Abstract
The study of surface morphology of Au deposited on mica is crucial for the fabrication of flat Au films for applications in biological, electronic, and optical devices. The understanding of the growth mechanisms of Au on mica allows to tune the process parameters to obtain ultra-flat film as suitable platform for anchoring self-assembling monolayers, molecules, nanotubes, and nanoparticles. Furthermore, atomically flat Au substrates are ideal for imaging adsorbate layers using scanning probe microscopy techniques. The control of these mechanisms is a prerequisite for control of the film nano- and micro-structure to obtain materials with desired morphological properties. We report on an atomic force microscopy (AFM) study of the morphology evolution of Au film deposited on mica by room-temperature sputtering as a function of subsequent annealing processes. Starting from an Au continuous film on the mica substrate, the AFM technique allowed us to observe nucleation and growth of Au clusters when annealing process is performed in the 573-773 K temperature range and 900-3600 s time range. The evolution of the clusters size was quantified allowing us to evaluate the growth exponent 〈z〉 = 1.88 ± 0.06. Furthermore, we observed that the late stage of cluster growth is accompanied by the formation of circular depletion zones around the largest clusters. From the quantification of the evolution of the size of these zones, the Au surface diffusion coefficient was evaluated in . These quantitative data and their correlation with existing theoretical models elucidate the kinetic growth mechanisms of the sputtered Au on mica. As a consequence we acquired a methodology to control the morphological characteristics of the Au film simply controlling the annealing temperature and time.
Highlights
Thin nanometric films play important role in various fields of the modern material science and technology [1,2]
We studied the evolution of the starting ultra-flat 28 nm sputter-deposited Au film as a consequence of the annealing processes performed in the 573-773 K temperature range and 0-3600 s time range
We can conclude that the 573 K-900 s annealing process determines the first stage of nucleation of Au clusters from the starting quasi-continuous film and that the following annealing processes cause their growth
Summary
Thin nanometric films play important role in various fields of the modern material science and technology [1,2]. Study of the observed structural changes to the process parameters such as deposition features (i.e. rate, time, etc.) [9,10,11,12,13] and features of subsequent processes (i.e. annealing temperatures and time, ion or electron beam energy and fluence, etc.) [14,15,16,17] In this framework, the study of the surface morphology of Au deposited on mica is crucial [18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39] in view of the fabrication of flat Au films for applications in biological, electronic, optical devices and techniques (i.e. surface enhanced Raman spectroscopy). The sputtering method is simpler than vacuum evaporation both for instrumentation and deposition procedure; with the deposition parameters properly chosen, the sputtered films exhibit superior surface planarity, even flatter than the smoothest evaporated films reported to date [28]
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