bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron-beam-induced current study of grain boundaries in multicrystalline silicon
Authors: Chen J. , Sekiguchi T. , Yang D. , Yin F. , Kido K. , Tsurekawa S.
Published: November 2004

The effects of grain boundary (GB) character and impurity contamination on the recombination activity of grain boundaries (GBs) in multicrystalline silicon (mc-Si) were systematically studied through an electron-beam-induced current (EBIC) technique. First, clean GBs of various characters were checked at 300 and 100K. The EBIC contrasts of these GBs were in the same range of 0%–2% at 300K and 2%–4% at 100K, suggesting that the recombination activity of clean GBs is weak and the GB character has no significant effect on it. Second, the effect of impurities was studied by comparing the EBIC contrasts of the same type of the GBs in mc-Si with different Fe contamination levels. The recombination activity of GBs became stronger as the contamination level rose. The variation in the recombination activity related to the GB character was also observed in these specimens. The random or high-Σ GBs showed a stronger EBIC contrast than the low-Σ GBs. Moreover, we found that the EBIC contrast was not uniform along one Σ3 GB. In a clean mc-Si, the variation in the EBIC contrast of different parts of the Σ3 GB was 1% at 300K, whereas it was more than 10% in the contaminated mc-Si. This indicates that not only the GB character but also the GB plane would affect the recombination activity of GBs. These results suggest that the recombination activity of GBs is principally determined by the gettering ability of GBs. Specifically, that random GBs may have the strongest gettering ability, whereas Σ3 {111} has the weakest.
Parameters required to simulate electric characteristics of SiC devices for n-type 4H–SiC
Authors: Kagamihara Sou , Matsuura Hideharu , Hatakeyama Tetsuo , Watanabe Takatoshi , Kushibe Mitsuhiro , Shinohe Takashi , Arai Kazuo
Published: November 2004

In order to obtain some of the parameters required to simulate the electric characteristics of silicon carbide (SiC) power electronic devices in a wide temperature range from startup temperatures (⩽30°C) to steady-operation temperatures (⩾200°C), we discuss the dependence of the two donor levels on the total donor density (ND) as well as the dependence of the electron mobility on the total impurity density (Nimp) and operating temperature (T) in the n-type 4H–SiC. The temperature-dependent electron concentration n(T) and electron mobility μn(T) in the n-type 4H–SiC epilayers with several nitrogen-doping densities are obtained from the Hall-effect measurements. By the graphical peak analysis method (free carrier concentration spectroscopy: FCCS) without any assumptions regarding the donor species, the two types of donor species are detected from n(T). Moreover, the energy level and density of each donor species are determined by the FCCS. Using these results, we obtain the parameters with which the dependence of each donor level on ND can be simulated. Using μn(T) at T>250K, moreover, we obtain the parameters with which the dependence of the electron mobility on Nimp and T can be simulated.
A strain gage method for determination of magnetic-moment intensity factors in through-cracked soft ferromagnetic plates
Authors: Horiguchi Katsumi , Shindo Yasuhide
Published: November 2004

This paper presents the results of a study on the effect of magnetic fields on the moment intensity factors in the through-cracked soft ferromagnetic plates with fixed ends. The experiments were conducted on a ferritic stainless steel with the through-cracked plate specimen geometries in a uniform, static transverse magnetic field. Strain gages were used to evaluate the magnetic-moment intensity factors. The experimental results were given for a single-internal crack, a single-edge crack, and two symmetric-edge cracks. The magnetic-moment intensity factor estimated from the measured strains was in good agreement with the theoretical calculations based on the authors’ previous work.
High capacitance organic field-effect transistors with modified gate insulator surface
Authors: Majewski L. A. , Schroeder R. , Grell M. , Glarvey P. A. , Turner M. L.
Published: November 2004

In this paper, we report on flexible, high capacitance, pentacene, and regioregular poly(3-hexylthiophene) (rr-P3HT) organic field-effect transistors fabricated on metallized Mylar films. The gate insulator, Al2O3, was prepared by means of anodization. We show that covering the anodized gate insulator with an octadecyltrichlorosilane self-assembled monolayer or apoly(α-methylstyrene) capping layer has the same effect on carrier mobility as for thermally grown silicon oxide. In addition, temperature-dependent measurements of mobility were performed on transistors fabricated with and without modification of the gate dielectric. In the case of both the pentacene and the rr-P3HT transistors, the μ(T) behavior shows that the cause of the mobility enhancement through surface modification is not a reduction in the level of energetic disorder (σ in Bässler’s model), as in the case of the fully amorphous organic semiconductor poly(triarylamine) [Veres et al., Adv. Funct. Mater. 13, 199 (2003)]. It appears that the surface modification improves mobility by changing the morphology of the semiconducting films.
Spectral response from modulus time domain data of disordered materials
Authors: Rivera A. , Blochowicz T. , Gainaru C. , Rössler E. A.
Published: November 2004

