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Dielectric Tensor of Microtextured Squaraine Thin Films Obtained by Imaging Mueller Matrix Ellipsometry


Manuela Schiek, S. Funke, M. Duwe, P. H. Thiesen, K. Hingerl, F. Balzer.

di-Iso-Butyl-anilino-Squaraine SQIB

transition dipole moment (TDM) along long molecular axis


Frenkel excitons incl. Davydov splitting ≥ 2 inequivalent molecules per unit cell


orthorhombic polymorph Pbcn CCDC 1567104 (4 inequivalent molecules in primitive unit cell) spincasting + thermal annealing @ 180°C formation of rotational domains with (110) orientation


Davydov splitting: 4 inequivalent molecules = 4 Davydov bands (2x UDC & 2x LDC)



linear combination of TDMs within one stack + interstack combination

SUM => LDC1 along b-axis & LDC2 along a-axis
DIFFERENCE => UDC1 along c-axis & UDC2 = 0 (dark state)


diagonal tensor for orthorhombic crystals: optical indicatrix is congruent with crystallographic axes


oscillator model to ensure Kramers-Kronig consistency negative real permittivity in vicinity of the strong resonances explains quasi-metallic shine of SQIB platelets



projected view onto (110) plane Davydov bands are polarized mutually perpendicular projected Davydov splitting ≈ 250 meV


spatially resolved polarized absorbance measured (circles) is well reproduced by calculated (solid lines) spectra transfer matrix optical calculations using εa and projection of εB and εy onto (110) plane

UDC along c-axis, effective LDC along projected a-b-axes



NanoFilm_EP4 imaging Mueller matrix ellipsometry system, Accurion GmbH, Göttingen


single compensator (PCSA-configuration): 11 normalized MM elements knife-edge illumination to suppress incoherent backside reflections collimated light beam spot diameter 1 mm lateral resolution 2 µm (λ = 400 nm) through microscopy objective, no focusing of incident beam selection of multiple ROIs reflection & transmission scans Theta Stage (TS): azimuthal Φ-rotation

app25 fig06

Funding & Acknowledgement

Linz Institute of Technology (LIT-2019-7-INC-313 SEAMBIOF) PRO RETINA Foundation (especially Franz Badura)
We are indebted to Dr. Matthias Schulz and Prof. Dr. Arne Lützen, University of Bonn, for providing SQIB powder.