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5 Apr 2010

Volume 96, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 96, 143103 (2010); http://dx.doi.org/10.1063/1.3378684 (3 pages)

Joshua A. Kellar, Justice M. P. Alaboson, Qing Hua Wang, and Mark C. Hersam
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On the effect of impurities in metallic glass formation

J. S. Yu, Y. Q. Zeng, T. Fujita, T. Hashizume, A. Inoue, T. Sakurai, and M. W. Chen

Appl. Phys. Lett. 96, 141901 (2010); http://dx.doi.org/10.1063/1.3373528 (3 pages) | Cited 1 time

Online Publication Date: 5 April 2010

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We report atomic-scale characterization of impurity elements in a Pd40Ni40P20 metallic glass by state-of-the-art atom probe tomography combining with transmission electron microscopy. The significant partitioning of the impurities in heterogeneous nanocrystals of the primarily crystallized glass provides compelling evidence that minor impurities dramatically influence the stability of supercooled liquids by manipulating heterogeneous crystallization of metallic glasses.
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64.70.pe Metallic glasses
64.70.Nd Structural transitions in nanoscale materials
61.43.Fs Glasses
64.70.kj Glasses

Dielectrophoresis of Janus particles under high frequency ac-electric fields

Lu Zhang and Yingxi Zhu

Appl. Phys. Lett. 96, 141902 (2010); http://dx.doi.org/10.1063/1.3378687 (3 pages) | Cited 13 times

Online Publication Date: 5 April 2010

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Janus polystyrene particles with gold and dielectric multilayer coatings on one hemisphere are shown to drastically alter the dielectrophoresis (DEP) behavior of homogeneous precursor particles under ac-electric fields. Alkanethiol coatings on the gold-coated hemisphere can effectively modify the DEP crossover frequency (ωc) with a negative (n) to positive (p) (p→n) DEP transition as increasing ac-frequency, in contrast to p→n DEP transition observed with precursor particles. All measured n→p DEP crossover frequencies with dependence on particle size, alkanethiol thickness, and medium conductivity are collapsed to yield a scaling with the resistance-capacitance (RC) time of the alkanethiol layer capacitance and the conductive medium resistance.
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82.45.-h Electrochemistry and electrophoresis
82.45.Mp Thin layers, films, monolayers, membranes
77.55.-g Dielectric thin films

Effect of doping on the mid-infrared intersubband absorption in GaN/AlGaN superlattices grown on Si(111) templates

P. K. Kandaswamy, H. Machhadani, Y. Kotsar, S. Sakr, A. Das, M. Tchernycheva, L. Rapenne, E. Sarigiannidou, F. H. Julien, and E. Monroy

Appl. Phys. Lett. 96, 141903 (2010); http://dx.doi.org/10.1063/1.3379300 (3 pages)

Online Publication Date: 6 April 2010

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We report on the effect of Si doping on the mid-infrared intersubband absorption in GaN/AlGaN superlattices. For increasing doping levels, interband luminescence displays a blueshift and a broadening of the band edge caused by the screening of the internal electric field and band-filling effects. The intersubband absorption energy is mainly governed by many-body effects like exchange interaction and depolarization shift, which increase the e1–e2 subband separation. The ISB blueshift induced by many-body effects can be more than 50% of the e1–e2 transition energy.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors

Anelastic anomalies and negative Poisson’s ratio in tetragonal BaTiO3 ceramics

Liang Dong, Donald S. Stone, and Roderic S. Lakes

Appl. Phys. Lett. 96, 141904 (2010); http://dx.doi.org/10.1063/1.3384996 (3 pages) | Cited 3 times

Online Publication Date: 6 April 2010

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Anelastic anomalies (sharp variations in modulus and damping with temperature) were observed in tetragonal BaTiO3 via broadband viscoelastic spectroscopy after aging at 50 °C for 15 h. The effect was most pronounced under electrical short circuit condition, at low frequency and under small excitation strain (10−6). Softening in bulk modulus and negative Poisson’s ratio were observed near 60 °C. Effects are attributed to an oxygen vacancy mechanism. A relaxational model cannot account for sharp response at smaller strains. Heterogeneity of negative stiffness is considered as a cause.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
61.72.jd Vacancies
62.20.dj Poisson's ratio
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Correlation of oxygen vacancy concentration and thermoelectric properties in Na0.73CoO2−δ

P. H. Tsai, T. Norby, T. T. Tan, R. Donelson, Z. D. Chen, and S. Li

Appl. Phys. Lett. 96, 141905 (2010); http://dx.doi.org/10.1063/1.3385264 (3 pages) | Cited 4 times

Online Publication Date: 6 April 2010

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In this work, oxygen vacancies were precisely controlled by manipulating oxygen partial pressure and the oxygen partial pressure dependence of thermoelectric properties of polycrystalline Na0.73CoO2−δ was investigated. The results suggest that resistivity and thermopower augment simultaneously with increasing concentration of oxygen vacancies δ due to the recombination of electrons and holes and average Co valence state. The total thermal conductivity can be reduced by minimizing δ. The dimensionless figure of merit was strongly affected by δ at lower operating temperature. The experimental results provide guideline for the variation in performance of this material system under different processing and operating environments.
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61.72.jd Vacancies
72.20.Pa Thermoelectric and thermomagnetic effects
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.80.Sk Insulators

