Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session U46: Focus Session: Advances in Scanned Probe Microscopy 2: High Frequencies and Optical Techniques |
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Sponsoring Units: GIMS Chair: Robert McMichael, NIST Room: Hilton Baltimore Holiday Ballroom 5 |
Thursday, March 21, 2013 11:15AM - 11:51AM |
U46.00001: Edge mode imaging in magnetic nanodisks using ferromagnetic resonance force microscopy Invited Speaker: Feng Guo Edge modes are trapped spin wave modes that can form at film edges. The spontaneous localization of edge modes makes them fine probes of edge properties and test objects for magnetic resonance imaging. We use ferromagnetic resonance force microscopy (FMRFM) to study the edge modes in magnetic nanodisks with an improved resolution of less than 100 nm. In this presentation we will describe imaging and spectroscopy of the normal modes in Permalloy disks, manipulation of edge modes to characterize the disk edges, and the disk-diameter dependence of the spectrum. Micromagnetic modeling of a 500 nm diameter, 25 nm thick disk predicts a main mode that is nearly uniform across the sample and three edge modes with higher resonance fields. The spectra measured with various tip positions are consistent with the modeling results. Besides the broad center mode, three distinct edge modes are observed and appear when the tip is near the disk edge. However, in contrast to the symmetric edge behavior predicted by the modeling, the measured left and right edge modes are detected at different resonance fields, suggesting inhomogeneity of the edge properties. By rotating the applied field, we are able to move the localized edge mode along the edge of a single structure and thus probe the inhomogeneity in edge properties. The fundamental edge mode with the highest resonance field is most sensitive to the edge inhomogeneity while the center mode is relatively isotropic. The disk size dependence of the edge mode is also investigated for disk diameters ranging from 100 nm to 750 nm. The number of trapped edge modes reduces with decreasing disk size in agreement with micromagnetic modeling. [Preview Abstract] |
Thursday, March 21, 2013 11:51AM - 12:03PM |
U46.00002: Magnetic imaging with shallow spins in nitrogen delta-doped diamond Bryan A. Myers, Jens Boss, Kenichi Ohno, Preeti Ovartchaiyapong, David D. Awschalom, Ania C. Bleszynski Jayich Nitrogen-vacancy (NV) electronic spins in diamond are atomic-size sensors of magnetism at the nanoscale. Shallow NVs with long spin coherence times ($T_2$) are desirable for ultrasensitive magnetometry. However, $T_2$ tends to decrease for shallow NVs, which couple most strongly to external spins. To optimize magnetic sensitivity, it was recently shown that delta-doping nitrogen during chemical vapor deposition of single-crystal diamond (SCD) can produce films with a $<5$ nm thick layer of NVs that retain long $T_2$ [1]. Here, using a magnetic field gradient produced by a scanning probe, we investigate optically-detected magnetic resonance measurement protocols to simultaneously determine the relative and absolute depths of the NVs in SCD films containing multiple doped layers separated by a few nm. A consistent comparison of NV properties, such as $T_2$, versus depth is important for engineering spin placement. Furthermore, this magnetic field gradient technique enables sub-diffraction imaging of NV centers, which itself will be explored for high resolution NV-based magnetometry. [1] K. Ohno et al., Appl. Phys. Lett. 101, 082413 (2012). [Preview Abstract] |
Thursday, March 21, 2013 12:03PM - 12:15PM |
U46.00003: Nanoscale Fourier-transform magnetic resonance imaging John Nichol, Tyler Naibert, William Rose, Eric Hemesath, Lincoln Lauhon, Raffi Budakian Magnetic resonance force microscopy is a promising technique for nanoscale magnetic resonance imaging, but the detection sensitivity must still be improved to reach the single proton level. Multiplexed imaging schemes, such as Fourier encoding, are used in clinical magnetic resonance imaging for sensitivity enhancement. Here, we report a method for Fourier encoding nanoscale samples, where statistical fluctuations dominate the spin polarization. The protocol uses periodic encoding pulses to create correlations in the spin fluctuations. We demonstrate this technique using a silicon nanowire mechanical oscillator as a force sensor to image $^{1}$H spins in a polystyrene sample. The sample is encoded using pulsed magnetic field gradients generated by a nanoscale current-carrying wire. We reconstruct a 2-dimensional projection of the proton density in the sample with 10~nm resolution. [Preview Abstract] |
