Bulletin of the American Physical Society
2008 APS March Meeting
Volume 53, Number 2
Monday–Friday, March 10–14, 2008; New Orleans, Louisiana
Session V36: Advances in Scanned Probe Microscopy IV: Optical and High Frequency Methods |
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Sponsoring Units: GIMS Chair: Phillip First, Georgia Institute of Technology Room: Morial Convention Center 228 |
Thursday, March 13, 2008 11:15AM - 11:27AM |
V36.00001: High-resolution element-selective microscopy using X-ray enhanced Scanning Tunneling Microscopy Volker Rose, John Freeland, Kenneth Gray, Stephen Streiffer, Matthias Bode Nanoscale structures are at the forefront of fundamental research as well as the keystone for whole new classes of potential applications. Proper understanding of these systems requires tools with both the ability to resolve the nanometer scale as well as provide detailed information about chemical, electronic and magnetic structure. Scanning probe microscopies achieve the requisite high spatial resolution; however, direct elemental determination is not easily accomplished. X-ray microscopies, on the other hand, provide elemental selectivity, but currently have spatial resolution only of tens of nanometers. We present a radically different concept that employs detection of local x-ray interactions utilizing a scanning probe that provides spatial resolution, and x-ray absorption directly yields chemical, electronic, and magnetic sensitivity. The achievement of nanometer spatial resolution with direct elemental selectivity will have a tremendous impact on our ability to probe and understand complex phenomena occurring in nanostructures. [Preview Abstract] |
Thursday, March 13, 2008 11:27AM - 11:39AM |
V36.00002: Scanning optical homodyne detection of high-frequency picoscale resonances in cantilever and tuning fork sensors J. C. Randel, G. Zeltzer, A. K. Gupta, R. Bashir, S.-H. Song, H. C. Manoharan Hybrid high-frequency sensors represent the next generation of scanned probe technology. In this work, higher harmonic modes in nanoscale silicon cantilevers and microscale quartz tuning forks are detected and characterized using a custom scanning optical homodyne interferometer. Capable of both mass and force sensing, these resonators exhibit high-frequency harmonic motion content with picometer-scale amplitudes detected in a 2.5 MHz bandwidth, driven by ambient thermal radiation. Quartz tuning forks additionally display both in-plane and out-of-plane harmonics. The first six electronically detected resonances are matched to optically detected and mapped fork eigenmodes. Mass sensing experiments utilizing higher tuning fork modes indicate greater than six times sensitivity enhancement over fundamental mode operation. (This work supported by NSF and ONR). [Preview Abstract] |
Thursday, March 13, 2008 11:39AM - 11:51AM |
V36.00003: Radio Frequency Scanning Tunneling Microscopy: Instrumentation and Applications Utku Kemiktarak, Tchefor Ndukum, Keith C. Schwab, Kamil L. Ekinci A severe limitation of the scanning tunneling microscope (STM) is its low temporal resolution, originating from the diminished high-frequency response of the tunnel current readout circuitry. In order to overcome this limitation, we have built a radio-frequency STM (RF-STM). Using this instrument, we can attain electronic bandwidths as high as 10 MHz by measuring the reflection from or transmission through the tunnel junction, which is embedded in a resonant inductor-capacitor (LC) circuit. This $\sim $100-fold bandwidth improvement upon the state-of-the-art translates into fast surface topography as well as delicate measurements in mesoscopic electronics and mechanics. Broadband noise measurements across the tunnel junction using this radio-frequency-STM (RF-STM) have allowed us to perform nanoscale thermometry. Furthermore, we have detected high-frequency mechanical motion with a sensitivity approaching 15 fmHz$^{-1/2}$. [Preview Abstract] |
Thursday, March 13, 2008 11:51AM - 12:03PM |
V36.00004: Thermomechanical Noise Measurements of Very High Frequency (VHF) Nanomechanical Resonators Carl Hart IV, Kamil Ekinci We have designed and built a near infrared (NIR) optical interferometer for ultra-sensitive displacement measurements on nanomechanical resonators. At moderate optical power levels, we are able to resolve the thermomechanical displacement fluctuations of stiff doubly-clamped beams with fundamental mode frequencies in the 100 MHz range. In a first set of noise measurements, we have determined the quality factors and resonant frequencies of the nanomechanical resonators under ambient atmospheric pressure at room temperature. We will compare these values to those extracted from driven resonance measurements and discuss sources of disagreement. Furthermore, we will discuss extraction of the local temperature of the nanomechanical resonators in order to assess the heating due to the optical probe. [Preview Abstract] |
Thursday, March 13, 2008 12:03PM - 12:15PM |
V36.00005: Development of an Evanescent Microwave Probe / Scanning Tunneling Microscope to study Localized Electron Spin Resonance Christian Long, Naoyuki Taketoshi, Ichiro Takeuchi, Haitao Yang, Xiao-Dong Xiang We have constructed a microwave microscope with an integrated scanning tunneling microscope. In addition to the measurement of complex dielectric constant and conductivity we also perform atomic resolution scanning tunneling microscopy (STM). In this work the probe is operated in a magnetic field, which causes unpaired spins in the sample to precess at the Larmor frequency. When the magnetic field is such that the Larmor frequency of the spins in the sample matches the resonant frequency of the resonator, the transmission coefficient of the resonator (S12) is changed. We measure local ESR by measuring the variation in S12 as a function of magnetic field. In this report, we give an outline of the experimental setup and preliminary spin detection data for various spin radical molecules (one unpaired spin each) on an HPOG substrate (no unpaired spins). Supported by the W. M. KECK Foundation and NSF MRSEC (DMR 0520471). [Preview Abstract] |
