Volume 52, Issue 6-7

The contamination of silicon wafers from dilute HF solutions containing ultratrace levels of metallic ion impurities is a subject of constant interest. The mechanism of copper electroless deposition from HF onto monocrystalline silicon was investigated using a new electrochemical cell, which proved to be a very sensitive detector for in situ characterization of silicon surfaces. Upon addition of copper trace amounts, the open-circuit potential was observed to shift rapidly towards more positive values at a rate nearly proportional to the copper concentration. All potential/ time curves tend to reach a limiting value of the potential, while quantitative measurements of radioactive tracers revealed that during a few tens of minutes, copper ions were continuously reduced on the silicon surface. Electrochemical potentials and voltammetric measurements were interpreted in terms of the mixed potential theory and led to the conclusion that copper nuclei act as a catalyst which enhances the cathodic activity for protons reduction. The model was supported by AFM observations which demonstrated the initiation of corrosion pits around the nuclei.

Numerical calculations of the NMR second moment in case of rotation and diffusion of molecules were performed. As an example computer simulations of molecular reorientation and self-diffusion in solid benzene have been performed. For each model and rate of motion the Van Vleck's second moment of the proton NMR absorption spectrum was calculated, and these values were compared with experimental data. It is concluded that restricted self-diffusion must be implied in order to obtain better agreement between calculated and experimental NMR second moments. The temperature at which self-diffusion was detected through NMR line-width narrowing was found to be about 120 K, nearly 80 K less than the temperature at which the self-diffusion was detected by T 1ρ relaxation measurements.

Solutions of 4-hydroxy-TEMPO(TANOL) in water and water-soyabean oil were investigated in the concentration range 0.1 mM-10mM. Dynamic nuclear polarization (DNP) and electronic relaxation time T 1e measurements were performed at each well resolved hyperfine line. In the TANOL/water-soyabean oil solutions, the effect of the presence of soyabean oil was an increase in the measured relaxation rates and a decrease in the observed enhancements. In addition, the observed enhancements diminished in time. For all of the samples, the relaxation rates decreased as the frequency of the transition increased.

The high pressure phase behaviour of a new liquid crystal, belonging to the series l-[4-«-alkylbiphenyl]-2-[4-isothio-cyanato-phenyl] ethane (nTPEB), n = 6, has been studied with differential thermal analysis. The pressure dependence of the phase transitions has been determined up to 300 MPa. No pressure-induced or pressure-limited phases are observed in this pressure range, the phase behaviour, however, depends on the thermal treatment. Enthalpy and volume changes accompanying the phase transitions have been calculated using the Clausius-Clapeyron equation.

The phase behaviour, the calorimetric and volumetric properties of 2,2,2-trichloro-ethanol (TCE) have been studied with differential thermal analysis (DTA) and pVT measurements in the pressure range 1 atm to 300 MPa and temperatures between 250 K to 355 K. TCE displays a metastable plastic phase (solid I') and a non-plastic solid phase II at atmospheric pressure. At least two pressure-induced solid phases have been detected: a stable plastic phase (solid I') and a non-plastic phase (solid III). There are two sets of triple points: a) 123 MPa and 308 K with the phases solid I, solid II and the liquid, b) 243 MPa and 316 K for solid I, II, III. Furthermore a metastable low-temperature brittle form (solid II') has been found, which transforms to solid I at a considerably lower temperature than solid II. The melting curve of solid I' can be pursued to higher pressures up to 260 MPa. On the other hand, the melting curve of the stable plastic phase solid I can be extrapolated beyond the triple point to pressures below 123 MPa. Volume and enthalpy changes are reported for all phase transitions.

The temperature dependences at 110 to 400 K of the : 1 H spin-lattice relaxation time (7\) of the phenethylammonium ion in phenethylammonium lead(II) halides, [C 6 H 5 CH 2 CH 2 NH 3 ] 2 PbX 4 (X = Cl, Br, I), revealed that this ion shows reorientation of the NH 3 moiety around the three-fold axis and torsional motion of the alkyl chain (CH 2 CH 2 ). Below room temperature, the chloride and the bromide yielded two minima of 1 H T 1 originating from NH 3 reorientation, whereas the iodide yielded only one minimum. These findings indicate that there are two kinds of NH 3 sites in the chloride and bromide but only one in the iodide. The T 1 minimum observed below room temperature gave similar activation energies of the NH 3 reorientation, E a = 15.7,15.1 and 15.5 kJ mol 1 for the chloride, bromide and iodide, respectively, suggesting that the corresponding NH 3 groups are located at similar environments. Above room temperature, the T 1 minimum in the chloride and bromide gave larger E a values of the NH 3 reorientation: E a - 23.6 and 20.2 kJ mol -1 for the chloride and bromide, respectively. These findings suggest that the NH 3 groups form stronger hydrogen bonding with halogen atoms (N-H ... X). Furthermore, the amplitude of the CH 2 CH 2 motion is discussed, using the two sites jump model. The activation energies for the CH 2 CH 2 motion in these compounds are almost equal (E a = 29.1, 30.0 and 28.2 kJ mol -1 for the chloride, bromide and iodide, respectively), but that the torsional angles become larger in the order iodide ⪡ bromide<chloride.

