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Jun 2008

Volume 79, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 79, 061301 (2008); http://dx.doi.org/10.1063/1.2938864 (11 pages)

John Melcher, Shuiqing Hu, and Arvind Raman

VEDA: Virtual Environment for Dynamic Atomic Force Microscopy, is a web-based suite of tools for the mathematical simulation of tip-sample interactions, probe dynamics, imaging instabilities and feedback control in the Atomic Force Microscope. The tools are freely accessible from the portal http://www.nanohub.org.

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Invited Article: VEDA: A web-based virtual environment for dynamic atomic force microscopy

John Melcher, Shuiqing Hu, and Arvind Raman

Rev. Sci. Instrum. 79, 061301 (2008); http://dx.doi.org/10.1063/1.2938864 (11 pages) | Cited 11 times

Online Publication Date: 24 June 2008

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We describe here the theory and applications of virtual environment dynamic atomic force microscopy (VEDA), a suite of state-of-the-art simulation tools deployed on nanoHUB (www.nanohub.org) for the accurate simulation of tip motion in dynamic atomic force microscopy (dAFM) over organic and inorganic samples. VEDA takes advantage of nanoHUB’s cyberinfrastructure to run high-fidelity dAFM tip dynamics computations on local clusters and the teragrid. Consequently, these tools are freely accessible and the dAFM simulations are run using standard web-based browsers without requiring additional software. A wide range of issues in dAFM ranging from optimal probe choice, probe stability, and tip-sample interaction forces, power dissipation, to material property extraction and scanning dynamics over hetereogeneous samples can be addressed.
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07.79.Lh Atomic force microscopes
07.05.-t Computers in experimental physics
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Direct measurement of beam size in a spectroscopic ellipsometry setup

Arthur Tay, Tuck Wah Ng, Yuheng Wang, and Shao Zhao

Rev. Sci. Instrum. 79, 063101 (2008); http://dx.doi.org/10.1063/1.2936262 (4 pages)

Online Publication Date: 2 June 2008

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Spectroscopic ellipsometry signals used in thin film analysis are dependent on the beam probe size. In this work, we report a technique to determine the beam size that uses the existing detection facilities in a spectroscopic ellipsometry setup without the need to rearrange the optical components. The intensity signal recorded with the technique comprises a coupled boundary diffraction and knife edge wave that can be isolated using nonlinear fitting. This then permitted an accurate measurement of the beam size with the stronger knife edge component. The technique has the added advantage of picking up chromatic aberration in the probing lens which may be a factor in ellipsometry measurement.
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07.60.Fs Polarimeters and ellipsometers
78.20.-e Optical properties of bulk materials and thin films

Time-resolved momentum imaging system for molecular dynamics studies using a tabletop ultrafast extreme-ultraviolet light source

Etienne Gagnon, Arvinder S. Sandhu, Ariel Paul, Kim Hagen, Achim Czasch, Till Jahnke, Predrag Ranitovic, C. Lewis Cocke, Barry Walker, Margaret M. Murnane, and Henry C. Kapteyn

Rev. Sci. Instrum. 79, 063102 (2008); http://dx.doi.org/10.1063/1.2930869 (14 pages) | Cited 8 times

Online Publication Date: 5 June 2008

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We describe a momentum imaging setup for direct time-resolved studies of ionization-induced molecular dynamics. This system uses a tabletop ultrafast extreme-ultraviolet (EUV) light source based on high harmonic upconversion of a femtosecond laser. The high photon energy (around 42 eV) allows access to inner-valence states of a variety of small molecules via single photon excitation, while the sub-–10-fs pulse duration makes it possible to follow the resulting dynamics in real time. To obtain a complete picture of molecular dynamics following EUV induced photofragmentation, we apply the versatile cold target recoil ion momentum spectroscopy reaction microscope technique, which makes use of coincident three-dimensional momentum imaging of fragments resulting from photoexcitation. This system is capable of pump-probe spectroscopy by using a combination of EUV and IR laser pulses with either beam as a pump or probe pulse. We report several experiments performed using this system.
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33.80.Eh Autoionization, photoionization, and photodetachment
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.30.-d Imaging and optical processing
42.72.Bj Visible and ultraviolet sources

Transmissive x-ray beam position monitors with submicron position- and submillisecond time resolution

