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28 Jan 2013

Volume 102, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 041101 (2013); http://dx.doi.org/10.1063/1.4777564 (5 pages)

K. Winkler, C. Schneider, J. Fischer, A. Rahimi-Iman, M. Amthor, A. Forchel, S. Reitzenstein, S. Höfling, and M. Kamp
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Elastic and anelastic properties close to the Curie temperature of Fe-based bulk metallic glass

J. Torrens-Serra, M. Stoica, J. Bednarcik, J. Eckert, and S. Kustov

Appl. Phys. Lett. 102, 041904 (2013); http://dx.doi.org/10.1063/1.4789776 (4 pages)

Online Publication Date: 28 January 2013

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Linear and non-linear ultrasonic damping, Young's modulus, and non-linear modulus defect have been studied in a Fe-based bulk metallic glass close to its Curie temperature, TC. We found that the acoustic technique used offers four different parameters which can be used to evaluate the TC. We show that ultrasonic measurements at a frequency of around 105 Hz detect both critical phenomena close to TC and intrinsic magnetomechanical damping in the ferromagnetic state. However, the values of absorption and Young's modulus anomaly observed over the critical range are quite low and do not permit reliable analysis of the critical exponents.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.80.+q Magnetomechanical effects, magnetostriction
62.20.de Elastic moduli

Thermally induced porous structures in printed gallium coating to make transparent conductive film

Shengfu Mei, Yunxia Gao, Haiyan Li, Zhongshan Deng, and Jing Liu

Appl. Phys. Lett. 102, 041905 (2013); http://dx.doi.org/10.1063/1.4789978 (4 pages)

Online Publication Date: 28 January 2013

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A directly printable gallium-based film with both optically transmissive and electrically conductive properties was proposed and demonstrated. The structures, electrical, and optical behaviors of the film printed on the substrate were experimentally investigated. It was disclosed that the porous structure induced inside the printed gallium film by thermal treatment is the main reason for the significant improvement of optical transmittance. A visible transmittance of 47% with a sheet resistance of 16.17 Ω/sq was obtained when the thermal treatment temperature and time are maintained at 400 °C and 40 min, respectively.
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73.61.At Metal and metallic alloys
78.66.Bz Metals and metallic alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology

Optical properties of SrTiO3 on silicon(100)

Yao Tian, Carolina Adamo, Darrell G. Schlom, and Kenneth S. Burch

Appl. Phys. Lett. 102, 041906 (2013); http://dx.doi.org/10.1063/1.4789752 (4 pages)

Online Publication Date: 29 January 2013

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Epitaxial buffer layers enable the many functionalities found in perovskites to be integrated with silicon. However, epitaxial growth of SrTiO3 on silicon is tricky and has so far only been achieved by molecular beam epitaxy. Nonetheless, previous investigations of these films were limited by the amorphous layer occurring at the interface. Through a combination of improved interface quality and an improved model, we report the optical properties of SrTiO3 films on Si(100) investigated by spectroscopic ellipsometry. We find that the data are best described by a model with two different SrTiO3 layers, potentially resulting from variations in the oxygen content.
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78.66.Nk Insulators
78.40.Ha Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators

Direct ab-initio molecular dynamic study of ultrafast phase change in Ag-alloyed Ge2Sb2Te5

B. Prasai, G. Chen, and D. A. Drabold

Appl. Phys. Lett. 102, 041907 (2013); http://dx.doi.org/10.1063/1.4789877 (4 pages) | Cited 1 time

Online Publication Date: 29 January 2013

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We employed ab-initio molecular dynamics to directly simulate the effects of Ag alloying (less than 5% Ag concentration) on the phase change properties of Ge2Sb2Te5. The short range order is preserved, whereas a slight improvement in the chemical order is observed. A slight decrease in the fraction of tetrahedral Ge (sp3 bonding) is reflected in the reduction of the optical band gap and in the increased dielectric constant. Simulations of the amorphous to crystalline phase change cycle revealed the fact that the crystallization speed in Ag0.5Ge2Sb2Te5 is not less than that in Ge2Sb2Te5. Moreover, the smaller density difference and the larger energy difference between the two phases of Ag0.5Ge2Sb2Te5 (compared to Ge2Sb2Te5) suggest a smaller residual stress in devices due to phase transition and improved thermal stability for Ag0.5Ge2Sb2Te5. The potential viability of this material suggests the need for a wide exploration of alternative phase change memory materials.
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64.70.dg Crystallization of specific substances
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Magnetic transition broadening and local lattice distortion in the negative thermal expansion antiperovskite Cu1−xSnxNMn3

