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Journal of Applied Physics

Issue 8 • Date Oct 2009

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Displaying Results 1 - 25 of 123
  • Photonic guiding structures in lithium niobate crystals produced by energetic ion beams

    Page(s): 081101 - 081101-29
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    A range of ion beam techniques have been used to fabricate a variety of photonic guiding structures in the well-known lithium niobate (LiNbO3 or LN) crystals that are of great importance in integrated photonics/optics. This paper reviews the up-to-date research progress of ion-beam-processed LiNbO3 photonic structures and reports on their fabrication, characterization, and applications. Ion beams are being used with this material in a wide range of techniques, as exemplified by the following examples. Ion beam milling/etching can remove the selected surface regions of LiNbO3 crystals via the sputtering effects. Ion implantation and swift ion irradiation can form optical waveguide structures by modifying the surface refractive indices of the LiNbO3 wafers. Crystal ion slicing has been used to obtain bulk-quality LiNbO3 single-crystalline thin films or membranes by exfoliating the implanted layer from the original substrate. Focused ion beams can either generate small structures of micron or submicron dimensions, to realize photonic bandgap crystals in LiNbO3, or directly write surface waveguides or other guiding devices in the crystal. Ion beam-enhanced etching has been extensively applied for micro- or nanostructuring of LiNbO3 surfaces. Methods developed to fabricate a range of photonic guiding structures in LiNbO3 are introduced. Modifications of LiNbO3 through the use of various energetic ion beams, including changes in refractive index and properties related to the photonic guiding structures as well as to the materials (i.e., electro-optic, nonlinear optic, lumine- scent, and photorefractive features), are overviewed in detail. The application of these LiNbO3 photonic guiding structures in both micro- and nanophotonics are briefly summarized. View full abstract»

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  • Electrostatic-discharge-induced degradation of 1.3 μm AlGaInAs/InP buried heterostructure laser diodes

    Page(s): 083101 - 083101-3
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    Degradation of 1.3 μm AlGaInAs buried heterostructure laser diodes due to electrostatic discharge (ESD) is studied. The degradation mechanism of this material has not previously been clear and so the ESD tolerance was evaluated. Degradation occurred at 0.5 and 2.5 kV for forward and reverse polarities, respectively. Because that ESD tolerance for forward polarity is insufficient for practical applications, we focused on it in analyzing the degradation mechanism. Elliptically shaped melted regions are observed in the active layer of the facet. Such regions developed inside a cavity under the application of ESD pulses. These results indicate that degradation is caused by melting due to optical absorption. View full abstract»

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  • Ultrafast and low-power photonic crystal all-optical switching with resonant cavities

    Page(s): 083102 - 083102-9
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    We theoretically investigate and discuss the response time, switching contrast, and pump power of all-optical switching in a nonlinear photonic crystal structure with high quality factor (high-Q) cavity. For the response time of all-optical switching, the drop and rise time are considered, respectively. Moreover, we find that when the duration of pump pulse is shorter than the lifetime, the response curve of all-optical switching is asymmetric, and the drop time is determined by both the lifetime of high-Q cavity and duration of pump pulse, and the rise time is mainly determined by lifetime of high-Q cavity. In contrast, when the duration of pump pulse is much longer than the lifetime, the dynamic response curve is symmetric, and both the drop and rise time are determined by the duration of pump pulse. On the other hand, the pump power can be significantly reduced by using a setup where the probe beam is located at the high-Q cavity mode with very narrow linewidth. Furthermore, if the central wavelength of pump pulse is also set to match with this or another high-Q cavity mode, the pump power will be reduced further due to the large field enhancement within the photonic crystal, and more importantly there is no extra prolonged response time of all-optical switching. By this method, the pump power as low as 210 KW/cm2 is observed in our model structure with the quality factor of only 32 096 for the ordinary polystyrene material. View full abstract»

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  • A Fresnel-reflection-based fiber sensor for simultaneous measurement of liquid concentration and temperature

