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Jul 2008

Volume 79, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 79, 071101 (2008); http://dx.doi.org/10.1063/1.2957649 (11 pages)

S. O. Reza Moheimani

Two-sensor-based feedback control structure for fast and accurate operation of a piezoelectric tube scanner.

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Invited Review Article: Accurate and fast nanopositioning with piezoelectric tube scanners: Emerging trends and future challenges

S. O. Reza Moheimani

Rev. Sci. Instrum. 79, 071101 (2008); http://dx.doi.org/10.1063/1.2957649 (11 pages) | Cited 40 times

Online Publication Date: 21 July 2008

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Piezoelectric tube scanners have emerged as the most widely used nanopositioning technology in modern scanning probe microscopes. Despite their impressive properties, their fast and accurate operations are hindered due to complications such as scan induced mechanical vibrations, hysteresis nonlinearity, creep, and thermal drift. This paper presents an overview of emerging innovative solutions inspired from recent advances in fields such as smart structures, feedback control, and advanced estimation aimed at maximizing positioning precision and bandwidth of piezoelectric tube scanners. The paper presents a thorough survey of the related literature and contains suggestions for future research prospects.
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07.79.-v Scanning probe microscopes and components
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.16.Ta Atom manipulation
37.10.-x Atom, molecule, and ion cooling methods
06.60.Sx Positioning and alignment; manipulating, remote handling
01.30.Rr Surveys and tutorial papers; resource letters
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A tabletop femtosecond time-resolved soft x-ray transient absorption spectrometer

Zhi-Heng Loh, Munira Khalil, Raoul E. Correa, and Stephen R. Leone

Rev. Sci. Instrum. 79, 073101 (2008); http://dx.doi.org/10.1063/1.2947737 (13 pages) | Cited 7 times

Online Publication Date: 1 July 2008

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A laser-based, tabletop instrument is constructed to perform femtosecond soft x-ray transient absorption spectroscopy. Ultrashort soft x-ray pulses produced via high-order harmonic generation of the amplified output of a femtosecond Ti:sapphire laser system are used to probe atomic core-level transient absorptions in atoms and molecules. The results provide chemically specific, time-resolved dynamics with sub-50-fs time resolution. In this setup, high-order harmonics generated in a Ne-filled capillary waveguide are refocused by a gold-coated toroidal mirror into the sample gas cell, where the soft x-ray light intersects with an optical pump pulse. The transmitted high-order harmonics are spectrally dispersed with a homebuilt soft x-ray spectrometer, which consists of a gold-coated toroidal mirror, a uniform-line spaced plane grating, and a soft x-ray charge coupled device camera. The optical layout of the instrument, design of the soft x-ray spectrometer, and spatial and temporal characterizations of the high-order harmonics are described. Examples of static and time-resolved photoabsorption spectra collected on this apparatus are presented.
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07.85.Nc X-ray and γ-ray spectrometers
42.55.Vc X- and γ-ray lasers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
07.60.Rd Visible and ultraviolet spectrometers
42.79.Bh Lenses, prisms and mirrors

Numerical fringe pattern demodulation strategies in interferometry

Jens Bethge and Günter Steinmeyer

Rev. Sci. Instrum. 79, 073102 (2008); http://dx.doi.org/10.1063/1.2938399 (8 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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The performance of two different numerical frequency demodulation strategies for evaluating sampled fringe patterns in interferometric applications and optics is discussed. Namely, these techniques involve traditional Fourier filtering techniques and a strategy based on the Gabor wavelets. While the latter is found to be more precise, it is generally difficult to implement wavelet-based frequency demodulation with equal performance as methods based on the fast Fourier transform. Here, we demonstrate a specialized fast wavelet algorithm that outperforms Fourier-based strategies for array sizes up to a few thousand data points and is yet more precise. The performance is investigated in numerical examples, indicating that the required choice of a global filter bandwidth is one of the main problems of the Fourier filtering strategy. Wavelet frequency demodulation, in contrast, always appears to perform slightly better, does not require judicious choice of filtering, and can often be made equally fast without loss of precision. Finally, applying this new algorithm to an ideal sinusoidal signal without noise, the precision of the numerical frequency demodulation is increased by nearly two orders of magnitude.
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42.50.St Nonclassical interferometry, subwavelength lithography
42.30.Kq Fourier optics
42.79.Ci Filters, zone plates, and polarizers

