Theoretical Simulation of Laser Emissions Describes Intensity and Polarization Properties of Semiconductor Nanowires
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shown previously to be biocompatible and nonadhesive to protein and cells. Details of the rubber casting and UV embossing techniques were previously published. The researchers found that the TiN mold can be used for more than 20 rubber castings without much dimensional change, which they attribute to the low surface energies of both TiN and silicone. Scanning probe microscopy (SPM) analysis shows that the roughness of the TiN master is about 4 nm, which the researchers present as evidence that FIB lithography of TiN produces surfaces smooth enough for nanopatterning. Similarly, successive generations of rubber moldings display little dimensional difference. However, scanning electron micrographs show that the structure resulting from the eighth consecutive PEGDA embossing (from the same silicone mold) displays some surface defects, although the major dimensions are replicated well. The researchers believe that increasing the hydrophobicity of the silicone and/or PEGDA can minimize surface defects. The researchers said that their technique is inexpensive and requires no special processing conditions, thereby allowing several tens to hundreds of UV-embossed PEGDA replications to be easily made from a single submicrometer-patterned TiN master mold. STEVEN TROHALAKI
Theoretical Simulation of Laser Emissions Describes Intensity and Polarization Properties of Semiconductor Nanowires Nanowires, which can have diameters of 20–200 nm, are capable of laser emission through the axial direction. While the smallerdiameter nanowires can only support emission with a mode similar to the fundamental hybrid mode of optical fibers, larger-diameter nanowires can give rise to different coexisting modes. Information on the properties of the far-field radiation is necessary to reveal the particular mode type involved. As a first approach toward analyzing the emissive modes of nanowire lasers, A.V. Maslov and C.Z. Ning from the Center for Nanotechnology at NASA Ames Research Center in California have developed a theoretical methodology to establish the mode type, deduced from the characteristics of the corresponding far-field radiation. They presented their research in the March 15 issue of Optics Letters. Maslov and Ning applied the finite-difference time-domain method to formulate their simulation. Initially, a current source excited two wave packets that traveled along the length of a vertically oriented nanowire toward the two ends of the nanowire, respectively. In their discussion, the researchers assumed that in a self-supporting nanowire in a steady-state regime, it was adequate to consider only the radiation that is incident on the top end. They then defined a domain using cylindrical coordinates: 100 cells in the ρ direction, 600 cells in the z direction, and a radius of 10 cells. After an excited wave packet arrived at the top of the nanowire, part of it was reflected, and the remainder left the nanowire so that an electronic field with two components, Eθ and Eφ , was created in the farfield region, where θ is the polar or elev
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