GRANT № 19-52-14006
Bi-lateral Russian-Austrian joint project (RFBR-FWF)
Self-aligned 2D material ribbons and plasmonic nanobelts
The overall goal of the project is to demonstrate two novel and complementary methods for the fabrication of nanoribbon networks of arbitrary 2D materials, and for decoration of the edges of these ribbon networks with metallic nanoparticles.
The goal of the first year was to explore various 2D material substrates and heterostructures for nanoribbon fabrication, to establish a set of parameters for organic semiconductor growth and reactive ion etching of monolayers, to probe laser ablation, and to find initial conditions for edge-specific decoration of 2D materials. Thus far the project results lead to one joint publication with the Austrian partner in ACS Omega.
The key results of the first year include the discovery of the unusual physical and chemical properties of structural domains occurring on the surface of bulk highly oriented pyrolytic graphite (HOPG). Based on co-localized imaging by Kelvin probe force microscopy and Raman spectroscopy, we made a conclusion about the existence of partially decoupled graphene layers in the structure of graphite. Further, these mismatched interfaces affect the adsorption of airborne species and the self-assembly of organic molecules on HOPG. These partially decoupled graphene layers on graphite provide a deeper understanding of graphite/graphene layer interaction and their impact on the electronic and optical responses.
The goal of the second year was to study various two-dimensional materials and heterostructures for creating nanoribbons, present nanoparticles edge decoration of nanoribbon networks, and demonstrate the level of control over nanoribbon edge type and termination. As a result of the work, one joint article with the Austrian partner was published in Carbon.
In order to characterize various two-dimensional materials (GaSe, MoS2, hBN, talc, Zn2In2S5) optically and electrically, highly-oriented pyrolytic graphite as a universal substrate was used for the investigation of 2D materials. Moreover, two-dimensional Zn2In2S5 was characterized for the first time. For this, a set of methods, such as atomic force microscopy, Raman spectroscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy were used. Obtained structures showed a number of fundamental properties: strong interaction between graphite and 2D material what makes the last one straining and leads to local modifications in reactivity, optical and electrical properties. By arising of local strain defects, it is possible to selectively deposit Ag nanoparticles exactly on the strained region accordingly to the plan the project.
February 10, 2021
Figure: Time evolution of surface potential images
TPU Scientists pinpoint the physical origin of the heterogeneous surface potential
TPU researchers jointly with their colleagues from the University of Leoben have investigated the presence of surface potential (SP) domains in HOPG and revealed that their physical origin is related to the formation of defects as rotationally miss-matched domains, i.e., twisted graphene layers in graphite.
The research findings are presented in Twisted graphene in graphite: Impact on surface potential and chemical stability, published in Carbon academic journal (Q1, IF 9.594).
"Highly oriented pyrolytic graphite (HOPG) is a popular source of graphene, from which single layers of carbon are separated using adhesive tape. Moreover, after the separation of graphene, an ideally clean and even surface remains; therefore, HOPG is used in many studies as a well-studied and predictable substrate with stable properties. We found that domains with different surface potentials appear on the HOPG surface over time. This is due to the fact that organic molecules from the air are deposited on its surface. But why don't they sit down everywhere? Probably, the matter is indifferent electrical properties of the surface, which are determined by the force of interaction of the upper layer with the graphite crystal itself. This means that such inhomogeneities will strongly affect the epitaxy of organic molecules on the HOPG surface," Tuan-Hoang Tran Ph.D. student of the TPU Research School of High-Energy Physics, explains.
The scientists offered their method. The graphite sample surface was prepared by cleavage of the top layer with adhesive tape. Different HOPG samples were measured with an AIST-NT Omegascope, an NT-MDT NTEGRA, and an Asylum Research MFP-3D AFM. The experiments were done in rooms with controlled humidity.
"Graphene is traditionally produced by exfoliation from highly-oriented pyrolytic graphite (HOPG). We discovered that the distribution of surface potential on HOPG is inhomogeneous due to the presence of defects. The origin of these defects was determined to be a mismatch angle between graphene layers in HOPG. This result is unexpected and can influence the self-assembly process of organic substances on HOPG," Raul D. Rodriguez Contreras, Professor of the TPU Research School of Chemistry and Applied Biomedical Sciences, says.
"By applying external potential between tip and sample, it’s possible in situ and at the nanoscale to remove organic substances on HOPG, which opens a new way to design and construct nanostructures"
The scientists from TPU and University of Leoben took part in the research work. The project is supported by the Russian Foundation for Basic Research № 19-52-14006.