Resumo em Inglês:

A short review on the diamond CVD origin, together with its state of the art and some prospects was given. New hybrid methods of the diamond CVD permit to gain 1.2 to 6 times of growth rate in comparison with ordinary diamond CVD's. Recent results on n-type diamond film synthesis through phosphorus doping in the course of the CVD process are briefly discussed. In comparison with high-pressure diamond synthesis, the CVD processes open new facets of the diamond as ultimate crystal for science and technology evolution. It was stressed that, mainly on the basis of new CVDs of diamond, the properties of natural diamond are not only reproduced, but can be surpassed. As examples, mechanical (fracture resistance), physical (thermal conductivity), and chemical (oxidation stability) properties are mentioned. Some present issues in the field are considered.

Resumo em Inglês:

A technique has been established to grow large diamonds up to 2 cm. The crystals are bulky polyhedron with yellow, blue, green or brown color as well as colorless, which depend on impurities. The impurities incorporated into the diamond are limited, i.e. nitrogen, boron, nickel, cobalt, silicon and phosphorus.

Resumo em Inglês:

This review summarizes our most recent findings in the structure and properties of amorphous and crystalline carbon nitride coatings, synthesized by reactive magnetron sputtering. By careful control of the plasma conditions via proper choice of process parameters such as substrate bias, target power and gas pressure, one can precisely control film structure and properties. With this approach, we were able to produce amorphous carbon nitride films with controlled hardness and surface roughness. In particular, we can synthesize ultrathin (1 nm thick) amorphous carbon nitride films to be sufficiently dense and uniform that they provide adequate corrosion protection for hard disk applications. We demonstrated the strong correlation between ZrN(111) texture and hardness in CNx/ZrN superlattice coatings. Raman spectroscopy and near-edge x-ray absorption show the predominance of sp³-bonded carbon in these superlattice coatings.

Resumo em Inglês:

Amorphous CNx and CNx:H have been prepared by the ion beam assisted deposition technique. Samples were characterized through X-ray and UV photoemission, IR absorption and Raman spectroscopies. These spectra have been interpreted with the aid of quantum chemical calculations based upon the Hartree-Fock theory on several molecular models. The understanding of the electronic and structural properties of the amorphous alloy as a function of nitrogen content could help in the task of synthesizing the metastable silicon-nitride like-phase beta-C3N4 , a solid which has been predicted to be as hard as diamond. The physical picture emerging from the present study helps to clarify the difficulties in obtaining the crystalline phase of the material, suggesting new experimental directions for syntheses.

Resumo em Inglês:

The infrared analysis of thin films on a thick substrate is discussed using the example of plasma-deposited, amorphous, hydrogenated carbon layers (a-C:H) on silicon substrates. The framework for the optical analysis of thin films is presented. The main characteristic of thin film optics is the occurrence of interference effects due to the coherent superposition of light multiply reflected at the various internal and external interfaces of the optical system. These interference effects lead to a sinusoidal variation of the transmitted and reflected intensity. As a consequence, the Lambert-Beer law is not applicable for the determination of the absorption coefficient of thin films. Furthermore, observable changes of the transmission and reflection spectra occur in the vicinity of strong absorption bands due to the Kramers-Kronig relation. For a sound data evaluation these effects have to be included in the analysis. To be able to extract the full information contained in a measured optical thin film spectrum, an experimentally measured spectrum has to be simulated using the full formalism including the Kramers-Kronig relation. Infrared absorption spectra and the resulting k spectra in the range of the CH vibrational bands around 3000 cm-1 are presented for a variety of a-C:H layers. The shape and the total intensity of the peak are quite sensitive to the film structure. Soft, polymerlike hydrocarbon layers are characterized by a well structured, intense IR absorption band, while hard, amorphous, hydrogenated carbon layers exhibit a structureless, broad IR absorption band with relative low intensity. The k spectra of the CH vibrational bands can be considered as fingerprint for the type of a-C:H film.

Resumo em Inglês:

The growth behaviour, film structure and mechanical properties of plasma-deposited amorphous hydrogenated carbon-nitrogen films are shortly reviewed. The effect of nitrogen-containing gas addition to the deposition to the hydrocarbon atmospheres used is discussed, considering the modifications observed in the chemical composition growth kinetics, carbon atom hybridisation and chemical bonding arrangements of a-C(N):H films. The overall structure behaviour is correlated to the variation of the mechanical properties.

