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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 4496-4500 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 11005-11010 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a comparative study of the photoinduced localized atomic reaction, LAR, of 1,2- and 1,4-dichlorobenzene (1,2- and 1,4-diClPh) on Si(111) 7×7, studied by scanning tunneling microscopy (STM). We observe different chlorine nearest-neighbor separations for the Cl–Si photoformed chemical "imprints" for the two adsorbates; the most probable separation of neighboring Cl's in the case of 1,2-dichlorobenzene being 8±3 Å, whereas that for 1,4-dichlorobenzene is 14±3 Å. These differing separations can be understood if the two C–Cl bonds in the respective adsorbates extend roughly linearly to chlorinate a nearby Si dangling-bond; for 1,2 diClPh the two C–Cl bonds are at 60° to one another leading to the chlorination of closely neighboring Si, whereas for 1,4 diClPh the two C–Cl bonds are at ∼180° leading to chlorination of sites twice as far apart, located to either side of the 1,4 diClPh adsorbate. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 17 (1984), S. 2756-2761 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 9905-9907 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron-induced reaction of chlorobenzene (ClPh) adsorbed on silicon [Si(111)7×7] is shown by scanning tunneling microscopy (STM) to result in "localized atomic reaction" (LAR), imprinting Cl as chemically-bound Cl–Si on the surface. Voltage pulses of −4 V from the STM tip give LAR restricted to the site of electron impact. Delocalized electron impact imprints the self-assembled pattern of ClPh(ad) on the surface as Cl–Si. The imprint is found to be on the same area of the unit cell as ClPh(ad), but at adjacent atomic sites. The occurrence of LAR is ascribed to a concerted reaction; this can only occur if the new bond (Cl–Si) is directly adjacent to the old one (Cl–Ph). © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 106 (1997), S. 6552-6563 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present dynamical studies of the surface photochemistry of dimethylcadmium (DMCd) adsorbed on GaAs(110) and CdTe(110) surfaces. This important precursor for chemical vapor deposition is studied using time-of-flight (TOF) spectroscopy in conjunction with temperature programmed desorption (TPD). For the case of greater than one monolayer coverages, on these surfaces, both photofragmentation and photodesorption are observed following irradiation. The relative probabilities of these two processes are found to be strongly dependent on adsorbate coverage and incident photon energy. Direct photoabsorption by the adsorbed molecule is found to dominate the photofragmentation process, with the substrate strongly reducing the probability of photofragmentation at low coverages due to the operation of substrate mediated channels for excited state relaxation. The CH3 fragments observed following photodissociation are found to have kinetic energies that are invariant with the energy of the exciting photon (193 and 248 nm), an effect attributed to an efficient curve crossing between excited states in this molecule. The molecular desorption process is found to exhibit an unusual coverage dependence which is linked to the probability of deposition of a significant amount of vibrational excitation in the overlayer via substrate mediated de-excitation processes. Following the adsorption of one monolayer on the GaAs substrate, the photochemistry observed is significantly different due to the thermal dissociation of DMCd to form adsorbed methylgallium moieties. In this case, multiple features are observed in the TOF spectrum with kinetic energies significantly different to those observed for the gas phase or physisorbed molecule. Correlation of the TOF spectral features with thermal desorption data allows these TOF features to be assigned to specific adsorbed intermediates. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular 1078 (1991), S. 411-417 
    ISSN: 0167-4838
    Keywords: 2-Arylpropionyl-CoA epimerase ; Ibuprofen isomerization ; Stereoselective drug metabolism
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 1500-1508 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Novolak resins provide the best overall performance for “g” and “i”-line photoresists. There is a continuing need for advanced novolak designs that will provide improved lithographic, thermal, and etch characteristics that may be reproducibly synthesized. A novolak synthesis process was developed using the solution condensation technique. Cresol mixtures with m-cresol and 3,5-xylenol at specific ratios provide reproducible novolaks with controlled molecular weights. In order to achieve high thermal and etch performance, while retaining photospeed and resolution characteristics, three basic approaches were investigated: (1) increase in molecular weight, which produces novolaks with Tg ranging from 120 to 130°C with relatively slow dissolution rates; (2) incorporation of multi-hydroxyphenols such as resorcinol to tailor the dissolution rate, resolution, thermal, etch, and adhesion characteristics; (3) partial esterification of multi-hydroxy novolaks giving a Tg range of 140 to 150°C. Lithographic evaluation of the novolak resins was performed by formulating with a 2,1,4-diazonaphthoquinone (DNQ) sensitizer. Results on resin synthesis, molecular weights, lithographic, thermal, and etch characteristics are discussed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 5 (1994), S. 28-40 
