Nanoindentation Techniques for the Evaluation of Silicon Nitride Thin Films

Silicon nitride thin films are of interest in the biomedical engineering field due to their biocompatibility and favorable tribological properties. Evaluation and understanding of the properties of these films under diverse loading and failure conditions is a necessary prerequisite to their use in biomedical devices. Three wafers of silicon nitride-coated silicon were obtained from Lawrence Livermore National Laboratory and used to create 96 samples. Samples were subjected to nanoindentation testing to evaluate the mechanical properties of the film. Samples were subjected to nanoimpact testing to compare the damage resistance of the film to separate nanoimpact types. Samples were subjected to nanoscratch testing to evaluate the consistency of the critical load of the film. Results showed that there were no significant differences in the mechanical properties of the film across the tested groups. There was a significant difference observed in the rate of damage to the film between pendulum oscillation nanoimpact testing and sample oscillation nanoimpact testing, with the former causing more damage with all experiment variables controlled for. Results showed that the critical load measure for the film was significantly different between different nanoscratch test parameters. The conclusions from this study will support future work for in vitro and in vivo testing of ceramic thin films for biomedical applications

Evaluation Of Elastic Modulus And Stress Gradient Of PECVD Silicon Nitride Thin Films

This study investigated the techniques for determining the elastic modulus and estimating the stress gradient of plasma-enhanced chemical vapor deposition (PECVD) silicon nitride thin films. The experimentally determined elastic modulus was then used in a finite element beam model to compute the stress distribution inside the thin films using a commercial finite element analysis package. The computed beam displacement caused by a given stress gradient was compared with the displacement experimentally evaluated using optical interference microscopy. This comparison allows the stress gradient of the PECVD silicon nitride membrane introduced by the fabrication process to be evaluated

W-Cr-C-N Nanocomposite Thin-Film Coatings via Reactive Magnetron Sputtering

While binary tungsten carbide can form smooth, hard films, these suffer from low fracture toughness. Tungsten nitride films are frequently harder, but are more brittle. Chromium nitride has excellent wear and oxidation resistance, but films often form with low hardness. Composites of these binary compounds offer a possibility to tailor the material for a desired combination of properties. To this end, we have used reactive RF-magnetron sputtering with Cr and WC targets to form quaternary composites, with nitrogen as the reactive gas. The coatings were deposited on Si, Ti, and steel substrates. The nitrogen partial pressure was varied to investigate the relationship between the film properties and the deposition conditions. Energy dispersive spectroscopy showed changes in the chemical composition as a result of the change in nitrogen partial pressure. X-ray diffraction illuminated the structure as either a solid solution with a B1 NaCl structure, or a nanocomposite with the average crystallite size under 11 nm. Optical interferometer revealed low compressive stresses. And nanoindentation established that the films are hard and adherent.U.S. National Science Foundation (DMR-0806521) and the Regional Council of Burgundy, Franc

Nanomechanical inhomogeneities in CVA-deposited titanium nitride thin films: Nanoindentation and Finite Element Method Investigations

Refractory metals that can withstand at high temperatures and harsh conditions are of utmost importance for solar-thermal and energy storage applications. Thin films of TiN have been deposited using cathodic vacuum arc deposition (CVA) at relatively low temperatures ~ 300 oC using the substrate bias ~ -60V. The nanomechanical properties of these films were investigated using nanoindentation and the spatial fluctuations were observed. The nanoindentation results were simulated using finite element method (FEM) through Johnson-Cook model. We have found the local nitridation plays an important role on nanomechanical properties of TiN thin films and confirms that the nitrogen deficient regions are ductile with low yield stress and hardening modulus. This study further opens the opportunities of modelling the nanoscale system using FEM analysis

Solar selective performance, Opto-dielectric and mechanical characteristics of vacuum fabricated metal nitride thin film coatings

