Marc Aucouturier

Electron spin resonance study of hydrogenation effects in polycrystalline silicon

Electron spin resonance spectra obtained on polycrystalline silicon produced by annealing of chemical vapor deposition silicon are investigated before and after plasma hydrogenation of the material. Before hydrogenation, two paramagnetic defects are observed, one of them remaining unidentified (g=2.0084). Hydrogenation decreases the total spin density, but the two defects are affected differently; the defect with g=2.0084 is more efficiently passivated. The results are discussed in terms of the inter‐ and intragranular nature of the paramagnetic defects and of hydrogen diffusivity in the polycrystal.

An Investigation of Gold/Ceramic and Gold/Glass Interfaces

This paper describes how various characterisation methods can be used to investigate the physicochemical and spectral properties of gold films in contact with glass or ceramic. The interface between the metal and substrate has been given special attention. The examples chosen to illustrate this include: liquid gold films (decorated and fired) or inlayed gold layers on ceramic wares and “sandwich” gold foils between two glass sheets for mosaic application. Characterisation methods include: microanalytical scanning electron microscopy, X-ray diffraction, ion beam analyses (PIXE: particle induced X-ray emission; RBS: Rutherford back-scattering spectrometry), photo-spectrometry and colorimetry. The adhesion mechanism and colour behaviour of the coated objects is discussed.

Gold like lustre: nanometric surface treatment for decoration of glazed ceramics in ancient Islam, Moresque Spain and Renaissance Italy

Abstract Lustre is one of the most fascinating surface decorative effects produced on glazed ceramics. This technique seems to have been born in the ninth century in factories created by the Arabs during their conquests in the Orient (Mesopotamia, Egypt and Persia). Arab potters spread their knowhow all over the Mediterranean basin, especially Spain. Italian Renaissance potters succeeded in applying it to their production. The technique is based on a specific firing of the glazed pottery in a reducing atmosphere in the presence of metallic salts. The result is a surface layer with a metallic appearance, exhibiting various colours, from gold to brown or red. This paper provides the chemical nature and the physical structure of ancient gold like lustre layers and compares them with contemporary lustres produced by a Spanish craftsman reproducing the traditional Islamic techniques. Various analytical investigations (atomic force microscopy, high resolution SEM, particle induced X-ray emission, Rutherford backscattering, TEM, X-ray induced photoelectron spectroscopy, time of flight SIMS and grazing X-ray diffraction) were carried out as well as investigations into the coloured appearance by spectrophotometry. The results show that the lustre layer consists of silver and copper particles of nanometric dimensions dispersed in a glassy matrix. A model of the lustre formation is proposed wherein the development of a new superficial glaze is described. Comparison between ancient and modern production shows how the techniques have varied through the ages.

Corrosion patina or intentional patina: contribution of non-destructive analyses to the surface study of copper-based archaeological objects

Publisher Summary This chapter discusses research into the type of intentional patination on archaeological objects. The study of the patinated surface found on various objects of different origins and periods, from ancient Egypt to the Roman Empire, presented in the chapter has shown that it is possible by laboratory non-destructive investigations to obtain a precise physico-chemical description of the surface layers intentionally elaborated for the purpose of coloration. The distinction between intentional patina and pure corrosion products remains a challenge in the general case. The investigation presented in the chapter has been greatly facilitated from that viewpoint by the active collaboration between the authors in charge of the physico-chemical analyses and those (museum curators, conservation–restoration experts) who brought the iconographic, historical, and archaeological insights. The result of that collaboration is that intentional patination and burial corrosion products could be clearly distinguished.

Intentional patina of metal archaeological artefacts: non-destructive investigation of Egyptian and Roman museum treasures

Abstract This paper describes microstructural analyses by X-ray portable diffraction and microdiffraction on intentional patina of the bronze museum objects from antique Egypt and the Roman Empire. They bring evidence of the presence in the true black bronze patinas of metallic gold and/or silver presumably as nanoparticles. Three other Egyptian patinas not belonging to black bronze are characterised. Apparent black patination on a Roman scalpel handle is discussed. The discovery of a new patination procedure on Roman artefacts from the Louvre museum is also related, based on intentional high temperature oxidation to obtain a dark patina on a lead bronze object. A presence of lead carbonate cerussite is an important observation.

