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19 May 2008

Volume 92, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 202101 (2008); http://dx.doi.org/10.1063/1.2927379 (3 pages)

Jasmin Aghassi, Matthias H. Hettler, and Gerd Schön
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Moderate to large magneto-optical signals in high Tc double perovskites

Hena Das, Molly De Raychaudhury, and T. Saha-Dasgupta

Appl. Phys. Lett. 92, 201912 (2008); http://dx.doi.org/10.1063/1.2936304 (3 pages) | Cited 4 times

Online Publication Date: 22 May 2008

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Using first-principles density functional calculations, we have computed the optical and magneto-optical properties of the Cr-based double perovskite compounds, Sr2CrB′O6 with B′ = W,Re,Os. Our computed magneto-optic spectra show substantially large Kerr rotations of about −2° to −2.5° for Sr2CrWO6 and Sr2CrReO6 and a moderately large Faraday rotation of about −0.25×106 deg/cm in insulating Sr2CrOsO6, indicating possible industrial applications. Our study should motivate experimental investigations in this yet to be explored area of Sr2CrB′O6 compounds.
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74.25.Ha Magnetic properties including vortex structures and related phenomena
74.70.-b Superconducting materials other than cuprates
78.20.Ls Magneto-optical effects
71.15.-m Methods of electronic structure calculations
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
74.25.Gz Optical properties

Icosahedral ordering in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass

X. Hui, H. Z. Fang, G. L. Chen, S. L. Shang, Y. Wang, and Z. K. Liu

Appl. Phys. Lett. 92, 201913 (2008); http://dx.doi.org/10.1063/1.2931702 (3 pages) | Cited 14 times

Online Publication Date: 22 May 2008

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This paper presents a computational evidence of icosahedral short and medium range ordering in Zr41Ti14Cu12.5Ni10Be22.5 bulk metallic glass using ab initio molecular dynamics simulation. It is found that 1551, 1541, and 1431 types of bond pairs are pronounced in both the liquid and glass states, resulting in icosahedral coordinate polyhedra at low temperatures. By linking the individual icosahedra through vertex-, edge-, face-, and intercross-shared atoms, icosahedral medium range ordering is formed. The predicted homogenized structure factor and pair correlation function of the glass structure have been confirmed to be in agreement with the experimental results.
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61.43.Fs Glasses
61.43.Bn Structural modeling: serial-addition models, computer simulation
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Excitation and photoluminescence of pure and Si-doped β-Ga2O3 single crystals

Kiyoshi Shimamura, Encarnación G. Víllora, Takekazu Ujiie, and Kazuo Aoki

Appl. Phys. Lett. 92, 201914 (2008); http://dx.doi.org/10.1063/1.2910768 (3 pages) | Cited 18 times

Online Publication Date: 23 May 2008

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Excitation and photoluminescence spectra of high purity and Si-doped β-Ga2O3 single crystals are investigated. Emission peaks in the UV and blue wavelength regions are observed. These are excited at two bands, which can be differentiated by polarized light. The features of the spectra are independent of excitation and emission wavelengths in the case of an undoped sample. On the contrary, after Si doping, the blue emission becomes strongly dependent. A model to interpret the characteristics of blue luminescence is proposed.
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78.55.Hx Other solid inorganic materials

High strength and utilizable ductility of bulk ultrafine-grained Cu–Al alloys

X. H. An, W. Z. Han, C. X. Huang, P. Zhang, G. Yang, S. D. Wu, and Z. F. Zhang

Appl. Phys. Lett. 92, 201915 (2008); http://dx.doi.org/10.1063/1.2936306 (3 pages) | Cited 21 times

Online Publication Date: 23 May 2008

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Lack of plasticity is the main drawback for nearly all ultrafine-grained (UFG) materials, which restricts their practical applications. Bulk UFG Cu–Al alloys have been fabricated by using equal channel angular pressing technique. Its ductility was improved to exceed the criteria for structural utility while maintaining a high strength by designing the microstructure via alloying. Factors resulting in the simultaneously enhanced strength and ductility of UFG Cu–Al alloys are the formation of deformation twins and their extensive intersections facilitating accumulation of dislocations.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.20.fk Ductility, malleability
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.10.Fq Growth from melts; zone melting and refining

