Rev. Sci. Instrum. - Review of Scientific Instruments

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Free-electron-laser-based biophysical and biomedical instrumentation

G. S. Edwards, R. H. Austin, F. E. Carroll, M. L. Copeland, M. E. Couprie, W. E. Gabella, R. F. Haglund, B. A. Hooper, M. S. Hutson, E. D. Jansen, K. M. Joos, D. P. Kiehart, I. Lindau, J. Miao, H. S. Pratisto, et al.

Rev. Sci. Instrum. 74, 3207 (2003); http://dx.doi.org/10.1063/1.1584078 (39 pages) | Cited 33 times

Online Publication Date: 24 June 2003

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A survey of biophysical and biomedical applications of free-electron lasers (FELs) is presented. FELs are pulsed light sources, collectively operating from the microwave through the x-ray range. This accelerator-based technology spans gaps in wavelength, pulse structure, and optical power left by conventional sources. FELs are continuously tunable and can produce high-average and high-peak power. Collectively, FEL pulses range from quasicontinuous to subpicosecond, in some cases with complex superpulse structures. Any given FEL, however, has a more restricted set of operational parameters. FELs with high-peak and high-average power are enabling biophysical and biomedical investigations of infrared tissue ablation. A midinfrared FEL has been upgraded to meet the standards of a medical laser and is serving as a surgical tool in ophthalmology and human neurosurgery. The ultrashort pulses produced by infrared or ultraviolet FELs are useful for biophysical investigations, both one-color time-resolved spectroscopy and when coupled with other light sources, for two-color time-resolved spectroscopy. FELs are being used to drive soft ionization processes in mass spectrometry. Certain FELs have high repetition rates that are beneficial for some biophysical and biomedical applications, but confound research for other applications. Infrared FELs have been used as sources for inverse Compton scattering to produce a pulsed, tunable, monochromatic x-ray source for medical imaging and structural biology. FEL research and FEL applications research have allowed the specification of spin-off technologies. On the horizon is the next generation of FELs, which is aimed at producing ultrashort, tunable x rays by self-amplified spontaneous emission with potential applications in biology. © 2003 American Institute of Physics.

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42.62.Be	Biological and medical applications
41.60.Cr	Free-electron lasers
87.80.-y	Biophysical techniques (research methods)
87.63.L-	Visual imaging
87.64.-t	Spectroscopic and microscopic techniques in biophysics and medical physics
87.59.-e	X-ray imaging
01.30.Rr	Surveys and tutorial papers; resource letters
42.65.Re	Ultrafast processes; optical pulse generation and pulse compression

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Extending the bandwidth of optical-tweezers interferometry

Erwin J. G. Peterman, Meindert A. van Dijk, Lukas C. Kapitein, and Christoph F. Schmidt

Rev. Sci. Instrum. 74, 3246 (2003); http://dx.doi.org/10.1063/1.1584085 (4 pages) | Cited 26 times

Online Publication Date: 24 June 2003

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High-resolution force and displacement measurements by laser interferometry, combined with optical tweezers in a light microscope, are frequently based on near-infrared lasers. With common silicon PN photodiodes the bandwidth of detection was found to be limited to about 5 kHz at 1064 nm laser wavelength. This is caused by the fact that silicon becomes increasingly transparent for wavelengths approaching the band gap energy, leading to the generation of charge carriers outside the depletion zone of the diode for wavelengths longer than about 850 nm. These charges have to diffuse before they can contribute to the photocurrent. In this technical note we demonstrate experimentally that the detection bandwidth can be extended to at least 100 kHz, either by using wavelengths below 850 nm, or by using different detectors at longer wavelengths: InGaAs PIN photodiodes or special-purpose fully depleted p-type silicon photodiodes. We measured the well-known power spectral density of the Brownian motion of micron-sized beads in optical tweezers and show that the optimized detectors do not cause attenuation within experimental noise. They are indeed linear enough to detect the weak inertial effects of the watery solvent on the power spectral density of the Brownian motion. © 2003 American Institute of Physics.

