Efstathios K. Polychroniadis

In situ observation of nickel metal-induced lateral crystallization of amorphous silicon thin films

The lateral crystallization of amorphous silicon thin films induced by nickel was studied in detail, performing in situ annealing experiments with a transmission electron microscope. The nickel-induced crystallization starts with the fast growth of thin needle-like crystallites of [110] orientation, which advance along the 〈111〉 directions within the film plane. The fast growth rate and the small probability of the crystallite exhibiting the [110] orientation result in large crystalline grains. These grains are, however, composed of many small misorientated subgrains. It is thought that this is because the needle-like crystallite does not grow continuously but grows by successive jumps. Our model is that after the nickel disilicide precipitate grows a thin crystalline slice epitaxially at the leading edge of the needle-like crystallite, the nickel moves to the new leading edge and forms the new nickel disilicide precipitates to maintain the needle-like crystalline growth.

Electrooxidation of ethylene glycol on Pt-based catalysts dispersed in polyaniline

Platinum dispersed in a polyaniline film is a better catalyst than smooth Pt for ethylene glycol electrooxidation in perchloric acid aqueous solutions. The catalytic activity of the platinum microparticles is further enhanced when Ru, Sn or both are codeposited. The PAni/Pt–Sn assembly shows the highest electrocatalytic activity of the electrodes examined. Underpotential deposition of Tl and Bi on dispersed Pt inhibits EG electrooxidation while Pb causes significant catalysis only with a specific preparation method electrocatalyst. The morphology and the identity of the metallic dispersion is examined by transmission electron microscopy.

Hexamethyldisilane/propane versus silane/propane precursors: application to the growth of high-quality 3C–SiC on Si

From a comparative evaluation of hexamethyldisilane (HMDS) and silane–propane (SP) precursor systems, it is shown that HMDS needs a small addition of propane to deposit heteroepitaxial layers of 3C–SiC on Si with superior crystalline properties. In this case, propane compensates for the secondary reactions induced by hydrogen reacting with carbon. Using atmospheric pressure chemical vapour deposition conditions, the new system (HMDS–propane) demonstrates several advantages. It is safer to handle than SP and allows a higher growth rate (up to 7 µm h−1 at 1350 °C) without any degradation of the layer morphology. However, when lowering the deposition temperature, HMDS is revealed to be more stable than silane. This is in contrast to most standard beliefs but explains why a high temperature (~1350 °C) is always necessary to grow high-quality material using HMDS.

Ion beam synthesis and characterization of thin SiC surface layers

Abstract Implantation of carbon into silicon with a concentration below 50 at.% and subsequently thermal treatment under high vacuum conditions results in the formation of a SiC surface layer. Crystalline Si 〈1 0 0〉 samples were implanted with 40 keV 13C ions at RT with a fluence of 3.8×1017 ions/cm2. The samples were thermally treated at different temperatures and for different annealing times using a scanned 20 keV electron beam. The influence of these parameters on the concentration-depth distribution of carbon was investigated by Narrow Resonance Reaction Analysis (NRRA) with the 13C(p,γ)14N reaction. An active oxidation process is proposed to be responsible for the redistribution of the implanted carbon atoms into a rectangular carbon-depth distribution. SiC-bonds were studied using Fourier Transform Infrared Spectroscopy (FTIR). A sharp and symmetric absorption peak of SiC appears after formation of the rectangular carbon distribution. The SiC surface layers were finally characterized by Transmission Electron Microscopy (TEM).

Morphology of platinum silicide films prepared by conventional and rapid thermal annealing and deep levels induced in silicon

Electron microscopic studies and the electrical properties of Pt contacts on n‐type Si annealed by conventional furnace and rapid thermal annealing (RTA) were investigated with scanning electron microscopy, transmission electron microscopy, x‐ray analysis, capacitance‐voltage, and deep‐level transient spectroscopy measurements. An incomplete reaction between Pt and Si is observed after furnace annealing at 550 °C due to the presence of oxygen in the ambient. An almost complete reaction between Pt and Si is achieved after silicidation by RTA at 550 °C. An acceptorlike level located 0.11 eV below the conduction‐band edge with a concentration of 2×1013 cm−3 is detected only after furnace annealing at 550 °C. Silicidation by RTA at 550 °C does not introduce traps in the Si band gap.

