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1 Dec 2008

Volume 104, Issue 11, Articles (11xxxx)

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Biosensors and tools for surface functionalization from the macro- to the nanoscale: The way forward

Liviu Nicu and Thierry Leïchlé

J. Appl. Phys. 104, 111101 (2008); http://dx.doi.org/10.1063/1.2973147 (16 pages) | Cited 16 times

Online Publication Date: 1 December 2008

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Most of review articles or even books dedicated to biosensing issues are organized by the generally admitted scheme of a biosensor. Subsequently, biological receptors, modified surfaces (and ways to specifically modify those surfaces using established biological and/or chemical recipes), and transduction techniques are thoroughly addressed in this precise order. In this review, we deliberately decided to break the conventional way of providing biosensing review by uniquely addressing biomolecules’ immobilization methods onto a solid surface and biosensing-related transduction techniques. The aim of this review is to provide a contemporary snapshot of the biosensing landscape without neglecting the seminal references or products where needed. The main guiding line of the review is the downscaling (from the macro- to the nanoscale) of biosensors and their respective most known applications. To conclude, a brief overview of the most popularized nanodevices applied to biology is given before attempting to comment on biosensors’ comparison criteria in terms of targeted applications.
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87.85.fk Biosensors
87.85.Rs Nanotechnologies-applications
82.45.Tv Bioelectrochemistry
87.15.R- Reactions and kinetics
82.80.Fk Electrochemical methods
82.47.Rs Electrochemical sensors
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Internal field effects on the lasing characteristics of InGaN/GaN quantum well lasers

G. E. Dialynas, G. Deligeorgis, M. Zervos, and N. T. Pelekanos

J. Appl. Phys. 104, 113101 (2008); http://dx.doi.org/10.1063/1.3021103 (7 pages) | Cited 5 times

Online Publication Date: 1 December 2008

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A theoretical investigation of InxGa1−xN/GaN single quantum well lasers with x in the range 0.05 ⩽ x ⩽ 0.3 is carried out via self-consistent Schrödinger–Poisson calculations in the effective mass approximation in order to quantify the adverse effects of the internal electric field on the lasing characteristics of these heterostructures. We find a nonzero optimum internal field value that minimizes the threshold current density Jth, and whose amplitude depends on the quantum well width, In content, and cavity losses. We demonstrate that the complete elimination of the internal field in In0.2Ga0.8N/GaN blue laser diodes with typical cavity losses should result in a decrease in Jth by as much as a factor of 4. Furthermore, for a wide range of In contents and cavity losses, we find that the optimum well width that minimizes Jth ranges between 2.5 and 4 nm. Finally, we show that the longest lasing wavelength that can be achieved from an InGaN/GaN quantum well laser is in the range of 480–500 nm depending on cavity losses.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Determination of large third-order optical nonlinearities in tetra-tert-butylphthalocyaninatogallium iodide film

Guang Shi, Yuxiao Wang, Dajun Liu, Xueru Zhang, Junyi Yang, Kun Yang, and Yinglin Song

J. Appl. Phys. 104, 113102 (2008); http://dx.doi.org/10.1063/1.3033518 (6 pages) | Cited 3 times

Online Publication Date: 1 December 2008

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Using the Z-scan technique with 532 nm 4 ns laser pulses at various energy levels and repetition rates, we investigated the optical nonlinearities of tetra-tert-butylphthalocyaninatogallium iodide (t-Bu)4PcGaI. As a result, we found that the soluble peripherally tert-butyl-substituted phthalocyanine bound with the core of gallium iodide exhibited a giant two-photon absorption coefficient and Kerr refractive index. This suggests the potential applications of this material in numerous fields of nonlinear optics. However, when tackling the large nonlinearly induced loss and phase distortion analytically, we failed to fit the corresponding experimental results with the existent series sum formulas, which retain only the first few terms in the expansion. We performed the fitting by retrieving the high-order terms and justified this approach by dealing with the light-matter interaction and wave propagation.
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42.65.-k Nonlinear optics
78.66.Qn Polymers; organic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
83.60.Uv Wave propagation, fracture, and crack healing
68.55.aj Insulators

