Bulletin of the American Physical Society
2008 Joint Fall Meeting of the Texas and Four Corners Sections of APS, AAPT, and Zones 13 and 16 of SPS, and the Societies of Hispanic & Black Physicists
Volume 53, Number 11
Friday–Saturday, October 17–18, 2008; El Paso, Texas
Session E3: Nanoscience |
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Chair: David Hough, Trinity University Room: Union East, 3rd Floor Smiley |
Friday, October 17, 2008 3:30PM - 3:42PM |
E3.00001: Fabrication and Analysis of Vertically Aligned and Patterned Silicon-Carbon Core Shell Nanotubes Jun Song, Richard Vanfleet, Robert Davis Silicon-carbon core shell nanotubes(SiCNTs) are synthesized on a vertically aligned and patterned carbon nanotube template. Vertical-aligned carbon nanotube(CNT) forests are grown from a patterned catalyst seed layer by standard thermal chemical vapor deposition (CVD) methods. Thin silicon films are deposited on the CNTs by low pressure chemical vapor deposition(LPCVD). Some features of these SiCNTs are controllable, such as the diameter, length, crystallization, and pattern, by varying details in the fabrication. [Preview Abstract] |
Friday, October 17, 2008 3:42PM - 3:54PM |
E3.00002: Purification of Semiconducting Single-walled Carbon Nanotubes by Isopycnic Centrifugation David Jones The single-walled carbon nanotube is a promising medium in the field of nanoelectronics. However, even the most advanced production methods yield aggregates of both metallic and semiconducting species. If carbon nanotubes are to be used in electrical applications, it is essential that they be isolated according to their electrical conductivity. We are using isopycnic centrifugation to isolate nanotubes. Absorption spectroscopy is used to identify nanotube species within a given sample before and after purification. Our current challenge is to quantify the purity of the isolated semiconducting nanotubes by way of direct measurement. Dielectrophoresis is used to align nanotubes upon electrodes after which individual electrical measurements can be performed. By performing direct measurements on a large sample size of purified semiconducting nanotubes, the effectiveness of this purification technique can be verified electrically. [Preview Abstract] |
Friday, October 17, 2008 3:54PM - 4:06PM |
E3.00003: Effects of radiation on switchable gratings and CdSe/ZnS nanostructures S.C. Sharma, R.A. Ramsey, J. Murphree, T. Chakraborty, C. Shive Switchable gratings formed in Polymer-Dispersed Liquid Crystals (PDLCs) and CdSe/ZnS quantum dots are of interest from scientific and technological points of views[1,2].The Bragg reflection and transmission PDLC gratings can be switched on/off by external fields. We present new results on the effects of synthesis parameters and radiation on the forward/reverse-mode gratings and PL spectra of CdSe/ZnS quantum dots. The PL emission from these nanostructures changes as a result of simultaneous irradiation by 532-nm laser and gamma-rays. The results of this study reaffirm the role of radiation-induced charges in modifying thin films, such as the ones studied in this work containing CdSe/ZnS nanostructures and switchable diffractive elements formed in PDLCs[3]. [1] T. J. Bunning, L. V. Natarajan, V. P. Tondiglia, R. L. Sutherland, Ann. Rev. Mat. Sci. 30, 83 (2000), [2] R. A. Ramsey and S. C. Sharma, Opt. Lett. 30, 592-594 (2005); S. C. Sharma, J. Murphree, T. Chakraborty, J. Lumin. 128, 1771,(2008); R. A. Ramsey and S. C. Sharma, Appl. Phys. B (in press)., [3] S. C. Sharma, L. Zhang, A. J. Tapiawala, P. C. Jain, Phys. Rev. Letts. 87, 105501 (2001). [Preview Abstract] |
Friday, October 17, 2008 4:06PM - 4:18PM |
E3.00004: High Aspect Ratio Carbon Nanotube MEMS Nick Morrill, David Hutchison, Robert Davis, Richard Vanfleet A new approach to the fabrication of microelectronic mechanical devices (MEMS) is a bottom-up design using carbon nanotubes (CNTs). A substrate, typically silicon, is prepared for MEMS construction by first depositing a sacrificial layer of SiO$_{2}$ for release. Then a 30nm layer of Al$_{2}$O$_{3}$ is deposited as a diffusion barrier for the CNT catalyst material (Fe). Next, using photolithography, resist is patterned and developed. A thin layer (4nm) of Fe is deposited on top of the resist and in the trenches where the resist was removed during development. Finally, ``lift-off,'' or removal of the remaining resist, leaves the surface with Fe patterned where CNTs are to be grown. CNTs are grown to various heights, providing high aspect ratios and well-defined features. The CNT ``forests'' can then be filled with various materials, of which we have tested and operated silicon and silicon nitride devices. To release MEMS devices for operation, the substrate is immersed in HF, removing part of the SiO$_{2}$ layer below. The new composite's properties were analyzed and compared to MEMS devices fabricated using conventional methods. [Preview Abstract] |
Friday, October 17, 2008 4:18PM - 4:30PM |
E3.00005: Low Temperature, High Pressure Cell for the Study of Single-Molecule Magnets Miguel Bencomo, Daniel M. Pajerowski, Eric L. Danielson, Mark W. Meisel We present a low temperature (T $>$ 1.5 K), high pressure (P $<$ 25 kbar) cell [1] configured to study the pressure dependence of the spin state of single-molecule magnets (SMMs). More specifically, the work focuses on two different Mn$_{7}$ samples with ground state spin states of S = 11 and S =16 arising from the subtle differences in their structures [2]. The change of the magnetic states is detected by using a resonant tank-circuit that operates between 2 -- 20 MHz and employs a tunnel-diode oscillator. The resonant frequency of the tank-circuit is sensitive to subtle changes in the inductor element, which are directly related to the magnetic susceptibility of the sample. [1] J.D. Thompson, \textit{Rev. Sci. Instrum.} 55 (1984) 232. [2] T.C. Stamatatos, K.M. Poole, D. Foguet-Albiol, K.A. Abboud, T.A. O'Brien, G. Christou, \textit{Inorg. Chem.} 47 (2008), 6593. [Preview Abstract] |
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