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20 Sep 2010

Volume 97, Issue 12, Articles (12xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 123101 (2010); http://dx.doi.org/10.1063/1.3490637 (3 pages)

Mark W. Licurse and Peter K. Davies
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Large optical bandwidth and polarization insensitive semiconductor optical amplifiers using strained InGaAsP quantum wells

H. Carrère, V. G. Truong, X. Marie, R. Brenot, G. De Valicourt, F. Lelarge, and T. Amand

Appl. Phys. Lett. 97, 121101 (2010); http://dx.doi.org/10.1063/1.3484151 (3 pages)

Online Publication Date: 20 September 2010

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The material gain of equal width InGaAsP/InGaAsP multi–quantum well active layers is calculated solving the Lüttinger–Kohn Hamiltonian, including tetragonal strain and confinement effects. The calculated optical bandwidth reaches 150 nm with a maximum polarization sensitivity of 1 dB between transverse electric (TE) and transverse magnetic (TM) emission over the −3 dB optical bandwidth. The corresponding device characterized by amplified spontaneous emission measurements shows an optical bandwidth with constant TE/TM ratio of almost 100 nm which can be improved up to 113 nm by increasing the barrier material band gap energy. Further enlargement of the optical bandwidth is expected by reducing the quantum well width.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
68.65.Fg Quantum wells

Temperature dependence of electronic transitions and optical properties in multiferroic BiFeO3 nanocrystalline film determined from transmittance spectra

W. W. Li (李文武), J. J. Zhu (诸佳俊), J. D. Wu (吴嘉达), J. Gan (干洁), Z. G. Hu (胡志高), M. Zhu (朱敏), and J. H. Chu (褚君浩)

Appl. Phys. Lett. 97, 121102 (2010); http://dx.doi.org/10.1063/1.3489926 (3 pages) | Cited 10 times

Online Publication Date: 21 September 2010

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The ultraviolet-infrared transmittance spectra of BiFeO3 nanocrystalline film have been studied in the temperature range 5.3–300 K. A redshift trend of the absorption edge and optical constants with increasing the temperature can be observed. Four interband electronic transitions can be uniquely assigned and strongly depend on the temperature. Moreover, two magnetic transitions located at about 150 and 200 K have been observed and can be interpreted as spin-reorientation transitions. It was found that the optical band gap decreases from 2.69±0.01 to 2.65±0.01 eV with increasing the temperature due to the modification of the electron-phonon interactions.
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77.55.Nv Multiferroic/magnetoelectric films
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
78.40.Ha Other nonmetallic inorganics
78.30.Hv Other nonmetallic inorganics
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
75.85.+t Magnetoelectric effects, multiferroics

Induced absorption dynamics in quantum dot based waveguide electroabsorbers

T. Piwonski, J. Pulka, E. A. Viktorov, G. Huyet, R. J. Manning, J. Houlihan, P. Mandel, and T. Erneux

Appl. Phys. Lett. 97, 121103 (2010); http://dx.doi.org/10.1063/1.3491805 (3 pages) | Cited 1 time

Online Publication Date: 22 September 2010

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Two-color pump-probe measurements are used to study the carrier dynamics of InAs/GaAs quantum dots in a waveguide structure under reverse bias conditions. For the case of initially populating the ground state (GS), we find relaxation dynamics that include both absorptive and bleaching components in the excited state (ES) wavelength range. We reproduce the main features of this induced absorption dynamics using a simple model with an additional term for induced absorption at the ES due to carriers injected at the GS. The induced absorption dynamics includes multiple recovery timescales which can be attributed to phonon-assisted processes of GS/ES interaction.
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77.22.Gm Dielectric loss and relaxation
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.05.Ea III-V semiconductors
71.20.Nr Semiconductor compounds

Long-period fiber gratings spontaneously written by a mechanism markedly different from Hill grating formation

