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18 Feb 2002

Volume 80, Issue 7, pp. 1111-1310

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Fast analog electro-optic effect in an achiral smectic C liquid crystal in a transverse electrode configuration

Chang-Jae Yu, Jin-Yun Kim, and Sin-Doo Lee

Appl. Phys. Lett. 80, 1111 (2002); http://dx.doi.org/10.1063/1.1450056 (3 pages) | Cited 4 times

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We demonstrated a fast analog electro-optic effect in an achiral smectic C (ASC) liquid crystal in a transverse electrode configuration. In this configuration, wide viewing characteristics are also achieved. The analog gray scales in the ASC mode are obtained in a dielectrically driving scheme as those in the nematic mode. The rising and falling times, 3.2 and 13.8 ms, are suitable for video-rate display applications. © 2002 American Institute of Physics.
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78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Two-photon absorption properties of commercial fused silica and germanosilicate glass at 264 nm

Adrian Dragomir, John G. McInerney, David N. Nikogosyan, and Peter G. Kazansky

Appl. Phys. Lett. 80, 1114 (2002); http://dx.doi.org/10.1063/1.1448387 (3 pages) | Cited 15 times

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Using high-intensity femtosecond pulses at λ = 264 nm, we have measured the two-photon absorption (TPA) coefficient in three fused silica samples Suprasil, Herasil, Infrasil (Heraeus) and in 3.5 mol % Ge-doped fused silica. While in fused silica samples the TPA coefficient value is about 2×10−11 cm/W, in germanosilicate glass it equals (42±3)×10−11 cm/W. © 2002 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Solvent-assisted dye-diffusion thermal transfer for electronic imaging applications

Chung-Chih Wu, Sun-Wen Lin, Chieh-Wei Chen, and Jui-Hung Hsu

Appl. Phys. Lett. 80, 1117 (2002); http://dx.doi.org/10.1063/1.1447001 (3 pages) | Cited 2 times

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Molecularly doped polymers processed by dye-diffusion thermal transfer (D2T2) have wide applications in electronic imaging. For the sake of stability, it is usually desired that the host polymers have high glass-transition temperatures (Tg), which however implies high processing temperatures. In this letter, we show that in an atmosphere of organic solvent vapor, effective dye-diffusion thermal transfer may be carried out at temperatures much below the Tg of a host polymer. The atmosphere of solvent vapor ensures incorporation of solvent molecules into the polymer throughout the process and causes the plasticization effect. As a consequence, the effective Tg of the system is lowered and the diffusion of dyes in the host polymer is enhanced. Through such a process, polymers of higher Tg and wider ranges of dye molecules may be used in D2T2 without losing the processing compatibility. Furthermore, carrying out D2T2 at lower temperatures is beneficial to the resolutions of transferred features due to the suppression of vaporization of dyes. © 2002 American Institute of Physics.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
66.30.J- Diffusion of impurities
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
64.70.F- Liquid-vapor transitions

Zero permittivity materials: Band gaps at the visible

N. Garcia, E. V. Ponizovskaya, and John Q. Xiao

Appl. Phys. Lett. 80, 1120 (2002); http://dx.doi.org/10.1063/1.1449529 (3 pages) | Cited 34 times

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We theoretically discuss the possibility of having materials with zero effective permittivity that would create band gaps in a wide range of frequencies up to the visible. The physical realization of these materials is also discussed in terms of embedding metallic nanoparticles and nanowires in a dielectric medium. In the limit of long wavelengths, these composites will behave like a homogeneous medium with zero permittivity that will completely reflect electromagnetic waves. We present transmittivity calculations by using finite-difference time domain for periodic structures that proves the concept and shows the validity of the long wavelength approximation. The striking result is that the cutoff frequency ωc is determined by the lattice parameter of the composite. By properly choosing the lattice constant of the composite and permittivity of metal and dielectric constituents, we can have full band gaps at any frequency range but especially in the visible. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)

