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15 Nov 2007

Volume 102, Issue 10, Articles (10xxxx)

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Investigation of the roundtrip cavity loss in laser diode pumped erbium:ytterbium-phosphate glass microchip lasers

Shujing Liu, Feng Song, Hong Cai, Teng Li, Xin Zhang, Zhaohui Wu, and Jianguo Tian

J. Appl. Phys. 102, 103101 (2007); http://dx.doi.org/10.1063/1.2805642 (4 pages) | Cited 1 time

Online Publication Date: 16 November 2007

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We present a method for determination of the roundtrip cavity loss in the laser diode pumped erbium:ytterbium-codoped phosphate glass microchip laser. Slope efficiency and laser threshold were measured in the experiment and their dependencies on roundtrip cavity loss were derived through rate equations. According to the energy levels, cumulative upconversion and cooperative upconversion are taken into consideration to ensure the accuracy of the derivation. Roundtrip cavity losses in different cavity configurations were investigated.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Sa Microcavity and microdisk lasers

Ghost imaging in Fourier space

Honglin Liu, Jing Cheng, and Shensheng Han

J. Appl. Phys. 102, 103102 (2007); http://dx.doi.org/10.1063/1.2812597 (4 pages) | Cited 3 times

Online Publication Date: 20 November 2007

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In experimentation we first find that a ghost diffraction image exists even when the coherent length on the object plane is larger than the character size of the object, and we explain the phenomenon in Fourier space. The analysis indicates that the resolution of the far-field diffraction image is determined by the coherent length on the back-focus plane, and the distribution of the wave vector of the illumination on the object determines the range of information of a pixel detector collecting in the signal arm.
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42.50.Dv Quantum state engineering and measurements
03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)

Strong tip effects in near-field scanning optical tomography

Jin Sun, P. Scott Carney, and John C. Schotland

J. Appl. Phys. 102, 103103 (2007); http://dx.doi.org/10.1063/1.2812545 (9 pages) | Cited 15 times

Online Publication Date: 21 November 2007

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A model for the interaction of the scanning probe in near-field scanning optical microscopy is presented. Multiple scattering of the illuminating field with the probe is taken into account. The implications of this so-called strong tip model for the solution of the associated inverse scattering problem are studied through simulations.
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07.79.Fc Near-field scanning optical microscopes

Iodine enhanced focused-ion-beam etching of silicon for photonic applications

Jonathan Schrauwen, Dries Van Thourhout, and Roel Baets

J. Appl. Phys. 102, 103104 (2007); http://dx.doi.org/10.1063/1.2815664 (7 pages) | Cited 3 times

Online Publication Date: 26 November 2007

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Focused-ion-beam etching of silicon enables fast and versatile fabrication of micro- and nanophotonic devices. However, large optical losses due to crystal damage and ion implantation make the devices impractical when the optical mode is confined near the etched region. These losses are shown to be reduced by the local implantation and etching of silicon waveguides with iodine gas enhancement, followed by baking at 300 °C. The excess optical loss in the silicon waveguides drops from 3500 to 1700 dB/cm when iodine gas is used, and is further reduced to 200 dB/cm after baking at 300 °C. We present elemental and chemical surface analyses supporting that this is caused by the desorption of iodine from the silicon surface. Finally we present a model to extract the absorption coefficient from the measurements.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.79.Gn Optical waveguides and couplers

Microstructured surface design for omnidirectional antireflection coatings on solar cells

Weidong Zhou, Meng Tao, Li Chen, and Hongjun Yang

J. Appl. Phys. 102, 103105 (2007); http://dx.doi.org/10.1063/1.2817470 (9 pages) | Cited 33 times

Online Publication Date: 27 November 2007

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We recently demonstrated a new process for the formation of partially spherical structures as an omnidirectional antireflection coating (omni-AR). In this paper, we report the simulation results of the angular and spectral dependences of the total reflectivity on various microstructured surfaces based on the rigorous coupled-wave analysis. Close to zero reflection can be achieved in these microstructured surfaces over an extended spectral region for large ranges of light incident angles. The impact of feature size, density, shape, and refractive index has all been investigated. The experimental results agree reasonably well with the theoretical work. Such an omni-AR structure offers an attractive solution to current crystalline silicon solar cells, as well as future thin film, quantum dot, and organic solar cells.
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68.35.-p Solid surfaces and solid-solid interfaces: structure and energetics
84.60.Jt Photoelectric conversion
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Temporal characteristics of an optical soliton with distributed Raman amplification

