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11 Aug 2003

Volume 83, Issue 6, pp. 1063-1275

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 1163 (2003); http://dx.doi.org/10.1063/1.1599972 (3 pages)

M. C. Rogge, C. Fühner, U. F. Keyser, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider
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Growth of a-plane InN on r-plane sapphire with a GaN buffer by molecular-beam epitaxy

Hai Lu, William J. Schaff, Lester F. Eastman, J. Wu, Wladek Walukiewicz, Volker Cimalla, and Oliver Ambacher

Appl. Phys. Lett. 83, 1136 (2003); http://dx.doi.org/10.1063/1.1599634 (3 pages) | Cited 45 times

Online Publication Date: 5 August 2003

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We report heteroepitaxial growth of InN on r-plane sapphire substrates with an AlN nucleation layer and GaN buffer using plasma-assisted molecular-beam epitaxy. The InN film was identified to be nonpolar (11math0) a-plane which follows the a-plane GaN buffer. Optical absorption and photoluminescence measurements of this material show that InN has a fundamental band gap of about 0.7 eV, which is also seen for growth on c-plane sapphire. The room-temperature Hall mobility of undoped a-plane InN is around 250 cm2/V s with a carrier concentration around 6×1018 cm−3. We also studied the electrical properties of the a-plane InN as a function of film thickness. In contrast to c-plane InN grown on c-plane sapphire, we did not observe apparent improvement of electrical properties of a-plane InN by growing thicker films. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
78.55.Cr III-V semiconductors

Defects in m-face GaN films grown by halide vapor phase epitaxy on LiAlO2

R. R. Vanfleet, J. A. Simmons, H. P. Maruska, D. W. Hill, M. M. C. Chou, and B. H. Chai

Appl. Phys. Lett. 83, 1139 (2003); http://dx.doi.org/10.1063/1.1599962 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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Free-standing wafers (50 mm diameter) of GaN were grown by halide vapor phase epitaxy on lattice-matched γ-LiAlO2. We report a transmission electron microscopy study of defects and defect densities in these wafers. The growth direction is [10math0]. Stacking faults in the basal plane are seen when viewing the specimen in the [1math10] direction with an average spacing of less than 100 nm. Convergent beam electron diffraction measurements show no switch in the polarity and thus the faults are proposed to be ABABACAC changes in the stacking. Threading dislocations are found to have a correlated arrangement with a density of 3×108 cm−2 when viewing the [1math10] direction and widely varying (depending upon location) when viewing in the [0001] direction. These dislocations act as “seeds” for postgrowth surface features that directly exhibit the correlated nature of these threading dislocations. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Lk Linear defects: dislocations, disclinations
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.35.B- Structure of clean surfaces (and surface reconstruction)

Electronic structure of Li(Co0.7−xAl0.3)MgxO2 studied by electron energy-loss spectroscopy

G. Chen, C. Li, X. Xu, J. Li, and U. Kolb

Appl. Phys. Lett. 83, 1142 (2003); http://dx.doi.org/10.1063/1.1599969 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2003

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Electronic structure of Li(Co0.7−xAl0.3)MgxO2 (x = 0.01, 0.03, and 0.05) is studied via electron energy-loss spectroscopy. Oxygen K edge and Co L2,3 edge were used to investigate the effect of Mg substitution on both the valence state of Co ion and the density of unoccupied states of O ion. A change in the ratio of the white lines of Co ion, L3/L2, is used to identify the change in the valence state in Co ion, which reveals that Mg substitution gives rise to an increase of the average valence of Co ion. This is a mixed valence state of Co3+ and Co4+ in Mg substitution materials. Relative lowering of the integrated intensity of prepeak in oxygen K edge with the Mg concentration connects with a lower covalency of the Co–O bond, which indicates a significant electron feeding back from Co 3d to O 2p. This makes the oxygen ions closer to the feature of closed shell, which helps electron hopping between Co3+ and Co4+ based on the double-exchange process. © 2003 American Institute of Physics.
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71.20.Ps Other inorganic compounds
79.20.Uv Electron energy loss spectroscopy
68.49.Jk Electron scattering from surfaces

