bluuebunny/crossref_metadata_2025 huggingface dataset:
Precise calibration for surface stress induced optical deflection measurements
Authors: Kury P. , Zahl P. , Hoegen M. Horn-von
Published: June 2004

Bending sample methods, like surface stress induced optical deflection, are powerful tools for the in situ determination of thin film and surface stress: the bending radius of a sample is measured via the deflection of reflected laser beams. In most setups split-segment position sensitive detectors are used. A precise method for calibrating those detectors is presented.
Effects of high temperature forming gas anneal on the characteristics of metal-oxide-semiconductor field-effect transistor with HfO2 gate stack
Authors: Choi Rino , Kang Chang Seok , Cho Hag-Ju , Kim Young-Hee , Akbar Mohammad S. , Lee Jack C.
Published: June 2004

The effects of high temperature forming gas (N2:H2=96:4) anneal (600 °C) prior to metallization have been evaluated in terms of the improvement in the carrier mobility of HfO2/nitride layer gate stack metal-oxide-semiconductor field-effect transistors with TaN gate electrode. The high-temperature forming gas anneal has been found to be effective in improving the interface quality by lowering both interface state density and interface charges. The improvements resulting in decreased Coulombic scattering centers can be attributed to hydrogen atoms that were concentrated near the interface.
A lead-free high-TC ferroelectric BaTi2O5: A first-principles study
Authors: Waghmare Umesh , Sluiter Marcel H. F. , Kimura Teiichi , Goto Takashi , Kawazoe Yoshiyuki
Published: June 2004

Previous experimental indications of ferroelectricity with Curie temperature (TC) of 747 K in BaTi2O5 are confirmed through assessment of its structural stability and estimation of its spontaneous polarization using first-principles density functional theory calculations. The present work establishes that the polarization is observed along b axis only and determines its structural origin with calculations of the Born effective charges. We find its piezoelectric response is comparable to that of PbTiO3, which with its high TC and nonperovskite structure should open up possibilities for new lead-free ferroelectric materials.
Electromechanically induced transition from nonohmic to ohmic behavior at contact interfaces
Authors: Kogut L. , Komvopoulos K.
Published: June 2004

A straightforward method for removing thin insulating films from contact interfaces of conductive surfaces that enables changing the contact behavior from nonohmic to ohmic was derived in this study. The efficacy of this method is demonstrated by experiments performed with a special microdevice consisting of polysilicon. It is shown that the native oxide film can be removed from asperity nanocontacts at the contact interface by electromechanical means without damaging the microdevice. Measurements of electrical contact resistance versus applied current are used to characterize the contact interface. The present approach for removing oxide surface films that are responsible for the nonohmic behavior at microdevice contact interfaces is straightforward and can easily be applied to other types of miniaturized devices to enhance their reliability and performance. An additional benefit of this method is the release of adhered microdevices by nondestructive means.
Controlled cleavage of single semiconducting nanowires and study on the suitability of their use as nanocavities for nanolasers
Authors: Chen Q. , Peng L.-M.
Published: June 2004

Single semiconducting nanowires have been cleaved to desired length at desired locations inside the scanning electron microscope (SEM) using a nanoprobe system. SEM and transmission electron microscope examinations of the cleaved nanowires revealed that the cleaved ends of the nanowires are in general atomic flat, but not without atomic steps. Possible use of the cleaved nanowire as nanocavity for nanolaser was considered, and several key parameters were estimated. In particular, our result shows that, for a semiconducting CdS nanowire, the effect of the atomic steps at the cleaved ends of the nanowire is negligible if the nanowire cavity is longer than several micrometers.
Size effects on exchange bias in sub-100 nm ferromagnetic–antiferromagnetic dots deposited on prepatterned substrates
Authors: Baltz V. , Sort J. , Rodmacq B. , Dieny B. , Landis S.
Published: June 2004

Exchange bias effects have been investigated in ferromagnetic (FM)–antiferromagnetic (AFM) square dots, with lateral sizes of 90 nm, sputtered on a prepatterned Si substrate. The magnetic behavior of the dots has been compared with that of a continuous FM–AFM bilayer with the same composition. Along the unidirectional direction, the dots exhibit square hysteresis loops and preserve an exchange bias field, HE, of 70 Oe at room temperature, which is about 40% smaller than HE in the continuous film. In addition, the distribution of blocking temperatures in the nanostructures is found to be shifted toward lower values with respect to that in the continuous film. These results can be interpreted assuming that the reduced lateral dimensions of the nanostructures impose some constraints on the formation and pinning of domain walls in the AFM layer.
Crystalline silicon oxycarbide: Is there a native oxide for silicon carbide?
Authors: da Silva Cesar R. S. , Justo João F. , Pereyra Inés
Published: June 2004

Using variable cell ab initio molecular dynamics, we have investigated hypothetical crystalline phases of silicon oxycarbide (Si1−xCxO2). We found that silicon oxide remains energetically stable with carbon incorporation, and the resulting oxycarbide material has a moderately large bulk modulus. Our results also indicated that there are at least two possible, and competing, crystalline phases for the Si2CO6. We discuss the possibility of those phases forming near the SiC/SiO2 interfaces.
Terahertz emission due to interminiband resonant Zener tunneling in wide-miniband GaAs/Al0.3Ga0.7As superlattices
Authors: Shimada Y. , Sekine N. , Hirakawa K.
Published: June 2004