Intraband absorption in solar cells with an intermediate band

Michael Y. Levy and Christiana Honsberg

J. Appl. Phys. 104, 113103 (2008); http://dx.doi.org/10.1063/1.3021449 (5 pages) | Cited 7 times

Online Publication Date: 1 December 2008

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This article presents a thermodynamic treatment of an intermediate band solar cell that includes photoinduced electronic transitions between two distinct states of the intermediate band. The treatment also allows for two black-body sources, interband photoinduced electronic transitions, overlapping absorption coefficients, multiple electron-hole pair generation, and nonradiative processes. A schematic of the device’s thermodynamic configuration shows that the solar cell is composed of three particle engines operating in tandem. The authors present detailed-balance results where it is assumed that when there is the physical possibility of both photoinduced intra- and interband electronic transitions at intermediate levels that the latter predominates. Results indicate that as the intermediate band’s width increases, the efficiencies saturate to those of two-stack tandem solar cells while the band structures approach that of a material that should operate as a black body. The authors conclude that the assumption that interband transitions predominate over intraband transitions, which is equivalent to ignoring or excluding intraband transitions, may yield results inconsistent with physical reality. The larger the difference between the intermediate band width and the smallest band gap in the system, the more pronounced will be the inconsistency.
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84.60.Jt Photoelectric conversion

H+ implanted channel waveguides in buried epitaxial crystalline YAG:Nd,Tm layers and infrared-to-blue upconversion characterization

Marta Szachowicz, Marie-France Joubert, Paul Moretti, Maurice Couchaud, Bemard Ferrand, Camelia Borca, and Azzedine Boudrioua

J. Appl. Phys. 104, 113104 (2008); http://dx.doi.org/10.1063/1.2976303 (9 pages)

Online Publication Date: 1 December 2008

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Nd,Tm:YAG codoped single crystal waveguides were studied in order to discover if the presence of Nd3+ ions favors blue luminescence at 486 nm. Innovative implantation techniques were applied to locally change Δn and form varied H+ implanted channel structures in Nd,Tm:YAG buried epitaxial waveguiding layers. The guided blue luminescence due to the Tm3+ 1G4→3H6 transition was studied under infrared excitation at 785 nm (Tm3+ absorption) and 808 nm (Nd3+ absorption) for the epitaxial planar waveguides of different Tm3+ and Nd3+ concentrations for all the implanted channel waveguide structures.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers

Comparison of optical parameters and luminescence between Er3+/Yb3+ codoped phosphate glass ceramics and precursor glasses

Xiaochen Yu, Feng Song, Wentao Wang, Lanjun Luo, Lin Han, Zhenzhou Cheng, Tongqing Sun, Jianguo Tian, and Edwin. Y. B. Pun

J. Appl. Phys. 104, 113105 (2008); http://dx.doi.org/10.1063/1.3028268 (6 pages) | Cited 12 times

Online Publication Date: 2 December 2008

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Er3+/Yb3+ codoped transparent phosphate precursor glasses and glass ceramics have been fabricated and characterized. The formation of ErPO4 and YbPO4 nanocrystals was studied using x-ray diffraction. The intensity parameters, the spontaneous radiative transition probabilities, the branching ratios, and the radiative lifetimes of Er3+ in both glass ceramics and precursor glasses were calculated based on the Judd–Ofelt theory, and the crystallization process in the glass ceramics is confirmed by the optical parameters obtained. Under 975 nm wavelength excitation intense 1.54 μm fluorescence and upconversion luminescence were observed in the glass ceramics, the quantum efficiency of the Er3+ 4I13/2→4I15/2 transition is 95%, and the transition mechanisms of the upconversion luminescence are due to a two-photon process.
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78.66.Jg Amorphous semiconductors; glasses
61.43.Fs Glasses
81.05.Pj Glass-based composites, vitroceramics
78.55.Qr Amorphous materials; glasses and other disordered solids

