bluuebunny/crossref_metadata_2025 huggingface dataset:
Contact injection into polymer light-emitting diodes
Authors: Conwell E. M. , Wu M. W.
Published: July 2002

The variation of current I with voltage V for poly(phenylene vinylene) and other polymer light-emitting diodes has been attributed to carriers tunneling into broad conduction and valence bands. In actuality the electrons and holes tunnel into polaron levels and transport is by hopping among these levels. We show that for small injection the I–V characteristic is determined mainly by the image force, for large injection by space charge effects, but in both cases the strong variation of mobility with field due to disorder plays an important role.
Control of diamond heteroepitaxy on nickel by optical reflectance
Authors: Yang P. C. , Schlesser R. , Wolden C. A. , Liu W. , Davis R. F. , Sitar Z. , Prater J. T.
Published: July 2002

Real time in situ laser reflectometry was used to investigate changes in surface morphology observed during the nucleation of oriented diamond on Ni in a hot filament chemical vapor deposition reactor. Characteristic features observed in the intensities of reflected and scattered light were interpreted by comparison with scanning electron micrographs of the diamond seeded substrates quenched at sequential stages of the process. Based on this analysis, a process was developed in which the scattered light signal was used as a steering parameter. Using this process, oriented nucleation and growth of diamond on Ni can be repeatedly achieved.
Isotopic tracing during rapid thermal growth of silicon oxynitride films on Si in O2, NH3, and N2O
Authors: Baumvol I. J. R. , Stedile F. C. , Ganem J.-J. , Trimaille I. , Rigo S.
Published: July 2002

We performed isotopic tracing of O, N, and H during rapid thermal growth of silicon oxynitride films on silicon in two different sequential, synergistic gas environments: O2, followed by NH3, then followed by N2O; and N2O, followed by NH3. Using nuclear reaction analysis and high resolution depth profiling, we demonstrate that the oxynitride films grow by means of thermally activated atomic transport involving the three traced species. Concomitantly, isotopic exchange processes take place. Growth in these sequential gas environments leads to oxynitride films with N concentration profiles and H concentrations different from those obtained by commonly used processes like thermal growth in N2O only or thermal nitridation of SiO2 films in NH3.
Band alignments in GaInP/GaP/GaAs/GaP/GaInP quantum wells
Authors: Kwok S. H. , Yu P. Y. , Uchida K. , Arai T.
Published: July 2002

Pressure-dependent photoluminescence (PL) in several GaInP(ordered)-GaAs quantum well structures grown by metal organic vapor phase epitaxy is reported. Quantum well emission from GaAs is observed only in structures where thin (∼2 nm) GaP layers are inserted between the GaAs well and the GaInP barrier. By extrapolating the energies of the various inter and intralayer PL transitions observed under pressures (up to 5.5 GPa) to zero pressure, the different band offsets of the heterostructure have been determined.
Defect formation in GeO2–SiO2 glass by poling with ArF laser excitation
Authors: Takahashi M. , Fujiwara T. , Kawachi T. , Ikushima A. J.
Published: July 2002

We have investigated formation of Ge-related defects in a GeO2–SiO2 glass fiber preformed by poling with ArF laser excitation. Electric field dependence of the induced-defect concentrations was measured by means of the optical absorption. Several color centers such as the germanium electron-trapped centers and the Ge E′ center were induced. Concentrations of the induced germanium electron-trapped centers and Ge E′ center increase with increasing the electric field. Conversion efficiency from the germanium electron-trapped centers to the Ge E′ center was found to be independent of the electric field. The present result strongly suggests that the poling with ArF laser excitation is effective in the present GeO2–SiO2 glass for the formation of germanium electron-trapped centers.
A possible mechanism for improved light-induced degradation in deuterated amorphous-silicon alloy
Authors: Wei Jeng-Hua , Sun Ming-Shyan , Lee Si-Chen
Published: July 2002

We have studied light-induced photoconductivity degradation in an intrinsic hydrogenated and deuterated amorphous-silicon (a-Si) alloy. Deuterated a-Si turns out to be more stable under light exposure. A possible mechanism is proposed to explain this phenomenon. It is attributed to the highly efficient coupling between the localized Si–D wagging modes (∼510 cm−1) and the extended Si–Si lattice vibration modes (∼495 cm−1). The energy released from electron or hole capture at silicon dangling bonds causes localized vibrations of nearby Si–D bonds. The energy dissipates quickly to the background lattice and a higher recombination rate at local sites is needed in deuterated a-Si than in hydrogenated amorphous silicon to accumulate enough energy to break the nearby weak bonds.
A physically based predictive model of Si/SiO2 interface trap generation resulting from the presence of holes in the SiO2
Authors: Lenahan P. M. , Conley J. F.
Published: July 2002

A physically based model is developed which explains apparently unrelated aspects of the Si/SiO2 interface trap generation process; the predictions of the model are in at least semiquantitative agreement with observations previously reported in the literature. The model involves interactions between molecular hydrogen and trivalent silicon dangling bond defects in the oxide (E′ centers) and at the Si/SiO2 interface (Pb centers). Our model is primarily directed at interface trap generation caused by ionizing radiation and by hot hole injection phenomena observed in short channel transistors.
Lateral electron current operation of vertical cavity surface emitting lasers with buried tunnel contact hole sources
Authors: Wierer J. J. , Evans P. W. , Holonyak N. , Kellogg D. A.
Published: July 2002