H. Tu, S. Shin, R. John, and S. A. Boppart

Appl. Phys. Lett. 97, 121104 (2010); http://dx.doi.org/10.1063/1.3491842 (3 pages) | Cited 1 time

Online Publication Date: 22 September 2010

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Pumping a nonlinear germanosilicate fiber with intense near-infrared femtosecond laser pulses for supercontinuum generation may invoke multiphoton-assisted photosensitivity of glasses to write a long-period fiber grating. In sharp contrast to the spontaneous formation of a Hill grating that resonates with the writing wavelength through first-order diffraction, the long-period fiber grating resonates with the writing wavelength through second-order diffraction. This finding highlights the surprising light-matter interaction in a waveguide.
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42.81.Wg Other fiber-optical devices
42.79.Dj Gratings
42.65.-k Nonlinear optics

Internal efficiency of InGaN light-emitting diodes: Beyond a quasiequilibrium model

W. W. Chow, M. H. Crawford, J. Y. Tsao, and M. Kneissl

Appl. Phys. Lett. 97, 121105 (2010); http://dx.doi.org/10.1063/1.3490232 (3 pages) | Cited 6 times

Online Publication Date: 23 September 2010

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We propose a model to better investigate InGaN light-emitting diode (LED) internal efficiency by extending beyond the usual total carrier density rate equation approach. To illustrate its capability, the model is applied to study intrinsic performance differences between violet and green LEDs. The simulations show performance differences, at different current densities and temperatures, arising from variations in spontaneous emission and heat loss rates. By tracking the momentum-resolved carrier populations, these rate changes are, in turn, traced to differences in bandstructure and plasma heating. The latter leads to carrier distributions that deviate from the quasiequilibrium ones at lattice temperature.
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85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling

High-sensitivity detection of terahertz waves using nonlinear up-conversion in an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate crystal

Hiroaki Minamide, Jun Zhang, Ruixiang Guo, Katsuhiko Miyamoto, Seigo Ohno, and Hiromasa Ito

Appl. Phys. Lett. 97, 121106 (2010); http://dx.doi.org/10.1063/1.3489097 (3 pages) | Cited 1 time

Online Publication Date: 23 September 2010

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We achieved high-sensitivity, rapid-response detection of terahertz (THz) waves using an organic nonlinear optical crystal, 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST). Nonlinear up-conversion in the crystal resulted in a shift of THz waves to near-infrared radiation at room temperature. A minimum THz-wave peak power of about 300 μW was measured at 19.2 THz by detecting the up-converted optical signal with an InGaAs-based photodetector. A noise equivalent power of about 6 nW/Hz1/2 was estimated in this experiment. Optimum conditions were obtained for THz-wave detection using a DAST crystal.
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42.65.-k Nonlinear optics
78.30.-j Infrared and Raman spectra
85.60.Gz Photodetectors (including infrared and CCD detectors)
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)

Enhancement of light power for strain-compensated hybrid InGaN/InGaN/MgZnO light-emitting diodes

Seoung-Hwan Park, Yong-Tae Moon, Jeong Sik Lee, Ho Ki Kwon, Joong Seo Park, and Doyeol Ahn

Appl. Phys. Lett. 97, 121107 (2010); http://dx.doi.org/10.1063/1.3493648 (3 pages)

Online Publication Date: 23 September 2010

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Electronic and optical properties of strain-compensated InGaN/InGaN/MgZnO quantum well (QW) structures using a MgZnO substrate are investigated using the multiband effective mass theory. A strain-compensated InGaN/InGaN/MgZnO QW structure with a larger strain shows larger matrix element than that with a smaller strain. The spontaneous emission peak rapidly increases with increasing compressive strain because the matrix element is enhanced for the strain-compensated QW structure with a larger strain. In addition, we find that the strain-compensated QW structure with the larger Mg composition in the substrate has greater spontaneous emission peak than the strain-compensated QW structure with the smaller Mg composition in the substrate.
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85.60.Jb Light-emitting devices