P. Tong, Despina Louca, Graham King, Anna Llobet, J. C. Lin, and Y. P. Sun

Appl. Phys. Lett. 102, 041908 (2013); http://dx.doi.org/10.1063/1.4790151 (4 pages) | Cited 1 time

Online Publication Date: 30 January 2013

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The local distortion indicated by the split of the Cu/Sn-Mn bonds for the negative thermal expansion (NTE) materials Cu1−xSnxNMn3 (x = 0.1 and 0.5) was observed using neutron pair distribution function. The distribution of Cu/Sn-Mn bonds upon Sn doping is suggested to be attributable to the fluctuation in the hybridization of Mn d with Sn p orbitals. Accordingly, the antiferromagnetic (AFM) coupling mediated by the p-d hybridization fluctuates in strength. Consequently, the AFM transition closely coupled with the volume change is broadened, leading to the NTE.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Ee Antiferromagnetics
65.40.De Thermal expansion; thermomechanical effects

Strain engineering enhancement of surface plasmon polariton propagation lengths for gold nanowires

Xue Ben and Harold S. Park

Appl. Phys. Lett. 102, 041909 (2013); http://dx.doi.org/10.1063/1.4790293 (4 pages)

Online Publication Date: 30 January 2013

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We present in this work the notion of using elastic strain engineering to reduce the intrinsic losses in a metal for subwavelength optical signal processing. By using a simple, analytical waveguide model, we demonstrate that application of uniaxial tensile strains below the yield strain of gold nanowires results in substantial increases of more than 70% in the surface plasmon polariton propagation lengths at optical frequencies. The enhancement is primarily due to a reduction in the core electron density, and is found to be size-independent for a wide range of nanowire diameters, while exhibiting a linear dependence on the applied tensile strain.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
72.20.Fr Low-field transport and mobility; piezoresistance
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Critical-temperature/Peierls-stress dependent size effects in body centered cubic nanopillars

Seung Min Han, Gang Feng, Joo Young Jung, Hee Joon Jung, James R. Groves, William D. Nix, and Yi Cui

Appl. Phys. Lett. 102, 041910 (2013); http://dx.doi.org/10.1063/1.4776658 (5 pages)

Online Publication Date: 30 January 2013

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The size-dependent plasticity of body centered cubic (bcc) metals is different from face centered cubic (fcc) metals: the size-effect exponent n varies for different bcc metal nanopillars (n = 0.8–1.0 for V, Nb; n = 0.3–0.5 for Ta, Mo, W). This inconsistency is first explained through a simple model based on the temperature-dependent Peierls stress. The bcc V nanopillars with a low critical temperature and Peierls stress showed a fcc-like size effect with n = 0.79, and our in-situ TEM compression study revealed that fcc-like dislocation starvation occurred in bcc V nanopillars, indicating that a small Peierls stress in V contributes to the fcc-like behavior.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.23.-c Structural classes of nanoscale systems

Self-organized Archimedean spiral pattern: Regular bundling of fullerene through solvent evaporation

Yong-Jun Chen, Kosuke Suzuki, Hitoshi Mahara, Kenichi Yoshikawa, and Tomohiko Yamaguchi

Appl. Phys. Lett. 102, 041911 (2013); http://dx.doi.org/10.1063/1.4789906 (5 pages)

Online Publication Date: 30 January 2013

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We report the spontaneous generation of an Archimedean spiral pattern of fullerene via the evaporation of solvent. The self-organized spiral pattern exhibited equi-spacing on the order of μm between neighboring stripes. The characteristics of the spirals, such as the spacing between stripes, the number of stripes, and the band width of stripes, could be controlled by tuning the thickness of the liquid bridge and the concentration of solution. The mechanism of pattern formation is interpreted in terms of a specific traveling wave on the liquid-solid interface accompanied by a stick-slip process of the contact line.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear

Novel pressure-induced phase transitions in Co3O4

Shigeto Hirai and Wendy L. Mao

Appl. Phys. Lett. 102, 041912 (2013); http://dx.doi.org/10.1063/1.4790387 (4 pages)

Online Publication Date: 31 January 2013

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Co3O4 represents an intriguing strongly correlated system since it is a spin liquid originating from A-site magnetic frustration. We conducted in-situ high pressure synchrotron x-ray diffraction experiments on Co3O4, and found two new monoclinic phases with the P121/c1 and C12/m1 structures. These high pressure phases are distinct from the high pressure structures that were previously reported for other 3d transition metal spinel oxides. The charge transfer does not drive the normal spinel to transform into a symmetry equivalent inverse spinel, and instead we observe transformations into the new monoclinic phases which have two distinct Co2+ and Co3+ octahedral sites.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.50.-p High-pressure effects in solids and liquids

Shape-anisotropic heterogeneous nucleation and magnetic Gibbs-Thomson effect in itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 magnetocaloric compound

A. Fujita, T. Kondo, M. Kano, and H. Yako

Appl. Phys. Lett. 102, 041913 (2013); http://dx.doi.org/10.1063/1.4789902 (5 pages)

Online Publication Date: 31 January 2013

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Macroscopic anisotropy of spatial selectivity in magnetic nucleation and growth was clarified for itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 by the time-dependent Ginzburg-Landau model combined with the Maxwell electromagnetic equation. Spontaneous generation of voltage supports symmetric growth in the longitudinal direction of the specimen as predicted by the simulation. The difference between nucleation-growth behaviors in thermally induced transition and those in field-induced transition is also elucidated. Electrical resistivity measurements also detect anisotropic growth of the induced phase. These results imply that the magnetic-dipole version of Gibbs-Thomson effect governs growth behavior.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Gw Magnetic anisotropy

Molecular beam epitaxy of high structural quality Bi2Se3 on lattice matched InP(111) substrates

S. Schreyeck, N. V. Tarakina, G. Karczewski, C. Schumacher, T. Borzenko, C. Brüne, H. Buhmann, C. Gould, K. Brunner, and L. W. Molenkamp

Appl. Phys. Lett. 102, 041914 (2013); http://dx.doi.org/10.1063/1.4789775 (4 pages) | Cited 3 times

Online Publication Date: 1 February 2013

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Epitaxial layers of the topological insulator Bi2Se3 have been grown by molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High resolution X-ray diffraction shows a significant improvement of Bi2Se3 crystal quality compared to layers deposited on other substrates. The measured full width at half maximum of the rocking curve is Δω = 13 arc sec, and the (ω−2θ) scans exhibit clear layer thickness fringes. Atomic force microscope images show triangular twin domains with sizes increasing with layer thickness. The structural quality of the domains is confirmed on the microscopic level by transmission electron microscopy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators

Random analysis on controlled buckling structure for energy harvesting

Yong Wang, Teng Ma, Hongyu Yu, and Hanqing Jiang

Appl. Phys. Lett. 102, 041915 (2013); http://dx.doi.org/10.1063/1.4789998 (5 pages) | Cited 1 time

Online Publication Date: 1 February 2013

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The controlled buckling piezoelectric structures can be used for stretchable energy harvesting due to the stretchability and piezoelectricity. In this paper, the ambient environmental excitation is modeled as a bound-limited white noise, and the random analysis is conducted to study the system response of controlled buckling structures. The spatial distribution of the harvestable energy is revealed, and the optimal locations of electrodes for maximal energy output are indicated. The optimal locations of electrodes are robust to the upper bound of environment excitation and the applied strain. This work provides a theoretical basis for stretchable energy harvesting using controlled buckling structures.
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84.60.-h Direct energy conversion and storage
88.05.-b Energy analysis
77.65.-j Piezoelectricity and electromechanical effects
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Atom probe study of Cu2ZnSnSe4 thin-films prepared by co-evaporation and post-deposition annealing

T. Schwarz, O. Cojocaru-Mirédin, P. Choi, M. Mousel, A. Redinger, S. Siebentritt, and D. Raabe

Appl. Phys. Lett. 102, 042101 (2013); http://dx.doi.org/10.1063/1.4788815 (4 pages) | Cited 2 times

