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24 Sep 2012

Volume 101, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 133101 (2012); http://dx.doi.org/10.1063/1.4752467 (5 pages)

Yen Husn Su and Wei-Yu Chen
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Anomalous temperature dependence of photoluminescence in self-assembled InGaN quantum dots

Jun Ma, Xiaoli Ji, Guohong Wang, Xuecheng Wei, Hongxi Lu, Xiaoyan Yi, Ruifei Duan, Junxi Wang, Yiping Zeng, Jinmin Li, Fuhua Yang, Chao Wang, and Gang Zou

Appl. Phys. Lett. 101, 131101 (2012); http://dx.doi.org/10.1063/1.4754533 (5 pages)

Online Publication Date: 24 September 2012

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Self-assembled InGaN quantum dots (QDs) were fabricated by metal-organic chemical vapor deposition. Abnormal temperature dependence of photoluminescence (PL) was observed. The integrated PL intensity of QDs sample shows a dramatic increase in a temperature range from 160 K to 215 K and reaches the maximum value at 215 K instead of 10 K as usual. To interpret this phenomenon, a theoretic model of temperature induced carrier redistribution mechanism is designed using rate equation, which fits closely with the experimental result. It is concluded that carriers’ redistribution from shallow QDs or wetting layer to deep QDs gives rise to the unique behavior for InGaN QDs structure.
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78.67.Hc Quantum dots
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.Dn Self-assembly
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Real-space mapping of nanoplasmonic hotspots via optical antenna-gap loading

S. Mastel, S. E. Grefe, G. B. Cross, A. Taber, S. Dhuey, S. Cabrini, P. J. Schuck, and Y. Abate

Appl. Phys. Lett. 101, 131102 (2012); http://dx.doi.org/10.1063/1.4754534 (4 pages) | Cited 2 times

Online Publication Date: 24 September 2012

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Plasmonic hotspots located in the nanogaps of infrared optical antennas are mapped in the near-field. The enhanced evanescent field resonance is shown to depend strongly on excitation wavelength, the excitation and detection laser polarization, and gap size. In addition, we demonstrate that in nanogap hotspot imaging using scattering probes, the probe tip can be considered as a load in the gap of the antenna, and the impedance of the load can then be tuned from inductive to capacitive or vice versa by changing the dielectric value of the tip load. Experimental results are in agreement with finite-difference time-domain simulations.
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42.30.-d Imaging and optical processing
84.40.Ba Antennas: theory, components and accessories

GaN-based light emitting diodes with micro- and nano-patterned structures by femtosecond laser nonlinear decomposition

Jiun-Ting Chen, Wei-Chih Lai, Yun-Chorng Chang, Jinn-Kong Sheu, and Wen-Chih Sen

Appl. Phys. Lett. 101, 131103 (2012); http://dx.doi.org/10.1063/1.4754569 (4 pages)

Online Publication Date: 24 September 2012

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The multiple micro/nano-patterning on p-GaN surface by femtosecond (fs) laser irradiation through a micro-ball lens array (MBLA) mask has been established to improve the light extraction efficiency of GaN-based light-emitting diodes (LEDs). This technique was meant for the high-speed surface micro/nano-patterning of a p-GaN surface on a large area using fs laser irradiation. Compared with conventional LEDs with flat surfaces, dual-scale roughened structures on p-GaN surface LEDs used in the present experiment scatter and increase the effective critical angle, increasing the escape probability of photons. The relationship of the hole size on p-GaN surface and the refractive index of the MBLA material would be also discussed. With an injection current of 20 mA, the output power of the experimental LEDs markedly improved by a magnitude of 48% compared with conventional GaN-based LEDs.
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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)
81.16.Rf Micro- and nanoscale pattern formation

Single-wavelength, all-optical switching based on exciton-polaritons

M. Steger, C. Gautham, B. Nelsen, D. Snoke, L. Pfeiffer, and K. West

Appl. Phys. Lett. 101, 131104 (2012); http://dx.doi.org/10.1063/1.4754575 (4 pages)

Online Publication Date: 24 September 2012

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We present a method for all-optical switching using a microcavity exciton-polariton system. Unlike many other switching methods, we use a single wavelength for both the signal and gate, which means that this method could be used for cascading optical logic gates and amplification within an all-optical circuit. We resonantly pump the sample at an angle with a laser beam and probe the sample with another beam at normal incidence. Upon saturation of the exciton-polariton states, the normal-incidence resonance increases in energy to permit the probe beam to be transmitted through the sample. Experimental results demonstrate switching using a GaAs/AlAs microcavity. Switching times on the order of ten picoseconds and on/off ratios on the order of 10:1 have been observed, and we propose design options to improve upon these.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.15.Eq Optical system design

