The adhesion of L-methionine amino acid through Dip Pen Nanolithography on silver thin films grown by Molecular Beam Epitaxy technique

Abstract The present work explore the fabrication of four silver thin films with controlled thicknesses of 30 nm, 60 nm, 90 nm and 120 nm, by using ultra-high vacuum (UHV) molecular beam epitaxy (MBE) technique. The peculiarities of their transformations depending on substrate quality, roughness and shape profile types were analyzed by Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDX) and Atomic Force Microscopy (AFM) scanning approaches. Topographical characteristics and structure modifications were highlighted depending on the deposition thicknesses. Within the increase of silver layers, Ag particles started to form a more uniform, clustered layer on the glass substrate. The improved regularity of Ag particles inside clusters defines better the cluster profiles, emphasizing a preferred orientation and arrangement of Ag particles. For the thicker layers of 90 nm and 120 nm, a well-ordered particles arrangement is present in a much higher amount, unifying the clusters with preferred regular orientations. This phenomenon has conducted to the formation of cluster islands, thus increasing the surface roughness. The reactivity of Ag thin films toward L-methionine amino acid was explored by Dip Pen Nanolithography (DPN). A clear dependence between the formation of distinct surface properties and the ease of direct-write patterning was demonstrated. An optimum linkage preference of molecular L-methionine for the most flat surface of 30 nm growth has been emphasized, while for the other substrates the writing process is critically affected by the surface roughness.