Showing papers in "Applied Physics Letters in 1995"
TL;DR: In this article, a nanoimprint process that presses a mold into a thin thermoplastic polymer film on a substrate to create vias and trenches with a minimum size of 25 nm and a depth of 100 nm has been demonstrated.
Abstract: A nanoimprint process that presses a mold into a thin thermoplastic polymer film on a substrate to create vias and trenches with a minimum size of 25 nm and a depth of 100 nm in the polymer has been demonstrated. Furthermore, the imprint process has been used as a lithography process to fabricate sub‐25 nm diameter metal dot arrays of a 100 nm period in a lift‐off process. It was found that the nanostructures imprinted in the polymers conform completely with the geometry of the mold. At present, the imprinted size is limited by the size of the mold being used; with a suitable mold, the imprint process should mold sub‐10 nm structures with a high aspect ratio in polymers. The nanoimprint process offers a low cost method for mass producing sub‐25 nm structures and has the potential to become a key nanolithography method for future manufacturing of integrated circuits and integrated optics.
2,749 citations
TL;DR: In this paper, the surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings, which can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed.
Abstract: The surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings. The gratings obtained are stable but can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed. Multiple gratings can be simultaneously written and gratings can be overwritten. Atomic force microscopy was used to investigate the gratings produced on the surfaces. Possible mechanisms responsible for the surface alteration are discussed.
1,183 citations
TL;DR: In this paper, the authors observed holographic surface relief gratings with relatively large amplitude on a second order nonlinear optical polymeric material, which were created upon exposure to polarized Ar+ laser beams at 488 nm without any subsequent processing steps.
Abstract: We report observation of holographic surface relief gratings with relatively large amplitude on a second order nonlinear optical polymeric material. Surface relief gratings on these polymer films were created upon exposure to polarized Ar+ laser beams at 488 nm without any subsequent processing steps. The surface structure of the relief gratings was investigated by atomic force microscopy. The depth of the surface relief in a typical case was 120 nm which is approximately 20% of the original film thickness. The diffraction efficiency of gold‐coated gratings was investigated as a function of wavelength and capability of recording orthogonal gratings on the same film was demonstrated.
1,079 citations
TL;DR: The electroluminescence of CdSe nanocrystallites (quantum dots) incorporated into thin films (1000 A) of polyvinyl carbazole (PVK) and an oxadiazole derivative (t‐Bu‐PBD) and sandwiched between ITO and Al electrodes was studied in this article.
Abstract: Electroluminescence is obtained from nearly monodisperse CdSe nanocrystallites (quantum dots) incorporated into thin films (1000 A) of polyvinylcarbazole (PVK) and an oxadiazole derivative (t‐Bu‐PBD) and sandwiched between ITO and Al electrodes. The electroluminescence and photoluminescence spectra (bandwidths ≤40 nm) are nearly identical at room temperature and are tunable from ∼530 to ∼650 nm by varying the size of the dots. Voltage studies at 77 K indicate that while only the dots electroluminesce at the lower voltages, both the dots and the PVK matrix electroluminesce at higher applied voltages. Variable temperature studies indicate that the electroluminescence efficiency increases substantially as the films are cooled down to cryogenic temperatures.
1,032 citations
TL;DR: In this paper, an aluminum coated tapered optical fiber is rigidly attached to one of the prongs of a high Q piezoelectric tuning fork, and the fork is mechanically dithered at its resonance frequency (33 kHz) so that the tip amplitude does not exceed 0.4 nm.
Abstract: An aluminum coated tapered optical fiber is rigidly attached to one of the prongs of a high Q piezoelectric tuning fork. The fork is mechanically dithered at its resonance frequency (33 kHz) so that the tip amplitude does not exceed 0.4 nm. A corresponding piezoelectric signal is measured on electrodes appropriately placed on the prongs. As the tip approaches within 20 nm above the sample surface a 0.1 nN drag force acting on the tip causes the signal to reduce. This signal is used to position the optical fiber tip to about 0 to 25 nm above the sample. Shear forces resulting from the tip‐sample interaction can be quantitatively deduced.
980 citations
TL;DR: In this article, the electrical, optical, and structural properties of light emitting diodes (LEDs) fabricated from the III-V nitride material system have been studied.
Abstract: The electrical, optical, and structural properties of light emitting diodes (LEDs) fabricated from the III–V nitride material system have been studied. LEDs with external quantum efficiencies as high as 4% were characterized by transmission electron microscopy and found to contain dislocation densities in excess of 2×1010 cm−2. A comparison to other III–V arsenide and phosphide LEDs shows that minority carries in GaN‐based LEDs are remarkably insensitive to the presence of structural defects. Dislocations do not act as efficient nonradiative recombination sites in nitride materials. It is hypothesized that the benign character of dislocations arises from the ionic nature of bonding in the III–V nitrides.
