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Dec 2010

Volume 81, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Rev. Sci. Instrum. 81, 121101 (2010); http://dx.doi.org/10.1063/1.3520482 (33 pages)

Young Jae Song, Alexander F. Otte, Vladimir Shvarts, Zuyu Zhao, Young Kuk, Steven R. Blankenship, Alan Band, Frank M. Hess, and Joseph A. Stroscio

Photograph of the ultra-high vacuum compatible dilution refrigerator for scanning probe microscopy. The left top inset shows a series of Landau level spectral prints of graphene as a function of magnetic field, ranging from 1 T (bottom) to 10 T (top). The right bottom inset shows a schematic of the four-fold degenerate spin and valley cyclotron orbits in graphene, which are measured in scanning tunneling spectroscopy (red curve). The spin sub-bands can split further into ½-fractional states under certain conditions as indicated in the schematic.

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Invited Review Article: A 10 mK scanning probe microscopy facility

Young Jae Song, Alexander F. Otte, Vladimir Shvarts, Zuyu Zhao, Young Kuk, Steven R. Blankenship, Alan Band, Frank M. Hess, and Joseph A. Stroscio

Rev. Sci. Instrum. 81, 121101 (2010); http://dx.doi.org/10.1063/1.3520482 (33 pages) | Cited 6 times

Online Publication Date: 29 December 2010

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We describe the design, development and performance of a scanning probe microscopy (SPM) facility operating at a base temperature of 10 mK in magnetic fields up to 15 T. The microscope is cooled by a custom designed, fully ultra-high vacuum (UHV) compatible dilution refrigerator (DR) and is capable of in situ tip and sample exchange. Subpicometer stability at the tip-sample junction is achieved through three independent vibration isolation stages and careful design of the dilution refrigerator. The system can be connected to, or disconnected from, a network of interconnected auxiliary UHV chambers, which include growth chambers for metal and semiconductor samples, a field-ion microscope for tip characterization, and a fully independent additional quick access low temperature scanning tunneling microscope (STM) and atomic force microscope (AFM) system. To characterize the system, we present the cooling performance of the DR, vibrational, tunneling current, and tip-sample displacement noise measurements. In addition, we show the spectral resolution capabilities with tunneling spectroscopy results obtained on an epitaxial graphene sample resolving the quantum Landau levels in a magnetic field, including the sublevels corresponding to the lifting of the electron spin and valley degeneracies.
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07.79.-v Scanning probe microscopes and components
81.05.ue Graphene
71.70.Di Landau levels
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back to top Optics; Atoms and Molecules; Spectroscopy; Photon Detectors

Development of a new photoelectron spectroscopy instrument combining an electrospray ion source and photoelectron imaging

A. R. McKay, M. E. Sanz, C. R. S. Mooney, R. S. Minns, E. M. Gill, and H. H. Fielding

Rev. Sci. Instrum. 81, 123101 (2010); http://dx.doi.org/10.1063/1.3505097 (9 pages)

Online Publication Date: 14 December 2010

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A new apparatus has been constructed that combines electrospray ionization with a quadrupole mass filter, hexapole ion trap, and velocity-map imaging. The purpose is to record photoelectron images of isolated chromophore anions. To demonstrate the capability of our instrument we have recorded the photodetachment spectra of isolated deprotonated phenol and indole anions. To our knowledge, this is the first time that the photodetachment energy of the deprotonated indole anion has been recorded.
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07.81.+a Electron and ion spectrometers
07.77.Ka Charged-particle beam sources and detectors

A twisted periscope arrangement for transporting elliptically polarized light without change in its polarization state

Ashish Arora and Sandip Ghosh

Rev. Sci. Instrum. 81, 123102 (2010); http://dx.doi.org/10.1063/1.3518949 (3 pages) | Cited 1 time

Online Publication Date: 20 December 2010

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The authors describe a dual-mirror 90∘ twisted periscope arrangement for transporting polarized light in air, wherein a general elliptic polarization state of the light is preserved at all wavelengths. It is experimentally demonstrated that in the wavelength range 400–1000 nm, this arrangement preserves the polarization state fairly well when using either metallic or dielectric mirrors.
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77.22.Ej Polarization and depolarization

