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3 May 1999

Volume 74, Issue 18, pp. 2569-2723

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Time-frequency spectroscopy of an InGaAs/InP quantum-well exciton Bragg reflector

Kensuke Ogawa and Yasuhiro Matsui

Appl. Phys. Lett. 74, 2569 (1999); http://dx.doi.org/10.1063/1.123900 (3 pages) | Cited 1 time

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Ultrafast absorption saturation in an exciton Bragg reflector, consisting of InGaAs quantum wells embedded in InP/InGaAsP Bragg layers, is characterized by pump-induced transient reflectance spectroscopy at room temperature. Spectral modulation of the reflected probe pulses is caused by ultrafast absorption saturation of excitons in the quantum wells. The spectral modulation leads to an optical phase shift of 1.6 π. The exciton-induced phase shift is more than four times as large as that induced by free carriers in a Bragg reflector. © 1999 American Institute of Physics.
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42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency
78.66.Fd III-V semiconductors
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
78.47.-p Spectroscopy of solid state dynamics
42.79.Hp Optical processors, correlators, and modulators
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.30.Fs III-V and II-VI semiconductors

Optically switchable gratings based on polymer-dispersed liquid crystal films doped with a guest–host dye

Andy Y.-G. Fuh, M.-S. Tsai, L.-J. Huang, and T.-C. Liu

Appl. Phys. Lett. 74, 2572 (1999); http://dx.doi.org/10.1063/1.123901 (3 pages) | Cited 38 times

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In this work, we add a small amount of a guest–host dye G-206 in the polymer-dispersed liquid crystal mixtures to fabricate holographic gratings. Following formation, the grating is irradiated by a single Ar+ laser beam while probed by a He–Ne laser. Experimental results indicate that the first-order diffracted intensity of the probe beam increases significantly. Such an optically switchable diffraction effect is attributed to thermal expansion. The G-206 dye absorbs the Ar+ laser, subsequently resulting in thermal expansion. The liquid crystal (LC) droplets are then squeezed so that the LC molecules within the droplets are reoriented collectively. Thus, the refractive index difference between the LC-rich and polymer-rich stripes Δn increases. © 1999 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
61.30.-v Liquid crystals
65.40.De Thermal expansion; thermomechanical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Linear sensing of speckle-pattern displacements using a photorefractive GaP crystal

Alexei A. Kamshilin, Yasuhiro Iida, Satoshi Ashihara, Tsutomu Shimura, and Kazuo Kuroda

Appl. Phys. Lett. 74, 2575 (1999); http://dx.doi.org/10.1063/1.123902 (3 pages) | Cited 10 times

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Linear transformation of lateral speckle-pattern displacements into the transmitted intensity modulation is achieved in a photorefractive GaP crystal using the polarization self-modulation effect. The optical system is very simple, self-referenced, and as sensitive as an interferometer. © 1999 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
42.30.Ms Speckle and moiré patterns

High second-order optical nonlinearities in thermally poled sol-gel silica

V. Pruneri, G. Bonfrate, P. G. Kazansky, H. Takebe, K. Morinaga, M. Kohno, K. Kuwasaki, and T. Takeuchi

Appl. Phys. Lett. 74, 2578 (1999); http://dx.doi.org/10.1063/1.123903 (3 pages) | Cited 5 times

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Silica glass samples prepared by a sol-gel process, the mixture of silica sol for gelation and colloidal silica particles, have been thermally poled in vacuum by continuous high voltage (8–12 kV) at elevated temperature (280 °C). High second-order nonlinearities (>1 pm/V), located under the anodic surface, have been measured and the values are higher than those obtained in fused silica glass, poled under the same conditions. A model for thermal poling is suggested which explains the experimental results in sol-gel silica and the difference between thermal poling of sol-gel and fused silica. The granular structure and the boundaries of sol-gel silica seem to play a major role in establishing the electrical properties of the depletion layer during and after poling. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ce Glasses, quartz
42.65.An Optical susceptibility, hyperpolarizability
81.05.Kf Glasses (including metallic glasses)
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions
61.43.Fs Glasses
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

A 2.0 μm cutoff wavelength separate absorption, charge, and multiplication layer avalanche photodiode using strain-compensated InGaAs quantum wells

J. Christopher Dries, Milind R. Gokhale, and Stephen R. Forrest

Appl. Phys. Lett. 74, 2581 (1999); http://dx.doi.org/10.1063/1.123904 (3 pages) | Cited 4 times

