VSOP23: Topics

Topic 1: General introduction to 2D materials and vdW heterostructures

Silicon-based scaling technology is reaching its limits and modern electronics is now requiring channel materials to be thinner and thinner. The advent of graphene with extraordinary properties has been expected to play an essential role in the so-called silicon-post era. Though the semimetal nature is not suited for the current electronic technology, graphene still promises a huge potential of applications. Other 2D materials also show interesting properties attractive to applications in electronics and optoelectronics, for instance, the 2D transition-metal dichalcogenides are stable in lattice structure and exhibit good semiconducting. With the aim of inspiring learners to a novel direction of research in condensed mater physics, lectures in this topic are designed to provide an overview of 2D materials and related heterostructures, including a perspective for the fundamental research and applications, the tendency and directions of research currently performed in the world, as well as difficulties and challenges to push this kind of materials into real applications.

Topic 2: Atomic structure and related properties

It used to be thought that due to reasons of thermodynamic fluctuations there could not exist any single-atomic layer material. The discovery of graphene, a single layer of carbon atoms forming the typical hexagonal lattice, using the exfoliation method however has changed that opinion. The exfoliation method has been then widely used to produce other high quality two-dimensional materials as small size flakes, which are not relevant for large scale applications, unfortunately. Epitaxial growth methods have thus been developed and optimized to the aim of producing large scale 2D material sheets. On the other hand, in order to be used in modern electronics, the large scale sheets of 2D materials must be processed. Unfortunately, it usually introduces structural defects, which may cause dramatic changes in properties of material sheets. Accordingly, understanding how individual atoms combine together and form stable lattices is paramount for fabricating and engineering properties of 2D materials. The lectures on this topic are designed to provide learners the understanding of which essential factors are governing the formation and stability of 2D material lattices, how the geometrical allotropes can be formed, how their properties can be changed in the presence of different kinds of defects, and other fundamental issues. To handle research activities, learners will also be taught efficient large-scale theoretical and computational methods to treat problems involving the lattice deformations of 2D materials which can be directly related to experimental studies based on the tunneling electron microscopy, scanning probe microscopy, scanning tunneling microscopy, etc.

Topic 3: Electronic structure

Given a material lattice, the electronic structure is the content considered first because it is the basis for the analysis of fundamental properties of a material, including the electronic, transport, optical, and magnetic properties. Lectures on this topic focus on theoretical methods which have been efficiently used to calculate the energy band structure of electrons in 2D materials, including those classified according to the environment-continuum approach, the empirical atomistic  approach, and the first-principles approach. The efficiency of presented methods is clarified through the treatment of the electronic structure of particular material systems. The typical electronic structure of 2D materials is presented and highlighted. Despite the focus of lectures, learners will also have a chance to understand the supplemental role of the theoretical research to experimental studies through the discussion of calculated and experimental data.

Topic 4: Fundamental electronic properties

Electronic, transport, optical, magnetic, and superconducting properties are fundamental of a material. Studying these properties does not only help to understand a material and/or the physics of electrons, but also suggest the application potential and ways of engineering materials for matching requirements of technology. Due to the fact that all atoms are on the material surfaces and electrons are ultimately confined in atomically thin layers, the fundamental properties of two-dimensional materials are drastically different from those of their 3D bulk mother materials. Lectures on this topic provide learners typical characteristics of 2D materials and show how essential factors, such as the confinement and the reduction of symmetries, govern the properties of 2D materials. Learners will also be taught theoretical methods which are fundamental to the investigation of material properties. Especially, to guide learners to advanced studies of the imperfection of material lattices as well as the crystalline fault when stacking 2D material layers to form vdW heterostructures, some typical large scale computational methods are also introduced as tools for treating nano-scale systems.

Topic 5: Application potential of 2D materials and related complex systems

One of the main reasons leading to the discovery of 2D materials is the rush for suitable materials to solve challenges in the era of post silicon. In spite of single or multiple atomic layer thickness, two-dimensional materials are stable, offer very good conduction of electricity and heat, are transparent but still interact strongly with light in the visible spectrum. All these features suggest the use of 2D materials in advanced flexible and transparent nanoelectronics and optoelectronics. Especially, due to the planar nature, 2D materials also open the possibility of constructing new device structures, for instance stacking material layers to form multilayered heterostructures and thus exploiting the vertical tunneling of electrons as the device operation. Fundamental studies in the field of application research require to systematically solve and assess many issues, e.g., the influence of metallic electrodes and insulator layers on the transport of electrons in the 2D materials conduction channel; the material layers stacking, etc., which control the operation of a system as a whole. Though the application potential of 2D materials is very large, lectures in this topic just focus on theoretical methods used to model and simulate the operation of novel electronic devices, including those based on the lateral and vertical transport of electrons in 2D materials. During lectures, learners will acquire the fundamentals in nanoelectronics, the tendency of modern electronics and technical challenges which need to be solved.