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07.60.Ly	Interferometers
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy
06.30.Bp	Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.10.Pz	Instruments for strain, force, and torque
85.60.Dw	Photodiodes; phototransistors; photoresistors

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Instrument and method for measuring second-order nonlinear optical tensors

Darrell J. Armstrong, Michael V. Pack, and Arlee V. Smith

Rev. Sci. Instrum. 74, 3250 (2003); http://dx.doi.org/10.1063/1.1581393 (8 pages) | Cited 2 times

Online Publication Date: 24 June 2003

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We describe an apparatus for measuring the second-order nonlinear tensor of crystals based on the measurement technique of separated-beam, nonphase matched, second-harmonic generation. This method is an improvement over traditional methods based on the analysis of Maker fringes. We illustrate our measurement technique and show some typical data for crystals of potassium dihydrogen phosphate and potassium niobate. We intend to maintain our apparatus to encourage rapid and complete characterization of new nonlinear crystals, and also to improve the nonlinear tensor data base for established nonlinear crystals. © 2003 American Institute of Physics.

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42.70.Mp	Nonlinear optical crystals
07.60.-j	Optical instruments and equipment
42.65.Ky	Frequency conversion; harmonic generation, including higher-order harmonic generation
06.20.Dk	Measurement and error theory
42.62.Eh	Metrological applications; optical frequency synthesizers for precision spectroscopy

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X-ray detection by an on-chip coil integrated superconducting tunnel junction

Keisuke Maehata, Tetsuya Ariyoshi, Akihito Hora, Naoto Mori, Kenji Ishibashi, Tohru Taino, Hiromi Sato, Hiroshi Nakagawa, Katsuya Kikuchi, Masahiro Aoyagi, Hiroshi Akoh, and Yuzuru Matsumoto

Rev. Sci. Instrum. 74, 3258 (2003); http://dx.doi.org/10.1063/1.1578155 (5 pages)

Online Publication Date: 24 June 2003

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An on-chip coil integrated superconducting tunnel junction (OC²-STJ) was used for x-ray detection by applying the magnetic field produced by a superconducting microstrip coil integrated into the superconducting tunnel junction chip. The fabricated OC²-STJ chip was mounted in a cooling capsule attached to the mixing chamber of a compact ³He–⁴He dilution refrigerator. The OC²-STJ chip was held at a constant temperature in the capsule against the Joule heat generated in the current feed line of the strip coil during the detection operation. Stable operation of the OC²-STJ was demonstrated without using the usual external electromagnets. © 2003 American Institute of Physics.

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07.85.Fv	X- and γ-ray sources, mirrors, gratings, and detectors
29.40.Wk	Solid-state detectors
85.25.Oj	Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)

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Single photon detector fabricated in a complementary metal–oxide–semiconductor high-voltage technology

A. Rochas, M. Gani, B. Furrer, P. A. Besse, R. S. Popovic, G. Ribordy, and N. Gisin

Rev. Sci. Instrum. 74, 3263 (2003); http://dx.doi.org/10.1063/1.1584083 (8 pages) | Cited 29 times

Online Publication Date: 24 June 2003

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In this article, a fully integrated single photon detector including a silicon avalanche photodiode and a quenching circuit is presented. The low doping concentrations, inherent to the complementary metal–oxide–semiconductor (CMOS) high-voltage technology used, favor the absorption of red and infrared photons at the depletion region. The detection probability rapidly increases with excess bias voltages up to 5 V. At this value, the detection probability is larger than 20% between 420 nm and 620 nm and still 7% at 750 nm. The photosensitive area is 7 μm in diameter. Cointegration of the diode and the quenching resistor allows a drastic reduction of parasitic capacitances. Though passively quenched, the single photon detector exhibits a dead time as low as 75 ns. The avalanche current is quickly quenched in less than 3.5 ns leading to a relatively low afterpulsing probability of 7.5% at 5 V excess bias voltage. The afterpulses are located in the first microseconds after the avalanche event. At room temperature, the dark count rate is about 900 Hz at 5 V excess bias voltage. Cooling of the sensor below 0 °C is of minor interest since the tunneling process becomes dominant. A remarkably short timing resolution has been obtained with values lower than 50 ps for excess bias voltage higher than 5 V. The industrial CMOS high-voltage technology used guarantees low production costs. In applications where the light can be focused on the small photosensitive area using a high magnification objective, the fabricated single photon avalanche photodiode overcomes the features of standard photomultiplier tubes. The CMOS integration opens the way to the fabrication of an extremely compact array. The design can be easily fitted to a dedicated application. Furthermore, by using an industrial CMOS process, the cointegration of data processing electronics to produce a smart sensor would be a feasible task. © 2003 American Institute of Physics.

