On the structure of surface active centers on CuO

It has been established that surface active centers on CuO can be associated with its surface defects, i.e. surface exits of twinning and screw dislocations where highly reactive oxygen and CO can be coordinated.

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Field effect in CdSe single-crystal films

The surface conductivity and effective mobility were studied as functions of the surface potential on CdSe single-crystal films having a conductivity of 1–10^–5 .cm^–1. The surface potential was varied by a constant external field. The formation of a conducting channel at the film surface is governed primarily by the change in the trapping factor as volume traps near the surface are filled. Field-effect data are used to evaluate the parameters of the exponential distribution of volume traps with respect to energy, the effective concentration of small donors, and the absolute values of the surface potential.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp.43–47, March, 1971.     

Photoelectron characteristics of diode structures based on quantum-well GaAs/InGaAs heteronanostructures with a Mn δ-doped layer

A GaAs layer over Mn is found to acquire p-type conductivity in Au(Ni)/n-GaAs/InGaAs diode heteronanostructures due to laser δ-doping of Mn with a density of 0.15–1.5 monolayers, yielding the formation of a p-n junction in the Schottky barrier. The effect of the shunting of diode structures by the ohmic resistance of the Mn δ-doped layer and a p-n junction outside the Schottky electrode is revealed. This effect is found to disappear after the formation of mesadiodes. The current-voltage characteristics of the mesadiodes with Mn cannot be described by the mechanism of thermionic emission through the barrier, and the current in these mesadiodes flows with the participation of thermal-field and field emission. A compensated region in the n-GaAs buffer layer, adjacent to the δ-doped layer, formed due to the laser deposition of a coating layer is found. The length of this region decreases with reduction in the layer-production temperature. A substantial increase in the effective surface potential barrier in the semiconductor (up to 1.05 V) in structures with Mn was revealed, and the photoelectric activity and depth of Mn layer occurrence in the forbidden band of GaAs energies is revealed.     

Mechanisms of Current Transport and Resistive Switching in Capacitors with Yttria-Stabilized Hafnia Layers

Technical Physics - The peculiarities of resistive switching in capacitors with yttria-stabilized hafnia layers were studied. The characteristics of current transport in the initial state and after...     

Efficient epoxidation of a terminal alkene containing allylic hydrogen atoms: trans-methylstyrene on Cu{111}

The selective oxidation of trans-methylstyrene, a phenyl-substituted propene that contains labile allylic hydrogen atoms, has been studied on Cu{111}. Mass spectrometry and synchrotron fast XPS were used to detect, respectively, desorbing gaseous products and the evolution of surface species as a function of temperature and time. Efficient partial oxidation occurs yielding principally the epoxide, and the behavior of the system is sensitive to the order in which reactants are adsorbed. The latter is understandable in terms of differences in the spatial distribution of oxygen adatoms; isolated adatoms lead to epoxidation, while islands of "oxidic" oxygen do not. NEXAFS data taken over a range of coverages and in the presence and absence of coadsorbed oxygen indicate that the adsorbed alkene lies essentially flat with the allylic hydrogen atoms close to the surface. The photoemission results and comparison with the corresponding behavior of styrene on Cu{111} strongly suggest that allylic hydrogen abstraction is indeed a critical factor that limits epoxidation selectivity. An overall mechanism consistent with the structural and reactive properties is proposed.     

Optimal detection of changes in probability characteristics

The article considers the problem of sequential discrimination of hypotheses using independent observations. An optimal sequential plan is developed for discrimination of hypotheses about a mismatch in the class of plans with bounded probabilities of making an incorrect decision.Translated from Statisticheskie Metody, pp. 189–204, 1980.     

Critical influence of adsorption geometry in the heterogeneous epoxidation of "allylic" alkenes: structure and reactivity of three phenylpropene isomers on Cu(111)

It has long been conjectured that the difficulty of heterogeneously epoxidizing higher alkenes such as propene is due to the presence in the molecule of "allylic" H atoms that are readily stripped off by the oxygenated surface of the metal catalyst resulting in combustion. Here, taking advantage of the intrinsically higher epoxidation selectivity of Cu over Ag under vacuum conditions, we have used three phenylpropene structural isomers to examine the correlation between adsorption geometry and oxidation chemistry. It is found that under comparable conditions alpha-methylstyrene, trans-methylstyrene, and allylbenzene behave very differently on the oxygenated Cu(111) surface: the first undergoes extensive epoxidation accompanied by relatively little decomposition of the alkene; the second leads to some epoxide formation and extensive alkene decomposition; and the third is almost inert with respect to both reaction pathways. This reactive behavior is understandable in terms of the corresponding molecular conformations determined by near-edge X-ray absorption fine structure spectroscopy and density functional theory calculations. The proximity to the surface of the C=C function and of the allylic H atoms is critically important in determining reaction selectivity. This demonstrates the importance of adsorption geometry and confirms that allylic H stripping is indeed a key process that limits epoxidation selectivity in such cases.     

Field effect as a method for controlling the quality of i-InP-based heteronanostructures with two-dimensional electron gases

The field effect in i-InP-based heteronanostructures has been studied in InP and In_0.52Al_0.48As layers with an In _x Ga_1?x As quantum well with a high Hall electron mobility in the frequency range of (20?2) × 10⁶ Hz and temperature range of 77?C450 K. It is shown that mobility in the field effect depends on the location of Si ??-doped areas with respect to the quantum well and on the doping level. The ??-doping level and the configurations of nanostructures have been determined for the case in which the values of the electron mobility in the field and Hall effects are close to each other and correspond to high values of mobility in the quantum well.