Date 2017-05-30 

■ Title: Two-dimensional materials: from fundamental studies to applications

■ Speaker: Prof. Chang Hyeon Ko (Sookmyeong Univ)


■ Date and time: 30th of May (Tue) 16:00


■ Venue: KAIST Applied Engineering B/D(W1), Multimedia Lecture Hall (1st Floor)


 Abstract: The recent upsurge of interest in two-dimensional (2D) materials originates with their exotic physical and chemical phenomena in the 2D limit as well as various novel device applications potentially relevant to overcoming the scaling limit of contemporary device technology as well as achieving mechanically-flexible devices.

 In the first of the talk, I will report on a two-dimensional AuSi eutectic system realized as a precursor layer gilding on the Au surface. Eutectics play an important role in growth kinetics, reactive wetting, and microstructure behavior in a wide range of alloy materials. AuSi has been brought a spotlight back on by virtue of the recent advance in nanostructure technology including Au-catalytic growth of Si. Moreremarkably, from the fundamental viewpoint, bulk metal-semiconductor eutectic liquids host extraordinary surface phase whose structure and composition distinctly differ from those of bulk counterparts, Au81Si19.

 It was observed in-situ that the atomically-thin eutectic layer is Si-enriched from the bulk eutectic and shows diffusion-limited growth kinetics with a remarkably faster spreading speed by three orders of magnitude than that of the geometrically opposite system, i.e. spreading of Au atoms on the Si surface hindered by interfacial reactions. Ab-initio molecular dynamics calculations reveal that the Si diffusion is facilitated by the surface migration of Au atoms while the permeation of Si atoms into the Au bulk is suppressed leading to the Si enrichment. These results may be relevant to the large-scale synthesis of novel 2D material system such as silicon monolayer called Silicene.

 In the second part of the talk, I will introduce an example of 2D material-based device application. High-performance non-volatile memory devices have been constructed interfacing 2D transition metal dichalcogenides (TMDs) with thin film ferroelectric (FE) oxides. Moreover, employing monolayer TMD/FE structures, a non-volatile optical memory effect has been also realized, in which the photoluminescence can be controlled reversibly in the wide range via the FE gating, closely pertaining to understanding the mechanisms of FE effects on 2D TMDs and probably leading to novel optoelectronic applications.