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28 May 2013

Volume 113, Issue 20 (partial)

Issue Cover Spotlight Figure

J. Appl. Phys. 113, 204101 (2013); http://dx.doi.org/10.1063/1.4801881 (6 pages)

Methee Promsawat, Anucha Watcharapasorn, Hamel N. Tailor, Sukanda Jiansirisomboon, and Zuo-Guang Ye
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back to top Lasers, Optics, and Optoelectronics

Optical properties of cubic and rhombohedral GeTe

David J. Singh

J. Appl. Phys. 113, 203101 (2013); http://dx.doi.org/10.1063/1.4807638 (5 pages)

Online Publication Date: 23 May 2013

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Calculations of the optical properties of GeTe in the cubic NaCl and rhombohedral ferroelectric structures are reported. The rhombohedral ferroelectric distortion increases the band gap from 0.11 eV to 0.38 eV. Remarkably, substantial changes in optical properties are found even at high energies up to 5 eV. The results are discussed in relation to the bonding of GeTe and to phase change materials based on it.
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78.40.Fy Semiconductors
61.66.Fn Inorganic compounds
77.80.-e Ferroelectricity and antiferroelectricity
78.30.Hv Other nonmetallic inorganics

Characteristics of terahertz pulses from antireflective GaAs surfaces with nanopillars

Chul Kang, Jung Woo Leem, Joong Wook Lee, Jae Su Yu, and Chul-Sik Kee

J. Appl. Phys. 113, 203102 (2013); http://dx.doi.org/10.1063/1.4807407 (4 pages)

Online Publication Date: 23 May 2013

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We investigated the characteristics of terahertz pulses generated from antireflective GaAs surfaces with nanopillars under femtosecond laser excitation. Although the antireflective nanostructures contribute to the enhancement of free photocarrier excitation in GaAs, they could reduce the transient photocurrent density and advance the start time of the photocurrent decay. Thus, the relative amplitudes of the high-frequency spectral components of terahertz pulses increased, whereas the energies of the pulses decreased. However, we showed that thinly distributed nanopillar structures could generate a short terahertz pulse without a reduction in the pulse energy.
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78.70.Gq Microwave and radio-frequency interactions
68.47.Fg Semiconductor surfaces
72.40.+w Photoconduction and photovoltaic effects
72.80.Ey III-V and II-VI semiconductors
73.25.+i Surface conductivity and carrier phenomena

Electronically tunable aperiodic distributed feedback terahertz lasers

O. P. Marshall, S. Chakraborty, Md. Khairuzzaman, T. Folland, A. Gholinia, H. E. Beere, and D. A. Ritchie

J. Appl. Phys. 113, 203103 (2013); http://dx.doi.org/10.1063/1.4807636 (8 pages)

Online Publication Date: 23 May 2013

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Focussed ion beam milling can be used to introduce aperiodic distributed feedback (ADFB) gratings into fully packaged, operational terahertz (THZ) quantum cascade lasers to achieve electronically controlled, discretely tunable laser emission. These aperiodic gratings—designed using computer-generated hologram techniques—consist of multiple slits in the surface plasmon waveguide, distributed along the length of the laser cavity. Tuning behaviour and output power in ADFB lasers operating around 2.9 THz are investigated with a variety of slit dimensions and grating scales. Mode selectivity and grating losses are found to be strongly dependent on milling depth into the upper waveguide layers, dramatically increasing as the metallic layers are penetrated, then rising more slowly with deeper milling into the laser active region. Grating scale and placement along the laser cavity length are also shown to influence mode selection.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Fc Modulation, tuning, and mode locking
42.40.Eq Holographic optical elements; holographic gratings
42.40.Jv Computer-generated holograms

First-principle prediction of single-carrier avalanche multiplication in chalcopyrite semiconductors

O. Rubel and A. Darbandi

J. Appl. Phys. 113, 203104 (2013); http://dx.doi.org/10.1063/1.4807650 (7 pages)

Online Publication Date: 23 May 2013

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A critical requirement for high gain and low noise avalanche photodiodes is the single-carrier avalanche multiplication. We propose that the single-carrier avalanche multiplication can be achieved in materials with a limited width of the valence band resulting in a restriction of kinetic energy for holes while allowing electrons to participate in the multiplication cascade. This feature of the electric structure is not common to the majority of technologically relevant semiconductors, but it can be anticipated in chalcopyrite Cu(AlGa)Se2 alloys based on the presented electric structure calculations.
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85.60.Dw Photodiodes; phototransistors; photoresistors

Threshold improvement in uniformly lying helix cholesteric liquid crystal laser using auxiliary π-conjugated polymer active layer

