Nanosecond pulsed laser irradiation resulting in material ablation and surface micro structuring of Yttria Stabilized Zirconia (YSZ) targets, has been investigated. Our study aims to evaluate suitable ablation conditions enabling either, creation of desired YSZ surfaces having micro porosity for directed use, or generation of YSZ vapors for deposition of homogenous, dense and particle free YSZ films via conventional Pulsed Laser Deposition (PLD) technique. The work being reported here involves a thermal model based theoretical simulation describing heat transport, melting and vaporization of a laser irradiated YSZ target. Our simulation has been validated against our experimental data on nanosecond laser ablation from a sample target of ceramic YSZ. Surface porosity generated on laser irradiated YSZ targets for low laser fluence levels ∼ 1 ​J/cm2 has been explained in terms of pore formation via entrapment of gas bubbles in the solidifying interface on laser melting and re-solidification thereafter, of the YSZ target. To understand surface crater formation on laser irradiated YSZ targets at high laser fluence levels ∼10 ​J/cm2 maximum temperature reached by the laser irradiated YSZ target has been compared with the thermodynamic critical temperature of YSZ. Our study confirms that judicious choice of laser fluence enables either, creation of surfaces having micro porosity of desired nature on YSZ target, or controlled generation of YSZ vapors for deposition of good quality YSZ films and coatings using laser deposition technique.

Experimental results and theoretical simulation of material ablation on nanosecond Nd:YAG laser irradiation of bioactive glass targets, is presented. The process of pulsed laser ablation critically affects both, laser based surface modification and pulsed laser deposition (PLD) of bioactive glass (BG). A thermal model based theoretical simulation has been carried out describing heat-transport, melting and vaporization of a laser irradiated BG target under near-threshold ablation conditions. Calculated mass ablation rate per laser pulse has been compared with our experimental observations over the average laser fluence of 0.5J/cm2 to 6J/cm2. With increasing laser fluence, possibility of material ablation approaching phase explosion has been discussed by comparing the calculated maximum temperature reached by the laser irradiated target and the estimated thermodynamic critical temperature for BG. Our investigations indicate that with average laser fluence restricted to ∼5 J/cm2 material ablation occurs largely via normal vaporization ensuring deposition of an uniform, homogeneous BG coating through PLD. Target surface temperatures estimated from our calculations also suggest that laser based surface modification of BG can be reproducibly carried out without causing target crystallization and surface damage through crater formation for irradiating laser fluence in the region of ∼ 5J/cm2.

Abstract A theoretical model has been used to simulate pulsed laser ablation of Lanthanum Phosphate (LaPO4) by nanosecond Nd:YAG laser irradiation. Material ablation rate per laser pulse was experimentally measured as a function of average incident laser fluence up to 12J/cm2. Calculations were performed by solving the heat conduction equation by an explicit finite‐difference technique to generate time evolution of temperature distribution, melt depth and ablation rate from the target during and after irradiation with a nanosecond laser pulse. Good agreement between our experimental and calculated ablation rates validates our theoretical model. The calculated maximum surface temperature of the LaPO4 target indicated that for laser fluence levels, up to 20J/cm2 material ejection from LaPO4 target is expected to occur via normal boiling and evaporation successfully avoiding explosive boiling. Our calculations confirm that operating with laser fluence at near ablation threshold levels for LaPO4 also restricts dissociation of the LaPO4 target to oxides with loss of gaseous products. Therefore, our study of pulsed laser ablation of LaPO4 target helps in making judicious selection of laser parameters for Pulsed Laser Deposition (PLD) of LaPO4 coatings and films of desired stoichiometric purity and homogeneity, while successfully ensuring phase stability of the target.

Radio-Frequency Plasma Enhanced Chemical Vapour Deposition (RF-PECVD), and Pulsed Laser Deposition (PLD) techniques were used to deposit boron carbide (BxC) thin films. Films were investigated to compare crystallinity, chemical composition, optical properties, and residual stress. X-ray diffraction analysis revealed that the film deposited by PLD was amorphous, while PECVD technique yielded crystalline BxC film. PLD technique provided films with better stoichiometric purity with B4C being the most dominant phase, as observed in XPS spectra. However, super-stoichiometric phase (BxC (x > 4)) was dominant in PECVD film. Moreover, the PECVD film had greater adhesion (Lc(3) similar to 29.5 N), hardness (similar to 2798 HK), and lubricity (COF similar to 0.03) compared to PLD deposited film. Optically, PECVD deposited film have higher value of refractive indices (1.82 at 600 nm) and lower extinction coefficient. Finally, residual stress measured via substrate curvature method revealed that for PLD 400 C film, the stress was compressive in nature while the same for PECVD -100 V film was tensile, with 10 times less in magnitude. Ultimately, this study provides the user with opportunity to weigh the advantages and disadvantages of PECVD and PLD techniques for deposition of functional BxC films.

