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24 Dec 2007

Volume 91, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages)

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu
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Pockels response in calcium barium niobate thin films

R. Helsten, L. Razzari, M. Ferrera, P. F. Ndione, M. Gaidi, C. Durand, M. Chaker, and R. Morandotti

Appl. Phys. Lett. 91, 261101 (2007); http://dx.doi.org/10.1063/1.2824455 (3 pages) | Cited 11 times

Online Publication Date: 26 December 2007

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The electro-optical response of calcium barium niobate ferroelectric thin films is characterized using a single beam setup in reflection geometry. Clear evidence of a Pockels response together with an r33 coefficient as high as 130 pm/V is found. This large value and the high Curie temperature of the material under study (>250 °C) can be considered as a promising feature for the fabrication of hybrid, integrated electro-optical modulators working at a high repetition rate.
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77.55.-g Dielectric thin films
78.20.Jq Electro-optical effects
77.80.B- Phase transitions and Curie point
78.66.-w Optical properties of specific thin films

Electrically driven light emission from hot single-walled carbon nanotubes at various temperatures and ambient pressures

Xinran Wang, Li Zhang, Yuerui Lu, Hongjie Dai, Y. K. Kato, and Eric Pop

Appl. Phys. Lett. 91, 261102 (2007); http://dx.doi.org/10.1063/1.2827281 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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Electroluminescence of individual single-walled carbon nanotubes down to ∼ 15 K is measured. We observe electrically driven light emission from suspended quasimetallic nanotubes in vacuum down to ∼ 15 K and under different gas pressures at room temperature. Light emission is found to originate from hot electrons in the presence of electrically driven nonequilibrium optical phonons. Reduced light emission is observed in exponential manner as electron and optical phonon temperatures in the nanotube are lowered by lower ambient temperature or higher gas pressure. The results reveal over wide ambient conditions, light emission in a suspended tube is from thermally excited electron-hole recombination.
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78.67.Ch Nanotubes
78.60.Fi Electroluminescence
73.63.Fg Nanotubes
72.20.Ht High-field and nonlinear effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Low resistance as-deposited Cr/Au contacts on p-type GaN

F. G. Kalaitzakis, N. T. Pelekanos, P. Prystawko, M. Leszczynski, and G. Konstantinidis

Appl. Phys. Lett. 91, 261103 (2007); http://dx.doi.org/10.1063/1.2828044 (3 pages) | Cited 3 times

Online Publication Date: 26 December 2007

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The influence of several predeposition surface treatments and different contact metals to the electrical properties of metal/p-GaN contacts was studied. A low resistance as-deposited Cr/Au Ohmic contact was achieved, using boiling aqua regia as surface treatment. The Ohmic resistance of Cr/Au contacts with 50 μm interspacing was found to be 50 Ω, while the specific contact resistivity value was measured 2.6×10−3 Ω cm2. Direct comparison with the standard oxidized Ni/Au contacts confirmed the superior characteristics of the Cr/Au contact scheme. Violet emission was readily obtained when the as-deposited Cr/Au contacts were used as the p electrode of a light emitting diode emitting at 385 nm.
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73.40.Ns Metal-nonmetal contacts
81.65.-b Surface treatments

Improved operational lifetime of semiconducting polymer lasers by encapsulation

S. Richardson, O. P. M. Gaudin, G. A. Turnbull, and I. D. W. Samuel

Appl. Phys. Lett. 91, 261104 (2007); http://dx.doi.org/10.1063/1.2826276 (3 pages) | Cited 11 times

Online Publication Date: 27 December 2007

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We report polymer distributed feedback lasers with dramatically extended operational lifetimes by using a simple encapsulation process. The lasers are configured as surface emitting, two-dimensional distributed feedback lasers based on the polymer poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene]. The microstructure is transferred to the polymer surface through solvent assisted micromolding. Once encapsulated, a 2500-fold improvement in lifetime is demonstrated under ambient conditions, compared to the unencapsulated device. A blueshift of the emission wavelength observed during operation is characterized by absorption and ellipsometry measurements and attributed to a change in effective index due to a loss of conjugation in the polymer.
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42.55.Px Semiconductor lasers; laser diodes

