bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of 0.5 wt % Cu addition in Sn–3.5%Ag solder on the dissolution rate of Cu metallization
Authors: Alam M. O. , Chan Y. C. , Tu K. N.
Published: December 2003

The dissolution of thin film under-bump-metallization (UBM) by molten solder has been one of the most serious processing problems in electronic packaging technology. Due to a higher melting temperature and a greater Sn content, a molten lead-free solder such as eutectic SnAg has a faster dissolution rate of thin film UBM than the eutectic SnPb. The work presented in this paper focuses on the role of 0.5 wt % Cu in the base Sn–3.5%Ag solder to reduce the dissolution of the Cu bond pad in ball grid array applications. We found that after 0.5 wt % Cu addition, the rate of dissolution of Cu in the molten Sn–3.5%Ag solder slows down dramatically. Systematic experimental work was carried out to understand the dissolution behavior of Cu by the molten Sn–3.5%Ag and Sn–3.5%Ag–0.5%Cu solders at 230–250 °C, for different time periods ranging from 1 to 10 min. From the curves of consumed Cu thickness, it was concluded that 0.5 wt % Cu addition actually reduces the concentration gradient at the Cu metallization/molten solder interface which reduces the driving force of dissolution. During the dissolution, excess Cu was found to precipitate out due to heterogeneous nucleation and growth of Cu6Sn5 at the solder melt/oxide interface. In turn, more Cu can be dissolved again. This process continues with time and leads to more dissolution of Cu from the bond pad than the amount expected from the solubility limit, but it occurs at a slower rate for the molten Sn–3.5%Ag–0.5%Cu solder.
Mechanism of electromigration-induced failure in the 97Pb–3Sn and 37Pb–63Sn composite solder joints
Authors: Nah J. W. , Paik K. W. , Suh J. O. , Tu K. N.
Published: December 2003

The electromigration-induced failure in the composite solder joints consisting of 97Pb–3Sn on the chip side and 37Pb–63Sn on the substrate side was studied. The under-bump metallization (UBM) on the chip side was 5 μm thick electroplated Cu coated on sputtered TiW/Cu and on the substrate side was electroless Ni/Au. It was observed that failure occurred in joints in a downward electron flow (from chip to substrate), while those joints having the opposite current polarity showed only minor changes. During electromigration, in addition to the compositional change by the moving of Pb atoms in the same direction as the electrons, current crowding was observed inside the UBM and it enhanced the phase transformation of Cu to Cu3Sn and to Cu6Sn5 at the UBM/solder interface. Due to the growth of Cu6Sn5, the Cu UBM was consumed rapidly, resulting in void formation-induced failure at the cathode side. The Cu6Sn5 intermetallic compound and void were first initiated from the upper left-hand side corner of the contact window which matches the current crowding region. The sequence of Cu UBM consumption and void formation is presented. The current crowding has been confirmed by simulation. The mechanism of electromigration-induced failure in the composite solder joint structure is discussed.
Photoluminescence excitonic linewidth in GaAsN alloys
Authors: Senger R. T. , Bajaj K. K.
Published: December 2003

We have calculated the variation of the photoluminescence excitonic linewidth, defined as the full width at half maximum, due to composition fluctuations as a function of nitrogen composition in completely random GaAs1−xNx alloys. We have considered the effects of a constant and of the composition dependent bowing parameter (and, thus, the energy band gap) on the excitonic linewidth. We have used two different recently proposed variations of the conduction electron mass with nitrogen composition. We have considered both the free and localized excitons. We find that the behavior of excitonic linewidth as a function of nitrogen composition, using two different bowing parameters, is qualitatively and quantitatively quite different.
SiGe relaxation on silicon-on-insulator substrates: An experimental and modeling study
Authors: Rehder E. M. , Inoki C. K. , Kuan T. S. , Kuech T. F.
Published: December 2003

The strain relaxation behavior of Si0.82Ge0.18 films on silicon-on-insulator (SOI) substrates was investigated for films grown beyond the critical thickness and strain-relaxed during growth and metastable films, grown beyond the critical thickness, which relaxed during subsequent thermal annealing. The thickness of the top silicon layer of the SOI substrate was varied over a range from 40 nm to 10 μm. In all cases, the SiGe film relaxation occurred via the nucleation and propagation of dislocations with the same onset of film relaxation and same relaxation rate for both SOI and bulk Si substrates. The SOI substrate does not serve as a compliant substrate but does alter the dislocation structure and motion. The buried amorphous oxide layer in the SOI substrate leads to the relaxation of the dislocation strain field through the removal of the dislocation line tension. This removal of the dislocation line tension drives dislocation motion and leads to the development of strain in the thin Si layer of the SOI substrate. Models of this dislocation behavior for SiGe growth on the SOI substrate are presented and calculation of the equilibrium strain of the thin Si substrate layer closely fits the measured strain of several SOI substrates. The article addresses the implications of the modified dislocation structure and kinetics for film relaxation on SOI substrates.
Structure and properties of artificial [(La0.7Sr0.3MnO3)m(SrTiO3)n]15 superlattices on (001)SrTiO3.
Authors: Lebedev O. I. , Verbeeck J. , Van Tendeloo G. , Dubourdieu C. , Rosina M. , Chaudouët P.
Published: December 2003