    Page(s): 083103 - 083103-5
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    We present a quasidistributed fiber sensor for simultaneous measurement of liquid concentration and temperature based on Fresnel reflection. Thin-film filters combined with an arrayed waveguide grating are utilized to achieve wavelength-division-multiplexing distributed sensing. By measuring the Fresnel-reflection signals from the sensing heads, each of which consists of two fiber sensing tips, simultaneous measurement of liquid concentration and temperature is obtained. The experimental results reveal that the sensing system can discriminate the concentration and temperature of a NaClH2O liquid with high concentration and temperature accuracies of ±0.07 % and ±0.35 °C, respectively. View full abstract»

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  • Ultrafast gain and refractive index dynamics in GaInNAsSb semiconductor optical amplifiers

    Page(s): 083104 - 083104-5
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    The gain and refractive index dynamics of dilute nitride antimonide semiconductor optical amplifiers are studied using heterodyne pump probe spectroscopy, both in forward and reverse bias regimes. In the forward biased absorption regime, both gain and refractive index relax on the same timescale indicating that both quantities are linked to the same relaxation process, interband recombination. Above transparency, in the forward biased gain regime, the gain and phase exhibit differing timescales resulting in a dynamical alpha factor that varies strongly with time. Reversed bias measurements suggest a recombination dominated absorption recovery where the recovery timescale increases with increasing reversed bias, possibly due to charge separation effects. View full abstract»

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  • Coupled mode analysis of nonlinear defects in photonic crystals

    Page(s): 083105 - 083105-5
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    We present a general analysis of the coupling of nonlinear photonic crystal cavities using coupled-mode theory. The nonlinear transmission properties of two coupled nonlinear cavities have been investigated. We validate the analysis by comparing the theoretical result with rigorous numerical simulations based on finite-difference time-domain techniques. A device consisting of two nonidentical photonic crystal cavities is proposed, by which we demonstrate that this theory can be employed for designing high-contrast all-optical switches or diodes. View full abstract»

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  • Wavelength-sized cavities in high aspect InP/InGaAsP/InP photonic crystals

    Page(s): 083106 - 083106-9
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    The photonic properties of two classes of wavelength-sized cavities are reported for deeply etched InP/InGaAsP/InP planar photonic crystals. The high aspect, deeply etched structures are studied as potential building blocks for nonmembrane type photonic devices in standard InP photonic integrated circuits. The first class consists of cavities of one unit cell in one direction and varying size in the other planar direction. The studied class includes a Fabry–Perot type cavity with one row of missing holes, a simple single missing hole defect cavity, and a cavity consisting of two holes which have been slightly shifted and reduced in hole radius. The best observed quality factor of 65 in this class is obtained for a single hole defect cavity. The second class is comprised of cavities which are derived from a three missing row defect in one direction and varying size in the other direction. This includes a Fabry–Perot type cavity with three rows of missing holes, a point defect cavity consisting of seven unetched holes and a six hole ring cavity. The best observed quality factor of 300 is obtained for the ring cavity in this second class of structures, which is adequate for applications. View full abstract»

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  • Changes to the network structure of Er–Yb doped phosphate glass induced by femtosecond laser pulses

    Page(s): 083107 - 083107-5
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    Changes to the glass network structure after modification with tightly focused 1043 nm, 400 fs laser pulses have been studied in Er–Yb doped phosphate glass using in situ confocal Raman microscopy. For femtosecond laser writing conditions that result in heat accumulation, the 710 and 1209 cm-1 Raman peaks, which are due to the (POP)sym and (PO2)sym network vibration modes, respectively, shift to both higher and lower wavenumbers. The differences in refractive index are shown to correlate spatially with the 1209 cm-1 Raman signal shifts. Systematic shifts in this Raman peak to higher and lower wavenumbers indicate an overall expansion and/or contraction of the phosphate network that depends on the femtosecond laser writing conditions. View full abstract»

