Scanning Tunneling Microscopy Study and Nanomanipulation of Graphene-Coated Water on Mica

Abstract

We study interfacial water trapped between a sheet of graphene and a muscovite (mica) surface using Raman spectroscopy and ultra-high vacuum scanning tunneling microscopy (UHV-STM) at room temperature. We are able to image the graphene-water interface with atomic resolution, revealing a layered network of water trapped underneath the graphene. We identify water layer numbers with a carbon nanotube height reference. Under normal scanning conditions, the water structures remain stable. However, at greater electron energies, we are able to locally manipulate the water using the STM tip. KEYWORDSGraphene, water, mica, scanning probe microscopy, atomic resolution, STM, RamanThe interface between water and various surfaces 1,2 at room temperature has been of great interest to scientists due to its relevance in geology, 3 biology, 4 and most recently, electronics. 5,6 It has been demonstrated that water behaves very differently at an interface than it does in the bulk state, forming semi-ordered "hydration layers" close to the solid surface. [7][8][9][10] However, the exact nature of these hydration layers are still not well understood and remains the source of much controversy. 11 Recent studies utilizing AFM and other methods have made 2 progress towards putting some of these controversies to rest, 6,11-14 but atomic-resolution imaging of the interface had not yet been achieved.Graphene 6,[15][16][17][18][19][20] has already been extensively characterized by surface imaging techniques on a variety of substrates, [21][22][23][24][25][26] but only recently has it started to see use as a template for studying other molecules, 13,27,28 Graphene is ideal for coating and trapping volatile molecules for both scanning probe microscopy 13,27,29 and electron microscopy 28 studies in that it is conductive, chemically inert, impermeable, 30 and atomically conforms to most substrates. 31 In this letter, we build upon the work performed by Xu et al. 13 and use the atomic resolution and cleanliness of the ultrahigh vacuum scanning tunneling microscope (UHV-STM) to characterize water confined between monolayer graphene and the mica surface at room temperature. Unlike previous studies of graphene on mica, 6,13,14,27,29,31,32 we use graphene grown on copper via chemical vapor deposition (CVD) 33,34 rather than graphene mechanically exfoliated from graphite. 19 While CVD graphene is inferior to exfoliated graphene in terms of carrier mobility, this drawback is offset by the ability to manufacture large, monolayer sheets and transfer them onto arbitrary substrates. 34Our CVD process uses a methane-to-hydrogen partial pressure ratio of 2:1, as lower ratios give higher monolayer coverage. 35,36 Previous work 33 and the supporting information give more details on our growth procedure. We transfer graphene to mica with polymethyl methylacrylate (PMMA) and use successive deionized (DI) water baths to clean the graphene films from etchant contamination. The final transfer occurs on a freshly cleaved mica surface within a DI bath in co...

Keeping argon under a graphene lid—Argon intercalation between graphene and nickel(111)

“…In this context, applications for gas containment, gas separation 38 [10][11][12], or protective coatings are discussed [13][14][15]. Gas separation 39 with modified graphene membranes was proposed to allow helium 40 separation from other gases, and helium isotope separation [16,17]. 41 Porous two-layer graphene membranes with various pore sizes, 42 prepared by focused ion beam etching and photo lithography, exhibit 43 good separation ratios for CO 2 and H 2 for pore diameters below 44 10 nm.…”

“…4a and b, and also in the quantitative anal- tercalated between graphene and Pt(111) to desorb at higher tempera-261 ture than from the bare Pt(111) [38]. Also, a higher desorption 262 temperature was found for water under graphene on mica [39]. (100) [40].…”

Evidence of Stranski–Krastanov growth at the initial stage of atmospheric water condensation

“…Different non-contact AFM and scanning polarization force microscopy methods have been developed to overcome many of these problems and have provided important results, but a disadvantage is that the large distance between the tip and the sample results in lower spatial resolution. Recently, graphene, albeit only one-atom thick, was found to not only prevent the evaporation of molecularly thin adlayers but also to act as an ideal template for studying the structures of ultrathin liquid adlayers on solid support under ambient conditions [10][11][12][13][14][15] . With the assistance of graphene, Xu et al 11 pioneered work on the observation of the first two ice-like water adlayers, increasing the humidity to 90%.…”

Communication: Growing room temperature ice with graphene

“…[1][2][3][4] Such layering effect has been experimentally evidenced recently by means of scanning probe microscopy measurements using protective graphene sheets as one of the confining surfaces. [5][6][7][8] When graphene sheets are deposited on cleaved mica surfaces in ambient conditions, room temperature (RT), and controlled relative humidity (RH), the trapped water layers grow in a two dimensional (2D) mode, forming atomically flat structures with heights of 0.37 nm, the distance between adjacent bilayers (BLs) in hexagonal ice (Ih).…”