Portable fiber sensors based on surface-enhanced Raman scattering

Xuan Yang, Zuki Tanaka, Rebecca Newhouse, Qiao Xu, Bin Chen, Shaowei Chen, Jin Z. Zhang, and Claire Gu

Rev. Sci. Instrum. 81, 123103 (2010); http://dx.doi.org/10.1063/1.3518957 (5 pages)

Online Publication Date: 20 December 2010

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Two portable molecular sensing systems based on surface-enhanced Raman scattering (SERS) have been experimentally demonstrated using either a tip-coated multimode fiber (TCMMF) or a liquid core photonic crystal fiber (LCPCF) as the SERS probe. With Rhodamine 6G as a test molecule, the TCMMF-portable SERS system achieved 2–3 times better sensitivity than direct sampling (focusing the laser light directly into the sample without the fiber probe), and a highly sensitive LCPCF-portable SERS system reached a sensitivity up to 59 times that of direct sampling, comparable to the sensitivity enhancement achieved using fiber probes in the bulky Renishaw system. These fiber SERS probes integrated with a portable Raman spectrometer provide a promising scheme for a compact and flexible molecular sensing system with high sensitivity and portability.
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42.81.Pa Sensors, gyros
42.81.Wg Other fiber-optical devices
42.70.Qs Photonic bandgap materials
87.64.kp Raman

Long distance fiber-optic displacement sensor based on fiber collimator

Wei Shen, Xiaowei Wu, Hongyun Meng, Guanbin Zhang, and Xuguang Huang

Rev. Sci. Instrum. 81, 123104 (2010); http://dx.doi.org/10.1063/1.3518971 (4 pages) | Cited 1 time

Online Publication Date: 20 December 2010

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A simple fiber-optic displacement sensor based on reflective intensity modulated technology is demonstrated using a fiber collimator. The sensing range is over 30 cm, which is over 100 times that of the conventional fiber-optic displacement sensor based on the normal single-mode fiber. The measured data are fitted into linear equation very well and the values of R-square are more than 0.995. The sensitivity of the device achieves 0.426 dB/cm over the range of 5–30 cm. By applying the relative technique, the errors resulted from the fluctuation of light source and influences of environment are effectively eliminated, and the stability for wide range measurement can be improved. The simplicity of the design, high dynamic range, stability and the ease of the fabrication make it suitable for applications in industries.
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42.81.Pa Sensors, gyros
42.79.Ag Apertures, collimators
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.79.Hp Optical processors, correlators, and modulators
42.15.Eq Optical system design

Real-time nonlinear correction of back-focal-plane detection in optical tweezers

Tanuj Aggarwal and Murti Salapaka

Rev. Sci. Instrum. 81, 123105 (2010); http://dx.doi.org/10.1063/1.3520463 (5 pages) | Cited 1 time

Online Publication Date: 22 December 2010

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Photodiode based detection of laser trapped beads using forward scattered light is a frequently employed technique for position measurement. There is a nonlinear relationship between photodiode outputs and bead position but for small displacements linear approximation holds well. Traditionally, the nonlinearity is compensated by normalizing the photodiode's position signal with the intensity signal and then using a polynomial fit in the range where voltage to position mapping is one to one. In this article, this range is extended by using the intensity signal as an independent input along with the two position signals. A map from the input signals to the actual position values is obtained. This mapping is one-to-one for a larger range that results in an increased detection range. An artificial neural network that facilitates implementation is employed for this purpose. This scheme is implemented on a Field Programmable Gate Array based data acquisition and control hardware with closed loop bandwidth of 50 kHz. Detection of the order of 350 nm from the center of detection laser is demonstrated for a 500 nm diameter bead compared to 180 nm achieved by a polynomial fit.
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87.80.Cc Optical trapping
42.79.Pw Imaging detectors and sensors
85.60.Dw Photodiodes; phototransistors; photoresistors
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)

