Electron-hole liquid and excitonic molecules in quasi-two-dimensional SiGe layers of Si/SiGe/Si heterostructures

The electron-hole liquid (EHL) in SiGe layers of Si/Si_{1 − x} Ge _x /Si quantum-confinement heterostructures is discovered. It is composed of quasi-two-dimensional holes in the quantum well formed by the SiGe layer and quasi-three-dimensional electrons, which occupy a wider region of space centered on this layer. The densities of electrons and holes in the EHL are determined to be p ₀ ≈ 8.5 × 10¹¹ cm⁻² and n ₀ ≈ 4.8 × 10¹⁸ cm⁻³, respectively. It is demonstrated that the gas phase consists of excitons and excitonic molecules. The conditions on the band parameters of the structure under which the formation of the EHL of this kind and biexcitons is possible are formulated.     

Metal Nanoparticles with PW11O397- and P2W17O6110- Heteropoly Anions as Stabilizing Agents: Radiation-Chemical Preparation and Properties

The radiation-chemical reduction of silver, copper, cadmium, thallium, lead, cobalt, and nickel ions to form stable metal nanoparticles was studied in the presence of PW₁₁O₃₉ ^7- and P₂W₁₇O₆₁ ^10- heteropoly anions in aqueous solutions containing sodium formate or isopropanol. The heteropoly anions were found to be efficient stabilizing agents for the resulting sols. The optical characteristics of the sols were determined.     

Synthesis and Structure of Perchloro-1λ5,3λ5-diphosphetane

Russian Journal of General Chemistry -     

Kinetics of film formation by interfacial polycondensation

An approximate analytical model of film formation by interfacial polycondensation is presented. The analysis requires knowledge of a minimal set of certain kinetic parameters (monomer diffusivities and reaction rate constants) and reaction conditions (monomer concentrations and thickness of the unstirred layer). The process proceeds as a succession of two or three markedly different kinetic regimes. Each regime (insipient film formation, slowdown, and diffusion-limited growth) sets a different pattern of local polymer accumulation, with important implications for the structure of the emerging film. At the incipient stage, a loose polymer film begins to emerge in a fixed narrow region inside the boundary layer, followed by gradual densification of the middle part of the film. A condition for film formation is thus formulated on the basis of our analysis. The model predicts that two different scenarios are possible, which depend on the permeability of the polymer: films with a low permeability to both monomers pass through an abrupt slowdown of film growth, whereas permeable films undergo a smooth transition between the incipient film formation and diffusion-limited regimes. The model incorporates the highly important effects of the accumulation of reactive end groups and the decrease of monomer diffusion with the polymer concentration on the kinetics of the process and film characteristics. In addition, the validity of the utilized mean-field approach is analyzed, and the analysis suggests a direct correlation between the roughness and the thickness of the film. The results are in good agreement with an earlier numerical study and the direct structural studies of polyamide membrane films.     

Anion substitution in zinc chalcogenides

Anion substitution effects on the structure and energy of zinc chalcogenides were studied with the semiempirical molecular orbital method MSINDO. Cyclic clusters of different sizes were chosen as model systems. The convergence of the bulk properties of the perfect clusters with increasing cluster size was tested. Single and multiple substitution of oxygen atoms in zinc oxide by sulfur and of sulfur atoms in zinc sulfide by oxygen served to determine the energetics of substitution for these two cases. It was found that the substitution of oxygen by sulfur in ZnO is easier than the substitution of sulfur by oxygen in ZnS in agreement with experimental results. The interaction between two oxygen atoms vs. two selenium atoms in zinc sulfide was investigated. Oscillations of the cluster energy in dependence of the distance between the two doping atoms were observed. These are explained by the relative sites of the doping atoms in the crystal lattice. The magnitude of the oscillations is smaller in ZnS:Se than in ZnS:O, because the difference between the anion radii of S2- and Se2- is smaller than between S2- and O2-. This is also reflected in the band gap.     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

MALDI produced ions inspected with a linear ion trap-orbitrap hybrid mass analyzer

A MALDI source is interfaced to a modified LTQ Orbitrap XL instrument. This work gives insight into the MALDI source design and shows results obtained with the MALDI source coupled to an accurate mass, high-resolution hybrid mass spectrometer. MALDI-produced ions and fragment ions thereof produced in the mass spectrometer may be analyzed and detected by the Orbitrap analyzer at a maximum mass resolution of 100,000 (FWHM) at m/z 400 with high mass accuracy. An accuracy of ≤2 ppm is achieved by internal mass calibration using lock mass functionality; using external mass calibration, an accuracy of ≤3 ppm is routinely obtained. External mass calibration of the hybrid mass spectrometer is performed using a standard calibration mixture of different peptides and matrix components. The instrumental capabilities are demonstrated for analytical methodologies such as Protein ID using Peptide Mass Fingerprint (PMF) and MS/MS analyses of small molecule samples. Stability of mass accuracy and signal-to-noise ratio for low samples loads (on plates) are demonstrated as well as the experimental dynamic range using α-cyano-4-hydroxy cinnamic acid (CHCA) matrix.     

Synthesis of 1-[(nitroxyalkoxy)methoxy]-1-triazene 2-oxides,new hybrid nitrogen monoxide donors

1-[(Nitroxyalkoxy)methoxy]-3,3-dialkyl-1-triazene 2-oxides were obtained by the reaction of 3,3-dialkyl-1-hydroxy-1-triazene 2-oxide sodium salts with β- or γ-nitroxyalcohol chloromethyl ethers or by the reaction of 3,3-dialkyl-1-(bromoalkoxymethoxy)-1-triazene 2-oxides with silver nitrate. These compounds can be of interest as new hybrid NO donors in living organisms.     

35Cl NQR Studies of the Geometry of Aromatic Imines

The preferred conformation of solidphase R4benzylidene3,4dichloroaniline molecules has been established by nuclear quadrupole resonance (NQR) combined with quantum chemical calculations. The conformational effect of substitutes reported previously is proved. The rotation angle of the plane of the aniline ring with respect to the plane of the azomethine bond is given.