Hiroyuki Yoshida, Yusuke Shiozaki, Yo Inoue, Masaya Takahashi, Yasuhiro Ogawa, Akihiko Fujii, and Masanori Ozaki

J. Appl. Phys. 113, 203105 (2013); http://dx.doi.org/10.1063/1.4807402 (5 pages)

Online Publication Date: 23 May 2013

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We propose a device structure to lower the lasing threshold of a uniformly lying helix cholesteric liquid crystal (ChLC) laser. We place a π-conjugated polymer active layer beneath the ChLC layer to provide auxiliary gain, and demonstrate an improvement in the lasing threshold by a factor of 2.3. We also perform finite difference time domain calculations coupled with rate equations for a four-level system, and clarify the effect of the additional active layer on both the photonic density of states and the inversion population density. Although the addition of an extra layer lowers the photonic density of states, the gain provided by the auxiliary layer is sufficient to overcome the losses and decrease the lasing threshold. Our concept is useful for obtaining high-performance ChLC lasers.
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42.55.-f Lasers
42.70.Df Liquid crystals
42.70.Hj Laser materials
42.70.Jk Polymers and organics
61.30.-v Liquid crystals
02.70.Bf Finite-difference methods
back to top Plasmas and Electrical Discharges

Hydrodynamics of the molten metal in a vacuum arc cathode spot at near-threshold currents

G. A. Mesyats and N. M. Zubarev

J. Appl. Phys. 113, 203301 (2013); http://dx.doi.org/10.1063/1.4807303 (4 pages)

Online Publication Date: 22 May 2013

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The extrusion of the molten metal from a microcrater formed on a metal cathode during the operation of a vacuum arc is considered. The problem is thought to be similar to the classical hydrodynamic problem of a liquid drop impact on a solid surface. Based on this analogy, the conditions are analyzed under which the liquid will change its regular behavior (spreading over the cathode surface) into a singular behavior (formation of microjets and droplets). It is shown that the conditions realized in vacuum arc cathode spots at near-threshold currents are close to the threshold conditions for splashing of the molten metal. This points to a considerable contribution of hydrodynamic processes to the self-sustained operation of a vacuum arc and, in particular, gives grounds to relate the existence of a threshold arc current to the existence of a splashing threshold for liquid metal.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Wq Discharge in liquids and solids
52.75.-d Plasma devices

Breathing oscillations in enlarged cylindrical-anode-layer Hall plasma accelerator

S. F. Geng, D. L. Tang, C. X. Wang, R. K. Y. Fu, X. M. Qiu, and Paul K. Chu

J. Appl. Phys. 113, 203302 (2013); http://dx.doi.org/10.1063/1.4807584 (4 pages)

Online Publication Date: 23 May 2013

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Breathing oscillations in the discharge of an enlarged cylindrical-anode-layer Hall plasma accelerator are investigated by three-dimensional particle-in-cell (PIC) simulation. Different from the traditional breathing mode in a circular Hall plasma accelerator, the bulk plasma oscillation here is trigged by the potential barrier generated by the concentrated ion beam and substantial enough to compete with the anode voltage. The electric field near the anode is suppressed by the potential barrier thereby decreasing the electron density by ∼36%. The discharge is restored to the normal level after the concentrated beam explodes and then it completes one cycle of electro-driven breathing oscillation. The breathing mode identified by the PIC simulation has a frequency range of ∼156 kHz–∼250 kHz and does not vary monotonically with the discharge voltage.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.65.Rr Particle-in-cell method
52.75.Di Ion and plasma propulsion
52.80.Qj Explosions; exploding wires
29.20.Ej Linear accelerators
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
back to top Structural, Mechanical, Thermodynamic, and Optical Properties of Condensed Matter

Effects of pressure, temperature, and hydrogen during graphene growth on SiC(0001) using propane-hydrogen chemical vapor deposition