The electric response of the glass-forming glycerol and crystalline ionic conductor Li0.18La0.61TiO3 is probed by modulus time domain measurements. A capacity correction algorithm is proposed to overcome the low capacitance limit of the technique. This method allows to Fourier-transform time domain data yielding undisturbed permittivity spectra. The algorithm is checked first in glycerol, where the dielectric data recorded in frequency and time domain show an overlap of several decades. It is also applied to match the dielectric data of the crystalline ionic conductor Li0.18La0.61TiO3 from modulus time domain with overlapping frequency domain data, forming data sets covering 11 decades in frequency. The extension of the electrical characterization to low frequencies allows the detection of an Arrhenius behavior for the dc ionic conductivity at low temperatures, in disagreement with previous analysis in terms of Vogel-Fulcher-Tammann laws.
Effects of high-temperature anneals on 4H–SiC Implanted with Al or Al and Si
Authors: Jones K. A. , Shah P. B. , Zheleva T. S. , Ervin M. H. , Derenge M. A. , Freitas J. A. , Harmon S. , McGee J. , Vispute R. D.
Published: November 2004

Co-implanting Si into 4H–SiC with Al hinders the ability of the Al acceptors to activate electrically at the lower annealing temperatures, but for annealing temperatures>1600°C, the effect is much less, suggesting that the activation energy for incorporating Al as an acceptor no longer controls the rate-determining step in this process. The cathodoluminescence data indicate that Al acceptors are trapped out by the DI defect, and this effect is more pronounced for the higher annealing temperatures. The increase in χmin with the annealing temperature at the higher temperatures can be explained by the nucleation and growth of structural defects, and the transmission electron miscroscopy results show that these defects are stacking faults. The stacking faults can be described as being quantum dots of different polytypes or domain walls with a point-defect periodic structure between the faulted and unfaulted regions, and they could be the source for the peaks associated with the DI defect. Also, we observed that the higher-energy peak in the DI doublet increases in intensity relative to the lower-energy peak as the annealing temperature and the initial implant damage increase.
Electrical resistivities and thermopowers of transparent Sn-doped indium oxide films
Authors: Li Z Q. , Lin J. J.
Published: November 2004

We have systematically measured the electrical resistivities and thermopowers of transparent tin-doped indium oxide films. We found that the resistivities obey the Bloch-Grüneisen law between 25 and 300K, whereas below 25K, the resistivities slightly increase logarithmically with the decreasing temperature due to the weak-localization and electron-electron interaction effects. The thermopowers are negative and decrease linearly with temperature from 300K down to 1.8K. Our results strongly indicate that the tin-doped indium oxide films behave as a good, free-electron-like conductor while being transparent.
Fabrication of conducting Si nanowire arrays
Authors: Beckman R. A. , Johnston-Halperin E. , Melosh N. A. , Luo Y. , Green J. E. , Heath J. R.
Published: November 2004

The recent development of the superlattice nanowire pattern transfer technique allows for the fabrication of arrays of nanowires at a diameter, pitch, aspect ratio, and regularity beyond competing approaches. Here, we report the fabrication of conducting Si nanowire arrays with wire widths and pitches of 10–20 and 40–50nm, respectively, and resistivity values comparable to the bulk through the selection of appropriate silicon-on-insulator substrates, careful reactive-ion etching, and spin-on glass doping. These results promise the realization of interesting nanoelectronic circuits and devices, including chemical and biological sensors, nanoscale mosaics for electronics, and ultradense field-effect transistor arrays.
Morphologic evolution and optical properties of nanostructured gold based on mesoporous silica
Authors: Kan Caixia , Cai Weiping , Li Cuncheng , Fu Ganhua , Zhang Lide
Published: November 2004

In this paper, we report the morphologic evolution and optical properties of nanostructured gold dispersed in monolithic mesoporous silica induced by soaking the silica into a HAuCl4 aqueous solution and subsequent treatments. It has been shown that the morphology of nanostructured Au depends on the subsequent treatments after soaking. If the HAuCl4-soaked mesoporous silica was dried at <100°C for enough time (>10h) and annealed at <300°C without any special reduction treatment, Au nanowires∕silica assembly can be formed. Corresponding optical-absorption spectra exhibit a broad absorption band around 1000nm. Subsequent step annealing from 300°C to 800°C results in a blueshift of the absorption band down to the visible region, accompanied by a decrease of the bandwidth. The corresponding morphology of the nanostructured Au evolves from the wire, rodlike to a spherical shape. This means that we can control the optical properties of this assembly in a large region by such a simple way. Further experiments reveal that the pore walls of silica have significant reduction effect on AuCl4− ions at a low temperature (<100°C). The interconnected channels in the silica host and drying at <100°C for enough time after soaking are crucial to form such Au nanowire∕silica assembly and hence to show tunable optical properties by subsequent step annealing. Not a single one of these conditions can be dispensed with. Otherwise, direct annealing the soaked monolithic silica at a high temperature (>300°C) or treating the soaked porous silica powders only leads to nearly spherical Au nanoparticles highly dispersed in silica, accompanying a normal surface plasmon resonance of Au around 540nm. It has been confirmed that the surface-mediated reducing groups (≡Si–OH) on the silica pore wall are responsible for the low-temperature reduction of Au3+ ions. The formation of the Au nanowires is attributed to the low nucleation rate, unidirectional diffusion of Au atoms along the pore channels and size confinement of pore channels.
The growth and optical properties of large, high-quality AlN single crystals
Authors: Strassburg Martin , Senawiratne Jayantha , Dietz Nikolaus , Haboeck Ute , Hoffmann Axel , Noveski Vladimir , Dalmau Rafael , Schlesser Raoul , Sitar Zlatko
Published: November 2004

