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10 Oct 2011

Volume 99, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 153101 (2011); http://dx.doi.org/10.1063/1.3646406 (3 pages)

H. T. Zhou, J. H. Mao, G. Li, Y. L. Wang, X. L. Feng, S. X. Du, K. Müllen, and H.-J. Gao
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High-reflectivity II-VI-based distributed Bragg reflectors for the blue-violet spectral range

S. Klembt, H. Dartsch, M. Anastasescu, M. Gartner, and C. Kruse

Appl. Phys. Lett. 99, 151101 (2011); http://dx.doi.org/10.1063/1.3644955 (3 pages) | Cited 4 times

Online Publication Date: 10 October 2011

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We report on the realization of a high quality distributed Bragg reflector for the blue-violet spectral range, with both high and low refractive index layers lattice matched to the GaAs substrate. Our structure is grown by molecular beam epitaxy (MBE). The high refractive index layer is made of ZnMgSSe, while the low index material consists of a short period superlattice containing MgS and ZnCdSe. The refractive index step of Δn = 0.43 results in a stop band width of 40 nm and the normalized reflectivity exceeds 99% for 21 Bragg pairs.
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68.55.ag Semiconductors
42.79.Dj Gratings
68.65.Cd Superlattices
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.66.Hf II-VI semiconductors
78.66.Fd III-V semiconductors

Intersubband absorption saturation in AlN-based waveguide with GaN/AlN multiple quantum wells grown by metalorganic vapor phase epitaxy

Hassanet Sodabanlu, Jung-Seung Yang, Takuo Tanemura, Masakazu Sugiyama, Yukihiro Shimogaki, and Yoshiaki Nakano

Appl. Phys. Lett. 99, 151102 (2011); http://dx.doi.org/10.1063/1.3650929 (3 pages) | Cited 1 time

Online Publication Date: 10 October 2011

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Intersubband absorption saturation at 1.57 μm wavelength was observed in a 400-μm long Si3N4-rib AlN-based waveguide with GaN/AlN multiple quantum wells (MQWs) fabricated by metalorganic vapor phase epitaxy (MOVPE). The self-saturation measurement was employed using a 1.56-μm short pulse laser which has a temporal width of 0.4 ps (full-width at half-maximum) and a repetition rate of 63 MHz. An intersubband absorption saturation by 5 dB was achieved using a pulse energy of 115 pJ. We have demonstrated the capability of MOVPE-grown GaN/AlN MQWs for intersubband optical devices operated at communication wavelength.
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78.67.De Quantum wells
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Fg Quantum wells
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Optical breakdown of air triggered by femtosecond laser filaments

Pavel Polynkin and Jerome V. Moloney

Appl. Phys. Lett. 99, 151103 (2011); http://dx.doi.org/10.1063/1.3651279 (3 pages) | Cited 7 times

Online Publication Date: 10 October 2011

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We report experiments on the generation of dense plasma channels in ambient air using a dual laser pulse excitation scheme. The dilute plasma produced through the filamentation of an ultraintense femtosecond laser pulse is densified via avalanche ionization driven by a co-propagating multi-Joule nanosecond pulse.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.80.-s Electric discharges
52.25.Jm Ionization of plasmas
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Plasmonic trapping with realistic dipole nanoantennas: Analysis of the detection limit

Andrea Lovera and Olivier J. F. Martin

Appl. Phys. Lett. 99, 151104 (2011); http://dx.doi.org/10.1063/1.3650267 (3 pages) | Cited 5 times

Online Publication Date: 11 October 2011

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We use numerical simulations based on the surface integral technique to study the detection limit of plasmonic trapping with realistic dipole antennas. The induced plasmon resonance shift due to the coupling between an antenna and a nanoparticle is studied for different antennas geometries, different positions, sizes, and materials for the trapped nanoparticle. The shift of the antenna resonance is found to be linear with the near-field intensity enhancement caused by the antenna and further dependents on the volume and refractive index of the trapped nanoparticle. Detection limit of 5 nm for plasmonic particles and 6.5 nm for high index dielectrics is reported.
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42.79.Pw Imaging detectors and sensors
84.40.Ba Antennas: theory, components and accessories
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
42.50.Wk Mechanical effects of light on material media, microstructures and particles
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Two-dimensional plasma grating by non-collinear femtosecond filament interaction in air