A. Michon, S. Vézian, E. Roudon, D. Lefebvre, M. Zielinski, T. Chassagne, and M. Portail

J. Appl. Phys. 113, 203501 (2013); http://dx.doi.org/10.1063/1.4806998 (8 pages)

Online Publication Date: 22 May 2013

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Graphene growth from a propane flow in a hydrogen environment (propane-hydrogen chemical vapor deposition (CVD)) on SiC differentiates from other growth methods in that it offers the possibility to obtain various graphene structures on the Si-face depending on growth conditions. The different structures include the (6√3 × 6√3)-R30° reconstruction of the graphene/SiC interface, which is commonly observed on the Si-face, but also the rotational disorder which is generally observed on the C-face. In this work, growth mechanisms leading to the formation of the different structures are studied and discussed. For that purpose, we have grown graphene on SiC(0001) (Si-face) using propane-hydrogen CVD at various pressure and temperature and studied these samples extensively by means of low energy electron diffraction and atomic force microscopy. Pressure and temperature conditions leading to the formation of the different structures are identified and plotted in a pressure-temperature diagram. This diagram, together with other characterizations (X-ray photoemission and scanning tunneling microscopy), is the basis of further discussions on the carbon supply mechanisms and on the kinetics effects. The entire work underlines the important role of hydrogen during growth and its effects on the final graphene structure.
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81.05.ue Graphene
68.35.bp Fullerenes
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
79.60.Jv Interfaces; heterostructures; nanostructures
68.35.Ct Interface structure and roughness
61.48.Gh Structure of graphene

Anisotropic optical and thermoelectric properties of In4Se3 and In4Te3

Xingfu Li, Bin Xu, Gongqi Yu, Li Xue, and Lin Yi

J. Appl. Phys. 113, 203502 (2013); http://dx.doi.org/10.1063/1.4807312 (6 pages)

Online Publication Date: 22 May 2013

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The anisotropic optical and thermoelectric properties of In4Se3 and In4Te3 are studied by the first-principles calculation using the full-potential linearized augmented plane-wave method and the semiclassical Boltzmann theory. The optical properties show highly anisotropic in the energy range between 0.0 and 12.0 eV for In4Se3 and between 0.0 and 10.0 eV for In4Te3 while it is isotropic in the higher energy range for In4Se3. In contrast to S, the anisotropies of the electrical conductivities and power factors are great affected by the change of the temperature. Their anisotropies become larger along three directions with the growth of the temperature. S2σ/τ along the y direction is much higher than that along the x and z directions for In4Se3, which shows that the thermoelectric thin films with excellent performance can be obtained along the (010) surface. By studying the anisotropy of transport properties, we find that the transport properties of In4Se3 are better than that of In4Te3, which mainly comes from the small band gap of In4Se3. The anisotropy of S2σ/τ for In4Se3 is larger than that for In4Te3, and the anisotropy of S2σ/τ is mainly due to the anisotropy of σ/τ.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Jc Other crystalline inorganic semiconductors
73.50.Lw Thermoelectric effects
78.30.Hv Other nonmetallic inorganics
71.15.-m Methods of electronic structure calculations

Creation of freestanding wrinkled nano-films with desired deformation properties by controlling the surface morphology of a sacrificial layer

Hiroyuki Hirakata, Tomohiro Maruyama, Akio Yonezu, and Kohji Minoshima

J. Appl. Phys. 113, 203503 (2013); http://dx.doi.org/10.1063/1.4807579 (13 pages)

Online Publication Date: 23 May 2013

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Various wrinkle patterns can be formed due to the buckling of a stiff thin film on a compliant substrate. However, most wrinkled films previously reported were fixed on a large deformable substrate and thereby the potential deformability of the film was mechanically constrained by the substrate. In this study, we developed a technique for forming various wrinkled structures on the surface of a sacrificial resin layer. Since the sacrificial layer can be subsequently removed with a solvent, freestanding wrinkled films are created using the sacrificial layer. We found that a wrinkled structure is formed on the surface of the layer by applying a compressive strain to the resin layer at the appropriate moment during the hardening process. The wrinkle pattern depends on the curing time and the timing of the straining in two in-plane orthogonal directions. In addition to conventional stripe and labyrinth patterns by simple uniaxial and equi-biaxial strains, respectively, it was found that independent biaxial strains induce interesting structures, such as an orthogonally ordered wrinkle pattern and a nonsymmetrical buckling structure, in which the stripe array produced by the first straining remains and many finer wrinkles appear in each stripe by the second straining in the orthogonal direction. We conducted tensile experiments for 300-nm-thick freestanding Cu films having these wrinkled structures. The wrinkled nano-films have a variety of mechanical properties: the stripe structure has extremely high deformability (more than 10% strain) and reversibility, the labyrinth structure shows planar isotropic deformation, and the nonsymmetrical buckling structure has an anisotropic modulus and strength. Finite element analysis on the wrinkle structures revealed that the local stress concentration dominates the fracture limits.
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68.55.-a Thin film structure and morphology
81.07.Bc Nanocrystalline materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.46.-w Structure of nanoscale materials

Theoretical and experimental characterization of promising new scintillators: Eu2+ doped CsCaCl3 and CsCaI3