Surface label-free sensing by means of a fluorescent multilayered photonic structure

Emiliano Descrovi, Francesca Frascella, Mirko Ballarini, Valeria Moi, Andrea Lamberti, Francesco Michelotti, Fabrizio Giorgis, and Candido Fabrizio Pirri

Appl. Phys. Lett. 101, 131105 (2012); http://dx.doi.org/10.1063/1.4754615 (4 pages) | Cited 2 times

Online Publication Date: 24 September 2012

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A fluorescent dielectric multilayer is exploited for label-free sensing in aqueous micro-environment. Fluorescence is laser-excited and collected through prism-coupling to a surface electromagnetic mode, also known as Bloch surface waves (BSW) localized at the interface between the multilayer and the outer aqueous medium. By detecting the spectral changes of the BSW-coupled light emission due to an external perturbation of the refractive index (Δn), a sensitivity of ∼2500 nm/RIU and a limit of detection down to Δn ∼ 3 × 10−6 are obtained.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.70.Qs Photonic bandgap materials

Broadband super-Planckian thermal emission from hyperbolic metamaterials

Yu Guo, Cristian L. Cortes, Sean Molesky, and Zubin Jacob

Appl. Phys. Lett. 101, 131106 (2012); http://dx.doi.org/10.1063/1.4754616 (5 pages) | Cited 6 times

Online Publication Date: 24 September 2012

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We develop the fluctuational electrodynamics of metamaterials with hyperbolic dispersion and show the existence of broadband thermal emission beyond the black body limit in the near field. This arises due to the thermal excitation of unique bulk metamaterial modes, which do not occur in conventional media. We consider a practical realization of the hyperbolic metamaterial and estimate that the effect will be observable using the characteristic dispersion (topological transitions) of the metamaterial states. Our work paves the way for engineering the near-field thermal emission using metamaterials.
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42.70.Qs Photonic bandgap materials

Influencing modulation properties of quantum-dot semiconductor lasers by carrier lifetime engineering

Benjamin Lingnau, Kathy Lüdge, Weng W. Chow, and Eckehard Schöll

Appl. Phys. Lett. 101, 131107 (2012); http://dx.doi.org/10.1063/1.4754588 (4 pages) | Cited 1 time

Online Publication Date: 25 September 2012

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The relaxation oscillation (RO) parameters and modulation properties of quantum-dot lasers are investigated depending on effective charge carrier scattering lifetimes of the confined quantum-dot states. We find three dynamical regimes of the laser, characterized by the level of synchronization between carrier dynamics in quantum-dots and quantum-well. For scattering rates similar to the RO frequency, a strong damping is found. On either side of this regime, simulations show low RO damping and improved dynamical response. Depending on the regime, the modulation response differs from conventional analytical predictions. Our results suggest the possibility of tailoring quantum-dot laser dynamical behavior via bandstructure engineering.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Rn Relaxation oscillations and long pulse operation

Record-low propagation losses of 154 dB/cm for substrate-type W1 photonic crystal waveguides by means of hole shape engineering

R. Kappeler, P. Kaspar, H. Jäckel, and Ch. Hafner

Appl. Phys. Lett. 101, 131108 (2012); http://dx.doi.org/10.1063/1.4753808 (4 pages) | Cited 1 time

Online Publication Date: 25 September 2012

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Large propagation losses in the order 600-1000 dB/cm were reported in the past for planar line-defect photonic crystal waveguides with a weak vertical refractive index contrast (substrate-type). Loss-relevant factors are a well-suited design of the photonic crystal pattern and a high-quality fabrication technology. Here, the focus is on the latter. Two methods—a thermally driven mass transport process and an ultra-slow, selective wet-etching process—are assessed with respect to their capability of enabling low-loss waveguides. With the resulting hole shape, we experimentally demonstrate record-low propagation losses of 154 dB/cm for W1 photonic crystal waveguides in the InP/InGaAsP system.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials

Direct observation of the terahertz optical free induction decay of molecular rotation absorption lines in the sub-nanosecond time scale

