bluuebunny/crossref_metadata_2025 huggingface dataset:
Rotating-field magnetoresistance of exchange-biased spin valves
Authors: Paul Amitesh , Buchmeier Matthias , Bürgler Daniel E. , Grünberg Peter
Published: January 2005

We investigate the magnetoresistance (MR) of spin valves by (i) varying the strength of the field applied in a fixed direction and (ii) rotating the field with fixed strength. The latter data reflect in general a mixture of giant and anisotropic magnetoresistance (GMR and AMR). We present an experimental procedure to suppress the AMR contributions of all ferromagnetic layers in the spin valve without disturbing the GMR response. The resulting angular MR curves are fitted with a single-domain model to determine with high precision the exchange bias field, the uniaxial anisotropies, the GMR ratio, and the interlayer coupling field. The application of the method to differently prepared Ta(5.0nm)∕NiFe(3.0nm)∕FeMn(15.5nm)∕NiFe(3.0nm)∕Co(2.0nm)∕Cu(3.5nm)∕Co(2.0nm)∕NiFe(7.0nm) spin valves with GMR ratios of 1.8% and 4% demonstrates the sensitivity and reveals differences of the order of a few percents of the exchange bias field for the uniaxial anisotropy fields of the free and pinned layer as well as for the interlayer coupling field.
Quantum reaction rate from higher derivatives of the thermal flux-flux autocorrelation function at time zero
Authors: Ceotto Michele , Yang Sandy , Miller William H.
Published: January 2005

A quantum theory of thermal reaction rates is presented which may be viewed as an extension of the recently developed “quantum instanton” (QI) model [W. H. Miller, Y. Zhao, M. Ceotto, and S. Yang, J. Chem. Phys. 119, 1329 (2003)]. It is based on using higher derivatives of the flux-flux autocorrelation function C(t) (as given by Miller, Schwartz, and Tromp) at t=0 to construct a short time approximation for C(t). Tests of this theory on 1d and collinear reactions, both symmetric and asymmetric, show it to be more accurate than the original QI model, giving rate constants to ∼5% for a wide range of temperature.
Characterization of methoxy adsorption on some transition metals: A first principles density functional theory study
Authors: Wang Gui-Chang , Zhou Yu-Hua , Nakamura Junji
Published: January 2005

Based on the gradient-density functional theory, calculation results of methoxy adsorption on Au(111), Ag(111), Cu(111), Pt(111), Pd(111), Ni(111), Rh(111), and Fe(100) surfaces are presented, and a consistent picture for some key physical properties determining the reactivity of metals appears. These eight metals belong to two groups: either with filled d electrons (group IB) or with unfilled but more than half filled d electrons (group VIII). The calculated adsorption energies are quite in agreement with the experimental data as well as the previous theoretical calculation results. Importantly, using the analysis of B. Hammer and J. K. Nørskov, Nature (London) 376, 232 (1995) and in Chemisorption and Reactivity on Supported Clusters and Thin Films, edited by R. M. Lambert and G. Pacchioni (Kluwer Academic, Dordrecht, 1997), pp. 285–351, the binding energies have selectively been linearly correlated to the d-band center and to the size of the metal d-band orbital overlapping with the adsorbate (coupling matrix element) for these two groups of metals. And by analyzing the nature of the adsorption bonding, the possible reason of this difference is suggested.
Reflection absorption infrared spectroscopy and temperature programmed desorption investigations of the interaction of methanol with a graphite surface
Authors: Bolina A. S. , Wolff A. J. , Brown W. A.
Published: January 2005

Reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) have been used to investigate the adsorption of methanol (CH3OH) on the highly oriented pyrolytic graphite (HOPG) surface. RAIRS shows that CH3OH is physisorbed at all exposures and that crystalline CH3OH can be formed, provided that the surface temperature and coverage are high enough. It is not possible to distinguish CH3OH that is closely associated with the HOPG surface from CH3OH adsorbed in multilayers using RAIRS. In contrast, TPD data show three peaks for the desorption of CH3OH. Initial adsorption leads to the observation of a peak assigned to the desorption of a monolayer. Subsequent adsorption leads to the formation of multilayers on the surface and two TPD peaks are observed which can be assigned to the desorption of multilayer CH3OH. The first of these shows a fractional order desorption, assigned to the presence of hydrogen bonding in the overlayer. The higher temperature multilayer desorption peak is only observed following very high exposures of CH3OH to the surface and can be assigned to the desorption of crystalline CH3OH.
A diffusion model for the fluids confined in micropores
Authors: Liu Ying-Chun , Wang Qi , Li Xiao-Feng
Published: January 2005

The self-diffusion coefficients were calculated by molecular dynamics simulations and the effects of pore width, temperature, and fluid density on diffusion behavior of simple fluid argon and polar fluid water confined in micropores were analyzed and studied. A mathematical model describing diffusion behavior of fluids confined in micropores was proposed from the theories of molecular dynamics and molecular kinematics, and validated on the basis of the simulation results at various conditions. The model indicates that the diffusion coefficient is proportional to the square root of the pore width and to the temperature divided by the density squared. It is applicable to either liquid or gas states and only two parameters are required.
Correlation of domain pattern and high-frequency response in pole-tip of inductive thin film head
Authors: Wei Dan , Zhang Xuan , Wu Guoguang , Wei Fulin , Yang Zheng
Published: January 2005

