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15 Aug 2009

Volume 106, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 106, 041101 (2009); http://dx.doi.org/10.1063/1.3207769 (21 pages)

Robert C. Runkle, L. Eric Smith, and Anthony J. Peurrung
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The photon haystack and emerging radiation detection technology

Robert C. Runkle, L. Eric Smith, and Anthony J. Peurrung

J. Appl. Phys. 106, 041101 (2009); http://dx.doi.org/10.1063/1.3207769 (21 pages) | Cited 7 times

Online Publication Date: 24 August 2009

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The resources devoted to interdicting special nuclear materials have increased considerably over the last several years in step with growing efforts to counter nuclear proliferation and nuclear terrorism. This changing landscape has led to a large amount of research and development that aims to improve the effectiveness of technology now deployed worldwide. Interdicting special nuclear materials is most commonly addressed by detecting and characterizing emitted gamma rays, but modest signature emissions can be obscured by attenuating material and must be differentiated from large and highly variable environmental background emissions. It is a daunting technical challenge to identify special nuclear materials via gamma-ray detection, but a host of new detection technologies is now emerging. This challenge motivates our review of special nuclear material signatures, the physics of detection approaches, emerging technologies, and performance metrics. The use of benchmark gamma-ray sources aids our discussion.
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29.40.-n Radiation detectors
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Visible to near infrared conversion in Ce3+–Yb3+ Co-doped YAG ceramics

Jumpei Ueda and Setsuhisa Tanabe

J. Appl. Phys. 106, 043101 (2009); http://dx.doi.org/10.1063/1.3194310 (5 pages) | Cited 33 times

Online Publication Date: 17 August 2009

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In Ce3+–Yb3+ co-doped Y3Al5O12 (YAG) ceramics, possibility of quantum cutting mechanism converting one visible photon into two NIR photons with optimum quantum efficiency approaching 200% have been investigated. In this material, Yb3+ emissions due to the 2F5/2-2F7/2 in the range of 1 μm were observed upon the excitation of 5d level of Ce3+. In addition, excitation spectra of Yb3+ emission corresponded to that of Ce3+ emission completely. Lifetime of the 5d level of Ce3+ decreased with increasing Yb3+ content. These results indicate the energy transfer (ET) from the 5d levels of Ce3+ to the 5F5/2 level of Yb3+. In (Y0.945Ce0.005Yb0.05) 3Al5O12 sample, the directly measured quantum yield (QY) of Yb3+ emission upon the excitation of 5d level of Ce3+ was about 12% and lower than QY (96%) that estimated from the ET efficiency which was calculated with the measured lifetime of Ce3+.
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78.55.Hx Other solid inorganic materials
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

High-temperature lasing characteristics of randomly assembled ZnO nanowires with a ridge waveguide

H. Y. Yang, S. F. Yu, H. K. Liang, C. Pang, B. Yan, and T. Yu

J. Appl. Phys. 106, 043102 (2009); http://dx.doi.org/10.1063/1.3200960 (5 pages) | Cited 6 times

Online Publication Date: 19 August 2009

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High-temperature lasing characteristics of randomly assembled ZnO nanowires at ultraviolet wavelength are investigated. Lasing emission was observed from the randomly assembled ZnO nanowires for temperature up to 500 K. The corresponding lasing mechanism is attributed to the coherent random lasing action via the formation of closed-loop cavity modes. Furthermore, ridge waveguide lasers using the randomly assembled ZnO nanowires as the active medium were fabricated. It is found that the width of the ridge waveguides restricted the size of the closed-loop cavity modes such that the corresponding characteristic temperature can be increased by 10 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Optical conductance and transmission in bilayer graphene

