ALBERT

Notes: We demonstrate a new circuit design for fast measurements of the voltage drop across the gap of a scanning tunneling microscope (STM) based on the simultaneous operation of two different amplifiers. The first is a fast instrumentation amplifier, sensing directly the voltage drop across the tunneling barrier, the second is a medium speed current amplifier with an overall gain of 108 V/A, suitable for normal STM operation. We obtained a time resolution of 10 ns measuring the plasma ignition under a STM tip during illumination with an intense 10 ns laser pulse. Possible applications include the study of STM point contacts. © 1999 American Institute of Physics.

Notes: For inspection of high aspect ratio structures like narrow semiconductor trenches, a thin membrane probe and a new force detection method have been proposed. Instead of conventional conical and pyramidal tips, a thin silicon nitride cantilever was set up vertically, and its edge was used as a tip. The membrane probe named as twist-probe (TP) was oscillated in the twisting resonance to detect a force from both vertical and lateral directions. About 100 μm long, 0.7 μm thick TP was fabricated as a trial. Amplitude versus distance curve measurements showed that the TP has a high spacing change sensitivity between the tip and a sample in both vertical and lateral directions. A trench cross-section imaging was demonstrated successfully with a TP and the twist resonant force detection method. © 1999 American Institute of Physics.

Notes: Expressions for the low frequency internal friction of a specimen and that of the vibration system of the internal friction measuring apparatus have been deduced for six linear mechanical models. It was found that in the case of forced vibration experiments, the internal friction expressions are different for different models. The relationships between the internal friction values of specimens and the vibration systems for different models have been obtained. © 1999 American Institute of Physics.

Notes: A custom-designed magnet/cryostat system is described which has demonstrated remarkably improved field stability over previous designs. To shield from external magnetic noise, a custom-fabricated flux-gate device remotely senses the changes in magnetic field and cancels them out at the site of the magnet/cryostat via a 1.7-m-diam Helmholtz coil. To provide further shielding, the basic superconducting solenoid includes a passive flux-stabilizing coil. To stabilize internal field shifts, the temperature of the materials in the immediate vicinity of the solenoid (which have a temperature-dependent susceptibility) is stabilized via the new cryostat geometry and by controlling the pressure of the evaporating liquid helium to a few parts per million. As a result, the total system now has a composite shielding factor of approximately 104 and an overall temporal stability on the order of 17(2) parts in 1012 per hour. This instrument, the heart of our new Penning trap mass spectrometer, has recently been used to determine a preliminary value of the proton's atomic mass to an accuracy of 1.4 parts in 1010. With the new magnet/cryostat system, this spectrometer now has a potential resolution which exceeds 2 parts in 1011 with 100 hours of data using a single carbon 4+ ion. © 1999 American Institute of Physics.

Notes: Standard emittance measurement techniques for bright electron beams are either insensitive to the emittance due to correlated effects like misaligned quadrupoles or a nonzero axial magnetic field at the cathode, or are unable to differentiate that emittance from the beam's intrinsic emittance corresponding to the beam's actual entropy. We describe a technique based on the standard quadrupole scan, in which the beam correlations leading to emittance growth can be directly measured, and the emittance from these correlations can be found for special cases. © 1999 American Institute of Physics.

Notes: A capacitive-type two-phase slug detection and characterization system has been developed. The main goal of this work consisted of developing a measurement technique that satisfies the following requirements: to be able to detect a wide range of liquid film thickness from a few millimeters up to the case when the channel is completely filled with water, to have a fast time response, to be nonintrusive and movable, to have a linear response for void fraction of up to 70%, and to be insensitive to the structure of the test section and to proximity effects. In order to detect very small changes in capacity required to fulfill these requirements, a nonlinear twin-T type bridge is used as the front end stage of the instrument. Furthermore, the linearity and stability response criteria are achieved by the appropriate selection of the geometry and topology of the electrodes; the calibration of the system shows an almost linear response for void fractions of up to 70%. The instrument is presently used to determine the slug propagation velocity and frequency in counter-current two-phase flow experiments. © 1999 American Institute of Physics.

Notes: A new experimental system has been constructed to detect evanescent fields of metal surface plasmons (SPs) using a metallic probe tip covered with fluorescence cadmium sulfide (CdS). The evanescent fields of the SPs sensitive to the metal interfaces were observed as fluorescent light from CdS on the tip. No additional lock-in detection technique with a vibrating probe tip is necessary in the system, in spite of the scattered light enhanced by SP due to the surface roughness. The fluorescent light measured for the Al film sample shows exponential decay with distance from the sample surface, indicating that the SP evanescent fields are detected with our apparatus. © 1999 American Institute of Physics.

Notes: A dynamic force distance control for scanning near-field optical microscopy (SNOM) based on a quartz tuning fork as piezoelectric force sensor is introduced. In contrast to a similar design for shear-force feedback, the tuning fork is aligned in such a way that forces perpendicular to the surface are detected. Various near-field probes can be attached to the end of the tuning fork and serve as force sensing tip. The high force sensitivity is demonstrated for two different near-field probes by imaging the topography of organic samples. The tetrahedral tip, an apertureless high-resolution near-field probe used up to now mainly with tunnel current distance control, is for the first time successfully combined with a force distance control for SNOM. A similar distance control was used in conjunction with an only few millimeters short aluminum-coated tapered fiber tip as near-field probe. The suitability of this design for near-field optical fluorescence imaging is demonstrated. Furthermore, the dynamic force distance control with a fiber tip was applied to a soft biological sample under water. The force sensitivity turned out to be sufficiently high to reveal corrugations in the order of 1 nm. © 1999 American Institute of Physics.

Notes: Shape and composition of electrochemically etched tungsten tips for use in scanning tunneling microscopy (STM) were investigated in a transmission electron microscope (TEM) with a Gathan imaging filter (GIP). The tips are prepared by a lamella drop-off technique. We observe typical tip radii of less than 10 nm. After a storage of some days under ambient conditions, an amorphous oxide film is detectable. The electron energy-loss spectroscopy confirms that the surface is contaminated by compounds that contain carbon, too. © 1999 American Institute of Physics.

Notes: Nanotip arrays have been fabricated on the distal faces of coherent fiber-optic bundles. A nanotip array comprised ∼6000 individual optical fibers that were etched chemically. Individual tips were ∼4 μm long with radii of curvatures as small as 15 nm. Nanotip arrays served as a template for a novel polymeric patterning process called photoimprint lithography. This lithographic method generated an array of polysiloxane microwells on glass surfaces. Individual wells had ∼1 μm diameters and were dispersed regularly ∼4 μm apart (center-to-center). Nanotip arrays were also used as templates for an imprint patterning process. This lithographic method generated an array of polystyrene microwells on glass surfaces dispersed regularly ∼4 μm apart with ∼1 μm diameters and ∼4 μm well depths. Both lithographic methodologies provide a simple, technically-expedient method to pattern surfaces with arrays of picoliter-volume wells suitable for microanalytical device utilization. © 1999 American Institute of Physics.

Notes: An experimental facility was developed to obtain real-time, quantitative, x-ray diffraction data in laboratory plate impact experiments. A powder gun, to generate plane wave loading in samples, was designed and built specifically to permit flash x-ray diffraction measurements in shock-compression experiments. Spatial resolution and quality of the diffracted signals were improved significantly over past attempts through partial collimation of the incident beam and the use of two-dimensional detectors to record data from shocked crystals. The experimental configuration and synchronization issues are discussed, and relevant details of the x-ray system and the powder gun are described. Representative results are presented from experiments designed to determine unit cell compression in shock-compressed LiF single crystals subjected to both elastic and elastic-plastic deformation, respectively. The developments described here are expected to be useful for examining lattice deformation and structural changes in shock wave compression studies. © 1999 American Institute of Physics.

Notes: A design for a liquid reaction apparatus is described which allows surfaces prepared in ultrahigh vacuum (UHV) to be reacted with solutions of a wide pH range under dry nitrogen atmosphere and subsequently returned to UHV for surface analysis. © 1999 American Institute of Physics.

Notes: The concept of utilizing a plasma generated by laser guided electric discharges in the atmosphere as the conducting element of an antenna was introduced in 1968. The principal objective was the development of an antenna with no physical structure, but with a large effective area. The goal of producing an ionized column of atmosphere for use as a practical antenna, or to direct lighting strikes, has proved to be elusive. The main difficulty in the production of a viable plasma antenna lies in the tendency of the plasma initially created to block the radiation required to maintain the plasma in a columnar geometry. Various strategies have been used to overcome this difficulty. We present the design of a novel lens with a focal column at a right angle to the principal plane. The design of the lens allows incident radiation to travel around any existing plasma, thereby limiting the blockage incurred by previous methods. Such a lens has application in the fields of plasma antennas and directed lighting strikes. © 1999 American Institute of Physics.

Notes: A multipurpose instrument for the measurement of reflectance and transmittance versus angle of incidence for both specular and diffuse samples in the solar wavelength range has been constructed and evaluated. The instrument operates in the single-beam mode and uses a common light source for three experimental setups. Two integrating spheres, 20 cm in diameter, are used for diffuse transmittance and reflectance measurements. The transmittance sphere can be turned around an axis through the sample to vary the angle of incidence. The reflectance sphere uses a center mounted sample and a special feature is the position of the detector, which is mounted on the sample holder at the center of the sphere. This way the detector always sees the same part of the sphere wall and no light can reach the detector directly from the sample. The third setup is an absolute instrument for specular samples. It uses a small averaging sphere as a detector. The detector is mounted on an arm which rotates around the center of the sample, and it can thus pick up both the reflected and transmitted beams including all multiply reflected components. The averaging sphere detector is insensitive to small side shifts of the detected beams and no multiple reflections between detector and optical system occur. In this report a number of calibration procedures are presented for the three experimental setups and models for the calculation of correct transmittance and reflectance values from measured data are presented. It is shown that for integrating sphere measurements, the geometry of the sphere and the diffusivity of the sample as well as the sphere wall reflectance and port losses are important factors that influence the result. For the center mounted configuration these factors are particularly important and special emphasis is given to the evaluation of the reflectance sphere model. All three instrument setups are calibrated using certified reference materials and nonscattering mirrors and substrates. The results are also compared to the results of a double-beam Beckman integrating sphere for near normal angles of incidence and Fresnel calculations. The results in this article show that good agreement is obtained between results from the different instruments if, and only if, proper evaluation procedures are applied to the measured signals. © 1999 American Institute of Physics.

