bluuebunny/crossref_metadata_2025 huggingface dataset:
A replaceable, low thermal mass hot stage for scanning probe microscopy
Authors: Trawick Matthew L. , Angelescu Dan E. , Chaikin Paul M. , Valenti Michael J. , Register Richard A.
Published: March 2003

We describe the design, construction, and characterization of a hot stage for use in scanning probe microscopy. The hot stage incorporates a heater and thermometer on a single 10×10×0.5 mm silicon chip, allowing rapid thermal response, uniform heat distribution, and low power operation. This design facilitates the incorporation of microfabricated features on the hot stage surface, which we illustrate with a SiNx step edge 30 nm high. Samples to be imaged can also be applied or fabricated directly on the chip. Individual chips can be easily inserted into and removed from a small sample holder, which provides spring contact electrodes to an external temperature controller; wire bonding is not required. The chip and holder combined are 15×15×12 mm.
A new simple method for decoding penumbra image: The filtered autocorrelation
Authors: Rouyer Alain
Published: March 2003

We present a new simple method for decoding penumbra image. Penumbral imaging is a coded aperture technique which uses a simple large circular aperture as coding aperture. Thus, the image of the object is coded and the information must be recovered through a decoding process. The proposed decoding method overcomes the classical problem related to the zero-crossing of the Fourier transform of the point spread function. This problem arises when using the usual methods based on inverse filtering in Fourier domain. Moreover, it allows to remove automatically the flat background which is often superimposed to the penumbra image, without requiring an evaluation of its mean level. Performance comparison with the classical pseudo-Wiener filtering are presented. The method has been applied to ICF neutron penumbra images recorded at the Omega Laser Facility of the LLE (University of Rochester, NY). Experimental results are presented.
Principle and performance of a superconducting angular accelerometer
Authors: Moody M. Vol , Paik Ho Jung , Canavan Edgar R.
Published: March 2003

A sensitive angular accelerometer has been developed. The accelerometer contains a superconducting test mass suspended by a weak flexure pivot and has a bandwidth exceeding 10 Hz. A superconducting quantum interference device amplifier and superconducting circuit are used to detect angular displacement of the test mass. Three nearly identical units have been constructed and tested. An analysis of the instrument is presented along with experimental results. At 4.2 K, performance better than 3×10−9 rad s−2 Hz−1/2 has been demonstrated. The measured noise floor has been traced to seismic motion and temperature fluctuations. The thermal noise contributes less than 10−10 rad s−2 Hz−1/2. Application of the superconducting angular accelerometer to gravity gradiometry is discussed.
Internal resistive heating in diamond anvil cell for in situ x-ray diffraction and Raman scattering
Authors: Zha Chang-Sheng , Bassett William A.
Published: March 2003

An internal resistive heater contained completely between the anvil faces of a diamond anvil cell has been used to conduct experiments up to 10 GPa and temperatures up to 3000 K. There is evidence that pressures up to 50 GPa can be achieved with smaller anvil faces and smaller heater assembly. The technique offers a very homogeneous temperature profile and excellent time stability for studying both metallic and nonmetallic materials. Temperature is measured by spectroradiometry as an image of the incandescent sample is projected onto the end of a fiber optic cable leading to a spectrometer. A very linear relationship between temperature and power provides accurate temperature measurements even when the temperature is below incandescence. The melting of gold determined by loss of diffraction peaks occurred at temperatures in good agreement with published values. In situ Raman spectra of SiO2 revealed the conversion of quartz to coesite. This method offers a larger heating volume with more stable and uniform temperature than laser heating techniques and at temperatures much greater than those that can be achieved by external resistive heating techniques.
CCD-area-based autocollimator for precision small-angle measurement
Authors: Yuan Jie , Long Xingwu
Published: March 2003

An optical method for precision small-angle measurement based on CCD-area-based autocollimator is proposed in this article. The autocollimator utilizes CCD area—an interline CCD image sensor in a video camera as its detector. A collimated image is taken by the video camera and captured into the memory of a personal computer by an image board with high performance, then the image is transformed into a digital image and can be further processed by software with special arithmetic. A small angular displacement is magnified twice by the collimator objective with a long focal length and the camera lens of the video camera. By using a cold-light source and special data processing arithmetic, the measuring resolution of the autocollimator has been greatly improved. The method is proved to be reliable by a prototype experiment. Although some inexpensive materials were used in the experiment, two-axis angular displacement can be measured simultaneously and a measuring accuracy of 0.01 arcsec has been achieved. If some expensive materials with lower temperature expansion coefficient are used, a measuring accuracy of about 0.005 arcsec or a much higher measuring accuracy can be achieved. Until now, this has been the highest measuring accuracy.
Factors affecting the performance of the bimorph-based dilatometer for field induced strain measurement of polymer films
Authors: Guo Shishang , Chan H. L. W. , Zhao X.-Z. , Choy C. L.
Published: March 2003

This article gives a detailed discussion about the design and performance of a bimorph-based dilatometer using different sensor heads and platforms both experimentally and theoretically. A current preamplifier in high-pass filter mode was used to optimize the signal and a protective circuit was introduced. The test results demonstrated that the best signal occurred when the lengths of stainless steel pin and bimorph were both 10.0 mm and that the resonant frequency was inversely proportional to the square of the sensor length. Some suggestions for reducing the noise and improving the sensitivity were also provided.
High-temperature bulge-test setup for mechanical testing of free-standing thin films
Authors: Kalkman A. J. , Verbruggen A. H. , Janssen G. C. A. M.
Published: March 2003

