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Showing papers in "Journal of Applied Physics in 1994"


Journal ArticleDOI
TL;DR: In this article, the authors compare the performance of SiC, GaN, and ZnSe for high-temperature electronics and short-wavelength optical applications and conclude that SiC is the leading contender for high temperature and high power applications if ohmic contacts and interface state densities can be further improved.
Abstract: In the past several years, research in each of the wide‐band‐gap semiconductors, SiC, GaN, and ZnSe, has led to major advances which now make them viable for device applications. The merits of each contender for high‐temperature electronics and short‐wavelength optical applications are compared. The outstanding thermal and chemical stability of SiC and GaN should enable them to operate at high temperatures and in hostile environments, and also make them attractive for high‐power operation. The present advanced stage of development of SiC substrates and metal‐oxide‐semiconductor technology makes SiC the leading contender for high‐temperature and high‐power applications if ohmic contacts and interface‐state densities can be further improved. GaN, despite fundamentally superior electronic properties and better ohmic contact resistances, must overcome the lack of an ideal substrate material and a relatively advanced SiC infrastructure in order to compete in electronics applications. Prototype transistors have been fabricated from both SiC and GaN, and the microwave characteristics and high‐temperature performance of SiC transistors have been studied. For optical emitters and detectors, ZnSe, SiC, and GaN all have demonstrated operation in the green, blue, or ultraviolet (UV) spectra. Blue SiC light‐emitting diodes (LEDs) have been on the market for several years, joined recently by UV and blue GaN‐based LEDs. These products should find wide use in full color display and other technologies. Promising prototype UV photodetectors have been fabricated from both SiC and GaN. In laser development, ZnSe leads the way with more sophisticated designs having further improved performance being rapidly demonstrated. If the low damage threshold of ZnSe continues to limit practical laser applications, GaN appears poised to become the semiconductor of choice for short‐wavelength lasers in optical memory and other applications. For further development of these materials to be realized, doping densities (especially p type) and ohmic contact technologies have to be improved. Economies of scale need to be realized through the development of larger SiC substrates. Improved substrate materials, ideally GaN itself, need to be aggressively pursued to further develop the GaN‐based material system and enable the fabrication of lasers. ZnSe material quality is already outstanding and now researchers must focus their attention on addressing the short lifetimes of ZnSe‐based lasers to determine whether the material is sufficiently durable for practical laser applications. The problems related to these three wide‐band‐gap semiconductor systems have moved away from materials science toward the device arena, where their technological development can rapidly be brought to maturity.

2,514 citations


Journal ArticleDOI
TL;DR: In this article, the metastable phase anatase has been shown to have a wider optical absorption gap than rutile thin films, which is consistent with the high mobility, bandlike conduction observed in anatase crystals.
Abstract: Electrical and optical spectroscopic studies of TiO2 anatase thin filmsdeposited by sputtering show that the metastable phase anatase differs in electronic properties from the well‐known, stable phase rutile. Resistivity and Hall‐effect measurements reveal an insulator–metal transition in a donor band in anatase thin films with high donor concentrations. Such a transition is not observed in rutile thin films with similar donor concentrations. This indicates a larger effective Bohr radius of donor electrons in anatase than in rutile, which in turn suggests a smaller electron effective mass in anatase. The smaller effective mass in anatase is consistent with the high mobility, bandlike conduction observed in anatase crystals. It is also responsible for the very shallow donor energies in anatase. Luminescence of self‐trapped excitons is observed in anatase thin films, which implies a strong lattice relaxation and a small exciton bandwidth in anatase. Optical absorption and photoconductivity spectra show that anatase thin films have a wider optical absorption gap than rutile thin films.

