摘要:

Some issues and examples of recent progress in the field of photochemistry at adsorbate–metal interfaces are overviewed.

ISSN:1071-1023    

DOI:10.1116/1.586298

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The mechanisms leading to anion electron stimulated desorption (ESD) at low energies (0–20 eV) are discussed with emphasis on the formation of transitory anions at surfaces decaying by dissociative attachment (DA). The results of recent measurements are summarized and briefly explained using as examples data on O−ESD from O2condensed on Pt and H−, CH−, and CH−2desorption from hydrocarbons also physisorbed on Pt. It is shown that, when O2and hydrocarbons are coadsorbed on Pt, O−ions formed by DA can undergo reactive scattering with other surface molecules; this reaction leads to the product OH−some of which desorb from the surface.

ISSN:1071-1023    

DOI:10.1116/1.586299

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Laser‐induced reactions of Ge(111), Si(111), GaAs(100), and InP(100) surfaces with chlorine under 355‐, 560‐, and 1064‐nm laser irradiation have been investigated using a supersonic beam technique and time‐resolved mass spectrometry. It has been found that the reaction yields depend not only on the laser fluence and wavelength, but also on the translational energy of the incident chlorine molecules. A possible mechanism of laser‐induced reactions is proposed.

ISSN:1071-1023    

DOI:10.1116/1.586302

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

We have studied the ultraviolet laser‐induced interaction of molecular chlorine with a well‐defined GaAs(110) surface under ultrahigh vacuum conditions. Without illumination, chlorine was found to adsorb both molecularly and dissociatively at 85 K. Illumination of a molecular chlorine‐covered surface at 85 K with 193, 248, and 351 nm radiation led to the desorption of Cl atoms and to the formation of AsCl3. We suggest that the surface reaction, that is responsible for the AsCl3formation, is initiated by molecular chlorine dissociation. While direct absorption by an individual Cl2molecule may be the cause for the chlorine dissociation at 351 nm, we propose an intermolecular charge–transfer absorption within the condensed Cl2overlayer for the cases of 248 and 193 nm. Support for this mechanism comes from the dependence of time‐of‐flight distributions and AsCl3coverage measurements on the molecular chlorine surface coverage, on the laser wavelengths and on the use of different substrates.

ISSN:1071-1023    

DOI:10.1116/1.586303

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Pulsed ultraviolet laser induced surface reactions of chlorine on silicon were investigated. The predominant chlorination products were SiCl and SiCl2. Laser fluence effects could be clearly divided into three regimes: under ≊150 mJ/cm2a nonthermal reaction occurred, from 200–400 mJ/cm2thermal effects play a significant role, and above this vaporization and plasma formation dominate. Wavelength effects were also apparent. Fluence thresholds for the appearance of products varied with 351 nm having the lowest, 308 nm the highest, and 248 nm intermediate values. The effect of wavelength upon product ratios suggests that a competing process of chlorine photodesorption is accessed at 308 nm. Increases in dopant concentration yielded increased production of silicon chlorides. The results of combined variations in dopant concentration and wavelength indicate the presence of at least two distinct mechanisms—one involving initial photon‐substrate interactions, the other photon‐adsorbate interactions. Under all conditions studied silicon chloride production was linear in chlorine gas pressure.

ISSN:1071-1023    

DOI:10.1116/1.586304

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The adsorption and decomposition kinetics of diethylsilane (DES), (CH3CH2)2SiH2, on silicon surfaces were studied using laser‐induced thermal desorption (LITD), temperature programmed desorption, and Fourier transform infrared (FTIR) spectroscopic techniques. LITD measurements determined that the initial reactive sticking coefficient of DES on Si(111) 7×7 decreased versus surface temperature from S0≊1.7×10−3at 200 K to S0≊4×10−5at 440 K. The temperature‐dependent sticking coefficients suggested a precursor‐mediated adsorption mechanism. FTIR studies on high surface area porous silicon surfaces indicated that DES adsorbs dissociatively at 300 K and produces SiH and SiC2H5surface species. Annealing studies also revealed that the hydrogen coverage on porous silicon increased as the SiC2H5surface species decomposed. CH2=CH2and H2were the observed desorption products at 700 and 810 K, respectively, following DES adsorption on Si(111) 7×7. The ethylene desorption and growth of hydrogen coverage during ethyl group decomposition were consistent with a β‐hydride elimination mechanism for the SiC2H5surface species, i.e., SiC2H5→SiH+CH2=CH2. Isothermal LITD studies monitored the decomposition kinetics of SiC2H5on Si(111) 7×7 as a function of time following DES exposures. The first‐order decomposition kinetics wereEd=36 kcal/mol and νd=2.7×109s−1. These decomposition kinetics suggest that the silicon surface catalyzes the β‐hydride elimination reaction.

ISSN:1071-1023    

DOI:10.1116/1.586305

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

The lifetime of a laser‐induced surface excitation on Al2O3(112̄0) that leads to detectable emission of neutral or positively charged particles and further to optical surface damage is measured to be a ∼200 ps by varying the delay between pairs of 80 ps pulses at 1064 nm. The dependence of the emission threshold fluence on the time delay between laser pulses suggests a low order absorption process.

ISSN:1071-1023    

DOI:10.1116/1.586306

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Synchrotron radiation in the energy range between 6 and 30 eV was used to study the photon‐stimulated field desorption (PSFD) from a water covered Ag‐field emitter. Above a threshold energy of 7.4 eV (extrapolated for zero electric field) a variety of protonated water clusters (H2O)n⋅H+,n=1,...,15, are observed. The influence of the surface temperature, electric field, photon energy, and photon flux on the PSFD spectra are measured. Under certain experimental conditions the predominance of themagicclusterion(H2O)4⋅H+is observed.

ISSN:1071-1023    

DOI:10.1116/1.586339

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Earlier work by Bringansetal. [R. D. Bringans and M. A. Olmstead, J. Vac. Sci. Technol. B7, 1232 (1989); R. I. C. Uhrberg, R. D. Bringans, M. A. Olmstead, R. Z. Bachrach, and J. E. Northrup, Phys. Rev. B35, 3945 (1987)] and by Woolf [D. A. Woolf, D. I. Westwood, and R. H. Williams, Semicond. Sci. Technol.4, 1127 (1989)] has shown that molecular‐beam epitaxy deposition of arsenic may be used to provide a capping and passivation layer on clean silicon surfaces both to protect the clean surface and to allow the transport of samples between laboratories for characterization purposes. In the present work we have shown that it is also possible to carry out such capping by means of photoassisted metalorganic vapor phase epitaxy using excimer laser radiation to decompose arsine. Suitable control of the laser beam intensity allows the deposition of films varying in thickness from one monolayer to several hundreds of angstroms.

ISSN:1071-1023    

DOI:10.1116/1.586340

出版商:American Vacuum Society    

年代:1992

数据来源: AIP

摘要:

Results obtained for deposition of hydrogenated amorphous silicon by infrared lasers and ultraviolet (UV) lasers are compared with plasma deposition data. Mechanistic information is extracted from the results obtained recently byinsitudiagnostic techniques andexsituanalysis of the film properties. A similar mechanism is proposed for the first stage of the deposition process including gas phase chemistry and chemisorption of film precursors for soft and energized processing. Characteristic differences are observed in the second dehydrogenation and solidification stage of the deposition process. Compared with CO2laser processing UV photons induce additional dehydrogenation The plasma environment has the potential to restrict the formation of polyhydrides and leads to the most efficient dehydrogenation.

ISSN:1071-1023    

DOI:10.1116/1.586341

出版商:American Vacuum Society    

年代:1992

数据来源: AIP