Hongjun Zheng, Shanliang Liu, Xin Li, and Zhen Tian

J. Appl. Phys. 102, 103106 (2007); http://dx.doi.org/10.1063/1.2817478 (4 pages) | Cited 6 times

Online Publication Date: 27 November 2007

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The effects of distributed Raman amplification (DRA) on temporal characteristics of an optical soliton that are numerically investigated by using the split-step Fourier method are compared with the experimental data measured by employing the second-harmonic generation frequency-resolved optical gating analyzer. It is found that the numerical results are consistent with the experimental data. DRA that can compensate the fiber loss does not change the temporal wave form of the soliton. The soliton width performs a various oscillation with propagation distance when considering the fiber loss and different Raman gain. Compensation of the fiber loss increases with the increase of the Raman pumping power.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Tg Optical solitons; nonlinear guided waves
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High energy pulsed inductive thruster modeling operating with ammonia propellant

Pavlos G. Mikellides and James K. Villarreal

J. Appl. Phys. 102, 103301 (2007); http://dx.doi.org/10.1063/1.2809436 (8 pages) | Cited 4 times

Online Publication Date: 16 November 2007

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Numerical modeling of the pulsed inductive thruster operating with ammonia propellant at high energy levels, utilized a time-dependent, two-dimensional, and axisymmetric magnetohydrodynamics code to provide bilateral validation of experiment and theory and offer performance insights for improved designs. The power circuit model was augmented by a plasma voltage algorithm that accounts for the propellant’s time-dependent resistance and inductance to properly account for plasma dynamics and was verified using available analytic solutions of two idealized plasma problems. Comparisons of the predicted current waveforms to experimental data exhibited excellent agreement for the initial half-period, essentially capturing the dominant acceleration phase. Further validation proceeded by comparisons of the impulse for three different energy levels, 2592, 4050, and 4608 J and a wide range of propellant mass values. Predicted impulse captured both trends and magnitudes measured experimentally for nominal operation. Interpretation of the modeling results in conjunction to experimental observations further confirm the critical mass phenomenon beyond which efficiency degrades due to elevated internal energy mode deposition and anomalous operation.
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52.75.Di Ion and plasma propulsion
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj Magnetohydrodynamic and fluid equation
02.60.Cb Numerical simulation; solution of equations

Laser-induced breakdown spectroscopy of trisilane using infrared CO2 laser pulses

J. J. Camacho, J. M. L. Poyato, L. Díaz, and M. Santos

J. Appl. Phys. 102, 103302 (2007); http://dx.doi.org/10.1063/1.2811870 (10 pages) | Cited 5 times

Online Publication Date: 20 November 2007

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The plasma produced in trisilane (Si3H8) at room temperature and pressures ranging from 50 to 103 Pa by laser-induced breakdown (LIB) has been investigated. The ultraviolet-visible-near infrared emission generated by high-power IR CO2 laser pulses in Si3H8 has been studied by means of optical emission spectroscopy. Optical breakdown threshold intensities in trisilane at 10.591 μm for laser pulse lengths of 100 ns have been measured as a function of gas pressure. The strong emission observed in the plasma region is mainly due to electronic relaxation of excited atomic H and Si and ionic fragments Si+, Si2+, and Si3+. An excitation temperature Texc = 5600±300 K was calculated by means of H atomic lines assuming local thermodynamic equilibrium. The physical processes leading to LIB of trisilane in the power density range 0.28 GW cm−2<J<3.99 GW cm−2 have been analyzed. From our experimental observations we can propose that, although the first electrons must appear via multiphoton ionization, electron cascade is the main mechanism responsible for the breakdown in trisilane.
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78.55.Hx Other solid inorganic materials

