On the nature of Surface States Stark Effect at clean GaN(0001) surface

Recently developed model allows for simulations of electric field influence on the surface states. The results of slab simulations show considerable change of the energy of quantum states in the electric field, i.e. Stark Effect associated with the surface (SSSE - Surface States Stark Effect). Detailed studies of the GaN slabs demonstrate spatial variation of the conduction and valence band energy revealing real nature of SSSE phenomenon. It is shown that long range variation of the electric potential is in accordance with the change of the energy of the conduction and valence bands. However, at short distances from GaN(0001) surface, the valence band follows the potential change while the conduction states energy is increased due to quantum overlap repulsion by surface states. It is also shown that at clean GaN(0001) surface Fermi level is pinned at about 0.34 eV below the long range projection of the conduction band bottom and varies with the field by about 0.31 eV due to electron filling of the surface states.Comment: 16 pages, 7 figure

Double step structure and meandering due to the many body interaction at GaN(0001) surface in N-rich conditions

Growth of gallium nitride on GaN(0001) surface is modeled by Monte Carlo method. Simulated growth is conducted in N-rich conditions, hence it is controlled by Ga atoms surface diffusion. It is shown that dominating four-body interactions of Ga atoms can cause step flow anisotropy. Kinetic Monte Carlo simulations show that parallel steps with periodic boundary conditions form double terrace structures, whereas initially V -shaped parallel step train initially bends and then every second step moves forward, building regular, stationary ordering as observed during MOVPE or HVPE growth of GaN layers. These two phenomena recover surface meandered pair step pattern observed, since 1953, on many semiconductor surfaces, such as SiC, Si or GaN. Change of terrace width or step orientation particle diffusion jump barriers leads either to step meandering or surface roughening. Additionally it is shown that step behavior changes with the Schwoebel barrier height. Furthermore, simulations under conditions corresponding to very high external particle flux result in triangular islands grown at the terraces. All structures, emerging in the simulations, have their corresponding cases in the experimental results.Comment: 25 pages, 8 figure

A comparative DFT study of electronic properties of 2H-, 4H- and 6H-SiC(0001) and SiC(000-1) clean surfaces: Significance of the surface Stark effect

Electric field, uniform within the slab, emerging due to Fermi level pinning at its both sides is analyzed using DFT simulations of the SiC surface slabs of different thickness. It is shown that for thicker slab the field is nonuniform and this fact is related to the surface state charge. Using the electron density and potential profiles it is proved that for high precision simulations it is necessary to take into account enough number of the Si-C layers. We show that using 12 diatomic layers leads to satisfactory results. It is also demonstrated that the change of the opposite side slab termination, both by different type of atoms or by their location, can be used to adjust electric field within the slab, creating a tool for simulation of surface properties, depending on the doping in the bulk of semiconductor. Using these simulations it was found that, depending on the electric field, the energy of the surface states changes in a different way than energy of the bulk states. This criterion can be used to distinguish Shockley and Tamm surface states. The electronic properties, i.e. energy and type of surface states of the three clean surfaces: 2H-, 4H-, 6H-SiC(0001), and SiC($000 \bar{1}$) are analyzed and compared using field dependent DFT simulations.Comment: 18 pages, 10 figures, 4 table

Odbicie społecznej nauki Kościoła katolickiego w programach głównych stronnictw politycznych II Rzeczypospolitej

The „Rerum novarum” encyclical, enacted in 1891 by pope Leon XIII significantly contributed to the rapid development of the Catholic social science. The next, important stage of that development was marked in 1931 by the encyclical of pope Pius XI. Catholic social thought was considerably developed in Poland at the time of the Second Republic by such prominent priests as: Antoni Szymański, Aleksander Wójcicki, Jan Piwowarczyk and Stefan Wyszyński - later cardinal and Primate of Poland. Some representatives of the Church’s hierarchy, like August cardinal Hlond, Primate of Poland, bishop Stanisław Adamski of Katowice and bishop Teodor Kubina of Częstochowa have also made an important contribution to the development of the Catholic church social science in Poland. At the same time in Poland - like in other countries - many different Catholic-social organizations were created, including political parties like Christian-Democracy and Labour Party. These parties, however, were not among the strongest ones in the Republic. The Catholic social science was fully incorporated - sometimes even developed - in their programs, but their possibilities to put these ideas into political action were much more limited. Some particular elements of social-Catholic thought appeared in programs of many political groups of the Second Republic, but often that was coincidence rather, than fully conscious choice of social Catholicism principles