Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F21: Focus Session: Advances in Scanned Probe Microscopy II: High Frequencies and Optical Techniques |
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Sponsoring Units: GIMS Chair: Fabian Natterer, National Institute of Standards and Technology Room: 201 |
Tuesday, March 3, 2015 8:00AM - 8:12AM |
F21.00001: Measurement of Radiation Pressure in an Ambient Environment Dakang Ma, Joseph Garrett, Jeremy Munday Light has momentum and thus exerts ``radiation pressure'' when it is reflected or absorbed due to the conservation of momentum. Micromechanical transducers and oscillators are suitable for measurement and utilization of radiation pressure due to their high sensitivities. However, other light-induced mechanical deformations such as photothermal effects often obscure accurate measurements of radiation pressure in these systems. In this work, we investigate the radiation pressure and photothermal force on an uncoated silicon nitride microcantilever under illumination by a 660 nm laser in an ambient environment. To magnify the mechanical effects, the cantilever is driven optically from dc across its resonance frequency, and the amplitude and phase of its oscillation are acquired by an optical beam deflection method and a lockin amplifier. We show that radiation pressure and photothermal effects can be distinguished through the cantilever's frequency response. Furthermore, in a radiation pressure dominant regime, our measurement of the radiation force agrees quantitatively with the theoretical calculation. [Preview Abstract] |
Tuesday, March 3, 2015 8:12AM - 8:24AM |
F21.00002: Sensitivity Improvement and Cryogenic Application of Scanning Microwave Microscope Hideyuki Takahashi, Yoshinori Imai, Atsutaka Maeda The technique to probe the spatial distribution of electric properties has been more important in modern material science. Scanning near-field microwave microscope (SMM) can be a powerful tool to study inhomogeneous materials. Recently we have developed scanning tunneling/microwave microscope (STM/SMM) with high sensitivity[1,2]. The SMM probe is a modified coaxial resonator whose resonant frequency is 10.7 GHz and Q-factor is 1200-1300 at room temperature. It is applicable to measurements at cryogenic environment. By downsizing the resonator probe, we achieved stable operation down to liquid helium temperature. Q-factor is enhanced to 2000-3000 below 77 K. As an example of application of our STM-SMM, we present the study on inhomogeneous iron-based superconductor K$_x$Fe$_y$Se$_2$. We successfully observed the characteristic mesoscopic phase separation of the metallic phase and the semiconducting phase by two different scanning modes; constant current mode and constant Q-factor mode. The spatial resolution is no worse than 200nm, which is comparable to curvature radius of a probe tip.\\ $\left[ 1 \right]$ A. Imtiaz and S. M. Anlage, J. Appl. Phys {\bfseries 100}, 044304 (2006). \\ $\left[ 2 \right]$ J. Lee et al., Appl. Phys. Lett. {\bfseries 97}, 183111 (2010). [Preview Abstract] |
Tuesday, March 3, 2015 8:24AM - 8:36AM |
F21.00003: Subsurface Imaging with the Scanning Microwave Microscope Joseph Kopanski, Lin You, Jonathan Michelson, Emily Hitz, Yaw Obeng The scanning microwave microscope (SMM) forms images from the reflected amplitude and phase of an incident RF ($\sim$ 2.3 GHz) signal. The reflected signal is a function of the properties of the tip-sample contact, but can also be influenced by buried interfaces and subsurface variations of the sample permittivity. This mechanism allows limited imaging of conductors buried within dielectrics, voids within metal, or multiple metal layers with different permittivity. Subsurface SMM data acquisition modes include passive and various active data acquisition modes. The theory of sub-surface imaging with SMM and COMSOL multi-physics simulations of specific situations will be presented. Measurements of specifically designed test structures and correlation with simulations show the sensitivity and resolution of the technique applied to imaging subsurface metal lines embedded in dielectric. Applications include metrology for back end of the line (BEOL) multi-level metallization and three-dimensional integrated circuits (3D-ICs). [Preview Abstract] |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F21.00004: Advances in imaging and quantification of electrical properties at the nanoscale