Blog

Abstract : Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical response, measured by pump-probe transient absorption (TA) spectroscopy, to explore the NP vibrational landscape. The fast Fourier transform analysis of the TA dynamics reveals specific vibration modes in the frequency range 15–150 GHz, further studied by numerical simulations based on the finite element method. While bare Au nanorods exhibit extensional and breathing modes, the bimetallic NPs undergo more complex motions, involving the displacement of facets, edges and corners. The amplitude and frequency of these modes are shown to depend on the Ag shell thickness, as the silver load modifies the NP aspect ratio and mass. Moreover, the contributions of the vibrational modes to the experimental TA spectra are shown to vary with the probe laser wavelength at which the signal is monitored. Using the combined simulations of the NP elastic and optical properties, we elucidate this influence by analyzing the effect of the mechanisms involved in the acousto-plasmonic coupling.

Tadele Otomalo 1, 2 Lorenzo Di Mario 3 Cyrille Hamon 4 Doru Constantin 4 Francesco Toschi 3 Khanh-Van Do 1 Vince Juvé 2 Pascal Ruello 2 Patrick O’Keeffe 3 Daniele Catone 3 Alessandra Paladini 3 Bruno Palpant 1
1 LuMIn – Laboratoire Lumière, Matière et Interfaces
2 IMMM – Institut des Molécules et Matériaux du Mans
3 CNR-ISM – Istituto di Struttura della Materia
4 LPS – Laboratoire de Physique des Solides

Abstract : The large tolerance of hybrid perovksites to the trapping of electrons by defects is a key asset in photovoltaic applications. Here, the ionic surface terminations of CH3NH3PbI3 are employed as a testbed to study the effect of electrostatic fields on the dynamics of excited carriers. We characterize the transition across the tetragonal to orthorhombic phase. The observed type II band offset and drift of the excited electrons highlight the important role that organic cations have on the screening of local electrostatic fields. When the orientation of organic cations is frozen in the orthorhombic phase, the positively charged termination induces a massive accumulation of excited electrons at the surface of the sample. Conversely, no electron accumulation is observed in the tetragonal phase. We conclude that the local fields cannot penetrate in the sample when the polarizability of freely moving cations boosts the dielectric constant up to ϵ = 120.

Marie Cherasse 1, 2 Jingwei Dong 1 Gaëlle Trippé-Allard 3 Emmanuelle Deleporte 3 Damien Garrot 4 Sebastian Maehrlein 2 Martin Wolf 2 Zhesheng Chen 5 Evangelos Papalazarou 5 Marino Marsi 5 Jean-Pascal Rueff 6 Amina Taleb-Ibrahimi 6 Luca Perfetti 1
1 LSI – Laboratoire des Solides Irradiés
2 Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society
3 LuMIn – Laboratoire Lumière, Matière et Interfaces
4 GEMAC – Groupe d’Etude de la Matière Condensée
5 LPS – Laboratoire de Physique des Solides
6 SSOLEIL – Synchrotron SOLEIL

Abstract : The debonding criterion of fibrils of soft adhesive materials is a key element regarding the quantitative modelisation of pressure sensitive adhesive tapes peeling energy. We present in this article an experimental study of the detachment of a commercial acrylic adhesive tape from the top surface of a single micrometric pillar of PDMS elastomer. During an experiment, the pillar and the adhesive, after being put in contact, are separated at a constant displacement rate, resulting in the formation, the elongation and the final detachment of a fibril of adhesive material. A systematic study allows us to uncover power laws for the maximum force and the critical elongation of the fibril at debonding as a function of the diameter of the cylindrical pillar which controls the diameter of the fibril. The scaling law evidenced for the critical elongation appears as a first step toward the understanding of the debonding criterion of fibrils of soft adhesive materials. In addition, viscoelastic digitation at the triple debonding line is observed during detachment for large pillar diameters. The wavelength and penetration length of the fingers that we report appear to be consistent with existing models based on pure elastic mechanical response.

Aymeric Duigou-Majumdar 1, 2 Pierre-Philippe Cortet 1 Christophe Poulard 2
1 FAST – Fluides, automatique, systèmes thermiques
2 LPS – Laboratoire de Physique des Solides

Abstract : The flow through a capillary tube with non-constant radius and where bubbles of yield stress fluid are injected is strongly non-linear. In particular below a finite yield pressure drop, PyPy, flow is absent, while a singular behaviour is expected above it. In this paper we compute the yield pressure drop statistics and the mean flow rate in two cases: (i) when a single bubble is injected, (ii) when many bubbles are randomly injected in the fluid.

Federico Lanza 1, 2 Alex Hansen 2 Alberto Rosso 1 Laurent Talon 3
1 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
2 NTNU – Norwegian University of Science and Technology [Trondheim]
3 FAST – Fluides, automatique, systèmes thermiques

Abstract : The behavior of shear-oscillated amorphous materials is studied using a coarse-grained model. Samples are prepared at different degrees of annealing and then subjected to athermal and quasi-static oscillatory deformations at various fixed amplitudes. The steady-state reached after several oscillations is fully determined by the initial preparation and the oscillation amplitude, as seen from stroboscopic stress and energy measurements. Under small oscillations, poorly annealed materials display shear-annealing, while ultra-stabilized materials are insensitive to them. Yet, beyond a critical oscillation amplitude, both kinds of materials display a discontinuous transition to the same mixed state composed of a fluid shear-band embedded in a marginal solid. Quantitative relations between uniform shear and the steady-state reached with this protocol are established. The transient regime characterizing the growth and the motion of the shear band is also studied.

Chen Liu 1 Ezequiel Ferrero 2 Eduardo Jagla 2 Kirsten Martens 3 Alberto Rosso 4 Laurent Talon 5
1 LPTENS – Laboratoire de Physique Théorique de l’ENS [École Normale Supérieure]
2 Centro Atómico Bariloche [Argentine]
3 LIPhy – Laboratoire Interdisciplinaire de Physique [Saint Martin d’Hères]
4 LPTMS – Laboratoire de Physique Théorique et Modèles Statistiques
5 FAST – Fluides, automatique, systèmes thermiques