H. M. Dong, J. Zhang, F. M. Peeters, and W. Xu

J. Appl. Phys. 106, 043103 (2009); http://dx.doi.org/10.1063/1.3200959 (6 pages) | Cited 1 time

Online Publication Date: 20 August 2009

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We present a theoretical study of the optoelectronic properties of bilayer graphene. The optical conductance and transmission coefficient are calculated using the energy-balance equation derived from a Boltzmann equation for an air/graphene/dielectric-wafer system. For short wavelengths (λ<0.2 μm), we obtain the universal optical conductance σ = e2/(2ℏ). Interestingly, there exists an optical absorption window in the wavelength range 10–100 μm, which is induced by different transition energies required for inter- and intra-band optical absorptions in the presence of the Moss–Burstein effect. As a result, the position and width of this absorption window depend sensitively on temperature, carrier density, and sample mobility of the system. These results are relevant for applications of recently developed graphene devices in advanced optoelectronics such as the infrared photodetectors.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.80.Sk Insulators
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.20.Fr Low-field transport and mobility; piezoresistance

Propagation characteristics of channel plasmon polaritons supported by a dielectric filled trench in a real metal

Triranjita Srivastava and Arun Kumar

J. Appl. Phys. 106, 043104 (2009); http://dx.doi.org/10.1063/1.3197362 (5 pages) | Cited 2 times

Online Publication Date: 21 August 2009

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We examine the propagation characteristics of channel plasmon polaritons supported by V-grooves and trenches embedded in a real metal. A dielectric filled trench is found to have superior characteristics as compared to a V-groove in terms of mode confinement and propagation length. A substantial decrease in the cutoff depth of the trench due to dielectric has also been observed, making the miniaturized optical components based on such waveguides possible.
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42.79.Gn Optical waveguides and couplers
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)

PbTe and SnTe quantum dot precipitates in a CdTe matrix fabricated by ion implantation

E. Kaufmann, T. Schwarzl, H. Groiss, G. Hesser, F. Schäffler, L. Palmetshofer, G. Springholz, and W. Heiss

J. Appl. Phys. 106, 043105 (2009); http://dx.doi.org/10.1063/1.3204499 (5 pages) | Cited 1 time

Online Publication Date: 25 August 2009

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We present rock-salt IV-VI semiconductor quantum dots fabricated by implantation of Pb+, Te+, or Sn+ ions into epitaxial zinc-blende CdTe layers. PbTe and SnTe nanoprecipitates of high structural quality are formed after implantation by thermal annealing due to the immiscibility of dot and matrix materials. For samples implanted only with Pb+, intense continuous-wave photoluminescence peaked at 1.6 μm at 300 K is found. In contrast, for PbTe quantum dots fabricated by coimplantation of Pb+ and Te+, the 300 K emission peak is observed at 2.9 μm, indicating luminescence from much larger dots.
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68.65.Hb Quantum dots (patterned in quantum wells)
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Jh Ion radiation effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments

Effect of laser fluence on yeast cell viability in laser-assisted cell transfer

Yafu Lin, Yong Huang, Gaoyan Wang, Tzeng-Rong J. Tzeng, and Douglas B. Chrisey

J. Appl. Phys. 106, 043106 (2009); http://dx.doi.org/10.1063/1.3202388 (7 pages) | Cited 7 times

Online Publication Date: 26 August 2009

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Matrix-assisted pulsed-laser evaporation direct-write (MAPLE DW) has been emerging as a promising biological construct fabrication technique. The post-transfer cell viability in MAPLE DW depends on various operation conditions such as the applied laser fluence; unfortunately, the effect of laser fluence on the post-transfer cell viability has not been well elucidated. This work aims to study the effect of laser fluence on the post-transfer cell viability and the cell recovery ability in MAPLE DW of yeast cells (Saccharomyces cerevisiae). It has been observed that (1) yeast cell viability decreases as the laser fluence increases from 85 to around 1500 mJ/cm2 and (2) some of the MAPLE DW process-induced cell damage is reversible. The post-transfer yeast cell recovery is a function of laser fluence; however, this dependence relationship is not monotonic. Future work is needed to better understand the physical and chemical mechanisms of the above observations.
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87.50.W- Optical/infrared radiation effects
42.62.-b Laser applications