Notes: A frequency modulated interferometer is developed, which uses a 94 GHz Gunn oscillator and a single sideband (SSB) upconverter as a frequency modulator. An SSB upconverter makes it possible to use a heterodyne phase measurement technique with one mm-wave source. In addition, the influence of frequency drift and phase noise of a mm-wave source on the phase measurement can be reduced. In this work, the performance of a SSB upconverter as a frequency modulator is examined. Also, overall performance of the mm-wave interferometer with a SSB upconverter and line density measurement results in a mirror device are described. © 1999 American Institute of Physics.

Notes: A spectrum analyzer with a sensitivity better than few pV/Hz in voltage noise measurements and better than 1 fA/Hz in current noise measurements is presented. It has two distinct and independent input amplifiers in parallel, connected to the same device under test (DUT) and is based on the suppression of their uncorrelated noises. The instrument is modular with different front-end amplifiers conceived to optimize the measurement of low impedance or high impedance DUTs. The instrument can cover 8 decades of frequency span, from 10 mHz to 1 MHz. The improvement of sensitivity with respect to a traditional system and the simplicity in the connection and biasing of the DUT makes it perfectly suited to measure ultralow noise levels in semiconductor devices, like trapping noise, shot noise associated with tunneling in fractional quantum Hall systems, 1/f and channel noise in metal–oxide–semiconductor field effect transistors operated below threshold. © 1999 American Institute of Physics.

Notes: The method of multilevel dynamical contrasting is applied to analyzing available data from tokamak plasmas. The results illustrate a possibility of extending the concept of the plasma percolating networks in dense Z pinches (and other inertially confined plasmas) to the case of magnetically confined plasmas. This extension suggests a necessity to append the conventional picture of the nonfilamentary plasma (which is nearly a fluid described by conventional magnetohydrodynamics) with a "network" component which is formed by the strongest long-living filaments of electric current and penetrate the "fluid" component. Signs of networking are found in visible light and soft x-ray images, and magnetic probing data. A diagnostic algorithm is formulated for identifying the role of plasma networking in observed phenomena of nonlocal (non-diffusive) heat transport in a tokamak. © 1999 American Institute of Physics.

Notes: The availability of compact cryogenic refrigerators is of importance for the development of both ground and space-borne instrumentation based on cryogenic detectors. In this article we report on the design and performance of a complete ground based cryogenic system consisting of a 3He cryosorption refrigerator, and designed to cool a 6×6 element detector array of tantalum based superconducting tunnel junctions (STJs). The refrigerator provides an operating temperature of 330 mK, with a hold time in excess of 7 h. The system is designed to be portable, to provide a very stable focal plane, and to minimize the use of magnetic materials. Such a system has been used to host the focal plane assembly of S-Cam, the first optical camera for ground based astronomy utilizing an array of STJs, recently installed at the William Herschel Telescope, in La Palma. © 1999 American Institute of Physics.

Notes: An eight channel electron cyclotron emission imaging (ECEI) diagnostic system is being developed for use on the helically symmetric experiment (HSX) stellarator. The system utilizes a linear Schottky diode mixer/receiver array, coupled with low cost conventional ECE radiometer IF boards under development at U.C. Davis, to measure the second harmonic x-mode radiation from the plasma. The array is fed with a fixed local oscillator, with single sideband operation enabled via a dichroic plate high pass filter whose cutoff frequency equals that of the local oscillator. A multithrow, high speed (〈100 ns switching times) microwave switch is utilized to sequentially connect the output from each mixer channel to the broadband IF receiver system, thus making the array capable of generating a high resolution two-dimensional image of the HSX electron temperature profile at rates exceeding 50 kHz. Instrument details of the system will be described. © 1999 American Institute of Physics.

Notes: A millimeter-wave two-dimensional imaging array has been developed for diagnostics of magnetically confined plasmas. It is applied to the plug cell of the GAMMA 10 tandem mirror, and measures time evolution of radial and axial line-density and electron cyclotron emission (ECE) profiles in one plasma shot. The monolithic-type GaAs Schottky diode detector having an antenna and built-in amplifier on a GaAs substrate is newly fabricated using monolithic microwave integrated circuit (MMIC) technology. This novel detector is developed to attain high frequency response up to submillimeter-wave region and wideband heterodyne characteristics, and is expected to be applied to ECE imaging in a large helical device. The response of the detector is compared with that of the hybrid-type detector using beam-lead Schottky barrier diodes. The first experimental result of the ECE measurement is reported using a heterodyne radiometer with the MMIC detector. © 1999 American Institute of Physics.

Notes: Correlations between electron density and temperature fluctuations have been measured in the core plasma of W7-AS. The simultaneous use of transmitting and receiving antennas of a heterodyne reflectometer by a crossed sightline ECE correlation radiometer enables the cross-correlation analysis of the reflectometer phase signal and ECE radiation temperature signals in overlapping plasma volumes. Correlations have been found in the spectral range 25–100 kHz, indicating an in-phase correlation between electron density and temperature fluctuations. © 1999 American Institute of Physics.

Notes: In this article we present experimental results obtained with a heterodyne/amplitude modulated (AM) reflectometer at W7-AS and simulations [two-dimensional (2D) (WKB)] of reflection on a rotating cutoff layer corrugated by turbulence for the W7-AS conditions. When the turbulence has a large amplitude and a small size relative to the illuminated spot, the calculations show the existence of a phase runaway and reproduce the typical behavior of the measured phase and amplitude signals. It is not possible to deduce the plasma rotation from the phase runaway value at "close to normal" incidence, as this value depends on the turbulence characteristics. When the illuminated cutoff surface is smooth, no runaway occurs, amplitude and phase signals are coherent and in certain poloidal wavelength ranges (∼1 to 2 cm for W7-AS conditions) their relative phase is π/2, conditions that have been observed experimentally during H mode. The phase runaway can affect the ne(r) measurements. However, the comparison between the measured carrier and AM phases shows that its effect is canceled by differential measurements of ne(r). © 1999 American Institute of Physics.

Notes: Here, we propose the heavy ion-beam probing (HIBP) project for the mega ampere spherical tokamak (MAST) to establish systematic research of the radial electric field as an idea to investigate both the reactor-related physics (H mode and advanced tokamak mode with reversed shear) and basic plasma physics (the nature of anomalous transport). The calculations of the probing beam trajectories made for typical MAST parameters: B0=0.6 T, Ipl=1 MA, and Cs+ probing ions show the applicability of HIBP for the spherical torus MAST with energy of about a few hundred keV. The detector line connecting the center and the edge of the plasma allows us to obtain a radial profile by variation of the energy shot by shot. A detector line of equal energy E=110 keV allows us to get a series of profiles in the internal part of the plasma 0〈ρ〈0.4 during a single shot by a fast scan of the injection angle. The effect of splitting of the sample volume due to the intersection of the secondary fan in a rapidly decreasing toroidal magnetic field of the spherical tokamak was observed: two sample volumes can appear instead of the conventional one. It changes the principles of HIBP: the notion of a detector grid became more general and a new problem appears: how to separate the signals coming from different sample volumes. Using this effect we can spread the detector grid and observe the outer part of the plasma, 0.4〈ρ〈1. It was shown that these two parts can be united and the total plasma profile can be observed in one shot. © 1999 American Institute of Physics.

Notes: The application of Kalman filtering is proposed for the numerical evaluation of plasma density profiles using noisy group delay data obtained from O-mode frequency-modulated broadband reflectometry. This method allows faster computation of the Abel inversion integral than the usual numerical methods (e.g., the trapezoidal rule) while maintaining a good accuracy in the presence of noise. In addition, density profiles with different degrees of smoothing can be produced by adjusting a single parameter. The algorithm seems promising in applications to plasma control in real time. © 1999 American Institute of Physics.

Notes: In this article the fabrication and characterization of two thermally actuated optical devices for the measurement of temperature and power are described. A transparent polymer having a high coefficient of thermal expansion—poly(dimethylsiloxane) (PDMS)—was used as the temperature-sensitive medium. Changes in the dimensions of the polymer on heating caused the observed optical responses of both devices. The temperature sensor based on the Fabry–Pérot cavity measures temperature differences to a precision of 0.005 °C within the linear working ranges of the device. The power sensor uses the architecture of a Mach–Zender interferometer; it is suitable for measurements of powers in the mW/cm2 range, delivered optically to the surface of the device in the visible wavelength region. The devices are inexpensive, easy to fabricate, and mechanically rugged. They offer alternatives to other sensors for measuring temperature and power. © 1999 American Institute of Physics.

