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We report an extensive experimental study of a detachment front dynamics instability, appearing at microscopic scales during the peeling of adhesive tapes. The amplitude of this instability scales with its period as $A_{\text{mss}} \propto T_{\text{mss}}^{1/3}$, with a pre-factor evolving slightly with the peel angle $\theta$, and increasing systematically with the bending modulus $B$ of the tape backing. Establishing a local energy budget of the detachment process during one period of this micro-instability, our theoretical model shows that the elastic bending energy stored in the portion of tape to be peeled is converted into kinetic energy, providing a quantitative description of the experimental scaling law., Comment: to be published in Phys. Rev. Lett

Prompted by intriguing events observed in certain particle-physics searches for rare events, we study light and acoustic emission simultaneously in some inorganic scintillators subject to mechanical stress. We observe mechanoluminescence in ${Bi}_4{Ge}_{3}{O}_{12}$, ${CdWO}_{4}$ and ${ZnWO}_{4}$, in various mechanical configurations at room temperature and ambient pressure. We analyze how the light emission is correlated to acoustic emission during fracture. For ${Bi}_4{Ge}_{3}{O}_{12}$, we set a lower bound on the energy of the emitted light, and deduce that the fraction of elastic energy converted to light is at least $3 \times 10^{-5}$.

We report the observation and characterization of field emission current from individual single- and few-layer graphene flakes laid on a flat SiO2/Si substrate. Measurements were performed in a scanning electron microscope chamber equipped with nanoprobes, used as electrodes to realize local measurements of the field emission current. We achieved field emission currents up to 1 {\mu}A from the flat part of graphene flakes at applied fields of few hundred V/{\mu}m. We found that emission process is stable over a period of several hours and that it is well described by a Fowler-Nordheim model for currents over 5 orders of magnitude.

Electron field emission characteristics of individual multiwalled carbon nanotubes have been investigated by a piezoelectric nanomanipulation system operating inside a scanning electron microscopy chamber. The experimental setup ensures a high control capability on the geometric parameters of the field emission system (CNT length, diameter and anode-cathode distance). For several multiwalled carbon nanotubes, reproducible and quite stable emission current behaviour has been obtained with a dependence on the applied voltage well described by a series resistance modified Fowler-Nordheim model. A turn-on field of about 30 V/um and a field enhancement factor of around 100 at a cathode-anode distance of the order of 1 um have been evaluated. Finally, the effect of selective electron beam irradiation on the nanotube field emission capabilities has been extensively investigated., Comment: 16 pages, 5 figures

Metallic cantilever in high vacuum atomic force microscope has been used as anode for field emission experiments from densely packed vertically aligned multi-walled carbon nanotubes. The high spatial resolution provided by the scanning probe technique allowed precise setting of the tip-sample distance in the submicron region. The dimension of the probe (curvature radius below 50nm) allowed to measure current contribution from sample areas smaller than 1um^2. The study of long-term stability evidenced that on these small areas the field emission current remains stable (within 10% fluctuations) several hours (at least up to 72 hours) at current intensities between 10-5A and 10-8A. Improvement of the current stability has been observed after performing long-time Joule heating conditioning to completely remove possible adsorbates on the nanotubes., Comment: 15 pages, 7 figures

We report on the application of Atomic Force Microscopy (AFM) for studying the Field Emission (FE) properties of a dense array of long and vertically quasi-aligned multi-walled carbon nanotubes grown by catalytic Chemical Vapor Deposition on a silicon substrate. The use of nanometric probes enables local field emission measurements allowing investigation of effects non detectable with a conventional parallel plate setup, where the emission current is averaged on a large sample area. The micrometric inter-electrode distance let achieve high electric fields with a modest voltage source. Those features allowed us to characterize field emission for macroscopic electric fields up to 250 V/$\mu$m and attain current densities larger than 10$^5$ A/cm$^2$. FE behaviour is analyzed in the framework of the Fowler-Nordheim theory. A field enhancement factor $\gamma \approx$ 40-50 and a turn-on field $E_{turn-on} \sim$15 V/$\mu$m at an inter-electrode distance of 1 $\mu$m are estimated. Current saturation observed at high voltages in the I-V characteristics is explained in terms of a series resistance of the order of M$\Omega$. Additional effects as electrical conditioning, CNT degradation, response to laser irradiation and time stability are investigated and discussed.

We study the roughness of a crack interface in a sheet of paper. We distinguish between slow (sub-critical) and fast crack growth regimes. We show that the fracture roughness is different in the two regimes using a new method based on a multifractal formalism recently developed in the turbulence literature. Deviations from monofractality also appear to be different in both regimes.

Slow crack growth in a model of homogenous brittle elastic material is described as a thermal activation process where stress fluctuations allow to overcome a breaking threshold through a series of irreversible steps. We study the case of a single crack in a flat sheet for which analytical predictions can be made, and compare them with results from the equivalent problem of a 2D spring network. Good statistical agreement is obtained for the crack growth profile and final rupture time. The specific scaling of the energy barrier with stress intensity factor appears as a consequence of irreversibility. In addition, the model brings out a characteristic growth length whose physical meaning could be tested experimentally., Comment: To be published in : Europhysics Letters

Direct comparison of scanning tunneling microscopy and high resolution core level photo-emission experiments provides a rationale for the mechanism of formation of a two dimensional (2D) binary alloy (1/3 mono-layer (ML) Sn(1- x)Six/Si(111)-\sqrt3X\sqrt3R30). In contrast with recent theoretical predictions, the pure metal surface (x=0) results partitioned into two classes (2/9 ML and 1/9 ML) of ad-atoms occupying non-equivalent T4 sites. During the formation of the alloy, Si ad-atoms preferably occupy the majority type adsorption site. This peculiar substitution mechanism leads to a mutual arrangement of ad-atoms which is not random even at room temperature, but shows the typical short range order universally observed in 2D and quasi 2D binary alloys, Comment: pdf only- 5 pages 3 figures. submitted to Phys. Rev. Lett