Search results for "etching"
showing 10 items of 186 documents
Evaluation of accelerated weathering effects on the surface of two coloured sicilian building stones
2007
The dark grey Breccia di Billiemi and the Ammonitico Rosso of Piana degli Albanesi, widely employed outdoor and indoor in monuments in Sicily, undergo significant alteration processes, affecting not only the chromatic aspect but also the state of aggregation. In a previous paper [1] the effects of accelerated weathering in laboratory was compared with natural ageing in the urban environment. The study included the description of lithofacies, the characterisation by means of petrographic and physical-chemical techniques and accelerated weathering experiments on both lithotypes.
Quantum size effects in solitary wires of bismuth
2007
We have performed four-probe electrical transport measurements on solitary highly crystalline wires of semimetallic bismuth with aspect ratios up to 60 at room and at cryogenic temperatures. By proper choice of the substrate material and the film deposition parameters, lithographic wires with lateral dimensions of down to one single grain, $\sim 250$ nm, were fabricated. The electrical resistance of each wire was measured against its thickness through successive reactive ion etching of the self-same wire. Quantum size effects revealed themselves as regular oscillations in the electrical resistance. Some evidence for the semimetal-to-semiconductor phase transition has been detected. The meas…
Silicon Nanocrystals Produced by Nanosecond Laser Ablation in an Organic Liquid
2011
Small (3−5 nm in diameter following HRTEM images) Si nanocrystals were produced in a two-stage process including (1) nanosecond laser ablation of a Si target in an organic liquid (chloroform) that results in formation of big composite polycrystalline particles (about 20−100 nm average diameter) and (2) ultrasonic post-treatment of Si nanoparticles in the presence of HF. The post-treatment is responsible for disintegration of the composite Si particles, release of small individual nanocrystals, and reduction of their size due to HF-induced etching of Si oxide. The downshift and broadening of the ∼520 cm−1 Raman phonon band of the small Si nanocrystals with respect to the bulk Si Raman band i…
Optical properties of ZnO deposited by atomic layer deposition (ALD) on Si nanowires
2018
International audience; In this work, we report proof-of-concept results on the synthesis of Si core/ ZnO shell nanowires (SiNWs/ZnO) by combining nanosphere lithography (NSL), metal assisted chemical etching (MACE) and atomic layer deposition (ALD). The structural properties of the SiNWs/ZnO nanostructures prepared were investigated by X-ray diffraction, Raman spectroscopy, scanning and transmission electron microscopies. The X-ray diffraction analysis revealed that all samples have a hexagonal wurtzite structure. The grain sizes are found to be in the range of 7-14 nm. The optical properties of the samples were investigated using reflectance and photoluminescence spectroscopy. The study o…
Blue lasing at room temperature in high quality factor GaN/AlInN microdisks with InGaN quantum wells
2007
The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at similar to 420 nm is achieved under pulsed excitation at room temperature for a peak power density of 400 kW/cm(2). The lasing emission linewidth is down to 0.033 nm.
Vortex diffusion and vortex-line hysteresis in radial quantum turbulence
2014
Abstract We study the influence of vortex diffusion on the evolution of inhomogeneous quantized vortex tangles. A simple hydrodynamical model to describe inhomogeneous counterflow superfluid turbulence is used. As an illustration, we obtain solutions for these effects in radial counterflow of helium II between two concentric cylinders at different temperatures. The vortex diffusion from the inner hotter cylinder to the outer colder cylinder increases the vortex length density everywhere as compared with the non-diffusive situation. The possibility of hysteresis in the vortex line density under cyclical variations of the heat flow is explored.
Troubled cosmic flows: turbulence, enstrophy and helicity from the assembly history of the intracluster medium
2021
Both simulations and observations have shown that turbulence is a pervasive phenomenon in cosmic scenarios, yet it is particularly difficult to model numerically due to its intrinsically multiscale character which demands high resolutions. Additionally, turbulence is tightly connected to the dynamical state and the formation history of galaxies and galaxy clusters, producing a diverse phenomenlogy which requires large samples of such structures to attain robust conclusions. In this work, we use an adaptive mesh refinement (AMR) cosmological simulation to explore the generation and dissipation of turbulence in galaxy clusters, in connection to its assembly history. We find that major mergers…
Strong etching formulation (time and rate) for PADC with deep depth bulk etch rate study
2021
Abstract Aqueous NaOH with ethanol (strong) etchant is widely used. It shortens etching time effectively compared to normal etching conditions (6.25N NaOH at 70 °C). Two equations have been proposed to calculate the etching time with NaOH molarity and ethanol volume. Another two empirical equations were introduced for estimating the bulk etch rates of PADC etched in strong etchant. Up to now, there were no such equations available in the literature that can predict etching time and V b of PADC with etchant molarity and ethanol volumes. The proposed equations were compared to fundamental V b models stemming from literature. Fast etching enables the follow-up of bulk etch rate variation versu…
Surface processing of TlBr single crystals used for radiation detectors
2009
Abstract The processing method for obtaining the high-quality surfaces of TlBr single crystals, providing removal of a mechanically destroyed surface layer by chemical etching, is developed. The crystals grown from the melt of purified materials by the Bridgman–Stockbarger method were used for the experiments. The Vickers microhardness as a structure-sensitive technique was used in a study of the crystal quality and properties of the plastically deformed surface layer created by cutting. It was shown that even under highly accurate conditions of cutting, the depth of the work-hardened surface layer with a high density of dislocations, vacancies and other structural defects exceeds 20 μm. Th…
Surface structure determination by SEM image processing and electrochemical impedance of graphite+polyethylene composite electrodes
2004
Abstract The electrochemical impedance behaviour of heterogeneous or/and rough electrodes has usually been associated with some geometrical parameters of the surface structure or to a statistical description of the surface properties. An experimental method for sample preparation of graphite + polyethylene composite electrodes based on plasma etching is proposed. After plasma etching, the statistical properties of the electrode, such as the graphite particle size distribution and fractional coverage are measured from scanning electron microscopy pictures using image processing software. The statistical information obtained for the surface is combined with impedance equations of independent …