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15 Aug 2011

Volume 99, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 073701 (2011); http://dx.doi.org/10.1063/1.3599706 (3 pages)

Miguel A. Santiago-Cordoba, Svetlana V. Boriskina, Frank Vollmer, and Melik C. Demirel
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Bipolar conductivity in amorphous HfO2

D. R. Islamov, V. A. Gritsenko, C. H. Cheng, and A. Chin

Appl. Phys. Lett. 99, 072109 (2011); http://dx.doi.org/10.1063/1.3626599 (3 pages) | Cited 1 time

Online Publication Date: 17 August 2011

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This study calculates the contribution of electrons and holes to HfO2 conductivity in Si/HfO2/Ni structures using experiments on injection of minority carriers from n- and p-type silicon. Results show that electrons and holes contribute to the conductivity of HfO2, allowing HfO2 to exhibit two-band conductivity.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
77.55.df For silicon electronics

Carbon nanotube thin film transistors on flexible substrates

Bhupesh Chandra, Hongsik Park, Ahmed Maarouf, Glenn J. Martyna, and George S. Tulevski

Appl. Phys. Lett. 99, 072110 (2011); http://dx.doi.org/10.1063/1.3622767 (3 pages) | Cited 6 times

Online Publication Date: 17 August 2011

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Carbon nanotube thin film transistors (CNT-TFTs) are fabricated on flexible substrates using purified, surfactant-based CNT suspensions, with >95% semiconducting CNT fraction. The TFTs are made up of local bottom-gated structures with aluminum oxide as the gate dielectric. The devices exhibit high ON current densities (0.1 μA/μm) and on-off ratios (∼105) with mobility values ranging from 10-35 cm2/Vs. A detailed numerical model is used to understand the TFT performance and its dependence on device parameters such as TFT channel length, CNT density, and purity.
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85.30.Tv Field effect devices
85.35.Kt Nanotube devices
85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
82.45.Un Dielectric materials in electrochemistry

Exchange interaction of electrons with Mn in hybrid AlSb/InAs/ZnMnTe structures

Ya. V. Terent’ev, C. Zoth, V. V. Bel’kov, P. Olbrich, C. Drexler, V. Lechner, P. Lutz, M. S. Mukhin, S. A. Tarasenko, A. N. Semenov, V. A. Solov’ev, I. V. Sedova, G. V. Klimko, T. A. Komissarova, S. V. Ivanov, et al.

Appl. Phys. Lett. 99, 072111 (2011); http://dx.doi.org/10.1063/1.3624921 (3 pages) | Cited 1 time

Online Publication Date: 17 August 2011

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Diluted magnetic semiconductor heterovalent AlSb/InAs/ZnMnTe quantum well (QW) structures with an electron channel have been designed and grown applying molecular-beam epitaxy. The enhanced magnetic properties of QWs as a result of the exchange interaction with Mn2+ ions, are proved by measuring the microwave radiation induced spin polarized electric currents.
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75.30.Et Exchange and superexchange interactions
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.70.Gm Exchange interactions

Diffusion of E centers in germanium predicted using GGA+U approach

H. Tahini, A. Chroneos, R. W. Grimes, U. Schwingenschlögl, and H. Bracht

Appl. Phys. Lett. 99, 072112 (2011); http://dx.doi.org/10.1063/1.3625939 (3 pages) | Cited 13 times

Online Publication Date: 17 August 2011

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Density functional theory calculations (based on GGA+U approach) are used to investigate the formation and diffusion of donor-vacancy pairs (E centers) in germanium. We conclude that depending upon the Fermi energy, E centers that incorporate for phosphorous and arsenic can form in their neutral, singly negatively or doubly negatively charged states whereas with antimony only the neutral or doubly negatively charged states are predicted. The activation energies of diffusion are compared with recent experimental work and support the idea that smaller donor atoms exhibit higher diffusion activation energies.
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71.20.Mq Elemental semiconductors
81.05.Cy Elemental semiconductors
61.72.jd Vacancies
61.72.Yx Interaction between different crystal defects; gettering effect
66.30.Lw Diffusion of other defects
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Understanding the intermediate initial state in TiO2−δ/La2/3Sr1/3MnO3 stack-based bipolar resistive switching devices

Y. S. Chen, B. Chen, B. Gao, L. P. Chen, G. J. Lian, L. F. Liu, Y. Wang, X. Y. Liu, and J. F. Kang

Appl. Phys. Lett. 99, 072113 (2011); http://dx.doi.org/10.1063/1.3626597 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2011

