bluuebunny/crossref_metadata_2025 huggingface dataset:
Aerosol optical depth and fine mode fraction variations deduced from Moderate Resolution Imaging Spectroradiometer (MODIS) over four urban areas in India
Authors: Ramachandran S.
Published: August 2007

Interannual and intra‐annual variations in aerosol optical depths (AOD) and fine mode fraction (FMF) analyzed from Moderate Resolution Imaging Spectroradiometer (MODIS) during 2001–2005 over four urban areas in India, Chennai, Mumbai, Kolkata and New Delhi, are investigated. MODIS derived AODs and FMFs are found to compare well with in situ Aerosol Robotic Network (AERONET) Sun photometer results over Kanpur. Monthly mean 550 nm AODs are higher than 0.30 in all the four locations and show prominent seasonal variations of summer high and winter low. FMF values are low during premonsoon and summer over Chennai, Mumbai and New Delhi, while they are 0.9 or higher over Kolkata during the entire year. AODs exhibit a positive correlation with rainfall. A strong convection in summer accompanied by a deeper boundary layer and hygroscopic growth of fine mode water soluble aerosols result in higher AODs during summer monsoon. The 5‐year mean AOD is 0.4 in Chennai and Mumbai while in Kolkata and New Delhi it is >0.55. AODs <0.4 contribute 50% or more in Chennai and Mumbai, while in Kolkata and New Delhi AODs in the 0.4–0.8 range contribute higher than 50%. Variation in annual mean FMF is the lowest in Kolkata and highest in New Delhi, consistent with seasonal variations in FMF values in these locations. In Chennai, Mumbai and Kolkata, FMF values >0.6 contribute higher than 75%, while over Kolkata FMF values in the 0.8–1.0 range contribute 94% which indicates the dominance of fine mode aerosols in Kolkata throughout the year.
Identification of domains influencing assembly and ion channel properties in α7 nicotinic receptor and 5‐HT3 receptor subunit chimaeras
Authors: Gee V J , Kracun S , Cooper S T , Gibb A J , Millar N S
Published: August 2007

Background and purpose:

Nicotinic acetylcholine receptors (nAChRs) and 5‐hydroxytryptamine type 3 receptors (5‐HT3Rs) are members of the superfamily of neurotransmitter‐gated ion channels. Both contain five subunits which assemble to form either homomeric or heteromeric subunit complexes. With the aim of identifying the influence of subunit domains upon receptor assembly and function, a series of chimaeras have been constructed containing regions of the neuronal nAChR α7 subunit and the 5‐HT3 receptor 3A subunit.

Experimental approach:

A series of subunit chimaeras containing α7 and 5‐HT3A subunit domains have been constructed and expressed in cultured mammalian cells. Properties of the expressed receptors have been examined by means of radioligand binding, agonist‐induced changes in intracellular calcium and patch‐clamp electrophysiology.

Key results:

Subunit domains which influence properties such as rectification, desensitization and conductance have been identified. In addition, the influence of subunit domains upon subunit folding, receptor assembly and cell‐surface expression has been identified. Co‐expression studies with the nAChR‐associated protein RIC‐3 revealed that, in contrast to the potentiating effect of RIC‐3 on α7 nAChRs, RIC‐3 caused reduced levels of cell‐surface expression of some α7/5‐HT3A chimaeras.

Conclusions and implications:

Evidence has been obtained which demonstrates that subunit transmembrane domains are critical for efficient subunit folding and assembly. In addition, functional characterization of subunit chimaeras revealed that both extracellular and cytoplasmic domains exert a dramatic and significant influence upon single‐channel conductance. These data support a role for regions other than hydrophobic transmembrane domains in determining ion channel properties.

British Journal of Pharmacology (2007) 152, 501–512; doi:10.1038/sj.bjp.0707429; published online 27 August 2007
Methylene blue and serotonin toxicity: inhibition of monoamine oxidase A (MAO A) confirms a theoretical prediction
Authors: Ramsay R R , Dunford C , Gillman P K
Published: August 2007

Background and purpose:

Monoamine oxidase inhibitors (MAOI) are known to cause serotonin toxicity (ST) when administered with selective serotonin reuptake inhibitors (SSRI). Methylene blue (methylthionium chloride, MB), a redox dye in clinical use, has been reported to precipitate ST in patients using SSRI. MB was assessed for MAO inhibition and so for its potential to precipitate ST.

Experimental approach:

Inhibition of purified human MAO was quantified using kinetic assays and visible spectral changes to study the interactions of MB with MAO A.

Key results:

MB was a potent (tight binding) inhibitor for MAO A. It also inhibited MAO B but at much higher concentration. Interactions of MB with the active site of MAO A were confirmed by its action both as an oxidising substrate and as a one‐electron reductant.

Conclusions and implications:

MB is a potent reversible inhibitor of MAO A with implications for gut uptake of amines when administered orally. At concentrations reported in the literature after intravenous administration, MAO B would be partially inhibited but MAO A would be completely inhibited. This inhibition of MAO A would be expected to lead to perturbations of 5‐hydroxytryptamine metabolism and hence account for ST occurring when administered to patients on SSRI treatment.

