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1 Mar 2008

Volume 103, Issue 5, Articles (05xxxx)

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A study on bending direction of sheet metal in laser forming

Yongjun Shi, Yancong Liu, Zhenqiang Yao, and Hong Shen

J. Appl. Phys. 103, 053101 (2008); http://dx.doi.org/10.1063/1.2887995 (6 pages)

Online Publication Date: 3 March 2008

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Concave laser forming and convex forming are all required for the complicated curved surface plate forming. Concave laser forming can be readily obtained by temperature gradient mechanism, while convex forming may be achieved based on buckling mechanism. To achieve precise control of bending direction of plate, buckling critical condition is analyzed when the buckling mechanism plays a dominant role, and a judgment criterion of working conditions of buckling mechanism, Fbuckling value, is derived. To verify the validity of the Fbuckling value, the experiments and numerical simulations are carried out. The results suggest that the bending direction of the plate can be exactly judged according to the Fbuckling value. In addition, the effects of the heating location and starting point on the bending direction are discussed, which provide further insight into the convex forming process and is helpful for the parameter selection of future process planning.
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46.32.+x Static buckling and instability
46.35.+z Viscoelasticity, plasticity, viscoplasticity
81.40.Lm Deformation, plasticity, and creep
68.35.Gy Mechanical properties; surface strains
79.20.Ds Laser-beam impact phenomena

Polarization selection with stacked hole array metamaterial

M. Beruete, M. Navarro-Cía, M. Sorolla, and I. Campillo

J. Appl. Phys. 103, 053102 (2008); http://dx.doi.org/10.1063/1.2841471 (4 pages) | Cited 10 times

Online Publication Date: 4 March 2008

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Polarization rotation or selection appears in materials with optical activity, or those with Faraday effect, or in liquid crystals. In this letter we present a structure, with an analogous response, using stacked extraordinary transmission subwavelength hole arrays modified to be nearly self-complementary. This produces a polarization selector because of the negative index of refraction for one of its linearly polarized eigenwaves. Simulation results and experiments at millimeter wavelengths confirm these features. Applications in miniaturized devices are envisioned as well as the possibility to scale to optical wavelengths.
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42.70.-a Optical materials
78.20.Ek Optical activity
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Ls Magneto-optical effects

Single mode photonic quantum ring laser fabricated in hyperboloid drum shape

Junho Yoon, Sung-Jae An, O’Dae Kwon, and Ja Kang Ku

J. Appl. Phys. 103, 053103 (2008); http://dx.doi.org/10.1063/1.2841418 (6 pages) | Cited 1 time

Online Publication Date: 5 March 2008

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From three dimensional whispering gallery cavities of GaAs photonic quantum ring fabricated in hyperboloid drum shape by chemically assisted ion beam etching with the central active region diameter of 0.9 μm, we have observed single mode lasing near 838 nm with a record low injection threshold of 300 nA (Jth = 47.1 A/cm2) in continuous wave operation at room temperature. This indicates that the quantum ring lasing phenomena associated with the three dimensional whispering gallery modes continue to persist, even at the submicron range overcoming the conventional two dimensional whispering gallery mode limit.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

High-resolution observations of an amorphous layer and subsurface damage formed by femtosecond laser irradiation of silicon

T. H. R. Crawford, J. Yamanaka, G. A. Botton, and H. K. Haugen

J. Appl. Phys. 103, 053104 (2008); http://dx.doi.org/10.1063/1.2885111 (7 pages) | Cited 10 times

Online Publication Date: 6 March 2008

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Using transmission electron microscopy (TEM), we observed the micro- and nanostructures of silicon after irradiation by ∼ 150 fs duration pulses centered at 800 nm wavelength. Specimens irradiated with a single pulse of 11 J/cm2 fluence and with five pulses, each with a fluence of 1.3 J/cm2, exhibited various structures which included amorphous phases. The amorphous phases were pure silicon, as was revealed by high-resolution TEM imaging, nanobeam diffraction patterns, high-angle annular dark-field images, conventional diffraction images, and energy-dispersive x-ray spectra. Irradiation with a single pulse of 1.5 J/cm2 produced neither amorphous material nor lattice defects. Single-pulse irradiation at a fluence of 33 J/cm2 and irradiation by four pulses at 11 J/cm2 led to substantial subsurface damage around the center of the laser spot. It is concluded that multiple-pulse irradiation produces crystallographic damage more readily than a single pulse.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.47.Fg Semiconductor surfaces
68.35.bj Amorphous semiconductors, glasses
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Og High-resolution transmission electron microscopy (HRTEM)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Focusing surface plasmons via changing the incident angle

