Selected Area X-ray Photoelectron Spectroscopy Research Articles

Selective atomic layer deposition on flexible polymeric substrates employing a polyimide adhesive as a physical mask

The rise of low-temperature atomic layer deposition (ALD) has made it very attractive to produce high-κ dielectric for flexible electronic devices. Similarly, selective deposition of ALD films is of great relevance for circuitry. We demonstrated a simple method of using a physical mask to block the film’s growth in selected polymeric and flexible substrate areas during a low-pressure ALD process. A low-cost silicone adhesive polyimide tape was used to manually mask selected areas of bare substrates and aluminum strips deposited by evaporation. 190 cycles of aluminum oxide (Al2O3) and hafnium oxide (HfO2) were deposited at temperatures ranging from 100 to 250 °C. Using x-ray photoelectron spectroscopy (XPS) analysis and energy dispersive x-ray spectroscopy (EDS), we showed that the mask was effective in protecting the areas under the tape. The mask did not show any modification of shape for an exposure of 10 h at 250 °C, hence keeping the form of the masked area intact. An analysis of the unmasked area by ellipsometry (632.8 nm) and x ray shows a regular film with a thickness variation under 2 nm for a given temperature and constant refractive index. EDS, selected-area XPS, and imaging XPS show an evident change of elemental content at the interface of two areas. By XPS, we established that the structure of the films was not affected by the mask, the films were stoichiometric, and there was no effect of outgassing from the adhesive film.

Ancient Mercury-Based Plating Methods: Combined Use of Surface Analytical Techniques for the Study of Manufacturing Process and Degradation Phenomena

Fire gilding and silvering are age-old mercury-based processes used to coat thesurface of less precious substrates with thin layers of gold or silver. In ancient times, these methods were used to produce and decorate different types of artefacts, such as jewels, statues, amulets, and commonly-used objects. Gilders performed these processes not only to decorate objects but also to simulate the appearance of gold or silver, sometimes fraudulently. From a technological point of view, the aim of these workmen over 2000 years ago was to make the precious metal coatings as thin and adherent as possible. This was in order to save expensive metals and to improve the resistance to the wear caused by continued use and circulation. Without knowledge about the chemical-physical processes, the ancient crafts-men systematically manipulated these metals to create functional and decorative artistic objects. The mercury-based methods were also fraudulently used in ancient times to produce objects such as jewels and coins that looked like they were made of silver or gold but actually had a less precious core. These coins were minted by counterfeiters but also by the official issuing authorities. The latter was probably because of a lack of precious metals, reflecting periods of severe economic conditions. In this Account, we discuss some representative cases of gold- and silver-coatedobjects, focusing on unique and valuable Roman and Dark Ages period works of art, such as the St. Ambrogio's altar (825 AD), and commonly used objects. We carried out the investigations using surface analytical methods, such as selected area X-ray photoelectron spectroscopy and scanning electron microscopy combined with energy-dispersive spectroscopy. We used these methods to investigate the surface and subsurface chemical features of these important examples of art and technology, interpreting some aspects of the manufacturing methods and of disclosing degradation agents and mechanisms. These findings may contribute to cultural heritage preservation, thus extending the applicability of the surface analytical techniques.

Ancient silver extraction in the Montevecchio mine basin (Sardinia, Italy): micro-chemical study of pyrometallurgical materials

Different pyrometallurgical materials such as slags, refractory materials and thermally treated lead ores likely related to smelting and extractive processes and chronologically related to Punic and Roman periods (IV–III BC) have been found at Bocche di Sciria and Conca e Mosu in the Montevecchio mine basin (south western Sardinia, Italy), where archaeological findings and classical authors locate extractive metallurgy activities since pre-Roman times. By means of the combined use of X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS), selected-area X-ray photoelectron spectroscopy (XPS) and optical microscopy (OM), micro-chemical and micro-structural investigations have been carried out in order to identify the nature of the pyrometallurgical materials, to decipher the processes carried out there and their technological steps and to determine the technological level of competence reached by the ancient metallurgists. The results confirm that the findings can be associated with smelting and extractive processes carried out close to the metal ore deposits first for the argentiferous lead production and, then, for the silver recovery via a cupellation process. Finally, the results disclose the high level of technological competence of the ancient metallurgists able to carry out complex high-temperature processes to treat the argentiferous lead ores and to recover low amounts of silver via high-temperature lead-selective oxidation.

