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21 July 2008

Volume 93, Issue 3,  Articles (03xxxx)

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Cover image from Di Xu, Kevin P. Chen, Kris Ohlinger, and Yuankun Lin, Appl. Phys. Lett. 93, 031101 (2008).

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LASERS, OPTICS, AND OPTOELECTRONICS

Holographic fabrication of diamondlike photonic crystal template using two-dimensional diffractive optical elements

Di Xu, Kevin P. Chen, Kris Ohlinger, and Yuankun Lin

Appl. Phys. Lett. 93, 031101 (2008) (3 pages)

Online Publication Date: 21 July 2008

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This letter demonstrates holographic fabrication of three-dimensional diamondlike photonic crystal templates in SU8 photoresist using a single diffractive optical element. Five coherent laser beams produced by a two-dimensional phase mask were used to construct face-centered-cubic or tetragonal interference patterns. The superposition of two interference patterns through double exposures yields diamondlike photonic crystal templates in SU8. Photonic bandgap calculation reveals a full bandgap in inverse structures based on the template. The utilization of the two-dimensional phase mask simplifies the fabrication configuration in multiple beam holographic lithography for three-dimensional photonic fabrication.
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42.40.Eq, 42.86.+b, 42.70.Qs, 42.40.Kw

Estimating threshold reduction for spin-injected semiconductor lasers

I. Vurgaftman, M. Holub, B. T. Jonker, and J. R. Meyer

Appl. Phys. Lett. 93, 031102 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The magnitude of threshold reduction in a semiconductor laser with electron spin injection is shown to depend on such intrinsic properties of the active region as the dominant recombination mechanism, the ratio of hole-to-electron densities of states, the active-region doping, and the available material gain as well as cavity properties such as the optical loss. The threshold reduction is expected to be greatest when the laser's active region is undoped, the recombination is strongly dominated by Auger processes, and the threshold gain is low. It can approach a factor of 3.5 for fully spin-polarized electrons in the active region.
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42.55.Px, 42.60.By, 85.35.Be

Simultaneous closure of multiple high voltage parallel spark channels without switch: A parametric study

Pallavi Raote, Gautam Patil, J. Padma Nilaya, and Dhruba J. Biswas

Appl. Phys. Lett. 93, 031103 (2008) (3 pages)

Online Publication Date: 21 July 2008

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Results of a detailed parametric study of a self-switched mutually inductively coupled high voltage parallel spark preionizer are presented. The maximal behavior exhibited by the breakdown voltage of the parallel gaps with respect to the number of mutually coupled turns has been explained. It has been found that there exists a threshold rise time of the current pulse beyond which simultaneous closure of the parallel gaps is not possible and that this threshold value is independent of the nature and geometry of the cores used for the mutual coupling. The degree of simultaneity of the closure of the self-switched parallel gaps matched that of the conventional operation of such gaps.
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52.80.Mg

Effect of waveguide sidewall roughness on the threshold current density and slope efficiency of quantum cascade lasers

Fatima Toor, Deborah L. Sivco, Hao E. Liu, and Claire F. Gmachl

Appl. Phys. Lett. 93, 031104 (2008) (3 pages)

Online Publication Date: 21 July 2008

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We report on a study to determine the effect of waveguide sidewall roughness on quantum cascade (QC) laser performance using two two-wavelength heterogeneous QC laser structures, one with emission wavelengths of 7.0  µm/11.2  µm, and the other with 8.7  µm/12.0  µm. For the range of roughness standard deviation values from about 0.4  to  1.0  µm, for which all four QC lasers were operating, the threshold current density increases by 12%–15% and the slope efficiency decreases by 30%–70% with stronger performance degradation for the shorter wavelength lasers, which is in agreement with a model based on Rayleigh scattering.
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42.55.Px, 42.60.Jf, 42.60.Lh

Transient carrier transfer in tunnel injection structures

V. G. Talalaev, J. W. Tomm, N. D. Zakharov, P. Werner, U. Gösele, B. V. Novikov, A. S. Sokolov, Y. B. Samsonenko, V. A. Egorov, and G. E. Cirlin

Appl. Phys. Lett. 93, 031105 (2008) (3 pages)

Online Publication Date: 23 July 2008

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InGaAs tunnel injection nanostructures consisting of a single quantum well as injector and a quantum dot layer as emitter are studied by time-resolved photoluminescence spectroscopy. The quantum dot photoluminescence undergoes substantial changes when proceeding from direct quantum dot excitation to quantum well excitation, which causes an indirect population of the dot ground states. This results in a lowered effective carrier temperature within the dots. Results on the carrier transfer versus barrier thickness are discussed within the Wentzel–Kramers–Brillouin approximation. Deviations for barrier thicknesses <5  nm are assigned to the formation of nanobridges that are actually detected by transmission electron microscopy.
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73.40.Kp, 73.63.Hs, 73.63.Kv, 73.40.Gk, 78.67.De, 78.67.Hc

Real-time optical reflectometry enabled by amplified dispersive Fourier transformation

Keisuke Goda, Daniel R. Solli, and Bahram Jalali

Appl. Phys. Lett. 93, 031106 (2008) (3 pages)

Online Publication Date: 23 July 2008

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The axial scan rate of optical frequency-domain reflectometry and optical coherence tomography can be increased to megahertz frequencies by dispersive Fourier transformation. However, the fundamental connection between dispersion and loss creates a trade-off between detection sensitivity and acquisition speed. Here we circumvent this predicament by using distributed Raman postamplification of the reflection from the sample. The Raman amplification enables measurement of weak signals, which are otherwise buried in detector noise. It extends the depth range without sacrificing the acquisition speed. Single-shot imaging with improved sensitivity at an axial scan rate of 36.6  MHz is demonstrated.
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07.60.Hv, 42.30.Kq

The effect of doping the M-barrier in very long-wave type-II InAs/GaSb heterodiodes

Darin Hoffman, Binh-Minh Nguyen, Edward Kwei-wei Huang, Pierre-Yves Delaunay, Manijeh Razeghi, Meimei Z. Tidrow, and Joe Pellegrino

Appl. Phys. Lett. 93, 031107 (2008) (3 pages)

Online Publication Date: 23 July 2008

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A variation on the standard homodiode type-II superlattice with an M-barrier between the pi-region and the n-region is shown to suppress the dark currents. By determining the optimal doping level of the M-superlattice, dark current densities of 4.95  mA/cm2 and quantum efficiencies in excess of 20% have been demonstrated at the moderate reverse bias of 50  mV; allowing for near background-limted performance with a Johnson-noise detectivity of 3.11×1010  cm  sqrt(Hz)/W at 77  K for 14.58  µm cutoff wavelength for large area diodes without passivation. This is comparable to values for the state-of-the-art HgCdTe photodiodes.
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85.60.Dw, 85.40.Ry

Thermally assisted magnetic recording on a bit-patterned medium by using a near-field optical head with a beaked metallic plate

Takuya Matsumoto, Kimio Nakamura, Tetsuya Nishida, Hiroyuki Hieda, Akira Kikitsu, Katsuyuki Naito, and Tetsunori Koda

Appl. Phys. Lett. 93, 031108 (2008) (3 pages)

Online Publication Date: 23 July 2008

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A near-field optical head with a beaked metallic plate was used for writing marks on a Co/Pd bit-patterned medium with a diameter of 20–25  nm and a pitch of 30  nm. Magnetic-force-microscope images of the medium show that the magnetizations of single bits were selectively reversed by the head. The light-utilization efficiency (defined as the ratio of the absorbed power in the medium to the incident light power) was estimated from the writing condition used and thermal modeling as about 5%.
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75.50.Ss, 75.60.Ej

A high speed, postprocessing free, quantum random number generator

J. F. Dynes, Z. L. Yuan, A. W. Sharpe, and A. J. Shields

Appl. Phys. Lett. 93, 031109 (2008) (3 pages)

Online Publication Date: 23 July 2008

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A quantum random number generator (QRNG) based on gated single photon detection of an In–GaAs photodiode at gigahertz frequency is demonstrated. Owing to the extremely long coherence time of each photon, each photons' wave function extends over many gating cycles of the photodiode. The collapse of the photon wave function on random gating cycles as well as photon random arrival time detection events are used to generate sequences of random bits at a rate of 4.01  Mbit/s. Importantly, the random outputs are intrinsically biasfree and require no postprocessing procedure to pass random number statistical tests, making this QRNG an extremely simple device.
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03.67.Lx, 85.60.Gz, 85.60.Dw

Fabry–Pérot microcavities with controllable resonant wavelengths in periodic dielectric waveguides

Yao Zhang, Wanwen Huang, and Baojun Li

Appl. Phys. Lett. 93, 031110 (2008) (3 pages)

Online Publication Date: 24 July 2008

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Fabry–Pérot microcavities with controllable resonant wavelengths and constant quality factors are constructed by introducing defects in periodic dielectric waveguides. Two-dimensional finite-difference time-domain method is used to simulate the field distributions in the cavities. The simulated electric field profile fits a cosine-Gaussian curve. The quadratic relation between the resonant wavelength and the defect length is theoretically discussed and numerically proved. Simulations show that the resonant wavelength can be simply controlled by shifting cylinders in the defects, and the value of quality factor keeps a constant of about 103.
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42.79.Gn

Single-frequency, Yb-free, resonantly cladding-pumped large mode area Er fiber amplifier for power scaling