Humeyra Caglayan, Irfan Bulu, and Ekmel Ozbay

J. Appl. Phys. 103, 053105 (2008); http://dx.doi.org/10.1063/1.2844552 (3 pages) | Cited 1 time

Online Publication Date: 7 March 2008

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We report a circular metallic aperture with a subwavelength circular slit in the microwave regime, in which we experimentally demonstrate that this aperture can excite and focus surface plasmons. Under normal illumination, there is no focusing of the surface plasmons. However, by changing the incident angle, it is possible to focus surface plasmons. We showed that under a 20° illumination angle surface plasmons focus at 4 cm away from the center on the surface of the aperture.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Do the grain boundaries of β-In2S3 thin films have a role in sub-band-gap photosensitivity to 632.8 nm?

R. Jayakrishnan, Teny Theresa John, C. Sudha Kartha, K. P. Vijayakumar, Deepti Jain, L. S. Sharath Chandra, and V. Ganesan

J. Appl. Phys. 103, 053106 (2008); http://dx.doi.org/10.1063/1.2841488 (6 pages) | Cited 3 times

Online Publication Date: 10 March 2008

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Highly photoconducting β-In2S3 thin films with conducting grain boundaries were obtained, using “chemical spray pyrolysis” technique. By varying the atomic ratio of the precursor solution used for spray pyrolysis, the photoconductivity of these films could be tailored. Conducting grain boundaries were found only for samples with a specific stoichiometry and these films exhibited photoresponse to intrinsic and extrinsic excitation wavelengths in the range of 325–532 nm. Postdeposition vacuum annealing of these films enhanced the grain boundary conductivity, caused the films to exhibit persistent photoconductivity for both intrinsic and extrinsic excitations and extended the extrinsic photoresponse to wavelengths beyond 632.8 nm. Photoresponse to excitation wavelength of 632.8 nm was observed in films with and without conducting grain boundaries which proved that the extrinsic photoresponse to this wavelength was an effect associated with the defect chemistry of the β-In2S3.
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68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
81.15.Rs Spray coating techniques
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.66.Bi Elemental solids
61.66.Dk Alloys
61.72.Mm Grain and twin boundaries
73.50.Pz Photoconduction and photovoltaic effects

A multiplexed fiber Bragg grating sensor for simultaneous salinity and temperature measurement

Liqiu Men, Ping Lu, and Qiying Chen

J. Appl. Phys. 103, 053107 (2008); http://dx.doi.org/10.1063/1.2890156 (7 pages) | Cited 14 times

Online Publication Date: 11 March 2008

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An in-line one-fiber approach to realize simultaneous measurement of salinity and temperature is proposed. The sensor system, which consists of multiplexed polymer-coated fiber Bragg gratings, showed that the polyimide-coated grating responds to variations of both temperature and salinity, while the acrylate-coated grating is only sensitive to the environmental temperature. The experimental results indicated that the temperature sensitivity of the acrylate-coated grating in water was 0.0102 nm/°C for redshifted Bragg wavelength with increasing temperature, and the temperature and the salinity sensitivities of the polyimide-coated grating were 0.0094 nm/°C (redshifted) and 0.0165 nm/M (blueshifted), respectively, which are in excellent agreement with the theoretical analysis.
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42.81.Pa Sensors, gyros
42.79.Dj Gratings
82.80.-d Chemical analysis and related physical methods of analysis