An efficient magneto-optical trap of metastable krypton atoms

C.-F. Cheng, W. Jiang, G.-M. Yang, Y.-R. Sun, H. Pan, Y. Gao, A.-W. Liu, and S.-M. Hu

Rev. Sci. Instrum. 81, 123106 (2010); http://dx.doi.org/10.1063/1.3520133 (3 pages)

Online Publication Date: 28 December 2010

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We report a magneto-optical trap of metastable krypton atoms with a trap loading rate of 3×1011 atoms/s and a trap capture efficiency of 3×10−5. The system starts with an atomic beam of metastable krypton produced in a liquid-nitrogen cooled, radio-frequency driven discharge. The metastable beam flux emerging from the discharge is 1.5×1014 atoms/s/sr. The flux in the forward direction is enhanced by a factor of 156 with transverse laser cooling. The atoms are then slowed inside a Zeeman slower before captured by a magneto-optic trap. The trap efficiency can be further improved, possibly to the 10−2 level, by gas recirculation. Such an atom trap is useful in trace analysis applications where available sample size is limited.
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85.70.Sq Magnetooptical devices
37.10.-x Atom, molecule, and ion cooling methods
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Modulated 3D cross-correlation light scattering: Improving turbid sample characterization

Ian D. Block and Frank Scheffold

Rev. Sci. Instrum. 81, 123107 (2010); http://dx.doi.org/10.1063/1.3518961 (7 pages)

Online Publication Date: 30 December 2010

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Accurate characterization using static light scattering (SLS) and dynamic light scattering (DLS) methods mandates the measurement and analysis of singly scattered light. In turbid samples, the suppression of multiple scattering is therefore required to obtain meaningful results. One powerful technique for achieving this, known as 3D cross-correlation, uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. Here we present a significant improvement to this method in which the two scattering experiments are temporally separated by modulating the incident laser beams and gating the detector outputs at frequencies exceeding the timescale of the system dynamics. This robust modulation scheme eliminates cross-talk between the two beam-detector pairs and leads to a fourfold improvement in the cross-correlation intercept. We measure the dynamic and angular-dependent scattering intensity of turbid colloidal suspensions and exploit the improved signal quality of the modulated 3D cross-correlation DLS and SLS techniques.
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07.60.-j Optical instruments and equipment
42.79.Hp Optical processors, correlators, and modulators
back to top Particle Sources, Optics and Acceleration; Particle Detectors

Experimental study of new laser-based alignment system at the KEK B-factory injector linear accelerator

T. Suwada, M. Satoh, and E. Kadokura

Rev. Sci. Instrum. 81, 123301 (2010); http://dx.doi.org/10.1063/1.3504370 (12 pages) | Cited 1 time

Online Publication Date: 10 December 2010

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A new laser-based alignment system for the precise alignment of accelerator components along an ideal straight line at the KEK B-factory injector linear accelerator (linac) is under development. This system is strongly required in the next generation of B-factories for the stable acceleration of high-brightness electron and positron beams with high bunch charges and also for maintaining the stability of injection beams with high quality. A new laser optics for the generation of a so-called Airy beam has been developed for the laser-based alignment system. The laser propagation characteristics both in vacuum and at atmospheric pressure have been systematically investigated in an 82-m-long straight section of the injector linac. The laser-based alignment measurements based on the new laser optics have been carried out with a measurement resolution of ±0.1 mm level by using an existing laser detection electronics. The horizontal and vertical displacements from a reference laser line measured using this system are in good agreement with those measured using a standard telescope-based optical alignment technique. In this report, we describe the experimental study in detail along with the basic designs and the recent developments in the new laser-based alignment system.
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29.20.Ej Linear accelerators
29.27.Fh Beam characteristics
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Single-shot microscopic electron imaging of intense femtosecond laser-produced plasmas

Shunsuke Inoue, Shigeki Tokita, Toshihiko Nishoji, Shinichiro Masuno, Kazuto Otani, Masaki Hashida, and Shuji Sakabe

