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info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

We report the first (in)elastic scattering measurement of with the capability to select and measure in a broad energy range the proton resonances in contributing to the reaction at type I x-ray burst energies. We measured spin-parities of four resonances above the threshold of that are found to strongly impact the rate. The new rate advances a state-of-the-art model to remarkably reproduce light curves of the GS clocked burster with mean deviation and permits us to discover a strong correlation between the He abundance in the accreting envelope of the photospheric radius expansion burster and the dominance of branch., SCOPUS: ar.j, info:eu-repo/semantics/published

Specular and off-specular neutron reflectometry have been used in a combined approach to study thin polymer films. Our goal in this work is to illustrate the power of the off-specular scattering technique to probe the properties of the buried interface of immiscible polymer bilayers of deuterated polystyrene and protonated poly(methyl methacrylate) (h-PMMA). The diffuse scattering stemming from these systems is discussed in relation to thermal fluctuations at the polymer/polymer interface, providing a means to extract in-plane correlation lengths from buried interfaces. In addition the onset of hole formation in the top layer is evidenced by the diffuse scattering, not easily detectable by specular reflection alone., SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published

An extended investigation of the low-spin structure of the Ni65 nucleus was performed at the Institut Laue-Langevin, Grenoble, France, via the neutron capture reaction Ni64(n,γ)Ni65, using the Fission Product Prompt Gamma-Ray Spectrometer High-Purity Ge array. The level scheme of Ni65 was significantly expanded, with two new levels and 87 newly found transitions. Angular correlation analyses were also performed, allowing us to assign spins and parities for a number of states and to determine multipolarity mixing ratios for selected γ transitions. The low-energy part of the experimental level scheme (up to about 1.4 MeV) was compared with Monte Carlo shell-model calculations, which predict spherical shapes for all states, apart from the 9/2+ and the second excited 1/2- states of oblate deformation., SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

info:eu-repo/semantics/published

Specular reflectivity (SR) and off-specular neutron scattering (OSS) are non-destructive scattering techniques, which, through deuteration (exchange of hydrogen atoms with deuterium), give a high contrast even among very similar chemical species and are therefore highly suitable for investigations of soft thin films. While readily available software exists for analysis of SR, there are no such existing tools for OSS. Through a combination of both, the former yielding a density profile in the direction normal to the sample surface and the latter yielding an in-plane lateral structure at each of the buried interfaces, one can obtain detailed information of buried morphology on length scales ranging from angstroms to 10 micrometres. OSS analysis was developed to analyze buried interfaces in absolute scale, with only structural parameters being free. Moreover, the SR and OSS are intricately linked and have to be fitted to the data simultaneously, constraining the model to a high degree. The OSS was applied to investigation of soft interfaces as model systems.The stability and instability of thin polymer layers have been studied extensively in the last decades, both as their applications as coatings have become part of our daily life, and in fundamental soft matter research. The mechanism of immiscible polymer film decomposition was investigated by preparing bilayers of deuterated polystyrene (d-PS) and protonated poly(methyl methacrylate) (h-PMMA) of different thicknesses on Si substrates. The in-plane lateral cutoff length was measured at the PS/PMMA interface as a function of d-PS thickness. For preannealed films with thickness of dPS below 250 angstroms, the result follows the prediction of the capillary waves cutoff length. For thicker films, spontaneous nucleation of the top layer, with a clear OSS signature, was observed. This was also the case for the non-preannealed samples, showing that preannealing causes irreversible adsorption on the substrate and thus stabi, Doctorat en Sciences, info:eu-repo/semantics/nonPublished

A substrate-supported phospholipid bilayer (SPB) is commonly used as a model bio-membranes on a solid substrate. The most common method to make SPBs is the adsorption followed by rupture of phospholipid vesicles on a substrate surface in contact with the vesicle solution. However, this method may present an applicability issue due to the limitation of combination of the phospholipids and substrates. On the other hand, adhesion of disklike micelles consisting of phospholipid, so-called bicelles, is a hopeful alternative method for making SPBs since they don't need the rupture process. The mechanism of the nanodisk adhesion on a substrate is, however, not fully understood yet. In this study, in-situ observation of the bicelle adhesion was performed using neutron reflectometry (NR), which can shed light on the depth profile of bilayer density at the interface between a substrate and bicelle solution. In addition, atomic force microscopy (AFM) was employed for the topographic imaging and force response measurement of the adhesion layer. These results presented that lamellae of phospholipid bilayers were aligned parallel to a surface of a bare Si substrate, whereas a fragile layer of unoriented phospholipid bilayers was formed on a NH2 coated Si substrate., SCOPUS: ar.j, info:eu-repo/semantics/published

