ICMCTF2004 Session D3: Functionalized Carbon-based and Nitrogen-based Materials

Friday, April 23, 2004 8:30 AM in Room Royal Palm 4-6

Friday Morning

Start	Invited?	Item
8:30 AM	Invited	D3-1 Thermal Properties, Processing and Applications of Highly Oriented Diamond Thin Films Scott D. Wolter (Duke University and US Army Research Office) Diamond is quite commonly regarded to as the ultimate semiconductor material because of its outstanding combination of materials properties. Yet, its relatively slow technological progress has limited its utility in commercial applications. A challenge exists for diamond technologists to seek out potential niche applications based on current capability as well as to advance the state-of-the-art in growth and device processing for next generation microelectronics. This presentation discusses early research surrounding bias-enhanced nucleation, a technique discovered circumstantially to promote diamond nucleation on pristine silicon. The discussion follows the progression of results from initial nucleation studies to later work involving epitaxial nucleation on Si(100) and TiC(111). This is truly an example of an enabling technology, as the epitaxially-textured films have been targeted for a host of applications. It was recognized very early in these studies that the substrate significantly affected the nucleation enhancement process, whereby the carbide formers appeared most suitable. While initial work was focused on negative DC substrate biasing, our attention later turned to cyclic and unipolar-pulsed biasing as a means of simplifying the processing of the highly oriented diamond. An investigation into duty cycle and bias frequency effects provided interesting and unanticipated results, enabling insight into this epitaxial nucleation process. The presentation then turns to an evaluation of the thermal attributes of bias-nucleated, epitaxially-textured diamond by comparing the in-plane thermal conductivity of highly oriented vs. randomly oriented diamond, and measuring their temperature-dependent thermal properties. Inferences may be made from this data regarding the defects responsible for their respective thermal properties. Finally, more recent efforts to wafer bond single-side polished Si(100) to smooth, epitaxially-textured diamond are presented. These silicon-on-diamond substrates were successfully fused at temperatures 750°C under an applied stress as low as ~10 MPa. This work highlights the effect of surface preparation on the bonding effectiveness and the materials reactions that occur at the fusion interface.
9:10 AM		D3-3 Use of Amorphous Carbon As High-pressure Cell for Investigating Trapped Noble Gases As a Function of Pressure P.F. Barbiere, M.H. Oliveira Jr, R.G. Lacerda (UNICAMP, Brazil); F.C. Marques (University of Campinas, Brazil) In the development of amorphous carbon it was found that hard films could be prepared under extreme stress. This stress is, in fact, a problem that hinders most technological applications. Nevertheless, this high stress can be useful for some scientific investigation. In this work we propose the use of amorphous carbon as high-pressure cell for trapping nobles gases under high pressure. This approach enables us to investigate the effects of the internal pressure on the implanted noble gases atoms subjected to the highly strained environment of the carbon matrix. This is an interesting approach to study noble gases under high pressure, because of the facility for handling the samples, which is a problem when using the conventional diamond anvil cells. Although these two systems provide different pressure characteristic, the use of trapped gases in a solid matrix alloys some investigation that is very hard to be carried out using the diamond cells. Using the above approach we studied the local environment of noble gases atoms implanted into an amorphous carbon (a-C) matrix. Thin a-C films were prepared by ion-beam-assisted deposition (IBAD) at 150 0C using noble gases. Photoemission spectroscopy (XPS/UPS), Electron Energy Loss Spectroscopy (EELS), and Raman scattering indicate that the material is composed of compressed and dense sp2 network (90% by EELS). By intentionally changing the a-C deposition conditions we were able to trap noble gas atoms under different internal pressure (intrinsic stress) ranging from 1 GPa up to 10 GPa. Extended x-ray absorption fine spectroscopy (EXAFS) was performed to investigate the interatomic distance of the implanted noble gases as a function of the intrinsic stress of the carbon matrix. The analysis of XANES (x-ray near edge spectroscopy) and the EXAFS indicate the clustering of the implanted noble gas atoms.
9:30 AM		D3-4 Gas Permeation Through Polymer Membranes Modified by A-C:H(n) Films Deposited using Butene, Butadiene and Nitrogen Gas Mixture C.A. Achete, E.F. Castro Vidaurre, R.A. Simao, A.C. Habert (Universidade Federal do Rio de Janeiro, Brazil) Pure amourphous hydrogenated carbon (a-C:H) and amorphous nitrogen incorporated (a-C:H(N)) films, with thickness up to 1 micron, were deposited onto asymmetric porous substrates of polysulfone (PSf) membranes by 13.56 MHz r. f. self bias glow discharge using pure Butadiene, Butene or mixtures with nitrogen. Several deposition parameters, namely bias voltage (Vb) , nitrogen partial pressure (PN) and total pressure P, were varied in a controlled way. The permeation of the gases N₂, and CO₂ was measured and the reduction of the permeability coefficient was correlated to composition and structure of the a-C:H(N) films obtained with different gases. The stoichiometry of the layers was analyzed using ion-beam techniques on films deposited onto silicon samples. The surfaces were analyzed using optical microscopy and atomic force microscopy (AFM). Room temperature conventional gas permeation measurements were performed on uncovered membranes and as a function of film thickness for layers deposited with different gases, Vb and PN. It was observed a general tendency of reduction of the permeability coefficient with the film thickness, reaching a minimum reduction of 95% for polymerlike layers of about 100 nm. Surprisingly, the barrier efficacy of the coating decreases with increasing a-C:H(N) film thickness or increasing bias voltage. This unexpected result is attributed to both, appearance of a network of cracks on the hole surface of the coating and the severe etching of the membrane surface during the deposition.
