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1 Nov 1999

Volume 75, Issue 18, pp. 2707-2859

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Dynamic response of the electro-optic effect in epitaxial KNbO3

B. H. Hoerman, B. M. Nichols, M. J. Nystrom, and B. W. Wessels

Appl. Phys. Lett. 75, 2707 (1999); http://dx.doi.org/10.1063/1.125123 (3 pages) | Cited 14 times

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The dynamic response of the electro-optic coefficient of epitaxial KNbO3 thin films was measured at room temperature. The effective electro-optic coefficient for these films at 100 kHz is 12 pm/V. The magnitude of the electro-optic response increased by seventy percent as the duration of the applied field was increased from 10 ns to 10 μs. A dispersion of the electro-optic coefficient is observed which follows a power law given by Atm. © 1999 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
78.20.Jq Electro-optical effects
78.66.Nk Insulators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Efficient polarization insensitive four-wave mixing using a semiconductor optical amplifier and one pump source in an optical loop

J. M. Tang, P. S. Spencer, and K. A. Shore

Appl. Phys. Lett. 75, 2710 (1999); http://dx.doi.org/10.1063/1.125124 (3 pages) | Cited 6 times

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An improved scheme for polarization insensitive four-wave mixing in semiconductor optical amplifiers (SOAs) is proposed, utilizing just one polarization insensitive SOA and one input pump wave, and without compromising the achievable conjugate power compared with that obtained from a conventional dual-pump co-propagating configuration. For frequency detuning larger than ∼ 300 GHz for a device length of say 500 μm, polarization sensitivity less than ∼ 0.8 dB can be obtained. © 1999 American Institute of Physics.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.55.Px Semiconductor lasers; laser diodes

Polymer gel light-emitting devices

Shun-Chi Chang and Yang Yang

Appl. Phys. Lett. 75, 2713 (1999); http://dx.doi.org/10.1063/1.125125 (3 pages) | Cited 6 times

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Polymers can be processed into several forms such as solid films, solutions, and gels. Traditional conjugated polymer electroluminescent devices are thin film, solid-state devices consisting of a thin polymer film sandwiched between two electrodes. Recently, a light-emitting device based on polymer solutions has been demonstrated. In this letter, we report the generation of luminescence from a polymer gel in a compact cell configuration. This unique polymer gel light-emitting device (GLED) consists of a thin layer of a polymer gel sandwiched between two electrode/glass substrates. The emission spectrum is consistent with the photoluminescence spectrum obtained from the polymer gel. The device shows an operating mechanism similar to the electrogenerated chemiluminescence. © 1999 American Institute of Physics.
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85.60.Jb Light-emitting devices
42.70.Jk Polymers and organics
82.70.Gg Gels and sols
78.60.Ps Chemiluminescence
78.60.Fi Electroluminescence

GaInNAs resonant-cavity-enhanced photodetector operating at 1.3 μm

J. B. Héroux, X. Yang, and W. I. Wang

Appl. Phys. Lett. 75, 2716 (1999); http://dx.doi.org/10.1063/1.125126 (3 pages) | Cited 55 times

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We demonstrate a GaAs-based p-i-n resonant-cavity-enhanced (RCE) GaInNAs photodetector operating near 1.3 μm. The device design was optimized using a transfer matrix method and experimental absorption spectra obtained from p-i-n structures grown without a resonant cavity. The RCE photodetector was fabricated in a single growth step by using GaAs/AlAs distributed Bragg reflectors for the top and bottom mirrors. A 72% quantum efficiency was obtained with a full width at half maximum of 11 nm. © 1999 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)

A five-period normal-incidence (In, Ga)As/GaAs quantum-dot infrared photodetector

Dong Pan, Elias Towe, and Steve Kennerly

Appl. Phys. Lett. 75, 2719 (1999); http://dx.doi.org/10.1063/1.125127 (3 pages) | Cited 51 times

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We have measured the optical and electrical properties of a five-period normal-incidence (In, Ga)As/GaAs quantum-dot infrared photodetector. A primary intersubband transition peak is observed at the wavelength of 10.2 μm and a secondary one at 9.4 μm. Excellent electron transport and peak detectivity of 7×109 cm Hz1/2/W are achieved at 30 K, with a low bias responsivity of up to 70 mA/W at 0.6 V. We believe that an observed avalanche gain process is initiated by intersubband absorption in the quantum dots. The maximum responsivity due to this avalanche multiplication process is about 4 A/W at a bias of 1.0 V. © 1999 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.50.Fq High-field and nonlinear effects
73.50.Pz Photoconduction and photovoltaic effects

