Energy Dispersive X-ray Reflectivity Research Articles

The Role of C60 Barrier Layer in Improving the Performances of Efficient Polymer-Based Photovoltaic Devices: An AFM/EDXR Time-Resolved Study

Here, we report an in situ study of the effect of morphological/structural aging processes on polymer-based photovoltaic cell performances. The devices were provided with a fullerene film as a barrier layer between the active element and the metallic cathode. The experimental method adopted consists of the joint use of atomic force microscopy (AFM) and energy dispersive X-ray reflectivity (EDXR), an original coupling particularly effective in the study of stratified media. These techniques were applied first to the intermediate stages of the device construction and, finally, to a complete cell. The problems related with the surface/interface modifications of the devices elements in operating conditions were investigated in depth, with particular concern on the role of the C60 barrier layer. The C60 film surface topography was monitored by AFM experiments during illumination, which evidenced a surface reorganization of the C60 layer molecules over time. Conversely, the C60 film bulk and its interface with ...

Assessment of potential toxic elements pollution of marine environment using African cuttlefish (Sepia bertheloti) from the Gulf of Guinea as an environmental bioindicator

Samples of African cuttlefish, Sepia bertheloti, were collected from the gulf of Guinea and analyzed using energy dispersive X-ray reflection fluorescence (EDXRF) analytical technique to assess potential toxic elements pollution of the marine environment. Eleven elements, namely, Cl, Sr, K, Ca, Br, Fe, Cu, Zn, Mn, Ni, and Se were detected. It is observed that Cl, K, Ca, Mn, Fe, Cu, and Zn identified in the cuttlefish exceeded their maximum recommended dietary reference intakes for individuals. This is supported by their calculated pollution index (PI > 1) indicating that the cuttlefish might have accumulated the elements via polluted marine environments. Comparison of the elemental composition of the cuttlefish with other common meats showed that the values of Ca, Mn, Ni, Cu, and Zn were comparatively high. Strong and significant positive correlation existed between Cl/Zn; Cl/Br; Ca/K; Se/Ni; Se/Cu; Se/Zn; Br/Cu; Br/Zn; Br/Se; Sr/K; and Sr/Ca signifying a common source or chemical similarity, while no strong and significant negative correlation existed between the elements detected.

Gas sensing (RuPc)2 thin films: Electrical response to NO2 gas and morphological changes induced by external moisture

The morphological changes induced in (RuPc)2 gas sensing thin films by hydration and de-hydration processes were investigated. Prior to this study a preliminary characterization was performed by conductivity measurements upon exposure to NO2 gas fluxes, to verify the electrical sensing response of the films. This response was correlated to the bulk morphological modification of the films. Subsequently, the effect of external moisture on the morphological stability of the films was addressed. This morphological characterization of the films was performed by using the energy dispersive X-ray reflectivity (EDXR) and atomic force microscopy (AFM) techniques, both ex situ and in situ, i.e. under operating conditions, during exposure of these films to 100% of relative humidity. The measurements allowed an accurate observation of both the surface morphology (i.e. its roughness obtained independently by EDXR and AFM). Moreover bulk evolution of the films was obtained by in situ EDXR and the morphological changes allowed to retrieve information on the water uptake dynamics. Moreover, the reversibility of the water/film interaction was studied and correlated to the sensing properties of the (RuPc)2.

Structural and magnetic properties of Mn 5Ge 3 nanoclusters dispersed in Mn xGe 1− x/Ge(0 0 1)2 × 1 diluted magnetic semiconductors

We investigated the structural and magnetic properties of Mn x Ge 1− x , with 0.02 ⩽ x ⩽ 0.1. The Mn x Ge 1− x samples were grown on Ge(0 0 1)2 × 1 by molecular beam epitaxy, at a substrate temperature of 520 K. The samples were characterized in situ by reflection high-energy electron diffraction and ex situ by high-resolution transmission electron microscopy, energy dispersive X-ray reflectivity and magneto-optical Kerr effect. From microscopy images we evidenced on all samples the presence of Mn 5Ge 3 nanocrystallites in addition to the Mn x Ge 1− x diluted magnetic semiconductor with an estimated Mn concentration x ≈ 1.5%. The size and the density of the Mn 5Ge 3 precipitates were found to increase with increasing the Mn concentration x. Magnetic analysis showed ferromagnetism with a Curie temperature of 280 K for all samples.

Multilayer characterization by energy dispersive X-ray reflectivity technique

An experimental setup was developed to verify the feasibility of silicon drift detector to be used for the multilayer characterization by means of multilayer energy dispersive X-ray reflectivity. Such a detector allows high count rates up to 3 × 10 5 cps and can be used in principle for the direct beam intensity measurement, which is to be done for the X-ray multilayer reflectivity patterns obtaining. A series of measurements were performed for Mo/B 4C multilayer sample. A quality of the experimentally obtained data turns out to be enough to perform a sample structure exploration using a numerical procedure of experimental data fitting. Due to low cost and short time, required for the measurements, an experimental technique proposed has a good perspective to be used for some practical applications in industry.

