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6 Aug 2012

Volume 101, Issue 6, Articles (06xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 062401 (2012); http://dx.doi.org/10.1063/1.4730997 (4 pages)

Mahdi Jamali, Kulothungasagaran Narayanapillai, Jae Hyun Kwon, and Hyunsoo Yang
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Highly compliant transparent electrodes

Samuel Shian, Roger M. Diebold, Alena McNamara, and David R. Clarke

Appl. Phys. Lett. 101, 061101 (2012); http://dx.doi.org/10.1063/1.4742889 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Adaptive optical devices based on electric field induced deformation of dielectric elastomers require transparent and highly compliant electrodes to conform to large shape changes. Electrical, optical, and actuation properties of acrylic elastomer electrodes fabricated with single-walled carbon nanotubes (SWCNTs) and silver nanowires (AgNWs) have been evaluated. Based on these properties, a figure of merit is introduced for evaluating the overall performance of deformable transparent electrodes. This clearly indicates that SWCNTs outperform AgNWs. Under optimal conditions, optical transparency as high as 91% at 190% maximum actuation strain is readily achievable using SWCNT electrodes.
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68.55.at Other materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.16.-c Methods of micro- and nanofabrication and processing

Partially sandwiched graphene as transparent conductive layer for InGaN-based vertical light emitting diodes

Liancheng Wang, Yiyun Zhang, Xiao Li, Zhiqiang Liu, Enqing Guo, Xiaoyan Yi, Junxi Wang, Hongwei Zhu, and Guohong Wang

Appl. Phys. Lett. 101, 061102 (2012); http://dx.doi.org/10.1063/1.4742892 (4 pages) | Cited 3 times

Online Publication Date: 6 August 2012

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InGaN-based vertical structure light emitting diodes (VLEDs) with multi-layer graphene transparent electrodes with higher optical output have been fabricated and tested. High temperature annealing introduced inter-diffusion of metal atoms and Ga atoms and generated the partially sandwiched graphene structure, which contributed to the performance improvement of VLEDs.
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85.60.Jb Light-emitting devices

Polarized light emission from GaInN light-emitting diodes embedded with subwavelength aluminum wire-grid polarizers

Ming Ma, David S. Meyaard, Qifeng Shan, Jaehee Cho, E. Fred Schubert, Gi Bum Kim, Min-Ho Kim, and Cheolsoo Sone

Appl. Phys. Lett. 101, 061103 (2012); http://dx.doi.org/10.1063/1.4744422 (4 pages)

Online Publication Date: 6 August 2012

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We demonstrate a back-emitting (sapphire-substrate emitting) linearly polarized GaInN light-emitting diode (LED) embedded with a subwavelength-sized aluminum wire-grid polarizer (WGP). Rigorous coupled wave analysis is implemented to study the polarization characteristics of such a WGP LED. The aluminum nanowire grating with a period of 150 nm is located on the sapphire backside of a GaInN LED structure and is fabricated by electron-beam lithography and inductively coupled plasma reactive-ion etching. A polarization ratio of 0.96 is demonstrated for a WGP GaInN LED in good agreement with simulation results.
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85.60.Jb Light-emitting devices
42.79.Ci Filters, zone plates, and polarizers
42.82.Cr Fabrication techniques; lithography, pattern transfer
81.65.Cf Surface cleaning, etching, patterning

Mid-infrared distributed-feedback interband cascade lasers with continuous-wave single-mode emission to 80 °C

C. S. Kim, M. Kim, J. Abell, W. W. Bewley, C. D. Merritt, C. L. Canedy, I. Vurgaftman, and J. R. Meyer

Appl. Phys. Lett. 101, 061104 (2012); http://dx.doi.org/10.1063/1.4744445 (3 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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We report continuous-wave (cw) distributed-feedback interband cascade lasers operating in a single spectral mode (λ = 3.7–3.8 μm) at temperatures between 20 and 80 °C. The first-order gratings were realized by patterning high-index germanium layers on top of narrow ridges with relatively thin top claddings. One device generated over 27 mW of cw single-mode output at 40 °C, with a side-mode-suppression ratio >30 dB, while at 80 °C it still emitted >1 mW. At 20 °C, a second device lased in a single spectral mode with <100 mW of drive power. The tuning range was 21.5 nm with temperature and 10 nm with current.
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42.55.-f Lasers

Scattering performance of plasmonic nanorod antennas in randomly tilted disordered and Fibonacci configurations