Continuous wave laser radiation at 1314 and 1386 nm and infrared to red self-frequency doubling in nonlinear LaBGeO5:Nd3+ crystal

J. Capmany, D. Jaque, and J. García Solé

Appl. Phys. Lett. 75, 2722 (1999); http://dx.doi.org/10.1063/1.125128 (3 pages) | Cited 2 times

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We report efficient generation of continuous wave laser radiation in the nonlinear LaBGeO5:Nd3+ crystal around 1.3 μm. The 4F3/2→4I13/2 laser channel of Nd3+ ions in this crystal leads to efficient generation of laser radiation at 1314 nm (π polarization) and at 1386 nm (σ polarization). Under resonant pumping with a Ti:sapphire laser at 800 nm in the GaAlAs laser diode emission spectral region, an absorbed power threshold of 26 mW is obtained for 1% output coupling. A slope efficiency of 40% is obtained for an output coupling of 3%. Visible red laser radiation at 657 nm is obtained by self-frequency doubling in a type I phase matched crystal. © 1999 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Hj Laser materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Photonic crystals as optical components

P. Halevi, A. A. Krokhin, and J. Arriaga

Appl. Phys. Lett. 75, 2725 (1999); http://dx.doi.org/10.1063/1.125129 (3 pages) | Cited 29 times

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Photonic crystals (PCs) have already found numerous applications associated with the photonic band gap. We point out that PCs could be also employed as custom-made optical components in the linear region well below the photonic gap. As an example, we discuss a birefringent PC lens that acts as a polarizing beam splitter. This idea is supported by a precise method of calculation of the optical constants of a transparent two-dimensional (2D) PC. Such a process of homogenization is performed for hexagonal arrays of polymer-based PCs and also for the mammalian cornea. Finally, 2D PCs are classified as optically uniaxial or biaxial. © 1999 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.50.-p Quantum optics
42.79.Fm Reflectors, beam splitters, and deflectors
42.79.Bh Lenses, prisms and mirrors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Fm Birefringence
42.70.Jk Polymers and organics
42.66.Ct Anatomy and optics of eye

Generation of first-order terahertz optical sidebands in asymmetric coupled quantum wells

C. Phillips, M. Y. Su, M. S. Sherwin, J. Ko, and L. Coldren

Appl. Phys. Lett. 75, 2728 (1999); http://dx.doi.org/10.1063/1.125130 (3 pages) | Cited 34 times

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We have generated first-order tetrahertz (THz) optical sidebands on a near-infrared (NIR) probe beam by driving an excitonic intersubband resonance with THz electric fields. We use THz radiation polarized along the noncentrosymmetric axis of a quantum well system to generate a comb of sidebands ωsideband = ωNIR+nωTHz. The n = 1 process offers an efficient means of modulating a NIR carrier beam at THz frequencies and yields new spectroscopic information on excitonic intersubband transitions. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.20.Jq Electro-optical effects
71.35.Gg Exciton-mediated interactions
78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Simple and convenient nonoptical shear force sensor for shear force and near-field optical microscopes

Y. Bai, J. D. White, G. Zhang, G. Chen, and X. Hou

Appl. Phys. Lett. 75, 2731 (1999); http://dx.doi.org/10.1063/1.125131 (3 pages) | Cited 1 time

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A simple, compact, and inexpensive method for shear force distance regulation is presented. A single piezoelectric cantilever is employed to both dither a fiber probe and to detect the decrease in piezotension-induced voltage as it approaches the sample surface. On resonance, the large piezotension-induced voltage (∼0.2 mV/nm) allows for simple electronics to be used. It is expected to find application both in shear force microscopy and for shear force distance regulation in near-field optical microscopy. © 1999 American Institute of Physics.
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07.10.Pz Instruments for strain, force, and torque
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
07.79.Sp Friction force microscopes
07.79.Fc Near-field scanning optical microscopes
07.68.+m Photography, photographic instruments; xerography
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Ion acceleration in the radially expanding plasma of the hot refractory anode vacuum arc

