HF elimination reaction, we combined the STM
data with the XPS chemical analysis. The C1s
core-level photoemission spectrum of P2 mole-
cules deposited on the rutile (011) surface at RT
(Fig. 4A) showed an asymmetric signal composed
of two peaks separated by ~2 eV in binding
energy (EB), which correspond to C–C (red line,
EB= 284.4 eV) and C–F (green line,EB= 286.3 eV)
contributions ( 36 , 37 ). Figure 4B presents the F1s
core-level region. For RT deposition, the singlepeak observed atEB= 686.8 eV is related to an
organofluorine component ( 13 , 36 , 37 ). The ab-
sence of a peak at ~684.5 eV suggests the lack of
aF–Ti component ( 38 ). Thus, the XPS analysis
confirmed that the C–F bonds in the precursor
molecules were intact after deposition on the
surface at RT.
Afterannealingat670Kfor10min,the
XPS signal from the C1s region consisted of
only a single peak atEB= 284.5 eV, corre-
sponding to a C–Ccomponent(Fig.4A),con-
firming global scission of C–FbondsinP2
molecules caused by efficient HF elimination.
The corresponding STM images (Fig. 3, A and
E) show that the flat-lying HBC molecules
were found on the newly formed reconstructed
areas of the surface, forming ad-islands attached
to TiO 2 (011)-(2×1) step edges or domain bound-
aries. These structures were not observed in a
control experiment, wherewedirectlydeposited
HBC molecules on the rutile (011) and annealed
thesampleto670K(seethesupplementaryma-
terials). Moreover, other halogenoarenes with
bromine ( 20 – 22 )oriodine( 21 )substituentsan-
nealed under similar conditions at rutile titania
surfaces did not produce the observed ad-islands.
An obvious hypothesis is that F atoms are
building blocks in these new structures. How-
ever,Fig.4Bshowsthatafterannealing,the
XPS signal from the F1s region was strongly
reduced, consisted of only organic fluorine
(<10% of the initial intensity), and provided
no indication of a F–Ti component at ~684.5 eV
(arrow). Lack of F at the surface region mo-
tivated us to look for fluorine-containing mol-
ecules desorbing from the rutile (011) surface
after the HF-zipping reaction by monitoring cor-
responding MS signals during controlled sample
heating from RT up to 770 K. We observed sig-
nals only for molecules of TiOF 2 (Fig. 4C) and
TiOF (see the supplementary materials). Despite
the sharp peak located at ~500 K, the main
fraction of TiOF 2 desorbed when the temperatureKolmeret al.,Science 363 ,57–60 (2019) 4 January 2019 3of4
Fig. 3. HF versus H 2 elimination.(A) STM image (+2 V, 50 pA) presenting molecules of
HBC and H2-HBC (arrows) formed from P2 after annealing at 670 K. (B) Cross sections along
purple and green lines in (A). (CandD) Optimized geometries of (C) HBC and (D) H2-HBC
molecules. Gray and white circles correspond to carbon and hydrogen atoms, respectively.
(E) High-resolution STM image (+2.7 V, 200 pA) of HBC and H2-HBC on newly formed
reconstruction of rutile (011). Scale bars in (C) to (E) are 1 nm.
Fig. 4. Chemical analysis.(A) XPS
C1s core-level spectra measured for P2
deposited on rutile (011) at RT (top)
and after annealing to 670 K (bottom).
arb., arbitrary. (B) XPS F1s core-level
spectra measured for P2 deposited
on rutile (011) at RT and after annealing
to 670 K. The arrow marks the energy
of the eventual F–Ti component. (C) Mass
spectrometer signals of a TiOF 2 molecule
(m/z= 101.8) registered during controlled
heating of bare and P2-covered rutile TiO 2 (011)
from RT to around 770 K. The main fraction
of thermally desorbed TiOF 2 molecules from the
P2-covered surface is registered for temper-
atures exceeding 670 K. (D) High-resolution STM
image (+2.7 V, 200 pA) presenting new recon-
struction of the ad-island with apparent
c(2×1) symmetry. (E) Calculated structure of
the hydroxylated rutile TiO 2 (011)-(1×1) surface
forming (2×1) reconstruction. Gray, red, and white circles correspond to titanium, oxygen, and hydrogen atoms, respectively. (F) Unoccupied-states
STM image simulation of the structure presented in (E). Scale bars in (D) to (F) are 0.5 nm. Purple rectangles mark corresponding unit cells.
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