Rev. Sci. Instrum. 81, 123302 (2010); http://dx.doi.org/10.1063/1.3514084 (6 pages) | Cited 1 time

Online Publication Date: 28 December 2010

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A simple technique for single-shot microscopic electron imaging was demonstrated for the study of intense femtosecond laser-produced plasmas. Passed through a permanent magnet lens designed for 110-keV electrons, hot electrons emitted from the plasma produced by a single laser pulse of 0.8 mJ with intensity of 3 × 1016 W/cm2 were successfully imaged. Analyzing this image, we found that electrons were emitted from an area of 3 μm in diameter. At higher laser intensity of 1018 W/cm2, distinct structures were observed in and near the focal spot of the laser; that is, the electrons were emitted from several separate spots. These results show that laser-plasma electron imaging is promising for studying the interactions of femtosecond lasers with high-density plasmas.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
back to top Nuclear Physics, Fusion and Plasmas

Detection of x-ray emission in a nanosecond discharge in air at atmospheric pressure

Cheng Zhang (章程), Tao Shao (邵涛), Yang Yu (于洎), Zheng Niu (牛铮), Ping Yan (严萍), and Yuanxiang Zhou (周远翔)

Rev. Sci. Instrum. 81, 123501 (2010); http://dx.doi.org/10.1063/1.3506637 (5 pages) | Cited 2 times

Online Publication Date: 2 December 2010

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Measurement of x-ray emission is an important parameter to investigate runaway behavior of fast electrons produced in nanosecond-pulse gas discharge. An online detection system of x rays is described in this paper, and the system consists of an x-ray detector with NaI (Tl) scintillator and photomultiplier tube, and an integrated multichannel analyzer. The system is responsible for detecting x-ray emission signal, processing the detected signals, and scaling the energy distribution. The calibration results show that every channel of the detection system represents a given x-ray energy and various x rays can be divided into different energy ranges between 10 and 130 keV. For a repetitive nanosecond-pulse breakdown between highly nonuniform gaps in open air, an energy distribution is obtained using the online detection system. It shows that the x-ray emission is a continuous spectrum and the x rays of above 60 keV dominate in the detected energy distribution.
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29.40.-n Radiation detectors
85.60.Ha Photomultipliers; phototubes and photocathodes

Flux and energy analysis of species in hollow cathode magnetron ionized physical vapor deposition of copper

L. Wu, E. Ko, A. Dulkin, K. J. Park, S. Fields, K. Leeser, L. Meng, and D. N. Ruzic

Rev. Sci. Instrum. 81, 123502 (2010); http://dx.doi.org/10.1063/1.3504371 (8 pages) | Cited 1 time

Online Publication Date: 3 December 2010

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To meet the stringent requirements of interconnect metallization for sub-32 nm technologies, an unprecedented level of flux and energy control of film forming species has become necessary to further advance ionized physical vapor deposition technology. Such technology development mandates improvements in methods to quantify the metal ion fraction, the gas/metal ion ratio, and the associated ion energies in the total ion flux to the substrate. In this work, a novel method combining planar Langmuir probes, quartz crystal microbalance (QCM), and gridded energy analyzer (GEA) custom instrumentation is developed to estimate the plasma density and temperature as well as to measure the metal ion fraction and ion energy. The measurements were conducted in a Novellus Systems, Inc. Hollow Cathode Magnetron (HCMTM) physical vapor deposition source used for deposition of Cu seed layer for 65–130 nm technology nodes. The gridded energy analyzer was employed to measure ion flux and ion energy, which was compared to the collocated planar Langmuir probe data. The total ion-to-metal neutral ratio was determined by the QCM combined with GEA. The data collection technique and the corresponding analysis are discussed. The effect of concurrent resputtering during the deposition process on film thickness profile is also discussed.
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85.40.Ls Metallization, contacts, interconnects; device isolation
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
68.55.at Other materials
81.15.Cd Deposition by sputtering
85.40.Sz Deposition technology

The rotating wall machine: A device to study ideal and resistive magnetohydrodynamic stability under variable boundary conditions

