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A novel and enhanced electrosynthesis protocol that allows the deposition of thin films of Co/Al and Co/Fe layered double hydroxides (LDHs) on different supports is hereby proposed. The approach is based on potentiodynamic cathodic reduction. All the films have been characterised by cyclic voltammetry, powder X-ray diffraction, scanning electron microscopy, and Raman and atomic emission spectroscopies. Moreover, LDHs electrosynthesised on carbonaceous materials have also been investigated by X-ray absorption spectroscopy to analyse their local metal structure. These substrates are particularly interesting for the plethora of LDH applications ranging from energy storage, sensing, and electrocatalysis, and are also of industrial importance, due to their low cost, ecocompatibility, and easy handling. In particular, the material was exploited for 5-(hydroxymethyl)furfural (HMF) electro-oxidation.

Films of the chemical precursor (t)Boc-quinacridone obtained by the spin-coating and bar-assisted meniscus shearing methods were subjected to thermal deprotection to recover the organic semiconductor quinacridone in its crystalline form. We found that the final crystal structure of the semiconductor on the Si/SiO2 substrate is in fact determined by the chemical precursor starting structure, which is in turn induced by the deposition method. Indeed, the samples prepared by spin coating display the precursor structure known from the literature, which transforms into the beta-quinacridone phase. The shearing technique instead yields highly homogeneous films composed of a novel (t)Boc-quinacridone polymorph, which acts as a trigger for the subsequent formation of a pure, well oriented alpha-quinacridone phase. Although this crystalline form is the least stable of the many quinacridone polymorphs, here it turns out to be selectively induced and stabilized. Finally, the organic field effect transistor charge mobility of the alpha-quinacridone films was measured., T. S. acknowledges the H2020-MSCA-COFUND-2014 Programme (P-SPHERE, Grant agreement 665919). This work was supported by the MIUR-PRIN project “From natural to artificial light-harvesting systems: unveiling fundamental processes towards a bio-inspired materials design” (HARVEST) protocol 201795SBA3. This work was funded by DGI (Spain) with the project GENESIS PID2019-111682RB-I00, the Generalitat de Catalunya (2017-SGR-918), and the Spanish Ministry of Economy and Competitiveness, through the “Severo Ochoa” Programme for Centers of Excellence in R&D (FUNFUTURE CEX2019-000917-S). The authors thank Dr Raphael Pfattner (ICMAB-CSIC) for fruitful discussions.

A method for structure solution in thin films that combines grazing incidence X-ray diffraction data analysis and crystal structure prediction was presented in a recent work (Braun et al. Cryst. Growth Des.2019, DOI: 10.1021/acs.cgd.9b00857). Applied to phenytoin form II, which is only detected in films, the approach gave a very reasonable, but not fully confirmed, candidate structure with Z = 4 and Z′ = 2. In the present work, we demonstrate how, by calculating and measuring the crystal Raman spectrum in the low wavenumber energy region with the aim of validating the candidate structure, this can be further refined. In fact, we find it to correspond to a saddle point of the energy landscape of the system, from which a minimum of lower symmetry may be reached. With the new structure, with Z = 4 and Z′ = 2, we finally obtain an excellent agreement between experimental and calculated Raman spectra., Experimental low wavenumber Raman spectroscopy validates the presence of a non-centrosymmetric packing arrangement that is energetically very close to a centrosymmetric saddle point structure.

