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15 Dec 2008

Volume 104, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 104, 121301 (2008); http://dx.doi.org/10.1063/1.3041061 (17 pages)

Junhang Dong, Y. S. Lin, Masakoto Kanezashi, and Zhong Tang
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Microporous inorganic membranes for high temperature hydrogen purification

Junhang Dong, Y. S. Lin, Masakoto Kanezashi, and Zhong Tang

J. Appl. Phys. 104, 121301 (2008); http://dx.doi.org/10.1063/1.3041061 (17 pages) | Cited 18 times

Online Publication Date: 18 December 2008

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The general mechanisms of gas separation in microporous inorganic membranes are reviewed in this article. Emphasis has been placed on discussing the requirements of membrane pore structure and material properties for high temperature hydrogen separation from other small gases involved in processes of hydrogen production from fossil fuels. The recent research progresses in developing the crystalline zeolite membranes, and amorphous silica-based membranes for high temperature hydrogen separation are critically reviewed. The fundamental issues associated with the zeolite and silica membranes relevant to the practical applications are analyzed based on the relationships between the separation performance and membrane structural and chemical properties.
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89.30.A- Fossil fuels
61.43.Gt Powders, porous materials
89.20.Kk Engineering
81.20.Ym Purification
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Tunable lateral shift and polarization beam splitting of the transmitted light beam through electro-optic crystals

Xi Chen, Ming Shen, Zhen-Fu Zhang, and Chun-Fang Li

J. Appl. Phys. 104, 123101 (2008); http://dx.doi.org/10.1063/1.3041423 (6 pages) | Cited 12 times

Online Publication Date: 16 December 2008

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We have investigated the tunable lateral shift and polarization beam splitting of the transmitted light beam through electro-optic crystals, based on the Pockels effect. The positive and negative lateral shifts could be easily controlled by adjusting the permittivity tensor, which is modulated by the external applied electric field. An alternative way to realize the polarization beam splitter was also proposed by the polarization-dependent lateral shifts. Numerical simulations for Gaussian-shaped incident beam have demonstrated the above theoretical results obtained by stationary phase method. All these phenomena have potential applications in optical devices.
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42.25.Bs Wave propagation, transmission and absorption
78.20.Jq Electro-optical effects
42.25.Gy Edge and boundary effects; reflection and refraction
42.79.Fm Reflectors, beam splitters, and deflectors

Absorption enhancement in solar cells by localized plasmon polaritons

Carsten Rockstuhl, Stephan Fahr, and Falk Lederer

J. Appl. Phys. 104, 123102 (2008); http://dx.doi.org/10.1063/1.3037239 (7 pages) | Cited 38 times

Online Publication Date: 17 December 2008

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By means of a rigorous diffraction theory, we investigate the possibility to enhance the absorption in solar cells by employing localized plasmon polaritons excited in metallic nanowires. The solar cells are assumed to be made of amorphous silicon. We identify two reasons for increased absorption; namely, the giant near-field enhancement and the enhanced scattering cross section upon exciting localized plasmon polaritons. It will be shown that by a careful and rational adjustment of the system parameters an enhancement in the number of absorbed photons from the solar spectrum up to a factor of 1.6 is feasible.
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84.60.Jt Photoelectric conversion
73.22.Lp Collective excitations
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Electrically injected InGaAs/GaAs photonic crystal membrane light emitting microcavity with spatially localized gain

Yong K. Kim, Victor C. Elarde, Christopher M. Long, James J. Coleman, and Kent D. Choquette

J. Appl. Phys. 104, 123103 (2008); http://dx.doi.org/10.1063/1.3040690 (5 pages) | Cited 3 times

Online Publication Date: 17 December 2008

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Electrically injected photonic crystal membrane light emitting microcavities with spatially localized optical gain are reported. The localization of the InGaAs quantum well inside the defect cavity of the photonic crystal allows for efficient coupling of the optical mode to the gain medium and reduces nonradiative carrier recombination. The use of a buried oxide layer under the semiconductor membrane enables optical and electrical confinement and a submicron diameter oxide aperture provides a current path. Enhancement of the electroluminescence intensity is observed as a result of the spatial localization of the quantum well, and the spectral characteristics at room temperature indicate the photonic crystal microcavity confinement.
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42.55.Sa Microcavity and microdisk lasers
42.70.Qs Photonic bandgap materials
85.60.Jb Light-emitting devices
42.55.Tv Photonic crystal lasers and coherent effects