A. Rashidi and H. Mosallaei

Appl. Phys. Lett. 101, 061105 (2012); http://dx.doi.org/10.1063/1.4738984 (3 pages)

Online Publication Date: 8 August 2012

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In this letter, we formulate and investigate the optical performance of finite arrays of plasmonic nanorod antennas in randomly tilted disordered and Fibonacci configurations. To efficiently model the scattering performance of a nanorod, we take advantage of characteristic basis function method in conjunction with macro basis functions. We study how random rotations of the nanorods, as a disorder, may affect their electromagnetic response. Also, the impact of quasi-periodic order on the performance of the array in the form of two-dimensional Fibonacci quasi-lattice comprising of plasmonic nanorods with two different lengths is studied.
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84.40.Ba Antennas: theory, components and accessories

High-resolution monitoring of wavelength shifts utilizing strong spatial dispersion of guided modes

Yi Wang (王毅), Xiaoguo Jiang (江孝国), Qin Li (李勤), Yuan Wang (王远), and Zhuangqi Cao (曹庄琪)

Appl. Phys. Lett. 101, 061106 (2012); http://dx.doi.org/10.1063/1.4740258 (4 pages)

Online Publication Date: 8 August 2012

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A prism-coupled metal-dielectric-metal waveguide structure is presented to detect slight variations in wavelength. Strong spatial dispersion ability is exhibited at the guided-mode resonance, which leads to a rapid changing of the reflected beam shift with respect to the light wavelength. It is demonstrated to be an effective way to enlarge the lateral shift of the reflected beam by increasing the guiding layer thickness, which helps to improve the sensitivity of the wavelength-shift monitoring. A wavelength resolution as high as 0.027 pm is achieved in the experiment.
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42.79.Gn Optical waveguides and couplers
42.79.Bh Lenses, prisms and mirrors

Unidirectional launching of surface plasmons with subwavelength metallic gratings around the plasmonic critical angle

Zhonghua Wang, Mingqian Zhang, Jia Wang, Fan Lu, Kun Li, and Anshi Xu

Appl. Phys. Lett. 101, 061107 (2012); http://dx.doi.org/10.1063/1.4745919 (5 pages)

Online Publication Date: 8 August 2012

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We find and verify that unidirectional surface plasmon polaritons (SPPs) are highly excited by subwavelength metallic gratings with back-side illumination around the plasmonic critical angle (PCA). The conditions and physical origins of the SPP excitation around the PCA are clarified. Moreover, the experimental results support our numerical calculations very well. Potential applications are also suggested.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
42.79.Dj Gratings
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Terahertz fingerprinting in presence of quasi-ballistic scattering

Mayank Kaushik, Brian W.-H. Ng, Bernd M. Fischer, and Derek Abbott

Appl. Phys. Lett. 101, 061108 (2012); http://dx.doi.org/10.1063/1.4745182 (5 pages)

Online Publication Date: 8 August 2012

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Recent years have seen significant advances in material diagnostics and analysis using terahertz (THz) time domain spectroscopy (TDS) and imaging. Despite its widespread application, the interaction between THz radiation and materials with random structure is not yet fully studied. Separation of absorption and scattering is required to extract the true absorption spectra, thus enabling direct comparison with pure samples in a spectral data base for automated recognition. Here, we present a discrete wavelet transform based iterative reconstruction technique that reduces the scattering contribution in THz-TDS measurements, in composites with absorbing constituents that exhibit sharp absorption features.
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78.70.Gq Microwave and radio-frequency interactions
84.40.-x Radiowave and microwave (including millimeter wave) technology
02.60.-x Numerical approximation and analysis
43.60.Hj Time-frequency signal processing, wavelets
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)

Acousto-optic couplings in two-dimensional phoxonic crystal cavities

Q. Rolland, M. Oudich, S. El-Jallal, S. Dupont, Y. Pennec, J. Gazalet, J. C. Kastelik, G. Lévêque, and B. Djafari-Rouhani

Appl. Phys. Lett. 101, 061109 (2012); http://dx.doi.org/10.1063/1.4744539 (4 pages) | Cited 4 times

