Weina Peng 1, a) , William J.I. DeBenedetti 1 , Seonjae Kim 1 , Melissa A. Hines 2 and Yves J.
Chabal 1
1
Department of Material Science and Engineering, University of Texas at Dallas
2
Department of Chemistry, Cornell University
S1. STM
For STM investigations, P-doped, 0.5–10

cm, single-side polished, Cz Si(100) wafers cut to within 0.9° of the (100) orientation were thermally oxidized to a depth of ~100 nm, diced, and cleaned in sequential baths of warm trichloroethylene, acetone, methanol and ultrapure H
2
O.
Immediately prior to imaging, the oxidized samples were chemically cleaned in sequential basic and acidic peroxide solutions at 80°C with thorough rinsing in ultrapure water after each step as described in Ref. 1. The thick thermal oxide was then removed by a 75 s etch in buffered oxide etchant (BOE, J. T. Baker, a 5:1 by volume mixture of 50% HF: 40% NH
4
F).
The final morphology was determined by the following etching step as verified by previous
research.
1 The HF-etched surfaces were etched for an additional 165 s etch in BOE, whereas the
quasi-atomically flat surfaces were etched for 2 min in 40% NH
4
F (aq), drawing the sample through the air/water interface every 15 sec. After etching, the samples were thoroughly rinsed in ultrapure water and an InGa ohmic contact applied to the backside before loadlocking into an ultrahigh vacuum chamber containing an Omicron variable temperature scanning tunneling microscope. The sample was imaged without further processing.
S2. FTIR
FTIR was performed with a Nicolet Nexus 6700 spectrometer equipped with a DTGS detector.
The entire instrument is installed in a constant N
2
purging glove box (O
2 and H
2
O < 0.1ppm) to minimize surface oxidation of hydrogen termination. For the reference as well as the sample spectra, three 500 scans (4 cm
-1
resolution) were taken at Brewster angle (~ 70.0

) in a transmission geometry and then averaged to yield the final spectra shown in Fig. 2(a).
S3. XPS

XPS was performed with a PHI 5600 ESCA system with a monochromaic Al K

source ( h

=
1486.6 eV). The spectra were scanned at a 45

take off angle with a band pass energy of 5.85 eV.
The spectra fitting is performed with Casa XPS program. A Shirley background has already been subtracted from the signal.
2500
2000
1500
1000
500
HF treated Si(100)
quasi atomically flat H-Si(100)
0
282 284 286 288 290
Binding Energy (eV)
292
Fig. S1 Comparison of C 1 s spectra for HF treated Si(100) surfaces and quasi-atomically flat H-
Si(100) surfaces. No obvious difference can be observed for the two surfaces.
10
12
10 11
10
10
10
9
0.10
HF treated Si(100) Atomically flat Si(111)
Quasi-atomically-flat Si(100)
MOS SiO
2
/Si(111) MOS SiO
2
/Si(100)
0.15
0.20
0.25
E-E i
(eV)
0.30
0.35
0.40
Fig. S2 The same graph as Fig. 4 but plotted on a log scale.
1 B. S. Aldinger, and M. A. Hines, J. Phys. Chem. C 116 , 21499 (2012).