Nanostructuring at the surface of low‐energy lead‐implanted silicon by electron beam annealing

Low‐energy lead ion implantation and high‐temperature electron beam annealing were used to study the potential of producing Pb nanostructures on Si. Pb⁺ ions were implanted at high dose into p‐type (100) Si to the depth of 8.0 nm. The implanted samples were annealed under high vacuum conditions with an electron beam at 200–700 °C for 15 s. Rutherford Backscattering Spectrometry (RBS) shows rapid out‐diffusion of Pb atoms above 400 °C. However, some Pb atoms are still present in the near‐surface region after annealing the implanted samples at 700 °C. Lead nanostructures were found on samples annealed above 300 °C. Annealing the samples at 450 °C causes the formation of nanostructures as tall as 4.1 ± 0.1 nm. Many of these are arranged in ‘web‐like’ strings that extend over micrometer distances. Occasionally, much larger nano‐features (as wide as 500 nm in diameter, average height of 1.5 nm) appear in the centre of the strings. Annealing samples well above the melting point of lead results in randomly distributed small nanometer‐sized Si nano‐dots. Copyright © 2008 John Wiley & Sons, Ltd.     

Chemical surface passivation of 3C‐SiC nanocrystals: A first‐principle study

The effect of the chemical surface passivation, with hydrogen atoms, on the energy band gap of porous cubic silicon carbide (PSiC) was investigated. The pores are modeled by means of the supercell technique, in which columns of Si and/or C atoms are removed along the [001] direction. Within this supercell model, morphology effects can be analyzed in detail. The electronic band structure is performed using the density functional theory based on the generalized gradient approximation. Two types of pores are studied: C‐rich and Si‐rich pores surface. The enlargement of energy band gap is greater in the C‐rich than Si‐rich pores surface. This supercell model emphasizes the interconnection between 3C‐SiC nanocrystals, delocalizing the electronic states. However, the results show a clear quantum confinement signature, which is contrasted with that of nanowire systems. The calculation shows a significant response to changes in surface passivation with hydrogen. The chemical tuning of the band gap opens the possibility plenty applications in nanotechnology. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem 110:2455–2461, 2010     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

Surface cavities produced by high‐dose nitrogen ion implantation into silicon

Nitrogen ion implantation (24 keV, 4.6 × 10¹⁷ cm^?2) into (100) a p‐type silicon wafer material and a subsequent electron beam annealing at 1100 °C for 15 s under high vacuum conditions leads to the formation of an uneven surface in the implanted region caused by nitrogen bubbles beneath the surface. Annealing at 1200 °C for 300 s results in surface cavities with a mean diameter of 350 nm and a surface coverage of 3–4% and an average depth of ～60 nm. Nuclear reaction analysis reveals that the nitrogen concentration in the as‐implanted state exceeds 57 at%, the value of stoichiometric Si₃N₄. Annealing at 1100 °C for 15 s slightly reduces the nitrogen peak concentration, whereas annealing at 1200 °C for 300 s induces a significant alteration to the shape of the nitrogen depth profile coupled with the lowering of the concentration close to the stoichiometry of Si₃N₄. The results present a new method of producing sub‐micrometre cavities embedded in a thin silicon nitride film on wafer silicon which may lead to novel micro‐electronic and biotechnology applications. Copyright © 2007 John Wiley & Sons, Ltd.     

XRD-Studies of SiC/Si layers on carbon substrates

Structural investigations of thin films of SiC, SiC with free silicon and various titanium suicides (TiSi₂, TiSi and Ti₅Si₃) are described. The crystal phases have been identified using X-ray diffractometry. The growth of reaction products from surface reactions between silicon and deposited titanium can be observed.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Chemical etching of hot‐pressed p‐type polycrystalline SiC surfaces by HF/K2S2O8 solutions

