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17 Mar 1997

Volume 70, Issue 11, pp. 1333-1482

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Photoluminescence microscopy of InGaN quantum wells

W. D. Herzog, R. Singh, T. D. Moustakas, B. B. Goldberg, and M. S. Ünlü

Appl. Phys. Lett. 70, 1333 (1997); http://dx.doi.org/10.1063/1.118600 (3 pages) | Cited 5 times

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Submicron spatial resolution photoluminescence is used to assess radiative efficiency and spatial uniformity of GaN/InGaN heterojunctions. Room temperature photoluminescence of multiple InGaN quantum wells with GaN barriers fabricated by electron-cyclotron resonance assisted molecular beam epitaxy was measured as a function of position on a facet perpendicular to the layer structure. Our high resolution studies reveal that the radiative recombination for the InGaN quantum wells is 50–60 times more efficient than for the underlying GaN film. © 1997 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Luminescent observation of multiphoton ionization-fragmentation of chromate ions adsorbed on a disperse SiO2 surface

Yuri D. Glinka

Appl. Phys. Lett. 70, 1336 (1997); http://dx.doi.org/10.1063/1.118572 (3 pages) | Cited 5 times

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Direct evidence for the multiphoton ionization with subsequent fragmentation of the chromate ions (CrO42−)adsorbed on a disperse SiO2 surface is provided by luminescence measurements using the Nd-doped yttrium aluminum garnet pulsed laser as a source of excitation. Experiments were done with the fundamental laser frequency (λ=1.064 μm; τp=20 ns). The multiphoton absorption proceeds through an intermediate three-photon resonance state. The luminescence response results from recombination of photoelectrons with ionized CrO42− ions and ionized surface oxygendeficient centers. The dynamics of this process include autoionization, which is stimulated by intermolecular perturbation in overexcited states, fragmentation of chromate ions, and annealing of the oxygen-deficient centers. © 1997 American Institute of Physics.  
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
78.55.Hx Other solid inorganic materials
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics

Photorefractive grating fixing in KNbO3 by ferroelectric domains

R. S. Cudney, P. Bernasconi, M. Zgonik, J. Fousek, and P. Günter

Appl. Phys. Lett. 70, 1339 (1997); http://dx.doi.org/10.1063/1.118573 (3 pages) | Cited 6 times

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We report observations of photorefractive grating fixing in potassium niobate at room temperature by means of ferroelectric domains. A grating is recorded while the crystal is simultaneously depoled. By repoling the crystal, the presence of a latent grating is revealed. This fixed grating diffracts light with an efficiency which increases when an electric field is subsequently applied and when it is uniformly illuminated. We explain these observations qualitatively using a previously developed model that involves charge compensation by domain walls, and a new aspect that invokes the creation of new trap sites at the ferroelectric domain walls. © 1997 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
78.20.-e Optical properties of bulk materials and thin films
42.79.Dj Gratings
77.22.Ej Polarization and depolarization

Double-end crosslinked electro-optic polymer modulators with high optical power handling capability

Yongqiang Shi, Wenshen Wang, Weiping Lin, David J. Olson, and James H. Bechtel

Appl. Phys. Lett. 70, 1342 (1997); http://dx.doi.org/10.1063/1.118574 (3 pages) | Cited 14 times

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Integrated Mach–Zehnder and straight channel electro-optic modulators have been fabricated with a double-end crosslinked polymer containing amino-sulfone chromophores. The optical power handling capability of these modulators was tested at 1.32 μm wavelength and at input optical power levels compatible with commercial analog transmitters. At a cw peak intensity of 0.9 MW/cm2 inside the waveguide, the double-end crosslinked polymer waveguide modulators exhibited no observable increase in optical loss or degradation of nonlinearity during the experiment period. The poled polymer showed a long-term thermal stability of the electro-optic coefficient at 100 °C and photochemical stability at 633 nm wavelength. © 1997 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.70.Jk Polymers and organics
42.65.-k Nonlinear optics

Room temperature infrared intersubband photoluminescence in GaAs quantum wells

S. Sauvage, Z. Moussa, P. Boucaud, F. H. Julien, V. Berger, and J. Nagle

Appl. Phys. Lett. 70, 1345 (1997); http://dx.doi.org/10.1063/1.118601 (3 pages) | Cited 11 times