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Bipolar resistive switching (RS) behavior was observed in epitaxially deposited TiO2−δ/La2/3Sr1/3MnO3 stacks. An intermediate initial state of this device demonstrated that the original resistive state would switch to either the higher or the lower state, depending only on the electrical polarity of the initial measurement. As the analogue intermediate states were obtained by device fabrication, the direct observation of these switching states was possible, knowing the microscopic physical origin of the RS effect. Based on x-ray photoelectron spectroscopy analysis, an understanding of this interesting phenomenon was proposed, well supporting the oxygen vacancy formation and recombination mechanism.
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84.30.Sk Pulse and digital circuits

The influence of dopant type and carrier concentration on the effective mass and Seebeck coefficient of GaNxAs1−x thin films

P. Pichanusakorn, Y. J. Kuang, C. J. Patel, C. W. Tu, and P. R. Bandaru

Appl. Phys. Lett. 99, 072114 (2011); http://dx.doi.org/10.1063/1.3626041 (3 pages) | Cited 4 times

Online Publication Date: 18 August 2011

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We probe whether an enhancement in the Seebeck coefficient (S) could be obtained in GaNxAs1−x through interactions between the N resonant states and the GaAs conduction band. Through experimental investigations, we then determined that an insufficient increase in the density of states effective mass (md) precludes such an enhancement. The relative influences of Group IV/VI dopants and the carrier concentration along with N passivation are discussed.
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72.20.Pa Thermoelectric and thermomagnetic effects
73.50.Lw Thermoelectric effects
73.61.Ey III-V semiconductors
81.65.Rv Passivation
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Field emission measure of the time response of individual semiconducting nanowires to laser excitation

M. Choueib, A. Ayari, P. Poncharal, C. Journet, C. S. Cojocaru, R. Martel, and S. T. Purcell

Appl. Phys. Lett. 99, 072115 (2011); http://dx.doi.org/10.1063/1.3627168 (3 pages) | Cited 1 time

Online Publication Date: 19 August 2011

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A simple technique is explored to determine the temporal photo-response, τ, of individual semiconducting SiC and Si nanowires (NWs), with a high time resolution. Laser-assisted field emission (LAFE) from the NWs is first shown to be highly sensitive to continuous laser illumination. Pulsed illumination is then combined with measurements of the total energy distributions to determine τ which were rather large, 4–200 μs. The time response scaled roughly with the square of the NWs length and could be attributed to laser-induced heating. LAFE is thus a new tool for quantifying rapid thermo-optical effects in such nano-objects.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.Gf Nanowires
78.20.nb Photothermal effects
81.40.Gh Other heat and thermomechanical treatments
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.60.Bm Clean metal, semiconductor, and insulator surfaces

High-quality 1.3 μm-wavelength GaInAsN/GaAs quantum wells grown by metalorganic vapor phase epitaxy on vicinal substrates

D. Fekete, R. Carron, P. Gallo, B. Dwir, A. Rudra, and E. Kapon

Appl. Phys. Lett. 99, 072116 (2011); http://dx.doi.org/10.1063/1.3623478 (3 pages) | Cited 7 times

Online Publication Date: 19 August 2011

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We investigated the composition and optical properties of GaInAsN/GaAs single quantum wells (QWs) grown on vicinal-(001) GaAs substrates using metallorganic vapor phase epitaxy with modulated nitrogen-precursor flux. A significant enhancement in N incorporation and photoluminescence efficiency is achieved with such optimized QW structures. Possible mechanisms of the observed increase in N uptake and reduction in defect density, related to the substrate vicinality, are discussed.
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68.65.Fg Quantum wells
78.55.Cr III-V semiconductors
78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.07.St Quantum wells
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Limiting mechanism of inversion channel mobility in Al-implanted lateral 4H-SiC metal-oxide semiconductor field-effect transistors

A. Frazzetto, F. Giannazzo, P. Fiorenza, V. Raineri, and F. Roccaforte

Appl. Phys. Lett. 99, 072117 (2011); http://dx.doi.org/10.1063/1.3627186 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2011