Multicolor fluorescence enhancement from a photonics crystal surface

A. Pokhriyal, M. Lu, C. S. Huang, S. Schulz, and B. T. Cunningham

Appl. Phys. Lett. 97, 121108 (2010); http://dx.doi.org/10.1063/1.3485672 (3 pages) | Cited 2 times

Online Publication Date: 24 September 2010

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A photonic crystal substrate exhibiting resonant enhancement of multiple fluorophores has been demonstrated. The device, fabricated uniformly from plastic materials over a ∼ 3×5 in.2 surface area by nanoreplica molding, utilizes two distinct resonant modes to enhance electric field stimulation of a dye excited by a λ = 632.8 nm laser (cyanine-5) and a dye excited by a λ = 532 nm laser (cyanine-3). Resonant coupling of the laser excitation to the photonic crystal surface is obtained for each wavelength at a distinct incident angle. Compared to detection of a dye-labeled protein on an ordinary glass surface, the photonic crystal surface exhibited a 32× increase in fluorescent signal intensity for cyanine-5 conjugated streptavidin labeling, while a 25× increase was obtained for cyanine-3 conjugated streptavidin labeling. The photonic crystal is capable of amplifying the output of any fluorescent dye with an excitation wavelength in the 532 nm<λ<633 nm range by selection of an appropriate incident angle. The device is designed for biological assays that utilize multiple fluorescent dyes within a single imaged area, such as gene expression microarrays.
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87.15.mq Luminescence
87.80.-y Biophysical techniques (research methods)

An efficiently tunable microring resonator using a liquid crystal-cladded polymer waveguide

Tao Cai, Qingkun Liu, Yaocheng Shi, Pengxin Chen, and Sailing He

Appl. Phys. Lett. 97, 121109 (2010); http://dx.doi.org/10.1063/1.3492848 (3 pages)

Online Publication Date: 24 September 2010

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An electrically tunable polymer microring resonator of large tunability and low applied voltage is demonstrated using active liquid crystal (LC) cladding. A large tuning range of 0.73 nm is achieved due to more homogenous LC molecular alignment and enhanced interaction of the light with the LC cladding in the simplified polymer waveguide structure. The operating voltage decreases to 10 V with a threshold of only 3 V by the utilization of interdigital electrodes.
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42.79.Gn Optical waveguides and couplers
42.70.Df Liquid crystals
07.10.Cm Micromechanical devices and systems

Temperature dependence of electroabsorption dynamics in an InAs quantum-dot saturable absorber at 1.3 μm and its impact on mode-locked quantum-dot lasers

M. A. Cataluna, D. B. Malins, A. Gomez-Iglesias, W. Sibbett, A. Miller, and E. U. Rafailov

Appl. Phys. Lett. 97, 121110 (2010); http://dx.doi.org/10.1063/1.3489104 (3 pages) | Cited 3 times

Online Publication Date: 24 September 2010

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We report temperature-dependent absorption recovery times in an InAs p-i-n ridge waveguide quantum-dot modulator under low reverse bias, investigated via subpicosecond pump-probe measurements. The measured decrease in absorption recovery time with increasing temperature (293–319 K) is in excellent agreement with a thermionic emission model. A similar trend in pulse duration with increasing temperature is also observed from a two-section mode-locked quantum-dot laser fabricated from a similar epitaxial structure. These measurements confirm the key role of the absorber recovery time in the reduction in the pulses generated by two-section mode-locked quantum-dot lasers, both at room and elevated temperatures.
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42.50.Gy Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Reduction in surface recombination and enhancement of light emission in silicon photonic crystals treated by high-pressure water-vapor annealing

Masayuki Fujita, Bernard Gelloz, Nobuyoshi Koshida, and Susumu Noda

Appl. Phys. Lett. 97, 121111 (2010); http://dx.doi.org/10.1063/1.3489419 (3 pages) | Cited 3 times

