Improvement of Nb/Cu adhesion and increase of Nb crystal size by laser radiation

Improvement of the first flux entry field by laser post-treatment of the thin Nb film on Cu

“…However, small holes emerged in both cases, with diameters from approximately 0.1 µm to about 1 µm. Similar features were also observed in [22,24] after laser irradiation. Possible explanations could be connected with melting, or even boiling of the Cu under the Nb film, also known as subsurface melting or lid effect [41].…”

“…The laser parameters used in this paper were chosen according to earlier study [22] in which the changes in structural properties of the Nb/Cu samples were in detail studied after laser irradiation.…”

“…Therefore, the thermal energy of a single laser pulse is the same for each dose. The number of laser pulses at the same spot (dose) has an accumulation character and influences the crystallinity of the material, decreases surface roughness, and improves adhesion Nb to Cu upto 36% according to [22]. These processes take place due to the inhomogeneous distribution of thermal energy in the Nb film.…”

“…The gradient of temperature with the maximum at the surface, during a laser pulse, takes place. Calculation of temperature distribution in Nb/Cu structure during the laser pulse is presented in [22].…”

“…The improvement of the Nb surface can be achieved by mitigation of the surface defects [18] with a small, disordered Nb grains, and slightly strained lattice parameters [19]. One of the promising solutions to improve the Nb structure and reduce the surface roughness is using laser irradiation which has already been used for the bulk Nb [20,21] as well as for thin Nb film on Cu [22][23][24].…”