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Role of double TiO2 layers at the interface of FeSe/SrTiO3 superconductors

Physical Review B 2016年第18期93卷 180506(R)-180506(R)页

作者： Ke Zou Subhasish Mandal Stephen D. Albright Rui Peng Yujia Pu Divine Kumah Claudia Lau Georg H. Simon Omur E. Dagdeviren Xi He Ivan Božović Udo D. Schwarz Eric I. Altman Donglai Feng Fred J. Walker Sohrab Ismail-Beigi Charles H. Ahn Department of Applied Physics Yale University New Haven Connecticut 06520 USA Center for Research on Interface Structures and Phenomena (CRISP) Yale University New Haven Connecticut 06520 USA Department of Physics Yale University New Haven Connecticut 06520 USA State Key Laboratory of Surface Physics Department of Physics and Advanced Materials Laboratory Fudan University Shanghai 200433 China Department of Mechanical Engineering and Materials Science Yale University New Haven Connecticut 06520 USA Condensed Matter Physics and Materials Science Department Brookhaven National Laboratory Upton New York 11973 USA Department of Chemical and Environmental Engineering Yale University New Haven Connecticut 06520 USA

We determine the surface reconstruction of SrTiO3 used to achieve superconducting FeSe films in experiments, which is different from the 1×1TiO2-terminated SrTiO3 assumed by most previous theoretical studies. In particular, we identify the existence of a double TiO2 layer at the FeSe/SrTiO3 interface that plays two important roles. First, it facilitates the epitaxial growth of FeSe. Second, ab initio calculations reveal a strong tendency for electrons to transfer from an oxygen deficient SrTiO3 surface to FeSe when the double TiO2 layer is present. The double layer helps to remove the hole pocket in the FeSe at the Γ point of the Brillouin zone and leads to a band structure characteristic of superconducting samples. The characterization of the interface structure presented here is a key step towards the resolution of many open questions about this superconductor.

关键词： surface reconstruction Superconductors Thin films Angle-resolved photoemission spectroscopy Density functional calculations Low-energy electron diffraction Reflection high-energy electron diffraction

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Photonic Crystals: Light‐Patterned Crystallographic Direction of a Self‐Organized 3D Soft Photonic Crystal (Adv. Mater. 42/2017)

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Advanced Materials 2017年第42期29卷

作者： Zhi‐Gang Zheng Cong‐Long Yuan Wei Hu Hari Krishna Bisoyi Ming‐Jie Tang Zhen Liu Pei‐Zhi Sun Wei‐Qiang Yang Xiao‐Qian Wang Dong Shen Yannian Li Fangfu Ye Yan‐Qing Lu Guoqiang Li Quan Li Department of Physics East China University of Science and Technology Shanghai 200237 China Liquid Crystal Institute and Chemical Physics Interdisciplinary Program Kent State University Kent OH 44242 USA National Laboratory of Solid State Microstructures Collaborative Innovation Center of Advanced Microstructures and College of Engineering and Applied Sciences Nanjing University Nanjing 210093 China Beijing National Laboratory for Condensed Matter Physics and CAS Key Laboratory of Soft Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China Visual and Biomedical Optics Lab Department of Ophthalmology and Visual Science and Department of Electrical and Computer Engineering Ohio State University Columbus OH 43212 USA

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Temperature-dependent isotropic-to-nematic transition of charged nanoplates

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Physical Review E 2014年第2期90卷 020504(R)-020504(R)页

作者： Huawei Li Xuezhen Wang Ying Chen Zhengdong Cheng Soft Matter Center Guangdong Provincial Key Laboratory on Functional Soft Condensed Matter School of Materials and Energy Guangdong University of Technology Guangzhou 510006 China Artie McFerrin Department of Chemical Engineering Texas A&M University College Station Texas 77843-3122 USA Mary Kay O’Connor Process Safety Center Artie McFerrin Department of Chemical Engineering Texas A&M University College Station Texas 77843-3122 USA Department of Materials Science and Engineering Texas A&M University College Station Texas 77843-3003 USA Professional Program in Biotechnology Texas A&M University College Station Texas 77843-3122 USA

Studies of temperature-dependent phase behaviors of discotic colloids are found infrequently in the literature. We establish here the isotropic-to-nematic (I-N) transition phase diagram of charged platelets in the temperature-versus-volume fraction plane. We discover that the N phase can be melted by increasing temperature, and that coexistent samples are more sensitive to polydispersity at higher temperature and higher concentration.