Vertical-type chiroptical spectrophotometer (I): Instrumentation and application to diffuse reflectance circular dichroism measurement

Takunori Harada, Hiroshi Hayakawa, and Reiko Kuroda

Rev. Sci. Instrum. 79, 073103 (2008); http://dx.doi.org/10.1063/1.2952674 (6 pages) | Cited 10 times

Online Publication Date: 2 July 2008

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We have designed and built a novel universal chiroptical spectrophotometer (UCS-2: J-800KCMF), which can carry out in situ chirality measurement of solid samples without any pretreatment, in the UV-vis region and with high relative efficiency. The instrument was designed to carry out transmittance and diffuse reflectance (DR) circular dichroism (CD) measurements simultaneously, thus housing two photomultipliers. It has a unique feature that light impinges on samples vertically so that loose powders can be measured by placing them on a flat sample holder in an integrating sphere. As is our first universal chiroptical spectrophotometer, UCS-1, two lock-in amplifiers are installed to remove artifact signals arising from macroscopic anisotropies which are unique to solid samples. High performance was achieved by theoretically analyzing and experimentally proven the effect of the photoelastic modulator position on the CD base line shifts, and by selecting high-quality optical and electric components. Measurement of microcrystallines of both enantiomers of ammonium camphorsulfonate by the DRCD mode gave reasonable results.
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07.60.Rd Visible and ultraviolet spectrometers
07.60.Dq Photometers, radiometers, and colorimeters

Monte Carlo simulations of microchannel plate detectors. I. Steady-state voltage bias results

Ming Wu, Craig A. Kruschwitz, Dane V. Morgan, and Jiaming Morgan

Rev. Sci. Instrum. 79, 073104 (2008); http://dx.doi.org/10.1063/1.2949119 (7 pages) | Cited 4 times

Online Publication Date: 10 July 2008

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X-ray detectors based on straight-channel microchannel plates (MCPs) are a powerful diagnostic tool for two-dimensional, time-resolved imaging and time-resolved x-ray spectroscopy in the fields of laser-driven inertial confinement fusion and fast Z-pinch experiments. Understanding the behavior of microchannel plates as used in such detectors is critical to understanding the data obtained. The subject of this paper is a Monte Carlo computer code we have developed to simulate the electron cascade in a MCP under a static applied voltage. Also included in the simulation is elastic reflection of low-energy electrons from the channel wall, which is important at lower voltages. When model results were compared to measured MCP sensitivities, good agreement was found. Spatial resolution simulations of MCP-based detectors were also presented and found to agree with experimental measurements.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.85.Nc X-ray and γ-ray spectrometers
29.30.Kv X- and γ-ray spectroscopy
29.40.Gx Tracking and position-sensitive detectors
02.50.Ng Distribution theory and Monte Carlo studies
29.85.-c Computer data analysis

Diffractive-refractive optics: X-ray collimator

Jaromír Hrdý and Peter Oberta

Rev. Sci. Instrum. 79, 073105 (2008); http://dx.doi.org/10.1063/1.2949386 (4 pages) | Cited 2 times

Online Publication Date: 10 July 2008

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Diffractive-refractive optics are x-ray focusing monochromators based on the diffraction on profiled crystal surface. Diffraction on longitudinal parabolic groove machined in crystal surface forms a sagittaly focused synchrotron radiation beam. Such kind of monochromator may be realized as a crystal with parabolic hole, where the beam is diffracted on the inner wall of the hole. Two such asymmetrically cut crystals set into antiparallel position, creating a dispersive (+,−,−,+) arrangement, form a sagittaly focusing x-ray monochromator which should be practically aberration-free. The focusing properties of such kind of monochromator are discussed in detail and it is shown for the first time that it can be used not only for focusing but also for creating highly parallel monochromatic beam in the broad region of the Bragg angles. This device with parabolic hole has not been tested experimentally yet.
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07.85.-m X- and γ-ray instruments
42.79.Ag Apertures, collimators

