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13 Jul 2009

Volume 95, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 023701 (2009); http://dx.doi.org/10.1063/1.3173808 (3 pages)

G. Devès, S. Roudeau, A. Carmona, S. Lavielle, K. Gionnet, G. Déléris, and R. Ortega
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Pseudoelasticity of Cu–Zr nanowires via stress-induced martensitic phase transformations

Q. Cheng, H. A. Wu, Y. Wang, and X. X. Wang

Appl. Phys. Lett. 95, 021911 (2009); http://dx.doi.org/10.1063/1.3183584 (3 pages) | Cited 13 times

Online Publication Date: 16 July 2009

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Atomistic simulations were performed to investigate the pseudoelastic effects induced by martensitic phase transformation from body-centered cubic (B2) to body-centered tetragonal (BCT) lattice in Cu–Zr nanowires. The phase transformation occurs through nucleation and propagation of {100} twin boundary, which differs from the {101} twin boundary for B2 Ni–Al nanowires. During unloading, extension strain up to 45% can be fully recovered through inverse phase transformation. The BCT lattice has also been verified to be metastable for Cu–Zr nanowires with an energy analysis along the epitaxial Bain path. Our work implies Cu–Zr nanowires may be excellent functional components for nanoelectromechanical systems.
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81.30.Kf Martensitic transformations
61.72.Mm Grain and twin boundaries
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.23.Hj Nanowires
64.60.qj Studies of nucleation in specific substances
64.70.kd Metals and alloys

Tuning the termination of the SrTiO3(110) surface by Ar+ sputtering

Zhiming Wang, Kehui Wu, Qinlin Guo, and Jiandong Guo

Appl. Phys. Lett. 95, 021912 (2009); http://dx.doi.org/10.1063/1.3180701 (3 pages) | Cited 4 times

Online Publication Date: 17 July 2009

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We report a scanning tunneling microscopy study on the SrTiO3(110) surface treated with Ar+ sputtering followed by annealing. Two types of termination coexist on the surface, which are spatially identified as the 4×1 reconstructed SrTiO layer and the O layer covered by Ti-rich oxide clusters, respectively. The relative areal ratio of the two types is tuned by sputtering dose reproducibly, and monophased surface with either SrTiO or O termination is obtained. The surface is stable at temperatures up to 1100 °C and under oxygen partial pressures from 6×10−5 mbar to ultra high vacuum, providing us a flexible epitaxial growth template.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
81.40.Gh Other heat and thermomechanical treatments
68.47.Gh Oxide surfaces
68.35.bt Other materials

Mechanism of compositional modulations in epitaxial InAlN films grown by molecular beam epitaxy

S.-L. Sahonta, G. P. Dimitrakopulos, Th. Kehagias, J. Kioseoglou, A. Adikimenakis, E. Iliopoulos, A. Georgakilas, H. Kirmse, W. Neumann, and Ph. Komninou

Appl. Phys. Lett. 95, 021913 (2009); http://dx.doi.org/10.1063/1.3184593 (3 pages) | Cited 13 times

Online Publication Date: 17 July 2009

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A mechanism for compositional modulations in InxAl1−xN films is described which considers growth kinetics during molecular beam epitaxy. InAlN crystalline films with various indium contents, grown on GaN or AlN buffer layers to create a variation in lattice mismatch conditions, were studied by transmission electron microscopy. Films comprise of columnar domains which are observed regardless of mismatch, with increasing indium concentration toward domain edges. We propose that indium is incorporated preferentially between adjacent dynamical InAlN platelets, owing to tensile strain generated upon platelet coalescence. The resulting In-rich boundaries are potential minima for further indium adatoms, creating a permanent indium composition gradient.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
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Formation of stable and reproducible low resistivity and high carrier concentration p-type ZnO doped at high pressure with Sb

J. M. Qin, B. Yao, Y. Yan, J. Y. Zhang, X. P. Jia, Z. Z. Zhang, B. H. Li, C. X. Shan, and D. Z. Shen

Appl. Phys. Lett. 95, 022101 (2009); http://dx.doi.org/10.1063/1.3153515 (3 pages) | Cited 7 times

