Determination of the optical constants of the SiSiO2 system by the method of the angular modulation of reflectance

The sensitivity of the method of the angular modulation of reflectance, recently developed by the authors, in the determination of the optical constants of the SiSiO₂ system is analyzed. This system, which can be approximated to a TFAS system in the visible region, is considered in the limit of small relative thicknesses $\text{d}{}_{\mathrm{<mtext>ox</mtext>}}\text{λ}$. The method proved sufficiently accurate to give the refractive index of the substrate n_s as well as the parameters of the oxide n_ox and d_ox with an accuracy of 2 % down to $\text{d}{}_{\mathrm{<mtext>ox</mtext>}}\text{= 200}\text{A}\text{?}$. The overall accuracy increases at larger oxide thicknesses.     

Large area extreme-UV lithography of graphene oxide via spatially resolved photoreduction

The ability to pattern graphene over large areas with nanometer resolution is the current request for nanodevice fabrication at the industrial scale. Existing methods do not match high throughput with nanometer resolution. We propose a high-throughput resistless extreme-UV (EUV) photolithographic approach operating with sub-micrometer resolution on large area (~10 mm(2)) graphene oxide (GO) films via spatially resolved photoreduction. The efficiency of EUV photoreduction is tested with 46.9 nm coherent light produced by a table top capillary discharge plasma source. Irradiated samples are studied by X-ray photoemission spectroscopy (XPS) and micro-Raman Spectroscopy (μRS). XPS data show that 200 mJ/cm(2) EUV dose produces, onto pristine GO, a 6% increase of sp(2) carbon bonds and a 20% decrease of C-O bonds. μRS data demonstrate a photoreduction efficiency 2 orders of magnitude higher than the one reported in the literature for UV-assisted photoreduction. GO patterning is obtained modulating the EUV dose with a Lloyd's interferometer. The lithographic features consist of GO stripes with modulated reduction degree. Such modulation is investigated and demonstrated by μRS on patterns with 2 μm periodicity.     

Fracture surfaces as multiscaling graphs

Fracture paths in quasi-two-dimensional (2D) media (e.g., thin layers of materials or paper) are analyzed as self-affine graphs h(x) of height h as a function of length x. We show that these are multiscaling, in the sense that nth order moments of the height fluctuations across any distance l scale with a characteristic exponent that depends nonlinearly on the order of the moment. Having demonstrated this, one rules out a widely held conjecture that fracture in 2D belongs to the universality class of directed polymers in random media. In fact, 2D fracture does not belong to any of the known kinetic roughening models. The presence of multiscaling offers a stringent test for any theoretical model; we show that a recently introduced model of quasistatic fracture passes this test.     

Evidence for a crossover in the frequency dependence of the acoustic attenuation in vitreous silica

We report measurements of the sound attenuation coefficient in vitreous silica, for sound waves of wavelength between 50 and 80 nm, performed with the new inelastic UV light scattering technique. These data indicate that in silica glass a crossover between a temperature-dependent (at low frequency) and a temperature-independent (at high frequency) acoustic attenuation mechanism occurs at Q approximately equal to 0.15 nm(-1). The absence of any signature in the static structure factor at this Q value suggests that the observed crossover should be associated with local elastic constant fluctuations.