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1 May 2006

Volume 88, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 181102 (2006); http://dx.doi.org/10.1063/1.2200148 (3 pages)

Yanyi Huang, Wei Liang, Joyce K. S. Poon, Yong Xu, Reginald K. Lee, and Amnon Yariv
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Optimized configuration for transmissive and reflective bistable chiral-splay nematic liquid crystal device

Seo Hern Lee, Tae-Hoon Yoon, and Jae Chang Kim

Appl. Phys. Lett. 88, 181101 (2006); http://dx.doi.org/10.1063/1.2198476 (3 pages) | Cited 3 times

Online Publication Date: 1 May 2006

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The optimized configurations to use a bistable chiral-splay nematic liquid crystal cell as transmissive and reflective display are calculated using the Mueller matrix method. By numerical calculation, nontwist 0° splay state of bistable states is optimized so that the dark state is completely achieved over the entire visible-wavelength range. Based on the optimized conditions, we have experimentally demonstrated a high-contrast ratio of 200:1 in transmissive display and 40:1 in reflective display without using a wideband retardation film.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.30.-v Liquid crystals
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Spiro-oxazine photochromic fiber optical switch

Yanyi Huang, Wei Liang, Joyce K. S. Poon, Yong Xu, Reginald K. Lee, and Amnon Yariv

Appl. Phys. Lett. 88, 181102 (2006); http://dx.doi.org/10.1063/1.2200148 (3 pages) | Cited 2 times

Online Publication Date: 2 May 2006

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A photochromic all-optical switch in telecommunication-grade fiber is fabricated by filling a fiber Bragg grating Fabry-Pérot resonator with a spiro-oxazine solution. The narrow linewidth of the resonator allows for a high sensitivity of the resonance wavelengths to the index change. The switch is controlled by low intensity UV light exposure, and operation at infrared telecommunication wavelengths is demonstrated. The switching speed on the order of minutes has been achieved.
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42.81.Wg Other fiber-optical devices
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Pc Optical bistability, multistability, and switching, including local field effects

Room-temperature operation of λ ≈ 7.5 μm surface-plasmon quantum cascade lasers

M. Bahriz, V. Moreau, J. Palomo, R. Colombelli, D. A. Austin, J. W. Cockburn, L. R. Wilson, A. B. Krysa, and J. S. Roberts

Appl. Phys. Lett. 88, 181103 (2006); http://dx.doi.org/10.1063/1.2198016 (3 pages) | Cited 17 times

Online Publication Date: 2 May 2006

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We report the pulsed, room-temperature operation of λ ≈ 7.5 μm quantum cascade lasers (QCLs) in which the optical mode is a surface-plasmon polariton excitation. Previously reported devices based on this concept operate at cryogenic temperatures only. The use of a silver-based electrical contact with reduced optical losses at the QCL emission wavelength allows a reduction of the laser threshold current by a factor of 2 relative to samples with a gold-based contact layer. As a consequence, the devices exhibit room-temperature operation with threshold current densities ∼ 6.3 kA/cm2. These devices could be used as all-electrical surface-plasmon generators at midinfrared wavelengths.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Dielectric characteristic of photoinduced isomerization in azo-dye doped polymeric matrices

Duanbin Luo and Li Deng

Appl. Phys. Lett. 88, 181104 (2006); http://dx.doi.org/10.1063/1.2200390 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2006

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The dielectric permittivities and losses of poly(methyl methacrylate) doped with different concentrations of azo dye are investigated under the irradiation of 532 nm light for the first time. The dielectric permittivities increase with the concentration of chromophores increasing, and the dielectric relaxation is mainly influenced by the doped azo-dye chromophores. Given the dye concentration, the dielectric permittivities depend on the pump power of 532 nm light. With the increase of pumping light power, the low frequency dielectric losses increase while the high frequency dielectric losses decrease. The results are explained based on the photoinduced isomerization of chromophores and the interaction between the chromophores and polymer matrices.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
82.50.Hp Processes caused by visible and UV light
82.30.Qt Isomerization and rearrangement

Anomalous dispersion measurement in terahertz frequency region by photomixing

G. Mouret, S. Matton, R. Bocquet, D. Bigourd, F. Hindle, A. Cuisset, J. F. Lampin, and D. Lippens

Appl. Phys. Lett. 88, 181105 (2006); http://dx.doi.org/10.1063/1.2200393 (3 pages) | Cited 16 times

