Scanning Tunneling Microscopy Studies of Temperature-Dependent Etching of Diamond (100) by Atomic Hydrogen Page: 3,370
VOLUME 86, NUMBER 15 PHYSICAL REVIEW LETTERS 9 APRIL 2001
FIG. 2. Nonhydrogen terminated diamond (100)-(2 X 1) sur-
face after atomic hydrogen exposure for 5 min at 200 C.
simply etching at that specific temperature. For example,
a film with the smooth morphology shown in Fig. 5 was
etched with atomic hydrogen at 200 C and converted to
a film with a rough morphology such as that shown in
Fig. 2. This rough morphology was then changed back to
the smooth morphology by etching at 1000 oC.
As shown in Fig. 2, exposure at 200 C results in a rough
surface at the atomic scale. The largest 2 X 1 domain size
is about 6 nm2, and there is no clear step direction. A
rough surface results when etching is isotropic in which
the probability of removal of a surface atom is independent
of its coordination . As shown in Fig. 3, exposure at
500 C results in a surface that is smoother at the atomic
scale with larger domains measuring about 100 nm2. In
addition, this surface contains large single atomic layer
vacancy islands, single height steps, and deep pits. The
pits have a pyramidal shape, as previously discussed for
Fig. 1(b). The vacancy islands have an average length
along the dimer rows that is 2.1 times greater than the
average length perpendicular to the dimer rows. Both SA
and SB steps are rough. These observations show that
etching occurs both parallel and perpendicular to the dimer
rows. As shown in Figs. 4 and 5, exposure at 1000 C
results in a smooth surface with the largest domains of
the three experiments measuring approximately 350 nm2.
Large pits are not observed and vacancy islands consist
mainly of single vacancy rows in the direction of the dimer
rows. SB steps are rough and SA steps are smooth, showing
that etching has a low probability of occurring at SA steps.
In addition, double type A steps, denoted DA in Figs. 4
and 5, are observed in which the middle SB step has been
completely etched. These observations show that etching
at 1000 C is highly anisotropic, with the etch rate along
the dimer rows much greater than that perpendicular to
the rows. In contrast, air STM experiments on epitaxial
diamond (100) films that are grown on viscinal diamond
(100) substrates and not etched by atomic hydrogen after
growth show a smooth surface consisting of double type
B, DB, steps formed by dimer row extension .
The anisotropic etching in the direction of dimer rows
supports recent theoretical models of the growth of smooth
diamond (100) films. Figure 6 shows a schematic of the
diamond (100)-(2 X 1):H surface. In theoretical models,
growth on this surface occurs by the adsorption of CH3 on
surface sites where hydrogen has been abstracted . The
adsorbates then form methylene bridges and dimers. In
the anisotropic etching model described in Ref. , ex-
tension of the dimer row at atoms 1 and 2 in Fig. 6 can oc-
cur as long as hydrocarbons have not adsorbed at the dimer
bonds to their right. For example, the presence of a methy-
lene bridge between atoms 3 and 4 will prevent adsorption
of CH3 at atoms 3 or 1 due to steric repulsion, and growth
will wait until this methylene bridge is etched. Growth
of dimers at SA steps, corresponding to atoms 5 and 6 in
Fig. 6, is not kinematically stable against etching because
all dimers grown at SA steps are similar to dimers at the
FIG. 3. Nonhydrogen terminated diamond (100)-(2 X 1) sur-
face after atomic hydrogen exposure for 5 min at 500 C.
FIG. 4. Nonhydrogen terminated diamond (100)-(2 X 1) sur-
face after atomic hydrogen exposure for 5 min at 1000 C.
VOLUME 86, NUMBER 15
PHYSICAL REVIEW LETTERS
9 APRIL 2001
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Stallcup, Richard E. & Pérez, José M. Scanning Tunneling Microscopy Studies of Temperature-Dependent Etching of Diamond (100) by Atomic Hydrogen, article, April 9, 2001; [College Park, Maryland]. (https://digital.library.unt.edu/ark:/67531/metadc84157/m1/3/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.