Dielectric degradation mechanism for copper interconnects capped with CoWP

T. L. Tan, C. L. Gan, A. Y. Du, C. K. Cheng, and J. P. Gambino

Appl. Phys. Lett. 92, 201916 (2008); http://dx.doi.org/10.1063/1.2929388 (3 pages) | Cited 2 times

Online Publication Date: 23 May 2008

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Time-dependent dielectric breakdown (TDDB) reliability of CoWP-capped copper/SiO2 interconnect structures are observed to be better than conventional SiN-capped structures. The activation energy for TDDB (Ea) is higher for CoWP-capped structures (0.66–0.84 eV) as compared to SiN-capped ones (0.47 eV), and is comparable to the Ea for intrinsic breakdown of SiO2. The TDDB degradation mechanism in CoWP-capped structures is postulated to be dominated by the properties of the intrametal dielectric, as opposed to being influenced by the properties of dielectric cap and associated interfaces. The presence of the dielectric cap lowers the Ea and increases leakage by Poole–Frenkel emission.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
77.22.Jp Dielectric breakdown and space-charge effects

Melt-dispersion mechanism for fast reaction of aluminum particles: Extension for micron scale particles and fluorination

Valery I. Levitas, Michelle L. Pantoya, and Kyle W. Watson

Appl. Phys. Lett. 92, 201917 (2008); http://dx.doi.org/10.1063/1.2936855 (3 pages) | Cited 7 times

Online Publication Date: 23 May 2008

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The theoretically predicted relationship for the relative flame rate versus relative particle size based on the melt dispersion mechanism (MDM), which was previously confirmed for oxidation of 40–120 nm diameter aluminum particles, is found to be in agreement with experiments for 1–3 μm diameter Al particles and fluorination. The main physical parameters for MDM (pressure in molten particle, cavitation threshold, and nanoclusters’ velocity) have been estimated for micron scale particles. The results suggest parameters that could be controlled during particle synthesis that would enable micron scale Al particles to react and achieve the performance of nanoscale Al particles.
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82.30.Nr Association, addition, insertion, cluster formation
36.40.Sx Diffusion and dynamics of clusters

Raman spectra of epitaxial graphene on SiC(0001)

J. Röhrl, M. Hundhausen, K. V. Emtsev, Th. Seyller, R. Graupner, and L. Ley

Appl. Phys. Lett. 92, 201918 (2008); http://dx.doi.org/10.1063/1.2929746 (3 pages) | Cited 94 times

Online Publication Date: 23 May 2008

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We present Raman spectra of epitaxial graphene layers grown on 6math×6math reconstructed silicon carbide surfaces during annealing at elevated temperature. In contrast to exfoliated graphene a significant phonon hardening is observed. We ascribe that phonon hardening to a minor part to the known electron transfer from the substrate to the epitaxial layer, and mainly to mechanical strain that builds up when the sample is cooled down after annealing. Due to the larger thermal expansion coefficient of silicon carbide compared to the in-plane expansion coefficient of graphite this strain is compressive at room temperature.
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78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
61.72.Cc Kinetics of defect formation and annealing
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.60.Bs Mechanical and acoustical properties
68.60.Wm Other nonelectronic physical properties
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Cotunneling assisted sequential tunneling in multilevel quantum dots

Jasmin Aghassi, Matthias H. Hettler, and Gerd Schön

Appl. Phys. Lett. 92, 202101 (2008); http://dx.doi.org/10.1063/1.2927379 (3 pages) | Cited 5 times

Online Publication Date: 19 May 2008

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We investigate the conductance and zero-frequency shot noise of interacting, multilevel quantum dots coupled to leads. We observe that cotunneling assisted sequential tunneling (CAST) processes play a dominant role in the transition region from Coulomb blockade to sequential tunneling. We analyze for intermediate coupling strength the dependence of the conductance due to CAST processes on temperature, coupling constant, and gate voltage. Remarkably, the width of the CAST transport feature scales only with temperature, but not with the coupling constant. While the onset of inelastic cotunneling is associated with a super-Poissonian noise, the noise is even stronger above the threshold for CAST processes.
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73.40.Gk Tunneling
73.23.Hk Coulomb blockade; single-electron tunneling
72.70.+m Noise processes and phenomena
73.21.La Quantum dots

Uniform resistive switching with a thin reactive metal interface layer in metal-La0.7Ca0.3MnO3-metal heterostructures

Musarrat Hasan, Rui Dong, H. J. Choi, D. S. Lee, D.-J. Seong, M. B. Pyun, and Hyunsang Hwang

