Growth morphology of Pb films on Ni3Al(111)

Scanning tunnelling microscopy (STM) and Auger electron spectroscopy (AES) have been used to investigate the growth morphology of ultra-thin Pb films on the Ni3Al(111) face at room temperature. A previous study [K. Migkow and A. Krupski Appl Surf Sci 273, 2013, 554] using low-energy electron diffraction (LEED) and real time Auger intensity recording has demonstrated that an initial two-dimensional growth of the first Pb monolayer thick 'wetting layer' takes place. With further deposition and for T = 300 K, flat three atomic-layer-high islands are grown. Above 350 K, the Stranski-Krastanov growth mode was observed. In the current study, the analysis of STM measurements indicate and confirm that for coverage theta = 1.0 ML two-dimensional growth of the first Pb monolayer took place. Above theta > 1.0 ML, a three-dimensional growth of the Pb islands was observed with a strongly preferred atomic-scale 'magic height (N),' hexagonal shape and flat-tops. At coverage theta = 3.5 ML, only islands containing N = 3, 5, 7 and 11 atomic layers of Pb are observed. At the higher coverage theta = 5.5 ML, three types of regular hexagonal islands with side lengths of 25, 30 and 45 nm are observed. Furthermore, three different island adsorption configurations rotated by 10 degrees +/- 1 degrees and 30 degrees +/- 6 degrees with respect to each other were observed. After an annealing at T= 400 K of 5.5 ML of lead deposited at RT on the Ni3Al(111) the morphology of the surface changes. Post-anneal, islands of Pb are observed above the 'wetting layer' with an estimated average size and diameter of 768 +/- 291 nm(2) and 38.17 +/- 6.56 nm and constant uniform height of two atomic layers (N = 2). (C) 2013 Elsevier Ltd. All rights reserved.