Zernike seminar: Pawel J. Kowalczyk "2D materials and their hybrids"

Recently, growing interest in 2D materials is observed initiated by exfoliation of graphene followed by
investigations of silicane, germanene and stanene all located in 14th group of periodic table. Elements
located in 15th group are also capable to crystalize in 2D form in layered A17 structure (black
phosphorus structure, α-form). The widely investigated α-phosphorene is best known example, however,
α-arsenene, α-antimonene, α-bismuthene and α-bismuth antimonidene can be synthesized. Interestingly,
Sb and Bi can also form stable hexagonal form i.e. β phase based on A7 structure (blue phosphorus).
After successive synthesis of these materials we investigate their properties and over years we found
number of interesting properties including unpinned Dirac states [1], nonsymorphic symmetries leading
to formation of Dirac points [2] and possible topologically protected edge states [3].
The other group of 2D materials is based on transition metal dichalcogenide (TMDC) compounds. From
this large group we will focus on TaS2 and WTe2 and their hybrids with graphene. These preliminary
research show presence of variety of moire patterns indicating great platform for twistroinics.
Finally, graphene can serve as electrode in many applications. To use it in photovoltaics its work function
(WF) has to be substantially increased. We started series of experiments with 2D oxide MoO3 growth [4,
5] which allowed us to tune graphene WF and create first working OLED in Poland.
All these experiments are conducted using surface sensitive techniques including SPM and ARPES.
Some of the experiments were conducted with LEEM/PEEM and STXM which are available only at
synchrotron facilities.
[1] Q. Lu et al., Nat. Comm. 13, 4603 (2022)
[2] P.J. Kowalczyk et al., ACS Nano 14, 1888 (2020)
[3] S. Salehitaleghani et al., 2D Mat. 10, 15020 (2022)
[4] D. Kowalczyk et al., 2D Mat. 8, 25005 (2021)
[5] D. Kowalczyk et al., ACS Appl. Mat. Int. 14, 44506 (2022)