bluuebunny/crossref_metadata_2025 huggingface dataset:
Giant fluctuation magnetoresistance in MnAs thin films
Authors: Grishin A. M. , Khartsev S. I. , Rao K. V.
Published: July 2002

We present the similarity in magnetic and transport properties of MnAs and perovskite La1−xCaxMnO3 thin films which exhibit a colossal magnetoresistance. Submicron thickness magnetic MnAs films exhibiting a continuous magnetic phase transition have been molecular beam epitaxy grown on sapphire substrates. A giant magnetoresistance (of order of 10% at H=10 kOe) arising from critical spin fluctuations in the vicinity of phase transition (T≊40 °C) is observed. The concomitant large pyromagnetic (d ln M/dT=−0.5 K−1) and pyroresistive (d ln R/dT=0.046 K−1) effects along with a high magnetoresistance make MnAs films promising for applications.
Infrared Raman scattering as a sensitive probe for the thermal conductivity of chemical vapor deposited diamond films
Authors: Wörner E. , Wagner J. , Müller-Sebert W. , Wild C. , Koidl P.
Published: July 2002

The infrared Raman spectrum of chemical vapor deposited (CVD) diamond films has been correlated with the in-plane thermal conductivity of the films. The scattering strength of the 1332 cm−1 zone-center phonon line of diamond, measured relative to the intensity of the nondiamond carbon phase, was found to increase strongly with increasing thermal conductivity. A good correlation between these two properties was found even for the highest quality CVD diamond films with peak thermal conductivities up to 54 W/cm K. The dependence of the peak thermal conductivity on the intensity of the 1332 cm−1 phonon line normalized to the scattering strength of the nondiamond carbon phase can be described by a power law with an exponent of 0.5.
Influence of backsurface argon bombardment on SiO2–Si interface characteristics
Authors: Lai P. T. , Huang M. Q. , Zeng X. , Zeng S. H. , Li G. Q.
Published: July 2002

A low-energy (550 eV) argon-ion beam was used to directly bombard the backsurface of polysilicon-gate metal-oxide-semiconductor (MOS) capacitors after the completion of all conventional processing steps. The interface characteristics of the MOS capacitors were investigated. The results show that, as the bombardment dose increases, the active dopant concentration near the oxide-semiconductor interface gets higher; maximum midgap energy increases; and interface-state density becomes lower. This simple technique is compatible with existing integrated-circuit processing, and can easily improve the interface characteristics, and therefore the electrical characteristics of MOS devices.
Type II mid-infrared quantum well lasers
Authors: Malin J. I. , Meyer J. R. , Felix C. L. , Lindle J. R. , Goldberg L. , Hoffman C. A. , Bartoli F. J. , Lin C.-H. , Chang P. C. , Murry S. J. , Yang R. Q. , Pei S.-S.
Published: July 2002

Pulsed, optically pumped four-constituent Type-II (InAs-Ga1−xInxSb-InAs-AlSb) quantum well lasers emitting at 3.9–4.1 μm were observed to lase up to 285 K with a characteristic temperature T0 of 35 K for 170 K ≤Top≤270 K. A theoretical analysis predicts dramatic further improvements once the potential for suppressing Auger recombination is fully realized.
Theoretical and experimental study of silicon-based angular filters
Authors: Sigalas M. M. , McCalmont J. S. , Ho K.-M. , Tuttle G.
Published: July 2002

We study periodic structures constructed by low resistivity Si wafers which allow only the transmission of electromagnetic waves incident at a certain angle. We call those materials angular filters. The angular width of the transmission peak can be controlled by changing the thickness of the structure and/or by changing the resistivity of Si wafers. The basic idea behind the unusual properties of those materials lies on the Borrman effect or anomalous transmission of x rays through the crystals. Measured responses are in good agreement with theoretical simulations. Although the present structure was designed and built to work at around 100 GHz, similar structures can be designed for any other frequency region.
Synchrotron radiation ablative photodecomposition and production of crystalline fluoropolymer thin films
Authors: Katoh T. , Zhang Y.
Published: July 2002

Deposition of crystalline thin films of polytetrafluoroethylene (PTFE) was carried out on Si(100) substrates by synchrotron irradiation of a PTFE target in vacuo. In situ mass spectrometric analysis of gaseous species evolved during the irradiation shows that, different from the laser ablation of PTFE for the deposition, the SR-induced reactions should be ablative photochemical decomposition (APD) rather than photothermal unzipping decomposition, yielding saturated fluorocarbons rather than monomers as the main gaseous products. Detection of a trace of CF3 in the deposited films by XPS and FTIR was consistent with our APD mechanism. In our processing, an increase in the target temperature made great improvements including considerable enhancement of the deposition rates, reduction of the CF3 component, and achievement of the crystalline features closer to the PTFE target, whereas an increase in the substrate temperature made the film surface rough.
Fabrication and fundamental properties of an edge-emitting device with step-index porous silicon waveguide
Authors: Araki Minoru , Koyama Hideki , Koshida Nobuyoshi
Published: July 2002

It is demonstrated that an edge-emitting device with a waveguide structure based on luminescent porous silicon (PS) operates at wavelengths in the visible region. The PS device is composed of an upper-side cladding Al thin film, an active PS layer, and a lower-side cladding PS layer with a smaller refractive index. When excited by an Ar ion laser with a wavelength of 458 nm, the device operates as an optical waveguide and consequently visible light can be observed from the cleaved facets of the device. The emitted light is significantly polarized along the direction of the transverse-electric (TE) mode due to the metal cladding layer. These results suggest that PS is useful as a component for silicon-based photonic integration.
A comparative study of ultraviolet emission with peak wavelengths around 350 nm from oxidized porous silicon and that from SiO2 powder
Authors: Qin G. G. , Lin J. , Duan J. Q. , Yao G. Q.
Published: July 2002