Jia Liu, Wenxue Li, Haifeng Pan, and Heping Zeng

Appl. Phys. Lett. 99, 151105 (2011); http://dx.doi.org/10.1063/1.3650709 (3 pages) | Cited 2 times

Online Publication Date: 11 October 2011

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We experimentally demonstrated that two-dimensional (2D) plasma gratings could be generated in air by nonlinear interaction of three femtosecond filaments. The intensity interference of non-collinearly overlapped filaments was self-projected along a relatively long distance and accompanied with a wavelength-scale periodic change of the refractive index in the encircling air due to periodic plasma density modulation. The 2D plasma gratings supported 2D diffraction of the generated third-harmonic pulses. By using in-line time-resolved holographic imaging and time-delayed diffraction, the 2D plasma gratings were evidenced to last a few tens picoseconds after the excitation pulses.
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52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.25.-b Plasma properties
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Subwavelength lithography by waveguide mode interference

Bing Wang, Ah Bian Chew, Jinghua Teng, Guangyuan Si, and Aaron J. Danner

Appl. Phys. Lett. 99, 151106 (2011); http://dx.doi.org/10.1063/1.3651274 (3 pages) | Cited 1 time

Online Publication Date: 11 October 2011

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A subwavelength lithography method is demonstrated theoretically and experimentally through the interference of transverse electric (TE) modes in a metal-dielectric waveguide (MDW). Like surface plasmon polaritons (SPPs) on metal surfaces, the TE modes have evanescent waves leaking out of the MDW and are used to do subwavelength patterning but with larger pattern area than SPPs for their low propagation loss. The patterning resolution and depth could be optimized by modifying the thickness of the dielectric layer in the MDW. Two-dimensional subwavelength patterning using TE modes is also proposed with azimuthally polarized light exposure.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Gn Optical waveguides and couplers
42.25.Ja Polarization
42.82.Cr Fabrication techniques; lithography, pattern transfer

Ultrafast spin-induced polarization oscillations with tunable lifetime in vertical-cavity surface-emitting lasers

N. C. Gerhardt, M. Y. Li, H. Jähme, H. Höpfner, T. Ackemann, and M. R. Hofmann

Appl. Phys. Lett. 99, 151107 (2011); http://dx.doi.org/10.1063/1.3651339 (3 pages) | Cited 8 times

Online Publication Date: 11 October 2011

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We report spin-induced polarization oscillations in vertical-cavity surface-emitting lasers above threshold and at room temperature. The oscillation frequency is 11.6 GHz, which is significantly higher than the modulation bandwidth of less than 4 GHz in the device. The oscillation frequency is determined by an additional resonance frequency in birefringence containing microcavities, which is potentially much higher than the conventional relaxation oscillation frequency. The damping of the oscillations can be controlled by the current, allowing for oscillation lifetimes much longer than the spin lifetime in the device as well as for short bursts potentially interesting for information transmission.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Px Semiconductor lasers; laser diodes
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Structural design of AlN/GaN superlattices for deep-ultraviolet light-emitting diodes with high emission efficiency

Katsumasa Kamiya, Yasuhiro Ebihara, Kenji Shiraishi, and Makoto Kasu

Appl. Phys. Lett. 99, 151108 (2011); http://dx.doi.org/10.1063/1.3651335 (3 pages) | Cited 6 times

Online Publication Date: 12 October 2011

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We demonstrate on the basis of first-principles calculations that a AlN/GaN superlattice with one or two GaN monolayers is efficient for near-band-edge C-plane emission of deep-ultraviolet light-emitting diodes. We find that such superlattices lead to a significant increase of the C-plane components of the optical matrix element up to 57% relative to GaN bulk. At the same time, the energy gap of these superlattices is in the deep-UV region, where the shortest emission wavelength is 224 nm. This is remarkably shorter than that in Al-rich AlGaN alloys.
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85.60.Jb Light-emitting devices

