bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical integrated diffusion-oxidation model for implanted nitrogen in silicon
Authors: Adam Lahir Shaik , Law Mark E. , Dokumaci Omer , Hegde Suri
Published: July 2002

Scaling the gate oxide thickness is one of many process development challenges facing device engineers today. Nitrogen implantation has been used to control gate oxide thickness. By varying the dose of the nitrogen implant, process engineers can have multiple gate oxide thicknesses in the same process. Although it has been observed that nitrogen retards gate oxidation kinetics, the physics of how this occurs is not yet well understood. Since the retardation in oxide growth is due to the diffusion of nitrogen and its subsequent incorporation at the silicon/silicon oxide interface, the study of the diffusion behavior of nitrogen in silicon becomes important. Further, it is also necessary to study how this diffusion behavior impacts oxide growth. Models have been developed to explore these issues. The diffusion model is based on ab initio results and is compared to experimental results at two temperatures. The oxide reduction model is based on the diffusion of nitrogen to the surface. The surface nitrogen is coupled to the surface reaction rate of silicon and oxygen to moderate oxide growth.
Reflection of infrared radiation from lamellar gratings on a silicon wafer: Spectroscopy of nonspecular orders
Authors: Hava S. , Ivri J. , Auslender M.
Published: July 2002

Spectral efficiencies in the wavelength range from 1.5 to 14 μm of nonspecular orders reflected by grating-on-silicon structures with periods comparable to the wavelengths have been measured. The measurements were carried out at varying incident and scattered angles while keeping their sum fixed. The spectra consist of broadened peaks at wavelengths close to those predicted by the grating equation. A mechanism of the broadening due to finite incident beam width has been discussed. Simulations using rigorous diffraction theory and wavelet analysis have been performed. The results obtained agree well with the experimental data.
Wall sheath and optimal bias in magnetic filters for vacuum arc plasma sources
Authors: Zhang T. , Zhang Y. C. , Chu P. K. , Brown I. G.
Published: July 2002

A plasma diffusion model is established to determine the optimal bias and sheath patterns in a positively biased magnetic filter of a metal arc plasma source. We determine the equation for the optimal bias on the magnetic filter. According to our model, the optimal bias is related to the electron speed, ion speed, ion mass, ion charge state, and plasma density in the filter. The optimal bias increases as these variables are increased with the exception of the electron speed. Even though the magnetic field is taken into account, it is not a variable in the final equation. Our experimental results confirm that the magnetic field has almost no influence on the optimal bias. An alternate design approach is suggested that should lead to enhanced plasma transport through the filter.
Polymer microring lasers with longitudinal optical pumping
Authors: Dou S. X. , Toussaere E. , Ben-Messaoud T. , Potter A. , Josse D. , Kranzelbinder G. , Zyss J.
Published: July 2002

We propose an optical pumping scheme for microring cavity lasers. The pump beam is end-fire coupled into the optical fiber that supports the microring cavity. When propagating along the fiber, the pump light is coupled into and excites the gain medium in the microring. We have demonstrated that this pumping geometry leads to an enhanced slope efficiency and significant reduction of the lasing threshold. In addition, as the excitation of the gain medium is uniform, certain effects that are prone to occur in the usual transversal pumping configuration because of nonuniform excitation can be avoided.
Activated dissociation via a trapping precursor: O2/Cu(001)-(2√×√)-O
Authors: Yata Masanori , Uesugi-Saitow Yuki
Published: July 2002

Dissociative adsorption of O2 on Cu(001)-(2√×√)-O was shown to induce Cu2O epitaxial islands on the surface. The initial dissociative sticking probability of O2 on Cu(001)-(2√×√)-O scaled with the total translational energy of incident O2, suggesting that the interaction potential was highly corrugated. The sticking probability decreased with increasing translational energy of incidence and increased with increasing surface temperature. For lower translational energy of incident O2 (⩽130 meV), the velocity distribution of the scattered molecules was of nonshifted Maxwellian-type, indicating trapping desorption. The translational temperature of the trapping desorption was lower than the surface temperature and increased linearly with surface temperature, suggesting that there was no barrier for desorption. Neither thermal desorption experiments nor velocity distribution analysis of the trapping desorption showed any evidences of recombination desorption. These results were interpreted as an activated dissociation via a trapping precursor. The activation barrier for dissociation was estimated as 330 meV. The angular distribution of the trapping desorption was fitted well by cos2 θ, which was in contrast to the expectation of a cosine angular distribution based on the detailed balance arguments. The discrepancy may have been attributable to preferential consumption of the parallel momentum of the trapped O2 for dissociation and imbalance between adsorbing and desorbing O2 flux.
Optically written solid-state lasers with broadly tunable mode emission based on improved poly (2,5-dialkoxy-phenylene-vinylene)
Authors: Kranzelbinder G. , Toussaere E. , Zyss J. , Pogantsch A. , List E. W. J. , Tillmann H. , Hörhold H.-H.
Published: July 2002

