bluuebunny/crossref_metadata_2025 huggingface dataset:
Test of collinear spectroscopy for precise high-voltage determination
Authors: Götte S. , Knaak K.-M. , Kotovski N. , Kluge H.-J. , Ewald G. , Wendt K. D. A.
Published: March 2004

Collinear spectroscopy holds promise for a precise determination of high dc voltages with an accuracy in the order of 10−6. For this purpose the velocity of ions, which are accelerated with the voltage to be measured, is determined by the analysis of the Doppler effect of their optical resonances. This article describes the construction and test of a prototype designed for measuring voltages from −20 up to −50 kV in collinear spectroscopy. In this way the feasibility of the method, its limitations, and the sources of uncertainty have been investigated experimentally. Thereby the frequencies of the two 3d 2D3/2,5/2→4p 2P3/2 transitions of Ca II have been measured with high accuracy.
Metrological large range scanning probe microscope
Authors: Dai Gaoliang , Pohlenz Frank , Danzebrink Hans-Ulrich , Xu Min , Hasche Klaus , Wilkening Guenter
Published: March 2004

We describe a metrological large range scanning probe microscope (LR-SPM) with an Abbe error free design and direct interferometric position measurement capability, aimed at versatile traceable topographic measurements that require nanometer accuracy. A dual-stage positioning system was designed to achieve both a large measurement range and a high measurement speed. This dual-stage system consists of a commercially available stage, referred to as nanomeasuring machine (NMM), with a motion range of 25 mm×25 mm×5 mm along x, y, and z axes, and a compact z-axis piezoelectric positioning stage (compact z stage) with an extension range of 2 μm. The metrological LR-SPM described here senses the surface using a stationary fixed scanning force microscope (SFM) head working in contact mode. During operation, lateral scanning of the sample is performed solely by the NMM. Whereas the z motion, controlled by the SFM signal, is carried out by a combination of the NMM and the compact z stage. In this case the compact z stage, with its high mechanical resonance frequency (greater than 20 kHz), is responsible for the rapid motion while the NMM simultaneously makes slower movements over a larger motion range. To reduce the Abbe offset to a minimum the SFM tip is located at the intersection of three interferometer measurement beams orientated in x, y, and z directions. To improve real time performance two high-end digital signal processing (DSP) systems are used for NMM positioning and SFM servocontrol. Comprehensive DSP firmware and Windows XP-based software are implemented, providing a flexible and user-friendly interface. The instrument is able to perform large area imaging or profile scanning directly without stitching small scanned images. Several measurements on different samples such as flatness standards, nanostep height standards, roughness standards as well as sharp nanoedge samples and 1D gratings demonstrate the outstanding metrological capabilities of the instrument.
Viscoelastic measurement techniques
Authors: Lakes R. S.
Published: March 2004

Methods for measuring viscoelastic properties of solids are reviewed. The nature of viscoelastic response is first presented. This is followed by a survey of time and frequency-domain considerations as they apply to mechanical measurements. Subresonant, resonant, and wave methods are discussed, with applications.
Measurement of x-ray coherence using two-beam interferometer with prism optics
Authors: Suzuki Yoshio
Published: March 2004

Two-beam x-ray interferometer using prism optics has been developed and applied to measurement of spatial coherence. Two-beam interferometry is made possible by using an x-ray prism as the beam deflector. A portion of the x-ray beam is deflected by the prism, and superimposed on the direct beam. This wavefront-dividing interferometer is essentially the same as well-known Fresnel’s mirror experiment in visible light optics. Quantitative analysis of spatial coherence can be performed by measuring visibility of interference fringes. The experiment has been done at the undulator beamline 20XU of SPring-8. The measured visibility at an x-ray wavelength of 1 Å agrees well with theoretical value. Spatially coherent area larger than 0.5 mm was confirmed by analyzing the visibility of fringes.
Ultrahigh vacuum glancing angle deposition system for thin films with controlled three-dimensional nanoscale structure
Authors: Robbie Kevin , Beydaghyan Gisia , Brown Tim , Dean Cory , Adams Jonathan , Buzea Cristina
Published: March 2004

An ultrahigh vacuum apparatus for the deposition of thin films with controlled three-dimensional nanometer-scale structure is described. Our system allows an alternate, faster, cheaper way of obtaining nanoscale structured thin films when compared to traditional procedures of patterning and etching. It also allows creation of porous structures that are unattainable with known techniques. The unique feature of this system is the dynamic modification of the substrate tilt and azimuthal orientation with respect to the vapor source during deposition of a thin film. Atomic-scale geometrical shadowing creates a strong directional dependence in the aggregation of the film, conferring control over the resulting morphological structure on a scale of less than 10 nm. Motion can create pillars, helixes, zig–zags, etc. Significant features of the apparatus include variable substrate temperature, insertion and removal of specimens from atmospheric conditions without venting the deposition system, computer controlled process parameters, and in situ analysis capabilities. The deposition system was successfully employed for the fabrication of a variety of nanostructured thin films with a wide range of potential applications.
Practical thermoreflectance design for optical characterization of layer semiconductors
Authors: Ho Ching-Hwa , Lee Horng-Wen , Cheng Zau-Hwang
Published: March 2004

