Mechanism of epitaxy -free oriented nanowire growth

1. Mechanism of epitaxy-free oriented nanowire growthEric E. Fullerton, University of California-San Diego, DMR 0906957 A general mechanism has been established for the oriented growth of transition-metal nanowire (NW) materials from metal-halide precursors using a chemical vapor deposition (CVD) technique. Both Ni and CrxSiy NWs have demonstrated a controlled vertical orientation with respect to the amorphous SiO2||Si growth substrates. The synthesis of these oriented NWs relies on the liberation of Si from the substrate through reaction with vapor phase products of precursor hydrolysis. A substrate surface bound Si-based film serves as a material sink for mobile adatoms and mediates incorporation of these atoms into the growing crystal. It is through the influence of the dimensionally confined Si-based mediator that vertically directed growth of NWs is achieved. The ability to dictate orientation in the absence of epitaxy promises substantial cost reductions in the controlled synthesis of nanoscale materials. Observations of NW morphology revealing the underlying growth mechanism. a) inert region is largely inactive, b) incorporation region results from primarily unidirectional growth, c) influx region actively introduces material to the growing NW. SEM images shown together with schematic depicting typical NW.

2. Mechanism of epitaxy-free oriented nanowire growth Eric E. Fullerton, University of California-San Diego, DMR 0906957 In addition to graduate student (K. Chan) undergraduate students are consistent participants and contributors to the NW Project. They are engaged in experimental work including sputter and chemical vapor deposition, photolithography, ion and chemical etching, magnetometry, and electrical transport measurements. D. Lam (B.S. 2010, ECE) worked on the growth of CoxNiy alloy NWs , C. Doran (B.S. 2010, ECE) on the fabrication of NW-based core-shell structured spin valves, J. Kan (BS 2010, Phys) on micromagnetic simulations. Current student, Trevor McCann (Junior, ECE) is involved in a study of Ni NW magneto-impedance. Two of the students (C. Doran and J. Kan) presented posters at international conferences and one co-authored a publication: IEEE Trans. Mag. 46, 2209 (2010). Undergraduate student Trevor McCann using a network analyzer to measure magneto-impedance in a NW device made from a vertically grown Ni NW (upper left).