C. Paz-Soldan, W. F. Bergerson, M. I. Brookhart, D. A. Hannum, R. Kendrick, G. Fiksel, and C. B. Forest

Rev. Sci. Instrum. 81, 123503 (2010); http://dx.doi.org/10.1063/1.3505487 (10 pages) | Cited 2 times

Online Publication Date: 7 December 2010

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The rotating wall machine, a basic plasma physics experimental facility, has been constructed to study the role of electromagnetic boundary conditions on current-driven ideal and resistive magnetohydrodynamic instabilities, including differentially rotating conducting walls. The device, a screw pinch magnetic geometry with line-tied ends, is described. The plasma is generated by an array of 19 plasma guns that not only produce high density plasmas but can also be independently biased to allow spatial and temporal control of the current profile. The design and mechanical performance of the rotating wall as well as diagnostic capabilities and internal probes are discussed. Measurements from typical quiescent discharges show the plasma to be high β ( ≤ p>2μ0/Bz2), flowing, and well collimated. Internal probe measurements show that the plasma current profile can be controlled by the plasma gun array.
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52.75.-d Plasma devices
52.70.Ds Electric and magnetic measurements
52.65.Kj Magnetohydrodynamic and fluid equation

Stray light analysis for the Thomson scattering diagnostic of the ETE Tokamak

L. A. Berni and B. F. C. Albuquerque

Rev. Sci. Instrum. 81, 123504 (2010); http://dx.doi.org/10.1063/1.3505485 (6 pages)

Online Publication Date: 14 December 2010

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Thomson scattering is a well-established diagnostic for measuring local electron temperature and density in fusion plasma, but this technique is particularly difficult to implement due to stray light that can easily mask the scattered signal from plasma. To mitigate this problem in the multipoint Thomson scattering system implemented at the ETE (Experimento Tokamak Esférico) a detailed stray light analysis was performed. The diagnostic system was simulated in ZEMAX software and scattering profiles of the mechanical parts were measured in the laboratory in order to have near realistic results. From simulation, it was possible to identify the main points that contribute to the stray signals and changes in the dump were implemented reducing the stray light signals up to 60 times.
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87.64.Cc Scattering of visible, uv, and infrared radiation
47.80.Fg Pressure and temperature measurements
06.30.Dr Mass and density

Diamagnetic flux measurement in Aditya tokamak

Sameer Kumar, Ratneshwar Jha, Praveen Lal, Chandresh Hansaliya, M. V. Gopalkrishna, Sanjay Kulkarni, and Kishore Mishra

Rev. Sci. Instrum. 81, 123505 (2010); http://dx.doi.org/10.1063/1.3514092 (7 pages)

Online Publication Date: 14 December 2010

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Measurements of diamagnetic flux in Aditya tokamak for different discharge conditions are reported for the first time. The measured diamagnetic flux in a typical discharge is less than 0.6 mWb and therefore it has required careful compensation for various kinds of pick-ups. The hardware and software compensations employed in this measurement are described. We introduce compensation of a pick-up due to plasma current of less than 20 kA in short duration discharges, in which plasma pressure gradient is supposed to be negligible. The flux measurement during radio frequency heating is also presented in order to validate compensation.
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52.55.Fa Tokamaks, spherical tokamaks
52.25.-b Plasma properties
52.70.-m Plasma diagnostic techniques and instrumentation
52.80.Pi High-frequency and RF discharges

Hard x-ray correlation analysis as a diagnostic tool for the measurement of magnetic turbulence in tokamaks

S. K. Saha, A. K. Hui, S. Chowdhury, Santwana Raychaudhuri, and D. Banik

Rev. Sci. Instrum. 81, 123506 (2010); http://dx.doi.org/10.1063/1.3516043 (6 pages)

