Reed Roeder Corderman

Kinetics and Initial Stages of Bismuth Telluride Electrodeposition

The kinetics and initial stages of Bi 2 Te 3 electrodeposition on gold from an aqueous electrolyte composed of bismuth and telluryl ions and nitric acid were investigated using voltammetry and chronopotentiometry. For tellurium alone, it is found that the reduction of tellurium ions to tellurium occurs with four exchanging electrons at -0.05 V vs Ag/AgCl (3 M KCl). At -0.6 V, tellurium reduces to H 2 Te under kinetic control and the following simultaneous diffusion-controlled reaction occurs with one exchange electron per tellurium atom: HTeO + 2 + H 2 Te + H + + 2e - → 2Te + 2H 2 O. Bismuth telluride deposition starts at more positive potential than bismuth and tellurium deposit individually. It is suggested that the electrodeposition of Bi 2 Te 3 proceeds via a Stransky-Krastanov mechanism. From the Bard correction to the Sand equation, the diffusion coefficients of bismuth and telluryl ions were determined to be 1.90 X 10 -5 and 1.39 X 10 -6 cm 2 /s, respectively, in the investigated solutions. Due to the low diffusivity and solubility of telluryl ions, the limiting current density for Bi 2 Te 3 deposition in the investigated solution is low; it is only 2 mA/cm 2 . Above the limiting current density, a smooth deposit cannot be obtained without agitation. A smooth deposit can be achieved when the depletion of anions is eliminated.

Heterogeneous integration of semiconducting and carbide nanowires on Si substrates

Integration of nanowires onto foreign substrates, and in functional devices, is widely recognized as a significant hurdle to further development of nanosystems based on quasi-one dimensional nanostructures. We describe methods for directly integrating relevant nanostructures on technologically relevant Si substrates using vapor phase synthesis of the nanowires. It is shown that ZnO nanowires may be directly integrated onto Si substrates containing patterned metal lines. Preferential growth from the edge of the metal lines has been achieved. We also show that growth of refractory transition metal carbides is also possible using catalytic growth. The electrical properties of such systems are also discussed. Finally, methods of integrating nanowires vertically on a Si substrate are also described.

Development of Nanostructured and Nanoparticle Dispersion-Reinforced Metallic Systems - Progress and Challenges

Investigations on nanostructured metallic systems have shown that exceptional property enhancements are potentially achievable through structural refinement to the nano-scale. While dramatic property improvements have been reported on these materials in the past, significant technical challenges exist in processing, as well as in retention of microstructural stability and useful properties at elevated temperatures. This presentation will summarize the key challenges in developing nanostructured metallic systems, and highlight our progress and selected successes in the understanding of structure-property relationships in bulk nanostructures as well as nanostructured multilayered systems. Work in nanoparticle dispersion-strengthened metallic systems will also be highlighted in this presentation.