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15 Feb 2007

Volume 101, Issue 4, Articles (04xxxx)

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Phenomenological characterization of photoactive centers in Bi12TiO20 crystals

Jaime Frejlich, Renata Montenegro, Nilson R. Inocente-Junior, Pedro V. dos Santos, Jean Claude Launay, Christophe Longeaud, and Jesiel F. Carvalho

J. Appl. Phys. 101, 043101 (2007); http://dx.doi.org/10.1063/1.2434009 (12 pages) | Cited 11 times

Online Publication Date: 16 February 2007

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We report optical and electrical measurements contributing for a better characterization of the relevant photoactive center levels in undoped photorefractive Bi12TiO20 (BTO) crystals grown in Brazil. Comparative results for Pb-doped BTO and Bi12GaO20 are also reported. A center responsible for photochromism was identified at 0.42–0.44 eV, probably below the conduction band (CB). The main electron and hole donor center is detected at 2.2 eV from the CB and the equilibrium Fermi level is pinned at this level. Other localized centers were identified at different positions in the band gap and their relation with the behavior of BTO under different wavelengths and operating conditions is discussed with particular attention to holographic recording.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials
42.70.Ln Holographic recording materials; optical storage media
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.40.-i Holography
42.79.Vb Optical storage systems, optical disks

Theoretical determination of lasing resonances in a microring

Reyhan Baktur, L. W. Pearson, and J. Ballato

J. Appl. Phys. 101, 043102 (2007); http://dx.doi.org/10.1063/1.2511634 (5 pages) | Cited 4 times

Online Publication Date: 20 February 2007

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We present a theoretical development for the lasing frequencies of a microring laser. Such a microring is typically made from an optically active polymer, which is fabricated on a metallic wire or glass optical fiber in order to provide a substrate of well-defined geometry. Lasing resonances of the microring are computed as zeros of characteristic equations, which can be arranged such that a whispering gallery term appears explicitly together with a residual term associated with waveguide modes. It is found that the residual term recedes as the thickness of the microring increases, leaving a characteristic equation associated with a pure whispering gallery mode (WGM). The resonant condition is examined to compute the lasing frequencies and the thickness of the microring that supports WGM. Computed data are compared with published experimental data on polymer microring lasers, and computed results match well with experiments.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.70.Jk Polymers and organics

Reactive ion etching of high optical quality GaN∕sapphire photonic crystal slab using CH4–H2 chemistry

S. Bouchoule, S. Boubanga-Tombet, L. Le Gratiet, M. Le Vassor d’Yerville, J. Torres, Y. Chen, and D. Coquillat

J. Appl. Phys. 101, 043103 (2007); http://dx.doi.org/10.1063/1.2433770 (7 pages) | Cited 4 times

Online Publication Date: 20 February 2007

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Reactive ion etching (RIE) using a CH4–H2 plasma is investigated for the fabrication of a GaN one-dimensional (1D) photonic crystal (PhC) slab. The dominant control parameter for the etch rate and the sidewall profile is the dc bias. The influence of operating pressure, CH4/H2 ratio, and total gas flow rate on the etching characteristics is also presented. An etch rate as high as 85 nm/min and an overcut angle as low as 5° obtained in this work are among the best values reported for conventional RIE technique. The CH4–H2 process is used to etch 1D PhCs with a lattice parameter ranging from 700 to 350 nm and an air filling factor of 0.30 into a 600‐nm-thick GaN∕sapphire slab. Sharp peaks corresponding to the resonant modes of the nanopatterned structures are observed in the experimental reflection spectra for all the lattice periods. Furthermore, the good optical quality of the nanostructures is evidenced by a resonantly enhanced second-harmonic generation experiment around 400 nm. A second-harmonic generation enhancement factor as high as 105 is obtained, compared with the unpatterned GaN reference slab. These results demonstrate that the CH4–H2 conventional RIE technique is well adapted to the etching of GaN PhC for the fabrication of next generation photonic devices exploiting nonlinear processes.
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42.70.Qs Photonic bandgap materials
52.77.Bn Etching and cleaning
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
81.65.Cf Surface cleaning, etching, patterning

