Graphene effect on mechanical response of copper film

This research is investigated the effect of the presence of a single layer graphene on the development of the contact plasticity inside a copper underlying substrate. As a matter of fact, a film of copper (deposited on a Si wafer) is the substrate used in the CVD process for graphene production, there is no need for transferring graphene which avoids any possible artifacts. Moreover, the adhesion between CVD-grown graphene and the underlying Cu film is larger than transferred graphene, since during transfer, wrinkles and ripples may form, thus weakening the interaction between graphene and the substrate. The bare Cu-film in the same condition as to produce graphene except that no methane was introduced into the chamber (the last step in graphene production). Nanoindentation was performed on the Cu-film with and without graphene. Nanoindentation was performed on the bare Cu-film also Cu-film with graphene. The same process, as the growth of graphene on Cu-film, was performed on bare Cu just without introducing the methane flow at the last step. The analysis of the force-displacement curves indicates that the presence of graphene modifies the onset of plasticity which appears in the form of a burst which is called pop-in. The first pop-in occurs at lower loads and the pop-in lengths are smaller with graphene in comparison to the bare Cu-film. The magnitude of the effect of the presence of a graphene cap layer varies also with respect to the orientation of the indented Cu grain. In order to understand the root causes of these effects of the presence of graphene on the plastic flow, transmission electron microscopy is used to compare samples after nanoindentation in terms of dislocation structures. 3D discrete dislocation dynamics simulations are performed to analyze the long-range back stress that are generated by the dislocation arrangements with and without graphene. To further extend this research and investigate the known effect of hardening by graphene insertion into metals, another system has been addressed which involves the deposition of a Cu film on top of the graphene layer, lying itself on top of the annealed Cu substrate. The presence of graphene caused marked effect on the indentation response in this case, even larger than in the first configuration

Longitudinal liver stiffness assessment in patient with chronic hepatitis C undergoing antiviral therapy.

BACKGROUND/AIMS:Liver stiffness (LS) measurement by means of transient elastography (TE) is accurate to predict fibrosis stage. The effect of antiviral treatment and virologic response on LS was assessed and compared with untreated patients with chronic hepatitis C (CHC). METHODS: TE was performed at baseline, and at weeks 24, 48, and 72 in 515 patients with CHC. RESULTS: 323 treated (62.7%) and 192 untreated patients (37.3%) were assessed. LS experienced a significant decline in treated patients and remained stable in untreated patients at the end of study (P<0.0001). The decline was significant for patients with baseline LS ≥ 7.1 kPa (P<0.0001 and P 0.03, for LS ≥ 9.5 and ≥ 7.1 kPa vs lower values, respectively). Sustained virological responders and relapsers had a significant LS improvement whereas a trend was observed in nonresponders (mean percent change -16%, -10% and -2%, for SVR, RR and NR, respectively, P 0.03 for SVR vs NR). In multivariate analysis, high baseline LS (P<0.0001) and ALT levels, antiviral therapy and non-1 genotype were independent predictors of LS improvement. CONCLUSIONS: LS decreases during and after antiviral treatment in patients with CHC. The decrease is significant in sustained responders and relapsers (particularly in those with high baseline LS) and suggests an improvement in liver damage

From St. Petersburg to Krushchev\u27s Boot

Program for the first annual RISD Cabaret held in Memorial Hall. Design and layout by Justin Kerr.https://digitalcommons.risd.edu/liberalarts_cabaret_programs/1000/thumbnail.jp

A crack-on-chip fracture mechanics method for freestanding ultra-thin films from brittle to ductile down to 2D materials

The characterization, control, and enhancement of the cracking resistance of freestanding thin films and 2D materials are major concerns for flexible electronics, MEMS/NEMS devices, and structural or functional coatings. In particular, environmentally-assisted cracking phenomena affect the reliability of many thin films/2D materials-based systems as a result of among others the adsorption, absorption, and surface reaction mechanisms with oxygen or moisture. This is a complex subject, along with the determination of the fracture toughness that constitutes an important subject that is insufficiently studied mostly because of experimental issues. The objective of the present research is to present a new on-chip technique ables to extract the static fracture toughness and to study the environmentally-assisted crack growth in freestanding thin films, 2D materials, as well as multilayers built from a combination of these films and 2D materials. The present method relies on a residual-stress-based-on-chip concept taking advantage of MEMS-based fabrication principles. The test configuration consists of a notched specimen attached to two long actuator beams involving tensile internal stress. Upon release, the relaxation of the residual stress leads to the deformation of the specimen. A crack initiates at the notch tip, propagates, and finally arrests. A data reduction scheme based on accurate finite element simulation of the test structures is used to determine the static fracture toughness. The method also provides the variation of the crack growth rate (da/dt) as a function of the stress intensity factor (K) under different temperature conditions and humidity levels. Several materials were tested over the last 4 years with this method varying from nominally brittle materials like SiN, SiO2, Al2O3 to ductile materials such as Cu, Ni and Al/Al2O3 multilayers revealing several interesting effects that will be presented. 2D materials like graphene (Gr) and heterostructures of graphene and hexagonal boron nitride (h-BN) were also successfully studied providing probably the first rigorous fracture mechanics statistically representative data on these materials