Bioactive glass 45S5 (BG) has been proposed as a biomaterial and extensively studied on account of its superior bioactive behavior. In this paper, we report our results on thin film deposition of BG on Ti6Al4V alloy using pulsed laser deposition (PLD) technique. ANd:YAG laser (532 nm) based pulsed laser deposition system has been used for this work. Post deposition, surface morphology, and chemical composition of the obtained films on Ti-alloy surface have been examined using scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDX). In vitro bioactivity of these PLD coated Ti-alloy samples was evaluated by immersing the BG coated Ti-alloy samples in simulated body fluid (SBF) for 10 days. SBF immersed samples have been analyzed using SEM, EDX, and micro Raman spectroscopic techniques. Superior growth of bone like apatite i.e. hydroxyapatite (HAP) have been observed on such BG coated Ti-alloy samples in comparison to uncoated Ti-alloy in our investigations. Also, biocompatibility tests carried out by us measuring tolerance of U2OS osteosarcoma cells to these PLD coated Ti6Al4V samples have shown positive results.

This study narrates the findings regarding investigation of tribological properties of BxC:Hy thin films deposited by Radio Frequency Plasma Enhanced Chemical Vapour Deposition (RF-PECVD) technique. To study tribological properties, two sets of films were prepared with variation in composition and thickness by tuning deposition parameters. Tribological properties were studied in ambience for three different applied vertical load values (5, 10 and 15 N). Lower self-bias (−75 V) seems advantageous for synthesis of BxC:Hy films offering superior hardness, lubricity and wear resistance in tribologically stressed conditions. For a given composition, the film with the highest thickness (∼3 μm) exhibited better friction and wear resistance, offering lowest co-efficient of friction (COF) ∼0.23 for 5 N load and specific wear rate of 2.56 × 10−5 mm3/Nm for 10 N load. Lower self-bias during deposition (−75 V) seems advantageous for synthesis of BxC:Hy films having high hardness (∼2800 HK) and excellent Co-efficient of friction (COF).

The present paper describes a failure investigation of a tube that had shown leakage in a shell and tube type heat-exchanger with 70/30 cupronickel tubes and mild steel baffles (13 nos.). Corrosion damage or thinning of the failed tube was found to have occurred from the outer surface at all the baffle locations. Further examination of the failed tube was done using an optical microscope, a scanning electron microscope equipped with energy dispersive spectroscopy, Raman spectroscopy and an instrumented microhardness indentation machine for hardness measurement. Based on the results, it was concluded that the failure and the loss in wall thickness of the tube at locations where it was in contact with the mild steel baffles were caused by fretting corrosion. The focus of this investigation is to bring out the metallurgical changes and the surface conditions (including changes in microstructure and microhardness, mode of corrosion attack and type of oxides/corrosion products) of the tube material undergoing fretting corrosion at micro level. Recommendations to avoid such a failure are also suggested.

This article reports our simulation results on a period of surface micro-protrusions, which are generated on titanium and stainless steel 304 target surfaces by femtosecond pulsed laser irradiation. The period of the generated micro-protrusions for varying laser fluence level has been estimated using an approach derived from the linear hydrodynamic Kuramoto Sivashinsky model. Some of the parameters, needed for calculating the period of surface micro-protrusions, have been estimated by numerically solving one-dimensional heat equations. Temperature evolution inside the target upon irradiation with a femtosecond laser pulse has been simulated using the two temperature model until the time electron and lattice subsystems attain thermal equilibrium. Thereafter, temperature evolution in the target has been simulated by defining a single temperature of the target at every position and time. We have validated our theoretical model by comparing simulated variation of period of surface micro-protrusions with incident laser fluence, ablation depth per pulse, and time required for thermalization between electrons and lattice subsystems with the reported experimental data for titanium target. Subsequently, the validated model has been used to simulate the period of surface micro-protrusions which are generated on the stainless steel 304 target via femtosecond laser irradiation.

Carbon nanowalls (CNWs) have been synthesized by electron-cyclotron resonance chemical vapour deposition (ECR-CVD) method on Si substrates. During deposition, processing gas compositions were varied to improve growth rate and it was found that replacing inflammable H-2 by safer and cheaper N-2 improves growth rate of CNWs. Energy dispersive x-ray spectroscopy and Fourier transform Infra-red spectroscopy results showed that N-2 did not take part in bond formation. Emissive probe diagnostics showed that increasing precursor gas to 90% of total gas mixture increases impinging ions' energy by 3.5 times leading to deposition of vertically oriented CNWs on Si substrate.

