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21 Feb 2011

Volume 98, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 081101 (2011); http://dx.doi.org/10.1063/1.3555489 (3 pages)

B. Cluzel, K. Foubert, L. Lalouat, J. Dellinger, D. Peyrade, E. Picard, E. Hadji, and F. de Fornel
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Addressable subwavelength grids of confined light in a multislotted nanoresonator

B. Cluzel, K. Foubert, L. Lalouat, J. Dellinger, D. Peyrade, E. Picard, E. Hadji, and F. de Fornel

Appl. Phys. Lett. 98, 081101 (2011); http://dx.doi.org/10.1063/1.3555489 (3 pages) | Cited 1 time

Online Publication Date: 22 February 2011

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In this letter, we fabricate a multislotted optical nanoresonator with several spatial field distributions which are all addressable by the wavelength. The reported structure consists in an array of evanescently coupled single mode photonic crystal nanocavities. By using a scanning near-field optical microscope, we quantify the morphology of the different optical mode volumes and show that they consist in grids of light confined at the subwavelength scale.
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42.82.-m Integrated optics
07.79.Fc Near-field scanning optical microscopes

Photonic properties of erbium doped InGaN alloys grown on Si (001) substrates

I. W. Feng, X. K. Cao, J. Li, J. Y. Lin, H. X. Jiang, N. Sawaki, Y. Honda, T. Tanikawa, and J. M. Zavada

Appl. Phys. Lett. 98, 081102 (2011); http://dx.doi.org/10.1063/1.3556678 (3 pages) | Cited 1 time

Online Publication Date: 22 February 2011

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Erbium doped InGaN alloys (InGaN:Er) were grown on Si (001) substrates using metal organic chemical vapor deposition. The growth of epitaxial films was accomplished by depositing InGaN:Er on GaN templates deposited on 7.3° off-oriented Si (001) substrates which were prepared by etching and subsequent selective area growth. X-ray diffraction measurements confirmed the formation of wurtzite InGaN (1math01) epilayers, which exhibit strong photoluminescence emission at 1.54 μm. The observed emission intensity at 1.54 μm was comparable to that from similar alloys grown on GaN/AlN/Al2O3 templates. These results indicate the high potential for on-chip integration of erbium based photonic devices with complementary metal oxide semiconductor technology.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors
81.65.Cf Surface cleaning, etching, patterning
78.55.Cr III-V semiconductors

Strong exciton-photon coupling with colloidal quantum dots in a high-Q bilayer microcavity

Noel C. Giebink, Gary P. Wiederrecht, and Michael R. Wasielewski

Appl. Phys. Lett. 98, 081103 (2011); http://dx.doi.org/10.1063/1.3558731 (3 pages) | Cited 4 times

Online Publication Date: 22 February 2011

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We demonstrate evanescently coupled bilayer microcavities with Q-factors exceeding 250 fabricated by a simple spin-coating process. The cavity architecture consists of a slab waveguide lying upon a low refractive index spacer layer supported by a glass substrate. For a lossless guide layer, the cavity Q depends only on the thickness of the low index spacer and in principle can reach arbitrarily high values. We demonstrate the versatility of this approach by constructing cavities with a guide layer incorporating CdSe/ZnS core/shell quantum dots, where we observe strong coupling and hybridization between the 1S(e)-1S3/2(h) and 1S(e)-2S3/2(h) exciton states mediated by the cavity photon. This technique greatly simplifies the fabrication of high-Q planar microcavities for organic and inorganic quantum dot thin films and opens up new opportunities for the study of nonlinear optical phenomena in these materials.
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42.79.Gn Optical waveguides and couplers
42.65.Wi Nonlinear waveguides
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Directionality control through selective excitation of low-order guided modes in thin-film InGaN photonic crystal light-emitting diodes

Elizabeth Rangel, Elison Matioli, Yong-Seok Choi, Claude Weisbuch, James S. Speck, and Evelyn L. Hu

Appl. Phys. Lett. 98, 081104 (2011); http://dx.doi.org/10.1063/1.3554417 (3 pages) | Cited 11 times