关键词： ISOTROPIC properties PHASE transformations (Physics) DISCOTIC liquid crystals PHASE diagrams POLYDISPERSE media

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Effects of Susceptor Geometry on GaN Growth on Si(111) with a New MOCVD Reactor

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MRS Online Proceedings Library 2011年第1期537卷 1-6页

作者： Yungeng Gao Daniel A. Gulino Ryan Higgins Department of Chemical Engineering and Condensed Matter and Surface Science Program Ohio University Athens USA Condensed Matter and Surface Science Program Ohio University Athens USA

High quality GaN films on AIN buffer layers were grown on Si(111) with a new, commercial, two-injector vertical rotating disk MOCVD reactor (CVD, Inc.). It was found that the geometry of the susceptor greatly affected the structural quality of the epilayers on Si. For the original susceptor geometry, though single crystal GaN films could be obtained, the films were dark gray in appearance with a rough morphology, and the best x-ray rocking curve FWHM was 2.33°. After modifying the susceptor geometry, transparent, mirror-like single crystal GaN films were obtained with the best x-ray rocking curve FWHM being 0.24°. Photoluminescence (PL) and infrared reflectance (IR) spectra of the grown films were compared. The film growth rate was found to increase with decrease of the growth pressure. A 2-D simulation of the flow, heat transfer, and chemical species transport in the reactor showed a more symmetric flow, larger velocity gradient, and lower upward velocity with the modified susceptor, which may be the main reason for the improvement of the structural quality of the films.

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Shear alignment and realignment of sphere-forming and cylinder-forming block-copolymer thin films

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Physical Review E 2010年第1期81卷 011503-011503页

作者： Andrew P. Marencic Douglas H. Adamson Paul M. Chaikin Richard A. Register Department of Chemical Engineering Princeton University Princeton New Jersey 08544 USA Department of Chemistry University of Connecticut Storrs Connecticut 06269 USA Polymer Program Institute of Materials Science University of Connecticut Storrs Connecticut 06269 USA Department of Physics New York University New York New York 10003 USA Center for Soft Condensed Matter Research New York University New York New York 10003 USA

In common with many other structured fluids, block copolymers can be effectively oriented by shear. This susceptibility to shear alignment has previously been shown to hold even in thin films, containing as few as two layers of spherical microdomains, or even a single layer of cylindrical microdomains. A phenomenological model has been proposed [M. W. Wu, R. A. Register, and P. M. Chaikin, Phys. Rev. E 74, 040801(R) (2006)] to describe the alignment of such block-copolymer films, yielding the microdomain lattice order parameter as a function of shearing temperature, stress, and time. Here we directly test the central idea of that model, that the grains which are most misaligned with the shear direction are selectively destroyed, to reform in a direction more closely aligned with the shear. Films are first shear aligned from a polygrain state into a monodomain orientation and are then subjected to a second shear, at a variable stress (σ) and misorientation angle (δθ) relative to the monodomain director, allowing the effects of σ and δθ to be independently and systematically probed. For both cylinder-forming and sphere-forming block copolymers, these experiments confirm the basic premise of the model, as the stress required for realignment increases monotonically as δθ becomes smaller. For a cylinder-forming block copolymer, we find that the characteristic stress σc required to realign cylinders from one monodomain orientation to another is indistinguishable from that required to generate a monodomain orientation from the polygrain state. By contrast, the hexagonal lattice of spheres requires a value of σc more than 3 times as high for reorientation than for generation of the initial monodomain orientation.

