Studying natural oxide on the surface of n-Si(111), n-Si(100), and p-Si(111) single crystal wafers by X-ray reflection spectroscopy

The state of the surface of standard phosphorus-doped n-Si(111) and n-Si(100) (KEF grade) and boron-doped p-Si(111) (KDB grade) single-crystal wafers treated in a 50% HF–70% HNO₃ (1: 3, v/v) polishing solution has been studied using soft X-ray reflection spectroscopy. The fine structure of the reflection spectra in the region of the Si L _2,3 ionization threshold has been analyzed. The dependence of the natural oxide thickness on the orientation of a silicon single crystal surface is established.     

Formation energies of two-dimensional nuclei randomly-generated on (001), (110), and (111) planes of a face-centered-cubic crystal

Monte-Carlo simulations of the two-dimensional crystal nucleus growth on (001), (110) and (111) crystal planes of a face-centeredcubic lattice have been conducted considering: (1) the adsorption of an atom from the surrounding gases, (2) its surface diffusion, (3) its annihilation, and (4) its being incorporated into the crystal nucleus. The energy of the formed nucleus was calculated using the bond-splitting model with reference to the energy of atoms at the half-crystal position and its dependence on the nucleus size were evaluated. The results implies that Pangarov's theory to explain the dependence of preferred orientation on the supersaturation might have to be amended in case above dynamic processes have a vital effect on the shape of nucleus of deposited thin films.     

Texture of CoSi2 films on Si(111), (110) and (001) substrates

Synchrotron radiation was used to study the texture of polycrystalline CoSi₂ films that were formed by a solid-state reaction between a 30 nm Co film and Si(111), (110) and (001) substrates. All films were strongly textured, and several texture components were identified. We discuss the simultaneous occurrence of axiotaxy (i.e. alignment of lattice planes across the interface) and several different types of epitaxy in each of the films. Comparison of the different texture components observed on the three substrate orientations suggests a strong preference for the alignment of CoSi₂{110} planes in the film with Si{110} planes in the substrate, and twinning around Si[111] directions.     

The growth and transformation of Pd2Si on (111), (110) and (100) Si

Thin Pd films on (111), (110), (100) and amorphous Si substrates form [001] fiber textured Pd₂Si in the temperature range 100°–700°C. The degree of texture is a function of substrate orientation, increasing in the order amorphous Si, (100) Si, (110) Si and (111) Si. Only on the (111) Si substrate is the Pd₂Si film epitaxially oriented. Temperature-dependent growth on this orientation can be characterized by [001] textured growth, epitaxial azimuth orientation at the Si interface and progressive layer by layer formation of the mosaic crystal to the thin film surface.During Pd deposition, rapid non-diffusion-controlled growth of epitaxial Pd₂Si on (111) Si occurs at substrate temperatures of 100° and 200°C. An unidentified palladium silicide of low crystallographic symmetry forms during Pd deposition onto a 50°C substrate. The diffusion-controlled growth of Pd₂Si on (111) Si follows a t^0.5 dependence. The velocity constant is

$\text{k = 7 × 10}{}^{\mathrm{?2}}\text{exp}\text{?}\text{29200±800}\text{RT}\text{cm}{}^2\text{/}\text{sec}$

Palladium deposited on 100°C (111) Ge substrates reacts during deposition to form epitaxially oriented Pd₂Ge. However, growth of this phase at higher temperatures results in a randomly oriented film. The transformation of Pd₂Ge to PdGe is kinetically controlled. After a 15 min anneal at 560°±10°C in N₂ only PdGe is detectable on (111) Ge.The high temperature stability of thin film Pd₂Si is controlled by time- temperature kinetics. For a given annealing cycle, the nucleation and growth rates of the PdSi phase are inversely related to the crystalline perfection of Pd₂Si. Decreasing transformation rates follow the order (100), (110), (111) Si. formation of thin film Pd₂Si occurs by the formation of PdSi and subsequent growth of Si within the PdSi phase. After a 30 min N₂ anneal, initial transformation occurs at 735°C on (100) Si, 760°C on (110) Si and 840°C on (111) Si. Extended high temperature annealing produces a two-phase structure of highly twinned and misoriented Si and small PdSi grains that penetrate as much as 3 μm into the Si.     

High-quality epitaxial Bi(111) films on Si(111) by isochronal annealing

Bi(111) films grown on Si(111) at room temperature show a significantly higher roughness compared to Bi films grown on Si(100) utilizing a kinetic pathway based on a low-temperature process. Isochronal annealing steps of 3 min duration each with temperatures up to 200 °C cause a relaxation of the Bi films' lattice parameter toward the Bi bulk value and yield an atomically flat Bi surface. Driving force for the relaxation and surface reordering is the magic mismatch of 11 Bi atoms to 13 Si atoms that emerges at annealing temperatures above 150 °C and reduces the remaining strain to less than 0.2%.     