We report an optical written distributed feedback (DFB) structure with broadly and continuously tunable mode emission (Δλ=30 nm) based on polycondensation-type poly[2methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH–PPV). In a Lloyd-mirror configuration we realize first-order feedback by dynamic photoinduced in-plane gratings, which can also be imprinted permanently. This technique is a versatile fabrication tool for polymeric DFB laser structures while also providing an efficient method to probe the lasing performance of organic solid-state laser materials. Furthermore, features of the photoinduced absorption spectra of improved MEH–PPV indicate favorable material properties towards further homopolymer solid-state laser applications.
Electronic and vibronic properties of Mg-doped GaN: The influence of etching and annealing
Authors: Tripathy S. , Chua S. J. , Ramam A. , Sia E. K. , Pan J. S. , Lim R. , Yu G. , Shen Z. X.
Published: July 2002

We report a systematic study of the effects of wet chemical treatment, inductively coupled plasma etching, and thermal annealing on the surface and optical properties of Mg-doped p-type GaN. The chemical bonding and surface stoichiometry of the GaN surface subjected to different processing steps are analyzed based on the results of x-ray photoelectron spectroscopy. Atomic force microscopy has been employed to characterize the surface morphology. Photoluminescence (PL) and micro-Raman techniques have been used to investigate the electronic and vibrational properties of plasma etched surface. We have correlated the surface changes induced by dry etching of p-type GaN to the corresponding changes in the defect and impurity related states, through their manifestation in the PL spectra. We have observed several local vibrational modes (LVMs) in p-type GaN subjected to various processing steps. A broad structure in the low-temperature Raman spectra around 865 cm−1 is attributed to the electronic Raman scattering from neutral Mg acceptors. In addition to the LVMs of Mg–Hn complexes, two new modes near 2405 and 2584 cm−1 are observed from the etched p-GaN surface. We have also carried out PL and micro-Raman analyses of Mg-doped GaN films annealed under different conditions.
A neutron scattering study of orientational ordering in the smectic and nematic phases of the liquid crystal, 2′,3′-difluoro-4-heptyl-4″-nonyl p-terphenyl
Authors: Hamley I. W. , Luckhurst G. R. , Richardson R. M. , Santos F.
Published: July 2002

The orientational order parameters P̄2, P̄4, and P̄6 have been determined by neutron scattering from a mixture of normal hydrogenous and deuterium labeled molecules in the nematic, smectic A and smectic C phases of the mesogen 2′,3′-difluoro-4-heptyl-4″-nonyl-p-terphenyl. Since the method relies on a knowledge of the molecular structure, the influence of different molecular conformations resulting from the terminal chains on the values determined was examined in detail. It was shown that the choice of conformation could significantly effect the resulting values of the order parameters. The order parameters were, therefore, determined by assuming a distribution of conformations for the alkyl chains. The relative contributions of these conformations were governed by the Flory rotational isomeric state model. The values for P̄2 were consistent with those determined by nuclear magnetic resonance but all the order parameters were generally much greater than those predicted by the Maier–Saupe theory.
Solvent-assisted dye-diffusion thermal transfer for electronic imaging applications
Authors: Wu Chung-Chih , Lin Sun-Wen , Chen Chieh-Wei , Hsu Jui-Hung
Published: July 2002

Molecularly doped polymers processed by dye-diffusion thermal transfer (D2T2) have wide applications in electronic imaging. For the sake of stability, it is usually desired that the host polymers have high glass-transition temperatures (Tg), which however implies high processing temperatures. In this letter, we show that in an atmosphere of organic solvent vapor, effective dye-diffusion thermal transfer may be carried out at temperatures much below the Tg of a host polymer. The atmosphere of solvent vapor ensures incorporation of solvent molecules into the polymer throughout the process and causes the plasticization effect. As a consequence, the effective Tg of the system is lowered and the diffusion of dyes in the host polymer is enhanced. Through such a process, polymers of higher Tg and wider ranges of dye molecules may be used in D2T2 without losing the processing compatibility. Furthermore, carrying out D2T2 at lower temperatures is beneficial to the resolutions of transferred features due to the suppression of vaporization of dyes.
Observation of magnetoresistance in core–shell Fe–Fe oxide systems
Authors: Savini L. , Bonetti E. , Bianco L. Del , Pasquini L. , Signoretti S. , Allia P. , Coisson M. , Moya J. , Selvaggini V. , Tiberto P. , Vinai F.
Published: July 2002

A negative magnetoresistance was measured between 15 and 300 K under a maximum field H=70 kOe on two granular systems obtained by compacting Fe nanoparticles surrounded by an oxide shell ∼2 nm thick. The effect depended on the Fe core average size D that was of 8 and 18 nm in the two samples, as by x-ray diffraction. The maximum relative resistance change, about 5%, was observed at 50 K in the sample with smaller D. The results have been interpreted considering intraparticle and interparticle magnetic correlations and microscopic mechanisms similar to those responsible for the magnetoresistance in other granular systems.
Effect of grain size dispersion on read/write properties in antiferromagnetically coupled recording media affected by thermal fluctuation
Authors: Nakatani Y. , Hayashi N. , Uesaka Y. , Fukushima H.
Published: July 2002

