Selected recent papers - please email Andrew Whittaker for copies of reprints or for more information.

Blakey, Idriss; Chen, Lan; Dargaville, Bronwin; Liu, Heping; Whittaker, Andrew; Conley, Will; Piscani, Emil; Rich, Georgia; Williams, Alvina; Zimmerman, Paul, 2007, Novel high-index resists for 193-nm immersion lithography and beyond, Proceedings of SPIE-The International Society for Optical Engineering, 6519, Pt. 1, Advances in Resist Materials and Processing Technology XXIV, 651909/1-651909/9
Abstract: A preliminary Quant. Structure Property Relationship (QSPR) model for predicting the refractive index of small mols. and polymers at 193 nm is presented. Although at this stage the model is only semiquant. we have found it useful for screening databases of com.-available compds. for high refractive index targets to include in our program of synthesis of high refractive index resist polymers. These resists are targeted for use in 2nd and 3rd generation 193 nm immersion lithog. Using this methodol. a range of targets were identified and synthesized via free radical polymn. Novel resist polymers were also synthesized via Michael addn. polymn. Preliminary dose to clear expts. identified a no. of promising candidates for incorporation into high refractive index resist materials. Furthermore, we have demonstrated imaging of a high index resist using water-based 193 nm immersion lithog. [on SciFinder (R)]

Chirila , Traian V.; Zainuddin; Hill, David, J. T.; Whittaker, Andrew, K.; Kemp, Anne, 2007, Effect of phosphate functional groups on the calcification capacity of acrylic hydrogels, Acta Biomater FIELD Full Journal Title:Acta biomaterialia, 3, 1, 95-102
Abstract: The incorporation of negatively charged groups into the structure of synthetic polymers is frequently advocated as a method for enhancing their calcification capacity required in orthopedic and dental applications. However, the results reported by various research groups are rather contentious, since inhibitory effects have also been observed in some studies. In the present study, phosphate groups were introduced in poly(2-hydroxyethyl methacrylate) (PHEMA) by copolymerization with 10% mol of either mono(2-acryloyloxyethyl) phosphate (MAEP) or mono(2-methacryloyloxyethyl) phosphate (MMEP). Incubation of these hydrogels for determined durations (1-9 weeks) in a simulated body fluid (SBF) solution induced deposition of calcium phosphate (CaP) deposits of whitlockite type. After 9 weeks, the amount of calcium deposited on the phosphate-containing polymers was four times lower than that found on PHEMA, as determined by X-ray photoelectron spectroscopy (XPS). Samples of copolymer HEMA-MAEP were implanted subcutaneously in rats and evaluated after 9 weeks. No CaP deposits could be detected on the copolymer by XPS or energy dispersive X-ray spectroscopy, while PHEMA samples were massively calcified. It was concluded that the presence of phosphate groups decreased the calcification capacity of the hydrogels, and that in the conditions of this study, the phosphate groups had an inhibitory effect on the deposition of CaP phases on HEMA-based hydrogels. [on SciFinder (R)]

Hogarth, Warren H. J.; Muir, Sean S.; Whittaker, Andrew K.; Diniz da Costa, Joao C.; Drennan, John; Lu, G. Q., 2007, Proton conduction mechanism and the stability of sol-gel titanium phosphates, Solid State Ionics, 177, 39-40, 3389-3394
Abstract: Proton conducting sol-gel titanium phosphates were synthesized and characterized with a specific focus on the structural characteristics of the materials which enable proton cond. and on testing the stability of the chem. groups which facilitate proton conduction under fuel cell conditions. The chem. structure of the materials before and after stability tests was probed using 31P MAS NMR, FTIR and powder X-Ray diffraction. After refluxing the materials in boiling water the cond. of the titanium phosphates at 100% relative humidity and 100 DegC was 0.0044 S cm-1 and 0.0019 S cm-1 for the two different samples. 31P MAS NMR and FTIR tests demonstrated that the presence of (H2PO4)- and (HPO4)2- groups in the materials, even after heat treatment, was responsible for the high cond. of the materials when in the presence of water vapor. Stable solid acid proton conductors such as these have the potential to extend the operating temp. of PEM fuel cells beyond the glass transition temps. of the current state of the art polymer technol. [on SciFinder (R)]