Complex [(La0.7Sr0.3MnO3)m(SrTiO3)n] [(LSMO)m/(STO)8]15 superlattices with different layer thicknesses (m=5, 8, 12, 16, 32) have been prepared using pulsed liquid injection metalorganic chemical vapor deposition. Transmission electron microscopy and electron diffraction reveal a very clear and well-separated layer sequence. The remarkable microstructure, as well as the ferromagnetic transition temperature, depends on the LSMO layer thickness. Apart from a very clear layer sequence, electron microscopy shows evidence of a self-assembled nanostructure formation: SrMnO3 nanoinclusions and associated SrTiO3–SrMnO3 thin walls. A formation model and growth mechanism for the self-assembled structure is proposed, based on high resolution and energy filtered elemental imaging.
Superparamagnetic behavior of ultrathin Fe films grown on Al2O3(0001) substrates
Authors: Shiratsuchi Yu , Yamamoto Masahiko , Endo Yasushi , Li Dongqi , Bader S. D.
Published: December 2003

We have studied superparamagnetic behavior of ultrathin Fe films grown on an Al2O3(0001) substrate at various growth temperatures. It is demonstrated that 1-nm-thick Fe films are in the superparamagnetic state, and the blocking temperature is strongly dependent on the growth temperature. The blocking temperature has a minimum value of 30 K for a growth temperature of 473 K, while it is ∼70 K at other growth temperatures. In order to clarify the behavior, we consider the Fe growth mechanism and the magnetic interactions between Fe particles. Fe grows as three-dimensional islands at all temperatures studied and forms particles. The volume of the particles is observed via atomic force microscopy to increase with increasing growth temperature. In the case of growth at 323 and 373 K, Fe forms small particles that are close together and that interact with each other. For growth at 673 and 773 K, Fe forms relatively large particles and the magnetic properties are dominated by the individual particles.
Near-infrared spectroscopic study of water at high temperatures and pressures
Authors: Jin Yusuke , Ikawa Shun-ichi
Published: December 2003

Near-infrared absorption of the OH stretching overtone transition of water has been measured at temperatures and pressures in the ranges of 373–673 K and 20–400 bar, respectively. The absorption profile at 673 K and 400 bar retains a mark of rotational structure, indicating that an appreciable proportion of water molecules can rotate quite freely. The molar absorption intensity decreases linearly with increasing pressure in the low-pressure region. Enthalpy for dimerization has been estimated to be 15±3 kJ/mol from the temperature dependence of the slopes. Plots of the molar absorption intensity against molar concentration are observed to be located on a single curve irrespective of the temperature. This fact indicates that the ratio of hydrogen-bond formation is largely dependent on the molar density only. A good correlation between the molar absorption intensity and the first moments of the band has been found out; this will be useful in the study of aqueous mixtures.
Characterization of thermally annealed tunnel junctions with preoxidized CoFe pinned electrode
Authors: Lee J. H. , Im D. H. , Yoon C. S. , Kim C. K. , Ando Y. , Kubota H. , Miyazaki T.
Published: December 2003

Postannealed structure and electron transport properties of the magnetic tunnel junctions with preoxidized CoFe pinned electrode were compared with those of the conventional plasma oxidized junctions. The preoxidized junction exhibited its peak tunneling magnetoresistance ratio at 375 °C which is well above the optimal annealing of the normal junction. Using Auger electron spectroscopy and x-ray photoelectron spectroscopy of the thermally annealed junctions, structural and chemical changes after annealing were observed in the tunnel barrier as well as near the interface for both types of the junctions and these changes closely corresponded to the respective postannealed electrical properties. X-ray magnetic circular dichroism analysis indicated that the Co moment in the preoxidized CoFe electrode rose near the tunnel barrier/electrode interface as the optimal annealing temperature was reached. Our results demonstrated that the magnitude of spin polarized tunneling current is very sensitive to the interface structure and that any changes near the barrier interface during thermal annealing can greatly alter the electrical properties of the magnetic tunnel junctions.
Production of gold nanoparticles by laser ablation in liquid alkanes
Authors: Compagnini G. , Scalisi A. A. , Puglisi O.
Published: December 2003

Pulsed laser ablation of Au target in n-alkanes generates Au sols. Experiments have been performed using the second harmonic of a Nd:yttritium–aluminum–garnet at 532 nm wavelength with a 5 ns pulse duration at a repetition rate of 10 Hz and fluences ranging from 1 to 200 J/cm2. Data coming from optical extinction show that the length of the hydrocarbon chain is able to tune the shape of the produced particles and the rate of formation in a controlled way. The data are supported by atomic force microscopy and transmission electron microscope observations.
Oxygen pressure and thickness dependent lattice strain in La0.7Sr0.3MnO3 films
Authors: Dho Joonghoe , Hur N. H. , Kim I. S. , Park Y. K.
Published: December 2003

We report magnetic and electronic properties of La0.7Sr0.3MnO3 (LSMO) thin films epitaxially grown on perovskite substrates by pulsed laser deposition, which are varied with oxygen background pressure and film thickness. The strains of the LSMO films are tuned by the two parameters but their resulting effects are somewhat different. The lattice strain induced by the oxygen pressure suppresses the ferromagnetic transition (TC) and metal–insulator transition (TMI) temperatures. With decreasing film thickness from 110 to 11 nm, however, small changes in both TC and TMI were observed. These results suggest that the physical properties of the LSMO films are strongly dependent on the oxygen content but less sensitive to the film thickness.
Morphology evolution and luminescence properties of porous GaN generated via Pt-assisted electroless etching of hydride vapor phase epitaxy GaN on sapphire
Authors: Dı́az Diego J. , Williamson Todd L. , Adesida Ilesanmi , Bohn Paul W. , Molnar Richard J.
Published: December 2003