SCOPUS: ar.j, info:eu-repo/semantics/published

The interaction between two immiscible materials is related to the number of contacts per unit area formed by the two materials. For practical reasons, this information is often parametrized by the interfacial free energy, which is commonly derived via rather cumbersome approaches, where properties of the interface are described by combining surface parameters of the single materials. These combining rules, however, neglect any effect that geometry might have on the strength of the interfacial interaction. In this Article, we demonstrate that the number of contacts at the interface between a thin polymer coating and its supporting substrate is altered upon confinement at the nanoscale level. We show that explicitly considering the effect of nanoconfinement on the interfacial potential allows a quantitative prediction of how sample geometry affects the number of contacts formed at the interface between two materials., SCOPUS: ar.j, info:eu-repo/semantics/published

A search for shape isomers in the Ni66 nucleus was performed, following old suggestions of various mean-field models and recent ones, based on state-of-the-art Monte Carlo shell model (MCSM), all considering Ni66 as the lightest nuclear system with shape isomerism. By employing the two-neutron transfer reaction induced by an O18 beam on a Ni64 target, at the sub-Coulomb barrier energy of 39 MeV, all three lowest-excited 0+ states in Ni66 were populated and their γ decay was observed by γ-coincidence technique. The 0+ states lifetimes were assessed with the plunger method, yielding for the 02+, 03+, and 04+ decay to the 21+ state the B(E2) values of 4.3, 0.1, and 0.2 Weisskopf units (W.u.), respectively. MCSM calculations correctly predict the existence of all three excited 0+ states, pointing to the oblate, spherical, and prolate nature of the consecutive excitations. In addition, they account for the hindrance of the E2 decay from the prolate 04+ to the spherical 21+ state, although overestimating its value. This result makes Ni66 a unique nuclear system, apart from U236,238, in which a retarded γ transition from a 0+ deformed state to a spherical configuration is observed, resembling a shape-isomerlike behavior., SCOPUS: ar.j, info:eu-repo/semantics/published

The neutron-rich nucleus Pt200 is investigated via in-beam γ-ray spectroscopy to study the shape evolution in the neutron-rich platinum isotopes towards the N=126 shell closure. The two-neutron transfer reaction Pt198(Se82, Se80)Pt200 is used to populate excited states of Pt200. The Advanced Gamma Ray Tracking Array (AGATA) demonstrator coupled with the PRISMA spectrometer detects γ rays coincident with the Se80 recoils, the binary partner of Pt200. The binary partner method is applied to extract the γ-ray transitions and build the level scheme of Pt200. The level at 1884 keV reported by Yates et al. [S. W. Yates, E. M. Baum, E. A. Henry, L. G. Mann, N. Roy, A. Aprahamian, R. A. Meyer, and R. Estep, Phys. Rev. C 37, 1889 (1988)] was confirmed to be at 1882.1 keV and assigned as the (61+) state. An additional γ ray was found and it presumably deexcites the (81+) state. The results are compared with state-of-the-art beyond mean-field calculations, performed for the even-even 190-204Pt isotopes, revealing that Pt200 marks the transition from the γ-unstable behavior of lighter Pt nuclei towards a more spherical one when approaching the N=126 shell closure., 0, SCOPUS: ar.j, info:eu-repo/semantics/published

When cooled at constant rate, a 25 nm thin film of poly(4-tert-butylstyrene) vitrifies 50 K lower than in bulk. This record sets the largest depression in thermal glass transition temperature (T) ever observed upon confinement at the nanoscale level. Same as for other supported polymer layers, this reduction in T has been attributed to the presence of a free surface, the ensemble of molecules at the interface with air remaining in the liquid state also at temperatures well below bulk T. Here, we verify that such tremendous shifts can be erased upon prolonged annealing in the liquid state, hinting at a metastable nature of confinement effects. We demonstrate that the recovery of bulk behavior and the manifestation of the free surface are enslaved to the kinetics of irreversible adsorption of chains on the supporting substrate.