We have investigated terahertz (THz) emission induced by high-field electron transport in biased wide-miniband GaAs/Al0.3Ga0.7As superlattices. With increasing bias electric fields, two distinct regimes are observed in the bias-field dependence of the emitted THz intensity. These two regimes are attributed to the intraminiband transport and interminiband Zener tunneling regimes, respectively. In the Zener tunneling regime, quasiperiodic structures are observed in the bias field dependence of the emitted THz intensity and are identified to be due to the resonant Zener tunneling between the Wannier–Stark ladders associated with the ground and excited minibands.
Direct observation of the barrier asymmetry in magnetic tunnel junctions
Authors: Koller P. H. P. , Swagten H. J. M. , de Jonge W. J. M. , Boeve H. , Coehoorn R.
Published: June 2004

A photoconductance method has been used to study directly the barrier asymmetry in TaOx magnetic tunnel junctions. Due to optical electron-hole pair generation in the barrier itself and subsequent transport in the electric field, the sign and magnitude of the barrier asymmetry can be determined quite accurately. The reliability of the technique is demonstrated by the independence on the direction of illumination. The oxidation time where the asymmetry becomes zero is found to coincide with a maximum in the magnetoresistance ratio. This is argued to be due to the complete oxidation of the barrier material, resulting in a symmetric tunnel barrier.
Multiwall nanotubes with intramolecular junctions (CNx/C): Preparation, rectification, logic gates, and application
Authors: Hu Ping’an , Xiao Kai , Liu Yunqi , Yu Gui , Wang Xianbao , Fu Lei , Cui Guanglei , Zhu Daoben
Published: June 2004

We prepared a large quantity of multiwall nanotubes with intramolecular junctions (CNx/C) by pyrolysis of iron phthalocyanine with or without an inlet of ammonia gas. The nanotubes consist of two sections, one section made of carbon nitride featuring bamboo-like structure and the other one made of carbon featuring empty hollow cylinder structure, and thus the intramolecular junctions were formed in the middle as a result of being doped or undoped with nitrogen. Nanodiode based on a single CNx/C junction shows reproducible rectifying behavior with a rectification ratio of 1.3×103 at ±2 V. In addition, the nanodiode demonstrated as a half-wave rectifier worked at an input sine wave of 1 kHz. Two CNx/C junctions were configured together to exhibit functions of OR and AND logic gates. Moreover, after substituting the wave-detection silicon diode in common transistor radio set with our nanodiode, the radio set still worked normally, representing an important step toward the potential application for nano-scale devices.
Large second-harmonic signal in thermally poled lead glass-silica waveguides
Authors: Luo Y. , Biswas A. , Frauenglass A. , Brueck S. R. J.
Published: June 2004

Thermal poling of silica-lead glass-silica waveguides formed by laser ablation of lead glass and e-beam evaporation of the silica cladding is reported. A large nonlinearity localized within the Pb-glass layer was found by scanning the probe laser beam across an angle-polished sample, and a peak second-order nonlinear susceptibility χ(2) as high as 15 pm/V was achieved in the Pb-glass layer. A simple theoretical model based on charge transport in the different materials during poling is proposed to explain complex χ(2) profile. The large third-order nonlinearity of lead glass plays a key role in the generation of the large second-harmonic signal.
Multiple relaxation mechanisms in SrTiO3/SrRuO3 heterostructures
Authors: Ban Z.-G. , Alpay S. P. , He Feizhou , Wells B. O. , Xi X. X.
Published: June 2004

We have studied stress relaxation mechanisms in epitaxial (001) SrTiO3 films grown on (001) LaAlO3 substrates with SrRuO3 buffer layers. A theoretical analysis has been undertaken to understand the variation of the lattice parameters of SrTiO3 epitaxial films, taking into account stress relaxation due to the formation of an orthorhombic polydomain structure in the SrRuO3 buffer layer as well as the formation of misfit dislocations at the LaAlO3/SrRuO3 and the SrTiO3/SrRuO3 interfaces. There exists a critical SrRuO3 buffer layer thickness, above which the SrRuO3 buffer layer can “screen” the effect of the LaAlO3 substrate. It is shown that the internal stress level in films can be controlled using buffer layers that exhibit a structural phase transformation.
Enhancement of third-order nonlinear optical susceptibilities in silica-capped Au nanoparticle films with very high concentrations
Authors: Hamanaka Y. , Fukuta K. , Nakamura A. , Liz-Marzán L. M. , Mulvaney P.
Published: June 2004

Third-order nonlinear optical susceptibilities (χ(3)) and response times have been investigated for silica-capped Au nanoparticles for various volume fractions, p, of Au nanoparticles ranging from 0.027 to 0.66. The imaginary part of χ(3)(Im χ(3)) around the surface plasmon resonance increases with increasing p up to 0.34, and decreases for p>0.39. In addition to the local field enhancement around the surface plasmon resonance in the composite system, an additional enhancement of Im χ(3) due to the interaction between nanoparticles for p<0.39 is observed.
Thickness-related features observed in GaN epitaxial layers
Authors: Castaldini A. , Cavallini A. , Polenta L.
Published: June 2004

Electrical properties of gallium nitride (GaN) epitaxially grown on sapphire show significant dependence on layer thickness. In this letter we show some of the main features observed by spectral photoconductivity (PC), electron beam induced current, and current–voltage characteristics. We focus our attention on the blueshift of the PC peak corresponding to the energy gap, which we associated to the strain acting in the GaN epilayers. The good energetic resolution of photoconductivity spectra allows for a direct study of the energy gap dependence on thickness.
Low-temperature growth and properties of ZnO nanowires
Authors: Wang Xuan , Li Qingwen , Liu Zhibo , Zhang Jin , Liu Zhongfan , Wang Rongming
Published: June 2004