Ultraviolet (UV) light emission with almost the same peak wavelengths from thermally oxidized porous silicon (OPS) (340, 355, and 370 nm) and SiO2 powder (340, 350, and 370 nm) has been observed. Photoluminescence excitation spectra of OPS without Si nanoscale particles (SNP) and those of SiO2 powder are very similar, however, very different from those of the OPS with SNP. Three types of luminescence centers with luminescence wavelengths around 350 nm are responsible for UV light emission, and photoexcitation in OPS with SNP occurs in SNP as well as in Si oxide layers covering SNP.
Single molecule fluorescence in inhomogeneous environments
Authors: Novotny Lukas
Published: July 2002

A single molecule in an inhomogeneous environment is studied theoretically using phenomenological theory. The molecule is located on a planar glass substrate and a finite sized, three dimensional object is scanned over the molecule at different heights. Lifetime and quantum yield are calculated as a function of the lateral position of the object. The analysis is based on a new field expansion method using Green’s functions of a layered reference system as basis functions. It is found that, near the edges of the object, the molecular lifetime is highly sensitive to the orientation of the transition dipole.
Optical transitions in GaN/AlxGa1−xN multiple quantum wells grown by molecular beam epitaxy
Authors: Smith M. , Lin J. Y. , Jiang H. X. , Salvador A. , Botchkarev A. , Kim W. , Morkoc H.
Published: July 2002

Time-resolved photoluminescence was employed to study optical transitions in GaN/AlxGa1−xN multiple quantum wells (MQWs). The effects of quantum confinement on the optical transitions as well as on the exciton-phonon interactions in MQW were investigated. Recombination lifetimes of optical transitions were measured at different emission energies and temperatures from 10 to 300 K. It was found that the exciton recombination lifetime increases linearly with temperature up to 60 K, which is a hallmark of radiative exciton recombination in MQW. Observed optical transitions and their dynamics in GaN/AlxGa1−xN MQW were also compared with those in GaN epilayers and GaAs/ AlxGa1−xAs MQW.
Ultrafast carrier dynamics and optical nonlinearities of low-temperature-grown InGaAs/InAlAs multiple quantum wells
Authors: Juodawlkis P. W. , McInturff D. T. , Ralph S. E.
Published: July 2002

Low-temperature-grown Be-doped In0.53Ga0.47As/In0.52Al0.48As multiple quantum wells are investigated via wavelength-dependent time-resolved nonlinear absorption measurements. Annealed Be-doped material, in contrast to annealed undoped material, is found to retain the carrier lifetime reduction induced by low-temperature growth in this narrow-gap material system. This is attributed to Be–As complexes which, in addition to producing high resistivity material, provide anneal–stable trap states. We also report that ultrafast band-edge and photoinduced absorption effects can produce subpicosecond absorption recovery in material exhibiting much longer (20 ps) defect-meditated carrier trapping.
Small valence-band offsets at GaN/InGaN heterojunctions
Authors: Van de Walle Chris G. , Neugebauer Jörg
Published: July 2002

The band discontinuities between GaN and InN, as well as InGaN alloys, are key parameters for the design of nitride-based light emitters. Values reported to date are subject to large uncertainties due to strain effects at this highly mismatched interface. We have investigated the band lineups using first-principles calculations with explicit inclusion of strains and atomic relaxations at the interface. We find that the “natural” valence-band offset between unstrained InN and GaN is 0.3 eV. Prescriptions are given, including the band shifts, due to strains at a pseudomorphic interface.
Controlled vertical manipulation of single CO molecules with the scanning tunneling microscope: A route to chemical contrast
Authors: Bartels L. , Meyer G. , Rieder K.-H.
Published: July 2002

A reliable procedure for controlled vertical transfer of single CO molecules between a Cu(111) surface and a scanning tunneling microscope tip and vice versa is demonstrated. It is shown that with a tip having a single CO molecule at its apex, chemical contrast is achieved allowing distinction of adsorbed CO molecules and oxgen atoms, which look very similar to the bare metal tip.
Synthesis of yttrium oxide thin films with and without the use of organic self-assembled monolayers
Authors: Agarwal M. , DeGuire M. R. , Heuer A. H.
Published: July 2002

Thin Y-containing films have been deposited at 80 °C from aqueous solutions of YNO3⋅5H2O and urea on bare single crystal Si wafers, and on Si wafers coated with sulfonate-functionalized organic self-assembled monolayers. The as-deposited films are believed to be an amorphous yttrium basic carbonate and can be completely transformed at 600 °C in air to crystalline Y2O3. Capacitance–voltage measurements on these films showed good dielectric properties, with a relative permitivity of 18, more than a factor of four higher than that of SiO2.
Conduction band spectra in self-assembled InAs/GaAs dots: A comparison of effective mass and an eight-band approach
Authors: Jiang Hongtao , Singh Jasprit
Published: July 2002

