Plastic deformation of synthetic quartz nanopillars by nanoindentation for multi-scale and multi-level security artefact metrics

Individual authentication using artefact metrics has received increasing attention, as greater importance has been placed on the security of individual information. These artefact metrics must satisfy the requirements of individuality, measurement stability, durability, and clone resistance, in addition to possessing unique physical features. In this study, we proposed that nanostructures of synthetic quartz (SQ) deposited on an SQ plate may provide sophisticated artefact metrics if morphological changes could be intentionally introduced into the SQ nanostructures at certain positions. We fabricated SQ nanopillars using a mass-production method (ultraviolet nanoimprint lithography) and investigated their mechanical deformation using nanoindentation with a spheroid diamond tip through a loading and unloading cycle. The SQ nanopillars with an aspect ratio of 1 (i.e., diameters D of 100 and 200 nm with corresponding heights H of 100 and 200 nm, respectively) could be plastically deformed without collapsing within a specified pillar-array format at programmed positions. The plastically deformed SQ nanopillar arrays demonstrated multi-scale (sub-millimetre, micrometre, and nanometre) and multi-level (shape, area, diameter, and height) individuality authentication and clone resistance. Because SQ is physically and chemically stable and durable, individuality authentication can be a highly reliable tool on Earth and in space.

Plastic Deformation of Synthetic Quartz Nanopillars by Nanoindentation for Multi-scale and Multi-level Security Artefact Metrics

Individual authentication using artefact metrics has received increasing attention as a greater importance has been placed on the security of individual information. These artefact metrics must satisfy the requirements of individuality, measurement stability, durability, and clone resistance, in addition to possessing unique physical features. In this study, we proposed that nanostructures of synthetic quartz (SQ) deposited on an SQ plate may provide such sophisticated artefact metrics if morphological changes can be intentionally introduced into the SQ nanostructures at certain positions. We fabricated SQ nanopillars using a mass-production method (namely ultraviolet nanoimprint lithography) and investigated their mechanical deformation using nanoindentation with a spherical diamond tip through loading and unloading cycles. The SQ nanopillars with an aspect ratio of 1 (i.e. diameters D of 100 and 200 nm and heights H of 100 and 200 nm, respectively) could be plastically deformed without collapsing within a specified pillar-array format at programmed positions. The plastically deformed SQ nanopillar arrays demonstrated multi-scale (sub-millimetre, micrometre, and nanometre) and multi-level (shape, area, diameter, and height) individuality authentication and clone resistance capabilities. Because SQ is physically and chemically stable and durable, the individuality authentication will be a highly reliable media on Earth and in space.

Strength of dry and wet quartz in the low–temperature plasticity regime: insights from nanoindentation

