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9 Apr 2012

Volume 100, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 100, 153701 (2012); http://dx.doi.org/10.1063/1.3700446 (3 pages)

Hsiao-lu D. Lee, Steffen J. Sahl, Matthew D. Lew, and W. E. Moerner
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Implications of twinning kinetics on the frequency response in NiMnGa actuators

Eilon Faran and Doron Shilo

Appl. Phys. Lett. 100, 151901 (2012); http://dx.doi.org/10.1063/1.3702459 (4 pages) | Cited 6 times

Online Publication Date: 9 April 2012

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The explicit kinetic relation for twin wall motion in NiMnGa is used to correlate basic material properties to magneto-mechanical actuation rates in these crystals. In particular, we identify two parameters: the Peierls energy barrier and the twin wall mobility, which directly determine the dynamic response of NiMnGa actuators at frequencies above 10 Hz. Comparison between the kinetics of type I and type II twin walls reveals a correlation between the Peierls energy barrier and the commonly used twinning stress property. However, it is shown that twinning stress dictates twin wall dynamics only at very slow frequencies, typically below 1 Hz.
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82.20.Pm Rate constants, reaction cross sections, and activation energies

Room temperature deposition of alumina-doped zinc oxide on flexible substrates by direct pulsed laser recrystallization

Martin Y. Zhang, Qiong Nian, and Gary J. Cheng

Appl. Phys. Lett. 100, 151902 (2012); http://dx.doi.org/10.1063/1.3702460 (4 pages) | Cited 1 time

Online Publication Date: 9 April 2012

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In this study, a method combining room temperature pulsed laser deposition (PLD) and direct pulsed laser recrystallization (DPLR) is introduced to deposit transparent conductive oxide (TCO) layer on low melting point flexible substrates. Alumina-doped zinc oxide (AZO), as one of the most promising TCO candidates, has now been widely used in solar cells. However, to achieve optimal, electrical, and optical properties of AZO on low melting point, flexible substrate is challenging. DPLR technique is a scalable, economic, and fast process to remove crystal defects and generate recrystallization at room temperature. It features selective processing by only heating up the TCO thin film and preserve the underlying substrate at low temperature. In this study, AZO thin film is pre-deposited by PLD on flexible and rigid substrates. DPLR is then introduced to achieve a uniform TCO layer on these substrates, i.e., commercialized Kapton polyimide film, micron-thick Al-foil, and sold lime glass (SLG). Both finite element analysis simulation and designed experiments are carried out to demonstrate that DPLR is promising in manufacturing high quality AZO layers without any damage to the underlying flexible substrates. The hall mobility of AZO after DPLR on Kapton and SLG reached 198 cm2/v · s and 398 cm2/v · s respectively, while the carrier concentrations are reduced to 2.68 × 1018 and 4.3 × 1019/cm−2, respectively. These characteristics are exactly what an ideal TCO layer should carry: high conductivity and high transmission. The property changes are due to the reduction of defect density after DPLR.
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81.15.Fg Pulsed laser ablation deposition
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.Ga II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors

Atomic crystal structure of ordered In3Sb1Te2 ternary alloy studied by high-resolution transmission electron microscopy

Chung Soo Kim, Jeong Yong Lee, and Yong Tae Kim

Appl. Phys. Lett. 100, 151903 (2012); http://dx.doi.org/10.1063/1.3702575 (3 pages)

Online Publication Date: 10 April 2012

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The atomic structure of In3Sb1Te2 was investigated by high-resolution transmission electron microscopy (HRTEM) and the National Center for Electron Microscopy Simulation System. In3Sb1Te2 has a disordered NaCl structure; In atoms are positioned in a face-centered cubic lattice, and Sb and Te atoms are located at randomly occupied octahedral sites. However, the observed HRTEM images of the ordered In3Sb1Te2 phase show that Sb and Te atoms are located in specific positions, that is, at the center and edge of the unit cell, respectively. The atomic model of the ordered In3Sb1Te2 is confirmed by simulated images, which match the experimental HRTEM images.
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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)
68.55.ag Semiconductors
68.55.J- Morphology of films
81.07.Gf Nanowires

Anisotropic oxidation of bismuth nanostructures: Evidence for a thin film allotrope of bismuth

P. J. Kowalczyk, D. Belic, O. Mahapatra, S. A. Brown, E. S. Kadantsev, T. K. Woo, B. Ingham, and W. Kozlowski

Appl. Phys. Lett. 100, 151904 (2012); http://dx.doi.org/10.1063/1.3701166 (3 pages) | Cited 1 time

Online Publication Date: 10 April 2012

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We present evidence that ultra-thin Bi(110) nanostructures oxidise from the edges, and that their top surfaces remain unoxidised. Even after prolonged oxidation, clean (unoxidised) bismuth is present in nanostructures that are less than 5 monolayers thick. Since the (110) surface of bulk bismuth is known to be readily oxidised, this is strong evidence for a thin film allotrope of bismuth. We present a comparison with calculated structures and the structures of polymeric nitrogen, which suggests that the allotrope is one of several complex or hybrid paired-layer structures.
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81.65.Mq Oxidation
61.46.Hk Nanocrystals
68.35.bd Metals and alloys