Initial epitaxial growth of (111) Au/(111) Cu and (111) Cu/(111) Au

The room temperature modes of growth of Au/(111) Cu and Cu/(111) Au are described. For the former growth mode initial deposits (2.4 Å) of gold on copper form smooth flat islands delineated by coincidence lattice misfit dislocations. For 6.0 Å of gold deposit, both thick and thin gold areas were observed with almost complete substrate coverage. For a 10 Å deposit, surface coverage was complete. Strain measurements and dislocation densities obtained on the (111) Au/(111) Cu films suggest the presence of two separate misfit dislocation networks at the interface. The coincidence lattice networks were large enough for transmission electron microscopy observation but contributed little to total overlayer strain. The (van der Merwe) natural lattice misfit dislocations were too closely spaced for direct observation but their presence was inferred because of the strain measurements. The initial epitaxy of Cu/(111) Au was similar to the Stranski-Krastanov model: the initial monolayer of copper (also delineated by coincidence misfit dislocations) grew smoothly on the gold; additional copper formed essentially stress-free “nuclei” on top of the initial copper layer.     

Self-assembly of rubrene on Cu(111)

We performed an ultra-high vacuum scanning tunneling microscopy (STM) investigation of the self-assembly of rubrene at room temperature on Cu(111), a metal surface with threefold symmetry. Rubrene self-assembles into two different structures called row and trimer. Both are different than the structures already observed on Cu(110) and Cu(100). Row and trimer structures have comparable molecular packing densities and are equally distributed across the surface. In the row structure the molecules are oriented with their backbone along the same high symmetry directions of the surface: [[Formula: see text]], [[Formula: see text]] or [[Formula: see text]]. The trimer structure is composed of units of three rubrene molecules, oriented along the high symmetry surface directions. These units are chiral, as revealed by height profile measurements by STM, and self-assemble in domains containing only one type of enantiomer.     

Low-temperature epitaxy of transferable high-quality Pd(111) films on hybrid graphene/Cu(111) substrate

Nano Research - The continuous pursuit of miniaturization in the electronics and optoelectronics industry demands all device components with smaller size and higher performance, in which thin metal...     

Diffusion processes in the Au(111)/Ag(111) thin film system

The diffusion mechanisms of silver through Au(111) films 360 Å thick for different temperatures and heating times are studied. By means of quantitative Auger electron spectroscopy and in-depth profiling techniques the composition of the first monolayer and the composition profiles of diffused silver against time and heating temperature are determined. After elimination of instrumental effects the bulk silver interdiffusion coefficients for different temperatures and the activation energy of diffusion are obtained. The extrapolation stages allows the time required for the diffused onto the surface in the first diffusion stages allows the time required for the first appearance to be determined. Comparison with two standard expressions gives the corresponding grain-boundary diffusion coefficients and the activation energy. A numerical formalism, which includes the variation of composition at the interface but makes no allowance for grain boundary-grain diffusion, is tested esing the calculated coefficients. The agreement between the experimental results and the theoretical surface compositions is satisfactory within the limitations of the proposed model.     

Si基GaN紫外光探测器

报道了以Si(111)为衬底的GaN光导型紫钙探测器的制备及其光电流性质,探测器的光谱响应表明,这种GaN探测器在紫外波段250－360nm有近于平坦的光电流响应,36nm附近陡峭的截止边,在357nm波长处,测得5V偏压下的响应度高达6．9A／W。响应度随外加偏压的增加而增加,5V时达到饱和,通过拟合光电流响应随入射光调制频率的变化关系,得到GaN探测器的响应时间为4．8ms。     

Co nanoislands on Au(111) and Cu(111) surfaces studied by scanning tunneling microscopy and spectroscopy

Co nanoislands on the Au(111) and Cu(111) surfaces have been studied by scanning tunneling microscopy and spectroscopy. The experimental results showed that Co nanoislands prefer to aggregate at the step edge and dislocation sites on the reconstructed Au(111) surface and at the step edge on the Cu(111) surface, respectively. In addition, based on dZ/dV-V spectra, in both the Co/Au(111) and the Co/Cu(111) systems, Gundlach oscillation was observed. From the peak shift of dZ/dV-V spectra between Co nanoisland and substrate surface, we can quantitatively obtain that the constant energy separation is -0.13 +/- 0.01 eV for the Co/Au(111) system, and 0.41 +/- 0.02 eV for the Co/Cu(111) system, respectively. These values indicate the work function difference between Co nanoisland and these surfaces.     

Structural coherency of graphene on Ir(111)

Low-pressure chemical vapor deposition allows one to grow high structural quality monolayer graphene on Ir(111). Using scanning tunneling microscopy, we show that graphene prepared this way exhibits remarkably large-scale continuity of its carbon rows over terraces and step edges. The graphene layer contains only a very low density of defects. These are zero-dimensional defects, edge dislocation cores consisting of heptagon-pentagon pairs of carbon atom rings, which we relate to small-angle in-plane tilt boundaries in the graphene. We quantitatively examined the bending of graphene across Ir step edges. The corresponding radius of curvature compares to typical radii of thin single-wall carbon nanotubes.     