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  • Excited-state absorption in erbium-doped silica fiber with simultaneous excitation at 977 and 1531 nm

    Page(s): 083108 - 083108-6
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    We report a study of the excited-state absorption (ESA) in erbium-doped silica fiber (EDF) pumped at 977 nm, when the fiber is simultaneously excited by signal radiation at 1531 nm. We show, both experimentally and theoretically, that ESA efficiency at 977 nm gets strongly enhanced only in the presence of signal power. Experimentally, this conclusion is supported through the detection of upconversion emission, a “fingerprint” of the ESA process, and through the measurements of the EDF nonlinear transmission coefficient for the pump wavelength, which is sensitive to the ESA value. It is shown that the experimental data are precisely modeled with an advanced five-level Er3+ model developed for the EDF. View full abstract»

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  • Reconstruction of polarized optical images in two- and three-dimensional vector holograms

    Page(s): 083109 - 083109-7
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    In the present paper, we extensively study the optical diffraction in two- and three-dimensional vector holograms and demonstrate the reconstruction of polarized optical images recorded in azobenzene-containing amorphous polymers (AP) and polymer-dissolved liquid-crystalline composites (PDLCC). The polarization states of the interference light are not modulated in the isotropic AP films, while modulated in the anisotropic PDLCC films. The information of the polarized optical image is recorded as the polarization induced anisotropy in the AP and PDLCC medium and is reconstructed as the polarized optical images. The theoretical consideration well explained the characteristics of the reconstructed polarized optical images from both two- and three-dimensional vector holograms. View full abstract»

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  • Influence of thin metal nanolayers on the photodetective properties of ZnO thin films

    Page(s): 083110 - 083110-4
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    We investigate the photoconductivity properties of ZnO thin films prepared by pulsed laser deposition with and without metals (Au or Pt) on the surface. The covering of nanostructured metals can largely enhance the photocurrent. Meanwhile, the dark currents have been increased significantly due to the increase in carrier concentration and mobility near the surface of ZnO thin film. Although plasmonic effect was observed by the photoluminescence enhancement, the main mechanism of the increase in the dark current and photoresponsivity for ZnO photoconductors has been interpreted by surface states, interface states, and persistent photoconductivity. View full abstract»

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  • Dynamic characterizations of high diffraction efficiency in volume Bragg grating formed by holographic photopolymerization

    Page(s): 083111 - 083111-6
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    Volume Bragg grating with 96% diffraction efficiency (DE) was efficiently formed by holographic photopolymerization in blend syrup of photocurable trimethylolpropane triacrylate monomer and nematic liquid crystal. The formation dynamics of the composite gratings was quantitatively characterized under the frame of one-dimensional reaction-diffusion model with a revision of individual decay constants for monomer diffusion and reaction. Initial parameters of diffusion and reaction were analytically determined from the measured first order DE at the beginning stage. Evolutions of the DE, both in curing and postcuring periods, were excellently simulated, especially with postcuring reaction been taken into account. View full abstract»

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  • Optical nonlinear absorption characteristics of AgInSbTe phase change thin films

    Page(s): 083112 - 083112-5
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    The AgInSbTe phase change thin films are very important as optical recording and the super-resolution mask materials in high density optical information storage. In this work, the effective nonlinear absorption coefficients of amorphous and crystalline AgInSbTe thin films were measured by the open-mode Z-scan method and no evidence of nonlinear refraction was found in the closed-mode Z-scan measurement. The effective nonlinear absorption coefficient βeff of amorphous AgInSbTe thin films is 7.53×10-3 m/W and the effective photon-absorption number n is 1.722; βeff of crystalline AgInSbTe thin films is 3.5×10-2 m/W, which is of an order lager than that of amorphous state, and the n value is 1.7011. The giant nonlinearity of AgInSbTe results from the free carrier absorption in the nanosecond time scale and this characteristic should be responsible for the mechanism of optical recording as well as the readout of super-resolution disk. View full abstract»

