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.     

Diffusion of nickel in silicon below 475 °C

Nickel films were deposited on (100) and (111) surfaces of single-crystal silicon and were then annealed. The conditions under which the nickel is deposited determine whether or not an NiSi compound forms on annealing. It is postulated that defects are necessary for the formation of an NiSi compound at annealing temperatures below at least 475 °C, although the presence of defects may not necessarily cause the formation of a silicide. For substrate temperatures below 70 °C, defects are created during the vapor deposition of nickel on silicon. These defects always result in the formation of nickel silicide when the sample is annealed at higher temperatures. When nickel is deposited on defect-free silicon at temperatures of about 250 °C no defects are generated and, although interdiffusion of nickel and silicon occurs, silicide formation does not take place upon subsequent annealing below 475 °C. The activation energies for the diffusion of nickel into (100) silicon and (111) silicon were determined.     

The solid state reaction of Fe with the Si(111) vicinal surface: splitting of bunched steps

The solid state reaction of deposited Fe (four monolayers, ML) with vicinal Si(111) substrate induced by subsequent thermal treatment has been studied using scanning tunnelling microscopy. At the lower range of annealing temperatures up to 400?°C the bunched steps of bare substrate are reproduced by the surface of the covering iron silicide layer. At 400?°C the onset of three-dimensional growth of iron silicide islands is observed. In comparison to the samples covered with smaller amounts of Fe it appears at a lower annealing temperature. Above 500?°C the bunched steps split into lower ones but more densely distributed due to proceeding reactions between Fe-rich iron silicide and Si substrate. As a consequence, at 700?°C the well-developed three-dimensional nanocrystallites of iron silicide are randomly distributed on the Si surface. This observation is in contrast to the formation of a regular array of iron silicide crystallites upon deposition of 2?ML of Fe.     

Structural properties of the PdSi interface: An investigation by reflection high energy electron diffraction

The first stages of the formation of silicide were studied at various temperatures during palladium deposition onto an Si(111) 7 × 7 surface using the reflection high energy electron diffraction technique.For temperatures below 200°C, the interaction of palladium with silicon leads to the formation of three-dimensional Pd₂Si crystallites.At more elevated temperatures (300–400°C) two-dimensional phases were distinguished that are denoted as follows: Si(111) √3 R(30°) Pd and Si(111) 2√3 R(30°) Pd.     

High resolution photoemission study of the formation and thermal stability of Mg silicide on silicon

The focus of this study is to use high resolution synchrotron based photoemission to investigate the initial growth mode of magnesium silicide which has been formed by both stepwise and continuous deposition of metallic Mg onto a thermally grown ultra-thin Si oxide surface. The findings suggest that stepwise deposition of Mg initially results in the growth of Mg silicide islands on the surface. Further magnesium deposition leads to the growth of metallic Mg on the surface of these silicide islands, along with the continued growth of silicide species on the uncovered oxide surface. However, it has been shown that continuous deposition of Mg results in considerably less silicide growth. The thermal stability of Mg silicide and a mechanism for high temperature silicide growth have also been studied using conventional X-ray photoelectron spectroscopy. The results suggest that the presence of oxidised Si acts as a barrier to Si diffusion during vacuum annealing, hence preventing the growth of further Mg silicide. It has also been shown that metallic Mg desorbs from the surface below 300 °C, while Mg silicide is not stable at temperatures above 500 °C in contrast to other metal silicides.     

Recrystallization on their substrates of Au (001)/NaCl (001) films into Au (111)/NaCl (001) Part I. Electron Microscopy and electron diffraction observations

The electron-gun evaporation technique for the deposition of Au and Ag films onto (001) NaCl leads to a decrease in the epitaxial temperatures of these materials to 75° and 50°C respectively. This decrease has enabled us to use a wide range of temperatures for film recrystallization without destruction of the substrate. The annealing of the films on their substrates leads to a change in their orientation from metal (001)/NaCl (001) to metal (111)/NaCl (001). In the present work the experimental and kinetic conditions of this transformation process are given.     