3.4 THz heterodyne receiver using a hot electron bolometer and a distributed feedback quantum cascade laser

P. Khosropanah, W. Zhang, J. N. Hovenier, J. R. Gao, T. M. Klapwijk, M. I. Amanti, G. Scalari, and J. Faist

J. Appl. Phys. 104, 113106 (2008); http://dx.doi.org/10.1063/1.3032354 (6 pages) | Cited 12 times

Online Publication Date: 2 December 2008

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We report a heterodyne receiver using a superconducting NbN hot electron bolometer (HEB) integrated with a tight winding spiral antenna as mixer and a distributed feedback (DFB) terahertz quantum cascade laser (QCL) operating at 3.42 THz as local oscillator. The aim is to demonstrate the readiness of both devices for the detection of OH lines at 3.5 THz in a real instrument. We show that the improved single-spot beam of the terahertz QCL can easily pump the HEB mixer. We measured a double sideband receiver noise temperature of 2100 K at the optimum local oscillator power of 290 nW. This noise temperature can be further reduced to 1100 K if we correct the loss due to the use of an uncoated lens, and the losses of the window and the air. Therefore, the combination of a HEB and such a DFB QCL can in principle be used to detect an OH line at 3.5 THz. However, a high input power of several watts, which is needed to operate the QCL in a liquid-helium cryostat, poses a big challenge to the receiver stability.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
42.55.Px Semiconductor lasers; laser diodes
42.62.Fi Laser spectroscopy
85.25.-j Superconducting devices

White light upconversion emissions from Tm3++Ho3++Yb3+ codoped tellurite and germanate glasses on excitation with 798 nm radiation

Neeraj Kumar Giri, D. K. Rai, and S. B. Rai

J. Appl. Phys. 104, 113107 (2008); http://dx.doi.org/10.1063/1.3033516 (5 pages) | Cited 18 times

Online Publication Date: 2 December 2008

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White light has been produced using 798 nm laser excitation in Tm3++Ho3++Yb3+ codoped tellurite and germanate glasses. These glasses simultaneously generate the three primary colors, red, green, and blue, on 798 nm excitation. Thus, multicolor emission obtained was tuned to white luminescence by adjusting the Ho3+ ion concentration and excitation power. UV excitation and fluorescence spectra of these triply doped glasses give additional emissions, which do not appear on 798 nm excitation.
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74.25.Gz Optical properties
42.70.Hj Laser materials
73.61.Jc Amorphous semiconductors; glasses
76.30.Kg Rare-earth ions and impurities
42.70.Ce Glasses, quartz

Plume dynamics and shielding characteristics of nanosecond scale multiple pulse in carbon ablation

Kedar Pathak and Alex Povitsky

J. Appl. Phys. 104, 113108 (2008); http://dx.doi.org/10.1063/1.3032937 (10 pages) | Cited 6 times

Online Publication Date: 3 December 2008

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The behavior of ablated plumes produced by nanosecond scale multiple laser pulses typical for carbon ablation is studied in order to understand the plume expansion dynamics and shielding effect of plume with special interest to ionization of plumes. The patterns of a planar plume (typical for channel cutting) and an axisymmetric plume (typical for hole drilling) appear to be quite different. Ionization in carbon plume is estimated using the Saha equation. An iterative procedure is developed to determine the local equilibrium temperature affected by ionization. It is shown that though shielding due to the presence of ionized particles in carbon plume is small, the effect of ionization on plume temperature can be considerable. Shielding effect is calculated for laser pulses with different time intervals between pulses. The effects of high temperature and low density of plume are conflicting and cause shielding behavior to be nonmonotonic. It is shown that the nonmonotonic dependence of the delivered laser energy, the pulse number, and the difference in shielding characteristics between planar and axisymmetric formulations increase with the time duration between two consecutive pulses.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.U- Carbon/carbon-based materials
81.16.-c Methods of micro- and nanofabrication and processing
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.20.Ds Laser-beam impact phenomena