Synchrotron radiation infrared microscopic study of non-bridging oxygen modes associated with laser-induced breakdown of fused silica

Manyalibo J. Matthews, Christopher W. Carr, Hans A. Bechtel, and Rajesh N. Raman

Appl. Phys. Lett. 99, 151109 (2011); http://dx.doi.org/10.1063/1.3651755 (3 pages) | Cited 5 times

Online Publication Date: 13 October 2011

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Nanosecond pulse laser-driven optical breakdown at SiO2 surfaces as probed by synchrotron-based Fourier transform infrared (SRFTIR) and photoluminescence (PL) microscopies is presented. SRFTIR mapping of laser damage identified localized non-bridging Si-O vibrational modes at ∼950 cm−1 which became stiffer as 355 nm laser pulse lengths were increased from 5 to 20 ns. The bridging Si-O-Si transverse optic mode frequency varied significantly across damaged regions indicating a wide range of average bond angles, softening slightly with increasing pulse length. 355 nm-excited PL images of laser modified regions could be directly correlated with the structural modifications identified through SRFTIR.
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78.30.Hv Other nonmetallic inorganics
78.47.jd Time resolved luminescence
78.55.Hx Other solid inorganic materials
61.82.Ms Insulators
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.50.Lt Crystal binding; cohesive energy

Switch-on dynamics of nanocavity laser devices

M. Lorke, T. R. Nielsen, and J. Mørk

Appl. Phys. Lett. 99, 151110 (2011); http://dx.doi.org/10.1063/1.3651765 (3 pages) | Cited 2 times

Online Publication Date: 13 October 2011

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Theoretical investigations of the switch-on behavior of semiconductor quantum dot based nanocavity laser devices are presented. From a microscopic treatment of the carrier-carrier and carrier-photon interaction, we find a fast switch-on of the laser device that is enabled by ultrafast carrier dynamics and heavily damped relaxation oscillations. We show that the timescales of the dynamics within the continuum states and the quantum dot states are strongly coupled and investigate the time dependence of the non-equilibrium scattering rates in detail.
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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

Wide depletion width of 1 eV GaInNAs solar cells by thermal annealing

I. R. Sellers, W.-S. Tan, K. Smith, S. Hooper, S. Day, and M. Kauer

Appl. Phys. Lett. 99, 151111 (2011); http://dx.doi.org/10.1063/1.3648110 (3 pages) | Cited 2 times

Online Publication Date: 13 October 2011

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We present high quality GaInNAs p-i-n solar cells with depletion widths in excess of 1 μm for material absorbing in the practically important 1 eV band gap regime. This is achieved through optimization of post-growth rapid thermal annealing at a temperature of ∼ 910 °C. Despite the improvements in material quality evidenced by a low background impurity concentration and improved minority carrier collection, the external quantum efficiency remains limited to ∼50%. This is attributed to losses due to efficient radiative recombination in the bulk GaInNAs intrinsic region enhanced via localization of carriers in alloy fluctuations.
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88.40.H- Solar cells (photovoltaics)

One-way cloak based on nonreciprocal photonic crystal

Cheng He, Xiao-Liu Zhang, Liang Feng, Ming-Hui Lu, and Yan-Feng Chen

Appl. Phys. Lett. 99, 151112 (2011); http://dx.doi.org/10.1063/1.3648112 (3 pages) | Cited 2 times

Online Publication Date: 13 October 2011

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We propose a physical concept of non-reciprocal transformation optics, by which a one-way invisible cloak is designed. The one-way invisible cloak is made of a coordinate-transformed nonreciprocal photonic crystal, showing a perfect cloaking for wave incident from one direction but acting as a perfect reflector for wave from the counter direction. The proposed design shows a high promise of applications in military, as protecting the own information to be detected but efficiently grabbing the information from the “enemy” side.
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42.79.-e Optical elements, devices, and systems
41.20.-q Applied classical electromagnetism
42.15.Eq Optical system design
42.70.Qs Photonic bandgap materials

Microphotonic parabolic light directors fabricated by two-photon lithography

J. H. Atwater, P. Spinelli, E. Kosten, J. Parsons, C. Van Lare, J. Van de Groep, J. Garcia de Abajo, A. Polman, and H. A. Atwater

