Effect of oligomers on the growth of amorphous silicon films in a PECVD reactor

A plasma-chemical model of processes in a PECVD reactor is constructed that is an extension of the earlier model and takes into account the formation of oligomers Si_nH_m (n ≤ 5). The corresponding scheme of chemical reactions is developed, and simulation of film growth is carried out. It is found that Si₂H₅ and Si₃H₇ components strongly influence the film growth. It is of interest to obtain more reliable experimental data dramatizing these effects.     

Upper bounds on Higgs-Boson masses in the Weinberg-Salam model with three Higgs doublets

In the Weinberg-Salam model with three Higgs doublets, the positivity of masses and tree graph unitarity applied on Higgs scattering lead to the following upper bounds on Higgs masses: m_H1^±, m_H2^± < 883 GeV, m_H1⁰ < 500 GeV, m_H2⁰, m_H3⁰ < (958–1633) GeV, m_H4⁰, m_H5⁰ < (360–883) GeV.     

Associated production of heavy Higgs boson with top quarks

Associated production of a heavy Higgs boson (m_H > 100 GeV) with top quarks at Juratron energies is studied. It is natural to differentiate between the “light” (2m_t < m_H < 2m_W) and “heavy” (m_H > 2m_W) Higgs search. It is assumed that the mass value of the top quarks is in the interval m_t ≈ 30–80 GeV. m_W is the W-boson mass. If m_H < 2m_W a dangerous background is given by the QCD production of four top quarks. We have calculated the cross sections for both the Higgs production and the background reaction. The disappointing result found is that the background is overwhelmingly large. However the Higgs search in this mass region is not hopeless. The associated production of the Higgs boson with a W-boson may have a clear experimental signature, its background given by the reaction $\text{p}\text{+}\text{p}\text{→}\text{W}\text{+}\text{t}\text{+}\text{t}$ might be suppressed. The difficulty with this mechanism is that the rate is rather low. If m_H > 2m_W the background is different and its contribution is expected to be small. The associated production of a Higgs boson with a pair of top quarks might be a useful method in the Higgs search in this case.     

Quantization and confinement effects in superconducting nanostructures

The confinement of the flux lines by a lattice of submicron holes (‘antidots’) has been studied in nanostructured superconducting Pb/Ge multilayers. By introducing regular arrays of sufficiently large antidots, multi-quanta vortex lattices have been stabilized. Sharp cusp-like magnetization (M) anomalies, appearing at matching fieldsH_m=mφ₀/Sin superconducting films with the antidot lattices having a unit cell areaS, are successfully explained. These anomalies are, analogues of the well-knownM(H) cusp atH_c1, but for the onset of multi-quanta (m+1)φ₀-vortices penetration at each subsequent matching fieldH_m. It is shown that theM(H) curve between the matching fieldsH_m<H<H_m+1follows a simpleM∝ln(H−H_m) dependence. These experimental observations have revealed an unusual expansion of validity of the London limit in superconductors with lattices of relatively large antidots. The successful high quality fit of theM(H,T) curves convincingly demonstrates that a new type of the critical stateB=const (‘single-terrace critical state’) can be realized in superconductors with the antidot lattices.     

Rotational spectra of mono-substituted asymmetric C6H6-H2O dimers

This paper reports the assignment of the rotational spectra of the m = 0 and 1 states of ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers. The m = 1 progression was not identified or assigned for both ¹³CC₅H₆-H₂O and C₆H₅D-H₂O in the earlier work, though for the symmetric isotopomers (C₆H₆-H₂O/D₂O/H₂¹⁸O), they were identified [H.S. Gutowsky, T. Emilsson, E. Arunan, J. Chem. Phys. 99 (1993) 4883]. The m = 1 transitions for ¹³CC₅H₆-H₂O and C₆H₅D-H₂O were split into two, unlike that of the parent C₆H₆-H₂O isotopomer. The splitting varied, somewhat randomly, with quantum numbers J and K. The m = 0 lines of ¹³CC₅H₆-H₂O had significant overlap with the m = 1 lines of the parent isotopomer, clouding proper assignment, and leading to an rms deviation of about 200 kHz in the earlier work. The general semi-rigid molecular Hamiltonian coupled to an internal rotor, described recently by Duan et al. [Y.B. Duan, H.M. Zhang, K. Takagi, J. Chem. Phys. 104 (1996) 3914], is used in this work to assign both m = 0 and 1 states of ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers. Consequently, the m = 0 fits for ¹³CC₅H₆-H₂O/D₂O have an rms deviation of only 4/7 kHz, comparable to experimental uncertainties. The fits for m = 1 transitions for ¹³CC₅H₆-H₂O and C₆H₅D-H₂O dimers have an rms deviation of about 200 kHz. However, it is of the same order of magnitude as that of the m = 1 state of the parent C₆H₆-H₂O dimer. The A rotational constants determined from the m = 0 fits for both ¹³CC₅H₆-H₂O and ¹³CC₅H₆-D₂O isotopomers are identical and very close to the C rotational constant for ¹³CC₅H₆. This provides a direct experimental determination for the C rotational constant of ¹³CC₅H₆, which has a negligible dipole moment.     