Broadside coupling to long-range surface plasmons in metal stripes using prisms, particles, and an atomic force microscope probe

Robert Charbonneau and Pierre Berini

Rev. Sci. Instrum. 79, 073106 (2008); http://dx.doi.org/10.1063/1.2952648 (9 pages) | Cited 6 times

Online Publication Date: 11 July 2008

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Techniques for broadside coupling to long-range surface plasmon waves propagating along metal stripes are investigated. The baseline technique consists of evanescently coupling an optical input beam originating from a polarization maintaining fiber to the plasmon wave via a right-angle prism positioned above the metal stripe, and providing an optical output some distance away through a mirror arrangement of identical elements. The technique is modeled theoretically using plane waves and implemented to measure the attenuation of the long-range plasmon wave propagating along a metal stripe supported by a thin freestanding dielectric membrane. An alternative technique for providing an output is proposed, whereby a tipless atomic force microscope probe physically contacts the metal stripe to generate out-of-plane scattering and a multimode fiber positioned nearby is used to capture a portion of the scattered light. This technique is easier to implement than the baseline technique, resulting in attenuation measurements of significantly better quality. The goodness of fit of the best fitting linear models to the measurements was significantly improved using this technique (0.93 and 0.99), and the measured attenuations were in very good agreement with the theoretical ones (6.01% and 0.27% error). This simple technique for optical probing and coupling could be applied to other surface plasmon waveguides and possibly to dielectric waveguides with modes having sufficient field strength in their evanescent tail. Output scattering using micron-sized particles located on the metal stripe was also investigated. The stability of the experimental setup was assessed and found to be about 0.01 dB peak to peak over a few minutes at constant temperature using a reference optical signal.
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07.79.Lh Atomic force microscopes
68.37.Ps Atomic force microscopy (AFM)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
42.79.Bh Lenses, prisms and mirrors

An ultrahigh stability, low-noise laser current driver with digital control

Christopher J. Erickson, Marshall Van Zijll, Greg Doermann, and Dallin S. Durfee

Rev. Sci. Instrum. 79, 073107 (2008); http://dx.doi.org/10.1063/1.2953597 (8 pages) | Cited 1 time

Online Publication Date: 11 July 2008

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We present a low-noise, high modulation-bandwidth design for a laser current driver with excellent long-term stability. The driver improves upon the commonly used Hall–Libbrecht design. The current driver can be operated remotely by way of a microprocessing unit, which controls the current set point digitally. This allows precise repeatability and improved accuracy and stability. It also allows the driver to be placed near the laser for reduced noise and for lower phase lag when using the modulation input. We present the theory of operation for our driver in detail, and give a thorough characterization of its stability, noise, set-point accuracy and repeatability, temperature dependence, transient response, and modulation bandwidth.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Mi Dynamical laser instabilities; noisy laser behavior

Development of a low-temperature photoelectron spectroscopy instrument using an electrospray ion source and a cryogenically controlled ion trap

Xue-Bin Wang and Lai-Sheng Wang

Rev. Sci. Instrum. 79, 073108 (2008); http://dx.doi.org/10.1063/1.2957610 (8 pages) | Cited 30 times

