Scanning probe microscopy studies of PbS surfaces oxidized in air and etched in aqueous acid solutions

Natural n-type PbS single crystals have been studied using AFM, STM and STS after long-term oxidation in air at ambient temperatures and extensive etching in aqueous acid solutions, in contrast to previous work devoted to initial corrosion of fresh surfaces. The exposure of PbS to atmosphere at high relative humidity for several days yields widespread loose oxidation products; the process is much slower at low humidity. Surface morphologies diverge after the treatment in 1 M perchloric and hydrochloric acid solutions at room temperature and become widely different at elevated temperatures, displaying commonly etch pits up to several micrometers in size and depth along with rather uniformly distributed 20-100 nm protrusions of PbS phase. The changes both in topography and semiconducting properties of PbS found by tunneling spectroscopy have been explained in terms of the non-uniform distribution of donor- and acceptor-type defects D⁺/D⁻ in the metal depleted surface layer, which are generated by chemical reactions and, in turn, determine the rates of the PbS corrosion. In particular, the D⁻ centers exhibit a self-catalyzing effect on the non-oxidative local dissolution of PbS in HCl media, resulting in the deep etch pits.     

Development of the Concept of High-Power Microwave Oscillators with Phase Locking by an External Signal

Radiophysics and Quantum Electronics - By simulations and experiments we develop a method for generation phase locking of a Ka-band subgigawatt nonstationary relativistic backward-wave oscillator...     

Crystal Structure and Properties of Acid Salt of Orthoperiodic Acid CsH9I2O12

The acid salt of orthoperiodic acid CsH₉I₂O₁₂crystallizes in the monoclinic system: base-centered unit cell, space group Cc. Unit cell parameters: a=18.473(5) Å, b= 5.439(2) Å, c= 10.481(3) Å, = 99.73°. The crystal structure consists of layers parallel to the yzcrystallographic axis. The layers are formed by the Cs⁺ions, the molecules of orthoperiodic acid IO(OH)₅, and by the IO₂(OH)^– ₄ions and are joined via hydrogen bonds. The studies of proton conductivity of ceramics reveal their transition into a superionic state at temperatures above 40°C.     

Mechanochemical synthesis of mixed-ligand europium β-diketonates with nitrogen-containing neutral ligands

The solid-phase reaction between europium salts of β-diketones and nitrogen-containing neutral ligands in a planetary mill produces luminescent mixed-ligand compounds Eu(β-dic)₃ · D, where β-dic stands for dibenzoylmethane (DBM), benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or benzoyltrifluoroacetone (BTFA); and D stands for 1,10-phenanethroline (Phen), 2,2-dipyridyl (Dipy), or diphenylguanidine (DPG). The mechanosynthesis and yield of lanthanide β-diketonates are studied as affected by the treatment parameters and the nature of the reagents. Powder X-ray diffraction demonstrates a staged course of the mechanochemical synthesis. Examination of formation-rate curves shows that grinding/stirring is the rate-controlling stage of the process. Thermogravimetric analysis (TGA) shows that the mechanosynthesis can proceed in the self-propagation mode. The relative luminescence intensity is determined as a function of treatment time. Particles of the mechanically activated mixture have sizes of 10–100 μm.     

Preparation and Structural and Electrochemical Characteristics of a Carbon-Containing Material Based on Aspen Bark Modified with Zinc and Iron Chlorides

Russian Journal of Applied Chemistry - The possibility of using aspen bark modified with zinc and iron chlorides for preparing highly porous materials with specific properties was examined. The...     

Oxidative transformations of labdane diols. III. Preparation of acids with a strobane skeleton from larixol

It has been shown that the oxidation of larixol with chromic acid mixture forms methyl 6-oxo-8α,13α-epoxystroban-14β-oate, methyl 6-oxo-8α,13α-epoxystroban-14α-oate, and 6,13-dioxo-14,15-bisnorlabd-7-en-17-oate.     

Oxidative transformations of labdane diols. III. Preparation of acids with a strobane skeleton from larixol

It has been shown that the oxidation of larixol with chromic acid mixture forms methyl 6-oxo-8,13-epoxystroban-14-oate, methyl 6-oxo-8,13-epoxystroban-14-oate, and 6,13-dioxo-14,15-bisnorlabd-7-en-17-oate.Novosibirsk Institute of Organic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 697–703, November–December, 1986.     

Characteristics of copper sulfide nanoparticles obtained in the copper sulfate–sodium thiosulfate system

Stable hydrosols of copper sulfide nanoparticles are synthesized by heating aqueous solutions with different ratios of sodium thiosulfate and copper sulfate in the presence of polyvinylpyrrolidone and studied by a number of physicochemical methods in situ (optical spectroscopy, dynamic light scattering) and ex situ (transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy). The main product is CuS covellite nanoparticles with some impurities of other phases (Cu₂S, Cu_1,8S, Cu₇S₄). With an increase in the initial molar ratio S₂O ^2?₃ / Cu from 0.2 to 5 the nanoparticle size increases from 1-5 nm to 30-50 nm and then decreases to 4 nm at a ratio of 10. A substantial increase in the intensity of plasmon absorption within 800-1500 nm is observed during the formation of planar nanoparticles with a lateral size of about 30 nm at S₂O ^2?₃:Cu = 5. A band gap obtained from both direct and indirect optical absorption spectra of sulfides (2.6 eV and 1.7 eV respectively) remains constant for all particles.