bluuebunny/crossref_metadata_2025 huggingface dataset:
Method for shallow impurity characterization in ultrapure silicon using photoluminescence
Authors: Broussell I. , Stotz J. A. H. , Thewalt M. L. W.
Published: November 2002

The advantages of very low excitation density photoluminescence for the quantitative determination of shallow impurity concentrations in ultrapure Si are demonstrated using the weakly-absorbed 1047 nm output of a Nd:YLF laser. Compared to the usual high excitation method, which uses an argon ion laser, the weak bound exciton luminescence is significantly enhanced relative to that of the free exciton, and competing luminescence from multiexcitonic species, which complicates the accurate determination of the bound exciton intensities, is eliminated. Also, the presence of the laser Raman line in the same spectral region as the luminescence allows for the accurate determination of relative luminescence quantum efficiencies and can reveal the presence of deep traps. Finally, we report calibrations for boron, phosphorus, and arsenic in the concentration range 1011 to 1015 cm−3.
Equation of state of bismuth to 222 GPa and comparison of gold and platinum pressure scales to 145 GPa
Authors: Akahama Yuichi , Kawamura Haruki , Singh Anil K.
Published: November 2002

Unit cell volumes of Bi, Pt, and Au have been measured simultaneously to megabar pressures by x-ray powder diffraction using a diamond anvil cell and a synchrotron radiation source. The body-centered cubic (bcc) phase of Bi was found to be stable up to 222 GPa. The equation of state (EoS) of bcc-Bi was determined using the Pt pressure scale. A fit of the Vinet EoS to the volume compression data gave B0=35.22(19) GPa, B0′=6.303(18), and 1 atm atomic volume V0=31.60(4) A3. Because of the high compressibility, the use of bcc-Bi as a pressure marker is expected to give improved precision in pressure measurement. The Pt and Au pressure scales were compared up to 145 GPa. The Au pressure scale gave lower pressure than the Pt pressure scale. The deviation between the two scales became noticeable at ∼30 GPa and diverged with increasing pressure, reaching ∼20 GPa at 145 GPa. A fit of the Vinet EoS to Au compression data on the Pt pressure scale gave: B0=166.34(77) GPa, and B0′=6.244(33).
The efficient optimization of molecular geometries using redundant internal coordinates
Authors: Bakken Vebjørn , Helgaker Trygve
Published: November 2002

The optimization of ab initio molecular geometries is discussed. Based on comparisons of 30 minimizations and 15 saddle-point optimizations, the most efficient combination of coordinate system, approximate and exact Hessians, and step control is determined. Use of a proposed set of extra-redundant internal coordinates is shown to reduce the number of geometry steps significantly relative to the use of redundant coordinates. Various update schemes are tested for minimum and saddle-point optimizations, including combination formulas. The complete expressions for the first and second derivatives of the Wilson B matrix are presented, thereby avoiding the need to calculate this by finite-difference methods. The presented scheme appears to be the most efficient, robust and generally applicable scheme to date.
Polarization consistent basis sets. III. The importance of diffuse functions
Authors: Jensen Frank
Published: November 2002

A sequence of diffuse functions to be used in connections with the previously defined polarization consistent basis sets are proposed based on energetic criteria and results for molecular properties. At the Hartree–Fock level the addition of a single set of diffuse s- and p-functions significantly improves the convergence of calculated electron affinities. A corresponding analysis at the density functional level indicates that only systems with high electron affinities have well-defined basis set limits with common exchange-correlation functionals that have electron self-interaction errors. The majority of reported density functional calculations of electron affinities appear to be artifacts of the limited basis set used. The good agreement with experiments for such calculations is most likely due to a reasonable modeling of the physics of the anionic species, rather than being a theoretically sound procedure. For molecular properties like dipole and quadrupole moments, and static polarizabilities, the addition of diffuse functions up to d-functions is required to reach the basis set limit in a consistent fashion, but higher order angular momentum functions are significantly less important.
A transferable polarizable electrostatic force field for molecular mechanics based on the chemical potential equalization principle
Authors: Chelli Riccardo , Procacci Piero
Published: November 2002

A polarizable electrostatic potential model for classical molecular mechanics is presented. Based on the chemical potential equalization (CPE) principle, the model is developed starting from the original formulation of Mortier, Ghosh, and Shankar [J. Am. Chem. Soc. 108, 4315 (1986)]. Following York and Yang [J. Chem. Phys. 104, 159 (1996)] we present an SP-basis CPE parametrization to describe realistically any sort of molecular system. By fitting ab initio electronic properties, such as dipole moment, polarizability and global molecular hardness of a restricted set of organic molecules, we derive atomic parameters to be applied to a more vast target set of compounds. We show, indeed, that the atomic CPE parameters calculated for the learning set of molecules give reliable values for several electronic properties of various compounds not included in the learning set. The multipole moments obtained by using the proposed CPE parametrization are compared to the results of a fixed charge parametrization like that used by a popular classical molecular mechanics force field, such as AMBER. We show that the fixed charge parametrization can well reproduce only the multipole moments of the molecular conformation or the isomer used for the fit, while being inaccurate when different molecular conformations or isomers are considered. On the contrary, the CPE model realistically reproduces the charge reorganization due to nuclear structural changes of the molecule, such as isomerization or conformational transition. The CPE model has been also tested on various molecular complexes to investigate the polarization response in the case of realistic molecule–molecule interactions. The main result of the paper is the demonstration that the construction of a general polarizable electrostatic force field for classical molecular mechanics is now a viable way.
Self-induced nonlinear Zernike filter realized with optically addressed liquid crystal spatial light modulator
Authors: Komorowska K. , Miniewicz A. , Parka J. , Kajzar F.
Published: November 2002