Recently, structural studies in the thin-film phase of 6,6′-dibromoindigo, the main component of the Tyrian purple dye, revealed the presence of surface-induced structures. This finding is important, as the system is a good candidate for applications in organic electronics, and knowledge of the film structure is needed to explain the physical properties of the conducting layer. In this work, combining the results of low-frequency Raman spectroscopy, X-ray diffraction, and accurate density-functional theory (DFT) calculations of the vibrational properties of the proposed surface-induced structures, we suggest that a newly detected 6,6′-dibromoindigo bulk crystal form is structurally closely related to the surface-induced modifications. Thus, 6,6′-dibromoindigo behavior shows similarities and differences at the same time, with respect to other investigated systems., We thank CINECA Supercomputing Center for providing computer time through the ISCRA scheme (project C—SCSCDFT). T.S. acknowledges the H2020-MSCA-COFUND-2014 Programme (P-SPHERE, Grant agreement 665919). The authors thank Prof. Roland Resel for the fruitful discussions. This work has been funded by the PRIN project “From natural to artificial light-harvesting systems: unveiling fundamental processes toward a bio-inspired materials design” (HARVEST) protocol 201795SBA3.

Indigo [2,2′-bis(2,3-dihydro-3-oxoindolyliden)], a commonly used natural dye, has been shown to exhibit a highly promising semiconducting behavior, allowing for the realization of ambipolar devices. Nevertheless, up to date, it is still unclear which crystal structure is present in the thin films, a piece of information relevant for device applications. In this work, we address this issue by an in-depth characterization of the polymorphs of Indigo in the bulk and in drop-cast films. To do this, X-ray diffraction (XRD) and micro-Raman spectroscopy have been employed jointly, with the support of state-of-the-art density functional theory calculations in the solid state. Structural and spectroscopic characterizations have established that the two known A and B polymorphs grow as concomitant in the bulk under most of the experimental conditions adopted in this work. In the drop-cast films, XRD cannot unambiguously identify the structure, but Raman spectroscopy is effective in establishing that only the B form is present. The calculations augment the experiments, providing valuable insights into the relative thermodynamic stability of the two forms as a function of temperature. They also allow for a more comprehensive characterization of the Raman modes.

We revisit the polymorphism of paracetamol by means of a micro-Raman technique, which has proved to be a powerful tool for structure recognition. Distinct lattice phonon spectra clearly identified the pure phases. Confocality enabled us to detect phase mixing between form II and either I or III on a micrometric scale in the same crystallite. Following the most recent findings on surface-mediated structures, we also investigated spin-coated films grown on glass, gold, and polystyrene substrates, confirming the selectivity of these surfaces for the metastable form III, which shows an unprecedented stability over a time span of several months. A mechanism of its transformation to phase II, via a partially ordered intermediate state, is suggested by polarized Raman measurements.

International audience; Thin films of the natural semiconductor indigo have been grown on Si/SiO2 substrates by physical vapour deposition under ultra-high vacuum conditions, monitoring the influence of the deposition rate on structure, morphology and thickness. This was done to allow well-defined films to be made in a controlled way, suitable for the manufacture of organic devices and the investigation of charge transport phenomena. The films have been characterized by X-ray diffraction, atomic force microscopy, microRaman spectroscopy and transmission electron microscopy, finding that the growth at the solid interface of polymorph B, the only phase present in the films, is governed by the formation of strong multiple hydrogen-bonds between neighbouring molecules, which play a predominant role in the interface organization of the molecular assemblies.

Thioindigo (2-(3-Oxo-1-benzothiophen-2(3H)-ylidene)-1-benzothiophen-3(2H)-one) is a synthetic dye related to the natural compound Indigo. Notwithstanding the interest aroused recently by its employment as a functional material in a number of applications, a satisfactory characterization of its solid state is still missing. In this work, we study the occurrence of the two thioindigo α and β polymorphs under various growth conditions, and find that their structural similarity implies they often coexist. However, whereas polymorph β is certainly predominant in the bulk phase, polymorph α grows preferentially on substrates, turning out to be the surface stabilized phase in highly homogeneous and ordered films obtained by the bar‐assisted meniscus shearing method (BAMS). DFT calculations support the experimental findings, aiding in the polymorph spectroscopic identification and to the interpretation of the order in the films of polymorph α., We thank CINECA Supercomputing Center for providing computer time through the ISCRA scheme (project C – HP10CA2TWT). The authors thank the Networking Research Center on Bioengineering, Biomaterials and Nanomedicine (CIBER-BBN), the DGI (Spain) project, FANCY CTQ2016-80030-R, the Generalitat de Catalunya (2017-SGR-918) and the Spanish Ministry of Economy and Competitiveness, through the ‘Severo Ochoa‘ Programme for Centres of Excellence in R&D (SEV- 2015–0496). We acknowledge the Elettra Synchrotron Trieste for beamtime allocation and thank Luisa Barba for assistance in using beamline XRD1. T.S. acknowledges the H2020-MSCA-COFUND-2014 Programme (P-SPHERE, Grant agreement 665919).

