Nanoindenter techniques have been used to investigate the mechanical properties of Ag-Al2O3 and Fe-SiO2 granular metal films. A discontinuity in the rate of change of hardness as a function of metal volume fraction p was observed. The discontinuity occurs at the percolation threshold pc of the metal, and appears to result from a change in the deformation mechanism at pc. A large peak in compliance (inverse modulus) as measured during indentation unloading was observed in the Ag-Al2O3 films near pc, but was not observed for the Fe-SiO2 films. The compliance peak displayed by Ag-Al2O3 is believed to result from debonding at the metal-ceramic interface and subsequent interfacial sliding, and is not an intrinsic materials property.

Copper-refractory metal composites/alloys are of interest for aerospace and related applications requiring good thermal conductivity and high strength at elevated temperatures[1]. These materials, due to generally very low mutual solubilities, may allow high strength microstructures to be developed which are stable at temperatures exceeding those suitable for precipitation strengthened alloys. Phase stability and mechanical property characteristics of bulk fabricated Cu-refractory metal composites were recently reviewed[2-3]. This paper reports the results of structure-property studies of a series of Cu1–xTax alloys created by RF sputter deposition. It will be shown that nanoscale face-centered-cubic and body-centered-cubic Ta particles form in the Cu matrix and that these Ta particles are very resistant to coarsening at temperatures up to 900ºC. Nanoindentation studies of these alloys reveal that their strengths are also essentially unaffected by exposure to 900ºC for times up to 100 hours.

Nanocrystalline gold and nickel thin films were prepared by both ion beam sputter deposition and electron beam evaporation techniques. The grain sizes were between 8–60 nm, depending on the processing. The deformation and fracture behavior of these nanostructural thin films were then investigated in a high resolution electron microscope (HREM) with atomic resolution. The behavior was a strong function of grain size. During slow strain rate deformation of small grain size materials (< 25 nm), nanopores formed and grew at grain boundary triple junctions in the front of crack and eventually linked with the main crack. The coalescence of the main crack with the growing nanopore, along with the elimination of the ligament between the two by a diffusive process, both indicated that diffusion played a role in deformation and fracture of these nanocrystalline thin films. In nickel films with larger grain sizes (> 25 nm), the cracks propagated in a mixed mode which was partially intergranular and partially transgranular. The transgranular propagation was crystallographic in nature, showing very fine, distinct crystallographic facets on the crack faces. It is suggested that a transition from intergranular propagation to a “cleavage-like” mechanism of propagation occurs with the increase of grain size.

Silicon single crystals have been ion implanted with Si ions at various energies and doses sufficient to achieve amorphisation to a depth of more than 1μm. This surface was subsequently annealed at 450°C for 30 minutes in vacuum to relax the implanted amorphous silicon. Mechanical properties of the different materials (crystalline, amorphous and annealed) were measured using a nominally 10 μm radius diamond tipped indenter and two indenting procedures; continuous loading and load partial-unloading. The crystalline material exhibited similar force-displacement behaviour to that observed by Weppelmann et al. [1] including a critical pressure to induce deformation on loading and a "pop-out" event during unloading. The amorphous and annealed materials showed a greater degree of plastic deformation but did not exhibit "pop-out" behaviour at lower loads (200 mN). The results are analysed to determine the difference of mean pressure with depth of penetration for all the materials. The onset of ductility was 5.5 to 6 GPa for the amorphous material and 10.9 GPa for the crystalline material. The depth dependence of hardness for the amorphous and annealed material showed substantial evidence of work hardening whereas the crystalline material did not.

Pyrolysis of polymer precursors (polysilazane) is a technologically and economically interesting way to produce thin ceramic coatings. However, many cracks appear and decohesion occurs during pyrolysis when the ceramic coatings (SiOCN) are thicker than 0.5 micrometers. In order to understand these cracking phenomena, the coatings are mechanically characterized by nanoindentation at different stages of the pyrolysis heat treatment.