I. I. Beilis, R. L. Boxman, S. Goldsmith, and V. L. Paperny

Appl. Phys. Lett. 75, 2734 (1999); http://dx.doi.org/10.1063/1.125132 (3 pages) | Cited 5 times

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The ion energy and plasma potential as a function of radial distance were measured in a vacuum arc mode—the hot refractory anode vacuum arc. A 175 A arc was sustained between a 30-mm-diam water-cooled Cu cathode and a thermally isolated graphite anode. The plasma potential and electron temperature were determined using a triple probe, and the ion energy distribution was measured with a retarding field analyzer. It was found that the electron temperature decreased from 1.2 to 0.6 eV with increasing radial distance from 3 to 18 cm. In the same distance range, the directed ion energy per unit charge increased from 8 to 20 eV. The 12 eV ion energy enhancement significantly exceeded the measured drop of the plasma potential of about 2 V, indicating that the ions were not accelerated electrostatically. © 1999 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.70.Ds Electric and magnetic measurements
52.25.Kn Thermodynamics of plasmas
52.30.-q Plasma dynamics and flow

Negative ion enhancement in caesium-seeded hydrogen discharges—a volume or surface effect?

P. G. Steen and W. G. Graham

Appl. Phys. Lett. 75, 2737 (1999); http://dx.doi.org/10.1063/1.125133 (3 pages) | Cited 4 times

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Measurements of plasma parameters, including H− ion densities, made in conjunction with wall temperature, visible and vacuum ultraviolet emission spectroscopy verify that there is little caesium in the plasma volume of the H− ion source. Surface work function measurements indicate that there is significant caesium coverage of the inner walls of the ion source. It is found that, as the work function of a test surface decreases due to caesium seeding, the H− ion fraction in the discharge volume increases. These observations combine to indicate that, in the present source, the H− ion enhancement mechanism is a surface dominated effect. © 1999 American Institute of Physics.
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52.80.-s Electric discharges
07.77.Ka Charged-particle beam sources and detectors
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Ds Electric and magnetic measurements
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Z-contrast imaging and electron energy-loss spectroscopy analysis of chromium-doped diamond-like carbon films

X. Fan, E. C. Dickey, S. J. Pennycook, and M. K. Sunkara

Appl. Phys. Lett. 75, 2740 (1999); http://dx.doi.org/10.1063/1.125134 (3 pages) | Cited 19 times

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Metal-doped diamond-like carbon films were produced for the purpose of an electrochemical nanoelectrode. In this study we use Z-contrast scanning transmission electron microscopy to directly observe metal cluster formation and distributions within the chromium-doped carbon films. At low doping (∼6 at. % Cr), Cr is uniformly distributed within the C matrix; at high doping (∼12 at. % Cr), Cr-rich clusters are formed. Analyzing electron energy loss spectroscopy Cr L2,3 white line ratios, we find that the Cr tends to be metallic-like when it is uniformly distributed in the C matrix and carbide-like in the Cr-rich clusters. The carbon is more diamond-like at low doping and more graphite/carbide-like at high doping according to the sp2/sp3 electron percentage measurements. © 1999 American Institute of Physics.
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68.55.-a Thin film structure and morphology
61.43.-j Disordered solids
79.20.Kz Other electron-impact emission phenomena
61.46.-w Structure of nanoscale materials

In situ high-resolution transmission electron microscopy of direct bonding processes between silicon tips with oxide surfaces at room temperature

Tokushi Kizuka and Kazue Hosoki

Appl. Phys. Lett. 75, 2743 (1999); http://dx.doi.org/10.1063/1.125135 (3 pages) | Cited 3 times

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Nanometer-sized silicon (Si) tips were mechanically bonded and retracted by piezo driving inside a high-resolution transmission electron microscope. The process was directly observed in situ at a spatial resolution of 0.2 nm. It was found that crystalline-Si/amorphous-Si oxide/crystalline-Si boundaries were produced by contact at room temperature. The deformation and strength of the boundaries were investigated. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.35.Gy Mechanical properties; surface strains
81.05.Cy Elemental semiconductors
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.07.-b Nanoscale materials and structures: fabrication and characterization

Effects of disorder on the optical gap of (Zn,Mg)(S,Se)