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We have observed mid-infrared photoluminescence at λ≈10 μm between conduction subbands in GaAs quantum wells. As for regular band-to-band interband photoluminescence spectroscopy, carriers are optically generated in the quantum wells using an interband optical pumping. At room temperature, the excited subbands of the quantum wells are thermally populated. Most of the carriers recombine nonradiatively through electron–phonon interactions, but a fraction of the carriers in the excited subbands recombine radiatively and give rise to the intersubband spontaneous emission in the 10 μm wavelength region. The intersubband photoluminescence is polarized along the growth axis of the quantum wells as expected from intersubband polarization selection rules. The emitted optical power is in the nW range and the quantum efficiency is found in agreement with calculations taking into account the radiative subband lifetimes. The emission is analyzed in terms of a blackbody emission of an electron gas in a two-dimensional confined system. © 1997 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Surface modification of indium tin oxide by plasma treatment: An effective method to improve the efficiency, brightness, and reliability of organic light emitting devices

C. C. Wu, C. I. Wu, J. C. Sturm, and A. Kahn

Appl. Phys. Lett. 70, 1348 (1997); http://dx.doi.org/10.1063/1.118575 (3 pages) | Cited 281 times

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We demonstrate the improvement of an indium tin oxide anode contact to an organic light emitting device via oxygen plasma treatment. Enhanced hole-injection efficiency improves dramatically the performance of single-layer doped-polymer devices: the drive voltage drops from >20 to <10 V, the external electroluminescence quantum efficiency (backside emission only) increases by a factor of 4 (from 0.28% to 1%), a much higher drive current can be applied to achieve a much higher brightness (maximum brightness ∼10,000 cd/m2 at 1000 mA/cm2), and the forward-to-reverse bias rectification ratio increases by orders of magnitude (from 102 to 106–107). The lifetime of the device is also enhanced by two orders of magnitude. © 1997 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.40.Ei Rectification
42.70.Jk Polymers and organics

Photo-pumped ZnCdSe/ZnCdMgSe blue-green quantum well lasers grown on InP substrates

Yongming Guo, Gregory Aizin, Y. C. Chen, Linfei Zeng, Abdullah Cavus, and Maria C. Tamargo

Appl. Phys. Lett. 70, 1351 (1997); http://dx.doi.org/10.1063/1.118576 (3 pages) | Cited 13 times

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We report the operation of new photo-pumped blue-green ZnCdSe/ZnCdMgSe graded-index separate confinement heterostructure single quantum well lasers grown lattice matched on InP substrates. Laser emission at 512 nm was observed. The T0 value is 150 K at room temperature. These materials are proposed as alternative materials for the fabrication of visible semiconductor lasers. © 1997 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Ry Gradient-index (GRIN) devices

Optical antenna: Towards a unity efficiency near-field optical probe

Robert D. Grober, Robert J. Schoelkopf, and Daniel E. Prober

Appl. Phys. Lett. 70, 1354 (1997); http://dx.doi.org/10.1063/1.118577 (3 pages) | Cited 120 times

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We demonstrate that an antenna can be used to realize a near-field optical probe that combines spatial resolution well below the diffraction limit with transmission efficiency approaching unity. The probe consists of a planar bow-tie antenna with an open-circuited gap at its apex. We present proof-of-principle measurements using microwave radiation and discuss scaling the antenna to the visible optical spectrum. © 1997 American Institute of Physics.
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07.57.Hm Infrared, submillimeter wave, microwave, and radiowave sources
42.30.-d Imaging and optical processing
84.40.Az Waveguides, transmission lines, striplines
78.40.Ha Other nonmetallic inorganics

Analog circuits simulation of communication with chaotic lasers

Renato M. de Moraes, Luiz de B. Oliveira-Neto, and José R. Rios Leite

Appl. Phys. Lett. 70, 1357 (1997); http://dx.doi.org/10.1063/1.118578 (3 pages) | Cited 3 times

