Mechanism of silicon epitaxy on porous silicon layers

The mechanism of silicon epitaxy on porous Si(111) layers is investigated by the Monte Carlo method. The Gilmer model of adatom diffusion extended to the case of arbitrary surface morphology is used. Vacancies and pendants of atoms are allowed in the generalized model, the activation energy of a diffusion hop depends on the state of the neighboring positions in the first and second coordination spheres, and neighbors located outside the growing elementary layer are also taken into account. It is shown that in this model epitaxy occurs by the formation of metastable nucleation centers at the edges of pores, followed by growth of the nucleation centers along the perimeter and the formation of a thin, continuous pendant layer. Three-dimensional images of surface layers at different stages of epitaxy were obtained. The dependence of the kinetics of the epitaxy process on the amount of deposited silicon is determined for different substrate porosities. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 7, 512–517 (10 April 1998)     

Experimental investigation of highly excited states of the 5,6He and 5,6Li nuclei in the (6Li, 7Be) and (6Li, 7Li) one-nucleon pickup reactions

The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions on ⁶Li and ⁷Li nuclei were investigated in the angular interval 0°–20° in the laboratory system at a ⁶Li energy of 93 MeV. In addition to low-lying states of the ^5,6He and ^5,6Li nuclei, broad structures were observed near the t(³He)+d and t(³He)+t thresholds at the excitation energies of 16.75 (3/2⁺) and ～20 MeV (for ⁵He), 16.66 (3/2⁺) and ～20 MeV (⁵Li), 14.0 and 25 MeV (⁶He), and ～20 MeV (⁶Li). The angular distributions measured in the ⁷Li(⁶Li, ⁷Be)⁶He reaction for transitions to the ground state (0⁺) and excited states at E _x=1.8 MeV (2⁺) and 14.0 MeV of the ⁶He nucleus were analyzed by the finite-range distorted-wave method assuming the 1p-and 1s-proton pickup mechanism. The (⁶Li, ⁷Be) and (⁶Li, ⁷Li) reactions were shown to proceed predominantly through the one-step pickup mechanism, and the broad structures observed at high excitation energies are considered as quasimolecular states of the t(³He)+d and t(³He)+t types.     

Imidazoline ring cleavage in 1,3,6,10-tetraazatetracyclo-[7.3.1.02,7.06,13]trideca-4, 11-dienes,leading to the formation of diquinoxalino[1,2-a∶2′,3′-d]pyrrole derivatives

Dibenzo[d,k]-1,3,6,10-tetraazatetracyclo[7.3.1.0^2,7.0^6,13]trideca-4,11-dienes undergo addition reactions at the C₍₂₎ carbon atom with alcohols and thiols, accompanied by cleavage of the C-N bond of the imidazoline ring, to generate diquinoxalino[1,2-a2,3-d]pyrrole derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 513–522, April, 1987.     

Spin-lattice relaxation of radicals in the solid state. Part 3

Some causes of spin-lattice relaxation in the solid state are considered. It is found that anisotropic hyperfine interaction can make an appreciable contribution to the spin-lattice relaxation time, which becomes dependent on the orientation of the radical relative to the external field and on the number of HS components. There is no appreciable contribution from frequency modulation of the vibrations (of the radical as a whole or purely intramolecular) caused by the lattice vibrations.     

Reaction of styrene with sulfur and triiron dodecacarbonyl and the molecular structure of the complex Fe2(CO)6(SCH2S)

Reaction of excess styrene with Fe₃(CO)₁₂ and sulfur (60°C, 15 h, Ar, S/Fe₃(CO)₁₂ 0.6 g-atom/mole) gave Fe₂(CO)₆S₂, Fe₃(CO)₉S₂, Fe₂(CO)₆(S₂CO), Fe₂(CO)₆S₂(PhCHCH₂), PhCHCH₂S₄, and a novel binuclear complex Fe₂(CO)₆(S₂CH₂S), whose structure was analyzed by x-ray crystallography. The crystals are monoclinic, a=7.764(3), b=13.205(4), c=6.628(6) Å, =98.97(3)°. V=671.2(7) ų, Z=2, space group P2₁/m. The bond lengths are Fe-Fe 2.520(2), Fe-S 2.236(2), S-S 2.078(4), C-S 1.825(12), Fe-CO 1.784(8), and CO 1.148(9) Å.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 930–934, April, 1991.     

Probing water interactions and vacancy production on gadolinia-doped ceria surfaces using electron stimulated desorption

Polycrystalline gadolinia-doped ceria (GDC) surfaces were studied using low-energy (5-400 eV) electron stimulated desorption (ESD). H(+), O(+), and H(3)O(+) were the primary cationic desorption products with H(+) as the dominant channel. H(+), H(3)O(+), and O(+) have a 22 eV threshold followed by a yield change around 40 eV. H(+) also has an additional yield change approximately 75 eV and O(+) has an additional change approximately 150 eV. The O(+) ESD yield change approximately 150 eV may indicate bond breaking of Gd-O and the involvement of oxygen vacancies. The H(+) and H(3)O(+) threshold data collectively indicate the presence of hydroxyl groups and chemisorbed water molecules on the GDC surfaces. ESD temperature dependence measurements show that the interaction of water with GDC surface defect sites, mainly oxygen vacancies, influences the desorption of H(+), O(+), and H(3)O(+). The temperature dependence of the O(+) ESD at 400 eV incident electron energy yields a 0.21 eV activation energy. This is close to the energy needed for oxygen vacancy production next to a pair of Ce(3+) on a CeO(2) surface. These results may indicate a correlation between the O(+) ESD yield and oxygen vacancy density on GDC surfaces and a potential correlation of O(+) ESD and GDC ionic conductivity.     

Nitroazines. 6. Direct introduction of indole residues into 6-nitroazolo[1,5-a]pyrimidines

Non-charge-activated 6-nitroazolo[1,5-a]pyrimidines have been reacted with indoles, and the effects of substituents in the azole moiety of the substrate molecule have been examined.For communication 5, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenni, No. 11, 1544–1549, November, 1986.     

Interaction of a low-pressure gas flame and heterogeneous catalytic processes on the reactor surface

Conclusions (1) It was shown that the Semenov theory in various modes of chain termination quantitatively describes oxyhydrogen combustion near the first ignition limit with allowance for the interaction between the flame and the catalytic processes on the reactor wall. (2) Numerical modeling of oxyhydrogen ignition in the diffusion-controlled chain-termination mode detected the dependence of the rate “constant” for heterogeneous chain initiation on the model of the reaction in the gas. (3) For the first time, the change in the specific rate of heterogeneous chain initiation during a single ignition was determined. (4) method for controlling the low-pressure flame mode by affecting tubes far from the reactor was proposed and applied. Original Russian Text ? E.N. Aleksandrov, S.N. Kozlov, N.M. Kuznetsov, 2006, published in Doklady Akademii Nauk, 2006, Vol. 407, No. 5, pp. 630–633. Presented by Academician A.E. Shilov October 5, 2005