ZnO nanowires were obtained through evaporation of zinc powders under a low temperature of 400 °C. These ZnO nanowires, in the diameter of ∼10 nm, were long and curved with lengths of tens of micrometers. High-resolution transmission electron microscopy showed these ZnO nanowires were mostly crystalline structure; however, the kink parts contained dislocations and stacking faults. Furthermore, the movement of dislocations was observed in the kink parts under e-beam irradiation. Photoluminescence and Raman spectra show that there exist oxygen vacancies in the ZnO nanowires. Possible reasons for the growth and properties of ZnO nanowires were discussed.
Strong red emission in heterojunctions of conjugated polymer blends
Authors: Li Zong-Long , Meng Hsin-Fei , Horng Sheng-Fu , Hsu Chain-Shu , Chen Lai-Cheng , Chang Shu-Mei
Published: June 2004

We demonstrate strong red electroluminescence in bilayer polymer light-emitting diodes with poly(3-hexylthiophene) and polyfluorene copolymers. The emission spectrum of the diode, peaked at 612 nm, is different from either of the two polymer layers, and is attributed to the exciplex state existing only at the heterojunction. The efficiency of this junction emission is very high for red polymer light-emitting diodes. Peak luminance of 3500 cd/m2 with yield 1.3 cd/A is achieved. The emission color can be made more saturated by blending red-emitting polymers into the polyfluorene to eliminate the small residual green emission.
Measurement of spin polarization by Andreev reflection in ferromagnetic In1−xMnxSb epilayers
Authors: Panguluri R. P. , Nadgorny B. , Wojtowicz T. , Lim W. L. , Liu X. , Furdyna J. K.
Published: June 2004

We carried out point contact Andreev reflection (PCAR) spin spectroscopy measurements on epitaxially grown ferromagnetic In1−xMnxSb epilayers with a Curie temperature of ∼9 K. The spin sensitivity of PCAR in this material was demonstrated by parallel control studies on its nonmagnetic analog, In1−yBeySb. We found the conductance curves of the Sn point contacts with In1−yBeySb to be fairly conventional, with the possible presence of proximity-induced superconductivity effects at the lowest temperatures. These measurements provided control data for subsequent PCAR measurements on ferromagnetic In1−xMnxSb, which indicated spin polarization in In1−xMnxSb to be 52±3%.
Giant optical rectification effect in nanocarbon films
Authors: Mikheev G. M. , Zonov R. G. , Obraztsov A. N. , Svirko Yu. P.
Published: June 2004

We present observations of the optical rectification effect in the nanocarbon film, which is excited by nanosecond pulses of a Nd:YAG laser in the absence of an external electric field. Effective second order susceptibility of the film material is found to be 10−6 CGSE, which is higher than that of conventional noncentrosymmetric crystals. The measured ratio of the dc voltage to the laser power is 500 and 650 mV/MW at the wavelengths of 1064 and 532 nm, respectively. This makes the nanocarbon materials a promising alternative to conventional semiconductor-based terahertz radiation sources.
Enhanced stability of the second-order optical nonlinearity in poled glasses
Authors: Deparis Olivier , Corbari Costantino , Kazansky Peter G. , Sakaguchi Koichi
Published: June 2004

Glasses in a wide range of chemical composition were thermally poled and the stability of the second-order optical nonlinearity induced was studied through isothermal annealing experiments. Enhanced stability was found in aluminosilicate and aluminoborosilicate with respect to silica (at least a five order of magnitude increase in lifetime). Such dramatic enhancement was explained by the strong decrease of the alkali ion mobility due to specific changes in glass composition.
Effects of thermal stress on interdiffusion in InGaAsN/GaAs quantum dots
Authors: Gao Q. , Tan H. H. , Fu L. , Jagadish C.
Published: June 2004

Thermal-stress controlled interdiffusion in InGaAsN/GaAs quantum dots (QDs) has been studied by deposition of titanium oxide (TiO2) layers combined with rapid thermal annealing. Without TiO2 cap layers, blueshifting of the band gap from 1.033 to 1.180 eV at 77 K has been observed after annealing at 850 °C for 30 s due to the thermal interdiffusion. The thermal interdiffusion has been effectively suppressed by depositing TiO2 layers on the samples without degrading the photoluminescence properties. By a combination of annealing temperature and TiO2 thickness, controlled blueshifting of the band gap has been achieved. We suggest that the mechanism of suppression of thermal interdiffusion is the thermal stress imposed on the QD structure generated by TiO2 layers during annealing.
Optical in-well pumping of a vertical-external-cavity surface-emitting laser
Authors: Schmid Marc , Benchabane Sarah , Torabi-Goudarzi Firuz , Abram Richard , Ferguson Allister I. , Riis Erling
Published: June 2004

A scheme is demonstrated for optical pumping of a vertical-external-cavity surface-emitting laser. The scheme is based on absorption of the pump light within the wells of the multiple-quantum-well gain structure rather than the conventional approach of absorption of a shorter wavelength in the barrier regions. The operation of a laser around 850 nm pumped by an 808 nm source demonstrates the potential of this technique for allowing operation at a significantly shorter range of wavelengths for these devices in general and specific application of high-brightness pump lasers for devices in this spectral region. A further advantage is the smaller quantum defect which results in reduced heating of the gain medium. These advantages are achieved while maintaining a slope efficiency of up to 18%, which is comparable to results obtained with a traditional pumping scheme with a similar gain medium.
Absolute H atom density measurement in pure methane pulsed discharge
Authors: Ganguly B. N. , Parish J. W.
Published: June 2004

