Electrospray Deposition of Diamond Nanoparticle Nucleation Layers for Subsequent CVD Diamond Growth
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1203-J17-27
Electrospray deposition of diamond nanoparticle nucleation layers for subsequent CVD diamond growth Oliver JL Fox, James OP Holloway, Gareth M Fuge, Paul W May, Michael NR Ashfold School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K. ABSTRACT Nucleation is the rate-determining step in the initial stages of most chemical vapour deposition processes. In order to achieve uniform deposition of diamond thin films it is necessary to seed non-diamond substrates. Here we discuss a simple electrospray deposition technique for application of 5 nm diamond seed particles onto substrates of various sizes. The influence of selected parameters, such as experimental spatial arrangement and colloidal properties, are analysed in optimizing the method by optical and electron microscopy, both before and after nanocrystalline diamond deposition on the seed layer. The advantages and limitations of the electrospray method are highlighted in relation to other commonly exploited nucleation techniques. INTRODUCTION The nucleation of non-diamond substrates prior to chemical vapour deposition (CVD) of nanocrystalline (NCD) and ultra-nanocrystalline diamond (UNCD) films is crucial for creating smooth, homogenous and uniform thin films. Substrates can be treated to promote surface nucleation in a variety of ways [1-3] including mechanical or ultrasonic abrasion [4-5], biasenhanced nucleation [6-7] and diamond-containing-photoresist coating [8]. Mechanical abrasion can be efficient at nucleating substrates for microcrystalline diamond (MCD) deposition, but the low surface roughness of NCD and UNCD films often demands a less aggressive nucleation technique. In previous studies, it has been shown that spraying diamond seed particles directly onto substrates can achieve nucleation densities of around 1011 cm-2 [9-10]. The electrostatic spray (“electrospray”) deposition technique uses a large potential difference to ionize nucleating particles (or droplets containing the particles) via the corona effect and accelerates them towards a grounded substrate. The technology has found many applications in the materials industry for application of particulates, paints and powders onto a variety of complex substrate forms and materials [11]. The technique has been employed successfully to seed silicon substrates prior to diamond CVD [12-13] using diamond powders suspended in water. In this case, the particles were forced through drying media (removing the majority of the liquid) by application of 30 psi pressure into an electrostatic spray gun (with an ionizing electrode at 80 kV) where they became charged and were then applied to the substrate. Here we describe a variation on this simple yet versatile electrospray deposition method for coating substrates with a nucleation layer comprised of 5 nm diamond particles. The main difference is that both the dispersion medium and the diamond particles exit through the electrode nozzle but the volatile liquid then evaporates before reaching the substrate, resulting in a uniform but dense coa
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