bluuebunny/crossref_metadata_2025 huggingface dataset:
The significance of a fluence threshold for ultraviolet laser ablation and etching of polymers
Authors: Srinivasan R. , Casey Kelly G. , Braren Bodil , Yeh Mildred
Published: July 2002

The minimum fluence at which a laser pulse (FWHM 20 ns; 248 nm) causes a change in the surface of a film of polyethylene terephthalate (=PET) or polyimide (KaptonTM) in air has been measured by probing the surfaces with visible laser pulses of <1 ns at delay times of 10–10 000 ns. At fluences at which a single pulse left a permanent etch pit, the probe pulse showed an intense and rapid (<60 ns) darkening of the surface which may be attributed to the scattering of the beam by gas bubbles at the polymer surface. In 100 ns, a blast wave was visible which could be tracked for over 1000 ns. At the end (∞ ns), the polymer surface was not darkened but an etch pit was apparent. Progressively decreasing the fluence showed that even at fluences <0.025 J/cm2 for PET and<0.050 J/cm2 for Kapton, a single pulse transiently blackened the surface but did not leave an etch pit. The threshold for the ablative photodecomposition of these polymers appears to lie at a value of the fluence that is well below the threshold for measurable etching by a single laser pulse.
Scanning tunneling microscopy on rough surfaces: Tip-shape-limited resolution
Authors: Reiss G. , Vancea J. , Wittmann H. , Zweck J. , Hoffmann H.
Published: July 2002

This paper discusses the reliability of scanning tunneling microscopy (STM) images of mesoscopically rough surfaces. The specific structure of these images represents a convolution between the real surface topography and the shape of the tip. In order to interpret these images quantitatively, the line scans of steep and high steps can be used to obtain an image of the tip itself. This image shows tip radii ranging typically from 5 to 15 nm and cone angles of about 30° over a length of 80 nm, and can in turn be used to recognize the limits of STM resolution on a rough surface: High-resolution transmission electron microscopy cross-section images of Au island films on a Au-Nb double layer are convoluted with the experimentally observed tip shape; the resulting line scans correspond very well with STM graphs of the same samples. Finally an overall criterion for the resolution of the STM on such surfaces is proposed.
Cu nuclear quadrupole resonance and magnetic phase transition in CuO
Authors: Ziolo J. , Borsa F. , Corti M. , Rigamonti A. , Parmigiani F.
Published: July 2002

Cu-nuclear quadrupole resonance (NQR) frequency and relaxation rates measurements in CuO, in the vicinity of the antiferromagnetic ordering temperature TN, are presented. As T→T+N divergent behaviors of the relaxation rates T−11,2 and an anomalous decrease in the NQR frequency are observed. These effects are discussed in light of the temperature dependence expected for conventional one-dimensional Heisenberg paramagnet and some anomalies are interpreted as possible results of valence fluctuations in the CuO bond character.
Analysis of the dominant modes of a slotted-helix-loaded cylindrical waveguide for use in plasma production
Authors: Ganguli A. , Appala Naidu P.
Published: July 2002

This paper is concerned with a detailed analysis of the dominant modes of a slotted helix loaded in an empty waveguide, with a view to improving the efficiency of plasma production using such structures. To this end the dispersion relation for a slotted helix loaded inside a cylindrical waveguide is first derived. As in the case of a tape-helix-loaded waveguide, the different dominant modes of the system can be identified by suitable asymptotic expansions of the exact dispersion relation. For large diameter helices (kvrh>1, where kv is the free-space wavelength of the wave and rh is the helix radius), the system has one slow wave and one fast wave as its dominant waves. The field patterns of these two modes are studied (for both slotted and tape helices) and the dominant field components corresponding to each type of helix and mode, identified from the point of view of ease in the excitation of the slow wave for plasma production. Since the fast and slow waves have overlapping dominant field components, methods are also discussed for suppressing the fast wave which can be excited more easily due to the presence of the waveguide. Finally, the state of polarization (left/right handedness) of the slow-wave mode is discussed with relevance to the coupling of the microwave to the plasma electrons in an external magnetic field.
MeV, self-ion implantation in Si at liquid nitrogen temperature; a study of damage morphology and its anomalous annealing behavior
Authors: Holland O. W. , White C. W. , El-Ghor M. K. , Budai J. D.
Published: July 2002

The damage formed by 1.25 MeV, self-ions in Si at liquid nitrogen temperature was studied. A dominant feature of the damage for moderate ion fluences is the presence of isolated amorphous regions over the range of the ions. The microstructure of this damage is detailed and formation mechanisms discussed. The amorphous regions are shown to give rise to strain in the surrounding crystal lattice which varies with ion dose in a complicated manner. The annealing behavior of the damage was studied and two distinct, low-temperature stages observed. Different mechanisms are shown to be responsible for each stage including a transient mechanism at 300 °C initiated by the release of defects from damage clusters, and enhanced crystallization of amorphous Si at 400 °C due to lattice stress.
Description of tantalum deformation behavior by dislocation mechanics based constitutive relations
Authors: Zerilli Frank J. , Armstrong Ronald W.
Published: July 2002

