Cross-sectional Nanoindentation Research Articles

Fracture-resistant thin-film metallic glass: Ultra-high plasticity at room temperature

We report the first example of room-temperature rubber-like deformation in thin-film metallic glasses (TFMGs), 260-nm-thick Zr60Cu24Al11Ni5 layers, under ultra-high shear strain. The TFMGs were deposited, with no external heating, on Zr-based bulk metallic glass (BMG) and Si(001) substrates by rf magnetron sputtering in a 3 mTorr Ar plasma. Cross-sectional transmission electron microscopy (XTEM) analyses and nanoindentation results reveal that the TFMGs undergo an incredibly large shear strain, estimated to be ∼4000%, during fatigue tests, and thickness reductions of up to 61.5%, with no shear-banding or cracking, during extreme nanoindentation experiments extending through the film and into the substrate. TFMG/BMG samples also exhibit film/substrate diffusion bonding during deformation as shown by high-resolution XTEM.

Microstructural shell strength of the Subantarctic pteropod Limacina helicina antarctica

Anthropogenic inputs of CO2 are changing ocean chemistry and will likely affect calcifying marine organisms, particularly aragonite producers such as pteropods. This work seeks to set a benchmark analysis of pteropod shell properties and variability using nanoindentation and electron microscopy to measure the structural and mechanical properties of Subantarctic pteropod shells (Limacina helicina antarctica) collected in 1998 and 2007. The 1998 shells were collected by a sediment trap deployed at 2000 m, 47°S, 142°E, and the 2007 shells were collected using nets from mixed-layer waters in the region (44°–54°S, 140°–155°E). Transmission electron microscopy revealed that the shells are composed of a polycrystalline structure, and no obvious porosity was visible. The hardness and modulus of the shells were measured using shell cross-section nanoindentation, across various regions of the shell from the inner to outer whorl. No change in mechanical properties was found with respect to the region of the shell cross-section probed. There was no statistically significant difference in the mean modulus or hardness of the shells between the 1998 and 2007 data sets. No major changes in the mechanical properties of these pteropod shells were detected between the 1998 and 2007 data sets, and we discuss the possible biases in the sampling techniques in complicating our analysis. However, quantifying the mechanical properties and microstructure of calcified may still provide insights into the responses of calcification to environmental changes, such as ocean acidification.

Microstructure-controlled depth gradients of mechanical properties in thin nanocrystalline films: Towards structure-property gradient functionalization

Although the influence of the grain size on the mechanical properties of polycrystalline materials is well understood, the occurrence of depth-gradients of grain size, microstructure, and residual stresses in nanocrystalline thin films and their effect on the functional properties is a phenomenon which has not yet been studied in detail. Hence in this work, single-layered polycrystalline and mosaic epitaxial as well as multilayered CrN thin films were characterized by a combination of averaging as well as depth-resolved experimental techniques, such as cross-sectional X-ray nanodiffraction and small-angle cross-sectional nanoindentation. The results reveal the fundamental relationship between gradients of grain size, microstructure, and stresses, controlled by the film growth conditions, and gradients of hardness and elastic modulus. The effect of the compressive stress and structural defects associated with high particle energy on the mechanical properties of nanocrystalline thin films was found to be dominant over the grain size and crystallographic texture. These findings open the way to functionalize structure-property gradients in nanocrystalline thin films through microstructural design as demonstrated for multilayered CrN films.

Cross-sectional nanoindentation (CSN) studies on the effect of thickness on adhesion strength of thin films

In this study the cross-sectional nanoindentation (CSN) technique has been employed to investigate the adhesion behavior of Titanium-Tungsten (TiW) thin films in various thicknesses on silicon substrate. Furthermore, the nanoindentation-induced blister (NIB) technique has been implemented on the same samples to evaluate the adhesion energy of the films with a different approach. The adhesion energy release rate of these thin films, derived by these two techniques, revealed a good agreement. Accordingly, the results show that as the thickness of the TiW layer increases, the adhesion toughness of the film decreases. It was suggested that three factors might be responsible for the superior adhesion strength of thin films with lower thicknesses: higher surface energy due to the smaller mean grain size; higher constraint from the substrate, which causes inferior fracture toughness of the coating and facilitates crack deflection from interface to surface; and, energy dissipation due to decohesion. The thickness dependency of the transition between delamination and decohesion mechanism in thin films has also been discussed and modelled.