1,560 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that the characteristics of light-emitting diodes based upon MEH-PPV are determined by tunneling both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes.
Abstract: In this paper it is demonstrated that the characteristics of light‐emitting diodes based upon MEH‐PPV [more fully known as poly(2‐methoxy,5‐(2’‐ethyl‐hexoxy)‐1,4‐phenylene‐ vinylene)] are determined by tunneling of both the holes and the electrons through interface barriers caused by the band offset between the polymer and the electrodes. It is shown that manipulating these offsets can control the useful operating voltage of the device as well as its efficiency. A model is developed that clearly explains the device characteristics of a wide range of diodes based upon MEH‐PPV. The turn‐on voltage for an ideal device is shown to be equal to the band gap, i.e., 2.1 eV for MEH‐PPV, and is slightly lower at 1.8 eV for an indium‐tin oxide/MEH‐PPV/Ca device. If there is a significant difference in the barrier height, the smaller of the two barriers controls the I–V characteristics, while the larger barrier determines the device efficiency. In indium‐tin‐oxide/MEH‐PPV/Ca devices, the barrier to hole injection is ...

1,435 citations


Journal ArticleDOI
TL;DR: This work examines the possible implementation of logic devices using coupled quantum dot cells, which use these cells to design inverters, programmable logic gates, dedicated AND and OR gates, and non‐interfering wire crossings.
Abstract: We examine the possible implementation of logic devices using coupled quantum dot cells. Each quantum cell contains two electrons which interact Coulombically with neighboring cells. The charge distribution in each cell tends to align along one of two perpendicular axes, which allows the encoding of binary information using the state of the cell. The state of each cell is affected in a very nonlinear way by the states of its neighbors. A line of these cells can be used to transmit binary information. We use these cells to design inverters, programmable logic gates, dedicated AND and OR gates, and non‐interfering wire crossings. Complex arrays are simulated which implement the exclusive‐OR function and a single‐bit full adder.

1,149 citations


Journal ArticleDOI
TL;DR: In this article, X-ray diffraction and Raman scattering are used to analyze the Raman spectrum of CeO2 and find that the single allowed Raman mode shifts to lower frequency with increasing doping level for all the rare earths.
Abstract: Powdered samples of the type Ce1−xRExO2−y, where RE=La, Pr, Nd, Eu, Gd, and Tb, are synthesized over the range 0≤x≤0.5 starting from nitrate solutions of the rare earths. X‐ray diffraction and Raman scattering are used to analyze the samples. These compounds, at least in the low doping regime and for strictly trivalent dopants, form solid solutions that maintain the fluorite structure of CeO2 with a change in lattice constant that is approximately proportional to the dopant ionic radius. The single allowed Raman mode, which occurs at 465 cm−1 in pure CeO2, is observed to shift to lower frequency with increasing doping level for all the rare earths. However, after correcting for the Gruneisen shift from the lattice expansion, the frequency shift is actually positive for all the strictly trivalent ions. In addition, the Raman line broadens and becomes asymmetric with a low frequency tail, and a new broad feature appears in the spectrum at ∼570 cm−1. These changes in the Raman spectrum are attributed to O va...

1,034 citations


Journal ArticleDOI
TL;DR: In this paper, a review of bolometric detectors for infrared and millimeter-wave measurements is presented, where the authors provide the background required by workers who wish to choose the appropriate bolometer technology for a given measurement or to evaluate a novel technology.
Abstract: This review describes bolometric detectors for infrared and millimeter waves. The introduction sketches the history of modern bolometers, indicates how they fit into the more general class of thermal detectors, and describes the types of applications for which they are the optimum solution. Section I is a tutorial introduction to the elementary theories of bolometer response, of thermal radiation, and of bolometer noise. Important results are derived from the laws of thermal physics in the simplest possible way. The more rigorous theories of bolometer response and noise that are required for quantitative understanding and optimization are then summarized. This material is intended to provide the background required by workers who wish to choose the appropriate bolometer technology for a given measurement, or to evaluate a novel technology. Section II, then describes the various components of an efficient bolometer and gives details of the fabrication and performance of modern bolometers. This discussion f...