Acousto-optic interaction in photonic crystals with defects

Xiao-Shi Qian, Jing-Ping Li, Ming-hui Lu, Yan-qing Lu, and Yan-feng Chen

J. Appl. Phys. 106, 043107 (2009); http://dx.doi.org/10.1063/1.3204018 (5 pages) | Cited 3 times

Online Publication Date: 26 August 2009

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The acousto-optic (AO) effects of photonic crystals (PCs) were studied. Both the PCs’ periodicity and their index distribution could be modulated instantly by the propagating acoustic wave. As a consequence, the PCs’ band structure becomes tunable. In addition to band gap shift in an ideal PC, AO frequency modulation was observed in a PC with single defect, which is quite different from normal AO tunable filters and gives rise to some interesting applications. Furthermore, in dual-defect situation, synchronized and desynchronized modulations were realized at different acoustic wavelengths. Interesting phenomena such as dual frequency sweeping and dual frequency Q-switching were demonstrated.
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42.70.Qs Photonic bandgap materials
42.55.Tv Photonic crystal lasers and coherent effects
42.60.Fc Modulation, tuning, and mode locking

Widely tunable lifetimes for donor-acceptor pair states created by displacing an intrinsic atom in photonic crystals

S. Nojima and M. Nakahata

J. Appl. Phys. 106, 043108 (2009); http://dx.doi.org/10.1063/1.3204175 (4 pages) | Cited 2 times

Online Publication Date: 26 August 2009

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This paper theoretically investigates the formation processes of intrinsic defect states in two-dimensional photonic crystals. We observe two types of defect states—what could be called the donor and acceptor states—created simultaneously by merely displacing a single rod atom from its regular site. The localization of light in the vicinity of these states is reasonably explained in terms of the stability of light around them. Finally, we demonstrate that the lifetimes of light trapped at these states can be tuned in a wide range by adjusting the position of the displaced rod appropriately.
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71.55.-i Impurity and defect levels
42.70.Qs Photonic bandgap materials
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Electromagnetic wave propagation through an overdense magnetized collisional plasma layer

C. Thoma, D. V. Rose, C. L. Miller, R. E. Clark, and T. P. Hughes

J. Appl. Phys. 106, 043301 (2009); http://dx.doi.org/10.1063/1.3195085 (8 pages)

Online Publication Date: 17 August 2009

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The results of investigations into the feasibility of using a magnetic window to propagate electromagnetic waves through a finite-sized overdense plasma slab are described. We theoretically calculate the transmission coefficients for right- and left-handed circularly polarized plane waves through a uniform magnetized plasma slab. Using reasonable estimates for the plasma properties expected to be found in the ionized shock layer surrounding a hypersonic aircraft traveling in the earth’s upper atmosphere (radio blackout conditions), and assuming a 1 GHz carrier frequency for the radio communications channel, we find that the required magnetic field for propagation of right-handed circularly polarized, or whistler, waves is on the order of a few hundred gauss. Transmission coefficients are calculated as a function of sheath thickness and are shown to be quite sensitive to the electron collision frequency. One-dimensional particle-in-cell simulations are shown to be in good agreement with the theory. These simulations also demonstrate that Ohmic heating of the electrons can be considerable. Two- and three-dimensional particle-in-cell simulations using a simplified waveguide and antenna model illustrate the same general transmission behavior as the theory and one-dimensional simulations. In addition, a net focusing effect due to the plasma is also observed in two and three dimensions. These simulations can be extended to design and analyze more realistic waveguide and antenna models.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.20.Fs Electron collisions
52.40.Kh Plasma sheaths
52.50.-b Plasma production and heating
52.65.-y Plasma simulation

Two-photon absorption laser-induced fluorescence of atomic oxygen in the afterglow of pulsed positive corona discharge

