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14 Nov 2011

Volume 99, Issue 20, Articles (20xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 201102 (2011); http://dx.doi.org/10.1063/1.3647979 (3 pages)

Shota Yamada, Bong-Shik Song, Takashi Asano, and Susumu Noda
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Long intersubband relaxation times in n-type germanium quantum wells

Michele Ortolani, Dominik Stehr, Martin Wagner, Manfred Helm, Giovanni Pizzi, Michele Virgilio, Giuseppe Grosso, Giovanni Capellini, and Monica De Seta

Appl. Phys. Lett. 99, 201101 (2011); http://dx.doi.org/10.1063/1.3662394 (3 pages)

Online Publication Date: 14 November 2011

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We measured the non-radiative intersubband relaxation time in n-type modulation-doped Ge/SiGe multi-quantum wells of different thickness by means of degenerate pump-probe experiments. The photon energy was tuned to be resonant with the lowest conduction band intersubband transition energy (14-29 meV), as measured by terahertz absorption spectroscopy and in agreement with band structure calculations. Temperature-independent lifetimes in excess of 30 ps were observed.
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81.07.St Quantum wells
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.63.Hs Quantum wells
78.70.Gq Microwave and radio-frequency interactions
81.05.Cy Elemental semiconductors

Silicon carbide-based photonic crystal nanocavities for ultra-broadband operation from infrared to visible wavelengths

Shota Yamada, Bong-Shik Song, Takashi Asano, and Susumu Noda

Appl. Phys. Lett. 99, 201102 (2011); http://dx.doi.org/10.1063/1.3647979 (3 pages) | Cited 1 time

Online Publication Date: 14 November 2011

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To realize nanophotonic devices that operate in both the infrared and visible wavelength ranges on a single wafer, we investigated the optical characteristics of silicon carbide (SiC)-based photonic crystal nanocavities. By fabricating nanocavities with lattice constants ranging from 150 to 600 nm, we experimentally demonstrated resonant wavelengths of individual cavities ranging from 550 to 1450 nm on a single SiC wafer. Furthermore, this ultra-broadband operation reveals the material dispersion of the thin SiC wafer, which is estimated as nSiC = 2.34 + 9.18 × 104/λ2, over the wide range of aforementioned wavelengths.
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42.79.-e Optical elements, devices, and systems
42.70.Qs Photonic bandgap materials
42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.82.Cr Fabrication techniques; lithography, pattern transfer
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Photonic bandstructure engineering of THz quantum-cascade lasers

A. Benz, M. Brandstetter, C. Deutsch, K. Unterrainer, H. Detz, A. M. Andrews, P. Klang, W. Schrenk, and G. Strasser

Appl. Phys. Lett. 99, 201103 (2011); http://dx.doi.org/10.1063/1.3661168 (3 pages)

Online Publication Date: 14 November 2011

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We present the design and realization of active photonic crystal (PhC) terahertz (THz) lasers operating in higher photonic bands. The structure consists of an array of isolated pillars fabricated from a THz quantum-cascade laser and embedded in a double-metal waveguide. The PhC geometry is adopted to achieve lasing in the first and second photonic bands. Thereby, the optical mode is pushed from the active pillars into the surrounding. The sensitivity of local sensors can be increased by almost one order of magnitude compared to designs operating in the lowest photonic band.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Tv Photonic crystal lasers and coherent effects
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers

Observation of spectral and temporal polarization oscillations of optical pulses in a silicon nanowaveguide

Brian A. Daniel, Jonathan Y. Lee, Philippe M. Fauchet, and Govind P. Agrawal

Appl. Phys. Lett. 99, 201104 (2011); http://dx.doi.org/10.1063/1.3662373 (3 pages)

Online Publication Date: 15 November 2011

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We observe both spectral and temporal oscillations in the polarization state of optical pulses propagating through a silicon nanowaveguide. The spectral oscillations are linear in nature and result from polarization-mode dispersion (PMD). The temporal oscillations are nonlinear in nature, and theoretical simulations clarify that they result from the combined effects of two-photon absorption generated free carriers and PMD.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers

A microsecond-response polymer-stabilized blue phase liquid crystal

Yuan Chen, Jin Yan, Jie Sun, Shin-Tson Wu, Xiao Liang, Shih-Hsien Liu, Pao-Ju Hsieh, Kung-Lung Cheng, and Jyh-Wen Shiu