E. N. Chesnokov, V. V. Kubarev, P. V. Koshlyakov, and G. N. Kulipanov

Appl. Phys. Lett. 101, 131109 (2012); http://dx.doi.org/10.1063/1.4754826 (4 pages) | Cited 1 time

Online Publication Date: 25 September 2012

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Optical free induction decay (FID) in the region of 60–75 cm−1 was detected using 120 ps pulses of free electron laser. Signals were detected in real time using ultra-fast Schottky diode detectors. The oscillations corresponding to the splitting of absorption lines in deuterated water vapor (Δf = 0.15 cm−1) and hydrogen bromide (Δf = 0.02 cm−1) were detected. At high optical density, we observed the oscillations arising from “top-hat” shape of absorption lines. Free induction decay signals could be detected in a single shot. This observation allowed obtaining a spectrum in one laser pulse, which facilitates studies of very fast processes.
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41.60.Cr Free-electron lasers
42.25.Bs Wave propagation, transmission and absorption
85.30.Kk Junction diodes

Degenerate parallel conducting layer and conductivity type conversion observed from p-Ge1−ySny (y = 0.06%) grown on n-Si substrate

Mee-Yi Ryu, Y. K. Yeo, M. Ahoujja, Tom Harris, Richard Beeler, and John Kouvetakis

Appl. Phys. Lett. 101, 131110 (2012); http://dx.doi.org/10.1063/1.4754625 (5 pages)

Online Publication Date: 26 September 2012

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Electrical properties of p-Ge1−ySny (y = 0.06%) grown on n-Si substrate were investigated through temperature-dependent Hall-effect measurements. It was found that there exists a degenerate parallel conducting layer in Ge1−ySny/Si and a second, deeper acceptor in addition to a shallow acceptor. This parallel conducting layer dominates the electrical properties of the Ge1−ySny layer below 50 K and also significantly affects those properties at higher temperatures. Additionally, a conductivity type conversion from p to n was observed around 370 K for this sample. A two-layer conducting model was used to extract the carrier concentration and mobility of the Ge1−ySny layer alone.
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73.61.Le Other inorganic semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
72.20.Fr Low-field transport and mobility; piezoresistance
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Influence of indium content and temperature on Auger-like recombination in InGaN quantum wells grown on (111) silicon substrates

B. Galler, P. Drechsel, R. Monnard, P. Rode, P. Stauss, S. Froehlich, W. Bergbauer, M. Binder, M. Sabathil, B. Hahn, and J. Wagner

Appl. Phys. Lett. 101, 131111 (2012); http://dx.doi.org/10.1063/1.4754688 (4 pages) | Cited 3 times

Online Publication Date: 26 September 2012

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High-efficiency InGaN-based light-emitting diodes have been grown on (111) silicon substrates and investigated with regard to efficiency and carrier lifetime as a function of current density. Using a single quantum well active layer ensures a well-defined active volume which enables the precise determination of the recombination coefficients in the ABC rate model for different emission wavelengths and junction temperatures. Good agreement of the resulting C values with calculated Auger coefficients is found both with respect to absolute value as well as their dependence on bandgap energy and temperature.
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85.60.Jb Light-emitting devices
73.63.Hs Quantum wells
79.20.Fv Electron impact: Auger emission

Polariton emission characteristics of a modulation-doped multiquantum-well microcavity diode

Ayan Das, Bo Xiao, Sishir Bhowmick, and Pallab Bhattacharya

Appl. Phys. Lett. 101, 131112 (2012); http://dx.doi.org/10.1063/1.4755777 (4 pages)

Online Publication Date: 26 September 2012

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The role of polariton-electron scattering on the performance characteristics of an electrically injected GaAs-based quantum well (QW) microcavity diode in the strong coupling regime has been investigated. An electron gas is introduced in the quantum wells by modulation doping with silicon dopants. It is observed that polariton-electron scattering suppresses the relaxation bottleneck in the lower polariton branch. However, it is not adequate to produce a degenerate coherent condensate at k∥ ∼ 0 and coherent emission.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.21.Fg Quantum wells
85.30.Kk Junction diodes

The reduction of efficiency droop by Al0.82In0.18N/GaN superlattice electron blocking layer in (0001) oriented GaN-based light emitting diodes

Roy B. Chung, Changseok Han, Chih-Chien Pan, Nathan Pfaff, James S. Speck, Steven P. DenBaars, and Shuji Nakamura

Appl. Phys. Lett. 101, 131113 (2012); http://dx.doi.org/10.1063/1.4756791 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2012

