Crystal morphology and growth in annealed rubrene thin films

Transcription

1 Supporting Information Crystal morphology and growth in annealed rubrene thin films Thomas R. Fielitz and Russell J. Holmes In the majority of this paper, the polymorph composition is inferred from the crystal growth mode and coloration. The orthorhombic and triclinic polymorphs differ significantly in crystal coloration and shape as shown in Figure d, which makes this analysis somewhat simpler. These crystal shape and coloration observations are drawn from phase pure samples on which x-ray diffraction had confirmed polymorph type. Scattering Intensity (a.u.) (00) (00) 50 o C Triclinic 70 o C Orthorhombic (00) (00) (0 ) (0 ) () ( o ) c b a c b a Substrate Figure S. XRD spectra of annealed films containing orthorhombic and triclinic rubrene, with unit cell orientations of the orthorhombic and triclinic unit cell inferred from D XRD with samples grown, annealed, and measured on silicon.

2 Orthorhombic Surface Area (%) nm 64 nm 39 nm Annealing Temperature ( o C) Figure S. Polymorphic composition of completely annealed rubrene films as a function of annealing temperature. Each data point represents multiple films on ITO, with the error bars describing the standard deviation between films. As the film thickness changes, the polymorphic composition also shifts. With increasing film thickness, the films exhibit a slightly higher onset temperature of orthorhombic crystallization and lower fraction of orthorhombic area, which supports a bulk kinetic mechanism being responsible for this transformation. These films also exhibit cross-nucleation, depicted below in Figure S3. This recently characterized phenomenon has been previously observed in systems growing from the melt or supercooled liquid but generally exhibits nucleation of a faster-growing polymorph upon a slower-growing polymorph, regardless of thermodynamic stability. 3,4 This is satisfied in annealed rubrene films, as the triclinic polymorph slows dramatically as the crystals grow, eventually slowing to a rate lower than that of the orthorhombic polymorph. This allows for competition at the growth front, with eventual nucleation and growth of the faster (orthorhombic) polymorph.

3 Orthorhombic Triclinic (d) (e) (f) Figure S3. Images showing the process of rubrene cross-nucleation and grain ripening on ITO at 70 C as a function of time after annealing begins. Amorphous film at t = 6. s; triclinic and orthorhombic nuclei at t = 0. s; cross-nucleation of orthorhombic grains on triclinic spherulites at t =.5 s, highlighted in white ovals; (d) continuing cross-nucleation and growth of orthorhombic rubrene at t = 6.9 s; (e) complete truncation of triclinic growth at t = 3.5 s; (f) grain ripening (t = 8.6 s), showing grain boundaries between different orthorhombic regions and cross-nucleation sites, as extracted from these boundaries, depicted by white dots. Images captured in situ with episcopic unpolarized light at 500x magnification. 3

4 Figure S4. Determination of crystallographic axes and correspondence to grain location at high temperature. and AFM images of rubrene on ITO, annealed at 70 C for 80 seconds and 80 C for 600 seconds, scale bars 3 μm. An optical micrograph is presented in to give broader context, with the nucleation sites labeled with a red X, grain boundary with a dashed blue line, and radii drawn to the AFM image location depicted in black. Cantilever width is approximately 40 μm. Table S. Comparison of calculated and measured facet angles corresponding to those measured in Figure S4 and. Plane Intersection Calculated Measured (Interior Angle) 70 C 80 C (00) {0} ± 5 6. ± 0.9 (0) ( 0) ± 5 7. ± 0.8 4

5 4 Figure S5. Contrast between films on ITO annealed past complete crystallization at 70 C, 80 seconds and 0 C, 300 seconds. is an atomic force micrograph, scale bar 3 μm; is an optical micrograph, scale bar 50 μm. At low temperature, the holes which appear in the ripening crystal are faceted and aligned across the crystal, whereas the high temperature crystals show a more centrosymmetric deterioration. REFERENCES () Jurchescu, O. D.; Meetsma, A.; Palstra, T. T. M. Low-Temperature Structure of Rubrene Single Crystals Grown by Vapor Transport. Acta Crystallogr. B. 006, 6 (Pt ), () Akopyan, Z. A.; Avoyan, R. L.; Struchkov, Y. T. Crystallographic Data on Certain Sterically Strained Naphthacene Derivatives. Zhurnal Strukt. Khimif 96, 3 (5), (3) Chen, S.; Xi, H.; Yu, L. Cross-Nucleation between ROY Polymorphs. J. Am. Chem. Soc. 005, 7 (3), (4) Yu, L. Nucleation of One Polymorph by Another. J. Am. Chem. Soc. 003, 5,