jap banner
  • Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Flickr Twitter UniPHY Group iResearch App Facebook

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue Next Issue

1 Oct 2007

Volume 102, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 102, 071101 (2007); http://dx.doi.org/10.1063/1.2787957 (12 pages)

A. Ashrafi and C. Jagadish
Enlarge Image | Read More
Page 1 of 8 Pages Next Page | Jump to Page
back to top
RSS Feeds

Review of zincblende ZnO: Stability of metastable ZnO phases

A. Ashrafi and C. Jagadish

J. Appl. Phys. 102, 071101 (2007); http://dx.doi.org/10.1063/1.2787957 (12 pages) | Cited 28 times

Online Publication Date: 1 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Common II-VI compound semiconducting materials are stable thermodynamically with zincblende phase, while the II-O materials such as zinc oxide (ZnO) and beryllium oxide (BeO) are stable with wurtzite phase, and cadmium oxide (CdO) and magnesium oxide (MgO) are stable in rocksalt phase. This phase disharmony in the same material family laid a challenge for the basic physics and in practical applications in optoelectronic devices, where ternary and quaternary compounds are employed. Thermodynamically the zincblende ZnO is a metastable phase which is free from the giant internal electric fields in the [001] directions and has an easy cleavage facet in the ⟨110⟩ directions for laser cavity fabrication that combined with evidence for the higher optical gain. The zincblende materials also have lower ionicity that leads to the lower carrier scattering and higher doping efficiencies. Even with these outstanding features in the zincblende materials, the growth of zincblende ZnO and its fundamental properties are still limited. In this paper, recent progress in growth and fundamental properties of zincblende ZnO material has been reviewed.
Show PACS
73.61.Ga II-VI semiconductors
78.55.Et II-VI semiconductors
71.55.Gs II-VI semiconductors
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.66.Fn Inorganic compounds
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
back to top
RSS Feeds

Voltage reduction in twisted nematic liquid crystals by reverse (negative) doping

M. D. Tillin

J. Appl. Phys. 102, 073101 (2007); http://dx.doi.org/10.1063/1.2785006 (4 pages) | Cited 4 times

Online Publication Date: 1 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The concept of reverse or negative doping of a liquid crystal is introduced, in which the sense of the twist of the helix induced by a chiral dopant in the unconstrained liquid crystal material is opposite to that induced by the alignment layers. Some considerations of the extent to which the liquid crystal may be negatively doped before reverse twist domains appear, and the effect of the threshold voltage, are presented. The concept is applied to a reflective liquid crystal display (LCD) and it is demonstrated how the data voltage and power consumption of twisted nematic reflective LCDs may be reduced.
Show PACS
42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.72.up Other materials

Influence of some design parameters on the efficiency of solar cells with down-conversion and down shifting of high-energy photons

Viorel Badescu and Alexis De Vos

J. Appl. Phys. 102, 073102 (2007); http://dx.doi.org/10.1063/1.2785026 (7 pages) | Cited 9 times

Online Publication Date: 2 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper we analyze the system proposed by Trupke et al. [J. Appl. Phys. 92, 1668 (2002) ] to increase solar cell efficiency. The system consists of adding to the solar cell a so-called down-converter, which is a device able to convert the high-energy incident photons into photons of lower energy. The contribution consists of taking account (i) the nonradiative recombination in both solar cell and converter, (ii) the refractive index of solar cell and converter materials, and (iii) the solar radiation concentration. Two configurations are studied: the cell and rear converter (C-RC) and front converter and cell (FC-C). The main conclusions of this work are as follow. (1) For ideal down-converters, with radiative recombination only, the solar energy conversion efficiency may be, or may not be, increased by adding a front (or a rear) down-converter to the cell, depending on the value of the solar cell refractive index. (2) More realistic systems, where nonradiative recombinations exist inside the converter, are also considered. The efficiency of the FC-C system is generally less than the efficiency of a single cell. C-RC systems perform better than the cell operating alone for some values of the refractive indices. (3) C-RC systems perform generally better than FC-C systems whatever the values of the refractive indices and the concentration ratio.
Show PACS
84.60.Jt Photoelectric conversion

Efficient initiation of photonuclear reactions using quasimonoenergetic electron beams from laser wakefield acceleration