British Journal of Pharmacology (2007) 152, 946–951; doi:10.1038/sj.bjp.0707430; published online 27 August 2007
Mechanical properties of AlxGa1−xN films with high Al composition grown on AlN/sapphire templates
Authors: Xu F. J. , Shen B. , Wang M. J. , Xu J. , Lu L. , Miao Z. L. , Yang Z. J. , Qin Z. X. , Zhang G. Y. , Lin B. , Bai S. L.
Published: August 2007

Mechanical properties of AlxGa1−xN thin films with high Al composition (0.33⩽x⩽1) grown on AlN/sapphire templates have been investigated by means of the nanoindentation technique. It is found that Young’s modulus E of the films increases with increasing Al composition. In addition, it is also found that the occurrence of the clear and sudden displacement discontinuity (“pop-in”) in the plastic deformation (PD) process is dependent on Al composition in AlxGa1−xN films. The higher Al composition results in less occurrence of the pop-in in the PD process of the films. With increasing Al composition, it is believed that the increase of the bond strength and the decrease of the lattice mismatch between AlxGa1−xN films and AlN/sapphire templates result in greater resistance to the formation of dislocations, which is responsible for the pop-in behavior in AlxGa1−xN films.
Midinfrared polarization spectroscopy of OH and hot water in low pressure lean premixed flames
Authors: Li Z. S. , Hu Changhong , Zetterberg J. , Linvin M. , Aldén M.
Published: August 2007

The application of midinfrared polarization spectroscopy (mid-IRPS) is demonstrated for sensitive detection of minor molecular species in combustion environments by probing rovibrational transitions. High resolution mid-IRPS spectra of low pressure flames were obtained in the spectral range around 3μm. Rotational lines of the fundamental vibrational band of the hydroxyl radical (OH) were fully resolved and properly assigned among the abundant hot water lines in the flame mid-IRPS spectra. The high signal-to-noise ratio of the recorded OH lines indicates the feasibility of sensitive mid-IRPS OH detection. This constitutes, to the best of our knowledge, the first reported OH flame detection in the midinfrared spectral range. A simulation of hot water mid-IRPS lines with molecular parameters extracted from the HITRAN/HITEMP database was performed and compared with the observed flame spectra. The proper prediction of the hot water lines may help to clarify the potential spectral interferences associated with minor species measurements.
Highly accurate determinations of CO2 line strengths using intensity-stabilized diode laser absorption spectrometry
Authors: Casa Giovanni , Parretta Donatella A. , Castrillo Antonio , Wehr Richard , Gianfrani Livio
Published: August 2007

An intensity-stabilized laser absorption spectrometer, which incorporates a mirror-extended cavity diode laser, a temperature-stabilized gas cell, and a Michelson interferometer, was developed and applied to a highly accurate investigation of line intensity factors within the ν1+2ν20+ν3 combination band of carbon dioxide, around 2μm wavelength, at a temperature of 296.0K. This relatively complex apparatus enables one to observe the absorption line shape with high precision and accuracy in such a way that it is possible to retrieve the integrated absorbance with a relative uncertainty better than 0.1%. The absorption spectra were interpolated with the uncorrelated strong-collision model of Rautian and Sobel’man in order to take into account Dicke narrowing effects, thus obtaining an agreement at a level of a few parts per 10−5. We report line strength values for the R(2)–R(18) transitions with an unprecedented level of accuracy, in the range between 0.1% and 0.15%. Finally, we discuss the possibility of providing a first experimental test of the theoretical model for molecular line strengths based on the Herman-Wallis expansion.
Theoretical investigation of the Rayleigh-Taylor instability in laser-produced plasmas driving into background gases
Authors: Rifai K. , Vidal F. , Johnston T. W.
Published: August 2007

Aluminum plasmas produced at moderate laser fluences in atmospheres of helium (a light gas) and argon (a heavy gas) are simulated by using a one-dimensional Lagrangian fluid code. The resulting data are used as input for Dimonte’s buoyancy-drag model for Rayleigh-Taylor instability development. The ablated matter and the shock wave generated in the gas are treated consistently by solving the fluid equations in both media. In helium, the Rayleigh-Taylor instability develops during the interface deceleration stage and grows for a considerable time. For the heavy argon gas, the instability operates only during the much shorter acceleration stage and is probably masked by interdiffusion. For the same laser fluence, the mixing width in helium is predicted to grow faster for ultrashort pulses than for nanosecond pulses. The relative size of the mixing width compared to the plume length is more significant at higher gas pressure.
Comment on the linear mirror instability near the threshold
Authors: Hellinger Petr
Published: August 2007

A linear threshold condition of the mirror instability in a homogeneous, multispecies collisionless plasma with a general class of distribution functions is obtained in the low-frequency, long-wavelength limit of the Vlasov-Maxwell equation. In the case of one cold species, the conditions of the validity of the threshold condition and the behavior of the instability near threshold are also presented. It is confirmed that finite Larmor radius effects do not change the threshold condition. The linear threshold condition is extended to the case of hot species with a general class of distribution functions. In this case the conditions of the validity of the threshold condition or the behavior of the instability near threshold are hard to get analytically. Previous analytical and numerical results are discussed.
Influence of γ-radiation doses on the properties of TeOx: (x=2–3) thin film
Authors: Dewan Namrata , Sreenivas K. , Gupta Vinay
Published: August 2007

The influence of γ-ray doses (10–50 Gy) on the optical and electrical properties of radio-frequency sputtered tellurium dioxide (TeOx) thin film was studied. The composition of the as-deposited TeOx films deposited under 25% oxygen and 100% oxygen in the sputtering gas mixture (Ar+O2) was x=2 and 3, respectively. TeO3 films were found to be highly sensitive to the γ-radiation doses and the value of optical band gap decrease from 4.18 to 3.56 eV with increasing radiation dose from 10 to 50 Gy. Current-voltage characteristics of the films showed an increase in the value of conductivity with increasing radiation doses. Monotonic decrease in the values of dielectric constant for the deposited films with increase in radiation dose was observed. The effect of γ-ray doses on the properties of TeOx film has been correlated with the rearrangement of the bipyramidal structure of amorphous TeOx thin film.
Anomalous exchange coupling in transition-metal-oxide based superlattices with antiferromagnetic spacer layers
Authors: Padhan P. , Prellier W. , Budhani R. C.
Published: August 2007