Dislocation mechanics based constitutive equation constants are determined for temperature, strain rate, work hardening, and polycrystal grain size influences on the deformation behavior of various tantalum materials. An analysis of the maximum load point strain provides a useful method of determining the work hardening constants. Different athermal stress constants and thermal activation related constants are obtained for certain groupings of the different tantalum materials. The variations are correlated with the annealing history of the materials and related to dislocation model parameters involved in the thermal activation strain rate analysis. Computed tantalum deformation results based on these constants are shown to agree with Gourdin’s reported expanding ring test measurements and with the deformed shape of a Taylor cylinder impact test specimen.
Physical study of laser-produced plasma in confined geometry
Authors: Fabbro R. , Fournier J. , Ballard P. , Devaux D. , Virmont J.
Published: July 2002

We study in this paper the different physical processes involved in laser-produced plasma in confined geometry. With this technique, a laser irradiates a target at an intensity of a few GW/cm2, and the produced plasma is confined by a transparent overlay to the laser which covers this target. This configuration has appeared necessary for example for metallurgical applications where, for a given laser energy, enhanced pressures must be realized in order to achieve high shock pressures. Therefore, a physical study of this method is useful in order to optimize this technique. We have first developed an analytical model which describes the different steps involved in this process, points out the interest of this technique, and compares it to the direct ablation regime. In the first stage, during the laser heating, the generated pressure is typically 4–10 times greater than the corresponding one obtained in direct ablation. The second step begins after the switch-off of the laser and is characterized by an adiabatic cooling of the plasma which maintains the applied pressure over a period which is about 2 times the laser-pulse duration. Finally, the third stage concerns also the adiabatic cooling of the recombined plasma, but during this period the exerted pressure is too small to realize a plastic deformation of the material.

We show that the impulse momentum given to the target is mainly generated during this step. This model allows us to also determine the velocities of thin foils accelerated with confined plasmas, and we show that very high hydrodynamic efficiencies can be achieved by this technique. Experimentally, we measured with quartz gauges, the pressures obtained in confined geometry, for 30-, 3-, and 0.6-ns laser-pulse duration. This study shows that short pulse durations are sensitive to the initial roughness of the interface, and such an effect should be suppressed by using a liquid confinement. Then, we conclude that a large fraction of the absorbed laser energy (80%–90%) is used for the ionization of the medium in these conditions of irradiation. Finally, we experimentally point out that the laser-induced breakdown of the confining medium is the main mechanism which limits the generated pressure and show the influence of the laser-pulse duration on this effect.
Hole transport in mixtures of 1,1-bis(di-4-tolylaminophenyl) cyclohexane and bisphenol-A-polycarbonate
Authors: Borsenberger P. M.
Published: July 2002

Hole mobilities have been measured in mixtures of 1,1-bis(di-4-tolylaminophenyl) cyclohexane and bisphenol-A-polycarbonate. The temperature and electric field dependencies can be described as exp-(T0/T)2 and exp(βE1/2), respectively. At high temperatures, T>316 K, the mobilities decrease with increasing electric field. The results are described within the framework of the disorder transport formalism introduced by Bässler and co-workers. The negative field dependence of the mobility is attributed to off-diagonal disorder and based on the assumption that fluctuations of the wavefunction overlap parameter increase with increasing temperature.
An investigation of Si-SiO2 interface charges in thermally oxidized (100), (110), (111), and (511) silicon
Authors: Vitkavage Susan C. , Irene Eugene A. , Massoud Hisham Z.
Published: July 2002

Trends in the electronic properties of the Si-SiO2 interface with various processing have been frequently reported. The present study focuses on silicon substrate orientation dependent trends in fixed oxide charge, Qf, and interface trap charge, Dit, for four silicon orientations: (100), (110), (111), and (511), for oxidation temperatures in the 750–1100 °C range, with and without hydrogen-containing post-metal anneals, and for processing within and without a cleanroom. It is found that the presence of mobile ionic charge in non-cleanroom processing and the lack of post-metal annealing can either obscure or enhance some trends. Both Qf and Dit increase for decreasing oxidation temperature for all silicon orientations. The orientational ordering of the charges varies with oxidation temperature and is dominated by the silicon atom areal density at the lowest temperatures with (110) Si having the highest charge, but a change to the (111) orientation is observed at higher oxidation temperatures. This orientational charge ordering parallels the orientational oxidation rate ordering but not the intrinsic stress. A model is proposed that considers the orientationally dominated oxidation rate, viscous relaxation, and strain accommodation across the interface as crucial processes.
PH3 surface chemistry on Si(111)-(7×7): A study by Auger spectroscopy and electron stimulated desorption methods
Authors: Wallace R. M. , Taylor P. A. , Choyke W. J. , Yates J. T.
Published: July 2002

The adsorption and decomposition of PH3 on Si(111)-(7×7) was investigated in ultrahigh vacuum by means of temperature programmed desorption, low-energy electron diffraction, Auger electron spectroscopy (AES), and electron stimulated desorption (ESD) methods. Phosphine adsorbs on Si(111)-(7×7) at T=120 K with an initial sticking coefficient of S0≂1 through a mobile (extrinsic) precursor state. Some PH3 dissociative adsorption at 120 K is observed. Thermal activation of the adsorbed species results in desorption of a molecular PH3 species up to 550 K. Further heating produces H2(g) desorption at T≂740 K and P2(g) desorption at T≂1010 K, thus indicating that PH3 decomposition has occurred. AES and ESD studies of the adsorbed species reveal that decomposition takes place by the breaking of PH bonds in PHx(a) to form SiH species on the surface for 120 K<T<700 K.
Diffusional relaxation and void growth in an aluminum interconnect of very large scale integration
Authors: Kato Masaharu , Niwa H. , Yagi H. , Tsuchikawa H.
Published: July 2002

