@article{harton_zhu_stevie_aoyama_ade_2007, title={Carbon-13 labeling for quantitative analysis of molecular movement in heterogeneous organic materials using secondary ion mass spectrometry}, volume={79}, ISSN={["1520-6882"]}, DOI={10.1021/ac070437q}, abstractNote={Secondary ion mass spectrometry (SIMS) is used to probe the movement of macromolecules in heterogeneous organic systems. Using 13C tracer labeling and two model systems, polystyrene/poly(2-vinylpyridine) (PS/P2VP) and polystyrene/poly(4-bromostyrene) (PS/P4BrS), the diffusion of 13C-labeled PS has been investigated near the respective heterogeneous interfaces using a CAMECA-IMS-6F magnetic sector mass spectrometer. 13C labeling has been shown to greatly minimize matrix effects (i.e., changes in secondary ion yields due to changing chemical environment) in heterogeneous systems. P2VP is a nitrogen-rich polymer (C7H7N monomer composition), making it an excellent model polymer for exploration of this technique for potential future use in biological applications, and probing the PS/P4BrS interface demonstrates the versatility of this technique for analysis of various heteroatom-containing materials. Results confirm that the 13C-labeling method does indeed allow for quantitative analysis of molecular movement in heterogeneous organic systems containing matrix-enhancing heteroatoms such as nitrogen. Therefore, extension of this method to more complicated biological systems involving multiple heteroatoms (oxygen, nitrogen, etc.), layers, and heterogeneous interfaces, as well as two- and three-dimensional profiling and imaging using SIMS, can be envisaged.}, number={14}, journal={ANALYTICAL CHEMISTRY}, author={Harton, Shane E. and Zhu, Zhengmao and Stevie, Frederick A. and Aoyama, Yoko and Ade, Harald}, year={2007}, month={Jul}, pages={5358–5363} }
 @article{hub_harton_hunt_fink_ade_2007, title={Influence of sample preparation and processing on observed glass transition temperatures of polymer nanocomposites}, volume={45}, ISSN={["1099-0488"]}, DOI={10.1002/polb.21249}, abstractNote={AbstractPolymer composites composed of poly(methyl methacrylate) (PMMA) and silica (14 nm diameter) have been investigated. The influences of sample preparation and processing have been probed. Two types of sample preparation methods were investigated: (i) solution mixture of PMMA and silica in methyl ethyl ketone and (ii) in situ synthesis of PMMA in the presence of silica. After removing all solvent or monomer, as confirmed using thermogravimetric analysis, and after compression molding, drops in Tg of 5–15 °C were observed for all composites (2–12% w/w silica) and even pure polymer reference samples. However, after additional annealing for 72 h at 140 °C, all previously observed drops in Tg disappeared, and the intrinsic Tg of bulk, pure PMMA was again observed. This is indicative of nonequilibrium trapped voids being present in the as‐molded samples. Field‐emission scanning electron microscopy was used to show well‐dispersed particles, and dynamic mechanical analysis was used to probe the mechanical properties (i.e., storage modulus) of the fully equilibrated composites. Even though no equilibrium Tg changes were observed, the addition of silica to the PMMA matrices was observed to improve the mechanical properties of the glassy polymer host. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2270–2276, 2007}, number={16}, journal={JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS}, author={Hub, Christian and Harton, Shane E. and Hunt, Marcus A. and Fink, Rainer and Ade, Harald}, year={2007}, month={Aug}, pages={2270–2276} }
 @article{harton_zhu_stevie_griffis_ade_2007, title={Mass fractionation of carbon and hydrogen secondary ions upon Cs+ and O-2(+) bombardment of organic materials}, volume={25}, ISSN={["1520-8559"]}, DOI={10.1116/1.2718957}, abstractNote={A phenomenon known as mass fractionation has been probed in organic materials using secondary ion mass spectrometry (SIMS). Mass fractionation occurs because two isotopes of a particular species (i.e., identical number of protons, but different number of neutrons) do not have identical secondary ion yields in a constant chemical environment. Two primary ion probes, Cs+ and O2+, have been utilized with detection of negative and positive secondary ions, respectively, using a magnetic sector mass spectrometer. These two analysis conditions have been found to yield considerably different mass fractionation effects as a result of different sputtering and ionization mechanisms. Also, as determined previously with SIMS analysis of inorganic materials, the lower molecular weight species carbon and hydrogen are particularly susceptible to mass fractionation effects. Because organic materials are primarily composed of carbon and hydrogen, and because isotopic labeling is often utilized to accurately analyze such materials, knowledge of these effects in organic materials is essential for quantitative SIMS analysis.}, number={3}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A}, author={Harton, Shane E. and Zhu, Zhengmao and Stevie, Frederick A. and Griffis, Dieter P. and Ade, Harald}, year={2007}, pages={480–484} }
