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28 Aug 2006

Volume 89, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 89, 093101 (2006); http://dx.doi.org/10.1063/1.2338808 (3 pages)

Nicholas Jabari Lee, Rajiv K. Kalia, Aiichiro Nakano, and Priya Vashishta
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Charge neutralization of dust particles in a plasma with negative ions

Robert L. Merlino and Su-Hyun Kim

Appl. Phys. Lett. 89, 091501 (2006); http://dx.doi.org/10.1063/1.2338790 (3 pages) | Cited 33 times

Online Publication Date: 28 August 2006

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Charging of dust grains in a plasma with negative ions is studied experimentally. When the relatively mobile electrons are attached to heavy negative ions, their tendency to charge the grains negatively is reduced. In a plasma in which a substantial fraction of the electrons are eliminated (positive ion/negative ion plasma), the grain charge can be reduced in magnitude nearly to zero (“decharging” or charge neutralization). If the positive ions are lighter than the negative ions, dust grains having a small net positive charge can be produced.
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52.27.Lw Dusty or complex plasmas; plasma crystals
52.20.Fs Electron collisions
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Fi Transport properties

Plasma-focus-based tabletop hard x-ray source for 50 ns resolution introspective imaging of metallic objects through metallic walls

C. Moreno, V. Raspa, L. Sigaut, R. Vieytes, and A. Clausse

Appl. Phys. Lett. 89, 091502 (2006); http://dx.doi.org/10.1063/1.2335631 (3 pages) | Cited 4 times

Online Publication Date: 28 August 2006

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A tabletop 4.7 kJ, 30 kV plasma focus device was used as a pulsed hard x-ray source for fast radiography (50 ns exposure time) of metallic pieces even through several millimeter thick metallic walls. An experimental estimation of the effective average energy of the x-ray beam (found to be around 100 keV) and a numerical estimation of the induced voltage on the focus during the compressional stage of a plasma focus are briefly discussed.
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52.59.Px Hard X-ray sources
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.75.-d Plasma devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.La X-ray and γ-ray measurements
07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors

Mechanism of laser plasma production and of plasma interaction with a target

I. I. Beilis

Appl. Phys. Lett. 89, 091503 (2006); http://dx.doi.org/10.1063/1.2345044 (3 pages) | Cited 8 times

Online Publication Date: 29 August 2006

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A model of plasma production by laser interaction with a solid target was developed taking into account plasma heating by the emitted electrons, as additional to the absorbed laser energy flux, and also target heating by ion bombardment, as additional heat source to the laser radiation. A system of equations, including equations for solid heat conduction, plasma generation, and the plasma expansion, was solved self-consistently. The proposed model allows to understand that the plasma, partially shielding the laser radiation from the target, also converts absorbed laser energies to kinetic and potential energy of the plasma particles, which transport this energy not only in the ambient vacuum but also through the electrostatic sheath to the solid surface.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.50.Gj Plasma heating by particle beams
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.40.Hf Plasma-material interactions; boundary layer effects

Theory and simulations of a gyrotron backward wave oscillator using a helical interaction waveguide

W. He, A. W. Cross, A. D. R. Phelps, K. Ronald, C. G. Whyte, S. V. Samsonov, V. L. Bratman, and G. G. Denisov

Appl. Phys. Lett. 89, 091504 (2006); http://dx.doi.org/10.1063/1.2345607 (3 pages) | Cited 16 times

Online Publication Date: 1 September 2006

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A gyrotron backward wave oscillator (gyro-BWO) with a helically corrugated interaction waveguide demonstrated its potential as a powerful microwave source with high efficiency and a wide frequency tuning range. This letter presents the theory describing the dispersion properties of such a waveguide and the linear beam-wave interaction. Numerical simulation results using the PIC code MAGIC were found to be in excellent agreement with the output measured from a gyro-BWO experiment.
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84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)
84.40.Az Waveguides, transmission lines, striplines
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Effect of surface morphology on the fracture strength of silicon nanobeams