Vertical cavity surface emitting lasers (VCSELs) are demonstrated with reverse-biased tunnel contact junctions allowing low-loss lateral electron current to support hole injection. A compact hybrid vertical cavity is employed consisting of a lower 6.5 period AlxOy/GaAs distributed Bragg reflector (DBR) formed by selective oxidation of high Al composition AlxGa1−xAs, and an electron-beam deposited 5 period SiO2/Si upper DBR. The cavity (active region) is defined also by selectively oxidizing a current-confining aperture. Lateral electron current drives a tunnel contact junction providing hole injection underneath the upper DBR through the oxide-defined current aperture. The p-type crystal in the VCSEL is reduced to a minimum, thus reducing resistive loss and device voltage.
Spatial distribution of neutrons guided through a monolithic tapered lens
Authors: Podurets K. M. , Sharov V. A. , Mildner D. F. R.
Published: July 2002

The cold neutron transmission through a monolithic polycapillary lens is studied by scanning a pinhole beam across the entrance cross section of the lens. The relative transmission as a function of bending radius of a tapered channel is obtained. The results are explained in terms of a reduced critical angle for total reflection for the tapered channels. A technique for qualitative examination of monolithic lenses is proposed.
Reduction of transient diffusion from 1–5 keV Si+ ion implantation due to surface annihilation of interstitials
Authors: Agarwal Aditya , Gossmann H.-J. , Eaglesham D. J. , Pelaz L. , Jacobson D. C. , Haynes T. E. , Erokhin Yu. E.
Published: July 2002

The reduction of transient enhanced diffusion (TED) with reduced implantation energy has been investigated and quantified. A fixed dose of 1×1014 cm−2 Si+ was implanted at energies ranging from 0.5 to 20 keV into boron doping superlattices and enhanced diffusion of the buried boron marker layers was measured for anneals at 810, 950, and 1050 °C. A linearly decreasing dependence of diffusivity enhancement on decreasing Si+ ion range is observed at all temperatures, extrapolating to ∼1 for 0 keV. This is consistent with our expectation that at zero implantation energy there would be no excess interstitials from the implantation and hence no TED. Monte Carlo modeling and continuum simulations are used to fit the experimental data. The results are consistent with a surface recombination length for interstitials of <10 nm. The data presented here demonstrate that in the range of annealing temperatures of interest for p-n junction formation, TED is reduced at smaller ion implantation energies and that this is due to increased interstitial annihilation at the surface.
Observation of oxide/Si(001)-interface during layer-by-layer oxidation by scanning reflection electron microscopy
Authors: Fujita S. , Watanabe H. , Maruno S. , Ichikawa M. , Kawamura T.
Published: July 2002

We have found that terrace contrast of oxidized Si(001) substrate observed with a scanning reflection electron microscopy (SREM) is reversed by progress in thermal oxidation by one atomic layer of Si. The cause for such terrace contrast reversion is that reflection electron intensity depends on Si-bond direction at oxide/Si interface. This fact was confirmed by calculations based on a multiple scattering theory. The motion of oxide/Si-bulk interface can be, thus, observed by SREM. The reversion and continuous change of the terrace contrast indicate that oxidation occurs monolayer by monolayer on Si(001) substrate.
Hydrogen-related photoluminescence in CdTe
Authors: Hamann J. , Blass D. , Casimir C. , Filz T. , Ostheimer V. , Schmitz C. , Wolf H. , Wichert Th. , Burchard A. , Deicher M. , Magerle R.
Published: July 2002

CdTe, nominally undoped, was exposed to a hydrogen plasma and to low energy H+ implantation. Under both conditions, seven typical photoluminescence lines are observed in the excitonic region. They are assigned to the presence of hydrogen in CdTe.
Effects of oxidation process on interface roughness of gate oxides on silicon: X-ray reflectivity study
Authors: Banerjee S. , Park Y. J. , Lee D. R. , Jeong Y. H. , Lee K.-B. , Yoon S. B. , Jo B. H. , Choi H. M. , Cho W.-J.
Published: July 2002

We report on the effects of the wet and dry oxidation processes on the interfacial roughness and time dependent dielectric breakdown (TDDB) characteristics of the poly-Si/SiO2/Si(100) trilayer. The interface roughness of the oxide layers buried under a thick poly-Si electrode has been investigated using an x-ray reflectivity technique. Analysis of x-ray reflectivity data for the trilayer samples and for a bare oxide film shows that interface roughness of poly-Si electrode/SiO2 interfaces depends on oxidation process while oxide layers have smooth SiO2/Si-subtstrate interfaces. TDDB of the SiO2 layer has also been observed to depend on the oxidation process, indicating that the interface roughness is a crucial factor affecting the TDDB characteristics. The wet oxidized SiO2 film is more stable to dielectric breakdown and has smoother interfaces than the dry oxidized sample.
The behavior of As precipitates in low-temperature-grown GaAs
Authors: Bourgoin J. C. , Khirouni K. , Stellmacher M.
Published: July 2002

We analyze the kinetics associated with the concentration and the growth of As precipitates during annealing in low-temperature-grown GaAs layers. We correlate them with that associated with the annealing of the As antisite related defect. This allows us to deduce that all these kinetics are governed by the mobility of the As interstitial whose migration energy is 0.44 eV.
Intraband transitions in semiconductor nanocrystals
Authors: Guyot-Sionnest P. , Hines M. A.
Published: July 2002

Intraband spectra of CdSe nanocrystal colloids are observed. The photoexcited nanocrystals, of average diameters 31.5, 38, and 43 Å, exhibit an isolated and strong infrared-induced absorption with peak energy between 0.5 and 0.3 eV. The energies and cross sections of the resonance are consistent with a one-electron transition between the delocalized 1Se and 1Pe states of the strongly confined quantum dots.
Bohm trajectories for the Monte Carlo simulation of quantum-based devices
Authors: Oriols X. , Garcı́a-Garcı́a J. J. , Martı́n F. , Suñé J. , González T. , Mateos J. , Pardo D.
Published: July 2002

