Orientated Langmuir-Blodgett Assembly of VO2 Nanowires

We report Langmuir-Blodgett (LB) based assembly of vanadium dioxide (VO2) nanowires. VO2 nanowires were functionalized with stearic acid (SA) and cetyltrimethylammonium bromide (CTAB) and then spread on the surface in an aqueous phase in a LB trough. Surface pressure-area (pi-A) isotherms were recorded on the LB trough and show hysteretic behavior. Scanning electron microscopy investigations of morphology and alignment of the VO2 nanowire films transferred at different points on the pi-A curve demonstrate that with increasing surface pressure there is a transition from well-separated domains of nanowires to compact and locally ordered nanowire monolayers, while aggregates of raftlike nanowire structures remain after expansion. Interestingly, X-ray diffraction studies show that VO2 nanowire LB films exhibit (00l) crystal plane orientation, which is attributed to preferential coordination of SA and CTAB-SA complex to (001) surface of VO2 nanowires thereby driving this orientation.