     

The adsorption of hydrogen on the (100) surfaces of silicon and diamond

Energy and structural calculations of hydrogen interacting with 9-atom clusters modelling the (100) surfaces of silicon and diamond, using the MINDO/3 and MNDO semiempirical quantum chemistry procedures, are reported. The equilibrium structure of the monohydride phases are symmetric dimers with stretched dimer bond lengths (2.53 Å for Si and 1.67 Å for C). The dihydrides have bulk-like structures with the H layer raised about 20% relative to tetragonal layer separations. We show that the dimer bonds on the monohydride phases are unstable against corrosion by atomic hydrogen (in contrast to the back bonds) and that there is a large difference between the desorption energies of the two phases, in agreement with the observed difference in thermal desorption temperatures. Values are calculated for the work function changes on formation of both hydride phases.     

Laser writing of a subwavelength structure on silicon (100) surfaces with particle-enhanced optical irradiation

Spherical 0.5-μm silica particles were placed on a silicon (100) substrate. After laser illumination with a 248-nm KrF excimer laser, hillocks with size of about 100 nm were obtained at the original position of the particles. The mechanism of the formation of the subwavelength structure pattern was investigated and found to be the near-field optical resonance effect induced by particles on the surface. Theoretically calculated near-field light intensity distribution was presented, which was in agreement with the experimental result. The method of particle-enhanced laser irradiation has potential applications in nanolithography.     

(111) facets as the origin of reconstructed Au(110) surfaces

The Au(110) surface has been investigated by scanning tunneling microscopy. The reconstructed surface consists of long ribbons of narrow (111) facets along the [1$\text{1}$0] direction with maximum three free rows. Two-row facets give rise to the 1 × 2 reconstruction of the missing-row type, while three-row facets account for the 1 × 3 reconstruction. Disorder arises from locally random sequences of the two facets.     

First-principles study on energetics of cBN(001) reconstructed surfaces

Total energies of various reconstructed configurations of cubic boron nitride (001) surfaces are studied systematically by the local density functional approach with ultrasoft pseudopotentials. Stable phases as a function of nitrogen chemical potential are predicted theoretically. Furthermore, we examine the validity of the electron counting rule, which plays an important role in the GaAs study, and obtain the supplemental factors to determine stable surface structures. The difference between cBN and GaAs surfaces is also discussed.     

Optical second-harmonic investigations of the isothermal desorption of SiO from the Si(100) and Si(111) surfaces

The isothermal desorption of SiO from the Si(100) and Si(111) surfaces was investigated by means of optical second-harmonic generation (SHG). Due to the high adsorbate sensitivity of this method, desorption rates could be measured over a wide range from 10⁻¹ to 10⁻⁶ ML s⁻¹. From their temperature dependence between 780 and 1000 K, activation energies of E_A=3.4±0.2 eV and E_A=4.0±0.3 eV and pre-exponential factors of ν₀=10^16±1 s⁻¹ and ν₀=10^20±1 s⁻¹ for SiO desorption were obtained for Si(100) and Si(111), respectively. In the case of the Si(100) surface, a pronounced decrease of the first-order rate constants was observed upon increasing the initial coverage from 0.02 to 0.6 ML. The results are interpreted in terms of coverage-dependent oxygen-binding configurations, which influence the stability of the oxide layer.