A generalization of the classical ensemble Monte Carlo (MC) device simulation technique is proposed to simultaneously deal with quantum-mechanical phase-coherence effects and scattering interactions in quantum-based devices. The proposed method restricts the quantum treatment of transport to the regions of the device where the potential profile significantly changes in distances of the order of the de Broglie wavelength of the carriers (the quantum window). Bohm trajectories associated to time-dependent Gaussian wave packets are used to simulate the electron transport in the quantum window. Outside this window, the classical ensemble MC simulation technique is used. Classical and quantum trajectories are smoothly matched at the boundaries of the quantum window according to a criterium of total-energy conservation. A self-consistent one-dimensional simulator for resonant tunneling diodes has been developed to demonstrate the feasibility of our proposal.
Improvement of (Pb1−xLax)(ZryTi1−y)1−x/4O3 ferroelectric thin films by use of SrRuO3/Ru/Pt/Ti bottom electrodes
Authors: Liu Kuo-Shung , Tseng Tzu-Feng , Lin I-Nan
Published: July 2002

This work deposits (Pb1−xLax)(ZryTi1−y)1−x/4O3 (PLZT) thin films, possessing good ferroelectric properties (Pr=14.4 μC/cm2), on Pt/Ti/SiO2/Si substrates, using SrRuO3 perovskite as bottom electrodes. Precoating a metallic Ru layer on Pt/Ti/SiO2/Si substrates prior to depositing SrRuO3 bottom electrode further improves the film electrical properties. The optimum ferroelectric properties achieved are Pr=25.6 μC/cm2, Ec=47.1 kV/cm, and εr=1204. Analyzing the elemental depth profiles using secondary ions mass spectroscopy reveals that the presence of the metallic Ru layer effectively suppresses the outward diffusion of Ti and Si species. The interdiffusion between the SrRuO3 layer and the subsequently deposited PLZT is also substantially reduced, an effect that is presumed to be the primary factor in improving ferroelectric properties for PLZT thin films.
A low pressure mercury vapor resonance ionization image detector
Authors: Matveev O. I. , Smith B. W. , Winefordner J. D.
Published: July 2002

Narrow-band spectrally selective image detection based upon the resonance ionization of mercury atoms in a low pressure cell is described. Image dimensions and intensities were measured versus the wavelength of ionizing laser radiation and the dependence upon the voltage applied to electrodes was studied. The position sensitive image of the electron beam, created by two-step resonance photoionization of mercury, was studied when the detected laser beam was scanned spatially. A distorting influence of space charge due to positive mercury ions on the electron beam image was observed. Means of eliminating these distortions are discussed.
The effect of composition on the thermal stability of Si1−x−yGexCy/Si heterostructures
Authors: Kulik L. V. , Hits D. A. , Dashiell M. W. , Kolodzey J.
Published: July 2002

The thermal stability of molecular beam epitaxy grown Si1−x−yGexCy/Si heterostructures (0⩽x<0.30, y∼0.008) was studied using infrared absorption spectroscopy. The local vibrational mode of C in Si and Si1−x−yGex was used to quantify the loss of C atoms from substitutional sites with high temperature annealing. The activation energy (Ea=4.9 eV) for the loss of substitutional C achieved a maximum for the strain compensated alloy (x∼0.1). An additional increase of Ge content resulted in a rapid decrease in Ea, which was found to be 3.4 eV for x∼0.27. The nonmonotonic behavior of Ea on Ge content is explained by the effect of the interface strain between the epitaxial layer and Si substrate.
Phases of cobalt-iron ternary disilicides
Authors: Dézsi I. , Fetzer Cs. , Szűcs I. , Langouche G. , Vantomme A.
Published: July 2002

Cobalt–iron transition-metal disilicides were investigated by Mössbauer effect and x-ray diffraction in order to determine the concentration range of their homogeneous and separate phase formation. Except at low Co or Fe concentrations, Co and Fe formed separate CoSi2 and FeSi2 phases. Up to 10 at % Co was found soluble in β-FeSi2; Fe dissolved in CoSi2 below 1.5 at % and was positioned at two different sites of cubic symmetry. The results obtained for the phase formation in thin layers of epitaxial CoSi2 on Si implanted with Fe were in agreement with the results obtained for the bulk samples.
Single-mode optical waveguide fabricated by oxidization of selectively doped titanium porous silicon
Authors: Nagata Seiichi , Domoto Chiaki , Nishimura Takehiro , Iwameji Kazuaki
Published: July 2002

Metal-organic compound molecules were selectively doped into the larger pores of a two-layered porous silicon (PS) which had different pore sizes. PS with a graded pore-size distribution was area-selectively formed by utilizing a thin film mask. Titanium-organic compound molecules were doped into the larger pores and the PS was oxidized to form an optical waveguide. Single-mode transmission of 1.55 μm wavelength laser light was successfully observed.
Relaxed Ge0.9Si0.1 alloy layers with low threading dislocation densities grown on low-temperature Si buffers
Authors: Peng C. S. , Zhao Z. Y. , Chen H. , Li J. H. , Li Y. K. , Guo L. W. , Dai D. Y. , Huang Q. , Zhou J. M. , Zhang Y. H. , Sheng T. T. , Tung C. H.
Published: July 2002