Structure Property Relationship of Suspension Thermally Sprayed WC-Co Nanocomposite Coatings

Tribomechanical properties of nanostructured coatings deposited by suspension high velocity oxy-fuel (S-HVOF) and conventional HVOF (Jet Kote) spraying were evaluated. Nanostructured S-HVOF coatings were obtained via ball milling of the agglomerated and sintered WC-12Co feedstock powder, which were deposited via an aqueous-based suspension using modified HVOF (TopGun) process. Microstructural evaluations of these hardmetal coatings included transmission electron microscopy, x-ray diffraction, and scanning electron microscopy equipped with energy dispersive x-ray spectroscopy. The nanohardness and modulus of the coated specimens were investigated using a diamond Berkovich nanoindenter. Sliding wear tests were conducted using a ball-on-flat test rig. Results indicated that low porosity coatings with nanostructured features were obtained. High carbon loss was observed, but coatings showed a high hardness up to 1000 HV2.9N. S-HVOF coatings also showed improved sliding wear and friction behavior, which were attributed to nanosized particles reducing ball wear in three-body abrasion and support of metal matrix due to uniform distribution of nanoparticles in the coating microstructure.

Sublimation Growth and Structural Characterization of 3C-SiC on Hexagonal and Cubic SiC Seeds

Epitaxial growth of cubic silicon carbide on 6H-SiC substrates, and 6H-SiC substrates with (111) 3C-SiC buffer layer, deposited by vapour liquid solid mechanism, was compared. The morphological details of the grown layers were studied by optical microscopy and their microstructure by transmission electron microscopy. The influence of the substrate on the nucleation of 3C-SiC, the initial homoepitaxial 6H-SiC nucleation before 3C-SiC as well as the formation of defects, are discussed.

Flash Lamp Supported Deposition of 3C-SiC (FLASiC) – a Promising Technique to Produce High Quality Cubic SiC Layers

This paper summarises latest advancements regarding FLASiC (Flash lamp supported deposition of 3C-SiC) as a new approach to produce high quality SiC-Si heteroepitaxial material. This concerns description of the process and equipment, microstructural results and modelling aspects. In this manner a new era of nanoscale liquid phase epitaxy could be born. Introduction The production of cubic SiC (3C-SiC) layers in device quality through the epitaxial growth on (100) Si wafers has remained a challenging task yet. Remembering back the last bigger effort it was at the ICSCRM ́95 at Kyoto that several groups presented their latest results regarding high quality material and discussed lively how to overcome the main problem: the high defect density of the SiC layer. Since then there has been not too much progress reported. Recently it was demonstrated that the use of Flash Lamp Processing (FLP) can support the production of high quality 3C-layers in a promising manner [1]. This process got the acronym FLASiC standing for Flash LAmp Supported Deposition of 3C-SiC [2].The FLASiC team –see the author and affiliation list aboveorganized within a project of the V. Framework of the European Community is currently extending this early work as a broader approach with the following main aspects: (i) Development of the epitaxial process including FLP: This includes not only the development of FLASiC as a basic version, but also the so-called i-FLASiC process [2] as the latest variant to overcome some problems of the basic FLASiC. In this case the ”i” stands for “inverse”, see below. (ii) Development of a prototype equipment for the FLP: Flash lamp processing or simply annealing was an early outcome of the euphoria in Laser annealing of semiconducting materials in the late seventies. The difference of FLP to Laser annealing is the longer annealing time in the msec Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 175-180 doi:10.4028/www.scientific.net/MSF.457-460.175

MnS clusters in natural zeolites

Abstract FTIR, ESR, optical absorption, photoconductivity, and luminescence measurements are used to evidence the nature of MnS clusters, synthesized by treating the Mn 2+ forms of natural zeolites with Na 2 S.

The existence of a new α’‐HgI2 phase and its use for growing single crystals of α‐HgI2

The existence of a new red α’‐HgI2 phase that occurs in a narrow temperature range prior to melting has been established. This phase allows the growth of single crystals within its stability range, which after quenching retain their monocrystallinity and transform to α‐HgI2. The method is used to prepare single crystals of any desired volume either pure or doped.