Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session P27: Focus Session: Advances in Scanned Probe Microscopy III: High Frequency and Optical Techniques |
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Sponsoring Units: GIMS Chair: Chris Hammel, Ohio State University Room: 329 |
Wednesday, March 18, 2009 8:00AM - 8:36AM |
P27.00001: Nanoscale Spectroscopy with Optical Antennas Invited Speaker: Antennas are devices that efficiently convert localized energy to free propagating radiation, and vice versa. They are a key enabling technology in the microwave and radiowave regime but their optical analogue is greatly unexplored. In order to understand antenna-coupled light emission and absorption we use a single molecule as an elementary light emitting device. With an optical antenna in the form of a simple gold particle we are able to increase the emission efficiency by more than a factor of 10. However, for very short distances between particle and molecule the fluorescence yield drops drastically because of nonradiative energy transfer. A simple gold particle is not an efficient optical antenna and it can be expected that favorably designed nanoplasmonic structures will yield much higher enhancement. Optical antennas can be employed as light sources for high-resolution optical microscopy and spectroscopy. We demonstrate vibrational (Raman scattering) and nonlinear imaging with spatial resolutions down to 10nm. [Preview Abstract] |
Wednesday, March 18, 2009 8:36AM - 8:48AM |
P27.00002: \textit{Nano-Prism} Probe for Nano-Optical Applications Taekyeong Kim, Byung Yang Lee, Seunghun Hong, Deok-Soo Kim, Zee Hwan Kim Recently, a \textit{nano-prism} structure has drawn attention as an optical nano-antenna due to its exotic optical properties, while it has been extremely difficult to prepare a probe terminated with a nano-prism for nano-optical applications. Herein, we report a method to mass-produce pristine nano-prism probes. Our fabrication process resulted in \textit{nano-prism with sharp edge at the end of the probe,} which significantly enhanced the electric field around it and made nano-prism probes ideal for nano-optical applications. We performed the apertureless near-field scanning optical microscopy on gold nanoparticles using a nano-prism probe, revealing the field localization at the vertices of the nano-prism. We also demonstrated the fabrication of multiple nano-prism probes in a parallel fashion. This method could be a major breakthrough and provide tremendous flexibility for SPM optical applications such as nano-TERS (tip enhanced Raman scattering) or FRET (fluorescent resonance energy transfer) because it allows one to mass-produce nano-probes terminated virtually general nanostructures. (Advanced Materials, in press) [Preview Abstract] |
Wednesday, March 18, 2009 8:48AM - 9:00AM |
P27.00003: Optical Response of Absorbates in the STM Environment; The Influence of the STM Tip and Plasmonic Effects Ping Chu, D.L. Mills STM is widely used to explore the excited states and related optical properties of adsorbates on metal surfaces. The adsorbate may be placed on a thin oxide layer that is grown on the metallic substrate. One may ignore the direct hybridization between the adsorbate electrons and those in the substrate. We have developed the theory of the optical response of adsorbates in such an environment. Electrons in the adsorbate may interact with the electronic degrees of freedom in the tip/substrate complex through the fluctuating electric fields generated by the zero point motions of electrons in the substrate and the tip. The coupled plasmons of the tip/substrate complex contribute to these fluctuating fields. We have developed a formalism which allows us to describe energy level shifts of the adsorbate orbitals and the non radiative decay rate of excited states from coupling to the electronic degrees of freedom in the tip and substrate. We have also developed a theory of plasmon enhanced radiation emission under the tip, where the coupled plasmons of the tip/substrate complex are responsible for the enhancement of the emission. [Preview Abstract] |
Wednesday, March 18, 2009 9:00AM - 9:12AM |
P27.00004: Ultrafast Stroboscopic Optical Interferometry of Nanoelectromechanical Devices in Damping Pressurized Gas Environment O. Svitelskiy, V. Sauer, N. Liu, K.M. Cheng, M.R. Freeman, W.K. Hiebert A broad range of prospective applications of nanoelectromechanical devices necessitates understanding their performance under varying external conditions. We report a comprehensive gas damping study of a series of Si nanobridges and nanocantilevers with thickness of 0.147 $\mu $m, widths ranging from 0.1 to 1 $\mu $m, and lengths from 0.5 to 12 $\mu $m. Free ring-down oscillations of the resonators, capacitively excited by 1 ns 50 V electric pulses, were measured via instantaneous optical interference pictures snapped by a femtosecond laser. The devices response to a range of damping environments was studied, including response to different gases (He, N$_{2}$, CO$_{2}$) in widely ranging pressures from deep vacuum up to 200 bar, all done in a specially designed scanning optical microscopy chamber [1]. The resonator parameters demonstrate three distinct regions of pressure behavior: high vacuum, free molecular flow, and viscous. For each region a qualitative model is presented.\newline [1] O.Svitelskiy et al, Rev.Sci.Instr,\textbf{79} 093701, 2008 [Preview Abstract] |