Negative characteristic temperature of long wavelength InAs/AlGaInAs quantum dot lasers grown on InP substrates

I. Alghoraibi, T. Rohel, R. Piron, N. Bertru, C. Paranthoen, G. Elias, A. Nakkar, H. Folliot, A. Le Corre, and S. Loualiche

Appl. Phys. Lett. 91, 261105 (2007); http://dx.doi.org/10.1063/1.2827177 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2007

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InAs quantum dot lasers grown on (311)B InP substrates with AlGaInAs barriers have been fabricated and studied. A large decrease of the threshold current with temperature was observed from 110 to 140 K. In the same temperature range, electroluminescence spectra showed a shape change, an energy shift with temperature, which cannot be fitted with a Varshni law, and a large decrease of the laser linewidth. These results can be related to a delayed thermalisation of carriers within quantum dot ensemble.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Micromachined optical well structure for thermo-optic switching

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu

Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages) | Cited 4 times

Online Publication Date: 28 December 2007

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This letter demonstrates the thermo-optic switching function using an adjustable optical well structure, which is constructed by a thin air gap sandwiched between two micromachined hemicylindrical prisms. The device is etched on a silicon-on-insulator wafer within a footprint of 400×400 μm2. In experiment, it measures an extinction ratio of 30.2 dB and a switching time of 2.2 μs. Compared with the other demonstrated switches that have optical barrier structures, this device is unique in the working principle and optical design, and shows various merits such as high extinction ratio, fast speed, low power consumption, and small size.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.79.Bh Lenses, prisms and mirrors
42.65.Pc Optical bistability, multistability, and switching, including local field effects
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Plasma-assisted laser ablation of tungsten: Reduction in ablation power threshold due to bursting of holes/bubbles

Shin Kajita, Noriyasu Ohno, Shuichi Takamura, Wataru Sakaguchi, and Dai Nishijima

Appl. Phys. Lett. 91, 261501 (2007); http://dx.doi.org/10.1063/1.2824873 (3 pages) | Cited 9 times

Online Publication Date: 27 December 2007

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Nanosecond laser ablation of tungsten (W) exposed to helium plasma is investigated using optical emission spectroscopy. Submicrometer-sized holes/bubbles are formed on the surface of W when it was exposed to the helium plasma at a sufficiently high temperature (≳1500–1600 K). The emissions from a virgin W (before the helium plasma irradiation) cannot be detected when the fluence is <1 J/cm2; however, the threshold fluence for the detection of neutral W emission after it was exposed to the helium plasma is ∼ 0.2 J/cm2. The physical mechanism of laser-induced bursting of holes/bubbles is proposed for achieving a significant reduction in ablation power threshold.
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52.38.Mf Laser ablation
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.40.Hf Plasma-material interactions; boundary layer effects

Field-aligned and transverse plasma-potential structures induced by electron cyclotron waves

K. Takahashi, T. Kaneko, and R. Hatakeyama

Appl. Phys. Lett. 91, 261502 (2007); http://dx.doi.org/10.1063/1.2827575 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2007

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It is demonstrated that potential structures of a magnetized plasma column can be controlled by electron cyclotron waves of azimuthal mode number m = ±1. A field-aligned plasma potential structure, i.e., an electric double layer with the potential jump corresponding to the ion flow energy is created around the electron cyclotron resonance point at the center and peripheral areas of the plasma column for m = +1 and −1 modes, respectively. As a result, transversely outward and inward electric fields are locally generated. Our experimental results show that the created potential structures are greatly relevant to the polarization profiles of the injected waves and the resultant heating profiles.
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52.25.Xz Magnetized plasmas
52.50.Sw Plasma heating by microwaves; ECR, LH, collisional heating
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
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A large-area bent crystal shield for deflection of high-energy ions

