Atomic structure of steps and defects on the clean diamond (100)-2 X 1 surface studied using ultrahigh vacuum scanning tunneling microscopy Page: 4,539
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Appl. Phys. Lett., Vol. 81, No. 24, 9 December 2002
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._ _ _FIG. 2. UHV STM image of the clean diamond (100)-2X 1 surface.
ment CVD reactor and were approximately 2 /tm thick. The
reactor is coupled to a UHV STM chamber at a pressure
<10-10 Torr via an all-metal through-valve. The CVD
growth pressure was 30 Torr with hydrogen and methane
flow rates of 200 and 0.5 sccm, respectively. The films were
doped with boron during growth using diborane gas at a
concentration of 10 ppm relative to hydrogen in order to
increase their conductivity for STM studies. The substrate
and filament temperatures were 900 and 2200 C, respec-
tively. After growth, the films were exposed to atomic hydro-
gen for 10 mmin at 900 OC to produce a smooth surface. This
was accomplished by shutting off the methane flow and
maintaining all of the other parameters for 10 min. The fila-
ment, sample heater and then the hydrogen flow were turned
off. The CVD reactor was evacuated to 1 X 10-s Torr using a
turbomolecular pump and the samples were transferred to the
UHV STM chamber via a linear translator without contami-
nating them by exposure to air. The samples were then
heated to 1000 C in UHV to desorb the hydrogen and pro-
duce a clean diamond (100)-2 X 1 surface. STM imaging
was performed for filled states using a sample bias of -1.0
to -1.5 V, and tunneling current of about 1 nA.
Figure 2 shows a UHV STM image of a clean diamond
(100)-2 X 1 surface prepared as described previously, show-
ing SB , SA , and DA steps. Figure 3(a) is a higher resolution
image showing that edge atoms on the bottom plane of an SB
step have a bonding configuration that is different than that
of a dimer row, as observed near regions marked "R." Figure
3(b) shows a high-resolution image of the SB step near the
center of Fig. 3(a), and a superimposed schematic of a reb-
onded SB step. As shown in Fig. 3(b), the distance from edge
dimers on the upper plane to the nearest full dimer row on
the bottom plane is 3 d, in agreement with a rebonded step.
The STM images of rebonded steps in Fig. 3 are similar to
those reported for the Si (100)-2 X 1 surface.2'9 In Fig. 3, the
rebonded rows consist of bright regions that occur at loca-
tions corresponding to atoms 1 and 2 in Fig. 1(a). We at-
tribute the bright regions to a bond between atoms 1 and 2.
In Fig. 3(b), the dimer row on the top plane, indicated by the
unmarked arrow, forms a local nonbonded step. Local non-
bonded steps on the Si (100)-2 X 1 surface have been ob-P
2 n
-_ 0.5 nm j
FIG. 3. (a) UHV STM image of the diamond (100)-2 x 1 surface showing
rebonded SB steps. (b) High-resolution UHV STM image of the SB step near
the center of (a) and a superimposed schematic of a rebonded SB step.
served and are thought to be stabilized by vacancies.2 There-
fore, we attribute the nonbonded step in Fig. 3(b) to vacancy
V shown in Fig. 3(a).
Figure 4 shows a UHV STM image of a DA step on the
diamond (100)-2 X 1 surface. Edge atoms on the bottom
plane have a bonding configuration that is the same as that
observed for rebonded SB steps, indicating a rebonded DA
step. All observed SB and DA steps were rebonded. These
observations contradict recent theoretical predictions that, on
the diamond (100)-2 X 1 surface, nonbonded SB and DA
steps are more favorable than rebonded ones.10
In addition, Figs. 2 and 3(a) show defects consisting of
dimer vacancies, indicated by V, that are single, multiple, and
arranged in rows parallel and perpendicular to dimer rows.
The density of single and multiple vacancies is about 8
X 10'2/cm2, less than in Si.2'3 Also observed are a large num-
SB
DA
S 1 nm -
FIG. 4. UHV STM image of the diamond (100)-2 x 1 surface showing a
rebonded DA step.Downloaded 24 Apr 2012 to 129.123.92.130. Redistribution subject to AlP license or copyright; see http:ilapl.aip.org/about/rights_and_permissions
R. E. Stallcup II and J. M. Perez 4539
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Stallcup, Richard E. & Pérez, José M. Atomic structure of steps and defects on the clean diamond (100)-2 X 1 surface studied using ultrahigh vacuum scanning tunneling microscopy, article, December 9, 2002; [College Park, Maryland]. (https://digital.library.unt.edu/ark:/67531/metadc83794/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT College of Arts and Sciences.