Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session Q21: THz and Impedance Spectroscopy |
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Sponsoring Units: GIMS Chair: Rachael Floyd, Janis Research Company Room: D161 |
Wednesday, March 23, 2011 11:15AM - 11:27AM |
Q21.00001: Bulk focused ion beam fabrication of nanoelectromechanical systems Wayne Hiebert, Doug Vick, Vince Sauer, Alastair Fraser, Oleksiy Svitelskiy, Mark Freeman Focused ion beam (FIB) nanomilling of NEMS devices out of bulk material will be presented. Ion impingement from multiple directions allows sculpting with considerable 3-dimensional control of device shape, including tapering and notching. Finite element modeling of device frequencies agrees with interferometric measurements, including for the effect of a localized notch. The measurements are sensitive enough to determine the thermomechanical noise floor of a bulk FIBed NEMS device with displacement sensitivity of 166 fm per root Hz, limited only by a combination of optical shot noise and detector dark current. We envision that bulk FIB fabrication will be useful for NEMS prototyping, milling of tough-to- machine materials, and generalized nanostructure fabrication with 3-dimensional shape control. [Preview Abstract] |
Wednesday, March 23, 2011 11:27AM - 11:39AM |
Q21.00002: Terahertz spectroscopy of ionized air and explosive vapor Benjamin Graber, Rongjia Tao, Dong Ho Wu In the past it has been demonstrated that terahertz spectroscopy could identify various chemical agents and explosives in solid and liquid phases. However peaks and dips in the terahertz spectra obtained from solid and liquid phases are not sharp and often ambiguous or ill-defined, as the interferences among the molecules in the solid or liquid obscure the molecule's characteristic resonances. Hence there has been considerable interest in obtaining terahertz spectrum of gas phase. Recently we have increased terahertz output power of our terahertz spectrometer, and measured terahertz spectra of gases, including water vapor, and ionized air produced by various ionization sources as well as explosive vapors. Our experiments revealed: (1) our terahertz spectrum of water vapor was highly consistent with other published data, (2) the spectra of ionized air produced by corona discharge and nuclear isotopes including Am-241, Bi-207, Ba-133, Co-60, Na-22 and Cs-137 were all different, and the characteristic spectrum changes largely depending on the type of ionization source, and (3) terahertz spectra of explosive vapor taken from TNT, PETN and RDX which were dissolved in acetonitrile or water exhibit very sharp resonance peaks and dips. We will present details of our experimental results. [Preview Abstract] |
Wednesday, March 23, 2011 11:39AM - 11:51AM |
Q21.00003: Characterization of high power near THz radiation from CMOS circuits using a Michelson Interferometer Daniel J. Arenas, Dongha Shim, Dimitrios Koukis, Eunyoung Seok, David B. Tanner, Kenneth K. O Recently, a high frequency SiGe BiCMOS Colpitts oscillator circuit was reported capable of emitting a second, third and fourth harmonic signal at 295, 442 and 589 GHz, respectively. The operating frequencies of the circuit and the emission powers were characterized using a Fourier transform interferometric spectrometer. The results show that this optical technique is an efficient way to characterize high-frequency circuits. The power emitted from the circuit at each frequency was also compared to that emitted from conventional blackbody sources. The results show that the high power emission of these circuits makes them ideal candidates for future spectroscopic applications. [Preview Abstract] |
Wednesday, March 23, 2011 11:51AM - 12:03PM |
Q21.00004: CNT Quantum dots as Terahertz detectors Mohamed Rinzan, Greg Jenkins, Dennis Drew, Serhii Shafranjuk, Paola Barbara We study Carbon Nanotube (CNT) quantum dots as detectors of THz radiation via photon assisted single electron tunneling. Although successful detection was recently demonstrated [1], the coupling between the CNT and THz radiations was very weak. Here, we implement a novel device design where the radiation is effectively coupled to the CNT quantum dot through broad band on-chip antennas. We show that the enhanced coupling yields a highly sensitive broad band Terahertz sensor. \\[4pt] [1] Y. Kawano, S. Toyokawa, T. Uchida and K. Ishibashi, THz photon assisted tunneling in carbon-nanotube quantum dots, Journal of Applied Physics 103, 034307 (2008). [Preview Abstract] |
Wednesday, March 23, 2011 12:03PM - 12:15PM |
