Papers

ICMCTF2003 Session D2-2: Growth and Applications of Diamond DLC, and other Wide Band Gap Materials

Thursday, May 1, 2003 8:30 AM in Room Royal Palm 1-3

Thursday Morning

Start	Invited?	Item
8:30 AM		D2-2-1 Building Organized Mesoscale Architectures Based on Multidirectionally Oriented Carbon Nanotube Bundles for Appllications G. Ramanath (Rensselaer Polytechnic Institute) There is widespread interest in harnessing carbon nanotubes for applications such as device interconnection, field emission, sensing, memory storage, molecular sieving, and skeletal reinforcement. In order to realize these possibilities, it is essential to controllably create meso-scale architectures of these nanoscale units, placed in desired locations and orientations, by a scaleable approach. This talk will describe our most recent results on creating meso-scale architectures comprised of nanotubes with multiple orientations with a high-degree of control over nucleation sites, substrate selectivity, orientation inheritance and length tunability. Our approach is based on a CVD technique that combines gas phase catalyst delivery, and results in selective growth of highly aligned nanotubes on silica surfaces. Spectacular growth morphologies including radially oriented or normally oriented nanotubes are possible to attain by manipulating the nucleation and growth modes. We combine lithographic chiseling of silica templates and selective growth normal to the surfaces, to controllably place and grow nanotube structures in any set of multiple (e.g., vertical + horizontal) predetermined directions at preselected locations. This approach can be used to create a variety of 2D and 3D mesoscale relief architectures with complex shapes, and porous membranes with a hierarchy of pore sizes. Strategies to achieve multilayered nanotube architectures and structures with nanotubes of different preselected lengths and/or orientations in close proximity will be demonstrated. Measurements of electrical and mechanical response characteristics of these architectures will also be described. If time permits, I will focus on emerging strategies for creating new device architectures by ion-assisted junction formation and selective anchoring nanoclusters to nanotube surfaces for fabricating molecular devices with nanotubes as building blocks.
9:10 AM		D2-2-3 Optical & Electrical Properties of Amorphous Carbon Films Deposited using Filtered Cathodic Vacuum Arc with Pulse Biasing J.Y.SZE Sze, B.K. Tay, D. Sheeja, L.K. Pan, S.P. Lau, P. Zhang, Z.W. Zhao (Nanyang Technological University, Singapore) The passive devices fabricated in metal containing amorphous (a-C) films are excellent. However, the difficulty in the etching of these films as well as their inferior inertness compared to pure a-C films led us to study the electrical and optical properties of pure a-C films deposited using Filtered cathodic vacuum arc system (FCVA) in conjunction with high substrate pulse basing. It is possible to control the sp² content and hence the properties, by varying the substrate pulse bias voltage. In the present study, the a-C films were prepared by varying the high substrate bias between 3kV and 11kV using Plasma Immersion Ion Implantation (PI3) system and which result in low stress, adhesive films. Characterization of these samples gives us an indication of the suitability of the films for integrated passive devices and other applications. Four-point probe measurement has been carried out to study the resistivity of the films deposited on quartz and SiO₂. The resistivity decreases with increasing the pulse bias voltage and which might probably be due to the increase in the sp² fraction in the film. The sp² content in the films are also estimated using XPS as well as Raman spectroscopy. Characterisation of optical properties of the films using Spectroscopic phase-modulated Ellipsometer as well as UV-visible spectrophotometer will also be discussed in the paper.
9:30 AM		D2-2-4 Structural and Optical Properties of In_xAl_1-xN, and In_xGa_1-xN Nanowires Grown by Metalorganic Chemical Vapor Deposition S.-C. Shi, C.-F. Chen (National Chiao Tung University, Taiwan, ROC); L.-C. Chen (National Taiwan University, Taiwan, ROC); K.-H. Chen (Academia Sinica, Taiwan, ROC) In this report the structural and optical properties of In_xAl_1-xN, and In_xGa_1-xN nanowires were studied. The nanowires were grown on the silicon substrate with Au as catalyst utilizing a simple resistive heated metalorganic chemical vapor deposition (MOCVD) system. Structural studies by high resolution transmission electron microscopy (HRTEM), scanning electron microscope (SEM), X-ray diffraction (XRD), and Raman spectroscopy of the nanowires were presented. Optical properties were obtained from both photoluminescence (PL) and cathodoluminescence (CL). While PL measurements are usually over a relative large area containing lots of nanowires, the CL technique allows us to measure luminescence signal from an individual nanowire. CL measurements of nanowires showed that CL spectral peaks shift to higher photon energy with increasing aluminum and gallium content. Size effects of nanowires on the CL spectra shift were also investigated.
9:50 AM		D2-2-5 Luminescence and SiC Formation from C and H Implanted Silicon Zhenghua An, R.K.Y. Fu, P. Chen (City University of Hong Kong); W.L. Liu (Shanghai Institute of Microsystem and Information Technology); P.K. Chu (City University of Hong Kong); C.L. Lin (Shanghai Institute of Microsystem and Information Technology) Since Canham reported intense visible photoluminescence (PL) from porous Si at room temperature, much effort has been made in an attempt to produce novel light-emitting materials to meet the demands of optoelectronic applications. Silicon carbide (SiC) may be one of the most promising candidates that can satisfy the need of blue light emission because of its wide optical band gap. Many PL studies have shown that porous SiC generally exhibits more intense visible luminescence than single crystal SiC at room temperature. The porous SiC samples prepared from bulk crystals of different polytypes such as 3C, 6H and 4H-SiC have almost identical PL spectra that are independent of the band-gap energy of a particular SiC polytype. Intense visible luminescence has also been observed from polycrystalline SiC at room temperature. All these developments show that SiC is a competing candidate for Si-based optoelectronics, although blue PL is still difficult to obtain from SiC. It has been reported that SiC can be formed by carbon implantation into silicon combined with high temperature annealing. In this work, we report our results on blue light emission from SiC samples formed by carbon implantation. Also, hydrogen implantation, together with subsequent heat treatment, is employed after SiC formation to create a buried porous structure and to passivate implantation damage, which always acts as non-radiative recombination centers. FTIR, Raman and SIMS are used to characterize the samples and the PL mechanism is discussed.
