Cyclic Nanoindentation Research Articles

CYCLIC NANOINDENTATION OF SEMICONDUCTOR AND METAL THIN FILMS

The nanoindentation technique was used to measure the hardness and Young's modulus of semiconductor and metal thin films on a Si(100) substrate under cyclic loading. The results showed that in all instances and at a constant cyclic load that the loading curves overlapped the previous unloading curve and had a small displacement after each cyclic nanoindentation. It was observed that the plastic energies of metal materials from the first loading–unloading cycle were much larger than that observed in semiconductor materials. Furthermore, the hardness and Young's modulus of the thin films decreased when the number of cyclic nanoindentations was increased. The effect of the cyclic loading on the hardness and Young's modulus of semiconductor material was much larger than that of the metal material. Young's modulus, the hardness and the contact stiffness of thin films conform to the relationship that Young's modulus was proportional to the contact stiffness and the square root of the thin film's hardness.

Optimization of the Ti-16.2Hf-24.8Nb-1Zr Alloy by Cold Working

The objective of the present work is to characterize the influence of cold work on the thermoelastic martensitic transformation and on the apparent elastic modulus of the Ni-free Ti-21.6Hf-23.7Nb-1Zr alloy in order to determine the key factor that promotes the desired shape memory properties and/or low apparent elastic modulus. A vacuum arc melted button of each alloy was heat treated at 1100 °C during 1.5 h and quenched with a mixture of ethanol/water at 0 °C. Samples of the alloy were cold rolled from 5% up to 95% and, finally, microstructurally and mechanically characterized. The apparent elastic modulus for each condition as well as the reversibility percentages were evaluated by instrumented nanoindentation using a Berkovich tip and a spherical tip, respectively. A higher proportion of martensite was found in the low cold work percentages compared to the untreated material as it was observed by optical and TEM microscopy. A decrease in the apparent elastic modulus was observed when increasing the cold work percentage. The lowest value was found in the 99% cold work condition with 44 GPa, value closer to that of cortical bone. Cyclic nanoindentation tests show an increase in the reversibility percentages in the cold worked condition compared to the untreated material.

Quasi-static cyclic loadings induced inelastic deformation in a Zr-based bulk metallic glass under nanoindentation

Cyclic nanoindentation tests were carried out on Zr50Cu40Al10 bulk metallic glass (BMG). From the designed quasi-static and incremental cyclic experiments at loading rates ranging from 250 to 2500 μN/s and at ambient temperature, we observed significant difference in inelastic deformation as a function of solicitation modes. Under incremental cyclic loadings, the hardness of the BMG increased each time when the sample was reloaded immediately after unloading and then gradually reduced before the next unloading. In contrast, we found that quasi-static cyclic loadings induced a mechanical softening which appears to be dependent on the number of cycles and the loading rates. The inelastic deformation was studied by analysing the remnant indent morphology using atomic force microscopy. A free-volume mechanism was proposed for interpreting these observations quantitatively.

Thermoelastic phase transformation in TiNi alloys under cyclic instrumented indentation

Austenitic and martensitic TiNi shape memory alloys were studied by means of cyclic instrumented indentation with the purpose of documenting the phase transformation. Recovery indexes were determined from the energy absorbed during loading, unloading and reloading and their relation with the microstructure and shape memory properties established. Significant changes on the load–displacement curves, associated to the transformation phenomenon, were exhibited by both materials. Under spherical cyclic nanoindentation, a classic pseudoelastic behavior was observed in the austenitic alloy, which was characterized by high recovery indexes and constitutes the first experimental evidence of this property under such testing conditions. On the other hand, the martensitic alloy showed lower recovery indexes, as a consequence of a faster stabilization process of the martensite plates.

On the hardness and the inherent ductility of chromium carbide nanostructured coatings prepared by RF sputtering

Homogenous and nanostructured chromium carbide thin coatings are prepared by RF sputtering. The nanoindentation tests are used to investigate the evolution of plastic deformation and hardness as a function of the grain size. The Cr 3C 2 films have been deposited on magnesium oxide substrates from a Cr 3C 2 target in pure argon atmosphere. Based on the effect of the deposition temperature, we have generated nanostructured Cr 3C 2 coatings with different mechanical properties. We have found that both crystalline texture and grain size increased with increasing the deposition temperature. The nanostructured chromiumcarbide film with grain size in the order of 5 nm, prepared at a deposition temperature of 600 °C, showed a higher hardness as well as a good ductility compared to the samples prepared at 850 °C or at room temperature. The cyclic nanoindentation measurements at constant loading rate allowed qualitative characterization of the change in the irreversible plastic work for the samples considered in this report.

