bluuebunny/crossref_metadata_2025 huggingface dataset:
Strained Si, SiGe, and Ge channels for high-mobility metal-oxide-semiconductor field-effect transistors
Authors: Lee Minjoo L. , Fitzgerald Eugene A. , Bulsara Mayank T. , Currie Matthew T. , Lochtefeld Anthony
Published: December 2004

This article reviews the history and current progress in high-mobility strained Si, SiGe, and Ge channel metal-oxide-semiconductor field-effect transistors (MOSFETs). We start by providing a chronological overview of important milestones and discoveries that have allowed heterostructures grown on Si substrates to transition from purely academic research in the 1980’s and 1990’s to the commercial development that is taking place today. We next provide a topical review of the various types of strain-engineered MOSFETs that can be integrated onto relaxed Si1−xGex, including surface-channel strained Si n- and p-MOSFETs, as well as double-heterostructure MOSFETs which combine a strained Si surface channel with a Ge-rich buried channel. In all cases, we will focus on the connections between layer structure, band structure, and MOS mobility characteristics. Although the surface and starting substrate are composed of pure Si, the use of strained Si still creates new challenges, and we shall also review the literature on short-channel device performance and process integration of strained Si. The review concludes with a global summary of the mobility enhancements available in the SiGe materials system and a discussion of implications for future technology generations.
Phase diagram of pseudobinary Pb(Yb1∕2Nb1∕2)O3−Pb(Sc1∕2Nb1∕2)O3 ceramic solid solution
Authors: Kim J.-H. , Kim H. , Choo W. K. , Koh K. S. , Setter N.
Published: December 2004

Crystal structure and dielectric properties of (1−x)Pb(Yb1∕2Nb1∕2)O3−xPb(Sc1∕2Nb1∕2)O3 (PYN1−xPSNx) (0⩽x⩽0.60) solid solution have been studied, and its pseudobinary phase diagram has been determined. The low-temperature crystal structure of PYN1−xPSNx becomes pseudocubic from the PYN’s orthothombic with increasing x. Also the x-ray diffraction line intensities ascribed, respectively, to the antiferroelectric (AFE) lattice modulation and the B-site ordering become gradually weaker and then they disappear altogether for x>0.37. In the PYN-rich composition range (0⩽x<0.37), the paraelectric (PE)-AFE phase transition occurs sharply and its transition temperature remains independent of the applied frequency. However, on further increasing Sc concentration (0.37<x⩽0.60), the dielectric constant versus temperature curve becomes gradually broader and displays a frequency-dependent ferroelectric (FE) relaxor behavior. Particularly near x=0.37, the frequency-dependent dielectric behavior near the dielectric maximum temperature changes to a frequency-independent one below a specific temperature. Particularly at this composition, this solid solution displays a sequence of PE-metastable AFE-FE-AFE phase transition.
Optoelectronic and microstructure attributes of epitaxial SrTiO3 on Si
Authors: Myhajlenko S. , Bell A. , Ponce F. , Edwards J. L. , Wei Y. , Craigo B. , Convey D. , Li H. , Liu R. , Kulik J.
Published: December 2004

We have investigated the optoelectronic characteristics of bulk single-crystal SrTiO3 (STO) and epitaxial STO on Si by photoluminescence and cathodoluminescence (CL) techniques. In particular, we have explored to what extent these techniques can offer information about crystal quality. We have complemented these observations with atomic force microscopy, transmission electron microscopy (TEM), and micro-Raman measurements. Panchromatic CL imaging of bulk STO revealed contrast features associated with growth-related striations, extended defects, and mechanical damage. CL imaging of undoped high-resistivity substrates was limited by beam charging effects. The weak nature of the CL signal from epitaxial STO (relative to bulk material) made it very difficult to visualize any features by analog detection. On the other hand, spectrally resolved CL measurements of epitaxial STO using single-photon counting techniques, revealed sensitivity to the defect content and film quality across a 3-in wafer. Preliminary results indicate a qualitative correlation in the room-temperature near band-edge luminescence properties (3.2–3.5eV) and crystalline quality as determined by micro-Raman spectroscopy and TEM.
Effect of YBa2Cu3O7−δ film thickness on the dielectric properties of Ba0.1Sr0.9TiO3 in Ag∕Ba0.1Sr0.9TiO3∕YBa2Cu3O7−δ∕LaAlO3 multilayer structures
Authors: Zhu Xiaohong , Peng Wei , Li Jie , Chen Yingfei , Tian Haiyan , Xu Xiaoping , Zheng Dongning
Published: December 2004

Ferroelectric and superconductor bilayers of Ba0.1Sr0.9TiO3 (BSTO)∕YBa2Cu3O7−δ (YBCO), with different YBCO film thicknesses, have been fabricated in situ by pulsed-laser deposition on 1.2° vicinal LaAlO3 substrates. The dielectric properties of BSTO thin films were measured with a parallel-plate capacitor configuration in the temperature range of 77–300K. We observed a strong dependence of the dielectric properties of BSTO thin films on the thickness of the YBCO layer. As the YBCO-film thickness increases, the temperature of the dielectric permittivity maximum of BSTO thin films shifts to higher values, and the leakage current and dielectric loss increase drastically, while the dielectric constant and dielectric tunability decrease remarkably. The results are explained in terms of the transformation in the growth mode of the YBCO layer from two-dimensional step flow to three-dimensional island that leads to significant deterioration in the dielectric properties of BSTO thin films. We propose that improved dielectric properties could be obtained by reasonably manipulating the growth mode of the YBCO layer in the multilayer structures.
Implications of nonparabolicity, warping, and inelastic phonon scattering on hole transport in pure Si and Ge within the effective mass framework
Authors: Rodríguez-Bolívar S. , Gómez-Campos F. M. , Gámiz F. , Carceller J. E.
Published: December 2004