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85.60.Gz	Photodetectors (including infrared and CCD detectors)
85.60.Dw	Photodiodes; phototransistors; photoresistors
85.40.Qx	Microcircuit quality, noise, performance, and failure analysis
07.07.Df	Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

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Feasibility of a synchrotron storage ring for neutral polar molecules

Hiroshi Nishimura, Glen Lambertson, Juris G. Kalnins, and Harvey Gould

Rev. Sci. Instrum. 74, 3271 (2003); http://dx.doi.org/10.1063/1.1578159 (8 pages) | Cited 5 times

Online Publication Date: 24 June 2003

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Using calculations and mathematical modeling, we demonstrate the feasibility of constructing a synchrotron storage ring for neutral polar molecules. The lattice is a racetrack type 3.6 m in circumference consisting of two 180° arcs, six bunchers, and two long straight sections. Each straight section contains two triplet focusing lenses and space for beam injection and experiments. The design also includes a matched injector and a linear decelerator. Up to 60 bunches can be loaded and simultaneously stored in the ring. The molecules are injected at 90 m/s but the velocity of the circulating beam can be decelerated to 60 m/s after injection. The modeling uses deuterated ammonia (¹⁴N²H₃) molecules in a weak-field seeking state. A beam that survives 400 turns (15 s), has horizontal and vertical acceptances of 35 and 70 mm mrad, respectively, and an energy acceptance of ±2%. © 2003 American Institute of Physics.

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37.20.+j	Atomic and molecular beam sources and techniques
29.20.db	Storage rings and colliders
29.20.dk	Synchrotrons

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Characterization of a high-density electron-cyclotron resonance plasma source operating in nitrogen

E. I. Toader, A. Fredriksen, and A. Aanesland

Rev. Sci. Instrum. 74, 3279 (2003); http://dx.doi.org/10.1063/1.1578154 (5 pages) | Cited 4 times

Online Publication Date: 24 June 2003

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Parametric characterization of a low-pressure and high-density electron-cyclotron resonance plasma source operating in nitrogen over a range of low-pressure 10⁻³–10⁻⁴ mbar, dissipated power 500 W, and magnetic field intensity 200–400 G, is presented. Internal parameters like electron energy distribution function, plasma density, electron temperature, plasma potential, and floating potential, were measured using a compensated Langmuir probe. The radial variation of internal parameters evidences two discharge modes, that is, a constricted mode for low-magnetic field values and a diffuse mode for high-magnetic field values. The electron energy distribution function is Maxwellian within the energy range of 0–15 eV and presents a structure with two prominent dips around 3.5 and 9.0 eV. The form of the structure and the position of the dips do not change significantly with the radial position or by changing the external parameters. © 2003 American Institute of Physics.

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52.50.Dg	Plasma sources
52.70.Ds	Electric and magnetic measurements

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Development and applications of time-bunched and velocity-selected positron beams

J. P. Merrison, M. Charlton, P. Aggerholm, H. Knudsen, D. P. van der Werf, J. Clarke, and M. R. Poulsen

Rev. Sci. Instrum. 74, 3284 (2003); http://dx.doi.org/10.1063/1.1581390 (9 pages) | Cited 2 times

Online Publication Date: 24 June 2003

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We describe the development of an instrument for the production of low energy positron beams that are bunched in time, and the use of a velocity selection device. The bunching unit was constructed from forty seven separate elements, coupled in series in a capacitor chain to reduce the delay time for propagation of the applied voltage pulse along the electrode system and to facilitate operation at frequencies up to 100 kHz. A parabolic potential distribution for time focusing was used. Tests with a dc positron beam produced from a radioactive source are described, together with measurements in which the buncher was used to compress positron pulses produced from an electron accelerator-based beam. Computer simulations of particle trajectories in the buncher have been performed resulting in a detailed evaluation of the factors that govern and limit the time resolution of the instrument. A sector magnet used to velocity-select intermediate energy positrons is described and its performance discussed. © 2003 American Institute of Physics.

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41.75.Fr	Electron and positron beams
07.77.Ka	Charged-particle beam sources and detectors
41.85.Lc	Particle beam focusing and bending magnets, wiggler magnets, and quadrupoles

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Thin tape target driver for laser ion accelerator

Takuya Nayuki, Yuji Oishi, Takashi Fujii, Koshichi Nemoto, Tsutomu Kayoiji, Yasuaki Okano, Yoichiro Hironaka, Kazutaka G. Nakamura, Ken-ichi Kondo, and Ken-ichi Ueda

Rev. Sci. Instrum. 74, 3293 (2003); http://dx.doi.org/10.1063/1.1578156 (4 pages) | Cited 31 times

Online Publication Date: 24 June 2003

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A thin tape target driver for laser ion acceleration was developed. The driver can move a copper tape of 5 μm thickness with a positioning reproducibility of less than 30 μm (peak to valley), which is sufficient for a laser irradiation target. Using this tape target and laser pulses of energy 350 mJ and duration 60 fs, protons of energies of over 1 MeV were accelerated in the forward direction. © 2003 American Institute of Physics.

