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8 Aug 2011

Volume 99, Issue 6, Articles (06xxxx)

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Appl. Phys. Lett. 99, 063701 (2011); http://dx.doi.org/10.1063/1.3622631 (3 pages)

Bomi Gweon, Mina Kim, Dan Bee Kim, Daeyeon Kim, Hyeonyu Kim, Heesoo Jung, Jennifer H. Shin, and Wonho Choe
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Mismatch relaxation by stacking fault formation of AlN islands in AlGaN/GaN structures on m-plane GaN substrates

Julita Smalc-Koziorowska, Marta Sawicka, Thilo Remmele, Czeslaw Skierbiszewski, Izabella Grzegory, and Martin Albrecht

Appl. Phys. Lett. 99, 061901 (2011); http://dx.doi.org/10.1063/1.3622642 (3 pages) | Cited 3 times

Online Publication Date: 8 August 2011

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We study the mismatch relaxation of 2-5 nm thin elongated AlN islands formed during growth of AlGaN on bulk m-plane GaN by molecular beam epitaxy. The relaxation of these m-plane AlN layers is anisotropic and occurs through the introduction of stacking faults in [0001] planes during island coalescence, while no relaxation is observed along the perpendicular [11math0] direction. This anisotropy in the mismatch relaxation and the formation of stacking faults in the AlN islands are explained by the growth mode of the AlN platelets and their coalescence along the [0001] direction.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Nn Stacking faults and other planar or extended defects

Thermoelectric properties of Ag1−xGaTe2 with chalcopyrite structure

Aikebaier Yusufu, Ken Kurosaki, Atsuko Kosuga, Tohru Sugahara, Yuji Ohishi, Hiroaki Muta, and Shinsuke Yamanaka

Appl. Phys. Lett. 99, 061902 (2011); http://dx.doi.org/10.1063/1.3617458 (3 pages) | Cited 12 times

Online Publication Date: 8 August 2011

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In the present study, we investigated the high-temperature thermoelectric (TE) properties of AgGaTe2 with chalcopyrite structure. We tried to enhance the TE properties of AgGaTe2 by reducing the Ag content. The reduction of Ag increased the carrier concentration, leading to enhancement of the dimensionless figure of merit (ZT). The maximum ZT value was 0.77 at 850 K obtained in Ag0.95GaTe2, which was approximately two times higher than that of stoichiometric AgGaTe2.
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72.20.Pa Thermoelectric and thermomagnetic effects
81.05.Hd Other semiconductors
61.66.Bi Elemental solids
61.66.Dk Alloys
72.20.My Galvanomagnetic and other magnetotransport effects

Effect of relaxation state on nucleation and grain growth of nanoscale quasicrystal in Zr-based bulk metallic glasses prepared under various cooling rates

Junji Saida, Albertus Deny Setyawan, and Eiichiro Matsubara

Appl. Phys. Lett. 99, 061903 (2011); http://dx.doi.org/10.1063/1.3622117 (3 pages) | Cited 4 times

Online Publication Date: 8 August 2011

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Zr65Al7.5Ni10Cu12.5Pd5 bulk metallic glasses (BMGs) in various relaxation states were prepared under different cooling rates. The grain growth rate of the primary quasicrystal was examined near the crystallization temperature. It was approximately 1 × 10−9 m/s in less relaxed BMGs and approximately twice as large in relaxed BMGs. In contrast, the calculated homogeneous nucleation rate of the less relaxed samples was five to ten times higher (5 × 1019–1 × 1020/m3s) than those in the relaxed BMGs. The results indicate that the relaxation state of glassy alloys has a marked effect on nucleation and grain growth behaviors.
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81.05.Kf Glasses (including metallic glasses)
64.60.qj Studies of nucleation in specific substances
64.70.kj Glasses
61.43.Fs Glasses
61.44.Br Quasicrystals
64.70.Nd Structural transitions in nanoscale materials

LaCrO3 heteroepitaxy on SrTiO3(001) by molecular beam epitaxy

L. Qiao, T. C. Droubay, M. E. Bowden, V. Shutthanandan, T. C. Kaspar, and S. A. Chambers

Appl. Phys. Lett. 99, 061904 (2011); http://dx.doi.org/10.1063/1.3624473 (3 pages) | Cited 3 times

Online Publication Date: 9 August 2011

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Stoichiometric, epitaxial LaCrO3 films have been grown on SrTiO3(001) by molecular beam epitaxy using O2 as the oxidant. Films grew in a layer-by-layer fashion, giving rise to coherently strained, structurally excellent films and surfaces which preserve the step-terrace structure of the substrate. The critical thickness is in excess of 500 Å. Cr(III) near the surface is easily oxidized to Cr(V) upon exposure to atomic oxygen and reduction back to Cr(III) is readily achieved by vacuum annealing, resulting in tunability of the charge state at the B-site cation.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.40.Gh Other heat and thermomechanical treatments
81.65.Mq Oxidation
68.55.aj Insulators
61.66.Bi Elemental solids
61.66.Dk Alloys