Tuncay Alan, Melissa A. Hines, and Alan T. Zehnder

Appl. Phys. Lett. 89, 091901 (2006); http://dx.doi.org/10.1063/1.2338649 (3 pages) | Cited 11 times

Online Publication Date: 28 August 2006

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The effect of nanoscale surface morphology on the fracture strength of 190-nm-thick, doubly clamped Si beams was measured experimentally. The surface morphology was controlled through aqueous etching and characterized by atomic force microscopy. The beams fractured along the primary cleavage planes, {111}. Fracture strength was extracted using finite element simulations of the experiment. Nanobeams etched with relatively smooth morphologies (0.4 nm rms) were able to sustain a tensile stress of 15.8 GPa, close to theoretical strengths predicted by previous atomistic calculations. In contrast, nanobeams decorated with nanometer-high step bunches (1.5 nm rms) had a 20% lower fracture strength, 12.8 GPa, suggesting that careful attention to processing is necessary for maximum strength.
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81.07.Bc Nanocrystalline materials
81.05.Cy Elemental semiconductors
68.47.Fg Semiconductor surfaces
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.65.Cf Surface cleaning, etching, patterning

X-ray diffuse scattering from stacking faults in thick 3C-SiC single crystals

A. Boulle, D. Chaussende, L. Latu-Romain, F. Conchon, O. Masson, and R. Guinebretière

Appl. Phys. Lett. 89, 091902 (2006); http://dx.doi.org/10.1063/1.2338787 (3 pages) | Cited 12 times

Online Publication Date: 28 August 2006

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Stacking faults in thick (001)- and (111)-oriented 3C-SiC single crystals are studied by high resolution x-ray diffraction. The authors demonstrate that the analysis of the diffuse scattering intensity distribution can be used as a nondestructive means to accurately determine the densities of Shockley-type stacking faults. The diffuse scattering intensity is simulated with a scattering model based on a difference-equation description of faulting in fcc materials. It is shown that the (001) SiC crystals exhibit an anisotropic fault distribution, whereas the (111) SiC crystals exhibit an isotropic fault distribution, in excellent quantitative agreement with transmission electron microscopy observations.
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61.72.Nn Stacking faults and other planar or extended defects
78.70.Ck X-ray scattering

Luminescence enhancement of (Ca,Zn)TiO3:Pr3+ phosphor using nanosized silica powder

D. Haranath, A. F. Khan, and Harish Chander

Appl. Phys. Lett. 89, 091903 (2006); http://dx.doi.org/10.1063/1.2338789 (3 pages) | Cited 11 times

Online Publication Date: 28 August 2006

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The results pertaining to luminescence enhancement due to high-temperature amalgamation of nanometer-sized silica powder and the oxide mixture of calcium, zinc, titanium, and praseodymium are presented. The (Ca,Zn)TiO3:Pr3+ phosphor showed an intense and narrow band emission at ∼ 614 nm under ambient light/ultraviolet excitation, which is associated with the typical math→math transition of Pr3+. The observed red emission is quite stable and long ( ∼ 60 min) for a dark-adapted human eye and shows no appreciable degradation in the optical properties for prolonged exposure to surrounding/atmosphere. With the addition of nanosized silica powder, the photoluminescence was augmented nearly 1.6 times as that of unadded sample. The present results are entirely different from those reported previously for Pr3+ doped-(Ca,Zn)TiO3 phosphor and silica-based persistent phosphors.
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78.55.Hx Other solid inorganic materials

Moisture-resistant ZnO transparent conductive films with Ga heavy doping

Osamu Nakagawara, Yutaka Kishimoto, Hiroyuki Seto, Yoshihiro Koshido, Yukio Yoshino, and Takahiro Makino

Appl. Phys. Lett. 89, 091904 (2006); http://dx.doi.org/10.1063/1.2337542 (3 pages) | Cited 26 times

