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13 Feb 2012

Volume 100, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 073501 (2012); http://dx.doi.org/10.1063/1.3682479 (3 pages)

S. Tongay, M. Lemaitre, J. Fridmann, A. F. Hebard, B. P. Gila, and B. R. Appleton
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Strain relaxation analysis of LaAlO3/SrTiO3 heterostructure using reciprocal lattice mapping

Wei Wei and Alp Sehirlioglu

Appl. Phys. Lett. 100, 071901 (2012); http://dx.doi.org/10.1063/1.3685463 (4 pages)

Online Publication Date: 13 February 2012

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Strain-relaxation in LaAlO3/SrTiO3 heterostructures was systematically investigated with LaAlO3 film thickness in the range 4.9-84 nm. Heterostructures were characterized using reciprocal lattice mapping (RLM), high resolution rocking curve, and x-ray reflectivity. RLM enables the measurement of lattice constant with accuracy of 10−6 nm. Lattice constant, mismatch, and strain are independently determined in both out-of-plane and in-plane directions. Heterostructures are tetragonally distorted over the entire range of film thickness, even in the film with thickness of 84 nm, in which plastic deformation occurred. This strain-relaxation analysis of LaAlO3/SrTiO3 heterostructure contributes, on the experimental basis, to the knowledge of the strained heterostructure interfaces from thin film growth point of view.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties

Depletion of nitrogen‐vacancy color centers in diamond via hydrogen passivation

A. Stacey, T. J. Karle, L. P. McGuinness, B. C. Gibson, K. Ganesan, S. Tomljenovic‐Hanic, A. D. Greentree, A. Hoffman, R. G. Beausoleil, and S. Prawer

Appl. Phys. Lett. 100, 071902 (2012); http://dx.doi.org/10.1063/1.3684612 (4 pages) | Cited 5 times

Online Publication Date: 13 February 2012

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We show reduction in the emission from nitrogen‐vacancy (NV) centers in single crystal diamond due to exposure to hydrogen plasmas ranging from 700 °C to 1000 °C. Significant fluorescence reduction was observed beneath the exposed surface to 80 μm depth after ∼10 min and did not recover after post‐annealing in vacuum for 7 h at 1100 °C. We attribute the fluorescence reduction to the formation of nitrogen‐vacancy‐hydrogen centers by the plasma‐induced diffusion of hydrogen. These results have important implications for the formation of NV centers for quantum applications, whilst also providing experimental evidence of long range hydrogen diffusion through intrinsic high‐purity diamond.
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61.72.jd Vacancies
81.65.-b Surface treatments
66.30.H- Self-diffusion and ionic conduction in nonmetals
81.40.Gh Other heat and thermomechanical treatments
78.55.-m Photoluminescence, properties and materials

Asymmetric coalescence of reactively wetting droplets

C. X. Zheng, W. X. Tang, and D. E. Jesson

Appl. Phys. Lett. 100, 071903 (2012); http://dx.doi.org/10.1063/1.3684616 (3 pages)

Online Publication Date: 13 February 2012

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Coalescence of droplets during reactive wetting is investigated for the liquid Ga/GaAs(001) system. In situ mirror electron microscopy reveals that coalescence predominantly involves the motion of one reactive droplet relative to the other. This behaviour differs significantly from coalescence in non-reactive systems and is associated with contact line pinning at a ridge/etch pit edge which is identified using atomic force microscopy and selective etching. A simple geometrical model is presented to describe the pinning.
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68.08.Bc Wetting
68.03.Cd Surface tension and related phenomena
81.65.Cf Surface cleaning, etching, patterning
68.37.Ps Atomic force microscopy (AFM)

Shear-band arrest and stress overshoots during inhomogeneous flow in a metallic glass

R. Maaß, D. Klaumünzer, G. Villard, P. M. Derlet, and J. F. Löffler

Appl. Phys. Lett. 100, 071904 (2012); http://dx.doi.org/10.1063/1.3684871 (4 pages) | Cited 2 times

Online Publication Date: 13 February 2012

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At the transition from a static to a dynamic deformation regime of a shear band in bulk metallic glasses, stress transients in terms of overshoots are observed. We interpret this phenomenon with a repeated shear-melting transition and are able to access a characteristic time for a liquidlike to solidlike transition in the shear band as a function of temperature, enabling us to understand why shear bands arrest during inhomogenous serrated flow in bulk metallic glasses.
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62.10.+s Mechanical properties of liquids
64.70.dj Melting of specific substances
64.70.pe Metallic glasses
61.25.Mv Liquid metals and alloys
47.15.St Free shear layers

Temperature dependent phonon Raman scattering of highly a-axis oriented CoFe2O4 inverse spinel ferromagnetic films grown by pulsed laser deposition

Y. Y. Liao (廖原愿), Y. W. Li (李亚巍), Z. G. Hu (胡志高), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 100, 071905 (2012); http://dx.doi.org/10.1063/1.3683520 (4 pages) | Cited 2 times

