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Feb 2013

Volume 84, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 84, 021101 (2013); http://dx.doi.org/10.1063/1.4789314 (14 pages)

Alexey Goncharov

Typical permanent magnet electrostatic plasma lens, characteristically about 15 cm long and 10 cm inner diameter. The magnets are shown in black between grey spacers. A set of cylindrical ring electrodes are located within the magnetic field region, with field lines connecting ring electrode pairs symmetrically about the lens midplane.

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back to top Microscopy and Imaging

A cryogenic scattering-type scanning near-field optical microscope

Honghua U. Yang, Erik Hebestreit, Erik E. Josberger, and Markus B. Raschke

Rev. Sci. Instrum. 84, 023701 (2013); http://dx.doi.org/10.1063/1.4789428 (6 pages)

Online Publication Date: 1 February 2013

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Scattering-type scanning near-field optical microscopy (s-SNOM) provides few nanometer optical spatial resolution and is compatible with nearly any form of linear and nonlinear optical spectroscopy. We have developed a versatile s-SNOM instrument operating under cryogenic and variable temperature (∼20–500 K) and compatible with high magnetic fields (up to 7 T). The instrument features independent tip and sample scanning and free-space light delivery with an integrated off-axis parabolic mirror for tip-illumination and signal collection with a numerical aperture of N.A. = 0.45. The optics operate from the UV to THz range allowing for continuous wave, broadband, and ultrafast s-SNOM spectroscopy, including different variants of tip-enhanced spectroscopy. We discuss the instrument design, implementation, and demonstrate its performance with mid-infrared Drude response s-SNOM probing of the domain formation associated with the metal-insulator transitions of VO2 (TMIT ≃ 340 K) and V2O3 (TMIT ≃ 150 K). This instrument enables the study of mesoscopic order and domains of competing quantum phases in correlated electron materials over a wide range of controlled electric and magnetic fields, strain, current, and temperature.
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07.79.Fc Near-field scanning optical microscopes
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
42.79.Bh Lenses, prisms and mirrors

Design of a high-speed electrochemical scanning tunneling microscope

Y. I. Yanson, F. Schenkel, and M. J. Rost

Rev. Sci. Instrum. 84, 023702 (2013); http://dx.doi.org/10.1063/1.4779086 (9 pages)

Online Publication Date: 5 February 2013

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In this paper, we present a bottom-up approach to designing and constructing a high-speed electrochemical scanning tunneling microscope (EC-STM). Using finite element analysis (FEA) calculations of the frequency response of the whole mechanical loop of the STM, we analyzed several geometries to find the most stable one that could facilitate fast scanning. To test the FEA results, we conducted measurements of the vibration amplitudes using a prototype STM setup. Based on the FEA analysis and the measurement results, we identified the potentially most disturbing vibration modes that could impair fast scanning. By modifying the design of some parts of the EC-STM, we reduced the amplitudes as well as increased the resonance frequencies of these modes. Additionally, we designed and constructed an electrochemical flow-cell that allows STM imaging in a flowing electrolyte, and built a bi-potentiostat to achieve electrochemical potential control during the measurements. Finally, we present STM images acquired during high-speed imaging in air as well as in an electrochemical environment using our newly-developed EC-STM.
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07.79.Cz Scanning tunneling microscopes
02.70.Dh Finite-element and Galerkin methods
07.10.-h Mechanical instruments and equipment

Calibration of measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy using a contact detection method

Zhen Liu, Younkoo Jeong, and Chia-Hsiang Menq

Rev. Sci. Instrum. 84, 023703 (2013); http://dx.doi.org/10.1063/1.4790194 (9 pages)

Online Publication Date: 6 February 2013

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An accurate experimental method is proposed for on-spot calibration of the measurement sensitivities of multiple micro-cantilever dynamic modes in atomic force microscopy. One of the key techniques devised for this method is a reliable contact detection mechanism that detects the tip-surface contact instantly. At the contact instant, the oscillation amplitude of the tip deflection, converted to that of the deflection signal in laser reading through the measurement sensitivity, exactly equals to the distance between the sample surface and the cantilever base position. Therefore, the proposed method utilizes the recorded oscillation amplitude of the deflection signal and the base position of the cantilever at the contact instant for the measurement sensitivity calibration. Experimental apparatus along with various signal processing and control modules was realized to enable automatic and rapid acquisition of multiple sets of data, with which the calibration of a single dynamic mode could be completed in less than 1 s to suppress the effect of thermal drift and measurement noise. Calibration of the measurement sensitivities of the first and second dynamic modes of three micro-cantilevers having distinct geometries was successfully demonstrated. The dependence of the measurement sensitivity on laser spot location was also experimentally investigated. Finally, an experiment was performed to validate the calibrated measurement sensitivity of the second dynamic mode of a micro-cantilever.
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06.20.fb Standards and calibration
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Kirkpatrick-Baez microscope for hard X-ray imaging of fast ignition experiments