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The mechanism limiting the channel mobility in metal-oxide-semiconductor field-effect transistors (MOSFETs) fabricated in Al-implanted 4H-SiC is discussed comparing different post-implantation annealings. In spite of the improved interfacial morphology in carbon capped samples during annealing, the observed reduction of the mobility (from 40 to 24 cm2 V−1 s−1) suggests that interfacial roughness does not significantly impact the transport in the channel. Furthermore, the temperature dependence of the mobility demonstrates that Coulomb scattering is the main degradation mechanism due to the presence of trapped charges at the SiO2/SiC interface.
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85.30.Tv Field effect devices
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Gh Other heat and thermomechanical treatments

Thermoelectric power factor enhancement by ionized nanoparticle scattering

Je-Hyeong Bahk, Zhixi Bian, Mona Zebarjadi, Parthiban Santhanam, Rajeev Ram, and Ali Shakouri

Appl. Phys. Lett. 99, 072118 (2011); http://dx.doi.org/10.1063/1.3625950 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2011

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We show theoretically that the thermoelectric power factor can be enhanced in degenerate semiconductors when embedded nanoparticles donate carriers to the matrix and replace conventional impurity dopants as scattering centers. Nanoparticle scattering rates calculated by the partial wave method indicate a mobility enhancement over materials with equivalent doping by isolated ionized impurities while the Seebeck coefficient remains nearly intact. We find that the thermoelectric power factor of In0.53Ga0.47As from 300 K to 800 K is enhanced by 15% – 30% by nanoparticles 3–4 nm in diameter.
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72.20.Pa Thermoelectric and thermomagnetic effects
72.80.Ey III-V and II-VI semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance

Optical detection of the defects associated with the magnetic properties observed in GaN:Gd layers grown by reactive molecular beam epitaxy

J. K. Mishra, B. P. Singh, and S. Dhar

Appl. Phys. Lett. 99, 072119 (2011); http://dx.doi.org/10.1063/1.3626034 (3 pages) | Cited 1 time

Online Publication Date: 19 August 2011

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The effect of annealing on the magnetic and the optoelectronic properties of Gd-doped GaN layers, which are grown by reactive molecular beam epitaxy technique, has been investigated using photoluminescence, photoconductivity, and vibrating sample magnetometry techniques. The study reveals that the multiple types of defects are formed in GaN layers during the Gd incorporation. However, the density of only one defect type, which results in a strong luminescence feature at 3.05 eV in the photoluminescence spectra recorded at low temperatures in GaN:Gd layers, has been found to decrease significantly upon annealing and at the same time, the saturation magnetization is also observed to reduce, suggesting that these defects are responsible for the magnetic properties observed in this system.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.40.Tv Optical and dielectric properties related to treatment conditions
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing

Suppression of planar defects in the molecular beam epitaxy of GaAs/ErAs/GaAs heterostructures

Adam M. Crook, Hari P. Nair, Domingo A. Ferrer, and Seth R. Bank

Appl. Phys. Lett. 99, 072120 (2011); http://dx.doi.org/10.1063/1.3626035 (3 pages) | Cited 4 times

Online Publication Date: 19 August 2011

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We present a growth method that overcomes the mismatch in rotational symmetry of ErAs and conventional III-V semiconductors, allowing for epitaxially integrated semimetal/semiconductor heterostructures. Transmission electron microscopy and reflection high-energy electron diffraction reveal defect-free overgrowth of ErAs layers, consisting of >2× the total amount of ErAs that can be embedded with conventional layer-by-layer growth methods. We utilize epitaxial ErAs nanoparticles, overgrown with GaAs, as a seed to grow full films of ErAs. Growth proceeds by diffusion of erbium atoms through the GaAs spacer, which remains registered to the underlying substrate, preventing planar defect formation during subsequent GaAs growth. This growth method is promising for metal/semiconductor heterostructures that serve as embedded Ohmic contacts to epitaxial layers and epitaxially integrated active plasmonic devices.
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73.40.Ns Metal-nonmetal contacts
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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Strain control spin reorientation transition in DyFeO3/SrTiO3 epitaxial film

T.-Y. Khim, M. J. Eom, J. S. Kim, B.-G. Park, J.-Y. Kim, and J.-H. Park

Appl. Phys. Lett. 99, 072501 (2011); http://dx.doi.org/10.1063/1.3623756 (3 pages) | Cited 1 time