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  • Photorefractive performance of polycarbazoylethylacrylate composites with photoconductive plasticizer

    Page(s): 083113 - 083113-5
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    Photorefractive quantities of diffraction efficiency, optical gain, and grating buildup speed were investigated for newly prepared polycarbazoylethylacrylate (PCzEA) composites with photoconductive plasticizer of carbazoylethylpropionate (CzEPA) in comparison with those with a commonly used plasticizer of benzyl n-butyl phthalate. CzEPA is a model compound of PCzEA and works as a good plasticizer with photoconductive performance. Diffraction efficiency of 7.5% and grating buildup speed of 4.3 s-1 (response time of 235 ms) were measured at lower electric field of 45 V μm-1 for the composite with CzEPA plasticizer. Furthermore stable optical gain of 51 cm-1 was measured because of lower absorption coefficient of 10 cm-1 at 632.8 nm. View full abstract»

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  • 2.7 μm emission of Nd3+, Er3+ codoped tellurite glass

    Page(s): 083114 - 083114-3
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    In this paper, we report on the observation of enhanced 2.7 μm midinfrared emission under 800 nm excitation in a Nd3+/Er3+ codoped tellurite glass. It is also found that the green upconversion emissions from Er3+ are effectively restricted, meanwhile the 4I13/2 level of Er3+ is depopulated in the Nd3+/Er3+ codoped tellurite glass. These results suggest that the midinfrared emission can be achieved in the oxyfluoride glasses and that codoping with Nd3+ can greatly improve the midinfrared emission performance. View full abstract»

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  • Theoretical prediction of GaN nanostructure equilibrium and nonequilibrium shapes

    Page(s): 083115 - 083115-7
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    A wide variety of nanostructure shapes have been observed for GaN under different growth conditions. These shapes include but are not limited to hexagonal pyramid, prismatic, triangular cross-section nanowires, and arrow-headed shapes. Using Wulff’s plot and kinetic Wulff’s plot for GaN under thermodynamic equilibrium and under various kinetic conditions, we present a model to theoretically predict and explain these faceted nanostructure shapes. Legendre transformation on Wulff’s plot and kinetic Wulff’s plot has been extensively utilized to obtain the faceted equilibrium shapes in equilibrium. In addition, equilibrium and nonequilibrium faceted geometry of nanostructures have also been predicted by numerical simulations using level set methods and the proposed kinetic Wulff’s plot. View full abstract»

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  • Gated pinhole camera imaging of the high-energy ions emitted by a discharge produced Sn plasma for extreme ultraviolet generation

    Page(s): 083301 - 083301-6
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    The origin and nature of the high-energy ions emitted by a discharge produced plasma source are studied using gated pinhole camera imaging. Time-of-flight analysis in combination with Faraday cup measurements enables characterization of the high-velocity component of the ionic debris. The use of an optional magnetic field allows mass-to-charge analysis of the first part of the Faraday cup signal. It is shown that this consists mainly of oxygen ions emitted from a region near the cathode. Time-resolved images of Sn ions with a kinetic energy of 45 keV visualize the regions in between the electrodes where the high-energy ion generation takes place. View full abstract»

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  • Temporal and spatial resolved optical emission behaviors of a cold atmospheric pressure plasma jet

