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27 Sep 1999

Volume 75, Issue 13, pp. 1821-1987

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Thermal and electrical transport properties of the single-phase quasicrystalline material: Al70.8Pd20.9Mn8.3

A. L. Pope, Terry M. Tritt, M. A. Chernikov, and M. Feuerbacher

Appl. Phys. Lett. 75, 1854 (1999); http://dx.doi.org/10.1063/1.124850 (3 pages) | Cited 36 times

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The electrical and thermal transport properties of a single-phase quasicrystalline material of composition Al70.8Pd20.9Mn8.3 have been measured as a function of temperature (T) over a range of 10 K<T<320 K. The following room-temperature values were found: electrical conductivity [640 (Ω cm)−1], Seebeck coefficient (85 μV/K), and thermal conductivity (1.6 W/m K). As the temperature was decreased from room temperature, the electrical conductivity decreased undergoing a minimum at T ≈ 50 K after which it increased slightly and the Seebeck coefficient decreased monotonically. The thermal conductivity decreased with temperature and exhibited a broad plateau region between 50 K<T<150 K. This class of materials is being investigated for potential thermoelectric applications. © 1999 American Institute of Physics.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys

Absorption spectra of nanocrystalline silicon embedded in SiO2 matrix

Zhixun Ma, Xianbo Liao, Gonglin Kong, and Junhao Chu

Appl. Phys. Lett. 75, 1857 (1999); http://dx.doi.org/10.1063/1.124851 (3 pages) | Cited 18 times

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Nanocrystalline silicon embedded SiO2 matrix is formed by annealing the SiOx films fabricated by plasma enhanced chemical vapor deposition technique. Absorption coefficient and photoluminescence of the films have been measured at room temperature. The experimental results show that there exists an exponential absorption in the spectral range of 2.0–3.0 eV. The relationship of (αhν)1/2∝(hν−Eg) demonstrates that the luminescent nanocrystalline silicon has an indirect band structure. The existence of Stokes shift between photoluminescence and absorption edge indicates that radiative combination can take place not only between shallow trap states of electrons and holes but also between quantized states of electrons and holes. © 1999 American Institute of Physics.
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78.66.Jg Amorphous semiconductors; glasses
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.40.Fy Semiconductors
71.20.Mq Elemental semiconductors
71.55.Cn Elemental semiconductors
78.55.Ap Elemental semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems

Grain growth in thin-film strontium sulfide electroluminescent phosphors

Y. B. Xin and C. J. Summers

Appl. Phys. Lett. 75, 1860 (1999); http://dx.doi.org/10.1063/1.124852 (3 pages)

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A comprehensive study of grain growth in strontium sulfide (SrS) thin-film electroluminescent (TFEL) phosphors is reported. It is suggested that the grain growth during annealing is influenced by the migration of the dopant ion from the grain boundary into a lattice position. The difference in the free energy of formation between SrS and the sulfur compounds of the dopants changes the activation energy for the grain boundary movement and promotes the grain growth. This understanding has successfully been used to explain the grain growth phenomena observed in SrS TFEL phosphors with different dopants, such as Cu, Ag, Mn, and Ga. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Fi Electroluminescence
61.72.Mm Grain and twin boundaries
66.30.J- Diffusion of impurities
78.66.Li Other semiconductors
61.72.Cc Kinetics of defect formation and annealing

Solid-state gadolinium–magnesium hydride optical switch

R. Armitage, M. Rubin, T. Richardson, N. O’Brien, and Yong Chen

Appl. Phys. Lett. 75, 1863 (1999); http://dx.doi.org/10.1063/1.124853 (3 pages) | Cited 30 times

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The optical switching properties of gadolinium–magnesium hydride have been demonstrated in a solid-state electrochromic device. With positive polarization of the hydride electrode, the visible reflectance approaches 35% with virtually zero transmission, while with negative polarization, the visible transmission exceeds 25% at 650 nm. The switching is reversible, with intermediate optical properties between the transparent and reflecting states. © 1999 American Institute of Physics.
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42.79.Bh Lenses, prisms and mirrors
78.20.Jq Electro-optical effects
78.66.Li Other semiconductors
78.40.Fy Semiconductors
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks

Evolution of the energy levels in quantum dot ensembles with different densities

S. Fafard, Z. R. Wasilewski, and M. Spanner

Appl. Phys. Lett. 75, 1866 (1999); http://dx.doi.org/10.1063/1.124854 (3 pages) | Cited 26 times

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Ensembles of self-assembled InAs/GaAs quantum dots (QDs) have been obtained with different densities by molecular beam epitaxy. The evolution of the structural and optical properties with coverage shows that lateral interactions are present for QD spacings of hundreds of nanometers (coverage> ∼ 109 QDs/cm2). Clear evidence for transfer of InAs from the wetting layer to the QDs is observed at the onset of the Stranski–Krastanow’s island formation for 1.83 monolayers (MLs). QDs with sharp electronic shell structures are observed by state-filling spectroscopy for the low density ensembles (1.83–1.91 ML). A decrease in the photoluminescence intensity is observed for more than 1.96 ML and is associated with the coalescence of the islands. © 1999 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Microscopical aspects of boron diffusion in ultralow energy implanted silicon