920 citations


Journal ArticleDOI
TL;DR: In this article, the authors compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of these materials.
Abstract: We compare the Raman spectra and other macroscopic properties of nearly one hundred amorphous carbon films deposited at five research laboratories by a total of five different methods in search of correlations useful for both process control and basic understanding of the structure of these materials. For the full range of carbon‐hydrogen alloys, including so‐called ‘‘amorphous diamond,’’ hydrogenated ‘‘diamondlike’’ carbon, and plasma‐polymers, a simple parametrization of the Raman spectrum in the usual 1000 cm−1 to 2000 cm−1 range can be used as a reliable predictor of hydrogenation and other properties (e.g., optical gap, hardness). Raman features in the 200 cm−1 to 1000 cm−1 range, a spectral region not usually reported for carbon films, may also be used as an indicator of hydrogenation. These growth method independent correlations greatly enhance the utility of Raman spectroscopy as a non‐destructive characterization and process control tool.

915 citations


Journal ArticleDOI
TL;DR: In this paper, the experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals.
Abstract: Photoemission spectromicroscopy was used to investigate the electronic structure of TiO2 anatase single crystals and polycrystalline thin films The stoichiometry and the degree of oxidation of as-grown crystals, as-deposited films, as well as of thermally annealed samples in different atmospheres, were analyzed, based on the Ti 2p and O 1s core levels, with an energy resolution of 04 eV The experimental density of states (DOS) was found to be in agreement with the theoretical DOS reported in the literature for anatase crystals, and shows some characteristics similar to the experimental DOS reported for rutile crystals In reduced samples, the experimental DOS is characterized by intense emission in the region of O 2p bonding orbitals, and does not exhibit an appreciable density of states in the band gap As-grown crystals exhibit small band gap emission (a few percent of the valence band VB signal) at about 08 eV, which is attributed to Ti3+ (3d) defect states Annealing the crystals at high temperatures in O2 or subsequent thermal reduction in an Ar-H2 Mixture (95%-5%) produces nearly stoichiometric surfaces with smaller or undetectable density of Ti3+ States In addition, some redistribution of the spectral weight is observed in the VB spectra

664 citations


Journal ArticleDOI
TL;DR: In this article, the authors proposed the ballistic transport of carriers in MOSFETs, and presented the currentvoltage characteristics of the ballistic n-channel MOS-FET.
Abstract: Experiments on ultra‐small metal‐oxide‐semiconductor field effect transistors (MOSFETs) less than 100 nm have been widely reported recently. The frequency of carrier scattering events in these ultra‐small devices is diminished, so that further suppression of carrier scattering may bring these devices close to the regime of ballistic transport. Carrier scattering is suppressed by constructing their channel regions with intrinsic Si and also by low temperature operation. This article proposes the ballistic transport of carriers in MOSFETs, and presents the current‐voltage characteristics of the ballistic n‐channel MOSFET. The current is expressed with the elementary parameters without depending on the carrier mobility. It is independent of the channel length and is proportional to the channel width. The current value saturates as the drain voltage is increased and the triode and the pentode operation are specified as in the conventional MOSFET. Similar current‐voltage characteristics in the ballistic transport regime are also investigated for the p‐channel MOSFET, the dual gate ultra‐thin silicon on insulator MOSFET, and the high electron mobility transistor device. The obtained current gives the maximum current limitation of each field effect transistor geometry. The current control mechanism of ballistic MOSFETs is discussed. The current value is governed by the product of the carrier density near the source edge in the channel, and the velocity with which carriers are injected from the source into the channel.Influence of optical phonon emission to the transport is discussed. It is suggested that if the device is operated with relatively low carrier density at low temperatures, and if the scattering processes other than the optical phonon emission are suppressed so as to attain the ballistic transport, the optical phonon emission is also suppressed and ballistic transport is sustained. A convenient figure of merit to show the ballisticity of carrier transport in an experimental MOSFET is proposed. Its value is estimated for some examples of the recent ultra‐small MOSFET experiment. The proposed current voltage characteristics are evaluated for a dual gate silicon on insulator MOSFET geometry. The result is compared with the recently reported elaborate Monte Carlo simulation with satisfactory agreement.