Archaeo-metallurgical studies of tuyeres and smelting slags found at Tharros (north-western Sardinia, Italy)

A large number of pyrometallurgical materials such as tuyeres, slags and refractory tools likely associated with metal extraction processes have been found at Tharros (north-western Sardinia, Italy) during archaeological excavations stratigraphically related to the Phoenician–Punic period (VI–III centuries BC). Micro-chemical, micro-structural and mineralogical studies have been carried out by means of the combined use of X-ray diffraction (XRD), selected-area X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) combined with energy-dispersive X-ray analysis (EDS) in order to identify pyrometallurgical processes and main relevant technological parameters. The results reveal that tuyeres, slags and refractory tools can be associated with an iron ore smelting process to extract the metal by slagging the unwanted by-products. Moreover, temperature and duration of the smelting process have been estimated through mineralogical studies and by a comparative analysis between the micro-chemical and structural features of thermally treated refractory materials and tuyeres. The results disclose the high level of technological competence of the ancient metallurgists able to carry out complex high-temperature processes to extract iron from ores by separating the metal from unwanted siliceous species.

Combined use of surface and micro-analytical techniques for the study of ancient coins

By means of the combined use of surface and micro-analytical techniques the surface chemical composition of ancient coins and some aspects of their manufacturing techniques and of degradation mechanisms have been elucidated. Two case histories are described concerning silver Roman Republican coins and some coins plated with thin films of silver and gold. In particular, the coinage methods, the silvering and gilding techniques and the origin of the embrittlement of these selected Roman coins have been studied by means of the combined use of selected-area X-ray photoelectron spectroscopy (SA-XPS) and scanning electron microscopy and energy-dispersive spectrometry (SEM+EDS). This innovative approach has been utilised in order to gain further insight into the microchemical structure of the external regions of the coins as well as of the bulk features. The results show the use of mercury to coat a copper or silver core with a thin film of precious metals that could be considered the most important advance in the technology of gilding to be made in antiquity. Furthermore, the microchemical investigation of brittle Roman silver coins has allowed us to identify the origin of this troublesome problem. The microchemical results indicate that brittleness is induced by the presence of a low amount of lead that is retained in supersaturated solution when the cast blank was produced. This latter element segregates at the grain boundaries during the coin production and the subsequent long-term ageing at room temperature, thus inducing the alloy fracturing along the weakened grain boundaries.

Microchemical and micromorphological features of gunshot residue observed by combined use of AFM, SA-XPS and SEM + EDS

Microchemical and micromorphological analytical methods have been used by law enforcement agencies to ascertain whether or not an individual has been involved recently in a firearm shooting by determining the presence of gunshot residue (GSR). In the present work, the microchemical and micromorphological features of the GSR particles deposited on the bullet and on the firing hands, collected using double-sided tape, have been studied by means of the combined use of scanning electron microscopy + energy-dispersive spectroscopy (SEM + EDS), atomic force microscopy (AFM) and selected-area x-ray photoelectron spectroscopy (SA-XPS). The results indicate that this advanced approach could disclose new micromorphological and microchemical features that could be useful for considerably increasing the confidence level of such determination. Copyright © 2002 John Wiley & Sons, Ltd.

Surface study of thin film gas sensors on a Si micro-machined substrate

The miniaturisation of gas sensors and the compatibility of their fabrication process with modern microelectronics technology are very important aspects of gas-sensing development. The reduction of power consumption could minimise not only thermal stresses and device degradation, but also enable to use battery operated sensors and smart sensor arrays.In the present work, variously surface-activated films of tin oxide deposited on a Si micro-machined substrate, which contained a Si3N4 membrane supporting the entire gas-sensing structure, have been investigated. Due to the very small thermal mass of the membrane, these devices can be operated in fast-pulsed temperature powering regime. The results of the measurements of gas sensitivity to aromatic hydrocarbons in fast-pulsed mode are presented and discussed. The gas sensitivity and device reliability are analysed on the basis of these results and the data of surface analysis of the sensors.The surface analysis of the samples has been carried out by using selected-area X-ray photoelectron spectroscopy (SA-XPS), SA-XPS depth profiling with cyclic Ar+ ion sputtering, scanning Auger microscopy (SAM) and scanning tunnelling microscopy (STM). These analytical techniques enable us to investigate the microchemical composition and morphology of the gas-sensing layers, both before and after the gas detecting cycles in real working conditions.

Microchemical study of the black gloss on red‐ and black‐figured Attic vases

The microchemistry of the black gloss decoration layer on black- and red-figured Attic vases (6th to 4th century BC) has been studied by means of selected-area x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS). The results show that the Attic black gloss is obtained from an illitic clay, enriched in iron oxide particles, that is applied on the vase body and fired in an oxidizing–reducing–oxidizing cycle at a top temperature of ∼950 °C. Furthermore, the results disclose the presence in the black gloss of iron grains with a complex structure, constituted by discrete areas of single phases with Fe3+, Fe2+ and Fe0. These particles are finely dispersed in a vitreous Al–K- and Fe-enriched silicate where also Fe–C and C–C carbon atoms are present. The information about the raw materials and the firing process shows that the production of Attic vases is important for the history of the art as well as of the ceramic technology. Copyright © 2000 John Wiley & Sons, Ltd.