Appl. Phys. Lett. 99, 201105 (2011); http://dx.doi.org/10.1063/1.3662391 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2011

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A polymer-stabilized blue-phase liquid crystal (BPLC) with microsecond response time is demonstrated using a vertical field switching cell. The measured decay time is 39 μs at room temperature (21 °C) and then decreases to 9.6 μs at 44.3 °C. Such a response time is 1-2 orders of magnitude faster than that of a typical BPLC device. The responsible physical mechanisms are the collective effects of short pitch length, strong polymer network, and low viscosity through temperature effect. The on-state voltage of our BPLC device is 44.2 V, hysteresis is below 0.7%, and contrast ratio is over 1300:1.
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42.79.Kr Display devices, liquid-crystal devices
61.30.Vx Polymer liquid crystals
83.80.Xz Liquid crystals: nematic, cholesteric, smectic, discotic, etc.

Single walled carbon nano-tube, ferroelectric liquid crystal composites: Excellent diffractive tool

A. K. Srivastava, E. P. Pozhidaev, V. G. Chigrinov, and R. Manohar

Appl. Phys. Lett. 99, 201106 (2011); http://dx.doi.org/10.1063/1.3661170 (3 pages) | Cited 2 times

Online Publication Date: 15 November 2011

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We present a switchable grating based on chiral single walled carbon nano-tube (SWCNT) doped ferroelectric liquid crystals (FLCs). The presence of SWCNTs improves the diffraction profile of the pure FLC. The diffraction efficiency, i.e., the ratio of intensities of first order and zero order maxima is more than 100% for the higher concentration of SWCNTs in pure FLC. This phenomenon has been explained by the decrease in ferroelectric domain periodicity, due to the doping of SWCNTs in pure FLC, and optical activity of the chiral SWCNTs. These gratings with very high diffraction efficiency may find application in many devices.
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77.80.Fm Switching phenomena
42.70.Df Liquid crystals
42.79.Dj Gratings
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
77.80.Dj Domain structure; hysteresis

Observing metamaterial induced transparency in individual Fano resonators with broken symmetry

Ranjan Singh, Ibraheem A. I. Al-Naib, Yuping Yang, Dibakar Roy Chowdhury, Wei Cao, Carsten Rockstuhl, Tsuneyuki Ozaki, Roberto Morandotti, and Weili Zhang

Appl. Phys. Lett. 99, 201107 (2011); http://dx.doi.org/10.1063/1.3659494 (3 pages) | Cited 1 time

Online Publication Date: 15 November 2011

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Metamaterial induced transparency is demonstrated using individual split ring resonators with two gaps on opposite side. For the symmetric structure, only a low quality dipolar resonance is witnessed at a normal incidence excited with electric field along the resonator gaps. Displacement of one gap from the centre breaks the symmetry and a higher order mode, inaccessible in the symmetric structure, is excited. Coherent interaction among the modes in the split ring resonator forms an extremely sharp narrowband transparency window centred directly at the dipole resonance. Such metamaterial could facilitate coherent manipulation of terahertz signals for delay, storage, and nonlinear applications.
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42.70.-a Optical materials
42.79.Ci Filters, zone plates, and polarizers
42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Strong modification of the reflection from birefringent layers of semiconductor nanowires by nanoshells

S. L. Diedenhofen, R. E. Algra, E. P. A. M. Bakkers, and Jaime Gómez Rivas

Appl. Phys. Lett. 99, 201108 (2011); http://dx.doi.org/10.1063/1.3662393 (3 pages)

Online Publication Date: 16 November 2011

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The propagation of light in layers of vertically aligned nanowires is determined by their unique and extreme optical properties. Depending on the nanowire filling fraction and their diameter, layers of nanowires form strongly birefringent media. This large birefringence gives rise to sharp angle dependent peaks in polarized reflection. We demonstrate experimentally the tunability of the reflection by adding shells of SiO2 with thicknesses ranging from 10 nm to 30 nm around the nanowires. The strong modification of the reflection peaks renders nanowire layers as a promising candidate for sensing applications.
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78.67.Uh Nanowires
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

In-well pumping of InGaN/GaN vertical-external-cavity surface-emitting lasers

Thomas Wunderer, John E. Northrup, Zhihong Yang, Mark Teepe, André Strittmatter, Noble M. Johnson, Paul Rotella, and Michael Wraback

