R. Ramaseshan

Response of magnetron sputtered AlN films to controlled atmosphere annealing

The present investigation deals with the examination of the response of amorphous AlN films to post-deposition annealing environments such as high vacuum (HV) and nitrogen atmosphere (NA). The c/a ratio values from GIXRD for both cases are around 1.602. The XPS profile of NA-AlN shows a deficiency of nitrogen on the surface, whereas the oxygen impurity level is negligible in the case of NA compared with HV. The PL spectra substantiate the nitrogen vacancies in NA-AlN. The amorphous AlN exhibits a nanoindentation hardness of 18 GPa.

Investigation of temperature dependent dielectric constant of a sputtered TiN thin film by spectroscopic ellipsometry

The temperature dependence of optical constants of titanium nitride thin film is investigated using Spectroscopic Ellipsometry (SE) between 1.4 and 5 eV in the temperature range of 300 K to 650 K in steps of 50 K. The real and imaginary parts of the dielectric functions e1(E) and e2(E) marginally increase with increase in temperature. A Drude Lorentz dielectric analysis based on free electron and oscillator model are carried out to describe the temperature behavior. With increase in temperature, the unscreened plasma frequency and broadening marginally decreased and increased, respectively. The parameters of the Lorentz oscillator model also showed that the relaxation time decreased with temperature while the oscillator energies increased. This study shows that owing to the marginal change in the refractive index with temperature, titanium nitride can be employed for surface plasmon sensor applications even in environments where rise in temperature is imminent.

Nanomechanical and optical properties of highly a-axis oriented AlN films

This paper reports optical and nanomechanical properties of predominantly a-axis oriented AlN thin films. These films were deposited by reactive DC magnetron sputtering technique at an optimal target to substrate distance of 180 mm. X-ray rocking curve (FWHM = 52 arcsec) studies confirmed the preferred orientation. Spectroscopic ellipsometry revealed a refractive index of 1.93 at a wavelength of 546 nm. The hardness and elastic modulus of these films were 17 and 190 GPa, respectively, which are much higher than those reported earlier can be useful for piezoelectric films in bulk acoustic wave resonators

Synthesis of nanostructured titanium nitride films by PLD through reactive processing

Abstract High quality TiN films were synthesised from elemental metallic target using reactive and plasma assisted pulsed laser deposition (RPLD and PAPLD) techniques. In these processes, a high pure titanium target is ablated using a nanosecond pulsed Nd:YAG laser operating at 1064 nm wavelength at different nitrogen pressures. In RPLD process, the titanium plume reacts directly with the nitrogen gas at pressures less than 0·07 mbar to yield TiN films. In PAPLD process, additional nitrogen plasma was generated and confined by a DC coil positioned between target and substrate. Resultant films were characterised for phase, composition and morphology using glancing incidence X-ray diffraction, Auger Electron Spectroscopy (AES), Rutherford back-scattering and Atomic Force Microscope (AFM). Reactive pulsed laser deposition grown TiN films were found to contain traces of unreacted titanium. The crystallite size is estimated to be 15 and 50 nm respectively by using X-ray diffraction and AFM. Rutherford backscattering investigations helped the authors in arriving at the stoichiometry and AES analysis revealed the formation of TiN with low oxygen contamination.

Preferentially oriented electron beam deposited TiN thin films using focused jet of nitrogen gas

A modified electron beam evaporator has been used to synthesise TiN thin films with (111) preferred orientation. This new design involved in creating local plasma by accelerating the secondary electrons emitted from the evaporating ingot by a positively biased semi-cylindrical anode plate (biased activated reactive evaporation). To accelerate the reaction to form TiN, a jet of gas has been focused towards the substrate as a reactive gas. We have observed a preferred orientation (111) with to the surface normal in pole figure analysis. The residual stress by the classical sin technique did not yield any tangible result due to the preferred orientation. The hardness and modulus measured by nanoindentation technique was around 19.5 and 214 GPa. The continuous multicycle indentation test on these films exhibited a stress relaxation.

Structural and optical properties of sputtered AlN thin films

Wurtzite type AlN thin films were grown on Si (100) substrate using DC reactive sputtering with varying substrate temperatures (35-600 °C). The phonon vibrational study of these films was performed by Raman Spectroscopy, where E2 (High) mode was observed with a movement of peak position from red shift to blue shift due to change in residual stress. Cross sectional TEM micrograph of these AlN films showed a columnar structure. Using phase modulated ellipsometry, refractive index and extinction co-efficient of the film were extracted based on new amorphous model and found to be 2.2 and 0.03 at a wavelength of 250 nm, respectively.