Hole mobility over a wide range of temperatures in pure Si and Ge is studied within the framework of effective mass theory using the Monte Carlo method. With this aim, we have implemented a three-band model (heavy, light, and split-off holes) introducing nonparabolicity even for the latter, which is usually considered parabolic in the literature. The warping in the heavy and light bands was taken into account, maintaining a spherical model for the split-off band. We also developed scattering rate expressions to be used in a Monte Carlo procedure with the nonparabolicity and warping effects included explicitly in the scattering rate expressions, an aspect neglected in the literature. In so doing, we calculated exactly the nonparabolicity functions for the valence band from the expressions provided by Kane [J. Phys. Chem. Solids 1, 82 (1956)]. Further, we modeled the acoustic phonons on an inelastic mechanism, generalizing previous work, and applying a temperature-dependent average to obtain typical values of the energy of the acoustic phonons involved in the scattering processes. We show that our treatment of hole transport provides results close to those reported experimentally and comparable to those obtained with more complex methods, but requiring much less computing time.
Modifications of ZnO thin films under dense electronic excitation
Authors: Kumar P. M. Ratheesh , Kartha C. Sudha , Vijayakumar K. P. , Singh F. , Avasthi D. K. , Abe T. , Kashiwaba Y. , Okram G. S. , Kumar M. , Kumar Sarvesh
Published: December 2004

Spray pyrolyzed ZnO films prepared using solution containing ethanol and water (volume ratio 1:1), exhibited optical transmission of 85% in the visible range and electrical resistivity of 78Ωcm. These samples were irradiated using 120MeV Au ion beam and then characterized using optical absorption and transmission, x-ray diffraction (XRD), electrical resistivity measurements, x-ray photoelectron spectroscopy (XPS), and photoluminescence studies. It appears that irradiation does not affect absorption edge while optical transmittance was slightly reduced. But intensities of peaks of XRD and photoluminescence were found to decrease continuously with increasing ion fluence. Electrical resistivity of the films decreased considerably (from 78to0.71Ωcm) with increase in ion fluence. Atomic concentration from XPS analysis showed that Zn∕O ratio is getting increased due to ion beam irradiation. Variations in carrier concentration were also measured using Hall measurements.
Experimental and theoretical investigation of the structural, chemical, electronic, and high frequency dielectric properties of barium cadmium tantalate–based ceramics
Authors: Liu Shaojun , Taylor Richard , Petrovic Novak S. , Budd Louisa , Van Schilfgaarde Mark , Newman N.
Published: December 2004

Single-phase Ba(Cd1∕3Ta2∕3)O3 powder was produced using conventional solid state reaction methods. Ba(Cd1∕3Ta2∕3)O3 ceramics with 2wt% ZnO as sintering additive sintered at 1550°C exhibited a dielectric constant of ∼32 and loss tangent of 5×10−5 at 2GHz. X-ray diffraction and thermogravimetric measurements were used to characterize the structural and thermodynamic properties of the material. Ab initio electronic structure calculations were used to give insight into the unusual properties of Ba(Cd1∕3Ta2∕3)O3, as well as a similar and more widely used material Ba(Zn1∕3Ta2∕3)O3. While both compounds have a hexagonal Bravais lattice, the P321 space group of Ba(Cd1∕3Ta2∕3)O3 is reduced from P3̱m1 of Ba(Zn1∕3Ta2∕3)O3 as a result of a distortion of oxygen away from the symmetric position between the Ta and Cd ions. Both of the compounds have a conduction band minimum and valence band maximum composed of mostly weakly itinerant Ta5d and Zn3d∕Cd4d levels, respectively. The covalent nature of the directional d-electron bonding in these high-Z oxides plays an important role in producing a more rigid lattice with higher melting points and enhanced phonon energies, and is suggested to play an important role in producing materials with a high dielectric constant and low microwave loss.
Downconversion and upconversion dynamics in Pr-doped Y3Al5O12 crystals
Authors: Özen G. , Forte O. , Di Bartolo B.
Published: December 2004

We have investigated the spectroscopic properties of praseodymium ion in a Y3Al5O12 sample. We obtained the luminescence spectra by exciting selectively the sample at 460 and 599nm, resulting in the excitation of the P03 and D21 levels, respectively. With excitation in the P03 level we obtained emission from this level and from the D21 level. We used time resolved spectra and decay pattern inspection to assign spectral lines to specific radiative transitions. With excitation in the D21 level we observed luminescence emitted by the same level and upconverted emission from the P03 level and the (4f5d) band. The experimental data indicate that the mechanism responsible for the upconversion processes is excited state absorption. We found the upconverted emission from P03 and the (4f5d) band to be proportional to the square of the excitation energy and to the cube of the excitation energy, respectively.
Correlation between Sm2(Fe,Ga)17 and its precursor Sm(Fe,Ga)9
Authors: Bessais L. , Dorolti E. , Djéga-Mariadassou C.
Published: December 2004