S. A. Reed, V. Chvykov, G. Kalintchenko, T. Matsuoka, V. Yanovsky, C. R. Vane, J. R. Beene, D. Stracener, D. R. Schultz, and A. Maksimchuk

J. Appl. Phys. 102, 073103 (2007); http://dx.doi.org/10.1063/1.2787159 (7 pages) | Cited 3 times

Online Publication Date: 3 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Pulses of nearly monoenergetic relativistic electrons have been generated by laser wakefield acceleration and used to perform photonuclear activation of carbon, copper, and photofission in uranium. Using bremsstrahlung converter targets, the electron beams generated by this technique have been shown to be effective in producing high energy γ-rays (tens of MeV) that are necessary to efficiently induce photonuclear reactions. Quantitative γ-ray spectroscopy of the irradiated C, Cu, and U samples indicates that more than 105 reactions were produced per joule of laser energy. The activation yield measurements have been compared with Monte Carlo modeling of electromagnetic cascade and photonuclear processes occurring in the targets to infer the characteristics of the laser accelerated electron beams.
Show PACS
25.20.-x Photonuclear reactions
23.20.Lv γ transitions and level energies
27.20.+n 6 ≤ A ≤ 19
27.50.+e 59 ≤ A ≤ 89
27.90.+b A ≥ 220
61.80.Fe Electron and positron radiation effects

Femtosecond carrier dynamics of InxGa1−xN thin films grown on GaN (0001): Effect of carrier-defect scattering

Emmanouil Lioudakis, Andreas Othonos, Eleftherios Iliopoulos, Katerina Tsagaraki, and Alexandros Georgakilas

J. Appl. Phys. 102, 073104 (2007); http://dx.doi.org/10.1063/1.2786610 (6 pages) | Cited 2 times

Online Publication Date: 4 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ultrafast carrier dynamics in ultrathin InxGa1−xN ternary alloys were investigated in detail, using femtosecond transient differential optical absorption measurements. Measurements were performed with probing wavelengths above and below the band edge of the materials. Furthermore, we performed a structural characterization by x-ray diffraction reciprocal space maps and we found that the alloys with the higher InN mole fraction (x = 0.89 and x = 0.43) present large lattice mismatch-strain relaxation whereas the lower InN content alloy was fully coherent with the underlying GaN (0001) layer. Our analysis showed that the observed nonradiative carrier dynamics was strongly related with the carrier-defect scattering of the materials. Our measurements in conjunction with the numerical analysis showed that when we excite these alloys with ultrashort laser pulses the background carrier concentration for In-rich InGaN samples participates to the photoexcited carrier relaxation process via carrier momentum scattering. For the higher InN content alloys (x = 0.89 and 0.43) the relaxation times were short (0.4–1.4 ps) whereas for the full strained alloy (x = 0.07) a slower nonradiative relaxation time ( ∼ 25 ps) was observed. Finally, the energy loss rate of this material (2.05±0.10 meV/fs) as well as the optical phonon lifetime (44±2 fs) were extracted.
Show PACS
73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
72.20.-i Conductivity phenomena in semiconductors and insulators
63.20.-e Phonons in crystal lattices

Enhancement of the high-order harmonic generation from the gold plume using the time-resolved plasma spectroscopy

Rashid A. Ganeev, Luc B. Elouga Bom, and Tsuneyuki Ozaki

J. Appl. Phys. 102, 073105 (2007); http://dx.doi.org/10.1063/1.2786026 (8 pages) | Cited 5 times

Online Publication Date: 4 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We present systematic time-resolved investigations of plasma conditions for achieving the maximum cutoff and maximum conversion efficiency of high-order harmonic generation from gold plasma within the plateau. We analyzed harmonic generation under different laser-plasma conditions. We also performed simulations to calculate the ionization state of the gold plasma, the free electron density, and singly charged ion density at different prepulse intensities. By optimizing the plasma conditions, we observed a harmonic cutoff at the 53rd order (λ = 15.09 nm). We estimate the conversion efficiency of the harmonics within the plateau region to be 2×10−6.
Show PACS
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.25.Jm Ionization of plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

In-fiber colloidal photonic crystals and the formed stop band in fiber longitudinal direction