    Page(s): 083302 - 083302-6
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    The propagation behavior of cold atmospheric pressure plasma jets has recently attracted lots of attention. In this paper, a cold He plasma jet generated by a single plasma electrode jet device is studied. The spatial-temporal resolved optical emission spectroscopy measurements are presented. It is found that the emission intensity of the He 706.5 nm line of the plasma behaves similarly both inside the syringe and in the surrounding air (plasma plume). It decreases monotonously, which is different from the emission lines, such as N2 337.1 nm line, N2+ 391.4 nm line, and O 777.3 nm line. For the discharge inside the syringe, the emission intensity of the He 706.5 nm line decays more rapidly than that of the other three spectral lines mentioned above. The N2 337.1 nm line behaves a similar time evolution with the discharge current. For the N2+ 391.4 nm line and the atomic O 777.3 nm line, both of them decay slower than that of the He 706.5 nm and the N2 337.1 nm. When the plasma plume propagates further away from the nozzle, the temporal behaviors of the emission intensities of the four lines tend to be similar gradually. Besides, it is found that, when the size of the plasma bullet appears biggest, the propagation velocity of the bullet achieves its highest value while the emission intensity of the N2+ 391.4 nm line reaches its maximum. Detailed analysis shows that the Penning effect between the metastable state Hem and the air molecules may play a significant role in the propagation of the plasma bullet in the open air. View full abstract»

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  • Experimental measurements of multiphoton enhanced air breakdown by a subthreshold intensity excimer laser

    Page(s): 083303 - 083303-8
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    This work presents density, spectroscopic temperature, and shockwave measurements of laser induced breakdown plasma in atmospheric air by subthreshold intensity (5.5×109 W/cm2) 193 nm laser radiation. Using molecular spectroscopy and two-wavelength interferometry, it is shown that substantial ionization (≫1016 cm-3) occurs that is not predicted by collisional cascade (CC) breakdown theory. While the focused laser irradiance is three orders of magnitude below the theoretical collisional breakdown threshold, the substantial photon energy at 193 nm (6.42 eV/photon) compared with the ionization potential of air (15.6 eV) significantly increases the probability of multiphoton ionization effects. By spectroscopically monitoring the intensity of the N2+ first negative system (B 2Σu+-X 2Σg+) vibrational bandhead (v=0,v=0) at low pressure (20 Torr) where multiphoton effects are dominant, it is shown that two photon excitation, resonant enhanced multiphoton ionization is the primary mechanism for quantized ionization of N2 to the N2+(B 2Σu+) state. This multiphoton effect then serves to amplify the collisional breakdown process at higher pressures by electron seeding, thereby reducing the threshold intensity from that required via CC processes for breakdown and producing high density laser formed plasmas. View full abstract»

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  • Optical Thomson scatter from a laser-ablated magnesium plume

    Page(s): 083304 - 083304-8
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    We have carried out an optical Thomson scatter study of a KrF laser-ablated Mg plume. The evolution of the electron temperature and density at distances 2–5 mm from the target surface has been studied. We have observed that the electron density falls more rapidly than the atomic density and believe that this is a result of rapid dielectronic recombination. A comparison of the electron density profile and evolution with simple hydrodynamic modeling indicates that there is a strong absorption of the laser in the plasma vapor above the target, probably due to photoionization. We also conclude that an isothermal model of expansion better fits the data than an isentropic expansion model. Finally, we compared data obtained from Thomson scatter with those obtained by emission spectroscopy under similar conditions. The two sets of data have differences but are broadly consistent. View full abstract»

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  • Characterization of a CO2/N2/Ar supersonic flowing discharge

    Page(s): 083305 - 083305-6
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    In this paper we are presenting the full characterization of a supersonic flowing CO2/N2/Ar discharge at static pressures of 1–20 Torr and Mach number 2.15. In all aspects besides the flow speed and gas temperature, these conditions correspond to Martian entry plasma. Plasma parameters were determined by optical emission spectroscopy techniques. The gas and vibrational temperature were found from analysis of the rotational and vibrational spectra of the CO B 1Σ+-A 1Π Ångstrom system, respectively. The electron density was determined from the absolute intensity of the N2 C 3Πu-B 3Πg second positive system. A kinetic model for the discharge was developed to calculate the electron density and compared with experimental data. View full abstract»

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  • Transient ion ejection during nanocomposite thermite reactions

