Patching of Lattice Defects in Two-Dimensional Diffusion Barriers

Two-dimensional crystals offer promise as diffusion barriers that can also facilitate electronic conduction through the barrier plane via tunneling. We present barriers in which crystal imperfections are patched, leaving the pristine regions of the crystal exposed and able to both prevent diffusion and allow electronic conduction. This is accomplished by atomic layer deposition, where nucleation of patch material is inhibited on the pristine crystal and promoted elsewhere. Demonstrations of the effectiveness of this technique are performed in the contexts of sulfur diffusion control in photovoltaic kesterite devices and oxygen diffusion control in oxide-based resistive switching devices

Fused Porphyrin–Single-Walled Carbon Nanotube Hybrids: Efficient Formation and Photophysical Characterization

A systematic study of the interaction between π-extended porphyrins and single-walled carbon nanotubes (SWNTs) is reported here. Zinc porphyrins with 1-pyrenyl groups in the 5,15-<i>meso</i> positions, <b>1</b>, as well as compounds where one or both of the pyrene groups have been fused at the <i>meso</i> and β positions of the porphyrin core, <b>2</b> and <b>3</b>, respectively, have been examined. The strongest binding to SWNTs is observed for porphyrin <b>3</b>, leading to debundling of the nanotubes and formation of stable suspensions of <b>3</b>–SWNT hybrids in a range of common organic solvents. Absorption spectra of <b>3</b>–SWNT suspensions are broad and continuous (λ = 400–1400 nm), and the Q-band of <b>3</b> displays a significant bathochromic shift of 33 nm. The surface coverage of the SWNTs in the nanohybrids was estimated by spectroscopic and analytical methods and found to reach 64% for (7,6) nanotubes. The size and shape of π-conjugated porphyrins were found to be important factors in determining the strength of the π–π interactions, as the linear <i>anti</i>-<b>3</b> isomer displays more than 90% binding selectivity compared to the bent <i>syn</i>-<b>3</b> isomer. Steady-state photoluminescence measurements show quenching of porphyrin emission from the nanohybrids. Femtosecond transient absorption spectroscopy reveals that this quenching results from ultrafast electron transfer from the photoexcited porphyrin to the SWNT (1/<i>k</i>_CT = 260 fs) followed by rapid charge recombination on a picosecond time scale. Overall, our data demonstrate that direct π–π interaction between fused porphyrins and SWNTs leads to electronically coupled stable nanohybrids