Sub-ps Pulsed Laser Deposition of Boron Films for Neutron Detector Applications.

In view of the demand for high-quality thermal neutron detectors, boron films have recently attracted widespread research interest because of their special properties. In this work, we report on the deposition of boron films on silicon substrates by sub-picosecond pulsed laser deposition (PLD) at room temperature. Particular emphasis was placed on the investigation of the effect of the laser energy density (fluence) on the ablation process of the target material, as well as on the morphological properties of the resulting films. In addition, based on the study of the ablation and deposition rates as a function of the fluence, the ablation/deposition mechanisms are discussed. We show that well-adherent and stable boron films, with good quality surfaces revealing a good surface flatness and absence of cracks, can be obtained by means of the PLD technique, which proves to be a reliable and reproducible method for the fabrication of thick boron coatings that are suitable for neutron detection technology.

Sub-ps Laser Deposited Copper Films for Application in RF Guns.

Copper thin films are intended to serve as a cover layer of photocathodes that are deposited by ablating copper targets in a high vacuum by temporally clean 600 fs laser pulses at 248 nm. The extremely forward-peaked plume produced by the ultrashort UV pulses of high-energy contrast ensures fast film growth. The deposition rate, defined as peak thickness per number of pulses, rises from 0.03 to 0.11 nm/pulse with an increasing ablated area while keeping the pulse energy constant. The material distribution over the surface-to-be-coated can also effectively be controlled by tuning the dimensions of the ablated area: surface patterning from airbrush-like to broad strokes is available. The well-adhering films of uniform surface morphology consist of densely packed lentil-like particles of several hundred nm in diameter and several ten nm in height. Task-optimized ultrashort UV laser deposition is thereby an effective approach for the production of thin film patterns of predetermined geometry, serving e.g., as critical parts of photocathodes.

Nanolayer Growth on 3-Dimensional Micro-Objects by Pulsed Laser Deposition.

Pulsed laser deposition on 3-dimensional micro-objects of complex morphology is demonstrated by the paradigmatic growth of cellulose and polymer/Y3Al5O12:Ce phosphor composite nanolayers. Congruent materials transfer is a result of multicomponent ablation performed by relatively low fluence (<200 mJ cm-2) ArF excimer laser pulses (λ = 193 nm). Films grown on optical and engineering components, having a thickness from ~50 nm to more than ~300 nm, are durable, well adherent and maintain the structural and functional properties of the parent solids. The results verify the unique capabilities of deep-ultraviolet pulsed laser deposition of novel functional nanostructures on arbitrary surface morphologies and highlight its potential in future 3-dimensional nanotechnologies.

Simulation of emission spectra from nonuniform reactive laser-induced plasmas.

We demonstrate that chemical reactions leading to the formation of AlO radicals in plasmas produced by ablation of aluminum or Ti-sapphire with ultraviolet nanosecond laser pulses can be predicted by the model of local thermodynamic equilibrium. Therefore, emission spectra recorded with an echelle spectrometer and a gated detector were compared to the spectral radiance computed for uniform and nonuniform equilibrium plasmas. The calculations are based on analytical solutions of the radiation transfer equation. The simulations show that the plasmas produced in argon background gas are almost uniform, whereas temperature and density gradients are evidenced in air. Furthermore, chemical reactions exclusively occur in the cold plume periphery for ablation in air. The formation of AlO is negligible in argon as the plasma temperature is too large in the time interval of interest up to several microseconds. Finally, the validity of local thermodynamic equilibrium is shown to depend on time, space, and on the elemental composition. The presented conclusions are of interest for material analysis via laser-induced breakdown spectroscopy and for laser materials processing.

Optical characterizations of ZnO, SnO2, and TiO2 thin films for butane detection.

The optogeometric properties of various sensitive thin films involved in gas sensing applications are investigated by using the m-line technique and atomic force microscopy. Variations of these optical properties are studied under butane and ozone exposure.