Strained epitaxy has been shown to produce high quality InAs/GaAs quantum dot structures by single step epitaxy. While effective mass-based approaches have been used for quantum structures, the nature of the strain and quantum confinement in self-assembled dots is such that this is not a good approximation. In this letter, we use an eight-band k⋅p formalism to find the electronic spectra in InAs/GaAs dots. The eight-band model shows that, in agreement with experiments, there are indeed several bound states in the conduction band well. Our results show that the simpler effective mass approaches cannot be used to quantitatively examine the physics of intersubband devices based on self-assembled quantum dots. Intersubband optical matrix elements and Coulomb blockade energy are also calculated in this letter.
Suppressing self-induced frequency scanning of a phase conjugate diode laser array using counterbalance dispersion
Authors: Lo/bel Martin , Petersen Paul M. , Johansen Per M.
Published: July 2002

Experimental results show that angular dispersion strongly influences the self-induced frequency scanning of a multimode broad-area diode laser array coupled to a photorefractive self-pumped phase conjugate mirror. Prisms or a dispersive grating placed in the external cavity opposing the material frequency dispersion of the phase conjugate BaTiO3 crystal suppress the frequency scanning and stabilize the center wavelength and the output power. We show that the dispersion of the crystal is crucial for the mechanism of the frequency scanning.
Electro-optic modulation using an organic single crystal film in a Fabry–Perot cavity
Authors: Xu Jianjun , Zhou Ligui , Thakur M.
Published: July 2002

Electro-optic modulation has been demonstrated using single crystal film of an organic electro-optic material, [N-(4-nitrophenyl)-L-prolinol] (NPP), placed in a Fabry–Perot cavity. The transverse geometry was used for electro-optic modulation. The cavity used had a finesse of about 50. The modulation depth achieved was about 0.7% for a low ac field of 0.5 V/μm applied along the charge-transfer (polar) axis on the film. The results are promising for applications of such films in high speed optical signal processing.
Monomolecular layer of squarylium dye J aggregates exhibiting a femtosecond optical response of delocalized excitons
Authors: Furuki Makoto , Pu Lyong Sun , Sasaki Fumio , Kobayashi Shyunsuke , Tani Toshiro
Published: July 2002

We report on the demonstration of the femtosecond nonlinear optical response from a two-dimensional monomolecular layer of squarylium dye J aggregate at 5 °C. The formation of a monomolecular layer Langmuir film was achieved by spreading squarylium dye modified by two propyl and two hexyl groups at the air–water interface, which resulted in a very strong J band (o.d.=0.3) at 777 nm. The transient absorption spectra in a resonant pump-probe measurement showed a low absorption saturation power (9.7×106 W/cm2) and an ultrafast response (300 fs), which are indicative of exciton delocalization over 18 molecules in this J aggregate, even at 5 °C.
Use of Kubo formalism to study transport beyond the Born approximation: Application to low-temperature transport in Si metal–oxide–semiconductor field-effect transistors
Authors: Zhang Yifei , Singh Jasprit
Published: July 2002

A formalism is developed to study transport in semiconductor devices under conditions where the Born approximation and independent scattering approximations break down. The approach based on the Kubo formalism is applied to Si metal–oxide–semiconductor field-effect transistors (MOSFETs) where interface roughness effects cause the approximations mentioned above to break down at low temperatures. Results presented are the outcome of a numerical method based on a three-dimensional approach to examine the interface roughness effects on the electronic spectrum as well as on the transport in the MOSFETs. The dependence of mobility on temperature and gate bias are reported and the shortcomings of the Born approximations are outlined. The approach is general and can be applied to problems where scattering is very strong and localization effects are significant, e.g., in amorphous semiconductor devices.
Excitation of higher harmonics in transient laser gratings by an ablative mechanism
Authors: Shen Y.-C. , Lomonosov A. , Frass A. , Hess P.
Published: July 2002

Laser-induced transient gratings were excited at the surface of an aluminum film by picosecond laser pulses. The counterpropagating surface acoustic waves with a fundamental frequency of 70 MHz that were launched were monitored outside the source region by laser probe beam deflection. The second and third harmonics were observed for ablative interaction of the laser radiation with the aluminum surface. A simple model is presented that describes the effects on the basis of nonlinear photoacoustic signal generation at the source due to a nonsinusoidal driving force.
Composition and crystal structure of carbon nitride films prepared by the electron cyclotron resonance plasma sputtering method
Authors: Tani Youji , Aoi Yoshifumi , Kamijo Eiji
Published: July 2002

Carbon nitride films were prepared on a Si(100) substrate by an electron cyclotron resonance plasma sputtering method using a carbon target and a nitrogen atmosphere. The maximum value of the N/C ratio in the film deposited at a substrate bias potential of about −55 V and ambient temperature was 1.35, which is close to the stoichiometric composition of C3N4. The surface morphology observed with scanning electron microscopy of the film deposited at 600 °C showed a crystalline structure with a 500 nm average grain diameter. The x-ray diffraction pattern of the film deposited at 600 °C and a substrate bias potential of −50 V indicates no amorphous phase in the film, which is composed of β- and α-C3N4 phases containing an unidentified C–N phase.
Low resistance spin-dependent tunnel junctions deposited with a vacuum break and radio frequency plasma oxidized
Authors: Sun J. J. , Soares V. , Freitas P. P.
Published: July 2002

