Self-Patterning Tetrathiafulvalene Crystalline Films

Tetrathiafulvalene (TTF) crystals grown from the melt are organized as spherulites in which helicoidal fibrils growing radially from the nucleation center twist in concert with one another. Alternating bright and dark concentric bands are apparent when films are viewed between crossed polarizers, indicating an alternating pattern of crystallographic faces exposed at the film surface. Band-dependent reorganization of the TTF crystals was observed during exposure to methanol vapor. Crystalline growth appears on bright bands at the expense of the dark bands. After a 24 h period of exposure to methanol vapor, the original spherulites were completely restructured, and the films comprise isolated, concentric circles of crystallites whose orientations are determined by the initial TTF crystal fibril orientation. While the surface of these outgrowths appears faceted and smooth, cross-sectional SEM images revealed a semiporous inner structure, suggesting solvent-vapor-induced recrystallization. Collectively, these results show that crystal twisting can be used to rhythmically redistribute material. Crystal twisting is a common and often controllable phenomenon independent of molecular or crystal structure and therefore offers a generalizable path to spontaneous pattern formation in a wide range of materials.

*stephlee@nyu.edu            Figure S13: AFM height profiles extracted from samples solvent vapor annealed for 0, 2, 8, 16, and 24 hours.A razor was used to scrape the TTF film away prior to scanning so the glass substrate could be used as a reference height (Figure S14), except in the case of the 24-hour sample, where glass was exposed between bands (Figure S15).  Figure S16: Scheme for growing "single crystal" from a twisted fibril.First, a banded spherulite film was made, then partially remelted by holding the sample near the melting point of TTF.Once the banded spherulite was partially remelted, the film was held at 100°C, causing a "single crystal" to nucleate from remaining banded spherulite edge.Once the single crystal formed, the banded portions of the film were scraped away, leaving a single crystal which was analyzed via grazing incidence x ray diffraction (POM inset).
Figure S17: Indexed grazing incidence x ray diffraction pattern of β TTF "single crystal" described in Figure S16.
Figure S19: Angles between faces were measured using the facet measurement function of Gwyddion AFM analysis software.By quantifying the vector normal to each facet of a single crystallite, the exterior angles between all facets were derived from the vector dot product equation.
Using Microsoft Excel, the angles between facets were tabulated and then quantitatively compared to all possible combinations of faces expected in the Mercury BFDH calculator (10 faces, 7 selected, 604,800 possible combinations).By calculating the percent difference between experimental AFM data and the theoretical exterior angle between planes from the single crystal structure, using the Excel solver, a difference minimized set of faces was found.

Figure
Figure S1: a) POM of TTF banded spherulite melt processed as a 9:1 mixture by weight with abietic acid.b) Circular retardance image of the same spherulite showing two zones of right and left handed heilicoidal crystal fibrils.

Figure S2 :
Figure S2: OMs of banded TTF films solvent vapor annealed with; a, b) ethyl acetate, c, d) acetone, and e, f) tetrahydrofuran at two magnifications.

Figure S3 :
Figure S3: Crystal structure of β-TTF (CCDC code: BDTOLE02) and powder diffraction patterns of films annealed from 0 to 64 hours.The black spectrum is the simulated β-TTF diffraction pattern calculated in Mercury using the aforementioned structure.

Figure
Figure S4: a) SEM image of banded TTF film melt processed and then held at 40 °C in a sealed vial for 4 hours.Dashed white lines roughly define the border between edge-on and face-on bands.b) expansion of an edge-on band from the SEM image in a).

Figure
Figure S5: a) AFM heightmap of banded TTF spherulite covering an area of four bands.b) A height profile of the same color line present in a).

Figure
Figure S6: SEM of TTF sample methanol solvent vapor annealed for 64 h.

Figure
Figure S7: a) GIWAX diffraction pattern of as processed TTF banded spherulite film.b) GIWAXS diffraction pattern of TTf banded spherulite mehtnaol solvent vapor anneaed for 24 hours.c) Azimuthally integrated GIWAXS difractino patterns of a) and b) compared to Mercury simulated patterns of β-TTF and abietic acid (CCDC refcode: YAWMOY10).

Figure
Figure S8: a) Top down SEM of area images in Fig 2f labelled with numbered arrows indicating ridges and valleys.The orange, oddnumbered arrows indicate the four ridges present in the cross-section, and the blue, even numbered arrows indicate valleys.b) The cross section from Fig 2f with crystallite layer outlined in red, and colored labels corresponding to the arrows in part a).

Figure
Figure S9: a) Top down SEM showing different crystallite tilts between bands of a TTF film where liquid methanol wet across the film surface for 4 seconds before rapidly air drying.b-c) Cross sectional SEM of the same film.

Figure S10 :
Figure S10: SEM cross-section of TTF banded spherulite film where spherulitic growth is parallel to the view, perpendicular to the crosssection cut.

Figure S11 :
Figure S11: SEM cross-section of a TTF banded spherulite film solvent vapor annealed for 8 hours.

Figure S12 :
FigureS12: SEM cross-section of a TTF banded spherulite film solvent vapor annealed for 2 hours.This image shows the area between bands where recrystallization occurs.The film interior appears to be suspended above the substrate due to crystallite growth downward from the bottom surface.The dashed white line indicates the approximate edge between a ridge and a valley.

Figure S14 :
Figure S14: Optical micrograph taken in AFM software of a TTF film solvent vapor annealed for 16 hours.Portions of the film were removed in lines with the edge of a razor blade.The triangle with a red laser spot is the AFM cantilever.

Figure S15 :
Figure S15: AFM height map of a TTF film solvent vapor annealed for 24 hours.