Correlation between density and structure. in boron nitride thin films by X-ray diffraction

* _ion=100 eV. Above E^* _ion the average density (deduced from X-ray reflectivity) shows a strong increase, indicating the sudden appearance of the cubic boron nitride phase consistent with the sp³ concentration deduced from IR absorption spectroscopy. The in-plane X-ray diffraction shows that this cubic phase consists of small nanocrystals of 70 Å linear size. Received: 26 November 1996/Accepted: 27 January 1997     

Proton activity and spontaneous strain of Cs3H(SeO4)2 in the phase transition at 369 K

We have investigated the origin of the change in proton activity in the phase transition at T_II-III (=369 K) in Cs₃H(SeO₄)₂ from the viewpoint of its ferroelasticity by using ¹H NMR and X-ray measurements. It is found that the second moment of the ¹H NMR absorption line rapidly decreases at T_II-III with increasing temperature. From this result, we conclude that the hopping motion of a proton, which is the precursor motion in the superprotonic phase, becomes more active above T_II-III. This result is consistent with the fact that the electrical conductivity in phase II is larger than that in phase III. Furthermore, it is also found that the spontaneous strain decreases abruptly at T_II-III. From these results, it is deduced that the decrease in the spontaneous strain at T_II-III causes the increase in the proton activity at T_II-III. In addition, it is deduced that the increase in proton activity and the decrease in the spontaneous strain at T_II-III are closely related with the appearance of the superprotonic phase transition at T_I-II (=456 K).     

Multi-instantons and exact results II: specific cases, higher-order effects, and numerical calculations

In this second part of the treatment of instantons in quantum mechanics, the focus is on specific calculations related to a number of quantum mechanical potentials with degenerate minima. We calculate the leading multi-instanton contributions to the partition function, using the formalism introduced in the first part of the treatise [Ann. Phys. (N. Y.) (previous issue) (2004)]. The following potentials are considered: (i) asymmetric potentials with degenerate minima, (ii) the periodic cosine potential, (iii) anharmonic oscillators with radial symmetry, and (iv) a specific potential which bears an analogy with the Fokker-Planck equation. The latter potential has the peculiar property that the perturbation series for the ground-state energy vanishes to all orders and is thus formally convergent (the ground-state energy, however, is non-zero and positive). For the potentials (ii), (iii), and (iv), we calculate the perturbative B-function as well as the instanton A-function to fourth order in g. We also consider the double-well potential in detail, and present some higher-order analytic as well as numerical calculations to verify explicitly the related conjectures up to the order of three instantons. Strategies analogous to those outlined here could result in new conjectures for problems where our present understanding is more limited.     

Mass and charge flow in the reaction 7.1 MeV/u197Au+63Cu

Mass-yield and angular-distribution data are presented for products from the reaction of 7.1 MeV/ ¹⁹⁷Au with⁶³Cu. With help from information derived from the latter, the former are classified into components corresponding to quasielastic transfer (580±80 mb), deep-inelastic transfer plus quasifission (1300±130 mb), fusionfission (195 mb), and sequential fission (195±45 mb). The fusion excitation function calculated with the Dynamic Capture model standard parameter set reproduces our deduced fusion-fission cross section well. Moreover, using this cross section as well as additional published data for the same reaction system, we extract ans-wave fusion-barrier shift (extra push) for this system of 35±7 MeV, which is in good agreement with the systematics derived from other fusion-barrier shifts which have been reported in the literature. Lastly, support is found for the Dissipative Diabatic Dynamics model prediction that dynamically-hindered fusion trajectories are reflected into quasielastic channels.Research supported by the Bundesministerium für Forschung und Technologie under contract number 06 MR 553     

Complete and incomplete fusion in12C+93Nb and16O+89Y reactions

Excitation functions for the evaporation residues for the reactions¹²C+⁹³Nb and¹⁶O+⁸⁹Y in the projectile energy range of 4 to 6.5 MeV/amu have been measured using off-line gamma spectrometry. The excitation functions for neutron(xn), proton(pxn) and one alpha(xn) emission channels are practically similar for both the reactions. However the products formed by two alpha(2xn) emission show much higher cross sections in the¹²C+⁹³Nb than the¹⁶O+⁸⁹Y system. This has been explained in terms of the incomplete fusion process involving transfer of an alpha particle from the projectile to the target in the former case.Authors thank Shri D.C. Ephraim for making the rolled metal foils and the operation crew of PELLETRON facility for their help in carrying out the irradiations. Authors are grateful to Dr. P.R. Natarajan, Head Radiochemistry Division for his keen interest in this work.     

Maximum excitation energy in fusion-evaporation reactions from light particle multiplicity measurements in32S+58Ni at 25 MeV/A

By using two 4 detector systems for charged particles and neutrons, we measured the evaporated light particles emitted in coincidence with evaporation residues (ER) produced in the reaction³²S+⁵⁸Ni atE(³²S) 820 MeV. From the analysis of the light particle multiplicities as a function of the ER velocity, we extracted the maximum excitation energy reached in fusion evaporation reactions for the studied system.Supported by the European Community Programme Human Capital and Mobility     

Cross sections of 102 element isotopes formation in the reactions of22Ne+236U and26Mg+232Th

The production cross sections of the isotopes²⁵²102,²⁵³102, and²⁵⁴102 were measured for the heavy ion fusion reactions of²²Ne+²³⁶U and²⁶Mg+²³²Th by using the kinematic separator VASSILISSA. The obtained excitation functions and the maximum production cross sections are compared with the ones for more asymmetric reactions leading to the same compound nucleus²⁵⁸102. The experimental cross sections and the results of statistical model calculations are compared and discussed.The authors express their gratitude to Prof. Yu. Ts. Oganessian for his great interest and support of this work, to Drs. E.A. Cherepanov, Yu.A. Muzychka and B.I. Pustylnik for the calculations and for the useful discussions.     

Lyapunov modes and time-correlation functions for two-dimensional systems

The relation between the Lyapunov modes (delocalized Lyapunov vectors) and the momentum autocorrelation function is discussed in two-dimensional hard-disk systems. We show numerical evidence that the smallest time-oscillating period of the Lyapunov modes is twice as long as the time-oscillating period of momentum autocorrelation function for both square and rectangular two-dimensional systems with hard-wall boundary conditions.     

Stoney equation limits for samples deformed as a cylindrical surface

This paper proposes a three-dimensional system for modelling stress in thin films deposited on thick substrates deformed as a small cylindrical surface by means of the minimization of the deformation energy. The results show the validity limits of the well-established Stoney equation and indicate the necessity of a correction term for substrates with Poisson ratio (ν_s) in the range of 0.25 < ν_s ≤ 0.4.     

Effects of O2 and H2O plasma immersion ion implantation on surface chemical composition and surface energy of poly vinyl chloride

Oxygen and water plasma immersion ion implantation (PIII) was used to modify poly vinyl chloride (PVC) to enhance oxygen-containing surface functional groups for more effective grafting. The modified surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), and contact angle measurements. Our experimental results show that both oxygen and water PIII can greatly improve the O to C ratios on the surface. The optimal plasma processing conditions differ for the two treatments. The hydrophilicity and surface energy of the plasma-implanted PVC are also improved significantly. Our results indicate that O₂ and H₂O PIII increase both the polar and dispersion interactions and consequently the surface energy. It can be explained by the large amount of oxygen introduced to the surface and that many CC bonds are transformed into more polar oxygen containing functional groups.