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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Enhancement and suppression of spontaneous emission by temperature tuning InAs quantum dots to photonic crystal cavities

D. G. Gevaux, A. J. Bennett, R. M. Stevenson, A. J. Shields, P. Atkinson, J. Griffiths, D. Anderson, G. A. C. Jones, and D. A. Ritchie

Appl. Phys. Lett. 88, 131101 (2006); http://dx.doi.org/10.1063/1.2189747 (3 pages) | Cited 21 times

Online Publication Date: 27 March 2006

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We report on the control of the spontaneous emission rates in InAs self-assembled quantum dots weakly coupled to the mode of a modified H1 defect cavity in a two-dimensional photonic crystal slab. Changes in sample temperature are used to spectrally tune the exciton emission from a single quantum dot to the monopole mode of the microcavity. A Purcell enhancement of the spontaneous emission rate of up to a factor of 11.4 is seen on-resonance, while suppression by up to a factor of 4.4 is seen off-resonance. Also, a two orders of magnitude increase in the intensity of light detected from the exciton is measured when compared to a quantum dot in bulk GaAs.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
42.82.Gw Other integrated-optical elements and systems
42.70.Qs Photonic bandgap materials
71.35.-y Excitons and related phenomena

Time-resolved and antibunching experiments on single quantum dots at 1300 nm

C. Zinoni, B. Alloing, C. Monat, V. Zwiller, L. H. Li, A. Fiore, L. Lunghi, A. Gerardino, H. de Riedmatten, H. Zbinden, and N. Gisin

Appl. Phys. Lett. 88, 131102 (2006); http://dx.doi.org/10.1063/1.2190466 (3 pages) | Cited 45 times

Online Publication Date: 27 March 2006

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We present time integrated and time-resolved photoluminescence (PL) measurements on a single InAs/GaAs quantum dot (QD), embedded in a planar microcavity, emitting in the 1300 nm telecom band. The results of both measurements clearly identify the exciton and biexciton transitions from a single QD. By optimizing the extraction efficiency of the QD PL into the single mode fibers and carefully tuning two InGaAs avalanche photodiodes, we were able to measure the second order correlation function with integration times comparable to those made with silicon based technology. These measurements demonstrate that our single QDs are efficient sources of triggered single photons for quantum key distribution in the O band.
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78.67.Hc Quantum dots
78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
42.82.Gw Other integrated-optical elements and systems
71.35.-y Excitons and related phenomena

A precise method for rotating single cells

Hiroaki Kobayashi, Ichirou Ishimaru, Ryoji Hyodo, Toshiki Yasokawa, Katsumi Ishizaki, Shigeki Kuriyama, Tsutomu Masaki, Seiji Nakai, Kaoru Takegawa, and Naotaka Tanaka

Appl. Phys. Lett. 88, 131103 (2006); http://dx.doi.org/10.1063/1.2190268 (2 pages) | Cited 10 times

Online Publication Date: 28 March 2006

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A precise method to rotate single cells is reported. In this method, the light pressure in the optical axis direction is harnessed as a rotating torque. Two proximal points in each cell are illuminated from different directions using two beams, and a light pressure is created that acts as a rotating torque. Using this proposed method, we could control the rotational direction of a microsphere regardless of the refractive index distribution in a noncontact operation. The microsphere could be rotated using proximal two-beam optical tweezers, and the rotational velocity could be controlled by changing the light intensity.
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87.63.L- Visual imaging
87.80.Cc Optical trapping
87.17.-d Cell processes
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.62.Be Biological and medical applications

Dopant profile engineering by near-infrared femtosecond laser activation

Yi-Chao Wang, Ci-Ling Pan, Jia-Min Shieh, and Bau-Tong Dai

Appl. Phys. Lett. 88, 131104 (2006); http://dx.doi.org/10.1063/1.2191095 (3 pages) | Cited 4 times

Online Publication Date: 28 March 2006

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Femtosecond laser annealing (FLA) was employed for activation of phosphorus (P)- and boron (B)-implanted silicons with negligible dopant diffusion. Preamorphizing implantation is not required. We found that the dopant profiles in FLA-activated samples essentially duplicate those of as-implanted ones even for junctions as deep as 100 nm below the surface. The measured sheet resistances and activation efficiencies of P- and B-implanted samples were in the range of 100–400 Ω/◻ and 28%–35%, respectively. Moreover, thermal-energy-assisted dopant diffusion by heating was observed for substrate temperature as low as 100 °C. The shallow activated-depth feature associated with FLA reduces the separation between end-of-range defects and high-concentration portion of dopants. This generates a steep interstitial gradient responsible for observed B and P uphill diffusions at a depth of about 60 nm below the surface.
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61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
66.30.J- Diffusion of impurities

