СТРУКТУРА И ЭЛЕКТРОННЫЕ СВОЙСТВА ДЕФЕКТОВ НА ГРАНИЦЕ СОЕДИНЕННЫХ ПЛАСТИН КРЕМНИЯ

Comprehensive studies of the structure and electronic properties of defects occurring on the connection boundary of disarranged n−type Si(001) wafers have been made by the methods of transmission electron microscopy, deep level transient spectroscopy (DLTS) and photoluminescence. The main revealed defects are two types of dislocation structure: orthogonal dislocation network composed of two screw dislocation families and zigzag mixed dislocations. The dislocation structures observed are sources of intense luminescence whose spectra are appreciably different from the standard dislocation luminescence spectra at all the investigated misfit angles of the Si bonded wafers. We show that an increase of the misfit angle results in a strong transformation of the dislocation luminescence spectra consisting in changes of the form of the spectra and a decrease in the integral luminescence intensity. In the samples in question the DLTS method revealed the presence of deep centers the concentration of which increased with increasing of twist misorientation of bonded wafers. It has been established that the deep centers are related to the dislocation structures observed by means of transmission electron microscopy. Методами просвечивающей электрон- ной микроскопии, нестационарной спектроскопии глубоких уровней и фотолюминесценции проведено ком- плексное исследование структуры и электронных свойств дефектов, воз- никающих на границе соединения разориентированных пластин Si(001) n−типа проводимости. Установлено, что основными выявленными де- фектами являются дислокационные структуры двух видов: ортогональная сетка дислокаций, состоящая из двух семейств винтовых дислокаций, и зигзагообразные смешанные дис- локации. Выявлено, что наблюдаемые дислокационные структуры являются источником интенсивной люминес- ценции, спектр которой значительно отличается от стандартного спектра дислокационной люминесценции при всех исследуемых углах поворотной разориентации пластин Si. Показано, что при увеличении угла разориен- тации происходит сильная транс- формация спектров дислокационной люминесценции, которая заключается в изменении формы спектров и умень- шении интегральной интенсивности люминесценции. Методом нестацио- нарной спектроскопии глубоких уров- ней в исследуемых образцах выявлено наличие глубоких центров, концентра- ция которых возрастает с увеличением угла разориентации пластин. Уста- новлено, что обнаруженные глубокие центры связаны с наблюдаемыми методом просвечивающей электрон- ной микроскопии дислокационными структурами.

Metallocavitins as Advanced Enzyme Mimics and Promising Chemical Catalysts

The supramolecular approach is becoming increasingly dominant in biomimetics and chemical catalysis due to the expansion of the enzyme active center idea, which now includes binding cavities (hydrophobic pockets), channels and canals for transporting substrates and products. For a long time, the mimetic strategy was mainly focused on the first coordination sphere of the metal ion. Understanding that a highly organized cavity-like enzymatic pocket plays a key role in the sophisticated functionality of enzymes and that the activity and selectivity of natural metalloenzymes are due to the effects of the second coordination sphere, created by the protein framework, opens up new perspectives in biomimetic chemistry and catalysis. There are two main goals of mimicking enzymatic catalysis: (1) scientific curiosity to gain insight into the mysterious nature of enzymes, and (2) practical tasks of mankind: to learn from nature and adopt from its many years of evolutionary experience. Understanding the chemistry within the enzyme nanocavity (confinement effect) requires the use of relatively simple model systems. The performance of the transition metal catalyst increases due to its retention in molecular nanocontainers (cavitins). Given the greater potential of chemical synthesis, it is hoped that these promising bioinspired catalysts will achieve catalytic efficiency and selectivity comparable to and even superior to the creations of nature. Now it is obvious that the cavity structure of molecular nanocontainers and the real possibility of modifying their cavities provide unlimited possibilities for simulating the active centers of metalloenzymes. This review will focus on how chemical reactivity is controlled in a well-defined cavitin nanospace. The author also intends to discuss advanced metal–cavitin catalysts related to the study of the main stages of artificial photosynthesis, including energy transfer and storage, water oxidation and proton reduction, as well as highlight the current challenges of activating small molecules, such as H2O, CO2, N2, O2, H2, and CH4

