197 research outputs found
Detection of second-order nonlinear optical magnetization by mapping normalized Stokes parameters
No full textA measurable magnetic (nonlocal) contribution to the second harmonic generation (SHG) of nonmagnetic materials is an intriguing issue related to chiral materials, such as biomolecules. Here we report the detection of an intensity-dependent optically induced magnetization of a chiral bacteriorhodopsin film under femtosecond pulse excitation (830 nm) and far from the material's resonance. The analysis of the pump intensity-dependent noncollinear SHG signal, by means of the polarization map of normalized Stokes parameters, allows one to improve the detection of the nonlinear optical magnetization M (2 omega) contribution to the SHG signal. (c) 2013 Optical Society of Americ
Cr, Sn and Ag/SnO2 interface formation studied by synchrotron radiation induced UPS
No full textThe room temperature (RT) formation of the interface between metals (Cr, Sn, Ag) and the SnO2 surface was studied by Synchrotron Radiation induced UPS. The Sn4d core level and the Valence Band were monitored as a function of metal growth starting from submonolayer regime. At low monolayer coverages a redox reaction with different rate and evolution depending on metal reactivity, arises between the Cr and Sn atoms and the SnO2 surface, oxidizing the overlayer and reducing the Sn cation at the interface. Deposition of less reactive Ag film leaves the stoichiometry of the substrate unchanged. However, in this case as well as for Cr, at high metal coverage the metallic tin segregation is observed
Surface effects for electron cloud
No full textThe ability of a low secondary electron yield coating to mitigate detrimental electron cloud effects potentially affecting accelerators’ performances has been convincingly validated. The interference of such coatings with other properties required to accelerator constructive materials (i.e. vacuum compatibility, magnetic permeability, high surface conductivity, etc.) is of great concern and has recently attracted a lot of interest and studies. For instance, the severe impedance budget constraint requires the highest conductivity in the surface layers within the skin depth (typically some μm) characteristic of the e.m. interaction. It is therefore of uttermost importance to define the minimum thickness one overlayer should have in order to be an eective electron cloud mitigator and minimize its impact to surface conductivity.To this purpose, XPS and secondary electron spectroscopy have been simultaneously applied to the prototypical system formed by increasing coverages of amorphous Carbon (a-C) deposited on atomically clean Cu. XPS has been successfully used to qualify and quantify the a-C thickness, rendering possible a detailed coverage dependent study. A significantly thin a-C layer, of about 5 to 7 nm, is surprisingly enough to lower the secondary emission properties of the whole system below 1. This observation opens up the possibility to develop, on industrial scale, thin enough electron cloud mitigators that will not affect impedance issues
Minimum thickness of carbon coating for multipacting suppression
No full textWe performed a combined secondary electron yield and x-ray photoelectron spectroscopy study on a prototypical system formed by increasing coverages of amorphous carbon (a-C) deposited on atomically clean Cu. A remarkably thin a-C layer, of about 6–8 nm, is surprisingly enough to lower below 1 the secondary emission yield of the whole system. This feature qualifies such low thickness coatings as a optimal multipacting suppressor that will not significantly affect impedance issues. The concomitant reduction of surface conductivity observed after antimultipacting coating is, in fact, a major drawback, reducing its applicability in many research fields. The consequences of this observation are discussed mainly for a-C coating applications to mitigate detrimental multipacting effects in radio-frequency devices and accelerators, but are expected to be of interest for other research fields and to hold for other conductive substrates and overlayers
Infrared radiation characterization of several stainless steel textiles in the 3.5-5.1 μm infrared range
No full textThe infrared emission of four stainless steel textiles was characterized in the mid-infrared range, i.e. 3.6÷5.1 μm, by observing their temperature evolution under heating regime. The investigated steel textiles differ by the type of fabrics, resulting in some variation in the infrared emission. Standard test method for measuring emissivity was applied to the set of metallic textiles using infrared imaging radiometers as well as a reference surface of known high emissivity. The obtained experimental results allowed to retrieve the infrared emissivity at different applied temperatures. The experimental data were interpreted by means of Plank's theory of black-body radiation. Finally, all the investigated textiles appear to be suitable for thermal shielding applications
Metamaterials approach for infrared radiation manipulation in dispersed nanowires systems
No full textIn recent years, much effort has been expended upon managing and tuning the radiative properties of structures and material surfaces in the infrared (IR) wavelength range for several applications, such as thermal radiation control as well as IR sensing. Metamaterials are artificial electromagnetic materials, composed by periodically or randomly arranged, subwavelength elements. Since the typical dimensions of the constitutive elements of a metamaterials are smaller than the interaction wavelengths, they behave as an effective medium and may give rise to peculiar electromagnetic properties, such as negative refraction, superlensing and cloaking, to name some. In the present work we review the use of metamaterials composed by dispersed nanowires systems into a dielectric matrix, for managing and tuning of the infrared emission. The main homogenization techniques effective medium approach are presented and discussed, along with several parameters such as filling factor, inclusions orientations and shape. We finally show some examples with different materials (metallic or polar nanowires) and many configurations in order to get spectral and/or spatial modulation of the resulting infrared emissivity. Taming and tuning the infrared radiation of a metamaterial allows the design of versatile optical elements as basic elements for further developments of infrared filters, thermal diodes and thermal logic gates
Interface formation between C60 and diethynyl-Zn-porphyrinato investigated by SR-induced photoelectron and near-edge X-ray absorption (NEXAFS) spectroscopies
No full textInterface formation between C60 and diethynyl-Zn-Porphyrin investigated by SR-induced photoelectron and near-edge X-ray absorption (NEXAFS) spectroscopies
No full textIn-plane thermal diffusivity measurements of polyethersulfone woven textiles by infrared thermography
No full textLock-in thermography was applied to the measurement of the in-plane thermal diffusivity of three polyethersulfone (PES) textiles characterized by different weaving pattern as well as different mass density of interlacing fibers. The experimental results showed that the in-plane thermal diffusivity in each direction decreased with the increase of the fibers’ linear mass density, thus leading to an anisotropic behavior of the thermal diffusivity in the specimen where PES fibers with different density were interlaced. A new theoretical model for the study of the heat diffusion in textiles was specifically developed and, thereafter, employed for the analysis of the experimental results. As such, our textile model approach, shedding light on the role of different textile and fibers parameters on the resulting thermal diffusivity, paves the way for the development and design of textiles with tailored thermal behavior
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