Dynamic formation of ring-shaped patterns of colloidal particles in microfluidic systems

David S. W. Lim, J. Patrick Shelby, Jason S. Kuo, and Daniel T. Chiu

Appl. Phys. Lett. 83, 1145 (2003); http://dx.doi.org/10.1063/1.1600532 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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This letter reports the formation of patterns of micrometer-sized beads within the steady-state recirculation flow of a microvortex generated in a microfluidic system. The mechanism by which these patterns form relies on a delicate balance between the centrifugal and displacement forces experienced by the recirculating particles with a lift force exerted on the particles near the solid boundary of the microcavity. Our observation was made possible by the small dimensions of the microchannels we used and by the presence of steep velocity gradients unique to microfluidic devices. © 2003 American Institute of Physics.
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47.54.-r Pattern selection; pattern formation
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
47.55.Kf Particle-laden flows
47.32.C- Vortex dynamics
47.85.Np Fluidics
82.70.Dd Colloids
47.60.-i Flow phenomena in quasi-one-dimensional systems
83.50.Ha Flow in channels

Epitaxial growth and large band-gap bowing of ZnSeO alloy

Y. Nabetani, T. Mukawa, Y. Ito, T. Kato, and T. Matsumoto

Appl. Phys. Lett. 83, 1148 (2003); http://dx.doi.org/10.1063/1.1600510 (3 pages) | Cited 19 times

Online Publication Date: 5 August 2003

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ZnSeO alloy was grown by molecular-beam epitaxy up to 1.3% O composition on GaAs substrate using rf plasma. The crystal structure of epitaxial ZnSeO alloy was zinc-blende. O composition was estimated by a strain-free lattice constant. No phase separation was observed by in situ reflection high-energy electron diffraction and x-ray diffraction. Photoluminescence intensity was larger than that of ZnSe. The peak energy shifted toward lower energies with increasing O composition. The band-gap energy determined by photoluminescence excitation spectra decreased with increasing O composition. A bowing parameter as high as 8 eV was obtained. This large band-gap bowing widens the controllable energy-gap range of II-VI semiconductor. © 2003 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Et II-VI semiconductors
61.66.Fn Inorganic compounds

Quantum mechanical predictions of nonscalar equations of state and nonmonotonic elastic stress-strain relations

Damian C. Swift and Graeme J. Ackland

Appl. Phys. Lett. 83, 1151 (2003); http://dx.doi.org/10.1063/1.1599043 (3 pages) | Cited 5 times

Online Publication Date: 5 August 2003

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In continuum mechanics, the isotropic part of the stress deviator (mean pressure) is routinely assumed to depend on the isotropic part of the strain deviator (compression). This assumption was tested using ab initio quantum mechanical calculations of elastic stress as a function of elastic strain and compression. Except for face-centered-cubic elements, the mean pressure varied significantly with shear strain as well as compression. In general, the shear stress did not increase monotonically with elastic shear strain. These phenomena may be important when comparing experimental data obtained on different time scales, particularly when interpreting dynamic response data from short-pulse laser experiments. © 2003 American Institute of Physics.
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46.05.+b General theory of continuum mechanics of solids
46.35.+z Viscoelasticity, plasticity, viscoplasticity
62.20.F- Deformation and plasticity
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Formation of vanadium-based ohmic contacts to n-GaN

June O Song, Sang-Ho Kim, Joon Seop Kwak, and Tae-Yeon Seong

Appl. Phys. Lett. 83, 1154 (2003); http://dx.doi.org/10.1063/1.1598284 (3 pages) | Cited 16 times

Online Publication Date: 5 August 2003

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We investigate vanadium (V)-based ohmic contacts on n-GaN (Nd = 2.0×1018 cm−3) as a function of annealing temperature. It is shown that the V (60 nm) contacts become ohmic with specific contact resistances of 10−3–10−4 Ω cm2 upon annealing at 650 and 850 °C. The V (20 nm)/Ti (60 nm)/Au (20 nm) contacts produce very low specific contact resistances of 2.2×10−5 and 4.0×10−6 Ω cm2 when annealed at 650 and 850 °C, respectively. A comparison shows that the use of the overlayers (Ti/Au) is very effective in improving ohmic property. Based on Auger electron spectroscopy and glancing-angle x-ray diffraction results, possible explanations for the annealing temperature dependence of the ohmic behavior of the V-based contacts are described and discussed. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.61.Ey III-V semiconductors
73.40.Cg Contact resistance, contact potential
79.20.Fv Electron impact: Auger emission

