The use of laser-induced breakdown spectroscopy (LIBS) for the sorting of polymers containing heavy metal impurity is
investigated. Our main attention is directed towards the detection of cadmium and lead in real-life waste materials and
certified reference polymer materials. UV (193 nm ArF) and IR (1064 nm Nd:YAG) laser radiation is employed for
ablation and plasma generation in air. The LIBS spectra are measured in the UV / VIS range by using an Echelle
spectrometer equipped with an ICCD camera. Spectra are compared for the different lasers. Sorted polymer materials are
investigated by reference analysis.
We combine laser processing and the technique of a scanning near-field optical microscope (SNOM) for realization of
laser-patterning on a nanoscale, laser ablation near the fiber tip, and micro-analysis of solid surface samples by laserinduced
breakdown spectroscopy (LIBS). We describe an universal SNOM-like setup allowing to produce near-field
laser patterns by laser heating and laser ablation, laser-induced breakdown spectroscopy, and atomic force microscope
(AFM) topography investigation with the same optical fiber tip, which is used as near-field emitter or as probe. With
solid Si and Al samples, three laser processing regimes were observed with increasing laser pulse energy: (1) cone
formation (only for Si, smallest features with 500 nm width and 100 nm height), (2) formation of small craters (smallest
features with 450 nm width and 250 nm depth), and (3) crater formation with a width of more than 2 μm with emission
of evaluable plasma emission line spectra.
Pulsed-laser deposition (PLD) is an excellent technique to grow thin films and multi-layers of complex oxide materials.
We present our recent results on deposition, characterization and nano-patterning of novel oxide high-temperature
superconductors (HTS) and piezoelectric materials. HTS thin films of improved superconducting properties are
fabricated from ceramic targets consisting of Y<sub>2</sub>Ba<sub>4</sub>CuMO<sub>y</sub> (M = metal) nano-particles embedded in YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub>
(YBCO) matrix. The nano-composite ceramics are UV-laser ablated and the optical plasma emission is monitored by
laser - induced breakdown spectroscopy. The HTS films reveal superconducting critical current densities that depend on
target composition and are strongly enhanced as compared to phase pure YBCO films. Application of HTS layers in
future nano-electronic devices requires novel techniques for nano-patterning. Masked ion-beam structuring enables the
nano-patterning of YBCO thin films in a direct and single-step process. Gallium orthophosphate (GaPO<sub>4</sub>) thin films and
piezoelectric ZnO multi-layers are reported also. GaPO<sub>4</sub> is an outstanding piezoelectric material with very high
transition temperature (~ 970 °C). Epitaxial GaPO<sub>4</sub> films are fabricated on quartz substrates by PLD and thermal post-annealing.
Long-term annealing at high temperature does not degrade the GaPO<sub>4</sub> films. Multi-layers of Al and Li doped
ZnO are pulsed-laser deposited on various substrates and investigated for applications in thin film sensors.
Solid Al alloy samples were analyzed by laser-induced breakdown spectroscopy (LIBS) either by employing an optical glass fiber as light waveguide or by direct laser irradiation in air. The samples had an Al content of 87.56 % to 99.2 % (w/w), a Si content of 0.07 % to 11.12 %, a Fe content of 0.15 % to 0.89 % and a Mg content of 0.005 % to 2.38 %. For the LIBS analyses, we used an Nd:YAG laser delivering 5 to 7 ns pulses with pulse energies from 50 to 500 mJ per pulse at a repetition rate of 10 or 20 Hz. The experiments were performed either at a wavelength of 1064 nm or (frequency doubled) at 532 nm. We obtained qualitatively similar results in experiments with direct laser irradiation in air and experiments where cleaved fibers were used as a laser light guide. Damage of the fibers sets an upper limit for the laser energy in the latter case. Experiments employing tapered fibers showed that a lateral resolution in the order of 10 &mgr;m is feasible with the presented setup.
We describe here the modification of various polymers (polytetrafluoroethylene, polyethyleneterephthalate, and
polyvinyl alcohol) by UV-irradiation with wavelengths below 200 nm in an inert or reactive atmosphere. The light
sources employed are F<sub>2-</sub> or excimer lasers and excimer lamps. The reactive gases include ammonia (NH<sub>3</sub>), acetylene
(C<sub>2</sub>H<sub>2</sub>), and oxygen (O<sub>2</sub>). Photo-dissociated fragments of these gases can react with the polymers or be deposited
thereon, resulting in new chemical groups at the surface. Special emphasis is put to improved adhesion of biological
cells at these modified surfaces. Potentials applications include cell coated medical implants and prostheses as well as
cell micro-arrays for high throughput screening.
The article describes the modification of fluoropolymers by UV-irradiation with wavelengths below 200 nm in a reactive or inert atmosphere. Light sources employed are excimer lamps, excimer-lasers or F<sub>2</sub>-lasers. Special emphasis is put on adhesion phenomena of fluids, biological cells and metal coatings at the modified surfaces.
Recent achievements in laser-induced surface patterning obtained in our group are summarized. Here, we have employed both a SNOM-type setup and two-dimensional lattices of SiO<sub>2</sub> microspheres formed by self-assembly processes. With the SNOM-type setup we have
demonstrated nanoscale photochemical and photothermal etching, mainly of Si in Cl<sub>2</sub> atmosphere. With 2D lattices of microspheres a large number of single features can be generated by a single or a few laser shots. Among the examples presented is the surface patterning by ablation, etching, deposition, and surface modification.
We report on rapid in-situ analysis of liquid and solid steel samples under reduced ambient pressure by laser-induced breakdown spectroscopy (LIBS) using a transportable system. LIBS denotes a technique where a pulsed laser beam is used to ablate small amounts of the target material. The characteristic optical emission line intensities of the excited species in the laser-generated plasma plume allow a quantitative chemical analysis of the target material. Over a wide range of parameters the expansion of the plume can be described by a generalized shock wave model. LIBS is a fast, non-contact method, which can be carried out under various atmospheric conditions allowing large working distances between the sample under investigation and the detection system. These properties make LIBS applicable to process control especially for vacuum devices used in metallurgy.
Polytetrafluoroethylene (Teflon PTFE) films were grown by pulsed-laser deposition (PLD). Films prepared by ablation from press-sintered targets are found to be highly crystalline, with spherulite sizes adjustable over more than one order in magnitude by suitable thermal annealing. As revealed by dielectric dilatometry, PLD-PTFE films show characteristics remarkably similar to those of conventional PTFE, i.e. the same structural first-order phase transitions. Dielectric losses are low and indicate no tendency to film oxidation. PLD-PTFE films additionally show an excellent charge-stability, comparable and even superior to commercially available Teflon-PTFE foils. PLD-PTFE enlarges the family of Teflon materials and may thus become interesting for potential miniaturized electret devices. Furthermore, dielectric dilatometry provides an elegant means for the determination of the coefficient of thermal expansion in thin nonpolar films.
UV-laser irradiation of polymers leads to different types of surface modifications, including the formation of structures with sub-micrometer dimensions. These structures may influence the adhesion of surface coatings. In this paper we investigate the temperature dependence of the growth of branched dendritic structures. Growth rates in excess of 1 nm/s were measured near the glass transition temperature of poly(ethylene terephthalate). Periodic surface structures are investigated with respect to physical formation processes.
In this paper we present recent results on laser-induce surface modifications and surface patterning by ablation. Different types of structure formation are discussed. The modeling of UV-laser ablation in nonstationary regimes is studied. Numerical calculations on the ablation rate are compared with experimental data.