Online Publication Date: 23 February 2011

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This letter explores the impact of quantum well placement and photonic crystal (PhC) etch depth on the emission directionality of thin-film InGaN PhC light-emitting diodes (LEDs). The far-field pattern of 800-nm-thick PhC LEDs is tuned by varying only the etch depth of a surface-patterned hexagonal PhC from 90 to 440 nm. This dependence on etch depth is shown to arise from the preferential excitation of a subset of the allowed guided modes. Selective excitation of the TE0 and TE1 modes is utilized to achieve a vertically directional emission pattern comprised of only these two modes.
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85.60.Jb Light-emitting devices

Pulsed laser induced switching of birefringence in nematic phase of photochromic molecules

J. Mysliwiec, M. Czajkowski, S. Bartkiewicz, K. Zygadlo, Z. Galewski, and B. Sahraoui

Appl. Phys. Lett. 98, 081105 (2011); http://dx.doi.org/10.1063/1.3559613 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2011

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Fast and dynamic switching of liquid-crystalline photochromic system birefringence induced by pulsed laser has been observed. The system consisted of photochromic molecules of 4-heptyl-4′-methoxyazobenzene showing liquid-crystalline nematic state close to the room temperature. Experiment of dynamic birefringence switching was done in optical Kerr effect (OKE) set-up, where for the sample excitation picosecond pulsed laser was used. Simultaneously, He–Ne laser was served as a probe beam source. Measurements were done for different voltages applied to the sample. Rise time constant was in the range of microseconds. Full reversibility of the OKE signal was observed.
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61.30.-v Liquid crystals
78.20.Fm Birefringence
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Nonlinear optical properties of covalently linked graphene-metal porphyrin composite materials

M. Bala Murali Krishna, V. Praveen Kumar, N. Venkatramaiah, R. Venkatesan, and D. Narayana Rao

Appl. Phys. Lett. 98, 081106 (2011); http://dx.doi.org/10.1063/1.3553500 (3 pages) | Cited 9 times

Online Publication Date: 23 February 2011

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The nonlinear optical (NLO) and optical limiting (OL) properties of covalently linked graphene-porphyrin composite materials were investigated using Z-scan technique in nanosecond regime. We observed enhanced NLO and OL properties of graphene-porphyrin composites in comparison to the individual graphene and porphyrins. The improved OL property of composites is attributed to energy transfer between porphyrin and graphene, which improved excited state absorption and nonlinear scattering. Nonlinear optical susceptibilities χ(3) of graphene and graphene-porphyrin composites were, in the order of 10−12 esu, measured using degenerate four wave mixing technique in nanosecond regime. High values of excited state absorption and two-photon absorption were observed for the composites.
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78.67.Sc Nanoaggregates; nanocomposites
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.An Optical susceptibility, hyperpolarizability

Direct measurement of versatile surface plasmon polaritons excited by split polarization

Tzu-Hsiang Lan, Chen-Yeh Ho, and Chung-Hao Tien

Appl. Phys. Lett. 98, 081107 (2011); http://dx.doi.org/10.1063/1.3552673 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2011

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We report on the concept, generation, and observation of versatile excited surface plasmon polariton (SPP) patterns via focused split polarization. Unlike the conventional subwavelength features such as holes array, grating, or other protrusion to satisfy the phase matching condition for SPP excitation, we utilized a structured focus to form either counterpropagating interference or a multiple casting plasmonic pattern by means of the arrangement of split polarization and corresponding focus position. The characteristics of the near-field SPP image are in close agreement with the finite-difference time-domain calculation and confirm its feasibility associated with SPP excitations in many areas.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Electromagnetically induced Talbot effect

Jianming Wen, Shengwang Du, Huanyang Chen, and Min Xiao

Appl. Phys. Lett. 98, 081108 (2011); http://dx.doi.org/10.1063/1.3559610 (3 pages) | Cited 5 times

Online Publication Date: 24 February 2011

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By modulating transmission function of a weak probe field via a strong control standing wave, an electromagnetically induced grating can be created in the probe channel. Such a nonmaterial grating may lead to self-imaging of ultracold atoms or molecules in the Fresnel near-field regime. This work may offer a nondestructive and lensless way to image ultracold atoms or molecules.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.25.Fx Diffraction and scattering
42.25.Hz Interference
07.60.Ly Interferometers
FREE