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We report an avalanche photodiode structure for use at wavelengths as long as 2.1 μm. Light is absorbed in a 100 period structure consisting of In0.83Ga0.17As quantum wells strain compensated by In0.83Ga0.17P barrier layers. Photogenerated electrons are injected into a high field In0.52Al0.48As (ionization rate ratio = 0.2) gain region initiating low noise avalanche multiplication. Primary dark currents of ∼5 nA and responsivities of 45 A/W at a wavelength of 1.9 μm are observed. © 1999 American Institute of Physics.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Microsecond photoresponse in liquid crystalline photoconductor doped with C70 under illumination of visible light

Masahiro Funahashi and Jun-ichi Hanna

Appl. Phys. Lett. 74, 2584 (1999); http://dx.doi.org/10.1063/1.123905 (3 pages) | Cited 10 times

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Steady-state and transient photocurrent measurements were carried out for C70-doped liquid crystalline photoconductor, 2-(4′-octylphenyl)-6-dodecyloxy-naphthalene (8-PNP-O12) in order to clarify its spectral photosensitization in visible region. The C70-doped liquid crystal cells exhibited a photoresponse in visible region of 400–700 nm corresponding to the optical absorption of C70. In the time-of-flight measurement, the fast transient photosignals with fast rise and decay on the order of microseconds were obtained even in a bulk excitation condition, which is governed by the carrier transit. These indicated that C70 can inject both electron and hole into 8-PNP-O12 when photoexcited and does not deteriorate the carrier transport, demonstrating a possible application of liquid crystalline photoconductors to high-speed photosensors with a fast response in microseconds. © 1999 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects

Red organic electroluminescence devices with a reduced porphyrin compound, tetraphenylchlorin

Y. Sakakibara, S. Okutsu, T. Enokida, and T. Tani

Appl. Phys. Lett. 74, 2587 (1999); http://dx.doi.org/10.1063/1.123906 (3 pages) | Cited 35 times

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We constructed red organic electroluminescence (EL) devices with a reduced porphyrin compound, tetraphenylchlorin, that was doped at various concentrations (0.5, 1.7, and 3.7 wt %) within a tris(8-hydroxyquinoline) aluminum (Alq3) host layer. We measured their EL properties and found that all three devices emitted a red EL band at 660 nm with a width of 20 nm. Emission color of the 1.7 and 3.7 wt % devices was red (chromaticity coordinates x = 0.67, y = 0.29 and x = 0.78, y = 0.21) and the luminance maximum was 100 and 24 cdm−2, respectively. The 0.5 wt % device emitted a green Alq3 EL band as well, and showed an increase in relative intensity of the Alq3 emission with increasing applied voltage. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.66.Qn Polymers; organic compounds
85.60.Pg Display systems

Amplified spontaneous emission and lasing in conducting polymers and fluorescent dyes in opals as photonic crystals

K. Yoshino, S. Tatsuhara, Y. Kawagishi, M. Ozaki, A. A. Zakhidov, and Z. V. Vardeny

Appl. Phys. Lett. 74, 2590 (1999); http://dx.doi.org/10.1063/1.123907 (3 pages) | Cited 48 times

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Spectral narrowing of photoluminescence (PL) and evolution of sharp emission lines upon optical excitation have been observed in opals made of SiO2 spheres infiltrated with conducting polymers such as OOPPV and MDDOPPV and also fluorescent dyes such as rhodamine 6G, NK-3483, and coumarin 120. Their emission properties are dependent on the sort of the opal and the solvents used for infiltration. With increasing optical excitation intensity, spectral narrowing and evolution of sharp lines have been observed in the green opal infiltrated with OOPPV, MDDOPPV, or rhodamine 6G but not in the infiltrated red and purple opals. With a solvent having a refractive index similar to that of SiO2, the evolution of the sharp emission lines is greatly suppressed and the lines exhibit a blueshift with decreasing refractive index. In NK-3483 and coumarin 120 which show red and purple PL, respectively, evolution of sharp lines is observed when they were infiltrated in red and purple opals, respectively, but not in other opals. These results are discussed in terms of amplified spontaneous emission and multimode lasing due to optical feedback in the opal matrix with a periodic structure. © 1999 American Institute of Physics.
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78.45.+h Stimulated emission
78.55.Kz Solid organic materials
42.70.Hj Laser materials
42.70.Qs Photonic bandgap materials
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems
42.70.Jk Polymers and organics
42.55.Rz Doped-insulator lasers and other solid state lasers

