TY  - JOUR
AU  - Haags, Anja
AU  - Rochford, Luke A.
AU  - Felter, Janina
AU  - Blowey, Phil J.
AU  - Duncan, David Andrew
AU  - Woodruff, D Phil
AU  - Kumpf, Christian
TI  - Growth and Evolution of TCNQ and K Coadsorption Phases on Ag(111)
JO  - New journal of physics
VL  - 22
SN  - 1367-2630
CY  - [London]
PB  - IOP
M1  - FZJ-2020-01585
SP  - 063028
PY  - 2020
AB  - 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.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000545698900001
DO  - DOI:10.1088/1367-2630/ab825f
UR  - https://juser.fz-juelich.de/record/874669
ER  -