The high frequency response of the soft magnetic pole tip in the thin film inductive head is crucial for the noise analysis of computer hard disk. A micromagnetic model is established in a mesoscopic soft magnetic thin film to analyze the domain pattern as well as the initial permeability in a wide frequency range from 10MHz to 18GHz. The simulated domain patterns in the pole tip, a vortex- and ladder-type, are chosen as the initial conditions for the high-frequency response studies. The scaling law of the permeability is analyzed at different amplitudes of the alternating external magnetic field. It is found that in the ladder-type domains the high frequency response is much better than that in the vortex-type domains, which agrees with experiment. A simplified explanation of the simulation result is discussed based on the analysis of the nonlinear Landau–Liftshitz equation.
Imaging of defect-mediated surface morphology of GaN(0001¯) grown on sapphire by molecular beam epitaxy
Authors: Liu B. , Leone Stephen R. , Kitajima T. , Zhang T. H. , Borca C.
Published: January 2005

In situ scanning tunneling microscopy and ex situ atomic force microscopy are used to study the surface morphology of GaN(0001¯) grown on sapphire substrates by plasma-assisted molecular beam epitaxy. Several types of defect-mediated surface morphologies are characterized, including surface terminations of screw and mixed dislocations, defect-induced grooves, and impurity-induced step bunching. In addition to the early theory of dislocation-enhanced crystal growth developed by Frank [F. C. Frank, Acta Crystallogr 4, 497 (1951)] step structures are also found to be critical to understand the formation of spiral growth hillocks around surface terminations of different types of threading dislocations. Growth experiments are also performed under different conditions, e.g., by varying III∕V flux ratio and growth temperature to further investigate the relationship between the final surface morphology and the early stages of growth, such as sapphire nitridation and the transition stage from the three-dimensional buffer layer growth under nitrogen-rich conditions to the two-dimensional active layer growth under slightly Ga-rich conditions.
Kirkendall void formation in eutectic SnPb solder joints on bare Cu and its effect on joint reliability
Authors: Zeng Kejun , Stierman Roger , Chiu Tz-Cheng , Edwards Darvin , Ano Kazuaki , Tu K. N.
Published: January 2005

The electronic packaging industry has been using electroless Ni(P)∕immersion Au as bonding pads for solder joints. Because of the persistence of the black pad defect, which is due to cracks in the pad surface, the industry is looking for a replacement of the Ni(P) plating. Several Cu-based candidates have been suggested, but most of them will lead to the direct contact of solder with Cu in soldering. The fast reaction of solder with Cu, especially during solid state aging, may be a concern for the solder joint reliability if the package will be used in a high temperature environment and is highly stressed. In this work, the reaction of eutectic SnPb solder with electrodeposited laminate Cu is studied. Emphasis is given to the evolution of the microstructure in the interfacial region during solid state aging and its effect on solder joint reliability. A large number of Kirkendall voids were observed at the interface between Cu3Sn and Cu. The void formation resulted in weak bonding between solder and Cu and led to brittle fracture at the interface in the ball shear and pull tests. The experimental results indicate that a barrier for Cu diffusion may be needed between the solder and the type of Cu used in the test vehicle for the packages that will experience high temperature (>100°C) and high stress.
Measurement of high viscosity with laser induced surface deformation technique
Authors: Yoshitake Y. , Mitani S. , Sakai K. , Takagi K.
Published: January 2005

A technique for viscosity measurement was developed based on the principle of laser-induced surface deformation. Light incident into liquids increases its momentum due to the difference in refractive index and gives the surface an upward force as a reaction. The plane surface thus swells up and deforms, and the shape is determined so that the force is balanced with the surface tension and the gravity. On sudden laser irradiation, the deformation inevitably accompanies a viscous flow and exhibits a relaxational behavior with a delay time, which gives the viscosity. Theoretical prediction of the step-response function was given that takes surface tension waves excited by the laser into consideration. Nd–yttritium–aluminum–garnet laser with 0.6W output was focused to ∼200μm beam waist and used for the pumping. The deformation process was observed sensitively with another probe laser illuminating the activated area. This system was tested with the standard liquids for viscosity ranging from 1 to 106cSt. The results demonstrated the validity of this technique, though a correction for the inertia effect was needed in the range lower than 10cSt. Further, effect of the thermal expansion by a slight optical absorption was discussed. This technique is especially useful at high viscosities since the measurement takes only a few seconds even in the specimen with 106cSt. Besides the rapidity, it has a great advantage of a noncontact feature and is appropriate for measuring the liquids that strongly dislike contamination. It has also potential applications in industries, measurement of liquids isolated in a production line, for instance.
Bending optical solitons in nonlinear photonic crystal waveguides
Authors: Chen Xiong-Wen , Lin Xu-Sheng , Lan Sheng
Published: January 2005

We investigate the propagation of optical solitons through nonlinear photonic crystal (PC) waveguide bends. Our studies focus on the waveguide bends in two-dimensional PC slabs which are widely used for the manipulation of photons. It is found that optical solitons are completely destroyed when trying to pass through the conventional waveguide bend. With appropriate modifications to the bend structure, however, perfect transmission of optical solitons can be realized. The criteria for the design of waveguide bends with low reflection loss are also generalized.
Comparison of density functionals for energy and structural differences between the high- [5T2g:(t2g)4(eg)2] and low- [1A1g:(t2g)6(eg)] spin states of iron(II) coordination compounds. II. More functionals and the hexaminoferrous cation, [Fe(NH3)6]2+
Authors: Fouqueau Antony , Casida Mark E. , Daku Latévi Max Lawson , Hauser Andreas , Neese Frank
Published: January 2005

