Order-disorder transition on Si(001)

A phase transition between c(4x2) and 2x1 structures on the Si(001) surface has been observed at 200 K by low-energy electron diffraction. This transition is a second order order-disorder transition of the asymmetric dimer configuration. The streak pattern remains up to well above the transition temperature. The temperature dependence of the width and the length of the streak can be described in terms of the effects of a strong anisotropic coupling between adjacent asymmetric dimers.     

Pathway for the strain-driven two-dimensional to three-dimensional transition during growth of Ge on Si(001)

The two-dimensional (2D) to three-dimensional (3D) morphological transition in strained Ge layers grown on Si(001) is investigated using scanning tunneling microscopy. The initial step takes place via the formation of 2D islands which evolve into small ( approximately 180 A) 3D islands with a height to base diameter ratio of approximately 0.04, much smaller than the 0.1 aspect ratio of 105-faceted pyramids which had previously been assumed to be the initial 3D islands. The "prepyramid" Ge islands have rounded bases with steps oriented along <110> and exist only over a narrow range of Ge coverages, 3.5-3.9 monolayers.     

Structural phase transition on Si(001) and Ge(001) surfaces

Among a variety of solid surfaces, Si(001) and Ge(001) have been most extensively studied. Although they seem to be rather simple systems, there have been many conflicting arguments about the atomic structure on these surfaces. We first present experimental evidence indicating that the buckled dimer is the basic building block and that the structural phase transition between the low-temperature c(4x2) structure and the high-temperature (2x1) structure is of the order-disorder type. We then review recent theoretical work on this phase transition. The real system is mapped onto a model Ising-spin system and the interaction parameters are derived from total-energy calculations for different arrangements of buckled dimers. The calculated critical temperature agrees reasonably well with the experimental one. It is pointed out that the nature of the phase transition is crucially affected by a small amount of defects on the real surfaces.     

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.     

Effect of strain on the appearance of subcritical nuclei of ge nanohuts on Si(001)

Real-time scanning tunneling microscopy observations of nucleation and heteroepitaxial growth of Ge nanocrystals (from germane) on Si(001) indicate that in the absence of Si-Ge intermixing the formation of full hut cluster islands is preceded by the nucleation of "subcritical" nuclei consisting of two adjacent truncated tetrahedral pyramids, which, upon unification, form a tiny square-based pyramidal "critical nucleus" It is suggested that such a precursor aids in surpassing the nucleation barrier and that the recently reported gradual faceting of prepyramids is characteristic of only Ge(Si) alloys.     

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     

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.     

Room-temperature epitaxial growth of CeO2(001) films on YSZ buffered Si(001) substrates

2 (001) epitaxial thin films deposited on Si(001) with yttria-stabilized zirconia buffers have been obtained for the first time at room temperature by pulsed-laser deposition. The influence of oxygen pressure on the crystal quality of CeO₂ was studied for the films deposited at 100 °C. The rocking curve full width at half maximum of the CeO₂(002) peak for films deposited at room temperature and 100 °C was between 1° and 2°, for oxygen pressures below 3×10^-2 mbar. The best crystal quality was obtained at around 3×10^-3 mbar. Epitaxial growth at room temperature was confirmed by cross-sectional transmission electron microscopy. Scanning electron microscopy and atomic force microscopy revealed very smooth surfaces for oxygen pressure below 3×10^-2 mbar, with rms roughness values around 0.3 nm over 5 μm×5 μm. Received: 25 September 1997/Accepted: 22 April 1998     

Dome-to-pyramid transition induced by alloying of Ge islands on Si(001)

Received: 19 October 1998/Accepted: 19 October 1998     

硅(001)图形衬底上锗硅纳米线的定位生长

纳米线的定位生长是实现纳米线量子器件寻址和集成的前提.结合自上而下的纳米加工和自下而上的自组装技术,通过分子束外延生长方法,在具有周期性凹槽结构的硅(001)图形衬底上首先低温生长硅锗薄膜然后升温退火,实现了有序锗硅纳米线在凹槽中的定位生长,锗硅纳米线的表面晶面为(105)晶面.详细研究了退火温度、硅锗的比例及图形周期对纳米线形成与否,以及纳米线尺寸的影响.     

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).     

First-principles molecular-dynamics study of native oxide growth on Si(001)

Through first-principles molecular dynamics we study the low-temperature oxidation of the Si(001) surface from the initial adsorption of an O2 molecule to the formation of a native oxide layer. Peculiar features of the oxidation process are the early, spontaneous formation of Si4+ species, and the enhanced reactivity of the surface while the reactions proceed, until saturation is reached at a coverage of 1.5 ML. The channels for barrierless oxidation are found to be widened in the presence of both boron and phosphorous impurities.     

铜（001）扭转晶界能的原子级计算

采用改进分析型嵌入原子法（MAEAM）计算了铜（001）未松弛扭转晶界的晶界能。结果表明，除扭转角为（完整晶体）时的能量为零外，对应和扭转角为36.87°时的晶界能为最小，和实验结果一致；对于其它扭转角，包括很小的扭转角1.94°，晶界能几乎为一常数；均匀膨胀和垂直于晶界面的膨胀都会使晶界能明显降低，尤其是后者。     

Novel pathway to the growth of diamond on cubic beta-SiC(001)

By carrying out first-principles calculations on diamond-forming processes, we predict a method for the heteroepitaxial growth of diamond on cubic beta-SiC(001). In the method, we used two processes: (i) the preformation of an sp(3)-like surface configuration of beta-SiC(001) by the adsorption of group-V surfactants; (ii) the successive growth of diamond by the segregation of the surfactants onto a surface and the desorption of surface hydrogen. Analyzing the segregation energies, we found that the atomic size effect plays a crucial role in the surfactant-mediated growth of diamond on beta-SiC(001).