@article{king_melville_rice_kashani_tonnele_raboui_swaraj_grant_mcafee_bender_et al._2021, title={Silicon Phthalocyanines for n-Type Organic Thin-Film Transistors: Development of Structure-Property Relationships}, volume={3}, ISSN={["2637-6113"]}, DOI={10.1021/acsaelm.0c00871}, abstractNote={Silicon phthalocyanines (SiPcs) have shown great potential as n-type or ambipolar organic semiconductors in organic thin-film transistors (OTFTs) and organic photovoltaics. Although properly designed SiPcs rival current state-of-the-art n-type organic semiconducting materials, relatively few structure–property relationships have been established to determine the impact of axial substituents on OTFT performance, hindering the intelligent design of the next generation of SiPcs. To address this omission, we have developed structure–property relationships for vapor-deposited SiPcs with phenoxy axial substituents. In addition to thorough electrical characterization of bottom-gate top-contact OTFTs, we extensively investigated SiPc thin films using X-ray diffraction, atomic force microscopy (AFM), grazing-incidence wide-angle X-ray scattering (GIWAXS), and density functional theory (DFT) modeling. OTFT performance, including relative electron mobility (μe) of materials, was in general agreement with values obtained through DFT modeling including reorganization energy. Another significant trend observed from device performance was that increasing the electron-withdrawing character of the axial pendant groups led to a reduction in threshold voltage (VT) from 47.9 to 21.1 V. This was corroborated by DFT modeling, which predicted that VT decreases with the square of the dipole induced at the interface between the SiPc pendant and substrate. Discrepancies between modeling predictions and experimental results can be explained through analysis of thin-film morphology and orientation by AFM and GIWAXS. Our results demonstrate that a combination of DFT modeling to select prospective candidate materials, combined with appropriate processing conditions to deposit molecules with a favorable thin-film morphology in an "edge-on" orientation relative to the substrate, yields high-performance n-type SiPc-based OTFTs.}, number={1}, journal={ACS APPLIED ELECTRONIC MATERIALS}, author={King, Benjamin and Melville, Owen A. and Rice, Nicole A. and Kashani, Somayeh and Tonnele, Claire and Raboui, Hasan and Swaraj, Sufal and Grant, Trevor M. and McAfee, Terry and Bender, Timothy P. and et al.}, year={2021}, month={Jan}, pages={325–336} }
 @article{swaraj_ade_2013, title={Differences in NEXAFS of odd/even long chain n-alkane crystals}, volume={191}, ISSN={["1873-2526"]}, DOI={10.1016/j.elspec.2013.10.006}, abstractNote={We present the near edge X-ray absorption fine structure (NEXAFS) spectra of several long chain n-alkanes crystallites formed on Silicon nitride (Si3N4) windows. Dichroic signature was investigated with the CC backbone aligned perpendicular to the substrate. Significant changes in the dichroic signature of spectral intensities at energies below the ionization edge (287.5 and 288.1 eV) have been observed. While the dichroic ratio corresponding to the spectral feature at 287.5 eV remains relatively unaffected by the overall length of CC backbone, it is noticeably affected by the parity (odd or even) of the number of Carbon atoms in the n-alkane backbone. Data obtained provide evidence of the influence of interaction of molecular orbitals with periodic lattice structure.}, journal={JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA}, author={Swaraj, Sufal and Ade, Harald}, year={2013}, month={Dec}, pages={60–64} }
 @article{pack_bobo_muir_yang_swaraj_ade_cao_korach_kashiwagi_rafailovich_2012, title={Engineering biodegradable polymer blends containing flame retardant-coated starch/nanoparticles}, volume={53}, ISSN={["1873-2291"]}, DOI={10.1016/j.polymer.2012.08.007}, abstractNote={We have shown that the addition of resorcinol di(phenyl phosphate) (RDP)-coated starch can improve the compatibility to either Ecoflex or poly(lactic acid) (PLA). The increased compatibilization enhanced the tensile properties such as yield strength and impact toughness. In particular, we examined the effect of addition of RDP-coated starch on thermal responses of a blend of Ecoflex/PLA. We found that the combination of RDP-coated starches with nanoclays could render the blends self-extinguishing since they are