Mark Dubinskii, Jun Zhang, and Igor Kudryashov

Appl. Phys. Lett. 93, 031111 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We report results for a single-frequency (SF) resonantly cladding-pumped Yb-free large mode area (LMA) erbium-doped fiber amplifier (EDFA) with nearly 50% slope efficiency based on a commercial 20/125  µm Er-doped double-clad LMA fiber with a core numerical aperture of 0.07. We believe that this is the original demonstration of a SF resonantly cladding-pumped LMA EDFA. We obtained a diffraction-limited SF output of 9.3  W, which is also a record power output obtained for resonantly cladding-pumped LMA EDFA.
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42.55.Wd, 42.60.By
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PLASMAS AND ELECTRICAL DISCHARGES

Development of a trielectrode plasma curtain at atmospheric pressure

H. Zastawny, R. Sosa, D. Grondona, A. Márquez, G. Artana, and H. Kelly

Appl. Phys. Lett. 93, 031501 (2008) (3 pages)

Online Publication Date: 23 July 2008

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The development of a nonequilibrium, low-power, trielectrode plasma curtain at atmospheric pressure is presented. The discharge is based on the combination of an ac dielectric barrier discharge with a dc corona discharge in a three electrode system, and can be sustained for large time periods and over interelectrode air gaps up to 20  mm and with an electrode length of ~10  cm in the transversal direction. The discharge is composed of a train of streamers, with a repetition frequency in the range 50–200  kHz, and carrying an average current in the range 0.1–0.4  mA. The geometry of the discharge makes it appropriate for gas decontamination.
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52.50.Dg, 52.80.Hc

Multiple substrate microwave plasma-assisted chemical vapor deposition single crystal diamond synthesis

J. Asmussen, T. A. Grotjohn, T. Schuelke, M. F. Becker, M. K. Yaran, D. J. King, S. Wicklein, and D. K. Reinhard

Appl. Phys. Lett. 93, 031502 (2008) (3 pages)

Online Publication Date: 23 July 2008

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A multiple substrate, microwave plasma-assisted chemical vapor deposition synthesis process for single crystal diamond (SCD) is demonstrated using a 915  MHz reactor. Diamond synthesis was performed using input chemistries of 6–8% of CH4/H2, microwave input powers of 10–11.5  kW, substrate temperatures of 1100–1200  °C, and pressures of 110–135  Torr. The simultaneous synthesis of SCD over 70 diamond seeds yielded good quality SCD with deposition rates of 14–21  µm/h. Multiple deposition runs totaling 145  h of deposition time added 1.8–2.5  mm of diamond material to each of the 70 seed crystals.
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81.15.Gh, 52.77.Dq, 68.55.aj

Influence of operating pressure on surface dielectric barrier discharge plasma aerodynamic actuation characteristics

Yun Wu, Yinghong Li, Min Jia, Huimin Song, Zhigang Guo, Ximing Zhu, and Yikang Pu

Appl. Phys. Lett. 93, 031503 (2008) (3 pages)

Online Publication Date: 24 July 2008

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This letter reports an experimental study of surface dielectric barrier discharge plasma aerodynamic actuation characteristics' dependence on operating pressure. As the pressure decreases, the N2(C  3[cyrillic PE]u) rotational temperature decreases, while its vibrational temperature decreases initially and then increases. In addition, the discharge mode changes from a filamentary type to a glow type at 45  Torr. In the filamentary mode, the electron density decreases with pressure, while the electron temperature remains almost unchanged. In the glow mode, however, both the electron density and the electron temperature increase while the pressure decreases. The induced velocity shows a maximum value at 445  Torr.
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52.30.-q, 52.35.Py, 52.80.Hc, 47.85.Gj

Modulating effects of the low-frequency source on ion energy distributions in a dual frequency capacitively coupled plasma

Xiao-Song Li, Zhen-Hua Bi, Da-Lei Chang, Zhi-Cheng Li, Shuai Wang, Xiang Xu, Yong Xu, Wen-Qi Lu, Ai-Min Zhu, and You-Nian Wang

Appl. Phys. Lett. 93, 031504 (2008) (3 pages)

Online Publication Date: 24 July 2008

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With the energy resolved quadrupole mass spectrometer and hybrid simulation, the influence of low-frequency (LF) source parameters on the ion energy distributions (IEDs) of argon ions impinging on the grounded electrode was studied, both experimentally and numerically, in a dual frequency capacitively coupled plasma. It was shown that for decreasing LF or increasing LF power, the high energy peak in IEDs shifts toward the high energy region significantly. The simulation results were in general agreement with the experimental data.
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52.25.-b, 52.50.Dg, 52.65.Ww, 52.70.Nc

Design of fine phosphor system for the improvement in the luminescent properties of the phosphor layer in the plasma display panel: Theoretical and experimental analysis

Chae-Woong Cho, Ungyu Paik, Do-Hyung Park, Yoon-Chang Kim, and Dong-Sik Zang

Appl. Phys. Lett. 93, 031505 (2008) (3 pages)

Online Publication Date: 25 July 2008

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Improvement in the luminescent properties of plasma display panels via phosphor size control was theoretically and experimentally investigated. From theoretical analyses of photon extraction and plasma efficiency, fine phosphor system was designed, which was compared with experimental data. The denser microstructure of finer phosphor-based layer promoted photon extraction efficiency by higher reflectivity. Also, the finer phosphor increased vacuum-ultraviolet discharge space and corresponding plasma efficiency via decrease in layer thickness. Based on the results, the phosphor size control improved the panel efficiency by the synergistic effect of improvements in photon extraction and plasma efficiency.
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85.60.Pg, 52.75.-d, 78.60.-b

Experimental observation of the inductive electric field and related plasma nonuniformity in high frequency capacitive discharge

S. K. Ahn and H. Y. Chang

Appl. Phys. Lett. 93, 031506 (2008) (3 pages)

Online Publication Date: 25 July 2008

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To elucidate plasma nonuniformity in high frequency capacitive discharges, Langmuir probe and B-dot probe measurements were carried out in the radial direction in a cylindrical capacitive discharge driven at 90  MHz with argon pressures of 50 and 400  mTorr. Through the measurements, a significant inductive electric field (i.e., time-varying magnetic field) was observed at the radial edge, and it was found that the inductive electric field creates strong plasma nonuniformity at high pressure operation. The plasma nonuniformity at high pressure operation is physically similar to the E-H mode transition typically observed in inductive discharges. This result agrees well with the theories of electromagnetic effects in large area and/or high frequency capacitive discharges.
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52.70.Ds, 52.80.Pi
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STRUCTURAL, MECHANICAL, THERMODYNAMIC, AND OPTICAL PROPERTIES OF CONDENSED MATTER

Phase transformation accommodated plasticity in nanocrystalline nickel

X. Y. Zhang, X. L. Wu, Q. Liu, R. L. Zuo, A. W. Zhu, P. Jiang, and Q. M. Wei

Appl. Phys. Lett. 93, 031901 (2008) (3 pages)

Online Publication Date: 21 July 2008

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Based on detailed x-ray diffraction and transmission electron microscopy we have found body-centered-cubic (bcc) Ni upon room-temperature rolling of nanocrystalline (nc) face-centered-cubic (fcc) Ni. The bcc phase forms via the Kurdjumov–Sachs (KS) martensitic transformation mechanism when the von Mises equivalent strain exceeds ~0.3, much higher than accessible in tensile testing. The fcc and bcc phases keep either the KS or the Nishiyama–Wasserman orientation relationship. Our results provide insights into the deformation physics in nc Ni, namely, the fcc-to-bcc phase transformation can also accommodate plasticity at large plastic strains.
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81.30.Kf, 64.70.kd, 81.40.Lm, 62.20.fq, 62.25.-g, 61.46.Df

In situ metal-organic chemical vapor deposition atomic-layer deposition of aluminum oxide on GaAs using trimethyaluminum and isopropanol precursors

Cheng-Wei Cheng and Eugene A. Fitzgerald

Appl. Phys. Lett. 93, 031902 (2008) (3 pages)

Online Publication Date: 21 July 2008

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In situ atomic-layer deposition (ALD) of Al2O3 on p-GaAs in metal-organic chemical vapor deposition system is demonstrated in this article. Isopropanol was chosen as the oxygen source for Al2O3 ALD, instead of common H2O. The ALD mechanism is discussed and it is proposed that water does not form in the process. The saturation growth rate of Al2O3 is about 0.8  Å/cycle. X-ray photoetectron spectroscopy depth profiles were performed and no arsenic oxide is observed at the interface. The capacitance-voltage measurements show a small accumulation capacitance dispersion and voltage shift in the depletion region. The interfacial defect density near the midgap of the GaAs bandgap has been determined with the conductance-frequency method. The interfacial defect density is determined as 2.5×1011  eV−1  cm−2 at the midgap of the GaAs.
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81.15.Ef, 81.15.Gh, 68.55.at, 81.15.Kk, 79.60.Bm

Giant effective g-factor in PbxEu1−xTe epitaxial films

E. Heredia, P. H. de Oliveira Rappl, P. Motisuke, A. L. Gazoto, F. Iikawa, and M. J. S. P. Brasil

Appl. Phys. Lett. 93, 031903 (2008) (3 pages)

Online Publication Date: 21 July 2008

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We investigated PbxEu1−xTe films with x<=0.2 by magneto-optical measurements. For x~0.01, the optical emission is similar to high quality EuTe films with two narrow lines attributed to excitonic recombinations associated with magnetic polarons. For increasing x, the emission becomes dominated by a broader lower energy band, which is very efficient as compared to the binary emission. The magneto-optical properties of the ternary films show various similarities with EuTe results, such as quenchings at similar temperatures and magnetic fields. Most remarkably, they also present a giant effective g-factor that makes this material a strong candidate for spintronic applications.
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78.66.Li, 78.20.Ls, 75.70.Ak, 78.55.Hx, 71.38.-k, 71.35.-y

