Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U16: Nanotechnology: Applications and Measurements |
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Sponsoring Units: FIAP Chair: S. Sridhar, Northeastern University Room: Baltimore Convention Center 312 |
Thursday, March 16, 2006 8:00AM - 8:12AM |
U16.00001: Development of Carbon Nanotube Based Isotropic X-ray Source for Cone-Beam Tomography Imaging Zejian Liu, Yueh Lee, Guang Yang, Jian Zhang, Jianping Lu, Otto Zhou We have developed a carbon nanotube based microfocus X-ray source with an isotropic focal spot. Two focusing electrodes were implemented in the design with one electrode harnessing the divergence of field-emitted electrons from gate and the other focusing electrons onto the anode. Isotropic X-ray focal spot was achieved by utilizing an elliptical cathode that forms elliptical electron probe on the anode after electrostatic focusing. Based on the design method, an x-ray source with an isotropic focal spot of 65 $\mu$m in diameter was experimentally demonstrated in X-ray projection images. This type of X-ray source sees wide applications in cone-beam tomography imaging studies. [Preview Abstract] |
Thursday, March 16, 2006 8:12AM - 8:24AM |
U16.00002: Stationary scanning x-ray source based on carbon nanotube field emitters Guang Yang, Jian Zhang, Yuan Cheng, Bo Gao, Qi Qiu, Yueh Lee, Jianping Lu, Otto Zhou Carbon nanotube is an ideal field emitter thanks to its large aspect ratio and small diameter. Based on its field emission property, we have developed a stationary scanning x-ray source, which can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key component of the device is a gated carbon nanotube field emission cathode with an array of electron emitting pixels that are individually addressable via a metal-oxide-semiconductor field effect transistor-based electronic circuit. The characteristics of this x-ray source are measured and its imaging capability is demonstrated. The device can potentially lead to a fast data acquisition rate for laminography and tomosynthesis. [Preview Abstract] |
Thursday, March 16, 2006 8:24AM - 8:36AM |
U16.00003: A New Thermionic Cathode Using Oxide Coated Carbon Nanotubes Christopher Day, Feng Jin, Yan Liu, Scott Little We have demonstrated a new type of thermionic cathode utilizing carbon nanotubes that exhibited superior electron emission properties. A field enhancement factor as high as 2000 was observed and thermionic electron emission current at least an order of magnitude higher than the emission from a conventional oxide cathode was obtained. This cathode combines the low work function of the oxide coating with a high field enhancement factor introduced by carbon nanotubes and we have demonstrated that it can be used as a highly efficient electron source. The cathode was fabricated by sputter deposition of a thin film of oxide materials on aligned carbon nanotubes, which were grown on a tungsten substrate with plasma enhanced chemical vapor deposition. [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U16.00004: Selective Adsorption and Alignment Phenomena of ZnO Nanorods on Molecular-Patterned Substrates for Large-Scale Integrated Device Fabrication Juwan Kang, Sung Myung, Seunghun Hong, Dongjin Oh, Gyutae Kim ZnO nanorods have been utilized for various device applications such as field effect transistor, UV sensor, etc. However, a major stumbling block holding back their practical applications is a lack of mass-production method of such devices. Since ZnO nanorods are first synthesized in solution, one has to pick up and assemble individual nanorods onto substrate for device fabrication, which is not an easy task. We studied the selective assembly and alignment phenomena of ZnO nanorods on molecule-patterned solid substrates. When the molecule-patterned substrate is placed in the solution of ZnO, ZnO nanorods are selectively adsorbed onto negatively charged surface region. Furthermore, we found the adsorbed nanorods slide on the substrate resulting in aligned nanorod structures. This presentation will discuss the systematic study of ZnO nanorod assembly process on patterned substrates and applications of this method for large-scale assembly of ZnO nanorod-based integrated devices. [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U16.00005: Atom selective force measurement with STM Aparna Deshpande, Violeta Iancu, Saw-Wai Hla Scanning tunneling microscope (STM) manipulation and spectroscopy is used to determine the strength of interactions necessary to manipulate individual silver and bromine atoms on a Ag(111) surface at 4.6 K. In order to distinguish between the two types of atoms, we use local atom extraction procedures: bromine atoms are extracted from individual molecules of cobalt porphyrin (5,10,15,20-Tetrakis-(4-bromophenyl)-porphyrin-Co(II)), which are deposited prior to this experiment, by selectively breaking the C-Br bonds with the STM tip. The individual silver atoms are extracted from the native Ag(111) surface by a controlled tip-crash procedure. Then, we laterally manipulate these two atoms using the same STM-tip along the close packed rows of the Ag(111) surface. The tip-height signals during manipulation are recorded as a function of the tip-atom distance, which include the force information necessary to move a halogen atom, bromine, and a metallic atom, silver, on this surface. This work is financially supported by US-DOE grant, DE-FG02-02ER46012. [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U16.00006: Nanofabrication Based on Nanoporous Membranes Zhen Wu, L. Tian, C. Richter, D Nagesha, S. Sridhar, L. Menon We describe