The effect of thermal fluctuation and grain-size dispersion on double-layered antiferromagnetically coupled (AFC) magnetic recording media is investigated by micromagnetic computer simulation. Calculations performed to obtain read/write properties show that the value of the underlayer saturation magnetization which yields maximum signal to noise ratio (SNR) is almost independent of the grain-size dispersion. The difference between the SNRs of the conventional and the AFC media was found not to depend on the grain-size dispersion but to be determined from other parameters such as the interlayer exchange constant, when the grains of both media are distributed with the same size dispersion. Thermal stability achieved by AFC was found to increase with increasing the interlayer exchange constant though the stabilization effect was seen to decrease as the grain-size dispersion is increased.
Current-controlled channel switching and magnetoresistance in an Fe3C island film supported on a Si substrate
Authors: Tang Jinke , Dai Jianbiao , Wang Kaiying , Zhou Weilie , Ruzycki Nancy , Diebold Ulrike
Published: July 2002

A film of magnetic Fe3C islands separated by nanochannels of graphite was prepared with pulsed laser deposition on a Si substrate with a native SiO2 surface. When the temperature is increased above 250 K the resistance suddenly drops because electron conduction switches from the film to the Si inversion layer underneath. The film shows a negative magnetoresistance. The inversion layer exhibits a large positive magnetoresistance. The transition to the low resistance channel can be reversed by applying a large measuring current, making possible current-controlled switching between two types of electron magnetotransport at room temperature.
Novel cylindrical, air-coupled acoustic levitation/concentration devices
Authors: Kaduchak Gregory , Sinha Dipen N. , Lizon David C.
Published: July 2002

A new class of devices for levitation and/or concentration of aerosols and small liquid/solid samples (up to several millimeters in diameter) in air has been developed. The novelty of these devices is their simplicity in design. These are inexpensive, low-power, and, in their simplest embodiment, do not require accurate alignment of a resonant cavity. Best of all, these can be off-the-shelf items. The devices are constructed from a hollow, cylindrical piezoelectric tube. The main design criteria requires a resonant mode of the tube to match a resonant mode of the interior air-filled cavity. Once matched, it is shown that drops of water in excess of 1 mm in diameter may be levitated inside the cylinder cavity against the force of gravity for less than 1 Watt of input electrical power. Efficient concentration/agglomeration of aerosol particles in air is also demonstrated.
Anti-Stokes emission in undoped YVO4
Authors: Ryba-Romanowski W. , Gołąb S. , Solarz P. , Dominiak-Dzik G. , Łukasiewicz T.
Published: July 2002

Single crystal of nominally undoped YVO4 exhibits a broad-band emission centered at 450 nm when excited at any wavelength between 620–440 nm with short pulses delivered by an optical parametric oscillator. The broad-band emission has been assigned to the transition from the lowest energy excited states T13, T23 to the ground A11 state of the VO43−, whereas the excitation mechanism is supposed to be an excited state absorption from a hitherto unidentified intermediate state. This state is likely to be related with V4+ and/or V3+ ions whose presence in YVO4 is generally recognized. The material may have a potential as a tunable source of blue radiation provided a way is found to increase the ground state absorption.
Spin blockade effects in chromium oxide intergrain magnetoresistance
Authors: Sokolov A. , Yang C.-S. , Yuan L. , Liou S.-H. , Cheng Ruihua , Xu B. , Borca C. N. , Dowben P. A. , Doudin B.
Published: July 2002

CrO 2 thin films with crystallites of a significant size permit investigation of the thin intergrain conduction between a limited numbers of crystals. Phoemission techniques reveal that the CrO2 films are covered by a 1–2-nm-thick Cr2O3 insulating barrier. The electronic band gap of the surface electrons is 3.4 eV at low temperatures, decreases sharply down to 2.8 eV at ambient. Electric transport though a few junctions in series shows a remarkable zero-bias anomaly, interpreted in terms of blockade effects. We show that the magnetoresistance is governed by low-bias blockade in these junctions.
On the mutual interaction between laser beams in plasmas
Authors: Ren C. , Duda B. J. , Evans R. G. , Fonseca R. A. , Hemker R. G. , Mori W. B.
Published: July 2002

The nonlinear interaction between light beams in a plasma is studied. In particular, nonlinearities due to relativistic mass corrections and density modulations from a plasma wave wake are considered; but the results can be generalized for other nonlinearities. A simple physical picture using the nonlinear phase velocity of the light wave in a plasma is developed to show that when two laser beams are coherent, the force can be repulsive or attractive, depending on their relative phase. When the two laser beams are polarized in mutually perpendicular directions, the force is always attractive. Using a variational method, a simple analytical expression for this attractive force is derived for Gaussian beams. The centers of the lasers move analogously to point masses under this attractive force with the laser power playing the role of the mass. Under an attractive force, solutions exist where the two lasers can spiral around each other. It is also shown that the plasma wave wake can cause the two spiraling lasers to become intertwined forming a braided pattern. The braiding is common to any nonlinearity which is not instantaneous. The analytical results concerning attraction, repulsion, and braiding have been confirmed using three dimensional particle-in-cell simulations. The simulations also show that angular momentum can radiate away leading to the coalescence of the remaining energy.
Temperature-dependent Hall measurements of molecular beam epitaxial grown Si-doped AlxGa1−xN for Al mole fraction up to 0.5
Authors: Ahoujja M. , Yeo Y. K. , Hengehold R. L. , Van Nostrand J. E.
Published: July 2002