formed as a shell-like chars on the exposure surface against heat, which can prevent the melt polymers against dripping. With an examination on the scanning transmission X-ray microscopy (STXM) images of the blends, the Ecoflex domains were well dispersed in the PLA matrix, while the domains became smaller when the RDP-coated starch was added. Moreover, we demonstrated that the introduction of either flat-like or tube-like clays could provide an increase of interfacial area on the RDP-coated starch surfaces, where each polymer chain preferentially segregates to either the starch or the clay surface. Thus, large complex in-situ grafts with polymers can be formed at the interfaces. Additionally, the complex in-situ grafts could influence flammability of the blends. We have shown that the addition of RDP-coated clays can decrease the mass loss rate of Ecoflex/Starch blends, while a lot of nanofiber are formed on the chars surface, which are entangled each other with the clay platelets. The mechanical properties of the chars structures were examined by nano-indentation, where a good elastic chars formation could keep the internal pressures built up with decomposed gases from melt polymers as well as ductility of the chars could play an important role on releasing the internal gases through small vents on its surface, steadily where a good elastic and ductile chars formation could require keeping the internal pressures built up with decomposed gases from melt polymers.}, number={21}, journal={POLYMER}, author={Pack, Seongchan and Bobo, Ezra and Muir, Neil and Yang, Kai and Swaraj, Sufal and Ade, Harald and Cao, Changhong and Korach, Chad S. and Kashiwagi, Takashi and Rafailovich, Miriam H.}, year={2012}, month={Sep}, pages={4787–4799} }
 @article{yan_wang_garcia_swaraj_gu_mcneill_schuettfort_sohn_kramer_bazan_et al._2011, title={Interfaces in organic devices studied with resonant soft x-ray reflectivity}, volume={110}, ISSN={["1089-7550"]}, DOI={10.1063/1.3661991}, abstractNote={Interfaces between donor and acceptor semiconducting polymers are critical to the performance of polymer light-emitting diodes and organic solar cells. Similarly, interfaces between a conjugated polymer and a dielectric play a critical role in organic thin-film transistors. Often, these interfaces are difficult to characterize with conventional methods. Resonant soft x-ray reflectivity (R-SoXR) is a unique and relatively simple method to investigate such interfaces. R-SoXR capabilities are exemplified by presenting or discussing results from systems spanning all three device categories. We also demonstrate that the interfacial widths between active layers can be controlled by annealing at elevated temperature, pre-annealing of the bottom layer, or casting from different solvent mixtures. The extension of R-SoXR to the fluorine K absorption edge near 698 eV is also demonstrated.}, number={10}, journal={JOURNAL OF APPLIED PHYSICS}, author={Yan, Hongping and Wang, Cheng and Garcia, Andres and Swaraj, Sufal and Gu, Ziran and McNeill, Christopher R. and Schuettfort, Torben and Sohn, Karen E. and Kramer, Edward J. and Bazan, Guillermo C. and et al.}, year={2011}, month={Nov} }
 @article{yan_swaraj_wang_hwang_greenham_groves_ade_mcneill_2010, title={Influence of Annealing and Interfacial Roughness on the Performance of Bilayer Donor/Acceptor Polymer Photovoltaic Devices}, volume={20}, ISSN={["1616-3028"]}, DOI={10.1002/adfm.201001292}, abstractNote={Abstract Through controlled annealing of planar heterojunction (bilayer) devices based on the polyfluorene copolymers poly(9,9‐dioctylfluorene‐co‐bis(N,N′‐(4,butylphenyl))bis(N,N′‐phenyl‐1,4‐phenylene)diamine) (PFB) and poly(9,9‐dioctylfluorene‐co‐benzothiadiazole) (F8BT) we study the influence of interface roughness on the generation and separation of electron–hole pairs at the donor/acceptor interface. Interface structure is independently characterized by resonant soft X‐ray reflectivity with the interfacial width of the PFB/F8BT heterojunction observed to systematically increase with annealing temperature from 1.6 nm for unannealed films to 16 nm with annealing at 200 °C for ten minutes. Photoluminescence quenching measurements confirm the increase in interface area by the three‐fold increase in the number of excitons dissociated. Under short‐circuit conditions, however, unannealed devices with the sharpest interface are found to give the best device