952 citations
TL;DR: In this article, free-space electro-optic sampling via the linear electro−optic effect (Pockels effect) offers a flat frequency response over an ultrawide bandwidth and the potential for simple cross-correlation signal of the terahertz and optical pulses.
Abstract: Free‐space electro‐optic sampling is an alternative method for the characterization of freely propagating terahertz beams with subpicosecond temporal resolution. In contrast to resonant photoconductive dipole antennas, free‐space electro‐optic sampling via the linear electro‐optic effect (Pockels effect) offers a flat frequency response over an ultrawide bandwidth and the potential for a simple cross‐correlation signal of the terahertz and optical pulses.
945 citations
TL;DR: In this paper, a superconducting transition edge sensor is proposed, where the temperature of a superconding film is held constant by feeding back to its position on the resistive transition edge.
Abstract: A novel type of superconducting transition edge sensor is proposed. In this sensor, the temperature of a superconducting film is held constant by feeding back to its position on the resistive transition edge. Energy deposited in the film is measured by a reduction in the feedback Joule heating. This mode of operation should lead to substantial improvements in resolution, linearity, dynamic range, and count rate. Fundamental resolution limits are below ΔE=√kT2C, which is sometimes incorrectly referred to as the thermodynamic limit. This performance is better than any existing technology operating at the same temperature, count rate, and absorber heat capacity. Applications include high resolution x‐ray spectrometry, dark matter searches, and neutrino detection.
714 citations
TL;DR: In this article, a single-layer white light-emitting organic electroluminescent devices were developed by using dyedispersed poly(Nvinylcarbazole) (PVK) which consists only of one polymer layer that is simply sandwiched between two electrodes, indium-tin oxide, and Mg:Ag.
Abstract: Bright single‐layer white light‐emitting organic electroluminescent devices were developed by using dye‐dispersed poly(N‐vinylcarbazole) (PVK) The active layer consists only of one polymer layer that is simply sandwiched between two electrodes, indium‐tin oxide, and Mg:Ag In order to achieve bipolarity in the single polymer emitter layer, PVK was molecularly dispersed with electron‐transporting additives such as 2‐(4‐biphenyl)‐5‐(4‐tert‐butylphenyl)‐1,3,4‐oxadiazole In addition, several fluorescent dyes, having different emission colors, were dispersed as emitting centers By adjusting the concentration of the fluorescent dyes, white light with a maximum luminescence of 4100 cd/m2 was obtained, which is the brightest white light ever observed for organic electroluminescent devices
627 citations
TL;DR: In this article, an equation for the threshold transition of liquid crystals was derived using the continuum elastic theory and an inversely proportional relationship between the threshold voltage and the gap between the substrates was found to hold.
Abstract: Electro‐optical characteristics related to the threshold behavior of liquid crystals when using the in‐plane switching (IPS) mode were investigated with interdigital electrodes. In order to analyze the switching behavior of liquid crystals, an equation, which expresses the threshold transition, was derived using the continuum elastic theory. It was made clear that it was the electric field and not the voltage that drives the liquid crystals in the IPS mode. Significantly, an inversely proportional relationship between the threshold voltage and the gap between the substrates was found to hold. Furthermore, the electro‐optical characteristics were recognized to change with the variation of the gap between the substrates. This behavior is due to the independence of electric field on liquid crystal layer normal.
603 citations
TL;DR: In this paper, high-power blue and violet light-emitting diodes (LEDs) based on III-V nitrides were grown by metalorganic chemical vapor deposition on sapphire substrates.
Abstract: High‐power blue and violet light‐emitting diodes(LEDs) based on III–V nitrides were grown by metalorganic chemical vapor deposition on sapphire substrates. As an active layer, the InGaN single‐quantum‐well‐structure was used. The violet LEDs produced 5.6 mW at 20 mA, with a sharp peak of light output at 405 nm, and exhibited an external quantum efficiency of 9.2%. The blue LEDs produced 4.8 mW at 20 mA and sharply peaked at 450 nm, corresponding to an external quantum efficiency of 8.7%. These values of the output power and the quantum efficiencies are the highest ever reported for violet and blue LEDs.
TL;DR: In this article, a nonlinear optical crystal CsLiB6O10 (CLBO) is described that can be grown from either stoichiometric melt or from solution, and a large, high quality single crystal with dimensions of 14×11×11 cm3 was obtained by the top-seeded Kyropoulos method.