Porous gallium nitride (PGaN) is produced by Pt-assisted electroless etching of hydride vapor phase epitaxy (HVPE)–GaN. Ultrathin Pt films are sputtered onto the GaN surface, and etching is carried out in a 1:2:1 solution of CH3OH:HF:H2O2. The evolution of the morphology proceeds by first forming a network of small pores, after which a ridge-trench morphology evolves, with ridges separated by a porous network in trenches between the ridges. As the etch progresses further the ridges evolve to a maximum size and then start to disappear. The formation and evolution of the ridge-trench morphology is explained by the presence of two different etch rates, an enhanced etch rate which generates the porous network and a slower etch rate that leads to the terraces of the ridge morphology. The rate at which the morphology evolves depends on the carrier concentration, with more heavily doped samples etching faster. In all cases, the final depth of the trenches between ridges is independent on the thickness of the starting GaN film. Cathodoluminescence (CL) spectroscopy of the unintentionally doped and the Si doped HVPE materials produce PGaN which shows only band gap emission at 368 nm before and after etching with only small shifts in the wavelength of maximum emission. The intensity of CL emission decreases with etch time as the GaN is consumed. CL spectroscopy and imaging show the ridges to be optically inactive, suggesting that the ridges might arise from grain boundaries or dislocations present in the starting GaN material.
Modeling and simulation of polycrystalline ZnO thin-film transistors
Authors: Hossain Faruque M. , Nishii J. , Takagi S. , Ohtomo A. , Fukumura T. , Fujioka H. , Ohno H. , Koinuma H. , Kawasaki M.
Published: December 2003

Thin-film transistors (TFTs) made of transparent channel semiconductors such as ZnO are of great technological importance because their insensitivity to visible light makes device structures simple. In fact, there have been several demonstrations of ZnO TFTs achieving reasonably good field effect mobilities of 1–10 cm2/V s, but the overall performance of ZnO TFTs has not been satisfactory, probably due to the presence of dense grain boundaries. We modeled grain boundaries in ZnO TFTs and performed simulation of a ZnO TFT by using a two-dimensional device simulator in order to determine the grain boundary effects on device performance. Polycrystalline ZnO TFT modeling was started by considering a single grain boundary in the middle of the TFT channel, formulated with a Gaussian defect distribution localized in the grain boundary. A double Schottky barrier was formed in the grain boundary, and its barrier height was analyzed as a function of defect density and gate bias. The simulation was extended to TFTs with many grain boundaries to quantitatively analyze the potential profiles that developed along the channel. One of the main differences between a polycrystalline ZnO TFT and a polycrystalline Si TFT is that the much smaller nanoscaled grains in a polycrystalline ZnO TFT induces a strong overlap of the double Schottky barriers with a higher activation energy in the crystallite and a lower barrier potential in the grain boundary at subthreshold or off-state region of its transfer characteristics. Through the simulation, we were able to estimate the density of total trap states localized in the grain boundaries for polycrystalline ZnO TFT by determining the apparent mobility and grain size in the device.
Dynamic turn-on behavior of organic light-emitting devices with different work function cathode metals under fast pulse excitation
Authors: Ichikawa Musubu , Amagai Junko , Horiba Yasuhiro , Koyama Toshiki , Taniguchi Yoshio
Published: December 2003

We investigate the electroluminescence (EL) response of organic light-emitting diodes (OLEDs) with different metal cathodes and device-area dependence. Moreover, we formulate the EL delay time, which is an indicator of the EL response. The EL response is fundamentally governed by the device area, i.e., the capacitance of the device, and this for the OLEDs with low work function metals as a cathode is fast. According to the formulation, we estimate electron mobility in an organic bilayer and the threshold electric fields for electron injection under fast-pulse excitation. It is consequently demonstrated that electron mobility in the bilayer showed mixed mobility characteristics for each layer, and the threshold electric field became smaller with a decrease in the work function of cathode metals. The low work function metal cathode device is identified as a high-speed EL response device.
Spin-current-assisted domain-wall depinning in a submicron magnetic wire
Authors: Kimura T. , Otani Y. , Tsukagoshi K. , Aoyagi Y.
Published: December 2003

We demonstrate experimentally the domain-wall depinning triggered by injecting the polarized spin current into the domain wall. The domain wall is pinned at the junction of a large pad and a narrow wire prior to the current injection experiment. When the polarized spin current is injected along the direction of the domain-wall propagation, the pinned domain wall is freed and pushed into the wire at the critical current that monotonously decreases by increasing the applied bias magnetic field. These results imply that the injection of the spin-polarized current into the domain wall causes additional magnetic pressure due to the spin-momentum transfer between the spin-polarized current and the localized magnetic moment.
Electron transport properties in Nb and NbN cluster-assembled films produced by a plasma–gas–condensation cluster source
Authors: Hihara T. , Yamada Y. , Katoh M. , Peng D. L. , Sumiyama K.
Published: December 2003

Nb and NbN cluster-assembled films were produced by a plasma–gas–condensation cluster deposition apparatus and examined by transmission electron microscopy, electrical resistivity, and ultraviolet photoemission spectroscopy. The electron diffraction patterns of the Nb and NbN clusters displayed body-centered-cubic and NaCl-type diffraction rings, respectively. The electrical sheet resistance, R□, of both Nb and NbN cluster-assembled films, however, showed no superconductivity down to 2 K. We found a linear relation in the log R□ versus T−1/4 plot for the Nb cluster assembly, suggesting an electron localization effect. For the NbN cluster-assembly, on the other hand, R□ showed a semiconductor type temperature dependence, which is consistent with the valence electron spectra.
Electrical properties of a highly oriented, textured thin film of the ionic conductor Gd:CeO2−δ on (001) MgO
Authors: Chen L. , Chen C. L. , Chen X. , Donner W. , Liu S. W. , Lin Y. , Huang D. X. , Jacobson A. J.
Published: December 2003

