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12 Jul 2010

Volume 97, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 023701 (2010); http://dx.doi.org/10.1063/1.3462979 (3 pages)

Pablo Dörig, Philipp Stiefel, Pascal Behr, Edin Sarajlic, Daniel Bijl, Michael Gabi, János Vörös, Julia A. Vorholt, and Tomaso Zambelli
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100 W peak-power 1 GHz repetition picoseconds optical pulse generation using blue-violet GaInN diode laser mode-locked oscillator and optical amplifier

Rintaro Koda, Tomoyuki Oki, Takao Miyajima, Hideki Watanabe, Masaru Kuramoto, Masao Ikeda, and Hiroyuki Yokoyama

Appl. Phys. Lett. 97, 021101 (2010); http://dx.doi.org/10.1063/1.3462942 (3 pages) | Cited 14 times

Online Publication Date: 12 July 2010

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We have generated single-transverse-mode optical pulses with 100 W peak power and 3 ps duration at 1 GHz repetition from a blue-violet GaInN mode-locked laser diode (MLLD) and a semiconductor optical amplifier (SOA) without the use of any pulse compression. The generation of clean optical pulses without subpulse components from the MLLD and the reduction in amplified spontaneous emission in the SOA by incorporating a flare waveguide structure resulted in effective amplification of optical pulses to produce over 100 W peak power.
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42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.Fc Modulation, tuning, and mode locking
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Antiguiding factor of GaN-based laser diodes from UV to green

W. G. Scheibenzuber, U. T. Schwarz, T. Lermer, S. Lutgen, and U. Strauss

Appl. Phys. Lett. 97, 021102 (2010); http://dx.doi.org/10.1063/1.3464172 (3 pages) | Cited 7 times

Online Publication Date: 13 July 2010

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We measure the antiguiding factor of (Al,In)GaN laser diodes emitting in the violet, blue and green spectral range by combining optical gain-spectroscopy with measurements of the charge-carrier induced refractive index change. A precise determination of the thermal resistance of the laser diodes allows us to keep the temperature of the active region constant during the whole measurement and thus to exclude any thermal effect on the refractive index. For laser diodes emitting in the range from 409 to 511 nm, the antiguiding factor at the laser wavelength is 4.1±0.5.
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42.55.Px Semiconductor lasers; laser diodes

Experimental study of Brillouin scattering in perfluorinated polymer optical fiber at telecommunication wavelength

Yosuke Mizuno and Kentaro Nakamura

Appl. Phys. Lett. 97, 021103 (2010); http://dx.doi.org/10.1063/1.3463038 (3 pages) | Cited 12 times

Online Publication Date: 13 July 2010

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Brillouin scattering properties in a perfluorinated graded-index polymer optical fiber (POF) with 120 μm core diameter were experimentally investigated using a laser with an operating wavelength of 1.55 μm. The Brillouin frequency shift and the Brillouin bandwidth were 2.83 GHz and 105 MHz, respectively. The calculated Brillouin gain coefficient of 3.09×10−11 m/W was comparable to that of fused silica fibers. The Brillouin threshold power of the 100 m POF was estimated to be 24 W, which we believe can be reduced by employing POFs with smaller cores.
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42.81.Ht Gradient-index (GRIN) fiber devices
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Four level, atomic Cs laser at 852.1 nm with a quantum efficiency above 98%: Observation of three body photoassociation

J. D. Readle, J. G. Eden, J. T. Verdeyen, and D. L. Carroll

Appl. Phys. Lett. 97, 021104 (2010); http://dx.doi.org/10.1063/1.3452338 (3 pages) | Cited 7 times