Modulation spectroscopy is a powerful characterization tool of semiconductors. In this article, we present a practical design for implementing the thermoreflectance (TR) measurements of sheet-type materials more effectively. Detailed design diagrams of the electronic circuits and heater structure of the TR measurements are described. Duty-cycle and frequency responses of the heated pulses used in the TR measurements of layered GaSe are tested. The heated pulses of low frequency and long duty cycle seem to be more efficient in the periodic thermal perturbation of the layered crystals. The thermoreflectance of layer-type GaSe0.9S0.1 and GaSe0.8S0.2 as well as the polarized thermoreflectance (PTR) of layered ReS2 and ReSe2 are, respectively, carried out. The experimental spectra are detailed analyzed and discussed. Experimental analyses show the well-behaved performance of this thermoreflectance design.
A dielectric slit die for in-line monitoring of polymer compounding
Authors: Bur Anthony J. , Roth Steven C. , Lee Yu-Hsin , McBrearty Michael
Published: March 2004

The dielectric slit die is an instrument that is designed to measure electrical, rheological, ultrasonics, optical, and other properties of a flowing liquid. In one application, it is connected to the exit of an extruder, pump or mixing machine that passes liquefied material such as molten plastic, solvents, slurries, colloidal suspensions, and foodstuffs into the sensing region of the slit-shaped die. Dielectric sensing is the primary element of the slit die, but in addition to the dielectric sensor, the die contains other sensing devices such as pressure, optical fiber, and ultrasonic sensors that simultaneously yield an array of materials property data. The slit die has a flexible design that permits interchangeability among sensors and sensor positions. The design also allows for the placement of additional sensors and instrumentation ports that expand the potential data package obtained. To demonstrate sensor operation, we present data from the extrusion and compounding of a polymer/clay nanocomposite. An analysis of the dielectric data involves a nonlinear fitting procedure that takes into account effects due to electrode polarization and dc conductivity. Light transmission through a filled polymer is analyzed in terms of a Beer’s law attenuation coefficient.
Performance of uncooled microcantilever thermal detectors
Authors: Datskos P. G. , Lavrik N. V. , Rajic S.
Published: March 2004

It has recently been shown that bimaterial microcantilevers can be used as uncooled infrared detectors. Bimaterial microcantilevers deform as their temperature changes due to the absorption of infrared photons. Infrared imaging using uncooled cantilever arrays has already been achieved by a number of groups. In this paper, we examined the performance of microcantilevers as uncooled infrared detectors with optical readout. As in the case of other kinds of uncooled thermal infrared detectors, temperature fluctuation noise and background fluctuation noise are fundamental limits to the performance of microcantilever thermal detectors. Since microcantilevers are mechanical devices, thermo-mechanical noise will also influence their performance. We fabricated a SiNx microcantilever thermal detector with an Al layer in the bimaterial region. For the microcantilever geometry and materials used, the background fluctuation noise equivalent temperature difference, NETDBF, calculated for f/1 optics and a 30 Hz frame rate was found to be 1.26 mK. The NETDTF, limited by temperature fluctuation noise, was calculated to be 7.4 mK while the thermo-mechanical NETDTM was calculated to be 5.3 mK. The sum of all fundamental noise sources, including the intrinsic noise of the “optical lever” readout, results in a total NETD of 9.2 mK. Absence of the readout noise would improve this parameter by only 2%.
Boron nitride nanotubes: Pronounced resistance to oxidation
Authors: Chen Ying , Zou Jin , Campbell Stewart J. , Le Caer Gerard
Published: March 2004

Boron nitride (BN) nanotubes have the same nanostructure as carbon nanotubes but are found to exhibit significant resistance to oxidation at high temperatures. Our systematic study has revealed that BN nanotubes are stable at 700 °C in air and that some thin nanotubes (diameter less than 20 nm) with perfect multiwalled cylindrical structure can survive up to 900 °C. Thermogravimetric analysis reveals an onset temperature for oxidation of BN nanotubes of 800 °C compared with only 400 °C for carbon nanotubes under the same conditions. This more pronounced resistance of BN nanotubes to oxidation is inherited from the hexagonal BN and also depends on the nanocrystalline structure. This high level of resistance to oxidation allows promising BN nanotube applications at high temperatures.
Tensile testing of ultrathin polycrystalline films: A synchrotron-based technique
Authors: Böhm J. , Gruber P. , Spolenak R. , Stierle A. , Wanner A. , Arzt E.
Published: March 2004

The mechanical properties of metallic thin films on the nanoscale acquire increasingly more importance as applications in microelectromechanical systems/NEMS as well as microelectronics have reached this size scale. Here, we present a synchrotron x-ray diffraction technique by which it is possible to characterize the evolution of mechanical stress in a metallic film thinner than 100 nm at measurement times shorter than 60 s per data point. This high data acquisition rate is achieved because no relative motions or tilting of specimen, x-ray source and detector (a large-area charge coupled device camera) are required. The technique comprises an initial “sin2 ψ” measurement to establish the absolute stress values followed by periodic “sin2 φ” measurements during straining to determine stress increments. We describe an experimental setup established at the synchrotron radiation source ANKA (Karlsruhe, Germany) which is specifically suited for monitoring the stress evolution during in situ tensile tests on thin films deposited on compliant polymeric substrates. First stress-strain curves, measured in this way, for a 40-nm-thick gold film are presented.
An electrolytically actuated micropump
Authors: Ateya Daniel A. , Shah Ashish A. , Hua Susan Z.
Published: March 2004

