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1 Nov 1999

Volume 75, Issue 18, pp. 2707-2859

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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 41 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 43 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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