Determination of free carrier bipolar diffusion coefficient and surface recombination velocity of undoped GaN epilayers

R. Aleksiejūnas, M. Sūdžius, T. Malinauskas, J. Vaitkus, K. Jarašiūnas, and S. Sakai

Appl. Phys. Lett. 83, 1157 (2003); http://dx.doi.org/10.1063/1.1599036 (3 pages) | Cited 24 times

Online Publication Date: 5 August 2003

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Time-resolved nondegenerate four-wave mixing experiments were performed on 2.6-μm-thick GaN epilayers grown by metalorganic chemical-vapor deposition using picosecond pulses at 355 and 1064 nm for grating recording and probing, respectively. Measurements of free carrier grating kinetics at various grating periods Λ in range from 3 to 10 μm allowed determination of nonequilibrium carrier bipolar diffusion coefficient D = 1.7 cm2/s at 300 K. Substitution of the D value into two-dimensional carrier transport model allowed fitting of the whole set of grating kinetics at various Λ varying surface recombination velocity S and linear recombination time τR. This procedure provided us a value of S = 5×104 cm/s as well as carrier lifetime of ∼1 ns. © 2003 American Institute of Physics.
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73.61.Ey III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.25.+i Surface conductivity and carrier phenomena

Enhanced room-temperature piezoconductance of metal–semiconductor hybrid structures

A. C. H. Rowe, D. R. Hines, and S. A. Solin

Appl. Phys. Lett. 83, 1160 (2003); http://dx.doi.org/10.1063/1.1600840 (3 pages) | Cited 13 times

Online Publication Date: 5 August 2003

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Metal–semiconductor hybrids (MSHs) are found to exhibit enhanced room-temperature piezoconductance in the presence of uniaxial tensile strain. The magnitude of the enhanced piezoconductance is more than five times greater than that of the homogeneous semiconductor alone and is strongly dependent on both the location and properties of the metal–semiconductor interface. MSHs may be useful in determining the electrical properties of low-resistance metal contacts on semiconductors. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.40.Cg Contact resistance, contact potential

Combined atomic force microscope and electron-beam lithography used for the fabrication of variable-coupling quantum dots

M. C. Rogge, C. Fühner, U. F. Keyser, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider

Appl. Phys. Lett. 83, 1163 (2003); http://dx.doi.org/10.1063/1.1599972 (3 pages) | Cited 2 times

Online Publication Date: 5 August 2003

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We have combined direct nanofabrication by local anodic oxidation with conventional electron-beam lithography to produce a parallel double quantum dot based on a GaAs/AlGaAs heterostructure. The combination of both nanolithography methods allows fabrication of robust in-plane gates and Cr/Au top-gate electrodes on the same device for optimal controllability. This is illustrated by the tunability of the interdot coupling in our device. We describe our fabrication and alignment scheme in detail and demonstrate the tunability in low-temperature transport measurements. © 2003 American Institute of Physics.
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81.16.Nd Micro- and nanolithography
81.16.Ta Atom manipulation
81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
68.47.Fg Semiconductor surfaces
68.65.Hb Quantum dots (patterned in quantum wells)
85.40.Hp Lithography, masks and pattern transfer
81.65.Mq Oxidation

Isoelectronic doping of AlGaN alloys with As and estimates of AlGaN/GaN band offsets

C. T. Foxon, S. V. Novikov, L. X. Zhao, and I. Harrison

Appl. Phys. Lett. 83, 1166 (2003); http://dx.doi.org/10.1063/1.1599635 (3 pages) | Cited 7 times

