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  • Elsevier  (239)
  • Wiley  (32)
  • American Institute of Physics (AIP)  (21)
  • Wiley-Blackwell  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Electronic states of the C6H6/Cu{111} system: Energetics, femtosecond dynamics, and adsorption morphology (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9155-9165 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two-photon-photoemission (2PPE) spectroscopy is employed to characterize electronic states of a bilayer C6H6/Cu{111} system at 85 K. The unoccupied benzene π* e2u state is observed with a binding energy of 4.6 eV above the Fermi level. This result agrees with inverse-photoemission (IPE) data and provides a case where the determination of the binding energy is identical for 2PPE and IPE. The π* e2u state is assigned in the 2PPE scheme as a final state which is the first observed final state in 2PPE of adsorbate-surface systems. The dependence of the electron dynamics on the morphology of an incomplete adsorption layer is also investigated. Two (n=1)-like image potential states A and B are observed which presumably originate from two different C6H6 adsorption geometries in the bilayer regime. The two image states A and B are characterized by electron effective masses of 1.1 and 1.9 me, binding energies of 3.30 and 3.45 eV above the Fermi level, and lifetimes of 40 and 20 fs, respectively. The dielectric continuum model and the Kronig–Penney model are employed to simulate the origin of (n=1)-like image states. The work function decreases from 4.9 eV at clean Cu{111} to 4.0 eV at bilayer coverage. The change of the work function and the observation of two image states suggest the redefining of the ratio of the numbers of benzene molecules in the first and the second layers of the bilayer regime to approximately 1:1 instead of 1:2, as previously reported. 2PPE is shown to be sensitive to the changes of morphologies, local work functions, and adsorbate-surface potentials during the layer formation. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477468
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  • 2
    Electronic Resource
    Electronic Resource
    Influence of the negative thermal-expansion coefficient on the luminescence properties of (CdMnMg)Te (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 8704-8711 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In zinc-blende II–VI alloys the thermal-expansion coefficient for low temperatures is negative and becomes positive at higher temperatures. We investigated the luminescence properties of molecular-beam-epitaxy-grown (CdMnMg)Te layers in the temperature range from 2 up to 200 K and show that the anomalous temperature dependence of the lattice constant is reflected in the luminescence properties of the excitonic recombination and the internal transition of manganese (ITM). The temperature behavior of the ITM energy is nonmonotonic and the existence of a minimum in the photon energy (at the temperature TMn) can be correlated to the change of sign of the thermal-expansion coefficient. The decay constants of the ITM begins to decrease drastically at TMn, too. Considering a lattice constant dependent energy transfer rate to the infrared emitting state (1.2 eV) of the manganese ion the variation of the lifetimes can also be explained by the temperature dependence of the lattice constant. Furthermore, we have measured the ITM in bulk layers and observed a different dependence of the ITM properties on the temperature, demonstrating the influence of the growing conditions on the microscopic surrounding of the manganese ions. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362496
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  • 3
    Electronic Resource
    Electronic Resource
    Desorption of CO from Ru(001) induced by near-infrared femtosecond laser pulses (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 9888-9897 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Irradiation of a Ru(001) surface covered with CO using intense femtosecond laser pulses (800 nm, 130 fs) leads to desorption of CO with a nonlinear dependence of the yield on the absorbed fluence (100–380 J/m2). Two-pulse correlation measurements reveal a response time of 20 ps (FWHM). The lack of an isotope effect together with the strong rise of the phonon temperature (2500 K) and the specific electronic structure of the adsorbate–substrate system strongly indicate that coupling to phonons is dominant. The experimental findings can be well reproduced within a friction-coupled heat bath model. Yet, pronounced dynamical cooling in desorption, found in the fluence-dependence of the translational energy, and in a non-Arrhenius behavior of the desorption probability reflect pronounced deviations from thermal equilibrium during desorption taking place on such a short time scale. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481626
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  • 4
    Electronic Resource
    Electronic Resource
    Far infrared laser magnetic resonance detection of CHD (X˜ 3A‘) (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 8706-8712 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Far infrared laser magnetic resonance (FIR-LMR) spectra of the CHD radical in its X˜3A‘ electronic ground state were observed and assigned. The radicals were generated in the reaction of Na atoms with CHDBr2. LMR spectra were observed using seven laser lines at wavelengths around 100 to 200 μm. The spectra were assigned to six different rotational transitions and the molecular parameters of CHD were determined by a least squares fit. A number of additional transitions, observed using a laser line at λ=184.3 μm but not yet assigned in detail, were attributed to a coupling between the accidentally almost degenerate NKaKc=505 and 413 rotational levels induced by the εab term in the spin–rotation Hamiltonian and by the off-diagonal components of the hyperfine coupling tensor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466726
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  • 5
    Electronic Resource
    Electronic Resource
    Weak ferromagnetism in low-dimensional cuprates Ba2Cu3O4Cl2 and Ba3Cu2O4Cl2 (2000)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 87 (2000), S. 6022-6024 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Ba2Cu3O4Cl2 is a two-dimensional quantum antiferromagnet with two Cu sublattices showing a small spontaneous magnetization M0. A group theoretical analysis shows that M0 may be due to (i) induced magnetization in the Cu II sublattice or (ii) spin canting of the Cu I moments, i.e., weak ferromagnetism (WFM). In case (i) the interaction is of pseudodipolar type. In case (ii) the Cu I moments are subject to some kind of anisotropy. The main reason for the occurrence of M0, compared to similar high-Tc cuprates related structures, is that the center between two Cu I moments is not an inversion center. Ba3Cu2O4Cl2 behaves like a classical antiferromagnet with a spin-flop transition. For this compound our analysis shows that, in the case where the magnetic and the crystallographic unit cells are identical, the Cu moments of equivalent sites should be parallel and the antiferromagnetic order is related to opposite directions of the moments at different sites. Weak antiferromagnetism but no WFM is permitted, in agreement with the experimental results. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.372600