Q21.00005: Highly absorbing metal nanolaminates for THz bi-material detectors Dragoslav Grbovic, Fabio Alves, Apostolos Karamitros, Gamani Karunasiri Interest in THz-ray sensing has significantly increased in recent years. It has been demonstrated that bi-material MEMS detectors show a great potential to be used for THz imaging. Our work aims to identify metal nanolaminates to improve the detector absorption in the range of interest. Using a finite element simulation tools we demonstrate that Chromium and Nickel films can absorb up to 50 and 35\%, respectively, between 1 and 5 THz, depending on the thickness of the layer. Different thickness of Cr and Ni layers were deposited on Si substrate using e-beam evaporation and the wafers were characterized using a FTIR expanded to THz range. The experimental results show excellent match with the simulations. Further analysis shows that by decreasing the surface filling fill-factor of Ni, it is possible to increase absorption closeup to the values obtained for the Cr films indicating that much lower stress Ni films can be used in bi-material MEMS detectors with absorption comparable with Cr films. [Preview Abstract] |
Wednesday, March 23, 2011 12:15PM - 12:27PM |
Q21.00006: Nanocoax arrays via NIL for high resolution sensing applications Binod Rizal, Patrick Jamieson, Svet Simidjiyski, Huaizhou Zhao, Dong Cai, Stephen Shepard, Thomas C. Chiles, Michael J. Naughton We have used nanoimprint lithography to fabricate nanocoax array-based chemical sensors, starting from SU-8 polymer replicas of silicon nanopillars. Nanocoaxes are formed by metalizing the polymer pillars, followed by oxide dielectric coating and outer metal deposition, and a polymer filling for stabilization. Chemical mechanical polishing and reactive ion etching were then used to open the ends of the coaxes and form coaxial cavity (with a nanoporous component) structures, respectively. Adsorption of water and organic solvent molecules into the coax annuli caused significant changes to the complex impedance of the coaxial capacitor array ($\Delta $C/C $>$ 100{\%} for 50{\%} relative humidity air). Impedance measurements with such coaxial nanocavity arrays thus provide highly sensitive and selective information for molecular detection, with ultimate sensitivity below 1 ppb, or $\sim $1 $\mu $g/m$^{3}$. [Preview Abstract] |
Wednesday, March 23, 2011 12:27PM - 12:39PM |
Q21.00007: A high performance humidity sensor based on dielectric detection with a novel coaxial nanostructure Dong Cai, Huaizhou Zhao, Binod Rizal, Timothy Kirkpatrick, Zhifeng Ren, Michael J. Naughton, Thomas C. Chiles High throughput coaxial nanocavity arrays are developed by overlaying porous Al$_{2}$O$_{3}$ and Al layers on vertically aligned carbon nanotube arrays. The porosity of Al$_{2}$O$_{3}$ was electrochemically characterized. The dielectric properties of the nanocoax structure were measured by impedance spectroscopy, from 10 mHz to 1 MHz. The capacitance of the sensor responded to humidity applied to the chip, $i.e.$ soaking the array with water increased the capacitance by 130{\%}. The detection mechanism was established for sensing changes to the dielectric constant due to adsorbed moisture in the porous Al$_{2}$O$_{3}$ coax annulus, with theoretical calculations based on~the Clausius-Mossotti equation~in agreement with the measurements.~ Highly sensitive humidity detection was demonstrated by applying relative humidity between 0.1{\%} and 100{\%}, with a power-law response, \textit{RH}$\sim x^{\alpha }$. This nanocoaxial structure thus offers the possibility of unprecedented performance of porous Al$_{2}$O$_{3}$-mediated capacitancer sensing for humidity detection. [Preview Abstract] |
Wednesday, March 23, 2011 12:39PM - 12:51PM |
Q21.00008: Capacitance response of porous and cavitized nanocoax arrays to various gases Patrick Jamieson, Binod Rizal, Svet Simidjiyski, Huaizhou Zhao, Dong Cai, Mark Hasenauer, Michelle Archibald, Stephen Shepard, Gregory McMahon, Michael J. Burns, Thomas C. Chiles, Michael J. Naughton Arrays of nanoscale coaxial electrodes with hollow or porous annuli offer the potential of highly sensitive detection and identification of gases and molecules. We report on the response of a porous and a partially hollow (cavitized) array to the introduction of various vaporized laboratory solvents. The response is measured as the capacitance and loss changes due to the introduction of molecules into the annuli, associated with the dielectric constant of the solvents, as well as the quantity and pressure. A monotonic dependence on concentration in dry nitrogen was observed. [Preview Abstract] |