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29.20.-c	Accelerators
41.75.Jv	Laser-driven acceleration
42.62.-b	Laser applications

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Development of movable mask system to cope with high beam current

Y. Suetsugu, K. Shibata, T. Sanami, T. Kageyama, and Y. Takeuchi

Rev. Sci. Instrum. 74, 3297 (2003); http://dx.doi.org/10.1063/1.1583860 (8 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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The KEK B factory (KEKB), a high current electron-positron collider, has a movable mask (or collimator) system to reduce the background noise in the BELLE detector coming from spent particles. The early movable masks, however, had severe problems of heating, arcing, and vacuum leaks over the stored beam current of several hundred mA. The cause is intense trapped higher order modes (HOMs) excited at the mask head, where the cross section of the beam chamber changed drastically. The mask head, made of copper–tungsten alloy or pure copper, was frequently damaged by hitting of the high energy beam at the same time. Since the problems of the mask were revealed, several kinds of improved masks have been designed employing rf technologies in dealing with the HOM and installed to the ring step by step. Much progress has come from adopting a trapped-mode free structure, where the mask was a bent chamber itself. Recently the further improved mask with a reduced HOM design or HOM dampers was developed to suppress the heating of vacuum components near the mask due to the HOM traveling from the mask. To avoid damage to the mask head, on the other hand, a titanium mask head was tried. The latest masks are working as expected now at the stored beam current of 1.5 A. Presented are the problems and experiences on the movable mask system for the KEKB, which are characteristic of and common in a high intensity accelerator. © 2003 American Institute of Physics.

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29.27.Eg	Beam handling; beam transport
29.20.db	Storage rings and colliders

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Transport beam line for ultraslow monoenergetic antiprotons

K. Yoshiki Franzen, N. Kuroda, H. A. Torii, M. Hori, Z. Wang, H. Higaki, S. Yoneda, B. Juhász, D. Horváth, A. Mohri, K. Komaki, and Y. Yamazaki

Rev. Sci. Instrum. 74, 3305 (2003); http://dx.doi.org/10.1063/1.1578160 (7 pages) | Cited 12 times

Online Publication Date: 24 June 2003

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A beam line for the transportation of slow antiprotons from a multiring electrode trap to an experimental chamber is described. The beam line is equipped with a three-stage differential pumping system in order to maintain a pressure lower than 1×10⁻¹² Torr in the trap region while simultaneously having a pressure of around 1×10⁻⁶ Torr in the chamber. Tests have shown that 10⁵ positive ions per trapping cycle were successfully extracted at 250 eV from the trap positioned in a superconducting solenoid. The ions were then further transported through three small apertures to the target area located 3.5 m downstream of the trap. Results from the first delivery of a 250 eV antiproton beam are described. © 2003 American Institute of Physics.

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29.27.Eg

Beam handling; beam transport

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Vacuum bench for the characterization of thermoionization ion sources

C. Guillermier, C. P. Lechene, J. Hill, and F. Hillion

Rev. Sci. Instrum. 74, 3312 (2003); http://dx.doi.org/10.1063/1.1584086 (5 pages) | Cited 1 time

Online Publication Date: 24 June 2003

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We have designed a vacuum bench to study the parameters of thermoionization sources with the ultimate goal of obtaining high spatial resolution for biomedical applications of secondary ion mass spectrometry. In the bench, the source ionizer can be directly heated with an electron gun positioned perpendicular to the axis of the ion beam and focused with an optical system including slit lenses and a magnetic sector. The source cross over diameter is measured by forming the image of the source using an Einzel lens at a 1×magnification. The ion beam current is measured in a Faraday cup placed after a movable diaphragm. The temperature of the diverse elements of the ionizer assembly is measured through a mirror with a micropyrometer. Using the vacuum bench with a cesium carbonate source, we measured a 35 μm minimum cross over size, and we calculated a 400 A/cm²/srmaximum brightness. We obtained an intense cesium ion beam when heating the ionizer with the electron gun. The vacuum bench will be used to compare the effect of the heating mode of the ionizer (i.e., indirect by filament electron emission or direct by electron beam) on the brightness of the cesium source, and to develop a thermoionization iodine negative ion source. © 2003 American Institute of Physics.

