Journal Article

FZJ-2020-01585

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Growth and Evolution of TCNQ and K Coadsorption Phases on Ag(111)

Haags, A.FZJ* ; Rochford, L. A. ; Felter, J. ; Blowey, P. J. ; Duncan, D. A. ; Woodruff, D. P. ; Kumpf, C. (Corresponding author)FZJ*

2020
IOP [London]

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Please use a persistent id in citations: http://hdl.handle.net/2128/27310  doi:10.1088/1367-2630/ab82  doi:10.1088/1367-2630/ab825f

Abstract: Alkali-doping is a very efficient way of tuning the electronic properties of active molecular layers in (opto-)electronic devices based on organic semiconductors. In this context, we report on the phase formation and evolution of charge transfer salts formed by 7,7,8,8-tetracyanoquinodimethane (TCNQ) in coadsorption with potassium on a Ag(111) surface. Based on an in-situ study using low energy electron microscopy and diffraction we identify the structural properties of four phases with different stoichiometries, and follow their growth and inter-phase transitions. We label these four phases α to δ, with increasing K content, the last two of which (γ and δ-phases) have not been previously reported. During TCNQ deposition on a K-precovered Ag(111) surface we find a superior stability of δ phase islands compared to the γ phase; continued TCNQ deposition leads to direct transition from the δ to the β-phase when the K:TCNQ ratio corresponding to this phase regime is reached, with no intermediate γ-phase formation. When, instead, K is deposited on a surface precovered with large islands of the low density commensurate (LDC) TCNQ phase that are surrounded by a TCNQ 2D-gas, we observe two different scenarios: On the one hand, in the 2D-gas phase regions, very small α-phase islands are formed (close to the resolution limit of the microscope, 10-15 nm), which transform to β-phase islands of similar size with increasing K deposition. On the other hand, the large (micrometer-sized) TCNQ islands transform directly to similarly large single-domain β-phase islands, the formation of the intermediate α-phase being suppressed. This frustration of the LDC-to-α transition can be lifted by performing the experiment at elevated temperature. In this sense, the morphology of the pure TCNQ submonolayer is conserved during phase transitions.

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Contributing Institute(s):

1. Funktionale Nanostrukturen an Oberflächen (PGI-3)

Research Program(s):

1. 899 - ohne Topic (POF3-899) (POF3-899)

Appears in the scientific report 2020

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Database coverage:
; ; ; ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; DOAJ Seal ; Ebsco Academic Search ; IF < 5 ; JCR ; Nationallizenz ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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