Photonic band gaps of polygonal and circular dielectric rods in square lattices

K. P. Chang, S. L. Yang, L. F. Shen, and T. J. Yang

J. Appl. Phys. 104, 113109 (2008); http://dx.doi.org/10.1063/1.3039213 (6 pages)

Online Publication Date: 4 December 2008

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The plane-wave method is employed to determine the band structures and the field patterns of the photonic crystals with polygonal and circular rods in square lattices. Isotropic and anisotropic N-fold polygonal rods are used to assess the effects of the shapes and symmetries of polygonal rods on E- and H-polarization modes. The photonic band structures of the polygonal rods approach those of the circular rods as N increases above a value that is determined by the optical properties of the photonic crystal. Moreover, for comparable geometric structures, anisotropic polygonal-rod photonic crystals can provide larger absolute photonic band gaps than isotropic photonic crystals.
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77.22.Ej Polarization and depolarization
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.-b Electron density of states and band structure of crystalline solids
42.70.Qs Photonic bandgap materials

Laser-induced magnesium production from magnesium oxide using reducing agents

M. S. Mohamed, T. Yabe, C. Baasandash, Y. Sato, Y. Mori, Liao Shi-Hua, H. Sato, and S. Uchida

J. Appl. Phys. 104, 113110 (2008); http://dx.doi.org/10.1063/1.2975969 (7 pages) | Cited 2 times

Online Publication Date: 4 December 2008

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Experiments for laser induced production of magnesium (Mg) from magnesium oxide (MgO) using reducing agents (R) were conducted. In these experiments, continuous wave CO2 focused laser is focused on a mixture of magnesium oxide and reducing agent. High power density of focused laser leads to high temperature and the reduction reaction resulting in Mg production. The resultant vapor is collected on a copper plate and analyzed in terms of magnesium deposition efficiency. Deposition efficiencies with various reducing agents such as Zr, C, and Si have been measured to be 60, 9.2, and 12.1 mg/kJ respectively. An excess addition of reducing agent over their corresponding reaction stoichiometric amounts is found to be optimum condition for the most of performed laser induced reactions. In addition, utilizing solar-pumped laser in Mg production with reducing agent will reduce CO2 emission and produce magnesium with high-energy efficiency and large throughput.
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81.05.Bx Metals, semimetals, and alloys
42.62.-b Laser applications
81.05.Cy Elemental semiconductors
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Holographic fabrication of photonic crystals using multidimensional phase masks

Yuankun Lin, Ahmad Harb, Daniel Rodriguez, Karen Lozano, Di Xu, and K. P. Chen

J. Appl. Phys. 104, 113111 (2008); http://dx.doi.org/10.1063/1.3037234 (6 pages) | Cited 3 times

Online Publication Date: 4 December 2008

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This paper reports the experimental approaches to the fabrication of two-layer integrated phase masks and the fabrication of photonic crystal templates using the phase mask based on holographic lithography technique. The photonic crystal template is formed by exposing photoresist mixtures to five-beam interference patterns generated through the phase mask. The fabricated phase mask consists of two layers of orthogonally oriented gratings produced in a liquid crystal and photoresist mixture. A polymerization-induced phase separation preserves the grating structure during the exposure. The vertical spatial separation between two layers of gratings produces a phase difference among diffracted laser beams, which enables the holographic fabrication of diamondlike photonic crystal structures. The fabricated photonic crystal structure is consistent with simulations based on the five-beam interference. The two-layer phase mask opens up an opportunity of direct printing photonic structures.
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42.40.Kw Holographic interferometry; other holographic techniques
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials

Visible luminescence mechanism in nano ZnO under weak confinement regime

Litty Irimpan, V. P. N. Nampoori, and P. Radhakrishnan

J. Appl. Phys. 104, 113112 (2008); http://dx.doi.org/10.1063/1.3032897 (5 pages) | Cited 2 times

Online Publication Date: 4 December 2008

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We describe the structure of luminescence spectrum in the visible region in nano-ZnO in colloidal and thin film forms under weak confinement regime by modeling the transition from excited state energy levels of excitons to their ground state. Measurements on nanocrystallites indicate the presence of luminescence due to excitonic emissions when excited with 255 nm. The relevant energy levels showing the transitions corresponding to the observed peaks in the emission spectrum of ZnO of particle size 18 nm are identified.
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78.66.Hf II-VI semiconductors
71.35.-y Excitons and related phenomena
82.70.Dd Colloids
78.55.Et II-VI semiconductors
71.20.Nr Semiconductor compounds

Electric field assisted dissolution of Au rods in gold-doped silicate glass

Zhiyu Zou, Xiangjun Chen, Qiang Wang, Shiliang Qu, and Xinyu Wang

J. Appl. Phys. 104, 113113 (2008); http://dx.doi.org/10.1063/1.3040555 (5 pages) | Cited 4 times

Online Publication Date: 8 December 2008

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Dissolution of Au rods in gold-doped silicate glass is observed experimentally during the dc electric field thermal poling. Scanning electron microscopy characterizations show that some Au rods with a high aspect ratio are dissolved to spherelike particles and others still keep an elongated structure, which is well accorded with the absorption spectroscopy results. The mechanism for dissolution of Au particles is attributed to electron tunneling conduction and Au cationic conduction, based on electrical measurements during the electric field assisted dissolution process. Electric field thermal poling provides a promising method for the controlling of structural and optical properties of noble metal-doped silicate glass.
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64.75.Bc Solubility
78.20.-e Optical properties of bulk materials and thin films
66.30.hh Glasses
61.43.Fs Glasses

Crack-free GaAs epitaxy on Si by using midpatterned growth: Application to Si-based wavelength-selective photodetector

Hui Huang, Xiaomin Ren, Jihe Lv, Qi Wang, Hailan Song, Shiwei Cai, Yongqing Huang, and Bo Qu

J. Appl. Phys. 104, 113114 (2008); http://dx.doi.org/10.1063/1.3035843 (5 pages) | Cited 3 times

Online Publication Date: 8 December 2008

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A monolithically integrated wavelength-selective photodetector, which consists of an 11.86 μm thick GaAs-based Fabry–Pérot filter and a 3.84 μm thick InP-based p-i-n absorption structure (with a 0.3 μm In0.53Ga0.47As absorption layer), was grown on a Si substrate. A crack-free and high-quality epilayer with an area of 800×700 μm2 was obtained by using midpatterned growth and thermal-cycle annealing. Long dislocations running parallel to the GaAs/Si interface were formed by thermal annealing. This kind of dislocation may effectively alleviate the thermal stress across a large patterned area and be responsible for the crack-free epilayer. A photodetector with a spectral linewidth of 1.1 nm (full width at half maximum) and a quantum efficiency of 9.0% was demonstrated.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
61.72.Lk Linear defects: dislocations, disclinations
61.72.Cc Kinetics of defect formation and annealing
85.60.Gz Photodetectors (including infrared and CCD detectors)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Dark current and band profiles in low defect density thick multilayered GaAs/InAs self-assembled quantum dot structures for infrared detectors

Tetsuya Asano, Anupam Madhukar, Krishnamurthy Mahalingam, and Gail J. Brown

J. Appl. Phys. 104, 113115 (2008); http://dx.doi.org/10.1063/1.3039799 (5 pages) | Cited 9 times

Online Publication Date: 9 December 2008

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We report results of a systematic study of the structural and photoresponse properties of GaAs/{InAs quantum dot (QD)/InGaAs quantum well/GaAs} ×m multiple quantum dot (MQD) structures with m from 1 to 20 placed in n-GaAs/i(MQD)/n-GaAs configuration to act as quantum dot infrared photodetectors (QDIPs). Extremely low dislocation densities inferred from cross-sectional and plan-view transmission electron microscopy and the observed linear increase in photoluminescence intensity with MQD thickness reveal the high quality of these QDIP structures. Temperature and bias dependent dark and photocurrent measurements reveal dark current activation energies (Ea) increasing with the number of QD layers in a manner that indicates that Ea represents the built-in potential in the MQD region. These studies indicate the need for more quantitative modeling to guide optimal doping strategies and profiles to realize high photocurrents while maintaining acceptable dark current.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Near-infrared emission properties and energy transfer of Tm3+-doped and Tm3+/Dy3+-codoped chalcohalide glasses