The effect of impurities and defects on the optical properties of AlN was investigated. High-quality AlN single crystals of more than 20mm2 size were examined. Different crucible materials and growth procedures were applied to the growth of bulk AlN by physical vapor transport method to vary the defect and the impurity concentrations. The crystalline orientation was investigated by Raman spectroscopy. Glow discharge mass spectrometry was used to determine the trace concentration of the incorporated impurities such as oxygen and carbon. The photoluminescence emission and absorption properties of the crystals revealed bands around 3.5 and 4.3eV at room temperature. Absorption edges ranging between 4.1 and 5.95eV were observed. Since no straight correlation of the oxygen concentration was obtained, a major contribution of oxygen or oxygen-related impurities was ruled out to generate the observed emission and absorption bands in the Ultraviolet spectral range. The carbon-related impurities and intrinsic defects might contribute to the observed optical properties. The absorption coefficient for AlN single crystals has been derived for the spectral range below the band edge.
Binary optoacoustic holography with a spatial light modulator
Authors: Meyer A. , Gspan S. , Bernet S. , Ritsch-Marte M.
Published: November 2004

A purely optical method to generate and to steer an ultrasonic beam is presented. The generation of the ultrasonic beam in the kilohertz to megahertz regime is achieved by using the optoacoustic effect in a layer attached to the surface of a water tank, which absorbs time-modulated laser pulses. In order to tailor the emitted acoustic wave, diffractive optics concepts are applied to acoustics. To this end, the laser light intensity distribution at the absorbing surface is controlled by sending a computer-calculated pattern to a transmissive high-resolution liquid-crystal display in the beam path. This results in an acoustic analog to the “diffractive optical elements” in laser optics, with the emitted ultrasonic wave emerging in a predetermined way. The proof of principle is demonstrated for examples such as phase gratings and binary Fresnel lenses. The optoacoustic ultrasound generation with holographic diffractive steering is a flexible method with the potential of new applications in ultrasound diagnostics.
Investigation of single electron traps induced by InAs quantum dots embedded in GaAs layer using the low-frequency noise technique
Authors: Hastas N. A. , Dimitriadis C. A. , Dozsa L. , Gombia E. , Mosca R.
Published: November 2004

The properties of the traps induced by InAs quantum dots (QDs), embedded in a GaAs layer grown by molecular beam epitaxy, are investigated by the low-frequency noise measurements using the Au∕n-GaAs Schottky diode as a test device. The forward current noise spectra are composed of two noise components: a 1∕f-like noise at low frequencies and a generation-recombination (g-r) noise at higher frequencies. The 1∕f noise is ascribed to the mobility fluctuations within the space-charge region. The obtained Hooge parameter (αH=6×10−5) is larger than the expected value considering the phonon or impurity scattering mechanism, indicating the presence of the defects associated with QDs. The analysis of the g-r noise gives a single trap of density of about 1.6×1014cm−3 in the part of the GaAs layer located above the QDs.
Stress reduction in tungsten films using nanostructured compliant layers
Authors: Karabacak Tansel , Picu Catalin R. , Senkevich Jay. J. , Wang Gwo-Ching , Lu Toh-Ming
Published: November 2004

The residual stress in thin films is a major limiting factor for obtaining high quality films. We present a strategy for stress reduction in sputter deposited films by using a nanostructured compliant layer obtained by the oblique angle deposition technique, sandwiched between the film and the substrate. The technique is all in situ, does not require any lithography steps, and the nanostructured layer is made from the same material as the deposited thin film. By using this approach we were able to reduce stress values by approximately one order of magnitude in sputter deposited tungsten films. These lower stress thin films also exhibit stronger adhesion to the substrate, which retards delamination buckling. This technique allows the growth of much thicker films and has enhanced structural stability. A model is developed to explain the stress relief mechanism and the stronger adhesion associated with the presence of the nanostructured compliant layer.
Measurement of the compression isentrope for 6061-T6 aluminum to 185GPa and 46% volumetric strain using pulsed magnetic loading
Authors: Hayes D. B. , Hall C. A. , Asay J. R. , Knudson M. D.
Published: November 2004

The Z accelerator at Sandia National Laboratories was used to measure the compression isentrope of 6061-T6 aluminum to 185GPa. The isentropic compression experimental technique uses a rapidly increasing, planar magnetic field to simultaneously subject multiple planar aluminum samples of different thicknesses to a ramped magnetic stress load. This magnetic stress load causes a ramped compression wave to propagate in the aluminum. Motion histories at the rear surface of each aluminum sample are measured through a LiF window using laser velocity interferometry. Backward and forward integration of the one-dimensional equations of motion are used to analyze the data. Imposing the requirement that each motion history comes from the same magnetic stress load is sufficient to determine both the stress load and the stress-strain behavior of the aluminum. Because of shocks that grow in the LiF, the usual VISAR interferometer analysis was modified. The measured compression curve obtained on different aluminum samples for volumetric strains to 46% agrees to within about 2% of peak stress with an isentrope obtained from the often-used Mie-Grüneisen equation of state that was derived from previous Hugoniot data.
Influence of Bi doping upon the phase change characteristics of Ge2Sb2Te5
Authors: Wang K. , Wamwangi D. , Ziegler S. , Steimer C. , Wuttig M.
Published: November 2004