Electrical properties of Si-doped AlxGa1−xN films grown on sapphire substrates with AlN buffer layers by gas source molecular beam epitaxy (MBE) have been investigated using temperature dependent Hall-effect measurements. These measurements show that the AlxGa1−xN sapphire interfacial layer significantly affect the electrical properties of the AlxGa1−xN layer doped with Si at a nominal value of 1×1018 cm−3. This study indicates that good quality AlxGa1−xN films can be grown for x⩽0.3 by gas source MBE, but lesser quality films are obtained for x>0.3.
Microstructure and magnetic properties of nanocomposite FePtCr–SiN thin films
Authors: Kuo P. C. , Chen S. C. , Yao Y. D. , Sun A. C. , Chiang C. C.
Published: July 2002

[ (FePt) 100−x Cr x ] 100–δ  –[ SiN ] δ nanocomposite thin films with x=0–25 at. %, and δ=0–30 vol. % were fabricated on a natural-oxidized Si(100) substrate by dc and rf magnetron cosputtering of FePt, Cr, and Si3N4 targets. The thickness of the films was kept at 10 nm in order to examine the possibility for applying in high-density magnetic recording media. Transmission electron microscopy (TEM) and electron diffraction analyses indicated that the face-centered-cubic (fcc) γ-phase FePt, body-centered-cubic (bcc) Cr, and amorphous SiN coexisted in as-deposited films. The as-deposited films were annealed in vacuum between 350 and 750 °C for 30 min, and then ice-water quench cooling, in order to transform the soft magnetic fcc γ-FePt phase to the hard magnetic face-centered-tetragonal (fct) γ1 phase. Cr was added to inhibit the FePt grain growth, and was observed by TEM and energy disperse spectrum analysis in the grain surface area of FePt grains. The TEM observation indicated that the structure of the film was an amorphous SiN matrix with FePtCr particles dispersed in it. The particle size of FePtCr in annealed film was increased with the annealing temperature but decreased with the increase of SiN and Cr contents. Magnetization measurements indicated that the optimum condition for high-density magnetic recording purpose of the film was found with x=10 at. % and δ=15 vol. %, annealing at 600 °C for 30 min. The average grain size of the FePtCr in this film is about 9.5 nm, the saturation magnetization is 450 emu/cm3, in-plane coercivity is 3.7 kOe, and in-plane squareness is about 0.75.
Electrical characteristics of TaSixNy/SiO2/Si structures by Fowler–Nordheim current analysis
Authors: Suh You-Seok , Heuss Greg P. , Misra Veena
Published: July 2002

In this letter, the Fowler–Nordheim tunneling in TaSixNy/SiO2/p-Si structures has been analyzed. The effective barrier height at the metal–oxide interface was extracted by Fowler–Nordheim current analysis. The barrier height was found to increase with increased annealing temperature. The barrier height was correlated with the extracted work function from capacitance–voltage analysis. This indicated that the work function of TaSixNy films changes under high temperature annealing from 4.2∼4.3 eV after 400 °C anneals to ∼4.8 eV after 900 °C anneals. We believe that the mechanism that causes the work function to increase is the formation of a Ta-disilicide layer at the interface between the electrode and the dielectric.
Test of the scaled particle theory for aligned hard spherocylinders using Monte Carlo simulation
Authors: Koda Tomonori , Ikeda Susumu
Published: July 2002

We obtained the chemical potential of a system of parallel hard spherocylinders by calculating the insertion probability of the particle. As a technique to obtain the insertion probability, we used a gradual insertion method together with Monte Carlo simulation. The simulation results provide a test of the scaled particle theory, suggesting a better approximation of the equation-of-state of the nematic phase of aligned long hard spherocylinders compared to the original scaled particle theory.
Band anticrossing in group II-Ox–VI1−x highly mismatched alloys: Cd1−xMnyOxTe1−x quaternaries synthesized by O ion implantation
Authors: Yu K. M. , Walukiewicz W. , Wu J. , Beeman J. W. , Ager J. W. , Haller E. E. , Miotkowski I. , Ramdas A. K. , Becla P.
Published: July 2002

Highly mismatched group II-Ox–VI1−x alloys have been synthesized by oxygen implantation into Cd1−yMnyTe crystals. In crystals with y>0.02, incorporation of O causes a large decrease in the band gap. The band gap reduction increases with y; the largest value observed is 190 meV in O-implanted Cd0.38Mn0.62Te. This striking behavior is consistent with the band anticrossing model which predicts that repulsive interaction between localized states of O and the extended states of the conduction band causes the band gap reduction. These large, O-induced effects provide a unique opportunity by which to control the optical and electronic properties in II–VI alloys.
Calibration of magnetic force microscopy using micron size straight current wires
Authors: Liu Congxiao , Lin Kingston , Holmes Rich , Mankey Gary J. , Fujiwara Hideo , Jiang Huaming , Seok Cho Hae
Published: July 2002

A circuit with two long parallel micron size wires was fabricated by photolithography to calibrate magnetic force microscopy (MFM) tips. The tip phase shift increased as the tip scan height decreased. With the tip scan height kept constant, a linear relationship was found between the current amplitude and the phase shift of the tip at the center position of the two wires separation. The estimated magnetic moment of the tip was one order larger than its nominal value. The results imply that with better control over the fabrication process, the micron size straight wires can be used to calibrate MFM tips.
Hole transport in polycrystalline pentacene transistors
Authors: Street R. A. , Knipp D. , Völkel A. R.
Published: July 2002