Optical transition energies as a probe of stress in polycrystalline CdTe thin films

Jian Li, Jie Chen, and R. W. Collins

Appl. Phys. Lett. 99, 061905 (2011); http://dx.doi.org/10.1063/1.3624536 (3 pages)

Online Publication Date: 9 August 2011

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In situ spectroscopic ellipsometry was applied to measure the dielectric functions ɛ of polycrystalline CdTe thin films prepared by magnetron sputtering. The observable critical point (CP) energies determined for the films in best fits to d2ɛ/dE2 are shifted relative to those for single crystal CdTe. The energy shift of the critical point designated as En is attributed to in-plane stress X with linear stress coefficient CX(En). By analyzing these shifts, it was found that stress (1) builds with thickness in as-deposited films, (2) relaxes with increasing substrate temperature at fixed thickness, and (3) is relaxed uniformly in CdCl2 treated films.
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81.05.Dz II-VI semiconductors
81.15.Cd Deposition by sputtering
68.60.Bs Mechanical and acoustical properties
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Hf II-VI semiconductors

Solar radiation shielding material for windows TiN studied from first-principles theory

Lihua Xiao, Yuchang Su, Hongyang Chen, Sainan Liu, Min Jiang, Ping Peng, and Sidong Liu

Appl. Phys. Lett. 99, 061906 (2011); http://dx.doi.org/10.1063/1.3624709 (3 pages) | Cited 1 time

Online Publication Date: 10 August 2011

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Using first-principles calculations in the framework of density functional theory, we studied the electronic structure and optical performance of TiN. It was found that the calculated structure parameter and optical performance are in better agreement with the latest relevant experimental data, and our theoretical studies showed that TiN is a perfect near infrared absorber with high visible light transmittance and could serve as references for future experimental study and its applications as solar radiation shielding material for windows.
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71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
78.40.Ha Other nonmetallic inorganics
61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Nanoscale multiplane shear and twin deformation in nanowires and nanocrystalline solids

I. A. Ovid'ko

Appl. Phys. Lett. 99, 061907 (2011); http://dx.doi.org/10.1063/1.3620934 (3 pages) | Cited 5 times

Online Publication Date: 10 August 2011

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A special physical micromechanism/mode of twin deformation in nanowires and nanocrystalline (NC) solids is suggested and theoretically described. This mode represents a nanoscale multiplane shear (NMS) defined as an ideal shear occurring within a nanometer-sized volume. We calculated the energy and stress characteristics of nanoscale twin deformation through NMS in Cu nanowires and NC Cu. It is shown that this deformation mode can occur in NC solids and defect-free nanowires at high stresses.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.Mm Grain and twin boundaries

Time-domain terahertz spectroscopy of spin state transition in [Fe(NH2 − trz)3]2+ spin crossover compounds

B. Viquerat, J. Degert, M. Tondusson, E. Freysz, C. Mauriac, and J. F. Létard

Appl. Phys. Lett. 99, 061908 (2011); http://dx.doi.org/10.1063/1.3624600 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2011

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We have measured the evolution of the THz spectrum of iron(II) spin crossover compounds within the low-spin/high-spin thermal hysteresis loop in the 0.6–6 THz frequency range. This study enabled to follow both the variations of the refractive optical index and absorption during the spin state transition. Marked absorptions centered ∼2 – 3 THz and ∼5 THz shifting with the spin state are revealed. Our work provides a means to store optically information and to read it out in the THz domain and also offers indications about the structural evolution occurring during the spin state transition.
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78.47.J- Ultrafast spectroscopy (<1 psec)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Pg Disordered solids

Microfocus infrared ellipsometry characterization of air-exposed graphene flakes

J. W. Weber, K. Hinrichs, M. Gensch, M. C. M. van de Sanden, and T. W. H. Oates

Appl. Phys. Lett. 99, 061909 (2011); http://dx.doi.org/10.1063/1.3624826 (3 pages)

Online Publication Date: 11 August 2011

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Graphene and ultrathin graphite flakes prepared by exfoliation were characterized by microfocus synchrotron infrared mapping ellipsometry. The dielectric function of graphene in a dry-air atmosphere is determined and compared to that of ultrathin graphite, bulk graphite, and gold. The imaginary part of graphene is revealed to be about an order of magnitude higher than that of graphite and comparable to that of gold. Comparing the conductivity to an optical model considering intraband transitions, we discuss the critical effects of environmental exposure, relevant for real-world applications.
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78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

In-assisted desorption of native GaAs surface oxides

L. H. Li (李联合), E. H. Linfield, R. Sharma, and A. G. Davies

Appl. Phys. Lett. 99, 061910 (2011); http://dx.doi.org/10.1063/1.3623424 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2011

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We demonstrate In-assisted desorption of native GaAs surface oxides at substrate temperatures of 480–550 °C. The oxides are removed through production of volatile Ga and In suboxides, Ga2O, and In2O. Compared to a Ga-assisted desorption process, excess In is easily removed at low substrate temperature, favouring a clean, smooth surface. The feasibility of using In-assisted desorption for the regrowth of high quality quantum dot structures is shown.
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68.43.Nr Desorption kinetics
81.07.Ta Quantum dots