Resumo em Inglês:

The hardness and stress of amorphous carbon films prepared by glow discharge and by ion beam assisting deposition are investigated. Relatively hard and almost stress free amorphous carbon films were deposited by the glow discharge technique. On the other hand, by using the ion beam assisting deposition, hard films were also obtained with a stress of the same order of those found in tetrahedral amorphous carbon films. A structural analysis indicates that all films are composed of a sp²-rich network. These results contradict the currently accepted concept that both stress and hardness are only related to the concentration of sp³ sites. Furthermore, the same results also indicate that the sp² sites may also contribute to the hardness of the films.

Resumo em Inglês:

We have shown that close to stoichiometry RF PECVD amorphous silicon carbon alloys deposited under silane starving plasma conditions exhibit a tendency towards c-SiC chemical order. Motivated by this trend, we further explore the effect of increasing RF power and H2 dilution of the gaseous mixtures, aiming to obtain the amorphous counterpart of c-SiC by the RF-PECVD technique. Doping experiments were also performed on ordered material using phosphorus and nitrogen as donor impurities and boron and aluminum as acceptor ones. For nitrogen a doping efficiency close to device quality a-Si:H was obtained, the lower activation energy being 0,12 eV with room temperature dark conductivity of 2.10-3 (omega.cm). Nitrogen doping efficiency was higher than phosphorous for all studied samples. For p-type doping, results indicate that, even though the attained conductivity values are not device levels, aluminum doping conducted to a promising shift in the Fermi level. Also, aluminum resulted a more efficient acceptor than boron, in accordance to observations in crystalline SiC material.

Resumo em Inglês:

CaF2 films were grown on <img src="http:/img/fbpe/bjp/v30n3/cem.gif" alt="cem.gif (148 bytes)"> silicon using the neutral cluster beam deposition technique. These films were highly crystalline and c-axis oriented. Superconducting YBCO thin films were grown on the CaF2 buffered silicon using the laser ablation technique. These films showed Tc(onset) at 90K and Tc(zero) at 86K. X-ray diffraction analysis showed that the YBCO lms were also oriented along the c-axis.

Resumo em Inglês:

We consider a model for gravity in which the linear part of the four-derivative terms <FONT FACE=Symbol>ò</FONT>R<FONT FACE=Symbol>mn</FONT> R<FONT FACE=Symbol>mn</FONT> <img src="http:/img/fbpe/bjp/v30n3/11eq01.gif" border="0" align="absmiddle">d4 x and <FONT FACE=Symbol>ò</FONT>R² <img src="http:/img/fbpe/bjp/v30n3/11eq01.gif" border="0" align="absmiddle">d4 x are included into the Fierz-Pauli gravitational action. Unitarity is discussed at the tree-level. The issue of the gravitational deflection of a light ray is also considered.

Resumo em Inglês:

Metal - glass metal, MGM, thin film devices are prepared using vacuum deposition of Sb2Pb1Se7 compound. The capacitance and the loss tangent variation as a function of temperature and frequency is studied. The observed characteristics are explained using small signal ac circuit analysis. It is shown that the theoretical curve generated using the ac circuit analysis gives excellent fitting with the experimental curve.

Resumo em Inglês:

Polycyclic aromatic hydrocarbons (PAHs) are a class of planar molecules, abundant in urban environment, which can induce chemical carcinogenesis. Their carcinogenic power varies in a large range, from very strong carcinogens to inactive ones. In a previous study, we proposed a methodology to identify the PAHs carcinogenic activity exploring electronic and topological indices. In the present work, we show that it is possible to simplify that methodology and expand its applicability to include methylated PAHs compounds. Using very simple rules, we can predict their carcinogenic activity with high accuracy (~ 89%).

Resumo em Inglês:

The field equations of a proposed nonsymmetric theory of gravitation are derived when electro-magnetic fields are present, by adopting a nonminimal coupling which ensures the validity of the equivalence principle. The static and spherically symmetric solution of the field of a charged point particle is obtained.