performance, despite the increase in interfacial area (and hence the number of excitons dissociated) in annealed devices. The decrease in device efficiency with annealing is attributed to decreased interfacial charge separation efficiency, partly due to a decrease in the bulk mobility of the constituent materials upon annealing but also (and significantly) due to the increased interface roughness. We present results of Monte Carlo simulations that demonstrate that increased interface roughness leads to lower charge separation efficiency, and are able to reproduce the experimental current‐voltage curves taking both increased interfacial roughness and decreased carrier mobility into account. Our results show that organic photovoltaic performance can be sensitive to interfacial order, and heterojunction sharpness should be considered a requirement for high performance devices.}, number={24}, journal={ADVANCED FUNCTIONAL MATERIALS}, author={Yan, Hongping and Swaraj, Sufal and Wang, Cheng and Hwang, Inchan and Greenham, Neil C. and Groves, Chris and Ade, Harald and McNeill, Christopher R.}, year={2010}, month={Dec}, pages={4329–4337} }
 @article{swaraj_wang_yan_watts_lüning jan_mcneill_ade_2010, title={Nanomorphology of Bulk Heterojunction Photovoltaic Thin Films Probed with Resonant Soft X-ray Scattering}, volume={10}, ISSN={1530-6984 1530-6992}, url={http://dx.doi.org/10.1021/nl1009266}, DOI={10.1021/nl1009266}, abstractNote={The bulk nanomorphology of organic bulk heterojunction devices, particularly of all-polymer devices, is difficult to characterize due to limited electron density contrast between constituent materials. Resonant soft X-ray scattering can overcome this problem and is used to show that the morphologies in chloroform cast and subsequently annealed polyfluorene copolymer poly(9,9'-dioctylfluorene-co-bis(N,N'-(4,butylphenyl))bis(N,N'-phenyl-1,4-phenylene)diamine) (PFB) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) blends exhibit a hierarchy of length scales with impure domains in as-cast films. With annealing, these domains first become purer at the smallest length scale and only then evolve in size with annealing. Even optimized cells using present fabrication methods are found to have a dominant domain size much larger than the exciton diffusion length. The observed morphology is far from ideal for efficient solar cell operation and very different from those achieved in high-efficiency fullerene-based devices. This strongly implies that lack of morphological control contributes to the relatively poor performance of the all-polymer PFB/F8BT devices and may be problematic for all-polymer devices in general. Novel processing strategies will have to be employed to harness the full potential these high open circuit voltage devices offer.}, number={8}, journal={Nano Letters}, publisher={American Chemical Society (ACS)}, author={Swaraj, Sufal and Wang, Cheng and Yan, Hongping and Watts, Benjamin and Lüning Jan and McNeill, Christopher R. and Ade, Harald}, year={2010}, month={Aug}, pages={2863–2869} }
 @article{ade_watts_swaraj_mcneill_thomsen_belcher_dastoor_2009, title={NEXAFS microscopy of polymeric materials: Successes and challenges encountered when characterizing organic devices}, volume={186}, ISBN={["*****************"]}, ISSN={["1742-6596"]}, DOI={10.1088/1742-6596/186/1/012102}, abstractNote={We summarize recent developments in x-ray microscopy of polymers by focusing on the characterization of organic electronic devices. The quantitative compositions of model polymer blends have been mapped at a resolution of ∼35 nm. Since it could be inferred that these devices have structures smaller than 35 nm, quantitative compositional mapping at length scales below the present resolution limit of x-ray microscopy is required. Organic devices thus serve to both highlight the success of NEXAFS microscopy to date, but to also outline the very real need for higher spatial resolution. New approaches to create improved optics or different acquisition modalities are required if x-ray microscopy is to make sustained contributions to such an important area of research as organic devices.}, journal={9TH INTERNATIONAL CONFERENCE ON X-RAY MICROSCOPY}, author={Ade, H. and Watts, B. and Swaraj, S. and McNeill, C. and Thomsen, L. and Belcher, W. and Dastoor, P. C.}, year={2009} }