Online Publication Date: 24 September 2010

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We propose and demonstrate the application of high-pressure water-vapor annealing (HWA) to silicon photonic crystals for surface passivation. We find that the photoluminescence intensity from a sample treated with HWA is enhanced by a factor of ∼ 6. We confirm that this enhancement originates from a reduction in the surface-recombination velocity (SRV) by a factor of ∼ 0.4. The estimated SRV is as low as 2.1×103 cm/s at room temperature. These results indicate that HWA is a promising approach for efficient surface passivation in silicon photonic nanostructures.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.55.Ap Elemental semiconductors
81.05.Cy Elemental semiconductors
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The nature of high voltage initiation of an electrical arc in a vacuum

I. I. Beilis

Appl. Phys. Lett. 97, 121501 (2010); http://dx.doi.org/10.1063/1.3491446 (3 pages) | Cited 1 time

Online Publication Date: 22 September 2010

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Generally the gap voltage at the moment of arc initiation in a vacuum is significantly larger than the voltage in developed arcs. This phenomenon was studied here suggesting a physical model for initially triggered at the bulk cathode plasma and then for appeared transient spot. The model allows calculating the transient energy flux to the cathode and the transient cathode potential drop (CPD). It was shown that the CPD at the moment of spot ignition is relatively large and significantly contributes to the arc voltage at arc ignition. The subsequent voltage decrease can be understood from the transient CPD behavior during arc development. The voltage oscillation in an arc was explained by suggested model taking into account the spot shifting on a cold location.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
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Photoluminescence from colloids containing aluminum hydroxide nanocrystals with uniform size

T. H. Li, L. Z. Liu, X. L. Wu, J. C. Shen, F. Gao, and Paul K. Chu

Appl. Phys. Lett. 97, 121901 (2010); http://dx.doi.org/10.1063/1.3491161 (3 pages) | Cited 2 times

Online Publication Date: 20 September 2010

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Aluminum hydroxide nanocrystals consisting of an amorphous shell and crystalline core are fabricated by pulsed laser ablation of an aluminum target in water. The colloid consisting of nanocrystals with a uniform size exhibits a size-independent photoluminescence (PL) band at ∼ 383 nm. According to the PL excitation spectra and time-resolved PL decay analysis, this PL band originates from oxygen vacancies in the amorphous shell and Förster energy transfer occurs between the oxygen vacancy levels in the crystalline core and amorphous shell. These phenomena are found to alter the PL excitation spectra.
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81.16.-c Methods of micro- and nanofabrication and processing
82.70.Dd Colloids

The effect of underlayer thin films on the surface-enhanced Raman scattering response of Ag nanorod substrates

Qin Zhou, Yongjun Liu, Yuping He, Zhengjun Zhang, and Yiping Zhao

Appl. Phys. Lett. 97, 121902 (2010); http://dx.doi.org/10.1063/1.3489973 (3 pages) | Cited 11 times

Online Publication Date: 21 September 2010

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The effect of underlayer thin films on the sensitivity of Ag nanorod surface-enhanced Raman scattering (SERS) substrates was studied both theoretically and experimentally. With the same Ag nanorod film, different materials (Ag, Al, Si, and Ti) with different thicknesses (25, 100, and 400 nm) were used as underlayers to alter the reflectivity systematically. The SERS intensity was found to increase linearly with the underlayer reflectivity, which can be explained by a modified Greenler’s model due to the contribution of reflected electric field from the substrate. This finding can be used to design high enhancement SERS substrates.
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78.30.Er Solid metals and alloys
82.80.Gk Analytical methods involving vibrational spectroscopy
78.67.Qa Nanorods
61.46.-w Structure of nanoscale materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

The shock-front structure of nanocrystalline aluminum

Wen Ma, Wenjun Zhu, and Fuqian Jing

Appl. Phys. Lett. 97, 121903 (2010); http://dx.doi.org/10.1063/1.3490643 (3 pages) | Cited 1 time