The ability of different density functionals to describe the structural and energy differences between the high- [5T2g:(t2g)4(eg)2] and low- [1A1g:(t2g)6(eg)0] spin states of small octahedral ferrous compounds is studied. This work is an extension of our previous study of the hexaquoferrous cation, [Fe(H2O)6]2+, [J. Chem. Phys. 120, 9473 (2004)] to include a second compound—namely, the hexaminoferrous cation, [Fe(NH3)6]2+—and several additional functionals. In particular, the present study includes the highly parametrized generalized gradient approximations (GGAs) known as HCTH and the meta-GGA VSXC [which together we refer to as highly parametrized density functionals (HPDFs)], now readily available in the GAUSSIAN03 program, as well as the hybrid functional PBE0. Since there are very few experimental results for these molecules with which to compare, comparison is made with best estimates obtained from second-order perturbation theory-corrected complete active space self-consistent field (CASPT2) calculations, with spectroscopy oriented configuration interaction (SORCI) calculations, and with ligand field theory (LFT) estimations. While CASPT2 and SORCI are among the most reliable ab initio methods available for this type of problem, LFT embodies many decades of empirical experience. These three methods are found to give coherent results and provide best estimates of the adiabatic low-spin–high-spin energy difference, ΔELHadia, of 12 000–13 000 cm−1 for [Fe(H2O)6]2+ and 9 000–11 000 cm−1 for [Fe(NH3)6]2+. All functionals beyond the purely local approximation produce reasonably good geometries, so long as adequate basis sets are used. In contrast, the energy splitting, ΔELHadia, is much more sensitive to the choice of functional. The local density approximation severely over stabilizes the low-spin state with respect to the high-spin state. This “density functional theory (DFT) spin pairing-energy problem” persists, but is reduced, for traditional GGAs. In contrast the hybrid functional B3LYP underestimates ΔELHadia by a few thousands of wave numbers. The RPBE GGA of Hammer, Hansen, and Nørskov gives good results for ΔELHadia as do the HPDFs, especially the VSXC functional. Surprisingly the HCTH functionals actually over correct the DFT spin pairing-energy problem, destabilizing the low-spin state relative to the high-spin state. Best agreement is found for the hybrid functional PBE0.
A gauge-independent zeroth-order regular approximation to the exact relativistic Hamiltonian—Formulation and applications
Authors: Filatov Michael , Cremer Dieter
Published: January 2005

A simple modification of the zeroth-order regular approximation (ZORA) in relativistic theory is suggested to suppress its erroneous gauge dependence to a high level of approximation. The method, coined gauge-independent ZORA (ZORA-GI), can be easily installed in any existing nonrelativistic quantum chemical package by programming simple one-electron matrix elements for the quasirelativistic Hamiltonian. Results of benchmark calculations obtained with ZORA-GI at the Hartree-Fock (HF) and second-order Møller-Plesset perturbation theory (MP2) level for dihalogens X2 (X=F,Cl,Br,I,At) are in good agreement with the results of four-component relativistic calculations (HF level) and experimental data (MP2 level). ZORA-GI calculations based on MP2 or coupled-cluster theory with single and double perturbations and a perturbative inclusion of triple excitations [CCSD(T)] lead to accurate atomization energies and molecular geometries for the tetroxides of group VIII elements. With ZORA-GI/CCSD(T), an improved estimate for the atomization energy of hassium (Z=108) tetroxide is obtained.
Efficient silicon surface and cluster modeling using quantum capping potentials
Authors: DiLabio Gino A. , Wolkow Robert A. , Johnson Erin R.
Published: January 2005

A one-electron, silicon quantum capping potential for use in capping the dangling bonds formed by artificially limiting silicon clusters or surfaces is developed. The quantum capping potentials are general and can be used directly in any computational package that can handle effective core potentials. For silicon clusters and silicon surface models, we compared the results of traditional hydrogen atom capping with those obtained from capping with quantum capping potentials. The results clearly show that cluster and surface models capped with quantum capping potentials have ionization potentials, electron affinities, and highest occupied molecular orbital-lowest unoccupied molecular orbital gaps that are in very good agreement with those of larger systems. The silicon quantum capping potentials should be applied in cases where one wishes to model processes involving charges or low-energy excitations in silicon clusters and surfaces consisting of more than ca. 150 atoms.
An application of the novel quantum mechanical/molecular mechanical method combined with the theory of energy representation: An ionic dissociation of a water molecule in the supercritical water
Authors: Takahashi Hideaki , Satou Wataru , Hori Takumi , Nitta Tomoshige
Published: January 2005

A novel quantum chemical approach recently developed has been applied to an ionic dissociation of a water molecule (2H2O→H3O++OH−) in ambient and supercritcal water. The method is based on the quantum mechanical/molecular mechanical (QM/MM) simulations combined with the theory of energy representation (QM/MM-ER), where the energy distribution function of MM solvent molecules around a QM solute serves as a fundamental variable to determine the hydration free energy of the solute according to the rigorous framework of the theory of energy representation. The density dependence of the dissociation free energy in the supercritical water has been investigated for the density range from 0.1 to 0.6 g/cm3 with the temperature fixed at a constant. It has been found that the product ionic species significantly stabilizes in the high density region as compared with the low density. Consequently, the dissociation free energy decreases monotonically as the density increases. The decomposition of the hydration free energy has revealed that the entropic term (−TΔS) strongly depends on the density of the solution and dominates the behavior of the dissociation free energy with respect to the variation of the density. The increase in the entropic term in the low density region can be attributed to the decrease in the translational degrees of freedom brought about by the aggregation of solvent water molecules around the ionic solute.
Rings-on-a-string chain structure in DNA
Authors: Miyazawa Naomi , Sakaue Takahiro , Yoshikawa Kenichi , Zana Raoul
Published: January 2005

