Stress and strain in titanium nitride thin films

Titanium nitride (TiN) films, with thickness ranging from 0.02 µm to 1.9 µm, were grown by reactive unbalanced magnetron sputter deposition on silicon substrates. The average film stress is highly compressive in thin films and less compressive in thicker films.Two films, with thicknesses of 0.53 µm and 1.63 µm, were subjected to detailed X-ray diffraction (XRD) analysis. Sin²Ψ analysis was performed, both on films attached to the substrate, as well as on free-standing flakes of the film. The flakes were obtained by dissolving the substrate. Sin²Ψ analysis, both on the films attached to the substrate as well as on the flakes, did not yield straight lines. By combining the sin²Ψ measurements on films attached to the substrate with the sin²Ψ measurements on the flakes we were able to distinguish between a residual deformation of the lattice and the deformation due to the biaxial stress. Following this procedure the stress obtained from wafer curvature and from XRD strain measurements coincides.A residual strain parallel to the growth direction of the crystallites with the <111> direction parallel to the growth direction combined with a changeover in film texture from <001> parallel to growth direction to <111> parallel to growth direction leads us to propose a model explaining the dependence of stress on film thickness in TiN thin films.     

Antibacterial effects of silver-doped hydroxyapatite thin films sputter deposited on titanium

Since many orthopedic implants fail as a result of loosening, wear, and inflammation caused by repeated loading on the joints, coatings such as hydroxyapatite (HAp) on titanium with a unique topography have been shown to improve the interface between the implant and the natural tissue. Another serious problem with long-term or ideally permanent implants is infection. It is important to prevent initial bacterial colonization as existing colonies have the potential to become encased in an extracellular matrix polymer (biofilm) that is resistant to antibacterial agents. In this study, plasma-based ion implantation was used to examine the effects of pre-etching on plain titanium. Topographical changes to the titanium samples were examined and compared via scanning electron microscopy. Hydroxyapatite and silver-doped hydroxyapatite thin films were then sputter deposited on titanium substrates etched at ? 700 eV. For silver-doped films, two concentrations of silver (~ 0.5 wt.% and ~ 1.5 wt.%) were used. Silver concentrations in the film were determined using energy dispersive X-ray spectroscopy. Hydroxyapatite film thicknesses were determined by measuring the surface profile using contact profilometry. Staphylococcus epidermidis and Pseudomonas aeruginosa adhesion studies were performed on plain titanium, titanium coated with hydroxyapatite, titanium coated with ~ 0.5 wt.% silver-doped hydroxyapatite, and titanium coated with ~ 1.5 wt.% silver-doped hydroxyapatite. Results indicate that less bacteria adhered to surfaces containing hydroxyapatite and silver; further, as the hydroxyapatite films delaminated, silver ions were released which killed bacteria in suspension.     

Study of adhesion of carbon nitride thin films on medical alloy substrates

The adhesion improvement of biocompatible thin films on medical metal alloy substrates commonly used for joint replacement implants is studied. Diamond-like carbon (DLC) and carbon nitride (CN) thin films are, because of their unique properties such as high hardness, wear resistance and low friction coefficient, candidates for coating of medical implants. However, poor adhesion on substrates with high thermal expansion coefficient limits their application. We deposited CN films by pulsed DC discharge vacuum sputtering of graphite target on CoCrMo and Ti6Al4V substrates. Surface nitridation of the substrate, changing the deposition parameters and use of interlayer led to improved adhesion properties of the films. Argon and nitrogen gas flow, thickness of the film and frequency of the deposition pulses had significant influence on the adhesion to the substrate. Properties of deposited films were analyzed using Scanning Electron Microscopy, Raman spectroscopy and tribology tests.     

Deposition and optical studies of silicon carbide nitride thin films

Thin films of silicon carbide nitride (SiCN) have been prepared by reactive radioactive frequency (r.f.) sputtering using SiC target and nitrogen as the reactant gas. Deposition rates are studied as a function of deposition pressures and argon-nitrogen flow ratios. The optical absorption studies indicated the band edge shifting of the films when the nitrogen ratios are increased during deposition. Fourier transform infrared spectroscopy (FTIR) analysis on the films indicated several stretching modes corresponding to SiC, SiN and CN compositions.     