Visualization of phase objects introducing small distortions to a plane wave front (such as turbulence of air) can be realized with the well-known Zernike filtering. In this work we discuss and present the use of an optically addressed liquid crystal spatial light modulator (OA LC SLM) performing self-induced nonlinear Zernike-type filtering. The OA LC SLM is made of a planar nematic liquid crystal layer sandwiched between a photoconductor (PVK:TNF 100-nm-thick polymer) and a polyimide orienting layer. The advantage of such a nonlinear Zernike filter over a conventional one is that no precise optical adjustment is necessary and the filtering is relatively easy to control by tuning the externally applied field to the modulator and the incoming light intensity.
Nonisothermal creep of bulk Zr52.5Ti5Cu17.9Ni14.6Al10 metallic glass
Authors: Berlev A. E. , Bobrov O. P. , Csach K. , Kaverin V. L. , Khonik V. A. , Kitagawa K. , Miškuf J. , Yurikova A.
Published: November 2002

The article presents the results of nonisothermal creep measurements of the Zr52.5Ti5Cu17.9Ni14.6Al10 bulk metallic glass in a wide range of heating rates well below and in the vicinity of the glass transition temperature Tg. It is shown that the shear viscosity η is strongly dependent on the heating rate Ṫ:η increases linearly with Ṫ−1 at TTg. It is argued that the heating rate dependence of the shear viscosity below the glass transition region is controlled by irreversible structural relaxation and can be quantitatively described by the directional structural relaxation model. A possible reason for the η(Ṫ) dependence in the glass transition region is discussed.
Double loop hysteresis in direct current dependent dielectric permittivity of SrTiO3
Authors: Gevorgian S. , Eriksson A. , Deleniv A. , Pandey D.
Published: November 2002

Experimental double loop hysteresis in dc field dependent dielectric permittivity in bulk single crystal SrTiO3 is reported. Small signal measurements of the permittivity are performed in the frequency range 0.5–1.5 GHz at temperatures below 77 K using electrically thin circular parallel-plate resonators. The dielectric permittivity is extracted form the measured resonant frequency. The double loop hysteresis may be caused by field induced local paraelectric/ferroelectric phase transitions, and/or switching (polarization reversal) in local opposing ferroelectric domains associated with symmetry breaking impurities/structural defects.
Compressively strained p-type InGaAs/AlGaAs quantum-well infrared photodetectors
Authors: Zhang D. H. , Shi W. , Li N. , Chu Junhao
Published: November 2002

The compressively strained p-type In0.15Ga0.85As/Al0.33Ga0.67As quantum-well infrared photodetectors (QWIPs) with different Be concentrations in their wells, which detect normal infrared incidence, were investigated. The QWIPs with a Be doping density of 1018 cm−3 in the wells show a cutoff wavelength of 7.9 μm and basically symmetric detectivities of about 8×108 cm Hz1/2/W at 600 Hz. By increasing the Be doping density in the wells to 2×1019 cm−3, the cutoff wavelength is blueshifted to about 7.25 meV and the photoresponsivity and detectivity become asymmetric. The detectivity is increased to about 1.4×109 cm Hz1/2/W at positive biases but significantly reduced at negative biases. The blueshift in the cutoff wavelength for the QWIP devices with heavy doping concentration in the wells is mainly due to the band-gap shrinkage and the increased well width while the asymmetric behavior in the photoresponsivity and detectivity is likely due to the inhomogenity resulting from dopant diffusion at high doping.
Calculated potential profile near charged threading dislocations at metal/semiconductor interfaces
Authors: Tivarus C. , Ding Y. , Pelz J. P.
Published: November 2002

We have made finite element calculations of the expected potential profile around negatively charged threading dislocations (TDs) close to a metal–semiconductor interface, using a Pt contact on n-type GaN as a specific case. The potential was calculated as a function of the assumed linear density and energy level of TD-related acceptors. Our model shows good agreement with the model of Read [W. T. Read, Philos. Mag. 45, 775 (1954); 46, 111 (1954)] for an infinite dislocation, far from any interface. Assuming 1 acceptor/c-axis lattice spacing (c=0.52 nm), we found for our near-surface modeling that acceptors levels deeper than 1.3 eV below the conduction band minimum (CBM) should be charged all the way to the Pt/GaN interface. This should produce a significant local increase in the potential barrier and at the Pt/GaN interface and should be observable by ballistic electron emission microscopy (BEEM). In fact recent BEEM measurements by Im et al. on molecular beam epitaxy-grown GaN films [Phys. Rev. Lett. 87, 106802 (2001)] showed no significant increased barrier at TDs indicating an acceptor energy within 1.3 eV of CBM and/or an acceptor density less then 1 acceptor/c-axis lattice spacing.
A molecular dynamics simulation study of the viscoelastic properties of polymer nanocomposites
Authors: Smith Grant D. , Bedrov Dmitry , Li Liwei , Byutner Oleksiy
Published: November 2002

