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15 Jan 2008

Volume 103, Issue 2, Articles (02xxxx)

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Blue luminescent silicon nanocrystals prepared by nanosecond laser ablation and stabilized in electronically compatible spin on glasses

Vladimir Švrček, Takeshi Sasaki, Yoshiki Shimizu, and Naoto Koshizaki

J. Appl. Phys. 103, 023101 (2008); http://dx.doi.org/10.1063/1.2830798 (8 pages) | Cited 4 times

Online Publication Date: 16 January 2008

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We investigated the blue luminescent silicon nanocrystal (Si-nc) preparation in liquid spin on glass (SOG) by nanosecond laser ablation of the Si target in SOG. The confinement of laser-generated plasma in liquids significantly enhanced the formation of Si-nc. Furthermore, the silicon-dioxide-based SOG inhibited Si-nc aggregation compared to the case of laser ablation in de-ionized water. The silicon-dioxide-based SOG during the solidification process accelerated Si-ncs surface oxidation and passivation. As a result, visible room temperature photoluminescence (PL) of stabilized Si-ncs in solid SOG was achieved with a maximum located at 2.9 eV. This PL spectrum was very similar to that from the Si-nc colloidal solution obtained by laser ablation of the Si target and subsequent aging for six months in de-ionized water. The mathematical description of dynamical Si-nc formation processes within laser plasma confined by liquid SOG was applied to qualitatively describe the obtained results. A Si-nc formation scheme could be described as serial processes of rapid formation and growth of embryotic Si particles, consecutive quick oxidation in SOG, and growth termination by quenching. The quantum confinement size effect and surface∕defect states in the surrounding silicon oxide were responsible for efficient blue PL. The solidification of Si-nc in SOG solution enabled the formation of self-supporting films with well-defined Si-nc concentrations that could be simply varied by laser fluence. The controllability of blue luminescent intensity from a film by laser fluence during laser ablation is of significance for optoelectronic applications.
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81.16.-c Methods of micro- and nanofabrication and processing
81.65.Rv Passivation
81.65.Mq Oxidation
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Ap Elemental semiconductors
81.30.Fb Solidification

Terahertz mobility measurements on poly-3-hexylthiophene films: Device comparison, molecular weight, and film processing effects

Okan Esenturk, Joseph S. Melinger, and Edwin J. Heilweil

J. Appl. Phys. 103, 023102 (2008); http://dx.doi.org/10.1063/1.2828028 (8 pages) | Cited 4 times

Online Publication Date: 17 January 2008

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We directly compare relative carrier mobilities in semiconducting organic polymer films measured using noncontact optical pump terahertz (THz) probe spectroscopy to those reported in electrical device studies. Relative transient signal amplitude measurements of photoinjected carrier mobility as a function of poly-3-hexylthiophene (P3HT) molecular weight correlate directly with electrical device test values, indicating that the THz method shows promise as a rapid material screening approach. We also present measurements on P3HT conducting films as a function of structural regularity, dispersing solvent, addition of C60 electron traps, sample temperature, and other growth parameters relevant to device manufacture.
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73.61.Ph Polymers; organic compounds
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
78.70.Gq Microwave and radio-frequency interactions

Upconversion in Nd3+-doped glasses: Microscopic theory and spectroscopic measurements

S. L. Oliveira, D. F. de Sousa, A. A. Andrade, L. A. O. Nunes, and T. Catunda

J. Appl. Phys. 103, 023103 (2008); http://dx.doi.org/10.1063/1.2826908 (8 pages) | Cited 3 times

Online Publication Date: 22 January 2008

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In this work, we report a systematic investigation of upconversion losses and their effects on fluorescence quantum efficiency and fractional thermal loading in Nd3+-doped fluoride glasses. The energy transfer upconversion (γup) parameter, which describes upconversion losses, was experimentally determined using different methods: thermal lens (TL) technique and steady state luminescence (SSL) measurements. Additionally, the upconversion parameter was also obtained from energy transfer models and excited state absorption measurements. The results reveal that the microscopic treatment provided by the energy transfer models is similar to the macroscopic ones achieved from the TL and SSL measurements because similar γup parameters were obtained. Besides, the achieved results also point out the migration-assisted energy transfer according to diffusion-limited regime rather than hopping regime as responsible for the upconversion losses in Nd-doped glasses.
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78.55.Hx Other solid inorganic materials
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
81.05.Kf Glasses (including metallic glasses)

