bluuebunny/crossref_metadata_2025 huggingface dataset:
Domain epitaxy: A unified paradigm for thin film growth
Authors: Narayan J. , Larson B. C.
Published: December 2002

We present a unified model for thin film epitaxy where single crystal films with small and large lattice misfits are grown by domain matching epitaxy (DME). The DME involves matching of lattice planes between the film and the substrate having similar crystal symmetry. In this framework, the conventional lattice matching epitaxy becomes a special case where a matching of lattice constants or the same planes is involved with a small misfit of less than 7%–8%. In large lattice mismatch systems, we show that epitaxial growth of thin films is possible by matching of domains where integral multiples of major lattice planes match across the interface. We illustrate this concept with atomic-level details in the TiN/Si(100) with 3/4 matching, the AlN/Si(100)with 4/5 matching, and the ZnO/α−Al2O3(0001) with 6/7 matching of major planes across the film/substrate interface. By varying the domain size, which is equal to intregral multiple of lattice planes, in a periodic fashion, it is possible to accommodate additional misfit beyond perfect domain matching. Thus, we can potentially design epitaxial growth of films with any lattice misfit on a given substrate with atomically clean surfaces. In situ x-ray diffraction studies on initial stages of growth of ZnO films on sapphire correctly identify a compressive stress and a rapid relaxation within 1 to 2 monolayers, consistent with the DME framework and the fact that the critical thickness is less than 1 monolayer. DME examples ranging from the Ge–Si/Si(100) system with 49/50 matching (2% strain) to metal/Si systems with 1/2 matching (50% strain) are tabulated, strategies for growing strain-free films by engineering the misfit to be confined near the interface are presented, and the potential for epitaxial growth of films with any lattice misfit on a given substrate with atomically clean surfaces is discussed.
Temperature dependence of the optical energy band gap in CuIn3Se5 and CuGa3Se5
Authors: Rincón C. , Wasim S. M. , Marı́n G. , Molina I.
Published: December 2002

The temperature dependence of the optical band gap EG in bulk crystals of CuIn3Se5 and CuGa3Se5 has been analyzed by separately considering the contributions due to electron–phonon interaction and thermal expansion. For the former contribution, we use an expression related to the mean frequency of phonons, defined by a temperature θ, that participate in the shift of the fundamental energy gap with temperature. For the latter, a term that explicitly takes into account the temperature variation of the thermal expansion coefficient and the pressure dependence of the band gap is employed.
Generation of radial electric field induced by collisionless internal kink mode with density gradient
Authors: Matsumoto Taro , Tokuda Shinji , Kishimoto Yasuaki , Naitou Hiroshi
Published: December 2002

Effects of density gradient on the collisionless m=1 (m/n=1/1) internal kink mode in a cylindrical tokamak plasma are studied by the gyrokinetic particle simulations. When the density gradient is not large enough to change the full reconnection process, the phenomena after the full reconnection, such as the secondary reconnection and the evolution of the safety factor profile, are changed considerably due to the self-generated radial electric field, i.e., the m/n=0/0 mode. The growing mechanism is explained by the difference of E×B drift motion between ions and electrons, which is caused by the fast parallel motion of electron. Once the radial electric field is triggered by the symmetrical flow induced by the 1/1 mode, the 0/0 mode grows up to the same level as the 1/1 mode, and drives an E×B plasma rotation in the ion diamagnetic direction, which breaks the symmetrical plasma flow induced by the 1/1 mode. The density and current distributions, and therefore minimum safety factor qmin after the full reconnection, are found to be affected by the asymmetrical flow driven by the 1/1 and 0/0 modes.
Measurement of the transverse Spitzer resistivity during collisional magnetic reconnection
Authors: Trintchouk F. , Yamada M. , Ji H. , Kulsrud R. M. , Carter T. A.
Published: December 2002

Measurement of the transverse resistivity was carried out in a reconnecting current sheet where the mean free path for the Coulomb collision is smaller than the thickness of the sheet. In a collisional neutral sheet without a guide field, the transverse resistivity is directly related to the reconnection rate. A remarkable agreement is found between the measured resistivity and the classical value derived by Spitzer. In his calculation the transverse resistivity for the electrons is higher than the parallel resistivity by a factor of 1.96. The measured values have verified this theory to within 30% errors.
Effect of surface induced nucleation of ferroelastic domains on polarization switching in constrained ferroelectrics
Authors: Ahluwalia Rajeev , Cao Wenwu
Published: December 2002

The role of the surface during polarization switching in constrained ferroelectrics is investigated using the time-dependent Ginzburg–Landau theory. The model incorporates the elastic and electrostrictive effects in the form of a long-range interaction that is obtained by eliminating the strain fields subject to the elastic compatibility constraint. A square-shaped finite sized constrained ferroelectric system with vanishing surface polarization is considered. Computer simulations of the hysteresis reveal that the corners of the constrained square act as nucleation sources for 90° domain structures. It is also found that no nucleation of the 90° domain structure takes place in a system with semi-infinite (corner free) geometry. For the corner free case, the polarization switches by 180° reorientations and a front of the reverse domains emerges from the surface, eventually sweeping over the entire system. Size dependence of the hysteresis loops is also studied.
Lateral composition modulation in InAs/GaSb superlattices
Authors: Stokes D. W. , Forrest R. L. , Li J. H. , Moss S. C. , Nosho B. Z. , Bennett B. R. , Whitman L. J. , Goldenberg M.
Published: December 2002