Thursday, March 13, 2008 12:15PM - 12:27PM |
V36.00006: High Frequency Piezoresponse Force Microscopy in the 1-10 MHz Regime Katyayani Seal, Stephen Jesse, Brian Rodriguez, Arthur Baddorf, Sergei Kalinin Imaging mechanisms in Piezoresponse Force Microscopy (PFM) in the high frequency regime above the first contact resonance are analyzed. High operation frequencies are expected to provide several advantages including (a) higher signal to noise ratios due to a larger number of oscillations per pixel time and increased separation from the 1/$f$ noise corner (b) imaging at cantilever resonances with an associated increase in mechanical signal amplification (c) inertial stiffening of the cantilever that minimizes the non-local electrostatic force contribution to the signal and improves tip-surface contact. Furthermore, high frequency operation is an essential component of the PFM-based ferroelectric data storage systems, currently limited by the bandwidth of electromechanical detection (1-10 kHz). At the same time, operation at a high mode number can give rise to several problems, including the (a) response averaging due to the finite size of the cantilever beam (b) loss of sensitivity if the tip-surface spring constant becomes smaller than the effective spring constant of the cantilever and (c) signal loss due to the bandwidth of the photodetector. Analytical expressions for these limits are considered. We analyze the operation mechanisms in PFM at high frequencies, and demonstrate high quality PFM imaging at 1-10 MHz. Prospects for imaging in the 10-100 MHz range are explored. [Preview Abstract] |
Thursday, March 13, 2008 12:27PM - 12:39PM |
V36.00007: Contrast sensitive imaging with a cantilever-based near-field microwave probe Keji Lai, Worasom Kundhikanjana, Michael Kelly, Zhi-xun Shen We have developed a procedure to systematically study the contrast mechanism of our cantilever-based near-field scanning microwave probes with separated excitation and sensing electrodes. Finite-element analysis was employed to model the small impedance change due to the tip-sample interaction. The near-field signal can then be calculated from the S-parameters of the matching network that routes the tip impedance to 50 Ohm feed lines. Using a common-mode cancellation scheme, the microwave electronics is sensitive down to 1aF capacitance change at our working frequencies near 1GHz. Experimental characterization of the microwave probes was performed on ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or topographical signals, in qualitative agreement with simulation, can be obtained using different reflection modes of the probe. Our microscope also shows very high contrast due to conductivity variations of the sample, which can lead to potential applications of the technique. [Preview Abstract] |
Thursday, March 13, 2008 12:39PM - 12:51PM |
V36.00008: STM and SNOM Type of Scanning Probe Microscopes in the Same Unit: Towards Electrical Modification and Optical Characterization at Nanoscale Ilya Sychugov, Hiroo Omi, Tooru Murashita, Yoshihiro Kobayashi Optical and electrical properties of nanostructures can be addressed using radiation or electrical current as a probe. In general, a near-field type of electromagnetic interaction is necessary for an optical probe to enter nanoscale regime. However, a typical scanning near-field microscope utilizes a dielectric fiber tip as an aperture, which makes it unsuitable for electrical measurements. Here, in order to realize both electrical and optical probing at nanoscale, we have combined it with a scanning tunneling microscope (STM). An STM-luminescence (STML) instrument with a conductive and transparent tip, featuring about 40 nm spatial resolution, was reported previously. We have complemented it with a beamsplitter unit in a configuration typical for the fluorescent microscopy. The excitation light is guided through a beamsplitter unit to the indium tin oxide (ITO) tip and the signal is collected via the same fiber transmission line in a spectroscopy mode or in a photon mapping regime. The influence of tip geometry on collection efficiency and spatial resolution as well as limitations of such an instrument are discussed. This approach may find its niche not only for combined electrical and optical measurements, but also for electrical modification with subsequent \textit{in situ} optical probing. [Preview Abstract] |
Thursday, March 13, 2008 12:51PM - 1:03PM |
V36.00009: A Unique Probe for Tip Enhanced Raman Scattering and Shadow NSOM Aaron Lewis, Hesham Taha, Rimma Dekhter, Galia Zinoviev, Galina Fish We present a unique atomic force microscope [AFM] probe for tip enhanced Raman scattering [TERS] and a new form of near-field microscopy, ``Shadow Near-field Scanning Optical Microscopy''. The probe consists of a single gold nanoparticle grown at the tip of a cantilevered nanopipette, exposed to the optical axis of an upright or inverted optical microscope. When these probes are used in combination with a Nanonics MV 2000 AFM/NSOM system, we show that a protocol for independent motion of the probe and the sample can produce enhancement or a shadow effect. Both of these effects are enhanced by the ability to affect different Raman spectra with the tip in {\&} out of contact while independently scanning the sample. We analyzed Raman signals of a thin nanometric strained Si layer deposited on bulk Si and developed an understanding of optical mechanisms of enhancement, scattering and shadowing. Our results show different optical mechanisms occur as a result of tip {\&} sample interactions, including TERS effect obtained by near-field interaction of the probe with the top layer of strained Si. Large enhancements of at least 4 orders of magnitude are seen and analyses of relative intensities of bulk and strained Si Raman peaks show an increase in light scattered by bulk or effective shadowing of the surface. [Preview Abstract] |