Online Publication Date: 28 August 2006

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Moisture-resistant ZnO transparent conductive films were formed with Ga heavy doping by off-axis-type rf magnetron sputtering. The resistivity of 12.4 wt % Ga-doped ZnO is 1.3×10−3 Ω cm and changes by less than 3% over a 2000 h reliability test at a temperature of 85 °C and a humidity of 85%. The crystal structural analysis of the heavily Ga-doped ZnO films indicates that the c axis grows along various directions, which is quite different from the conventional c-axis oriented growth. The effect of heavy doping is discussed based on the crystal structural transformation and carrier compensation by excess Ga segregated in the film.
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81.05.Dz II-VI semiconductors
73.61.Ga II-VI semiconductors
81.15.Cd Deposition by sputtering
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Effect of the misorientation of the 4H-SiC substrate on the open volume defects in GaN grown by metal-organic chemical vapor deposition

E. Tengborn, M. Rummukainen, F. Tuomisto, K. Saarinen, M. Rudzinski, P. R. Hageman, P. K. Larsen, and A. Nordlund

Appl. Phys. Lett. 89, 091905 (2006); http://dx.doi.org/10.1063/1.2338887 (3 pages) | Cited 3 times

Online Publication Date: 28 August 2006

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Positron annihilation spectroscopy has been used to study GaN grown by metal-organic chemical vapor deposition on misoriented 4H-SiC substrates. Two kinds of vacancy defects are observed: Ga vacancies and larger vacancy clusters in all the studied layers. In addition to vacancies, positrons annihilate at shallow traps that are likely to be dislocations. The results show that the vacancy concentration increases and the shallow positron trap concentration decreases with the increasing substrate misorientation.
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61.72.J- Point defects and defect clusters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.80.Fe Electron and positron radiation effects
78.70.Bj Positron annihilation
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Prospective emission efficiency and in-plane light polarization of nonpolar m-plane InxGa1−xN/GaN blue light emitting diodes fabricated on freestanding GaN substrates

T. Koyama, T. Onuma, H. Masui, A. Chakraborty, B. A. Haskell, S. Keller, U. K. Mishra, J. S. Speck, S. Nakamura, S. P. DenBaars, T. Sota, and S. F. Chichibu

Appl. Phys. Lett. 89, 091906 (2006); http://dx.doi.org/10.1063/1.2337085 (3 pages) | Cited 41 times

Online Publication Date: 28 August 2006

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Prospective equivalent internal quantum efficiency (ηint) of approximately 34% at 300 K was demonstrated for the blue emission peak of nonpolar m-plane (1math00) InxGa1−xN/GaN multiple quantum well light emitting diodes (LEDs) fabricated on freestanding m-plane GaN substrates. Although the ηint value is yet lower than that of conventional c-plane blue LEDs (>70%), the results encourage one to realize high performance green, amber, and red LEDs by reducing the concentration of nonradiative defects, according to the absence of the quantum-confined Stark effects due to the polarization fields parallel to the quantum well normal. The electric field component of the blue surface emission was polarized perpendicular to the c axis with the in-plane polarization ratio of 0.58 at 300 K.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Reorientation of the crystalline planes in confined single crystal nickel nanorods induced by heavy ion irradiation

Abha Misra, Pawan K. Tyagi, Padmnabh Rai, D. S. Misra, Jay Ghatak, P. V. Satyam, and D. K. Avasthi

Appl. Phys. Lett. 89, 091907 (2006); http://dx.doi.org/10.1063/1.2337544 (3 pages) | Cited 2 times