Using the previously obtained stress distributions in an Al line after relaxation by plastic deformation, another possible relaxation process by diffusion was analyzed. Even after this relaxation occurs, some stresses still remain in the Al line. If these remaining stresses are large enough, they can be responsible for the growth of voids causing line failure. Using a theory for diffusional growth of grain-boundary voids, the time to failure of the Al line was estimated analytically. The previous and present papers together constitute a full analysis of the so-called ‘‘stress migration’’ phenomenon.
High-dose neutron generation from plasma ion implantation
Authors: Uhm Han S. , Lee W. M.
Published: July 2002

Based on a theoretical estimation, a simple new scheme to generate high-dose, steady-state neutrons is presented. This new high-dose neutron source makes use of the plasma ion implantation, which consists of a cylindrical palladium rod saturated with deuterium atoms and immersed in a deuterium or tritium plasma. The plasma is contained by a grounded conducting chamber. The palladium rod is connected to a high-power modulator, which provides a series of negative-voltage pulses. During these negative pulses, deuterium or tritium ions fall into the palladium rod and collide with the deuterium atoms in it, initiating fusion reactions and emitting neutrons. This neutron device will be portable, reliable and almost free from radiation hazards except for the neutrons themselves. For reasonable system parameters allowed by present technology, we find from a theoretical calculation that the average neutron production rate 〈dN/dt〉 = 2.3 × 1012 s−1 for D-T reaction, which may be more than enough for most applications. The average neutron production rate for D-D reaction is two order of magnitude less than that for D-T reaction.
Ionization by electron impact in an indirectly heated Penning source
Authors: Sato Y. , Yamada T. , Ogawa H. , Yamada S.
Published: July 2002

ion-production mechanism in an indirectly heated Penning source has been studied at NIRS. Taking the number of primary electron passages between two cathodes into account, we calculated the effective electron current density, Ji ; it is the order of kA/cm2 for Ar, where the index ‘‘i’’ is the charge state. In a pulsed arc condition of 2.6 A and 1300 V with a neutral atom density of 4×1013/cm3(cw), the calculated ionization times for Ar5+→Ar6+ and Ar6+→Ar7+ are 18 and 28 μs if their production process is step-by-step. These values agree well with the experimental value of 20 μs. Ji is proportional to the arc voltage and inversely proportional to the neutral-atom density N. The yield of multiply charged ions is in proportion to 1/Ni−2. This expression agrees well with the experimental results, which suggest that multiply charged ions are produced from Ar2+ through step-by-step ionization by primary electrons.
The anisotropy of R2Fe17Cx (R=Sm and Tm)
Authors: Grössinger R. , Kou X. C. , Jacobs T. H. , Buschow K. H. J.
Published: July 2002

The temperature dependence of the anisotropy field of Sm2Fe17Cx and Tm2Fe17Cx has been determined over the entire uniaxial ferro- or ferrimagnetic temperature range using the singularity point detection technique. The temperature dependence of the ac initial susceptibility was measured on these two systems from 4.2 to 300 K. The Curie temperature, lattice constants, spin-reorientation temperature (of Tm2Fe17Cx) and the magnetic anisotropy field are increasing with increasing carbon concentration. A ‘‘magnetic-phase-like transition’’ is observed in Sm2Fe17Cx for x<0.7 at low temperatures, which is proved not to be a spin reorientation. Additionally, the transition temperature increases systematically with increasing carbon concentration. However, the nature of this transition is not yet well understood.
Self-organized behavior in thin-film recording media
Authors: Zhu Jian-Gang , Bertram H. Neal
Published: July 2002

Magnetization domain structures in thin metallic films utilized as recording media are modeled by a cellular automation on a two-dimensional triangular lattice. This alternative approach permits significantly large arrays (≳ 106 grains) to be investigated as compared to an exact calculation (≊ 5 × 103 grains). Thus a study of the statistical distribution of the domain sizes and their power spectra can be made. Magnetostatic interactions and intergranular exchange coupling are included in a simple manner so that collective behavior is incorporated. It is found that away from the saturation remanent state, the distribution of the size of the avalanches (or the number of sites reversed in a single reversal sequence) follows a power-law behavior: D(S) = AS−α where S is the avalanche size and α varies in the vicinity of 1 depending on the interaction strength. The reversal field keeps the system marginally stable. It is found that the reproduce noise power varies as the derivative of the M-H loop.
Removal of SO2 from gas streams using a dielectric barrier discharge and combined plasma photolysis
Authors: Chang Moo Been , Balbach Jeanne H. , Rood Mark J. , Kushner Mark J.
Published: July 2002