Relaxed GexSi1−x epilayers with high Ge fractions but low threading dislocation densities have been successfully grown on Si (001) substrate by employing a stepped-up strategy and a set of low-temperature GeySi1−y buffers. We show that even if the Ge fraction rises up to 90%, the threading dislocation density can be kept lower than 5×106 cm−2 in the top layers, while the total thickness of the structure is no more than 1.7 μm.
Detection of single infrared, optical, and ultraviolet photons using superconducting transition edge sensors
Authors: Cabrera B. , Clarke R. M. , Colling P. , Miller A. J. , Nam S. , Romani R. W.
Published: July 2002

We have demonstrated the use of superconducting transition edge sensors for the wide-band detection of individual photons from the mid infrared (IR), through the optical, and into the far ultraviolet (UV). These tungsten transition edge sensors are squares about 18 μm on a side and detect single photon events above a threshold of 0.3 eV (4 μm wavelength), with an energy resolution of 0.15 eV full width at half maximum, and with a risetime (falltime) of .5 μs (60 μs). The calibration data extend up to the UV cutoff of the fiber optic feed at 3.5 eV (350 nm).
Luminescence quenching in Er-doped BaTiO3 thin films
Authors: Yi G.-C. , Block B. A. , Ford G. M. , Wessels B. W.
Published: July 2002

Luminescence quenching in Er-doped epitaxial BaTiO3 thin films was investigated. From transient photoluminescence, nonradiative decay processes were measured, and a nonradiative resonant energy transfer model was developed. The nonradiative transition rate is linearly proportional to the OH impurity concentration in the films, indicating it is responsible for the observed quenching behavior.
Fabrication of midgap metal gates compatible with ultrathin dielectrics
Authors: Buchanan D. A. , McFeely F. R. , Yurkas J. J.
Published: July 2002

A process has been described which can produce a midgap tungsten gate compatible with the current and future complementary metal–oxide–semiconductor technology. The tungsten was deposited directly onto a 3.0 nm SiO2 gate dielectric without measurable degradation of any of its electrical properties. The tungsten deposition process yields no reactive or corrosive by-products that affect the gate dielectric integrity. The tungsten film is found to be pure within the limits of several analytical techniques and the resistivity of the tungsten films was found to be within a factor of 2 of the bulk value.
Time-gated x-ray tomography
Authors: Grätz M. , Kiernan L. , Wahlström C.-G. , Svanberg S. , Herrlin K.
Published: July 2002

Time-gated x-ray tomography with scatter reduction is demonstrated using a laser-produced plasma as an ultrashort-pulse x-ray source in combination with a time-resolving streak-camera detector. Backprojections of a phantom imbedded in 9 cm of water show an effective 50% increase in contrast when scattered x-ray quanta (being delayed in time) are suppressed by gating on the prompt, nonscattered photons. Implications for future volumetric tomography, in particular concerning possible dose reductions, are discussed.
Activation fields in ferroelectric thin film capacitors: Area dependence
Authors: Song T. K. , Aggarwal S. , Gallais Y. , Nagaraj B. , Ramesh R. , Evans J. T.
Published: July 2002

We report the activation field characteristics of (La,Sr)CoO3/Pb(Nb,Zr,Ti)O3/(La,Sr)CoO3 capacitors with areas varying from 13 to 9600 μm2. Switching properties such as maximum current and switching time depend on the capacitor area and measuring circuit elements, but the activation field is independent of capacitor area and measuring circuit parameters. Area independence of activation fields is also confirmed in (Pb,La)(Zr,Ti)O3 thin film capacitors. Two different approaches have been used to determine the activation field, yielding similar results. It is concluded that activation field is an intrinsic property and is a good quantitative measure of the ferroelectric switching properties.
Cubic-phase GaN light-emitting diodes
Authors: Yang Hui , Zheng L. X. , Li J. B. , Wang X. J. , Xu D. P. , Wang Y. T. , Hu X. W. , Han P. D.
Published: July 2002

The feasibility of growing device-quality cubic GaN/GaAs(001) films by metal organic chemical vapor deposition has been demonstrated. The optical quality of the GaN films was characterized by room-temperature photoluminescence measurements, which shows a full width at half maximum of 46 meV. The structural quality of the films was investigated by transmission electron microscopy. There are submicron-size grains free from threading dislocations and stacking faults. More importantly, a cubic-phase GaN blue light-emitting diode has been fabricated. The device process, which is very simple and compatible with current GaAs technology, indicates a promising future for the blue light-emitting diode.
Control of silica cap properties by oxygen plasma treatment for single-cap selective impurity free vacancy disordering
Authors: Helmy A. Saher , Murad S. K. , Bryce A. C. , Aitchison J. S. , Marsh J. H. , Hicks S. E. , Wilkinson C. D. W.
Published: July 2002

By exposing the SiO2 films used as annealing caps in the process of impurity free vacancy disordering (IFVD) to an oxygen plasma, which is produced in a reactive ion etching machine, the effect of the exposed caps on quantum well intermixing can be substantially controlled. The effect of the oxygen treatment is manifested in inhibiting the Ga outdiffusion from GaAs/AlGaAs heterostructures. A selective IFVD process using identical silica caps has been obtained by selective exposure of the caps to oxygen plasma. Differential band gap shifts in excess of 100 meV were achieved with control samples exhibiting band gap shifts less than 10 meV.
Controlled spontaneous emissions from current-driven semiconductor microcavity triodes
Authors: Yamashita S. , Nakamura S. , Kobayashi S. , Ueda T. , Kadoya Y. , Yamanishi M.
Published: July 2002