During pyrolysis, the cracking temperature is detected by in-situ optical observation. The thickness of the coatings varies during pyrolysis from 3 micrometers at the polymeric state to 1 micrometer at the ceramic state. The coatings' properties, hardness and Young's modulus are evaluated after heat treatment, taking into account the substrate's influence. A large variation of these properties occurs at the cracking temperature. Both the hardness and the Young's modulus are multiplied by a factor of 10. By analysing these results, we show that cracking is correlated with the evolution of the coatings' mechanical properties during the transformation.

Thin films of tantalum oxide 1 μm thick were deposited by oxygen ion-assisted electron-beam evaporation onto silicon and glass substrates. The packing density and optical properties of the films were controlled by the degree of ion assistance during growth. The films were characterized for hardness by ultra-micro indentation measurement and density by RBS. A strong correlation of hardness, and optical properties was found with the ion-to-vapor arrival ratio at the substrate during deposition. Evaporated films without ion assistance were found to be relatively soft with hardness values of 5.3 GPa and 6.5 GPa on glass and silicon respectively when measured with a Berkovich indenter. When the ion bombardment was increased the film hardness increased to a maximum hardness of 10 GPa for 1000 eV O2 ion bombardment. The measured microhardness of the films was found to be influenced by the nature of the substrate for all depositions with higher microhardness values being recorded for films deposited onto silicon. The films were found to be amorphous and homogeneous. Additional ultra-microhardness measurements with a spherical tipped indenter enabled the depth dependence of hardness and modulus to be determined.

TiN films are prepared by reactive rf magnetron sputtering on carbon steel substrates which are widely applied as structural materials. The electroless Ni-P plating is introduced as an interlayer in the surface modification of TiN coating. The electroless Ni-P deposit crystallizes during rf sputtering due to the elevated sputtering temperature and thus a TiN/Ni3P/Fe coating assembly is formed.

The employment of electroless Ni-P deposit results in an increase in the surface microhardness and adhesion strength. The surface hardness as high as 2266HK1 close to the hardness of bulk TiN can be achieved in the Ni3P interlayer modified TiN coating. With respect to the wear-resistance, the adhesion of the TiN coating plays an important role for the sliding wear-resistance and the interlayer Ni3P acts as a hard , barrier instead of the soft carbon steel substrate.

Thick r.f.-sputtered alumina is used as an overcoat material in microelectronic applications. The stress in the material is compressive and its magnitude is influenced by the sputtering conditions including the power, gas pressure and r.f. substrate bias. These parameters also affect the deposition rate, stoichiometry and sputter gas (argon) content of the material and its etch rate in hydroxide solutions. Nanoindentation measurements of the elastic modulus and hardness are presented for alumina sputtered under different bias conditions and show that the zero bias material appears to be harder and suffer than material deposited at -100V bias.

A nanoindenter has been used to obtain Young's modulus and hardness data for a variety of dielectric thin films including silicon carbide, boron nitride, silicon carbonitride, and silicon oxide. These films, were synthesized by low pressure and plasma enhanced chemical vapor deposition, and had a thickness from 0.25 to a few microns. For the BN films, the modulus and hardness of the films decreased significantly as the deposition temperature increased while the reverse was true for the SiC films. In both cases, these changes were related to variations in the compositions of the deposits due to the onset of different reactions as the temperature is increased. Silicon carbonitride films oxidized slowly when synthesized at temperatures below 200º C and the Young's modulus of these films increased at higher deposition temperatures. For silicon dioxide, there was little change in the composition of the films over the deposition temperature range investigated (375–475º C), thus correspondingly, small variations in the micromechanical properties of the material. However, moisture and hydrogen removal caused by an anneal at 800º C resulted in an significant increase in the modulus and hardness of these films.

Production of thin (10 to 200 microns thick) metallic (Cu, Co and Ni-P) foils is performed by electrodeposition on various substrates. A competition between substrate-induced and electroplating-induced inhibition of crystal growth appears. Film structures observed by SEM, TEM and X-Ray diffraction are related to the mechanical properties of the films (stress-strain curves, microhardness and work hardening bend test).

In some cases, copper thin films with a large number of submicron crystals are obtained. These films recrystallize at room temperature and their mechanical properties are completely modified by this ageing process.