Online Publication Date: 13 July 2009

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Stable p-type Sb-doped ZnO (ZnO:Sb) was fabricated reproducibly by sintering mixture of ZnO and Sb2O3 powders under 5 GPa at temperatures of 1100–1450 °C. The best p-type ZnO:Sb with resistivity of 1.6×10−2 Ω cm, carrier concentration of 3.3×1020 cm−3, and mobility of 12.1 cm/V s was obtained by doping 4.6 at. % Sb and sintering at 1450 °C. The p-type conduction is due to complex acceptor formed by one substitutional Sb at Zn site and two Zn vacancies. The acceptor level was measured to be 113 meV. Effect of pressure on formation and electrical properties of the p-type ZnO:Sb is discussed.
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72.20.Fr Low-field transport and mobility; piezoresistance
61.72.uj III-V and II-VI semiconductors
71.55.Gs II-VI semiconductors
61.72.jd Vacancies
62.50.-p High-pressure effects in solids and liquids
72.80.Ey III-V and II-VI semiconductors

Germanium oxynitride gate dielectrics formed by plasma nitridation of ultrathin thermal oxides on Ge(100)

Katsuhiro Kutsuki, Gaku Okamoto, Takuji Hosoi, Takayoshi Shimura, and Heiji Watanabe

Appl. Phys. Lett. 95, 022102 (2009); http://dx.doi.org/10.1063/1.3171938 (3 pages) | Cited 15 times

Online Publication Date: 13 July 2009

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Germanium oxynitride (GeON) gate dielectrics with surface nitrogen-rich layers were fabricated by plasma nitridation of thermally grown oxides (GeO2) on Ge(100). Insulating features of ultrathin GeO2 layers of around 2-nm-thick were found to improve with plasma treatment, in which leakage current was drastically reduced to over four orders of magnitude. Consequently, Au/GeON/Ge capacitors of an equivalent oxide thickness down to 1.7 nm were achieved while keeping sufficient leakage reduction merit. The minimum interface state density values of GeON/Ge structures as low as 3×1011 cm−2 eV−1 were obtained for both the lower and upper halves of the bandgap without any postnitridation treatments. These results were discussed based on the effects of plasma nitridation on a degraded GeO2 surface for recovering its electrical properties by creating stable nitride layers.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
77.55.-g Dielectric thin films
73.61.Ng Insulators
84.32.Tt Capacitors
52.77.-j Plasma applications
71.20.Ps Other inorganic compounds

The role of threading dislocations and unintentionally incorporated impurities on the bulk electron conductivity of In-face InN

Chad S. Gallinat, Gregor Koblmüller, and James S. Speck

Appl. Phys. Lett. 95, 022103 (2009); http://dx.doi.org/10.1063/1.3173202 (3 pages) | Cited 28 times

Online Publication Date: 13 July 2009

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The origin of bulk electrons in In-face InN has been studied by considering the effects of both unintentionally incorporated impurities and threading dislocation densities on electron transport properties. The concentration of unintentionally incorporated oxygen and hydrogen scaled with the bulk electron concentration while threading dislocations had no discernable effect on the electron concentration. We conclude that unintentional impurities were the significant source of electrons and threading dislocations acted only as scattering centers limiting the electron mobility in as-grown InN films. Further, we present In-face InN growth techniques controlling the incorporation of oxygen and hydrogen and reducing threading dislocation densities.
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71.55.Eq III-V semiconductors
61.72.jj Interstitials
61.72.jd Vacancies
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors

Carrier transport mechanisms in nonvolatile memory devices fabricated utilizing multiwalled carbon nanotubes embedded in a poly-4-vinyl-phenol layer

Won Tae Kim, Jae Hun Jung, and Tae Whan Kim

Appl. Phys. Lett. 95, 022104 (2009); http://dx.doi.org/10.1063/1.3174913 (3 pages) | Cited 4 times