Spin-dependent tunnel junctions with resistance-area products (RJ×A) down to 1.8 kΩ×μm2 and tunneling magnetoresistance (TMR)⩾15% were fabricated. Junction areas vary from 6 to 45 μm2. A systematic study of junction resistance and TMR versus deposited Al thickness (tAl=7, 9, 11, and 13 Å), and oxidation time (from 4 to 90 s) is presented. The TMR is maximum (25% to 27%) for tAl=11 Å, with 6 s oxidation time (RJ×A=10 to 20 kΩ×μm2). At 6–10 s oxidation time, reducing the Al thickness from 11 to 7 Å reduces the resistance-area products from 10–20 kΩ×μm2 to 1–3 kΩ×μm2, while TMR decreases from 22%–27% to 13%–17%. Excess oxidation or incomplete oxidation of the Al layer leads to current–voltage curve asymmetry.
Observation of local tilted regions in strain-relaxed SiGe/Si buffer layers using x-ray microdiffraction
Authors: Mooney P. M. , Jordan-Sweet J. L. , Noyan I. C. , Kaldor S. K. , Wang P.-C.
Published: July 2002

The microstructure of strain-relaxed Si1−xGex/Si films that relaxed by different dislocation nucleation mechanisms has been investigated using x-ray microdiffraction with a diffracted beam footprint of 1 μm×5μm. Intensity variations in the x-ray microtopographs of samples having step-graded intermediate layers, which relaxed by dislocation multiplication, are due to the presence of local tilted regions which are larger in area than the diffracted x-ray beam. In contrast, microtopographs of uniform composition layers, which relaxed by surface roughening and subsequent random dislocation nucleation, show little intensity contrast as the local tilted regions in these samples are much smaller than the diffracted x-ray beam. The difference in microstructure arises from the different distributions of 60 ° misfit dislocations in these two types of samples.
Femtosecond near-field optical spectroscopy of implantation patterned semiconductors
Authors: Nechay B. A. , Siegner U. , Morier-Genoud F. , Schertel A. , Keller U.
Published: July 2002

We have developed a femtosecond-resolved near-field scanning optical microscope, using a diffraction-limited pump and near-field probe configuration, which allows us to measure carrier dynamics with a spatial resolution of ∼150 nm and a time resolution of ∼250 fs. This instrument is used for near-field degenerate pump–probe studies of carrier dynamics in GaAs/AlGaAs single quantum well samples locally patterned by focused-ion-beam (FIB) implantation. We find that lateral carrier diffusion across the nanometer-scale FIB pattern plays a significant role in the decay of the excited carriers.
On the observation of 2.8 μm emission from diode-pumped Er3+- and Yb3+-doped low silica calcium aluminate glasses
Authors: de Sousa D. F. , Zonetti L. F. C. , Bell M. J. V. , Sampaio J. A. , Nunes L. A. O. , Baesso M. L. , Bento A. C. , Miranda L. C. M.
Published: July 2002

In this letter, we investigate the midinfrared photoluminescence of a series of diode-pumped Er3+-doped and Er3+, Yb3+-codoped low-silica content aluminosilicate glasses. Emission at 2.8 μm was observed in both single doped and codoped samples. The effect of Yb3+ codoping of the Er3+-doped samples was such that, for example, for a 2 wt % Er3+-doped, the photoluminescence yield at 2.8 μm was found to be roughly three times larger than that of the single 2 wt % Er3+-doped sample. This behavior was attributed to the efficient sensitization of Er3+ by Yb3+ in our oxide based host glasses. The results reported in this letter, together with the outstanding mechanical, chemical, and thermal properties of these glasses, suggest that rare-earth doped calcium aluminate glasses may become an attractive host for the development of solid state lasers operating in the midinfrared.
Enhancing defect-related photoluminescence by hot implantation into SiO2 layers
Authors: Im S. , Jeong J. Y. , Oh M. S. , Kim H. B. , Chae K. H. , Whang C. N. , Song J. H.
Published: July 2002

Visible photoluminescence around an orange band of 580 nm wavelength are observed from 300 nm thin SiO2 layers implanted by Si or Ge ions at both substrate temperatures of 25 °C [room temperature (RT)] and 400 °C (hot). Si implantations at an energy of 30 keV were performed with doses of 5×1015, 3×1016, and 1×1017 cm−2 while Ge implantations were done at 100 keV with a dose of 5×1015 cm−2. Samples implanted at 400 °C always show much higher intensities of luminescence than those implanted at room temperature. Electron spin resonance signals of the hot-implanted samples indicate relatively smaller amounts of nonradiative defects than those of RT-implanted samples. It is concluded that the hot-implantation effectively enhances the intensity of defect-related photoluminescence by reducing the density of the nonradiative defects and introducing the radiative defects, which contribute to the luminescence in SiO2 layers.
Oxide electrodes as barriers to hydrogen damage of Pb(Zr,Ti)O3-based ferroelectric capacitors
Authors: Aggarwal S. , Perusse S. R. , Nagaraj B. , Ramesh R.
Published: July 2002

The ferroelectric properties of Pb(Zr,Ti)O3 films are known to degrade when subjected to forming gas anneals. In an earlier publication we established that although there may be loss of oxygen and lead during forming gas anneal, the primary mechanism for loss of ferroelectricity is the incorporation of hydrogen and subsequent formation of [OH]−1 bonds between the ionized hydrogen and oxygen ions along the polarization axis in the octahedra. In this study, we show that (La,Sr)CoO3 oxide electrodes can act as a diffusion barrier to hydrogen during forming gas anneals. Forming gas anneal at lower temperatures such as 200 and 300 °C does not lead to a measurable loss of polarization. There is some loss of polarization during forming gas anneals at 450 °C for 12 h, however the capacitors still exhibit ferroelectric properties. The capacitors show no fatigue up to 1011 cycles, no imprint, good logic state retention characteristics, and similar slopes for the pulse width dependent polarization values before and after forming gas anneal in the measured range. More importantly, we have demonstrated that even a bare La0.5Sr0.5CoO3 top electrode can prevent the complete loss of ferroelectricity during forming gas treatment.
Direct current glow discharges in atmospheric air
Authors: Stark Robert H. , Schoenbach Karl H.
Published: July 2002

