Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session G24: Focus Session: Advances in Scanned Probe Microscopy II: High Frequencies and Optical Techniques |
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Sponsoring Units: GIMS Chair: Sebastian Loth, Max Plank Institute for Structure and Dynamics Room: 504 |
Tuesday, March 4, 2014 11:15AM - 11:51AM |
G24.00001: Nanoscale cantilevers with integrated optomechanical readout: increasing speed and sensitivity Invited Speaker: Vladimir Aksyuk Decreasing a mechanical probe size and mass into the nanoscale and sub-picogram range offers a way to increase the transduction bandwidth while maintaining the desired mechanical stiffness and, ideally, maintaining or lowering the mechanical damping and the associated fundamental thermal force noise. Such transducers require a new approach to low noise and fast motion readout that is also stable, practical, low power and capable of operating over a wide temperature range. We are using on-chip cavity optomechanical sensing for realizing fast, sensitive and practical integrated AFM probes. Integrated micrometer-scale silicon microdisk high Q optical cavities evanescently couple to sense motion of suspended silicon beams with nanoscale cross sections (e.g. 100 nm x 260 nm). The sensors achieve sub- fm/Hz$^{0.5}$ motion sensitivity, which is near the standard quantum limit for these beams, with dissipated optical power under 300 $\mu $W and the readout bandwidth of approximately 1 GHz. The mechanical properties of the beams are broadly adjustable by design, covering four decades of mechanical stiffness (0.01 N/m to 290 N/m) and frequencies from 250 kHz to 110 MHz, with similar motion readout sensitivity across the range. Combining the low mass mechanical transducer with the ultraprecise readout potentially opens up new regimes of operation while also posing design tradeoffs in gain, bandwidth and dynamic range. The mechanical probe can be excited and the dynamics can be tuned by optomechanical effects as well as application of optical and electrostatic forces via feedback. Effective stiffness modification, regenerative oscillation as well as optomechanical and feedback damping can be useful in different modalities of probe operation. Unresolved sideband operation gives the readout bandwidth larger than the mechanical frequency, which is particularly useful for broadband feedback actuation, e.g. to modify the transfer function, extend the useful measurement bandwidth and cool the sensor motion to reduce nonlinearity and mechanical backaction of the mechanical probe on the sample. [Preview Abstract] |
Tuesday, March 4, 2014 11:51AM - 12:03PM |
G24.00002: Detection of thin film NMR spectrum by Magnetic Resonance Force Microscopy Seung-Bo Saun, Sungmin Kwon, Soonchil Lee, Soonho Won NMR is widely used in many fields due to its powerful advantages such as nondestructive, chemically selective detection, and local probing. However, because of its low sensitivity, it is difficult to investigate thin film samples by conventional NMR. MRFM is the combined technic of NMR and Scanning Probe Microscopy (SPM), and it enabled exceptional sensitivity increasement of NMR detection. We succeeded in detecting general thin film NMR spectrum for the first time by modifying the MRFM. CaF$_{2}$ 34nm thin film NMR was detected and we observed 20 Gauss spectrum in proximity to bulk spectrum which is about 10 Gauss. [Preview Abstract] |
Tuesday, March 4, 2014 12:03PM - 12:15PM |
G24.00003: Implementation of NMR pulse sequences for Magnetic Resonance Force Microscopy Bradley Moores, Alexander Eichler, Christian Degen Magnetic resonance force microscopy (MRFM) is a scanning microscopy technique that allows measuring nuclear spin densities with a resolution of a few nanometers. Ongoing efforts are aiming at improving this resolution, which might ultimately facilitate non-destructive 3D scans of complex molecules or solid state systems with atomic resolution. Here, we review our current efforts to utilize in an MRFM experiment pulsing techniques borrowed from the nuclear magnetic resonance community. The use of advanced pulsing schemes may improve signal-to-noise ratio, imaging resolution, and allow the investigation of novel phenomena. [Preview Abstract] |
Tuesday, March 4, 2014 12:15PM - 12:27PM |