Online Publication Date: 21 September 2010

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The shock-front structures of nanocrystalline Al are investigated in detail by exploring the relationship between the evolution of stress, particle velocity distributions, and the atomistic structures through molecular dynamics simulations. It is found that in nanocrystalline Al the contribution of grain boundary-mediated plasticity to the shock-front width is significant in comparison with dislocation-mediated plasticity. Due to different deformation mechanisms and time sequences, the shock front can be separated into following three stages: elastic, grain boundary dominated plasticity, and dislocation emission and propagation.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.72.Bb Theories and models of crystal defects
62.20.F- Deformation and plasticity
61.46.Hk Nanocrystals
61.72.Mm Grain and twin boundaries
62.25.-g Mechanical properties of nanoscale systems

Persistent two-dimensional growth of (110) manganite films

R. Bachelet, D. Pesquera, G. Herranz, F. Sánchez, and J. Fontcuberta

Appl. Phys. Lett. 97, 121904 (2010); http://dx.doi.org/10.1063/1.3490713 (3 pages) | Cited 9 times

Online Publication Date: 21 September 2010

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We have deposited La2/3Sr1/3MnO3(110) thin films by pulsed laser deposition, changing the ratio of surface diffusivity to deposition flux (D/F) by adjusting substrate temperature and laser repetition rate. We show that persistent two-dimensional layer-by-layer growth, at least up to 30 nm, can be achieved by exploiting diffusion-limited growth (small D/F ratio), giving rise to atomically-flat epitaxial films. The results are of interest in spintronic applications such as tunnel magnetoresistance devices, and the approach presented here can be extended to other functional films of high surface energy.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Dd Nonmetallic ferromagnetic materials
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.35.Fx Diffusion; interface formation
81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials

Mechanically generated surface chirality: Control of chiral strength

Sameh Ferjani, Joel Pendery, and Charles Rosenblatt

Appl. Phys. Lett. 97, 121905 (2010); http://dx.doi.org/10.1063/1.3491157 (3 pages) | Cited 1 time

Online Publication Date: 21 September 2010

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A substrate coated with an achiral polyimide alignment layer was scribed with the stylus of an atomic force microscope having a line-to-line force profile FAFBFCFAFBFC…. The strength of the resulting chiral surface was examined using the nematic liquid crystal electroclinic effect induced by the surface. The magnitude of the electroclinic effect was found to increase with increasing scribing force, which suggests a method for controlling the chiral strength. Additionally, the electroclinic magnitude divided by the rms surface roughness was approximately constant with scribing force, suggesting that the azimuthal anchoring strength coefficient is nearly independent of the scribing force.
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61.30.-v Liquid crystals

Theory of a three-dimensional nanoporous silicon lattice with unsaturated bonding

Feng Zhang, Dragan S. Stojkovic, and Vincent H. Crespi

Appl. Phys. Lett. 97, 121906 (2010); http://dx.doi.org/10.1063/1.3491240 (3 pages)

Online Publication Date: 21 September 2010

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Several molecules are known to contain stable silicon double or triple bonds that are sterically protected by bulky side groups. Through first-principles computation, we demonstrate that well-defined π bonds can also be stabilized in a prototypical crystalline Si structure: Schwarzite Si-168, when modest negative pressures are applied to a nanoscale porous framework. The sp2-bonded Si-168 is thermodynamically preferred over diamond silicon at a negative pressure of −2.5 GPa. Ab-initio molecular dynamics simulations of Si-168 at 1000 K reveal significant thermal stability. Si-168 is metallic at P = 0 in density functional theory, but a gap (between π-like and π∗-like bands) opens around the Fermi level at the transition pressure of −2.5 GPa. Alternatively, a band gap buried below the Fermi level at P = 0 can be accessed via hole doping in semiconducting Si144B24.
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61.50.Lt Crystal binding; cohesive energy
73.20.At Surface states, band structure, electron density of states
61.43.Bn Structural modeling: serial-addition models, computer simulation