Abstract: A new nonlinear optical crystal CsLiB6O10 (CLBO), is described that can be grown from either stoichiometric melt or from solution. A large, high quality single crystal with dimensions of 14×11×11 cm3 was obtained by the top‐seeded Kyropoulos method. Fourth harmonic and fifth harmonic generations of the 1.064 μm Nd:YAG laser radiation with type‐I phase matching were realized in the CLBO crystal. Output pulse energies obtained were 110 mJ at 266 nm and 35 mJ at 213 nm.
TL;DR: In this paper, N-channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element, showing on-off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V
Abstract: N‐channel field effect transistors with excellent device characteristics have been fabricated by utilizing C60 as the active element. Measurements on C60 thin films in ultrahigh vacuum show on‐off ratios as high as 106 and field effect mobilities up to 0.08 cm2/V s.
TL;DR: In this article, a photomixer consisting of an epitaxial layer of LTG GaAs with interdigitated electrodes fabricated on the top surface is used to generate coherent continuous-wave output radiation from microwave frequencies up to 3.8 THz.
Abstract: Low‐temperature‐grown (LTG) GaAs is used as an optical‐heterodyne converter or photomixer, to generate coherent continuous‐wave output radiation from microwave frequencies up to 3.8 THz. The photomixer consists of an epitaxial layer of LTG GaAs with interdigitated electrodes fabricated on the top surface. Terahertz photocurrents are generated in the gaps between the electrodes, and power is radiated into free space through a three‐turn self‐complementary spiral antenna. In a photomixer having a 0.27‐ps electron‐hole lifetime and small electrode capacitance, the output power is practically flat up to about 300 GHz and then rolls off at a rate of approximately 12 dB/oct.
TL;DR: In this article, the authors used oscillating silicon nitride microcantilevers coated with a thin gold film to detect adsorbed vapors with picogram mass resolution and found that cantilever resonance frequency changes due to surface mass loading as a result of adsorption of mercury vapor.
Abstract: Oscillating silicon nitride microcantilevers coated with a thin gold film have been used to detect mercury vapor in air. Cantilever resonance frequency changes due to surface mass loading as a result of adsorption of mercury vapor. Furthermore, cantilever bending is also altered due to changes in surface stress induced by mercury adsorption on the gold overlayer. Both of these phenomena can be used to quantitatively detect adsorbed vapors with picogram mass resolution.
TL;DR: In this article, thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition.
Abstract: Thin films of novel superhard composite materials consisting of TiN nanocrystals in an amorphous Si3N4 matrix have been prepared by means of plasma chemical vapor deposition. The films show a high Vickers hardness of 5000 kg/mm2 and elastic modulus of ≳500 GPa, and they are resistant against oxidation in air up to ≥800 °C. The theoretical background of these unusual properties are briefly discussed and practical rules suggested according to which similar properties should be expected for composites of other ternary systems.
TL;DR: In this article, the luminous efficiency was obtained to be 1.5 lm/W. The external quantum efficiency was estimated to be 2.4%, which is one of the highest efficiencies ever reported in blue emitting organic EL devices.
Abstract: We report that organic electroluminescence devices with a distyrylarylene (DSA) emitting layer including a new dopant realized highly efficient and bright emission in blue region. This dopant was amino‐substituted DSA. The luminous efficiency was obtained to be 1.5 lm/W. The external quantum efficiency was estimated to be 2.4%, which is one of the highest efficiencies ever reported in blue emitting organic EL devices.
TL;DR: In this paper, the application of the atomic force microscope (AFM) to manipulate and position nanometer-sized particles with nanometer precision is described. And the technique, which can be regarded as a nanometerscale analogy to atomic level manipulation with the scanning tunneling microscope, allowed them to form arbitrary nanostructures, under ambient conditions, by controlled manipulation of individual 30 nm GaAs particles.
Abstract: We report on the application of the atomic force microscope (AFM) to manipulate and position nanometer‐sized particles with nanometer precision. The technique, which can be regarded as a nanometer‐scale analogy to atomic level manipulation with the scanning tunneling microscope, allowed us to form arbitrary nanostructures, under ambient conditions, by controlled manipulation of individual 30 nm GaAs particles. A whole new set of nanodevices can be fabricated particle‐by‐particle for studies of quantum effects and single electron tunneling. We also demonstrate a method, based on the AFM manipulation, to determine the true lateral dimensions of nano‐objects, in spite of the tip‐sample convolution.
