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G. KAUPP
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ABSTRACT: The application of atomic force microscopy (AFM) to photodimerization of crystalline chalcones provides new insights into the detailed mechanisms of solid-state reactions on the molecular level. Well-directed long-range transport phenomena are found which reach far beyond the crystal lattice distances. Reactions occur in the surface region where the light is absorbed. Characteristic features are built up that depend on crystal structure and crystal face. This could not be foreseen by previous theories based solely on a topochemical postulate/principle. There is now a much more intimate correlation of crystal structure with solid-state reactivity and this is directly studied and proven experimentally by AFM. Even solid-state reactions which are in opposition to topochemistry can be studied and understood on a molecular basis. The three-dimensional resolution of undisturbed insulating surfaces which is obtained by AFM is not available by any other technique.
Journal of Microscopy 08/2011; 174(1):15 - 22. · 1.63 Impact Factor
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Journal of Materials Chemistry. 01/2011; 21(23):8389-8390.
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Wood Material Science and Engineering. 01/2011; 6(3):140-146.
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ABSTRACT: The analysis of published loading curves reveals the exponent 3/2 to the depth for nanoindentations with sharp pyramidal or conical tips. This has geometric reasons, as it occurs independent on the bonding states and indentation mechanisms. Nevertheless, most mathematical deductions and finite element simulations of nanomechanical parameters in the literature continue using the experimentally not supported Hertzian exponent 2. Therefore, numerous published loading curves of various authors are plotted using the experimental exponent 3/2 to present unbiased proof for its generality with metals, oxides, semiconductors, biomaterials, polymers, and organics. Linearity is independent of equipment and valid for load controlled, or depth controlled, or continuous stiffness, or AFM force measurements. The linearity with exponent 3/2 often extends from the nano- into the microindentation ranges. The tip rounding and taper influence of the "geometrical similar" indenters are discussed. When kinks occur in such linear plots through the origin, these indicate change of the materials' mechanical properties under pressure by phase transition. These events are discussed for nanoindentations with respect to the known hydrostatic transformation pressures that are, of course, always higher than the necessary indentation mean pressure. Numerous Raman, as well as X-ray and electron diffraction results from the literature support the phase transitions that are now easily detected. Nanoporous materials first fill the pores upon indentation. Published loading curves exhibit more information than hitherto assumed.
Scanning 10/2010; 32(5):265-81. · 1.07 Impact Factor
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Scanning. 01/2010; 32:265-281.
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ChemSusChem. 01/2009; 2:248-254.
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ChemSusChem. 01/2009; 2:83-88.
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European Journal of Organic Chemistry. 01/2009;
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Macromolecular Symposia. 01/2008; 274:72-80.
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International Journal of Materials Research. 01/2007; 98:438-445.
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Zeitschrift fuer Metallkunde/Materials Research and Advanced Techniques. 01/2005; 96:1226-1236.
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Metall. 01/2005; 59:293-296.
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CrystEngComm. 01/2005; 7:402-410.
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ABSTRACT: Thin films of protonated meso-tetraphenylporphine were studied by IR spectroscopy and contact atomic force microscopy. Thin films of protonated porphine were shown to contain large amount of bound water, the most of which, however, can be removed by hygroscopic CsI. All water bands of the IR spectrum of a thin film are similar to those of liquid water including the broad band at 2000–2400 cm1. The changes in the doublet at 1440 and 1473 cm–1 characteristic of the IR spectrum of tetraphenylporphine pressed with KBr tablet indicate the donor–acceptor interaction between its molecules in thin films. Spherical nanoparticles with a diameter of 30–80 nm, as well as larger nanoparticles with different plasticity of water–porphine core, were detected using atomic force microscope. These particles are formed in a solution and shape a peculiar relief of thin films upon their sticking and sedimentation; this relief is represented by the isolated nanoparticles, submicroscopic grains, and microscopic domains.
Colloid Journal 01/2004; 66(4):489-494. · 0.71 Impact Factor
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Zeitschrift fuer Metallkunde/Materials Research and Advanced Techniques. 01/2004; 95:297-305.
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CrystEngComm. 01/2003; 5:474-479.
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Journal of Physical Organic Chemistry. 01/2003; 16:905-912.
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Tetrahedron. 01/2003; 59:3753-3760.
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Chemistry - A European Journal. 01/2003; 9:4156-4160.
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ABSTRACT: The thermal isomerizations of meso- and rac-3,4-dibromo-1,6-diphenyl-1,6-bis(p-tolyl)-1,2,4,5-hexatetraene (1) to give stereospecifically the 3,4-bis(phenyl-p-tolylmethylene)-1,2-dibromocyclobutenes 3 and 5 + 6 were studied in the solid state using atomic force microscopy (AFM) and interpreted on the basis of known crystal structural data. These isomerizations run to completion in the bulk and include highly space-demanding internal rotations around the central bond. Far-reaching anisotropic molecular movements are detected on the major faces that align the surface features along cleavage planes in the initial phase rebuilding stage. Only one of three identified cleavage planes of meso-1 is successful, owing to closer interactions of the bromine substituents in the non-used cleavage planes. Thus, very fine details can be correlated and predicted for the occurrence of internal rotations and molecular movements in the crystal lattice. The second stage in these intramolecular isomerizations, the phase transformation, produces very high features up to 100 nm and still parallel to the preferred cleavage plane of meso-1 but in the µm range without relation to the initial crystal structure in the case of rac-1. Copyright © 2002 John Wiley & Sons, Ltd.
Journal of Physical Organic Chemistry 01/2002; 15(3):148 - 153. · 1.96 Impact Factor