Thursday, March 21, 2013 12:15PM - 12:27PM |
U46.00004: On infrared and terahertz imaging of surface plasmons in high-Tc superconductors H.T. Stinson, Z. Fei, A.S. Rodin, A.S. McLeod, M.M. Fogler, D.N. Basov Recent scattering-mode scanning near-field optical microscopy (s-SNOM) experiments have imaged surface plasmons in graphene at infrared frequencies.\footnote{Z. Fei et al., Nature, \textbf{487}, 82 (2012).} The scanning probe launches surface plasmons and detects their standing-wave interference pattern upon reflection from the sample edge. The surface plasmon dispersion relation directly relates the standing wave fringe separation and amplitude decay to the optical constants of the sample. We have modeled surface plasmon s-SNOM imaging for high-Tc superconductor (HTSC) thin films. Our results indicate that surface plasmons can be imaged in HTSCs at frequencies near or below the superconducting gap. This would allow for a direct measurement of HTSC optical constants below the gap. For known HTSCs such as YBCO, this is in the far-IR or terahertz range. Our simulations show that this method can also distinguish between superconducting and normal states at the nanoscale. [Preview Abstract] |
Thursday, March 21, 2013 12:27PM - 12:39PM |
U46.00005: Quantifying the Stochastic Dynamics of the Elastic Probe used in Cavity Optomechanical Force Micropscopy Stephen Epstein, Mark Paul Atomic force microscopy has revolutionized surface science and is now as essential tool for micro and nanoscale studies in science and engineering. Cavity optomechanical force microscopy consists of an atomic force microscopy probe that is placed in close proximity to a microfabricated optical cavity. The interaction between the probe and the optical cavity is used to quanitfy the probe dynamics. Cavity optomechaincal force microscopy extends conventional atomic force microscopy by being more sensitive with increased frequency resolution. In many situations of interest the probe operates while immersed in a viscous fluid which can strongly affect the probe dynamics. In this talk we quantify the stochastic dynamics of the elastic probe when driven by Brownian motion where the dominant source of dissipation is the surrounding viscous fluid. We use deterministic finite-element numerical simulations with the fluctuation-dissipation theorem to quantify the stochastic dynamics of the probe for the precise conditions and geometries used in current experiments. [Preview Abstract] |
Thursday, March 21, 2013 12:39PM - 12:51PM |
U46.00006: Enhanced Electroluminescence from A Nanocavity Due to Dynamical Coupling of Plasmonic and Molecular Emissions Xiaoguang Li, Gong Chen, Zhenchao Dong, Jian Shen, Zhenyu Zhang We investigate the electroluminescence from a nanocavity formed by a luminescent molecule within the tip-substrate junction of a scanning tunneling microscope. The light emissions from the molecular luminescence and plasmonic radiation are evaluated using respectively a density matrix approach and classical electromagnetic theory. The molecular luminescence is described in two different components: the radiation associated with the excited states effectively pumped by the tunneling electrons and the spontaneous emission enhanced by the plasmonic field. In particular, by explicitly treating the near field of the plasmons, we explore in detail the dynamical coupling between the plasmonic and molecular emissions, and identify conditions for enhanced electroluminescence. We discuss these results in comparison with experiments. [Preview Abstract] |
Thursday, March 21, 2013 12:51PM - 1:03PM |