We developed a bulge-test setup which enables measurement of the elastic and plastic properties of free-standing thin film samples between room temperature and at least 300 °C. Mechanical stress is applied to the film by a differential gas pressure across the sample and the bulge height is measured by a scanning laser beam technique. To prevent sample oxidation the pressure cell containing the sample is mounted in a vacuum chamber. The correct operation of the setup is demonstrated by measurement of the thermal expansion of free-standing Al films. Creep experiments and tensile tests demonstrate measurement of the plastic deformation of these films at temperatures up to 200 °C.
Spectral and thermal properties of quasiphase-matching second-harmonic-generation in Nd3+ :Sr0.6 Ba0.4 (NbO3)2 multiself-frequency-converter nonlinear crystals
Authors: Romero J. J. , Aragó C. , Gonzalo J. A. , Jaque D. , Garcı́a Solé J.
Published: March 2003

Quasiphase-matching second-harmonic-generation experiments have been performed on the Nd3+-doped strontium barium niobate multiself-frequency-converter nonlinear crystals. Optical microscopy has been used to determine the size dispersion of cylindrical ferroelectric domains appearing in as-grown crystals. A broad distribution of domain sizes (ranging between 1.5 and 8 μm) has been obtained. This gives the possibility of broadband second-harmonic generation in the 800–1200 nm range. The dependence of second-harmonic efficiency on crystal temperature has been found to be correlated with the thermal behavior of the spontaneous polarization, so that second-harmonic efficiency is almost temperature independent in the 25–50 °C range.
Si doping for n- and p-type conduction in AlxGa1−x As grown on GaAs(311)A by molecular-beam epitaxy
Authors: Kassa S. Tibebu , Hey R. , Ploog K. H.
Published: March 2003

For Si-doped AlxGa1−xAs(311)A with 0⩽x⩽1 grown by molecular-beam epitaxy, a systematic study of electrical properties is performed depending on growth conditions. A phase diagram for the conversion of the conduction type as a function of growth temperature and V/III beam-equivalent pressure ratio is established for AlxGa1−xAs layers. To achieve n-type conduction in AlxGa1−xAs layers, high arsenic flux and growth temperatures not exceeding about 550 °C are required, whereas low arsenic flux and higher growth temperatures lead to p-type conduction. For Si-doped AlxGa1−xAs(311)A layers with x>0.5, p-type conduction is reported with a Si doping efficiency above 90%. Based on these results, all-Si-doped strained-layer In0.2Ga0.8 As/GaAs(311)A quantum-well laser structures with x=0.5 and 0.8 in the cladding layers were grown. Compared with reference laser structures grown on GaAs(100) and doped with Be, a better lasing performance of the all-Si-doped (311)A-oriented single quantum-well laser structures is obtained. For 1.5 mm long conventional broad area lasers, we achieve a lower threshold current density (280 A/cm2), an internal quantum efficiency of about 85%, and an internal optical loss of 9 cm−1.
Continuous model for the shear modulus as a function of pressure and temperature up to the melting point: Analysis and ultrasonic validation
Authors: Nadal Marie-Hélène , Le Poac Philippe
Published: March 2003

The aim of the present study is to propose a predictive model for the shear modulus versus pressure and temperature G(P,T) to complete the principal known elasto-plastic models implemented in hydrodynamic computer codes. The relevance of the proposed G(P,T) model is discussed in detail. The generic approach is to model G(T) by considering Lindemann theory at the melting point. This article focuses on analysis of the mechanical elastic behavior of a solid to confirm that the melting point and the shear component attenuation are closely connected. The drastic fall of G(T) at the melting point is discussed and compared to experimental data mainly derived from ultrasonics. The original part of this work is the experimental work concentrating on direct measurement of the shear wave velocity. The five materials of interest have melting points ranging from that of tin (505 K) to that of tantalum (3269 K). The corresponding Lindemann constant is determined, leading to an average value of 0.103 for cubic crystalline symmetry (Ta, Cu, Au, and Al) and 0.060 for tetragonal crystalline symmetry (Sn). We propose a relationship between G(P,T) and the melting temperature.
Defects in ZnO thin films grown on ScAlMgO4 substrates probed by a monoenergetic positron beam
Authors: Uedono A. , Koida T. , Tsukazaki A. , Kawasaki M. , Chen Z. Q. , Chichibu SF. , Koinuma H.
Published: March 2003

Zinc oxide (ZnO) thin films grown on ScAlMgO4 substrates were characterized by means of positron annihilation. We measured Doppler broadening spectra of annihilation radiation and photoluminescence spectra for the ZnO films deposited by laser molecular-beam epitaxy and single-crystal ZnO. Although the lifetime of positrons in single-crystal ZnO was close to the lifetime of positrons annihilated from the free state, the diffusion length of positrons was shorter than that for typical defect-free materials. We attribute this to the scattering of positrons by native defects. For the ZnO films, we observed a correlation between the defects and the lifetime of bound exciton emissions τEx; the main defect species detected by positron annihilation was Zn vacancies or other related defects. Isochronal annealing at 750–850 °C was found to introduce additional vacancy-type defects into the film, although the value of τEx was scarcely changed by the annealing.
High-resolution transmission electron microscopy study of metastable silicon phases produced by nanoindentation
Authors: Ge Daibin , Domnich Vladislav , Gogotsi Yury
Published: March 2003