Gao Tang, Cunming Liu, Zhiyong Yang, Lan Luo, and Wei Chen

J. Appl. Phys. 104, 113116 (2008); http://dx.doi.org/10.1063/1.3040030 (6 pages) | Cited 6 times

Online Publication Date: 10 December 2008

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Near-infrared emission properties of Tm3+ in GeSe2–Ga2Se3–CsI glasses were investigated. The increase in emission intensity ratio I1.47 μm/I1.22 μm and the large increase in the lifetime of the Tm3+:3H4 level from 189 to 2480 μs can be obtained as CsI concentration changes from 20% to 40%. These improved emission properties result from the appearance of I-containing structural units, which have low phonon energy and are located near the Tm3+ ions, dominating the multiphonon relaxation and cross relaxation. Radiative parameters of Tm3+ were calculated based on the Judd–Ofelt analysis. The potential use of Tm3+-doped GeSe2–Ga2Se3–CsI glasses for S-band fiber amplifiers was discussed. Additionally, the intensity and lifetime of 1.2, 1.3, and 1.47 μm infrared fluorescence on Tm3+/Dy3+-codoped GeSe2–Ga2Se3–CsI glasses were studied, and the energy transfer mechanisms were discussed.
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78.55.Qr Amorphous materials; glasses and other disordered solids
78.55.Hx Other solid inorganic materials
78.66.Jg Amorphous semiconductors; glasses
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

Terahertz emission from femtosecond laser illuminated (112) surfaces of InSb

V. L. Malevich, A. Krotkus, A. Bičiūnas, and V. Pačebutas

J. Appl. Phys. 104, 113117 (2008); http://dx.doi.org/10.1063/1.3040691 (6 pages) | Cited 8 times

Online Publication Date: 10 December 2008

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Polarized terahertz radiation generated from (112)-oriented InSb surfaces is investigated as a function of the sample azimuthal orientation under excitation from femtosecond Yb:KGW laser pulses. The expressions describing the optical rectification and the surface electric-field-induced optical rectification in reflection from zinc-blende crystals, such as InSb, are calculated. It is shown the contributions of both these effects should be taken into account when describing terahertz emission from InSb surfaces.
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79.20.Ds Laser-beam impact phenomena
78.20.Jq Electro-optical effects
78.68.+m Optical properties of surfaces
42.65.-k Nonlinear optics
78.70.Gq Microwave and radio-frequency interactions

Light absorption in the near field around surface plasmon polaritons

Antonio Luque, Antonio Martí, Manuel J. Mendes, and Ignacio Tobías

J. Appl. Phys. 104, 113118 (2008); http://dx.doi.org/10.1063/1.3014035 (8 pages) | Cited 8 times

Online Publication Date: 12 December 2008

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A semiclassical method is developed to calculate the energy absorption of an electronic system located in the near field of a metal nanoparticle sustaining surface plasmons. The results are found to be similar to those of photon absorption from ordinary transversal radiation. However, they are affected by a geometrical factor that can increase the absorption by several orders of magnitude. As example, we investigate ellipsoidal-shaped metal nanoparticles which, under favorable conditions, may provide near field aborption enhancements almost as large as 104, and in many cases above 10.
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73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Optical measurement of the thermal diffusivity of intact thermal barrier coatings