Polarity- and voltage-controlled color-variable light-emitting devices based on conjugated polymers

Y. Z. Wang, R. G. Sun, D. K. Wang, T. M. Swager, and A. J. Epstein

Appl. Phys. Lett. 74, 2593 (1999); http://dx.doi.org/10.1063/1.123952 (3 pages) | Cited 16 times

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There is increased interest in developing multilayer color-variable light-emitting devices. So far, the multilayer color-variable light-emitting devices mainly have focused on polarity-controlled two-color light-emitting devices. We report here the fabrication and study of voltage- and polarity-controlled multilayer multicolor light-emitting devices based on pyridine-containing conjugated polymers and derivatives of polyacetylene. The devices emit red light under forward bias and multiple colors of light (from orange-red to green) under reverse bias. The colors under reverse bias are controlled by the magnitude of the applied voltages. © 1999 American Institute of Physics.  
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42.70.Jk Polymers and organics
78.66.Qn Polymers; organic compounds
85.60.Jb Light-emitting devices

Enhancement of the photoluminescence intensity in short-period GaAs/AlAs superlattices with different well and barrier thickness

S. Krylyuk, D. V. Korbutyak, V. G. Litovchenko, R. Hey, H. T. Grahn, and K. H. Ploog

Appl. Phys. Lett. 74, 2596 (1999); http://dx.doi.org/10.1063/1.123908 (3 pages) | Cited 12 times

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The transition from an indirect to a direct energy band structure has been induced in short-period GaAs/AlAs superlattices by going from a symmetric to an asymmetric distribution of the well and the barrier thickness within the unit cell of the superlattice. Reducing the barrier thickness dB to half the well thickness dW moves the lowest state in the conduction band from the X point in the AlAs barrier to the Γ point in the GaAs well. For dW = 2dB, the band structure becomes therefore direct for all values of dW. This change in the type of energy gap is accompanied by a significant enhancement of the integrated photoluminescence intensity for asymmetric superlattices. © 1999 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
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Plasma vacuum ultraviolet emission in an electron cyclotron resonance etcher

C. Cismaru and J. L. Shohet

Appl. Phys. Lett. 74, 2599 (1999); http://dx.doi.org/10.1063/1.123909 (3 pages) | Cited 25 times

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This work investigates the vacuum ultraviolet (VUV) emission from various feed gases producing plasmas in an electron cyclotron resonance etcher. Absolute measurements of plasma VUV emission at typical pressures for processing between 0.5 and 5 mTorr, and microwave powers between 700 and 1300 W, show levels of irradiance at the wafer position of the order of tenths of mW/cm2 and integrated photon fluxes in the 1014 photons/cm2 s range. The reported level of VUV emission is sufficient to induce radiation damage in typical metal–oxide–semiconductor devices in the form of flatband voltage shift and inversion of lightly doped substrates. © 1999 American Institute of Physics.
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52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
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Epitaxial aluminum carbide formation in 6H–SiC by high-dose Al+ implantation

J. Stoemenos, B. Pécz, and V. Heera

Appl. Phys. Lett. 74, 2602 (1999); http://dx.doi.org/10.1063/1.123910 (3 pages) | Cited 5 times

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Aluminum carbide precipitates are formed after Al ion implantation with dose 3×1017 cm−2 at 500 °C into single crystalline 6H–SiC. The aluminum carbide (Al4C3) precipitates are in epitaxial relation with 6H–SiC matrix, having the following orientation relation, [0001]6H–SiC//[0001]Al4C3, and [11math0]6H–SiC//[11math0]Al4C3, as transmission electron microscopy reveals. The aluminum carbide appears around the maximum of the Al depth distribution. Silicon precipitates were also detected in the same zone. © 1999 American Institute of Physics.
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61.82.Fk Semiconductors
61.72.up Other materials
85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Hd Other semiconductors
81.30.Mh Solid-phase precipitation
64.75.-g Phase equilibria
61.80.Jh Ion radiation effects