Measurements of pentacene thin-film transistors are used to explore hole transport mechanisms. The grain-boundary barrier model does not account for the data, since no field dependence of the mobility is observed over a wide range of gate and drain voltages. Instead, trapping provides a more satisfactory qualitative and quantitative interpretation. The subthreshold characteristics are attributed to deep acceptors in the pentacene film, and the conclusions are supported by numerical modeling.
Holographic fabrication of multiple layers of grating inside soda–lime glass with femtosecond laser pulses
Authors: Li Yan , Watanabe Wataru , Yamada Kazuhiro , Shinagawa Taishi , Itoh Kazuyoshi , Nishii Junji , Jiang Yongyuan
Published: July 2002

Gratings have been holographically fabricated inside soda–lime glass by two-beam interference of a single 130 fs laser pulse at a wavelength of 800 nm. Because the grating was localized in the focal volume and the depth at which the grating was formed can be controlled by translation of the sample, multiple layers of grating can be fabricated. As an example, three layers of grating have been recorded at depths of ∼200, ∼400, and ∼600 μm, respectively. These gratings can be read by either of the two recording beams with reduced energy, which demonstrates their potential applications in integrated optics and optical storage.
Dynamics of many bodies in a liquid: Added-mass tensor of compounded bodies and systems with a fast oscillating body
Authors: Ragazzo Clodoaldo Grotta
Published: July 2002

An explicit set of ordinary differential equations that approximately describe the dynamics of many rigid bodies (without any hypothesis on their geometry) inside an ideal fluid is presented. Two applications of these equations are made. At first, it is shown how to use these equations to compute the added-mass tensor of a single body made up of simpler units (like spheres, cylinders, and ellipsoids). Then the hydrodynamic force and torque that a small-amplitude fast oscillating body induces on another body that can freely move in its vicinity is computed. The noticeable result is that if the free body is sufficiently far from the oscillating one then the averaged interaction force is attractive if and only if the density of the free body is larger than the density of the fluid. Finally, computations for a pendulum system are presented. It seems that the latter system is suitable for experimentation.
Origin of transconductance oscillations in silicon-on-insulator metal–oxide–semiconductor field-effect transistors with an ultrathin 6-nm-thick active Si layer
Authors: Ueno H. , Tanaka M. , Morikawa K. , Takahashi T. , Miura-Mattausch M. , Omura Y.
Published: July 2002

Transconductance oscillations were observed for silicon-on-insulator metal–oxide–semiconductor field-effect transistors with 50 nm channel length and 6 nm Si-layer thickness in the temperature range of 39–50 K. By investigating the temperature dependence of the oscillations it was found that the oscillations were caused by two reasons. One reason is the roughness at the Si/insulator interface responsible for the low-gate-voltage oscillations. The roughness results in different thicknesses of the Si layer along the channel, causing different quantized energy levels, which act as barriers for carriers moving in the channel. The other reason is the tunneling through the potential barrier at the p/n junctions between the contacts and the channel, which is responsible for the high-gate-voltage oscillations.
Injection and accumulation of electric charge in MgO single crystals
Authors: Farhat N. , Ditchi T. , Holé S. , Lewiner J.
Published: July 2002

We describe the space charge dynamics in MgO single crystals under high voltage at room temperature. The space charge profiles are measured in a nondestructive way using light induced pressure pulses. The build up of a positive space charge near the anode and of a negative space charge near the cathode are observed. The amplitude and extension of these charges depend on the electrode materials. Hole and electron injections at the interfaces can explain the charge distributions observed.
Simultaneous existence and atomic arrangement of CuPt-type and CuAu-I type ordered structures near ZnTe/ZnSe heterointerfaces
Authors: Lee H. S. , Lee J. Y. , Kim T. W. , Lee D. U. , Choo D. C. , Kim M. D.
Published: July 2002

Selected area electron diffraction pattern and high-resolution transmission electron microscopy measurements on a ZnTe/ZnSe heterointerface grown on a GaAs(001) substrate showed two structures of the CuPtB-type ordering structures, one for each direction of the doublet periodicity on the {111} lattice planes along the [110] axis, and superstructure spots related to CuAu-I-type ordering. Auger electron spectroscopy measurements showed that the Se atoms were interdiffused into the ZnTe thin film and that the diffused Se atoms formed a ZnSexTe1−x layer, which might be related to the coexistence of the two types of ordered structures. The coexisting behavior of the two ordered structures are discussed. The present results can help improve the understanding of the formation mechanism and the coexisting behaviors of the two ordered structure near the ZnTe/ZnSe heterointerface.
Transverse demagnetizing factors of long rectangular bars. II. Numerical calculations for arbitrary susceptibility
Authors: Pardo Enric , Sanchez Alvaro , Chen Du-Xing
Published: July 2002

For an infinitely long bar with rectangular cross section 2a×2b and constant susceptibility χ in a uniform transverse applied field Ha along dimension a, the fluxmetric and magnetometric demagnetizing factors Nf,m as functions of a/b and χ are accurately computed using a finite-elements method. By comparison of the computed results with exact analytical results for χ=−1,0,∞ and with a set of conjugate relations derived in this work, the elements distributions have been optimized to give a minimum discretization error. This error is further greatly reduced in the final results of Nf,m by using an error correction approach previously proposed in a similar work for cylinders.
Influence of light intensity on the photoluminescence of silicon nanostructures
Authors: Amans D. , Guillois O. , Ledoux G. , Porterat D. , Reynaud C.
Published: July 2002

