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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 7306-7312 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Molecular stacking structures in epitaxial crystals of oxotitanium and oxovanadium phthalocyanines (TiOPc and VOPc) prepared by physical vapor deposition (PVD) and molecular beam epitaxy (MBE), respectively, onto the (001) face of a KBr substrate were investigated by means of x-ray and electron diffraction studies. In thin epitaxial film of VOPc deposited by MBE at a substrate temperature of 20 °C, the flat-lying molecules oriented in the (3×3) commensurate square lattice (a=1.40 nm) were alternately stacked with body-centered head-to-head and a/4-slipped face-to-face dimeric bilayers. The crystal structure determined was the triclinic space group P1¯ with a=b=1.40, c=1.06 nm, α=109.2, β=133.9, γ=90.0°, Z=2. When TiOPc was thickly deposited by PVD at a substrate temperature of 200 °C, islandlike crystals epitaxially grew in a truncated pyramidal morphology and assumed the same orientation. In the pyramidal crystals the thick molecular layer stacking separate from the KBr surface was relaxed and had a square lattice with a shorter constant (a=1.33 nm). The three-dimensional stacking structure explained the observed grain boundary formation and asymmetric pyramidal morphology. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4990-4996 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxial growth of C60 was found in vapor-deposited crystals on the KI (001) cleavage surface. C60 molecules deposited on the KI surface, which was preheated at 400 °C, then kept at 195 °C during deposition, crystallized in the face-centered cubic form with two types of morphologies. Truncated pyramidal crystals epitaxially grew along the KI 〈110〉 directions, taking its C60 (001) face parallel to the KI (001) surface. This epitaxial nucleation occurred at a corner of the crossing steps along the KI 〈100〉 directions which were caused by thermal etching of the KI surface. Molecular mechanics and dynamics calculations revealed that a three-dimensional (2×2) commensurate lattice matching between the C60 {100} planes and the KI {100} faces at the step corner attributed to the epitaxial nucleation of the pyramidal crystal, in spite of the lower stability of the monolayer interaction of the C60 (001) face with the KI (001) surface. On the other hand, platelike crystals grew, with the C60 (111) face parallel to the KI (001) surface. A stable monolayer nucleation of the close-packed C60 (111) face made this two-dimensional growth of the platelike crystals possible to occur on the (001) terrace of the etched KI surface. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2061-2068 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Structure dependence of electrical properties was investigated for amorphous and epitaxial thin films of chloroaluminumphthalocyanine vacuum deposited on both glass and KCl. The extrinsic conductivity in the dark was improved by elevating substrate temperatures, depending on the morphological change from granular, discontinuous films deposited at a substrate temperature of 25 °C to uniform, continuous ones at 250 °C. The photocurrents under monochromatic light illumination increased in proportion to the amount of adsorbed O2 in the amorphous films on glass. A regular doping form of O2 in the epitaxial film on KCl could enhance photocarrier generation. The granular, discontinuous morphology in the films caused a frequent charge-carrier recombination at the grain boundaries and defect sites. In the intrinsic region the amorphous films exhibited a higher dark conductivity due to the π-electron interaction between the randomly arranged molecules and gave a moderate activation energy for conduction. The epitaxial film with a regular orientation exhibited a significantly higher activation energy for intrinsic dark conduction because of a weak molecular interaction between the standing molecular columns.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 3812-3819 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxial thin films of naphthalocyanines (Nc's) were prepared on the (001) surface of alkali halide (AX) by a vacuum-deposition technique. Two types of molecular stacking and orientation were found depending on the molecular structure. Metal-free Nc(H2Nc) and divalent zinc Nc(ZnNc) took the face-to-face, eclipsed stacking, P orientation, in which their molecular planes came into a parallel contact to the substrate surface. Trivalent chloroaluminum Nc(AlNcCl) and fluorogallium Nc(GaNcF), and tetravalent vanadyl Nc(VONc) took the eclipsed, slipped stacking, I orientation, holding their molecular planes slightly inclined to the substrate surface. In the latter orientation an unexpected face-to-face stacking caused a stacking defect structure. The tetragonal lattice of the Nc crystals demonstrated five types of commensurate matchings to the ionic lattice of AX, depending on the lattice parameters of the Nc and AX crystals. On NaCl unidirectional AX(001)(4×4)R+45°-Nc was a predominant orientation, and on KCl and KBr bidirectional AX(001)((square root of)10 ×(square root of)10)R±26.5°-Nc was mainly found.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5146-5153 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Zinc 2,3-naphthalocyanine (ZnNc) was vacuum evaporated onto glass, NaCl, and highly oriented pyrolytic graphite (HOPG) substrates, and the molecular orientation was investigated by x-ray-diffraction, Fourier-transform-infrared–reflection-absorption spectroscopy, electronic spectroscopy, transmission electron microscopy, and scanning electron microscopy observations. Three types of molecular orientations were assigned for the deposited thin films depending on the different substrates kept at 250 °C. ZnNc molecules deposited on glass formed columnar crystals taking N orientation, in which molecular planes oriented perpendicularly to the substrate surface. Unidirectional epitaxic growth was observed in the film deposited on NaCl. ZnNc molecules seemed to be stacked in parallel having P orientation, where the molecular planes were parallel to the NaCl(001) surface. The ZnNc square lattice made an angle of 45° to the NaCl[100] direction (4×4-type orientation). The film deposited on HOPG exhibited I orientation, in which ZnNc molecular planes were inclined to the HOPG basal plane. The tilting molecules stacked in the direction normal to the surface. These different orientations in ZnNc thin films resulted in significant electronic spectral change in the longer-wavelength region.