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6 Dec 2010

Volume 97, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 233101 (2010); http://dx.doi.org/10.1063/1.3523252 (3 pages)

Hoonkyung Lee, Marvin L. Cohen, and Steven G. Louie
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Systematic investigation of self-absorption and conversion efficiency of 6.7 nm extreme ultraviolet sources

Takamitsu Otsuka, Deirdre Kilbane, Takeshi Higashiguchi, Noboru Yugami, Toyohiko Yatagai, Weihua Jiang, Akira Endo, Padraig Dunne, and Gerry O’Sullivan

Appl. Phys. Lett. 97, 231503 (2010); http://dx.doi.org/10.1063/1.3526383 (3 pages) | Cited 10 times

Online Publication Date: 10 December 2010

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We have investigated the dependence of the spectral behavior and conversion efficiencies of rare-earth plasma extreme ultraviolet sources with peak emission at 6.7 nm on laser wavelength and the initial target density. The maximum conversion efficiency was 1.3% at a laser intensity of 1.6×1012 W/cm2 at an operating wavelength of 1064 nm, when self-absorption was reduced by use of a low initial density target. Moreover, the lower-density results in a narrower spectrum and therefore improved spectral purity. It is shown to be important to use a low initial density target and/or to produce low electron density plasmas for efficient extreme ultraviolet sources when using high-Z targets.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.50.Dg Plasma sources
42.72.Bj Visible and ultraviolet sources
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
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Imaging ellipsometry of graphene

Ulrich Wurstbauer, Christian Röling, Ursula Wurstbauer, Werner Wegscheider, Matthias Vaupel, Peter H. Thiesen, and Dieter Weiss

Appl. Phys. Lett. 97, 231901 (2010); http://dx.doi.org/10.1063/1.3524226 (3 pages) | Cited 8 times

Online Publication Date: 6 December 2010

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Imaging ellipsometry studies of graphene on SiO2/Si and crystalline GaAs are presented. We demonstrate that imaging ellipsometry is a powerful tool to detect and characterize graphene on any flat substrate. Variable angle spectroscopic ellipsometry is used to explore the dispersion of the optical constants of graphene in the visible range with high lateral resolution. In this way, the influence of the substrate on graphene’s optical properties can be investigated.
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78.67.Wj Optical properties of graphene
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Significant elastic anisotropy in Ti1−xAlxN alloys

Ferenc Tasnádi, Igor A. Abrikosov, Lina Rogström, Jonathan Almer, Mats P. Johansson, and Magnus Odén

Appl. Phys. Lett. 97, 231902 (2010); http://dx.doi.org/10.1063/1.3524502 (3 pages) | Cited 6 times

Online Publication Date: 6 December 2010

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Strong compositional-dependent elastic properties have been observed theoretically and experimentally in Ti1−xAlxN alloys. The elastic constant, C11, changes by more than 50% depending on the Al-content. Increasing the Al-content weakens the average bond strength in the local octahedral arrangements resulting in a more compliant material. On the other hand, it enhances the directional (covalent) nature of the nearest neighbor bonds that results in greater elastic anisotropy and higher sound velocities. The strong dependence of the elastic properties on the Al-content offers new insight into the detailed understanding of the spinodal decomposition and age hardening in Ti1−xAlxN alloys.
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81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dq Other elastic constants
62.65.+k Acoustical properties of solids
64.75.Op Phase separation and segregation in alloying
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging

Effect of substrate misorientation on the material properties of GaAs/Al0.3Ga0.7As tunnel diodes

H. W. Yu, E. Y. Chang, H. Q. Nguyen, J. T. Chang, C. C. Chung, C. I. Kuo, Y. Y. Wong, and W. C. Wang

Appl. Phys. Lett. 97, 231903 (2010); http://dx.doi.org/10.1063/1.3525158 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2010

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The effect of substrate misorientation on the material quality of the N++–GaAs/P++–AlGaAs tunnel diodes (TDs) grown on these substrates is investigated. It is found that the misorientation influences both surface roughness and interface properties of the N++–GaAs/P++–AlGaAs TDs. Smooth surface (rms roughness: 1.54 Å) and sharp interface for the GaAs/Al0.3Ga0.7As TDs were obtained when the (100) tilted 10° off toward [111] GaAs substrate was used. Besides, the oxygen content in N++–GaAs and P++–AlGaAs layers grown on the 10° off GaAs substrates was reduced due to the reduction of sticking coefficient and number of anisotropic sites.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Size-dependent strain in epitaxial (001) gadolinium-doped ceria nanoislands