Online Publication Date: 9 August 2012

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We investigate the acousto-optic coupling, based on both photo-elastic and opto-mechanical mechanisms, in periodic structures with simultaneous photonic and phononic band gaps. The investigations are focused on a cavity defect in which the strong confinement of acoustic and optic waves enhances the interaction. We calculate the modulation of each photonic mode frequency by each phononic mode confined in the cavity. We compare the strength for the photo-elastic and opto-mechanical effects in the different cases. Both mechanisms can be in phase or out of phase and produce additive or subtractive effects in the total acousto-optic coupling.
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42.70.Qs Photonic bandgap materials
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects

Nonthermal carrier distributions in the subbands of 2-phonon resonance mid-infrared quantum cascade laser

Andrzej Kolek, Grzegorz Hałdaś, and Maciej Bugajski

Appl. Phys. Lett. 101, 061110 (2012); http://dx.doi.org/10.1063/1.4745013 (4 pages) | Cited 1 time

Online Publication Date: 10 August 2012

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Nonequilibrium Green’s functions model of mid-infrared quantum cascade laser that utilizes double-phonon resonance scheme is analyzed. Good agreement with experimental data is found. For quantities not accessible experimentally, it is shown that electronic distributions in lower active region subbands are nonthermal and have local maximum at higher in-plane energy. In upper subband, carrier distribution is thermal-like. Upper state lifetime is strongly reduced from optical phonon value by interface roughness and alloy scatterings. Net gain originates from population inversion at subbands bottom which is not suppressed by high-k absorption because of nonparabolicity which shifts absorption peak to lower frequencies.
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42.55.Px Semiconductor lasers; laser diodes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
02.30.-f Function theory, analysis
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Electromechanical properties of freestanding graphene functionalized with tin oxide (SnO2) nanoparticles

L. Dong, J. Hansen, P. Xu, M. L. Ackerman, S. D. Barber, J. K. Schoelz, D. Qi, and P. M. Thibado

Appl. Phys. Lett. 101, 061601 (2012); http://dx.doi.org/10.1063/1.4745780 (4 pages)

Online Publication Date: 8 August 2012

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Freestanding graphene membranes were functionalized with SnO2 nanoparticles. A detailed procedure providing uniform coverage and chemical synthesis is presented. Elemental composition was determined using scanning electron microscopy combined with energy dispersive x-ray analysis. A technique called electrostatic-manipulation scanning tunneling microscopy was used to probe the electromechanical properties of functionalized freestanding graphene samples. We found ten times larger movement perpendicular to the plane compared to pristine freestanding graphene and propose a nanoparticle encapsulation model.
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81.05.ue Graphene
77.65.-j Piezoelectricity and electromechanical effects
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Hard x-ray photoelectron spectroscopy study of As and Ga out-diffusion in In0.53Ga0.47As/Al2O3 film systems

C. Weiland, P. Lysaght, J. Price, J. Huang, and J. C. Woicik

Appl. Phys. Lett. 101, 061602 (2012); http://dx.doi.org/10.1063/1.4745207 (4 pages) | Cited 2 times

Online Publication Date: 9 August 2012

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Hard x-ray photoelectron spectroscopy (HAXPES) was performed on In0.53Ga0.47As/Al2O3 gate stacks as deposited and annealed at 400 °C, 500 °C, and 700 °C to test for out-diffusion of substrate elements. Ga and As core-level intensities increase with increasing anneal temperature, while the In intensity decreases. HAXPES was performed at two different beam energies to vary the surface sensitivity; results demonstrate Ga and As out-diffuse into the Al2O3 film. Analysis suggests the presence of an interlayer containing Ga and As oxides, which thickens with increasing anneal temperature. Further diffusion, especially of Ga, into the Al2O3 film is also observed with increasing anneal temperature.
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82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.at Other materials
68.55.J- Morphology of films
61.72.Cc Kinetics of defect formation and annealing
66.30.Lw Diffusion of other defects
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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Resonant actuation of microcantilever by pulse wave of one-nth the resonant frequency

Zhaobin Feng, Duo Liu, Zhiyuan Zuo, Qian Yu, Ruijun Wang, and Xiangang Xu

Appl. Phys. Lett. 101, 061901 (2012); http://dx.doi.org/10.1063/1.4742859 (3 pages)

Online Publication Date: 6 August 2012

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We achieve the resonant actuation of a microcantilever by using a pulse wave of one-nth the microcantilever resonant frequency. Our studies on the relationship between pulse duration and microcantilever resonant amplitude reveal that the most effective actuation can be acquired when the pulse duration is odd multiples of the half period of microcantilever resonant oscillation. This actuation method is generally applicable and may find applications in ultrahigh frequency actuation of microcantilever or similar resonant systems for high sensitivity detection.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Transparent Ce:Y3Al5O12 ceramic phosphors for white light-emitting diodes