Stretchability of encapsulated electronics

J. Wu, Z. J. Liu, J. Song, Y. Huang, K.-C. Hwang, Y. W. Zhang, and J. A. Rogers

Appl. Phys. Lett. 99, 061911 (2011); http://dx.doi.org/10.1063/1.3624848 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2011

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Stretchable and flexible electronics offer the performance of conventional wafer-based systems but can be stretched like a rubber band, twisted like a rope, and bent over a pencil. Such a technology offers new application opportunities, in areas of surgical and diagnostic implements that naturally integrate with the human body to provide advanced capabilities, to curvilinear devices such as hemispherical “eyeball” cameras. In practice, stretchable and flexible electronic systems require encapsulation layers to provide mechanical and environmental protection. This paper establishes a simple, analytical model for the optimal design of encapsulation.
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87.85.-d Biomedical engineering
42.66.-p Physiological optics

Dependence on composition of the optical polarization properties of m-plane InxGa1−xN commensurately grown on ZnO

Hiroaki Tamaki, Atsushi Kobayashi, Jitsuo Ohta, Masaharu Oshima, and Hiroshi Fujioka

Appl. Phys. Lett. 99, 061912 (2011); http://dx.doi.org/10.1063/1.3624462 (3 pages) | Cited 1 time

Online Publication Date: 11 August 2011

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We have grown m-plane InxGa1−xN (x = 0.24-0.43) commensurately on m-plane ZnO by the use of a low temperature epitaxial growth technique and investigated its optical properties. We found that the critical thickness for strain relaxation in the InGaN films prepared by the present technique is at least one order of magnitude larger than those reported by the other techniques. Polarized optical absorption measurements revealed that the allowed optical transition between the conduction band and the topmost valence band in m-plane InxGa1−xN (x = 0.24−0.43) on ZnO is for light polarized along c-axis. We found that the valence band splitting energy strongly depends upon the In composition. The values of the deformation potentials of InN were determined as D3 = 2.4 eV, D4 = −6.3 eV, and D5 = −1.2 eV, by fitting the experimental results with theoretical calculations based on the k·p approach.
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81.05.Ea III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.60.Bs Mechanical and acoustical properties
71.20.Nr Semiconductor compounds
78.66.Fd III-V semiconductors

Pressure induced high spin-low spin transition in FeSe superconductor studied by x-ray emission spectroscopy and ab initio calculations

Ravhi S. Kumar, Yi Zhang, Yuming Xiao, Jason Baker, Andrew Cornelius, Sathishkumar Veeramalai, Paul Chow, Changfeng Chen, and Yusheng Zhao

Appl. Phys. Lett. 99, 061913 (2011); http://dx.doi.org/10.1063/1.3621859 (3 pages) | Cited 2 times

Online Publication Date: 11 August 2011

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FeSe is a simple binary system in the iron based superconducting family and exhibits a significant pressure induced increase in the superconducting transition temperature (Tc). In addition to pressure effect, spin fluctuations, magnetic ordering, and crystal structure all play vital roles in altering Tc. Even though various experiments and theoretical simulations explain the connection among them and superconductivity, the interplay between these important parameters is still not clearly understood. Here, we report the pressure effect on the spin state of Fe in FeSe superconductor studied using synchrotron x-ray emission spectroscopy at ambient and low temperatures down to 8 K near Tc. Pressure induced high spin to low spin transition was observed at both ambient and low temperatures with continuous suppression of Fe magnetic moments under increasing pressure. The spin transition is closely related to the pressure induced tetragonal to orthorhombic structural transition.
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74.62.Fj Effects of pressure
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
78.70.En X-ray emission spectra and fluorescence
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
74.62.Bf Effects of material synthesis, crystal structure, and chemical composition

Formation of m-plane InGaN/GaN quantum dots using strain engineering of AlGaN/AlN interlayers

Xuelin Yang, Munetaka Arita, Satoshi Kako, and Yasuhiko Arakawa

Appl. Phys. Lett. 99, 061914 (2011); http://dx.doi.org/10.1063/1.3626589 (3 pages) | Cited 2 times

Online Publication Date: 12 August 2011

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We demonstrate the growth of m-plane InGaN/GaN quantum dots by metalorganic chemical vapor deposition. Formation of the InGaN quantum dots on the GaN layer is achieved only when AlGaN/AlN interlayers are deposited prior to the GaN layer. Structural analysis shows that the AlGaN/AlN layers which introduce a compressive strain for the GaN layer play a crucial role in the formation of the quantum dots. The strong photoluminescence emission observed at room temperature as well as the reduction of quantum confinement Stark effect in the m-plane InGaN quantum dots opens the possibility of using such systems as efficient single photon sources.
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68.55.ag Semiconductors
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.67.Hc Quantum dots
81.07.Ta Quantum dots
78.55.Cr III-V semiconductors
78.20.Jq Electro-optical effects
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