Optical anisotropy in [hkil]-oriented wurtzite semiconductor quantum wells

Chun-Nan Chen, Sheng-Hsiung Chang, Meei-Ling Hung, Jih-Chen Chiang, Ikai Lo, Wan-Tsang Wang, Ming-Hong Gau, Hsiu-Fen Kao, and Meng-En Lee

J. Appl. Phys. 101, 043104 (2007); http://dx.doi.org/10.1063/1.2423139 (9 pages) | Cited 9 times

Online Publication Date: 21 February 2007

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An 8×8 band edge potential matrix of the [hkil]-oriented wurtzite Hamiltonian is developed and applied to explore optical anisotropy in [hkil]-oriented wurtzite semiconductor quantum wells. The wave-vector-dependent optical matrix elements are expressed entirely in terms of Hamiltonian matrix elements, thus avoiding the requirement to introduce any additional optical parameters. To accommodate the noncubic symmetry of the wurtzite lattice, spinor rotation is taken into account when performing the calculations for different crystal orientations. The optical matrix elements are formulated and calculated for both the real finite-barrier-height case and the approximate infinite-barrier-height case. It is found that giant anisotropy of the optical matrix elements appears in the [10math0]- and [10math2]-oriented well planes.
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78.67.De Quantum wells
68.65.Fg Quantum wells
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

A model of CaF2 indentation

Q. Zhang and J. C. Lambropoulos

J. Appl. Phys. 101, 043105 (2007); http://dx.doi.org/10.1063/1.2496128 (6 pages)

Online Publication Date: 22 February 2007

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A finite element model (FEM) of calcium fluoride (CaF2) with a rate-dependent mesoplastic constitutive formulation was developed and compared with nanoindentation tests. Indentations on the three main crystallographic planes (100), (110), and (111) of (CaF2) were analyzed. Appropriate material parameters were obtained by correlating the FEM results and the corresponding experimental load-displacement curves. The simulations show a value in the range of 74–110 MPa for the initial shear yield strength and a value in the range of 100–180 MPa for the self-hardening modulus. Such estimates can be used to examine the detailed stress distribution induced by the indentation.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Nanosecond-laser plasma-assisted ultradeep microdrilling of optically opaque and transparent solids

Stanley Paul, Sergey I. Kudryashov, Kevin Lyon, and Susan D. Allen

J. Appl. Phys. 101, 043106 (2007); http://dx.doi.org/10.1063/1.2434829 (8 pages) | Cited 9 times

Online Publication Date: 23 February 2007

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A mechanism of ultradeep (up to tens of microns per pulse, submillimeter total hole depths) plasma-assisted ablative drilling of optically opaque and transparent materials by high-power nanosecond lasers has been proposed and verified experimentally using optical transmission and contact photoacoustic techniques to measure average drilling rates per laser shot versus laser intensity at constant focusing conditions. The plots of average drilling rates versus laser intensity exhibit slopes which are in good agreement with those predicted by the proposed model and also with other experimental studies. The proposed ultradeep drilling mechanism consists of a number of stages, including ultradeep “nonthermal” energy delivery into bulk solids by the short-wavelength radiation of the hot ablative plasma, bulk heating and melting, accompanied by subsurface boiling in the melt pool, and resulting melt expulsion from the target.
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52.38.Mf Laser ablation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.20.Wk Machining, milling
52.77.-j Plasma applications
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Conductors, semiconductors, and insulators irradiated with short-wavelength free-electron laser

J. Krzywinski, R Sobierajski, M. Jurek, R. Nietubyc, J. B. Pelka, L. Juha, M. Bittner, V. Létal, V. Vorlíček, A. Andrejczuk, J. Feldhaus, B. Keitel, E. L. Saldin, E. A. Schneidmiller, R. Treusch, et al.