Wednesday, March 18, 2009 9:12AM - 9:24AM |
P27.00005: An Ultra High Vacuum Radio Frequency Scanning Tunneling Microscope Utku Kemiktarak, Keith Schwab, Kamil Ekinci Radio frequency scanning tunneling microscope (RF-STM) utilizes a \textit{LC} resonant circuit to achieve impedance matching between the STM tunnel junction and 50-$\Omega $ high frequency electronics. This technique allows measurement bandwidths up to 10 MHz. We have built an ultra high vacuum (UHV) RF-STM system with in-situ tip and surface treatment as well as sample, tip and matching circuit exchange. In this talk, we will describe the basic operation of this system and discuss the application of UHV RF-STM to high frequency displacement detection. We will argue that UHV RF-STM is a suitable tool to measure back-action forces of tunneling electrons and other tip-sample interactions. [Preview Abstract] |
Wednesday, March 18, 2009 9:24AM - 9:36AM |
P27.00006: Development of a scanning probe microscope for localized ferromagnetic resonance measurements Christian Long, Naoyuki Taketoshi, Haitao Yang, Ichiro Takeuchi We present an update on our research into the development of a scanning probe microscope capable of performing localized ferromagnetic resonance measurements. The system is based on near-field microwave microscopy using a resonant microwave cavity. Using near-field microwave microscopy allows us to produce a GHz frequency magnetic field which is confined to the region around the probe tip. By recording the change in the transmission coefficient of the resonator (S12) as a function of applied DC magnetic field, we measure the absorption of RF energy by the sample. The resulting ferromagnetic resonance spectrum allows us to map the magnetic properties of the material under the probe tip. The possibility to perform localized ferromagnetic resonance measurements using a scanning probe geometry promises to yield new insight into the properties of magnetic thin films. [Preview Abstract] |
Wednesday, March 18, 2009 9:36AM - 9:48AM |
P27.00007: Scanning magnetic resonance microscopy: Spatially resolved imaging of ferromagnetic resonance on yttrium iron garnet disk. Toshu An, Toyoaki Eguchi, Yukio Hasegawa We developed a radio frequency (RF) probe which can be implemented into scanning probe microscope aiming for its spatially resolved imaging. The probe is composed of a sharp tip attached at the end of a semi-rigid coaxial cable which transmits RF over 10 GHz. To measure ferromagnetic resonance (FMR) of a sample, the probe is set close to the sample, and the S$_{11}$ parameter was measured by using a network analyzer. As a test magnetic sample, a 10 mm-diameter and 1 mm-thickness polycrystalline YIG (yttrium iron garnet) disk was used. By locating the RF probe at the center of the YIG disk, FMR signal was detected as an absorption dip at 2.8 GHz in the S$_{11}$ measurements under in-plane static magnetic field of 458 Oe. The detected FMR signal has a sharper dip compared with that obtained in the coplanar wave guide method, and by moving the RF probe to the edge of the YIG disk, two different frequencies of FMR signal appears depending on the moving direction parallel or perpendicular to the applied magnetic field. The detected spatially dependent FMR signals are well explained by the magnetostatic waves. [Preview Abstract] |
Wednesday, March 18, 2009 9:48AM - 10:00AM |
P27.00008: Design and Fabrication of a Nanoscale Force Sensor for High-Speed Atomic Force Microscopy J. M. Campbell, B. Lucht, R. G. Knobel The atomic force microscope (AFM) has become an important tool in many fields ranging from materials science to biology. Conventional microfabricated AFM cantilevers have resonance frequencies of 10--300~kHz; some specialized cantilevers are available with frequencies up to 2~MHz. However, this represents the practical limit of the resonance frequency of microcantilevers. Three modeling methods were used to design a 200~MHz silicon nitride cantilever suitable for integration into an atomic resolution, frequency-modulation AFM. A process was developed to fabricate the cantilever coupled to an atomic point contact (APC) displacement detector, a device first demonstrated by Flowers-Jacobs et al.~(2007). The cantilever mask and APC electrodes were defined through electron-beam lithography and triple-angle evaporation. The cantilever pattern was transferred to the nitride layer through focused ion beam milling and a subsequent wet etch into the underlying Si substrate suspended the structure. Then, using an active feedback system similar to that developed by Strachan et al.~(2005), electromigration was used to form the APC at 77~K and $10^{-6}$~Torr. Progress toward measuring cantilever motion with the APC displacement detector through microwave reflectometry will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 10:00AM - 10:12AM |
P27.00009: Interferometric and Synthetic Aperture Real-Time Terahertz Imaging Ke Su, Zhiwei Liu, Dale E. Gary, John F. Federici, Robert B. Barat, Zoi-Heleni Michalopoulou Over the past several years, several methods of real-time THz imaging have been developed. In this presentation, we describe a synthetic aperture imaging method of THz imaging. A 4-element THz detector array is used to reconstruct 2-D images of a point source through the interferometric synthetic aperture imaging method. A capture rate up to 63frames/s can be achieved. The recorded video showing the movement of the terahertz source in real time can be viewed at http://www.njit.edu/$\sim $ks265/imagingvideo.html after baseline and phase correction. Furthermore, a high power THz source will be integrated in this CW THz system for longer stand-off imaging distances. [Preview Abstract] |