Vyacheslav F. Solovyov, Marta Gibert, Teresa Puig, and Xavier Obradors

Appl. Phys. Lett. 97, 231904 (2010); http://dx.doi.org/10.1063/1.3527079 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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We report size-dependent strain in epitaxial gadolinium doped ceria nanoislands, which was determined by synchrotron x-ray diffraction. Reciprocal space sections of symmetric, (004) and asymmetric, (224) reflections are approximated by a model assuming size-dependent strain of the islands using real-space size distribution obtained by atomic force microscopy. We show that the islands smaller than 40 nm are subjected to a high level of lateral tensile strain and normal compression. The lateral to normal strain ratio determined from the reciprocal map analysis suggests that lateral tension is the primary stress generator, possibly due to oxygen vacancy ordering on the island-substrate interface.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology

Enhancing visibility of graphene on arbitrary substrates by microdroplet condensation

Hugo Gonçalves, Michael Belsley, Cacilda Moura, Tobias Stauber, and Peter Schellenberg

Appl. Phys. Lett. 97, 231905 (2010); http://dx.doi.org/10.1063/1.3527081 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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In order to take advantage of the enormous potential of graphene for future electronic microcircuits and other applications it is necessary to develop reliable, rapid, and widely applicable methods to visualize graphene-based structures. We report here on a microdroplet condensation technique, which allows for quick visual identification of graphene on a variety of substrates, including some which were previously considered unsuitable for the visualization of carbon layers. The technique should also be applicable to visualize artificially patterned graphene structures which are expected to be key technologically enabling components in electronic microcircuits and other applications.
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78.67.Wj Optical properties of graphene
61.48.Gh Structure of graphene
78.30.Na Fullerenes and related materials

Photoluminescence and extinction enhancement from ZnO films embedded with Ag nanoparticles

M. Liu, S. W. Qu, W. W. Yu, S. Y. Bao, C. Y. Ma, Q. Y. Zhang, J. He, J. C. Jiang, E. I. Meletis, and C. L. Chen

Appl. Phys. Lett. 97, 231906 (2010); http://dx.doi.org/10.1063/1.3525171 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2010

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ZnO films embedded with Ag nanoparticles are deposited at 750 °C with a reactive radio-frequency magnetron sputtering. The films are found to have a large enhancement in the intensity of photoluminescence emission and in the extinction of incident light. The enhancement is assigned to be from the interaction between the localized surface plasmons in the Ag nanoparticels and the light. The surface plasmons in the films can be excited in a wide range, from ultraviolet to near infrared wavelength of light.
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78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.16.-c Methods of micro- and nanofabrication and processing
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
68.55.-a Thin film structure and morphology
78.55.Et II-VI semiconductors

Identification of zinc and oxygen vacancy states in nonpolar ZnO single crystal using polarized photoluminescence

J. Liu, Y. Zhao, Y. J. Jiang, C. M. Lee, Y. L. Liu, and G. G. Siu

Appl. Phys. Lett. 97, 231907 (2010); http://dx.doi.org/10.1063/1.3525714 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2010

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Polarized photoluminescence spectra of the nonpolar ZnO single crystals annealed at different temperatures in air were investigated, for which the whole emission spectra from visible up to ultraviolet range for zinc and oxygen defects states are taken separately via the parallel and the crossed polarization geometries, respectively. It is also deduced from the spectra that the density of oxygen vacancy defects attains minimum for the sample annealed at 400 °C, and above which both anharmonic effects of ultraviolet emission and enhancement of defect-related deep band emission band due to the increase of oxygen and zinc vacancy defects are observed.
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71.55.Gs II-VI semiconductors
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.jd Vacancies

Promotion of hydrogen production using spectrally controlled thermal radiation

Yuriko Maegami, Fumitada Iguchi, and Hiroo Yugami

Appl. Phys. Lett. 97, 231908 (2010); http://dx.doi.org/10.1063/1.3525164 (3 pages)