The removal of SO2 from simulated gas streams (N2/O2/H2O/SO2) is experimentally investigated using a dielectric barrier discharge, and by computer modeling. Conversion of SO2 to primarily H2SO4 is found to be limited by the generation of OH radicals. Increasing the concentrations of O2 and H2O increases the generation of OH radicals and results in more removal of SO2 from gas streams. Removal efficiencies of ≳80% were experimentally achieved. Results from the model suggest that more efficient removal is obtained with a series of short, high E/N current pulses rather than a single, low E/N current pulse. Results from the model also suggest that uv illumination of the plasma to photolyze O3 will improve the removal of SO2 from the gas stream. Photolysis of O3 produces O(1D) atoms which generate OH radicals by H abstraction from H2O, thereby increasing the removal of SO2.
Nanofabrication with a scanning tunneling microscope
Authors: Yau S.-T. , Saltz D. , Wriekat A. , Nayfeh M. H.
Published: July 2002

Nanometer-scale structures as small as 1 nm were fabricated on graphite surfaces using a scanning tunneling microscope in the presence of low-pressure (10−4 Torr) trimethylaluminum. The studies were performed under controlled conditions of gas purity and gas pressure, allowing systematic measurements. We studied the voltage threshold and other features of the fabrication process as a function of the tip-surface biasing voltage and the tunneling current. The studies lead us to believe that the structures were formed by bombardment of the graphite surface by ions produced by electron-assisted field ionization localized in the region of the tunneling gap.
Ultraviolet photoablation of p-tetrafluoroethylene: Rotational energy distributions of the CF radical and time-resolved mass spectra
Authors: Goodwin P. M. , Otis C. E.
Published: July 2002

Gas-phase products from the nanosecond ultraviolet excimer ablation of polytetrafluoroethylene (Teflon©) have been characterized using mass-resolved vacuum ultraviolet laser photoionization techniques. Picosecond and nanosecond vacuum ultraviolet (10.5 eV) photoionization mass spectra recorded following the ablation of polytetrafluoroethylene display a significant dependence on the ablation wavelength. Polymer fragments ranging in mass from 31 to greater than 300 amu are observed following the 193 nm ablation of the polymer, whereas using 248 and 308 nm, the mass spectra consist almost entirely of the monomer (C2F4). Rotationally resolved resonant two-photon ionization (R2PI) spectra of the CF radical, recorded following the 193 nm ablation, were used to estimate the rotational temperature of this species in the ablation plume; temperatures ranged from 500 to 800 K.
Self-consistent determination of the perpendicular strain profile of implanted Si by analysis of x-ray rocking curves
Authors: Tsai C. J. , Dommann A. , Nicolet M. A. , Vreeland T.
Published: July 2002

Results of a determination of strain perpendicular to the surface and of the damage in (100) Si single crystals irradiated by 250-keV Ar+ ions at 77 K are presented. Double-crystal x-ray diffraction and dynamical x-ray diffraction theory are used. Trial strain and damage distributions were guided by transmission electron microscope observations and Monte Carlo simulation of ion energy deposition. The perpendicular strain and damage profiles, determined after sequentially removing thin layers of Ar+-implanted Si, were shown to be self-consistent, proving the uniqueness of the deconvolution. Agreement between calculated and experimental rocking curves is obtained with strain and damage distributions which closely follow the shape of the trim simulations from the maximum damage to the end of the ion range but fall off more rapidly than the simulation curve near the surface. Comparison of the trim simulation and the strain profile of Ar+-implanted Si reveals the importance of annealing during and after implantation and the role of complex defects in the final residual strain distribution.
Free carrier induced changes in the absorption and refractive index for intersubband optical transitions in AlxGa1−xAs/GaAs/AlxGa1−xAs quantum wells
Authors: Kuhn Kelin J. , Iyengar Gita U. , Yee Sinclair
Published: July 2002

The changes in the real index of refraction and the optical absorption for conduction intersubband transitions in AlxGa1−xAs/GaAs/AlxGa1−xAs quantum wells are examined as a function of the carrier density. Various values for the input optical field and quantum well width are considered in the calculations. The linear contribution due to χ(1) as well as the nonlinear contribution from χ(3) is included. The relationship of the results to device applications such as waveguides and optical modulators is discussed.
Ion channeling study of strained ErAs films on (001) GaAs
Authors: Wilkens B. J. , Martinez J. A. , Mounier S. , Palmstro/m C. J.
Published: July 2002

Epitaxial thin films of ErAs were grown by molecular beam epitaxy on (100) GaAs. The lattice mismatch induced strain and subsequent lattice relaxation were studied using Rutherford backscattering spectrometry and ion channeling. The channeling results showed a strong thickness dependence for the backscattered minimum yield. Channeled angular scans showed the thin films to be fully strained up to 15 nm in thickness. Thicker films were found to relax with full relaxation not being reached until the 100-nm thickness range. The thick films were found to tilt up to 0.26° with respect to the crystal axes of the substrate. The tilt is apparently a result of the strain relaxation mechanism.
Microscopic and macroscopic effects of electron irradiation on ferroelectric poly(vinylidene fluoride-TrFe) copolymers
Authors: Daudin B. , Legrand J. F. , Macchi F.
Published: July 2002

The effect of electron irradiation on ferroelectric poly(vinylidene-trifluoroethylene) copolymers has been studied from both microscopic and macroscopic points of view. Microscopically, it is found by x-ray photoemission spectroscopy analysis and ultraviolet absorption that the irradiation damaging is mainly through dehydrofluorination and leads to double-bond production and crosslinking. On the other hand, dielectric permittivity, internal friction, x-ray diffraction, and differential scanning calorimetry experiments show that both the ferroelectric transition temperature Tc and the melting temperature Tm are lowered under irradiation. These various experimental features are consistently analyzed taking into account three main mechanisms resulting from the electron irradiation: (i) reduction of the crystallite mean size, (ii) changes in the internal pressure, and (iii) reduction of the dipolar energy.
Intersubband absorption in Ga1−xAlxSb/AlSb superlattices for infrared detection
Authors: Xie H. , Piao J. , Katz J. , Wang W. I.
Published: July 2002