Highly oriented ionic conductor gadolinium-doped CeO2−δ (Ce0.8Gd0.2O2−δ) thin films have been grown on single-crystal (001) MgO substrates by pulsed-laser ablation. The films are highly c-axis oriented with cube-on-cube epitaxy, as shown by x-ray diffraction and electron microscopy. The interface relationship is, surprisingly, found to be (001)film//(001)sub and [100]film//[100]sub with an extremely large lattice misfit of more than 28%. Ac impedance measurements in the temperature range of 500 to 800 °C reveal that electrical conductivity is predominantly ionic over a very broad oxygen partial pressure range from pO2 from 1×10−19 atm to 1 atm. The activation energy Ea for ionic conductivity measured on unannealed films is 0.86 eV, but after heat treatment, Ea decreases to 0.74 eV.
Characterization of porous materials with a rigid frame via reflected waves
Authors: Fellah Z. E. A. , Mitri F. G. , Depollier C. , Berger S. , Lauriks W. , Chapelon J. Y.
Published: December 2003

The inverse problem for waves reflected by porous material is solved at oblique incidence, and an inverse scattering calculation of porosity and tortuosity is given for air-saturated plastic foam samples. The interaction of the sound pulse with the fluid-saturated porous material is described by a time-domain equivalent fluid model. The sensitivity of the porosity and tortuosity is studied and it shows their effect on the reflection coefficient at the first interface. This study shows that porosity is much more sensitive than tortuosity to reflection, especially when the incident angle is less than its critical value, at which the reflection coefficient vanishes. Some advantages and perspectives of this method are discussed.
Photovariation of grating-assisted coupling of terahertz waves into a silicon waveguide
Authors: Aquistapace F. , Duvillaret L. , Garet F. , Roux J.-F. , Coutaz J.-L.
Published: December 2003

Using terahertz (THz) time-domain spectroscopy, we study the coupling of THz waves into a silicon waveguide by means of a grating coupler. We vary the efficiency of the coupling coefficient for selected frequencies up to 20% in amplitude (40% in intensity) by generating photocarriers in the silicon material through illumination of the waveguide with white light. The experimental data are well fitted using the differential method to model the grating diffraction.
Control of ferromagnetic coupling by in situ interface modification
Authors: Nickel Janice H. , Tran Lung , Portier Xavier , Petford-Long Amanda K.
Published: December 2003

Ferromagnetic coupling is a major factor in the engineering of magnetic multilayer devices. This article describes a method for controlling the interface roughness, which contributes to ferromagnetic coupling. Specifically, we report a process whereby the amplitude of the roughness profile can be systematically modified. Although the data presented is for pinned layer systems of NiFe on MnFe, this process is equally effective in other materials systems, such as CoFe and NiFeCo on IrMn. A reduction of the ferromagnetic coupling is evidenced by a decrease in the offset of the magnetic hysteresis loops from zero field, a reduction of roughness of the films, and an improvement in resistance uniformity.
Step-wise Fréedericksz transition in a nematic liquid crystal
Authors: Shioda Tatsutoshi , Wen Bing , Rosenblatt Charles
Published: December 2003

The stylus of an atomic force microscope is used to rub a polyimide-coated substrate with a spatial period of 10 μm. A spatial periodicity is thereby introduced into the anchoring strength coefficient, resulting in a shoulder in the intensity–voltage curve above the Fréedericksz transition threshold of a nematic liquid crystal.
Thermoelectric properties of LaNi1−xCoxO3 solid solution
Authors: Migiakis P. , Androulakis J. , Giapintzakis J.
Published: December 2003

We present the results of a systematic investigation of the thermal conductivity, Seebeck coefficient and electrical resistivity for selected members (x=0.3, 0.7, 0.8, and 1) of the LaNi1−xCoxO3 solid solution in the temperature range of 80⩽T⩽320 K. Substitution of Ni by Co drives the system from n-type metallic phase with low thermopower values into p-type semiconducting phase with high thermopower values of the order of hundreds of μV/K. But the thermal conductivity observed varies only slightly with the composition, x, over the temperature range investigated. The latter effect also holds true for the lightly hole doped x=0.8 member (in substituting Sr for La). Our results suggest that semiconducting members of the LaNi1−xCoxO3 solid solution can be classified as “phonon glass and electron crystal” systems. The highest room temperature figure of merit was exhibited by the x=0.8 member (ZT=0.022), which is comparable to that of single crystal NaCo2O4 (ZT=0.03).
Combined field-induced dielectrophoresis and phase separation for manipulating particles in microfluidics
Authors: Bennett Dawn J. , Khusid Boris , James Conrad D. , Galambos Paul C. , Okandan Murat , Jacqmin David , Acrivos Andreas
Published: December 2003

Experiments were conducted in microfluidics equipped with dielectrophoretic gates arranged perpendicular to the flow. Under the action of a high-gradient ac field and shear, flowing suspensions were found to undergo a phase separation and to form a distinct front between the regions enriched with and depleted of particles. We demonstrate that this many-body phenomenon, which originates from interparticle electrical interactions, provides a method for concentrating particles in focused regions and for separating biological and nonbiological materials. The evolution of the particle patterns formation is well described by a proposed electrohydrodynamic model.
Low-temperature calorimetric evaluation of aluminum–lithium alloys
Authors: Wang C. R. , Neeleshwar S. , Chen Y. Y. , Ho J. C.
Published: December 2003

