Bruno Guelorget

Strong Improvements of Localized Surface Plasmon Resonance Sensitivity by Using Au/Ag Bimetallic Nanostructures Modified with Polydopamine Films

In the present work, the standard monometallic localized surface plasmon resonance (LSPR) biosensing sensitivity is highly improved when using a new system based on glass substrates modified with high-temperature annealed gold/silver bimetallic nanoparticles (Au/Ag bimetallic NPs) coated with polydopamine films before biomolecule specific immobilization. Thus, different zones of bimetallic NPs are spatially created onto a glass support thanks to a commercial transmission electron microscopy (TEM) grid marker in combination with two sequential evaporations of continuous films of gold (4 nm) and silver (2 nm) and followed by annealing at 500 °C for 8 h. By using the scanning electron microscopy (SEM), it is found that annealed Au/Ag bimetallic NPs have uniform size and shape distribution that exhibited a sharper well-defined LSPR resonant peak when compared with that of monometallic Au NPs and thereby contributing to an improved sensitivity in LSPR biosensor application. The controlled micropatterns consisting of bimetallic particles are used in the construction of LSPR biochips for high-throughput detection of different concentrations of a model antigen named bovine serum albumin (BSA) on a single glass sample, with a lower limit of detection of 0.01 ng/mL under the optimized conditions.

Extracting the plastic properties of metal materials from microindentation tests: Experimental comparison of recently published methods

Experimental verifications have been performed on three engineering metals to verify recent methods proposed for extracting stress–strain curves from indentation tests. Their sensitivity to data errors is evaluated. Finally, the factors that might cause the inaccuracy and instability of the proposed methods are discussed, providing information that can be useful for further improving these methods.

New Gold Nanoparticles Adhesion Process Opening the Way of Improved and Highly Sensitive Plasmonics Technologies

Gold nanostructures have very suitable physical properties for plasmonic applications but do not stick on glass substrates. One usually uses a chromium adhesion layer that gives good mechanical adhesion but quench the plasmon. We developed a new adhesion process that permits a covalent bonding between gold and glass thanks to an MPTMS molecular layer throughout nanolithography process. We demonstrate that this new adhesion layer allows an improvement of the optical properties of the gold nanoparticles as well as an essential improvement of their surface-enhanced Raman scattering performances.

Numerical simulation and experimental validation of the microindentation test applied to bulk elastoplastic materials

The main objective of this work is to compare numerically simulated load?indentation depth curves together with deformation and stress fields underneath a sharp indenter for a set of mystical materials. Firstly, a numerical simulation and experimental validation of the microindentation test applied to three different bulk elastoplastic materials (copper, stainless steel and pure aluminium) using two indenters (Berkovich and spherical) are presented. The simulation of these microindentation tests is carried out using the finite element large strain elastoplastic and contact models. The corresponding results are particularly aimed at addressing the following aspects: the influence of the indenter geometry on both the load?indentation depth curve and range of plastic strains involved in the test, the comparison of the 3D results for the sharp indenter with those of the 2D approximation, the capabilities of the modelling through experimental validation of the numerical predictions and, in addition, an assessment of the indentation size effect. Secondly, the numerical results of Berkovich indentation applied to a set of mystical materials are exhaustively discussed. Although it is effectively shown that these mystical materials exhibit indistinguishable load?penetration depth curves during the loading phase, an important aspect that has not been previously addressed is that some clear differences in their responses are obtained for the unloading stage. Finally, the deformation and stress contours at the maximum indentation force and after unloading are particularly analysed.

Determination of forming limits of sheet metals by speckle interferometry

Forming Limit Diagrams (FLD’s) can be defined by the criteria of either diffuse or localized necks. We used Electronic Speckle Pattern Interferometry (ESPI) in commercial 1100 aluminum sheet metals annealed at 400°C to determine the strains at which both types of neck started in uniaxial tension (U) and in quasi plane strain tension (PS) tests. In biaxial (B) loading we observed only the localized neck, but we were also able to detect a small defective spot at which fracture was incubated. The strains that produced the diffuse neck and the defective spot were approximately comparable to those predicted by Swift’s criterion for plastic instability. The difference between the FLD defined by a diffuse neck or by a defective spot leading to fracture and the one defined by a localized neck was found to be very noticeable in the U tests and less important, but still significant, in the PS and B tests. We found also that maximum load occurred at some point within the diffuse neck region and that afterwards the load carrying capacity was still substantial. We thus conclude that the decision on the criterion to use should be based on parts quality, safety and costs.

Evaluation of Damage and Plastic Properties by Microindentation and Inverse Method

Local determination of Young’s modulus and hardness is performed through microindentation on a longitudinal section of a semi-hard copper sheet, which was broken in a tensile machine. (i) the shorter the distance between the measured point and the fracture, the higher the hardness; (ii) local variations of Young’s modulus in the neighbouring of the fracture gives access to local damage variations. Using an inverse method, yield stress and strain hardening coefficient are evaluated in the localized neck.

Uncertainty evaluation of strain and strain rate measurements by ESPI during a tensile test

Localization of plastic strain has been studied by measuring strain and strain rate during tensile test1. Pictures were continuously recorded during the experiment and in-plane Electronic Speckle Pattern Interferometry (ESPI) pictures were generated afterwards, by subtracting couples of images. A square grid of 3 mm separation was drawn on the specimen to determine the true stress-true strain curve, while fringe patterns gave an access to relative displacements. Strain, average strain and strain rate were deduced. An uncertainty evaluation on these parameters was carried out applying the so-called law of propagation of uncertainties (ISO 07-0202).

Strain Localization Analysis by a Combination of the Espi With a Bulge Test

The problem of strain localization is important in sheet metal forming, as it determines the forming limit diagram of the material. To analyze this process, engineers use a variety of tests. One of them is the bulge test. In it, an initially flat specimen is placed between a matrix and a blank holder, and hydraulic pressure is applied on one of its surfaces. An approximately equi-biaxial strain loading path is obtained [1,2].

Analysis of localization of strains by ESPI, in equibiaxial loading (bulge test) of copper sheet metals

In this paper, an original application of ESPI in materials engineering has been described. The technique was used to analyze a bulge test in order to study strain localization by following the strain rate progress. Results show that ESPI allows detecting clearly the two stages of localization, namely, the diffuse and localized necks. Using this technique, forming limit diagrams can thus be established accurately.

Synchrotron Radiation and Instrumented Indentation Studies of Compressive Plastic Deformation in Zr-Based Bulk Metallic Glasses

X-ray diffraction using synchrotron radiation and instrumented indentation experiments has been carried out to trac k free volume changes and local reodering following plastic straining by indentation below the glass transition temperature Tg in the Zr60Ni10Cu20Al10, Zr 65 Ni 10 Cu 15 Al 10 and Zr 65 Ni 10 Cu 7.5 Al 7.5 Pd10 metallic glass forming systems. A quantitative diffraction line profiles modifications are observed during scanning strained and unstrained zones of the same specimen. We have found that the first diffractogram maximum intensity in transmission and the average inter-atomic spacing position are significantly affected in the overlapping shear bands around impressions. The surface uplift of the pile-up around indents has been assessed using a profilometer. It is shown that the inhomogeneous deformation results in an inhomogeneous distribution of free volume concentration. Substantial plastic deformation is determined form hysteresis loops recorded during nanoindentation experiments. While the ratio of the dissipated energy to total indentation work is quite similar for Zr-based metallic glasses, continuous stiffness measurements showed an appreciable difference in the evolution of the elastic modulus and hardness as function of penetration depth.