Online Publication Date: 29 August 2006

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In a recent letter Tyagi et al. [Appl. Phys. Lett. 86, 253110 (2005)] have reported the special orientation of nickel planes inside multiwalled carbon nanotubes (MWCNTs) with respect to the tube axis. Heavy ion irradiation has been performed with 1.5 MeV Au2+ and 100 MeV Au7+ ions on these nickel filled MWCNTs at fluences ranging from 1012 to 1015 ions/cm2 at room temperature. Ion-induced modifications have been studied using high-resolution transmission electron microscopy. The diffraction pattern and the lattice imaging showed the presence of ion-induced planar defects on the tube walls and completely amorphized encapsulated nickel nanorods. The results are discussed in terms of thermal spike model.
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61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
61.82.Rx Nanocrystalline materials
61.46.Hk Nanocrystals

Increase of blue electroluminescence from Ce-doped SiO2 layers through sensitization by Gd3+ ions

J. M. Sun, S. Prucnal, W. Skorupa, M. Helm, L. Rebohle, and T. Gebel

Appl. Phys. Lett. 89, 091908 (2006); http://dx.doi.org/10.1063/1.2338892 (3 pages) | Cited 12 times

Online Publication Date: 29 August 2006

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Efficient blue electroluminescence peak at around 440 nm with a maximum output power density of 34 mW/cm2 was obtained from Ce and Gd coimplanted metal-oxide-semiconductor light emitting devices. Energy transfer from Gd3+ to Ce3+ ions was observed during the excitation process, leading to a more than threefold increase of the external quantum efficiency of the blue Ce3+ luminescence up to 1.8%. This is evidenced by the increase of the excitation cross section of Ce3+ ions from 4.8×10−13 to 3.5×10−12 cm2 and the simultaneous reduction of the decay time and the impact cross section of Gd3+ ions.
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85.30.-z Semiconductor devices
85.60.Jb Light-emitting devices

Stranski-Krastanov growth in Mg0.37Zn0.63O/ZnO heteroepitaxy: Self-organized nanodots and local composition separation

Hiroaki Matsui, Noriyuki Hasuike, Hiroshi Harima, Takanori Tanaka, and Hitoshi Tabata

Appl. Phys. Lett. 89, 091909 (2006); http://dx.doi.org/10.1063/1.2339027 (3 pages) | Cited 7 times

Online Publication Date: 29 August 2006

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Heteroepitaxy of strained Mg0.37Zn0.63O layers on ZnO (0001) substrates introduces a transition from two-dimensional to Stranski-Krastanov growth accompanying lattice relaxation at a critical thickness, as indicated by the nanodots formation on the growing planar layer. Due to differences in the atomic size of Mg and Zn, the strained layer was compressively distorted at the heterointerface and alloy compositions fluctuated locally. Elastic strain induced by the lattice misfit acted as a driving force for the self-organization of surface nanodots. Moreover, a strained field generated by alloy fluctuation caused local composition separation with a correlation between surface roughening and a lateral Mg segregation.
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81.05.Dz II-VI semiconductors
81.16.Dn Self-assembly
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.65.Hb Quantum dots (patterned in quantum wells)
81.07.Ta Quantum dots

Induced free carrier modulation of photonic crystal optical intersection via localized optical absorption effect

Selin H. G. Teo, A. Q. Liu, J. B. Zhang, and M. H. Hong

Appl. Phys. Lett. 89, 091910 (2006); http://dx.doi.org/10.1063/1.2344840 (3 pages) | Cited 5 times

Online Publication Date: 29 August 2006

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This letter reports demonstration of optically induced signal modulation in two-dimensional photonic crystal (PhC) optical intersections. High resolution and high aspect ratio PhC was fabricated for optical communication wavelengths. Besides characterization of the silicon PhC static properties, dynamic modulations through spatially localized applications of high intensity pump radiation were also demonstrated to yield normalized modulations of 15 dB for incident intensity of 70 MW/cm2—corresponding well with first principles simulations. The effective modulation range and pump limit of the method were therefore determined and the potential of such a modulation scheme as a practical means of developing tunable PhC devices was realized.
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42.70.Qs Photonic bandgap materials

Nonradiative losses in Yb:KGd(WO4)2 and Yb:Y3Al5O12

Subrat Biswal, Shawn P. O’Connor, and Steven R. Bowman

Appl. Phys. Lett. 89, 091911 (2006); http://dx.doi.org/10.1063/1.2335774 (3 pages) | Cited 2 times