Development of human mesenchymal stem cells on DC sputtered titanium nitride thin films

The biocompatible properties of titanium nitride (TiN) have opened a new field of applications for this material. In the present work, TiN coatings with thicknesses around 1 m have been prepared by DC magnetron sputtering. The aim has been to evaluate the adherence, growth and proliferation of human pluripotent mesenchymal stem cells (hMSCs) on the surface of TiN films with contrasted structural, electrical, and mechanical properties. For this purpose, the films were characterized by X-ray diffraction, scanning electron microscopy, sheet resistance measurements, and nanoindentation. Biological tests show that hMSCs adhere and proliferate onto TiN surfaces. The combination of the mechanical, electrical, and biological responses suggest that TiN coatings present appropriate properties to induce the in vitro stimulated differentiation of hMSCs. This possibility gives an added value to TiN based biomaterial coatings.     

Influence of aluminum nitride interlayers on crystal orientation and piezoelectric property of aluminum nitride thin films prepared on titanium electrodes

Highly c-axis-oriented aluminum nitride (AlN) thin films have been prepared on titanium (Ti) bottom electrodes by using AlN interlayers. The AlN interlayers were deposited between Ti electrodes and silicon (Si) substrates, such as AlN/Ti/AlN/Si. The crystallinity and crystal orientation of the AlN films and Ti electrodes strongly depended on the thickness of the AlN interlayers. Although the sputtering conditions were the same, the X-ray diffraction intensity of AlN (0002) and Ti (0002) planes drastically increased, and the full-width at half-maximum (FWHM) of the X-ray rocking curves decreased from 5.1° to 2.6° and from 3.3° to 2.0°, respectively. Furthermore, the piezoelectric constant d₃₃ of the AlN films was significantly improved from − 0.2 to − 4.5 pC/N.     

Bacterial adhesion to bisphosphonate coated hydroxyapatite

Staphylococcus aureus (S. aureus) is commonly associated with microbial infection of orthopaedic implants. Such infections often lead to osteomyelitis, which may result in failure of the implant due to localised bone destruction. Bacterial adhesion and subsequent colonisation of the device may occur as a consequence of contamination during surgery, or by seeding from a distant site through the blood circulation. Coating of the hydroxyapatite (HA) ceramic component of artificial hip joints with the bisphosphonates clodronate (C) and pamidronate (P) has been proposed as a means to minimise osteolysis and thereby prevent loosening of the implant. However, the effect of the bisphosphonate coating on bacterial adhesion to the HA materials must be determined before this approach can be implemented. In this study coated HA materials were incubated with the S. aureus and the number of adherent bacteria determined using the Modified Vortex Device (MVD) method. The number of bacteria adherent to the P coated HA material was significantly greater than that adherent to uncoated HA (60-fold increase) or to the C coated HA (90-fold increase). Therefore, even though earlier studies suggested that P bound to HA may improve osseointegration, the results presented would suggest that the use of this coating may be limited by the potential increased susceptibility of the coated device to infection.     

Nitrogen pulsing to modify the properties of titanium nitride thin films sputter deposited

TiN _x thin films were grown on (100) Si and glass substrates by dc reactive magnetron sputtering. A titanium target was sputtered in Ar + N₂ atmosphere using a pulsing flow rate of the nitrogen gas. A constant pulsing period was used for every deposition whereas the nitrogen injection time was changed. The systematic variation of the nitrogen injection time led to a gradual decrease of the deposition rate and to a controlled modulation of the chemical composition of the TiN _x films (x between 0 and 1.05). Analysis of the crystallographic structure by X-ray diffraction showed that both Ti and TiN phases coexisted and a change of the preferential orientation from (200) to (111) occurred. The electrical conductivity and colour measurements in the CIE-L*a*b* system of colourimetry were also performed and correlated with the evolution of the N/Ti ratio.     

Vacuum annealing studies of the structure and of mechanical properties of thin titanium nitride films deposited by activated reactive evaporation

Thin titanium nitride layers were deposited by activated reactive evaporation onto two different substrates: high chromium steel strips and steel ball-bearings 10 mm in diameter. Several characteristics of the layers as deposited and after various stages of vacuum annealing in the temperature range 1070–1370 K were investigated: chemical composition, phase composition, morphology and mechanical properties such as microhardness, wear rate and coefficient of friction. As the result of the annealing the mechanical properties change markedly: the microhardness increases by between 20% and 180% and the wear rate decreases by about one order of magnitude. Such significant changes in these two properties were explained in terms of structural changes, which, among others, consist in the creation of a fully recrystallized single δ-TiN phase in place of primary phases, which disappear.     

