Bulletin of the American Physical Society
78th Annual Meeting of the Southeastern Section of the APS
Volume 56, Number 9
Wednesday–Saturday, October 19–22, 2011; Roanoke, Virginia
Session GC: Condensed Matter Physics/Nanophysics I |
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Chair: Hans Robinson, Virginia Polytechnic Institute and State University Room: Crystal Ballroom C |
Friday, October 21, 2011 8:30AM - 8:42AM |
GC.00001: Capturing Ion-Solid Interactions with MOS structures R. Shyam, D.A. Field, S. Chambers, W.R. Harrell, C.E. Sosolik We have fabricated metal-oxide-semiconductor (MOS) devices for a study of implantation rates and damage resulting from low energy ion-solid impacts. Specifically, we seek to capture ion irradiation effects on the oxides. Fabrication of the MOS devices follows a standard procedure where Ohmic contacts are first created on the wafer backside followed by the thermal growth of various thicknesses of SiO$_{2}$ (from 50 nm to 200 nm) on the wafer frontside. As-grown SiO$_{2}$ layers are then exposed to various singly-charged alkalis ions with energies in the range of 100 eV to 10 keV in our beamline setup. Following this exposure, the MOS devices are completed in situ with the deposition of a top Al contact. Characterization of the ion-modified devices involves the standard device technique of biased capacitance-voltage (C-V) measurements where a field is applied across the MOS structure at an elevated temperature to move implanted ions resulting in changes in surface charge density that are reflected as shifts in the flatband voltage (V$_{FB})$. Similarly, a triangular voltage sweep (TVS) test can be utilized to measure the ionic displacement current as it is driven by a slow linear voltage ramp and it should reveal the total ionic space charge in an MOS. [Preview Abstract] |
Friday, October 21, 2011 8:42AM - 8:54AM |
GC.00002: Free flux flow in two single crystals of V$_{3}$Si with differing pinning strengths O. Gafarov, A.A. Gapud, S. Moraes, J.R. Thompson, D.K. Christen, A.P. Reyes Results of measurements on two very clean, single-crystal samples of the A15 superconductor V$_{3}$Si are presented. Magnetization and transport data have confirmed the ``clean'' quality of both samples, as manifested by: (i) high residual electrical resistivity ratio, (ii) very low critical current densities Jc, and (iii) a ``peak'' effect in the field dependence of critical current. The (H,T) phase line for this peak effect is shifted down for the slightly ``dirtier'' sample, which consequently also has higher critical current density J$_{c}$(H). Large Lorentz forces are applied on mixed-state vortices via large currents, in order to induce the highly ordered free flux flow (FFF) phase, using experimental methods developed previously. The traditional model by Bardeen and Stephen (BS) predicts a simple field dependence of flux flow resistivity \textit{$\rho $}$_{f}$\textit{(H) $\sim $ H/H}$_{c2}$, presuming a field-independent flux core size. A model by Kogan and Zelezhina (KZ) takes into account the effects of magnetic field on core size, and predict a clear deviation from the linear BS dependence. In this study, $\rho _{f}$(H) is confirmed to be consistent with predictions of KZ. [Preview Abstract] |
Friday, October 21, 2011 8:54AM - 9:06AM |
GC.00003: Double-Paddle Oscillators for the Mechanical Spectroscopy of Ion-Surface Modifications D.A. Field, T.H. Metcalf, C.E. Sosolik We discuss the use of silicon double-paddle oscillators (DPOs) as a technique for following atomistic changes in mechanical properties under energetic ion irradiation conditions in ultra high vacuum (UHV). For these DPOs, it is well known that at low temperatures ($\sim $4k) the internal friction or Q$^{-1}$ of the anti-symmetric oscillator eigenmode is lower than 10$^{-8}$ and that it increases to 10$^{-5}$ as temperature is increased (up to 673K). This small damping or high Q allows for sensitive measurements of the mechanical properties of thin deposited films or of the oscillator structure itself. Using an incident ion beam we will investigate changes in the mechanical properties of the DPO due to mass loss during ion bombardment. In initiating these measurements, a basic frequency sweep setup has been utilized under ambient atmospheric conditions in order to finalize the required electronics and to demonstrate the various DPO eigenmodes that have been seen in earlier studies. A more advanced electronics and DPO mount design will follow as the system is transitioned to UHV operation. [Preview Abstract] |
Friday, October 21, 2011 9:06AM - 9:18AM |
GC.00004: Measurement of DC resistivity of new quasi-one-dimensional conducting platinate A.A. Gapud, J. Alexander, R.I. Leatherbury, O. Gafarov, A.P. Weber, L. Pham, R.E. Sykora, A. Khan Cs$_{4}$[Pt(CN)$_{4}$](CF$_{3}$SO$_{3})_{2}$ (TCP) is the newest palatinate, quasi-one-dimensional conductors with parallel ``chains'' of Pt maintained by peripheral materials and with well known properties, especially in the potassium-containing material, KCP. Unlike KCP, however, we are finding properties unique to TCP. First, we discuss technical difficulties in measuring the DC resistivity of this material: Unlike with KCP, the samples of TCP were relatively small and very fragile, their contact surface had an insulating film, and the crystal had a very sensitive pressure dependence, coupled with significant thermal contraction/expansion. These issues were addressed with reasonable success, using proper handling methods, sputtered electrical contacts, and a floating sample mount, as will be discussed. The resulting temperature dependence of resistivity is radically different from KCP, showing an anomalous ``peak'' at around 150 K. [Preview Abstract] |
Friday, October 21, 2011 9:18AM - 9:30AM |