Notes: We present a reliable method to account for the magnetoresistance of resistance sensors which are used as thermometers in many low temperature (T≤20 K) experiments carried out in high magnetic fields (to 31 T). To apply the method, a set of isothermal magnetoresistance data, and a zero magnetic field temperature calibration are first necessary. A simple algorithm, which uses this data set, can then be applied to compute the temperature from the measured resistance at any field. The method is particularly useful for temperature dependent measurements at fixed field, or where, in cases where the temperature may change unpredictably during a change in magnetic field. We apply this method to the treatment of data in two separate experiments with the two different thermometers, RuO2 (below 1 K) and Cernox (above 1 K) sensors, respectively. © 1999 American Institute of Physics.

Notes: The dynamics and noise of a dc superconducting quantum interference device (SQUID) with the McCumber parameter βc=2πR2IcC/Φ0 close to the unity (where Ic, R, C are the critical current, the shunt resistance, and the capacitance of the Josephson junctions comprising the SQUID, respectively, and Φ0=2.07×10−15 Wb is the magnetic flux quantum) integrated with a planar spiral input coil have been experimentally studied. The length of the spiral input coil was chosen to match its λ/4 microwave resonance frequency to the plasma resonance frequency of the SQUID. The input coil resonance enhances the overall quality factor Q of the Josephson oscillations in the SQUID and, as a result, increases the dynamic resistance Rd and the gradient of the flux-to-voltage characteristics ∂V/∂Φ without hysteresis. This relaxes the tolerance for the βc parameter, simplifies the technological process, and improves the yield of devices. A dc SQUID with loop inductance L=31.4 pH, βc=0.72, and a six turn input coil has demonstrated a nondistorted quasisinusoidal flux-to-voltage transfer function with an exceptionally large modulation depth of approximately 140 μV peak-to-peak. A spectral density of the intrinsic magnetic flux noise as low as 3.5×10−7 Φ0/Hz1/2 has been measured in the double stage configuration at a temperature of 4.2 K using direct read-out electronics. This corresponds to the intrinsic energy resolution of ε=12.5h. In combination with an intermediary transformer, the current resolution of the SQUID is as low as 1.25 pA/Hz1/2 with an input coil inductance of 58 nH. The coupled energy resolution is εc=45h in the white noise region. © 1999 American Institute of Physics.

Notes: In this article we describe a new slit grating spectrograph which is based on an e-beam written 10 000 linepairs/mm freestanding transmission diffraction grating. In combination with a thinned, back-illuminated charge coupled device (CCD), the spectrograph allows for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength region λ=1–20 nm. Calibration of grating and CCD allow for the possibility to measure absolute photon fluxes, currently within the wavelength region λ=1–6 nm. The compact spectrograph is easy to align and flexible in its use. Absolutely calibrated spectra were obtained from a liquid-jet laser-plasma source in the water window, with a spectral resolution λ/Δλ≥330 at λ=3.37 nm. A simple change in experimental geometry allowed single-shot spectra to be recorded with λ/Δλ≥60 at the same wavelength. In addition, spectra from this laser-plasma source were measured within the range λ=9–20 nm. © 1999 American Institute of Physics.

Notes: Utilizing the chaos control technique of occasional proportional feedback (OPF), we designed and constructed an inexpensive and easy to assemble electronic OPF controller. A number of built-in features provide ample versatility to enable the controller to be used with a wide variety of chaotic experimental systems. The controller has a standard OPF correction signal output, but also allows for the addition of a modulated signal to the correction. The rate and active duration of the correction pulse, the offset voltage, and the effective window width are variable. We present the basic principles of OPF control and discuss the individual component functions of the OPF controller. We have successfully used this controller to stabilize chaotic fluctuations in the frequency emission from a tunable lead–salt stripe geometry infrared diode laser. © 1999 American Institute of Physics.

Notes: The inversion problem of angle dependent chord integrals is theoretically studied and a rotating type optical probe is developed for its application. The proposed solution is computationally efficient and robust to measurement additive noise. The probe system constructed is tested in an inductively coupled plasma source by measuring a spectral line intensity of argon plasma. © 1999 American Institute of Physics.

Notes: In this article we describe evanescent field imaging of material nonuniformities with a record resolution of 0.4 μm at 1 GHz (λg/750 000), using a resonant stripline scanning microwave probe. A chemically etched tip is used as a point-like evanescent field emitter and a probe–sample distance modulation is employed to improve the signal-to-noise ratio. Images obtained by evanescent microwave probe, by optical microscope, and by scanning tunneling microscope are presented for comparison. Probe was calibrated to perform quantitative conductivity measurements. The principal factors affecting the ultimate resolution of evanescent microwave probe are also discussed. © 1999 American Institute of Physics.

Notes: The recently described tests of the synchrotron imaging photoelectron spectromicroscope MEPHISTO (Microscope à Emission de PHotoélectrons par Illumination Synchrotronique de Type Onduleur) were complemented by further resolution improvements and tests, which brought the lateral resolution down to 20 nm. Images and line plot profiles demonstrate such performance. © 1999 American Institute of Physics.

Notes: We present an apparatus that permits quasisimultaneous measurements of several vibrating modes in a vibrating reed experiment. Position detection by laser beam deflection offers a simple setup and good sensitivity for higher modes of flexural as well as torsional vibrations. Frequency and damping from free decay data are determined by software which permits high accuracy, especially at low damping. This is particularly interesting for the measurement of the mechanical properties of thin films deposited on a low damping vibrating reed. As an example results on an Al film on a microstructurized silicon resonator are shown. © 1999 American Institute of Physics.

Notes: An experimental method was developed to perform picosecond time-resolved electronic spectroscopy in single-event, plate impact, shock wave experiments. Several experimental difficulties had to be addressed due to the fast time resolution (100 ps) and short time duration (12.7 ns) of such experiments. Procedures are described to address the following experimental issues: (i) synchronization of the light source, detection equipment, and the shock event within the experimental duration, (ii) incorporation of a Nd:YAG laser (operative in a repetitive mode) into the experimental configuration, and (iii) sources of temporal dispersion. Representative results are shown from experiments performed on single crystal CdS. The developments described here are also expected to be useful for shock wave experiments involving Raman, fluorescence, or other types of spectroscopy which require the use of a laser. © 1999 American Institute of Physics.

Notes: We discuss practical aspects of Kelvin probe force microscopy (KFM) which are important to obtain stable images of the electric surface potential distribution at high spatial resolution (〈100 nm) and high potential sensitivity (〈1 mV) on conducting and nonconducting samples. We compare metal-coated and semiconducting tips with respect to their suitability for KFM. Components of the metal coating can become detached during scanning, introducing sudden offset jumps in the potential maps (typically up to 350 mV between adjacent scan lines). However, n-doped silicon tips show no substantial tip alterations and, therefore, provide a stable reference during the experiment (offset jumps typically up to 40 mV between adjacent scan lines). These semiconducting tips must be electrically connected via contact pads. We use InGa and colloidal silver pads which are easily applied to the substrate supporting the cantilever and have a low enough differential contact resistance (350 Ω and 2.2 kΩ, respectively). Furthermore, we introduce a simple procedure to fine tune the feedback which detects the electric surface potential and show how the basic KFM setup has to be modified to gain access to the necessary control signals. © 1999 American Institute of Physics.

Notes: Dynamic contact mode electrostatic force microscopy (DC-EFM) was developed as a new operation mode of scanning probe microscope (SPM). By operating EFM in a contact mode with an ac modulation bias, we have improved the spatial resolution and also achieved a complete separation of the topographic effect from other electrostatic force effect overcoming the mixing problem of a topographic effect with other electrostatic effects frequently encountered in the conventional noncontact EFM measurement. DC-EFM can be utilized either as a force microscopy for the surface hardness, or as a potentiometry for the surface potential distribution, or as a charge densitometry for the surface charge density study. This is also applicable to the measurement and control of the domain structure in ferroelectric materials that have a bound surface charge. © 1999 American Institute of Physics.

Notes: We describe the fabrication of micron-sized Hall probes from a Si/SiGe heterostructure. The magnetic field response of the Hall probes shows a very high sensitivity of ∼60 Ω/kG. Below a temperature of 80 K, the Hall probes exhibit a highly linear field dependence of the Hall resistance. The onset of the quantum Hall effect at very low temperatures and high magnetic fields causes only small deviations from the linear field response. We demonstrate the performance of the device as a sensitive local magnetization probe in high-temperature superconducting crystals of Bi2Sr2CaCu2O8. With a linear array of Hall probes we track both the spatial and temporal evolution of the magnetization profile across the crystal. In this way surface and bulk contributions to the overall magnetization can be delineated. © 1999 American Institute of Physics.

Notes: A new apparatus for magneto-optical investigations of high temperature superconducting (HTS) films as large as 20×20 cm2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field (magneto-optical scanning technique, MOST). The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1×1 cm2 is presented for the first time. The results are compared to inductive jc measurements as well as to micrographs [optical microscope (OM), scanning electron microscopy (SEM)] and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical current density, which is the relevant parameter for an application of the superconducting thin films. Moreover, it could be shown that MOST has appreciable advantages compared to inductive jc scans and microscopy (OM, SEM). In particular it is possible to observe defects, which are below the optical resolution of the MOST setup. © 1999 American Institute of Physics.

Notes: The construction of a single-crystal nuclear magnetic resonance (NMR) probe with a new two-axis geometry for the goniometer has improved the sensitivity of the NMR response from small crystals. This allows studies of the smallest crystals used so far in single-crystal NMR. The goniometer of the probe uses only two different mountings of the crystal, and the rotation axis of the goniometer is tilted 45° with respect to the direction of the magnetic field. By moving the goniometer outside the radio frequency coil, the filling factor and the probe sensitivity increase. The improved sensitivity for the probe is illustrated by the 31P-{1H} cross-polarization spectrum of a 0.088 mm3 crystal of (NH4)2HPO4 and a 87Rb single-pulse spectrum of a 0.048 mm3 crystal of RbZn2(HPO4)PO4. Moreover, the capability to determine precise parameters for the solid-state NMR interactions using the new probe is demonstrated by 23Na and 87Rb single-crystal studies of NaNO3 and RbClO4. © 1999 American Institute of Physics.