Appl. Phys. Lett. 99, 201109 (2011); http://dx.doi.org/10.1063/1.3663575 (3 pages)

Online Publication Date: 16 November 2011

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In-well-pumped blue InGaN/GaN vertical-external-cavity surface-emitting lasers are demonstrated. The laser structures were grown on bulk GaN substrates by using metal-organic vapor phase epitaxy near atmospheric pressure. The active zone consisted of up to 20 InGaN quantum wells distributed in a resonant periodic gain configuration. High-reflectivity dielectric distributed Bragg-reflectors were used as mirrors. Laser emission with a single longitudinal mode at 440 nm was achieved by exclusively pumping the quantum wells with the 384 nm emission line of a dye-/N2-laser.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.Bh Lenses, prisms and mirrors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

High-resolution single-mode fiber-optic distributed Raman sensor for absolute temperature measurement using superconducting nanowire single-photon detectors

Michael G. Tanner, Shellee D. Dyer, Burm Baek, Robert H. Hadfield, and Sae Woo Nam

Appl. Phys. Lett. 99, 201110 (2011); http://dx.doi.org/10.1063/1.3656702 (3 pages)

Online Publication Date: 17 November 2011

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We demonstrate a distributed fiber Raman sensor for absolute temperature measurement with spatial resolution on the order of 1 cm at 1550 nm wavelength in a single-mode fiber using superconducting nanowire single-photon detectors. Rapid measurements are shown, with less than 60 s integration period, allowing the demonstration of temperature evolution in an optical fiber recorded at over 100 resolvable, 1.2 cm spaced positions along the fiber simultaneously. This distributed sensor has potential application as a primary reference standard, in which high-accuracy, high-spatial-resolution temperature measurements can be obtained without the need for a separate temperature calibration standard.
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42.81.Pa Sensors, gyros
07.20.Dt Thermometers
85.25.-j Superconducting devices
81.07.Gf Nanowires

Optical and luminescence properties of Co:AgCl0.2Br0.8 crystals and their potential applications as gain media for middle-infrared lasers

I. Zakosky-Neuberger, I. Shafir, L. Nagli, and A. Katzir

Appl. Phys. Lett. 99, 201111 (2011); http://dx.doi.org/10.1063/1.3661171 (3 pages)

Online Publication Date: 18 November 2011

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Infrared absorption and luminescence emission of cobalt doped silver halide crystals were investigated at room temperature and at low temperatures. A broad absorption band was observed in the near-infrared (1.4–2.5 µm) and a broad emission band in the middle-infrared (3.5–5.2 µm). The emission lifetime varied between 1.73 ms at low temperatures and 5 µs at room temperature. Based on the measured parameters and theoretical calculations, we believe that there is an excellent chance that these crystals would lase in the mid-IR. Moreover, it would be possible to extrude fibers from the crystals and obtain mid-IR fiber lasers.
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42.55.Wd Fiber lasers
42.70.-a Optical materials
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Effect of mesh bias on the properties of the lateral conductivity of intrinsic microcrystalline silicon films deposited by low-frequency inductively coupled plasma

W. S. Yan, S. Xu, C. C. Sern, and D. Y. Wei

Appl. Phys. Lett. 99, 201501 (2011); http://dx.doi.org/10.1063/1.3662419 (3 pages)

Online Publication Date: 15 November 2011

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A meshgrid is installed to study the effect of mesh bias on the lateral conductivity properties of intrinsic microcrystalline silicon films deposited by low frequency inductively coupled plasma. When a mesh bias is increased from 0 to −15 V, the dark conductivity remarkably decreases by three orders of magnitude, whereas the ratio of the photo and dark conductivity improves by one order. On contrary, the applied substrate bias has only a marginal effect on the lateral conductivity. It is revealed from the measured electron energy distribution functions that the sheath layer induced ion bombardment is responsible for the drastic change.
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73.61.Cw Elemental semiconductors
81.05.Cy Elemental semiconductors
68.55.ag Semiconductors
52.77.Dq Plasma-based ion implantation and deposition
72.80.Cw Elemental semiconductors
73.50.Pz Photoconduction and photovoltaic effects