620 citations


Journal ArticleDOI
TL;DR: In this article, the authors showed that near the band edge of a one-dimensional photonic band gap structure the photon group velocity approaches zero, which implies an exceedingly long optical path length in the structure.
Abstract: Near the band edge of a one‐dimensional photonic band gap structure the photon group velocity approaches zero. This effect implies an exceedingly long optical path length in the structure. If an active medium is present, the optical path length increase near the photonic band edge can lead to a better than fourfold enhancement of gain. This new effect has important applications to vertical‐cavity surface‐emitting lasers.

605 citations


Journal ArticleDOI
TL;DR: In this paper, an experimental method is introduced to directly and quantitatively determine the domain-wall and intrinsic contributions to the piezoelectric and dielectric responses of a ferroelectric material.
Abstract: By making use of the fact that domain‐wall motions do not produce volumetric changes, an experimental method is introduced to directly and quantitatively determine the domain‐wall and intrinsic contributions to the piezoelectric and dielectric responses of a ferroelectric material. Utilizing this method, the contributions from the domain walls and intrinsic part as well as their temperature dependence for lead zirconate‐titanate (PZT) 52/48 and PZT‐500 ceramics are evaluated. The data show that at temperatures below 300 K, the large change in the dielectric and piezoelectric constants with temperature is due to the change in the domain‐wall activities in the materials. The results confirm that most of the dielectric and piezoelectric responses at room temperature for the materials studied is from the domain‐wall contributions. The data also indicate that in PZT‐500, both 180° wall and non‐180° walls are possibly active under a weak external driving field.

Journal ArticleDOI
TL;DR: In this article, the normal load method is used to measure the coefficients for PZT thin films with various compositions prepared by the solgel technique or by organometallic chemical vapor deposition (OMCVD).
Abstract: This article presents measurements of piezoelectric coefficients of lead zirconate titanate (PZT) thin films. The normal load method is used to measure the coefficients for PZT films with various compositions prepared by the sol‐gel technique or by organometallic chemical vapor deposition (OMCVD). The as‐deposited OMCVD films have a piezoelectric coefficient of 20–40×10−12 m/V, whereas the unpoled sol‐gel films are not piezoelectric. After poling the thin films having a composition near the morphotropic phase boundary; these values increase to 200×10−12 m/V for OMCVD films and 400×10−12 m/V for sol‐gel films. The difference may arise from an incomplete poling of the OMCVD films.

Journal ArticleDOI
TL;DR: In this article, a number of properties such as thermal expansion coefficient, sound velocity, thermal conductivity, electrical conductivity and Seebeck coefficient have been measured by hot isostatic pressing of powders.
Abstract: Polycrystalline p‐type samples of IrSb3 and Ir0.5Rh0.5Sb3 have been made by hot isostatic pressing of powders. A number of properties such as thermal expansion coefficient, sound velocity, thermal conductivity, electrical conductivity, Seebeck coefficient, and carrier concentration have been measured. These compounds show promise as thermoelectric materials.

Journal ArticleDOI
TL;DR: In this paper, the authors calculated the electron mobility in GaN and InN as a function of temperature for carrier concentrations of 1016, 1017, and 1018 cm−3 with compensation ratio as a parameter.
Abstract: Electron mobilities in GaN and InN are calculated, by variational principle, as a function of temperature for carrier concentrations of 1016, 1017, and 1018 cm−3 with compensation ratio as a parameter. Both GaN and InN have maximum mobilities between 100 and 200 K, depending on the electron density and compensation ratio, with lower electron density peaking at lower temperature. This is due to the interplay of piezoelectric acoustic phonon scattering at low carrier concentrations and ionized impurity scattering at higher carrier concentrations. Above 200 K, polar mode optical phonon scattering is the mobility limiting process. The 300 and 77 K electron and Hall mobilities as functions of carrier concentration in the range of 1016–1020 cm−3 and compensation ratio are also calculated. The theoretical maximum mobilities in GaN and InN at 300 K are about 1000 and 4400 cm2 V−1 s−1, respectively, while at 77 K the limits are beyond 6000 and 30 000 cm2 V−1 s−1, respectively. We compare the results with experimental data and find reasonable correlation, but with evidence that structural imperfection and heavy compensation play important roles in the material presently available. Only phonon limited scattering processes are considered in the calculation of the mobility in AlN since it is an insulator of extremely low carrier concentration. We find a phonon limited electron mobility of about 300 cm2 V−1 s−1 at 300 K.

