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Shake It Up – printing thin film organic devicesJoel D. Brock, Cornell University, DMR 0936384

Journal cover uses this work to highlighting new methodology and insight to ensure that drying solutions crystallizes in optimal ways to promote carrier transport in organic FETs.

Li, R., Khan, H. U., Payne, M. M., Smilgies, D.-M., Anthony, J. E. and Amassian, A. (2013), Heterogeneous Nucleation Promotes Carrier Transport in Solution-Processed Organic Field-Effect Transistors. Adv. Funct. Mater., 23: 291–297. doi: 10.1002/adfm.201201264

Intellectual Merit: There is great interest in being able to “print” electronics using liquids. Unfortunately, it is often difficult to use traditional surface science tools to analyze fast-drying liquid processes, with the consequence that it has been difficult to understand and improve methods to “print” electronics. Aram Amassian at King Abdullah University of Science and Technology (KAUST) and his coworkers from University of Kentucky and CHESS, have now shown that careful measurement of solution concentration and crystallization throughout the drying of the solution allows one to control the way in which the solution to solid phase transformation takes place. This was done by combining quartz crystal monitoring with dissipation (QCM-D) with grazing incidence wide-angle x-ray scattering (GIWAXS) at CHESS coupled in an environmental chamber to provide a unique quantitative insight into the time-evolution of the concentration of the solution, the onset of nucleation, and the mode of growth of the organic semiconductor under varied drying conditions.

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In-situ measurements performed during drop-casting from solution in a controlled environment. The gas flow through the closed vapor chamber controls the drying speed.

Li, R., Khan, H. U., Payne, M. M., Smilgies, D.-M., Anthony, J. E. and Amassian, A. (2013), Heterogeneous Nucleation Promotes Carrier Transport in Solution-Processed Organic Field-Effect Transistors. Adv. Funct. Mater., 23: 291–297. doi: 10.1002/adfm.201201264

Broader Impacts: The production of thin films underlies much of modern technology, from flexible flat screen monitors to future applications of “plastic electronics” in cases such as luminaires, smart tags, and solar energy conversion. While the common process of vacuum deposition of thin film materials onto substrates is well understood, much less is known about how a molecular thin film forms from a liquid solution. This is important because liquid solution methods will enable fast, inexpensive printing of electronics, solar cells and batteries. High performance devices require that scientists control the microstructure and morphology of solution-cast thin films, which develop via nucleationand growth processes, to exhibit a high degree ofcrystallinity, a high purity of lamellar texturing, a low density of grain/domain boundaries, low crystallographic misorientation at boundaries, and high surface coverage of the substrate. These characteristics can be quantified via in-situ x-ray techniques coupled to sophisticated specimen chambers.

Shake It Up – printing thin film organic devicesJoel D. Brock, Cornell University, DMR 0936384

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Student Award for Nanocrystal Designer SolidsJoel D. Brock, Cornell University, DMR 0936384

Artist’s view of a BCC superlattice of cuboctahedral lead sulfite nanocrystals displaying orientational order (ligands not shown for clarity). As the solvent in the thin film of the suspension evaporated, interfacial forces went into action. Van der Waals interactions at the interface between the substrate and the liquid gave rise to a beautiful square layer; this arrangement maximizes the interfacial contact with the substrate and neighboring nanocubes.

Kaifu Bian, Joshua J. Choi, Ananth Kaushik, Paulette Clancy, Detlef-M. Smilgies, and Tobias Hanrath; "Shape-anisotropy Driven Symmetry Transformations in Nanocrystal Superlattice Polymorphs", ACS Nano 5 2815–2823 (2011)

Joshua J. Choi, Kaifu Bian, William J. Baumgardner, Detlef-M. Smilgies, and Tobias Hanrath; "Interface-Induced Nucleation, Orientational Alignment and Symmetry Transformations in Nanocube Superlattices", Nano Lett. 12, 4791–4798 (2012)

Intellectual Merits: Despite intense research efforts by research groups worldwide, the potential of self-assembled nanocrystal superlattices (NCSLs) has not been realized due to an incomplete understanding of the fundamental molecular interactions governing the self-assembly process. The Hanrath group has worked with CHESS to develop in-situ techniques for isolating and tuning growth conditions to achieve a high degree of structural control over fcc, bcc, and intermediate bct symmetries. Cornell students Josh Choi and Kaifu Bian investigated the complex growth of simple PbS nanocubes in-situ with a combination of grazing incidence small- and wide-angle x-ray scattering. Small-angle scattering revealed the superlattice symmetry and orientation, wide-angle scattering the orientation of the nanocubes within the superlattices. Both techniques showed unambiguously the co-existence of both interface-induced nanocube orientations.

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Hooey awardee, Kaifu Bian (right) and his advisor Tobias Hanrath (left), both from the Cornell Department of Chemical and Biochemical Engineering

Kaifu Bian, Joshua J. Choi, Ananth Kaushik, Paulette Clancy, Detlef-M. Smilgies, and Tobias Hanrath; "Shape-anisotropy Driven Symmetry Transformations in Nanocrystal Superlattice Polymorphs", ACS Nano 5 2815–2823 (2011)

Broader Impacts: Cornell chemical engineering student Kaifu Bian was recently awarded the 2012 Austin Hooey Award for Outstanding Thesis Research. The Hooey Graduate Research Excellence Recognition Award is the highest award given to a graduate student by Cornell’s School of Chemical and Biomolecular Engineering. This award recognizes excellence in graduate research and service to the research group, department and community. Kaifu’s research focused on fundamental processing-structure-property relationships of nanocrystal assemblies as designer solids. Kaifu’s work in the group of Tobias Hanrath provides important new insights into the fundamental forces governing: (i) the self-assembly of nanocrystal superlattice and (ii) the stability and collective properties of the formed superstructures. These advances were enabled by access to world-class X-ray scattering facilities at CHESS.

Student Award for Nanocrystal Designer SolidsJoel D. Brock, Cornell University, DMR 0936384

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Women in physics network, mentor at conferenceJoel Brock, Cornell University, DMR 0936384

Cara Esposito, of Saint Joseph's University, presents a scientific poster to students at the Conference for Undergraduate Women in Physics.

Broader Impacts: A Cornell conference for women in physics and other physical sciences drew close to 200 participants, Jan. 18-20, 2013. Professor of physics Ritchie Patterson gave brief opening remarks to kick off the three-day conference. Patterson, who is also director of the Cornell Laboratory for Accelerator-Based Sciences and Education (CLASSE), was the principal investigator on the joint National Science Foundation and Department of Energy proposal that provided the funding for the event. Organized by Cornell students and Lora Hine, director of education for CLASSE, the Northeast Conference for Undergraduate Women in Physics was one of six events happening simultaneously throughout the U.S. About 140 female undergraduates and 40 invited guests, including speakers, panelists and faculty members, attended the Cornell event. The conference offered many activities, including the opportunity for students to give talks or present posters to practice communicating their scientific work to general audiences. At each event, Cornell faculty and staff volunteers provided feedback and advice.