Origin of electrical signals for plasma etching endpoint detection

Mark A. Sobolewski

Appl. Phys. Lett. 99, 201502 (2011); http://dx.doi.org/10.1063/1.3662973 (3 pages)

Online Publication Date: 18 November 2011

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Electrical signals are used for endpoint detection in plasma etching, but the origin of the electrical changes observed at endpoint is not known. They may be caused by changes in the gas-phase densities of etch products and reactants or by changes in substrate surface properties such as photoemitted or ion-induced electron yield. To investigate these effects, experiments were performed in an inductively coupled, rf-biased reactor, during CF4/Ar etches of SiO2 films on Si wafers. The rf bias impedance was measured vs. time during etching, simultaneous with Langmuir probe measurements. At endpoint, a decrease in impedance coincided with increases in ion current and electron energy. The data, analyzed by a numerical model of the discharge, indicate that changes in electron emission yield were relatively insignificant or entirely absent. Thus the impedance change is not a surface effect but is, instead, predominantly or entirely a gas-phase phenomenon.
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52.77.Bn Etching and cleaning
52.80.Pi High-frequency and RF discharges
81.65.Cf Surface cleaning, etching, patterning
52.25.Fi Transport properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.Ds Electric and magnetic measurements
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Chirality- and curvature-dependent bending stiffness of single layer graphene

Tinghua Ma, Bin Li, and Tienchong Chang

Appl. Phys. Lett. 99, 201901 (2011); http://dx.doi.org/10.1063/1.3660739 (3 pages)

Online Publication Date: 14 November 2011

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An analytical molecular mechanics model is developed to relate the bending properties of a single layer graphene to its atomic structure. Explicit expression for the bending stiffness of graphene with arbitrary chirality is derived. The results show that the bending stiffness of graphene depends significantly on the chiral angle, especially when the bending curvature is large. Curvature can induce significant anisotropic bending properties of graphene. The present analytical results are helpful for understanding of chirality- and curvature-dependent bending properties of graphene and thus useful for potential applications of graphene as a bending component of nano devices.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Large oscillatory forces generated by interfacial water under lateral modulation between two hydrophilic surfaces

Byung I. Kim, Jared A. Rasmussen, and Edward J. Kim

Appl. Phys. Lett. 99, 201902 (2011); http://dx.doi.org/10.1063/1.3662008 (3 pages)

Online Publication Date: 14 November 2011

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We observed remarkable oscillatory forces with amplitude of 60-90 nN and periodicity of 3–4 water molecule diameters in an ambient environment between two silicon surfaces as the tip-sample distance decreased using the cantilever-based optical interfacial force microscope with lateral modulation. As the humidity increased, the oscillatory forces changed from being large at lower relative humidities, below 40%, to progressively becoming smaller as the humidity went higher than 40%. The frequency of oscillatory forces increased with the existence of lateral tip-modulation and with the slower approaching tip-speed. Its starting point distance has been found to originate from the topographic water structure.
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47.35.-i Hydrodynamic waves
47.80.Jk Flow visualization and imaging
68.08.De Liquid-solid interface structure: measurements and simulations

Influence of the interface on growth rates in AlN/GaN short period superlattices via metal organic vapor phase epitaxy

L. E. Rodak and D. Korakakis

Appl. Phys. Lett. 99, 201903 (2011); http://dx.doi.org/10.1063/1.3658734 (3 pages)

Online Publication Date: 15 November 2011

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AlN/GaN short period superlattices are well suited for a number of applications including, but not limited to, digital alloys, intersubband devices, and emitters. In this work, AlN/GaN superlattices with periodicities ranging from 10 to 20 Å have been grown via metal organic vapor phase epitaxy in order to investigate the influence of the interface on the binary alloy growth rates. The GaN growth rate at the interface was observed to decrease with increasing GaN thickness while the AlN growth rate remained constant. This has been attributed to a decrease in the decomposition rate of GaN at the hetero-interface as seen in other III-V hetero-structures.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.55.ag Semiconductors

Metal-glass nanocomposite for optical storage of information

Andrei Stalmashonak, Amin Abdolvand, and Gerhard Seifert

Appl. Phys. Lett. 99, 201904 (2011); http://dx.doi.org/10.1063/1.3660740 (3 pages)

