bluuebunny/crossref_metadata_2025 huggingface dataset:
The ωσ method: A new contactless comparison method for measuring electrical conductivity of nonferromagnetic conductors
Authors: Miletić M. B. , Nikolić P. M. , Vasiljević-Radović D. , Bojičić A. I.
Published: July 2002

A novel, very simple, eddy current method for measuring the electrical conductivity of nonferromagnetic conductors is described. This method is relative, i.e., we measure the ratio of conductivities of two samples of the same shape and size (this shape and size may be arbitrary). For one of them, conductivity is known, this is the reference sample, whereas the conductivity of the other is unknown and it is to be determined. Consequently, in this method it is necessary to have a reference sample of known conductivity. On the other hand, in this method no other calibration is necessary; the ratio of two conductivities we obtain directly as the ratio of two frequencies, without any calibration. The principle of this method is as follows: It turns out, based on Maxwell’s equations, that if we have a coil through which a sinusoidal current of an angular frequency ω flows and in whose magnetic field a given conductive, nonferromagnetic sample is placed, the effective inductance (i.e., the ratio of the reactive part of the impedance to the frequency ω) depends on ω and on the conductivity of the sample σ only through their product ωσ. Therefore, if it is found that with a sample of conductivity σ 1 at frequency ω1 the effective inductance is equal to that of a sample with conductivity σ 2 and frequency ω2 (the samples being of the same shape and size, both nonferromagnetic, and both placed in the same position relative to the coil), this means that equality ω1σ1=ω2σ2 is valid. Hence, if σ1 is known and σ2 is unknown, σ2 can be calculated.
Impedance-matching system for a flexible surface-coil-type resonator
Authors: Hirata Hiroshi , Ono Mitsuhiro
Published: July 2002

This article describes an impedance-matching system for a flexible surface-coil-type resonator (FSCR) used in electron paramagnetic resonance (EPR) experiments. To design the matching system, the input impedance of the FSCR was formulated using transmission line theory, and then the parameters of a matching circuit using varicap diodes were calculated. Experimental measurements of input impedance showed the validity of the formulation and the usefulness of the matching system. The matching circuit made by the varicap diodes 1SV186 offered the tunable bandwidth of 50 MHz for the prototype FSCR. Such a matching system also offers the possibility of remotely tuning EPR resonators electronically.
Utility of videomicroscopy in the characterization of single crystals of air sensitive compounds to be studied by x-ray crystallography
Authors: Evans William J. , Broomhall-Dillard Randy N. R.
Published: July 2002

We describe here how modern videomicroscopy can be used to enhance the selection of single crystals for x-ray crystallography and provide a permanent record of crystal shape and color. The cost/advantage ratio of this technique is such that we expect it to become a standard practice in the future.
Measurements of fast electrons produced in solid targets by laser intensities of 5×1019 W/cm2 (abstract)
Authors: Wharton K. , Zakharenkov Y. , Hammel B. , Herman S. , Miller J. , Moody J. , Offenberger A. , Pennington D. , Perry M. , Stuart B. , Brown C. , Yanovsky Y. , Wilks S.
Published: July 2002

We report on experiments using the 100 TW laser at LLNL (40J, 400 fs, 5×1019 W/cm2 focal intensity) and planar multilayer targets (Mo/Sn) to study the generation and transport of electrons with MeV energies. Such fast electrons are of prime importance to many proposed applications, e.g., the fast ignitor fusion concept. X-ray emission spectroscopy is used to study the electron transport. Characteristic K α photon emission produced by the fast electrons in the front (Mo) and rear (Sn) layers of the target is measured with a charge-coupled device detector (single photon counting mode) to infer the electron energy deposition. The electron energy spectrum is measured by varying the thickness of the Mo layer to attenuate the electrons by different amounts. Penumbral imaging of the K α emission is used to give information about the angular distribution of the fast electron emission. Details of the measurement techniques and experimental results will be discussed and compared with modeling calculations.
Characteristics of the beams generated by a “hollow cathode” electron gun
Authors: Ciullo G. , Sharapa A. N. , Shemyakin A. V. , Tecchio L.
Published: July 2002

The characteristics of a beam generated by a “hollow cathode” gun, intended for electron cooling purposes, are thoroughly investigated. Attention was focused on the details of the current density and temperature distributions across the electron beam. Consequently a high quality beam was obtained, comparable with the beams generated by standard guns. Much insight was gained on the vacuum and alignment conditions for this new configuration.
Negative hydrogen ions and evidence for a potential dip in an electron cyclotron resonance discharge for highly charged ions
Authors: Bolshukhin D. , Meyer D. , Wolters U. , Wiesemann K.
Published: July 2002

By means of photodetachment we have detected negative hydrogen ions in an electron cyclotron resonance (ECR) discharge under conditions where highly charged ions are present in the plasma if hydrogen is absent. From the time delay between the laser pulse and the photodetachment (PD) signals we obtained the location of the negative ion clouds in the halo of the plasma. It coincides with the location found for atomic hydrogen ions in previous ion cyclotron resonance heating experiments. The confinement of the ions to these places must be due to the presence of local potential maxima. These maxima imply a potential dip in the core of the plasma. Furthermore, these H− ions indicate the presence of cold electrons even under conditions where high charge states are produced.
A miniature metal–ceramic x-ray source for spacecraft instrumentation
Authors: Koppel L. N. , Marshall J. R.
Published: July 2002