Martin R. Fuchs, Karsten Holldack, Mark Bullough, Susanne Walsh, Colin Wilburn, Alexei Erko, Franz Schäfers, and Uwe Mueller

Rev. Sci. Instrum. 79, 063103 (2008); http://dx.doi.org/10.1063/1.2938400 (9 pages) | Cited 1 time

Online Publication Date: 6 June 2008

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We present the development of fast transmissive center-of-mass x-ray beam position monitors with a large active area, based on a thinned position sensitive detector in both a duo- and a tetra-lateral variant. The detectors were tested at BESSY beamlines BL14.1, KMC-1, and KMC-2 and yielded signal currents of up to 3 μA/100 mA ring current at 10 keV photon energy using the monochromatic focused beam of BL14.1. The active area sizes were 1×1 and 3×3 mm2 for the duo-lateral and 5×5 mm2 for the tetra-lateral devices, with the duo-lateral detectors currently being available in sizes from 1×1 to 10×10 mm2 and thicknesses between 5 and 10 μm. The presented detectors’ thicknesses were measured to be 5 and 8 μm with a corresponding transmission of up to 93% at 10 keV and 15% at 2.5 keV. Up to a detection bandwidth of 10 kHz, the monitors provide submicron position resolution. For lower detection bandwidths, the signal-to-noise reaches values of up to 6×104 at 10 Hz, corresponding to a position resolution of better than 50 nm for both detector sizes. As it stands, this monitor design approach promises to be a generic solution for automation of state-of-the-art crystal monochromator beamlines.
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07.85.-m X- and γ-ray instruments
29.40.Gx Tracking and position-sensitive detectors

Compact electron beam ion trap for spectroscopy of moderate charge state ions

Nobuyuki Nakamura, Hiroyuki Kikuchi, Hiroyuki A. Sakaue, and Tetsuya Watanabe

Rev. Sci. Instrum. 79, 063104 (2008); http://dx.doi.org/10.1063/1.2939393 (4 pages) | Cited 17 times

Online Publication Date: 11 June 2008

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A compact electron beam ion trap (EBIT) has been constructed for spectroscopic studies of moderate charge state ions. The electron beam energy range of the present EBIT is 100–1000 eV, for which it is rather difficult to operate an ordinary EBIT which used to be designed for operation with higher electron energy ( ∼ 10 keV or more). To cut down the running costs, a superconducting wire with a high critical temperature is used for the central magnet so that it can be operated without liquid helium. The performance of the compact EBIT has been investigated through visible spectroscopy of highly charged krypton and iron ions.
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07.60.Rd Visible and ultraviolet spectrometers
41.75.Fr Electron and positron beams

A whole-field polariscope using a liquid crystal polarization rotator

Pin Wang and Anand Asundi

Rev. Sci. Instrum. 79, 063105 (2008); http://dx.doi.org/10.1063/1.2943417 (5 pages) | Cited 1 time

Online Publication Date: 24 June 2008

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A novel polariscope using a liquid crystal (LC) polarization rotator is proposed for full-field subfringe photoelastic stress analysis. The system uses a light-emitting diode-based modified Senarmont polariscope with an added liquid crystal polarization rotator to generate phase shifts by applying suitable voltages to the LC element. Four phase shift polariscope images are captured and analyzed to get the stress distribution. A comparative study with the gray-field polariscope method which uses a rotating analyzer shows good agreement.
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07.60.Fs Polarimeters and ellipsometers
42.79.Ci Filters, zone plates, and polarizers
85.60.Jb Light-emitting devices
42.79.Kr Display devices, liquid-crystal devices

A Mach–Zehnder interferometer for the detection and noninvasive optical amplification of polarization rotation

Joshua M. LaForge and Geoffrey M. Steeves

Rev. Sci. Instrum. 79, 063106 (2008); http://dx.doi.org/10.1063/1.2948309 (7 pages)

Online Publication Date: 25 June 2008

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We present the theory and design of a Mach–Zehnder interferometer with orthogonally polarized arms that passively, noninvasively, optically amplifies polarization rotation in one arm of the interferometer. Theoretical analysis of the electric fields in the two arms is used to compare the significance of device optimizations. Design of the beam alignment, beam recombination, noise isolation, and active stabilization to enable reliable measurements are thoroughly discussed. Finally, we review a comparison between the interferometer with an optical gain factor of ∼ 4.5 and the optical bridge (OB) technique for polarization rotation detection that shows the interferometer offers better performance than the OB.
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07.60.Ly Interferometers
42.15.Eq Optical system design
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
02.60.Pn Numerical optimization