Using fluorescence microscopy (FM), which permits the observation of single molecules, we found that a pearling structure is generated on a single long DNA molecule upon the addition of a gemini (dimeric) surfactant. This pearling structure was further investigated by performing atomic force microscopy measurements on the same DNA molecules as observed by FM. These observations revealed that the pearling structure is composed of many rings that are interconnected by elongated coil parts along a single DNA molecule, i.e., rings-on-a-string structure. The mechanism of the formation of such an intrachain segregated structure in terms of microphase separation on a single polyelectrolyte chain is discussed.
Mass-analyzed threshold ionization spectroscopy of the rotamers of p-n-propylphenol cations and configuration effect
Authors: Li Changyong , Lin Jung Lee , Tzeng Wen Bih
Published: January 2005

Two-color resonant two-photon mass-analyzed threshold ionization (MATI) spectroscopy was used to record the vibrationally resolved cation spectra of the selected rotamers of p-n-propylphenol. The adiabatic ionization energies of the trans, gauche-A, and gauche-B rotamers are determined to be 65 283±5, 65 385±5, and 65 369±5 cm−1, which are less than that of phenol by 3342, 3240, and 3256 cm−1, respectively. This suggests that the n-propyl substitution causes a greater degree in lowering the energy level in the cationic than the neutral ground state. Analysis on the MATI spectra of the selected rotamers of p-n-propylphenol cation shows that the relative orientation of the p-n-alkyl group has little effect on the in-plane ring vibrations. However, the low-frequency C3H7 bending vibrations appear to be active only for the two gauche forms of the cation.
Molecular beam studies of the F atom reaction with propyne: Site specific reactivity
Authors: Ran Qin , Yang Chung Hsin , Lee Yuan T. , Lu I-Chung , Shen Guanlin , Wang Ling , Yang Xueming
Published: January 2005

The dynamics of the F atom reaction with propyne (CH3CCH) has been investigated using a universal crossed molecular beam apparatus. Two reaction channels have been clearly observed: H+C3H3F and HF+C3H3. The substitution of F for H occurs mainly via a complex formation mechanism, producing reaction products with some contribution from a direct reaction mechanism. The HF product, however, appears to be dominantly forward scattered relative to the F atom beam direction, suggesting that the HF formation occurs via a direct abstraction mechanism. Branching ratios for the two observed reaction channels are also determined. The H formation channel is found to be the major reaction pathway, while the HF formation channel is also significant. From the measurements of DF versus HF products from the F atom reaction with deuterated propyne, the H atom picked up by the F atom in the reaction with normal propyne seems to come mostly from the CH3 group. In addition, the H atom produced in the H atom formation channel appears to be mostly from the CH3 group with some contribution from the CCH group.
A study of InxGa1−xN growth by reflection high-energy electron diffraction
Authors: Liu Y. , Xie M. H. , Cao Y. G. , Wu H. S. , Tong S. Y.
Published: January 2005

Epitaxial growth of InxGa1−xN alloys on GaN(0001) by plasma-assisted molecular-beam epitaxy is investigated using the in situ reflection high-energy electron-diffraction (RHEED) technique. Based on RHEED pattern changes over time, the transition of growth mode from two-dimensional (2D) nucleation to three-dimensional islanding is studied for various indium compositions. RHEED specular-beam intensity oscillations are recorded during the 2D wetting-layer growth, and the dependences of the oscillation period/frequency on the substrate temperature and source flux are established. By measuring the spacing between diffraction spots in RHEED, we also estimated indium composition, x, in alloys grown under different flux combinations. Incorporation coefficients of both gallium and indium are derived. Possible surface segregation of indium atoms is finally examined.
Peculiar temperature aging effects on the piezoelectric constant of Pb(Mg1∕3Nb2∕3)O3-PbTiO3 single crystal near the morphotropic phase boundary
Authors: Xu Guisheng , Wang Xiaofeng , Yang Danfeng , Duan Ziqing , Feng Chude , Chen Kai
Published: January 2005

After temperature aging, peculiar changes of the piezoelectric response of 0.67Pb(Mg1∕3Nb2∕3)O3-0.33PbTiO3 crystals appeared. The piezoelectric constant d33 of the (001)-cut crystals with TRT∼35°C abruptly rose more than 1000pC∕N in some regions after heat treatment at 65°C for 12h. For the (001)-cut crystals with TRT∼74°C, in spite of a fall of 40–100pC∕N after heat treatment at 65°C for 12h, the values of d33 rose 50–100pC∕N unexpectedly after the subsequent heat treatment at 85°C for 4h. The structure adjustment caused by the internal stress relaxation during heat treatment at T>TRT accounted for the enhancement of d33.
Cooling rate dependence of specific heat in systems out of equilibrium
Authors: Tao T. , Odagaki T. , Yoshimori A.
Published: January 2005

The anomaly of specific heat in systems out of equilibrium, especially the measurement procedure dependence of specific heat, is investigated by means of free energy landscape. Introducing measurement procedure which is based on experimental method, we propose a calculation method of specific heat in systems out of equilibrium and find an abrupt change in specific heat between annealed and quenched states. For longer observation time the change in specific heat occurs at lower temperature and becomes sharper. For slower cooling of a system the transition temperature becomes lower. This cooling rate dependence of the transition temperature is consistent with experiments and thus the abrupt change in specific heat can be regarded as the glass transition which is thermally identified.
Further application of the constrained fluid λ-integration method
Authors: Grochola Gregory
Published: January 2005