Definitive mineralogical identification of materials with x-ray diffraction and fluorescence on remote planetary probes requires the development of a rugged miniature x-ray source that complies with the mass, power, thermal, and electrical management constraints imposed by space missions. Conventional x-ray tubes are generally fragile, glass-envelope designs with heat-sensitive seals. They are too brittle and bulky for planetary missions, and usually require cumbersome and power-consuming cooling systems. Here we describe the development of a novel, rugged miniature x-ray source employing a ceramic BeO substrate upon which a metal target material is deposited. Conventional thermionic emission and high-voltage acceleration of electrons to strike the metal target material produce an x-ray yield comparable to conventional x-ray tubes. Thermal management of the x-ray source is achieved with the excellent heat transport properties of the BeO target substrate coupled with a passive heatpipe.
Novel loop-gap probe head for time-resolved electron paramagnetic resonance at 9.5 GHz
Authors: Elger G. , Törring J. T. , Möbius K.
Published: July 2002

A novel probe head with a two-loop-one-gap resonator for X-band (9.5 GHz) time-resolved transient electron paramagnetic resonance measurements with direct detection is described. The low quality factor Q of the resonator allows time resolution in the order of 10 ns while the high filling factor guarantees a sensitivity which is at least comparable to that of conventional cavity resonators. A novel feature of the resonator is the coupling mechanism which exploits the field distribution in the microwave shield. The type of the resonator and the microwave coupling scheme chosen provide high mechanical stability of the setup. This is particularly important for pulsed laser excitation and gas stream cooling of the sample. The advantages of the probe head are demonstrated by relaxation measurements on the photoexcited triplet state of zinc-tetratolylporphyrin, for which the high time resolution allows the determination of fast anisotropic relaxation. This relaxation behavior can be attributed to the dynamic Jahn–Teller effect.
Introductory overview of research instruments for recording the electrical activity of neurons in the human brain
Authors: Garell P. C. , Granner M. A. , Noh M. D. , Howard M. A. , Volkov I. O. , Gillies G. T.
Published: July 2002

Scientific advancement is often spurred by the development of new instruments for investigation. Over the last several decades, many new instruments have been produced to further our understanding of the physiology of the human brain. We present a partial overview of some of these instruments, paying particular attention to those which record the electrical activity of the human brain. We preface the review with a brief primer on neuroanatomy and physiology, followed by a discussion of the latest types of apparatus used to investigate various properties of the central nervous system. A special focus is on microelectrode investigations that employ both intracellular and extracellular methods of recording the electrical activity of single neurons; another is on the modern electroencephalographic, electrocorticographic, and magnetoencephalographic methods used to study the spontaneous and evoked field potentials of the brain. Some examples of clinical applications are included, where appropriate.
Spins and parities of levels in fission fragments
Authors: Jones M. A. , Urban W. , Phillips W. R.
Published: July 2002

Efficient methods for using triple and fourfold γ-ray coincidence data to give information on spins and parities of levels in secondary fission fragments are described. Triple-γ angular correlations and double-γ angular correlations culled from triple coincidences with one γ ray observed isotropically for selectivity have been used to give information on the multipole nature of transitions; directional linear polarization data culled from fourfold coincidences with one isotropically observed γ ray have been used to provide parity information. Results for known cascades agree with predicted correlation and polarization patterns. Examples of the techniques applied to transitions in Mo106 produced in the decay of Cm248 are given.
Nonperturbing meaurement of energy distribution function of confined D-T fusion alpha particles in Joint European Torus plasmas using impurity induced neutralization (abstract)
Authors: Korotkov A. A. , Gondhalekar A. , Akers R. J.
Published: July 2002

We present measurements of the energy distribution function of fusion α particles in the range 0.8⩽E(MeV)⩽3 in hot-ion H-mode plasmas, using a NPA. Two contributions to the measured atomic flux are distinguished: (i) alpha particles due to direct neutralization effected in double charge–exchange reactions with intrinsic plasma impurities C4+, Be2+, and He0, and (ii) MeV energy deuterons formed by elastic scattering on fusion alpha particles, their neutralization effected by reactions with C5+, Be3+, He1+, and D0. Application of the impurity induced neutralization model to the measurements is presented. Deduced fusion α particle and knock-on deuteron energy distribution functions are compared with Fokker–Planck simulations in which measured time-dependent α-particle source and collisionality are used.
Enhancing electron beam induced current images
Authors: Ong Vincent K. S. , Wu Dethau
Published: July 2002

Image processing techniques can be used on electron beam induced current (EBIC) images to reveal information hidden in the images. The method proposed in this article is similar to that used in ion beam induced charge collection in which different signal strengths are channelled to different windows. An image processing algorithm has been developed to mimic the effect of separating different signal strength into different windows. On top of that, the algorithm also stretches the strength of the signal, and this greatly enhances the capability of the technique. An EBIC image of a transistor is used to demonstrate this technique and the results are presented in this article.
Distributed-feedback dye laser for picosecond ultraviolet and visible spectroscopy
Authors: Yaney Perry P. , Kliner Dahv A. V. , Schrader Paul E. , Farrow Roger L.
Published: July 2002