Online Publication Date: 3 May 2006

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Photomixing and coherent homodyne detection have been used to measure the absorption and dispersion of dielectric media. The signal to noise ratio was sufficient to allow the dispersion and absorption characteristics of a polytetrafluoroethylen (Teflon) sample to be extracted up to a frequency of 1.6 THz. Due to the relatively narrow spectral linewidth of terahertz source, estimated to be in order of 5 MHz, the anomalous dispersion in the vicinity of a rotational transition of carbonyl sulfide is clearly observed, with a refractive index variation of about 10−4 being measured at frequencies within 40 MHz of the transition.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
78.70.Gq Microwave and radio-frequency interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Near-anode phase separation in thermally poled soda lime glass

Honglin An and Simon Fleming

Appl. Phys. Lett. 88, 181106 (2006); http://dx.doi.org/10.1063/1.2200394 (3 pages) | Cited 3 times

Online Publication Date: 3 May 2006

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Soda lime glass was thermally poled at 280 °C with dc voltages up to 2 kV. Second-order nonlinearity was found in a layer ∼ 1.7 μm beneath the anode surface with second-harmonic microscopy. Scanning electron microscopy was employed to examine the microstructure of the poled glass under the anode. In the depletion region, pillar-shaped phase separations were found which could impede ion migration and enhance the stability of the induced second-order nonlinearity in the poled soda lime glass.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
77.22.Ej Polarization and depolarization
61.43.Fs Glasses
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
66.30.H- Self-diffusion and ionic conduction in nonmetals

Probing carrier dynamics in implanted and annealed polycrystalline silicon thin films using white light

Emmanouil Lioudakis, Andreas Othonos, and A. G. Nassiopoulou

Appl. Phys. Lett. 88, 181107 (2006); http://dx.doi.org/10.1063/1.2200745 (3 pages) | Cited 6 times

Online Publication Date: 3 May 2006

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Polycrystalline silicon thin film samples implanted and annealed at various temperatures have been studied using ultrafast laser pulse excitation. Nondegenerate pump-probe technique has been utilized to investigate carrier dynamics in the highly implanted samples at a relatively small fluence. A model based on two coupled differential equations has been used to fit the experimental data, giving a simple but adequate picture of the dynamics of this system. Basic sample parameters such as carrier trapping times, diffusion coefficient, and penetration depths have been extracted, providing a dependence on the annealing temperature for the samples under investigation.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.66.Db Elemental semiconductors and insulators
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Cc Kinetics of defect formation and annealing
61.72.uf Ge and Si
73.61.Cw Elemental semiconductors

High Q-factor colloidal nanocrystal-based vertical microcavity by hot embossing technology

Luigi Martiradonna, Luigi Carbone, Milena De Giorgi, Liberato Manna, Giuseppe Gigli, Roberto Cingolani, and Massimo De Vittorio

Appl. Phys. Lett. 88, 181108 (2006); http://dx.doi.org/10.1063/1.2200748 (3 pages) | Cited 9 times

Online Publication Date: 3 May 2006

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We report on the fabrication and optical characterization of vertical hybrid microcavities in which a layer of colloidal nanocrystals dispersed in an organic matrix is embedded between two inorganic mirrors. The devices are fabricated by a technique based on the unconventional use of the hot embossing technology, which allows a very fine control of the cavity length. The technique exploits a λ-thick microstructured dielectric top mirror pressed onto the bottom one, previously coated with the active layer, to sandwich the cavity and precisely control its thickness. Room-temperature photoluminescence measurements show a Q factor as high as 146 for our devices.
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42.82.Gw Other integrated-optical elements and systems
42.79.Bh Lenses, prisms and mirrors

Soft x-ray polarizer for optical productions of any orthogonal state of the linear and circular polarization modes

Dae-Eun Jeong, Ki-Suk Lee, and Sang-Koog Kim

Appl. Phys. Lett. 88, 181109 (2006); http://dx.doi.org/10.1063/1.2200753 (3 pages) | Cited 2 times