J. Appl. Phys. 101, 043107 (2007); http://dx.doi.org/10.1063/1.2434989 (4 pages) | Cited 13 times

Online Publication Date: 23 February 2007

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The results of a study of irreversible changes induced at surfaces of metals, semiconductors, and insulators by extreme ultraviolet (λ<100 nm) ultrashort pulses provided by TESLA Test Facility Free-Electron Laser, Phase 1 (TTF1 FEL) are reported and discussed. The laser was tuned at 86, 89, and 98 nm during the experiments reported here. Energy spectra of ions ejected from the irradiated surfaces are also reported. Special attention is paid to the difference in the ablation behavior of (semi)conductors and insulators that we have observed. The difference is dramatic, while the absorption coefficients are similar for all materials at the TTF1 FEL wavelength.
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79.20.Ds Laser-beam impact phenomena
61.82.Bg Metals and alloys
61.82.Fk Semiconductors
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Measurement of the twist elastic constant of nematic liquid crystals using pi-cell devices

P. D. Brimicombe, C. Kischka, S. J. Elston, and E. P. Raynes

J. Appl. Phys. 101, 043108 (2007); http://dx.doi.org/10.1063/1.2432311 (8 pages) | Cited 4 times

Online Publication Date: 26 February 2007

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We present a fast and accurate method for measurement of the twist elastic constant of nematic liquid crystals using pi-cell devices. We observe that there are two bifurcations during the transition from the bend state to the planar 180° twisted state, each of which leads to a voltage threshold. The Fréedericksz threshold voltage due to a tilt bifurcation occurs at a lower voltage and is “softened” by the required surface pretilt in the device. The higher of the two thresholds is due to a bifurcation between left- and right-handed 180° twisted states and we term this the T to V state threshold. This voltage threshold is independent of device thickness, and is not softened by the pretilt. We show that the T to V state threshold is highly sensitive to changes in the twist elastic constant, K22, and use this threshold to evaluate the magnitude of K22 for a variety of materials. These results show very good agreement with those obtained using the standard magnetic Fréedericksz twist threshold experiment. This method does not require a complex experimental setup and has an accuracy of better than ±8%.
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62.10.+s Mechanical properties of liquids
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Enhanced focusing of laser beams in semiconductor plasmas

D. N. Gupta and H. Suk

J. Appl. Phys. 101, 043109 (2007); http://dx.doi.org/10.1063/1.2654873 (4 pages) | Cited 2 times

Online Publication Date: 26 February 2007

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The beating of two copropagating laser beams (having frequency difference Δω ≈ ωp, where ωp is the plasma frequency) can resonantly excite a large amplitude plasma wave in a narrow-gap semiconductor [ V. I. Berezhiani and S. M. Mahajan, Phys. Rev. B 55, 9247 (1997) ]. The higher ponderomotive force on the electrons due to the plasma beat wave makes the medium highly nonlinear. As a result, the incident laser beams become self-focused due to the nonlinearity by the ponderomotive force. In this paper, we show the self-focusing and spot size evolution of the laser beams in semiconductor plasmas.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
72.30.+q High-frequency effects; plasma effects

Spectroscopic properties and Judd-Ofelt theory analysis of Dy3+ doped oxyfluoride silicate glass

Zhongchao Duan, Junjie Zhang, and Lili Hu

J. Appl. Phys. 101, 043110 (2007); http://dx.doi.org/10.1063/1.2434809 (6 pages) | Cited 11 times

Online Publication Date: 28 February 2007

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Dy3+ doped oxyfluoride silicate glass was prepared and its optical absorption, 1.3 μm emission, and upconversion luminescence properties were studied. Furthermore, the Judd-Ofelt [Phys. Rev. 127, 750 (1962) ; J. Chem. Phys. 37, 511 (1962)] intensity parameters, oscillator strengths, spontaneous transition probability, fluorescence branching ratio and radiative lifetime were calculated by Judd-Ofelt theory, while stimulated emission cross section of 6H9/2+6F11/2→6H15/2 transition was calculated by McCumber theory [ Phys. Rev. A. 134, 299 (1964) ]. According to the obtained Judd-Ofelt intensity parameters Ω2 = 2.69×10−20 cm2, Ω4 = 1.64×10−20 cm2, and Ω6 = 1.64×10−20 cm2, the radiative lifetime was calculated to be 810 μs for 1.3 μm emission, whose full width at half maximum and σe were 115 nm and 2.21×10−20cm2, respectively. In addition, near infrared to visible upconversion luminescence was observed and evaluated. The results suggest that Dy3+ doped oxyfluoride silicate glass can be used as potential host material for developing broadband optical amplifiers and laser applications.
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78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
78.45.+h Stimulated emission
42.70.Hj Laser materials