A direct correlation is seen between the coercive field (HC) and the magnetic-field-dependent resistivity (MR) in SrMnO3/SrRuO3 superlattices of perpendicular magnetic anisotropy. The magnetoresistance shows a sharp jump at HC for in-plane current and the out-of-plane magnetic field. Both HC and high-field MR also oscillate with the thickness of the SrMnO3 spacer layers separating the metallic ruthenate. Since the spacer in these superlattices has no mobile carriers to facilitate an oscillatory coupling, we attribute the observed behavior to the spin-polarized quantum tunneling of electrons between the ferromagnetic layers and antiferromagnetically ordered t2g spins of SrMnO3.
Photoconductivity in sprayed β-In2S3 thin films under sub-band-gap excitation of 1.96 eV
Authors: Jayakrishnan R. , Sebastian Tina , John Teny Theresa , Kartha C. Sudha , Vijayakumar K. P.
Published: August 2007

β -In 2 S 3 thin films with a band gap of ∼2.67eV exhibited persistent photoconductivity when excited using photons with energy of 1.96 eV. The photoconductive response to extrinsic photoexcitation could be removed when the film stoichiometry was changed. Photoluminescence studies in the films revealed an emission of 1.826 eV, due to donor–acceptor pair (DAP) recombination, which was absent in the film not responding to extrinsic excitation. Hence, it was concluded that presence of the DAP was responsible for the extrinsic photoconductivity under the 1.96 eV excitation. This study can initiate further a methodology for tailoring the photoresponse of this semiconducting thin film by spatially controlling the film stoichiometry.
Ink-jet printing of carbon nanotube thin film transistors
Authors: Beecher P. , Servati P. , Rozhin A. , Colli A. , Scardaci V. , Pisana S. , Hasan T. , Flewitt A. J. , Robertson J. , Hsieh G. W. , Li F. M. , Nathan A. , Ferrari A. C. , Milne W. I.
Published: August 2007

Ink-jet printing is an important process for placing active electronics on plastic substrates. We demonstrate ink-jet printing as a viable method for large area fabrication of carbon nanotube (CNT) thin film transistors (TFTs). We investigate different routes for producing stable CNT solutions (“inks”). These consist of dispersion methods for CNT debundling and the use of different solvents, such as N-methyl-2-pyrrolidone. The resulting printable inks are dispensed by ink-jet onto electrode bearing silicon substrates. The source to drain electrode gap is bridged by percolating networks of CNTs. Despite the presence of metallic CNTs, our devices exhibit field effect behavior, with effective mobility of ∼0.07 cm2/V s and ON/OFF current ratio of up to 100. This result demonstrates the feasibility of ink-jet printing of nanostructured materials for TFT manufacture.
Substrate-dependent wetting layer formation during GaN growth: Impact on the morphology of the films
Authors: Sidorenko A. , Peisert H. , Neumann H. , Chassé T.
Published: August 2007

We have compared epitaxial growth of GaN films on 6H-SiC(0001)-(3×3)R30°−Ga and on (0001)-sapphire. Predeposited Ga layers were nitrided by ion beam assisted molecular beam epitaxy. Whereas on SiC the initially deposited Ga covers the substrate surface completely, on sapphire only Ga droplets are present. The different distribution of the predeposited Ga affects the morphology of GaN significantly. Scanning electron microscopy and atomic force microscopy analysis of the grown films show that the complete wetting of the SiC substrate with Ga enhances finally the size and the flatness of GaN terraces and thus the quality of the film. X-ray photoelectron spectroscopy measurements reveal that metallic Ga resides also on top of the GaN films during the growth.
Thermal stability of molecularly functionalized mesoporous silica thin films
Authors: Singh A. P. , Gandhi D. D. , Moore R. , Ramanath G.
Published: August 2007

We report the stability of ordered mesoporous silica (MPS) thin films functionalized with mercaptan- and cyanide-terminated organosilanes upon annealing at temperatures up to 500 °C in vacuum, nitrogen, and air. Electron spectroscopy analyses indicate that the molecules are attached to the surfaces of the films as well as the pores inside the films. The cyanide-functionalized MPS films are stable up to 500 °C in vacuum, N2, and air ambient. In contrast, mercaptan-functionalized MPS films are stable only up to 400 °C in vacuum due to the higher reactivity of mercaptan with oxygen. Our results provide insights into effects of temperature and gas environments on the properties of molecularly functionalized porous dielectrics, and would be important considerations for developing new options for interlayer electrical isolation of nanodevice wiring.
Local heating and viscosity drop during shear band evolution in bulk metallic glasses under quasistatic loading
Authors: Zhang Hongwen , Subhash Ghatu , Maiti Spandan
Published: August 2007