Original surface treatment of copper alloy in ancient Roman Empire: chemical patination on a Roman strigil

Abstract Metal polychromy has been widely used for decorating metallic artworks from ancient antiquity. In Hellenistic and Roman periods, the famous Corinthian bronzes (Corinthium aes) are a typical example of the skill of metallurgical craftsmen striving to obtain various coloured surfaces on copper based alloys; but the existing investigations are devoted mainly to the ‘black bronzes’ obtained by oxidation in a wet medium of copper–gold alloys. The present study is part of a general programme devoted to research into different kinds of special surface oxidation treatments on copper alloys and their environmental behaviour. For archaeological objects, such treatments are difficult to observe, as a consequence of corrosion degradation. The examination and analysis of objects kept in the Department of Greek, Etruscan and Roman Antiquities of the Louvre Museum have evidenced the occurrence on one of them, a strigil dated from the first century AD, of a new type of decoration. The strigil is made of copper–zinc alloy, and its decoration exhibits orange-red coloured motifs visibly obtained by chemical oxidation. The present paper describes analyses performed using different techniques: microscopy, particle induced X-ray emission, X-ray diffraction, Rutherford backscattering spectrometry, micro-Raman spectroscopy, spectrophotocolorimetry and optical profilometry. The steps of the decoration process are detailed: the motifs were coloured together with the neighbouring surface. This neighbouring surface was further cleaned by a mechanical process to make the motif coloration appear. The present paper attempts to describe how the Roman craftsman obtained the decorated appearance.

Gilding of cultural heritage artefacts: an elaborated technology

Abstract Gilding has been used to decorate, one may say sublimate, the surface appearance of artworks since the beginning of gold use in art. Gold foils and leaves were used first, thanks to the high ductility of that metal, and the progress of gilding art through centuries has been linked to: (1) the evolution of the thickness of the gold film used for the process; (2) the continuous research for efficient adhesive materials adapted to the various substrates; and (3) the development of techniques of direct adhesion of the gold coating, especially on metals. This paper, based on recent laboratory results obtained through laboratory studies of various museum artworks, discusses these three aspects. First, it shall develop a mechanical modelling of gold leaf beating. Second, it shall detail the properties of the main classes of adhesive materials used for leaf gilding on various materials. Finally, the importance of the diffusion phenomena at the interface between a metal substrate and a gold coating shall be discussed, especially in the case of gilding involving a high temperature treatment.

Organometallic based gold decoration, formation and durability

Abstract The present study proposes a complete characterisation of the liquid gold silver layer on glass, from the application of the initial product, to the final metallic film obtained. The decomposition of organometallic compounds, during the heating, has been followed using different spectroscopic methods (infrared, nuclear magnetic resonance, mass spectrometry, etc.) which were coupled with thermal analyses and microscope observations (SEM, TEM, etc.). In the present paper the steps of the formation of the film will be briefly described, and a special attention is given to the study of the adhesion mechanisms which operates at the interface between the gold film and the glass substrate. Specific adhesion tests have been performed by aging the system in controlled solutions and observing the loss of adhesion after a given immersion duration. In depth concentration profiles obtained by secondary ion mass spectrometry and Rutherford back-scattering spectrometry reveal, during the process, a migration of the precious metals into the substrate. That migration ensures a good adhesion for the film. That ‘diffusion’ of gold into the glass substrate does not follow the classical diffusion laws and does not seem to be the only explanation for the occurrence of a good adhesion between to two partners. The results also suggest an essential role played by flux agents as vanadium, whose interaction with the alkaline modifiers of the bulk glass constitutes a critical factor for the durability of decorations.

Comparative XPS and SIMS depth profile analysis of Cu-implanted silicon: evidence of segregation effects

Abstract Copper concentration profiles in copper-implanted silicon have been analysed comparatively by XPS and SIMS techniques. The results are compared to theoretically computed concentration profiles, obtained by the TRIM procedure. Differences between experimental profiles and computed ones may be explained in terms of ion beam-induced segregation. The effect is strongly dependent on the sputtering rate: a shift and broadening of the concentration peak is induced in the XPS analysis, under relatively slow sputtering.

Grain Boundary Segregation. Grain Boundary Diffusion

In polycrystalline materials, grain boundaries differ from the monocrystalline bulk by : i) their structure, ii) their electronic properties, iii) their chemical composition, iv) the atomic mobility of all the species.