We report the analysis of lateral composition modulation in (InAs)m/(GaSb)m superlattices by x-ray diffraction. Vertical and lateral satellite peaks for a 140 period structure were observed. The lateral modulation wavelength, average superlattice composition, and vertical superlattice wavelength were determined. The lateral modulation was observed only along one in-plane direction resulting in quantum wire-like structures along the [11̄0] direction. The unconventional structure of the lateral composition modulation, in which the stacking of the layers leads to a doubling of the vertical superlattice period, is discussed.
Radiation driven capsules for fast ignition fusion
Authors: Slutz Stephen A. , Herrmann Mark C.
Published: December 2002

The energy required to ignite compressed deuterium–tritium fuel decreases strongly with fuel density. Thermal radiation is an effective way of driving inertial fusion capsules to high density. The achievable fuel density increases with peak radiation temperature, since the ablation pressure depends strongly on the radiation temperature. Through a series of detailed numerical simulations, peak fuel densities have been calculated as a function of the peak radiation drive temperature. In these calculations, the time dependence of the radiation temperature has been optimized to obtain maximum density for each scaling point. These results are then used with the fast ignition scaling of Atzeni [S. Atzeni, Phys. Plasmas 6, 3316 (1999)] to obtain ignition energy as peak drive temperature.
Effect of crystal defects on the electrical properties in epitaxial tin dioxide thin films
Authors: Dominguez J. E. , Fu L. , Pan X. Q.
Published: December 2002

Epitaxial (101) tin dioxide thin films with thickness ranging from 6 and 100 nm were deposited on the (101̄2) α-Al2O3 substrate by femtosecond pulsed laser ablation. Due to the lattice and thermal expansion mismatch with the substrate, the SnO2 film shows interfacial misfit dislocations, antiphase boundaries (APBs), and partial dislocations. The APBs lie along the (1̄01) planes with a displacement of 1/2[101]. The densities of APBs and partial dislocations vary with film thickness, whereas the average spacing of misfit dislocations remains constant. Hall effect measurements showed that both electron concentration and mobility decrease with a reduction in the film thickness, which is ascribed to the scattering of electrons by crystal defects and interfaces and the effect of a native space charge region at the near-surface region of the films. The response of the films to reducing gases was found to depend on the electron concentration of the film and the relative fraction, with respect to film thickness, of material that is depleted of electrons.
Kinetics of electric-field-enhanced crystallization of amorphous silicon in contact with Ni catalyst
Authors: Kim Hae-Yeol , Kim Binn , Bae Jong-Uk , Hwang Kwang-Jo , Seo Hyun-Sik , Kim Chang-Dong
Published: December 2002

Electric-field-enhanced crystallization of hydrogenated amorphous silicon in contact with nickel catalyst (Ni/a-Si:H) has been investigated. In order to elucidate the crystallization kinetics quantitatively, in situ conductivity measurement was used. With the change of Ni dose (4×1013∼1.3×1015 cm−2) and annealing temperature (550∼500 °C), crystallization rate varied drastically at the electric field of 33 V cm−1. The activation energy for the crystallization was found to be strongly dependent on the Ni dose, 85 kJ mol−1 for 1.3×1015 Ni cm−2, 243 kJ mol−1 for 6×1014 Ni cm−2, and 276 kJ mol−1 for 4×1013 Ni cm−2, respectively. The polycrystalline silicon films were composed of needle-like crystallites of ∼5 μm (long axis) and their thin-film transistors (TFTs) showed field effect mobility of 43 cm2 V−1 s−1.
Bulk and surface contributions to resonant second-harmonic generation from Si(001) surfaces
Authors: Qiang An Yong , Cundiff Steven T.
Published: December 2002

The spectra of the isotropic and anisotropic contributions to second-harmonic generation from modified Si(001) surfaces are separated using polarization selection and rotational anisotropy. A bulk anisotropic resonance is observed at a two-photon energy of 3.42±0.01 eV. The isotropic surface contributions for native oxide Si and thermal oxide Si show peaks at 3.39±0.01 eV and 3.35±0.01 eV, respectively. Interference between these contributions and the bulk signal can shift the apparent resonance position if they are not separated. The surface produces a noninterfering contribution that is comparable to the interfering contribution for H-terminated Si but negligible for oxidized silicon.
Electronic structure and interband transitions of metallic carbon nanotubes
Authors: D’yachkov P. N. , Hermann H. , Kirin D. V.
Published: December 2002

Band structure of the metallic (n,n) carbon nanotubes (coefficients n are the indices of the two-dimensional primitive lattice vectors of the graphene lattice) is calculated in terms of a linear augmented cylindrical wave method. The results are used to correlate the minimum direct energy gaps E11 between the conduction and valence band singularities with the nanotube diameter d and optical absorption spectra. Significant deviations from the equation E11∼d−1 are observed. The ππ* gap energy increases monotonically with 1/d, whereas the σπ* gap width shows a minimum at n=10. In the (3, 3) tube, the conduction band singularity coincides with the Fermi level, resulting in a drastic increase of the density of states on this level.
Si doping of high-Al-mole fraction AlxGa1−xN alloys with rf plasma-induced molecular-beam-epitaxy
Authors: Hwang Jeonghyun , Schaff William J. , Eastman Lester F. , Bradley Shawn T. , Brillson Leonard J. , Look David C. , Wu J. , Walukiewicz Wladek , Furis Madalina , Cartwright Alexander N.
Published: December 2002