Based on the facts that the thickness of a shear band in bulk metallic glasses (BMGs) is a few tens of nanometers, the shear displacement across the band is few micrometers, and the time for their formation is in submicrosecond duration, the local strain rates within the shear band can be as high as 109∕s. To capture such dynamic effects, a thermo-micromechanical model based on momentum diffusion mechanism, free-volume theory, and heat diffusion analysis is proposed. The model has been shown to capture the characteristic rate effects, i.e., significant local temperature rise and a dramatic drop in viscosity during shear band evolution in BMGs. The model also takes into account the effects of normal stress component on the deformation behavior of BMGs. While the predicted maximum temperature rise under quasistatic deformation in the absence of normal component of stress is low (300 K), significant temperature rise well above 1000 K accompanied by a sudden drop in viscosity has been predicted under dynamic loads at high normal pressures. It is also predicted that temperature rise and viscosity drop are negligible during the early phase of shear band formation but increase significantly towards the final phase of shear band evolution and cause subsequent fracture, as has been theorized by many researchers in the literature.
Effect of low fluence laser annealing on ultrathin Lu2O3 high-k dielectric
Authors: Darmawan P. , Lee P. S. , Setiawan Y. , Ma J. , Osipowicz T.
Published: August 2007

The effect of low fluence single pulse laser annealing on a pulsed laser deposited high-k dielectric, Lu2O3 is reported. With low fluence laser irradiation, high “k” of 45 is achieved with an equivalent oxide thickness of 0.39nm, without taking into account the quantum mechanical tunneling effect. High-resolution transmission electron microscopy micrograph revealed well-ordered epitaxial-like interfacial layer. High-resolution Rutherford backscattering confirmed the presence of Lu-based silicate layer at the interface. It was proposed that the high dielectric constant was caused by the increased ionic polarizability in the film, thereby increasing the ionic contribution of the dielectric constant.
Long-lifetime emission in luminescent colloidal silica
Authors: Soriano Ronald B. , Kpatcha Essoyodou , Jakob Adam M. , Merkert Jon W. , Carlin Clifford M. , Schmedake Thomas A.
Published: August 2007

Calcination of aminopropylsilica spheres generates colloidal silica with tailorable luminescence properties depending on the calcination conditions. After calcining at 550°C for 20h, photoexcited luminescent colloidal silica exhibits a bright blue emission (λmax=375nm, 3.3eV) followed by a long-lifetime green photoluminescence centered around 500nm (2.5eV), which lasts for more than 10s at room temperature. Time resolved temperature studies indicate that the long-lifetime green photoluminescence can be fitted by a multiexponential decay function consisting of a regular exponential term and a stretched exponential term with a temperature independent beta parameter consistent with a hopping mechanism.
Ferromagnetic semiconductor Ge1−xCrxTe with a Curie temperature of 180K
Authors: Fukuma Y. , Asada H. , Moritake N. , Irisa T. , Koyanagi T.
Published: August 2007

A IV-VI ferromagnetic semiconductor Ge1−xCrxTe (x∼0.06) with Curie temperature TC up to 180K is grown by molecular-beam epitaxy. The magnetization is well reproduced from anomalous Hall effect. As the Te∕Cr flux ratio increases during the growth of Ge1−xCrxTe, the spontaneous magnetization and the magnetic anisotropy are decreased and TC is increased. On the other hand, the Te∕Cr flux ratio over 3.6 leads to formation of Cr–Te precipitations. The magnetoresistance measurements reveal that the increase of TC is attributed to the decrease of nonstoichiometric defects.
Effect of Ga∕In ratio on the optical and electrical properties of GaInZnO thin films grown on SiO2∕Si substrates
Authors: Kang Donghun , Song Ihun , Kim Changjung , Park Youngsoo , Kang Tae Dong , Lee Ho Suk , Park Jun-Woo , Baek Seoung Ho , Choi Suk-Ho , Lee Hosun
Published: August 2007

Amorphous GaInZnO and polycrystalline ZnO thin films are grown by rf magnetron sputtering. Their optical properties are investigated by spectroscopic ellipsometry. The optical gap of the GaInZnO film increases with the increase of Ga content and by annealing. These are attributed to the large band-gap energy of Ga2O3 and the structural relaxation after annealing, respectively. The changes in optical properties show a strong correlation to the device characteristics of GaInZnO thin film transistors: The turn-on voltage increases as the optical gap increases with increasing Ga∕In ratio. This study shows that the GaInZnO thin films are as excellent as transparent oxide semiconductors.
Spin-polarized transport in dilute magnetic semiconductor tunnel junctions
Authors: Bunder J. E.
Published: August 2007

The author considers transport properties of a trilayer junction consisting of an insulator sandwiched between two dilute magnetic semiconductors (DMSs). The magnetization directions of the two DMSs are not parallel but at a relative angle of θ. After calculating the transmission probabilities, the author calculates the conductance using the Landauer formula. The author defines a ratio R(θ,T), related to the tunneling magnetoresistance, which compares the θ=0 to the θ≠0 conductance at temperature T. The author also calculates R(θ,T) semiclassically using the well-known Julliere formula. The author shows that, in general, R(θ,T) obtained from the Julliere formula poorly approximates R(θ,T) obtained from the Landauer formula.
Evaluation of microwave dielectric properties of giant permittivity materials by a modified resonant cavity method
Authors: Li Lei , Chen Xiang Ming , Ni Lei , Fu Mao Sen
Published: August 2007

A modified resonant cavity method was developed to evaluate the microwave dielectric properties of giant permittivity materials, which were difficult to determine accurately using previous methods. A small-sized sample was used for measurement in the present work, and the microwave dielectric properties could be measured accurately over a wide frequency range with the aid of low-loss reference ceramics. The measurement was conducted on CaCu3Ti4O12 ceramics from 3.38to10.16GHz. The permittivity of CaCu3Ti4O12 ceramics was around 84 over the above frequency range and decreased slightly with increasing frequency, while the dielectric loss decreased significantly from 0.17 to 0.055.
Piezoelectricity and ferroelectric cluster size in relaxor ferroelectrics
Authors: Wang L.-F. , Liu J.-M.
Published: August 2007

