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20 Sep 1999

Volume 75, Issue 12, pp. 1655-1810

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Lithium tetra-(8-hydroxy-quinolinato) boron for blue electroluminescent applications

X. T. Tao, H. Suzuki, T. Wada, H. Sasabe, and S. Miyata

Appl. Phys. Lett. 75, 1655 (1999); http://dx.doi.org/10.1063/1.124832 (3 pages) | Cited 36 times

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We report the optical and electroluminescent properties of the organometallic complex lithium tetra-(8-hydroxy-quinolinato) boron (LiBq4). The complex was prepared by the reaction of lithium borohydride with 8-hydroxyquinoline and shows absorption cutoff wavelength of 410 nm and bright blue photoluminescence with a peak wavelength at 466 nm. The ionization potential of LiBq4 was determined to be ∼5.6 eV by a photoemission apparatus. Electroluminescence (EL) properties of three-layer light-emitting diodes (LED) of ITO/PVK:TPD/LiBq4/Alq3/Mg with LiBq4 as the active layer were characterized. The EL spectra of the three-layer device are similar to the PL spectrum of the single layer LiBq4 but with peak wavelength at 475 nm. The results indicate that boron complexes are potential blue emitters for LED applications. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials

Amplification of Raman scattering by stimulated emission in a stretched free-standing poly(p-phenylenevinylene) film

Seungwoo Shin, Jeongmi Shin, Hongki Kim, Jung Hoon Ro, Heayoung Choi, Kwanghee Lee, and Myoungsik Cha

Appl. Phys. Lett. 75, 1658 (1999); http://dx.doi.org/10.1063/1.124784 (3 pages)

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Photoexcitation of a stretched poly(p-phenylenevinylene) thick film results in a light emission with a very narrow linewidth when the excitation intensity exceeds a threshold. By measuring the excitation and the Raman spectra, we found that the narrow emission is an amplification of Raman scattering during waveguide propagation. © 1999 American Institute of Physics.
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78.66.Qn Polymers; organic compounds
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
78.30.Jw Organic compounds, polymers
78.45.+h Stimulated emission
78.55.Kz Solid organic materials
42.70.Jk Polymers and organics

Room-temperature optically pumped CdHgTe vertical-cavity surface-emitting laser for the 1.5 μm range

C. Roux, E. Hadji, and J.-L. Pautrat

Appl. Phys. Lett. 75, 1661 (1999); http://dx.doi.org/10.1063/1.124831 (3 pages)

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The demonstration of a room-temperature CdHgTe surface-emitting laser is reported. A planar heterostructure with two high-index contrast dielectric mirrors deposited after growth and after etching off the substrate has been realized. The emission wavelength of 1.57 μm is nearly independent of temperature (dλ/dT = 0.02 nm/K) and the multimode linewidth is 10 meV. The pulsed threshold power is as low as 21 mW for a 300 μm spot. Lasing is observed up to 300 K and the peak output power exceeds 700 mW © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.79.Bh Lenses, prisms and mirrors
81.65.Cf Surface cleaning, etching, patterning

Switching dynamics of near-infrared vertical-cavity surface-emitting lasers by injection of near-infrared and midinfrared femtosecond pulses

D. Fortusini, K. C. Burr, F. Robert, and C. L. Tang

Appl. Phys. Lett. 75, 1664 (1999); http://dx.doi.org/10.1063/1.124785 (3 pages) | Cited 1 time

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We report the switch-off and recovery dynamics of a vertical-cavity surface-emitting semiconductor laser induced by injection of near-infrared or midinfrared femtosecond optical pulses. The laser is switched off by carrier-density depletion or carrier-heating effects, depending on the spectral range of the injected pulses. In both cases, the recovery of the laser output can be described by standard rate equations. © 1999 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

High collection efficiency in fluorescence microscopy with a solid immersion lens

Kazuko Koyama, Masahiro Yoshita, Motoyoshi Baba, Tohru Suemoto, and Hidefumi Akiyama

Appl. Phys. Lett. 75, 1667 (1999); http://dx.doi.org/10.1063/1.124833 (3 pages) | Cited 32 times

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High efficiency of light collection was demonstrated by applying solid immersion lenses (SILs) with refractive indices n = 1.845 and 1.687 to fluorescence microscopy of 0.11-μm-radius dye-doped polystyrene sphere beads. This was analyzed with theories on the radiation of dipoles near the surface of the dielectric medium. The estimated collection efficiency with the NA = 0.8 objective and the n = 1.845 SIL was about 60%–70%, which well exceeds the diffraction-limit value of 50% for 2π-solid angle collection in conventional methods. © 1999 American Institute of Physics.
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07.60.Pb Conventional optical microscopes
42.79.Bh Lenses, prisms and mirrors
42.15.Eq Optical system design
78.55.Kz Solid organic materials