Low dielectric electromagnetic absorbing material in 18–40 GHz using large scale photonic crystal structures

T. Narita, K. Matsumura, and Y. Kagawa

J. Appl. Phys. 101, 043111 (2007); http://dx.doi.org/10.1063/1.2710278 (4 pages) | Cited 1 time

Online Publication Date: 28 February 2007

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The interaction behavior between a monolithic low dielectric block with unidirectionally aligned through holes and an electromagnetic wave at a frequency range from 18 to 40 GHz has been studied. Hexagonally aligned through holes, whose diameters are 8.0, 9.0, and 10.0 mm, are introduced to a polymethylmethacrylate block. The electromagnetic wave reflection and transmission spectra perpendicular to the hole axis show a unique structure dependence, which is related to the diameter of the hole and its arrangement. A large decrease in the reflectance and transmittance appears in the spectra, which originates from the interference effect between the electromagnetic wave and material. It is concluded that the material has a potential for controlling the electromagnetic wave at a tailored target frequency and is expected to be usable as monolithic low dielectric electromagnetic wave absorbing material.
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42.70.Qs Photonic bandgap materials
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Induced emission cross section of a possible laser line in Nd:Y2O3 ceramics at 1.095 μm

Akihiro Fukabori, Masami Sekita, Takayasu Ikegami, Nobuo Iyi, Toshiki Komatsu, Masayuki Kawamura, and Makoto Suzuki

J. Appl. Phys. 101, 043112 (2007); http://dx.doi.org/10.1063/1.2709867 (7 pages) | Cited 3 times

Online Publication Date: 28 February 2007

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In this study, we measured the change of the optical transmittance for calcination temperatures, in steps of 10°, at two different sintering temperatures. It was found that the optical transmittance is highly dependent on the calcination temperature. The highest optical transmittance obtained was 70% for the transparent Y2O3 (yttria) ceramics produced without the use of additives and high injection presure in this study, higher than the highest reported value of 65%. Optical absorption and emission spectra of Nd:Y2O3 obtained from a low temperature synthesis process were measured. The energy level structure of Nd3+ in the Y2O3 ceramics was determined for a 1 mol % Nd concentration. The induced emission cross section was calculated to be in the range of 3.2×10−19–1.1×10−17 cm2 for the 1 mol % Nd-doped Y2O3 ceramics. Furthermore, a laser line possibly has been identified in this study, in the Nd:Y2O3 ceramic at 1.095 μm.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.60.By Design of specific laser systems
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Simplified calculation of nonlocal thermodynamic equilibrium excited state populations contributing to 13.5 nm emission in a tin plasma

J. White, A. Cummings, P. Dunne, P. Hayden, and G. O’Sullivan

J. Appl. Phys. 101, 043301 (2007); http://dx.doi.org/10.1063/1.2434965 (14 pages) | Cited 9 times

Online Publication Date: 16 February 2007

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Extreme ultraviolet lithography schemes for the semiconductor industry are currently based on coupling radiation from a plasma source into a 2% bandwidth at 13.5 nm (91.8 eV). In this paper, we consider the case for a laser-produced plasma (LPP) and address the calculation of ionic level populations in the 4p64dN, 4p64dN−14f1, 4p54dN+1, and 4p64dN−15p1 configurations in a range of tin ions (Sn6+ to Sn13+) producing radiation in this bandwidth. The LPP is modeled using a one-dimensional hydrodynamics code, which uses a hydrogenic, average atom model, where the level populations are treated as l degenerate. Hartree-Fock calculations are used to remove the l degeneracy and an energy functional method to calculate the nl level populations involved in n = 4−4 transitions as a function of distance from the target surface and time. Detailed data are presented for the tin ions that contribute to in-band emission.
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52.25.Kn Thermodynamics of plasmas
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
47.85.Dh Hydrodynamics, hydraulics, hydrostatics
52.30.-q Plasma dynamics and flow

Numerical study of nanosecond laser interactions with micro-sized single droplets and sprays of xenon