We have shown that the out-of-equilibrium hexagonal P6∕mmm phase adopts the stoichiometry Sm(Fe,Ga)9 in the Sm–Fe–Ga system. X-ray diffraction analysis has been combined with Mössbauer spectrometry. A specific program for the Wigner–Seitz cell (WSC) volume calculation of the equilibrium and of the metastable structure, deduced from the results given by the Rietveld analysis, was used. The Mössbauer spectra have been simulated with a model based on: (i) the multinomial law related to the statistical distribution of Ga and Sm vacancies obtained by the crystallographic approach, and (ii) the correlation between the WSC volume and the isomer shift of each inequivalent crystallographic site. The specific behavior of the 3g site isomer shift evolution corroborates the structure model. The Curie temperatures of the Sm(Fe,Ga)9 series are higher than those of the Sm2(Fe,Ga)17 alloys. Sm(Fe,Ga)9 represents an interesting host lattice for interstitial C or N atoms, with possible permanent magnet applications.
Influence of alternating current electrokinetic forces and torque on the elongation of immobilized DNA
Authors: Germishuizen W. A. , Tosch P. , Middelberg A. P. J. , Wälti C. , Davies A. G. , Wirtz R. , Pepper M.
Published: December 2004

The authors investigate the elongation and orientation of different-sized deoxyribose nucleic acid (DNA) molecules, tethered onto gold electrodes via a terminal thiol, under the influence of high frequency ac electric fields. The DNA molecules are elongated from a random coil into an extended conformation and orientated along the electric field lines as a result of the forces acting on the molecules during the application of the ac electric fields. Elongation was observed in the frequency range 100kHz–1MHz, with field strengths of 0.06–1.0MV∕m. Maximum elongation for all DNA fragments tested, irrespective of size, was found for frequencies between 200 and 300kHz. The torque acting on the induced dipole in the DNA molecules, complemented by a directional bias force, opposite in direction to the dielectrophoretic force, provides the main contribution to the elongation process. The length of elongation is limited to either half the distance between opposing electrodes or to the contour length of the DNA, whichever is shorter. Further, the authors show that the normalized length of the elongated DNA molecules is independent of the contour length of the DNA.
Time-resolved x-ray diffraction in a molecular crystal
Authors: Rozgonyi Tamás , Sauerbrey Roland , Feurer Thomas
Published: December 2004

The application of time-resolved x-ray diffraction for monitoring large amplitude coherent intramolecular vibrations in a molecular crystal is considered. The coherent vibrations are induced in the electronically excited state by an ultrashort optical pump pulse and the x-ray diffraction intensity based on a model crystal consisting of diatomic molecules is derived. Time-resolved diffraction signals are calculated for an iodine molecular crystal.
Structural and anisotropic transport properties of (Hg,Re)Ba2CaCu2Oy vicinal films
Authors: Ogawa A. , Sugano T. , Wakana H. , Kamitani A. , Adachi S. , Tarutani Y. , Tanabe K.
Published: December 2004

Approximately 160-nm-thick (Hg0.9Re0.1)Ba2CaCu2Oy [(Hg,Re)-1212] epitaxial thin films were fabricated on 2°–18.4°-tilt SrTiO3 vicinal substrates with thin buffer layers. The vicinal films had superior crystallinity and superconducting properties comparable to those for conventional films with no tilt. X-ray diffraction measurements revealed that the tilt angles of the c axes of the (Hg,Re)-1212 are slightly larger by 0.5°–1.5° than the substrate tilt angles, which is attributed to deformation of crystal structure due to lattice mismatch in the c-axis direction. The resistivity and critical current density along the c-axis direction (ρc and Jc-c) were estimated to be ρc=500mΩcm at room temperature and Jc-c=(1.0–1.4)×105A∕cm2 at 10K from transport measurements for different in-plane directions of the vicinal films. The ρc clearly exhibited semiconductor-like temperature dependence below 180K. The temperature dependence of Jc-c almost agreed with the theoretical relationship for superconductor-insulator-superconductor junctions. The current–voltage characteristics in the directions across their a–b planes exhibited a multiple branch structure of intrinsic Josephson junctions with voltage jumps at intervals of approximately 20mV at 4–40K.
Perpendicular magnetic anisotropy of Co∕Rh(111) distorted superlattices
Authors: Tokano H. , Yanagihara H. , Kita Eiji
Published: December 2004

We have investigated the relationship between perpendicular magnetic anisotropy (PMA) and the magnetoelastic effect of Co∕Rh(111) epitaxial superlattices as a large mismatch system and found the PMA for the thin Co layer to be less than 12Å. The magnitude of the PMA is comparable to those of typical PMA systems such as Co∕Pd and Co∕Pt. By taking account of the Co-thickness-dependent magnetoelastic anisotropy KME, arising from the lattice strain due to the 7% mismatch between Co and Rh, we found that the thickness-dependent PMA can be reproduced with no adjustable parameter.
Resonant tunneling transients and decay for a one-dimensional double barrier potential
Authors: Delgado F. , Muga J. G. , Austing D. G. , García-Calderón G.
Published: December 2004