We have carried out molecular dynamics simulations of model polymer–nanoparticle composites (PNCs) consisting of coarse-grained bead-necklace polymer chains and roughly spherical nanoparticles comprised of like beads for the purpose of gaining understanding of the influence of the nanoparticle–polymer interface on the viscoelastic properties of PNCs. The dynamic shear modulus Gc(t) and viscosity ηc of the PNCs were determined as a function of nanoparticle volume fraction, specific nanoparticle–polymer interfacial area, and the nature of the nanoparticle–polymer interaction. The viscoelastic properties of the PNCs were well described as a product of a polymer matrix dynamic shear modulus or viscosity and a particle volume fraction dependent effect independent of particle size, analogous to treatments of conventional particle composites. In contrast to many conventional composites, however, the viscoelastic properties of the polymer matrix were strongly perturbed by the nanoparticles and depended upon the nature of the nanoparticle–polymer interactions.
Self-diffusion coefficient of dense fluids from the pair correlation function
Authors: Bretonnet Jean-Louis
Published: November 2002

An analysis of the entropy dependence of the diffusion coefficient is presented in terms of the positional correlations in a fluid of hard spheres, with the objective to investigate the scaling law relating the diffusion coefficient and the excess entropy proposed many years ago and established empirically by the simulations. It is found that the exponential behavior between the reduced diffusion coefficient and the excess entropy is observable over a restricted range of densities, where the hydrodynamic behavior of the hard-sphere fluid is readily describable by a nearly exponential velocity autocorrelation function as prescribed by the Enskog theory. From this analysis, a semiempirical expression for the diffusion coefficient of the dense fluids is proposed in terms of the pair correlation function.
Vibrational predissociation of van der Waals molecules: An internal collision, angular momentum model
Authors: McCaffery Anthony J. , Marsh Richard J.
Published: November 2002

We describe an “internal collision” model of vibrational predissociation (vpd) in triatomic van der Waals (vdW) molecules based on the angular momentum (AM) model of collision-induced vibration–rotation transfer. The probability of vpd is related to the probability of disposing the vibrational energy into rotational and orbital AM. In T-shaped species, two internal collision configurations are likely to dominate namely, the turning points of excursions by the weakly bound species relative to the diatomic. These two geometries result in a bimodal distribution of final rotational states. Velocity-AM diagrams demonstrate why halogen and hydride vdW molecules have very different properties and illustrate the physics of quantitative calculations that reproduce experimental distributions in a wide range of vdW molecules. We introduce an analogy between a metastable dissociative state and the optical resonator and define a quality factor (Qjl) that relates vpd lifetime to stored energy and to ease of generating rotational and orbital AM by dissociation. Data on vdW molecules of OH are analyzed using the Qjl concept and the accelerated dissociation on forming the vdW complex with an efficient energy acceptor is likened to the formation of a particularly low-Q molecular resonator.
Double-resonance spectroscopy of quasi-linear Rydberg states of water
Authors: Glab W. L.
Published: November 2002

We have studied quasi-linear autoionizing Rydberg states of the water molecule with three quanta of bending vibration using double-resonance excitation through the quasi-linear (Ã)3pb2 state. The use of double resonance resulted in vibrational and rotational selectivity which led to simple, easily understood spectra. We have identified and performed an analysis on one ns series and two nd series (σ and π), yielding quantum defects for the series and an improved value of the energy of the ionic state which is the convergence limit for these Rydberg states. At low n, the 4dπ state showed vibronic splitting consistent with the Σ–Δ splitting in the ion core. This splitting vanished at high n as the Rydberg electron uncoupled from the ion core. Comparison of the spectra of bent and linear states in the same energy region displayed the effects of linear-bent interactions on the Rydberg spectrum.
Statistical angular correlation coefficients of atomic Hartree–Fock orbitals
Authors: Koga Toshikatsu , Kawata Yoshihisa
Published: November 2002

When the probe function f(r) is chosen to be f(r)=r, the statistical correlation coefficient τ[f] reduces to the angular correlation coefficient τ[r], which provides an overall measure of the difference between the electron-pair density and the product of single-electron densities. For a pair of atomic Hartree–Fock spin–orbitals i and j, the characteristics of the angular correlation coefficient τij[r] are studied. The coefficient τij[r] is found to be negative for two spin–orbitals with the same spin and with azimuthal quantum numbers different by unity and zero for other cases. It is shown that τij[r] is expressible in terms of the generalized electron-pair moments 〈q2〉(a,b)ij relevant to the spin–orbitals i and j. Especially, the relation for a=b=1 means that τij[r] is nothing but the difference between the center-of-mass motion and relative motion contributions of two electrons in those spin–orbitals. A numerical examination of 102 neutral atoms shows that the angular correlation is generally largest between the outermost s and p subshells.
Electrically induced charge separation and resistance change in Xe-doped and F-doped amorphous SiOx double layer thin films
Authors: Okada Fumio
Published: November 2002