An electrolytically actuated bubble micropump capable of precise dosing at high pumping speed is discussed. The fluid displacement is achieved by sequentially generating electrolytic gas bubbles directly inside the microfluidic channels. The operation of the pump thus requires no moving mechanical parts. A series of phase-shifted dc voltage pulses (ranging from 3.3 to 4.5 V) were applied to inflate the bubbles. Results show that the liquid displacement and pumping rate can be easily and accurately controlled by adjusting the applied voltage, pulse width, and pulse interval. An optimized pump rate of 24 nl/min, corresponding to a flow velocity of 640 μm/s was achieved for a channel size of 25×25 μm in cross section. The measured volume displacements and pump rates were found to be in close agreement with the Faraday bubble growth mechanism. Results also show that the pump can reliably operate at high backpressure (up to 110.1 kPa), and a decrease in pump rate due to elevated backpressure can be offset simply by a small increase in voltage or pulse width.
Effect of interfaces in Monte Carlo computer simulations of ferroelectric materials
Authors: Bolten D. , Böttger U. , Waser R.
Published: March 2004

In this article, Monte Carlo simulation methods were used to investigate the influence of interface layers between the ferroelectric core material and the electrodes on the hysteresis loop in ferroelectric thin films. The hysteresis loops were calculated using an existing Monte Carlo model. For certain interface configurations, the simulations resulted in asymmetric hysteresis loops, similar to imprinted loops, due to asymmetric nucleation kinetics. Although the results might not offer a new explanation for imprint in ferroelectric thin films, they provide insight into the often observed phenomenon of initially imprinted hysteresis loops of as-prepared thin-film samples.
Modification of critical current density of MgB2 films irradiated with 200 MeV Ag ions
Authors: Shinde S. R. , Ogale S. B. , Higgins J. , Choudhary R. J. , Kulkarni V. N. , Venkatesan T. , Zheng H. , Ramesh R. , Pogrebnyakov A. V. , Xu S. Y. , Li Qi , Xi X. X. , Redwing J. M. , Kanjilal D.
Published: March 2004

The effect of 200 MeV Ag ion irradiation on the temperature and field dependence of critical current density (JC) of high quality MgB2 thin films is studied. Substantial increase in JC is observed over a certain field range for the film irradiated at a dose of 1012 ions/cm2. Our analysis suggests that columnar defects are not formed under irradiation conditions used in these studies, which correspond to an electronic energy loss of about 16 keV/nm. Defects clusters are likely to be responsible for the observed improvement in JC.
Enhanced thermoelectric figure of merit of CoSb3 via large-defect scattering
Authors: Shi X. , Chen L. , Yang J. , Meisner G. P.
Published: March 2004

We have measured the structural, chemical, and transport properties of a series of CoSb3 skutterudite samples modified by fullerene additions of 0, 0.52, 3.28, 3.90, 4.77, and 6.54 mass%. Fullerene is a 60-atom carbon molecule that forms microsize clusters between the grain boundaries of CoSb3. We observed that the dominant scattering mechanism in the electrical transport changes from impurity scattering to grain-boundary scattering near a C60 content of ∼5–6 mass%, and that thermal conductivity decreases with increasing C60 content. A significant increase in the thermoelectric figure of merit is achieved for 6.54 mass% C60 compared to the pure CoSb3.
Demonstration of a 256×256 middle-wavelength infrared focal plane array based on InGaAs/InGaP quantum dot infrared photodetectors
Authors: Jiang J. , Mi K. , Tsao S. , Zhang W. , Lim H. , O’Sullivan T. , Sills T. , Razeghi M. , Brown G. J. , Tidrow M. Z.
Published: March 2004

We report a demonstration of an infrared focal plane array based on InGaAs/InGaP quantum dot infrared photodetectors. The middle-wavelength infrared quantum-dot infrared photodetector (QDIP) structure was grown via low-pressure metal organic chemical vapor deposition. A detectivity of 3.6×1010 cm Hz1/2/W was achieved at T=95 K and a bias of −1.4 V. The background limited temperature of our QDIP was 140 K with a 45° field of view. A 256×256 detector array was fabricated with dry etching, and hybridized to a Litton readout chip by indium bumps. Thermal imaging was achieved at temperatures up to 120 K. At T=77 K, the noise equivalent temperature difference was measured as 0.509 K with a 300 K background and f/2.3 optics.
Controlled deposition of picoliter amounts of fluid using an ultrasonically driven micropipette
Authors: Larson Bradley J. , Gillmor Susan D. , Lagally Max G.
Published: March 2004

A fluid microplotter that uses ultrasonics to deposit small fluid features has been constructed. It consists of a dispenser, composed of a micropipette fastened to a piece of lead zirconate titanate piezoelectric, attached to a precision positioning system. When an electrical signal of the appropriate frequency and voltage is applied, solution in the tip of the micropipette wicks to the surface in a controlled fashion. The gentle pumping of fluid to the surface occurs when the micropipette is driven at frequencies in the range of 400–700 kHz. Spots with diameters smaller than several microns can be deposited in this manner. Continuous lines can also be produced. Several examples of deposited patterns and structures are described. This means of deposition represents a higher-resolution alternative to standard fluid deposition techniques in the fabrication of biological microarrays or polymer-based circuits.
Band-pass magnetostatic wave resonators on micromachined silicon substrate
Authors: Marcelli Romolo , Sajin George , Cismaru Alina
Published: March 2004