The influence of Bi doping upon the phase change characteristics of Ge2Sb2Te5 alloys has been investigated using four-point-probe electrical resistance measurements, grazing incidence x-ray diffraction (XRD), x-ray reflectometry (XRR) and variable incident angle spectroscopic ellipsometry, a static tester and atomic force microscopy. For a Ge2Sb2Te5 alloy doped with 3% Bi, two transition temperatures are observed in the temperature dependent sheet resistance measurements at 136°C and 236°C, respectively. The evolution of structures upon annealing, investigated by XRD, reveals that the first transition is caused by the crystallization of the amorphous film to a NaCl-type structure, while the second transition is related to the transition to a hexagonal structure. The density values of 5.87±0.05gcm−3, 6.33±0.05gcm−3, and 6.41±0.05gcm−3 are measured by XRR for the film in the amorphous, NaCl-type, and hexagonal structure, respectively. Ultrafast crystallization, which is correlated with a single NaCl-structure phase and the reduced activation barrier, is demonstrated. Sufficient optical contrast is exhibited and can be correlated with the density change upon crystallization.
Continuous magnetophoretic separation of blood cells in microdevice format
Authors: Han Ki-Ho , Bruno Frazier A.
Published: November 2004

This paper presents a method for continuous magnetophoretic separation of red and white blood cells from whole blood based on their native magnetic properties. The microsystem separates the blood cells using a high gradient magnetic separation method without the use of additives such as magnetic tagging or inducing agents. A theoretical model of the magnetophoretic microseparator is derived and verified by comparison with finite element simulation. The microseparator is fabricated using microfabrication technology, enabling the integration of microscale magnetic flux concentrators in an aqueous microenvironment, providing strong magnetic forces, and fast separations. Experimental tests are performed using a permanent magnet to create an external magnetic flux of 0.2T, and measuring the movement of red blood cells within the microchannel of the microseparator. The experimental results correlate well with the theoretical results.
Polarization response of proton irradiated 0.9Pb(Mg1∕3Nb2∕3)O3-0.1PbTiO3∕polyvinylidene fluoride-trifluoroethylene 0-3 composites
Authors: Lam K. H. , Chan H. L. W.
Published: November 2004

Polyvinylidene fluoride-trifluoroethylene [P(VDF-TrFE) 70∕30mol%] copolymer can be transformed from a normal ferroelectric to a relaxor ferroelectric material after proton irradiation. The phase transition peak broadens and shifts towards lower temperature as the measurement frequency decreases. The occurrence of a slim polarization-electric field loop is another evidence of the effect of proton irradiation. In the present study, 0-3 composites are fabricated by incorporating 0.9Pb(Mg1∕3Nb2∕3)O3-0.1PbTiO3 ceramic powder into a P(VDF-TrFE) 70∕30mol% copolymer matrix. 0.9PMN-0.1PT ceramic is a relaxor ferroelectric with high dielectric permittivity. It was found that the relative permittivity of an unirradiated PMN-PT∕P(VDF-TrFE) 0-3 composite increases with increasing ceramic volume fraction. With a dosage of 1000kGy (where 1Gy=100rad), the composite exhibits a broad peak in the relative permittivity. In the unirradiated composites, the remnant polarization increases gradually with PMN-PT volume fraction. After irradiation, the remnant polarization of the composites with different PMN-PT volume fractions is similar to that of the irradiated copolymer. Energy storage capabilities of the samples were evaluated which showed that proton irradiated composites have a potential for energy storage applications.
Investigation of incubation in ArF excimer laser irradiated poly(methyl-methacrylate) using pulsed force mode atomic force microscopy
Authors: Hopp B. , Smausz T. , Kokavecz J. , Kresz N. , Bor Z. , Hild S. , Marti O.
Published: November 2004

An atomic force microscopic method to study the incubation states of UV laser irradiated polymer samples is presented. Targets were illuminated by different number of pulses at 5.8 and 8.9mJ∕cm2 fluences. The induced adhesive and morphological changes were investigated simultaneously by an atomic force microscope equipped with a pulsed force mode extension. Importantly, below 100 pulses morphological changes were not observable while significant changes in the adhesion were found as a result of the incubation at 8.9mJ∕cm2 fluence. This method allows the imaging and detection of the whole laser modified area with nanometer resolution.
Large spontaneous magnetostrictive softening below the Curie temperature of Fe3C Invar particles
Authors: Duman E. , Acet M. , Hülser T. , Wassermann E. F. , Rellinghaus B. , Itié J. P. , Munsch P.
Published: November 2004

Fe 3 C incorporates only Fe as a metallic element and is an Invar material with valence electron concentration 8.67. We have studied the equation of state up to 20GPa of Fe3C particles (d∼40nm) below and above the Curie temperature (room temperature and 550K, respectively) to search for a softening associated with a magnetovolume instabilities characteristic of Invar-type material. The isothermal bulk modulus of Fe3C particles at room temperature was found to be about 13% smaller than that of the value at 550K. This difference is comparable with the relative difference in the bulk modulus of Fe65Ni35 Invar in a similar temperature range around the Curie temperature.
Heterolayered lead zirconate titanate thin films of giant polarization
Authors: Zhou Z. H. , Xue J. M. , Li W. Z. , Wang J. , Zhu H. , Miao J. M.
Published: November 2004