Online Publication Date: 15 November 2011

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We demonstrate an all-optical data storage and readout technique on a medium that has proved to be stable over centuries—glass containing metallic nanoparticles. Using ultra-short laser pulses to persistently change the shapes of the nanoparticles dependent of the laser polarization, well-defined local dichroism in the focal volume can be produced. The latter could be utilized for multi-bit encoding in spot sizes down to the diffraction limit, where the information can be read out very fast by wavelength- and polarization-sensitive detection of the transmitted light. The storage capacity of the proposed technique is comparable with that of blu-ray discs.
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42.79.Vb Optical storage systems, optical disks
78.20.Fm Birefringence
81.05.uj Diamond/nanocarbon composites
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Photoinduced variable stiffness of spiropyran-based composites

E. Samoylova, L. Ceseracciu, M. Allione, A. Diaspro, A. C. Barone, and A. Athanassiou

Appl. Phys. Lett. 99, 201905 (2011); http://dx.doi.org/10.1063/1.3662401 (3 pages)

Online Publication Date: 16 November 2011

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A quantitative demonstration of reversible stiffness upon appropriate light stimulus in a spiropyran-polymeric composite is presented. The polymeric films containing 3% wt. of the photochromic spiropyran were irradiated with alternating ultraviolet and visible light and the storage modulus was measured. A reversible change in modulus of about 7% was observed. The modulus change was attributed to an interaction of the polar merocyanine with the polymeric chains and/or to a variation of effective free volume induced by merocyanine aggregates formed in the polymer upon ultraviolet irradiation. The effect is fully reversed when the merocyanine isomers turn back to the spiropyran state after visible irradiation.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.40.Me Organic compounds and polymers

Mode separation of a single-frequency bi-modal elastic wave pulse by a phononic crystal

Pyung Sik Ma, Hoe Woong Kim, Joo Hwan Oh, and Yoon Young Kim

Appl. Phys. Lett. 99, 201906 (2011); http://dx.doi.org/10.1063/1.3662446 (3 pages)

Online Publication Date: 16 November 2011

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Multiple wave modes in a signal can be effectively separated by frequency filtering or frequency-based methods as long as the modes propagate at different frequencies. However, they cannot be applied for the separation of multiple modes that propagate at the same frequency. This work shows that two wave modes contained in a single-frequency bi-modal signal can be separated if a specially engineered phononic crystal (PC) is employed. For demonstration, guided elastic wave experiments were performed in a thin aluminum plate in the middle of which a PC is inserted for mode separation.
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62.30.+d Mechanical and elastic waves; vibrations

Direct visualization and characterization of chemical bonding and phase composition of grain boundaries in polycrystalline diamond films by transmission electron microscopy and high resolution electron energy loss spectroscopy

I. Y. Koenka, Y. Kauffmann, and A. Hoffman

Appl. Phys. Lett. 99, 201907 (2011); http://dx.doi.org/10.1063/1.3660582 (3 pages)

Online Publication Date: 16 November 2011

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Polycrystalline diamond films are composed of diamond grains, interconnected by grain boundaries of ill defined nature. In this study we characterized the local phase composition, chemical bonding, and structure of the grain boundaries by electron energy loss spectroscopy (EELS) in the plasmonic and core-level ragimes, using a monochromated and high resolution transmission electron microscope. Peaks at 283.5, 286.3, and 287.5 eV in the C(1s) pre-edge structure provide direct evidence for the preferential presence of amorphous carbon and hydrogen bonding at grain boundaries. Plasmonic EELS reveals a high amorphous carbon component in the grain boundaries region.
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61.72.Mm Grain and twin boundaries
81.05.ug Diamond
68.37.Og High-resolution transmission electron microscopy (HRTEM)
68.55.Nq Composition and phase identification
79.20.Uv Electron energy loss spectroscopy

Resonant x-ray reflectivity study of perovskite oxide superlattices

N. Kemik, M. Gu, F. Yang, C.-Y. Chang, Y. Song, M. Bibee, A. Mehta, M. D. Biegalski, H. M. Christen, N. D. Browning, and Y. Takamura

Appl. Phys. Lett. 99, 201908 (2011); http://dx.doi.org/10.1063/1.3660719 (3 pages)

