Surface chirality of CuO thin films.
We present X-ray photoelectron spectroscopy (XPS) and X-ray photoelectron diffraction (XPD) investigations of CuO thin films electrochemically deposited on an Au(001) single-crystal surface from a solution containing chiral tartaric acid (TA). The presence of enantiopure TA in the deposition process results in a homochiral CuO surface, as revealed by XPD. On the other hand, XPD patterns of films deposited with racemic tartaric acid or the "achiral" meso-tartaric acid are completely symmetric. A detailed analysis of the experimental data using single scattering cluster calculations reveals that the films grown with l(+)-TA exhibit a CuO(1) orientation, whereas growth in the presence of d(-)-TA results in a CuO(11) surface orientation. A simple bulk-truncated model structure with two terminating oxygen layers reproduces the experimental XPD data. Deposition with alternating enantiomers of tartaric acid leads to CuO films of alternating chirality. Enantiospecifity of the chiral CuO surfaces is demonstrated by further deposition of CuO from a solution containing racemic tartaric acid. The pre-deposited homochiral films exhibit selectivity toward the same enantiomeric deposition pathway.
Widmer
Roland
R
Empa, Swiss Federal Laboratories for Materials Testing and Research, nanotech@surfaces Laboratory, Feuerwerkerstrasse 39, CH-3602 Thun, Switzerland. roland.widmer@empa.ch
Haug
Franz-Josef
FJ
Ruffieux
Pascal
P
Gröning
Oliver
O
Bielmann
Michael
M
Gröning
Pierangelo
P
Fasel
Roman
R
D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D013057:Spectrum Analysis / Q000379:methods; D013237:Stereoisomerism; D013499:Surface Properties; D014965:X-Rays
D003300:Copper; C030973:cupric oxide