Sequential multiphoton strategy for semiconductor-based terahertz detectors

Fabrizio Castellano, Rita C. Iotti, and Fausto Rossi

J. Appl. Phys. 104, 123104 (2008); http://dx.doi.org/10.1063/1.3043577 (10 pages) | Cited 2 times

Online Publication Date: 17 December 2008

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A semiconductor-based terahertz-detector strategy, exploiting a bound-to-bound-to-continuum architecture, is presented and investigated. In particular, a ladder of equidistant energy levels is employed, whose step is tuned to the desired detection frequency and allows for sequential multiphoton absorption. Our theoretical analysis demonstrates that the proposed multisubband scheme could represent a promising alternative to conventional quantum-well infrared photodetectors in the terahertz spectral region.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.30.De Semiconductor-device characterization, design, and modeling

Biexcitonic cavity quantum electrodynamics effect on nonlinear spectra of a quantum dot

Hiroshi Ajiki and Hajime Ishihara

J. Appl. Phys. 104, 123105 (2008); http://dx.doi.org/10.1063/1.3043627 (8 pages) | Cited 1 time

Online Publication Date: 17 December 2008

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We theoretically study cross-polarized pump-probe spectra of a quantum dot (QD) embedded in a microcavity in the cavity quantum electrodynamics treatment. Recently, observations of a vacuum Rabi splitting for a QD in microcavity have been reported. The vacuum Rabi splitting is the level separation of one-excitation dressed states (1e states). However, two-excitation dressed states (2e states) have not been observed in this system. We discuss the possibility to observe pump-probe signal coming from the cross-polarized 2e states, in which the energy levels of a QD are modeled by a four-level system consisting of the ground state, right- and left-polarized excitons, and a biexciton. The signal peaks due to the cross-polarized 2e states are found when the quality factor of the cavity is extremely large. The spectral intensity is dramatically enhanced due to the cavity effect. The enhancement rate is independent of the coupling constants between the exciton (biexciton) and a cavity photon when a well-defined vacuum Rabi splitting is formed. However, a strong suppression of the signal occurs at a condition where the energy of the 1e state coincides with the energy difference between 1e and cross-polarized 2e states.
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03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
03.67.Mn Entanglement measures, witnesses, and other characterizations
78.67.De Quantum wells

Enhanced efficiency and reduced spectral shift of green light-emitting-diode epitaxial structure with prestrained growth

Chi-Feng Huang, Tzu-Chi Liu, Yen-Cheng Lu, Wen-Yu Shiao, Yung-Sheng Chen, Jyun-Kai Wang, Chih-Feng Lu, and C. C. Yang

J. Appl. Phys. 104, 123106 (2008); http://dx.doi.org/10.1063/1.3046582 (7 pages) | Cited 8 times

Online Publication Date: 18 December 2008

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The enhanced emission efficiency and reduced spectral shifts of a green InGaN/GaN quantum-well (QW) light-emitting-diode epitaxial structure by using the prestrained growth technique when compared with a control sample of the same emission spectrum with conventional growth are demonstrated. By adding an ∼ 7%-indium InGaN/GaN QW to the structure before the growth of designated emitting high-indium QWs, the growth temperature of the emitting QWs can be raised by 30 °C while keeping about the same emission wavelength around 544 nm in photoluminescence (PL) and 525 nm in electroluminescence (EL). The internal quantum efficiency, room-temperature PL intensity, and EL intensity at the injection current of 20 mA are increased by ∼ 167%, ∼ 140%, and ∼ 182%, respectively. Also, the spectral blueshift range in increasing injection current in the range of 50 mA is decreased by 46%. Based on the pump-power dependent PL measurement, it is found that the quantum-confined Stark effect (QCSE) becomes weaker in the prestrained growth sample. Also, from the calibration of the Arrhenius plots, the carrier localization effect is observed to become weaker under prestrained growth. Therefore, the enhanced emission efficiency is mainly attributed to the decreased defect density and the reduced QCSE in the prestrained sample.
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78.67.De Quantum wells
78.60.Fi Electroluminescence
68.65.Fg Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors

Experimental observation of intermodal dispersion in photonic crystal directional couplers

Francisco Cuesta-Soto, Alejandro Martínez, and Javier Martí

J. Appl. Phys. 104, 123107 (2008); http://dx.doi.org/10.1063/1.3043641 (4 pages)

Online Publication Date: 18 December 2008

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The intrinsic multimode nature of a directional coupler responsible for its functionality leads to intermodal dispersion. In this work, the authors experimentally demonstrate at microwave frequencies that the energy components of a pulse coupled to each of the supermodes of the photonic crystal directional coupler travel at different velocities. An intermodal dispersion of 5 ns/m is measured, which is in good agreement with the theoretical results. This value is more than two orders of magnitude higher than that reported from conventional two-core fiber couplers.
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42.79.Gn Optical waveguides and couplers
42.25.Bs Wave propagation, transmission and absorption
42.70.Qs Photonic bandgap materials

Silicon nanocluster-sensitized emission from erbium: The role of stress in the formation of silicon nanoclusters

I. Ahmad, M. P. Temple, A. Kallis, M. Wojdak, C. J. Oton, D. Barbier, H. Saleh, A. J. Kenyon, and W. H. Loh

J. Appl. Phys. 104, 123108 (2008); http://dx.doi.org/10.1063/1.3050324 (5 pages) | Cited 3 times

Online Publication Date: 18 December 2008

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Erbium-doped silicon-rich silicon oxide films deposited by plasma enhanced chemical vapor deposition suffer from compressive stress as deposited, which converts to a large tensile stress on annealing due to the release of hydrogen. Although the cracking that results from this stress can be avoided by patterning the films into ridges, significant stress remains along the ridge axis. Measurements of erbium photoluminescence sensitized by silicon nanoclusters in stressed and relaxed films suggest an important role for internal film stresses in promoting the phase separation of excess silicon into nanoclusters, which has previously been thought of as a thermally driven process.
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68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.77.Dq Plasma-based ion implantation and deposition
81.40.Gh Other heat and thermomechanical treatments
78.55.Hx Other solid inorganic materials

Light extraction and optical loss mechanisms in organic light-emitting diodes: Influence of the emitter quantum efficiency

Stefan Nowy, Benjamin C. Krummacher, Jörg Frischeisen, Nils A. Reinke, and Wolfgang Brütting

J. Appl. Phys. 104, 123109 (2008); http://dx.doi.org/10.1063/1.3043800 (9 pages) | Cited 53 times

Online Publication Date: 18 December 2008

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The internal quantum efficiency of organic light-emitting diodes (OLEDs) can reach values close to 100% if phosphorescent emitters to harvest triplet excitons are used; however, the fraction of light that is actually leaving the device is considerably less. Loss mechanisms are, for example, waveguiding in the organic layers and the substrate as well as the excitation of surface plasmon polaritons at metallic electrodes. Additionally, absorption in the organic layers and the electrodes can play a role. In this work we use numerical simulations to identify and quantify different loss mechanisms. Changing simulation parameters, for example, the distance of the emitter material to the cathode or thicknesses of the various layers, enables us to study their influence on the fraction of light leaving the OLED. An important parameter in these simulations and for the actual device is the radiative quantum efficiency q, which is defined as the efficiency of radiative exciton decay in an unbounded space filled by the emitting dye and its matrix. The simulations show that due to microcavity effects the radiative decay channel can be considerably changed in an OLED as compared to free space emission of a dipole. Thus the knowledge of the radiative quantum efficiency is crucial for the optimization of OLEDs. As an example, we present simulations of bottom-emitting OLEDs based on the well-known green emitter tris-(8-hydroxyquinoline) aluminum with transparent indium tin oxide anode and a calcium/aluminum cathode.
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85.60.Jb Light-emitting devices