Residual strain in thermally annealed periodic mesoporous silica revealed by x-ray scattering

G. Chen and C. Wan

Appl. Phys. Lett. 96, 141906 (2010); http://dx.doi.org/10.1063/1.3380663 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2010

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We have applied x-ray scattering to characterize residual strain in nanostructured glasses. The first sharp diffraction peak (FSDP) and the nanostructures of periodic mesoporous silica were investigated as a function of annealing temperature. It is found that position and width of the FSDP exhibit different temperature dependencies, which correspond to two types of residual strain caused by defects and constrained nanostructures, respectively. The latter appear to be inherent to the periodic mesoporous material as confirmed by the small-angle x-ray scattering analysis. Our study has implications for the structural properties of periodic mesoporous materials.
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78.70.Ck X-ray scattering
61.43.Gt Powders, porous materials
61.43.Fs Glasses
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
81.16.-c Methods of micro- and nanofabrication and processing

Establishing the mechanism of thermally induced degradation of ZnO:Al electrical properties using synchrotron radiation

M. Vinnichenko, R. Gago, S. Cornelius, N. Shevchenko, A. Rogozin, A. Kolitsch, F. Munnik, and W. Möller

Appl. Phys. Lett. 96, 141907 (2010); http://dx.doi.org/10.1063/1.3385024 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2010

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X-ray absorption near edge structure and x-ray diffraction studies with synchrotron radiation have been used to relate the electrical properties of ZnO:Al films to their bonding structure and phase composition. It is found that Al-sites in an insulating metastable homologous (ZnO)3Al2O3 phase are favored above a certain substrate temperature (TS) leading to deterioration of both the crystallinity and the electrical properties of the films. The higher film resistivity is associated with lower carrier mobility due to increased free electron scattering. Lower metal to oxygen flux ratios during deposition expand the range of TS at which low-resistivity films are obtained.
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73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
73.50.Dn Low-field transport and mobility; piezoresistance
78.70.Dm X-ray absorption spectra
81.15.Cd Deposition by sputtering
68.55.ag Semiconductors

Influence of Sn Migration on phase transition in GeTe and Ge2Se3 thin films

Archana Devasia, Santosh Kurinec, Kristy A. Campbell, and Simone Raoux

Appl. Phys. Lett. 96, 141908 (2010); http://dx.doi.org/10.1063/1.3385781 (3 pages) | Cited 4 times

Online Publication Date: 9 April 2010

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Phase transitions in GeTe/SnSe and Ge2Se3/SnTe are investigated using time resolved x-ray diffraction. GeTe exhibits a structural transition from rhombohedral to the cubic phase at 300 °C, which is ∼ 100 °C lower than that of pure GeTe. This is facilitated by incorporation of Sn from SnSe. Sn migration is observed explicitly in Ge2Se3/SnTe by separation of SnSe phase. Amorphous Ge2Se3 is also found to crystallize at a lower temperature of 300 °C resulting in orthorhombic GeSe and monoclinic GeSe2. Thus, inclusion of a Sn containing layer may offer a means to tailor phase transition in Ge-chalcogenide thin films for phase change memory applications.
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64.70.kd Metals and alloys
68.55.aj Insulators

Gigantic uphill diffusion during self-assembled growth of Ge quantum dots on strained SiGe sublayers

M. Ya. Valakh, P. M. Lytvyn, A. S. Nikolenko, V. V. Strelchuk, Z. F. Krasilnik, D. N. Lobanov, and A. V. Novikov

Appl. Phys. Lett. 96, 141909 (2010); http://dx.doi.org/10.1063/1.3383241 (3 pages) | Cited 1 time

Online Publication Date: 9 April 2010

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Raman spectroscopy and atomic-force microscopy were applied to study the morphology of nanoislands grown on strained Si1−xGex sublayers. It was shown that the growth of nanoislands on strained Si1−xGex sublayer not only induces the effect of their spatial ordering but also enhances the role of interdiffusion processes. Unusual high island volume increase during the epitaxy is explained by anomalous strong material diffusion from the sublayer into the islands, induced by nonuniform field of elastic strains.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
66.30.Pa Diffusion in nanoscale solids
81.07.Ta Quantum dots

Austenite–martensite interface in shape memory alloys

C. H. Lei, L. J. Li, Y. C. Shu, and J. Y. Li

Appl. Phys. Lett. 96, 141910 (2010); http://dx.doi.org/10.1063/1.3385278 (3 pages) | Cited 5 times

Online Publication Date: 9 April 2010

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A two-scale phase field simulation is developed for austenite–martensite interface to understand the effects of crystalline symmetry and geometric compatibilities on the reversibility of structural phase transformations in shape memory alloys. It is observed that when the middle eigenvalue of martensite transformation strain is equal to zero, an exact austenite–martensite interface is formed with negligible elastic energy. On the other hand, when the middle eigenvalue is different from 0, an inexact interface between austenite and martensitic twin is formed, and the corresponding elastic energy increases with the increased magnitude of the middle eigenvalue, resulting in substantially higher energy barrier for austenite–martensite transformation, and thus higher thermal hysteresis in shape memory alloys.
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64.70.K- Solid-solid transitions
62.20.fg Shape-memory effect; yield stress; superelasticity
81.30.Kf Martensitic transformations
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
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