Online Publication Date: 5 August 2003

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The isoelectronic doping of AlxGa1−xN alloys with arsenic in films grown by molecular-beam epitaxy has been investigated. In photoluminescence spectra of AlxGa1−xN layers, with an increase in Al mole faction, there is a progressive shift of the position of the blue band emission towards higher energies. The observed energy shift for blue band emission is less than the corresponding increase in the band gap of AlxGa1−xN. A model is presented, which can explain the observed shift in the energy of the blue band emission. This model also allows the AlxGa1−xN/GaN valence band offset to be estimated. © 2003 American Institute of Physics.
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78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
78.55.Cr III-V semiconductors
73.20.At Surface states, band structure, electron density of states
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Composition dependence of polarization fields in GaInN/GaN quantum wells

A. Hangleiter, F. Hitzel, S. Lahmann, and U. Rossow

Appl. Phys. Lett. 83, 1169 (2003); http://dx.doi.org/10.1063/1.1601310 (3 pages) | Cited 37 times

Online Publication Date: 5 August 2003

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We report an experimental determination of the internal polarization field in GaInN/GaN quantum wells, due to piezoelectric and spontaneous polarization, utilizing the quantum confined Stark effect, with fields as large as 3.1 MV/cm at 22% In. From its dependence on quantum well composition and strain, we find that the total field in GaInN is a linear combination of polarization charges from GaN and InN. The piezoelectric constants d31 for GaN and InN derived from our data are 1.05±0.05 pm/V and 3.7±0.5 pm/V, in fair agreement with theoretical data. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
77.22.Ej Polarization and depolarization
77.65.Bn Piezoelectric and electrostrictive constants
78.67.De Quantum wells
78.20.Jq Electro-optical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
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Anomalous temperature dependence of coercivity in precipitation hardened Pr–Co–Cu–Ti magnets

Jian Zhang, Hui Liu, Chuan-bin Rong, Hong-wei Zhang, Shao-ying Zhang, Bao-gen Shen, Yuan-qiang Bai, and Bao-he Li

Appl. Phys. Lett. 83, 1172 (2003); http://dx.doi.org/10.1063/1.1597747 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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The anomalous temperature dependence of coercicity, Hc(T), has been observed in precipitation hardened PrCo6.7−xCuxTi0.3 (x = 0.2–1) magnets. Transmission electron microscopy reveals that they exhibit a cellular microstructure. With an increase of Cu content, the Curie temperature of the 2:17 phase remains nearly unchanged whereas that of the 1:5 phase decreases. The peak of Hc(T) becomes higher, broader and shifts towards low temperature while the room temperature coercivity remains low and does not change with an increase of Cu content. There is a strong correlation between the Curie temperature of the 1:5 phase and the peak of Hc(T). The effect of Cu on Hc(T) cannot be explained by a traditional domain wall pinning model. It is highly likely that their magnetization reversal is controlled by the nucleation of reverse domains in isolated 2:17 cells. © 2003 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
75.50.Vv High coercivity materials
81.40.Rs Electrical and magnetic properties related to treatment conditions
75.50.Cc Other ferromagnetic metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure

Dynamic orientation ratio in longitudinal recording media

S. N. Piramanayagam, J. H. Yin, H. B. Zhao, J. Kasim, Y. J. Chen, J. Zhang, and C. H. Hee

Appl. Phys. Lett. 83, 1175 (2003); http://dx.doi.org/10.1063/1.1599045 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2003

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The origin of orientation ratio (OR) in longitudinal recording media has been controversial in the literature. In the past, the observation of a higher OR for thinner magnetic films has been attributed to stress or thermal effects. Our measurements, carried out over a larger range of time scales, confirm that the thermal effects play a major role in the observation of a higher OR for thinner magnetic films. We point out that the OR is dynamic and follows a ln(t) behavior at larger time scales (5–1000 s). Our studies indicate that a larger OR and a more dynamic behavior of OR will be observed when KuV/kBT values are smaller. We also propose that the slope of dynamic OR can be used to compare the recording performance of media indirectly. © 2003 American Institute of Physics.
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75.50.Ss Magnetic recording materials
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.70.Ak Magnetic properties of monolayers and thin films

Electronic structures of two-phase microstructures α and β in heavily Pb-doped Bi2Sr2CaCu2Oy single crystals investigated by scanning tunneling microscopy/spectroscopy