10:10 AM		D2-2-6 "Cold" and "Hot" Hydrogenation of CVD Diamond Films V. Richter, Y. Avyigal (Technion-Israel Institute of Technology, Israel) The potential use of CVD diamond coating as a cold cathode material is limited by several factors associated with a material degradation induced by interaction that gives rise to secondary electron emission. In particular, the negative electron affinity (NEA) loss which is attributed to Hydrogen detachment from the film surface, happens during ion or electron bombardment and seriously affects secondary electron emission. We show here the possibility of surface hydrogenation performed at relatively low temperature of 350°C to cause complete hydrogen termination of CVD diamond film surface. Subsequent low dose proton bombardment causes significant decrease in ion induced electrom emission (IIEE) coefficient γ. Repeated "cold" and "hot" rehydrogenation of CVD diamond film only partially recovers the emission properties implying an existance of residual Boron-defect complexes.
10:30 AM		D2-2-7 An Intermediate Hybridization in Diamond: Edge Shared Tetrahedra A. Badzian, T. Badzian (The Pennsylvania State University) The crystal structure of diamond is a model for a whole family of group IV elements and AIIIBV and AIIBIV semiconductor compounds. A common feature of these structures is a connection of tetrahedra at the corners. It take place in cubic diamond (sphalerite), hexagonal diamond (wurtzite) and polytypes. Stacking faults and twinnig on {111} planes are well-established defects of tetrahedral family of structures based on the connection at the corners. The exact atomic configurations of carbon atoms in disordered CVD diamond materials are not known. We respond to the present ambiguity about the sp³/sp² concepts created by the assignment of sp³ to diamond and sp² to graphite structure. We consider a hypothesis of twinning on (001) plane as a new type of defect. The (001) twinning implicates that the tetrahedra share edges. This is contrary to accepted rules of crystal chemistry. The tetrahedra are connected along the <110> direction, and the twinning on (001) create chains of carbon atoms arranged as rhombuses lying in the (1-10) plane. The interatomic distance in such four-member rings is anticipated to be an intermediate between diamond and graphite. This particular atomic configuration is considered as an intermediate hybridization in between single and double bonds. We think that oriented growth of diamond on (001) silicon generates (001) twins in diamond structure. Raman spectra from these materials show non-cubic diamond features. We suggest their connection to twinning. Scanning Tunneling Microscopy images of hydrogenated (001) diamond surface revealed disturbances of dimmers in the <110> direction. It is possible that linear defect with tetrahedra sharing edges is observed there.
10:50 AM		D2-2-8 Effect of Substrate Bias on the Adhesion of the Diamond Film Deposited on the WC-Co Cutting Inserts by HFCVD J.-K. Park, D.-H. Kim, W.-S. Lee, Y.-J. Baik (Korea Institute of Science and Technology, South Korea) The adhesion of diamond film deposited on WC-Co insert was investigated according to the substrate bias. SPGN type of WC-Co was used as substrate where diamond was deposited by hot filament chemical vapor deposition (HFCVD) at 60 torr with H₂-2%~3%CH₄ mixed gas. Pulsed DC bias was applied to the insert with the range between 0V and -120V. For comparison, 3-kinds of specimen were prepared, in which the bias was applied after the deposition of 5h, 7.5h and 10 h, respectively. The adhesion of the deposited diamond films was measured by indentation method. The machining test was performed with Al-Si alloy, and the surface roughness of the machined workpiece was measured. The grain size of diamond film deposited on WC-Co insert decreased with increase in negative bias voltage. The grain size refinement was more enhanced near the edge than the center of the insert. For the diamond films with same thickness, the adhesion was measured to be better when the bias was applied later. The surface roughness value of the machined Al-Si alloy became smaller when using the diamond-coated tool with smaller grain size induced by DC biasing. The effect of negative DC biasing during diamond deposition on adhesion of diamond film and roughness of the machined workpiece will be discussed.
11:10 AM		D2-2-9 Growth and Applications of Large Area CVD-Diamond W. Mueller-Sebert, C. Wild, E. Woerner, P. Koidl (Fraunhofer-Institut für Angewandte Festkoerperphysik, Germany) For many applications of CVD-diamond, high purity large area films or free standing layers are required. We report on the development of microwave-plasma reactors for the deposition of such films and their processing to a variety of diamond products. Based on FEM-simulations for the distribution of the electric field and the resulting plasma position, a range of differently sized MW-plasma reactors with an ellipsoidal resonator has been built. With our 2.45 GHz system, films up to 75 mm in diameter have been produced, a scaled up 915 MHz system has the capability of depositing layers with diameters up to 150 mm. Thicknesses up to 2 mm have been realized. Processing techniques to prepare free standing diamond wafers or windows have been developed. Three dimensional diamond components have been realized either by laser processing or by engraving structures into the substrates with subsequent overgrowth. We have developed a variety of innovative diamond products for optical, acoustical and thermal applications. In detail we will report on the preparation of optical and microwave windows, diamond lenses, flexible diamond heat spreaders and diamond tweeter domes for integration in high-end loudspeaker systems.