Biological Applications of Nanocrystalline Diamond
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0956-J05-01
Biological Applications of Nanocrystalline Diamond Oliver A.. Williams1,2, Michael Daenen1, and Ken Haenen1,2 1 Institute for Materials Research, Wetenschapspark 1, Diepenbeek, 3590, Belgium 2 IMEC vzw, Division IMOMEC, Wetenschapspark 1, Diepenbeek, 3590, Belgium
ABSTRACT Nanocrystalline diamond films have generated substantial interest in recent years due to their low cost, extreme properties and wide application arena. Diamond is chemically inert, has a wide electrochemical window and is stable in numerous harsh environments. Nanocrystalline diamond has the advantage of being readily grown on a variety of substrates at very low thickness, resulting in smooth conformal coatings with high transparency. These films can be doped from highly insulating to metallically conductive and at very high concentrations become superconducting.
INTRODUCTION Diamond has a number of properties that make it ideal for biological applications. The extreme chemical inertness, tuneable surface wettability, wide electrochemical window and high transparency are well documented properties1. More specific to diamond is the stability of functionalisation strategies, crucial for long term bio-sensing2. Hydrogen terminated diamond also exhibits p type surface conductivity3 and strong pH sensitivity4.
EXPERIMENTAL PROCEDURE AND RESULTS Nanocrystalline diamond films were grown by Microwave Plasma Enhanced Chemical Vapour Deposion (MWPEVCD). Prior to deposition, substrates were immersed in ethanol / diamond powder suspensions and bath ultrasonicated for 30 mins. Growth parameters were 1-3% CH4 in H2 gas phase, 2-3.5kW, 20-40 torr, 700 ºC for a duration depending on desired thickness. Temperature was monitored by two colour pyrometry. Doping was achieved by the addition of trimethylboron (TMB) to the gas phase. Figure 1 shows a plot of growth rate against substrate temperature at 700 ºC and 3500 W. It can be seen from this figure that the growth rate increases with CH4 fraction as expected.
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Figure 1: Growth rate against methane fraction for nanocrystalline diamond deposition at 700 ºC and 3500 W. Figure 2 (a) is a Scanning Electron Microscopy image of a standard film of NCD grown from 1% CH4 in H2, this film exhibits one colour uniformity over 2”. This film exhibits grain sizes less than 50nm and is around 50nm thick. The grain size is reasonably uniform in this film, and it is found that films grown with higher methane content usually show a much wider distribution of crystallite size. 1500
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This NCD obviously shows clear faceting at this length scale unlike UNCD [ref]. Figure 2(b) is a Raman spectrum of a general NCD filom. It can be seen that unlike UNCD, NCD exhibits clear sp3 bonding ion Raman due to its strong crystalline faceting as seen in figure 2(b). A clear 1332 cm-1 peak is se
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