G. Kinoda, T. Hasegawa, S. Nakao, T. Hanaguri, K. Kitazawa, K. Shimizu, J. Shimoyama, and K. Kishio

Appl. Phys. Lett. 83, 1178 (2003); http://dx.doi.org/10.1063/1.1594826 (3 pages) | Cited 8 times

Online Publication Date: 5 August 2003

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We have performed scanning tunneling microscopy/spectroscopy (STM/STS) of a high-Jc superconductor, heavily Pb-doped Pb0.6Bi1.4Sr2CaCu2Oy, at low temperatures below Tc. The obtained STM images showed a lamella-type phase separation into Pb-poor and Pb-rich regions. At 4.3 K, values of energy gap Δ, deduced from STS spectra, showed considerable inhomogeneity in the range of 20–80 meV, while Δ variations across the phase boundaries were less significant. At 63 K, in contrast, we found that Δ altered sharply at the boundaries particularly in the annealed samples, resulting from the suppression of electronic inhomogeneity in each phase. This suggests that the phase boundaries act as strong pinning centers at higher temperatures. © 2003 American Institute of Physics.
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74.25.Jb Electronic structure (photoemission, etc.)
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Microstructure and high critical current density of in situ processed MgB2 tapes made by WSi2 and ZrSi2 doping

Yanwei Ma, H. Kumakura, A. Matsumoto, and K. Togano

Appl. Phys. Lett. 83, 1181 (2003); http://dx.doi.org/10.1063/1.1600508 (3 pages) | Cited 23 times

Online Publication Date: 5 August 2003

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WSi2- and ZrSi2-doped Fe-sheathed MgB2 tapes were prepared through the in situ powder-in-tube method. Both WSi2- and ZrSi2-doped tapes were found to have significantly increased critical current density Jc at 4.2 K in magnetic fields up to 12 T than their undoped counterpart. Scanning electron microscopy investigation revealed that the WSi2 and ZrSi2, doping enhanced intergranular connectivity, thus raising Jc by more than a factor of 2.2 and 3.4, respectively. Moreover, the critical temperature for the doped tapes decreased slightly (less than 0.7 K). It was also found that the improved field dependence of the WSi2 tapes was due to the pinning by possible segregates or defects caused by the WSi2 addition. This role of WSi2 and ZrSi2 may be very beneficial in the fabrication of MgB2 tapes for a large range of applications. © 2003 American Institute of Physics.
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74.10.+v Occurrence, potential candidates
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.62.Dh Effects of crystal defects, doping and substitution
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
74.70.Dd Ternary, quaternary, and multinary compounds (including Chevrel phases, borocarbides, etc.)
61.72.-y Defects and impurities in crystals; microstructure
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)

Nanoscale observation of room-temperature ferromagnetism on ultrathin (La,Ba)MnO3 films

Teruo Kanki, Run-Wei Li, Yasuhisa Naitoh, Hidekazu Tanaka, Takuya Matsumoto, and Tomoji Kawai

Appl. Phys. Lett. 83, 1184 (2003); http://dx.doi.org/10.1063/1.1599971 (3 pages) | Cited 21 times

Online Publication Date: 5 August 2003

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We have fabricated La0.8Ba0.2MnO3 ultrathin films with an atomically flat surface and have systematically investigated the magnetism for film thickness dependence. The 20-nm-thick film showed a maximum peak of TC (310 K). It was found that even the 5-nm-thick film showed a TC of 290 K near room temperature, which opens up the possibility of spin devices working at room temperature. Furthermore, we have adopted noncontact magnetic force microscopy to evaluate local magnetization in ultrathin (La,Ba)MnO3 films, and confirmed that several tens of nanocale ferromagnetic domains appear at room temperature. © 2003 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ch Domain walls and domain structure
75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Dd Nonmetallic ferromagnetic materials
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Rt Magnetic force microscopy (MFM)
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Analysis of ultrathin SiO2 interface layers in chemical vapor deposition of Al2O3 on Si by in situ scanning transmission electron microscopy