H. Friesen, H. F. Tiedje, D. S. Hey, M. Z. Mo, A. Beaudry, R. Fedosejevs, Y. Y. Tsui, A. Mackinnon, H. S. McLean, and P. K. Patel

Rev. Sci. Instrum. 84, 023704 (2013); http://dx.doi.org/10.1063/1.4776670 (8 pages)

Online Publication Date: 7 February 2013

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A Kirkpatrick-Baez X-ray microscope has been developed for use on the Titan laser facility at the Lawrence Livermore National Laboratory in Fast Ignition experiments. It was developed as a broadband alternative to narrow band Bragg crystal imagers for imaging Kα emission from tracer layers. A re-entrant design is employed which allows for alignment from outside the chamber. The mirrors are coated with Pt and operate at a grazing incident angle of 0.5° providing higher resolution than an equal brightness pinhole and sufficient bandwidth to image thermally shifted characteristic Kα emission from heated Cu tracer layers in Fast Ignition experiments. The superpolished substrates (<1 Å rms roughness) had a final visible wavelength roughness of 1.7 Å after coating, and exhibited a reflectivity corresponding to an X-ray wavelength roughness of 7 ± 1 Å. A unique feature of this design is that during experiments, the unfiltered direct signal along with the one-dimensional reflections are retained on the detector in order to enable a live indication of alignment and incident angle. The broad spectral window from 4 to 9 keV enables simultaneous observation of emission from several spectral regions of interest, which has been demonstrated to be particularly useful for cone-wire targets. An experimentally measured resolution of 15 μm has been obtained at the center of the field of view.
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52.70.La X-ray and γ-ray measurements
41.50.+h X-ray beams and x-ray optics
42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings

Diagonal control design for atomic force microscope piezoelectric tube nanopositioners

B. Bhikkaji, Y. K. Yong, I. A. Mahmood, and S. O. R. Moheimani

Rev. Sci. Instrum. 84, 023705 (2013); http://dx.doi.org/10.1063/1.4790474 (8 pages)

Online Publication Date: 12 February 2013

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Atomic Force Microscopes (AFM) are used for generating surface topography of samples at micro to atomic resolutions. Many commercial AFMs use piezoelectric tube nanopositioners for scanning. Scanning rates of these microscopes are hampered by the presence of low frequency resonant modes. When inadvertently excited, these modes lead to high amplitude mechanical vibrations causing the loss of accuracy, while scanning, and eventually to break down of the tube. Feedback control has been used to damp these resonant modes. Thereby, enabling higher scanning rates. Here, a multivariable controller is designed to damp the first resonant mode along both the x and y axis. Exploiting the inherent symmetry in the piezoelectric tube, the multivariable control design problem is recast as independent single-input single-output (SISO) designs. This in conjunction with integral resonant control is used for damping the first resonant mode.
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45.80.+r Control of mechanical systems
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
89.20.Kk Engineering
02.30.Rz Integral equations
02.30.Yy Control theory
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A near-field scanning microwave microscope based on a superconducting resonator for low power measurements

S. E. de Graaf, A. V. Danilov, A. Adamyan, and S. E. Kubatkin

Rev. Sci. Instrum. 84, 023706 (2013); http://dx.doi.org/10.1063/1.4792381 (7 pages) | Cited 1 time

Online Publication Date: 21 February 2013

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We report on the design and performance of a cryogenic (300 mK) near-field scanning microwave microscope. It uses a microwave resonator as the near-field sensor, operating at a frequency of 6 GHz and microwave probing amplitudes down to 100 μV, approaching low enough photon population (N ∼ 1000) of the resonator such that coherent quantum manipulation becomes feasible. The resonator is made out of a miniaturized distributed fractal superconducting circuit that is integrated with the probing tip, micromachined to be compact enough such that it can be mounted directly on a quartz tuning-fork, and used for parallel operation as an atomic force microscope (AFM). The resonator is magnetically coupled to a transmission line for readout, and to achieve enhanced sensitivity we employ a Pound-Drever-Hall measurement scheme to lock to the resonance frequency. We achieve a well localized near-field around the tip such that the microwave resolution is comparable to the AFM resolution, and a capacitive sensitivity down to 6.4 × 10−20 F/math, limited by mechanical noise. We believe that the results presented here are a significant step towards probing quantum systems at the nanoscale using near-field scanning microwave microscopy.
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07.79.Fc Near-field scanning optical microscopes
85.25.-j Superconducting devices
84.40.Az Waveguides, transmission lines, striplines