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To investigate the effect of Al0.82In0.18N electron blocking layer (EBL) on the efficiency droop, (0001) oriented InGaN light emitting diodes (LEDs) were grown with two different types of EBLs—single Al0.82In0.18N:Mg layer and Al0.82In0.18N:Mg (2 nm)/GaN:Mg (2 nm) superlattice (SL) structure with 7 periods. It was found that the output power and operating voltage of single Al0.82In0.18N EBL LED were sensitive to EBL thickness due to the difficulty in growing high quality Mg doped Al0.82In0.18N. On the other hand, LED with SL EBL showed no deterioration of optical power and operating voltage while its efficiency droop (17% at 300 A/cm2) reduced by more than a half compared to a conventional Al0.2Ga0.8N (20 nm) EBL LED (36% at 300 A/cm2).
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85.60.Jb Light-emitting devices

Direct measurement of laser-induced frequency shift rate of ultracold cesium molecules by analyzing losses of trapped atoms

Yichi Zhang, Jie Ma, Yuqing Li, Jizhou Wu, Linjie Zhang, Gang Chen, Lirong Wang, Yanting Zhao, Liantuan Xiao, and Suotang Jia

Appl. Phys. Lett. 101, 131114 (2012); http://dx.doi.org/10.1063/1.4756801 (4 pages)

Online Publication Date: 28 September 2012

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We report on a quantitative experimental determination of the laser-induced frequency shift rate of the ultracold cesium molecules formed via photoassociation (PA) by means of the trap loss measurement of the losses of trapped atoms in a standard magneto-optical trap. The experiment was directly performed by varying the photoassociation laser intensity without any additional frequency monitor technologies. Our experimental method utilized dependences of the losses on the laser-induced frequency shift rate based on the conditions of the identified photoassociation spectral shape. We demonstrated that the method is sensitive enough to determine small frequency shifts of rovibrational levels of ultracold cesium molecules.
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82.30.Nr Association, addition, insertion, cluster formation
82.37.Vb Single molecule photochemistry
82.50.Hp Processes caused by visible and UV light
33.57.+c Magneto-optical and electro-optical spectra and effects
33.15.Mt Rotation, vibration, and vibration-rotation constants

Photophoretic trampoline—Interaction of single airborne absorbing droplets with light

Michael Esseling, Patrick Rose, Christina Alpmann, and Cornelia Denz

Appl. Phys. Lett. 101, 131115 (2012); http://dx.doi.org/10.1063/1.4755761 (4 pages) | Cited 2 times

Online Publication Date: 28 September 2012

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multimedia

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We present the light-induced manipulation of absorbing liquid droplets in air. Ink droplets from a printer cartridge are used to demonstrate that absorbing liquids—just like their solid counterparts—can interact with regions of high light intensity due to the photophoretic force. It is shown that droplets follow a quasi-ballistic trajectory after bouncing off a high intensity light sheet. We estimate the intensities necessary for this rebound of airborne droplets and change the droplet trajectories through a variation of the manipulating light field.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
82.70.Rr Aerosols and foams
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Pulsed laser ablation of complex oxides: The role of congruent ablation and preferential scattering for the film stoichiometry

S. Wicklein, A. Sambri, S. Amoruso, X. Wang, R. Bruzzese, A. Koehl, and R. Dittmann

Appl. Phys. Lett. 101, 131601 (2012); http://dx.doi.org/10.1063/1.4754112 (5 pages) | Cited 1 time

Online Publication Date: 24 September 2012

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By combining structural and chemical thin film analysis with detailed plume diagnostics and modeling of the laser plume dynamics, we are able to elucidate the different physical mechanisms determining the stoichiometry of the complex oxides model material SrTiO3 during pulsed laser deposition. Deviations between thin film and target stoichiometry are basically a result of two effects, namely, incongruent ablation and preferential scattering of lighter ablated species during their motion towards the substrate in the O2 background gas. On the one hand, a progressive preferential ablation of the Ti species with increasing laser fluence leads to a regime of Ti-rich thin film growth at larger fluences. On the other hand, in the low laser fluence regime, a more effective scattering of the lighter Ti plume species results in Sr rich films.
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81.15.Fg Pulsed laser ablation deposition
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.55.aj Insulators
78.70.En X-ray emission spectra and fluorescence
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films

Water droplets on a hydrophobic insulator surface under high voltages: A thermal perspective