Online Publication Date: 10 December 2010

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By controlling the thermal radiation spectrum using surface grating technologies, we promote the methane steam reforming to produce hydrogen. We fabricated a two-dimensional surface grating to tune its thermal emittance peak to the vibrational absorption bands of methane and water. We demonstrated that hydrogen production strongly depends on the spectral intensity within the resonant wavelength range, and that the hydrogen production rate is four times greater than that obtained when the spectrally controlled thermal radiation is not tuned to vibrational resonances. The optical excitation of the vibrational energy levels of gas molecules is found to effectively promote hydrogen production.
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88.30.E- Hydrogen production with renewable energy

Effect of relative humidity on contact angle and particle deposition morphology of an evaporating colloidal drop

Viral H. Chhasatia, Abhijit S. Joshi, and Ying Sun

Appl. Phys. Lett. 97, 231909 (2010); http://dx.doi.org/10.1063/1.3525167 (3 pages) | Cited 2 times

Online Publication Date: 10 December 2010

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The deposition behavior of inkjet-printed aqueous colloidal drops on a glass substrate has been investigated by using fluorescence microscopy and a high resolution goniometer. Real-time side-view images of a pinned colloidal drop show that the contact angle during evaporation is a function of the relative humidity (RH). The RH also affects the extent to which the drop is able to spread after impacting a substrate, the evaporation rate at the drop surface, and the evaporatively driven flow inside the drop that drives the suspended particles toward the contact line. Results show that the particle deposition area and pattern change significantly with the RH.
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68.03.Fg Evaporation and condensation of liquids
47.57.J- Colloidal systems
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
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Valence-band splittings in cubic and hexagonal AlN, GaN, and InN

Luiz Cláudio de Carvalho, André Schleife, Frank Fuchs, and Friedhelm Bechstedt

Appl. Phys. Lett. 97, 232101 (2010); http://dx.doi.org/10.1063/1.3524234 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2010

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Modern parameter-free band-structure calculations are applied to the uppermost valence bands near the Γ point. They are based on a nonlocal exchange-correlation starting point for the iteration of the quasiparticle equation and include spin-orbit interaction. The Ga 3d and In 4d electrons remarkably influence the valence-band splittings. Quasiparticle effects shrink the crystal-field splitting Δcf for GaN and increase the inverted Γ1−Γ5 distance for AlN. Beyond the quasicubic approximation, we find a small anisotropy of the spin-orbit splittings. While for AlN Δso does only weakly depend on the crystal structure, variations are found between zinc blende and wurtzite for GaN or InN.
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71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.70.Ch Crystal and ligand fields
61.66.Fn Inorganic compounds
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High switching endurance in TaOx memristive devices

J. Joshua Yang, M.-X. Zhang, John Paul Strachan, Feng Miao, Matthew D. Pickett, Ronald D. Kelley, G. Medeiros-Ribeiro, and R. Stanley Williams

Appl. Phys. Lett. 97, 232102 (2010); http://dx.doi.org/10.1063/1.3524521 (3 pages) | Cited 20 times

Online Publication Date: 6 December 2010

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We demonstrate over 1×1010 open-loop switching cycles from a simple memristive device stack of Pt/TaOx/Ta. We compare this system to a similar device stack based on titanium oxides to obtain insight into the solid-state thermodynamic and kinetic factors that influence endurance in metal-oxide memristors.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)

Stable bipolar surface potential behavior of copper-doped zinc oxide films studied by Kelvin probe force microscopy

Meng Fei Wong, Tun Seng Herng, Zhongkun Zhang, Kaiyang Zeng, and Jun Ding

Appl. Phys. Lett. 97, 232103 (2010); http://dx.doi.org/10.1063/1.3521281 (3 pages) | Cited 2 times

Online Publication Date: 7 December 2010

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The surface potential of undoped and copper-doped zinc oxide (ZnO:Cu) films has been studied using the Kelvin probe force microscopy at ambient condition. In contrast to the undoped ZnO with unipolar behavior, the ZnO:Cu film exhibits a bipolar surface potential behavior under a dc bias. The localized hole trapping phenomenon is attributed to the presence of Cu ions in ZnO films. With an appropriate amount of the Cu ions ( ∼ 8 at. %), the charge trapping is reasonably stable over a period of 20 h, which can be associated with the presence of oxygen vacancies. This coexistence of Cu ions and oxygen vacancies in ZnO gives rise to stable bipolar behavior, paving way to potential charge storage application.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.jd Vacancies

Work function shifts, Schottky barrier height, and ionization potential determination of thin MgO films on Ag(001)