TL;DR: In this article, two cantilevers were fabricated and operated in parallel in a new mode for imaging with the atomic force microscope (AFM) in a constant force mode, where the actuator provided over 4 μm of deflection at low frequencies (dc) and over 30 μm at the first resonant frequency.
Abstract: We have fabricated and operated two cantilevers in parallel in a new mode for imaging with the atomic force microscope (AFM). The cantilevers contain both an integrated piezoresistive silicon sensor and an integrated piezoelectric zinc oxide (ZnO) actuator. The integration of sensor and actuator on a single cantilever allows us to simultaneously record two independent AFM images in the constant force mode. The ZnO actuator provides over 4 μm of deflection at low frequencies (dc) and over 30 μm deflection at the first resonant frequency. The piezoresistive element is used to detect the strain and provide the feedback signal for the ZnO actuator.
TL;DR: In this article, the molecular design of hole transport materials (HTMs) for producing high durability in organic layered electroluminescent (EL) diodes was elucidated.
Abstract: The molecular design of hole transport materials (HTMs) for producing high durability in organic layered electroluminescent (EL) diodes was elucidated. The durability tests were examined using fourteen hole transport materials in the cell structure of an anode/hole transport layer (HTL)/emitter layer (EML)/cathode. The ionization potential (Ip) of HTLs was found to be the dominant factor for obtaining high durability in organic EL devices. The formation of the small energy barrier at the interface of a HTL/anode was required for high durability. Moreover, no straightforward relations between melting point, glass transition temperature of the HTMs, and durability of the EL devices were observed. The EL device using the HTM having a low Ip (5.08 eV) showed an especially remarkable stability. In this case, the half‐life period of the initial luminance was beyond 500 h.
TL;DR: In this paper, an improved mid-wave infrared diode laser structure based on InAs•Ga1−xInxSb• InAs−Ga•Sb Type•II multiple quantum wells was proposed, which combines strong optical coupling, 2D dispersion for both electrons and holes, suppression of the Auger recombination rate and excellent electrical and optical confinement.
Abstract: We discuss an improved mid‐wave infrared diode laser structure based on InAs‐Ga1−xInxSb‐ InAs‐Ga1−xAlxSb Type‐II multiple quantum wells. The proposed design combines strong optical coupling, 2D dispersion for both electrons and holes, suppression of the Auger recombination rate, and excellent electrical and optical confinement.
TL;DR: In this article, the drift mobility of electrons and holes in thin, vapordeposited films of tris(8−hydroxyquinolinolato•N1,O8) aluminum using a time of flight photoconductivity technique was measured.
Abstract: We have measured the drift mobility of electrons and holes in thin, vapor‐deposited films of tris(8‐hydroxyquinolinolato‐N1,O8) aluminum using a time of flight photoconductivity technique. The drift of mobility of both carriers is dispersive and strongly electric field and temperature dependent. At ambient temperature and an electric field of 4×105 V cm−1, the effective mobility of electrons and holes is 1.4×10−6 and 2×10−8 cm2 V−1 s−1, respectively, in a 400 nm thick sample.
TL;DR: Ferroelectric SrBi2Ta2O9 thin films were synthesized on Pt/Ti/SiO2/Si substrates using a solution deposition process, and structural and electrical properties were investigated as discussed by the authors.
Abstract: Ferroelectric SrBi2Ta2O9 thin films were synthesized on Pt/Ti/SiO2/Si substrates using a solution deposition process, and structural and electrical properties were investigated. The spin‐on films crystallized during firing above 700 °C. The films showed high diffraction peaks of (105) and (200), while little peaks from (00l) planes were observed. Good ferroelectric properties were obtained for a 280 nm thick film; Pr and Ec were 10.0 μC/cm2 and 38 kV/cm, respectively. Fatigue endurance was excellent; the hysteresis loop does not change up to 109 switching cycles. These properties are very attractive for nonvolatile memory application.
TL;DR: In this article, the topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations.
Abstract: The atomically ultrasmooth surfaces with atomic steps of sapphire substrates were obtained by annealing in air at temperatures between 1000 and 1400 °C. The terrace width and atomic step height of the ultrasmooth surfaces were controlled on an atomic scale by changing the annealing conditions and the crystallographic surface of substrates. The obtained ultrasmooth surface was stable in air. The topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations.
TL;DR: In this article, a critical assessment of thermal models for laser sputtering at high fluences is presented, and it is argued that the model explaining such sputtering by involving a subsurface superheating effect misinterprets the meaning of "vaporization" and "boiling" and as a result inappropriate boundary conditions are used, including those for both the surface temperature and for surface temperature gradient.