Enhancing the surface passivation of TiO2 coated silicon wafers

B. S. Richards, J. E. Cotter, and C. B. Honsberg

Appl. Phys. Lett. 80, 1123 (2002); http://dx.doi.org/10.1063/1.1445810 (3 pages) | Cited 24 times

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In this letter, we demonstrate good surface passivation of lightly diffused n-type solar cell emitters using titanium dioxide (TiO2) thin films treated with a furnace oxidation process. Transient-photoconductance decay, x-ray photoelectron spectroscopy, and scanning electron microscopy measurements indicate that the silicon dioxide layer formed at the TiO2:Si interface provides excellent surface passivation. Emitter dark saturation current densities of 4.7×10−14 A/cm2 are achieved by this method, demonstrating that TiO2 films are compatible with high-efficiency solar cell structures. © 2002 American Institute of Physics.
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81.65.Rv Passivation
84.60.Jt Photoelectric conversion
73.50.Pz Photoconduction and photovoltaic effects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.61.Le Other inorganic semiconductors

High-gain coupled InGaAs quantum well InAs quantum dot AlGaAs–GaAs–InGaAs–InAs heterostructure diode laser operation

G. Walter, T. Chung, and N. Holonyak

Appl. Phys. Lett. 80, 1126 (2002); http://dx.doi.org/10.1063/1.1451989 (3 pages) | Cited 20 times

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Data are presented showing that a single-layer InAs quantum dot (QD) laser in the AlGaAs–GaAs–InGaAs–InAs heterostructure system is improved in gain and continuous wave (cw) room temperature operation by coupling, via tunneling, auxiliary strained-layer InGaAs quantum wells (QWs) to the single InAs QD layer to assist carrier collection and thermalization. A QW-assisted single-layer InAs QD laser, a QD+QW laser, is demonstrated that operates cw (300 K), and at diode length 150 μm in pulsed operation exhibits gain as high as ∼ 100 cm−1. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
78.67.Hc Quantum dots

Above-room-temperature optically pumped 4.12 μm midinfrared vertical-cavity surface-emitting lasers

F. Zhao, H. Wu, Lalith Jayasinghe, and Z. Shi

Appl. Phys. Lett. 80, 1129 (2002); http://dx.doi.org/10.1063/1.1449540 (3 pages) | Cited 16 times

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Optically pumped lead salt vertical-cavity surface-emitting lasers (VCSELs) with a nine period PbSe/PbSrSe quantum well active region operating above room temperature in pulsed mode are reported. The gain peak and cavity mode of the VCSEL structure are in resonance at 300 K. A power output of 40 mW is obtained at room temperature and it does not show saturation. The room-temperature threshold pump density is 200 kW/cm2. The lasing wavelength of λ = 4.12 μm remains nearly constant over a temperature range of 280–310 K. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
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T-junction tuning system for large-area surface-wave plasma sources

Jozef Kudela, Tibor Terebessy, Igor Odrobina, and Masashi Kando

Appl. Phys. Lett. 80, 1132 (2002); http://dx.doi.org/10.1063/1.1448399 (3 pages) | Cited 6 times

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A tuning system for large-area surface-wave plasma source is proposed. The system is based on T-junction tuning elements applied directly on the plasma-dielectric resonator and it provides remarkable control of microwave discharges sustained on large areas. Along with the control of matching, it enables also the control of discharge diameter and, most importantly, control of the radial plasma density profile. Considering its principle of operation, the system is applicable to any large-area guided-wave plasma source, magnetized or unmagnetized. © 2002 American Institute of Physics.
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52.50.Dg Plasma sources
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Elasticity and magnetoelasticity of Fe–Ga solid solutions

Manfred Wuttig, Liyang Dai, and James Cullen

Appl. Phys. Lett. 80, 1135 (2002); http://dx.doi.org/10.1063/1.1450045 (3 pages) | Cited 64 times