Influence of exposure to 980 nm laser radiation on the luminescence of Si:Er/O light-emitting diodes

A. Karim, C.-X. Du, and G. V. Hansson

J. Appl. Phys. 104, 123110 (2008); http://dx.doi.org/10.1063/1.3050316 (6 pages)

Online Publication Date: 19 December 2008

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Erbium (Er) codoping with oxygen (O) in Si is a well-known method for producing electroluminescent material radiating at 1.54 μm through a 4f shell transition of Er3+ ions. In this work the influence of exposure to 980 nm radiation on the electroluminescence (EL) of reverse biased Si:Er/O light-emitting diodes (LEDs), which give a strong room temperature 1.54 μm intensity, is presented and discussed. All the device layers, including Er/O doped Si sandwiched between two Si0.82Ge0.18 layers, have been grown on silicon on insulator substrates using molecular beam epitaxy and processed to fabricate edge emitting Si:Er/O waveguide LEDs. Electromagnetic mode confinement simulations have been performed to optimize the layer parameters for waveguiding. The temperature dependence of the 1.54 μm EL intensity exhibits an abnormal temperature quenching with a peak near −30 °C, and at −160 °C it has decreased by a factor of 5. However, irradiating the devices with a 980 nm laser gives an enhancement of the 1.54 μm EL intensity, which is more dramatic at low temperatures (e.g., −200 °C) where the quenched EL signal is increased up to almost the same level as at room temperature. The enhancement of the EL intensity is attributed to the photocurrent generated by the 980 nm laser, reducing the detrimental avalanche current.
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85.60.Jb Light-emitting devices
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.79.Gn Optical waveguides and couplers
78.55.Ap Elemental semiconductors
61.72.uf Ge and Si
78.60.Fi Electroluminescence

Properties of O2(1Δ)–I(2P1/2) laser medium with a dc glow discharge iodine atom generator

Pavel A. Mikheyev and Valeriy N. Azyazov

J. Appl. Phys. 104, 123111 (2008); http://dx.doi.org/10.1063/1.3050339 (6 pages) | Cited 7 times

Online Publication Date: 19 December 2008

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Experiments were carried out in a flow cell apparatus under conditions corresponding to those of a typical oxygen-iodine laser. The cell was equipped with a chemical jet type singlet oxygen generator and an electric discharge for the production of iodine atoms. The properties of the discharge generator and the active medium were studied using laser-induced fluorescence and emission spectroscopy. I2 or CH3I entrained in a carrier flow of Ar were used as atomic iodine precursors. About 50% of the iodine contained in CH3I molecules was extracted in the generator. 2.6% of the electric power loaded into the discharge was used in CH3I dissociation. Right after the discharge 80%–90% of the iodine flow consisted of atoms. However, due to recombination during transport, only 20%–50% of atoms remained at the point of injection into the oxygen flow. A straightforward comparison of two methods of oxygen-iodine medium production—conventional, by means of I2 dissociation in the singlet oxygen flow and with iodine atoms produced externally in the electric discharge—was performed. It was found that the lifetime for the energy stored in singlet oxygen was about 30% longer, when atomic iodine was produced from CH3I in the discharge, as compared to the conventional chemical dissociation of I2 in the singlet oxygen flow.
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42.55.Ks Chemical lasers
42.60.By Design of specific laser systems
42.70.Hj Laser materials
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Influence of carbon on the thermoluminescence and optically stimulated luminescence of α-Al2O3:C crystals