The strong visible photoluminescence (PL) of nanostructured silicon, such as porous Silicon and silicon nanocrystals, is studied as a function of the power and the wavelength of the excitation laser source. The position of the PL peak is a function of the fluence: when the incident fluence is increased, the PL peak is blueshifted, and it is redshifted to its initial position when the fluence is decreased back. The PL yield is strongly attenuated with the increasing fluence and this decrease is partially irreversible. The behavior is also found to be a function of the wavelength of excitation: the shorter the excitation wavelength, the stronger the fluence effect. The PL temporal behavior has also been studied and appears to be weakly sensitive to the fluence. Fluence effects are compared to temperature effects and both are noticeably different, proving the absence of heating effects in our experiment for a wide range of incident power. Auger effect and state filling are discussed in order to understand the experimental results in the framework of the quantum confinement process.
Direct crystallization of the peritectic Nd2Fe14B1 phase by undercooling of bulk alloy melts
Authors: Volkmann Thomas , Gao Jianrong , Herlach Dieter M.
Published: July 2002

Electromagnetic levitation was used to melt and solidify containerlessly Nd–Fe–B alloys. A method was developed to reduce and evaporate stable solid Nd oxides at the surface of the liquid samples. The oxides otherwise limit the undercoolability of the highly reactive Nd-based alloys. In such a way, undercoolings up to 150 K of the levitation processed samples were achieved. Owing to the large undercooling range, the intermetallic Nd2Fe14B1 phase with the hard magnetic properties was primarily crystallized at undercoolings exceeding 50 K. Solidification of the pro-peritectic γ-Fe with soft magnetic properties was successfully suppressed. At the largest undercoolings, a metastable phase, likely to be of the composition Nd2Fe17Bx (x≈1) is primarily formed while the crystallization of Nd2Fe14B1 phase is followed up in a subsequent step.
Electronic structure, optical, and magneto-optical properties of Gd5(Si2Ge2) compound
Authors: Harmon B. N. , Antonov V. N.
Published: July 2002

The electronic structure, optical, and magneto-optical spectra of the strongly magnetocaloric Gd5(Si2Ge2) compound are investigated theoretically from first principles, using the fully relativistic Dirac linear muffin tin orbital band structure method. The electronic structure is obtained with the local spin-density approximation (LSDA), as well as with the so-called LSDA+U approach. The Coulomb repulsion Ueff strongly influences the electronic structure of Gd5(Si2Ge2) and for the Gd3+ ions seven spin up 4f bands are fully occupied and situated at the bottom of Si and Ge s states, while the 4f hole levels are completely unoccupied and well above the Fermi level hybridized with Gd 5d states. LSDA+U theory predicts that the magneto-optical spectra are much more sensitive to the α→β phase transition in comparison with the regular nonmagnetic optical properties.
Dielectric tunability of coherently strained LaAlO3/SrTiO3 superlattices
Authors: Fuchs D. , Adam M. , Schweiss P. , Schneider R.
Published: July 2002

Dielectric LaAlO3 and SrTiO3 thin films and LaAlO3/SrTiO3 multilayers were grown epitaxially by pulsed laser deposition on (001) oriented (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates. Their structural characterization was carried out by x-ray diffraction and cross section transmission electron microscopy, which allowed us to determine the degree of strain in the dielectric material. For a film thickness of 200 nm we observed significant structural relaxation of the LaAlO3 and SrTiO3 single layers toward their single crystal lattice parameters in contrast to LaAlO3/SrTiO3 multilayer structures, where the dielectric material remained coherently strained. The influence of strain on the dielectric properties was studied by impedance spectroscopy in the frequency range of 40 Hz–10 MHz at room temperature. The measurements were performed on parallel plate capacitors, using epitaxial La0.4Sr0.6CoO3 films as bottom and top electrodes. The dielectric constant ε of partially relaxed and coherently strained material was nearly the same. However, the dielectric tunability, i.e., the influence of a direct current bias voltage on ε, was found to be significantly larger for coherently strained dielectrics. For [LaAlO3(30 Å)/SrTiO3(60 Å)]20 multilayers we observed a tunability of nearly 20% at room temperature for a bias voltage of only 1 V, corresponding to an electric field strength of 50 kV/cm. The total dielectric loss of the multilayer capacitors is below 1% for frequencies above 1 MHz and depends only slightly on the bias voltage.
Laser ablation of thin films with very high induced stresses
Authors: Dömer H. , Bostanjoglo O.
Published: July 2002

The ablation of chromium films by nanosecond laser pulses was tracked by triple-frame high-speed transmission electron microscopy and selected area diffraction (exposure time ≈7–11 ns, frame spacings 20 ns–10 μs). At lower fluences the films were shattered during heatup and cooldown, producing debris with huge in-plane accelerations up to 1010 m/s2 and rotations with 106 rps. At higher fluences the ablation is proceeded by a domain-patterned evaporation. These effects are responsible for the high damage in laser-produced patterns in chromium films. They were all explained as being due to stress waves, launched by an extremely fast nonthermal 3%–4% expansion/contraction of the bcc lattice constant during heating/cooling.
Magnesium-diboride ramp-type Josephson junctions
Authors: Mijatovic Dragana , Brinkman Alexander , Oomen Ingrid , Rijnders Guus , Hilgenkamp Hans , Rogalla Horst , Blank Dave H. A.
Published: July 2002