Mohit Tyagi, M. Zhuravleva, and C. L. Melcher

J. Appl. Phys. 113, 203504 (2013); http://dx.doi.org/10.1063/1.4807401 (9 pages)

Online Publication Date: 23 May 2013

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An integrated approach was used to characterize Eu2+ doped CsCaCl3 and CsCaI3 crystals theoretically and experimentally. The temperature dependence of photoluminescence excitation, emission, and decay time was studied to better understand the energy transport and migration mechanism in these materials. The broadening and redshift of emission with increasing temperature was explained for both crystals by simultaneous quenching of emission and interaction of emission states with lattice vibration. The unusual increase of photoluminescence decay time with increasing temperature was ascribed to the presence of states with a lowered radiative rate slightly above the emitting states. The electronic and optical properties were also calculated theoretically with the help of Density functional theory in order to explain the Eu2+ emission properties in these crystals. The calculation explains the better scintillation light output and proportionality in CsCaI3. The promising cross-luminescent efficiency of these materials is also explained with the help of electronic band structure and dispersion of the partial density of the states of constituent atoms. Despite structural anisotropy, the calculated optical properties of CsCaI3 are nearly isotropic, and therefore the synthesis of optically transparent polycrystalline ceramics may be possible.
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78.55.Hx Other solid inorganic materials
78.70.Ps Scintillation
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

Effect of silane/hydrogen ratio on microcrystalline silicon thin films by remote inductively coupled plasma

Y. N. Guo, D. Y. Wei, S. Q. Xiao, S. Y. Huang, H. P. Zhou, and S. Xu

J. Appl. Phys. 113, 203505 (2013); http://dx.doi.org/10.1063/1.4807404 (5 pages)

Online Publication Date: 23 May 2013

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Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by remote low frequency inductively coupled plasma (ICP) chemical vapor deposition system, and the effect of silane/hydrogen ratio on the microstructure and electrical properties of μc-Si:H films was systematically investigated. As silane/hydrogen ratio increases, the crystalline volume fraction Fc decreases and the ratio of the intensity of (220) peak to that of (111) peak drops as silane flow rate is increased. The FTIR result indicates that the μc-Si:H films prepared by remote ICP have a high optical response with a low hydrogen content, which is in favor of reducing light-induced degradation effect. Furthermore, the processing window of the phase transition region for remote ICP is much wider than that for typical ICP. The photosensitivity of μc-Si:H films can exceed 100 at the transition region and this ensures the possibility of the fabrication of microcrystalline silicon thin film solar cells with a open-circuit voltage of about 700 mV.
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73.61.Cw Elemental semiconductors
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
61.72.-y Defects and impurities in crystals; microstructure

Characteristics of ultrafast optical responses originating from non-equilibrium carrier transport in undoped GaAs/n-type GaAs epitaxial structures

Takayuki Hasegawa, Yoshihiro Takagi, Hideo Takeuchi, Hisashi Yamada, Masahiko Hata, and Masaaki Nakayama

J. Appl. Phys. 113, 203506 (2013); http://dx.doi.org/10.1063/1.4807405 (6 pages)

Online Publication Date: 23 May 2013

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We have investigated the characteristics of ultrafast optical responses originating from a carrier transport process in undoped GaAs/n-type GaAs (i-GaAs/n-GaAs) epitaxial structures with the use of a reflection-type pump-probe technique at room temperature. The built-in electric field in the i-GaAs top layer, whose strength is controlled by its thickness d, accelerates the transit of photogenerated carriers through the i-GaAs layer. We systematically observed that the decay time of a carrier-induced reflectivity change shortens with an increase in built-in electric field strength resulting from a decrease in d: 6.1, 12, and 28 kV/cm for d = 1200, 500, and 200 nm, respectively. In the i-GaAs/n-GaAs sample with d = 200 nm, which has the highest built-in electric field strength, the decay time is much shorter than the oscillation period of longitudinal optical (LO) phonon. From the spectrally resolved detection of the reflected light, it was found that the energy relaxation of the photogenerated carriers by the LO-phonon scattering hardly occurs in the i-GaAs layer, which indicates a quasiballistic transport. This finding demonstrates that the i-GaAs/n-GaAs structure with the non-equilibrium carrier transport process is useful for ultrafast optical applications.
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78.47.J- Ultrafast spectroscopy (<1 psec)
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport
73.50.Fq High-field and nonlinear effects
73.61.Ey III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Low temperature investigations and surface treatments of colloidal narrowband fluorescent nanodiamonds