Absolute atomic hydrogen and methyl radical production resulting from direct electron impact dissociative excitation of CH4 has been measured in pulsed discharge by two-photon allowed laser induced fluorescence. For 20 Torr pure methane discharge with 480 ns pulse duration, 4–6 kV voltage applied, and 6–11.5 mJ input electrical energy yield of 10–22×1015 cm−3 hydrogen atoms, i.e., up to 4.5% dissociation of CH4 is achieved by direct electron impact with 50% energy conversion efficiency.
Varying the effective buoyancy of cells using magnetic force
Authors: Guevorkian Karine , Valles James M
Published: June 2004

We introduce a magnetic force buoyancy variation (MFBV) technique that employs intense inhomogeneous magnetic fields to vary the effective buoyancy of cells and other diamagnetic systems in solution. Nonswimming Paramecia have been suspended, forced to sediment and driven to rise in solution using MFBV. Details of their response to MFBV have been used to determine the magnetic susceptibility of a single Paramecium. The use of MFBV as a means by which to suspend cell cultures indefinitely is also described.
Effect of operating temperature and film thickness on the pyroelectric response of ferroelectric materials
Authors: Sharma A. , Ban Z.-G. , Alpay S. P. , Mantese J. V.
Published: June 2004

The influence of the operating temperature and film thickness on the pyroelectric properties of (001) Ba0.6Sr0.4TiO3 (BST 60/40) epitaxial films on (001) LaAlO3, MgO, and Si substrates is investigated theoretically via a thermodynamic model. The results are presented using contour maps that can be used to identify “design windows” for film thickness and operating temperature for optimum pyroelectric response. For BST 60/40 on LAO and MgO large pyroelectric coefficients (∼0.7 μC cm−2 K−1) are observed at near room temperature for moderate film thickness (50–200 nm). The pyroresponse of films on Si is suppressed by two orders of magnitude compared to bulk BST 60/40 due to internal stresses. Significant recovery in the pyroelectric coefficient on Si is expected for lower growth temperatures due to the reduction of thermal stresses.
High microwave permittivity of multiwalled carbon nanotube composites
Authors: Wu Junhua , Kong Lingbing
Published: June 2004

Complex permittivity spectra of the multiwalled carbon nanotube (MWNT)-epoxy composites with mass concentrations up to 25.9% were measured from 10 MHz to 20 GHz. The composites exhibit high real and imaginary relative permittivities over broad bandwidth, showing strong dependence on the MWNT loading. It is observed that distinct resonance takes place at ∼1.5 GHz, with the corresponding resonant frequency shifts downward as the MWNT concentration increases. The origin of the dielectric properties is explained in terms of the dielectric relaxation/resonance and electrical conduction behavior of the nanotube composites, substantiated by the agreement between simulation and experimental data.
Critical point transitions of wurtzite AlN in the vacuum–ultraviolet spectral range
Authors: Chen J. , Shen W. Z. , Ogawa H. , Guo Q. X.
Published: June 2004

The optical reflection spectra have been measured on a high-quality wurtzite aluminum nitride (AlN) single crystal with synchrotron radiation in the range of 6–16 eV at different temperatures. The energy positions of the dominant structures due to the critical point (CP) transitions have been extracted by employing Adachi’s dielectric function model. By the aid of the band structure of AlN, we have assigned up to ten CP transitions in the reflection spectra. The crystal-field splitting at the center of the Brilliouin zone is observed to be 110 meV. We have further revealed the temperature dependencies of these interband transitions.
Ion implant simulations: Kinetic Monte Carlo annealing assessment of the dominant features
Authors: Martin-Bragado I. , Jaraiz M. , Castrillo P. , Pinacho R. , Rubio J. E. , Barbolla J.
Published: June 2004

The atomistic physically based kinetic Monte Carlo method has been used in conjunction with the binary collision approximation (BCA) to elucidate the implant mechanisms most relevant for modeling transient-enhanced diffusion (TED). For the cases studied, we find that: (i) The spatial correlation of the interstitial, vacancy (I,V) Frenkel pairs is not critical, (ii) the interstitial supersaturation in simulations which include full I, V profiles or only the net I–V is the same, (iii) quick and noisy BCA implant I, V distributions can be directly used (or after smoothing them out) as they can still yield accurate annealing simulations, and (iv) when there is an impurity concentration comparable to the net I–V excess, the full I and V profiles have to be used in order to correctly reproduce the impurity clustering/deactivation. Finally, some practical implications for TED simulations are drawn.
Carbon nanotube filaments in household light bulbs
Authors: Wei Jinquan , Zhu Hongwei , Wu Dehai , Wei Bingqing
Published: June 2004

Household light bulbs made from macroscopic single-walled and double-walled carbon nanotube filaments were fabricated and tested. The nanotube bulbs are found to possess several interesting features when compared to a conventional tungsten filament in safelight (36 V, 40 W), such as lower threshold voltage for light emission and higher brightness at high voltages. Electrically induced excited peaks at 407, 417, 655 nm were identified to be an intrinsic property of nanotubes and these peaks are observed to become stronger in the light emission spectra at high temperatures which cannot be explained easily with the concept of blackbody emission.
Martensitic transformation from α-Ti to β-Ti on rapid heating
Authors: Zhang W. , Zhao W. S. , Li D. X. , Sui M. L.
Published: June 2004

Instead of conventional quenching martensitic transformation from β-Ti to α-Ti, unusual martensitic transformation from α-Ti to β-Ti induced by rapid heating has been achieved simply by using an electric current pulse. A large amount of the high-temperature martensitic phase remained in a Ti–6Al–4V alloy. We verified that such transformation is structurally and kinetically achievable, which agrees well with the phenomenological crystallographic theory of martensitic transformation.
Structure of the glycerol liquid/vapor interface studied by sum-frequency vibrational spectroscopy
Authors: Oh-e Masahito , Yokoyama Hiroshi , Baldelli Steven
Published: June 2004

