Characterisation of Pb thin films prepared by the nanosecond pulsed laser deposition technique for photocathode application

Abstract

Pb thin films were prepared by the ns pulsed laser deposition technique on Si (100) and polycrystalline Nb substrates for photocathode application. As the photoemission performances of a cathode are strongly affected by its surface characteristics, the Pb films were grown at different substrate temperatures with the aim of modifying the morphology and structure of thin films. Atomic force microscopy and scanning electron microscopy analyses showed a strong morphological change in the deposited films with the substrate temperature, and the formation of spherical grains at higher temperatures with the nucleation of large voids on the film surface. X-ray diffraction measurements showed that a preferred orientation of Pb (111)

Morphology and structure of Pb thin films grown on Si(111) by pulsed laser deposition

“…For example, while semiconductor photocathodes have the advantage of lower work functions and higher quantum efficiencies, metallic photocathodes (Cu, Mg, Y, etc.) are considered as a dependable alternative [7][8][9][10] due to their shorter response time, better robustness, and longer lifetime. Quantum emission measurements of Mg and Y thin film photocathodes revealed a value of 1.8×10-3 for the Mg photocathode and 3.3×10-4 for the Y photocathode [35].…”

“…Pb (lead) thin films are of particular interest for photocathode applications in superconducting radiofrequency guns, solid lubricants, and aerospace and junction electrode applications [7]. Lead has a critical temperature 7.2 K, which is close to that of niobium (9.3 K), and it has higher quantum efficiency (around 7.5 x10-5 at 250 nm vs. niobium quantum efficiency of 1x10-5 at 250 nm) [10,34].…”

Structural and morphological properties of metallic thin films grown by pulsed laser deposition for photocathode application

“…They are very adherent [18] to the substrates, even with depositions performed at room temperature, most likely due to high energy species of the plasma plume characterized by single and double charged states of ions [19,20]. It is worth to say that the goal of obtaining good-quality thin films by this deposition technique, in terms of morphology and crystalline structure, is strongly related to the choice of experimental parameters, which have to be evaluated very carefully for each specific target material.…”

“…The working laser fluence was chosen close to the laser ablation threshold of Pb, Fthr =0.52 J/cm 2 [18], in order to reduce the laser thermal effects on the target due to the relatively low melting point of such material (327 °C). The target-substrate distance was set at 4 cm in order to increase the deposition rate, as the low laser fluence constrained by the low melting point of Pb caused a low deposition rate with respect to Y.…”

Nanomechanical and electrical properties of Nb thin films deposited on Pb substrates by pulsed laser deposition as a new concept photocathode for superconductor cavities

“…Until now, no material has been 12 found to satisfy these requirements, so it is necessary to make a compromise between 13 both QE and electrical performance. The obvious solution to such a compromise is 14 Pb, which presents a QE around 2×10 -5 at 266 nm [3], much higher than Nb (7.4×10…”