E. Neu, F. Guldner, C. Arend, Y. Liang, S. Ghodbane, H. Sternschulte, D. Steinmüller-Nethl, A. Krueger, and C. Becher

J. Appl. Phys. 113, 203507 (2013); http://dx.doi.org/10.1063/1.4807398 (7 pages)

Online Publication Date: 23 May 2013

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We report fluorescence investigations and Raman spectroscopy on colloidal nanodiamonds (NDs) obtained via bead assisted sonic disintegration (BASD) of a polycrystalline chemical vapor deposition film. The BASD NDs contain in situ created silicon vacancy (SiV) centers. Whereas many NDs exhibit emission from SiV ensembles, we also identify NDs featuring predominant emission from a single bright SiV center. We demonstrate oxidation of the NDs in air as a tool to optimize the crystalline quality of the NDs via removing damaged regions resulting in a reduced ensemble linewidth as well as single photon emission with increased purity. We furthermore investigate the temperature dependent zero-phonon-line fine-structure of a bright single SiV center as well as the polarization properties of its emission and absorption.
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81.65.Mq Oxidation
61.72.jd Vacancies
78.30.Na Fullerenes and related materials
78.55.Hx Other solid inorganic materials
78.66.Tr Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
back to top Electronic Structure and Transport

Effect of growth oxygen pressure on anisotropic-strain-induced phase separation in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films

Bowen Zhi, Guanyin Gao, Zhen Huang, Lingfei Wang, Xuelian Tan, Pingfan Chen, and Wenbin Wu

J. Appl. Phys. 113, 203701 (2013); http://dx.doi.org/10.1063/1.4807293 (5 pages)

Online Publication Date: 22 May 2013

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The effect of deposition oxygen pressure (PO) on phase separation (PS) induced in epitaxial La0.67Ca0.33MnO3/NdGaO3(001) films was investigated. Fully oxygenated films grown at high PO are anisotropically strained. They exhibit PS over a wide temperature range, because of the large orthorhombicity of NdGaO3 substrates. The paramagnetic insulator-to-ferromagnetic metal (FM) and FM-to-antiferromagnetic insulator (AFI) transitions gradually shift to lower temperatures with decreasing PO. The AFI state is initially weakened (PO ≥ 30 Pa), but then becomes more robust against the magnetic field (PO < 30 Pa). The out-of-plane film lattice parameter increases with decreasing PO. For films grown at PO ≥ 30 Pa, the slight oxygen deficiency may enlarge the lattice unit cell, reduce the anisotropic strain, and suppress the AFI state. Films deposited at PO < 30 Pa instead experience an average compressive strain. The enhanced compressive strain and structural defects in the films may lead to the robust AFI state. These results aid our understanding of PS in manganite films.
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68.55.A- Nucleation and growth
68.60.-p Physical properties of thin films, nonelectronic
75.30.Gw Magnetic anisotropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
62.50.-p High-pressure effects in solids and liquids

Cu-substitution effect on thermoelectric properties of the TiNi-based shape memory alloys

B. Ramachandran, R. C. Tang, P. C. Chang, Y. K. Kuo, C. Chien, and S. K. Wu

J. Appl. Phys. 113, 203702 (2013); http://dx.doi.org/10.1063/1.4807397 (7 pages)

Online Publication Date: 23 May 2013

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We have studied the effects of Cu substitution on thermoelectric properties of Ti50Ni50-xCux (0 ≤ x ≤ 30 at. %) shape memory alloys by means of electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) measurements. From the electrical resistivity and Seebeck coefficient studies, it is found that the Cu substituted TiNi alloys show a metallic nature in the entire temperature range. However, thermal hysteresis behavior was observed in all the TiNi-based alloys near martensitic transition, which confirms the first order phase transition. Transformation starting temperature of B19′ martensite (Ms) is found to be decreased with increase in Cu substitution (x > 5), whereas that of B19 martensite (M′s) increased gradually with Cu content, and the thermal hysteresis behavior becomes weaker upon substitution of Cu. It is also found that the separation between B19 and B19′ phases in the 7.5% Cu doped TiNi alloy is clearly evident in the Seebeck coefficient measurement, which is not seen in the resistivity data. Finally, analysis of thermal conductivity reveals that the anomalous feature in κ at the B19 ↔ B19′ transformation for 7.5, 10, and 15% Cu-substituted TiNi alloys which can be mainly attributed to the electronic contribution, while a large anomalous peak observed at the B19 → B2 transformation in the warming process is due to change in the lattice thermal conductivity. The relative change in thermal conductivity (Δκ/κ) near martensitic transformation is found to be increased with increase in Cu content, reaches a giant value of 200% for 10% Cu-substituted TiNi alloy and then starts to decrease with further Cu substitution.
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72.15.Jf Thermoelectric and thermomagnetic effects
81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
66.70.Df Metals, alloys, and semiconductors
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Interfacial electronic structure of trimethyl-aluminum and water on an In0.20Ga0.80As(001)-4 × 2 surface: A high-resolution core-level photoemission study