Yuankun Lin, Peter R. Herman, and Wei Xu

J. Appl. Phys. 102, 073106 (2007); http://dx.doi.org/10.1063/1.2786038 (4 pages) | Cited 5 times

Online Publication Date: 4 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report a microfluid-guided growth of colloidal photonic crystals inside a twin-hole optical fiber. The microfluid is pumped by the vapor pressure and capillary force of the solvent sealed in a vial. A face-centered-cubic lattice-type structure has been achieved for colloidal photonic crystals grown inside the twin-hole optical fiber. The colloidal crystal growths at air-colloid interfaces, fiber microchannel-colloid interfaces, and crystal-colloid boundaries are studied with scanning electronic microscope. Optical reflection measurement reveals a stop band along the fiber longitudinal direction due to the Bragg diffraction of in-fiber colloidal photonic crystals. The in-fiber photonic crystal adds an optical function to the microstructure optical fiber by incorporating spectral control through a structural resonance in the cladding region of the optical fiber.
Show PACS
42.81.Bm Fabrication, cladding, and splicing
47.85.-g Applied fluid mechanics
81.10.Dn Growth from solutions
42.70.Qs Photonic bandgap materials
82.70.Dd Colloids

Responsivity of ZnTe/n-GaAs heterostructures formed by infrared nanosecond laser deposition

K. P. Acharya, B. Ullrich, and A. Erlacher

J. Appl. Phys. 102, 073107 (2007); http://dx.doi.org/10.1063/1.2786890 (5 pages) | Cited 4 times

Online Publication Date: 5 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
With nanosecond laser pulses at 1064 nm, ZnTe was ablated and deposited onto n-GaAs. The intrinsic and extrinsic room temperature responsivities of the heteropairing was investigated with lock-in technique employing various optical chopping frequencies. The work brings to light two peculiar features: The photocurrent of the structure possesses a frequency independent (isosbestic) point and the dominating photocurrent, i.e., defect or bulk related, crossing the sample can be sensitively altered via the sign of the bias. The reported features here, which cannot be achieved with GaAs itself, might open useful technological calibrating applications for light detectors.
Show PACS
81.15.Fg Pulsed laser ablation deposition
79.60.-i Photoemission and photoelectron spectra

Ambipolar charge transport in bulk heterojunction of poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene)/C60 composite

Quanmin Shi, Yanbing Hou, Hui Jin, and Yunbai Li

J. Appl. Phys. 102, 073108 (2007); http://dx.doi.org/10.1063/1.2779257 (6 pages) | Cited 9 times

Online Publication Date: 10 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Using the time-of-flight technique (TOF), the influence of C60 concentrations on ambipolar charge transport in poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV)/C60 composite has been investigated. Adding C60 to the blend increases both electron and hole mobilities, compared to the pristine polymer. In the pristine MEH-PPV, the mobility of electrons is below the measurable range. However, electron mobility (10−7 cm2 V−1 s−1) could be calculated when the weight ratio of C60: MEH-PPV increased to 1:18. The temperature and electric field dependence of mobility is analyzed in the disorder formalism. It is observed that above ∼ 290 K the slope of the electric field dependence of the electron mobility becomes negative. The occurrence of negative field dependence in composite samples is attributed to the large positional disorder (Σ = 4).
Show PACS
73.90.+f Other topics in electronic structure and electrical properties of surfaces, interfaces, thin films, and low-dimensional structures (Restricted to new topics in section 73)

Atomic and molecular emissions of the laser-induced plasma during zinc and zinc oxide target ablation

S. Acquaviva, E. D’Anna, and M. L. De Giorgi

J. Appl. Phys. 102, 073109 (2007); http://dx.doi.org/10.1063/1.2786711 (7 pages) | Cited 4 times

Online Publication Date: 11 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Optical emission spectroscopic investigations of the plasma produced during KrF excimer laser ablation of Zn and ZnO targets, in vacuum and in oxygen gas environment, are presented. The plume luminescence is mainly due to Zn excited atoms and ions, but the contribution of atomic and molecular oxygen, as well as of particulates, cannot be neglected. In particular, we detect emissions in the spectral regions around 380 and 530 nm, corresponding to the UV and green photo-luminescence bands of the zinc oxide. Moreover, we study the temporal evolution of atomic and ionic ejected species by space- and time-resolved spectroscopy and analyze the results by means of empirical models, in order to infer information about plasma dynamics.
Show PACS
52.38.Mf Laser ablation
42.55.Lt Gas lasers including excimer and metal-vapor lasers
31.50.Df Potential energy surfaces for excited electronic states