Formation and characterization of semiconductor Ca2Si layers prepared on p-type silicon covered by an amorphous silicon cap

Formation of calcium silicide on three types of templates: Si(111)7 × 7, 2D Mg₂Si, and 3D Mg₂Si, was studied during Ca deposition at 120 °C in situ by Auger and electron energy loss spectroscopy, and by differential optical reflectance spectroscopy. A continuous Ca₂Si layer is formed on 2D and 3D Mg₂Si templates; but, on an atomically clean silicon surface (Si(111)7 × 7), a mixture of Ca₂Si with another Ca silicide was found. The growth of a Si cap layer over the Ca silicide layers at about 100 °C studied by in situ methods demonstrated the full embedding of Ca silicide in amorphous silicon, independent of the used template. Transmission electron microscopy, Rutherford backscattering spectrometry, atomic force microscopy, and electrical characterization of Schottky junctions revealed the Ca₂Si and Mg₂Si nanoparticles and the redistribution of Mg and Ca during the silicon cap growth and its effect on the electronic properties of the structures. Reproduction of the experiments on higher doped and better purity substrates is needed to understand better the role of Mg- and Ca-related defects, and defects of silicon generated by the growth process.     

Low energy electron diffraction,Auger electron spectroscopy and angle-resolved photoemission from silver films on Si(100) and Si(111)

We studied the growth of thin silver films on Si(100)2 × 1 and Si(111) 7 × 7 between room temperature and 300 °C. At room temperature and with a silver flux of 2.4 × 10¹² atoms s^-1 cm^-2 a nearly exponential dependence of the Si L_2,3 VV and Ag M₄ VV Auger intensities indicates layer-by-layer (Frank-van der Merwe) growth up to a film thickness of a few monolayers. With increasing coverage θ silver grows in form of three-dimensional islands even at room temperature. In spite of the existence of the well-known Si(111)?(√3 × √3)R30° Ag surface structure after annealing (which we observe for θ = 1) we did not find an ordered Si-Ag interface layer for silver on Si(100). For elevated temperatures the growth of this system may therefore be described by the Volmer-Weber (pure three-dimensional island growth) mechanism, whereas silver condenses on Si(111) according to the Stranski-Krastanov (interface layer plus three-dimensional islands) growth mode.     

Formation of epitaxial NiSi2 nanowires on Si(100) surface by atomic force microscope nanolithography

Ni nanowries were fabricated by atomic force microscope nanolithography, evaporation, lift-off and annealing processes. Epitaxial NiSi2 nanowires on a Si(100) surface along Si(110) and (100) directions were formed by the rapid thermal annealing treatment of the Ni nanowires at 400 degrees C. The silicide nanowires along the Si(110) direction had coherent type-A Si(111) and Si(100) interfaces, while those along the Si(100) direction had a type-A Si(110) interface. Silicide nanowires were agglomerated when the Ni nanowires were annealed at high temperature (> or = 500 degrees C). The mechanism of formation of a faceted nanowire was discussed based on the minimization of the total surface energy.     

Synthesis and characterization of indium monoselenide (InSe) nanowires

Indium monoselenide (InSe) nanowires were grown by the thermal evaporation method in argon atmosphere without the presence of any catalysts using InSe polycrystalline powder as the source material. No nanostructure growth was observed at deposition temperatures below 580 °C. The nanostructures were discernable at temperatures above 620 °C. Pure InSe nanowires were obtained at the deposition temperature of 660 °C for 50 min. The diameters of the nanowires were from 50 to 240 nm and their lengths were up to several micrometers. X-ray diffraction spectrum reveals that the synthesized products were single-crystalline of the β-phase hexagonal structure of InSe with lattice constants a = 4.006 Å and c = 16.642 Å. The strong peak due to the reflection from the (004) crystal plane reveals that most nanowires grow with a strong preferred orientation.     

