Chemisorption of Au on Si（001） surface

The chemisorption of one monolayer of Au atoms on an ideal Si(001) surface is studied by using the self-consistent tight binding linear muffin-tin orbital method. Energies of the adsorption system of a Au atom on different sites are calculated. It is found that the most stable position is A site (top site) for the adsorbed Au atoms above the Si(001) surface. It is possible for the adsorbed Au atoms to sit below the Si(001) surface at the B_1 site(bridge site), resulting in a Au－Si mixed layer. This is in agreement with the experiment results. The layer projected density of states is calculated and compared with that of the clean surface. The charge transfer is also investigated.     

Phosphine dissociation on the Si(001) surface

Density functional calculations are performed to identify features observed in STM experiments after phosphine (PH3) dosing of the Si(001) surface. On the basis of a comprehensive survey of possible structures, energetics, and simulated STM images, three prominent STM features are assigned to structures containing surface bound PH2, PH, and P, respectively. Collectively, the assigned features outline for the first time a detailed mechanism of PH3 dissociation and P incorporation on Si(001).     

Second-harmonic spectroscopy of Ge/Si(001) and Si1-xGex(001)/Si(001)

0.9 Ge_0.1(001)/Si(001) films with SH photon energies 3.1<2hν<3.5 eV near the bulk E₁ critical point of Si(001) or Si_0.9Ge_0.1(001). Ge was deposited on Si(001) by using atomic layer epitaxy cycles with GeH₄ or Ge₂H₆ deposition at 410 K followed by hydrogen desorption. As Ge coverage increased from 0 to 2 monolayers the SH signal increased uniformly by a factor of seven with no detectable shift in the silicon E₁ resonant peak position. SH signals from Si_0.9Ge_0.1(001)/Si(001) were also stronger than those from intrinsic Si(001). Hydrogen termination of the Si_0.9Ge_0.1(001) and Ge/Si(001) surfaces strongly quenched the SH signals, which is similar to the reported trend on H/Si(001). We attribute the stronger signals from Ge-containingsurfaces to the stronger SH polarizability of asymmetric Ge-Si and Ge-Ge dimers compared to Si-Si dimers. Hydrogen termination symmetrizes all dimers, thus quenching the SH polarizability of all of the surfaces investigated. Received: 13 October 1998 / Revised version: 18 January 1999     

STM observation of pit formation and evolution during the epitaxial growth of Si on Si(001) surface

Pit formation and surface morphological evolution in Si(001) homoepitaxy are investigated by using scanning tunneling microscopy. Anti-phase boundary is found to give rise to initial generation of pits bound by bunched D B steps. The terraces break up and are reduced to a critical nucleus size with pit formation. Due to anisotropic kinetics, a downhill bias diffusion current, which is larger along the dimer rows through the centre area of the terrace than through the area close to the edge, leads to the prevalence of pits bound by {101} facets. Subsequent annealing results in a shape transition from {101}-faceted pits to multi-faceted pits.     

Chemisorption of Fe on Au-passivated Si（001） surface

The chemisorption of one monolayer of Fe atoms on a Au-passivated Si(001) surface is studied by using the self-consistent tight-binding linear muffin-tin orbital method. The Fe adatom chemisorption on an ideal Si(001) surface is also considered for comparison. The chemisorption energy and layer projected density of states for a monolayer of Fe atoms on Au-passivated Si(001) surface are calculated and compared with that of the Fe atoms on an ideal Si(001) surface. The charge transfer is investigated. It is found that the most stable position is at the fourfold hollow site for the adsorbed Fe atoms, which might sit below the Au surface. Therefore there will be a Au－Fe mixed layer at the Fe/Au－Si(100) interface. It is found that the adsorbed Fe atoms cannot sit below the Si surface, indicating that a buffer layer of Au atoms may hinder the intermixing of Fe atoms and Si atoms at the Fe/Au－Si(001) interface effectively, which is in agreement with the experimental results.     

