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We demonstrate that the deposition of methylammonium lead iodide (MAPbI3) on native nominally undoped (100) GaAs substrates generates an enhancement in the GaAs photoluminescence (PL) intensity by more than 3 orders of magnitude. We attribute this pronounced PL enhancement to some very efficient MAPbI3-induced passivation schemes of the GaAs surface. Time-resolved PL experiments reveal greatly enhanced carrier lifetimes next to the GaAs surface, in agreement with a passivation process. X-ray photoelectron spectroscopy measurements on ultrathin MAPbI3/GaAs and PbI2/GaAs samples suggest some Pb-related deoxygenation of the GaAs surface, as an atomistic mechanism possibly related to the passivation effect. Notably, the whole process is fully reversible, as it suffices to immerse the MAPbI3/GaAs sample in salt water and the MAPbI3layer is completely removed, while the PL intensity and spectral features of the GaAs substrate return to their pristine condition.

Grazing Incidence X-ray Diffraction (GIXD) is a widely used characterization technique, applied for the investigation of the structure of thin films. As far as organic films are concerned, the confinement of the film to the substrate results in anisotropic 2-dimensional GIXD patterns, such those observed for polythiophene-based films, which are used as active layers in photovoltaic applications. Potential malfunctions of the detectors utilized may distort the quality of the acquired images, affecting thus the analysis process and the structural information derived. Motivated by the success of Morphological Component Analysis (MCA) in image processing, we tackle in this study the problem of recovering the missing information in GIXD images due to potential detector’s malfunction. First, we show that the geometrical structures which are present in the GIXD images can be represented sparsely by means of a combination of over-complete transforms, namely, the curvelet and the undecimated wavelet transform, resulting in a simple and compact description of their inherent information content. Then, the missing information is recovered by applying MCA in an inpainting framework, by exploiting the sparse representation of GIXD data in these two over-complete transform domains. The experimental evaluation shows that the proposed approach is highly efficient in recovering the missing information in the form of either randomly burned pixels, or whole burned rows, even at the order of 50% of the total number of pixels. Thus, our approach can be applied for healing any potential problems related to detector performance during acquisition, which is of high importance in synchrotron-based experiments, since the beamtime allocated to users is extremely limited and any technical malfunction could be detrimental for the course of the experimental project. Moreover, the non-necessity of long acquisition times or repeating measurements, which stems from our results adds extra value to the proposed approach.

A detailed study of Spectroscopic Ellipsometry (SE) spectra of uniaxially stressed, 12μm thick poly(ethylene terephthalate) (PET) membranes were realized in both IR (900‐3500 cm−1) and Vis‐FUV (1.5 to 6.5 eV) spectral regions and in various orientation angles ∅︁between the plane of incidence and the machine direction (MD) of the PET membranes. In the IR spectra, the three main modes of the ester group at ∼1126, 1256 and 1721 cm−1are observed. The first two of these peaks show identical polarization dependence, with preferential orientation ∅︁≈0° (i.e. the plane of reflection parallel to the MD), while the peak at ∼1721 cm−1is excited in the perpendicular direction, ∅︁≈90°. In the Vis‐FUV SE spectra, the dependence of the characteristic electronic absorption bands on the orientation angle ∅︁is studied. Besides the well known benzene band centered at ∼5 eV, a doublet of less intense peaks appear just above the absorption edge between 4.1 and 4.3 eV with the most striking characteristic that they show polarization selection rules opposing to that of the benzene band. The above characteristics of the electronic Vis‐FUV spectra of PET are discussed in a manner comparative to the corresponding IR spectra. The discussion becomes in the context of determining the molecular orientation of PET using a non‐destructive technique such as SE.

The use of Resonant Soft X-rays Scattering (RSOXS) for the investigation of block copolymer micelles within a thin homopolymer film is demonstrated in this work. Thin films of polystyrene-block-polyisoprene, PS-b-PI, copolymer within a high molecular weight polystyrene, PS, matrix were coated onto Si3N4 substrates. The formation of copolymer micelles with a polyisoprene core and a polystyrene corona was verified by the RSOXS measurements. The thin film samples are difficult to study with hard x-rays or neutrons, and well-suited to the RSOXS approach having stronger cross-sections. The core radius of the PS-b-PI micelles was estimated from the experimental data and was found to be in good agreement with measurements in the bulk and with that theoretically predicted. Increasing copolymer concentration resulted in an increase in the number density of micelles in the films; however, no ordering of the confined micelles was observed, even at high copolymer concentrations, possibly because of the segregation of significant fraction of the PS-b-PI copolymer chains to the air/polymer and polymer/substrate interfaces. In order to overcome this problem polystyrene-block-poly(methyl methacrylate), PS-b-PMMA, was utilized. A PS-b-PMMA/PS film of high copolymer concentration was spin-coated on a pre-treated Si3N4 substrate and RSOXS revealed the formation of dense micelle assemblies within the PS matrix.