G24.00004: Development of Low Temperature Nuclear Magnetic Resonance Force Microscopy (NMRFM) Experiments for Probing Nanoscale Films and Microcrystals Jeremy Paster, Daniel Tennant, Shirin Mozaffari, John Markert Force detection of nuclear spins is accomplished by coupling NMR spin-flip sequences to a mechanical oscillator. A thin ferromagnet deposited on the tip of the oscillator sets up a large gradient magnetic field in the vicinity of the spins. This provides a magnetic force signature which we can distinguish from the thermal noise of the oscillator. The gradient field also traces out a slice in space in which spins are resonantly tuned to the RF field. We review the advantages of various strategies for inducing nuclear spin flips including cantilever-driven and RF-modulation techniques. We also report on the current state of the project, highlighting important developments and experimental results. In particular, we've adapted a low temperature NMRFM probe for easy transition between thin-film and microcrystal experiments. In one configuration, we orient the oscillator perpendicular to the sample plane so we can work in the region where the ferromagnet's field gradient is largest. Conversely, we can rotate the oscillator 90 degrees to change the geometry of the gradient field. With this orientation we maximize resolution in one dimension by using the flat part of the resonance slice to pick up as many in-plane nuclei as we can. [Preview Abstract] |
Tuesday, March 4, 2014 12:27PM - 12:39PM |
G24.00005: Scanning capacitance microscopy of atomically-precise donor devices in Si Ezra Bussmann, M. Rudolph, S.M. Carr, G. Subramania, G. Ten Eyck, J. Dominguez, M.P. Lilly, M.S. Carroll Recently, a scanning tunneling microscopy (STM) technique to fabricate atomically-precise dopant-based nanoelectronics in Si has been developed. Phosphorus donors are placed via an atomic-precision template formed by STM H-depassivation lithography, then capped with epi-Si and lastly metal contacts are made to the buried donor layer using conventional microfabrication. New challenges are introduced with this approach that center around difficulties to locate and characterize the pattern of buried donors. In this talk, we show that scanning capacitance microscopy (SCM) can image these buried donor nanostructures with sub-100-nm tip-limited resolution. The technique is used to successfully locate and characterize buried donor nanostructures relative to surface alignment marks. This approach relaxes alignment requirements for the STM lithography step and can offer improved alignment of subsequent metallization steps. The SCM technique is also used to nondestructively image the shape of the electronic carrier distribution and characterize the relative doping levels. This work, performed in part at the Center for Integrated Nanotechnologies, a U.S. DOE Office of Basic Energy Sciences user facility, was supported by Sandia's Lab Directed Research and Development Program. Sandia is a multi-program lab operated by Sandia Corp, a Lockheed-Martin Company, for U. S. DOE under Contract DE-AC04-94AL85000. [Preview Abstract] |
Tuesday, March 4, 2014 12:39PM - 12:51PM |
G24.00006: Quantum Many-Body Dynamics in Luminescence from Molecular Exciton and Plasmon Induced by Scanning Tunneling Microscopy Kuniyuki Miwa, Mamoru Sakaue, Branko Gumhalter, Hideaki Kasai In scanning-tunneling-microscope (STM)-induced light emission (STM-LE) from clean and molecule-covered metal surfaces, surface plasmons localized near the tip-substrate gap region play important roles in electronic excitations and radiative decays of molecules. A recent experiment succeeded to observe that the dynamics of the molecule (e.g., luminescence and energy absorption) have an influence on the luminescence spectral profiles of surface plasmons. To understand this from a microscopic point of view, there is a need to investigate the dynamics of the molecule and surface plasmons within the framework of quantum many-body theory. In this study, we construct the effective model of the system and investigate the effects of coupling between a molecular exciton and a surface plasmon (exciton-plasmon coupling) on the luminescence properties using the nonequilibrium Green's function method. It is found that in addition to the dynamics of the molecule, the dynamics of surface plasmons plays an essential role in determining the luminescence spectral profiles of surface plasmons. Prominent peak and dip structure observed in recent experiments are interpreted by the developed theory. The details of exciton-plasmon coupling on the luminescence properties will be discussed. [Preview Abstract] |