 @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{harton_stevie_zhu_ade_2006, title={Carbon-13 labeled polymers: An alternative tracer for depth profiling of polymer films and multilayers using secondary ion mass spectrometry}, volume={78}, ISSN={["1520-6882"]}, DOI={10.1021/ac060133o}, abstractNote={13C labeling is introduced as a tracer for depth profiling of polymer films and multilayers using secondary ion mass spectrometry (SIMS). Deuterium substitution has traditionally been used in depth profiling of polymers but can affect the phase behavior of the polymer constituents with reported changes in both bulk-phase behavior and surface and interfacial interactions. SIMS can provide contrast by examining various functional groups, chemical moieties, or isotopic labels. 13C-Labeled PS (13C-PS) and unlabeled PS (12C-PS) and PMMA were synthesized using atom-transfer radical polymerization and assembled in several model thin-film systems. Depth profiles were recorded using a Cameca IMS-6f magnetic sector mass spectrometer using both 6.0-keV impact energy Cs+ and 5.5-keV impact energy O2+ primary ion bombardment with detection of negative and positive secondary ions, respectively. Although complete separation of 12C1H from 13C is achieved using both primary ion species, 6.0-keV Cs+ clearly shows improved detection sensitivity and signal-to-noise ratio for detection of 12C, 12C1H, and 13C secondary ions. The use of Cs+ primary ion bombardment results in somewhat anomalous, nonmonotonic changes in the 12C, 12C1H, and 13C secondary ion yields through the PS/PMMA interface; however, it is shown that this behavior is not due to sample charging. Through normalization of the 13C secondary ion yield to the total C (12C + 13C) ion yield, the observed effects through the PS/PMMA interface can be greatly minimized, thereby significantly improving analysis of polymer films and multilayers using SIMS. Mass spectra of 13C-PS and 12C-PS were also analyzed using a PHI TRIFT I time-of-flight mass spectrometer, with 15-keV Ga+ primary ion bombardment and detection of positive secondary ions. The (12)C7(1)H7 ion fragment and its 13C-enriched analogues have significant secondary ion yields with negligible mass interferences, providing an early indication of the potential for future use of this technique for cluster probe depth profiling of high molecular weight 13C-labeled fragments.}, number={10}, journal={ANALYTICAL CHEMISTRY}, author={Harton, S. E. and Stevie, F. A. and Zhu, Z. and Ade, H.}, year={2006}, month={May}, pages={3452–3460} }
 @article{harton_stevie_ade_2006, title={Carbon-13 labeling for improved tracer depth profiling of organic materials using secondary ion mass spectrometry}, volume={17}, ISSN={["1879-1123"]}, DOI={10.1016/j.jasms.2006.03.018}, abstractNote={13C labeling is introduced as an alternative to deuterium labeling for analysis of organic materials using secondary ion mass spectrometry (SIMS). A model macromolecular system composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) was used to compare the effects of isotopic labeling using both deuterium substitution (dPS) and 13C labeling (13C-PS). Clear evidence is shown that deuterium labeling does introduce changes in the thermodynamic properties of the system, with the observation of segregation of dPS to an hPS:dPS/hPMMA interface. This type of behavior could significantly impact many types of investigations due to the potential for improper interpretation of experimental results as a consequence of labeling-induced artifacts. 13C labeling is shown to provide a true tracer for analysis using SIMS.}, number={8}, journal={JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY}, author={Harton, S. E. and Stevie, F. A. and Ade, H.}, year={2006}, month={Aug}, pages={1142–1145} }