M. B. H. Breese

Appl. Phys. Lett. 91, 261901 (2007); http://dx.doi.org/10.1063/1.2824457 (3 pages)

Online Publication Date: 26 December 2007

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A large-area bent crystal shield which is capable of deflecting high-energy ions of all atomic numbers is described. Its effect on the transmitted angular distribution of high-energy ions is characterized using Monte Carlo channeling simulations. Ions up to an energy limit set by the bent crystal curvature radius are deflected by the full bend angle. A shield with a surface area of 1×1 cm2 which is capable of deflecting ions with energies up to 100 GeV/nucleon has been fabricated in which the lattice planes across the entrance surface are uniformly aligned.
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61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
81.20.-n Methods of materials synthesis and materials processing

Interface electronic structure of the organic light-emitting devices: Photoemission and x-ray absorption studies of Al/KF/Alq3 interface

J. Lee, J. S. Lim, H. J. Shin, and Y. Park

Appl. Phys. Lett. 91, 261902 (2007); http://dx.doi.org/10.1063/1.2824464 (3 pages) | Cited 3 times

Online Publication Date: 26 December 2007

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The chemistry of organic light-emitting diode interface composed of KF sandwiched between the Al and Alq3 was investigated using near-edge x-ray absorption fine structure (NEXAFS) as well as x-ray and ultraviolet photoelectron spectroscopy techniques. At the earliest stages of KF deposition on Alq3, changes in F K-edge NEXAFS spectra indicated a strong chemical reaction, which is responsible for the dipole layer formation seen in valence-band spectra. For Al deposition on KF/Alq3, the reactions inferred from observed spectral changes are not consistent with the commonly believed KF dissociation and AlF3 formation scenarios.
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85.60.Jb Light-emitting devices

Effects of plasma surface modification on interfacial behaviors and mechanical properties of carbon nanotube-Al2O3 nanocomposites

Yan Guo, Hoonsung Cho, Donglu Shi, Jie Lian, Yi Song, Jandro Abot, Bed Poudel, Zhifeng Ren, Lumin Wang, and Rodney C. Ewing

Appl. Phys. Lett. 91, 261903 (2007); http://dx.doi.org/10.1063/1.2824865 (3 pages) | Cited 9 times

Online Publication Date: 26 December 2007

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The effects of plasma surface modification on interfacial behaviors in carbon nanotube (CNT) reinforced alumina (Al2O3) nanocomposites were studied. A unique plasma polymerization method was used to modify the surfaces of CNTs and Al2O3 nanoparticles. The CNT-Al2O3 nanocomposites were processed by both ambient pressure and hot-press sintering. The electron microscopy results showed ultrathin polymer coating on the surfaces of CNTs and Al2O3 nanoparticles. A distinctive stress-strain curve difference related to the structural interfaces and plasma coating was observed from the nanocomposites. The mechanical performance and thermal stability of CNT-Al2O3 nanocomposites were found to be significantly enhanced by the plasma-polymerized coating.
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61.46.Fg Nanotubes
52.40.Hf Plasma-material interactions; boundary layer effects
82.35.Np Nanoparticles in polymers
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Jj Elasticity and anelasticity, stress-strain relations

Precise measurements of electron and hole g factors of single quantum dots by using nuclear field

R. Kaji, S. Adachi, H. Sasakura, and S. Muto

Appl. Phys. Lett. 91, 261904 (2007); http://dx.doi.org/10.1063/1.2827572 (3 pages) | Cited 10 times

