Papers by Author: X.H. Qi

Abstract: Single-phase nanocrystalline diamond composite is very difficult to sinter because of a huge amount of oxygen-containing and nitrogen-containing functional groups adsorbed on the surface of nanocrystalline diamond going against the yielding of diamond-to-diamond bonding. In this paper, silicon film was deposited on nanocrystalline diamond by means of atomic layer deposition (ALD) using silane as precursor, which would promote the sintering of nanocrystalline diamond as the bond. The structure and the morphology of Si-deposited nanocrystalline diamond were thoroughly studied by X-ray diffraction (XRD), high-resolution electron microscopy (HREM) and Fourier transform infrared (FTIR) spectra. The results confirmed that silicon film grew uniformly on every primary particle and functional groups adsorbed on the surface of nanocrystalline diamond were removed by this method.

Abstract: Nanocrystalline diamond compact possesses not only the advantageous performance of polycrystalline diamond but also the high strength and the high toughness of nano-ceramics. However, single-phase nanocrystalline diamond compact is very difficult to sinter because of a huge amount of oxygen-containing and nitrogen-containing functional groups absorbed on the surface of nanocrystalline diamond. In this paper, atomic layer deposition (ALD) method has been used to coat nanocrystalline diamond with titanium, which will promote the bonding of nanocrystalline diamond as the bond in polycrystalline diamond. In vacuum, the H2 and TiCl4 reactants were employed alternately in an ABAB… binary reaction sequence to achieve Ti layer, which reacted with diamond matrix and formed TiC in the coating, realizing strong chemical bonding between the coating and the diamond. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were utilized to study the structure and the morphology of the coating. The results confirmed the formation of titanium carbide at the depositing temperature 500°C. The darker spots and strips observed on nanocrystalline diamond particles by TEM were proved to be TiC and the nucleation and subsequent growth of TiC preferentially occurred in the defects as twin zones and dislocation areas on diamond surfaces.

Abstract: A new species of single-cell magnetotactic bacteria, the NMV-1 bacteria, has been found by us. Each NMV-1 bacterium synthesizes itself a chain of magnetic nanoparticles inside its body. When an external magnetic field is applied, long bacteria chains come into being in the direction of the field in the water. More than 30 µm long chains of live bacteria have been observed. Length of bacteria chains is field dependant: the higher the magnetic field is, the longer the bacteria chains are. The bacteria chains orientation is controllable and the chains can be stably trapped. The mechanism of the assembly of long bacteria chains is also discussed. The results show that, while an external magnetic field is applied, the NMV-1 bacteria have strong enough interactions between each other to assemble long bacteria chains. After positioning the bacteria chain, cellular membranes of the bacteria were removed by cell lysis, leaving long chains of magnetic nanoparticles on a substrate. These magnetic nanochains can be potentially used as building blocks for magnetic nanostructures.