Calculated temperature rise in midinfrared laser irradiated Hg0.72Cd0.28Te

Asta Katrine Storeboe, Trond Brudevoll, and Knut Stenersen

J. Appl. Phys. 103, 053108 (2008); http://dx.doi.org/10.1063/1.2890751 (9 pages) | Cited 3 times

Online Publication Date: 11 March 2008

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We present results from a numerical study on heating in a 10 μm thick layer of Hg0.72Cd0.28Te induced by 1 μs long laser pulses at photon energies close to the band gap of the material. A number of highly nonlinear mechanisms contribute to the heating, their relative importance being dependent on laser wavelength, instantaneous irradiance, and material temperature. Mechanisms studied include one- and two-photon absorptions across the band gap, intervalence band absorption between light- and heavy hole bands, electron-hole recombination, free-carrier absorption, excess carrier temperatures, and refractive index changes. The increase in band gap with temperature eventually terminates one-photon absorption from the valence to the conduction band, and further heating is driven by much weaker absorption processes. The varying band gap also introduces changes in electron- and light hole masses and thereby in the separation between the light- and heavy hole bands, thus strongly affecting intervalence band absorption. At the shortest laser wavelength of 3.8 μm, the simulations indicate that surface melting will occur at fluence levels in the range of 2–3 J/cm2, while more than 10 J/cm2 will be required for melting at wavelengths beyond 5 μm.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Fk Semiconductors
71.20.Nr Semiconductor compounds
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
64.70.dj Melting of specific substances

Excitonic and pair-related photoluminescence in ZnSe nanowires

Ankur Saxena, Suxia Yang, U. Philipose, and Harry E. Ruda

J. Appl. Phys. 103, 053109 (2008); http://dx.doi.org/10.1063/1.2885729 (7 pages) | Cited 5 times

Online Publication Date: 11 March 2008

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It has been established that deviations from stoichiometry during the growth of ZnSe crystals result in point defects, which influence its electronic properties. We report on detailed photoluminescence results and their systematic analysis for ZnSe nanowires. We studied photoluminescence from vapor-phase grown undoped ZnSe nanowires grown under excess Zn conditions, and in particular the dependence on excitation intensity. Luminescence spectra were characterized by strong near-band-edge luminescence with negligible deep-level emission. We observed excitonic emission at 2.794 eV related to the neutral donor at VSe. The binding energy of the exciton was found to be 7 meV, and that of the donor was 35 meV. Two donor-acceptor pair transitions at 2.714 and 2.686 eV were also observed, which can be related to the defect complexes of native defects with other native defects or with common unintentional shallow donors and acceptors. The ionization energies of both donors were 27 meV, whereas those of the acceptors were 102 and 139 meV, respectively.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
71.55.Gs II-VI semiconductors
73.22.Lp Collective excitations
71.15.Nc Total energy and cohesive energy calculations

Direct observations for the superprism effect in photonic crystals utilizing negative refraction

S. Y. Yang, J. Y. Wu, H. E. Horng, Chin-Yih Hong, and H. C. Yang

J. Appl. Phys. 103, 053110 (2008); http://dx.doi.org/10.1063/1.2890390 (4 pages) | Cited 1 time

Online Publication Date: 14 March 2008

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In this work, we experimentally explored the negative-refraction superprism effect in photonic crystals by investigating the frequency-dependent negative refractive index of photonic crystals at microwave frequencies from 8.2 to 8.4 GHz. By detecting the spatially distributed intensity of a transmitted microwave whose incident angle is well controlled, we determined the propagating path, the refractive angle, and the refractive index of the transmitted microwave. The highly dispersive relationship between the negative refractive index and the frequency of microwave observed indicates potential applicability of this method for being used in a microwave wavelength demultiplexer by utilizing the negative-refraction superprism effect in photonic crystals.
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42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.25.Gy Edge and boundary effects; reflection and refraction
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Characteristics of low energy atom and molecule beams generated by the charge exchange reaction

Yasuhiro Hara, Seigo Takashima, Koji Yamakawa, Shoji Den, Hirotaka Toyoda, Makoto Sekine, and Masaru Hori