Nian Wei, Tiecheng Lu, Feng Li, Wei Zhang, Benyuan Ma, Zhongwen Lu, and Jianqi Qi

Appl. Phys. Lett. 101, 061902 (2012); http://dx.doi.org/10.1063/1.4742896 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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We present our recent achievement of a transparent ceramic able to produce white light when directly combined with commercially available blue light emitting diodes. The photoluminescence properties of ceramic phosphor (Y1-xCex)3Al5O12 are studied as a function of doping fraction (x = 0.0005–0.0020). The emission color is tunable by variations of Ce3+ concentration and ceramic phosphor thickness. A maximum luminous efficacy exceeding 93 lm/W at a low correlated color temperature of ∼4600 K is obtained, which is superior to samples made from commercial phosphor powders. Hence, the present transparent ceramic phosphor is expected to be an ideal candidate for generating white light.
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85.60.Jb Light-emitting devices
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.55.Hx Other solid inorganic materials

Recrystallization of an amorphized epitaxial phase-change alloy: A phoenix arising from the ashes

P. Rodenbach, A. Giussani, K. Perumal, M. Hanke, M. Dubslaff, H. Riechert, R. Calarco, M. Burghammer, A. V. Kolobov, and P. Fons

Appl. Phys. Lett. 101, 061903 (2012); http://dx.doi.org/10.1063/1.4742919 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2012

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Epitaxial Ge2Sb2Te5 films grown on Si(111) by molecular beam epitaxy were reversibly switched between crystalline and amorphous states over a large area using femtosecond laser pulses. The structural and spatial homogeneity of the as-grown epitaxial and laser-switched areas on the sample were investigated by synchrotron nanofocus high resolution x-ray diffraction. The investigation clearly demonstrated that the single crystalline metastable cubic phase of Ge2Sb2Te5 is restored after switching. No polycrystalline features, not only on the average but even on the nanometer scale of the x-ray beam, were observed.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
64.70.kg Semiconductors
68.55.ag Semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)

Blue-white tunable luminescence for white light-emitting diodes and wideband near-infrared luminescence from Sm3+-doped borophosphate glass

Qiuchun Sheng, Yinglong Shen, Shuang Liu, Wentao Li, and Danping Chen

Appl. Phys. Lett. 101, 061904 (2012); http://dx.doi.org/10.1063/1.4743008 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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Highly transparent samarium (Sm3+) doped borophosphate glasses were prepared using the melt-quenching technique. The tunable light emission and wideband near-infrared luminescence properties of Sm3+-doped glasses were investigated systemically. Tuning the Sm3+ concentration and excitation wavelength can generate hues that vary from blue to white. Two wide luminescence bands in the 850 nm to 1070 nm range and in the 1100 nm to 1250 nm range, respectively, were also achieved. The results suggest that Sm3+-doped borophosphate glasses can be used as conversion materials for blue light-emitting diode chips to generate white light-emitting diodes and for optical amplification.
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85.60.Jb Light-emitting devices

Enhanced internal quantum efficiency in graphene/InGaN multiple-quantum-well hybrid structures

Huei-Min Huang, Chiao-Yun Chang, Yueh-Shan Hsu, Tien-Chang Lu, Yu-Pin Lan, and Wei-Chi Lai

Appl. Phys. Lett. 101, 061905 (2012); http://dx.doi.org/10.1063/1.4745211 (4 pages) | Cited 1 time

Online Publication Date: 6 August 2012

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The enhanced internal quantum efficiency of InGaN/GaN multiple-quantum-wells (MQWs) structure is demonstrated by paving the graphene layers on the MQWs surface. Compared to the conventional MQWs, the internal quantum efficiency of the graphene/InGaN MQWs hybrid structure exhibits a remarkable 2-fold increase. The high charge carrier density in graphene layer is accounted for the enhanced internal quantum efficiency. Moreover, the negligible photoluminescence emission peak shift with increasing the excitation power as well as the decrease of radiative recombination lifetime are attributed to the reduced quantum-confined Stark effect, which correlates to the screening of the polarization field in the c-plane nitride-based quantum well structure.
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78.55.Cr III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Quantum mechanical study of plasmonic coupling in sodium nanoring dimers