Jack, Kevin; Liu, Heping; Blakey, Idriss; Hill, David; Wang, Yueh; Cao, Heidi; Leeson, Michael; Denbeaux, Greg; Waterman, Justin; Whittaker, Andrew, 2007, The rational design of polymeric EUV resist materials by QSPR modelling, Proceedings of SPIE-The International Society for Optical Engineering, 6519, Pt. 2, Advances in Resist Materials and Processing Technology XXIV, 65193Z/1-65193Z/8
Abstract: We present the initial results of the development of a qual. structure property relationship (QSPR) model to guide in the design and synthesis of high-sensitivity, non-CAR materials for EUV lithog. The model was developed using the fragmentation data of low mol. wt. species at 70 eV using a mass spectrometer (MS) with an electron ionization source as the input parameter. The preliminary model has highlighted a no. of structural elements which will be important in the future design of resists, however, limitations with the current set of input data for mols. which fragment readily have been identified and these are currently being addressed. Addnl., a correlation between g (1 MeV) and EUV (92 eV) radiolysis of selected polymers has been established and it is proposed that the higher energy (1 MeV) irradn. source is a suitable model process for EUV and can, therefore, be used in the future screening of polymeric materials. [on SciFinder (R)]

Tan, Ihwa; Flanagan, Bernadine M.; Halley, Peter J.; Whittaker, Andrew K.; Gidley, Michael J., 2007, A Method for Estimating the Nature and Relative Proportions of Amorphous, Single, and Double-Helical Components in Starch Granules by 13C CP/MAS NMR, Biomacromolecules, 8, 3, 885-891
Abstract: An improved method to analyze the 13C NMR spectra of native starches, which considers the contribution of the V-type conformation and the nature of the amorphous component, was developed. Starch spectra are sepd. into amorphous and ordered subspectra, using intensity at 84 ppm as a ref. point. The ordered subspectra of high amylose starches show the presence of both V-type single helixes and B-type double helixes. Relative proportions of amorphous, single, and double-helical conformations are estd. by apportioning intensity of C1 peak areas between conformational types on the basis of ordered and amorphous subspectra of the native starch. Quant. anal. shows that the V-type single-helical component increases with amylose content of starches. Different amorphous subspectra are needed to provide a consistent anal. of granular starches from diverse sources. The method of prepn. was found to be more important than the starch botanical origin in detg. 13C NMR spectral features of amorphous samples. [on SciFinder (R)]

Varcoe, Kylie M.; Blakey, Idriss; Chirila, Traian V.; Hill, Anita J.; Whittaker, Andrew K., 2007, The effect of synthetic conditions on the free volume of poly(2-hydroxyethyl methacrylate) as studied by 1H NMR, 129Xe NMR, and position annihilation spectroscopy, ACS Symposium Series, 963, New Approaches in Biomedical Spectroscopy, 391-409
Abstract: The porous structure of PHEMA hydrogels prepd. under a range of conditions has been examd. using three distinct probes. Positron annihilation lifetime spectroscopy and 129Xe NMR are sensitive to pores in the range 0.1-10 nm, while 1H NMR of water within the hydrogel provides information on a range of sizes up to several microns. PHEMA samples were prepd. in soln. with from 5-30 wt. % of water in the polymn. mixt. Below 30 wt. % the water exists in nanometer-sized pores, and above this a substantial proportion reside in micron sized pores. The PALS and 129Xe NMR results support the existence of relatively hydrophobic domains of sub-nanometer size. [on SciFinder (R)]

Whittaker, Andrew K.; Blakey, Idriss; Chen, Lan; Dargaville, Bronwin; Liu, Heping; Conley, Will; Zimmerman, Paul A., 2007, Rational design of high-RI resists for 193nm immersion lithography, Journal of Photopolymer Science and Technology, 20, 5, 665-671
Abstract: We have developed a Quant. Structure Property Relationship (QSPR) model for predicting the refractive index of small mols. and polymers at 193 nm. This model has been useful for screening databases of compds. for high refractive index to include in our program of synthesis of polymer having high RI. A range of novel target structures were identified and prepd. via free radical polymn. In addn. polymers were also synthesized via Michael addn. polymn. Preliminary dose-to-clear and imaging expts. identified a no. of promising candidates for incorporation into high refractive index resist materials. The platforms presented may be limited by relatively high intrinsic absorbance, and so design limits for incorporation of sulfur are given. [on SciFinder (R)]