Plan-view transmission electron microscopy (TEM) and Raman microspectroscopy were used to identify metastable silicon phases in nanoindentation. A mixture of metastable Si-III and Si-XII phases was observed by both selected area diffraction in TEM and Raman analysis. High resolution TEM observations provided detailed structural information about the metastable phases of silicon and the interfaces between different silicon structures. A mechanism of dislocation-induced lattice rotation that leads to a phase transition and distortion-induced amorphization in nanoindentation is proposed.
Modeling planar leaky optical waveguides
Authors: Pogossian S. P. , Le Gall H.
Published: March 2003

A simple theoretical model is proposed for a description of light propagation in ion-implanted leaky waveguides. It permits interpretation of existing published experimental results. A single parameter, the imaginary component of the refractive index, is sufficient to describe losses in the barrier. Simple analytical expressions are obtained for both the lateral resonance condition and the confinement coefficient. For each quasiguided mode, we calculate an optimal barrier thickness which gives the lowest attenuation coefficient. Interestingly, for thick barriers, high-order modes give the best confinement coefficient. Our approach can also describe prism-loaded slab type waveguides.
Interface-layer formation in microcrystalline Si:H growth on ZnO substrates studied by real-time spectroscopic ellipsometry and infrared spectroscopy
Authors: Fujiwara Hiroyuki , Kondo Michio , Matsuda Akihisa
Published: March 2003

By applying real-time spectroscopic ellipsometry and infrared attenuated total reflection spectroscopy (ATR), we have characterized interface-layer formation in microcrystalline silicon (μc-Si:H) growth on ZnO substrates in a conventional rf plasma-enhanced chemical vapor deposition. With an increase in the hydrogen dilution ratio (R=[H2]/[SiH4]), we find a significant increase in the interface-layer thickness from 0 (R=0) to 48 Å (R=100). In contrast, no interface-layer formation was observed in μc-Si:H growth on SiO2 substrates. Detailed analyses show that the interface layer formed on ZnO is porous amorphous Si:H with a large amount of SiH2 bonds (16 at. %). During the early stage of interface-layer formation, we observed almost no film deposition and a dramatic increase in free-carrier concentration within the ZnO substrate due to a chemical reduction of ZnO by H-containing plasma. Real-time ATR spectra revealed the predominant formation of SiHnO4−n (n=1−2) species on the ZnO surface prior to interface-layer formation. These SiHnO4−n species are chemically inactive and remain at the μc-Si:H/ZnO interface. Based on these findings, we propose that the SiHnO4−n formation that results from ZnO reduction reaction by H suppresses chemical reactivity on the ZnO surface and induces porous interface-layer formation during the initial deposition process.
Influence of the postplasma process conditions on the surface conductivity of hydrogenated diamond surfaces
Authors: Snidero E. , Tromson D. , Mer C. , Bergonzo P. , Foord John S. , Nebel C. , Williams Oliver A. , Jackman Richard B.
Published: March 2003

It is a common observation that diamond surface conductivity rises after exposure to hydrogen plasmas. Hydrogenation treatments are known to induce a p-type conductive layer, which is not present on non-hydrogenated samples. However, the particular mechanisms predominant in the plasma treatment process are still controversial, and several antagonist conditions have been reported to be of importance, such as sample temperature (500 °C to 800 °C), duration (a few seconds to 1 h), and microwave (MW) power density, etc. Further, the post-plasma step is also crucial, especially since the surface conductivity has been reported to be affected by the presence of an adsorbate layer on the diamond surface. By setting up the arrangement to enable the in situ measurement of the surface conductivity after treatment, we have been able to control all parameters that could affect the surface conductivity, in order to determine those of importance. Among the parameters studied, we were able to analyze the influence of the surface temperature, the gas phase exposure (dry air, wet air, neutral gas, CH4, O2, and H2), the MW plasma conditions (O2,H2) as well as the exposure to UV (Hg and deuterium) and the importance of the sequence and duration of each of these treatments. We found that hydrogenated surfaces are strongly influenced by the combination of wet air exposure and UV light. We noticed that the effect of UV light is persistent and cannot be related to direct photoconduction and has to be attributed to a modification of the trapped defect population. This can, therefore, be compared with the modification of filled defect density as observed in persistent photoconduction.
Comment on “Unified compact theory of tunneling gate current in metal–oxide–semiconductor structures: Quantum and image force barrier lowering” [J. Appl. Phys. 92, 3724 (2002)]
Authors: Fischetti M. V.
Published: March 2003

Quan, Kim, and Cho [J. Appl. Phys. 92, 3724 (2002)] have proposed a compact model to evaluate the tunneling current across the insulator of metal–oxide–semiconductor structures and have claimed to have “shown conclusively that image force lowering of the oxide barrier is negligible for the oxide as thin as 1 nm.” Unfortunately, the model is based on a questionable approximation for the “transparency factor.” Most importantly, the argument brought forward to explain the negligible effect of the image-induced barrier-lowering ignores simple concepts of electrostatics.
Reply to “Comment on ‘Unified compact theory of tunneling gate current in metal-oxide-semiconductor structures: Quantum and image force barrier lowering’ [J. Appl. Phys. 92, 3724 (2002)]”
Authors: Quan Wu-yun , Kim Dae M. , Cho Myoung Kwan
Published: March 2003