A large Kerr constant polymer-stabilized blue phase liquid crystal

Linghui Rao, Jin Yan, Shin-Tson Wu, Shin-ichi Yamamoto, and Yasuhiro Haseba

Appl. Phys. Lett. 98, 081109 (2011); http://dx.doi.org/10.1063/1.3559614 (3 pages) | Cited 31 times

Online Publication Date: 24 February 2011

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A polymer-stabilized blue phase liquid crystal (BPLC) composite with a large Kerr constant (K ∼ 13.7 nm/V2) is developed and its electro-optic properties characterized. In addition to the reduced operating voltage, this BPLC also exhibits a fast response time ( ∼ 1 ms), high contrast ratio (>1000:1), and relatively small hysteresis (<6%). It will undoubtedly accelerate the emergence of BPLC for next-generation display and photonic devices.
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61.30.Vx Polymer liquid crystals
78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
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AlGaN based deep ultraviolet light emitting diodes with high internal quantum efficiency grown by molecular beam epitaxy

Yitao Liao, Christos Thomidis, Chen-kai Kao, and Theodore D. Moustakas

Appl. Phys. Lett. 98, 081110 (2011); http://dx.doi.org/10.1063/1.3559842 (3 pages) | Cited 15 times

Online Publication Date: 24 February 2011

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We report the development of AlGaN based deep ultraviolet light emitting diodes (UV-LEDs) by molecular beam epitaxy. By growing the AlGaN well layer under Ga-rich conditions to produce strong potential fluctuations, internal quantum efficiency of a quantum well structure emitting at 300 nm was found to be 32%. By combining such Ga-rich growth condition in the active region with polarization field enhanced carrier injection layers, deep UV-LEDs emitting at 273 nm were obtained with output power of 0.35 mW and 1.3 mW at 20 mA continuous wave and 100 mA pulsed drive current, respectively. The maximum external quantum efficiency was 0.4%.
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85.60.Jb Light-emitting devices

Oriented polaritons in strongly-coupled asymmetric double quantum well microcavities

Gabriel Christmann, Alexis Askitopoulos, George Deligeorgis, Zacharias Hatzopoulos, Simeon I. Tsintzos, Pavlos G. Savvidis, and Jeremy J. Baumberg

Appl. Phys. Lett. 98, 081111 (2011); http://dx.doi.org/10.1063/1.3559909 (3 pages) | Cited 2 times

Online Publication Date: 24 February 2011

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Replacing independent single quantum wells inside a strongly-coupled semiconductor microcavity with double quantum wells produces a special type of polariton. Using asymmetric double quantum wells in devices processed into mesas allows the alignment of the electron levels to be voltage-tuned. At the resonant electronic tunneling condition, we demonstrate that “oriented polaritons” are formed, which possess greatly enhanced dipole moments. Since the polariton–polariton scattering rate depends on this dipole moment, such devices could reach polariton lasing, condensation, and optical nonlinearities at much lower threshold powers.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Ultrasharp ministop-band edge for subnanometer tuning resolution

N. Shahid, N. Speijcken, S. Naureen, M. Y. Li, M. Swillo, and S. Anand

Appl. Phys. Lett. 98, 081112 (2011); http://dx.doi.org/10.1063/1.3559915 (3 pages) | Cited 4 times

Online Publication Date: 24 February 2011

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We propose and demonstrate a method that enables spectral tuning with subnanometer accuracy, and is based on the transmission ministop-band (MSB) in line-defect multimode photonic crystal (PhC) waveguides. The fabricated MSB filter has ultrasharp edges which show a 30 dB drop in transmission in a 4 nm wavelength span. The use of the ultrasharp MSB edge to (optically) determine PhC fabrication accuracy is demonstrated. The wavelength position of the MSB could be tuned by temperature, with a coefficient of 0.1 nm/°C. The spectral characteristics of the MSB realized in this work are promising for sensing, tuning, and modulation applications.
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42.79.-e Optical elements, devices, and systems
42.70.Qs Photonic bandgap materials

Room temperature circularly polarized lasing in an optically spin injected vertical-cavity surface-emitting laser with (110) GaAs quantum wells

Satoshi Iba, Shinji Koh, Kazuhiro Ikeda, and Hitoshi Kawaguchi

Appl. Phys. Lett. 98, 081113 (2011); http://dx.doi.org/10.1063/1.3554760 (3 pages) | Cited 9 times

