The structure of 2D charge transfer salts formed by TCNQ/alkali metal coadsorption on Ag(111)

P. J. Blowey; L. A. Rochford; D. A. Duncan; P. T.P. Ryan; D. A. Warr; T. L. Lee; G. Costantini; D. P. Woodruff

doi:10.1016/j.susc.2020.121687

The structure of 2D charge transfer salts formed by TCNQ/alkali metal coadsorption on Ag(111)

P. J. Blowey, L. A. Rochford, D. A. Duncan, P. T.P. Ryan, D. A. Warr, T. L. Lee, G. Costantini, D. P. Woodruff^*

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

1 Citation (Scopus)

Abstract

The structure of coadsorption phases formed on Ag(111) by TCNQ (7,7,8,8-tetracyanoquinodimethane) with Cs are compared with previously reported coadsorption phases formed with K, following investigation by scanning tunnelling microscopy (STM), low energy electron diffraction, soft X-ray photoelectrons spectroscopy and normal incidence X-ray standing waves (NIXSW). For each alkali we identify two ordered phases, one with an alkali: TCNQ stoichiometry of 1:1 and the other 2:1. STM images show the molecular organisation is the same for Cs and K, although only the K₂TCNQ phase is commensurate with the substrate. A previously-published detailed structure determination of the K₂TCNQ phase, complemented by density function theory calculations that identify bonding strengths, showed that the binding within the layer is much stronger than that of the layer to the substrate. Insensitivity to commensuration is thus to be expected. The situation for KTCNQ and CsTCNQ is less clear; these ordered incommensurate overlayers clearly have strong intralayer bonding, but the relative strength of the average overlayer-substrate bonding is unknown. NIXSW data show that the alkalis in these phases occupy adsorption sites far more distant from the substrate than the TCNQ molecules when compared to the near coplanar alkali-TCNQ geometry of K₂TCNQ and Cs₂TCNQ. Ultraviolet photoelectron spectra show increasing bonding shifts of TCNQ orbital states with alkali coverage.

Original language	English
Article number	121687
Journal	Surface Science
Volume	701
DOIs	https://doi.org/10.1016/j.susc.2020.121687
Publication status	Published - Nov 2020

Bibliographical note

Funding Information:
The authors thank Diamond Light Source for allocations SI15899 and NT18191 of beam time at beamline I09 that contributed to the results presented here. P.J.B. acknowledges financial support from Diamond Light Source and EPSRC . G.C. acknowledges financial support from the EU through the ERC Grant “VISUAL-MS” (Project ID: 308115 ).

Publisher Copyright:
© 2020 Elsevier B.V.

Keywords

Alkali adsorption
Charge transfer
NIXSW
STM
Surface structure
TCNQ

ASJC Scopus subject areas

Condensed Matter Physics
Surfaces and Interfaces
Surfaces, Coatings and Films
Materials Chemistry

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@article{39661270010d4907808a0857996db202,

title = "The structure of 2D charge transfer salts formed by TCNQ/alkali metal coadsorption on Ag(111)",

abstract = "The structure of coadsorption phases formed on Ag(111) by TCNQ (7,7,8,8-tetracyanoquinodimethane) with Cs are compared with previously reported coadsorption phases formed with K, following investigation by scanning tunnelling microscopy (STM), low energy electron diffraction, soft X-ray photoelectrons spectroscopy and normal incidence X-ray standing waves (NIXSW). For each alkali we identify two ordered phases, one with an alkali: TCNQ stoichiometry of 1:1 and the other 2:1. STM images show the molecular organisation is the same for Cs and K, although only the K2TCNQ phase is commensurate with the substrate. A previously-published detailed structure determination of the K2TCNQ phase, complemented by density function theory calculations that identify bonding strengths, showed that the binding within the layer is much stronger than that of the layer to the substrate. Insensitivity to commensuration is thus to be expected. The situation for KTCNQ and CsTCNQ is less clear; these ordered incommensurate overlayers clearly have strong intralayer bonding, but the relative strength of the average overlayer-substrate bonding is unknown. NIXSW data show that the alkalis in these phases occupy adsorption sites far more distant from the substrate than the TCNQ molecules when compared to the near coplanar alkali-TCNQ geometry of K2TCNQ and Cs2TCNQ. Ultraviolet photoelectron spectra show increasing bonding shifts of TCNQ orbital states with alkali coverage.",

keywords = "Alkali adsorption, Charge transfer, NIXSW, STM, Surface structure, TCNQ",

author = "Blowey, {P. J.} and Rochford, {L. A.} and Duncan, {D. A.} and Ryan, {P. T.P.} and Warr, {D. A.} and Lee, {T. L.} and G. Costantini and Woodruff, {D. P.}",

note = "Funding Information: The authors thank Diamond Light Source for allocations SI15899 and NT18191 of beam time at beamline I09 that contributed to the results presented here. P.J.B. acknowledges financial support from Diamond Light Source and EPSRC . G.C. acknowledges financial support from the EU through the ERC Grant “VISUAL-MS” (Project ID: 308115 ). Publisher Copyright: {\textcopyright} 2020 Elsevier B.V.",

year = "2020",

month = nov,

doi = "10.1016/j.susc.2020.121687",

language = "English",

volume = "701",

journal = "Surface Science",

issn = "0039-6028",

publisher = "Elsevier",

}

TY - JOUR

T1 - The structure of 2D charge transfer salts formed by TCNQ/alkali metal coadsorption on Ag(111)

