Diamond CVD onto different substrates
We are investigating various methods to seed non-diamond surfaces to allow growth of CVD diamond layers. Manual abrasion using 1-3 μm of diamond grit is simple, but damages the substrate and is not very useful for thin layers (< 100 nm). An alternative is ultrasonic abrasion - a suspension of nanodiamond powder is made in a liquid (usually water but it can be methanol or IPA) and agitated in an ultrasonic bath or using an ultrasonic probe (see picture, right). This breaks up large agglomerates and keeps the suspension stable. The Si substrate is added to the sonicating suspension and the nanodiamond particles attach to the surface via van der Waals forces.
Another method, pioneered here at Bristol, is electrospray. A diamond suspension is put into a plastic syringe, and draw out of the tip via application of high voltage (30 kV) between the metal tip and a grounded substrate a few cm away. This causes the suspension to spray across the chamber towards the substrate, coating it uniformly in nanodiamond. This technique has the advantage of being fast, uniform and can coat 3D shapes. The substrate is rotated using an electric motor for uniformity. Photos of the electrospray kit can be seen below.
- O.J.L. Fox, J.O.P. Holloway, G.M. Fuge, P.W. May, M.N.R. Ashfold, "Electrospray deposition of diamond nanoparticle nucleation layers for subsequent CVD diamond growth", in Diamond Electronics and Bioelectronics - Fundamentals to Applications III, edited by P. Bergonzo, J.E. Butler, R.B. Jackman, K.P. Loh, M. Nesladek (Mater. Res. Soc. Symp. Proc. Volume 1203, Warrendale, PA, 2010), paper J17-27.