Heterolayered Pb(Zr1−xTix)O3 (PZT) films consisting of alternating PbZr0.8Ti0.2O3 and PbZr0.2Ti0.8O3 layers, which were successfully synthesized via a multistep sol-gel route, demonstrate giant polarizations. They show (001)/(100) preferred orientation, the degree of which is strongly affected by both the combination sequence and the number of alternating layers as well as the processing temperature. There occurs a strong interaction between the layers of the two different compositions, leading to the preferred orientations. Both the ferroelectric and dielectric properties are dependent on the number of alternating layers. The six-heterolayered PZT film shows a giant remnant polarization of as high as 71.9μC∕cm2 and a dielectric permittivity of 905, which can easily double those of the conventional polycrystalline PZT films. Studies of the polarization behaviors under subswitching fields suggest a domain wall pinning mechanism. The giant polarization observed at high electric field can be accounted for by the coupling and interactions between the rhombohedral and tetragonal layers.
Temperature induced polytype conversion in cubic silicon carbide studied by Raman spectroscopy
Authors: Püsche R. , Hundhausen M. , Ley L. , Semmelroth K. , Schmid F. , Pensl G. , Nagasawa H.
Published: November 2004

In this paper, we study the polytype transformation of cubic silicon carbide (3C-SiC) by micro Raman spectroscopy. Two sets of samples are investigated. First, physical vapor transport (PVT) grown samples, grown on chemical vapor deposition (CVD) substrates at growth temperatures between 1800 and 1950°C. The microscopic images of the cross sections and the Raman spectra taken on these grown crystals show a growing fraction of 6H-SiC inclusions with increasing growth temperature. To decide whether these polytype inclusions are induced by the PVT growth process or by the temperature treatment of the CVD substrates, we studied the temperature induced polytype coversion of cubic CVD substrates grown on undulant Si(100) surfaces which were used as seed crystals for the PVT growth. The CVD substrates were annealed in the temperature range between 1700 and 2100°C. The results of this annealing series are similar to the results we find in the PVT grown samples. Therefore we argue that the polytype conversion is not induced by the PVT growth process but a result of the heat treatment of the CVD seed crystals.
An oscillating bubble near an elastic material
Authors: Klaseboer E. , Khoo B. C.
Published: November 2004

A method is presented to describe the behavior of an oscillating bubble in a fluid near a second elastic (biological) fluid. The elasticity of the second fluid is modeled through a pressure term at the interface between the two fluids. The Laplace equation is assumed to be valid in each of the fluids, and a difference in the respective densities is allowed. A relationship between the two velocity potentials just above and below the fluid-fluid interface can be found. The boundary integral method is then used to solve for the unknown normal velocities at both the bubble interface and fluid-fluid interface. These said normal velocities are subsequently utilized to update the position of the interface(s) for the next time step. For bubbles oscillating near a second nonelastic fluid, the bubbles can develop a jet towards or away from the fluid-fluid interface (depending on the distance of the bubble from the fluid-fluid interface and the density ratios of the two fluids). This behavior can be greatly modified when the second fluid possesses some elastic properties. The elasticity causes a small perturbation to travel along the surface of the bubble. A complex interaction between this growing perturbation and the bubble in its collapse phase can lead to the bubble assuming a “mushroom” shape and/or even breakup into two smaller bubbles. These phenomena have not been observed when the elasticity is absent in the second fluid. Excellent agreement with experimental data was obtained for a wide range of parameters.
Analytical band Monte Carlo simulation of electron impact ionization in In0.53Ga0.47As
Authors: Choo K. Y. , Ong D. S.
Published: November 2004

An analytical band Monte Carlo model has been developed to study electron transport and impact ionization in In0.53Ga0.47As. Our simulations show that it is important to include the second conduction band at X7 because impact ionization becomes significant in this higher band at fields above 100kV∕cm. The higher ionization rate here is found to be responsible for the strong field dependence of the ionization coefficient for electric fields above 180kV∕cm. At lower fields the weak field dependence results from the large energy separation between the Γ6 and X7 valleys which confines most of the electrons to the first conduction band, where the ionization rate is lower. Although the electron impact ionization coefficient of InGaAs is comparable to that of GaAs at 300kV∕cm, the average electron energy at impact ionization is 1.59eV lower than in GaAs and the average time to impact ionization is almost twice that in GaAs, indicating a slower drift of electrons in InGaAs prior to impact ionization
Photoluminescence and lasing characteristics of InGaAs∕InGaAsP∕InP quantum dots
Authors: Pyun S. H. , Lee S. H. , Lee I. C. , Kim H. D. , Jeong Weon G. , Jang J. W. , Kim N. J. , Hwang M. S. , Lee D. , Lee J. H. , Oh D. K.
Published: November 2004

The InGaAs quantum dots (QDs) were grown with InGaAsP(λg=1.0–1.1μm) barrier, and the emission wavelength was controlled by the composition of InGaAs QD material in the range between 1.35 and 1.65μm. It is observed that the lateral size increases and the height of the QDs decreases with the increase in relative concentration of trimethylgallium to trimethylindium supplied during InGaAs QD growth. It is seen that the higher concentration of group III alkyl supply per unit time leads to higher QD areal density, indicating that the higher concentration causes more QDs to nucleate. By optimizing the growth conditions, the QDs emitting at around 1.55μm were grown with an areal density as high as 8×1010cm−2. The lasing action between the first excited subband states at the wavelength of 1.488μm has been observed from the ridge waveguide lasers with five QD stacks up to 260K. The threshold current density of 3.3kA∕cm2 at 200K and a characteristic temperature of 118K were measured.
Effects of field dependent mobility and contact barriers on liquid crystalline phthalocyanine organic transistors
Authors: Cherian Samir , Donley Carrie , Mathine David , LaRussa Lynn , Xia Wei , Armstrong Neal
Published: November 2004