We describe the design and operation of a tunable, picosecond laser system for use in time-resolved spectroscopic measurements in the visible and ultraviolet (UV) spectral region. The laser is designed for fine tuning and high wavelength stability. A Nd:YAG-pumped distributed-feedback dye laser (DFDL) generates pulses that are ∼100 ps in duration with a nearly transform-limited linewidth (∼5 GHz) at a 20 Hz repetition rate. The DFDL pulses are amplified in two bow-tie amplifiers, providing pulse energies of up to 3.0 mJ; the amplified pulses may be frequency doubled to the UV spectral region, providing up to 1.0 mJ. The DFDL wavelength is computer stabilized to within ±0.8 pm (±0.7 GHz, two standard deviations), allowing the wavelength to be stationed on a narrow atomic or molecular transition or permitting nearly continuous spectral scans. Application of the laser system to studies of OH energy transfer has been demonstrated; both laser-induced-fluorescence and degenerate-four-wave-mixing spectra have been recorded.
Neutral-donor-bound exciton recombination dynamics in GaN grown by metalorganic chemical vapor deposition
Authors: Chen G. D. , Smith M. , Lin J. Y. , Jiang H. X. , Khan M. Asif , Sun C. J.
Published: July 2002

Neutral-donor-bound exciton recombination (I2) dynamics have been studied by photoluminescence in an unintentionally doped n-type GaN epitaxial layer grown by metalorganic chemical vapor deposition. The luminescence emission line shape, peak position, and intensity as functions of temperature have been measured. In particular, time-resolved emission spectroscopy has been employed to study the dynamic processes of the bound exciton recombination, from which the temperature and the emission energy dependencies of the recombination lifetime of this transition have been obtained.
Growth modes in atomic hydrogen-assisted molecular beam epitaxy of GaAs
Authors: Okada Yoshitaka , Fujita Tomoya , Kawabe Mitsuo
Published: July 2002

It has been shown that irradiation with atomic hydrogen during the growth of GaAs in molecular beam epitaxy (MBE) promotes an ideal layer-by-layer two-dimensional nucleation and step-flow growth mode on GaAs(001) substrates, thereby resulting in atomically flat surfaces. Fundamentally important observations related to elementary processes have been presented based on the reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) measurements. A growth model for the atomic hydrogen-assisted GaAs MBE has been postulated.
MgO seed layers for CoCrPt/Cr longitudinal magnetic recording media
Authors: Lee Li-Lien , Cheong B. K. , Laughlin D. E. , Lambeth D. N.
Published: July 2002

Sputter deposited MgO thin films with the B1 crystal structure and (002) film texture are used as seed layers to improve the texture and magnetic properties of the CoCrPt/Cr magnetic thin films on glass substrates for longitudinal recording. The desired (002) textured Cr underlayers are usually obtained by sputtering Cr onto heated substrates. However, it is found that the MgO seed layers can induce the (002) film texture in the Cr underlayers without using a heated substrate and hence, the overlying CoCrPt films are formed with the (112̄0) texture. Vibrating-sample magnetometry measurements show greatly improved in-plane coercivities that are suitable for future high density recording media can be easily obtained.
SiO2 deposition from oxygen/silane pulsed helicon diffusion plasmas
Authors: Charles C. , Boswell R. W. , Kuwahara H.
Published: July 2002

Near-stoichiometric SiO2 films, with little H incorporation and wet etch rates 1.5–3 times that of thermal oxide, have been deposited in a low pressure oxygen/silane helicon diffusion plasma, which has been pulsed with a 50% duty cycle at frequencies from 0.005 Hz to 1 kHz. At low pulse frequencies, the deposition rate is about 50% of the continuous rate, but as the pulse frequency increases from 0.1 to 100 Hz, the deposition rate increases and equals that for a continuous plasma. A likely explanation is that deposition from silane radicals and oxygen continues to take place in the afterglow after the plasma has extinguished. A simple model gives a time constant for this process of about 200 ms.
Lateral quantization effects in lithographically defined CdZnSe/ZnSe quantum dots and quantum wires
Authors: Illing M. , Bacher G. , Kümmell T. , Forchel A. , Andersson T. G. , Hommel D. , Jobst B. , Landwehr G.
Published: July 2002

Quantum dots and quantum wires based on CdZnSe/ZnSe single quantum well heterostructures have been achieved using electron beam lithography and wet chemical etching. Photoluminescence spectra of the dot and wire structures show a blue shift due to lateral quantization for lateral dimensions below 40 nm. For the dot ground state, a lateral confinement energy of 16 meV is obtained for 28 nm diameter structures. For wires with widths on the order of 20 nm, lateral confinement energies of about 5 meV are observed. The dot diameter and wire width dependence of the emission energies can be described based on a square well potential and the measured sizes of the structures.
Metal–semiconductor junctions on p-type strained Si1−xGex layers
Authors: Nur O. , Willander M. , Turan R. , Sardela M. R. , Hansson G. V.
Published: July 2002

The electrical properties of Schottky junctions on high-quality p-type strained Si1−xGex layers have been studied for Ge fractions 0≤x≤0.24. A multicrystal high-resolution x-ray diffractometer was used to investigate the sample’s quality and the strain state and to accurately determine the Ge fraction in the fabricated devices. Several different metals, having a wide range of barrier heights, were used to reach conclusions on the variation of barrier height with the Ge content in the grown strained Si1−xGex layers. It has been found that the Schottky barrier height decreases with increasing Ge fraction in the Si1−xGex layer for the different metals investigated. The change in the barrier height with x has been found to be directly correlated to the valence band discontinuity in the Si/Si1−xGex heterojunction.
Structure and hardness studies of CNx/TiN nanocomposite coatings
Authors: Li Dong , Lin Xi-Wei , Cheng Shang-Cong , Dravid Vinayak P. , Chung Yip-Wah , Wong Ming-Show , Sproul William D.
Published: July 2002