关键词： alignment realignment films

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Environmental effect on the fluorescence lifetime and quantum yield of single extended luminescent conjugated polymers

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Journal of Physical Chemistry C 2009年第43期113卷 18681-18688页

作者： Rassamesard, Areefen Huang, Yi-Fang Lee, Hsu-Yang Lim, Tsong-Shin Li, Ming Chung White, Jonathon David Hodak, Jose Hector Osotchan, Tanakorn Peng, K.Y. Chen, S.A. Hsu, Jui-Hung Hayashi, Michitoshi Fann, Wunshain Institute of Atomic and Molecular Sciences Academia Sinica P.O. Box 23-166 Taipei 106 Taiwan Department of Physics Faculty of Science Mahidol University Rama 6 Rd. Bangkok 10400 Thailand Department of Physics Tunghai University Taichung 407 Taiwan Department of Chemistry National Tsing Hua University Hsinchu 30013 Taiwan Molecular Science and Technology Program Taiwan International Graduate Program Academia Sinica Taipei 115 Taiwan Center for Condensed Matter Sciences National Taiwan University Taipei 106 Taiwan Department of Photonics Engineering Yuan Ze University Taoyuan Taiwan ThEP Center Commission of Higher Education 328 Si Ayuthaya Rd Bangkok 10400 Thailand Department of Chemical Engineering National Tsing Hua University Hsinchu 300 Taiwan Department of Materials and Optoelectronic Science National Sun Yat-sen University Kaohsiung Taiwan Institute of Polymer Science and Engineering National Taiwan University Taipei 106 Taiwan Department of Physics National Taiwan University Taipei 106 Taiwan

To investigate the local environment's effect on the lifetime and quantum yield of extended polymer chains in the absence of intra-and interchain aggregation, short, rodlike polymers of poly(2,5-di-n-octyloxy-1,4- phenylenevinylene) (DO-PPV) were dissolved in chloroform and then embedded in a polystyrene matrix. The fluorescence lifetime was found to increase by 45% in moving from the solution to the matrix form. By using the absorption and emission spectra of the chloroform solution to estimate the radiative and nonradiative rate constants for the polymer in solution, along with calculations based on an exciton model, the corresponding decay rate constants for the polymer embedded in the matrix were obtained. The close agreement between the calculated and experimental values of fluorescent lifetime in the matrix proved the applicability of the exciton model used. On the basis of the model, the average quantum yield of isolated polymers in the matrix was calculated to be a factor of 2 higher than in solutionsan effect arising from a 59% decrease in the nonradiative rate constant and, to a smaller extent, from a 20% increase in the radiative decay rate due to the different dielectric constants of the environments. These results suggest that by extending and isolating single luminescent polymers, high quantum yield devices are possible. © 2009 American chemical Society.

关键词： Rate constants

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Effect of Externally-Imposed Radial Strain on the Piezoelectric Response of MOCVD-Grown Gallium Nitride

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MRS Online Proceedings Library 2001年第1期639卷 11581-115811页

作者： Himes, Jennifer A. Willis, James R. Gulino, Daniel A. Department of Chemical Engineering and Condensed Matter and Surface Science Program Ohio University Athens USA

The large piezoelectric constants of GaN suggest possible application of GaN-based materials in piezoelectric sensors, among other areas. GaN’s wide band gap implies that these sensors will fare well over a broad temperature range and/or in a harsh environment. In this work, films of gallium nitride approximately 0.75 micron thick and grown by MOCVD were subject to an externally-imposed radial stress condition. Deposition was performed in a commercial MOCVD reactor (CVD, Inc.) at 1323K using trimethylgallium and ammonia as the chemical precursors. The substrate was one-inch diameter silicon (111). After deposition, titanium dots were deposited in various locations, including the wafer center, by evaporation. Stress was applied to the film/substrate system using a modified micrometer head (Mitutoyo) mounted to an Ionic Systems Basic Stressgauge (model 30285). Stress levels were calculated based on the magnitude of the imposed deflection as read from the micrometer head display, and the piezoelectric response at any particular dot with respect to the center dot was measured by measuring the voltage difference using a digital multimeter (Keithley 175). The micrometer head impinged on the center dot and served as one electrical contact point. Effective piezoelectric coefficients were measured as a function of imposed radial stress. Applied stresses in the range of 1 to 5 GPa resulted in effective piezoelectric coefficients ranging from -0.6 to -2.0 × 10-5 C/m2

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Effects of susceptor geometry on GaN growth on Si(111) with a new MOCVD reactor

Effects of susceptor geometry on GaN growth on Si(111) with ...