Xin-Bo Yang, Hong-Jun Li, Qun-Yu Bi, Yan Cheng, Qiang Tang, and Jun Xu

J. Appl. Phys. 104, 123112 (2008); http://dx.doi.org/10.1063/1.3050344 (6 pages) | Cited 5 times

Online Publication Date: 22 December 2008

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α-Al2O3:C crystal shows excellent thermoluminescence (TL) and optically stimulated luminescence (OSL) properties but the real role carbon plays in this crystal is still not clearly understood so far. In this work, α-Al2O3:C crystal doping with different amounts of carbon were grown by the temperature gradient technique, and TL and OSL properties of as-grown crystals were investigated. Additionally, a mechanism was proposed to explain the role of carbon in forming the TL and OSL properties of α-Al2O3:C. TL and OSL intensities of as-grown crystals increase with the increasing amount of carbon doping in the crystal, but no shift is found in the glow peak location at 465 K. As the amount of carbon doping in the crystals decreases, OSL decay rate becomes faster. With the increase in heating rate, the integral TL response of as-grown crystals decreases and glow peak shifts to higher temperatures. TL response decrease rate increases with the increasing amount of carbon doping in the crystals. All the TL and OSL response curves of as-grown crystals show linear-sublinear-saturation characteristic, and OSL dose response exhibits higher sensitivity and wider linear dose range than that of TL. The crystal doping with 5000 ppm carbon shows the best dosimetric properties. Carbon plays the role of a dopant in α-Al2O3:C crystal and four-valent carbon anions replace the two-valent anions of oxygen during the crystal growth process, and large amounts of oxygen vacancies were formed, which corresponds to the high absorption coefficient of F and F+ centers in the crystals.
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78.60.Kn Thermoluminescence
78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
61.72.jd Vacancies
61.72.jn Color centers

Grating couplers on porous silicon planar waveguides for sensing applications

X. Wei, C. Kang, M. Liscidini, G. Rong, S. T. Retterer, M. Patrini, J. E. Sipe, and S. M. Weiss

J. Appl. Phys. 104, 123113 (2008); http://dx.doi.org/10.1063/1.3043579 (5 pages) | Cited 10 times

Online Publication Date: 22 December 2008

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We study the use of polymer gratings as light couplers into porous silicon planar waveguides for sensing applications. Experimental evidence of a guided mode in a grating-coupled porous silicon structure is presented, along with a study of its detuning due to waveguide infiltration with a chemical linker. All the measurements are in good agreement with simulations obtained by means of a Fourier modal method, where the porous silicon birefringence is considered. These results demonstrate that this system is potentially useful for chemical and biological sensing applications.
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42.79.Gn Optical waveguides and couplers
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Dj Gratings

The effect of shot noise on the start up of the fundamental and harmonics in free-electron lasers

H. P. Freund, L. Giannessi, and W. H. Miner, Jr.

J. Appl. Phys. 104, 123114 (2008); http://dx.doi.org/10.1063/1.3040689 (11 pages) | Cited 5 times

Online Publication Date: 23 December 2008

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The problem of radiation start up in free-electron lasers (FELs) is important in the simulation of virtually all FEL configurations including oscillators and amplifiers in both seeded master oscillator power amplifier (MOPA) and self-amplified spontaneous emission (SASE) modes. Both oscillators and SASE FELs start up from spontaneous emission due to shot noise on the electron beam, which arises from the random fluctuations in the phase distribution of the electrons. The injected power in a MOPA is usually large enough to overwhelm the shot noise. However, this noise must be treated correctly in order to model the initial start up of the harmonics. In this paper, we discuss and compare two different shot noise models that are implemented in both one-dimensional wiggler-averaged (PERSEO) and non-wiggler-averaged (MEDUSA1D) simulation codes, and a three-dimensional non-wiggler-averaged (MEDUSA) formulation. These models are compared for examples describing both SASE and MOPA configurations in one dimension, in steady-state, and time-dependent simulations. Remarkable agreement is found between PERSEO and MEDUSA1D for the evolution of the fundamental and harmonics. In addition, three-dimensional correction factors have been included in the MEDUSA1D and PERSEO, which show reasonable agreement with MEDUSA for a sample MOPA in steady-state and time-dependent simulations.
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41.60.Cr Free-electron lasers
42.60.By Design of specific laser systems
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Mi Dynamical laser instabilities; noisy laser behavior
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Sheath criterion and Sagdeev potential for both electronegative and electropositive plasmas