Online Publication Date: 24 February 2011

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We fabricated a (110)-oriented vertical-cavity surface-emitting laser (VCSEL) with GaAs/AlGaAs quantum wells (QWs) and characterized the lasing properties of the VCSEL under optical spin injection. We demonstrated circularly polarized lasing at a high degree of circular polarization of 0.96 for our VCSEL at room temperature that originated from a long electron spin relaxation time of 0.7 ns in the (110) GaAs QWs despite a really small initial electron spin polarization of 0.04, which was well reproduced by using a rate equation analysis.
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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

Interference-free superposition of nonzero order light modes: Functionalized optical landscapes

T. Čižmár, H. I. C. Dalgarno, P. C. Ashok, F. J. Gunn-Moore, and K. Dholakia

Appl. Phys. Lett. 98, 081114 (2011); http://dx.doi.org/10.1063/1.3552202 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2011

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In this paper, we utilize the incoherent superposition of nonzero order light modes. We show that this approach brings an additional degree of freedom to the generation of optical fields and notably the formation of superpositions that are otherwise unattainable through the use of refractive or diffractive optical elements and coherent or incoherent light sources. We employ this technique in two exemplary cases: first to create a field with tunable orbital angular momentum whose spatial intensity distribution remains unchanged and second to form an unusual type of “nondiffracting” light beam.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Self-phase modulation in high-power stimulated Brillouin compression

A. I. Erokhin and I. V. Smetanin

Appl. Phys. Lett. 98, 081115 (2011); http://dx.doi.org/10.1063/1.3559624 (3 pages)

Online Publication Date: 25 February 2011

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The spectrum of the stimulated Brillouin—compressed subnanosecond laser radiation is studied experimentally in a wide range of pump intensities up to the eightfold threshold value. It is found that at intensities increasing four times the threshold, the spectrum splits and acquires a two-humped shape, which is explained by the phase modulation near the Brillouin resonance. Analytical model of self-phase modulation in stimulated Brillouin compression is developed, which describes the observed spectral splitting and formation of the frequency chirp.
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42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Fano resonance of three-dimensional spiral photonic crystals: Paradoxical transmission and polarization gap

Wen-Jie Chen, Jeffrey Chi Wai Lee, Jian-Wen Dong, Cheng-Wei Qiu, and He-Zhou Wang

Appl. Phys. Lett. 98, 081116 (2011); http://dx.doi.org/10.1063/1.3560338 (3 pages) | Cited 3 times

Online Publication Date: 25 February 2011

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Extraordinary Fano resonance with right handedness is present in a right-handed polarization gap of compound spiral photonic crystals. The structure is composed of unit cells with double helices of π phase shift arranged in square lattice. Such a paradoxical phenomenon is derived from mode interferences between left-handed propagating modes along spiral axis and negative group velocity modes in extended Brillouin zone. By analyzing Fourier spectra and chirality of photonic eigenmodes, intrinsic mechanism is well understood by mode coupling theory.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Ultrafast linear kinetic inductive photoresponse of YBa2Cu3O7−δ meander-line structures by photoimpedance measurements

Haig A. Atikian, Behnood G. Ghamsari, Steven M. Anlage, and A. Hamed Majedi

Appl. Phys. Lett. 98, 081117 (2011); http://dx.doi.org/10.1063/1.3561742 (3 pages)

Online Publication Date: 25 February 2011

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We report the experimental demonstration of the linear kinetic-inductive photoresponse of thin-film YBa2Cu3O7−δ meander line structures, where the photoresponse amplitude, full-width-half-maximum, and rise time are bilinear in the incident optical power and bias current. This bilinear behavior reveals a trade-off between obtaining high responsivity and high speed photodetection. We also report a rise time as short as 29 ps in our photoimpedance measurements.
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74.25.Gz Optical properties
74.78.-w Superconducting films and low-dimensional structures
78.47.J- Ultrafast spectroscopy (<1 psec)
74.72.-h Cuprate superconductors
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X-ray Raman compression via two-stream instability in dense plasmas

S. Son and Sung Joon Moon

Appl. Phys. Lett. 98, 081501 (2011); http://dx.doi.org/10.1063/1.3554723 (3 pages)