Online Publication Date: 14 July 2010

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Lasing on the D2 (6p 2P3/2→6s 2S1/2) transition of atomic Cs at 852.1 nm has been observed with a four level system in which the Cs 6p 2P3/2 state is pumped by the photoassociation and subsequent dissociation of Cs-rare gas collision pairs. Characterized by a quantum efficiency >98%, this laser requires no atomic precursor to the upper laser level and provides oscillation on an alkali transition inaccessible to three level, photopumped alkali laser systems. Measurements of photoabsorption and pump energy threshold in Cs–Ar–Kr mixtures reveal the influence of three body photoassociation.
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03.75.Pp Atom lasers
42.50.-p Quantum optics

Ultrabroadband terahertz generation using 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate single crystals

I. Katayama, R. Akai, M. Bito, H. Shimosato, K. Miyamoto, H. Ito, and M. Ashida

Appl. Phys. Lett. 97, 021105 (2010); http://dx.doi.org/10.1063/1.3463452 (3 pages) | Cited 5 times

Online Publication Date: 14 July 2010

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Ultrabroadband terahertz generation up to 200 THz has been demonstrated using a 5 fs Ti:sapphire laser and a 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) crystal. The high-frequency components beyond 100 THz are much stronger than those generated using conventional electro-optic crystals such as GaSe. A simple simulation of the difference frequency generation in the DAST crystal by considering the refractive index dispersion can reproduce the broadband generation of the terahertz wave and its chirp dependence. Because the generated terahertz wave is coherent and has a broad bandwidth, it can serve as a suitable light source for ultrabroadband terahertz time-domain spectroscopy of a material.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.70.Jk Polymers and organics

Complete spectral gap in coupled dielectric waveguides embedded into metal

Wei Liu, Andrey A. Sukhorukov, Andrey E. Miroshnichenko, Chris G. Poulton, Zhiyong Xu, Dragomir N. Neshev, and Yuri S. Kivshar

Appl. Phys. Lett. 97, 021106 (2010); http://dx.doi.org/10.1063/1.3458694 (3 pages) | Cited 1 time

Online Publication Date: 14 July 2010

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We study a plasmonic coupler involving backward (TM01) and forward (HE11) modes of dielectric waveguides embedded into an infinite metallic background. The simultaneously achievable contradirectional energy flows and codirectional phase velocities in different channels lead to a spectral gap, despite the absence of periodic structures along the waveguide. We demonstrate that a complete spectral gap can be achieved in a symmetric structure composed of four coupled waveguides.
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42.79.Gn Optical waveguides and couplers
78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

A scanning microcavity for in situ control of single-molecule emission

C. Toninelli, Y. Delley, T. Stöferle, A. Renn, S. Götzinger, and V. Sandoghdar

Appl. Phys. Lett. 97, 021107 (2010); http://dx.doi.org/10.1063/1.3456559 (3 pages) | Cited 4 times

Online Publication Date: 14 July 2010

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We report on the fabrication and characterization of a scannable Fabry–Perot microcavity, consisting of a curved micromirror at the end of an optical fiber and a planar distributed Bragg reflector. Furthermore, we demonstrate the coupling of single organic molecules embedded in a thin film to well-defined resonator modes. We discuss the choice of cavity parameters that will allow sufficiently high Purcell factors for enhancing the zero-phonon transition between the vibrational ground levels of the electronic excited and ground states.
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42.82.Gw Other integrated-optical elements and systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.79.Bh Lenses, prisms and mirrors

Production of ozone and nitrogen oxides by laser filamentation

Yannick Petit, Stefano Henin, Jérôme Kasparian, and Jean-Pierre Wolf

Appl. Phys. Lett. 97, 021108 (2010); http://dx.doi.org/10.1063/1.3462937 (3 pages) | Cited 8 times

Online Publication Date: 15 July 2010

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We have experimentally measured that laser filaments in air generate up to 1014, 3×1012, and 3×1013 molecules of O3, NO, and NO2, respectively. The corresponding local concentrations in the filament active volume are 1016, 3×1014, and 3×1015 cm−3, and allows efficient oxidative chemistry of nitrogen, resulting in concentrations of HNO3 in the parts per million range. The latter forming binary clusters with water, our results provide a plausible pathway for the efficient nucleation recently observed in laser filaments.
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82.50.-m Photochemistry
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Three-dimensional microfluidic liquid-core/liquid-cladding waveguide