Practical sensor for nitrogen in direct current glow discharges

D. Popović, V. Milosavljević, and S. Daniels

J. Appl. Phys. 102, 103303 (2007); http://dx.doi.org/10.1063/1.2816254 (7 pages) | Cited 3 times

Online Publication Date: 29 November 2007

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This paper presents a method for precise measurement of atomic and molecular nitrogen in an oxygen-nitrogen dc plasma. This is achieved by monitoring the intensities of the atomic nitrogen spectral line at 821.6 nm and the molecular nitrogen bandhead at 337.1 nm, relative to the atomic oxygen spectral line at 844.7 nm. Oxygen is one of the most frequently used gases for surface chemical treatment, including deposition and etching, therefore the ability to measure and control the process and chemical composition of the process is essential. To validate this oxygen actimometry method for N2-xO2 (where x varies from 0 to 1) dc plasmas, threshold tests have been performed with Ar actinometry. The optical measurements have been performed using two methods. The first approach uses a USB2000 fiber optic spectrometer, calibrated with a Gigahertz–Optik BN-0102-1 reference standard source, to record the desired spectral lines. The second approach uses narrow bandwidth optical filters ( ∼ 0.7–0.07 nm) with central wavelengths of 821.6, 337.1, and 844.69 nm and photodiodes to detect the emission intensity, also calibrated with the same standard source. Optical data are collected for a range of experimental conditions in a flowing glow discharge of N2-xO2 mixture. The maximum dc voltage is 2.2 kV and maximum chamber pressure is 266 Pa. Data from both optical methods are compared and used to interpret the relative atomic and molecular nitrogen concentrations under various operating conditions.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.80.Hc Glow; corona

A double-band high-power microwave source

Yu-Wei Fan, Hui-Huang Zhong, Zhi-Qiang Li, Ting Shu, Jian-De Zhang, Jun Zhang, Xiao-Ping Zhang, Jian-Hua Yang, and Ling Luo

J. Appl. Phys. 102, 103304 (2007); http://dx.doi.org/10.1063/1.2817254 (3 pages) | Cited 12 times

Online Publication Date: 29 November 2007

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In order to increase the power conversion efficiency of a magnetically insulated line oscillator (MILO), an axially extracted virtual cathode oscillator (VCO) is introduced to utilize the load current in the MILO, so it is called the MILO-VCO. In this device, the MILO and VCO are operated synchronously and generate high-power microwaves. The MILO-VCO is investigated in detail with particle-in-cell (PIC) methods (KARAT code). In simulation, the diode voltage is 640 kV and the current is 50 kA. The total peak power of the MILO-VCO is 5.22 GW and the corresponding power conversion efficiency is 16.3%. In the MILO-VCO, the peak power of the MILO is 3.91 GW and its frequency is 1.76 GHz; the peak power of the VCO is 1.33 GW and its frequency is 3.79 GHz.
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84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Instability of relativistic electron-beam–dielectric system as a mechanism for microwave generation

Ling-Bao Kong, Chao-Hai Du, Pu-Kun Liu, and Liu Xiao

J. Appl. Phys. 102, 103305 (2007); http://dx.doi.org/10.1063/1.2817642 (3 pages) | Cited 7 times

Online Publication Date: 30 November 2007

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The dispersion relation of relativistic rectilinear electron beam propagating along a guide magnetic field in a dielectric is investigated by cold fluid model. In such a system, due to anomalous Doppler effect, the instability occurs when the electron velocity exceeds the wave phase velocity. The growth rate and spatial growth rate are studied analytically and the nonlinear saturated efficiency is given analytically for the first time. Numerical results show that the saturated efficiency approaches about 10%–30%. The distinctive interaction mechanism is promising for the design of a new kind of compact high-power microwave generation devices.
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41.75.Ht Relativistic electron and positron beams
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
41.20.Jb Electromagnetic wave propagation; radiowave propagation
84.40.-x Radiowave and microwave (including millimeter wave) technology
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Relationship between the optical absorption and the density of deep gap states in microcrystalline silicon

Stefan Klein, Friedhelm Finger, Reinhard Carius, Thorsten Dylla, and Josef Klomfass