The infrared absorption from intersubband transitions between the lowest two superlattice conduction minibands is investigated for n-type Ga1−xAlxSb/AlSb superlattices. In such an indirect semiconductor superlattice, intersubband transitions can be induced by normally incident light because of the effective-mass anisotropy and the tilted orientation of conduction-band valleys with respect to the growth direction. The absorption coefficients and peak transition wavelengths are calculated for superlattices grown in the [001], [110], and [111] directions for both normal and parallel incidence. In the [110] Ga1−xAlxSb/AlSb superlattice, peak absorption coefficients of 5000–7000 cm−1 are obtained for both normally and parallel incident radiation in the wavelength range of 8–14 μm with moderate sheet doping concentrations of 1012 cm−2. The ability to detect normally incident radiation and to achieve absorption comparable to that in the GaAs/Ga1−xAlxAs detectors makes the Ga1−xAlxSb/AlSb devices promising for future applications in long-wavelength infrared detection.
Growth of Al nitride layers on GaAs(100) by reaction with condensed ammonia
Authors: Park Ken T. , Cao Jianming , Gao Y. , Wicks G. W. , Ruckman M. W.
Published: July 2002

An Al nitride-GaAs(100) bilayer formed by deposition of Al into a solid ammonia overlayer on GaAs(100) at T=100 K is studied using synchrotron radiation photoemission. Al does not react with NH3 to an appreciable amount at 100 K, but stable AlN layers are formed as the temperature of the substrate is raised to room temperature. The Al1−xNx layer formed is stable upon annealing up to 600 K, and detectable amounts of AlAs are not observed during deposition of 20 Å of Al into NH3 or after heating the sample to 300 K and higher.
Electrical and optical properties of CuAlSe2 grown by iodine chemical vapor transport
Authors: Chichibu S. , Shishikura M. , Ino J. , Matsumoto S.
Published: July 2002

Resistivities, carrier concentrations, optical absorption, and photoluminescences of undoped and Cd,Zn-doped CuAlSe2 single crystals grown by chemical vapor transport were studied. The electrical and optical properties were almost unchanged after annealing under Se pressure. However, the resistivity increased about seven orders of magnitude after annealing in vacuum. The resistivity also increased by Cd or Zn doping. The samples showed p-type conduction even when Cd or Zn was doped. An acceptor ionization energy of about 65 meV was obtained. The mobility showed the dominance of lattice scattering for temperatures between 80 and 200 K. Two independent, broad, red luminescences having their own excitation energies were observed at relatively low temperature. We have proposed the configuration coordinate model for this characteristic emission. The emission can be interpreted as radiative transitions from a deep center to the respective A or C valence bands, accompanied by a lattice relaxation.
Time evolution of capture cross sections of radiation-induced Si/SiO2 interface traps studied by single-frequency ac conductance technique
Authors: Chen Wenliang , Ma T.-P.
Published: July 2002

We report the time-dependent evolution of the capture cross sections of interface traps in metal/SiO2/Si capacitors after they are created by x-ray irradiation. A single-frequency ac conductance technique was used in this study. The capture cross section decreases significantly right after irradiation, and gradually recovers over a time scale similar to that of the interface-trap transformation process reported previously [T. P. Ma, Semicond. Sci. Technol. 4, 1061 (1989)]. The x-ray dose dependence and the effect of PMA (post-metal anneal) will also be presented.
Reply to ‘‘Comment on ‘Spreading of liquid droplets on cylindrical surfaces: Accurate determination of contact angle’ ’’ [J. Appl. Phys. 6
7, 1352 (1990)]
Authors: Wagner H. D.
Published: July 2002

A brief reply to the Comment is provided. Both the procedure I suggested and the tables presented by Carroll [Textile Res. J. 47, 56 (1977)] allow easy and fast estimation of contact angles.
Quantitative measurement of space-charge effects in lead zirconate-titanate memories
Authors: Scott J. F. , Araujo C. A. , Melnick B. M. , McMillan L. D. , Zuleeg R.
Published: July 2002

By combining Auger data on the width of an oxygen depletion layer near the Pt electrodes with a modified Langmuir–Child law for the leakage current: I(V) = aV + bV2, we deduce parameters related to the space-charge density and field in 210-nm-thick PbZr1−xTixO3 memories. The results are compared with the space charge fields inferred by Okazaki (∼10 kV/cm for PZT), which involve measuring the switching speeds ts(E) for positive and negative voltages. Differences in the voltage dependencies of the leakage current are found after fatigue and are related to specific electrochemical processes involving oxygen deposition on electrode surfaces.
Influences of a high excitation frequency (70 MHz) in the glow discharge technique on the process plasma and the properties of hydrogenated amorphous silicon
Authors: Finger F. , Kroll U. , Viret V. , Shah A. , Beyer W. , Tang X. -M. , Weber J. , Howling A. , Hollenstein Ch.
Published: July 2002

