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13 Sep 2010

Volume 97, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 97, 113701 (2010); http://dx.doi.org/10.1063/1.3487998 (3 pages)

Sarah E. Baker, Michael D. Pocha, Allan S. P. Chang, Donald J. Sirbuly, Stefano Cabrini, Scott D. Dhuey, Tiziana C. Bond, and Sonia E. Létant
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Single crystal-like selection rules for unipolar-axis oriented tetragonal Pb(Zr,Ti)O3 thick epitaxial films

Mitsumasa Nakajima, Takashi Fujisawa, Yoshitaka Ehara, Tomoaki Yamada, Hiroshi Funakubo, Hiroshi Naganuma, Soichiro Okamura, Ken Nishida, Takashi Yamamoto, and Minoru Osada

Appl. Phys. Lett. 97, 111901 (2010); http://dx.doi.org/10.1063/1.3488015 (3 pages)

Online Publication Date: 13 September 2010

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We investigated the polarized Raman spectra of a strain-free, unipolar-axis oriented tetragonal Pb(Zr,Ti)O3 thick epitaxial film. We evaluated the single crystal-like selection rules of the A1- and E-symmetry components, and found an anomalous behavior in the angular dependence of the A1(1TO)-mode intensity similar to that observed in high-Tc superconductor single crystals. Raman tensor analyses of the A1(1TO) mode revealed complex phases may exist between two independent Raman-tensor components even in the single 180° domain state.
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78.30.Hv Other nonmetallic inorganics
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.55.Px Epitaxial and superlattice films

Dielectric functions and interband transitions of In1−xAlxSb alloys

J. J. Yoon, T. J. Kim, Y. W. Jung, D. E. Aspnes, Y. D. Kim, H. J. Kim, Y. C. Chang, S. H. Shin, and J. D. Song

Appl. Phys. Lett. 97, 111902 (2010); http://dx.doi.org/10.1063/1.3488827 (3 pages) | Cited 2 times

Online Publication Date: 13 September 2010

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Pseudodielectric functions 〈ε〉 of In1−xAlxSb ternary alloy films were determined from 1.5 to 6.0 eV by spectroscopic ellipsometry. Overlayer effects were minimized by performing in situ chemical etching to more accurately determine intrinsic bulk dielectric responses. Critical-point (CP) energies of structures were determined from numerically calculated second energy derivatives. Where necessary, Brillouin-zone origins were identified by electronic band structure calculations done with the linear augmented Slater-type orbital method. These calculations also showed increasing separation of the E2 and E2′ CP structures with increasing Al-composition
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71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
71.20.Gj Other metals and alloys

Nanoductility induced brittle fracture in shocked high performance ceramics

Paulo S. Branicio, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta

Appl. Phys. Lett. 97, 111903 (2010); http://dx.doi.org/10.1063/1.3478003 (3 pages) | Cited 3 times

Online Publication Date: 13 September 2010

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Nanoductility induced crack nucleation mechanism mediated by a single dislocation core is revealed in a 300 million-atom molecular dynamics simulation of shocked silicon carbide ceramic. The atomistic damage mechanism involves dynamic transitions between clearly delineated regimes—from shock-induced structural transformation to plastic deformation to brittle fracture. Such atomistic understanding may help in the design of nanocrack suppression strategies to realize predictive modeling of complex damage processes in high-performance ceramics.
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81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
62.20.mt Cracks
62.20.fk Ductility, malleability
62.50.Ef Shock wave effects in solids and liquids

Subterahertz characterization of ethanol hydration layers by microfluidic system

S. Laurette, A. Treizebre, F. Affouard, and B. Bocquet

Appl. Phys. Lett. 97, 111904 (2010); http://dx.doi.org/10.1063/1.3488832 (3 pages) | Cited 6 times

Online Publication Date: 13 September 2010

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Characterizations of ethanol hydration layers are examined through subterahertz spectroscopy of water/ethanol mixtures by using a microfluidic system. A three-component model is used to explain measurements discrepancies with the Lambert–Beer law and to determine ethanol hydration shell absorption. Moreover, the hydration shell distribution is compared with molecular dynamics simulations with a good agreement. Ethanol hydration number is then computed and it can quickly characterize only the first water hydration layer or the whole hydration shell, depending on the chosen extraction model.
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47.85.Np Fluidics
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

The TiAl channel mechanism for enhanced (de)hydrogenation kinetics in Mg-based films

Shiqiang Hao

Appl. Phys. Lett. 97, 111905 (2010); http://dx.doi.org/10.1063/1.3489672 (3 pages) | Cited 4 times

