Size-controllable synthesis of 2D Mn3O4 triangular-shaped nanosheets by thermal chemical vapor deposition

Abstract

In this study, monolayer up to few-layer of Mn 3 O 4 nanosheets grown on c-Si (111) substrates using a thermal chemical vapor deposition (TCVD) technique were investigated in detail, where the growth reaction pressure was varied from 0.12 to 0.72 mbar. The morphology of the triangular-shaped Mn 3 O 4 nanosheet greatly depends on the atomic ratio of O to Mn, which eventually determines the horizontal growth rate of the triangle's edges that forms the shape of the nanosheet. A low O/Mn ratio results in the formation of a triangle with a longer edge as compared to a high O/Mn ratio which produces a shorter edge. The 2D triangular-shaped Mn 3 O 4 nanosheets prepared at 0.42 mbar exhibited a thickness of ∼1.10–2.29 nm (equivalent to the approximate thickness of monolayer-bilayer) with a maximum edge length of ∼850 nm, whereas ultrathin nanosheets with a thickness of ∼1.93–4.68 nm (equivalent to ∼2–3 layers) with an edge length of <250 nm were found at the highest reaction pressure of 0.72 mbar. The results imply a synthesis of 2D Mn 3 O 4 nanosheets with controllability of thickness and edge length that vary from monolayer to ultrathin nanosheets at different O/Mn ratios. By presuming that the Mn 3 O 4 growth along the [001] direction, we performed first-principles density-functional theory calculations to validate the structure and electronic properties of these 2D Mn 3 O 4 nanosheets. Our calculated lattice parameters for the 2D Mn 3 O 4 were considerably close to the experimental measurements. The band structure calculations predicted that the 2D Mn 3 O 4 possessed metallic characteristics. This paper discusses the seed-assisted growth mechanism of these 2D Mn 3 O 4 nanosheets. • Thermal CVD grown Mn 3 O 4 nanosheet. • The atomic ratio between O and Mn controlled the morphologies of the triangular-shaped Mn 3 O 4 nanosheet. • A low O/Mn ratio produced monolayer 2D triangular shaped with a longer edge. • A high O/Mn ratio produced ultrathin nanosheets with thickness up to 3 layers and shorter edge. • Based on DFT calculations, 2D Mn 3 O 4 nanosheet exhibited metallic characteristics.