Appl. Phys. Lett. 92, 202102 (2008); http://dx.doi.org/10.1063/1.2932148 (3 pages) | Cited 38 times

Online Publication Date: 19 May 2008

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A thin samarium (Sm) metal layer was introduced to improve the resistive hysteresis and switching uniformity. Sm reacts with the La0.7Ca0.3MnO3 and forms a thin interface oxide layer, which is responsible for the switching. The switching occurs without any forming process. Compared with conventional resistive memory device based on localized filament formation, Sm/La0.7Ca0.3MnO3 devices show area-dependent resistance which indicates uniform resistive switching. Under a positive bias, electromigration of oxygen ions (O2−) forms thicker oxide (SmOx), which dissociates under a negative bias, causes high and low resistance states, respectively. Estimated data retention of more than 10 yr was observed at 85 °C.
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73.40.Sx Metal-semiconductor-metal structures
77.80.Dj Domain structure; hysteresis
66.30.Qa Electromigration

X-ray characterization of dislocation density asymmetries in heteroepitaxial semiconductors

B. Yarlagadda, A. Rodriguez, P. Li, R. Velampati, J. F. Ocampo, E. N. Suarez, P. B. Rago, D. Shah, J. E. Ayers, and F. C. Jain

Appl. Phys. Lett. 92, 202103 (2008); http://dx.doi.org/10.1063/1.2936078 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2008

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We demonstrate an x-ray rocking curve method which allows detection of an asymmetry in the dislocation densities in an heteroepitaxial (001) zinc blende semiconductor layer. These dislocations exist on two types of slip systems with their misfit dislocation line segments oriented along either a [1−10] direction (type A) or a [110] direction (type B). An imbalance in the densities of dislocations on these slip systems produces an observable azimuthal variation in the rocking curve width for symmetric x-ray reflections. An approximate quantitative model allows the estimation of the dislocation densities on the two types of slip systems.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Concentration dependence of self-interstitial and boron diffusion in silicon

Wolfgang Windl

Appl. Phys. Lett. 92, 202104 (2008); http://dx.doi.org/10.1063/1.2936081 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2008

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We show that recent experimental data and ab initio calculations agree on the charge state as a function of the Fermi energy of the dominant species for diffusion of self-interstitials (+, +, and 0) and boron atoms (+) in silicon. By mapping the experimental data onto the activation energy versus Fermi-level representation commonly used to display ab initio results, we can show that the experimental results are consistent with each other. While theoretical values for the boron activation energy as a function of the Fermi level agree well with experiment, values for self-interstitials are low, despite using total-energy corrections.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
66.30.Dn Theory of diffusion and ionic conduction in solids
66.30.J- Diffusion of impurities
61.72.jj Interstitials
61.72.sd Impurity concentration
71.20.Mq Elemental semiconductors

Resistivity of V2O3 thin films deposited on a-plane (110) and c-plane (001) sapphire by pulsed laser deposition

B. S. Allimi, S. P. Alpay, C. K. Xie, B. O. Wells, J. I. Budnick, and D. M. Pease

Appl. Phys. Lett. 92, 202105 (2008); http://dx.doi.org/10.1063/1.2921787 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2008

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Thin films of V2O3 with thickness of 215 nm were grown on a- and c-plane sapphire by pulsed laser deposition with (001)V2O3∥(001)Al2O3 and (110)V2O3∥(110)Al2O3 epitaxy. The effects of the growth direction on the electrical resistivity of the films were examined. Films on c-plane sapphire displayed a metal-to-insulator transition at T = 180 K compared to T = 160 K in single-crystal V2O3. The films on a-plane sapphire, however, showed an insulator-to-insulator transition at T = 186 K. The variation in the phase transformation characteristics and the resistivity can be attributed to different levels of strain and commensurate changes in the film morphology.
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73.61.Ng Insulators
68.55.A- Nucleation and growth
81.15.Fg Pulsed laser ablation deposition
64.70.K- Solid-solid transitions
71.30.+h Metal-insulator transitions and other electronic transitions

Line defects of M-plane GaN grown on γ-LiAlO2 by plasma-assisted molecular beam epitaxy

Ikai Lo, Chia-Ho Hsieh, Yen-Liang Chen, Wen-Yuan Pang, Yu-Chi Hsu, Jih-Chen Chiang, Ming-Chi Chou, Jenn-Kai Tsai, and D. M. Schaadt

