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15 Feb 1999

Volume 74, Issue 7, pp. 899-1050

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Photoinduced alignment control of photoreactive side-chain polymer liquid crystal by linearly polarized ultraviolet light

Nobuhiro Kawatsuki, Tohei Yamamoto, and Hiroshi Ono

Appl. Phys. Lett. 74, 935 (1999); http://dx.doi.org/10.1063/1.123414 (3 pages) | Cited 26 times

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Alignment control of mesogenic groups in a photocrosslinkable polymer liquid crystalline film was achieved by linearly polarized (LP) ultraviolet (UV) irradiation followed by heating. The alignment direction was parallel to the electric vector of the incident LPUV light and the tilt angle of the mesogenic groups could be controlled by a one-step slantwise LPUV irradiation. The photoinduced birefringence dn was 0.07 and the order parameter of the mesogenic group was 0.28. © 1999 American Institute of Physics.
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42.70.Df Liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.66.Qn Polymers; organic compounds
78.20.Fm Birefringence
61.82.Pv Polymers, organic compounds
82.50.-m Photochemistry
61.41.+e Polymers, elastomers, and plastics

Optical anisotropy of uniaxially drawn and silver-dispersed polyimide films

Takashi Sawada, Shinji Ando, and Shigekuni Sasaki

Appl. Phys. Lett. 74, 938 (1999); http://dx.doi.org/10.1063/1.123415 (3 pages) | Cited 8 times

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Distinct anisotropy in optical transmittance in the visible and near-infrared region for uniaxially drawn and silver-dispersed polyimide films was observed. The films were prepared in a one-step operation that involves thermal curing and simultaneous uniaxial drawing of poly(amic acid) (PAA) films, which were made by dissolving silver nitrate in the PAA solution at a 1:4 mol ratio. The polyimide molecular chains with a rod-like structure were oriented along the drawing direction during curing, and this orientation accompanied the generation of silver nanoparticles with elongated shapes. An anisotropy in the optical transmittance of 5:1 was obtained for a 22-μm-thick film at 850 nm with transmittance of 68% perpendicular to the drawing direction. The optical and mechanical properties of this film were retained after annealing at 300 °C for 1 h. © 1999 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
78.20.Fm Birefringence
42.70.Jk Polymers and organics
81.05.Qk Reinforced polymers and polymer-based composites
68.55.-a Thin film structure and morphology
61.41.+e Polymers, elastomers, and plastics

Selective epitaxial growth of organic molecules on patterned alkali halide substrates

Toshihiro Shimada, Takafumi Sakurada, and Atsushi Koma

Appl. Phys. Lett. 74, 941 (1999); http://dx.doi.org/10.1063/1.123416 (3 pages) | Cited 2 times

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Selective epitaxial growth of organic materials is found and analyzed. It is observed during the molecular beam epitaxy of organic molecules and charge transfer complexes on ionic surfaces. The selectivity comes from lattice matching condition on critical nuclei formation in contrast to compound semiconductors for which covalent chemical bonding plays essential roles. It can be utilized to fabricate micropatterns of crystalline organic materials accompanied by lithography processes of alkali halides using NH3 plasma. Feasibility of building three-dimensional microstructures has also been shown, which is readily applicable to make photonic crystals from optically functional organic materials. © 1999 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.-a Thin film structure and morphology
42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
81.65.Cf Surface cleaning, etching, patterning

Thermomechanical properties and moisture uptake characteristics of hydrogen silsesquioxane submicron films

Jie-Hua Zhao, Irfan Malik, Todd Ryan, Ennis T. Ogawa, Paul S. Ho, Wei-Yan Shih, Andrew J. McKerrow, and Kelly J. Taylor

Appl. Phys. Lett. 74, 944 (1999); http://dx.doi.org/10.1063/1.123417 (3 pages) | Cited 28 times