Longitudinally excited N2 lasers without high-voltage switches

Kazuyuki Uno, Kenshi Nakamura, Tatsumi Goto, and Takahisa Jitsuno

Rev. Sci. Instrum. 79, 063107 (2008); http://dx.doi.org/10.1063/1.2936872 (5 pages) | Cited 1 time

Online Publication Date: 25 June 2008

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We have developed novel excitation circuits without high-voltage switches for two longitudinally excited N2 lasers (wavelength: 337 nm). One uses a single tube without a trigger and the other uses a tandem tube with a trigger. In both systems, the discharge tube acts as a switch. In the single-tube system, the laser output energy was 125.8 μJ and the efficiency was 0.16% at 18 Torr (2.4 kPa) when a slow-rising voltage pulse of −28 kV was applied (rise time: 21.3 μs). In the tandem-tube system, the laser output energy was 259.4 μJ and the efficiency was 0.11% at 18 Torr when a slow-rising voltage pulse of −48 kV was applied (rise time: 27 μs).
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

A photoelectron-photoion coincidence imaging apparatus for femtosecond time-resolved molecular dynamics with electron time-of-flight resolution of σ = 18 ps and energy resolution ΔE/E = 3.5%

Arno Vredenborg, Wim G. Roeterdink, and Maurice H. M. Janssen

Rev. Sci. Instrum. 79, 063108 (2008); http://dx.doi.org/10.1063/1.2949142 (9 pages) | Cited 21 times

Online Publication Date: 27 June 2008

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We report on the construction and performance of a novel photoelectron-photoion coincidence machine in our laboratory in Amsterdam to measure the full three-dimensional momentum distribution of correlated electrons and ions in femtosecond time-resolved molecular beam experiments. We implemented sets of open electron and ion lenses to time stretch and velocity map the charged particles. Time switched voltages are operated on the particle lenses to enable optimal electric field strengths for velocity map focusing conditions of electrons and ions separately. The position and time sensitive detectors employ microchannel plates (MCPs) in front of delay line detectors. A special effort was made to obtain the time-of-flight (TOF) of the electrons at high temporal resolution using small pore (5 μm) MCPs and implementing fast timing electronics. We measured the TOF distribution of the electrons under our typical coincidence field strengths with a temporal resolution down to σ = 18 ps. We observed that our electron coincidence detector has a timing resolution better than σ = 16 ps, which is mainly determined by the residual transit time spread of the MCPs. The typical electron energy resolution appears to be nearly laser bandwidth limited with a relative resolution of ΔEFWHM/E = 3.5% for electrons with kinetic energy near 2 eV. The mass resolution of the ion detector for ions measured in coincidence with electrons is about ΔmFWHM/m = 1/4150. The velocity map focusing of our extended source volume of particles, due to the overlap of the molecular beam with the laser beams, results in a parent ion spot on our detector focused down to σ = 115 μm.
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37.20.+j Atomic and molecular beam sources and techniques
07.81.+a Electron and ion spectrometers
32.80.-t Photoionization and excitation
33.80.-b Photon interactions with molecules
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Production of pulsed, mass-selected beams of metal and semiconductor clusters

Omar Kamalou, Jimmy Rangama, Jean-Marc Ramillon, Patrick Guinement, and Bernd A. Huber

Rev. Sci. Instrum. 79, 063301 (2008); http://dx.doi.org/10.1063/1.2937646 (5 pages) | Cited 2 times

Online Publication Date: 5 June 2008

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We report on the development of a beam line for mass-selected metal and semiconductor clusters. The cluster source combines the principles of plasma sputtering and gas condensation. Both techniques together allow to produce clusters in a wide size range. With the aid of a time-of-flight system, small clusters (i.e., Cun+, n<100) are selected and pure beams containing only one cluster size are provided. For large clusters (containing several thousands of atoms), a beam with a narrow size distribution is obtained. A 90° quadrupole deviator is used to separate charged clusters from neutral ones.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
52.77.-j Plasma applications
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Plasma cell adaptation to enhance particle acceleration