Appl. Phys. Lett. 92, 202106 (2008); http://dx.doi.org/10.1063/1.2924288 (3 pages) | Cited 3 times

Online Publication Date: 19 May 2008

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The edge and threading dislocations of M-plane GaN epilayers grown on γ-LiAlO2 have been studied by high-resolution transmission electron microscope. We found that edge dislocations were grown in [1math00] direction while threading dislocations were generated along a1 or −a2 axes. We also observed a single stacking fault in the M-plane GaN epilayer.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
61.72.Nn Stacking faults and other planar or extended defects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors

Effects of hydrogen implantation temperature on InP surface blistering

Peng Chen, Zengfeng Di, M. Nastasi, Elena Bruno, Maria Grazia Grimaldi, N. David Theodore, and S. S. Lau

Appl. Phys. Lett. 92, 202107 (2008); http://dx.doi.org/10.1063/1.2926682 (3 pages) | Cited 7 times

Online Publication Date: 19 May 2008

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We have investigated the effects of hydrogen implantation temperature on the ion-cut process of InP by examining the correlation between surface blistering and the ion induced damage, hydrogen distribution, and strain. Using Rutherford backscattering spectrometry, elastic recoil detection, and x-ray diffraction, it was found that both the point defects induced by the hydrogen implantation and the in-plane compressive stress were necessary for hydrogen trapping and H-platelet nucleation and growth. The control of implantation temperature is crucial for creating sufficient defects and strain to induce surface blistering or layer exfoliation.
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61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
61.72.J- Point defects and defect clusters
61.72.jd Vacancies

High-temperature quenching of electrical resistance in graphene interconnects

Q. Shao, G. Liu, D. Teweldebrhan, and A. A. Balandin

Appl. Phys. Lett. 92, 202108 (2008); http://dx.doi.org/10.1063/1.2927371 (3 pages) | Cited 43 times

Online Publication Date: 19 May 2008

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The authors reported on the experimental investigation of the high-temperature electrical resistance of graphene. The test structures were fabricated by using the focused ion beam from the single and bilayer graphene produced by mechanical exfoliation. It was found that as temperature increases from 300 to 500 K, the resistance of the single, and bilayer graphene interconnects drops down by 30% and 70%, respectively. The quenching and temperature dependence of the resistance were explained by the thermal generation of the electron-hole pairs and carrier scattering by acoustic phonons. The obtained results are important for the proposed graphene interconnect applications in integrated circuits.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
81.40.Gh Other heat and thermomechanical treatments
85.40.Ls Metallization, contacts, interconnects; device isolation
72.10.Di Scattering by phonons, magnons, and other nonlocalized excitations

Laterally coupled self-assembled InAs quantum dots embedded in resonant tunnel diode with multigate electrodes

S. Amaha, T. Hatano, S. Teraoka, A. Shibatomi, S. Tarucha, Y. Nakata, T. Miyazawa, T. Oshima, T. Usuki, and N. Yokoyama

Appl. Phys. Lett. 92, 202109 (2008); http://dx.doi.org/10.1063/1.2920205 (3 pages) | Cited 12 times

Online Publication Date: 20 May 2008

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We study the electronic properties of submicron vertical resonant tunneling structures containing several self-assembled InAs quantum dots (SADs) surrounded by four gate electrodes. The four gates are designed not only to squeeze the conductive channel containing a few SADs but also to differently modulate the electrochemical potential of each SAD. We measure the stability diagram and distinguish the features of lateral interdot coupling, such as the type of coupling (quantum mechanical or capacitive), the number of coupled dots, and the relative coupled dot position. This technique will be useful in characterizing the electronic properties of coupled SAD systems.
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85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)

Barrier breakdown in multiple quantum well structure

Aurore Gomez, Vincent Berger, Nicolas Péré-Laperne, and Louis-Anne De Vaulchier

Appl. Phys. Lett. 92, 202110 (2008); http://dx.doi.org/10.1063/1.2927472 (3 pages) | Cited 7 times

Online Publication Date: 20 May 2008

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We explore a regime of unipolar electronic transport in a multiple quantum well structure with very large current discontinuities—up to five orders of magnitude. Magnetotransport experiments reveal different transport regimes. Quantum well impact ionization shifts the structure from a resistive “down” state, where the current flows through interwell quantum tunneling, to a highly conductive “up” state. In the latter regime, the current leaks through a barrier suddenly broken down because of an efficient ionization of the first quantum well. This mechanism might open the way to original devices based on unipolar impact ionization.
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81.07.St Quantum wells
75.75.-c Magnetic properties of nanostructures
75.47.-m Magnetotransport phenomena; materials for magnetotransport
73.63.Hs Quantum wells

