Molecular transport through capillaries made with atomic-scale precision

Abstract

Nanometre-scale pores and capillaries have long been studied because of their importance in many natural phenomena and their use in numerous applications. A more recent development is the ability to fabricate artificial capillaries with nanometre dimensions, which has enabled new research on molecular transport and led to the emergence of nanofluidics. But surface roughness in particular makes it challenging to produce capillaries with precisely controlled dimensions at this spatial scale. Here we report the fabrication of narrow and smooth capillaries through van der Waals assembly, with atomically flat sheets at the top and bottom separated by spacers made of two-dimensional crystals with a precisely controlled number of layers. We use graphene and its multilayers as archetypal two-dimensional materials to demonstrate this technology, which produces structures that can be viewed as if individual atomic planes had been removed from a bulk crystal to leave behind flat voids of a height chosen with atomic-scale precision. Water transport through the channels, ranging in height from one to several dozen atomic planes, is characterized by unexpectedly fast flow (up to 1 metre per second) that we attribute to high capillary pressures (about 1,000 bar) and large slip lengths. For channels that accommodate only a few layers of water, the flow exhibits a marked enhancement that we associate with an increased structural order in nanoconfined water. Our work opens up an avenue to making capillaries and cavities with sizes tunable to ångström precision, and with permeation properties further controlled through a wide choice of atomically flat materials available for channel walls.

Electrowetting on conductors: anatomy of the phenomenon

“…This is related to recently observed phenomena such as the ultra-rapid transport of water through carbon nanotubes and precision "nano-capillaries" fabricated between graphite flakes using graphene "spacers" as the capillary walls. 31,32 PPFs can be viewed as "disordered" graphitic materials, which, despite their relatively low surface roughness, are believed to contain a higher number of H-terminated (i.e. sp 3 carbon atoms) at their surface.…”

Reversible structural transition in nanoconfined ice

“…density of confined water can be higher than 1g/cm 3 . The latter causes a complex rearrangements of the H-bonds network and unexpected water flow, slip length and viscosity of confined water 10,27,28 .…”

In situ direct observation of photocorrosion in ZnO crystals in ionic liquid using a laser-equipped high-voltage electron microscope

“…Graphene is a promising thin film for sealing or channeling liquid around a specimen. [13][14][15] On the other hand, high-voltage electron microscopy (HVEM) is advantageous due to the transparency of its electron beam in order to eliminate the limitation of the maximum thickness of such a film. Although in situ HVEM observation is a promising way to examine specimens on the nanometer-to-micrometer scale while maintaining high resolution, there is little work on observing chemical reactions in liquid while applying electric fields, photon beam irradiation, or ion irradiation.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] In general, specimen evaporation during TEM often causes critical damage to the electron gun and specimen chamber, so researchers have tried to seal such specimens in holders made from membranes of silicon nitride or SiO 2 . 1-6 By accelerating electrons through such sets of thin membranes, researchers have managed to observe specimens in solution.…”