M. S. Ragheb

Rev. Sci. Instrum. 79, 063302 (2008); http://dx.doi.org/10.1063/1.2912953 (8 pages) | Cited 1 time

Online Publication Date: 16 June 2008

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A plasma study is performed in order to construct a cell for plasma acceleration purpose. As well, a multicell design is introduced for the injection of beam driver application. The suggested idea is experimentally demonstrated for two plasma cell configuration. The preformed plasma is obtained by a symmetrically driven capacitive audio frequency discharge. It is featured by its moderate pressure of 0.1–0.2 Torr, low consumption power of 130 W maximum, low discharge voltage and frequency up to 950 V and 20 kHz, respectively, and high plasma density from 1011 to 1015 cm−3. The electron temperature obtained by Langmuir double probe varies from 1 up to 16 eV. It is observed that the increases of the discharge voltage and frequency enlarge the plasma parameters to their maximum values. The plasma cell filled with different gases demonstrates that the Ar and He gases manifest the highest ionization efficiency exceeding 100% at 950 V and 20 kHz. The formed plasma is cold; its density is uniform and stable along the positive column for long competitive lifetime. Showing that it follows the conditions to enhance particle acceleration and in conjunction with its periphery devices form a plasma cell that could be extended to serve this purpose. Demonstrating that an injected electron beam into the extended preformed plasma could follow, to long distance, a continuous trajectory of uniform density. Such plasma generated by H2 or Ar gases is suggested to be used, respectively, for low-density or higher density beam driver.
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52.70.Ds Electric and magnetic measurements
52.80.-s Electric discharges
52.25.-b Plasma properties

A ceramic radial insulation structure for a relativistic electron beam vacuum diode

Tao Xun, Hanwu Yang, Jiande Zhang, Zhenxiang Liu, Yong Wang, and Yansong Zhao

Rev. Sci. Instrum. 79, 063303 (2008); http://dx.doi.org/10.1063/1.2936884 (5 pages) | Cited 2 times

Online Publication Date: 30 June 2008

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For one kind of a high current diode composed of a small disk-type alumina ceramic insulator water/vacuum interface, the insulation structure was designed and experimentally investigated. According to the theories of vacuum flashover and the rules for radial insulators, a “cone-column” anode outline and the cathode shielding rings were adopted. The electrostatic field along the insulator surface was obtained by finite element analysis simulating. By adjusting the outline of the anode and reshaping the shielding rings, the electric fields were well distributed and the field around the cathode triple junction was effectively controlled. Area weighted statistical method was applied to estimate the surface breakdown field. In addition, the operating process of an accelerator based on a spiral pulse forming line (PFL) was simulated through the PSPICE software to get the waveform of charging and diode voltage. The high voltage test was carried out on a water dielectric spiral PFL accelerator with long pulse duration, and results show that the diode can work stably in 420 kV, 200 ns conditions. The experimental results agree with the theoretical and simulated results.
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84.47.+w Vacuum tubes
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
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Analysis of magnetic probe signals including effect of cylindrical conducting wall for field-reversed configuration experiment

Taeko Ikeyama, Masanori Hiroi, Yuuichi Nemoto, and Yasuyuki Nogi

Rev. Sci. Instrum. 79, 063501 (2008); http://dx.doi.org/10.1063/1.2937205 (10 pages) | Cited 2 times

Online Publication Date: 3 June 2008

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A confinement field is disturbed by magnetohydrodynamic (MHD) motions of a field-reversed configuration (FRC) plasma in a cylindrical conductor. The effect of the conductor should be included to obtain a spatial structure of the disturbed field with a good precision. For this purpose, a toroidal current in the plasma and an eddy current on a conducting wall are replaced by magnetic dipole and image magnetic dipole moments, respectively. Typical spatial structures of the disturbed field are calculated by using the dipole moments for such MHD motions as radial shift, internal tilt, external tilt, and n = 2 mode deformation. Then, analytic formulas for estimating the shift distance, tilt angle, and deformation rate of the MHD motions from magnetic probe signals are derived. It is estimated from the calculations by using the dipole moments that the analytic formulas include an approximately 40% error. Two kinds of experiment are carried out to investigate the reliability of the calculations. First, a magnetic field produced by a circular current is measured in an aluminum pipe to confirm the replacement of the eddy current with the image magnetic dipole moments. The measured fields coincide well with the calculated values including the image magnetic dipole moments. Second, magnetic probe signals measured from the FRC plasma are substituted into the analytic formulas to obtain shift distance and deformation rate. The experimental results are compared to the MHD motions measured by using a radiation from the plasma. If the error included in the analytic formulas and the difference between the magnetic and optical structures in the plasma are considered, the results of the radiation measurement support well those of the magnetic analysis.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.58.Lq Z-pinches, plasma focus, and other pinch devices