Online Publication Date: 28 January 2013

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We use atom probe tomography (APT) for resolving nanometer scale compositional fluctuations in Cu2ZnSnSe4 (CZTSe) thin-films prepared by co-evaporation and post-deposition annealing. We detect a complex, nanometer–sized network of CZTSe and ZnSe domains in these films. Some of the ZnSe domains contain precipitates having a Cu- and Sn-rich composition, where the composition cannot be assigned to any of the known equilibrium phases. Furthermore, Na impurities are found to be segregated at the CZTSe/ZnSe interface. The insights given by APT are essential for understanding the growth of CZTSe absorber layers for thin-film solar cells and for optimizing their optoelectronic properties.
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81.15.Dj E-beam and hot filament evaporation deposition
64.75.-g Phase equilibria
68.55.ag Semiconductors

Defect enhanced funneling of diffusion current in silicon

S. Azimi, Z. Y. Dang, J. Song, M. B. H. Breese, E. Vittone, and J. Forneris

Appl. Phys. Lett. 102, 042102 (2013); http://dx.doi.org/10.1063/1.4789849 (5 pages) | Cited 1 time

Online Publication Date: 29 January 2013

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We report a current transport mechanism observed during electrochemical anodization of ion irradiated p-type silicon, in which a hole diffusion current is highly funneled along the gradient of modified doping profile towards the maximum ion induced defect density, dominating the total current flowing and hence the anodization behaviour. This study is characterized within the context of electrochemical anodization but relevant to other fields where any residual defect density may result in similar effects, which may adversely affect performance, such as in wafer gettering or satellite-based microelectronics. Increased photoluminescence intensity from localized buried regions of porous silicon is also shown.
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66.30.Lw Diffusion of other defects
78.55.Ap Elemental semiconductors
81.65.-b Surface treatments

Resistive switching mechanism in silicon highly rich SiOx (x < 0.75) films based on silicon dangling bonds percolation model

Yuefei Wang, Xinye Qian, Kunji Chen, Zhonghui Fang, Wei Li, and Jun Xu

Appl. Phys. Lett. 102, 042103 (2013); http://dx.doi.org/10.1063/1.4776695 (5 pages)

Online Publication Date: 29 January 2013

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The unipolar resistive switches are investigated in silicon highly rich SiOx (x < 0.75) films. The as-deposited SiO0.73 films contain high concentration (1.0 × 1019 cm−3) of silicon dangling bonds (Si-DBs) and are rich in SiO2≡Si–Si and O3≡Si–Si configurations. Unlike the currently reported normal silicon-rich SiOx (x > 1.8) based devices, our Pt/SiO0.73/Pt devices operate at lower voltage regime (<2.0 V) and exhibit much lower resistance (∼30 Ω). The reset voltage (∼0.7 V) is lower than set voltage (∼1.7 V) and the performance is reduced in the vacuum environment. We propose a Si-DBs percolation model to explain the above characteristics. The experimental evidences for supporting our model are presented and discussed.
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72.60.+g Mixed conductivity and conductivity transitions
77.55.-g Dielectric thin films
FREE

High mobility ambipolar MoS2 field-effect transistors: Substrate and dielectric effects

Wenzhong Bao, Xinghan Cai, Dohun Kim, Karthik Sridhara, and Michael S. Fuhrer

Appl. Phys. Lett. 102, 042104 (2013); http://dx.doi.org/10.1063/1.4789365 (4 pages) | Cited 7 times

Online Publication Date: 29 January 2013

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We fabricate MoS2 field effect transistors on both SiO2 and polymethyl methacrylate (PMMA) dielectrics and measure charge carrier mobility in a four-probe configuration. For multilayer MoS2 on SiO2, the mobility is 30–60 cm2/Vs, relatively independent of thickness (15–90 nm), and most devices exhibit unipolar n-type behavior. In contrast, multilayer MoS2 on PMMA shows mobility increasing with thickness, up to 470 cm2/Vs (electrons) and 480 cm2/Vs (holes) at thickness ∼50 nm. The dependence of the mobility on thickness points to a long-range dielectric effect of the bulk MoS2 in increasing mobility.
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85.30.Tv Field effect devices

On the mechanism of recombination at oxide precipitates in silicon

J. D. Murphy, K. Bothe, V. V. Voronkov, and R. J. Falster

Appl. Phys. Lett. 102, 042105 (2013); http://dx.doi.org/10.1063/1.4789858 (5 pages)