    Page(s): 083306 - 083306-8
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    We observe an intense ion pulse from nanocomposite thermite reactions, which we temporally probe using a recently developed temperature jump/time of flight mass spectrometer. These ion pulses are observed to be much shorter in duration than the overall thermite reaction time. Ion ejection appears in stages as positive ions are ejected prior to nanocomposite thermite ignition, and ignition of the thermite mixtures leads to a second ionization step which is primarily dominated by negative species. The positive species are identified from mass spectrometric measurements and the results show that the positive ion species are comprised of Na ions with minor species of Al and K ions. This observation can be explained by a diffusion based ion-current mechanism, in which strong Al ion diffusion flux formed through the oxide shell, and the surface Na and K ions from salt contaminations are ejected by the strong electrostatic repulsion. The fact that the negative ionization step occurs during the ignition event suggests a strong relation between the nanocomposite thermite reaction and the negative ionization process. View full abstract»

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  • Coherent optical control of the ultrafast dephasing and mobility in a polar semiconductor

    Page(s): 083501 - 083501-8
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    Using the nonperturbative many-body time-dependent approach, we investigate the nonequilibrium dynamics of the coherent longitudinal optical phonon-plasmon coupled (LOPC) modes in a polar semiconductor and explore their coherent optical control and eventually the carrier mobility of the semiconductor. The basic idea for a control of the carrier mobility is to manipulate the ultrafast dephasing of the coherent carrier-relevant LOPC mode. We theoretically propose two possible options to realize the idea and reach the final goal. One is to optimize a semiconductor by finely balancing two kinds of carrier densities by chemical doping and optical doping (or photodoping), where the relaxation of the coherent carrier-relevant LOPC mode would respond in a (weak) singular way. It is found that, in this way, the carrier mobility could be enhanced by a few tens of percent. The other is to optimize the optical pumping laser. In this option, the pulse train creating pure virtual carriers through the below-band-gap excitation would be incorporated for an optical pumping, which can make possible the dephasing-free dynamics of the coherent carrier-relevant LOPC mode. The carrier mobility can then be efficiently controlled and dramatically enhanced by synchronizing the pulse train with its coherent oscillation. This might imply one of ultimate ways to control the carrier mobility of the semiconductor. View full abstract»

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  • Mechanisms of nonstoichiometry in HfN1-x

    Page(s): 083502 - 083502-4
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    Density functional theory is used to calculate defect structures that can accommodate nonstoichiometry in hafnium nitride: HfN1-x, 0≤×≤0.25. It is predicted that a mechanism assuming simple distributions of nitrogen vacancies can accurately describe the variation in the experimentally observed lattice parameter with respect to the nitrogen nonstoichiometry. Although the lattice parameter changes are remarkably small across the whole nonstoichiometry range, the variations in the bulk modulus are much greater. View full abstract»

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  • Molecular dynamics simulation of delamination of a stiff, body-centered-cubic crystalline film from a compliant Si substrate

    Page(s): 083503 - 083503-7
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    Compliant substrate technology offers an effective approach to grow high-quality multilayered films, of importance to microelectronics and microelectromechanical systems devices. By using a thin, soft substrate to relieve the mismatch strain of an epitaxial film, the critical thickness of misfit dislocation formation in the overlayer is effectively increased. Experiments have indicated that stiff films deposited onto Si substrates can delaminate at the interface. However, the atomic mechanisms of the deformation and the fracture of the films have not been well studied. Here, we have applied molecular dynamics simulations to study the delamination of a stiff body-centered-cubic crystalline film from a compliant Si substrate due to tensile loading. The observed mechanical behavior is shown to be relatively independent of small changes in temperature, loading rate, and system size. Fracture occurs at the interface between the two materials resulting in nearly atomically clean surfaces. Dislocations are seen to nucleate in the body-centered-cubic film prior to delamination. At higher strains, a phase change to a face centered cubic is observed within the body-centered-cubic film, facilitating extensive dislocation growth and interaction. The various defects that form prior to fracture are discussed and related to the mechanical properties of the system. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory