Optical Study of GaAs quantum dots embedded into AlGaAs nanowires

We report on the photoluminescence characterization of GaAs quantum dots embedded into AlGaAs nano-wires. Time integrated and time resolved photoluminescence measurements from both an array and a single quantum dot/nano-wire are reported. The influence of the diameter sizes distribution is evidenced in the optical spectroscopy data together with the presence of various crystalline phases in the AlGaAs nanowires.Comment: 5 page, 5 figure

Spin 1/2 Particle with Two Masses in External Magnetic Field

Equation for spin 1/2 particle with two mass states is investigated in presence of magnetic field. The problem reduces to a system of 4 linked 2-nd order differential equations. After diagonalization of the mixing term, separate equations for four different functions are derived, in which the spectral parameters coincide with the roots of a 4-th order polynomial. Solutions are constructed in terms of confluent hypergeometric functions; four series of energy spectrum are found. Numerical study of the spectra is performed. Physical energy levels for the two mass fermion differ from those for the ordinary Dirac fermion

Understanding hysteresis in carbon dioxide sorption in porous metal-organic frameworks

Two new isostructural microporous coordination frameworks [Mn3(Hpdc)2­(pdc)2] (1) and [Mg3(Hpdc)2­(pdc)2] (2) (pdc2– = pyridine-2,4-dicarboxylate) showing primitive cubic (pcu) topology have been prepared and characterized. The pore aperture of the channels is too narrow for the efficient adsorption of N2; however, both compounds demonstrate substantially higher uptake of CO2 (119.9 mL·g–1 for 1 and 102.5 mL·g–1 for 2 at 195 K, 1 bar). Despite of their structural similarities, 2 shows a typical reversible type I isotherm for adsorption/desorption of CO2, while 1 features a two-step adsorption process with a very broad hysteresis between the adsorption and desorption curves. This behavior can be explained by a combination of density functional theory calculations, sorption, and X-ray diffraction analysis and gives insights into the further development of new sorbents showing adsorption/desorption hysteresis

Stoichiometry and absolute atomic concentration profiles obtained by combined Rutherford backscattering spectroscopy and secondary-ion mass spectroscopy: InAs nanocrystals in Si

Abstract Rutherford backscattering spectroscopy (RBS) and secondary-ion mass spectroscopy (SIMS) were combined to achieve depth profiling calibrated in absolute atomic concentrations. This method was applied to InAs nanocrystals, grown by molecular beam epitaxy (MBE), buried in a Si matrix. By means of RBS, with its capability of accessing the buried layers, we determined the depth-integrated areal densities of As and In. These were used to calibrate the SIMS profiles with their high depth resolution and dynamic range in absolute atomic concentrations. This allowed us to identify, besides a well confined layer of stoichiometric InAs nanocrystals, significant diffusion of In and As into the Si matrix in despite of their larger atomic radii, and an excess of As due to its non-reactive deposition on Si from the excess As 4 flux during the MBE growth. On the basis of these findings, we suggest measures to optimize the MBE process for InAs/Si and similar systems

Experimental model of normotrophic pseudarthrosis of a rabbit’s tibia

Background. The formation of a pseudarthrosis is one of the most severe complications of bone fractures. Pseudarthrosis occurs as a result of a disorder in the fracture union, has a poor prognosis and requires long-term treatment and repeated surgeries. A small number of representative pseudarthrosis models makes it difficult to conduct preclinical studies of promising pharmacological substances, bone replacement materials and surgical methods of treatment.The aim. To develop and to validate an experimental model of normotrophic pseudarthrosis of a rabbit’s tibia by creating diastasis between bone fragments, forming local vascularization disturbance and using unstable fixation.Materials and methods. The study was carried out on Soviet Chinchilla rabbits. The animals were divided into 2 groups: in experimental group, we formed tibial pseudarthrosis; in control group, we made a simple transverse tibial fracture. The pseudarthrosis was formed by segmental resection (5 mm) of the middle third of the tibia, bone fragments dilatation for 5 mm, removal of periosteum and bone marrow within 5 mm followed by daily destabilization of a fracture in an external fixation device. The duration of the experiment was 6 weeks. X-ray examination of the fracture area was carried out weekly, multi-layer spiral computed tomography (MSCT) and histological examinations were carried out at the end of the experiment.Results. The survival value in the experiment was 100 %. According to weekly X-ray examination, fracture union was registered only in the control group and occurred on average on the 22,8 ± 5,1 day, while the formation of pseudarthrosis was observed only in the experimental group, and radiographic signs of a pseudarthrosis were noted on average on the 33,6 ± 3,5 day. The formation of a pseudarthrosis by the end of the experiment was confirmed by MSCT and histological studies.Conclusions. The developed model of the normotrophic pseudarthrosis of a rabbit’s tibia can be used for experimental tests of various factors for stimulating reparative regeneration and methods for treatment of the pseudarthrosis

Halochromic coordination polymers based on a triarylmethane dye for reversible detection of acids

Chromeazurol B (Na2HL) is a pH-sensitive (halochromic) dye based on a hydroxytriarylmethane core and two carboxylate functional groups, which makes it suitable for the synthesis of coordination polymers. Two new coordination polymers [NaZn4(H2O)3(L)3]·3THF·3H2O (1) and [Zn3(H2O)3(μ2- OH2)(μ3-OH)(HL)2(H2L)]·2THF·3H2O (2) incorporating Chromeazurol B linkers have been prepared and characterised. The structure of 1 comprises pentanuclear heterometallic {Zn4Na} nodes linked by six L3– anions to give a layered structure with a honeycomb topology. 2 crystallizes as a double-chain ribbon (ladder) structure with two types of metal node: a mononuclear Zn(II) cation and tetranuclear {Zn(II)}4 cluster. Chromeazurol B anions link each tetranuclear cluster to four individual Zn(II) cations and each Zn(II) cation with four tetranuclear clusters. Both compounds show pH-sensitivity in water solution which can be observed visually, giving the first example of a halochromic coordination polymer. The halochromic properties of 1 towards HCl vapors were systematically investigated. As-synthesized violet-grey 1 reversibly changes color from orange to pink in the presence of vapors of 2M and 7M HCl, respectively. The coordination of the Chromeazurol B anion at each color stage was examined by diffuse reflectance spectroscopy and FT-IR measurements. The remarkable stability of 1 to acid and the observed reversible and reproducible color changes provide a new design for multifunctional sensor materials