Ingo Hussla

Infrared photodesorption: Vibrational excitation and energy transfer processes on surfaces

Abstract Photon-stimulated desorption due to internal vibrational excitation of adsorbed molecules is a resonant phenomenon and has recently attracted considerable experimental and theoretical attention. n this paper, a brief review of prior studies is given. New results on NH3, ND3 and Xe in neatly adsorbed and co-adsorbed states excited by a tunable infrared laser and photodesorbed from Cu(100), NaCl and Ag films are presented to elucidate desorption mechanisms. Both single-photon and multiphoton excitation processes are examined and the velocity distributions of desorbed particles are analyzed. Various energy transfer and relaxation processes related to desorption are evaluated and a model for infrared photodesorption with particular emphasis on assessing the quantum and thermally-assisted effects is also discussed.

Ablation of metal surfaces by pulsed ultraviolet lasers under ultrahigh vacuum

A review of recent studies of ablation of metal surfaces by pulsed ultraviolet lasers under ultrahigh vacuum conditions is presented. Techniques employed include optical emission spectroscopy, time-resolved mass spectrometry, and reflectance measurements. The results are discussed in terms of optical and thermal mechanisms that could account for the observed ablation phenomena.

Infrared spectroscopic investigation of the adsorption of fluoromethane on sodiumchloride surfaces under ultra high vacuum

Abstract The adsorption of CH 3 F on NaCl between 77 K and 250 K was investigated using infrared spectroscopy under ultra high vacuum conditions. All internal normal modes of the adsorbate were observed and assigned. Three adsorption phases were detected. The largest frequency shift with respect to the gas takes place for the most intense mode, the C-F stretch ν 3 , − 102 cm −1 ( 10 %) for α-CH 3 F-NaCl(film) on NaCl(100), while the other modes were much less influenced. No splitting of the vibrations degenerate in the gas occurs. Adsorption isotherms and the isosteric heats of adsorption were determined.

Selective desorption from the binary coadsorbate C2H6CH3FNaCl by resonant vibrational excitation with laser infrared radiation

Abstract After measuring the linear infrared absorption spectrum of the coadsorbate, selective desorption of CH 3 F from the binary coadsorbate C 2 H 6 -CH 3 F-NaCl under ultrahigh vacuum conditions at 12o K stimulated by resonant CO 2 laser pulses of small fluence ∼0.1 J·cm −2 has been carried out. No desorption of ethane, which is slightly more volatile, but has no significant infrared absorption at the laser frequency, was observed. The primary activation step is the resonant multiphoton excitation of the most intense internal CH 3 F-NaCl adsorbate vibration, the C-F stretching mode v3. The substance separation seems to indicate high localisation of the activation in this desorption and could be of interest for applications.

Laser-Assisted Chemical Etching of Inorganic Materials: Mechanistic Studies

Recent advances in applications of lasers to induce chemical etching and vapor deposition have raised the firm expectation that the laser chemical techniques may have significant impact on processing materials for microelectronics. In laser-induced chemical etching, it has been shown in various laboratories that a rather wide range of solid materials can be potentially processed by lasers [1,2]. These include the etching of semiconductors such as Si [3–9], Ge [10], GaAs [11–13] and InP [11], metals such as Ta [14], Te [15,16], Ni and Fe [lb], insulators such as SiO2 [15,17,18], and magnetic and ceramic materials such as MnZn ferrites [1a,9a] and TiC-Al2O3 [1b, 16], by various halogen-containing gases excited by ultraviolet, visible and infrared lasers. The laser-enhanced etch rates can be greater than 50 μm/sec and submicron spatial resolution has also been demonstrated.

Molecule-Surface Interactions Stimulated by Laser Radiation

Laser photons can interact with a gas-solid system to promote heterogeneous reactions and to stimulate desorption. Two classes of photo-enhanced surface processes have been extensively investigated in our studies. The first one involves laser-induced chemical etching of solids examplified by the silicon-fluorine reaction affected by visible photons. Recent time-resolved mass spectrometric measurements have revealed interesting surface interaction characteristics quite different from steady-state reactions. The second one involves infrared laser photodesorption initiated by excitation of internal molecular vibrations. New results on ammonia photodesorbed from Cu(100) and NaC1 surfaces are presented to elucidate desorption mechanisms. Both single-photon and multi-photon excitation processes are examined and the velocity distributions of desorbed particles are analyzed. Various energy transfer and relaxation processes related to desorption are evaluated and a model for infrared photodesorption with particular emphasis on assessing the quantum and thermally-assisted effects is also discussed.

Infrared laser-induced photodesorption of adsorbed and condensed phases

Abstract Infrared laser-induced photodesorption occurs via pulsed excitation of internal vibrational modes of molecules adsorbed on surfaces. A review of these experiments is given. Excitation of the second overtone of the molecule-surface bond has been proposed theoretically as alternative photodesorption channel. Experimental results are reported for CO-Cu(100). No desorption was detected even though the overtone occurred within the CO 2 laser range and incident intensities up to 100 MW/cm 2 were used.

Selective Desorption from the Binary Coadsorbate C2H6-CH3F-NaCl By Resonant Vibrational Excitation with Laser Infrared Radiation

Abstract After measuring the linear infrared absorption spectrum of the coadsorbate, selective desorption of CH 3 F from the binary coadsorbate C 2 H 6 -CH 3 F-NaCl under ultrahigh vacuum conditions at 12o K stimulated by resonant CO 2 laser pulses of small fluence ∼0.1 J·cm −2 has been carried out. No desorption of ethane, which is slightly more volatile, but has no significant infrared absorption at the laser frequency, was observed. The primary activation step is the resonant multiphoton excitation of the most intense internal CH 3 F-NaCl adsorbate vibration, the C-F stretching mode v3. The substance separation seems to indicate high localisation of the activation in this desorption and could be of interest for applications.