Online Publication Date: 20 December 2010

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A diagnostic has been developed for the measurement and characterization of the magnetic turbulence occurring in the core region of a tokamak. A specially shielded detector looking in the tangential direction has been employed to measure the thin target bremsstrahlung from the core plasma. The thick target bremsstrahlung from the limiter is also recorded at the same time. Auto- and cross-correlation analyses have been shown to yield, respectively, the stochasticity of the magnetic fluctuations in the core region and the consequent diffusion coefficient of the nonthermal electrons. The measured stochasticity bears a relationship with the diffusion coefficient. Data obtained from internal magnetic probes corroborate the above trend but the hard x-ray measurement data are shown to be more reliable than those obtained from magnetic probes.
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52.55.Fa Tokamaks, spherical tokamaks
28.52.Fa Materials
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.70.La X-ray and γ-ray measurements
52.35.Ra Plasma turbulence

Development of a digital integrator for the KSTAR device

Seong-Heon Seo, Andreas Werner, and M. Marquardt

Rev. Sci. Instrum. 81, 123507 (2010); http://dx.doi.org/10.1063/1.3519303 (4 pages) | Cited 1 time

Online Publication Date: 21 December 2010

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The development of an integrator for magnetic diagnostics becomes more important as the pulse length of fusion devices gets longer and longer, especially for present-day superconducting fusion devices. A small offset in the signal can cause a significant drift in the integrator output for long pulse experiments. A lock-in amplifying digital integrator has been developed for Wendelstein 7-X (W7-X). It succeeds in suppressing the drift to a low value but requires about 100 ms for data processing. To shorten the data processing time, a Field Programmable Gate Array (FPGA) built in the digitizer is utilized. Since there is no need to transfer the data to an external computer, the integration can be done in real time. The microprocessor built in the digitizer directly transfers the data integrated in the internal FPGA into the reflective memory installed in the same compact Peripheral Component Interconnect chassis. These features result in a very compact system design. The design and the preliminary results of the digital integrator will be presented.
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84.30.Sk Pulse and digital circuits

Design and implementation of a full profile sub-cm ruby laser based Thomson scattering system for MAST

T. O’Gorman, P. J. Mc Carthy, S. Prunty, M. J. Walsh, M. R. Dunstan, R. B. Huxford, G. Naylor, Emmanuel Maguet, R. Scannell, and S. Shibaev

Rev. Sci. Instrum. 81, 123508 (2010); http://dx.doi.org/10.1063/1.3511556 (7 pages)

Online Publication Date: 22 December 2010

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A major upgrade to the ruby Thomson scattering (TS) system has been designed and implemented on the Mega-ampere spherical tokamak (MAST). MAST is equipped with two TS systems, a Nd:YAG laser system and a ruby laser system. Apart from common collection optics each system provides independent measurements of the electron temperature and density profile. This paper focuses on the recent upgrades to the ruby TS system. The upgraded ruby TS system measures 512 points across the major radius of the MAST vessel. The ruby laser can deliver one 10 J 40 ns pulse at 1 Hz or two 5 J pulses separated by 100–800 μs. The Thomson scattered light is collected at F/15 over 1.4 m. This system can resolve small (7 mm) structures at 200 points in both the electron temperature and density channels at high optical contrast; ∼50% modulated transfer function. The system is fully automated for each MAST discharge and requires little adjustment. The estimated measurement error for a 7 mm radial point is <4% of Te and <3% of ne in the range of 40 eV to 2 keV, for a density of ne = 2×1019 m−3. The photon statistics at lower density can be increased by binning in the radial direction as desired. A new intensified CCD camera design allows the ruby TS system to take two snapshots separated with a minimum time of 230 μs. This is exploited to measure two density and temperature profiles or to measure the plasma background light.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
52.55.Fa Tokamaks, spherical tokamaks
42.79.Pw Imaging detectors and sensors
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Impurities removal by laser blow-off from in-vacuum optical surfaces on RFX-mod experiment

A. Alfier, S. Barison, A. Fassina, S. Fiameni, L. Giudicotti, R. Pasqualotto, V. Cervaro, and L. Lotto

Rev. Sci. Instrum. 81, 123509 (2010); http://dx.doi.org/10.1063/1.3511557 (10 pages)

