6
of Figure 6A. Figure 6C, the section analysis of Figure 6A,
confirms that the surface roughness increases a little bit
when malachite surface contacts a high concentration of
OHA. Figure 6D is the deflection image of Figure 6A with
a 5 nm data scale.
To verify the adsorption of the OHA on malachite in
solution, after Figure 6 is obtained, a 1 µm × 1 µm area is
scanned for one time with a much larger scan force being
applied to intentionally remove the adsorbate. Further, the
same position is scanned again in a 5 µm × 5 µm area with
a normal scan force being applied and the result is shown
as Figure 7. One can see from Figure 7A, the height image,
that a 1 µm × 1 µm blank ‘window’ is shown in the center
of the image due to the removal of the adsorbate from min-
eral surface under the previously applied large scan force.
That is, the ‘window’ in the center is the bare malachite
surface and the surrounding area is the mineral surface
still covered by the adsorbate without being disturbed the
applied large scan force. By comparing Figure 7B, the 3-D
image of Figure 7A, to igure 6B, one can easily observe a
deep pit showing on mineral surface with adsorbate cover-
ing the surrounding area. Figure 7C is the section analysis
of Figure 7A and it shows the height difference between
the blank ‘window’ (as shown by the red markers) and the
surrounding area being covered with adsorbate (as shown
by the red markers). Figure 7D is the deflection image of
Figure 7A with a 5 nm data scale.
Figure 8 shows the AFM images of a malachite sur-
face soaked in 5×10–4 M OHA solution for 10 minutes. By
comparing Figure 8A, the height image, to Fig.2A, one can
find that there is some adsorbate showing up on malachite
when the mineral surface contacts 5×10–4 M OHA solu-
tion. Figure 8B is the 3-D image of Figure 8A. Figure 8C,
the section analysis and Figure 8D is the deflection image
with a 5 nm data scale.
AFM Force Measurement
Figure 9 shows that the detach force measured between an
AFM probe and malachite surface in air is about 10 nN, and
the force is due to the adhesion, which arises from the van
der Waals force, between two objects in contact. When the
malachite surface contacts water, the detach force decreases
to 5 nN and it is due to the reduced Hamaker constant
of Amalachite/water/SiN when compared to Amalachite/
air/SiN. When malachite surface contacts 5×10–5 M
OHA solution, the detach force value is very low, suggest-
ing a very weak adhesion between malachite surface and
the AFM probe in solution. The facts that the “jump-off”
point is sharp and the “jump-off” occurs at the place where
the separation is close to 0 nm separation suggest that the
Figure 6. AFM images of a malachite surface soaked in 1×10–4 M
OHA solution for 10 minutes. A) the 2 µm × 2 µm height image
with a data scale of 20 nm B) the 3-D image C) the section
analysis and D) the deflection image with a data scale of 5 nm
of Figure 6A. Figure 6C, the section analysis of Figure 6A,
confirms that the surface roughness increases a little bit
when malachite surface contacts a high concentration of
OHA. Figure 6D is the deflection image of Figure 6A with
a 5 nm data scale.
To verify the adsorption of the OHA on malachite in
solution, after Figure 6 is obtained, a 1 µm × 1 µm area is
scanned for one time with a much larger scan force being
applied to intentionally remove the adsorbate. Further, the
same position is scanned again in a 5 µm × 5 µm area with
a normal scan force being applied and the result is shown
as Figure 7. One can see from Figure 7A, the height image,
that a 1 µm × 1 µm blank ‘window’ is shown in the center
of the image due to the removal of the adsorbate from min-
eral surface under the previously applied large scan force.
That is, the ‘window’ in the center is the bare malachite
surface and the surrounding area is the mineral surface
still covered by the adsorbate without being disturbed the
applied large scan force. By comparing Figure 7B, the 3-D
image of Figure 7A, to igure 6B, one can easily observe a
deep pit showing on mineral surface with adsorbate cover-
ing the surrounding area. Figure 7C is the section analysis
of Figure 7A and it shows the height difference between
the blank ‘window’ (as shown by the red markers) and the
surrounding area being covered with adsorbate (as shown
by the red markers). Figure 7D is the deflection image of
Figure 7A with a 5 nm data scale.
Figure 8 shows the AFM images of a malachite sur-
face soaked in 5×10–4 M OHA solution for 10 minutes. By
comparing Figure 8A, the height image, to Fig.2A, one can
find that there is some adsorbate showing up on malachite
when the mineral surface contacts 5×10–4 M OHA solu-
tion. Figure 8B is the 3-D image of Figure 8A. Figure 8C,
the section analysis and Figure 8D is the deflection image
with a 5 nm data scale.
AFM Force Measurement
Figure 9 shows that the detach force measured between an
AFM probe and malachite surface in air is about 10 nN, and
the force is due to the adhesion, which arises from the van
der Waals force, between two objects in contact. When the
malachite surface contacts water, the detach force decreases
to 5 nN and it is due to the reduced Hamaker constant
of Amalachite/water/SiN when compared to Amalachite/
air/SiN. When malachite surface contacts 5×10–5 M
OHA solution, the detach force value is very low, suggest-
ing a very weak adhesion between malachite surface and
the AFM probe in solution. The facts that the “jump-off”
point is sharp and the “jump-off” occurs at the place where
the separation is close to 0 nm separation suggest that the
Figure 6. AFM images of a malachite surface soaked in 1×10–4 M
OHA solution for 10 minutes. A) the 2 µm × 2 µm height image
with a data scale of 20 nm B) the 3-D image C) the section
analysis and D) the deflection image with a data scale of 5 nm