Figures from "Morphology and Dissolution Processes of Metal Sulfide Minerals Observed with the Electrochemical Scanning Tunneling Microscope", S.R. Higgins and R.J. Hamers, J. Vac. Sci. Technol. B 14(2), Mar/Apr 1996.

All original binhex and zipped figures are Adobe Photoshop TIFF documents unless otherwise noted.

Figure 1

Diagram of the electrochemical STM instrumentation showing the incorporation of a syringe pump mechanism. Also, the electrode connections via a biopotentiostat are shown. T=tip electrode, R=reference electrode, C=counter electrode, and W=working electrode.


Figure 2

(2a) 3000 x 3000 Å STM image of the covellite [CuS(0001)] cleavage surface immersed in 0.5 M NaClO4 near the open circuit potential (OCP). Esample = 0.0 V, Etip = -0.35 V, Itip = 1 nA.
(2b) 800 x 800 Å image of the pyrite [FeS2(001)] natural surface. The solution conditions in this image were identical to those of figure 2a. The sample was imaged at the OCP. Esample = +0.2 V, Etip = +0.75 V, Itip = 0.2 nA.
(2c) 2800 x 2800 Å image of a galena [PbS(001)] cleavage surface shortly after immersion in 0.5 M Na2SO4 at a pH of 1.3. Esample = +0.11 V, Etip = -0.14 V, Itip = 0.58 nA.


Figure 3

Real time sequence of STM images of the galena(001) surface showing the dissolution process.
(3a) 6250 x 6250 Å image.
(3b-3d) 2000 x 2000 Å images. The time to acquire each image was approximately 3 minutes. The imaging conditions were identical to those in figure 2c.


Figure 4

Diagram of the PbS(001) surface structure showing the atomic arrangements at the [100] and [110] step edges.


Figure 5

100 x 100 Å atomic resolution STM image (empty states) of the defect structure on the galena(001) surface. Esample = +0.17 V, Etip = -0.10 V, Itip = 1 nA.


Figure 6

Sequence of 4000 x 4000 Å STM images of the galena(001) surface showing the effect of chloride ions on the surface morphology and dynamics at the OCP.
(6a) taken in 1 M NaClO4 at pH = 1.7.
After the acquisition of (a), 20 mL of a 1 M NaCl solution at pH = 1.7 was introduced into the cell.
(6b-6c) images acquired immediately following chloride incorporation. Esample = +0.27 V, Etip = +0.67 V, Itip = 0.28 nA.


Last updated February 3, 1998