R. F. Klie, N. D. Browning, A. Roy Chowdhuri, and C. G. Takoudis

Appl. Phys. Lett. 83, 1187 (2003); http://dx.doi.org/10.1063/1.1597415 (3 pages) | Cited 12 times

Online Publication Date: 5 August 2003

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The development of Al2O3 as an alternative gate dielectric for microelectronic applications depends on the ability to grow a high-quality nanoscale thin film that forms an atomically abrupt interface with Si. Here, the combination of in situ Z-contrast imaging, electron energy loss spectroscopy and x-ray photoelectron spectroscopy of amorphous Al2O3 films grown by metalorganic chemical vapor deposition shows that excess oxygen incorporated into the film routinely reacts with the Si substrate to form an amorphous SiO2 interface layer during postdeposition annealing. The intrinsic oxygen-rich environment of all films grown by such techniques and the necessity of postdeposition processing in device applications implies that control and optimization of the SiO2 interface layers could be of utmost interest for high-κ dielectric stacked structures. © 2003 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Nq Composition and phase identification
68.37.Lp Transmission electron microscopy (TEM)
61.72.Cc Kinetics of defect formation and annealing

Electrostrictive behavior of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)

J. T. Garrett, C. M Roland, A. Petchsuk, and T. C. Chung

Appl. Phys. Lett. 83, 1190 (2003); http://dx.doi.org/10.1063/1.1600515 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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The mechanism underlying the large electric-field-induced strains in terpolymers of vinylidene fluoride, trifluoroethylene, and chlorotrifluoroethylene was investigated. The electrostrictive strain increased by an order of magnitude with increasing temperature, up to the Curie transition, and was essentially invariant to temperature thereafter. Infrared absorption spectra, obtained as a function of both temperature and electric field strength, revealed no change in the crystal phase structure for electric fields sufficient to induce longitudinal strains of ∼ 1%. Thus, the electrostriction observed herein is not due to crystal phase conversion. The Maxwell strain was also negligible under all conditions, because of the terpolymer’s high mechanical modulus (10 to 100 MPa). The mechanical properties exhibit an anomalous change in behavior near the Curie transition, whose origin is unclear. © 2003 American Institute of Physics.
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77.65.Bn Piezoelectric and electrostrictive constants
78.30.Jw Organic compounds, polymers
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.41.+e Polymers, elastomers, and plastics

The enhanced and optimal piezoelectric coefficients in single crystalline barium titanate with engineered domain configurations

Dan Liu and JiangYu Li

Appl. Phys. Lett. 83, 1193 (2003); http://dx.doi.org/10.1063/1.1600517 (3 pages) | Cited 23 times

Online Publication Date: 5 August 2003

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In this letter, we report a micromechanical analysis to explain the enhanced piezoelectric coefficients in ferroelectric single crystals poled along a nonpolar axis, where the coexistence of several variants leads to a complicated domain configuration. The engineered domain configuration in the crystal is constructed first using energy minimization approach, and the effective moduli of single crystal with engineered domain configuration is then determined using homogenization theory. Following this procedure, we calculate the effective electromechanical moduli of tetragonal barium titanate poled along [111] direction, where the piezoelectric coefficient d33 is found to be 70% higher than those poled along [001], consistent with experimental observation. Piezoelectric coefficient d32 is also found to be 114% higher. In addition, we notice that poling along [111] direction does not lead to the optimal domain configuration, since barium titanate poled along [110] direction has much higher d32 and d33. The analysis reveals that much higher electromechanical coupling can be obtained in ferroelectric crystals with engineered domain configurations, and offers insight on the design and optimization of ferroelectrics for enhanced functional properties. © 2003 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Polarization dynamics over broad time and field domains in modified ferroelectrics

Christelle Jullian, J. F. Li, and D. Viehland

Appl. Phys. Lett. 83, 1196 (2003); http://dx.doi.org/10.1063/1.1600823 (3 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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The dynamics of polarization switching have been investigated over extremely broad time (10−8<t<102 s) and field ranges for various modified Pb-based perovskite ferroelectrics. The results unambiguously demonstrate the presence of extremely broad relaxation time distributions for switching, which can extend over decade(s) in orders of magnitude in time. © 2003 American Institute of Physics.
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77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
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Is there a thermodynamic size limit of nanowires grown by the vapor-liquid-solid process?