Guoxin Xie, Jianbin Luo, Ye Yang, Dan Guo, and Lina Si

Appl. Phys. Lett. 101, 131602 (2012); http://dx.doi.org/10.1063/1.4754689 (4 pages)

Online Publication Date: 25 September 2012

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The thermal characteristics in the interaction process between water droplets on a hydrophobic insulator surface under high direct current voltages have been investigated with the infrared thermography. Discharge inception under a sufficiently high electric field resulted in the temperature rise between droplets and the formation of a liquid channel. The channel was transient for low conductivity droplets followed by their coalescence while stable for highly conductive ones. Asymmetric temperature distributions in the associated droplets appeared, and localized drying in the low conductivity droplet near the higher potential electrode initiated intermittent discharge. Mechanisms of these experimental phenomena have been discussed.
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66.25.+g Thermal conduction in nonmetallic liquids

Thermoelectric properties of YBa2Cu3O7−δ–La2/3Ca1/3MnO3 superlattices

S. Heinze, H.-U. Habermeier, G. Cristiani, S. Blanco Canosa, M. Le Tacon, and B. Keimer

Appl. Phys. Lett. 101, 131603 (2012); http://dx.doi.org/10.1063/1.4754707 (4 pages)

Online Publication Date: 26 September 2012

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We report measurements of the thermoelectric power and electrical resistivity of superlattices composed of the high-temperature superconductor YBa2Cu3O7−δ (YBCO) and the metallic ferromagnet La2/3Ca1/3MnO3 (LCMO) with individual layer thicknesses between 5 and 50 nm. Whereas YBCO and LCMO reference films prepared under the same conditions exhibit negative Seebeck coefficients, in excellent agreement with data on bulk compounds of identical composition, those of all superlattices are positive, regardless of the individual layer thickness. Having ruled out lattice strain and incomplete oxygenation, we attribute the observed sign reversal of the Seebeck coefficient to a long-range electronic reconstruction nucleated at the YBCO-LCMO interfaces.
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74.25.fg Thermoelectric effects
74.72.-h Cuprate superconductors

S-parameter and perfect pinning of the Fermi level at nonpolar (11-20) a-plane p-GaN surfaces

Yunju Choi, Keun Man Song, and Hyunsoo Kim

Appl. Phys. Lett. 101, 131604 (2012); http://dx.doi.org/10.1063/1.4755839 (3 pages) | Cited 1 time

Online Publication Date: 26 September 2012

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We investigated the Schottky barrier height and S-parameter at nonpolar (11-20) a-plane p-GaN surfaces by using Schottky diodes fabricated with various metals, including Ti, Cu, Ni, and Pt. A barrier inhomogeneity model was used to explain anomalous carrier transport behavior at the nonpolar p-GaN surfaces, yielding the mean barrier heights of 2.01, 1.73, 1.82, and 1.92 eV for the Ti, Cu, Ni, and Pt contacts, respectively. The extracted S-parameter was as low as 0.02, indicating perfect pinning of the surface Fermi level at around 1.9 eV above the valence band.
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71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions

Superstructure of self-aligned hexagonal GaN nanorods formed on nitrided Si(111) surface

Praveen Kumar, Mohit Tuteja, Manoj Kesaria, U. V. Waghmare, and S. M. Shivaprasad

Appl. Phys. Lett. 101, 131605 (2012); http://dx.doi.org/10.1063/1.4751986 (4 pages) | Cited 1 time

Online Publication Date: 28 September 2012

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We present here the spontaneous formation of catalyst-free, self-aligned crystalline (wurtzite) nanorods on Si(111) surfaces modified by surface nitridation. Nanorods grown by molecular beam epitaxy on bare Si(111) and non-stoichiometric silicon nitride interface are found to be single crystalline but disoriented. Those grown on single crystalline Si3N4 intermediate layer are highly dense c-oriented hexagonal shaped nanorods. The morphology and the self-assembly of the nanorods shows an ordered epitaxial hexagonal superstructure, suggesting that they are nucleated at screw dislocations at the interface and grow spirally in the c-direction. The aligned nanorod assembly shows high-quality structural and optical emission properties.
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81.16.Dn Self-assembly
78.67.Qa Nanorods
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Manganese induced modifications in yttria stabilized zirconia

Manoj K. Mahapatra, Prabhakar Singh, and Scott T. Misture

Appl. Phys. Lett. 101, 131606 (2012); http://dx.doi.org/10.1063/1.4755776 (4 pages)

