@article{watts_swaraj_nordlund_luning_ade_2011, title={Calibrated NEXAFS spectra of common conjugated polymers}, volume={134}, number={2}, journal={Journal of Chemical Physics}, author={Watts, B. and Swaraj, S. and Nordlund, D. and Luning, J. and Ade, H.}, year={2011} }
 @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{watts_belcher_thomsen_ade_dastoor_2009, title={A Quantitative Study of PCBM Diffusion during Annealing of P3HT: PCBM Blend Films}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma901444u}, abstractNote={Scanning transmission X-ray microscopy has been used to quantitatively map the composition of P3HT:PCBM blend films in the vicinity of PCBM crystals formed during annealing at 140 °C. The observed PCBM concentration profiles around these crystals have been fitted to Fick’s second law of diffusion and the diffusion constant found to be 2.5 × 10−14 m2 s−1. The PCBM concentration at the crystal boundary was found to be 19% (v/v) and is interpreted, together with the annealing temperature of 140 °C, as a point on the bimodal line of the composition−temperature phase diagram. The diffusion of PCBM through P3HT is observed to be bulk-dominated, in contrast to the surface/interface-dominated diffusion observed in MDMO-PPV:PCBM blend films by Yang et al.(1, 2)}, number={21}, journal={MACROMOLECULES}, author={Watts, Benjamin and Belcher, Warwick J. and Thomsen, Lars and Ade, Harald and Dastoor, Paul C.}, year={2009}, month={Nov}, pages={8392–8397} }
 @article{mcneill_watts_thomsen_belcher_greenham_dastoor_ade_2009, title={Evolution of Laterally Phase-Separated Polyfluorene Blend Morphology Studied by X-ray Spectromicroscopy}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma801816r}, abstractNote={The morphological evolution of laterally phase-separated polyfluorene blends composed of poly(9,9′-dioctylfluorene-co-bis-N,N′-(4-butylphenyl)-bis-N,N′-phenyl-1,4-phenylenediamine) (PFB) and poly(9...}, number={9}, journal={MACROMOLECULES}, author={McNeill, Christopher R. and Watts, Benjamin and Thomsen, Lars and Belcher, Warwick J. and Greenham, Neil C. and Dastoor, Paul C. and Ade, Harald}, year={2009}, month={May}, pages={3347–3352} }
 @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} }
 @inproceedings{lucovsky_long_chung_seo_watts_vasic_ulrich_2009, title={Predeposition plasma nitridation process applied to Ge substrates to passivate interfaces between crystalline-Ge substrates and Hf-based high-K dielectrics}, volume={27}, number={1}, booktitle={Journal of Vacuum Science & Technology. B, Microelectronics and Nanometer Structures}, author={Lucovsky, G. and Long, J. P. and Chung, K. B. and Seo, H. and Watts, B. and Vasic, R. and Ulrich, M. D.}, year={2009}, pages={294–299} }
 @article{burke_belcher_thomsen_watts_mcneill_ade_dastoor_2009, title={Role of Solvent Trapping Effects in Determining the Structure and Morphology of Ternary Blend Organic Devices}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma802632y}, abstractNote={We present results of scanning transmission X-ray microscopy (STXM) measurements of bulk heterojunction organic solar cells built from a ternary blend of poly(3-hexylthiophene) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and [2,3,12,13-tetracyano-5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrinato]copper(II) (Cu(CN)4P) porphyrin. These results show evidence of solvent trapping due to porphyrin in the film. Upon annealing, submicrometer depressions are observed in the ternary blend films, corresponding to the evolution of solvent that is associated with the small porphyrin aggregates that phase segregate in the middle of the depressions. The areal density and size of the depressions change systematically with porphyrin concentration in the ternary blend. The relationship of the observed morphologies to the previously measured device performance is discussed.}, number={8}, journal={MACROMOLECULES}, author={Burke, Kerry B. and Belcher, Warwick J. and Thomsen, Lars and Watts, Benjamin and McNeill, Christopher R. and Ade, Harald and Dastoor, Paul C.}, year={2009}, month={Apr}, pages={3098–3103} }
 @article{watts_queen_kilcoyne_tyliszczak_hellman_ade_2009, title={Soft X-Ray Beam Induced Current Technique}, volume={186}, ISBN={["*****************"]}, ISSN={["1742-6596"]}, DOI={10.1088/1742-6596/186/1/012023}, abstractNote={Direct mapping of the charge transport efficiency of polymer solar cell devices using a soft X-ray beam induced current (SoXBIC) method is described. By fabricating a polymer solar cell on an x-ray transparent substrate, we demonstrate the ability to map polymer composition and nanoscale structure within an operating solar cell device and to simultaneously measure the local charge transport efficiency via the short-circuit current. A simple model is calculated and compared to experimental SoXBIC data of a PFB:F8BT bulk-heterojunction device in order to gain greater insight into the device operation and physics.}, journal={9TH INTERNATIONAL CONFERENCE ON X-RAY MICROSCOPY}, author={Watts, B. and Queen, D. and Kilcoyne, A. L. D. and Tyliszczak, T. and Hellman, F. and Ade, H.}, year={2009} }