Localized mechanical property assessment of SiC/SiC composite materials

SiC fiber-reinforced SiC matrix composites (SiC/SiC) are under consideration as a structural material for a range of nuclear applications. While these materials have been studied for decades, recently new small scale materials testing techniques have emerged which can be used to characterize SiC/SiC materials from a new perspective. In this work cross section nanoindentation was performed on SiC/SiC composites revealing that both the hardness and Young’s modulus was substantially lower in the fiber compared to the matrix despite both being SiC. Using scanning electron microscopy it was observed that the grain growth of the matrix during formation was radially out from the fiber with a changing grain structure as a function of radius from the fiber center. Focused ion beam machining was used to manufacture micro-cantilever samples and evaluate the fracture toughness and fracture strength in the matrix as a function of grain orientation in the matrix. Additionally microstructural characterization techniques like Raman spectroscopy, X-ray diffraction, and microtomography were used to evaluate differences in the matrix and fibers of the composite.

Direct Imaging of Mechanical and Chemical Gradients Across the Thickness of Graded Organosilicone Microwave PECVD Coatings

The characterization of variations in the chemical composition and ensuing mechanical properties across the thickness of coatings with continuously varying compositions through their thickness (graded coatings) presents considerable challenges for current analytical techniques in materials science. We report here the direct imaging of nanomechanical and chemical gradients across cross-sections of an organosilicone coating fabricated via microwave plasma enhanced chemical vapor deposition (PECVD). Cross-sectional nanoindentation was used to determine the mechanical properties of uniform and graded organosilicone coatings. Both hardness and modulus across the coatings were directly measured. Additionally, "modulus mapping" on cross-sections was used to map the complex modulus. For the graded coating, it was found that variations in the complex modulus was predominantly due to varying storage modulus. It was observed that at the interface with the substrate there was a low storage modulus, which linearly increased to a relatively high storage modulus at the surface. It is proposed that the increase in stiffness, from the substrate interface to the outer surface, is due to the increasing content of a cross-linked O-Si-O network. This mechanical gradient has been linked to a change in the Si:O ratio via direct compositional mapping using ToF-SIMS. Direct mapping of the mechanical and compositional gradients across these protective coatings provides insight into the changes in properties with depth and supports optimization of the critical mechanical performance of PECVD graded coatings.

Microstructural and Nanoindentation Studies Across Diffusion-bonded Interfaces in Al/Cu Metal Intermetallic Laminates

In this study, alternate layers of Al and Cu were diffusion bonded to obtain a Metal Intermetallic Laminate (MIL). Intermetallic compounds form at the Al/Cu interface due to in-situ reactions between the metals. The type of compounds formed, their individual mechanical properties and the strength of the interface play a central role in determining the mechanical response of these laminates. In this context, we have characterized the Al/Cu interface and the interfacial intermetallics by means of SEM- based microstructural studies, X-ray diffraction and cross-sectional nanoindentation studies. Microstructural characterization, composition profiles and X-ray diffraction reveal the formation of three intermetallic phases at the interface. Furthermore, nanoindentation studies suggest that the intermetallic phases are not only stiff and hard, but are also well-bound to the abutting metal layers. This suggests the possibility of enhanced mechanical properties for the laminate.