Online Publication Date: 16 November 2011

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Resonant x-ray reflectivity (XRR) is utilized to characterize the structural properties of La0.7Sr0.3MnO3/La0.7Sr0.3FeO3 superlattices. XRR spectra at the Mn and Fe absorption edges provide additional structural information compared to spectra obtained with a conventional Cu x-ray source. We demonstrate that this technique provides individual layer thicknesses and intermixing behavior of perovskite superlattices with small density contrast in a non-destructive manner. These results are consistent with scanning transmission electron microscopy and electron energy loss spectroscopy.
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68.65.Cd Superlattices

Mechanical properties of rare earth stannate pyrochlores

J. Feng, B. Xiao, Z. X. Qu, R. Zhou, and W. Pan

Appl. Phys. Lett. 99, 201909 (2011); http://dx.doi.org/10.1063/1.3659482 (3 pages)

Online Publication Date: 16 November 2011

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The RE2Sn2O7 series compounds (RE = La, Nb, Sm, Gd, Er, Yb) with a pyrochlore structure are prepared by co-precipitation method. The bulk, shear, Young’s moduli, B/G, and Poisson’s ratios are calculated using density functional theory and also measured by ultrasonic resonance method. The theoretical values of lattice constants and mechanical moduli are smaller than experimental results. The electronic structures of RE2Sn2O7 are analogous to RE2Zr2O7. La2Sn2O7 exhibits stronger ionic bonds than others. The covalent interactions are slightly enhanced in the heavy rare earth stannate pyrochlores. The Vickers harnesses of RE2Sn2O7 are measured experimentally, which are smaller than theoretical predictions.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.de Elastic moduli
62.20.dj Poisson's ratio
62.20.Qp Friction, tribology, and hardness
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Real-time imaging of acoustic rectification

S. Danworaphong, T. A. Kelf, O. Matsuda, M. Tomoda, Y. Tanaka, N. Nishiguchi, O. B. Wright, Y. Nishijima, K. Ueno, S. Juodkazis, and H. Misawa

Appl. Phys. Lett. 99, 201910 (2011); http://dx.doi.org/10.1063/1.3662930 (3 pages)

Online Publication Date: 17 November 2011

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We image gigahertz surface acoustic waves normally incident on a microscopic linear array of triangular holes—a generic “acoustic diode” geometry—with a real-time ultrafast optical technique. Spatiotemporal Fourier transforms reveal wave diffraction orders in k-space. Squared amplitude reflection and transmission coefficients for incidence on both sides of the array are evaluated and compared with numerical simulations. We thereby directly demonstrate acoustic rectification with an asymmetric structure.
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68.35.Iv Acoustical properties
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Combined visible light photo-emission and low temperature thermionic emission from nitrogen doped diamond films

Tianyin Sun, Franz A. M. Koeck, Chiyu Zhu, and Robert J. Nemanich

Appl. Phys. Lett. 99, 202101 (2011); http://dx.doi.org/10.1063/1.3658638 (3 pages)

Online Publication Date: 14 November 2011

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This study reports a photoemission threshold of ∼1.5 eV from nitrogen-doped nanocrystalline diamond, which ranks among the lowest photo-threshold of any non-cesiated material. Diamond films on molybdenum substrates have been illuminated with light from 340 to 550 nm, and the electron emission spectrum has been recorded from ambient to ∼320 °C. The results display combined thermionic and photo-electron emission limited by the same low work function and indicate that the two emission processes are spatially separated. These results indicate the potential for a solar energy conversion structure that takes advantage of both photoemission and thermionic emission.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
79.40.+z Thermionic emission

Ion implantation synthesized copper oxide-based resistive memory devices

S. M. Bishop, H. Bakhru, S. W. Novak, B. D. Briggs, R. J. Matyi, and N. C. Cady

Appl. Phys. Lett. 99, 202102 (2011); http://dx.doi.org/10.1063/1.3662036 (3 pages)

Online Publication Date: 14 November 2011

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Copper oxide resistive memory layers have been synthesized by ion implantation. Devices fabricated from off-stoichiometric Cu2O exhibited unipolar switching in forward/reverse bias without a forming voltage. The on-state conduction of these devices is likely dominated by a metallic filament, which ruptures via Joule heating to transition the device to the high resistance off-state. Technology scaling was achieved by oxygen implanting copper filled vias. The resulting via-based memory devices exhibited unipolar resistive switching down to 48 nm in diameter.
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84.30.Sk Pulse and digital circuits
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