Bauke Heeg and David R. Clarke

J. Appl. Phys. 104, 113119 (2008); http://dx.doi.org/10.1063/1.3035942 (7 pages) | Cited 3 times

Online Publication Date: 12 December 2008

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The thermal diffusivity of vapor deposited thermal barrier coatings is measured using an all-optical approach. The method combines CO2 laser heating of the coating surface with detection of the temperature variation in the laser induced Cr3+ luminescence signal from the thermally grown oxide (TGO) formed under the coating during service. The thermal diffusivity is determined from the delay between a surface heating laser pulse and the heating of the TGO. Data analysis is performed using a three layer heat equation model. Various locations on several coatings were investigated with different average heating laser powers and modulation frequencies. The normalized standard deviation was found to be of the order of 20%, which is thought to be largely due to localized variations in coating thickness and density. The advantage of the method described here is that it does not require knowledge of either the thermal properties of the alloy, its temperature, or thickness, and is therefore well suited for measurement on coated parts of complex shape, such as a hot section gas turbine blade.
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
66.30.Xj Thermal diffusivity
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
79.20.Ds Laser-beam impact phenomena
81.65.-b Surface treatments

An extended model for upconversion in solar cells

Viorel Badescu

J. Appl. Phys. 104, 113120 (2008); http://dx.doi.org/10.1063/1.3040692 (10 pages) | Cited 10 times

Online Publication Date: 15 December 2008

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Here we analyze the system proposed by Trupke et al. (J. Appl. Phys. 92, 4117 (2002) ) to increase solar cell efficiency. The system consists in adding to the cell a so-called upconverter, which is a device able to convert the low-energy (subband-gap) incident solar photons into photons of higher energy. The model takes account of (i) the nonradiative recombination in both solar cell and converter and (ii) the refractive index of both cell and converter. Two configurations are studied: cell and rear converter (C-RC) and front converter and cell. The main conclusions are as follows. (1) When nonradiative recombination is neglected for both cell and converter, the energy conversion efficiency of a C-RC system slightly exceeds the efficiency of a solar cell operating alone (under 1 sun illumination). (2) When similar realistic values for the radiative recombination efficiency are considered for both cell and converter, the energy conversion efficiency of a C-RC system is lower than the efficiency of a solar cell operating alone (under 1 sun illumination). (3) Adding a rear upconverter to the solar cell is beneficial in the case of present-day quality solar cells under concentrated solar radiation. (4) At small values of the cell refractive index (roughly less than 2), the conversion efficiency does not depend on the converter refractive index. (5) At higher values of the cell refractive index, the conversion efficiency decreases by increasing the converter refractive index. (6) The energy conversion efficiency does not increase by adding a front upconverter to the cell, whatever the values of the radiative recombination efficiency and solar radiation concentration ratio are.
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84.60.Jt Photoelectric conversion
72.40.+w Photoconduction and photovoltaic effects
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Quantification of the ion and momentum fluxes toward the substrate during reactive magnetron sputtering

S. Mahieu, K. Van Aeken, and D. Depla

J. Appl. Phys. 104, 113301 (2008); http://dx.doi.org/10.1063/1.3031527 (7 pages) | Cited 8 times

Online Publication Date: 1 December 2008

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The ion and momentum fluxes toward the growing film during reactive magnetron sputtering of a Ti target in a mixture of Ar and N2 are determined. For the ion flux and ion energy distribution a retarding field energy analyzer has been employed. The results were confronted with planar and cylindrical probe measurements, two more common used techniques. For the momentum flux, energy resolved mass spectrometry and simulations with the binary collision Monte Carlo code SIMTRA were performed to determine the contribution to this flux by the impact of ions and sputtered and reflected particles. Based on the quantification of both fluxes, it can be concluded that there is a relation between the hardness and elastic modulus of the TiN films and the momentum flux.
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81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli

Characteristics of streamer discharge development between the dielectric-coated sphere-plane electrodes in water