Motivated by recent experimental work on quantum dots subjected to voltage pulses we consider a simple model to study the transition between off-resonance and on-resonance scattering states with the same incident energy in response to a sudden change in the well depth of a double barrier potential structure. The change displaces the real part of the resonance energy to coincide with the incident energy. The resonance buildup is not given by a pure exponential growth due to the interference between incident and resonance components represented by nearby poles, but the resonance lifetime is a relevant time scale. The reverse process (resonance depletion) that follows the opposite change in the well depth detunes the resonance level and the incident energy but, except for short and long time deviations, the decay is exponential with the lifetime of the displaced resonance. For a larger change in the well depth beyond a critical depth, trapping dominates rather than decay since the resonance becomes a bound state.
Influence of the AlGaN buffer layer on the biaxial strain of GaN epilayers grown on 6H-SiC (0001) by molecular-beam epitaxy
Authors: Jeganathan K. , Shimizu M. , Okumura H.
Published: December 2004

The role of AlxGa1−xN buffers in the control of residual strain in GaN epitaxial layers grown on 6H-SiC (0001) substrates by molecular-beam epitaxy was investigated. The initial GaN layer on the AlxGa1−xN (x=0%–10%) buffer nucleates in two-dimensional form, which promotes a step-flow growth mode in subsequently grown GaN layers. As the Al content in the AlxGa1−xN (x∼20%) buffer was increased, GaN began to nucleate as incoherent polygonal islands, coalescing as the thickness increased to 15nm. The overall residual strain induced in GaN is tensile (εxx) for GaN grown directly on SiC and compressive (−εxx) for GaN grown using an AlGaN buffer. The stiffness coefficient (−2C13∕C33) of GaN on the AlxGa1−xN (x∼10%) buffer was estimated to be −0.53 assuming that the defect-induced hydrostatic stress of unstrained GaN (c0∕a0) was constant.
Characterization of epitaxial (Y,Bi)3(Fe,Ga)5O12 thin films grown by metal-organic decomposition method
Authors: Ishibashi Takayuki , Mizusawa Aiko , Nagai Masataka , Shimizu Shinichiro , Sato Katsuaki , Togashi Naoto , Mogi Takayuki , Houchido Michio , Sano Hiroaki , Kuriyama Kazuo
Published: December 2004

Epitaxial (Y,Bi)3(Fe,Ga)5O12 garnet thin films have been prepared on Gd3Ga5O12 (111) substrates by a metal-organic decomposition (MOD) method using carboxylic acids. The chemical compositions of the films prepared in this study are Y2BiFe5O12 (YBFO), Y3Fe4GaO12 (YFGO), and Y2BiFe4GaO12 (YBFGO). Epitaxy of these films was confirmed by x-ray diffraction and Rutherford backscattering (RBS) measurements. Full width of half maximum values of the 444 diffraction peaks of YFGO and YBFGO were 0.4° and 0.04°, respectively. RBS channeling was clearly observed for the YFGO film with a minimum yield χmin along the [111] direction of ∼7.5%. These garnet films could also be reproducibly obtained by the MOD method without any deterioration in the MOD solutions over two years.
Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85−xAgx (⩽x⩽0.20) glasses
Authors: Pattanayak Pulok , Asokan S.
Published: December 2004

Temperature modulated alternating differential scanning calorimetric studies show that Se rich Ge0.15Se0.85−xAgx (0⩽x⩽0.20) glasses are microscopically phase separated, containing Ag2Se phases embedded in a Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase percolates in the Ge–Se matrix, with a well-defined percolation threshold at x=0.10. A signature of this percolation transition is shown up in the thermal behavior, as the appearance of two exothermic crystallization peaks. Density, molar volume, and microhardness measurements, undertaken in the present study, also strongly support this view of percolation transition. The superionic conduction observed earlier in these glasses at higher silver proportions is likely to be connected with the silver phase percolation.
Field-emission properties of macroporous silicon grown at high anodization voltages
Authors: Baranauskas V. , Fontana M. , Guo Zhao Jing , Ceragioli H. J. , Peterlevitz A. C.
Published: December 2004

In this work, the electron field emission properties, photoluminescence, and structure of porous silicon emitters as a function of the anodizing voltages have been studied. Morphological features, such as sharp nanometer-scale tip geometries, or micrometer-scale asperities, and large hexagonlike porosity, have been observed in porous silicon using atomic force microscopy for samples prepared at low or high anodization voltages, respectively. Threshold fields for electron emission of 16.6Vμm−1 and of 11.4Vμm−1 have been obtained for samples prepared at anodizing voltages of 10V and 150V, respectively, which are close to values required for technological applications. Possible mechanisms of field enhancement are discussed.
Microwave permeability of Co2Z composites
Authors: Rozanov K. N. , Li Z. W. , Chen L. F. , Koledintseva M. Y.
Published: December 2004