The dipole configuration and electromechanical behaviors of dipole-disorder induced relaxor ferroelectrics (RFs) are investigated using a phenomenological model. In comparison to normal ferroelectric lattice, the RF lattice shows spatially inhomogeneous cluster configuration but no breaking of the dipole orientation symmetry is identified. A clean relationship between the piezoelectric response and the characteristic size of the ferroelectric clusters is established, which predicts a broad peak of the piezoelectric coefficient in response to the dipole disorder degree.
Temperature-insensitive photonic crystal fiber interferometer for absolute strain sensing
Authors: Villatoro Joel , Finazzi Vittoria , Minkovich Vladimir P. , Pruneri Valerio , Badenes Gonçal
Published: August 2007

The authors report a highly sensitive (∼2.8pm∕με) wavelength-encoded strain sensor made from a piece of photonic crystal fiber (PCF) spliced to standard fibers. The authors intentionally collapse the PCF air holes over a short region to enlarge the propagating mode of the lead-in fiber which allows the coupling of only two modes in the PCF. The transmission spectrum of the interferometer is stable and sinusoidal over a broad wavelength range. The sensor exhibits linear response to strain over a large measurement range, its temperature sensitivity is very low, and for its interrogation a battery-operated light emitting diode and a miniature spectrometer are sufficient.
Universality of electron accumulation at wurtzite c- and a-plane and zinc-blende InN surfaces
Authors: King P. D. C. , Veal T. D. , McConville C. F. , Fuchs F. , Furthmüller J. , Bechstedt F. , Schley P. , Goldhahn R. , Schörmann J. , As D. J. , Lischka K. , Muto D. , Naoi H. , Nanishi Y. , Lu Hai , Schaff W. J.
Published: August 2007

Electron accumulation is found to occur at the surface of wurtzite (112¯0), (0001), and (0001¯) and zinc-blende (001) InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low Γ-point conduction band minimum lying significantly below the charge neutrality level.
Subnanosecond ellipticity detector for laser radiation
Authors: Ganichev S. D. , Kiermaier J. , Weber W. , Danilov S. N. , Schuh D. , Gerl Ch. , Wegscheider W. , Prettl W. , Bougeard D. , Abstreiter G.
Published: August 2007

A room temperature detector of terahertz laser radiation ellipticity has been developed based on the simultaneous measurements of three different photoelectric phenomena: circular photogalvanic effect, linear photogalvanic effect, and photon drag effect. Each of these effects, which have subnanosecond time constants, is monitored by different detector units stacked together in one detector.
Multi-quantum-well spin oscillator
Authors: Bonilla L. L. , Escobedo R. , Carretero M. , Platero G.
Published: August 2007

A dc voltage biased II-VI semiconductor multi-quantum-well structure attached to normal contacts exhibits self-sustained spin polarized current oscillations if one or more of its wells are doped with Mn. Without magnetic impurities, the only configurations appearing in these structures are stationary. Analysis and numerical solution of a nonlinear spin transport model yield the minimal number of wells (four) and the ranges of doping density and spin splitting needed to find oscillations.
Effects of alloying and localized electronic states on the resonant Raman spectra of Zn1−xMgxO nanocrystals
Authors: Ye J. D. , Teoh K. W. , Sun X. W. , Lo G. Q. , Kwong D. L. , Zhao H. , Gu S. L. , Zhang R. , Zheng Y. D. , Oh S. A. , Zhang X. H. , Tripathy S.
Published: August 2007

Using resonant Raman spectroscopy, the authors report on the alloying effect and localization of electronic states in Zn1−xMgxO (x<0.15) nanostructures with average sizes in the range of 20–150nm. Anomalous intensity enhancement of the second-order longitudinal optical phonon has been observed, which is due to Fröhlich interaction via the localized exciton as the resonant intermediate electronic states. The alloying-induced disorder due to Mg incorporation led to the enhancement of exciton localization as well as the asymmetric broadening of longitudinal optical phonon line shape. The composition in ZnMgO could be determined by the first-order longitudinal optical phonon frequency via a bowinglike quadratic fit. This simple relationship is in perfect match to the modified random-element-isodisplacement model and provides a nondestructive approach to probe the quantitative composition distributions in wurtzite ZnMgO alloy system.
Stability and electronic structures of CuxTe
Authors: Da Silva Juarez L. F. , Wei Su-Huai , Zhou Jie , Wu Xuanzhi
Published: August 2007

In this work, the authors study the stability and electronic properties of CuxTe as a function of the Cu∕Te ratio using first-principles calculations. They find that CuxTe shows bistability with energy minimum at x≈1.25 and x≈1.75. At low x, CuxTe is more stable in the tetragonal-based structures, whereas for x>1.47, it is more stable in the trigonal-based structures. The valence-band maximum of Cu2Te is found to be 0.7eV higher than that of CdTe, indicating that it can easily be doped p type. The Cu diffusion barriers and hole density decrease with increasing Cu concentration, indicating that for x∼2, ionic conductivity may play a role.
Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors enabled by self-assembled nanodielectrics
Authors: Lin H. C. , Kim S. K. , Chang D. , Xuan Y. , Mohammadi S. , Ye P. D. , Lu G. , Facchetti A. , Marks T. J.
Published: August 2007