Ultra micro-indentation tests on Ni and Cu samples showed increasing hardness with decreasing penetration depth over a range from 200 to 2000 nm. The results suggest increased strain hardening with decreased indentation depth. To establish that this is a real material effect, a series of tests were conducted on amorphous materials, for which strain hardening is not expected. The hardness of Metglas® was found to be independent of depth. A simple model of the dislocation densities produced under the indenter tip describes the data well. The model is based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness. At large depths, the density of geometrically necessary dislocations is sufficiently small to have little effect on hardness, and the measured hardness approaches the intrinsic hardness of the material.

The adhesion of Pt thin films to NiO substrates has been studied using the continuous microscratch technique. Films of Pt ranging from 65 to 1080 nm in thickness were sputter deposited onto single crystals of NiO. Continuous microscratch experiments were performed by driving a conical diamond indenter, with a nominal radius of 5 μm, simultaneously into and across the film until a load drop was observed indicating that the film had delaminated. The practical work of adhesion was calculated using a theoretical model developed for metal-ceramic systems. The practical work of adhesion increases from 0.03 to 4.7 J/m2 as the film thickness increases from 65 to 1080 nm. The practical work of adhesion includes the true work of adhesion — the energy to produce two new surfaces — and terms involving the plastic deformation of the film and substrate. Extrapolation of the practical work of adhesion versus film thickness data to zero thickness yields a first order estimate of the true work of adhesion. The true work of adhesion for the as-sputtered Pt/NiO system is determined to be 0.025 J/m2, a value of the same order as the Van der Waal’s energy.

Adhesion of Cr, SiO2, TiO2 and Ta2O5 films with thicknesses between 40 nm and 380 nm has been investigated using a new scratch-test method based on a vibrating diamond micro-indenter. The oxide films are produced on different substrates by sol-gel technique (SG), reactive evaporation (RE), reactive ion plating (IP) and plasma impulse chemical vapor deposition (PICVD); Cr-layers are deposited by sputtering (SP) on quartz. Large variations in adhesion are found for different coating techniques and deposition conditions, especially the substrate temperature. The adhesion can be correlated with microscopic properties in the film-substrate interface where differences are analyzed in term of hydrogen content, film growth and density. The adhesion is also connected with other macroscopic film quantities.

We have investigated the tribomechanical properties of ion-beam-densified sol-gel zirconia overlayers on bulk zirconia. Ion irradiation of the sol-gel films leads to hydrogen, oxygen, and carbon losses as indicated by Rutherford backscattering spectrometry and forward recoil energy spectroscopy. Ellipsometry measurements show that the film thickness decreases with increasing dose. The microhardness exhibits an increase and subsequent decrease with dose. Friction measurements along with profilometry measurements indicate that severe abrasive wear of the film takes place in the first 1000 cycles after which point the substrate is in direct contact with the pin.

Thin (0.1 μm) LPCVD polycrystalline silicon (poly-Si) films are shown to exhibit permeability and suffer structural degradation when exposed to concentrated hydrofluoric acid. Analysis by TEM and SEM reveals two attack mechanisms. (1) Poly-Si films deposited onto phosphosilicate glass (PSG) at 605ºC exhibit tensile residual stress and degrade immediately upon exposure to HF, a phenomenon which we attribute to stress-corrosion cracking. Phosphorus from the PSG layer enters the poly-Si during the deposition, resulting in a microstructural gradient which contributes to the cracking mechanism. (2) As-deposited tensile poly-Si films on phosphorus-free LPCVD SiO2 (LTO) and annealed films on LTO and PSG blister at different rates in HF due to penetration at foreign particle inclusion sites and other film defects. Unannealed compressive films deposited at 650ºC onto PSG do not show any evidence of attack.

Silicon rooftop structures 30 µm high and of 1 µm linewidth were fabricated in a microelectronics facility using anistropic KOH etching. Aluminum-1% silicon was sputter-deposited to investigate the effects of a ductile thin film on the fracture toughness of a brittle material. The rooftop structures were indented by a Knoop indenter purposely placed off-center so that the indenter was wedge-shaped. Deformation and cracks were photographed by SEM. Crack threshold load per unit width are reported for normal cracks, running perpendicular to the roofline. Fracture toughness is calculated by first order approximation and finite element modeling using SEM measurements of the length of normal cracks. Without a thin film, values for silicon are in reasonable agreement with the literature. With a thin film of only 600 Å, fracture toughness is increased by 45%. Cracks nearly parallel to the roofline also appeared at higher load values. Characteristics of both types of cracks are discussed.