Previously we proposed a three stage, and recently a single stage nonphysical λ-integration path for thermodynamically coupling bulk solid and liquid states directly. In this work we further apply these paths, specifically the newer single stage path, to the calculation of the complete truncated and shifted Lennard-Jones (Rcutoff=2.5σ) and aluminum glue potential melting lines, and the zero pressure melting point for a commonly used gold glue potential. The results showed accurate agreement with presently available literature. We found the single stage constrained fluid λ-integration methodology to be robust in terms of reversibility over this extended range of temperatures, pressures, and intermolecular potentials.
Electronic properties of artificial Au chains with individual Pd impurities
Authors: Wallis T. M. , Nilius N. , Mikaelian G. , Ho W.
Published: January 2005

Artificial Au atomic chains with individual Pd impurities were assembled from single metal atoms with a scanning tunneling microscope on a NiAl(110) surface. Scanning tunneling spectroscopy (STS) revealed an electronic resonance 2.15 eV above the Fermi energy localized within 4 Å of single Pd atom impurities and two electronic resonances 2.25 eV and 2.95 eV above the Fermi energy localized within 8 Å of Pd dimer impurities. The emergence of these localized resonances was studied by STS at each stage of the atom-by-atom assembly. Additionally, conductance images of the chains revealed delocalized electronic density oscillations in the pure Au segments of the chains.
Domain wall coupling and collective switching in interacting mesoscopic ring magnet arrays
Authors: Kläui M. , Vaz C. A. F. , Bland J. A. C. , Heyderman L. J.
Published: January 2005

The effects of magnetostatic domain wall coupling on the magnetic switching are investigated for micrometer-sized cobalt ring arrays with edge-to-edge spacings varying between 80 nm and 8μm. The various transitions between the different equilibrium states in rings are affected differently with increasing magnetostatic interaction (leading to an increased or reduced switching field) depending on the details of the particular switching mechanism. The switching field distribution width is strongly reduced for narrowly spaced ring arrays due to collective switching between adjacent rings where the domain walls couple magnetostatically. The interaction is found to increase with increasing film thickness due to the increased stray field.
Electrical properties of polycrystalline SrSi2
Authors: Imai Motoharu , Naka Takashi , Furubayashi Takao , Abe Hideki , Nakama Takao , Yagasaki Katsuma
Published: January 2005

The electrical properties of polycrystalline SrSi2 were examined by electrical resistivity measurements at temperatures ranging from 2 to 760 K and Hall coefficient measurements at temperatures ranging from 10 to 300 K. These measurements revealed that SrSi2 is a narrow-gap semiconductor with an energy gap of 0.035 eV whose dominant carriers are holes.
Thermal characterization of liquids and polymer thin films using a microcalorimeter
Authors: Zhang Yuyan , Tadigadapa Srinivas
Published: January 2005

This paper presents an integrated microfluidic thermal sensor that can be used to characterize the thermal properties of nanoliter quantities of fluids and polymer thin films. The device consists of a polycrystalline silicon (polysilicon) heater located in close proximity to the hot junctions of p+-polysilicon/gold microthermopiles fabricated on a thermally isolated membrane. ac calorimetric measurements were performed by introducing a periodic heat signal using the heater and detecting the frequency-dependent thermal signal response in the presence of various fluids and polymers. The thermal conductivity of different fluids and five typical polymers used in microfabrication was measured using this device.
High sensitivity of positive magnetoresistance in low magnetic field in perovskite oxide p–n junctions
Authors: Lu H. B. , Dai S. Y. , Chen Z. H. , Zhou Y. L. , Cheng B. L. , Jin K. J. , Liu L. F. , Yang G. Z. , Ma X. L.
Published: January 2005

Large positive magnetoresistance (MR) and high MR sensitivity in low magnetic fields have been discovered in the Sr-doped LaMnO3 and Nb-doped SrTiO3 p–n junctions fabricated by laser molecular-beam epitaxy. The MR ratios, defined as ΔR∕R0, ΔR=RH−R0, are observed as large as 11% in 5Oe, 23% in 100Oe, and 26% in 1000Oe at 290K; 53% in 5Oe, 80% in 100Oe, and 94% in 1000Oe at 255K. The MR sensitivities are 85Ω∕Oe at 290K, 246Ω∕Oe at 255K, and 136Ω∕Oe at 190K, respectively, with the applied magnetic field changed from 0to5Oe. The positive MR ratios and high MR sensitivities of the p–n junctions are very different from that of the LaMnO3 compound family.
Formation and electrical properties of Ni1−xFex nanocrystals embedded in a polyimide layers for applications as nonvolatile flash memories
Authors: Kim J. H. , Jin J. Y. , Jung J. H. , Lee I. , Kim T. W. , Lim Sung K. , Yoon C. S. , Kim Y.-H.
Published: January 2005

Self-assembled Ni1−xFex nanoparticles embedded in a polyimide (PI) matrix were formed by curing Ni1−xFex thin films with PI precursor layers. Transmission electron microscopy images and selected area electron-diffraction patterns showed that Ni1−xFex nanocrystals were created inside the PI layer. Capacitance-voltage measurements on Al/PI/nanocrystalline Ni1−xFex∕PI∕n-Si structures at 300K showed a metal-insulator-semiconductor behavior with a large flatband voltage shift due to the quantum confinement effect of the Ni1−xFex nanocrystals in spite of the possible existence of a thick tunnel PI layer, and conductance-voltage measurements showed a broad conductance peak around the flatband voltage. The present results suggest that self-assembled Ni1−xFex nanocrystals embedded in a PI layer hold promise for potential applications in nonvolatile flash memories with floating gates consisting of Ni1−xFex nanocrystals embedded in a PI layer.
Estimation of elastic compliances of planar interfacial cracks from homogeneous solutions
Authors: Gorbatikh Larissa , Popova Marina
Published: January 2005

