Kitty Baert

The formation and characterisation of ultra-thin films containing Ag nanoparticles

A simple three step method for creating ultra-thin films, which contain Ag nanoparticles, on both glass and stainless steel surfaces, is presented. First, during the immersion into N-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (DIAMO) a monolayer of DIAMO is attached on the sample surface after which immersion in silver nitrate is performed and a complex between the two amino groups of DIAMO and silver ions forms, leading to large clusters on the surface. During the annealing step these silver containing clusters are converted into silver nanoparticles which are homogeneously distributed and bound to the surface. The formation of the film was characterised using UV/Vis, FE-SEM and FE-AES. Additionally, SERS activity of the surface and the effect of the attachment of the nanoparticles on their antibacterial nature were also investigated.

Morphology, Structure and Photoelectrocatalytic Activity of TiO2 / WO3 Coatings Obtained by Pulsed Electrodeposition onto Stainless Steel

A simple two-step pulsed electrodeposition/ electrosynthesis technique is employed for the preparation of a bicomponent photocatalyst, TiO2/WO3, onto metal substrates. TiO2 can be activated under UV light illumination and is well known for its water detoxification capabilities. The coupling between this wide band-gap semiconductor with a suitable narrow band-gap one, WO3, is used for effective separation of the photogenerated charge carriers. Besides the reduced surface recombinetion due to directional charge transfer, the combination with the visible light (Vis)-activated WO3 entails an extended photoactivity towards Vis wavelengths. In addition, the photocatalytic decomposition of organic water pollutants at TiO2/WO3 layers supported on conductive substrates can be further enhanced by applying a positive bias in an appropriate electrochemical cell. Drawing the electrons away from the surface through the external circuit reduces surface recombination rates of photogenerated electron-hole pairs. Recently, bilayer TiO2/WO3 photocatalysts were prepared onto stainless steel substrates by continuous cathodic electrodeposition of WO3 followed by TiO2 electrosynthesis [1, 2]. Their photoelectrocatalytic efficiency is very promising and superior to both their single-component counterparts. Also, there have been indications of the considerable impact of composition, morphology and structure on photoelectrocatalytic activity [3]. This implicates the necessity for appropriate monitoring and design of these factors. By applying a consecutive pulsed electrodeposition/electrosynthesis method for WO3 and TiO2, a favorable modification of the electronic properties at the TiO2-WO3 junction and an increased catalyst surface area has been sought. The morphology, structure and related composition distribution of the pulsed-deposited films onto metal substrates have been characterized by high resolution Field Emission SEM (FE SEM) (Fig. 1), SEMEDS and Raman spectroscopy. The photocurrents at photoanodes with various loadings, structure and morphology have been evaluated in the presence and absence of the model pollutants Na-oxalate and 4chlorophenol under UV and Vis light illumination. Similar to the case of continuous electrodeposition [3], a trend was observed of the impact and the need for optimization of the TiO2/WO3 loading ratio, surface morphology, structure and composition distribution to design high-performance photocatalysts. The performance for bulk photo-decomposition of 4-chlorophenol has been evaluated at photoanodes WO3 and TiO2/WO3 prepared by continuous electrodeposition and compared with that at pulsed-plated TiO2/WO3. Long-term photoelectrolysis at constant potential was applied, using spectrophotometry to monitor the variation of the pollutant concentration.

Optical spectroscopy applied to the analysis of medieval and post-medieval plain flat glass fragments excavated in Belgium

Window glass fragments from four Belgian sites were studied and for a set of eighty-five samples the UV-VIS-NIR transmission spectra were analyzed. This collection contains historical and archaeological finds originating from religious buildings namely the Basilica of Our Lady of Hanswijk in Mechelen (17th-20thc) and the Church of Our Lady in Bruges (16th-20thc) as well as from secular buildings as a private house/Antwerp (18th-1948) and the castle of Middelburg-in-Flanders (1448-17thc). All sites contain material on the hinge point between the medieval and the industrial tradition. The variation in composition of the analyzed samples can be explained by the use of different glassmaking recipes, more specifically the use of different raw materials. The composition of window glass differs essentially in the type of flux, using a potash rich fluxing agent until the post-medieval times and industrial soda from the 19th century onwards. A second difference concerns the iron impurities in the glass. For all fragments a clear compositional classification could be made based on the iron concentration. These conclusions were based on archaeological research and drawn after submitting samples to expensive, complex, time-consuming and destructive chemical analyzing methods. Our study indicates that similar conclusions could be made applying the proposed optical based methodology for plain window glass. As a whole, the obtained results make it possible to cluster the fragments for a particular site based on three different sensing parameters: the UV absorption edge, the color and the presence of characteristic absorption bands. This information helps in identifying trends to date window glass collections and indicating the use of different raw materials, production technologies and/or provenance.

Laser ablation- and plasma etching-based patterning of graphene on silicon-on-insulator waveguides.

We present a new approach to remove monolayer graphene transferred on top of a silicon-on-insulator (SOI) photonic integrated chip. Femtosecond laser ablation is used for the first time to remove graphene from SOI waveguides, whereas oxygen plasma etching through a metal mask is employed to peel off graphene from the grating couplers attached to the waveguides. We show by means of Raman spectroscopy and atomic force microscopy that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method.

