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  • American Institute of Physics (AIP)  (69)
  • Molecular Diversity Preservation International  (34)
  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10895-10902 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: Using symplectic integrator schemes, we calculate the classical trajectory of a Rydberg electron in external electric and magnetic fields. We also solve the equation of motion obtained by taking the mean values over one revolution of the electron in the undisturbed motion. The resulting secular motion is periodic. When only an electric field F is applied, as long as the modulation period in the orbital angular momentum l is longer than the revolution period, the motion agrees with the secular one and the duration for which l is much larger than its low initial value is stretched. The residence time (RT), namely, the probability of finding the electron at the distance r, is hence smaller than that at F=0. In crossed electric and magnetic fields, the secular motion predicts that an additional time stretching due to a magnetic field occurs up to the critical value of magnetic field strength, Bc=33nF (n is the principal action). In the actual simulations, the RT near the core is smaller than that at B=0 even beyond Bc, regardless of the magnitude of the non-Coulombic interaction C2/r2. Slow modulations in l are generated by transitions to secular motions that maintain high l, in addition to the fast modulation originating from the secular motion. When the magnetic field is so strong as to induce chaotic motion (∼4000 G for the energy of −5 cm−1), the RT is one order of magnitude as large as those in weak field cases around 40 G. In the intermediate region (〉 a few hundred Gauss), without a non-Coulombic interaction, the RT monotonically increases as B increases. In the presence of C2/r2, transitions from low l states to high l states occur: the RT decreases. The motions in high l states can be explained by the well-known model in which an electron bound to the core by a harmonic force moves in a magnetic field. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 7707-7716 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The state-selected differential cross section (DCS) and rotational angular momentum polarization for the reaction O(1D)+H2O→OH+OH have been measured by utilizing the polarized Doppler-resolved laser-induced fluorescence probing technique. Stereodynamics of the reaction channel forming the newly formed OH in the specific vibrational level v′=2 is discussed on the basis of the vector properties. A nearly isotropic DCS for the product OH(2Π3/2, v′=2, j′=5.5) most probably indicates that the reaction is dominated by an insertion mechanism involving a collisional HOOH complex with a lifetime comparable to its rotational period. The extremely asymmetrical energy partitioning between the two OH fragments, therefore, suggests that the redistribution of the available energy does not occur on a time scale comparable to the rotational period of the complex. Furthermore, it has been found that the product rotational angular momentum vector j′ is predominantly perpendicular to the collision plane spanned by k and k′ (the relative velocity vectors of the reactants and products, respectively) both for the forward- and backward-scattered products. It suggests that the initially excited bending motion of the H–O–O moiety in the collisional HOOH complex primarily contributes to the product rotation. © 1999 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 80 (1996), S. 3804-3807 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We observe the formation of an ordered structure in Si1−xGex films grown on Ge(100) substrates, as well as on Si(100) substrates, by molecular beam epitaxy. The structural characterization of these ordered films is performed. The degree of order in the films is quantitatively measured using x-ray diffraction. The dependence of the degree of order on Ge composition is similar between films on Ge(100) and Si(100) substrates. By careful x-ray diffraction analysis, we find that the degree of order is not equivalent in variants. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 3805-3811 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Control of the orientation of (Ca,Sr)CuO2 films with (001) and (101) texture on glass substrates, and (110) and (101) texture on (001) MgO substrates was obtained by changing the sputtering conditions. Although (110) and (101) films on (001) MgO substrates were epitaxial, they showed a double positioning and fourfold rotation symmetry structure. Calculations using the cohesive energy between the film and the MgO single crystal substrate were used to confirm the epitaxial relationships between the film and the MgO substrate. The reason for the change in the texture of the films as a function of the substrate is also discussed. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 7084-7088 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have proposed ReMnO3 (Re: rare earth) thin films for nonvolatile memory devices. We examine the growth mechanism of YMnO3 films on (0001)ZnO:Al/(0001) sapphire substrate using rf magnetron sputtering and pulsed laser deposition methods with oxide compound target. We have succeeded in obtaining (0001) epitaxial YMnO3 films on (111) MgO and (0001)ZnO:Al/(0001) sapphire substrate, and polycrystalline films on (111)Pt/(111)MgO. For an optimal structure, the film needed much less oxygen from the gas phase compared to other oxide films. The composition (Y/Mn ratio) of the YMnO3 films changed drastically by varying the partial oxygen pressure in the sputtering gas. In addition the Y/Mn ratio slinfled with sputter time due to target surface modification, probably caused by Y segregation. An extremely small amount of oxygen is required to form the YMnO3 crystal. This was confirmed by pulsed laser deposition experiments. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 472-477 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We investigated the initial stage of native oxide growth on an atomically flat hydrogen terminated silicon (Si) (111) surface by immersion in pure water using Fourier transformed infrared attenuated total reflection spectroscopy and reflection absorption spectroscopy. There is a sharp absorption peak at 2083 cm−1 arising from silicon monohydrides at surface terraces, this peak decreases and broadens with immersion time and seems to separate into two components. This broadening is considered to reflect the progress of very early native oxide growth. The experiment on a vicinal Si(111) surface showed that the absorption peaks arising from monohydrides at the terraces and at the steps on the surface decrease at approximately the same rate with immersion time. This indicates that the native oxide growth arises in spite of terraces and steps on the silicon surface. Furthermore, the large amount of silicon-hydrogen (Si–H) bonds not related with oxygen atoms suggests that the native oxide growth mechanism is not layer-by-layer oxidation. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 2169-2176 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It is argued that epitaxial films of ionically bonded materials are more easily achieved than those of covalently bonded materials. Good epitaxy can be achieved despite a relatively large lattice mismatch with the substrate. However, a strong influence of interfacial energy can result in difficulty in controlling the orientation of epitaxial films. The crystallographic orientation of ionically bonded LiNbO3 films was therefore studied. Growth orientation was controlled by paying attention to the sharing between octahedra in the structure and to the formation of the octahedra containing lithium and niobium ions. The orientation of the film on R-cut (011¯2) sapphire changed from (011¯2) to (101¯0) via (112¯0) by increasing the Li concentration in the film. Lithium concentration could be increased by increasing the rf power, O2 partial pressure and total gas pressure, and decreasing the substrate temperature during sputtering deposition. The (011¯2) and (101¯0) films were epitaxial with respect to the substrate. The (101¯0) epitaxial film, in particular, was of excellent quality. Detailed studies on the crystallinity and the formation mechanism of LiNbO3 film with a new epitaxial orientation (101¯0) on (011¯2) sapphire was performed. Based on the degree of freedom in sharing of octahedra containing Li and Nb, sufficient Li concentration and effects of the interfacial restriction are considered to promote the formation of the (101¯0) epitaxial film. If deposition is performed under the conditions by which (101¯0) epitaxial film is formed, excellent epitaxial film can be formed because the interface between (101¯0) LiNbO3 and (011¯2) sapphire has a larger cohesive energy.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 592-599 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: We have measured the product state-selected differential cross-section (DCS), and the rotational angular momentum polarization, together with the energy distributions for the reaction O(1D)+N2O→NO+NO by utilizing Doppler-resolved polarization spectroscopy. The reaction dynamics of the vibrational channel forming the product NO(v′=0) is discussed based on both the scalar and vector properties. The product rotational and center-of-mass translational energy distributions are described as Boltzmann distributions with Trot(approximate)10 000 K and Ttr(approximate)13 000 K, respectively. These energy distributions are close to statistical predictions. The product DCS has substantial intensities over the whole angular range with a slight preference for backward scattering. The product rotational angular momentum vector j′ does not have a noticeable angular correlation with either k or k′ (the relative velocity vectors of the reactant and product, respectively). This nearly isotropic angular distribution of j′ indicates that both in-plane and out-of-plane motions of the collisional ONNO complex contribute to the product rotation to almost the same degree. Considering that this reaction has no potential well deep enough for the formation of a long-lived complex, these nearly statistical scalar and isotropic vector properties suggest that the energy redistribution among the internal modes of the collisional ONNO complex efficiently takes place. It implies that there are strong couplings among the internal modes. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 9318-9331 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: A new approach to locally design a control pulse is proposed. This locally optimized control pulse is explicitly derived, starting with optimal control formalism, and satisfies the necessary condition for a solution to the optimal control problem. Our method requires a known function, g(t), a priori, which gives one of the possible paths within the functional space of the objective functional. A special choice of g(t)≡0 reduces the expression of the control pulse to that derived by Kosloff et al. For numerical application, we restrict ourselves to this special case; however, by combining an appropriate choice of the target operator together with the backward time-propagation technique, we apply the local control method to population inversion and to wave packet shaping. As an illustrative example, we adopt a two-electronic-surface model with displaced harmonic potentials and that with displaced Morse potentials. It is shown that our scheme successfully controls the wave packet dynamics and that it can be a convenient alternative to the optimal control method for wave packet shaping. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8338-8346 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: State-selected differential cross sections (DCSs) have been measured for the OH radicals produced from the reactions of O(3P) with saturated hydrocarbons by utilizing Doppler-resolved polarization spectroscopy. Stereodynamics in the reactions of secondary (c-C6H12) and tertiary (i-C4H10) hydrogen atoms are discussed based on the dependences of the DCSs on the collision energy and the structure of these hydrocarbons. For the c-C6H12 reaction, the DCS of the OH(2Π3/2,v′=1,j′=3.5,A′) shows predominant intensities in the backward hemisphere with reference to the incident O(3P) atom at a mean collision energy of 〈Ecoll〉=12 kJ/mol. When the collision energy is raised to 〈Ecoll〉=33 kJ/mol, the OH radicals scattered in the forward hemisphere grow almost to match those in the backward hemisphere. The observed increase in the forward scattering implies that the collision energy makes the large impact parameter collisions contribute to the reactive scattering. At a similar collision energy of 〈Ecoll〉=31 kJ/mol the forward scattering component in the DCS of the i-C4H10 reaction does not exceed that of the c-C6H12. This shows that the cone of acceptance is not enlarged in the i-C4H10 reaction from that in the c-C6H12 reaction, as opposed to the expectation based on the height of activation barrier. The absence of the enlargement of the cone of acceptance can be attributed to a large steric hindrance caused by the three bulky methyl groups surrounding the reactive tertiary C–H bond of i-C4H10. The difference in the steric hindrance can explain the difference in the temperature-dependent pre-exponential factors of the macroscopic reaction rates between the abstraction of the secondary and tertiary C–H bonds. The collision energy dependence of the DCS as well as the internal excitation of alkyl radical products reveal that the O(3P)+alkane reactions are not always dominated by the simple rebound mechanism, which has long been believed. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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