T. Jaouen, G. Jézéquel, G. Delhaye, B. Lépine, P. Turban, and P. Schieffer

Appl. Phys. Lett. 97, 232104 (2010); http://dx.doi.org/10.1063/1.3525159 (3 pages) | Cited 3 times

Online Publication Date: 8 December 2010

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The electronic band structure and the work function of MgO thin films epitaxially grown on Ag(001) have been investigated using x-ray and ultraviolet photoelectron spectroscopy for various oxide thicknesses. The deposition of thin MgO films on Ag(001) induces a strong diminution in the metal work function. The p-type Schottky barrier height is constant at 3.85±0.10 eV above two MgO monolayers and the experimental value of the ionization potential is 7.15±0.15 eV. Our results are well consistent with the description of the Schottky barrier height in terms of the Schottky–Mott model corrected by an MgO-induced polarization effect.
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73.30.+y Surface double layers, Schottky barriers, and work functions
68.55.aj Insulators
68.55.jd Thickness
78.40.Ha Other nonmetallic inorganics
79.60.Dp Adsorbed layers and thin films
71.20.Ps Other inorganic compounds

Surface polar phonon dominated electron transport in graphene

X. Li, E. A. Barry, J. M. Zavada, M. Buongiorno Nardelli, and K. W. Kim

Appl. Phys. Lett. 97, 232105 (2010); http://dx.doi.org/10.1063/1.3525606 (3 pages) | Cited 7 times

Online Publication Date: 9 December 2010

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The effects of surface polar phonons on the electronic transport properties of monolayer graphene are studied by using a Monte Carlo simulation. Specifically, the low-field electron mobility and saturation velocity are examined for different substrates (SiC, SiO2, and HfO2) in comparison to the intrinsic case. While the results show that the low-field mobility can be substantially reduced by the introduction of surface polar phonon scattering, corresponding degradation of the saturation velocity is not observed for all three substrates at room temperature. It is also found that surface polar phonons can influence graphene’s electrical resistivity even at low temperature, leading potentially to inaccurate estimation of the acoustic phonon deformation potential constant.
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72.20.Fr Low-field transport and mobility; piezoresistance
68.35.Ja Surface and interface dynamics and vibrations
73.61.Wp Fullerenes and related materials

High conductive gate leakage current channels induced by In segregation around screw- and mixed-type threading dislocations in lattice-matched InxAl1−xN/GaN heterostructures

J. Song, F. J. Xu, X. D. Yan, F. Lin, C. C. Huang, L. P. You, T. J. Yu, X. Q. Wang, B. Shen, K. Wei, and X. Y. Liu

Appl. Phys. Lett. 97, 232106 (2010); http://dx.doi.org/10.1063/1.3525713 (3 pages) | Cited 5 times

Online Publication Date: 9 December 2010

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A correlation between microstructures and high gate leakage current density of Schottky contacts on lattice-matched InxAl1−xN/GaN heterostructures has been investigated by means of current-voltage measurements, conductive atom force microscopy (C-AFM), and transmission electron microscopy (TEM) investigations. It is shown that the reverse-bias gate leakage current density of Ni/Au Schottky contacts on InxAl1−xN/GaN heterostructures is more than two orders of magnitude larger than that on AlxGa1−xN/GaN ones. C-AFM and TEM observations indicate that screw- and mixed-type threading dislocations (S/M-TDs) are efficient leakage current channels in InxAl1−xN barrier and In segregation is formed around S/M-TDs. It is believed that In segregation around S/M-TDs reduces local Schottky barrier height to form conductive channels and leads to high leakage current density of Schottky contacts on InxAl1−xN/GaN heterostructures.
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81.05.Ea III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.30.+y Surface double layers, Schottky barriers, and work functions
64.75.-g Phase equilibria
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Demonstration of AlGaN/GaN high-electron-mobility transistors on 100 mm diameter Si(111) by plasma-assisted molecular beam epitaxy

K. Radhakrishnan, N. Dharmarasu, Z. Sun, S. Arulkumaran, and G. I. Ng

Appl. Phys. Lett. 97, 232107 (2010); http://dx.doi.org/10.1063/1.3518717 (3 pages)