J. Appl. Phys. 103, 053301 (2008); http://dx.doi.org/10.1063/1.2842402 (5 pages) | Cited 2 times

Online Publication Date: 5 March 2008

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A low energy NB source, which consisted of a surface wave plasma (SWP) source and two large diameter carbon electrodes, was developed for damageless etching of ultralarge-scale integrated devices. Ion beams were extracted from the SWP using two carbon electrodes, accelerated and injected to the process chamber, and then neutralized without energy loss by a charge exchange reaction. The energy distribution functions of an Ar ion beam and an Ar atom beam was observed using a quadrupole mass spectroscope equipped with an energy analyzer. The energy of the Ar ion beam and the Ar atom beam was controlled by the acceleration voltage. N2 ion and N ion beams were also extracted from a nitrogen plasma source. The intensity ratio of the N ion beam to the N2 ion beam was 5:9, indicating that N ions were efficiently generated in the nitrogen SWP. The N2 ion and N ion beams were changed to N2 molecule and N atom beams, respectively, through a charge exchange reaction without energy loss. The energy of these beams was controlled by the acceleration voltage and was in the region less of than 100 eV. When the acceleration voltage is higher than 40 V, not only the primary peaks due to the N2 ion beam or N ion beam were observed but also a low energy second peak was observed in the energy distribution. The energy of the low energy second peak was controlled by the acceleration voltage. It was concluded that the low energy second peak corresponds to the N2 molecule ion beam and the N ion beam, which is extracted from the second plasma generated in the space between the two carbon electrodes.
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52.50.Dg Plasma sources
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
52.77.Bn Etching and cleaning

Numerical analysis of the production profile of H0 atoms and subsequent H− ions in large negative ion sources

N. Takado, H. Tobari, T. Inoue, J. Hanatani, A. Hatayama, M. Hanada, M. Kashiwagi, and K. Sakamoto

J. Appl. Phys. 103, 053302 (2008); http://dx.doi.org/10.1063/1.2887996 (12 pages) | Cited 2 times

Online Publication Date: 5 March 2008

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The production and transport processes of H0 atoms are numerically simulated using a three-dimensional Monte Carlo transport code. The code is applied to the large JAEA 10 ampere negative ion source under the Cs-seeded condition to obtain a spatial distribution of surface-produced H− ions. In this analysis, the amount of H0 atoms produced through dissociation processes of H2 molecules is calculated from the electron temperature and density obtained by Langmuir probe measurements. The high-energy tail of electrons, which greatly affects H0 atom production, is taken into account by fitting a single-probe characteristic as a two-temperature Maxwellian distribution. In the H0 atom transport process, the energy relaxation of the H0 atoms, which affects the surface H− ion production rate, is taken into account. The result indicates that the surface H− ion production is enhanced near the high-electron-temperature region where H0 atom production is localized.
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34.35.+a Interactions of atoms and molecules with surfaces
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.70.Ds Electric and magnetic measurements
34.80.Dp Atomic excitation and ionization
52.65.Pp Monte Carlo methods

Probe measurements in a nonstationary plasma

Yu. P. Bliokh, Yu. L. Brodsky, Kh. B. Chashka, J. Felsteiner, and Ya. Z. Slutsker

J. Appl. Phys. 103, 053303 (2008); http://dx.doi.org/10.1063/1.2838227 (7 pages) | Cited 5 times

Online Publication Date: 6 March 2008

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Single and double probes are simple and common tools for plasma measurements. In the case of nonstationary plasmas, the values of the plasma density obtained with these tools may differ significantly from the correct values measured, e.g., by microwave methods. The reason for such discrepancy could be the Bohm criterion failure during the plasma transition to the steady state. Indeed, the Bohm criterion, which is commonly used as a boundary condition at the plasma-sheath edge, directly determines the ion saturation current to the probe surface. The transition-time duration is studied and explained quantitatively for various plasmas produced by a version of a ferroinductor-coupled plasma source, which has its magnetic core fully immersed in the plasma. Corresponding conversion factors for probe measurements have been evaluated. Also, the influence of a certain amount of “hot” non-Maxwellian electrons on probe characteristics has been investigated.
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52.50.Dg Plasma sources
52.70.-m Plasma diagnostic techniques and instrumentation