B. Alterkop

J. Appl. Phys. 104, 123301 (2008); http://dx.doi.org/10.1063/1.3041629 (5 pages) | Cited 2 times

Online Publication Date: 16 December 2008

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The sheath criterion was considered for electronegative as well as electropositive plasma in contact with a material boundary that is either more negative than the plasma space potential or more positive than the space potential. A fluid model accounted for the inertia and pressures of all the plasma components and the Sagdeev potential in the whole sheath without any power series expansion were used. The criterion was specified for several special cases of both electronegative and electropositive plasmas. In the cases, a cold ion critical velocity at the sheath entrance was greater by a factor of 1.585 for qϕ>0 than that for qϕ<0, where q is the ion charge and ϕ is the electrical potential in the sheath. In the case of a plasma with Boltzmann electrons and positive ions and a cold ion beam, this conclusion is true only for q<0 and ϕ<0.
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52.40.Kh Plasma sheaths
52.30.Ex Two-fluid and multi-fluid plasmas
52.40.Hf Plasma-material interactions; boundary layer effects

Dissociation of O2 in low pressure glow discharges in He–O2, Ne–O2, and Ar–O2 gas mixtures

Mohammad Aslam Khan and Abdulaziz M. Al-Jalal

J. Appl. Phys. 104, 123302 (2008); http://dx.doi.org/10.1063/1.3043886 (5 pages) | Cited 2 times

Online Publication Date: 17 December 2008

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Low-pressure glow discharges in He, Ne, or Ar gases containing small amounts of O2 can produce considerable dissociation of O2 molecules. High-lying metastable states in these noble gases play a predominant role in this process. Due to the difference in energies of metastable states of the noble gas atoms, there is a significant variation in the product states of O atoms created as a result of dissociation. Apparently, for He and Ne, superexcited O2 molecules are formed through collisions with high-lying metastable states of the noble gases. The superexcited O2 molecule could either autoionize to form an O2+ ion that subsequently captures an electron and dissociates or it could directly dissociate through some curve-crossing interactions yielding at least one atom in highly excited state. However, in the case of Ar, the formation of superexcited O2 may be possible through a prior creation of Ar2+ ion. We report some interesting observations on spectral emissions from O atoms in the three gas mixtures covering transition from 5d, 4d 3,5D, and 5s 3,5S, to 3p 3,5P levels and 4p and 3p 3,5P to 3s 3,5S levels. The emission from the b 4Σg−−a 4Πu system of O2+ ions is also reported. In general, populations of the above-stated O and O2+ levels are highest in the case of He–O2 mixture and lowest for the Ar–O2 mixture. However, the Ne–O2 mixture appears to strongly populate the 4p 5P levels, while the Ar–O2 mixture strongly populates the 3p 3P levels. The He–O2 mixture appears to be more efficient among the three gas mixtures considered in dissociating the O2 molecules.
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52.80.Hc Glow; corona
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Analysis of plasma profile over KTiOAsO4 surface produced by 532 and 1064 nm laser radiations

Yuming Sun, Ming Chen, Yufei Li, Huanjun Qi, Mingwen Zhao, and Xiangdong Liu

J. Appl. Phys. 104, 123303 (2008); http://dx.doi.org/10.1063/1.3040155 (4 pages)

Online Publication Date: 18 December 2008

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Optical emission studies are carried out on the plasma generated by nanosecond radiation of the 532 and 1064 nm lasers on KTiOAsO4 (KTA) samples with the intensity of 108–109 GW/cm2. Our studies indicate that the amount of evaporated matter in plasma evolution depends on the laser wavelength. The dimension of the self-regulating region shows a clear laser-intensity dependence, which increases from 3 mm at 0.22 GW/cm2 to 8.5 mm at 1.72 GW/cm2. This work is expected be helpful for optimizing the experimental parameters of growing KTA thin films using pulsed laser deposition.
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52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Tx Emission, absorption, and scattering of particles
81.15.Fg Pulsed laser ablation deposition
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.70.-m Plasma diagnostic techniques and instrumentation
52.77.Dq Plasma-based ion implantation and deposition