Online Publication Date: 26 December 2007

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We demonstrated the cancellation of the external magnetic field by the nuclear field at one edge of the nuclear polarization bistability in single InAlAs quantum dots. The cancellation for the electron Zeeman splitting gives the precise value of the hole g factor. In combination with the exciton g factor that is obtained from the Zeeman splitting for linearly polarized excitation, the magnitude and the sign of the electron and hole g factors in the growth direction are evaluated.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
71.35.-y Excitons and related phenomena
81.05.Dz II-VI semiconductors

Effects of carbon on ion-implantation-induced disorder in GaN

S. O. Kucheyev, J. E. Bradby, C. P. Li, S. Ruffell, T. van Buuren, and T. E. Felter

Appl. Phys. Lett. 91, 261905 (2007); http://dx.doi.org/10.1063/1.2827587 (3 pages) | Cited 10 times

Online Publication Date: 26 December 2007

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Wurtzite GaN films bombarded with 40 keV C ions to high doses (5×1017 and 1×1018 cm−2) are studied by a combination of Rutherford backscattering/channeling spectrometry, transmission electron microscopy, and soft x-ray absorption spectroscopy. Results show that, contrary to other ion species, implanted C forms nitrilelike carbon-nitride bonds (–C≣N) and suppresses ion-beam-induced material decomposition involving the formation and agglomeration of ≳5-nm-large N2 gas bubbles.
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81.05.Ea III-V semiconductors
79.20.Kz Other electron-impact emission phenomena
78.70.Dm X-ray absorption spectra

Mechanical properties of carbon nanocones

J. X. Wei, K. M. Liew, and X. Q. He

Appl. Phys. Lett. 91, 261906 (2007); http://dx.doi.org/10.1063/1.2813017 (3 pages) | Cited 11 times

Online Publication Date: 26 December 2007

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In this paper, the elastic and plastic properties of single-walled carbon nanocones (CNCs) under tension are investigated employing molecular dynamics simulation. The force-deformation responses of CNCs are obtained and compared with those of carbon nanotubes (CNTs). CNCs with a larger apex angle present a larger failure strength but a smaller maximum strain under tension. Following this law, CNTs exhibit the smallest failure strength but greatest maximum strain due to their zero conical angles. The mechanical properties such as Young’s modulus, elastic strain limit, and ultimate force are determined and discussed.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep

Strong excitonic transition of Zn1−xMgxO alloy

H. Tampo, H. Shibata, K. Maejima, A. Yamada, K. Matsubara, P. Fons, S. Niki, T. Tainaka, Y. Chiba, and H. Kanie

Appl. Phys. Lett. 91, 261907 (2007); http://dx.doi.org/10.1063/1.2828031 (3 pages) | Cited 16 times

Online Publication Date: 26 December 2007

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A strong excitonic optical transition in a Zn1−xMgxO alloy grown by radical source molecular beam epitaxy was observed using both optical reflectivity measurements and photoluminescence (PL) measurements. Clear and strong reflectance peaks at room temperature (RT) were observed from 3.42 eV (x = 0.05) to 4.62 eV (x = 0.61) from ZnMgO layers at RT. Distinct clear PL spectra at RT were also observed for energies up to 4.06 eV (x = 0.44). The peak intensity of the reflected signal increased for x values up to x ∼ 0.2 simultaneously with an increase in PL intensity; however, a Stokes shift between the reflectance peak and the PL peak was not observed for x values below 0.2. These facts suggest that the oscillator strength of ZnMgO is enhanced by alloying, and the underlying mechanism is discussed. Furthermore, we demonstrate that the strong reflectance properties even at RT provide an easy method to determine the Mg composition of a thin ZnMgO layer in a ZnMgO/ZnO heterostructure.
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71.35.-y Excitons and related phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors

Characterization of fatigue-induced free volume changes in a bulk metallic glass using positron annihilation spectroscopy

R. S. Vallery, M. Liu, D. W. Gidley, M. E. Launey, and J. J. Kruzic

Appl. Phys. Lett. 91, 261908 (2007); http://dx.doi.org/10.1063/1.2825427 (3 pages) | Cited 6 times