T. Auguste, F. de Gaufridy de Dortan, T. Ceccotti, J. F. Hergott, O. Sublemontier, D. Descamps, and M. Schmidt

J. Appl. Phys. 101, 043302 (2007); http://dx.doi.org/10.1063/1.2432870 (13 pages)

Online Publication Date: 20 February 2007

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We present a thorough numerical study on interactions of a nanosecond laser with micro-sized xenon droplets. We developed a code which allows simulation of laser interactions with a single droplet as well as a spray. We give a detailed description of the code, and we present results on the dynamics of a microplasma produced by irradiation of a single xenon droplet with a laser focused at peak vacuum intensity in the 5×1010−5×1012 W/cm2 range. We find that the heating of the plasma depends dramatically on the laser parameters (duration, pulse shape, and intensity) on one hand, and on the droplet diameter on the other. We also present results obtained with a spray which show that the dynamics of the microplasmas is very sensitive to the position of the droplets in the interaction volume. The predictions of our model agree well with recent experimental observations performed on laser-produced plasma sources for extreme ultraviolet lithography. In particular, the postprocessing of our data with a sophisticated atomic physics code has allowed us to reproduce quite well the spectrum emitted in the extreme ultraviolet range by a xenon plasma generated by laser irradiation of a spray of droplets.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.50.Dg Plasma sources

Numerical study on xenon positive column discharges of mercury-free lamp

Jiting Ouyang, Feng He, Jinsong Miao, Jianqi Wang, and Wenbo Hu

J. Appl. Phys. 101, 043303 (2007); http://dx.doi.org/10.1063/1.2432024 (7 pages) | Cited 12 times

Online Publication Date: 23 February 2007

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In this paper, the numerical study has been performed on the xenon positive column discharges of mercury-free fluorescent lamp. The plasma discharge characteristics are analyzed by numerical simulation based on two-dimensional fluid model. The effects of cell geometry, such as the dielectric layer, the electrode width, the electrode gap, and the cell height, and the filling gas including the pressure and the xenon percentage are investigated in terms of discharge current and discharge efficiency. The results show that a long transient positive column will form in the xenon lamp when applying ac sinusoidal power and the lamp can operate in a large range of voltage and frequency. The front dielectric layer of the cell plays an important role in the xenon lamp while the back layer has little effect. The ratio of electrode gap to cell height should be large to achieve a long positive column xenon lamp and higher efficiency. Increase of pressure or xenon concentration results in an increase of discharge efficiency and voltage. The discussions will be helpful for the design of commercial xenon lamp cells.
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52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.65.Kj Magnetohydrodynamic and fluid equation
52.40.Hf Plasma-material interactions; boundary layer effects
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Charge-state-resolved ion energy distribution functions of cathodic vacuum arcs: A study involving the plasma potential and biased plasmas

André Anders and Efim Oks

J. Appl. Phys. 101, 043304 (2007); http://dx.doi.org/10.1063/1.2561226 (6 pages) | Cited 3 times

Online Publication Date: 23 February 2007

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Charge-state-resolved ion energy distribution functions were measured for pulsed cathodic arcs taking the sheath into account that formed between the plasma and the entrance of a combined energy and mass spectrometer. An electron emitting probe was employed to independently determine the plasma potential. All results were obtained by averaging over several individual measurements because the instantaneous energy distributions and the plasma potential show large amplitude fluctuations due to the explosive nature of the arc plasma generation. It was found that the ion energy distribution functions in the plasma were independent of the ion charge state. This is in contrast to findings with continuously operating, direct-current arcs that employ a magnetic field at the cathode to steer the cathode spot motion. The different findings indicate the important role of the magnetic steering field for the plasma properties of direct-current arcs. The results are further supported by experiments with “biased plasmas” obtained by shifting the potential of the anode. Finally, it was shown that the ion energy distributions were broader and shifted to higher energy at the beginning of each arc pulse. The characteristic time for relaxation to steady state distributions is about 100 μs.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.50.Dg Plasma sources
52.40.Kh Plasma sheaths
52.70.Ds Electric and magnetic measurements
52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties

Detailed study of the plasma-activated catalytic generation of ammonia in N2-H2 plasmas

J. H. van Helden, W. Wagemans, G. Yagci, R. A. B. Zijlmans, D. C. Schram, R. Engeln, G. Lombardi, G. D. Stancu, and J. Röpcke

