Electrically-functionalised nanoindenter dedicated to local capacitive measurements: experimental set-up and data-processing procedure for quantitative analysis

International audienceIn this work, we report the experimental development and the application of a new characterisation tool combining mechanical testing and dielectric characterisation. The experimental setup is essentially a nanoindentation head functionalised for capacitive measurements. First the experimental procedure for the characterisation of dielectric thin films is given: detailed setup description, procedure for the capacitance-vs-voltage (C-V) measurements, stray capacitance,... Secondly, a complete data-processing method is proposed to perform the quantitative analysis of capacitance data. To this end, a fully analytical model has been developed, able to relate the C-V curves to the system characteristics (set-up geometry and specimen properties) without any fitting parameter. Finally dielectric films with different thicknesses and relative permittivities have been tested to validate both the characterisation tool and the data-processing method. The analytical model has been used to predict the permittivity of each dielectric thin film. The extracted data have been compared to data obtained from a calibrated macro-scale technique and showed remarkable agreement. One of the strengths of the data-processing method is to eliminate the stray capacitance which usually disturbs local capacitance measurements. Even though the effect of mechanical load is not investigated in the present study, the experimental proof-of-principle is shown and the data-processing method is validated. This work opens prospects for local and quantitative dielectric characterisations under mechanical loads. It should also fill a gap between quantitative characterisations at macro-scales and spatially highly-resolved characterisations at nano-scale

Compression of gold sub-micron crystallites: Method and experiments

Understanding and characterizing the mechanical response of individual nanostructure is of great importance for both fundamental prospects and device reliability. Higher flow stress with decreasing sample size is observed together with jerky flow. Compression of pristine submicron gold crystallites yield at very large stress in a stochastic manner, followed by large displacement bursts reaching up to 50% of the initial height [1,2]. In this work, by collecting a large set of measurements, we investigate the small and large strain behavior of crystallites loaded in compression. Large arrays of [111] oriented gold crystallites are prepared by solid state dewetting of initial cylinders of different volumes on sapphire substrates. Dedicated flat punch compression in-situ a FEG-SEM (figure 1a) has been carried out in load controlled mode [3]. Microstructure of defects is investigated using synchrotron radiation by nanoscale 3D imaging (Bragg Coherent X-ray Diffraction Imaging) [4] and Atomic Force Microscopy observations. The analysis of the plastic instability and its amount of deformation is carried out taking into account the inertial effect of the instrument, using a 1D dynamic model and Finite Element Method calculations. Simulations are made with different estimates of the shape of each individual crystallite, from an ideal cylinder of equivalent volume to the one based on SEM or AFM observations. We show that prior to the displacement burst, plastic events take place and that the sudden displacement does not necessarily relates to the onset of dislocation nucleation (figure 1b). Moreover, using the collection of measurements, we show that a unique stress-strain response can be obtained which can be used as a lower bound estimate of the mechanical response in compression of the crystallites. Please click Additional Files below to see the full abstract

Resistive-nanoindentation: contact area monitoring by real-time electrical contact resistance measurement

International audienceIn the past decades, efforts have been made to couple nanoindentation with resistive measurements in order to monitor the real-time contact area, as an alternative to the use of traditional analytical models. In this work, a novel and efficient stand-alone method is proposed to compute contact area using resistive-nanoindentation of noble metals (bulk or thin films). This method relies on three steps: tip shape measurement, setup calibration, application to the sample to be characterized. The procedure is applied to nanoindentation tests on a sample with film-on-elastic-substrate rheology and is successfully validated against experimental measurements of the contact area

High-temperature scanning indentation: A new technique to assess microstrutural changes along thermal ramping

Thanks to recent developments in high temperature nanoindentation testing, investigation of thermally activated mechanisms at small length scales can now be carried out [1]. In-situ anisothermal measurements at the micron-scale of hardness, Young modulus and creep properties are now feasible. The development of the High Temperature Scanning Indentation [2] technique, based on a specific high-speed loading procedure, allows quasi-continuous determination of those properties in temperature in only few hours. Please click Download on the upper right corner to see the full abstract

Resistive-nanoindentation on gold: Experiments and modeling of the electrical contact resistance

International audienceThis paper reports the experimental, analytical, and numerical study of resistive-nanoindentation tests performed on gold samples (bulk andthin film). First, the relevant contributions to electrical contact resistance are discussed and analytically described. A brief comparison of testsperformed on gold and on natively oxidized metals highlights the high reproducibility and the voltage-independence of experiments on gold(thanks to its oxide-free surface). Then, the evolution of contact resistance during nanoindentation is fully explained in terms of electronictransport regimes: starting from tunneling, electronic transport is then driven by ballistic conduction before ending with pure diffusive con-duction. The corresponding analytical expressions, as well as their validity domains, are determined and compared with experimental data,showing excellent agreement. From there, focus is made on the diffusive regime. Resistive-nanoindentation outputs are fully described byanalytical and finite-element modeling. The developed numerical framework allows a better understanding of the main parameters: it firstassesses the technique capabilities (validity domains, sensitivity to tip defect, sensitivity to rheology, effect of an oxide layer, and so on), butit also validates the different assumptions made on current line distribution. Finally, it is shown that a simple calibration procedure allows awell-resolved monitoring of the contact area during resistive-nanoindentation performed on samples with complex rheologies (ductile thinfilm on an elastic substrate). Comparison to analytical and numerical approaches highlights the strength of resistive-nanoindentation forcontinuous area monitoring

High-Temperature Scanning Indentation: A new method to investigate in situ metallurgical evolution along temperature ramps

A new technique, High-Temperature Scanning Indentation (HTSI), is proposed to investigate metallurgical evolution occurring during anisothermal heat treatments. This technique is based on the use of high-speed nanohardness measurements carried out during linear thermal ramping of the system with appropriate settings. A specific high-speed loading procedure, based on a quarter sinus loading function, a creep segment and a three-step unloading method, permits the measurement of elastic, plastic and creep properties. The indentation cycle lasts one second to minimize thermal drift issues. This approach enables quasi-continuous measurements of elastic modulus and hardness as a function of temperature in much shorter times than previous techniques. The HTSI technique is validated on fused silica and pure aluminum. The application to cold-rolled aluminum undergoing thermal cycling highlights the potential of the HTSI technique to investigate in situ thermally activated mechanisms linked with microstructural changes such as viscoplasticity, static recovery and recrystallization mechanisms in metals. Results on aluminum were confirmed using Electron Back-Scattering Diffraction measurement

Better understand the crystallization dynamics of ZrCu TFMGs: Benefits of combining global and local in situ approaches

International audienceThis work describes crystallization mechanisms in a model ZrCu thin film metallic glass, synthesized through magnetron sputtering. Global-scale characterization techniques, including differential scanning calorimetry and X-ray diffraction, are compared with local-scale characterization obtained through in situ transmission electron microscopy during isothermal heating. This multi-scale approach establishes the crystallization sequence of ZrCu thin film metallic glasses. Furthermore, it highlights the role of oxidation as a nucleation site, initiating the crystallization process. Once initiated, crystallization progresses as a propagating front, scanning and transforming the amorphous matrix. The combination of both global and local approaches yields consistent key thermodynamic values. Additionally, monitoring the advancing crystallization front during in situ high-temperature transmission electron microscopy provides access to crucial kinetic parameters, such as diffusion coefficients