Three-dimensional simulation schemes for discrete dislocation dynamics (DDD) have been used successfully to investigate plasticity of bulk materials. The adaptation of these DDD schemes to a description of thin-film plasticity requires detailed modeling of the interfaces and surfaces of the film. One possible method is to compensate for the normal stresses that a dislocation distribution exerts on a surface by appropriate point loads. This traction-compensation method is extended to a free standing film (two opposing surfaces). The extension to a thin film on a substrate is possible.

This work investigates the sintering kinetics and residual stresses which develop in thin layered ceramic structures when sintered on a rigid substrate. A continuum constitutive framework to model the evolution of the microstructure and stresses in the sintering layers under non-isothermal conditions is presented. The sintering model is used to investigate the constrained sintering behaviour of layered ceramic structures used in solid oxide fuel cells (SOFC). Samples of a 50 μm thick SOFC film were screen-printed on a fully dense yttriastabilised zirconia substrate and then sintered at temperatures ranging from 1100°C to 1300°C. Measured values of relative density and average grain size are compared with model predictions. A correlation between residual stresses extracted from curvature measurements and analytical predictions revealed these stresses to have been mostly relieved during the subsequent cooling by microcrack formation.

A molecular dynamics simulation of amorphous SiO2 thin films has been made to investigate the structure and internal stress. The atomic configuration of the amorphous structure is investigated through the radial distribution function and the distribution of Si-O-Si bond angles. Distribution of internal stress through the specimen is evaluated from the volume and the shape of the SiO4 tetrahedron, which is the elementally unit of amorphous SiO2.

By use of dc-magnetron sputtering, (111) textured Ag/Ni multilayered thin films were deposited with nominal bilayer repeat lengths ranging from 2 nm to 250 nm. Bulk and interface stresses were obtained from X-ray diffraction and measurements of substrate curvatures. Both in-plane and out-of-plane expansions were observed in the Ni layers, and a compressive interface stress of −2.24±0.21 J/m2 was found. This is in agreement with a previously published result of the interface stress in Ag/Ni thin films which had, as opposed to the present multilayers, a high level of total stress.

Elementary dislocation arrays are applied to multilayered thin films to predict the critical stress required to propagate dislocation loops within individual layers and to study the tendency for deformation to be uniform or localized. The analyses suggest that shearing normal to layers is a mechanically unstable, softening process while stretching parallel to layers produces substantial hardening. Further, films with smaller layer thickness, h, require larger plastic strains to initiate pile-up modes of slip. Although the initial stress required to propagate an isolated loop within a single layer scales as ln(h)/h, there is a minimum h below which the critical stress is predicted to depend only on the resistance of the interface to dislocation transmission.

A detailed study of microhardness of multilayered films has been strongly needed to reveal effects of film layer structures and deposition conditions on the film hardness. A nanoindentation method is a useful method to investigate mechanical properties of thin films prepared on substrate materials. In this respect we have deposited a several types of Ti/TiN multilayered films and estimated their hardness by a nanoindentation method. The desired compositional modulation was obtained by changing the flow rate of N2 gas periodically using a computer system. The modulation period has been varied from 10 to 40nm by changing a flow rate control pattern. The total thickness of the film was about 500nm including the underlayer of the TiO2(50nm)/Ti(50nm) multilayer for all samples with different modulation period. Substrates used in the experiment were borosilicate glass and not heated during film deposition. The compositional distribution toward to the film depth orientation was estimated by Auger electron spectroscopy. The dynamic hardness of the films has been estimated by a nanoindenter as a function of the modulation period. It was found that there existed an optimum modulation period of 20nm to enhance the film hardness by multilayer structure.. The maximum value of microhardness obtained for the optimum modulation period was 29GPa, which was much larger than that of the monolithic TiN coating of 15GPa. The hardness measurement results show that the behavior for dynamic hardness was different from that for plastic deformation hardness obtained.