Central configurations of the collinear three-body problem and singular surfaces in the mass space

This Letter is to provide a new approach to study the phenomena of degeneracy of the number of the collinear central configurations under geometric equivalence. A direct and simple explicit parametric expression of the singular surface H₃ is constructed in the mass space (m₁,m₂,m₃)∈³(R⁺). The construction of H₃ is from an inverse respective, that is, by specifying positions for the bodies and then determining the masses that are possible to yield a central configuration. It reveals the relationship between the phenomena of degeneracy and the inverse problem of central configurations. We prove that the number of central configurations is decreased to 3!/2−1=2, m₁, m₂, and m₃ are mutually distinct if m∈H₃. Moreover, we know not only the number of central configurations but also what the nonequivalent central configurations are.     

Investigation of the magnetization vector hodographs corresponding to the 90° pulse magnetization of ferrite-garnet films with easy-plane anisotropy

The magnetization vector hodographs corresponding to the regime of 90° pulse magnetization of ferrite-garnet films with easy-plane anisotropy have been analyzed. It is found that when the magnetizing pulse amplitude H _m exceeds some threshold value H*_m (≈15 Oe), magnetization occurs through the mechanism of uniform magnetization vector rotation. The weak dependence of the intensity of nonlinear oscillations (accompanying the magnetization process) on the rise time of the magnetizing pulse, observed in the fields H _m > H*_m, is explained by the presence of biaxial anisotropy in the plane of real films.     

Photoelectron spectroscopy of some thiocyanates,isocyanates and isothiocyanates

Photoelectron spectra of some thiocyanates (RSCN, R = CH₃, C₂H₅, n-C₄H₉), isocyanates (RNCO, R = C₂H₅, n-C₄H₉) and isothiocyanates (RNCS, R = C₂H₅, n-C₄H₉) have been measured, to study interactions between nonbonding and π orbitals, mainly localized on the SCN, NCO or NCS fragments. The spectral interpretation of CH₃SCN is based on semiempirical CNDO/S calculations, sum-rule considerations, and intensity differences between He(I) and HE(II) spectra. For the larger molecules, comparison of the spectra is used as an aid in the interpretation. In a number of aromatic isocyanates (o?, m?, p-tolylisocyanate and m?, p-chlorophenylisocyanate), interactions between the isocyanate group and the highest occupied π and σ orbitals of the phenyl ring are studied. Spectra are assigned on the basis of semiempirical INDO/S calculations.     

Structures of proton solvates in the HCl-H2O-(CH3)2NCHO system as determined by IR spectroscopy and quantum-chemical calculations

The structures of proton solvates in the HCl-H₂O-(CH₃)₂NCHO (DMFA) system at H₂O: DMFA ratios ranging from 1: 1 to 21: 1 are studied by the IR spectroscopy method. It is demonstrated that H₂O?H⁺?OH₂ ions and (CH₃)₂NCHO?H⁺?OH₂ mixed solvates with a strong quasi-symmetrical hydrogen bond are formed in solutions. With an increase in the DMFA concentration, the fraction of H₅O ₂ ⁺ ions decreases. At HCl: H₂O ≥ 1: 3 and arbitrary DMFA concentrations, only mixed proton solvates are formed. The continuous absorption coefficients for the (CH₃)₂NCHO?H⁺?OH₂ ions are determined. The results obtained are compared with the results of quantum-chemical calculations of the structure and relative stability of the (DMFA) _m H⁺(H₂O) _n (m = 0–2, n = 0–3) positively charged complexes which were performed by the B3LYP/6-31++G(d,p) DFT method. We identified 19 stable configurations with chain, cyclic, and branched structures. Most of these configurations contain the (CH₃)₂NCHO?H⁺?OH₂ fragment. The parameters of the O?H⁺?O bridge show that some configurations have a strong quasi-symmetrical hydrogen bond. In some cases, the proton is located between two DMFA molecules. The H₂O?H⁺?OH₂ bridge is observed in none of the stable configurations of the (DMFA) _m H⁺(H₂O) _n (m ≠ 0) complexes.     