Evolution of valence-band alignment with nitrogen content in GaNAs/GaAs single quantum wells

Jun Shao, Wei Lu, M. Sadeghi, Xiang Lü, S. M. Wang, Lili Ma, and A. Larsson

Appl. Phys. Lett. 93, 031904 (2008) (3 pages)

Online Publication Date: 21 July 2008

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We report on experimental evidence for the transition of valence-band alignment from type I to type II in GaNxAs1−x/GaAs single quantum wells by photoreflectance measurements. The substitutional nitrogen content covers a range of 1.4%–5.9%. The turning point of the type I–type II transition occurs at x>~4.7%. The experimental observations can be well interpreted by a combination of band anticrossing model and model-solid theory when nonlinear behavior of either the shear deformation potential or the average valence-band energy is taken into account. The effect of dilute nitrogen on the valence-band offset of GaNAs/GaAs quantum well structure is hence clarified.
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73.21.Fg, 78.67.De

Modulus mapping of nanoscale closure variants in Ni–Mn–Ga

Yaniv Ganor and Doron Shilo

Appl. Phys. Lett. 93, 031905 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The twinned magnetic microstructure of Ni2MnGa ferromagnetic shape-memory alloy is investigated by high resolution nanoscale modulus mapping. A surprisingly fine near-surface nanoscale substructure of closure magnetic twin variants was observed. The lateral distance between adjacent closure variants was found to be 100  nm. The small size of twin variant prisms provides a unique opportunity for evaluating the twin boundary energy by considering the competition between the magnetic field and interface energies. Our estimate shows a relatively small twin boundary energy of 3  ergs/cm2, which suggests the ability of Ni2MnGa to form nanoscale structures of magnetic twin variants.
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61.72.Mm, 75.50.Cc, 81.40.Lm, 68.35.Md, 62.20.F-

Improved GaN film overgrown with a molybdenum nanoisland mask

Chaotong Lin, Guanghui Yu, Xinzhong Wang, Mingxia Cao, Hang Gong, Ming Qi, and Aizhen Li

Appl. Phys. Lett. 93, 031906 (2008) (3 pages)

Online Publication Date: 21 July 2008

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We report the improved crystalline and optical quality of GaN film overgrown by hydride vapor phase epitaxy adopting a molybdenum (Mo) nanoisland mask (MNM). The MNM is fabricated following thermal annealing of the nanometer-thick Mo film deposited by electron-beam evaporation. The full width at half maximum values of high-resolution x-ray diffraction (HRXRD) rocking curves for the GaN film with MNM are 188  arc  sec (002 reflection) and 219  arc  sec (102 reflection), while those for the GaN film without MNM are 256 and 364  arc  sec, respectively. This result indicates a significant reduction of dislocation density in the overgrown GaN film with MNM. Photoluminescence spectra measurements reveal the compressive strain relaxation and improvement in the quality of the overgrown GaN film with MNM as compared to the regrown GaN film without MNM, which is consistent with the trend observed by HRXRD.
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81.05.Ea, 81.15.Kk, 68.55.ag, 42.70.Nq, 78.66.Fd, 78.55.Cr

Shear band melting and serrated flow in metallic glasses

K. Georgarakis, M. Aljerf, Y. Li, A. LeMoulec, F. Charlot, A. R. Yavari, K. Chornokhvostenko, E. Tabachnikova, G. A. Evangelakis, D. B. Miracle, A. L. Greer, and T. Zhang

Appl. Phys. Lett. 93, 031907 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Scanning electron microscopy observations of shear steps on Zr-based bulk metallic glasses show direct evidence of shear band melting due to heat generated by elastic energy release. The estimated range of attained temperatures and the observed morphologies are consistent with shear steps forming at a subsonic speed limited by a required redistribution of local microscopic stresses. The calculations indicate that a 0.2  µm layer melts in the vicinity of a shear band forming a 1  µm shear step. The plastic part of the stress strain curve is serrated but a majority of shear events are not associated to serrations.
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81.40.Lm, 62.20.fq, 62.20.de, 61.43.Fs, 81.40.Jj, 64.70.dj

Mechanical twinning and omega transition by <111> {112} shear in a metastable beta titanium alloy

H. Xing and J. Sun

Appl. Phys. Lett. 93, 031908 (2008) (3 pages)

Online Publication Date: 23 July 2008

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{112} <111> mechanical twinning and stress-induced omega transition were observed by high-resolution transmission electron microscope in a metastable beta titanium alloy with chemical composition of Ti-23Nb-0.7Ta-2Zr-1.2O at. % after deformation. The orientation relationships between the omega phase and beta parent matrix are ([overline 1]010)omega||(211)beta, [1[overline 2]10]omega||[0[overline 1]1]beta and [0001]omega||[[overline 1]11]beta, and the habit plane of ([overline 1]010)omega||(211)beta for the stress-induced omega transition is different from that of (0001)omega||(111)beta often observed for the thermal omega transition. Both mechanical twinning and omega transition arise from the shear along <111> {112}. A dislocation mechanism for mechanical twinning and stress-induced omega transition was discussed additionally.
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61.72.Mm, 61.72.Ff, 81.30.Hd, 64.70.kd, 81.40.Lm, 62.20.F-

Voltage dependent director of a homeotropic negative liquid crystal cell

L. Z. Ruan, Fuzi Yang, and J. R. Sambles

Appl. Phys. Lett. 93, 031909 (2008) (2 pages)

Online Publication Date: 23 July 2008

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Thin layers of obliquely (60° to normal) thermally evaporated SiOx lead to homeotropic alignment of a nematic liquid crystal (LC) having negative dielectric anisotropy. Under application of an ac voltage the director, as characterized by the fully leaky waveguide technique, is found to realign with a voltage controlled tilt along the evaporation direction. This behavior is in complete contrast with that of a LC having positive dielectric anisotropy and may have important implications for modern LC display technology.
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42.79.Kr, 61.30.Eb

Deformation twin formed by self-thickening, cross-slip mechanism in nanocrystalline Ni

X. L. Wu, J. Narayan, and Y. T. Zhu

Appl. Phys. Lett. 93, 031910 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We report the observation of a deformation twin formed by a recently proposed self-thickening, cross-slip twinning mechanism. This observation verifies one more twinning mechanism, in addition to those reported before, in nanocrystalline face-centered-cubic metals. In this mechanism, once the first Shockley partial is emitted from a grain boundary, and cross slips onto another slip plane, a deformation twin could nucleate and grow in both the primary and cross-slip planes without requiring the nucleation of additional Shockley partials from the grain boundary.
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81.40.Lm, 62.20.F-, 61.72.Mm, 61.46.Hk

Spherical indentation of a finite poroelastic coating

M. Galli and M. L. Oyen

Appl. Phys. Lett. 93, 031911 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Indentation testing of a finite poroelastic layer is considered. Finite element modeling was used to investigate spherical contact creep tests, with emphasis on the influence of layer thickness and of finite rise time on the time-dependent deformation. Thin layers are stiffened by the substrate constraint even at very small relative indenter penetrations and reach steady state more quickly than thick layers. The degree of consolidation following loading is affected by the interaction of layer thickness and rise time and cannot be predicted from either alone. These results provide guidance for micro- and nanoindentation testings of hydrogel coatings for biomedical applications.
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81.40.Np, 62.20.M-, 81.40.Jj, 62.20.D-, 81.70.Bt, 81.40.Lm, 62.20.F-

Unusual surface reliefs from photoinduced creeping and aggregation behavior of azopolymer

Seungwoo Lee, Yong-Cheol Jeong, and Jung-Ki Park

Appl. Phys. Lett. 93, 031912 (2008) (3 pages)

Online Publication Date: 24 July 2008

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We report the spontaneous formation of unusual surface reliefs, in which two sets of sinusoidal gratings were hierarchically structured, merely by single-step holographic inscription on amorphous azopolymer films. By monitoring of growth behavior of surface reliefs during holographic inscription, we found that the formation of additional grating is caused by the creeping and resulting aggregation of dome structures. Our direct observation of creeping and aggregation behavior is expected to contribute to enhancing the understanding of unusual surface reliefs, and also in fabricating complex surface reliefs.
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42.70.Jk, 42.40.Eq, 61.41.+e

High strength Ni–Zr binary ultrafine eutectic-dendrite composite with large plastic deformability

Jin Man Park, Tae Eung Kim, Sung Woo Sohn, Do Hyang Kim, Ki Buem Kim, Won Tae Kim, and Jürgen Eckert

Appl. Phys. Lett. 93, 031913 (2008) (3 pages)

Online Publication Date: 24 July 2008

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A Ni–8Zr high strength ultrafine eutectic-dendrite composite with large plasticity has been developed in the Ni–Zr binary eutectic system. The excellent mechanical properties are attributed to the specific heterogeneous microstructure with distinctly different length scales, i.e., micrometer-size ductile dendrites combined with an ultrafine eutectic matrix. The plastic deformation mainly proceeds through a shear banding mechanism. However, there is no significant shear localization due to the constraint effect of ductile solid solution Ni phases including dendrites and/or alternating lamellar layers. Furthermore, excessive shear stress and accumulated shear strain can be effectively released and accommodated by delocalization and multiplication of shear bands.
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81.40.Lm, 62.20.fk

Thin film NiTi coatings on optical fiber Bragg sensors

K. P. Mohanchandra, S. Karnani, M. C. Emmons, W. L. Richards, and G. P. Carman

Appl. Phys. Lett. 93, 031914 (2008) (3 pages)