Low temperature calorimetric measurements have been made on a series of binary aluminum alloys containing 1–10 at. % lithium. The heat capacity data are analyzed in terms of an electronic and a lattice contribution. Accordingly, the low level of lithium addition yields appreciable changes in the electronic density-of-states at Fermi level and the characteristic Debye temperature of lattice. These results reflect certain degrees of electron localization between aluminum and lithium atoms, providing a fundamental basis for solid solution strengthening in the lightweight materials with great potential in aerospace applications.
Electron paramagnetic resonance of Cr2+ and Cr4+ ions in CdGeAs2 crystals
Authors: Garces N. Y. , Giles N. C. , Halliburton L. E. , Nagashio K. , Feigelson R. S. , Schunemann P. G.
Published: December 2003

Electron paramagnetic resonance (EPR) has been used to investigate chromium ions in single crystals of CdGeAs2 grown by the horizontal gradient freeze technique. Signals from Cr2+ and Cr4+ ions were observed near 12 K. The Cr2+ ions have the 3d4 configuration with S=2 and substitute at the cadmium sites, while the Cr4+ ions have the 3d2 configuration with S=1 and substitute at the germanium sites. As a result, each impurity represents a neutral center. Both EPR spectra display the tetragonal symmetry of the lattice, which suggests that the centers most likely are not perturbed by nearby defects. The ratio of Cr2+ ions to Cr4+ ions in a particular CdGeAs2 crystal depends on the growth conditions and stoichiometry.
Charge transfer between thermally deposited α-naphthyl-phenyl-diamine and chemical-vapor-deposited homoepitaxial diamond films
Authors: Chun M. , Teraji T. , Ito T.
Published: December 2003

Substantial charge transfers between overlayered N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′biphenyl-4,4″diamine (α-NPD) films and three different chemical-vapor-deposited (CVD) homoepitaxial diamond substrates have been evidenced mainly from Hall effect measurements in the temperature range from 100 to 300 K. It is found that substantial reductions in the hole concentrations were observed after the α-NPD depositions while the conductivities increased at sufficiently high temperatures of ⩾230 K, compared with those prior to the α-NPD depositions. These indicate substantial amounts of hole transfers from the CVD diamond substrates to the deposited α-NPD films as well as a substantial contribution of the α-NPD overlayer to the electrical conductivity at the high temperatures. Both two- and three-carrier models are employed to discuss possibilities of the CVD diamond both as a hole transfer layer and as a transparent electrode.
Nitrogen-activated bowing of dilute InyGa1−yAs1−xNx based on photoreflectance studies
Authors: Fahmi M. M. E. , Khan Arif , Griffin J. A. , Harris G. L. , Robins Lawrence H. , Birdwell A. G. , Kang Youn-Seon , Smith David J. , Steiner Todd , Mohammad S. Noor
Published: December 2003

The dependence of the fundamental band gap and higher-lying critical-point energies of dilute-nitrogen Ga1−yInyAs1−xNx epilayers on nitrogen mole fraction (x), for x⩽0.0125, and temperature, from 20 to 300 K, was investigated by photoreflectance spectroscopy. The band gap, EG, was found to decrease with increasing x in a highly nonlinear manner. The bowing parameter (the second-order parameter b in a quadratic expression for the dependence of EG on x) was found to become less negative with increasing x; the value of b changed from −50 eV, at very low nitrogen fraction, to −20 eV, at x>0.01. These results strongly suggest that nitrogen-related impurity levels arise within the band gap of dilute-nitrogen Ga1−yInyAs1−xNx alloys.
Effect of low-temperature annealing on the luminescent lifetime and negative differential resistance of silicon-implanted borosilicate glass
Authors: Lin Gong-Ru
Published: December 2003

The silicon-implanted borosilicate glass (BSO:Si+) low-temperature (500 °C) annealed at a different time are structurally, electrically, and optically characterized. The weak and broadened x-ray diffraction reveal insignificant Si nano-crystallization even after long-term annealing, whereas the redshifted photoluminescence (PL) interprets the change in category and the decrease in density of irradiative defects in BSO:Si+. Time-resolved PL analysis reveals a lengthening luminescent lifetime of BSO:Si+ from 1.7 to 2.8 ns, which indicates that the density ratio of nonradiative defects in as-implanted BSO:Si+ are reduced by one-tenth after annealing for 60 min. Transmission line mode analysis shows that both the leakage current and the contact resistance of a metal–BSO:Si+–metal diode has dramatically changed by three orders of magnitude. A strong negative differential resistance (NDR) and associated double-barrier electron tunneling phenomenon are observed with a threshold electric field of 290–350 kV/cm. The decreasing barrier height of the metal–BSO:Si+ junction from 3.0 to 1.9 eV is mainly contributed by deep-level defects with activation energy of ∼1 eV. After annealing, the NDR effect significantly diminishes, the barrier height raises to >2.4 eV, and most electrical characteristics of the metal–BSO:Si+ junction have recovered back to be comparable with those of the metal–BSO junction due to the elimination of these defects.
Coherent acoustic phonons in hexagonal manganite LuMnO3
Authors: Lim D. , Averitt R. D. , Demsar J. , Taylor A. J. , Hur N. , Cheong S. W.
Published: December 2003