Direct current glow discharges have been operated in atmospheric air by using 100 μm microhollow cathode discharges as plasma cathodes. The glow discharges were operated at currents of up to 22 mA, corresponding to current densities of 3.8 A/cm2 and at average electric fields of 1.2 kV/cm. Electron densities in the glow are in the range from 1012 to 1013 cm−3. Varying the current of the microhollow cathode discharge allows us to control the current in the atmospheric pressure glow discharge. Large volume atmospheric pressure air plasmas can be generated by operating microhollow cathode discharges in parallel.
Anti-Stokes photoluminescence in colloidal semiconductor quantum dots
Authors: Poles Ehud , Selmarten Donald C. , Mićić Olga I. , Nozik Arthur J.
Published: July 2002

We report anti-Stokes photoluminescence (photon energy up-conversion) from size-quantized CdSe and InP nanocrystalline colloids. The observed up-conversion is highly efficient and occurs at very low excitation intensities. With low temperatures the intensity of the up-converted photoluminescence decreases while that of the usual Stokes photoluminescence increases; the up-converted photoluminescence is also restricted to energies corresponding to the band gaps of the quantum dots that are present in the colloid ensemble. The anti-Stokes photoluminescence is explained by a model that involves surface states.
The dependence of electron emission on ferroelectric properties of Pb(ZrxTi1−x)O3
Authors: Kim Yong Tae , Yoon Ki Hyun , Kim Tae Heui , Park Kyung Bong
Published: July 2002

The characteristics of pulse electric field induced electron emission from the Pb(ZrxTi1−x)O3 ceramics have been investigated with a particular emphasis on the relationship to the ferroelectric properties. The emission charge of the negative pulse field to the rear electrode was smaller and more stable than that of the positive field. The emission threshold field and the emission charge were indeed affected by the coercive field and polarization change. However, the emission properties were minimally affected by the dielectric constant. The emission charge increased exponentially with the pulse field and polarization change. The electron emission can be regarded as a field emission by polarization change.
Ionochromism in a light-emitting electrochemical cell with low response time based on an ionic conductive poly-phenylene vinylene
Authors: Holzer L. , Wenzl F. P. , Tasch S. , Leising G. , Winkler B. , Dai L. , Mau A. W. H.
Published: July 2002

Characterizations of red-orange light-emitting electrochemical cells (LECs) based on poly[1,4-(2,5-bis(1,4,7,10-tetraoxaundecyl))phenylene vinylene], (BTEM-PPV), are presented, BTEM-PPV combines good electronic conductivity with ionic conductivity due to its conjugated backbone and side chains consisting of oligo(ethylene oxide). The use of this polymer in LECs leads to relatively bright light emitting devices with low response times which are obtained without blending an additional ionic conductive polymer into the film. The response times of the BTEM-LECs driven with a square wave form pulse were determined to be about 480 μs. The value for the turn-on voltage of the electroluminescence is 2 V and at 3 V a brightness of around 35 cd/m2 was obtained. BTEM-PPV complexed with metal ions shows an ionochromic effect in the absorption spectrum and also in the electroluminescence spectrum due to the covalent linkage of the glymelike side chains to the PPV backbone, which represents an approach toward chemical sensors.
Fully sealed, high-brightness carbon-nanotube field-emission display
Authors: Choi W. B. , Chung D. S. , Kang J. H. , Kim H. Y. , Jin Y. W. , Han I. T. , Lee Y. H. , Jung J. E. , Lee N. S. , Park G. S. , Kim J. M.
Published: July 2002

A fully sealed field-emission display 4.5 in. in size has been fabricated using single-wall carbon nanotube (CNT)-organic binders. The fabricated displays were fully scalable at low temperature, below 415 °C, and CNTs were vertically aligned using paste squeeze and surface rubbing techniques. The turn-on fields of 1 V/μm and field emission current of 1.5 mA at 3 V/μm (J=90 μA/cm2) were observed. Brightness of 1800 cd/m2 at 3.7 V/μm was observed on the entire area of a 4.5 in. panel from the green phosphor-indium–tin–oxide glass. The fluctuation of the current was found to be about 7% over a 4.5 in. cathode area.
Above-room-temperature continuous-wave mid-infrared photoluminescence from PbSe/PbSrSe quantum wells
Authors: McCann P. J. , Namjou K. , Fang X. M.
Published: July 2002

Strong photoluminescence between 3 and 4 μm was observed at temperatures as high as 55 °C from PbSe/PbSrSe multiple-quantum-well structures grown on BaF2 (111) substrates by molecular-beam epitaxy. Fabry–Perot interference fringes dominated the spectra, indicating that the luminescence was primarily due to stimulated emission processes. Peak emission energies were determined by fitting Gaussian functions to the spectra, and they showed that emission energies at 25 °C decreased from 402 to 312 meV as quantum-well thickness increased from 40 to 200 Å. The temperature tuning coefficient was also observed to decrease from 0.400 meV/K for a 200 Å multiple-quantum-well sample to 0.313 meV/K for a 40 Å multiple-quantum-well sample.
Two-photon fluorescence imaging and spectroscopy of nanostructured organic materials using a photon scanning tunneling microscope
Authors: Shen Yuzhen , Jakubczyk Daniel , Xu Faming , Swiatkiewicz Jacek , Prasad Paras N. , Reinhardt Bruce A.
Published: July 2002

