Photocurrent generation in carbon nanotube/cubic-phase HfO(2) nanoparticle hybrid nanocomposites

A hybrid material consisting of nonfunctionalized multiwall carbon nanotubes (MWCNTs) and cubic-phase HfO(2) nanoparticles (NPs) with an average diameter of 2.6 nm has been synthesized. Free standing HfO(2) NPs present unusual optical properties and a strong photoluminescence emission in the visible region, originating from surface defects. Transmission electron microscopy studies show that these NPs decorate the MWCNTs on topological defect sites. The electronic structure of the C K-edge in the nanocomposites was probed by electron energy loss spectroscopy, highlighting the key role of the MWCNT growth defects in anchoring HfO(2) NPs. A combined optical emission and absorption spectroscopy approach illustrated that, in contrast to HfO(2) NPs, the metallic MWCNTs do not emit light but instead expose their discrete electronic structure in the absorption spectra. The hybrid material manifests characteristic absorption features with a gradual merger of the MWCNT π-plasmon resonance band with the intrinsic defect band and fundamental edge of HfO(2). The photoluminescence of the nanocomposites indicates features attributed to combined effects of charge desaturation of HfO(2) surface states and charge transfer to the MWCNTs with an overall reduction of radiative recombination. Finally, photocurrent generation under UV–vis illumination suggests that a HfO(2) NP/MWCNT hybrid system can be used as a flexible nanodevice for light harvesting applications.