Gallium nitride metal-semiconductor-metal photodetectors prepared on silicon substrates

R. W. Chuang, S. P. Chang, S. J. Chang, Y. Z. Chiou, C. Y. Lu, T. K. Lin, Y. C. Lin, C. F. Kuo, and H. M. Chang

J. Appl. Phys. 102, 073110 (2007); http://dx.doi.org/10.1063/1.2786111 (4 pages) | Cited 4 times

Online Publication Date: 11 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Gallium nitride (GaN) ultraviolet metal-semiconductor-metal photodetectors (PDs) grown on Si substrates were demonstrated. The dark current of PDs fabricated on Si substrates was substantially smaller in magnitude compared to identical devices prepared on sapphire substrates. With an incident wavelength of 359 nm, the maximum responsivities of the n−‐GaN MSM photodetectors with TiW and Ni/Au contact electrodes were 0.187 and 0.0792 A/W, corresponding to quantum efficiencies of 64.7% and 27.4%, respectively. For a given bandwidth of 1 kHz and a given bias of 5 V, the corresponding noise equivalent powers of our n−‐GaN MSM photodetectors with TiW and Ni/Au electrodes were 1.525×10−12 and 5.119×10−12 W, respectively. Consequently, the values of detectivity (D*) determined for devices with TiW and Ni/Au electrodes were then calculated to be 1.313×1012 and 3.914×1011 cm Hz0.5 W−1, respectively.
Show PACS
73.40.Sx Metal-semiconductor-metal structures
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects

Decoupling of silicon carbide optical sensor response for temperature and pressure measurements

A. Chakravarty, N. R. Quick, and A. Kar

J. Appl. Phys. 102, 073111 (2007); http://dx.doi.org/10.1063/1.2786889 (12 pages) | Cited 2 times

Online Publication Date: 11 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Single crystal silicon carbide is a chemically inert transparent material with superior oxidation-resistant properties at elevated temperatures compared to black polycrystalline silicon carbide substrates. These improved properties make crystalline silicon carbide a good optical sensor material for harsh environments such as combustion chambers and turbine systems. Interferometric optical sensors are orders of magnitude more sensitive than electrical sensors and are proposed for these applications. Silicon carbide itself behaves as a Fabry-Pérot etalon eliminating the need for an external interferometer for any measurement using this silicon carbide as a sensor. The principle of the optical sensor in this study is the temperature- and pressure-dependent refractive index of silicon carbide, which can be used to determine the temperatures and pressures of gases that are in contact with silicon carbide. Interference patterns produced by a silicon carbide (4H-SiC) wafer due to multiple reflections of a helium-neon laser beam of wavelength of 632.8 nm have been obtained at temperatures up to 500 °C and pressures up to 600 psi. The pattern changes for the same gas at different temperatures and pressures and for different gases at the same temperature and pressure. The refractive index at the wafer-gas interface is calculated from the interference pattern and the refractive index gradients with respect to temperature and pressure, respectively, are also determined. Decoupling temperature and pressure using these gradients and the measured reflectivity data are discussed in this paper.
Show PACS
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.-e Optical elements, devices, and systems
42.79.Pw Imaging detectors and sensors

Deterministic processing of alumina with ultrashort laser pulses

J. Furmanski, A. M. Rubenchik, M. D. Shirk, and B. C. Stuart

J. Appl. Phys. 102, 073112 (2007); http://dx.doi.org/10.1063/1.2794376 (4 pages)

Online Publication Date: 12 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Ultrashort pulsed lasers can accurately ablate materials which are refractory, transparent, or are otherwise difficult to machine by other methods. The typical method of machining surfaces with ultrashort laser pulses is by raster scanning, or the machining of sequentially overlapping linear trenches. Experiments in which linear trenches were machined in alumina at various pulse overlaps and incident fluences are presented, and the dependence of groove depth on these parameters established. A model for the machining of trenches based on experimental data in alumina is presented, which predicts and matches observed trench geometry. This model is then used to predict optimal process parameters for the machining of trenches for maximal material removal rate for a given laser.
Show PACS
52.38.Mf Laser ablation
81.65.-b Surface treatments