We have observed coherent acoustic phonons in the hexagonal manganite LuMnO3 using two-color femtosecond optical pump-probe spectroscopy. The dependence of the oscillatory component of the photoinduced reflectivity on the probe wavelength and incident angle is consistent with a propagating strain pulse. Moreover, the frequency, dephasing, and phase of the oscillation are found to be temperature dependent. In particular, a large phase shift occurs in the vicinity of the Néel temperature (TN), which we relate to the temperature-dependent on-site Mn d–d transition that is coupled to antiferromagnetic ordering, as recently observed in optical conductivity measurements.
Hybrid electro-optic polymer/sol–gel waveguide modulator fabricated by all-wet etching process
Authors: Enami Y. , Meredith G. , Peyghambarian N. , Jen A. K.-Y.
Published: December 2003

A simple all-wet-etch process fabricates a hybrid electro-optic-polymer (EOP)/sol–gel waveguide modulator, confining the EOP laterally in the sol–gel overcladding. The structure enables an adiabatic transition between the passive sol–gel waveguides and the active EOP overlayers without lateral radiation. Intensity is confined well in a 0.9-μm-thick EOP overlayer, resulting in a low half-wave voltage (Vπ) due to the larger overlap integral. This lateral confinement technique allowed the reduction of Vπ (at 1550 nm) by a factor of 4.
Effect of external strain on the conductivity of AlGaN/GaN high-electron-mobility transistors
Authors: Kang B. S. , Kim S. , Kim J. , Ren F. , Baik K. , Pearton S. J. , Gila B. P. , Abernathy C. R. , Pan C.-C. , Chen G.-T. , Chyi J.-I. , Chandrasekaran V. , Sheplak M. , Nishida T. , Chu S. N. G.
Published: December 2003

The changes in the conductance of the channel of Al0.3Ga0.7N/GaN high-electron-mobility transistor structures during the application of both tensile and compressive strain were measured. For a fixed Al mole fraction, the changes in the conductance were roughly linear over the range up to 2.7×108 N cm−2, with coefficients for planar devices of −6.0+/−2.5×10−10 S N−1 m−2 for tensile strain and +9.5+/−3.5×10−10 S N−1 m−2 for compressive strain. For mesa-isolated structures, the coefficients were smaller due to the reduced effect of the AlGaN strain, with values of 5.5+/−1.1×10−13 S N−1 m−2 for tensile strain and 4.8×10−13 S N−1 m−2 for compressive strain. The large changes in the conductance demonstrate that simple AlGaN/GaN heterostructures are promising for pressure and strain sensor applications.
High-quality heterojunction between p-type diamond single-crystal film and n-type cubic boron nitride bulk single crystal
Authors: Wang Cheng-Xin , Yang Guo-Wei , Zhang Tie-Chen , Liu Hong-Wu , Han Yong-Hao , Luo Ji-Feng , Gao Chun-Xiao , Zou Guang-Tian
Published: December 2003

We presented the results on the fabrication and characterization of high-quality heterojunction between p-type diamond single-crystalline film and n-type cubic boron nitride (c-BN) bulk single crystal. By employing a simple surface diffusion, we prepared the n-type c-BN bulk single crystals with relatively low resistivity (1.0×10−1 Ω cm). Combining p-type diamond films grown by chemical vapor deposition with n-type c-BN, we fabricated a high-quality heterojunction bipolar p–n diode, which the turn-on voltage of the heterojunction was 0.85 V, and the current density reached to 170 A/m2 when the forward bias was applied to 3 V.
Structural changes on supercooling liquid silicon
Authors: Jakse Noël , Hennet Louis , Price David L. , Krishnan Shankar , Key Thomas , Artacho Emilio , Glorieux Benoit , Pasturel Alain , Saboungi Marie-Louise
Published: December 2003

X-ray diffraction experiments and ab initio molecular dynamics (AIMD) simulations have been performed to investigate the atomic structure of liquid silicon into the deeply supercooled region. The levitation technique used has made it possible to extend the measurements down to a temperature of 1458 K, 230 K below the equilibrium melting point. The x-ray and AIMD results, which are in reasonable agreement, show conclusively that the tetrahedral order is reinforced and that the coordination number decreases as the liquid is supercooled, with implications for the liquid–liquid phase transition.
Surface kinetics: Step-facet barriers
Authors: Huang Hanchen , Wang Jian
Published: December 2003

This letter presents a concept of surface kinetic barrier: The step–facet barrier. This concept is demonstrated for two face-centered-cubic metals, aluminum and copper, through molecular statics calculations. Our numerical results show that the step–facet barrier is substantially larger than step–step or diffusion barriers on flat surfaces; true for both metals. Based on the relative magnitudes of kinetic barriers, we discuss implications of the step–facet barrier on surface processing, particularly the step flow. This discussion shows that the kinetic barrier potentially may enable us to pattern nanowires on a metal surface.
Observations of near-zero linewidth enhancement factor in a quantum-well coupled quantum-dot laser
Authors: Kondratko Piotr Konrad , Chuang Shun-Lien , Walter Gabriel , Chung Theodore , Holonyak Nick
Published: December 2003

Amplified spontaneous emission (ASE) measurements of a quantum-well coupled quantum-dot (QW–QD) laser are investigated in our experimental study. Fabry–Perot ASE spectrum taken below threshold of this device allows the extraction of gain, index of refraction change, and linewidth enhancement factor. Our experimental study includes continuous wave and pulsed measurements. The QW–QD laser consists of an auxiliary QW which assists in carrier collection while tunneling of carriers takes place from the well to the dot region. Our experimental analysis reveals a low linewidth enhancement factor of 0.15 over a flat spectrum for these GaAs–InGaAs–InAs QW–QD lasers.
Ferroelectric inverse opals with electrically tunable photonic band gap
Authors: Li Bo , Zhou Ji , Li Longtu , Wang Xing Jun , Liu Xiao Han , Zi Jian
Published: December 2003