Online Publication Date: 26 December 2007

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Depth-profiled Doppler broadening spectroscopy of positron annihilation on the cyclic fatigue-induced fracture surfaces of three amorphous Zr44Ti11Ni10Cu10Be25 metallic glass specimens reveals the presence of a 30–50 nm layer of increased free volume that is generated by the propagating fatigue crack tip. The presence and character of this fatigue transformation zone is independent of the initial amount of bulk free volume, which was varied by structural relaxation via annealing, and the voids generated in the zone by intense cyclic deformation are distinct from those typical of the bulk.
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81.05.Kf Glasses (including metallic glasses)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.43.Fs Glasses
78.70.Bj Positron annihilation
81.40.Gh Other heat and thermomechanical treatments
81.40.Lm Deformation, plasticity, and creep

Friction of soft elastomeric surfaces with a defect

Charles J. Rand and Alfred J. Crosby

Appl. Phys. Lett. 91, 261909 (2007); http://dx.doi.org/10.1063/1.2828136 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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We consider a simple problem that provides insight into the building blocks of friction for topographically patterned surfaces and fundamental understanding into the general friction of coatings. The problem focuses on the effect of a line defect, such as a pattern’s edge, on the lateral force of a sliding soft interface. The line defect presents a discontinuity in the stress at the sliding interface, changing the lateral stiffness and decreasing the sliding force. We relate the decrease in sliding shear force to the changes in lateral stiffness through relationships that account for contact splitting and lateral confinement effects.
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68.35.Af Atomic scale friction
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations

Crack-free GaN grown on AlGaN/(111)Si micropillar array fabricated by polystyrene microsphere lithography

Guan-Ting Chen, Jen-Inn Chyi, Chia-Hua Chan, Chia-Hung Hou, Chii-Chang Chen, and Mao-Nan Chang

Appl. Phys. Lett. 91, 261910 (2007); http://dx.doi.org/10.1063/1.2828137 (3 pages) | Cited 6 times

Online Publication Date: 26 December 2007

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The authors report on the growth of GaN on AlGaN/(111)Si micropillar array by metal-organic chemical vapor deposition. Using the substrates with micropillar array, 2-μm-thick GaN films without cracks can be achieved. Transmission electron microscopy, atomic force microscopy, and micro-Raman studies indicate that the dislocation density and residual stress of the GaN grown on micropillar array are also reduced. The results reveal the potential of this type of substrates for growing GaN-based devices as well as preparing GaN freestanding substrates.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.60.Bs Mechanical and acoustical properties

Complicated three-dimensional photonic crystals fabricated by holographic lithography

Wei-Dong Mao, Guan-Quan Liang, Yi-Ying Pu, He-Zhou Wang, and Zhaohua Zeng

Appl. Phys. Lett. 91, 261911 (2007); http://dx.doi.org/10.1063/1.2827565 (3 pages) | Cited 6 times

Online Publication Date: 27 December 2007

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We have fabricated a kind of three-dimensional photonic crystal in a single exposure by two sets of conventional laser holographic configurations. Specific structural features, such as a kagomelike lattice with p6mm symmetry on the top surface and a chainlike lattice on a cleavage plane, are possessed in this large-area and high-quality complicated microstructure, and many interesting properties such as skyrocketlike diffraction pattern exist. This work demonstrates that holographic lithography is a good method for the fabrication of photonic materials with crystal structure differing from the electronic crystals.
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42.70.Qs Photonic bandgap materials
42.40.My Applications
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Size dependence of the electronic structures and electron-phonon coupling in ZnO quantum dots

S. C. Ray, Y. Low, H. M. Tsai, C. W. Pao, J. W. Chiou, S. C. Yang, F. Z. Chien, W. F. Pong, M.-H. Tsai, K. F. Lin, H. M. Cheng, W. F. Hsieh, and J. F. Lee

