Nanomechanics of Ultrathin Carbon Nanomembranes.

Ultrathin carbon nanomembranes (CNMs) are two-dimensional materials (2DM) of a few nm thickness with sub-nm intrinsic pores that mimic the biofiltration membranes found in nature. They enable highly selective, permeable, and energy-efficient water separation and can be produced at large scales on porous substrates with tuned properties. The present work reports the mechanical performance of such CNMs produced by p-nitrobiphenyl phosphonic acid (NBPS) or polyvinylbiphenyl (PVBP) and their composite membranes of microporous supporting substrates, which constitute indispensable information for ensuring their mechanical stability during operation. Measuring the nanomechanical properties of the ultrathin material was achieved by atomic force microscopy (AFM) on membranes both supported on flat substrates and suspended on patterned substrates ("composite membrane"). The AFM analysis showed that the CNMs presented Young's modulus in the range of 2.5-8 GPa. The composite membranes' responses were investigated by tensile testing in a micro-tensile stage as a function of substrate thickness and substrate pore density and diameter, which were found to affect the mechanical properties. Thermogravimetric analysis was used to investigate the thermal stability of composite membranes at high temperatures. The results revealed the structural integrity of CNMs, while critical parameters governing their mechanical response were identified and discussed.

Controlled polymerization of substituted diacetylene self-organized monolayers confined in molecule corrals.

We have shown that STM-tip-induced chain polymerization of 10,12-tricosadiynoic acid (TCDA) in a self-organized monolayer at the liquid-solid interface of TCDA on highly oriented pyrolytic graphite is possible. The oligomers thus produced started at the point where a voltage pulse was applied between the STM tip and the sample during a short period when the feedback condition was momentarily suspended (as it is for scanning tunneling spectroscopy). Polymerization probabilities depended upon the length of the applied voltage pulse and were generally higher for longer pulse widths in the 10-ms to 100-micros time scales, approaching unit probability for the former and decreasing quickly to a few tens of percent for the latter. The polymerization could be confined to certain nanometer-sized areas by using "molecule corrals,"and polymerization appeared to be governed by topochemical constraints. Polymerization across domain boundaries, or over molecule corral edges, was never observed in over approximately 150 observations. Due to the constant supply of nonpolymerized molecules from the covering solution, a dynamic exchange between molecules on the surface and in the solution was possible. This exchange occurred on a time scale that was comparable to the image acquisition time (approximately 10(1) s), and appeared to depend weakly upon the length of the desorbing oligomer. The desorption process was probably also influenced by interactions with the STM tip.