Our transparency factor, Peff using the effective triangular approximation is shown to practically match PWKB given in the comment. It indicates that Peff can model the effect of image force lowering (if it exists) on the gate current (Ig) in the Fowler–Nordheim regime as accurately as the Wentzel–Kramers–Brillouin method. The experimentally extracted value of α≈0 indicates that PWKB incorporating the image potential still overestimates Ig. Additionally, physics underlying the image force lowering in metal-oxide-silicon systems is briefly discussed in light of the wave nature of electrons and other reported experimental data.
Effect of water adsorption on microscopic friction force on SrTiO3(001)
Authors: Iwahori Koichiro , Watanabe Shunji , Kawai Maki , Kobayashi Kei , Yamada Hirofumi , Matsushige Kazumi
Published: March 2003

A friction force microscope study in ultrahigh vacuum was conducted on an atomically flat SrTiO3(001) surface, where SrO and TiO2 domains were distinguished by the difference in friction force. It is revealed that the friction on the SrO became stronger with water adsorption relative to the TiO2 layer. The selective change in friction is attributed to the chemical reaction occurring on the SrO layer, which is supported by the results of x-ray photoelectron spectroscopy.
Interface properties and reliability of ultrathin oxynitride films grown on strained Si1−xGex substrates
Authors: Samanta S. K. , Chatterjee S. , Maikap S. , Bera L. K. , Banerjee H. D. , Maiti C. K.
Published: March 2003

The role of nitrogen in improving the interface properties and the reliability of oxynitride/SiGe interfaces and the dielectric properties of oxynitride films has been studied using constraint theory. Ultrathin (<3 nm) oxynitride films were grown using N2O followed by N2 annealing on strained Si0.82Ge0.18 layers. Silicon dioxide films grown on strained Si0.82Ge0.18 layers were also nitrided in N2O by rapid thermal processing. The nitrogen distribution in the oxynitride films was investigated by time-of-flight secondary ion mass spectrometry. The interface state density, charge trapping properties, and interface state generation with constant current and voltage stressing were studied. It is observed that dielectric films grown in N2O ambient and subsequently annealed in N2 have excellent electrical properties. A low stress-induced leakage current and a high time dependent dielectric breakdown are also observed in these films. Improvements in the electrical properties are shown to be due to the creation of a large number of strong Si–N bonds both in bulk and in the SiON–Si1−xGex interface region of the dielectric.
Combined effect of thickness and stress on ferroelectric behavior of thin BaTiO3 films
Authors: Huang G-F. , Berger S.
Published: March 2003

Thin BaTiO3 (BTO) layers were deposited by magnetron sputtering on a Si substrate between two thin LaNiO3 (LNO) electrodes (LNO/BTO/LNO/Si structure). The thickness of the BTO layer was varied between 35 nm and 1 μm. The stress, dielectric permittivity, and ferroelectric hysteresis loop were measured after deposition and during heating. It was found that the BTO layers are under tensile stress at the Curie temperature. The tensile stress increases with decreasing layer thickness leading to a shift of the Curie point to a lower temperature, a decrease of remanent polarization, and an increase of the coercive field. The effect of tensile stress on the Curie temperature is dominant within a restricted range of stresses between 300 and 450 mega Pascals (MPa), where the Curie temperature decreases linearly by about 0.16 °C/MPa. A good correlation was found between stress and dielectric measurements with respect to the temperature of the Curie point. The ferroelectric hysteresis loops showed that the ferroelectric-paraelectric phase transition starts at the Curie temperature of the BTO layer and continues within a range of temperatures until about the Curie temperature of the bulk BTO material. The ferroelectric behavior indicates dominance of domains within the interior part of the BTO layer and minor contribution of surface domains. The results are compared with a theoretical approach of size-driven phase transition in stress-induced ferroelectric thin films.
Calorimetric measurements of phase transformations in thin films of amorphous Te alloys used for optical data storage
Authors: Kalb J. , Spaepen F. , Wuttig M.
Published: March 2003

Sputtered amorphous Ag0.055 In0.065 Sb0.59 Te0.29, Ge4 Sb1 Te5, and Ge2 Sb2 Te5 thin films were studied by differential scanning calorimetry. The crystallization temperature and the heat of crystallization of the amorphous phases, the melting temperature and the heat of fusion of the crystalline phases, and the heat capacities of crystalline and liquid AgInSbTe were measured. The entropies of fusion are large (⩾2R), which suggests a change of bonding type between liquid and crystal. In contrast to amorphous AgInSbTe and Ge4 Sb1 Te5, which upon heating crystallize to a single phase within a small temperature interval, the crystallization of amorphous Ge2 Sb2 Te5 is complicated by a subsequent cubic-to-hexagonal transformation. No thermal evidence of a glass transition was found below the crystallization temperature. The ratio of the glass transition temperature (approximated as the crystallization temperature) to the liquidus temperature is 0.49–0.56, which identifies the materials as marginal glass formers. The heat capacity measurements on AgInSbTe were used to estimate the temperature dependence of the difference in enthalpy, entropy, and Gibbs free energy between the undercooled liquid and the crystal.
Photoinduced nonlinear optics in Ca4GdO(BO3)3 nanocrystallites embedded within a polymer matrix
Authors: Gruhn W. , Kityk I. V. , Sahraoui B.
Published: March 2003

