Stability enhancement of organic photovoltaic devices utilizing partially reduced graphene oxide as the hole transport layer: nanoscale insight into structural/interfacial properties and aging effects

A powerful insight into the structural and interfacial properties of post-fabricated bulk heterojunction (BHJ) organic photovoltaic (OPV) devices, utilizing partially reduced graphene oxide as the hole transport layer, is reported.

Spatially-resolved in-situ structural study of organic electronic devices with nanoscale resolution: the plasmonic photovoltaic case study

A novel high spatial resolution synchrotron X-ray diffraction stratigraphy technique has been applied in-situ to an integrated plasmonic nanoparticle-based organic photovoltaic device. This original approach allows for the disclosure of structure-property relations linking large scale organic devices to length scales of local nano/hetero structures and interfaces between the different components.

Ferromagnetic Mn-doped Si0.3Ge0.7 nanodots self-assembled on Si(100)

Densely packed epitaxial Mn-doped Si(0.3)Ge(0.7) nanodots self-assembled on Si(100) have been obtained. Their structural properties were studied using reflection high-energy electron diffraction, energy dispersive x-ray diffraction, atomic force microscopy, extended x-ray absorption fine structure measurements and high-resolution transmission electron microscopy. Mn(5)Ge(1)Si(2) crystallites embedded in Si(0.3)Ge(0.7) were found. They exhibit a ferromagnetic behaviour with a Curie temperature of about 225 K.

Self-amplified spontaneous emission free-electron laser with an energy-chirped electron beam and undulator tapering

We report the first experimental implementation of a method based on simultaneous use of an energy chirp in the electron beam and a tapered undulator, for the generation of ultrashort pulses in a self-amplified spontaneous emission mode free-electron laser (SASE FEL). The experiment, performed at the SPARC FEL test facility, demonstrates the possibility of compensating the nominally detrimental effect of the chirp by a proper taper of the undulator gaps. An increase of more than 1 order of magnitude in the pulse energy is observed in comparison to the untapered case, accompanied by FEL spectra where the typical SASE spiking is suppressed.

Crystallization process of carbonate substituted hydroxyapatite nanoparticles in toothpastes upon physiological conditions: an in situ time-resolved X-ray diffraction study

The crystallization process in recently developed toothpastes, containing nanoparticles of carbonate substituted hydroxyapatite (nano-CHA), was investigated. For this purpose, the non-conventional Energy Dispersive X-Ray Diffraction technique, that demonstrated to be a powerful tool to follow in situ phase transformations, was applied, for the first time, to products of pharmaceutical-cosmetic interest. Two types of toothpastes, containing 15 and 20 wt% of nano-CHA, respectively, have been studied. It was observed that, after mixing the toothpastes with water and saliva in order to reproduce in vivo conditions, a crystallization of nano-CHA takes place. Such process occurs in a characteristic time of (22 +/- 1) min for the toothpaste containing 15 wt% of nano-CHA and of (3.9 +/- 0.5) min for the one containing 20% of nano-CHA. For both toothpastes, a 10% increase in grain dimensions was observed over an average characteristic time of (55 +/- 5) min.

Selective energy dispersive diffraction peak fitting by using genetic algorithm

Accurate and precise estimates of X-Ray diffraction peak parameters is mandatory, when small dynamic changes of lattice parameters have to be quantitatively analyzed. To follow in real time such changes, a large set of patterns must be usually collected, so that the position of certain peaks of interest can be tracked. To calculate the positions, a fitting procedure of the peaks is required and several algorithms are reported in the literature for this purpose. However, these algorithms are mainly focused on the determination of parameters based on a model of the cell geometry. Here, we present a new algorithm allowing to carry out the fitting procedure on a portion only of the pattern, with neither tight constraints on the dataset, nor restrictive hypotheses on the sample structure. In our case, a coarse estimate of the detector resolution and of the positions of the peaks to fit are the only initial conditions required. This method can be regarded as a hybrid technique, as it makes use of a genetic algorithm approach, mixed with an intensive multiple random generation of the population, that makes it similar to a Monte Carlo technique. Moreover, adaptive genetic operators have been implemented in the data processing code. These properties result in a fast and efficient algorithm, a fundamental requirement when, as in the present case, the Energy Dispersive X-ray Diffraction method is applied to observe structural changes, which implies the acquisition of many patterns in a relatively short time. The result of this application is shown by some practical examples.

Angular calibration in energy dispersive X-Ray diffraction by using genetic algorithms

In Energy Dispersive X-Ray diffraction measurements, the estimate of momentum transfer q, on which the diffracted intensity depends, should be as accurate as possible. Since q, in turn, depends on both the energy and the scattering angle, an error on the latter due to an incorrect positioning of the sample, to the asymmetric angular spread induced by the collimation slits or, in general, to any uncertainty on the geometric setup, results in an uncertainty on the q value. Here, a new self calibration method to correct such errors, based on a genetic algorithm is presented. It is robust, fast and completely automatic. Results obtained by carrying out Energy Dispersive X-Ray Diffraction measurements on reference samples are reported and discussed. They show how the application of such genetic algorithm may provide a fast esteem of the two parameters required when multiple angle pattern collection is performed, namely the effective starting angle and the angular step. In this way, reliable q-values of all the diffraction pattern features (Bragg peaks for crystalline, and diffused bumps for non-crystalline samples) are obtained.

Energy dispersive X-ray diffraction study of phase development during hardening of calcium phosphate bone cements with addition of chitosan

The aim of this work was to study the phase transformation during the setting reaction of two calcium phosphate bone cements based on either alpha tricalcium phosphate (alpha-TCP) or tetracalcium phosphate (TetCP) initial solid phase, and a magnesium carbonate-phosphoric acid solution as the hardening liquid. Low molecular weight (38.2 kDa) chitosan was used to retard the cement's setting reaction. To follow the kinetics of the phase development, an energy dispersive X-ray diffraction technique was applied. This technique allowed the collection of diffraction patterns from the cement pastes in situ starting from 1 min of the setting process. In the case of the TetCP-based cement, the appearance and evolution of an intermediate phase was detected.

Energy-dispersive X-ray diffraction on thin films and its application to superconducting samples

Energy-dispersive X-ray diffraction is applied to investigate double-layer PBCO/YBCO thin films deposited by laser ablation. The merits of this technique for the structural study of films are discussed. It is shown that the rocking curves of the Bragg reflections of a film along thecdirection can be simultaneously collected, allowing the accurate evaluation of its angular spread. A systematic displacement of the rocking curves of the film with respect to those of the substrate was found, revealing a slight divergence of the growth direction from the normal to the substrate surface.