Online Publication Date: 28 September 2012

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We have investigated the role of manganese oxide on the crystallographic and morphological modifications of cubic 8 mol. % yttria stabilized zirconia (YSZ). X-ray diffraction studies indicate that manganese dissolution leads to partial transformation of cubic YSZ into the tetragonal polymorph along with contraction of the unit cell. Evolution of an undulated surface with 2–15 nm roughness has been observed using electron and atomic force microscopies.
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61.66.Fn Inorganic compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.75.Bc Solubility
68.35.bt Other materials
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Laser triggered sequential folding of microstructures

Kate E. Laflin, Christopher J. Morris, Tanziyah Muqeem, and David H. Gracias

Appl. Phys. Lett. 101, 131901 (2012); http://dx.doi.org/10.1063/1.4754607 (4 pages) | Cited 3 times

Online Publication Date: 24 September 2012

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In order to fabricate complex origami inspired devices, it is necessary to control folding pathways and enable sequential folding. We demonstrate sequential folding of microstructures from afar by the directed heating of pre-stressed hinges using low power, 40–80 mW handheld, commercial lasers. We observed that the hinge-actuation and consequently folding time varied with laser irradiance, wavelength, and distance. We highlight possible applications by sequential folding of patterned and nested microstructures.
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07.10.Cm Micromechanical devices and systems

Minimizing scattering from antireflective surfaces replicated from low-aspect-ratio black silicon

Alexander B. Christiansen, Jeppe Clausen, N. Asger Mortensen, and Anders Kristensen

Appl. Phys. Lett. 101, 131902 (2012); http://dx.doi.org/10.1063/1.4754691 (4 pages)

Online Publication Date: 24 September 2012

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The scattering properties of randomly structured antireflective black silicon polymer replica have been investigated. Using a two-step casting process, the structures can be replicated in Ormocomp on areas of up to 3 in. in diameter. Fourier analysis of scanning electron microscopy images of the structures shows that the scattering properties of the surfaces are related to the spatial periods of the nanostructures. Structures with a dominating spatial period of 160 nm, a height of 200 nm, and aspect ratio of 1.3 show insignificant scattering of light with wavelength above 500 nm and lower the reflectance by a factor of two.
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78.66.Db Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Fy Semiconductors

On the nature of enthalpy relaxation below and above the glass transition of metallic glasses

Yu. P. Mitrofanov, A. S. Makarov, V. A. Khonik, A. V. Granato, D. M. Joncich, and S. V. Khonik

Appl. Phys. Lett. 101, 131903 (2012); http://dx.doi.org/10.1063/1.4754710 (4 pages) | Cited 2 times

Online Publication Date: 24 September 2012

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Within the framework of the interstitialcy theory, we derived a simple and testable expression for the heat flow (enthalpy relaxation rate) occurring upon warming of glass at a constant rate. Formally, this heat flow is mostly determined by the shear moduli of glass and parent crystal. The underlying physical reason is relaxation of an intrinsic interstitialcy-like defect system. An extensive check of the derived heat flow law for temperatures near the glass transition showed good agreement with the experiment specially performed on two Pd-based metallic glasses.
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64.70.pe Metallic glasses
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
81.05.Kf Glasses (including metallic glasses)
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.jj Interstitials
62.20.de Elastic moduli

Polymer-stabilized supercooled blue phase

Hyunseok Choi, Hiroki Higuchi, Yukiko Ogawa, and Hirotsugu Kikuchi

Appl. Phys. Lett. 101, 131904 (2012); http://dx.doi.org/10.1063/1.4752461 (5 pages)

Online Publication Date: 24 September 2012

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We report a method to prepare a polymer-stabilized liquid-crystal blue phase that is effective over a wide range of temperature. There are two main key points about this method: (1) A precursor solution is injected into the cell at an enough high temperature above the blue phase–isotropic phase transition point, and (2) a photo-polymerization process with a deeply supercooled blue phase of the precursor solution stabilizes the phase. Thus, a polymer-stabilized “supercooled” blue phase is achieved through photo-polymerization over a wide range of temperature. The proposed method will be very beneficial for manufacturing blue-phase-mode liquid crystal displays.
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61.30.Mp Blue phases and other defect-phases
82.35.-x Polymers: properties; reactions; polymerization
64.70.mj Experimental studies of liquid crystal transitions
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