Online Publication Date: 24 July 2008

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This paper describes the sputter deposition and characterization of nickel titanium (NiTi) thin film shape memory alloy onto the surface of an optical fiber Bragg grating. The NiTi coating uniformity, crystallinity, and transformation temperatures are measured using scanning electron microscope, x-ray diffraction, and differential scanning calorimeter, respectively. The strain in the optical fiber is measured using centroid calculation of wavelength shifts. Results show distinct and abrupt changes in the optical fiber signal with the four related transformation temperatures represented by the austenite-martensite forward and reverse phase transformations. These tests demonstrate a coupling present between optical energy and thermal energy, i.e., a modified multiferroic material.
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42.81.Pa, 81.15.Cd, 42.79.Wc, 42.79.Dj, 42.81.Bm, 42.81.Cn

Bilinear responses and rippling morphologies of multiwalled carbon nanotubes under torsion

Xu Huang, Jian Zou, and Sulin Zhang

Appl. Phys. Lett. 93, 031915 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We present coarse-grained simulations of torsion induced rippling deformation morphology of multiwalled carbon nanotubes (MWCNTs). Our simulations reveal that beyond the torsional bifurcation, the rippling pattern propagates from outer to inner layers, with the two innermost layers acting as a hard core that hardly ripples. Despite the highly nonlinear rippling deformation, the mechanical response of MWCNTs follows a simple bilinear law, with a nearly constant ratio (~60%) of post- to prerippling torsional rigidities. The bifurcation torsion scales inversely with the square of tube radius. This bilinear constitutive relation may be exploited by large-scale simulations of MWCNT-based materials and devices.
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81.40.Lm, 81.07.De, 61.46.Fg

Microstructural evolution in H ion induced splitting of freestanding GaN

O. Moutanabbir, R. Scholz, S. Senz, U. Gösele, M. Chicoine, F. Schiettekatte, F. Süßkraut, and R. Krause-Rehberg

Appl. Phys. Lett. 93, 031916 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We investigated the microstructural transformations during hydrogen ion-induced splitting of GaN thin layers. Cross-sectional transmission electron microscopy and positron annihilation spectroscopy data show that the implanted region is decorated with a high density of 1–2  nm bubbles resulting from vacancy clustering during implantation. These nanobubbles persist up to 450  °C. Ion channeling data show a strong dechanneling enhancement in this temperature range tentatively attributed to strain-induced lattice distortion. The dechanneling level decreases following the formation of plateletlike structures at 475  °C. Extended internal surfaces develop around 550  °C leading to the exfoliation of GaN thin layer.
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61.72.U-, 61.72.jd, 61.80.Jh, 78.70.Bj, 47.55.D-, 61.72.Qq

A study of the pair distribution function of self-organized Ge quantum dots

Marco Bernardi, Anna Sgarlata, Massimo Fanfoni, Adalberto Balzarotti, and Nunzio Motta

Appl. Phys. Lett. 93, 031917 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We explore the use of the pair distribution function to study the self-organization process of Ge quantum dots on both nanopatterned and nonpatterned oxidized Si(001) surfaces. Dots formation and ordering upon annealing of a Ge thin film are analyzed. The method we use is not limited to this case study. We show how it can be applied to determine short and long range self-ordering of nanostructures. We support our results by applying a software routine to simulate patterns of dots to finally spot the relevant physical aspects of Ge islands self-assembly.
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81.16.Dn, 68.65.Hb, 61.72.Cc, 68.55.ag

Temperature independence of pressure-induced amorphization of the phase-change memory alloy Ge2Sb2Te5

M. Krbal, A. V. Kolobov, J. Haines, A. Pradel, M. Ribes, P. Fons, J. Tominaga, C. Levelut, R. Le Parc, and M. Hanfland

Appl. Phys. Lett. 93, 031918 (2008) (3 pages)

Online Publication Date: 25 July 2008

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In the temperature range from room temperature to about 150  °C, the prototypic phase-change material Ge2Sb2Te5 becomes amorphous upon hydrostatic compression. In the studied temperature range, the onset of amorphization is at about 15  GPa and the material completely amorphizes at 25  GPa; these values do not depend on temperature. Upon decompression, the amorphous phase is stable at lower temperatures, yet at higher temperatures (145  °C), the initial fcc phase is recovered upon decompression. A possible mechanism of pressure-induced amorphization and its implications for phase-change memories are discussed.
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64.70.K-, 81.30.Hd, 61.43.-j

Elasticity of ideal single-walled carbon nanotubes via symmetry-adapted tight-binding objective modeling

D.-B. Zhang and T. Dumitrică

Appl. Phys. Lett. 93, 031919 (2008) (3 pages)

Online Publication Date: 25 July 2008

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The elastic response for a large catalog of carbon nanotubes subjected to axial and torsional strain is derived from atomistic calculations that rely on an accurate tight-binding description of the covalent binding. The application of the computationally expensive quantum treatment is possible due to the simplification in the number of atoms introduced by accounting for the helical and angular symmetries exhibited by the elastically deformed nanotubes. The elasticity of nanotubes larger than ~1.25  nm in diameter can be represented with an isotropic elastic continuum.
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81.40.Jj, 81.40.Lm, 62.25.-g, 62.23.-c, 62.20.D-, 62.20.F-
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ELECTRONIC TRANSPORT AND SEMICONDUCTORS

Stretched-exponential a-Si:H/c-Si interface recombination decay

Stefaan De Wolf, Sara Olibet, and Christophe Ballif

Appl. Phys. Lett. 93, 032101 (2008) (3 pages)

Online Publication Date: 23 July 2008

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The electronic properties of hydrogenated amorphous silicon (a-Si:H) relax following stretched exponentials. This phenomenon was explained in the past by dispersive hydrogen diffusion, or by retrapping included hydrogen motion. In this letter, the authors report that the electronic passivation properties of intrinsic a-Si:H/crystalline silicon (c-Si) interfaces relax following a similar law. Carrier injection dependent a-Si:H/c-Si interface recombination calculations suggest this originates from amphoteric interface state (or Si dangling bond) reduction, rather than from a field effect. These findings underline the similarity between a-Si:H/c-Si interface recombination and the electronic properties of a-Si:H bulk material.
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73.40.Lq, 81.65.Rv, 72.20.Jv, 73.25.+i

Bias-controlled spin polarization in quantum wires

T.-M. Chen, A. C. Graham, M. Pepper, I. Farrer, and D. A. Ritchie

Appl. Phys. Lett. 93, 032102 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We demonstrate that a source-drain bias creates a fully spin-polarized current as the 0.25(2e2/h) plateau in quantum wires even in zero magnetic field. When a source-drain bias lifts the momentum degeneracy, the dc measurements show that it is possible to achieve a unidirectional ferromagnetic order and this ordered spin array is destroyed once transport in both directions commences. The spin polarization of currents, between full spin polarization and partial spin polarization (or spin degeneracy), is thus simply controlled by source-drain bias and split-gate voltage, something of considerable value for spintronics.
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73.63.Nm, 72.25.-b

Highly stable amorphous-silicon thin-film transistors on clear plastic

Bahman Hekmatshoar, Kunigunde H. Cherenack, Alex Z. Kattamis, Ke Long, Sigurd Wagner, and James C. Sturm

Appl. Phys. Lett. 93, 032103 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Hydrogenated amorphous-silicon (a-Si:H) thin-film transistors (TFTs) have been fabricated on clear plastic with highly stable threshold voltages. When operated at a gate field of 2.5×105  V/cm, the threshold voltage shift extrapolated to only ~1.2  V after ten years. This stability is achieved by a high deposition temperature for the gate silicon nitride insulator which reduces charge trapping and high hydrogen dilution during a-Si:H growth to reduce defect creation in a-Si:H. This gate field of 2.5×105  V/cm is sufficient to drive phosphorescent organic light emitting diodes (OLEDs) at a brightness of 1000  Cd/m2. The half-life of the TFT current is over ten years, slightly longer than the luminescence half-life of high quality green OLEDs.
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85.30.Tv, 85.40.-e, 85.60.Jb

Evidence of low interface trap density in GeO2/Ge metal-oxide-semiconductor structures fabricated by thermal oxidation

Hiroshi Matsubara, Takashi Sasada, Mitsuru Takenaka, and Shinichi Takagi

Appl. Phys. Lett. 93, 032104 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We have fabricated GeO2/Ge metal-oxide-semiconductor (MOS) structures by direct thermal oxidation of Ge substrates. The interface trap density (Dit) of Al/GeO2/Ge MOS structures, measured by the low temperature conductance method including the effect of the surface potential fluctuation, is found to be reduced as the oxidation temperature increases. The minimum values of Dit can be obtained for the oxidation around 575  °C, which is in the maximum temperature range where GeO volatilization does not occur under atmospheric pressure of O2. It is also found that the hydrogen annealing before Al gate formation is effective for the passivation of GeO2/Ge interface states. It is clarified, as a result, that the minimum Dit value lower than 1011  cm−2  eV−1 can be obtained for GeO2/Ge MOS interfaces fabricated by direct oxidation of Ge substrates.
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73.20.-r, 73.40.Qv, 61.72.Cc, 81.65.Mq, 81.65.Rv