Tuesday, March 4, 2014 12:51PM - 1:03PM |
G24.00007: Enhancing Stimulated Emission based Fluorescence Detection with Interferometric Setup Fu-Jen Kao Stimulated emission, being spatially coherent, supports unattenuated fluorescence detection at extended distance with low NA optics. We have demonstrated stimulated emission (SE) imaging in a long-working distance configuration. Additionally, the corresponding fluorescence lifetime imaging is realized by electronically controlling the time delay between the excitation and the SE pulses in the nanosecond ranges through pump-probe configuration. The fluorescence lifetime of selected fluorophores is accurately determined through the pump-probe configuration. However, the sensitivity of SE based fluorescence detection is usually limited by the dynamic range and saturation of photodetectors. We are showing that interferometric setup can greatly enhance the detection sensitivity by reducing the DC level of the stimulation beam with destructive interference. The results show that there are many interesting possibilities by combining interferometric techniques with stimulated emission based fluorescence detection. [Preview Abstract] |
Tuesday, March 4, 2014 1:03PM - 1:15PM |
G24.00008: Sub-Hz Linewidth harmonics in a microwave frequency comb generated by focusing a mode-locked ultrafast laser on the tunneling junction of a scanning tunneling microscope Mark Hagmann, Frank Stenger, Dmitry Yarotski A microwave frequency comb (MFC) with hundreds of measurable harmonics superimposed on the DC tunneling current is generated by optical rectification when focusing a mode-locked ultrafast laser on the tip-sample junction of a scanning tunneling microscope (STM). Using a Kerr-lens passively mode-locked Ti:Sapphire laser (CompactPro, Femtolasers) having a pulse repetition frequency of 74.25 MHz with a STM (UHV700, RHK Technology) operated in air, 200 harmonics from 74.25 MHz to 14.85 GHz have reproducible measured linewidths equal to the 1 Hz resolution bandwidth (RBW) of the spectrum analyzer. At the 200$^{\mathrm{th}}$ harmonic the signal-to-noise ratio is 20 dB. When the RBW exceeds 1 Hz the measured linewidth increases to remain equal to the RBW. However, for a RBW of 0.1 Hz the measured linewidth is distributed from 0.1 Hz to 1.2 Hz which we attribute to the stochastic behavior of the pulse repetition frequency in the unstabilized laser. Measurements of drift in the pulse repetition frequency and a derivation showing the effects of timing jitter support this hypothesis. [Preview Abstract] |
Tuesday, March 4, 2014 1:15PM - 1:27PM |
G24.00009: Variable temperature nano-optics in correlated electronic systems Adrian Gozar, Rainer Held, Darrell Schlom We report on the development and performance of instrumentation designed to study nano-scale optical properties of correlated electronic systems in a cryogenic environment. The main capability of our Variable-Temperature scattering-based Scanning Near-Field Optical Microscope (VT-SNOM) is to measure the complex dielectric function with a spatial resolution of 20-30 nm in a 10 K - 300 K temperature range. VT-SNOM measurements around the metal-insulator transition on 20 nm thick subsurface EuO films will be presented. [Preview Abstract] |
Tuesday, March 4, 2014 1:27PM - 1:39PM |
G24.00010: Imaging and quantification of electrical properties at the nanoscale using Scanning Microwave Impedance Microscopy (sMIM) Stuart Friedman, Oskar Amster Scanning Microwave Impedance Microscopy (sMIM) is a novel mode for AFM-enabling imaging of unique contrast mechanisms and measurement of local permittivity and conductivity at the 10's of nm length scale. We will review the state of the art, including imaging studies of microelectronic devices as well as novel materials and nanostructures, such as graphene and patterned optical crystals and ferro-electrics. In addition to imaging, the technique is suited for a variety of metrology applications where specific physical properties are determined quantitatively. We will present research results on quantitative measurements of dielectric constant (permittivity) and conductivity (e.g. dopant concentration). For samples where properties such as dielectric constant are known the technique can be used to measure film thickness. [Preview Abstract] |