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Proceedings of the 1998 MRS Fall Meeting - Symposium on 'GaN and Related Alloys'

作者： Gao, Yungeng Gulino, Daniel A. Higgins, Ryan Department of Chemical Engineering Condensed Matter and Surface Science Program Ohio University Athens OH 45701 United States Condensed Matter and Surface Science Program Ohio University Athens OH 45701 United States

High quality GaN films on AlN buffer layers were grown on Si(111) with a new, commercial, two-injector vertical rotating disk MOCVD reactor (CVD, Inc.). It was found that the geometry of the susceptor greatly affected the structural quality of the epilayers on Si. For the original susceptor geometry, though single crystal GaN films could be obtained, the films were dark gray in appearance with a rough morphology, and the best x-ray rocking curve FWHM was 2.33°. After modifying the susceptor geometry, transparent, mirror-like single crystal GaN films were obtained with the best x-ray rocking curve FWHM being 0.24°. Photoluminescence (PL) and infrared reflectance (IR) spectra of the grown films were compared. The film growth rate was found to increase with decrease of the growth pressure. A 2-D simulation of the flow, heat transfer, and chemical species transport in the reactor showed a more symmetric flow, larger velocity gradient, and lower upward velocity with the modified susceptor, which may be the main reason for the improvement of the structural quality of the films.

关键词： Semiconducting gallium compounds

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Contributory presentations/posters

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Journal of Biosciences 1999年第1期24卷 33-198页