Increase in the density of β-FeSi2 nanoclusters on a Si(111) surface by means of Si(111) √3 × √3R30°-B reconstruction

The formation of iron disilicide (β-FeSi₂) nanoclusters as a result of solid-state epitaxy at T = 500–700°C and an iron coverage of 0.05–0.5 monolayer on a boron-modified Si(111)√3 × √3 R30° surface has been studied by scanning tunneling microscopy. It is established that the number density of β-FeSi₂ nanoclusters on the Si(111) √3 × √3 R30°-B surface significantly exceeds the density of silicide clusters formed on the atomically clean Si(111) surface with a 7 × 7 reconstruction for the analogous iron coverages and annealing temperatures. At the same time, the density of point defects and clusters possessing metallic conductivity on the Si(111) √3 × √3 R30°-B surface is several orders of magnitude lower than on the Si(111)7 × 7 surface treated under identical conditions.     

锰及其硅化物在Si(100)表面的反应外延生长

采用超高真空分子束外延-扫描隧道显微镜(UHVMBE-STM)系统研究了不同温度下锰及其硅化物在Si(100)-2 ×1重构表面上的外延生长情况.实验结果表明当生长过程中衬底温度控制在室温到135℃时,生成大小基本一致的锰纳米团簇;当衬底温度达到210℃时锰与硅开始发生反应,形成硅化物,并有纳米线结构出现;当衬底温度达到330℃时,纳米线完全被棒状物或不规则的三维岛状硅化物取代.随着沉积时衬底温度升高,生成物的成核密度与生长温度的关系与经典的二维岛成核理论相符合.     

A study of the temperature dependence of adsorption and silicidation kinetics at the Mg/Si(111) interface

The adsorption studies of magnesium on Si(111) substrate have been performed using AES, LEED and EELS at various substrate temperatures. It is observed that the sticking coefficient of magnesium on the silicide surface is close to zero for temperatures greater than 100 °C. It has been shown that the magnesium silicide grows as continuous films on Si substrate at temperature 100-140 °C, while for temperatures higher than 170 °C the magnesium silicide grows in the form of islands.     

Effects of nitrogen annealing on surface structure,silicide formation and magnetic properties of ultrathin films of Co on Si(100)

Effects of nitrogen annealing on structural and magnetic properties of Co/Si (100) up to 700°C has been studied in this paper. Ultrathin Co films having a constant thickness of 50 Å were grown on Si (100) substrates using electron-beam evaporation under very high vacuum conditions at room temperature. Subsequently, the samples were annealed at temperatures ranging from 100–700°C in a nitrogen environment at atmospheric pressure. Sample quality and surface morphology were examined using atomic force microscopy. Silicide formation and the resultant variation in crystallographic arrangement were studied using X-ray diffractometer. The magnetization measurements done using a vibrating sample magnetometer indicate a decrease in coercivity and retentivity values with increase in annealing temperature. Resistivity of the samples measured using a four-point probe set up shows a decrease in resistivity with increase in annealing temperature. Formation of various silicide phases at different annealing temperatures and the resultant variation in the magnetic susceptibility has been thoroughly studied and quantified in this work.     

Interfacial reaction and adhesion between SiC and thin sputtered nickel films

Thin sputtered nickel films grown on SiC were annealed in an Ar/4 vol % H2 atmosphere at temperatures between 550 to 1450 °C for various times. The reactivity and the reaction-product morphology were characterized using optical microscopy, surface profilometry, X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The reaction with the formation of silicides and carbon was observed to first occur above 650 °C. Above 750 °C, as the reaction proceeded, the initially formed Ni3Si2 layer was converted to Ni2Si and carbon precipitates were observed within this zone. The thin nickel film reacted completely with SiC after annealing at 950 °C for 2 h. The thermodynamically stable Ni2Si is the only observed silicide in the reaction zone up to 1050 °C. Above 1250 °C, carbon precipitated preferentially on the outer surface of the reaction zone and crystallized as graphite. The relative adhesive strength of the reaction layers was qualitatively compared using the scratch test method. At temperatures between 850 to 1050 °C the relatively higher critical load values of 20–33 N for SiC/Ni couples are formed. This revised version was published online in November 2006 with corrections to the Cover Date.     