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Continuous-wave measurements of the shear elastic constants of bcc Fe–Ga solid solutions show that the constant C44 is independent of the gallium composition while the constant ½(C11–C12) decreases linearly and extrapolates to zero at 26 at. % Ga. This result indicates that the Fe–Ga solid solution is inhomogeneous and contains clusters consisting of embryos of a martensitic phase. The increasing softness of ½(C11–C12) then reflects an increase of the embryo density. A model assuming that the clusters are centered around next-nearest Ga pairs reproduces the known composition dependence of the magnetostrictive constant λ100 in the composition range 0<XGa<0.23 with only one adjustable parameter. Its value suggests a cluster size of 12 atoms. © 2002 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions

Effect of composition inhomogeneity on the photoluminescence of InGaN/GaN multiple quantum wells upon thermal annealing

Chang-Cheng Chuo, Mao Nan Chang, Fu-Ming Pan, Chia-Ming Lee, and Jen-Inn Chyi

Appl. Phys. Lett. 80, 1138 (2002); http://dx.doi.org/10.1063/1.1450262 (3 pages) | Cited 9 times

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The optical properties of thermally annealed InGaN/GaN multiple quantum wells were investigated by low-temperature photoluminescence measurements. It is found that the photoluminescence peak exhibits a redshift followed by a blueshift as the annealing time is increased. In contrast, the assigned photoluminescence peak from an In-rich dot-like structure shows a monotonic blueshift with more annealing time. Transmission electron microscopic observation confirms that the density of dot-like structures is reduced after thermal annealing, indicating that phase separation does not take place in these samples. Instead, in-plane and out-plane outdiffusion of dot-like structures is proposed to account for the spectral shift with more annealing time. Based on this diffusion model, a quantized state transition in the quantum well along with the composition inhomogeneity and piezoelectric field is considered to be the dominant luminescence mechanism. © 2002 American Institute of Physics.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.Cc Kinetics of defect formation and annealing
68.65.Fg Quantum wells

Spatially resolved cathodoluminescence of laterally overgrown GaN pyramids on (111) silicon substrate: Strong correlation between structural and optical properties

Yong-Hoon Cho, H. M. Kim, T. W. Kang, J. J. Song, and W. Yang

Appl. Phys. Lett. 80, 1141 (2002); http://dx.doi.org/10.1063/1.1450250 (3 pages) | Cited 6 times

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Spatially resolved optical emission properties of laterally overgrown GaN hexagonal pyramids on (111) Si substrates are investigated by cathodoluminescence (CL) spectroscopy and mapping techniques. The results are compared with structural properties obtained by scanning and transmission electron microscopic techniques. To clarify the origin of the band edge and yellow-band emissions from the GaN pyramids, wavelength-resolved CL properties of normal and cleaved GaN pyramids are investigated in top and/or cross-sectional view configurations. The cross-sectional view CL images for cleaved GaN pyramid samples show significant differences between the overgrown areas on top of the mask and the coherently grown regions over the windows. Precise reverse (identical) contrast between the band-edge (yellow-band) emission intensity and threading dislocation density is observed by comparing the cross-sectional view CL and transmission electron microscopic images. It is demonstrated that a strong correlation exists between structural defects and optical properties in laterally overgrown GaN hexagonal pyramids. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.-a Thin film structure and morphology

Role of hydrogen for the elastic properties of alumina thin films

Jochen M. Schneider, Karin Larsson, Jun Lu, Eva Olsson, and Björgvin Hjörvarsson

Appl. Phys. Lett. 80, 1144 (2002); http://dx.doi.org/10.1063/1.1448389 (3 pages) | Cited 37 times