Intersubband spectroscopy of quantum cascade lasers under operating conditions

D. G. Revin, L. R. Wilson, J. W. Cockburn, A. B. Krysa, J. S. Roberts, and R. J. Airey

Appl. Phys. Lett. 88, 131105 (2006); http://dx.doi.org/10.1063/1.2189911 (3 pages) | Cited 9 times

Online Publication Date: 28 March 2006

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A technique is described that enables the mid infrared spectroscopic study of the intersubband electron distribution in quantum cascade lasers under operating conditions. By measuring the transmission of a broadband thermal source through the waveguide of a λ ∼ 7.4 μm InGaAs/AlInAs/InP quantum cascade laser, the redistribution of the electrons in the active region confined levels has been investigated for a wide range of operating currents and temperatures. This technique also allows direct determination of key parameters such as the temperature of the core region under operating conditions, the modal gain coefficient, and the waveguide loss.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Ultralow noise optical pulse generation in an actively mode-locked quantum-dot semiconductor laser

Myoung-Taek Choi, Ji-Myung Kim, Wangkuen Lee, and Peter J. Delfyett

Appl. Phys. Lett. 88, 131106 (2006); http://dx.doi.org/10.1063/1.2190443 (3 pages) | Cited 6 times

Online Publication Date: 28 March 2006

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We report excellent noise performance of an external-cavity actively mode-locked laser based on quantum-dot gain medium. Optical pulse trains with less than 7.5 fs residual timing jitter (1 Hz to 10 MHz) for a 12.8 GHz harmonically mode-locked ring laser were obtained. This result represents, to our knowledge, the lowest residual jitter reported from actively mode-locked semiconductor lasers, and shows that quantum-dot mode-locked lasers are promising as sources of ultralow noise optical pulse trains.
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42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Photoinduced currents in carbon nanotube/metal heterojunctions

Jia-Lin Sun, Jinquan Wei, Jia-Lin Zhu, Dong Xu, Xiaomeng Liu, Hongsan Sun, De-Hai Wu, and Nian-Le Wu

Appl. Phys. Lett. 88, 131107 (2006); http://dx.doi.org/10.1063/1.2189454 (3 pages) | Cited 18 times

Online Publication Date: 29 March 2006

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Significant photoinduced currents have been explored in carbon nanotube/metal heterojunctions, i.e., heterodimension junctions containing macrolong carbon nanotubes (CNTs). The experimental measurements clearly show that the net transport direction of the photoexcited electrons is from the lower dimensional CNTs to higher dimensional CNTs or metal electrodes and the photoinduced currents dramatically depend on the laser spot position relative to the junction interface. The currents increase linearly with the increase of the laser intensity as the intensity is not very large. A prototype sensor has been constructed to illustrate applications of the heterodimension junctions in photoelectronics.
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73.40.Ns Metal-nonmetal contacts
73.50.Pz Photoconduction and photovoltaic effects
73.63.Fg Nanotubes

Nonlinear magneto-optical rotation with amplitude modulated light

W. Gawlik, L. Krzemień, S. Pustelny, D. Sangla, J. Zachorowski, M. Graf, A. O. Sushkov, and D. Budker

Appl. Phys. Lett. 88, 131108 (2006); http://dx.doi.org/10.1063/1.2190457 (3 pages) | Cited 12 times

Online Publication Date: 29 March 2006

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The technique of nonlinear magneto-optical rotation with amplitude modulated light is developed. The technique is an alternative to its counterpart with frequency modulated light and can be applied to sensitive measurements of magnetic fields ranging from microgauss to the Earth-field level. The rotation signals exhibit nontrivial features such as narrowed non-Lorentzian line shapes and multicomponent resonances.
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32.60.+i Zeeman and Stark effects
42.65.-k Nonlinear optics
32.70.Jz Line shapes, widths, and shifts
07.77.-n Atomic, molecular, and charged-particle sources and detectors
31.50.Df Potential energy surfaces for excited electronic states