Development of ion source with a washer gun for pulsed neutral beam injection

T. Asai, N. Yamaguchi, H. Kajiya, T. Takahashi, H. Imanaka, Y. Takase, Y. Ono, and K. N. Sato

Rev. Sci. Instrum. 79, 063502 (2008); http://dx.doi.org/10.1063/1.2936255 (3 pages) | Cited 2 times

Online Publication Date: 9 June 2008

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A new type of economical neutral beam source has been developed by using a single washer gun, pulsed operation, and a simple electrode system. We replaced the conventional hot filaments for arc-discharge-type plasma formation with a single stainless-steel washer gun, eliminating the entire dc power supply for the filaments and the cooling system for the electrodes. Our initial experiments revealed successful beam extraction up to 10 kV and 8.6 A, based on spatial profile measurements of density and temperature in the plasma source. The system also shows the potential to control the beam profile by controlling the plasma parameters in the ion accumulation chamber.
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29.25.Ni Ion sources: positive and negative
07.77.Ka Charged-particle beam sources and detectors
52.50.Gj Plasma heating by particle beams
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.25.-b Plasma properties
52.50.Dg Plasma sources

Bipolar high-repetition-rate high-voltage nanosecond pulser

Fuqiang Tian, Yi Wang, Hongsheng Shi, and Qingquan Lei

Rev. Sci. Instrum. 79, 063503 (2008); http://dx.doi.org/10.1063/1.2943413 (5 pages) | Cited 1 time

Online Publication Date: 17 June 2008

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The pulser designed is mainly used for producing corona plasma in waste water treatment system. Also its application in study of dielectric electrical properties will be discussed. The pulser consists of a variable dc power source for high-voltage supply, two graded capacitors for energy storage, and the rotating spark gap switch. The key part is the multielectrode rotating spark gap switch (MER-SGS), which can ensure wider range modulation of pulse repetition rate, longer pulse width, shorter pulse rise time, remarkable electrical field distortion, and greatly favors recovery of the gap insulation strength, insulation design, the life of the switch, etc. The voltage of the output pulses switched by the MER-SGS is in the order of 3–50 kV with pulse rise time of less than 10 ns and pulse repetition rate of 1–3 kHz. An energy of 1.25–125 J per pulse and an average power of up to 10–50 kW are attainable. The highest pulse repetition rate is determined by the driver motor revolution and the electrode number of MER-SGS. Even higher voltage and energy can be switched by adjusting the gas pressure or employing N2 as the insulation gas or enlarging the size of MER-SGS to guarantee enough insulation level.
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52.75.Kq Plasma switches (e.g., spark gaps)
89.60.-k Environmental studies
52.80.Hc Glow; corona
52.25.Mq Dielectric properties

Subcutoff microwave driven plasma ion sources for multielemental focused ion beam systems

Jose V. Mathew, Abhishek Chowdhury, and Sudeep Bhattacharjee

Rev. Sci. Instrum. 79, 063504 (2008); http://dx.doi.org/10.1063/1.2943341 (5 pages) | Cited 11 times

Online Publication Date: 20 June 2008

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A compact microwave driven plasma ion source for focused ion beam applications has been developed. Several gas species have been experimented including argon, krypton, and hydrogen. The plasma, confined by a minimum B multicusp magnetic field, has good radial and axial uniformity. The octupole multicusp configuration shows a superior performance in terms of plasma density ( ∼ 1.3×1011 cm−3) and electron temperature (7–15 eV) at a power density of 5–10 W/cm2. Ion current densities ranging from a few hundreds to over 1000 mA/cm2 have been obtained with different plasma electrode apertures. The ion source will be combined with electrostatic Einzel lenses and should be capable of producing multielemental focused ion beams for nanostructuring and implantations. The initial simulation results for the focused beams have been presented.
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52.59.-f Intense particle beams and radiation sources
52.55.-s Magnetic confinement and equilibrium
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.77.Dq Plasma-based ion implantation and deposition