The characterisation of iron-containing intermetallic phases within industrially cast aluminium

57Fe conversion electron Mossbauer spectroscopy has been used to investigate the intermetallic phases near the surface of a D.C. cast aluminium ingot. The CEMS data is used with SAAES (selected area Auger electron spectroscopy) and SAXPS (selected area X-ray photoelectron spectroscopy) data to propose a model of the surface region above the grain boundaries.

Microchemical study of the black gloss on red- and black-figured Attic vases

The microchemistry of the black gloss decoration layer on black- and red-figured Attic vases (6th to 4th century BC) has been studied by means of selected-area x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS). The results show that the Attic black gloss is obtained from an illitic clay, enriched in iron oxide particles, that is applied on the vase body and fired in an oxidizing–reducing–oxidizing cycle at a top temperature of ∼950 °C. Furthermore, the results disclose the presence in the black gloss of iron grains with a complex structure, constituted by discrete areas of single phases with Fe3+, Fe2+ and Fe0. These particles are finely dispersed in a vitreous Al–K- and Fe-enriched silicate where also Fe–C and C–C carbon atoms are present. The information about the raw materials and the firing process shows that the production of Attic vases is important for the history of the art as well as of the ceramic technology. Copyright © 2000 John Wiley & Sons, Ltd.

Role of the substrate deoxidation process in the growth of strained InAs/InP heterostructures

We have investigated the role of the arsenic flux used during the substrate deoxidation process in the MBE (molecular beam epitaxy) growth of strained InAs/InP heterostructures. Two different experiments were performed: (i) thermal cleaning of the InP wafer under an As flux at different exposure times and (ii) the growth of very thin InAs layers (3–9 ML). The samples grown were characterized by Raman spectroscopy and selected area X-ray photoelectron spectroscopy. The results obtained demonstrated the formation of an InAs x P 1− x sublayer at the interface of the InAs/InP system. The annealing of InP under an As flux promotes not only As → P substitution on the surface, but also the subsequent diffusion of As atoms into the deeper subsurface region of InP.

Depth profiling of InAs/InP and [formula omitted] heterostructures grown by molecular beam epitaxy

Highly strained InAs/InP heterostructures and In x Ga 1−x As/InAs single quantum wells on InP(100) substrates were grown by molecular beam epitaxy. The fabricated heterostructures were investigated by means of the selected-area X-ray photoelectron spectroscopy (SAXPS) depth profiling technique. The depth resolution of the SAXPS profiling was found to be limited mainly by the photoelectron information depth. It was demonstrated that the ternary compound InAs x P x is formed on the InP substrate during its deoxidation under an arsenic flux. The thickness of the InAs x P 1−x interfacial sublayer was determined and the segregation of indium on the sample and substrate surfaces was revealed from the SAXPS profiles.

Characterization study of CdS passivation layers on [formula omitted

Hg x Cd 1−x Te epitaxial samples were passivated using an anodic non-aqueous sulphidation technique. The chemical composition and thickness of the CdS thin films deposited were investigated by selected-area X-ray photoelectron spectroscopy combined with Ar + ion sputtering. The CdS films formed on Hg x Cd 1−x Te were found to be nearly stoichiometric; their thickness varied with the sulphidation temperature and time. The lateral non-homogeneity of the CdS passivation layers was studied by means of scanning Auger microscopy. The chemical composition and origin of the “holes” observed in the CdS films deposited were revealed by the Auger chemical images obtained.

Characterization study of strained InxGa1−xAs/GaAs superlattices

InxGa1−xAs/GaAs strained layer superlattices were studied by means of double-crystal x-ray diffractometry (DCXD), transmission electron microscopy (TEM), and selected area x-ray photoelectron spectroscopy (SAXPS) depth profiling techniques. The quality of superlattices, strain in the sublayers, and their thickness and chemical composition were evaluated. The effect of the real superlattice structure on the shape of x-ray rocking curves has been revealed. It was concluded that full identification of nonperiodic defects and the initial stage of stress relaxation can be determined by combining DCXD and TEM methods. The results of SAXPS depth profiling were found to be in good quantitative agreement with DCXD and TEM data. The linear dependence of depth resolution Δz on the sputtering depth, caused by sputtering induced development of heterointerface roughness was determined in SAXPS profiles.