 @article{swaraj_wang_araki_mitchell_liu_gaynor_deshmukh_yan_mcneill_ade_2009, title={The utility of resonant soft x-ray scattering and reflectivity for the nanoscale characterization of polymers}, volume={167}, ISSN={["1951-6355"]}, DOI={10.1140/epjst/e2009-00946-3}, journal={EUROPEAN PHYSICAL JOURNAL-SPECIAL TOPICS}, author={Swaraj, S. and Wang, C. and Araki, T. and Mitchell, G. and Liu, L. and Gaynor, S. and Deshmukh, B. and Yan, H. and McNeill, C. R. and Ade, H.}, year={2009}, month={Feb}, pages={121–126} }
 @article{mcneill_watts_swaraj_ade_thomsen_belcher_dastoor_2008, title={Evolution of the nanomorphology of photovoltaic polyfluorene blends: sub-100 nm resolution with x-ray spectromicroscopy}, volume={19}, ISSN={["1361-6528"]}, DOI={10.1088/0957-4484/19/42/424015}, abstractNote={We investigate the influence of annealing on the morphology of intimately mixed blends of the conjugated polymers poly(9,9'-dioctylfluorene-co-bis-N,N'-(4-butylphenyl)-bis-N,N'-phenyl-1,4-phenylene-diamine) (PFB) and poly(9,9'-dioctylfluorene-co-benzothiadiazole) (F8BT) with scanning transmission x-ray microscopy (STXM). Through the use of a zone plate with theoretical Rayleigh resolution of 30 nm, we are able to resolve sub-100 nm bulk structure in these films. Surprisingly, for unannealed films spin-coated from chloroform we observe features with an average diameter of 85 nm. The high degree of photoluminescence quenching in these as-spun films (>95%) implies that there is significant intermixing within the 85 nm structures, indicating that a hierarchy of phase separation exists even on the length scale of less than 100 nm. With annealing up to 160 °C, close to the T(g) of the components, there is little change in the feature sizes observed by STXM, although an increase in variation of the composition is observed. With annealing above 160 °C the imaged features begin to evolve in size, increasing to 225 nm in extent, alongside large changes in composition with annealing to 200 °C. Comparing the evolution of morphology imaged by STXM with the change in photoluminescence quenching with annealing, we propose that phase separation first evolves via the evolution of relatively pure phases on the length scale of a few to tens of nanometres within the larger 85 nm structures. Once the length scale of compositional fluctuations exceeds 85 nm (for anneal temperatures above 160 °C) the hierarchy of phase separation is lost and the subsequent morphological evolution is readily imaged by STXM. Applying the results of an exciton diffusion and quenching model, we find good agreement between the size of the domains measured by STXM (above 180 °C) and the results of the model for an exciton diffusion length of 15 nm. The growth in domain size and towards purer structures has also been observed with resonant soft x-ray scattering.}, number={42}, journal={NANOTECHNOLOGY}, author={McNeill, C. R. and Watts, B. and Swaraj, S. and Ade, H. and Thomsen, L. and Belcher, W. and Dastoor, P. C.}, year={2008}, month={Oct} }
 @article{swaraj_oran_lippitz_unger_2008, title={Surface chemical analysis of plasma-deposited copolymer films prepared from feed gas mixtures of ethylene or styrene with allylamine}, volume={5}, ISSN={["1612-8869"]}, DOI={10.1002/ppap.200700106}, abstractNote={Abstract Plasma deposited ethylene/allylamine and styrene/allylamine copolymer films were prepared and analyzed using XPS, NEXAFS and ToF‐SIMS. The relative partial flow rate of the each monomer was used as the variable deposition parameter, while the other deposition parameters were kept constant at optimized values for the retention of functional groups. The effect of the variation in the relative partial flow rates of co‐monomers on various chemical aspects of the films like unsaturation, nitrogen retention and branching was investigated revealing several non‐linear correlations. This observation is taken as an indication for chemical copolymerization processes during film deposition. An attempt is made to compare these non‐linear correlations with approaches which have been developed for classic radical copolymerization processes. The aging behavior of these plasma copolymer films was also studied; the results indicated a stabilization against oxidation in comparison to the aging of allylamine plasma homopolymers. magnified image}, number={1}, journal={PLASMA PROCESSES AND POLYMERS}, author={Swaraj, Sufal and Oran, Urnut and Lippitz, Andreas and Unger, Wolfgang E. S.}, year={2008}, month={Jan}, pages={92–104} }