Spectral tuning of plasmon-enhanced silicon quantum dot luminescence

Julie S. Biteen, Nathan S. Lewis, Harry A. Atwater, Hans Mertens, and Albert Polman

Appl. Phys. Lett. 88, 131109 (2006); http://dx.doi.org/10.1063/1.2191411 (3 pages) | Cited 71 times

Online Publication Date: 31 March 2006

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In the presence of nanoscale silver island arrays, silicon quantum dots exhibit up to sevenfold luminescence enhancements at emission frequencies that correspond to the collective dipole plasmon resonance frequency of the Ag island array. Using electron-beam lithography to alter the pitch and particle diameter, this wavelength-selective enhancement can be varied as the metal array resonance wavelength is tuned from 600 to 900 nm. The luminescence intensity enhancement upon coupling is attributed to an increase in the radiative decay rate of the silicon quantum dots.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.67.Hc Quantum dots
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces

Absolute calibration of optical tweezers

N. B. Viana, A. Mazolli, P. A. Maia Neto, H. M. Nussenzveig, M. S. Rocha, and O. N. Mesquita

Appl. Phys. Lett. 88, 131110 (2006); http://dx.doi.org/10.1063/1.2189148 (3 pages) | Cited 24 times

Online Publication Date: 31 March 2006

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As a step toward absolute calibration of optical tweezers, a first-principles theory of trapping forces with no adjustable parameters, corrected for spherical aberration, is experimentally tested. Employing two very different setups, we find generally very good agreement for the transverse trap stiffness as a function of microsphere radius for a broad range of radii, including the values employed in practice, and at different sample chamber depths. The domain of validity of the WKB (“geometrical optics”) approximation to the theory is verified. Theoretical predictions for the trapping threshold, peak position, depth variation, multiple equilibria, and “jump” effects are also confirmed.
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06.20.fb Standards and calibration
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
31.15.A- Ab initio calculations
42.15.Fr Aberrations

Optical control of recovery speed of photoinduced third-harmonic generation in azo-copolymer thin films

Jian Hung Lin, Ngoc Diep Lai, and Chia Chen Hsu

Appl. Phys. Lett. 88, 131111 (2006); http://dx.doi.org/10.1063/1.2185078 (3 pages) | Cited 1 time

Online Publication Date: 31 March 2006

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Recovery speed of photoinduced third-harmonic (TH) generation in azo-copolymer thin films can be controlled by a nanosecond laser excitation. When the excitation is tuned on, the TH signal decreases because of angular hole burning and angular redistribution effects. After turning off the excitation, the TH signal can recover to its original level either within 1 min (high intensity excitation) or longer than several days (low intensity excitation). The fast recovery of the TH signal is attributed to the increase of temperature in the sample that causes molecules to more easily reorient and return to the original trans form.
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42.70.Jk Polymers and organics
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Qn Polymers; organic compounds
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Low-temperature lasing action in a metal-backed monosubstituted polyacetylene

Yuan Ming Huang, Fufang Zhou, and Kaitian Xu

Appl. Phys. Lett. 88, 131112 (2006); http://dx.doi.org/10.1063/1.2191429 (3 pages) | Cited 1 time

Online Publication Date: 31 March 2006

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Within a metal-backed feedback structure, low-temperature laser action has been observed in a highly luminescent monosubstituted polyacetylene, poly(n-[(4′-hexylcarbonyl-biphenyl-4-oxy)]-1-propyne}(PBP), at a low pump intensity of about 4 kW/cm2. Sandwiched between a finely polished copper plate and a quartz plate, solid films of the polymer PBP begin to give off sharp line emission at 570 nm when the temperature drops below 200 K. Both the temperature and the pump intensity dependences of the sharp line emission are investigated. Our results suggest that low-temperature lowered threshold makes lasing feasible in PBP at a considerably low pumping intensity.
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78.45.+h Stimulated emission
42.70.Jk Polymers and organics
42.70.Hj Laser materials
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Efficient single-active-layer organic light-emitting diodes with fluoropolymer buffer layers

H. F. Wang, L. D. Wang, Z. X. Wu, D. Q. Zhang, J. Qiao, Y. Qiu, and X. G. Wang

Appl. Phys. Lett. 88, 131113 (2006); http://dx.doi.org/10.1063/1.2191470 (3 pages) | Cited 7 times