Journal ArticleDOI
TL;DR: In this paper, the authors developed temperature dependent stability maps that predict the stable domain structure that forms during the paraelectric to ferroelectric transition (PE→FE) and discussed the role of dislocation stabilization of domain patterns.
Abstract: Possible mechanisms for strain relaxation in ferroelectric thin films are developed. The models are applicable to tetragonal thin film ferroelectrics grown epitaxially on (001) cubic single crystal substrates. We assume growth at temperatures in excess of the Curie temperature (Tc). The extent of strain accommodation by misfit dislocations is considered at the growth temperature (Tg). On cooling to Tc, further misfit dislocation generation is possible due to differences in thermal expansion behavior of the film and substrate. During the paraelectric to ferroelectric transition (PE→FE) additional strains develop in the film. The total strain for the FE phase may be relieved either by further misfit generation or by domain formation. We have developed temperature dependent stability maps that predict the stable domain structure that forms during the PE→FE transition. The stability maps incorporate the role of the following parameters: (i) substrate lattice parameter, (ii) differential thermal expansion characteristics between the film and substrate, (iii) cooling rate, and (iv) depolarizing fields and electrode geometry. Further, the role of dislocation stabilization of domain patterns is discussed.

Journal ArticleDOI
TL;DR: In this article, a simple model accounts for the time-scale dependence of coercivity in terms of the thermally assisted crossing of an energy barrier whose height is reduced by the applied field.
Abstract: Coercivity and other experimental measures of switching field depend upon the time scale of interest. This time‐scale dependence has practical importance in magnetic recording, because the effective time scales of writing and storage are very different. A simple model accounts for the time‐scale dependence of coercivity in terms of the thermally assisted crossing of an energy barrier whose height is reduced by the applied field. Fitting this barrier‐crossing model to data provides an estimate of the volume that must switch magnetization direction in overcoming the barrier. The assumption of Stoner–Wohlfarth reversal is used to obtain an initial estimate of the dependence of the barrier height on the field. With some adjustment of the resulting energy expression, the model gives good agreement between calculated switching volume and actual particle volume for advanced recording particles of three types: acicular oxide, acicular metal, and barium ferrite platelets. The model can be used to estimate minimum ...

Journal ArticleDOI
TL;DR: In this article, resistivity, thermopower, and Hall-effect measurements on large single crystals of the anatase form of TiO2 all indicate high mobility n-type carriers that are produced by thermal excitation from a density of ∼1018 cm−3 putatively present shallow donor states.
Abstract: Resistivity, thermopower, and Hall‐effect measurements on large single crystals of the anatase form of TiO2 all indicate high mobility n‐type carriers that are produced by thermal excitation from a density of ∼1018 cm−3 putatively present shallow donor states. The decrease of the mobility with increasing temperature is consistent with the scattering of carriers by the optical phonons of TiO2.

Journal ArticleDOI
TL;DR: In this article, a detailed discussion of spectral features of the photoluminescence spectra of undoped, p−doped and n−doping AlxGa1−xAs (0≤x≤1) alloys is given.
Abstract: A thorough discussion of the various features of the photoluminescence spectra of undoped, p‐doped and n‐doped AlxGa1−xAs (0≤x≤1) alloys is given. This review covers spectral features in the energy region ranging from the energy band gap down to ≂0.8 eV, doping densities from isolated impurities to strongly interacting impurities (heavy‐doping effects) and lattice temperatures from 2 to 300 K. The relevance of photoluminescence as a simple but very powerful characterization technique is stressed also in comparison with other experimental methods. The most recent determinations of the Al concentration dependence of some physical properties of the alloy (energy gaps, carrier effective masses, dielectric constants, phonon energies, donor and acceptor binding energies, etc.) are given. The main physical mechanisms of the radiative recombination process in semiconductors are summarized with particular emphasis on the experimental data available for AlxGa1−xAs. The effects of the nature of the band gap (direct ...

