P. Perfetti

In situ energy dispersive x-ray reflectometry measurements on organic solar cells upon working

The change in the morphology of plastic solar cells was studied by means of time-resolved energy dispersive x-ray reflectivity (XRR). This unconventional application of the XRR technique allowed the follow up of in situ morphological evolution of an organic photovoltaic device upon working. The study consisted of three steps: A preliminary set of XRR measurements on various samples representing the intermediate stages of cell construction, which provided accurate data regarding the electronic densities of the different layers; the verification of the morphological stability of the device under ambient condition; a real-time collection of XRR patterns, both in the dark and during 15h in artificial light conditions which allowed the changes in the system morphology at the electrode-active layer interface to be monitored. In this way, a progressive thickening of this interface, responsible for a reduction in the performances of the device, was observed directly.

In situ studies of electrodic materials in Li-ion cells upon cycling performed by very-high-energy x-ray diffraction

A very high-energy synchrotron radiation source (87 keV) was utilized for in situ sampling of the structural changes occurring in the electrodic materials of a Li-ion cell during charge–discharge cycling. The real-time evolution of their crystal lattice was obtained as a function of the degree of Li intercalation. As a result, new information on two electrodic materials, Li–Ti “zero strain” and Li–Ni–Co oxide, both of extreme interest for generation of rechargeable batteries, was gained. The actual change of the Li–Ti oxide lattice parameter upon cycling was observed in greater detail than before, and provided evidence of unexpected behavior in some intervals of the cycle. In the Li–Ni–Co sample, a new phase formed during the early stages of cycling that remained stable in the subsequent cycles was revealed.

Controlling photoinduced degradation in plastic photovoltaic cells: A time-resolved energy dispersive x-ray reflectometry study

The electrode-active layer interface of organic photovoltaic cells, a critical point in the development of organic devices, was studied by the energy dispersive x-ray reflectivity (EDXR) technique applied in situ. An EDXR-based protocol allowing discrimination between the possible mechanisms that produce the aging process at the interface was established. The study detects photoinduced oxidation of the electrode at the buried interface, to which fading of the device performances could be attributed. This conclusion was further confirmed by results obtained on a new cell, of selectively modified architecture, whose performances turned out to be stable in time.

The SPARC project: a high-brightness electron beam source at LNF to drive a SASE-FEL experiment

Abstract The Project Sorgente Pulsata e Amplificata di Radiazione Coerente (SPARC), proposed by a collaboration among ENEA–INFN–CNR–Universita’ di Tor Vergata–INFM–ST, was recently approved by the Italian Government and will be built at LNF. The aim of the project is to promote an R&D activity oriented to the development of a coherent ultra-brilliant X-ray source in Italy. This collaboration has identified a program founded on two main issues: the generation of ultra-high peak brightness electron beams and of resonant higher harmonics in the SASE-FEL process, as presented in this paper.

Refined, in-situ EDXD structural analysis of the Li[Li1/3Ti5/3]O4 electrode under lithium insertion–extraction

An in-situ energy dispersive X-ray diffraction (EDXD) analysis has been run on the Li[Li1/3Ti5/3]O4 compound upon Li intercalation–deintercalation process. The results confirm that this process is accompanied by a very small variation of the host lattice parameter, i.e., confined between 1‰ over the entire cycle. This value, which agrees with previous literature information, concurs to demonstrate that Li[Li1/3Ti5/3]O4 may indeed be considered as a zero-strain intercalation compound, this being a characteristic of key technological importance since lattice strains upon cycling are among the main causes of capacity decays in lithium battery electrodes. In addition, this work confirms that EDXD is a quite convenient technique for electrochemical measurements since, allowing in-situ lattice parameter determinations, may lead to a complete evaluation of the intermediate stages of the intercalation process and, possibly, to detect differences among the various cycles.

Time-resolved energy dispersive x-ray reflectometry measurements on ruthenium phthalocyanine gas sensing films

The energy dispersive (ED) variant of the conventional x-ray reflectivity (XR) provides an atomic scale determination of the morphological characteristics of thin films, such as their thickness and surface roughness. We report on the in situ EDXR measurements of the (minimal) morphological changes of ruthenium phthalocyanine gas sensing thin films. A series of reflectivity spectra have been collected, during the exposure of the films to a gas flux of nitrogen oxides (NOx) molecules. The measurements allowed a very high density time sampling of the evolution of the two morphological parameters, providing important information on the gas-film interaction.

Experimental evidence of a two-step reversible absorption/desorption process in ruthenium phtalocyanine gas sensing films by in situ energy dispersive x-ray reflectometry

An in situ energy dispersive x-ray reflectivity technique was used to study the morphological changes of gas sensing thin films of ruthenium phtalocyanine (RuPc)2 induced by gas absorption/desorption processes. The time-resolved collection of reflectivity spectra during the exposure of each film to a gas flux of nitrogen oxides provided the evolution of the morphological parameters (thickness and roughness). The gas absorption process develops in two stages: The first induces morphological changes characteristic of a surface (adsorption) process, while the second is dominated by a bulk effect. This two-step behavior is also observed in the desorption process: When the thermal treatment is performed at 130°C, the gas is released from the bulk only. Conversely, at higher temperatures, the gas is fully released, i.e., also from the surface, and the initial film thickness is regained. Finally, a further in situ study upon a second absorption treatment was carried out: In this case, only the film bulk diffusio...

Evidence of a rearrangement of the surface structure in titanium phthalocyanine sensors induced by the interaction with nitrogen oxides molecules

Thin-film samples of titanium phthalocyanine, a sensor of environmental pollutants, were studied by time resolved energy-dispersive x-ray reflectivity (EDXR). This original method demonstrated to be an ideal tool to follow the evolution of the films morphology upon gas exposure, in situ, also allowing an unexpected response of the sensors to be detected. Indeed, while the increase in thickness showed the characteristic feature of a “breathing-like” expansion, already observed in other metal-Pc, the curve of roughness versus exposure time exhibited a peak. This effect, in some cases evident by observation with the naked eye the EDXR data, was attributed to a surface structure rearrangement process.

Morphological variations as nonstandard test parameters for the response to pollutant gas concentration: An application to Ruthenium Phthalocyanine sensing films

A systematic time-resolved energy dispersive x-ray reflectometry study was performed in situ on Ruthenium Phthalocyanine thin fims to estimate the morphological detection limits of this material as NO2 transducer and the influence of the gas concentration on the gas-film interaction mechanisms. The work validates the use of this unconventional method—based on the observation of the morphological parameters change—for evaluating the response of novel sensing materials in alternative to more standard procedures. Indeed, the morphological monitoring is shown to be sensitive to the gas concentration in a range comparable to the usual electroresistive measurements. Moreover, while the latter is only able to give the information on whether the gas is interacting with the sensor, the former is also able to discriminate among interaction processes of a different nature (in the present case the interaction limited to the film surface and the one involving the material bulk).

In situ energy dispersive x-ray reflectometry to investigate the (RuPc)2∕NOx interaction process evidenced by ex situ measurements

A systematic energy dispersive x-ray reflectometry study of different ruthenium phthalocyanine (RuPc)2 thin films was performed in order to investigate their reactivity with the oxidizing NOx gas. A preliminary ex situ analysis, consisting of the comparison between the morphological parameters of different films (before and after the exposure to the gas), was performed. It suggests that a reaction involving two different mechanisms takes place. The following in situ (while fluxing the gas) reflectometry analysis confirms this hypothesis, and clarifies the temporal evolution, also revealing that the first mechanism is limited to the film surface, while the second is a bulk diffusion process.