Bubble-assisted microstreaming during electrode deposition of Mn2O3 energy harvesters.

The deposition of energy-harvesting Mn2O3 onto the "Cu" electrode is reported using pulsed laser ablation at the manganese-water interface. Conventionally, laser-induced plasma deposition is carried out by orthogonally placing the substrate (electrodes) in the plasma expansion. Here, underwater material deposition is observed on electrodes placed parallel to the plasma expansion. The possible role played by the fluid dynamically assisted microbubbles in transporting the materials onto electrodes is investigated here. To verify the influence of microbubbles, external electric fields are employed, and implications for the electrodes are characterized. The studies reveal that the external field intensifies the flow of the microbubbles towards the walls, which assists in the deposition of Mn2O3 on the electrodes.

Experimental demonstration of in situ surface and thickness profile measurements of thin film during deposition using a grating array based wavefront sensor.

Here we introduce an in situ and non-intrusive surface and thickness profile monitoring scheme of thin-film growth during deposition. The scheme is implemented using a programmable grating array based zonal wavefront sensor integrated with a thin-film deposition unit. It provides both 2D surface and thickness profiles of any reflecting thin film during deposition without requiring the properties of the thin-film material. The proposed scheme comprises a mechanism to nullify the effect of vibrations which is normally built in with the vacuum pumps of thin-film deposition systems and is largely immune to the fluctuations in the probe beam intensity. The final thickness profile obtained is compared with independent off-line measurement and the two results are observed to be in agreement.

Fabrication of photoluminescent nc-Si:SiO2 thin films prepared by PLD.

In the present report, the structural, compositional, morphological, and photoluminescence properties of nanostructured non-stoichiometric silicon oxide (nc-Si:SiO2 or SiOx) thin films fabricated by pulsed-laser ablation of silicon in the presence of oxygen pressure, from 10-4 to 0.5 mbar, are presented. X-ray diffraction spectra and Raman spectra confirmed the formation of nanocrystalline Si within the films while electron diffraction X-ray spectroscopy confirmed the increase in oxygen content with increasing O2 pressure. Scanning electron microscopy images of the SiOx films showed spreading of the micron-sized clusters on the otherwise uniform background, while Raman maps confirm the presence of nanocrystalline Si in these clusters embedded in a uniform matrix comprising oxidized amorphous silicon. A systematic blue shift in the band gap energy from 1.55 to 2.80 eV was observed with increasing O2 pressure in the SiOx films due to a shift in the stoichiometry of the films from x = 0.03 to 2.14 respectively. The films with higher oxygen content exhibited broad and intense PL emissions with multiple peaks originating from quantum confined (QC) Si nanocrystals as well as oxygen defects like NBOH and VO centers. The variation in PL intensity as a function of excitation intensity displays an initial linear increase followed by saturation, a characteristic feature of emissions from QC nc-Si.

Effect of focusing conditions on laser-induced shock waves at titanium-water interface.

The spatial and temporal evolution of laser-induced shock waves at a titanium-water interface was analyzed using a beam deflection setup. The focusing conditions of the source laser were varied, and its effect onto the dynamics of shock waves was elucidated. For a tightly focused condition, the speed of the shock wave was ~6.4 Km/s, whereas for a defocused condition the velocities reduced to <3 km/s at the vicinity of the titanium-water interface. When the laser is focused a few millimeters above the target, i.e., within the water, the emission of dual shock waves was observed toward the rear side of the focal volume. These shock waves originate from the titanium-water interface as well as from the pure water breakdown region, respectively. The shock wave pressure is estimated from the shock wave velocity using the Newton's second law across a shock wave discontinuity. The shock wave pressure for a tightly focused condition was 18 GPa, whereas under a defocused condition the pressure experienced was ≤1 GPa in the proximity of target.

Efficacy of cellulose paper treated with Cu and Ag oxide nanoparticles synthesized via pulsed laser ablation in distilled water in the annihilation of bacteria from contaminated water.

In the present work, nanoparticles of copper and silver synthesized via pulsed laser ablation of the respective targets in distilled water are applied to cellulose filter paper to check their effectiveness in the annihilation of bacteria from contaminated water. The treatment of the filter paper with the nanoparticles is found to be an excellent way to get rid of two common bacteria, Staphylococcus aureus and Escherichia coli, from contaminated water. The spread plate method on agar, employed to test the antibacterial efficacy of the nanoparticle-treated papers, clearly shows the absence of bacterial growth upon coming into contact with the nanoparticles in the filter paper. These results were further substantiated by the growth kinetic study of the bacteria that exhibited slow growth of the bacteria that were exposed to the nanoparticles. The morphology of the bacteria that came into contact with the nanoparticles is found to be adversely affected by the nanoparticles. Both copper and silver nanoparticles show a similar extent of antibacterial activity.