Photon scanning tunneling microscopy and spectroscopy using femtosecond two-photon excitation are demonstrated. The measurement of both intensity dependence and spectral dependence is performed on a two-photon chromophore. A subdiffraction-limited resolution is obtained, and the domain-size dependence of spatial and spectral features is observed, which indicates the high degree of molecular order in the isolated nanoparticle. It is shown that the light confinement due to a quadratic dependence of the fluorescence intensity leads to an optical contrast enhancement with a coated probe.
Magnetoquenched superconducting valve with bilayer ferromagnetic film for uniaxial switching
Authors: Clinton T. W. , Johnson Mark
Published: July 2002

A bilayer ferromagnetic film, consisting of a soft- and hard-magnetic layer separated by a nonmagnetic layer, has been incorporated into a magnetoquenched superconducting valve, making it possible to control the valve with uniaxial magnetic fields. Device switching is demonstrated with fields as small as 20 Oe. The switch is inherently nonvolatile, has linear output characteristics, and requires a single inductively coupled “write wire” for integrated operation, all of which make it promising for application as a storage cell in a high-density superconducting random-access memory.
Simulation of a picosecond laser ablation plasma
Authors: Mao Samuel S. , Mao Xianglei , Greif Ralph , Russo Richard E.
Published: July 2002

A theoretical model has been developed to simulate plasma formation and evolution during the early stage of picosecond laser ablation of solids. Surface electron emission was implemented as one boundary condition for plasma development above the target. The simulation results indicate that a plasma forms, with electron density on the order of 1020 cm−3, during the picosecond laser pulse. Laser induced gas breakdown assisted by electron emission from the target was found to be the origin of the plasma. In agreement with experimental measurements, longitudinal movement of the electrons inside the plasma was suppressed after the laser pulse. The suppression of the plasma can be attributed to the development of a strong electric field above the target.
Switching characteristics and magnetization vortices of thin-film cobalt in nanometer-scale patterned arrays
Authors: Girgis E. , Schelten J. , Shi J. , Janesky J. , Tehrani S. , Goronkin H.
Published: July 2002

The switching characteristics and magnetization vortices of 15 nm thick cobalt structures patterned to different widths of 100, 200, and 600 nm were investigated. The effects of linewidth and aspect ratio (length/width) were systematically studied using an alternating gradient magnetometer (AGM), an atomic force microscope/magnetic force microscope (MFM) and superconducting quantum interference device. The AGM and MFM show that trapped magnetization vortices appear in structures with low aspect ratios (length/width)=1.5, 2, but not in structures with high aspect ratio (length/width)=3,4. It is found that the magnetization vortices of these patterned elements are strongly dependent on the width of the element with narrower linewidth more clearly showing the presence of magnetization vortices.
Pr–Zr–Co precipitation-hardened magnet
Authors: Gabay A. M. , Zhang Yong , Hadjipanayis G. C.
Published: July 2002

Hard magnetic properties have been found in homogenized and subsequently aged Pr–Zr–Co alloys. Transmission electron microscopy reveals a microstructure consisting of a Pr2(Co, Zr)17 matrix with (Pr, Zr)Co5 precipitates formed after aging the homogenized alloys with the (Pr, Zr)Co5+δ structure. This microstructure is similar to that of the Sm–Co–Cu–Zr precipitation-hardened magnets. However, unlike Sm2Co17, the easy magnetization direction (EMD) of Pr2Co17 lies in a basal plane. The coexistence of the 2:17 matrix phase with EMD∥(001) and the 1:5 cell-boundary phase with EMD∥[001] results in unusual alignment effects. Anisotropic Pr11.5Zr4Co85 powders with coercivity of 4.1 kOe and energy product of 7.2 MGOe were obtained.
Alkali ion drift model for data retention in stacked gate structures
Authors: Tanaka Sumio
Published: July 2002

A model for data retention in stacked gate structures has been formulated, considering that an alkali ion drift toward the negatively charged floating gate is a cause of degradation. A charge conservation law is obtained for the alkali ions, which reduces to a differential equation concerning the threshold voltage variation. A simple analytical expression for the threshold voltage variation has been obtained whose form is identical to the conventional model; however, the physical meaning is quite different. In the proposed model, the low activation energy is attributed to the potential barrier height formed by silicon dioxide atoms for alkali ions and the inconsistency in the conventional model can be solved.
Predicted thermally induced stresses in, and the bow of, a circular substrate/thin-film structure
Authors: Suhir E.
Published: July 2002

An easy-to-apply analytical (“mathematical”) stress model is developed for the prediction of the stresses in, and the bow of, a circular substrate/thin-film structure subjected to a change in temperature. The model can be helpful for stress–strain analyses and physical design of thin film systems fabricated on circular substrates, experiencing thermally induced bending deformations. Structures of this type are widely used in microelectronics and photonics packaging engineering.
Determination of the substitution scheme of gallium and magnetic features of Nd2Fe14−xGaxB
Authors: Chacon Cyril , Isnard Olivier
Published: July 2002