using Scanning Microwave Impedance Microscopy (sMIM) Stuart Friedman, Yongliang Yang, Oskar Amster Scanning Microwave Impedance Microscopy (sMIM) is a mode for Atomic Force Microscopy (AFM) enabling imaging of unique contrast mechanisms and measurement of local permittivity and conductivity at the 10's of nm length scale. Recent results will be presented illustrating high-resolution electrical features such as sub 15 nm Moire' patterns in Graphene, carbon nanotubes of various electrical states and ferro-electrics. In addition to imaging, the technique is suited to a variety of metrology applications where specific physical properties are determined quantitatively. We will present research activities on quantitative measurements using multiple techniques to determine dielectric constant (permittivity) and conductivity (e.g. dopant concentration) for a range of materials. Examples include bulk dielectrics, low-k dielectric thin films, capacitance standards and doped semiconductors. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:00AM |
F21.00005: Analytical quantitative theory of RF-SPM for nanocarbon electronics Slava V. Rotkin Among a variety of Scanning Probe Microscopy (SPM) tools RF- or microwave-SPM has recommended itself as a versatile characterization tool, recently demonstrated capability to map electronic properties of nanocarbon materials non-destructively and with nanometer resolution. The transparent theory of RF-SPM sensing mechanism is however lacking, mostly limited to numerical or empirical solutions, especially when studying low-dimensional quantum objects, such as nanotubes/nanowires (NT/NW), where the classical description is often invalid. One-dimensional electronic structure of the NT/NW, weak screening of Coulomb interaction and finite e-e compressibility were successfully taken into account to provide an analytic form of its quasi-stationary (due to low RF frequency of the excitation) selfconsistent response. SPM tip response function was, in turn, efficiently analyzed in multipole series, and non-perturbatively diagrammatically summed in the sense of the Random Phase Approximation. Resulting theory shows transparently the physics of RF-SPM sensing mechanism, simultaneously allowing a quantitative analysis of recent RF-SPM data on nanotube electronic devices [E. Seabron, S. MacLaren, X. Xie, SV. Rotkin, JA. Rogers, WL. Wilson, unpublished]. [Preview Abstract] |
Tuesday, March 3, 2015 9:00AM - 9:12AM |
F21.00006: Ferromagnetic Resonance detection using stroboscopic magneto optical Kerr effect Seungha Yoon, Takahiro Moriyama, Robert McMichael Ferromagnetic resonance (FMR) is a powerful method for measuring the magnetic properties of ferromagnets. A number of related optical techniques have become popular, including time-resolved magneto-optical Kerr effect (TR-MOKE) microscopy and Brillouin light scattering (BLS). In this presentation we describe a new, stroboscopic method of measuring FMR based on the magneto-optical Kerr effect (MOKE). We use a polarized telecommunications fiber laser (wavelength $=$ 1550 nm) and a fiber modulator driven at a frequency of interest (1 GHz to 10 GHz) to create pulsed, linearly polarized light incident on a CoFeB thin film sample. Precession in the sample is driven via a coplanar waveguide in the sample holder while the reflected light is split by a polarizing beam splitter and detected by a balanced detector. As the magnetic field is swept, oscillations in the Kerr angle and in the light intensity mix to produce a DC resonance signal. The spectra are Lorentzian, with a superposition of symmetric and anti-symmetric shapes that depends on the phase of the optical and microwave signals. In the presentation, we will also discuss phase sensitive measurements with this technique as well as the advantages over other FMR techniques. [Preview Abstract] |
Tuesday, March 3, 2015 9:12AM - 9:48AM |