Dispersion of magnetic plasmon polaritons in perforated trilayer metamaterials

Tao Li, Shu-Ming Wang, Hui Liu, Jia-Qi Li, Fu-Ming Wang, Shi-Ning Zhu, and Xiang Zhang

J. Appl. Phys. 103, 023104 (2008); http://dx.doi.org/10.1063/1.2828178 (4 pages) | Cited 16 times

Online Publication Date: 22 January 2008

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Multiple magnetic plasmon polariton (MPP) modes were recently explored in a well-known system—metal∕insulator∕metal layered structure perforated with periodic holes array [ Appl. Phys. Lett. 90, 251112 (2007) ]. Now, we consequently study the dispersions of the MPP modes in similar systems with rectangular hole arrays by analyzing the detailed optical transmittances at oblique incidences. Significantly, our results provide a definite polarization-dependent dispersion property of MPP modes: strong dispersive MPP(±1,±1) modes with the degeneration broken up and a remained degenerate MPP(0,±1) mode for s-polarization and almost flat dispersions of all MPP modes for p-polarization. Such a phenomenon is explained by the different coupling intensities among the artificial “magnetic atoms.” This finding helps us to make a deeper understanding on the artificial magnetic excitations in this trilayer metamaterial.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.66.-w Optical properties of specific thin films

Pump excited state absorption in holmium-doped fluoride glass

André Felipe Henriques Librantz, Stuart D. Jackson, Laércio Gomes, Sidney José Lima Ribeiro, and Younes Messaddeq

J. Appl. Phys. 103, 023105 (2008); http://dx.doi.org/10.1063/1.2833436 (8 pages) | Cited 13 times

Online Publication Date: 23 January 2008

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The primary excited state absorption processes relating to the 5I6→5I7 3 μm laser transition in singly Ho3+-doped fluoride glass have been investigated in detail using time-resolved fluorescence spectroscopy. Selective laser excitation of the 5I6 and 5I7 energy levels established the occurrence of two excited state absorption transitions from these energy levels that compete with previously described energy transfer upconversion processes. The 5I7→5I4 excited state absorption transition has peak cross sections at 1216 nm (σesa = 2.8×10−21 cm2), 1174 nm (σesa = 1×10−21 cm2), and 1134 nm (σesa = 7.4×10−22 cm2) which have a strong overlap with the 5I8→5I6 ground state absorption. On the other hand, it was established that the excited state absorption transition 5I6→5S2 had a weak overlap with ground state absorption. Using numerical solution of the rate equations, we show that Ho3+-doped fluoride fiber lasers employing pumping at 1100 nm rely on excited state absorption from the lowest excited state of Ho3+ to maintain a population inversion and that energy transfer upconversion processes compete detrimentally with the excited state absorption processes in concentrated Ho3+-doped fluoride glass.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.D- Time resolved spectroscopy (>1 psec)
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Wavelength tuning predictions and experiments for type II antimonide lasers

G. C. Dente, M. L. Tilton, A. P. Ongstad, and R. Kaspi

J. Appl. Phys. 103, 023106 (2008); http://dx.doi.org/10.1063/1.2836785 (4 pages) | Cited 3 times

Online Publication Date: 28 January 2008

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After a review of pseudopotential models for superlattices, we use the superlattice empirical pseudopotential method to predict the wavelength tuning of type II antimonide lasers. We then compare the predictions with a large set of experimental data on a series of optically pumped lasers operating from 2.2 to 9.2 μm.
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42.60.Fc Modulation, tuning, and mode locking
42.55.Ah General laser theory
42.55.Px Semiconductor lasers; laser diodes

Photoinduced absorption in B-doped hydrogenated amorphous silicon alloys applied to all-optical modulators