J. Appl. Phys. 102, 103501 (2007); http://dx.doi.org/10.1063/1.2815645 (5 pages) | Cited 8 times

Online Publication Date: 19 November 2007

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We have measured the subgap optical absorption of undoped microcrystalline silicon samples with photothermal deflection spectroscopy and compared it with the spin density measured by electron spin resonance. The material was prepared using the hot wire chemical vapor deposition technique with a broad range of deposition parameters, yielding materials with a wide variety of structural, optical, and electronic properties. A nearly linear correlation between the spin densities and the subgap absorption coefficient at photon energy of 0.7 eV over three orders of magnitude indicates that the optical absorption in this region is due to the dominating paramagnetic defects, likely dangling bonds. However, the structural composition of the material, determined by Raman spectroscopy, has also some influence on the optical and electronic properties, which leads to some deviation from a straightforward relationship between optical absorption and spin or defect density.
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78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.55.Cn Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
76.30.Mi Color centers and other defects

Strain effects and microstructural evolution in Ge–Si system materials prepared by ion implantation and by ultrahigh vacuum chemical vapor deposition

Hailing Tu, Qinghua Xiao, and Tongda Ma

J. Appl. Phys. 102, 103502 (2007); http://dx.doi.org/10.1063/1.2811850 (5 pages)

Online Publication Date: 19 November 2007

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Appropriately utilizing some microstructures may be very helpful to acquire desirable Ge–Si system materials. In this work, the Ge–Si system materials have been prepared either by ion implantation or ultrahigh vacuum chemical vapor deposition (UHVCVD). The interesting microstructures including half-loop dislocations, SiGe nanoclusters, and dislocation dipoles have been found in these two kinds of Ge–Si system materials. It is demonstrated that the evident surface strain state and adequate surface layer quality have been realized by employing these microstructures. Compared with the dipole dislocations in the Ge–Si systems deposited by UHVCVD on the compliant silicon on insulator, the half-loop dislocations and the SiGe nanoclusters induced by Ge ion implantation and subsequent annealing can relax the SiGe layer more effectively and lead to relatively large strain in the surface silicon. It may provide some new approaches to the control of misfit strains for fabricating desirable Ge–Si system materials.
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61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.80.Jh Ion radiation effects
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing

Optical properties of Co silicides: Experiment and density functional theory

Y. V. Kudryavtsev, V. A. Oksenenko, Y. P. Lee, J. Y. Rhee, and Y. D. Kim

J. Appl. Phys. 102, 103503 (2007); http://dx.doi.org/10.1063/1.2812552 (7 pages) | Cited 2 times

Online Publication Date: 19 November 2007

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The dielectric functions of Co2Si, CoSi, and CoSi2 compounds have been measured and compared with the calculated ones. All three compounds have very common features in their density of states, especially near the Fermi level: Co 3d-dominated characteristics with very small amounts of Co and Si sp characteristics. Consequently, the features observed in the optical conductivity (OC) spectra of 0.5–5.0 eV for all the compounds also have very similar characteristics. Since in this energy range both the occupied and empty states involved in the interband-absorption peak formation have a 3d character in an energy range, the major factor contributing to the features observed in the OC spectra is the joint-density-of-states (JDOS) effects, and the optical-transition-matrix elements do not play an important role. Co2Si, whose crystal structure is orthorhombic, has a strong optical anisotropy, as expected. The structural dependence of the electronic band structure for Co silicides has also been evaluated by examining the optical properties of the disordered and the crystalline Co-Si alloy films of the CoSi and CoSi2 stoichiometry. The change in the OC spectra can be explained by “simple” JDOS effects in the DOS curves.
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78.66.Bz Metals and metallic alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Be Transition metals and alloys
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Modification of local structures in multicrystals revealed by spatially resolved x-ray rocking curve analysis

Noritaka Usami, Kentaro Kutsukake, Kozo Fujiwara, and Kazuo Nakajima

J. Appl. Phys. 102, 103504 (2007); http://dx.doi.org/10.1063/1.2816207 (4 pages) | Cited 4 times

Online Publication Date: 20 November 2007

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We show that spatially resolved x-ray rocking curve analysis can be a useful technique to investigate local structures in bulk multicrystals and their modification during crystal growth when combined with appropriate samples. For this purpose, a model crystal growth experiment was carried out using a Si seed crystal with artificially controlled 〈110〉 tilted grain boundaries. The growth orientation was chosen as the scan axis for rocking curve measurements in different crystal grains. Thanks to the superior angle resolution, the gradual structural changes can be monitored by the changes in the rocking curve profile such as the peak shift and the peak splitting. The amount as well as the sign of the peak shift was found to be strongly dependent on the initial grain boundary structure. Furthermore, the technique was applied to investigate local structures of Si multicrystals with controlled grain orientation grown without any seeds.
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81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.66.Bi Elemental solids
61.72.Mm Grain and twin boundaries