Hydrogenated amorphous silicon has been prepared at a plasma excitation frequency in the very-high-frequency band at 70 MHz with the glow discharge technique at substrate temperatures between 280 and 50 °C. The structural properties have been studied using hydrogen evolution, elastic recoil detection analysis, and infrared spectroscopy. The films were further characterized by dark and photoconductivity and by photothermal deflection spectroscopy. With respect to films prepared at the conventional frequency of 13.56 MHz considerable differences concerning the electronic and structural properties are observed as the substrate temperature is decreased from 280 to 50 °C. Down to a substrate temperature of 150 °C the electronic film properties change only a little and the total hydrogen content cH and the degree of microstructure that can be directly correlated to cH increase only moderately. Below 150 °C the electronic properties deteriorate in the usual manner but still the total hydrogen content does not exceed 21 at. % even at a substrate temperature of 50 °C. It is argued that the influence of the higher excitation frequency on the plasma and on the growth kinetics plays a key role in this context by allowing a highly effective dissociation of the process gas with the maximum ion energies remaining at low levels. It is concluded that deposition processes at higher excitation frequencies can have important technological implications by allowing a decrease of the deposition temperature without losses in the material quality.
Formation of ferroelectric domains in a copolymer P(VDF–TrFE)
Authors: Ohigashi H. , Kagami N. , Li G. R.
Published: July 2002

The effects of reannealing on the depolarization and phase transition behaviors of poled ferroelectric copolymer film of P(VDF–TrFE) (75/25) are studied by using differential scanning calorimetry (DSC) and piezoelectric resonance techniques from a viewpoint of formation of ferroelectric domains. It is found that the DSC peak at Curie point (Tc) splits into two peaks by reannealing at temperatures around Tc, the broader one appearing at a lower temperature and the sharper one at a higher temperature TcH. As the annealing temperature increases, the peak at TcH shifts to the higher temperature side, and its peak intensity decreases less rapidly than the macroscopic polarization of the film. To explain these phenomena we propose that ferroelectric domains possibly composed of 60° and 180° domains are developed within lamellar single crystals during the reannealing process at temperatures around Tc.
Time-resolved reflectivity of ArF laser-irradiated polyimide
Authors: Ediger M. N. , Pettit G. H.
Published: July 2002

The time-resolved reflectivity of ArF laser-irradiated polyimide has been investigated. Substantial attenuation of the trailing portion of the reflected laser pulse is observed, and the initiation of detectable pulse clipping coincides with the ablation threshold fluence. Examination of laser light scattered into small and moderate angles shows no evidence of significant ablation-plume scattering of the reflected beam. The time course of the recovery of the ultraviolet reflectivity of the irradiation site has also been studied using pump-probe techniques. These results indicate that for ablative fluences the ultraviolet reflectivity of the site does not return to its preablation value until nearly 1 ms after the incident pulse. The dynamic reflectivity is at least partially due to optical changes in the solid polymer.
Raman and ion channeling analysis of damage in ion-implanted GaAs: Dependence on ion dose and dose rate
Authors: Desnica U. V. , Wagner J. , Haynes T. E. , Holland O. W.
Published: July 2002

Raman scattering and ion channeling techniques were used to investigate the damage in GaAs implanted at room temperature with 100-keV Si+ ions. The ion-induced damage was analyzed for different ion doses and dose rates (current densities). The development of different damage components was monitored by comparing a Raman signal which is specific to amorphization in GaAs to ion channeling results which are sensitive to small-volume crystalline defects, as well as to amorphous regions. Raman analysis showed that the rate of growth of the amorphous fraction with implant dose was comparable to the growth rate of the total damage as determined by ion channeling. However, while Raman analysis indicated a weak dependence of damage on dose rate, the ion channeling results showed a substantially stronger dependence. These results demonstrate that the damage morphology in GaAs is dependent upon both dose and dose rate, and that the dose-rate-dependent component of the total damage consists primarily of crystalline defects.
Hot carriers and the frequency response of quantum well lasers
Authors: Lester L. F. , Ridley B. K.
Published: July 2002

A simple analytical model is obtained to describe the effect of carrier heating on the frequency response of a quantum well laser. The principal factors are taken to be injection heating, recombination heating, and hot phonons. The model is applied to the GaAs/GaInAs strained layer system and is shown to qualitatively account for many of the nonideal features observed. The nonlinear effects cannot be described satisfactorily by a single phenomenological ‘‘gain suppression’’ factor. However, at low drives the conventional gain suppression factor can be expressed in terms of the phonon lifetime and the temperature-relaxation time. The response is mediated by several time constants which, in our example, combine to give an effective time constant of about 10 ps. The modulation frequency response becomes seriously impaired when the differential gain is lowered by a factor of 2 and the time constants describing scattering and phonon lifetime are increased by a factor of 2.
SiO2 precipitate strain relief in Czochralski Si: Self-interstitial emission versus prismatic dislocation loop punching
Authors: Taylor W. J. , Gösele U. , Tan T. Y.
Published: July 2002