The microwave permittivity and permeability of Co2Z barium ferrite composite samples are measured as functions of frequency and volume fraction of the ferrite. Magnetostatic properties of the bulk ferrite are determined. This allows Snoek’s law [J. L. Snoek, Physica 14, 204 (1948)] to be verified by comparing the microwave and magnetostatic Snoek’s constants. The modification of Snoek’s law for hexagonal ferrites suggested recently by Acher et al. [Phys. Rev. B 62, 11324 (2000)] is also verified. Acher’s constant is found from microwave measurements to agree with the value calculated from the magnetostatic properties of bulk ferrite, but microwave and magnetostatic Snoek’s constant do not agree. This may be attributed to the effect due to demagnetizing factors of ferrite inclusions that are not considered in the derivation of Snoek’s and Acher’s laws. The measured frequency-dependent permeability of composites satisfies the Lorentzian dispersion law and is consistent with the Maxwell Garnett approximation [J. C. Maxwell Garnett, Philos. Trans. R. Soc. London 203, 385 (1904)]. According to the theoretical analysis based on the Lorentzian dispersion law and the Maxwell Garnet mixing rule, both Snoek’s and Acher’s constants must be linear functions of the volume fraction, independent of whether microwave values of the constants are in agreement with the magnetostatic values. In contrast, the experimental measurements reveal a steady decrease of both constants with the volume fraction. The disagreement is discussed in terms of the influence of effective medium in composite on the inherent permeability of ferrite particles.
Nonlinear optical susceptibilities for magnetization-induced third-harmonic generation
Authors: Shimura Jusuke , Hashimoto Kazuhito , Ohkoshi Shin-ichi
Published: December 2004

This paper describes a method for evaluating the magnetization-induced element in a third-order nonlinear optical susceptibility tensor. One difficulty in estimating this element is that the Faraday effects at fundamental and harmonic wavelengths are entangled with the polarization state of the outgoing harmonic wave. Using our method, the contribution of the Faraday effects can be isolated and removed from the rotation angle and the ellipticity of the outgoing harmonic wave. The theoretical expressions for the right- and left-handed circularly polarized components of the outgoing harmonic wave from magnetic media are derived. A formula for evaluating the magnetization-induced element is then determined from these expressions. Applying this formula to a bismuth-aluminum-doped yttrium-iron garnet thin film gives the magnetization-induced element ∣χxyyy(3),m∣=4×10−21m2∕V2 at the fundamental wave of 1.17eV (third-harmonic wave: 3.50eV) in a magnetic field of +1kOe.
In situ synthesis of Mn-doped ZnO multileg nanostructures and Mn-related Raman vibration
Authors: Yang L. W. , Wu X. L. , Huang G. S. , Qiu T. , Yang Y. M.
Published: December 2004

Mn-doped ZnO multileg nanostructures were synthesized via in situ thermal oxidation of Zn and MnO2 powder. Spectroscopic measurements show that Mn ions have been doped into the lattice positions of Zn ions, which strongly induce growth of the observed ZnO multileg nanostructure. It is revealed that the growth mechanism of this kind of multileg ZnO:Mn nanostructure is different from the traditional vapor–solid or vapor–liquid–solid nucleation model of ZnO nanostructures. A possible mechanism is discussed on the basis of the growth process of a tetrapod ZnO nanostructure. Furthermore, we report the observation of an additional Raman peak. This peak is considered to have an origin related to Mn dopant in the ZnO nanostructure. This Raman feature can be regarded as an indicator for the incorporation of Mn ions into the lattice positions of the multileg ZnO nanostructure.
Crystalline structure and transition behavior of recrystallized-irradiated P(VDF-TrFE) 65∕35 copolymer
Authors: Li Zhi-Min , Li Sui-Qiong , Cheng Z.-Y.
Published: December 2004

The effect of recrystallization on the crystalline structure and properties of P(VDF-TrFE) 65∕35mol% samples that had previously been irradiated with high-energy electrons at doses of 60, 85, and 100Mrad was studied. The crystallinity of the recrystallized samples was found to be lower than that of corresponding irradiated samples and the size of the crystalline regions in the recrystallized samples was smaller. For 60- and 85-Mrad irradiated samples, the crystalline regions in the recrystallized samples contained more Tm>3 conformations than in the corresponding irradiated samples, while for 100-Mrad irradiated samples, the crystalline regions in the recrystallized samples had fewer Tm>3 conformations. Based on their melting and structure transformation behaviors, the crystalline regions in the unrecrystallized irradiated samples have a much higher surface energy, probably originating from the compressive stress induced by crosslinking on the surface of the crystalline regions. Although the recrystallized samples have a lower surface energy, the crosslinking caused the crystalline regions in the polymer to have a partially ordered region on the surface of the crystalline regions. This partially ordered surface, i.e., the interfacial layer, results in a high polarization level in the recrystallized samples. Additionally, the recrystallized sample has a lower dielectric loss. These findings combined to make such recrystallized polymers strong candidates for use in applications requiring high-performance electroactive polymers.
Structure formation on the surface of indium phosphide irradiated by femtosecond laser pulses
Authors: Bonse J. , Munz M. , Sturm H.
Published: December 2004

Laser-induced periodic surface structures (LIPSS; ripples) with different spatial characteristics have been observed after irradiation of single-crystalline indium phosphide (c-InP) with multiple linearly polarized femtosecond pulses (130fs, 800nm) in air. With an increasing number of pulses per spot, N, up to 100, a characteristic evolution of two different types of ripples has been observed, i.e., (i) the growth of a grating perpendicular to the polarization vector consisting of nearly wavelength-sized periodic lines and (ii), in a specific pulse number regime (N=5–30), the additional formation of equally oriented ripples with a spatial period close to half of the laser wavelength. For pulse numbers higher than 50, the formation of micrometer-spaced grooves has been found, which are oriented perpendicular to the ripples. These topographical surface alterations are discussed in the frame of existing LIPSS theories.
Evolution of surface waviness in thin films via volume and surface diffusion
Authors: Panat Rahul , Hsia K. Jimmy , Cahill David G.
Published: December 2004