Online Publication Date: 30 January 2013

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Oxide precipitates are well known to degrade minority carrier lifetime in silicon, but the mechanism by which they act as recombination centres is not fully understood. We report minority carrier lifetime measurements on oxide precipitate-containing silicon which has been intentionally contaminated with iron. Analysis of the injection-dependence of lifetime demonstrates the same recombination centres exist in iron-contaminated and not intentionally contaminated samples, with the state density scaling with iron loss from the bulk. This shows that recombination activity arises from impurity atoms segregated to oxide precipitates and/or surrounding crystallographic defects.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
81.30.Mh Solid-phase precipitation
61.72.sh Impurity distribution
64.75.Qr Phase separation and segregation in semiconductors

Mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi

G. Vardar, S. W. Paleg, M. V. Warren, M. Kang, S. Jeon, and R. S. Goldman

Appl. Phys. Lett. 102, 042106 (2013); http://dx.doi.org/10.1063/1.4789369 (4 pages)

Online Publication Date: 30 January 2013

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We have examined the mechanisms of droplet formation and Bi incorporation during molecular beam epitaxy of GaAsBi. We consider the role of the transition from group-V-rich to group-III-rich conditions, i.e., the stoichiometry threshold, in the presence of Bi. For As-rich GaAsBi growth, Bi acts as a surfactant, leading to the formation of droplet-free GaAsBi films. For films within 10% of the stoichiometric GaAsBi growth regime, surface Ga droplets are observed. However, for Ga-rich GaAsBi growth, Bi acts as an anti-surfactant, inducing Ga-Bi droplet formation. We propose a growth mechanism based upon the growth-rate-dependence of the stoichiometry threshold for GaAsBi.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
81.05.Ea III-V semiconductors

Orbital structure of FeTiO3 ilmenite investigated with polarization-dependent X-ray absorption spectroscopy and band structure calculations

S. W. Chen, M. J. Huang, P. A. Lin, H. T. Jeng, J. M. Lee, S. C. Haw, S. A. Chen, H. J. Lin, K. T. Lu, D. P. Chen, S. X. Dou, X. L. Wang, and J. M. Chen

Appl. Phys. Lett. 102, 042107 (2013); http://dx.doi.org/10.1063/1.4789992 (4 pages)

Online Publication Date: 30 January 2013

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We explored the orbital structure of FeTiO3 with polarization-dependent x-ray absorption spectra complemented with electronic structure calculations. The electronic structure, near the bottom of conduction band, is composed of O 2p and Ti 3d orbitals. Ti 3d/4p hybridization dominantly lies on the ab plane. The highly delocalized Ti 4p orbital might hybridize with O 2p orbital and even extend to the next-neighbor Fe atom whereby establishing a linear orbital combination of Ti-O-Fe. A clear picture of the orbital construction in FeTiO3 will help to elucidate the paths of pressure-induced charge transfer and other physical or magnetic characteristics.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra

The role of the products of the decay of optical phonons

A. Dyson and B. K. Ridley

Appl. Phys. Lett. 102, 042108 (2013); http://dx.doi.org/10.1063/1.4790280 (3 pages)

Online Publication Date: 1 February 2013

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The decay of nonequilibrium longitudinal optical phonons is investigated by abandoning the usual assumption that the decay products remain in thermodynamic equilibrium. The case when only the grand-daughter modes remain in thermodynamic equilibrium is studied. The effective lifetime of the LO mode, which is the one that would be measured by experiment, is found to decrease with increasing occupancy of the LO mode.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
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Detecting p-type conduction in Ba-doped InN

Q. Y. Xie, W. M. Xie, J. L. Wang, H. P. Zhu, J. H. Yang, L. Sun, and X. S. Wu

Appl. Phys. Lett. 102, 042109 (2013); http://dx.doi.org/10.1063/1.4790281 (4 pages)

Online Publication Date: 1 February 2013

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The buried p-type conduction is demonstrated in InN with Ba ion implantation dose increases up to 1 × 1015 ions/cm−2. The in-plane lattice parameter increases by about 1.2% deep in the film due to larger Ba replacing smaller indium (In). The n-type conductivity is also detected at the surface, which may results from the N-deficiency. First-principles calculations show that holes at the surface, induced by Ba ion implantation, are compensated by extra electrons from the In adlayer. The p-type carriers dominate in the bulk layers, which is in good agreement with the experimental results.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
73.25.+i Surface conductivity and carrier phenomena