Crystalline CNx/TiN multilayer composite coatings have been synthesized using an opposed cathode unbalanced magnetron sputtering system. Electron microscopy studies showed that the CNx/TiN coatings were fully crystalline and dense at small bilayer thicknesses. An amorphous phase was formed when the CNx layer thickness exceeded 4–5 nm. Two new d spacings extracted by Fourier transform of digitized images of the crystalline CNx region cannot be matched by known compounds formed by the detected elements. This provides limited evidence for the possible formation of a new carbon–nitrogen compound. Nanoindentation hardness about 45–55 GPa was reproducibly achieved for coatings produced under low nitrogen partial pressure and high substrate bias (−150 to −250 V). TiN (111) preferred orientation was strongly correlated to the high coating hardness.
The role of vertical quantum wells in carrier trapping in v-groove quantum wire lasers
Authors: Kiener C. , Rota L. , Maciel A. C. , Freyland J. M. , Ryan J. F.
Published: July 2002

We report a theoretical investigation of carrier trapping in GaAs v-groove quantum wire structures. Our results show that trapping is fast in wires confined by AlGaAs alloy barriers where the growth process creates a Ga-rich vertical quantum well at the center of the v-groove: this acts as a highly effective scattering channel into quantum wires states. The results indicate that with suitable growth engineering, high-efficiency quantum wire structures can be obtained.
Low-temperature AlGaAs/GaAs multiple quantum well structure and its application to photorefractive devices
Authors: Feng W. , Yu Y. , Chen H. , Huang Q. , Zhou J. M.
Published: July 2002

We report the low-temperature (LT) growth of a AlGaAs/GaAs multiple quantum well (MQW) structure by molecular beam epitaxy and demonstrate its application to photorefractive devices. The samples are semi-insulating as grown, and show large electro-optic effect. Resistivity up to 108 Ω cm has been observed. The electroabsorption approaches 3000 cm−1 and the electrorefraction is higher than 1.5% for dc electric field of 15 kV/cm. The effect of annealing on electrical and optical properties of LT AlGaAs/GaAs MQW has also been investigated.
Reduction of low-frequency excess noise in superconducting quantum interference devices by applying high-frequency magnetic fields
Authors: Schöne S. , Mück M. , Heiden C.
Published: July 2002

We have investigated a possible reduction of low-frequency excess noise and the dependence of the flux signal on temperature changes in direct current superconducting quantum interference devices, dc SQUIDs, generated by trapped flux. Niobium thin film dc SQUIDs, carefully cooled down in a well shielded environment, have been exposed to switching transients. The thereby generated low-frequency excess noise and in some case an excess white noise, could substantially be reduced by applying a rf magnetic field of sufficiently high frequency to the SQUID. The temperature dependence of the flux signal of the SQUID and the magnetic field dependence of the drift could also be reduced in these cases, where the drift is caused by movement of trapped vortices.
Microwave power dependence of YBa2Cu3O7 thin-film Josephson edge junctions
Authors: Oates D. E. , Nguyen P. P. , Habib Y. , Dresselhaus G. , Dresselhaus M. S. , Koren G. , Polturak E.
Published: July 2002

Using a stripline resonator technique, we measured the dependence on microwave current of the impedance of fabricated superconductor/normal-metal/superconductor Josephson junctions in YBa2Cu3O7 thin films. The results are compared with predictions of a resistively shunted junction model that yields good agreement at low and intermediate values of the microwave current. At high currents deviations from the model predictions are observed, which we propose are due to flux penetration into the junction. The results are consistent with previously proposed explanations of the rf power dependence of the high-Tc materials.
Correlation between two dielectric breakdown mechanisms in ultra-thin gate oxides
Authors: Satake Hideki , Yasuda Naoki , Takagi Shin-ichi , Toriumi Akira
Published: July 2002

The origin of stressing polarity dependence of charge-to-breakdown, Qbd, in thin SiO2 is discussed based on the temperature dependence of Qbd for both stressing polarities using wet and dry oxides. It was found that the temperature dependence of Qbd, which increases with decreasing temperature in the high temperature region and tends to saturate in the low temperature region, is identical irrespective of the stressing polarity and the oxidation condition. It has been proposed that the strain gradient from Si/SiO2 interface to SiO2/gate electrode interface determines directly both the Si–H bond density which dominates Qbd in high temperature region and the strained Si–O bond density which dominates Qbd in the low temperature region, irrespective of gate polarity and of oxidation condition.
Ultrafast interstitial injection during transient enhanced diffusion of boron in silicon
Authors: Huizing H. G. A. , Visser C. C. G. , Cowern N. E. B. , Stolk P. A. , de Kruif R. C. M.
Published: July 2002

The injection of interstitials during annealing of nonamorphizing Si implants has been monitored by means of sharp boron-doped marker layers grown by reduced pressure chemical vapor deposition. The boron diffusivity enhancement measured during the initial annealing stages (t<15 s) at 700 °C is at least an order of magnitude larger than the enhancement during subsequent annealing. The high supersaturation of interstitials during the early stages of the anneal induces immobilization of boron down to concentrations of ≊1×1017 cm−3, consistent with interstitial-driven boron clustering. The ultrafast diffusion sets lower limits for the silicon and boron interstitial diffusivities at 700 °C of 2×10−10 cm2 s−1 and 2×10−13 cm2 s−1, respectively.
Semiconducting Ge–Si–Fe alloy grown on Si(100) substrate by reactive deposition epitaxy
Authors: Chen H. , Han P. , Huang X. D. , Hu L. Q. , Shi Y. , Zheng Y. D.
Published: July 2002