Titanium and its alloy are most widely used implant materials in dental and orthopaedic fields. However, infections occurring during implantation leads to implant failure in most of the cases. Here, we have demonstrated antibacterial behavior of Ti6Al4V alloy achieved when surface modified using femtosecond laser beam. Post laser treatment conical microstructures were observed on the Ti6Al4V alloy surface. Generation of different sub-oxide phases of titanium dioxide were detected on laser treated samples using X-ray diffraction and X-ray photoelectron spectroscopy. Wettability of Ti6Al4V alloy surface changed significantly after interaction with the laser. Adhesion and growth of two gram positive; Staphylococcus aureus and Streptococcus mutans and one gram negative Pseudomonas aeruginosa bacteria have been explored on pristine, as well as, on laser textured Ti6Al4V alloy surfaces. In-vitro investigation on agar plate showed inhibition of bacterial growth on most of the laser treated surface. Superior surface roughness and occurrence of magneli phases of titanium dioxide on laser treated surface were probably responsible for the antibacterial behavior exhibited by the laser treated samples. Therefore, femtosecond laser surface treatment of Ti6Al4V alloy could find potential application in the development of infection free medical implants for dental and orthopedic usages.

Biological performances such as osseointegration and biocompatibility of Ti6Al4V alloy primarily depends on topological and chemical properties of the surface of the bio-material. Here, a nanosecond pulsed Nd:YAG laser has been used to generate microstructures on Ti6Al4V surface by irradiating with 6000 number of laser shots per site. Formation of ripple structure and generation of sub-oxide phases on laser treated titanium surface supported uniform and dense growth of HAP on the sample. In contrast, discrete nucleation of HAP with comparable higher precipitation of calcium occurred on untreated Ti6Al4V sample when subjected to similar in vitro tests by exposing the sample to simulated body fluid. Initial interaction and growth of U2OS cells on untreated and laser treated Ti6Al4V substrates were quantified using MTT assay. More numbers of cell were attached to laser treated sample in comparison to untreated sample as observed in confocal microscope images. Our results suggested that surface patterning of Ti6Al4V alloy using nanosecond pulsed laser promoted bio-integration without compromising its biocompatibility. Copyright © VBRI Press.

In this paper we report our results on nanosecond laser based surface micro (mu)-structuring of Tantalum (Ta) samples and their field emission behavior. Surface micro-structuring has been carried out using a typical laser fluence of 0.9 J cm(-2) and varying number of incident laser pulses in the range of 3000 to 9000. Laser treated samples have been characterized in terms of surface morphology, chemical phase and field emission behavior. Nanosecond laser irradiation resulted in formation of self assembled surface mu-protrusions in the laser treated region. Peak height of the generated mu-protrusions and average roughness of the laser treated region increased with increasing number of irradiating laser pulses. Laser treated specimens have shown enhanced field emission in comparison to pristine Ta specimen. Specimens mu-structured using 3000, 6000 and 9000 laser pulses per spot have shown field emission with turn on field (E-on) of 6.6 V-1 mu m(-1), 4.8 V-1 mu m(-1) and 3.7 V-1 mu m(-1), respectively. Also, maximum emission current density delivered by these laser modified specimens was found to increase with increasing number of laser pulses. Although, Ta specimen mu-structured with 9000 laser pulses has shown highest emission current density, emission current stability of this sample was poorer in comparison to specimens modified using 3000 and 6000 laser pulses.

A thermal model based simulation of nanosecond laser irradiation of a Ti6Al4V alloy has been described. Material ablation rates per laser pulse for a laser fluence of up to 15J/cm(2) experimentally measured by the author have shown good agreement with results of the model calculations, duly validating the theoretical approach. Calculated ablation threshold is also in agreement with the experimental data on Ti6Al4V. Calculated maximum temperature reached by a laser irradiated Ti6Al4V target has been compared with an estimated thermodynamic critical temperature for titanium, indicating that for laser fluence below 20J/cm(2) target ablation occurred largely through normal boiling and vaporization. Following this, a simulation based approach allows selection of optimum laser parameters successfully avoiding the onset of explosive boiling in the case of Ti6Al4V targets. Maintaining laser fluence close to the ablation threshold ensures surface texturing of Ti6Al4V with minimum associated surface damage.

Nanocrystalline cobalt boride (Co-B) thin films prepared by pulsed laser deposition were used as an anode catalyst to study the water oxidation reaction in alkaline medium. Elemental depth profiling revealed the bulk of the film to be metallic, which helps in improving conduction of charges, while the surface of the film was rich in CoOOH-type species to facilitate the oxygen evolution reaction (OER). Comparison of OER performance with boron-free samples suggests that inclusion of B helps in improving the OER rate by preventing the conversion of surface Co to stable oxides. The Co-B film achieved a current density of 10 mA/cm(2) at merely 280 mV, with potentiostatic stability for 45 h in alkaline medium, highlighting its superior performance than the powder catalyst. This work not only establishes the advantage of developing thin-film catalysts but also presents a new approach to understand the OER mechanism in metal borides.

