Micro-Raman spectroscopy of nanomaterials : applications in Archaeology

“Nanomaterials” is a generic term used to describe nano-sized crystals and bulk homogenous materials with a structural disorder at the nanoscale. Ancient (and modern) ceramics and glasses derive some of their properties (eg. pliability and low sintering temperature) from the fact that their raw material namely natural clay is nanosized. Furthermore the pigments used to colour ceramics and glasses need to have particle sizes <500 nm for the object to appear homogenously coloured to the human eye. Raman spectroscopy intrinsically probes chemical bonds and is therefore one of the few techniques that has been proven useful to provide information at the nanoscale. It is an excellent tool to study ceramics and glasses as a Raman spectrum can be used to identify phases, analyse amorphous domains in the silicate network and identify pigments on a nano-scale. The characteristics of a glass, ceramic or ceramic glaze derived through its Raman spectrum can then be linked to the technology used to produce an artefact and in this way provide information about its relative age and provenance. Likewise, the identification of pigments and binders in San rock art might provide information about production techniques and assist in the developement of conservation procedures. In this thesis micro-Raman spectroscopy (with X-ray fluorescence, X-ray powder diffraction, electronmicroscopy and photoluminescence as supportive techniques) was utilised to study archaeological artefacts from the Mapungubwe Collection and San rock art. It was possible to re-date celadon shards excavated on Mapungubwe hill in 1934 to the Yuan or even later Ming dynasty in stead of its original classification as Song. A profile of the glass technology used to produce the Mapungubwe oblates, small trade beads from the “royal burials” on Mapungubwe hill was determined and quite a few unique characteristics of the beads may eventually help to establish their provenance. The possible influence of the presence of rock hyraces at rock art sites on the deterioration of rock art were investigated and during the study very rare polymorphs of CaCO3 (vaterite and monohydrocalcite) were discovered in rock hyrax urine. This study was extended to analyse a San rock art fragment and another first was the identification of animal fat on the fragment, but the exact origin of the fat has to be verified by similar experiments.Thesis (PhD)--University of Pretoria, 2009.Physicsunrestricte

Raman classification of the glass beads excavated on Mapungubwe Hill and K2, two archaeological sites in South Africa

About 200 coloured glass beads (red, yellow, green, blue, white, black, pink, plum) excavated on Mapungubwe hill and at K2, archaeological sites in the Limpopo valley South Africa, were studied with Raman scattering. This is also the most southern site in Africa where evidence for glass reworking has been found. The glass matrix of the beads was classified according to its Raman signature into three main subgroups and corroded glass could also be identified. At least seven different chromophores or pigments (lazurite, lead tin yellow type II, Ca/Pb arsenate, chromate, calcium antimonate, Fe–S ‘amber’ and a spinel) were identified. Many of the pigments were manufactured after the 13th century, confirming the presence of modern beads in the archaeological record. This calls for further research to find a way to reconcile the carbon dating of the hill, which currently gives the last occupation date on the hill as 1290 AD with the physical evidence of the modern beads excavated on the hill. The results are discussed in terms of the glass production origin of the beads (Europe, Mediterranean area, India, China).http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1097-4555hb2013ai201

Infrared reflectance spectroscopy as an analytical technique for the study of residues on stone tools : potential and challenges

FTIR (Fourier transform infrared) spectroscopy is a non-destructive analytical method that has been used successfully to analyse both inorganic and organic archaeological material. Using a microscope attachment has the additional benefit of analysing very small spots (diameter 100 mm) directly on an artefact without sample preparation or destruction. It is therefore a suitable method to study residues on prehistoric stone tools. However, using a microscope without an ATR (attenuated total reflection) microscope objective, results in a combination of reflection and transmission/absorbance FTIR spectra, which is not always as easy to interpret as directly measured transmission/absorbance spectra. In order to improve the interpretation of spectra recorded on archaeological samples, the method was tested with replicated Middle Stone Age stone points used during hunting and butchery experiments on parts of a blue wildebeest (Connochaetes taurinus) published in 2004 (Lombard et al., 2004). In this case, the residues on the tools were known and post-depositional contamination was eliminated. Additional samples of the organic materials, and the minerals from which the tools were made were also available. Therefore, we could assess the viability of FTIR reflectance spectra for distinguishing between bone, fat and protein residues.NRF, the Universities of Pretoria, the Witwatersrand and Johannesburghttp://www.elsevier.com/locate/jashb2014ai201