E. Napolitani, A. Carnera, E. Schroer, V. Privitera, F. Priolo, and S. Moffatt

Appl. Phys. Lett. 75, 1869 (1999); http://dx.doi.org/10.1063/1.124855 (3 pages) | Cited 25 times

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The transient enhanced diffusion of ultralow energy implanted B is reported in this letter. The mechanism giving rise to an enhancement of the diffusion during postimplantation anneal is investigated in detail by monitoring the diffusion of B as a function of temperature in the range 600–750 °C, for implant energies of 500 eV and 1 keV. The contribution of several classes of defect clusters to the anomalous diffusion phenomenon has been detected and interpreted. Both an ultrafast diffusion, occurring during the ramp-up of the thermal process, and a transient enhancement of the diffusion with characteristic decay times shorter by orders of magnitude than the known transient enhanced diffusion lifetimes, have been evidenced. The activation energy for the enhanced diffusion has been measured and found to be 1.7 eV. © 1999 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.uf Ge and Si
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Amplified stain-rate dependence of deformation in polymer-dispersed liquid-crystal materials

Darran R. Cairns, Guy M. Genin, Amy J. Wagoner, Clyde L. Briant, and Gregory P. Crawford

Appl. Phys. Lett. 75, 1872 (1999); http://dx.doi.org/10.1063/1.124856 (3 pages) | Cited 8 times

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The mechanical properties of polymer-dispersed liquid crystals (PDLCs) are investigated to elucidate their fundamental microstructural and mechanistic underpinnings, and overall structural integrity under deformation. High strain-rate loading experiments and quasistatic compression tests on PDLC materials reveal an amplified strain-rate dependence relative to the matrix material. A finite-element micromechanical model of PDLC materials explains this behavior in terms of strain-rate concentrations at the equators of the spherical liquid-crystal droplets. The model also predicts a weak dependence of the aspect ratio of deforming liquid-crystal droplets on their volume fraction. © 1999 American Institute of Physics.
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62.10.+s Mechanical properties of liquids
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.

Synthesizing boron nitride nanotubes filled with SiC nanowires by using carbon nanotubes as templates

Weiqiang Han, Philipp Redlich, Frank Ernst, and Manfred Rühle

Appl. Phys. Lett. 75, 1875 (1999); http://dx.doi.org/10.1063/1.124857 (3 pages) | Cited 40 times

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A method is described to synthesize silicon carbide (SiC)-filled boron nitride (BN) nanotubes (NT) simultaneously in high yield by using carbon nanotubes (CNTs) as templates. This method combines both carbon nanotube-substitution reaction and confined reaction. Through the CNT-substitution reaction, CNTs react with boron oxide vapor in the presence of nitrogen gas to form BN NTs, whose diameters and lengths are similar to those of the starting CNTs. The formation of the SiC filling is proceeded by the penetration of SiO vapor into the cavity of the nanotubes and subsequent reaction of SiO vapor with the inner carbon layers or volatile carbon mono-oxide in the interior to form SiC nanowires. The filled length can be up to the entire length of the nanotubes. SiC-filled (BN)xCy nanotubes also form in the product. © 1999 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials

Photoinduced surface relief gratings on azopolymer films: Analysis by a fluid mechanics model

K. Sumaru, T. Yamanaka, T. Fukuda, and H. Matsuda

Appl. Phys. Lett. 75, 1878 (1999); http://dx.doi.org/10.1063/1.124858 (3 pages) | Cited 42 times

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Photoinduced surface relief grating (SRG) formation on azopolymer films is discussed precisely using a fluid mechanics model which takes depth dependence of photoinduced driving force and velocity distribution in the film surface into account. Formulation for the SRG dynamics is derived analytically as a function of film thickness and interference wave number. The film thickness dependence of diffraction efficiency, which is observed experimentally, agrees well with the theoretical value in the entire range of film thickness. The dependence of SRG driving force on interference wave number is also discussed in terms of the experimental data using proposed model. © 1999 American Institute of Physics.
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42.79.Dj Gratings
42.70.Jk Polymers and organics

Macroscopic residual stress in chemical-vapor-deposition free-standing diamond films by x-ray diffraction analyses

O. Durand, J. Olivier, R. Bisaro, P. Galtier, J. K. Krüger, C. J. Brierley, and G. R. Kennedy

Appl. Phys. Lett. 75, 1881 (1999); http://dx.doi.org/10.1063/1.124859 (3 pages) | Cited 9 times

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We present a structural analysis of plasma-assisted chemical-vapor-deposition self-supporting diamond films with different qualities, black, gray and white. Experimental results show a weak fiber texture and a large average grain size at the growth side, consistent with the model usually used to described chemical-vapor-deposition growth with a preferred orientation of the grains. Macroscopic residual stresses have been determined by means of x-ray measurements, through the sin2 ψ method. Compressive and tensile stresses are reported at both faces of the samples. We show that stresses present at both growth face and nucleation face cannot be explained by the usual models involving the average grain size. For some samples, a closer analysis of the sin2 ψ curves reveals a shift from the linear behavior. This effect comes from various stress states and/or lattice parameters between the grains belonging to the texture and the randomly oriented grains. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Radiation damage to fullerite (C60) in the transmission electron microscope