Journal ArticleDOI
TL;DR: In this article, thermally induced decay of fiber Bragg gratings patterned by ultraviolet irradiation in germanium-doped silica fiber has been investigated, and the decay is well characterized by a power-law function of time with a small exponent.
Abstract: We report measurements of thermally induced decay of fiber Bragg gratings patterned by ultraviolet irradiation in germanium‐doped silica fiber. The decay is well characterized by a ‘‘power‐law’’ function of time with a small exponent, which is consistent with the rapid initial decay followed by a substantially decreasing rate of decay. We propose a decay mechanism in which carriers excited during writing are trapped in a broad distribution of trap states, and the rate of thermal depopulation is an activated function of the trap depth. This model is consistent with the observed power‐law behavior. An important consequence of this mechanism is that the decay of the induced index change can be accelerated by increasing temperature. A decelerated‐aging experiment verifies this prediction. This result demonstrates that it is possible to preanneal a device incorporating ultraviolet‐induced refractive‐index changes, wiping out the portion of the index change that would decay over the lifetime of the device, and keeping only the very stable portion of the index change.

Journal ArticleDOI
TL;DR: In this paper, the utility of Raman spectroscopy for the simultaneous determination of composition and strain in thin GexSi1−x layers has been investigated using data from the literature and new data for the strain shift of the SiSi phonon mode presented here.
Abstract: The utility of Raman spectroscopy for the simultaneous determination of composition and strain in thin GexSi1−x layers has been investigated. Using data from the literature and new data for the strain shift of the Si‐Si phonon mode presented here, we show how Raman spectra provide several different means of measuring composition and strain in samples as thin as 200 A. We demonstrate that for largely relaxed layers with compositions near x=0.30, Raman scattering can measure the composition, x, with an accuracy of ±0.015 and the strain, e, with an accuracy ±0.0025. The accuracy of the alloy composition obtained from Raman spectra is comparable or, in the case of very thin layers, superior to that measured by other techniques such as x‐ray diffraction, electron microprobe, and Auger electron spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, a dimensionless solution is presented for the surface recombination component τs of the effective lifetime τeff of the fundamental mode of excess carrier decay in semiconductors. But the problem is solved in terms of dimensionless variables, and the solution obtained is a general one.
Abstract: A dimensionless solution is presented for the surface recombination component τs of the effective lifetime τeff of the fundamental mode of excess carrier decay in semiconductors. The case of different surface recombination velocities S1 and S2 is analyzed. As the problem is solved in terms of dimensionless variables, the solution obtained is a general one. A normalized surface lifetime τ *s is plotted as a function of normalized surface recombination velocities S*1 and S*2. This allows rapid calculation and visualization of the influence of surface recombination on τs, for all possible cases of recombination parameters. That is, for any value of S1, S2, W (the width of a sample), and D (the diffusion constant) a solution for the surface lifetime τs can be found from the one graphical solution. It is a useful tool for rapidly interpreting the effect of surface recombination in transient lifetime measurement experiments. For the cases where S=S1=S2, or where S1 or S2 is zero, this approach is an elegant too...

Journal ArticleDOI
TL;DR: In this paper, high-brightness InGaN/AlGaN double-heterostructure blue-green light-emitting diodes with a luminous intensity of 2 cd were fabricated by increasing an indium mole fraction of the active layer up to 0.23.
Abstract: High‐brightness InGaN/AlGaN double‐heterostructure blue‐green‐light‐emitting diodes with a luminous intensity of 2 cd were fabricated by increasing an indium mole fraction of the InGaN active layer up to 0.23. Both Zn and Si were codoped into the InGaN active layer to afford relatively stronger luminescence. The blue‐green emission intensity of room‐temperature photoluminescence became maximum when the electron carrier concentration of the InGaN active layer was around 1×1019 cm−3. Donor‐acceptor pair recombination is a dominant emission mechanism of the InGaN active layer. The external quantum efficiency was as high as 2.4% at a forward current of 20 mA at room temperature. The peak wavelength and the full width at half‐maximum of the electroluminescence were 500 and 80 nm, respectively.