Evaluations of DLC coated polycarbonates have been carried out via high speed projectile impact, three point bend, and continuous microscratch tests. Radial and circumferential microcracks appeared on the back surfaces and near the regions of impact as a result of the high speed impact stresses. Despite the impact, the adhesion of the DLC coating in the area between the cracks remained, except in the immediate vicinity of impact. In the three point bend tests, transverse cracks developed and propagated in the DLC coating when the applied strain reached the fracture limit of the coating. No delamination occurred in the continuous microscratch tests; instead, cracking of the coating was observed in DLC coated polycarbonates. Microcracking was the dominant mode of failure which was consistent in these three diversed mechanical tests. Results of the SEM studies further confirmed microcracking prior to delamination as observed in the high speed impact tested coupons.

Continuous microscratch experiments have been carried out to investigate the effect of various heat treatments on adhesion in the Cr/Al2O3 system. After samples were prepared by vapor depositing 0.32 µm thick Cr films on (1102) surfaces of single crystal sapphire substrates, they were annealed at different temperatures at controlled oxygen partial pressures. In the subsequent continuous microscratch tests, a conical diamond indenter with a 1 µm tip radius was driven simultaneously into and across the sample until a load drop occurred. Optical and scanning electron microscopy observations demonstrate that a portion of the Cr film delaminated from the Al2O3 substrate at that point. The interfacial strain energy release rate was calculated from the load at failure combined with the size and geometry of the delaminated region. The work of adhesion was found to decrease dramatically on annealing in an H2-Ar mixture at 250°C.

Interface structure and adhesion between a Si substrate after an Ar ion bombardment pretreatment and Ni(100–1500 nm)/Ti(250 nm) double layers prepared in a dc magnetron sputtering apparatus have been investigated.

Two extra layers were generated between the Ti layer and the Si substrate in as-deposited condition. One was an amorphous Si (a-Si) layer(∼ 2 nm) formed on the single crystal Si substrate surface which contains Ar atoms. Another is an amorphous Ti-Si (a-Ti · Si) mixed layer( ∼ 3 nm) on the a-Si layer. A peeling test with an adhesive tape showed that the peeling occurred at the interface between the a-Si and the a-Ti · Si. Ar atoms appeared to be distributed at the interface and the direct contact of the a-Ti · Si layer with the Si substrate seems to be prevented.

After preparing the film and subjecting it to heat treatment at 623 K for 30 min, the adhesion decreased by the accumulation of Ar atoms at the interface. At 723 K for 30 min treatment, however, the adhesion increased probably because of Ar atoms diffusion. It is considered that the Ar atoms incorporated at the interface plays an important role on adhesion of the layer.

Amorphous hydrogenated silicon carbide (a-Si1-xCx:H) films (x = 0.65 to 1) were deposited by radio frequency plasma assisted chemical vapour deposition (RF-PACVD). Their friction and wear properties were investigated by means of a conventional ball-on-disk apparatus. The results were correlated with film mechanical properties. It was found that adding silicon to a-C:H (also called diamond-like carbon (DLC)) films reduces the hardness, elastic modulus and internal stress values by 15 to 30 %. Scratch testing induces film spallation from stainless steel substrates at low loads (1 N). In the low normal load (1 N) ball-on-disk tests under humid N2 conditions, a-Si1-xCx:H films (0.7 < x < 0.9) combine a very low wear rate of both the film and the counterbody with a steady state low friction coefficient below 0.1. For higher loads (5 and 10 N), however, this low friction coefficient only lasts for a relatively short time. In this case, the harder diamond-like carbon films perform tribologically better because of their higher wear resistance, low wear rate of the counterbody and generally low friction coefficients between 0.15 and 0.35 in a humid ambient atmosphere. In a dry N2 atmosphere, pure DLC films perform tribologically better than a-S1-xCx:H films in all respects.