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Masked signal communication between two chaotic lasers, described by rate equations, was implemented using analog circuits. Digital modulation of the gain parameter in the master circuit generated the messages. It is shown that there is a level of modulation for which the receiver circuit decodes the signal by on-off synchronization while the Poincaré sections, the first return maps and the time of return maps recovered directly from the master signal could not distinguish the bits. The circuits simulate the dynamics of two optically coupled CO2 lasers with intracavity saturable absorber. The signal appears to be unbreakable in such low dimensional systems because they operate at homoclinic chaos which corresponds to multibranched one-dimensional return maps. © 1997 American Institute of Physics.
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42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Four-wave mixing in a distributed-feedback laser

J. Minch, C. S. Chang, and S. L. Chuang

Appl. Phys. Lett. 70, 1360 (1997); http://dx.doi.org/10.1063/1.118579 (3 pages) | Cited 6 times

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We present a detailed study of four-wave mixing in a long-wavelength distributed-feedback (DFB) laser for both nearly degenerate and nondegenerate pump-probe detunings. We characterize scaling laws of the power dependence of multiple conjugate waves on the pump and probe power levels for the nearly degenerate case. We also measure the output ratio of the probe and conjugate waves up to a detuning of 500 GHz and report the cavity enhancement of the DFB laser on this output ratio. © 1997 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Spatial soliton robustness against spatially anisotropic phase perturbations

Jin U. Kang, C. J. Hamilton, J. S. Aitchison, and G. I. Stegeman

Appl. Phys. Lett. 70, 1363 (1997); http://dx.doi.org/10.1063/1.118580 (3 pages) | Cited 3 times

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We demonstrate experimentally that spatial solitons in AlGaAs waveguides are resilient against spatially anisotropic perturbations in their phase caused by introducing a wedge in the soliton propagation path. In agreement with numerical simulations, the solitons maintained their initial beam shape and width, independent of the fraction of the soliton beam intercepted by the wedge. © 1997 American Institute of Physics.
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42.65.Tg Optical solitons; nonlinear guided waves
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays

Femtosecond continuously tunable second harmonic generation over the entire-visible range in orthorhombic acentric Gd2(MoO4)3 crystals

H. Nishioka, W. Odajima, M. Tateno, K. Ueda, A. A. Kaminskii, A. V. Butashin, S. N. Bagayev, and A. A. Pavlyuk

Appl. Phys. Lett. 70, 1366 (1997); http://dx.doi.org/10.1063/1.118581 (3 pages) | Cited 11 times

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Second harmonic generation over the entire visible range in Nd3+ doped and undoped Gd2(MoO4)3 crystals under ultrashort hypercontinuum pumping is presented. The continuous tuning ranges from 487 to 790 nm in a single crystal. © 1997 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.-e Optical elements, devices, and systems
77.80.-e Ferroelectricity and antiferroelectricity
62.20.F- Deformation and plasticity

An enhancement of pump efficiency of a Ti:sapphire tube laser with an inner spectrum converter

Jae-Tae Seo, Kwang S. Han, and Ja H. Lee

Appl. Phys. Lett. 70, 1369 (1997); http://dx.doi.org/10.1063/1.118571 (3 pages)

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An inner spectrum converter was employed to enhance the pump efficiency of a Ti:sapphire laser system. The inner converter was inserted along the hollow of the laser tube for additional spectrum conversions of the photons transmitted through the outer converter jacket and the laser-tube wall. The pump source was an array of hypocycloidal pinches that produced intense broad-band, rich in the near-ultraviolet, emissions. The increase of laser efficiency is attributable to the inner converter which offered an efficient spectral coupling into the center of the Ti:sapphire absorption band and a better geometric coupling than the outer converter. © 1997 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.79.Nv Optical frequency converters
42.60.By Design of specific laser systems

High resolution visualization of acoustic wave fields within surface acoustic wave devices

T. Hesjedal, E. Chilla, and H.-J. Fröhlich

Appl. Phys. Lett. 70, 1372 (1997); http://dx.doi.org/10.1063/1.119323 (3 pages) | Cited 8 times

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We present the submicron visualization of surface acoustic wave (SAW) fields within interdigital transducers (IDTs) obtained by a scanning acoustic force microscope. Utilizing the nonlinear force curve of the tip-to-surface interaction, a periodic deflection of the cantilever appears when the SAWs are excited intermittently. This deflection depends on the amplitude of the surface oscillation and was measured by lock-in technique. SAWs with operating frequencies above 600 MHz were detected. The influence of the mass loading on the local oscillation amplitude was studied for various layer thicknesses of the IDT electrodes. © 1997 American Institute of Physics.
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43.38.Rh Surface acoustic wave transducers
43.38.Fx Piezoelectric and ferroelectric transducers
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.58.Ls Acoustical lenses and microscopes

