ICMCTF2005 Session H1-2: Nanostructured Coatings and Novel Deposition Strategies

Thursday, May 5, 2005 8:30 AM in Room Royal Palm 4-6

Thursday Morning

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8:30 AM H1-2-1 Carbon Nanotube Peapods: A New Form of Nano-Carbon
H. Shinohara (Nagoya University, Japan)

One of the fascinating features of metallofullerene-peapods (CNT encaging fullerenes) such as GdC82 peapods is that we can perform a local band gap engineering at the site where a fullerene is endothermally inserted. Previous TEM images and electron energy loss spectra suggested that the metallofullerenes1 can be spaced regularly as close as 1.1 nm in a high-density peapods structure, while 1.1 - 3 nm spacing was often observed in a low-density peapod. In the present GdC82 peapod samples, about 10% of over 200 SWNT images showed locally modified semiconducting band gaps2-5.

Scanning tunneling microscopy and spectroscopy (dI/dV) give bias-dependent topographic images and local density of states (LDS) on carbon nanotubes near the fermi level. In the STS map, two strong VHS peaks corresponding to conduction and valence band edges are clearly seen with two smaller ones at higher bias voltages. The original band gap of 0.43 eV is narrowed down to 0.17 eV where the fullerene is expected to be located.

Furthermore, GdC82 peapods exhibit ambipolar FET behavior with both n- and p-channels easily accessible by simple electrostatic gates. Similar results were obtained from more than 10 independent devices composed of a small bundle of GdC82 peapods. Such ambipolar behavior has never been observed for C60 peapods.

1H.Shinohara, Rep.Prog.Phys.63, 843(2000).
2K.Hirahara et al. Phys.Rev.Lett. 85, 5384(2000).
K.Suenaga et al. Phys.Rev.Lett., 90, 055506 (2003).
K.Suenaga, Science, 290, 2280-2281 (2000).
J.Lee et al. Nature 415, 1005(2002).

9:10 AM H1-2-3 Engineered Nano-Rare Earth Coatings for Corrosion Prevention
S. Seal (University of Central Florida)
Fe-Cr-Ni alloys are usually subjected to high temperature oxidation during their various processing stages like rolling, forging and heat treatment. Extensive scaling losses are found to occur in these components in such aggressive environments at elevated temperatures. Therefore, development of coating that imparts oxidation resistance to Fe base alloys is important not only for applications of these alloys at elevated temperatures but also to protect the oxidation losses during high temperature processing. The present study investigates the effectiveness of nano-ceria coating to enhance high temperature oxidation resistance of austenitic steels. The coatings are formed by self assembly on the alloy substrate. High temperature oxidation kinetics showed the effectiveness of nanoceria over micro ceria in corrosion prevention. Surface chemistry and scale morphology were characterized using SEM, SIMS, XPS and HRTEM.
9:50 AM H1-2-5 A Survey of Nanostructured Thin Films Created with Glancing Angle Deposition
C. Elliott, K. Robbie, C. Buzea, K. Kaminska, J. Yang (Queen's University, Canada)
Design of structured porous thin films has been dramatically advanced by glancing angle deposition (GLAD). Controlled substrate rotation, combined with variation in vapour incidence angle, creates porous nanostructures, affecting optical, thermal, magnetic, and biological response. A survey of the more significant structures will give us a broad perspective of the morphology achievable at the nanoscale and the possibilities available to the nano-designer. Structures include columns, pillars, helices, fractal cauliflower-like structures, and zig-zags. Potential applications for structured nanofilms made by glancing angle deposition include optical filters, photonic crystal hybrids, high efficiency power applications, and nano-scale biomaterials. A survey of attainable GLAD nanostructures will be presented from scanning electron microscope images of many previously unpublished structures.
10:10 AM H1-2-6 Nanostructure Growth by Glancing Angle Ion Beam Assisted Deposition
E. Schubert, F. Frost, Th. Hoeche, B. Rauschenbach (Leibniz-Institut fuer Oberflachenmodifizierung, Germany)
Nanostructures with a complex geometry promise a high application potential for instance as photonic band gap materials, magnetic storage devices or sensors. Glancing angle deposition in combination with a computer controlled substrate rotation is a sophisticated method to customize manifold nanostructure varieties. Ion beam sputtering of a silicon target is performed to generate a particle flux, which arrives at the [001] silicon substrate with an extremely oblique angle of incidence (typically 5 deg). By means of atomic shadowing, highly porous thin films are created, which consist of slanted amorphous silicon needles with a diameter from 20 nm to 50 nm. By adding a simultaneous substrate rotation, the nanostructure geometry can be tailored. Chevrons and quadratic spirals are created with a symmetric stepwise substrate rotation of 180 deg and 90 deg, respectively. The fabrication of circular spirals, spirellis and vertical posts is realised by a constant substrate rotation, and the nanostructure geometry depends on the ratio from deposition rate to substrate rotation speed. The growth of the nanostructures is studied in dependence of the substrate temperature, substrate prepatterning, substrate rotation speed, and deposition rate by using scanning electron microscopy and high-resolution scannning force microscopy. The nanostructure nucleation and growth processes are discussed by means of competitive growth mechanism due to atomic shadowing. Regular nanostructure arrays are demonstrated by using prepatterned substrates, and a self-ordering phenomenon depending on the substrate rotation symmetry is found for the nanostructure growth on unseeded substrates.
10:30 AM H1-2-7 Two-Component Nanopillars Arrays Grown by Glancing Angle Deposition
S.V. Kesapragada, D. Gall (Rensselaer Polytechnic Institute)
Periodic arrays of straight and zigzag shaped Si/Au, Cr/Si, and CrN multi-stack nanopillars, 20-100 nm wide, were grown by Glancing Angle sputter Deposition (GLAD) for use as high sensitivity sensors and complex three dimensional nanoarchitectures. Initial surface patterning was employed to control the nanopillar spacing from 20-160 nm. Si (100) substrates were patterned by dispersing monolayers of 20-160 nm diameter silica spheres to form a periodic close-packed array. Nanopillars grow perpendicular to the substrate surface when the substrate is continuously rotated about the polar axis during deposition. In contrast, a stationary substrate yields columns that are tilted towards the deposition flux, and zigzag pillars are obtained by rotating the substrate 180° during subsequent deposition steps. The azimuthal angle between the incident flux and the surface normal, which was varied from 66-88°, controls the width and broadening of the nanopillars as a function of layer thickness.
10:50 AM H1-2-8 Change of Preferential Orientation of Ru Films by Sputtering in Ar-N2 Mixed Gas
M. Kawamura, K. Yagi, Y. Abe, K. Sasaki (Kitami Institute of Technology, Japan)

