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- 2000 (21) (entfernen)
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- Femtosecond laser ablation (3)
- Ablation (2)
- Polymer (2)
- Titanium nitride (2)
- Activated ester (1)
- Auger electron spectroscopy (1)
- Batteries (1)
- Bismuth (1)
- Buried interface (1)
- Conducting polyalkylthiophene (1)
Micromachining experiments were performed with Ti:sapphire laser pulses (130 fs - 150 fs, 800 nm, approximately 10 Hz) in air. Employing the direct focusing technique, highly absorbing titanium nitride (TiN) and weakly absorbing polyimide (PI) and polymethylmethacrylate (PMMA) served as target materials. The lateral and vertical precision of the laser ablation and morphological features were characterized by scanning force (SFM), scanning electron (SEM) and optical microscopy. For TiN, incubation can be observed, i.e. the single-pulse surface damage threshold (0.26 J/cm2) is by a factor of two greater than the threshold for 100 pulses. Ablation rates below 10 nm per pulse can be achieved. The evolution of sub-wavelength ripples is presented in dependence on pulse number and laser fluence, respectively. The incubation behavior of the polymers can be described by an accumulation model as for TiN. Experiments on PI with varying focal lengths result in the same modification thresholds. Different polarization states of light (linear, circular) lead to a variation of the ablation rate and to various morphological patterns in the ablation craters (wavelength ripples, cones). Swelling of PMMA occurred at fluences below the ablation threshold.
The present study concerns the cleaning of matenats using pulsed laser irradiarton and it summarises the most recent results obtalned by the collaborative research of different European groups, within the kamework of a European program for tralnlng and mobillrv of researchers. A series of pulsed lasers, which emit at various wavelengths (liom UV to IR) wit11 short duration of pulse (few nano-, pico- or fernto-seconds), is used for the removal of metallic, ceramic and organic pollutants kom contaminated solid surfaces of different natures. The scientific results obtained so far are focused on the laser cleaning of silicon wafers from sub-micrometer particles, tile theoretical modelling of particles removal mechanism during dry laser cleaning, the removal of oxide layers from oxidised metals and alloys, as well as on the development of laser imaging as a diagnostrc tool for the estimation of the efficiency of the proposed cleaning technique.
Ablation of indium phosphide wafers in air was performed with 130 fs laser pulses at a wavelength of 800 nm at a low repetition rate of 10 Hz. In order to evaluate the role of the incubation effects, the relationship between the number of laser pulses used for the ablation and the threshold fluence was studied. Particular attention was paid to the chemical composition, surface morphology and structural variations of the ablated area.
Summary form only given. Machining investigations of crystalline silicon have been performed with laser pulses at a wavelength of 780 nm in the range between 5 fs and 400 fs. Applying 100 pulses per spot, surface damage thresholds were determined by the measurement of the damage diameter. In this pulse duration regime, the threshold fluences were nearly constant. Single-pulse investigations with 5 fs pulses yielded a value of about 0.15 J cm-2 identical to the multi-pulse experiment. This is in contradiction to the behaviour of dielectrics where incubation effects alter the optical properties down to the 5 fs pulse regime. Employing laser pulses with a duration of 130 fs at a wavelength of 800 nm, single-pulse ablation thresholds of 0.23 J cm-2 and 0.16 J cm-2 were determined for Si and InP in air, respectively. The threshold fluence was calculated from the linear relation between the square of the diameters versus the logarithm of the laser fluences.
Gradient Composite Replicas from Protein Crystal Layer Templates produced by Pulsed Laser Deposition
(2000)
Ultrashort pulse laser microstructuring (pulse duration 130 fs, wavelength 800 nm, repetition rate 2 Hz) of titanium nitride (TiN) films on silicon substrates was performed in air using the direct focusing technique. The lateral and vertical precision of laser ablation was evaluated. The TiN ablation threshold changed with the number of pulses applied to the surface due to an incubation effect. An ablation depth per pulse below the penetration depth of light was observed. Columnar structures were formed in the silicon substrate after drilling through the TiN layer.
Ablation experiments with ultrashort laser pulses (pulse duration 150 fs, wavelength 800 nm) on polymers (PC, PMMA) relevant for biomedical technology have been performed in air. The lateral and vertical machining precision was evaluated by optical, atomic force and scanning electron microscopy. The ablation threshold reaches values in the range of 0.52.5 J/cm2 and depends significantly on the number of laser pulses applied to the same spot. The hole diameters are influenced by the laser fluence and the number of laser pulses. The relation between the ablation threshold and the number of laser pulses applied to the same spot is described in accordance with an incubation model.
Three new thiophene derivatives containing different activated ester groups covalently attached to the thiophene ring via a linear undecyl spacer have been synthesized. Electropolymerization of these monomers in acetonitrile led to stable electroactive polymers, while activated functional groups withstand the polymerization conditions and were correctly incorporated in the resulting polymers. These polymers show the characteristic electrochemical behavior of poly(3-alkylthiophene)s with the reversible redox transition in the range of 0.70.9 V. UV/Vis spectra of them exhibit an absorption maximum at around 460 nm. Conductivity measurements on oxidized films of these polymers by means of the two-probe method gave values in the range of 10-310-2 S cm-1. The reactivity of the pendant activated ester groups was demonstrated by the reaction with butylamine, (4-amino-2-oxabutyl) ferrocene and 2-aminoanthraquinone. Spectroscopic studies and electrochemical characterization confirmed that the immobilized amino compounds are covalently bound to the polymer surfaces. These results suggest that the obtained new polymers can be used as electrically conducting carrier materials for the immobilization of biochemically interesting molecules.