An YBCO film as a Josephson medium near T c : Frequency and field dependences and scaling relationships

The diamagnetic response of a laser-deposited YBCO film was studied in weak exciting magnetic fields H _ac =H ₀sinωt (H ₀=2–500 mOe, ω/2π=1–30 kHz). An analysis of the experimentally measured diamagnetic response showed evidence of a ring character of the electric field flowing in the sample at small H ₀ values. The plots of T _m (the temperature of maximum dissipative losses χ″₁) versus H ₀ measured at various frequencies showed the existence of a certain critical field strength H*(ω) at which the (1?T _m /T _c ) versus H ₀ ^2/3 plots exhibit a break. A logarithmic dependence of T _m on the frequency ω of the exciting field H _ac is reliably valid only in the region of (ω/2π)>5 kHz. Verification of the scaling relationship showed that this relationship is valid (to within the experimental accuracy) for the frequencies ω above 5 kHz and the field amplitudes H ₀>H*(ω). However, the exponent n in the scaling relationship under consideration is not correlated with the exponent n in the power relationship describing the current-voltage characteristic.     

Low-field AC susceptibility study of critical current density in Eu:123 and Bi:2223 superconductors

Low-field AC susceptibility measurements have been made, at different values of AC field amplitude H_m (26–600 A/m), on Eu:123 and Bi:2223 samples. Analysis of the temperature dependence of the AC susceptibility has been done employing Beans’ critical state model. The intergranular critical current density (J_c) is calculated as a function of both H_m and temperature for both samples, respectively. It is found that J_c increases with increasing H_m for both samples and its values are generally higher in Bi sample than in Eu sample. Our results are discussed in terms of zero-temperature pinning potential βI(0) in both systems.     

Magnetic irreversibility and metastability in a CuMn alloy

Our magnetic measurements on a CuMn alloy reveal that T_m, the temperature of the susceptibility peak, is marked by a qualitative change in the magnetization-vs.-field behavior. The magnetization process at and above T_m is reversible at all fields, whereas below T_m an irreversibility sets in at a threshold field H₁ and persists up to a second threshold field H₂. The irreversibility results in an isothermal remanence whose saturation value (attained when the field removed exceeds H₂) equals the saturation value of the thermoremanence (attained after cooling from above T_m in a field larger than H₂). Both states of remenence are characterized by a magnetization which is completely reversed by a small reverse field but returns to its original polarity when the field is removed. The hysteresis loop remains thus displaced as long as the cycling field is less than H₁.     

Percolation magnetoresistance in ferromagnetic superconductors

It is shown that the magnetoresistance (as a function of magnetic field H) in polycrystalline magnetic superconductors has the percolation character which is the consequence of the anisotropy of magnetic susceptibility. The magnetoresistance R_m(H), and the upper critical field H_c2(T) of ErRh₄B₄ are evaluated and compared with the experimental data.     

On the decays of heavy Higgs bosons

The decay of a neutral heavy Higgs bosonH to a weak vector bosonV+lepton pair is discussed and found to be relevant. Its width is strongly growing with increasingm _H and fromm _H≈200 GeV it exceeds ≈10 MeV.     

On the initial conditions for super-exponential inflation

In a higher-dimensional theory of gravity containing higher-derivative terms and a cosmological constant, a period of super-exponential inflation of the physical spacetime is possible, during which the Hubble parameter H increases with time, as discovered by Shafi and Wetterich. This means that the initial value H₀ must be small H₀ < 6 × 10⁻⁵m_p. We discuss the meaning of this initial condition from the standpoint of quantum cosmology.     

Electrical conductivity, DSC, XRD, and 7Li NMR studies of rotator crystals n-C21H43COOLi x K(1 − x) (0.33 ≤ x ≤ 0.50), n-C m H(2m + 1)COOLi, and n-C m H(2m + 1)COOK (m = 13, 15, 17, 19, and 21)

