Number Of Ablation Pulses Research Articles

Pulsed laser deposition of silver nanoparticles on prosthetic heart valve material to prevent bacterial infection

Pyrolytic carbon (PyC) is a biomaterial widely employed as artificial heart valve but prone to bacterial infections like endocarditis. The aim of this investigation was to prevent bacterial colonisation by coating the surface of PyC with a thin film of silver nanoparticles (AgNPs) using pulsed laser deposition (PLD) technique. Thin films were deposited at 5000, 7500, 10,000, 12,500 and 15,000 ablation pulses and characterised by surface profilometer, scanning electron microscopy, energy dispersive X-ray analysis and atomic force microscopy. The antibacterial activity of AgNPs films was evaluated against gram-positive and gram-negative bacteria including methicillin resistant Staphylococcus aureus (MRSA) by the zone of inhibition method. The mean particle sizes of all AgNPs were below 30 nm and the film thickness, roughness and particle size increased with the increase in number of ablation pulses. All films of AgNPs showed significant antibacterial effect against all tested pathogens except that films prepared at 12,500 pulses alone had antibacterial activity against MRSA. The AgNPs coating had led to the betterment of haemocompatibility of PyC especially at 7500 and 10,000 ablation pulses. Film roughness as well as AgNPs’ particle size which are in nano range can be attributed to the inhibition of bacterial growth. The coating of AgNPs thin films on PyC samples using PLD technique had improved haemocompatibility properties and potential to prevent bacterial attack of the biomaterial surface.

Growth temperature dependent surface plasmon resonances of densely packed gold nanoparticles’ films and their role in surface enhanced Raman scattering of Rhodamine6G

Localized surface plasmon resonance (LSPR) characteristics of gold nanoparticles films grown at different substrate temperatures and mass thicknesses with and without alumina capping were studied. At different film mass thicknesses, the LSPR response was observed mainly in the films grown at high substrate temperatures. About 300°C substrate temperature was found to be optimum for producing narrow and strong LSPR band in both uncapped and alumina capped gold nanoparticles films. The LSPR wavelength could be tuned in the range of 600–750nm by changing either number of ablation pulses or decreasing target to substrate distance (TSD) and alumina layer capping. Though the alumina capping re-sputtered the gold films still these films exhibited stronger LSPR response compared to the uncapped films. Atomic force microscopic analysis revealed formation of densely packed nanoparticles films exhibiting strong LSPR response which is consistent with the package density of the nanoparticles predicted by the theoretical calculations. The average size of nanoparticles increased with substrate temperature, number of ablation pulses and decreasing the TSD. For the same mass thickness of gold films grown at different substrate temperatures the surface enhanced Raman scattering (SERS) intensity of Rhodamine6G dye was found to be significantly different which had direct correlation with the LSPR strength of the films at the excitation wavelength.

Coherence effects in surface roughness induced by vacuum ultraviolet F_2 laser ablation

We analyze statistical fluctuations in the pulse-to-pulse spatial fluence distribution of a highly multimode F2 laser beam and the influence that coherence effects have on the attainable smoothness of an ablated surface. The magnitude of fluctuations is predicted to be a few percent, with associated roughness increasing as m1/2, where m is the number of ablation pulses. By use of a white-light optical interferometer, measurements have been made of roughness induced on N-BK7 glass surfaces ablated with a 157-nm laser, and reasonable agreement with predictions based on this roughening mechanism has been found.

Multielemental Laser-Enhanced Ionization Spectrometry for the Determination of Lead at the Trace Level in Pelletized Coal Using Laser Ablation and Internal Standard Signal Normalization

Laser ablation laser-enhanced ionization (LA-LEI) was used for the simultaneous measurement of lead and indium in pelletized graphite and coal samples. UV Laser ablation of the solid samples was performed in an ablation cell and the ablated material was carried by a flow of gas to a miniature LEI flame where lead was detected. The influence of parameters such as binder content of the solid pellets and dispersion of the analytes spiked in the sample material, as well as the number of ablation pulses per crater on signal repeatability and on the size and shape of ejected particles was examined. Measurement repeatability values of 2 to 5% of relative standard deviation were obtained using indium as an internal standard to correct for variations in the ablation rate. A limit of detection of 120 nanograms per gram was calculated for the determination of Pb in high-purity graphite. The Pb concentration in the NIST 1632c Bituminous Coal certified reference material was determined to within 1% of its certified value, using graphite as the matrix-matching material and In as the internal standard in pelletized solid samples.