U46.00007: Measurement of optical force in plasmonic resonant cavities using dynamic mode AFM Dongshi Guan, Zhihong Hang, Zsolt Marcet, Hui Liu, Ivan Kravchenko, Cheting Chan, Hobun Chan, Penger Tong We report an experimental study of the optical force induced by a plasmonic resonance mode in metallic cavities using dynamic mode atomic force microscopy (AFM). The plasmonic cavity is made of a (upper) gold coated glass sphere and a (lower) quartz substrate patterned with an array of gold disks, whose diameter $d$ varies from 250 to 750 nm. The gold coated sphere is glued to an AFM cantilever, by which we measure the optical force acted on the sphere using AFM and phase-sensitive lock-in amplifier. With this technique the sensitivity of the force measurement is significantly increased to $\sim$0.1 pN, which may have many applications in precise force measurement. The measured optical force is found to have a strong resonance dependence on the cavity separation $r$, as well as the diameter of gold disk $d$. The conventional optical force obtained in the far-field ($r$$>$3$\mu$m) for different values of $d$ agrees well with the measured transmission. In the near-field ($r$$<$0.5$\mu$m), resonance is excited in the plasmonic cavity and the induced force by an infrared laser is found to be increased by an order of magnitude compared with the photon pressure generated by the same laser light. *Work supported by the Research Grants Council of Hong Kong SAR. [Preview Abstract] |
Thursday, March 21, 2013 1:03PM - 1:15PM |
U46.00008: Nano-FTIR: infrared spectroscopic chemical identification of materials at the nanoscale Florian Huth, Alexander Govyadinov, Sergiu Amarie, Wiwat Nuansing, Fritz Keilmann, Rainer Hillenbrand Recently, we applied the principles of FTIR to scattering-type Scanning Near-field Optical Microscopy (s-SNOM). s-SNOM employs an externally illuminated sharp metallic tip to create a nanoscale hot-spot at its apex which greatly enhances the near-field interaction between the probing tip and the sample. The light backscattered from the tip transmits the information about this near-field interaction to the far zone where the FTIR spectra can be recorded. The result is a novel nano-FTIR technique, which is capable to perform near-field spectroscopy and imaging with nanoscale resolution. Here we demonstrate nano-FTIR with a coherent-continuum infrared light source. We show that the method can be used to determine the fingerprint IR absorption spectrum of organic samples with a spatial resolution of 20 nm. Corroborated by theory, the nano-FTIR absorption spectra correlate well with conventional FTIR absorption spectra, as experimentally demonstrated with PMMA samples. Nano-FTIR can thus make use of standard infrared databases of molecular vibrations to identify organic materials in ultra-small quantity and at ultrahigh spatial resolution. [Preview Abstract] |
Thursday, March 21, 2013 1:15PM - 1:27PM |
U46.00009: Broadband vibrational nano-spectroscopy with a synchrotron infrared source Hans A. Bechtel, Robert L. Olmon, Eric A. Muller, Benjamin Pollard, Markus B. Raschke, Michael C. Martin Scattering-scanning near-field optical microscopy (s-SNOM) is capable of providing chemical contrast with deep sub-wavelength spatial resolution of a few 10's of nanometers. Unfortunately, the wide applicability of the technique has been hindered by the lack of suitable broadly-tunable or broadband IR sources that can provide the necessary high spectral irradiance. Here, we demonstrate broadband, Fourier-transform infrared spectroscopic s-SNOM using infrared synchrotron radiation from the Advanced Light Source (ALS). We show near-field spectra spanning the full mid-infrared, including the fingerprint absorption region (700 cm$^{-1}$ --- 4000 cm$^{-1}$) and spectroscopic multi-modal imaging in combination with laser-based IR sources. We discuss the potential of the approach for a wide range of soft and hard matter nanoscale spectroscopic applications. [Preview Abstract] |
Thursday, March 21, 2013 1:27PM - 1:39PM |
U46.00010: The Lightning Rod Model: a Genesis for Quantitative Near-Field Spectroscopy Alexander McLeod, Gregory Andreev, Gerardo Dominguez, Mark Thiemens, Michael Fogler, D.N. Basov Near-field infrared spectroscopy has the proven ability to resolve optical contrasts in materials at deeply sub-wavelength scales across a broad range of infrared frequencies. In principle, the technique enables sub-diffractional optical identification of chemical compositions within nanostructured and naturally heterogeneous samples. However current models of probe-sample optical interaction, while qualitatively descriptive, cannot quantitatively explain infrared near-field spectra, especially for strongly resonant sample materials. We present a new first-principles model of near-field interaction, and demonstrate its superb agreement with infrared near-field spectra measured for thin films of silicon dioxide and the strongly phonon-resonant material silicon carbide. Using this model we reveal the role of probe geometry and surface mode dispersion in shaping the measured near-field spectrum, establishing its quantitative relationship with the dielectric properties of the sample. This treatment offers a route to the quantitative determination of optical constants at the nano-scale. [Preview Abstract] |
