排序方式: 共有6条查询结果,搜索用时 62 毫秒
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Kris A. Bertness Aric W. Sanders Devin M. Rourke Todd E. Harvey Alexana Roshko John B. Schlager Norman A. Sanford 《Advanced functional materials》2010,20(17):2911-2915
The location of GaN nanowires is controlled with essentially perfect selectivity using patterned SiNx prior to molecular beam epitaxy growth. Nanowire growth is uniform within mask openings and absent on the mask surface for over 95% of the usable area of a 76 mm diameter substrate. The diameters of the resulting nanowires are controlled by the size of the mask openings. Openings of approximately 500 nm or less produce single nanowires with symmetrically faceted tips. 相似文献
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Alexana Roshko Loren F. Goodrich David A. Rudman Richard Moerman Leila R. Vale 《Journal of Electronic Materials》1995,24(12):1919-1922
The influence of microstructure on the critical current density of laser ablated YBa2Cu3O7−δ thin films has been examined. Scanning tunneling microscopy was used to examine the morphologies of YBa2Cu3O7−δ films and the morphology data were then correlated with measurements of the critical current density. The films were found
to grow by an island nucleation and growth mechanism. The critical current densities of the films are similar to those of
films with screw dislocation growth, indicating that screw dislocation growth is not necessary for good pinning. The data
suggest that the critical current density in applied magnetic field may be higher in films with higher densities of growth
features. 相似文献
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AM Herrero PT Blanchard A Sanders MD Brubaker NA Sanford A Roshko KA Bertness 《Nanotechnology》2012,23(36):365203
The development of Ni/Au contacts to Mg-doped GaN nanowires (NWs) is examined. Unlike Ni/Au contacts to planar GaN, current-voltage (I-V) measurements of Mg-doped nanowire devices frequently exhibit a strong degradation after annealing in N(2)/O(2). This degradation originates from the poor wetting behavior of Ni and Au on SiO(2) and the excessive void formation that occurs at the metal/NW and metal/oxide interfaces. The void formation can cause cracking and delamination of the metal film as well as reduce the contact area at the metal/NW interface, which increases the resistance. The morphology and composition of the annealed Ni/Au contacts on SiO(2) and the p-GaN films were investigated by scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD) measurements. Adhesion experiments were performed in order to determine the degree of adhesion of the Ni/Au films to the SiO(2) as well as observe and analyze the morphology of the film's underside by SEM. Device degradation from annealing was prevented through the use of a specific adhesion layer of Ti/Al/Ni deposited prior to the nanowire dispersal and Ni/Au deposition. I-V measurements of NW devices fabricated using this adhesion layer showed a decrease in resistance after annealing, whereas all others showed an increase in resistance. Transmission electron microscopy (TEM) on a cross-section of a NW with Ni/Au contacts and a Ti/Al/Ni adhesion layer showed a lack of void formation at the contact/NW interface. Results of the XRD and TEM analysis of the NW contact structure using a Ti/Al/Ni adhesion layer suggests Al alloying of the Ni/Au contact increases the adhesion and stability of the metal film as well as prevents excessive void formation at the contact/NW interface. 相似文献
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Masayuki Fujimoto Yet-Ming Chiang Alexana Roshko W. David Kingery 《Journal of the American Ceramic Society》1985,68(11):300-C
In sodium-diffused strontium titanate internal-boundary-layer capacitors exhibiting good varistor properties, high-resolution transmission electron microscopy and scanning transmission electron microscopy revealed sodium segregation at grain boundaries in the absence of intergranular phases. The segregation layer is narrow (≅10 nm), unlike much broader diffused boundary layers which have also been observed. The nonohmic behavior in these and in potassium-diffused specimens suggests that segregated acceptor alkali ions act as grain-boundary electron traps leading to varistor electrical barriers. 相似文献
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