Formation of cracks in a material as a result of the damage accumulation may change (weaken) material effective properties. The present letter suggests an approach to estimate such changes when cracks form at interfaces of dissimilar materials (for example, at matrix/inclusion boundaries or film/substrate interfaces). Generally, solution of an interface problem is required to predict compliances of interfacial cracks, with the exception of planar cracks. We show that planar cracks possess a special property in the sense that their normal compliances may be approximated from solutions in a homogeneous medium. The method is then applied to analyze elastic compliances of the rectilinear, penny-shaped, elliptical, and annular interfacial cracks.
Growth of ZnO∕MgZnO quantum wells on sapphire substrates and observation of the two-dimensional confinement effect
Authors: Zhang B. P. , Binh N. T. , Wakatsuki K. , Liu C. Y. , Segawa Y. , Usami N.
Published: January 2005

Zn O ∕ Mg Zn O single quantum wells (QWs) in which the well width changes continuously were grown on sapphire (112¯0) substrates by metalorganic chemical vapor deposition. Photoluminescence (PL) measurement revealed two emission peaks: one is position dependent and the other is not. Polarized PL spectra obtained from cleaved facets demonstrated perfect two-dimensional features of the position-dependent emission peak. The position-dependent peak was attributed to emissions due to excitons confined in the ZnO well layer, and the position-independent peak was attributed to emissions due to excitons in MgZnO barrier layers. The width dependence of the emission energy from the ZnO QW was interpreted by a simple theoretical model. Typical PL decay time of the QW emission was 360ps at 77K. It was shorter than that of the MgZnO barrier, 470ps, due to the enhanced confinement effect in the QW.
Investigation of the initial stage of growth of HfO2 films on Si(100) grown by atomic-layer deposition using in situ medium energy ion scattering
Authors: Chang Hyo Sik , Hwang Hyunsang , Cho Mann-Ho , Moon Dae Won
Published: January 2005

The initial stage of growth of HfO2 films on p-type Si(100) grown by atomic-layer deposition (ALD) was investigated using in situ medium energy ion scattering (MEIS). The interaction between adsorbed HfCl4 molecules and the oxidized Si surface was examined as a function of growth cycles. The results clearly show that island-like growth occurs during the initial HfO2 growth and the islands are then merged into a continuous atomic layer with an increase in ALD cycles. The morphology of thicker HfO2 films remained essentially unchanged with growth cycles. Interfacial reactions between Hf and Si during the initial growth stage were minimal. As a result, the effect of insufficient nucleation density is a dominant factor in the initial stage of growth of hafnium oxide on the oxidized Si substrate, resulting in nonlinear growth behavior.
Self-assembled patterns of nanospheres with symmetries from submicrons to centimeters
Authors: Chen Kun , Taflove Allen , Kim Young L. , Backman Vadim
Published: January 2005

We report pattern formations during the drying of a sheet of an aqueous suspension of nanospheres. The structures self-assembled by nanospheres span several centimeters and exhibit order at scales ranging from nanometers to centimeters, although the substrate has no predefined pattern. Within these structures, several regular patterns can be identified, including two-dimensional periodic gratings generated by crack networks with a characteristic spatial frequency linearly depending on the evaporation speed, and three-dimensional flower-like structures. This phenomenon potentially provides a simple and inexpensive method to grow structures having unique electromagnetic and/or biological properties.
Rare earth ion size effects and enhanced critical current densities in Y2∕3Sm1∕3Ba2Cu3O7−x coated conductors
Authors: MacManus-Driscoll J. L. , Foltyn S. R. , Maiorov B. , Jia Q. X. , Wang H. , Serquis A. , Civale L. , Lin Y. , Hawley M. E. , Maley M. P. , Peterson D. E.
Published: January 2005

The influence of rare earth (RE) ion size on critical current density (Jc) in epitaxial films of superconducting REBa2Cu3O7−x was studied, where RE is the mixture of two or three rare earth ions. No systematic dependence of Jc on RE ion size was found. However, strongly enhanced critical current densities (Jc’s) were found for the composition Y2∕3Sm1∕3Ba2Cu3O7−x (YSmBCO). In ∼1-μm-thick films, Jc’s as high as 4.7×106Acm−2 (75.5K,0T) and 11×104Acm−2 (75.5K,5T) were obtained on single crystals and 6×104Acm−2 (75.5K,5T) on buffered metal. The values are up to a factor of 3 higher than for comparative YBCO samples.
Properties of nonpolar a-plane InGaN∕GaN multiple quantum wells grown on lateral epitaxially overgrown a-plane GaN
Authors: Chakraborty Arpan , Keller Stacia , Meier Cedrik , Haskell Benjamin A. , Keller Salka , Waltereit Patrick , DenBaars Steven P. , Nakamura Shuji , Speck James S. , Mishra Umesh K.
Published: January 2005