Online Publication Date: 14 July 2009

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Transmission electron microscopy images showed that multiwalled carbon nanotubes (MWCNTs) were dispersed in a poly-4-vinyl-phenol (PVP) layer. Capacitance-voltage (C-V) measurements on the Al/MWCNTs embedded in a PVP layer/p-Si (100) devices at 300 K showed a clockwise hysteresis with a large flatband voltage shift due to the existence of the MWCNTs. The magnitude of the flatband voltage shift in the C-V curve for the devices increased with increasing MWCNT concentration. The carrier transport mechanisms for the writing and the erasing processes for the Al/MWCNTs embedded in PVP/p-Si devices are described on the basis of the C-V results.
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84.30.Sk Pulse and digital circuits
72.20.Fr Low-field transport and mobility; piezoresistance
68.37.Og High-resolution transmission electron microscopy (HRTEM)
73.63.Bd Nanocrystalline materials
61.46.Fg Nanotubes

Photoconductivity of iron doped amorphous carbon films on n-type silicon substrates

Caihua Wan, Xiaozhong Zhang, Xin Zhang, Xili Gao, and Xinyu Tan

Appl. Phys. Lett. 95, 022105 (2009); http://dx.doi.org/10.1063/1.3177190 (3 pages) | Cited 9 times

Online Publication Date: 14 July 2009

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The Fe doped a-C films on n-type silicon substrates were deposited by pulse laser deposition. The Fe doped a-C films are p-type semiconductor and they are rich in sp2 ( ∼ 75%). I-V characteristics and photoconductivity of the structures were measured in the current in-plane geometry. The photoconductivity with magnitude of 170 ∼ 220 was observed under white light illumination with power of 20 mW/cm2 at room temperature. The photoconductivity is ascribed to the p-n junction formed between the p-type a-C: Fe film and the n-type Si substrate whose reverse-biased saturation current increases intensively under illumination.
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73.50.Pz Photoconduction and photovoltaic effects
81.15.Fg Pulsed laser ablation deposition
73.61.Jc Amorphous semiconductors; glasses
81.05.Gc Amorphous semiconductors
61.72.up Other materials
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Direct injection tunnel spectroscopy of a p-n junction

Edward M. Likovich, Kasey J. Russell, Venkatesh Narayanamurti, Hong Lu, and Arthur C. Gossard

Appl. Phys. Lett. 95, 022106 (2009); http://dx.doi.org/10.1063/1.3177191 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2009

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We demonstrate spectroscopic measurements on an InGaAs p-n junction using direct tunnel injection of electrons. In contrast to the metal-base transistor design of conventional ballistic electron emission spectroscopy (BEES), the base layer of our device is comprised of a thin, heavily doped p-type region. By tunneling directly into the semiconductor, we observe a significant increase in collector current compared to conventional BEES measurements. This could enable the study of systems and processes that have thus far been difficult to probe with the low-electron collection efficiency of conventional BEES, such as luminescence from single-buried quantum dots.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Gk Tunneling
81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
73.63.Kv Quantum dots
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors

Correlation of high temperature x-ray photoemission valence band spectra and conductivity in strained LaSrFeNi oxide on SrTiO3(110)

A. Braun, X. Zhang, Y. Sun, U. Müller, Z. Liu, S. Erat, M. Ari, H. Grimmer, S. S. Mao, and T. Graule

Appl. Phys. Lett. 95, 022107 (2009); http://dx.doi.org/10.1063/1.3174916 (3 pages) | Cited 1 time

Online Publication Date: 15 July 2009

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Reversible and irreversible discontinuities at around 573 and 823 K in the electric conductivity of a strained 175 nm thin film of (La0.8Sr0.2)0.95Ni0.2Fe0.8O3−δ grown by pulsed laser deposition on SrTiO3 (110) are reflected by valence band changes as monitored in photoemission and oxygen K-edge x-ray absorption spectra (XAS). The irreversible jump at 823 K is attributed to depletion of doped electron holes concomitant with reduction of Fe3+ toward Fe2+, as evidenced by oxygen and iron core level soft XAS, and possibly of a chemical origin, whereas the reversible jump at 573 K possibly originates from structural changes.
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79.60.Dp Adsorbed layers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
73.61.Ng Insulators
78.66.Nk Insulators
68.55.jd Thickness
71.27.+a Strongly correlated electron systems; heavy fermions
81.15.Fg Pulsed laser ablation deposition
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.70.Dm X-ray absorption spectra