Investigation of the photoplastic effect in vitreous semiconductors by cyclic nanoindentation

The dynamics of photoinduced changes in the internal friction and the Young’s modulus for films in the As-Se system is investigated by cyclic nanoindentation at infralow frequencies. It is revealed that the irradiation of the films leads to an increase in the Young’s modulus, a retardation of relaxation processes, and a decrease in the viscosity and nanohardness of the material. The results obtained are discussed in the framework of the concept of microheterogeneous glass structure.

Identification of viscoelastic model parameters by means of cyclic nanoindentation testing

Abstract A method for the identification of model parameters describing the time-dependent material behavior by means of cyclic nanoindentation is presented. The complex shear modulus of the material sample is determined from the prescribed amplitude in the load history, the measured amplitude in the penetration history, and the phase shift between the peak values for the load and the penetration. The parameters for a specific viscoelastic model are obtained by comparing the experimentally-obtained storage and loss moduli – both depending on the frequency used during cyclic testing – with the analytical expressions for the respective viscoelastic model. The presented method is applied to low-density polyethylene, giving access to the parameters of the fractional dash-pot which is used to describe the viscoelastic behavior. The results are compared with results from nanoindentation (static) creep tests, considering different maximum loads. Finally, the performance of the presented method is assessed by comparing the creep-compliance functions corresponding to the model parameters identified by nanoindentation with the macroscopic creep-compliance function obtained from bending-beam-rheometer tests.

Cyclic Depth-Sensing Indentation of Gold Wire

Conventional depth-sending indentation and novel cyclic indentation were performed to study the mechanical properties and strengthening mechanism of pure gold and Ca-doped gold of up to 90 ppm. The system was chosen because it is popular materials for microelectronics interconnection, yet the strengthening mechanism is not well-understood. Conventional depthsensing indentation showed an increase in hardness and modulus of gold with increasing Ca content of up to 90 ppm, which remained significantly higher after annealing. Cyclic depth sensing indentation, where the specimen is loaded to a specific value, unloaded and immediately reloaded, produced a cyclic loop between unloading and reloading curves. The path of the unloading and reloading curves tell the story of the different response of the dislocations generated under the indentation, in different materials, pure gold and Ca-doped gold at different level. Thus their dislocation movement and deformation behavior could be studied by cyclic depth-sensing indentation method. This paper reports cyclic indentation study performed in calcium doped gold widely used in wire bonding and shows that a few ppm level of calcium could result in dislocationssolute interactions, leading to significant strengthening of the materials. TEM micrographs of the material shows that it consists of elongated grains parallel to the drawing direction about 200 nanometers in diameter and a few micrometers in length. It is concluded that cyclic nanoindentation could be used as an extended technique to extract sensitive material information that are not reflected in the conventional test.

Study of Delamination of Thin Film Coating on Cyclic Nano-Indentation Test

The aim of this paper is to evaluate the cyclic interfacial strength between thin film and its substrate by cyclic nano-indentation tests. The specimen used in this study is PET substrate/ITO coatings layered specimen. From the indentation load and displacement curve, we proposed an evaluation method for the interfacial strength. The results are good agreement with the interfacial strength evaluated by peel test. After cyclic indentations, the surface profile was observed by atomic force microscope. The number of elongates increased with indentation cycles when the indentation load is low, whereas elongates number is almost constant under high load cases. These phenomena can be explained by simple models. In this study, two types of fracture modes are proposed. They are “subsidiary fracture mode” and “buckling mode”.

Laser-induced collective effects in glassy semiconductor films

Photoinduced variations in the structure of glassy semiconductor films are considered from the standpoint of the theory of self-organization, including the formation of dissipative structures and their subsequent transformation under laser irradiation, which drives the system to the new state with minimum dissipated energy of the external mechanical field. Direct experimental evidence for the existence of cooperative (synergetic) self-organization processes is provided by the results of cyclic nanoindentation measurements in films of a chalcogenide glass with As2Se3 stoichiometric composition exposed to band-gap light (hv ≥ Eg)).

Reverse Plasticity in Nanoindentation

AbstractThis paper summarises our recent cyclic nanoindentation experiment studies on a range of materials including single crystal and nanocrystalline copper, single crystal aluminium and bulk metallic glasses with different glass transition temperatures. The unloading and reloading processes of the nanoindentation curves have been analysed. The reverse plasticity will be discussed in the context of plastic deformation mechanisms involved. The effect of loading rates on the mechanical properties of materials upon cyclic loading will also be discussed.