Online Publication Date: 17 July 2008

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The ability to control ion temperatures is critical for gas phase spectroscopy and has been a challenge in chemical physics. A low-temperature photoelectron spectroscopy instrument has been developed for the investigation of complex anions in the gas phase, including multiply charged anions, solvated species, and biological molecules. The new apparatus consists of an electrospray ionization source, a three dimensional (3D) Paul trap for ion accumulation and cooling, a time-of-flight mass spectrometer, and a magnetic-bottle photoelectron analyzer. A key feature of the new instrument is the capability to cool and tune ion temperatures from 10 to 350 K in the 3D Paul trap, which is attached to the cold head of a closed cycle helium refrigerator. Ion cooling is accomplished in the Paul trap via collisions with a background gas and has been demonstrated by observation of complete elimination of vibrational hot bands in photoelectron spectra of various anions ranging from small molecules to complex species. Further evidence of ion cooling is shown by the observation of H2-physisorbed anions at low temperatures. Cold anions result in better resolved photoelectron spectra due to the elimination of vibrational hot bands and yield more accurate energetic and spectroscopic information. Temperature-dependent studies are made possible for weakly bonded molecular and solvated clusters, allowing thermodynamic information to be obtained.
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07.81.+a Electron and ion spectrometers
07.75.+h Mass spectrometers
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

A modification of the laser detonation-type hyperthermal oxygen atom beam source for a long-term operation

Hiroshi Kinoshita, Shunsuke Yamamoto, Hideaki Yatani, and Nobuo Ohmae

Rev. Sci. Instrum. 79, 073109 (2008); http://dx.doi.org/10.1063/1.2957613 (4 pages) | Cited 3 times

Online Publication Date: 21 July 2008

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It has been an impedimental problem, for the laser detonation-type atom beam generator, that a poppet in the pulsed supersonic valve is rapidly eroded by the irradiation of powerful laser light and high temperature plasma. In order to operate the atom beam source for a long duration, a modification was made to hide the poppet from direct irradiation of laser and plasma. The alteration of device configuration resulted in great improvement in endurance of poppet more than 300 000 repetitions. Morphology of a polyimide film exposed to approximately 200 000 pulses of hyperthermal oxygen atom beam showed a shaglike carpet structure, which is a characteristic to that exposed to energetic oxygen atoms. A flux of the oxygen atom beam was estimated to be 5×1014 atoms/cm2/pulse at a location of 30 cm away from the nozzle throat.
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52.50.Dg Plasma sources
68.55.J- Morphology of films
61.82.Pv Polymers, organic compounds
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
61.80.Lj Atom and molecule irradiation effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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Absolute calibration of photostimulable image plate detectors used as (0.5–20 MeV) high-energy proton detectors

A. Mančić, J. Fuchs, P. Antici, S. A. Gaillard, and P. Audebert

Rev. Sci. Instrum. 79, 073301 (2008); http://dx.doi.org/10.1063/1.2949388 (6 pages) | Cited 19 times

Online Publication Date: 1 July 2008

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In this paper, the absolute calibration of photostimulable image plates (IPs) used as proton detectors is presented. The calibration is performed in a wide range of proton energies (0.5–20 MeV) by exposing simultaneously the IP and calibrated detectors (radiochromic films and solid state detector CR39) to a source of broadband laser-accelerated protons, which are spectrally resolved. The final result is a calibration curve that enables retrieving the proton number from the IP signal.
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42.79.Pw Imaging detectors and sensors
06.20.F- Units and standards
29.40.Gx Tracking and position-sensitive detectors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Reflection-time-of-flight spectrometer for two-electron (e,2e) coincidence spectroscopy on surfaces

J. Kirschner, G. Kerhervé, and C. Winkler

Rev. Sci. Instrum. 79, 073302 (2008); http://dx.doi.org/10.1063/1.2949869 (6 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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In this article, a novel time-of-flight spectrometer for two-electron-emission (e,2e/γ,2e) correlation spectroscopy from surfaces at low electron energies is presented. The spectrometer consists of electron optics that collect emitted electrons over a solid angle of approximately 1 sr and focus them onto a multichannel plate using a reflection technique. The flight time of an electron with kinetic energy of Ekin ≃ 25 eV is around 100 ns. The corresponding time- and energy resolution are typically ≈ 1 ns and ≈ 0.65 eV, respectively. The first (e,2e) data obtained with the present setup from a LiF film are presented.
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07.75.+h Mass spectrometers

Laser ablation source for formation and deposition of size-selected metal clusters

