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14 May 2012

Volume 100, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 100, 203104 (2012); http://dx.doi.org/10.1063/1.3701731 (4 pages)

Z. Y. Jiang, X. X. Jiang, S. Su, X. P. Wei, S. T. Lee, and Y. He
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On the characteristic length scales associated with plastic deformation in metallic glasses

P. Murali, Y. W. Zhang, and H. J. Gao

Appl. Phys. Lett. 100, 201901 (2012); http://dx.doi.org/10.1063/1.4717744 (4 pages) | Cited 2 times

Online Publication Date: 14 May 2012

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Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale ℓc that governs Poisson’s ratio ν, shear band thickness tSB, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest ℓc, thinnest tSB, lowest ν, and brittle fracture; CuZr exhibits largest ℓc, thickest tSB, highest ν, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest ℓc as a fundamental measure of the shear transformation zone size in metallic glasses.
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81.05.Kf Glasses (including metallic glasses)
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.fq Plasticity and superplasticity
81.05.Bx Metals, semimetals, and alloys

Ring-shaped NdFeB-based magnetic tweezers enables oscillatory microrheology measurements

Jun Lin and Megan T. Valentine

Appl. Phys. Lett. 100, 201902 (2012); http://dx.doi.org/10.1063/1.4717988 (4 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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We present the design and characterization of a magnetic tweezers device that employs a ring-shaped neodymium iron boron (NdFeB) magnet. Because the gradient of the magnetic field generated by ring magnets changes sign along its symmetry axis, magnetic tweezers devices that employ ring magnets can both push and pull on microscale magnetic beads, opening new avenues for the micromanipulation of soft materials. We demonstrate the application of such a device to oscillatory microrheology measurements of soft networks of microtubules, an essential cellular biopolymer.
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85.70.Ay Magnetic device characterization, design, and modeling
87.17.-d Cell processes

Nonlinear size-dependent melting of the silica-encapsulated silver nanoparticles

Chengying Tang (唐成颖), Yun-Mo Sung, and Joonho Lee

Appl. Phys. Lett. 100, 201903 (2012); http://dx.doi.org/10.1063/1.4712599 (3 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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In spite of the recent report of the in situ high-resolution transmission electron microscopy observation of the melting of Ag nanoparticles (NPs) in Chen et al. [Appl. Phys. Lett. 96, 253104 (2010)], no consistent experimental investigation coupled with theoretical analysis has been reported so far. We report the size-dependence of the melting temperature (Tm) of Ag NPs by both differential scanning calorimetry experiments and thermodynamic assessments. Thermodynamically calculated Tm for the Ag NPs showed a nonlinear function with respect to the inverse of the particle size and agreed well with the present and reported experimental results within an error of 1 K.
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64.70.Nd Structural transitions in nanoscale materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Optical and acoustic phonon modes in strained InGaAs/GaAs rolled up tubes

T. Angelova, N. Shtinkov, Ts. Ivanov, V. Donchev, A. Cantarero, Ch. Deneke, O. G. Schmidt, and A. Cros

Appl. Phys. Lett. 100, 201904 (2012); http://dx.doi.org/10.1063/1.4714542 (4 pages) | Cited 1 time

Online Publication Date: 14 May 2012

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Rolled-up semiconductor tubes of various diameters made of alternating In0.215Ga0.785As/GaAs layers have been investigated by means of Raman scattering. The optical and acoustic phonon modes of individual tubes have been studied and compared with the characteristics of the surrounding material. After tube formation, the frequency of the phonon modes shifts with respect to the as-grown material and disorder activated modes are observed. The frequency shifts are related to the residual strain in the tubes through the deformation potential approximation. Good agreement with atomistic valence force field simulations and x-ray micro-diffraction measurements is found. By comparison with x-ray data, a Raman strain constant K = 0.65 is proposed for In0.215Ga0.785As. In the low frequency range, acoustic mode doublets are observed on the tubes that are absent in the surrounding material. They show clear evidence of the formation of periodic superlattices after the rolling-up process, and give insight into the quality of their interfaces.
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78.66.Fd III-V semiconductors
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
68.65.Cd Superlattices
78.30.-j Infrared and Raman spectra
78.30.Fs III-V and II-VI semiconductors

Magnitude-tunable sub-THz shear phonons in a non-polar GaN multiple-quantum-well p-i-n diode

Chien-Cheng Chen, Huei-Min Huang, Tien-Chang Lu, Hao-Chung Kuo, and Chi-Kuang Sun