Surface-specific sum-frequency vibrational spectroscopy has been used to study the structures of the glycerol liquid/vapor interface. The results show that the molecules at the glycerol surface are highly polar ordered with the CH2 and CH groups projecting into the vapor and the OH group remaining at the surface or pointing into the bulk. More quantitatively, we have also determined how the CH2 groups of the molecules are oriented at the surface.
Silicon nanowhiskers grown on 〈111〉Si substrates by molecular-beam epitaxy
Authors: Schubert L. , Werner P. , Zakharov N. D. , Gerth G. , Kolb F. M. , Long L. , Gösele U. , Tan T. Y.
Published: June 2004

Silicon nanowhiskers in the diameter range of 70 to 200 nm were grown on 〈111〉-oriented silicon substrates by molecular-beam epitaxy. Assuming the so-called “vapor–liquid–solid” (VLS) growth process to operate, we initiated the growth by using small clusters of gold at the silicon interface as seeds. The in situ generation of the Au clusters as well as the growth parameters of the whiskers are discussed. The experimentally observed radius dependence of the growth velocity of the nanowhiskers is opposite to what is known for VLS growth based on chemical vapor deposition and can be explained by an ad-atom diffusion on the surface of the whiskers.
Quasiperiodic photonic crystal microcavity lasers
Authors: Nozaki Kengo , Baba Toshihiko
Published: June 2004

We fabricated a 12-fold symmetric quasiperiodic photonic crystal (QPC) point defect laser, and obtained the lasing action at room temperature. When photopumping a seven-hole-missing defect or a uniform QPC part, the lasing occurred by different modes. The finite-difference time-domain analysis showed that the defect mode is a whispering gallery mode, which is confined by the photonic gap or the boundary reflection. It also indicated that the defect-free mode is an extended but partly localized mode, which cannot be seen in photonic crystals.
Writing polarization bits on the multiferroic BiMnO3 thin film using Kelvin probe force microscope
Authors: Son J. Y. , Kim Bog G. , Kim C. H. , Cho J. H.
Published: June 2004

We report the multiferroic properties of epitaxially (100) oriented BiMnO3 thin film on (100) LaAlO3 substrate and preferentially (111) oriented BiMnO3 thin film on (111) Pt/TiO2/SiO2/Si substrate. Nano-size bits of ferroelectric polarization on the BiMnO3 thin film on (111) Pt/TiO2/SiO2/Si substrate can be easily written and read by Kelvin force microscope (KFM). We found that, for the preferentially (111) oriented BiMnO3 thin film, only ferroelectric polarization has been induced at the low writing biases, which makes the writing and reading process simple. This suggests that the preferentially oriented BiMnO3 thin film is a potential candidate for the high-density data storage device based on KFM.
Determination of dielectric constant of a thin and low-dielectric film in the millimeter wave region
Authors: Kawate Etsuo , Ishii Kenichi
Published: June 2004

This letter presents a method for measuring free-space transmittance to study the dielectric property of a thin and low-dielectric film in the millimeter wave region. We found that multireflection keeps the height of the repeated peaks of the transmittance almost constant and that their widths quickly narrow with increase in the incident angle. We further show how the dielectric constant is set for a 20-μm-thick silicon dioxide film on a 700-μm-thick silicon substrate near the electromagnetic waves of frequency 65 GHz.
Noncollinear magnetism and enhancement of magnetocrystalline anisotropy at the Σ3(111) grain boundary in ferromagnetic Fe
Authors: Nakamura Kohji , Ito Tomonori , Freeman A. J. , Zhong Lieping , Fernandez-de-Castro Juan
Published: June 2004

Magnetic structures and magnetocrystalline anisotropy of the Σ3[11̄0](111) grain boundary (GB) in ferromagnetic Fe are investigated by the first-principles full-potential linearized augmented plane-wave method including intra-atomic noncollinear magnetism. In breaking the spatial translation symmetry in a crystalline solid, the GB is found to give rise to a magnetic noncollinearity, where the magnetic moments at both sides of the GB orient at an angle of about 10° with respect to each other. Importantly, the presence of the GB enhances the magnetocrystalline anisotropy energy by one order of magnitude from its bulk value and may induce a pinning effect on the magnetization rotation or magnetic domain wall motion.
Controllable excimer-laser fabrication of conical nano-tips on silicon thin films
Authors: Georgiev D. G. , Baird R. J. , Avrutsky I. , Auner G. , Newaz G.
Published: June 2004

We have found conditions for the reproducible, direct laser fabrication of sharp conical tips with heights of about 1 μm and apical radii of curvature of several tens of nanometers. An individual cone is formed when single-crystalline silicon on a silica substrate is irradiated with a single pulse from a KrF excimer laser, homogenized and shaped to a circular spot several microns in diameter. Atomic force microscopy and field-emission scanning electron microscopy were used to characterize these structures. A simple mechanism of formation based on movement of melted material is proposed. Our results suggest that this technique could produce even smaller structures by optimizing the laser processing geometry.
Leakage mechanism in GaN and AlGaN Schottky interfaces
Authors: Hashizume Tamotsu , Kotani Junji , Hasegawa Hideki
Published: June 2004