Germanium nanowire epitaxy: shape and orientation control

Epitaxial growth of nanowires along the 111 directions was obtained on Ge(111), Ge(110), Ge(001), and heteroepitaxial Ge on Si(001) substrates at temperatures of 350 degrees C or less by gold-nanoparticle-catalyzed chemical vapor deposition. On Ge(111), the growth was mostly vertical. In addition to 111 growth, 110 growth was observed on Ge(001) and Ge(110) substrates. Tapering was avoided by the use of the two-temperature growth procedure, reported earlier by Greytak et al.     

Self-organization of CrSi2 nanoislands on Si(111) and growth of monocrystalline silicon with buried multilayers of CrSi2 nanocrystallites

The process of self-organization of CrSi2 nanosize islands on Si(111)7 x 7 surface has been investigated during reactive deposition (RDE) of Cr at 500 degrees C by methods of low energy diffraction (LEED) and differential reflectance spectroscopy (DRS). Morphology of grown samples has been studied by atomic force microscopy (AFM). DRS data have demonstrated the semiconductor nature of silicide islands from the beginning of Cr deposition at 500 degreesC. The optimal temperature (750 0C) and optimal Si thickness (50 nm) have been determined for silicon molecular epitaxy (MBE) growth atop CrSi2 nanosize islands. Monolithic silicon-silicide heterostructures with multilayers of CrSi2 nanosize crystallites have been grown.     

Effects of annealing on the formation of Mg2Si film prepared by resistive thermal evaporation method

The effects of annealing time and temperature on the formation and structure of magnesium silicide (Mg₂Si) films were investigated. Magnesium films of 380 nm thickness were deposited on Si (111) substrates using resistive thermal evaporation method. The films were then annealed in an annealing furnace under a low vacuum atmosphere of 10^?1–10^?2 Pa. The results showed that the crystallization quality of Mg₂Si films was strongly affected by the annealing time and temperature. Annealing at 400 °C for 4 h was the optimal preparation conditions for Mg₂Si films.     

Effect of Si(100)-<Emphasis Type="Italic">c</Emphasis>(4 × 12)-Al and Si(111)-(5.55 × 5.55)-Cu reconstructions on the deposition of cobalt onto silicon surface

The use of surface reconstructions for modifying properties of single crystal silicon substrates with a view to the creation of new nanostructures is a promising direction in the development of nanotechnologies. Systems Si(100)-c(4 × 12)-Al and Si(111)-(5.55 × 5.55)-Cu occupy special positions among stable reconstructions of the silicon surface, which have been recently demonstrated to be promising templates. The adsorption of cobalt on these surfaces at various temperatures has been studied using scanning tunneling microscopy. The room-temperature deposition leads to the formation of a weakly ordered layer of metallic Co with retained initial reconstructions at the Co/Si interface. An increase in the temperature leads to the formation of faceted cobalt silicide islands on both reconstructed surfaces.     

Ion-induced transformations of a W–Si interface

Tungsten silicide formation in multilayer tungsten/silicon structure was investigated. The W–Si multilayers were deposited on thermally oxidized silicon wafers using the dual-target magnetron sputtering. Deposition of the whole stack of sublayers was carried out without breaking vacuum in order to eliminate contamination or oxidation of the interfaces between sublayers. Samples were annealed in the RTA furnace at temperatures ranging from 700 °C up to 1050 °C. Some of the structures were irradiated with argon ion beam before annealing. Reactions between sublayers were studied using SEM imaging of cross-sectional cleavages and by X-ray diffraction analysis. Influence of the irradiation with argon ion beam on structural transformations was investigated using RBS analysis. It has been found that tungsten silicide formation depends on the deposition sequence. The reaction was more effective on interfaces between silicon layer deposited on tungsten then on interface between tungsten deposited on silicon. Ion beam mixing experiment showed that ion–target interaction promotes formation of the WSi₂ phase.