Appl. Phys. Lett. 91, 262101 (2007); http://dx.doi.org/10.1063/1.2824396 (3 pages) | Cited 5 times

Online Publication Date: 26 December 2007

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The electronic structures and optical properties of various sizes of ZnO quantum dots (QDs) were studied using x-ray absorption, photoluminescence, and Raman spectroscopy. The increase in the intensity ratio of the second-order Raman spectra of longitudinal optical mode and its fundamental mode, which is related to the strength of the electron-phonon coupling (EPC), is found to increase with the size of QD. The trend of EPC also correlates with the increase of the intensity ratio of the O 2pπ (Iπ) and 2pσ (Iσ) orbital features in the O K-edge x-ray absorption near-edge structure (XANES) as the size of QD increases. The EPC and XANES results suggest that the crystal orientations of ZnO QDs are approximately aligned with the c axis parallel with the polarization of x-ray photons.
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71.20.Nr Semiconductor compounds
78.30.Fs III-V and II-VI semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.67.Hc Quantum dots

Electron mobility in InGaN channel heterostructure field effect transistor structures with different barriers

J. Xie, J. H. Leach, X. Ni, M. Wu, R. Shimada, Ü. Özgür, and H. Morkoç

Appl. Phys. Lett. 91, 262102 (2007); http://dx.doi.org/10.1063/1.2824461 (3 pages) | Cited 9 times

Online Publication Date: 26 December 2007

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InGaN possesses higher electron mobility and velocity than GaN, and therefore is expected to lead to relatively better performances for heterostructure field effect transistors (HFETs). However, the reported mobilities for AlGaN/InGaN HFETs are lower than GaN channel HFETs. To address this issue, we studied the effect of different barriers on the Hall mobility for InGaN channel HFETs grown by metal organic chemical vapor deposition. Unlike the conventional AlGaN barrier, the AlInN barrier can be grown at the same temperature as the InGaN channel layer, alleviating some of the technological roadblocks. Specifically, this avoids possible degradation of the thin InGaN channel during AlGaN growth at high temperatures; and paves the way for better interfaces. An undoped In0.18Al0.82N/AlN/In0.04Ga0.96N HFET structure exhibited a μH = 820 cm2/V s, with a ns = 2.12×1013 cm−2 at room temperature. Moreover, with an In-doped AlGaN barrier, namely, Al0.24In0.01Ga0.75N, grown at 900 °C, the μH increased to 1230 cm2/V s with a ns of 1.09×1013 cm−2 for a similar InGaN channel. Furthermore, when the barrier was replaced by Al0.25Ga0.75N grown at 1030 °C, μH dropped to 870 cm2/V s with ns of 1.26×1013 cm−2 at room temperature. Our results suggest that to fully realize the potential of the InGaN channel HFETs, AlInN or AlInGaN should be used as the barrier instead of the conventional AlGaN barrier.
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85.30.Tv Field effect devices
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Thickness dependence of the electronic properties in V2O3 thin films

C. Grygiel, Ch. Simon, B. Mercey, W. Prellier, R. Frésard, and P. Limelette

Appl. Phys. Lett. 91, 262103 (2007); http://dx.doi.org/10.1063/1.2824465 (3 pages) | Cited 13 times

Online Publication Date: 26 December 2007

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High quality vanadium sesquioxide V2O3 films (170–1100 Å) were grown using the pulsed laser deposition technique on (0001)-oriented sapphire substrates, and the effects of film thickness on the lattice strain and electronic properties were examined. X-ray diffraction indicates that there is an in-plane compressive lattice parameter (a), close to −3.5% with respect to the substrate and an out-of-plane tensile lattice parameter (c). The thin film samples display metallic character between 2 and 300 K, and no metal-to-insulator transition is observed. At low temperature, the V2O3 films behave as a strongly correlated metal, and the resistivity (ρ) follows the equation ρ = ρ0+AT2, where A is the transport coefficient in a Fermi liquid. Typical values of A have been calculated to be 0.14 μΩ cm K−2, which is in agreement with the coefficient reported for V2O3 single crystals under high pressure. Moreover, a strong temperature dependence of the Hall resistance confirms the electronic correlations of these V2O3 thin film samples.
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73.20.At Surface states, band structure, electron density of states
73.61.-r Electrical properties of specific thin films
71.27.+a Strongly correlated electron systems; heavy fermions
72.20.My Galvanomagnetic and other magnetotransport effects
68.60.Bs Mechanical and acoustical properties