Conductive-atomic force microscopy study of local electron transport in nanostructured titanium nitride thin films

Simultaneous local current and topography measurements were made on the surface of titanium nitride thin films by conductive-atomic force microscopy (C-AFM). Two compositions, stoichiometric TiN and sub-stoichiometric TiN_0.76 were investigated. Local variation of current at grain and grain boundaries was examined. The current flow is filamentary in nature, with the number of percolation paths being smaller for sub-stoichiometric titanium nitride. Current-voltage characteristics of stoichiometric TiN reveal that the grain interiors are electrically conductive, while in sub-stoichiometric TiN_0.76 thin film, grains are electrically resistive, i.e., a potential barrier to electron transport exists at the junction between the grain and the grain boundary in sub-stoichiometric TiN_0.76. Therefore, electron transport in this film is due to tunneling through the junction, which leads to increased resistivity. The total resistance of the samples measured using the four probe technique is 1 and 400 kΩ for TiN and TiN_0.76 respectively. In both type of compounds the grain and grain boundary resistances are of the order of MΩ. The grain and grain boundaries are connected in a manner that causes the total resistivity to be lower than the local resistivity.     

X-ray analysis of heat-treated titanium nitride films

Titanium nitride films deposited onto steel substrates maintained at 423 K were heat treated in the temperature interval 773–1173 K. Samples were studied by electron probe microanalysis and X-ray diffraction. The high values of the microhardness observed for the as-deposited films decreased after annealing for 3 h at 973 K to nearly bulk values. This decrease is mainly due to the improvement in the microstructure of the films. It is accompanied by strong decreases in strain, stress and the lattice parameter of δ-TiN_x. Growth of the ε-Ti₂N phase at the expense of the δ-TiN_x phase was observed in a film with 34 at .% N when it was annealed for 3 h at 973 K. The lattice parameter and strain in the substrate increased after film deposition, most probably due to a dissolution of nitrogen or titanium atoms in the lattice of -Fe.     

Impedance studies of free-standing,flexible thin films of PVDF filled with gallium nitride nanoparticles

Flexible, free-standing composite films of poly(vinylidene fluoride) (PVDF) with Gallium Nitride (GaN) as fillers, in varying concentrations, were synthesized by sol–gel method. Modulations in the microstructural, morphological and dielectric properties, due to the addition of fillers, were investigated. Modifications in the spherocrystal structure, their dimensions and their number density were observed. Microstructural studies confirmed the presence of GaN nanoparticles in the matrix. FTIR and Raman spectroscopy revealed the presence of the three polymorphs of PVDF in the composite films. The dielectric constant of the composite films were found to increase with the increase in the filler concentration, to almost?~?6 times that of the value for the pristine film due to the interfacial polarization playing between the polymer chains and the filler nanoparticles. Low values of dielectric constant at higher frequencies were observed due to the contribution of dipolar polarization. A peak-to-peak voltage of ~?5.4?V, from a triboelectric nanogenerator fabricated using a 1 wt% composite films, was obtained.

     

氮化碳薄膜的电化学沉积及其电阻率研究

在ITO导电玻璃基底上,采用二氰二胺分散在DMF(N,N-二甲基甲酰胺)中形成的溶液做沉积液,阴极电化学沉积了CNx薄膜。X射线光电子能谱(XPS)和傅立叶转换红外光谱(FTIR)的分析结果表明,沉积的CNx薄膜的N/C比为0.7左右,碳和氮主要以C-N、C=N的形式成键,有少量的碳和氮以C≡N的形式成键。拉曼光谱测试发现其存在多个吸收峰,对其进行分析的结果表明薄膜样品中含有α-C3N4和β-C3N4相的成分。电阻率测试表明,氮化碳薄膜的电阻率值达到1012～1013Ω·cm。     

Pulsed laser deposition of hydroxyapatite thin films

Hydroxyapatite is a bioactive ceramic material that mimics the mineral composition of natural bone. This material does not possess acceptable mechanical properties for use as a bulk biomaterial; however, it does demonstrate significant potential for use as a coating on metallic orthopaedic and dental prostheses. This paper reviews recent developments involving pulsed laser deposition of hydroxyapatite thin films for medical and dental applications. The structural, mechanical, and biological properties of hydroxyapatite thin films are described. In addition, future directions in pulsed laser deposition of hydroxyapatite thin films are discussed.