Heterodyne speckle velocimetry of Poiseuille flow

M. D. Alaimo, M. A. C. Potenza, D. Magatti, and F. Ferri

J. Appl. Phys. 102, 073113 (2007); http://dx.doi.org/10.1063/1.2786905 (8 pages) | Cited 2 times

Online Publication Date: 12 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We review the technique named heterodyne speckle velocimetry and present two applications for testing the method with a fluid moving under the conditions of Poiseuille flow. The fluid was seeded with small tracking particles (diameter 300 nm) and fluxed between the two parallel planes of a cell with constant or variable cross section. In the first case the velocity distribution was constant along the direction parallel to the planes and was in excellent agreement with the expected Poiseuille profile along the orthogonal direction. In the second case, where velocity gradients were present also along the planes, the technique was able to reconstruct both the orthogonal Poiseuille profile and the in-plane two dimensional mapping of the velocity vectors, with the possibility of measuring the fluid flux within an accuracy of 1%.
Show PACS
47.80.Cb Velocity measurements
47.15.Rq Laminar flows in cavities, channels, ducts, and conduits

Photoluminescence of Ga-doped ZnO film grown on c‐Al2O3 (0001) by plasma-assisted molecular beam epitaxy

H. C. Park, D. Byun, B. Angadi, D. Hee Park, W. K. Choi, J. W. Choi, and Y. S. Jung

J. Appl. Phys. 102, 073114 (2007); http://dx.doi.org/10.1063/1.2783956 (5 pages) | Cited 14 times

Online Publication Date: 12 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
High quality gallium doped ZnO (Ga:ZnO) thin films were grown on c‐Al2O3(1000) by plasma-assisted molecular beam epitaxy, and Ga concentration NGa was controlled in the range of 1×1018–2.5×1020/cm3 by adjusting∕changing the Ga cell temperature. From the low-temperature photoluminescence at 10 K, the donor bound exciton I8 related to Ga impurity was clearly observed and confirmed by comparing the calculated activation energy of 16.8 meV of the emission peak intensity with the known localization energy, 16.1 meV. Observed asymmetric broadening with a long tail on the lower energy side in the photoluminescence (PL) emission line shape could be fitted by the Stark effect and the compensation ratio was approximately 14–17% at NGa ≥ 1×1020/cm3. The measured broadening of photoluminescence PL emission is in good agreement with the total thermal broadening and potential fluctuations caused by random distribution of impurity at NGa lower than the Mott critical density.
Show PACS
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
78.20.Jq Electro-optical effects
81.15.Jj Ion and electron beam-assisted deposition; ion plating
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors

Optical properties of a Si delta-doped InGaN/GaN quantum well with ultraviolet emission

Min-Ki Kwon, Il-Kyu Park, Ja-Yeon Kim, Jeom-Oh Kim, Seong-Bum Seo, Seong-Ju Park, Kyeongik Min, and Gil-Han Park

J. Appl. Phys. 102, 073115 (2007); http://dx.doi.org/10.1063/1.2794714 (4 pages) | Cited 2 times

Online Publication Date: 15 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We report on the effect of the position of the Si delta-doped layer within a GaN barrier layer on the optical properties of a InGaN/GaN single quantum well (SQW) with an emission wavelength of 374 nm. When the Si delta-doped layer was very close to the SQW layer, the potential well of the Si delta-doped layer overlapped the SQW potential, reducing photoluminescence (PL) intensity. When the Si delta-doped layer was very far away from the SQW layer, carrier injection from the Si delta-doped layer into the SQW layer was not observed. However, the Si delta-doped layer located 12 nm away from the SQW layer showed enhanced PL intensity due to effective electron injection from the Si delta-doped layer into the SQW layer and to an increase in hole confinement in the valence band.
Show PACS
78.67.De Quantum wells
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
back to top
RSS Feeds

Spatiotemporal behavior of excited Xe*(1s4,1s5) and Kr*(1s5) atoms measured by laser-absorption spectroscopy in unit cell of a plasma display panel with Xe–Kr–Ne ternary gas mixture

Jun-Seok Oh and Kunihide Tachibana

J. Appl. Phys. 102, 073301 (2007); http://dx.doi.org/10.1063/1.2786609 (9 pages) | Cited 1 time

Online Publication Date: 4 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We have studied the effects of ternary gas mixtures of Xe(10%)–Kr(20% and 40%)–Ne on the luminous efficiency in ac plasma display panels. Spatiotemporal behaviors of near infrared (IR) emission was measured by an intensified charge-coupled device camera equipped with a narrow bandpass filter and absolute densities of excited Xe* and Kr* atoms in the lowest resonance (1s4) and metastable (1s5) levels were measured by a technique of microscopic laser absorption spectroscopy. We have found interesting features from both emission and absorption experiments, such as longer near-IR emission (0.3–0.4 μs) and different temporal behaviors between the excited Kr*(1s5) atoms and Xe*(1s4,1s5) atoms. We have also found that the order of magnitude of the peak density of excited Kr*(1s5) atoms ( ∼ 1012 cm−3) was ten times smaller than that of Xe*(1s4,1s5) atoms, and that their decay time was remarkably short ( ∼ 0.3 μs). These results have then been compared with those for a binary gas mixture of Xe(10%)–Ne. At a certain range of the sustain voltage, the production rate of Xe*(1s4,1s5) atoms and the luminous efficiency have turned out to be slightly improved for the ternary gas mixtures, compared to the binary gas mixture.
Show PACS
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics

Effect of collisions on dust particle charging via particle-in-cell Monte-Carlo collision

B. Rovagnati, M. Davoudabadi, G. Lapenta, and F. Mashayek

J. Appl. Phys. 102, 073302 (2007); http://dx.doi.org/10.1063/1.2786032 (9 pages) | Cited 10 times

Online Publication Date: 4 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
In this paper, the effect of collisions on the charging and shielding of a single dust particle immersed in an infinite plasma is studied. A Monte-Carlo collision (MCC) algorithm is implemented in the particle-in-cell DEMOCRITUS code to account for the collisional phenomena which are typical of dusty plasmas in plasma processing, namely, electron-neutral elastic scattering, ion-neutral elastic scattering, and ion-neutral charge exchange. Both small and large dust particle radii, as compared to the characteristic Debye lengths, are considered. The trends of the steady-state dust particle potential at increasing collisionality are presented and discussed. The ions and electron energy distributions at various locations and at increasing collisionality in the case of large particle radius are shown and compared to their local Maxwellians. The ion-neutral charge-exchange collision is found to be by far the most important collisional phenomenon. For small particle radius, collisional effects are found to be important also at low level of collisionality, as more ions are collected by the dust particle due to the destruction of trapped ion orbits. For large particle radius, the major collisional effect is observed to take place in proximity of the presheath. Finally, the species energy distribution functions are found to approach their local Maxwellians at increasing collisionality.
Show PACS
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Tx Emission, absorption, and scattering of particles
52.27.Lw Dusty or complex plasmas; plasma crystals

Plasma irradiation damages to magnetic tunneling junction devices

Tomonori Mukai, Butsurin Jinnai, Yoshiyuki Fukumoto, Norikazu Ohshima, Hiromitsu Hada, and Seiji Samukawa

J. Appl. Phys. 102, 073303 (2007); http://dx.doi.org/10.1063/1.2785849 (4 pages) | Cited 2 times

Online Publication Date: 10 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We exposed magnetic tunneling junction (MTJ) devices—fabricated using Ar-ion milling—to the reactive plasma commonly used in etching to determine the mechanism of the damage caused by the exposure. Exposing MTJ devices to the conventional continuous-wave (CW) plasma widely used in plasma etching significantly degrades their magnetic characteristics. However, exposure to a pulse-time-modulated (TM) plasma does not degrade the MTJ devices’ magnetic characteristics. Analysis of transmission electron microscopy cross sections of the MTJ device structures revealed that the structure of the CoFe pinned layer was damaged in the MTJ devices exposed to a conventional CW plasma. This structural damage degraded the MTJ devices’ magnetic characteristics. No damage to the structure of the MTJ devices was seen in those exposed to a TM plasma. Therefore, using the TM plasma offers an effective, damage-free method of etching MTJ devices as part of their manufacturing process.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
52.77.-j Plasma applications

Fast electron temperature measurements using a “multicolor” optical soft x-ray array

L. F. Delgado-Aparicio, D. Stutman, K. Tritz, M. Finkenthal, R. Bell, J. Hosea, R. Kaita, B. LeBlanc, L. Roquemore, and J. R. Wilson

J. Appl. Phys. 102, 073304 (2007); http://dx.doi.org/10.1063/1.2786034 (7 pages) | Cited 7 times

Online Publication Date: 12 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
A fast ( ⩽ 0.1 ms) and compact “multicolor” scintillator-based optical soft x-ray (OSXR) array has been developed for time- and space-resolved measurements of the electron temperature [Te(R,t)] profiles in magnetically confined fusion plasmas. The 48-channel tangential multicolor OSXR prototype was tested on the National Spherical Torus Experiment. Each sight line views the same plasma volume at the midplane (0 ⩽ r/a ⩽ 1), in three distinct energy ranges determined by beryllium foils with different thicknesses. A tangential view of the toroidally (circular) symmetric plasma allows an Abel inversion of the line-integrated SXR brightness to obtain the x-ray emissivity profiles which are then used to constrain the reconstruction of the fast Te(R,t). The first assessment of the electron temperature is obtained by modeling the slope of the continuum radiation with the ideal double-foil method using both the line-integrated intensity measurements as well as the inverted SXR emissivity profiles.
Show PACS
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
07.85.-m X- and γ-ray instruments
52.55.Jd Magnetic mirrors, gas dynamic traps
back to top
RSS Feeds

Formation characteristics of shape-engineered InAs/InAlGaAs quantum dots grown on InP substrates

Jin Soo Kim, Cheul-Ro Lee, In Hwan Lee, Jae-Young Leem, Jong Su Kim, and Mee-Yi Ryu

J. Appl. Phys. 102, 073501 (2007); http://dx.doi.org/10.1063/1.2785001 (5 pages) | Cited 2 times

Online Publication Date: 1 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
This article reports the structural and optical properties of shape-engineered InAs/InAlGaAs quantum dots (QDs) on InP substrates formed using an alternate growth method (AGQDs), where a thin InAs layer (0.8 or 1 monolayer) and a thin InAlGaAs layer (1 monolayer) were deposited alternately. For five-stacked AGQD layers, a double-peak feature was observed in the photoluminescence (PL) spectra. The two peaks were related to two different QD branches as confirmed by excitation-power-dependent PL. Observation of a double-peak feature in the PL spectra indicated that the growth conditions for the AGQD layers were not optimized. A slight increase in growth temperature resulted in the merging of the double-peak feature to a single peak with a relatively narrow PL linewidth.
Show PACS
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Characterization of hot wall grown silver phthalocyanine films

Himani Gupta, R. K. Bedi, and Aman Mahajan

J. Appl. Phys. 102, 073502 (2007); http://dx.doi.org/10.1063/1.2785016 (4 pages) | Cited 1 time

Online Publication Date: 1 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
Silver phthalocyanine (AgPc) has attracted considerable interest because of its outstanding chemical stability, optical and electrical properties, and wide variety of potential applications in modern optical recording and optoelectronic devices. To improve the performance of devices based on AgPc, hot wall technique has been used to grow thin layers of AgPc onto the glass substrates kept at different temperatures in a vacuum of 10−5 Torr. The films so obtained are annealed and studied for structural, electrical, and optical characterization. The x-ray diffraction and scanning electron microscopy pattern of these films show a crystalline behavior of films. The films deposited at higher substrate temperature suggest the formation of more ordered and crystalline films. An analysis of optical absorption measurements on the films indicates that the interband transition energies lie in the range 4.1–4.13 eV.
Show PACS
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Hd Other semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.66.Qn Polymers; organic compounds
73.61.Ph Polymers; organic compounds
68.55.-a Thin film structure and morphology

Thin-film evolution equation for a strained solid film on a deformable substrate: Numerical steady states