We present a scheme for tuning the photonic band gap (PBG) by an external electric field in a ferroelectric inverse opal structure. The inverse opals, consisting of ferroelectric (Pb,La)(Zr,Ti)O3 (PLZT) ceramics, were synthesized by a sol–gel process. Optical reflection spectra show that the PBG of the PLZT inverse opals shifts continuously with the change in the applied electric field. As the photonic crystals (PCs) consist of the high-refractive-index constituent and possess an “all-solid” structure, it should supply a more reliable mode to tune the PBG by the electric field for the superprism effect in PCs. It should be of high interest in device applications.
Gigahertz-band electroacoustic devices based on AlN thick films sputtered on Al2O3 at low temperature
Authors: Caliendo Cinzia
Published: December 2003

Piezoelectric aluminum nitride films, 1.4–6.2 μm thick, have been grown on z-cut Al2O3 substrates by reactive rf sputtering at 180 °C. The films were clear, uniform, stress free, and highly adhesive to the substrate. Surface acoustic wave (SAW) delay lines with harmonic modes operating at frequencies up to about 2.4 GHz were obtained using only conventional optical lithography at 7.5 μm line width resolution. The phase velocity and the electromechanical coupling factor of SAWs propagating along zx-Al2O3/AlN and zy-Al2O3/AlN structures were investigated and found to be in good agreement with the theoretical predictions. The Al2O3/AlN first-order temperature coefficient of frequency was estimated for different film thickness to wavelength ratio values, and the temperature-compensated SAW delay line was obtained.
Epitaxial growth of SrTiO3 films on CeO2/yttria-stabilized zirconia/Si(001) with TiO2 atomic layer by pulsed-laser deposition
Authors: Yamada Tomoaki , Wakiya Naoki , Shinozaki Kazuo , Mizutani Nobuyasu
Published: December 2003

Epitaxial SrTiO3 (STO) films were fabricated on CeO2/yttria-stabilized zirconia(YSZ)/Si(001) substrates by the insertion of a TiO2 atomic layer by pulsed-laser deposition. X-ray diffraction and reflection high-energy electron diffraction showed that epitaxial STO films with different out-of-plane orientations have been obtained by controlling the thickness of the TiO2 atomic layer. A stoichiometric STO film directly deposited on CeO2/YSZ/Si was preferentially (110) oriented with a STO[1̄10]∥CeO2[100] epitaxial relationship. On the other hand, 1 monolayer (ML) TiO2-covered CeO2/YSZ/Si resulted in STO(001) film epitaxially growth with a STO[110]∥CeO2[100] relationship. However, as the TiO2 thickness exceeded 1 ML, the orientation of STO film drastically changed to (111) orientation having a STO[011̄]∥CeO2[100] epitaxial relationship. These results indicate that the atomic layer thickness dramatically controls the film epitaxial growth.
Anisotropy in thermo-optic coefficients of polyimide films formed on Si substrates
Authors: Terui Yoshiharu , Ando Shinji
Published: December 2003

The temperature dependence of in-plane and out-of-plane refractive indices (i.e., thermo-optic coefficients dn/dT) was measured for seven kinds of aromatic polyimide (PI) films formed on silicon substrates. The absolute values of dnTE/dT (polarization parallel to the film plane) are significantly larger than dnTM/dT (perpendicular to the film plane). The dn/dT for average refractive indices (nav) are −94 to −58 ppm/K, independent of film thickness. The anisotropies (dnTE/dT−dnTM/dT) are −9 to −39 ppm/K. Although the values of nav are independent of film thickness, the anisotropies slightly increase as the film thickness decreases for flexible PI films. As expected from the temperature derivative of the Lorentz–Lorenz (LL) equation, the amorphous PI films exhibiting high nav show large dnav/dT, however, significant anisotropies are observed even for the PI films exhibiting very small birefringence.
Fabrication of periodic nanostructures by phase-controlled multiple-beam interference
Authors: Klein-Wiele Jan-Hendrik , Simon Peter
Published: December 2003

A special beam splitting scheme based on distributed beam splitting with diffractive elements is presented. Multiple beams are created, whose phase relations can be controlled with almost arbitrary precision by only changing the distance between the applied diffractive elements. Integration of this scheme into a reflective imaging system ensures temporal and spatial overlap of all selected beams in the target plane, and enables the use of femtosecond radiation. Manifold photonic structures can be fabricated in this way by phase-controlled multiple-beam interference. We demonstrate the capability of the method for femtosecond laser treatment of solids. Using subpicosecond laser pulses at 248 nm, submicron sized periodic structures with different shapes and feature sizes in the range of 100 nm are ablated on the surface of polycarbonate samples.
Low-loss as-grown germanosilicate layers for optical waveguides
Authors: Ay Feridun , Aydinli Atilla , Agan Sedat
Published: December 2003

We report on systematic growth and characterization of low-loss germanosilicate layers for use in optical waveguide technology. The films were deposited by plasma-enhanced chemical vapor deposition technique using silane, germane, and nitrous oxide as precursor gases. Fourier transform infrared spectroscopy was used to monitor the compositional properties of the samples. It was found that addition of germane leads to decreasing of N–H- and O–H-related bonds. The propagation loss values of the planar waveguides were correlated with the decrease in the hydrogen-related bonds of the as-deposited waveguides and resulted in very low values, eliminating the need for high-temperature annealing as is usually done.
Chemical states of Co and Fe in a specularly reflective oxide layer in spin valves
Authors: Hong Jongill , Lee Youngjun , Lee Min Kyu , Song Ha Jin , Shin Hyun-Joon , Yoo Yonggoo , Suh Jeongdae
Published: December 2003