Photonic stopbands and light transmission characteristics in GaAs-based three dimensional waveguides with large index contrast

Pallab Bhattacharya, Weidong Zhou, Donghai Zhu, and Jayshri Sabarinathan

Appl. Phys. Lett. 75, 1670 (1999); http://dx.doi.org/10.1063/1.124786 (3 pages) | Cited 3 times

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A relatively simple technique to realize a III–V semiconductor based quasi-three-dimensional photonic crystal material with a refractive index contrast ∼2 is described. Fourier transform infrared spectroscopy measurement reveals a stop band between 15 and 20 μm for a sample with scattering center spacing of 6.3 μm. Another narrow transmittance dip is observable in the wavelength range of 1.1–1.58 μm, with an attenuation of 12 dB at 1.18 μm. The relation between transmission T and waveguide length L, as measured by 1.15 μm wavelength light is either T−L−2 or T−exp(−L/L0), indicating photon localization in the weakly disordered system. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.82.Et Waveguides, couplers, and arrays
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Backswitch poling in lithium niobate for high-fidelity domain patterning and efficient blue light generation

Robert G. Batchko, Vladimir Y. Shur, Martin M. Fejer, and Robert L. Byer

Appl. Phys. Lett. 75, 1673 (1999); http://dx.doi.org/10.1063/1.124787 (3 pages) | Cited 66 times

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In nonlinear optics applications employing quasiphase matching, short-pitch domain gratings are generally required for the efficient generation of visible and ultraviolet light. Here we introduce an improved electric-field poling technique, which incorporates spontaneous backswitching and leads to uniform short-pitch domain structures. The total volume of backswitched material, and hence the duty cycle of the backswitched domain grating, can be accurately controlled. First-order single-pass continuous-wave second harmonic generation of 60 mW at 460 nm is achieved at 6.1%/W efficiency in 0.5-mm-thick 4-μm-period backswitch-poled lithium niobate. © 1999 American Institute of Physics.
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42.70.Mp Nonlinear optical crystals
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena

A numerical study of optical second-harmonic generation in a one-dimensional photonic structure

G. T. Kiehne, A. E. Kryukov, and J. B. Ketterson

Appl. Phys. Lett. 75, 1676 (1999); http://dx.doi.org/10.1063/1.124788 (3 pages) | Cited 9 times

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We present a band-gap engineering approach for obtaining a finite photonic-band-edge-resonant stratified periodic dielectric structure in the presence of material dispersion. When the structure contains second-order nonlinear optical materials, enhanced phase-matched optical second-harmonic (SH) generation may be obtained. Using a transfer-matrix technique, we computed the transmitted and reflected SH power for a GaAs/AlAs Bragg grating and found that a substantial enhancement of the SH power is obtained for a modest number of periods. Asymptotically for a large number of periods, we found the SH power to scale as the eighth power of the total structure thickness. © 1999 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Qs Photonic bandgap materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.79.Dj Gratings
78.66.Fd III-V semiconductors

Built-in field electroabsorption spectroscopy of polymer light-emitting diodes incorporating a doped poly(3,4-ethylene dioxythiophene) hole injection layer

T. M. Brown, J. S. Kim, R. H. Friend, F. Cacialli, R. Daik, and W. J. Feast

Appl. Phys. Lett. 75, 1679 (1999); http://dx.doi.org/10.1063/1.124789 (3 pages) | Cited 218 times

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We report electroabsorption measurements of polymer light-emitting diodes, (LEDs), fabricated with poly(4-4′-diphenylene diphenylvinylene), PDPV, as the emissive layer, Ca–Al cathodes, and indium tin oxide (ITO) anodes, with and without a doped conducting polymer hole injection/transport layer, namely poly(3,4-ethylene dioxythiophene), PEDOT, doped with poly(styrene sulfonate), PSS−. In these structures, the bias at which the electroabsorption signal is null corresponds to the difference between the electrodes’ work functions. We find that such a built-in voltage increases by 0.5 V when a PEDOT:PSS film is incorporated between the ITO electrode and the emissive layer. This leads to a marked reduction of the anode barrier height at the hole-injecting interface, and accounts for a variety of improvements brought about by the PEDOT insertion, namely: (a) the increase of luminescence efficiency, (b) the reduction of the turn-on voltage, and (c) the increase of the device lifetime. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
73.61.Ph Polymers; organic compounds
78.66.Qn Polymers; organic compounds
78.20.Jq Electro-optical effects
78.60.Fi Electroluminescence