Large optical polarization anisotropy due to anisotropic in-plane strain in m-plane GaInN quantum well structures grown on m-plane 6H-SiC

H. Jönen, H. Bremers, T. Langer, U. Rossow, and A. Hangleiter

Appl. Phys. Lett. 100, 151905 (2012); http://dx.doi.org/10.1063/1.3702786 (4 pages)

Online Publication Date: 11 April 2012

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We investigated the optical polarization anisotropy of m-plane GaInN/GaN quantum well structures on m-plane SiC and bulk GaN substrates. On bulk GaN, the degree of polarization increases with increasing indium content according to the larger strain-induced separation of the topmost valence bands. On m-plane SiC, however, we observe constantly large polarization ratios of around 90% and more. From an x-ray strain state analysis and calculations of the valence band energies, we find that an anisotropic strain of the GaN buffer layer leads to a very strong separation of the topmost valence bands resulting in a large degree of polarization.
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78.66.Fd III-V semiconductors
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds
68.65.Fg Quantum wells

High Eu 4f low-energy oscillator strength in the isostructural rare-earth Zintl compounds EuIn2X2 (X = P,As)

N. Singh and U. Schwingenschlögl

Appl. Phys. Lett. 100, 151906 (2012); http://dx.doi.org/10.1063/1.3702787 (5 pages) | Cited 3 times

Online Publication Date: 11 April 2012

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The isostructral Zintl compounds EuIn2X2 (X = P,As) are investigated within density functional theory. We employ the local spin density approximation with onsite interaction (LSDA + U) for varying U from 0 eV to 7 eV to model the Coulomb repulsion of the Eu 4f electrons. The LSDA + U optical conductivity disagrees with the experimental spectrum, while the simple LSDA is successful. Contrary to the expectation, it is found that EuIn2X2 (X = P,As) has a large oscillator strength for the f → d transitions in the low-energy range (below 1.5 eV) in which effects of the joint density of states play a key role. The materials show a sizeable magneto-optical Kerr effect.
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73.20.At Surface states, band structure, electron density of states
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.20.Ls Magneto-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Ps Other inorganic compounds

Free-suspended graphene synthesis via carbon diffusion through platinum-based metal

Aziz Zenasni, Alexandru Delamoreanu, and Caroline Rabot

Appl. Phys. Lett. 100, 151907 (2012); http://dx.doi.org/10.1063/1.3702808 (3 pages) | Cited 1 time

Online Publication Date: 11 April 2012

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Some advances in chemical vapor deposition process have provided noteworthy results toward the growth of large scale graphene. However, in contact with a neighboring material, graphene performances are usually reduced. Decoupling graphene from the substrate by suspension or intercalation is foreseen to recover its intrinsic properties. This work reports an original way for graphene suspension which occurs during its growth on platinum metal. This suspension arises above platinum silicide clusters which form during the annealing and induce the metal dewetting. The stretched graphene is highly corrugated because the clusterization of silicides structures induces additional stress.
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81.05.ue Graphene
61.48.Gh Structure of graphene
82.70.Kj Emulsions and suspensions
81.40.Gh Other heat and thermomechanical treatments

Stark shifts and exciton dissociation in CdSe nanoparticle grafted conjugated polymer

Mohan Singh Mehata

Appl. Phys. Lett. 100, 151908 (2012); http://dx.doi.org/10.1063/1.3701719 (4 pages)

Online Publication Date: 11 April 2012

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Electroabsorption (E-A) and electrophotoluminescence (E-PL) responses of polymer films of CdSe quantum dots (QDs) incorporated sulfide-substituted poly(1,4-phenylene vinylene) derivative CdSe-S3PPV were measured. The observed Stark shift both in E-A and E-PL responses is likely to be caused by a substantial contribution of change in molecular polarizability (Δmath) and change in electric dipole moment (|Δμ|) following photoexcitation. Together with Stark shift, field-induced photoluminescence (PL) quenching and enhancement were observed depending on excitation energy. The quenching of PL of CdSe-S3PPV film is interpreted in terms of an exciton model-a breaking of electron-hole pairs in the presence of electric field.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.55.-a Thin film structure and morphology
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.60.Fi Electroluminescence

Temperature-dependent preferential formation of quantum structures upon the droplet epitaxy

Y. Y. Cao and G. W. Yang

Appl. Phys. Lett. 100, 151909 (2012); http://dx.doi.org/10.1063/1.3702813 (4 pages) | Cited 3 times