Injection of carriers from a ZnO nanostructured shell to a ZnS based microsphere core

Sung Il Ahn, Seong Eui Lee, Yong-Hoon Cho, Gi Ryoung Kim, Song-Mei Li, Kyung Cheol Choi, and Won Hee Lee

Appl. Phys. Lett. 95, 022108 (2009); http://dx.doi.org/10.1063/1.3177066 (3 pages) | Cited 1 time

Online Publication Date: 15 July 2009

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ZnO nanostructures were synthesized on a microsphere ZnS:Cu,Cl (ZC) with various optical emission bands. Using an electroluminescence (EL) device with a semiliquid type of active layer, the carrier injection phenomenon through the nanostructure was observed. The EL from ZnO nanorods on the cubic ZC and the ZnO plate on the hexagonal ZC showed a nonlinear voltage-color characteristic and deep blue color, respectively, as explained by the carrier injection through the ZnO nanostructures. Both carrier injection cases appear to have been caused by the lowered band-gap energy at the boundary and by the structural factors that focused the applied electric field.
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73.63.Bd Nanocrystalline materials
73.22.-f Electronic structure of nanoscale materials and related systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
85.60.Jb Light-emitting devices
78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
81.16.-c Methods of micro- and nanofabrication and processing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Different resistance switching behaviors of NiO thin films deposited on Pt and SrRuO3 electrodes

J. S. Choi, J.-S. Kim, I. R. Hwang, S. H. Hong, S. H. Jeon, S.-O. Kang, B. H. Park, D. C. Kim, M. J. Lee, and S. Seo

Appl. Phys. Lett. 95, 022109 (2009); http://dx.doi.org/10.1063/1.3173813 (3 pages) | Cited 22 times

Online Publication Date: 16 July 2009

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We have compared resistance switching of NiO films deposited on Pt and SrRuO3 (SRO): unipolar switching in Pt/NiO/Pt and bipolar switching in Pt/NiO/SRO. Linear fitted current-voltage curves and capacitance-voltage results show that on- and off-states conductions in unipolar switching are dominated by inductive Ohmic behavior and Poole–Frenkel effect, respectively. However, the conductions of on- and off-states in bipolar switching follow capacitive Ohmic behavior and Schottky effect, respectively. Therefore, we infer that the mechanisms of the unipolar and bipolar switching behaviors in NiO films are related with changes in bulk-limited filamentary conduction and interfacial Schottky barrier, respectively.
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73.30.+y Surface double layers, Schottky barriers, and work functions
81.15.Cd Deposition by sputtering
73.50.Fq High-field and nonlinear effects
68.55.jd Thickness
73.61.-r Electrical properties of specific thin films
72.60.+g Mixed conductivity and conductivity transitions

Large magnetoresistances and non-Ohmic conductivity in EuWO1+xN2−x

A. Kusmartseva, M. Yang, J. Oró-Solé, A. M. Bea, A. Fuertes, and J. P. Attfield

Appl. Phys. Lett. 95, 022110 (2009); http://dx.doi.org/10.1063/1.3180813 (3 pages) | Cited 8 times

Online Publication Date: 16 July 2009

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The magnetic field and voltage dependent electronic transport properties of EuWO1+xN2−x ceramics are reported. Large negative magnetoresistances are observed at low temperatures, up to 70% in the least doped (x = 0.09) material. Non-Ohmic conduction emerges below the 12 K Curie transition. This is attributed to a microstructure of ferromagnetic conducting and antiferromagnetic insulating regions resulting from small spatial fluctuations in the chemical doping.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
61.72.up Other materials
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics
75.47.De Giant magnetoresistance

High-performance dinaphtho-thieno-thiophene single crystal field-effect transistors

Simon Haas, Yukihiro Takahashi, Kazuo Takimiya, and Tatsuo Hasegawa

Appl. Phys. Lett. 95, 022111 (2009); http://dx.doi.org/10.1063/1.3183509 (3 pages) | Cited 27 times

