摘要:

A new model for laser‐induced desorption is proposed based on a master equation for the photon population in a closely coupled subsystem involving the relevant degrees of freedom. The validity of approximations such as the Born and Markovian approximations is discussed in terms of the laser pulse duration and multiple time scales of the adspecies‐surface system. The desorption rate is numerically calculated from the photon population and the threshold number of photons absorbed by the adspecies. The effects of anharmonicity, dephasing and laser detuning on the desorption rate are examined. The mechanism of dephasing and the possible direct and indirect desorption channels are discussed.

ISSN:1071-1023    

DOI:10.1116/1.582978

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

Vibrational energy transfer between an IR laser, a solid surface, and an adatom is studied by a genralized master equation which includes memory effects. Numerical problems associated with the temporally delocalized memory kernel are overcome by introducing the isomnesic approximation. Results obtained for time scales ranging from 2 ps to 2 μs for H(H20)/KCl(001) show that effective vibrational excitation is possible with low‐power lasers (1 W/cm2) in spite of fast phonon relaxation. Detailed time evolution of the system is seen to differ radically from that predicted by Markovian theories, even for fairly long time scales.

ISSN:1071-1023    

DOI:10.1116/1.582979

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

The suitability of several Sn‐containing molecules (tetramethyltin, tetrabutyltin, dibutyltin dibromide, and stannic chloride) as gas phase sources of Sn for use in molecular beam epitaxy of GaAs was evaluated.InsituAuger electron spectroscopy showed that the Sn molecules absorbed at approximately the monolayer level at room temperature on GaAs (001) epilayer surfaces and pyrolytically decomposed before desorption. Capacitance–voltage and secondary ion mass spectrometry profiles demonstrated that the pyrolytic Sn deposits incorporated as ann‐type dopant into newly regrown GaAs epilayers. Sn films were ultraviolet (UV) photolytically deposited on GaAs from each of these Sn‐containing molecules and characterized by x‐ray photoelectron spectroscopy.

ISSN:1071-1023    

DOI:10.1116/1.582980

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

We report on a large decrease of surface‐enhanced Raman scattering (SERS) of pyridine on cold and island Ag films due to Pd submonolayers. In contradistinction, it is shown that very thin (∼1 monolayer) Ag deposits give rise to SERS unobserved before the Ag deposition. Auger and reflectivity measurements are also presented.

ISSN:1071-1023    

DOI:10.1116/1.582981

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

The temperature dependence of the sputtering yield and velocity distribution of sputtered neutral Ca and Cr atoms has been studied by Doppler shift laser fluorescence spectroscopy (DSLFS) for 15‐keV‐Ar+ion bombardment.These investigations have been performed in the search for thermal spike effects and radiation‐enhanced sublimation in sputtering at elevated temperatures. Ca targets have been studied up to about 270 °C and Cr targets up to 750 °C. The shapes of the velocity distributions do not change in the respective temperature ranges for both target materials. Furthermore, the absolute yield of sputtered neutral ground state atoms does not increase with temperature.This indicates that no radiation‐enhanced thermal contribution is of relevant importance. Moreover, we can explain the velocity distributions in both cases by the linear cascade theory of sputtering. The thermal contribution due to thermal evaporation increases drastically above 230 °C for Ca and 550 °C for Cr. In both cases the corresponding velocity distribution can be fitted by a Boltzmann distribution.

ISSN:1071-1023    

DOI:10.1116/1.582982

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

Doppler shift laser fluorescence spectroscopy (DSLFS) has been developed in the last few years as a powerful tool to measure densities and energy distributions of neutral particles. Its main application described in this paper is the study of particles ejected from surfaces under impact of atoms, ions or electrons. Complications and controversies in the interpretation of DSLFS spectra will be discussed. The major achievements and applications of the method over the last few years will be presented. One of the most important results has been a deeper insight into the composition of the particle fluxes ejected from surfaces under ion beam bombardment in respect to the degree of surface oxidation. This has been possible due to the fact that DSLFS enables us to measure the densities and energy distributions of neutral particles in specific electronic states. As a direct consequence, a large amount of information on sputtered excited atoms has recently been obtained by DSLFS.

ISSN:1071-1023    

DOI:10.1116/1.582983

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

We report on metal atom segregation within an oxide matrix as a consequence of absorption of short (≂12 ns) excimer laser pulses at 249 nm. The segregation phenomenon is investigated by the example of Au‐TeO2thin films on glass substrates using transient reflectivity and transmissivity techniques as well as ESCA analysis. ESCA depth profiles show drastic modification of the film composition upon laser exposure. Whereas the distribution of Au and TeO2is homogeneous for the as‐deposited films, the laser‐irradiated areas show a total depletion of Au in the surface region exposed to the laser. We interpret this as a laser‐driven segregation of TeO2to the surface and correspondingly of Au towards the substrate. The time‐resolved optical experiments show that the segregation takes place within 30 ns following the laser pulse. The reflectivity and transmissivity changes are characterized by a sharp fluence threshold corresponding to the melting of the film surface.

ISSN:1071-1023    

DOI:10.1116/1.582984

出版商:American Vacuum Society    

年代:1985

数据来源: AIP

摘要:

High resolution electron microscopy (HREM) has been applied to the characterization of surfaces and surface rearrangements using the profile imaging method. This review paper outlines the basic principles of the technique and then surveys the recent atomic‐level observations of metal, semiconductor, and oxide particle surfaces. Advantages and possible drawbacks of the technique are briefly discussed.

ISSN:1071-1023    

DOI:10.1116/1.582985

出版商:American Vacuum Society    

年代:1985

数据来源: AIP