C. Summonte, F. G. Della Corte, M. A. Nigro, and A. Desalvo

J. Appl. Phys. 103, 023107 (2008); http://dx.doi.org/10.1063/1.2833325 (7 pages) | Cited 2 times

Online Publication Date: 29 January 2008

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All-optical modulators have been fabricated, based on the infrared photoinduced absorption produced within an optical waveguide upon visible light illumination. The modulation data are analyzed by means of simulation software based on a numerical mode solver. It is found that the modulation depth increases for pump illumination energy closer to the energy gap of the guiding material, while illumination at varying intensity shows a sublinear dependence of the photoinduced absorption. The results are discussed in terms of occupation statistics of gap states. It is shown that the major contribution to the photoinduced signal derives from the modulation of the occupation of tail states under illumination. Modeling of the phenomenon allows one to predict the behavior of a given device and opens the way to practical applications.
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42.79.Hp Optical processors, correlators, and modulators
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.82.-m Integrated optics

Blue emission from Eu2+-doped high silica glass by near-infrared femtosecond laser irradiation

Yanbo Qiao, Danping Chen, Jinjun Ren, Botao Wu, Jianrong Qiu, and Tomoko Akai

J. Appl. Phys. 103, 023108 (2008); http://dx.doi.org/10.1063/1.2837055 (3 pages) | Cited 8 times

Online Publication Date: 30 January 2008

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Eu2+-doped high silica glass (HSG) is fabricated by sintering porous glass which is impregnated with europium ions. Eu2+-doped HSG is revealed to yield intense blue emission excited by ultraviolet (UV) light and near-infrared femtosecond laser. The emission profile obtained by UV excitation can be well traced by near-infrared femtosecond laser. The upconversion emission excited by 800 nm femtosecond laser is considered to be related to a two-photon absorption process from the relationship between the integrated intensity and the pump power. A tentative scheme of upconverted blue emission from Eu2+-doped HSG was also proposed. The HSG materials presented herein are expected to find applications in high density optical storage and three-dimensional color displays.
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78.55.Mb Porous materials
78.47.-p Spectroscopy of solid state dynamics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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Characterization of plasma waves in gated two-dimensional electron systems

Koichi Narahara and Yuta Suzuki

J. Appl. Phys. 103, 023301 (2008); http://dx.doi.org/10.1063/1.2826909 (4 pages) | Cited 1 time

Online Publication Date: 16 January 2008

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The characteristics of plasma waves in gated two-dimensional electron gas systems are discussed. We numerically discuss the effect of the intrinsic nonlinearity of plasma waves on their propagation. Moderate nonlinearity results in the development of solitons, as suggested by [ Govorov et al., JETP Lett. 70, 488 (1999) ]. In addition, backward-traveling pulses develop when the degree of nonlinearity becomes large.
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52.70.-m Plasma diagnostic techniques and instrumentation
52.35.Sb Solitons; BGK modes
52.25.Fi Transport properties

Electron dynamics and acceleration study in a magnetized plasma-filled cylindrical waveguide

Sandeep Kumar and Moohyun Yoon

J. Appl. Phys. 103, 023302 (2008); http://dx.doi.org/10.1063/1.2831223 (7 pages) | Cited 3 times

Online Publication Date: 16 January 2008

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In this article, EH01 field components are evaluated in a cylindrical waveguide filled with plasma in the presence of external static magnetic field applied along the direction of the mode propagation. The electron acceleration inside the plasma-filled cylindrical waveguide is investigated numerically for a single-electron model. It is found that the electron acceleration is very sensitive to the initial phase of mode-field components, external static magnetic field, plasma density, point of injection of the electron, and microwave power density. The maximum amplitude of the EH01 mode’s field components is approximately 100 times greater than the vacuum-waveguide case for operating microwave frequency f = 7.64 GHz, plasma density n0 = 1.08×1017 m−3, initial phase angle ϕ0 = 60°, and microwave power ∼ 14 MW in a cylindrical waveguide with a radius of 2.1 cm. An electron with 100 keV gets 27 MeV energy gain in 2.5 cm along the waveguide length in the presence of external power ∼ 14 MW with a microwave frequency of 7.64 GHz. The electron trajectory is also analyzed under the effects of magnetic field when the electron is injected in the waveguide at r = R/2.
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52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.25.-b Plasma properties
84.40.Az Waveguides, transmission lines, striplines

Roles of oxidizing species in a nonequilibrium atmospheric-pressure pulsed remote O2/N2 plasma glass cleaning process

