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Abstract: Mg-based films have been prepared by pulsed laser deposition technique for photocathode applications. We have investigated the influence of pulse laser duration on morphology and photoemissive properties. Two laser sources have been used, generating pulses of 30ns at 308nm (XeCl excimer laser), 5ps and 500fs at 248nm (KrF excimer laser) to grow Mg films onto Si and Cu substrates in high vacuum (∼10−7 Pa) and at room temperature. Morphological investigations carried out by scanning electron microscopy (SEM) have revealed that, in our experimental conditions, the number and the mean size of the droplets on the films surfaces decreases as the pulse laser duration shortens. The contamination level of Mg film surfaces have been studied by energy dispersive X-ray spectroscopy (EDX). The photoelectron performances in terms of quantum efficiency (QE) and emission stability have been tested in a UHV DC photodiode cell (10−7 Pa). Measures of the QE of the samples surfaces have revealed a decrease on the initial value for Mg-based photocathodes prepared by fs laser (from 7.8×10−4 to 6.6×10−4) PLD with respect to ps (from 6.2×10−4 to 7.4×10−4) and ns lasers (from 5.0×10−4 to 1.6×10−3). A comparison among Mg-based photocathodes prepared by ns, ps and fs PLD for the production of high brightness electron beams has been presented and discussed. [Copyright &y& Elsevier]

Abstract: Advanced high brightness radio frequency (RF) gun injectors require photocathodes with a fast response, high quantum efficiency (QE) and good surface uniformity. Metal films deposited by various techniques on the gun back wall could satisfy these requirements. A new deposition technique has been recently proposed, i.e. pulsed laser ablation. Several Mg samples have been deposited by this technique: the emission performance and morphological changes induced on the cathode surface during laser activation are compared and discussed. [Copyright &y& Elsevier]

Abstract: In this study, pulsed laser ablation of pure Mg targets (99.99%) using an XeCl excimer laser (λ =308nm, τ =30ns) was used to grow Mg coatings on Cu substrates. A thin layer of Mg (100–200nm) was deposited in UHV of 5×10−6 Pa to ensure high purity. A second ultra-thin layer of MgO of 10–20nm was deposited in oxygen at 10−2 Pa pressure to protect the previous layer from atmospheric contamination. Measurements for determining the electron yield of the deposited samples under UV irradiation were performed on a diode structure in another UHV apparatus evacuated to 10−6 Pa. [Copyright &y& Elsevier]

Abstract: Nanostructured tin oxide films were deposited on Si(100) substrates at room temperature using the PLAD method. Depositions were achieved by using a XeCl* laser, with a fluence of 10J/cm2 to ablate a SnO2 target either in vacuum or in an atmosphere containing a relatively low partial pressure (10−2 to 100Pa) of O2. A range of spectroscopic diffraction and real space imaging techniques, SEM, EDS, XRD, and XPS were used in order to characterize the surface morphology, structure, and composition of films. XPS results indicate that the film deposited in vacuum comprises a mixture of Sn, SnO and SnO2. In contrast, films deposited in oxygen comprise only SnO and SnO2. This indicates that the deposition of tin oxide films in relatively low partial pressures of O2 prevents the accumulation of unreacted tin metal within the resulting film. SEM studies reveal a sub-micron grain size structure, while XRD analyses indicate that the samples are crystalline, with no evidence for the presence of amorphous material. In this paper we discuss the significance and implications of these findings in terms of the optimization of tin oxide films for use in gas sensing devices and other technological applications. [Copyright &y& Elsevier]

The changes of the laser ablated target morphology and the corresponding plume deflection angle have been studied. As the number of laser pulses/site increases, the target morphology changes and produces a visible deviation of the plasma plume. Scanning electron microscopy analyses of the target surface allowed us to correlate the plume deflection angle to the target roughness and, hence, to the number of laser pulses/site. The deflection effect has been observed for all the targets used (Ti, Si, Cu, Al–Sn alloy, graphite and magnetic compounds) and for whatever target surface morphology produced by laser irradiation. As earlier models explaining the origin of the plume deflection are not universal and less than ever satisfactory, we suggest a simple model that seems to be more realistic and general. [Copyright &y& Elsevier]

Hastelloy thin films have been deposited on carbon steel substrates at room temperature by pulsed laser ablation of bulk Hastelloy targets. Different numbers of laser pulses were used in order to obtain films of various thicknesses. Scanning electron microscopy (SEM) was used to analyze the surface morphology of the deposited films. Energy dispersion X-ray (EDX) spectroscopy and X-ray diffraction (XRD) have shown that the laser ablation process was almost congruent, and the crystallographic structure was retained in the films. In order to relate the microstructure of the film surface with its corrosion behavior, electrochemical tests in aqueous CO2 environment, such as potentiodynamic curves and linear polarization resistance, were performed. The film characteristics and their dependence on deposition parameters are presented and discussed. [Copyright &y& Elsevier]