Differential scanning calorimetry (DSC) thermograms, X-ray diffraction (XRD) analysis, electrical conductivity (σ), and ⁷Li NMR spectroscopy characterization of n-C _m H_(2m?+?1)COOM solids (M = Li, Na, K; m?=?13, 15, 17, 19, 21) and mixed crystals n-C₂₁H₄₃COOLi _x K_(1???x) (0.25?≤?x?≤?0.75) was performed as a function of temperature. DSC thermograms of n-C _m H_(2m?+?1)COOM revealed several solid-solid phase transitions with large entropy changes. Electrical conductivity studies established that n-C _m H_(2m?+?1)COOLi crystals are poor electrical conductors. In contrast, n-C _m H_(2m?+?1)COOK salts were found to have σ values of 10^???7–10^???8 S·cm^???1. Since the crystal structures and phase-transition temperatures of both n-C _m H_(2m?+?1)COOLi and n-C _m H_(2m?+?1)COOK crystals were similar, they were able to form mixed crystals with the structure n-C _x H_(2m?+?1)COOLi _x K_(1???x). DSC thermograms of the mixed crystals showed a small entropy change at the melting point (ΔS _mp?<?13 J K^???1 mol^???1), in addition, large ΔS values at the solid-solid phase transition temperature. The σ values obtained for mixed crystals were roughly one order of magnitude greater than those determined for n-C₂₁H₄₃COOK crystals. ⁷Li NMR spectra of the mixed crystals recorded at various temperatures suggested that the self-diffusion of Li^?+? ions was excited in the highest-temperature solid phase. Based on these results, we have classified these mixed crystals as rotator crystals.     

Photocatalytic abilities of gel-derived P-doped TiO2

P-doped TiO₂ nanoparticles were synthesized through hydrolysis and condensation of Ti(OC₂H₅)₄ with H₃PO₄ additions. Effects of [H₃PO₄]/[Ti(OC₂H₅)₄] molar ratios on the anatase-to-rutile phase transformation, crystallite sizes, surface areas, and photocatalytic abilities of the gel-derived P-doped TiO₂ were investigated. The P-doped TiO₂ nanoparticles prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 were composed of anatase monophase even at 900 ^oC and possessed very strong photocatalytic ability. Kinetic studies on the P-doped TiO₂ to photocatalytically decompose methylene blue under irradiation of 365 nm UV light found that the P-doped TiO₂ prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 and calcined at 800 ^oC had the specific reaction rates, at 25 °C, k_A,m=0.76 m³/(kg min) (based on the mass of P-doped TiO₂) and k_A,BET=46.2×10⁻⁶ m/min (based on the BET surface area of P-doped TiO₂), which is superior to the performance of a commercial product, P25 (k_A,m=0.22 m³/(kg min) and k_A,BET=4.8×10⁻⁶ m/min).     

Coercivity of anisotropic γ-Fe2O3 particles at high temperatures

The coercivity of five different samples of anisotropic γ-Fe₂O₃ particles is studied in the temperature range 0°–600°C. It is found that their relative coercive force h _c = H _c (T)/H _c (0) is almost a linear function of the relative magnetization of the particles m _s = M _s (T)/M _s (0), where H _c (0) and M _s (0) are the values of H _c and M _s of the particles at 0°C. It is experimentally found that h _c = βm _s + α, where β = 1.103 ± 0.015 and α = ?0.114 ± 0.009. This character of the dependence of h _c on m _s suggests that, at high temperatures, H _c of anisotropic γ-Fe₂O₃ particles can depend on both their shape anisotropy and other factors. It is assumed that, as the temperature increases, anisotropic γ-Fe₂O₃ particles in a zero magnetic field are divided into small structurally and magnetically unstable nanoclusters with magnetization spontaneously changing its direction. As a result, H _c disappears near the Curie temperature, although the saturation magnetization of the particles in a field of 1 T is still retained at this temperature.     

On the metastability of the Standard Model vacuum

If the Higgs mass m_H is as low as suggested by present experimental information, the Standard Model ground state might not be absolutely stable. We present a detailed analysis of the lower bounds on m_H imposed by the requirement that the electroweak vacuum be sufficiently long-lived. We perform a complete one-loop calculation of the tunnelling probability at zero temperature, and we improve it by means of two-loop renormalization-group equations. We find that, for m_H=115 GeV, the Higgs potential develops an instability below the Planck scale for m_t>(166±2) GeV, but the electroweak vacuum is sufficiently long-lived for m_t<(175±2) GeV.     

On the Meissner effect in gauge theories

The phase structure of spontaneously broken scalar electrodynamics in an external electromagnetic field is analyzed. With no external field, the spectrum comprises a scalar boson of mass m_H and a vector boson of mass m_W. If m_H ≤ m_W, it is shown that in the tree approximation, as the external field is increased, a first order phase transition to a restored symmetry phase occurs, and the critical field strength is calculated. Below the critical point the external field is completely screened, this being the analogue of the Meissner effect in superconductivity. If m_H > m_W, a third phase, characterized by vortex solutions of the field equations, occurs. Quantum effects, such as pair production in an electric field, are considered at the one (and two) loop level in the massless theory (the Coleman-Weinberg model). The leading correction to the critical magnetic field strength is calculated, and it is shown that for an external electric field the phase transition does not exist.