AU - Blowey, P. J.

AU - Rochford, L. A.

AU - Duncan, D. A.

AU - Ryan, P. T.P.

AU - Warr, D. A.

AU - Lee, T. L.

AU - Costantini, G.

AU - Woodruff, D. P.

N1 - Funding Information: The authors thank Diamond Light Source for allocations SI15899 and NT18191 of beam time at beamline I09 that contributed to the results presented here. P.J.B. acknowledges financial support from Diamond Light Source and EPSRC . G.C. acknowledges financial support from the EU through the ERC Grant “VISUAL-MS” (Project ID: 308115 ). Publisher Copyright: © 2020 Elsevier B.V.

PY - 2020/11

Y1 - 2020/11

N2 - The structure of coadsorption phases formed on Ag(111) by TCNQ (7,7,8,8-tetracyanoquinodimethane) with Cs are compared with previously reported coadsorption phases formed with K, following investigation by scanning tunnelling microscopy (STM), low energy electron diffraction, soft X-ray photoelectrons spectroscopy and normal incidence X-ray standing waves (NIXSW). For each alkali we identify two ordered phases, one with an alkali: TCNQ stoichiometry of 1:1 and the other 2:1. STM images show the molecular organisation is the same for Cs and K, although only the K2TCNQ phase is commensurate with the substrate. A previously-published detailed structure determination of the K2TCNQ phase, complemented by density function theory calculations that identify bonding strengths, showed that the binding within the layer is much stronger than that of the layer to the substrate. Insensitivity to commensuration is thus to be expected. The situation for KTCNQ and CsTCNQ is less clear; these ordered incommensurate overlayers clearly have strong intralayer bonding, but the relative strength of the average overlayer-substrate bonding is unknown. NIXSW data show that the alkalis in these phases occupy adsorption sites far more distant from the substrate than the TCNQ molecules when compared to the near coplanar alkali-TCNQ geometry of K2TCNQ and Cs2TCNQ. Ultraviolet photoelectron spectra show increasing bonding shifts of TCNQ orbital states with alkali coverage.

AB - The structure of coadsorption phases formed on Ag(111) by TCNQ (7,7,8,8-tetracyanoquinodimethane) with Cs are compared with previously reported coadsorption phases formed with K, following investigation by scanning tunnelling microscopy (STM), low energy electron diffraction, soft X-ray photoelectrons spectroscopy and normal incidence X-ray standing waves (NIXSW). For each alkali we identify two ordered phases, one with an alkali: TCNQ stoichiometry of 1:1 and the other 2:1. STM images show the molecular organisation is the same for Cs and K, although only the K2TCNQ phase is commensurate with the substrate. A previously-published detailed structure determination of the K2TCNQ phase, complemented by density function theory calculations that identify bonding strengths, showed that the binding within the layer is much stronger than that of the layer to the substrate. Insensitivity to commensuration is thus to be expected. The situation for KTCNQ and CsTCNQ is less clear; these ordered incommensurate overlayers clearly have strong intralayer bonding, but the relative strength of the average overlayer-substrate bonding is unknown. NIXSW data show that the alkalis in these phases occupy adsorption sites far more distant from the substrate than the TCNQ molecules when compared to the near coplanar alkali-TCNQ geometry of K2TCNQ and Cs2TCNQ. Ultraviolet photoelectron spectra show increasing bonding shifts of TCNQ orbital states with alkali coverage.

KW - Alkali adsorption

KW - Charge transfer

KW - NIXSW

KW - STM

KW - Surface structure

KW - TCNQ

UR - http://www.scopus.com/inward/record.url?scp=85087857276&partnerID=8YFLogxK

U2 - 10.1016/j.susc.2020.121687

DO - 10.1016/j.susc.2020.121687

M3 - Article

AN - SCOPUS:85087857276

SN - 0039-6028

VL - 701

JO - Surface Science

JF - Surface Science

M1 - 121687

ER -

The structure of 2D charge transfer salts formed by TCNQ/alkali metal coadsorption on Ag(111)

Abstract

Bibliographical note

Keywords

ASJC Scopus subject areas

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