Online Publication Date: 30 August 2006

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Photothermal deflection spectroscopy was used to measure nonradiative losses in Yb:KGW and Yb:YAG (for both crystal and for the first time in ceramic form). Fluorescent quantum efficiencies for both materials were found to be greater than 98.9%. The reduction of nonradiative losses due to annealing of Yb:YAG is also presented.
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78.55.Hx Other solid inorganic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.-a Optical materials
81.40.Gh Other heat and thermomechanical treatments

Light propagation and transmission in hybrid-aligned nematic liquid crystal cells: Geometrical optics calculations

Carlos I. Mendoza and J. Adrian Reyes

Appl. Phys. Lett. 89, 091912 (2006); http://dx.doi.org/10.1063/1.2345042 (3 pages)

Online Publication Date: 30 August 2006

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The authors present a geometrical approach to calculate the transmission of light in a hybrid-aligned nematic cell under the influence of an applied electric field. Using the framework of geometrical optics they present results for the ray tracing as well as the transmission of light as a function of the applied low frequency voltage. Dispersion effects are included through a wavelength dependent dielectric function. Their results for the transmittance as a function of the applied voltage show oscillations that are in good qualitative agreement with previously obtained experimental measurements.
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42.70.Df Liquid crystals
61.30.-v Liquid crystals
42.15.Dp Wave fronts and ray tracing
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effects of high pressure on the optical absorption spectrum of scintillating PbWO4 crystals

D. Errandonea, D. Martínez-García, R. Lacomba-Perales, J. Ruiz-Fuertes, and A. Segura

Appl. Phys. Lett. 89, 091913 (2006); http://dx.doi.org/10.1063/1.2345228 (3 pages) | Cited 22 times

Online Publication Date: 30 August 2006

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The pressure behavior of the absorption edge of PbWO4 was studied up to 15.3 GPa. It redshifts at −71 meV/GPa below 6.1 GPa, but at 6.3 GPa the band gap collapses from 3.5 to 2.75 eV. From 6.3 to 11.1 GPa, the absorption edge moves with a pressure coefficient of −98 meV/GPa, undergoing additional changes at 12.2 GPa. The results are discussed in terms of the electronic structure of PbWO4 which attribute the behavior of the band gap to changes in the local atomic structure. The changes observed at 6.3 and 12.2 GPa are attributed to phase transitions.
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62.50.-p High-pressure effects in solids and liquids
78.20.-e Optical properties of bulk materials and thin films
64.70.K- Solid-solid transitions
71.20.Nr Semiconductor compounds
78.55.Hx Other solid inorganic materials

Zn1−xCdxO systems with visible band gaps

Junji Ishihara, Atsushi Nakamura, Satoshi Shigemori, Toru Aoki, and Jiro Temmyo

Appl. Phys. Lett. 89, 091914 (2006); http://dx.doi.org/10.1063/1.2345232 (2 pages) | Cited 34 times

Online Publication Date: 30 August 2006

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Zn1−xCdxO films in the range of the content x from x = 0 to x = 1 were grown by remote-plasma-enhanced metal organic chemical vapor deposition. The crystal structure of Zn1−xCdxO film changed with increase of the content x from wurtzite structure to rocksalt structure around x = 0.7. The relationship between the cadmium content and axis length in the Zn1−xCdxO films was studied. Photoluminescence spectra were observed from the wurtzite Zn1−xCdxO films in the range of 3.3–1.8 eV at room temperature. Stokes’s shift in the restricted composition range was compared with the previous results.
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78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
68.55.-a Thin film structure and morphology
71.20.Nr Semiconductor compounds

Measuring interface strains at the atomic resolution in depth using x-ray Bragg-surface diffraction