Copper phthalocyanine (CuPc) transistors were fabricated using the Langmuir-Blodgett technique to produce bottom contact organic field effect transistors (OFETs) on silicon substrates. The resultant devices were measured and the performance was analyzed using a two-dimensional numerical simulation of the device structure. A hole barrier at the Au∕phthalocyanine source and drain contacts was seen from the experimental data. The numerical simulations were used to extract a barrier height of 0.415eV at the Au∕phthalocyanine contacts. Also, a Frenkel-Poole mobility model was used to account for the drain current in the transistors and a high field mobility of 0.018cm2∕Vsec was extracted from the experimental data. The resultant device parameters were compared to simple analytical results and the benefits of enhanced two-dimensional modeling of OFETs are shown.
Thermoelectric properties of semiconductorlike intermetallic compounds TMGa3 (TM=Fe, Ru, and Os)
Authors: Amagai Y. , Yamamoto A. , Iida T. , Takanashi Y.
Published: November 2004

Transport properties of polycrystalline TMGa3 (TM=Fe, Ru, and Os) compounds are reported in the temperature range 313K<T<973K. These compounds exhibit semiconductorlike behavior with relatively high Seebeck coefficient and electrical resistivity. Hall carrier concentrations at room temperature are reported in the range of 1017–1018cm−3. Seebeck coefficient measurements indicate that FeGa3 and OsGa3 are n-type material at the operating temperature; on the other hand, the Seebeck coefficient of RuGa3 changes its sign rapidly from large positive value to large negative value around 450K. The thermal conductivity of these compounds is estimated to be 3.5W∕mK at room temperature and decreases with increasing temperature. The absolute value of the lattice thermal conductivity for FeGa3, RuGa3, and OsGa3 is 3.5W∕mK at room temperature, and decreases down to 2W∕mK at high temperature. The resulting thermoelectric figure of merit ZT at 945K for RuGa3 reaches 0.18.
Cadmium sulfide thin-film transistors fabricated by low-temperature chemical-bath deposition
Authors: Voss C. , Subramanian S. , Chang C.-H.
Published: November 2004

In this paper, we report the characterization and analysis of the dc electrical characteristics of thin-film transistors fabricated from low-temperature chemical-bath-deposited CdS as the channel layer. Our analysis shows that the device can be operated either in the depletion mode or in the accumulation mode. In the depletion mode, the channel lies completely within the bulk of the CdS layer. In the accumulation mode, the current is carried by an accumulation channel at the SiO2∕CdS interface and a buried channel that lies in the bulk of the CdS layer. Using our device analysis, we have extracted the threshold voltage, the carrier concentration in CdS, and the carrier mobility in the bulk channel as well as in the surface channel. The extracted value of the surface channel mobility is found to be greater than 1cm2∕Vs, which shows that the CdS deposited by this method has a great promise for applications that require low-temperature processing (e.g., in plastic electronics).
Quasiparticle charge imbalance, first-order phase transition and quantum criticality in ferromagnet∕superconductor∕ferromagnet double-tunnel junctions
Authors: Jin Biao , Su Gang , Zheng Qing-Rong
Published: November 2004

Spin-dependent transport in ferromagnet∕superconductor∕ferromagnet double-tunnel junctions is revisited by taking both the spin and quasiparticle charge imbalances into account. It is shown that even a small quasiparticle charge imbalance can lead to remarkable changes of the superconducting and transport properties. In particular, it is found that a first-order phase transition from an inhomogeneous superconducting state to the normal state will take place in both the antiparallel and parallel alignments of magnetizations, as the bias voltage is increased to a critical value. A quantum critical point is specified.
Small polaron formation in porous WO3−x nanoparticle films
Authors: Ederth J. , Hoel A. , Niklasson G. A. , Granqvist C. G.
Published: November 2004

Porous tungsten oxide nanoparticle films were prepared by reactive gas evaporation. The structure was studied by x-ray diffraction and scanning electron microscopy, and the oxygen nonstoichiometry was inferred by x-ray photoelectron spectroscopy, elastic recoil detection analysis, and neutron scattering. Specifically, the films consisted of WO3−x with 0.25<x<0.4. The optical and electrical data were consistent with the formation of small polarons having a radius of 5–6Å. The infrared optical data, used to extract information on phonon energies, were instrumental to reach this conclusion. The polaron hopping energy was about half the polaron binding energy, as expected from the theory.
Evidence for a little ice age and recent warming from a borehole temperature data inversion procedure
Authors: Fivez J. , Thoen J.
Published: November 2004

In this article, we apply our analytical theory, published earlier in this journal, to obtain information on the earth surface temperature history from some borehole temperature data. Compared to the results of the five different methods applied to the same temperature data, our method seems to be easier, assumption-free, and yields internally consistent results. The results suggest a cooling a few centuries ago, followed by a continuing warming up to these days, in agreement with a little ice age scenario.
Modeling of diamond radiation detectors
Authors: Milazzo L. , Mainwood A.
Published: November 2004