Haifeng Yin and Hong Zhang

Appl. Phys. Lett. 101, 061906 (2012); http://dx.doi.org/10.1063/1.4745654 (5 pages) | Cited 1 time

Online Publication Date: 7 August 2012

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In sodium nanoring dimers, plasmon resonances and the plasmon-induced field enhancement are investigated by time-dependent density functional theory. The optical absorption, the induced charge response, and the frequency dependent current demonstrate that the main plasmon resonance modes are the charge transfer plasmon mode and the bonding dimer plasmon mode (BDP). Moreover, there are also two small hybridized plasmon modes. The induced field enhancement of each spatial region depends on the gap distance and the plasmon mode. For the narrow gap, the field enhancement at different positions of the straight line segments between two nanorings is almost uniformly distributed. However, for large separations, along the axial direction, the field enhancement gradually decreases in the region within the radius of the sodium atom. Then, the change of the field enhancement is nonlinear. For different plasmon modes, there is a different number of field enhancement extrema. The largest extreme value is located in the middle region. These findings are expected to play an important role in designing plasmonic nanostructures for practical applications that require coupled metallic nanoparticles with enhanced electric fields.
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73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
03.65.-w Quantum mechanics
71.70.-d Level splitting and interactions

Kinetic study of GeO disproportionation into a GeO2/Ge system using x-ray photoelectron spectroscopy

Sheng Kai Wang, Hong-Gang Liu, and Akira Toriumi

Appl. Phys. Lett. 101, 061907 (2012); http://dx.doi.org/10.1063/1.4738892 (4 pages) | Cited 3 times

Online Publication Date: 7 August 2012

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GeO disproportionation into GeO2 and Ge is studied through x-ray photoelectron spectroscopy. Direct evidence for the reaction 2GeO → GeO2 + Ge after annealing in ultra-high vacuum is presented. Activation energy for GeO disproportionation is found to be about 0.7 ± 0.2 eV through kinetic and thermodynamic calculations. A kinetic model of GeO disproportionation is established by considering oxygen transfer in the GeO network. The relationship between GeO disproportionation and GeO desorption induced by GeO2/Ge interfacial reaction is discussed, and the apparent contradiction between GeO desorption via interfacial redox reaction and GeO disproportionation into Ge and GeO2 is explained by considering the oxygen vacancy.
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82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.20.Fd Collision theories; trajectory models
82.20.Pm Rate constants, reaction cross sections, and activation energies
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Viscous damping of microcantilevers with modified surfaces and geometries

O. Ergincan, G. Palasantzas, and B. J. Kooi

Appl. Phys. Lett. 101, 061908 (2012); http://dx.doi.org/10.1063/1.4744951 (4 pages)

Online Publication Date: 7 August 2012

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Noise measurements were performed to determine the quality factor Q and the resonating frequency shift as a function of gas pressure P for microcantilevers with modified surfaces and geometries. In the molecular and continuum regimes, energy loss is dominated by the surrounding fluid leading to reduction of the Q factor and shift of the resonance frequency by Δf, which becomes significant in the continuum regime showing sensitivity on surface changes. This is shown via three methods: frequency shift Δf vs. P, Q factor vs. P, and direct calculation using surface roughness details acquired via atomic force microscopy.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Microelectromechanical systems based Stewart platform with sub-nano resolution

Seung Ho Yang, Yong-Sik Kim, Jae-Myung Yoo, and Nicholas G. Dagalakis

Appl. Phys. Lett. 101, 061909 (2012); http://dx.doi.org/10.1063/1.4739517 (5 pages)

Online Publication Date: 7 August 2012

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There have been difficulties in the fabrication of microelectromechanical systems (MEMS) based Stewart platforms [D. Stewart, Proc. Inst. Mech. Eng. 180(15), 371 (1965)]. The macroscale positioning technology, such as universal joints, ball and roller bearings, and commercial actuators, used for building the macro Stewart platforms could not be fit into MEMS version machines. In this paper, we report that these difficulties were overcome at the National Institute of Standards and Technology (NIST). A prototype of NIST’s MEMS-based Stewart platform showed six degree-of-freedom kinematic capability with sub-nano-scale resolution. This MEMS Stewart platform can be adopted as a precision stage for sub nano-scale applications, such as the atomic force microscope and manipulation of molecules.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Dynamic characteristics of the exciton and the biexciton in a single InGaN quantum dot