J. Appl. Phys. 101, 043305 (2007); http://dx.doi.org/10.1063/1.2645828 (12 pages) | Cited 9 times

Online Publication Date: 27 February 2007

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We investigated the efficiency and formation mechanism of ammonia generation in recombining plasmas generated from mixtures of N2 and H2 under various plasma conditions. In contrast to the Haber-Bosch process, in which the molecules are dissociated on a catalytic surface, under these plasma conditions the precursor molecules, N2 and H2, are already dissociated in the gas phase. Surfaces are thus exposed to large fluxes of atomic N and H radicals. The ammonia production turns out to be strongly dependent on the fluxes of atomic N and H radicals to the surface. By optimizing the atomic N and H fluxes to the surface using an atomic nitrogen and hydrogen source ammonia can be formed efficiently, i.e., more than 10% of the total background pressure is measured to be ammonia. The results obtained show a strong similarity with results reported in literature, which were explained by the production of ammonia at the surface by stepwise addition reactions between adsorbed nitrogen and hydrogen containing radicals at the surface and incoming N and H containing radicals. Furthermore, our results indicate that the ammonia production is independent of wall material. The high fluxes of N and H radicals in our experiments result in a passivated surface, and the actual chemistry, leading to the formation of ammonia, takes place in an additional layer on top of this passivated surface.
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82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Nr Association, addition, insertion, cluster formation
82.20.Hf Product distribution

Probing of a surface plasma wave by an obliquely incident laser on the metal surface

D. B. Singh, Gagan Kumar, and V. K. Tripathi

J. Appl. Phys. 101, 043306 (2007); http://dx.doi.org/10.1063/1.2472281 (4 pages)

Online Publication Date: 28 February 2007

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A surface plasma wave (SPW) of frequency ω1 and wave number k1 propagating along a metal-free space boundary exerts a ponderomotive force on the free electrons, creating an electron density perturbation at frequency 2ω1. When a laser of frequency ω2 and wave number k2 is incident at a suitable angle on the metal surface, it gives rise to the oscillatory velocity of electrons at frequency ω2. This oscillatory velocity couples with the density perturbation to generate a nonlinear current at frequency 2ω1+ω2. The nonlinear current derives a radiating wave under suitable conditions. By measuring the amplitude of the radiating wave, the SPW field can be probed.
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52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Fi Transport properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
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A micromechanical model for nonlinear acoustic properties of interfaces between solids

Jin-Yeon Kim and Jun-Shin Lee

J. Appl. Phys. 101, 043501 (2007); http://dx.doi.org/10.1063/1.2434939 (9 pages) | Cited 5 times

Online Publication Date: 16 February 2007

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A micromechanical model for an interface between two solids in elastoplastic contact is presented to predict the acoustic linear and nonlinear interfacial stiffnesses during loading-unloading cycle. This interface is a representative model for apparently closed cracks and imperfect bonds that are interacting with ultrasonic waves sent for evaluating quality of their interfaces. For a better physical description of the elastoplastic contact behavior of the interface, the previous model [ Kim et al., J. Mech. Phys. Solids 52, 1911 (2004) ] is improved in two important aspects: the unloading model for unit contact element (asperity) and the geometrical and statistical parameters of the interface. The model is validated with experimental results. The interface parameters are obtained by fitting measured reflection coefficients during loading-unloading cycle with the theoretical model. Using so obtained parameters, the linear and second-order interfacial stiffnesses and the nonlinearity in transmitted longitudinal waves are calculated. The theoretical nonlinear transmission amplitude is in good comparison with the experimental result, demonstrating the capability of the present modeling framework in predicting both linear and nonlinear ultrasonic responses of imperfect interfaces. It is observed that the effect of adhesive force, which is not taken into account in the model, can be important in a certain stage of the unloading phase.
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68.35.Iv Acoustical properties
68.35.Ja Surface and interface dynamics and vibrations
62.65.+k Acoustical properties of solids
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Asymmetric transient enhanced intermixing in Pt/Ti