Kang Soo Lee, Sang Bok Kim, Kyung Heon Lee, Hyung Jin Sung, and Sang Soo Kim

Appl. Phys. Lett. 97, 021109 (2010); http://dx.doi.org/10.1063/1.3460279 (3 pages) | Cited 3 times

Online Publication Date: 15 July 2010

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This letter describes a three-dimensional liquid-core/liquid-cladding optical waveguide system. The core fluid was focused in the vertical direction by a transverse secondary flow (produced by a Dean vortex) and focused in the horizontal direction by two parallel sheath flows. The waveguide introduced less optical loss between the core fluid and the channel wall. Diffusion between the core fluid and the cladding fluid was reduced by high fluid velocities. The present system can be considered as a graded-index waveguide due to the diffusion effect. The width of the core fluid was manipulated by adjusting the sheath flow rates. Numerical simulations were conducted to support and interpret the experimental results.
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42.79.Gn Optical waveguides and couplers
42.79.Ry Gradient-index (GRIN) devices
42.82.Et Waveguides, couplers, and arrays
47.85.Np Fluidics
47.61.-k Micro- and nano- scale flow phenomena

Physical limits of semiconductor laser operation: A time-resolved analysis of catastrophic optical damage

Mathias Ziegler, Martin Hempel, Henning E. Larsen, Jens W. Tomm, Peter E. Andersen, Sønnik Clausen, Stella N. Elliott, and Thomas Elsaesser

Appl. Phys. Lett. 97, 021110 (2010); http://dx.doi.org/10.1063/1.3463039 (3 pages) | Cited 6 times

Online Publication Date: 15 July 2010

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The early stages of catastrophic optical damage (COD) in 808 nm emitting diode lasers are mapped by simultaneously monitoring the optical emission with a 1 ns time resolution and deriving the device temperature from thermal images. COD occurs in highly localized damage regions on a 30 to 400 ns time scale which is determined by the accumulation of excess energy absorbed from the optical output. We identify regimes in which COD is avoided by the proper choice of operation parameters.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Terahertz metamaterials with VO2 cut-wires for thermal tunability

Qi-Ye Wen, Huai-Wu Zhang, Qing-Hui Yang, Yun-Song Xie, Kang Chen, and Ying-Li Liu

Appl. Phys. Lett. 97, 021111 (2010); http://dx.doi.org/10.1063/1.3463466 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2010

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An active terahertz (THz) metamaterial with vanadium dioxide (VO2) cut-wire resonators fabricated on glass substrate was proposed, and THz time-domain spectroscopy was used to probe the temperature-tuned electromagnetic properties. By thermal-triggering the insulator-metal phase transition of VO2, THz transmission signals through the metamaterial exhibit a significant decline with amplitude over 65%. Numerical simulations confirm the observations are due to the metallization of the VO2 film with increasing temperature.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.70.Gq Microwave and radio-frequency interactions
71.30.+h Metal-insulator transitions and other electronic transitions

Light direction-dependent plasmonic enhancement in quantum dot infrared photodetectors

S. C. Lee, S. Krishna, and S. R. J. Brueck

Appl. Phys. Lett. 97, 021112 (2010); http://dx.doi.org/10.1063/1.3454776 (3 pages) | Cited 3 times

Online Publication Date: 16 July 2010

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Plasmonic enhancement of a quantum dot infrared photodetector (QDIP) integrated with a metal photonic crystal (MPC) depends on the direction of the incident light, air-side versus substrate-side illumination. Compared with air-side illumination, substrate-side illumination on the same photodetector results in more than 2× enhancement in detectivity. This is explained by more efficient excitation of surface plasma waves (SPWs) at the MPC/QDIP interface in the back-side geometry. The air/MPC/semiconductor structure is optically asymmetric and has different SPW coupling leading to higher photoresponse for substrate-side illumination. This agrees with simulation and provides direct evidence that the detectivity enhancement is due to the coupling to SPWs and is crucially affected by light incident direction.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.70.Qs Photonic bandgap materials