Deformation mechanisms involving mass transport by stress driven diffusion influence a large number of technological problems. We study the formation of undulations on surfaces of stressed films at high temperature by exploring the deformation kinetics governed by volume and surface diffusion. A governing equation is derived that gives the amplitude change of such surfaces as a function of time. A parametric study is then carried out using a range of practically important input values of the film material properties. The results show that at the dominant instability wavelength, under high average stresses (giga pascal range), only surface diffusion contributes to film surface morphology evolution whereas under low stress and high-temperature conditions, both surface diffusion and volume diffusion contribute to film surface morphology evolution. Furthermore, the contribution of volume diffusion depends on the sign of the film stress, with compressive stress promoting surface roughening and tensile stress promoting surface smoothing.
Photoluminescence of ZnTe and ZnTe:Cr grown by molecular-beam epitaxy
Authors: Luo Ming , VanMil B. L. , Tompkins R. P. , Myers T. H. , Giles N. C.
Published: December 2004

Photoluminescence (PL) from undoped and chromium-doped ZnTe epilayers was studied in the spectral range from 0.3to2.4eV over the temperature range from 5K to room temperature. Films approximately 2μm thick were grown by molecular-beam epitaxy on GaAs substrates. For undoped ZnTe, spectra are dominated by a sharp acceptor-bound-exciton line related to arsenic, with only weak emission observed due to substitutional oxygen (OTe). An analysis of strain-induced shifts in excitonic energies was performed to clarify transition assignments for two PL bands near 2.375 and 2.379eV. For ZnTe:Cr epilayers, the infrared Cr2+ emission near 2.5μm (0.5–0.6eV) was found to be a function of both doping concentration and Zn∕Te beam-equivalent-pressure ratio. Direct excitation of the Cr2+ ions with 1.89-μm light produced emission up to room temperature. Indirect excitation with 514.5-nm light produced emission that could be detected up to 180K. Luminescence decay curves measured from a ZnTe:Cr film ([Cr]∼1×1018cm−3) using pulsed excitation at 355 and at 532nm indicated two lifetimes: τ1=3(±1)μs and τ2⩾10μs. The shorter lifetime agrees with values reported previously for Cr-doped ZnTe bulk crystals and thin films under 1.9-μm pulsed excitation.
Shock wave compression of the ferroelectric ceramic Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3: Depoling currents
Authors: Setchell Robert E.
Published: December 2004

Shock wave compression of poled Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (PZT 95/5-2Nb) results in rapid depoling and release of bound charge. In the current study, planar-impact experiments with this material were conducted on a gas-gun facility to determine Hugoniot states, to examine constitutive mechanical properties during shock propagation, and to investigate shock-induced depoling characteristics. A previous article summarized results from the first two of these areas, and this article summarizes the depoling studies. A baseline material, similar to materials used in previous studies, was examined in detail. More limited experiments were conducted with other materials to investigate the effects of different porous microstructures. Experiments were conducted over a wide range of conditions in order to examine the effects of varying shock strength, poling orientation, input wave shape, electric field strength, porous microstructure at a fixed density, and initial density. Depoling currents were recorded in an external circuit under either short-circuit or high-field conditions, and provide a convenient means of examining the kinetics associated with the ferroelectric–to–antiferroelectric phase transition. For sufficiently strong shock waves, the measured short-circuit currents indicate that the phase transition is very rapid and essentially complete. As shock strengths are reduced, short-circuit currents show increasing rise times and decreasing final levels at the end of shock transit. These features indicate that the transition kinetics can be characterized in terms of both a transition rate and a limiting degree of transition achieved in a given shock experiment. The presence of a strong electric field does not appear to have a significant effect on transition kinetics at high shock stresses, but has a strong effect at low stresses. As was found for constitutive mechanical properties, only small effects on measured currents resulted from differences in the porous microstructure of common-density materials, but large effects were observed when initial density was varied. To examine transition kinetics in more detail, short-circuit currents obtained with the baseline material and several approximate methods were used to estimate values for the rate and degree of transition as functions of shock properties. Differences between these currents and currents measured in high-field experiments using the same impact conditions were used to examine field effects on transition kinetics and corresponding dielectric properties.
Modulated spot heating for the measurement of thermal diffusivity
Authors: Lakestani Fereydoun , Salerno Antonio , Volcan Alberto
Published: December 2004

The method described in this article performs thermal diffusivity measurements on bulk materials using a modulated spot heating of the sample surface and measuring the surface temperature on the spot with an infrared detector at different modulation frequencies. Since the method is single sided and it can be performed on a bulk, it does not require the preparation of a sample. Furthermore it does not require a precise alignment nor a movement of the heating source nor of the infrared detector. The diffusivity measurement on a sample of unknown thermal diffusivity requires the knowledge of the shape of the heating and of the sensitivity profile of the infrared detector on the sample surface. This information, difficult to obtain, is not necessary in case a first measurement is performed on a reference sample of known thermal diffusivity and subsequent measurements on samples of unknown thermal diffusivity are performed by positioning them with their surface precisely in the same location as the reference one.
Determination of anisotropic elastic constants of superlattice thin films by resonant-ultrasound spectroscopy
Authors: Nakamura Nobutomo , Ogi Hirotsugu , Hirao Masahiko , Ono Teruo
Published: December 2004

