Origin of Ubiquitous Stripes at the Graphite–Water Interface

Abstract

The investigation of solid−liquid interfaces is pivotal for understanding processes like wetting, corrosion, and mineral dissolution and growth. The graphite−water interface constitutes a prime example for studying the water structure at a seemingly hydrophobic surface. Surprisingly, in a large number of atomic force microscopy (AFM) experiments, well-ordered stripes have been observed at the graphite−water interface. Although many groups have reported on the observation of stripes at this interface, fundamental properties and, in particular, the origin of the stripes are still under debate. Proposed origins include contamination, interplanar stacking of graphene layers, formation of methanol−water nanostructures, and adsorption of nitrogen molecules. Especially, the latter interpretation has received considerable attention because of its potential impact on explaining the long-range nature of the hydrophobic interaction. In this study, we demonstrate that these stripes readily form when using standard plastic syringes to insert the water into the AFM instrument. In contrast, when clean glass syringes are used instead, no such stripes form even though nitrogen was present. We, therefore, conclude that contaminations from the plastic syringe rather than nitrogen constitute the origin of the stripes we observe. We provide high-resolution AFM data that reveal detailed structural insights into the arrangement of the stripes. The rich variability of our data suggests that the stripes might be composed of several different chemical species. Still, we cannot rule out that the stripes observed in the literature might originate from other sources; our study offers a rather straightforward explanation for the origin of the stripes. In the view of these results, we propose to carefully reconsider former assignments.

Organic contaminants and atmospheric nitrogen at the graphene–water interface: a simulation study

“…However, despite several decades of study and the topographical and chemical simplicity of the graphene and graphene-like surfaces, the detailed structure of graphene-water and graphite-water interfaces under typical experimental conditions remains controversial. In particular, contact angle 1,2 and capacitance measurements, 3 infrared spectroscopy, 2 and atomic force microscopy (AFM) [4][5][6][7][8][9][10][11] suggest the presence of contaminants of some nature that rapidly accumulate on even freshly cleaved graphite surfaces exposed to water or air under typical laboratory conditions. The identity of these contaminants remains somewhat unclear and likely depends on the details of the environment to which the sample has been exposed; however, two major hypotheses are that these contaminants consist of (i) a mixture of hydrocarbon species or (ii) a condensed form of a major atmospheric gas, with most attention being given to N 2 .…”

Zigzag gas phases on holey adsorbed layers

“…42 It has been also reported that the stripe structures, which are similar to the ordered layers, are formed by the adsorption of airborne hydrocarbon contaminant. [43][44][45] Although we tried to acquire the Raman shis of the micropancakes and adsorbed layers to determine the component of them, no peaks derived from them were observed because they are too thin and sparse to be detected by the Raman spectroscopy (see ESI Note S6 †). However, Hwang's group have showed the strong relationship between the nucleation of the interfacial domains and the dissolved gas concentration in water.…”

The composition and structure of the ubiquitous hydrocarbon contamination on van der Waals materials

“…During the last decade several groups reported 1D ordered structures on the surface of graphitic materials [6][7][8][9][10][11][12][13][14][15][16][17] , e.g. parallel stripes with 4-6 nm period, and suggested explanations for the stripe structure as the organized adsorption of molecules.…”

“…parallel stripes with 4-6 nm period, and suggested explanations for the stripe structure as the organized adsorption of molecules. First, Lu et al 6,7 proposed that the stripes can be built up from a self-assembled layer of molecular nitrogen, later a monolayer of organic chain-like molecules was also suggested 14,15 . Despite the large number of observations [6][7][8][9][10][11][12][13][14][15][16][17] there is no consensus on the chemical composition, nor the origin of the molecular layer.…”

“…First, Lu et al 6,7 proposed that the stripes can be built up from a self-assembled layer of molecular nitrogen, later a monolayer of organic chain-like molecules was also suggested 14,15 . Despite the large number of observations [6][7][8][9][10][11][12][13][14][15][16][17] there is no consensus on the chemical composition, nor the origin of the molecular layer. It is suggested in many of these reports that the stripe structure possibly follows the zigzag or the armchair direction of the surface's hexagonal lattice.…”