Synthèse de NP anisotropes Au, Pd / Au et Pd par évaporation oblique sur du verre: applications de détection et de résonance Plasmon

International audienceGold metal nanoparticles (NPs) display localised surface plasmon resonances (LSPR) in the visible to close infra-red range. The wavelength position of the LSPR depends strongly on the shape of the NPs. Typically, elongated NPs such as nanorods display a high (low) wavelength LSPR for polarisation of light along the large (short) axis. This property opens the path to elaborate dichroic films based on plasmonic metal NPs.In order to obtain such dichroic samples, multiple methods could be used. Should it be a bottom-up method through the chemical synthesis of nanoparticles [1], which allows one to greatly control their shape and, consequently, their LSPR, though makes it difficult to organise them on a surface or in a matrix, as it has been shown in our group [2]. An alternative is the top-down method using primarily lithographic techniques, which allow one to get a very controlled pattern, though limiting the minimum size of a feature to around 100nm [3,4]; or using evaporation onto a prior nanostructured substrate [5,6] In this poster, another method was chosen known as oblique angle deposition. It consists to evaporate metals at a grazing angle to a non-structured substrate. As long as the metal does not wet the substrate e.g. gold on glass, anisotropic nano-islands form with a preferential orientation, which leads to a global optical anisotropy. Although this method does not produce as defined features as the methods mentioned above, it has the advantage of being very simple and easy to put in place. Furthermore, in this way very small particles can be synthesised, which can have applications for chemical reactivity or catalysis issues. The shape of the NPs and the optical anisotropy can be tuned by varying the angle of deposition as well as the amount evaporated. The morphology of the NPs was analysed using scanning tunnelling microscopy (SEM) and compared to results obtained by atomic force microscopy (AFM) which is limited due to the effect of convolution of the tip. The samples obtained in such way display a strong dichroism, which can be tuned by varying the elaboration parameters. It was measured by transmission spectroscopy and by reflectance anisotropy spectroscopy (RAS). This is illustrated in Fig.1, where the absorption of a gold film is drawn for two perpendicular polarisations of light

Optical properties of silicene, Si/Ag(111) and Si/Ag(110)

We present a state-of-the-art study of the optical properties of free-standing silicene and of single-layer Si one- and two-dimensional (1D and 2D) nanostructures supported on Ag(110) and Ag(111) substrates. Ab initio simulations of reflectance anisotropy spectroscopy (RAS) and surface differential reflectivity spectroscopy (SDRS) applied to the clean Ag surface and Si/Ag interfaces are compared with new measurements. For Si/Ag(110), we confirm a pentagonal nanoribbon geometry, strongly bonded to the substrate, and rule out competing zigzag chain and silicenelike models. For Si/Ag(111), we reproduce the main experimental features and isolate the optical signal of the epitaxial silicene overlayer. The absorption spectrum of a silicene sheet computed including excitonic and local field effects is found to be quite similar to that calculated within an independent particle approximation and shows strong modifications when adsorbed on a Ag substrate. Important details of the computational approach are examined and the origins of the RAS and SDRS signals are explained in terms of the interface and substrate response functions. Our study does not find any evidence for Si adlayers that retain the properties of freestanding silicene

Reflectivity Anisotropy Spectra of Cu- and Ag- (110) surfaces from {\it ab initio} theory

We are able to disentagle the effects of the intraband and interband parts of the bulk dielectric function on the bare dielectric anisotropy of the surface. We show how the position, sign and amplitude of the structures observed in such spectra depend on the above quantities. The lineshape of all the calculated structures agree very well with the ones observed experimentally for samples treated by suitable surface cleaning. In particular, we reproduce the observed single peak structure of Ag at high energy, found to represent a state of the clean surface different from the one giving the originally observed double peak structure. This results is not reproduced by the 'local field' model.Comment: 4 pages, 3 figures. submitted to Phys. Rev. Let

Anisotropic optical response of the diamond (111)-2x1 surface

The optical properties of the 2$\times$1 reconstruction of the diamond (111) surface are investigated. The electronic structure and optical properties of the surface are studied using a microscopic tight-binding approach. We calculate the dielectric response describing the surface region and investigate the origin of the electronic transitions involving surface and bulk states. A large anisotropy in the surface dielectric response appears as a consequence of the asymmetric reconstruction on the surface plane, which gives rise to the zigzag Pandey chains. The results are presented in terms of the reflectance anisotropy and electron energy loss spectra. While our results are in good agreement with available experimental data, additional experiments are proposed in order to unambiguously determine the surface electronic structure of this interesting surface.Comment: REVTEX manuscript with 6 postscript figures, all included in uu file. Also available at http://www.phy.ohiou.edu/~ulloa/ulloa.html Submitted to Phys. Rev.

The China miracle in a technological and socio-political framework—The role of institutions

China’s economy has grown at an average annual rate of around 9.5% in the past four decades, which is often hailed as the China Miracle. This paper proposes a new theoretical model to analyse the causes of China’s phenomenal growth in a technological and socio-political framework. In our new framework, the contemporary technology (T) determines what an economy can achieve; the objective (O) of the society has a fundamental impact on its economic growth; the performance (P) in implementing the social objective largely determines the growth rate of the economy; and the stability (S) of the society determines the sustainability of the economic growth. China’s institutions have played key roles in the TOPS framework to initiate and sustain China’s rapid growth in the past four decades. Socio-political changes caused by economic growth might affect the capacity of these institutions to promote economic growth in future

Crowds in or crowds out? The effect of foreign direct investment on domestic investment in Chinese cities

This study investigates the empirical relationship between foreign direct investment (FDI) and domestic investment (DI) in China using a comprehensive city-level panel over the period from 2003 to 2011. System-generalized method-of-moment estimation reveals mixed results. At the national level, FDI neither crowds in nor crowds out DI, indicating a neutral FDI–DI nexus. However, when the full sample is segmented by geographical topology, a positive and significant FDI–DI nexus can be found in eastern and, to a lesser extent, central cities. A negative, although insignificant, association is reported among western cities. Further, the empirical nexus is conditional on several local absorptive capacities including human capital, financial development, and institutional quality. These findings suggest that a region-based FDI strategy in general and local governments should strengthen their absorptive capacities to fully internalize FDI spillovers

Regional development gaps in Argentina: A multidimensional approach to identify the location of policy priorities

Spatial inequalities within Latin American countries have historically attracted the interest ofacademics, policy-makers, and international agencies. This article aims to provide amultidimensional diagnosis of provincial development gaps in Argentina, in order to identifythe location of policy priorities. Therefore, we built a large database, which covers sevendevelopment dimensions, and applied multivariate analysis techniques to overcome someanalytical limitations of previous studies. Results show the stability of provincial developmentgaps between 2003 and 2013 and some heterogeneity within geographic regions. Instead,cluster analysis offers a better classification of Argentine provinces according to theirdevelopment gaps, which can help the government to prioritize the places wheredevelopment policies are strategic.Fil: Niembro, Andrés Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Río Negro; ArgentinaFil: Sarmiento, Jesica Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Río Negro; Argentin