S. Vučković, M. Svanqvist, and V. N. Popok

Rev. Sci. Instrum. 79, 073303 (2008); http://dx.doi.org/10.1063/1.2952503 (8 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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This work describes construction of a source and optimisation of its parameters for production of cluster ion beams using material ablation by the second harmonic of a Nd:YAG laser (532 nm). The influence of different source parameters such as carrier gas pressure, laser power, delay time between gas, and laser pulses as well as nozzle configuration on the cluster formation are studied. For the current experiments the laser ablation cluster source was optimized for production of Con+ cluster ions. Clusters with n up to 150 atoms are registered by a time-of-flight mass spectrometer. Deposition of size-selected Co50+ clusters with kinetic energies in the interval of 250–4850 eV/cluster on highly ordered pyrolytic graphite is studied. At the highest impact energies the clusters are implanted. Craters and well-like structures can be seen by scanning tunneling microscopy at impact spots. A decrease in cluster kinetic energy leads to formation of bumplike structures which probably represent damaged graphite areas with incorporated Co atoms. Further decrease in the cluster impact energy to the level of 450–250 eV/cluster creates condition for so-called cluster pinning when the cluster constituents are intact but the energy transferred to the graphite is still enough to produce radiation defects to which the cluster is bound.
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79.20.Ds Laser-beam impact phenomena
81.65.-b Surface treatments
36.40.-c Atomic and molecular clusters
42.55.Rz Doped-insulator lasers and other solid state lasers

A high-current microwave ion source with permanent magnet and its beam emittance measurement

Zeen Yao, Xinjian Tan, Hongxin Du, Ben Luo, and Zhanwen Liu

Rev. Sci. Instrum. 79, 073304 (2008); http://dx.doi.org/10.1063/1.2954967 (5 pages) | Cited 1 time

Online Publication Date: 11 July 2008

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The progress of a 2.45 GHz high-current microwave ion source with permanent magnet for T(d,n)4He reaction neutron generator is reported in this paper. At 600 W microwave power and 22 kV extraction voltage, 90 mA peak hydrogen ion beam is extracted from a single aperture of 6 mm diameter. The beam emittance is measured using a simplified pepper-pot method. The (x,x′) emittance and the (y,y′) emittance for 14 keV hydrogen ion beam are 55.3π and 58.2π mm mrad, respectively. The normalized emittances are 0.302π and 0.317π mm mrad, respectively.
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29.25.Dz Neutron sources
29.25.Lg Ion sources: polarized
29.25.Ni Ion sources: positive and negative
29.27.Ac Beam injection and extraction
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A 1 MA, variable risetime pulse generator for high energy density plasma research

J. B. Greenly, J. D. Douglas, D. A. Hammer, B. R. Kusse, S. C. Glidden, and H. D. Sanders

Rev. Sci. Instrum. 79, 073501 (2008); http://dx.doi.org/10.1063/1.2949819 (5 pages) | Cited 28 times

Online Publication Date: 1 July 2008

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COBRA is a 0.5 Ω pulse generator driving loads of order 10 nH inductance to >1 MA current. The design is based on independently timed, laser-triggered switching of four water pulse-forming lines whose outputs are added in parallel to drive the load current pulse. The detailed design and operation of the switching to give a wide variety of current pulse shapes and rise times from 95 to 230 ns is described. The design and operation of a simple inductive load voltage monitor are described which allows good accounting of load impedance and energy dissipation. A method of eliminating gas bubbles on the underside of nearly horizontal insulator surfaces in water was required for reliable operation of COBRA; a novel and effective solution to this problem is described.
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84.30.Jc Power electronics; power supply circuits
84.30.Ng Oscillators, pulse generators, and function generators
84.30.Sk Pulse and digital circuits
52.59.Qy Wire array Z-pinches
52.50.Lp Plasma production and heating by shock waves and compression

On the reliability of scrape-off layer ion temperature measurements by retarding field analyzers

M. Kočan, J. P. Gunn, M. Komm, J.-Y. Pascal, E. Gauthier, and G. Bonhomme

Rev. Sci. Instrum. 79, 073502 (2008); http://dx.doi.org/10.1063/1.2955465 (10 pages) | Cited 21 times