Modeling of dielectric barrier discharge plasma actuator

Balaji Jayaraman, Young-Chang Cho, and Wei Shyy

J. Appl. Phys. 103, 053304 (2008); http://dx.doi.org/10.1063/1.2841450 (15 pages) | Cited 7 times

Online Publication Date: 11 March 2008

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Glow discharge at atmospheric pressure using a dielectric barrier discharge can induce fluid flow and operate as an actuator for flow control. In this paper, we simulate the physics of a two-dimensional asymmetric actuator operating in helium gas using a high-fidelity first-principles-based numerical modeling approach to help improve our understanding of the physical mechanisms associated with such actuators. Fundamentally, there are two processes in the two half-cycles of the actuator operation, largely due to the difference in mobility between faster electrons and slower ions, and the geometric configurations of the actuator (insulator and electrodes). The first half-cycle is characterized by the deposition of the slower ion species on the insulator surface while the second half-cycle by the deposition of the electrons at a faster rate. A power-law dependence on the voltage for the resulting force is observed, which indicates that larger force can be generated by increasing the amplitude. Furthermore, one can enhance the effectiveness of the actuator by either increasing the peak value of the periodic force generation or by increasing the asymmetry between the voltage half-cycles or both. Overall, the increase in the lower electrode size, applied voltage, and dielectric constant tends to contribute to the first factor, and the decrease in frequency of applied voltage tends to contribute to the second factor. However, the complex interplay between the above factors determines the actuator performance.
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47.85.L- Flow control
89.20.Kk Engineering
52.75.-d Plasma devices

Modeling of dielectric barrier discharge plasma actuator in air

Alexandre V. Likhanskii, Mikhail N. Shneider, Sergey O. Macheret, and Richard B. Miles

J. Appl. Phys. 103, 053305 (2008); http://dx.doi.org/10.1063/1.2837890 (13 pages) | Cited 20 times

Online Publication Date: 11 March 2008

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A detailed physical model for asymmetric dielectric barrier discharge (DBD) in air at low voltages (1.5–2 kV) is developed. Modeling of DBD with an applied sinusoidal voltage is carried out in two dimensions. The leading role of charging the dielectric surface by electrons in the cathode phase is shown to be critical, acting as a harpoon that pulls positive ions forward and accelerates the gas in the anode phase. The positive ion motion back toward the exposed electrode is shown to be a major source of inefficiency in the sinusoidal or near-sinusoidal voltage cases. Based on understanding of the DBD physics, an optimal voltage waveform is proposed, consisting of high repetition rate, short (a few nanoseconds in duration), negative pulses combined with a positive dc bias applied to the exposed electrode.
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52.80.-s Electric discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Measurement of x-ray free-electron-laser pulse energies by photoluminescence in nitrogen gas

S. P. Hau–Riege, R. M. Bionta, D. D. Ryutov, and J. Krzywinski

J. Appl. Phys. 103, 053306 (2008); http://dx.doi.org/10.1063/1.2844478 (9 pages) | Cited 7 times

Online Publication Date: 11 March 2008

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We discuss the physics of a photoluminescence-based pulse-energy detector that will be used to characterize hard x-ray free-electron-laser pulses at the Linac Coherent Light Source. We tested the detector in a quasi-steady-state mode of operation at the conventional synchrotron light source Stanford positron electron assymetric ring 3 at the Stanford Synchrotron Radiation Laboratory. We also developed a Monte-Carlo model for the x-ray interaction with the nitrogen gas and the resulting ultraviolet signal and found good agreement with the experimental data. Remaining discrepancies can, to a large extent, be attributed to the varying luminescence behavior of different chamber wall materials.
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41.60.Cr Free-electron lasers