Bulk and micromachined magnetostatic wave frequency tunable resonators have been designed, realized, and tested. Four resonator configurations, two on a silicon bulk substrate and other two on a micromachined silicon membrane, have been characterized and compared by measuring their S parameter responses at different dc magnetic bias fields. The frequency has been swept between 2 GHz and 5 GHz for silicon bulk resonators and between 2 GHz and 6.5 GHz for the resonators supported by the silicon membrane. By using the membrane technological solution, the insertion losses for membrane supported resonators decrease by about 18 dB with respect to the bulk silicon supported ones. Moreover, the quality factor measured for these configurations was QL≈450, about twice that for silicon bulk supported straight edge resonators. The obtained results demonstrate both: (i) the possibility to combine the magnetostatic wave technology with the micromachining one, and (ii) the improvement of the electrical performances for the resonators supported on a silicon membrane, with a strong decrease in the insertion losses and a doubling of the value for the quality factor. Finally, the obtained electrical response is quite good as compared to the classical alumina-based devices, with the novelty to have realized the resonators in an all-silicon environment.
Observation of dust stream formation produced by low current, high voltage cathode spots
Authors: Foster John E.
Published: March 2004

Macroparticle acceleration driven by low current, high voltage cathode spots has been investigated for potential applications ranging from micrometeoroid simulation to nanoparticle deposition/implantation. Acceleration by this process was observed to occur when nanometer and micrometer-sized particles were exposed to a high voltage pulse in the presence of a plasma discharge. The applied negative voltage pulse initiates the formation of multiple, high voltage, low current cathode spots which provide the mechanism of actual acceleration of the charged dust particles. Dust streams generated by this process were detected using laser scattering techniques. Cathode spot behavior was also documented. The particle impact craters observed at the surface of downstream witness badges were documented using scanning electron microscopy and light microscopy. The observed impacts suggest the presence of energetic macroparticles formed during this process.
Modified gaseous electronics conference reference cell for the study of plasma-surface-gas interactions
Authors: Goeckner M. J. , Marquis J. M. , Markham B. J. , Jindal A. K. , Joseph E. A. , Zhou B.-S.
Published: March 2004

The inductively coupled plasma (ICP) gaseous electronics conference (GEC) reference cell provides a standard system for the study of plasma sciences. In this article, we present a version of the ICP GEC cell that has been designed to allow studies of the interactions between a plasma, gas-phase chemistry, and surface-phase chemistry. Specifically, this modified GEC reference cell has specially designed interior walls that can be heated/cooled (10 to 200 °C) and moved. In addition, these walls can be coated with various materials (Al2O3, SiO2, Si, etc.). Design specifications and initial results are presented. These initial results provide an indication of the flexibility of this modified tool and the types of experiments that it should allow.
Dependence of leakage mechanisms on dielectric barrier in Cu–SiOC damascene interconnects
Authors: Ngwan V. C. , Zhu Chunxiang , Krishnamoorthy Ahila
Published: March 2004

Leakage mechanisms of low-dielectric constant (low-k) carbon-doped silicon oxide (SiOC) were investigated in Cu damascene structure integrated with amorphous SiC or SiN as Cu diffusion barrier at low electric fields (0–1.36 MV/cm) and various temperatures (25–250 °C). Conduction mechanisms of SiOC integrated with SiC were found to be different from that with SiN. Schottky emission over a barrier height of 0.70 eV at Ta/SiOC interface dominates in SiC–SiOC structures while Poole–Frenkel emission over a trap potential well of 0.69 eV dominates in SiN–SiOC structures. Traps in the SiN/SiOC interface are the main sources of leakage in Cu low-k damascene structures with SiN barrier.
Effects of interlayer and annealing on chemical states of HfO2 gate insulators studied by photoemission spectroscopy
Authors: Toyoda S. , Okabayashi J. , Kumigashira H. , Oshima M. , Ono K. , Niwa M. , Usuda K. , Liu G. L.
Published: March 2004

We have performed photoemission spectroscopy of high-k gate insulators HfO2/HfSiON/Si to investigate the interlayer formation by Hf metal predeposition and the annealing effect systematically. Comparing the line shapes of core-level photoemission spectra for two systems with and without Hf-metal predeposition, we found that Hf-metal predeposition effectively reduces the growth of interface layer. Hf 4f core-level spectra revealed that the annealing at 1000 °C for both samples causes the formation of the metallic Hf and Hf-silicide clusters. Surface morphology was also observed by atomic force microscopy.
Coherent control of inhomogeneously broadened system by area-regulated pulse sequence
Authors: Tsurumachi Noriaki , Komori Kazuhiro , Hattori Toshiaki
Published: March 2004

We have proposed a coherent control method that is available even for inhomogeneously broadened systems, which uses an area-regulated laser pulse sequence. It is expected to be applied to ultrafast optical devices without restriction of energy relaxation time.
Direct carrier multiplication due to inverse Auger scattering in CdSe quantum dots
Authors: Califano Marco , Zunger Alex , Franceschetti Alberto
Published: March 2004

Many optoelectronic devices could achieve much higher efficiencies if the excess energy of electrons excited well above the conduction band minimum could be used to promote other valence electrons across the gap rather than being lost to phonons. It would then be possible to obtain two electron–hole pairs from one. In bulk materials, this process is inherently inefficient due to the constraint of simultaneous energy and momentum conservation. We calculated the rate of these processes, and of selected competing ones, in CdSe colloidal dots, using our semi-empirical nonlocal pseudopotential approach. We find much higher carrier multiplication rates than in conventional bulk materials for electron excess energies just above the energy gap Eg. We also find that in a neutral dot, the only effective competing mechanism is Auger cooling, whose decay rates can be comparable to those calculated for the carrier multiplication process.
Free carrier absorption in heavily doped silicon layers
Authors: Isenberg Joerg , Warta Wilhelm
Published: March 2004