Superlattice thin films are expected to show elastic anisotropy because of lattice misfits at interfaces among different elements. This study demonstrates that resonant-ultrasound spectroscopy and laser-Doppler interferometry can determine anisotropic elastic constants of superlattice thin films. Mechanical resonance frequencies of a layered specimen composed of a substrate and deposited thin film depend on the elastic constants, mass densities, and dimensions of the substrate and thin film. X-ray diffraction measurement determines accurately the total thiskness of a multilayer thin film. Therefore, the elastic constants of the multilayer thin film can be derived from measured resonance frequencies, provided that mode identification on observed resonance frequencies is achieved. We measure the resonance frequencies by a piezoelectric tripod and identify the vibration modes by measuring the displacement distributions on the specimen surface using laser-Doppler interferometry. We apply the present method to a Co/Pt multilayer [Co(4Å)∕Pt(16Å)]500 showing the perpendicular magnetic anisotropy. The in-plane elastic constants are larger than those of bulks by 1%–7%. This is attributed to internal strain due to lattice misfit at the Co–Pt interfaces through interatomic anharmonicity.
Erbium-implanted silicon–germanium
Authors: Touboltsev V. , Jalkanen P.
Published: December 2004

Rutherford backscattering/channeling technique complemented by transmission electron microscopy has been used to study the composition dependence and the effect of carbon codoping on thermal and structural properties of unstrained Si1−xGex (x=0.1–0.8) alloys implanted with Er+ at 70keV to a fluence of the order of ∼1015cm−2. It has been shown that implantation in the low-temperature regime (350°C) led to the formation of a ternary solid solution with a peak Er concentration of around 1at.%. Implanted Er atoms were found randomly distributed in the heavily damaged host matrix. Postimplantation annealing at different temperatures up to 600°C was observed to induce solid phase epitaxial regrowth leading to the recrystallization of the damaged matrix and the simultaneous removal of almost all the implanted Er. Both rate and activation temperature of the epitaxy in Si1−xGex were found to depend strongly on the stoichiometry of the alloy. Implantation of Er in the high-temperature regime (550°C) was found to lead to the spontaneous recovery of the host matrix crystallinity and the incorporation of Er atoms on regular lattice sites. Specific lattice positions Er can occupy were identified and they were found to have a strong dependence on both the alloy composition and foreign impurity (C codoping). Based on the channeling analysis, an interpretation of the diverse Er occupancy in Si1−xGex observed in our experiments is proposed.
Numerical simulations and experimental measurements of stress relaxation by interface diffusion in a patterned copper interconnect structure
Authors: Singh N. , Bower A. F. , Gan D. , Yoon S. , Ho P. S. , Leu J. , Shankar S.
Published: December 2004

We describe a series of experiments and numerical simulations that were designed to determine the rate of stress-driven diffusion along interfaces in a damascene copper interconnect structure. Wafer curvature experiments were used to measure the rate of stress relaxation in an array of parallel damascene copper lines, which were encapsulated in a dielectric, and passivated with an overlayer of silicon nitride or silicon carbide. The stress relaxation was found to depend strongly on the choice of passivation. Three-dimensional finite element simulations were used to model the experiments, and showed that this behavior is caused by changes in the diffusivity of the interface between the copper lines and the passivation. By fitting the predicted stress relaxation rates to experimental measurements, we have identified the interfaces that contribute to stress relaxation in the structure, and have estimated values for their diffusion coefficients.
Composition dependent magnetic properties of iron oxide-polyaniline nanoclusters
Authors: Sharma Raksha , Lamba Subhalakshmi , Annapoorni S. , Sharma Parmanand , Inoue Akihisa
Published: December 2004

γ - Fe 2 O 3 prepared by sol gel process was used to produce nanocomposites with polyaniline of varying aniline concentrations. Transmission electron microscopy (TEM) shows the presence of chain like structure for lower polyaniline concentration. The room temperature hysteresis curves show finite coercivity of ∼160Oe for all the composites, while the saturation magnetization was found to decrease with increasing polymer content. Zero field cooled-field cooled magnetization measurements indicate high blocking temperatures. It is believed that this indicates a strongly interacting system, which is also shown by our TEM results. Monte Carlo simulations performed on a random anisotropy model with dipolar and exchange interactions match well with experimental results.
Cathodoluminescence and solid phase epitaxy in Ba-irradiated α-quartz
Authors: Dhar S. , Sahoo P. K. , Gąsiorek S. , Vetter U. , Kulkarni V. N. , Lieb K. P.
Published: December 2004

The luminescent properties of quartz and silica doped with photoactive ions depend on the structural and chemical properties of the matrix and doping elements. The dynamic solid phase epitaxy of α-quartz during Ba+-ion implantation at 300–1170K and its relationship to cathodoluminescence emission are investigated in this work. Rutherford backscattering channeling analysis revealed that the amorphous layer created by 1×1015 175keVBaions∕cm2 at 300K almost disappeared when the implantation temperature was raised to 1120K. Between 770 and 1100K the cathodoluminescence spectra taken at room temperature exhibit dramatic changes with the implantation temperature and allow to distinguish between color centers related to quartz, ion-irradiated silica, and implanted Ba ions. After achieving almost complete epitaxial recovery, only a violet band at 3.4eV remained, which we attribute to Ba-related luminescence centers. Samples first implanted with Ba ions and then postannealed in air or O218 atmosphere up to 1320K did not show full epitaxy of the amorphized layer.
Electron-irradiation effects on CdSe thin films investigated by thermally stimulated current method
Authors: Ion L. , Antohe S.
Published: December 2004