Red organic light-emitting diodes using an emitting assist dopant

Yuji Hamada, Hiroshi Kanno, Tsuyoshi Tsujioka, Hisakazu Takahashi, and Tatsuro Usuki

Appl. Phys. Lett. 75, 1682 (1999); http://dx.doi.org/10.1063/1.124790 (3 pages) | Cited 178 times

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We propose an emitting assist (EA) dopant system for obtaining organic light-emitting diodes (OLEDs) with pure red emission. The EA dopant (rubrene) did not itself emit but assisted the energy transfer from the host (Alq3) to the red emitting dopant (DCM2). The cell structure used was {indium tin oxide/hole injection layer [(20 nm), CuPc/hole transport layer (50 nm), NPB/emitting layer (40 nm), Alq3+DCM2 (2%)+rubrene (5 wt %)]/MgIn}. (CuPc: Copper (II) phthalocyanine, NPB: N, N′-Di(naphthalen-1-yl)-N, N′-diphenyl-benzidine, DCM2: 4-Dicyanomethylene- 2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-8-yl)vinyl]-4H-pyran). A stable red emission (chromaticity coordinates: x = 0.64, y = 0.36) was obtained in this cell within the luminance range of 100–4000 cd/m2. When the cell was not doped with rubrene, the emission color changed from red to orange as the luminance increased. The EA dopant system is a promising method for obtaining red OLEDs. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
71.55.Ht Other nonmetals
78.60.Fi Electroluminescence

Plasmon-based terahertz emission from quantum well structures

P. Bakshi, K. Kempa, A. Scorupsky, C. G. Du, G. Feng, R. Zobl, G. Strasser, C. Rauch, Ch. Pacher, K. Unterrainer, and E. Gornik

Appl. Phys. Lett. 75, 1685 (1999); http://dx.doi.org/10.1063/1.124791 (3 pages) | Cited 14 times

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Growing coherent plasma oscillations (plasma instability) can be generated in quantum well structures, where a sufficient population inversion is maintained in the carrier distribution by appropriate injection–extraction configurations. The collective response characteristics of such structures have been calculated. Such structures have been grown, and their radiation emission spectra observed. The experimental results are in agreement with the theoretical predictions. The emission maximum is in the terahertz frequency range, and occurs at an intersubband plasmon frequency. This shows that population inversion is achieved in these structures. © 1999 American Institute of Physics.
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73.50.Mx High-frequency effects; plasma effects
84.40.-x Radiowave and microwave (including millimeter wave) technology
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.61.Ey III-V semiconductors

Ultraviolet-blue emission and electron-hole states in ZnSe quantum dots

C. A. Smith, H. W. H. Lee, V. J. Leppert, and S. H. Risbud

Appl. Phys. Lett. 75, 1688 (1999); http://dx.doi.org/10.1063/1.124834 (3 pages) | Cited 34 times

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We observed the quantum-confined band edge emission from ZnSe quantum dots and the size dependence of the energy states, spin-orbit interaction, and Stokes shift. The band edge emission occurs in the ultraviolet blue. The energy gap = Eg+C/dn where d is the diameter and n is 1.19±0.13 and 1.21±0.13 for the first and second electron-hole transitions, respectively. The separation between these transitions approaches the bulk spin-orbit splitting, while the Stokes shift decreases with particle size. Effective mass theories cannot explain these results. Trap emission is observed in some samples in the green and red, resulting from Se-related traps. © 1999 American Institute of Physics.
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78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.40.Fy Semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Subwavelength resolution in a transmission acoustic microscope configuration using fiber-tip sensors

Christian Koch

Appl. Phys. Lett. 75, 1691 (1999); http://dx.doi.org/10.1063/1.124835 (3 pages)

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Subwavelength resolution in a transmission acoustic microscope configuration is demonstrated using optical fiber-tip sensors as small-sized acoustic probes. A slit with a width of 1/20 of the acoustic wavelength Λ representing the object was detected with a lateral resolution of the outer fiber diameter which was ≈1/10 Λ, and with a proper signal-to-noise ratio. Fiber preparation techniques may raise the resolution to the fiber core dimensions, and simultaneous detection of an acoustic and an optical image is proposed. © 1999 American Institute of Physics.
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43.58.Ls Acoustical lenses and microscopes
07.79.-v Scanning probe microscopes and components
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Colloidal CdTe/HgTe quantum dots with high photoluminescence quantum efficiency at room temperature