GC.00005: NMR study of $^{133}$Cs in new quasi-one-dimensional conducting platinate R.I. Leatherbury, J. Alexander, O. Gafarov, A.A. Gapud, A.P. Weber, L. Pham, R.E. Sykora, A.P. Reyes, P. Kuhns Cs$_{4}$[Pt(CN)$_{4}$](CF$_{3}$SO$_{3})_{2}$ (TCP) is a new Krogmann's salt, consisting of quasi-one-dimensional conducting chains of Pt with well known properties, especially in the potassium-containing material, KCP. Unlike KCP, however, there are properties unique to TCP, e.g., longer Pt-Pt separation, insulating at room temperature, and non-magnetic. Previous NMR studies on KCP have mainly been on $^{195}$Pt, which does not produce a usable NMR signal in TCP; our study utilizes $^{133}$\textbf{Cs} instead, which are peripheral to the Pt chains. Splitting of spin states due to quadrupole interaction with local electric field gradient has been measured as a function of orientation versus applied static field. Modeling of the frequency shifts reveals consistency with the known symmetry axes of $^{133}$\textbf{Cs} determined by single-crystal x-ray diffraction. Relaxation time T1 versus temperature reveals a weak relaxation mechanism and absence of magnetism. Relaxation data has a sharp anomaly around 119 K where T1 jumps 3 orders of magnitude, consistent with critical fluctuations but not yet well understood. [Preview Abstract] |
Friday, October 21, 2011 9:30AM - 9:42AM |
GC.00006: Controlled release from stimuli-sensitive microgel capsules Hassan Masoud, Alexander Alexeev We introduce a mesoscale computational model for responsive gels, i.e. chemically cross-linked polymer networks immersed in Newtonian fluids, and use it to probe the release of nanoparticles from hollow microgel capsules that swell and deswell in response to external stimuli. Our model explicitly describes the transport of nanoparticles in swelling/deswelling polymer networks with complex geometries and associated fluid flows. Our simulations reveal that responsive microcapsules can be effectively utilized for steady and pulsatile release of encapsulated solutes. Steady, diffusive release of nanoparticle takes place from swollen gel capsules, whereas capsule deswelling cause burst-like discharge of solutes driven by a flow from the shrinking capsule interior. We demonstrate that this hydrodynamic release can be regulated by introducing rigid microscopic rods inside the capsule. Our calculations indicate that the rods stretch the deswelling membrane and promote the formation of large pores in the shell, which allow massive flow-driven release of nanoparticles. Thus, our findings unveil a new approach for regulating the release from stimulus responsive micro-carriers that will be especially useful for designing new drug delivery systems. [Preview Abstract] |
Friday, October 21, 2011 9:42AM - 9:54AM |
GC.00007: Study the friction behaviour of poly[2-(dimethylamino)ethyl methacrylate] brush with AFM probes in contact mechanics Maryam Raftari, Zhenyu Zhang, Graham J. Leggett, Mark Geoghegan We have studied the frictional behaviour of grafted poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) films using friction force microscopy (FFM). The films were prepared on native oxide-terminated silicon substrates using the technique of atom transfer radical polymerization (ATRP). We show that single asperity contact mechanics (Johnson-Kendall-Roberts(JKR) and Derjaguin-Muller-Toporov(DMT)) as well as a linear (Amontons) relation between applied load and frictional load depending on the pH of the FFM probe. Measurements were made using functionalized and unfunctionalized silicon nitride triangular probes. Functionalized probes included gold-coated probes, and ones coated with a self-assembled monolayer of dodecanethiol (DDT). The frictional behaviour between PDMAEMA and all tips immersed in pH from 3 to 11 are corresponded to the DMT or JKR model and are linear in pH=1, 2, and 12. These results show that contact mechanics of polyelectrolytes in water is complex and strongly dependent on the environmental pH. [Preview Abstract] |
Friday, October 21, 2011 9:54AM - 10:06AM |
GC.00008: Dynamics of Polydisperse Foam-like Emulsion Harry Hicock, Klebert Feitosa Foam is a complex fluid whose relaxation properties are associated with the continuous diffusion of gas from small to large bubbles driven by differences in Laplace pressures. We study the dynamics of bubble rearrangements by tracking droplets of a clear, buoyantly neutral emulsion that coarsens like a foam. The droplets are imaged in three dimensions using confocal microscopy. Analysis of the images allows us to measure their positions and radii, and track their evolution in time. We find that the droplet size distribution fits a Weibull distribution characteristics of foam systems. Additionally, we observe that droplets undergo continuous evolution interspersed by occasional large rearrangements in par with local relaxation behavior typical of foams. [Preview Abstract] |
Friday, October 21, 2011 10:06AM - 10:18AM |
GC.00009: Patterning the adhesive properties of amine-rich polymer films Stefan Stoianov, Chalongrat Daengngam, Malihe Borhani, Yong Xu, Hans Robinson Full integration of top-down and bottom-up nanofabrication technologies will require the ability to accurately place nanostructures onto well-defined locations on a surface, where the nanostructures initially only exist suspended in a liquid. As the nanostructures may be quite fragile, perhaps the best way to do this is to pattern the adhesiveness of the surface in order to guide assemblies to the desired locations. We have demonstrated two routes for achieving this using the amine-rich, nm thick polymer films based on poly(allylamine hydrochloride). The adhesive properties of the films can be patterned with standard lithographic techniques, where adhesion to selected portions of the surface is suppressed either by treatment with acetic anhydride or by direct exposure to ultraviolet light. We applied these techniques both to flat and curved substrates and demonstrate spatial resolution better than 100 nm. [Preview Abstract] |
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