ICMCTF2005 Session H1-1: Nanostructured Coatings and Novel Deposition Strategies
Time Period WeA Sessions | Abstract Timeline | Topic H Sessions | Time Periods | Topics | ICMCTF2005 Schedule
| Start | Invited? | Item |
|---|---|---|
| 3:50 PM | Invited |
H1-1-8 Self-Organization of Nanostructures in Semiconductor Heteroepitaxy
C. Teichert (University of Leoben, Austria) Exploitation of strain-induced self-organization phenomena during semiconductor heteroepitaxy is an elegant and efficient route towards fabrication of large-scale arrays of uniform nanostructures. This will be demonstrated for the Stranski-Krastanov growth of SiGe films on vicinal Si(001) substrates1. In this system, the growth front undergoes a series of strain-relief mechanisms. This includes the formation of {105}-faceted three-dimensional crystallites and the evolution of a misfit dislocation network. By tuning substrate miscut and film thickness or growing SiGe/Si superlattices, a variety of patterns with different symmetries can be obtained. Atomic-force microscopy has been applied to obtain quantitative information on nanostructure uniformity and arrangement as a function of growth conditions. Strain driven self-organization can also be observed in heteroepitaxial growth of organic thin films. A recent example of nanostructure self-alignment in oligophenylene films2 on a variety of substrates will be presented. The mechanisms of pattern formation - which are not at all restricted to semiconductor systems - will be explained in the framework of continuum elasticity theory. Finally, analogies to pattern formation during ion erosion of semiconductor surfaces3 will be discussed. |
| 4:30 PM |
H1-1-10 Spatially-Defined Arrays of Metal Oxide Quantum Dots on SrTiO3 (100)
Y. Du, J.F. Groves (University of Virginia); I. Lyubinetsky, S. Thevuthasan, D. Baer (Pacific Northwest National Lab) Many lattice mismatched material systems form self-assembled quantum dots (QDs) during epitaxial thin film growth. To harness this phenomenon into engineered devices, the QD size, size distribution, inter-dot spacing and properties must be precisely controlled. We report the results of efforts to grow arrays of metal oxide QDs on SrTiO3 (100). In this work, a focused ion beam (FIB) tool has been used to define the growth location of individual QDs by injecting gallium ions into each selected growth site on the single crystal surface. Following subsequent surface annealing and cleaning, oxygen plasma assisted molecular beam epitaxy has been used to grow arrays of metal oxide QDs. Results will be presented, illustrating single-phased Cu2O QD synthesis under carefully controlled temperature and oxygen partial pressure. Results for other metal oxide systems will also be discussed. Under selected conditions, islands form first in the FIB-generated surface topography and grow in size before reaching a critical limit, and then, with continuous deposition, islands form elsewhere on the unmodified surface. Island size, shape and relation to local FIB modifications are studied. In-situ X-ray photoelectron spectroscopy and Auger electron spectroscopy analysis were used to verify the final QD phase; x-ray diffraction was performed to confirm QD epitaxy. We will report upon the extent to which QD size, size distribution, and inter-dot spacing has been controlled. It will also describe differences in QD growth motivated by changes to the specific FIB surface patterning parameters employed. The photocatalytic decomposition of water on metal oxide surfaces under visible light irradiation has been reported. Well defined metal oxide island arrays on the SrTiO3 substrate could be an efficient, clean means of producing hydrogen for fuel cells. Control of QD growth as reported here also has implications for nanoscale electronics, magnetics, and related fields of use. |
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| 4:50 PM |
H1-1-11 Preparation and Characterization of Nanocrystalline Porous TiO2/WO3 Composite Thin Films
C.S. Hsu, C.K. Lin, C.C. Chan, C.C. Chang (Feng Chia University, Taiwan) TiO2 materials possessing not only photocatalytic but also electrochromic properties have attracted many research and development interests. Though WO3 exhibits excellent electrochromic properties, the much higher cost of WO3 as compared with the TiO2 may restrict the practical application of WO3 materials. In the present study, the feasibility of preparing nanocrystalline porous TiO2/WO3 composite thin films was investigated. Precursors of TiO2, WO3 sol gels and polystyrene spheres with various mixed ratios were used to prepare nanocrystalline TiO2/WO3 composite thin films by spin coating. The as-deposited thin films were then heat treated at high temperature to remove the polystyrene spheres. Thus nanocrystalline porous TiO2/WO3 composite thin films can be prepared successfully. The porous films were characterized by X-ray diffraction, scanning electron microscopy, and UV/Visible spectroscopy techniques. The preliminary experimental results showed that, by controlling the mixed ratio of starting materials and post heat treatment temperature, we can control the porous structure and thus the properties of the nanocrystalline TiO2/WO3 composite thin films. |
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| 5:10 PM |
H1-1-12 Self-Organization of the Coating Deposited by Gas-Dynamical Method
J.S. Gershman (All-Russian Railway Research Institute, Russia); S.I. Soldatenkov (Moscow State Industrial University, Russia) In the present work self-organizing of the coating deposited by gas-dynamical method is considered. The coating is a mixture copper and zinc powders. This powders mixture has bee deposited on a copper substrate surface using the gas - carrier with the speed within a range of sound (around 330 m/s). This type of deposition can be considered as a "cold" one, since the temperature of the gas - carrier (in this case-air) is no more than 300°С. The powder particles are deformed and stick to the surface of copper substrate during the impact. The similar method of deposition was applied, when it was necessary to deposit a few mm thick layer of coating at high speed (around 1 m/min) on the area around 10 mm wide. The heating of a substrate material should be prevented during the deposition. This technology of deposition has been developed for restoration of the worn out copper contact of the railways wires. Spontaneous separation of the powders mixture into components is revealed in the coating after deposition. In this case two sub-layers have been formed that are enriched, with copper and zinc accordingly. The sublayer rich in zinc was formed closer to the cooper substrate. Adhesion of the deposited layer with separation of elements was much higher as compared to the non-separated one. In the latter case a spallation usually occurred. Entropy of the layer with the separated components is lower than entropy of layer with uniform distribution of the components. It corresponds to process of self-organizing. In this case self-organizing results in adhesion to substrate (bonding) increase. Self-organizing phenomenon was studied. The chemical composition, mechanical properties of the deposited coating was optimized to improve its wear intensity. |