CHESS DMR Pi stacking improves organic semiconductors Joel Brock, Cornell University, DMR Inducing different in- and out-of-plane molecular orientations in contorted hexabenzocoronene (HBC) thin-films via hexane vapor, thermal annealing, and physical contact. A. M. Hispanski, S. S. Lee, H. Wang, A. R. Woll, C. Nuckolls and Y.-L. Loo, "Post Deposition Processing Methods To Induce Preferential Orientation in Contorted Hexabenzocoronene Thin Films," ACS Nano, vol. 7, pp , Intellectual Merit: A group of researchers from Princeton University, led by Professor Yueh-Lin Loo, developed post-deposition processing techniques that induce crystallization in thin-films of the organic semiconductor hexabenzocoronene (HBC). Using Grazing Incidence X-ray Diffraction at the G1 beam-line of CHESS, Loo’s group measured the molecular orientation distribution of post-deposition processed thin-films of HBC. In the PDMS case, post-deposition processing produces a progressive increase in edge-on molecular orientation, which corresponds to a greater degree of in-plane, π-stacking. The enhanced alignment increases the carrier mobility by two orders of magnitude in TFT devices. This research clearly demonstrates their ability to tune the molecular orientation, which is critical to optimize the electronic properties of organic thin-films.

CHESS DMR a) PDMS contact processing and b) hexane vapor annealing of hexabenzocoronene thin films as seen by x- ray scattering. Alignment of the conjugated π bonds results in higher charge mobility. A. M. Hispanski, S. S. Lee, H. Wang, A. R. Woll, C. Nuckolls and Y.-L. Loo, "Post Deposition Processing Methods To Induce Preferential Orientation in Contorted Hexabenzocoronene Thin Films," ACS Nano, vol. 7, pp , Broader Impacts: Flexible electronic devices, such as plastic displays, wearable radio frequency identification (RFID) tags, and roll up solar panels, based on π- bonded organic semiconductors are highly desirable due to their light weight and high level of durability. These devices benefit greatly from relatively low manufacturing costs and ease of scaling. However, poor charge mobility, and thus, poor device performance can occur unless the molecules of the organic thin film are properly oriented with respect to one another. In organic semiconductors, charge is transported preferentially along the direction of π-stacking of the aromatic rings of the constituent molecules. This research demonstrated the ability to tune the molecular orientation of organic thin-films through a suite of post-deposition treatments, resulting in organic semiconductor thin-films with enhanced properties for organic electronics applications. Pi stacking improves organic semiconductors Joel Brock, Cornell University, DMR

CHESS DMR Organic Transistors: A Little Vapor Goes a Long Way Joel Brock, Cornell University, DMR Hadayat Ullah Khan, Ruipeng Li, Yi Ren, Long Chen, Marcia M. Payne, Unnat S. Bhansali, Detlef-M. Smilgies, John E. Anthony and Aram Amassian, "Solvent Vapor Annealing in the Molecular Regime Drastically Improves Carrier Transport in Small- Molecule Thin-Film Transistors", ACS Appl. Mater. Interfaces 5, 2325−2330 (2013). Intellectual Merit: KAUST and CHESS scientists tuned charge carrier transport device performance by controlling solvent vapor annealing while depositing organic electronic devices onto a quartz substrate. Analysis indicates that processing occurs in two stages. Initially, the crystalline structure, as monitored by in-situ X-ray scattering measurement on CHESS D-line, improves with exposure to solvent. More importantly, the carrier mobility in transistors increases by up to two orders of magnitude. This suggests that a very small dose of solvent vapor in the molecular regime is capable of dramatically transforming the morphology of the film. With continued exposure to solvent, a second stage follows that is associated with significant coarsening in the lateral size of grains. The large isolated crystallites suggest both intra- and inter-grain mass transport occurs during processing. This second stage is associated with dewetting of the film from the substrate, producing low substrate coverage and decay of carrier mobility. These results demonstrate the need for precise control during solvent vapor annealing, in order to optimize the performance of organic thin film transistors. TIPS-pentacene molecules ordering on a flexible substrate under the influence of toluene vapor.