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87.64.-t	Spectroscopic and microscopic techniques in biophysics and medical physics
82.80.Ms	Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
29.25.Ni	Ion sources: positive and negative
07.77.Ka	Charged-particle beam sources and detectors

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Field-ionization electron detector at low temperature of 10 mK range

M. Shibata, M. Tada, Y. Kishimoto, K. Kominato, T. Haseyama, I. Ogawa, S. Matsuki, S. Yamada, H. Funahashi, and K. Yamamoto

Rev. Sci. Instrum. 74, 3317 (2003); http://dx.doi.org/10.1063/1.1582392 (7 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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Selective field-ionization electron detector at low temperature of 10 mK range was developed with a channel electron multiplier. The field-ionization electrode system is attached to the bottom plate of the mixing chamber of a dilution refrigerator and ionized electrons are transported to a channel electron multiplier at the 1 K temperature pumping stage through a series of ring focusing electrodes. The channel electron multiplier is heated up to more than 20 K with a heating coil to maintain its long-term operational conditions, while keeping its environment temperature to 1 K. Rydberg states in Rb with 80≲n≲150 were successfully field ionized and detected with this system at the long-term operating temperature of 12–15 mK. © 2003 American Institute of Physics.

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85.60.Ha	Photomultipliers; phototubes and photocathodes
29.40.-n	Radiation detectors

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A fiber–optic interferometer for in situ measurements of plasma number density in pulsed-power applications

L. M. Smith, D. R. Keefer, and N. W. Wright

Rev. Sci. Instrum. 74, 3324 (2003); http://dx.doi.org/10.1063/1.1582389 (5 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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A fiber–optic-based interferometer has been designed, constructed, and applied to plasma measurements in pulsed-power systems. The beam from a 1310 nm solid-state diode laser is coupled into a single-mode fiber and split into two beams, one of which was passed through an acousto-optic modulator to frequency shift the light. Both beams travel through approximately 30 m of fiber, with the probe volume consisting of a short air or vacuum gap in the probe beam fiber where the light is collimated and collected by lenses. The beams are then recombined on a photodiode, producing a time-varying sinusoidal intensity signal that is phase modulated with the presence of a plasma in the probe volume. This configuration allows for remote measurements of plasma electron number density, and is robust with respect to vibration in the plasma source and electromagnetic interference. Tests indicate that phase measurement accuracies of ±0.045 rad corresponding to number density accuracies of ±1.2×10¹⁹ m⁻² at 1310 nm are achievable with this device. A description of this interferometer, including refinements needed to achieve these accuracies, is presented along with the results of tests performed on a coaxial plasma gun. © 2003 American Institute of Physics.

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42.81.Pa	Sensors, gyros
52.70.Kz	Optical (ultraviolet, visible, infrared) measurements
07.60.Ly	Interferometers
84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables

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Effect of accelerating electrode rotation on ion beam optics

Elizabeth Surrey

Rev. Sci. Instrum. 74, 3329 (2003); http://dx.doi.org/10.1063/1.1578153 (6 pages)

Online Publication Date: 24 June 2003

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The effect of a rotation of the electrode used to accelerate a positive ion beam is treated analytically for the Joint European Torus (JET) Positive Ion Neutral Injector (PINI) tetrode accelerator. The rotation is taken to be about an axis in the plane of the electrode and perpendicular to the beam axis, so the effect is that of a tilt in the alignment of the affected electrode. The effect of such a tilt in either of the two multiaperture accelerating electrodes is to introduce an additional steering of the beam, the magnitude of which depends upon the ratio of the potentials across the first and second accelerating gaps and the position of the beamlet with respect to the tilt axis. The direction of the steering is dependent upon which electrode is displaced. Steering angles of the order 10 mrad can be generated by this effect, which is significant compared to the alignment precision required from high power neutral injectors such as those on JET. The presence of a grid rotation also affects the total perveance of a multiaperture system and this can be used to obtain information on the position of the tilt axis. Typical values are calculated for the JET PINI geometry and compared to observation.

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29.27.Ac	Beam injection and extraction
41.75.Ak	Positive-ion beams
41.85.Ar	Particle beam extraction, beam injection

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Prescription for density profile reconstruction using a heavy ion beam probe

A. Fujisawa, M. Kitazawa, A. Shimizu, S. Ohshima, and H. Iguchi

Rev. Sci. Instrum. 74, 3335 (2003); http://dx.doi.org/10.1063/1.1581360 (6 pages) | Cited 4 times

Online Publication Date: 24 June 2003

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This article presents a method for density profile reconstruction using a heavy ion beam probe. A model calculation is performed to demonstrate the feasibility of the proposed method. The possibility to infer the density profile widely extends the applicability of the heavy ion beam probe by providing fine structural measurements of density profile that is, in principle, continuous in space, with a high temporal resolution of milliseconds. © 2003 American Institute of Physics.