Online Publication Date: 14 February 2012

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Lattice vibrations of highly a-axis oriented CoFe2O4 (CFO) films have been investigated by Raman scattering in the temperature range of 80-873 K. The five phonon modes T1g(2), T1g(3), Eg, A1g(1), A1g(2), and their evolutions can be uniquely distinguished. It was found that an electron transfer between Co2+ and Fe3+ cations occurs in octahedral sites at about 173 K. The structure disorder in the CFO films appears with increasing the temperature, which indicates the cation migration between tetrahedral and octahedral sites. The phenomena suggest the structural transformation trend from inverse spinel to normal spinel at the elevated temperatures.
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78.30.Hv Other nonmetallic inorganics
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Sample size effects on the large strain bursts in submicron aluminum pillars

Zhang-Jie Wang, Qing-Jie Li, Zhi-Wei Shan, Ju Li, Jun Sun, and Evan Ma

Appl. Phys. Lett. 100, 071906 (2012); http://dx.doi.org/10.1063/1.3681582 (3 pages) | Cited 5 times

Online Publication Date: 14 February 2012

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In situ transmission electron microscope compression testing of submicron Al pillars shows two sample size regimes with contrasting behavior underlying the large strain bursts. For small pillars, the bursts originate from explosive and highly correlated dislocation generation, characterized by very high collapse stresses and nearly dislocation-free post-collapse microstructure. For larger pillars, the bursts result from the reconstruction of jammed dislocation configurations, featuring relative low stress levels and retention of dislocation network after bursts.
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61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
81.70.Bt Mechanical testing, impact tests, static and dynamic loads
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity

Temperature dependence of Raman-active optical phonons in Bi2Se3 and Sb2Te3

Y. Kim, X. Chen, Z. Wang, J. Shi, I. Miotkowski, Y. P. Chen, P. A. Sharma, A. L. Lima Sharma, M. A. Hekmaty, Z. Jiang, and D. Smirnov

Appl. Phys. Lett. 100, 071907 (2012); http://dx.doi.org/10.1063/1.3685465 (3 pages) | Cited 4 times

Online Publication Date: 15 February 2012

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Inelastic light scattering spectra of Bi2Se3 and Sb2Te3 single crystals have been measured over the temperature range from 5 K to 300 K. The temperature dependence of dominant A1g2 phonons shows similar behavior in both materials. The temperature dependence of the peak position and linewidth is analyzed considering the anharmonic decay of optical phonons and the material thermal expansion. This work suggests that Raman spectroscopy can be used for thermometry in Bi2Se3- and Sb2Te3-based devices in a wide temperature range.
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78.30.Hv Other nonmetallic inorganics
65.40.De Thermal expansion; thermomechanical effects
63.20.D- Phonon states and bands, normal modes, and phonon dispersion

Diffusion-controlled formation mechanism of dual-phase structure during Al induced crystallization of SiGe

Tian-Wei Zhang, Fei Ma, Wei-Lin Zhang, Da-Yan Ma, Ke-Wei Xu, and Paul K. Chu

Appl. Phys. Lett. 100, 071908 (2012); http://dx.doi.org/10.1063/1.3685712 (3 pages) | Cited 1 time

Online Publication Date: 15 February 2012

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Aluminum induced crystallization of amorphous SiGe at low temperature is studied and a dual-phase stacked structure with different compositions emerges when the annealing temperature is higher than a critical value. This behavior is very sensitive to the oxidization state of the interlayer. A model based on energetics is proposed to elucidate this temperature dependent behavior. Thermodynamically, it can be ascribed to the competition between grain-boundary-mediated and interface-mediated crystallization and kinetically, it stems from the different diffusion rates of Si and Ge. The results are useful to the design and fabrication of high-efficiency solar cells.
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61.43.Dq Amorphous semiconductors, metals, and alloys
61.72.Mm Grain and twin boundaries
64.70.kg Semiconductors
66.30.-h Diffusion in solids

Role of aluminum as an oxygen-scavenger in zirconium based bulk metallic glasses

Jochen Heinrich, Ralf Busch, Frank Müller, Samuel Grandthyll, and Stefan Hüfner

Appl. Phys. Lett. 100, 071909 (2012); http://dx.doi.org/10.1063/1.3685492 (3 pages) | Cited 1 time

Online Publication Date: 16 February 2012

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In order to investigate a way to diminish the impact of oxygen onto the critical cooling rate of Zr-based alloys, the bonding chemistry of the elements in Zr-Cu-Ni-Al-Nb-Si bulk metallic glasses with different oxygen contents is studied by x-ray photoelectron spectroscopy. Complementary undercooling experiments lead to continuous-cooling-transformation diagrams for the studied alloys. The experimental results demonstrate that Al not only acts as a scavenger for both absorbed and intrinsic oxygen but the dissolution of its oxide on atomic length scales refrains from heterogeneous nucleation. The combined effect is an enhancement of oxygen tolerance in the investigated alloy.
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61.43.Fs Glasses
61.50.Lt Crystal binding; cohesive energy
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
81.30.Dz Phase diagrams of other materials
79.60.Ht Disordered structures
64.60.qj Studies of nucleation in specific substances