P. Süle, M. Menyhárd, L. Kótis, J. Lábár, and W. F. Egelhoff, Jr.

J. Appl. Phys. 101, 043502 (2007); http://dx.doi.org/10.1063/1.2437661 (8 pages) | Cited 6 times

Online Publication Date: 16 February 2007

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The ion-sputtering induced intermixing is studied by Monte Carlo transport of ions in matter (TRIM), molecular-dynamics (MD) simulations, and Auger electron spectroscopy depth profiling (AES-DP) analysis in Pt/Ti/Si substrate (Pt/Ti) and Ta/Ti/Pt/Si substrate (Ti/Pt) multilayers. Experimental evidence is found for the asymmetry of intermixing in Pt/Ti, and in Ti/Pt. In Ti/Pt we obtain a much weaker interdiffusion (broadening at the interface) than in Pt/Ti. The unexpected enhancement of the interdiffusion of the Pt atoms into the Ti substrate has also been demonstrated by simulations. We are able to capture the essential features of intermixing using TRIM and MD simulations for ion-beam sputtering and find reasonable values for interface broadening which can be compared with the experimental measurements. We explain the asymmetry of IM by the possible occurrence of transient enhanced diffusion in Pt/Ti which manifests in the exponential high diffusity tail of the AES concentration profile.
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66.30.Ny Chemical interdiffusion; diffusion barriers
64.75.-g Phase equilibria
79.20.Fv Electron impact: Auger emission

Structural and elastic characterization of Cu-implanted SiO2 films on Si(100) substrates

J. Shirokoff, C. K. Young, L. C. Brits, G. T. Andrews, B. Johannessen, and M. C. Ridgway

J. Appl. Phys. 101, 043503 (2007); http://dx.doi.org/10.1063/1.2437690 (6 pages) | Cited 1 time

Online Publication Date: 16 February 2007

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Cu-implanted SiO2 films on Si(100) have been studied and compared to unimplanted SiO2 on Si(100) using x-ray methods, transmission electron microscopy, Rutherford backscattering, and Brillouin spectroscopy. The x-ray results indicate the preferred orientation of Cu {111} planes parallel to the Si substrate surface without any directional orientation for Cu-implanted SiO2/Si(100) and for Cu-implanted and annealed SiO2/Si(100). In the latter case, transmission electron microscopy reveals the presence of spherical nanocrystallites with an average size of ∼ 2.5 nm. Rutherford backscattering shows that these crystallites (and the Cu in the as-implanted film) are largely confined to depths of 0.4−1.2 μm below the film surface. Brillouin spectra contain peaks due to surface, film-guided and bulk acoustic modes. Surface (longitudinal) acoustic wave velocities for the implanted films were ∼ 7% lower ( ∼ 2% higher) than for unimplanted SiO2/Si(100). Elastic constants were estimated from the acoustic wave velocities and film densities. C11 (C44) for the implanted films was ∼ 10% higher (lower) than that for the unimplanted film. The differences in acoustic velocities and elastic moduli are ascribed to implantation-induced compaction and/or the presence of Cu in the SiO2 film.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids

Atomistic simulations of shock induced microstructural evolution and spallation in single crystal nickel

S. G. Srinivasan, M. I. Baskes, and G. J. Wagner

J. Appl. Phys. 101, 043504 (2007); http://dx.doi.org/10.1063/1.2423084 (7 pages) | Cited 20 times

Online Publication Date: 16 February 2007

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Spallation in single crystalline nickel was studied using molecular dynamics simulations. The shock waves—incident waves, the waves reflected from sample free surfaces, and interference between reflected waves—create and destroy many microstructural features. These features, though unimportant in determining the spall strength, control the spall nucleation site. Spall occurs by cavitation at a grain boundary junction in cold, defective, tensile regions of the sample. Atomistic calculations and experiments, though separated by six orders of magnitude in strain rates, follow a universal strain rate behavior.
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62.50.-p High-pressure effects in solids and liquids
61.72.Mm Grain and twin boundaries

Thermal analysis and topographical characterization of latex films by scanning probe microscopy