In the present study, metal nitride based sputtered thin film coatings such as Mo/Si, CrN/Si, and Mo:CrN/Si were investigated for their solar selective surface and mechanical applications. Despite a large number of literature is available in the area of solar selective applications of metal nitride based thin film coatings, these materials are still to be commercialized for their practical device applications. In view of this, we chose metal nitride based thin film coatings e.g., Mo, CrN and Mo:CrN to realize their structural, morphological, elemental compositions, optical, dielectric and mechanical properties in as-deposited, and annealed conditions. Detail analyses of these features were carried out using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-Ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy and FTIR, nanoindentation and finite element modeling (FEM). In addition to these, the first principle based density functional theory (DFT) integrated with the B3LYP hybrid functional plus LANL2DZ basis sets based infrared (IR), Raman and ultraviolet-visible (UV-Vis) analysis were also carried out to probe the electronic structural and optical properties of pristine and Mo-doped CrN clusters in the non-crystalline phase. Optical analysis showed that in the visible range of the solar spectrum, the CrN coatings exhibit the highest solar absorptance of 66% while the lowest thermal emittance value of 5.67 was recorded for the CrN coating doped with Mo. As a result, the highest solar selectivity of 9.6, and the energy band-gap of 2.88 eV were achieved with the Mo-doped CrN coatings. On the other hand, optical studies of the annealed coatings showed that with the rise in annealing temperature up to 700 °C, the solar absorptance of CrN coatings increased from 61% to 89% and slightly decreased at 800 °C, while the optical band-gap energy dropped from 2.62 to 1.38 eV but slightly increased to 1.48 eV at 800 °C. Nanoindentation results indicated that as the annealing progresses, the hardness and elastic modulus values of CrN coatings are lowered. Further optical studies of Mo-doped CrN coatings showed that as the annealing temperature increased up to 700 oC, the solar absorptance is increased from 55% to its maximum value of 86%, and the optical band-gaps were dropped from 2.48 to 1.14 eV. Nanoindentation and finite element modeling studies of Mo-doped CrN coatings indicated that as the annealing progresses, both the hardness and elastic modulus values of these coatings reduced. A first principle based DFT simulation on Cr4N4, Cr4MoN3, Cr4Mo2N2, Cr3MoN4, Cr3Mo2N3, and Cr2Mo2N4 clusters indicated that the Cr4Mo2N2 structure was chemically and energetically the most stable species among the six clusters considered. The DFT based electronic analysis revealed that Cr4MoN3 and Cr3Mo2N3 clusters possess magnetic susceptibility while the infrared (IR), Raman and ultraviolet-visible (UV-Vis) studies indicated that the clusters formed by Cr4N4 and Cr4Mo2N2 are naturally stable and able to function as light harnessing materials to be used in solar selective surfaces

Effect of thermal annealing and carbon implantation on the functional properties of nanocomposite TiSiN coatings on steel

This PhD research contributes to the part of advanced materials technology. The machining industry currently faces tremendous pressures with the need for durable cutting tools suitable for eco-friendly high speed machining operations becoming acute. In this thesis innovative design and synthesis strategies are explored to tailor the properties of nanocomposite coatings. Advanced characterisation techniques are applied to identify the mechanisms that control the mechanical, tribological, and corrosion behaviours of these coatings. Cutting tools protected by these coatings are anticipated to exhibit a unique combination of superior toughness and greater resistance to wear and corrosion, providing significant economic and environmental benefits. The thin ceramic coatings are commonly applied to various kinds of steel cutting and machining tools to enhance their mechanical and tribological properties. The most common ceramic coating is TiN. But the major issues that hamper the application of TiN are high friction co-efficient (typically~0.5), lower hardness, lower thermal stability (~5000 C) and lower corrosion resistance. To address some of these problems, TiSiN nanocomposite coatings are developed, which have super-hardness, better thermal stability (~10000C) and better corrosion resistance. But the as-deposited TiSiN coating still has high co-efficient of friction (~0.4) and high residual stress (~7-9 GPa) which consequently affect the adhesion and toughness of the coating. This project aims to address these problems by (a) the application of carbon implantation to modify the structure and chemistry of the surface layer of the nanocomposite coatings with reduced friction and residual stress; and (b) thermal annealing of the nanocomposite coating to reduce the residual stress with enhanced fracture toughness, better corrosion resistance and more thermal stability. In addition, the role of microstructure, residual stress and defects of these hard coating in corrosive environment will be studied. For this research, a combination of microstructural and mechanical properties characterization, corrosion analysis, tribological test and finite element modelling facilities will be used. The study includes focused ion beam (FIB) milling and transmission electron microscopy (TEM), Synchrotron X-Ray Diffraction (XRD), X-ray Photo Spectroscopy (XPS), Energy dispersive X-Ray (EDX), nanoindentation, nano-scratching, potentio-dynamic polarization cell and Atomic force microscopy(AFM)

Alumiininitridi-ohutkalvojen mekaaninen luotettavuus

The purpose of this Master's Thesis is to study the mechanical reliability of aluminum nitride thin films. This is done by measuring the relevant mechanical properties of the thin films through use of the bulge test. The Young's moduli, residual stresses, ultimate tensile strengths and fracture toughness of AlN thin films are measured. A fatigue cycling experiment is conducted in order to study the effects of cyclic loading on these films. The measurements are conducted on films of two thicknesses produced by sputtering (54 and 220 nm) and on a 126 nm film deposited with MOVPE. The implications of the results are analyzed in detail with an error analysis, and the way these material properties can be used in design for reliability is presented.Tämän diplomityön tarkoitus on tutkia alumiininitridi-ohutkalvojen mekaanista luotettavuutta. Tutkimus on toteutettu mittaamalla bulge test-testimetodin avulla näiden ohutkalvojen relevantit mekaaniset ominaisuudet. Alumiininitridi-ohutkalvojen kimmokertoimet, jäännösjännitteet, murtolujuudet ja murtositkeydet on mitattu. Kalvojen väsymisominaisuuksia tutkittiin syklitystestillä. Mittaukset on tehty kahdella eri pinnoitustekniikalla (sputterointi ja MOVPE) tuotetuille kalvoille. Testatut sputteroidut kalvot ovat 54 nm ja 220 nm paksuja, ja MOVPE-kalvot 126 nm paksuja. Tuloksien luotettavuus, sekä tuloksista tehtävissä olevat johtopäätökset ovat esitelty yksityiskohtaisesti. Tapoja, joilla tuloksia voi käyttää luotettavien alumiininitridi-ohutkalvoja käyttävien sovellusten suunnittelemisessa, on annettu