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We describe the role of the presence of hydrogen on the elastic properties of AlxOyHz (0.32 ⩽ x ⩽ 0.4; 0.54 ⩽ y ⩽ 0.6; 3×10−4 ⩽ z ⩽ 0.14) films. The films were deposited by reactive magnetron sputtering in an Ar/O2/H2O discharge and were studied by Rutherford backscattering spectrometry, nuclear resonance analysis, selected area electron diffraction, as well as nanoindentation. As the hydrogen concentration is increased from 0.03% to 13.9% the measured elastic modulus value is reduced by approximately 53%. The measured elastic modulus is in excellent agreement with our electronic structure calculations. The large scattering in the reported values of the elastic properties of amorphous alumina thin films can readily be understood by hydrogen incorporation during synthesis. © 2002 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.Nq Composition and phase identification
68.35.Gy Mechanical properties; surface strains
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
82.80.-d Chemical analysis and related physical methods of analysis
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.43.Er Other amorphous solids

Formation and decay mechanisms of electron–hole pairs in amorphous SiO2

T. Uchino, M. Takahashi, and T. Yoko

Appl. Phys. Lett. 80, 1147 (2002); http://dx.doi.org/10.1063/1.1448173 (3 pages) | Cited 6 times

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We present theoretical evidence for the creation of an electron–hole pair at an edge-sharing SiO4 site that is supposed to exist in a-SiO2 as an intrinsic structural defect. The present electron–hole pair consists of a nonbridging oxygen hole center and an E′ center, but these paramagnetic defects do not form a close pair but are separately located by over ∼4 Å. The subsequent decay mechanism along with the related radiolytic process is also discussed. © 2002 American Institute of Physics.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.43.Er Other amorphous solids

Investigation of nanoscale structure in digital layers of Mn/GaAs and MnGa/GaAs

G. Kioseoglou, S. Kim, Y. L. Soo, X. Chen, H. Luo, Y. H. Kao, Y. Sasaki, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 80, 1150 (2002); http://dx.doi.org/10.1063/1.1448658 (3 pages) | Cited 10 times

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Grazing incidence x-ray scattering (GIXS) and x-ray diffraction (XRD) techniques have been employed to study the microscopic structure of magnetic digital layers of Mn/GaAs and MnGa/GaAs. Samples with various GaAs layer thickness (8 to 16 monolayers) and a half monolayer of either Mn or MnGa were prepared by low-temperature molecular-beam epitaxy. All digital alloys consist of 50 periods of magnetic layers separated by GaAs. High crystalline quality was verified and the periodicity and layer thickness were determined from the GIXS and XRD data. In order to investigate the magnetic properties, we performed magnetization measurements on all samples using superconducting quantum interference device magnetometry (SQUID). © 2002 American Institute of Physics.
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75.75.-c Magnetic properties of nanostructures
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
72.25.Dc Spin polarized transport in semiconductors
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Cc Other ferromagnetic metals and alloys

Preparation of polycrystalline boron carbide thin films at room temperature by pulsed ion-beam evaporation

H. Suematsu, K. Kitajima, T. Suzuki, W. Jiang, K. Yatsui, K. Kurashima, and Y. Bando

Appl. Phys. Lett. 80, 1153 (2002); http://dx.doi.org/10.1063/1.1449539 (3 pages) | Cited 10 times

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Polycrystalline boron carbide (B4C) thin films have been prepared by a pulsed ion-beam evaporation technique without heating substrates or annealing samples. Here, we clearly demonstrate the possibility of preparing B4C thin films for electronic device applications. © 2002 American Institute of Physics.
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81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.05.Hd Other semiconductors
68.55.A- Nucleation and growth

Photorefractive polymer composites fabricated by injection molding

J. A. Herlocker, C. Fuentes-Hernandez, J. F. Wang, N. Peyghambarian, B. Kippelen, Q. Zhang, and S. R. Marder

Appl. Phys. Lett. 80, 1156 (2002); http://dx.doi.org/10.1063/1.1451990 (3 pages) | Cited 1 time

