Anand Kumar Sharma

Vanadium oxide-molybdenum oxide (VO-MO) thin (21–475 nm) films were grown on quartz and silicon substrates by pulsed RF magnetron sputtering technique by altering the RF power from 100 to 600 W. Crystalline VO-MO thin films showed the mixed phases of vanadium oxides e.g., V₂O₅, V₂O₃ and VO₂ along with MoO₃. Reversible or smart transition was found to occur just above the room temperature i.e., at ~45–50 °C. The VO-MO films deposited on quartz showed a gradual decrease in transmittance with increase in film thickness. But, the VO-MO films on silicon exhibited reflectance that was significantly lower than that of the substrate. Further, the effect of low temperature (i.e., 100 °C) vacuum (10⁻⁵ mbar) annealing on optical properties e.g., solar absorptance, transmittance and reflectance as well as the optical constants e.g., optical band gap, refractive index and extinction coefficient were studied. Sheet resistance, oxidation state and nanomechanical properties e.g., nanohardness and elastic modulus of the VO-MO thin films were also investigated in as-deposited condition as well as after the vacuum annealing treatment. Finally, the combination of the nanoindentation technique and the finite element modeling (FEM) was employed to investigate yield stress and von Mises stress distribution of the VO-MO thin films.

The purpose of this present study was to evaluate the effect of vacuum (i.e., 10⁻⁵ mbar) heat treatment at 300 to 1100 °C on morphological, thermo-optical, mechanical and tribological properties of 75 μm thin SS304 foils. Microstructural, morphological and surface properties of the foils were characterized by field emission scanning electron microscopy (FESEM), profilometry, x-ray photoelectron spectroscopy (XPS) and water contact angle (WCA) measurement techniques, respectively. The x-ray diffraction (XRD) was employed to identify the phase of SS304 foils after different heat treatment temperatures. Thermo-optical properties such as solar absorptance (α _s), reflectance (ρ _s) and IR emittance (ε _ir) were also evaluated. The nanomechanical properties i.e., nanohardness (H) and Young's modulus (E) of as-received and heat treated SS304 foils were evaluated by the nanoindentation technique. Tribological and tensile properties i.e., yield strength (σ _y) and percentage of elongation of different heat treated foils were also investigated by single pass scratch tests and universal testing machine, respectively. Noteworthy grain growth of SS304 was observed beyond vacuum heat treatment temperature of 700 °C. As a consequence, the magnitudes of both H and E data of SS304 were significantly decreased beyond the vacuum heat treatment temperature of 700 °C. Further, the hardness data followed the well known Hall–Petch relationship. On the other hand, the tribological property of SS304 was significantly deteriorated beyond the vacuum heat treatment temperature of 700 °C. The tensile strength of the foils was also altered after the heat treatment.

A combined nanoindentation experiment and finite element modeling (FEM) approach was utilized in the present work to evaluate the effects of variations in the ratio ( h / t ) of indentation depth ( h ) to film thickness ( t ) on the nanomechanical behavior of 2.3–6.2 μ m vanadium pentoxide (V ₂ O ₅ ) films. The soft V ₂ O ₅ films were deposited by pulsed radio frequency magnetron sputtering on a relatively hard silicon (Si) substrate. The elasto-plastic properties of the V ₂ O ₅ films as well as the Si substrate were evaluated using a power law-based nonlinear material model. Based on the present nanoindentation and FEM results the critical penetration depth to film thickness ratio ( h / t ) _c , i.e. critical depth ratio (CDR) was predicted as 7.9%,,confirming thereby that there is no universal critical penetration depth beyond which the mechanical properties of the substrate start to affect the evaluated nanomechanical properties (e.g. nanohardness H , Young’s modulus E, etc) of a given soft film on a given hard substrate. The experimental data showed that at h ~ 0.5 t the magnitudes of E and H were approximately two times the values measured at h ⩽ 0.1 t . The FEM results obtained in the present work successfully predicted the effects of variations in the h / t ratio on the indenter displacements as well as the distributions of the von Mises stress for the soft V ₂ O ₅ films on the hard Si substrate system.