Nanostructured surfaces, Nanocomposites and nanomaterials
Colloidal 2D nanomaterials: shape and dimensionality control opens intriguing properties
Lesyuk R.I.1,2
1 Intitute of Physics, University of Rostock, Germany 
E-mail: rostyslav.lesyuk@uni-rostock.de
2 Pidstryhach Institute for applied problems of mechanics and mathematics of NASU, Lviv, Ukraine; Photonics Department, Lviv Polytechnic National University, Lviv, Ukraine.

Colloidal synthesis of two-dimensional metal chalcogenides (CdX, PbX, CuX, ZnX (X=Se,S,Te)) presents solution-based chemical route for extensive and low-cost nanomaterials fabrication with unprecedented level of shape and surface chemistry control 1. Driving mechanisms responsible for the 2D formation mode are anisotropic growth, confined growth in a surfactant mesophase due to templating effect and oriented attachment. Presence of specific ligands, crystal structure anisotropy, nanopraticles self-organization and kinetic mode of reaction are main factors necessary for the obtaining of quasi-two-dimensional morphology of the product. 
The properties of colloidal 2D nanomaterials can be tuned in terms of quantum confinement and distinct faceting possibilities to govern the optical absorption, photoluminescence spectrum, lifetime and quantum yield, conductivity anisotropy, mobility, FET performance etc. Moreover, on the example of lead sulfide, the complete switch of semiconducting to metallic properties can be possible 2. The comparative study of PbS nanostripes and nanowires by means of individual contacting and electronic probing, TEM, XRD, SAED, XPS and HAADF-tomography reveal that appropriate faceting of the nanocrystal with lead-rich {111} face is able to alter the fundamental properties of the material dramatically changing its temperature coefficient and specific conductivity by orders of magnitude. Probing at cryogenic temperatures gives the sign of transition to the superconductivity state in PbS zig-zag nanowires. DFT simulations support the surface-induced metallicity in nanostructured lead sulfide with exposed {111} surface. Understanding of the mechanisms behind observed effects opens new prospects in shape and dimensionality control and applicability of colloidal nanomaterials.    

1.	Wang, F., Wang, Y., Liu, Y. H., Morrison, P. J., Loomis, R. A., & Buhro, W. E. Two-dimensional semiconductor nanocrystals: properties, templated formation, and magic-size nanocluster intermediates // Accounts of chemical research.-2015.-48(1).-P. 13-21.
2.	Ramin M.M.M., Kull S.,... Lesyuk R., & Klinke C. Function Follows Form: From Semiconducting to Metallic toward Superconducting PbS Nanowires by Faceting the Crystal // Advanced Functional Materials.-2020.- 30(19).-P. 1910503.