Online Publication Date: 10 December 2010

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AlGaN/GaN high-electron-mobility transistor structures grown on 100 mm high-resistivity Si(111) substrates using plasma-assisted molecular beam epitaxy are reported. The two-dimensional electron gas (2DEG) formation in the heterostructures was realized by the growth optimization of two-step low temperature and high temperature AlN layers and GaN buffer layer. High-electron mobility of 1100 cm2/V s with a sheet carrier density of 9×1012 cm−2 was achieved. The presence of 2DEG in the AlGaN/GaN interface was confirmed by temperature dependent Hall measurements and capacitance-voltage carrier profiling. The fabricated 1.5 μm gate length high electron mobility transistor exhibited a maximum drain current density of 530 mA/mm and a peak extrinsic transconductance of 156 mS/mm.
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85.30.Tv Field effect devices
85.40.Sz Deposition technology
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CoIr-carbon complexes with magnetic anisotropies larger than 0.2 eV: A density-functional-theory prediction

Ruijuan Xiao, Michael D. Kuz’min, Klaus Koepernik, and Manuel Richter

Appl. Phys. Lett. 97, 232501 (2010); http://dx.doi.org/10.1063/1.3520488 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2010

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We report a density-functional study of the heteronuclear CoIr dimer adsorbed on benzene or graphene. In either case, CoIr prefers an upright position above the center of a carbon hexagon with the Co atom next to it. The Ir atom stays away from the carbon ring and thus preserves its free-atom-like properties. This results in a very large magnetic anisotropy of more than 0.2 eV per dimer. So high a value should suffice for long-term data storage at the temperature of liquid nitrogen.
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75.30.Gw Magnetic anisotropy
31.15.es Applications of density-functional theory (e.g., to electronic structure and stability; defect formation; dielectric properties, susceptibilities; viscoelastic coefficients; Rydberg transition frequencies)

Intrinsic room temperature ferromagnetism in boron-doped ZnO

X. G. Xu, H. L. Yang, Y. Wu, D. L. Zhang, S. Z. Wu, J. Miao, Y. Jiang, X. B. Qin, X. Z. Cao, and B. Y. Wang

Appl. Phys. Lett. 97, 232502 (2010); http://dx.doi.org/10.1063/1.3524493 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2010

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We report room temperature ferromagnetism in boron-doped ZnO both experimentally and theoretically. The single phase Zn1−xBxO films deposited under high oxygen pressure by pulsed laser deposition show ferromagnetic behavior at room temperature. The saturation magnetization increases monotonically from 0 to 1.5 emu/cm3 with the increasing boron component x from 0% to 6.8%. The first-principles calculations demonstrate that the ferromagnetism in the B-doped ZnO originates from the induced magnetic moment of oxygen atoms in the nearest neighbor sites to B–Zn vacancy pairs. The calculated total magnetic moment shows an increasing trend with the boron component which is consistent with experiment.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition

Single picojoule pulse switching of magnetization in ferromagnetic (Ga,Mn)As

A. H. M. Reid, G. V. Astakhov, A. V. Kimel, G. M. Schott, W. Ossau, K. Brunner, A. Kirilyuk, L. W. Molenkamp, and Th. Rasing

Appl. Phys. Lett. 97, 232503 (2010); http://dx.doi.org/10.1063/1.3524525 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2010

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The recently demonstrated photoinduced reduction of the coercive field in (Ga,Mn)As is shown to display a pronounced increase in efficiency when triggered by short laser pulses. This is due to the relaxation timescale of the effect that is measured to be about 1.5 ns. In addition, a single 100-fs-pulse with only 80 pJ of energy is found to be sufficient to write a magnetic domain.
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75.70.Ak Magnetic properties of monolayers and thin films
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.50.Dd Nonmetallic ferromagnetic materials
78.47.J- Ultrafast spectroscopy (<1 psec)
75.50.Pp Magnetic semiconductors
78.66.Nk Insulators
78.20.Ls Magneto-optical effects

The peculiar magnetic property evolution along RCu3Mn4O12 (R = Y, La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu): A first-principles study

Xiaojuan Liu, Shuhui Lv, hongping Li, and Jian Meng

Appl. Phys. Lett. 97, 232504 (2010); http://dx.doi.org/10.1063/1.3524527 (3 pages)

Online Publication Date: 6 December 2010

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Within RCu3Mn4O12 (R = Rare earth), besides the expected ferrimagnetic order of Mn and Cu ions below TC1, R magnetic moments also play an important role at lower temperatures TC2, leading to their peculiar magnetic behavior. By first-principles calculation, we found that along the series from La to Lu, TC1 monotonically increased due to the ionic radius (IR) induced chemical pressure, as experimentally observed, while TC2 is closely related to the atomic radius of R. Additionally, the magnetic anisotropy energy (ΔEani) along the series is found to be correlated with the total magnetic moment of R ion.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy
75.50.Gg Ferrimagnetics