Nanoscale Pseudoelasticity of Single-crystal Cu–Al–Ni shape-memory Alloy Induced by Cyclic Nanoindentation

Nanoscale Pseudoelasticity of Single-crystal Cu–Al–Ni shape-memory Alloy Induced by Cyclic Nanoindentation

Cyclic loading as an extended nanoindentation technique

Conventional depth sensing nanoindentation test which produces a load–depth curve for a monotonically increasing load can be used to determine many mechanical properties. Alternatively, if the specimen is loaded to a specific value, unloaded and immediately reloaded, a cyclic nanoindentation curve is produced. The unloading–reloading paths do not necessarily overlap in all materials. The reason for this is thought to be the different response of the dislocations generated under the indentation, in different materials. The dislocation behaviour will be controlled by the chemistry and microstructure of the material. Therefore, sensitive dislocation–microstructure interactions may be detectable in the unloading–reloading curves during cyclic indentation. This paper reports such cyclic nanoindentation investigation done in calcium-doped gold used in wire bonding. It is shown that calcium, even in ppm levels, can influence the cyclic load–depth curves to measurable extents. The loading and unloading profiles obtained are reported and the effect of increasing dopant level is evident in them. This is attributed to dislocation–solute interactions. The microstructure of the material consists of elongated (drawn) grains of diameter of about 200 nm and length of a few micrometers. It is concluded that cyclic nanoindentation could be used as an extended technique to extract sensitive material information that are not reflected in the conventional test.

3013 繰り返しナノインデンテーションによるコーティング薄膜のはく離(S38 皮膜の磨耗および残留応力特性(2),S38 コーティング材料の皮膜特性とその評価)

The aim of this paper is to evaluate the cyclic interfacial strength by cyclic nanoindentation tests. The specimen used in this study is PET substrate/ITO coatings layered specimen. In this study mono cycle nanoindentation test and 10 cycle nanoindentation were conducted on each load, and these results were compared. From indentation load and displacement curves, we classified those results into 3 types (A-C). These three types relate the maximum loads. After the cyclic indentation, we observed the surface profile by the function of atomic force microscope. On Type A, the deviations were observed on the edge on indentations. On Type B, some elongates were observed in the indentations. In addition the number of elongates increased by repeating nanoindentation. These phenomena can be explained by simple models. In this study, two types of fracture modes are proposed. They are "subsidiary fracture mode" and "buckling mode". From the deviation of indentation load and displacement curve, we proposed the method to estimate the energy used for thin film delamination and the interfacial strength was evaluated. The results are good agreement with the interfacial strength evaluated by peel test.

Deformation of nanostructured materials: insights from experimental observations

Increased interest in nanoscale deformation has been spurred by the rapid miniaturization of features and components in microelectronic devices, magnetic storage media, and MEMS/NEMS, i.e., microand nanoelectromechanical systems, respectively. Materials for these applications are often chosen because of their electronic, optical, or magnetic properties. Frequently, however, the mechanical properties are the performance-limiting factor. Until recently, the techniques used to produce samples resulted in a high number of induced artefacts and, hence, irregular mechanical properties. Thanks to progress in processing methods, we can now make nanograin samples of high purity and high density that, under experimental conditions, show reproducible characteristics. Such fully dense materials are excellent candidates for fundamental mechanical property studies as well as for high-performance applications. Compared with their microcrystalline counterparts,nanostructured metals with grain size smaller than 100nm possess attractive properties such as high yield and fracture strength and improved wear resistance. But evidence also suggests that miniaturization may influence their microstructural and mechanical stability, resulting in undesirable shape change, mechanical response, thermal behavior, and electrical performance. These instability phenomena are the main focus of our research efforts. Small sample size generally rules out standardized tests, such as tensile and compression tests. But advances in methods such as nanoindentation accommodate very small amounts of material. Traditional nanoindentation testing measures the elastic modulus and hardness of engineering materials by pushing a probe into the material while monitoring load and penetration depth. Now, instrumentation offers new possibilities. For example, we perform cyclic nanoindentation tests with up to a million load Figure 1. Shown is the grain structure of nickel following 10 loading cycles using a pyramidal tip. The initial grain size was 30nm. Some areas of the indented region (along the edge as indicated in the insert) show significantly larger grains and increased surface roughness after cyclic contact loading, as marked by arrows.

Microstructure and mechanical properties of porous Ti 3SiC 2

A ≈43 vol.% porous Ti 3SiC 2 ternary compound was fabricated by the reactive sintering of elemental powders. Under cyclic compression, the first loading cycle resulted in a measurable deformation, but subsequent cycles to the same load resulted in fully reversible, closed hysteresis loops that were smaller in area than the first loop. Cyclic nanoindentation loadings on solid bridges separating pores displayed behavior that was qualitatively similar to the uniaxial compression testing results. The results are interpreted in light of our kink band formation model. The significantly larger areas associated with the porous material than the fully dense sample with comparable grain size are ascribed to the formation of more incipient and regular kink bands as a consequence of the lack of constraint due to the presence of pores. The technological implications of having a porous material that dissipates more energy – on an absolute scale – than its fully dense counterpart are discussed.