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This letter describes measurement of the biaxial modulus, coefficient of thermal expansion (CTE), and moisture uptake characteristics of hydrogen silsesquioxane (HSQ) thin films. The biaxial modulus and CTE were determined using a bending beam method, and moisture uptake was studied using a quartz crystal microbalance method. The biaxial modulus and CTE of a 0.5 μm HSQ film were measured on Si and Ge substrates and found to be 7.07 GPa and 20.5 ppm/°C, respectively. The value determined for the diffusion constant of water in a 0.7-μm-thick HSQ films is 3.61×10−10 cm2/s at room temperature. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.60.Dv Thermal stability; thermal effects
65.40.De Thermal expansion; thermomechanical effects
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
77.55.-g Dielectric thin films
62.20.D- Elasticity
66.30.J- Diffusion of impurities
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Evidence for multiple atomic structure for the {10math0} inversion domain boundaries in GaN layers

V. Potin, G. Nouet, and P. Ruterana

Appl. Phys. Lett. 74, 947 (1999); http://dx.doi.org/10.1063/1.123418 (3 pages) | Cited 18 times

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Atomic structure investigation has been carried out on {10math0} inversion domain boundaries in GaN layers grown by molecular beam epitaxy. A method based on the comparison of the stacking sequences of GaN on both sides of the boundary is proposed in order to distinguish between different models. Experimental evidence is shown for two atomic configurations of the boundary plane. Depending probably on the growth conditions, the Holt model, which has been theoretically characterized as highly energetic, can also exist for the {10math0} inversion domain boundaries in GaN epitaxial layers. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Mm Grain and twin boundaries

Selective area oxide desorption by electron irradiation in a H2 ambient on GaAs (100)

S. J. Brown, T. M. Burke, M. P. Smith, D. A. Ritchie, M. Pepper, K. B. T. Tang, and R. E. Palmer

Appl. Phys. Lett. 74, 950 (1999); http://dx.doi.org/10.1063/1.123419 (3 pages)

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The selective area removal of oxides from the surface of exposed GaAs (100) has been achieved by irradiating the sample with a broad, low energy electron beam in a H2 ambient. It is proposed that electrons dissociate the molecular hydrogen to create ionized species which react with the surface. The surfaces of samples decontaminated at 365 °C, up to electron energies of 200 eV, were undamaged as revealed by atomic force microscopy. Moreover, quantum well structures epitaxially grown on these surfaces exhibited luminescence. A possible reaction mechanism responsible for the oxide removal is described. © 1999 American Institute of Physics.
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68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.20.La Photon- and electron-stimulated desorption
61.82.Fk Semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.35.Dv Composition, segregation; defects and impurities

Wiedemann–Franz law at boundaries

G. D. Mahan and M. Bartkowiak

Appl. Phys. Lett. 74, 953 (1999); http://dx.doi.org/10.1063/1.123420 (2 pages) | Cited 29 times

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The full equations are derived for the resistances to the transport of heat and electricity through boundaries of thermoelectrics. We show that the boundary resistances of heat and electricity are proportional. This relationship is a boundary form of the Wiedemann–Franz law. We also show there is a boundary Seebeck coefficient. © 1999 American Institute of Physics.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
73.50.Lw Thermoelectric effects
73.61.-r Electrical properties of specific thin films

In situ texture monitoring for growth of oriented cubic boron nitride films

Dmitri Litvinov and Roy Clarke

Appl. Phys. Lett. 74, 955 (1999); http://dx.doi.org/10.1063/1.123421 (3 pages) | Cited 29 times

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We report evidence for oriented growth of pure-phase cubic boron nitride on silicon (100) substrates. The films are deposited at high temperatures (up to 1200 °C) by reduced-bias ion-assisted sputtering. The growth technique produces highly textured c-BN films with relatively large grain size (∼1000 Å) and reduced residual stress as the bias voltage is decreased. We have been able to grow thick (up to 2 μm) cubic boron nitride films containing 100% of the cubic phase with the (001) crystallographic axis of c-BN oriented perpendicular to the surface of the film. We show how reflection high-energy electron diffraction applied to texture monitoring in polycrystalline films can be used as an in situ process control technique that allows texture identification and quantitative characterization of its angular spread. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering
61.05.jh Low-energy electron diffraction (LEED) and reflection high-energy electron diffraction (RHEED)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.60.Bs Mechanical and acoustical properties