Petri Ihalainen, Kaj Backfolk, Petri Sirviö, and Jouko Peltonen

J. Appl. Phys. 101, 043505 (2007); http://dx.doi.org/10.1063/1.2429722 (10 pages) | Cited 2 times

Online Publication Date: 20 February 2007

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Scanning probe microscopy (SPM) was utilized to study the thermal behavior of latex films dried under different conditions. Using the SPM probe resonance frequency method, the resonance frequency (ω) of the oscillating probe above the sample surface was followed as a function of temperature (T). Two different approaches for detecting thermal transitions were used and compared. In the heating-by-the-sample approach, the SPM probe acts as a thermal sensor detecting the heat dissipated by the heated sample. In the heating-by-the-probe approach, the SPM probe is utilized simultaneously as an actuator and a sensor: the heated probe both dissipates heat and detects the heat reflected from the sample surface. Thermal transitions in the polymer films could be observed in the Δω-T curves. The results were consistent with those observed by differential scanning calorimetry, but also additional information about the characteristics of the transitions was obtained. The heating-by-the-probe method showed higher surface sensitivity and more localized effects than the other approach. Furthermore, the progress of the latex film formation and the effect of the different drying conditions on film topography were studied by SPM imaging and roughness analysis. Skewness and local surface curvature are demonstrated to serve as useful numerical measures with which to distinguish different levels of particle deformation and the formation of a continuous film. Preannealing of the samples at high temperature influenced not only the topography (roughness) but also the characteristics of the thermal transitions.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
68.55.-a Thin film structure and morphology
68.35.B- Structure of clean surfaces (and surface reconstruction)

Spatial distribution of refractive index variations induced in bulk fused silica by single ultrashort and short laser pulses

I. M. Burakov, N. M. Bulgakova, R. Stoian, A. Mermillod-Blondin, E. Audouard, A. Rosenfeld, A. Husakou, and I. V. Hertel

J. Appl. Phys. 101, 043506 (2007); http://dx.doi.org/10.1063/1.2436925 (7 pages) | Cited 17 times

Online Publication Date: 20 February 2007

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We correlate phase-contrast microscopy of modification tracks induced by tightly focused single ultrashort and short laser pulses inside fused silica with numerical simulations of nonlinear laser excitation footprints. Different pulse durations on the femtosecond and picosecond range are compared in order to validate the experimental and theoretical observations on the subsequent refractive index variations in a regime where linear and nonlinear contributions play a comparable role. The nature of the laser-induced structural changes depends essentially on the characteristics of pulse propagation in different regions of the irradiated zone. Numerical simulations of laser pulse propagation in the excited region show that accumulation of excess energy and swift nonlinear absorption contribute to the formation of either positive or negative phase-shift regions within the same single-pulse-induced damage trace. The decrease in the refractive index can be unambiguously correlated with the regions of maximum energy deposition during prolonged exposure times.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Ce Glasses, quartz
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Experimental and theoretical study of heterogeneous iron precipitation in silicon

A. Haarahiltunen, H. Väinölä, O. Anttila, M. Yli-Koski, and J. Sinkkonen

J. Appl. Phys. 101, 043507 (2007); http://dx.doi.org/10.1063/1.2472271 (6 pages) | Cited 15 times

Online Publication Date: 20 February 2007

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Heterogeneous iron precipitation in silicon was studied experimentally by measuring the gettering efficiency of oxide precipitate density of 1×1010 cm−3. The wafers were contaminated with varying iron concentrations, and the gettering efficiency was studied using isothermal annealing in the temperature range from 300 to 780 °C. It was found that iron precipitation obeys the so-called s-curve behavior: if iron precipitation occurs, nearly all iron is gettered. For example, after 30 min annealing at 700 °C, the highest initial iron concentration of 8×1013 cm−3 drops to 3×1012 cm−3, where as two lower initial iron concentrations of 5×1012 and 2×1013 cm−3 remain nearly constant. This means that the level of supersaturation plays a significant role in the final gettering efficiency, and a rather high level of supersaturation is required before iron precipitation occurs at all. In addition, a model is presented for the growth and dissolution of iron precipitates at oxygen-related defects in silicon during thermal processing. The heterogeneous nucleation of iron is taken into account by special growth and dissolution rates, which are inserted into the Fokker-Planck equation. Comparison of simulated results to experimental ones proves that this model can be used to estimate internal gettering efficiency of iron under a variety of processing conditions.
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61.72.Yx Interaction between different crystal defects; gettering effect
81.65.Tx Gettering
81.30.Mh Solid-phase precipitation
61.72.Cc Kinetics of defect formation and annealing
64.75.-g Phase equilibria
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