Heavily doped and fully compensated Ge single-crystalline films on GaAs

V. F. Mitin

Appl. Phys. Lett. 92, 202111 (2008); http://dx.doi.org/10.1063/1.2931704 (3 pages) | Cited 2 times

Online Publication Date: 20 May 2008

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Heavily doped and fully compensated Ge single-crystalline thin ( ∼ 0.1 μm) films were epitaxially grown in vacuum on semi-insulating GaAs substrates. Such films have high resistivity (up to 140 Ω/cm), conductance activation energy as high as half the band gap of Ge, low free charge carrier mobility ( ∼ 50 cm2/V⋅s) and concentration ( ∼ 1014 cm−3). The transport properties of the films were studied and explained involving the theory of two-dimensional potential fluctuations and percolation.
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81.05.Cy Elemental semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.ag Semiconductors
73.61.Cw Elemental semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
71.20.Mq Elemental semiconductors
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Interpretation of nanoscale conducting paths and their control in nickel oxide (NiO) thin films

I. K. Yoo, B. S. Kang, Y. D. Park, M. J. Lee, and Y. Park

Appl. Phys. Lett. 92, 202112 (2008); http://dx.doi.org/10.1063/1.2936087 (3 pages) | Cited 12 times

Online Publication Date: 21 May 2008

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The behavior of unipolar resistance switching in NiO thin film was investigated. The switching current and the switching voltage alone did not follow statistical distribution. Instead, it was observed that product of switching current and switching voltage; namely, switching power follows Poisson’s distribution. An electrical manipulation—pulse train, for example—was suggested in order to minimize switching failure based on the above Poisson’s distribution behavior.
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73.61.Ng Insulators
68.55.-a Thin film structure and morphology

Anomalously large measured thermoelectric power factor in Sr1−xLaxTiO3 thin films due to SrTiO3 substrate reduction

Matthew L. Scullin, Choongho Yu, Mark Huijben, Subroto Mukerjee, Jan Seidel, Qian Zhan, Joel Moore, Arun Majumdar, and R. Ramesh

Appl. Phys. Lett. 92, 202113 (2008); http://dx.doi.org/10.1063/1.2916690 (3 pages) | Cited 12 times

Online Publication Date: 21 May 2008

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We report the observation that thermoelectric thin films of La-doped SrTiO3 grown on SrTiO3 substrates yield anomalously high values of thermopower to give extraordinary values of power factor at 300 K. Thin films of Sr0.98La0.02TiO3, grown via pulsed laser deposition at low temperature and low pressure (450 °C, 10−7 Torr), do not yield similarly high values when grown on other substrates. The thin-film growth induces oxygen reduction in the SrTiO3 crystals, doping the substrate n type. It is found that the backside resistance of the SrTiO3 substrates is as low ( ∼ 12Ω/◻) as it is on the film side after film growth.
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73.50.Lw Thermoelectric effects
73.61.Ng Insulators
81.15.Fg Pulsed laser ablation deposition
68.55.aj Insulators

Preparation and thermoelectric properties of high-performance Sb additional Yb0.2Co4Sb12+y bulk materials with nanostructure

Han Li, Xinfeng Tang, Xianli Su, and Qingjie Zhang

Appl. Phys. Lett. 92, 202114 (2008); http://dx.doi.org/10.1063/1.2936277 (3 pages) | Cited 34 times

Online Publication Date: 22 May 2008

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High-performance Sb excess Yb0.2Co4Sb12+y (y = 0,0.3,0.6,1.0) bulk materials with nanostructure have been prepared by combining melt spinning technique with spark plasma sintering. Average grain size of the bulk samples is about 150 nm when y = 0 and 0.3, and the grain size increases with the increase of y. Moderately superfluous Sb may improve the electrical transport properties effectively and the thermal conductivity of the bulk samples decreases markedly due to the nanostructure. The thermoelectric performance of the samples is significantly improved, and the maximum figure of the merit reaches 1.26 for the Yb0.2Co4Sb12.3 compound at 800 K.
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81.05.Bx Metals, semimetals, and alloys
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
73.63.Bd Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Characterization of Mn1.56Co0.96Ni0.48O4 films for infrared detection