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52.25.-b	Plasma properties
52.70.Nc	Particle measurements

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A computerized Langmuir probe system

L. S. Pilling, E. L. Bydder, and D. A. Carnegie

Rev. Sci. Instrum. 74, 3341 (2003); http://dx.doi.org/10.1063/1.1581362 (6 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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For low pressure plasmas it is important to record entire single or double Langmuir probe characteristics accurately. For plasmas with a depleted high energy tail, the accuracy of the recorded ion current plays a critical role in determining the electron temperature. Even for high density Maxwellian distributions, it is necessary to accurately model the ion current to obtain the correct electron density. Since the electron and ion current saturation values are, at best, orders of magnitude apart, a single current sensing resistor cannot provide the required resolution to accurately record these values. We present an automated, personal computer based data acquisition system for the determination of fundamental plasma properties in low pressure plasmas. The system is designed for single and double Langmuir probes, whose characteristics can be recorded over a bias voltage range of ±70 V with 12 bit resolution. The current flowing through the probes can be recorded within the range of 5 nA–100 mA. The use of a transimpedance amplifier for current sensing eliminates the requirement for traditional current sensing resistors and hence the need to correct the raw data. The large current recording range is realized through the use of a real time gain switching system in the negative feedback loop of the transimpedance amplifier. © 2003 American Institute of Physics.

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52.70.Ds	Electric and magnetic measurements
52.25.Fi	Transport properties
52.25.-b	Plasma properties
07.05.Hd	Data acquisition: hardware and software
07.05.Dz	Control systems

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Dehong Hu, Miodrag Micic, Nicholas Klymyshyn, Yung Doug Suh, and H. Peter Lu

Rev. Sci. Instrum. 74, 3347 (2003); http://dx.doi.org/10.1063/1.1581359 (9 pages) | Cited 17 times

Online Publication Date: 24 June 2003

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A near-field optical imaging approach is demonstrated for simultaneous topographic and spectroscopic imaging with spatial resolution beyond the optical diffraction limit. The method combines metallic-tip-based tapping-mode atomic force microscopy (AFM) with fluorescence lifetime imaging microscopy (FLIM). The AFM metallic tip was formed by sputter coating a Si tapping mode tip with Au, in a way that forms a globular tip apex. Such tip apex generates high local electric field enhancement under laser illumination, which provides a strong electric-field interaction between the AFM tip and the fluorescent molecules under the tip. The tip perturbation of fluorescence gives the fluorescence lifetime changes that provide the AFM–FLIM imaging contrast. A finite element method simulation was used to further evaluate the electric near-field enhancement and electric field distribution originating from the metallic Au-coated AFM tapping-mode tip. We have demonstrated that spatially mapping the change in fluorescence lifetime and intensity is a promising approach to spectroscopic imaging at an AFM spatial resolution typically defined by the apex diameter of the AFM tips. The globular Au-coated AFM tip not only gives adequate spatial AFM tapping-mode imaging spatial resolution but also is “environmentally friendly” to soft samples, such as polymeric dye-labeled nanospheres and even biological specimens such as POPO-3 labeled DNA. © 2003 American Institute of Physics.

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07.79.Fc	Near-field scanning optical microscopes
87.64.Dz	Scanning tunneling and atomic force microscopy
87.64.M-	Optical microscopy

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Thermal microstrains measured by atomic force microscopy

F. Avilés, O. Ceh, and A. I. Oliva

Rev. Sci. Instrum. 74, 3356 (2003); http://dx.doi.org/10.1063/1.1578704 (6 pages) | Cited 4 times

Online Publication Date: 24 June 2003

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Microdeformations observed in atomic force microscopy (AFM) images on the surface of metallic films when an electrical current (dc) flows through the film were analyzed on a film–substrate system. The electrical current flow causes an increase in temperature on the thin film and a step in the AFM topography while imaging. Experiments realized with AFM explain the nature of such a step and allow one to quantify these microdeformations. Theoretical bending models mainly derived from modifications of the Stoney equation support our experimental results. Theoretical predictions show reasonable agreement with AFM measurements, and demonstrate that the major contribution to the observed deformation step (about 90%) is due to the thermal bending effect of the AFM cantilever. The remaining deformation is due to the nature of bimaterial effects in the film–substrate system and thermal expansion of the substrate, with the expansion of the film being negligible. The possibility of electric and magnetic effects in the AFM cantilever (due to current flow through the film) is also discussed. The existence of a strong thermal effect on the AFM cantilever is outlined. Hence, a slight variation in temperature during AFM measurements could turn out to be misinterpretation of the results obtained. Consequently, we recommend strict control of the temperature during AFM imaging, in order to improve the reliability and accuracy of the instrument. © 2003 American Institute of Physics.