Si(001)表面稀土金属硅化物纳米结构

稀土金属元素的硅化物在n型硅衬底上具有高电导率和低肖特基势垒的特点,在大规模集成的微电子器件领域具有很好的应用价值.文章系统介绍了在Si(001)表面自组装生长的稀土金属硅化物纳米结构的研究进展,较全面地讨论了退火温度、退火时间以及稀土金属表面覆盖度等生长条件对纳米结构生长的影响作用,并在此基础上分析了纳米线、纳米岛的晶化结构,衬底对纳米结构生长的影响,以及纳米结构的演化过程.搞清楚这些内在的生长机理,有助于人们今后实现可严格控制稀土金属硅化物纳米结构的形貌尺寸和分布的自组装生长.此外,文章还介绍了目前人们对稀土金属硅化物纳米线电学性质的研究进展.     

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.     

Oxidation of the Si(001) surface: lateral growth and formation of P(b0) centers

More than 100 oxygen-adsorbed configurations with oxygen coverage of up to two monolayers (ML) were studied through first-principles calculations. It was found that oxidation proceeds almost laterally. When the coverage exceeds 1.25 ML, oxygen atoms introduced between the second and third layers are captured at a bridging site in the second layer, generating twofold-coordinated Si atoms. Emission of such twofold-coordinated Si atoms leaves weakly bonded Si pairs in the fourth layer. When such pairs happen to be generated close to each other, they transform into a chain of Si trimers with one P(b0) center at each end.     

Characterization of epitaxial MgO growth on Si(001) surface

MgO epitaxial growth on a Si(001) surface by ultrahigh-vacuum molecular beam epitaxy was investigated. Epitaxial orientation and crystalline quality were characterized based on the three-dimensional reciprocal map obtained by Weissenberg RHEED. The epitaxial orientation and crystallinity were strongly dependent on the initial condition of the substrate. When MgO was deposited on a clean Si(001) surface at room temperature a MgO(001) film grew on the Si(001) substrate with two in-plane orientations:MgO[110]//Si[100] and MgO[100]//Si[100]. This is the first observation of MgO epitaxy with the former orientation, which has a smaller mismatch than the latter orientation. When the substrate was exposed to O₂ or thermally oxidized, the latterorientation predominantly grew on the substrate. Deposition of Mg on the substrate also produced the latter orientation. These results imply that nucleation sites on the initial substrate play an important role in determining the epitaxial orientation.     

Barrierless formation and faceting of SiGe islands on Si(001)

The initial stages of the formation of SiGe islands on Si(001) pose a long-standing puzzle. We show that the behavior can be consistently explained by one simple assumption-that for strained SiGe, (001) is a stable orientation but not a facet orientation. Calculations of energy and morphology reproduce the key features of "prepyramid" and "pyramid" islands, and explain the initial formation and subsequent shape transition. Scanning tunneling microscopy measurements confirm the key assumptions and predictions of the model.     

Surface electromigration of metals on Si(001): In/Si(001)

The possibility of surface electromigration (SE) of metals of In, Ga, Sb and Ag on a very flat Si(001)2×1 substrate (single domain 2×1) was examined by SEM, μ-RHEED and μ-AES under UHV conditions. It was found that Ga, Sb and Ag show no SE on Si(001) surface even at DC annealing temperatures for the desorption of these metals. For In on Si(001), a very fast SE (8000 μm/min) towards the cathode side was found that suddenly sets in at 450°C DC annealing, which was related to a surface phase transition. μ-RHEED and μ-AES observation showed that the SE is related to an ordered 4×3-In phase together with two-dimensional In gas phase over the 4×3-In phase and an In-disordered phase at the front end of SE. Single domain 4×3-In phases were found to occur under sequences of In deposition and DC annealing which involve the In SE on Si(001).     

Formation mechanism of one-dimensional Si islands on a H/Si(001) surface

The formation mechanism of one-dimensional Si islands on a H/Si(001)-(2x1) surface is studied using scanning tunneling microscopy/spectroscopy and first-principles calculations. We observed that one-dimensional islands that are made from dimer chains are formed at the initial growth stages similar to the bare Si(001) surface. It is found that the number of odd-numbered dimer chains is larger than that of even-numbered dimer chains. We propose the growth processes of the two types of growth edges to explain the observation.