The photoinduced nonlinear optical effects in large-sized (up to 20 nm) Ca4(GdO(BO3)3) GdCOB nanocrystallites incorporated within an oligoether photopolymer matrix have been studied. The photoinduced optical second harmonic generation (SHG) was measured at the fundamental wavelength 1.06 μm. A nitrogen pulsed laser (λ=0.337 μm) was used as the source of photoinducing light. We found that with increasing ultraviolet (UV) illumination power density, the output doubled frequency SHG signal (λ=0.53 μm) increases and achieves its maximum value at a UV power density about 1.4 GW/cm2 and nanocrystallite size about 5.5 nm. The absolute SHG values were about 15% less than for the d222 tensor of potassium dihydrogen phosphate single crystals. With decreasing temperature below 18 K, the SHG signal increases. Probe-pump measurements indicate the occurrence of a SHG maximum at a pump-probe delay time of about 27 ps. This effect is explained within the framework of the anharmonic electron-phonon interaction due to creation of photoinduced electrostricted phonons. Third-order two-photon absorption was also investigated. We showed that the BO3 structural fragments play a crucial role in the observed photoinduced effects. The results obtained show that the mentioned composites can be used as a powerful tool for creation of UV-operated nonlinear optical devices.
Luminescent properties of nanostructured Dy3+- and Tm3+-doped lanthanum chloride prepared by reactive atmosphere processing of sol-gel derived lanthanum hydroxide
Authors: Soga Kohei , Wang Wenzhong , Riman Richard E. , Brown J. Bryan , Mikeska Kurt R.
Published: March 2003

Dy 3+ - and Tm3+-doped lanthanum chloride was prepared via reactive atmosphere processing (RAP) of sol-gel derived hydroxide powders. The low-phonon energy chloride host facilitated the 1.3-μm emission from Dy3+ and the 1.2- and 1.4-μm emissions from Tm3+. The emission intensities of the Dy3+ and Tm3+ ions increased logarithmically with increasing RAP temperature. The dependence of emission intensities and lifetimes on the rare-earth (RE) concentration was also investigated. The emission intensity was found to increase up to 1 mole % RE for both ions. Luminescence quenching was observed for concentrations exceeding 1 mole % for Tm3+ and 0.1 mole % for Dy3+.
Band-gap bowing effects in BxGa1−xAs alloys
Authors: Shan W. , Walukiewicz W. , Wu J. , Yu K. M. , Ager J. W. , Li S. X. , Haller E. E. , Geisz J. F. , Friedman D. J. , Kurtz Sarah R.
Published: March 2003

Photomodulation spectroscopy studies of the transitions at the Γ point of the Brillouin zone of thin films of BxGa1−xAs alloys grown by metal-organic chemical-vapor deposition are presented. A very small increase of the fundamental band gap is found in samples with B content up to 3%. Under hydrostatic pressure, the band gap increases at a rate almost identical to the pressure dependence of the GaAs band gap. In contrast to the case of N incorporation at similar concentrations into GaAs, the experimental results show that B incorporation does not cause large modifications of the conduction-band structure in BxGa1−xAs alloys.
Remanent polarization of evaporated films of vinylidene fluoride oligomers
Authors: Noda Kei , Ishida Kenji , Kubono Atsushi , Horiuchi Toshihisa , Yamada Hirofumi , Matsushige Kazumi
Published: March 2003

A remanent polarization of 130±3 mC/m2, large among the values reported for organic materials, and rectangular D–E hysteresis curves were realized in synthesized vinylidene fluoride (VDF) oligomer [CF3(CH2CF2)17I] film evaporated onto a platinum surface around liquid nitrogen temperature. The results suggested that the VDF oligomer film has an extremely high crystallinity, and the electric dipoles arrange almost perfectly perpendicular to the film surface, and that a Lorentz local field factor of ferroelectric VDF oligomer crystals is nearly zero. Moreover, the obtained value of the coercive field, which was larger than those of ferroelectric polymers, might be attributed to the steric hindrance arising from the existence of iodine atoms at the VDF oligomer chains.
Temperature dependence of single-axis acoustic levitation
Authors: Xie W. J. , Wei B.
Published: March 2003

The temperature-dependent physical conditions for single-axis acoustic levitation are theoretically analyzed with consideration of the deviation of the actual acoustic field from the plane standing wave approximation. The effects of temperature variation on the resonant conditions, levitation force and threshold pressures pm (the minimum entrapping pressure) and pM (the maximum pressure to keep the integration of a liquid drop) are discussed by assuming a quasi-static heating and cooling process. The first resonant spacing H1 between the reflector and emitter is larger than that predicted for plane standing waves, and its temperature dependence comes mainly from the variation of wavelength, which is proportional to T1/2. The maximum levitation force FM has a drastic decreasing tendency with temperature rise due to its sensitivity to the ratios of the geometric parameters to wavelength. For the containerless processing of water and the Pb–Sn eutectic alloy, pm decreases whereas pM increases with the enhancement of temperature, which narrows the allowed pressure range for the safe and stable levitation of the processed drops at higher temperatures. As an experimental application of these analyses, the acoustically levitated water and the Pb–Sn eutectic alloy melt are highly undercooled by up to 24 and 38 K, respectively.
Static screening by conducting nanospheres
Authors: Krčmar Maja , Saslow Wayne M. , Zangwill A.
Published: March 2003