Evidence of turbulence in laser-induced plasmas

S. D. Roberson, C. Akpovo, E.-D. Mezonlin, and J. A. Johnson, III

J. Appl. Phys. 103, 053307 (2008); http://dx.doi.org/10.1063/1.2841770 (6 pages) | Cited 1 time

Online Publication Date: 12 March 2008

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By focusing a pulsed single mode Nd:YAG laser, we created low temperature plasmas at various pressures with various target gases and collected spectral light emissions to investigate the possibility of turbulent behavior in these types of plasmas. Characteristic fluctuation frequencies, chaotic dimensions, spectral indices, and turbulent fluctuation energies are determined from fluctuations in these spectral light emissions. Values calculated for the spectral index and the chaotic index for each plasma event are found to be within the known values for other turbulent plasma systems. Thus, turbulent fluctuations on a nanosecond time scale are confirmed in the time evolutions of various singly ionized and neutral spectral lines of various gases.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.35.Ra Plasma turbulence
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Investigation of plasma immersion ion implantation of nickel-titanium rod by multiple-grid particle-in-cell simulation

Dixon T. K. Kwok, Shuilin Wu, Xiangmei Liu, Ricky K. Y. Fu, and Paul K. Chu

J. Appl. Phys. 103, 053308 (2008); http://dx.doi.org/10.1063/1.2890157 (5 pages) | Cited 3 times

Online Publication Date: 13 March 2008

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A multiple-grid-particle-in-cell numerical method has been developed. This method uses grids of different cell sizes and details are needed in only one part of the simulation region and not others. Hence, there are fewer nodes in the simulation thereby reduced computational time without sacrificing details. In the multiple-grid system, a phenomenon is identified to arise at the interface between two grids and a half-cell weighting method is utilized to solve the weighting issue at the boundary. It is shown that the expression of the change of momentum has no weighting function. This method is employed to numerically simulate the plasma immersion ion implantation process into a nickel titanium rod measuring 50 mm long and 4.8 mm in diameter used in orthopaedic surgery. To conduct more uniform implantation, the NiTi rod is elevated on the sample stage by a metal rod. The nitrogen implantation fluences and depth profiles are simulated and compared to experimental values determined by x-ray photoelectron spectroscopy.
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61.72.up Other materials
52.77.Dq Plasma-based ion implantation and deposition
61.72.S- Impurities in crystals

Anodic plasma in Hall thrusters

Michael Keidar

J. Appl. Phys. 103, 053309 (2008); http://dx.doi.org/10.1063/1.2844495 (5 pages) | Cited 2 times

Online Publication Date: 13 March 2008

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In this paper plasma dynamics and ionization of propellant gas are modeled within the anode holes used for gas injection of a Hall thruster. Under conditions of anode coating with dielectric material, the discharge current should close within these holes, which results in ionization and formation of plasma jets emanating from the openings. The model shows that gas ionization inside the anode holes is very significant. For instance, the electron density increases by two orders of magnitude under certain conditions. The potential drop in the anode region which includes the electrostatic sheath inside the hole and potential drop along the hole might be positive or negative, depending on the anode hole radius.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.80.-s Electric discharges
52.75.-d Plasma devices

Environmentally harmonized CF3I plasma for low-damage and highly selective low-k etching

Seiji Samukawa, Yoshinari Ichihashi, Hiroto Ohtake, Eiichi Soda, and Shuichi Saito

J. Appl. Phys. 103, 053310 (2008); http://dx.doi.org/10.1063/1.2887987 (7 pages) | Cited 2 times

Online Publication Date: 13 March 2008

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Low-damage, high-rate, and highly selective low-k etching can be simultaneously satisfied using a plasma with an environmentally harmonized gas chemistry (CF3I). Such a CF3I plasma can drastically reduce the irradiation damage by ultraviolet (UV) photons during low-k etching, because the intensity of UV in CF3I plasma is much lower than that in conventional CF4 plasma. The etching selectivity of SiOCH to a photoresist can be drastically improved by using CF3I plasma because of reducing F radical generation. In addition, pulse-time-modulated CF3I plasma causes a drastic increase in the etching rate because a large amount of negative ions can be generated. These results show that CF3I plasma is a very promising candidate for low-damage and highly selective low-k etching.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.Cf Surface cleaning, etching, patterning
52.77.-j Plasma applications
61.43.Gt Powders, porous materials
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Spectroscopic and structural studies of Sm2+ doped orthophosphate KSrPO4 crystal