Study of FePt films prepared by reactive sputtering

In the present study, 57FePt films are prepared with reactive ion beam sputtering using mixture of argon and nitrogen gases. Energy-dispersive X-ray reflectivity is used to estimate the thickness of the as-deposited films. Structural and magnetic properties of the as-deposited and annealed films are studied using grazing incidence X-ray diffraction (GIXRD), magneto-optical Kerr effect (MOKE) and conversion electron Mossbauer spectroscopy (CEMS). Significant difference in structural and magnetic properties i.e., formation of ordered L1 0 phase and perpendicular magnetic anisotropy are observed for the films prepared with mixture of nitrogen and argon as compared to the film prepared with argon only. From the GIXRD, peaks corresponding to the ordered face-centred tetragonal FePt phase are observed for the films prepared with mixture gas. The results of CEMS clearly show the perpendicular magnetic anisotropy (PMA) for the films prepared with mixture of nitrogen and argon. The observed enhanced chemical ordering and the development of PMA in the films prepared with mixture gas is due to the role played by the defects created as a consequence of nitrogen escape in the films with high temperature annealing.

Energy-dispersive X-ray reflectivity and GID for real-time growth studies of pentacene thin films

We use energy-dispersive X-ray reflectivity and grazing incidence diffraction (GID) to follow the growth of the crystalline organic semiconductor pentacene on silicon oxide in-situ and in real-time. The technique allows for monitoring Bragg reflections and measuring X-ray growth oscillations with a time resolution of 1 min in a wide q-range in reciprocal space extending over 0.25–0.80 Å − 1 , i.e. sampling a large number of Fourier components simultaneously. A quantitative analysis of growth oscillations at several q-points yields the evolution of the surface roughness, showing a marked transition from layer-by-layer growth to strong roughening after four monolayers of pentacene have been deposited.

Influence of thermal curing on the fabrication and properties of thin organosilane films coated on low carbon steel substrates

Silane coupling agents seem to be one of the most promising alternatives for the chromium and phosphate mainly due to its excellent corrosion protection and adhesion properties to organic coatings and a non-toxic pretreatment. The organosilane film was produced by thermal curing after low carbon steel substrates were immersed in γ-glycidoxypropyltrimethoxysilane (γ-GPS) solution. The present paper is intended to provide a deeper insight into the effect of thermal curing on the fabrication and properties of this film. Characterizations of the film were performed by energy dispersive X-ray spectrometer (EDS) and reflection–absorption infrared spectroscopy (RAIR). The adhesion of the film to the substrates was also tested by pull-off method. The analytical results from EDS showed that the distribution of silicon and iron atomic concentration changed with the curing temperature. The maximum adhesion of 3.65 MPa was obtained for films cured at 150 °C for 1 h. Results of RAIR showed that the thermal curing had a great effect on the chemical structure of the films, and the reaction between silanols caused to the formation of dense films with siloxane bonds.

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.

Morphological and magnetic properties of Ge/Mn xGe 1− x/Ge(0 0 1)2 × 1 diluted magnetic semiconductor

We studied morphological and magnetic properties of Ge/Mn x Ge 1− x /Ge(0 0 1)2 × 1, x = 0.02–0.04. Several Mn x Ge 1− x alloys were grown on Ge(0 0 1)2 × 1 by molecular beam epitaxy, as a function of substrate temperature and Mn concentration. The samples were characterized in situ by RHEED, and ex situ by energy dispersive X-ray reflectivity (EDXR) and magneto-optical Kerr effect, (MOKE). From RHEED analysis we found an optimal growth temperature T epi = 523 K to achieve 2D epitaxial Mn x Ge 1− x ( x = 0.02–0.04) alloy on a Ge(0 0 1) substrate. X-ray reflectivity measurements provided: the film roughness, the Mn x Ge 1− x scattering length density, and the average thickness for all samples. MOKE analysis showed ferromagnetism with Curie temperature T C = 270 K for samples grown at T epi = 523 K.

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.

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.

Elemental composition and reflectance of ambient fine particles at 21 European locations

We sampled fine particles (PM2.5) over a 1-year period at 21 central urban monitoring sites in 20 cities of the European Community Respiratory Health Survey (ECRHS). Particle filters were then analysed for elemental composition using energy dispersive X-ray fluorescence spectrometry and reflectance (light absorption). Elemental analyses yielded valid results for 15 elements (Al, As, Br, Ca, Cl, Cu, Fe, K, Mn, Pb, S, Si, Ti, V, Zn). Annual and seasonal means of PM2.5, reflectance, and elements show a wide range across Europe with the lowest levels found in Iceland and up to 80 times higher concentrations in Northern Italy. This pattern holds for most of the air pollution indicators. The mass concentration of S did constitute the largest fraction of the analysed elements of PM2.5 in all locations. The crustal component varies from less than 10% up to 25% across these cities. Temporal correlations of daily values vary considerably from city to city, depending on the indicators compared. Nevertheless, correlations between estimates of long-term exposure, such as annual means, are generally high among indicators of PM2.5 from anthropogenic sources, such as S, metals, and reflectance. This highlights the difficulty to disentangle effects of specific sources or PM constituents in future health effect analyses using annual averages.