Notes: The receiver of the Joint European Torus (JET) energetic ion and alpha particle collective Thomson scattering diagnostic is calibrated assuming blackbody emission from the torus vacuum vessel (VV) and using electron cyclotron emission (ECE). The 32 receiver channels are absolutely calibrated with a mechanical chopper in the quasioptical arm of the receiver, alternating the receiver view between the torus vacuum at 320 °C and room temperature. This calibration is noisy due to the small difference between torus and room temperatures. A more accurate relative calibration is achieved with the ECE during plasma shots. The intensity of the ECE is found to be a smooth function of frequency, which enables the combination of the ECE calibration with the VV calibration. The accuracy of the absolute VV calibration is hereby improved to nearly the same standard as the relative ECE calibration. ECE signals measured by the calibrated receiver agree well with standard JET ECE diagnostics. Based on mathematical considerations presented here, noise is injected into the receiver final intermediate frequency stage during VV calibrations to provide more bit transitions for accurate analog-to-digital (AD) conversion of the low level calibration signals. This yields a resolution which is better than 1% of an (AD) step. © 1999 American Institute of Physics.

Notes: The time integrated neutron yield on TEXTOR is measured with an activation system which pneumatically sends the samples near to and from the plasma edge. After irradiation the samples are counted by an absolutely calibrated high purity germanium (HPGe) detector. The uncertainty in the calibration of the HPGe detector is less than 2%. By using threshold reactions for indium and silicon samples it is possible to distinguish between the 2.5 and 14 MeV neutron emission. MCNP code simulations have been performed in order to determine the neutron fluence and energy distribution at the irradiation position. This allows calculation of an activation coefficient which relates the activation of the sample to the total yield from the TEXTOR plasma. For the 2.5 MeV neutron emission the corresponding error is less than 15%. Details on the measuring procedure as well as on the calibration method of the HPGe detector are provided. Results of calibration monitoring of the neutron source strength measurements and the triton burnup measurements are presented. © 1999 American Institute of Physics.

Notes: A simple technique has been developed to image intense pulsed proton beams with radiachromic film and to measure their spatial distribution. The optical density (OD) of 50 μm thick film, sufficient to stop 1.5 MeV protons, is measured to infer the incident beam fluence. The OD increases nearly linearly with fluence up to 0.25 cal/cm2. This film is used to measure the uniformity of large-area beams as well as the detector in a multiple-pinhole camera to determine the source uniformity and divergence of applied-magnetic field and pinched-beam ion diodes. © 1999 American Institute of Physics.

Notes: Mechanical investigations with single molecules have opened a rich spectrum of new experiments, ranging from molecular recognition over polymer elasticity and DNA unzipping to protein unfolding. Here we present the design of a novel instrument, where the force is applied to the molecule via magnetic fields acting on a magnetic cantilever for atomic force microscopy. The performance of this instrument was demonstrated by measuring the binding force of biotin/avidin complexes. A new and technically very appealing detection scheme for measurements of unbinding forces was introduced, which consists of picking up the induced voltage pulse caused by a discontinuous change of the magnet position upon bond rupture. © 1999 American Institute of Physics.

Notes: This article presents the design criteria, the prototype development, and application results of a low-cost four quadrants infrared (IR) detector. The detector was specifically developed as a position sensor for the alignment of low power IR laser diode beams, especially for spectroscopic applications. The detector consists of a polyvinilidene difluoride pyroelectric radiation sensor of 4×4 mm2 total surface area and of a four-channel high gain transimpedance amplifier, followed by a narrow bandwidth resonant filter for noise rejection. The overall single pixel responsivity resulted 3590 V root mean square /W¯ at 5.8 μm, and modulation frequency of 85 Hz. The beam spot centroid of a square-wave modulated laser diode emitting 85 μW¯ was determined using an algorithm evaluating the difference signals between diagonal elements along vertical and horizontal scanning directions. An uncertainty in the centroid position of 6 μm, in both directions, was obtained, mainly limited by the digitizing resolution of the 12-bit acquisition system. © 1999 American Institute of Physics.

Notes: A compact optical pressure cell tested at pressures up to 400 MPa is presented. The cell has been used within the temperature range 10–350 K. The cell has a small mass of 0.2 kg which facilitates rapid changes in temperature. A new high-pressure window seal is presented which allows the cell to be mounted directly in vacuum with no leak over its entire temperature and pressure range. A method of attaching the cell to common coldhead-type cryostats and closed-cycle refrigerators is presented. © 1999 American Institute of Physics.

Notes: A molecular beam apparatus which was formerly used for crossed molecular beam chemiluminescence experiments under high vacuum conditions has been modified into an ultrahigh vacuum apparatus with a rotatable mass spectrometer detector equipped with an electron bombardment ionizer to study (1) the molecule-surface scattering process, (2) molecular beam-surface reaction dynamics, and (3) light-excited molecular desorption. Every flange surface originally sealed using a Viton o ring is sealed with a combination of an inner spring-loaded Teflon or aluminum seal with an outer Viton o ring, the intermediate region being pumped with a diffusion pump. Due to the limited space available for a rotatable detector chamber and to make the neutral flight length in time-of-flight (TOF) measurements as long as possible, the electron bombardment ionizer is installed at the farthest end of a triply differentially pumped detector chamber; thus, the ions formed are extracted toward the reverse direction of the scattered neutral molecular beam, mass selected with a quadrupole mass filter, and detected by an electron multiplier. Using this apparatus, angular and TOF distributions have been measured for Xe scattered from crystalline graphite surface and for the desorbed product, SiCl2, from the etching reaction of Si(111) with a beam of hyperthermal Cl2 molecules. © 1999 American Institute of Physics.

Notes: Plasma immersion ion implantation is a burgeoning surface modification technique and not limited by the line-of-sight restriction plaguing conventional beam-line ion implantation. It is therefore an excellent technique to treat interior surfaces as well as components of a complex shape. To enhance the implant uniformity and increase the thickness of the modified layer, we are using a high frequency, low-voltage process to achieve high temperature and dose rate to increase the thickness of the modified layer. The low voltage conditions also lead to a thinner sheath more favorable to conformal implantation. In this article, we will describe our special modulator consisting of a single ended forward converter with a step-up transformer. The modulator is designed to operate from 5 to 35 kHz and the output voltage is adjustable to an upper ceiling of 5000 V that is deliberately chosen to be our voltage limit for the present experiments. We will also present experimental data on SS304 stainless steel materials elucidating the advantages of our modulator and high frequency, low-voltage experimental protocols. © 1999 American Institute of Physics.

Notes: A PC plug-in card for on-line time resolved fluorescence detection of single dye molecules based on a new time-correlated single photon counting (TCSPC) module is described. The module contains all electronic components constant fraction discriminators (CFDs), time-to-amplitude converter (TAC), analog-to-digital converter (ADC), multichannel analyzer (MCA timers) on board required for TCSPC. A fast TAC design in combination with a fast flash ADC and an error-correcting ADC/MCA principle results in a maximum count rate of 8 MHz (dead time 125 ns). A dual memory architecture allows for unlimited recording of decay curves with collection times down to 150 μs without time gaps between subsequent recordings. Applying a short-pulse diode laser emitting at 640 nm with a repetition rate of 60 MHz in combination with a confocal microscope, we studied bursts of fluorescence photons from individual dye labeled mononucleotide molecules (Cy5-dCTP) in a cone shaped microcapillary with an inner diameter of 0.5 μm at the end of the tip. The flow of the conjugates was controlled by electrokinetic forces. The presented technique permits the counting and identification of all labeled analyte molecules present in a given sample due to their characteristic velocities, burst sizes, and fluorescence decay times. © 1999 American Institute of Physics.

Notes: A new trace gas detection system, using the high surface area properties of an aerosol to adsorb specific gas species and the high sensitivity and near real time capabilities of the infrared aerosol analyzer, has been successfully demonstrated. A new technique is described that allows certain chemical vapor species to be detected in time frames on the order of 2 min. The technique uses aerosols of selected materials to adsorb the vapor from an air sample, concentrating the vapor onto the surface of the aerosol, then depositing the particles onto a substrate for infrared analysis. For 1 min sample collection times, discernable signals were observed for SO2 levels as low as 2.3 ppm and NH3 concentrations as low as 1.5 ppm. Dimethyl methyl phosphonate (DMMP) vapors from a room temperature container were also detected. Preliminary results indicate that the measured absorbance is a monotonic function of the quantity of the trace gas injected, which gives encouraging evidence that a quantitative determination of the amounts of trace gases present in the atmosphere can be made in many cases. Trace gas detection is dependent upon the aerosol material chosen as the absorbent. For this work, copper (II) chloride and copper (II) sulfate were found to adsorb NH3, SO2, and DMMP. The copper compounds did not absorb NO or NO2. This enables the system to reduce the myriad potential interferences that can exist when sampling the atmosphere. The ammonia complex detected by this technique could be one of many such complexes that can be formed by properly matching the aerosol material and trace gas. As such, the process could be tailored to specific gas/aerosol combinations that could be used to unambiguously identify gaseous effluents of interest. © 1999 American Institute of Physics.

Notes: We have devised compact optics for the forward-box configuration in degenerate four-wave mixing spectroscopy. The core of the optical setup is the successive use of a pair of polarization-based beam splitters that divide the laser beam into four parallel beams. This setup is compact, easy to assemble, and adaptable for laser light over a wide spectral range. Selection of the combination of beam polarization produces two types of transient grating: either a polarization grating or an intensity grating. © 1999 American Institute of Physics.