S. Amloy, E. S. Moskalenko, M. Eriksson, K. F. Karlsson, Y. T. Chen, K. H. Chen, H. C. Hsu, C. L. Hsiao, L. C. Chen, and P. O. Holtz

Appl. Phys. Lett. 101, 061910 (2012); http://dx.doi.org/10.1063/1.4742343 (4 pages) | Cited 1 time

Online Publication Date: 7 August 2012

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The dynamics of the exciton and the biexciton related emission from a single InGaN quantum dot (QD) have been measured by time-resolved microphotoluminescence spectroscopy. An exciton-biexciton pair of the same QD was identified by the combination of power dependence and polarization-resolved spectroscopy. Moreover, the spectral temperature evolution was utilized in order to distinguish the biexciton from a trion. Both the exciton and the biexciton related emission reveal mono-exponential decays corresponding to time constants of ∼900 and ∼500 ps, respectively. The obtained lifetime ratio of ∼1.8 indicates that the QD is small, with a size comparable to the exciton Bohr radius.
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71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)
78.47.D- Time resolved spectroscopy (>1 psec)
78.47.jd Time resolved luminescence

Fast excited state diffusion in a-As2Se3 chalcogenide films

Abhishesh Regmi, Ashtosh Ganjoo, Donghui Zhao, Himanshu Jain, and Ivan Biaggio

Appl. Phys. Lett. 101, 061911 (2012); http://dx.doi.org/10.1063/1.4745612 (3 pages)

Online Publication Date: 8 August 2012

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Transient grating experiments after optical band-gap pulsed illumination of amorphous a-As2Se3 thin films reveal the existence of a well defined transport process occurring on length- and time-scales of the order of micrometers and microseconds, respectively. We tentatively assign this fast process, corresponding to a mobility of 0.04 ± 0.005  cm2 V−1 s−1, to the diffusion of photoexcited charge carriers with microsecond lifetime.
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73.61.Jc Amorphous semiconductors; glasses
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Jg Amorphous semiconductors; glasses
71.35.-y Excitons and related phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Multiple-band transmission of acoustic wave through metallic gratings

Dong-Xiang Qi, Ren-Hao Fan, Ru-Wen Peng, Xian-Rong Huang, Ming-Hui Lu, Xu Ni, Qing Hu, and Mu Wang

Appl. Phys. Lett. 101, 061912 (2012); http://dx.doi.org/10.1063/1.4742929 (5 pages)

Online Publication Date: 8 August 2012

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In this work, we demonstrate that acoustic waves can achieve extremely flat transmission through a metallic grating under oblique incidence within multiple frequency bands separated by Wood’s anomalies. At the low-frequency band, the transmission of acoustic wave is independent of the frequency and presents a flat curve with the transmission efficiency reaching about 100%; while at high-frequency bands, the transmission decreases to be lower flat curves due to the diffraction effect. The transmission efficiency is insensitive to the thickness of the grating. This phenomenon is verified by experiments, numerical simulations, and an analytical model. The broadband high transmission is attributed to the acoustic impedance matching between the air and the grating. This research may open up a field for various potential applications of acoustic gratings, including broadband sonic imaging and screening, grating interferometry, and antireflection cloaking.
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62.65.+k Acoustical properties of solids
72.30.+q High-frequency effects; plasma effects
43.20.-f General linear acoustics

Transforming carbon nanotube forest from darkest absorber to reflective mirror

Tanveer Saleh, Mehran Vahdani Moghaddam, Mohamed Sultan Mohamed Ali, Masoud Dahmardeh, Charles Alden Foell, Alireza Nojeh, and Kenichi Takahata

Appl. Phys. Lett. 101, 061913 (2012); http://dx.doi.org/10.1063/1.4744429 (4 pages)

Online Publication Date: 8 August 2012

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Carbon nanotube (CNT) forests are known to be among the darkest materials on earth. They can absorb the entire visible range of electromagnetic wave more efficiently than any other known black material. We have attempted controlled mechanical processing of the CNTs and, surprisingly, observed mirror-like reflection from the processed area with 10%–15% reflectivity, a level higher than typical reflectivity of pure forests by over two orders of magnitude, for a wide range of the spectrum (570–1100 nm). Patterning of micro mirrors in the forest is demonstrated to show its potential application for producing monolithically integrated reflector-absorber arrays in the material.
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81.05.U- Carbon/carbon-based materials
42.79.Bh Lenses, prisms and mirrors
42.82.-m Integrated optics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Ch Nanotubes
81.07.De Nanotubes
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