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Many wooden artworks are contaminated by DDT (dichlorodiphenyltrichloroethane) as a result of a surface treatment by means of Hylotox-59©. The liquid preservative was used until the end of the 80s. DDT crystal structures are formed on the wood surfaces by the "blooming" of chlorine compounds. Contaminated waste wood with natural biocide ageing, gilded and wood carved elements of an old picture frame and wooden samples with paint layers were provided by the Schlossmuseum Sondershausen.
The removal of DDT was evaluated employing femtosecond and nanosecond laser radiation and cold atmospheric plasma technique using different working gases (air, nitrogen, and argon).
Before laser application, a chlorine measurement is done by X-ray fluorescence (XRF) analysis as reference. After laser processing, the XRF analysis is used again at the same surface position to determine depletion rates. Additionally, a documentation and characterization of the sample surface is done before and after laser and plasma treatment using optical microscopy. For plasma processing with various systems a chlorine measurement is done by gas chromatographic-mass spectrometry (GCMS) analysis.
For laser treatment a depletion of the chlorine concentration of 55-70% and 75% was achieved for 1064-nm nanosecond pulses and 800-nm femtosecond pulses, respectively. For the application of 30-fs laser pulses, no crystalline DDT residues remain on the sample surfaces. This holds also for the plasma processing with nitrogen as working gas.
Degradation behavior of thin polystyrene films on exposure to Ar plasma and its emitted radiation
(2013)
Spin-coated films of amorphous polystyrene (PS) were exposed to argon plasma for a few seconds to several minutes. The PS film was either in direct contact with the plasma or was shielded from the direct plasma contact by filters with different cutoff wavelengths in the vacuum UV region or by a Faraday cage (FC) made from metal mesh to prevent the impinging of charged species. Only energy-rich neutrals and plasma radiation may be operative in presence of the FC. lithium fluoride (LiF) filter protects the sample from direct contact with the plasma. Wavelengths of plasma radiation shorter than c. 105 nm (≈ 11.8 eV) were cut off. Glass filters made of fused SiO2 have a cutoff at λ ≈175?nm completely the vacuum UV radiation of plasma (ca. 175 nm ≈ 7.0 eV). These energies are sufficient to produce C–C, C–H bond scissions in case of direct Ar plasma exposure and Ar plasma exposure with use of the LiF filter. Only quartz glass shielding did not produce significant effects on the polymer surface in comparison to the reference PS, either in surface energy or O/C ratio or in IR spectra. Oxygen plasma has worked most aggressive and had etched the PS film, thus establishing a steady state between introduction of new oxygen functionalities and polymer etching. Ar plasma exposure produces also oxidation and etching of the polymer films as the oxygen plasma. Using of a FC during Ar plasma exposure or the LiF filter a slightly weaker oxidation was observed.
Recently, time-of-flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) instrumentation has been used to address areas of interest within micro-fluidic devices providing full access to the surface chemistry established at the bottom of micro-channels therein. After careful calibration, information on surface chemistry as obtained by ToF-SIMS or XPS can be interpreted in terms of wettability expressed as contact angles which are then characteristic for the inner walls of micro-channels. Standard contact angle measurement is not applicable in micro-channels. The approach has been demonstrated to be successful with two different micro-fluidic devices hot embossed into high-end quality poly(methyl methacrylate) (PMMA) or Polycarbonate wafers. A pre-selected surface chemistry at micro-channel walls can be established by plasma technologies but ageing and rinsing effects have to be under control. A combination of ToF-SIMS, XPS and contact angle measurement techniques has been demonstrated to provide the required information. Finally, it is shown by ToF-SIMS and XPS analysis that in the production of micro-fluidic parts during practical processing using hot embossing technologies, material originating from cover foils will reside on the polymer wafer's surface. Moreover, residues of releasing agents as silicone oil used during processing can be detected by ToF-SIMS. Both cover foil residues and silicones are issues of trouble shooting in micro-fluidics because they will change contact angles efficiently.
Laser and plasma processing of materials is a rapidly growing field in fundamental science and materials technology requiring both a multidisciplinary approach and a wide-ranging knowledge. The topical issue Laser and plasma processing for advanced materials of the Journal of Optoelectronics and Advanced Materials covers a number of recent research highlights. The production of thin functionalized films, nanoparticles and nanocomposites using pulsed laser ablation (PLA) and deposition (PLD) or plasma treatment is discussed in a number of papers. Additionally, experiments using matrix assisted pulsed laser evaporation (MAPLE) are described. It is shown in this book that nanoparticles are generated and/or processed by laser or plasma interaction in very different environments ranging from gaseous and liquid to solid phase. Material properties change if the particle size is reduced below a critical limit allowing e.g. optical, electronic, biomedical, and environmental applications. Micro- and nanostructuring of surfaces (2D) and within the bulk of transparent materials (3D) is presented in various articles. In many cases, ultrashort laser pulses were applied. Furthermore, nanoparticles interacting with laser radiation can be used for nanostructuring purposes. Apart from experimental investigations, numerical modeling of the interaction of femtosecond laser pulses with materials has also been performed to understand structure formation theoretically. Especially for bio-functionalization, selective deposition of sensitive materials (e.g. proteins, cells) on surfaces is needed. A sophisticated process used for this purpose is known as laser induced forward transfer (LIFT). Recent findings regarding the LIFT method are depicted in this issue. Laser annealing of implanted dopants and thin films aiming to enhance structural and electrical properties, sensor dicing by laser radiation, and laser or plasma surface modification for the improvement of solar cells or polymer wettability change are but a few of the subjects focusing on applied research. Additionally, hybrid processes combining plasma spraying and laser-induced melting to control microstructure of coatings are introduced. Last but not least, achievements regarding analytical techniques are outlined. Laser induced breakdown spectroscopy (LIBS) make up a large part of this class. Additionally, the contributions to optical emission spectroscopy and mass spectrometry of plasma processes are significant.
The X-ray-induced sample damage during mono XPS analysis of an oxygen-plasma-oxidized and subsequently wet-chemically reduced poly(propylene) film was investigated as a showcase for plasma-modified or plasma-deposited samples. By doing this, the degradation index approach as introduced by Beamson and Briggs in the Scienta ESCA300 high-resolution XPS database of organic polymers has been adopted. As to be expected, the sample degrades by loosing oxygen as revealed by observation of decreasing O/C and COR/Csum ratios. However, the X-ray degradation indices are definitely higher than those of conventional reference polymers. Moreover, the COR/Csum degradation index is significantly higher in comparison with one obtained for the O/C ratio. In that context, there is no difference between the plasma sample and a conventional poly(vinyl alcohol) polymer. It is concluded that for reliable quantitative surface chemical analysis, the quality of spectra in terms of acquisition times must be optimized aimed to a minimization of X-ray degradation. Finally, it is proposed to describe the photon flux of an X-ray gun in an XPS experiment, which defines the degradation rate at the end, by using the sample current simply measured with a carefully grounded sputter-cleaned reference silver sample.
The production of chemically-defined plasma polymers and the introduction of monotype functional groups onto polymer surfaces are described. One method is to lower the energetic level of low-pressure plasmas. Pressure- and plasma-pulsed plasmas were successfully tested for the production of chemically-defined plasma polymers by increasing the monomer supply during the plasma-off period. Well-defined ultra-thin polymer films with regular structure were deposited from atmospheric plasmas by electrospray techniques. Post-plasma wet-chemical processing was also applied, as were gas/liquid-based aerosols and underwater plasmas.