Magnetic flux array for spontaneous magnetic reconnection experiments

A. Kesich, J. Bonde, J. Egedal, W. Fox, R. Goodwin, N. Katz, and A. Le

Rev. Sci. Instrum. 79, 063505 (2008); http://dx.doi.org/10.1063/1.2937193 (5 pages) | Cited 5 times

Online Publication Date: 24 June 2008

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Experimental investigation of reconnection in magnetized plasmas relies on accurate characterization of the evolving magnetic fields. In experimental configurations where the plasma dynamics are reproducible, magnetic data can be collected in multiple discharges and combined to provide spatially resolved profiles of the plasma dynamics. However, in experiments on spontaneous magnetic reconnection recently undertaken at the Versatile Toroidal Facility at MIT, the reconnection process is not reproducible and all information on the plasma must be collected in a single discharge. This paper describes a newly developed magnetic flux array which directly measures the toroidal component of the magnetic vector potential, Aϕ. From the measured Aϕ, the magnetic field geometry, current density, and reconnection rate are readily obtained, facilitating studies of the three-dimensional dynamics of spontaneous magnetic reconnection. The novel design of the probe array allows for accurate characterization of profiles of Aϕ at multiple toroidal angles using a relatively small number of signal channels and with minimal disturbance of the plasma.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Vd Magnetic reconnection
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Compact two-dimensional coarse-positioner for scanning probe microscopes

Anjan K. Gupta, Rajiv Shankar Sinha, and Reetesh Kumar Singh

Rev. Sci. Instrum. 79, 063701 (2008); http://dx.doi.org/10.1063/1.2940234 (3 pages) | Cited 4 times

Online Publication Date: 16 June 2008

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We report on the design and fabrication of a compact two-dimensional xy-positioner for scanning probe microscopes. This positioner uses three piezoelectric bimorphs in flexing or length-change mode by appropriate selection of electrodes and voltage polarities. One end of these bimorphs is fixed to a rectangular metal frame while on each of the free ends two sapphire disks are fixed which can slide against the polished plates of a platform movable in the xy-plane. For moving the platform by one step, the bimorphs are deformed sequentially in one mode and they are brought back to their undeformed state simultaneously. The motion of the positioner has been tested with an optical microscope and a homemade scanning tunneling microscope.
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07.79.Cz Scanning tunneling microscopes
07.60.Pb Conventional optical microscopes

Single beam optical tweezers setup with backscattered light detection for three-dimensional measurements on DNA and nanopores

Andy Sischka, Christoph Kleimann, Wiebke Hachmann, Marcus M. Schäfer, Ina Seuffert, Katja Tönsing, and Dario Anselmetti

Rev. Sci. Instrum. 79, 063702 (2008); http://dx.doi.org/10.1063/1.2938401 (7 pages) | Cited 6 times

Online Publication Date: 18 June 2008

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We introduce a versatile and high precision three-dimensional optical tweezers setup with minimal optical interference to measure small forces and manipulate single molecules in the vicinity of a weak reflective surface. Our tweezers system integrates an inverted optical microscope with a single IR-laser beam that is spatially filtered in an appropriate way to allow force measurements in three dimensions with remarkably high precision when operated in backscattered light detection mode. The setup was tested by overstretching a λ-DNA in x and z directions (perpendicular and along the optical axis), and by manipulating individual λ-DNA molecules in the vicinity of a nanopore that allowed quantitative single molecule threading experiments with minimal optical interference.
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87.80.Cc Optical trapping
87.14.gk DNA
42.79.Ci Filters, zone plates, and polarizers

Modeling and characterization of a cantilever-based near-field scanning microwave impedance microscope

K. Lai, W. Kundhikanjana, M. Kelly, and Z. X. Shen

Rev. Sci. Instrum. 79, 063703 (2008); http://dx.doi.org/10.1063/1.2949109 (6 pages) | Cited 4 times