Very high levels of n-type doping of AlxGa1−xN alloys were recently achieved by rf plasma-induced molecular-beam epitaxy on sapphire substrates and Si as a dopant. Electron concentrations were obtained up to 1.25×1020 cm−3 when the Al mole fraction was 50%, and 8.5×1019 cm−3 electrons were measured even when the Al mole fraction was 80%. Other material properties were determined by optical absorption, photoluminescence, cathodoluminescence, x-ray diffraction, and atomic force microscopy measurements and high optical and morphological qualities were shown.
Jourdain’s variational equation and Appell’s equation of motion for nonholonomic dynamical systems
Authors: Wang Li-Sheng , Pao Yih-Hsing
Published: December 2002

Based on Jourdain’s variational equation proposed in 1909, we deduce a minimal set of general equations of motion for nonholomic dynamical systems of particles and rigid bodies. This equation of motion for the system, which differs slightly from the Gibbs–Appell equation, appears to be the same as the equation derived by Kane in 1961. Since the same equation was established by Appell in 1903 on the basis of D’Alembert’s principle, the newly derived equation is named Appell’s equation.
From Cbits to Qbits: Teaching computer scientists quantum mechanics
Authors: Mermin N. David
Published: December 2002

A strategy is suggested for teaching mathematically literate students, with no background in physics, just enough quantum mechanics for them to understand and develop algorithms in quantum computation and quantum information theory. Although the article as a whole addresses teachers of physics well versed in quantum mechanics, the central pedagogical development is addressed directly to computer scientists and mathematicians, with only occasional asides to their teacher. Physicists uninterested in quantum pedagogy may be amused (or irritated) by some of the views of standard quantum mechanics that arise naturally from this unorthodox perspective.
An Intergroup Phase III Comparison of Standard Radiation Therapy and Two Schedules of Concurrent Chemoradiotherapy in Patients With Unresectable Squamous Cell Head and Neck Cancer
Authors: Adelstein David J. , Li Yi , Adams George L. , Wagner Henry , Kish Julie A. , Ensley John F. , Schuller David E. , Forastiere Arlene A.
Published: December 2002

Purpose: The Head and Neck Intergroup conducted a phase III randomized trial to test the benefit of adding chemotherapy to radiation in patients with unresectable squamous cell head and neck cancer.

Patients and Methods: Eligible patients were randomly assigned between arm A (the control), single daily fractionated radiation (70 Gy at 2 Gy/d); arm B, identical radiation therapy with concurrent bolus cisplatin, given on days 1, 22, and 43; and arm C, a split course of single daily fractionated radiation and three cycles of concurrent infusional fluorouracil and bolus cisplatin chemotherapy, 30 Gy given with the first cycle and 30 to 40 Gy given with the third cycle. Surgical resection was encouraged if possible after the second chemotherapy cycle on arm C and, if necessary, as salvage therapy on all three treatment arms. Survival data were compared between each experimental arm and the control arm using a one-sided log-rank test.

Results: Between 1992 and 1999, 295 patients were entered on this trial. This did not meet the accrual goal of 362 patients and resulted in premature study closure. Grade 3 or worse toxicity occurred in 52% of patients enrolled in arm A, compared with 89% enrolled in arm B (P < .0001) and 77% enrolled in arm C (P < .001). With a median follow-up of 41 months, the 3-year projected overall survival for patients enrolled in arm A is 23%, compared with 37% for arm B (P = .014) and 27% for arm C (P = not significant).

Conclusion: The addition of concurrent high-dose, single-agent cisplatin to conventional single daily fractionated radiation significantly improves survival, although it also increases toxicity. The loss of efficacy resulting from split-course radiation was not offset by either multiagent chemotherapy or the possibility of midcourse surgery.
Defects of blastogenesis
Authors: Opitz John M. , Zanni Ginevra , Reynolds James F. , Gilbert‐Barness Enid
Published: December 2002

Ever more frequent and closer involvement by clinical geneticists and counselors in the prenatal assessment of development mandates a better understanding of all stages of human ontogeny, but especially those of earliest development during which most of the lethal and all of the gross, multiple and complex defects of morphogenesis arise. Because of the phenomenon of universality, i.e., identical molecular inductive mechanisms involved in the process of embryonic pattern formation in all vertebrates, experimental animals indeed are a most valuable approach to an understanding of the causal and formal aspects of development and are beginning to forge essential, strong bonds between molecular biologists and clinicians in a mutually supportive discipline of developmental biology. However, to grieving parents of a stillborn fetus with, say, Pentalogy of Cantrell, sirenomelia or otocephaly, mouse data offer little comfort or reassurance about recurrence; thus, it is imperative to make ever more effective a science of human teratology (sensu lato) with participating reproductive geneticists, obstetricians, neonatologists, ultrasonographers, pediatric/fetal pathologists, cytogeneticists and pediatric geneticists to generate the diagnostic, pathogenetic and causal data necessary to counsel and to comfort the parents. Few molecular data exist on causes of blastogenetic defects in humans; however, the phenomenon of parsimony, whereby the same “morphogenetic” molecule, say, sonic hedgehog (SHH), is “deployed” simultaneously or sequentially during the morphogenesis (and even the histogenesis) of several/many embryonic primordia, makes it likely that a genetic/epigenetic disturbance of such an inductive system will have multiple effects on blastogenetic, organogenetic and perhaps also histogenetic events in the embryo. If causally defined, such a pattern of anomalies constitutes pleiotropy, and the embryo/fetus can be said to have a syndrome. If cause is unknown, the presumption of pleiotropy is less certain, and the fetus/infant may be said to have an “association” with low empiric recurrence risk. © 2002 Wiley‐Liss, Inc.
Peripheral axotomy affects nicotinamide adenine dinucleotide phosphate diaphorase and nitric oxide synthases in the spinal cord of the rabbit
Authors: Lukáčová Nadežda , Čížková Dáša , Križanová Olga , Pavel Jaroslav , Maršala Martin , Maršala Jozef
Published: December 2002