Appl. Phys. Lett. 100, 201905 (2012); http://dx.doi.org/10.1063/1.4718524 (4 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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Coherent transverse acoustic phonons are optically generated and detected through the piezoelectric coupling between the build-in electric fields and shear strains of a non-polar GaN multiple quantum wells embedded in a p-n junction. By optical transient transmission change measurement, the phonon frequency is observed to be 0.4 THz which corresponds to a wavelength of 12.5 nm, the periodicity of the multiple quantum wells, and the estimated phonon velocity corresponds to the transverse acoustic phonon velocity in GaN. Moreover, we can magnify the driving amplitude of the generated shear phonons by increasing the reverse bias of the p-i-n diode.
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85.30.Kk Junction diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Anomalous phase change characteristics in Fe-Te materials

X. T. Fu, W. D. Song, H. W. Ho, R. Ji, L. Wang, and M. H. Hong

Appl. Phys. Lett. 100, 201906 (2012); http://dx.doi.org/10.1063/1.4719074 (4 pages) | Cited 1 time

Online Publication Date: 16 May 2012

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Phase change materials have become significantly attractive due to its unique characteristics for its extensive applications. In this paper, a kind of phase change material, which consists of Fe and Te components, is developed. The crystallization temperature of the Fe-Te materials is 180 °C for Fe1.19Te and can be adjusted by the Fe/Te ratio. High-speed phase change in the Fe-Te materials has been demonstrated by nanosecond laser irradiation. Comparing to conventional phase change materials, the Fe-Te materials exhibit an anomalous optical property that has higher reflectivity at amorphous than crystalline state, which is useful for data storage design.
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61.43.-j Disordered solids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.40.Kc Metals, semimetals, and alloys

Nano-sized Ba2NaNb5O15–NaNbO3 co-crystallized glass-ceramics in phosphoniobate system

Yoshihiro Takahashi, Nobuhiro Fujie, and Takumi Fujiwara

Appl. Phys. Lett. 100, 201907 (2012); http://dx.doi.org/10.1063/1.4719034 (4 pages) | Cited 2 times

Online Publication Date: 17 May 2012

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Glass-ceramics (GC) consisting of nano-sized Nb-dielectrics were fabricated in BaO–Na2O–P2O5–Nb2O5 system, and their crystallization and physical features were studied. Precursor of 0.67(2BaO–0.5Na2O)–1P2O5–2.5Nb2O5 glass co-crystallized Ba2NaNb5O15 (BNN) and NaNbO3 phases, which are about 10 nm in size, and resulting GC possessed an optical transparency comparable to the precursor glass, and optical band-gap of the GC was close to that of BNN. It is suggested that the fabricated GC is not merely a GC with transparency but Nb-dielectric GC, in which light scattering due to the crystallized phases evolution is minimized, i.e., practically transparent GC material.
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81.07.Bc Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Carbon nanotube fibers as torsion sensors

A. S. Wu, X. Nie, M. C. Hudspeth, W. W. Chen, T.-W. Chou, D. S. Lashmore, M. W. Schauer, E. Towle, and J. Rioux

Appl. Phys. Lett. 100, 201908 (2012); http://dx.doi.org/10.1063/1.4719058 (4 pages) | Cited 1 time

Online Publication Date: 17 May 2012

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Carbon nanotube fibers possess the ability to respond electrically to tensile loading. This research explores their electrical response to torsional loading; results demonstrate that applied twist compacts the fiber, resulting in increased electrical contact between carbon nanotubes. Shear strains in excess of 24% do not result in permanent changes in electrical resistance along uninfused fibers, while irreversible changes in electrical resistance arise from applied shear strains of 12.9% in epoxy infused fibers. Bulk shear modulus is approximated to be 0.40 ± 0.02 GPa for unreinforced and 2.79 ± 0.64 GPa for infused fibers.
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07.10.Cm Micromechanical devices and systems

Three-dimensional distribution of Al in high-k metal gate: Impact on transistor voltage threshold

F. Panciera, S. Baudot, K. Hoummada, M. Gregoire, M. Juhel, and D. Mangelinck

Appl. Phys. Lett. 100, 201909 (2012); http://dx.doi.org/10.1063/1.4717742 (4 pages) | Cited 1 time

Online Publication Date: 18 May 2012

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The three-dimensional spatial distribution of Al in the high-k metal gates of metal-oxide-semiconductor field-effect-transistors is measured by atom probe tomography. Chemical distribution is correlated with the transistor voltage threshold (VTH) shift generated by the introduction of a metallic Al layer in the metal gate. After a 1050 °C annealing, it is shown that a 2-Å thick Al layer completely diffuses into oxide layers, while a positive VTH shift is measured. On the contrary, for thicker Al layers, Al precipitation in the metal gate stack is observed and the VTH shift becomes negative.
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85.30.Tv Field effect devices
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