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  • 1
    Electronic Resource
    Electronic Resource
    Laser induced photodissociation and desorption. II. CH2I2 adsorbed on Ag (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3332-3338 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The adsorbate- and the substrate-mediated chemical processes induced by ultraviolet (UV) laser pulses have been identified for the CH2I2/Ag system. In contrast to CH2I2 on Al2O3, little photodissociation or desorption is observed for the molecules adsorbed on an Ag surface at submonolayer coverages. Photochemical effect is evident at coverages higher than a monolayer. Explosive desorption dominates at high surface coverages and high laser fluences. The explosive behavior is elucidated and its implications relevant to material ablation by lasers is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455887
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  • 2
    Electronic Resource
    Electronic Resource
    Laser induced photodissociation and desorption. I. CH2I2 adsorbed on Al2O3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3318-3331 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: CH2I2 molecules adsorbed on Al2O3 and Ag surfaces are used as model systems for studying the photofragmentation and desorption processes on solid surfaces involving electronic excitation of the adsorbate. The molecules are activated into an antibonding state by a ultraviolet (UV) light pulse and the desorption behavior is monitored by time-of-flight mass spectrometry. The surface coverage and chemical changes due to laser irradiation are determined by x-ray photoemission and thermal desorption spectroscopies. The desorption yields as well as the mass and the translational energy distributions are measured as a function of the surface coverage, the laser fluence, and the number of laser pulses. The UV radiation effect on a mixture of CH2I2 and NH3 as coadsorbates on Al2O3 is also examined. The results reveal the characteristic electronic, thermal, and "explosive'' desorption effects depending on both the gaseous exposure and the laser irradiation conditions. The quantum yields, the molecular selectivities, the energetics of dissociation and the desorption mechanisms are discussed based on the experimental observations. For clarity, the results and analyses are presented in two parts: CH2I2/Al2O3 in paper I and CH2I2/Ag in paper II of this series.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455886
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  • 3
    Electronic Resource
    Electronic Resource
    The effect of adsorbed noble gas atoms on vibrational relaxation of hydroxyl group in zeolite (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 279-288 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: By means of tunable infrared pump–probe experiment, vibrational relaxation rates (v=1→0) of OH stretching mode of Brønsted acidic hydroxyl groups in a mordenite zeolite, which were interacting with noble gases (He, Ar, Kr, or Xe), were measured. The population lifetime, T1, decreased with the increase of the interaction with noble gases, e.g., 170 ps and 58 ps for isolated hydroxyl groups and ones interacting with Xe, respectively. Using a simple linear chain model, the mechanism for the enhancement of the relaxation rate was studied. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471873
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  • 4
    Electronic Resource
    Electronic Resource
    Picosecond infrared pump–probe spectrum of D2O adsorbed at acid OD group of zeolite (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 2460-2466 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Spectroscopic and dynamic features of the vibrationally excited D2O/zeolite system have been investigated by two-color infrared–infrared pump–probe experiment. The frequency- and delay-scanned probe intensities were measured by tuning the pump laser to the OD stretching bands of the D2O molecule hydrogen bonded to the acidic OD group of mordenite zeolite. Two types of pump-induced signals were observed: the ones which have the population lifetime of 43±5 ps and display frequency shift by the pumping frequency, and the others, which have the lifetime of about 15 ps and exhibit no such frequency shift. Possible origins of the signals are discussed. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476816
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  • 5
    Electronic Resource
    Electronic Resource
    Transient absorption spectra of vibrationally excited OH/OD groups in mordenite zeolites: Effect of Xe adsorption (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 6665-6672 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Transient spectra following the v=1←0 excitation of the OH stretching mode of Brønsted acidic hydroxyl groups in normal and deuterated mordenite zeolites have been measured by a two-color picosecond pump–probe technique. When the OH and OD stretching bands were excited by resonant IR pulses, transient bleaching of the fundamental band (v=1←0) and the transient hot band (v=2←1) absorption signal were observed. For the OH and OD groups free of adsorbates, the spectral widths of the pump-induced signals were broadened by ∼4 cm−1 due to pure dephasing from the convoluted width of the pump and probe IR pulses. When the OH and OD groups were adsorbed by a Xe atom, the frequencies of the ν(OH) and ν(OD) bands shifted to lower frequency and at the same time the widths of both the transient bleaching and the transient hot band absorption were much broader than those of the isolated hydroxyl groups by the factor of more than three. Actually, the widths of the transient signals were about the same as those of the linear absorption signals. An adiabatic approximation has been employed to interpret the observed broadening/shift of the IR bands by making use of the results of DFT (density functional theory) calculations performed on a model cluster consisting of a Xe atom and an H3Si–(OH)–AlH3 substrate. The result agreed well with the observed spectral features. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471849
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of strain on interfacial recombination in AlGaInP/GaInP double heterostructures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 3629-3630 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using time-resolved photoluminescence, we examined the carrier-recombination process in strained AlGaInP/GaInP double heterostructures grown by metal-organic vapor phase epitaxy. We found that interfacial recombination dominates the process at room temperature, and that the interfacial recombination is enhanced by tensile strain and reduced by compressive strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111226
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  • 7
    Electronic Resource
    Electronic Resource
    Interwell inhomogeneity of carrier injection in InGaN/GaN/AlGaN multiquantum well lasers (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 2775-2777 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simulation of current flow for an InGaN/GaN/AlGaN multiquantum well (MQW) laser showed that generation of the optical gain is inhomogeneous across the MQW due to inhomogeneous carrier injection. Laser diodes with three and five wells in MQW were compared to experimentally investigate inhomogeneous carrier injection. We found that external quantum efficiency was significantly improved by a reduction in the number of wells from five to three. The result was explained quantitatively by the fact that the five-well laser had a larger internal loss and a poorer internal quantum efficiency due to the inhomogeneous carrier injection. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.122587
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  • 8
    Electronic Resource
    Electronic Resource
    Analysis of recombination centers in (AlxGa1−x)0.5In0.5P quaternary alloys (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 4946-4949 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We studied nonradiative recombination centers in undoped (AlxGa1−x)0.5In0.5Pgrown by metalorganic vapor phase epitaxy using transient capacitance spectroscopy. We found three deep energy levels, including a mid-gap level. We drew an equation to get a capture cross section for minority carriers, and obtained it using isothermal capacitance transient spectroscopy measurement. The mid-gap level had an electron capture cross section of 2 × 10−10 cm2 and a hole capture cross section of 1 × 10−15 cm2. The time constant of nonradiative recombination through the mid-gap level was found to be comparable to that of radiative recombination. We concluded that the mid-gap level is an effective nonradiative recombination center that reduces photoluminescence intensity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349041
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  • 9
    Electronic Resource
    Electronic Resource
    Origin of the nonradiative 〈112¯0〉 line defect in lateral epitaxy-grown GaN on SiC substrates (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 2547-2549 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nonradiative line defects are observed by cathodoluminescence in 〈2¯110〉 directions in [11¯00]-oriented GaN stripes grown by lateral epitaxy on SiC substrates. Using transmission electron microscopy, the origin is determined to be principally screw dislocations. We observe the screw dislocations in vertically [0001] stacked configurations and forming dislocation loops and half loops contained in two of the three planes of the form {11¯00}. The dislocations are believed to serve to relax the anisotropic stresses experienced in the lateral epitaxy-overgrown stripes. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.126404
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  • 10
    Electronic Resource
    Electronic Resource
    Erratum: "Lasing mechanism of InGaN/GaN/AlGaN multiquantum well laser diode" [Appl. Phys. Lett. 72, 1359 (1998)] (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2766-2766 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121084
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