Direct-current and radio-frequency characterizations of GaAs metal-insulator-semiconductor field-effect transistors (MISFETs) with very thin self-assembled organic nanodielectrics (SANDs) are presented. The application of SAND on compound semiconductors offers unique opportunities for high-performance devices. Thus, 1μm gate-length depletion-mode n-channel SAND/GaAs MISFETs exhibit low gate leakage current densities of 10−2–10−5A∕cm2, a maximum drain current of 260mA∕mm at 2V forward gate bias, and a maximum intrinsic transconductance of 127mS∕mm. These devices achieve a current cutoff frequency (fT) of 10.6GHz and a maximum oscillation frequency (fmax) of 6.9GHz. Nearly hysteresis-free Ids-Vgs characteristics and low flicker noise indicate that a high-quality SAND-GaAs interface is achieved.
Fast, precise, tomographic measurements of thin films
Authors: Ghim Young-Sik , Kim Seung-Woo
Published: August 2007

The authors describe a nondestructive measurement method that enables them to obtain the cross-sectional thickness profile of thin-film layers fast with a single operation of measurement. The method is based on spectrally resolved white-light interferometry, being capable of reconstructing the tomographic height map of thin films with depth resolutions in the nanometer range. In terms of the measuring speed and resolution, the proposed method is well suited for the in-line high-speed inspection of microelectronics devices produced in large quantities particularly in the semiconductors and flat panel displays industries.
Effect of gas pressure on current-voltage characteristics of amorphous carbon film/silicon heterojunction
Authors: Gao Xili , Xue Qingzhong , Hao Lanzhong , Li Qun , Zheng Qingbin , Tian Ping
Published: August 2007

Amorphous carbon film/n-Si (a-C∕Si) junctions have been fabricated by direct current magnetron sputtering and their current-voltage (I-V) characteristics have been investigated. The results show that the gas pressure has a large effect on the reverse bias I-V characteristics of the junctions. For example, the reverse current can increase by 3300% when the gas pressure decreases from 100000to100Pa. The effect of gas pressure may be attributed to the physisorption process of gas molecules which increases the space charge width and changes the surface states of the junction.
Some comments on contact charge relaxation
Authors: Ireland Peter M.
Published: August 2007

The established contact charge relaxation scheme of Matsuyama and Yamamoto [J. Phys. D 28, 2418 (1995); 30, 2170 (1997)] is reassessed in light of the observations of Horn and Smith [Science 256, 362 (1992)] and Horn et al. [Nature (London) 366, 442 (1993)] of charge relaxation between separated charged surfaces. The multiple partial discharges observed in these studies are inconsistent with a scheme where onset and extinction are both described by a single Paschen curve. A modified version of the established scheme is therefore proposed.
Atomic scale nitrogen depth profile control during plasma enhanced atomic layer deposition of high k dielectrics
Authors: Maeng W. J. , Kim H.
Published: August 2007

Nitrogen incorporation produces several benefits in the performance of high k gate oxides. However, since too much nitrogen incorporation at the interface of gate dielectric can result in device degradation, the atomic scale control of nitrogen depth profile is desirable. In this study, the authors have improved electrical properties and interface properties by depth profile control of in situ nitrogen incorporation during plasma enhanced atomic layer deposition. The best electrical properties in terms of hysteresis, equivalent oxide thickness, and interface states were obtained when the nitrogen is incorporated in the middle of the thin film, which has not been achievable by other techniques.
Raman tensor elements for tetragonal BaTiO3 and their use for in-plane domain texture assessments
Authors: Deluca Marco , Higashino Masayuki , Pezzotti Giuseppe
Published: August 2007

A quantitative assessment of c-axis oriented domains in a textured BaTiO3 (BT) single crystal has been carried out by polarized Raman microprobe spectroscopy. The relative intensity modulation of the Raman phonon modes has been theoretically modeled as a function of crystal rotation and linked to the volume fraction of c-axis oriented domains. Raman tensor elements have also been experimentally determined for the Ag and B1 vibrational modes. As an application, the internal in-plane texture and the volume fraction of c-oriented domains in the BT single crystal have been nondestructively visualized by monitoring the relative intensity of Ag and B1 Raman modes.
Transmission increase upon switching of VO2 thin films on microstructured surfaces
Authors: Karakurt I. , Boneberg J. , Leiderer P. , Lopez R. , Halabica A. , Haglund R. F.
Published: August 2007

The authors compare transmission measurements of near-infrared light through VO2 thin films on smooth substrates and on ordered arrays of silica microspheres. When the samples are heated above the critical temperature for the semiconductor-metallic phase transition, smooth thin films show reduced transmission independent of thickness; however, the VO2 film deposited on the microspheres may show either reduced or enhanced transmission, depending on VO2 film thickness. They show that this at a first glance, unexpected behavior is directly related to the change of scattering efficiency upon the phase transition. This suggests that optical transmission through thin-film microstructures could be tuned by an appropriate combination of microsphere ordering and VO2 film thickness.
Electronic structure and work function of metal gate Mo–W system
Authors: Gong H. R. , Cho Kyeongjae
Published: August 2007

First principles calculation reveals that the Mo–W interface dipole is formed due to an equal loss of electrons of interface atoms, and the interface formation is energetically unfavorable with positive interface energy, signifying a tendency of phase separation of Mo and W atoms. Calculation also shows that Mo surface segregation has an important effect in reducing the work function of Mo–W alloys, and that after Mo surface segregation, the Mo–W work function becomes relatively stable when W is between 0–70at.%. Interestingly, such a composition range seems good for work function modulation of metal gate Mo–W system.
Stability of photovoltage and trap of light-induced charges in ferroelectric WO3-doped (Pb0.97La0.03)(Zr0.52Ti0.48)O3 thin films
Authors: Qin Meng , Yao Kui , Liang Yung C. , Gan Bee Keen
Published: August 2007