Formation of SiO2 precipitates in Czochralski Si is associated with a volume expansion of more than 100%. The needed extra volume for precipitate growth to occur is primarily supplied by emission of Si self-interstitials (I) into the Si matrix, in balance with a compressive growth residual strain. During cooling after the anneal, an additional compressive cooling strain component also develops because of the different thermal expansion coefficients of SiO2 and Si. For precipitates grown to a sufficiently large size, the growth residual strain and/or the cooling strain can be further relieved by punching interstitial type prismatic dislocation loops into the Si matrix. Otherwise, only I emission can occur. Up to now, there have been no quantitatively determined strain values, which constitute in a given experiment a measure of the I emission efficiency on the one hand, and a basis for determining whether prismatic punching can also occur on the other. In this study, we have calculated the strain values and obtained a quantitative criterion for prismatic punching to occur. In the order of ∼10−3–10−2, the growth residual strain component values indicate that I emission has attained an efficiency of relieving the precipitate growth strain by ∼90%–99%. Available experimental data on the precipitate size dependence of prismatic dislocation loop punching have been satisfactorily fitted using the obtained strain values and the punching criterion, indicating that these calculated values are in acceptable accuracy ranges.
Interstitial supersaturation during oxidation of silicon in steam ambients
Authors: Jeng Nanseng , Dunham Scott T.
Published: July 2002

The supersaturation of interstitials during oxidation in pyrogenic steam at 900 and 1000 °C was determined through measurements of enhanced phosphorus diffusion. At 900 °C, the supersaturation during steam oxidation was found to be significantly less than that observed during dry oxidation at the same growth rate, and the interstitial supersaturation varied as the square root of the oxidation rate as predicted in previous work. At 1000 °C, interstitial supersaturation was similar to that observed in dry O2, and the interstitial concentration showed only a 0.25 power dependence on oxidation rate. It was also observed that the inert-ambient annealing of an oxide deposited at low temperature resulted in enhanced phosphorus diffusion.
Room temperature epitaxial growth of Ag on low-index Si surfaces by a partially ionized beam
Authors: Nason T. C. , You L. , Lu T.-M.
Published: July 2002

The room temperature growth of 1000–1500 Å Ag films on HF-dipped Si substrates is studied as a function of self-ion (Ag+) energy during deposition. In all cases the films contained a mixture of epitaxial grains and randomly oriented (111) grains. The orientations observed were Ag(111)/Si(111) with both type A (Ag〈110〉//Si〈110〉) and type B (Ag〈110〉//Si〈114〉) twins; Ag(110)/Si(110) with Ag〈001〉//Si〈001〉; and Ag(100)/Si(100) with Ag〈011〉//Si〈011〉. All three constructions match three Si atomic rows with four Ag rows. As judged by the ratio of epitaxial to nonepitaxial grains, the strength of the epitaxy was seen to decrease in the order (111)≳(110)≳(100). Increasing the Ag+ ion energy during the deposition was generally seen to decrease this ratio. Annealing of the Ag/Si(100) films induced preferential (100) grain growth.
Defect models in electron-irradiated n-type GaAs
Authors: Ziebro B. , Hemsky J. W. , Look D. C.
Published: July 2002

1 MeV electron irradiation has been performed in degenerate, n-type (n≂2×1017 cm−3), molecular beam epitaxial GaAs layers, and Hall effect measurements have been carried out during the irradiation in order to get accurate defect production data. The results have been fitted with statistical models, and are most consistent with the usual E1 (EC−0.045 eV) and E2 (EC−0.15 eV) levels being the (−/0) and (0/+) transitions of the As vacancy, respectively. Also, an acceptor well below EC−0.15 eV is produced at a much higher rate than that of E1 and E2.
Effects of rapid thermal annealing on lasing properties of InGaAs/GaAs/GaInP quantum well lasers
Authors: Zhang G. , Näppi J. , Ovtchinnikov A. , Asonen H. , Pessa M.
Published: July 2002

Thermal processing of strained-layer InGaAs/GaAs/GaInP separated confinement heterostructure single quantum well lasers, grown by gas-source molecular beam epitaxy, is investigated. Rapid thermal annealing (RTA) significantly increases room-temperature photoluminescence from the quantum well and decreases the threshold current density of the lasers, due to a removal of nonradiative centers from the InGaAs/GaAs interfaces. On the other hand, RTA reduces the characteristic temperature and external differential quantum efficiency of the lasers, due to interdiffusion of Ga and In atoms at high temperatures.
Magnetic structure of Fe/Cr/Fe trilayers
Authors: Idzerda Y. U. , Tjeng L. H. , Lin H.-J. , Meigs G. , Chen C. T. , Gutierrez J.
Published: July 2002

The magnetic structure of Cr films deposited on single crystal Fe(001)/GaAs(001) substrates is investigated by soft x-ray magnetic circular dichroism (SXMCD) of the L2 and L3 absorption edges. We find that 0.25 ML Cr coverages result in Cr moments aligned with each other and antialigned to the underlying Fe moment direction. The Cr moment is measured to be 0.6±0.2 μB. Additional Cr deposition results in a monotonically reducing averaged moment consistent with the island growth of ferromagnetic Cr sheets of a single layer, antialigned with adjoining sheets. SXMCD measurements of the trilayer structures clearly show the antiferromagnetic coupling of the two Fe films through the interlying Cr film.
Effect of well coupling on the optical gain of multi-quantum-well lasers
Authors: Akhtar A. I. , Guo C.-Z. , Xu J. M.
Published: July 2002