Online Publication Date: 13 September 2010

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The transport properties of hydrogen in metal additives are very important for understanding the enhanced kinetic processes of (de)hydrogenation in metal hydrides. Based on the first-principles calculations, we found that the H2 dissociation rates on TiAl surfaces are very facile and the dissociated H diffusion in TiAl lattice is much faster than that in host material MgH2. We propose that the “catalytic” effect of additives Ti and Al is the H transport channel within the Mg and MgH2 host materials for the enhanced reaction kinetics.
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82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.43.Mn Adsorption kinetics
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
68.43.Bc Ab initio calculations of adsorbate structure and reactions
82.20.-w Chemical kinetics and dynamics

Evaporation temperature-tuned physical vapor deposition growth engineering of one-dimensional non-Fermi liquid tetrathiofulvalene tetracyanoquinodimethane thin films

I. Sarkar, M. Laux, J. Demokritova, A. Ruffing, S. Mathias, J. Wei, V. Solovyeva, M. Rudloff, S. S. Naghavi, C. Felser, M. Huth, and M. Aeschlimann

Appl. Phys. Lett. 97, 111906 (2010); http://dx.doi.org/10.1063/1.3489098 (3 pages) | Cited 3 times

Online Publication Date: 14 September 2010

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We describe the growth of high quality tetrathiofulvalene tetracyanoquinodimethane (TTF-TCNQ) organic charge-transfer thin films which show a clear non-Fermi liquid behavior. Temperature dependent angle resolved photoemission spectroscopy and electronic structure calculations show that the growth of TTF-TCNQ films is accompanied by the unfavorable presence of neutral TTF and TCNQ molecules. The quality of the films can be controlled by tuning the evaporation temperature of the precursor in physical vapor deposition method.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.A- Nucleation and growth
64.70.fm Thermodynamics studies of evaporation and condensation

Spectral analysis of resonance ultrasonic spectroscopy: Kramers–Kronig analysis, Fano profiles, and the case of precursor softening in SnTe:Cr

D. J. Safarik, E. K. H. Salje, and J. C. Lashley

Appl. Phys. Lett. 97, 111907 (2010); http://dx.doi.org/10.1063/1.3489376 (3 pages) | Cited 4 times

Online Publication Date: 14 September 2010

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The analysis of resonant ultrasound spectroscopy (RUS) spectra is exemplified by the study of elastic softening in single-crystal Sn0.995Cr0.005Te near the ferroelastic phase transition at T ≃ 100 K. Kramers–Kronig analysis of the resonance peaks shows that the elastic response is linear over the entire temperature range. In the paraelastic phase the Cole–Cole plots of the RUS spectra are circles with small gaps that are related to linear damping. In the ferroelastic phase strong coupling with domain boundary movement occurs, and results in distortion of the Cole–Cole circles. The RUS line profiles in the ferroelastic phase are well-described by the sum of a resonance term and a Fano spectrum with a Fano parameter of q = 0.46. The general equations and some simple approximations, which can conveniently be used to analyze RUS spectra, are summarized. We expect that this analysis is transportable to a large parameter space and can be applied to most RUS spectra for both ferroic and nonferroic materials.
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78.20.-e Optical properties of bulk materials and thin films
72.25.-b Spin polarized transport
79.60.-i Photoemission and photoelectron spectra

Two-dimensional electron gas in Zn-polar ZnMgO/ZnO heterostructure grown by metal-organic vapor phase epitaxy

J. D. Ye, S. Pannirselvam, S. T. Lim, J. F. Bi, X. W. Sun, G. Q. Lo, and K. L. Teo

Appl. Phys. Lett. 97, 111908 (2010); http://dx.doi.org/10.1063/1.3489101 (3 pages) | Cited 7 times

Online Publication Date: 15 September 2010

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We report the formation of two-dimensional electron gas (2DEG) at the Zn1−xMgxO/ZnO interface grown by metal-organic vapor phase epitaxy on sapphire substrates. The existence of the 2DEG is confirmed by the observation of Shubnikov–de Haas oscillations and the integer quantum Hall effect. In particular, the Zn0.8Mg0.2O/ZnO heterostructure shows a high Hall mobility of 2138 cm2/V s with a carrier sheet density of 3.51×1012 cm−2 at 1.4 K. We attribute the origin of 2DEG to be the donor states on ZnMgO surface. The dependence of carrier sheet density of 2DEG on ZnMgO layer thickness and Mg composition (x) are also investigated.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
61.72.uj III-V and II-VI semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.A- Nucleation and growth
72.20.My Galvanomagnetic and other magnetotransport effects
72.20.-i Conductivity phenomena in semiconductors and insulators
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Correlation of Mn charge state with the electrical resistivity of Mn doped indium tin oxide thin films