The stability of photovoltage in WO3-doped (Pb0.97La0.03)(Zr0.52Ti0.48)O3 (PLWZT) ferroelectric thin films was investigated. For in-plane polarized configuration, with a greatly enhanced electrode gap, the reduction ratio of photovoltage during multicycle UV illumination was significantly smaller and stability of photovoltage was greatly improved over the sandwich capacitor configuration. The ferroelectric-metal interfacial effects including Schottky barriers and polarization screening due to the trap of photoinduced charges at interfaces were found to determine the magnitude, stability, and even the polarity of the photovoltage, particularly for the electrode-sandwiched PLWZT thin films.
Application of parameter-induced stochastic resonance to target detection in shallow-water reverberation
Authors: Xu Bohou , Zhang Huiquan , Zeng Lingzao , Li Jianlong , Wu Xingxing , Jiang Zhong-Ping
Published: August 2007

A method based on parameter-induced stochastic resonance is proposed for target echo detection in the presence of shallow-water reverberation. The signal received by the horizontal sensor array is normalized and delayed to form the input to a bistable system. The system parameters are tuned properly to maximize the detection performance based on parameter-induced stochastic resonance techniques. Considering the limitation on the length of receiving arrays, the space-time unfolding method is suggested to largely improve the detection performance.
Luminescence properties of Tb3+–Sm3+ codoped glasses for white light emitting diodes
Authors: Liang Xiaoluan , Yang Yunxia , Zhu Chaofeng , Yuan Shuanglong , Chen Guorong , Pring Allan , Xia Fang
Published: August 2007

Photoluminescence properties of silicate and borosilicate glasses codoped with Tb3+ and Sm3+ ions have been characterized by excitation and emission spectroscopies. When excited by ultraviolet light the glasses emit a combination of green and orange-red wavelengths giving white light. The ratio of the intensities of orange-red to green emissions can be tuned by varying both the concentration of the Sm3+ ion and an the composition of the glass matrix. The excitation and emission spectra show a self-quenching effect for the Sm3+ ions and an energy transfer from Tb3+ (D45) to Sm3+ (G5∕24).
Doping level dependence of electron irradiation-induced minority carrier diffusion length increase in Mg-doped GaN
Authors: Lopatiuk-Tirpak O. , Chernyak L. , Wang Y. L. , Ren F. , Pearton S. J. , Gartsman K.
Published: August 2007

The electron irradiation-induced increase of minority carrier diffusion length was studied as a function of hole concentration in Mg-doped GaN. Variable-temperature electron beam induced current measurements yielded activation energies of 264, 254, 171, and 144meV for samples with hole concentrations of 2×1016, 9×1016, 3×1018, and 7×1018cm−3, respectively. This carrier concentration dependence of the activation energy for the effects of electron irradiation was found to be consistent with Mg acceptors, indicating the involvement of the latter levels in the irradiation-induced diffusion length increase.
Carrier statistics and quantum capacitance of graphene sheets and ribbons
Authors: Fang Tian , Konar Aniruddha , Xing Huili , Jena Debdeep
Published: August 2007

In this work, fundamental results for carrier statistics in graphene two-dimensional sheets and nanoscale ribbons are derived. Though the behavior of intrinsic carrier densities in two-dimennsional graphene sheets is found to differ drastically from traditional semiconductors, very narrow (sub-10nm) ribbons are found to be similar to traditional narrow-gap semiconductors. The quantum capacitance, an important parameter in the electrostatic design of devices, is derived for both two-dimensional graphene sheets and nanoribbons.
Electronic transport in Ta2O5 resistive switch
Authors: Sakamoto Toshitsugu , Lister Kevin , Banno Naoki , Hasegawa Tsuyoshi , Terabe Kazuya , Aono Masakazu
Published: August 2007

The authors examined the electronic transport of a solid electrolyte resistive switch. Using element analysis and the temperature dependence of its electronic transport, they deduced that the conductive path is composed of Cu metal precipitated in the solid electrolyte film by an electrochemical reaction. Furthermore, they observed Coulomb blockade phenomena at 4K when the switch was in the off state. Their observations and experimental results suggest that the metallic conductive path consists of metallic islands separated by tunneling barriers and that switching between the on and off states originates from modulation in the tunneling barriers.
Observation of 394nm electroluminescence from low-temperature sputtered n-ZnO∕SiO2 thin films on top of the p-GaN heterostructure
Authors: Chen Cheng Pin , Ke Min Yung , Liu Chien Cheng , Chang Yuan Jen , Yang Fu Hsiang , Huang Jian Jang
Published: August 2007

The authors report on the 394nm UV light emission from low-temperature sputtered n-ZnO∕SiO2 thin films on top of the p-GaN heterostructure. They compare samples with and without a SiO2 current blocking layer. With a SiO2 layer, electroluminescence spectrum shows a sharp emission peak at 394nm, which is attributed to the recombination of accumulated carriers between n-ZnO∕SiO2 and p-GaN∕SiO2 junctions. As for the sample without a SiO2 layer, a broadband ranging from 400to800nm is observed, which is due to Mg+ deep-level transition in the GaN along with defects in the ZnO layers.
Tunable current-voltage characteristics in polycrystalline calcium copper titanate
Authors: Chung Sung-Yoon , Choi Jin-Hoon , Choi Jong-Kwan
Published: August 2007