T. W. Pi (皮敦文), H. Y. Lin (林孝于), T. H. Chiang (江宗鴻), Y. T. Liu (劉雅婷), G. K. Wertheim, J. Kwo (郭瑞年), and M. Hong (洪銘輝)

J. Appl. Phys. 113, 203703 (2013); http://dx.doi.org/10.1063/1.4807400 (5 pages)

Online Publication Date: 23 May 2013

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In atomic-layer deposition (ALD), organoaluminum as trimethyl-aluminum (TMA) on a freshly molecular beam epitaxy grown In0.20Ga0.80As(001)-4 × 2 surface has three forms: Al bonding with 1, 2, and 3 methyl groups. The ALD method of using one pulse (0.1 s) of TMA plus one pulse (0.1 s) of water was ineffective in passivating the surface, as demonstrated by the increased intensity of the reacted surface components with high numbers of pulses. The intact TMA was physisorbed on the trough In atoms, while the methyl-deficient precursors are either bridged with two As atoms or on the row-edge As atoms. After the water pulse on the TMA-covered surface, a bond in the bridged As atoms was scissored off to produce the As-Al-CH3 and As-OH, and the physisorbed TMA was unaffected. TMA removed some row In atoms, which allowed the In and Ga atoms in the second layer to form OH bonds after the water exposure. The appearance of the As-OH bonds may cause interfacial defect density (Dit) a peak at the midgap.
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73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
68.35.bg Semiconductors
61.50.Lt Crystal binding; cohesive energy
68.43.Mn Adsorption kinetics

Atomic and electronic structure of La2CoMnO6 on SrTiO3 and LaAlO3 substrates from first principles

Shuhui Lv, Zhongchang Wang, Mitsuhiro Saito, and Yuichi Ikuhara

J. Appl. Phys. 113, 203704 (2013); http://dx.doi.org/10.1063/1.4807410 (11 pages)

Online Publication Date: 23 May 2013

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Adhesion energies, atomic structures, electronic states, and bonding nature of the La2CoMnO6(001)/SrTiO3(001) and La2CoMnO6(001)/LaAlO3(001) interfaces are systematically investigated from first principles by taking into account strain effect, electron correlation effect, and polarity continuity. A total of sixteen candidate geometries are considered for each interface, and the fundamental impact of strain on interfacial atomic structures is found to be minor, but its electronic impact is significant. For the La2CoMnO6/SrTiO3 interface where La2CoMnO6 suffers tensile strain, the 3d states of Co and Mn overlap Fermi level, demonstrating a metallic nature for this interface. Electrons are found to be injected into the Ti of SrTiO3 at this interface and spread layers away from interface, inducing an ordering of the in-plane dxy orbital. On the other hand, the compression strained La2CoMnO6/LaAlO3 interface takes on a half-metallic nature with a large degree of hybridization of interfacial Mn 3d with O 2p at Fermi level. We also find an ordering of the out-of-plane dz2 orbital for the interfacial and sub-interfacial Mn atoms and an ordering of the pz orbital for the O neighboring Mn. By applying several analytic methods, we have thoroughly characterized the electronic structure and have determined the interfacial bonding to be covalent for the La2CoMnO6/SrTiO3 interface, yet mixed covalent and ionic for the La2CoMnO6/LaAlO3 interface.
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73.40.-c Electronic transport in interface structures
79.20.Kz Other electron-impact emission phenomena
68.35.Np Adhesion
71.15.-m Methods of electronic structure calculations
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Energy-band alignment of II-VI/Zn3P2 heterojunctions from x-ray photoemission spectroscopy

Jeffrey P. Bosco, David O. Scanlon, Graeme W. Watson, Nathan S. Lewis, and Harry A. Atwater

J. Appl. Phys. 113, 203705 (2013); http://dx.doi.org/10.1063/1.4807646 (8 pages)

Online Publication Date: 23 May 2013

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The energy-band alignments for zb-ZnSe(001)/α-Zn3P2(001), w-CdS(0001)/α-Zn3P2(001), and w-ZnO(0001)/α-Zn3P2(001) heterojunctions have been determined using high-resolution x-ray photoelectron spectroscopy via the Kraut method. Ab initio hybrid density functional theory calculations of the valence-band density of states were used to determine the energy differences between the core level and valence-band maximum for each of the bulk materials. The ZnSe/Zn3P2 heterojunction had a small conduction-band offset, ΔEC, of −0.03 ± 0.11 eV, demonstrating a nearly ideal energy-band alignment for use in thin-film photovoltaic devices. The CdS/Zn3P2 heterojunction was also type-II but had a larger conduction-band offset of ΔEC = −0.76 ± 0.10 eV. A type-III alignment was observed for the ZnO/Zn3P2 heterojunction, with ΔEC = −1.61 ± 0.16 eV indicating the formation of a tunnel junction at the oxide–phosphide interface. The data also provide insight into the role of the II-VI/Zn3P2 band alignment in the reported performance of Zn3P2 heterojunction solar cells.
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79.60.Jv Interfaces; heterostructures; nanostructures
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.20.At Surface states, band structure, electron density of states