Well-to-well non-uniformity in InGaN/GaN multiple quantum wells characterized by capacitance-voltage measurement with additional laser illumination

Tae-Soo Kim, Byung-Jun Ahn, Yanqun Dong, Ki-Nam Park, Jin-Gyu Lee, Youngboo Moon, Hwan-Kuk Yuh, Sung-Chul Choi, Jae-Hak Lee, Soon-Ku Hong, and Jung-Hoon Song

Appl. Phys. Lett. 100, 071910 (2012); http://dx.doi.org/10.1063/1.3685717 (4 pages) | Cited 2 times

Online Publication Date: 16 February 2012

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We experimentally investigated well-to-well non-uniformity in InGaN/GaN multiple quantum well (MQW) structures by using capacitance-voltage measurements with additional laser illumination. By varying the illuminating power of the resonant excitation, well-to-well non-uniformity through the MQWs was clearly revealed. The quantum wells (QWs) close to the n-GaN side show higher carrier accumulations and larger position shift as the excitation power is increased, relative to the p-side QWs. Both results were attributed to the existence of stronger piezoelectric fields in the n-side QWs induced by subsequent partial relaxation of strain through the MQWs.
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73.61.Ey III-V semiconductors

Dirac cones at math = 0 in acoustic crystals and zero refractive index acoustic materials

Fengming Liu, Xueqin Huang, and C. T. Chan

Appl. Phys. Lett. 100, 071911 (2012); http://dx.doi.org/10.1063/1.3686907 (4 pages) | Cited 9 times

Online Publication Date: 16 February 2012

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We show that two-dimensional acoustic crystals (ACs) can be designed to exhibit Dirac cone dispersion at math = 0. Effective medium theory finds that some of these ACs can have effectively zero reciprocal of bulk modulus 1/κeff and zero mass density ρeff, and thus zero refractive indices at the Dirac point. Numerical simulations are used to demonstrate various phenomena associated with the zero spatial phase change inside such materials.
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62.65.+k Acoustical properties of solids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
62.20.de Elastic moduli
81.40.Jj Elasticity and anelasticity, stress-strain relations

Temperature-dependent decay dynamics in highly mismatched ZnSe1−xTex alloy

Yan-Cheng Lin, Wei-Shi Jiang, Wu-Ching Chou, Wei-Kuo Chen, Wen-Hao Chang, Chin-Hau Chia, Cheng-Yu Chen, and Jen-Inn Chyi

Appl. Phys. Lett. 100, 071912 (2012); http://dx.doi.org/10.1063/1.3687187 (4 pages)

Online Publication Date: 17 February 2012

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This study investigates the temperature-dependent decay dynamics in highly mismatched ZnSe0.950Te0.050 alloy using photoluminescence (PL) and time-resolved PL spectroscopy. The PL peak energy exhibits a V-shaped dependence on temperature (10–300 K), indicating strong carrier localization. Kohlrausch’s stretched exponential law, in which the deduced stretching exponent β is highly consistent with the V-shaped PL peak shift, closely corresponds to the complex decay curves over a wide temperature range. Additionally, the PL lifetime τ initially increases and then monotonically declines as the temperature increases. These findings agree excellently with the low electron-hole binding energy upon thermal ionization of weakly bound electrons.
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73.61.Ga II-VI semiconductors
78.66.Hf II-VI semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.20.Nr Semiconductor compounds
78.55.Et II-VI semiconductors
78.47.jd Time resolved luminescence

Properties of InxGa1−xN films in terahertz range

A. Gauthier-Brun, J. H. Teng, E. Dogheche, W. Liu, A. Gokarna, M. Tonouchi, S. J. Chua, and D. Decoster

Appl. Phys. Lett. 100, 071913 (2012); http://dx.doi.org/10.1063/1.3684836 (5 pages) | Cited 1 time

Online Publication Date: 17 February 2012

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In this letter, we report the characterization of the refractive indices and complex conductivities of a set of GaN films with different carrier concentrations, InN film, and InxGa1−xN films with indium content varying from x = 0.07 to x = 0.14 grown by metalorganic chemical vapor deposition for frequencies ranging from 0.3 to 3 THz using terahertz time-domain spectroscopy (THz-TDS). The refractive indices of InxGa1−xN films at THz range are reported. The carrier density and mobility determined using THz-TDS method show good agreement with four-probe Hall measurements.
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73.61.Ey III-V semiconductors
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
68.55.ag Semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.80.Ey III-V and II-VI semiconductors
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