Enhancement of the conversion efficiency of GaN-based photovoltaic devices with AlGaN/InGaN absorption layers

C. C. Yang, J. K. Sheu, Xin-Wei Liang, Min-Shun Huang, M. L. Lee, K. H. Chang, S. J. Tu, Feng-Wen Huang, and W. C. Lai

Appl. Phys. Lett. 97, 021113 (2010); http://dx.doi.org/10.1063/1.3463469 (3 pages) | Cited 1 time

Online Publication Date: 16 July 2010

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InGaN/sapphire-based p-i-n type photovoltaic (PV) devices were shown to have Al0.14Ga0.86N/In0.21Ga0.79N heterostructures that enhance the extraction of photogenerated carriers from active layers. With an appropriately increased barrier height in AlGaN/InGaN absorption layers, PV devices exhibit lower RS despite the increase in conduction-band discontinuity compared with GaN/InGaN superlattice absorption layers. This improvement can be attributed to polarization-induced electric fields enhanced by the incorporated aluminum in barrier layers. The enhancement is beneficial to increase built-in electric fields. Subsequently, the photogenerated carriers can escape more easily from recombination or scattering centers. Under 1 sun air-mass 1.5 standard testing conditions, the Al0.14Ga0.86N/In0.21Ga0.79N PV device exhibits high VOC (2.10 V) as well as an enhanced fill factor (0.66) and JSC (0.84 mA/cm2) corresponding to a power conversion efficiency of 1.16%.
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84.60.Jt Photoelectric conversion
85.30.De Semiconductor-device characterization, design, and modeling

Photocurrent spectra of heavily doped terahertz quantum well photodetectors

X. G. Guo, R. Zhang, H. C. Liu, A. J. SpringThorpe, and J. C. Cao

Appl. Phys. Lett. 97, 021114 (2010); http://dx.doi.org/10.1063/1.3458829 (3 pages) | Cited 1 time

Online Publication Date: 16 July 2010

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Terahertz (THz) quantum well photodetectors (QWPs) are an important candidate for THz imaging and THz free space communication. Low absorption efficiency of THz QWPs is the main factor limiting the performance of this kind of THz detectors. To increase the absorption efficiency, three heavily doped THz QWPs were fabricated. The band structure calculations show that the second subband falls into the quantum well with increasing Si doping concentration, which decreases the escape probability of the photon-excited electrons in the second subband. This effect is responsible for the blueshift and broadening of the photocurrent peak with increasing Si doping.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
72.40.+w Photoconduction and photovoltaic effects
61.72.U- Doping and impurity implantation
84.40.-x Radiowave and microwave (including millimeter wave) technology
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Energetics of local clusters in Cu64.5Zr35.5 metallic liquid and glass

S. Q. Wu, C. Z. Wang, S. G. Hao, Z. Z. Zhu, and K. M. Ho

Appl. Phys. Lett. 97, 021901 (2010); http://dx.doi.org/10.1063/1.3464164 (3 pages) | Cited 12 times

Online Publication Date: 12 July 2010

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Correlation between the cluster energy and its population and dynamics can provide a better understanding of the complicated energy landscape of disordered metallic systems. We propose a method to analyze the cluster energy distribution for different kinds of short-range order (local clusters) in liquid and glass systems. By applying this analysis to an interesting and important glass forming system—Cu64.5Zr35.5 we observe a direct correlation between the energy and dynamics of the cluster in this realistic glass-forming system. This study suggests that dynamic arrest originates from the environment-dependent energetics of local clusters.
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61.25.Mv Liquid metals and alloys
61.20.Ja Computer simulation of liquid structure
61.43.Fs Glasses
64.70.pe Metallic glasses