We use methods of nonlinear dynamics to describe the effect of periodic inhibition on the patterns of action potentials generated by regular spiking rat cortical neuron in vitro. Both direct measurements and our mathematical model reveal that chaotic patterns of discharge can be evoked at certain frequencies of inhibitory stimulation. We use detailed biophysical simulation of a cortical neuron to explain the firing patterns in terms of known membrane ionic conductances.

The complete bifurcation diagram as well as the basin of attraction for the logistic map is presented for the whole range of the control parameters, namely -2≤a≤4 where the system remains finite. Equivalence of the newly found bifurcation branch to the conventional branch is shown.

The peculiarities of the 35 Cl, 79 Br NQR spectra of the chalcogenhalide complexes are explained in terms of intraspheric effect of ligands, formation of secondary intra-and intermolecular bonds, and electronic structure of metal atom. In the 35 Cl spectra of [TeCl 3 ] 2 [OsCl 6 ] 1, [SeCl 3 ] 2 [OsCl 6 ]2 and [TeCl 3 ] 2 [ReCl 6 ]3 the 7-10% increase in frequency in the low-frequency multiplet are accounted for by the disturbance of the p Hal -d M π-interaction due to the formation of the peripheral coordination polyhedra [SeCl 6 ] and [TeCl 6 ]. The peculiarities of the 35 Cl and 79 Br spectra of [MoS 2 Cl 3 (SeCl 2 )] 2 4, [MoS 2 Br 3 (SeCl 2 )] 2 5, [WS 2 Cl 3 (SeCl 2 )] 2 6 and [WS 2 Br 3 (SeBr 2 )] 2 7 are attributed to the disturbance of the p Hal- d M π-interaction under the influence of the coordination of the SeCl 2 and SeBr 2 ligands and formation of secondary intramolecular bonds. For [RhCl 3 (SeCl 2 ) 2 ] 2 8, [IrCl 3 (SeCl 2 ) 2 ] 2 9 and [SCl 3 ][IrCl 4 (SCl 2 ) 2 ]10, the appearance of frequencies at 25 MHz in low-frequency triplets is attributed to the intraspheric effect of weak donors-neutral SCl 2 and SeCl 2 molecules; the frequencies at 18 MHz are assigned to bridging chlorine atoms. This assignment was confirmed by the dimeric structure, which was established by an X-ray structure analysis.

X-ray diffraction measurements were performed on liquid LiBr • 5H 2 O and Lil • 5H 2 O at temperatures from -30 to 25 °C. The total radial distribution functions did show that on supercooling the hydration shell of the halide ions becomes more structured, while that of the lithium ions becomes distorted. The larger the halide ion, the stronger becomes the water-water interaction around halide ions with lowering temperature. However, the distance between the water molecules in the hydration shells of the halide ions depends little on their size. On the basis of the present results, together with those of our previous investigation on LiCl • 5H 2 O at temperatures from - 135 to 100°C, the effects of temperature and the size of the halide ions on the structure of the solution are discussed.

The stability of the plane interface separating two Rivlin-Ericksen elastico-viscous superposed fluids of uniform densities when the whole system is immersed in a uniform horizontal magnetic field has been studied. The stability analysis has been carried out, for mathematical simplicity, for two highly viscous fluids of equal kinematic viscosities and equal kinematic viscoelasticities. It is found that the stability criterion is independent of the effects of viscosity and viscoelasticity and is dependent on the orientation and magnitude of the magnetic field. The magnetic field is found to stabilize a certain wave-number range of the unstable configuration. The behaviour of growth rates with respect to kinematic viscosity and kinematic viscoelasticity parameters are examined numerically.

In a recent paper, Englert et al. reject Bohm's reinterpretation of quantum mechanics as "surrealistic." Responses to this by Dewdney et al. and Durr et al. have generally missed the point of this somewhat strange characterization of the interpretation. In this paper I explain the experiment which is supposed to illustrate the surrealism. I argue that what is really being objected to is the non-locality of the interpretation. While this is an undesirable feature of Bohm's interpretation, it is not a feature of which the standard interpretation gives a more satisfactory account.