Appl. Phys. Lett. 99, 151113 (2011); http://dx.doi.org/10.1063/1.3648115 (3 pages) | Cited 7 times

Online Publication Date: 13 October 2011

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We have fabricated microphotonic parabolic light directors using two-photon lithography, thin-film processing, and aperture formation by focused ion beam lithography. Optical transmission measurements through upright parabolic directors 22 μm high and 10 μm in diameter exhibit strong beam directivity with a beam divergence of 5.6°, in reasonable agreement with ray-tracing and full-field electromagnetic simulations. The results indicate the suitability of microphotonic parabolic light directors for producing collimated beams for applications in advanced solar cell and light-emitting diode designs.
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42.79.-e Optical elements, devices, and systems
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.15.Dp Wave fronts and ray tracing

Electro-absorption modulation in horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguides

Shiyang Zhu, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 99, 151114 (2011); http://dx.doi.org/10.1063/1.3653240 (3 pages) | Cited 10 times

Online Publication Date: 13 October 2011

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An ultracompact, broadband, and fully complementary metal-oxide-semiconductor (CMOS) compatible Si nanoplasmonic electro-absorption modulator is proposed based on the recently developed horizontal metal-insulator-silicon-insulator-metal nanoplasmonic slot waveguide. The modulation relies on a highly accumulated electron layer at the insulator/Si interface induced by an applied voltage. Proof-of-concept devices are fabricated using standard Si CMOS technology. A 3-dB modulation around 1550 nm is measured under ∼6.5 V bias for a device with total length of only 4 μm. The design suggests that larger modulation could be achieved by using high-κ dielectrics as the insulator, thinning down the insulator thickness, and narrowing the Si core of the nanoplasmonic waveguide.
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85.40.-e Microelectronics: LSI, VLSI, ULSI; integrated circuit fabrication technology
42.79.Gn Optical waveguides and couplers
42.79.Hp Optical processors, correlators, and modulators
77.55.D- High-permittivity gate dielectric films

Control of spontaneous emission in a volume of functionalized hyperbolic metamaterial

T. Tumkur, G. Zhu, P. Black, Yu. A. Barnakov, C. E. Bonner, and M. A. Noginov

Appl. Phys. Lett. 99, 151115 (2011); http://dx.doi.org/10.1063/1.3631723 (3 pages) | Cited 8 times

Online Publication Date: 13 October 2011

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We have developed a simple method to fabricate lamellar metal-dielectric hyperbolic metamaterials on flat, flexible, and curvilinear substrates, which allows for functionalization of dielectric layers by dye molecules. The control of spontaneous emission of dye molecules with hyperbolic metamaterials has been studied in two different sample configurations, and the effect has been found to be much stronger when emitters are placed inside the metamaterial rather than on its surface.
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42.70.-a Optical materials
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
42.50.-p Quantum optics

Effect of stimulated emission on the transport characteristics of terahertz quantum-cascade lasers

R. Sharma, L. Schrottke, M. Wienold, K. Biermann, R. Hey, and H. T. Grahn

Appl. Phys. Lett. 99, 151116 (2011); http://dx.doi.org/10.1063/1.3653262 (3 pages) | Cited 1 time

Online Publication Date: 13 October 2011

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We investigate the effect of stimulated emission on the transport characteristics of terahertz quantum-cascade lasers operating in a frequency range between 4.3 and 4.6 THz. The impact of stimulated emission is varied by changing the mirror losses via damaging one or two facets. In the case of voltage-driven measurements, a reduction in the current density near the onset of stimulated emission is observed for the facet-damaged lasers as compared to the original one. The measurements are in qualitative agreement with results of numerical simulations including the effect of stimulated emission.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Critical optical coupling between a GaAs disk and a nanowaveguide suspended on the chip

C. Baker, C. Belacel, A. Andronico, P. Senellart, A. Lemaitre, E. Galopin, S. Ducci, G. Leo, and I. Favero

Appl. Phys. Lett. 99, 151117 (2011); http://dx.doi.org/10.1063/1.3651493 (3 pages) | Cited 3 times