Online Publication Date: 16 July 2009

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We fabricated high-performance single crystal organic field-effect transistors (SC-OFETs) based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene (DNTT). Among various device geometries and contact types, best performance is obtained for a lamination-type SC-OFET composed of a Cytop-treated SiO2 gate dielectric and top-contact gold/tetrathiafulvalene-tetracyanoquinodimethane electrodes, which results in hysteresis-free device characteristics with optimum mobility of 8.3 cm2/V s and an on/off ratio of >108. The achieved performance is promising for use of the air-stable DNTT in future studies of intrinsic properties of molecular crystals.
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85.30.Tv Field effect devices
82.45.Fk Electrodes

A modified scheme of charge sensitive infrared phototransistor

Zhihai Wang, S. Komiyama, T. Ueda, and N. Nagai

Appl. Phys. Lett. 95, 022112 (2009); http://dx.doi.org/10.1063/1.3173819 (3 pages) | Cited 5 times

Online Publication Date: 17 July 2009

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Charge sensitive infrared phototransistors (CSIP) realized in a GaAs/AlGaAs double quantum well (QW) structure have so far exploited the tunneling of excited electrons from an isolated island of upper QW to the lower two-dimensional electron gas layer. Another type of CSIP is developed by using a GaAs/AlGaAs double QW crystal, in which inter-QW tunneling is suppressed. Instead of “vertical” tunneling, excited electrons in the upper QW flow in and out the isolated island “laterally” via translational motion through gate-induced potential barriers. The scheme is demonstrated for wavelengths ≈ 14.6 μm but is suitable for expanding toward longer wavelengths.
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85.60.Dw Photodiodes; phototransistors; photoresistors
73.40.Gk Tunneling
73.63.Hs Quantum wells
73.21.Fg Quantum wells

Using a two-dimensional electron gas to study nonequilibrium tunneling dynamics and charge storage in self-assembled quantum dots

B. Marquardt, M. Geller, A. Lorke, D. Reuter, and A. D. Wieck

Appl. Phys. Lett. 95, 022113 (2009); http://dx.doi.org/10.1063/1.3175724 (3 pages) | Cited 10 times

Online Publication Date: 17 July 2009

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We demonstrate a strong influence of charged self-assembled quantum dots (QD) on the conductance of a nearby two-dimensional electron gas (2DEG). A conductance measurement of the 2DEG allows us to probe the charge tunneling dynamics between the 2DEG and the QDs in nonequilibrium as well as close to equilibrium. Measurements of hysteresis curves with different sweep times and time-resolved conductance measurements enable us to unambiguously identify the transients as tunneling events between the 2DEG and QD states.
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73.63.Kv Quantum dots
73.40.Gk Tunneling

Spin polarization control by electric stirring: Proposal for a spintronic device

Yu. V. Pershin, N. A. Sinitsyn, A. Kogan, A. Saxena, and D. L. Smith

Appl. Phys. Lett. 95, 022114 (2009); http://dx.doi.org/10.1063/1.3180494 (3 pages) | Cited 2 times

Online Publication Date: 17 July 2009

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We propose a spintronic device to generate spin polarization in a mesoscopic region by purely electric means. We show that the spin Hall effect in combination with the stirring effect are sufficient to induce measurable spin polarization in a closed geometry. Our device structure does not require the application of magnetic fields, external radiation or ferromagnetic leads, and can be implemented in standard semiconducting materials.
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72.25.Dc Spin polarized transport in semiconductors
72.20.My Galvanomagnetic and other magnetotransport effects
73.23.-b Electronic transport in mesoscopic systems
73.63.-b Electronic transport in nanoscale materials and structures

High-quality single-crystal Ge stripes on quartz substrate by rapid-melting-growth

Masanobu Miyao, Kaoru Toko, Takanori Tanaka, and Taizoh Sadoh

Appl. Phys. Lett. 95, 022115 (2009); http://dx.doi.org/10.1063/1.3182795 (3 pages) | Cited 28 times