Antonino Marco Saitta, Stefano de Gironcoli, and Stefano Baroni

Appl. Phys. Lett. 75, 2746 (1999); http://dx.doi.org/10.1063/1.125136 (3 pages) | Cited 8 times

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The electronic properties and optical gap of (Zn,Mg)(S,Se) wide-gap solid solutions are studied using ab initio techniques and starting from the previously determined atomistic structure of the alloy. Compositional disorder is shown to close the gap substantially with respect to the predictions of the virtual-crystal approximation. The bowing of the fundamental gap versus composition predicted by our calculations is in very good agreement with experiments available for the Zn(S,Se) pseudobinary alloy. At temperatures typical of molecular-beam epitaxy growth, the quaternary alloy displays a rather large amount of short-range order whose effect is to slightly but unmistakably open the gap. Our results agree well with recent experimental data for the quaternary alloy. © 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)
71.20.Nr Semiconductor compounds
71.15.-m Methods of electronic structure calculations
78.66.Li Other semiconductors

Thermal strain in GaAs layers grown by epitaxial lateral overgrowth on Si substrates

Z. R. Zytkiewicz and J. Domagala

Appl. Phys. Lett. 75, 2749 (1999); http://dx.doi.org/10.1063/1.125137 (3 pages) | Cited 8 times

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X-ray diffraction was used to study deformation of GaAs layers grown on Si substrates by liquid phase epitaxial lateral overgrowth (ELO). We show that, in the direction perpendicular to seeding lines, the GaAs ELO stripes bend outwards from the mask due to the tensile strain in the GaAs buffer layer. As narrow as 94 arcsec (004) rocking curves have been measured for the laterally grown parts of ELO stripes what indicates the high quality of ELO GaAs layers grown on GaAs-coated Si substrates. We use our model of strain relaxation via bending of laterally grown parts of ELO layers to explain some recently published results on bending of ELO GaN layers on SiC and sapphire substrates. © 1999 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
62.20.F- Deformation and plasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Controlled arrangement of self-organized Ge islands on patterned Si (001) substrates

G. Jin, J. L. Liu, S. G. Thomas, Y. H. Luo, K. L. Wang, and Bich-Yen Nguyen

Appl. Phys. Lett. 75, 2752 (1999); http://dx.doi.org/10.1063/1.125138 (3 pages) | Cited 68 times

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We report the ability to arrange self-organized Ge islands on patterned Si (001) substrates. Selective epitaxial growth of Si is carried out with gas-source molecular beam epitaxy to form Si mesas followed by subsequent Ge growth. Self-aligned and regularly spaced Ge islands are formed on the 〈110〉-oriented ridges of the Si stripe mesas. A mono-modal size distribution of the islands has been observed on the ridges. Using preferential nucleation sites allows us to place Ge islands at predetermined positions. The controlled arrangement of self-organized nanostructures offers the potential applications of island arrays for the implementation in nanoelectronics and quantum computation. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.05.Cy Elemental semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Geometrical structure and electronic properties of atomically resolved multiwall carbon nanotubes

A. Hassanien, M. Tokumoto, S. Ohshima, Y. Kuriki, F. Ikazaki, K. Uchida, and M. Yumura

Appl. Phys. Lett. 75, 2755 (1999); http://dx.doi.org/10.1063/1.125139 (3 pages) | Cited 11 times

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Multiwall carbon nanotubes (MWNTs) are predicated to exhibit various electronic properties depending on their diameters and chiralities. The existence of multishells offers the possibility of switching between high and low conducting states within the same nanotube. So far, it has been a big challenge to probe the structure and the electronic properties of different MWNT shells. Here we report the nanostructure measurements of MWNT together with their electronic properties as revealed by a scanning tunneling microscope. The images show tubes with different chiralities (0°–30°) and diameters (4–9 nm). Upon thermal oxidation in air, we have observed diameter-dependent tube opening. MWNTs with large diameters (7–9 nm) show open ends while smaller diameters have closed ends. The structure of open end shows unsaturated bonds, which offers rich chemistry to develop molecular technology based on carbon nanotubes. Finally, we present the structure of the inner shells of MWNT. © 1999 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
71.20.Tx Fullerenes and related materials; intercalation compounds
72.80.Rj Fullerenes and related materials
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
68.37.Ps Atomic force microscopy (AFM)
68.37.Rt Magnetic force microscopy (MFM)
68.37.Uv Near-field scanning microscopy and spectroscopy