Online Publication Date: 15 July 2008

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The retarding field analyzer (RFA) is one of the only widely accepted diagnostics for measurements of ion temperature Ti in the tokamak scrape-off layer. In this paper we analyze some instrumental effects of the RFA and their influence on Ti measurements. It is shown that selective ion transmission through the RFA slit is responsible for an overestimation of Ti by less than 14%, even for a relatively thick slit plate. Therefore, thicker slit plates are preferable, since they reduce, e.g., the risk of melting during off-normal events, and the effect of positive space charge inside the cavity. The influence of the electron repelling grid, as well as misalignment of the slit with respect to the magnetic field on Ti measurements are negligible.
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52.55.Fa Tokamaks, spherical tokamaks
52.70.-m Plasma diagnostic techniques and instrumentation

Digital smoothing of the Langmuir probe I-V characteristic

F. Magnus and J. T. Gudmundsson

Rev. Sci. Instrum. 79, 073503 (2008); http://dx.doi.org/10.1063/1.2956970 (8 pages) | Cited 11 times

Online Publication Date: 15 July 2008

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Electrostatic probes or Langmuir probes are the most common diagnostic tools in plasma discharges. The second derivative of the Langmuir probe I-V characteristic is proportional to the electron energy distribution function. Determining the second derivative accurately requires some method of noise suppression. We compare the Savitzky–Golay filter, the Gaussian filter, and polynomial fitting to the Blackman filter for digitally smoothing simulated and measured I-V characteristics. We find that the Blackman filter achieves the most smoothing with minimal distortion for noisy data.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.80.-s Electric discharges
84.30.Vn Filters
84.30.Sk Pulse and digital circuits

Pulse compression radar reflectometry to measure electron density in plasma with parasitic reflections

Bin Li, Hong Li, Zhipeng Chen, Chen Luo, Huihui Wang, Song Geng, Lei Feng, Qiuyan Liu, and Wandong Liu

Rev. Sci. Instrum. 79, 073504 (2008); http://dx.doi.org/10.1063/1.2947734 (5 pages)

Online Publication Date: 29 July 2008

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Pulse compression radar reflectometry is used to obtain electron density profile in plasma with parasitic reflections in this article. The pulse compression radar relies on the relation between the temporal width of a pulse and the frequency bandwidth of this pulse: Δt∝1/Δf. So a set of sweep-frequency microwaves within a bandwidth Δf can be introduced sequentially into the plasma to obtain the same information as the one obtained by a real pulse. By applying a Fourier transform to the data of reflectivity array in the frequency domain, the temporal response in the time domain is obtained. The limitation of the parasitic reflections on measurement can be eliminated from the temporal response by the method of time gate. This is a prominent advantage when this method is compared to the traditional reflectometry. For this method, an appropriate compromise between the spatial resolution and the electron density resolution is important. Experimental results show that the profile obtained from pulse compression radar reflectometry is similar to that from a double Langmuir probe.
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52.70.Gw Radio-frequency and microwave measurements
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
52.25.-b Plasma properties
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Improving the electrical performance of a conductive atomic force microscope with a logarithmic current-to-voltage converter

L. Aguilera, M. Lanza, M. Porti, J. Grifoll, M. Nafría, and X. Aymerich

Rev. Sci. Instrum. 79, 073701 (2008); http://dx.doi.org/10.1063/1.2952058 (5 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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A new configuration of conductive atomic force microscope (CAFM) is presented, which is based in a standard CAFM where the typical I-V converter has been replaced by a log I-V amplifier. This substitution extends the current dynamic range from 1–100 pA to 1 pA–1 mA. With the broadening of the current dynamic range, the CAFM can access new applications, such as the reliability evaluation of metal-oxide-semiconductor gate dielectrics. As an example, the setup has been tested by analyzing breakdown spots induced in SiO2 layers.
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07.79.Lh Atomic force microscopes

Simultaneous sensing and actuation with a piezoelectric tube scanner

S. O. Reza Moheimani and Yuen K. Yong

Rev. Sci. Instrum. 79, 073702 (2008); http://dx.doi.org/10.1063/1.2952506 (5 pages) | Cited 9 times