 @article{harton_stevie_ade_2006, title={Investigation of the effects of isotopic labeling, at a PS/PMMA interface using SIMS and mean-field theory}, volume={39}, ISSN={["1520-5835"]}, DOI={10.1021/ma052236z}, abstractNote={Isotopic labeling (deuteration) is known to affect the phase behavior of polystyrene (PS) and poly- (methyl methacrylate) (PMMA) blends, but little is known regarding the changes in the interfacial properties at the PS/PMMA interface due to deuteration of PS and/or PMMA. To investigate these potential changes, secondary ion mass spectrometry (SIMS) was used to measure real-space depth profiles of dPS in hPS:dPS/hPMMA bilayers, with the hPS:dPS blend being well within the single-phase region of the phase diagram. Profound changes in the thermodynamic behavior of this system at the polymer/polymer interface are observed in the form of significant segregation of dPS to the hPS:dPS/hPMMA interface. The observation of a depletion hole during the formation of an equilibrium excess of dPS implies that the energetic gain at the interface per dPS chain has to be >kT. These results cannot be described, even qualitatively, using previously reported changes in for PS/PMMA due to isotopic labeling. The previously reported values of for dPS/hPMMA and hPS/hPMMA actually predict a depletion of dPS at the hPS:dPS/hPMMA interface rather than the observed segregation. The observed interfacial excess is quantified by generating theoretical profiles, using self-consistent mean-field theory (SCMF), and fitting an effective interaction energy parameter ¢ p as a function of temperature. This parameter represents the asymmetry in dPS/hPMMA and hPS/PMMA interactions. The temperature dependency of ¢ p was found to be a factor of 3-4 greater than any of those reported for of PS/PMMA. It was also found that SCMF theory accurately describes the concentration dependency of dPS segregation at a constant dPS molecular weight using a concentration-independent ¢ p; however, ¢ p was found to be dependent on dPS molecular weight.}, number={4}, journal={MACROMOLECULES}, author={Harton, SE and Stevie, FA and Ade, H}, year={2006}, month={Feb}, pages={1639–1645} }
 @article{harton_luning_betz_ade_2006, title={Polystyrene/poly(methyl methacrylate) blends in the presence of cyclohexane: Selective solvent washing or equilibrium adsorption?}, volume={39}, ISSN={["0024-9297"]}, DOI={10.1021/ma061401n}, abstractNote={Cyclohexane has been frequently used as a selective solvent to remove PS layers or domains from polystyrene:poly(methyl methacrylate) (PS:PMMA) blends and for reorganization or self-assembly of polymer brushes and block copolymers. We have found that cyclohexane is not efficient at PS removal, observing significant residual PS at PMMA surfaces. In contrast, 1-chloropentane was found to be a far greater selective solvent (i.e., residual PS was essentially nonexistent). These results were compared to PMMA surfaces after PS was allowed to adsorb to the surface from a dilute theta solution in cyclohexane. Using near-edge X-ray absorption fine structure spectroscopy and inverse gas chromatography, coupled with self-consistent mean-field theory calculations, we have demonstrated that selectively washing a polymer from a polymer blend is nearly identical to adsorption of a polymer to a "soft" surface from a dilute solution. Improved knowledge about the effects of selective solvents will improve experimental analysis of washed systems as well as manipulation of block copolymers and polymer brushes for reorganization or self-assembly.}, number={22}, journal={MACROMOLECULES}, author={Harton, Shane E. and Luning, Jan and Betz, Heike and Ade, Harald}, year={2006}, month={Oct}, pages={7729–7733} }
 @article{harton_stevie_griffis_ade_2006, title={SIMS depth profiling of deuterium labeled polymers in polymer multilayers}, volume={252}, ISSN={["0169-4332"]}, DOI={10.1016/j.apsusc.2006.02.146}, abstractNote={Thin planar polymer films are model systems for probing physical phenomena related to molecular confinement at polymer surfaces and polymer/polymer interfaces. Existing experimental techniques such as forward recoil spectrometry (FRES) and neutron reflectometry (NR) have been used extensively for analysis of these systems, although they suffer from relatively low depth resolution (FRES) or difficulties associated with inversion to real space (NR). In contrast, secondary ion mass spectrometry (SIMS) can provide real-space depth profiles of tracer labeled polymers directly with sufficient depth resolution for optimal analyses of these systems. Deuterated polystyrene (dPS) has been employed as the tracer polymer and has been embedded in a matrix of either unlabeled polystyrene (PS) or poly(cyclohexyl methacrylate) (PCHMA). These doped films have been placed on either poly(methyl methacrylate) (PMMA) or poly(2-vinyl pyridine) (P2VP) and thermally annealed. Varied analysis conditions for a magnetic sector SIMS instrument (CAMECA IMS-6f) were used to optimize the depth resolution and detection sensitivity while minimizing matrix effects and sample charging. Both Cs+ and O2+ primary ions have been used along with detection of negative and positive secondary ions, respectively. Impact energy and primary ion species have been shown to affect matrix secondary ion count rate for the various films studied.}, number={19}, journal={APPLIED SURFACE SCIENCE}, author={Harton, Shane E. and Stevie, Fred A. and Griffis, Dieter P. and Ade, Harald}, year={2006}, month={Jul}, pages={7224–7227} }