Stephen V. Kershaw, Mike Burt, Mike Harrison, Andrey Rogach, Horst Weller, and Alex Eychmüller

Appl. Phys. Lett. 75, 1694 (1999); http://dx.doi.org/10.1063/1.124792 (3 pages) | Cited 37 times

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We have used an aqueous colloidal growth technique to form hybrid CdTe/HgTe quantum dots with a broad, strong fluorescence in the infrared (800–1200 nm). The quantum efficiency is high, around 44%, when pumped in the visible (488 nm), and the excited state lifetime is around 130 ns, making the material interesting as an optical amplifier medium. Using a pump-probe experiment, we have demonstrated weak optical amplification in a dilute aqueous suspension of CdTe/HgTe dots in the short wavelength wing of the emission spectrum at 808 nm. © 1999 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.35.-y Excitons and related phenomena

Quasicrystals in a partially devitrified Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass

M. W. Chen, T. Zhang, A. Inoue, A. Sakai, and T. Sakurai

Appl. Phys. Lett. 75, 1697 (1999); http://dx.doi.org/10.1063/1.124793 (3 pages) | Cited 131 times

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A quasicrystalline phase was discovered in a Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glass annealed in the supercooled liquid range. Through systematical transmission electron microscopy rotation analyses, the selected area electron diffraction patterns are obtained corresponding to fivefold, threefold, and twofold rotational symmetry, demonstrating that the precipitated phase is an icosahedral quasicrystalline phase with good rotational symmetry. It is concluded that the addition of Ag in the Zr-based metallic glass promotes the formation of the quasicrystalline phase. The present experimental result implies that there is a natural relationship between the Zr-based bulk metallic glasses and icosahedral quasicrystalline. © 1999 American Institute of Physics.
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61.44.Br Quasicrystals
61.43.Fs Glasses
64.75.-g Phase equilibria

Electron field emission from silicon nanowires

Frederick C. K. Au, K. W. Wong, Y. H. Tang, Y. F. Zhang, I. Bello, and S. T. Lee

Appl. Phys. Lett. 75, 1700 (1999); http://dx.doi.org/10.1063/1.124794 (3 pages) | Cited 82 times

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Silicon nanowires (SiNWs) were synthesized using laser ablation. A continuous SiNW film was prepared by grinding the pieces of sponge-like SiNWs to powder, then dispersing and sticking the powder onto a Si wafer. The field emission characteristics of the SiNW film were studied based on current–voltage measurements and the Fowler–Nordheim equation. The electron field emission increased with decreasing diameter of SiNWs. A hydrogen plasma treatment of the SiNW film aimed at reducing the oxide overlayer improved the emission uniformity of the film. © 1999 American Institute of Physics.
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79.70.+q Field emission, ionization, evaporation, and desorption

Factors influencing the interfacial roughness of InGaAs/GaAs heterostructures: A scanning tunneling microscopy study

Kuo-Jen Chao, Ning Liu, Chih-Kang Shih, D. W. Gotthold, and B. G. Streetman

Appl. Phys. Lett. 75, 1703 (1999); http://dx.doi.org/10.1063/1.124795 (3 pages) | Cited 12 times

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Using cross-sectional scanning tunneling microscopy, we have investigated factors which influence interfacial roughness in InGaAs/GaAs heterostructures and have found that the roughness of the growth front and In segregation are two major factors influencing the interfacial roughness. In addition, we noticed no preferential clustering of indium atoms along the [001] growth direction as previously reported by others. Furthermore, a growth procedure which combines substrate temperature ramping with a growth interruption results in an atomically smooth interface. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
64.75.-g Phase equilibria
68.35.Fx Diffusion; interface formation

High-quality coalescence of laterally overgrown GaN stripes on GaN/sapphire seed layers

P. Fini, L. Zhao, B. Moran, M. Hansen, H. Marchand, J. P. Ibbetson, S. P. DenBaars, U. K. Mishra, and J. S. Speck

Appl. Phys. Lett. 75, 1706 (1999); http://dx.doi.org/10.1063/1.124796 (3 pages) | Cited 54 times