Josephson junctions have been realized in which two superconducting magnesium-diboride (MgB2) layers are separated by a thin MgO barrier layer, using the ramp-type configuration. Their current–voltage characteristics follow the behavior described by the resistively shunted junction model, with an excess current of about 30% of the critical current Ic. A suppression of 70% of Ic was achieved in applied magnetic fields. Shapiro steps were observed by irradiating the junctions with 10.0 GHz microwaves, and the dependence of the step height on applied rf current is well described by a current–source model. Reference samples prepared without the MgO layer showed strong-link behavior with large Ic values.
Role of nitrogen related complexes in the formation of defects in silicon
Authors: Karoui A. , Karoui F. Sahtout , Kvit A. , Rozgonyi G. A. , Yang D.
Published: July 2002

Defect size and density distributions were obtained as a function of depth in nitrogen doped CZ silicon (N-CZ) following Hi–Lo–Hi and Lo–Hi annealing, using an oxygen precipitate profiler. The defects were also delineated by Wright etching and Nomarski optical microscopy on both cleaved and bevel polished samples. In addition to the enhanced precipitation and absence of voids previously reported for N-CZ Si, an unexpected mode of precipitation has been found near the annealed wafer surface, just above the traditional denuded zone. This oxynitride precipitate is discussed with regard to N-related complex interactions and point defect supersaturations/injection. High resolution transmission electron microscopy revealed that most precipitates have an octahedral shape with two distinct amorphous phases, which reflect a transition from an initial phase containing both N and O to one with primarily O, as verified with Z-contrast TEM and electron energy loss spectroscopy.
Change of quasilattice constant during amorphous-to-quasicrystalline phase transformation in Zr65Al7.5Ni10Cu7.5Ag10 metallic glass
Authors: Jiang J. Z. , Rasmussen A. R. , Jensen C. H. , Lin Y. , Hansen P. L.
Published: July 2002

The amorphous-to-quasicrystalline phase transformation in a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass has been investigated by monitoring the quasilattice constant and the composition of quasicrystalline particles in the samples annealed in vacuum at 663 K for various times. It is found that the quasilattice constant decreases with annealing time and saturates after 90 min while the zirconium and silver contents in quasicrystalline particles differ from those in the remaining amorphous matrix. The results provide evidence that the amorphous-to-quasicrystalline phase transformation in the Zr65Al7.5Ni10Cu7.5Ag10 metallic glass is a nonpolymorphous reaction.
Transient response of a bilayer organic light emitting diode: Building-up of external and recombination currents
Authors: Hassine L. , Bouchriha H. , Roussel J. , Fave J.-L.
Published: July 2002

Using a theoretical model of a bilayer organic light emitting diode, we calculate numerically the evolution of carrier densities and electric fields inside the device. The obtained results allow us to detail injection and accumulation of carriers during transient excitation. Charge densities as a function of applied voltage present two distinct thresholds which determine three operating ranges: no injection, unipolar injection, and bipolar injection. Dynamically these thresholds depend on the rise time of the applied voltage and have a clear signature in the current densities. We show that the electroluminescence threshold has static and dynamic values which may be different. Calculated external current in response to a voltage ramp presents two steps related to the evolution of the capacity of the device. This capacitive behavior is observed experimentally.
Compositionally graded hafnium silicate studied by chemically selective scanning tunneling microscopy
Authors: Lee Jung-Ho , Ichikawa Masakazu
Published: July 2002

Taking a tradeoff between channel carrier mobility and overall k value into account, compositionally graded ultrathin (1–2 nm) hafnium silicate has been investigated and suggested as an interfacial layer for an alternative high-permittivity (high-k) gate dielectric. Attempts to confirm whether a compositional gradation could occur in such a thin thickness range were performed by thermal annealing of 1-ML-thick Hf deposited on 1-nm-thick SiO2 in an ultrahigh vacuum chamber. Compositionally graded features varying from topmost HfOx-like to SiO2-like at the interface with Si could be analyzed with subnanometer resolution by scanning tunneling microscopy utilizing a local variation in the position of the conduction-band minimum within the insulator band gap as an identifier.
Midinfrared intersubband electroluminescence of Si/SiGe quantum cascade structures
Authors: Bormann I. , Brunner K. , Hackenbuchner S. , Zandler G. , Abstreiter G. , Schmult S. , Wegscheider W.
Published: July 2002

Unipolar intersubband lasers like quantum cascade laser structures might be realized not only in III–V semiconductors but also in Si/SiGe multiple layer structures since no optical transitions across the indirect band gap are involved. We report on well-defined intersubband electroluminescence emission of Si/SiGe quantum cascade structures with different active quantum wells parameters. The complex valence band structure and a nonradiative relaxation rate of about 400 fs were calculated by multiband k⋅p formalism including Si/Ge segregation effects. The observed spectral shift of the electroluminescence peak from 146 to 159 meV is described well by quantum confinement of the two lowest heavy hole subbands. The electroluminescence observed reveals transverse magnetic polarization, a spectral line shape that changes with the direction of the current, and low-energy line broadening with an increase in temperature and current. All these features are described well by the k⋅p model calculation.
Molecular beam epitaxial growth of SrCu2O3: Metastable structures and the role of epitaxy
Authors: Ingle N. J. C. , Hammond R. H. , Beasley M. R.
Published: July 2002