The unsolved question of the location of the gallium atoms within the Nd2Fe14B structure is addressed. We have performed a high-resolution neutron diffraction investigation on Nd2Fe14−xGaxB powder samples evidencing a preferential substitution of Ga in the Fe (4c), Fe (8j1), and Fe (16k2) sites of the structure. The crystal structure has been investigated using the Rietveld method and the evolution of the shorter iron–iron interatomic distances has been linked to the observed increase of the Curie temperature when the Ga concentration increases. The combined use of neutron diffraction investigation and of scanning electron microscope analysis reveals that the solubility limit of Ga is equal to 1.8 atoms per formula unit. The effects of Ga for Fe substitution on the structural and magnetic properties of the Nd2Fe14−xGaxB compounds have been studied. The magnetic moment values of each atom and the saturation magnetization are clearly sensitive to the Ga for Fe substitution but also to the temperature. A significant modification of the Nd atoms near neighborhood is observed via the evolution of the interatomic distances and the influence of the Ga concentration on the spin reorientation temperature is discussed. The angle of tilt of the magnetization away from the c axis has been determined below the spin reorientation temperature for both Nd2Fe13GaB and Nd2Fe12.2Ga1.8B phases. Finally, a comparison with the influence of Ga on the structural properties of R2Fe17 compounds is presented.
A classical ensemble model of three-body collisions in the point contact approximation and application to alignment effects in near-resonant energy transfer collisions of He atoms with Rydberg Ca atoms
Authors: Shafer-Ray Neil E. , Morrison Michael A. , Parker Gregory A.
Published: July 2002

A classical ensemble model of three-body energy transfer in the point contact approximation is presented. This model yields cross sections for transitions between initial and final states defined by energy, magnitude of angular momentum, and projection of angular momentum along an axis of spatial quantization corresponding to the quantum numbers of the initial and final stationary states, n,l,m and n′,l′,m′. Using a cross section that is differential in the final-state quantum numbers, the spatial constraints imposed by conservation of energy and angular momentum can be investigated even for comparatively small quantum numbers. When applied to the Ca(17d)+He→Ca(18p)+He energy transfer processes, the model sheds light on recently discovered alignment phenomena in collisions of rare-gas atoms with initially aligned Rydberg atoms. Materials for the implementation of this model are available from the authors via the Internet.
Ultrasonic stress measurement using PC based and commercial flaw detectors
Authors: Santos Auteliano A. , Bray Don E.
Published: July 2002

The determination of the stress field inside metallic parts is one of the most important challenges to the designer. Although the prediction of the stress distribution can be done by several numerical and empirical methods, the real stress value is almost always unknown. Several destructive and nondestructive techniques have been tested to accomplish this task, including the application of x rays, saw cut, neutron diffraction and so on, but none of them seems to have a suitable correlation between cost and applicability. Ultrasonic techniques have been used for flaw detection since the 1950s. The main application was in the identification of cracks and voids. In this work we present the application of ultrasound in the evaluation of a one-dimensional stress field using the longitudinal critically refracted waves (LCR). A new ultrasonic LCR probe is presented and its performance is evaluated using PC based instrumentation. Also, the LCR waves’ sensitivity is verified using a low cost commercial flaw detector. The results show that the technique can be applied to quantify the magnitude of the stresses in bars, using either the PC based or the commercial flaw detector system, as long as the high sensitivity longitudinal critically refracted waves are used.
On the numerical treatment of viscous singularities in wall-confined thermocapillary convection
Authors: Kasperski G. , Labrosse G.
Published: July 2002

Confined thermocapillary flows often present a viscous singularity where free and solid surfaces meet. Any computational treatment of these flows must filter this singularity, either explicitly by modifying the boundary conditions of the problem, or implicitly by using finite precision methods. The effect of an explicit polynomial filtering is here examined for an axisymmetric side-heated liquid bridge, leading to two results: (i) thermally convective flows converge very slowly with the filtering scale; the numerical experiments must therefore be conducted carefully in order to get physically relevant results; (ii) stream-function and temperature are not suitable test variables for estimating this convergence.
Modeling electromigration-induced stress evolution and drift kinetics with a stress-dependent diffusivity
Authors: Chizhik S. A. , Matvienko A. A. , Sidelnikov A. A. , Proost J.
Published: July 2002

Clement and Thompson have justified that it is necessary to take into account the stress dependence of atomic mobility when describing stress evolution in a metal conductor caused by electromigration [J. J. Clement and C. V. Thompson, J. Appl. Phys. 78, 900 (1995)]. In the present contribution the role of this dependence is considered in more detail, leading to qualitatively new results concerning stress evolution and drift kinetics. The stationary stress distribution over the length of the elastic zone of the conductor was shown to be nonlinear and asymmetrical at superthreshold conditions, with the zone of compressive stress being more extended than that of tensile stress. This also results in an asymmetrical pattern for plastic deformation, the hillocking zone being more extended than the voiding region at the cathode. The drift rate was shown to achieve its maximum value during the nonstationary stage of stress evolution and then to drop down to its stationary value. The duration of the nonstationary stage of stress evolution is proportional to the conductor length and inversely proportional to the current density. This is essentially different from the result obtained in all previous works. Our model also predicts that for conductors with a length much longer than the critical one, the nonstationary stage of stress evolution corresponds to a quasistationary stage for drift kinetics, during which a constant drift rate is observed. Finally, we will consider the consequences of taking into account the stress dependence of mobility when describing the effects of passivation and thermal stress on drift kinetics.
Nonstationary driven oscillations of a magnetic cavity
Authors: Ruderman M. S. , Wright A. N.
Published: July 2002