Tensile strain in arsenic heavily doped Si

G. Borot, L. Rubaldo, L. Clement, R. Pantel, D. Dutartre, K. Kuitunen, J. Slotte, F. Tuomisto, X. Mescot, M. Gri, and G. Ghibaudo

J. Appl. Phys. 102, 103505 (2007); http://dx.doi.org/10.1063/1.2816251 (5 pages) | Cited 5 times

Online Publication Date: 20 November 2007

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In this paper we highlight the existence of tensile stress in heavily arsenic-doped epitaxial silicon (Si:As) prepared by low pressure chemical vapor deposition. Despite the large size of As atoms compared to Si ones, we demonstrate with x-ray diffraction and convergent electron beam diffraction that the heavily doped epitaxial layers show a tetragonal lattice with a reduced out of plane parameter. Using positron annihilation spectroscopy, we highlight the formation of arsenic-vacancies defects during the growth. We show that the tensile strain is related to this type of defects involving inactive As atoms and not to the As active concentration.
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61.66.Bi Elemental solids
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Local strain measurements in shallow trench insulator structures using near-ultraviolet Raman spectroscopy: Simulation and experiment

Eddy Latu-Romain, Michel Mermoux, Alexandre Crisci, Dominique Delille, and Laurens F. Tz. Kwakman

J. Appl. Phys. 102, 103506 (2007); http://dx.doi.org/10.1063/1.2811947 (8 pages) | Cited 3 times

Online Publication Date: 20 November 2007

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Shallow trench insulator (STI) stress induced in active lines has been investigated both by near-ultraviolet (UV) Raman spectroscopy and mechanical modelization. Two different STI processes have been compared. The influence of the linewidth is also studied. After adjusting some instrumental and material parameters, all components of the stress tensors have been determined accurately. The polarization of the incoming light is discussed, showing that the selection rules are no longer respected at the edges of the STIs. Some of the limitations in spatial resolution of the Raman spectroscopy have been overcome, making use of the mechanical model and taking benefit from the higher spatial resolution of the UV excitation. In turn, the mechanical model has been refined from comparisons with experiments. It is therefore suggested that coupling these techniques may provide a relevant method to measure stress in the silicon for the integrated circuit industry. From a practical viewpoint, it is demonstrated that the use of the subatmospheric chemical vapor deposition process allows significant reduction of the compressive stress in the center of the active lines.
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07.10.Pz Instruments for strain, force, and torque
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
85.30.De Semiconductor-device characterization, design, and modeling

Formation and optical properties of CdTe/ZnTe nanostructures with different CdTe thicknesses grown on Si (100) substrates

H. S. Lee, H. L. Park, I. Lee, and T. W. Kim

J. Appl. Phys. 102, 103507 (2007); http://dx.doi.org/10.1063/1.2812557 (5 pages) | Cited 1 time

Online Publication Date: 20 November 2007

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Atomic force microscopy (AFM) and photoluminescence (PL) measurements were carried out to investigate the formation and the optical properties of CdTe/ZnTe nanostructures with various CdTe thicknesses grown on Si (100) substrates by using molecular beam epitaxy and atomic layer epitaxy. AFM images showed that uniform CdTe/ZnTe quantum dots with a CdTe layer thickness of 2.5 ML (monolayer) were formed on Si (100) substrates. The excitonic peaks corresponding to transitions from the ground electronic subband to the ground heavy-hole band in the CdTe/ZnTe nanostructures shifted to a lower energy with increasing thickness of the CdTe layer. The activation energies of the carriers confined in the CdTe/ZnTe nanostructures grown on Si (100) substrates were obtained from the temperature-dependent PL spectra. The present observations can help improve understanding of the formation and the optical properties in CdTe/ZnTe nanostructures with different CdTe thicknesses grown on Si (100) substrates.
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81.07.Ta Quantum dots
81.05.Dz II-VI semiconductors
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Monte Carlo simulations of defect recovery within a 10 keV collision cascade in 3C–SiC

