Automated self-assembly and electrical characterization of nanostructured films
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esearch Letter
Automated self-assembly and electrical characterization of nanostructured films Rafael C. Hensel and Kevin L. Rodrigues, Department of Applied Physics, “Gleb Wataghin” Institute of Physics, University of Campinas––UNICAMP, 13083-970, Campinas, SP, Brazil Vinicius do L. Pimentel, Information Technology Center Renato Archer, 13069-901, Campinas, SP, Brazil Antonio Riul Jr. and Varlei Rodrigues, Department of Applied Physics, “Gleb Wataghin” Institute of Physics, University of Campinas––UNICAMP, 13083-970, Campinas, SP, Brazil Address all correspondence to Varlei Rodrigues at varlei@ifi.unicamp.br (Received 11 January 2018; accepted 19 March 2018)
Abstract Significant progress in nanoscience was achieved through the development of methods and instruments to better comprehend nanoscale properties. We present here a methodology and automated setup to measure layer-by-layer films capacitance in the air immediately after polyelectrolytes adsorption. It presents high accuracy (∼0.01 pF) to check the capacitance stabilization during spontaneous drying process in the air, with sensitivity to show electrical signal alternation accordingly to the outermost polyelectrolyte layer. Besides, a linear trend in capacitance was observed similar to UV–vis measurements. This method allows analyzing films electrical properties, affording better choice of materials, thickness, and molecular architecture.
Introduction Organic thin films have attracted great interest due to their ability to interact with surfaces, tailoring specific properties for a myriad of applications.[1] In this context, the layer-by-layer (LbL) technique is a simple method to modify large area surfaces.[2] This method forms multilayered nanostructured films by spontaneous adsorption of polyelectrolytes due to noncovalent intermolecular interactions (electrostatic, van der Waals, and hydrogen bonding). LbL film properties such as optical absorption,[3] roughness,[4] and conductivity[5] depend on the assembled materials, the way they are nanostructured, and the number of adsorbed layers,[6] demanding a precise control of the adsorption process during the LbL assembly. Consequently, new methods and instruments are fundamental to precisely track the film properties during the LbL growth at each deposited layer, independently of adsorption steps. The use of capacitive devices such as electrolyte–insulator– semiconductor (EIS) capacitor to analyze DNA immobilization and hybridization inspired their use to monitor LbL film growth.[7,8] As an example, Poghossian et al. tracked the growth of LbL films formed by poly(allylamine hydrochloride) (PAH) and poly(sodium 4-styrenesulfonate) (PSS) in a (PAH/ PSS)n architecture (n being the number of deposited bilayers) by means of capacitance as a function of voltage measurements (C–V) on EIS devices after each deposition step.[9,10] The observed alternation in the polarization voltage according to the deposited polyelectrolyte layer demonstrated a dependence between the polarization voltage amplitude displacement
as a function o
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