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2 Apr 2012

Volume 100, Issue 14, Articles (14xxxx)

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Appl. Phys. Lett. 100, 144101 (2012); http://dx.doi.org/10.1063/1.3697983 (4 pages)

H. Xu (徐涵), Wei Yu (余玮), M. Y. Yu (郁明阳), A. Y. Wong (黄燿煇), Z. M. Sheng (盛政明), M. Murakami (村上匡且), and J. Zhang (张杰)
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Design of ductile bulk metallic glasses by adding “soft” atoms

N. Zheng, R. T. Qu, S. Pauly, M. Calin, T. Gemming, Z. F. Zhang, and J. Eckert

Appl. Phys. Lett. 100, 141901 (2012); http://dx.doi.org/10.1063/1.3700721 (4 pages) | Cited 6 times

Online Publication Date: 2 April 2012

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We propose a strategy for the design of ductile bulk metallic glasses (BMGs) through minor substitution using relatively large atoms, which make the bonding nature become more metallic and with it less shear resistant. Such a locally modified structure results in topological heterogeneity, which appears to be crucial for achieving enhanced plasticity. This strategy is verified for Ti-Zr-Cu-Pd glassy alloys, in which Cu was replaced by In, and seems to be extendable to other BMG systems. The atomic-scale heterogeneity in BMGs is somewhat analog to defects in crystalline alloys and helps to improve the overall plasticity of BMGs.
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81.05.Kf Glasses (including metallic glasses)
61.72.-y Defects and impurities in crystals; microstructure
81.20.-n Methods of materials synthesis and materials processing
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Surface morphological stabilization of stressed crystalline solids by simultaneous action of applied electric and thermal fields

Dwaipayan Dasgupta, Georgios I. Sfyris, M. Rauf Gungor, and Dimitrios Maroudas

Appl. Phys. Lett. 100, 141902 (2012); http://dx.doi.org/10.1063/1.3698360 (4 pages)

Online Publication Date: 2 April 2012

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We examine the surface morphological stability of electrically and thermally conducting crystalline elastic solids in uniaxial tension under the simultaneous action of an electric field and a temperature gradient. We use linear stability analysis of a surface mass transport model that accounts for surface electromigration and thermomigration induced by the applied fields and for surface diffusional anisotropy. We find that a properly oriented applied thermal gradient can reduce the critical electric-field strength requirement for stabilization of the planar surface morphology. The temperature dependence of the solid material’s properties does not affect the critical strength requirement of the applied fields.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
66.30.Qa Electromigration
68.35.Fx Diffusion; interface formation
73.25.+i Surface conductivity and carrier phenomena
62.20.D- Elasticity
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Origin of size-dependent photoluminescence decay dynamics in colloidal γ-Ga2O3 nanocrystals

Manu Hegde, Ting Wang, Zoran L. Miskovic, and Pavle V. Radovanovic

Appl. Phys. Lett. 100, 141903 (2012); http://dx.doi.org/10.1063/1.3698390 (5 pages) | Cited 2 times

Online Publication Date: 2 April 2012

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We studied size-dependent dynamics of defect-based photoluminescence of colloidal γ-Ga2O3 nanocrystals in the framework of the donor-acceptor pair model. Two theoretical models were developed based on relative positioning of donor and acceptor sites: (1) for random distribution of defects throughout the nanocrystal volume and (2) for surface segregation of defects. The results of the modeling indicate that defect sites are predominantly located in the vicinity of nanocrystal surfaces and that the density of defects increases with decreasing nanocrystal size. The donor Bohr radius obtained as a fitting parameter suggests an increase in the donor binding energy with decreasing nanocrystal size.
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78.55.Hx Other solid inorganic materials
82.70.Dd Colloids
61.72.jd Vacancies
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.35.Dv Composition, segregation; defects and impurities
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Notable internal thermal effect on the yielding of metallic glasses

W. D. Liu and K. X. Liu

Appl. Phys. Lett. 100, 141904 (2012); http://dx.doi.org/10.1063/1.3700923 (4 pages) | Cited 1 time

Online Publication Date: 3 April 2012

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We revealed a notable internal thermal effect on the yielding of metallic glasses with the aid of a newly developed microscopic model focusing on the interaction of incipient localized shear events. It is shown that at the high strain rate, localized heating in metallic glasses instead of localized structure change plays the dominant role in shear softening. Using the modified cooperative shear model with the ingredient of the thermal effect, we captured the sudden decrease of the strength of metallic glasses after a critical strain rate, which was found in experiments.
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81.40.Lm Deformation, plasticity, and creep
61.43.Fs Glasses
63.20.Pw Localized modes
62.20.F- Deformation and plasticity