Online Publication Date: 22 December 2010

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An in situ window cleaning system by laser blow-off through optical fiber has been developed on the basis of a feasibility study previously presented. The beam generated by a Q-switched Nd:YAG laser is launched in a vacuum box into a high damage threshold optical fiber through a lens. The fiber output is focused on the impurities-coated surface of a vacuum window exposed to the plasma of the RFX-mod experiment, and it is remotely controlled with an xy motion system to scan the entire surface. We first investigate the energy density threshold necessary to ablate the deposited impurity substrate on removed dirty windows: above threshold, a single laser pulse recovers ∼95% of the window transmission before its exposure to the plasma, while below it the efficiency of the cleaning process is too poor. The system so conceived was then used to clean the three collection windows of the Main Thomson scattering diagnostic on RFX-mod. We also present results obtained applying the same technique to the SiO-protected Al mirror used for the Zeff diagnostic: an energy threshold for efficient impurity removal without mirror damage is first identified, then ablation tests are executed and analyzed in terms of recovered reflectivity. The SIMS technique is used both with windows and mirror to study the composition of surfaces before and after the ablation
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52.25.Vy Impurities in plasmas
52.38.Mf Laser ablation
52.77.Dq Plasma-based ion implantation and deposition
52.55.Fa Tokamaks, spherical tokamaks
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
back to top Microscopy and Imaging

An alternative flat scanner and micropositioning method for scanning probe microscope

Wei Cai, Guangyi Shang, Yusheng Zhou, Ping Xu, and Junen Yao

Rev. Sci. Instrum. 81, 123701 (2010); http://dx.doi.org/10.1063/1.3505781 (5 pages)

Online Publication Date: 8 December 2010

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An alternative flat scanner used for combining a scanning probe microscope with an inverted optical microscope is presented. The scanner has a novel structure basically consisting of eight identical piezoelectric tubes, metal flexure beams, and one sample mount. Because of the specially designed structure, the scanner is able to carry a sample of more than 120 g during imaging. By applying voltages of ±150 V, scanning range of more than 30 μm in three dimensions can be achieved. To improve the reliability of the stick-slip motion, a new method for sample micropositioning is proposed by applying a pulsed voltage to the piezotubes to produce a motion in the z-axis. Reliable translation of the sample has been thus accomplished with the step length from ∼700 nm to 9 μm over a range of several millimeters. A homemade scanning probe microscope–inverted optical microscope system based on the scanner is described. Experimental results obtained with the system are shown.
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42.79.Ls Scanners, image intensifiers, and image converters
07.60.Pb Conventional optical microscopes
07.79.-v Scanning probe microscopes and components
06.60.Sx Positioning and alignment; manipulating, remote handling

Ferrule-top atomic force microscope

D. Chavan, G. Gruca, S. de Man, M. Slaman, J. H. Rector, K. Heeck, and D. Iannuzzi

Rev. Sci. Instrum. 81, 123702 (2010); http://dx.doi.org/10.1063/1.3516044 (5 pages) | Cited 2 times

Online Publication Date: 16 December 2010

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Ferrule-top cantilevers are a new generation of all-optical miniaturized devices for utilization in liquids, harsh environments, and small volumes [G. Gruca et al., Meas. Sci. Technol. 21, 094033 (2010)]. They are obtained by carving the end of a ferruled fiber in the form of a mechanical beam. Light coupled from the opposite side of the fiber allows detection of cantilever deflections. In this paper, we demonstrate that ferrule-top cantilevers can be used to develop ultra compact AFMs for contact mode imaging in air and in liquids with sensitivity comparable to that of commercial AFMs. The probes do not require any alignment procedure and are easy to handle, favoring applications also outside research laboratories.
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07.79.Lh Atomic force microscopes

Effect of tip shape on line edge roughness measurement based on atomic force microscopy

Ning Li, Fei Wang, and Xuezeng Zhao

Rev. Sci. Instrum. 81, 123703 (2010); http://dx.doi.org/10.1063/1.3518973 (3 pages)