This article examines the static screening of a uniform electric field by nonideal conducting nanospheres; that is, those with a finite (rather than an infinite) density of states at the Fermi surface. The theory characterizes the spheres with a nonzero screening length ℓ and a dielectric constant ε≠1. We study bulk spheres, spherical shells, and bulk spheres with localized and delocalized surface states. The results should be applicable to nanospheres with a quasicontinuous distribution of energy levels such as metallic and semiconducting nanoparticles and fullerene complexes such as carbon onions. A companion article uses the same theory to treat the electrostatics of nonideal conducting nanocylinders.
Electrostatics of conducting nanocylinders
Authors: Krčmar Maja , Saslow Wayne M. , Zangwill Andrew
Published: March 2003

This article calculates the capacitance and transverse polarizability of nonideal conducting nanocylinders. It employs a semiclassical theory that characterizes the cylinders with a nonzero screening length ℓ and a dielectric constant ε≠1. Cylinders both with and without free surface states are considered. The results should be relevant to cylinders with a quasicontinuous distribution of energy levels such as nanowires and nanotubes. The theory yields very acceptable agreement with random phase approximation calculations for the radius dependence of the polarizability of single-wall carbon nanotubes. The same type of theory has already been applied to the capacitance of nanospheres, and in a companion article is applied to static screening by nanospheres.
Miniaturized electrostatic analyzer manufactured using photolithographic etching
Authors: Enloe C. L. , Krause L. Habash , Haaland R. K. , Patterson T. T. , Richardson C. E. , Lazidis C. C. , Whiting R. G.
Published: March 2003

A design for a new type of electrostatic analyzer, comprised of an arrangement of thin, patterned, conducting, and insulating plates and suitable for extreme miniaturization, is presented. The prototype, destined for use on a microsatellite-based experiment, is fabricated from photolithographically etched stainless steel plates with Teflon insulating layers. Results from tests on the prototype using a highly monoenergetic electron beam show that, as predicted, the device operates as a bandpass energy filter. The energy resolution and angular field of view of this design depend on the relative geometries of the apertures in the conducting plates and can be tailored to specific applications by varying these parameters.
Vector measurements with combined magnetic and electric field sensors
Authors: Prance R. J. , Clark T. D. , Harland C. J. , Prance H.
Published: March 2003

In this article we describe a vector measurement system consisting of a highly sensitive induction magnetometer and a novel electric field sensor. These elements are combined over a broad range of frequencies (10 Hz–10 kHz) using an active phase shift network to provide real-time vector information about the signal.
Thomson scattering system for the diagnosis of the ETE spherical tokamak plasma
Authors: Berni L. A. , Ueda M. , Del Bosco E. , Ferreira J. G. , Oliveira R. M. , Vilela W. A.
Published: March 2003

A 10 J ruby laser Thomson scattering system was implemented on the ETE spherical tokamak to measure the density ne and temperature Te profiles. The laser probes the plasma at the horizontal midplane of the torus and the collection optics allows the observation of up to 22 points inside the plasma in the same plane. Radial profiles of plasma density and electron temperature were obtained for different times during the discharge by shot-to-shot procedure. Temperatures of up to 160 eV and densities of 2.2×1019 m−3 were measured. Since the level of stray light was too high, the calibration of the Thomson scattering system for density measurements was made using the nitrogen Raman technique instead of the usually applied Rayleigh method.
The flexible and modern open source scanning probe microscopy software package GXSM
Authors: Zahl Percy , Bierkandt Markus , Schröder Stefan , Klust Andreas
Published: March 2003

GXSM is a full featured and modern scanning probe microscopy (SPM) software. It can be used both in stand alone mode for powerful image processing and analysis and connected to an instrument operating many different flavors of SPM, e.g., scanning tunneling microscopy and atomic force microscopy or in general two-dimensional multichannel data acquisition instruments. The GXSM core can handle different data types, e.g., integer and floating point numbers. An easily extendable plug-in architecture provides many image analysis and manipulation functions. A digital signal processor subsystem runs the feedback loop, generates the scanning signals, and acquires the data during SPM measurements. In addition it performs sophisticated spectroscopy tasks such as scanning tunneling spectroscopy. The GXSM software is released under the GNU general public license and can be obtained via the Internet.
Long afterglow phosphorescent sensor materials for fiber-optic thermometer
Authors: Aizawa H. , Katsumata T. , Takahashi J. , Matsunaga K. , Komuro S. , Morikawa T. , Toba E.
Published: March 2003