W. C. Sun, H. C. Chang, B. K. Wu, Y. R. Chen, C. H. Chu, S. L. Chang, M. Hong, M. T. Tang, and Yu. P. Stetsko

Appl. Phys. Lett. 89, 091915 (2006); http://dx.doi.org/10.1063/1.2345023 (3 pages) | Cited 6 times

Online Publication Date: 31 August 2006

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A generic x-ray diffraction method, using three-wave Bragg-surface diffraction, is developed to measure strains at the interface of molecular beam epitaxial Au/GaAs(001), where grazing-incidence diffraction cannot be applied due to the difference in refractive index between Au and GaAs. Changes in diffraction images of the surface reflection (1−13) of GaAs(006)/(1−13) three-wave Bragg-surface diffraction and the (−1−13) of GaAs(006)/(−1−13) at different azimuth and Bragg angles give the depth penetration of 2 Å resolution and variations of lattice constant, −49%, −27%, and 2%, along the surface normal [001] and in-plane directions [−1−10] and [1−10] within the depths of 18, 72, and 72 Å, respectively.
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81.05.Bx Metals, semimetals, and alloys
68.35.Gy Mechanical properties; surface strains
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Misfit strain relaxation in strained-Si layers on silicon-germanium-on-insulator substrates

Norio Hirashita, Yoshihiko Moriyama, Naoharu Sugiyama, Eiji Toyoda, and Shin-ichi Takagi

Appl. Phys. Lett. 89, 091916 (2006); http://dx.doi.org/10.1063/1.2345250 (3 pages) | Cited 2 times

Online Publication Date: 1 September 2006

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The critical thickness of tensile-strained-Si layers grown at 600 °C on (001) surfaces of silicon-germanium-on-insulator substrates is experimentally studied for a tensile strain range between 0.4% and 1.2% and is found to be rather thinner than Houghton’s critical thickness [ J. Appl. Phys. 70, 2136 (1991) ] for compressively mismatched SiGe/Si (001) system. The thinner critical thickness in tensile-strained Si is attributed to the fact that the stress-relieving misfit dislocations are 90° partial dislocations, instead of 60° misfit dislocations for compressive SiGe layers on Si (001) substrates. Although 60° misfit dislocation is found to be increasingly formed with increasing strained-Si layer thickness, the strain relaxation is sluggish and the tensile strain mostly remains for supercritical thickness ten times thicker than the critical thickness.
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68.35.Gy Mechanical properties; surface strains
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Lk Linear defects: dislocations, disclinations
68.60.Bs Mechanical and acoustical properties

Evaluation of glass-forming ability for metallic glasses based on order-disorder competition

Mingxu Xia, Shuguang Zhang, Chaoli Ma, and Jianguo Li

Appl. Phys. Lett. 89, 091917 (2006); http://dx.doi.org/10.1063/1.2345259 (3 pages) | Cited 11 times

Online Publication Date: 1 September 2006

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The authors propose a calculable parameter ε, defined as a negative ratio of mixing entropy to mixing enthalpy, to evaluate the glass-forming ability (GFA) of metallic glasses from the viewpoint of a competition of disordering against ordering. It is found that the GFAs of most typical metallic glasses linearly distribute with ε and the likely formation area of bulk metallic glass could be conservatively restricted within 0.25<ε<0.6 K−1. The prediction of Tb–Fe–Al glassy alloys shows promise for rapidly locating glass formers with less cost.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
64.75.-g Phase equilibria
61.43.Fs Glasses

Negative strain rate sensitivity in bulk metallic glass and its similarities with the dynamic strain aging effect during deformation

Florian H. Dalla Torre, Alban Dubach, Marco E. Siegrist, and Jörg F. Löffler

Appl. Phys. Lett. 89, 091918 (2006); http://dx.doi.org/10.1063/1.2234309 (3 pages) | Cited 26 times