Thursday, March 21, 2013 1:39PM - 1:51PM |
U46.00011: Interferometric Scanning Microwave Microscope for Nanotechnology Application Nicolas Clement, Thomas Dargent, Hassan Tanbakuchi, Katsuhiko Nishiguchi, Ragavendran Sivakumarasamy, Fei Wang, Akira Fujiwara, Damien Ducatteau, Gilles Dambrine, Dominique Vuillaume, Bernard Legrand, Didier Th\'eron Scanning probe microscopes (SPMs) allow scientists to image, characterize and even manipulate material structures at exceedingly small scales including features of atomic dimensions. Although most microelectronics devices operate at high frequency, SPMs have mainly been used with electrical excitation at DC (Conducting Atomic Force Microscope) or kHz (Electric Force Microscope, Kelvin Force Microscope). The main reason is that at GHz frequency, nanoscale objects are far from the standard impedance of 50ohms and almost all the signal is reflected. Here we show, using an interferometer to enable extraction and amplification of the signal of interest, that Scanning Microwave Microscopes (SMM) are ideal tools for tiny capacitances imaging. We demonstrate applications in several fields of nanotechnology with capacitance evaluation down to aF of nanoscale integrated capacitors, biased nanotransistors, molecular junctions and biomolecule flow in a nanofluidic channel. The frequency range of excitation varied from 2 GHz to 20 GHz. With a finite element analysis, we discuss the limits of such microscope. [Preview Abstract] |
Thursday, March 21, 2013 1:51PM - 2:03PM |
U46.00012: Highly enhanced green emission of ZnO via plasmonic resonance of a tungsten tip Huiqi Gong, Xiaodong Guo, Li Dong, Nan Xie, Shichao Yan, Xinyan Shan, Yang Guo, Jimin Zhao, Qian Sun, Xinghua Lu We present a systematic investigation of the photoluminescence of a single crystal ZnO with the aid of a metallic tungsten tip in a pulse laser assisted scanning tunneling microscope. When excited with 740nm laser pulses and as the tip approaches ZnO surface up to the tunneling region ($\sim$ 1nm), an enhancement in green emission (centered at 560nm), up to a factor of 70, is observed. The photoluminescence is a two-photon excitation process, which is evident by the observation of the second-harmonic peak of excitation light and the up-converted luminescence. By measuring the green emission intensity as a function of incidence power, wavelength, and tip-sample distance, we illustrate the critical role of plasmonic resonance of the tungsten tip for the enhanced green emission. The observed broad plasmonic response (680nm to 1080nm) implies possible applications in designing novel solar cells with the aid of tungsten plasmon. [Preview Abstract] |
Thursday, March 21, 2013 2:03PM - 2:15PM |
U46.00013: Single \& Multiprobe Apertureless Thermal Imaging of Electromagnetic Excitation Over A Wide Range of Wavelengths Rimma Dekhter, Aaron Lewis, Sophia Kokotov, Patricia Hamra, Boaz Fleischman, Hesham Taha Near-field optical effects have generally been detected using photodetectors. There are no reports on the use of the temperature changes caused by electromagnetic radiation using thermal sensing probes for scanned probe microscopy. In this paper we apply our development of such probes to monitor the effects of electromagnetic radiation at a number of different wavelengths using the heating caused in a sample by specific wavelengths and their propagation. The paper will catalogue effects over a wide spectrum of wavelengths from the near to mid infrared. The thermal sensing probes are based on glass nanopipettes that have metal wires that make a contact at the very tip of a tapered glass structure. These probes are cantilevered and use normal force tuning fork methodology to bring them either into contact or near-contact since this feedback method has no jump to contact instability associated with it. Data will be shown that defines the resolution of such thermal sensing to at least the 32 nm level. In addition the probes have the important attribute of having a highly exposed tip that allows for either optical sensing methodologies with a lens either from directly above or below or heat sensing with a single or additional probe in a multiprobe scanning probe system. [Preview Abstract] |
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