Long duration phosphorescent SrAl2O4 phosphors doped with various auxiliary activators (Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) have been evaluated for the fiber-optic thermometer application. In this thermometer, temperature was measured based on the temperature dependence of the lifetime and/or intensity of the afterglow phosphorescence which was dominated by the thermal excitation of trapped carriers. Characteristics of the long phosphorescent fiber-optic thermometer are quite different from those of the conventional thermometer using fluorescent lifetime of the phosphors. Lifetime and intensity of the afterglow phosphorescence from the long afterglow phosphorescent sensor heads show large positive temperature coefficients in the narrow temperature region around room temperature. Sensitivity and temperature range of the long phosphorescent fiber-optic thermometer depend strongly on the trap depth and the trap density of phosphors. Since the trap depth and the trap density vary with auxiliary activator elements, a variety of fiber-optic thermometers with high sensitivity in various temperature ranges will be able to be developed using Eu2+ doped SrAl2O4 codoped with various auxiliary activator Ln3+ ions (Ln=Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu).
A three-frame Mach–Zehnder interferometer for measuring dense magnetized plasmas
Authors: Wang Xinxin , Zou Xiaobing , Liu Zhen , Han Min , Luo Chengmu , Ma Ruili
Published: March 2003

A three-frame Mach–Zehnder interferometer (TFMZI) was developed for taking three pictures of the imploding plasma produced by one shot of fast pulsed discharge. TFMZI consists of a YAG laser, a beam splitter, and a Mach–Zehnder interferometer. By passing through the beam splitter the laser beam was split into three beams with an interbeam delay of 13 ns and each laser beam will give a snapshot of the implosion state. The measurements with the TFMZI were conducted on a small gas-puff z-pinch device and gave good results. In principle an upgraded four or (more) frame Mach–Zehnder interferometer could be constructed if much improvement was made on the TFMZI.
Comparison of cryogenic filters for use in single electronics experiments
Authors: Bladh K. , Gunnarsson D. , Hürfeld E. , Devi S. , Kristoffersson C. , Smålander B. , Pehrson S. , Claeson T. , Delsing P. , Taslakov M.
Published: March 2003

We have analyzed six different cryogenic filters for applications in single electronics. Each filter is evaluated with respect to its construction, cryogenic compatibility, principle of operation, and performance. The filters were measured at 4.2 K in a 50 Ω environment between 20 kHz and 8 GHz. We have also combined some of the best properties of these filters into a single, highly effective filter that covers the entire frequency spectrum.
Optical measurements of structure and orientation in sheared carbon-nanotube suspensions
Authors: Hobbie E. K. , Wang H. , Kim H. , Han C. C. , Grulke E. A. , Obrzut J.
Published: March 2003

We describe an optical metrology for measuring shear-induced structure and orientation in dilute dispersions of multiwalled carbon nanotubes. Small-angle polarized light scattering and optical microscopy are combined in situ to quantify the structural anisotropy of multiwalled carbon nanotubes in semidilute, surfactant-stabilized aqueous suspensions under simple shear flow. Measurements performed as a function of the applied shear rate are used to demonstrate the capabilities and limitations of the experimental technique, which should be suitable for probing the shear response of polymer-nanotube melts and solutions.
Acoustic modes in free and embedded quantum dots
Authors: Rufo Salvador , Dutta Mitra , Stroscio Michael A.
Published: March 2003

Acoustic phonon spectra were calculated for different quantum dots for the free-standing case and for the case in which the quantum dot is embedded in a selection of different matrix materials including semiconductors, plastic, and water. The case of water as a matrix embedding a quantum dot is of special interest in biology where quantum dots are being used as biological tags. The acoustic phonon modes can be normalized in the free-standing case and the Hamiltonians for the deformation potential interactions derived. The results demonstrate that the matrix can have a large effect on the acoustic phonon spectrum and therefore it should be included when calculating the acoustic modes of the quantum-dot heterostructures. Simple analytic results are used to specify completely the lowest-order spherical breathing mode for free-standing quantum dots.
Fabrication of microlenses in Ag-doped glasses by a focused continuous wave laser beam
Authors: Antonov I. , Bass F. , Kaganovskii Yu. , Rosenbluh M. , Lipovskii A.
Published: March 2003

A technique for the fabrication of small (2–10 μm in diameter) microlenses on the surface of glass with embedded silver nanoclusters in a subsurface diffusion layer is demonstrated. The dependence of the microlens size on the exposure time and the laser power of a focused continuous wave (cw) laser beam is discussed. It is shown that the optical transmission of the lenses increases with increasing laser power used for the exposure. The temperature distribution in the glass around the focal spot is calculated taking into account the temperature dependence of heat conductivity, shape of the beam, and decrease of absorption coefficient with depth through the diffusion layer containing Ag clusters. The measured microlens sizes are in good agreement with the calculations.
Optical constants of cubic GaN/GaAs(001): Experiment and modeling
Authors: Muñoz Martı́n , Huang Y. S. , Pollak Fred H. , Yang Hui
Published: March 2003

The optical constants ε(E)=ε1(E)+iε2(E) of unintentionally doped cubic GaN grown on GaAs(001) have been measured at 300 K using spectral ellipsometry in the range of 1.5–5.0 eV. The ε(E) spectra display a structure associated with the critical point at E0 (direct gap) and some contribution mainly coming from the E1 critical point. The experimental data over the entire measured spectral range (after oxide removal) has been fit using the Holden–Muñoz model dielectric function [M. Muñoz et al., J. Appl. Phys. 92, 5878 (2002)]. This model is based on the electronic energy-band structure near critical points plus excitonic and band-to-band Coulomb-enhancement effects at E0, E0+Δ0 and the E1, E1+Δ1, doublet. In addition to evaluating the energy of the E0 critical point, the binding energy (R1) of the two-dimensional exciton related to the E1 critical point was estimated using the effective mass/k⋅p theory. The line shape of the imaginary part of the cubic-GaN dielectric function shows excitonic effects at room temperature not withstanding that the exciton was not resolved.
On the lower limiting velocity of a dynamic crack in brittle solids
Authors: Beery Ilan , Lev Uri , Sherman Dov
Published: March 2003