The microstructures and mechanical properties of Cu/Cr multilayers prepared by sputtering onto {100} Si substrates at room temperature are presented. The films exhibit columnar grain microstructures with nanoscale grain sizes. The interfaces are planar and abrupt with no intermixing, as expected from the phase diagram. The multilayers tend to adopt a Kurdjumov- Sachs (KS) orientation relationship: {110}Cr //{111}Cu, <111>Cr //<110>Cu. The hardness of the multilayered structures, as measured by nanoindentation, increase with decreasing layer thickness for layer thicknesses ranging from 200 nm to 50 nm, whereas for lower thicknesses the hardness of the multilayers is independent of the layer thickness. Dislocation-based models are used to interpret the variation of hardness with layer periodicity. The possible effects of factors such as grain size within the layers, density and composition of films and residual stress in the multilayers are highlighted. Comparisons are made to the mechanical properties of sputtered polycrystalline Cu/Nb multilayers which, like Cu/Cr, exhibit sharp fcc/bcc interfaces with no intermixing and a KS orientation relationship, but have a small shear modulus mismatch.

During growth of Cu/Pd multilayers the apparent stress in the Cu layers changes from compressive to tensile during the growth of a single Cu layer. The apparent stress in the Pd layers is initially either tensile or compressive depending on the thickness of the underlying Cu layer. It has been speculated that this stress behaviour may be either a result of island growth of Cu on Pd or alloying at the Cu/Pd interface[I]. We have observed that the stress behavior is similar in Cu/Pd and Pd/Pt multilayers and continue to study these systems to better understand the origins of stress in metal multilayers. Stress evolution during growth is monitored by in-situ substrate curvature measurement using a multiple parallel laser beam technique. High angle superlattice spectra for the multilayers are found from symmetric x-ray diffraction scans in order to determine crystallographic texture. Information about interfacial disorder and alloying in the layers is obtained from simulation of the superlattice diffraction patterns. Stress behaviour is correlated with possible modes of growth of the layers, and with atomic peening and coherency effects.

The magneto-mechanical properties of Terfenol-D thin films deposited on Si substrates were studied by magnetic and mechanical measurements of film/substrate composite cantilevers. The AE effect and mechanical damping of the film were measured simultaneously. The stress in the film was controlled by annealing and deposition at different temperatures as well by the selection of the substrate material below the recrystallization temperature and determined to vary from -500 MPa, compression, in as deposited films to +480MPa, tension, in annealed films. This paper highlights the magneto-mechanical response of tensioned 1 m nanocrystalline Terfenol-D films on 50 Pim Si substrates display a pronounced damping maximum at a magnetic field of about 1.5kOe oriented perpendicular to the plane of the film. The phenomenon is critically dependent on the orientation of the magnetic field and is the result of a magneto-mechanical instability in the Terfenol film.

Dislocation segments which extend through the thickness of a film can move through the film only if dislocation line length is deposited or removed at the film/substrate and film/passivation (if any) interfaces. The dislocation density and, therefore, the energy stored in the film increase during plastic deformation. The reverse process, that is, the reduction of strain energy in the film by the reduction of dislocation line length, is here suggested to be the origin of a number of unexplained features of experimentally obtained stress-temperature curves, including very low (or even “negative”) yield stresses in compression, tensile-compressive flow stress asymmetries, increasing strength with increasing temperature upon heating, and a very strong Bauschinger-like effect which has been seen in thin Cu films. The results of stress-temperature measurements of passivated Cu thin films on silicon substrates are presented.

The hardness, elastic modulus, and fracture toughness of chemical vapor deposited (CVD) polycrystalline diamond have been investigated on several thick (∼100 μm) free-standing films with regard to the grain size, impurity content and failure mechanisms. Micro-hardness measurements using Vickers indentation, in conjunction with Young's modulus measurement techniques such as nano-indentation, were employed to estimate the indentation fracture toughness. The toughness of CVD diamond was increased through the addition of non-diamond carbon, which promoted intergranular fracture and enhanced the toughness by grain bridging.