Based on detailed temperature-dependent current–voltage (I–V–T) measurements the mechanism of leakage currents through GaN and AlGaN Schottky interfaces is discussed. The experiments were compared to calculations based on thin surface barrier model in which the effects of surface defects were taken into account. Our simulation method reproduced the experimental I–V–T characteristics of the GaN and AlGaN Schottky diodes, and gave excellent fitting results to the reported Schottky I–V curves in GaN for both forward and reverse biases at different temperatures. The present results indicate that the barrier thinning caused by unintentional surface-defect donors enhances the tunneling transport processes, leading to large leakage currents through GaN and AlGaN Schottky interfaces.
Microwave generation by a direct current spin-polarized current in nanoscale square magnets
Authors: Xi Haiwen , Gao Kai-Zhong , Shi Yiming
Published: June 2004

Theoretical calculation for a simple nanoscale magnetoelectronic device to function as a microwave generator based on the spin-transfer torque effect is presented. The device is unique because the output amplitude and frequency can be continuously tuned by the electrical current in the microwave frequency range. Analysis and discussion of the device structure, function, and realization are provided.
Cascaded light-emitting devices based on a ruthenium complex
Authors: Bernards Daniel A. , Slinker Jason D. , Malliaras George G. , Flores-Torres Samuel , Abruña Héctor D.
Published: June 2004

We use a transition metal complex to demonstrate a cascaded device architecture in which the same metal electrode acts as an anode for one device and a cathode for its neighbor. This architecture does not require patterning of the organic layer and allows monolithic fabrication of panels that show intrinsic fault tolerance to short circuits and are amenable to scaling to large areas.
Vacancy defects in O-doped GaN grown by molecular-beam epitaxy: The role of growth polarity and stoichiometry
Authors: Rummukainen M. , Oila J. , Laakso A. , Saarinen K. , Ptak A. J. , Myers T. H.
Published: June 2004

Positron annihilation spectroscopy is used to study vacancy defects in GaN grown by molecular-beam epitaxy due to different polar directions and varying stoichiometry conditions during oxygen doping. We show that Ga-polar material is free of compensating Ga vacancies up to [O]=1018 cm−3 in Ga stable growth, but high concentrations of VGa are formed in N-stable conditions. We also show that vacancy clusters are formed in N-polar material grown in Ga stable conditions, which may be related to the higher reactivity of the N-polar surface. These clusters have no apparent influence on the electrical properties of the material. We thus infer that their charge state is neutral.
Imaging Joule heating in a conjugated-polymer light-emitting diode using a scanning thermal microscope
Authors: Boroumand F. A. , Voigt M. , Lidzey D. G. , Hammiche A. , Hill G.
Published: June 2004

We have used a scanning thermal microscope to image Joule heating in a conjugated-polymer light-emitting diode (LED). Our LEDs had an active diameter of 100 μm, which was defined using an insulating layer of silicon nitride patterned onto the LED anode. At an average power input of 0.2 mW into the LED, we find that the center of the cathode is some 0.2 K warmer than its periphery. The observed temperature distribution across the pixel is slightly asymmetric, an effect which may be correlated with spatial inhomogeneity in the local current density across the device. We present a finite element analysis thermal model which is able to accurately describe the observed temperature distribution across the LED cathode.
Light amplification by dye-doped holographic polymer dispersed liquid crystals
Authors: Lucchetta D. E. , Criante L. , Francescangeli O. , Simoni F.
Published: June 2004

In this letter we report a “one-step” fabrication technique of an optical active organic photonic band gap (PBG) structure allowing the onset of the amplification spontaneous emission effect and narrowing of the corresponding band. This result has been achieved through the addition of the dye rhodamine 6G to a standard holographic polymer dispersed liquid crystal pre-polymer mixture. The effects of the dye addition on the optical properties of the polymerized PBG structure have been analyzed. The spectra emitted by this optically active periodic structure have been studied as a function of the excitation energy.
Tomographic measurement of femtosecond-laser induced stress changes in optical fibers
Authors: Dürr F. , Limberger H. G. , Salathé R. P. , Hindle F. , Douay M. , Fertein E. , Przygodzki C.
Published: June 2004

The tomographic measurement of the residual stress profile in femtosecond-laser irradiated standard SMF-28 germanium-doped telecommunication fiber is demonstrated. The fiber is irradiated with weakly focused pulses to realize long-period fiber gratings. In the irradiated grating regions, an asymmetrical increase in axial core stress up to 6.2 kg/mm2 is found. The increase in stress is attributed to a densification of the irradiated glass matrix. The stress-induced anisotropic index distribution is calculated and related to the absolute index change in the irradiated regions.
Atom motion of Cu and Co in Cu damascene lines with a CoWP cap
Authors: Hu C.-K. , Gignac L. M. , Rosenberg R. , Herbst B. , Smith S. , Rubino J. , Canaperi D. , Chen S. T. , Seo S. C. , Restaino D.
Published: June 2004

Electromigration of Cu and diffusion of Co in Cu damascene bamboo-like grain structure lines capped with CoWP have been studied for sample temperatures between 350 and 425 °C. Void growth from the Cu line/W via interface was observed. Bulk-like activation energy for electromigration of 2.4±0.2 eV was obtained for these samples suggesting that electromigration damage is greatly diminished for these on-chip Cu interconnections. The solubility and diffusivity of Co in Cu was determined from line resistance measurements of thermally annealed Cu lines which were affected by Co diffusion into the Cu line.
Coarsening of monodisperse wet microfoams
Authors: Gañán-Calvo A. M. , Fernández J. M. , Marquez Oliver A. , Marquez M.
Published: June 2004

