Nanocolumnar Crystalline Vanadium Oxide-Molybdenum Oxide Antireflective Smart Thin Films with Superior Nanomechanical Properties

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 similar to 45-50 degrees 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 degrees 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

Effect of denture cleansers on color stability, surface roughness, and hardness of different denture base resins

Aim: The purpose of this study was to evaluate the effect of different denture cleansers on the color stability, surface hardness, and roughness of different denture base resins. Materials and Methods: Three denture base resin materials (conventional heat cure resin, high impact resin, and polyamide denture base resin) were immersed for 180 days in commercially available two denture cleansers (sodium perborate and sodium hypochlorite). Color, surface roughness, and hardness were measured for each sample before and after immersion procedure. Statistical Analysis: One-way analysis of variance and Tukey's post hoc honestly significant difference test were used to evaluate color, surface roughness, and hardness data before and after immersion in denture cleanser (α =0.05). Results: All denture base resins tested exhibited a change in color, surface roughness, and hardness to some degree in both denture cleansers. Polyamides resin immersed in sodium perborate showed a maximum change in color after immersion for 180 days. Conventional heat cure resin immersed in sodium hypochlorite showed a maximum change in surface roughness and conventional heat cure immersed in sodium perborate showed a maximum change in hardness. Conclusion: Color changes of all denture base resins were within the clinically accepted range for color difference. Surface roughness change of conventional heat cure resin was not within the clinically accepted range of surface roughness. The choice of denture cleanser for different denture base resins should be based on the chemistry of resin and cleanser, denture cleanser concentration, and duration of immersion

Evaluation of critical depth ratio for soft V2O5 film on hard Si substrate by finite element modeling of experimentally measured nanoindentation response

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 mu m vanadium pentoxide (V2O5) films. The soft V2O5 films were deposited by pulsed radio frequency magnetron sputtering on a relatively hard silicon (Si) substrate. The elasto-plastic properties of the V2O5 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 similar to 0.5t the magnitudes of E and H were approximately two times the values measured at h <= 0.1t. 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 V2O5 films on the hard Si substrate system

Evaluation of elasto-plastic properties of ITO film using combined nanoindentation and finite element approach

Here we report for the first time the combined nanoindentation experiments and finite element modeling to investigate the in-depth nanomechanical behavior of similar to 1.25 mu m indium tin oxide (ITO) film. The ITO film is grown on silicon substrate by a reactive direct current (DC) magnetron sputtering technique. Here, the contributions of both film and substrate are considered in a power law based nonlinear material model. Based on experimental data a detailed study is carried out in the present work to investigate the stress strain behavior, the related von-Mises stress and equivalent plastic strain of the ITO film. In addition, the effect of the nanoindentation response of the ITO film on the silicon substrate is also evaluated. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Simulation of nanoindentation experiment on RF magnetron sputtered nanocolumnar V2O5 film using finite element method

The present work reports the nanomechanical behavior of a pulsed radio frequency (RF) magnetron sputtered vanadium pentoxide (V2O5) film deposited on silicon (Si) substrate using a combination of nanoindentation experiments and a finite element model (FEM). Deposited V2O5 film is characterized by x-ray diffraction (XRD), nanoprofilometry, field emission scanning electron microscopy (FESEM), nanoindentation and FEM. The phase pure 6.16 mu m V2O5 film shows a nanocolumnar structure. The film exhibits nanohardness (H) of 0.16 +/- 0.013 GPa and Young's modulus (E) of about 12.05 +/- 1.41 GPa. The FEM reproduces experimentally obtained load versus depth (P-h) plot and subsequently give yield stress and strain hardening component data of V2O5 film on Si substrate. Stress-strain behavior and von-Mises stress distribution of the V2O5 film with Si substrate system are also simulated. The FE model confirms the local maximum equivalent stress active underneath the nanoindenters to be nearly twice as high as the yield stress and thereby explains the plastic deformation observed in the V2O5 film

Effect of low temperature vacuum annealing on microstructural, optical, electronic, electrical, nanomechanical properties and phase transition behavior of sputtered vanadium oxide thin films

Vanadium oxide thin films were deposited on quartz substrate by pulsed RF magnetron sputtering technique at 400-600 W and subsequently annealed at 100 degrees C in vacuum (1.5 x 10(-5) mbar). Phase analysis, surface morphology and topology of the films e.g., both as-deposited and annealed were investigated by x-ray diffraction, field emission scanning electron microscopy and atomic force microscopy techniques. X-ray photoelectron spectroscopy (XPS) was employed to understand the elemental oxidation of the films. Transmittance of the films was evaluated byUV-vis-NIR spectrophotometer in the wavelength range of 200-1600 nm. Sheet resistance of the films was measured by two-probe method both for as-deposited and annealed conditions. XPS study showed the existence of V5+ and V4+ species. Metal to insulator transition temperature of the as-deposited film decreased from 339 degrees C to 326 degrees C after annealing as evaluated by differential scanning calorimetric technique. A significant change in transmittance was observed in particular at near infrared region due to alteration of surface roughness and grain size of the film after annealing. Sheet resistance values of the annealed films decreased as compared to the as-deposited films due to the lower in oxidation state of vanadium which led to increase in carrier density. Combined nanoindentation and finite element modeling were applied to evaluate nanohardness (H), Young's modulus (E), von Mises stress and strain distribution. Both H and E were improved after annealing due to increase in crystallinity of the film