Graphene Microcapsule Arrays for Combinatorial Electron Microscopy and Spectroscopy in Liquids

Abstract

Atomic-scale thickness, molecular impermeability, low atomic number, and mechanical strength make graphene an ideal electron-transparent membrane for material characterization in liquids and gases with scanning electron microscopy and spectroscopy. Here, we present a novel sample platform made of an array of thousands of identical isolated graphene-capped micro-channels with high aspect ratio. A combination of a global wide field of view with high resolution local imaging of the array allows for high throughput in situ studies as well as for combinatorial screening of solutions, liquid interfaces and immersed samples. We demonstrate the capabilities of this platform by studying a pure water sample in comparison with alkali halide solutions, a model electrochemical plating process and beam induced crystal growth in liquid electrolyte. Spectroscopic characterization of liquid interfaces and immersed objects with Auger and X-ray fluorescence analysis through the graphene membrane are also demonstrated

2D Material Membranes for Operando Atmospheric Pressure Photoelectron Spectroscopy

“…The adhesion of the graphene to its support must therefore also be carefully considered, as if this is not strong enough the environment within the reaction cell will be able to bypass the graphene membrane and leak out along the graphenesupport. Metallic films are therefore commonly deposited onto these supports prior to graphene transfer to try and improve this adhesion, as well as minimise charging by making the support more conductive [38,108]. The intercalation of species beneath 2D materials has been studied on a range of transition metal supports [29,107,109,110], with a strong interaction between a 2D material and its support shown to be critical to preventing intercalation [29].…”

“…Copyright 2018 American Chemical Society using higher-quality graphene with fewer defects would reduce the number of sites for preferential attack, but this is practically limited by the quality of graphene that can be reliably obtained by CVD. Stacking multiple graphene layers may also be beneficial, as the probability of two defects overlapping will correspond to the square of the defect density of SLG, and this approach has indeed been used in several reports to improve stability [98,99,108,133], although it comes at the expense of reduced photoelectron transmission, as discussed earlier. Instead of this, other 2D materials could be employed which are more resistant to oxidative attack such as h-BN [134], however its insulating behaviour is likely to result in undesirable charging during measurement.…”

“…More recently, Kolmakov et al have focussed on using multichannel static cells in combination with PEEM and other microscopic methods. This has included X-ray absorption measurements of the O K-edge of liquid water acquired in partial electron yield (PEY) mode [98], as well as similar Auger electron spectroscopy (AES) measurements [108]. This approach has also been applied to detect Cu ions in aqueous solutions of CuSO 4 and H 2 SO 4 during electrochemical cycling [133].…”

“…In addition to the powerful surface-sensitive chemical information that XPS can provide, in many experimental situations combining this with high spatial resolution would provide more profound understanding of the surface under investigation. A number of surface-sensitive spectromicroscopy techniques have already been used including scanning photoelectron microscopy (SPEM) [96], photoemission electron microscopy (PEEM) [98], and scanning AES [108], particularly with the multichannel static cell geometry, to identify which cells have and have not leaked. However, the resolution of these techniques is of the order of tens of nanometres, which is insufficient for revolving small nanoparticles let alone the atomic-scale structure of the surface, which is of primary interest in many cases.…”

Radiation Damage on Liquid Electrolyte during Spatially Resolved Soft X-ray Photoemission Measurements

“…A liquid cell sample platform was made as an array of electrolyte filled several thousand isolated micro-channels, with a diameter of 2 to 5 μm and encapsulated with bilayer graphene (BLG) on the front side and with water-immiscible epoxy on the backside (Fig. 1A) [6]. Highly focused Xray beam was rastered over the graphene covered channel to elucidate chemical composition of the electrode-electrolyte interface and its evolution during metal plating/stripping reactions.…”