We demonstrate the alteration of spontaneous emissions in semiconductor microcavity triodes, in which the carriers are injected by current into a single quantum well (QW) active region and the emission wavelength was varied by the voltage applied to the QW through the quantum confined Stark effect. The clear changes in the emission spectra and radiation patterns with the change of the voltage manifest that the spontaneous emission is well modified by the microcavity under the control of the applied voltage.
Surface energetics, pit formation, and chemical ordering in InGaN alloys
Authors: Northrup J. E. , Romano L. T. , Neugebauer J.
Published: July 2002

We present first-principle calculations of the structure and energetics of the GaN(101_1) surface, and present models for the reconstructions. A strong preference for In surface segregation and occupation of specific surface sites is demonstrated. We argue that inverted pyramid defect formation is enhanced by segregation of In on (101_1) facets. We propose that the chemical ordering recently observed in InGaN alloys is driven by the preference for In incorporation at the sites of reduced N coordination present at step edges during growth on the (0001) and (0001_) surfaces.
Growth and study of self-organized Ge quantum wires on Si(111) substrates
Authors: Jin G. , Tang Y. S. , Liu J. L. , Wang K. L.
Published: July 2002

Self-organized Ge quantum wires were grown on regular atomic steps formed along [1̄10] direction on Si(111) substrates by annealing at 870 °C in vacuum. The samples were then studied by atomic force microscopy, polarization-dependent Raman scattering, and low temperature photoluminescence spectroscopy. The results suggest that good quality Ge quantum wires were formed and clear quantum confinement-induced quantization in the wires was observed.
Oxidation kinetics in La0.67Ba0.33MnO3−δ epitaxy on SrTiO3 (001) during pulsed-laser deposition
Authors: Zhu X. D. , Si Weidong , Xi X. X. , Li Qi , Jiang Q. D. , Medici M. G.
Published: July 2002

Using an oblique-incidence optical reflectance difference technique, we study the kinetics of La0.67Ba0.33MnO3−δ (LBMO) epitaxy on SrTiO3(001) during pulsed-laser deposition. By monitoring the recovery of the optical response function from one-monolayer-deposited LBMO, we found that under the conditions studied, the epitaxy was rate limited by the oxidation of the as-deposited monolayer with an activation barrier of 1 eV/atom or 23 kcal/mol. The result reveals the origin of oxygen deficiency often found in manganite thin films.
Electron paramagnetic resonance of radiation defects in hydrogen-implanted silicon detected by spin-dependent microwave photoconductivity
Authors: Laiho R. , Vlasenko L. S. , Vlasenko M. P. , Kozlov V. A. , Kozlovski V. V.
Published: July 2002

Electron paramagnetic resonance (EPR) spectra of radiation defects induced by low-energy protons (100 keV) in a thin near-surface layer (L<1 μm) of silicon crystals are detected with spin-dependent microwave photoconductivity. It is found that EPR spectra of the excited triplet states of oxygen+vacancy complexes and spectra related to carbon-containing defects are formed at low proton irradiation doses of about 2×1012–1013 cm−2. When the irradiation dose is increased from 1013 to 5×1013 cm−2, a fast decrease of the intensity of the detected EPR spectra takes place. This effect is explained by passivation of the radiation defects by hydrogen.
Highly-ordered carbon nanotube arrays for electronics applications
Authors: Li J. , Papadopoulos C. , Xu J. M. , Moskovits M.
Published: July 2002

Highly-ordered arrays of parallel carbon nanotubes were grown by pyrolysis of acetylene on cobalt within a hexagonal close-packed nanochannel alumina template at 650 °C. The nanotubes are characterized by a narrow size distribution, large scale periodicity, and high densities. Using this method ordered nanotubes with diameters from 10 nm to several hundred nm and lengths up to 100 μm can be produced. The high level of ordering and uniformity in these arrays is useful for applications in data storage, field emission displays and sensors, and offers the prospect of deriving computational functions from the collective behavior of symmetrically coupled nanotubes. The fabrication method used is compatible with standard lithographic processes and thus enables future integration of such periodic carbon nanotube arrays with silicon microelectronics.
Band gap and wave guiding effect in a quasiperiodic photonic crystal
Authors: Jin Chongjun , Cheng Bingying , Man Baoyuan , Li Zhaolin , Zhang Daozhong , Ban Shouzheng , Sun Bo
Published: July 2002

A two-dimensional octagonal quasiperiodic photonic crystal composed of alumina cylinders is prepared. The transmission spectra of the quasicrystal are measured in the microwave region for the TM wave. We find that the position and width of the band gap do not depend on the incident direction, while the band structure can appear for quite a small piece of the quasicrystal. Two types of waveguide, a straight guide and a bending guide with two sharp 90° corners, are fabricated by removing three rows of cylinders. The measured transmittances show that the guiding efficiency for both waveguides is high.
Microscopical aspects of boron diffusion in ultralow energy implanted silicon
Authors: Napolitani E. , Carnera A. , Schroer E. , Privitera V. , Priolo F. , Moffatt S.
Published: July 2002

The transient enhanced diffusion of ultralow energy implanted B is reported in this letter. The mechanism giving rise to an enhancement of the diffusion during postimplantation anneal is investigated in detail by monitoring the diffusion of B as a function of temperature in the range 600–750 °C, for implant energies of 500 eV and 1 keV. The contribution of several classes of defect clusters to the anomalous diffusion phenomenon has been detected and interpreted. Both an ultrafast diffusion, occurring during the ramp-up of the thermal process, and a transient enhancement of the diffusion with characteristic decay times shorter by orders of magnitude than the known transient enhanced diffusion lifetimes, have been evidenced. The activation energy for the enhanced diffusion has been measured and found to be 1.7 eV.
Er doped nanocrystalline ZnO planar waveguide structures for 1.55 μm amplifier applications
Authors: Mais N. , Reithmaier J. P. , Forchel A. , Kohls M. , Spanhel L. , Müller G.
Published: July 2002