Schottky barrier height extraction from forward current-voltage characteristics of non-ideal diodes with high series resistance

Khaled Ahmed and Tony Chiang

Appl. Phys. Lett. 102, 042110 (2013); http://dx.doi.org/10.1063/1.4789989 (3 pages)

Online Publication Date: 1 February 2013

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Forward bias current-voltage (I-V) characteristics measured at room temperature were used to extract Schottky barrier heights in sulfur-implanted PtSi/n-Si and NiGe/n-Ge contacts. It is found that I-V data claimed to support barrier height reductions of ∼700 meV and ∼500 meV are more consistent with ∼300 meV and 100 meV reductions, respectively. These estimates should better guide attempts aiming at finding physical models for the observed reductions.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Ns Metal-nonmetal contacts
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High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

F. Cossu, N. Singh, and U. Schwingenschlögl

Appl. Phys. Lett. 102, 042401 (2013); http://dx.doi.org/10.1063/1.4789506 (4 pages)

Online Publication Date: 28 January 2013

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First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.
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68.65.Cd Superlattices
73.23.Hk Coulomb blockade; single-electron tunneling
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Ee Antiferromagnetics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Site-preference and valency for rare-earth sites in (R-Ce)2Fe14B magnets

Aftab Alam, Mahmud Khan, R. W. McCallum, and D. D. Johnson

Appl. Phys. Lett. 102, 042402 (2013); http://dx.doi.org/10.1063/1.4789527 (4 pages)

Online Publication Date: 28 January 2013

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Rare-earth (R) permanent magnets of R2Fe14B have technological importance due to their high energy products, and they have two R-sites (Wyckoff 4f and 4g, with four-fold multiplicity) that affect chemistry and valence. Designing magnetic behavior and stability via alloying is technologically relevant to reduce critical (expensive) R-content while retaining key properties; cerium, an abundant (cheap) R-element, offers this potential. We calculate magnetic properties and Ce site preference in (R1−xCex) 2Fe14B [R = La,Nd] using density functional theory (DFT) methods—including a DFT + U scheme to treat localized 4f-electrons. Fe moments compare well with neutron data—almost unaffected by Hubbard U, and weakly affected by spin-orbit coupling. In La2Fe14B, Ce alloys for 0 ≤ x ≤ 1 and prefers smaller R(4f) sites, as observed, a trend we find unaffected by valence. Whereas, in Nd2Fe14B, Ce is predicted to have limited alloying (x ≤ 0.3) with a preference for larger R(4g) sites, resulting in weak partial ordering and segregation. The Curie temperatures versus x for (Nd,Ce) were predicted for a typical sample processing and verified experimentally.
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75.50.Ww Permanent magnets
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
75.10.Lp Band and itinerant models
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Bb Fe and its alloys

Significant ferrimagnetisms observed in superlattice composed of antiferromagnetic LaFeO3 and YMnO3

Y. B. Chen, Jian Zhou, Shan-Tao Zhang, Fei-Xiang Wu, Shu-Hua Yao, Zheng-Bin Gu, Di Wu, and Yan-Feng Chen

Appl. Phys. Lett. 102, 042403 (2013); http://dx.doi.org/10.1063/1.4789753 (5 pages)

Online Publication Date: 28 January 2013

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Show Abstract
A series of LaFeO3/YMnO3 superlattices with various thicknesses are synthesized epitaxially on (001) and (111) SrTiO3 substrates. X-ray diffraction, high-resolution cross-sectional transmission electron microscopy, and sub-nanometer-scale resolved electron energy loss spectroscopy characterizations prove that grown superlattices have designed layer-by-layer structures, and there is atomically sharp interface between two successive constituent layers. Temperature-dependent magnetization and magnetic hysteresis loop measurements substantiate that there is significant ferrimagnetism generated at LaFeO3/YMnO3 interfaces. The generated ferrimagnetism is discussed by considering the magnetic structures in each constituent layer.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Gg Ferrimagnetics
75.50.Ee Antiferromagnetics
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