Phase evolution of vanadium oxides obtained through temperature programmed calcinations of ammonium vanadate in hydrogen atmosphere and their humidity sensing properties

The possibility of obtaining vanadium dioxide (VO2) [wherein the vanadium ionic state is 4þ] from a precursor of ammonium metavanadate (NH4VO3) bearing the ion V5þ is investigated. The reduction is carried out by calcining the NH4VO3 powders in similar concentrations of H2 flow at varying temperatures. The resulting powders have been studied by several techniques including XRD, Raman spectroscopy, FTIR, TEM, BET and DSC. It is found that remnants of bright yellow V5þ still exist up to calcination temperatures of 100 C after which the sky-blue VO2 dominates at calcination temperatures of 150 C e250 C. There is a population surge of metastable dark-blue V6O13 (where V is in between V4þ and V5þ ionic states) between 250 C and 300 C. However above 350 C the material reverts to the stable V5þ in the yellow-orange V2O5. XPS/EDS and VSM confirm the order of appearance to be VO2(150 C) / V6O13(200 C) / V2O5 (350 C).India-Brazil-South Africa trilateral cooperation under the National Research Foundation (NRF) grant number HGER24X.http://www.elsevier.com/locate/matchemphyshb201

Towards refining the classification of glass trade beads imported into Southern Africa from the 8th to the 16th century AD

Tracing the origin of glass trade beads excavated at archaeological sites can contribute significantly to dating a site and reconstructing prehistoric trade routes. Wood developed a temporally sensitive bead sequence dating from the 8th to the 16th century AD for beads excavated at southern African sites that is commonly used by archaeologists to classify beads according to their morphology. In this study we develop a multidisciplinary methodology to refine the classification of glass beads based on morphology alone. Glass trade beads excavated at 11 sites along the upper reaches of the Limpopo River in east-central Botswana are used as case study. The beads were visually classified according to their morphological properties (colour, size, etc.) and analysed with Raman spectroscopy and portable X-ray fluorescence (XRF). Energy Dispersive Spectroscopy (EDS) of one bead showed that two types of glass were sintered together to form a recycled product, explaining the divergence of Raman spectra recorded on different zones. The study confirms the value of a morphological classification based on existing data sets as a first approach, but demonstrates that both Raman and XRF measurements can contribute to a more exact classification of glass beads imported into southern Africa from the East before the 17th century AD.Farahnaz Koleini and Linda C. Prinsloo acknowledge the financial contribution from the National Research Foundation (NRF) of South Africa and Philippe Colomban from EGIDE PROTEA.http://www.journals.elsevier.com//journal-of-cultural-heritage2017-05-31hb2016Anthropology and ArchaeologyPhysic

Raman spectroscopic investigation of radiation damage in carbon implanted diamond

