The interest in 2D materials has accelerated exponentially since 2004, when graphene was produced for the first using the 'Scotch Tape' method. The interest in van der Waals bonded layers stems from their remarkable physical (e.g. mechanical, transport...) properties, while being the thinnest possible layers. Integrating these 2D materials with existing Si technology (heterogenous integration) opens a world of new opportunities and applications (e.g. wearables, optical devices (modulators, detectors), bio devices, transistors...).
Chemical vapour deposition is a proven method to synthesize 2D materials, and the best results are obtained when the 2D materials are grown on an epitaxial template (i.e. sapphire/Cu(111) for graphene and sapphire for transition metal dichalcogenides (TMDCs)) at high temperatures (>700oC). Using these epitaxial templates enables oriented growth of 2D materials which minimizes the occurrence of grain boundaries. After 2D material growth, a strong coupling between the 2D material and the growth substrate often exists, resulting in high adhesion between the 2D material and its growth template. It is important to understand this interaction, as these 2D materials need to be transferred to enable heterogeneous integration. Moreover, if one can modify the interaction, and partially or fully decouple the 2D material from the substrate on which it is grown, this would open exciting new opportunities for innovative transfer methods.
The first results of ultra-low energy (ULE) noble gas implantation in sapphire/Cu(111)/graphene indicate that a graphene layer can be electronically decoupled from the Cu layer using ULE implantations. Modifying this 2D/growth wafer interaction is a first important step, but fundamental understanding of this effect is still in its infancy. Several open questions still need to be answered, such as: What is the mechanism underlying this decoupling? How does it depend on implanted element and implantation parameters?... Furthermore, it is unclear if this effect can be applied to other 2D materials (i.e. TMDCs) as well, and if this decoupling can be beneficial fur subsequent 2D material dry transfer approaches. Such a dry transfer is a necessary ingredient to enable heterogenous integration.
The challenge underlying this project is the use of an innovative implantation technique to alter the 2D/growth substrate interface. As it is an interfacial effect, measuring it is already challenging on its own. As the environment has a direct influence on the 2D material, measuring the 2D material properties can be an indirect indication of the changed surrounding after ULE implantation. Possible measurement techniques include scanning tunnelling microscopy and spectroscopy (STM/STS), angle-resolved photoemission spectroscopy (ARPES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, photoluminescence, transport measurements, etc. Furthermore, a combination of molecular dynamics (MD) and density functional theory (DFT) simulations will shed light on the dynamic implantation process.
As this multidisciplinary topic deals with the understanding of interfaces, knowledge of several characterization techniques is preferred. You are a self-motivated and a handy person. The ability to communicate fluently in English is an absolute requirement in our international environment. Furthermore, this PhD is a joint collaboration between the Department of Physics and Astronomy of the KU Leuven (Quantum Solid State Physics unit) and Imec. Therefore, it is important that the candidate is open to work together with different teams and spend time at international large-scale facilities in Europe, e.g. to characterize the materials using synchrotron radiation techniques.
Required background: Physics, Material Engineering, Engineering Science, Engineering Technology
Type of work: 60% experimental (fabrication, characterization), 40% data analysis and theory
Supervisor: Stefan De Gendt, ,
Daily advisor: Steven Brems
The reference code for this position is 2020-006. Mention this reference code on your application form.