Yanlin Huang, Weifang Kai, Yonggang Cao, Kiwan Jang, Ho Sueb Lee, Ilgon Kim, and Eunjin Cho

J. Appl. Phys. 103, 053501 (2008); http://dx.doi.org/10.1063/1.2890152 (7 pages) | Cited 6 times

Online Publication Date: 3 March 2008

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Sm2+ ions doped KSrPO4 were prepared by high-temperature solid-state reaction method. The samples were investigated by x-ray powder diffraction, photoluminescence excitation and emission spectra, and luminescence decay measurements. After excitation into the 4f55d1 levels, the emission of Sm2+ ions showed 5D0→7FJ (J = 0,1,2) emission together with the broad 5d→4f emission band. The luminescence of Sm2+ ions was sensitive to the temperature. With the decreasing of the temperature, the broad 5d→4f emission band of Sm2+ ions gradually quenched, while 5D0→7FJ (J = 0,1,2) emission lines could be clearly detectable. Based on the luminescence properties of Sm2+ ions and structure of KSrPO4 crystal, the crystallographic sites and the energy structure correlated with 4f→5d transitions of Sm2+ ions in KSrPO4 were discussed.
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78.55.Hx Other solid inorganic materials
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.72.up Other materials

Monte Carlo simulation of cross-plane thermal conductivity of nanostructured porous silicon films

Jaona Randrianalisoa and Dominique Baillis

J. Appl. Phys. 103, 053502 (2008); http://dx.doi.org/10.1063/1.2841697 (11 pages) | Cited 2 times

Online Publication Date: 4 March 2008

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This paper presents a Monte Carlo (MC) modeling of heat conduction in heavily doped (p+ and n+) porous silicon (PS) films known as mesoporous silicon (meso-PS). A three-dimensional pore network generator is developed to better reproduce the structure of low porosity (fv<50%) meso-PS. The submicron scale heat conduction modeled by the Boltzman transport equation is simulated using the MC method in which the nonlinear phonon dispersion curves of bulk silicon and the phonon lifetime dependent on temperature, frequency, and polarization are taken into account. The proposed method has been applied to predict the effect of the porosity (10%–47%), pore sizes (10–20 nm), pore arrangement (p+- and n+-type), temperature (50–500 K), and film thickness (50 nm–1 μm) on the cross-plane thermal conductivity of meso-PS films. Moreover, the simulation results enable to deduce the scattering mean free path (MFP) of phonons in the PS and the scattering MFP due to phonon-pore wall interaction. At room temperature, the thermal conductivity of meso-PS is shown one to two orders of magnitude smaller than that of bulk silicon. A drastic simplification of the phonon dispersion curves and phonon MFP, such as in the Debey approximation, results in an overestimation (by about three times) of the thermal conductivity of meso-PS. The thermal conductivity decreases when the pore size decreases or the porosity increases. For a given porosity and pore size, the thermal conductivity of doped p+-type PS is much smaller than that of doped n+-type PS. Finally, the simulations of thermal conductivity of doped p+-type PS are shown in good agreement with available experimental data which confirms the validity of the current modeling.
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66.70.Df Metals, alloys, and semiconductors
68.55.ag Semiconductors
61.43.Gt Powders, porous materials
61.46.-w Structure of nanoscale materials
63.22.Dc Free films
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Self-assembly of multiwalled carbon nanotubes from quench-condensed CNi3 films