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We report on the fabrication of bulk samples of photorefractive polymers using the injection molding technique. The photorefractive properties of these materials are evaluated by four-wave mixing and two-beam coupling experiments. Samples with good optical quality, high diffraction efficiency, and net optical gain are obtained. © 2002 American Institute of Physics.
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42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
81.10.Fq Growth from melts; zone melting and refining
42.86.+b Optical workshop techniques

Fine crystalline grain model for the determination of the morphology of ultrathin amorphous silicon films

Sukti Hazra, Isao Sakata, Mitsuyuki Yamanaka, and Eiichi Suzuki

Appl. Phys. Lett. 80, 1159 (2002); http://dx.doi.org/10.1063/1.1450046 (3 pages) | Cited 8 times

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To obtain the morphology of ultrathin hydrogenated amorphous silicon (a-Si:H) films with thicknesses of 2–10 nm grown by thermal chemical-vapor deposition, we have utilized spectroscopic ellipsometry and introduced a model, called the fine crystalline grain model. This model resolves that the growth of the amorphous silicon matrix starts with the formation of dense deformed crystallites or paracrystallites. A better fit to the experimental data has been obtained with this model when the a-Si:H film thickness is below 20 nm. The fine grain component gradually decreases with the film growth. It has been clarified that the presence of deformed crystallites in the starting a-Si:H films acts as a constraint for their crystallization by rapid thermal annealing. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.05.Gc Amorphous semiconductors
81.05.Cy Elemental semiconductors
61.43.Dq Amorphous semiconductors, metals, and alloys

Photoluminescence behavior of poly(quinoline)s in silica glasses via the sol–gel process

W. Y. Huang, S. W. Ho, T. K. Kwei, and Y. Okamoto

Appl. Phys. Lett. 80, 1162 (2002); http://dx.doi.org/10.1063/1.1450040 (3 pages) | Cited 15 times

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A full color display with its spectra covering the entire visible color range using a single polymer is presented here. Different concentrations of poly(2,6-[4-phenylquinoline]) and poly(2,6-[p-phenylene]-4-phenylquinoline) were incorporated into silica gels via the sol–gel technique. At high concentrations, the conjugated polymers form multiple excimers in the channels within the silica network, leading to the emission of red light (∼600 nm). At low concentrations, the polymer chains are isolated and are being trapped individually in the silica domain, which results in the emission of blue light (∼400 nm). For concentrations in-between, moderate extensive chain interaction leads to the emission of green, yellow, and orange colors. Therefore, the color tunability can be achieved by simply varying the concentration of quinoline polymers in the silica glasses. © 2002 American Institute of Physics.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Kz Solid organic materials
81.07.Bc Nanocrystalline materials
81.05.Pj Glass-based composites, vitroceramics
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)

Quantitative measurement of Cr segregation in Co0.8−xCrxPt0.1B0.1 recording media by scatter diagram analysis

Werner Grogger, Kannan M. Krishnan, Roger A. Ristau, Thomas Thomson, Samuel D. Harkness, and Rajiv Ranjan

Appl. Phys. Lett. 80, 1165 (2002); http://dx.doi.org/10.1063/1.1450039 (3 pages) | Cited 9 times

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We describe the scatter diagram analysis of chemically resolved energy-filtered transmission electron microscopy (EFTEM) images and demonstrate its application in obtaining quantitative information about the segregation of Cr on the nanometer scale. The recording performance of Co–Cr based magnetic media depends critically on the microstructure of the thin film alloy, i.e., the degree of segregation of Cr to the grain boundaries determines the extent of magnetic isolation that can be achieved. Magnetic isolation of the grains reduces transition widths and thereby allows increased recording densities. The EFTEM results obtained correlate well with both the magnetic properties and recording performance of the media; i.e., a higher Cr content of 16 at. % (compared with a 10 at. % sample) shows substantial segregation of Cr with about 8% (0.06%) of the image area, most of it at the grain boundaries, having a Cr concentration which is higher than 24 at. %, and a medium signal to noise ratio of 17.8 dB (15.3 dB). © 2002 American Institute of Physics.
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61.72.Mm Grain and twin boundaries
75.50.Ss Magnetic recording materials
64.75.-g Phase equilibria
85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
68.37.Lp Transmission electron microscopy (TEM)
81.30.Mh Solid-phase precipitation