Monitoring remineralization of enamel subsurface lesions by optical coherence tomography

Optical coherence tomography (OCT) is a potential clinical tool for enamel lesion monitoring. Swept-source OCT findings were compared with cross-sectional nanohardness findings of enamel. Subsurface bovine enamel lesions in three groups were subjected to (1) deionized water (control), (2) phosphoryl oligosaccharide of calcium (POs-Ca) or (3) POs-Ca with 1 ppm fluoride for 14 days. B-scans images were obtained at 1310-nm center wavelength on sound, demineralized and remineralized areas after 4, 7, and 14 days. The specimens were processed for cross-sectional nanoindentation. Reflectivity from enamel that had increased with demineralization decreased with remineralization. An OCT attenuation coefficient parameter (μt), derived based on the Beer-Lambert law as a function of backscatter signal slope, showed a strong linear regression with integrated nanohardness of all regions (p<0.001, r=-0.97). Sound enamel showed the smallest, while demineralized enamel showed the highest μt. In group three, μt was significantly lower at four days than baseline, but remained constant afterwards. In group two, the changes were rather gradual. There was no significant difference between groups two and three at 14 days in nanohardness or μt POs-Ca with fluoride-enhanced nanohardness of the superficial zone. OCT signal attenuation demonstrated a capability for monitoring changes of enamel lesions during remineralization.

Gum Containing Calcium Fluoride Reinforces Enamel Subsurface Lesions in situ

The aim of this study was to assess the effect of chewing gum containing phosphoryl oligosaccharides of calcium (POs-Ca) and a low concentration of fluoride (F) on the hardness of enamel subsurface lesions, utilizing a double-blind, randomized, and controlled in situ model. Fifteen individuals wore removable lingual appliances with 3 bovine-enamel insets containing subsurface demineralized lesions. Three times a day for 14 days, they chewed one of the 3 chewing gums (placebo, POs-Ca, POs-Ca+F). After the treatment period, cross-sectional mineral content, nanoindentation hardness, and fluoride ion mapping by time-of-flight secondary ion mass spectrometry (TOF-SIMS) were evaluated. Although there were no statistical differences in overall mineral content and hardness recovery rates between POs-Ca and POs-Ca+F subsurface lesions (p > 0.05), nanoindentation at 1-μm distance increments from the surface showed statistical differences in hardness recovery rate between POs-Ca and POs-Ca+F in the superficial 20-μm region (p < 0.05). Fluoride mapping revealed distribution of the ion up to 20 μm from the surface in the POs-Ca+F group. Nanoindentation and TOF-SIMS results highlighted the benefits of bioavailability of fluoride ion on reinforcement of the superficial zone of subsurface lesions in situ (NCT01377493).

Structure and mechanical properties of swift heavy ion irradiated tungsten-bearing delta-phase oxides Y6W1O12 and Yb6W1O12

We report on the relationship between structure and mechanical properties of complex oxides whose structures are derivatives of fluorite, following irradiation with swift heavy ion (92MeVXe) which approximately simulates fission product irradiation, where the electronic energy loss dominates. The two compounds of interest in this paper are Y6W1O12 and Yb6W1O12. These compounds possess an ordered, fluorite derivative crystal structure known as the delta (δ) phase, a rhombohedral structure belonging to space group R3¯.Structural changes induced by irradiation were examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD investigations indicated an irradiation-induced amorphization in these compounds. This result is consistent with our previous study on Y6W1O12 under displacive radiation environment in which the nuclear energy loss is dominant. High resolution TEM also revealed that individual ion tracks was amorphized. The mechanical properties of both irradiated compounds, were determined by cross-sectional nano-indentation measurements as a function of ion penetration depth. The decreases in Young’s modulus, E, and hardness, H (both by about 40% at the irradiated surface) suggest amorphization beyond simple defect accumulation occurs under this irradiation condition.

Cross-sectional nanoindentation and nanoscratch of compositionally graded mullite films