Amplifying planar waveguide structures in Er-doped nanocrystalline II/VI semiconductor layer systems were developed by photolithography and wet chemical etching. 2 μm thick planar waveguides on glass substrates with lateral dimensions down to 5 μm with rectangular cross section were realized. By optical excitation a maximum gain of 82 cm−1 could be determined, which is sufficiently high to allow the design of compact planar amplifiers in this material system. The influence of a thermal sintering step on the gain spectrum and on the fluorescence lifetime has been investigated. By increasing the sintering temperature to 800 °C a consistent increase of gain and fluorescence lifetime was observed.
The use of thickness graded samples to investigate the elastic to plastic relaxation in ZnSe/GaAs(001)
Authors: Etgens V. H. , Capelle B. , Carbonell L. , Eddrief M.
Published: July 2002

The strain relaxation process of ZnSe grown by molecular beam epitaxy on GaAs(001) has been studied using high resolution x-ray diffraction. One single sample with a tailored thickness gradient has been used, allowing us to continuously follow the strain in a wide range of thicknesses. The relaxation starts around 1300 Å with the coexistence of fully strained and partially relaxed regions of the ZnSe and continues up to 1600 Å. These findings can be explained by the formation of misfit dislocations on the top surface with subsequent migration to the ZnSe/GaAs interface.
Two-stage amplifier based on a double relaxation oscillation superconducting quantum interference device
Authors: Podt M. , van Duuren M. J. , Hamster A. W. , Flokstra J. , Rogalla H.
Published: July 2002

A low-noise single-chip two-stage superconducting quantum interference device (SQUID) system with a double relaxation oscillation SQUID as the second stage has been realized. The system was operated in a direct voltage readout mode, with a closed loop bandwidth up to 1 MHz. Operated at 4.2 K, the white flux noise measured in flux locked loop was 1.3 μΦ0/√Hz, corresponding to an energy sensitivity of ε≈27h. Owing to the large flux-to-voltage transfer of up to 3.6 mV/Φ0, the room-temperature preamplifier noise did not dominate the overall flux noise.
Conduction mechanism under quasibreakdown of ultrathin gate oxide
Authors: He Y. D. , Guan Hao , Li M. F. , Cho Byung Jin , Dong Zhong
Published: July 2002

The conduction mechanism under quasibreakdown of ultrathin gate oxide has been studied systematically in both n and p metal–oxide–semiconductor field effect transistors (MOSFETs) with a 3.7 nm gate oxide. The carrier separation experiment is conducted to investigate the evolutions of gate, source/drain, and substrate currents before and after quasibreakdown. It is shown that after quasibreakdown, the substrate current and the source-drain current versus the gate voltage curves are surprisingly analogous to those curves observed in fresh MOSFET with a gate oxide of direct tunneling thickness. This strongly supports the quasibreakdown model based on the local physically damaged region by which the effective oxide thickness is reduced. When direct tunnelings of conduction band electrons, valence band electrons and holes through the effectively thinned gate oxide are taken into account, the major experimental observations in the quasibreakdown can be explained in a unified way.
Time-resolved photoluminescence studies of InxGa1−xAs1−yNy
Authors: Mair R. A. , Lin J. Y. , Jiang H. X. , Jones E. D. , Allerman A. A. , Kurtz S. R.
Published: July 2002

Time-resolved photoluminescence spectroscopy has been used to investigate carrier decay dynamics in a InxGa1−xAs1−yNy (x∼0.03, y∼0.01) epilayer grown on GaAs by metal organic chemical vapor deposition. Time-resolved photoluminescence (PL) measurements, performed for various excitation intensities and sample temperatures, indicate that the broad PL emission at low temperature is dominated by localized exciton recombination. Lifetimes in the range of 0.07–0.34 ns are measured; these photoluminescence lifetimes are significantly shorter than corresponding values obtained for GaAs. In particular, we observe an emission energy dependence of the decay lifetime at 10 K, whereby the lifetime decreases with increasing emission energy across the PL spectrum. This behavior is characteristic of a distribution of localized states, which arises from alloy fluctuations.
Unprecedented magnetoresistance in Cd-substituted Tl2Mn2O7 pyrochlores
Authors: Alonso J. A. , Velasco P. , Martı́nez-Lope M. J. , Casais M. T. , Martı́nez J. L. , Fernández-Dı́az Marı́a T. , de Paoli J. M.
Published: July 2002

Moderate pressure techniques (P=20 kbar) have been used to prepare Tl2−xCdxMn2O7 (0⩽x⩽0.4) pyrochlore-like materials. The x=0.2 compound has been characterized by neutron powder diffraction, magnetic, magnetotransport, and Hall measurements. This material is ferromagnetic below TC=110 K. Both electrical resistance and magnetoresistance (MR) are enhanced with respect to stoichiometric Tl2Mn2O7, due to the drastic reduction in the number of carriers (electrons) induced by hole doping. MR(0.5 T) is higher than 106% at 120 K, and MR(9 T) is 30% at room temperature. We show that hole doped derivatives of Tl2Mn2O7 are promising candidates in which to search for large bulk magnetoresistance.
Nanoquasicrystalline phase produced by devitrification of Hf–Pd–Ni–Al metallic glass
Authors: Louzguine D. V. , Ko M. S. , Inoue A.
Published: July 2002