Yun Hou, Zhiming Huang, Yanqing Gao, Yujian Ge, Jing Wu, and Junhao Chu

Appl. Phys. Lett. 92, 202115 (2008); http://dx.doi.org/10.1063/1.2936292 (3 pages) | Cited 9 times

Online Publication Date: 22 May 2008

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Mn1.56Co0.96Ni0.48O4 films with spinel structure were prepared on Al2O3 substrate by chemical solution deposition method. The microstructure of the films was studied by atomic force microscope and field-emission scanning electron microscope. The current-voltage characteristics showed Ohmic conductivity in the temperature range of 245–295 K. The conduction was described by a variable range hopping model for a parabolic density of states. The advantages of high characteristic temperature, as well as high transition temperature (201 K) between ferromagnetic and paramagnetic phases make the Mn1.56Co0.96Ni0.48O4 films very promising for infrared detection, especially for functional devices by integrating magnetic and electronic properties of the materials.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
73.61.Ng Insulators

Resistivity reduction of boron-doped multiwalled carbon nanotubes synthesized from a methanol solution containing boric acid

Satoshi Ishii, Tohru Watanabe, Shinya Ueda, Shunsuke Tsuda, Takahide Yamaguchi, and Yoshihiko Takano

Appl. Phys. Lett. 92, 202116 (2008); http://dx.doi.org/10.1063/1.2930677 (3 pages) | Cited 4 times

Online Publication Date: 22 May 2008

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Boron-doped multiwalled carbon nanotubes (MWNTs) were synthesized using a methanol solution of boric acid as a source material. Accurate measurements of the electrical resistivity of an individual boron-doped MWNT was performed with a four-point contact, which was fabricated using an electron beam lithography technique. The doped boron provides conduction carriers, which reduces the resistivity of the MWNT.
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73.63.Fg Nanotubes
81.07.De Nanotubes

Subgap states in transparent amorphous oxide semiconductor, In–Ga–Zn–O, observed by bulk sensitive x-ray photoelectron spectroscopy

Kenji Nomura, Toshio Kamiya, Hiroshi Yanagi, Eiji Ikenaga, Ke Yang, Keisuke Kobayashi, Masahiro Hirano, and Hideo Hosono

Appl. Phys. Lett. 92, 202117 (2008); http://dx.doi.org/10.1063/1.2927306 (3 pages) | Cited 63 times

Online Publication Date: 22 May 2008

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We investigated the electronic states in amorphous In–Ga–Zn–O films with high carrier concentrations by optical absorption and hard x-ray photoelectron spectroscopy (HX-PES). Films having different Hall mobilities were prepared and their annealing effects were examined. All HX-PES spectra showed Fermi edge structures and extra subgap densities of states (DOSs). Tail-like structures observed in the optical spectra originate from subgap DOSs (⪢1020 cm−3) near valence band maximas (VBMs). Subgap DOSs near VBMs provide a reason why In–Ga–Zn–O thin film transistors show hard saturation in off states and are difficult to operate in an inversion p-channel mode.
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71.23.Cq Amorphous semiconductors, metallic glasses, glasses
73.61.Jc Amorphous semiconductors; glasses
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.66.Jg Amorphous semiconductors; glasses
61.72.Cc Kinetics of defect formation and annealing
72.20.My Galvanomagnetic and other magnetotransport effects

Electrical conductivity and lattice expansion of β-Ga2O3 below room temperature

Encarnación G. Víllora, Kiyoshi Shimamura, Takekazu Ujiie, and Kazuo Aoki

Appl. Phys. Lett. 92, 202118 (2008); http://dx.doi.org/10.1063/1.2910770 (3 pages) | Cited 7 times

Online Publication Date: 23 May 2008

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The temperature dependence of the electrical properties of β-Ga2O3 is analyzed from liquid helium to room temperature by Hall measurements. Below 100 K, the carrier motion takes place within the impurity conduction band and it shows a power-law dependence. An electrostructural coupling is ascertained. Thermal activation in the conduction band is observed above 100 K, with an activation energy Ea = 7 meV. Thermal conductivity is measured to 13 W m−1 K−1. Further, it is shown that Ti is a good Ohmic electrode for n-type β-Ga2O3 substrates.
Show PACS
72.80.Sk Insulators
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
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