Small scale fracture behaviour of multilayer TiN/CrN systems: Assessment of bilayer thickness effects by means of ex-situ tests on FIB-milled micro-cantilevers

TiN/CrN multilayered PVD coatings are known to exhibit outstanding micromechanical properties and wear resistance. On the other hand, information on their small scale fracture behaviour is rather scarce. The present work aims to address it by testing to failure FIB-milled microbeams of multilayer TiN/CrN systems with different bilayer periods (8, 19 and 25 nm). In doing so, these micrometric specimens are first FIB notched, and thus deflected by means of a nanoindentation system. It is found that multilayer architecture translates into a beneficial synergic effect regarding critical load for reaching unstable failure; and thus, on energy absorption at fracture. Such behaviour is associated with small scale crack deflection as main toughening mechanism.Peer ReviewedPostprint (author's final draft

Investigation Of Reactively Sputtered Boron Carbon Nitride Thin Films

Research efforts have been focused in the development of hard and wear resistant coatings over the last few decades. These protective coatings find applications in the industry such as cutting tools, automobile and machine part etc. Various ceramic thin films like TiN, TiAlN, TiC, SiC and diamond-like carbon (DLC) are examples of the films used in above applications. However, increasing technological and industrial demands request thin films with more complicated and advanced properties. For this purpose, B-C-N ternary system which is based on carbon, boron and nitrogen which exhibit exceptional properties and attract much attention from mechanical, optical and electronic perspectives. Also, boron carbonitride (BCN) thin films contains interesting phases such as diamond, cubic BN (c-BN), hexagonal boron nitride (h-BN), B4C, β-C3N4. Attempts have been made to form a material with semiconducting properties between the semi metallic graphite and the insulating h-BN, or to combine the cubic phases of diamond and c-BN (BC2N heterodiamond) in order to merge the higher hardness of the diamond with the advantages of c-BN, in particular with its better chemical resistance to iron and oxygen at elevated temperatures. New microprocessor CMOS technologies require interlayer dielectric materials with lower dielectric constant than those used in current technologies to meet RC delay goals and to minimize cross-talk. Silicon oxide or fluorinated silicon oxide (SiOF) materials having dielectric constant in the range of 3.6 to 4 have been used for many technology nodes. In order to meet the aggressive RC delay goals, new technologies require dielectric materials with

Enhancing Diamond-Like Carbon Adhesion on AISI 316L Stainless Steel Using Chromium Nitride Interlayers

Energy losses in moving components due to high friction and wear are one of the biggest challenges faced by industries. AISI 316L stainless steel (SS) is one of the most widely used alloyed steel for moving parts in corrosive environments. However, its poor tribological properties result in limited longevity and performance. As lubrication is not an option for food processing and biomedical devices, surface modification of the SS is usually required. Nitriding and carburizing can enhance its wear resistance but result in a high coefficient of friction (COF) and poor corrosion resistance. Coating Diamond-like carbon (DLC) films are very promising to lower its COF and increase its wear and corrosion resistance as well as biocompatibility. However, the application has been limited due to its poor adhesion to SS substrates. The present thesis work aims to use a chromium nitride (CrN) thin film as an interlayer to enhance DLC adhesion on the SS substrate. CrN thin films with various microstructures and thicknesses were first deposited onto the SS substrate using radio frequency magnetron sputtering under different deposition conditions. DLC coatings were then deposited on the CrN interlayered SS substrates using ion beam deposition (IBD). The deposited CrN interlayers and DLC coatings were then characterized by various techniques including grazing incidence X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy, optical profilometry, nanoindentation, Rockwell C indentation, and ball-on-disc tribological testing. The results show that the microstructure and the corresponding mechanical properties of the sputtered CrN thin films can be tailored by changing deposition parameters. CrN films deposited at 470 °C and 10 mTorr pressure had a dense, net-like structure with a hardness of 8 GPa, and significantly enhanced DLC adhesion on the steel. The interlayer, deposited with a thickness ranging from 0.4 to 2.1 µm, was found to play an important role in improving DLC adhesion. The thicker the interlayer, the better the adhesion. Furthermore, good DLC adhesion on the steel was achieved by doping DLC with nitrogen at a thinner CrN interlayer of 1.1 µm because of the reduced intrinsic stress in nitrogen doped DLC coatings. Finally, wear testing results showed that DLC coating can decrease COF and wear rate of the steel when sliding with AISI 302 ball