Online Publication Date: 24 February 2011

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A Raman compression scheme suitable for x-rays, where the Langmuir wave is created by an intense beam rather than the ponderomotive potential between the seed and pump pulses, is proposed. The required intensity of the seed and pump pulses enabling the compression could be mitigated by more than a factor of 100 compared to conventionally available other Raman compression schemes. The relevant wavelength of x-rays ranges from 1 to 10 nm.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.38.Ph X-ray, γ-ray, and particle generation
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Possible routes for synthesis of new boron-rich Fe–B and Fe1−xCrxB4 compounds

A. F. Bialon, T. Hammerschmidt, R. Drautz, S. Shah, E. R. Margine, and A. N. Kolmogorov

Appl. Phys. Lett. 98, 081901 (2011); http://dx.doi.org/10.1063/1.3556564 (3 pages) | Cited 2 times

Online Publication Date: 22 February 2011

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We use ab initio calculations to examine thermodynamic factors that could promote the formation of recently proposed unique oP10-FeB4 and oP12-FeB2 compounds. We demonstrate that these compact boron-rich phases are stabilized further under pressure. We also show that chromium tetraboride is more stable in the new oP10 rather than the reported oI10 structure which opens up the possibility of realizing an oP10-(FexCr1−x)B4 pseudobinary material. In addition to exhibiting remarkable electronic features, oP10-FeB4 and oP12-FeB2 are expected to be harder than the known Fe–B compounds commonly used for hard coating applications.
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61.66.Fn Inorganic compounds
81.65.Kn Corrosion protection
71.20.Ps Other inorganic compounds
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
71.15.-m Methods of electronic structure calculations

Reversible switching between isotropic and anisotropic wetting by one-direction curvature tuning on flexible superhydrophobic surfaces

Si-Zhu Wu, Jian-Nan Wang, Li-Gang Niu, Jia Yao, Dong Wu, and Ai-Wu Li

Appl. Phys. Lett. 98, 081902 (2011); http://dx.doi.org/10.1063/1.3556585 (3 pages) | Cited 2 times

Online Publication Date: 22 February 2011

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In this letter, we report a kind of smart surfaces with reversible switching between isotropy and anisotropic wetting, which was realized by one-direction curvature tuning on flexible superhydrophobic surfaces. Along the curvature change, the wettability of this flexible film was changed from isotropic state (150°/150°) into anisotropic state confirmed by its anisotropic contact angles (150°/160°) and sliding properties (30°/65°). Further investigation revealed that the surface wettability was changed from composited pinned state into transitional state. This was attributed to the increase in roughness factor and the decrease in the contact area between the water droplet and the pillar array. At last, we demonstrate that the wetting states between isotropy and anisotropy on this flexible superhydrophobic film could be reversibly switched by curvature for many times (>10).
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68.03.Cd Surface tension and related phenomena
68.08.Bc Wetting
68.55.am Polymers and organics
68.35.bm Polymers, organics

Strain-mediated electric-field control of photoinduced demagnetization in La0.8Ca0.2MnO3 thin films

E. J. Guo, J. Gao, and H. B. Lu

Appl. Phys. Lett. 98, 081903 (2011); http://dx.doi.org/10.1063/1.3556613 (3 pages) | Cited 11 times

Online Publication Date: 22 February 2011

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La0.8Ca0.2MnO3 (LCMO) thin films have been epitaxially grown on ferroelectric 0.67Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (PMN-PT) substrates. The substrate-induced strain effects on the transport and photoinduced demagnetization in LCMO films were investigated. The photoinduced resistances (PRs) of LCMO systematically changed versus temperature before and after ferroelectric-poling on PMN-PT, indicating that photoexcited extra carriers in LCMO may suppress the neighboring spin correlation due to the photoassisted hopping of anti-Jahn–Teller polarons. Moreover, a significant modulation on PR by electric fields applied across PMN-PT was observed. In situ x-ray diffraction indicates that the observed variations result from substrate-induced strain due to the ferroelectric polarization or converse piezoelectric effect.
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81.15.Fg Pulsed laser ablation deposition
77.22.Ej Polarization and depolarization
75.70.Ak Magnetic properties of monolayers and thin films
77.55.fp Other ferroelectric films
73.50.Pz Photoconduction and photovoltaic effects
73.50.Dn Low-field transport and mobility; piezoresistance