Cerium oxide nanocrystals for nonvolatile memory applications

Shao-Ming Yang, Chao-Hsin Chien, Jiun-Jia Huang, Tan-Fu Lei, Ming-Jinn Tsai, and Lurng-Shehng Lee

Appl. Phys. Lett. 91, 262104 (2007); http://dx.doi.org/10.1063/1.2821367 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2007

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The characteristics of silicon-oxide-nitride-oxide-silicon-type memories embedded with cerium oxide nanocrystals were demonstrated. They were fabricated by depositing a thin CeO2 film on the SiO2 tunneling layer and subsequently rapid-thermal annealing process. The mean size and aerial density of the CeO2 nanocrystals embedded in SiO2 are estimated to be about 8–10 nm and (3–7)×1011/cm−2 after a high-temperature annealing with different ambients on 900 °C. The program/erase behaviors and data retention characteristics were described to demonstrate its advantages for nonvolatile memory device applications.
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84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices
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Improvement in electric and dielectric properties of nanoferrite synthesized via reverse micelle technique

Sangeeta Thakur, S. C. Katyal, and M. Singh

Appl. Phys. Lett. 91, 262501 (2007); http://dx.doi.org/10.1063/1.2824454 (3 pages) | Cited 10 times

Online Publication Date: 26 December 2007

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Nano nickel zinc ferrite (Ni0.58Zn0.42Fe2O4) with fascinating dielectric properties which reveal a direction for application was synthesized by reverse micelle technique. Dielectric constant and dielectric losses are controlled up to a measurement temperature of around 473 K at higher frequency range of 9–19 MHz. The dielectric loss of the sample investigated at room temperature is only 0.003 at 19 MHz. The presently studied nanoferrite also exhibits a high value of dc resistivity, 108 Ω cm. High resistivity and low dielectric constant and loss can be corelated to small grain size and better compositional stoichiometry obtained as a result of processing via reverse micelle technique at low sintering temperature (773 K).
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73.63.Bd Nanocrystalline materials
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

X-ray absorption spectroscopy and x-ray magnetic circular dichroism of epitaxially grown Heusler alloy Co2MnSi ultrathin films facing a MgO barrier

Toshiaki Saito, Toshikazu Katayama, Takayuki Ishikawa, Masafumi Yamamoto, Daisuke Asakura, and Tsuneharu Koide

Appl. Phys. Lett. 91, 262502 (2007); http://dx.doi.org/10.1063/1.2824856 (3 pages) | Cited 10 times

Online Publication Date: 26 December 2007

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Show Abstract
We element specifically studied the electronic and magnetic states of epitaxially grown full-Heusler alloy Co2MnSi (CMS) 1.1 nm (4 ML) thick ultrathin films facing an epitaxial MgO(001) tunnel barrier by means of x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). In situ reflection high-energy electron-diffraction observations indicated that the CMS films grew into the L21 structure. The observed XAS and XMCD spectra revealed that the CMS ultrathin film was not oxidized. The ratio of Mn and Co spin magnetic moments obtained by applying the sum rules was about 2.7, close to a theoretical value of 2.8 for CMS with the L21 structure.
Show PACS
75.70.Ak Magnetic properties of monolayers and thin films
78.70.Dm X-ray absorption spectra
75.30.Cr Saturation moments and magnetic susceptibilities
73.20.At Surface states, band structure, electron density of states
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