W. T. Tekalign and B. J. Spencer

J. Appl. Phys. 102, 073503 (2007); http://dx.doi.org/10.1063/1.2785024 (7 pages) | Cited 10 times

Online Publication Date: 1 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
We consider the nonlinear behavior of the thin-film evolution equation for a strained solid film on a substrate. The evolution equation describes morphological changes to the film by surface diffusion in response to elastic energy, surface energy, and wetting energy. Due to the thin-film approximation, the elastic response of the film is determined analytically, resulting in a self-contained evolution equation which does not require separate numerical solution of the full three-dimensional elasticity problem. Using a pseudospectral predictor-corrector method we numerically determine the family of steady state solutions to this evolution equation which correspond to quantum dot and quantum ridge morphologies.
Show PACS
68.55.-a Thin film structure and morphology
68.35.Fx Diffusion; interface formation
68.35.Md Surface thermodynamics, surface energies
68.60.Bs Mechanical and acoustical properties

Tensile strength and fracture toughness of brittle materials

Francisco G. Emmerich

J. Appl. Phys. 102, 073504 (2007); http://dx.doi.org/10.1063/1.2785008 (12 pages) | Cited 4 times

Online Publication Date: 2 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The fracture properties of brittle materials under tension have been explained by many authors; however, questions such as the dependence of the tensile strength on the crack tip radius of curvature and the scatter of fracture toughness are still not well explained from fundamental principles. This work aims to address this question by using a force-atomistic approach: we analyze the forces that act in the solid down to the smallest dimensions in an atomistic context, verifying the satisfaction of the static equilibrium condition given by Newton’s second law up to the beginning of the rupture. We take into account the forces due to the applied stress, which may be very large at crack tips, and the material cohesion forces, particularly at the point of largest local strain and stress concentration, where the local hyperelasticity of the material plays a governing role. By considering and connecting microstructure and atomicity, and using an experimentally proved maximum tensile-stress criterion for fracture, here we obtain an expression for the tensile strength of the brittle materials, where an effective local cohesive stress is defined. Thus, we explain in a unified framework from fundamental principles a set of established experimental results of brittle fracture of materials under tension, including the dependence of the tensile strength on the crack tip radius of curvature and some scatter in reported values of fracture toughness and cleavage surface energy. This work can be useful to make more realistic predictions of fracture properties of brittle materials taking into account microstructure and atomicity.
Show PACS
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity
62.20.D- Elasticity

Effects of the high-temperature-annealed self-buffer layer on the improved properties of ZnO epilayers grown by helicon-wave-excited-plasma sputtering epitaxy on a-plane sapphire substrates

T. Koyama, A. N. Fouda, N. Shibata, and S. F. Chichibu

J. Appl. Phys. 102, 073505 (2007); http://dx.doi.org/10.1063/1.2786090 (4 pages) | Cited 2 times

Online Publication Date: 2 October 2007

Full Text: Read Online (HTML) | Download PDF

Show Abstract
The use of the high-temperature-annealed self-buffer layer (HITAB) enabled to observe free A-and B-exciton emissions at 9 K from ZnO heteroepitaxial films grown by the sputtering epitaxy method using a helicon-wave-excited plasma on uniaxially nearly lattice-matched (11math0) Al2O3 substrates. The result was correlated with a twofold decrease in the densities of threading dislocations having both the screw and edge components, according to the dislocation concealing in ZnO HITAB due to lateral mass transport of low-temperature deposited ZnO nanocrystalline grains during high temperature annealing.
Show PACS
61.72.Cc Kinetics of defect formation and annealing
71.35.-y Excitons and related phenomena
Page 1 of 8 Pages Next Page | Jump to Page
Close

Google Calendar

ADVERTISEMENT

Your Recent History Recent History Help

Recently Viewed

  1. Magnetocaloric effect in reactively-milled LaFe11.57Si1.43Hy intermetallic compounds
  2. Enhanced backward wave propagation in evanescent waveguides loaded with split ring resonators
  3. Cherenkov radiation by an electron bunch moving in Hermitian medium
  4. Characteristic temperatures of exchange biased systems
  5. Effect of switching field gradient for thermally assisted magnetic recording
Go to AIP Home
Copyright © American Institute of Physics
close