Tuesday, March 4, 2014 1:39PM - 1:51PM |
G24.00011: Scanning near field microwave microscopy based on an active resonator Naser Qureshi, Oleg Kolokoltsev, Cesar Leonardo Ordonez-Romero A large number of recent implementations of near field scanning microwave microscopy (NFSMM) have been based on the perturbation of a resonant cavity connected to a sharp scanning probe. In this work we present results from an alternative approach: the perturbation of a microwave source connected to a scanning tip. Based on a yittrium iron garnet (YIG) cavity ring resonator this scanning probe system has a quality factor greater than 10$^{6}$, which allows us to detect very small frequency shifts, which translates to a very high sensitivity in sample impedance measurements. Using a selection of representative semiconductor, metal and biological samples we show how this approach leads to unusually high sensitivity and spatial resolution. [Preview Abstract] |
Tuesday, March 4, 2014 1:51PM - 2:03PM |
G24.00012: Spectral frustration and coherence in thermal near-field spectroscopy Brian O'callahan, William Lewis, Andrew Jones, Markus Raschke The thermal near-field is characterized by fundamentally distinct spatial, spectral, and coherence properties compared to far-field thermal radiation. Scattering scanning near-field microscopy (s-SNOM) has recently opened spectroscopic access to the enhanced electromagnetic local density of states associated with electronic and vibrational resonances. We study the influence of the tip on the scattered near-field spectral response due to the frustration of the evanescent thermal field by the tip. With the example of the extrinsic resonance of the surface phonon polariton (SPhP) in SiC we demonstrate redshifts by $0$ cm$^{-1}$ to $50$ cm$^{-1}$ of the unperturbed 948 cm$^{-1}$ resonance. We model the behavior as a result of tip-sample coupling or effective medium change due to the presence of the tip. We show that the effect is most significant for momentum dependent and strongly dispersive resonances. In addition, distance dependence measurements demonstrate a competition between scattering of the near-field associated with the thermally driven stochastically fluctuating optical polarization and that of the spatially coherent SPhP which is excited. The results indicate the possibility for local tuning of SPhP resonant conditions via evanescent thermal near-field coupling. [Preview Abstract] |
Tuesday, March 4, 2014 2:03PM - 2:15PM |
G24.00013: Highest resolution Confocal Raman-AFM-SNOM: Advantages and new insights for Graphene characterization Wei Liu, Ute Schmidt, Thomas Dieing An important goal of graphene study is precisely determining the number of layers forming the graphene flake. The aim of this contribution is to show how the confocal Raman AFM - SNOM can contribute to the characterization of graphene. In the past two decades, AFM (Atomic Force Microscopy)was one of the main techniques used to characterize the morphology of nano-materials. From such images it is possible to gain information about the physical dimensions of the material, but not their chemical composition, crystallinity or stress state. On the other hand, Raman spectroscopy is known to be used to unequivocally determine the chemical composition of a material. By combining the chemical sensitive Raman spectroscopy with high resolution confocal optical microscopy, the analyzed material volume can be reduced below 0.02 $\mu$m$^{3}$, thus leading to the ability to acquire diffraction limited resolution Raman images. Furthermore, using SNOM (Scanning Near-field Optical Microscopy) technology, it will be shown for the first time how the transparency of different graphene sheets is changing as a function of the number of layers. The combination of confocal Raman microscopy with AFM and SNOM is a breakthrough in microscopy. Using such a combination, the topographic information obtained with an AFM can be directly linked to the chemical information provided by confocal Raman and transparency properties obtained with SNOM. [Preview Abstract] |
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