Online Publication Date: 31 March 2006

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In the present Letter, efficient organic light-emitting diodes (OLEDs) with tris(8-hydroxyquinolino) aluminum (Alq3) as a single-active layer have been prepared by using a series of fluoropolymer buffer layers. The OLEDs with a 10-nm-thick poly(tetrafluroethylene-perfluoroalkylvinylethers) (PFA) buffer layer had a current efficiency of 4.46 cd/A at a current density of 2000 A/m2, whereas conventional double-layer OLEDs with N,N′-bis-(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) and Alq3 showed a current efficiency of only 3.81 cd/A at the same condition in our experiment. The effect of the insulating fluoropolymer buffer layers could be interpreted to enhance hole injection and improve carrier balance.
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85.60.Jb Light-emitting devices

Measuring the role of surface chemistry in silicon microphotonics

Matthew Borselli, Thomas J. Johnson, and Oskar Painter

Appl. Phys. Lett. 88, 131114 (2006); http://dx.doi.org/10.1063/1.2191475 (3 pages) | Cited 28 times

Online Publication Date: 31 March 2006

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Utilizing a high quality factor (Q ∼ 1.5×106) optical microresonator to provide sensitivity down to a fractional surface optical loss of αs′ ∼ 10−7, we show that the optical loss within Si microphotonic components can be dramatically altered by Si surface preparation, with αs′ ∼ 1×10−5 measured for chemical oxide surfaces as compared to αs′ ⩽ 1×10−6 for hydrogen-terminated Si surfaces. These results indicate that the optical properties of Si surfaces can be significantly and reversibly altered by standard microelectronic treatments, and that stable, high optical quality surface passivation layers will be critical in future Si micro- and nanophotonic systems.
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78.66.Db Elemental semiconductors and insulators
81.65.Rv Passivation
42.79.-e Optical elements, devices, and systems

Exciton fine structure splitting in dot-in-a-well structures

A. I. Tartakovskii, R. S. Kolodka, H. Y. Liu, M. A. Migliorato, M. Hopkinson, M. N. Makhonin, D. J. Mowbray, and M. S. Skolnick

Appl. Phys. Lett. 88, 131115 (2006); http://dx.doi.org/10.1063/1.2191476 (3 pages) | Cited 2 times

Online Publication Date: 31 March 2006

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A range of dot-in-a-well structures designed for long-wavelength (>1.3 μm) emission is studied in polarization- and time-resolved differential transmission measurements. Quantum beats observed in differential transmission are employed to measure the fine structure splitting (EFS) of the bright exciton states. A strong dependence of EFS on In content in the InGaAs well surrounding the dots is observed. Large magnitudes of EFS up to 87 μeV are found.
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78.67.De Quantum wells
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.47.-p Spectroscopy of solid state dynamics
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Temperature measurement in a high pressure dielectric barrier discharge using pressure induced line broadening and frequency shift

Robert J. Leiweke and Biswa N. Ganguly

Appl. Phys. Lett. 88, 131501 (2006); http://dx.doi.org/10.1063/1.2190453 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2006

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We have demonstrated two gas temperature measurement methods which are applicable to high pressure discharges where the pressure induced line broadening and frequency shift dominate over thermal broadening of atomic transitions. We have used diode-laser absorption spectroscopic measurements of argon 1s3→2p2 transition Doppler linewidth, Lorentzian broadening, and frequency shift to measure gas temperature in a dielectric barrier discharge operating from 5 up to 500 Torr with temperature rise less than 100 K.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.Yr Discharges for spectral sources (including inductively coupled plasma)
52.25.Kn Thermodynamics of plasmas
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Viscoelastic properties of polymer surfaces investigated by nanoscale dynamic mechanical analysis

A. Chakravartula and K. Komvopoulos

Appl. Phys. Lett. 88, 131901 (2006); http://dx.doi.org/10.1063/1.2189156 (3 pages) | Cited 26 times