nanofabrication methods to produce nanopore array templates in aluminum oxide and titanium dixode films. The method is based on anodization of thin films of aluminum and titanium under \textit{dc} conditions in an acid. We also describe non-lithographic means of transferring the pore pattern from such nanoporous membranes onto a generic substrate. This is based on reactive ion etching through the nanoporous template grown directly on the substrate. In our demonstration, a thin alumina template consisting of a hexagonal array of pores $\sim $50nm in diameter is first deposited on the substrate. The pores reach within 10-20 nm of aluminum, which is protected by an alumina barrier layer. By controlling reactive ion etching conditions, we demonstrate highly anisotropic etching through the aluminum layer, barrier alumina layer and into the substrate. The 50nm pore layer is thus directly transferred to create nanoporous and nanopillar arrays of a variety of materials such as Al, Si, GaN, GaAs, etc. Such nanoporous, nanopillar arrays will be useful in a variety of applications involving biosensors, optoelectronic and spintronic devices. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U16.00007: Resonant Operation of Nanoelectromechanical Systems in a Viscous Fluid Devrez Karabacak, Kamil L. Ekinci Up to date, most work on nanoelectromechanical systems (NEMS) has been done in high vacuum. Yet, many applications may require fluidic NEMS operation. Here, we present measurements of the quality ($Q)$ factor and resonance frequency in nanomechanical doubly-clamped beam resonators as a function of surrounding gas pressure --- from high vacuum to atmospheric conditions. Atmospheric $Q$s obtained are $\sim $10$^{2}$. The experimental results also suggest that viscous effects become less severe in high frequency devices. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U16.00008: Experimental Measurement of Elastic Contact Diameter Charles Ying Manipulation of nano-objects, as well as further development of the MEMS technology, needs an understanding and control of surface forces, including friction and adhesion forces, which depend on contact area in the nanoscale. Meaningful measurements of surface forces and correct interpretation of the force data require knowledge of contact area. Due to experimental difficulties of contact area measurements, a common practice today in surface force research using atomic force microscopy (AFM) is to compute the contact area using the contact mechanics theories. In this talk, I will present a method of experimental determination of contact diameter, or contact width, between a diamond tip and a flat silicon surface. The experiments used diamond tips with their surface geometry determined by AFM imaging. The measured elastic contact widths for diamond tips with a spherical shape, under controlled magnitudes of force in the surface normal direction, agree with the Hertzian contact mechanism. The technique has also been used successfully to obtain contact widths for non-spherical tip geometry. [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U16.00009: Preparation of different protected bimetallic nanoelectrodes with 30nm gapwidth and access window Stephan Kronholz, Silvia Karth\"{a}user, Rainer Waser Reproducible fabrication of 30 nm metallic nanogaps on silicon chips and their electrochemical characterization are presented. The fabrication of the chip is a combination of an optical lithography step and two electron-beam (e-beam) steps. An optimized adhesion layer/metal layer combination (Ti/Pt/Au) and an adopted two layer e-beam resist are used. Specifically the chip has been covered with different protection layers, except of an access window located on top of the nanogaps, calibration electrodes and contact pads, respectively (Fig.1). After characterising the gaps and of the protection layer by cyclical voltammetry in 0.1 M H$_2$SO$_4$ aqueous electrolyte, the deposition of Cu onto the nanogaps will be presented. Fig.1: Different Nanoelectrode Strcutures with access window on top covered by SiO$_2$/Si$_3$N$_4$/SiO$_2$ used as protection layer. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:00AM |
U16.00010: Nanoscale metal thermometry using a radiofrequency single electron transistor Loren Swenson, David Wood, Andrew Cleland We report on the development of single electron transistors for thermometric readout of nanoscale normal metal volumes. Due to the weak electron-phonon interaction at low temperatures, the electron gas in a normal metal can be heated to a temperature significantly greater than that of the surrounding lattice. Below 100 mK, the electron-phonon coupling time is on the order of microseconds to milliseconds, making direct measurements of the electron temperature's time dependence possible. Achieving sensitive and high frequency readout of this system is of critical importance for applications in nanocalorimetry and nanobolometry. We will describe the use of a radiofrequency single electron transistor to time-resolve the temperature of the electron gas in a submicron scale normal metal volume. [Preview Abstract] |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U16.00011: Electrothermal Tuning of Nanomechanical Resonators Michael Manolidis, Seong Chan Jun, X.M. Henry Huang, J. Hone A highly effective electrothermal tuning method has been demonstrated for Al-SiC nanomechanical resonators. Doubly clamped beam devices are actuated and read out using a magnetomotive technique under moderate vacuum. DC current applied to a beam heats the structure and shifts the resonance frequency downward. Frequency shifts of 10 percent are