9:50 AM		D3-5 Organometallic Precursors for Deposition of Metal Nitrides and Metal Carbides L. McElwee-White, C.B. Wilder, L.L. Reitfort, O.J. Bchir, K.M. Green, T.J. Anderson (University of Florida) Chemical properties of organometallic complexes, such as bond strengths, mass spectrometry fragmentation patterns and solution substitution chemistry, can be used in the design and evaluation of precursors for deposition of metal nitride and carbide films. Target materials include tungsten nitride and zirconium carbide. Correlation of film properties and deposition conditions to chemical structure will be discussed.
10:10 AM		D3-6 High Quality Zirconium Carbide Thin Films Grown by Pulsed Laser Deposition V. Craciun, J.M. Howard, T.J. Anderson (University of Florida) The growth of thin films of zirconium carbide on Si wafers by the pulsed laser deposition technique has been investigated. Structural information for the films was obtained by x-ray diffraction and grazing incidence x-ray diffraction. The thickness, density and interfacial and surface roughness were investigated by x-ray reflectivity and variable angle spectroscopic ellipsometry. Surface morphology of the films was also characterized by atomic force microscopy and scanning electron microscopy. Chemical composition and bonding was obtained by x-ray photoelectron spectroscopy. Current emission properties of films were also investigated. It has been found that crystalline films could be grown only by using fluences above 6 J/cm² and substrate temperatures in excess of 500°C. For a fluence of 10 J/cm² and a substrate temperature of 700°C, highly (100)-textured ZrC films exhibiting a cubic structure (a=0.469 nm) and a density of 6.7 g/cm³ were deposited. The use of a low-pressure atmosphere of C₂H₂ had a beneficial effect on crystallinity, stoichiometry, and field emission characteristics of the films. All films contained high levels of oxygen contamination, especially in the surface region, because of the rather reactive nature of Zr atoms.
10:30 AM	Invited	D3-7 Flat Screen Displays Based on Carbon Nanotube Films K.A. Dean (Motorola Inc.) A conductive surface that is functionalized with carbon nanotubes can become an excellent electron source. At Motorola, we have learned to selectively coat regions of a surface with carbon nanotubes below 550°C while controlling the nanotube size, orientation, and spatial distribution. We describe how this technique enables us to catalytically grow nanotubes into the device structures of field emission displays on commercial display glass substrates. We characterize the electrical, mechanical, and surface science properties of these nanotubes that lead to good electron emission behavior. Finally, we demonstrate recent success in the development of flat screen displays based on these nanotube electron emitters.
11:10 AM		D3-9 Carbon Nanoflake Synthesized by RF PECVD on Si and Metal Surfaces M. Zhu, J. Wang, R. Outlaw, X. Zhao, N. Theodore (College of William and Mary); V.P. Mammana (International Technology Center); B.C. Holloway, D.M. Manos (College of William and Mary) This paper reports the synthesis of a novel morphological form of carbon, which we call carbon nanoflake (CNF). Using high-density RF inductively coupled plasma enhanced chemical vapor deposition, we have deposited this high-surface area, high-aspect ratio material on a variety of substrates including Si, SiO_x, and most importantly continuous metal films. SEM and TEM images show that the carbon nanoflakes have edges less than 5 nm wide, heights over 100 nm, and are insensitive to probe beam heating. TEM and TED indicate that the material contains well-ordered graphene sheets. Kelvin Probe measurements yield a contact potential (work function) of CNF that is close to graphite. Raman spectra show that the ratio of D to G peaks is a function of the gas composition, which correlates to changes in morphology seen in SEM images. Since two possible areas of application are energy storage and field emission, surface area measurements and I-V curve data will also be discussed as well the capability to grow CNF’s without catalytic pretreatment of the surface.
11:30 AM		D3-10 Large Area Formation of Platinum Nanoparticles on Arrayed CN_x Nanotubes C.-L. Sun, K.H. Chen (Academia Sinica, Taiwan, R.O.C.); L.S. Hong, M.-C. Su (National Taiwan University of Science and Technology, Taiwan, R.O.C.); C.-Y. Hsu, L.C. Chen (National Taiwan University, Taiwan, R.O.C.); T.-F. Chang, L. Chang (National Chiao Tung University, Taiwan, R.O.C.) Arrayed CN_x nanotube-platinum (Pt) nanoparticle composites have been synthesized and investigated in this report. The CN_x nanotube arrays were grown by microwave-plasma-enhanced chemical vapor deposition (MPECVD) at first then acted as the template and support for Pt dispersion in the following sputtering process. Under the same sputtering condition, it was found that well-separated Pt nanoparticles would form with an average diameter of 2 nm on the arrayed nanotubes while a continuous Pt thin film was observed on the bare Si substrate. Furthermore, the effect of sputtering on the nitrogen bonding in nanotubes was also studied by X-ray photoelectron spectroscopy (XPS). XPS spectra revealed that the sputtering process would cause the decrease of nitrogen content in CN_x nanotubes and also result in the change of peak shape in C1s spectra. Implications of these bonding changes and the nanotube-Pt composite structures will be discussed. Finally, it is suggested that the much larger sidewall surface area of nanotubes would be helpful for catalyst application with uniform fine Pt dispersion.