Study of the effect of natural oxidation and thermal annealing on microstructures of AlOx in the magnetic tunnel junction by high-resolution transmission electron microscopy

Jun Soo Bae, Kyung Ho Shin, Taek Dong Lee, and Hyuck Mo Lee

Appl. Phys. Lett. 80, 1168 (2002); http://dx.doi.org/10.1063/1.1451988 (3 pages) | Cited 13 times

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In a magnetic tunnel junction, the formation of an insulator is sensitive and critical to the stable performance and reproducibility of the junction. The oxidation path and the microstructural change with time of the insulator in natural oxidation have been studied by the high-resolution transmission electron microscopy. It has been observed that the oxidation path is primarily through the grain boundary at an early stage of oxidation and then through the grains at a later stage. The morphology of the oxide layer was rugged and modulated. There also occurred an isotropic volume expansion with increased oxidation. It was observed that the ferromagnetic Co layer below an insulator was partially oxidized because of the preferred grain boundary oxidation. When this multilayer was annealed, the locally oxidized Co layer was reduced and the metallic layer formed as a continuous film type, thereby improving the interface. © 2002 American Institute of Physics.
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75.47.De Giant magnetoresistance
81.65.Mq Oxidation
68.65.Ac Multilayers
72.25.Mk Spin transport through interfaces
61.72.Mm Grain and twin boundaries
61.72.Cc Kinetics of defect formation and annealing

Study of intermixing in a GaAs/AlGaAs quantum-well structure using doped spin-on silica layers

L. Fu, R. W. v. d. Heijden, H. H. Tan, C. Jagadish, L. V. Dao, and M. Gal

Appl. Phys. Lett. 80, 1171 (2002); http://dx.doi.org/10.1063/1.1449522 (3 pages) | Cited 9 times

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The effect of two different dopants, P and Ga, in spin-on glass (SOG) films on impurity-free vacancy disordering (IFVD) in GaAs/AlGaAs quantum-well structures has been investigated. It is observed that by varying the annealing and baking temperatures, P-doped SOG films created a similar amount of intermixing as the undoped SOG films. This is different from the results of other studies of P-doped SiO2 and is ascribed to the low doping concentration of P, indicating that the doping concentration of P in the SiO2 layer is one of the key parameters that may control intermixing. On the other hand, for all the samples encapsulated with Ga-doped SOG layers, significant suppression of the intermixing was observed, making them very promising candidates with which to achieve the selective-area defect engineering that is required for any successful application of IFVD. © 2002 American Institute of Physics.
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68.65.Fg Quantum wells
81.05.Ea III-V semiconductors
81.05.Kf Glasses (including metallic glasses)
81.07.St Quantum wells
71.55.Eq III-V semiconductors
73.21.Fg Quantum wells
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Role of atomic arrangements at interfaces on the phase control of epitaxial TiO2 films

B. H. Park, J. Y. Huang, L. S. Li, and Q. X. Jia

Appl. Phys. Lett. 80, 1174 (2002); http://dx.doi.org/10.1063/1.1450249 (3 pages) | Cited 13 times

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Epitaxial rutile-TiO2 and anatase-TiO2 films were grown at 800 °C on Al2O3(math10math) and LaAlO3(001), respectively, using pulsed laser deposition. Both films showed high crystalline quality, evidenced by x-ray diffraction and high-resolution electron microscopy. The formation of different phases on different substrates could be qualitatively explained by the atomic arrangements at the interfaces. We also deposited epitaxial rutile-TiO2 and anatase-TiO2 films on conductive RuO2 and La0.5Sr0.5CoO3 electrodes, respectively. Using a Kelvin probe, we measured the photovoltaic properties of these multilayer structures. A rutile-TiO2 film grown on RuO2 showed a very broad peak in the visible light region. An epitaxial anatase-TiO2 film grown on La0.5Sr0.5CoO3 showed a strong peak with a threshold energy of 3.05 eV. © 2002 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
73.50.Pz Photoconduction and photovoltaic effects
73.61.Le Other inorganic semiconductors
68.35.Ct Interface structure and roughness