Using nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry and nitric oxide synthase (NOS) immunocytochemistry combined with radioassay of calcium‐dependent NOS activity, we examined the occurrence of NADPHd staining and NOS immunoreactivity (NOS‐IR) in the dorsal root ganglia (DRG) neurons, dorsal root afferents, and axons projecting via gracile fascicle to gracile nucleus 14 days after unilateral sciatic nerve transection in the rabbit. Mild to moderate NADPHd staining and NOS‐IR appeared in a large number of small and medium‐sized to large neurons in the ipsilateral L4–L6 DRG, accompanied by enhanced NOS‐IR of thick myelinated fibers in the ipsilateral L4–L6 dorsal roots. A noticeable increase in the density of punctate NADPHd staining occurred throughout laminae I–IV in the ipsilateral medial part of the dorsal horn in L4–L6 segments. Concurrently, a statistically significant decrease in the number of small NADPHd‐exhibiting neurons in laminae I–II and, in contrast to this, a statistically significant increase of medium‐sized to large NADPHd‐stained somata in the ipsilateral laminae III–VI of L4–L6 segments were found. A detailed compartmentalization of L4–L6 segments into gray and white matter regions disclosed substantially increased catalytic NOS activity and inducible NOS mRNA levels in the dorsal horn and dorsal column ipsilaterally to the peripheral injury. A noticeable increase in the number of thick myelinated NADPHd‐exhibiting and NOS‐IR axons was noted in the ipsilateral gracile fascicle, terminating in dense, punctate NADPHd staining in the neuropil of the gracile nucleus. These observations indicate that the de novo‐synthesized NOS in the lesioned primary afferent neurons resulting after sciatic nerve transection may be involved in an increase in NADPHd staining and NOS‐IR in the ipsilateral dorsal roots and dorsal horn of L4–L6 segments, whence NOS could be supplied to ascending axons of the gracile fascicle. © 2002 Wiley‐Liss, Inc.
DNA repair gene O6‐methylguanine‐DNA methyltransferase: Promoter hypermethylation associated with decreased expression and G:C to A:T mutations of p53 in brain tumors
Authors: Yin Dong , Xie Dong , Hofmann Wolf‐Karsten , Zhang Wenxuan , Asotra Kamlesh , Wong Rex , Black Keith L , Koeffler H. Phillip
Published: December 2002

The DNA repair enzyme O6‐methylguanine‐DNA methyltransferase (MGMT) removes alkylating adducts from the O6 position of guanine and protects cells from cytotoxic and mutagenic effects. Expression of MGMT is decreased in some cancers, which may be the result of methylation of CpG islands of both the promoter and coding regions of the gene. We studied the methylation status of the MGMT promoter in a very large collection of brain tumors (85) using methylation‐specific polymerase chain reaction (PCR). Aberrant methylation occurred in 48% of 85 human brain tumor samples. Quantitative real‐time PCR showed that expression of MGMT mRNA levels was significantly decreased (P < 0.001) in those brain tumors that had methylation of the promoter region of their MGMT gene. MGMT can prevent G to A mutations by removing alkyl groups from the O6 position of guanine. We found a significantly increased frequency of G:C to A:T mutations of the p53 gene in brain tumors having a methylated MGMT promoter compared with those having an unmethylated MGMT promoter (P < 0.05), and all the non–CpG dinucleotide G:C to A:T mutations of p53 were in samples with a methylated MGMT promoter. © 2002 Wiley‐Liss, Inc.
Mid-Holocene Hydrologic Model of the Shingobee Watershed, Minnesota
Authors: Filby Sheryl K. , Locke Sharon M. , Person Mark A. , Winter Thomas C. , Rosenberry Donald O. , Nieber John L. , Gutowski William J. , Ito Emi
Published: December 2002

A hydrologic model of the Shingobee Watershed in north-central Minnesota was developed to reconstruct mid-Holocene paleo-lake levels for Williams Lake, a surface-water body located in the southern portion of the watershed. Hydrologic parameters for the model were first estimated in a calibration exercise using a 9-yr historical record (1990–1998) of climatic and hydrologic stresses. The model reproduced observed temporal and spatial trends in surface/groundwater levels across the watershed. Mid-Holocene aquifer and lake levels were then reconstructed using two paleoclimatic data sets: CCM1 atmospheric general circulation model output and pollen-transfer functions using sediment core data from Williams Lake.