Online Publication Date: 14 October 2011

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We report on an integrated GaAs disk/waveguide system. A millimeter-long waveguide is suspended and tapered on the chip over a length of 25 μm to evanescently couple to high Q optical whispering gallery modes of a GaAs disk. The critical coupling regime is obtained both by varying the disk/guide gap distance and the width of the suspended nanoscale taper. Experimental results are in good agreement with predictions from coupled mode theory.
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42.82.Et Waveguides, couplers, and arrays

Temperature dependence of the gain peak in p-doped InAs quantum dot lasers

M. Hutchings, I. O’Driscoll, P. M. Smowton, and P. Blood

Appl. Phys. Lett. 99, 151118 (2011); http://dx.doi.org/10.1063/1.3652702 (3 pages)

Online Publication Date: 14 October 2011

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Gain peak shifts with injection in undoped and p-doped InAs quantum dot laser structures between 200 K and 350 K are measured. The blue-shift with increasing injection, due to state-filling of the inhomogeneous distribution, is temperature independent for a fixed peak gain in the undoped sample, but temperature dependent in the doped sample. This is due to the wide electron state distribution and lowering of the electron quasi Fermi level by p-doping relative to the undoped device. While p-doping reduces the temperature dependence of the threshold current, it comes at the expense of increasing the temperature sensitivity of the wavelength.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
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Enhanced transmission of THz radiation through sub-wavelength, asymmetry metallic hole arrays

M. X. Qiu, S. C. Ruan, H. Su, C. D. Wang, M. Zhang, R. L. Wang, and H. W. Liang

Appl. Phys. Lett. 99, 151501 (2011); http://dx.doi.org/10.1063/1.3633269 (3 pages) | Cited 1 time

Online Publication Date: 12 October 2011

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Strongly enhanced transmission of terahertz radiation pulses through asymmetry rectangular hole arrays with various hole lengths are obtained experimentally. The transmission magnitudes increase and their positions shift to lower frequency with increasing hole length. The maximum transmittance peak is observed for the sample with a hole length of 400 μm. Apparent angle-dependent behavior is observed in the transmission spectra of the 200 × 400 μm2 hole array, which due to the size effect of the rectangular hole along the two orthogonal axes. The resonance frequencies are deduced according to the surface plasmon polaritons modes. Our experiment results closely match the theoretical calculations.
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78.70.Gq Microwave and radio-frequency interactions
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)
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Theoretical analysis of the formation of face-centered cubic Si nanocrystals by magnetron sputtering

Shengliang Hu, Jingqi Zhang, Jinlong Yang, Jun Liu, and Shirui Cao

Appl. Phys. Lett. 99, 151901 (2011); http://dx.doi.org/10.1063/1.3651485 (3 pages) | Cited 2 times

Online Publication Date: 10 October 2011

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To have a clear insight into the physical origin of the nucleation of face-centered cubic Si in the magnetron sputtering condition, a theoretical model was proposed by taking the capillary effect of the nanosized curvatures of the critical nucleus and the concave surface on the substrate into account. The calculation shows that the size and energy of the critical nucleation depend on the radius of the concave surface on the substrate and the temperature. Both the smaller radius of concave surface and the higher temperature are propitious to the formation of face-centered cubic Si nanocrystals.
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81.07.Bc Nanocrystalline materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.15.Cd Deposition by sputtering

Photoluminescence and cathodoluminescence from nanostructured silicon surface

Manas Ranjan Gartia, Yi Chen, and Gang Logan Liu

Appl. Phys. Lett. 99, 151902 (2011); http://dx.doi.org/10.1063/1.3648108 (3 pages) | Cited 1 time

Online Publication Date: 10 October 2011

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We report the photoluminescence (PL) and cathodoluminescence (CL) study of nanostructured poly-crystalline silicon surface fabricated by lithography-less, reactive ion etching process. Photoluminescence in visible range at room temperature with peak position between 630 nm and 720 nm is observed without any oxidation or annealing steps. X-ray photoemission (XPS) and Auger electron spectroscopy (AES) revealed the presence of silicon oxide. The observed cathodoluminescence in green and red regions of the visible spectrum are due to nano-scaled tips and their coating with nonstoichiometric silicon oxide.
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78.55.Ap Elemental semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
81.07.Bc Nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing
81.65.Cf Surface cleaning, etching, patterning
73.20.At Surface states, band structure, electron density of states