Impact of ion implantation boundary dimensionality on boron transient diffusion in submicron scale patterns

Wei Yen Woon (溫偉源) and Chia Ling Chen (陳佳伶)

Appl. Phys. Lett. 97, 121907 (2010); http://dx.doi.org/10.1063/1.3492840 (3 pages) | Cited 1 time

Online Publication Date: 22 September 2010

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We investigate two-dimensional boron transient diffusion in sub-micron scale patterns by plane view scanning capacitance microscopy (SCM). Submicron long strips and squares ion implantation windows of systematically varying sizes have been designed and fabricated. Boron ion implantation and spike annealing were followed to activate the dopant and cause diffusion. Square opening windows show more enhanced diffusion than the long strip counterparts, especially at larger length scales. We explain the observation and fit the experimental data by a nonlinear logistics model. The implication to modern microelectronic circuit design and conventional dopant profiling methodology are discussed.
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85.40.Ry Impurity doping, diffusion and ion implantation technology
81.05.Cy Elemental semiconductors
61.72.uf Ge and Si
61.72.Cc Kinetics of defect formation and annealing
68.35.Fx Diffusion; interface formation
61.72.jj Interstitials

Carbon nanotube-induced chirality in an achiral liquid crystal

Rajratan Basu, Krysta A. Boccuzzi, Sameh Ferjani, and Charles Rosenblatt

Appl. Phys. Lett. 97, 121908 (2010); http://dx.doi.org/10.1063/1.3492844 (3 pages) | Cited 4 times

Online Publication Date: 22 September 2010

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A small quantity of carbon nanotubes was dispersed in an achiral liquid crystal (LC), and the mixture was found to exhibit a weak degree of chirality. The induced chirality in the LC was probed by means of the electroclinic effect in the LC’s smectic-A phase, which showed significant pretransitional behavior on approaching the smectic-A–smectic-C transition temperature from above. The results suggest that there is a net chirality associated with the carbon nanotubes, which is transmitted into the LC.
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61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
61.25.-f Studies of specific liquid structures
64.70.M- Transitions in liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Structural and optical properties of GaInP grown on germanium by metal-organic chemical vapor deposition

W. He, S. L. Lu, J. R. Dong, Y. M. Zhao, X. Y. Ren, K. L. Xiong, B. Li, H. Yang, H. M. Zhu, X. Y. Chen, and X. Kong

Appl. Phys. Lett. 97, 121909 (2010); http://dx.doi.org/10.1063/1.3492854 (3 pages) | Cited 7 times

Online Publication Date: 22 September 2010

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Structural and optical properties of Si-doped as well as nominally undoped GaInP epilayers grown on Germanium substrates by metal-organic chemical vapor deposition have been investigated by high resolution transmission electron microscope and photoluminescence (PL). Si incorporation results in an increased inner band PL transition and a blue shift of PL energy with increasing temperature, which arises from the trapping states around Ge-GaInP interface due to Ge diffusion to GaInP epilayer as well as Si doping. For the inter band PL transition, a competition between the emission processes near the band edge and in the ordered GaInP domains is responsible for the inverted S shape temperature dependence of PL peaks. By analyzing the time-resolved PL results, we attribute this emission near the ordered states to the localized states due to the potential fluctuation, which is induced by the compositional inhomogeneity of Ga and In in the partially ordered GaInP.
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78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.U- Doping and impurity implantation
68.55.ag Semiconductors

Observation of coherent phonons in metallic carbon nanotubes

Keiko Kato, Katsuya Oguri, Atsushi Ishizawa, Hideki Gotoh, Hidetoshi Nakano, and Tetsuomi Sogawa

Appl. Phys. Lett. 97, 121910 (2010); http://dx.doi.org/10.1063/1.3491220 (3 pages) | Cited 1 time

