Istraživanje silicijevih oksinitridnih filmova bogatih vodikom metodom EPR

We studied hydrogen rich silicon oxynitrides deposited from nitrous oxide and silane gas mixture by a plasma enhanced chemical vapour deposition apparatus on single crystal silicon substrates. Annealing study showed that hydrogen outdiffusion depends on the film composition and is particularly retarded for oxygen content x = 1.4. EPR analysis demonstrated that this film contains the highest concentration of D centres. However, the maximum concentration of charged dangling bond-like centres does not coincide with D centres. Therefore, we conclude that D centres act as hydrogen traps and are responsible for the peculiar hydrogen behaviour observed in the studied films.Istraživali smo silicijeve oksinitridne filmove bogate vodikom, dobivene na monokristalnoj silicijevoj podlozi iz mješavine silana i dušik-(1)-oksida s pomoću uređaja za plazmom stimulirano kemijsko nanošenje iz pare. Proučavanje otpuštanja je pokazalo da izlaženje vodika ovisi o sastavu sloja, a posebice je usporeno pri sadržaju kisika x = 1.4. EPR mjerenja pokazuju da takav sloj sadrži najveću koncentraciju D centara. Zaključuje se da D centri djeluju kao zamke za vodik i uzrokuju neobična svojstva vodika u istraživanim filmovima

Optimization of Copper Stain Removal from Marble through the Formation of Cu(II) Complexes in Agar Gels

Copper complexes with different ligands (ethylenediaminetetraacetic acid, EDTA, ammonium citrate tribasic, TAC, and alanine, ALA) were studied in aqueous solutions and hydrogels with the aim of setting the optimal conditions for copper stain removal from marble by agar gels, with damage minimization. The stoichiometry and stability of copper complexes were monitored by ultraviolet-visible (UV-Vis) spectroscopy and the symmetry of Cu(II) centers in the different gel formulations was studied by electron paramagnetic resonance (EPR) spectroscopy. Cleaning effectiveness in optimized conditions was verified on marble laboratory specimens through color variations and by determining copper on gels by inductively coupled plasma-mass spectrometry (ICP-MS). Two copper complexes with TAC were identified, one having the known stoichiometry 1:1, and the other 1:2, Cu(TAC)2, never observed before. The stability of all the complexes at different pH was observed to increase with pH. At pH 10.0, the gel\u2019s effectiveness in removing copper salts from marble was the highest in the presence of ALA, followed by EDTA, TAC, and pure agar gel. Limited damage to the marble surface was observed when gels with added EDTA and TAC were employed, whereas agar gel with ALA was determined to be the most efficient and safe cleaning material

Change of cobalt magnetic anisotropy and spin polarization with alkanethiolates self-assembled monolayers

International audience; We demonstrate that the deposition of a self-assembled monolayer of alkanethiolates on a 1 nm thick cobalt ultrathin film grown on Au(111) induces a spin reorientation transition from in-plane to out-of-plane magnetization. Using ab initio calculations, we show that a methanethiolate layer changes slightly both the magnetocrystalline and shape anisotropy, both effects almost cancelling each other out for a 1 nm Co film. Finally, the change in hysteresis cycles upon alkanethiolate adsorption could be assigned to a molecular-induced roughening of the Co layer, as shown by STM. In addition, we calculate how a methanethiolate layer modifies the spin density of states of the Co layer and we show that the spin polarization at the Fermi level through the organic layer is reversed as compared to the uncovered Co. These results give new theoretical and experimental insights for the use of thiol-based self-assembled monolayers in spintronic devices

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

Spectroscopic ellipsometry measurements on an anisotropic organic crystal : potassium acid phtalate

Spectroscopic ellipsometry in the range from 300 to 800 nm is applied for the determination of the optical properties of potassium acid phtalate crystals, of particular interest for their use as substrates for the epitaxial deposition of highly oriented polymers. The study is based on the analysis of measurements performed on differently oriented samples at different angles of incidence. Such measurements are used to reduce uncertainty in the analysis

Optical properties of polycrystalline silicon thin films deposited by single-wafer chemical vapor deposition

The ellipsometric study of polycrystalline silicon films deposited using a single wafer rapid thermal chemical vapor deposition reactor under varying conditions of temperature and doping is presented. In particular, using spectroscopic ellipsometry in the visible spectral range, we determined the thickness of the films and the structural changes as a function of the deposition temperature. A different film structure, from amorphous to polycrystalline, has been found for the different deposition temperatures. A shift to lower values of the transition temperature which marks the structural change and a decrease in the deposition rate as the doping level is increased are observed. Moreover, from the ellipsometric results the optical functions of the different samples were evaluated

Oxidation of Crystalline Rubrene Films: Evidence of an Epitaxial Native Oxide Layer

Rubrene (RUB) is a benchmark organic semiconductor since the record exciton diffusion length and high charge carrier mobility are demonstrated in its orthorhombic single-crystal phase. In this respect, great research efforts on the growth and study of crystalline RUB thin films, the most suitable choice for device applications, are made, even though its oxidation remains a still open problem. Here, the oxidation of crystalline RUB thin films is focused, by studying and modeling the so-formed interface between RUB and its oxide. Optical spectroscopy carried out on freshly grown and aged crystalline RUB films gives evidence that oxidation occurs without altering the original crystal structure of the RUB films. To deeply analyze the process, a direct characterization of rubrene endoperoxide (RUBox) is proposed: after synthesizing a microcrystalline powder, its crystal structure and Raman response are determined. The joint results achieved on the RUBox powder and on aged RUB films demonstrate that RUBox forms as a crystalline native oxide layer with a well-defined epitaxial interface with the underlying RUB. Finally, structural constraints at the RUBox/RUB interface are shown to limit surface oxidation, with the oxide acting as a passivation layer against further oxidation