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Surface functionalization of low-dimensional nanomaterials offers a means to tailor their optoelectronic and chemical characteristics. However, functionalization reactions are sensitive to the inherent surface features of nanomaterials, such as defects, grain boundaries, and edges. Conventional optical characterization methods, such as Raman spectroscopy, have limited sensitivity and spatial resolution and, therefore, struggle to visualize reaction sites and chemical species. Here, we demonstrate the capability of spatially and chemically sensitive tip-enhanced Raman spectroscopy imaging to map the distribution of molecules in covalently functionalized graphene. Hyperspectral vertex component analysis and density functional theory are necessary to interpret the nature of binding sites and extract information from the spatially and spectrally heterogeneous datasets. Our results clarify the origin of heterogeneous surface functionalization, resolving preferential binding at edges and defects. This work demonstrates the potential of nanospectroscopic tools combined with unsupervised learning to characterize complex, partially ordered optoelectronic nanomaterials. 

The nanoscale spectral heterogeneity of graphene oxide provides insight into the mechanism of self-reduction. 

Covalent bonding interactions determine the energy–momentum (E–k) dispersion (band structure) of solid-state materials. Here, we show that noncovalent interactions can modulate theE–kdispersion near the Fermi level of a low-dimensional nanoscale conductor. We demonstrate that low energy band gaps may be opened in metallic carbon nanotubes through polymer wrapping of the nanotube surface at fixed helical periodicity. Electronic spectral, chiro-optic, potentiometric, electronic device, and work function data corroborate that the magnitude of band gap opening depends on the nature of the polymer electronic structure. Polymer dewrapping reverses the conducting-to-semiconducting phase transition, restoring the native metallic carbon nanotube electronic structure. These results address a long-standing challenge to develop carbon nanotube electronic structures that are not realized through disruption of π conjugation, and establish a roadmap for designing and tuning specialized semiconductors that feature band gaps on the order of a few hundred meV.