Characterization of nonthermal Ne–N2 mixture radio frequency discharge

N. U. Rehman, M. Zakaullah, F. U. Khan, and S. Naseer

J. Appl. Phys. 104, 123304 (2008); http://dx.doi.org/10.1063/1.3021356 (9 pages) | Cited 2 times

Online Publication Date: 30 December 2008

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This paper deals with optical emission spectroscopic studies of low pressure (p = 0.1⇒0.5 mbar) Ne–N2 capacitively coupled radio frequency (rf) plasma that can be used for plasma nitriding, etc. It reports the methods to calculate the electron temperature (Te) in nonthermal plasmas. Since, the selected Ne I lines, used to calculate electron temperature, are found in corona balance; therefore, it allows us to use modified Boltzmann technique to calculate electron temperature. Langmuir probe is also used to calculate electron temperature and electron energy distribution functions (EEDFs). The measurements are worked out for different discharge parameters like neon percentage, filling pressure and RF power. It is found that electron temperature increases with the increase in neon percentage and decreases with the increase in pressure, whereas excitation temperature (Texc) increases with power, neon percentage, and decreases with pressure. It is also observed that electron temperature measured by Langmuir probe technique is slightly greater than the one measured via modified Boltzmann plot method. The tails of the EEDFs gain height and extend toward the higher energy with the increase in neon percentage in the mixture.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges
52.80.Hc Glow; corona
52.77.-j Plasma applications
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Band gap bowing parameter of In1−xAlxN

R. E. Jones, R. Broesler, K. M. Yu, J. W. Ager, III, E. E. Haller, W. Walukiewicz, X. Chen, and W. J. Schaff

J. Appl. Phys. 104, 123501 (2008); http://dx.doi.org/10.1063/1.3039509 (6 pages) | Cited 19 times

Online Publication Date: 16 December 2008

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We report a band gap bowing parameter for In1−xAlxN of 4.7 eV from a study of high quality and homogenous samples with x = 0.017–0.60. Optical absorption data were modeled to extract the band gaps in order to consider the complications of the band structure of In-rich InAlN, including the Burstein–Moss shift, nonparabolic conduction band, and broadening of the absorption edge. The alloy compositions were accurately determined using Rutherford backscattering spectrometry and the sample quality was evaluated using x-ray diffraction and channeling-RBS.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Fd III-V semiconductors
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
71.20.Nr Semiconductor compounds

Quantum dots in strained layers—preventing relaxation through the precipitate hardening effect

R. Beanland, J. P. R. David, and A. M. Sanchez

J. Appl. Phys. 104, 123502 (2008); http://dx.doi.org/10.1063/1.3028270 (4 pages) | Cited 1 time

Online Publication Date: 16 December 2008

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The internal strain in epitaxial layers due to lattice misfit has long been recognized as a limiting factor in the design of semiconductor structures. In strained layer structures above a critical thickness hc, this strain is relaxed by the introduction of misfit dislocations. Here, we show that the interaction between the strain fields of a self-assembled quantum dot and a dislocation can lead to a threading dislocation being trapped, or pinned, by the quantum dot. The strength of this interaction is always larger than the force exerted on the dislocation by a surrounding layer with lower misfit strain. This gives a significant increase in the critical thickness for relaxation hc(QD). In layers between hc and hc(QD), threading dislocations can at best move only small distances, effectively preventing relaxation. Furthermore it is not possible to destabilize such a layer by the deposition of strained layers above it. The classical critical thickness condition thus does not apply to these structures, and they can be produced with essentially no limits to thickness before relaxation occurs. This may be expected to have significant technological consequences and allow a much wider range of structures to be produced than is possible using current strained layer design rules.
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81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
68.65.Hb Quantum dots (patterned in quantum wells)
68.35.Gy Mechanical properties; surface strains
61.72.Lk Linear defects: dislocations, disclinations

Characterization of magnetic force microscopy probe tip remagnetization for measurements in external in-plane magnetic fields

Tanja Weis, Ingo Krug, Dieter Engel, Arno Ehresmann, Volker Höink, Jan Schmalhorst, and Günter Reiss

