We describe the use of single-wall carbon nanotube (SWNT) thin films as transparent and conducting electrodes for hole collection in poly(hexyl)thiophene-[6-6]phenyl-C61-butyric acid methyl ester (P3HT-PCBM) organic photovoltaics. We report a power conversion efficiency of 1%, with a fill factor of 0.3 and a short-circuit current of 6.5mA∕cm2 under 100mW∕cm2 polychromatic white light illumination measured in air. These values are comparatively higher than reference cells of similar thickness made on indium tin oxide (ITO) glass substrates. This is attributed to the three-dimensional nature of the interface between the SWNTs and the P3HT-PCBM nanocomposite. Our results indicate that solution processed SWNT thin films are a viable alternative to ITO for photovoltaic devices, eliminating an expensive vacuum deposition step in the fabrication of organic solar cells.

A study based on two-dimensional percolation theory yielding quantitative parameters for optimum connectivity of transparent single-wall carbon nanotube (SWNT) thin films is reported. Optimum SWNT concentration in the filtrated solution was found to be 0.1 mg/L with a volume of 30 mL. Such parameters lead to SWNT fractions in the films of approximately Phi = 1.8 x 10(-3), much below the metallic percolation threshold, which is found to be approximately PhiC = 5.5 x 10(-3). Therefore, the performance of transparent carbon nanotube thin-film transistors is limited by the metallic SWNTs, even below their percolation threshold. We show how this effect is related to hopping or tunneling between neighboring metallic tubes.

We describe the use of C 60 fullerene molecules as the charge storage medium in an insulating poly-vinyl-phenol (PVP) polymer. The simple metal-organic-metal (MOM) sandwich structure devices deposited from solution exhibit distinct high and low conduction states, which can be used to program read, write and erase memory operations. The charge transfer and retention in C 60 molecules at room temperature has been confirmed by capacitance-voltage and Raman spectroscopy measurements. Conducting atomic force microscopy has been used to demonstrate that high and low conductance states persist even at the nanoscale.

Mechanical systems can display topological characteristics similar to that of topological insulators. Here we report a large class of topological mechanical systems related to the BDI symmetry class. These are self-assembled chains of rigid bodies with an inversion centre and no reflection planes. The particle-hole symmetry characteristic to the BDI symmetry class stems from the distinct behaviour of the translational and rotational degrees of freedom under inversion. This and other generic properties led us to the remarkable conclusion that, by adjusting the gyration radius of the bodies, one can always simultaneously open a gap in the phonon spectrum, lock-in all the characteristic symmetries and generate a non-trivial topological invariant. The particle-hole symmetry occurs around a finite frequency, and hence we can witness a dynamical topological Majorana edge mode. Contrasting a floppy mode occurring at zero frequency, a dynamical edge mode can absorb and store mechanical energy, potentially opening new applications of topological mechanics.

Memory devices based on C 60 fullerene molecules and polystyrene and poly 4-vinyl phenol polymers are described. It is shown that the bistability in the I-V characteristics can be used to perform read-write-erase memory functions. In addition, it is demonstrated that mild thermal annealing enhances the stability of the devices. Specifically, after annealing, the hysteresis in our devices can be preserved up to 85°C in 60% humidity. Furthermore, memory retention tests show that it is possible to preserve a state even after annealing at 85°C in 60% humidity for 30 min.

A simple optical method based on absorption of monochromatic light to investigate the dynamics of single walled carbon nanotube ͑SWCNT͒ suspensions is described. The well dispersed suspensions display a complex behavior, exhibiting peaks due to resonant scattering from SWCNT bundles with increasing diameters as a function of time. The results indicate that the bundling of SWCNTs initiates almost immediately after termination of sonication ͑after ϳ0.1 h͒ and continues to increase up to a critical time ͑ϳ10 h͒, above which precipitation according to the Stokes relationship occurs. The absorbance behavior can be explained by the depletion of the effective medium as well as the Mie scattering from growth of bundles. A semiquantitative analysis of the experimental data based on the Mie theory of light scattering from cylindrical particles allows the extraction of diameters at the nucleation and growth of SWCNT bundles. The bundling dynamics have been correlated with the electrical properties such as the sheet resistance and transistor characteristics of the SWCNT thin films. Our work is a useful step toward reproducible solution processed electronics because it provides a simple method to monitor the quality of SWCNT suspensions in real time and correlate it to device characteristics.

In this paper, we describe an all organic molecular memory device that combines the advantages of molecular and organic electronics. We accomplish this by combining C 60 molecules with poly(4-vinylphenol) (PVP) and co-dissolving them in iso-propanol. The currentvoltage measurements show a large hysteresis in the blend devices, in contrast to pure PVP devices. The thin blend films have been thoroughly characterized using Raman spectroscopy, atomic force microscopy and scanning electron microscopy.

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