Metallization contacts to nonpolar a-plane n-type GaN

Hyunsoo Kim, Sung-Nam Lee, Yongjo Park, Joon Seop Kwak, and Tae-Yeon Seong

Appl. Phys. Lett. 93, 032105 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We have investigated the electrical characteristics of metallization contacts to nonpolar a-plane and polar c-plane n-type GaN. Pd Schottky diodes and x-ray photoemission spectroscopy measurements show that the Schottky barrier height of the a-plane GaN is lower than that of the c-plane GaN by 0.24 and 0.30  eV, respectively. Ti/Al Ohmic contacts to the a-plane n-GaN produce lower contact resistivity than that of the c-plane samples when annealed at 500  °C. However, Ti/Al contacts to the c-plane and a-plane GaN show opposite electrical behavior when annealed at temperatures above 500  °C, which is attributed to the absence of polarization-induced surface charges for a-plane GaN.
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85.40.Ls, 73.40.Ns, 79.60.Bm, 73.30.+y, 85.30.Kk, 73.40.Cg

Formation of a manganese oxide barrier layer with thermal chemical vapor deposition for advanced large-scale integrated interconnect structure

Koji Neishi, Shiro Aki, Kenji Matsumoto, Hiroshi Sato, Hitoshi Itoh, Shigetoshi Hosaka, and Junichi Koike

Appl. Phys. Lett. 93, 032106 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Advanced large-scale integrated interconnect structure faces a major challenge in forming a thin and conformal diffusion barrier layer. We deposited a Mn oxide layer by thermal chemical vapor deposition (CVD) on SiO2 substrates and investigated deposition behavior and diffusion barrier property. A thin Mn oxide layer was formed with a uniform thickness of 2.6–10  nm depending on deposition temperature between 100 and 400  °C. Heat-treated samples of Cu/CVD-Mn oxide/SiO2 indicated no interdiffusion at 400  °C for 100  h. The CVD of the Mn oxide layer was found to be an excellent barrier formation process.
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85.40.Ls, 81.15.Gh

Radiotracer diffusion of cobalt, iron, and chromium in dislocation-free germanium

L. Lerner and N. A. Stolwijk

Appl. Phys. Lett. 93, 032107 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Diffusion of the transition metals Co, Fe, and Cr into single-crystal germanium is found to be fast processes at temperatures relevant to the fabrication of semiconductor devices. These results were obtained from experiments in which electronic-grade Ge samples were provided with a radioactive surface source and short time annealed in a lamp furnace at temperatures ranging from 600  to  900  °C. Diffusion coefficients were determined from penetration profiles of the radioisotopes 57Co, 59Fe, and 51Cr. The results are interpreted within the framework of interstititial-substitutional diffusion and compared with earlier diffusion data on Ge crystals.
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66.30.J-, 61.72.Cc, 61.72.jj, 81.05.Cy

High-temperature annealing behavior of deep levels in 1  MeV electron irradiated p-type 6H-SiC

Giovanni Alfieri and Tsunenobu Kimoto

Appl. Phys. Lett. 93, 032108 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We report on the thermal stability of deep levels detected after 1  MeV electron irradiated p-type 6H-SiC. The investigation was performed by deep level transient spectroscopy, and an isochronal annealing series was carried out in the 373–2073  K temperature range. We found seven traps located between 0.23 and 1.3  eV above the valence band edge (EV). Two traps anneal out at temperatures below 1273  K, while the others display a high thermal stability up to 2073  K. The nature of the detected traps is discussed on the basis of their annealing behavior and previous data found in the literature.
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71.55.Ht, 73.20.At, 61.72.Cc, 81.40.Gh

Ti/Al/Mo/Au Ohmic contacts to all-binary AlN/GaN high electron mobility transistors

Liang Wang, Ilesanmi Adesida, Amir M. Dabiran, Andrew M. Wowchak, and Peter P. Chow

Appl. Phys. Lett. 93, 032109 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Electrical and microstructural characterizations of the Ti/Al/Mo/Au Ohmic contacts to ultrathin AlN/GaN heterostructures were carried out. It was found that as-deposited contacts had linear I-V behavior due to high tunneling current across the thin AlN barrier. A contact resistance of 0.455  Omega mm was obtained for samples annealed at 800 °C without any premetallization plasma treatment. Transmission electron microscopy studies showed that despite the use of Ti, the AlN layer remained intact. Mushroom-shaped TiN protrusions were formed only along threading dislocations, which terminated in the AlN layer. The TiN protrusions acted as metal plugs/spikes thereby aiding carrier transport.
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85.30.Tv, 85.75.Hh

Isotope disorder of phonons in GaN and its beneficial effect on high power field effect transistors

Jacob B. Khurgin, Debdeep Jena, and Yujie J. Ding

Appl. Phys. Lett. 93, 032110 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We analyze the influence of isotope disorder on longitudinal optical (LO) phonon modes in GaN and then study the scattering by disordered LO phonons in the channel of high power transistor. Results indicate that as a larger number of LO phonons gets excited, a more efficient cooling of electrons can be accomplished and most of the spurious hot phonon effects can be mitigated leading to significant improvement in the saturation velocity. To the best of our knowledge this is the first ever example of disorder playing constructive role in the performance of room-temperature electronic devices.
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85.30.Tv

Studies on the Bi/Si(100)−(2×1) interface

A. Bannani, C. A. Bobisch, and R. Möller

Appl. Phys. Lett. 93, 032111 (2008) (3 pages)

Online Publication Date: 25 July 2008

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Epitaxial Bi(111) films on the Si(100)−(2×1) surface were studied by two different scanning probe techniques, to obtain information on the buried interface. Ballistic electron emission microscopy reveals that the transmission across the Schottky barrier depends on the type of substrate terrace. The thermovoltage in scanning tunneling microscopy exhibits alternating signals for substrate step edges, which can be related to SA and SB steps, characteristic for the uncovered Si(100)−(2×1) surface. In addition to information about the growth mode of Bi, it was found that typical features of the Si(100)−(2×1) surface reconstruction are maintained.
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68.35.bg, 73.30.+y, 73.40.Ns

Repeated epitaxial growth and transfer of arrays of patterned, vertically aligned, crystalline Si wires from a single Si(111) substrate

Joshua M. Spurgeon, Katherine E. Plass, Brendan M. Kayes, Bruce S. Brunschwig, Harry A. Atwater, and Nathan S. Lewis

Appl. Phys. Lett. 93, 032112 (2008) (3 pages)

Online Publication Date: 25 July 2008

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Multiple arrays of Si wires were sequentially grown and transferred into a flexible polymer film from a single Si(111) wafer. After growth from a patterned, oxide-coated substrate, the wires were embedded in a polymer and then mechanically separated from the substrate, preserving the array structure in the film. The wire stubs that remained were selectively etched from the Si(111) surface to regenerate the patterned substrate. Then the growth catalyst was electrodeposited into the holes in the patterned oxide. Cycling through this set of steps allowed regrowth and polymer film transfer of several wire arrays from a single Si wafer.
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81.05.Cy, 81.07.Vb, 82.65.+r

p-channel thin-film transistor using p-type oxide semiconductor, SnO

Yoichi Ogo, Hidenori Hiramatsu, Kenji Nomura, Hiroshi Yanagi, Toshio Kamiya, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 93, 032113 (2008) (3 pages)

Online Publication Date: 25 July 2008

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This paper reports that among known p-type oxide semiconductors, tin monoxide (SnO) has a high hole mobility and produces good p-type oxide thin-film transistors (TFTs). Device-quality SnO films were grown epitaxially on (001) yttria-stabilized zirconia substrates at 575  °C by pulsed laser deposition. These exhibited a Hall mobility of 2.4  cm2  V−1  s−1 at room temperature. Top-gated TFTs, using epitaxial SnO channels, exhibited field-effect mobilities of 1.3  cm2  V−1  s−1, on/off current ratios of ~102, and threshold voltages of 4.8  V.
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85.30.Tv, 81.15.Fg

Effects of the compensation level on the carrier lifetime of crystalline silicon

S. Dubois, N. Enjalbert, and J. P. Garandet

Appl. Phys. Lett. 93, 032114 (2008) (3 pages)

Online Publication Date: 25 July 2008

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This study focuses on the evolution of the carrier lifetime with the compensation level in crystalline silicon. Especially we show that an increase in the compensation level reduces the recombination strength of doping species and of some metal impurities. These theoretical results are confirmed by the chemical and electrical characterizations of strongly compensated multicrystalline silicon wafers. These results are of paramount importance since an accurate control of the compensation level can lead to strong improvements in silicon solar cells efficiencies.
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72.20.Jv, 72.80.Cw, 61.72.uf, 61.72.sd, 81.05.Cy
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MAGNETISM AND SUPERCONDUCTIVITY

Piezoelectric disks used as metamaterial inclusions

O. Acher, M. Ledieu, A. Bardaine, and F. Levassort

Appl. Phys. Lett. 93, 032501 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The permeability of inclusions consisting of commercially available piezoelectric disks was investigated, leading to the observation of several resonances in the 100  MHz–3  GHz range. This could be described through a simple analytical relation, and the inclusions were deemed attractive for manufacturing metamaterials with negative permeabilities over a significant frequency range. Moreover, they can be used as reference permeability samples.
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77.65.-j, 84.40.-x, 77.22.Ch

Effect of magnetic field on domain-wall structures in two antiferromagnetically coupled Co/Pt multilayers

Z. Y. Liu, N. Li, F. Zhang, B. Xu, J. L. He, D. L. Yu, Y. J. Tian, and G. H. Yu

Appl. Phys. Lett. 93, 032502 (2008) (3 pages)