The existence of forbidden velocity gap in dynamic crack propagation in brittle crystals has been proposed previously, based on analytical calculations and numerical simulations. These suggested that the minimal velocity of a dynamically propagating crack is a significant portion of the Rayleigh wave speed. On the other hand, theoretical analysis based on continuum mechanics does not identify any lower limit to the crack velocity. In this work, we studied experimentally the crack velocity in glass and single-crystal silicon, in a geometry that constrains the crack profile to a nearly quarter elliptical shape, such that at a certain part of the crack it is forced to move appreciably slowly. Direct measurements show that the crack velocity along this profile decreases to less than 1% of the Rayleigh wave speed, both at room temperature and at 77 K, which is notably below the expected velocity gap.
Spin-state effects on the outer core-level multiplet structures for high-spin Mn molecular clusters
Authors: Nelson A. J. , Reynolds John G. , Christou George
Published: March 2003

Oxo-bridged manganese polynuclear complexes have applications in a variety of technologies, such as single-molecule nanomagnets, catalysis, and photosynthetic redox chemistry. X-ray photoemission spectroscopy was used to study the Mn 3p, 3s, and valence band electronic behavior as a function of Mn cluster structural properties, where the cluster size and nuclearity are systematically varied. Results show a chemical shift of the Mn 3p3/2,1/2 spin–orbit pair related to the cluster size and nuclearity. In addition, the Mn 3s S7 and S5 final state multiplet components shift since they involve the binding energy of a ligand valence electron. In addition, the branching ratio of the S7:S5 states is related to the 3s–3d electron correlation. Specifically, in the S7 state, the remaining 3s electron is well correlated with 3d electrons of parallel spin, while in the S5 state, the two spins are antiparallel. Changes in this electron correlation are clearly observed in the S7:S5 branching ratio as a function of cluster size and ligand electronegativity.
Photoluminescence of InGaN/GaN multiple quantum wells originating from complete phase separation
Authors: Chen P. , Chua S. J. , Miao Z. L.
Published: March 2003

The photoluminescence (PL) spectra of InGaN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition were investigated by varying the PL temperature and excitation power density. Two different sapphire substrates, an exact c-plane and a c-plane with a 2° offset towards the a-plane, were used. The MQW samples were grown under the same conditions. A shift of the PL peak position to a longer wavelength was observed on the off-axis substrate. At all temperatures, the PL spectra from InGaN/GaN MQWs grown on the on-axis substrate showed a double-peak structure, while those from the MQWs grown on the off-axis substrate showed a single-peak structure. With increasing excitation power density, a larger blueshift was found on the off-axis substrate. These experimental results were discussed based on the segregation effect in InGaN MQWs. The high In composition regions on the off-axis substrate play an important role in the radiative recombination process.
Excitation energy transfer and population dynamics in a quantum dot system induced by optical near-field interaction
Authors: Sangu S. , Kobayashi K. , Shojiguchi A. , Kawazoe T. , Ohtsu M.
Published: March 2003

Energy transfer and exciton population dynamics in a two-quantum dot system coupled with a phonon heat-bath system are examined using the density matrix formalism. In such a system, optical near-field interactions induce energy transfer between quantum dots, and exciton–phonon interactions guarantee the unidirectional excitation energy transfer. Our theoretical investigation shows that the population dynamics change drastically depending on the coupling strengths due to optical near-field interactions and exciton–phonon heat-bath interactions. The temperature effect promotes frequent energy back-transfer from the heat-bath to the quantum dot system. Applying our theoretical formulation, we numerically calculate the time evolution of populations, and estimate energy transfer time or state-filling time for a CuCl quantum dot system. The estimated time is suitable for the elements in our proposed optical nano-switch and nano-photonic devices.
Exciton–phonon coupled states in CdTe/Cd1−xZnxTe quantum dots
Authors: El Moussaouy A. , Bria D. , Nougauoi A. , Charrour R. , Bouhassoune M.
Published: March 2003

This article presents a theoretical analysis of the dependence of the exciton binding energy and exciton–LO-phonon coupling on the cylindrical quantum dot (QD) size. The effect of the temperature on the integrated photoluminescence line intensity is also investigated. Calculations were performed within the effective-mass approximation by using a variational method. Specific applications of these results are given for CdTe QDs embedded in a Cd1−xZnxTe matrix. The excitonic confinement is described by a finite, deep potential well. We observe, on the one hand, an enhancement of the exciton binding energy and the exciton–LO-phonon coupling energy with decreasing dot size. On the other hand, at high temperature, the LO phonon has a noticeable effect on the photoluminescence intensity. This last physical parameter also shows a great dependence on QD size and on the potential level induced by the barrier material.
Photothermal wave propagation in media with thermal memory
Authors: Galović S. , Kostoski D.
Published: March 2003

Generalized expressions of photothermal wave propagation are derived, including the thermal memory effects. The focus is on optically opaque solids. The models of photothermal spectra based on the suggested descriptions are discussed for a semi-infinite sample and two limiting cases of backing—an ideal insulator and an ideal conductor backing. The results are compared with previous models.