We report experiments on the aging of monodisperse wet microfoams. We use the flow focusing technique to produce perfectly monodisperse microbubbles from 50 to 80 μm in diameter. This results in a foam of spherical bubbles of the same size ordered in random ordered lattices like “crystal grains” above the foam/liquid interface. We observe two different behaviors while the foam drains without any interference. At early times, the foam bubble size is almost constant from 10 to 20 min depending on the initial diameter of the bubbles. For longer times, the foam reaches a scaling state where the bubbles mean diameter growth agrees with the theoretical prediction t1/3.
Analysis of optical emission from high-aluminum AlGaN quantum-well structures
Authors: Wieczorek S. , Chow W. W. , Lee S. R. , Fischer A. J. , Allerman A. A. , Crawford M. H.
Published: June 2004

The letter presents theoretical analysis of spontaneous emission in AlGaN wurtzite quantum wells. It is found that the combined effects of strain, internal electric field, and many-body Coulomb interactions lead to a significant dependence of optical properties on quantum-well configuration. In particular, the effects of the internal electric field are mitigated for certain Al concentration in the quantum well. Calculations of the emitted photon energy show good agreement with experimental measurements. Presented results are of interest for applications such as ultraviolet light-emitting diodes and lasers.
X-ray studies of the growth of smooth Ag films on Ge(111)-c(2×8)
Authors: Basile L. , Hong Hawoong , Czoschke P. , Chiang T.-C.
Published: June 2004

We have performed in situ reflectivity measurements using synchrotron radiation of Ag films deposited on Ge(111) over the thickness range of 3–12 atomic layers. The films deposited at a substrate temperature of 110 K are not well ordered, but become well ordered upon annealing, as evidenced by substantial changes in the x-ray reflectivity data. The thickness distribution for each annealed film, deduced from a fit to the reflectivity data, is remarkably narrow, with just two or three adjacent discrete thicknesses present, despite the large lattice mismatch between Ag and Ge. In some cases, the film thickness is nearly atomically uniform. The results are discussed in connection with recent models and theories of electronic effects on the growth of ultrathin metal films.
Short-range structure of Zr41Ti14Cu12.5Ni10Be22.5 glass prepared by shock wave
Authors: Yang L. , Chao Y. , Saksl K. , Franz H. , Sun L. L. , Wang W. K. , Jiang N. P. , Wu X. J. , Jiang J. Z.
Published: June 2004

Short-range structure of a Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass prepared by shock-wave treatment was investigated by x-ray diffraction using synchrotron radiation with a wavelength of 0.112 71 Å. The radial distribution function was obtained from S(Q) with a large Q value up to 20 Å−1. The oscillation in S(Q) of the glass definitely persists up to Q∼14 Å−1. The shoulder on the high Q side of the second peak is observed in the bulk glass. It is found that the glass has higher coordination numbers in the range of r∼2.4–5.6 Å and lower numbers in the range of r∼5.6–9.5 Å than those for a water-quenched glass while the shell distances are similar in both glasses prepared by shock-wave and water-quenching methods. In the shock-waved glass, atomic configurations in the first, fourth, or fifth coordination shells are modified, i.e., atoms are packed denser in the first two coordination shells and less (or more free volume) in the third and fourth coordination shells as compared to those for the water-quenched glass. This atomic configuration for shock-waved glass might have different physical properties.
Position noise in scanning superconducting quantum interference device microscopy
Authors: Lee Su-Young , Matthews J. , Wellstood F. C.
Published: June 2004

Experimentally obtained magnetic field images contain not only magnetic field noise, but also uncertainty in the position at which the data points are recorded. Such position noise degrades the images where the magnetic field gradients are strongest. Our high-Tc scanning superconducting quantum interference device (SQUID) microscope was found to be limited by a position noise of about 0.145 μm. For a straight wire carrying 500 μA with a rms magnetic noise of 0.185 nT, and source–sample separation 150 μm, we find that the rms position noise must be less than 62 nm for it to have less impact on the image quality than intrinsic magnetic SQUID noise.
High Curie temperatures in ferromagnetic Cr-doped AlN thin films
Authors: Kumar D. , Antifakos J. , Blamire M. G. , Barber Z. H.
Published: June 2004

Al 1−x Cr x N thin films with 0.02⩽x⩽0.1 were deposited by reactive co-sputtering onto c-plane (001) sapphire. Room-temperature ferromagnetism with a coercive field of 85 Oe was observed in samples with chromium contents as low as x=0.027 (2.7%). With increasing Cr content the mean magnetic moment is strongly suppressed, with a maximum saturation moment of 0.62 and 0.71 μB per Cr atom at 300 and 50 K, respectively. We show that the Curie temperature of Al1−xCrxN for x=0.027 is greater than 900 K.
Positive colossal magnetoresistance in a multilayer p–n heterostructure of Sr-doped LaMnO3 and Nb-doped SrTiO3
Authors: Lu H. B. , Yang G. Z. , Chen Z. H. , Dai S. Y. , Zhou Y. L. , Jin K. J. , Cheng B. L. , He M. , Liu L. F. , Guo H. Z. , Fei Y. Y. , Xiang W. F. , Yan L.
Published: June 2004

A positive colossal magnetoresistance (CMR) has been discovered in an epitaxial multilayer p–n heterostructure fabricated with Sr-doped LaMnO3 and Nb-doped SrTiO3 by laser molecular-beam epitaxy. In contrast to the negative CMR of the LaMnO3 compound family, positive CMR is observed in the temperature range from 100 to 300 K. The largest value of the magnetoresistance (MR) ratio (ΔR/R0,ΔR=RH−R0), 517%, is one order of magnitude larger than that of simple p–n junctions of the same materials previously reported. A very large MR ratio, 297%, remains in a low field of 0.01 T. Even at a temperature as high as 300 K, a MR ratio as large as 17.3% is still observed.
High power polymer dye laser with improved stability
Authors: Kytina I. G. , Kytin V. G. , Lips K.
Published: June 2004