Online Publication Date: 25 June 2008

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This paper presents a detailed modeling and characterization of a microfabricated cantilever-based scanning microwave probe with separated excitation and sensing electrodes. Using finite-element analysis, we model the tip-sample interaction as small impedance changes between the tip electrode and the ground at our working frequencies near 1 GHz. The equivalent lumped elements of the cantilever can be determined by transmission line simulation of the matching network, which routes the cantilever signals to 50 Ω feed lines. In the microwave electronics, the background common-mode signal is canceled before the amplifier stage so that high sensitivity (below 1 aF capacitance changes) is obtained. Experimental characterization of the microwave microscope was performed on ion-implanted Si wafers and patterned semiconductor samples. Pure electrical or topographical signals can be obtained from different reflection modes of the probe.
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07.79.-v Scanning probe microscopes and components
84.40.-x Radiowave and microwave (including millimeter wave) technology
07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
02.70.Dh Finite-element and Galerkin methods

Feed-forward compensation of surface potential in atomic force microscopy

Dominik Ziegler, Nicola Naujoks, and Andreas Stemmer

Rev. Sci. Instrum. 79, 063704 (2008); http://dx.doi.org/10.1063/1.2947740 (4 pages) | Cited 5 times

Online Publication Date: 26 June 2008

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We introduce a feed-forward technique for lift-mode Kelvin probe force microscopy to minimize electrostatically induced errors in topography scans. Such errors typically occur when a grounded tip is scanned over a heterogeneous sample with differences in local work function or areas of local surface charging. To minimize electrostatic forces during the topography scan we bias the tip with the surface potential recorded in the previous Kelvin probe scan line. With this method we achieve an error free topography on samples with large variations in local surface potential. Compared to conventional tapping mode, we further observe a significant reduction of tip-induced surface charge modifications on charge patterns written in electret films.
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07.79.Lh Atomic force microscopes
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The use of symmetry to correct Larmor phase aberrations in spin echo scattering angle measurement

Roger Pynn, W. T. Lee, P. Stonaha, V. R. Shah, A. L. Washington, B. J. Kirby, C. F. Majkrzak, and B. B. Maranville

Rev. Sci. Instrum. 79, 063901 (2008); http://dx.doi.org/10.1063/1.2927251 (8 pages) | Cited 2 times

Online Publication Date: 4 June 2008

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Spin echo scattering angle measurement (SESAME) is a sensitive interference technique for measuring neutron diffraction. The method uses waveplates or birefringent prisms to produce a phase separation (the Larmor phase) between the “up” and “down” spin components of a neutron wavefunction that is initially prepared in a state that is a linear combination of in-phase up and down components. For neutrons, uniformly birefringent optical elements can be constructed from closed solenoids with appropriately shaped cross sections. Such elements are inconvenient in practice, however, both because of the precision they demand in the control of magnetic fields outside the elements and because of the amount of material required in the neutron beam. In this paper, we explore a different option in which triangular-cross-section solenoids used to create magnetic fields for SESAME have gaps in one face, allowing the lines of magnetic flux to “leak out” of the solenoid. Although the resulting field inhomogeneity produces aberrations in the Larmor phase, the symmetry of the solenoid gaps causes the aberrations produced by neighboring pairs of triangular solenoids to cancel to a significant extent. The overall symmetry of the SESAME apparatus leads to further cancellations of aberrations, providing an architecture that is easy to construct and robust in performance.
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76.60.Lz Spin echoes
85.70.Sq Magnetooptical devices
85.70.Ay Magnetic device characterization, design, and modeling

Simultaneous measurement of magnetization and magnetostriction in 50 T pulsed high magnetic fields

M. Doerr, W. Lorenz, T. Neupert, M. Loewenhaupt, N. V. Kozlova, J. Freudenberger, M. Bartkowiak, E. Kampert, and M. Rotter

Rev. Sci. Instrum. 79, 063902 (2008); http://dx.doi.org/10.1063/1.2919882 (5 pages) | Cited 2 times

