AFM analysis of morphology-density-transport relationships in carbon nanotube thin films

The dependence of the electrical properties of carbon nanotube (CNT) network films on the nanoscale film morphology and structure as determined by atomic force microscopy (AFM) was investigated. CNT films were prepared over a controlled density range by steam-assisted solution deposition, and the structure and morphology were analysed by automated density mapping and height-distribution analysis of the AFM images. This allowed a measure of the densification and bundling of the films with deposition time. Electrical properties of the films were measured after deposition of contacts by current-voltage (I-V) and Van der Pauw measurements. It was found that increased bundling in the film structure correlated inversely with film resistance, linking morphology to electronic behaviour. Sparse films (< ∼110 junctions/µm²) exhibited high resistance and non-linear, Schottky-limited transport, whereas dense bundle-rich networks(>∼160 junctions/µm²) showed near-linear or ohmic conduction through metallic percolation. Although the transition between transport regimes is density-dependent; it was found that highly dense networks can still exhibit elevated resistance due to complex inter-tube contacts. These results showed that AFM height-distribution analysis provides a rapid and predictive morphology-based framework for relating CNT-film structure to electrical performance, with broader potential for morphology-property studies in CNT-film devices.