Glass transition in ultrathin polymer films: A thermal expansion study

The glass transition process gets affected in ultrathin films having thickness comparable to the size of the molecules. We observe systematic broadening of the glass transition temperature (T(g)) as the thickness of an ultrathin polymer film reduces below the radius of gyration but the change in the average T(g) was found to be very small. The existence of reversible negative and positive thermal expansion below and above T(g) increased the sensitivity of our thickness measurements performed using energy-dispersive x-ray reflectivity. A simple model of the T(g) variation as a function of depth expected from sliding motion could explain the results.

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 diffusion process takes place.

Transition from two-dimensional to three-dimensional melting in Langmuir-Blodgett films

Results of energy-dispersive x-ray reflectivity and grazing incidence diffraction studies of Langmuir-Blodgett films exhibited evolution of conventional three-dimensional melting from continuous melting, characteristic of two-dimensional systems, as a function of deposited monolayers. Continuous expansion followed by a sharp phase transition of the in-plane lattice was observed before the melting point and found to be independent of number of deposited layers. Evolution of conventional melting with an increase in the number of monolayers could be quantified by measuring stiffness against tilting of the vertical stack of molecules, which are kept together by an internal field. The internal field as defined in this model reduces as the in-plane lattice expands and the sample temperature approaches melting point. The sharpness of the melting transition, which has been approximated by a Langevin function, increases with the number of deposited monolayers.

Technology of production of red figure pottery from Attic and southern Italian workshops

Samples from Greek figure vases were investigated by scanning electron microscopy coupled with energy dispersive X-ray analysis, X-ray diffraction, thermomechanical analysis and reflectance spectroscopy to achieve a technological characterisation. The vases, dating from the end of the sixth to the fourth century BC, had been excavated at Locri Epizephiri (Calabria, Italy) and attributed to Attic or local workshops, respectively. Information on the morphology of black slip areas and firing temperatures was compared with that previously obtained for Attic and local black gloss pottery from the same site; results show that the peculiar technique required for the production of black slips was mastered by both Attic and local potters and employed for monochrome and figured products. The black coating is usually well vitrified and 15- to 20-microm thick; the evaluated maximum firing temperature is around 900 degrees C, while a temperature lower than 800 degrees C is generally estimated for ceramic body re-oxidation.

Energy dispersive X-ray reflectivity to study phase transitions in thin films

We present here characteristics of energy dispersive X-ray reflectivity (EDR) technique that is suitable for studying phase transitions in thin films at both laboratory and synchrotron sources. In spite of the poorer resolution of this technique as compare to more widely used angle dispersive reflectivity technique, rapid data collection capability of the EDR technique will find applications in the studies of nano-structured thin films. We demonstrate merit of this technique here using results of thermal properties of thin organic films.

Energy dispersive x-ray reflectivity technique to study thermal properties of polymer films

A method to study temperature dependent thickness variation of thin films has been developed based on angle and energy dispersive x-ray reflectivity (EDR) techniques. The data analysis scheme developed for this method combines both energy and angle dispersive x-ray reflectivity (ADR) profiles. The ADR technique provides the electron density profile on an absolute scale and the EDR technique facilitates rapid collection of reflectivity data as a function of temperature. We demonstrate the utility of the developed method with results of a study of thermal expansion of single and bilayer polymer films. We could detect a change of the thickness of the film in angstroms and could demonstrate interplay of negative and positive thermal expansions of dissimilar polymer layers in determining density profiles of polymer–polymer interface as a function of temperature.

Ni-containing spinel aluminates glass-ceramic materials obtained from cordieritic bulk glasses

Monolithic glasses with compositions 2MO · 2Al 2O 3 · 5SiO 2, being M=Ni and equimolar mixtures of Ni and Mg, were prepared at 1650 °C by melting mixtures of raw materials. The crystallization of monoliths was produced by heat-treatment at several temperatures up to 1200 °C. The crystallization sequence was followed by differential thermal analysis (DTA), X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray (EDX) and diffuse reflectance spectroscopies. Surprisingly, the only crystalline phase formed after heating up to 1100 °C was a nickel-containing aluminate spinel for both compositions. The microstructural characterization indicated the volume crystallization of well formed octahedral crystals of spinel with smaller size than 500 nm. Finally, it has been proved that nickel-containing aluminosilicate glasses could be converted into μ- or α-cordierite- and spinel-based glass-ceramics by thermal treatment of powdered glasses and monolithic bodies, respectively.