D.S. Misra

High-resolution transmission electron microscopy mapping of nickel and cobalt single-crystalline nanorods inside multiwalled carbon nanotubes and chirality calculations

The nickel and cobalt nanorods of the diameters in the range of 6–20nm with lengths of 0.29–0.9μm are formed using multiwalled carbon nanotubes as templates. The nickel and cobalt nanorods as described in our letter are perfect single crystals inside the nanotube with their Miller planes inclined with respect to the tube axis in a particular fashion. The (111) planes of face-centered-cubic nickel and cobalt are inclined at angles 39.6° and 39.4°, respectively, while the hexagonal-closed-packed cobalt (002) planes incline at an angle 53.4°. The inclination of these planes is studied in detail and results are discussed in terms of elastic energy and surface tension. The chirality of the carbon nanotubes, in intimate contact with the nanorod, is determined using the mapping of Ni and C atoms in a graphene sheet. We believe this could pave a way for synthesizing the tubes with known chirality.

Microstructure, flux pinning and critical current density in YBa2Cu3O7-δ films grown by laser ablation

Abstract Thin films of YBa2Cu3O7−δ (YBCO) are deposited by laser ablation at substrate temperatures (Ts) ranging from 575 to 850 °C. The microstructure and growth behaviour of the films are found to be a sensitive function of Ts. We also find that the critical current density (Tc) of the films isstrongly related to the microstructure. It is proposed that the boundaries between a-axis and c-axis grains may act as pinning centres.

DC electrical conductivity of chemical vapour deposited diamond sheets: a correlation with hydrogen content and paramagnetic defects

Diamond sheets were grown on p-type Si( 100) substrates varying the deposition pressure from 20 to 140 Torr at 1163 K by a hot filament chemical vapour deposition (HFCVD) process. A mixture of 0.8% methane in balance hydrogen was used as a precursor gas. Diamond sheets deposited at low pressures are translucent with very low concentration of hydrogen and non-diamond impurities, The amount of non-diamond impurities and the hydrogen content increase in the sheets significantly with the growth pressure. A systematic variation in the value of the room temperature DC electrical conductivity (σ 300 ) of diamond sheets was observed. Highly pure sheets show very high values of σ 300 . It is suggested that the paramagnetic defects intrinsic to CVD diamond might be one of the controlling parameters of σ 300 of the sheets.

Diamond nucleation and growth on zeolites

Abstract In this work, we report the use of zeolites as substrates for the deposition of porous diamond films. Films were deposited in a hot-filament chemical vapor deposition (HFCVD) apparatus. The HFCVD system was fed with a mixture of methane (0.8%) with the balance being hydrogen. A series of depositions were done in the pressure range 20–120 Torr and at substrate temperature 880 °C. The morphologies of the as-deposited films were analyzed by scanning electron microscopy and show isolated diamond grains in the initial nucleation stages, which develop into a microporous film in the next stage and form a continuous film after long time deposition. Raman spectroscopy was used to investigate the crystal morphology, structure and non-diamond impurities in the films deposited at various growth conditions. The nature of the hydrogen bonding with sp 3 and sp 2 network and the quantitative analysis were done by Fourier transform infrared spectroscopy.

Growth of (100) oriented diamond grains by the application of lateral temperature gradients across silicon substrates

Polycrystalline diamond films with a predominant (100) texture were deposited onto silicon substrates using hot-filament chemical vapor deposition. During film deposition, different temperature gradients were created and imposed laterally across the substrate materials. Films grown under a gradient of 100 °C cm −1 displayed large (100) oriented grains. No crystallite (100) orientation was observed in the as-grown films prepared without a temperature gradient. It was observed that the diamond grain size varied as a function of the gradient. The lower gradient resulted in smaller grains and vice versa. Furthermore, the size of the grains was a function of the deposition time. The orientation of the diamond grains changed gradually across the substrate from (100) to (110) orientation as we scanned from the high-temperature to the low-temperature zone. The films were characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy. XRD showed strong (400) reflections in the oriented samples. SEM results indicated the presence of smooth diamond surfaces consisting of predominantly (100) oriented platelets. As the (100) oriented diamond grains were grown on top of the (100) oriented silicon substrates, the faces were mostly aligned parallel to the substrate surface resulting in the deposition of a smooth diamond surface. AFM observations revealed the presence of steps located at the boundaries of the oriented grains. FTIR results showed the characteristic difference in hydrogen bonding in the oriented samples and gave useful information about mechanisms responsible for the orientation. Quantitative analysis was carried out to measure the H content in the films, and it was found that the oriented films contained less hydrogen. Our findings suggest that high saturation of carbon and a concentration gradient of sp 3 CH 2 species can be the key factor in the oriented growth of (100) diamond grains.