Journal ArticleDOI
TL;DR: In this paper, a review of magnetoinductive and magneto-impedance effects in FeCoSiB amorphous wires is presented, showing that at low frequencies (1-10 kHz) the inductive voltage drops by 50% for a field of 2 Oe (25%/Oe) reflecting a strong field dependence of the circumferential permeability.
Abstract: Recent experiments have discovered giant and sensitive magneto‐impedance and magneto‐inductive effects in FeCoSiB amorphous wires. These effects include a sensitive change in an ac wire voltage with the application of a small dc longitudinal magnetic field. At low frequencies (1–10 kHz) the inductive voltage drops by 50% for a field of 2 Oe (25%/Oe) reflecting a strong field dependence of the circumferential permeability. At higher frequencies (0.1–10 MHz) when the skin effect is essential, the amplitude of the total wire voltage decreases by 40%–60% for fields of 3–10 Oe (about 10%/Oe). These effects exhibit no hysteresis for the variation of an applied field and can be obtained even in wires of 1 mm length and a few micrometer diameter. These characteristics are very useful to constitute a highly sensitive microsensor head to detect local fields of the order of 10−5 Oe. In this paper, we review recently obtained experimental results on magneto‐inductive and magneto‐impedance effects and present a detail...

Journal ArticleDOI
TL;DR: In this paper, consistent sets of Ar++Ar and Ar+++Ar differential and integral cross sections for modeling ion scattering that take into account differential scattering data and the fact that symmetric charge transfer collisions are one aspect of elastic scattering collisions are presented.
Abstract: We suggest consistent sets of Ar++Ar and Ar+++Ar differential and integral cross sections for modeling ion scattering that take into account differential scattering data and the fact that symmetric charge transfer collisions are one aspect of elastic scattering collisions. These suggestions make possible a considerable improvement in the accuracy of future Monte Carlo calculations of the angular, energy, and temporal distributions of Ar+ and Ar++ ions passing through the electrode sheaths of low‐pressure, rf, and dc discharges in Ar. The cross sections necessary for a proper modeling of the energy dissipation in the gas and at the electrodes by fast neutral Ar atoms formed in symmetric‐charge‐transfer collisions of Ar+ and Ar++ with Ar are also reviewed.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated visible photoluminescence excited by an Ar-ion laser (488 nm, 2.54 eV) at room temperature from Si+implanted silica glass, as-implanted and after subsequent annealing in vacuum.
Abstract: We have investigated visible photoluminescence excited by Ar‐ion laser (488 nm, 2.54 eV) at room temperature from Si+‐implanted silica glass, as‐implanted and after subsequent annealing in vacuum. We found two visible luminescence bands: one peaked around 2.0 eV, observed in as‐implanted specimens and annealed completely after heating to about 600 °C, the other peaked around 1.7 eV observed only after heating to about 1100 °C, the temperature at which Si segregates from SiOx. It was found that the 2.0 eV band anneals parallel to the E’ centers, as detected by electron spin resonance studies. It was also found that Raman lines around 520 cm−1, due to Si—Si bonds, grow and that interference patterns are induced by annealing Si+‐implanted silica glass. Based on these studies, we ascribe the 2.0 eV band to the electron‐hole recombination in Si‐rich SiO2 and the 1.7 eV band to the electron‐hole recombination in the interface between the Si nanocrystal and the SiO2 formed by segregation of crystalline Si from SiOx.