The standard parametrization of free carrier absorption in silicon predicting a linear dependence of the absorption on carrier concentration is revised, finding that due to several simplifications, it is only applicable up to carrier densities of about 3×1016 cm−3. A parametrization applicable for both p- and n-type silicon and for doping densities as high as 1021 cm−3 is introduced. Using this parametrization, considerably better agreement between the emitter sheet resistance of diffused layers measured by IR transmission and electrical measurements is found, proving the applicability of the enhanced model even for heavily doped layers. Additionally, parameters for the dependence of the refractive index of silicon on doping concentration are given.
GaN epitaxy on thermally treated c-plane bulk ZnO substrates with O and Zn faces
Authors: Gu Xing , Reshchikov Michael A. , Teke Ali , Johnstone Daniel , Morkoç Hadis , Nemeth Bill , Nause Jeff
Published: March 2004

ZnO is considered as a promising substrate for GaN epitaxy because of stacking match and close lattice match to GaN. Traditionally, however, it suffered from poor surface preparation which hampered epitaxial growth in general and GaN in particular. In this work, ZnO substrates with atomically flat and terrace-like features were attained by annealing at high temperature in air. GaN epitaxial layers on such thermally treated basal plane ZnO with Zn and O polarity have been grown by molecular beam epitaxy, and two-dimensional growth mode was achieved as indicated by reflection high-energy electron diffraction. We observed well-resolved ZnO and GaN peaks in the high-resolution x-ray diffraction scans, with no Ga2ZnO4 phase detectable. Low-temperature photoluminescence results indicate that high-quality GaN can be achieved on both O- and Zn-face ZnO.
Passivation of Mn acceptors in GaMnAs
Authors: Brandt M. S. , Goennenwein S. T. B. , Wassner T. A. , Kohl F. , Lehner A. , Huebl H. , Graf T. , Stutzmann M. , Koeder A. , Schoch W. , Waag A.
Published: March 2004

The effects of hydrogen and deuterium on ferromagnetic GaAs doped with high concentrations of Mn (≈1021 cm−3) are studied. Secondary ion mass spectroscopy depth profiles show that D is incorporated in the same concentration as Mn. The epilayers change from metallic to semiconducting behavior upon hydrogenation. Fourier transform infrared absorption measurements show the As–H and As–D local vibrational modes characteristic for the complexes of hydrogen with group-II acceptors in GaAs.
Preparation of organic bulk heterojunction photovoltaic cells by evaporative spray deposition from ultradilute solution
Authors: Ishikawa Takamasa , Nakamura Makiko , Fujita Katsuhiko , Tsutsui Tetsuo
Published: March 2004

An organic bulk heterojunction photovoltaic cell (OPC) having a thin layer consisting of a functionalized fullerene and a poly-p-phenylenevinylene (PPV) derivative was prepared from a highly diluted tetrahydrofuran solution at the concentration below 1 ppm by the evaporative spray deposition from ultradilute solution (ESDUS) technique. The power conversion efficiency of the OPC prepared from 1:1 mixture solution of fullerene/PPV derivative at the concentration of 1 ppm was 0.69%, which was almost comparable to that prepared by the conventional spin coating technique from 0.5 wt % chlorobenzene solution of the mixture. Although the bulk heterojunction OPCs are known to show relatively high power conversion efficiency, they have two major problems for development of higher device performance. One is a solubility problem of used materials and the other is a strong dependence of the device performance on the preparation solvent. The former has been a stumbling block to improve the performance by examining various combinations of organic materials. The latter has compelled to use relatively toxic solvents such as a chlorobenzene to prepare the devices. Those problems could be solved by the ESDUS technique to fabricate an organic film of almost insoluble materials.
Mechanical response of KD2xH2(1−x)PO4 crystals during nanoindentation
Authors: Kucheyev S. O. , Siekhaus W. J. , Land T. A. , Demos S. G.
Published: March 2004

The deformation behavior of rapidly grown tetragonal KD2xH2(1−x)PO4 (KDP and DKDP) single crystals, with a deuteration degree x of 0.0, 0.3, and 0.6, is studied by nanoindentation with a 1 μm radius spherical indenter. Within experimental error, the deformation behavior is found to be independent of the deuterium content and different for (001) and (100) surfaces. Multiple discontinuities (so-called “pop-in” events) in force-displacement curves are observed during indentation loading, but not during unloading. Slip is identified as the major mode of plastic deformation in DKDP, and pop-in events are attributed to the initiation of slip.
Liquid-tin-jet laser-plasma extreme ultraviolet generation
Authors: Jansson P. A. C. , Hansson B. A. M. , Hemberg O. , Otendal M. , Holmberg A. , de Groot J. , Hertz H. M.
Published: March 2004

We demonstrate the applicability of liquid-metal jets in vacuum as regenerative targets for laser-plasma generation of extreme ultraviolet (EUV) and soft x-ray radiation. This extends the operation of liquid-jet laser-plasma sources to high-temperature, high-Z, high-density, low-vapor-pressure materials with new spectral signatures. The system is demonstrated using tin (Sn) as the target due to its strong emission around λ≈13 nm, which makes the material suitable for EUV lithography. We show a conversion efficiency of 2.5% into (2%BW×2π×sr) and report quantitative measurements of the ionic/atomic as well as particulate debris emission.
GaN micro-light-emitting diode arrays with monolithically integrated sapphire microlenses
Authors: Choi H. W. , Liu C. , Gu E. , McConnell G. , Girkin J. M. , Watson I. M. , Dawson M. D.
Published: March 2004