Online Publication Date: 22 September 2010

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We investigated the ultrafast dynamics of coherent phonons with sub-10 fs laser pulses in metallic single-walled carbon nanotubes (m-SWCNTs). We identified radial breathing mode (RBM), D-mode, and G-mode coherent phonons in m-SWCNTs. We also resolved G−- and G+-mode coherent phonons, which correspond to the longitudinal and transverse optical phonon modes, respectively. The frequencies of the RBM coherent phonons shift with increases in laser intensity, suggesting that photocarriers modify the phonon frequency.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
63.20.kd Phonon-electron interactions

The transition in hydrogen sensing behavior in noncontinuous palladium films

Thomas Kiefer, Luis Guillermo Villanueva, Frédéric Fargier, Frédéric Favier, and Jürgen Brugger

Appl. Phys. Lett. 97, 121911 (2010); http://dx.doi.org/10.1063/1.3491263 (3 pages) | Cited 5 times

Online Publication Date: 22 September 2010

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The morphological transition in ultrathin palladium (Pd) films around the percolation threshold and the related transition in hydrogen sensing behavior is investigated. We find that besides the transition from continuous to discontinuous Pd, an intermediate - semicontinuous-state must be considered. It shows hydrogen sensing features of both continuous and discontinuous film types, simultaneously. This study focuses on the discontinuous-semicontinuous transition. Experimental evidence is supported by studying the evolution of the electrical resistance with temperature, under hydrogen exposure and after thermal annealing. The results are highly relevant for the optimization of nanogap based hydrogen sensors.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.-d Chemical analysis and related physical methods of analysis

Congruent evaporation temperature of GaAs(001) controlled by As flux

Z. Y. Zhou, C. X. Zheng, W. X. Tang, D. E. Jesson, and J. Tersoff

Appl. Phys. Lett. 97, 121912 (2010); http://dx.doi.org/10.1063/1.3491552 (3 pages) | Cited 1 time

Online Publication Date: 22 September 2010

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The congruent evaporation temperature Tc is a fundamental surface characteristic of GaAs and similar compounds. Above Tc the rate of As evaporation exceeds that of Ga during Langmuir (free) evaporation into a vacuum. However, during molecular beam epitaxy (MBE) there is generally an external As flux F incident on the surface. Here we show that this flux directly controls Tc. We introduce a sensitive approach to measure Tc based on Ga droplet stability, and determine the dependence of Tc on F. This dependence is explained by a simple model for evaporation in the presence of external flux. The capability of manipulating Tc via changing F offers a means of controlling congruent evaporation with relevance to MBE, surface preparation methods, and droplet epitaxy.
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64.70.kg Semiconductors
64.70.fh Boiling and bubble dynamics
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
47.55.dk Surfactant effects

Selective area growth of high quality InP on Si (001) substrates

G. Wang, M. R. Leys, R. Loo, O. Richard, H. Bender, N. Waldron, G. Brammertz, J. Dekoster, W. Wang, M. Seefeldt, M. Caymax, and M. M. Heyns

Appl. Phys. Lett. 97, 121913 (2010); http://dx.doi.org/10.1063/1.3491554 (3 pages) | Cited 4 times

Online Publication Date: 22 September 2010

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In this work, we demonstrate the selective area growth of high quality InP layers in submicron trenches on exactly (001) oriented Si substrates by using a thin Ge buffer layer. Antiphase domain boundaries were avoided by annealing at the Ge surface roughening temperature to create additional atomic steps on the Ge buffer layer. The mechanism of Ge surface atomic step formation and the corresponding step density control method are illustrated. The elimination of antiphase boundaries from the optimized Ge buffer layer, together with the defect necking effect, yield defect-free top InP layers inside the trenches.
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68.37.-d Microscopy of surfaces, interfaces, and thin films
68.55.ag Semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
81.40.Lm Deformation, plasticity, and creep
73.40.Ns Metal-nonmetal contacts
68.47.Fg Semiconductor surfaces
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