Above-room-temperature photoluminescence from a strain-compensated Ge/Si0.15Ge0.85 multiple-quantum-well structure

P. H. Wu, D. Dumcenco, Y. S. Huang, H. P. Hsu, C. H. Lai, T. Y. Lin, D. Chrastina, G. Isella, E. Gatti, and K. K. Tiong

Appl. Phys. Lett. 100, 141905 (2012); http://dx.doi.org/10.1063/1.3700804 (3 pages) | Cited 7 times

Online Publication Date: 4 April 2012

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Photoluminescence (PL) of a strain-compensated Ge/Si0.15Ge0.85 multiple-quantum-well (MQW) structure was studied above room temperature, in the range of 300–440 K. Both direct and indirect radiative recombination PL features were observed. The relative intensity of direct to indirect recombination markedly increases with the increase of temperature. The enhancement of PL from direct recombination above RT has been attributed to the thermal excitation of carriers from L-type to Γ-type confined states. This extends the potential applicability of Ge/SiGe MQW as light emitters on a Si-based platform and is favorable for applications in metal-oxide-semiconductor integrated circuits which normally operate above RT.
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78.55.Ap Elemental semiconductors
78.67.De Quantum wells

Nano-precipitates made of atomic pillars revealed by single atom detection in a Mg-Nd alloy

W. Lefebvre, V. Kopp, and C. Pareige

Appl. Phys. Lett. 100, 141906 (2012); http://dx.doi.org/10.1063/1.3701272 (5 pages)

Online Publication Date: 5 April 2012

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We report on the atomic architecture of metastable precipitates in a model Mg-0.5 at. %Nd system. High resolution Z-contrast observations in scanning transmission electron microscopy demonstrate that a common elementary structure, made of Nd atomic pillars, is shared by precipitates involved in the early decomposition of the system. A combination of Z-contrast projections has been used to establish the accurate location of Nd atoms in the atomic pillars, therefore allowing the determination of structure and composition of precipitates. Other precipitates compositions are extrapolated by means of a quantitative analysis.
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81.16.-c Methods of micro- and nanofabrication and processing
61.46.-w Structure of nanoscale materials
81.30.Mh Solid-phase precipitation

Probing the electrode-polymer interface in conjugated polymer devices with surface-enhanced Raman scattering

Dongbo Li, Nicholas J. Borys, and John M. Lupton

Appl. Phys. Lett. 100, 141907 (2012); http://dx.doi.org/10.1063/1.3701278 (4 pages) | Cited 1 time

Online Publication Date: 6 April 2012

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A crucial consideration in organic devices is the role of the interface between a metal electrode and the active polymer material. Here, we use the conjugated polymer poly[2-methoxy-5-(2-ethylhexyl-oxy)-1,4-phenylene-vinylene] (MEH-PPV) with model gold and silver electrodes to perform surface-enhanced Raman scattering (SERS) on the metal-MEH-PPV interface. We observe significant differences between the SERS spectra on the two metals, which we assign to conformational changes of the phenyl rings within the polymer. The difference between gold and silver interfaces can be removed upon thermal annealing, suggesting structural relaxation. Resonance Raman spectra of the two interfaces are identical, implying that the overall conformation of the polymer backbone which supports the pi-electron transition remains unaffected by the different metals. SERS is uniquely sensitive to the interfacial metal/organic layer and provides an important in situ tool to optimizing organic device structures.
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85.60.Jb Light-emitting devices

Structural and optical characterization of SixGe1−x−ySny alloys grown by molecular beam epitaxy

Hai Lin, Robert Chen, Weisheng Lu, Yijie Huo, Theodore I. Kamins, and James S. Harris

Appl. Phys. Lett. 100, 141908 (2012); http://dx.doi.org/10.1063/1.3701732 (4 pages) | Cited 1 time

Online Publication Date: 6 April 2012

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SixGe1−x−ySny alloys were grown by molecular beam epitaxy at low temperature, followed by ex-situ annealing. The crystal quality of SixGe1−x−ySny layers was characterized by atomic force microscopy and transmission electron microscopy. The compositions and lattice constants of the alloys were studied by x-ray photoelectron spectroscopy and x-ray diffraction. The results show that Vegard’s law is a good approximation for SixGe1−x−ySny alloys. Photoreflectance spectroscopy at room temperature was used to determine the direct bandgap energy of SixGe1−x−ySny layers. Analyzing the relationship between composition and direct bandgap energy reveals a negative energy bowing parameter for SiSn.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.10.Bk Growth from vapor
81.40.Gh Other heat and thermomechanical treatments
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.66.Dk Alloys
71.20.Gj Other metals and alloys
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