ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
Collection
Years
  • 1
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The wavelength dependence of photoinduced dissociation of CH3Br via dissociative electron attachment (DEA) of "hot" electrons for one monolayer CH3Br adsorbed on GaAs(110) has been measured. The cross section for dissociation is found to decrease monotonically by two orders of magnitude as the incident wavelength is varied from 308 to 550 nm. There is an apparent threshold near 490 nm (2.5 eV), well below the gas phase photodissociation threshold near 250 nm (5.0 eV), but in good agreement with a simple estimate based on expected values for the decrease in the photoemission threshold and the lowering of the molecular affinity level upon adsorption of CH3Br on a semiconductor surface. The observed threshold is found to move to higher energy as dissociation of the monolayer proceeds. Based on the work of Hasselbrink and co-workers [F. Weik, A. de Meijere, and E. Hasselbrink, J. Chem. Phys. 99, 682 (1993)], a simple theoretical model is developed which considers the tunneling of hot electrons through the interfacial barrier between the physisorbed CH3Br and the GaAs. The results of our theoretical model in conjunction with those of earlier ab initio calculations [S. Black, R. Friesner, P. H. Lu, and R. M. Osgood, Jr., Surf. Sci. 382, 154 (1997)] suggest that the adsorbate affinity level is centered at ∼0.6 eV above the (adsorbate- modified) vacuum level of the substrate. This value corresponds to a ∼1.8 eV stabilization of the negative ion resonance upon adsorption. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6552-6563 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present dynamical studies of the surface photochemistry of dimethylcadmium (DMCd) adsorbed on GaAs(110) and CdTe(110) surfaces. This important precursor for chemical vapor deposition is studied using time-of-flight (TOF) spectroscopy in conjunction with temperature programmed desorption (TPD). For the case of greater than one monolayer coverages, on these surfaces, both photofragmentation and photodesorption are observed following irradiation. The relative probabilities of these two processes are found to be strongly dependent on adsorbate coverage and incident photon energy. Direct photoabsorption by the adsorbed molecule is found to dominate the photofragmentation process, with the substrate strongly reducing the probability of photofragmentation at low coverages due to the operation of substrate mediated channels for excited state relaxation. The CH3 fragments observed following photodissociation are found to have kinetic energies that are invariant with the energy of the exciting photon (193 and 248 nm), an effect attributed to an efficient curve crossing between excited states in this molecule. The molecular desorption process is found to exhibit an unusual coverage dependence which is linked to the probability of deposition of a significant amount of vibrational excitation in the overlayer via substrate mediated de-excitation processes. Following the adsorption of one monolayer on the GaAs substrate, the photochemistry observed is significantly different due to the thermal dissociation of DMCd to form adsorbed methylgallium moieties. In this case, multiple features are observed in the TOF spectrum with kinetic energies significantly different to those observed for the gas phase or physisorbed molecule. Correlation of the TOF spectral features with thermal desorption data allows these TOF features to be assigned to specific adsorbed intermediates. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Temperature programmed desorption (TPD) spectra of CH3X (X=Cl, Br, I) from GaAs(110) were recorded with a heating rate of 5 K/s for coverages from less than 0.1 to 2 ML, where methyl halides desorb molecularly, i.e., without dissociation. The shapes of the TPD spectra are strongly coverage dependent with the peak temperature of desorption decreasing with increasing coverage, especially for the submonolayer region. A model incorporating dipole–dipole repulsive interactions between the adsorbed molecules and which was previously proposed for the desorption of adsorbed molecules from metal surfaces has been employed to fit our TPD spectra. The fit gives the activation energy, effective dipole moment, and effective polarizability for the adsorbate. The resulting dipole moment and polarizability are less than the gas-phase molecular values, suggesting the importance of an ordered adsorption orientation. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...