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68.37.Ps	Atomic force microscopy (AFM)
07.10.Pz	Instruments for strain, force, and torque
07.79.Lh	Atomic force microscopes
68.60.Bs	Mechanical and acoustical properties
68.60.Dv	Thermal stability; thermal effects

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An improved wedge calibration method for lateral force in atomic force microscopy

M. Varenberg, I. Etsion, and G. Halperin

Rev. Sci. Instrum. 74, 3362 (2003); http://dx.doi.org/10.1063/1.1584082 (6 pages) | Cited 66 times

Online Publication Date: 24 June 2003

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An improved wedge calibration method for quantitative lateral force measurement in atomic force microscopy is presented. The improved method differs from the original one in several aspects. It utilizes a much simpler, commercially available, calibration grating and can be performed at any single specified applied load. It enables calibration of all types of probes, both integrated with sharp tips, and colloidal with any radius of curvature up to 2 μm. The improved method also simplifies considerably the calculation of the calibration factor by using flat facets on the calibration grating to cancel out system errors. A scheme for the data processing for on-line calibration of the lateral force is also presented. © 2003 American Institute of Physics.

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07.79.Lh	Atomic force microscopes
06.20.F-	Units and standards
07.10.Pz	Instruments for strain, force, and torque

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Scanning Auger microscopy study of W tips for scanning tunneling microscopy

L. Ottaviano, L. Lozzi, and S. Santucci

Rev. Sci. Instrum. 74, 3368 (2003); http://dx.doi.org/10.1063/1.1581392 (11 pages) | Cited 17 times

Online Publication Date: 24 June 2003

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Tungsten tips used in scanning tunneling microscopy (STM) (prepared via electrochemical etching with a 2 N KOH or NaOH solution) have been studied with state of the art scanning Auger microscopy (SAM) with chemical lateral resolution of 10 nm. The experiments were focused on the investigation of the W tips’ apex shape and surface composition, for tips as etched, or after various postetching treatments performed for cleaning, sharpening, and surface oxide removal purposes. Ultrasonic cleaning likely bend the tip apex. Hydrofluoride etching successfully removes the native WO₃ oxide layer, but this happens at the expense of the tip sharpness. Ion sputtering in ultrahigh vacuum is not always effective in sharpening and cleaning the tungsten tip apex, and we sometimes observed the formation of needle like nanotips, mostly composed of WO₃. Direct resistive annealing of the tip (operated in the STM at 10 V, 50 nA set-point sample bias voltage and current, respectively) to remove the oxide layer, produces a coiling of the tip apex. In this case, atom transfer from the sample to the tip is directly demonstrated with Auger spectra taken at the tip apex. © 2003 American Institute of Physics.

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68.37.Hk	Scanning electron microscopy (SEM) (including EBIC)
81.05.Bx	Metals, semimetals, and alloys
79.20.Fv	Electron impact: Auger emission
82.80.Pv	Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Jk	Electron scattering from surfaces
07.78.+s	Electron, positron, and ion microscopes; electron diffractometers
81.65.Cf	Surface cleaning, etching, patterning
68.35.B-	Structure of clean surfaces (and surface reconstruction)
68.47.De	Metallic surfaces
68.35.Dv	Composition, segregation; defects and impurities
61.72.Cc	Kinetics of defect formation and annealing
81.40.Gh	Other heat and thermomechanical treatments

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Charge-coupled device area detector for low energy electrons

Miroslav Horáček

Rev. Sci. Instrum. 74, 3379 (2003); http://dx.doi.org/10.1063/1.1583863 (6 pages) | Cited 5 times

Online Publication Date: 24 June 2003

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A fast position-sensitive detector was designed for the angle- and energy-selective detection of signal electrons in the scanning low energy electron microscope (SLEEM), based on a thinned back-side directly electron-bombarded charged-coupled device (CCD) sensor (EBCCD). The principle of the SLEEM operation and the motivation for the development of the detector are explained. The electronics of the detector is described as well as the methods used for the measurement of the electron-bombarded gain and of the dark signal. The EBCCD gain of 565 for electron energy 5 keV and dynamic range 59 dB for short integration time up to 10 ms at room temperature were obtained. The energy dependence of EBCCD gain and the detection efficiency are presented for electron energy between 2 and 5 keV, and the integration time dependence of the output signals under dark conditions is given for integration time from 1 to 500 ms. © 2003 American Institute of Physics.