Characteristics of a high temperature vertical spin valve

Debashish Basu, Hyun Kum, Pallab Bhattacharya, and Dipankar Saha

Appl. Phys. Lett. 97, 232505 (2010); http://dx.doi.org/10.1063/1.3524820 (3 pages) | Cited 1 time

Online Publication Date: 6 December 2010

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We demonstrate high temperature electrical spin injection and detection in degenerately p-doped GaAs in vertical spin valves using valence band electron tunneling. The maximum measured magnetoresistance at 10 and 300 K is 40% and ∼ 1%, respectively. Spin relaxation in these devices was found to be relatively insensitive to temperature (T) for T>125 K. The spin injection and detection efficiencies are mostly dominated by the ferromagnetic contact polarization and spin independent transport at the ferromagnet/semiconductor interface.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.25.-b Spin polarized transport
73.61.Ey III-V semiconductors
73.20.At Surface states, band structure, electron density of states

Magnetic properties of full-Heusler alloy Co2Fe1−xMnxAl films grown by molecular-beam epitaxy

K. K. Meng, S. L. Wang, P. F. Xu, L. Chen, W. S. Yan, and J. H. Zhao

Appl. Phys. Lett. 97, 232506 (2010); http://dx.doi.org/10.1063/1.3525376 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2010

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We have investigated magnetic properties of single-crystalline full-Heusler alloy Co2Fe1−xMnxAl films (0<x<1) grown on GaAs (001) by molecular-beam epitaxy at different temperatures. It is found that as x increases, the films grown at 160 °C have complex magnetic phases, but show pure ferromagnetic properties when grown at 280 °C. We attribute this magnetic behavior to the competition between ferromagnetic and antiferromagnetic Mn–Mn interactions, which are proved by x-ray magnetic circular dichroism measurements. Moreover, we have investigated in-plane magnetic anisotropies of Co2Fe1−xMnxAl films with pure ferromagnetic phases and deduced the corresponding anisotropy constants which also remarkably depend on x.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Bb Fe and its alloys
78.20.Ls Magneto-optical effects
75.30.Gw Magnetic anisotropy
75.50.Ee Antiferromagnetics
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Magnetization dynamics triggered by surface acoustic waves

S. Davis, A. Baruth, and S. Adenwalla

Appl. Phys. Lett. 97, 232507 (2010); http://dx.doi.org/10.1063/1.3521289 (3 pages)

Online Publication Date: 7 December 2010

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Investigations into fast magnetization switching are of both fundamental and technological interest. Here we present a low-power, remote method for strain driven magnetization switching. A surface acoustic wave propagates across an array of ferromagnetic elements, and the resultant strain switches the magnetization from the easy axis into the hard axis direction. Investigations as a function of applied magnetic field as well as unidirectional anisotropy (the exchange bias) reveal excellent agreement with prediction, confirming the viability of this method.
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75.78.-n Magnetization dynamics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.30.Gw Magnetic anisotropy
62.65.+k Acoustical properties of solids
68.35.Iv Acoustical properties

Ultrathin Co/Pt and Co/Pd superlattice films for MgO-based perpendicular magnetic tunnel junctions

K. Yakushiji, T. Saruya, H. Kubota, A. Fukushima, T. Nagahama, S. Yuasa, and K. Ando

Appl. Phys. Lett. 97, 232508 (2010); http://dx.doi.org/10.1063/1.3524230 (3 pages) | Cited 19 times

Online Publication Date: 9 December 2010

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Ultrathin [Co/Pt]n and [Co/Pd]n superlattice films consisting of 0.14–0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering. A large perpendicular magnetic anisotropy [(3–9)×106 ergs/cm3] and an ideal square out-of-plane hysteresis loop were attained even for ultrathin superlattice films with a total thickness of 1.2–2.4 nm. The films were stable against annealing up to 370 °C. MgO-based perpendicular magnetic tunnel junctions with this superlattice layer as the free layer showed a relatively high magnetoresistance ratio (62%) and an ultralow resistance-area product (3.9 Ω μm2) at room temperature. The use of these films will enable the development of gigabit-scale nonvolatile memory.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
72.15.Gd Galvanomagnetic and other magnetotransport effects
81.15.Cd Deposition by sputtering
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