Online Publication Date: 2 July 2008

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Piezoelectric tube scanners with quartered external electrodes are the most widely used nanopositioning technology in modern scanning probe microscopes. There has been increasing interest in utilizing feedback control techniques to improve bandwidth and accuracy of these nanopositioners. The use of feedback requires a sensor to be incorporated into the nanopositioning device. Noncontact displacement sensors, e.g., capacitive and inductive sensors, have been used for this purpose. However, their measurements contain a significant noise component if operated over large bandwidths. The piezoelectric voltage induced in a tube nanopositioner has been proposed recently as an alternative measure of displacement with a much improved noise figure, up to three orders of magnitude better than capacitive sensors. In this arrangement, an electrode is used to actuate the tube, while the opposite electrode is used as a sensor. This approach has two drawbacks: (i) the operating range of the tube is reduced to half and (ii) the tube is not driven symmetrically, thus the opposite sides of the tube experience asymmetric stresses, i.e., in this mode of operation, the scanner is not a perfectly collocated system. In this paper, we present a new electrode pattern for piezoelectric tube scanners which addresses the above problems and allows simultaneous sensing and actuation of the tube in an efficient way.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
07.07.Mp Transducers

Investigation of blind tip estimation

P. Bakucz, R. Krüger-Sehm, and L. Koenders

Rev. Sci. Instrum. 79, 073703 (2008); http://dx.doi.org/10.1063/1.2901616 (9 pages)

Online Publication Date: 8 July 2008

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In this work we study functions for maximum likelihood estimation in blind tip estimation. We will implement the expectation maximization (EM), the stochastic EM, and stochastic approximation EM algortithms to estimate the unknown tip geometry. To demonstrate the functionality of the algorithms we applied it to dilated artificial input signal.
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02.60.-x Numerical approximation and analysis
02.50.-r Probability theory, stochastic processes, and statistics

An integrated approach to piezoactuator positioning in high-speed atomic force microscope imaging

Yan Yan, Ying Wu, Qingze Zou, and Chanmin Su

Rev. Sci. Instrum. 79, 073704 (2008); http://dx.doi.org/10.1063/1.2956980 (9 pages) | Cited 8 times

Online Publication Date: 15 July 2008

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In this paper, an integrated approach to achieve high-speed atomic force microscope (AFM) imaging of large-size samples is proposed, which combines the enhanced inversion-based iterative control technique to drive the piezotube actuator control for lateral x-y axis positioning with the use of a dual-stage piezoactuator for vertical z-axis positioning. High-speed, large-size AFM imaging is challenging because in high-speed lateral scanning of the AFM imaging at large size, large positioning error of the AFM probe relative to the sample can be generated due to the adverse effects—the nonlinear hysteresis and the vibrational dynamics of the piezotube actuator. In addition, vertical precision positioning of the AFM probe is even more challenging (than the lateral scanning) because the desired trajectory (i.e., the sample topography profile) is unknown in general, and the probe positioning is also effected by and sensitive to the probe-sample interaction. The main contribution of this article is the development of an integrated approach that combines advanced control algorithm with an advanced hardware platform. The proposed approach is demonstrated in experiments by imaging a large-size (50 μm) calibration sample at high-speed (50 Hz scan rate).
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07.79.Lh Atomic force microscopes
06.20.F- Units and standards
07.07.Tw Servo and control equipment; robots
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Development of eddy current microscopy for high resolution electrical conductivity imaging using atomic force microscopy

V. Nalladega, S. Sathish, K. V. Jata, and M. P. Blodgett

Rev. Sci. Instrum. 79, 073705 (2008); http://dx.doi.org/10.1063/1.2955470 (11 pages) | Cited 3 times