作者： N. Manoj V. R. Srinivas A. Surolia M. Vijayan K. Suguna R. Ravishankar R. Schwarzenbacher K. Zeth Diederichs G. M. Kostner A. Gries P. Laggner R. Prassl Madhusudan Pearl Akamine Nguyen-huu Xuong Susan S. Taylor M. Bidva Sagar K. Saikrishnan S. Roy K. Purnapatre P. Handa U. Varshney B. K. Biswal N. Sukumar J. K. Mohana Rao A. Johnson Vasantha Pattabhi S. Sri Krishna Mira Sastri H. S. Savithri M. R. N. Murthy Bindu Pillai Kannan M. V. Hosur Mukesh Kumar Swati Patwardhan K. K. Kannan B. Padmanabhaa S. Sasaki-Sugio M. Nukaga T. Matsuzaki S. Karthikevan S. Sharma A. K. Sharma M. Paramasivam P. Kumar J. A. Khan S. Yadav A. Srinivasan T. P. Singh S. Gourinath Neelima Alam A. Srintvasan Vikas Chandra Punit Kaur Ch. Betzel S. Ghosh A. K. Bera S. Bhattacharya S. Chakraborty A. K. Pal B. P. Mukhopadhyay I. Dey U. Haldar Asok Baneriee Jozef Sevcik Adriana Solovicova K. Sekar M. Sundaralingam N. Genov Dong-cai Liang Tao Jiang Ji-ping Zhang Wen-rui Chang Wolfgang Jahnke Marcel Blommers S. C. Panchal R. V. Hosur Bindu Pillay Puniti Mathur S. Srivatsun Ratan Mani Joshi N. R. Jaganathan V. S. Chauhan H. S. Atreya S. C. Sahu K. V. R. Chary Girjesh Govil Elisabeth Adjadj Éric Quinjou Nadia Izadi-Pruneyre Yves Blouquit Joël Mispelter Bernadette Heyd Guilhem Lerat Philippe Milnard Michel Desmadreil Y. Lin B. D. Nageswara Rao Vidva Raghunathan Mei H. Chau Prashant Pesais Sudha Srivastava Evans Coutinho Anil Saran Leizl F. Sapico Jayson Gesme Herbert Lijima Raymond Paxton Thamarapu Srikrishnan C. R. Grace G. Nagenagowda A. M. Lynn Sudha M. Cowsik Sarata C. Sahu S. Chauhan A. Bhattacharya G. Govil Anil Kumar Maurizio Pellecchia Erik R. P. Zuiderweg Keiichi Kawano Tomoyasu Aizawa Naoki Fujitani Yoichi Hayakawa Atsushi Ohnishi Tadayasu Ohkubo Yasuhiro Kumaki Kunio Hikichi Katsutoshi Nitta V. Rani Parvathy R. M. Kini Takumi Koshiba Yoshihiro Kobashigawa Min Yao Makoto Demura Astushi Nakagawa Isao Tanaka Kunihiro Kuwajima Jens Linge Seán O. Donoghue Michael Nilges G. Chakshusmathi Girish S. Ratnaparkhi P. K. Madhu R. Varadarajan C. Tetreau Molecular Biophysics Unit Indian Institute of Science Bangalore India Austrian Academy of Sciences Institute of Biophysics and X-ray Structure Research Graz Austria Faculty of Biology University of Konstanz Germany Institute of Medical Biochemistry University of Graz Austria Howard Huges Medical Institute Department of Chemistry & Biochemistry University of California La Jolla USA Department of Chemistry & Biochemistry University of California San Diego La Jolla USA Molecular Biophysics Unit India Department of Microbiology &Cell Biology Indian Institute of Science Bangalore India Macromolecular Structure Laboratory NCI - Frederick Cancer Research and Development Center ABL - Basic Research Program Frederick USA Department of Crystallography and Biophysics University of Madras Chennai Biochemistry Department Indian Institute of Science Bangalore India Condensed Matter Physics Division B.A.R.C. Trombay Mumbai Condensed Matter Physics Division Bhabha Atomic Research Centre Trombay Mumbai IMCB The University of Tokyo Tokyo Japan Mitsubishi Chemical Corporation Yokohama Research Center Yokohama Japan Faculty of Pharmaceutical Sciences Chiba University Chiba Japan Department of Biophysics All India Institute of Medical Sciences New Delhi India Department of Biophysics All India Institute of Medical sciences New Delhi India Institüt Physiologische Chemie Hamburg Germany Biophysics Department Bose Institute Calcutta India Slovak Academy of Sciences Institute of Molecular Biology Bratislava Slovakia Indian Institute of Science Bioinformatics Centre Bangalore Departments of Chemistry and Biochemistry Biological Macromolecular Structure Center USA Bulgarian Academy of Sciences Institute of Organic Chemistry Sofia Bulgaria Chinese Academy of Sciences Institute of Biophysics Beijing China Novartis Pharma AG Preclinical Research Basel Switzerland Department of Chemical Sciences Tata Institute of Fundamental Research Mumbai India Solid State Physics Div

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Aluminum Oxide Films for Thermo-Oxidative Protection of Polyimide-Based Composites

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MRS Online Proceedings Library 1993年第1期305卷 191-196页

作者： Larry M. Miller Daniel A. Gulino Department of Chemical Engineering and Condensed Matter and Surface Science Program Ohio University Athens Greece

Polyimide-based composites offer one of the best opportunities to bring the advantages of high modulus-to-density ratio materials to higher temperature applications, such as jet engines. In the present work, thin films (1000 – 2000Å) of aluminum oxide have been deposited by plasma-enhanced chemical vapor deposition from aluminum tri- isopropoxide precursor on polyimide composite substrates. The films were characterized for stoichiometry, thickness uniformity, and adhesion, and their effectiveness in the prevention of thermo-oxidative degradation of the composite at temperatures up to 371 °C has been examined and compared to that provided by other thin film materials. These preliminary results indicate that Al2O3 is not as successful as SiO2 at preventing oxidative degradation, although significant variability in the quality of the polyimide composite substrate makes precise comparison difficult.

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