Thursday, March 13, 2008 1:03PM - 1:15PM |
V36.00010: Chemical Imaging of the Surface of Polymeric Nanostructures Using Apertureless Near-Field IR Microscopy Zahra Fakhraai, Kerstin Mueller, Melissa Paulite, Xiujuan Yang, Gilbert C. Walker The chemical composition of the surfaces of thin films of polystyrene-poly (methyl methacrylate) (PS-PMMA) diblock copolymers are investigated using apertureless near-field IR microscopy. In this technique a tunable IR beam is scattered from an oscillating atomic force microscopy tip. The scattered light is enhanced using a reference signal with the same optical frequency (homodyne) or slightly shifted IR frequency (heterodyne) and detected after demodulation in order to eliminate the background scattering. Using this technique a lateral chemical imaging resolution of $<$20 nm is achievable. It is demonstrated that this technique can be successfully used to image the surface of PS-PMMA diblock copolymers. It is shown that an increase in the IR absorption is observed in the PMMA rich domains with a wavenumber dependence that is consistent with the bulk absorption spectrum. The results indicate that even though a topography induced artifact can be observed, when homodyne detection technique is used, the chemical signature of the sample can be detected clearly. This technique can be further used in a variety of different systems to detect the surface structure of polymers or proteins. [Preview Abstract] |
Thursday, March 13, 2008 1:15PM - 1:27PM |
V36.00011: Scanning thermal microscopy with a fluorescent nanoprobe Benjamin Samson, Elika Saidi, Lionel Aigouy, Peter Low, Beomjoon Kim, Christian Bergaud, Michel Mortier We have developed a scanning thermal microscope that uses a fluorescent particle settled at the extremity of an atomic force microscope tip as a nanoscale temperature sensor. When a temperature change occurs, a modification of fluorescence is detectable, enabling to perform thermal images and to determine the local temperature. We will describe the technique in details and present some thermal images on submicron sized nickel nanoheaters heated by an electrical current. We will show that this apparatus works in both DC and AC regimes, in a low frequency range whose upper limit is around the kilohertz. By performing tip approach/retraction curves on a heated wire, we will describe the different thermal transfer mechanisms between the surface and the fluorescent probe. [Preview Abstract] |
Thursday, March 13, 2008 1:27PM - 1:39PM |
V36.00012: A versatile technique for fabrication of SiC SPM probes Joel Therrien, Daniel Schmidt, Sheetal Barrot, Bhavin Patel To date SPM probes have largely been fabricated via methods borrowed from the semiconductor industry for fabricating Micro Electro Mechanical Systems. Although these techniques have enabled SPM to see widespread use, the processes put significant limitations on what structures can be made. We report our progress on fabricating SPM cantilevers composed of Silicon Carbide using polymer molding techniques. A pre-ceramic polymer is molded into the desired probe shape and then converted to SiC via pyrolisys. We will also report on progress in using photo-sterolithography for fabrication of even more complex geometries. In addition to opening up a much larger set of probe structures, the use of SiC leads to improved wear resistance of the resulting probes. Among the potential applications, this method enables the fabrication of low spring constant, high resonant frequency cantilevers via cross sectional geometries not accessible to standard fabrication techniques. Such probes are required for high speed tapping and non-contact imaging. [Preview Abstract] |
Thursday, March 13, 2008 1:39PM - 1:51PM |
V36.00013: \textit{In-situ} broadband microwave calibrations and measurements using cryogenic probe stations Jeffrey Lindemuth, Scott Yano Until recently, calibration of microwave measurements in cryogenic environments required custom fixtures [1,2]. These fixtures were necessary to accommodate the limited space in typical ``down bore'' cryostat designs. The typical three measurements (through, short, load, for example) required removing the fixtures from the cryostat three times before loading the sample of interest. We will show that with a 4-probe cryogenic probe station it is possible to simultaneously load a commercially available calibration test strip and the measurement sample. We will demonstrate calibration of the complete S matrix of the microwave network analyzer at each temperature followed by measurement of the sample. In addition, the temperature-dependent effects of the calibration can be determined. We will show short term and long term calibration stability. \newline [1] Broadband calibration of long lossy microwave transmission lines at cryogenic temperatures using nichrome films, M. L. Stutzman, Mark Lee, and R. F. Bradley, Rev. Sci. Instrum. 71, 4596 (2000) \newline [2] Broadband microwave spectroscopy in Corbino geometry for temperatures down to 1.7 K [Preview Abstract] |
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