GaN micro-light-emitting diodes (micro-LEDs) with monolithically integrated microlenses have been demonstrated. Microlenses, with a focal length of 44 μm and a root mean square roughness of ∼1 nm, have been fabricated on the polished back surface of a sapphire substrate of an array of micro-LEDs by resist thermal reflow and plasma etching. The optical properties of the microlenses have been demonstrated to alter the emission pattern of the LED emitters. The cone of light emitted from this hybrid device is significantly less divergent than a conventional broad-area device. This combination of micro-LED and microlens technologies offers the potential for further improvement in the overall efficiency of GaN-based light emitters.
Crossover between extrinsic and intrinsic dielectric loss mechanisms in SrTiO3 thin films at microwave frequencies
Authors: Astafiev K. F. , Sherman V. O. , Tagantsev A. K. , Setter N. , Kaydanova T. , Ginley D. S.
Published: March 2004

The dc bias field dependence of the dielectric loss in SrTiO3 thin films deposited onto MgO substrate is investigated. The experimental data obtained at different frequencies of the ac field (8 and 16 GHz) from differently processed films (as deposited and oxygen annealed) strongly suggest the occurrence of a crossover in the dominant loss mechanism. The crossover is driven by the dc bias field: at weak fields the loss is governed by an extrinsic mechanism(s) whereas, at higher fields, the contribution of an intrinsic mechanism (dc field-induced quasi-Debye loss) becomes predominant.
Large positive magnetoresistance in nonstoichiometric NiMnSb thin films on silicon
Authors: Branford W. R. , Clowes S. K. , Syed M. H. , Bugoslavsky Y. V. , Gardelis S. , Androulakis J. , Giapintzakis J. , Grigorescu C. E. A. , Berenov A. V. , Roy S. B. , Cohen L. F.
Published: March 2004

We report a systematic study of the transport properties of pulsed-laser-deposited NiMnSb films on silicon as a function of film thickness. A low-temperature upturn is observed in the resistivity for film thicknesses of 130 nm and below. The resistivity minimum corresponds to the maximum in the positive magnetoresistance for all samples. As the film thickness decreases, the magnitude of both the resistivity upturn and the magnetoresistance increase. There is no feature associated with the upturn in the low-field Hall resistivity, which becomes systematically more electron dominated as the film thickness decreases and the temperature increases. This has implications for the use of NiMnSb as a spin injector for spintronic applications. The positive magnetoresistance of the 5 nm sample is greater than 100% at 200 K in 8 T. Further enhancement of the magnetoresistance occurs for field parallel, rather than perpendicular, to the film surface. The magnetoresistance behavior is compared to various model systems, including the band-gap tuning found in the silver chalcogenides, disorder-induced weak localization, and the emerging class of “bad metal” ferromagnets.
Ultrafast control of electronic motion in quantum-well structures
Authors: Matos-Abiague A. , Berakdar J.
Published: March 2004

An ultrashort half-cycle pulse (HCP) is a fast (<1 ps) unipolar pulse, followed by a much longer (∼100 ps) and weaker unipolar pulse of opposite polarity. We show that such pulses can be utilized to localize, within femtoseconds, and control, for picoseconds, the electronic motion in a AlxGa1−xAs based symmetric double quantum well. The results are obtained by (i) deriving analytically for a model system the type of HCPs that lead to a fast and sustainable localization of a desirable final electron state and (ii) by solving numerically exactly the time-dependent Schrödinger equation for the quantum-well structure in the presence of the HCPs.
Effect of adhesion on dynamic and static friction in surface micromachining
Authors: Corwin A. D. , de Boer M. P.
Published: March 2004

We measure friction of monolayer-lubricated microelectromechanical systems surfaces under both static and dynamic conditions while continuously controlling the applied normal load at positive or negative values (i.e., compression or tension). The dynamic friction experiment methodology we have devised enables fitting to the complete one-dimensional equation of motion. We observe friction at zero applied load, and quantitatively attribute this to interfacial adhesion. Within error, the adhesive force is the same under static and dynamic conditions.
Detection of nondelayed photons in the forward-scattering of picosecond pulses
Authors: Andreoni A. , Bondani M. , Brega A. , Paleari F. , Spinelli A. S. , Zambra G.
Published: March 2004

We perform time-correlated single-photon counting measurements on 9 ps pulses from a cw mode-locked Nd laser passed through highly turbid water suspensions of Intralipid™, which is a phantom medium widely used for light propagation studies. By detecting photons emerging at very small angles with a system whose pulse-response duration is ∼34 ps full width at half-maximum, we obtain time-of-flight distributions in which the contributions of photons nondelayed by scattering events are evident up to very high values of Intralipid concentrations.
Dielectric/metal sidewall diffusion barrier for Cu/porous ultralow-k interconnect technology
Authors: Chen Zhe , Prasad K. , Li C. Y. , Lu P. W. , Su S. S. , Tang L. J. , Gui D. , Balakumar S. , Shu R. , Kumar Rakesh
Published: March 2004