Online Publication Date: 17 July 2009

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Single-crystal Ge on a transparent insulating substrate is desired to achieve advanced thin-film transistors (TFTs) with high speed operation. We have developed the rapid-melting-growth process of amorphous Ge by using polycrystalline Si islands as the growth seed. High-quality and dominantly (100)-oriented single-crystal Ge stripes with 400 μm length are demonstrated on quartz substrates. The temperature dependence of the electrical conductivity shows a high hole mobility of 1040 cm2/V s. This method opens up a possibility of Ge-channel TFT with the high carrier mobility.
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73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Cw Elemental semiconductors
85.30.Tv Field effect devices
73.61.Jc Amorphous semiconductors; glasses

CoAl2O4–Fe2O3 p-n nanocomposite electrodes for photoelectrochemical cells

Kwang-Soon Ahn, Yanfa Yan, Moon-Sung Kang, Jin-Young Kim, Sudhakar Shet, Heli Wang, John Turner, and Mowafak Al-Jassim

Appl. Phys. Lett. 95, 022116 (2009); http://dx.doi.org/10.1063/1.3183585 (3 pages) | Cited 6 times

Online Publication Date: 17 July 2009

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CoAl2O4–Fe2O3 p-n nanocomposite electrodes were deposited on Ag-coated stainless-steel substrates and annealed at 800 °C. Their photoelectrochemical (PEC) properties were investigated and compared with that of p-type CoAl2O4 films. We found that the nanocomposite electrodes exhibit much improved PEC photoresponse as compared to the reference p-type CoAl2O4 electrodes. We speculate that the enhancement is due to the formation of a three-dimensional junction between p-type CoAl2O4 and n-type Fe2O3 nanoparticles, which improves electron-hole separation, thus reducing charge recombination upon light illumination.
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82.47.Jk Photoelectrochemical cells, photoelectrochromic and other hybrid electrochemical energy storage devices
82.45.Fk Electrodes
82.45.Yz Nanostructured materials in electrochemistry
72.40.+w Photoconduction and photovoltaic effects
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
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Converse magnetoelectric effect in ferromagnetic shape memory alloy/piezoelectric laminate

S. Y. Chen, D. H. Wang, Z. D. Han, C. L. Zhang, Y. W. Du, and Z. G. Huang

Appl. Phys. Lett. 95, 022501 (2009); http://dx.doi.org/10.1063/1.3179146 (3 pages) | Cited 17 times

Online Publication Date: 13 July 2009

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In laminates, the converse magnetoelectric (CME) effect is often achieved by an elastic coupling between magnetostrictive and piezoelectric layers. Here the authors report on an alternative mechanism for obtaining CME. In a transition-metals-based ferromagnetic shape memory alloy/piezoelectric ceramic laminated composite, the stress-induced martensitic transformation is utilized to gain the magnetic changes, which gives rise to a giant CME effect consequently. The strong CME is observed at room temperature over a broad bandwidth, under weak magnetic bias and electric field.
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75.80.+q Magnetomechanical effects, magnetostriction
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
75.50.Cc Other ferromagnetic metals and alloys
64.70.K- Solid-solid transitions

Spin reorientation transitions in Pt/Co/Pt films under low dose Ga+ ion irradiation

J. Jaworowicz, A. Maziewski, P. Mazalski, M. Kisielewski, I. Sveklo, M. Tekielak, V. Zablotskii, J. Ferré, N. Vernier, A. Mougin, A. Henschke, and J. Fassbender

Appl. Phys. Lett. 95, 022502 (2009); http://dx.doi.org/10.1063/1.3179147 (3 pages) | Cited 10 times

Online Publication Date: 13 July 2009

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An elegant route for tuning the magnetic anisotropy of ultrathin Co films by Ga+ ion irradiation is presented. The magnetic anisotropy of a Pt/Co(2.6 nm)/Pt film is first changed from in-plane to out-of-plane by uniform low dose Ga+ ion irradiation at 30 keV. When increasing the dose, a second spin reorientation transition toward the sample plane is also evidenced. This could be a way to design magnetic nanowires with perpendicular anisotropy, embedded in an in-plane magnetized environment, either by irradiation through a mask or focused ion beam. Tentative explanations on the origin of these two successive spin reorientations are proposed.
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75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
68.55.at Other materials
75.30.Gw Magnetic anisotropy
61.80.Jh Ion radiation effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

A bias voltage dependent positive magnetoresistance in Cox–C1−x/Si heterostructure