Online Publication Date: 23 July 2008

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In antiferromagnetically coupled [Pt  (5  Å)/Co  (4  Å)]4/NiO  (11  Å)/[Co  (4  Å)/Pt  (5  Å)]4 multilayer with perpendicular anisotropy, net ferromagnetic stripes are created in demagnetized state between the relatively shifted domain walls in the two Co/Pt multilayers owing to the competition between magnetostatic and exchange energies. With an external field applied antiparallel to the wall magnetization, involvement of Zeeman energy of net ferromagnetic stripes in the competition makes the net ferromagnetic stripes shrink, and the stripe width varies with field in an inversely proportional way in the low field range.
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75.70.Cn, 75.60.Ch, 75.50.Cc, 75.50.Ee, 75.30.Gw, 75.60.Ej

Critical fields and anisotropy of NdFeAsO0.82F0.18 single crystals

Ying Jia, Peng Cheng, Lei Fang, Huiqian Luo, Huan Yang, Cong Ren, Lei Shan, Changzhi Gu, and Hai-Hu Wen

Appl. Phys. Lett. 93, 032503 (2008) (3 pages)

Online Publication Date: 23 July 2008

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By using flux method, we have grown single crystals of NdFeAsO0.82F0.18 at ambient pressures. Resistive measurements reveal a surprising discovery that the anisotropy Gamma=(mc/mab)1/2 is below 5, which is much smaller than the theoretically calculated value. The data measured up to 400  K show a curved feature, which prevents a conjectured linear behavior for an unconventional metal. The upper critical fields determined based on the Werthamer–Helfand–Hohenberg formula [N. R. Werthamer et al., Phys. Rev. 147, 295 (1966)] are H<sub>c2</sub><sup>ab</sup>(T=0  K)[approximate]  304  T and H<sub>c2</sub><sup>c</sup>(T=0  K)[approximate]62–70  T. These high values indicate very encouraging applications of the new superconductors.
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74.10.+v, 74.70.-b, 74.25.Fy, 74.25.Ha

Ultrafast optical control of coercivity in GaMnAs

K. C. Hall, J. P. Zahn, A. Gamouras, S. March, J. L. Robb, X. Liu, and J. K. Furdyna

Appl. Phys. Lett. 93, 032504 (2008) (3 pages)

Online Publication Date: 24 July 2008

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Femtosecond optical control of the magnetization and coercive field is demonstrated in GaMnAs using time-resolved magneto-optical Kerr effect techniques. These experiments reveal a near-complete, subpicosecond collapse of the hysteresis loop, consistent with femtosecond demagnetization. On longer time scales (~300  ps) an increase in coercivity is observed, attributed to hole-mediated enhancement of the domain wall energy.
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75.60.Ej, 75.60.Ch, 78.47.jc, 75.50.Pp, 78.20.Ls

Direct chemical synthesis of high coercivity air-stable SmCo nanoblades

C. N. Chinnasamy, J. Y. Huang, L. H. Lewis, B. Latha, C. Vittoria, and V. G. Harris

Appl. Phys. Lett. 93, 032505 (2008) (3 pages)

Online Publication Date: 25 July 2008

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Ferromagnetic air-stable SmCo nanoparticles have been produced directly using a one-step chemical synthesis method. X-ray diffraction studies confirmed the formation of hexagonal SmCo5 as a dominant phase. High resolution transmission electron microscopy confirms the presence of uniform, anisotropic bladelike nanoparticles approximately 10  nm in width and 100  nm in length. Values of the intrinsic coercivity and the magnetization in the as-synthesized particles are 6.1  kOe and 40  emu/g at room temperature and 8.5  kOe and 44  emu/g at 10  K, respectively. This direct synthesis process is environmentally friendly and is readily scalable to large volume synthesis to meet the needs for the myriad of advanced permanent magnet applications.
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75.60.Ej, 75.50.Tt, 75.50.Vv, 75.50.Ww, 75.50.Cc, 61.66.Dk

Granular L10 FePt:TiO2 (001) nanocomposite thin films with 5  nm grains for high density magnetic recording

Y. F. Ding, J. S. Chen, B. C. Lim, J. F. Hu, B. Liu, and G. Ju

Appl. Phys. Lett. 93, 032506 (2008) (3 pages)

Online Publication Date: 25 July 2008

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FePt:TiO2 (001) thin films were deposited on CrRu/MgO underlayers by dc magnetron cosputtering. The effects of TiO2 content on microstructure and magnetic properties of the epitaxial FePt (001) films were studied. Experimental results showed that even with 20  vol  % TiO2 doping, FePt films could keep a (001) preferred orientation and perpendicular anisotropy. The FePt:TiO2 (001) film with 5  nm grain size, adjustable coercivity, and reduced exchange coupling was obtained by doping 20  vol  % TiO2 into FePt film, showing great potential as low noise ultrahigh density perpendicular magnetic recording media.
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75.70.Ak, 75.50.Ss, 75.30.Gw, 81.15.Cd, 68.55.jm, 61.72.-y
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DIELECTRICS AND FERROELECTRICITY

Low voltage operating InGaZnO4 thin film transistors using high-k MgO–Ba0.6Sr0.4TiO3 composite gate dielectric on plastic substrate

Dong Hun Kim, Nam Gyu Cho, Ho-Gi Kim, Hyun-Suk Kim, Jae-Min Hong, and Il-Doo Kim

Appl. Phys. Lett. 93, 032901 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The authors report on the dielectric and leakage current properties of room temperature grown MgO-Ba0.6Sr0.4TiO3 (MgO-BST) composite thin films to be utilized InGaZnO4 thin films transistors (TFTs) fabricated on a polyethylene terephthalate (PET) substrate. The InGaZnO4 TFTs with MgO-BST gate dielectrics exhibited low operation voltage of 4  V, high on/off current ratio of 4.13×106, and high field effect mobility of 10.86  cm2/V  s. These results verify that a room temperature grown MgO-BST gate dielectric is a good candidate for producing high performance InGaZnO4 TFTs on plastic substrates.
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85.30.Tv

Dielectric and polarization experiments in high loss dielectrics: A word of caution

M. Maglione and M. A. Subramanian

Appl. Phys. Lett. 93, 032902 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The recent quest for improved functional materials like high permittivity dielectrics and/or multiferroics has triggered an intense wave of research. Many materials have been checked for their dielectric permittivity or their polarization state. In this report, we call for caution when samples are simultaneously displaying an insulating behavior and a defect-related conductivity. Many oxides containing mixed valent cations or oxygen vacancies fall into this category. In such cases, most of the standard experiments may result in an effective high dielectric permittivity, which may not be related to ferroelectric polarization. Here we list a few examples of possible discrepancies between measured parameters and their expected microscopic origin.
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77.22.Ch, 77.22.Gm, 77.84.Bw, 77.80.-e, 61.72.jd, 77.22.Ej

Evolution of the neutron quasielastic scattering through the ferroelectric phase transition in 93%PbZn1/3Nb2/3O3–7%PbTiO3

G.-M. Rotaru, S. N. Gvasaliya, B. Roessli, S. Kojima, S. G. Lushnikov, and P. Günter

Appl. Phys. Lett. 93, 032903 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We show that the neutron diffuse scattering in relaxor ferroelectric (1−x)PZN−xPT (x=0.07) consists of two components. The first component is strictly elastic but extended in q-space and grows below 600  K. The second component, which was not reported before for the (1−x)PZN−xPT relaxor ferroelectrics, is quasielastic with a linewidth that has a similar temperature dependence as the width of the central peak observed by Brillouin spectroscopy. The temperature dependence of the susceptibility of the quasielastic scattering has a maximum at the ferroelectric transition.
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77.80.Bh, 77.84.Dy, 78.35.+c

Ferroelectric polarization and piezoelectric properties of layer-structured K0.5Bi4.5Ti4O15 single crystals

Yuji Noguchi, Muneyasu Suzuki, Yuuki Kitanaka, Shunsuke Teranishi, and Masaru Miyayama

Appl. Phys. Lett. 93, 032904 (2008) (3 pages)

Online Publication Date: 24 July 2008

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Single crystals of ferroelectric K0.5Bi4.5Ti4O15 with a Bi-layered structure were grown by the flux method, and the properties of polarization hysteresis, piezoelectric strain, and leakage current were investigated along the polar a axis at 25  °C. K0.5Bi4.5Ti4O15 crystals exhibited a large remanent polarization of 31  µC/cm2, which suggests that K0.5Bi4.5Ti4O15 has the largest spontaneous polarization among Bi layer-structured ferroelectrics with four TiO6 layers in the perovskite blocks. Strain measurements showed that the piezoelectric strain constant was 31  pm/V.
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77.80.Dj, 77.22.Ej, 77.84.Dy, 77.65.-j, 81.10.Dn

Epitaxy of single crystalline PrO2 films on Si(111)

T. Weisemoeller, C. Deiter, F. Bertram, S. Gevers, A. Giussani, P. Zaumseil, T. Schroeder, and J. Wollschläger

Appl. Phys. Lett. 93, 032905 (2008) (3 pages)

Online Publication Date: 24 July 2008

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A film of praseodymium sesquioxide with hexagonal structure, that has been deposited on Si(111) by molecular beam epitaxy, was annealed in oxygen atmosphere to obtain a PrO2 film for improved heteroepitaxy as buffer dielectric for alternative semiconductor layer integration. The film structure is characterized by x-ray diffraction and x-ray reflectometry. The film is single crystalline with Fm[overline 3]m (fluorite) structure. It is B oriented with respect to Si and has lattice constants close to bulk PrO2. The cubic lattice of the PrO2 film is slightly distorted due to residual oxygen vacancies which increase the diameter of Pr ions.
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68.55.-a, 68.55.J-, 68.55.Ln
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NANOSCALE SCIENCE AND DESIGN

Device study, chemical doping, and logic circuits based on transferred aligned single-walled carbon nanotubes