With the acknowledged insufficiency of traditional Ta or TaN barriers, deposited by physical vapor deposition (PVD), in the Cu/porous ultralow-k intermetal dielectric integration, an amorphous hydrogenated SiC (a-SiC:H)/Ta bilayer sidewall diffusion barrier has been fabricated using 0.13 μm Cu/porous ultralow-k [Porous-SiLK (Proprietary product from Dow Chemical Corporation, USA), k∼2.2] single damascene process. The electrical tests show that the line-to-line leakage current and the electrical breakdown field (EBD) of samples with this a-SiC:H/Ta dielectric/metal bilayer structure are significantly improved compared to the conventional PVD multi-stacked Ta(N) sidewall barrier. This improvement is mostly due to surface roughness modification after the deposition of a-SiC:H film, which, in addition to being a good barrier to Cu diffusion, can effectively “seal” the weak points on the surface of porous low-k material that are responsible for the sidewall barrier failure.
Electrical characterization of phosphorus-doped n-type homoepitaxial diamond layers by Schottky barrier diodes
Authors: Suzuki Mariko , Yoshida Hiroaki , Sakuma Naoshi , Ono Tomio , Sakai Tadashi , Koizumi Satoshi
Published: March 2004

Temperature-dependent current–voltage (I–V), capacitance–voltage (C–V) measurements, and frequency-dependent C–V measurements have been carried out to investigate electrical properties of phosphorus (P)-doped n-type homoepitaxial diamond layers. We have fabricated lateral dot-and-plane (with ring-shaped-gap) Schottky barrier diodes. Frequency-dependent capacitance measurements revealed the existence of a deep donor level. C–V measurements deduced that the net donor concentration was 6.2×1017 cm−3 and the corresponding built-in potential was 4.0 eV, when the P concentration was 8.3×1017 cm−3. Phosphorus electrical activity was 0.75 in the P-doped diamond layer. The carrier thermal activation energy (the donor level) was evaluated to be 0.6 eV from the relation between the net donor concentration and the carrier concentration.
The temporal expression profile of
Mycobacterium tuberculosis
infection in mice
Authors: Talaat Adel M. , Lyons Rick , Howard Susan T. , Johnston Stephen Albert
Published: March 2004

Infection with
Mycobacterium tuberculosis
causes the illness tuberculosis with an annual mortality of ≈2 million. Understanding the nature of the host-pathogen interactions at different stages of tuberculosis is central to new strategies for developing chemotherapies and vaccines. Toward this end, we adapted microarray technology to analyze the change in gene expression profiles of
M. tuberculosis
during infection in mice. This protocol provides the transcription profile of genes expressed during the course of early tuberculosis in immune-competent (BALB/c) and severe combined immune-deficient (SCID) hosts in comparison with growth in medium. The microarray analysis revealed clusters of genes that changed their transcription levels exclusively in the lungs of BALB/c, SCID mice, or medium over time. We identified a set of genes (
n
= 67) activated only in BALB/c and not in SCID mice at 21 days after infection, a key point in the progression of tuberculosis. A subset of the lung-activated genes was previously identified as induced during mycobacterial survival in a macrophage cell line. Another group of
in vivo
-expressed genes may also define a previously unreported genomic island. In addition, our analysis suggests the similarity between mycobacterial transcriptional machinery during growth in SCID and in broth, which questions the validity of using the SCID model for assessing mycobacterial virulence. The
in vivo
expression-profiling technology presented should be applicable to any microbial model of infection.
Inhibition of Epstein-Barr virus-induced growth proliferation by a nuclear antigen EBNA2-TAT peptide
Authors: Farrell Christopher J. , Lee Jae Myun , Shin Eui-Cheol , Cebrat Marek , Cole Philip A. , Hayward S. Diane
Published: March 2004

Epstein-Barr virus (EBV) causes infectious mononucleosis and is associated with cancers in immunocompromised populations. Antiviral drugs targeted against lytic viral replication have limited efficacy in these disease settings. EBV infection of peripheral blood mononuclear cells induces growth proliferation and the EBV latency Epstein-Barr virus-encoded nuclear antigen (EBNA)2 transcriptional transactivator (TAT) is essential for this response. EBNA2 targets the cellular DNA-binding protein CBF1 to mimic activated Notch signaling. A 10-aa peptide from the CBF1 interaction domain of EBNA2 was synthesized as a fusion with the protein transduction domain of HIV-1 TAT. The EBNA2-TAT peptide blocked EBNA2-CBF1 interaction in an
in vitro
GST affinity assay and labeling with fluorescein confirmed that the EBNA2-TAT peptide efficiently entered cultured B cells. Neither EBNA2-TAT, nor a mutant peptide with a 2-aa substitution that was unable to block the EBNA2-CBF1 interaction, significantly affected the growth of non-EBNA2-expressing EBV(-) B cells or Burkitt's lymphoma Akata cells. However, treatment of an EBV-immortalized lymphoblastoid cell line with the EBNA2-TAT peptide stopped cell growth and reduced cell viability. RT-PCR analyses of gene expression in the peptide-treated lymphoblastoid cell line cultures revealed that EBNA2-TAT treatment down-regulated the EBNA2-responsive viral LMP1 and LMP2 genes and cellular CD23, intercellular adhesion molecule 1, BATF, and Cdk1 genes while up-regulating expression of the cyclin-dependent kinase inhibitor p21. EBV-induced outgrowth of B cells from cultured peripheral blood mononuclear cells was also blocked in a dose-responsive manner by the EBNA2-TAT peptide. This study suggests that cell-permeable EBNA2 peptides may have potential as novel anti-EBV therapeutics.
Disease-causing mutant WNK4 increases paracellular chloride permeability and phosphorylates claudins
Authors: Yamauchi Kozue , Rai Tatemitsu , Kobayashi Katsuki , Sohara Eisei , Suzuki Tatsunori , Itoh Tomohiro , Suda Shin , Hayama Atsushi , Sasaki Sei , Uchida Shinichi
Published: March 2004