R. F. Egerton and Manabu Takeuchi

Appl. Phys. Lett. 75, 1884 (1999); http://dx.doi.org/10.1063/1.124860 (3 pages) | Cited 5 times

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Electron energy-loss spectroscopy was used to monitor structural damage to solid C60 as a function of electron exposure. The characteristic dose was found to be in the range 300–700 C/cm2 for incident energies in the range 100–200 keV and specimen temperatures between 100 and 300 K. The absolute value of this dose, and its energy and temperature dependence, suggest that the damage mechanism is predominantly electronic rather than knock-on displacement. © 1999 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
61.82.Rx Nanocrystalline materials
61.80.Fe Electron and positron radiation effects
79.20.Kz Other electron-impact emission phenomena

Structural and optical quality of GaN/metal/Si heterostructures fabricated by excimer laser lift-off

W. S. Wong, Y. Cho, E. R. Weber, T. Sands, K. M. Yu, J. Krüger, A. B. Wengrow, and N. W. Cheung

Appl. Phys. Lett. 75, 1887 (1999); http://dx.doi.org/10.1063/1.124861 (3 pages) | Cited 26 times

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Gallium nitride (GaN) thin films grown on sapphire substrates were successfully bonded and transferred onto Si substrates using a Pd–In metallic bond. After bonding, a single 600 mJ/cm2, 38 ns KrF (248 nm) excimer laser pulse was directed through the transparent sapphire followed by a low-temperature heat treatment to remove the substrate. Channeling-Rutherford backscattering measurements revealed the thickness of the defective interfacial region to be approximately 350 nm. The full width at half maximum, low-temperature (4 K), donor-bound exciton photoluminescence (PL) peak was larger by 25% on the exposed interfacial layer compared to the original GaN surface. Ion milling of the exposed interface to a depth of 400 nm was found to remove the interfacial layer and associated defects. The minimum channeling yield and PL linewidths from the exposed interface were found to be comparable to those obtained from the original GaN surface after ion milling. © 1999 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
42.62.-b Laser applications
78.66.Fd III-V semiconductors
81.65.Cf Surface cleaning, etching, patterning
73.40.Vz Semiconductor-metal-semiconductor structures
78.55.Cr III-V semiconductors
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
85.40.Hp Lithography, masks and pattern transfer

Anisotropic propagation of light in planar waveguides containing InGaAs–InP quantum wells

T. Guettler, O. Krebs, P. Voisin, G. Faini, D. Rondi, and C. Alibert

Appl. Phys. Lett. 75, 1890 (1999); http://dx.doi.org/10.1063/1.124862 (3 pages) | Cited 2 times

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We report on the observation of anisotropy of the propagation index with respect to propagation direction in planar waveguides containing InGaAs–InP quantum wells. We discuss the relation between this effect and the recently discovered in-plane polarization anisotropy of the absorption observed for light propagating along the growth axis. © 1999 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
78.66.Fd III-V semiconductors
78.30.Fs III-V and II-VI semiconductors
42.25.Ja Polarization

Elastic constants of tetrahedral amorphous carbon films by surface Brillouin scattering

A. C. Ferrari, J. Robertson, M. G. Beghi, C. E. Bottani, R. Ferulano, and R. Pastorelli

Appl. Phys. Lett. 75, 1893 (1999); http://dx.doi.org/10.1063/1.124863 (3 pages) | Cited 73 times

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The elastic constants of tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H) thin films were determined nondestructively by surface Brillouin scattering. Besides the usual Rayleigh surface mode, we also observe a new pseudosurface acoustic mode of longitudinal polarization, which is a modified version of the longitudinal guided mode usually found in slow-on-fast supported films. The Young’s modulus E of a ta-C with 88% sp3 is 757 GPa, and the shear modulus G is 337 GPa. The moduli of ta-C:H with 70% sp3 and 30 at. % H are lower, E = 300 GPa and G = 115 GPa. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.66.Jg Amorphous semiconductors; glasses
68.35.Gy Mechanical properties; surface strains

Electroluminescence of polymer/J-aggregate composites

Eugene I. Mal’tsev, Dmitry A. Lypenko, Boris I. Shapiro, Maria A. Brusentseva, George H. W. Milburn, Jeffrey Wright, Andre Hendriksen, Vladimir I. Berendyaev, Boris V. Kotov, and Anatoly V. Vannikov

Appl. Phys. Lett. 75, 1896 (1999); http://dx.doi.org/10.1063/1.124864 (3 pages) | Cited 31 times

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Efficient electroluminescence was revealed in single-layer light-emitting diodes based on electron-hole conducting polymers containing the nanocrystalline phase of cyanine dyes (J-aggregates). These species exhibit a very narrow emission band with a maximum in the red to infrared spectrum range. The J-aggregates play an active role in the charge carrier transport of the composites. © 1999 American Institute of Physics.
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78.60.Fi Electroluminescence
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