    ISSN: 1042-7147
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The synthesis and lithographic characterization of the three positional isomers of polyhydroxystyrene is described. Large differences in dissolution rates are found as a function of the position of the hydroxy group, which are explained in terms of intra- vs. intermolecular hydrogen bonding and steric shielding of the hydroxy group by the polymer backbone. In plots of log (dissolution rate) vs. developer strength, linear plots are observed for the 2- and 4-isomers, while for poly(3-hydroxystyrene), a break occurs in the plot, leading to two linear regions. While the 2-hydroxy isomer is too slow and the 4-hydroxy isomer too fast for use in conventional dissolution inhibition systems, the copolymerization of both allows any dissolution rate between these extremes to be chosen ( “dial a dissolution rate” copolymers). Determination of the copolymerization parameters of the corresponding 4- and 2-acetoxystyrene precursors by the method of Kelen and Tüdös shows the polymerization to be nearly ideal and azeotropic (r1 = 0.76, r2 = 0.94). Analysis of the dissolution rates as a function of developer strength according to the Huang-Reiser-Kwei equation shows that the critical concentrations c* are a linear function of copolymer composition, whereas the penetration exponents in show a minimum near unity in the region of the 1 : 1 copolymer, down from the values of 3.2-3.3 observed for all three homopolymers. The 1 : 1 copolymer shows a dissolution rate comparable to novolak resins, and when formulated into a photoresist together with a diazonaphthoquinone sensitizer resolved 0.4μm features at a dose of 340 mJ/cm2. The thermal flow resistance of the resist was found to be improved over that of novolak resists although not to the degree expected from the increased Tg of the 1:1 copolymer.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 22 (1984), S. 213-223 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The effect of parasubstituents on the radiation chemistry of poly(α-methylstyrene) (PMS) was compared for the fluoro (PFMS), chloro (PCMS), bromo (PBMS), isopropyl (PiPMS), and methoxy (PMeOM) derivatives. Radiolysis yields, ESR spectra, and GC—MS analysis of products were obtained. PMS and PFMS have similar low radiolysis yields, products, and product distributions. Only main-chain radicals which persist to 200° were observed. PCMS has increased values of Gs, Gx, and Gr. The product analysis results suggest that the presence of chlorine contributes to the primary process by dissociative electron capture and enhances the cleavage of α-methyl group. Irradiation of PBMS caused crosslinking and yielded few volatile products. PMeOMS and PiPMS gel readily by γ-irradiation and may be useful as negative radiation resists.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 22 (1984), S. 195-211 
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Homopolymers of 2,2,2-trifluoroethyl(methacrylate) (TFEMA) and 2,2,2-trichloroethyl-(methacrylate) (TCEMA) and copolymers with methyl-α-chloroacrylate (MCA) in a range of compositions were synthesized. The reactivity ratios were obtained; the two copolymerizations were close to ideal. Poly(MCA) showed Gs = 7.4 and Gs = 0.9 by γ-radiolysis. On the other hand, poly(TFEMA) and poly(TCEMA) and Gs values of 2.0 and 2.4, respectively, and Gx = 0. Radiolysis of copolymers was initiated to a large degree by dissociative electron capture by the halogen atoms in both comonomers, as revealed by the ESR spectra of radicals derived from them. Germinal recombinations in irradiated poly(TFEMA) suggested the presence of radicals in proximity. This process was absent in the copolymers. GC-MS analysis of volatile products and other supporting evidence showed that TFEMA monomers tended to depolymerize; the TCEMA monomers did not. The radiolysis yields varied monotonically with the comonomer composition for the MCA-TFEMA system but the yield-composition relationship was irregular in MCA-TCEMA copolymers. Four noncrosslinking systems are potential radiation resists arranged in increasing order of promise: poly(TFEMA) (Gs = 2.0, Tg = 70°); poly(TCEMA) (Gs = 2.7, Tg = 142°); poly(94MCA-co-6TCEMA) (Gs = 2.7, Tg = 142°); and poly(68MCA-co-32TFEMA) (Gs = 3.0, Tg = 112°). These materials merit further investigation for E-beam or x-ray lithographic applications. Mechanisms of radiolysis for these materials, based on ESR, GC-MS, and radiolysis yield data, were discussed.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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