Stable hexagonal-wurtzite silicon phase by laser ablation

Yan Zhang, Zafar Iqbal, Sankaran Vijayalakshmi, and Haim Grebel

Appl. Phys. Lett. 75, 2758 (1999); http://dx.doi.org/10.1063/1.125140 (3 pages) | Cited 18 times

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A stable phase of relatively large hexagonal-wurtzite silicon crystals (up to 20 μm) was directly deposited at low pressure using ultraviolet laser ablation. The films were grown on a variety of substrates at room temperature from a single crystal, cubic silicon target. Crystallites of the hexagonal-wurtzite phase of silicon were clearly identified using selected area electron diffraction. Further support for this identification was provided by confocal scanning micro-Raman spectroscopy. The deposition of hexagonal silicon films may lead to novel two-dimensional optoelectronic devices, and pave the way to studies of the electronic properties of this lower symmetry, uncommon silicon phase. © 1999 American Institute of Physics.
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81.05.Cy Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
81.15.Fg Pulsed laser ablation deposition
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology

Photoluminescence and ultraviolet lasing of polycrystalline ZnO thin films prepared by the oxidation of the metallic Zn

Sunglae Cho, Jing Ma, Yunki Kim, Yi Sun, George K. L. Wong, and John B. Ketterson

Appl. Phys. Lett. 75, 2761 (1999); http://dx.doi.org/10.1063/1.125141 (3 pages) | Cited 191 times

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We report a simple method for preparing polycrystalline ZnO thin films with good luminescent properties: the oxidization of metallic Zn films. In photoluminescence (PL) studies at room temperature for wavelengths between 370 and 675 nm, we have observed a single exciton peak around 390 nm without any deep-level emission and a small PL full width at half maximum (23 meV), indicating that the concentrations of the defects responsible for the deep-level emissions are negligible. We have also observed optically pumped lasing action in these films. The threshold intensity for lasing was ∼9 MW/cm2. © 1999 American Institute of Physics.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Fy Semiconductors
42.55.Px Semiconductor lasers; laser diodes

Microwave synthesis of fullerenes from chloroform

Su-yuan Xie, Rong-bin Huang, La-jia Yu, Jie Ding, and Lan-sun Zheng

Appl. Phys. Lett. 75, 2764 (1999); http://dx.doi.org/10.1063/1.125142 (3 pages) | Cited 7 times

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Fullerenes C60 and C70 were synthesized continuously via microwave plasma from chloroform at low pressure argon atmosphere, and identified in toluene extracts of soot, using high-performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry and diode-array spectrophotometric detection. Yield of C60 (0.3%–1.3%) and C70 (0.1%–0.3%) and their ratio depend on the temperature gradient and the collision probability. Besides fullerenes, a series of perchlorinated carbon clusters were found in the synthesis products. Since frameworks of the products are fragments of fullerenes, the further investigation of this process may lead to a better knowledge of the formation mechanisms of fullerenes. © 1999 American Institute of Physics.
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81.05.ub Fullerenes and related materials
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
82.80.Bg Chromatography
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
61.48.-c Structure of fullerenes and related hollow and planar molecular structures

Direct nanoimprint of submicron organic light-emitting structures

Jian Wang, Xiaoyun Sun, Lei Chen, and Stephen Y. Chou

Appl. Phys. Lett. 75, 2767 (1999); http://dx.doi.org/10.1063/1.125143 (3 pages) | Cited 56 times

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We have demonstrated a method to directly pattern organic light-emitting structures with a submicron resolution without any degradation in optical properties. Both small molecules and polymer-based light-emitting structures were patterned by nanoimprint at 150 °C in a vacuum. The comparison of luminescence efficiency before and after patterning shows that nanoimprint did not cause degradation in the optical property of the materials. Nanoimprint offers a low-cost, high-throughput, high-resolution patterning technique that opens a way for realizing novel photonic devices based on organic light-emitting materials. © 1999 American Institute of Physics.
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42.70.Jk Polymers and organics
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Nanocrystallization of ZrTiCuNiBeC bulk metallic glass under high pressure