Laser-based method for fabricating monodisperse metallic nanoparticles

J. Bosbach, D. Martin, F. Stietz, T. Wenzel, and F. Träger

Appl. Phys. Lett. 74, 2605 (1999); http://dx.doi.org/10.1063/1.123911 (3 pages) | Cited 50 times

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An experimental method is presented for fabrication of almost monodisperse metal nanoparticles on substrate surfaces. It relies on substantial narrowing of broad size distributions through irradiation with short laser pulses by exploiting the size dependent optical absorption coefficient of the metal particles. Successive irradiation by applying two laser wavelengths completely removes the smallest clusters of the distribution and causes a size reduction of the largest particles. Finally, only clusters with diameters in a very narrow size interval remain on the surface. By using this method, Ag clusters with mean diameters of 〈d〉 = 10 nm and size distributions with standard deviations of Δd/〈d〉 = 0.13 have been prepared. © 1999 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys

Quantum box size effect on vertical self-alignment studied using cross-sectional scanning tunneling microscopy

B. Legrand, J. P. Nys, B. Grandidier, D. Stiévenard, A. Lemaître, J. M. Gérard, and V. Thierry-Mieg

Appl. Phys. Lett. 74, 2608 (1999); http://dx.doi.org/10.1063/1.123912 (3 pages) | Cited 23 times

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InAs quantum boxes separated by GaAs spacer layers are known to exhibit a vertical self-organization along the growth direction. The alignment probability between two sets of quantum boxes depends strongly on the spacer layer thickness Zs. In this letter, we study samples containing multiple arrays of quantum boxes separated by GaAs spacer layers of various thicknesses, using cross-sectional scanning tunneling microscopy. This work experimentally evidences that the spacer layer characteristic thickness Zs0 below which a vertical self-alignment occurs, depends on the size of the quantum boxes. These results are interpreted using a theoretical two-dimensional model. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Migration and coalescence of Xe nanoprecipitates in Al induced by electron irradiation at 300 K

C. W. Allen, R. C. Birtcher, S. E. Donnelly, K. Furuya, N. Ishikawa, and M. Song

Appl. Phys. Lett. 74, 2611 (1999); http://dx.doi.org/10.1063/1.123913 (3 pages) | Cited 13 times

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Effects of 1 MeV electron irradiation on Xe precipitates in Al, formed by ion implantation, have been observed in situ by high-voltage transmission electron microscopy. Individual Xe precipitates undergo melting and recrystallization, migration which leads to coalescence, and shape changes. These processes are driven by the production of defects without either cascade defect production or the introduction of additional Xe atoms. Precipitate migration is due to an irradiation-induced surface diffusion process on the Xe/Al interfaces. Coalescence of close precipitates is enhanced by directed motion as a result of the net displacement of Al atoms out of the volume between them. © 1999 American Institute of Physics.
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64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
61.80.Fe Electron and positron radiation effects
61.82.Bg Metals and alloys
61.72.Qq Microscopic defects (voids, inclusions, etc.)
61.72.up Other materials
68.35.Fx Diffusion; interface formation
66.30.Lw Diffusion of other defects

Thermal crystallization of amorphous Si/SiO2 superlattices

M. Zacharias, J. Bläsing, P. Veit, L. Tsybeskov, K. Hirschman, and P. M. Fauchet

Appl. Phys. Lett. 74, 2614 (1999); http://dx.doi.org/10.1063/1.123914 (3 pages) | Cited 89 times

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Annealing of amorphous Si/SiO2 superlattices produces Si nanocrystals. The crystallization has been studied by transmission electron microscopy and x-ray analysis. For a Si layer thinner than 7 nm, nearly perfect nanocrystals are found. For thicker layers, growth faults and dislocations exist. Decreasing the a-Si layer thickness increases the inhomogeneous strain by one order of magnitude. The origin of the strain in the crystallized structure is discussed. The crystallization temperature increases rapidly with decreasing a-Si layer thickness. An empirical model that takes into account the Si layer thickness, the Si/SiO2 interface range, and a material specific constant has been developed. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.72.Cc Kinetics of defect formation and annealing
61.46.-w Structure of nanoscale materials
61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Nn Stacking faults and other planar or extended defects

Simulation and characterization of the selective area growth process

M. A. Alam, R. People, E. Isaacs, C. Y. Kim, K. Evans-Lutterodt, T. Siegrist, T. L. Pernell, J. Vandenberg, S. K. Sputz, S. N. G. Chu, D. V. Lang, L. Smith, and M. S. Hybertsen