CHESS DMR Hadayat Ullah Khan, Ruipeng Li, Yi Ren, Long Chen, Marcia M. Payne, Unnat S. Bhansali, Detlef-M. Smilgies, John E. Anthony and Aram Amassian, "Solvent Vapor Annealing in the Molecular Regime Drastically Improves Carrier Transport in Small-Molecule Thin-Film Transistors", ACS Appl. Mater. Interfaces 5, 2325−2330 (2013). Broader Impacts: For the industrial production of flexible electronics for the consumer market, post-deposition annealing is an important processing step. The purpose of the annealing step is to optimize performance in printed organic circuits. The KAUST and CHESS team developed a new way to investigate and control the solvent vapor annealing of solution-cast organic semiconductor thin films. Using time-resolved grazing incidence wide angle X-ray scattering (GIWAXS) and complementary static atomic force microscopy (AFM), they demonstrate that solvent vapor annealing in the molecular regime can cause significant performance improvements in organic thin film transistors (OTFTs), whereas allowing the solvent to percolate and form a liquid phase results in catastrophic reorganization and dewetting of the film, making the process counter- productive. Using these lessons they devised processing conditions which prevent percolation of the adsorbed solvent vapor molecules for extended periods, thus extending the benefits of solvent vapor annealing and improving carrier mobility by nearly two orders of magnitude. Overview of the KAUST results: A bottom gate transistor (top left) was kept in a closed chamber (bottom left) with a quartz- crystal monitor. A similar chamber could also be used for the x-ray scattering experiments. The right panel shows the hole mobility as a function of time, as the organic transistor is exposed to toluene vapor at high or low vapor pressure. Organic Transistors: A Little Vapor Goes a Long Way Joel Brock, Cornell University, DMR

CHESS DMR CHESS User Gaurav Giri receives the SSRL Melvin P. Klein Scientific Development Award Joel Brock, Cornell University, DMR Gino preparing another in-situ real-time coating experiment at CHESS D1 station. Gaurav Giri, known to his friends as Gino, received the 2013 Melvin P. Klein Award for his work on solution shearing of organic semiconducting molecules. The Klein Award recognizes outstanding research accomplishments by students and postdocs at SSRL and promotes dissemination of research results. Gino is currently a Stanford graduate student working with Zhenan Bao in the Department of Chemical Engineering. His award cited ambitious work started two years ago with KAUST collaborator Aram Amassian and CHESS Staff Scientist Detlef Smilgies to watch organic thin films crystallize in-situ and in real-time during the solution shearing process. The idea grew out of Gino’s prior work at SSRL to analyze shear-coated molecular films after deposition using beamline 11-3, which led to the discovery of a strained TIPS-pentacene polymorph with very high mobility. This prior work recently resulted in a letter to Nature [1]. Gino worked with Smilgies to develop a miniature coater that fits on an x-ray sample goniometer [2], but can replicate the coating conditions that he had explored earlier on his large- scale lab system at Stanford. We congratulate Gino on a well-deserved Klein-Award! [1] G. Giri et al, Nature 480, (2011). [2] D.-M. Smilgies et al., Physica Status Solidi - Rapid Res. Lett. 7, (2013).

CHESS DMR Revamp Camp connects kids with science skills and software engineering Joel Brock, Cornell University, DMR CHESS electrical engineer Eric Edwards shows Revamp Camp participants how many computers are needed to carry out x-ray experiments at the CHESS A2 end station.. The autonomous walking/barking dog was just one of eight Arduino-based projects designed and built by students participating in the week-long Revamp Camp co-sponsored by Xraise, the outreach program at CHESS and Ithaca Generator (IG), the Makerspace in downtown Ithaca. Education Coordinators envisioned the summer camp where youth with a passion for science, computer programming and electronics engineering could design and innovate. Xraise and IG outreach staff planned the week’s activities around the ultimate goal of having each student chose their own physical computing project using an Arduino Uno. Reasonably priced and open source, these programmable microcontroller development boards provide an ideal way to prototype circuits with a wide variety of inputs and outputs - distance sensors, flex and tilt sensors, push buttons, moisture and temperature sensors, led's, motors, and more. This accessible prototyping platform has limitless applications for inventive youth and professional scientists alike.