Teh Y. Tan, Na Li, and Ulrich Gösele

Appl. Phys. Lett. 83, 1199 (2003); http://dx.doi.org/10.1063/1.1599984 (3 pages) | Cited 28 times

Online Publication Date: 5 August 2003

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For nanowires grown by the vapor-liquid-solid (VLS) process, expressions of the thermodynamically allowed minimum sizes of the wire and the liquid droplet are derived using Si nanowires (SiNW) grown from metal–silicon (M–Si) liquid as the model case. The liquid droplet minimum size is determined by a unique set of external M and Si vapor phase pressure values. The SiNW minimum size expression contains two contributions, one depending on composition of the liquid and one depending on the droplet size. These expressions do not predict a limit on the attainable VLS SiNW minimum size, implying ever smaller SiNW can be grown until reaching some growth kinetic limit which is presently unknown. © 2003 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.07.-b Nanoscale materials and structures: fabrication and characterization

Infusing metal into self-organized semiconductor nanostructures

Hideo Kohno and Seiji Takeda

Appl. Phys. Lett. 83, 1202 (2003); http://dx.doi.org/10.1063/1.1599970 (2 pages) | Cited 9 times

Online Publication Date: 5 August 2003

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We show that more complex nanoheterostructures can be formed readily by using templates through a self-organized process. We fabricated silicon/silicide/oxide-heterostructured nanowires by infusing metal into chains of crystalline-silicon nanospheres. The structure and composition were studied using transmission-electron-microscopy-based approaches. © 2003 American Institute of Physics.
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68.65.La Quantum wires (patterned in quantum wells)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Lp Transmission electron microscopy (TEM)
61.46.-w Structure of nanoscale materials

Doping of the nanocrystalline semiconductor zinc oxide with the donor indium

Th. Agne, Z. Guan, X. M. Li, H. Wolf, Th. Wichert, H. Natter, and R. Hempelmann

Appl. Phys. Lett. 83, 1204 (2003); http://dx.doi.org/10.1063/1.1598289 (3 pages) | Cited 33 times

Online Publication Date: 5 August 2003

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Doping of the nanocrystalline semiconductor ZnO with the donor 111In was achieved by the incorporation of 111In atoms during the growth process followed by a hydrothermal treatment at 473 K. The incorporation of 111In on substitutional Zn sites was shown by the perturbed γγ angular correlation technique. The structural quality of nanocrystalline ZnO with a mean grain size of 11 nm is significantly improved by annealing at 473 K, as revealed by x-ray diffraction, transmission electron microscopy, optical absorption measurements, and photoluminescence spectroscopy. It is shown that the incorporation of 111In on undisturbed Zn sites in nanocrystalline ZnO seems to be supported by the onset of crystal growth and by the removal of intrinsic defects. © 2003 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.46.-w Structure of nanoscale materials
81.07.Bc Nanocrystalline materials
78.55.Et II-VI semiconductors

Growth of vertically aligned carbon nanofibers by low-pressure inductively coupled plasma-enhanced chemical vapor deposition

J. B. O. Caughman, L. R. Baylor, M. A. Guillorn, V. I. Merkulov, D. H. Lowndes, and L. F. Allard

Appl. Phys. Lett. 83, 1207 (2003); http://dx.doi.org/10.1063/1.1597981 (3 pages) | Cited 26 times

Online Publication Date: 5 August 2003

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Vertically aligned carbon nanofibers (VACNFs) have been grown using a low-pressure, plasma-enhanced, chemical vapor deposition process. The nanofibers are grown from a nickel catalyst that can be patterned to form arrays of individual, isolated VACNFs. The fibers are grown at pressures below 100 mTorr, using an inductively coupled plasma source with a radio-frequency bias on the sample substrate to allow for independent control of the ion energies. Plasma conditions are related to growth results by comparing optical emission from the plasma to the physical structure of the nanofibers. We find that the ratio of etching species in the plasma to depositing species is critical to the final shape of the carbon structures that are formed. © 2003 American Institute of Physics.
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81.05.U- Carbon/carbon-based materials
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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