We report ultrahigh density assembly of aligned single-walled carbon nanotube (SWNT) two-dimensional arrays via AC dielectrophoresis using high-quality surfactant-free and stable SWNT solutions. After optimization of frequency and trapping time, we can reproducibly control the linear density of the SWNT between prefabricated electrodes from 0.5 SWNT/μm to more than 30 SWNT/μm by tuning the concentration of the nanotubes in the solution. Our maximum density of 30 SWNT/μm is the highest for aligned arrays via any solution processing technique reported so far. Further increase of SWNT concentration results in a dense array with multiple layers. We discuss how the orientation and density of the nanotubes vary with concentrations and channel lengths. Electrical measurement data show that the densely packed aligned arrays have low sheet resistances. Selective removal of metallic SWNTs via controlled electrical breakdown produced field-effect transistors with high current on-off ratio. Ultrahigh density alignment reported here will have important implications in fabricating high-quality devices for digital and analog electronics.

We demonstrate assembly of solution-processed semiconducting enriched (99%) single-walled carbon nanotubes (s-SWNTs) in an array with varying linear density via ac dielectrophoresis (DEP) and investigate detailed electronic transport properties of the fabricated devices. We show that (i) the quality of the alignment varies with frequency of the applied voltage and that (ii) by varying the frequency and concentration of the solution, we can control the linear density of the s-SWNTs in the array from 1/μm to 25/μm. The DEP assembled s-SWNT devices provide the opportunity to investigate the transport property of the arrays in the direct transport regime. Room temperature electron transport measurements of the fabricated devices show that with increasing nanotube density the device mobility increases while the current on-off ratio decreases dramatically. For the dense array, the device current density was 16 μA/μm, on-conductance was 390 μS, and sheet resistance was 30 kΩ/◻. These values are the best reported so far for any semiconducting nanotube array.

High performance lacey reduced graphene oxide nanoribbons (LRGONR) were chemically synthesized. Holes created during the LRGONR synthesis not only enhanced the electrolytic accessibility but destacked all the graphene layers through protrusion at edge planes and corrugation in individual graphene. LRGONR in a supercapacitor cell showed ultrahigh performance in terms of specific capacitance and capacity retention. Consistently in aqueous, nonaqueous, and ionic electrolytes, LRGONR symmetric supercapacitor exhibited exceptionally high energy/power density, typically 15.06 W h kg(-1)/807 W kg(-1) in aqueous at 1.7 A g(-1), 90 W h kg(-1)/2046.8 W kg(-1) in nonaqueous at 1.8 A g(-1), and 181.5 W h kg(-1)/2316.8 W kg(-1) in ionic electrolyte at ∼1.6 A g(-1).

An electrical noise is one of the key parameters determining the performance of modern electronic devices. However, it has been extremely difficult, if not impossible, to image localized noise sources or their activities in such devices. We report a "noise spectral imaging" strategy to map the activities of localized noise sources in graphene domains. Using this method, we could quantitatively estimate sheet resistances and noise source densities inside graphene domains, on domain boundaries and on the edge of graphene. The results show high activities of noise sources and large sheet resistance values at the domain boundary and edge of graphene. Additionally, we showed that the top layer in double-layer graphene had lower noises than single-layer graphene. This work provides valuable insights about the electrical noises of graphene. Furthermore, the capability to directly map noise sources in electronic channels can be a major breakthrough in electrical noise research in general.

The localized noise-sources and those induced by external-stimuli were directly mapped by using a conducting-AFM integrated with a custom-designed noise measurement set-up. In this method, current and noise images of a poly(9,9-dioctylfluorene)-polymer-film on a conducting-substrate were recorded simultaneously, enabling the mapping of the resistivity and noise source density (NT). The polymer-films exhibited separate regions with high or low resistivities, which were attributed to the ordered or disordered phases, respectively. A larger number of noise-sources were observed in the disordered-phase-regions than in the ordered-phase regions, due to structural disordering. Increased bias-voltages on the disordered-phase-regions resulted in increased NT, which is explained by the structural deformation at high bias-voltages. On photo-illumination, the ordered-phase-regions exhibited a rather large increase in the conductivity and NT. Presumably, the illumination released carriers from deep-traps which should work as additional noise-sources. These results show that our methods provide valuable insights into noise-sources and, thus, can be powerful tools for basic research and practical applications of conducting polymer films.