In this letter, we report a semiconducting Ge–Si–Fe alloy thin film grown on Si(100) by reactive deposition epitaxy using high vacuum evaporation technique. This work is based on the idea that the band structure of β-FeSi2 will be changed with part of the Si atoms in the lattice replaced by Ge atoms. An iron film was first deposited on a SiGe/Si(100) structure, then the alloy was formed during an annealing process. Auger electron spectroscopy and x-ray diffraction results indicate that the new alloy film can be regarded as a distorted β-FeSi2 thin film with the participation of Ge. The direct band gap of the Ge–Si–Fe alloy is determined to be 0.83 eV by optical transmission measurements, which indicate a redshift of the band gap with regard to that of β-FeSi2 (Eg=0.87 eV) thin films.
Nanostructured magnetic networks
Authors: Barnard J. A. , Fujiwara H. , Inturi V. R. , Jarratt J. D. , Scharf T. W. , Weston J. L.
Published: July 2002

Nanostructured contiguous networks of Fe well suited to fundamental studies of the effects of confinement are described. The Fe networks are prepared by sputter deposition onto the surface of nanochannel alumina. One of the most obvious consequences of confining the magnetic material to a nanostructured network is a dramatic enhancement in the coercivity when compared to a continuous Fe film of the same thickness.
Microstructural development and optical properties of epitaxial Ge1−xCx alloys on Si(100)
Authors: Krishnamurthy M. , Yang Bi-Ke , Weber W. H.
Published: July 2002

We report on the microstructural development and optical properties of epitaxial Ge1−xCx alloys (0<x<0.1) grown on Si(100) by low-temperature (200 °C) molecular-beam epitaxy. Films with C concentrations below 2%–3% grow in 2D layers, while films with C higher than 5% form 3D islands after initial layer growth. X-ray-diffraction indicates that less than 1% C may have been substitutionally incorporated. Spectroscopic ellipsometry measurements of the films’ optical constants show small systematic changes with increasing C concentration. These changes occur primarily near 2 eV, the E1 critical point in Ge. No new features attributable to Ge–C vibrational modes could be identified using Raman spectroscopy.
Giant grown-in octahedral inclusions in as-grown silicon: voids versus silicon oxide precipitates
Authors: Vanhellemont Jan
Published: July 2002

Straightforward thermodynamic considerations on critical precipitate size suggest that interstitial oxygen assisted void nucleation and growth during the cooling of a Czochralski grown silicon crystal after solidification from the melt is a likely process. The observed void sizes are in agreement with vacancy diffusion limited growth in the temperature range above 1100 °C.
In-plane periodic bicrystallinity in magnetic thin films
Authors: Sussiau M. , Nguyen-Van-Dau F. , Galtier P. , Schuhl A.
Published: July 2002

Magnetic thin films have been deposited by molecular beam epitaxy on vicinal Si(111) substrates misoriented towards [11-2]. The substrates were thermally pretreated in order to activate the step bunching mechanism, which results in a laterally modulated surface topology with a period of ∼800 Å. Cobalt or permalloy layers grown on such surfaces exhibit an in-plane uniaxial magnetic anisotropy. This anisotropy is associated with the lateral pseudoperiodic variation of the crystalline orientation of the metallic layers as observed by transmission electron microscopy. Magnetoresistance measurements on microstructured films reveal a single-domain behavior with a magnetization reversal by rotation.
InAs/GaSb(001) valence-band offset: Independence of interface composition and strain
Authors: Montanari Barbara , Peressi Maria , Baroni Stefano , Molinari Elisa
Published: July 2002

The InAs/GaSb(001) valence-band offset is calculated for the two inequivalent GaAs-like and InSb-like interfaces and found to coincide to within ≊30 meV. This result is rationalized and generalized to arbitrary composition profiles and induced strain by using a simple model, based on the linear response theory, which is validated by a number of accurate first-principles calculations for intermixed interfaces.
Suppressed angular color dispersion in planar microcavities
Authors: Tessler N. , Burns S. , Becker H. , Friend R. H.
Published: July 2002

We report an improved microcavity design which allows the suppression of the viewing angle dependence of the color emitted by a planar device. This is demonstrated for luminescent conjugated polymer based cavities, for which the wavelength change is reduced from ∼60 to 10 nm at an angle of 60°. We introduce the concept of cavity optical length dispersion and suggest structures for which the wavelength change with viewing angle is reduced to 5 nm at a viewing angle of 60° irrespective of the emissive material.
Fabrication of buried epitaxial CoSi2 layer through selective diffusion
Authors: Prabhakaran K. , Sumitomo K. , Ogino T.
Published: July 2002

The incorporation of metallic layers into the bulk of semiconductors is gaining tremendous attention for device applications. This is mainly achieved by ion beam synthesis. In the ultrathin film regime, however, this technique is not practical due to the damage incurred. Here we report a technique by which fabrication of buried epitaxial CoSi2 is achieved by making use of the selective diffusion behavior of Co. Co atoms diffuse through a Ge overlayer on a Si(111) substrate and are terminated by reaction with the Si atoms underneath. Ion scattering as well as high resolution microscopy results confirm that the CoSi2 layer thus formed is in epitaxial form. This method would help in providing functionality to nanostructure based devices.
Anisotropic piezoelectric effect in lateral surface superlattices
Authors: Skuras E. , Long A. R. , Larkin I. A. , Davies J. H. , Holland M. C.
Published: July 2002