Calculated paleo-lake levels based on pollen-derived paleoclimatic reconstructions indicated a 3.5-m drop in simulated lake levels and were in good agreement with the position of mid-Holocene beach sands observed in a Williams Lake sediment core transect. However, calculated paleolake levels based on CCM1 climate forcing produced only a 0.05-m drop in lake levels. We found that decreases in winter precipitation rather than temperature increases had the largest effect on simulated mid-Holocene lake levels. The study illustrates how watershed models can be used to critically evaluate paleoclimatic reconstructions by integrating geologic, climatic, limnologic, and hydrogeologic data sets.
Interdomain interaction through helices A and B of DnaK peptide binding domain
Authors: Moro Fernando , Fernández Vanesa , Muga Arturo
Published: December 2002

In order to better define the structural elements involved in allosteric signalling, wild‐type DnaK and three deletion mutants of the peptide binding domain have been characterized by biophysical (steady‐state and time‐resolved fluorescence) and biochemical methods. In the presence of ATP the chemical environment of the single tryptophan residue of DnaK, located in the ATPase domain, becomes less polar, as seen by a blue shift of the emission maximum and a shortening of the fluorescence lifetime, and its accessibility to polar quenchers is drastically reduced. These nucleotide‐dependent modifications are also observed for the deletion mutant DnaK1‐537, but not for DnaK1‐507 or DnaK1‐385, and thus rely on the presence of residues 507–537 (helices A and the N‐terminal half of B) of the peptide binding domain. These data indicate that αA and half αB contribute to the allosteric communication of DnaK. In the presence of ATP, they promote a conformational change that displaces a residue(s) of the peptide binding domain towards a region of the ATPase domain where the tryptophan residue (W102) is located. A putative role for these helical segments as regulators of the position of the lid is discussed.
The European Social Policy Model: Progress since the Early 1980s
Authors: Castles Francis G.
Published: December 2002

This article uses a simple statistical technique to examine whether there is a distinct European social policy model and whether such a model has consolidated during the 1980s and 1990s. In terms of total social expenditure and its major aggregates, it shows that Europe as a whole, and the countries presently constituting the EU, are somewhat more similar to each other than are the countries constituting a wider OECD grouping, but that this similarity is probably insufficient to warrant the label of European social policy model. In respect of individual programmes like pensions, health and unemployment benefits differences between Europe and the wider OECD are even less distinct. Over time, there is a general tendency for there to be greater coherence in total spending levels and in levels of expenditure on poverty alleviation and health care, but less coherence in respect of levels of social security spending. While the evidence for any kind of encompassing European social model is weak, the article does identify a Northern European grouping of countries, which, in several respects, manifests an expenditure profile quite distinct from OECD nations in general.
The Institutional Framework of Privatised Public Pension Plans: The Case of Former Socialist Economies
Authors: Kahn Peter L.
Published: December 2002

The success of some Latin American countries in creating ‘privatised’ public pension systems has led to proposals that similar systems be created elsewhere. Such proposals warrant a high degree of scepticism, particularly in those countries in transition to capitalist economics with inadequately developed legal systems. Pension fund management presents opportunities for self-dealing and mismanagement, sometimes for political reasons. There must be effective legal means of addressing these problems. There is little reason to expect the marketplace alone to do so. Ensuring that investment managers behave in a reasonably responsible manner requires at least three elements. There must be some ability to oversee the activities of the manager, and assurances that managers' incentives are aligned with those of the system, and legal institutions capable of enforcing these obligations. On all counts, countries in transition from socialism to capitalism make poor candidates for privatised pension systems.
NOBEL LECTURE: A Half-Century of Neurotransmitter Research: Impact on Neurology and Psychiatry
Authors: Carlsson Arvid
Published: December 2002

The effect that research on dopamine and other neutro trasmitters has on disciplines like neurology and psychiatry is described.
Photoluminescence of Ge nanoparticles embedded in SiO2 glasses fabricated by a sol–gel method
Authors: Yang Heqing , Wang Xingjun , Shi Huazhong , Xie Songhai , Wang Fujian , Gu Xiaoxiao , Yao Xi
Published: December 2002

Ge nanoparticles with different sizes in silica glasses were prepared by a sol–gel method using Cl3–Ge–C2H4–COOH as a Ge source. The size of the Ge nanoparticles decreases with a reduction in the content of Ge in the starting materials, and thus the optical absorption edge shifts to a higher energy. Silica gel glasses doped with Ge nanoparticles showed a strong room-temperature photoluminescence with peaks at 568, 607, 672, 722, and 775 nm. The peak position of photoluminescence spectrum scarcely depends on the Ge/Si ratio. However, the photoluminescence intensity increases sharply as the Ge/Si ratio is reduced. The photoluminescence arises from the Ge clusters of diameter of <1–2 nm with a molecular character instead of nanocrystalline Ge with the diamond structure.
Epitaxial lateral overgrowth of GaN on Si (111)
Authors: Feltin E. , Beaumont B. , Vennéguès P. , Vaille M. , Gibart P. , Riemann T. , Christen J. , Dobos L. , Pécz B.
Published: December 2002

Completely coalesced epitaxial lateral overgrowth (ELO) of GaN on silicon (111) is presented for ELO layer thicknesses below 3 μm. Fast lateral expansion of the ELO-GaN was achieved by metalorganic vapor phase epitaxy at high growth temperature (1120 °C), low pressure (100 mbar), and a high V/III ratio of 8000. Thus full coalescence and a smooth surface (roughness of 5 nm across 100 μm2) are accomplished for wide SixNy masks along 〈11_00〉GaN with a 10 μm period and 3 μm openings. Atomic force microscopy and transmission electron microscopy are used to assess the quality of the layers. The density of dislocations is reduced from 8×109 cm−2 in the GaN template down to 8×108 cm−2 above the mask openings, and finally to 5×107 cm−2 in the laterally overgrown regions. The corresponding strong improvement of the optical properties and the stress present within the epilayer are evidenced by scanning cathodoluminescence microscopy.
Hysteretic ferromagnetic resonance as a probe for coercivity, exchange bias, and loop asymmetry
Authors: Punnoose A. , Morales E. H. , Wang Y. , Lederman D. , Seehra M. S.
Published: December 2002

