Supporting Information
Surface morphology of atomic nitrogen on Pt(111)
Zhu Liang,1 Hyunjin Yang,2,3 Yousoo Kim,2 and Michael Trenary1,a)
1
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago,
Illinois 60607, United States
2
Surface and Interface Science Laboratory, RIKEN, 2-1 Hirosawa, Wako-shi, Saitama 351-
0198, Japan
3
Department of Advanced Materials Science, The University of Tokyo, 5-1-5 Kashiwanoha,
Kashiwa, Chiba 277-8561, Japan
FIG. S1. STM images of p(2×2)-N (a) before and (b) after dissociation of an NH molecule
(indicated by solid arrow). For both images: area = 4 nm  4 nm, Vs = 50 mV, It = 0.5 nA.
After injecting tunneling electrons (2.4 nA, 0.7 V, 4 sec) into the NH molecule at the topleft corner of Fig. S1(a), indicated by an arrow, an undisturbed p(2×2)-N structure was
observed as shown in Fig. S1(b). The NH molecule was converted to an H atom (not observed
under these conditions) and an N atom, which sits at the same fcc-hollow site.
a) mtrenary@uic.edu.
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FIG. S2. Model of p(2×2)-N. N atom occupies (a) fcc-hollow site; (b) hcp-hollow site. Blue
and purple rhombuses indicate the unit cells of p(2×2)-N and p(2×2)-Pt, respectively.
Nitrogen atoms are colored blue, Pt (visible) purple, and Pt (2nd layer) brown.
A triangle in the six-membered ring connects three Pt atoms that are visible in STM
images, and is centered at the hollow of that ring. Such a triangle in Fig. S1(a) is rotated by 60°
compared to that in Fig. S1(b) if the N atoms sit at different hollow sites. Rotated triangles are
not observed in the images.
FIG. S3. Polarity effects on the appearance of p(2×2)-N. For all images, area = 3 nm × 3 nm,
It = 0.6 nA. (a) Vs = ±10 mV (17 MΩ); (b) Vs = ±50 mV (50 MΩ). Blue and black circles
indicate the position of N and Pt atoms, respectively.
In Fig. S3(a) and (b), images in the upper panels were obtained at negative sample bias (−),
while those in the bottom panels were obtained at positive sample bias (+). In Fig. S3(a),
images are almost identical under (+) and (−) biases. In Fig. S3(b), the relative brightness
(apparent height) of a Pt atom to a N atom is slightly higher under (+) bias than that under (−)
bias. However, inversion of contrast was not observed, which means Pt atoms are always
brighter than N atoms under either (+) or (−) biases at 50 MΩ gap resistance.
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