Reactivity of Ozone with Solid Potassium Iodide Investigated by Atomic Force Microscopy Page: 2 of 5
This article is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
Initially there is no KIO3 present on the surface and a
stoichiometric iodide to potassium ratio is measured. As the
sample is exposed to increasing amounts of ozone there is a
decrease in the iodide to potassium ratio and an increase in the
iodate to potassium ratio. The surface concentration of KIO3
saturates following prolonged exposures to ozone. The average
reactive sticking coefficient is 1.4 ( 0.7) x 10-4.10
AFM images presented in Figure 2 show the initial reaction
to form KIO3 at the KI surface. The original KI (100) plane
(following a brief exposure to water vapor) is shown in Figure
2A. The surface has a RMS roughness of 0.3 A, due mostly to
instrument error. As the relative humidity is increased, surface
ions become solvated and mobile, facilitating redistribution
across the cleaved plane in order to dissipate surface static
charge that is generated during the cleavage process.
Rounding of the step edges results from a reduction in the
surface energy.3 The onset of reactive uptake with ozone is
shown in Figure 2B. The reaction initially proceeds along step
edges, decorating the length of the edge with small particles of
KIO3 that are -3.8 A in height, consistent with a single iodate
sitting on the surface. Following reactivity of the step edge
sites, the oxidation then takes place across the sample terraces
as shown in Figure 3A. Small domains of potassium iodate
nucleate before growing into nanometer sized particles of
potassium iodate as the surface is exposed to increasing
amounts of ozone (Figure 3B).
n-a -- -------
reaction proceeds further, domains of KIO3 are generated on
the flat terraces of the sample. As these domains, which serve
as nucleation sites, grow into particles with increasing ozone
exposure, similar substrate pits are formed. Figure 4B shows a
small particle of KIO3, 1.5 nm in height on a flat terrace. The
corresponding section is shown in Figure 4D. Erosion of the
underlying KI surface has resulted in a pit from which the
material has been transferred to the newly formed KIO3
- I I I I I I
0 100 200 300 400 500
Figure 2: Topographic images of the KI surface during initial
oxidation to form KI03. The KI surface with monotonic step edges
~3.5 A in height is shown in (A). As the reaction begins, the step edges
become decorated with small particles of KI3 (B).
Initial oxidation occurs along the step edge and material
migrates to form small particles along the edge. Figure 4A
shows small particles of K103 that have decorated a step edge
of the KI (100) surface. The corresponding section through a
single particle is shown in Figure 4C. The section reveals that
there is mass transport of material from the KI substrate during
island growth, leaving pits adjacent to the islands. As the
0 100 200 300 400 500
Figure 3: Topographic images of the KI surface during oxidation to
form KI03. With increasing ozone exposure, oxidation occurs across
the sample terraces, nucleating additional islands of KI03 (A), which
grow with increasing exposure to ozone (B).
Figure 5 shows the KI surface following extended exposure
to ozone in which the surface is saturated in KIO3. The small
domains of KIO3 initially decorating the step edges and across
the flat terraces seen in Figures 2 and 3 have grown in size and
are now 10-30 nm in width, 4-6 nm in height and are densely
packed across the entire sample surface. No further evolution
of the island structure was observed in dry environments.
When the oxidized KI surface was imaged in AFM contact
mode, the iodate islands were easily displaced by the scanning
tip, consistent with a weak interaction between the particle and
the substrate due to an island-substrate lattice mismatch and
Oxidation of the KI (100) surface by ozone to form K103
does not take place as a simple layer-by-layer process. We
believe the passivating layer is comprised of small particles of
K103, residing on top of the underlying KI surface. Additional
electrostatic (Kelvin probe) AFM experiments, which we do
not describe here in detail, were carried out on a partially
reacted but not yet passivated surface. These experiments
show a difference in contact potential between islands and the
flat unreacted terraces, consistent with a difference in
composition. Also, the XPS study suggests that the flat terrace
regions could have at most 1 or 2 iodate layers of coverage.0
Here’s what’s next.
This article can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Article.
Mulleregan, Alice; Brown, Matthew A.; Ashby, Paul D.; Ogletree, D. Frank; Salmeron, Miquel & Hemminger, John C. Reactivity of Ozone with Solid Potassium Iodide Investigated by Atomic Force Microscopy, article, April 14, 2008; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc894501/m1/2/: accessed April 18, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.