A high-pressure atomic force microscope for imaging in supercritical carbon dioxide

Abstract

A high-pressure atomic force microscope (AFM) that enables in situ, atomic scale measurements of topography of solid surfaces in contact with supercritical CO 2 (scCO 2 ) fluids has been developed. This apparatus overcomes the pressure limitations of the hydrothermal AFM and is designed to handle pressures up to 100 atm at temperatures up to ∼350 K. A standard optically-based cantilever deflection detection system was chosen. When imaging in compressible supercritical fluids such as scCO 2 , precise control of pressure and temperature in the fluid cell is the primary technical chal-lenge. Noise levels and imaging resolution depend on minimization of fluid density fluctuations that change the fluid refractive index and hence the laser path. We demonstrate with our apparatus in situ atomic scale imaging of a calcite (CaC0 3 ) mineral surface in scCO 2 ; both single, monatomic steps and dynamic processes occurring on the (101 4) surface are presented. This new AFM provides unprecedented in situ access to interfacial phenomena at solid-fluid interfaces under pressure.

Water in Inhomogeneous Nanoconfinement: Coexistence of Multilayered Liquid and Transition to Ice Nanoribbons

“…The strategy of varying density to mimic the change in lateral pressure has been widely used to study the behavior of confined water in MD simulations. , It is expected that, in future AFM experiments to verify our findings, the pressure (water density) could be readily increased (or decreased) by filling the AFM chamber with compressed gas at a certain high pressure (or evacuating some amount of air from the chamber). Alternatively, a high water density may also be achieved by using a so-called high-pressure AFM that was employed to image supercritical CO 2 at pressures of ∼100 atm …”

“…Alternatively, a high water density may also be achieved by using a so-called high-pressure AFM that was employed to image supercritical CO 2 at pressures of ∼100 atm. 32 The bottom plate is composed of a triangular arrangement of monolayer atoms, with the neighboring bond length being fixed at 0.23 nm. The x and y components of each atom position in the convex top plate are also in a triangular arrangement, while z components lie on a circle with a radius of R. The waterÀplate (or wall) interactions were modeled by a 6À12 Lennard-Jones (LJ) potential with the parameters σ (O-wall) = 0.316 nm, σ (H-wall) = 0.284 nm and ε (O-wall) = 0.831 kJ/mol, ε (H-wall) = 0.415 kJ/mol, which approximately reproduce the van der Waals (vdW) interaction between a water molecule and a quartz (SiO 2 ) surface.…”

CO2 Adhesion on Hydrated Mineral Surfaces

“…17 Measuring these forces directly is difficult because of the elevated pressures that are involved. 34 Atomic force microscopy (AFM) is one of the most accurate tools for measuring adhesive forces and active research is underway to carry it out under supercritical CO 2 conditions. 35 Studies of adhesion between solid surfaces have employed 'stick-peel-crack' type measurements where surfaces are placed in contact with each other and then pulled apart while measuring the force needed to separate the surfaces.…”

“…Measuring these forces directly is difficult because of the elevated pressures that are involved . Atomic force microscopy (AFM) is one of the most accurate tools for measuring adhesive forces and active research is underway to carry it out under supercritical CO 2 conditions .…”

The ReactorAFM: Non-contact atomic force microscope operating under high-pressure and high-temperature catalytic conditions

“…A more advanced approach uses a high-pressure flow cell that is separated from the piezo of the AFM scanner by a flexible membrane, to operate up to 423 K and 6 bar in liquids, 15 or up to 350 K and 100 atm in supercritical CO 2 . 16 These two instruments are limited to static AFM (i.e., contact mode) and constant temperature (long equilibration times), but could in principle be applied to catalytic systems. The ReactorAFM uses a similar concept with a high-pressure cell that is separated from the scanner, but has superior characteristics for catalysis research.…”