Bulk-suppressed and surface-sensitive Raman scattering by transferable plasmonic membranes with irregular slot-shaped nanopores.

Raman spectroscopy enables the non-destructive characterization of chemical composition, crystallinity, defects, or strain in countless materials. However, the Raman response of surfaces or thin films is often weak and obscured by dominant bulk signals. Here we overcome this limitation by placing a transferable porous gold membrane, (PAuM) on the surface of interest.

Freestanding and Permeable Nanoporous Gold Membranes for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman spectroscopy (SERS) demands reliable, high-enhancement substrates in order to be used in different fields of application. Here we introduce freestanding porous gold membranes (PAuM) as easy-to-produce, scalable, mechanically stable, and effective SERS substrates. We fabricate large-scale sub-30 nm thick PAuM that form freestanding membranes with varying morphologies depending on the nominal gold thickness.

Macroscopic Salt Rejection through Electrostatically Gated Nanoporous Graphene.

Atomically thin porous graphene is emerging as one of the most promising candidates for next-generation membrane material owing to the ultrahigh permeation. However, the transport selectivity relies on the precise control over pore size and shape which considerably compromises the scalability. Here, we study electrolyte permeation through a sheet of large-area, porous graphene, with relatively large pore sizes of 20 ± 10 nm.

Assessing the Thickness-Permeation Paradigm in Nanoporous Membranes.

Driven by the need of maximizing performance, membrane nanofabrication strives for ever thinner materials aiming to increase permeation while evoking inherent challenges stemming from mechanical stability and defects. We investigate this thickness rationale by studying viscous transport mechanisms across nanopores when transitioning the membrane thickness from infinitely thin to finite values. We synthesize double-layer graphene membranes containing pores with diameters from ∼6 to 1000 nm to investigate liquid permeation over a wide range of viscosities and pressures.

Multifunctional wafer-scale graphene membranes for fast ultrafiltration and high permeation gas separation.

Reliable and large-scale manufacturing routes for perforated graphene membranes in separation and filtration remain challenging. We introduce two manufacturing pathways for the fabrication of highly porous, perforated graphene membranes with sub-100-nm pores, suitable for ultrafiltration and as a two-dimensional (2D) scaffold for synthesizing ultrathin, gas-selective polymers. The two complementary processes-bottom up and top down-enable perforated graphene membranes with desired layer number and allow ultrafiltration applications with liquid permeances up to 5.

Enhanced Chemical Separation by Freestanding CNT-Polyamide/Imide Nanofilm Synthesized at the Vapor-Liquid Interface.

In chemical separation, thin membranes exhibit high selectivity, but often require a support at the expense of permeance. Here, we report a pinhole-free polymeric layer synthesized within freestanding carbon nanotube buckypaper through vapor-liquid interfacial polymerization (VLIP). The VLIP process results in thin, smooth and uniform polyamide and imide films.

Understanding the interaction between energetic ions and freestanding graphene towards practical 2D perforation.

We report experimentally and theoretically the behavior of freestanding graphene subjected to bombardment of energetic ions, investigating the capability of large-scale patterning of freestanding graphene with nanometer sized features by focused ion beam technology. A precise control over the He(+) and Ga(+) irradiation offered by focused ion beam techniques enables investigating the interaction of the energetic particles and graphene suspended with no support and allows determining sputter yields of the 2D lattice. We found a strong dependency of the 2D sputter yield on the species and kinetic energy of the incident ion beams.

Contact transfer length investigation of a 2D nanoparticle network by scanning probe microscopy.

Nanoparticle network devices find growing application in sensing and electronics. One recurring challenge in the design and fabrication of this class of devices is ensuring a stable interface via robust yet unobstructive electrodes. A figure of merit which dictates the minimum electrode overlap required for optimal charge injection into the network is the contact transfer length.

Water-assisted growth of uniform 100 mm diameter SWCNT arrays.

We report a simple method for growing high-quality single-walled carbon nanotube (SWCNT) arrays on 100 mm wafers via the addition of water vapor to highly purified gases during the CNT growth step. We show that adding a small amount of water during growth helps to create a uniform catalyst distribution and yields high-quality (Raman G/D of 26 ± 3), high-density (up to 6 × 10(11) cm(-2)) and uniform SWCNT arrays on 100 mm large wafers. We rationalize our finding by suggesting that the addition of water decreases catalyst mobility, preventing its coarsening at higher temperatures.

Ultimate permeation across atomically thin porous graphene.

A two-dimensional (2D) porous layer can make an ideal membrane for separation of chemical mixtures because its infinitesimal thickness promises ultimate permeation. Graphene--with great mechanical strength, chemical stability, and inherent impermeability--offers a unique 2D system with which to realize this membrane and study the mass transport, if perforated precisely. We report highly efficient mass transfer across physically perforated double-layer graphene, having up to a few million pores with narrowly distributed diameters between less than 10 nanometers and 1 micrometer.