A polymer dye laser was developed suitable for high-power and high-repetition-rate pump lasers. A maximum output power of the dye laser of 1.5 W was achieved. The output power of the polymer gain medium is demonstrated to be absolutely stable for 4 h within 3% accuracy in a cyclic operation mode with a duty cycle of 83%. The enhanced stability of the gain medium stems from a partial recovery of photodegradation due to the dissociation of intermediate chemically active products which are detected with electron spin resonance and are shown to be produced much faster at elevated temperature.
Overheating threshold and its effect on time–temperature-transformation diagrams of zirconium based bulk metallic glasses
Authors: Mukherjee S. , Zhou Z. , Schroers J. , Johnson W. L. , Rhim W. K.
Published: June 2004

A pronounced effect of overheating is observed on the crystallization behavior for the three zirconium-based bulk metallic glasses: Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr57Cu15.4Ni12.6Al10Nb5, and Zr52.5Cu17.9Ni14.6Al10Ti5. A threshold overheating temperature is found for each of the three alloys, above which there is a drastic increase in the undercooling level and the crystallization times. Time–temperature-transformation (TTT) diagrams were measured for the three alloys by overheating above their respective threshold temperatures. The TTT curves for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5 are very similar in shape and scale with their respective glass transition temperatures, suggesting that system-specific properties do not play a crucial role in defining crystallization kinetics in these alloys. The critical cooling rates to vitrify the alloys as determined from the TTT curves are about 2 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and 10 K/s for Zr57Cu15.4Ni12.6Al10Nb5. The measurements were conducted in a high-vacuum electrostatic levitator.
Phase-matched third-harmonic generation from nematic liquid crystals
Authors: Kosugi Jun-ichi , Kajikawa Kotaro
Published: June 2004

The type-II phase-matching condition of the direct third-harmonic generation originated from third-order nonlinearity (3ω=ω+ω+ω) is performed in nematic liquid crystals with a fundamental light at 1064 nm. Since the phase-matching condition can be achieved in normal incidence of the fundamental light, the walk-off angle is zero. Thus, the interaction length is equal to the thickness of the liquid crystal film. Although the conversion efficiency in the present system is still low, 9.1×10−8, it will become 10−2 as discussed in this letter.
All-pass transmission or flattop reflection filters using a single photonic crystal slab
Authors: Suh Wonjoo , Fan Shanhui
Published: June 2004

We show that a single photonic crystal slab can function either as optical all-pass transmission or flattop reflection filter for normally incident light. Both filter functions are synthesized by designing the spectral properties of guided resonance in the slab. The structure is extremely compact along the vertical direction. We expect this device to be useful for optical communication systems.
Organic nonvolatile memory by controlling the dynamic copper-ion concentration within organic layer
Authors: Ma Liping , Xu Qianfei , Yang Yang
Published: June 2004

Copper (Cu) migration into semiconductor materials like silicon is a well-known and troublesome phenomenon often causing adverse effect on devices. Generally a diffusion barrier layer is added to prevent Cu metallization. We demonstrate an organic nonvolatile memory device by controlling the Cu-ion (Cu+) concentration within the organic layer. When the Cu+ concentration is high enough, the device exhibits a high conductive state due to the metallization effect. When the Cu+ concentration is low, the device displays a low conductance state. These two states differ in their electrical conductivity by more than seven orders of magnitude and can be precisely switched by controlling the Cu+ concentration through the application of external biases. The retention time of both states can be more than several months, and the device is promising for flash memory application. Discussions about the device operation mechanism are provided.
Electroluminescent ceramics excited by low electrical field
Authors: Liu Yun , Xu Chao-Nan
Published: June 2004

Strong green-light emission occurs in Eu:SrAl2O4 ceramics and Eu:SrAl2O4/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) composites when excited by a lower dc or ac voltage. That emission is caused by strong electric-mechanic-optic interaction. The composite shows stronger luminescent emission intensity in comparison to similar ceramics because of an enhanced piezoelectric effect from P(VDF-TrFE)—a typical piezoelectric polymer.
Nitrogen bonding, stability, and transport in AlON films on Si
Authors: Soares G. V. , Bastos K. P. , Pezzi R. P. , Miotti L. , Driemeier C. , Baumvol I. J. R. , Hinkle C. , Lucovsky G.
Published: June 2004

The chemical environment of N in nitrided aluminum oxide films on Si(001) was investigated by angle-resolved x-ray photoelectron spectroscopy. Two different bonding configurations were identified, namely N–Al and N–O–Al, suggesting the formation of the AlN and AlO2N compounds. The near-surface region is N-rich and AlN compounds therein are more abundant than AlO2N, whereas in bulk regions the proportions of these two compounds are comparable. Rapid thermal annealing at 1000 °C for 10 s in vacuum or in low-pressure oxygen atmosphere led to the breakage of N–Al bonds in AlN, releasing N and Al. The mobile N is partly lost by desorption from the surface and partly fixed by reacting with the network to form AlO2N. The released Al atoms, which remain immobile, react with oxygen from the film or from the gas phase. Characterization of the films outermost surfaces by low-energy ion scattering revealed that the migration of Si atoms from the substrate across the films, reaching the surface and being oxidized therein, is not entirely inhibited in AlON/Si, although this migration is largely reduced as compared to nonnitrided Al2O3 films.