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07.78.+s	Electron, positron, and ion microscopes; electron diffractometers
29.40.Gx	Tracking and position-sensitive detectors

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Real time technique to measure the electrical resistivity of ultrathin films during growth in plasma environments

E. V. Barnat, D. Nagakura, and T.-M. Lu

Rev. Sci. Instrum. 74, 3385 (2003); http://dx.doi.org/10.1063/1.1556947 (5 pages) | Cited 5 times

Online Publication Date: 24 June 2003

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A technique used to obtain the evolution of the electrical resistivity of ultrathin films during growth in a plasma environment is described. Details are given on the physical construction of the substrate assembly that house specially prepared substrates used for film growth. Discussion on the considerations that were needed for proper design of the circuitry to minimize or eliminate the effects of the plasma and any electrode bias on the measurement of the resistivity is given. Operation of the final design is demonstrated through measurements of the current and induced voltages obtained in real time for ultrathin copper sputter deposited onto silicon dioxide. The measured signals are then used to calculate the resistivity as a function of the thickness of the film. © 2003 American Institute of Physics.

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84.37.+q	Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)
73.61.At	Metal and metallic alloys
81.15.Cd	Deposition by sputtering
52.77.Dq	Plasma-based ion implantation and deposition

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A new instrument to measure the surface resistance of superconducting samples at 400 MHz

E. Mahner, S. Calatroni, E. Chiaveri, E. Haebel, and J. M. Tessier

Rev. Sci. Instrum. 74, 3390 (2003); http://dx.doi.org/10.1063/1.1578157 (5 pages) | Cited 3 times

Online Publication Date: 24 June 2003

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A 400-MHz niobium quadrupole resonator has been manufactured to study the rf properties of superconducting bulk and thin film samples at low temperatures. We describe the apparatus, i.e., the construction of the resonator, field calculations with MAFIA, and the experimental procedure. In first validation tests the surface resistance R_s of a reactor-grade bulk niobium sample as a function of temperature and applied rf field has been investigated by using a calorimetric “rf-dc-compensation” method. A critical temperature T_c = 9.15±0.02 K, a thermal conductivity λ(4.2 K) = 6.9±0.7 W/mK, a residual resistance R_res = 19.0±0.3 nΩ, and a superconducting energy gap of Δ/k_BT_c = 1.82±0.01 have been measured. At 4.2 K we achieved a calorimetric detection limit for R_s of 0.16 nΩ at a peak field of 25 mT. © 2003 American Institute of Physics.

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85.25.Qc	Superconducting surface acoustic wave devices and other superconducting devices
84.37.+q	Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

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Use of a double-paddle oscillator for the study of metallic films at high temperatures

P. Rösner, K. Samwer, R. O. Pohl, and S. Schneider

Rev. Sci. Instrum. 74, 3395 (2003); http://dx.doi.org/10.1063/1.1584087 (5 pages) | Cited 11 times

Online Publication Date: 24 June 2003

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We demonstrate the use of silicon double-paddle oscillators for the study of mechanical properties of thin films in the temperature range of 300–673 K under ultrahigh vacuum conditions. It is shown that even at these temperatures the damping coefficient Q⁻¹ of one particular eigenmode of the bare paddle is lower than 10⁻⁵ and is explained through thermoelastic damping. This small background damping provides a sufficient sensitivity for investigations of mechanical properties of thin films above room temperature. As an application, shear modulus and internal friction are presented for a glassy metallic Zr₆₅Al_7.5Cu_27.5 film of 300 nm thickness, deposited by simultaneous electron-beam evaporation of the pure elements. Glass transition and crystallization are observed. © 2003 American Institute of Physics.

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07.10.-h	Mechanical instruments and equipment
68.60.Bs	Mechanical and acoustical properties
62.40.+i	Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.20.D-	Elasticity
81.40.Jj	Elasticity and anelasticity, stress-strain relations

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Jul 2003

Volume 74, Issue 7, pp. 3207-3582

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