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We have characterized GaN stripes grown by lateral epitaxial overgrowth on large-area (2 in.) SiO2/GaN/Al2O3 wafers by low-pressure metalorganic chemical vapor deposition before and after coalescence. Using scanning electron microscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscope (AFM), it is shown that by first obtaining “wings” (laterally overgrown material) with low tilt relative to the “seed” (underlying) GaN, very few extended defects are formed when wings from neighboring stripes coalesce. After wings with a tilt of ∼0.1° are coalesced and an additional ∼10 μm of GaN is grown, it is found with XRD that peak splitting due to tilt is no longer detectable. TEM and AFM results show that few dislocations (with a linear density <4×103 cm−1) are formed at coalescence fronts. © 1999 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.B- Structure of clean surfaces (and surface reconstruction)
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

X-ray imaging and diffraction from surface phonons on GaAs

W. Sauer, M. Streibl, T. H. Metzger, A. G. C. Haubrich, S. Manus, A. Wixforth, J. Peisl, A. Mazuelas, J. Härtwig, and J. Baruchel

Appl. Phys. Lett. 75, 1709 (1999); http://dx.doi.org/10.1063/1.124797 (3 pages) | Cited 22 times

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Surface acoustic waves (SAWs) are excited on the GaAs (001) surface by using interdigital transducers, designed for frequencies of up to 900 MHz. The emitted phonons with wavelengths down to 3.5 μm are visualized and characterized by combined x-ray diffraction techniques. Using stroboscopic topography, the SAW emission of a parallel and a focusing transducer geometry are imaged. High-resolution x-ray diffraction profiles show up to 12 phonon-induced satellite reflections besides the GaAs (004) reflection, with a width of 9 arcsec each. The diffraction pattern is simulated numerically, applying the kinematical scattering theory to a model crystal. From fits to measured diffraction profiles at different excitation voltages, the SAW amplitudes were calculated and found to be in the sub-nm range. © 1999 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
68.35.Gy Mechanical properties; surface strains
68.35.B- Structure of clean surfaces (and surface reconstruction)

Ultrafast response of nonlinear refractive index of silver nanocrystals embedded in glass

Y. Hamanaka, A. Nakamura, S. Omi, N. Del Fatti, F. Vallée, and C. Flytzanis

Appl. Phys. Lett. 75, 1712 (1999); http://dx.doi.org/10.1063/1.124798 (3 pages) | Cited 50 times

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Ultrafast Kerr-type nonlinearities and relaxation dynamics of photoexcited electrons in silver nanocrystals embedded in glass have been investigated by means of femtosecond pump and probe spectroscopy. The transient absorption spectrum induced by the surface plasmon excitation shows a redshift and broadening of the surface plasmon band. The additional broadening is ascribed to the increase of surface plasmon damping and the redshift originates from a change in the real part of the dielectric function of the silver nanocrystals due to nonequilibrium electron heating. The observed redshift yields the nonlinear refractive index n2 of +2.4×10−10 esu and its time response is 1.9 ps. © 1999 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
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
77.22.Ch Permittivity (dielectric function)

Long-lasting phosphorescence in Ce3+-doped Ca2Al2SiO7 and CaYAl3O7 crystals

Nobuhiro Kodama, Tomoko Takahashi, Mitsuo Yamaga, Yoshifumi Tanii, Jianrong Qiu, and Kazuyuki Hirao

Appl. Phys. Lett. 75, 1715 (1999); http://dx.doi.org/10.1063/1.124799 (3 pages) | Cited 56 times

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Long-lasting phosphorescence is observed in Ce3+-doped Ca2Al2SiO7 (CASM) and CaYAl3O7 (CYAM) crystals at room temperature. UV irradiation at 365 nm produces broadband emissions with peaks at 417 nm for CASM and 425 nm for CYAM, which persist for not less than 1 h after the removal of the irradiating light. Based on the time dependence of the intensity of the phosphorescence, the long-lasting phosphorescence in these crystals is considered to be due to the electron–hole recombination at shallow traps, which occurs by a thermally activated process. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
71.55.Ht Other nonmetals

Structural models of amorphous carbon surfaces

Rainer Haerle, Giulia Galli, and Alfonso Baldereschi

Appl. Phys. Lett. 75, 1718 (1999); http://dx.doi.org/10.1063/1.124836 (3 pages) | Cited 8 times

