Growth of MnWO4 nanowires on W(110) by high-temperature oxygen-assisted molecular beam epitaxy

We describe the growth of synthetic hübnerite (MnWO₄) by high-temperature oxygen-assisted molecular beam epitaxy on W(110). The hübnerite nanowires have widths of hundreds of nanometers, heights of tens of nanometers and lengths in the range of millimeters. The growth was followed in real time by low-energy electron microscopy (LEEM). The nanowires were characterized in situ by low-energy electron microscopy, X-ray absorption and X-ray photoelectron spectroscopy in photoemission microscopy, as well as ex situ by atomic force microscopy, optical microscopy and Raman spectroscopy. Hübnerite can be grown on W(110) by dosing only manganese in a molecular oxygen environment, likely due to the formation of highly mobile WO_x species with diffusion lengths of the order of hundreds of micrometers. These species can react with the deposited Mn and be efficiently incorporated into the wolframite structure of hübnerite. The strongly anisotropic growth observed may stem from the inherent anisotropy of the wolframite lattice. We propose that this method may be applicable to the growth of other tungstates as well.