An electronic material, a rare gas- and halogen-doped amorphous thin film, has been designed and developed applying the excitation and charge separation mechanisms of excimers in condensed phases. Xe-doped and F-doped amorphous SiOx double layer thin films were fabricated using a conventional sputtering method, aiming at the creation of a functioning material that utilizes electrically induced charge separation in the films. The films showed a constant resistance of 20 Ω upon applying AC voltages of 0–12 V, and the current increased linearly with increasing applied voltage. However, when the threshold voltage of 13 V was applied, the resistance of the films suddenly and dramatically increased to more than 40 MΩ, the upper measurable limit of the tester, resulting in no current through the film. The order of magnitude in resistance increment is much greater than those of conventional substances, such as positive temperature coefficient materials. A model, in which electrically induced charge transfer from Xe to F gives rise to the formation of an electrically neutral layer, is proposed.
Thermal return reflection method for resolving emissivity and temperature in radiometric measurements
Authors: Woskov P. P. , Sundaram S. K.
Published: November 2002

A radiometric method for resolving emissivity ε and temperature T in thermal emission measurements is presented. Thermal radiation from a viewed source is split by a beamsplitter between a radiometer and a mirror aligned to return a part of the thermal radiation back to the source. The ratio of the thermal signal with and without a return reflection provides a measurement of the emissivity without need of any other probing sources. The analytical expressions that establish this relationship are derived taking into account waveguide/optic losses and sources between the radiometer and viewed sample. The method is then applied to thermal measurements of several refractory materials at temperatures up to 1150 °C. A 137 GHz radiometer is used to measure the emissivity and temperature of an alumina brick, an Inconel 690 plate, and two grades of silicon carbide. Reasonable temperature agreement is achieved with an independent thermocouple measurement. However, when the emissivity approaches zero, as in the case of the Inconel plate, radiometric temperature determinations are inaccurate, though an emissivity near zero is correctly measured. This method is expected to be of considerable value to noncontact thermal analysis applications of materials.
Acceptor binding energy in δ-doped GaAs/AlAs multiple-quantum wells
Authors: Zheng W. M. , Halsall M. P. , Harmer P. , Harrison P. , Steer M. J.
Published: November 2002

A series of Be δ-doped GaAs/AlAs multiple-quantum wells with the doping at the well center were grown by molecular beam epitaxy. The photoluminescence spectra were measured at 4, 20, 40, 80, 120, and 200 K, respectively. The two-hole transitions of the acceptor-bound exciton from the ground state, 1S3/2(Γ6), to the first-excited state, 2S3/2(Γ6), have been clearly observed and the acceptor binding energy measured. A variational calculation is presented to obtain the acceptor binding energy as a function of well width. It is found that the experimental results are in good agreement with the theory.
Ab initio x-ray scattering of liquid water
Authors: Krack Matthias , Gambirasio Alfredo , Parrinello Michele
Published: November 2002

A direct calculation of the coherent x-ray scattering spectrum of liquid water under ambient conditions is presented using ab initio density functional theory. The experimental data are compared with the calculated x-ray scattering spectra retrieved from the trajectories of two Car–Parrinello molecular dynamics runs of about 10 ps with 32 and 64 water molecules in the simulation cell, respectively. Furthermore, the x-ray spectra obtained from molecular dynamics runs of 20 ps for 128 water molecules using empirical water models are presented. All calculations were performed with the QUICKSTEP code, which includes an all-electron implementation of the Gaussian augmented plane wave method. It is shown that by this approach one can assess how well different models describe the structural properties of water.
Enhancement of the activation energy in coupled CdTe/ZnTe quantum dots and quantum-well structures with a ZnTe thin separation barrier
Authors: Lee H. S. , Lee K. H. , Choi J. C. , Park H. L. , Kim T. W. , Choo D. C.
Published: November 2002

Temperature-dependent photoluminescence measurements showed that the activation energy of CdTe/ZnTe quantum dots (QDs) coupled with a quantum well is much larger than that of the QDs alone, This behavior is attributed to the tunneling of carriers via a thin separation layer from the quantum well to the QDs. The present observations can help improve understanding of the enhancement of the activation energy in coupled CdTe/ZnTe nanostructures.
Large-scale atomistic simulations of atomic displacements, stresses, and strains in nanoscale mesas: Effect of mesa edges, corners, and interfaces
Authors: Makeev Maxim A. , Madhukar Anupam
Published: November 2002

Large-scale atomistic simulations are performed to study the atomic displacements, stresses, and strains in the Stillinger–Weber model of nanoscale Si(001) bare and Ge overlayer covered mesas. Considerable inhomogeneity in the atomic displacement fields in the vicinity of the mesa edges, corners, and at the lattice-mismatched Ge/Si interface is observed, maximum displacements being as large as 0.6 Å even for an uncovered mesa. For Ge overlayer covered mesas, relaxation in the mesa interior and deep into the substrate is observed. The relationship between the off-diagonal components of the stress and strain tensors is found to become non-linear in the vicinity of the mesa edges for both bare and covered mesas.
Green ErIII luminescence in fractal ZnO nanolattices
Authors: Kohls Marco , Bonanni Marc , Spanhel Lubomir , Su Dangsheng , Giersig Michael
Published: November 2002