Formation of nanocrystalline structure of TaSi2 films on silicon

The nanocrystalline structure and mechanical properties of TaSi2 films deposited by sputtering of TaSi2 target have been investigated by x-ray diffraction, cross-sectional transmission electron microscopy (TEM), four-point electrical resistance measurement, and cyclic depth-sensitive nanoindentation. The purpose of this work is to study the formation of nanocrystalline structure in TaSi2 films on a silicon substrate. As revealed, a decrease in the deposition rate leads to an increase in the O and C impurity content in the films. Contamination of the film by O and C atoms during a low-rate deposition causes the formation of an amorphous phase in the deposited films. Upon annealing, the amorphous structures crystallize into mixtures of disilicide and a small amount of polysilicide, i.e. TaSi2 and Ta5Si3, respectively. After annealing at 970 K, the formation of a nanocrystalline structure with a grain size about 10 nm takes place in the film produced at a deposition rate of 0.2 nm/sec. The formation of a nanocrystalline structure changes drastically the mechanical properties of the film. The nanohardness and elastic modulus increase significantly, and the film becomes brittle and overstressed. After deposition in the film produced at the 1 nm/sec deposition rate mainly Ta disilicide and the amorphous phase are observed. After annealing, the amorphous phase near the Si substrate coexists with column-shape grains of Ta disilicide of size 150 × 500 nm. The annealed thin film becomes nonuniform in thickness. The nanohardness and elastic modulus increase.

The transition from elastic to plastic behaviour in an Al-Cu-Fe quasicrystal studied by cyclic nanoindentation

Abstract Comparative mechanical tests of an Al-Cu-Fe quasicrystal and a tungsten (001) single crystal have been carried out using cyclic nanoindentation by a Berkovich indenter. The first loading-unloading cycle up to 30 mN formed the initial indent. On reloading of the indenter up to 50 mN, a transition from elastic to plastic deformation of the material was observed. To reveal the region of the transition better, the reloading curve was differentiated with respect to time. It was found that, for tungsten, the transition from elastic to plastic behaviour was smooth. The transition began at 25 mN and terminated at 34mN only. During the transition the strain rate in the indent trebled. In the Al-Cu-Fe quasicrystal, the transition from elastic to plastic deformation was very abrupt. No evidence of plastic deformation in the indent was observed up to 32 mN. Only a further increase in the load by 0.35mN caused the onset of plastic deformation. A pop-in was observed in the reloading curve at this point. The di...

The transition from elastic to plastic behaviour in an Al-Cu-Fe quasicrystal studied by cyclic nanoindentation

Abstract Comparative mechanical tests of an Al-Cu-Fe quasicrystal and a tungsten (001) single crystal have been carried out using cyclic nanoindentation by a Berkovich indenter. The first loading-unloading cycle up to 30 mN formed the initial indent. On reloading of the indenter up to 50 mN, a transition from elastic to plastic deformation of the material was observed. To reveal the region of the transition better, the reloading curve was differentiated with respect to time. It was found that, for tungsten, the transition from elastic to plastic behaviour was smooth. The transition began at 25 mN and terminated at 34mN only. During the transition the strain rate in the indent trebled. In the Al-Cu-Fe quasicrystal, the transition from elastic to plastic deformation was very abrupt. No evidence of plastic deformation in the indent was observed up to 32 mN. Only a further increase in the load by 0.35mN caused the onset of plastic deformation. A pop-in was observed in the reloading curve at this point. The displacement increased by about 10 nm and the pressure in the indent dropped by 360 MPa. This was probably due to the destruction of the quasicrystalline structure and the formation of the crystalline structure. A plastic crystalline phase appeared to be pressed between the indenter and the hard quasicrystal substrate and then to be extruded from the indent. Because of this, the pressure in the quasicrystal drops during the transition from elastic to plastic deformation.

Nanoindentation studies of ion implanted silicon

Cyclic nanoindentation studies were conducted on (111) single-crystal silicon modified by implanting O +, N + 2, P +, As +, and Ar + ions with different doses ranging from 1 × 10 16 to 5 × 10 17 ions cm -2 at 200 keV. Hysteresis in cyclic indentation and discontinuity kinks during unloading are considerably reduced by the ion implantation. Ion implantation of compound-forming species O + and N + 2 into silicon improves the resistance to deformation, which is defined as the ratio of hardness to the square of Young's modulus. By contrast, the implantation of P +, As +, and Ar + species that do not form compounds reduced the resistance to deformation to almost half. Based on this study, it is concluded that the ion implantation with an appropriate ion species can be used to modify resistance to deformation.