Science - USA (2019-01-04)

exceeded 670 K, consistent with our previous
experimental observations.
Desorption of TiOF 2 points to strong Ti–F
covalent bonding of F to the surface during the
HF zipping, which may indirectly explain the
observed surface reconstruction under newly
formed HBC molecules. Adsorbates strongly in-
teracting with the surface are known to induce
changes in rutile titania reconstructions, as pre-
viously reported for (110) ( 39 ) and (011) ( 40 , 41 )
faces. Recent work by Balajkaet al.( 41 )reported
a water-induced reconstruction of a rutile (011)
surface to form a bulk-terminated (1×1) face
covered with a hydroxyl group overlayer form-
ing (2×1) reconstruction. In the case of a HF
elimination reaction, the desorption of TiOF 2
species also formally leads to the formation of
water molecules, TiO 2 +2HF→TiOF 2 +H 2 O,
which then could dissociate and locally create
the hydroxyl-rich reconstruction. Close inspec-
tion of the ad-island structure performed by
high-resolution STM characterization (Fig. 4D)
shows bright protrusions forming rows along the
[01-1] direction, with neighboring ones shifted
by half of the lattice, giving apparent pseudo-
hexagonalc(2×1) symmetry. Results of our den-
sity functional theory calculations shown in Fig.
4E present the exact structure of the ad-islands
with four hydroxyl groups (two dissociated water
molecules) per (2×1) unit cell. Corresponding
unoccupied-states STM image simulation (Fig.
4F) confirmed that for high positive bias volt-
ages, this (2×1) surface reconstruction gave the
apparentc(2×1) symmetry observed in the ex-
perimental data. These results support the rutile
titania surface participation in intermediate
states of the cyclodehydrofluorination and re-
flect its crucial role in this process. Our results
provide a pathway toward custom-designed
sp^2 carbon–based nanostructure formation by
direct on-surface synthesis methods on tech-

nologically relevant semiconducting or insulat-

ing surfaces.

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ACKNOWLEDGMENTS

Funding:The research was supported by the Polish Ministry

of Science and Higher Education, contract no. 0341/IP3/2016/74.

R.Z. acknowledges support received from the National

Science Center, Poland (2017/24/T/ST5/00262). A.K.S. and

K.A. thank the Deutsche Forschungsgemeinschaft (DFG-SFB

953 “Synthetic Carbon Allotropes”project A6, and AM407) for

financial support. Work was partially conducted at the Center

for Nanophase Materials Sciences (CNMS), which is a DOE

Office of Science User Facility. The research was partially

supported from basic and statutory funds of the Jagiellonian

University in Krakow provided by the Polish Ministry of Science

and Higher Education.Author contributions:K.A. and M.K.

conceived the project. K.A. and A.K.S. carried out the precursor

synthesis and analysis. M.K. and R.Z. conducted the on-surface

synthesis and low-temperature STM, XPS, and MS analyses

with support from L.Z., S.G., and M.S. M.E. conducted the

computations. M.K. and K.A. prepared the manuscript with

feedback from all other authors.Competing interests:None

declared.Data and materials availability:All data needed to

evaluate the conclusions in the paper are present in the paper or

the supplementary materials.

SUPPLEMENTARY MATERIALS

http://www.sciencemag.org/content/363/6422/57/suppl/DC1

Materials and Methods

Supplementary Text

Figs. S1 to S34

Table S1

References ( 42 – 45 )

21 September 2018; accepted 16 November 2018

10.1126/science.aav4954

Kolmeret al.,Science 363 ,57–60 (2019) 4 January 2019 4of4

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