Bipolar resistive switching properties of Ti-CuO/(hexafluoro-hexa-peri-hexabenzocoronene)-Cu hybrid interface device: Influence of electronic nature of organic layer

Bharti Singh, B. R. Mehta, Deepak Varandani, Govind, A. Narita, X. Feng, and K. Müllen

J. Appl. Phys. 113, 203706 (2013); http://dx.doi.org/10.1063/1.4807411 (7 pages)

Online Publication Date: 23 May 2013

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This study reports the change in the structural and junction properties of Ti-CuO-Cu structure on incorporation of a 2-dimensional (2D) organic layer comprising of n-type hexafluoro-hexa-peri-hexabenzocoronene (6F-HBC). A bipolar resistive switching is observed in the device having interface between sputter deposited copper oxide (CuO) and vacuum sublimated 6F-HBC hybrid interface. The CuO/6F-HBC hybrid interface exhibits rectifying I-V characteristics in complete contrast to the ohmic and rectifying characteristics of junctions based on individual 6F-HBC and CuO layers. Large change in resistive switching property from unipolar resistive switching in CuO/HBC to bipolar resistive switching in CuO/6F-HBC interface was observed. At the CuO/6F-HBC interface, C1s peak corresponding to fluorinated carbon is shifted by 0.68 eV towards higher binding energy (BE) side and O1s peak due to non-lattice oxygen is shifted by 0.6 eV towards lower BE, confirming the interaction of O2− ion in CuO with fluorinated carbon atoms in 6F-HBC at the hybrid interface. Correlation between conductive atomic force microscopy images and atomic force microscopy topography images, I-V characteristics in conducting, non-conducting, and pristine regions along with x-ray photoelectron spectroscopy results establishes the important role of hybrid interface to determining the resistive switching properties. This study demonstrates that the resistive switching and interface properties of a hybrid device based on inorganic and organic 2D materials can be modified by changing the electronic properties of organic layer by attaching suitable functional groups.
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73.40.Sx Metal-semiconductor-metal structures
81.15.Cd Deposition by sputtering
68.35.Ct Interface structure and roughness
68.37.-d Microscopy of surfaces, interfaces, and thin films
68.37.Ps Atomic force microscopy (AFM)
73.40.Ei Rectification
back to top Magnetism and Superconductivity

Nanorods of Co/Pd multilayers fabricated by glancing angle deposition for advanced media

Hao Su, Anusha Natarajarathinam, and Subhadra Gupta

J. Appl. Phys. 113, 203901 (2013); http://dx.doi.org/10.1063/1.4807168 (4 pages)

Online Publication Date: 22 May 2013

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Perpendicular anisotropy magnetic nanorods composed of Co/Pd multilayers have been successfully fabricated by glancing angle deposition (GLAD) in a planetary sputtering system. Co and Pd layer thickness, ratio, and bilayer number were optimized for both normal and GLAD depositions. Scanning electron micrographs estimated the nanorods to be about 12 nm in diameter. M-H loops showed that the coercivity for the GLAD nanorods increased from 1.3 kOe for the normally deposited continuous films to 2.9 kOe for the GLAD nanorod array, a 123% increase.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
75.75.Cd Fabrication of magnetic nanostructures
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Expanding the longitudinal magnetoimpedance sensor range by direct bias current

M. Ipatov, V. Zhukova, A. Zhukov, and J. Gonzalez

J. Appl. Phys. 113, 203902 (2013); http://dx.doi.org/10.1063/1.4807296 (6 pages)

Online Publication Date: 22 May 2013

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We investigated the effects of induced helical anisotropy and application of dc bias current IB on longitudinal magnetoimpedance (MI) in amorphous microwires both separately and together. We demonstrated that when both parameters are present, i.e., a dc bias current IB is applied to the microwire with induced helical anisotropy, the longitudinal MI sensor range can be considerably extended up to the fields considerably higher than its anisotropy field as the slope of MI curve dZ/dHE remains rather high. A highly asymmetric longitudinal MI dependence with a rather high slope at the zero-field point was obtained. Reversing the bias current IB causes reversal of the bias field direction and results in a mirroring of the MI dependence. This gives a possibility to determine both the sign and the magnitude of the external magnetic field. The obtained results can be used in development of the longitudinal MI sensors with increased sensitivity and/or range.
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07.55.-w Magnetic instruments and components