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 568-576 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Photovoltaic solar cells were constructed by successive vacuum deposition of chloroaluminum phthalocyanine (AlPcCl) and Au on a single-crystal n-Si wafer. By controlling the thickness and morphology of the AlPcCl deposits in the Au/AlPcCl/n-Si cells, an improved photovoltaic efficiency was obtained as compared to the Au/n-Si Schottky-type cell. The cell with a homogeneous, ultrathin (10 nm thickness) AlPcCl film, which was prepared by deposition on an n-Si substrate kept at −20 °C, exhibited a high photovoltage (Voc=0.45 V) and strongly sensitized photocurrents in the Q-band absorption region (600–800 nm) of AlPcCl chromophore. This improved photoresponse was attributed to a space-charge layer generated inside the AlPcCl film, where the intervening AlPcCl layer prevented the n-Si surface from forming surface states because of noncontact with the Au top electrode. When discontinuous island crystallites of AlPcCl were formed on the n-Si surface kept at 200 °C, the Au/AlPcCl/n-Si cell also exhibited an improved efficiency with a high photovoltage (Voc=0.42 V).The discontinuous AlPcCl coverage, providing both the Au/n-Si Schottky contact and AlPcCl/n-Si heterojunction, modulated a diffusion potential at the space-charge region to give rise to a steep barrier gradient at the edges of the AlPcCl island. Its high photovoltaic response was attributed to an efficient charge-carrier separation from excitons that were generated on the uncoated n-Si area and diffused at the AlPcCl-island edge.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 1355-1357 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: In view of practical handling of single-walled carbon nanotubes (SWNTs), here we present cutting procedures and spontaneous ordering of SWNTs deposited on highly oriented pyrolytic graphite (HOPG). Purified SWNTs were cut by ultrasonication in H2SO4/HNO3 mixture and further in de-ionized water. Thus, prepared short SWNTs were resuspended in methanol and dropped on a freshly cleaved HOPG surface. Scanning tunneling microscopy under a vacuum revealed that the short tubes of 20–100 nm in length were aligned along the basal axis of the HOPG lattice. Tunneling spectroscopy obtained from the oriented tubes indicated a semiconducting behavior, which was characterized in relation to their helical structure. The observed orientation of SWNTs was attributed to their one-dimensional electronic nature along the tube axis with the HOPG lattice. © 2001 American Institute of Physics.
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  • 8
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 73 (1998), S. 563-565 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxial structuring of blue light-emitting molecules, p-phenylene oligomers (p-nP, n=3,4,5,6), was investigated in thin crystals vapor deposited on the (001) surface of a KCl single crystal. Their molecular orientation and morphology changed depending on the molecular length and substrate temperatures during deposition. As the length of p-nP was longer and the substrate temperature was lower, the orientation of the molecular axis changed from standing to lying on the KCl surface due to an increase of molecule–substrate interactions. p-terphenyl (3P) hardly adsorbed on the KCl (001) surface, but a portion of the standing molecules stuck along the step edge of KCl and formed a walllike structure. Long needlelike crystals of p-hexaphenyl (6P) epitaxially grew in two orthogonal KCl [110] directions taking lying orientation even at a higher substrate temperature. In these epitaxial needles, the transition dipoles parallel to the molecular axis gave rise to blue fluorescence sharply polarized along the KCl [110] directions. © 1998 American Institute of Physics.
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  • 9
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 76 (2000), S. 3406-3408 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Epitaxially oriented crystals of a π-conjugating blue light-emitting molecule, 1,4-bis[2-(5phenyloxazolyl)]benzene (POPOP), were prepared by vapor deposition onto the KCl (001) surface. Rodlike crystals with submillimeter length grew along the KCl 〈110〉 directions having the (102) plane of the monoclinic cell contact with the KCl surface. The POPOP molecules were aligned parallel on this plane taking the herringbone structure. Due to this orientation, the electronic transition dipoles between the frontier molecular orbitals were all lying, so that the fluorescence emitted from the crystals under ultraviolet excitation was highly polarized in parallel to the substrate surface. This polarized emission with the transverse-electric mode was partly confined within the crystals and self-waveguided along their rod axes. © 2000 American Institute of Physics.
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  • 10
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 187-189 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Highly polarized and self-waveguided blue light emission was observed in oriented organic crystals of p-sexiphenyl (6P). The 6P molecules were epitaxially grown in needlelike crystals with a submillimeter length by mask-shadowing vapor deposition on the KCl (001) surface. In the crystals, the molecular axes are oriented parallel to the [110] direction of the KCl substrate and perpendicular to the needle axis of the crystal. Under ultraviolet excitation, the blue light emission was confined within the crystal and self-waveguided along the needle axis with the transverse-electric mode, then radiated from the tips of the needles. This self-waveguided emission in the crystal was based on the uniaxially oriented transition dipoles which lay on the KCl surface and were aligned perpendicular to the needle axis in the crystal. © 1999 American Institute of Physics.
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