Journal ArticleDOI
TL;DR: In this article, it was demonstrated that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers, which results in high contrast at large viewing angles, and gray scale.
Abstract: It is demonstrated that the reflective properties and bistability of cholesteric liquid crystals can be controlled by proper surface treatment and dispersed polymers. Dispersing a polymer in the liquid crystal or using a cell with an inhomogeneous surface anchoring creates permanent defects which result in long‐term bistability, high contrast at large viewing angles, and gray scale. The wide‐angle, reflective feature makes cholesteric materials suitable for displays without backlights and bistability provides flicker‐free operation.

Journal ArticleDOI
TL;DR: In this paper, a quantum magnetic disk scheme that is based on uniformly embedding single-domain magnetic structures in a nonmagnetic disk is proposed, which can be used to store one bit of information, therefore such nanomagnetic pillar array storage offers a rather different paradigm than the conventional storage method.
Abstract: Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon that have a uniform diameter of 35 nm, a height of 120 nm, and a period of 100 nm were fabricated. The density of the pillar arrays is 65 Gbits/in.2—over two orders of magnitude greater than the state‐of‐the‐art magnetic storage density. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. Each pillar can be used to store one bit of information, therefore such nanomagnetic pillar array storage offers a rather different paradigm than the conventional storage method. A quantum magnetic disk scheme that is based on uniformly embedding single‐domain magnetic structures in a nonmagnetic disk is proposed.

Journal ArticleDOI
TL;DR: In this article, the authors measured the Ramaman spectra of n-type gallium nitride with different carrier concentrations and found that the phonon band shifted towards the high frequency side and broadened with an increase in carrier concentration.
Abstract: Raman spectra of n‐type gallium nitride with different carrier concentrations have been measured. The LO phonon band shifted towards the high‐frequency side and broadened with an increase in carrier concentration. Results showed that the LO phonon was coupled to the overdamped plasmon in gallium nitride. The carrier concentrations and damping constants were determined by line‐shape fitting of the coupled modes and compared to values obtained from Hall measurements. The carrier concentrations obtained from the two methods agree well. As a result, the dominant scattering mechanisms in gallium nitride are deformation‐potential and electro‐optic mechanisms.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the coercive field is independent of thickness having a value of 2.4 V/μm and the ratio ebl/dbl is in the range 20−28 nm−1; the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 Vm2/C; and (iv) the polarization depends on the electric field in the PZT layer.
Abstract: Ferroelectric capacitors having Pt bottom and top electrodes and a ferroelectric film of composition PbZr0.51Ti0.49O3 (PZT) were fabricated and investigated. The PZT films of thicknesses varying from 0.12 to 0.69 μm were prepared by organometallic chemical‐vapor deposition. Annealed capacitors were investigated by capacitance, hysteresis, and pulse switching measurements. It is found that the thickness dependence of the reciprocal capacitance, the coercive voltage, and the polarization measured by pulse switching can all be explained by a blocking layer model, in which a dielectric layer of thickness dbl and relative permittivity ebl is situated between the PZT film and an electrode. It is shown that (i) the coercive field is independent of thickness having a value of 2.4 V/μm; (ii) the ratio ebl/dbl is in the range 20–28 nm−1; (iii) the voltage across the blocking layer is proportional to the polarization, Vbl=cP, where c=4.1±0.5 V m2/C; and (iv) the polarization depends on the electric field in the PZT layer, independent of thickness. Pulse switching endurance measurements showed that in the saturation range the fatigue for these ferroelectric capacitors is determined by the pulse voltage and is independent of the thickness.

Journal ArticleDOI
TL;DR: In this paper, a colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La•Ca•Mn•O thin films.
Abstract: A colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La‐Ca‐Mn‐O thin films. The effect is negative and isotropic with respect to the field orientations. The magnetoresistance is strongly temperature dependent, and exhibits a sharp peak that can be shifted to near room temperature by adjusting processing parameters. Near‐room‐temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be detrimental to achieving very large magnetoresistance in the lanthanum manganite films. The orders of magnitude change in electrical resistivity could be useful for various magnetic and electric device applications.