The in-plane angular variation of hysteretic ferromagnetic resonance (HFMR) at 9.57 GHz, in increasing and decreasing field sweeps, is used to determine both coercivity HC and exchange bias HE in a ferromagnetic/antiferromagnetic Co/MnPt bilayer. The angular dependence of HC and HE is in excellent agreement with micromagnetic models in which the interfacial exchange energy is approximately equal to the domain-wall energy in the antiferromagnet. The HFMR linewidths show a systematic angular variation, indicating that domain formation is important.
Nonlinear absorption of a short intense laser pulse in a nonuniform plasma
Authors: Andreev A. A. , Platonov K. Yu. , Okada T. , Toraya S.
Published: December 2002

The analytical solutions of nonlinear relativistic hydrodynamic equations for inhomogeneous plasmas are considered and the model of laser pulse absorption when the laser and plasma parameters are varied over a wide range of values is developed. The absorption coefficient has a local maxima at an optimal plasma density gradient for the given laser intensity, and that absorption then increases with scale length, in agreement with our particle-in-cell simulation results. The simulations and model have shown that the absorption of the foil target increases with laser intensity because of plasma density deepness and the spreading of the resonant area of laser plasma wave interaction.
Theoretical mass, liquid, and polymer sensitivity of acoustic wave sensors with viscoelastic guiding layers
Authors: McHale Glen , Newton Michael Ian , Martin Fabrice
Published: December 2002

The theoretical sensitivity of Love wave and layer-guided shear horizontal acoustic plate mode (SH-APM) sensors for viscoelastic guiding layers and general loading by viscoelastic materials is developed. A dispersion equation previously derived for a system of three rigidly coupled elastic mass layers is modified so that the second and third layers can be viscoelastic. The inclusion of viscoelasticity into the second, wave guiding layer, introduces a damping term, in addition to a phase velocity shift, into the response of the acoustic wave system. Both the waveguiding layer and the third, perturbing layer, are modeled using a Maxwell model of viscoelasticity. The model therefore includes the limits of loading of both nonguided shear horizontal surface acoustic wave and acoustic plate mode (APM) sensors, in addition to Love wave and layer-guided SH-APM sensors, by rigidly coupled elastic mass and by Newtonian liquids. The three-layer model is extended to include a viscoelastic fourth layer of arbitrary thickness and so enable mass deposition onto an immersed Love wave or layer-guided SH-APM sensor to be described. A relationship between the change in the complex velocity and the slope of the complex dispersion curve is derived and the similarity to the mass and liquid sensor response of quartz crystal microbalances is discussed. Numerical calculations are presented for the case of a Love wave device in vacuum with a viscoelastic waveguiding layer. It is shown that, while a particular polymer relaxation time may be chosen such that the effect of viscoelasticity on the real part of the phase speed is relatively small, it may nonetheless induce a large insertion loss. The potential or the use of insertion loss as a sensor parameter is discussed.
Magnetic inhomogeneity and valence state in Sr2CrWO6 double perovskite
Authors: Wang Jinhui , Liu Gongqiang , Zhong Wei , Du Youwei
Published: December 2002

The magnetic inhomogeneities in the double perovskite Sr2CrWO6 ceramics have been investigated by means of ferromagnetic resonance spectra and magnetization measurements. The experimental results show that the peak-to-peak linewidth increases with decreasing temperature from 450 to 294 K. Meanwhile, the samples exhibit a remarkable coercivity up to 1050 Oe at room temperature in magnetic field of 18.3 kOe, and hard to attain saturation in magnetization. All these behaviors are symptomatic of magnetic inhomogeneities in the samples. The magnetoresistance (MR), arising from spin-polarized carriers tunneling at the grain boundaries, is about 24% at 6 K in magnetic field of 50 kOe. The MR decreases with elevating temperature and is nearly zero at room temperature. These studies clearly reveal that the magnetically soft character in this system is a prerequisite to enhance low-field magnetoresistance at room temperature. The investigation of x-ray photoemission spectra indicates that the ground state of Sr2CrWO6 adopts Cr3+–W5+ configuration. The superexchange interaction between Cr and W ions leads to ferrimagnetic ordering below Curie temperature TC∼473 K.
Optical properties of nanocrystalline diamond films by prism coupling technique
Authors: Sharda T. , Soga T. , Jimbo T.
Published: December 2002

Measurement of optical properties such as the refractive index and thickness of nanocrystalline or smooth diamond films is carried out by the prism coupling technique. The films observed to be absorbing for a standard operating wavelength of 633 nm and higher wavelengths, i.e., 830 and 1300 nm, were used to obtain sharp guided modes and the refractive index and thickness of the films could be measured independently with high accuracy. The index of the nanocrystalline diamond films was found to be homogeneous within the films with negligible changes observed at the film–substrate interface. Information on absorption was also obtained from the half width of the guided modes and was correlated to the graphitic concentration of the films measured by Raman spectroscopy. The thickness measured by the prism coupling technique was found to be in agreement with the thickness measured by cross-sectional transmission electron microscopy. The overall results indicate that the prism coupling technique can be very useful for rapid, easy accurate measurement of the refractive index and thickness of smooth diamond films.
Evolution of vacancy ordering structures in epitaxial YbSi2−x thin films on (111) and (001)Si
Authors: Chi K. S. , Tsai W. C. , Chen L. J.
Published: December 2002