Online Publication Date: 3 May 2006

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An efficient soft x-ray polarizer that is able to optically convert a linear polarization state to any orthogonal state of not only linear but also circular polarization modes is found by means of numerical calculations of the intensities of individual orthogonal polarization components in reflected waves. Calculation results, using the known linear-polarization-mode based Kerr matrix as well as a newly derived circular-polarization-mode based Kerr matrix, indicate that a +45° or −45° linearly polarized incident wave can be readily converted to any orthogonal states of both circular and linear polarization modes, i.e., left- and right-handed circular and s- and p-linear polarizations through reflection, at certain grazing angles of incidence near the critical angle from a simple ferromagnetic thin film of Co(9.0 nm)/Si substrate. The intensities of almost pure circularly or linearly polarized reflected waves are about 10% or less in a certain spectral soft x-ray range just below the absorption edges of constituent magnetic elements. The counterpart orthogonal states of the linear as well as circular modes can be rapidly switched simply by reversing oppositely the orientation of longitudinal magnetizations. These results suggest that the orthogonal polarization states of the circular- and linear-polarization modes converted from such a polarizing optical element through reflection can be practically used in probing the vector quantities of element specific magnetizations in multicomponent magnetic materials.
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07.85.-m X- and γ-ray instruments
42.79.Ci Filters, zone plates, and polarizers
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
75.50.Cc Other ferromagnetic metals and alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Pulse-width selective all-optical switching

Youfa Wang and Wenfeng Wang

Appl. Phys. Lett. 88, 181110 (2006); http://dx.doi.org/10.1063/1.2200755 (3 pages)

Online Publication Date: 3 May 2006

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The coupled nonlinear Schrödinger equations governing the optical pulse coupling in a nonlinear directional coupler are solved numerically. The numerical results show that the optical pulse can be coupled back and forth efficiently between the two-coupled waveguides by varying the input pulse duration. The energy transfer efficiency between the two-coupled waveguide can be greater than 90%. It implies that the pulse-width dependent all-optical switching can be realized in a nonlinear directional coupler.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.79.Gn Optical waveguides and couplers

Enhanced hard x-ray emission from microdroplet preplasma

M. Anand, S. Kahaly, G. Ravindra Kumar, M. Krishnamurthy, A. S. Sandhu, and P. Gibbon

Appl. Phys. Lett. 88, 181111 (2006); http://dx.doi.org/10.1063/1.2200761 (3 pages) | Cited 8 times

Online Publication Date: 3 May 2006

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We perform a comparative study of hard x-ray emission from femtosecond laser plasmas in 15 μm methanol microdroplets and Perspex target. The hard x-ray yield from droplet plasmas is ≃ 68 times more than that obtained from solid plasmas at 2×1015 W cm−2. A 10 ns prepulse at about 5% of the main pulse appears to be essential for hard x-ray generation from droplets. Hot electron temperature of 36 keV is measured from the droplets at 8×1014 W cm−2, whereas a three times higher intensity is needed to obtain similar hot electron temperatures from Perspex plasmas. Particle-in-cell simulations with very long scale-length density profiles support experimental observations.
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52.59.Px Hard X-ray sources
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Ph X-ray, γ-ray, and particle generation
52.65.Rr Particle-in-cell method

Three-dimensional metallic photonic crystals fabricated by soft lithography for midinfrared applications

Jae-Hwang Lee, Chang-Hwan Kim, Yong-Sung Kim, Kai-Ming Ho, Kristen Constant, and Cha Hwan Oh

Appl. Phys. Lett. 88, 181112 (2006); http://dx.doi.org/10.1063/1.2201621 (3 pages) | Cited 14 times

Online Publication Date: 3 May 2006

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We present an efficient method of fabricating freestanding three-dimensional metallic photonic crystals using soft lithography. Low cost and ease of fabrication are achieved through gold sputter deposition on a freestanding woodpile polymer template. We compare experimental results to theoretical calculations for tetragonal and face-centered-tetragonal structures as a function of the number of layers. The photonic crystals behave like full metallic structures with a photonic band edge at a wavelength of 3.5 μm. The rejection rates of the structures are about 10 dB/layer.
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42.70.Qs Photonic bandgap materials
81.16.Nd Micro- and nanolithography
81.15.Cd Deposition by sputtering

Fabrication and efficiency improvement of micropillar InGaN/Cu light-emitting diodes with vertical electrodes

W. K. Wang, S. Y. Huang, S. H. Huang, K. S. Wen, D. S. Wuu, and R. H. Horng

Appl. Phys. Lett. 88, 181113 (2006); http://dx.doi.org/10.1063/1.2201622 (3 pages) | Cited 14 times