Vacuum ultraviolet absorption spectroscopy for absolute density measurements of fluorine atoms in fluorocarbon plasmas

K. Sasaki, Y. Kawai, and K. Kadota

Appl. Phys. Lett. 70, 1375 (1997); http://dx.doi.org/10.1063/1.118582 (3 pages) | Cited 12 times

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Absolute densities of fluorine (F) atoms at the ground state (2p5 2P°) were measured in helicon-wave excited high-density CF4 plasmas by vacuum ultraviolet (VUV) absorption spectroscopy. By employing an electron cyclotron resonance CF4 plasma as a light source in the VUV wavelength range, an absorption spectroscopy system with no vacuum windows was constructed. As a result, the density of F atoms was approximately 1×1013 cm−3 for an rf power of 1 kW and a CF4 gas pressure of 2.5 mTorr, which was one-order higher than the density of CFx radicals and was one-order lower than the density of the parent gas. © 1997 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties

Piezoelectric properties of c-axis oriented Pb(Zr,Ti)O3 thin films

I. Kanno, S. Fujii, T. Kamada, and R. Takayama

Appl. Phys. Lett. 70, 1378 (1997); http://dx.doi.org/10.1063/1.118583 (3 pages) | Cited 95 times

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Piezoelectric properties of the c-axis oriented Pb(Zr,Ti)O3 (PZT) thin films were investigated. The PZT films with a composition near the morphotropic phase boundary were epitaxially grown on (100)Pt-coated MgO substrates by rf-magnetron sputtering. The PZT films exhibited excellent ferroelectricity with a remanent polarization more than 50 μC/cm2. In order to examine intrinsic piezoelectric properties, cantilever structures were microfabricated with the PZT films. The piezoelectric coefficient d31 of PZT films, which were not subjected to poling treatments, was measured directly from the transverse expansion of the cantilever beams. The measurements revealed that the PZT films were naturally polarized and had a relatively large piezoelectric coefficient d31 of 100×10−12 m/V without poling. © 1997 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization

Deposition of n-type diamondlike carbon by using the layer-by-layer technique and its electron emission properties

Kyu Chang Park, Jong Hyun Moon, Suk Jae Chung, Jin Jang, Myung Hwan Oh, and W. I. Milne

Appl. Phys. Lett. 70, 1381 (1997); http://dx.doi.org/10.1063/1.119076 (3 pages) | Cited 19 times

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We have studied the electron emission behavior of the diamondlike carbon (DLC) films by plasma enhanced chemical vapor deposition using a layer-by-layer deposition, in which the deposition of a thin layer of DLC and a CF4 plasma exposure on its surface were carried out alternatively. The electron emission current increases with CF4 plasma exposure time. The increase in emission current appears to be due to the n-type behavior of the DLC. © 1997 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Cy Elemental semiconductors
79.70.+q Field emission, ionization, evaporation, and desorption

Effect of applied electric field on the molecular orientation of epitaxially grown organic films

Kouichi Hayashi, Shin’ichi Kawato, Yasuhiro Fujii, Toshihisa Horiuchi, and Kazumi Matsushige

Appl. Phys. Lett. 70, 1384 (1997); http://dx.doi.org/10.1063/1.118584 (3 pages) | Cited 9 times

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In order to control and obtain desired molecular orientations, we investigated the effects of applying an electric field during the epitaxial growth of organic crystals in this study. We deposited interdigitated gold electrodes on polished KCl (001) substrates, and then grew copper phthalocyanine (CuPc) thin films, applying the voltages during evaporation process. Using an energy dispersive grazing incidence x-ray diffraction system, we evaluated the orientations of α-CuPc crystals relative to the KCl substrates. The CuPc crystals with applied electric fields were found to orient in different directions from those of the usual epitaxially grown films without applied electric fields. These facts suggest that the combination of applying an electric field and epitaxial growth provide us a new method to control the molecular orientation in the organic thin films. © 1997 American Institute of Physics.
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81.05.Hd Other semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