The evolution of vacancy ordering structures in epitaxial YbSi2−x thin films on both (111) and (001)Si has been studied by transmission electron microscopy (TEM). Epitaxial YbSi2−x thin films were grown on Si by either room temperature deposition with subsequent thermal annealing or deposition at elevated temperature. Epitaxial YbSi2−x was found to form in samples annealed at 300 °C for 30 min and the appearance of additional diffraction spots is attributed to the formation of an ordered vacancy superstructure in the epitaxial YbSi2−x thin films. In other samples, the split or streaking of extra diffraction spots is attributed to the formation of out-of-step structures. The variation of out-of-step structures with the annealing temperature is correlated to a change in vacancy concentration that makes compressive stress in the Si sublattice relax. From studying plan-view and cross-sectional TEM samples in conjunction with simulated diffraction patterns, the three-dimensional structures of vacancy ordering were determined. The vacancy ordering structures are expected to exert a strong influence on the physical properties of epitaxial rare-earth silicide nanowires grown on (001)Si.
Ion-matrix sheaths related to planar targets with semicylindrical grooves
Authors: Demokan O. , Filiz Y.
Published: December 2002

In this work, the ion-matrix sheaths near planar targets with infinitely long, semicylindrical grooves are studied analytically to optimize ion implantation, concerning a broad range of industrial products. The potential profiles inside and outside the groove are derived and the velocity components inside the groove are estimated. The variation of the angle of incidence on the surface of the groove and the constant potential contours outside the groove are obtained. Results are observed to be in good agreement with the numerical simulations. Finally, suggestions for improving the uniformity of implantation on the surfaces of such grooves are stated.
Monolithic integration of room-temperature cw GaAs/AlGaAs lasers on Si substrates via relaxed graded GeSi buffer layers
Authors: Groenert Michael E. , Leitz Christopher W. , Pitera Arthur J. , Yang Vicky , Lee Harry , Ram Rajeev J. , Fitzgerald Eugene A.
Published: December 2002

GaAs/Al x Ga (1−x) As quantum well lasers have been demonstrated via organometallic chemical vapor deposition on relaxed graded Ge/GexSi(1−x) virtual substrates on Si. A number of GaAs/Ge/Si integration issues including Ge autodoping behavior in GaAs, reduced critical thickness due to thermal expansion mismatch, and complications with mirror facet cleaving have been overcome. Despite unoptimized laser structures with high series resistance and large threshold current densities, surface threading dislocation densities for GaAs/AlGaAs lasers on Si substrates as low as 2×106 cm−2 permitted continuous room-temperature lasing at a wavelength of 858 nm. The laser structures are uncoated edge-emitting broad-area devices with differential quantum efficiencies of 0.24 and threshold current densities of 577 A/cm2. Identical devices grown on commercial GaAs substrates showed similar behavior. This comparative data agrees with previous measurements of near-bulk minority carrier lifetimes in GaAs grown on Ge/GeSi/Si substrates.
Characteristics of microstructure and glass transition of (Zr0.59Ti0.06Cu0.22Ni0.13)100−xAlx bulk metallic glasses
Authors: Wen Ping , Wang Ru Ju , Pan Ming Xiang , Zhao D. Q. , Wang Wei Hua
Published: December 2002

The glass transition and the microstructural characteristics of (Zr0.59Ti0.06Cu0.22Ni0.13)100−xAlx (10⩽x⩽16) bulk metallic glasses (BMG) are investigated as function of Al content. It is found that the Al content has strong effects on the glass transition, microstructure, and properties of the alloy. The marked increase of the Debye temperature and shear modulus with increasing Al content indicates that the different Al incorporations result in microstructural change in atomic short range of the BMG. The increase of the glass transition temperature with the increase Al content is consistent with the large variation of properties with increase of Al content. The change of the microstructure of the glass-forming alloy is responsible for the change of the properties.
Laser-induced optical changes in amorphous multilayers
Authors: Malyovanik M. , Ivan S. , Csik A. , Langer G. A. , Beke D. L. , Kökényesi S.
Published: December 2002

It is shown that the well-known blueshift of the fundamental absorption edge in as-deposited compositionally modulated amorphous Si/Ge and As6Se94/Se80Te20 multilayers (with periods of 4–8 nm) is further enhanced due to the thermal or laser-induced intermixing of adjacent layers. The laser-induced intermixing process, as supported by experiments and model calculations, can be attributed to both the local heating and photo-effects in As6Se94/Se80Te20 multilayers, while only the thermal effects were observed for Si/Ge multilayers. Structural transformations, based on this enhanced interdiffusion, provide good capability for spatially patterning optoelectronic devices and digital information recording.
On the relation between the compressibility and the static structure factor of a fluid with a state-dependent pair-potential
Authors: Tejero C. F. , Baus M.
Published: December 2002