Taiyun Zhu, Lanjun Yang, Zhijie Jia, and Qiaogen Zhang

J. Appl. Phys. 104, 113302 (2008); http://dx.doi.org/10.1063/1.3026529 (5 pages) | Cited 2 times

Online Publication Date: 2 December 2008

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This paper presents the characteristics of the streamer discharge development between the dielectric-coated sphere-plane electrodes in water. In order to study the streamer propagation mechanism, the factors such as polarities, water conductivity, and ambient pressure were taken into consideration. Experimental results demonstrate that the water conductivity and amplitude of applied voltage both have a great influence on mean velocity and brightness of the streamer. When the ambient pressure decreases from 0.1 to 0.0065 MPa, the pressure has little influence on the mean velocities of the streamer in both distilled and tap water for fast streamer. The existence of dielectric coating causes a lower initiation voltage of the streamer for negative polarity than that for positive one. Also, the 10% breakdown voltage (U10%) is decreased by 20% under the pressure of 0.0065 MPa than that under the pressure of 0.1 MPa in distilled water, while the U10% is almost the same under different pressures in tap water. Based on the analysis of the discharge images and current waveforms as well as the above experimental results, it can be concluded that the streamer propagation is composed of the generation of the microbubbles and the discharge in the bubbles. For subsonic streamer, the generation of the bubbles is more likely a thermal process, whereas for supersonic streamer, the ionization and dissociation of water molecules in high electric field are involved in the bubble generation process.
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52.80.Wq Discharge in liquids and solids
52.25.Jm Ionization of plasmas

Evolution of an electron energy distribution function in a weak dc magnetic field in solenoidal inductive plasma

Min-Hyong Lee and Seong Wook Choi

J. Appl. Phys. 104, 113303 (2008); http://dx.doi.org/10.1063/1.3035838 (7 pages) | Cited 4 times

Online Publication Date: 4 December 2008

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We investigated the evolution of the electron energy distribution function (EEDF) in a solenoidal inductively coupled plasma surrounded by an axial dc magnetic field. The increase in the dc magnetic field caused the EEDF to evolve from a bi-Maxwellian to a Maxwellian distribution. At the discharge center, the number of low energy electrons was significantly reduced while the high energy electron population showed little change when a weak dc magnetic field was present. However, at the discharge radial boundary, the high energy electron population decreased significantly with the magnetic field while the change in low energy population was not prominent compared to the discharge boundary. These changes in EEDFs at the boundary and center of the discharge are due to the radial confinement and the restriction of radial transport of electrons by dc magnetic field.
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52.25.-b Plasma properties
52.55.-s Magnetic confinement and equilibrium
52.40.Hf Plasma-material interactions; boundary layer effects
52.80.-s Electric discharges

Plasma-chemical processes in microwave plasma-enhanced chemical vapor deposition reactors operating with C/H/Ar gas mixtures

Yuri A. Mankelevich, Michael N. R. Ashfold, and Jie Ma

J. Appl. Phys. 104, 113304 (2008); http://dx.doi.org/10.1063/1.3035850 (11 pages) | Cited 19 times

Online Publication Date: 10 December 2008

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Microwave (MW) plasma-enhanced chemical vapor deposition (PECVD) reactors are widely used for growing diamond films with grain sizes spanning the range from nanometers through microns to millimeters. This paper presents a detailed description of a two-dimensional model of the plasma-chemical activation, transport, and deposition processes occurring in MW activated H/C/Ar mixtures, focusing particularly on the following base conditions: 4.4%CH4/7%Ar/balance H2, pressure p = 150 Torr, and input power P = 1.5 kW. The model results are verified and compared with a range of complementary experimental data in the companion papers. These comparators include measured (by cavity ring down spectroscopy) C2(a), CH(X), and H(n = 2) column densities and C2(a) rotational temperatures, and infrared (quantum cascade laser) measurements of C2H2 and CH4 column densities under a wide range of process conditions. The model allows identification of spatially distinct regions within the reactor that support net CH4→C2H2 and C2H2→CH4 conversions, and provide a detailed mechanistic picture of the plasma-chemical transformations occurring both in the hot plasma and in the outer regions. Semianalytical expressions for estimating relative concentrations of the various C1Hx species under typical MW PECVD conditions are presented, which support the consensus view regarding the dominant role of CH3 radicals in diamond growth under such conditions.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.aj Insulators
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.77.Dq Plasma-based ion implantation and deposition
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