Online Publication Date: 1 September 2006

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Detailed investigations were carried out on the deformation behavior of Zr-based monolithic bulk metallic glass and bulk metallic glass matrix composites. The latter, due to splitting and multiplication of shear bands, exhibits larger compressive strains than the former, without significant loss of strength. Serrated flow in conjunction with a negative strain rate sensitivity was observed in both materials. This observation, together with an increase in stress drops with increasing strain and their decrease with increasing strain rate, indicates phenomenologically close similarities with the dynamic strain aging deformation mechanism known for crystalline solids. The micromechanical mechanism of a shear event is discussed in light of these results.
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81.05.Kf Glasses (including metallic glasses)
81.05.Bx Metals, semimetals, and alloys
61.43.Fs Glasses
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

High pressure crystalline phase formation during nanoindentation: Amorphous versus crystalline silicon

S. Ruffell, J. E. Bradby, and J. S. Williams

Appl. Phys. Lett. 89, 091919 (2006); http://dx.doi.org/10.1063/1.2339039 (3 pages) | Cited 26 times

Online Publication Date: 1 September 2006

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Phase transformations induced by indentation at different unloading rates have been studied in crystalline and amorphous silicon via Raman microspectroscopy and transmission electron microscopy. Unloading was performed at a “slow” rate of ∼ 0.9 mN/s which is known to create volumes of high pressure phases (Si-III and Si-XII) in crystalline silicon as well as “rapid” unloading ( ∼ 1000 mN/s), where amorphous phases are expected. Stark differences between the resulting structures are observed depending on whether the starting material is amorphous or crystalline silicon. Interestingly, amorphous silicon transforms to high pressure phases much more readily than crystalline silicon even after rapid unloading.
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64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
78.30.Am Elemental semiconductors and insulators
78.20.Jq Electro-optical effects
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Organic-inorganic hybrid dielectrics with low leakage current for organic thin-film transistors

Sunho Jeong, Dongjo Kim, Sul Lee, Bong-Kyun Park, and Jooho Moon

Appl. Phys. Lett. 89, 092101 (2006); http://dx.doi.org/10.1063/1.2338753 (3 pages) | Cited 21 times

Online Publication Date: 28 August 2006

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Using a thermally cross-linkable organosiloxane-based organic-inorganic hybrid material, a solution-processable gate dielectric layer for organic thin-film transistors has been fabricated. The hybrid dielectric was synthesized by a sol-gel process, followed by heat treatment at below 190 °C. Dielectric strength of 1.4–1.65 MV/cm was measured and it was confirmed that the leakage current is governed by the Poole-Frenkel emission mechanism in which the silanol groups act as trap sites. An organic thin-film transistor utilizing the hybrid dielectric shows similar electrical performance to a transistor fabricated using surface-modified thermally grown SiO2.
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85.30.Tv Field effect devices
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Junction characteristics of SrTiO3 or BaTiO3 on p-Si (100) heterostructures

D. Hunter, K. Lord, T. M. Williams, K. Zhang, A. K. Pradhan, D. R. Sahu, and J.-L. Huang

Appl. Phys. Lett. 89, 092102 (2006); http://dx.doi.org/10.1063/1.2338764 (3 pages) | Cited 12 times

Online Publication Date: 28 August 2006

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The authors report the fabrication of p-n junctions, consisting of n-type SrTiO3 or BaTiO3 and p-type Si substrates, by the pulsed-laser deposition technique. The BaTiO3/Si junction exhibits excellent rectifying behavior and significantly reduced leakage current at 300 K exceeding breakdown voltage of −25 V with leakage current <0.5 μA, while SrTiO3/Si with an interfacial layer shows moderate junction characteristics. It was demonstrated that the BaTiO3/Si grown at an optimum growth temperature of 650 °C displayed superior performance which is promising for electronic devices. Both junctions show photocurrent at 300 K due to electron injection following the photoexcitation of n-type perovskite.
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73.40.Ei Rectification
72.40.+w Photoconduction and photovoltaic effects
77.22.Jp Dielectric breakdown and space-charge effects
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth
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