The compressibility equation of a fluid with an effective, state-dependent, pair-potential is derived. It is shown that the thermodynamic states for which the infinite wavelength limit of the static structure factor diverges are not consistent with the thermodynamic states for which the compressibility diverges whenever the effective potential is density-dependent. This result is in agreement with some recent numerical simulations.
Stabilization and fine control of Ge dot structure on Si (100) by C cover layer
Authors: Wakayama Y. , Sokolov L. V. , Zakharov N. , Werner P. , Gösele U.
Published: December 2002

A very thin layer of carbon deposited on a Ge dot surface was found to stabilize Ge dot structures. When the Ge dots were covered by the C layers, a hut with an elongated structure was maintained even after thermal annealing and a dome with a high aspect ratio was formed in Si matrix. Morphological analysis using atomic force microscopy and transmission electron microscopy revealed that stability of the Ge dot depends on the thickness of C cover layer. These results provide a method for a fine control of size and structure of the Ge dot on nanometer scale.
In situ transmission electron microscopy study of irradiation induced dewetting of ultrathin Pt films
Authors: Hu Xiaoyuan , Cahill David G. , Averback Robert S. , Birtcher Robert C.
Published: December 2002

Irradiation induced dewetting of 3–10 nm Pt thin films from SiO2 and SiNx substrates is studied using real-time in situ transmission electron microscopy (TEM). Fissures in the initial films form dry patches, which serve as nuclei for the dewetting process. Upon 800 keV Kr++ irradiation, the dry patches undergo filling-in, growth and coalescence. The dose range for these three stages of dewetting depends on the film thickness. Due to the effects of line tension, the growth of fissures is anisotropic, turning elongated fissures into rounded ones. The evolution of the area and width of individual fissures was extracted from a sequence of TEM images for 3 nm Pt/SiO2 under 800 keV Kr++ irradiation. We calculate the average velocity of receding contact lines to be ∼0.55±0.2 m/s during the thermal spike.
Strong blue emission from anodic alumina membranes with ordered nanopore array
Authors: Huang G. S. , Wu X. L. , Mei Y. F. , Shao X. F. , Siu G. G.
Published: December 2002

We have investigated the photoluminescence (PL) from anodic alumina membranes with an ordered nanopore array formed on bulk Al foils. Most of the membranes fabricated by anodization in oxalic acid showed a strong PL peak in the blue. Due to an obvious asymmetry, the PL peak can be Gaussian divided into two bands around 405 and 455 nm, having a slight shift with the sample formed in different acid concentrations. The PL excitation (PLE) spectral examinations and analyses revealed that the two blue PL bands originate from optical transitions in two kinds of different oxygen-deficient defect centers, F (oxygen vacancy with two electrons) and F+ (oxygen vacancy with only one electron) centers. Their distributions were discussed on the basis of the observed PL and PLE behaviors. Our experimental results improve the understanding of the blue-emitting property of anodic alumina membranes.
Experimental observation of electron velocity overshoot in AlN
Authors: Collazo R. , Schlesser R. , Sitar Z.
Published: December 2002

The energy distribution of electrons transported through intrinsic AlN heteroepitaxial films grown on 6H-SiC was directly measured as a function of the applied electric field. Following the transport, electrons were extracted into vacuum through a semitransparent Au electrode and their energy distribution was measured using an electron spectrometer. Transport through 80-nm-thick layers indicated the onset of quasiballistic transport for fields greater than 510 kV/cm. This was evidenced by a symmetric energy distribution centered at energies above the conduction band minimum. Drifted Fermi–Dirac energy distribution was fitted to the measured energy distribution, with the energy scale referenced to the bottom of the AlN conduction band. The drift energy and the carrier temperature were obtained as fitting parameters. Overshoots as high as five times the saturation velocity were observed and a transient length of less than 80 nm was deduced. In addition, the velocity-field characteristic was derived from these observations.
Exploring the propagator of a particle in a box
Authors: Fulling S. A. , Güntürk K. S.
Published: December 2002

The propagator of a particle in a one-dimensional box is quite different from the propagator for infinite space. It has a complicated but regular structure of everywhere dense singularities. We investigate the case of periodic boundary conditions both numerically and theoretically, leaving the slightly more complicated case of reflecting boundary conditions to the suggested problems. The singularity structure is shown to match up with the fractional revivals observed by many authors in wave packet studies.
An exact solution of the Lippmann–Schwinger equation in one dimension
Authors: Yang T. R. , Dvoynenko M. M. , Goncharenko A. V. , Lozovski V. Z.
Published: December 2002

We consider a one-dimensional scattering problem and establish a system of two integral equations for the local (self-consistent) electric field. The equations are derived using the standard Green’s function method. Their solution yields the local fields at any point of the system. To illustrate the efficacy of this approach, we apply it to a film and obtain analytical solutions that are identical to the Fabry–Perot solution. Some potential applications of the approach are also discussed.
Phase transition-like behavior in a low-pass filter
Authors: Krivine H. , Lesne A.
Published: December 2002

We discuss an iterative electric circuit for which the limits of infinite number of elements and zero dissipation in each element do not commute. The circuit is taken from the Feynman lectures, where it was argued on physical considerations that an infinite circuit made only of inductances and capacitances would behave as a dissipative system with nonvanishing resistance below a threshold frequency. The understanding of this behavior requires that the two limits be taken in the appropriate order. This simple example illustrates that caution in multiple limiting procedures is necessary to obtain the correct physical behavior. A close analogy with the standard ferromagnetic transition of the Ising model is drawn.