J. Appl. Phys. 104, 123503 (2008); http://dx.doi.org/10.1063/1.3040025 (4 pages) | Cited 3 times

Online Publication Date: 16 December 2008

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A quantitative analysis of magnetic force microscopy (MFM) images taken in external in-plane magnetic fields is difficult because of the influence of the magnetic field on the magnetization state of the magnetic probe tip. We prepared calibration samples by ion bombardment induced magnetic patterning with a topographically flat magnetic pattern magnetically stable in a certain external magnetic field range for a quantitative characterization of the MFM probe tip magnetization in point-dipole approximation.
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07.79.Pk Magnetic force microscopes
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
06.20.F- Units and standards

Intense white photoluminescence emission of V-implanted zinc oxide thin films

Sven Müller, Michael Lorenz, Christian Czekalla, Gabriele Benndorf, Holger Hochmuth, Marius Grundmann, Heidemarie Schmidt, and Carsten Ronning

J. Appl. Phys. 104, 123504 (2008); http://dx.doi.org/10.1063/1.3041652 (7 pages) | Cited 9 times

Online Publication Date: 16 December 2008

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Pulsed laser deposited ZnO films were implanted with vanadium ions using ion energies between 30 and 250 keV with different fluences yielding vanadium concentrations in the range between 0.8 and 5 at. %. After annealing under oxygen ambient at 800 °C, a broad luminescence band observed by photoluminescence covers nearly the total visible spectral region. This luminescence is a superposition of different bands triggered by the incorporated V and remaining implantation defects. The visual impression of the bright whitish emission of the implanted ZnO has been quantified using the color space map of the Commission internationale de l’Éclairage. Furthermore, the intensity of the white emission strongly increases with increasing V concentration, whereas Ar-implanted reference sample shows only weak white emission.
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78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.40.Ha Other nonmetallic inorganics
61.72.uj III-V and II-VI semiconductors

Impact response of titanium from the ambient temperature to 1000 °C

E. B. Zaretsky

J. Appl. Phys. 104, 123505 (2008); http://dx.doi.org/10.1063/1.3042229 (10 pages) | Cited 6 times

Online Publication Date: 16 December 2008

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The yield and spall strengths of polycrystalline high purity (99.99%) and commercial (grade 2) titanium were studied in a series of planar impact experiments with the initial sample temperature ranging from 20 to 1000 °C. In a separate series of impact experiments, the temperature dependence of the longitudinal speed of sound in pure Ti was measured making use of the reverberation of the stress pulse generated in the 3 mm Ti sample by an aluminum impactor. In all the experiments, the velocity of the sample free surface was continuously monitored by VISAR. The stress-strain diagrams of the two kinds of samples were derived from the free surface velocity profiles using the simple wave approximation. Analysis of these diagrams made allowed revealing the sequence of the dislocation-based processes governing the plastic flow in the two materials, from the ambient to some 100 °C above the hcp-bcc transformation temperature. On the basis of the spall data obtained from impact experiments with pure titanium, the limits of existence of nonequilibrium titanium phases were outlined.
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81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
61.72.Lk Linear defects: dislocations, disclinations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

A two-dimensional model for enhanced adhesion of film-terminated fibrillar interfaces by crack trapping

Lulin Shen, Chung-Yuen Hui, and Anand Jagota

J. Appl. Phys. 104, 123506 (2008); http://dx.doi.org/10.1063/1.3035908 (8 pages) | Cited 5 times

Online Publication Date: 16 December 2008

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Experiments on a recently developed bioinspired film-terminated fibrillar array show significantly enhanced adhesion compared to a flat unstructured control sample. Adhesion is enhanced because the interfacial crack is trapped close to fibril edges. Using a finite element method and approximate analysis, we study a two-dimensional version of the fibrillar structure to understand the behavior observed in experiments. Several experimental observations are explained by the model: (1) the work to separate a unit area of the interface (W+) is larger than the work of adhesion (Wad) of the flat control sample; (2) the work to heal a unit area of the interface (W−) is smaller than the work of adhesion of the flat control sample; (3) W+ increases with fibril spacing; (4) W+ decreases with film thickness; and (5) W+ decreases with fibril height.
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68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
68.55.jd Thickness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks
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