In this work we investigate the mechanism of product formation of the aluminothermic reaction of Fe 2 O 3 in the presence of Al 2 O 3 using Ball Milling and Self-propagating High-temperature techniques. Results obtained by experiments under either argon or air atmosphere are analysed by X-ray diffraction and Mössbauer spectroscopy, together with microstructure observations. It is shown that ball milling products are strongly affected by the kind of atmosphere, while self-propagating high-temperature ones are only weakly influenced. Reaction mechanisms taking place in these cases are proposed. While ball milling involves only solid state reactions, the formation of a melt occurs under self-propagating high-temperature conditions.

The influence of the cations on the condensation of the anions in the salts (A´)Zn(II) Br 4 and (A) 2 Zn(II)Br 4 is studied by 81 Br NQR and X-ray crystal structure analysis. (A´)Zn(II)Br 4 (A´ = [H 3 N(CH 2 ) 3 NH 3 ] 2+ ) (1) shows a phase transition at 474 K. The phase II of (1) crystallizes with isolated [ZnBr 4 ] 2- tetrahedra: monoclinic P2 1 /n, Z = 4, a = 1108.4 (5), b = 1096.8 (2), c = 1118.5 (6) pm, and β= 117.07(4)° at 296 K. A quartet was observed in the 81 Br NQR spectrum of phase II: 61.634,58062, 56.675, and 53.673 MHz (77K); 59.193, 57.448, 56.015, and 52.515 MHz (301 K).(A) 2 ZnBr 4 (A = [n-H 3 C(CH 2 ) 2 NH 3 ] + (2) and [n-H 3 C(CH 2 ) 3 NH 3 ] + (3)) also show structures with isolated [ZnBr 4 ] 2- tetrahedra. The compound (2) crystallizes with P2 1 /c, Z = 4, a = 771.8(3), b = 1061.9(4), c = 2054.2 (7) pm, and β = 106.75(1)° at 291 K. The compound (3) crystallizes with P2 1 /c, Z = 4, a = 768.9(4), b = 2229.6(10), c = 1071.6(5) pm, and β = 91.70(3)° at 295 K. 81 Br NQR and DSC measurements on [H 3 N(CH 2 ) 4 NH 3 ]ZnBr 4 (4), and [n-H 3 C(CH 2 ) 4 NH 3 ] 2 ZnBr 4 (5) were also performed. The compound (4) shows several phase transitions at 349 K and higher temperatures, and a quartet in the 81 r NQR spectrum could be observed between 77 and 330 K: 65.992,65.544, 59.900, and 50.162 MHz (77 K); 63.787, 62.963, 59.928, and 50.364 MHz (320 K). The compound (5) shows also a phase transition at 244 K, and a quartet of 81 Br lines could be observed in the NQR spectrum between 77 and 244 K: 61.279, 58.933, 57.869, and 56.485 MHz (77 K); 59.712, 56.936, 57.409, and 54.793 MHz (240 K). The various influences of the cations, such as size and hydrogen bonds on the condensation of [MX 4 ] 2- (M = Zn, Cd; X = C1, Br) are discussed.

For 56 years, researchers have sought, with varied success, to determine the mass of a roton. However, with the recent emergence of the author's theory of superfluid 4 He, the time may soon be at hand when the roton's mass is determined unequivocally. This letter reports the first quantitative results of the new theory of helium II. Using data from a neutron scattering experiment, the mass of a roton was calculated. It was found that the roton mass is 2.12 x 10 -27 kg or approximately 0.32 m He , where m He is the mass of a helium atom.

Electric polarizabilities and hyperpolarizabilities were calculated from accurate self-consistent field wavefunctions for P 2 . The following values are reported, using the experimental bond length of 1.8934 Å: dipole polarizability α zz = 69.83 and α xx = 41.20 e 2 a 0 2 Eh -1 , second dipole hyperpolarizability γ zzzz = 17 040, γ xxxx = 11 581 and γ xxzz = 4724 e 4 a 0 4 E h -3 , quadrupole polarizability, C zz „zz = 276.14, C xz,xz = 232.64 and C xx,xx = 151.25 e 2 a 0 4 E h -1 , dipole-octopole polarizability, E z,zzz , = 331.00 and E x,xxx = -154.66 e 2 a 0 4 E h -1 and for the dipole-dipole-quadrupole hyperpolarizability, B zz,zz = - 2441, B xz,xz = - 1442, B xx,zz = 866 and B xx,xx = - 1411 e 3 a 0 4 Eh -2 .

Mean Amplitudes of Vibration of the "Onium" Cations H 3 O + , H 3 S + and H 3 Se + Mean amplitudes of vibration of H 3 O + , H 3 S + and H 3 Se + have been calculated from spectroscopic data in a wide temperature range. The results are briefly discussed in comparison with data of related species.