Diamond deposition on modified silicon substrates: Making diamond atomic force microscopy tips for nanofriction experiments

Fine-crystalline diamond particles are grown on standard Si atomic force microscopy tips, using hot filament-assisted chemical vapor deposition. To optimize the conditions for diamond deposition, first a series of experiments is carried out using silicon substrates covered by point-topped pyramids as obtained by wet chemical etching. The apexes and the edges of the silicon pyramids provide favorable sites for diamond nucleation and growth. The investigation of the deposited polycrystallites is done by means of optical microscopy, scanning electron microscopy and micro-Raman spectroscopy. The resulting diamond-terminated tips are tested in ultra high vacuum using contact-mode atomic force microscope on a stepped surface of sapphire showing high stability, sharpness, and hardness. (C) 2003 American Institute of Physics.status: publishe

The adhesion of hot-filament CVD diamond films on AISI type 316 austenitic stainless steel

Steel ball indentation and scratch adhesion testing of hot filament chemical vapour deposited diamond films onto AISI type 316 austenitic stainless steel substrates using two different interlayer systems, namely chromium nitride and borided steel, have been investigated. In order to compare the adhesion of these films with that of a well-known and strongly adherent system, detailed adhesion tests were performed on diamond films grown on molybdenum substrates as well. Scanning electron microscopy analysis of various indented regions on the diamond-coated steel and molybdenum samples in combination with the measurement of the acoustic emission signals during loading, indicate that the adhesion of the coatings on the stainless steel substrates with the CrN interlayer is comparable and only slightly less than that of the strongly adhering diamond films on the molybdenum samples. The critical load value derived from the acoustic emission signals at which partial delammation of the diamond films is first observed, is significantly lower for the diamond-coated steel with the boride interlayer than that obtained with the CrN interlayer for the present deposition conditions used. The steel ball indentation tests also show that the hardness and thickness of the interlayer have a strong effect on the penetration depths of the indents. Scratch tests performed on the diamond coated stainless steel specimens with the boride interlayer show no significant coating failure for loads up to 80 N. (C) 2003 Elsevier B.V. All rights reserved.status: publishe

The applicability of ultra thin silicon films as interlayers for CVD diamond deposition on steels

In this study, the use of thin Si interlayers (35-150 nm) for promoting diamond deposition onto steel is investigated. The diamond films are deposited by hot filament CVD onto AISI type 316 stainless and high-speed steels. Single stage deposition at substrate temperatures. ranging from as low as 475 to 750 degreesC is found to result only in non-continuous films with low number densities of diamond crystallites. A composite film of diamond and carbides is formed at intermediate temperatures of about 650 degreesC. It is believed that the formation of iron silicide phases at the exposed steel substrate surfaces leads to diffusion barriers for free iron from the steel matrix, so that graphitic soot formation is significantly avoided. Utilizing a two-stage deposition process, the density and uniformity of the deposited diamond films are increased and a nearly continuous cauliflower shaped diamond film is obtained. Micro-Raman spectroscopy, scanning electron microscopy and X-ray diffraction techniques are employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers.status: publishe

Atomic force microscopy studies on the surface morphology of {111} tabular AgBr crystals

Both ex situ and in situ atomic force microscopy have been applied to study the (1 1 1) and (1 0 0) surfaces of tabular silver bromide crystals grown from dimethyl sulphoxide-water solutions. This resulted in observations of monosteps, macrosteps, etch pits, pinning of steps and nucleated crystals showing twin planes. These examinations indicate that the growth and dissolution of both the (1 0 0) and the polar (1 1 1) faces occur via steps in many configurations. The registered 40-nm distance between the parallel twin planes of the nucleated crystals agrees with transmission electron microscopy measurements done on tabular crystals grown by the industrial double-jet precipitation method. (C) 2000 Elsevier Science B.V. All rights reserved.status: publishe

The effect of nitriding on the diamond film characteristics on chromium substrates

In this report, we present a study of diamond deposition on pure and nitrided chromium substrates using the hot filament-assisted chemical vapour deposition technique. Deposition was performed at substrate temperatures varying from 475 to 750 degreesC for different exposure times. Scanning electron microscopy (SEM), micro-Raman spectroscopy and X-ray diffraction (XRD) techniques were employed to study the modified interlayers and diamond films. The high solubility and diffusivity of carbon in pure chromium result in an increased incubation time for diamond nucleation. However, even a 4-5-mum-thick nitrided layer is efficient as a diamond-nucleating surface, with a reduced incubation time as compared to pure chromium. Fully covering and adhering diamond films were obtained on the nitrided Cr specimens at temperatures between 550 and 750 degreesC. As a result of the nitriding process, the nitride diffusion layer reduces the carbon solubility at the substrate surface, thereby reducing the incubation time for diamond nucleation. Due to the strong chemical and mechanical bonding of the diamond films to the nitrided Cr substrates, the residual compressive stresses are accommodated, leading to adherent, continuous diamond films. The present study, however, also indicates an optimal low-temperature deposition condition to obtain a continuous diamond film directly on pure Cr. (C) 2002 Elsevier Science B.V. All rights reserved.status: publishe

Enhancement of the nucleation of smooth and dense nanocrystalline diamond films by using molybdenum seed layers

