Projects Synthesis Materials Fabrication Devices Characterization Theory
Facile Hydrothermal   Electroless Deposition at the Nanoscale  
Vapor Phase Transport Growth in Thermal CVD   Chemical deposition method  
Facile Hydrothermal
Hydrothermal route can be defined as the use of water as reaction medium in a sealed reaction container when the temperature is raised above 100°C. Autogeneous pressure which is self-developed and not externally applied is generated under these conditions. The pressure within the sealed reaction container increases dramatically with temperature, but also will depend on other experimental factors, such as the percentage fill of the vessel and any dissolved salts as illustrated in the figure below. A high percentage fill allows access to pressures of hundreds of atmospheres when the temperature is below the critical point of water, and even below 200°C. One remarkable advantage of the use of hydrothermal conditions is that it has significant effects on the reactivity of inorganic solids and the solubility of diverse compounds under conditions of elevated pressure and temperatures. Secondly, the chemical reactivity of usually insoluble reagents can be much enhanced and a lot of sluggish solid state reactions can be initiated under hydrothermal conditions.
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Electroless Deposition at the Nanoscale
With a seed layer acting as a catalyst, metal can be electrolessly deposited onto various insulating substrates, i.e. no potential is applied to the substrate. A key application is that metal can be deposited and be surrounded by insulator such as is often required on PCB board. The catalytic activity of the seed layer changes at the nanoscale requiring changes to the electrolyte and desposition conditions. In addition, it is often advantageous, with increasingly smaller patterns to achieve native-metal catalysis thereby having pure single metal structures and not, for example Ag-Cu or Pd-Cu. In this effort we are develping a copper seed layer that is active for electroless deposition of Cu over the length scale from bulk to 50nm line widths. The seed layer can be patterned via electron beam lithography or nanocontact printing. We are also modifying the seed layer for photolithographic patterning.
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Vapor Phase Transport Growth in Thermal CVD
We synthesis various transition metal oxide nanowires and nanostructures via vapor phase growth in thermal chemical vapor deposition systems, including NiO, VO2 and ZnO nanowires and CuO and Cu2O nanostructures. The phase diagrams of these systems often imply high temperature conditions, i.e. above 12000C. By using organo-metal solid sources or solid sources mixed with graphite we are able to reduce the synthetic temperature. Depending on the material system we grow our nanowires epitaxially with no catalyst on specific substrates. Nanostructures can be grown on a variety of substrates including glass, SiO2 and Si. Our research also involves in-situ doping of the wires and nanostructures and controlling the oxygen content to modify electrical and sensing behaviors. In addition we develop techniques to control the density of the nanowire growth.
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Chemical deposition method
We have developed a new facile method that yields single crystalline nanowires on various substrates including glass, ITO-glass, SiO2, sapphire, and Si. A chemical solution is prepared that is then spin-coated or dip-coated onto the substrate. Upon drying and heating at typically sub-5000C temperatures in laboratory air, single crystalline nanowires naturally grow from nuclei self assembled on the substrate. This method's advantages are many and currently we are using this technique to grow doped and compound transition metal oxides, incluing pure and doped V2O5 and MoO3 nanowires and compounds. The technique centers around the careful preparation of the solution and the thickness of the layer as well as the interaction with the subtrate upon heating.
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