Xin Zhang, Xiaozhong Zhang, Caihua Wan, and Lihua Wu

Appl. Phys. Lett. 95, 022503 (2009); http://dx.doi.org/10.1063/1.3179152 (3 pages) | Cited 12 times

Online Publication Date: 13 July 2009

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Cox–C1−x granular films were deposited on n-type Si substrates by pulsed laser deposition method. The heterostructure, investigated in current-perpendicular-to-plane geometry, has a bias voltage dependent positive magnetoresistance (MR), and at room temperature, the MR value reaches 16% at magnetic field H = 2.5 kOe and bias voltage of 6 V. All MRs have saturated behavior when H>2.5 kOe. The mechanism of this MR is attributed to that the applied magnetic field and local random magnetic field modulate the ratio of singlet and triplet spin states leading to the MR.
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72.20.My Galvanomagnetic and other magnetotransport effects
68.55.jd Thickness
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.15.Fg Pulsed laser ablation deposition
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators

A model of the exchange bias setting process in magnetic read sensors

J. Barker, B. Craig, R. Lamberton, A. Johnston, R. W. Chantrell, and O. Heinonen

Appl. Phys. Lett. 95, 022504 (2009); http://dx.doi.org/10.1063/1.3179154 (3 pages) | Cited 2 times

Online Publication Date: 13 July 2009

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A model of the acquisition of exchange bias during the high temperature annealing process used to set the bias direction in the antiferromagnet is described. The model is applied to the investigation of the process of setting the bias direction in the antiferromagnetic layer, which comprises a high-temperature anneal in a field sufficiently large to saturate the ferromagnetic layers. It is shown that there is an optimal setting temperature depending on the material parameters. The temperature dependence of the antiferromagnetic anisotropy is shown to be an important factor in achieving maximum exchange bias.
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75.50.Ss Magnetic recording materials
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.60.Nt Magnetic annealing and temperature-hysteresis effects

Frustration driven stripe domain formation in Co/Pt multilayer films

J. E. Davies, O. Hellwig, E. E. Fullerton, M. Winklhofer, R. D. Shull, and Kai Liu

Appl. Phys. Lett. 95, 022505 (2009); http://dx.doi.org/10.1063/1.3179553 (3 pages) | Cited 11 times

Online Publication Date: 13 July 2009

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We report microscopic mechanisms for an unusual magnetization reversal behavior in Co/Pt multilayers where some of the first-order reversal curves protrude outside of the major loop. Transmission x-ray microscopy reveals a fragmented stripe domain topography when the magnetic field is reversed prior to saturation, in contrast to an interconnected pattern when reversing from a saturated state. The different domain nucleation and propagation behaviors are due to unannihilated domains from the prior field sweep. These residual domains contribute to random dipole fields that impede the subsequent domain growth and prevent domains from growing as closely together as for the interconnected pattern.
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75.60.Jk Magnetization reversal mechanisms
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.40.-s Critical-point effects, specific heats, short-range order

Micromagnet-superconducting hybrid structures with directional current flow dependence for persistent current switching

Ali Esad Ozmetin, Murat Kaya Yapici, Jun Zou, Igor F. Lyuksyutov, and Donald G. Naugle

Appl. Phys. Lett. 95, 022506 (2009); http://dx.doi.org/10.1063/1.3176481 (3 pages) | Cited 2 times

Online Publication Date: 13 July 2009

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This letter reports on a microfabricated magnet-superconducting hybrid structure (Co–SiO2–Pb82Bi18) showing the dependence of the critical current (Ic) on the current flow direction. With external magnetic field, intermittent superconducting and normally conducting regions are formed on the Pb82Bi18 film due to field localization created by the Co stripes, which is verified by scanning Hall probe microscopy measurements. Superconducting and normal conduction paths are created parallel and perpendicular to the Co stripes, providing directional dependency on the current flow. By changing the orientation of the ferromagnetic stripes with respect to the superconducting film, the hybrid structure could be adapted to realize a low-power persistent current switch.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
68.37.-d Microscopy of surfaces, interfaces, and thin films
74.25.Sv Critical currents
74.78.-w Superconducting films and low-dimensional structures
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