Online Publication Date: 27 March 2006

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The viscoelastic properties of polymer surfaces were investigated by nanoscale dynamic mechanical analysis (nano-DMA) involving contact force modulation in the frequency range of 10–200 Hz. Nano-DMA experiments were performed with a Berkovich diamond tip of nominal radius of curvature equal to ∼ 100 nm under a mean contact force of 8–10 μN and alternating force equal to 2% of the mean force. Variations in the loss tangent, storage modulus, and loss modulus of low- and high-density polyethylene and ultrahigh molecular weight polyethylene with the force frequency demonstrated significantly different viscoelastic behaviors for shallow depths (<40 nm) than for relatively large depths (i.e., 75–100 nm). The effects of alternating force frequency and indentation depth on the viscoelastic properties of the different polyethylene materials are interpreted in terms of the microstructure characteristics and the molecular chain mobility at the polymer surfaces. The results show that nano-DMA is an effective technique for nanoscale studies of the viscoelastic behavior of polymer surfaces.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.35.Gy Mechanical properties; surface strains
61.41.+e Polymers, elastomers, and plastics
77.22.Gm Dielectric loss and relaxation
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

A 200 nm thick glass-forming metallic film for fatigue-property enhancements

C. L. Chiang, J. P. Chu, F. X. Liu, P. K. Liaw, and R. A. Buchanan

Appl. Phys. Lett. 88, 131902 (2006); http://dx.doi.org/10.1063/1.2189917 (3 pages) | Cited 22 times

Online Publication Date: 27 March 2006

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In this letter, we report the fatigue-property enhancement by a thin layer of glass-forming film. The fatigue life of a 316L stainless steel is considerably improved by at least 30 times, depending on the maximum applied stress when it is coated with a 200 nm thick Zr47Cu31Al13Ni9 film. The application of the sputtered film yields an increase of the fatigue limit by 30%. The smooth surface, good adhesion, and compressive residual stress are found to play beneficial roles in achieving superior fatigue properties, revealing the glass-forming film as a potential material to enhance fatigue properties.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Size reduction of nanoparticle ink patterns by fluid-assisted dewetting

Cedric P. R. Dockendorf, Tae-Youl Choi, Dimos Poulikakos, and Andreas Stemmer

Appl. Phys. Lett. 88, 131903 (2006); http://dx.doi.org/10.1063/1.2187410 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2006

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A novel method is proposed to considerably reduce the size of partially wetting patterns of nanopaticle solutions (nanoinks) on a substrate. A nanoink prepared by suspending gold nanoparticles in toluene was deposited on a glass substrate by writing a thin line with the width of 70 μm. A water droplet of about 100 μl covering the pattern was employed to shrink the pattern by transport of the toluene from the nanoink to the water region triggered by controlled heat addition from the substrate, which increased the solubility of toluene into water (these two liquids are practically immiscible at room temperature). During the dewetting phase, the three-phase-contact line is pulled by the uncompensated Young’s force. The dewetting dynamics is explained by the action of thermocapillarity enhanced by the convection microflow generated in the water layer.
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68.08.Bc Wetting
82.70.Kj Emulsions and suspensions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.75.-g Phase equilibria
47.55.P- Buoyancy-driven flows; convection

Two-way indent depth recovery in a NiTi shape memory alloy

Yijun Zhang, Yang-Tse Cheng, and David S. Grummon

Appl. Phys. Lett. 88, 131904 (2006); http://dx.doi.org/10.1063/1.2189201 (3 pages) | Cited 4 times

Online Publication Date: 28 March 2006

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Controlled reversible changes in surface texture and topography are of interest to many applications, including information storage, optical communication devices, micro-fluidic instruments for drug delivery, and smart tribological surfaces for friction and wear control. Here, we demonstrate a method of inducing two-way reversible changes in an indentation made on the surface of a shape memory NiTi alloy. The two-way indent shape change is accomplished by thermomechanical training of spherical indents in NiTi shape memory alloy. After training, spherical indents exhibit two-way depth recovery: Shallow indent depth at high temperature and deep indent depth at low temperature. The reversible depth change is about 45% of the total indent depth and is stable over many cycles. The reversible depth change can have a wide range of engineering applications.
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81.40.Lm Deformation, plasticity, and creep
68.47.De Metallic surfaces
68.35.Gy Mechanical properties; surface strains
64.70.K- Solid-solid transitions
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Pq Friction, lubrication, and wear

Raman spectroscopy of pressure-induced amorphous boron carbide

X. Q. Yan, W. J. Li, T. Goto, and M. W. Chen

Appl. Phys. Lett. 88, 131905 (2006); http://dx.doi.org/10.1063/1.2189826 (3 pages) | Cited 26 times

