I report gas and water flow measurements through microfabricated membranes in which aligned carbon nanotubes with diameters of less than 2 nanometers serve as pores. Molecular dynamics simulations have raised the expectation that gas and water transport through carbon nanotubes should occur at much faster rates compared with the rate shown by conventional nanopores. Water transport through carbon nanotubes is important due to the biological similarity of their internal space to water-permeable transmembrane channels in a human body. For the first time, this study carried out experimental measurement of mass transport through sub-2-nanometer carbon nanotubes.

I successfully realized a novel MEMS-compatible microfabrication scheme to make void-free, silicon-nitride-matrix membranes containing double walled carbon nanotubes of less than 2 nanometers in diameters.

The measured gas flow exceeds predictions of the Knudsen diffusion model by more than one to two orders of magnitude. It exceeds predictions of the unified gas flow model by one order of magnitude. The measured gas flow rates in this study agree well with the prediction by molecular dynamics simulations quantitatively. The tangential momentum accommodation coefficient is, to my knowledge, much smaller than the values for any other surfaces experimentally reported so far. Single component gas selective study shows a possibility of separating hydrocarbon gas species from inert and inorganic species.

The measured water flow rate exceeds values calculated from continuum hydrodynamics models by more than three orders of magnitude. The failure in predicting the nanoscale flow rates with the models rooted to the continuum-based momentum transfer mechanism led me, inspired by MD simulations, to hypothesize a nanoscale momentum transfer mechanism for water flow in a narrow carbon nanotube based on the "material" layer assumption, hydrophobicity and friction-shielding effect.

Understanding the fast mass transport through such narrow carbon nanotubes is important because of the filtration of entities larger than the size of the carbon-nanotube pores. In addition, the success in development of the carbon-nanotube-based membranes will lay a cornerstone for the realization of devices with biomimetic functionalities. It is concluded that these membranes have strong potential for enabling a number of significant applications, including (1) fundamental studies of mass transport in confined environments, (2) more energy-efficient nanoscale filtration, and (3) biomimetic device development.