Online Publication Date: 15 August 2011

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We grew single phase DyFeO3 (110) epitaxial films on SrTiO3(001) substrates in the layer-by-layer mode using the pulsed laser deposition. The Fe L2,3-edge x-ray magnetic linear dichroism and magnetic hysteresis confirm that the film shows the spin-canted antiferromagnetism at room temperature and undergoes the spin reorientation transition (SRT) upon cooling as the bulk. The SRT temperature is significantly reduced in the thin films due to the compressive strain and becomes below 5 K for the thickness ≲ 50 Å.
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75.30.Ds Spin waves
75.30.Wx Spin crossover
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Fg Pulsed laser ablation deposition

Suppression of the spin pumping in Pd/Ni81Fe19 bilayers with nano-oxide layer

Duck-Ho Kim, Hong-Hyoun Kim, and Chun-Yeol You

Appl. Phys. Lett. 99, 072502 (2011); http://dx.doi.org/10.1063/1.3626593 (3 pages) | Cited 1 time

Online Publication Date: 17 August 2011

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We demonstrate that the spin pumping effect can be effectively suppressed with a nano-oxide layer. Spin pumping effect manifests itself by an enhancement of the Gilbert damping parameter in normal metal/ferromagnetic hetero-structures, while many spintronics devices prefer smaller damping parameter. Since the spin pumping effect is directly related with the spin dependent interface conductance, we can modify the spin pumping by altering the interface conductance with the nano-oxide layer. We prepared series of Pd/Ni81Fe19 bilayers with different pausing time between Pd and Ni81Fe19 depositions in order to control the interface conductance. The Gilbert damping parameters are determined from the line-width measurements in the ferromagnetic resonance spectra for each pausing time sample. They are 0.0490, 0.0296, 0.0278, and 0.0251 for 0, 6, 30, and 60 s pausing time, respectively. We find that the damping parameter of Pd/Ni81Fe19 is almost recovered to one of the Cu/Ni81Fe19 bilayer with 60 s pausing time, while the static magnetic properties are not noticeably changed.
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81.05.Bx Metals, semimetals, and alloys
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.76.+j Spin transport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)

First principles study of the electric field effect on magnetization and magnetic anisotropy of FeCo/MgO(001) thin film

K. H. He, J. S. Chen, and Y. P. Feng

Appl. Phys. Lett. 99, 072503 (2011); http://dx.doi.org/10.1063/1.3626598 (3 pages) | Cited 6 times

Online Publication Date: 17 August 2011

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The magnetization and magnetic anisotropy of FeCo/MgO(001) thin film under electric field were investigated by the first-principles calculations. Three different interface configurations were considered: Co/Fe/MgO, Fe/Co/MgO, and FeCo/FeCo/MgO. It was found that the perpendicular anisotropy was preferred for all the configurations and enhanced with increasing electric field, which was consistent with experimental results. Furthermore, our calculations indicated that the FeCo/FeCo/MgO was the most stable configuration and had the largest perpendicular magnetic anisotropy energy. The results also showed that the FeCo/FeCo/MgO and Fe/Co/MgO configurations had larger magnetoelectric coefficients than those of the Co/Fe/MgO configuration and previous report about the Fe/MgO interface.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
71.15.-m Methods of electronic structure calculations
75.30.Gw Magnetic anisotropy
75.85.+t Magnetoelectric effects, multiferroics
77.55.Nv Multiferroic/magnetoelectric films
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Strain analysis of multiferroic BiFeO3-CoFe2O4 nanostructures by Raman scattering

O. Chaix-Pluchery, C. Cochard, P. Jadhav, J. Kreisel, N. Dix, F. Sánchez, and J. Fontcuberta

Appl. Phys. Lett. 99, 072901 (2011); http://dx.doi.org/10.1063/1.3626595 (3 pages) | Cited 7 times

Online Publication Date: 15 August 2011

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We report a Raman scattering investigation of columnar BiFeO3-CoFe2O4 (BFO-CFO) epitaxial thin film nanostructures, where BFO pillars are embedded in a CFO matrix. The feasibility of a strain analysis is illustrated through an investigation of two nanostructures with different BFO-CFO ratios. We show that the CFO matrix presents the same strain state in both nanostructures, while the strain state of the BFO pillars depends on the BFO/CFO ratio with an increasing tensile strain along the out-of-plane direction with decreasing BFO content. Our results demonstrate that Raman scattering allows monitoring strain states in complex 3D multiferroic pillar/matrix composites.
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78.30.Hv Other nonmetallic inorganics
77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials
68.55.-a Thin film structure and morphology
75.50.Dd Nonmetallic ferromagnetic materials