This paper presents our results on surface micro-structuring of tantalum samples using femtosecond (fs) pulsed laser irradiation and its effect on field emission performance. Micro-structuring of Ta targets has been carried by varying laser fluence in the range 0.35–0.55 J/cm2 while keeping target scan speed constant at 25 µm/s. Laser-treated surfaces have shown the formation of high density micro-protrusions and an oxide phase mainly consisting of crystalline Ta2O5. Our results showed substantial improvement in field emission performance of laser micro-structured surfaces in comparison to pristine Ta surface. Areal number density of micro-protrusions decreases from 8.8 × 105 to 3.5 × 105 protrusions/cm2 as incident laser fluence varied from 0.35 to 0.55 J/cm2. Ta sample micro-structured with 0.55 J/cm2 laser fluence has shown low turn on field (~ 4.0 ± 0.6 Vµm− 1) and high-field enhancement factor (4500 ± 500).

Results on nanosecond pulsed laser irradiation and ablation of graphite are presented. Theoretical simulation based on a thermal model describing heat-transport and vaporization from a graphite target has been employed to calculate mass ablation rate per laser pulse. Attenuation of the incident laser beam in the generated vapor plume has been incorporated in terms of two coefficients, a and b, that serve as the only fitting parameters for our simulation model. Comparison between experimentally measured data and calculated mass ablation rate per pulse confirmed that the laser ablation mechanism was largely normal vaporization, in the incident laser fluence range of 10–25 J/cm2. Calculated maximum temperature reached by graphite target surface on laser irradiation and its dependence on average laser fluence enabled us to assess the possibility of the onset of explosive boiling in the target. A good agreement between model calculations and experimental results on the ablation rate for laser fluence below ∼30 J/cm2 validates our theoretical model. Our study facilitates a proper selection of laser fluence successfully minimizing laser induced explosive boiling in graphite targets, thereby ensuring deposition of pulsed laser ablation based carbon films and coatings with good microstructural and mechanical properties.

Plasma is probably the most underused tool applied for nuclear waste management. To study the feasibility of putting this technology in practice, a non-thermal microwave based atmospheric pressure plasma jet (APPJ) had been developed. The device was characterized by spectroscopic technique prior to its actual deployment inside glove box to narrow down its operational regime and also tested on Ta, a known surrogate of Pu which showed its efficacy in etching. The device was then used for removal of Pu based synthetic radioactive wastes inside radioactive glove box. Thereafter, optimization studies were conducted to maximize decontamination efficiency and it was seen that oxygen in plasma plays a significant role. The same device was later scaled up to a multi-electrode model and used for similar radioactive waste removal. Both these devices under optimized condition could remove ∼92% radioactive wastes and the scaled up model reduced duration by 50%.

Advance designs of random lasers towards development of miniature laser systems are in demand. We demonstrated random lasing from Rhodamine-B dye attached to polystyrene micro-spheres. Bare polystyrene spheres were used as scatterers and these provided optical feedback to the gain. Random lasing was successfully demonstrated in two different disordered environments, in binary colloidal mixture solution and in photonic glass. Incoherent feedback occurred in both the cases and single wavelength lasing were obtained. The lasing threshold in case of photonic glass was lower in comparison to binary colloidal mixture solution. This was because of higher index contrast and larger filling fraction of micro-particles in case of photonic glass. Longer fluorescence lifetime of embedded dye was observed in photonic glass environment in comparison to ethanolic solution of the Rhodamine-B dye. Lasing results obtained for photonic glass were compared with our previous results of Bloch lasing in photonic crystal synthesized using similar dye doped polystyrene micro-spheres.

A single electrode microwave based atmospheric pressure plasma jet (APPJ) had been developed, characterized and applied for decontamination of Pu based synthetic radioactive waste. Argon plasma with small amount of CF4 and O2 was used for this purpose. The device was initially characterized by optical emission spectroscopy (OES) to determine its operational regime and used on Ta, a known surrogate of Pu for testing its efficacy in etching. Parametric optimization studies had been conducted thereafter on solid radioactive wastes of Pu and it was seen that presence of oxygen in plasma plays a crucial role in efficient removal of contamination. A scaled up multi-electrode version of this device was later designed and employed inside the glove box for similar studies. It was seen that 92 optimized condition with both the devices and the scaled up APPJ device reduced operation time by 50