Within the study of oxide materials, high pressure bulk growth has generated a number of new and interesting materials. More recently, attention has been paid to using epitaxy to stabilize these high pressure oxide materials as thin films. In this article we report on the molecular beam epitaxial growth of SrCu2O3; a high pressure, highly correlated, model oxide. We find that the choice of substrate can significantly alter not only the structure but also the chemistry of the resulting film. For growth on SrTiO3 substrates the epitaxially stabilized structure for single phase films with a SrCu2O3 composition is based on a tetragonal unit cell. For identical growth conditions, but on a LaAlO3 substrate, a single phase film with the composition and structure of the infinite layer material (SrCuO2) is formed. We also review the literature for the successes and failures of epitaxy to stabilize high pressure structures.
Quaternary GaInAsN with high In content: Dependence of band gap energy on N content
Authors: Serries D. , Geppert T. , Ganser P. , Maier M. , Köhler K. , Herres N. , Wagner J.
Published: July 2002

Quaternary pseudomorphically strained GaInAsN films and double-quantum wells were grown by plasma assisted molecular-beam epitaxy on an InP substrate. The In content ranged from 53% to 70% while the N content was varied between 0% and 2.4%. A reduction of compressive strain and a low-energy shift of photoluminescence (PL) peak position was observed with increasing N concentration, accompanied by a reduction in PL peak intensity and increase in linewidth. The net effect of N incorporation on the GaInAsN band gap energy was calculated from the measured PL peak energies. The thus obtained composition dependent GaInAsN band gap energy was fitted using the band anticrossing model, yielding values for the interaction parameter CMN for high In-containing GaInAsN being only slightly smaller than that reported for low In-content GaInAsN on GaAs.
Extended phase diagrams for guiding plasma-enhanced chemical vapor deposition of silicon thin films for photovoltaics applications
Authors: Ferlauto A. S. , Koval R. J. , Wronski C. R. , Collins R. W.
Published: July 2002

Real time spectroscopic ellipsometry has been applied to develop extended phase diagrams that can guide the deposition of hydrogenated silicon (Si:H) thin films for highest performance solar cells. Previous such studies have shown that optimization of amorphous Si:H intrinsic layers by rf plasma-enhanced chemical vapor deposition (PECVD) is achieved using the maximum possible H2 dilution of SiH4 while avoiding a transition to the mixed-phase (amorphous+microcrystalline) growth regime. In this study, we propose that optimization of amorphous Si:H in higher rate rf PECVD processes further requires the largest possible thickness onset for a surface roughening transition detected in the amorphous film growth regime.
Experimental determination of equivalent oxide thickness of gate insulators
Authors: Hiraiwa Atsushi , Sakai Satoshi , Ishikawa Dai , Nakazawa Masatoshi
Published: July 2002

We propose an experimental method of determining the equivalent oxide thickness (EOT) of gate insulators based on the principle that the capacitance associated with the bandbendings in the Si substrate and the gate (Si capacitance) depends only on the Si surface field. To do this we experimentally obtained the Si surface field by using the capacitance–voltage (CV) integration method, and we used x-ray reflectometry to measure the physical thickness of thermal oxides. We then determined the relationship between the Si capacitance and the Si surface field. The relationship among the Si capacitance, the Si surface field, the EOT, and gate voltage minus the flatband voltage was also experimentally obtained. From these two relationships, we produce ideal CV curves for any given EOT and determined EOTs in such a way that the ideal CV curves fit best with the experimental results. Accordingly, our method is free of errors that accompany modeling the quantum mechanics of the gate electrode and Si substrate, and any errors that it does contain are independent of the film thickness. We further simplified the method for practical application by approximating the above relationships using rational polynomials. The results obtained by this simplified method were in good agreement with the experiments for the whole range of thicknesses. In contrast, the conventional quantum mechanical simulators produced CV curves that showed no small difference from the measured ones in the case of thin oxides in the 1-nm-thick range, and led to an overestimate of the EOT. Our method of EOT derivation provides an important basis for developing high-performance metal–oxide–semiconductor transistors.
Defects in silicon-on-insulator wafers and their hydrogen interaction studied by monoenergetic positron beams
Authors: Uedono Akira , Chen Zhi Quan , Ogura Atsushi , Suzuki Ryoichi , Ohdaira Toshiyuki , Mikado Tomohisa
Published: July 2002

Vacancy-type defects in separation-by-implanted oxygen wafers were probed using monoenergetic positron beams. We measured the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positrons. The species of the defects in Si-on-insulator (SOI) layers were identified as oxygen clusters or small oxygen precipitates, and the positrons are considered to be trapped by open spaces adjacent to such defects. The mean size of the open spaces was estimated to be larger than that of a hexavacancy. After annealing in a hydrogen atmosphere at 600 °C, both the lifetime of positrons trapped by the defects and the annihilation probability of positrons with high-momentum electrons decreased. These facts were attributed to the trapping of hydrogen atoms by the open spaces. The defects in bond-and-etchback SOI wafers and their interaction with hydrogen were also studied.