Wednesday, March 23, 2011 12:51PM - 1:03PM |
Q21.00009: Damping effects of capacitive comb fingers on biomimetic MEMS directional microphone John Roth, Michael Touse, Jose Sinibaldi, Gamani Karunasiri MEMS directional sound sensors that use two coupled wings moving in air are subjected to viscous damping. The amplitude of oscillation of the sensors is read out by measuring the capacitance of interdigitated comb fingers along the edges of the wings. In this presentation, effects of damping on MEMS sensors with and without comb fingers will be described. It was found that the sensors with comb fingers have a significantly larger damping indicating that the longer perimeter due to combs is responsible for the observed increase [1]. However, the increase in damping reduces the quality factor which improves the response time of the device. \\[4pt] [1] W. Zhang and K. Turner, \textit{Sensors \& Actuators: A.} \textbf{134} p.594 (2007). [Preview Abstract] |
Wednesday, March 23, 2011 1:03PM - 1:15PM |
Q21.00010: Attofarad capacitance measurement on organic thin films using Scanning Microwave Microscopy Shijie Wu, Jing-Jiang Yu Scanning microwave microscopy (SMM) is a recent development in SPM technique that combines the lateral resolution of AFM and the measurement precision of microwave analysis. It consists of an AFM interfaced with a vector network analyzer (VAN). In the reflection mode (S11 measurement), the measured complex reflection coefficient of the microwave from the contact point directly correlates to the impedance of the sample under test. The maximum sensitivity of the measurement is obtained at the resonance where the impedance of the sample under test matches the characteristic impedance. Since the measured load impedance is largely determined by the impedance of the sample under test, SMM can be used to measure the capacitances over dielectric thin films. In this presentation, we report the calibration of SMM using a capacitance standard developed by NIST. Then SMM is used to measure the minute capacitance difference between decanethiol and octadecanthiol SAM layers. The coexistence of two different SAMs on the same substrate with a well-known height difference of 0.88 nm is achieved via an AFM-based nanolithography method known as Nanografting. The measured capacitance difference is about 24 attofarads under the condition that the effective tip/sample contact area was estimated to be about 60nm in diameter. [Preview Abstract] |
Wednesday, March 23, 2011 1:15PM - 1:27PM |
Q21.00011: Intermodulation Spectral Analysis and The Intermodulation Lockin David Haviland, Erik Th\"olen, Daniel Platz, Daniel Forchheimer, Carsten Hutter High quality factor oscillators are very useful for sensitive measurement. A weak perturbation to the oscillator gives a large change of response near resonance, which is typically analyzed to first order as change in the linear response (e.g. shift of resonance frequency). In many cases the measurement can be greatly enhanced by detecting higher order nonlinear response. With a single drive frequency, high order non-linearity gives response at high frequency harmonics, which are filtered out by the high $Q$ oscillator. With two drive frequencies, high-order nonlinear response can be crowded near resonance by intermodulation, or frequency mixing. The intermodulation spectrum near resonance is highly correlated and from its analysis one can reconstruct high-order non-linearity\footnote{C. Hutter et al. Phys. Rev. Lett. {\bf 104}, 050801 (2010)} without high frequency spectral data. We developed a general-purpose lockin measurement instrument and software analysis algorithms for preforming this type of measurement. The instrument drives a system with two pure tones while simultaneously measuring both quadratures of response at 32 intermodulation product frequencies.\footnote{E. A. Th\"olen et al. submitted to RSI, arXiv:1008.2722} [Preview Abstract] |
Wednesday, March 23, 2011 1:27PM - 1:39PM |