Zainuddin; Hill, David J. T.; Whittaker, Andrew K., 2007, Mineralization of radiation-crosslinked polyvinyl alcohol/polyvinyl pyrrolidone hydrogels, Journal of biomedical materials research. Part A, 83, 2, 354-61
Abstract: A study of the calcification of the polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) hydrogels during their exposure to a calcium chloride solution or a simulated body fluid has been carried out. On the basis of the experiments, using a two-compartment permeation cell, the diffusion of calcium ions and their subsequent deposition in the hydrogels were elucidated. Steady-batch experiments were also performed to further elaborate the deposition pattern and the types of calcium deposits. It was demonstrated that Fick's second law of diffusion can describe the diffusion of calcium ions through PVA/PVP hydrogels at 310 K. The diffusion coefficient was determined to be (4.4 +/- 0.1) x 10(-10) m(2)/s and the partition coefficient for the hydrogels was 0.06. Formation of calcium deposits was noticed taking place both on the surface and inside the hydrogels. The deposits formed on the surface have flake morphology, while the deposits inside the hydrogels are more like globular aggregates. Both types of deposits have been characterized as being comprised calcium and hydroxyl ion deficient apatites with chloride ions the most likely substituting species at the hydroxyl sites. (c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res 2007. [on SciFinder (R)]

Zainuddin; Hill, D. J. T.; Whittaker, A. K.; Lambert, L.; Chirila, T. V., 2007, Preferential interactions of calcium ions in poly(2-hydroxyethyl methacrylate) hydrogels, Journal of Materials Science: Materials in Medicine, 18, 6, 1141-1149
Abstract: An investigation of the preferential interaction of calcium ions with oxygen atoms in poly(2-hydroxyethyl methacrylate) (PHEMA)-based hydrogels was carried out. The formation of polymer-Ca complexes was achieved by exposing powd. or fully hydrated samples with 5 mM, 0.1-0.5 M, or satd. CaCl2 solns. for certain periods of time. The characteristics of the polymer-Ca complexes were deduced from the effect of the solute on the equil. water content, and from NMR, at. absorption and IR spectroscopies. The absence of significant changes in the NMR chem. shift and IR vibrational wavenumbers for the various functional groups confirmed that polymer complexation with Ca2+ ions involves only weak interactions, possibly electrostatic or ion-dipole interactions. Among the 3 types of oxygen atoms in PHEMA, hydroxyl oxygen atoms seem to be the most sensitive to the presence of Ca2+ ions. Complexation at the ester oxygen atoms was also evidenced by a new band in the IR spectra at 1,550 cm-1. On the other hand, there were no indications that the hydrophobic domains in the backbone and the Me groups at the side chain of PHEMA interact significantly with Ca2+ ions. [on SciFinder (R)]

Zimmerman, Paul A.; van Peski, Chris; Rice, Bryan; Byers, Jeff; Turro, Nicholas J.; Lei, Xuegong; Gejo, Juan Lopez; Liberman, Vladimir; Palmacci, Steve; Rothschild, Mordy; Whittaker, Andrew; Blakey, Idriss; Chen, Lan; Dargaville, Bronwin; Liu, Heping, 2007, Status of high-index materials for generation-three 193nm immersion lithography, Journal of Photopolymer Science and Technology, 20, 5, 643-650
Abstract: Generation-three (Gen-3) immersion lithog. can be an enabler for the 32nm half-pitch node. For Gen-3 lithog. to be successful, however, there must be three major breakthroughs in materials development: high refractive index (\"high-index\") lenses, high-index immersion fluids, and high-index photo-resists. Currently a material for a high-index lens element, lutetium aluminum garnet (LuAG), has been identified. However, suitable materials choices remain elusive for both the Gen-3 fluid and resist. This paper reviews the successes and failures in the search for Gen-3 high-index materials. [on SciFinder (R)]