Simone Pentzien

Laser interaction with coated collagen and cellulose fibre composites: fundamentals of laser cleaning of ancient parchment manuscripts and paper

Laser cleaning of delicate biological composite materials such as ancient parchment manuscripts from the 15th and 16th century and printed paper from the 19th century is demonstrated with an ultraviolet excimer pulsed laser at 308 nm. Laser fluence levels must stay below the ablation and destruction threshold of the parchment or paper substrate, and have to surpass the threshold of the contaminant matter. Foreign layers to be removed must exhibit a higher optical density than the artifact substrates. Synthetic carbonaceous dirt modelled by water-soluble black crayons showed a characteristically weak featureless laser-induced plasma spectroscopy spectrum near the noise limit. It turned out that laser-induced plasma spectroscopy is of limited use in monitoring halting points (or etch-stops) because it relies on the destruction not only of the laterally inhomogenously distributed contaminant but also of pigment phases on a microscopically rough parchment substrate. Laser-induced fluorescence spectroscopy, however, promises to be a valuable non-destructive testing technique for etch-stop monitoring.

Near-UV and visible pulsed laser interaction with paper

The applicability of excimer laser at 308 nm and Nd:YAG laser at 532 nm with fluences below 0.86 J/cm2 for cleaning of cellulose and paper materials was evaluated. The extent of degradation of purified cotton cellulose and Fabriano paper after laser treatment as well as after a period of accelerated humid oven ageing was determined by following the changes in the degree of polymerization. While irradiation of paper with the excimer laser at 308 nm results in depolymerization of cellulose accompanied by a decrease in ISO brightness, no detrimental effects of Nd:YAG laser treatments were observed.

Pulsed-laser deposition and boron-blending of diamond-like carbon (DLC) thin films

Abstract Diamond-like carbon (DLC) films, both pure and doped with boron, were prepared by pulsed laser deposition (PLD) with a XeCl excimer laser employing polycrystalline graphite and boron carbide targets. As substrates served silicon(111) wafers. The deposition parameters such as the laser intensity, vacuum, supporting gas conditions, substrate temperature, target-substrate distance, substrate combination and composition could be controlled independently, and thus, were used to modify the film properties and composition. Optical emission diagnostics of the laser plasma was performed at various locations between the target and the substrate. In the high power regime (> 108 W cm−2), pulsed laser evaporation resulted in the emission of excited C2 molecule radicals. High incident energies were necessary for surmounting potential barriers to the formation of sp3 bonds. Films with the highest sp3 content were formed with small distance between target and substrate, high laser intensities (I ≈ 109 W cm−2), and low base pressures (

Template electrodeposition of nanowire arrays on gold foils fabricated by pulsed-laser deposition

Abstract A novel procedure to generate stable and rigid metal nanowire arrays with diameters between 100 and 600 nm and densities of ∼10 8 cm −2 is presented. It combines 1. (a) pulsed-laser deposition of an adherent and homogeneous gold cathode foil on a polycarbonate track-etch template 2. (b) reinforcement and levelling by electroplating, and 3. (c) the potentiostatic growth of the nanowire array through the etch tracks under convection control in an electrochemical jet cell.

Diagnostics of parchment laser cleaning in the near-ultraviolet and near-infrared wavelength range: a systematic scanning electron microscopy study

A detailed diagnostic study of the interaction of nanosecond laser pulses from the near-ultraviolet to the near-infrared wavelength range with various types of contemporary and ancient parchments is presented. The advantages of laser cleaning due to the absence of chemical agents, spectroscopic selectivity, micro-precision and computer-aided handling can only be verified when physico-chemical diagnostics guarantee destructionless processing. Scanning electron microscopy data are correlated with chemical degradation and morphological changes dependent on the laser fluence and wavelength. It is also shown how transmission electron microscopy, diffuse reflectance infrared Fourier transform spectroscopy, and pyrolysis capillary gas chromatography can be employed in the chemical diagnostics of laser cleaning of parchment. This study suggests that the ageing status of parchment artefacts plays a major role in assessing the laser cleaning limits.

Near-UV laser interaction with contaminants and pigments on parchment: laser cleaning diagnostics by SE-microscopy, VIS-, and IR-spectroscopy

Abstract Potentials and limitations of the near-UV pulsed laser cleaning of parchment (wavelength 308 nm, pulse duration 17 ns) are demonstrated by the application of scanning electron microscopy (SEM), colour metrics and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) at model contamination/pigment/parchment systems. Pigment-binder systems stable and unstable against near-UV laser treatment could be identified. A chemical degradation threshold fluence of a goat parchment model substrate was determined which practically coincided with its ablation threshold fluence. This indicates that the fluence range of destructionless laser cleaning at 308 nm is almost not impaired by chemical modfications below the ablation limit. Nevertheless, spectroscopic diagnostics are necessary to guarantee destructionless cleaning for practical cases where the chemical conversion threshold fluence deviates from the ablation threshold to lower values.