Directed crystal growth often requires considerable experimental effort to achieve epitaxial control. In this work a simple solution step is shown to yield crystals of two different molecules simultaneously within a thin film and with defined epitaxial relations to each other. This was achieved by dissolving simultaneously carbamazepine (CBZ), a drug molecule, and iminostilbene (ISB), its precursor, in a single solution. When the sample is prepared using slow solvent evaporation rates, both molecules grow into needle-shaped crystals. The ISB crystals contact the substrate surface and extend for hundreds of μm. CBZ tends to minimize the contact with the substrate and assembles on top or is ledge-directed. In both cases a defined inclination of CBZ to the underlying ISB crystals is seen with optical microscopy showing a 36° inclination of the elongated crystals. In a similar way to pole figure measurements, rotating grazing incidence X-ray diffraction allows the determination of crystallographic properties and epitaxial relation, i.e. how the unit cells of both molecules align with respect to each other in terms of contact plane and azimuthal orientation. A point-on-line coincidence was identified, which can be related to the herringbone packing in the ISB crystals. Furthermore, changing the solute content as well as the processing times/kinetics, the appearance and the quality of crystal growth changes, but with the epitaxial relations remaining unaffected; crystals grow more frequent on top when processed slowly and when processed fast, growth takes place more often at facet inclined 90° from the top one., The authors want to thank the NAWI Graz for support. Elettra synchrotron is acknowledged for providing beamtime at the XRD1 beamline. The authors want to thank Luisa Barba and Nicola Demitri for excellent support.

Layered double hydroxides (LDHs) have been widely studied for their plethora of fascinating features and applications. The potentiostatic electrodeposition of LDHs has been extensively applied in the literature as a fast and direct method to substitute classical chemical routes. However, the electrochemical approach does not usually allow for a fine control of the M-II/M-III ratio in the synthesized material. By employing a recently proposed potentiodynamic method, LDH films of controlled composition are herein prepared with good reproducibility, using different ratios of the trivalent (Fe or Al) to bivalent (Co) cations in the electrolytic solution. All the obtained materials are shown to be effective oxygen evolution reaction (OER) catalysts, and are thoroughly characterized by a multi-technique approach, including FE-SEM, XRD, Raman, AES and a wide range of electrochemical procedures.

Thin films of Al, and Co or Ni based Layered Double Hydroxides (LDH) have been electrochemically deposited on four different supports (Grafoil, Toray Carbon Paper, Carbon Cloth and Nickel Foam) through a potentiostatic or a potentiodynamic approach. The obtained films have been fully characterized to compare their properties in dependence on the different deposition techniques and substrates. Finally, the Grafoil support modified with a Ni /Al-LDH has been employed as cathode in combination with a Grafoil anode modified with poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) also electrosynthesized, in order to develop an all-binder-free hybrid supercapacitor as a proof of concept to demonstrate the applicability in the field of energy storage.

Per quanto la spettroscopia Raman sia una tecnica consolidata nello studio del polimorfismo, l'attenzione alla zona spettrale dei modi reticolari (fononi ottici) non ha ancora assunto il rilievo che merita la sua potenzialità di indagine. In questo articolo si illustra brevemente lo stato dell'arte al riguardo, con rilevanti applicazioni nel campo della tecnologia e della farmaceutica.