S. R. Sarath Kumar, Mohamed Nejib Hedhili, H. N. Alshareef, and S. Kasiviswanathan

Appl. Phys. Lett. 97, 111909 (2010); http://dx.doi.org/10.1063/1.3481800 (3 pages) | Cited 3 times

Online Publication Date: 15 September 2010

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Correlation of charge state of Mn with the increase in resistivity with Mn concentration is demonstrated in Mn-doped indium tin oxide films. Bonding analysis shows that Mn 2p3/2 core level can be deconvoluted into three components corresponding to Mn2+ and Mn4+ with binding energies 640.8 eV and 642.7 eV, respectively, and a Mn2+ satellite at ∼ 5.4 eV away from the Mn2+ peak. The presence of the satellite peak unambiguously proves that Mn exists in the +2 charge state. The ratio of concentration of Mn2+ to Mn4+ of ∼ 4:1 suggests that charge compensation occurs in the n-type films causing the resistivity increase.
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81.05.Hd Other semiconductors
73.61.Le Other inorganic semiconductors
71.15.Nc Total energy and cohesive energy calculations
61.50.Lt Crystal binding; cohesive energy

Energy band structure of the single crystalline MgO/n-Ge(001) heterojunction determined by x-ray photoelectron spectroscopy

Kun-Rok Jeon, Sang-Jun Lee, Chang-Yup Park, Hun-Sung Lee, and Sung-Chul Shin

Appl. Phys. Lett. 97, 111910 (2010); http://dx.doi.org/10.1063/1.3486116 (3 pages) | Cited 2 times

Online Publication Date: 16 September 2010

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We report the energy band structure of the single crystalline MgO/n-Ge(001) heterojunction characterized by x-ray photoelectron spectroscopy. The valence band offset of ΔEV = 3.64±0.07 eV with a 1.49±0.02 eV band bending was obtained. Given the experimental band gap of MgO (7.83 eV), a type-I band alignment with a conduction band offset of ΔEC = 3.52±0.07 eV is found. The band alignment of the MgO/n-Ge heterojunction including the large band bending was analyzed by a theoretical model taking into account the formation of the interface dipole.
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71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures
79.60.Bm Clean metal, semiconductor, and insulator surfaces
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Lattice site location of optical centers in GaN:Eu light emitting diode material grown by organometallic vapor phase epitaxy

K. Lorenz, E. Alves, I. S. Roqan, K. P. O’Donnell, A. Nishikawa, Y. Fujiwara, and M. Boćkowski

Appl. Phys. Lett. 97, 111911 (2010); http://dx.doi.org/10.1063/1.3489103 (3 pages) | Cited 6 times

Online Publication Date: 16 September 2010

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Eu-doped GaN was grown by organometallic vapor phase epitaxy at temperatures from 900 to 1100 °C. Eu incorporation is influenced by temperature with the highest concentration found for growth at 1000 °C. In all samples, Eu is incorporated entirely on substitutional Ga sites with a slight displacement which is highest ( ∼ 0.2 Å) in the sample grown at 900 °C and mainly directed along the c-axis. The major optical Eu3+ centers are identical for in situ doped and ion-implanted samples after high temperature and pressure annealing. The dominant Eu3+ luminescence lines are attributed to isolated, substitutional Eu.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.ag Semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
81.15.Kk Vapor phase epitaxy; growth from vapor phase

Observation of electron confinement in InP/GaAs type-II ultrathin quantum wells

S. D. Singh, V. K. Dixit, S. Porwal, Ravi Kumar, A. K. Srivastava, Tapas Ganguli, T. K. Sharma, and S. M. Oak

Appl. Phys. Lett. 97, 111912 (2010); http://dx.doi.org/10.1063/1.3486470 (3 pages) | Cited 6 times

Online Publication Date: 17 September 2010

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The issue of type-II band alignment for InP/GaAs heterostructure is addressed by means of simple layer architecture of ultrathin quantum wells (QWs). From specific signatures of the radiative recombination in type-II QWs especially the cube root dependence of blueshift in the lowest excitonic transition energy on excitation power in photoluminescence measurements indicates that the observed luminescence is originating from spatially separated electrons and holes. Such a blueshift is seen to increase with the QW thickness again confirming a type-II band alignment. A direct evidence of electron confinement in the conduction band of InP is provided by the capacitance voltage measurements.
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68.65.Fg Quantum wells
81.07.St Quantum wells
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
81.05.Ea III-V semiconductors
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