 @article{harton_stevie_ade_2005, title={Diffusion-controlled reactive coupling at polymer-polymer interfaces}, volume={38}, ISSN={["0024-9297"]}, DOI={10.1021/ma047421b}, abstractNote={Reactive coupling of an end-functionalized polymer A with another endor chain-functionalized polymer B at an A-B interface is technologically referred to as reactive compatibilization. It is a proven means by which to reduce interfacial tension and improve adhesion between domains in polymer blends.1 In reactive systems, whether small-molecule or macromolecular in nature, the two regimes that generally describe the ratelimiting mechanism of the reaction are classified as diffusionand reaction-controlled (DC and RC, respectively) regimes.2 A dimensionless Damkohler number (NDa) as defined below can be used to determine which regime dominates a particular reaction.3}, number={9}, journal={MACROMOLECULES}, author={Harton, SE and Stevie, FA and Ade, H}, year={2005}, month={May}, pages={3543–3546} }
 @article{harton_koga_stevie_araki_ade_2005, title={Investigation of blend miscibility of a ternary PS/PCHMA/PMMA system using SIMS and mean-field theory}, volume={38}, ISSN={["1520-5835"]}, DOI={10.1021/ma051595r}, abstractNote={Poly(cyclohexyl methacrylate) (PCHMA) and polystyrene (PS) are miscible with each other, but each is highly immiscible with PMMA. Identifiable by the asymmetries in the binary mean-field interaction parameters χ, PS preferentially segregates to the PCHMA/PMMA interface. Secondary ion mass spectrometry was used to provide real-space depth profiles of deuterated PS (dPS) in a miscible blend with PCHMA. The initial dPS concentration was varied from 5 to 20% (v/v), and the blend film was annealed at 150 °C on a film of PMMA for 42 h. X-ray reflectometry was used to determine the interfacial width between PCHMA and PMMA at 150 °C. Using self-consistent mean-field theory, good agreement was found between the experimental and theoretical interfacial excess Z* of dPS at each concentration. Because of their similar glass transition temperatures (∼100 °C for PS and PCHMA) and the ability of PS and PCHMA to be controllably synthesized with low polydispersities, we anticipate this blend to be a model system for futur...}, number={25}, journal={MACROMOLECULES}, author={Harton, SE and Koga, T and Stevie, FA and Araki, T and Ade, H}, year={2005}, month={Dec}, pages={10511–10515} }
 @article{harton_stevie_spontak_koga_rafailovich_sokolov_ade_2005, title={Low-temperature reactive coupling at polymer–polymer interfaces facilitated by supercritical CO2}, volume={46}, ISSN={0032-3861}, url={http://dx.doi.org/10.1016/j.polymer.2005.07.085}, DOI={10.1016/j.polymer.2005.07.085}, abstractNote={Supercritical CO2 (scCO2) has been used to facilitate reactions in thin film bilayers between functionalized polystyrene and poly(methyl methacrylate) at temperatures far below the glass transition temperatures of the respective polymers. Secondary ion mass spectrometry (SIMS) is used to monitor the reaction progression directly by measuring the interfacial excess of deuterated PS. Complementary X-ray reflectometry (XR) yields the interfacial width and surface roughness of bilayer films for reactive systems with and without the addition of scCO2, and comparisons are made with unreactive reference systems. From XR and SIMS analyses, the interfacial width and roughness have been found to be effectively independent of the reaction conditions employed here, and the primary impact of incorporated scCO2 is enhanced mobility of the reactive polymer chains. The use of scCO2 can change polymer mobility significantly enough over a very small temperature range (DTw15 8C) so that both diffusion- and reaction-controlled type behavior can be observed for otherwise identical systems. q 2005 Elsevier Ltd. All rights reserved.}, number={23}, journal={Polymer}, publisher={Elsevier BV}, author={Harton, S.E. and Stevie, F.A. and Spontak, R.J. and Koga, T. and Rafailovich, M.H. and Sokolov, J.C. and Ade, H.}, year={2005}, month={Nov}, pages={10173–10179} }