The role of the (111) texture on the exchange bias and interlayer coupling effects observed in sputtered NiFe/IrMn/Co trilayers

I. L. Castro, V. P. Nascimento, E. C. Passamani, A. Y. Takeuchi, C. Larica, M. Tafur, and F. Pelegrini

J. Appl. Phys. 113, 203903 (2013); http://dx.doi.org/10.1063/1.4804671 (10 pages)

Online Publication Date: 23 May 2013

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Magnetic properties of sputtered NiFe/IrMn/Co trilayers grown on different seed layers (Cu or Ta) deposited on Si (100) substrates were investigated by magnetometry and ferromagnetic resonance measurements. Exchange bias effect and magnetic spring behavior have been studied by changing the IrMn thickness. As shown by X-ray diffraction, Ta and Cu seed layers provoke different degrees of (111) fcc-texture that directly affect the exchange bias and indirectly modify the exchange spring coupling behavior. Increasing the IrMn thickness, it was observed that the coupling angle between the Co and NiFe ferromagnetic layers increases for the Cu seed system, but it reduces for the Ta case. The results were explained considering (i) different anisotropies of the Co and IrMn layers induced by the different degree of the (111) texture and (ii) the distinct exchange bias set at the NiFe/IrMn and IrMn/Co interfaces in both systems. The NiFe and Co interlayer coupling angle is strongly correlated with both exchange bias and exchange magnetic spring phenomena. It was also shown that the highest exchange bias field occurs when an unstressed L12 IrMn structure is stabilized.
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75.30.Et Exchange and superexchange interactions
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.15.Cd Deposition by sputtering
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Origin of ferromagnetism in transition metal doped BaTiO3

I. N. Apostolova, A. T. Apostolov, Safa Golrokh Bahoosh, and Julia M. Wesselinowa

J. Appl. Phys. 113, 203904 (2013); http://dx.doi.org/10.1063/1.4807412 (4 pages)

Online Publication Date: 23 May 2013

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We have calculated the temperature, magnetic field, and ion doping dependence of the magnetic and electric properties in Fe-doped BaTiO3 using a microscopic model and the Green's function technique. It is shown that the ferromagnetic and multiferroic properties observed at room temperature in Fe doped BaTiO3 could be due to the super exchange interactions between Fe3+ ions in different occupational sites associated with oxygen vacancies and to the exchange coupling of Fe ions with mixed valence, Fe3+ and Fe4+. There is a multiferroic region which depends strongly on the Fe-doping concentration.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
61.72.jd Vacancies
61.72.sd Impurity concentration

Co-existence of ferrimagnetism and spin-glass state in the spinel Co2SnO4

Subhash Thota and M. S. Seehra

J. Appl. Phys. 113, 203905 (2013); http://dx.doi.org/10.1063/1.4807294 (5 pages)

Online Publication Date: 23 May 2013

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The nature of magnetic ordering in the inverted spinel Co2SnO4 = [Co2+][Co2+Sn4+]O4 is investigated by measuring the temperature dependence of its magnetization (M) and ac-susceptibilities (χ′ and χ″) in different magnetic fields (H) using a superconducting quantum interference device magnetometer. The polycrystalline sample with a grain size of 3–5 μm was prepared by the solid-state route and characterized by x-ray diffraction and scanning electron microscopy. Above the ferrimagnetic Néel temperature TN = 41 K, χdc = M/H fits well with the Néel' expression for the two-sublattice model of ferrimagnetism. The ferrimagnetic ordering is suggested to result from different magnetic moments of Co2+ on the A sites (3.87 μB) and B sites (4.16 μB) and antiferromagnetic molecular field constants with magnitudes NAA = 13.6, NBB = 36.8, and NAB = 33.2. The temperature variations of χ′ and χ″ under various dc-bias fields suggest the existence of a spin-glass (SG) phase for T < TSG = 39.1 K in which only the transverse spin components are frozen below TSG. This co-existence of longitudinal ferrimagnetic order below TN = 41 K and transverse SG state below TSG = 39.1 K is suggested to result from the presence of non-magnetic Sn4+ ions on the B sites.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Ee Antiferromagnetics
75.50.Gg Ferrimagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.10.Nr Spin-glass and other random models
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