Notes: Design study of an x-ray crystal spectrometer for the HANBIT mirror machine is presented. The x-ray emissivity of HANBIT plasmas is rather low as a result of the low values of the electron temperature and density. The design difficulty from the low x-ray emissivity can be overcome by utilizing a vacuum spectrometer sightline parallel to the long axial length of HANBIT and using an x-ray sensitive vacuum charge-coupled device camera as a detector. © 1999 American Institute of Physics.

Notes: A new type of high-resolution x-ray imaging crystal spectrometers is described for implementation on the National Spherical Torus Experiment (NSTX) to provide spatially and temporally resolved data on the ion temperature, toroidal and poloidal plasma rotation, electron temperature, impurity ion-charge state distributions, and impurity transport. These data are derived from observations of the satellite spectra of heliumlike argon, Ar XVII, which is the dominant charge state for electron temperatures in the range from 0.4 to 3.0 keV and which is accessible to NSTX. Experiments at the Torus Experiment for Technology Oriented Research (TEXTOR) demonstrate that a throughput of 2×105 photons/s (corresponding to the count-rate limit of the present detectors) can easily be obtained with small, nonperturbing argon gas puffs of less than 1×10−3 Torr l/s, so that it is possible to record spectra with a small statistical error and a good time resolution (typically 50 and 1 ms in some cases). Employing a novel design, which is based on the imaging properties of spherically bent crystals, the spectrometers will provide spectrally and spatially resolved images of the plasma for all experimental conditions, which include ohmically heated discharges as well as plasmas with rf and neutral-beam heating. The conceptual design, experimental results on the focusing properties, and relevant spectral data from TEXTOR are presented. © 1999 American Institute of Physics.

Notes: Two groups of well-known suspensions are described in the early part of this article. Their viscosity and other properties can be changed by means of the electric and magnetic field. The main goal of this article is to present new types of suspensions with properties which can be changed by means of both the above mentioned fields. These suspensions consist of sodium chloride and magnetite particles or nickel-zinc ferrite dispersed in transformer oil. The method of producing these suspensions is described. Also given are the results from an analysis of their magnetic permeability and their dielectric constant induced changes. A comparison and discussion of the results obtained are presented in the final part of the article. © 1999 American Institute of Physics.

Notes: The design, fabrication, and performance of an apparatus for measurements of rf penetration depth in superconducting samples are described. The instrument makes use of a close-cycle helium refrigerator and is capable of measuring vortex dynamics in superconducting sample of volume as small as 1×10−3 cm3 with a signal-to-noise ratio of 1400. The system has been tested for a tunnel diode oscillator and an IC 74LS04 oscillator in the 3–5 MHz frequency range. Both magnetic field magnitude and angular variations to the resolution of 1 G and 0.05°, respectively, are possible with the apparatus. The system performance is evaluated by measuring the dynamical behavior of vortices in platelet samples of Bi2Sr2CaCu2O8 and (Bi-Pb)2Sr2Ca2Cu3O10 superconductors. © 1999 American Institute of Physics.

Notes: The construction principles of a new heatable large volume high-pressure cell for neutron powder diffraction, the Kiel–Berlin Cell II, are presented. The basic design is of the piston/cylinder type. The cell is designed to operate up to pressures of 3.5 GPa and temperatures above 800 K. First tests showed the mechanical stability of the cell to be ensured up to the corresponding necessary sample load of 50 tons and a prestress of 110 tons. The cell is intended for use at reactor-based neutron sources. The use of a large sample (1.5 cm3) allows rapid data collection. There are no major geometrical restrictions in the scattering plane. The projected temperature could be reached simultaneously to the application of pressure. First neutron experiments revealed a good signal-to-noise ratio of the diffracted neutrons. For the present layout of the Ti/Zr pressure cylinders and upper stability limit of 1.2 GPa was determined. © 1999 American Institute of Physics.

Notes: A digital quadrature detection technique for the acquisition of the nuclear magnetic resonance signal is proposed. It is demonstrated with experimental results that the suggested method is superior to the conventional quadrature detection (QD) technique. The superiority arises mainly from the fact that only one channel of analog circuit is utilized and no spectral distortion due to unbalance between two channels used by the QD occurs. As a result, no phase cycling for canceling the distortion mentioned above is necessary. © 1999 American Institute of Physics.

Notes: We describe a novel device which can measure, with low dissipation and high resolution, the level of a dielectric liquid. This device can also be used with cryogenic liquids, in particular with liquid helium. The high degrees of stability and of reproducibility make this apparatus an instrument of performances largely competitive with respect to others commonly used. © 1999 American Institute of Physics.

Notes: A uniform plasma of large volume is produced by using a new waveguide-surfatron. The plasma is uniform within ±5% in a diameter over 160 mm in the diffusion area. The plasma density is 1010–1011 cm−3 with electron temperature 2–4 eV at a microwave power of 500–900 W and a pressure of 10–50 Pa. © 1999 American Institute of Physics.

Notes: The ion temperature and toroidal rotation velocity with high time resolution (τ∼1 ms) using charge exchange spectroscopy in JT-60U tokamak plasma have been measured. The method uses three interference filters that have slightly different peak wavelengths. These filters are selected according to the ion temperature and rotation velocity expected at the measured position. The system with a time resolution of 1 ms was applied to the analysis of fast plasma phenomena. As an example, the time evolution of the C VI ion temperature and toroidal rotation velocity across the L–H transition has been measured. The toroidal rotation at a normalized minor radius (r/a=0.3) increases gradually after the L–H transition, while that at the edge changes from a speed of 5 km/s before the transition to −40 km/s after the transition within a time of 5–10 ms. © 1999 American Institute of Physics.

Notes: Local plasma emissivity of TJ-II plasmas will be determined using pyroelectric detectors. For tomographic reconstructions three fan-like arrays, 20 channels each, will be installed at the top, side, and bottom ports of the same sector. The designed compact in-vessel systems will use folding support structures to introduce the arrays through small diameter flanges and translation and rotary drives to position them at their measuring sites. Special individual "honeycomb-like" collimators (transparency of around 50% and spatial resolution of about 2 cm at the plasma center) have been designed to optimize the signal level and to act as a microwave filter. In the first stage, radial profiles of plasma emissivity will be obtained with a single detector, on the basis of frozen plasma parameters during a few ms. This detector is equipped with a rotary slit that scans the whole plasma cross section from 10–20 times per shot. To perform power balances, global plasma emission is monitored with three pyroelectric detectors. Collimators are movable slits that enable probing either the full plasma cross section or narrow central chords; when fully closed they protect detectors during wall conditioning and permit background noise characterization. © 1999 American Institute of Physics.

Notes: In recent years the necessity of understanding the physics concerning new tokamak results has clearly shown the limits of the actual diagnostic capability of existing devices, in terms of reliability, precision, spatial localization, and temporal resolution of measurements. This appears even more evident when next-step tokamak devices are considered. For example, the formation and evolution of the plasma internal transport barriers and the regulation of its positions by a detailed tailoring of the current spatial profile and plasma heating gives demanding requests to a complex set of diagnostics including motional Stark effect as well as incoherent Thomson scattering (ITS). The measurement of detachment of plasma in a divertor puts some requirements on a dedicated ITS. The rotational stabilization of ideal magnetohydrodynamic modes puts some important accent to the plasma rotation measurements. The coherent (or collective) Thomson scattering giving ion temperature can be useful in a prototype fusion reactor to monitor the ignition process. A state-of-the-art review for these diagnostics is carried out trying to outline the perspectives that are seen from the point of view of physics studies. A discussion of the present limits is presented and new directions of development identified, since a step foreward in the physics studies implies a parallel refinement and/or new conception of diagnostic equipment. © 1999 American Institute of Physics.

Notes: A versatile remotely controlled fast reciprocating Langmuir probe has been developed for the TJ-II stellarator. The main components of the system are a removable head, containing the measurement tips, and a displacement system that enables the probe to be displaced in vacuum. The probe displacement system has two different components: a slow one (course length≤0.8 m) to set the probe at the initial measurement position, and a fast one (run length=0.1 m) to obtain the desired measurements within an adjustable time interval during the plasma discharge. The radial movement of the probe is controlled remotely by means of a programmable logical control system, with a radial resolution of better than 1 mm. The fast displacement of the probe (up to 1.7 m/s) is achieved by using a pneumatic system. Its position as a function of time is monitored by means of the on-line response of a linear resistor attached to the fast displacement system. © 1999 American Institute of Physics.

Notes: A method to determine the spring constant of a rectangular atomic force microscope cantilever is proposed that relies solely on the measurement of the resonant frequency and quality factor of the cantilever in fluid (typically air), and knowledge of its plan view dimensions. This method gives very good accuracy and improves upon the previous formulation by Sader et al. [Rev. Sci. Instrum. 66, 3789 (1995)] which, unlike the present method, requires knowledge of both the cantilever density and thickness. © 1999 American Institute of Physics.

Notes: We have designed and constructed an improved two-dimensional X pendulum vibration–isolation table. It achieved a lower resonant frequency (7 s) than previous prototypes, and the effects of many parasitic elastic resonances have been reduced by careful balancing, leading to much improved vibration isolation around a few hertz. © 1999 American Institute of Physics.

Notes: In order to measure the very weak interaction between a gravitational wave and a resonant-mass detector the antenna must be vibrationally isolated from all external excitations. In this article we describe an analytical and experimental study of the final support to a spherical antenna. We derive an analytical procedure for optimizing the dimensions of the support for maximum attenuation. The results of a finite element analysis are also presented that takes into account the elasticity of the sphere. The described techniques were used for designing the final support of a room-temperature prototype antenna. We found the measurements on this system to be in good agreement with the expected transfer functions. © 1999 American Institute of Physics.