Appl. Phys. Lett. 74, 2617 (1999); http://dx.doi.org/10.1063/1.123915 (3 pages) | Cited 17 times

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A simple three-dimensional vapor phase model is used to interpret and clarify the selective area growth process. The model predicts both normal and anomalous profiles of thickness and composition, including long range effects. These are verified by an extensive set of experiments. © 1999 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.40.Sz Deposition technology

Bonding modifications in carbon nitride films induced by thermal annealing: An x-ray absorption near edge study

I. Jiménez, W. M. Tong, D. K. Shuh, B. C. Holloway, M. A. Kelly, P. Pianetta, L. J. Terminello, and F. J. Himpsel

Appl. Phys. Lett. 74, 2620 (1999); http://dx.doi.org/10.1063/1.123916 (3 pages) | Cited 33 times

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The thermal stability of nonstoichiometric carbon nitride films has been studied by x-ray absorption near edge spectroscopy. Amorphous carbon nitride thin films were annealed in vacuum up to 1150 °C revealing the presence of nitrogen in different bonding configurations. Annealing to 450 °C results in the loss of ∼50% of the nitrogen. The remaining nitrogen is bonded to carbon within a graphitic framework and it evolves into a more stable configuration with increasing temperature without significant N loss up to 820 °C. Beyond this temperature, nitrogen loss occurs without important structural changes. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Dv Thermal stability; thermal effects
78.70.Dm X-ray absorption spectra
61.50.Lt Crystal binding; cohesive energy
61.72.Cc Kinetics of defect formation and annealing

Light-controlled erasure of induced χ(2) in thermally poled glasses

S. Montant, A. Le Calvez, E. Freysz, A. Ducasse, V. Nazabal, E. Fargin, and G. Le Flem

Appl. Phys. Lett. 74, 2623 (1999); http://dx.doi.org/10.1063/1.123917 (3 pages) | Cited 3 times

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We demonstrate that the induced second order nonlinearity χ(2) generated in thermal poled doped borosilicate glasses can be erased by a prolonged exposure to near IR laser radiation. The evolution of the second harmonic signal with respect to laser time exposure, intensity and wavelength is reported. The IR laser radiation induced relaxation of the χ(2) is mainly related to two-photon absorption of the glass. The nonexponential time dependence of the second harmonic signal agrees with a simple model involving diffusion of photoexcited carriers. The reversible erasure process is also observed when the sample is exposed to near ultraviolet laser radiation. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Ce Glasses, quartz
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability
81.40.Tv Optical and dielectric properties related to treatment conditions

Interfacial defects in thin refractory metal films imaged by low-energy electron microscopy

W. Świȩch, M. Mundschau, and C. P. Flynn

Appl. Phys. Lett. 74, 2626 (1999); http://dx.doi.org/10.1063/1.123918 (3 pages) | Cited 6 times

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Low-energy electron microscopy is employed to image defects at buried interfaces through the strains they cause at the front surface. The interfacial defects studied here occur in high quality films of Mo(110) grown by molecular beam epitaxy on Al2O3(11math0). The defects include steps and inclusions on the original sapphire surface and interfacial dislocations created where epitaxial strain causes slip. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.Dv Composition, segregation; defects and impurities
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Plasmon energy shift in mesoporous and double length-scale ordered nanoporous silica

J. S. Yin and Z. L. Wang

Appl. Phys. Lett. 74, 2629 (1999); http://dx.doi.org/10.1063/1.123919 (3 pages) | Cited 9 times

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Electron energy-loss spectroscopy studies are reported on three different types of structures: solid silica spheres, mesoporous silica, and the double length-scale ordered (DLSO) porous silica. The mesoporous silica has porosity at the length scale of nanometers. The DLSO porous silica has an additional ordering on submicron hollows created by the template polystyrene spheres. The plasmon energy of the porous silica shows a significant shift in comparison to that of the bulk, suggesting that the local density of the bound electrons in the porous structures is lower than that in the bulk. This gives the possibility of tuning the electronic structure of silica by varying its porosity, leading to even lower dielectric loss. © 1999 American Institute of Physics.
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
79.20.Kz Other electron-impact emission phenomena
61.43.Gt Powders, porous materials
77.22.Gm Dielectric loss and relaxation
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Characteristics of homoepitaxial 4H-SiC films grown on c-axis substrates offcut towards 〈1100〉 or 〈1120〉