 @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 Tg 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{watts_ade_2008, title={A simple method for determining linear polarization and energy calibration of focused soft X-ray beams}, volume={162}, ISSN={["1873-2526"]}, DOI={10.1016/j.elspec.2007.08.008}, abstractNote={Although critical to quantitative linear dichroism studies of molecular orientation, the degree of linear polarization of focused soft X-ray beams delivered by X-ray microscopes has not been previously measured. Here, we present a scaled-down version of a recently developed technique in which the π∗ near edge X-ray absorption fine structure (NEXAFS) resonance of highly oriented pyrolytic graphite (HOPG) is used to probe the electric field intensity in each direction and hence deduce the degree of linear polarization of the incident X-ray beam. Applying this technique to the soft X-ray microscope at beamline 5.3.2 of the Advanced Light Source in Berkeley, CA, yielded a measured value of 79±11%, for the first Stokes parameter of 0.79±0.11 or as a Stöhr P factor of 0. 89±0.06. It is expected that the error margin could be significantly reduced via the use of an in-vacuum rotation actuator. We have also calibrated the energy of the graphite exciton to be 291.65±0.025 eV, improving the utility of graphite as an energy calibration standard for NEXAFS and allowing the convenience of both energy calibration and polarization determination with a single inexpensive sample.}, number={2}, journal={JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA}, author={Watts, B. and Ade, H.}, year={2008}, month={Feb}, pages={49–55} }
 @article{wang_araki_watts_harton_koga_basu_ade_2007, title={Resonant soft x-ray reflectivity of organic thin films}, volume={25}, ISSN={["0734-2101"]}, DOI={10.1116/1.2731352}, abstractNote={At photon energies close to absorption edges in the soft x-ray range, the complex index of refraction, n=1−δ−iβ, of organic materials varies rapidly as a function of photon energy in a manner that strongly depends on the chemical moieties and functionalities present in the material. The authors present details of how these molecular structure specific variations in the complex index of refraction can be utilized to enhance and tune the contrast in reflectivity experiments of organic films. This near edge contrast enhancement mimics the specific contrast achieved through deuterium labeling in neutron reflectivity (NR). This relatively new x-ray approach, resonant soft x-ray reflectivity (RSoXR), thus combines aspects of NR and conventional x-ray reflectivity (XR), yet does not require special chemical procedures. The capabilities of RSoXR are exemplified using a number of polymeric bi- and multilayers. Furthermore, a direct comparison of RSoXR to conventional x-ray reflectivity and NR for polystyrene and poly(methyl methacrylate) bilayers verifies that RSoXR is an excellent alternative tool for the characterization of organic thin films. The influence of the longitudinal and transverse coherence properties as well as the divergence of the x-ray or neutron beam on the capabilities and limitations of each reflectivity variant is discussed.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Wang, Cheng and Araki, Tohru and Watts, Benjamin and Harton, Shane and Koga, Tadanori and Basu, Saibal and Ade, Harald}, year={2007}, pages={575–586} }
 @article{mcneill_watts_thomsen_ade_greenham_dastoor_2007, title={X-ray microscopy of photovoltaic polyfluorene blends: Relating nanomorphology to device performance}, volume={40}, ISSN={["1520-5835"]}, DOI={10.1021/ma070132d}, abstractNote={The composition of blend films of poly(9,9‘-dioctylfluorene-co-bis-N,N‘-(4-butylphenyl)-bis-N,N‘-phenyl-1,4-phenylenediamine) (PFB) and poly(9,9‘-dioctylfluorene-co-benzothiadiazole) (F8BT) used in prototype polymer solar cells has been quantitatively mapped using scanning transmission X-ray microscopy (STXM). The resolution of the STXM technique is 50 nm or better, allowing the first nanoscale lateral chemical mapping of this blend system. For 1:1 blend films spin-coated from xylene we find that the F8BT-rich domain is over 90% pure (by weight) and the PFB-rich domain contains 70% PFB. For 5:1 and 1:5 blend films processed from xylene, the minority phases are found to be intermixed, containing as much as 50% by weight of the majority polymer. Films prepared from chloroform with a 1:1 weight ratio have also been imaged but show no features on the length scale of 50 nm or greater. Additionally, the performance of photovoltaic devices fabricated using films prepared in an identical fashion to those prepared...}, number={9}, journal={MACROMOLECULES}, author={McNeill, Christopher R. and Watts, Benjamin and Thomsen, Lars and Ade, Harald and Greenham, Neil C. and Dastoor, Paul C.}, year={2007}, month={May}, pages={3263–3270} }
 @article{mcneill_watts_thomsen_belcher_kilcoyne_greenham_dastoor_2006, title={X-ray spectromicroscopy of polymer/fullerene composites: Quantitative chemical mapping}, volume={2}, number={12}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={McNeill, C. R. and Watts, B. and Thomsen, L. and Belcher, W. J. and Kilcoyne, A. L. D. and Greenham, N. C. and Dastoor, P. C.}, year={2006}, pages={1432–1435} }