Notes: An integrated humidity sensor able to detect and measure a very low humidity concentration and higher relative humidity (RH) levels as well with the possibility of industrial application has been designed and fabricated using very large scale integration technology where thin porous Al2O3 film acts as humidity sensing material. The porous structure of Al2O3 has been obtained by anodic oxidation of a thin film of Al in sulfuric acid. During anodic oxidation, a few top atomic layers of Ta are also oxidized into Ta2O5 whose properties affect the normal sensing properties of Al2O3 and a better quality of sensor with higher sensitivity and speed is obtained. The gate insulator structure of the field-effect transistor is SiO2/Si3N4/Ta/Ta2O5/Al2O3. The device is basically an enhancement mode metal–oxide–semiconductor field-effect transistor. The drain current ID of the device is measured at constant gate and drain voltages at 25 °C and found to be sensitive up to less than ∼1 ppmv moisture concentration. The response time of the sensor in ppmv level is less than 1 s. The device is also found to be very sensitive at higher RH levels and shows a linear dependency on RH. The response and recovery times of the sensor are 2 and 6 s, respectively. © 1999 American Institute of Physics.

Notes: A time-to-digital converter (TDC) for digital storage oscilloscopes has been developed. The TDC utilizes an analog interpolation scheme named a pulse stretcher of very high stretching ratio of about 5000 to achieve fine timing resolution. With the high stretching ratio, high single-shot accuracy can be achieved with a relatively low counting clock frequency. The start and stop inputs of the TDC are the trigger pulse and the 250 MHz sampling clock respectively, so they have at most a 4 ns time interval. The time interval between two inputs is stretched by a pulse stretcher with a high discharging–charging ratio, and the stretched interval is counted with a coarse counter. The resulting count is the output of the TDC which is proportional to the time interval between the two inputs. The least-significant-bit step and the root-mean-squared deviation of the TDC output were measured to be 7.80 and 14.1 ps. The TDC was used in a 250 MS/s data acquisition system for interpolating the 4 ns sampling clock period and its interpolation capability was verified. © 1999 American Institute of Physics.

Notes: A newly designed bulge-testing apparatus for the mechanical testing of the tensile properties of free-standing thin films has been constructed and tested. With this instrument it is possible to measure the elastic modulus, tensile and compressive growth stress, and plain strain yield strength in thin films. The setup features a high strain resolution (4E-10), and a high stress resolution, e.g., 〉0.2 MPa for bulge heights larger than 10 μm. In our setup, thin films are stressed by a differential gas pressure across the film, while the deflection is measured by a scanning laser beam. The scanning laser beam measures the curvature of the bulge rather than the bulge height. This makes the setup insensitive to a possible initial nonflatness of the film. This also provides the possibility to measure the growth stress of films that were deposited under a compressive stress. We show the results of measurements of the plane strain modulus on thin tungsten films and on both flat and nonflat aluminum (alloy) film samples. © 1999 American Institute of Physics.

Notes: To understand surface reaction dynamics in III–V compound semiconductor growth, we have developed an apparatus to study both surface chemical reactions and epitaxial growth. This apparatus has double supersonic III and V compound molecular beam cells and an analytical chamber with a rotatable differentially pumped liquid-nitrogen-cooled quadrupole mass spectrometer to measure angular and time-of-flight distribution of reflected beams. It also has reflection high-energy electron diffraction to analyze surface structures. Tertiarybutylarsine beam energies of 1.6 eV were obtained for He, 0.22 eV for Ar, and 0.06 eV for Xe seeding. An organometallic molecular beam of translational energy is varied over a wide range, enabling source molecules to be brought to a well-defined epitaxial surface in well-characterized ways. High-purity GaAs layers were grown by alternatively supplying triethylgallium and tertiarybutylarsine molecules to the analytical chamber. Our apparatus bridges the gap of studies between epitaxial growth and surface chemical reactions. Dynamic measurement on the growth surface revealed a number of interesting reactions not ordinarily observed on well-defined surfaces. © 1999 American Institute of Physics.

Notes: Some diagnostic components in ITER will be subject to high levels of radiation (neutrons and gammas) and changes in their physical properties can result. During the ITER EDA an extensive range of tests on relevant materials, e.g., window materials, metals, and insulators, have been carried out and the changes in their physical properties have been measured. The effects examined include radiation induced electrical damage (RIED) and radiation induced conductivity (RIC) in potential insulators; radiation induced absorption and radio luminescence in potential optical materials; and changes to the reflectivity and surface properties of bulk metal mirrors. The results give a database of information which is of use to the designers of ITER diagnostic systems. Recent and planned work is concentrating on the testing of diagnostic prototypes in relevant radiation fields. The results obtained thus far will be summarized and the planned work outlined. © 1999 American Institute of Physics.

Notes: A complex of probe diagnostics allows extensive characterization of the plasma parameters in the H-1 heliac. The probes used on H-1 include quadruple probes, poloidal and radial "fork" probes, a Mach probe, a 24-channel probe array, and a retarding field energy analyzer. This article provides details of the probe design and a brief description of the experimental techniques involved. Different techniques are compared. Sample results in two different modes of confinement in H-1 are presented. The capabilities of the probe diagnostics used in different combinations are discussed. © 1999 American Institute of Physics.

Notes: A magnetic inductive method for investigating the magnetic properties of ferromagnetic substances over a broad range of temperatures under pressure in diamond-anvil cells is described. The proposed method exploits the fact that ferromagnetic substances change their dynamic magnetic susceptibility during magnetization by a constant external magnetic field up to the point of saturation. With increasing magnetic field, however, the magnetic properties of components of the high-pressure cell are essentially invariant. Therefore, the signal from the sample can be distinguished from that of the background caused asymmetries in the inductance system and the disposition of metal parts in the diamond-anvil cell. Measurements on CdCr2Se4 and iron demonstrate the feasibility of the method. © 1999 American Institute of Physics.

Notes: A chopper wheel apparatus to characterize the time response of a nitric oxide detector is described. At low chopping rates, fast Fourier transform analysis of the output signal indicates that the instrument has a response time of about 0.45±0.14 s with respect to a periodic input signal. This detector has an "e-folding" response time of about 0.3±0.1 s to a simple step change in input signal, demonstrating reasonable agreement within experimental uncertainty between the two techniques. © 1999 American Institute of Physics.

Notes: In the article on which we comment, the authors have in fact only determined the group index of the materials. © 1999 American Institute of Physics.

Notes: In this article, we describe the manufacture and characterization of linear silicon Bragg–Fresnel lenses (BFLs) with outermost zone widths of 100 nm. This is, to our knowledge, a factor of 3 smaller than any other device of this kind reported so far. Furthermore, we give the first detailed description of an accurate and robust method to measure the diffraction efficiency of BFLs. The first-order diffraction efficiency of our lenses at 13.25 keV photon energy was 26%±0.5%. The combination of wide aperture angle, high efficiency, and large size of our devices results in a significant gain in achievable x-ray flux. © 1999 American Institute of Physics.

Notes: A first focusing test of the undulator radiation at SPring-8 has been done using two types of x-ray refractive lenses in thin glass capillaries. One (lens No. 1) contained bubbles in a glue whereas the other (lens No. 2) contained bubbles in glycerol. The capillaries had inner diameters of 0.2 and 0.8 mm, respectively. Using x rays of 17–18 keV, the undulator source image was investigated at the focal plane. The spherical aberrations and the field distortions were carefully examined by taking the images of a gold mesh. Lens No. 1 had an advantage of high transmissivity in the hard x-ray region (18% at 18 keV) and high tolerance to severe radiation damage, e.g., ∼5×1012 photons/s/0.03 mm2 of the 18 keV x rays for an exposure time of 1 h. On the other hand, lens No. 2 had an advantage of a large aperture, 0.8 mm, and a small field distortion, e.g., less than 10% inside a diameter of 300 μm. © 1999 American Institute of Physics.

Notes: As a novel method to obtain a low divergence laser beam, a self-injection locking oscillator system has been developed for a copper vapor laser. The system is made of one laser tube, and uses temporal superposition of two pulsed discharges, predischarge and main discharge. The laser pulse is produced in the main discharge by amplifying a seeded laser pulse produced by the predischarge. By optimizing the discharge conditions including an interval period between the two pulsed discharges, a high quality laser beam containing 80% of the whole laser beam energy in divergence as small as eight times diffraction limited has been obtained. The quality of the laser beam is comparable to that obtained with a conventional injection locking oscillator system consisting of two separate laser tubes. © 1999 American Institute of Physics.

Notes: The use of a charge-coupled device (CCD) camera for the detection of mercuric bromide (HgBr2) vapor at low concentrations by laser photofragment fluorescence (PFF) spectroscopy was investigated. The CCD detection system (camera+monochromator) offers reasonable sensitivity plus spectral information, thus enhancing PFF as a technique for the environmental monitoring of airborne mercury compounds. The experiment used laser radiation at 222 nm to photolyze HgBr2 and produce excited atomic mercury (Hg*). The PFF was monitored at 253.7 nm. Our unenhanced CCD detection limit was about 30 ppb HgBr2 in the absence of air. The CCD response remained linear up to 20 ppm. Observed nonlinearity of the PFF signal at higher concentrations is discussed. With the same collection optics and under the same experimental conditions, the sensitivity of a photomultiplier tube (PMT) with interference filters (253.7 nm) was also investigated for comparison. The detection limit for our PMT system was 10 ppb without signal averaging, but the linear dynamic range ended at 0.7 ppm. It is expected that the CCD detection system would be more versatile for measuring metal compound species by PFF spectroscopy in any future airborne metals monitor. © 1999 American Institute of Physics.