Contactless electroreflectance study of band bending in Be-doped GaInNAs/GaAs quantum wells: The origin of photoluminescence enhancement

R. Kudrawiec, M. Gladysiewicz, J. Misiewicz, V.-M. Korpijärvi, J. Pakarinen, J. Puustinen, P. Laukkanen, A. Laakso, M. Guina, M. Dumitrescu, and M. Pessa

Appl. Phys. Lett. 97, 021902 (2010); http://dx.doi.org/10.1063/1.3462299 (3 pages) | Cited 1 time

Online Publication Date: 12 July 2010

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Contactless electroreflectance (CER) has been applied to study band bending in Be-doped GaInNAs/GaAs quantum wells (QWs). It has been shown that (i) the sign of GaAs-related CER signal changes from positive to negative due to Be-doping and (ii) QW-related CER resonances disappear for Be-doped QWs whereas they are clearly observed for un-doped QWs. The two observations indicate a Be-related shift in the Fermi level above the hole levels in the QW region, i.e., the change in band bending in this system. The results point out that the experimentally-observed enhancement in QW photoluminescence upon Be-doping is associated with a better collection/confinement of photogenerated carriers by the Be-doped GaInNAs QW.
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78.20.Jq Electro-optical effects
78.55.Cr III-V semiconductors
73.21.Fg Quantum wells
71.55.Eq III-V semiconductors
61.72.uj III-V and II-VI semiconductors
78.67.De Quantum wells

Experimental determination of the principal dielectric functions in silver nanowire metamaterials

Jyotirmayee Kanungo and Joerg Schilling

Appl. Phys. Lett. 97, 021903 (2010); http://dx.doi.org/10.1063/1.3462311 (3 pages) | Cited 7 times

Online Publication Date: 12 July 2010

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The polarization dependent optical properties of silver nanowire arrays are investigated by angular resolved transmission measurements. The corresponding spectra show clear Fabry–Perot oscillations, which exhibit an unusual shift toward longer wavelengths for the extraordinary waves. From the peak shift both principal dielectric functions of the metamaterial are determined and compared with effective medium theories. Their different signs lead to a hyperbolic wave vector surface for the extraordinary waves and cause the observed peculiar peak shift.
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77.22.Ch Permittivity (dielectric function)
78.67.Uh Nanowires
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.-a Optical materials
77.22.Ej Polarization and depolarization

Photoluminescence emission in deep ultraviolet region from GaN/AlN asymmetric-coupled quantum wells

Guan Sun, Yujie J. Ding, Guangyu Liu, G. S. Huang, Hongping Zhao, Nelson Tansu, and Jacob B. Khurgin

Appl. Phys. Lett. 97, 021904 (2010); http://dx.doi.org/10.1063/1.3462324 (3 pages) | Cited 4 times

Online Publication Date: 12 July 2010

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We have investigated the photoluminescence spectra from GaN/AlN asymmetric-coupled quantum wells grown by metal-organic chemical vapor deposition. Deep ultraviolet photoluminescence peaks with photon energies up to 5.061 eV and dramatically improved intensities at low temperatures are identified due to recombination of electrons in the AlN coupling barrier with heavy holes in the GaN quantum wells. Photoluminescence quenching caused by relocation of photogenerated electrons under large internal electric fields, inherent in GaN/AlN asymmetric-coupled quantum wells, is observed.
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81.07.St Quantum wells
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.67.De Quantum wells
78.55.Cr III-V semiconductors

Determination of band gap energy (Eg) of Cu2ZnSnSe4 thin films: On the discrepancies of reported band gap values

SeJin Ahn, Sunghun Jung, Jihye Gwak, Ara Cho, Keeshik Shin, Kyunghoon Yoon, Doyoung Park, Hyeonsik Cheong, and Jae Ho Yun