Morphological control and structural characteristics of crystalline Ge–C systems: Carbide nanorods, quantum dots, and epitaxial heterostructures

David C. Nesting, J. Kouvetakis, and David J. Smith

Appl. Phys. Lett. 74, 958 (1999); http://dx.doi.org/10.1063/1.123422 (3 pages) | Cited 6 times

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Chemical precursors are used to grow crystalline Ge–C materials with unusual morphologies that depend on the molecular design of the precursor and the C concentration. Ge–C nanorods with overall C content of about 13–15 at. % and lattice constants close to that of pure Si grew very rapidly from the surface of a 40 nm Ge–C epitaxial film. Coherent carbide islands are formed after epitaxial growth of 20 nm Ge1−xCx (x = 9 at. %) on (100)Si. Lower reaction temperatures resulted in extremely low growth rate of epitaxial Ge1−xCx (x = 3–5 at. %) heterostructures with very flat surfaces implying two-dimensional layer-by-layer growth. The use of precursor chemistry as reported here to control morphology and composition in the Ge–C system may provide a simple and reliable synthetic route to a new family of Si-based heterostructures. © 1999 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
68.55.Nq Composition and phase identification
81.05.Hd Other semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Enhancing defect-related photoluminescence by hot implantation into SiO2 layers

S. Im, J. Y. Jeong, M. S. Oh, H. B. Kim, K. H. Chae, C. N. Whang, and J. H. Song

Appl. Phys. Lett. 74, 961 (1999); http://dx.doi.org/10.1063/1.123423 (3 pages) | Cited 13 times

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Visible photoluminescence around an orange band of 580 nm wavelength are observed from 300 nm thin SiO2 layers implanted by Si or Ge ions at both substrate temperatures of 25 °C [room temperature (RT)] and 400 °C (hot). Si implantations at an energy of 30 keV were performed with doses of 5×1015, 3×1016, and 1×1017 cm−2 while Ge implantations were done at 100 keV with a dose of 5×1015 cm−2. Samples implanted at 400 °C always show much higher intensities of luminescence than those implanted at room temperature. Electron spin resonance signals of the hot-implanted samples indicate relatively smaller amounts of nonradiative defects than those of RT-implanted samples. It is concluded that the hot-implantation effectively enhances the intensity of defect-related photoluminescence by reducing the density of the nonradiative defects and introducing the radiative defects, which contribute to the luminescence in SiO2 layers. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
61.72.up Other materials
61.80.Jh Ion radiation effects
71.55.Ht Other nonmetals
76.30.Lh Other ions and impurities

Surface smoothing of GaAs microstructure by atomic layer epitaxy

S. Hirose, A. Yoshida, M. Yamaura, and H. Munekata

Appl. Phys. Lett. 74, 964 (1999); http://dx.doi.org/10.1063/1.123424 (3 pages) | Cited 10 times

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We report a method to smooth the rough surface of GaAs microstructures. This method is based on the nucleation process for atomic layer epitaxy which involves the self-limiting two-dimensional (one-monolayer) island formation. The method has been applied successfully to smooth the (111)A surfaces of chemically etched V-grooved GaAs structures as well as the (110) and (111)B side walls of selectively grown GaAs stripe structures. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Cf Surface cleaning, etching, patterning
81.05.Ea III-V semiconductors

Time-dependent diffusivity of boron in silicon oxide and oxynitride

K. A. Ellis and R. A. Buhrman

Appl. Phys. Lett. 74, 967 (1999); http://dx.doi.org/10.1063/1.123425 (3 pages) | Cited 14 times

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The diffusivities of boron in silicon oxide and oxynitride have been determined from secondary ion mass spectroscopy measurements of annealed metal-oxide-silicon structures. The results clearly show a decrease in diffusivity with increasing anneal time which is approximately exponential in form. This effect implies a similar time dependence in the concentration of a secondary species, such as hydrogen, or a defect within the dielectric, which promotes diffusion even in a nominally pure oxide. © 1999 American Institute of Physics.
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66.30.J- Diffusion of impurities
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals
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