F21.00007: Time-resolved scanning tunneling microscopy for studies of nanoscale magnetization dynamics Invited Speaker: Sebastian Loth The time resolution of the scanning tunneling microscope can be boosted greatly by use of electronic pump probe measurement schemes. Pulse shaping of the input pulses can even overcome bandwidth limitations of the instrument and enables sub-nanosecond time resolution [1]. In this talk we will focus on applications of this technique for measurements of fast spin dynamics in nanomagnets. We use the probe tip of a low-temperature STM to arrange magnetic atoms into arrays of our own design. Thin insulating films decouple the atoms from the supporting metallic substrate so that the nanostructures show quantum-magnetic properties with discrete spin states. The time-domain information gained in pump probe spectroscopy quantifies the spin relaxation between metastable spin states [2]. It enables isolating the interaction between the nanomagnet and its environment. In particular, we find that the magnetic atoms of a spin-polarized STM tip interact significantly with the surface even at moderate tunneling conditions. This interaction acts analogously to a highly localized magnetic field. It depends exponentially on the tip-nanomagnet distance and can reach a strength of several tesla. We use this atomically localized magnetic field to control the spin state mixing of a nanomagnet in an avoided level crossing of low-energy spin states [3]. Furthermore, pump probe spectroscopy enables non-local measurements of magnetic states and highlights pathways to design and control magnetism at the single atom level. \\[4pt] [1] C. Grosse, M. Etzkorn, K. Kuhnke, S. Loth, K. Kern, Appl. Phys. Lett. 103, 183108 (2013).\\[0pt] [2] S. Loth, M. Etzkorn, C.P. Lutz, D.M. Eigler, A.J. Heinrich, Science 329, 1628 (2010).\\[0pt] [3] S. Yan, D.-J. Choi, J.A.J. Burgess, S. Rolf-Pissarczyk, S. Loth, Nat. Nanotechnol. doi:10.1038/nnano.2014.281 (2014). [Preview Abstract] |
Tuesday, March 3, 2015 9:48AM - 10:00AM |
F21.00008: A low temperature ultrahigh vacuum scanning tunneling microscope with high-NA optics to probe optical interactions at the atomic scale Haigang Zhang, Joseph Smerdon, Ozgun Suzer, Heath Kersell, Jeffrey Guest The optical and photophysical properties of single molecules/atoms, defects, and nanoscale structures at surfaces hinge on structure at the atomic scale. In order to characterize and control this structure and unravel these correlations, we are developing a low temperature (LT) laser-coupled ultrahigh vacuum (UHV) scanning tunneling microscope (LT Laser UHV STM) based on the Pan-style STM scanner with integrated high-numerical-aperture (NA) optics for single particle spectroscopy measurements under the STM tip. Using slip-stick inertial piezo steppers, the sample stage can be coarsely translated in X and Y directions. For optical measurements, high-NA optics behind and above the sample focus laser excitation on and collect photons emitted from the tip-sample junction. The STM is cooled by a liquid helium bath surrounded by a liquid nitrogen jacket for operation near 5 K; two separate ultrahigh vacuum chambers are used for sample preparation and STM measurements, respectively. We will describe our progress in demonstrating this instrument and plans for experiments studying the correlation between structure and optical function in nanoscale systems. [Preview Abstract] |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F21.00009: Metal-Insulator Phase transition of VO$_2$ nano crystals studied by near-field nanoscopy Yohannes Abate Near-field dipolar plasmon interactions of multiple infrared antenna structures in the strong coupling limit are studied using scattering-type scanning near-field optical microscope (s-SNOM) and theoretical finite-difference time-domain (FDTD) calculations. We monitor in real-space the evolution of plasmon dipolar mode of a stationary antenna structure as multiple resonantly matched dipolar plasmon particles are closely approaching it. Interparticle separation, length and polarization dependent studies show that the cross geometry structure favors strong interparticle charge--charge, dipole--dipole and charge--dipole Coulomb interactions in the nanometer scale gap region, which results in strong field enhancement in cross-bowties and further allows these structures to be used as polarization filters. The nanoscale local field amplitude and phase maps show that due to strong interparticle Coulomb coupling, cross-bowtie structures redistribute and highly enhance the out-of-plane (perpendicular to the plane of the sample) plasmon near-field component at the gap region relative to ordinary bowties. Preliminary results on using VO$_{2}$ film to tune infrared plasmonic antenna resonances will be presented. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F21.00010: Determination of the dielectric function of materials with scattering-type scanning near field optical microscopy Peng Xu, T.J. Huffman, M.M. Qazilbash, Inhae Kwak, Amlan Biswas Apertureless scattering-type near field optical and infrared microscopy has been widely employed for imaging a variety of systems at the nanoscale including semiconductor nanostructures, organic bio-systems, and phase coexistence during metal-insulator transitions. In apertureless, scattering-type near field infrared microscopy, one can measure both the near field amplitude and phase. To obtain the complex dielectric function of the material at nanometer length scales from the measured amplitude and phase, the inverse problem of near field interaction needs to be solved. We employed the lightning rod model [1] to analyze the near field interaction and obtain the dielectric function numerically. We present results for near-field infrared measurements on transition metal oxides including those that exhibit optical contrast due to coexisting phases. [1] A. S. McLeod et al. , Phys. Rev. B 90, 085136 (2014) [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F21.00011: Generalized method of eigenoscillations for near-field optical microscopy Bor-Yuan Jiang, Lingfeng Zhang, Antonio Castro Neto, Dimitri Basov, Michael Fogler Electromagnetic interaction between a sub-wavelength particle (the ``probe'') and a material surface (the ``sample'') is studied theoretically. The interaction is shown to be governed by a series of resonances (eigenoscillations), corresponding to surface polariton modes localized near the probe. The resonance parameters depend on the dielectric function and geometry of the probe, as well as the surface reflectivity of the material. Calculation of such resonances is carried out for several axisymmetric particle shapes (spherical, spheroidal, and pear-shaped). For spheroids an efficient numerical method is proposed, capable of handling cases of large or strongly momentum-dependent surface reflectivity. The method is applied to modeling near-field spectroscopy studies of various materials. For highly resonant materials such as aluminum oxide (by itself or covered with graphene) a rich structure of the simulated signal is found, including multi-peak spectra and nonmonotonic approach curves. These features have a strong dependence on physical parameters, e.g., the probe shape. For less resonant materials such as silicon oxide the dependence is weaker, and the spheroid model is generally applicable. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F21.00012: Cryogenic Near-Field Microscopy in Correlated Electronic Systems Adrian Gozar We present results on the performance of a scattering-based scanning near-field optical microscope. The instrument was designed for measuring nano-scale complex dielectric properties of materials in a variable-temperature environment. The setup has a 20 - 30 nm spatial resolution with sample temperatures in the 10 - 300 K range. Spectral operation is in the infrared to visible and 0.1 - 1 THz regions. We illustrate these capabilities with results in graphene and ultra-thin sub-surface oxide films. [Preview Abstract] |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F21.00013: Radiation pressure excitation of Low Temperature Atomic Force {\&} Magnetic Force Microscope (LT-AFM/MFM) for Imaging Ozgur Karci, Umit Celik, Ahmet Oral We describe a novel method for excitation of Atomic Force Microscope (AFM) cantilevers by means of radiation pressure for imaging in an AFM for the first time. Piezo excitation is the most common method for cantilever excitation, but it may cause spurious resonance peaks. A fiber optic interferometer with 1310 nm laser was used both to measure the deflection of cantilever and apply a force to the cantilever in a LT-AFM/MFM from NanoMagnetics Instruments. The laser power was modulated at the cantilever`s resonance frequency by a digital Phase Lock Loop (PLL). The force exerted by the radiation pressure on a perfectly reflecting surface by a laser beam of power P is F $=$ 2P/c. We typically modulate the laser beam by $\sim$ 800 $\mu$W and obtain 10nm oscillation amplitude with Q $\sim$ 8,000 at 2.5x10$^{-4}$ mbar. The cantilever's stiffness can be accurately calibrated by using the radiation pressure. We have demonstrated performance of the radiation pressure excitation in AFM/MFM by imaging a hard disk sample between 4-300K and Abrikosov vortex lattice in BSCCO single crystal at 4K to for the first time. [Preview Abstract] |
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