Zhouwen Rong, Fei Gao, William J. Weber, and Gerhard Hobler

J. Appl. Phys. 102, 103508 (2007); http://dx.doi.org/10.1063/1.2812701 (7 pages) | Cited 8 times

Online Publication Date: 26 November 2007

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A kinetic lattice Monte Carlo (KLMC) model is developed to investigate the recovery and clustering of defects during annealing of a single 10 keV cascade in cubic silicon carbide. The 10 keV Si cascade is produced by molecular dynamics (MD), and a method of transferring the defects created by MD simulations to the KLMC model is developed. The KLMC model parameters are obtained from MD simulations and ab initio calculations of defect migration, recombination, and annihilation. The defects are annealed isothermally from 100 K to 1000 K in the KLMC model. Two distinct recovery stages for close Frenkel pairs are observed at about 200 and 550 K, and the growth of complex clusters is observed above 400 K. These simulation results are in good agreement with available experimental results.
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81.05.Hd Other semiconductors
61.72.Cc Kinetics of defect formation and annealing

Forces, charges, and light emission during the rupture of adhesive contacts

Takashi Miura, Michael Chini, and Roland Bennewitz

J. Appl. Phys. 102, 103509 (2007); http://dx.doi.org/10.1063/1.2817403 (6 pages) | Cited 2 times

Online Publication Date: 27 November 2007

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Pulling forces and light emission have been recorded simultaneously while rupturing the contact between 1/16 in. balls and adhesive tape. The force curve reveals the formation of glue filaments between the tape and the balls. Multiple light flashes originating in air discharge from the rupturing contact indicate the number of filaments. The charge separation in the moment of rupture has been evaluated by comparison with the light intensity of electric microgap discharges. The charge density is found to be one or two magnitudes larger than previously reported residual contact electrification for adhesive tape.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
78.60.Mq Sonoluminescence, triboluminescence

Application of contact theory to metal-metal bonding of silicon wafers

H. L. Leong, C. L. Gan, C. V. Thompson, K. L. Pey, and H. Y. Li

J. Appl. Phys. 102, 103510 (2007); http://dx.doi.org/10.1063/1.2811724 (9 pages) | Cited 7 times

Online Publication Date: 27 November 2007

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A model is presented which relates the applied load and surface roughness to the integrity of metal-metal wafer-level thermocompression bonds. Using contact theory, the true contact area is calculated as a function of the applied load and surface roughness as characterized using atomic force microscopy. The relationship between the nominal and true contact areas quantifies the effects of applied load and surface roughness on the bond integrity of the bonded wafers as indicated by the dicing yield. Experiments on Cu–Cu bonds show that the true contact area provides a better indicator of bond integrity than either the nominal contact area or applied force, taken together or separately.
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81.05.Bx Metals, semimetals, and alloys
81.05.Cy Elemental semiconductors
81.20.Vj Joining; welding

The effect of coupling barrier thickness on structural and optical properties in asymmetrically coupled GaN/Al0.5Ga0.5N/GaN multiquantum wells

Young S. Park, Chang Mo Park, Bo Ra Hwang, T. W. Kang, Yongmin Kim, Hyunsik Im, and Myung-Soo Han

J. Appl. Phys. 102, 103511 (2007); http://dx.doi.org/10.1063/1.2817480 (5 pages)

Online Publication Date: 27 November 2007

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The structural and optical properties of coupled, multiquantum-well structures, consisting of GaN(10 Å)/Al0.5Ga0.5N(12 or 22 Å)/GaN(20 Å) bounded by Al0.5Ga0.5N (100 Å) barriers, were investigated by high resolution x-ray diffraction, transmission electron microscopy, and photoluminescence measurements. We studied the carrier dynamics in asymmetric double quantum wells by analyzing the temperature-dependent and time-resolved photoluminescence spectra. Carrier tunneling between the coupled quantum wells affected the optical properties. In our analysis of the effect of the carrier tunneling in terms of free-carrier screening, the effect was much weaker for the sample with Tib = 12 Å than for that with Tib = 22 Å.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
68.65.Fg Quantum wells
73.63.Hs Quantum wells