On the presence of molecular nitrogen in nitrogen-implanted amorphous carbon

S. Grigull, W. Jacob, D. Henke, A. Mücklich, C. Spaeth, and L. Sümmchen

Appl. Phys. Lett. 70, 1387 (1997); http://dx.doi.org/10.1063/1.118585 (3 pages) | Cited 8 times

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Hard amorphous carbon (ta-C) films were implanted with 20 keV N+ ions into saturation at two different temperatures. Monitoring the composition ratio [N]/[C] using in situ elastic recoil detection analysis, saturation levels [N]/[C] of 0.35 and 0.16 have been found for implantations at room temperature and 400 °C, respectively. Raman and x-ray photoelectron spectroscopy analyses of the implanted films indicate the presence of N2 molecules inside room-temperature implanted samples, but not for the case of implantation at 400 °C. Cross-section transmission electron microscopy images show the presence of near-surface voids, interpreted as remnants of N2-filled bubbles, in the former case. Annealing experiments show that about 50% of the total N inventory consists of nitrogen only weakly trapped inside the carbon matrix in room-temperature implanted films, this fraction being significantly reduced in samples held at 400 °C during implantation. © 1997 American Institute of Physics.
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61.43.Er Other amorphous solids
79.60.Ht Disordered structures
78.30.Hv Other nonmetallic inorganics
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Layer splitting process in hydrogen-implanted Si, Ge, SiC, and diamond substrates

Q.-Y. Tong, K. Gutjahr, S. Hopfe, U. Gösele, and T.-H. Lee

Appl. Phys. Lett. 70, 1390 (1997); http://dx.doi.org/10.1063/1.118586 (3 pages) | Cited 97 times

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Si, Ge, SiC, and diamond samples were implanted with H2+ at 120–160 keV with 5.0×1016 ions/cm2 (corresponding to 1.0×1017 H+ ions/cm2) and annealed at various temperatures to introduce hydrogen filled microcracks. An effective activation energy was determined for the formation of optically detectable surface blisters from the time required to form such blisters at various temperatures. The measured effective activation energies are close to the respective bond energies in all four materials. The time required to completely split hydrogen implanted layers from bonded silicon substrates and to transfer them onto oxidized silicon wafers is a factor of about 10 longer. Both processes, blister formation and layer splitting, show the same activation energy. © 1997 American Institute of Physics.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Cy Elemental semiconductors
62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Gh Other heat and thermomechanical treatments
61.72.uf Ge and Si
61.72.up Other materials
61.80.Jh Ion radiation effects

Highly oriented ferroelectric CaBi2Nb2O9 thin films deposited on Si(100) by pulsed laser deposition

S. B Desu, H. S Cho, and P. C. Joshi

Appl. Phys. Lett. 70, 1393 (1997); http://dx.doi.org/10.1063/1.118587 (3 pages) | Cited 24 times

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We report the successful deposition of highly c-axis oriented CaBi2Nb2O9 (CBN) thin films directly on p-type Si(100) substrates by pulsed laser deposition. The CBN thin films exhibited good structural, dielectric, and CBN/Si interface characteristics. The electrical measurements were conducted on CBN thin films in a metal–ferroelectric–semiconductor (MFS) capacitor configuration. The typical measured small signal dielectric constant and the dissipation factor at a frequency of 100 kHz were 80 and 0.051, respectively. The leakage current of the MFS capacitor structure was governed by the Schottky barrier conduction mechanism and the leakage current density was lower than 10−7A/cm2 at an applied electric field of 100 kV/cm. The capacitance–voltage measurements on MFS capacitors established good ferroelectric polarization switching characteristics. © 1997 American Institute of Physics.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.15.Fg Pulsed laser ablation deposition
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
73.30.+y Surface double layers, Schottky barriers, and work functions
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
84.32.Tt Capacitors

Improvement of the dielectric properties of Ta2O5 through substitution with Al2O3

R. J. Cava, W. F. Peck, J. J. Krajewski, G. L. Roberts, B. P. Barber, H. M. O’Bryan, and P. L. Gammel

Appl. Phys. Lett. 70, 1396 (1997); http://dx.doi.org/10.1063/1.119088 (3 pages) | Cited 38 times