Online Publication Date: 16 July 2008

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We present a high resolution electrical conductivity imaging technique based on the principles of eddy current and atomic force microscopy (AFM). An electromagnetic coil is used to generate eddy currents in an electrically conducting material. The eddy currents generated in the conducting sample are detected and measured with a magnetic tip attached to a flexible cantilever of an AFM. The eddy current generation and its interaction with the magnetic tip cantilever are theoretically modeled using monopole approximation. The model is used to estimate the eddy current force between the magnetic tip and the electrically conducting sample. The theoretical model is also used to choose a magnetic tip–cantilever system with appropriate magnetic field and spring constant to facilitate the design of a high resolution electrical conductivity imaging system. The force between the tip and the sample due to eddy currents is measured as a function of the separation distance and compared to the model in a single crystal copper. Images of electrical conductivity variations in a polycrystalline dual phase titanium alloy (Ti-6Al-4V) sample are obtained by scanning the magnetic tip–cantilever held at a standoff distance from the sample surface. The contrast in the image is explained based on the electrical conductivity and eddy current force between the magnetic tip and the sample. The spatial resolution of the eddy current imaging system is determined by imaging carbon nanofibers in a polymer matrix. The advantages, limitations, and applications of the technique are discussed.
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84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
07.79.Lh Atomic force microscopes

Tip-enhanced near-field Raman spectroscopy with a scanning tunneling microscope and side-illumination optics

K. J. Yi, X. N. He, Y. S. Zhou, W. Xiong, and Y. F. Lu

Rev. Sci. Instrum. 79, 073706 (2008); http://dx.doi.org/10.1063/1.2956977 (8 pages) | Cited 3 times

Online Publication Date: 16 July 2008

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Conventional Raman spectroscopy (RS) suffers from low spatial resolution and low detection sensitivity due to the optical diffraction limit and small interaction cross sections. It has been reported that a highly localized and significantly enhanced electromagnetic field could be generated in the proximity of a metallic tip illuminated by a laser beam. In this study, a tip-enhanced RS system was developed to both improve the resolution and enhance the detection sensitivity using the tip-enhanced near-field effects. This instrument, by combining RS with a scanning tunneling microscope and side-illumination optics, demonstrated significant enhancement on both optical sensitivity and spatial resolution using either silver (Ag)-coated tungsten (W) tips or gold (Au) tips. The sensitivity improvement was verified by observing the enhancement effects on silicon (Si) substrates. Lateral resolution was verified to be below 100 nm by mapping Ag nanostructures. By deploying the depolarization technique, an apparent enhancement of 175% on Si substrates was achieved. Furthermore, the developed instrument features fast and reliable optical alignment, versatile sample adaptability, and effective suppression of far-field signals.
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07.60.Rd Visible and ultraviolet spectrometers
07.79.Cz Scanning tunneling microscopes
42.62.Fi Laser spectroscopy
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Development of an ion beam alignment system for real-time scanning tunneling microscope observation of dopant-ion irradiation

Takefumi Kamioka, Kou Sato, Yutaka Kazama, Takanobu Watanabe, and Iwao Ohdomari

Rev. Sci. Instrum. 79, 073707 (2008); http://dx.doi.org/10.1063/1.2957608 (4 pages) | Cited 1 time

Online Publication Date: 17 July 2008

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An ion beam alignment system has been developed in order to realize real-time scanning tunneling microscope (STM) observation of “dopant-ion” irradiation that has been difficult due to the low emission intensity of the liquid-metal-ion-source (LMIS) containing dopant atoms. The alignment system is installed in our original ion gun and STM combined system (IG/STM) which is used for in situ STM observation during ion irradiation. By using an absorbed electron image unit and a dummy sample, ion beam alignment operation is drastically simplified and accurized. We demonstrate that sequential STM images during phosphorus-ion irradiation are successfully obtained for sample surfaces of Si(111)-7×7 at room temperature and a high temperature of 500 °C. The LMIS-IG/STM equipped with the developed ion beam alignment system would be a powerful tool for microscopic investigation of the dynamic processes of ion irradiation.
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07.79.Cz Scanning tunneling microscopes
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.47.Fg Semiconductor surfaces
61.80.Jh Ion radiation effects
61.72.uf Ge and Si
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