<p>The strength of experimentally deformed natural and synthetic quartz is strongly affected by the intracrystalline water content. Water–related defects weaken quartz by either decreasing the resistance to dislocation motion (Peierls stress) or by enhancing the nucleation of dislocations, during what is commonly referred to as hydrolytic weakening. However, hydrolytic weakening has been observed predominantly in synthetic quartz grains, with water contents higher than 20–30 wt ppm H<sub>2</sub>O and at high-homologous temperatures, for which the activation of dislocation climb and recovery processes is enhanced.</p><p>In the low-temperature plasticity (LTP) regime, at low-homologous temperatures and high stress conditions, quartz plasticity is mainly controlled by dislocation glide. At these conditions, the possible effect of intracrystalline water on quartz strength is still a matter of debate.</p><p>In order to analyse the effects of intracrystalline water content on the plastic yield and hardness of quartz in the LTP regime, natural samples from recrystallized quartz domains of a granulite-facies migmatitic gneiss, presenting different water contents and microstructures, have been investigated through a series of spherical and Berkovich nanoindentation tests at room conditions. Nanoindentation tests have been integrated with measurements of intracrystalline water contents of the indented grains with secondary ion-mass spectrometry (SIMS), and with electron backscatter diffraction (EBSD) measurements of the crystallographic orientation of the indented grains.</p><p>Water content of indented quartz grains ranges between 2 and 104 wt ppm H<sub>2</sub>O. Samples and related nanoindentation tests were thus classified as either “dry” (DQ, for water contents < 20 wt ppm H<sub>2</sub>O) or “wet” (WQ, for water content > 20 wt ppm H<sub>2</sub>O). Spherical nanoindentation tests revealed comparable yield stresses (ranging between 3.5 and 8.8 GPa, depending on the crystal orientation) for DQ and WQ grains. In addition, significant strain hardening was observed in both DQ and WQ grains. Berkovich nanoindentation tests also resulted in comparable hardness (ranging from 8.0 to 13.5 GPa) in both DQ and WQ grains. The hardness also increases with indentation depth, which is consistent with the “size-effect” on mineral strength during LTP.</p><p>These results suggest that, for the investigated range of water contents, the yield strength and flow stress of quartz in the LTP regime is not affected by the intracrystalline water content of the indented grain. Both the dry and wet quartz experienced significant crystal plastic deformation prior to the nanoindentation tests, as evidenced by the occurrence of undulatory extinction, misorientation bands, subgrains, and recrystallized grains. This pre-indentation strain history may have had a major role in generating the dislocation density, which then controlled the yield stresses during low-temperature plasticity in our experiments. Hence, inherited strain history, crystallographic orientation, and grain size may play a more important role than water in controlling the strength of the continental crust at the brittle–ductile transition, where LTP is dominant and quartz is the most abundant phase.</p>

Experimental and numerical demonstrations for development of composite planar fabrics in fault zones

<p>Many experimental works have previously performed to understand frictional properties of various kinds of rocks and minerals by using friction apparatus at various orders of sliding velocities ranging from nm/s to m/s together with microscopic observation. However, friction experiments at wide range of velocities on a single type of rock or mineral have been rarely reported. Here we conducted friction experiments using powdered pyroclastic samples at velocities ranging from 0.0002 m/s to 1 m/s, 1.5–3.0 MPa normal stress, 10 m slip distance and dry and wet conditions. We also performed numerical simulation by using discrete element method (DEM) that focused on the changes of distances to adjacent particles (referred as CAP) and forces particles experiencing during frictional slip. At higher velocities, the sample showed relatively drastic decrease of friction coefficient and boundary-parallel Y shears. In contrast, R1 shears, oblique to shear direction, were observed in the samples at lower velocities. Numerical simulations at higher velocities of 0.1 and 1 m/s resulted in slip weakening and development of larger CAP lines parallel to boundary. At lower velocities, larger forces and CAPs were concentrated locally. These results could imply that the development of composite planar fabrics has a dependency on slip velocity. Now we are investigating the relationship using synthetic quartz powders, and will show the preliminary results of re-experiments, numerical simulations, and microscopic observations.</p>

Спектральные и амплитудно-временные характеристики излучения Черенкова при возбуждении прозрачных материалов пучком электронов

Interest in the study of the characteristics of the Vavilov-Cherenkov (VCR) radiation has increased in connection with the work on the creation of runaway electron (RE) detectors for TOKAMAK-type installations. This review presents the results of studies of the spectral, amplitude-temporal, and spatial characteristics of VCR, obtained mainly in recent years when transparent substances are excited by an electron flux with energies of tens to hundreds of keV. The VCR spectra in diamond (natural and synthetic), quartz glass, sapphire, leucosapphire are given, and the VCR registration in MgF2, Ga2O3 and other transparent samples is reported. A comparison of the spectra and amplitude-time characteristics of the VCR and pulsed cathodoluminescence (PCL) at various electron energies is carried out. For a number of samples, the VCR spectra were calculated taking into account the dispersion of the refractive index, as well as the energy distribution of the beam electrons and the decrease in the electron energy during their deceleration in the sample material. The emission spectrum of polymethyl methacrylate (PMMA), which is used as a material for radiators in Cherenkov detectors and optical fibers transmitting radiation in scintillation dosimeters, as well as a plastic base in organic scintillators, has been investigated.