Nanocrystalline Diamond Surface Research Articles

Nanocrystalline diamond surface functionalization in radio frequency plasma

Here we present data on growth of thin nanocrystalline diamond (NCD) layers on silicon and glass substrates by microwave plasma-enhanced chemical vapor deposition. The typical NCD layer thickness is below 500 nm with a typical grain size about 50 nm. NCD films are optically transparent, have a smooth surface and a low background photoluminescence. We have applied a radio-frequency (RF) plasma discharge in vaporized silane coupling agent N-(6-aminohexyl) aminopropyl trimethoxysilane to successfully functionalize the NCD surface with the primary amino group NH 2 as confirmed by using fluorescamine-in-acetone spray as a fluorescence marker.

Nanocrystalline diamond surface is resistant to bacterial colonization

Susceptibility of medical steel, titanium and medical steel coated with nanocrystalline diamond (NCD) to bacterial colonization was investigated. Number of bacteria at the surface was estimated with fluorescence microscopy inspection. It was found that efficiency of bacterial settlement depends on the presence of proteins in the surrounding media and that NCD surface exhibits the highest resistance to this process, significantly higher than that of titanium. The resistance of medical steel is very poor.

DNA-modified nanocrystalline diamond thin-films as stable, biologically active substrates.

Diamond, because of its electrical and chemical properties, may be a suitable material for integrated sensing and signal processing. But methods to control chemical or biological modifications on diamond surfaces have not been established. Here, we show that nanocrystalline diamond thin-films covalently modified with DNA oligonucleotides provide an extremely stable, highly selective platform in subsequent surface hybridization processes. We used a photochemical modification scheme to chemically modify clean, H-terminated nanocrystalline diamond surfaces grown on silicon substrates, producing a homogeneous layer of amine groups that serve as sites for DNA attachment. After linking DNA to the amine groups, hybridization reactions with fluorescently tagged complementary and non-complementary oligonucleotides showed no detectable non-specific adsorption, with extremely good selectivity between matched and mismatched sequences. Comparison of DNA-modified ultra-nanocrystalline diamond films with other commonly used surfaces for biological modification, such as gold, silicon, glass and glassy carbon, showed that diamond is unique in its ability to achieve very high stability and sensitivity while also being compatible with microelectronics processing technologies. These results suggest that diamond thin-films may be a nearly ideal substrate for integration of microelectronics with biological modification and sensing.

Surface acoustic waves on nanocrystalline diamond

Surface acoustic wave (SAW) devices based on polycrystalline diamond have recently achieved success as microwave filters. This is due in part to the large acoustic wavelength of diamond at microwave frequencies, a consequence of its high surface wave velocity, and the resulting ability to use photolithography for transducer fabrication. Since nanocrystalline diamond has a smooth surface and is elastically isotropic, it may offer considerable advantages over thick films of polycrystalline diamond. We have studied the propagation of surface waves on nanocrystalline diamond prepared by microwave plasma chemical vapor deposition (CVD) on silicon substrates. Films were synthesized on 75-mm Si wafers using input gas mixtures consisting of Ar with 1% CH4 and 0–4% H2. The deposition parameters studied included pressure, 2.45 GHz microwave power, and total gas flow rate. Film thicknesses up to 23 μm were produced. SAW transducers were fabricated by photolithography on as-grown nanocrystalline diamond surfaces covered with a 1–3 μm overlayer of oriented polycrystalline piezoelectric ZnO prepared by reactive dc sputtering. The device response was analyzed with frequency and time domain methods. The resonant frequencies of the devices agree with the results of numerical solutions for sound propagation in layered media. Several surface acoustic modes exist at frequencies between 0.5 and 1 GHz that exhibit appreciable dispersion. We have propagated surface waves in nanocrystalline diamond over distances varying from 0.1 to 3 mm with low attenuation. For a film with mean grain size of approximately 30 nm, the SAW velocity is similar to test devices on thick polycrystalline diamond. We conclude that nanocrystalline diamond is a highly attractive substrate material for SAW devices, possessing the high sound velocity of diamond but requiring less materials processing.