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Materials (Basel). 2018 Dec 15;11(12). pii: E2556. doi: 10.3390/ma11122556.

Fingerprints of sp¹ Hybridized C in the Near-Edge X-ray Absorption Spectra of Surface-Grown Materials.

Author information

1
ETSF and Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria, 16, I-20133 Milano, Italy. guido.fratesi@unimi.it.
2
ETSF and Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria, 16, I-20133 Milano, Italy. simona.achilli@unimi.it.
3
ETSF and Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria, 16, I-20133 Milano, Italy. nicola.manini@fisica.unimi.it.
4
ETSF and Dipartimento di Fisica, Università degli Studi di Milano, Via Celoria, 16, I-20133 Milano, Italy. Giovanni.Onida@mi.infn.it.
5
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi, 55, 20125 Milano, Italy. a.baby@campus.unimib.it.
6
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi, 55, 20125 Milano, Italy. a.ravikumar@campus.unimib.it.
7
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi, 55, 20125 Milano, Italy. a.ugolotti@campus.unimib.it.
8
Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi, 55, 20125 Milano, Italy. gianpaolo.brivio@unimib.it.
9
Department of Energy, Politecnico di Milano via Ponzio 34/3, I-20133 Milano, Italy. alberto.milani@polimi.it.
10
Department of Energy, Politecnico di Milano via Ponzio 34/3, I-20133 Milano, Italy. carlo.casari@polimi.it.

Abstract

Carbon structures comprising sp 1 chains (e.g., polyynes or cumulenes) can be synthesized by exploiting on-surface chemistry and molecular self-assembly of organic precursors, opening to the use of the full experimental and theoretical surface-science toolbox for their characterization. In particular, polarized near-edge X-ray absorption fine structure (NEXAFS) can be used to determine molecular adsorption angles and is here also suggested as a probe to discriminate sp 1 /sp 2 character in the structures. We present an ab initio study of the polarized NEXAFS spectrum of model and real sp 1 /sp 2 materials. Calculations are performed within density functional theory with plane waves and pseudopotentials, and spectra are computed by core-excited C potentials. We evaluate the dichroism in the spectrum for ideal carbynes and highlight the main differences relative to typical sp 2 systems. We then consider a mixed polymer alternating sp 1 C 4 units with sp 2 biphenyl groups, recently synthesized on Au(111), as well as other linear structures and two-dimensional networks, pointing out a spectral line shape specifically due to the the presence of linear C chains. Our study suggests that the measurements of polarized NEXAFS spectra could be used to distinctly fingerprint the presence of sp 1 hybridization in surface-grown C structures.

KEYWORDS:

C 1s absorption; carbynes; density functional theory; near edge X-ray absorption spectroscopy; on-surface chemistry; self-assembly

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