Probing the limits of paper and parchment laser cleaning by multispectral imaging

Paper and parchment cleaning with lasers provides the advantage to be a contact-less and dry process. The absence of chemical agents, its spectroscopic selectivity, micro-precision, computer-aided handling, and the combination with on-line diagnostic techniques makes it attractive for restoration applications. This technique, however, is not only limited by the evaporation of such delicate protein or cellulose fibre structures (i.e. the ablation threshold) or by discolorations, which can be easily detected by the naked eye or by microscopic inspection. Even when the aesthetic appearance is not altered, invisible irreversible chemical modifications may affect the long-term aging behavior negatively. In such cases, only diagnostic tools sensitive for chemical changes can probe the limits of laser cleaning. Deviations of chemical conversion threshold fluences from the well-established ablation threshold fluence values were investigated by multi-spectral imaging techniques at parchment or paper model systems and historical originals. Ultraviolet, visible and infrared reflection, but also visible fluorescence were employed using an imaging system, which operates in a spectral range from 320 nm to 1550 nm. Visible imaging allowed an accurate documentation of the color appearance of the artwork before and after the laser treatment. In-depth information of chemical modifications could be gained by the infrared imaging mode. Surface chemical identification was performed by both diffuse-reflection imaging in the ultraviolet range between 320 and 400 nm, and by visible fluorescence imaging using a 365 nm light source. The results for excimer laser treatment at 308 nm show that not only the laser fluence but also the age of the artefact strongly affects the chemical conversion threshold. Most substrates older than at least several decades exhibited much higher chemical stability than new model systems. This is a strong indication that the aging status of both parchment and paper artefact plays a major role in assessing the laser cleaning limits. That means that the laser processing behavior of model systems can be compared with that of original fibrous artworks to only a very limited extent, and that original artefacts have to be treated rather as individual specimens.

Pulsed-laser metal contacting of biosensors on the basis of crystalline enzyme-protein layer composites

Abstract Crystalline bacterial cell surface layers (S-layers) composed of monomolecular arrays of protein subunits are accessible to a wide variety of possible proteinchemical reactions. This enables the attachment and immobilization of enzyme molecules in a tightest packing, which has not been achieved with other immobilization matrices. When immobilized to an S-layer lattice, the enzyme entities are surrounded by nanometer pores. Thus, they can react electrochemically with the analyte liquid streaming through these pores. The control over this process has to take place by way of an inert electrical contact in a distance of less than 1 nm. The relatively voluminous, but specially shaped sensor enzyme molecules have to be connected with an optimum metallic contact, which must not disturb the protein structure. Previously, platinum films were applied on enzyme layers immobilized on S-layer protein by argon sputtering. This conventional technique, however, exhibits substantial limitations. One, for instance, is the volume change of the S-layer/enzyme composite system when it is introduced into a conventional vacuum coating apparatus. This coating problem can be circumvented by a completely new deposition method, i.e. the pulse-laser-deposition (PLD) on protein crystal composite films with optimized laser parameters and reaction atmospheres. Enzyme activities of 70–80% were achieved, thus demonstrating that composite systems consisting of the 2D-protein-layer/enzyme/metal sequence can successfully serve as highly efficient sensor systems.

Traditional and Laser Cleaning Methods of Historic Picture Post Cards

1 Institute of Science and Technology in Art, Academy of Fine Arts, Schillerplatz 3, 1010 Vienna, Austria ◦ present address: Freiberger Compound Materials, Am Junger Lowe Schacht 5, 09599 Freiberg, Germany 2 Institute of Conservation and Restoration, Academy of Fine Arts, Schillerplatz 3, 1010 Vienna, Austria, h.holle@akbild.ac.at 3 Division Surface Technologies, Federal Institute for Materials Research and Testing (BAM), Unter den Eichen 87, 12205 Berlin, Germany 4 Department of Physical Chemistry, University of Vienna, Waehringer Str. 42, 1090 Vienna, Austria

Technical analysis of a Central Asian wall painting detached from a Buddhist cave temple on the northern Silk Road

A great number of Central Asian wall paintings, archeological materials, architectural fragments, and textiles, as well as painting fragments on silk and paper, make up the so called Turfan Collection at the Asian Art Museum in Berlin. The largest part of the collection comes from the Kucha region, a very important cultural center in the third to ninth centuries. Between 1902 and 1914, four German expeditions traveled along the northern Silk Road. During these expeditions, wall paintings were detached from their original settings in Buddhist cave complexes. This paper reports a technical study of a wall painting, existing in eight fragments, from the Buddhist cave no. 40 (Ritterhöhle). Its original painted surface is soot blackened and largely illegible. Grünwedel, leader of the first and third expeditions, described the almost complete destruction of the rediscovered temple complex and evidence of fire damage. The aim of this case study is to identify the materials used for the wall paintings. Furthermore, soot deposits as well as materials from conservation interventions were of interest. Non-invasive analyses were preferred but a limited number of samples were taken to provide more precise information on the painting technique. By employing optical and scanning electron microscopy, energy dispersive X-ray spectroscopy, micro X-ray fluorescence spectroscopy, X-ray diffraction analysis, and Raman spectroscopy, a layer sequence of earthen render, a ground layer made of gypsum, and a paint layer containing a variety of inorganic pigments were identified.