The properties of nonpolar a-plane InGaN∕GaN multiple-quantum wells (MQWs), grown simultaneously on lateral epitaxially overgrown (LEO) a-plane GaN and planar a-plane GaN, were studied. High-resolution x-ray diffraction analysis revealed that the In mol fraction in the MQWs grown on LEO-GaN was significantly lower than that on planar a-plane GaN. The lower In incorporation was confirmed by microphotoluminescence (μ-PL) and wide-area photoluminescence measurements, which showed a redshift of the MQW emission from 413 nm for the nearly defect-free laterally overgrown regions to 453 nm for the defective “window” regions of the LEO a-plane GaN, to 478 nm for the high-defect density planar a-plane GaN. μ-PL measurements also demonstrated that the emission from the nearly defect-free wings of the LEO a-plane GaN was more than ten times stronger than the emission from the defective windows.
Corner overgrowth: Bending a high mobility two-dimensional electron system by 90°
Authors: Grayson M. , Schuh D. , Huber M. , Bichler M. , Abstreiter G.
Published: January 2005

Introducing an epitaxial growth technique called corner overgrowth, we fabricate a quantum confinement structure consisting of a high-mobility GaAs∕AlGaAs heterojunction overgrown on top of an ex situ cleaved substrate corner. The resulting corner-junction quantum-well heterostructure effectively bends a two-dimensional electron system (2DES) at an atomically sharp 90° angle. The high-mobility 2DES demonstrates fractional quantum Hall effect on both facets. Lossless edge-channel conduction over the corner confirms a continuum of 2D electrons across the junction, consistent with Hartree calculations of the electron distribution. This growth technique differs distinctly from cleaved-edge overgrowth and enables a complementary class of embedded quantum heterostructures.
Plasmon scattering from a single gold nanoparticle collected through an optical fiber
Authors: Eah Sang-Kee , Jaeger Heinrich M. , Scherer Norbert F. , Wiederrecht Gary P. , Lin Xiao-Min
Published: January 2005

A single gold nanoparticle is attached to the end of a chemically etched fiber axicon microlens tip by modifying the tip surface with linker molecules. The high collection efficiency of the fiber axicon microlens allows plasmon scattering of a single nanoparticle to be measured directly through the optical fiber. The portable nature of this probe allows direct optical sensing of environmental changes using a single nanoparticle.
Millimeter wave mixing using plasmon and bolometric response in a double-quantum-well field-effect transistor
Authors: Lee Mark , Wanke M. C. , Reno J. L.
Published: January 2005

Heterodyne mixing characteristics of a double-quantum-well field-effect transistor (DQW FET) from 94 to 145GHz are reported. The DQW FET exhibits two physically distinct mixing responses. Near pinch-off, the device behaves as a broadband bolometric mixer with intermediate frequency (IF) bandwidth of 620MHz. Away from pinch-off it shows an electrically tunable resonant plasmon response. Mixing on a plasmon resonance yields an IF with significant harmonic distortion, signaling a complicated nonlinear mechanism, and shows a wide IF bandwidth >2GHz.
Josephson junctions with nonlinear damping for rapid single-flux-quantum - qubit circuits
Authors: Zorin A. B. , Khabipov M. I. , Balashov D. V. , Dolata R. , Buchholz F.-I. , Niemeyer J.
Published: January 2005

We demonstrate that shunting of superconductor-insulator-superconductor (S-I-S) Josephson junctions by superconductor-insulator-normal metal (S-I-N) structures having pronounced nonlinear I–V characteristics can remarkably modify the Josephson dynamics. In the regime of Josephson generation the phase behaves as an overdamped coordinate, while in the superconducting state the damping and current noise are strikingly small, that is vitally important for application of such junctions for readout and control of Josephson qubits. Superconducting Nb/AlOx/Nb junction shunted by Nb/AlOx/AuPd junction of S-I-N type was fabricated and, in agreement with our model, exhibited nonhysteretic I–V characteristics at temperatures down to at least 1.4 K.
Probing the size and density of silicon nanocrystals in nanocrystal memory device applications
Authors: Feng Tao , Yu Hongbin , Dicken Matthew , Heath James R. , Atwater Harry A.
Published: January 2005

Structural characterization via transmission electron microscopy and atomic force microscopy of arrays of small Si nanocrystals embedded in SiO2, important to many device applications, is usually difficult and fails to correctly resolve nanocrystal size and density. We demonstrate that scanning tunneling microscopy (STM) imaging enables a much more accurate measurement of the ensemble size distribution and array density for small Si nanocrystals in SiO2, estimated to be 2–3 nm and 4×1012–3×1013cm−2, respectively, in this study. The reflection high energy electron diffraction pattern further verifies the existence of nanocrystallites in SiO2. The present STM results enable nanocrystal charging characteristics to be more clearly understood: we find the nanocrystal charging measurements to be consistent with single charge storage on individual Si nanocrystals. Both electron tunneling and hole tunneling processes are suggested to explain the asymmetric charging∕discharging processes as a function of bias.
Effect of double-sided (Pb0.72La0.28)Ti0.93O3 buffer layers on the ferroelectric properties of Pb(Zr0.52Ti0.48)O3 thin films
Authors: Lee Eun Sun , Chung Hyun Woo , Lim Sung Hoon , Lee Sang Yeol
Published: January 2005