Electron-phonon interaction effects on the direct gap transitions of nanoscale Si films

V. K. Kamineni and A. C. Diebold

Appl. Phys. Lett. 99, 151903 (2011); http://dx.doi.org/10.1063/1.3650470 (3 pages) | Cited 1 time

Online Publication Date: 10 October 2011

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This study shows that the dielectric function of crystalline Si quantum wells (c-Si QW) is influenced by both carrier confinement and electron-phonon interactions. The energy shifts and lifetime broadening of the excitonic E1 direct gap transition of c-Si QWs from 2 to 10 nm are found to have a significant dimensional and temperature dependence that can be traced to changes in the phonon dispersion of nanoscale films. The influence of electron-phonon interactions on the dielectric function was verified by altering the phonon dispersion using different dielectric layers above a 5 nm c-Si QW.
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81.07.St Quantum wells
73.63.Hs Quantum wells
63.22.Np Layered systems
63.20.kd Phonon-electron interactions
81.05.Cy Elemental semiconductors
77.22.Ch Permittivity (dielectric function)

Q-factor control of a microcantilever by mechanical sideband excitation

Warner J. Venstra, Hidde J. R. Westra, and Herre S. J. van der Zant

Appl. Phys. Lett. 99, 151904 (2011); http://dx.doi.org/10.1063/1.3650714 (3 pages) | Cited 11 times

Online Publication Date: 10 October 2011

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We demonstrate the coupling between the fundamental and second flexural modes of a microcantilever. A mechanical analogue of cavity-optomechanics is then employed, where the mechanical cavity is formed by the second vibrational mode of the same cantilever, coupled to the fundamental mode via the geometric nonlinearity. By exciting the cantilever at the sum and difference frequencies between fundamental and second flexural modes, the motion of the fundamental mode of the cantilever is damped and amplified. This concept makes it possible to enhance or suppress the Q-factor over a wide range.
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46.40.Ff Resonance, damping, and dynamic stability
43.40.-r Structural acoustics and vibration

Simultaneous self-collimation of fundamental and second-harmonic in sonic crystals

E. Soliveres, I. Pérez-Arjona, R. Picó, V. Espinosa, V. J. Sánchez-Morcillo, and K. Staliunas

Appl. Phys. Lett. 99, 151905 (2011); http://dx.doi.org/10.1063/1.3643497 (3 pages) | Cited 1 time

Online Publication Date: 11 October 2011

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Simultaneous self-collimation of sound beams with different frequencies, corresponding to fundamental wave and to its second harmonic, is proposed theoretically and demonstrated experimentally. The result is obtained when the isofrequency contours for each harmonics, corresponding to different propagation bands, develop flat segments along the same direction. The effect can be utilized for managing (enhancement and control) of nonlinear frequency mixing of narrow sound beams.
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43.25.Ed Effect of nonlinearity on velocity and attenuation
43.35.Cg Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in solids; elastic constants

Effect of carbon doping on the structure of amorphous GeTe phase change material

G. E. Ghezzi, J. Y. Raty, S. Maitrejean, A. Roule, E. Elkaim, and F. Hippert

Appl. Phys. Lett. 99, 151906 (2011); http://dx.doi.org/10.1063/1.3651321 (3 pages) | Cited 6 times

Online Publication Date: 11 October 2011

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Carbon-doped GeTe is a promising material for use in phase change memories since the addition of C increases the stability of the amorphous phase. By combining x-ray total scattering experiments and ab initio molecular dynamics, we show that carbon deeply modifies the structure of the amorphous phase through long carbon chains and tetrahedral and triangular units centered on carbon. A clear signature of these units is the appearance of an additional interatomic distance, around 3.3 Å in the measured pair distribution function. Besides, the first Ge-Ge and Ge-Te distances are almost not affected by doping.
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61.43.Er Other amorphous solids
78.70.Ck X-ray scattering
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