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For bulk ceramic materials, small substitutions of Al2O3 in Ta2O5 are shown to cause a moderate enhancement of the dielectric constant. For compositions near 0.95Ta2O5–0.05Al2O3, the temperature coefficient of the dielectric constant at 20 °C dramatically decreases, from more than 200 ppm/°C for pure Ta2O5 to less than 20 ppm/°C. The quality factors (Q) at 1 MHz, are 2000–5000. Measurements to 14 GHz at 20 °C show that the dielectric constant is maintained to microwave frequencies, with a Q of ∼600 at 5 GHz. © 1997 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Micron-sized control of molecular orientation: Thin film deposition of liquid crystalline polymer on polyimide layer exposed with a linearly polarized laser

Toshiaki Itadani, Koichi Saito, Hiroyuki Niino, and Akira Yabe

Appl. Phys. Lett. 70, 1399 (1997); http://dx.doi.org/10.1063/1.118588 (3 pages) | Cited 4 times

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Linearly polarized laser chemical vapor deposition of liquid crystalline polymer was carried out on the polyimide layer which was exposed with a linearly polarized laser. We used 4[ω(2-methylpropenoyloxy)hexyloxy]-4′-cyanobiphenyl as a source of polymer film and a KrF excimer laser as an UV laser light source. Before deposition, exposure to a polyimide layer on a substrate was performed through a photomask. In both exposed and nonexposed areas, the film was deposited during laser irradiation. The molecular orientation of the film in the exposed area was perpendicular to the polarization of the exposed laser beam while that in the nonexposed area was parallel to the polarization of a deposition laser beam. © 1997 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.15.+e Liquid thin films
61.25.H- Macromolecular and polymers solutions; polymer melts
61.30.-v Liquid crystals

Lateral composition modulation in AlAs/InAs short period superlattices grown on InP(001)

J. Mirecki Millunchick, R. D. Twesten, D. M. Follstaedt, S. R. Lee, E. D. Jones, Yong Zhang, S. P. Ahrenkiel, and A. Mascarenhas

Appl. Phys. Lett. 70, 1402 (1997); http://dx.doi.org/10.1063/1.118589 (3 pages) | Cited 43 times

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Spontaneous lateral composition modulation as a consequence of the deposition of a (AlAs)n/(InAs)m short period superlattice on an InP(001) substrate is examined. Transmission electron microscopy images show distinct composition modulation appearing as vertical regions of In- and Al-rich materials alternating in the [110] projection. The periodicity of the modulation is 130 Å, and is asymmetric. The transmission electron and x-ray diffraction patterns from the structure exhibit distinct satellite spots which correspond to the lateral periodicity. Transmission electron microscopy images show that the individual superlattice layers possess cusplike undulations, which directly correlate with the composition modulation. Composition modulation in this sample appears to be coupled to morphological and compositional instabilities at the surface due to strain. © 1997 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Electrical properties and microstructures of Pt/Ba0.5Sr0.5TiO3/SrRuO3 capacitors

Mitsuaki Izuha, Kazuhide Abe, Mitsuo Koike, Shiro Takeno, and Noburu Fukushima

Appl. Phys. Lett. 70, 1405 (1997); http://dx.doi.org/10.1063/1.118590 (3 pages) | Cited 41 times

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Thin film polycrystalline Ba0.5Sr0.5TiO3 capacitors employing conductive perovskite oxide SrRuO3 as a bottom electrode were fabricated on Si substrates by rf-magnetron sputtering. Dielectric constants of these capacitors were observed to be 206, 214, and 146 for 60, 40, and 20 nm Ba0.5Sr0.5TiO3 (BSTO) thicknesses, respectively. The lowest SiO2 equivalent thickness of 0.54 nm was obtained for 20-nm-thick BSTO capacitors; their leakage current density was less than 1×10−7 A/cm2 for ±1.8 V bias. The cross-sectional transmission electron microscope observation revealed that BSTO and SrRuO3 (SRO) formed continuous columnar grains and showed epitaxial growth at the interface of BSTO/SRO within each column; this microstructure of the capacitors was tentatively designated “local epitaxial film.” © 1997 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.35.Ct Interface structure and roughness
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