Masahiro Iwasaki, Yuto Matsudaira, Keigo Takeda, Masafumi Ito, Eiji Miyamoto, Takuya Yara, Tsuyoshi Uehara, and Masaru Hori

J. Appl. Phys. 103, 023303 (2008); http://dx.doi.org/10.1063/1.2830982 (7 pages) | Cited 10 times

Online Publication Date: 17 January 2008

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Atmospheric pressure plasma treatments have attracted attention for various application processes. The effect of O2 additions below 0.2% to N2 was investigated for the efficiency of removing organic contaminants on a glass surface using nonequilibrium atmospheric-pressure pulsed plasma. A remarkably high efficiency of cleaning was obtained by a plasma treatment with ca. 0.03% O2 additions to N2. The concentration of ozone (O3) and the ground-state oxygen radical [O(3P2)] were measured using ultraviolet absorption spectroscopy and vacuum ultraviolet laser absorption spectroscopy, respectively. It was found that the key factors for surface cleaning were the scission of carbon bonds due to ultraviolet irradiation and subsequent oxidation due to O(3P), and that the surface cleaning proceeded in broad areas due to the photodissociation of O3.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.77.Bn Etching and cleaning
81.65.-b Surface treatments

Dependence of electron peak current on hollow cathode dimensions and seed electron energy in a pseudospark discharge

S. O. Cetiner, P. Stoltz, P. Messmer, and J.-L. Cambier

J. Appl. Phys. 103, 023304 (2008); http://dx.doi.org/10.1063/1.2832507 (9 pages) | Cited 3 times

Online Publication Date: 18 January 2008

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The prebreakdown and breakdown phases of a pseudospark discharge are investigated using the two-dimensional kinetic plasma simulation code OOPIC™ PRO. Trends in the peak electron current at the anode are presented as function of the hollow cathode dimensions and mean seed injection velocities at the cavity back wall. The plasma generation process by ionizing collisions is examined, showing the effect on supplying the electrons that determine the density of the beam. The mean seed velocities used here are varied between the velocity corresponding to the energy of peak ionization cross section, 15 times this value and no mean velocity (i.e., electrons injected with a temperature of 2.5 eV). The reliance of the discharge characteristics on the penetrating electric field is shown to decrease as the mean seed injection velocity increases because of its ability to generate a surplus plasma independent of the virtual anode. As a result, the peak current increases with the hollow cathode dimensions for the largest average injection velocity, while for the smallest value it increases with the area of penetration of the electric field in the hollow cathode interior. Additionally, for a given geometry an increase in the peak current with the surplus plasma generated is observed. For the largest seed injection velocity used a dependence of the magnitude of the peak current on the ratio of the hole thickness and hollow cathode depth to the hole height is demonstrated. This means similar trends of the peak current are generated when the geometry is resized. Although the present study uses argon only, the variation in the discharge dependencies with the seed injection energy relative to the ionization threshold is expected to apply independently of the gas type. Secondary electrons due to electron and ion impact are shown to be important only for the largest impact areas and discharge development times of the study.
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52.80.-s Electric discharges
52.65.-y Plasma simulation
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Crystallization kinetics of amorphous equiatomic NiTi thin films: Effect of film thickness

X. Wang, M. Rein, and J. J. Vlassak

J. Appl. Phys. 103, 023501 (2008); http://dx.doi.org/10.1063/1.2829811 (6 pages) | Cited 7 times

Online Publication Date: 16 January 2008

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We have investigated the crystallization of amorphous equiatomic NiTi thin films sandwiched between two protective silicon nitride barrier films using optical, atomic force, and transmission electron microscopies. Crystallite nucleation occurs homogeneously inside the NiTi films because small composition shifts at the interfaces between NiTi and surrounding layers suppress heterogeneous nucleation at these interfaces. The crystallite growth rate is independent of film thickness for films thicker than 600 nm. Below 600 nm, the growth rate decreases rapidly and has an apparent activation energy that increases with decreasing film thickness. We suggest that diffusion of hydrogen from the film interfaces may be responsible for this unusual behavior.
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64.70.kd Metals and alloys
68.55.at Other materials
68.55.jd Thickness
61.43.Dq Amorphous semiconductors, metals, and alloys

Meniscus model for noncontacting and contacting sphere-on-flat surfaces including elastic-plastic deformation