Appl. Phys. Lett. 97, 021905 (2010); http://dx.doi.org/10.1063/1.3457172 (3 pages) | Cited 43 times

Online Publication Date: 13 July 2010

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We demonstrate experimental data to elucidate the reason for the discrepancies of reported band gap energy (Eg) of Cu2ZnSnSe4 (CZTSe) thin films, i.e., 1.0 or 1.5 eV. Eg of the coevaporated CZTSe film synthesized at substrate temperature (Tsub) of 370 °C, which was apparently phase pure CZTSe confirmed by x-ray diffraction (XRD) and Raman spectroscopy, is found to be around 1 eV regardless of the measurement techniques. However, depth profile of the same sample reveals the formation of ZnSe at CZTSe/Mo interface. On the other hand, Eg of the coevaporated films increases with Tsub due to the ZnSe formation, from which we suggest that the existence of ZnSe, which is hardly distinguishable from CZTSe by XRD, is the possible reason for the overestimation of overall Eg.
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73.61.Le Other inorganic semiconductors
68.43.Mn Adsorption kinetics

Gigantic transverse voltage induced via off-diagonal thermoelectric effect in CaxCoO2 thin films

Kouhei Takahashi, Tsutomu Kanno, Akihiro Sakai, Hideaki Adachi, and Yuka Yamada

Appl. Phys. Lett. 97, 021906 (2010); http://dx.doi.org/10.1063/1.3464286 (3 pages) | Cited 8 times

Online Publication Date: 13 July 2010

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Gigantic transverse voltages exceeding several tens volt have been observed in CaxCoO2 thin films with tilted c-axis orientation upon illumination of nanosecond laser pulses. The voltage signals were highly anisotropic within the film surface showing close relation with the c-axis tilt direction. The magnitude and the decay time of the voltage strongly depended on the film thickness. These results confirm that the large laser-induced voltage originates from a phenomenon termed the off-diagonal thermoelectric effect, by which a film out-of-plane temperature gradient leads to generation of a film in-plane voltage.
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73.61.Ng Insulators
73.50.Lw Thermoelectric effects
42.62.-b Laser applications
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

The noise of the needle: Avalanches of a single progressing needle domain in LaAlO3

Richard J. Harrison and Ekhard K. H. Salje

Appl. Phys. Lett. 97, 021907 (2010); http://dx.doi.org/10.1063/1.3460170 (3 pages) | Cited 12 times

Online Publication Date: 13 July 2010

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The propagation of a single ferroelastic needle domain under weak elastic stress consists of two parts: a continuous front propagation and jerky avalanches. Optical observation and themodynamic analysis show that the continuous behavior is thermally activated. The avalanches follow power law behavior with an energy exponent ε = −1.8±0.2 in agreement with self-similar avalanches close to the depinning threshold. Our experiments on ferroelastic LaAlO3 exclude nucleation of secondary domains, so that the observed behavior is related exclusively to the statistical behavior of one single needle domain.
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62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Phase diagram and composition optimization for magnetic shape memory effect in Ni–Co–Mn–Sn alloys

D. Y. Cong, S. Roth, M. Pötschke, C. Hürrich, and L. Schultz

Appl. Phys. Lett. 97, 021908 (2010); http://dx.doi.org/10.1063/1.3454239 (3 pages) | Cited 4 times

Online Publication Date: 13 July 2010

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The composition dependent phase transformation and magnetic properties of the Ni50−xCoxMn39Sn11 (0 ≤ x ≤ 10) alloys were systematically investigated. Based on the obtained results, the phase diagram of this alloy system was established. Considering the combination of large magnetization difference across phase transformation ΔM and small transformation entropy change ΔS, the optimal composition range of 5 ≤ x ≤ 8 for magnetic-field-induced phase transformation (MFIPT) and consequently magnetic shape memory effect was figured out. Furthermore, the decrease in martensitic transformation temperatures by magnetic fields and almost fully reversible MFIPT from martensite to austenite were confirmed in the alloys within this composition range.
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81.30.Kf Martensitic transformations
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
65.40.gd Entropy
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
64.70.kd Metals and alloys