The effect of coupling between quantum wells on the optical gain has been examined here. Although the results of the calculations mostly agree with previous qualitative expectations of gain suppression with coupling, there are some important exceptions. It is shown that the dependence of peak gain or threshold current density is not a monotonic function of the barrier thickness, and more importantly there are barrier thicknesses (beyond the almost opaque barrier case) for which optical gain can be enhanced and threshold current density reduced as compared to the values for an uncoupled structure. Results and discussion for the gain peak and threshold current density of a GaAs/Al0.3Ga0.7As double quantum well system are presented as a specific example
Improvement of breakdown characteristics of a GaAs power field-effect transistor using (NH4)2Sx treatment
Authors: Lee Jong-Lam , Kim Dojin , Maeng Sung Jae , Park Hyung Ho , Kang Jin Young , Lee Yong Tak
Published: July 2002

A (NH4)2Sx solution treatment technique was applied to a GaAs metal-semiconductor field-effect transistor (MESFET) to improve the electrical properties of the transistor. The gate leakage current of the MESFET remarkably decreased while the drain breakdown voltage doubled to 30 V with the (NH4)2Sx treatment. The (NH4)2Sx treatment was found to effectively suppress the formation of donor-type defects at the GaAs surface and to increase the Schottky barrier height.
A slow positron beam study of vacancy formation in fluorine-implanted silicon
Authors: Fujinami M. , Chilton N. B.
Published: July 2002

The subsurface vacancy profile in Czochralski (Cz) Si(100) implanted to a dose of 2×1014 cm−2 with 120 keV fluorine ions has been determined using a slow positron beam. The unique sensitivity of the positron technique to vacancy concentrations of part per million (ppm) order is utilized. We demonstrate the presence of vacancies at ppm concentrations at depths up to 1 μm greater than the depth predicted by Monte Carlo modeling. The vacancies caused by the implantation process are suggested to consist of an immobile and a mobile component, the latter component being able to diffuse to such depths.
Positron studies of metal-oxide-semiconductor structures
Authors: Au H. L. , Asoka-Kumar P. , Nielsen B. , Lynn K. G.
Published: July 2002

Positron annihilation spectroscopy provides a new probe to study the properties of interface traps in metal-oxide semiconductors (MOS). Using positrons, we have examined the behavior of the interface traps as a function of gate bias. We propose a simple model to explain the positron annihilation spectra from the interface region of a MOS capacitor.
An explanation for the directionality of interfacet migration during molecular beam epitaxical growth on patterned substrates
Authors: Guha S. , Madhukar A.
Published: July 2002

An explanation of the interfacet migration behavior observed in molecular beam epitaxical growth of GaAs and AlGaAs on patterned GaAs(100) substrates is presented on the basis of the nature of the ledge–ledge interaction.
Effects of carrier and dispersion on propagation of a directed electromagnetic pulse
Authors: Hafizi B.
Published: July 2002

Propagation of a directed pulse of electromagnetic radiation in a vacuum and in a rarefied, temporally dispersive medium is investigated. The pulse belongs to the class of broadband directed radiation beams termed electromagnetic ‘‘missiles’’ and is superposed on a carrier wave. First the propagation characteristics of the pulse in a vacuum are reviewed. In a vacuum the far-field time-integrated Poynting flux U(z) of the pulse drops off as 1/z1+4ν, with ‖ν‖≤1/4. In the corresponding expression for U(z) in a dispersive medium the leading term also varies as 1/z1+4ν since the high-frequency end of the spectrum experiences very little dispersion. In a dispersive medium the propagation of the precursors and of the carrier signal is examined in certain limits and expressions for the spatial variation of the vector potential are given.
Measurement of the Stark broadening and shift parameters for several ultraviolet lines of singly ionized aluminum
Authors: Colón C. , Hatem G. , Verdugo E. , Ruiz P. , Campos J.
Published: July 2002

The Stark broadening parameters of the 1990.53, 2631.55, 2669.17, 2816.18, 3900.68, and 5593.23 Å lines of Al(II) have been measured in a plasma produced by ablation with a Nd:YAG laser of an aluminum target. In order to obtain suitable experimental conditions for the homogeneity and stability of the plasma a study of the spatial and temporal plasma evolution in helium, argon, and nitrogen at different pressures was made. The broadening parameters were obtained with the aluminum target placed in molecular nitrogen at 1000 mbar, which provides appropriate measurements conditions. The Al(II) 4663.05 Å line was used to determine the electron density in all cases. For this line the Stark shift parameter has been measured. Contributions to broadening arising from mechanism different than Stark broadening were estimated for every studied line.
Preparation and properties of Bi4Ti3O12 single-crystal thin films by atmospheric pressure metalorganic chemical vapor deposition
Authors: Wang H. , Fu L. W. , Shang S. X.
Published: July 2002

Bismuth titanate (Bi4Ti3O12) thin films have been grown on (100) silicon substrates at 550 °C by atmospheric pressure metalorganic chemical vapor deposition using Bi (C6H5)3 and Ti (OC4H9)4 as the source materials. The x-ray diffraction analysis and reflection electron diffraction pattern revealed that the film is a single crystal with a (100) orientation. Ferroelectric properties were confirmed by polarization hysteresis curve observation. The remanent polarization and coercive field were found to be 38 μC/cm2 and 45 kV/cm, respectively. The measured dielectric constant and loss tangent were 93 and 0.05, respectively, at room temperature.