Nanoindentation and nanoscratch have become well-established techniques for measuring mechanical properties of thin films. Conventionally, these tests are performed on the surface of the films to evaluate their mechanical integrity: elastic modulus, hardness and adhesion strength. However, in complex systems such as compositionally graded thin films, small spatial variations in mechanical properties are difficult to distinguish using this approach. In this work, the evaluation of the above parameters was conducted on cross-sections of compositionally graded mullite coatings, chemical-vapor deposited on silicon carbide substrates. To assess the intrinsic mechanical properties and their spatial variation, nanoindentation tests were carried out on mullite coatings with constant and graded Al/Si ratios. Additionally, transverse nanoscratch tests to evaluate the cohesive and adhesive resistance of the coatings as well as the coating/substrate systems, respectively, were performed. Different damage morphologies were identified within the coating and at the interface by using complementary characterization techniques. In the case of functionally graded coatings a gradual rise in the hardness and elastic modulus with increasing distance from the coating/substrate interface was observed. Nanoscratch tests on the cross-sections allowed determining the critical loads for cohesive and adhesive damage by following this approach. Compositionally graded mullite coatings exhibited the best combination of hardness/stiffness and cohesive/adhesive scratch strength.

Crack propagation in multilayer thin-film structures of electronic packages using the peridynamic theory

This paper presents an application of the peridynamic theory to predict crack paths in multilayer thin-film structures of electronic packages. The peridynamic theory is a nonlocal continuum theory that has an inherent crack initiation and growth criterion. Specifically, the peridynamic theory is employed to model cross-sectional nanoindentation, an experimental technique used for characterizing interfacial adhesion and observing crack paths. Cross-sectional indentation experiments previously conducted on blanket and patterned thin-film structures were simulated. The predicted crack propagation paths in both blanket and patterned multilayer thin-film structures compare well with the results from cross-sectional nanoindentation experiments.

Characterization of the adhesion of thin film by Cross-Sectional Nanoindentation: Analysis of the substrate edge chipping and the film delamination

Cross-Sectional Nanoindentation (CSN) is a recent method for adhesion measurement of nanoscale thin films in Ultra-Large Scale Integrated circuits. In the case of ductile thin films, the motion of the substrate chip implies significant plastic deformation of the film and complex geometry of delaminated areas. This article recalls first the experimental procedure and the two main features observed in this test performed on various plane copper films deposited on silicon: the critical force producing silicon edge chipping increases linearly with the distance of the indenter to the interface; on the section the delaminated length of the film ( a − b ) is proportional to the residual silicon chip displacement u f and the ratio S = u f / ( a − b ) depends on the manufacturing process of the film, and is so related to its adhesion to the substrate. One proposes a simple analysis of the silicon edge chipping. Then a model of pull-off of an elastic-strain hardening plastic film is developed, which suggests an explanation for the delamination process. Application of the model to experimental results starting from films plastic properties deduced from nanoindentation measurements provides plausible results. Some improvements for performing the CSN test are proposed in order to make easier its interpretation.

Composition, microstructure and mechanical properties of boron containing multilayer coatings for hot forming tools

The tribological conditions of hot forming processes are much different from those at room temperature. Thus classical wear-resistant coating like CrN, CrAlN, TiAlN in most cases are not sufficient for hot forming tools in industrial applications.Additionally the use of lubricants is limited, thermal shock conditions and the increase of sticking work piece material are leading to severe wear.This paper presents examples for ternary boron based Ti–B–N gradient coatings in specific multilayer designs obtained through plasma enhanced chemical vapor deposition. After a thorough characterization of the chemical composition by Auger electron spectroscopy, the microstructure by X-ray diffraction and the mechanical properties by microindentation and small-angle cross section nanoindentation, the coatings were applied onto hot forming tools made from DIN 1.2367 tool steel. The coated tools were tested in hot forging of AISI 1043 raw parts in an automatic press and have been compared in terms of adhesion and wear resistance. In this study an optimum design has been found which significantly reduces sticking of work piece material and wear. This allows an efficient production without interruptions for a reworking of the tools and enables to increase the process reliability paired with a longer tool life.

Thermal evolution and mechanical properties of hard Ti–Cr–B–N and Ti–Al–Si–B–N coatings

Surface properties modification is an effective way to improve the performances of materials subjected to thermo-mechanical stress. Nanocomposite Ti–B–N based coatings have high hardness, while their behavior at elevated temperatures can be enhanced through the addition of other elements. Mechanical properties and oxidation behavior of Ti–Cr–B–N and Ti–Al–Si–B–N coatings, deposited through ion implantation assisted magnetron sputtering on Si are presented. Microstructure investigation by XRD and TEM, hardness and Young's modulus by in plane and cross sectional nanoindentation, were performed on as-deposited coatings and after annealing in air at 900 °C. Evolution of morphology and microstructure and its relationship with coatings hardness is described.