Mechanism for shear banding in nanolayered composites

N. A. Mara, D. Bhattacharyya, J. P. Hirth, P. Dickerson, and A. Misra

Appl. Phys. Lett. 97, 021909 (2010); http://dx.doi.org/10.1063/1.3458000 (3 pages) | Cited 25 times

Online Publication Date: 13 July 2010

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Recent studies have shown that two-phase nanocomposite materials with semicoherent interfaces exhibit enhanced strength, deformability, and radiation damage resistance. The remarkable behavior exhibited by these materials has been attributed to the atomistic structure of the bimetal interface that results in interfaces with low shear strength and hence, strong barriers for slip transmission due to dislocation core spreading along the weak interfaces. In this work, the low interfacial shear strength of Cu/Nb nanoscale multilayers dictates a new mechanism for shear banding and strain softening during micropillar compression. Our findings, supported by molecular dynamics simulations, provide insight on the design of nanocomposites with tailored interface structures and geometry to obtain a combination of high strength and deformability. High strength is derived from the ability of the interfaces to trap dislocations through relative ease of interfacial shear, while deformability can be maximized by controlling the effects of loading geometry on shear band formation.
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68.65.Ac Multilayers
61.46.-w Structure of nanoscale materials
62.20.F- Deformation and plasticity
62.25.-g Mechanical properties of nanoscale systems
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Strongly enhanced incorporation of oxygen into barium titanate based multilayer ceramic capacitors using water vapor

M. Kessel, R. A. De Souza, H.-I. Yoo, and M. Martin

Appl. Phys. Lett. 97, 021910 (2010); http://dx.doi.org/10.1063/1.3460156 (3 pages) | Cited 2 times

Online Publication Date: 14 July 2010

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The reoxidation of sintered BaTiO3-based multilayer ceramic capacitors (MLCCs) is currently an empirically determined, but poorly understood, procedure. In this work, the incorporation of oxygen into BaTiO3-based MLCCs has been studied by means of isotope exchange annealing (18O2/16O2, 1H218O/1H216O or 2H216O/1H216O) and subsequent determination of the isotope profiles in the solid by secondary ion mass spectrometry. Oxygen isotope profiles in the barium titanate dielectric can be described by a bulk diffusion coefficient D∗ and a surface exchange coefficient k∗. The values obtained for k∗ indicate that oxygen incorporation from H2O is much faster than from dry O2; it thus plays the key role in the reoxidation process.
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84.32.Tt Capacitors
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
81.40.Gh Other heat and thermomechanical treatments

Graphene strain tuning by control of the substrate surface chemistry

M. Bruna, A. Vaira, A. Battiato, E. Vittone, and S. Borini

Appl. Phys. Lett. 97, 021911 (2010); http://dx.doi.org/10.1063/1.3463460 (3 pages) | Cited 3 times

Online Publication Date: 15 July 2010

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We show that the Raman spectrum of graphene is sensitive to the surface chemistry of the substrate where the atomic plane is deposited. Two types of functionalized SiO2 surface are experimentally compared: OH-terminated and NH2-terminated. In the case of NH2-terminated surface, the graphene Raman bands are significantly redshifted with respect to the peaks observed on the hydroxylated surface. The observed phonon softening can be ascribed to a biaxial strain induced into graphene by its interaction with the substrate. Therefore, the control of the substrate surface chemistry may be envisaged as a route to graphene strain engineering.
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78.67.Wj Optical properties of graphene
78.30.Na Fullerenes and related materials
62.25.-g Mechanical properties of nanoscale systems
63.22.Rc Phonons in graphene
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
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