229 research outputs found
Ion beam sputtered surface dynamics investigated with two-time correlation functions : a model study
Ion beam sputtering is a widely used technique to obtain patterned surfaces. Despite the large use of this approach on different materials to create surface
nanostructures, the theoretical model to explain the time evolution of the erosion process is still debated. We show with the help of simulations, that two-time correlation
functions can serve to assess the validity of different models. These functions can be measured experimentally with the X-ray photon correlation spectroscopy technique
On the use of two-time correlation functions for X-ray photon correlation spectroscopy data analysis
Multi-time correlation functions are especially well suited to study non-equilibrium processes. In particular, two-time correlation functions are widely used in X-ray photon correlation experiments on systems out of equilibrium. One-time correlations are often extracted from two-time correlation functions at different sample ages. However, this way of analysing two-time correlation functions is not unique. Here, two methods to analyse two-time correlation functions are scrutinized, and three illustrative examples are used to discuss the implications for the evaluation of the correlation times and functional shape of the correlations
Ageing dynamics of ion bombardment induced self-organization processes
Instabilities caused during the erosion of a surface by an ion beam can lead to the formation of self-organized patterns of nanostructures. Understanding the self-organization process requires not only the in-situ characterization of ensemble averaged properties but also probing the dynamics. This can be done with the use of coherent X-rays and analyzing the temporal correlations of the scattered intensity. Here, we show that the dynamics of a semiconductor surface nanopatterned
by normal incidence ion beam sputtering are age-dependent and slow down with sputtering time. This work provides a novel insight into the erosion dynamics and opens new perspectives for the understanding of self-organization mechanisms
Absence of Structural Impact of Noble Nanoparticles on P3HT: PCBM Blends for Plasmon Enhanced Bulk-Heterojunction Organic Solar Cells Probed by Synchrotron Grazing Incidence X-Ray Diffraction
The incorporation of noble metal nanoparticles, displaying localized surface
plasmon resonance, in the active area of donor-acceptor bulk-heterojunction
organic photovoltaic devices is an industrially compatible light trapping
strategy, able to guarantee better absorption of the incident photons and give
an efficiency improvement between 12% and 38%. In the present work, we
investigate the effect of Au and Ag nanoparticles blended with P3HT: PCBM on
the P3HT crystallization dynamics by synchrotron grazing incidence X-ray
diffraction. We conclude that the presence of (1) 80nm Au, (2) mix of 5nm,
50nm, 80nm Au, (3) 40nm Ag, and (4) 10nm, 40nm, 60nm Ag colloidal
nanoparticles, at different concentrations below 0.3 wt% in P3HT: PCBM blends,
does not affect the behaviour of the blends themselves
Impact of ambient oxygen on the surface structure of α-Cr2O3(0001)
Surface x-ray diffraction has been employed to quantitatively assess the surface structure of α-Cr2O3(0001) as a function of oxygen partial pressure at room temperature. In ultrahigh vacuum, the surface is found to exhibit a partially occupied double layer of chromium atoms. At an oxygen partial pressure of 1×10−2 mbar, the surface is determined to be terminated by chromyl species (CrO), clearly demonstrating that the presence of oxygen can significantly influence the structure of α-Cr2O3(0001)
The formation of a nanohybrid shish-kebab (NHSK) structure in melt-processed composites of poly (ethylene terephthalate) (PET) and multi-walled carbon nanotubes (MWCNTs)
The combination of synchrotron Small- and Wide-Angle X-ray scattering (SAXS/WAXS), and thermal analysis was used to follow the evolution of crystalline morphology and crystallization kinetics in a series of melt-processed composites of poly(ethylene terephthalate) (PET) and multiwall carbon nanotubes (MWCNT). The as-extruded PET-MWCNT composites underwent both hot and cold isothermal crystallizations where a final oriented nanohybrid shish-kebab (NHSK) crystalline structure was observed. An oriented NHSK structure was seen to persist even after melting and recrystallization of the composites. From the scattering data, we propose a model whereby the oriented MWCNTs act as heterogeneous nucleation surfaces (shish) and the polymer chains wrap around them and the crystallites (kebabs) grow epitaxially outwards during crystallization. However, depending on crystallization temperature, unoriented crystallites also grow in the polymer matrix, resulting in a combination of a NHSK and lamellar morphology. In contrast, the neat PET homopolymer showed the sporadic nucleation of a classic unoriented lamellar structure under the same isothermal crystallization conditions. These results provide a valuable insight into the distinctive modification of the crystalline morphology of melt-processed polymer-MWCNT composites prior to any secondary processing, having a significant impact on the use of MWCNTs as fillers in the processing and modification of the physical and mechanical properties of engineering polymers
Sinkrotroi erradiazioa: azaugarriak eta historia
Artikulu honetan, sinkrotroi erradiazioaren propietate garrantzitsuenak aurkezten dira. Halaber, sinkrotroi erradiazioaren historia gainbegiratu egiten da, eredu teorikoa garatu zenetik gaur egunera arte. Ondoren, gaur egungo sinkrotroi baten funtzionamendua era errazean esplikatzen da eta sinkrotroi erradiazioa erabiltzen duten zenbait alor aipatzen dira. Azken paragrafoan etorkizunari buruz hitz egiten da
In situ Rheo-GISANS of triblock copolymers : gelation and shear effects on quasi-crystalline structures at interfaces
The behaviour of polymeric systems at surfaces and under flow is extremely important in many applications, ranging from drug delivery to lubrication. We have studied a model triblock copolymer in deuterated water combining in situ rheology and grazing incidence small angle neutron scattering. Several thermotropic phases appear as a function of the temperature, including a bicontinuous phase not present in the bulk. Moreover, gelation can occur following a different route depending on the concentration. We show that shearing can be used to monitor the structural integrity of the micellar systems and in some cases as a tool for modifying the thermotropic phases: an fcc (face centred cubic) phase is sheared into a hcp (hexagonally close packed) phase, and is then recovered by cycling the temperature
Perfil, hábitos e atitudes do consumidor do presunto de Chaves
Esta comunicação tem por objectivos traçar o perfil do consumidor do Presunto de Chaves; conhecer os seus hábitos, as suas preferências e as suas atitudes; determinar o grau de influência de características, designadamente, pessoais, sociais, geográficas, económicas e contextuais, na decisão de compra deste produto e verificar a existência de diferenças de atitudes e comportamentos entre grupos no que diz respeito ao consumo deste tipo de produto. Esta investigação apoia-se em dados primários obtidos através da aplicação de um questionário a 200 turistas e ou visitantes do concelho de Chaves no período de Julho a Outubro do ano de 2006
Structure of a model TiO2 photocatalytic interface
The interaction of water with TiO2 is crucial to many of its practical
applications, including photocatalytic water splitting. Following the first
demonstration of this phenomenon 40 years ago there have been numerous studies
of the rutile single-crystal TiO2(110) interface with water. This has provided
an atomic-level understanding of the water-TiO2 interaction. However, nearly
all of the previous studies of water/TiO2 interfaces involve water in the
vapour phase. Here, we explore the interfacial structure between liquid water
and a rutile TiO2(110) surface pre-characterized at the atomic level. Scanning
tunnelling microscopy and surface X-ray diffraction are used to determine the
structure, which is comprised of an ordered array of hydroxyl molecules with
molecular water in the second layer. Static and dynamic density functional
theory calculations suggest that a possible mechanism for formation of the
hydroxyl overlayer involves the mixed adsorption of O2 and H2O on a partially
defected surface. The quantitative structural properties derived here provide a
basis with which to explore the atomistic properties and hence mechanisms
involved in TiO2 photocatalysis
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