Phase Transition of Graphene-Templated Vertical Zinc Phthalocyanine Nanopillars.

Author(s) Arellano, L.Gonzalez; Burnett, E.K.; Uzun, S.Demirci; Zakashansky, J.A.; Iii, V.K.Champagn; George, M.H.; Mannsfeld, S.C.B.; Briseno, A.L.
Journal J Am Chem Soc
Date Published 2018 Jun 07

We report on the graphene-assisted growth, crystallization, and phase transition of zinc phthalocyanine (ZnPc) vertically-oriented single crystal nanopillars. Post-crystallization thermal annealing of the nanostructures results in a molecular packing change while maintaining the vertical orientation of the single crystals orthogonal to the underlying substrate. Grazing incidence X-ray diffraction and high resolution TEM studies characterized this phase transition from a metastable crystal phase to the more stable β-phase commonly observed in bulk crystals. These vertical arrays of crystalline nanopillars exhibit a high-surface-to-volume ratio, which is advantageous for applications such as gas sensors. We fabricated chemiresistor sensors with ZnPc nanopillars grown on graphene and demonstrated its selectivity for ammonia vapors, and improvement in sensitivity in the β-phase crystal packing pillars due to their molecular orientation increasing the exposure of the Zn2+ ion to the ammonia analyte. This work highlights the first morphology-retentive phase transition in organic single crystal nanopillars through simple post-processing thermal annealing. This study opens up the possibility of molecular packing control without large variations in morphology, a necessity for high per-formance devices and establishing structure-property relations.

DOI 10.1021/jacs.8b03078
ISSN 1520-5126
Citation J Am Chem Soc. 2018.

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