We have built up a computer simulation of the detection mechanism in the diamond radiation detectors. The diamond detectors can be fabricated from a chemical vapour deposition polycrystalline diamond film. In this case, the trapping-detrapping and recombination at the defects inside the grains and at the grain boundaries degrade the transport properties of the material and the charge induction processes. These effects may strongly influence the device’s response. Previous simulations of this kind of phenomena in the diamond detectors have generally been restricted to the simple detector geometries and homogeneous distribution of the defects. In our model, the diamond film (diamond detector) is simulated by a grid. We apply a spatial and time discretization, regulated by the grid resolution, to the equations describing the charge transport and, by using the Shockley-Ramo theorem, we calculate the signal induced on the electrodes. In this way, we can simulate the effects of the nonhomogeneous distributions of the trapping, recombination, or scattering centers and can investigate the differences observed when different particles, energies, and electrode configurations are used. The simulation shows that the efficiency of the detector increases linearly with the average grain size, that the charge collection distance is small compared to the dimensions of a single grain, and that for small grains, the trapping at the intragrain defects is insignificant compared to the effect of the grain boundaries.
Electron cyclotron resonance deposition, structure, and properties of oxygen incorporated hydrogenated diamondlike amorphous carbon films
Authors: Adamopoulos G. , Godet C. , Zorba T. , Paraskevopoulos K. M. , Ballutaud D.
Published: November 2004

Oxygen-incorporated hydrogenated amorphous carbon films were grown by the integrated distributed electron cyclotron resonance plasma technique from a mixture of acetylene and oxygen. It has been found that the increase of the oxygen to acetylene gas ratio results in more oxygen incorporation up to O∕(O+C)=0.2 with a decrease in the hydrogen concentration within the film as measured by the nuclear reaction analysis (NRA) and a combination of the elastic recoil detection analysis and Rutherford backscattering techniques. The spectroscopic ellipsometry in the range of 1.5–5eV showed a negligible decrease of the E04 optical band gap for increasing the oxygen content. At the same time, the decrease of the refractive index from 2.2 to 2.0 denotes the decrease of the films density, which was independently estimated by NRA. The visible (488nm) Raman spectroscopy showed that the increase of the oxygen content favors the clustering of the six-fold sp2C rings. The Fourier transform infrared spectroscopy gives evidence of both C–O and CO bonding configurations. No evidence of O–H bonds formation is found. Simultaneously, the chemisorption of CO2 seems to increased with increasing the oxygen to acetylene gas ratio, which is consistent with the lower film density. The previously trends denote the “softening” of the films, which is consistent with the significant decrease (of about 35%) of the compressive stress allowing the growth of thicker but still transparent films.
Electrically switchable spatial filter based on polymer-dispersed liquid crystal film
Authors: Fuh Andy Y.- G. , Lin Tsung-Hsien
Published: November 2004

This work demonstrates the feasibility of using polymer-dispersed liquid crystal (PDLC) films as electrically switchable spatial filters in the optical signal process. The fabrication relies on the fact that the size of the liquid crystal droplet formed in a PDLC film is inversely proportional to the intensity of curing. Controlling the driving voltage on the PDLC sample can filter particular spatial frequencies in the Fourier optical signal process. A simulation is also performed, and the results are highly consistent with those of experiments.
Raman spectra of Nd∕Sn cosubstituted Ba6−3xSm8+2xTi18O54 microwave dielectric ceramics
Authors: Wu S. Y. , Li Y. , Chen X. M.
Published: November 2004

The Raman spectra and dielectric properties of Nd∕Sn cosubstituted Ba6−3xSm8+2xTi18O54 (x=2∕3) microwave dielectric ceramics were discussed as the functions of composition and sintering time. The peaks in 753cm−1 were caused by the second order scatter. The peaks in 425 and 403cm−1 became sharper with prolonging sintering time, and this reflected the increased lattice defects. The shoulder peak near 292cm−1 was caused by the octahedral tilt when A site is Nd3+. The Raman shifts in 590, 520, 280, and 232cm−1 indicated no obvious change in position, but all peaks became sharper with prolonging sintering time. This indicated the increased ordering degree of A-site cations. With prolonging sintering time, the Qf factor (Q is the inverse of dielectric loss, tan δ, and f is the resonant frequency) increased, and the temperature coefficient of resonant frequency significantly decreased or became more negative, while the dielectric constant indicated no significant variation.
Influence of nitrogen on tunneling barrier heights and effective masses of electrons and holes at lightly-nitrided SiO2∕Si interface
Authors: Ng C. Y. , Chen T. P. , Liu Y. , Sun C. Q. , Fung S.
Published: November 2004

We have determined both the effective masses and the barrier heights for electrons and holes in pure SiO2 and lightly nitrided oxides with various nitrogen concentrations up to 4.5 at %. In contrast to previous studies which were usually carried out by assuming a value for either the effective mass or the barrier height, this study does not make such an assumption. The approach is proven to be reliable by examining the result for the well-studied pure SiO2 thin films. It is observed that with the increase of the nitrogen concentration the effective masses increase while both the barrier heights and the energy gap decrease.
Magnetic and structural properties of GaN thin layers implanted with Mn, Cr, or V ions
Authors: Guzenko V. A. , Thillosen N. , Dahmen A. , Calarco R. , Schäpers Th. , Houben L. , Luysberg M. , Schineller B. , Heuken M. , Kaluza A.
Published: November 2004