Online Publication Date: 12 April 2012

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A theoretical model has been established to pursue the stability of quantum rings (QRs) and quantum dots (QDs) with respect to thermal effects in the droplet epitaxy. Adding thermal fluctuations to the energetic model within the statistical mechanics frame, we found that a critical temperature provides a means to separate regimes of preferential QR and QD formation. Thermal fluctuations play a crucial role in the temperature-dependent shape evolution. These theoretical results are in good agreement with experiments, which implied that the developed theory can be used to control ring or dot formation in droplet epitaxy.
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81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.ag Semiconductors
81.07.Ta Quantum dots
05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion

Coherent acoustic wave oscillations and melting on Ag(111) surface by time resolved x-ray diffraction

Ali Oguz Er, Jie Chen, Jau Tang, and Peter M. Rentzepis

Appl. Phys. Lett. 100, 151910 (2012); http://dx.doi.org/10.1063/1.3703122 (5 pages) | Cited 2 times

Online Publication Date: 12 April 2012

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The transient structural disorder on the Ag(111) crystal after excitation with fs pulses was studied by means of time resolved x-ray diffraction. The lattice disorder after UV irradiation is detected by changes in the XRD rocking curve including peak shift, broadening, and total diffraction intensity. We have observed blast and pressure wave formation and melting and mosaic crystal formation during re-crystallization. A blast force was formed within 2 ps after fs UV irradiation of the crystal, followed lattice contraction, melting phase transition, and mosaic crystal formation as the temperature decreases below melting. The experimental data are also supported by theoretical simulations.
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68.35.Iv Acoustical properties
78.66.Bz Metals and metallic alloys
62.50.Ef Shock wave effects in solids and liquids
64.70.dg Crystallization of specific substances
64.70.dj Melting of specific substances

The anharmonic vibration of Li in lithium amide

B. Paik, T. Hasegawa, I. Ishii, A. Michigoe, T. Suzuki, M. Udagawa, N. Ogita, T. Ichikawa, and Y. Kojima

Appl. Phys. Lett. 100, 151911 (2012); http://dx.doi.org/10.1063/1.3703586 (4 pages) | Cited 1 time

Online Publication Date: 12 April 2012

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A large amplitude rattling-type anharmonic vibration of Li is possible without guest-host type structure, as we report here for tetragonal LiNH2 crystal. The low temperature (0.4–300 K) specific heat capacity and Raman spectroscopy support the phonon model of site-specific Li activities governed by the symmetry of the potential energy distribution around the Li atoms in LiNH2, which yields the anharmonic Li3 vibration (optical) in one direction (either X or Y axis of the crystal), while the Li1 and Li2 atoms remain silent. Our finding may help to correlate ionic conductivity, thermal, and hydrogenation properties of LiNH2.
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78.30.Er Solid metals and alloys
65.40.Ba Heat capacity
66.30.H- Self-diffusion and ionic conduction in nonmetals
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
82.30.-b Specific chemical reactions; reaction mechanisms
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Nucleation of metals by strong electric fields

M. Nardone and V. G. Karpov

Appl. Phys. Lett. 100, 151912 (2012); http://dx.doi.org/10.1063/1.3703611 (4 pages) | Cited 4 times

Online Publication Date: 13 April 2012

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Recent work on phase transitions in chalcogenides (underlying phase change memory) led to a theory of symmetry-breaking field effects, predicting needle-shaped metallic nuclei and exponentially accelerated nucleation rates. Here, we predict that, in general, any insulator will eventually form metallic inclusions if immersed in a sufficient electric field. These phase transitions are driven, not simply enhanced, by an electric field. Hence, metals can be formed under conditions where they would be otherwise unexpected. This opens the venue of field induced materials synthesis. As a technologically important example, we consider the field driven synthesis of metallic hydrogen at normal pressure.
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64.60.qj Studies of nucleation in specific substances
64.60.qe General theory and computer simulations of nucleation
82.60.Nh Thermodynamics of nucleation

Nonreciprocal optical Bloch-Zener oscillations in ternary parity-time-symmetric waveguide lattices

Shulin Ding and Guo Ping Wang

Appl. Phys. Lett. 100, 151913 (2012); http://dx.doi.org/10.1063/1.4703937 (4 pages) | Cited 1 time

Online Publication Date: 13 April 2012

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We demonstrate a kind of ternary parity-time (PT)-symmetric complex waveguide arrays to observe nonreciprocal optical Bloch-Zener oscillations (OBZOs) at the PT thresholds. The waveguide arrays are periodically constructed with a unit of a dielectric waveguide sandwiched by a loss and a gain waveguides. The nonreciprocal optical Bloch-Zener oscillations are attributed to the unidirectional Bragg scattering behaviors of light in the systems, which can be controlled by the propagation constant mismatch between dielectric waveguides and loss or gain waveguides through independently tuning the propagation constants of the dielectric waveguides of the units.
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42.79.Gn Optical waveguides and couplers
42.50.Wk Mechanical effects of light on material media, microstructures and particles
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