Tetrahedral [Zn4O(OAc)6]-clusters grow in alcohol in the presence of ErIII and SiIV ions to self-similar tetrahedral ZnO nanocrystals (with sizes d=5–6 nm). The nanoparticulate ZnO films prepared from these colloids show green ErIII fluorescence. The Klafter–Blumen theory is used to fit the fluorescence decay data. From this fit, the donor life time τD and the exponent β were determined to be τD=4.3 μs and β=0.289, indicating that the interior space of the codoped ZnO nanocrystallites is fractal.
Stacking fault formation in highly doped 4H-SiC epilayers during annealing
Authors: Chung H. J. , Liu J. Q. , Skowronski M.
Published: November 2002

Stacking fault formation in n+ 4H-SiC epilayers (n=9×1019 cm−3) deposited on the 4H-SiC substrates (n=5×1018 cm−3) has been observed by conventional and high-resolution transmission electron microscopy (HRTEM). Formation of faults occurred during annealing in Ar at 1150 °C for 90 min. All faults were identical double layer Shockley faults formed by the glide of partial dislocations on two neighboring basal planes. The sign of the Burgers vector for several of the partial dislocations bounding the faults at the epilayer/substrate interface has been determined by HRTEM. Approximately half the dislocations had a sign corresponding to the extra half-plane inserted into the epilayer, while the other half resulted in the removal of the same half-plane from the film. In one case, two faults bounded by opposite sign dislocations were separated by only 80 nm. This result is inconsistent with mechanical stress due to the doping difference between the epilayer and the substrate as a driving force of fault expansion.
Infrared spectroscopy of hydrogen in ZnO
Authors: McCluskey M. D. , Jokela S. J. , Zhuravlev K. K. , Simpson P. J. , Lynn K. G.
Published: November 2002

Zinc oxide (ZnO) is a wide-band gap semiconductor that has attracted tremendous interest for optical, electronic, and mechanical applications. First-principles calculations by [C. G. Van de Walle, Phys. Rev. Lett. 85, 1012 (2000)] have predicted that hydrogen impurities in ZnO are shallow donors. In order to determine the microscopic structure of hydrogen donors, we have used IR spectroscopy to measure local vibrational modes in ZnO annealed in hydrogen gas. An oxygen–hydrogen stretch mode is observed at 3326.3 cm−1 at a temperature of 8 K, in good agreement with the theoretical predictions for hydrogen in an antibonding configuration. The results of this study suggest that hydrogen annealing may be a practical method for controlled n-type doping of ZnO.
Selectively excited photoluminescence of GaAs1−xSbx/GaAs single quantum wells
Authors: Luo X. D. , Hu C. Y. , Xu Z. Y. , Luo H. L. , Wang Y. Q. , Wang J. N. , Ge W. K.
Published: November 2002

GaAsSb/GaAs single quantum wells grown by molecular-beam epitaxy are studied by selectively excited photoluminescence measurements. We have simultaneously observed the photoluminescence (PL) from both type-I and type-II transitions in the samples. The two transitions exhibit different PL behavior under different excitation energies. As expected, the peak energy of the type-I emission remains constant in the entire excitation energy range we used, while the type-II transition shows a significant blueshift with increasing excitation energy. The observed blueshift can be well explained by an electron–hole charge separation model at interface. This result, along with the excitation-power-dependent PL and the measured longer carrier decay time, provides more direct information on the type-II nature of the band alignment in GaAsSb/GaAs quantum well structures.
A Raman scattering study of self-assembled pure isotope Ge/Si(100) quantum dots
Authors: Kolobov A. V. , Morita K. , Itoh K. M. , Haller E. E.
Published: November 2002

Use of self-assembled Ge/Si(100) quantum dots (QDs) grown from pure isotope Ge70 and Ge76 sources provides a unique possibility to experimentally deconvolute contributions from Ge QDs and Si substrate into the Raman spectrum. We demonstrate that raw Raman spectra of Ge/Si(100) QDs are dominated by the Si substrate. We further show that intermixing in the QDs depends on the dot size and is stronger in smaller dots, and that the Ge-rich area exists as a core of the dots. It is also shown that the amplitude of the Raman peak is not directly proportional to the number of the corresponding bonds.
Cis→trans conversion of formic acid by dissipative tunneling in solid rare gases: Influence of environment on the tunneling rate
Authors: Pettersson M. , Maçôas E. M. S. , Khriachtchev L. , Lundell J. , Fausto R. , Räsänen M.
Published: November 2002

The relaxation of the higher-energy cis conformer of formic acid to the lower-energy trans form by a tunneling mechanism has been investigated in low-temperature rare gas matrices. In the temperature range 8–60 K, the tunneling takes place dominantly from the vibrational ground state of the cis form and the temperature dependence of the tunneling rate constant is influenced by the interactions with the environment. The temperature-dependent tunneling rates for HCOOH and DCOOH in solid Ar, Kr, and Xe are measured including data for molecules in different local environments within each host. It was found that the medium and the local environment has a significant influence on the tunneling rate.
Nanoindentation and Raman spectroscopy studies of boron carbide single crystals
Authors: Domnich Vladislav , Gogotsi Yury , Trenary Michael , Tanaka Takaho
Published: November 2002