Xiaojie Xue and Andreas A. Polycarpou

J. Appl. Phys. 103, 023502 (2008); http://dx.doi.org/10.1063/1.2830863 (9 pages) | Cited 5 times

Online Publication Date: 16 January 2008

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Single asperity adhesive contact is a fundamental problem in physics and mechanics and a significant body of research works have been published on capillary adhesion of noncontacting and contacting spheres and surfaces in general. The existing works, however, do not specifically consider the change of the projected meniscus area due to the solid asperity deformation when contacting with the flat solid surface. In this paper, accounting for the effects of both elastic and plastic deformations, we present an improved meniscus model for a deformable sphere on a rigid flat surface covering a large range of interference values from noncontact to a fully plastic contact. For elastic contact, the real contact area, the deformed sphere profile, and the projected meniscus area were determined by the Hertzian solution. For elastic-plastic contact, a finite element-based spherical solution was used to calculate the real wetted area and meniscus force. The model predicts that due to the spherical deformation, the meniscus force increases with increasing interference. The effects of asperity radius, humidity level, and different liquid environments, as well as the valid range of the model, were also discussed.
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68.35.Gy Mechanical properties; surface strains
68.35.Ja Surface and interface dynamics and vibrations
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.fq Plasticity and superplasticity
81.40.Lm Deformation, plasticity, and creep

Engineering the electronic, magnetic, and gap-related properties of the quinternary half-metallic Heusler alloys

K. Özdoğan, E. Şaşıoğlu, and I. Galanakis

J. Appl. Phys. 103, 023503 (2008); http://dx.doi.org/10.1063/1.2831224 (10 pages) | Cited 6 times

Online Publication Date: 17 January 2008

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We study the electronic and magnetic properties of the quinternary full Heusler alloys of the type Co2[Cr1−xMnx][Al1−ySiy] employing three different approaches: (i) the coherent potential approximation; (ii) the virtual crystal approximation; and (iii) supercell calculations. All three methods give similar results, and the local environment manifests itself only for small details of the density of states. All alloys under study are shown to be half-metals, and their total spin moments follow the so-called Slater–Pauling behavior of the ideal half-metallic systems. We especially concentrate on the properties related to the minority-spin band gap. We present the possibility to engineer the properties of these alloys by changing the relative concentrations of the low-valent transition metal and sp atoms in a continuous way. Our results show that for realistic applications, compounds rich in Si and Cr are ideal since they combine large energy gaps (around 0.6 eV), robust half-metallicity with respect to defects (the Fermi level is located near the middle of the gap), and high values of the majority-spin density of states around the Fermi level, which are needed for large values of the perfectly spin-polarized current in spintronic devices like spin valves or magnetic tunnel junctions.
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71.20.Gj Other metals and alloys
71.15.-m Methods of electronic structure calculations
75.30.Cr Saturation moments and magnetic susceptibilities
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.47.Np Metals and alloys

Microstructure and dislocation of epitaxial InN films revealed by high resolution x-ray diffraction

B. Liu, R. Zhang, Z. L. Xie, H. Lu, Q. J. Liu, Z. Zhang, Y. Li, X. Q. Xiu, P. Chen, P. Han, S. L. Gu, Y. Shi, Y. D. Zheng, and W. J. Schaff

J. Appl. Phys. 103, 023504 (2008); http://dx.doi.org/10.1063/1.2832753 (4 pages) | Cited 7 times

Online Publication Date: 17 January 2008

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This article reports on the study of microstructure and dislocation of InN films using high resolution x-ray diffraction grown on sapphire (0001) both by metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE). The mosaic tilt, twist, and correlation lengths of InN films are determined by using symmetrical and asymmetrical reflections as well as reciprocal space mapping. Deducing from these results, MBE-grown InN film exhibits the edge-type dislocations of 4.0×109 cm−2, which is about ten times higher than the density of screw-type dislocations. In MOCVD-grown InN sample, the edge-type dislocations density is as high as 2.1×1010 cm−2, and the screw-type dislocations density is 1.3×109 cm−2. They indicate that edge type is the predominant dislocation type in the InN films. By comparing the reported transmission electron microscopy results, the accuracy of evaluation for the dislocation density using the mosaic model is proved.
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61.72.Bb Theories and models of crystal defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
68.37.Og High-resolution transmission electron microscopy (HRTEM)