The nonlinear current-voltage relationship and the subsequent threshold voltage in polycrystalline CaCu3Ti4O12 are found to be easily controlled by simply doping a small amount of supervalent cations, Nb5+ and Ta5+. The authors show that the dopants have a significant effect on the reduction of the electrostatic potential at the grain boundaries, scarcely changing the conductance of the bulk grains. Through microcontact analysis and impedance spectroscopy, the control of the potential barrier at the boundaries was demonstrated to be a key factor for governing the overall current-voltage characteristics. Plausible compensation mechanisms for the excess charge of the added dopants are also discussed.
Electrostatic ion trap and Fourier transform measurements for high-resolution mass spectrometry
Authors: Bhushan K. G. , Gadkari S. C. , Yakhmi J. V. , Sahni V. C.
Published: August 2007

We report on the development of an electrostatic ion trap for high-resolution mass spectrometry. The trap works on purely electrostatic fields and hence trapping and storing of ions is not mass restrictive, unlike other techniques based on Penning, Paul, or radio frequency quadrupole ion traps. It allows simultaneous trapping and studying of multiple mass species over a large mass range. Mass spectra were recorded in “dispersive” and “self-bunching” modes of ions. Storage lifetimes of about 100ms and mass resolving power of about 20 000 could be achieved from the fifth harmonic Fourier transform spectrum of Xe ions recorded in the self-bunching mode.
Flushing time of solutes and pollutants in the central Great Barrier Reef lagoon, Australia
Authors: Wang Yonghong , Ridd Peter V. , Heron Mal L. , Stieglitz Thomas C. , Orpin Alan R.
Published: August 2007

The flushing time of the central Great Barrier Reef lagoon was determined by using salinity as a tracer and developing both an exchange model and a diffusion model of the shelf exchange processes. Modelling suggests that the cross-shelf diffusion coefficient is approximately constant for the outer half of the lagoon but decays rapidly closer to the coast. The typical outer-shelf diffusion coefficient is ~1400 m2 s–1, dropping to less than 100 m2 s–1 close to the coast. Flushing times are around 40 days for water close to the coast and 14 days for water in the offshore reef matrix.
Investigating the association between pelagic fish and dimethylsulfoniopropionate in a natural coral reef system
Authors: DeBose Jennifer L. , Nevitt Gabrielle A.
Published: August 2007

Dimethylsulfoniopropionate (DMSP) is a biogenic chemical produced by marine algae that is associated with areas of high primary and secondary productivity in the ocean. In laboratory experiments, DMSP has been shown to be an effective feeding attractant for a variety of fresh and saltwater fishes, suggesting that it might also function as a foraging cue in the natural environment. Here we explore whether free-roaming pelagic fishes associate with periodic elevations of DMSP in their natural foraging habitat. Working in the vicinity of the coral reefs of the Flower Garden Banks in the Gulf of Mexico, we found that daily changes in the number of pelagic jack fishes (Carangidae) were significantly correlated with natural changes in concentrations of DMSP in the water column. These results provide the first evidence of a correlation between variation in the number of pelagic fishes and a specific habitat-associated chemical cue in the ocean.
Influence of upwelling on movement of southern bluefin tuna (Thunnus maccoyii) in the Great Australian Bight
Authors: Willis Jay , Hobday Alistair J.
Published: August 2007

Large pelagic predators move quickly in and out of local ecosystems that may be separated by long distances: their trophic effects are determined by their behaviour while present. To investigate movement and local residence times of one such predator we implanted 29 acoustic tags into juvenile southern bluefin tuna (Thunnus maccoyii) (SBT) in the Great Australian Bight. We used acoustic detectors at a reef known to attract tuna and detected fifteen SBT on 941 occasions over 62 days. SBT were tagged at the reef, 40 km, and 120 km distant. A total of 100% of local and 60% of SBT tagged 40 km away were subsequently recorded at the reef. Presence and absence was related to an upwelling event. Water temperature decreased just after SBT departure from the monitoring region. The immediate area was aerially surveyed 22 times for SBT schools during the experiment. We combined aerial survey observations with computer simulation, calibrated against field studies of SBT movement, to test the hypothesis that tuna could be well simulated by a correlated random walk throughout the area of known occurrence. The most plausible explanation for the observed behaviour was short-term (hours) fidelity to schools combined with medium-term (weeks) fidelity to bathymetric features. The present study illustrates how dynamic models aid interpretation of experiments designed to understand trophic effects of large pelagic predators.
Evidence of genetic subdivision among populations of blacklip abalone (Haliotis rubra Leach) in Tasmania
Authors: Temby Nepelle , Miller Karen , Mundy Craig
Published: August 2007

The scale over which populations exchange individuals (migration) is central to ecology, and important for understanding recruitment and connectivity in commercial species. Field studies indicate that blacklip abalone (Haliotis rubra) have localised larval dispersal. However, genetic studies show differentiation only at large scales, suggesting dispersal over more than 100 km. Most genetic studies, however, have failed to test for subdivision at scales equivalent to field experiments. We used microsatellite DNA to investigate genetic structure at small scales (100 m to 10 km) in blacklip abalone in south-east Tasmania. We found significant subdivision (FST = 0.021; P < 0.05) among sites, and hierarchical FST analysis indicated 64% of genetic variation was at the smallest scale, supporting field studies that concluded larval dispersal is less than 100m. We also tested if genetic differentiation varied predictably with wave exposure, but found no evidence that differences between adjacent sites in exposed locations varied from differences between adjacent sites in sheltered populations (mean FST = 0.016 and 0.017 respectively). Our results show the usefulness of microsatellites for abalone, but also identify sampling scales as critical in understanding gene flow and dispersal of abalone larvae in an ecologically relevant framework. Importantly, our results indicate that H. rubra populations are self-recruiting, which will be important for the management of this commercial species.