Spinodal decomposition in BxGa1−xN and BxAl1−xN alloys

L. K. Teles, L. M. R. Scolfaro, J. R. Leite, J. Furthmüller, and F. Bechstedt

Appl. Phys. Lett. 80, 1177 (2002); http://dx.doi.org/10.1063/1.1450261 (3 pages) | Cited 15 times

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We present first-principles calculations of the structural and thermodynamic properties of cubic BxGa1−xN and BxAl1−xN alloys. The calculations are based on the generalized quasichemical approach to disorder and composition effects and a pseudopotential-plane-wave approximation. The bulk moduli and lattice constants are found to vary linearly with the alloy composition. Due to the large lattice mismatch between BN and binaries GaN and AlN, the phase diagrams display large miscibility gaps in the temperature range usually adopted to grow the corresponding alloys. This explains the difficulties reported in growing these alloys with boron content higher than 0.1. © 2002 American Institute of Physics.
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64.75.-g Phase equilibria
65.40.G- Other thermodynamical quantities
62.20.D- Elasticity
61.66.Fn Inorganic compounds

Measurement of debonding in cracked nanocomposite films by ultrasonic force microscopy

A. P. McGuigan, B. D. Huey, G. A. D. Briggs, O. V. Kolosov, Y. Tsukahara, and M. Yanaka

Appl. Phys. Lett. 80, 1180 (2002); http://dx.doi.org/10.1063/1.1450058 (3 pages) | Cited 9 times

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This letter reports the application of ultrasonic force microscopy (UFM) to investigate subsurface fracture mechanisms during tensile loading of nanocomposite films consisting of a brittle glass on a ductile polyethylene terephthalate (PET) substrate. Such materials are used in packaging applications where a gas barrier is required to maintain the product quality. Cracking or debonding of the surface glass layer results in destruction of the gas barrier properties of the film. Accurate evaluation of the continuity or discontinuity at the crack edge within the layered material is crucial for the correct characterization of both adhesive failure and crack propagation. Here simultaneous atomic force microscopy and UFM images are compared for a range of tensile strains to identify debonded regions of the glass film from the PET. Debonding occurred for strains greater than 6%. In some films, this debonding increased with applied strain. © 2002 American Institute of Physics.
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62.25.-g Mechanical properties of nanoscale systems
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
68.37.Tj Acoustic force microscopy
81.05.Pj Glass-based composites, vitroceramics
62.20.M- Structural failure of materials

Anti-Stokes emission in undoped YVO4

W. Ryba-Romanowski, S. Gołąb, P. Solarz, G. Dominiak-Dzik, and T. Łukasiewicz

Appl. Phys. Lett. 80, 1183 (2002); http://dx.doi.org/10.1063/1.1451991 (3 pages) | Cited 8 times

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Single crystal of nominally undoped YVO4 exhibits a broad-band emission centered at 450 nm when excited at any wavelength between 620–440 nm with short pulses delivered by an optical parametric oscillator. The broad-band emission has been assigned to the transition from the lowest energy excited states 3T1, 3T2 to the ground 1A1 state of the VO43−, whereas the excitation mechanism is supposed to be an excited state absorption from a hitherto unidentified intermediate state. This state is likely to be related with V4+ and/or V3+ ions whose presence in YVO4 is generally recognized. The material may have a potential as a tunable source of blue radiation provided a way is found to increase the ground state absorption. © 2002 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
71.35.-y Excitons and related phenomena
78.55.Hx Other solid inorganic materials
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