Online Publication Date: 28 March 2006

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We report low- and high-temperature Raman spectroscopy of pressure-induced amorphous boron carbide (a-B4C). Coarsening of carbon clusters in a-B4C was characterized during heating, whereas unusual temperature coefficients of a-B4C Raman peak shifts were observed during cooling. These results experimentally evidence that the amorphization of B4C is associated with the destruction of the C–B–C chains and a-B4C is composed of sp2 carbon aromatic rings and boron clusters. This disordered structure with relatively weak carbon sp2 bonds is believed to be responsible for the loss of B4C shear strength at high pressures.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.43.Er Other amorphous solids
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
62.20.-x Mechanical properties of solids

Free volume kinetics during sub-Tg structural relaxation of a bulk Pd40Ni40P20 metallic glass

Osami Haruyama and Akihisa Inoue

Appl. Phys. Lett. 88, 131906 (2006); http://dx.doi.org/10.1063/1.2189833 (2 pages) | Cited 15 times

Online Publication Date: 28 March 2006

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The structural relaxation of bulk Pd40Ni40P20 metallic glass was examined under glass transition region. Assuming the isoconfigurational structural change, the room temperature density was measured after relaxing the bulk sample at 549 K for any given time. The density relaxation was manifested by the process with a spectrum of relaxation times. The data were well described by a stretched exponential function with an average relaxation time of 1389 s and Kohlrausch exponent of 0.66. The relaxation of reduced free volume was impossible to reproduce by means of bimolecular model for flow defect concentration.
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61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Excellent soft-ferromagnetic bulk glassy alloys with high saturation magnetization

Baolong Shen, Masahiro Akiba, and Akihisa Inoue

Appl. Phys. Lett. 88, 131907 (2006); http://dx.doi.org/10.1063/1.2189910 (3 pages) | Cited 29 times

Online Publication Date: 28 March 2006

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The development of Fe-based bulk glassy alloys (BGAs) with high glass-forming ability has become a very hot research topic, not only because of the soft-magnetic properties, but also of the high fracture strength. Here we report the discovery of excellent soft-ferromagnetic BGAs in FeMoPCBSi system, without the expensive element Ga, which can be cast into glassy alloy rods with diameters range up to 4 mm by copper mold casting. These low cost Fe-based ferromagnetic BGAs exhibit high saturation magnetization of 1.27–1.44 T and superhigh initial permeability of 13 400–25 000 at 1 kHz under a field of 1 A/m.
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75.50.Bb Fe and its alloys
81.05.Bx Metals, semimetals, and alloys
81.20.-n Methods of materials synthesis and materials processing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Microstructural refinement mechanism by controlling heating process in multiphase materials with particular reference to γ-TiAl

Hanliang Zhu, K. Maruyama, and J. Matsuda

Appl. Phys. Lett. 88, 131908 (2006); http://dx.doi.org/10.1063/1.2190076 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2006

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The microstructural refinement mechanism by controlling heating rate was investigated in TiAl alloys as an example of multiphase materials. During heating in the α+γ dual phase field of TiAl alloys, the phase transformation of γ to α takes place. The increase in heating rate raises the extent of superheating, leading to increases in driving force and the nucleation rate of the α phase. At higher heating rate, numerous α nuclei form and lengthen, resulting in a fine α2/γ lamellar microstructure after subsequent cooling. The theoretical prediction was demonstrated by the experimental results obtained on a fully lamellar Ti-48Al alloy.
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81.05.Bx Metals, semimetals, and alloys
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
64.70.K- Solid-solid transitions

Fast synthesis method and phase diagram of hydrogen clathrate hydrate

Konstantin A. Lokshin and Yusheng Zhao

Appl. Phys. Lett. 88, 131909 (2006); http://dx.doi.org/10.1063/1.2190273 (3 pages) | Cited 24 times

Online Publication Date: 29 March 2006

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We report a very fast method for hydrogen clathrate production. The formation of hydrogen clathrate from H2 gas and ice-Ih at 77–273 K occurs at least 100 times faster compared to the reaction with water. This effect is probably the result of a partial penetration of hydrogen into the ice-Ih body, which favors clathrate formation. With the ice method, the ice-Ih/48H2*136H2O system can quickly trap and release up to 3.77 mass % of hydrogen, which gives it an advantage over other chemical-bonding hydrogen storage technologies. New data on the hydrogen-water phase diagram are presented and discussed.
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81.30.Dz Phase diagrams of other materials
84.60.-h Direct energy conversion and storage
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