Defects determining the electrical properties of CdSe thin films, before and after irradiation with high-energy electrons, have been investigated by thermally stimulated current technique. Thin films of CdSe, 30 μm thick, prepared by thermal-vacuum evaporation on glass substrate at a temperature of 220 °C were subjected to irradiation with 6-MeV electrons to a fluency of 5×1013e∕cm2. The main defect (D1), controlling the electrical properties of the films both before and after irradiation, is located at 0.38 eV below the conduction-band edge. Some other defects existing in lower densities and having lower ionization energies (0.24 eV, D2; 0.17 eV, D3; and 0.14 eV, D4) were also identified. Electron irradiation induces in significant increase in the peaks associated with the defects D1, D2, and D3, especially in the first one. The parameters characterizing all the detected traps were determined.
Enhanced bulk metallic glass formability by combining chemical compatibility and atomic size effects
Authors: Guo F. Q. , Poon S. J. , Shiflet G. J.
Published: December 2004

The glass formability (GFA) of Y- and Ca-based alloys is enhanced by inserting elements that yield a more uniform separation in the atomic sizes, as well as a wider atomic size distribution range, in agreement with the analytical findings of Miracle, Senkov, and others. The degree of the GFA improvement depends on the chemical compatibility of the addition elements with the existing components. By combining this observation with similar results noted in other alloys that form large-size bulk metallic glasses, the importance of the atomic size effect and chemical compatibility in glass forming alloys is revealed. The atomic size effect and chemical compatibility are discussed along with other glass forming factors.
Combining drought tolerance and responsiveness to summer moisture availability in cocksfoot (Dactylis glomerata L.) germplasm grown in Mediterranean environments
Authors: Piano E. , Pecetti L. , Annicchiarico P. , Carroni A. M. , Fornasier F. , Romani M.
Published: December 2004

Drought-tolerant cocksfoot cultivars capable of exploiting off-season moisture could be useful for the Mediterranean region. This study aimed to assess drought tolerance and responsiveness to summer irrigation in 2 sets of materials, namely, 8 populations including Mediterranean and non-Mediterranean ssp. glomerata cultivars and 2 Mediterranean ssp. hispanica natural populations, and 28 half-sib progenies issued by previous phenotypic selection of Mediterranean parent germplasm under summer irrigation. Dry matter (DM) yield under rainfed and summer-irrigated conditions was observed in summer and the following cool season and it was related to plant survival at the end of summer, concentration of soluble sugars and total nitrogen before and at full imposition of the summer treatments, and leaf-extension rate at early treatment imposition. The results indicated that: (i) a complete vegetative arrest under stress is a prerequisite for summer survival in Mediterranean environments; (ii) selected Mediterranean material may exhibit a level of responsiveness to moisture availability in summer that is comparable, in some cases, with that of non-Mediterranean germplasm; (iii) responsiveness to summer irrigation may not exert a detrimental effect on the subsequent cool-season regrowth in selected Mediterranean germplasm, whereas a detrimental effect is evident in unselected ssp. hispanica material; (iv) DM yield responses under rainfed and irrigated conditions are genetically compatible, as shown by the moderate positive genetic correlation (rg = 0.51); (v) the selection for responsiveness to summer irrigation in Mediterranean germplasm of ssp. glomerata or ssp. hispanica can be effective; and (vi) Mediterranean germplasm accumulates soluble sugars during the dry period, but the value of this or other physiological traits as an indirect selection criterion within adapted Mediterranean germplasm is questionable.
Measurement of trace metal influx in plants: a case study with Co
Authors: Reid Rob , Liu Juhong
Published: December 2004

The analysis of transport systems involved in the uptake of trace metals in plants is complicated by technical difficulties associated with measurement of uptake and by the likely presence of multiple transporters with broad specificity. In this study, influx of Co was used to illustrate the problems involved and potential solutions. Issues surrounding kinetic descriptions of transport, multiple uptake systems, specificity of transporters, pH effects and the role of membrane surface charge in determining fluxes are addressed. A list of criteria for validation of flux measurements is provided.
Microvascular patterning is controlled by fine-tuning the Akt signal
Authors: Sun Jing Fang , Phung Thuy , Shiojima Ichiro , Felske Terri , Upalakalin J. Nalinee , Feng Dian , Kornaga Tad , Dor Talia , Dvorak Ann M. , Walsh Kenneth , Benjamin Laura E.
Published: December 2004

We investigated the functions of Akt during vascular development and remodeling by using an inducible endothelial cell-specific driver of the dominant-active myrAkt. We found that sustained signaling in response to overexpression of myrAkt led to embryonic lethality, edema, and vascular malformations. In addition to the morphological malformations, the vascular phenotype was consistent with a failure in remodeling, such that the normal patterning and vessel hierarchy was disturbed. Examination of the well studied retinal vasculature during the remodeling phases revealed that transient expression of myrAkt was capable of altering the normal response to oxygen-induced remodeling without causing vascular malformations. These findings suggest that physiological levels of Akt signaling modulated microvascular remodeling and support the hypothesis that, although Akt may be required for vascular growth and homeostasis, appropriate down-regulation is also an essential aspect of normal vascular patterning.