Online Publication Date: 3 May 2006

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We present a micropillar surface structure based on the enhancement of the light extraction efficiency of the near-ultraviolet (409 nm) vertical-conducting InGaN light-emitting diode (LED) with an electroplated Cu substrate. The micropillar InGaN/Cu LED (chip size: 1×1 mm2) was fabricated using a combination of patterned sapphire substrate (PSS), laser lift-off, and copper electroplating processes. The PSS and Cu substrate can offer the advantages of dislocation reduction and thermal heat sink, respectively. It was found that the light output power (at 350 mA) of the micropillar InGaN/Cu LED sample can be improved by 39% as compared with that of the conventional InGaN/Cu LED one. This significant enhancement in output power could be attributed to the increase of the extraction efficiency which is a result of the increase in photon escaping probability caused by scattering the emission light at the micropillar surface. The light extraction efficiency can be further optimized by tuning the micropillar spacing, as evidenced by the ray-tracing simulation result.
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85.60.Jb Light-emitting devices
81.15.Pq Electrodeposition, electroplating

Three-photon absorption in water-soluble ZnS nanocrystals

Jun He, Wei Ji, Jun Mi, Yuangang Zheng, and Jackie Y. Ying

Appl. Phys. Lett. 88, 181114 (2006); http://dx.doi.org/10.1063/1.2198823 (3 pages) | Cited 22 times

Online Publication Date: 3 May 2006

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We report on large three-photon absorption (3PA) in glutathione-capped ZnS semiconductor nanocrystals (NCs), determined by both Z-scan and transient transmission techniques with 120 fs laser pulses. The monodispersed, water-soluble ZnS NCs are synthesized by a modified protocol with a mean diameter of 2.5 nm. Their 3PA cross section is determined to be ∼ 2.7×10−78 cm6 s2 photon−2 at an optimal wavelength of commercial Ti:sapphire femtosecond lasers. This value is nearly one order of magnitude greater than that of CdS NCs, and four to five orders of magnitude higher than those of the previously reported common UV fluorescent dyes.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.70.-a Optical materials
78.47.-p Spectroscopy of solid state dynamics

Evidence for a “dark exciton” state of PbS nanocrystals in a silicate glass

R. Espiau de Lamaëstre, H. Bernas, D. Pacifici, G. Franzó, and F. Priolo

Appl. Phys. Lett. 88, 181115 (2006); http://dx.doi.org/10.1063/1.2201885 (3 pages) | Cited 11 times

Online Publication Date: 4 May 2006

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PbS nanocrystals (diameter of 5–7 nm) were synthesized via sulfur ion implantation in Pb-based glasses and postannealing. They display strong emission at around 1.5 μm due to quantum confinement, and a very large photoluminescence (PL) excitation cross section. The PL intensity and decay rate temperature dependences provide evidence for a large energy splitting (ca. 30 meV) of the emitting exciton ground state fine structure, presumably due to the complex PbS electronic band structure.
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71.35.-y Excitons and related phenomena
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials

Remote angular displacement sensor based on Faraday effect: Experiment and modeling

C. M. Park, Y. Melikhov, and S. J. Lee

Appl. Phys. Lett. 88, 181116 (2006); http://dx.doi.org/10.1063/1.2201892 (3 pages) | Cited 4 times

Online Publication Date: 4 May 2006

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Recently, we have reported a magneto-optic angular displacement (MOAD) sensor where both the incident and reflected laser beams pass through a magneto-optic (MO) film. In this letter, we report a modified MOAD sensor where only a reflected laser beam passes through the MO film. With the modified configuration, the modified MOAD sensor is a truly remote sensor such that the MO film can be located close to the detector and far from the sample. Furthermore, the modified sensor system can measure angular displacements with an improved resolution of 1×10−3 deg, which is ten times better than that previously reported.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
06.30.Bp Spatial dimensions (e.g., position, lengths, volume, angles, and displacements)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
85.70.Sq Magnetooptical devices
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy

Enhanced performance of an InGaN–GaN light-emitting diode by roughening the undoped-GaN surface and applying a mirror coating to the sapphire substrate

Wei Chih Peng and YewChung Sermon Wu

Appl. Phys. Lett. 88, 181117 (2006); http://dx.doi.org/10.1063/1.2199613 (3 pages) | Cited 18 times

Online Publication Date: 4 May 2006

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An InGaN–GaN light-emitting diode (LED) with a roughened undoped-GaN surface and a silver mirror on the sapphire substrate was fabricated through a double transfer method. It was found that, at an injection current of 20 mA, its luminance intensity was 100% larger than conventional LEDs. Its output power was 49% larger than conventional LEDs.
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85.60.Jb Light-emitting devices
68.47.Fg Semiconductor surfaces
42.79.Wc Optical coatings