Formation processes of iron silicide nanoparticles studied by ex situ and in situ transmission electron microscopy

Jonghan Won, András Kovács, Muneyuki Naito, Manabu Ishimaru, and Yoshihiko Hirotsu

J. Appl. Phys. 102, 103512 (2007); http://dx.doi.org/10.1063/1.2815649 (7 pages) | Cited 4 times

Online Publication Date: 28 November 2007

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The formation processes of iron silicide nanoparticles dependent on thermal annealing were examined by ex situ and in situ transmission electron microscopy (TEM). An Fe thin film with a thickness of ∼ 2 nm was deposited on a Si(100) substrate at room temperature using an electron-beam evaporation method, followed by thermal annealing at temperatures ranging from 573 to 1173 K. Ex situ TEM observations showed that pyramidal β-FeSi2 particles (1173 K) were formed via the ε-FeSi layer (573 K) and the γ-FeSi2 particle (873 K). Detailed observations by in situ TEM indicated that an amorphous Fe-Si layer was formed on the Si substrate in the as-deposited specimen. This amorphous layer was crystallized into ε-FeSi after thermal annealing and then hemispherical ε-FeSi particles together with metastable γ-FeSi2 were formed just beneath the surface of the Si substrate. With increasing annealing temperature, the ε phase changed to hemispherical γ-FeSi2 nanoparticles and finally the γ-FeSi2 particles transformed into pyramidal β-FeSi2 particles. We discuss the formation mechanism of the iron silicide nanoparticles at the atomic scale.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.16.-c Methods of micro- and nanofabrication and processing
81.40.Gh Other heat and thermomechanical treatments
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.70.Nd Structural transitions in nanoscale materials

A density functional study of the effect of hydrogen on the strength of an epitaxial Ag/ZnO interface

Zheshuai Lin and Paul D. Bristowe

J. Appl. Phys. 102, 103513 (2007); http://dx.doi.org/10.1063/1.2815646 (6 pages) | Cited 5 times

Online Publication Date: 29 November 2007

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A density functional calculation of a Ag (111)/ZnO (0001) interface with 30° rotated epitaxy reveals that the strength of the interface, as determined from the work of separation, is significantly lowered by the presence of hydrogen. This interface has been observed in magnetron sputtered thin-film systems and could be present in optical multilayers used to coat architectural glass for solar-control and energy efficiency. The weakening of the hydrogen-modified interface, which originates in the Ag-H bond, could partly explain the observed delamination of the interface during processing or service in a hydrogen-rich or humid environment.
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68.43.Mn Adsorption kinetics
42.70.Ce Glasses, quartz
73.40.Ns Metal-nonmetal contacts
42.79.Wc Optical coatings

Characterization of defects in ZnO nanocrystals: Photoluminescence and positron annihilation spectroscopic studies

A. K. Mishra, S. K. Chaudhuri, S. Mukherjee, A. Priyam, A. Saha, and D. Das

J. Appl. Phys. 102, 103514 (2007); http://dx.doi.org/10.1063/1.2817598 (6 pages) | Cited 8 times

Online Publication Date: 29 November 2007

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Defects present in ZnO nanocrystals prepared by a wet chemical method have been characterized by photoluminescence (PL) and positron annihilation spectroscopy (PAS) techniques. The as-prepared sample was heat treated at different temperatures to obtain nanocrystals in the size range of 19–39 nm. X ray diffractograms confirmed the single-phase wurtzite structure formation. Photoluminescence measurements showed a strong violet band at 434 nm, which has been identified as due to electronic transitions from the zinc interstitial defect level to the top of the valence band. A marked decrease in the intensity of the violet emission with increasing heat-treatment temperature has been observed, which is attributed to recombination of zinc interstitials with zinc vacancies. Positron annihilation spectroscopy has been employed to understand the dynamics of the vacancy-type defects and their annealing behavior. The observed variation of the defect related lifetime components with heat-treatment temperature has been successfully explained by using a three-state trapping model. The results of PL and PAS studies in the present case are found to be complementary to each other.
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78.55.Et II-VI semiconductors
78.70.Bj Positron annihilation
81.07.Bc Nanocrystalline materials
81.16.Be Chemical synthesis methods
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