Ryo Ono, Kei Takezawa, and Tetsuji Oda

J. Appl. Phys. 106, 043302 (2009); http://dx.doi.org/10.1063/1.3190530 (5 pages) | Cited 7 times

Online Publication Date: 17 August 2009

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Atomic oxygen is measured in the afterglow of pulsed positive corona discharge using time-resolved two-photon absorption laser-induced fluorescence. The discharge occurs in a 14 mm point-to-plane gap in dry air. After the discharge pulse, the atomic oxygen density decreases at a rate of 5×104 s−1. Simultaneously, ozone density increases at almost the same rate, where the ozone density is measured using laser absorption method. This agreement between the increasing rate of atomic oxygen and decreasing rate of ozone proves that ozone is mainly produced by the well-known three-body reaction, O+O2+M→O3+M. No other process for ozone production such as O2(v)+O2→O3+O is observed. The spatial distribution of atomic oxygen density is in agreement with that of the secondary streamer luminous intensity. This agreement indicates that atomic oxygen is mainly produced in the secondary streamer channels, not in the primary streamer channels.
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52.80.Hc Glow; corona
52.80.-s Electric discharges

Intensity distributions of enhanced H emission from laser-induced low-pressure He plasma and a suggested He-assisted excitation mechanism

Zener Sukra Lie, Marincan Pardede, Rinda Hedwig, Maria Margaretha Suliyanti, Eden Steven, Maliki, Koo Hendrik Kurniawan, Muliadi Ramli, Syahrun Nur Abdulmadjid, Nasrullah Idris, Kurnia Lahna, Kiichiro Kagawa, and May On Tjia

J. Appl. Phys. 106, 043303 (2009); http://dx.doi.org/10.1063/1.3195087 (6 pages) | Cited 2 times

Online Publication Date: 18 August 2009

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An experimental study was conducted on the spatial distributions of hydrogen emission intensities from low-pressure plasmas generated by laser ablation of zircaloy-4 and black stone targets in nitrogen and helium ambient gases. In addition to confirming the previously observed intensity enhancement effect in ambient helium gas, the hydrogen and helium emission intensities measured along the plasma expansion direction revealed remarkable extended spatial distributions featuring unexpected maxima near the far end of the plasma where the available shock-wave generated thermal excitation energy should have been significantly reduced. This “anomalous” feature necessarily implied the presence of an additional excitation process beside the well known shock-wave excitation process which is responsible for the plasma emission of heavy atoms in low-pressure ambient gas. Further analysis of the data led to a suggested physical mechanism explaining the possible contribution of a helium metastable excited state to the unusual phenomenon observed in this experiment.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Mf Laser ablation
52.50.Lp Plasma production and heating by shock waves and compression
52.35.Tc Shock waves and discontinuities

Ionic debris measurement of three extreme ultraviolet sources

J. Sporre, C. H. Castaño, R. Raju, and D. N. Ruzic

J. Appl. Phys. 106, 043304 (2009); http://dx.doi.org/10.1063/1.3176494 (7 pages) | Cited 1 time

Online Publication Date: 19 August 2009

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Generation of debris in extreme ultraviolet (EUV) light sources is an inherent and real threat to the lifetime of collection optics. Debris measurement of these sources is useful to enable source suppliers to estimate collector lifetime. At the Center for Plasma Material Interactions (CPMI) at the University of Illinois, an Illinois calibrated spherical sector electrostatic energy analyzer (ICE) was built to measure the ion debris flux in absolute units. In addition to ion flux, the detector is also capable of identifying different ion species present in the plasma utilizing energy-to-charge ratio discrimination. The lifetime of the collector optics is calculated using the measured ion flux. In the current investigation we compare the measurement of ion debris production in three different EUV sources: the Energetiq EQ-10M, the AIXUV-100, and the XTREME XTS 13-35. In the EQ-10M source, three angular measurements are coupled with three variations in operating pressure to measure consequent effects on debris production. These measurements reveal four predominant ion species in the energetic debris analysis: C+, Si+, Xe+, and Xe2+. The amount of debris is reduced as pressure is increased. Various debris mitigation methods are implemented in the AIXUV-100 source and results reveal that four ion species are observed (Ar+, Xe+, Xe2+, and W+), though there does not seem to be a dominant species. The first mitigation technique, backstreaming argon toward the source, reduces the amount of Ar+, Xe2+, and W+, yet increases the amount of Xe+ The increase in Xe+ flux is explained based on charge exchange phenomena. The ICE machine was then attached 1.92 m away from the pinch of XTS 13-35 source, and placed at 25° away from the normal line. The comparison of results reveals that the XTS 13-35 and the EQ-10M sources produced comparable amounts of energetic ion flux per watt of EUV light produced. The AIXUV-100 source generated more ion debris flux per watt of EUV light than the other two sources, though it should be noted that the AIXUV-100 source was capable of producing more than ten times the amount of EUV light power compared to any of the other sources.
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52.50.Dg Plasma sources
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.70.Nc Particle measurements
52.75.-d Plasma devices

Off-axis stability of intense continuous relativistic beams

Luciano C. Martins, Felipe B. Rizzato, and Renato Pakter

J. Appl. Phys. 106, 043305 (2009); http://dx.doi.org/10.1063/1.3204972 (4 pages)

Online Publication Date: 24 August 2009

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This paper investigates the stability of off-axis continuous intense relativistic beams propagating inside a circular conducting pipe. The equations of motion for the centroid and the envelope of slightly off-axis beams are derived and used to determine equilibrium and stability conditions for the beam transport. It is shown that depending on the parameters of the system, beams propagating along the pipe axis may become unstable due to the presence of the wall, imposing a fundamental limitation in the effective area that an equilibrium beam can occupy inside the conductor.
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41.75.-i Charged-particle beams

Parametric study of expanding plasma plume formed by laser-blow-off of thin film using triple Langmuir probe

Ajai Kumar, R. K. Singh, Jinto Thomas, and S. Sunil

J. Appl. Phys. 106, 043306 (2009); http://dx.doi.org/10.1063/1.3204946 (8 pages) | Cited 4 times

Online Publication Date: 28 August 2009

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The triple probe technique has been used to study the parameters of flowing plasma plume formed by laser-blow-off (LBO) of a multicomponent LiF–C target. The advantages of triple Langmuir probe over the single probe have been discussed with regard to the present study. Our results show that triple probe is better suited for parametric measurements close to the target. The spatiotemporal evolutions of electron density and temperature were measured in different ambient environments and for various laser fluences. The angular distribution of electron density and temperature was also measured. It was found that the presence of ambient gas drastically affects the electron density and temperature of the LBO plume. Large enhancement in ne and Te at intermediate pressures (10−2 Torr) is expected due to increase in collisional processes. On the other hand, laser fluence does not affect the observed ne and Te significantly. In vacuum, a new phenomenon, i.e., an oscillation in the trailing portion of the plasma plume at a closer distance from the target, is also reported.
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52.70.Ds Electric and magnetic measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Effects of tube diameter and chirality on the stability of single-walled carbon nanotubes under ion irradiation

Zijian Xu, Wei Zhang, Zhiyuan Zhu, Cuilan Ren, Yong Li, and Ping Huai

J. Appl. Phys. 106, 043501 (2009); http://dx.doi.org/10.1063/1.3194784 (13 pages) | Cited 3 times

Online Publication Date: 17 August 2009

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Using molecular dynamics method, we investigated the influence of tube diameter and chirality on the stability of single-walled carbon nanotubes (CNTs) under ion irradiation. We found that in the energy range below 1 keV, the dependence of CNT stability on the tube diameter is no longer monotonic under C ion irradiation, and the thinner (5, 5) CNT may be more stable than the thicker (7, 7) CNT, while under Ar irradiation, the CNT stability increases still monotonically with the CNT diameter. This stability behavior was further verified by the calculations of the threshold ion energies to produce displacement damage in CNTs. The abnormal stability of thin CNTs is related to their resistance to the instantaneous deformation in the wall induced by ion pushing, the high self-healing capacity, as well as the different interaction properties of C and Ar ions with CNT atoms. We also found that under ion irradiation the stability of a zigzag CNT is better than that of an armchair CNT with the same diameter. This is because of the bonding structure difference between the armchair and the zigzag CNTs with respect to the orientations of graphitic networks as well as the self-healing capacity difference.
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61.82.Rx Nanocrystalline materials
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
61.80.Jh Ion radiation effects
62.25.-g Mechanical properties of nanoscale systems

A plasmonic “ac Wheatstone bridge” circuit for high-sensitivity phase measurement and single-molecule detection

T. J. Davis, K. C. Vernon, and D. E. Gómez

J. Appl. Phys. 106, 043502 (2009); http://dx.doi.org/10.1063/1.3195071 (6 pages) | Cited 5 times

Online Publication Date: 17 August 2009

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In this paper, a plasmonic “ac Wheatstone bridge” circuit is proposed and theoretically modeled for the first time. The bridge circuit consists of three metallic nanoparticles, shaped as rectangular prisms, with two nanoparticles acting as parallel arms of a resonant circuit and the third bridging nanoparticle acting as an optical antenna providing an output signal. Polarized light excites localized surface plasmon resonances in the two arms of the circuit, which generate an optical signal dependent on the phase-sensitive excitations of surface plasmons in the antenna. The circuit is analyzed using a plasmonic coupling theory and numerical simulations. The analyses show that the plasmonic circuit is sensitive to phase shifts between the arms of the bridge and has the potential to detect the presence of single molecules.
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84.30.-r Electronic circuits
84.40.Ba Antennas: theory, components and accessories

Ambipolar diffusion and spatial and time-resolved spectroscopies in semiconductor heterostructures

Áurea R. Vasconcellos, M. J. S. P. Brasil, Roberto Luzzi, A. A. P. Silva, and A. H. S. Leite

J. Appl. Phys. 106, 043503 (2009); http://dx.doi.org/10.1063/1.3173176 (9 pages) | Cited 2 times

Online Publication Date: 17 August 2009

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An analysis of the hydrodynamic motion of the fluid of photoinjected carriers in polar semiconductors is presented. Experiments of time-resolved photoluminescence, which provide relevant insights into the dynamical behavior of heterostructures, are analyzed. We study the propagation and recombination of carriers in semiconductor devices with a large cap layer, where carriers are photoinjected, and a quantum well where they recombine. The movement of the photoinjected, and away from equilibrium, carriers along such cap layer consists, to a good degree of approximation, in an ambipolar diffusivelike one, which decays in time as a result of recombination and the coupling, via Coulomb interaction, with the optical and acoustic plasma waves. The density of the electrons arriving at the interface with the quantum well can be determined; these electrons are transferred through the interface to recombine in the quantum well, and the resulting intensity of the time-resolved luminescence is obtained. Comparison with experimental data shows a good agreement.
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78.47.D- Time resolved spectroscopy (>1 psec)
73.63.Hs Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
66.30.Ny Chemical interdiffusion; diffusion barriers
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Functionally grading the shape memory response in NiTi films: Laser irradiation

A. J. Birnbaum, G. Satoh, and Y. L. Yao

J. Appl. Phys. 106, 043504 (2009); http://dx.doi.org/10.1063/1.3183950 (8 pages)

Online Publication Date: 18 August 2009

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A new process and mechanism are presented for controlling the shape memory response spatially within monolithic NiTi thin film structures. This technique is shown to effectively control the martensitic phase transformation temperature and exhibits control over aspects of the mechanical and shape memory responses as well. Specifically, the martensitic phase transformation temperature decreases with incident laser energy density. Concomitant modifications are observed in both the mechanical and shape memory responses in laser processed films. Analysis and characterization are performed via temperature controlled optical microscopy, x-ray diffraction, atomic force microscopy, and nanoindentation.
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81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.kd Metals and alloys
68.60.Bs Mechanical and acoustical properties
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Amorphization of crystalline Si due to heavy and light ion irradiation

P. D. Edmondson, D. J. Riley, R. C. Birtcher, and S. E. Donnelly

J. Appl. Phys. 106, 043505 (2009); http://dx.doi.org/10.1063/1.3195081 (8 pages) | Cited 4 times

Online Publication Date: 19 August 2009

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The formation of amorphous silicon in crystalline silicon by bombardment with light (Si) and heavy (Xe) ions has been investigated by transmission electron microscopy with in situ ion irradiation. Experiments have been carried out at room temperature and low temperature (50 K) and the results are compared to a simple numerical model for amorphization. The results indicate that the amorphization mechanisms for both irradiations are heterogeneous in nature and that numerous overlaps of the collision cascade are generally required to render the crystal amorphous. Following from this, the nature of the material within the confines of collision cascades will be discussed and it will be shown that the individual cascade volume is not necessarily amorphous as previously described in the scientific literature but contains varying degrees of damage depending on the energy deposited within the cascade.
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64.70.kg Semiconductors
61.80.Jh Ion radiation effects

Experimental and theoretical studies on the elasticity of molybdenum to 12 GPa

Wei Liu, Qiong Liu, Matthew L. Whitaker, Yusheng Zhao, and Baosheng Li

J. Appl. Phys. 106, 043506 (2009); http://dx.doi.org/10.1063/1.3197135 (4 pages) | Cited 1 time

Online Publication Date: 19 August 2009

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Experiments have been conducted to measure compressional (VP) and shear wave (VS) velocities as well as unit-cell volumes (densities) of molybdenum to 12.0 GPa at room temperature using ultrasonic interferometry in conjunction with synchrotron x-radiation. Both VP and VS as well as the adiabatic bulk (KS) and shear (G) moduli exhibit monotonic increase with increasing pressure. A finite strain equation of state analysis of the directly measured velocities and densities yields KS0 = 260.7(5) GPa, G0 = 125.1(2) GPa, KS0′ = 4.7(1), and G0′ = 1.5(1) for the elastic bulk and shear moduli and their pressure derivatives at ambient conditions. Complimentary to the experimental data, VP and VS as well as the elastic bulk and shear moduli were also computed using density functional theory (DFT) at pressures comparable to the current experiment. Comparing with experimental results, the velocities and elastic moduli from DFT calculations exhibit close agreement with the current experimental data both in their values as well as in their pressure dependence.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids

Re-entrance phase and excited metastable electronic spin states in one-dimensional spin crossover compounds explained by atom-phonon coupling model

Aurelian Rotaru, Jorge Linares, Sebastien Mordelet, Alexandru Stancu, and Jamil Nasser

J. Appl. Phys. 106, 043507 (2009); http://dx.doi.org/10.1063/1.3186055 (5 pages) | Cited 4 times

Online Publication Date: 19 August 2009

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An unusual behavior of the disappearance and the reappearance of the hysteresis loop of the spin crossover compounds under external pressure was observed experimentally by Garcia et al. [Hyperfine Interact. 139/140, 543 (2002)] and modeled within the framework of the “atom-phonon coupling” model. In this contribution we explain the evolution of the hysteresis width versus the applied pressure. Using the same model, we also show the existence of stable as well as metastable and unstable states at very low temperatures. These excited metastable electronic spin states at low temperature can be associated to the “out of equilibrium” states in the light-induced electronic spin state trapping.
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75.30.Wx Spin crossover
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
63.20.K- Phonon interactions

Structural properties of tensily strained Si layers grown on SiGe(100), (110), and (111) virtual substrates

V. Destefanis, D. Rouchon, J. M. Hartmann, A. M. Papon, L. Baud, A. Crisci, and M. Mermoux

J. Appl. Phys. 106, 043508 (2009); http://dx.doi.org/10.1063/1.3187925 (10 pages) | Cited 5 times

Online Publication Date: 19 August 2009

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We have studied the structural properties of tensily strained Si (t-Si) layers grown by reduced pressure–chemical vapor deposition on top of SiGe(100), (110), and (111) virtual substrates (VSs). Chemical mechanical planarization has been used beforehand to eliminate the as-grown surface crosshatch on all orientations and reduce by 10 up to 100 times the surface roughness. A definite surface roughening has occurred after the epitaxy of t-Si on (110) and (111). For the lowest Ge contents investigated, top Si(100) and (110) layers are locally “defect-free” whereas numerous {111} stacking faults are present in the t-Si(111) layers. For higher Ge content SiGe VS, a degradation of the crystallographic quality of (110) and (111) t-Si layers has been evidenced, with the presence of dislocations, stacking faults, and twins. Quantification of the strain level in the t-Si layers has been carried out using visible and near-UV Raman spectroscopy. The Ge contents in the VS determined by Raman spectroscopy were very close to the ones previously obtained by secondary ion mass spectrometry or x-ray diffraction. Stress values obtained for t-Si(100) layers were whatever the Ge content similar to those expected. Stress values corresponding to pseudomorphic t-Si growths have been obtained on (110) and (111) SiGe VSs, for Ge contents up to 35% and 25%, respectively. The stress values obtained on (110) surfaces for such Ge contents were high, with a noticeable anisotropy along the [001] and [1-10] directions. Degradations of the (110) and (111) Raman profiles likely coming from twin-assisted strain relaxation have been noticed for t-Si layers on SiGe VS with Ge contents higher than 35% and 25%, respectively. UV and visible Raman mapping of the growth plane strain fluctuations has finally been carried out. Original surface arrays have been highlighted for each surface orientation. Such strain fields are related to the plastic relaxation of strain in the SiGe graded layer underneath through the emission of misfit dislocations, twins, and stacking faults. Promising results have been obtained for t-Si layers on (110) SiGe VS while the technological usefulness of the (111) ones is more questionable.
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68.55.ag Semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Mm Grain and twin boundaries
81.65.Ps Polishing, grinding, surface finishing
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators

Ultraviolet Raman microscopy of single and multilayer graphene

Irene Calizo, Igor Bejenari, Muhammad Rahman, Guanxiong Liu, and Alexander A. Balandin

J. Appl. Phys. 106, 043509 (2009); http://dx.doi.org/10.1063/1.3197065 (5 pages) | Cited 33 times

Online Publication Date: 20 August 2009

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We investigated Raman spectra of single-layer and multilayer graphene under ultraviolet laser excitation at the wavelength λ = 325 nm. It was found that while graphene’s G peak remains pronounced in UV Raman spectra, the 2D-band intensity undergoes severe quenching. The evolution of the ratio of the intensities of the G and 2D peaks, I(G)/I(2D), as the number of graphene layers n changes from n = 1 to n = 5, is different in UV Raman spectra from that in conventional visible Raman spectra excited at the 488 and 633 nm wavelengths. The 2D band under UV excitation shifts to larger wave numbers and is found near 2825 cm−1. The observed UV Raman features of graphene were explained by invoking the resonant scattering model. The obtained results contribute to the Raman nanometrology of graphene by providing an additional metric for determining the number of graphene layers and assessing its quality.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Hx Other solid inorganic materials
78.30.Na Fullerenes and related materials

Structural, magnetic, and energetic properties of Na2FePO4F, Li2FePO4F, NaFePO4F, and LiFePO4F from ab initio calculations

M. Ramzan, S. Lebègue, P. Larsson, and R. Ahuja

J. Appl. Phys. 106, 043510 (2009); http://dx.doi.org/10.1063/1.3202384 (6 pages) | Cited 4 times

Online Publication Date: 21 August 2009

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In this paper, we report on Na2FePO4F and Li2FePO4F, which are materials that are used as cathodes in batteries, using density functional theory with the LDA, LDA+U, GGA, or GGA+U approximations. Specifically, we study their crystal structure, electronic structure, and magnetic properties and provide similar information about the intermediate compounds LiFePO4F and NaFePO4F. Finally, the intercalation voltages of the corresponding batteries are calculated using various exchange-correlation approximations and conclusions are drawn about which one is the most suitable to use for the study of this class of materials.
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71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
82.47.Cb Lead-acid, nickel-metal hydride and other batteries
82.45.Fk Electrodes
71.70.Gm Exchange interactions
61.66.Fn Inorganic compounds
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