The identification of chromophores in ancient glass by the use of UV-VIS-NIR spectroscopy

In this publication optical spectroscopy is considered to be a supplementary technique to study ancient colored glass. It results from a systematic study of the UV-VIS-NIR transmission spectra of intentionally colored glass fragments from various archaeological and historical sites and dated from the Roman period to the 21th century AD. The main goal consists of defining optical sensing parameters for this type of material. The considered colorants are iron, cobalt, manganese, copper and chromium. It is proved that many cases exist where optical spectroscopy can be seen as a straightforward, non-destructive, low-cost and in-situ applicable technique in identifying authentic material or to obtain information about the origin of the material. Possible sensing parameters are defined as the absence/presence of absorption bands characteristic for a specific coloring metal oxide and the spectral position of these bands. These parameters could reveal information about the applied furnace conditions and/or to the composition of the glass matrix. It is shown that the cobalt absorption band situated around 535 nm for soda rich glasses (Roman and industrial times) is shifted towards 526 nm for potash rich glasses (medieval and post-medieval times).

A XANES study of chromophores: the case of black glass

We studied the Fe K-edge X-ray absorption near edge (XANES) spectra of several Roman black glass fragments in order to determine the Fe3+/ΣFe ratio of these materials. The selected archaeological glass samples cover the period 1st–5th century AD in nine different sites of the North Western provinces of the Roman Empire. The fragments belong to two different compositional groups demonstrating a diachronic evolution: early Roman HMG (High Magnesia Glass) and Roman Imperial LMG (Low Magnesia Glass). The first group contains natural Fe levels (below 2 wt% as Fe2O3), while the LMG has concentrations above 5 wt%. This difference is also reflected by Fe3+/ΣFe values. Low iron glass was produced under strongly reducing conditions in order to obtain the black colour, with average Fe3+/ΣFe values ≈ 0.17. LMG glass is somewhat more oxidised (Fe3+/ΣFe ≈ 0.4–0.5). While HMG glass required active control of the furnace environment, LMG was made under ambient atmosphere and its higher oxidation degree is mainly determined by the chemistry of the raw glass.

Evaluation of the Yasuda parameter for the atmospheric plasma deposition of allyl methacrylate

This work studies the influence of the proportional change in discharge power and the monomer feed on the morphology and the chemistry of atmospheric plasma deposited films. Atmospheric plasma coatings of allyl methacrylate were deposited using dielectric barrier discharge plasma under different conditions but always under the same ratio between the discharge power and monomer feed (W/FM). It is shown that a constant W/FM does not necessarily provide the same chemistry and the same morphology for atmospheric pressure plasma. This is explained by the higher discharge power of the plasma resulting in an increase of streamers which alter the distribution of energy among the plasma species. On the surface of the deposited coatings, globular-like features were observed, which are suggested to be formed in the volume of the discharge. The deposition rate is also influenced. providing thicker coatings, when high monomer feed/high power are used. Finally, infrared spectra showed a higher retention of the ester functionality at high power/high monomer feed.

In situ electrochromic efficiency of a nickel oxide thin film: origin of electrochemical process and electrochromic degradation

Electrochromic nickel oxide (NiOx) thin films are one of the most promising anodic colored materials. However, there is lack of accurate description of their electrochemical process and degradation mechanism. In this study, a novel approach involving in situ electrochromic efficiency is proposed to reveal the electrochemical origin of an electrochromic NiOx thin film cycled in a Li+-ion electrolyte. The results indicate that the coloring process of the NiOx thin film refers to the oxidation reactions of Ni2+ to Ni3+ and Ni2+ to Ni4+ (in two forms of Ni3O4 and Ni2O3), and the bleaching process is associated with the reduction reactions of Ni4+ to Ni2+, Ni4+ to Ni3+, and Ni3+ to Ni2+. The irreversible reduction of Ni4+ to Ni3+ plays a dominant role in the activation procedure of NiOx. It is deduced that the Li+-ion trapping in the bleaching process along with the reduction reactions of Ni4+ to Ni3+ and Ni3+ to Ni2+ causes the degradation of the electrochromic properties. This study provides a further insight into the electrochromic mechanism and is conducive to the improvement of the long-term cyclic durability for Li+-based electrochromic NiOx. Moreover, the study significantly establishes a direct connection between an electrochemical process and a variation in the optical absorbance of materials.

Growth mechanisms of spatially separated copper dendrites in pores of a SiO2 template

Abstract n-Si/SiO2(Cu) structures with different morphologies of copper deposits are produced using the template synthesis method. Deposition of Cu nanostructures and their structural features is thoroughly studied, and mechanisms for the formation of compact and dendrite-like deposits in the pores of the SiO2 template on the n-type single-crystal silicon substrate are established. Spatially separated copper dendrites are obtained and used to investigate the efficiency of Raman scattering enhancement using the aqueous solution of the Rhodamine 6G dye.

Using optical spectroscopy to characterize the material of a 16th c. stained glass window

In this paper we studied the transmittance spectra of a collection of several glass samples taken from a 16th century stained window of the Church of Our Lady in Bruges, Belgium. We recorded the optical spectra for all the samples in the region between 350 and 1600 nm. The goal of our research was to reveal information about the composition of the glass artifacts in a fast and non-destructive way. Analysis of the optical spectra allowed us in the first place to identify the type of colorants that were used. It was possible to recognize metal ions, such as Fe2+, Fe3+, Co2+, Mn3+, Cr3+ and Cu2+. Also colors made of metal nanoparticles, such as silver and copper colloids were successfully identified. The recognition of the coloring agents is of particular interest in dating the glass pieces. This is because some colorants were only used in certain periods. Green glass colored by chromium was produced only after the mid 19th century onwards. Our study showed that 3 of the 10 pieces were colored by this element and they originate as such from a later period. A second conclusion refers to the applied fluxing agent. By analyzing the spectral position of the first cobalt absorption band, we were able to classify the glass pieces as potash based (used in medieval times) or soda-based (used in modern times) and therefore to classify them as original or as restoration material. From the 10 blue colored samples, 7 of them were recognized as original material. Finally, for the naturally colored parts the analysis of the spectra allowed us to group them based on cobalt impurities.