A new adaptive light beam focusing principle for scanning light stimulation systems

L. A. Bitzer, M. Meseth, N. Benson, and R. Schmechel

Rev. Sci. Instrum. 84, 023707 (2013); http://dx.doi.org/10.1063/1.4791795 (4 pages)

Online Publication Date: 22 February 2013

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In this article a novel principle to achieve optimal focusing conditions or rather the smallest possible beam diameter for scanning light stimulation systems is presented. It is based on the following methodology: First, a reference point on a camera sensor is introduced where optimal focusing conditions are adjusted and the distance between the light focusing optic and the reference point is determined using a laser displacement sensor. In a second step, this displacement sensor is used to map the topography of the sample under investigation. Finally, the actual measurement is conducted, using optimal focusing conditions in each measurement point at the sample surface, that are determined by the height difference between camera sensor and the sample topography. This principle is independent of the measurement values, the optical or electrical properties of the sample, the used light source, or the selected wavelength. Furthermore, the samples can be tilted, rough, bent, or of different surface materials. In the following the principle is implemented using an optical beam induced current system, but basically it can be applied to any other scanning light stimulation system. Measurements to demonstrate its operation are shown, using a polycrystalline silicon solar cell.
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42.79.Pw Imaging detectors and sensors
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

Three-dimensional imaging of copper pillars using x-ray tomography within a scanning electron microscope: A simulation study based on synchrotron data

N. Martin, J. Bertheau, P. Bleuet, J. Charbonnier, P. Hugonnard, D. Laloum, F. Lorut, and J. Tabary

Rev. Sci. Instrum. 84, 023708 (2013); http://dx.doi.org/10.1063/1.4792377 (5 pages)

Online Publication Date: 25 February 2013

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While microelectronic devices are frequently characterized with surface-sensitive techniques having nanometer resolution, interconnections used in 3D integration require 3D imaging with high penetration depth and deep sub-micrometer spatial resolution. X-ray tomography is well adapted to this situation. In this context, the purpose of this study is to assess a versatile and turn-key tomographic system allowing for 3D x-ray nanotomography of copper pillars. The tomography tool uses the thin electron beam of a scanning electron microscope (SEM) to provoke x-ray emission from specific metallic targets. Then, radiographs are recorded while the sample rotates in a conventional cone beam tomography scheme that ends up with 3D reconstructions of the pillar. Starting from copper pillars data, collected at the European Synchrotron Radiation Facility, we build a 3D numerical model of a copper pillar, paying particular attention to intermetallics. This model is then used to simulate physical radiographs of the pillar using the geometry of the SEM-hosted x-ray tomography system. Eventually, data are reconstructed and it is shown that the system makes it possible the quantification of 3D intermetallics volume in copper pillars. The paper also includes a prospective discussion about resolution issues.
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85.40.Ls Metallization, contacts, interconnects; device isolation
07.85.Tt X-ray microscopes
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Atomic force microscope infrared spectroscopy on 15 nm scale polymer nanostructures

Jonathan R. Felts, Hanna Cho, Min-Feng Yu, Lawrence A. Bergman, Alexander F. Vakakis, and William P. King

Rev. Sci. Instrum. 84, 023709 (2013); http://dx.doi.org/10.1063/1.4793229 (6 pages)

Online Publication Date: 27 February 2013

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We measure the infrared spectra of polyethylene nanostructures of height 15 nm using atomic force microscope infrared spectroscopy (AFM-IR), which is about an order of magnitude improvement over state of the art. In AFM-IR, infrared light incident upon a sample induces photothermal expansion, which is measured by an AFM tip. The thermomechanical response of the sample-tip-cantilever system results in cantilever vibrations that vary in time and frequency. A time-frequency domain analysis of the cantilever vibration signal reveals how sample thermomechanical response and cantilever dynamics affect the AFM-IR signal. By appropriately filtering the cantilever vibration signal in both the time domain and the frequency domain, it is possible to measure infrared absorption spectra on polyethylene nanostructures as small as 15 nm.
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07.79.Lh Atomic force microscopes
07.60.-j Optical instruments and equipment
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