B. E. Landini and G. R. Brandes

Appl. Phys. Lett. 74, 2632 (1999); http://dx.doi.org/10.1063/1.123920 (3 pages) | Cited 9 times

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Substrate orientation plays a critical role in determining SiC epilayer quality, but limited work has been done to examine the effect of offcut directions on 4H-SiC epilayers. 4H-SiC epilayers were grown on substrates offcut 8° towards either the 〈1100〉 or the 〈1120〉 crystalline direction. Epilayers up to 15.5 μm thick, possessing smooth morphologies free of large-scale step bunching, were grown on both substrate orientations. Triangular defects were observed primarily on the wafer periphery, and the triangular defect density depended only on offcut angle. Atomic force microscopy analysis confirmed smooth surfaces for epilayers up to 15.5 μm thick grown on 〈1100〉 offcut substrates. Low-energy electron diffraction analysis of epilayers grown on substrates offcut towards 〈1100〉 showed an ordered surface. Nitrogen and aluminum doping were successfully obtained for epilayers grown on substrates offcut towards 〈1100〉, and n-type and p-type doping control were demonstrated. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Hd Other semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Qq Microscopic defects (voids, inclusions, etc.)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Polymerization in nematic emulsions

J. Lanzo, F. P. Nicoletta, G. De Filpo, and G. Chidichimo

Appl. Phys. Lett. 74, 2635 (1999); http://dx.doi.org/10.1063/1.123921 (3 pages) | Cited 8 times

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This letter deals with a procedure to obtain polymer-dispersed liquid-crystal films by photopolymerization of nematic emulsions. The major advantage of such a procedure is that homogeneously micron-sized liquid-crystal droplets in an organic monomer matrix can be obtained before polymerization takes place. The electro-optical changes induced in nematic emulsions by the polymerization of the fluid matrix are reported. The effects due to the application of an external field during the polymerization process on the resulting films are also discussed. © 1999 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
82.35.-x Polymers: properties; reactions; polymerization
82.70.Kj Emulsions and suspensions
78.20.Jq Electro-optical effects
82.50.-m Photochemistry
68.15.+e Liquid thin films
64.70.M- Transitions in liquid crystals

The influence of atomic structure on the formation of electrical barriers at grain boundaries in SrTiO3

N. D. Browning, J. P. Buban, H. O. Moltaji, S. J. Pennycook, G. Duscher, K. D. Johnson, R. P. Rodrigues, and V. P. Dravid

Appl. Phys. Lett. 74, 2638 (1999); http://dx.doi.org/10.1063/1.123922 (3 pages) | Cited 44 times

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An experimental atomic resolution analysis of an undoped Σ5 36° [001] tilt grain boundary in SrTiO3 shows that the structure contains incomplete oxygen octahedra. These incomplete octahedra act as effective oxygen vacancies and lead to a fixed, positive boundary charge. Annealing the boundary in the presence of MnO2 does not change the atomic structure of the boundary plane, and results in a high concentration of Mn3+ (acceptor) enrichment at the specific Ti4+ locations in closest proximity to the effective oxygen vacancies. This result can be explained in terms of standard charge compensation models and indicates that the formation of electrical barriers at oxide grain boundaries may be influenced by the atomic structure of the boundary plane. © 1999 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
71.55.Ht Other nonmetals
61.72.J- Point defects and defect clusters
79.20.Kz Other electron-impact emission phenomena
61.72.Cc Kinetics of defect formation and annealing

Atomic force microscopy of work functions on the nanometer scale

M. P. O’Boyle, T. T. Hwang, and H. K. Wickramasinghe

Appl. Phys. Lett. 74, 2641 (1999); http://dx.doi.org/10.1063/1.123923 (2 pages) | Cited 14 times

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The Kelvin probe force microscope, introduced some years ago, has opened up several avenues of investigation. In this letter, we demonstrate that the technique is capable of distinguishing constituents of a metal alloy through their work-function differences. The intermetallics in the alloy are clearly resolved. We discuss the basic principles of the measurement technique and present our results on aluminum/copper surfaces. The limits of the technique are also discussed. © 1999 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.35.Dv Composition, segregation; defects and impurities
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy
73.40.Cg Contact resistance, contact potential
07.79.Lh Atomic force microscopes
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