In general, metal films are deposited in pure Ar gas by sputtering method. On amorphous substrate, metal films tend to show preferential orientation with the closest packed plane to minimize the surface energy of the films. However, an influence of reactive gas addition into the sputtering chamber on obtained film texture has been reported. Ru film with hcp structure generally tends to orient its c-plane (00l) parallel to the substrate surface. The influence of N2 addition into the sputtering gas on the crystal orientation of the films was investigated.

An rf magnetron sputtering apparatus with a Ru target (99.9%) was used for the deposition. Glass substrate heated at 100°C or 100°C was used and total flow rate of Ar and N2 was fixed to 1.0 cc/min. For the obtained films, crystal structure, chemical composition and electrical properties were investigated.

At 0% N2 flow ratio and 100°C of the substrate temperature (Ts), (002) peak was dominant by XRD measurement. By adding N2 into the sputtering gases, intensity of the (002) peak lowered and finally disappeared at 50%. By the surface analysis, it was shown that Ru films deposited in Ar-N2 mixed gas contain nitrogen. After annealing the films in vacuum at 400°C, nitrogen in the films was removed but orientation remained the same as before the annealing. Consequently, c-plane oriented and c-plane suppressed Ru films can be obtained by controlling N2 flow ratio. At 300°C of Ts, interaction between Ru atoms and nitrogen becomes weaker and c-plane remained preferentially oriented.

11:10 AM H1-2-10 Characterization of Elecrophoretically Deposited Nanocrystalline Titanium Dioxide Composite Thin Films
C.K. Lin, T.J. Yang, C.H. Lee (Feng Chia University, Taiwan); C.Y. Su (National Taipei University of Technology, Taiwan); P.Y. Lee (National Taiwan Ocean University, Taiwan)
TiO2 materials possessing photocatalytic properties have attracted many research and development interests. In the present study, nanocrystalline TiO2 powders were elecrophoretically deposited on the surface of a stainless steel substrate with or without following electroless plating treatment. The as-prepared nanocrystalline TiO2 and TiO2/Ni composite thin films were post heat treated to improve the adhesion strength. The as-prepared and heat-treated samples were characterized by atomic force microscopy, scanning electron microscopy, x-ray diffraction, synchrotron x-ray absorption spectroscopy, and UV-Visible spectroscopy. Preliminary experimental results show that the as-deposited nanocrystalline TiO2 films exhibited anatase phase. The reduction of Ni+2 to Ni nanoparticles can be revealed by the synchrotron x-ray absorption spectroscopy. The photocatalytic properties of the nanocrystalline TiO2 and TiO2/Ni composite thin films were investigated.
11:30 AM H1-2-11 Reactively Sputtered N-Doped Titanium Oxide Films as Visible Light Photocatalysts
M.S. Wong, H.B. Chou, S.H. Wang, T.K. Chen, T.S. Yang (National Dong Hwa University, Taiwan)
Titanium oxide (TiO2) and nitrogen-doped titanium oxide (TiO2-xNx) films were prepared by reactive d.c.-magnetron sputtering of Ti metal target in plasma of Ar+O2 and Ar+O2+N2 mixtures, respectively. The relationship among the processing parameters, film structures and photocatalytic properties was explored. The aim is to shift the absorption edge of the films from ultraviolet to visible region and to promote their photocatalytic performance, e.g., photodegradation of methylene blue (MB) and photoreduction of silver-ions under visible-light irradiation. The absorption edges of TiO2-xNx films are shifted from 400 to 510 nm gradually with the increasing nitrogen fraction in the gas feed. The TiO2-xNx films with well-crystallized anatase phase exhibit excellent photocatalytic performance under visible light irradiation, while undoped TiO2 film shows nearly no visible-light induced photocatalytic activity. The smooth TiO2-xNx films of nanocrystalline grains exhibit the best photodegradation of MB. The water contact angle is decreased and the amount of reduced silver is increased with increasing surface roughness of TiO2-xNx films.
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