PNNL-13501 - Pacific Northwest National Laboratory

in Figure 1. This optical image (10X) was obtained using
an optical microscope built into the atomic force
microscopy instrument. The curving lower boundary of
the regular crystalline arrays is the boundary of the drop.
The edge of the calcite crystal is seen at the bottom of the
image. The upper right boundary of the deposit was
formed as the drop evaporated (the drop initially covered
the bare upper right region). Another 10X optical image
of the combination of large crystals and dendrites is
shown in Figure 2. The preferred orientation of both
crystals and dendrites, from upper left to lower right, is
apparent.
Figure 1. 10X optical image of neptunium(V) crystalline
deposits at the edge of 10 µL drop coverage
Figure 2. 10X optical image showing combination of Np(V)
large crystals and dendrites
Figure 3 is a close-up of Figure 2, showing the dendrites
in more detail. Figure 4 is a scan of the tip of the large
crystal shown in Figure 3, using the atomic force
microscopy scanning tip. This scan provided high spatial
360 FY 2000 Laboratory Directed Research and Development Annual Report
resolution in three dimensions. The thickness of this
relatively small portion of the crystal was 5 µm,
indicating that the total thickness of the large crystals was
greater than this. Figure 5 is a closeup atomic force
microscopy scan of Figure 4, showing crystalline terraces
that form the large crystal. Figure 6 is an atomic force
microscopy scan of the dendrites just to the right of the
large crystal in Figure 3. The dendrites were 5 µm to
10 µm wide, 50 µm to 100 µm (or more) long, and had
many parallel branches arrayed along their long edges.
The line analysis capability of the atomic force
microscopy software was used to determine the 100 nm to
150 nm thickness of the dendrites. The surface of the
dendrites was found to be very flat, as shown in Figure 7.
The height variation is less than 0.16 nm, probably within
the error of this measurement.
Figure 3. Close-up of Figure 2 (30X total) showing dendrites
in more detail
Figure 4. Atomic force microscopy scan of the tip of the
large crystal shown in Figure 3. Crystal thickness is over
5 µm.