easily achievable, and the thermal time constant of these structures is in the $\mu $s range. The initial frequency and frequency tunability are studied for beams of varying Al thickness, and the device performance can be accurately modeled using simple mechanical and thermal models. Because of the different mechanical properties of SiC and Al, both the initial frequency and the frequency tunability can be modified by varying the Al layer thickness. This approach has the potential to become an important tool for effective frequency tuning in deployable SiC-based NEMS devices and systems for applications that would benefit from SiC as the structural material. [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U16.00012: Resonant absorption in micrometer and nanometer absorbing particles Eshel Faraggi, Bernard Gerstman Resonance effects can occur in laser absorption by micrometer and nanometer sized particles when a train of pulses is used. The pressure generated by the train of pulses may be significantly different than the pressure generated by a single pulse with the same total energy. For pulsed lasers with a gap duration between pulses that is an integer multiple of the characteristic oscillation time of the absorber, constructive interference occurs and the pressure generated inside the absorber is approximately the same as that generated by a single laser pulse. For pulsed lasers with a gap duration between pulses that is not an integer multiple of the characteristic oscillation time, destructive interference occurs and the pressure is significantly decreased. We present numerical computations comparing this effect in two model systems: 1 micrometer melanosome and a 100 nm gold absorber. The resonance effects have implications for both damage thresholds and therapeutic applications of laser radiation. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U16.00013: Optical Trapping and Integration of Semiconductor Nanowire Assemblies in Water Aleksandra Radenovic, Eliane Trepagnier, Hari Shroff, Jan Liphardt, Peter Pauzauskie, Peidong Yang The use of nanowires in scientific, biomedical, and microelectronic applications is greatly restricted due to a lack of methods to assemble nanowires into complex heterostructures with high spatial and angular precision. Here we show that an infrared single-beam optical trap can be used to individually trap, transfer, and assemble high-aspect-ratio semiconductor nanowires into arbitrary structures in a fluid environment. Nanowires with diameters as small as 20 nm and aspect ratios of above 100 can be trapped and transported in three dimensions, enabling the construction of nanowire architectures which may function as active photonic devices. Moreover, nanowire structures can now be assembled in physiological environments, offering novel forms of chemical, mechanical, and optical stimulation of living cells. [Preview Abstract] |
Thursday, March 16, 2006 10:36AM - 10:48AM |
U16.00014: Low temperature internal friction peak in Boron doped nanocrystalline diamond Thomas Metcalf, Brian Houston, James Butler, Tatyana Feygelson Recent measurements of the low-temperature internal friction ($Q^{-1}$) of nanocrystalline diamond films have revealed that these films have a broad but distinct internal friction peak at approximately 2K. In contrast to the off-peak baseline low-temperature $Q^{-1}$ of these films, which show no measureable variation over a factor of 4 span in amplitude, the $Q^{-1}$ at the peak decreases by as much as 60\% when the measurement amplitude is increased by a factor of 4. The similarity of this peak with a low-temperature peak previously observed in boron-doped silicon led to the possibility that the peak is the result of boron contamination of the diamond films. To further investigate this, diamond films with varying degrees boron doping were grown and measured between room temperature and 400 mK. The films are typically 0.5 $\mu$m thick and are grown on silicon double paddle oscillator substrates, which have an extremely low internal friction background and enable highly sensitive measurements of the mechanical properties of thin films. Preliminary results show an upwards shift in temperature of the peak with increasing boron levels. [Preview Abstract] |
Thursday, March 16, 2006 10:48AM - 11:00AM |
U16.00015: Microwave Dielectric Resonance and Negative Permittivity Behavior in Al$_{2}$O$_{3}$-CuO-Cu Nanocomposites Jeffrey Calame, Jacob Battat The frequency-dependent microwave (0.1-18 GHz) complex permittivity of nanocomposites based on the Al$_{2}$O$_{3}$/CuO/Cu system is investigated. The composites are formed by solution infusion of copper precursors into a porous Al$_{2}$O$_{3}$ matrix, followed by thermal decomposition to copper oxides and localized formation of CuAl$_{2}$O$_{4}$ spinels, and finally partial reduction by H$_{2}$ firing. The final material has a complicated microstructure and exhibits strong amplitude, relatively narrowband dielectric resonance in the microwave regime at intermediate concentrations ($\sim $15-18{\%} by volume) of Cu. The resonances are superficially similar in structure to plasmon and Reststrahlen resonances typically seen in conductors at far-infrared to optical frequencies, but occurring at much lower frequencies in the composites. This is in contrast to the usual broadband induced-polarization dielectric relaxations observed in standard composites. Large concentrations of copper cause negative permittivity behavior below 6 GHz. Permittivity data, SEM micrographs, and possible explanations will be presented. [Preview Abstract] |
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