We report on magnetic and structural properties of n- and p-type GaN layers implanted with Mn, Cr, and V. The samples were subsequently annealed in a N2 atmosphere at a constant temperature in the range between 700 and 1050°C. Measurements of the magnetization as a function of magnetic field as well as of the temperature show typical paramagnetic behavior. In addition, a weak antiferromagnetic coupling between the implanted ions was observed. 3d-metal rich precipitates of crystalline nature are revealed by high resolution transmission electron microscopy.
Ionization and ablation phenomena in an ablative plasma accelerator
Authors: Keidar M. , Boyd I. D. , Beilis I. I.
Published: November 2004

Several interrelated phenomena near the surface ablated into a discharge plasma, such as ablation and ionization in accelerated plasma are studied. Two characteristic ablation modes are identified, namely, ablation mode with a velocity at the Knudsen layer edge smaller than the local sound speed and a velocity at the Knudsen layer edge close to the sound speed. The existence of these two ablation modes is determined by the current density in the acceleration region. The nonequilibrium ionization region in the presence of strong electromagnetic plasma acceleration is studied. In the subsonic regime, the ionization region thickness is proportional to the ionization rate and inversely proportional to the magnetic field. Conditions for ionization equilibrium in the accelerating plasma are determined. The specific example of a micropulsed plasma thruster is considered. It is concluded that both the equilibrium and nonequilibrium ionization regimes occur in this device.
Regulatory actions of the A-kinase anchoring protein Yotiao on a heart potassium channel downstream of PKA phosphorylation
Authors: Kurokawa Junko , Motoike Howard K. , Rao Jenny , Kass Robert S.
Published: November 2004

A-kinase anchoring proteins (AKAPs) are thought to be passive members of protein complexes that coordinate the association of cAMP-dependent protein kinase A (PKA) with cellular substrates to facilitate targeted PKA protein phosphorylation. I
Ks
, the slow heart postassium current, is carried by the I
Ks
potassium channel, a substrate for PKA phosphorylation in response to sympathetic nerve stimulation, is a macromolecular complex that includes the KCNQ1 α subunit, the KCNE1 regulatory subunit, and the AKAP Yotiao. Disruption of this regulation by mutation in the long QT syndrome is associated with elevated risk of sudden death. Here, we have studied the effects of the AKAP Yotiao on the function of the I
Ks
channel that had been mutated to simulate channel phosphorylation, and we report direct AKAP-mediated alteration of channel function distinct from its role in the coordination of channel phosphorylation by PKA. These data reveal previously undescribed actions of Yotiao that occur subsequent to channel phosphorylation and provide evidence that this adaptor protein also may serve as an effector in regulating this important ion channel.
Crystal structures of 2-acetylaminofluorene and 2-aminofluorene in complex with T7 DNA polymerase reveal mechanisms of mutagenesis
Authors: Dutta Shuchismita , Li Ying , Johnson Donald , Dzantiev Leonid , Richardson Charles C. , Romano Louis J. , Ellenberger Tom
Published: November 2004

The carcinogen 2-acetylaminofluorene forms two major DNA adducts:
N
-(2′-deoxyguanosin-8-yl)-2-acetylaminofluorene (dG-AAF) and its deacetylated derivative,
N
-(2′-deoxyguanosin-8-yl)-2-aminofluorene (dG-AF). Although the dG-AAF and dG-AF adducts are distinguished only by the presence or absence of an acetyl group, they have profoundly different effects on DNA replication. dG-AAF poses a strong block to DNA synthesis and primarily induces frameshift mutations in bacteria, resulting in the loss of one or two nucleotides during replication past the lesion. dG-AF is less toxic and more easily bypassed by DNA polymerases, albeit with an increased frequency of misincorporation opposite the lesion, primarily resulting in G → T transversions. We present three crystal structures of bacteriophage T7 DNA polymerase replication complexes, one with dG-AAF in the templating position and two others with dG-AF in the templating position. Our crystallographic data suggest why a dG-AAF adduct blocks replication more strongly than does a dG-AF adduct and provide a possible explanation for frameshift mutagenesis during replication bypass of a dG-AAF adduct. The dG-AAF nucleoside adopts a
syn
conformation that facilitates the intercalation of its fluorene ring into a hydrophobic pocket on the surface of the fingers subdomain and locks the fingers in an open, inactive conformation. In contrast, the dG-AF base at the templating position is not well defined by the electron density, consistent with weak binding to the polymerase and a possible interchange of this adduct between the
syn
and
anti
conformations.
A screen for genes that suppress loss of contact inhibition: Identification of
ING4
as a candidate tumor suppressor gene in human cancer
Authors: Kim Suwon , Chin Koei , Gray Joe W. , Bishop J. Michael
Published: November 2004

We have devised a screen for genes that suppress the loss of contact inhibition elicited by overexpression of the protooncogene
MYCN
. The initial application of this screen detected nine distinctive suppressors within a representative human cDNA library. One of these genes was
ING4
, a potential tumor suppressor gene that maps to human chromosome 12p13. Ectopic expression of
ING4
suppressed the loss of contact inhibition elicited by either
MYCN
or
MYC
but had no direct effect on cellular proliferation. Pursuing the possibility that
ING4
might be a tumor suppressor gene, we found inactivating mutations in
ING4
transcripts from various human cancer cell lines. In addition, we used comparative genomic hybridization to detect deletion of the
ING4
locus in 10-20% of human breast cancer cell lines and primary breast tumors. Ectopic expression of
ING4
attenuated the growth of T47D human breast cancer cells in soft agar. We conclude that
ING4
is a strong candidate as a tumor suppressor gene.