No abstract

We report a comparative study of the ultraviolet laser ablation of graphite, in vacuum, using nanosecond (34 ns), picosecond (5 ps), and femtosecond (450 fs) pulses of 248 nm radiation, focusing on the plume characteristics as revealed by wavelength, time- and spatially resolved optical emission spectroscopy. Nanosecond pulsed ablation gives a distinctively different optical emission spectrum from that observed with the two shorter pulse durations. Emissions attributable to electronically excited C*, C+* and C2* fragments are identified in the former, while the spectra obtained when using the shorter duration, higher intensity pulses contain additional lines attributable to C2+* species but none of the C* emission lines. As before [Claeyssens et al., J. Appl. Phys. 89, 697 (2001)], we consider that each atomic emission is a step in the radiative cascade that follows when an electron recombines with a Cn+ species (where n is one charge state higher than that of the observed emitter) formed in the original ablation process. Broadband visible radiation attributable to blackbody emission from larger particulates is also observed following ablation with any of the three laser pulse durations. Time gated imaging studies allow estimation of the velocity distributions of various of these emitting species within the plume, and their variation with incident laser fluence and/or intensity. The deduced multicomponent structure of the plume emission following excitation with short duration laser pulses is rationalized in terms of contributions from both nonthermal and thermal mechanisms for material ejection from the target. Use of longer duration (nanosecond) laser pulses offers the opportunity for additional laser-plume interactions, which we suggest are responsible for much of the observed emission in the nanosecond pulsed laser ablation of graphite.

No abstract

No abstract

We report on thin film deposition by matrix-assisted pulsed laser evaporation of simple hydroxyapatite (HA) or silver (Ag) doped HA combined with the natural biopolymer organosolv lignin (Lig) (Ag:HA-Lig). Solid cryogenic target of aqueous dispersions of Ag:HA-Lig composite and its counterpart without silver (HA-Lig) were prepared for evaporation using a KrF* excimer laser source. The expulsed material was assembled onto TiO2/Ti substrata or silicon wafers and subjected to physical-chemical investigations. Smooth, uniform films adherent to substratum were observed. The chemical analyses confirmed the presence of the HA components, but also evidenced traces of Ag and Lig. Deposited HA was Ca deficient, which is indicative of a film with increased solubility. Recorded X-ray Diffraction patterns were characteristic for amorphous films. Lig presence in thin films was undoubtedly proved by both X-ray Photoelectron and Fourier Transform Infra-Red Spectroscopy analyses. The microbiological evaluation showed that the newly assembled surfaces exhibited an inhibitory activity both on the initial steps of biofilm forming, and on mature bacterial and fungal biofilm development. The intensity of the anti-biofilm activity was positively influenced by the presence of the Lig and/or Ag, in the case of Staphylococcus aureus, Pseudomonas aeruginosa and Candida famata biofilms. The obtained surfaces exhibited a low cytotoxicity toward human mesenchymal stem cells, being therefore promising candidates for fabricating implantable biomaterials with increased biocompatibility and resistance to microbial colonization and further biofilm development.

No abstract

Synthesis of nanostructured thin films of pure and oxidized levan exopolysaccharide by matrix-assisted pulsed laser evaporation is reported. Solutions of pure exopolysaccharides in dimethyl sulfoxide were frozen in liquid nitrogen to obtain solid cryogenic pellets that have been used as targets in pulsed laser evaporation experiments with a KrF* excimer source. The expulsed material was collected and assembled onto glass slides and Si wafers. The contact angle studies evidenced a higher hydrophilic behavior in the case of oxidized levan structures because of the presence of acidic aldehyde-hydrogen bonds of the coating formed after oxidation. The obtained films preserved the base material composition as confirmed by Fourier transform infrared spectroscopy. They were compact with high specific surface areas, as demonstrated by scanning electron and atomic force microscopy investigations. In vitro colorimetric assays revealed a high potential for cell proliferation for all coatings with certain predominance for oxidized levan.

Additive manufacturing with an emphasis on 3D printing has recently become popular due to its exceptional advantages over conventional manufacturing processes. However, 3D printing process parameters are challenging to optimize, as they influence the properties and usage time of printed parts. Therefore, it is a complex task to develop a correlation between process parameters and printed parts’ properties via traditional optimization methods. A machine-learning technique was recently validated to carry out intricate pattern identification and develop a deterministic relationship, eliminating the need to develop and solve physical models. In machine learning, artificial neural network (ANN) is the most widely utilized model, owing to its capability to solve large datasets and strong computational supremacy. This study compiles the advancement of ANN in several aspects of 3D printing. Challenges while applying ANN in 3D printing and their potential solutions are indicated. Finally, upcoming trends for the application of ANN in 3D printing are projected.