Wei Hua Wang, D. W. He, D. Q. Zhao, Y. S. Yao, and M. He

Appl. Phys. Lett. 75, 2770 (1999); http://dx.doi.org/10.1063/1.125144 (3 pages) | Cited 40 times

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Nanocrystallization of Zr41Ti14Cu12.5Ni9Be22.5C1 bulk metallic glass (BMG) under high pressure is investigated. It is found that the nanocrystallization is pressure assisted, and the primary nanocrystallization temperature decreases as the applied pressure increases. Pressure annealing of the BMG in the supercooled liquid region produces a composite with dispersion of very fine nanocrystallites in the amorphous matrix. A fully nanocrystallization is obtained by pressure annealing under 6 GPa at 723 K. The pressure also controls the phase selection during the crystallization. The mechanism for the pressure-assisted nanocrystallization is discussed. © 1999 American Institute of Physics.
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61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
62.50.-p High-pressure effects in solids and liquids
81.40.Vw Pressure treatment
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Nanotube electronic states observed with thermal field emission electron spectroscopy

Kenneth A. Dean, Oliver Groening, Olivier M. Küttel, and L. Schlapbach

Appl. Phys. Lett. 75, 2773 (1999); http://dx.doi.org/10.1063/1.125145 (3 pages) | Cited 27 times

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We observe nonmetallic electronic states above the Fermi level in single-walled carbon nanotubes by measuring the energy distribution of thermal-field-emitted electrons. This measurement method examines electronic states associated with the nanotube cap or end termination, and with it, we resolve electronic states greater than 3 eV above the Fermi level. The observed emitting states are broad at high temperatures (0.7–1.5 eV full width at half maximum), and the peak positions shift linearly with applied voltage. We present possible mechanisms responsible for these states. © 1999 American Institute of Physics.
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71.20.Tx Fullerenes and related materials; intercalation compounds
68.37.Vj Field emission and field-ion microscopy
79.70.+q Field emission, ionization, evaporation, and desorption
73.40.Gk Tunneling

Determination of the critical layer thickness in the InGaN/GaN heterostructures

C. A. Parker, J. C. Roberts, S. M. Bedair, M. J. Reed, S. X. Liu, and N. A. El-Masry

Appl. Phys. Lett. 75, 2776 (1999); http://dx.doi.org/10.1063/1.125146 (3 pages) | Cited 42 times

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We present an approach to determine the critical layer thickness in the InxGa1−xN/GaN heterostructure based on the observed change in the photoluminescence emission as the InxGa1−xN film thickness increases. From the photoluminescence data, we identify the critical layer thickness as the thickness where a transition occurs from the strained to unstrained condition, which is accompanied by the appearance of deep level emission and a drop in band edge photoluminescence intensity. The optical data that indicate the onset of critical layer thickness, was also confirmed by the changes in InxGa1−xN surface morphology with thickness, and is consistent with x-ray diffraction measurements. © 1999 American Institute of Physics.
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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
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
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Control of surface states in GaSb/AlxGa1−xAsySb1−y/GaxIn1−xSb/AlxGa1−xAsySb1−y quantum well structures

D. K. Johnstone, Y. K. Yeo, R. L. Hengehold, and G. W. Turner

Appl. Phys. Lett. 75, 2779 (1999); http://dx.doi.org/10.1063/1.125147 (3 pages) | Cited 2 times

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GaSb-based lasers show advanced capabilities over other material for the far-infrared wavelength range. However, for quantum-well (QW) laser structures of AlxGa1−xAsySb1−y/GaxIn1−xAsySb1−y/AlxGa1−xAsySb1−y grown on GaSb, each component element etches at a different rate, making it difficult to achieve quality surfaces sufficiently free of defects. Thus, in this letter, the effects on the surface quality of GaSb-based laser materials have been studied using phosphoric acid etching, boron trichloride reactive ion etching (RIE), and a postetch sulfur treatment. In addition, the quality of the surface is compared for two barriers of AlAs0.07Sb0.93 and Al0.9Ga0.1As0.07Sb0.93, based on current–voltage measurements as a function of temperature. The best surfaces were produced by RIE and by using as much Ga in the barriers as the device operation allows. A generation center in the Ga0.81In0.19As0.12Sb0.88 was found at 0.14 eV for QW diodes with low surface conduction. © 1999 American Institute of Physics.
Show PACS
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
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