Correlation between surface scaling behavior and surface plasmon resonance properties of semitransparent nanostructured Cu thin films deposited via PLD.

The surface scaling behavior of nanostructured Cu thin films, grown on glass substrates by the pulsed laser deposition technique, as a function of the deposition time has been studied using height-height correlation function analysis from atomic force microscopy (AFM) images. The scaling exponents α, ß, 1/z and γ of the films were determined from AFM images. The local roughness exponent, α, was found to be ∼0.86 in the early stage of growth of Cu films deposited for 10 minutes while it increased to 0.95 with a longer time of deposition of 20 minutes and beyond this, it was nearly constant. Interface width w (rms roughness) scales with depositing time (t) as ∼ t ß , with the value of the growth exponent, ß, of 1.07 ± 0.11 and lateral correlation length ξ following ξ = t 1/z and the value of 1/z = 0.70 ± 0.10. These exponent values convey that the growth dynamics of PLD Cu films can be best described by a combination of local and non-local models under a shadowing mechanism and under highly sticking substrate conditions. From the scaling exponents and power spectral density function, it is concluded that the films follow a mound like growth mechanism which becomes prominent at longer deposition times. All the Cu films exhibited SPR properties where the SPR peak shifts towards red with increasing correlation length (ξ) whereas bandwidth increases initially with ξ and thereafter decreases gradually with ξ.

Role of confining liquids on the properties of Cu@Cu2O nanoparticles synthesized by pulsed laser ablation and a correlative ablation study of the target surface.

The effect of confining liquid on the properties of copper nanoparticles synthesized by pulsed laser ablation in two organic solvents, methanol and 2-propanol is investigated along with the effect of the laser irradiation time on the synthesized nanoparticles. To understand the role of confining liquids on the formation mechanism of the nanoparticles in different environments, the results obtained in the organic solvents are compared to those obtained in distilled water. The increase in the average size of the nanoparticles from 7-19 nm with the laser irradiation time from 15-60 minutes is accompanied by a shift in the plasmonic peak towards longer wavelength from 606-621 nm, respectively in methanol. In the case of nanoparticles synthesized in 2-propanol, the average size of the nanoparticles increases from 9-17 nm and there is a corresponding shift in the SPR peak from 581-601 nm, respectively. The increase in the size of the nanoparticles with the increase in irradiation time in the organic solvents is the reverse trend of that obtained for nanoparticles synthesized in distilled water. The range of the plasmonic peak positions is blue shifted for the nanoparticles synthesized in methanol and 2-propanol as compared to that of 626-641 nm for the nanoparticles synthesized in distilled water indicating the formation of insufficiently oxidized nanoparticles in organic solvents. Formation of core-shell spherical copper nanoparticles with carbon encapsulation in methanol and 2-propanol is another interesting observation. The origin of the dependence of properties of the synthesized nanoparticles on the ambient liquid lies in the way the laser beam interacts with the target surface in the ambient. A detailed ablation study on the laser produced crater in all the three liquids is carried out to understand the factors that affect the properties of the nanoparticles.

Note: large area deposition of Rh single and Rh/W/Cu multilayer thin films on stainless steel substrate by pulsed laser deposition technique.

Mirror like thin films of single layer Rh and multilayer Rh/W/Cu are deposited on highly polished 50 mm diameter stainless steel substrate by Pulsed Laser Deposition (PLD) technique for first mirror application in fusion reactors. For this, the conventional PLD technique has been modified by incorporating substrate rastering stage for large area deposition via PLD. Process optimization to achieve uniformity of deposition as estimated from fringe visibility and thickness is also discussed.

Note: epitaxial ruby thin film based photonic sensor for temperature measurement.

Deposition of optical quality C-axis oriented epitaxial thin film of ruby via pulsed laser deposition technique on sapphire substrate is reported. The film is characterized by Raman spectra and photoluminescence spectra. The peak positions of R-line and the corresponding linewidth are observed to be temperature dependent. The sensitivity of R(1)-line position, υ, with the temperature, (dυ/dT), in the range of 138-368 K shows linear behavior confirming its applicability as temperature sensor.

Mirrorlike pulsed laser deposited tungsten thin film.

Mirrorlike tungsten thin films on stainless steel substrate deposited via pulsed laser deposition technique in vacuum (10(-5) Torr) is reported, which may find direct application as first mirror in fusion devices. The crystal structure of tungsten film is analyzed using x-ray diffraction pattern, surface morphology of the tungsten films is studied with scanning electron microscope and atomic force microscope. The film composition is identified using energy dispersive x-ray. The specular and diffuse reflectivities with respect to stainless steel substrate of the tungsten films are recorded with FTIR spectra. The thickness and the optical quality of pulsed laser deposition deposited films are tested via interferometric technique. The reflectivity is approaching about that of the bulk for the tungsten film of thickness ∼782 nm.