We have studied the potential induced by lateral surface superlattices deposited on a GaAs/AlGaAs heterostructure as a function of bias and orientation of the gates. By using the gates to null the total potential, we extracted the contribution to this potential in the absence of gate bias. Its angular dependence shows that it is dominated by strain from the gates coupled to the electrons by the piezoelectric effect.
Achievement of zero temperature coefficient of resistance with RuOx thin film resistors
Authors: Kim Yong Tae
Published: July 2002

The temperature coefficient of resistance (TCR) for an as-deposited RuO2.2 thin film resistor changes from −131.6 to 1007.95 ppm/°C after the annealing at 600 °C for 30 min. Typically, a near zero TCR about 0±0.12 ppm/°C can be obtained after annealing at 300 °C for 30 min in an Ar ambient. The changes of TCR from negative to positive is attributed to the grain growth of RuOx films from fine grain (30–40 Å) to a larger one (500–800 Å) during the annealing process. Rutherford backscattering spectroscopy and in situ x-ray photoemission spectroscopy show that the ratio of O/Ru in the RuOx film decreases from 2.2 to 2.0, due to the out diffusion of oxygen during the annealing process, which is independent of the changes in TCR.
Characterization of bond and etch-back silicon-on-insulator wafers by photoluminescence under ultraviolet excitation
Authors: Tajima M. , Ibuka S. , Aga H. , Abe T.
Published: July 2002

Photoluminescence (PL) spectroscopy under the ultraviolet (UV) light excitation has been used for the characterization of bond and etch-back silicon-on-insulator (BESOI) wafers. Since the UV light can excite only the silicon-on-insulator (SOI) layer and the SOI structure prevents the photoexcited carriers from diffusing into the base wafer, the PL light is emitted only from the SOI layer. We have detected defects induced during the photoassisted chemical etching process in BESOI wafers. The defect-related emission disappears and the electron-hole droplet signal appears after annealing at 800 °C for 30 min. This allows us to suggest that the annealed SOI layer is comparable in crystalline quality with that of conventional bulk Si wafers and that the recombination velocity at the interfaces is low.
Determination of optical dispersion and film thickness of semiconducting disordered layers by transmission measurements: Application for chemically vapor deposited Si and SnO2 film
Authors: Davazoglou D.
Published: July 2002

A method is presented for the determination of the optical dispersion and thickness of thin semiconducting disordered layers, or stacks of such layers, deposited on fully or partly transparent substrates using transmission measurements. The method consists in fitting to the experimentally recorded spectra, theoretical ones, generated simulating the optical dispersion of the films involved with the help of the physical model proposed by Forouhi and Bloomer for amorphous semiconductors [Phys. Rev. B 34, 7018 (1986)]. The fit is made using standard regression analysis techniques that allow determination of the model parameters corresponding to these films. This method is applied for amorphous Si layers deposited on fused silica substrates by low pressure chemical vapor deposition (CVD) and SnO2 films grown by atmospheric pressure CVD on glass substrates and give results that are in agreement with those reported in the literature.
Optimization of sub 3 nm gate dielectrics grown by rapid thermal oxidation in a nitric oxide ambient
Authors: Kumar Kiran , Chou Anthony I. , Lin Chuan , Choudhury Prasenjit , Lee Jack C. , Lowell John K.
Published: July 2002

The vertical scaling of oxide thickness in the ultra large scale integrated era places stringent requirements on oxide quality. In this letter we report optimization studies in the growth of ultrathin oxynitrides in the sub 3 nm range. The oxynitride growth technique used involved self-limiting growth in nitric oxide (NO) followed by reoxidation in oxygen or nitrous oxide (N2O) ambient. This method allows tight control of oxide thickness and resulted in consistently low leakage currents over a range of thicknesses from 2 to 3 nm. The reliability of the oxynitrides is characterized using QBD, stress-induced leakage and surface charge and contact potential difference measurements. Charge-to-breakdown (QBD) data indicate that the reliability of the oxide degrades with increasing nitridation times in an NO ambient. Increasing reoxidation times in O2 have a similar effect. It is found that an improvement in reliability can be obtained by reoxidation in an N2O ambient. Surprisingly, reoxidizing in N2O proceeds at a higher rate than in O2 and this enables the use of lower thermal budgets.
Gallium self-diffusion in gallium phosphide
Authors: Wang Lei , Wolk J. A. , Hsu L. , Haller E. E. , Erickson J. W. , Cardona M. , Ruf T. , Silveira J. P. , Briones F
Published: July 2002

Ga self-diffusion in gallium phosphide (GaP) is measured directly in isotopically controlled GaP heterostructures. Secondary ion mass spectroscopy (SIMS) is used to monitor intermixing of Ga69 and Ga71 between isotopically pure GaP epilayers which are grown by molecular beam epitaxy (MBE) on GaP substrates. The Ga self-diffusion coefficient in undoped GaP is determined to be D=2.0 cm2 s−1 exp(−4.5 eV/kBT) between 1000 and 1190 °C under phosphorus-rich condition. The self-diffusion entropy is found to be ∼4 kB.
Effect of adding Ar on the thermal stability of chemical vapor deposited fluorinated silicon oxide using an indirect fluorinating precursor
Authors: Chang Kow Ming , Wang Shih Wei , Li Chii Horng , Yeh Ta Hsun , Yang Ji Yi
Published: July 2002