Effect of phase transition in shock-recovered silicon

Hiroaki Kishimura and Hitoshi Matsumoto

J. Appl. Phys. 103, 023505 (2008); http://dx.doi.org/10.1063/1.2830805 (6 pages) | Cited 5 times

Online Publication Date: 18 January 2008

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A series of shock-recovery experiments on a single crystal of silicon up to 38 GPa and characterizations of the recovered samples by x-ray diffraction analysis, Raman spectroscopy, and microscopic observations were performed for a better understanding of residual effects after shock loading by using a propellant gun. The x-ray diffraction trace of each sample revealed the absence of additional constituents including metastable phases and high-pressure phases of silicon except for 11 and 38 GPa. At 11 GPa, small amounts of metastable phases of silicon were obtained. The formation of copper silicide (Cu3Si) was confirmed in the sample shocked at 38 GPa. Considering the surface morphology revealed by microscopic observation, a thermochemical reaction through the melting of silicon resulted in the formation of Cu3Si. An additional band and the center frequency deviation of a peak were shown in the Raman spectroscopy results. The results of x-ray diffraction and Raman spectroscopy indicated that crystalline size reduction rather than the formation of metastable phases occurred. Structural deformation rather than the thermal effect caused by a shock-induced temperature rise may be responsible for the disappearance of metastable phases, which were observed in other high-pressure experiments.
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78.30.Am Elemental semiconductors and insulators
62.50.Ef Shock wave effects in solids and liquids
64.70.kg Semiconductors
68.35.bg Semiconductors
82.60.-s Chemical thermodynamics

Determination of the dissolution mechanism of Al2O3 in CaO-Al2O3-SiO2 liquids using a combined experimental-numerical approach

F. Verhaeghe, J. Liu, M. Guo, S. Arnout, B. Blanpain, and P. Wollants

J. Appl. Phys. 103, 023506 (2008); http://dx.doi.org/10.1063/1.2830852 (8 pages) | Cited 1 time

Online Publication Date: 18 January 2008

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Experimental results obtained from the in situ observation of the dissolution of spherical Al2O3 particles in CaO-Al2O3-SiO2-containing melts at elevated temperatures are analyzed using a lattice Boltzmann dissolution model. Through a comparison of the experimental dissolution curve with analytical predictions and numerical simulations, the rate-limiting step is identified as diffusion control. Estimations of the effective binary diffusion coefficient are obtained, together with an estimate of the activation energy for the diffusion process.
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64.75.Bc Solubility
66.10.C- Diffusion and thermal diffusion

Structure and optical properties of pulsed sputter deposited CrxOy/Cr/Cr2O3 solar selective coatings

Harish C. Barshilia, N. Selvakumar, K. S. Rajam, and A. Biswas

J. Appl. Phys. 103, 023507 (2008); http://dx.doi.org/10.1063/1.2831364 (11 pages) | Cited 11 times

Online Publication Date: 18 January 2008

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Spectrally selective CrxOy/Cr/Cr2O3 multilayer absorber coatings were deposited on copper (Cu) substrates using a pulsed sputtering system. The Cr targets were sputtered using asymmetric bipolar-pulsed dc generators in Ar+O2 and Ar plasmas to deposit a CrxOy (bottom layer)/Cr/Cr2O3 (top layer) coating. The compositions and thicknesses of the individual component layers have been optimized to achieve high absorptance (0.899–0.912) and low emittance (0.05–0.06). The x-ray diffraction data in thin film mode showed that the CrxOy/Cr/Cr2O3 coating consists of an amorphous phase; the Raman data of the coating, however, showed the presence of A1g and Eg modes, characteristic of Cr2O3. The x-ray photoelectron spectroscopy (XPS) data from near-surface region of the absorber suggested that the chemical state of Cr was in the form of Cr3+ and no phases of CrO2 and CrO3 were present. The experimental spectroscopic ellipsometric data have been fitted with theoretical models to derive the dispersion of the optical constants (n and k). The optical constants of the three layers indicate that the bottom two layers are the main absorber layers and the top Cr2O3 layer, which has higher oxygen content, acts as an antireflection coating. In order to study the thermal stability of the CrxOy/Cr/Cr2O3 coatings, they were subjected to heat treatment (in air and vacuum) at different temperatures and durations. The coating deposited on Cu substrates exhibited high solar selectivity (α/ε) of 0.895/0.06 even after heat treatment in air up to 300 °C for 2 h. At higher temperatures, the solar selectivity decreased significantly (e.g., α/ε = 0.855/0.24 at 350 °C in air), which is attributed to oxidation of Cr crystallites, increased surface roughness, and formation of CuO. The formation of CuO and the increase in Cr3+ vacancies due to the outward diffusion of Cr at higher annealing temperatures were confirmed by XPS. In the case of vacuum annealing, for temperatures greater than 500 °C the outward diffusion of Cu was the dominating degradation mechanism. The microstructural stability of the absorber coatings heat treated in air (up to 325 °C) and vacuum (up to 600 °C) was confirmed by micro-Raman spectroscopy measurements. Studies on the accelerated aging tests indicated that the absorber coatings on Cu were stable in air up to 250 h at 250 °C with a solar selectivity of 0.898/0.11.
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81.15.Cd Deposition by sputtering
78.30.-j Infrared and Raman spectra
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Fx Diffusion; interface formation
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
68.55.-a Thin film structure and morphology