Mechanical properties of titanium nitride (TiNx) thin films have been investigated using the bulge test and the depth sensing nanoindentation measurements. The bulge test was performed on the square free standing membranes made by means of standard micromachining of silicon wafers, while the nanoindentation was conducted on the films adhered to their supporting substrate. Thin layeres of titanium nitride (t = 300 – 1000 nm) were deposited in a r. f. magnetron sputtering system on the Si(100) wafers containing a layer of low stress LPCVD silicon nitride (SiNy). The bulge test was first conducted on the silicon nitride film to determine its proper residual stress and Young's modulus. Then, the composite membrane made of TiNx together with underlying silicon nitride was bulged and the related load-displacement variation was measured. Finally, using a simple rule of mixture formula the elastic mechanical properties of TiNx coatings were calculated. Both the Young's modulus and residual stress showed increasing values with negative bias voltage and nitrogen to titanium ratio, but the substrate temperature between 50–570°C was found less significant as compared to the other parameters. Nanoindentation data extracted from dynamically loading-unloading of TiN films converged to the bulge test measurements for compact coatings, but diverged from the bulge test data for porous coatings. Scanning electron microscopy observation of the cross sectioned specimens showed that TiN films first grow by formation of the nanocrystallites of size mostly between 10 – 15 nm. These nanocrystallites give rise to the columnar morphology beyond a thickness of 50–100 nm. The columns change their aspect with deposition parameters, but remain nearly perpendicular to the film surface. Relationship between microstructural evolution of columns and mechanical properties of coatings are discussed in terms of deposition parameters.

Using standard deposition and micromachining techniques, silicon substrates with square and rectangular windows covered with membranes of polycrystalline silicon (polysilicon) have been fabricated. Pressure-displacement curves obtained during the bulge testing of membranes with the above geometries have been used to determine the elastic constants E and v of the polysilicon. The results obtained (E = 162± 4 GPa and v = 0.19±0.03) are in good agreement with literature values for bulk polycrystalline silicon.

Low temperature diamond deposition on metal substrates is motivated by the need to reduce thermal stress so that the film adhesion is satisfactory. Although the use of oxygen-con- taining gas mixtures have been shown to extend the temperature range for which diamond can grow as well as to improve film quality, most studies have focused on the use of silicon as sub- strates and have neglected technologically important metallic systems. To this end, microwave plasma chemical vapor deposition (MPCVD) was used to grow diamond films on Ti-6A1-4V alloy at low temperature (615 to 780 C) using CH4/O2/H2 and CO/H2 gas mixtures. In-situ pyrometric interferometry (ISPI) shows that as the oxygen concentration increases, the onset time for dia- mond nucleation and subsequent film surface roughness increases while the average growth rate decreases. Micro-Raman spectroscopy shows improved film quality and suggests a trend toward increasing in-plane compressive stress with increasing oxygen concentration. Glancing-angle x- ray diffraction (XRD) was complimentary to the Raman data and indicates the presence of a TiC interfacial layer thickness which decreases with increasing oxygen concentration. We found that the CO/H2 mixture resulted in poorly adhered “white soot” films with low diamond content whereas the CH4/O2/H2 mixture yielded well adhered high quality diamond films.

Thin films of B4C and SiC deposited by magnetron sputtering as components of multilayers have the potential to provide significant property improvements over current wear resistant coating technology. B4C and SiC have previously been found to be amorphous and possibly nanocrystalline under the deposition conditions used. This study reports results of synchrotron x-ray scattering experiments providing information on the degree of crystallinity, strain, average density, and coordination number in 2000 Å films of these compounds on Si substrates. Radial distribution functions from B4C and SiC thin films were obtained and used to model the structure. Strain results are compared with Double Crystal x-ray Diffraction Topography (DCDT) results as a means for establishing a standard strain state.