The discussions on the nanoconfinement effect on the glass transition and glassy dynamics phenomena have yielded many open questions. Here, the thickness dependence of the thermal glass transition temperature Tgtherm of thin films of a PVME/PS blend is investigated by ellipsometry. Its thickness dependence was compared to that of the dynamic glass transition (measured by specific heat spectroscopy) and the deduced Vogel temperature (T0). While Tg therm and T0 showed a monotonous increase, with decreasing film thickness, the dynamic glass transition temperature (Tgdyn) measured at a finite frequency showed a nonmonotonous dependence that peaks at 30 nm. This was discussed by assuming different cooperativity length scales at these temperatures, which have different sensitivities to composition and thickness. This nonmonotonous thickness dependence of Tgdyn disappears for frequencies characteristic for T0. Further analysis of the fragility parameter showed a change in the glassy dynamics from strong to fragile, with decreasing film thickness., SCOPUS: ar.j, info:eu-repo/semantics/published

When cooled at constant rate, a 25 nm thin film of poly(4-tert-butylstyrene) vitrifies 50 K lower than in bulk. This record sets the largest depression in thermal glass transition temperature (Tg) ever observed upon confinement at the nanoscale level. Same as for other supported polymer layers, this reduction in Tg has been attributed to the presence of a free surface, the ensemble of molecules at the interface with air remaining in the liquid state also at temperatures well below bulk Tg. Here, we verify that such tremendous shifts can be erased upon prolonged annealing in the liquid state, hinting at a metastable nature of confinement effects. We demonstrate that the recovery of bulk behavior and the manifestation of the free surface are enslaved to the kinetics of irreversible adsorption of chains on the supporting substrate., SCOPUS: ar.j, info:eu-repo/semantics/published

We investigated the impact of irreversible adsorption on the mechanisms of thermal expansion of 1D confined polymer layers. For spincoated films (polystyrene on aluminum) of constant thickness, the thermal expansion coefficient of the melt drops upon annealing following the kinetics of irreversible adsorption of the chains onto the supporting substrate, while the thermal expansion of the glass is annealing invariant. These perturbations are explained in terms of the reduction in free volume content, upon immobilization of monomers onto the substrate. To shed more light on this phenomenon, we performed an extensive investigation of the thermal expansion of irreversibly adsorbed layers of polystyrene on silicon oxide. We verified that, contrarily to recent speculations, these films cannot be modeled as dead layers - immobilized slabs lacking of segmental relaxation. On the contrary, thin adsorbed layers show an increase in thermal expansion with respect to the bulk, due to packing frustration. Immobilization plays a role only when the thickness of the adsorbed layers overcomes ∼10 nm. Finally, we show that for adsorbed layers the difference in thermal expansion between the melt and the glass is sufficiently high to investigate the glass transition down to 3 nm. Owing to this unique feature, not shared by spincoated films, adsorbed layers are the perfect candidate to study the properties of extremely thin polymer films., SCOPUS: ar.j, info:eu-repo/semantics/published

Film forming properties of semiconducting organic molecules comprising alkyl-chains combined with an aromatic unit have a decisive impact on possible applications in organic electronics. In particular, knowledge on the film formation process in terms of wetting or dewetting, and the precise control of these processes, is of high importance. In the present work, the subtle effect of temperature on the morphology and structure of dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) films deposited on silica surfaces by spin coating is investigated in situ via X-ray diffraction techniques and atomic force microscopy. Depending on temperature, bulk C8-BTBT exhibits a crystalline, a smectic A and an isotropic phase. Heating of thin C8-BTBT layers at temperatures below the smectic phase transition temperature leads to a strong dewetting of the films. Upon approaching the smectic phase transition, the molecules start to rewet the surface in the form of discrete monolayers with a defined number of monolayers being present at a given temperature. The wetting process and layer formation is well defined and thermally stable at a given temperature. On cooling the reverse effect is observed and dewetting occurs. This demonstrates the full reversibility of the film formation behavior and reveals that the layering process is defined by an equilibrium thermodynamic state, rather than by kinetic effects., SCOPUS: ar.j, info:eu-repo/semantics/published

Controlling polymer/substrate interfaces without modifying chemistry is nowadays possible by finely tuning the formation of adsorbed layers. The complex processes leading to irreversible attachment of chains onto solid substrates are governed by two mechanisms: molecular rearrangement and potential-driven adsorption. Here we introduce an analytical method to differentiate these two mechanisms. By analyzing experiments and simulations, we investigate how changes in thermal energy and interaction potential affect equilibrium and nonequilibrium components of the adsorption kinetics. We find that the adsorption process is thermally activated, with activation energy comparable to that of local noncooperative processes. On the other hand, the final adsorbed amount depends on the interface interaction only (i.e. it is temperature independent in experiments). We identify a universal linear relation between the growth rates at short and long adsorption times, suggesting that the monomer pinning mechanism is independent of surface coverage, while the progressive limitation of free sites significantly limits the adsorption rate., SCOPUS: ar.j, info:eu-repo/semantics/published