Q21.00012: A Study of Ionic Transport Through Randomly-Aligned Silica Nanospring Using Electrochemical Impedance Spectroscopy Yukta P. Timalsina, Joshua Branen, Eric Aston, Ken Noren, David N. McIlroy A study of ionic transport through randomly aligned (silica) nanospring (RANS) using electrochemical impedance spectroscopy is presented. The device used for this study is a parallel plate capacitor consisting of two conducting surfaces with RANS as the dielectric spacer layer. The device response is evaluated with test solutions consisting of sodium chloride in a phosphate buffer. The experimental impedance data is analyzed using a model equivalent resistor-inductor-capacitor (RLC) circuit. The solution resistance through RANS and electric double layer formed at solution- electrode interface are elements of equivalent circuit that are more responsive and are more likely to be affected by changes of ionic concentrations. From our analysis we have determined that an electric double layer forms at the solution- RANS interface, which acts as a barrier to diffusion of ions from the solution into the RANS, and vice versa. We have also determined that ion diffusion is impeded by the RANS, as illustrated by changes in the resistance of the element of the equivalent circuit that corresponds to diffusion of ions through the RANS. The linear response of the RANS-based device below 10 kHz is potentially useful for many sensing applications. [Preview Abstract] |
Wednesday, March 23, 2011 1:39PM - 1:51PM |
Q21.00013: Gas Sensing Properties of Hybrid SnO$_{2}$/Carbon Nanotubes Azlin Biaggi-Labiosa, Laura J. Evans, Jennifer C. Xu, Gary W. Hunter, Gordon Berger, Francisco Sola Chemical sensors involving nanostructured materials can be developed into sensor systems with unique properties and improved performance. One approach is to combine different nanomaterials in order to form hybrid structures with properties different than that of the constituent materials. Hybrid nanostructures consisting of tin oxide (SnO$_{2})$ nanocrystals distributed on the surface of multiwalled carbon nanotubes (MWCNTs) and singlewalled carbon nanotubes (SWCNTs) were fabricated and incorporated on a sensor platform in a controlled and efficient manner with a novel approach that combines dielectrophoresis with standard microprocessing techniques. Current vs. voltage and current vs. temperature curves were taken at different concentrations of hydrogen (H$_{2})$, hydrocarbons and nitrogen oxides (NO$_{x})$ at various operating temperatures for the hybrid nanostructures and were compared with their counterparts without SnO$_{2}$ nanocrystals. The tests showed that the hybrid nanostructures exhibit room temperature sensing capability when exposed to low concentration gases in contrast to the high operating temperature typically required for SnO$_{2}$ nanocrystals alone. High resolution electron microscopy and electron energy-loss spectroscopy will also be presented. [Preview Abstract] |
Wednesday, March 23, 2011 1:51PM - 2:03PM |
Q21.00014: Development of a Tunnel Diode Resonator technique for magnetic measurements in Electrostatic Levitation chamber N.S. Spyrison, P. Prommapan, H. Kim, J. Maloney, G.E. Rustan, A. Kreyssig, A.I. Goldman, R. Prozorov The incorporation of the Tunnel Diode Resonator (TDR) technique into an ElectroStatic Levitation (ESL) apparatus was explored. The TDR technique is known to operate and behave well at low temperatures with careful attention to coil-sample positioning in a dark, shielded environment. With these specifications a frequency resolution of $10^{-9}$ in a few seconds counting time can be achieved.\footnote{C. V. Degrift, ``Tunnel diode oscillator for 0.001 ppm measurements at low temperatures,'' Rev. Sci. Instrum. \textbf{46}, 599 (1975).} Complications arise when this technique is applied in the ESL chamber where a sample of molten metal is levitating less then 10 mm from the coil in a large electrostatic field. We have tested a variety of coils unconventional to TDR; including Helmholtz pairs and Archimedean spiral coils. [Preview Abstract] |
Wednesday, March 23, 2011 2:03PM - 2:15PM |
Q21.00015: Microwave impedance imaging on semiconductor memory devices Worasom Kundhikanjana, Keji Lai, Yongliang Yang, Michael Kelly, Zhi-Xun Shen Microwave impedance microscopy (MIM) maps out the real and imaginary components of the tip-sample impedance, from which the local conductivity and dielectric constant distribution can be derived. The stray field contribution is minimized in our shielded cantilever design, enabling quantitative analysis of nano-materials and device structures. We demonstrate here that the MIM can spatially resolve the conductivity variation in a dynamic random access memory (DRAM) sample. With DC or low-frequency AC bias applied to the tip, contrast between n-doped and p-doped regions in the dC/dV images is observed, and p-n junctions are highlighted in the dR/dV images. The results can be directly compared with data taken by scanning capacitance microscope (SCM), which uses unshielded cantilevers and resonant electronics, and the MIM reveals more information of the local dopant concentration than SCM. [Preview Abstract] |
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