Analog and digital structures can be written into thin surface layers of semiconductors by using focused ion beams of submicron dimensions. By inducing the phase transition from the crystalline (c) to the amorphous state (a) optical contrast is generated between areas of different exposure. The aim of this study was to investigate the properties of diamond as a high-density optical recording medium and to determine the corresponding irradiation parameters. To this end, single crystals of diamond were irradiated with self-ions of 75 key energy with fluences between F=0.3-l0xlO15 C/cm2 at about 100 K. The radiation damage, persisting after annealing treatments between 300-1700 K, was studied by Raman measurements, monitoring changes in the atomic bonding arrangements. Since the scattering cross-section of C sp2 bonds is 50x that of C sp3 bonds, this is an extremely sensitive technique in detecting changes in the initially purely sp3 state. The position and linewidth of the characteristic first-order phonon of crystalline diamond at 1332 cm-l reflect crystallinity and stress level, while bands between 1350-1700 cm-l indicate disorder. In utilizing the microscopic resolution of a Raman facility additional information was obtained on the spatial variation of the damage level. The optimum annealing temperature was found to be 1500 K. For F > 3xlO15C/cm2, the damage was irreversible, for F = 3xlO15C/cm2 the damage was only partly repaired after annealing at 1500 K and, for F < 3xlO15C/ cm2, the crystalline/amorphous contrast was reversible. For F < lxl015C/ cm2 Raman spectroscopy was not sensitive enough to detect the incurred damage. Infrared spectroscopy was used to classify the diamond samples according to type.Dissertation (MSc (Chemistry))--University of Pretoria, 2006.Chemistryunrestricte

A Raman spectroscopic study of the Mapungubwe oblates: glass trade beads excavated at an Iron Age archaeological site in South Africa

Oblate seed beads excavated on Mapungubwe hill, an Iron Age site in South Africa, were analyzed using raman microscopy and supportive techniques to determine the glass technology and pigments used to produce the beads. Corrosion of the black beads was also investigated and an organic phase detected on the beads, which might influence the corrosion process. This detailed profile of the glass technology used to produce the Mapungubwe oblates might eventually help to determine their provenance.National Research Foundation Laboratoire Dynamique, Interactions et Reactivite (Ladir) CNRS- Universite Pierre et Marie Curie Francewww.interscience.wiley.co

Hyraceum, the fossilized metabolic product of rock hyraxes (Procavia capensis), shows GABA-benzodiazepine receptor affinity

Hyraceum, an accretion of urine and dung of rock hyraxes (also known as rock dassies), when fossilized with age, has been used in South Africa for the traditional treatment of epilepsy.We report on tests of 14 hyraceum samples, collected at various geographical locations in South Africa, and assayed for GABA-benzodiazepine receptor affinity. Ethanolic extracts of four of the hyraceum samples assayed positive, whereas all aqueous extracts were inactive. Qualitative TLC resolution of the ethanolic extracts shows a complex mixture of constituents, with no feature being a distinguishing pattern for all four active samples. These preliminary results are not in conflict with the traditional use of hyraceum as a treatment for epilepsy by the settlers of Gamkaskloof

Unusual coloration in scarabaeid beetles

In this paper we investigate the reflection of circularly polarized light from the exocuticle of the scarabaeid beetle Gymnopleurus virens. Reflection spectra are deeply modulated, exhibiting a number of relatively narrow well-defined peaks, which differ from previously studied specimens. By comparing model calculations and electron microscopy work with the recorded spectra, we can propose the presence of specific structural defects responsible for the unusual spectra

Re-dating of Chinese celadon sherds excavated on Mapungubwe Hill, a 13th Century Iron Age site in South Africa, using Raman spectroscopy, XRF and XRD

Chinese celadon shards of the Longquan type, believed to date from the Southern Song dynasty (1127-1279 AD), were excavated in 1934 on Mapungubwe Hill, a 13th century Iron Age site in the Limpopo valley, South Africa. We studied the shards with Raman spectroscopy, X-ray fluorescence spectroscopy (XRF) and X-ray diffractometry (XRD). The Raman polymerization index (Ip), calculated from the spectra of the glaze of the shards, indicated a higher firing temperature than expected for the relatively calcium rich Longquan glazes of the Southern Song dynasty. XRF analysis of the glaze and XRD measurements of the bulk of the shards supported this view and dates the shards to possibly the Yuan (1279-1368 AD) or even early Ming (1368-1644 AD) dynasties. These results have an impact on the chronology of the history of the region and therefore call for further research of a comparative nature of other Chinese celadon shards excavated on archaeological sites in Africa, as well as additional carbon dates of Mapungubwe hill.www.interscience.wiley.co