Density and refractive index of supercritical CO2 as a function of pressure up to 140 atm for temperature isotherms 310–350K. Large changes in slope at specific temperature and pressure conditions reflect the potential for considerable noise in the optical detection system induced by temperature and pressure fluctuations.
Schematic of the high-pressure AFM head showing sapphire window (A), window cover (B), fluid cell (C), optical head base plate (E), scanner housing (K), translational components (I,L–Q), stepper motor housing (R,S), stepper motor housing window (T), and stepper motor housing window cover (U).
Schematic of the fluid cell portion of the high-pressure AFM head. The fluid cell region consists of a sapphire window (A), window cover (B), titanium cantilever holder (C), cantilever (D), optical head base plate (E), titanium fluid cell (F), the titanium sample disk (G), Macor™ spacer (H), piezoelectric scanner (I), Kalrez® membrane (J), and scanner housing (K).
Schematic of the fluid delivery system. Valves are labeled A–F.
Noise comparison between a cantilever freely suspended in a Multimode AFM in its standard configuration at ambient conditions (black) and one freely suspended in the test cell filled with supercritical CO2 at 343 K and 92.0 atm (gray). The rms noise for the AFM in its standard configuration is calculated to be 5.9 mV and is greater than the rms noise for the test cell, calculated to be 2.7 mV.
(a) A 5 μm × 5 μm topographic image of a freshly cleaved calcite () surface under dry scCO2 at 308.2 K and 99.3 atm using a flow rate of 500 μl min−1. 3.2 Å monatomic steps are visible in this image. (b) A 40 μm × 40 μm topographic image of a calibration grid with 3 μm periodicity at 308.3 K.
7 μm × 7 μm topographic images of the () surface of calcite initially exposed to ambient air for ∼20 h prior to imaging under scCO2 at 308.3 K and 82.0 atm as a function of time using a flow rate of 500 μl min−1. Images (a)–(c), taken 6 min apart, show dynamic processes occurring on the mineral surface. Image (d) is a cross section of a portion of image (a) (line shown) showing height of the terrace is about 1.2 nm.
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