Structure changes in the Hf–Al–Ni–Pd metallic glass on heating have been studied by x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. It has been found that the first stage of the devitrification process is related to the precipitation of fine particles of an icosahedral phase from about 5 to 15 nm in size. A direct evidence of the formation of the icosahedral phase has been done using nanobeam diffraction in transmission electron microscope.
Generating-function method for fusion rules
Authors: Bégin L. , Cummins C. , Mathieu P.
Published: July 2002

This is the second of two articles devoted to an exposition of the generating-function method for computing fusion rules in affine Lie algebras. The present paper focuses on fusion rules, using the machinery developed for tensor products in the companion article. Although the Kac–Walton algorithm provides a method for constructing a fusion generating function from the corresponding tensor-product generating function, we describe a more powerful approach which starts by first defining the set of fusion elementary couplings from a natural extension of the set of tensor-product elementary couplings. A set of inequalities involving the level are derived from this set using Farkas’ lemma. These inequalities, taken in conjunction with the inequalities defining the tensor products, define what we call the fusion basis. Given this basis, the machinery of our previous paper may be applied to construct the fusion generating function. New generating functions for sp∧(4) and su∧(4), together with a closed form expression for their threshold levels are presented.
The ONIOM (our own N-layered integrated molecular orbital + molecular mechanics) method for the first singlet excited (S1) state photoisomerization path of a retinal protonated Schiff base
Authors: Vreven Thom , Morokuma Keiji
Published: July 2002

By testing a large number of ONIOM (our own N-layered integrated molecular orbital + molecular mechanics) combinations against the standard complete active space self-consistent field (CASSCF) method with the 6-31G(d) basis set, we have investigated the suitability of the ONIOM (molecular orbital + molecular orbital) method for the investigation of the first singlet excited state (S1) photoisomerization pathways in protonated Schiff bases (PSBs). For the isomerization reaction of an 11-nonhydrogen (H) PSB (10-non-H Schiff base plus one methyl group), ONIOM can accurately reproduce the standard CASSCF(10e/10o) (10 active electrons in 10 orbitals) results for only 10% of the computer time. The model system, which includes the protonated Schiff base group as well as the isomerization bond, was always treated at the CASSCF level. With the unrestricted Hartree–Fock first triplet state (T1) in the low level, the S1 energy profile is reproduced accurately, while time-dependent Hartree–Fock or single excitation configuration interaction in the low level reproduces the difference between the singlet ground state (S0) and S1 states very well. Using our ONIOM method, we also computed the first S1 isomerization energy profile of the entire retinal protonated Schiff base.
Abnormal selection rules of interface modes in ultrathin GaAs/AlAs superlattice
Authors: Zhang S. L. , Zhang J. , Yang C. L. , Li L. Y. , Zhang L. , Planel R.
Published: July 2002

We observed a violation of the normal Raman selection rule in the resonant Raman spectra of interface (IF) phonon modes of the ultrathin (GaAs)4/(AlAs)2 superlattice. Contrary to the prediction of conventional theories, all four IF modes were observed in both (XX) and (XY) geometries. The result can be interpreted as a consequence of the deep penetration of the electron wave function in the GaAs wells into the AlAs barriers and a lack of definite parity of the electron wave function. Furthermore, our result indicates that conventional theory for bulk (thicker) systems may need to be modified and further developed to be applicable to ultrathin systems.
Patterns of glow peak movement in rare earth doped lanthanum fluoride
Authors: Yang B. , Townsend P. D.
Published: July 2002

Low temperature thermoluminescence data from rare earth doped lanthanum fluoride is characterized by numerous glow peaks. These differ in temperature as a function of the substituted rare earth ion, dopant concentration and thermal annealing. Analysis of the component bands in terms of activation energy, frequency factor and kinetic order reveals simple patterns in which the movement of the glow peaks is related to the ionic radii of the rare earth ions. Models for the thermoluminescence signals resulting from close association of the dopant recombination sites and the charge traps are discussed. Further consideration of a preference for impurity clustering, in order to reduce lattice strain, is used to explain the concentration and annealing induced changes.
Non-L2 solutions to the Seiberg–Witten equations
Authors: Adam Christoph , Muratori Bruno , Nash Charles
Published: July 2002

We show that a previous paper of Freund describing a solution to the Seiberg–Witten equations has a sign error rendering it a solution to a related but different set of equations. The non-L2 nature of Freund’s solution is discussed and clarified and we also construct a whole class of solutions to the Seiberg–Witten equations.
An ultralow supply voltage circuit for driving blue light emitting diodes
Authors: Liao Tai-Shan , Chang Chun-Ming
Published: July 2002

A low-cost and simple circuit for driving blue light emitting diodes with ultralow supply voltage is demonstrated. By using only three transistors and two voltage multipliers, a blue light emitting diode was driven with a supplied voltage as low as 0.8 V.
The ceramic-cup microwave ion source for sealed-tube neutron generator
Authors: Jing Shiwei , Li Wensheng , Gu Li , Liu Linmao
Published: July 2002

A microwave proton source for sealed-tube neutron generator has been built in the radiation Technology Institute of Northeast Normal University. The plasma resonance chamber is made of 95%Al2O3 ceramic material. The microwave absorption as a function of the magnetic field and the pressure is studied. The microwave absorption efficiencies, (Pi−Pr)/Pi are more than 90% when the magnetic field at the microwave windows is 0.095 T and incident microwave power is 300–500 W, at the same time, the impedance between the microwave circuit and the plasma source is well matched. Two-grid multi-hole extraction electrodes are employed to extract ion. The maximum proton current of 30 mA is obtained when the extraction voltage is 5.4 KV and the incident microwave power is 300 W.
Strain relaxation and defect reduction in InxGa1−xAs/GaAs by lateral oxidation of an underlying AlGaAs layer
Authors: Chang K. L. , Epple J. H. , Pickrell G. W. , Lin H. C. , Cheng K. Y. , Hsieh K. C.
Published: July 2002