The problem of transition to the steady state of driven oscillations in a magnetic cavity in a cold resistive plasma is addressed. The foot point driving polarized in the inhomogeneous direction is considered, and it is assumed that the cavity length in the direction of the equilibrium magnetic field is much larger than the cavity width in the inhomogeneous direction. The latter assumption enables one to neglect the variation of the magnetic pressure in the inhomogeneous direction, which strongly simplifies the analysis. The explicit solution describing the nonstationary behavior of the magnetic pressure and the velocity is obtained. This solution is used to study the properties of the transition to the steady state of oscillation. The main conclusion is that, in general, there are two different characteristic transitional times. The first time is inversely proportional to the decrement of the global mode. It characterizes the transition to the steady state of the global motion, which is the coherent oscillation of the cavity in the inhomogeneous direction. The second time is the largest of the two times, the first transitional time and the phase-mixing time, which is proportional to the magnetic Reynolds number in 13 power. It characterizes the transition to the steady state of the local motion, which is oscillations at the local Alfvén frequencies, and the saturation of the energy damping rate. An example from solar physics shows that, in applications, the second transitional time can be much larger than the first one.
Optical absorption and Hall effect in (220) and (400) oriented polycrystalline silicon films
Authors: Kamiya T. , Nakahata K. , Sameshima T. , Watanabe T. , Mouri T. , Shimizu I.
Published: July 2002

Carrier transport properties were investigated for polycrystalline silicon (poly-Si:H:F) films fabricated at 300 °C by 100 MHz plasma enhanced chemical vapor deposition from gaseous mixture of SiF4 and H2. Analysis of free carrier optical absorption (FCA) revealed that 1 μm thick (400) oriented phosphorus-doped poly-Si:H:F films with a carrier concentration of 5×1019 cm−3 had the average electron mobility in crystalline grains at 40 cm2/V s, while the electron mobility of the (220) oriented phosphorus-doped poly-Si:H:F films was only 12 cm2/V s. These results indicated that (400) oriented poly-Si:H:F films had excellent quality crystalline grains. Analyses of the FCA combined with Hall effect current measurements revealed that the electrical conductivity at grain boundaries of top doped films increased as the underlying film thickness increased from 0 to 280 nm for (400) oriented phosphorus-doped/undoped double layered samples, but grain boundaries still acted as large resistive regions limiting the effective conductivity.
Simulation of pulsed high-frequency breakdown in hydrogen
Authors: Lacoste A. , Alves L. L. , Ferreira C. M. , Gousset G.
Published: July 2002

We present a simulation of the breakdown stage of high-power, short-pulse high-frequency discharges in hydrogen, produced when an electric field of the form E(t)=EmaxIW(1−e−t/τ)sin(ωt) is applied to a cylindrical resonant cavity. Typical discharge operating conditions considered are applied powers 1–15 kW, gas pressures 0.1–20 Torr, cavity diameter of 25.71 cm, tube radius of 0.8 cm, field frequency ω/2π=1.12 GHz, pulse width tP=10 μs, and rising times τ of a few microseconds. Under these conditions, discharge breakdown occurs before the electric field reaches its maximum amplitude EmaxIW, this situation corresponding to the so-called increasing wave (IW) regime. The simulation is based on a Monte Carlo model to calculate the breakdown times, tb, and fields, Eb, for different field rising slopes EmaxIW/τ≃10−1−103 V cm−1 ns−1. The results obtained show that a breakdown criterion based on the electron energy balance (εgain=εloss, where εgain and εloss are, respectively, the mean electron energy gain and loss) yields excellent agreement between calculated and measured values of tb and Eb, while the classical particle rate balance criterion (νgain=νloss, where νion and νloss are, respectively, the mean electron production and loss frequencies) is satisfied only at pressures below 0.5 Torr. It is further shown that: (i) the IW limit for long breakdown times (tb≃τ→∞) corresponds to the continuous wave regime; and (ii) there is an equivalence between pulsed excitation, with pulse width tP, and IW regimes, for short breakdown times such that tb=tP≪τ.
Morphological aspects of continuous and modulated epitaxial growth of (GaIn)P
Authors: Jiang Jiechao , Schaper Andreas K. , Spika Zeljko , Stolz Wolfgang
Published: July 2002

In contrast to the continuous metalorganic vapor phase epitaxy of (GaIn)P, a modulated growth process yields higher degrees of superlattice ordering along with a more complex domain hierarchy. Using cross-sectional as well as plan view transmission electron microscopy, we have studied the two-dimensional contrast modulation which occurs at a deposition cycle of 1 monolayer (ML) GaP/1 ML InP. The interlocking modulation waves create a columnar domain morphology coexisting with an antiphase domain structure. The lateral size of the domain columns ranges from 25 to 50 nm depending on the misorientation of the GaAs substrate. Dark-field imaging and atomic force microscopy investigations provided clear evidence of stress relief involved in the domain formation. At zero off cut, complementary single ordering variant superdomains are formed in parallel with faceting of the growth front. The 4°–6° B facets appear the energetically more stable growth planes compared to the exact (001) crystallographic plane.
Dust streams from Jupiter and Saturn
Authors: Horányi Mihály
Published: July 2002

This is a brief review of the recent in situ observations and modeling of the dynamics of dust particles that are ejected from Jupiter’s magnetosphere due to dusty plasma effects. Dust grains exposed to plasma and UV radiation collect electrostatic charges and their dynamics can be altered due to electric and magnetic fields. Hence, magnetospheric effects can shape the size and spatial distributions of micron-sized and smaller dust grains. Based on the observations and the theory of the dust streams ejected from Jupiter’s magnetosphere, analogous processes are expected to operate in Saturn’s magnetosphere as well.