For a low dielectric constant intermetal dielectric application, fluorinated silicon oxide (FxSiOy) films were deposited in an electron cyclotron resonance chemical vapor deposition system, with SiH4, O2, and CF4 as the reaction gases. Since the CF4 is an indirect fluorinating precursor, the fluorinating mechanism resembles that of the oxide etching by a fluorocarbon plasma. Thermal stability of the incorporated fluorine (and hence, the dielectric constant) relies heavily on the deposition parameters and technologies. According to experimental results, adding Ar gas during deposition can improve the thermal stability of incorporated fluorine. Such an improvement is due to the fact that Ar sputtering enhances the removal of weakly bonded silicon fluoride on the as-deposited film surface, thereby elevating the mean bonding strength of fluoride remaining in the oxide.
Valence subband structures of (101̄0)-GaN/AlGaN strained quantum wells calculated by the tight-binding method
Authors: Niwa Atsuko , Ohtoshi Tsukuru , Kuroda Takao
Published: July 2002

The effect of biaxial strain on the valence bands in (101̄0)-GaN/AlGaN quantum wells (QWs) is theoretically investigated, using the sp3 tight-binding method. The effective mass around the valence band edge in unstrained (101̄0) QWs is reduced to about 1/2 that of (0001) QWs. Under compressive strain, the subband non-parabolicity near the band edge is further reduced due to heavy-hole/light-hole splitting. The optical matrix elements of [112̄0] polarization in these QWs are twice as large as those in (0001) QWs. The reduced effective mass and large optical matrix elements in the (101̄0) QWs are an advantage for short-wavelength laser diodes based on wurtzite GaN.
Polymer waveguides with optimized overlap integral for modal dispersion phase-matching
Authors: Wirges W. , Yilmaz S. , Brinker W. , Bauer-Gogonea S. , Bauer S. , Jäger M. , Stegeman G. I. , Ahlheim M. , Stähelin M. , Zysset B. , Lehr F. , Diemeer M. , Flipse M. C.
Published: July 2002

Modal dispersion phase-matched second harmonic generation is demonstrated in new poled polymer waveguide geometries with a nonlinear optical core consisting of two side-chain polymers with different glass transition temperatures. After poling above and between the respective glass transitions, the sign of the nonlinear optical coefficient is reversed in the two polymers, thereby improving the overlap integral. Conversion efficiencies up to 7%/W cm2 were achieved in the first experiments.
Sequential tunneling current through semiconductor superlattices under intense THz radiation
Authors: Platero Gloria , Aguado Ramón
Published: July 2002

Recent transport measurements in GaAs–GaAlAs superlattices under THz radiation show evidence of dynamical localization and electron pumping in the opposite direction to the dc bias in the linear response regime. The ac field induces absorption and emission processes in the multiwell structure which assist the tunnel and which are reflected as new features in the current density. A calculation within the framework of the Bardeen Hamiltonian has been performed to evaluate the tunneling current through the superlattice in the presence of an ac field. By means of this model these new features are reproduced in the current which can be explained in terms of the new induced tunneling channels and of the charge occupation in the wells.
Noise gain in single quantum well infrared photodetectors
Authors: Carbone A. , Mazzetti P.
Published: July 2002

A new approach to the calculation of current noise in single quantum well infrared photodetectors is proposed. The modulation noise due to the fluctuation of the emitter barrier potential is taken into account by considering the correlation between the elementary pulses constituting the excess current injected from the emitter when the quantum well is depleted by electrons. A simple relationship between the noise gain and the photoconductive gain of the device is obtained. A comparison with experiments is also reported.
Ferroelectric properties of (Pb0.97La0.03)(Zr0.66Ti0.34)0.9875O3 films deposited on Si3N4-coated Si substrates by pulsed laser deposition process
Authors: Tseng Tzu-Feng , Yang Rong-Pyng , Liu Kuo-Shung , Lin I-Nan
Published: July 2002

( Pb 0.97 La 0.03 )( Zr 0.66 Ti 0.34 ) 0.9875 O 3 , PLZT, thin films deposited on either LaNiO3 (LNO) or LNO/Pt coated Si3N4/Si substrates, possessing good ferroelectric properties, were successfully obtained by the pulsed laser deposition process. Using LNO/Pt as double layer electrodes not only resulted in PLZT films with superior electric properties, but also of better handling endurance. The former is attributed to the low surface resistivity of electrode materials (i.e., ρLNO/Pt=0.5 mΩ cm) due to the bypassing effect of the Pt layer, whereas the latter is ascribed to the induction of compressive stress on PLZT and LNO layers due to a relatively larger thermal expansion coefficient (CTE) of the Pt layer. The ferroelectric properties of (PLZT )LNO/pt films were Pr=16.5 μC/cm2 and Ec=63.5 kV/cm, while the dielectric constant and leakage current were K=1.028 and Je⩽8×10−6 A/cm2 (under 150 kV/cm), respectively. Their fatigue life was longer than 2×109cycles under action of 300 kV/cm pulse.
Influence of reactive gas on ion energy distributions in filtered cathodic vacuum arcs
Authors: Bilek M. M. M. , Chhowalla M. , Milne W. I.
Published: July 2002