Online Publication Date: 5 June 2008

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To simultaneously perform magnetization and magnetostriction measurements in high magnetic fields, a miniaturized device was developed that combines an inductive magnetometer with a capacitive dilatometer and, therefore, it is called “dilamagmeter.” This combination of magnetic and magnetoelastic investigations is a new step to a complex understanding of solid state properties. The whole system can be mounted in a 12 mm clear bore of any cryostat usually used in nondestructive pulsed high field magnets. The sensitivity of both methods is about 10−5 A m2 for magnetization and 10−5 relative changes in length for striction measurements. Measurements on a GdSi single crystal, which are corrected by the background signal of the experimental setup, agree well with the results of steady field experiments. All test measurements, which are up until now performed in the temperature range of 4–100 K, confirm the perfect usability and high stability in pulsed fields up to 50 T with a pulse duration of 10 ms.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.80.+q Magnetomechanical effects, magnetostriction

Construction and development of a time-resolved x-ray magnetic circular dichroism–photoelectron emission microscopy system using femtosecond laser pulses at BL25SU SPring-8

Keiki Fukumoto, Tomohiro Matsushita, Hitoshi Osawa, Tetsuya Nakamura, Takayuki Muro, Kuniaki Arai, Takashi Kimura, Yoshichika Otani, and Toyohiko Kinoshita

Rev. Sci. Instrum. 79, 063903 (2008); http://dx.doi.org/10.1063/1.2937648 (5 pages) | Cited 4 times

Online Publication Date: 10 June 2008

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A femtosecond pulsed laser system has been installed at the BL25SU soft x-ray beamline at SPring-8 for time-resolved pump-probe experiments with synchronization of the laser pulses to the circularly polarized x-ray pulses. There are four different apparatuses situated at the beamline; for photoemission spectroscopy, two-dimensional display photoelectron diffraction, x-ray magnetic circular dichroism (XMCD) with electromagnetic coils, and photoelectron emission microscopy (PEEM). All four can be used for time-resolved experiments, and preliminary investigations have been carried out using the PEEM apparatus to observe magnetization dynamics in combination with XMCD. In this article, we describe the details of the stroboscopic pump-probe XMCD-PEEM experiment, and present preliminary data. The repetition rate of the laser pulses is set using a pulse selector to match the single bunches of SPring-8’s hybrid filling pattern, which consists of several single bunches and a continuous bunch train. Electrons ejected during the bunch train, which do not provide time-resolved signal, are eliminated by periodically reducing the channel plate voltage using a custom-built power supply. The pulsed laser is used to create 300 ps long magnetic field pulses, which cause magnetic excitations in micron-sized magnetic elements which contain magnetic vortex structures. The observed frequency of the motion is consistent with previously reported observations and simulations.
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42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
41.85.Ct Particle beam shaping, beam splitting
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
07.85.-m X- and γ-ray instruments

An optical NMR spectrometer for Larmor-beat detection and high-resolution POWER NMR

J. G. Kempf, J. A. Marohn, P. J. Carson, D. A. Shykind, J. Y. Hwang, M. A. Miller, and D. P. Weitekamp

Rev. Sci. Instrum. 79, 063904 (2008); http://dx.doi.org/10.1063/1.2936257 (9 pages) | Cited 2 times

Online Publication Date: 11 June 2008

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Optical nuclear magnetic resonance (ONMR) is a powerful probe of electronic properties in III-V semiconductors. Larmor-beat detection (LBD) is a sensitivity optimized, time-domain NMR version of optical detection based on the Hanle effect. Combining LBD ONMR with the line-narrowing method of POWER (perturbations observed with enhanced resolution) NMR further enables atomically detailed views of local electronic features in III-Vs. POWER NMR spectra display the distribution of resonance shifts or line splittings introduced by a perturbation, such as optical excitation or application of an electric field, that is synchronized with a NMR multiple-pulse time-suspension sequence. Meanwhile, ONMR provides the requisite sensitivity and spatial selectivity to isolate local signals within macroscopic samples. Optical NMR, LBD, and the POWER method each introduce unique demands on instrumentation. Here, we detail the design and implementation of our system, including cryogenic, optical, and radio-frequency components. The result is a flexible, low-cost system with important applications in semiconductor electronics and spin physics. We also demonstrate the performance of our systems with high-resolution ONMR spectra of an epitaxial AlGaAs/GaAs heterojunction. NMR linewidths down to 4.1 Hz full width at half maximum were obtained, a 103-fold resolution enhancement relative any previous optically detected NMR experiment.
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07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
07.60.-j Optical instruments and equipment
73.20.-r Electron states at surfaces and interfaces
76.60.-k Nuclear magnetic resonance and relaxation
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