In this work, an experimental study on the etching of p‐type hot‐pressed silicon carbide (SiC) was carried out in HF/K₂S₂O₈ solutions. The SiC wafers used in this work were p‐type polycrystalline materials, supplied by Goodfellow, with an acceptor concentration of 2.31 × 10¹² cm^?3. The SiC substrate was a hot‐pressed material, the latter realized from a mixture of 1 part of SiO₂ with 3 parts of C (carbon) ‘1SiO₂ + 3C’ heated in an oven at 2500 °C. In order to facilitate the chemical etching of the SiC substrate, a thin aluminium film was deposited on the SiC substrate. The morphology of the etched surface was examined with varying K₂S₂O₈ concentration. The surfaces of the etched samples were analysed using secondary ions mass spectrometry (SIMS), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR) and photoluminescence (PL). The surface morphology of the samples etched in HF/K₂S₂O₈ is shown to depend on the solution composition. The investigation of the effect of the HF/K₂S₂O₈ solution on SiC samples shows that as K₂S₂O₈ concentration increases, the chemical etching reveals defects with random geometry. Finally, chemical etching of p‐type SiC induces a decrease in the PL intensity, which indicates clearly the defects on the polycrystalline SiC surface. In addition, the result is very interesting, as to date no chemical etching solution at low temperature (<100 °C) has been developed for SiC. Finally, we have proposed a dissolution mechanism of SiC in 2HF/1K₂S₂O₈ solutions. Copyright © 2007 John Wiley & Sons, Ltd.     

SiC表面Ni沉积超疏水膜层的形成机理

前期采用环境友好方法制备的改性碳化硅颗粒,经较长时间放置,发现其由亲水性转变为超疏水性,接触角为156°。为解释这一新的现象,采用扫描电子显微镜、能谱、(高分辨)透射电子显微镜、X射线光电子能谱(XPS)对原粉碳化硅、改性后碳化硅及久置碳化硅进行了测试与分析。结果显示：改性后碳化硅经较长时间放置,表面胞状颗粒增大并出现凸起物,粗糙度增加,存在类似于荷叶的微纳米结构。改性后颗粒的主要成分为Ni、Si、O,其中凸起处Ni、O元素的含量明显高于凹陷处。Ni颗粒表面出现清晰的膜层,膜层厚度为2～3 nm,但结晶度偏低。XPS测试结果显示金属镍的特征峰正向移动近4 eV,与镍的氧化态特征峰相一致,从而解释了颗粒表面形态发生细小改变,自发形成超疏水膜层的机理。     

SiC表面Ni沉积超疏水膜层的形成机理

前期采用环境友好方法制备的改性碳化硅颗粒,经较长时间放置,发现其由亲水性转变为超疏水性,接触角为156°。为解释这一新的现象,采用扫描电子显微镜、能谱、(高分辨)透射电子显微镜、X射线光电子能谱(XPS)对原粉碳化硅、改性后碳化硅及久置碳化硅进行了测试与分析。结果显示：改性后碳化硅经较长时间放置,表面胞状颗粒增大并出现凸起物,粗糙度增加,存在类似于荷叶的微纳米结构。改性后颗粒的主要成分为Ni、Si、O,其中凸起处Ni、O元素的含量明显高于凹陷处。Ni颗粒表面出现清晰的膜层,膜层厚度为2~3 nm,但结晶度偏低。XPS测试结果显示金属镍的特征峰正向移动近4eV,与镍的氧化态特征峰相一致,从而解释了颗粒表面形态发生细小改变,自发形成超疏水膜层的机理。     

Interpretation of Auger depth profiles of thin SiC layers on Si

Silicon carbide thin films, prepared by carbonization of Si-wafers are analysed by Auger depth profiling. The influence of atomic mixing is simulated with a Monte Carlo model. By using mixing simulations the dependence of the two mixing parameters (width of the mixing zone and recoil depth) on ion beam energy, incidence angle and ion mass can be calculated. For comparison of the simulated data with Auger measurements an Auger electron escape depth correction is necessary. The simulated and -corrected data of several layer structures show good qualitative agreement with Auger depth profiles of thin carbonized SiC-layers.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

Focused ion beam implantation of Ga in Si and Ge: fluence‐dependent retention and surface morphology