Mutations in the WNK4 gene cause pseudohypoaldosteronism type II (PHAII), an autosomal-dominant disorder of hyperkalemia and hypertension. The target molecules of this putative kinase and the molecular mechanisms by which the mutations cause the phenotypes are currently unknown. Although recent reports found that expression of WNK4 in
Xenopus
oocytes causes inhibition of the thiazide-sensitive NaCl cotransporter and the renal K channel ROMK, there may be additional targets of WNK4. For example, an increase in paracellular chloride permeability has been postulated to be a mediator of PHAII pathogenesis, a possibility supported by the localization of WNK4 at tight junctions
in vivo
. To determine the validity of this hypothesis, we measured transepithelial Na and Cl permeability in Madin-Darby canine kidney II cells stably expressing wild-type or a pathogenic mutant of WNK4. We found that transepithelial paracellular Cl permeability was increased in cells expressing a disease-causing mutant WNK4 (D564A) but that Na permeability was decreased slightly. Furthermore, WNK4 bound and phosphorylated claudins 1-4, major tight-junction membrane proteins known to be involved in the regulation of paracellular ion permeability. The increases in phosphorylation of claudins were greater in cells expressing the mutant WNK4 than in cells expressing wild-type protein. These results clearly indicate that the pathogenic WNK4 mutant possesses a gain-of-function activity and that the claudins may be important molecular targets of WNK4 kinase. The increased paracellular “chloride shunt” caused by the mutant WNK4 could be the pathogenic mechanism of PHAII.
Mycobacterial polyketide-associated proteins are acyltransferases: Proof of principle with
Mycobacterium tuberculosis
PapA5
Authors: Onwueme Kenolisa C. , Ferreras Julian A. , Buglino John , Lima Christopher D. , Quadri Luis E. N.
Published: March 2004

Mycobacterium tuberculosis
(
Mt
) produces complex virulence-enhancing lipids with scaffolds consisting of phthiocerol and phthiodiolone dimycocerosate esters (PDIMs). Sequence analysis suggested that PapA5, a so-called polyketide-associated protein (Pap) encoded in the PDIM synthesis gene cluster, as well as PapA5 homologs found in
Mt
and other species, are a subfamily of acyltransferases. Studies with recombinant protein confirmed that PapA5 is an acetyltransferase. Deletion analysis in
Mt
demonstrated that
papA5
is required for PDIM synthesis. We propose that PapA5 catalyzes diesterification of phthiocerol and phthiodiolone with mycocerosate. These studies present the functional characterization of a Pap and permit inferences regarding roles of other Paps in the synthesis of complex lipids, including the antibiotic rifamycin.
Percolation and criticality in a mitochondrial network
Authors: Aon Miguel A. , Cortassa Sonia , O'Rourke Brian
Published: March 2004

Synchronization of mitochondrial function is an important determinant of cell physiology and survival, yet little is known about the mechanism of interorganellar communication. We have recently observed that coordinated cell-wide oscillations in the mitochondrial energy state of heart cells can be induced by a highly localized perturbation of a few elements of the mitochondrial network, indicating that mitochondria represent a complex, self-organized system. Here, we apply percolation theory to explain the mechanism of intermitochondrial signal propagation in response to oxidative stress. A global phase transition (mitochondrial depolarization) is shown to occur when a critical density of mitochondria accumulate reactive oxygen species above a threshold to form an extended spanning cluster. The scaling and fractal properties of the mitochondrial network at the edge of instability agree remarkably well with the idea that mitochondria are organized as a percolation matrix, with reactive oxygen species as a key messenger.
Effect of sulfide structure on enantioselectivity in catalytic asymmetric epoxidation of aldehydes: Mechanistic insights and implications
Authors: Aggarwal Varinder K. , Charmant Jonathan , Dudin Leo , Porcelloni Marina , Richardson Jeffery
Published: March 2004

Bridged bicyclic sulfide 1 was originally found to provide high levels of asymmetric induction in sulfur ylide-mediated epoxidations. This sulfide possesses chirality in the [2.2.1] thioether moiety and the [2.2.1] camphor-derived carbocyclic moiety. To determine whether the optimal sulfide had been used, a diastereomer of sulfide 1 in which the stereochemistry of the [2.2.1] carbocycle was reversed (sulfide 5) was prepared and studied as an epoxidation catalyst. This diastereomer gave considerably lower levels of asymmetric induction than the original sulfide 1. From computational and x-ray studies it was found that sulfide 5 gave rise to a more hindered ylide, which reacted more reversibly with aldehydes leading to lower enantioselectivity. Conditions that reduced reversibility were also tested and high enantioselectivities were returned for sulfide 5 (similar to sulfide 1). The implications for the synthesis of chiral sulfides for asymmetric epoxidations are discussed.
Toward efficient asymmetric hydrogenation: Architectural and functional engineering of chiral molecular catalysts
Authors: Noyori Ryoji , Kitamura Masato , Ohkuma Takeshi
Published: March 2004

Asymmetric hydrogenation uses inexpensive, clean hydrogen gas and a very small amount of a chiral molecular catalyst, providing the most powerful way to produce a wide array of enantio-enriched compounds in a large quantity without forming any waste. The recent revolutionary advances in this field have entirely changed the synthetic approach to producing performance chemicals that require a high degree of structural precision. The means of developing efficient asymmetric hydrogenations is discussed from a mechanistic point of view.