Fast coherent all-optical flip-flop memory

Jani Oksanen and Jukka Tulkki

Appl. Phys. Lett. 88, 181118 (2006); http://dx.doi.org/10.1063/1.2199971 (3 pages) | Cited 2 times

Online Publication Date: 5 May 2006

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Coherent nonlinear feedback is shown to eliminate the most critical transient problems in the known active integrated all-optical flip-flop structures, potentially increasing the operating speed by an order of magnitude. The nonlinearity is based on the interference of two coherent optical fields and on operating the pertinent laser amplifiers only above the laser threshold. Therefore the lasers have an approximately constant carrier density and an ever present photon population in the laser mode. This enables fast switching. Numerical analysis based on coupled rate equations demonstrates switching times below 25 ps (40 GHz).
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42.79.Vb Optical storage systems, optical disks
42.55.Px Semiconductor lasers; laser diodes

Laser emission at 0.8 μm from photopumped luminescent polymer microresonators

Takeyuki Kobayashi, Martin Djiango, Grace Jordan, Manuel Rüther, Werner J. Blau, Yasuhiro Suzuki, and Toshikuni Kaino

Appl. Phys. Lett. 88, 181119 (2006); http://dx.doi.org/10.1063/1.2198478 (3 pages) | Cited 11 times

Online Publication Date: 5 May 2006

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We present the results of a study on laser emission from luminescent polymer microresonators containing a near-infrared emitting dye, 2-(6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl)-3-methyl-benzothiazolium perchlorat. Poly(1-vinyl-2-pyrrolidone) microrings doped with the dye are fabricated around a 200-μm-diameter silica optical fiber by self-assembly and are shown to lase at around 835 nm under nanosecond photopumping at 532 nm. The threshold for lasing is found to be 311±87 μJ/cm2 (62.2±17.3 kW/cm2). The lower limit of the cavity quality factor is estimated to be 1.8×103.
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42.55.Mv Dye lasers
42.55.Sa Microcavity and microdisk lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Interdigitated multipixel arrays for the fabrication of high-power light-emitting diodes with very low series resistances

Arpan Chakraborty, L. Shen, H. Masui, S. P. DenBaars, and U. K. Mishra

Appl. Phys. Lett. 88, 181120 (2006); http://dx.doi.org/10.1063/1.2201878 (3 pages) | Cited 5 times

Online Publication Date: 5 May 2006

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We report on the fabrication of high-power light-emitting diodes (LEDs) with very low series resistance by employing a mask design consisting of interdigitated multipixel arrays. The reduction in the series resistance was mainly achieved by reducing the bulk n resistance and the n-contact resistance by increasing the effective perimeter of the mesa. The small separation of the p and n contacts of the individual pixel improved lateral current spreading. The distributed array of pixels also resulted in improved thermal management, effectively rendering high continuous-wave (cw) drive current operation. Significant improvement in electrical and optical performances was observed when the mask was applied to a 400 nm InGaN/GaN violet LED wafer, compared to a standard square-shaped LED with equal active area and fabricated from the same epitaxial wafer. Series resistance of less than 1 Ω was measured for 300 μm devices. A peak output power of 115 mW was obtained at 3.15 A cw drive current for the unpackaged device.
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85.60.Jb Light-emitting devices
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Resonance enhancement of optical second harmonic generation in a ZnO nanowire

R. Prasanth, L. K. van Vugt, D. A. M. Vanmaekelbergh, and H. C. Gerritsen

Appl. Phys. Lett. 88, 181501 (2006); http://dx.doi.org/10.1063/1.2200230 (3 pages) | Cited 23 times

Online Publication Date: 3 May 2006

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Two-photon absorption measurement has been carried out in a single 80 nm×10 μm ZnO nanowire using femtosecond laser pulses in the wavelength range of 700–800 nm. In addition to the deep-level green emission around 530 nm due to surface defects and the near band-edge ultraviolet emission around 360 nm due to the exciton, a second harmonic peak has been observed. The strength of the frequency-doubled component is found to enhance while the two-photon absorption wavelength is tuned towards the exciton wavelength of the nanowire. This behavior can be ascribed to the resonant exciton absorption in ZnO nanowires.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.67.Lt Quantum wires
78.47.-p Spectroscopy of solid state dynamics
71.55.Ht Other nonmetals
78.55.Hx Other solid inorganic materials
73.21.Hb Quantum wires

