Detecting the nir fingerprint of colors: The characteristic response of modern blue pigments

Reflectance spectroscopy in the ultraviolet (UV), visible (Vis), and near infrared (NIR) range is widely applied to art studies for the characterization of paints and pigments, with the advantages of non-invasive techniques. Isolating and detecting the fingerprint of pigments, especially in the NIR range, is quite challenging, since the presence of vibrational transitions of the most common organic functional groups prevents to relate the optical spectrum of a composite sample, as an artwork is, to each one of its elements (i.e., support, binder, and specific pigment). In this work, a method is presented to obtain the UV-Vis-NIR optical response of the single components of a model composite sample reproducing an artwork, i.e., the support, the binder, and the pigment or dye, by using diffuse reflectance spectroscopy. This allowed us to obtain the NIR spectral fingerprint of blue pigments and to identify specific features possibly applicable for detecting cobalt and phthalocyanine blue colors in artwork analysis

Chemical separation of acrylic color components enabling the identification of the pigment spectroscopic response

Acrylic colors are mixtures of several components that can be identified as pigments, binders, and fillers, so that, when analyzed, the characteristic response of the different components may not be recognizable. This limits the accuracy of spectroscopic techniques, nonetheless particularly useful as they are noninvasive and can be applied in situ on real artworks. Here, a method is proposed to chemically separate and identify the different components of acrylic colors, in order to be able to study their spectroscopic response separately, in particular by ultraviolet visible near infrared diffuse reflectance. The results clearly show that the chemical and analytical method developed here is fully reliable, with the advantage of clearly separating the response of the different components without any change of their chromatic chemical properties. As a case study, the new method is applied here to original acrylic colors used by the Italian artist Ico Parisi, in view of building a spectra databas

Stratigraphic analysis of intercalated graphite electrodes in aqueous inorganic acid solutions

A detailed stratigraphic investigation of the intercalation mechanism when graphite electrodes are immersed inside diluted perchloric HClO4 and sulfuric H2SO4 electrolytes is obtained by comparing results when graphite crystals are simply immersed in the same acid solutions. By combining time of flight secondary ion mass spectrometry ToF SIMS and in situ atomic force microscopy AFM , we provide a picture of the chemical species involved in the intercalation reaction. The depth intensity profile of the ion signals along the electrode crystal clearly shows a more complex mechanism for the intercalation process, where the local morphology of the basal plane plays a crucial role. Solvated anions are mostly located within the first tens of nanometers of graphite, but electrolytes also diffuse inside the buried layers for hundreds of nanometers, the latter process is also aided by the presence of mesoscopic crystal defects. Residual material from the electrolyte solution was found localized in well defined circular spots, which represent preferential interaction areas. Interestingly, blister like micro structures similar to those observed on the highly oriented pyrolytic graphite HOPG surface were found in the buried layers, confirming the equivalence of the chemical condition on the graphite surface and in the underneath layer

Uniaxial Alignment of a Monolayer of Flat-on Free-Base Porphyrins on an Exfoliable Insulating Substrate

Porphyrins are an extremely valuable class of molecules engaged in a variety of roles spanning from biology to optoelectronics. Manipulation of the chemical and physical properties of the inner cavity of porphyrins has been recognized as crucial for the exploitation of these systems in organic devices, particularly when porphyrins self-organize at the interface with a flat-on orientation of the macrocycle. Such an orientation has been mostly observed on metallic surfaces. Unfortunately, the physical-chemical properties of the molecules result in being largely perturbed due to the molecule-metal interaction. In addition, conducting substrates are unsuited to exploit electrically driven devices based on organic layers. To overcome these issues, we performed a topology-based analysis of insulating organic single crystal structures to identify a surface which (i) ensures easy exfoliation through mechanical methods, (ii) ensures epitaxial match with an overlayer of close-packed flat-on porphyrin molecules, and (iii) displays chirality. The outcome of this work is represented by a unique crystal of mixed 2,5-diketopiperazine and fumaric acid in a 1:1 ratio. We demonstrate that the (110) surface of this crystal fulfills the aforementioned requirements and, thanks to its peculiar subnanometric corrugations, allows one to grow uniaxially aligned monolayers of flat-on porphyrin molecules assembled through van der Waals interactions

Contact potential and scanning Kelvin force microscopy measurements on sulphate-anion intercalated graphite

In the current interpretative model of graphite anion intercalation, the characteristic blisters, formed after the incipient surface oxidation, have the same structural behaviour of pristine graphite. However, this result is deduced from scanning tunneling microscopy data, which cannot give a chemical finger- print of the electrode surface. Conversely, the contact potential difference between a reference tip and a sample depends on the chemical as well as on the structural conditions of the surface. As a consequence, in this paper, we combine a contact potential measurement with a scanning Kelvin force microscopy analysis, in order to extract information on electronic changes occurring to the electrode with a sub- micrometre investigation of the surface morphology after the incipient graphite oxidation process in diluted sulphuric acid. The results suggest that, as well as the structural properties, no significant electronic differences occur between blisters and the graphite basal plane after the intercalation process