Impact of the transient formation of molecular hydrogen on the microcrack nucleation and evolution in H-implanted Si (001)

S. Personnic, K. K. Bourdelle, F. Letertre, A. Tauzin, N. Cherkashin, A. Claverie, R. Fortunier, and H. Klocker

J. Appl. Phys. 103, 023508 (2008); http://dx.doi.org/10.1063/1.2829807 (9 pages) | Cited 14 times

Online Publication Date: 22 January 2008

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We study the implant-induced hydrogenated defects responsible for the Smart Cut™ layer transfer of Si (001) films. Different experimental methods are used to quantify the time dependence of the defect evolution and interactions during isothermal annealings. An optical characterization technique was developed for the statistical analysis of the formation and growth of micrometer size microcracks in the buried implanted layer. We show that the formation of molecular hydrogen is dominated by a transient phenomenon related to the rapid dissociation of the hydrogenated point defects. The impact of the H2 formation kinetics on the microcrack evolution is described and the physical mechanisms involved in their growth are identified. A comprehensive picture of the fracture phenomenon in H implanted Si leading to the full layer transfer is proposed and discussed.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.20.mt Cracks
68.55.ag Semiconductors
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si

Modulation of hard x-ray beam profiles by Borrmann pyramid

G. Xu and J. Britten

J. Appl. Phys. 103, 023509 (2008); http://dx.doi.org/10.1063/1.2832429 (4 pages) | Cited 1 time

Online Publication Date: 22 January 2008

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Spatial modulation of hard x-ray beam profiles is reported, using the “Borrmann pyramid” formed in dual Bragg diffraction of a single crystal, where a small angular change of the incident beam is magnified to span the entire pyramid base. As an attempt, it is demonstrated using hard x rays by (1) the linear shift of a micrometer sized mask; (2) the partial blockade of a two micron beam; and (3) the millimeter shadow of a nanoscale gold strip, which shows the potential application of Borrmann pyramids in the form of an enlarged x-ray image.
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07.85.Jy Diffractometers
07.85.-m X- and γ-ray instruments

Ab initio molecular dynamics simulations for thermal equation of state of B2-type NaCl

Shigeaki Ono, John P. Brodholt, Dario Alfè, Maria Alfredsson, and G. David Price

J. Appl. Phys. 103, 023510 (2008); http://dx.doi.org/10.1063/1.2832632 (5 pages) | Cited 9 times

Online Publication Date: 22 January 2008

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The pressure as a function of volume and temperature has been investigated for B2-type NaCl over the pressure range of 20–360 GPa and at temperatures between 300 and 3000 K. The simulations were performed using ab initio molecular dynamics method within the density-functional theory framework. A Vinet equation of state fitted to the 300 K data yielded a bulk modulus of BTa = 128.66 GPa and a pressure derivative of BTa′ = 4.374 at standard state pressure of 30 GPa. The thermal pressure contribution was determined to be of the form ΔPth = [αBT(Va)+(∂BT/∂T)V ln(Va/V)]ΔT. When αBT(Va) is assumed to be constant, the fit to the data yielded αBT(Va) = 0.0033 GPa/K at standard volume, corresponding to the pressure of 30 GPa. In contrast, the volume dependence of the thermal pressure was very small, and fitting yielded (∂BT/∂T)V = 0.000 87.
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64.30.Jk Equations of state of nonmetals
62.20.de Elastic moduli
62.50.-p High-pressure effects in solids and liquids