Analytical solution of space charge limited current for spherical and cylindrical objects

L. Oksuz

Appl. Phys. Lett. 88, 181502 (2006); http://dx.doi.org/10.1063/1.2201469 (3 pages) | Cited 4 times

Online Publication Date: 3 May 2006

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Analytical solutions for space charge limited currents in collisionless, electron-free sheaths are given for Cartesian, spherical, and cylindrical geometries. Constant current and current density are assumed. Until now, the problem of space charge limited current has not been solved either directly, in terms of series expansions, or numerically, for spherical and cylindrical objects. Analytical results show that the geometry of the system is important for determining the space charge limited current, sheath thickness, and sheath potential profile. This solution method can be used to solve similar nonlinear differential equations.
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52.25.Fi Transport properties
52.40.Kh Plasma sheaths
52.40.Hf Plasma-material interactions; boundary layer effects
02.60.Lj Ordinary and partial differential equations; boundary value problems
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Excited-state dynamics and nonlinear optical response of Ge nanocrystals embedded in silica matrix

Luca Razzari, Andrea Gnoli, Marcofabio Righini, Aykutlu Dâna, and Atilla Aydinli

Appl. Phys. Lett. 88, 181901 (2006); http://dx.doi.org/10.1063/1.2201550 (3 pages) | Cited 4 times

Online Publication Date: 1 May 2006

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We use a dedicated Z-scan setup, arranged to account for cumulative effects, to study the nonlinear optical response of Ge nanocrystals embedded in silica matrix. Samples are prepared with plasma-enchanced chemical-vapor deposition and post-thermal annealing. We measure a third-order nonlinear refraction coefficient of γ = 1×10−16 m2/W. The nonlinear absorption shows an intensity-independent coefficient of β = 4×10−10 m/W related to fast processes. In addition, we measure a second β component around 10−9 m/W with a relaxation time of 300 μs that rises linearly with the laser intensity. We associate its origin to the absorption of excited carriers from a surface-defect state with a long depopulation time.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
61.72.Cc Kinetics of defect formation and annealing
73.20.At Surface states, band structure, electron density of states
71.55.Cn Elemental semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Variation of surface morphology and electronic behavior under dynamic tensile conditions

W. Li, M. Cai, Z. Zong, and S. Yu

Appl. Phys. Lett. 88, 181902 (2006); http://dx.doi.org/10.1063/1.2193048 (3 pages) | Cited 7 times

Online Publication Date: 1 May 2006

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Mechanical deformation can lead to various surface changes such as surface electronic behavior. The effect of deformation on work function (WF) has been studied extensively, but the mechanism responsible for such effect has been unclear. In this study, we measured the variations in the WF typically of an Al–Mn alloy with respect to deformation under dynamic tensile conditions using a scanning Kelvin probe. Furthermore, we also investigate the contribution of surface morphology, represented by roughness, caused by different deformation conditions to the WF. It was demonstrated that the WF depends strongly on both deformation and deformation speed, whereas roughness depends on deformation but hardly deformation speed. The present study therefore suggests a significant role of dislocation mechanism in determining the WF although surface morphology or roughness associated with deformation also affects the WF.
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81.05.Bx Metals, semimetals, and alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.35.Gy Mechanical properties; surface strains
73.20.At Surface states, band structure, electron density of states

Semiconducting chalcogenide buffer layer for oxide heteroepitaxy on Si(001)

D. A. Schmidt, Taisuke Ohta, C.-Y. Lu, Aaron A. Bostwick, Q. Yu, Eli Rotenberg, F. S. Ohuchi, and Marjorie A. Olmstead

Appl. Phys. Lett. 88, 181903 (2006); http://dx.doi.org/10.1063/1.2199451 (3 pages) | Cited 4 times

Online Publication Date: 2 May 2006

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We report controlled laminar growth of a crystalline transition metal oxide on Si(001) without SiOx or silicide formation by utilizing the chalcogenide semiconductor gallium sesquiselenide (Ga2Se3) as a nonreactive buffer layer. Initial nucleation of both pure and Co-doped anatase (TiO2) is along Ga2Se3 nanowire structures, coalescing to a flat, multidomain film within two molecular layers. Arsenic-terminated Si(001) [Si(001):As] is stable against pure O2, but oxidizes when both Ti and O2 are present. The Si–TiO2 valence band offset using either buffer layer is about 2.8 eV, producing a staggered band alignment.
Show PACS
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
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