Growth and characterization of a-axis oriented Cr-doped AlN films by DC magnetron sputtering

Wurtzite type Cr-doped AlN thin films were grown on Si (100) substrates using DC reactive magnetron sputtering with a function of N2 concentration (15 to 25%). Evolution of crystal structure of these films was studied by GIXRD where a-axis preferred orientation was observed. The electronic binding energy and concentration of Cr in these films were estimated by X-ray photoemission spectroscopy (XPS). We have observed indentation hardness (HIT) of around 28.2 GPa for a nitrogen concentration of 25%.

Evaluation of the nanostructure of cervical third cementum in health and chronic periodontitis: An in vitro study.

Background: During the progression of periodontal disease, the cementum undergoes alterations in its structure and composition. Understanding the nanostructure of cementum, in terms of its mechanical properties, will provide an insight into the milieu that periodontal ligament cells encounter in health and chronic periodontitis. This study aims to analyze the nanomechanical properties of the cervical third of the cementum (transverse section) in health and chronic periodontitis. Materials and Methods: Twenty teeth (10 healthy and 10 periodontally diseased) were collected and the nanomechanical properties of the transverse section of the cervical third cementum were evaluated with depth-sensing nanoindentation technique under dry conditions. A total of 100 nanoindentations were performed to analyze the modulus of elasticity and hardness of cervical third of the cementum. Results: The nanomechanical properties of the healthy cervical third cementum sections were significantly higher (P < 0.05) (hardness: 0.720 ± 0.305 GPa; modulus: 15.420 ± 3.902 GPa) than the diseased cementum section (hardness: 0.422 ± 0.157 GPa; modulus: 11.056 ± 3.434 GPa). Conclusion: The results of our study indicate that the hardness and modulus of elasticity of the cervical third cementum decreases significantly in chronic periodontitis.

Surface modification and mechanical property studies of Ti 6 Al 4 V alloy using high power diode laser in nitrogen atmosphere

Ti6Al4V alloy was surface modified by Laser surface nitridation with a high power diode laser (HDPL) in a nitrogen atmosphere in an acrylic chamber. In this report, a complete study of structure and mechanical properties of two scanning speeds (5, 10 mm/sec) presented, by keeping the power (3 kW) and nitrogen gas flow (75 l/min) as constant after a complete study of various powers and nitrogen gas flow. A complete conversion of Ti6Al4V alloy to TiN on the surface was observed by X-ray diffraction in the case of slow scanning speed (5 mm/sec), whereas unreacted Ti was observed in the fast scanning speed (10 mm/sec). The surface roughness of slow scanning speed (5 mm/sec) was larger than the fast scanning speed (10 mm/sec). Nanoindentation hardness of slow scanning speed and fast scanning speed were 18 GPa and 16 GPa, respectively. Friction coefficient of unmodified Ti6Al4V alloy was measured as 0.7, whereas slow and fast scanning speed was 0.42 and 0.62, respectively.

Structural and nano-mechanical characterization of TiN / Ti 1−x Al x N multilayered thin films

Nanostructured multilayers have high interface area densities along with other factors such as periodicity, single layer thickness, sharpness, in general lead to improved mechanical properties. In this study, we have selected a combination of two metallic hard materials, such as cubic TiN and metastable cubic TiAlN sub-layers to synthesize a periodic multilayer thin films. Advantage of TiAlN as a sub-layer is the stability against oxidation due to the formation of dense Al2O3, which prevents further oxidation. These periodic TiN/TiAlN multilayers were synthesized by reactive magnetron co-sputtering technique on SS 304 LN substrates with TiN as a starting sub-layer and TiAlN as next with bi-layer thicknesses 7 nm to 60 nm. GIXRD results confirm the formation of metastable TiAlN with NaCl structure which is similar to TiN with a shift in the peak position. The individual layers were resolved by X-TEM and Secondary Ion Mass Spectroscopy to understand the architecture. Depth sensing nanoindentation was used to study the surface hardness which clearly explains the reverse Hall-Petch relationship (change in the periodicity). The maximum surface hardness of 34 GPa was obtained for a bi-layer thickness of 30 nm.