Wednesday, March 18, 2009 10:12AM - 10:24AM |
P27.00010: Fabrication of MEMS Bimaterial Sensors for Uncooled THz Imaging. Dragoslav Grbovic, Gamani Karunasiri Recently, there has been a significant interest in Terahertz (THz) technology, primarily its applications in concealed object detection and medical imaging. THz region of the spectrum has been underutilized due to lack of compact and efficient sources and detectors. THz imaging has recently been achieved using uncooled, microbolometer infrared (IR) camera and quantum cascade laser (QCL) operating as a THz illuminator. However, bolometer IR cameras are not optimized for the THz band and fabrication of their focal plane arrays (FPAs) is complex due to requred monolithic integration of detectors and readout electronics. Recent developments in bi-material based IR FPAs with optical readout, substantially simplify the fabrication process by decoupling readout from sensing. This presentation describes the design and fabrication of THz-optimized bi-material FPAs, as well as integration of the real-time imaging system. The detection scheme involves detector deformation to minute temperature changes due to absorption of THz radiation. Individual detector deformations are simultaneously probed by shining visible light on entire FPA and reflecting it into a CCD camera. Optical readout eliminates the self-heating effects, enabling longer integration times and, better signal-to-noise ratio. [Preview Abstract] |
Wednesday, March 18, 2009 10:24AM - 10:36AM |
P27.00011: Detection of terahertz radiation from 410 GHz CMOS circuit and other high-frequency oscillators using a Fourier Transform Interferometer Eunyoung Seok, Daniel J. Arenas, Dongha Shim, Kenneth K. O, David B. Tanner Recently, a record-setting operating frequency of 410 GHz was reported for a CMOS circuit, fabricated using 45 nm technology. To measure the emission from this and related devices, we employed a Bruker 113v fourier transform interferometer. The radiation from an on-chip patch antenna attached to the 410 GHz push-push oscillator circuit was measured by placing the chip in the lamp housing of the interferometer. Emission was detected in the first and second harmonics of the oscillator fundamental. Power was estimated by comparison to that from quasi-blackbody sources (globar and mercury lamp). Possible applications will be discussed. [Preview Abstract] |
Wednesday, March 18, 2009 10:36AM - 10:48AM |
P27.00012: Measuring Spin-Lattice and Spin-Spin Relaxation Times Using a Continuous Wave Electron Paramagnetic Resonance Spectrometer Michael R. Page, M.R. Herman, K.C. Fong, D.V. Pelekhov, P.C. Hammel The spin-spin and spin-lattice relaxation times, known as $T_2$ and $T_1$, respectively, provide information about the spins in a material. This information can be used as an imaging technique in Magnetic Resonance methods. $T_1$ and $T_2$ can be measured by a Continuous Wave Electron Paramagnetic Resonance Spectrometer, provided the relationship between the input power and oscillating magnetic field is known. The advantage to this is that Continuous Wave Electron Paramagnetic Resonance Spectrometers are much cheaper than Pulse Electron Paramagnetic Resonance Spectrometers. The relationship between the input power and the oscillating magnetic field is determined by using a sample with known $T_1$ and $T_2$, measuring the absorption at different power levels, and fitting the distribution of absorptions to a curve. We show the results of this measurement with a Bruker EMX 2.7 Continuous Wave Electron Paramagnetic Resonance Spectrometer. This work was supported by The U.S. Army Research Office MURI under contract W911NF-05-1-0414 and by The U.S. Army Research Office DURIP under contract W911NF-07-1-0305. [Preview Abstract] |
Wednesday, March 18, 2009 10:48AM - 11:00AM |
P27.00013: Terahertz Near-Field Nanoscopy of Mobile Carriers in Single Semiconductor Nanodevices Andreas J. Huber, Fritz Keilmann, J. Wittborn, Javier Aizpurua, Rainer Hillenbrand We introduce ultraresolving Terahertz (THz) near-field microscopy based on THz scattering at atomic force microscope tips. Nanoscale resolution is achieved by THz field confinement at the very tip apex to within 30 nm, which is in good agreement with full electro-dynamic calculations. Imaging semiconductor transistors, we provide first evidence of 40 nm ($\lambda$/3000) spatial resolution at 2.54 THz (wavelength $\approx$ 118 $\mu$m) and demonstrate the simultaneous THz recognition of materials and mobile carriers in a single nanodevice. We find that the mobile carrier contrast can be directly related to near-field excitation of THz-plasmons in the doped semiconductor regions. This opens the door to quantitative studies of local carrier concentration and mobility at the nanometer scale. The THz near-field response is extraordinary sensitive, providing contrast from less than 100 mobile electrons in the probed volume. Future improvements could allow for THz characterization of even single electrons or biomolecules. [Preview Abstract] |
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