Focused ion beam implantation of 30‐keV Ga⁺ ions in single‐crystalline Si and Ge was investigated by SIMS, using Cs⁺ primary ions for sputtering. Nine different implantation fluences ranging from 1 × 10¹³ to 1 × 10¹⁷ Ga⁺‐ions/cm² were used, with implanted areas of 40 × 40 µm². The Ga concentration distributions of these implants were determined by SIMS depth profiling. Such 30‐keV Ga implantations were also simulated by a dynamic Monte‐Carlo code that takes into account the gradual change of the near‐surface composition due to the Ga incorporation. In both approaches, an essentially linear increase of the Ga peak concentrations with fluence is found up to ～1 × 10¹⁶cm^?2; for higher fluences, the Ga content approaches a saturation level which is reached at about (1–2) × 10¹⁷cm^?2. The measured and simulated peak concentrations of the Ga distributions are in good agreement. The most probable ranges obtained from the experiments correspond closely with the respective values from the simulations. The surface morphology caused by Ga⁺ implantation was investigated by atomic force microscopy (AFM). The AFM data indicate that for low fluences (<3 × 10¹⁵cm^?2) the surface within the implanted areas is growing outward (i.e. is swelling). For increasingly higher fluences, sputter‐induced erosion of the surface becomes dominant and distinct craters are formed for fluences above ～1 × 10¹⁶cm^?2. At the boundary of the implanted region a wall‐like structure is found to form upon Ga implantation; its height is growing with increasing fluence, reaching a value of ～15 nm at 1 × 10¹⁷ Ga⁺‐ions/cm². Copyright © 2008 John Wiley & Sons, Ltd.     

Initial formation of contact layers on Ni/SiC samples studied by XPS

This study deals with the quantitative assessment of the coverage and thickness of Ni silicide films formed during annealing of SiC substrates with sputtered thin films of Ni. The analytical approach involves the use of XPS and depth profiling by means of successive ion etchings and XPS analyses. For either 3 or 6 nm initial Ni film thickness, a 10 nm Ni₂Si product is formed. On top of this product, the C released is accumulated in a very thin (1–2 nm) film. In neither case, the Ni₂Si covers the whole surface, although the coverage is almost complete (～90%) in the latter case. For the greater initial Ni‐film thickness of 17 nm, the thickness of the Ni₂Si product corresponds well to the value of 25 nm expected from the Ni/Ni₂Si stoichiometric relationship. This thickness is significantly greater than a critical level and the film covers the whole surface. Carbon is similarly accumulated in a very thin layer on the top surface, although the major part of C (～70%) is found inside the main reaction product layer. Copyright © 2008 John Wiley & Sons, Ltd.     

Chemically assisted ion beam etching of silicon and silicon dioxide using SF6

A chemical flux of sulfur hexafluoride (SF₆) in conjunction with low-energy Ar-ion bombardment has been used for chemically assisted ion beam etching (CAIBE) of silicon and silicon dioxide. The study has shown a large degree of independent control over the selectivity and anisotropy in dry etching. The total etch rate could be controlled by varying either the Ar-ion milling parameters or the chemical flux of SF₆. Etch rate enhancement of 7–8 for silicon and 3–4 for silicon dioxide have been obtained over pure physical etching.     

Long‐Term Stable Silver Subsurface Ion‐Exchanged Glasses for SERS Applications

We report on the formation of silver subsurface ion‐exchanged metal oxide (silver SIMO) glasses and their surface‐enhanced Raman scattering (SERS) activity. The samples were prepared by a combined thermal and chemical three‐step methodology and characterized by transmission electron microscopy (TEM), atomic force microscopy (AFM), environmental electron scanning microscopy (ESEM), and UV/Vis spectroscopy. This unique method provides SERS substrates with protection against contamination and strong, reliable and reproducible SERS enhancement. The Raman enhancement factors of the long‐term stable SIMO glasses were estimated to approximately 10⁷.     

X‐ray diffraction study of low‐energy carbon‐ion implanted Si(001)

In the search for Si‐ and C‐based crystalline phases in low‐energy ion implanted and electron‐beam annealed Si surface layers, X‐ray diffraction (XRD) measurements were performed at grazing incidence on samples of large SiC nanocrystals grown on a 90 nm thick Si layer containing C atoms. Diffraction patterns and reciprocal space maps did not reveal XRD patterns originating from the nanocrystals or the implanted layer, but did show that distortions of the Si crystal structure were introduced into the implanted layer. After annealing, the strain in the implanted layer is reduced, possibly by carbon atoms that have moved to locations close to dislocations and dislocation loops. This investigation underpins the growth theory of the SiC nanocrystals on Si, with carbon atoms migrating to form the nanostructures. Copyright © 2007 John Wiley & Sons, Ltd.     

