Numerical Analysis of a Tubular Phononic Crystal Sensor

International audienceWe present a theoretical investigation of the dispersion and transmission properties of a tubular phononic crystal for sensing application. We show the existence of modes confined in a cavity with displacement field spreading over both the solid and fluid parts. Therefore, the frequency of the transmission peak associated to this mode should be sensitive to the sound velocity of the fluid filling the tube

Directional elastic wave propagation in high-aspect-ratio photoresist gratings: liquid infiltration and aging

Determination of the mechanical properties of nanostructured soft materials and their composites in a quantitative manner is of great importance to improve the fidelity in their fabrication and to enable the subsequent reliable utility. Here, we report on the characterization of the elastic and photoelastic parameters of a periodic array of nanowalls (grating) by the non-invasive Brillouin light scattering technique and finite element calculations. The resolved elastic vibrational modes in high and low aspect ratio nanowalls reveal quantitative and qualitative differences related to the two-beam interference lithography fabrication and subsequent aging under ambient conditions. The phononic properties, namely the dispersion relations, can be drastically altered by changing the surrounding material of the nanowalls. Here we demonstrate that liquid infiltration turns the phononic function from a single-direction phonon-guiding to an anisotropic propagation along the two orthogonal directions. The susceptibility of the phononic behavior to the infiltrating liquid can be of unusual benefits, such as sensing and alteration of the materials under confinement.E. A. R. and G. F. thank D. Schneider for his support in the initial stage of the BLS study and acknowledge the support from ERC SuPro 340391 and ERC SmartPhon 694977, respectively. S. Y. acknowledges the support by the National Science Foundation (NSF), Grant #CMMI-0900468. B. G. and C. M. S. T. gratefully acknowledge support from the EC project MERGING (GA nr. 309150), the Spanish project PHENTOM (FIS2015-70862P) and the Severo Ochoa Program (MINECO, Grant SEV-2013-0295). B. G. acknowledges the Alexander von Humboldt foundation for support.Peer Reviewe

Imprinting isolated single iron atoms onto mesoporous silica by templating with metallosurfactants

International audienceHypothesisOne of the main drawbacks of metal-supported materials, traditionally prepared by the impregnation of metal salts onto pre-synthesized porous supports, is the formation of large and unevenly dispersed particles. Generally, the larger are the particles, the lower is the number of catalytic sites. Maximum atom exposure can be reached within single-atom materials, which appear therefore as the next generation of porous catalysts.ExperimentsHerein, we designed single iron atom-supported silica materials through sol-gel hydrothermal treatment using mixtures of a non-ionic surfactant (Pluronic P123) and a metallosurfactant (cetyltrimethylammoniumtrichloromonobromoferrate, CTAF) as porogens. The ratio between the Pluronic P123 and the CTAF enables to control the silica structural and textural properties. More importantly, CTAF acts as an iron source, which amount could be simply tuned by varying the non-ionic/metallo surfactants molar ratio.FindingsThe fine distribution of iron atoms onto the silica mesopores results from the iron distribution within the mixed micelles, which serve as templates for the polymerization of the silica matrix. Several characterization methods were used to determine the structural and textural properties of the silica material (XRD, N2 sorption isotherms and TEM) and the homogeneous distribution and lack of clustering of iron atoms in the resulting materials (elemental analysis, magnetic measurements, pair distribution function (PDF), MAS-NMR and TEM mapping). The oxidation and spin state of single-iron atoms determined from their magnetic properties were confirmed by DFT calculations. This strategy might find straightforward applications in preparing versatile single atom catalysts, with improved efficiency compared to nanosized ones

Spin density in YTiO 3 : I. Joint refinement of polarized neutron diffraction and magnetic x-ray diffraction data leading to insights into orbital ordering

International audienceOrbital ordering below 30 K was previously observed in the ferromagnetic YTiO 3 compound both by polarized neutron diffraction (PND) and x-ray magnetic diffraction (XMD). In this paper we report a procedure for the joint refinement of a unique spin-density model based on both PND and XMD data. The distribution of the unpaired 3d electron of titanium is clearly seen on the magnetization density reconstructed by the maximum entropy method from the PND data collection at 5 K. The Ti 3+ 3d orbital populations obtained by joint model refinement are discussed in terms of the orbital ordering scheme. Small but significant magnetic moments on apical oxygen O 1 and yttrium atoms are found. The agreement between experimental and theoretical spin densities obtained using density functional theory is discussed

Spin density in YTiO 3 : II. Momentum-space representation of electron spin density supported by position-space results

International audienceUnpaired electrons in YTiO 3 ferromagnetic crystal (below 30 K) were studied by polarized neutron diffraction (PND) and incoherent x-ray magnetic Compton scattering (MCS). These experiments provide both position and momentum representations of the electrons at the origin of the magnetic behavior, mostly those in the t 2g state of Ti atoms. A two-dimensional reconstruction was conducted from experimental and theoretical directional magnetic Compton profiles to obtain the two-dimensional magnetic electron momentum density. A " superposition " method is proposed to examine the coherence between results for position and momentum spaces, respectively. This model-free approach allows a straightforward cross-checking of PND and MCS experiments. An " isolated Ti model " is proposed to emphasize the role played by O 1 in the ferromagnetic coupling between Ti and its neighboring atoms