Abstract: A critical assessment of thermal models for laser sputtering at high fluences is presented. It is argued that the model explaining such sputtering by involving a subsurface superheating effect misinterprets the meaning of ‘‘vaporization’’ and ‘‘boiling’’. As a result inappropriate boundary conditions are used, including those for both the surface temperature and for the surface temperature gradient. On the contrary, it is shown that explosive boiling (also termed phase explosion) in the sense pioneered by Martynyuk and by Fucke and Seydel remains the only thermal mechanism able to explain laser sputtering at high fluences.
TL;DR: In this paper, optical heterodyne measurements with distributed Bragg reflector diode-laser pumps demonstrate that low-temperature grown (LTG) GaAs photomixers will be useful in a compact all-solid-state terahertz source.
Abstract: Recent optical heterodyne measurements with distributed‐Bragg‐reflector diode‐laser pumps demonstrate that low‐temperature‐grown (LTG) GaAs photomixers will be useful in a compact all‐solid‐state terahertz source. Electrical 3 dB bandwidths as large as 650 GHz are measured in mixers with low electrode capacitance. These bandwidths appear to be independent of pump‐laser wavelength over the range 780–850 nm. Shorter wavelength pumping results in a significant reduction of the bandwidth. The best LTG‐GaAs photomixers are used to generate coherent continuous‐wave output radiation at frequencies up to 5 THz.
TL;DR: The preferred orientation of polycrystalline TiN films grown by ultrahigh-vacuum reactive magnetron sputter deposition on amorphous SiO2 at 350°C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N) as mentioned in this paper.
Abstract: The preferred orientation of polycrystalline TiN films grown by ultrahigh‐vacuum reactive‐magnetron sputter deposition on amorphous SiO2 at 350 °C in pure N2 discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratio Ji/JTi from 1 to ≥5 with the N+2 ion energy Ei maintained constant at ≂20 eV (≂10 eV per incident accelerated N). All samples were slightly over‐stoichiometric with N/Ti=1.02±0.03. Films deposited with Ji/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 μm. However, films grown with Ji/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from ≂0 to 1 as Ji/JTi was varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240...
TL;DR: A silicon surface tunneling transistor structure, based on lateral band-to-band tunneling, is presented in this article, which is controlled by the bias on the gate of the device which modulates the width of the tunneling barrier.
Abstract: A silicon surface tunneling transistor structure, based on lateral band‐to‐band tunneling, is presented The theory, fabrication, and operation of the device is described Band‐to‐band tunneling is controlled by the bias on the gate of the device which modulates the width of the tunneling barrier The operation of the device is confirmed in both experimental results and two‐dimensional computer simulations Dramatic differences in drain current are observed for different gate bias
TL;DR: In this article, a low temperature positioning mechanism with a single chip miniature superconducting quantum interference device (SQUID) magnetometer is combined with a novel low-temperature positioning mechanism to form an extremely sensitive new magnetic microscope, with a demonstrated spatial resolution of ∼10 μm.
Abstract: We have combined a novel low temperature positioning mechanism with a single‐chip miniature superconducting quantum interference device (SQUID) magnetometer to form an extremely sensitive new magnetic microscope, with a demonstrated spatial resolution of ∼10 μm. The design and operation of this scanning SQUID microscope will be described. The absolute calibration of this instrument with an ideal point source, a single vortex trapped in a superconducting film, will be presented, and a representative application will be discussed.
TL;DR: In this paper, superconducting and mechanical properties of YBa2Cu3O7−δ (YBCO) films on Ni-based alloys with a textured yttria-stabilized zirconia (YSZ) buffer layer were reported.
Abstract: We report superconducting and mechanical properties of YBa2Cu3O7−δ (YBCO) thick films on Ni‐based alloys with a textured yttria‐stabilized zirconia (YSZ) buffer layer. The YBCO and YSZ layers were deposited by pulsed laser deposition and ion beam assisted deposition, respectively. It was found that the transport critical current density (Jc) correlates very well with the YBCO mosaic spread. Jc over 1×10 6 A/cm2 at 75 K and ∼1×107 A/cm2 at 4 K were obtained in the 1‐μm thick YBCO films. Zero field critical current of 120 amps at 75 K was obtained in a 2‐μm‐thick and 1‐cm‐wide YBCO film. Angular dependence measurement revealed Jc peaks for both H∥c and H∥a‐b. The peak for H∥c implies additional pinning due to defects such as small angle grain boundaries or twin boundaries. Bending tests at 75 K showed that the YBCO thick films on the metallic substrates could sustain a strain of 0.4% and over 1% for tension and compression, respectively.