A method for the nucleation enhancement of nanocrystalline diamond (NCD) films on silicon substrates at low temperature is discussed. A sputter deposition of a Mo seed layer with thickness 50 nm on Si substrates was applied followed by an ultrasonic seeding step with nanosized detonation diamond powders. Hot-filament chemical vapor deposition (HF-CVD) was used to nucleate and grow NCD films on substrates heated up at 550 °C. The nucleation of diamond and the early stages of NCD film formation were investigated at different methane percentages in methane/ hydrogen gas mixtures by atomic force microscopy, micro-Raman spectroscopy, scanning electron microscopy, and grazing incidence x-ray analyses in order to gain specific insight in the nucleation process of NCD films. The nucleation kinetics of diamond on the Mo-coated Si substrates was found to be up to ten times higher than on blank Si substrates. The enhancement of the nucleation of diamond on thin Mo interlayers results from two effects, namely, (a) the nanometer rough Mo surface shows an improved embedding of ultrasonically introduced nanosized diamond seeds that act as starting points for the diamond nucleation during HF-CVD and (b) the rapid carbonization of the Mo surface causes the formation of Mo₂C onto which diamond easily nucleates. The diamond nucleation density progressively increases at increasing methane percentages and is about 5 x 10¹⁰ cm¯² at 4.0% methane. The improved nucleation kinetics of diamond on Mo interlayers facilitates the rapid formation of NCD films possessing a very low surface roughness down to ~6 nm, and allows a submicron thickness control.status: publishe

Comparison of GaN and AlN nucleation layers for the oriented growth of GaN on diamond substrates

In this study, {0001} oriented GaN crystals have been grown on freestanding, polycrystalline diamond substrates using AlN and GaN nucleation layers (NLs). XRD measurements and SEM analysis showed that the application of a thin AlN NL gives the best structural results, because AlN has a thermal expansion coefficient in between GaN and diamond and thus delocalizes the stress to two interfaces. The optical quality of the layers, investigated with Raman microscopy and photoluminescence spectroscopy, is similar. Although no lateral epitaxy is obtained, new insight is gained on the nucleation of GaN on diamond substrates facilitating the growth of GaN epilayers on polycrystalline diamond substrates. (C) 2009 Elsevier B.V. All rights reserved.status: publishe

CVD diamond deposition on steel using arc-plated chromium nitride interlayers

This paper reports on hot filament CVD diamond deposition onto steel using arc-plated chromium nitride (CrN) as the interlayer. Direct deposition of diamond onto steel leads to the formation of a non-adhering layer of graphitic soot covered by poor-quality diamond. However, if are-plated CrN coatings with a thickness of 2.5 mu.m are used, diamond formation takes place. Adherent and good-quality diamond coatings are obtained after several hours of deposition at a substrate temperature as low as 650 degreesC. Micro-Raman spectroscopy, scanning electron microscopy, X-ray diffraction and EDAX analysis have been employed to study the phases, morphology, composition, quality and residual stresses of the grown diamond layers and the modified substrate interlayers. The Scotch tape test is used to assess the adhesion of the diamond coatings. (C) 2002 Elsevier Science B.V. All rights reserved.status: publishe

Growth of GaN on nano-crystalline diamond substrates

In this study GaN has been grown on nano-crystalline diamond substrates utilizing metal-organic chemical vapour deposition (MOCVD). It is shown that the growth of closed GaN films onto synthetic diamond substrates is feasible, when applying the correct buffer layer and growth parameters. XRD measurements showed that the GaN formed is of wurzite structure and polycrystalline, but the high intensity of the (0002) diffraction peak indicates a preferential crystallite orientation. This preferred 100011 orientation was confirmed by SEM analysis. The optical quality of the deposited GaN layer was investigated using cathodoluminescence and showed a large yellow luminescence peak. This work comprises a first step in preparing heterogeneous layers and GaN devices with a diamond heat sink as a substrate, facilitating the thermal management of these devices. (C) 2009 Elsevier B.V. All rights reserved.status: publishe

Pitting corrosion behaviour of diamond coated tool steel

Using a hot filament chemical vapour deposition reactor, diamond films of approximately 2-3 mum in thickness were deposited on tool steel specimens with three different interlayer systems, namely CrN, Si and borided steel. The morphology, defect densities and residual stresses of the diamond films were strongly governed by the type of interlayer used. Electrochemical potentiodynamic polarisation studies have been carried out on the diamond deposited tool steel specimens in NaCl solutions of two different concentrations, 0.01 M and 0.50 M, respectively. The type of interlayer used for diamond coating on tool steel has a strong influence on the corrosion potential. The maximum shift in the equilibrium corrosion potential is observed for the silicon interlayer. However, it leads to selective dissolution of the carbide phase upon anodic polarisation. A near total resistance to pitting of the CrN coated tool steel specimens is observed with the introduction of a very thin diamond layer of 2 - 3 mum. With increasing chloride ion concentration in the electrolyte, reverse trends in the shift of EO, are observed for the blank tool steels in comparison to the diamond-coated specimens. Detailed SEM characterisation of the corrosion-tested specimens indicates the possible operating mechanisms. (C) 2004 Elsevier B.V All rights reserved.status: publishe