The measurements of hardness and elastic modulus have been conducted on the (0001) and (101̄1) faces of B4.3C single crystals using nanoindentation. The results are in good agreement with the corresponding values obtained using a conventional microhardness technique on polycrystalline ceramics. Raman microspectroscopy analysis of the nanoindentations shows the appearance of several bands which suggest dramatic structural changes in the indented material. Localized contact loading may lead to damage in boron carbide resulting in disorder or a pressure-induced solid state phase transformation in the region under the indenter, although the exact mechanism responsible for the observed Raman spectra could not be identified at this time. This may explain why little variation in mechanical properties was observed with respect to the crystallographic orientation.
Fabrication of submicron-scale SrTiO3−δ devices by an atomic force microscope
Authors: Pellegrino L. , Pallecchi I. , Marré D. , Bellingeri E. , Siri A. S.
Published: November 2002

By applying a negative voltage to the conducting tip of an atomic force microscope, we modify on submicron-scale semiconducting oxygen deficient SrTiO3−δ thin films grown on LaAlO3 substrates. In comparison with the as-grown film, the modified regions present different electrical and structural properties, which can be exploited to realize submicrometer circuits. After a discussion on the mechanisms of the process, we report a prototype of a SrTiO3−δ-based sidegate field-effect transistor, showing a 4% modulation of channel resistivity with gate voltages up to 40 V.
Interaction corrections to transport due to quasibound states in open quantum dots
Authors: Indlekofer K. M. , Bird J. P. , Akis R. , Ferry D. K. , Goodnick S. M.
Published: November 2002

We formulate a many-body model of transport in open quantum dots, which is based upon the idea of an enhanced electron–electron interaction in the vicinity of a quasibound state. Our studies suggest that the effect of including this peaked interaction is to increase the amplitude of the conductance fluctuations, beyond the value expected from a single-particle treatment. While the role of interactions in transport through open dots has attracted little theoretical attention, our results demonstrate the presence of interaction-induced corrections to the transport in these structures.
Flexible mirrorless laser based on a free-standing film of photopolymerized cholesteric liquid crystal
Authors: Matsui Tatsunosuke , Ozaki Ryotaro , Funamoto Kazuhiro , Ozaki Masanori , Yoshino Katsumi
Published: November 2002

Optically pumped mirrorless laser action has been observed in a dye-doped flexible free-standing film of photopolymerized cholesteric liquid crystal (PCLC). In the PCLC film, self-organized helical structure acts as one-dimensional (1D) photonic crystal. At high excitation intensity above the threshold, a laser action is observed at an edge of the 1D photonic band of the PCLC helical structure. This PCLC film laser possesses an excellent mechanical flexibility, and the laser action is also observed in a bent film of PCLC. This implies that the one-dimensional periodic structure for the laser action is maintained even in the deformed film. Using such flexibility of the PCLC film, a focusing effect of laser emission is demonstrated in a circularly deformed film. Moreover, the helical pitch of the PCLC has no temperature dependence in contrast to that of unpolymerized cholesteric liquid crystal. This means that the operation wavelength of laser action is thermally stable, which is the great advantage for the device application.
Emergence of a dominant design in probiotic functional food development
Authors: Nordström Katrina , Biström Mikaela
Published: November 2002

This study explores technological factors influencing the development of functional food products. The specific aim was to investigate if the concept of a dominant design holds true for functional foods. By using consumer acceptance as the measure of product dominance, it is postulated that market pressure inherent to functional foods becomes established by the perceived value to consumers. This value is due to the inherent and documented health advantages, taste, user convenience and competitive price. Switching costs, which create barriers to entry, for functional foods are due to the establishment of a technological solution, patenting, meeting regulatory approval and brand assets in connection to marketing. It is also postulated that in the development of functional foods, a product innovation phase leads into process innovation alternatives. These alternatives arise from different precursors of dominant designs.
Creating competitive advantage through effective management education
Authors: Longenecker Clinton O. , Ariss Sonny S.
Published: November 2002

States that the twenty‐first century has brought with it the global marketplace, and with it unparalleled business opportunities which have competitive pressures. Discusses how organizations can use management education to create competitive advantage. Concludes that management education and development is essential in order for an organization to remain competitive.
Getting from good to great: a conversation with Jim Collins
Authors: Finnie William C. , Abraham Stanley C.
Published: November 2002