Notes: The emission properties of a Steigerwald-type electron gun are reexamined. Several optical parameters were experimentally determined, and they indicate that the original telefocus mechanism proposed by Steigerwald in 1949 needs to be revised. "Remote focusing" is found to be nonexistent in most of the telefocus electron guns deployed in high-energy electron scattering experiments. Instead, almost parallel beams with variable beam diameters were found. The physical mechanism responsible for producing a very narrow, monochromatic, and highly collimated beam without limiting apertures is explained in this article with supporting evidences from measurements. We think the new emission model proposed here can help new types of electron or ion gun designs and applications using electron gun in electron optical systems. © 1999 American Institute of Physics.

Notes: A gold neutral beam probe system was improved by adopting a multichannel ion detector and adding sweeping functions of beam energy, deflector voltage, and electrode voltage of the analyzer to the system to measure the fluctuations and time evolution of the two-dimensional space potentials with fast resolving time during one shot. Positions of the beam spot on the multichannel detector corresponding to the ionizing points of the beam in the plasma were simulated precisely as a function of the beam energy and the injection angle. A potential derivation formula was determined taking into consideration both the numerical and experimental results, and the reproducibility of the potential profile was checked. Two-dimensional potential profiles were measured in the optimization experiment of the microwave injection angles for formation of the plug potential. © 1999 American Institute of Physics.

Notes: The swept homodyne reflectometer installed on the RFX experiment is composed of five units which cover the frequency range 26.5–110 GHz. This diagnostic system is based on solid state IMPATT sources and can be operated in the O or X mode. During the first operation, at a sweep rate of 0.1 GHz/μs, the typical density fluctuations present in the reversed field pinch configuration usually prevented correct profile reconstruction, which was possible only in some special cases. To increase the sweep speed and overcome this limit, a new IMPATT driver has been built and IF amplifiers, control, and acquisition systems have been modified accordingly. The new configuration has been extensively tested in the 34–38 GHz range with a modulation rate exceeding 4 GHz/μs on many different plasma conditions. Measurements on plasma showed that both the phase and reflected power level can be correctly recovered from the IF signals. These results indicated the criteria necessary to extend the fast sweep capability to the full 26.5–110 GHz range. In this article we present how the fast sweep capability is now being extended to the whole reflectometric diagnostic and the first successful plasma measurements obtained using a test reflectometric system. © 1999 American Institute of Physics.

Notes: Recent results from the high resolution edge x-ray imaging diagnostic at Alcator C-Mod are presented. The diagnostic measures the soft x-ray emissivity using an array of 38 photodiodes viewing the plasma through a narrow aperture. A 10 μm beryllium foil located in the aperture filters away photons below 600 eV and has close to 100% transmission above 2 keV photon energy. The viewing chords are separated by about 1 mm in the plasma region and have minimal overlap. The absolute position of the chords with respect to the vessel has been determined within 1 mm. The chord integrated data are inverted into emissivity as a function of midplane radius assuming that the emissivity is constant on a flux surface. The full three-dimensional geometry is used in the inversion. The emissivity profiles have a radial resolution of 1.7 mm at the midplane and a temporal resolution of 12 μs. Results show that L-mode discharges have very low edge x-ray emission. During H mode, the edge x-ray emissivity is an order of magnitude higher than in the L mode, and has a pronounced pedestal shape with widths in the range 1.5–8 mm. The width is determined as a function of time by fitting a modified tanh function to each profile. Results for width scalings with local parameters such as ρpi and ρi, as well as time resolved edge localized mode data will be presented. © 1999 American Institute of Physics.

Notes: A frequently used method for determination of impurity transport coefficients is the analysis of the radial and temporal time evolution of the impurity density of injected tracer impurities. In cases when the impurity density cannot be measured directly, e.g., by active charge exchange recombination spectroscopy, the impurity density has to be reconstructed from impurity radiation as measured, e.g., by the soft-x camera. Due to the energy integrated information, assumption about the spatial ionization state distribution, e.g., coronal equilibrium, is necessary. This might not be valid in cases of large transport. Consequently, the transport quantities, derived under the preliminary assumption of radial coronal distribution, are used again in an iterative way to improve the density reconstruction in order to approach more realistic transport quantities. The procedure was applied to plasma discharges in the stellarator Wendelstein 7-AS. © 1999 American Institute of Physics.

Notes: Accurate experimental measurements of the equation of state for strongly coupled plasmas (Γ≥1), relevant to astrophysical, geologic and inertial confinement fusion applications, have been extremely difficult. In this pursuit, we have designed a one-dimensional dual-crystal x-ray microscope for making high-resolution measurements of shocks launched by laser pulses in high-density aluminum plasmas. Optical ray-tracing analysis of the design is presented including effects of surface aberrations. The spherically bent mica crystals are arranged at near normal incidence to operate at energies of 1.35 and 4.75 keV using the second and seventh order reflections, respectively. With a magnification of 45×, the microscope's spatial resolution is predicted to be better than 2 μm when coupled to an x-ray streak camera. The addition of a grazing-incidence optic perpendicular to the imaging direction partially compensates astigmatism. This compensation provides an increase in collection efficiency at the streak camera slit by a factor of ∼15. © 1999 American Institute of Physics.

Notes: We developed a two-dimensional spatial resolved high-speed UV sampling camera (HISAC) to study energy transport in laser-produced plasmas. The HISAC is composed of an optical bundle of fibers coupled to a streak camera to obtain a two-dimensional spatial resolution with a temporal resolution of less than a few 10 ps. This HISAC system was demonstrated in the experiments on inferred uniformity measurements of laser-ablation pressures as well as on energy transport in ultraintense laser-plasma interactions. Two-dimensional shock heating was temporally resolved in a hemispherical target, resulting in the distribution of the ablation pressure as a function of laser incidence angle. © 1999 American Institute of Physics.

Notes: One of the most critical quantities to be measured for better understanding of the ablative Rayleigh–Taylor (RT) instability is the cutoff wavelength below which the RT instability is stabilized. Unfortunately, this wavelength is expected to be below or close to spatial resolutions of most x-ray imagers used in the RT experiments. We propose and test a new technique using moiré interferometry to convert short wavelength perturbations to longer wavelength perturbations. The RT target is backlit by x rays and imaged just like in conventional experiments, but a grid mask is inserted between the target and the x-ray imager. The grid mask is one dimensional grid with a period slightly different from the wavelength of the RT target. It is set so that the grid and the RT perturbation groove are parallel to each other. With this operation, the long wavelength moiré interference is measured as the beat with the RT target. As an initial test, we use a grid mask with 10 μm period coupled to RT targets with 8 and 12 μm perturbation wavelengths. The corresponding moiré interference wavelengths are 40 and 60 μm, respectively.© 1998 American Institute of Physics.

Notes: The set of diagnostics that are being installed in TJ–II are meant to cover the full photon energy range expected in TJ–II during the electron cyclotron resonance heating phase. The obtained information will be used to evaluate the energy contained in the superthermal electron populations and its possible relevance in the global power balance as well as for standard electron temperature estimations. Two NaI(Tl) detectors located at the equatorial plane of the machine will be used to analyze the highest energy photons (over 50 keV). One Si(Li) and a planar Ge detector will be used to obtain the emission spectra between 1 and 100 keV. Tomographic reconstruction of plasma emissivity (up to 10 keV) will be carried out using four p-n silicon photodiodes arrays of 16 detectors, located at the same poloidal section. An additional camera will be used to detect toroidal asymmetries. © 1999 American Institute of Physics.

Notes: Microchannel plate intensified (MPI) x-ray detectors are commonly used for imaging and spectral measurements in the 100–1500 eV photon energy range. Using a laser-produced plasma x-ray source, we measured the integrated detector response versus incident x-ray intensity and the relative efficiency versus photon energy of a MPI x-ray detector. Two identical 2000 lines/mm transmission grating spectrometers simultaneously record broadband plasma source emission from a tantalum target. The relative efficiency was determined by comparing the spectrum recorded with an absolutely calibrated x-ray CCD reference detector on one spectrometer to the spectrum recorded with a MPI x-ray detector on the other spectrometer. The integrated detector response versus incident x-ray intensity was measured by simultaneously illuminating the CCD reference detector and the MPI detector with step-wedge-filtered magnesium plasma emission. The aluminum step wedge x-ray filters pass the 1s–2p emission lines of H-like Mg at 1470 eV and the 1s2–1s2p emission lines of He-like Mg at 1350 eV, and provide a four order of magnitude range in incident intensity on the detectors.© 1999 American Institute of Physics.

Notes: Resistive bolometry is an accurate, robust, spectrally broadband technique for measuring absolute x-ray fluence and flux. Bolometry is an independent technique for x-ray measurements that is based on a different set of physical properties than other diagnostics such as x-ray diodes, photoconducting detectors, and P-I-N diodes. Bolometers use the temperature-driven change in element resistivity to determine the total deposited energy. The calibration of such a device is based on fundamental material properties and its physical dimensions. We describe the use of nickel and gold bolometers to measure x rays generated by high-power z pinches on Sandia's Saturn and Z accelerators. The Sandia bolometer design described herein has a pulse response of ∼1 ns. We describe in detail the fabrication, fielding, and data analysis issues leading to highly accurate x-ray measurements. The fundamental accuracy of resistive bolometry will be discussed. © 1999 American Institute of Physics.

