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

Institute of Solid State Physicsx-ray reflectivity: structural characterisationof thin films for organic electronicsRoland Resel, Oliver Werzer,Institute of Solid State Physics, Graz University of TechnologyProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20091

Institute of Solid State PhysicsDHS900contentx-ray reflectivity - introductionpolymer thin films - PS, P3HT, F8T2molecular monolayers - pentaceneself assembled monolayers - SAMsconclusionBRUKER D8 DiscoverProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20092

Institute of Solid State Physicsx-ray reflectivity refraction of x-rays at interfacesα in < 1r eclassical electron radiusρ e electron density in the solidμ xlinear absorption coefficientn 1 itypical values: δ ~ 10 -5 ...10 -6β ~ 10 -7 ...10 -822r e e4xcritical 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 2001Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20093

intensityInstitute of Solid State Physicsx-ray reflectivityoptical reflection of x-rays on surfaces and interfacesinterference between the surface reflected and the interface reflected beams most accurate method of layer thickness determination (1nm … 700 nm) only possible for homogenous thick layerslayer thicknesslargelayer thicknesssmalln = 1n ~ 1α iα fα fmedium1n ~ 1medium2fitting parameters:film thicknesssurface roughnessinterface roughnesselectron densityα iH. Kissig, Ann. Physik (1931)α iF. Schreiber, X-ray Scattering on Thin Films and SurfacesProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20094

Institute of Solid State Physicspolymer thin films spin coated films from different concentrations effect of annealingO. Werzer, et al., Thin Solid Films, 2007Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20095

Institute of Solid State Physicspolymer thin films film preparation by spin coatingrotation speed: 1000 rpm / 9 sec. + 1500rpm / 30 sec.O. Werzer, PhD thesisProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20096

Institute of Solid State Physicspentacene sub-monolayer physical vapour deposition on SiOxnom. t ... nominal thicknesscov afm… coverage2µmProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20097

Institute of Solid State Physicssub-monolayer - x-ray reflectivityvariabled=15.4ÅvariablefixedO. Werzer, et al., Eur. J. Phys. , (2009)Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20098

Institute of Solid State Physicsself assembled monolayerschloro-quinquethienyl-undecyl-dimethylsilane prepared on SiOx prepared in solution space concept from liquid crystals monofunctional anchoring groupprevents uncontrolled polymerisationE. C. P. Smith, et al., Nature (2008)Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 20099

Institute of Solid State Physicsfilm preparation:substrate: plasma etching, surface activation by HCl, rinse by waterSAM preparation : 0.5 … 2 days in toluene solution, rinse with dry toluene0.5 days in solution 1 day 2 daysProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200910

Institute of Solid State Physicsx- ray reflectivity fitting by a double layer model before / after heat treatment @ 120°CE. C. P. Smith, et al., Nature (2008)Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200911

Institute of Solid State Physicsgrazing incidence x-ray diffraction 2-dimensional crystallographyangle 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) 599Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200912

Institute of Solid State Physicsgrazing incidence x-ray diffraction appearance of Bragg rodshalf a day in solutionE. C. P. Smith, et al., Nature (2008)Professor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200913

Institute of Solid State Physicsstructural models 2-dimensional crystal herringbone packing of thiophene unitsProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200914

Institute of Solid State Physicsconclusionx-ray reflectivity for organic thin film characterisationfilm thicknesssurface roughnessinterface roughnesstotal electron density control film quality also multilayer structures interface characterisation (e.g. gold penetration into organics) in combination with ellipsometry:determination of optical refractive indicesProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200915

Institute of Solid State PhysicsAcknowledgementsB. Stadlober, A. Haase,NMP WeizE.C.P. Smith, H. Wondergem, D. de Leeuw,Philips EindhovenF. Zontone, O. Konovalov,ID10B, ESRF, GrenobleD. SmilgiesG2-line, CHESS, Cornell University, Ithaca, NYProfessor Roland Resel Horst Cerjak, 19.12.2005Bologna, 17 February 200916