Strategy & Leadership contributing editors interviewed researcher Jim Collins. Collins is author of two influential books: Built to Last: Successful Habits of Visionary Companies co‐authored with Jerry Porras, and Good to Great: Why Some Companies Make the Leap … and Others Don’t. Some key points Collins makes are: The transition from good to great all began with a Level 5 leader. The essence of Level 5 leadership is having an ambition for the cause of the work‐the outcome, the company, the organization‐above the self; also, at the same time, having the ferocious, frightening, terrifying willfulness to act upon that ambition. Most Level 5 leaders understand that their report card only comes in when their successor succeeds. In most cases, but not all, their successors were even more successful than they were. That’s different from the comparison cases, where a number of the executives defined their success in terms of their successor failing. All the good‐to‐great CEOs said “I am not going to answer the ‘What to do’ question until I’ve got the right people. And we will not determine where to drive this bus until we decide who should be on the bus, who should be off the bus, and who should be in what seat.” In the comparison companies, you have leaders who often came in with “the what” and then tried to get everybody to go there, whereas the good‐to‐great companies had leaders who began with the “who” and then figured it out from there. The idea that you first get the right team and only later figure out where to drive the bus is absolutely contrary to what everyone learned in business school. The great companies understood what they could absolutely be the best in the world at. And also, “If we can’t be the best in the world at it then we shouldn’t be doing it.” They wanted to have a profound understanding of their economics and how to fundamentally change them. And they put a high premium on things that they were very passionate about.
A comparison of upward‐only and turnover leases
Authors: Hendershott Patric H.
Published: November 2002

The upward‐only lease is the dominant rental contract in the UK, while the turnover lease is widely used in the US retail sector. This paper compares and contracts the landlord rent options in these two leases, interpreting and extending the earlier simulation analysis of Booth and Walsh and of Hendershott and Ward. While the options are similar, the ability of the turnover rent lease to induce greater landlord effort and co‐operation between tenants and the landlord suggest that both UK investors and UK consumers would be well served by greater use of the turnover lease.
Analysis of Belt-Driven Mechanics Using a Creep-Rate-Dependent Friction Law
Authors: Leamy M. J. , Wasfy T. M.
Published: November 2002

An analysis of the frictional mechanics of a steadily rotating belt drive is carried out using a physically appropriate creep-rate-dependent friction law. Unlike in belt-drive mechanics analyzed using a Coulomb friction law, the current analysis predicts no adhesion zones in the belt-pulley contact region. Regardless of this finding, for the limiting case of a creep-rate law approaching a Coulomb law, all predicted response quantities (including the extent of belt creep on each pulley) approach those predicted by the Coulomb law analysis. Depending on a slope parameter governing the creep-rate profile, one or two sliding zones exist on each pulley, which together span the belt-pulley contact region. Closed-form expressions are obtained for the tension distribution, the sliding-zone arc magnitudes, and the frictional and normal forces per unit length exerted on the belt. A sample two-pulley belt drive is analyzed further to determine its pulley angular velocity ratio and belt-span tensions. Results from this analysis are compared to a dynamic finite element solution of the same belt drive. Excellent agreement in predicted results is found. Due to the presence of arbitrarily large system rotations and a numerically friendly friction law, the analytical solution presented herein is recommended as a convenient comparison test case for validating friction-enabled dynamic finite element schemes.
Are Lower-Order Gradient Theories of Plasticity Really Lower Order?
Authors: Volokh K. Yu. , Hutchinson J. W.
Published: November 2002

An explicit example of one-dimensional shearing is used to illustrate the necessity of extra boundary conditions for a class of incremental theories of plasticity regarded as otherwise conventional apart from a dependence of the tangential moduli on gradients of plastic strain.
Hamiltonian Mechanics for Functionals Involving Second-Order Derivatives
Authors: Tabarrok B. , Leech C. M.
Published: November 2002

Hamilton’s principle was developed for the modeling of dynamic systems in which time is the principal independent variable and the resulting equations of motion are second-order differential equations. This principle uses kinetic energy which is functionally dependent on first-order time derivatives, and potential energy, and has been extended to include virtual work. In this paper, a variant of Hamiltonian mechanics for systems whose motion is governed by fourth-order differential equations is developed and is illustrated by an example invoking the flexural analysis of beams. The variational formulations previously associated with Newton’s second-order equations of motion have been generalized to encompass problems governed by energy functionals involving second-order derivatives. The canonical equations associated with functionals with second order derivatives emerge as four first-order equations in each variable. The transformations of these equations to a new system wherein the generalized variables and momenta appear as constants, can be obtained through several different forms of generating functions. The generating functions are obtained as solutions of the Hamilton-Jacobi equation. This theory is illustrated by application to an example from beam theory the solution recovered using a technique for solving nonseparable forms of the Hamilton-Jacobi equation. Finally whereas classical variational mechanics uses time as the primary independent variable, here the theory is extended to include static mechanics problems in which the primary independent variable is spatial.
Electron emission suppression characteristics of molybdenum grids coated with carbon film by ion beam assisted deposition
Authors: Liu Xianghuai , Ren Congxin , Jiang Bingyao , Zhu Hong , Liu Yanyuan , Wu Jingxian
Published: November 2002

Carbon was coated on the surface of molybdenum grids by ion beam assisted deposition. The electron emission characteristics from the grids with and without carbon, which were contaminated by an active electron emission substance of the cathode, was measured using an analogous diode method. The results show that electron emission from the carbon-coated Mo grid was much less than that from the Mo grid without carbon. The cathode emission substance deposited on the carbon surface of the grid was analyzed by x-ray photoelectron spectroscopy and electron probes. Analysis results revealed that the carbon-coated Mo grid could effectively reduce the accumulation of the cathode emitting substances Ba and BaO on the grid surface. The reason for the suppression of electron emission of the carbon-coated Mo grid is discussed. The carbon-coated Mo grids were used in pulsed-controlled grid traveling wave tubes and the working lifetime of the tube was increased from tens of hours to over 1000 h.
Investigation of the hydrogenation properties of Zr films under unclean plasma conditions
Authors: Shi L. Q. , Yan G. Q. , Zhou J. Y. , Luo S. Z. , Peng S. M. , Ding W. , Long X. G.
Published: November 2002