Notes: Microchannel plates (MCPs) are used in many diagnostic systems to study laser-plasma interactions. Typically the front surface of a MCP is coated with some photocathode (PC) material to convert x ray to electron. This is followed by electron multiplication along the microchannels. Materials such as CsI, Al, and Au have been identified as good PC materials, but the overall quantum efficiencies of these materials are low, so that electron multiplication along the channel has been the only path to signal amplification. This approach is known to have some problems (J. D. Wiedwald, University of California UCRL-JC-110906, August 1992). We investigated the effect of pairing transmission PC to standard MC's and found that CsI and Au foils used in multilayered configuration, significantly enhance the overall quantum efficiency of the combination. The findings could lead to better MCP design and fabrication.

Notes: A method of the mid-IR-laser microscopy has been recently proposed for the investigation of the large-scale electrically and recombination active defects in semiconductors and nondestructive inspection of semiconductor materials and structures in the industries of microelectronics and photovoltaics. The basis for this development was laid with a wide cycle of the investigations on the low-angle mid-IR-light scattering in semiconductors. The essence of the technical idea was to apply the dark-field method for spatial filtering of the scattered light in the scanning mid-IR-laser microscope. This approach enabled the visualization of large-scale electrically active defects which are the regions enriched with ionized electrically active centers. The photoexcitation of excess carriers within a small volume located in the probe mid-IR-laser beam enabled the visualization of the large-scale recombination-active defects like those revealed in the optical or electron beam induced current methods. Both these methods of the scanning mid-IR-laser microscopy are now introduced in detail in the present article as well as a summary of techniques used in the standard method of the low-angle mid-IR-light scattering itself. Besides the techniques for direct observations, methods for analyses of the defect composition associated with the mid-IR-laser microscopy are also discussed in the article. Special attention is paid upon potential applications of the above methods as characterization and testing techniques in the semiconductor science and industry. It is concluded that elastic midinfrared laser light scattering is a basis for the development of a variety of research techniques and instruments which could be useful in different branches of basic and applied research work in the field of defect engineered semiconductors as well as for the development of devices for quality inspections in the semiconductor industry. Being contactless, nondestructive and nonpolluting, techniques based on midinfrared light scattering could also find many applications for automation of the technological process control as well as the process remote monitoring. © 1999 American Institute of Physics.

Notes: We describe a technique for measuring the thermal diffusivity of substrate-supported polymer films based on the early-time electrothermal response following a 100 ns pulse from a Q-switched ruby laser. Data for a polyimide film spin coated on a p-doped Si[111] substrate are used to demonstrate the technique. From the late-time decay of the signal, we also obtain an estimate of the interfacial thermal-transport coefficient of the polymer–semiconductor interface. © 1999 American Institute of Physics.

Notes: We describe a magnetic field scanning instrument designed to extend the spatial resolution of scanning superconducting quantum interference device microscopy into the submicron regime. This instrument, the scanning Josephson junction microscope, scans a single Josephson junction across the surface of a sample, detecting the local magnetic field by the modulation of the junction critical current. By using a submicron junction and a scanning tunneling microscope feedback system to maintain close proximity to the surface, magnetic field sensitivity of 10 μG with a spatial resolution of 0.3 μm should be attainable, opening up new opportunities for imaging vortex configurations and core structure in superconductors and magnetic domains in magnetic materials. © 1999 American Institute of Physics.

Notes: We report a vacuum cryogenic (80 K〈T〈350 K), near-field microwave scanning system based on a 90 GHz transmitting/receiving resonant slit antenna with a capacitive measurement of the probe-sample separation. The probe allows local measurement of resistance as a function of temperature with the spatial resolution of 20-50 μm. The mm-wave probe is integrated with the eddy-current probe which allows global measurement of resistance of conducting and superconducting samples. This integrated probe is used for local study of the superconducting transition in high-Tc superconducting thin films. The sensitivity of our present mm-wave probe is sufficient for probing conductivity in the normal state and in the superconducting state close to Tc however not yet sufficient for probing conductivity variations far below superconducting transition temperature. © 1999 American Institute of Physics.

Notes: Tritium on the inside walls of the Tokamak Fusion Test Reactor was detected by configuring the vacuum vessel as an ionization chamber and measuring the secondary electron current from the tritium beta decay. The vessel was typically filled with (approximate)5 Torr of dry nitrogen and the secondary electron current was collected by an internal electrode biased to about +15 V with respect to the vessel wall. The measured variations of the collected current with gas pressure, bias voltage, and applied magnetic fields are described, as well as an in situ calibration made by injecting a known amount of tritium gas. Improved versions of this diagnostic may be useful to track the in-vessel content of surface tritium in future fusion devices. © 1999 American Institute of Physics.

Notes: A new spectrophotometric technique has been developed in which the absorption is sampled by short flashes produced by an optical parametric oscillator (OPO) pumped by the third harmonic of a Nd:YAG laser. Continuously tunable monochromatic flashes (6 ns duration, 1 nm bandwidth) are obtained in a domain ranging from 415 to 680 nm and 730 to 2000 nm. Light-induced absorption changes can be analyzed in a time window ranging from 10 ns to 100 s, with a 10−5 noise level. This new technique opens areas of research which are not accessible to previously existing spectrophotometers. Indeed, the high energy of the detecting flashes allows the analysis of samples of large optical density such as leaves, in the blue region of the spectrum. A few examples of application of this method to the analysis of electron transfer reactions in different types of photosynthetic apparatus (leaves, unicellular algae, and bacteria) are presented. This technique is also well suited to analyze the photodissociation of ligands associated with hemoproteins, in solution or in living cells. © 1999 American Institute of Physics.

Notes: A large sized synthetic diamond window assembly was installed on a 170 GHz gyrotron. An aperture and a thickness of the window are 83 and 2.23 mm, respectively, whose edge was directly cooled by water. Gyrotron performances of 520 kW at 6.2 s and 450 kW at 8 s were attained. A temperature increase of the window stabilized after ∼5 s, whereas the power had been limited to below 170 kW with conventional windows. This drastic improvement of a deliverable power was obtained from the outstanding properties of the diamond, that is, an extremely high thermal conductivity (∼1800 W/mK) and a low value of loss tangent (tan δ〈1.3×10−4). The gyrotron was inspected after the ∼1300 times operation at 520 kW (〉1 s), but no damage nor trouble was found both on the gyrotron and the diamond window. These results give a prospect for a multimegawatt power output from the gyrotron, i.e., the diamond window gives a solution for the window problem which has been regarded as the most serious issue on the development of high power long pulse gyrotron. © 1999 American Institute of Physics.

Notes: An ultrahigh vacuum, cryogenic scanning tunneling microscope (STM) has been developed for imaging and current–voltage spectroscopy. Design details and results from initial studies are presented. The microscope design is based on the Besocke "beetle" style STM with some significant modifications. In particular, the placement of the tip and sample have been interchanged to facilitate in-vacuum transfer of tips and samples. The STM operates in a cryostat submerged in liquid helium or liquid nitrogen. Imaging of the 22×3 reconstruction of the Au(111) surface and atomic resolution of graphite are demonstrated. A current versus voltage spectrum showing Coulomb charging features and level quantization in a 29 000 amu Au nanocrystal is also presented to show the spectroscopic capability of the instrument. © 1999 American Institute of Physics.

Notes: Beam line optics for synchrotron facilities are generally designed from geometric calculations wherein the bending magnet, undulator, or wiggler photon source is approximated by a high divergence point source. In this article we will, however, show that in the case of a synchrotron radiation source with very small divergence (such a source can be encountered at an undulator based third generation facility) the imaging properties resemble those of a laser source. This implies certain criteria for the focusing properties of the optical elements in the beam line. For instance, a beam waist is found close to the back focal plane of the optical element, with its position and size dependent on the divergence. If the divergence is determined predominantly by the diffraction part, this also means that the size and position of the beam waist is photon energy dependent. The study has been carried out by analytic treatment, numerical simulations as well as beam profile measurements carried out at beam line I511 at the MAX II synchrotron in Lund, Sweden. © 1999 American Institute of Physics.

Notes: Several advances have been made toward the achievement of quantitative two-dimensional dopant and carrier profiling. To improve the dielectric and charge properties of the oxide–silicon interface, a method of low temperature heat treatment has been developed which produces an insulating layer with consistent quality and reproducibility. After a standard polishing procedure is applied to cross-sectional samples, the samples are heated to 300 °C for 30 min under ultraviolet illumination. This additional surface treatment dramatically improves dielectric layer uniformity, scanning capacitance microscopy (SCM) signal to noise ratio, and C–V curve flat band offset. Examples of the improvement in the surface quality and comparisons of converted SCM data with secondary ion mass spectrometry (SIMS) data are shown. A SCM tip study has also been performed that indicates significant tip depletion problems can occur. It is shown that doped silicon tips are often depleted by the applied SCM bias voltage causing errors in the SCM measured profile. Worn metal coated and silicided silicon tips also can cause similar problems. When these effects are tested for and eliminated, excellent agreement can be achieved between quantitative SCM profiles and SIMS data over a five-decade range of dopant density using a proper physical model. The impact of the tip size and shape on SCM spatial accuracy is simulated. A flat tip model gives a good agreement with experimental data. It is found that the dc offset used to compensate the C–V curve flat band shift has a consistently opposite sign on p- and n-type substrates. This corresponds to a positive surface on p-type silicon and to a negative surface on n-type silicon. Rectification of the large capacitance probing voltage is considered as a mechanism responsible for the apparent flat band shift of (0.4–1) V measured on the samples after heating under UV irradiation. To explain the larger flat band shift of (1–5) V, tip induced charging of water-related traps is proposed and discussed. © 1999 American Institute of Physics.