Resumo em Inglês:

A four-fermion model with additional higher-derivative terms is investigated in an external electromagnetic field. The effective potential in the leading order of large-N expansion is calculated in external constant magnetic and electric fields. It is shown that, in contrast to the former results concerning the universal character of "magnetic catalysis" in dynamical symmetry breaking, in the present higher-derivative model the magnetic field restores chiral symmetry broken initially on the tree level. Numerical results describing a second-order phase transition that accompanies the symmetry restoration at the quantum level are presented.

Resumo em Inglês:

The global multiplicative properties of the Laplacian on j — forms and related zeta functions are analyzed. The explicit form of the multiplicative and conformal anomalies in closed oriented hyperbolic manifolds gamma<img src="http:/img/fbpe/bjp/v30n3/16eq01.gif" border="0">d are derived.

Resumo em Inglês:

The ratio of positron/electron fluxes originated in nuclear spallation reactions in the Earth's magnetosphere is considered. It is supposed that positrons as well as electrons are produced in the decay of charged pions (pi±<FONT FACE=Symbol>® m</FONT>± ->e±) born in nuclear collisions of trapped relativistic inner zone protons with the residual atmosphere. These positrons and electrons are captured in the magnetosphere and create positron and electron radiation belts of nuclear origin. The positron/electron trapped magnetospheric fluxes formed with this mechanism are simulated and the resulting computed e+/e- flux ratio ~ 4 appears in agreement with the recent observations. This ratio is significantly different from the ratio ~1 obtained from the primary cosmic ray source through the same mechanism.

Resumo em Inglês:

Taking into account the stringent limits from helioseismology observations on possible matter density fluctuations described by magnetohydrodynamics theory, we find the corresponding time variations of solar neutrino survival probability due to the resonant spin-flavor precession phenomenon with amplitude of order O(10%). We discuss the physics potential of high statistics real time experiments, like as Superkamiokande, to observe the effects of such magnetohydrodynamics fluctuations on their data. We conclude that these observations could be thought as a test of the resonant spin-flavor precession solution to the solar neutrino anomaly.

Resumo em Inglês:

We present a Hamiltonian treatment of the Landau-Ginzburg theory of phase transitions in the case of incommensurate ferroelectric systems like (NH4)2BeF4. This formulation has the advantage of treating the system as an example of a nonlinear dynamical system.

Resumo em Inglês:

We show that ambiguities and symmetry violations arising in one loop calculations can always be avoided provided the regularization scheme employed satisfies three consistency conditions. Our calculations are effected by assuming only implicitly the presence of a regulator in the integrand. We demonstrate in this way that there is a set of three relations involving divergent integrals of the same degree of divergence which are the source of both ambiguities and symmetry violations in Quantum Electrodynamics. Moreover we give analytical expressions for the finite parts of amplitudes off the mass shell systematized in terms of a set of special functions. Ward identities require hightly nom trivial relations involving those functions which we also derive.

Resumo em Inglês:

Several aspects of the Thermodynamics of systems away from equilibrium are considered. Particular attention is given to the question of the concepts of entropy and temperature in arbitrary nonequilibrium conditions. Even though such state function and thermodynamic variable are elusive in such conditions, it is elaborated and discussed an approach to them that can be obtained in the framework of the so-called Informational Statistical Thermodynamics. This is the approach to Thermodynamics based on the statistical-mechanical foundations provided by a Gibbs ensemble-like algorithm in nonequilibrium situations. The resulting nonequilibrium temperature-like variable - dubbed as quasitemperature - is shown to be a quantity measurable with appropriate "thermometric devices". A comparison of quasitemperatures that arise in different approximated nonequilibrium statistical-thermodynamic descriptions of the dissipative system is done. The validity of these different approximations is evaluated, and (in the framework of the theory) generalized Gibbs, Clausius, and Boltzmann's relations, as well as properties of the corresponding entropy-like function (or informational entropy in Jaynes-Shannon sense), that the theory introduces, are presented. Conceptual and physical aspects of the question are also discussed, and a partial comparison of these concepts with those arising in other approaches to irreversible thermodynamics is briefly attempted. This article is an enlargement of a paper in Fortschritte der Physik/Progress of Physics, 47, 9 (1999), where have been added extensive comments on the subject.