Growth and Field Emission Study of Molybdenum Oxide Nanostars

The field emission properties of MoO 2 nanostars grown on a silicon substrate and their emission performance in various vacuum gaps are reported in this article. A new structure of molybdenum oxides, named a nanostar, is grown by thermal vapor deposition with a length of ∼1 μm, a thickness of ∼50 nm, and its width in the range of 500−700 nm. The morphology, structure, composition, and chemical states of the prepared nanostars were characterized by scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). According to XRD analysis, the grown nanostructures are composed of both crystalline Mo 4 O 11 and crystalline MoO 2 structures. XPS analysis showed that the synthesized nanostructures contained ∼21.2% Mo 6+, ∼16.2% Mo 5+, ∼39.8% Mo 4+, and ∼22.8% Mo δ+ (where 0 < δ < 4). TEM observations indicate that the synthesized sample consists of MoO 2 nanostars over a crystalline thin film containing Mo 4 O 11 nanoparticles. The turn-on emission field and the enhancement factor of nanostars are found to be 1.0 V/μm and 19 070 at the vacuum gap of 500 μm, respectively. These excellent emission properties are attributed to the special structure of the nanostars. Therefore, these nanostars can be used in vacuum microelectronic applications.