A monocarboxylate-bridged diiron(III) mu-oxido complex that catalyzes alkane oxidation by hydrogen peroxide

Reaction of the ligand 2-(N-isopropyl-N-{(2-pyridyl)methyl}aminomethyl)- 6-(N-(carboxymethyl)-N-((2-pyridyl)-methyl) aminomethyl)- 4-methylphenol (H2IPCPMP) with two equivalents of Fe(ClO4)(2) and two equivalents of sodium pivalate in air leads to the formation of the mu-oxido, mu-carboxylato-bridged diiron complex [{Fe(H-IPCPMP)}(2)(mu-O)(Piv)]ClO4 (1) (Piv = pivalate). Complex 1 is capable of catalysing the oxidation of cyclohexane or 1,2-cis-dimethylcyclohexane by hydrogen peroxide, leading to the formation of the corresponding cyclohexanone and cyclohexanol, as well as a small amount of cyclohexyl hydroperoxide

Synthesis and Characterization of Iron(III) Complexes of a New Ligand Containing a Potentially Bridging Carboxylate; Structural Characterization of Helical Tetranuclear Iron Complex

Reaction of the new polydentate ligand 2,6-bis{3-[N,N-di(2-pyridylmethyl)amino]propoxy}benzoic acid (LH) with Fe(ClO4)3 followed by addition of chloroacetic acid leads to the formation of the tetranuclear complex [{Fe2OL(ClCH2- CO2)2}2](ClO4)4, the crystal structure of which reveals that it consists of two FeII2(µ-O)(µ-RCO2)2 cores that are linked via the two L ligands in a helical structure, with the carboxylate moieties of the two ligands forming a hydrogen-bonded pair at the center of the helix

Catalytic C-H oxidations by nonheme mononuclear Fe(II) complexes of two pentadentate ligands: Evidence for an Fe(IV) oxo intermediate

The oxidation reactions of alkanes with hydrogen peroxide and peracids (peracetic acid (PAA) and m-chloroperoxybenzoic acid (mCPBA)) catalysed by two Fe(II) complexes of pentadentate {N5}-donor ligands have been investigated. Kinetic isotope effect experiments and the use of other mechanistic probes have also been performed. While the total yields of oxidized products are similar regardless of oxidant (e.g. 30–39% for oxidation of cyclohexane), the observed alcohol/ketone ratios and kinetic isotope effects differ significantly with different oxidants. Catalytic reactions in H2O2 medium are consistent with the involvement of hydroxyl radicals in the CH bond cleavage step, and resultant low kinetic isotope effect values. On the other hand, catalytic reactions performed using peracid media indicate the involvement of an oxidant different from the hydroxyl radical. For these reactions, the kinetic isotope effect values are relatively high (within a range of 4.2–5.1) and the C3/C2 selectivity parameters in adamantane oxidation are greater than 11, thereby excluding the presence of hydroxyl radicals in the CH bond cleavage step. A low spin Fe(III)-OOH species has been detected in the H2O2-based catalytic system by UV/Vis, mass spectrometry and EPR spectroscopy, while an Fe(IV)-oxo species is postulated to be the active oxidant in the peracid-based catalytic systems. Computational studies on the CH oxidation mechanism reveal that while the hydroxyl radical is mainly responsible for the H-atom abstraction in the H2O2-based catalytic system, it is the Fe(IV)-oxo species that abstracts the H-atom from the substrate in the peracid-based catalytic systems, in agreement with the experimental observations.This work was financially supported by the Robert A. Welch Foundation (grant B-1093 ) and the Wenner-Gren Foundation