Abnormal sub-Tg enthalpy relaxation in the CuZrAl metallic glasses far from equilibrium

Lina Hu, Yuanzheng Yue, and Chunzhi Zhang

Appl. Phys. Lett. 98, 081904 (2011); http://dx.doi.org/10.1063/1.3556659 (3 pages) | Cited 3 times

Online Publication Date: 22 February 2011

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The sub-Tg enthalpy relaxation in glasses far from equilibrium (i.e., hyperquenched glasses) is usually manifested as a monotonic increase in both the onset temperature and the extent of enthalpy recovery with increasing the annealing temperature. Here we report an abnormal three-steplike relaxation pattern in hyperquenched Cu45Zr45Al10 and Cu48Zr48Al4 glasses below Tg, i.e., the usual monotonic increase is inverted when the annealing temperature increases to a critical value. This abnormal relaxation pattern could be attributed to the high extent of chemical heterogeneity in the CuZrAl supercooled liquids, and present a thermodynamic evidence for the dynamic fragile-to-strong transition in metallic glass-forming liquids.
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65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
64.70.pe Metallic glasses
81.40.Gh Other heat and thermomechanical treatments
65.20.Jk Studies of thermodynamic properties of specific liquids
61.43.Fs Glasses

Hydrogenation of magnesium nanoblades: The effect of concentration dependent hydrogen diffusion

B. Yang, Y.-P. He, and Y.-P. Zhao

Appl. Phys. Lett. 98, 081905 (2011); http://dx.doi.org/10.1063/1.3557056 (3 pages) | Cited 5 times

Online Publication Date: 22 February 2011

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By assuming the H diffusion coefficient and H adsorption rate to be exponentially and linearly dependent on concentration, a physical model is developed to predict the hydrogenation process of Mg nanoblades. The predicted H uptake curves agree well with the experimental data from V-coated Mg nanoblades. The obtained H diffusion coefficients in MgHx between Mg and MgH2 have nearly three orders of magnitude variation. The characteristic time of H surface adsorption is longer than that of H diffusion in Mg but shorter than that in MgH2 for 100 nm thick nanoblades. A hydride shell is not formed during the hydrogenation.
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68.43.Mn Adsorption kinetics
66.30.Pa Diffusion in nanoscale solids
88.30.R- Hydrogen storage

Formation mechanism of shear bands in ultrafine lamellar Ti–Fe eutectics

F. Zhu, H. N. Tian, X. Li, G. H. Cao, D. Gerthsen, C.-G. Oertel, and W. Skrotzki

Appl. Phys. Lett. 98, 081906 (2011); http://dx.doi.org/10.1063/1.3559220 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2011

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Shear bands with alternating lamellar and serrated structures were observed on the fracture surface of an Ti–Fe ultrafine eutectic. The shear bands are composed of coalesced subgrains. Hence, a subgrain rotational mechanism is proposed to explain their formation. The work is a direct experimental evidence of the hypothetical rotational mechanism.
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62.20.F- Deformation and plasticity
62.20.mm Fracture

Huge binding energy of localized biexcitons in Al-rich AlxGa1−xN ternary alloys

Ryo Kittaka, Hirotaka Muto, Hideaki Murotani, Yoichi Yamada, Hideto Miyake, and Kazumasa Hiramatsu

Appl. Phys. Lett. 98, 081907 (2011); http://dx.doi.org/10.1063/1.3559226 (3 pages)

Online Publication Date: 23 February 2011

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Excitonic optical properties of Al-rich AlxGa1−xN ternary alloy epitaxial layers have been studied by means of photoluminescence excitation spectroscopy. On the basis of the energy separation between exciton resonance and two-photon biexciton resonance, the binding energy of biexcitons was estimated to be 56±5 and 48±5 meV for the sample with x = 0.81 and 0.89, respectively. The biexciton binding energy of 56 meV was approximately three times as large as the biexciton binding energy of 19 meV in AlN. The large enhancement of the biexciton binding energy resulted from the strong localization of biexcitons due to alloy disorder.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
68.55.-a Thin film structure and morphology
71.35.-y Excitons and related phenomena
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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