Sign reversal of dielectric anisotropy of ferroelectric liquid crystals doped with cadmium telluride quantum dots

A. Kumar, P. Silotia, and A. M. Biradar

Appl. Phys. Lett. 99, 072902 (2011); http://dx.doi.org/10.1063/1.3627179 (3 pages) | Cited 6 times

Online Publication Date: 19 August 2011

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A small amount of cadmium telluride quantum dots (CdTe QDs) has been doped into various ferroelectric liquid crystals (FLCs) to observe the modifications in the alignment and dielectric anisotropy (Δɛ) of the composites. The CdTe QDs have induced a uniform homeotropic (HMT) alignment in most of the FLC mixtures. We observed an unexpected switching (from HMT to homogeneous configuration) of CdTe QDs doped FLC CS1026 (having positive Δɛ) by the application of high dc bias. This reverse switching has been attributed to the interaction between FLC molecules and CdTe QDs which caused the sign reversal of Δɛ of FLC CS1026.
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77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.80.Fm Switching phenomena
61.30.Jf Defects in liquid crystals
42.70.Df Liquid crystals
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Homogeneity improvement of field emission beam from metallic nano-tip arrays by noble-gas conditioning

S. Tsujino, M. Paraliev, E. Kirk, and H.-H. Braun

Appl. Phys. Lett. 99, 073101 (2011); http://dx.doi.org/10.1063/1.3624705 (3 pages) | Cited 2 times

Online Publication Date: 15 August 2011

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The authors explored control of field-emission electron beam homogeneity emitted from metallic nano-tips fabricated by molding. Improved beam homogeneity and increased maximum bunch charge were observed after DC operation of cathodes in low-pressure argon gas environment. They also observed average current per tip of 4.5 μA from a 1 × 104 emitter array device after conditioning in neon gas. Evolution of Fowler-Nordheim parameters as a result of noble-gas conditioning was discussed.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption

High charge carrier density at the NaTaO3/SrTiO3 hetero-interface

S. Nazir and U. Schwingenschlögl

Appl. Phys. Lett. 99, 073102 (2011); http://dx.doi.org/10.1063/1.3625951 (3 pages) | Cited 6 times

Online Publication Date: 15 August 2011

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The formation of a (quasi) two-dimensional electron gas between the band insulators NaTaO3 and SrTiO3 is studied by means of the full-potential linearized augmented plane-wave method of density functional theory. Optimization of the atomic positions points to only small changes in the chemical bonding at the interface. Both the p-type (NaO)−/(TiO2)0 and n-type (TaO2)+/(SrO)0 interfaces are found to be metallic with high charge carrier densities. The effects of O vacancies are discussed. Spin-polarized calculations point to the formation of isolated O 2p magnetic moments, located in the metallic region of the p-type interface.
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71.20.Ps Other inorganic compounds
61.72.jd Vacancies
71.10.Ca Electron gas, Fermi gas
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Enhanced gas-flow-induced voltage in graphene

Jun Yin, Jianxin Zhou, Xuemei Li, Yaqing Chen, Guoan Tai, and Wanlin Guo

Appl. Phys. Lett. 99, 073103 (2011); http://dx.doi.org/10.1063/1.3624590 (3 pages) | Cited 2 times

Online Publication Date: 15 August 2011

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We find experimentally that gas-flow-induced voltage in monolayer graphene is more than twenty times of that in bulk graphite. Examination over samples with sheet resistances ranging from 307 to 1600 Ω/sq shows that the induced voltage increases with the electric resistance and can be further improved by controlling the quality and doping level of graphene. The induced voltage is nearly independent of the substrate materials and can be well explained by the interplay of Bernoulli’s principle and the carrier density dependent Seebeck coefficient. The results demonstrate that graphene has great potential for flow sensors and energy conversion devices.
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73.61.Wp Fullerenes and related materials
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.up Other materials
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces

Observation and interpretation of adjacent Moire patterns of different shapes in bilayer graphene