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  • 6
    Electronic Resource
    Electronic Resource
    The adsorbate state specific photochemistry of dioxygen on Pd(111) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5327-5336 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ultraviolet-photochemistry of molecularly adsorbed oxygen on Pd(111) has been studied using pulsed laser light with 6.4 eV photon energy. Three processes occur upon irradiation: desorption of molecular oxygen, conversion between adsorption states, and dissociation to form adsorbed atomic oxygen. By using time-of-flight spectroscopy to detect the desorbing molecular oxygen and post-irradiation thermal desorption spectroscopy (TDS) to characterize the adsorbate state, a detailed picture of the photochemical processes is obtained. The data indicate that the O2 molecules desorbing with low translational energies from the saturated surface as well as the conversion of adsorbed molecules between binding states are induced by the photoinduced build-up of atomic oxygen on the surface. Analysis of a proposed reaction model reproduces the observed data and yields detailed rates. Polarization analysis indicates that the photochemical processes are initiated by electronic excitations of the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459652
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  • 7
    Electronic Resource
    Electronic Resource
    Dynamics of the ultraviolet photochemistry of water adsorbed on Pd(111) (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 4609-4619 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: UV-laser irradiation (hν=6.4 eV and 5.0 eV) of the water bilayer adsorbed on a Pd(111) surface leads to molecular desorption and to conversion of the adsorbed state as manifested in thermal desorption spectra. The latter effect is attributed to photodissociation of water on the surface. Time-of-flight measurements show that water molecules desorb with a translational energy of about 600 K for both photon energies indicating a nonthermal process. While desorption is largely suppressed with adsorbed multilayers, conversion within the first layer still proceeds. The dependence of the desorption yield on angle of incidence and polarization of the light reveals substrate excitations as the dominant primary step. A strong variation of cross sections with isotopic substitution is observed. This is interpreted as evidence for the operation of a mechanism involving excitation onto an isotope-independent excited potential energy surface followed by rapid deexcitation to the ground state so that, of the total number of species excited, only a small mass dependent fraction actually fragments or desorbs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460589
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  • 8
    Electronic Resource
    Electronic Resource
    Cross sections and NO product state distributions resulting from substrate mediated photodissociation of NO2 adsorbed on Pd(111) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3154-3169 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultraviolet irradiation of NO2 adsorbed on top of a NO saturated Pd(111) surface causes the photodissociation of NO2/N2O4 and results in the desorption of NO molecules. This process has been studied using excitation energies between 3.5 and 6.4 eV. At a photon energy of 6.4 eV, a cross section of 3×10−18 cm2 is found. Using laser-induced fluorescence to detect the desorbed NO molecules, fully state-resolved data detailing the energy channeling into different degrees of freedom has been obtained. Two desorption channels are found, one characterized by nonthermal state populations, and one showing accommodation to the surface. The yield of the fast channel shows a marked increase above 4 eV photon energy. The slow channel is interpreted as being due to NO molecules which, after formation, undergo a trapping–desorption process. A polarization experiment indicates that the photodissociation is initiated by excitation of metal electrons rather than direct absorption by the adsorbate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457913
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  • 9
    Electronic Resource
    Electronic Resource
    Ultraviolet-laser induced dissociation and desorption of water adsorbed on Pd(111) (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1509-1510 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ultraviolet-laser irradiation (6.4 eV and 5.0 eV) of the first layer of water adsorbed on a Pd(111) surface at 90 K leads to desorption of H2O and to conversion of the adsorbed state as manifested in the thermal desorption spectra. The latter effect is attributed to photodissociation of water on the surface. Time-of-flight measurements show that water molecules desorb with the same translational energy of about 600 K for both photon energies. While desorption is suppressed with adsorbed multilayers, conversion within the first layer still proceeds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458111
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  • 10
    Electronic Resource
    Electronic Resource
    Photochemical decomposition of AsH3 on GaAs(100) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 605-615 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular AsH3, adsorbed on Ga-rich GaAs(100) at 115 K, dissociates readily upon uv irradiation with 193, 248, and 351 nm excimer laser light. In the initial photodissociation step one As–H bond cleaves, leaving all the AsH2, and a large fraction of the H, adsorbed to As. The AsH2 further photodissociates to give As–H and Ga–H. The final steps, photochemical removal of hydrogen from Ga–H and As–H, lead to As deposition. The photodissociation cross section decreases sharply with the extent of photolysis. The wavelength dependence, compared to the gas-phase absorption cross section, extends to much lower photon energies and indicates that substrate-mediated excitation dominates the observed chemistry. There are strong isotope effects in all the cross sections; these are related to mass-dependent substrate-mediated quenching of the excited states. Implications for photon-assisted organometallic chemical vapor deposition are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463556
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