Chuan Wang, Koungmin Ryu, Alexander Badmaev, Nishant Patil, Albert Lin, Subhasish Mitra, H.-S. Philip Wong, and Chongwu Zhou

Appl. Phys. Lett. 93, 033101 (2008) (3 pages)

Online Publication Date: 21 July 2008

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In this paper, high-performance back-gated carbon nanotube field-effect transistors based on transferred aligned carbon nanotubes were fabricated and studies found that the on/off ratio can reach 107 and the current density can reach 1.6  µA/µm after electrical breakdown. In addition, chemical doping with hydrazine was used to convert the p-type aligned nanotube devices into n-type. These devices were further utilized to demonstrate various logic circuits, including p-type metal-oxide-semiconductor inverters, diode-loaded inverters, complementary metal-oxide-semiconductor inverters, NAND, and NOR gates. This approach could work as the platform for future nanotube-based nanoelectronics.
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85.35.Kt, 85.30.Tv, 84.30.Sk, 85.40.-e, 85.30.Kk, 85.40.Ry

Back-gate ZnO nanowire field-effect transistors each with a top Omega shaped Au contact

W. Q. Yang, L. Dai, R. M. Ma, C. Liu, T. Sun, and G. G. Qin

Appl. Phys. Lett. 93, 033102 (2008) (3 pages)

Online Publication Date: 21 July 2008

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We have fabricated depletion and enhancement modes (D-mode and E-mode) back-gate metal-insulator-semiconductor field-effect-transistors (MISFETs), using two kinds of ZnO nanowires (NWs) labeled as A and B, respectively. The NWs A and B were synthesized via the vapor phase transport method with ZnO/C admixture and Zn as the sources, respectively. Each of the MISFETs has a top Omega shaped Au contact on the conductive channel. Compared to that without any top Au contact, the on/off ratio (~106) of the ZnO NW A MISFET increases by a factor of 103, and is the highest one among the back-gate ZnO NW MISFETs ever reported; while the ZnO NW B MISFET changes from D-mode to E-mode when a top Au contact is added. The effects of the Au/ZnO NW contacts on the performances of the NW A and B MISFETs were discussed.
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85.30.Tv

Chromium and tantalum site substitution patterns in Ni3Al  (L12) gamma[prime]-precipitates

Christopher Booth-Morrison, Zugang Mao, Ronald D. Noebe, and David N. Seidman

Appl. Phys. Lett. 93, 033103 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The site substitution behavior of Cr and Ta in the Ni3Al  (L12)-type gamma[prime]-precipitates of a Ni–Al–Cr–Ta alloy is investigated by atom-probe tomography (APT) and first-principles calculations. Measurements of the gamma[prime]-phase composition by APT suggest that Al, Cr, and Ta share the Al sublattice sites of the gamma[prime]-precipitates. The calculated substitutional energies of the solute atoms at the Ni and Al sublattice sites indicate that Ta has a strong preference for the Al sites, while Cr has a weak Al site preference. Furthermore, Ta is shown to replace Cr at the Al sublattice sites of the gamma[prime]-precipitates, altering the elemental phase partitioning behavior of the Ni–Al–Cr–Ta alloy.
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71.15.Mb, 64.75.Op, 82.30.Hk

Conductivity enhancement of carbon nanotube composites by electrolyte addition

Hui-Ching Li, Sheng-Yi Lu, Sen-Hong Syue, Wen-Kuang Hsu, and Shih-Chin Chang

Appl. Phys. Lett. 93, 033104 (2008) (3 pages)

Online Publication Date: 23 July 2008

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The conductivity of carbon nanotubes and polyvinyl alcohol composites is significantly improved by addition of Fe2(SO4)3. The coordinated cations between nanotubes play a crucial role in lowering intertube hopping magnitude.
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81.05.Tp, 61.48.De

Silicon nanowires for rechargeable lithium-ion battery anodes

Kuiqing Peng, Jiansheng Jie, Wenjun Zhang, and Shuit-Tong Lee

Appl. Phys. Lett. 93, 033105 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Large-area, wafer-scale silicon nanowire arrays prepared by metal-induced chemical etching are shown as promising scalable anode materials for rechargeable lithium battery. In addition to being low cost, large area, and easy to prepare, the electroless-etched silicon nanowires (SiNWs) have good conductivity and nanometer-scale rough surfaces; both features facilitate charge transport and insertion/extraction of Li ions. The electroless-etched SiNWs anode showed larger charge capacity and longer cycling stability than the conventional planar-polished Si wafer.
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82.45.Yz, 68.47.Fg, 82.47.Aa, 82.45.Fk, 82.45.Vp, 73.63.Nm

Precise in situ thickness analysis of epitaxial graphene layers on SiC(0001) using low-energy electron diffraction and angle resolved ultraviolet photoelectron spectroscopy

C. Riedl, A. A. Zakharov, and U. Starke

Appl. Phys. Lett. 93, 033106 (2008) (3 pages)

Online Publication Date: 23 July 2008

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We demonstrate an easy and practical method for the thickness analysis of epitaxial graphene on SiC(0001) that can be applied continuously during the preparation procedure. Fingerprints in the spot intensity spectra in low energy electron diffraction (LEED) allow for the exact determination of the number of layers for the first three graphene layers. The LEED data have been correlated with the electronic bandstructure around the [overline K]-point of the graphene Brillouin zone as investigated by laboratory based angle resolved ultraviolet photoelectron spectroscopy using He II excitation. The morphology and homogeneity of the graphene layers can be analyzed by low energy electron microscopy.
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68.55.jd, 61.46.-w, 79.60.Bm

Carrier dynamics of type-II InAs/GaAs quantum dots covered by a thin GaAs1−xSbx layer

Wen-Hao Chang, Yu-An Liao, Wei-Ting Hsu, Ming-Chih Lee, Pei-Chin Chiu, and Jen-Inn Chyi

Appl. Phys. Lett. 93, 033107 (2008) (3 pages)

Online Publication Date: 23 July 2008

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Carrier dynamics of InAs/GaAs quantum dots (QDs) covered by a thin GaAs1−xSbx layer were investigated by time-resolved photoluminescence (PL). Both the power dependence of PL peak shift and the long decay time constants confirm the type-II band alignment at the GaAsSb–InAs interface. Different recombination paths have been clarified by temperature dependent measurements. At lower temperatures, the long-range recombination between the QD electrons and the holes trapped by localized states in the GaAsSb layer is important, resulting in a non-single-exponential decay. At higher temperatures, optical transitions are dominated by the short-range recombination with the holes confined to the band-bending region surrounding the QDs.
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72.20.Jv, 72.80.Ey, 78.55.Cr, 78.66.Fd

Resistance-pressure sensitivity and a mechanism study of multiwall carbon nanotube networks/poly(dimethylsiloxane) composites

C. H. Hu, C. H. Liu, L. Z. Chen, Y. C. Peng, and S. S. Fan

Appl. Phys. Lett. 93, 033108 (2008) (3 pages)

Online Publication Date: 23 July 2008

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In this work, we explored the electrical resistance-pressure sensitivity of multiwall carbon nanotube (MWNT) networks/poly(dimethylsiloxane) (PDMS) composites and proposed a deformation-induced property transition mechanism of the nanotubes to explain this behavior. The thermoelectric coefficients of the MWNT networks/PDMS composites and MWNT mat under pressure were also measured and discussed to support our proposition. Our results revealed that the relative resistances of MWNT networks/PDMS composites with lower MWNT loadings are more sensitive on the applied pressure. Furthermore, the I-V characteristic of the MWNT networks/PDMS composites modulated with pressure on one side has shown a well rectified behavior.
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73.40.Ei, 72.80.Tm, 72.20.Pa, 81.05.Qk, 81.40.Lm, 62.20.F-

Electric charging and nanostructure formation in polymeric films using combined amplitude-modulated atomic force microscopy-assisted electrostatic nanolithography and electric force microscopy

Michael A. Reagan, Dmytro Kashyn, Shane Juhl, Richard A. Vaia, and Sergei F. Lyuksyutov

Appl. Phys. Lett. 93, 033109 (2008) (3 pages)

Online Publication Date: 24 July 2008

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A hybrid technique, combining lithography which exploits atomic force microscope tip manipulation with modified electric force microscopy was used to study surface electric charging (deposition and evolution) of polymethyl methacryalate and polystyrene films. Upon charging the films past a threshold voltage, two distinct regimes were observed: (1) stable feature formation related to electric breakdown and mass transport resulting in stable film deformation due to the negative surface charging (negative tip bias) and (2) no stable feature formation regime attributed to viscoelastic deformation of polymer surface followed by the surface relaxation in the case of positive surface charging (positive tip bias).
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73.61.Ph, 68.55.am, 61.41.+e, 81.16.Nd, 81.40.Lm, 62.20.F-

Ultrasensitive immunoassay for prostate specific antigen using scanning tunneling microscopy-based electrical detection

Jeong-Woo Choi, Byung-Keun Oh, Yong-Hark Jang, and Da-Yeon Kang

Appl. Phys. Lett. 93, 033110 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We characterized a vertically configured electrical detection system that used scanning tunneling microscopy (STM) to detect antigen-antibody binding. This technique could be used to easily construct a multiple measurement system in a protein chip. We utilized immunocomplexes comprised of our model protein, prostate specific antigen (PSA), corresponding antibody fragments, and gold nanoparticle-antibody conjugates. The electrical tunneling current between the STM tip and these complexes exhibited a peaklike pulse, the frequency of which depended on the surface density of the bound complexes. We could therefore quantitatively measure PSA concentrations as low as 10  fg/mL using periodogram analysis of this peak frequency.
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87.64.Dz, 87.85.Rs, 87.15.K-, 87.15.Fh, 87.15.Pc, 87.85.-d