Online Publication Date: 20 December 2010

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Atomic force microscopy (AFM) is an important tool in line edge roughness (LER) measurements, where accuracy for line edge identification is influenced by the shape of the tip. In this article, the effect of tip shape on LER measurement based on AFM is studied theoretically. The formulas for calculating the distance between the measured and actual line edge of the sample are presented. The effects of the three kinds of tips with different shapes are experimentally compared for validation. Suggestions on how to reduce measuring error caused by tip shape are also given.
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07.79.Lh Atomic force microscopes
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
68.37.Ps Atomic force microscopy (AFM)
06.20.Dk Measurement and error theory

Wavefield characterization of nearly diffraction-limited focused hard x-ray beam with size less than 10 nm

Takashi Kimura, Hidekazu Mimura, Soichiro Handa, Hirokatsu Yumoto, Hikaru Yokoyama, Shota Imai, Satoshi Matsuyama, Yasuhisa Sano, Kenji Tamasaku, Yoshiki Komura, Yoshinori Nishino, Makina Yabashi, Tetsuya Ishikawa, and Kazuto Yamauchi

Rev. Sci. Instrum. 81, 123704 (2010); http://dx.doi.org/10.1063/1.3509384 (5 pages)

Online Publication Date: 29 December 2010

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In situ wavefront compensation is a promising method to realize a focus size of only a few nanometers for x-ray beams. However, precise compensation requires evaluation of the wavefront with an accuracy much shorter than the wavelength. Here, we characterized a one-dimensionally focused beam with a width of 7 nm at 20 keV using a multilayer mirror. We demonstrate that the wavefront can be determined precisely from multiple intensity profiles measured around the beamwaist. We compare the phase profiles recovered from intensity profiles measured under the same mirror condition but with three different aperture sizes and find that the accuracy of phase retrieval is as small as λ/12.
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07.85.-m X- and γ-ray instruments

Nanoscale potential measurements in liquid by frequency modulation atomic force microscopy

Naritaka Kobayashi, Hitoshi Asakawa, and Takeshi Fukuma

Rev. Sci. Instrum. 81, 123705 (2010); http://dx.doi.org/10.1063/1.3514148 (4 pages) | Cited 2 times

Online Publication Date: 29 December 2010

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We have developed a method for local potential measurements in liquid using frequency modulation atomic force microscopy. In this method, local potential is calculated from the first and second harmonic vibrations of a cantilever induced by applying an ac bias voltage between a tip and a sample. The use of an ac bias voltage with a relatively high frequency prevents uncontrolled electrochemical reactions and redistribution of ions and water. The nanoscale resolution of the method is demonstrated by imaging potential distribution of a dodecylamine thin film deposited on a graphite surface in 1 mM NaCl solution.
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07.79.Lh Atomic force microscopes

The effect of exit beam phase aberrations on parallel beam coherent x-ray reconstructions

S. O. Hruszkewycz, R. Harder, X. Xiao, and P. H. Fuoss

Rev. Sci. Instrum. 81, 123706 (2010); http://dx.doi.org/10.1063/1.3514085 (5 pages)

Online Publication Date: 29 December 2010

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Diffraction artifacts from imperfect x-ray windows near the sample are an important consideration in the design of coherent x-ray diffraction measurements. In this study, we used simulated and experimental diffraction patterns in two and three dimensions to explore the effect of phase imperfections in a beryllium window (such as a void or inclusion) on the convergence behavior of phasing algorithms and on the ultimate reconstruction. A predictive relationship between beam wavelength, sample size, and window position was derived to explain the dependence of reconstruction quality on beryllium defect size. Defects corresponding to this prediction cause the most damage to the sample exit wave and induce signature error oscillations during phasing that can be used as a fingerprint of experimental x-ray window artifacts. The relationship between x-ray window imperfection size and coherent x-ray diffractive imaging reconstruction quality explored in this work can play an important role in designing high-resolution in situ coherent imaging instrumentation and will help interpret the phasing behavior of coherent diffraction measured in these in situ environments.
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07.85.-m X- and γ-ray instruments
42.30.Wb Image reconstruction; tomography
42.30.Va Image forming and processing
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