PTCDA on Cu(111) partially covered with NaCl

The organic molecule 3,4,9,10-perylene-tetracarboxylic dianhydride (PTCDA) was studied by means of scanning tunneling microscopy (STM) on thin insulating NaCl films grown on a Cu(111) single crystal. The deposition of approximately two monolayers (ML) of sodium chloride onto a Cu(111) substrate at a sample temperature of about 350 K causes a rather rough growth of (100)-oriented NaCl islands up to a local height of 4 ML. For submonolayer coverages (0.1 and 0.4 ML) of PTCDA on a Cu(111) surface partly covered with NaCl, two different rod structures of PTCDA were found on the copper surface, which are in contrast to previously published data for PTCDA on Cu(111) showing a herringbone-like arrangement. These findings can be explained by the formation of a Na(x)-PTCDA complex. On NaCl covered areas, single PTCDA molecules adsorb at vacancies of [010] and [001] oriented steps of the NaCl(100) islands. In this case, the electrostatic forces between the polar step edges and the PTCDA molecules are dominant. The terraces of the alkali halide surface are free of PTCDA molecules.     

Orientation of ethyl mercaptan on Cu(111) surface

X-Ray photoelectron spectroscopy (XPS) and near edge X-ray absorption fine structure (NEXAFS) studies have been performed on ethyl mercaptan adsorbed on a clean Cu(111) surface at 85 K. At submonolayer coverage (0.36 ML), two different states of sulfur (thiolate) are identified with the aid of XPS investigations. Polarization dependence of S K-edge NEXAFS of the submonolayer phase indicates that the S---C bond for the two thiolate phases are tilted 33±7° and 30±7° from the surface.     

Nucleation and growth of germanium on silicon (111)

The nucleation and growth of Ge on Si(111) substrates were investigated by transmission electron microscopy (TEM). It was found that growth is initiated by the formation of three-dimensional islands. At a very early stage of growth a polycrystalline layer was obtained. The orientation of this Ge film, however, improved as growth proceeded, resulting in an epitaxial film when the islands were fully coalesced. It was found that the major defects present in the Ge epilayer were microtwins (primary and secondary twins) occurring on the inclined {111} planes of Ge.     

Ag films formed simultaneously on (111) and (100) NaCl

The ranges of epitaxial deposition have been explored for Ag evaporated simultaneously under high vacuum onto three NaCl substrate surfaces designated (111), (100)_E and (100)_c. The first substrate consisted of a thin (111)-oriented monocrystalline NaCl film deposited onto air-cleaved mica. The substrate designated (100)_E consisted of a thin (100)-oriented monocrystalline NaCl film evaporated onto air-cleaved NaCl, and that designated (100)_c consisted of air- cleaved NaCl. The occurrence of monocrystalline and polycrystalline films and their microstructure were determined by transmission electron microscopy and diffraction as a function of deposition rare R and substrate temperature T. The results are presented on 1n R versus$\text{1}\text{T}$ plots. Activation energies for the transition from a low temperature polycrystalline region to a higher temperature monocrystalline region were determined as approximately 0.8 and 1.0 eV respectively for (111) and (100)_E NaCl substrates. No such transition was found in the case of (100)_c substrates. In the case of (100)_E substrates a steep high temperature demarcation line (activation energy 3.9 eV) was found to separate the monocrystalline region from a high temperature polycrystalline region. The latter region was identified with the coalescence stage of film growth. These results agree with earlier reports suggesting that the coalescence stage rather than the nucleation stage is pre-eminent in determining the occurrence of epitaxy.     

Cu films formed simultaneously on (111) and (100) NaCl

Copper films were deposited simultaneously in high vacuum on three different monocrystalline NaCl substrates: evaporated (111) NaCl on mica, evaporated (100) NaCl and air-cleaved (100) NaCl. The occurence and microstructure of monocrystalline or polycrystalline copper films were determined by transmission electron microscopy and diffraction as a function of deposition rate R and substrate temperature T. When log R was plotted against 1/T, straight lines could be drawn separating the monocrystalline and the polycrystalline regions. Activation energies for the polycrystalline to monocrystalline transition of Cu films were calculated to be 1.48, 1.22 and 1.27 eV for the (111), evaporated (100) and air-cleaved (100) NaCl substrates respectively. It is shown that these results can be related to the atomistic theory of nucleation by Walton. Moreover, the results indicate that both the binding energy U between a single adatom and a growing oriented cluster and the atomic adsorption energy Q_ad on the substrate surface are proportional to the planar atom densities in the growing cluster and in the substrate surface respectively. It is further shown that while the activation energies for Cu films formed on the two (100) substrate surfaces are about the same, the actual epitaxial temperatures for the same R are significantly different.     

Contents of Volume 111 (2001)

Volume Contents

Contents of Volume 111 (2001)