Ab initio potential energy surface and vibration‐rotation energy levels of silicon dicarbide,SiC2

The accurate ground‐state potential energy surface of silicon dicarbide, SiC₂, has been determined from ab initio calculations using the coupled‐cluster approach. Results obtained with the conventional and explicitly correlated coupled‐cluster methods were compared. The core‐electron correlation, higher‐order valence‐electron correlation, and scalar relativistic effects were taken into account. The potential energy barrier to the linear SiCC configuration was predicted to be 1782 cm^?1. The vibration‐rotation energy levels of the SiC₂, ²⁹SiC₂, ³⁰SiC₂, and SiC¹³C isotopologues were calculated using a variational method. The experimental vibration‐rotation energy levels of the main isotopologue were reproduced to high accuracy. In particular, the experimental energy levels of the highly anharmonic vibrational ν₃ mode of SiC₂ were reproduced to within 6.7 cm^?1, up to as high as the v₃ = 16 state.     

Effect of Cu pre‐deposition on the interface structure between the C‐SiC coatings and stainless steel

The copper dispersion‐strengthened matrix composites (Cu/C? SiC) were fabricated on the stainless steel by using magnetron sputtering and ion‐beam mixing. The pre‐deposition of Cu element is used to modify the interface structure, and hence, to develop the compatibility between Fe substrate and C‐SiC coating. The results show that the copper layer can effectively broaden the transition layer, where the elements of the coating could be completely mixed with the elements of the substrate. The following heat treatment on it can further broaden the transition layer, i.e. heat treatment can provide more compatibility between C‐SiC coating and Fe substrate. Copyright © 2008 John Wiley & Sons, Ltd.     

用透射电子显微技术研究Si3N4/纳米SiC复相陶瓷的微观结构与力学性能

利用透射电子显微镜,观察了Si3N4/纳米SiC复相陶瓷材料的显微结构特点、分析比较了纳米复相陶瓷与单相Si3N4陶瓷的显微结构差异、讨论了复相陶瓷材料的力学性能与其微观结构的关系,并提出在材料中引入纳米SiC粒子后,可以起到抑制Si3N4晶体长大,使材料的力学性能得到显著提高.     

Study in the effect of annealing on hydrogen retention properties of C‐90%SiC films

Carbon‐rich silicon carbide (C‐90%SiC) films as hydrogen barriers were deposited on the surface of stainless steel substrates with magnetron sputtering, and then bombarded by argon ion beam. In order to remove the argon atoms reserved during films preparation, some samples with the prepared C‐90%SiC films were thermally annealed for 30 min at 473, 673 and 873 K in vacuum, respectively. These samples together with the un‐annealed ones were then irradiated by a 5 keV hydrogen ion beam. SEM was used to investigate the surface micrograph of those films and SIMS was used to measure the mass spectra of positive species and the depth distribution of argon and hydrogen in the samples. A remarkable decrease in hydrogen intensity in the substrates with annealing indicates that annealing for removing argon can effectively improve hydrogen retention properties of the C‐90%SiC films. Copyright © 2008 John Wiley & Sons, Ltd.     

Evaluation of exchange‐correlation functionals in comparison to B3LYP for the description of silicon and Cu‐doped silicon clusters

Several developed exchange‐correlation functionals in density functional theory have been systematically applied to describe the geometries and electronic properties of small silicon (Si_n+1, n < 5) and doped silicon (CuSi_n) clusters. The performance of the various approaches is done with their critical comparison with B3LYP and available high level wave function methods. Our calculations indicate that all functional give reasonable results. Further, OLYP/6‐311+G* approach generally agrees with B3LYP results. The good performance of OLYP is of significant interest knowing that the hybrid functionals are computationally more demanding than nonhybrid schemes. So, we recommend OLYP/6‐311+G* approach for studying the doped silicon clusters and understanding the electronic properties of silicon by the presence of doped metal impurities. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008