From 2D Transition Metal Di-chalcogenides to the 3D Transition Metal Oxides; Growth, Processing and Device Applications
Abstract: Two dimensional (2D) materials have achieved recently an unpredictable research interest owing to their special properties such as indirect-to-direct band gap transition from bulk regime to monolayer, band structure tunability with strain, large optical absorption coefficient and naturally having a passivated surface (due to the chalcogen bonds). Nowadays, this research interest has resulted in more than hundred different 2D materials, which initiated a new class of 2D materials. This class of material system apparently are including all the different type of materials that we know, such as semiconductors, superconductors, magnetic materials, insulators, semimetals and etc. In this class of materials system, transition metal di-chalcogenides (TMDCs), namely WS2, MoS2, WSe2 and MoSe2, are the promising semiconductor 2D materials. One of the challenging issue for these materials is obtaining large area monolayers. Although, there are reported many different methods to obtain very high quality TMDCs, all these methods lack of growth of continues, homogeneous thin films. In the first part of my talk, I will be showing how we control the growth from 2D WS2 and MoS2 continues and homogeneous thin films to 3D vertical nanowalls by simple sputtering method. Then I will be showing the field effect transistor (FET) applications from these materials that we grew. In addition, MoS2-WS2 hetero-junction FET results will be shown. Second part of my talk, I will be moving to researches that we recently focused on 3D nanowalls MoS2 and WS2 conversion into the MO3 and WO3 without changing the morphology by controlling the oxidation process with in-situ measurement that we set up. Then I will be finishing my talk with the results of device applications, chromic and gas sensors, from these obtained very large surface / volume ratio MoO3 and WO3 nanowalls.