The energy with which depositing species impinge on a growth surface is one of the main factors influencing the microstructure and properties of the thin films fabricated in plasma deposition processes. In this letter, we examine the effects of a variety of deposition parameters on the ion energy distribution beyond the magnetic filter in a filtered cathodic vacuum arc (FCVA). The results indicate that the ion energy distributions do not vary significantly with the magnetic field strength, magnetic field configuration, lateral position in the beam, or bias on the filter duct wall in the ranges studied. The energy distribution was however strongly affected by the presence of a reactive background gas. A reduction of 10 eV was recorded for a background pressure of 10−3 Torr of N2 gas in a carbon FCVA. This result has implications for all FCVA depositions carried out in a gas atmosphere and is consistent with the view that ion transport in the magnetic filter occurs due to an electrostatic guiding potential well.
Velocity distributions of molecules ejected in laser ablation
Authors: Zhigilei Leonid V. , Garrison Barbara J.
Published: July 2002

Based on the results of molecular dynamics simulations, we propose an analytical expression for the velocity distributions of molecules ejected in laser ablation. The Maxwell-Boltzmann distribution on a stream velocity, commonly used to describe the measured velocity distributions, is modified to account for a range of stream velocities in the ejected plume. The proposed distribution function provides a consistent description of the axial and radial velocity distributions. The function has two parameters that are independent of the desorption angle and have clear physical meaning, namely, the temperature of the plume and the maximum stream velocity or velocity of the plume propagation.
Electron emission from disordered tetrahedral carbon
Authors: Weiss B. L. , Badzian A. , Pilione L. , Badzian T. , Drawl W.
Published: July 2002

Electron field-emission tests have been performed on films grown by a modified microwave plasma assisted chemical vapor deposition diamond process. This modification includes the addition of N2 and O2 during the growth stage. Characterization of these films shows the presence of a disordered tetrahedral carbon structure. Raman spectroscopy indicates a disturbance in the cubic symmetry of the lattice and x-ray diffraction indicates a disordered tetrahedral structure. Field-emission testing indicate that current densities of 0.5 mA/cm2 can be obtained for applied fields of 5–8 V/μm. The results are explained in terms of a change in the band structure and the formation of electronic states in the band gap.
Noise in single quantum well infrared photodetectors
Authors: Ershov M. , Korotkov A. N.
Published: July 2002

The spectral density of current fluctuations in single quantum well infrared photodetectors is calculated using the Langevin approach. The noise gain and photocurrent gain are expressed in terms of basic transport parameters. Fluctuations of the incident photon flux are taken into account.
Ga vacancies in low-temperature-grown GaAs identified by slow positrons
Authors: Gebauer J. , Krause-Rehberg R. , Eichler S. , Luysberg M. , Sohn H. , Weber E. R.
Published: July 2002

A systematic investigation of GaAs layers grown at low temperatures was carried out by means of positron annihilation. The vacancy defects in undoped as-grown material were identified to be mainly Ga vacancies (VGa) by comparing the annihilation parameters to those of Ga vacancies in highly Si-doped GaAs. The characteristic S parameter for positron annihilation in Ga vacancies was determined to be S(VGa)=1.024(1). The VGa concentration increases up to 1018 cm−3 by decreasing the growth temperature to 200 °C. The vacancy concentration can account for the compensation of AsGa+ antisites as was previously assumed.
The process and efficiency of ultraviolet generation from gallium nitride blue light emitting diodes
Authors: Basrur J. P. , Choa F. S. , Liu P.-L. , Sipior J. , Rao G. , Carter G. M. , Chen Y. J.
Published: July 2002

To obtain small size, high speed ultraviolet sources, we studied the ultraviolet (UV) generation process and efficiency of gallium nitride (GaN) blue light emitting diodes (LEDs). The blue and UV emissions follow a four-level recombination model. Depending on the pump pulse amplitude, the UV-to-blue generation ratio increases and then saturates with increasing pump pulse duration. High efficiency, up to 450 μW UV power at 380 nm, can be obtained from a 1.2 mW blue LED.
Ce-substituted yttrium iron garnet films prepared on Gd3Sc2Ga3O12 garnet substrates by sputter epitaxy
Authors: Shintaku Toshihiro , Tate Akiyuki , Mino Shinji
Published: July 2002

Ce-substituted yttrium iron garnet films are epitaxially grown in situ on (111)-oriented substrates of Gd3Sc2Ga3O12 garnet by conventional rf diode sputtering for application to magneto-optic waveguide devices in optical communication systems. The lattice constant of the substrates is larger than that of the previously used (Gd,Ca)3(Ga,Mg,Zr)5O12 garnet substrates whose lattice constant is smaller than that of the films. The lowest ever reported propagation losses of 9.7 dB/cm in the TE mode and 5.8 dB/cm in the TM mode are obtained for a film thickness of 0.5 μm at λ=1.55 μm.
Vertical strain and doping gradients in thick GaN layers
Authors: Siegle H. , Hoffmann A. , Eckey L. , Thomsen C. , Christen J. , Bertram F. , Schmidt D. , Rudloff D. , Hiramatsu K.
Published: July 2002

We report on spatially-resolved low-temperature luminescence and Raman experiments on a 220-μm-thick GaN layer grown on sapphire by hydride vapor phase epitaxy. Our measurements reveal that the peak position of the near-band-gap luminescence strongly depends on the distance to the substrate interface. The luminescence shifts continuously to lower energies with decreasing distance but a strong blue shift occurs directly at the interface. We correlate these effects with the inhomogeneous free-carrier distribution and the strain gradient found by our Raman experiments.