Nonlocal continuum theories of beams for the analysis of carbon nanotubes

J. N. Reddy and S. D. Pang

J. Appl. Phys. 103, 023511 (2008); http://dx.doi.org/10.1063/1.2833431 (16 pages) | Cited 81 times

Online Publication Date: 22 January 2008

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The equations of motion of the Euler–Bernoulli and Timoshenko beam theories are reformulated using the nonlocal differential constitutive relations of Eringen [International Journal of Engineering Science 10, 1–16 (1972) ]. The equations of motion are then used to evaluate the static bending, vibration, and buckling responses of beams with various boundary conditions. Numerical results are presented using the nonlocal theories to bring out the effect of the nonlocal behavior on deflections, buckling loads, and natural frequencies of carbon nanotubes.
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46.70.De Beams, plates, and shells
46.32.+x Static buckling and instability
46.35.+z Viscoelasticity, plasticity, viscoplasticity
46.40.-f Vibrations and mechanical waves
81.40.Lm Deformation, plasticity, and creep
62.25.-g Mechanical properties of nanoscale systems

Faraday magneto-optical rotation in compositionally graded films

X. P. Miao, L. Gao, and P. Xu

J. Appl. Phys. 103, 023512 (2008); http://dx.doi.org/10.1063/1.2831489 (5 pages)

Online Publication Date: 23 January 2008

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We present a two-step homogenization method for studying the Faraday magneto-optical effect in graded metal-dielectric composite films of width W, in which the volume fraction of metal particles in a slice varies along the direction perpendicular to the film surface. First, we adopt the effective-medium theory to formulate the equivalent (local) dielectric permittivity tensor for a z slice. Second, the graded composite films are homogenized with an effective (overall) dielectric permittivity tensor including the diagonal and off-diagonal elements. Faraday rotation is studied as a function of the graded profile p(z) with the same total volume fraction. For a power-law form p(z) = a(z/W)m with different m, it is found that with increasing m, the magnitude of Faraday rotation becomes weak near the surface plasmon resonant band, accompanied with the redshift of the resonant center. Interestingly, it is possible to achieve strongly enhanced Faraday rotation in the high-frequency region, and to change the direction of rotation in the low-frequency one. Moreover, the magnitude can be further enhanced for needle-like particles. In the dilute limit, we show that Faraday rotation is indeed independent of m within Maxwell-Garnett theory.
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77.22.Ch Permittivity (dielectric function)
78.20.Ek Optical activity
78.20.Ls Magneto-optical effects
78.66.-w Optical properties of specific thin films

Surface-wave suppression band gap and plane-wave reflection phase band of mushroomlike photonic band gap structures

Long Li, Qiang Chen, Qiawei Yuan, Changhong Liang, and Kunio Sawaya

J. Appl. Phys. 103, 023513 (2008); http://dx.doi.org/10.1063/1.2832401 (10 pages) | Cited 1 time

Online Publication Date: 23 January 2008

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Mushroomlike photonic band gap (PBG) structures exhibit two band gap characteristics: surface-wave suppression and in-phase reflectivity. The fundamental electromagnetic properties and the relationship between the surface-wave suppression band gap and the plane-wave reflection phase band are investigated and clarified by a finite-element full-wave analysis. The results of the plane-wave bistatic reflection experiments on mushroomlike PBG plates in an anechoic chamber are in good agreement with those of numerical simulation, confirming the phenomenon of dual in-phase reflection, i.e., dual-resonant behavior, for a transverse magnetic polarization plane wave at oblique incidence on a mushroomlike PBG surface. A modified local resonance cavity cell model of a PBG structure is presented to provide insight into the physical mechanism of dual-resonant behavior.
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42.70.Qs Photonic bandgap materials
41.20.Jb Electromagnetic wave propagation; radiowave propagation
33.40.+f Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance)
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