By the means of non-Rutherford backscattering spectroscopy and elastic recoil detection analysis, the plasma hydrogenation of Zr films with and without a Ni overlayer were investigated. Close to the theoretical maximum hydrogen storage capacity (H/Zr=2) was attained when the sample was exposed to plasma with relative low contamination and a hydrogen pressure of ∼2 Pa and a substrate temperature of 393 K for 10 min. This reaction rate is much higher than obtained for gas hydrogenation. In an unclean plasma condition, the absorption of hydrogen is retarded by C and O contamination occurring on the sample surface. Though the oxide layer does not act as an efficient permeation barrier to atomic hydrogen, the maximum equilibrium hydrogen content dropped drastically with increasing contamination. In contrast to theoretical prediction, the hydrogen capacity for Ti is lower than Zr due to sample contamination. Also, the influence of the Ni overlayer on the plasma hydrogenation is discussed.
Angle-resolved x-ray photoelectron spectroscopy of ultrathin Al2O3 films grown by atomic layer deposition
Authors: Renault O. , Gosset L. G. , Rouchon D. , Ermolieff A.
Published: November 2002

Thin (45 nm) and ultrathin (4.5–1 nm) Al2O3 layers deposited on HF-stripped Si or thin SiO2 surfaces by atomic layer deposition were studied by angle-resolved x-ray photoelectron spectroscopy, before and after rapid thermal annealing (RTA) at 800 °C for 15 min in N2 or annealing in a conventional furnace under ultrahigh vacuum (UHV) (p=10−6 mbar) and N2 at the same temperature. Samples were characterized in terms of chemical defects and interfacial regrowth upon annealing. Chemical defects as Al–OH groups are evidenced from the O 1s spectra even after RTA. Interfacial regrowth, estimated from the Si 2p components intensity, was found (1) to occur upon every kind of annealing, (2) to be dependent on the initial Al2O3 thickness (the thicker the layer the greater the regrowth), and (3) to be significantly reduced on SiO2 surfaces as thin as 0.5 nm. In agreement with previous studies, we also consistently found the presence of an oxidized Si component at the Al2O3/substrate interface centered at 102 eV for which an assignment to silicate groups (Si–O–Al) is proposed, on the basis of other x-ray photoelectron spectroscopy parameters. Given the influence of UHV annealing in interfacial regrowth, Al–OH defects may play an important role in interface oxidation.
Time development of microstructure and resistivity for very thin Cu films
Authors: Rossnagel S. M. , Kuan T. S.
Published: November 2002

The electrical resistance of thin, 4–100 nm sputter-deposited (physical vapor deposition) Cu films was measured in situ in the deposition chamber. The Cu was deposited on silicon dioxide surfaces to reduce surface pinning or adhesion effects and allow high mobility. During, and following the deposition, the electrical resistance was measured under vacuum for periods of up to several thousand minutes, and in each case the electrical resistivity decreased 13%–50% over that time period. This is consistent with reports of room temperature grain growth in electrodeposited thin films. X-ray diffraction data showed significant increases in (111) crystallinity. At very small thicknesses (4.5 nm), it appears that a second mechanism occurs prior to grain growth which may be related to the agglomeration of nearly discontinuous islands on the surface. Similar Cu films deposited on Ta adhesion layers showed little, if any, change in resistance over time, indicating the role of the substrate interface in limiting grain growth.
Correlation of surface chemistry of GaAs substrates with growth mode and stacking fault density in ZnSe epilayers
Authors: Hong Soon-Ku , Chang Ji-Ho , Hanada Takashi , Kurtz Elisabeth , Oku Masaoki , Yao Takafumi
Published: November 2002

We report on the correlation of surface chemistry of GaAs substrates with growth mode and stacking fault density in ZnSe epilayers. High quality ZnSe epilayers with low stacking fault density have been directly grown on commercial epiready GaAs (001) substrates without GaAs buffer layer growth. It is found that proper pregrowth treatments of epiready GaAs (001) substrates to obtain clean surfaces are crucial to two-dimensional layer-by-layer growth and suppression of generation of stacking faults. The surface oxide layers of epiready GaAs substrates before and after chemical etching using a NH4OH-based solution are carefully characterized by angle-resolved x-ray photoelectron spectroscopy. The surface oxide layer is composed of Ga2O3 and As2O3. The chemical etching is found to reduce not only the thickness of the oxide layers but also the ratio of Ga2O3 to As2O3 to about half of that before etching. A clean GaAs (001) surface typically characterized by a (4×1) reconstruction is obtained in the present case after thermal cleaning. Prior to ZnSe growth Zn preexposure is carried out. Reflection high-energy electron diffraction intensity oscillations with more than 50 periods are observed even from the beginning of ZnSe growth on such cleaned GaAs substrates. High quality ZnSe layers with a stacking fault density of low-105 cm−2 range are grown.