New growth modes of molybdenum oxide layered 1D structures using alternative catalysts: transverse mode vs. axial mode

Abstract

Different from the common metal catalysts (e.g., Au) employed in catalyst-assisted growth of one-dimensional (1D) structures, a variety of molybdenum oxide (MoO₃) layered 1D structures were synthesized using a group of alternative alkali metal based catalysts. In contrast to the sole axial growth mode found in conventional catalyst-assisted growth, two different growth modes were observed for the MoO₃ 1D growth here: transverse growth and axial growth. In the transverse mode, the 1D structures grow perpendicularly to the catalyst-deposition axis with the catalyst particles sitting on the side surfaces of the 1D structures; whereas in the axial mode, the growth direction is along the catalyst-deposition axis. The growth modes were explained by a modified vapor–solid–solid (VSS) mechanism, and the factors that affect the growth were explored. Based on the proposed growth mechanism, the growth was extended to a large family of alkali metal based catalysts and hierarchical structures were realized by multiple-growth approaches. This growth mechanism provides a new approach to control the orientation of 1D structures and can be applied to different layered materials.