J. B. Jasinski, S. Dumpala, G. U. Sumanasekera, M. K. Sunkara, and P. J. Ouseph

Appl. Phys. Lett. 99, 073104 (2011); http://dx.doi.org/10.1063/1.3624703 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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In transmission electron micrography of few-layer thick graphene samples, two distinct regions, a region of superlattice and an adjacent region of parallel straight bands, are seen. These two features are explained as Moire patterns produced by (1) rotation of top part of one of the graphene layers and (2) a small change in the shape of the bottom part of the same layer. It is interesting to note that for the first time, Moire pattern of parallel straight bands is observed and satisfactorily explained.
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61.48.Gh Structure of graphene
68.65.Cd Superlattices

Effect of electric and stress field on structures and quantum conduction of Cu nanowires

C. He, L. Qi, W. X. Zhang, and H. Pan

Appl. Phys. Lett. 99, 073105 (2011); http://dx.doi.org/10.1063/1.3626284 (3 pages) | Cited 3 times

Online Publication Date: 16 August 2011

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The ballistic transport properties of Cu nanowires under different electric and stress fields are investigated for future application in microelectronics using first-principles density-function theory. Relative to the case with the electric field only, the stability and quantum conduction of both nonhelical and helical atomic strands are enhanced by applying a stress field F. Under V = 1 V/Å, the most excellent quantum conductivity is exhibited at F = 1.5 nN for the nonhelical atomic strands while at F = 2 nN for the helical ones, and the latter is more stable with collapse-resistant F high as 3 nN compared to the former as 2 nN.
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73.61.Cw Elemental semiconductors
73.63.Nm Quantum wires
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
72.20.Ht High-field and nonlinear effects
73.23.Ad Ballistic transport

Multiferroic coupling in nanoscale BiFeO3

Sudipta Goswami, Dipten Bhattacharya, P. Choudhury, B. Ouladdiaf, and T. Chatterji

Appl. Phys. Lett. 99, 073106 (2011); http://dx.doi.org/10.1063/1.3625924 (3 pages) | Cited 7 times

Online Publication Date: 16 August 2011

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Using the results of x-ray and neutron diffraction experiments, we show that the ferroelectric polarization, in ∼22 nm particles of BiFeO3, exhibits a jump by ∼30% around the magnetic transition point TN (∼635 K) and a suppression by ∼7% under 5T magnetic field at room temperature (≪TN). These results confirm the presence of strong multiferroic coupling even in nanoscale BiFeO3 and thus could prove to be quite useful for applications based on nanosized devices of BiFeO3.
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75.85.+t Magnetoelectric effects, multiferroics
77.80.B- Phase transitions and Curie point
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Gg Ferrimagnetics
75.50.Tt Fine-particle systems; nanocrystalline materials
77.22.Ej Polarization and depolarization

Charge-transfer-induced suppression of galvanic replacement and synthesis of (Au@Ag)@Au double shell nanoparticles for highly uniform, robust and sensitive bioprobes

Dao Thi Ngoc Anh, Prerna Singh, Cheshta Shankar, Derrick Mott, and Shinya Maenosono

Appl. Phys. Lett. 99, 073107 (2011); http://dx.doi.org/10.1063/1.3626031 (3 pages) | Cited 4 times

Online Publication Date: 16 August 2011

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The synthesis of double shell (Au@Ag)@Au nanoparticles is accomplished through suppression of the galvanic replacement reaction caused by an electron transfer phenomenon. The resulting nanoparticles are monodisperse with a thin and uniform second Au shell. These particles are ultimately expected to lead to sensitive probes for biomolecular sensing and diagnostics.
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82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Effects of GaAsSb capping layer thickness on the optical properties of InAs quantum dots

Wei-Ting Hsu, Yu-An Liao, Feng-Chang Hsu, Pei-Chin Chiu, Jen-Inn Chyi, and Wen-Hao Chang

Appl. Phys. Lett. 99, 073108 (2011); http://dx.doi.org/10.1063/1.3624464 (3 pages) | Cited 3 times

Online Publication Date: 17 August 2011

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The optical properties of GaAsSb-capped InAs quantum dots (QDs) with different capping layer thickness are investigated. Both the emission energy and the recombination lifetime are found to be correlated with the capping layer thicknesses. Theoretical calculations indicate that the quantum confinement and the wave function distribution of hole states are sensitive to the GaAsSb capping layer thickness. The Sb induced change in QD size also plays a role in the optical properties of GaAsSb-capped QDs. Controlling the GaAsSb capping layer thickness is a feasible way to tailor the InAs QDs for long-wavelength applications.
Show PACS
78.67.Hc Quantum dots
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
78.55.Cr III-V semiconductors
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