ENERGY RELEASE RATE OF INTERFACE DELAMINATION BETWEEN A THIN COATING AND AN ELASTIC SUBSTRATE

The mechanical properties of materials such as elastic modulus, hardness, and fracture toughness, can be measured by nanoindentation. For a thin film coated on an elastic substrate, the cross-sectional nanoindentation technique can decrease the influence of plastic deformation around the nanoindenter apex on fracture toughness for interface delamination. Considering the effect of the elastic substrate, the theory of an elastic beam bonded to an elastic foundation is further developed to obtain the energy release rate of interfacial debonding. Explicit closed-form solutions are determined, and the influence of the substrate on the energy release rate is shown graphically.

Influence of Residual Stresses on the Interfacial Toughness Measurement by Cross-Sectional Nanoindentation

Cross-sectional nanoindentation (CSN) is a new method for measuring interface adhesion of thin films. The interfacial energy release rate (G), characterizing interfacial adhesion, is calculated from the material and geometrical parameters relevant to the test. Effects of residual stresses on G and crack tip phase angle Ψ, have been studied by finite element simulation in this study. The results show tensile residual stresses increase G and compressive stresses reduce it, and they have similar effects on the magnitude of Ψ.

Cross-sectional nanoindentation for copper adhesion characterization in blanket and patterned interconnect structures: experiments and three-dimensional FEM modeling

Cross-sectional nanoindentation (CSN) is a recent method for adhesion measurement of nanoscale thin films in ultra-large scale integrated circuits. In the case of ductile thin films, plastic deformation during the test and complex geometry of delaminated areas require 3D finite element modeling (FEM) for adhesion energy calculation. In this paper the adhesion of various copper (Cu) films on blanket and patterned structures is studied by CSN test. The experimental procedure and qualitative analysis of the test are presented in detail. Crack propagation is studied on blanket and patterned substrates. The dimensions of delaminated blisters are measured by scanning electron microscope (SEM) for each sample. Results show that a geometrical ratio can be used to give a quick and qualitative measurement of adhesion. A new 3D FEM model is then proposed to assess quantitative analysis of CSN test. The deformation energy of Cu blister is calculated for each sample. The mechanical properties of the Cu films required for numerical calculations are measured by instrumented indentation. The influence on these measurements of the evolution of the Cu deformation with penetration depth is discussed in detail with the aid of 2D numerical simulation. The results of numerical modeling correlate well with qualitative evaluation of adhesion.

Fracture characterization in patterned thin films by cross-sectional nanoindentation

A testing technique based on cross-sectional nanoindentation has been used to assess the mechanical reliability of interconnect structures. A Berkovich indenter was used to initiate fracture in a silicon substrate and cracks propagated through the structure. To better control crack growth and to convert the problem into two dimensions, a trench parallel to the indentation surface was previously machined using a focused ion beam. The crack lengths obtained for different material systems in the interconnect structure correlate well with the fracture energies measured for the same materials in blanket films. Finite element model simulations incorporating cohesive elements have been used to model the fracture processes and to explain the different cracking behaviour observed.

Hard multilayer coatings containing TiN and/or ZrN: A review and recent progress in their nanoscale characterization

In the first part of this article, a comprehensive literature review on hard multilayer coatings, which contain TiN and/or ZrN as a component is given. The developments made in this field, starting with the first published results in 1987 and ending with the latest articles in 2005, were summarized and critically evaluated in order to serve as a starting point for future research in this area. In the second part, recent progress in the nanoscale characterization of multilayers and their interfaces by the small-angle cross-section nanoindentation method and atomic force microscopy is demonstrated on TiN∕ZrN multilayers. These nanoscale multilayers were deposited by reactive dc-magnetron sputtering of metallic titanium and zirconium targets in argon/nitrogen plasma onto hard metal and silicon substrates.