In an examination of near-edge x-ray absorption fine structure spectra and magnetoresistance responses of a spin valve with a partially oxidized Co90Fe10 layer, we found that oxygen preferentially reacted with the solute Fe rather than with the solvent Co, and the very oxidized Fe likely enhanced specular reflections leading to an increase in the magnetoresistance value. Most Fe oxides transformed into α-Fe2O3, which further improved the magnetoresistance response after the spin valves were annealed. Our results show that obtaining appropriate oxide phases and controlling their quantity are the key to optimizing the magnetoresistance performance and magnetic properties of spin valves with specularly reflective oxide layers.
Electrical-field control of metal–insulator transition at room temperature in Pb(Zr0.2Ti0.8)O3/La1−xBaxMnO3 field-effect transistor
Authors: Kanki Teruo , Park Young-Geun , Tanaka Hidekazu , Kawai Tomoji
Published: December 2003

We have constructed field-effect transistor structures that consist of a ferromagnetic (La,Ba)MnO3 channel and a ferroelectric PbZr0.2Ti0.8O3 gate insulator with the aim of controlling the metal–insulator transition at room temperature by applying an electric field. Investigations have revealed that the transition temperature changed from 237.0 K to 242.0 K for the La0.90Ba0.10MnO3 channel layer by ferroelectric remnant polarity (±50 μC/cm2) and from 280.5 K to 283.0 K (±26 μC/cm2) for the La0.85Ba0.15MnO3 channel layer. These shifts, which are linearly proportional to the magnitude of ferroelectric remnant polarization, are induced by the accumulation charge due to the electric field.
Synthesis of zinc oxide varistors with a breakdown voltage of three volts using an intergranular glass phase in the bismuth–boron–oxide system
Authors: Ohashi Naoki , Kataoka Ken , Ohgaki Takeshi , Miyagi Takahira , Haneda Hajime , Morinaga Kenji
Published: December 2003

Zinc oxide (ZnO) crystals joined by using an intergranular glass phase were investigated in order to develop surge filters for low-voltage applications and to clarify the current transport mechanism through the junction. The junctions having a ZnO/glass/ZnO sandwich structure were synthesized by using an interfacial glass phase of the Bi–B–O system. A highly nonlinear current–voltage curve was obtained for the ZnO/glass/ZnO junction with Co-doped ZnO single crystals, and the current through the junction at the breakdown voltage was proportional to the 30th power of the bias voltage. Dielectric measurements revealed that a double-sided depletion layer was formed at the interface, and the observed high nonlinearity was ascribed to the corresponding potential barrier formed at the interface.
High-pressure phase transformation of silicon nitride
Authors: Patten John , Fesperman Ronnie , Kumar Satya , McSpadden Sam , Qu Jun , Lance Michael , Nemanich Robert , Huening Jennifer
Published: December 2003

We provide evidence for a high-pressure phase transformation (HPPT) in the ceramic material silicon nitride. This HPPT is inferred by a high-pressure diamond anvil cell, Raman spectroscopy, scanning/transmission electron microscopy, and optical and acoustic microscope inspection. In the case of silicon nitride, the HPPT involves a ductile or metallike behavior that is observed in severe deformation processes, such as nanoindentation and micromachining. This pressure-induced plasticity is believed to be similar to that found in silicon and germanium with its origin in the high-pressure metallic β-Sn phase formation.
In-situ nanostructured film formation during physical vapor deposition
Authors: Zhang Chi , Kalyanaraman Ramki
Published: December 2003

An approach to directly make controlled nanostructured films in situ with physical vapor thin film deposition is presented. Co films were formed into lines with 3.2±0.8 nm thickness and were regularly spaced 550±20 nm apart on a Si(100) surface. The line pattern results during pulsed laser deposition of Co simultaneous with two-beam laser interference irradiation of the Si surface. Preliminary results indicate that preferential evaporation is not the primary mechanism. This patterning is likely due to anisotropic diffusion modified growth of Co under thermal gradients. This one step patterning process, without need of any pre- or post-patterning of the substrate or film, is promising as an economical and simple nanostructured film fabrication approach.
Single-crystalline InN films with an absorption edge between 0.7 and 2 eV grown using different techniques and evidence of the actual band gap energy
Authors: Bhuiyan Ashraful Ghani , Sugita Kenichi , Kasashima Ken , Hashimoto Akihiro , Yamamoto Akio , Davydov Valery Yu.
Published: December 2003

Single crystalline InN films with an absorption edge between 0.7 and 2 eV have been grown using a variety of different techniques, including conventional metal-organic vapor-phase epitaxy (MOVPE), ArF-laser assisted MOVPE (la-MOVPE), and plasma-assisted molecular-beam epitaxy (pa-MBE). Analysis of samples grown using different methods has led to important evidence for determining the actual band gap energy of InN. In an effort to find the origin of the change in absorption edge, this evaluation was focused on the la-MOVPE of InN. This deposition technique enables InN film deposition over a wide range of growth temperatures, ranging from room temperature to a very high temperature (700 °C). Characterization of InN films grown over a wide range of temperatures strongly suggests that oxygen contamination leads to a larger band gap absorption energy value than the actual value, even in the case of single crystalline films. In films grown at low temperatures, oxygen appeared to form an alloy, resulting in a larger absorption edge, whereas, in films grown at high temperatures oxygen was present as a donor, which resulted in a larger absorption edge due to a Burstein–Moss shift.