x-ray reflectivity: structural characterisation of thin films for organic electronics

Transcription

1 x-ray reflectivity: structural characterisation of thin films for organic electronics Roland Resel, Oliver Werzer, Institute of Solid State Physics, Graz University of Technology 1

2 DHS900 content x-ray reflectivity - introduction polymer thin films - PS, P3HT, F8T2 molecular monolayers - pentacene self assembled monolayers - SAMs conclusion BRUKER D8 Discover 2

3 x-ray reflectivity refraction of x-rays at interfaces α i n < 1 r e classical electron radius ρ e electron density in the solid μ x linear absorption coefficient n 1 i typical values: δ ~ β ~ r e e 4 x critical angle of total external reflection: Θ C..= (2δ) = 0.1 (organics) 0.4 (gold) J. Als-Nielsen, et al., Elements of Modern X-ray Physics, Wiley & Sons

4 intensity Institute of Solid State Physics x-ray reflectivity optical reflection of x-rays on surfaces and interfaces interference between the surface reflected and the interface reflected beams most accurate method of layer thickness determination (1nm 700 nm) only possible for homogenous thick layers layer thickness large layer thickness small n = 1 n ~ 1 α i α f α f medium1 n ~ 1 medium2 fitting parameters: film thickness surface roughness interface roughness electron density α i H. Kissig, Ann. Physik (1931) α i F. Schreiber, X-ray Scattering on Thin Films and Surfaces 4

5 polymer thin films spin coated films from different concentrations effect of annealing O. Werzer, et al., Thin Solid Films,

6 polymer thin films film preparation by spin coating rotation speed: 1000 rpm / 9 sec rpm / 30 sec. O. Werzer, PhD thesis 6

7 pentacene sub-monolayer physical vapour deposition on SiOx nom. t... nominal thickness cov afm coverage 2µm 7

8 sub-monolayer - x-ray reflectivity variable d=15.4å variable fixed O. Werzer, et al., Eur. J. Phys., (2009) 8

9 self assembled monolayers chloro-quinquethienyl-undecyl-dimethylsilane prepared on SiOx prepared in solution space concept from liquid crystals monofunctional anchoring group prevents uncontrolled polymerisation E. C. P. Smith, et al., Nature (2008) 9

10 film preparation: substrate: plasma etching, surface activation by HCl, rinse by water SAM preparation : days in toluene solution, rinse with dry toluene 0.5 days in solution 1 day 2 days 10

11 x- ray reflectivity fitting by a double layer model before / after heat 120 C E. C. P. Smith, et al., Nature (2008) 11

12 grazing incidence x-ray diffraction 2-dimensional crystallography angle of incidence: α i ~ Θ C (critical angle) Yoneda peak at k(α f = Θ C )!! I. K. Robinson, et al., Rep. Prog. Phys. 55 (1992)

13 grazing incidence x-ray diffraction appearance of Bragg rods half a day in solution E. C. P. Smith, et al., Nature (2008) 13

14 structural models 2-dimensional crystal herringbone packing of thiophene units 14

15 conclusion x-ray reflectivity for organic thin film characterisation film thickness surface roughness interface roughness total electron density control film quality also multilayer structures interface characterisation (e.g. gold penetration into organics) in combination with ellipsometry: determination of optical refractive indices 15

16 Acknowledgements B. Stadlober, A. Haase, NMP Weiz E.C.P. Smith, H. Wondergem, D. de Leeuw, Philips Eindhoven F. Zontone, O. Konovalov, ID10B, ESRF, Grenoble D. Smilgies G2-line, CHESS, Cornell University, Ithaca, NY 16