We deposited the Pb(Zr0.52Ti0.48)O3 (PZT) thin films with single and double-sided (Pb0.72La0.28)Ti0.93O3 (PLT) buffers by using a pulsed-laser deposition method. With the PLT buffer layers, the remanent polarization values increased, and a remanent polarization value of 33.4μC∕cm2 was obtained when 10-nm-thick double-sided PLT buffer layers were used. While the coercive field of films slightly increased only with a single-sided PLT buffer, it decreased again by adding the top PLT buffer layer. The film with double-sided PLT buffer also exhibited good fatigue endurance after 109 switching cycles even without oxide electrodes, mainly because the accumulated charges were compensated at the interface junction between the PLT buffer layer and the electrode.
Investigation of plasma hydrogenation and trapping mechanism for layer transfer
Authors: Chen Peng , Chu Paul K. , Höchbauer T. , Lee J.-K. , Nastasi M. , Buca D. , Mantl S. , Loo R. , Caymax M. , Alford T. , Mayer J. W. , Theodore N. David , Cai M. , Schmidt B. , Lau S. S.
Published: January 2005

Hydrogen ion implantation is conventionally used to initiate the transfer of Si thin layers onto Si wafers coated with thermal oxide. In this work, we studied the feasibility of using plasma hydrogenation to replace high dose H implantation for layer transfer. Boron ion implantation was used to introduce H-trapping centers into Si wafers to illustrate the idea. Instead of the widely recognized interactions between boron and hydrogen atoms, this study showed that lattice damage, i.e., dangling bonds, traps H atoms and can lead to surface blistering during hydrogenation or upon postannealing at higher temperature. The B implantation and subsequent processes control the uniformity of H trapping and the trap depths. While the trap centers were introduced by B implantation in this study, there are many other means to do the same without implantation. Our results suggest an innovative way to achieve high quality transfer of Si layers without H implantation at high energies and high doses.
Characterization of femtosecond light pulses coupled to hollow-pyramid near-field probes: Localization in space and time
Authors: Labardi M. , Zavelani-Rossi M. , Polli D. , Cerullo G. , Allegrini M. , De Silvestri S. , Svelto O
Published: January 2005

We perform the in situ characterization, by second-order optical autocorrelation, of femtosecond pulses transmitted by near-field optical probes. We demonstrate that transmission through hollow pyramid probes with diameter down to 65 nm has negligible effects on the duration of pulses as short as 30 fs. We also show that such probes allow obtaining, at their output, sufficient peak power to perform nonlinear optical experiments in the near field on such a space and time scale.
Influence of the gate leakage current on the stability of organic single-crystal field-effect transistors
Authors: de Boer R. W. I. , Iosad N. N. , Stassen A. F. , Klapwijk T. M. , Morpurgo A. F.
Published: January 2005

We investigate the effect of a small leakage current through the gate insulator on the stability of organic single-crystal field-effect transistors (FETs). We find that, irrespective of the specific organic molecule and dielectric used, leakage current flowing through the gate insulator results in an irreversible degradation of the single-crystal FET performance. This degradation occurs even when the leakage current is several orders of magnitude smaller than the source-drain current. The experimental data indicate that a stable operation requires the leakage current to be smaller than 10−9A∕cm2. Our results also suggest that gate leakage currents may determine the lifetime of thin-film transistors used in applications.
Reconstruction of refractive index discontinuities from truncated phase-contrast tomography projections
Authors: Shi Daxin , Anastasio Mark A. , Pan Xiaochuan
Published: January 2005

Propagation-based phase-contrast tomography is a noninterferometric imaging technique that can reconstruct the complex refractive index distribution of an object. To accomplish such a reconstruction using existing methods, however, there must be no truncation of the phase-contrast projection data in the detector planes at each tomographic view angle. We demonstrate that local tomography reconstruction theory can be applied for reconstruction of refractive index discontinuities in two-dimensional objects from truncated phase-contrast projections acquired in the near-Fresnel zone. Numerical results are presented to corroborate our theoretical assertions.
Demonstration of low-cost Si-based tunable long-wavelength resonant-cavity-enhanced photodetectors
Authors: Mao R. W. , Zuo Y. H. , Li C. B. , Cheng B. W. , Teng X. G. , Luo L. P. , Yu J. Z. , Wang Q. M.
Published: January 2005

A simple process for fabricating low-cost Si-based continuously tunable long-wavelength resonant-cavity-enhanced (RCE) photodetectors has been investigated. High-contrast SiO2∕Si(Δn∼2) was employed as mirrors to eliminate the need to grow thick epitaxial distributed Bragg reflectors. Such high-reflectivity SiO2∕Si mirrors were deposited on the as-grown InGaAs epitaxy layers, and then were bonded to silicon substrates at a low temperature of 350 °C without any special treatment on bonding surfaces, employing silicate gel as the bonding medium. The cost is thus decreased. A thermally tunable Si-based InGaAs RCE photodetector operating at 1.3–1.6 μm was obtained, with a quantum efficiency of about 44% at the resonant wavelength of 1476 nm and a tuning range of 14.5 nm. It demonstrates a great potential for industry processes.
Photonic quasicrystal single-cell cavity mode
Authors: Kim Sun-Kyung , Lee Jee-Hye , Kim Se-Heon , Hwang In-Kag , Lee Yong-Hee , Kim Sung-Bock
Published: January 2005

We propose and realize the photonic quasicrystal (PQC) single-cell resonator based on a InP-InGaAsP freestanding slab. A well-defined hexapole-like localized state following a C6ν symmetry is identified from the PQC single-cell resonator. In this type of hexapole mode, the electromagnetic energy is strongly concentrated on the dielectric region, in contrast to that in a triangular lattice photonic crystal. By tailoring the structural parameters, the hexapole mode shows a maximum theoretical quality factor of ∼20000. The PQC single-cell resonator lases in a single hexapole mode with a threshold of ∼0.6mW at room temperature.