D. P. Young, A. B. Karki, P. W. Adams, Johnpeter N. Ngunjiri, Jayne C. Garno, Hongwei Zhu, Bingqing Wei, and D. Moldovan

J. Appl. Phys. 103, 053503 (2008); http://dx.doi.org/10.1063/1.2888571 (4 pages) | Cited 4 times

Online Publication Date: 4 March 2008

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Freestanding, vertical, multiwalled carbon nanotubes (MWCNTs) are formed during the vacuum deposition of thin films of the metastable carbides CT3 (T = Ni, Co) onto fire-polished glass substrates. In contrast to widely used chemical and laser vapor deposition techniques, we utilize direct e-beam evaporation of arc-melted CT3 targets to produce MWCNTs that are self-assembled out of the CT3-film matrix. The depositions are made in an ambient vapor pressure that is at least six orders of magnitude lower than the 1−100 Torr typically used in chemical vapor techniques. Furthermore, the substrates need not be heated, and, in fact, we observe a robust nanotube growth on liquid nitrogen cooled glass and sapphire substrates. High-resolution atomic force microscopy reveals that MWCNTs of heights 1−40 nm are formed in films with nominal thicknesses in the range of 5−60 nm. We show that the growth parameters of the nanotubes are very sensitive to the grain structure of the films. This is consistent with a precipitation mediated root-growth mechanism.
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81.16.Dn Self-assembly
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Irreversible volume growth in polymer-bonded powder systems: Effects of crystalline anisotropy, particle size distribution, and binder strength

Amitesh Maiti, Richard H. Gee, D. Mark Hoffman, and Laurence E. Fried

J. Appl. Phys. 103, 053504 (2008); http://dx.doi.org/10.1063/1.2838319 (5 pages) | Cited 1 time

Online Publication Date: 5 March 2008

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Pressed-powdered crystallites of intrinsically anisotropic materials have been shown to undergo irreversible volume expansion when subjected to repeated cycles of heating and cooling. In a previous letter publication [ R. H. Gee et al., Appl. Phys. Lett. 70, 254105 (2007) ], we developed a coarse-grained (micron-scale) interaction Hamiltonian for such a system and quantitatively reproduced experimentally observed irreversible growth through explicit molecular dynamics simulations. In this paper, we report (1) recent experiments with a high-density fluoropolymer binder that significantly lowers irreversible growth, (2) identification of a critical interaction parameter of our model that has a strong correlation with binder properties, (3) sensitivity of irreversible growth to the details of particle size and alignment distribution, and (4) a physical picture of irreversible growth in terms of particle displacements.
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61.41.+e Polymers, elastomers, and plastics
61.43.Gt Powders, porous materials
61.43.Bn Structural modeling: serial-addition models, computer simulation

Examining the effects of wall numbers on buckling behavior and mechanical properties of multiwalled carbon nanotubes via molecular dynamics simulations

Y. Y. Zhang, C. M. Wang, and V. B. C. Tan

J. Appl. Phys. 103, 053505 (2008); http://dx.doi.org/10.1063/1.2890146 (9 pages) | Cited 4 times

Online Publication Date: 6 March 2008

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Molecular dynamics simulations are performed on multiwalled carbon nanotubes (MWCNTs) under axial compression to investigate the effects of the number of walls and their van der Waals (vdW) interaction on the buckling behaviors and mechanical properties (Young’s modulus and Poisson’s ratio). The Brenner second-generation reactive empirical bond order and Lennard–Jones 12-6 potential have been adopted to describe the short-range bonding and long-range vdW atomic interaction within the carbon nanotubes, respectively. In the presence of vdW interaction, the buckling strain and Young’s modulus of MWCNTs increase as the number of tubes is increased while keeping the outermost tube diameter constant, whereas Poisson’s ratio was observed to decrease. On the other hand, when the MWCNTs are formed by progressively adding outer tubes while keeping the innermost tube diameter constant, Young’s modulus and buckling strain were observed to decrease, whereas Poisson’s ratio increases. The buckling load increases with increasing the number of walls due to the larger cross-sectional areas. Individual tubes of MWCNTs with a relatively large difference between the diameters of the inner and outer tubes buckle one at a time as opposed to simultaneously for MWCNTs with a relatively small difference in diameters.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.dj Poisson's ratio
62.20.F- Deformation and plasticity
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