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Using tight-binding molecular dynamics, we have constructed structural models of amorphous carbon surfaces, by imposing tensile strain on computer generated networks containing 512 carbon atoms until fracture is produced and two surfaces are formed. Different tensile strains are applied along different directions, in order to mimic the effect of preparation conditions. The surfaces generated with different strains from networks with a given bulk atomic density, exhibit similar structures and formation energies differ by a few 0.01 eV/Å2. Surface roughness increases with the amount of the graphitic component in the bulk sample. The calculated surface thicknesses are consistent with recent experimental data. © 1999 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
61.43.Bn Structural modeling: serial-addition models, computer simulation
68.35.Md Surface thermodynamics, surface energies
68.35.Gy Mechanical properties; surface strains
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Synthesis of uniformly distributed carbon nanotubes on a large area of Si substrates by thermal chemical vapor deposition

Cheol Jin Lee, Dae Woon Kim, Tae Jae Lee, Young Chul Choi, Young Soo Park, Won Seok Kim, Young Hee Lee, Won Bong Choi, Nae Sung Lee, Jong Min Kim, Yong Gak Choi, and Soo Chang Yu

Appl. Phys. Lett. 75, 1721 (1999); http://dx.doi.org/10.1063/1.124837 (3 pages) | Cited 64 times

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We have synthesized carbon nanotubes by thermal chemical vapor deposition of C2H2 on transition metal-coated silicon substrates. Multiwalled carbon nanotubes are uniformly synthesized on a large area of the plain Si substrates, different from previously reported porous Si substrates. It is observed that surface modification of transition metals deposited on substrates by either etching with dipping in a HF solution and/or NH3 pretreatment is a crucial step for the nanotube growth prior to the reaction of C2H2 gas. We will demonstrate that the diameters of carbon nanotubes can be controlled by applying the different transition metals. © 1999 American Institute of Physics.
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81.05.ub Fullerenes and related materials
78.66.Tr Fullerenes and related materials
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Na Fullerenes and related materials
81.65.Cf Surface cleaning, etching, patterning

Epitaxial switchable yttrium-hydride mirrors

D. G. Nagengast, J. W. J. Kerssemakers, A. T. M. van Gogh, B. Dam, and R. Griessen

Appl. Phys. Lett. 75, 1724 (1999); http://dx.doi.org/10.1063/1.124800 (3 pages) | Cited 39 times

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By means of x-ray scattering and scanning probe microscopy it is shown that high-quality epitaxial Y films can be deposited on (111)-CaF2 substrates. The films can reversibly be switched from metallic YH2 to transparent insulating YH3−δ. Although hydrogen absorption involves an expansion of the lattice and a symmetry change from hcp to fcc, the epitaxiality of the film remains intact during the switching process. The transparency and the insulating nature of the substrate opens unique possibilities to investigate electrically and optically these switchable mirror films in the single crystalline state. © 1999 American Institute of Physics.
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78.66.Bz Metals and metallic alloys
68.55.-a Thin film structure and morphology
72.60.+g Mixed conductivity and conductivity transitions
42.79.Bh Lenses, prisms and mirrors
73.61.At Metal and metallic alloys
42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Nk Insulators

Laser-induced direct formation of C54 TiSi2 films with fine grains on c-Si substrates

S. Y. Chen, Z. X. Shen, Z. D. Chen, L. H. Chan, and A. K. See

Appl. Phys. Lett. 75, 1727 (1999); http://dx.doi.org/10.1063/1.124801 (3 pages) | Cited 7 times

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In this letter, we report on the direct synthesis of C54 TiSi2 films with fine grains by pulsed-laser irradiation from Ti deposited on Si substrates, using a Q-switched Nd:YAG laser. The films were characterized using micro-Raman spectroscopy, high-resolution transmission electron microscopy, and atomic force microscopy. In comparison with the C54 TiSi2 using the conventional rapid thermal annealing (RTA) of 35 nm thick Ti/Si, which has an average grain size of about 110 nm and film thickness of 50 nm, the laser-induced C54 TiSi2 films vary from 13 to about 42 nm in thickness with different laser scanning speed and the grain size is 85 nm on average. The TiSi2/substrate Si interface is smooth on the atomic scale. Our results demonstrate the unique advantages of the laser-induced formation technique and its potential in deep submicron semiconductor technology. We propose that the C54 phase is formed by solid-state diffusion, rather than melting. © 1999 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.-a Thin film structure and morphology
81.05.Bx Metals, semimetals, and alloys
68.35.Fx Diffusion; interface formation
42.62.Cf Industrial applications
78.66.Bz Metals and metallic alloys
68.35.Ct Interface structure and roughness
78.30.Er Solid metals and alloys
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