Determination of the stiffness of cellulose nanowhiskers and the fiber-matrix interface in a nanocomposite using Raman spectroscopy

Rafeadah Rusli and Stephen J. Eichhorn

Appl. Phys. Lett. 93, 033111 (2008) (3 pages)

Online Publication Date: 25 July 2008

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The stiffness of 10 nm diameter cellulose nanowhiskers is reported. These whiskers are produced by acid hydrolysis. These whiskers are dispersed in epoxy resin and placed on the surface of a beam of the same material and deformed in tension and compression using a four-point bending device. By following the molecular deformation of the whiskers using Raman spectroscopy it is shown that, by theoretical models of their dispersion and matrix reinforcement, their stiffness can be derived. The effects of debonding, matrix yielding, and buckling of whiskers are also discussed using this method as a means for studying nanocomposite materials.
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81.05.Qk, 81.40.Jj, 62.20.D-, 81.40.Lm, 62.20.mq, 78.30.Ly

Ion bombardment effects on ZnO nanowires during plasma treatment

H.-W. Ra, K. S. Choi, C. W. Ok, S. Y. Jo, K. H. Bai, and Y. H. Im

Appl. Phys. Lett. 93, 033112 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We present the effects of ion bombardment on ZnO nanowires caused by their exposure to an Ar inductively coupled plasma. The conductivity of the individual ZnO nanowire was increased in up to 3 orders of magnitude due to increase in both carrier concentration and mobility, with a substantial negative shift in the threshold gate voltage also being observed. The drastic changes in the electrical properties were attributed to the decrease in species adsorbed on the surface, as well as to the increase in oxygen vacancies near the surface caused by ion bombardment.
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73.63.Nm, 52.77.-j, 68.43.-h, 68.49.Sf, 79.20.Rf, 72.20.Fr

Localized surface plasmon polaritons in Ag/SiO2/Ag plasmonic thermal emitter

Yi-Han Ye, Yu-Wei Jiang, Ming-Wei Tsai, Yi-Tsung Chang, Chia-Yi Chen, Dah-Ching Tzuang, Yi-Ting Wu, and Si-Chen Lee

Appl. Phys. Lett. 93, 033113 (2008) (3 pages)

Online Publication Date: 25 July 2008

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The reflection dispersion relation and emission spectra of Ag/SiO2/Ag trilayer plasmonic thermal emitters with different lattice constant and Ag line width were investigated. The top Ag film is perforated with parallel line-shape hole array. The induced Ag/SiO2 surface plasmons at both top and bottom Ag/SiO2 interface are found coupled together. The coupling effect results in the localized surface plasmon polaritons confined at the top Ag/SiO2 interface which exhibit the Fabry–Pérot resonance. The thermal emission peak position coincides with the reflection minimum in the dispersion relation and shifts to long wavelength as the Ag line width increases, which proves that the emission is due to the excitation of localized surface plasmon polaritons. Moreover, the emitted light is polarized perpendicular to the parallel metal lines.
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73.20.Mf, 71.36.+c, 61.66.Fn, 78.55.Hx, 68.55.A-

Room-temperature ferromagnetism in single crystal Fe1.7Ge thin films of high thermal stability grown on Ge(111)

R. Jaafar, Y. Nehme, D. Berling, J. L. Bubendorff, A. Mehdaoui, C. Pirri, G. Garreau, and C. Uhlaq-Bouillet

Appl. Phys. Lett. 93, 033114 (2008) (3 pages)

Online Publication Date: 25 July 2008

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We report on the epitaxial growth of ultrathin ferromagnetic Fe1.7Ge layers on Ge(111) wafer. These single crystal intermetallic layers adopt the InNi2 (B82) crystallographic structure. They are ferromagnetic with a Curie temperature well above room temperature. The interface between the ferromagnet layer and the Ge wafer is of high perfection. Interestingly, the annealing of the sample up to 300  °C alters neither the crystallographic structure, nor the interface quality, nor the magnetic properties but leads to a nearly perfect smoothening of the germanide layer surface. This high thermal robustness should open the way for the growth of fully epitaxial iron germanide/Ge hybrid structures.
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75.70.Cn, 68.35.Ct, 81.40.Gh, 75.30.Kz, 75.50.Bb, 75.70.Ak
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ORGANIC ELECTRONICS AND PHOTONICS

FREE

Effect of Ag interlayer on the optical and passivation properties of flexible and transparent Al2O3/Ag/Al2O3 multilayer

Jin-A. Jeong, Han-Ki Kim, and Min-Su Yi

Appl. Phys. Lett. 93, 033301 (2008) (3 pages)

Online Publication Date: 21 July 2008

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We report on the characteristics of a flexible Al2O3/Ag/Al2O3 multilayer passivation grown on a polyethylene terephthalate (PET) substrate as a function of Ag thickness. Due to the surface plasmon resonance (SPR) effects and the ductility of the Ag layer that is sandwiched between the dielectric Al2O3 layer, the flexible Al2O3/Ag/Al2O3 multilayer passivation exhibits a high transparency of 86.44% and improved flexibility at a Ag thickness of 10  nm. We found that SPR effects in the Ag layer occur at the transition region from distinct islands to a continuous film at a critical thickness (~10  nm). In addition, the water vapor transmission rate of the Al2O3/Ag/Al2O3/PET sample decreased as the thickness of the Ag layer increased. Using synchrotron x-ray scattering and field emission scanning electron microscopy, we suggest a possible mechanism to explain the SPR in the Ag layer of the flexible and transparent Al2O3/Ag/Al2O3 multilayer passivation.
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81.65.Rv, 68.65.Ac, 73.20.Mf, 81.40.Lm, 62.20.F-, 78.70.Ck
FREE

Multifolded polymer solar cells on flexible substrates

Yinhua Zhou, Fengling Zhang, Kristofer Tvingstedt, Wenjing Tian, and Olle Inganäs

Appl. Phys. Lett. 93, 033302 (2008) (3 pages)

Online Publication Date: 21 July 2008

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Arrays of reflective multijunction polymer solar cell were demonstrated by folding four separated cells fabricated on a single plastic substrate using conducting polymer poly(3, 4-ethylene-dioxythiophene):polystyrenesulfonate as an anode. The combination of flexible substrate and polymer solar cells (PSCs) makes the construction of multifolded PSCs on one substrate possible. The power conversion efficiency (PCE) of the multifolded reflective PSCs was enhanced by 62%±12% with the folded opening angle of 30° compared to the planar cells. In series connection of four solar cells, an open-circuit voltage (Voc) of 3.65  V was obtained.
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84.60.Jt
FREE

Origin of high mobility within an amorphous polymeric semiconductor: Space-charge-limited current and trap distribution

Dae Sung Chung, Dong Hoon Lee, Chanwoo Yang, Kipyo Hong, Chan Eon Park, Jong Won Park, and Soon-Ki Kwon

Appl. Phys. Lett. 93, 033303 (2008) (3 pages)

Online Publication Date: 21 July 2008

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To elucidate the origin of the high field-effect mobility ([approximate]0.02  cm2/V  s) of amorphous poly[(1,2-bis-(2[prime]-thienyl)vinyl-5[prime],5[double-prime]-diyl)-alt-(9,9-dioctyldecylfluorene-2,7-diyl], we investigated the current density–voltage (J-V) and mobility–voltage (µ-V) relationships as a function of temperature. By using the power law model and the Gaussian hopping model, we determined a characteristic trap energy of 67  meV, an energetic disorder parameter of 64  meV, and a total trap density of 2.5×1016  cm−3, comparable to that of poly(3-hexylthiophene). We conclude that the relatively low trap density, which originates from the grain-boundary-free amorphous nature of the semiconductor, enables this high field-effect mobility.
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72.20.Ht, 72.20.Ee, 72.80.Le, 72.80.Ng
FREE

Charge trapping induced current instability in pentacene thin film transistors: Trapping barrier and effect of surface treatment

T. Miyadera, S. D. Wang, T. Minari, K. Tsukagoshi, and Y. Aoyagi

Appl. Phys. Lett. 93, 033304 (2008) (3 pages)

Online Publication Date: 21 July 2008

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The current instability of pentacene thin film transistors is described by the energetic distribution of the barrier height for the trapping of mobile charges at the organic/insulator interface. The trapping energy was quantitatively analyzed by measuring the temperature dependence of current decay, which follows a stretched exponential function. The distribution of the barrier becomes higher and narrower by the use of a self assembled monolayer (SAM) on the insulator surface, whereas the pentacene film morphology has little influence on the trapping barriers. The increase in the barrier height in the SAM-treated device suppresses charge trapping, resulting in stable device operation.
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85.30.Tv
FREE

High mobility electron-conducting thin-film transistors by organic vapor phase deposition

C. Rolin, K. Vasseur, S. Schols, M. Jouk, G. Duhoux, R. Müller, J. Genoe, and P. Heremans

Appl. Phys. Lett. 93, 033305 (2008) (3 pages)

Online Publication Date: 21 July 2008

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In this letter, we report on the growth of thin films of N,N[prime]-ditridecylperylene-3,4,9,10-tetracarboxylic diimide (PTCDI-C13H27) by organic vapor phase deposition (OVPD). Uniform films are deposited with a material utilization efficiency of 59±4% and deposition rates up to 15  Å/s. Top-contact transistors based on OVPD-grown PTCDI-C13H27 show high n-type mobilities (up to 0.3  cm2/V  s) and reproducible characteristics. The influence of deposition parameters on electrical properties is discussed.
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85.30.Tv