The strain relaxation in In0.25Ga0.75As and In0.4Ga0.6As grown on GaAs substrates at low temperature has been studied before and after laterally oxidizing an underlying Al0.98Ga0.02As layer. The relaxation as a function of layer thickness has been measured by cross-sectional transmission electron microscopy and x-ray analysis. It is found that oxidation of the Al0.98Ga0.02As layer improves the relaxation of the strained InxGa1−xAs layer. Moreover, the interfacial misfit dislocations have been removed, and the threading dislocation density has decreased approximately by one order of magnitude after oxidation.
Magnetization pattern of ferromagnetic nanodisks
Authors: Raabe J. , Pulwey R. , Sattler R. , Schweinböck T. , Zweck J. , Weiss D.
Published: July 2002

We explore the magnetization pattern of Co and permalloy disks with diameters between 80 nm and 1 μm by using two complementary experimental techniques: Lorentz microscopy and magnetic force microscopy (MFM). By means of Lorentz microscopy we show that the dominating magnetization pattern of the disks is a vortex structure with closed flux lines in the plane of the disks. Complementary MFM measurements demonstrate that the magnetization in the center of the disks is tilted out of the plane of the disk. The experimental findings closely agree with corresponding micromagnetic calculations.
Correlation between compositional and refractive index profiles in LiNbO3:Zn diffused optical waveguides
Authors: Nevado R. , Cussó F. , Lifante G. , Caccavale F. , Sada C. , Segato F.
Published: July 2002

Waveguides fabrication in Z- and X-cut LiNbO3 crystals by vapor zinc diffusion has been studied by secondary ion mass spectrometry and optical measurements. Compositional analysis of diffused substrates shows the formation of a Zn rich superficial layer, followed by a deeper region with decreasing Zn concentration. A subsequent thermal annealing process has been performed to let zinc ions further diffuse into the substrates. The composition profiles have been correlated with the refractive index profiles, reconstructed by optical reflectivity measurements. The results and the nature of the detected layers are discussed and correlated with previous x-ray studies obtained in the same samples.
Hydrogen passivation of deep levels in n–GaN
Authors: Hierro A. , Ringel S. A. , Hansen M. , Speck J. S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

Differential postgrowth hydrogen passivation of deep levels in n–GaN grown by metal-organic chemical vapor deposition has been directly observed by means of both deep level transient spectroscopy and deep level optical spectroscopy. Two deep levels found at Ec−Et=0.62 and 1.35 eV show strong H passivation effects, with their concentrations decreasing by a factor of ⩾30 and ∼14, respectively. The decrease in the 0.62 eV trap concentration together with its correlation with the presence of Mg in n–GaN is consistent with Mg–H complex formation. A band of closely spaced deep levels observed at Ec−Et=2.64–2.80 eV narrows to Ec−Et=2.74–2.80 eV after hydrogenation, consistent with hydrogen complexing with VGa3− defects as anticipated by earlier theoretical results. Finally, a deep level at Ec−Et=3.22 eV likely related to background acceptors remains unaffected by hydrogen.
Ferromagnetic resonance spectroscopy with a micromechanical calorimeter sensor
Authors: Moreland John , Löhndorf Markus , Kabos Pavel , McMichael R. D.
Published: July 2002

We describe a new type of ferromagnetic resonance (FMR) spectroscopy that is based on a calorimeter sensor. We use an atomic force microscopy cantilever coated with a ferromagnetic thin film as a bimaterial sensor to measure absorption of microwaves at 9.17 GHz. The spectra show a peak in the cantilever deflection as a function of applied magnetic field corresponding to a peak in the absorbed microwave power that occurs at the FMR resonance of the ferromagnetic film. The saturation magnetization Meff and the damping factor α were determined from the FMR microwave absorption spectra for Co, NiFe, and Ni thin films. The data correlate well with conventional FMR spectra taken with a tuned cavity spectrometer. Our instrument can detect magnetic moments as small as 1.3×10−12 A m2 (1.3×10−9 emu) with prospects for sensitivity improvements to the 1×10−16 A m2 (1×10−12 emu) level. The technique provides a potentially superior way to make quantitative measurements of saturation magnetization of thin-film samples with very small total magnetic moments.
Reaction kinetics in zeolites as a random walk problem: Theory versus experiment
Authors: Barzykin A. V. , Hashimoto S.
Published: July 2002

We present a continuous time random walk (CTRW) model for the kinetics of pseudo-first-order long-range reactions in zeolites assisted by migration between the adsorption sites. Both Markovian and non-Markovian formulations admit a simple matrix solution in terms of the lattice Green’s function. Diffuse-reflectance transient absorption study of triplet anthracene quenching by azulene in NaY zeolite is reported giving a direct visual indication of the long-range reaction between molecules residing in the neighboring cages, reflecting an open structure of the cage network. The Markovian model with unbiased nearest-neighbor CTRW on a diamond lattice of NaY supercages explains the experimental decay data. This practical example demonstrates a general possibility to consistently recover information about intercage transport in zeolites and related microporous materials by using an indicator reaction and an appropriate theoretical interpretation, complementary to conventional NMR techniques.