on the IUVSTA Workshop on
in Surface Science and Thin Films
The purpose of the IUVSTA Workshop on Lasers in Surface Science and Thin Films was to bring together scientists working at the frontiers of the applications of lasers in the fields of Surface Science and Thin Films. The workshop is sponsored by the Surface Science Division and the Thin Film Division of IUVSTA. The workshop was co-organised by Wolfgang Husinsky (Institut fur Algemeine Physik, Technische Universitaet Wien, Austria; local organiser) and Aart W. Kleyn (FOM-Institute for Atomic and Molecular Physics, Amsterdam, the Netherlands). Prof. Y. Murata (University of Electrocommunications,Tokyo, Japan) and Prof. H. Helvajian (Aerospace Corp., USA) were advisory members of the organising committee. The workshop was held at the Bundessportheim Kitzsteinhorn, at a remote location at an altitude of 2500 meters. The site has excellent conference facilities for small groups. In addition to the scientific programmes the participants could enjoy skiing and hiking together in the mountains, leading to a very relaxed atmosphere and very strong mutual interactions. The workshop was attended by 24 participants from: Austria, 6; Germany, 5; Japan, 5; The Netherlands, 3; United States, 3; Sweden, 1; United Kingdom, 1. The number of participants was lower than the organisers had aimed at, but the turned out to be very good for the intensity of discussions and ample time for each presentation.
The scientific programme consisted of 5 invited lectures of 1 hour and 16 contributed papers of 30-40 minutes. Each paper was followed by 5-15 minutes discussed. In addition, there were very lively discussions outside of the sessions. The programme highlighted the use of lasers both at a fundamental and applied level. Specific topics addressed were:
most basic work presented was the study of hot electron dynamics in metals.
Petek (Hitachi, Japan) showed how information concerning the interaction
between excited electrons and the electrons in Cu or Ag surfaces could
be studied using femtosecond laser pulses. It was shown that relaxation
of excited electrons in electron-electron collisions occurred at a timescale
on the order of tens of femtoseconds. The relaxation dynamics could approximately
be described using Fermi liquid theory but many uncertainties remained.
Using interferometric methods in some cases a time resolution of less
than one femtosecond could be obtained.
The information that the thermalisation of electrons occurs on a very short timescale was exploited by Heinz (Columbia University, New York, USA). He showed that the relaxation of the hot (2000 K) electron gas occurs on a timescale of a picosecond in electron-phonon collisions. The subsequent relaxation of the phonon system leading to complete thermalisation of the solid occurs at much longer times. Hence desorption induced by femtosecond laser pulses (100 Fs) is mainly due to the rapid heating of the electronic system. The hot electrons induce electronic transitions in the adsorbate-surface system leading to desorption. The time the system spends in the electronically excited state is very short (a few Fs) and re-excitation during the time the electrons are hot can occur. This leads to a strongly enhanced desorption probability when compared to experiments with longer light pulses. Dissociation was not observed with femtosecond pulses.
Photochemistry by longer laser pulses (nanoseconds) was discussed by Hasselbrink (Fritz-Haber Institute, Berlin, D). In this case multiple excitation could be excluded due to the lower laser power present when the nanosecond pulse is on. Photochemistry occurs for those cases when the adsorbate-surface system survives in its excited state. This probability is several order of magnitude lower than for femtosecond pulses with comparable energy. Hasselbrink showed very nicely that several characteristics of the desorbed molecule, such as the rotational excitation, could be described with simple empirical potential energy surfaces for both the excited and ground state potential. New result on he photodesorption of NH3 and ND3 from Pd(111) were shown.
The link between those basic studies and laser ablation was made by Leuchtner (University of New Hampshire, USA). He showed that several regimes for desorption of adsorbates and the surface itself exist. At low powers simple thermal heating can account for desorption. At higher laser powers per cm2, exceeding those of the previous several non-linear effects were observed. These effects were attributed to several electronic effects. At first the high laser powers lead to deformation of the surfaces. The irregular structures thus formed allow a number of electronic effects, leading to laser power absorption and ejection of particles. At very high laser powers the ejection of charged particles leads to the formation of a plasma.
Laser processing of materials was discussed by Buerle (Linz, Austria). Processing can be done by ablation, putting the principles introduced by Leuchtner to work, by laser reactive etching, and by laser induced deposition. In the latter case laser induced dissociation of molecules before the surface, at the surface by electronic processes or at the surface by pyrolytic processes could lead to deposition of materials. The process was used for instance to make metallic interconnects for custom made ICs and in IC repair.
In addition to the invited talks contributed talks contributed papers highlighted recent development in the areas introduced by the invited speakers. In addition, some work concerning related developments concerning internal surfaces of porous materials was presented. The presentations at the conference are listed below.
Hrvoje Petek, Japan (review paper)
Dynamics in Metals: A Critical Comparison between Experiment and Fermi
fast electron dynamics of image potential states
Processes Induced by Femtosecond Laser Pulses: Experiment and Theory
dynamics explored in more than one dimensions
mechanism in surface photochemistry
Alignment in the UV-Laser Induced Desorption of CO from Cr2O3(0001)
desorption of NO and CO from Pt and Pt-Ge surface alloys
reactions of water and potassium coadsorbed on graphite
photochemistry of large physisorbed molecules on Ag(l11)
Studies of Fundamental Processes in Laser Ablation and Desorption
Desorption and Surface Structural Changes on Si(111)7x7 Surface
Time-Resolved Study of Laser-lnduced Desorption from Si(111)7x7 Surface
Pulse Laser Ablation of Thin Films
Ablation of biological Material: Mass spectrometry of ablated material
Direct Writing and 3D Patterning
of pyrolytic laser direct writing: non coherent structures and instabilities
monolayer template for patterning of strongly bound adsorbates
Simulations of Laser-Induced Surface Structures
Harmonic Generation on Diamond Interfaces
dephasing mechanisms in hydrogen-bonded systems
The dynamics of infrared photodissociation of methanol clusters in zeolites and in solution