Magneto-optical studies of CdTe/CdMnTe semimagnetic semiconductor superlattices under high pressure

Abstract

The photoluminescence (PL) of a CdTe/CdMnTe superlattice has been studied at pressures up to 4.1GPa, where the phase transition occurs. PL is observed up to this pressure, and it moves to higher energy with pressure at 66meV/GPa. This result is consistent with theory. Magnetic fields decrease the band-gap of the semimagnetic CdMnTe barriers and this reduces the PL energy. The pressure dependence of this effect is expected to provide a stringent test of the theory of semimagnetic materials and of superlattices.     

A re-interpretation of the absorption and excitation spectra of a-Si: H

The absorption spectrum of a-Si: H below the gap consists of an exponential tail whose slope is independent of temperature (up to ≈ 400 K). The excitation spectrum of the 1.4 eV photoluminescence follows the absorption closely. We interpret this in terms of a zero-phonon model for the absorption and emission transitions, and show that this model is compatible with the known behaviour of the photoluminescence.     

An Algorithm for Solving a Resource Allocation Problem

The paper discusses the solution of a resource allocation problem and a new method for solving a special case of the problem. An algorithm for solving the general problem is presented, and computational experience comparing it with existing methods is given.     

The passivation of atomic scale defects present on III–V semiconductor laser facets: an STM/STS investigation

The work presented in this paper is based on the use of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) to study the passivation of atomic scale defect-induced surface states on cleaved III–V (1 1 0) surfaces. This is based on the use of thin Si layers deposited in situ on to the atomically clean surface. The simultaneous STM and STS measurements allowed direct correlation of the structural and electronic properties at the nanoscopic level. The preferential adsorption of Si clusters onto surface defects was achieved using elevated temperature growth on the GaAs(1 1 0) substrate. The STS results clearly indicated local electronic passivation of both step defects and vacancy clusters when the interface is formed at 280 °C. This observation was also confirmed on a macroscopic level using X-ray photoelectron spectroscopy (XPS) under identical conditions. The results are interpreted in terms of the surface bonding of Si with the defect sites. Furthermore, this STM/STS study has been extended to real laser devices where comparable defect features are observed. The implications of defect passivation in nanotechnology are also discussed.     

Thermochemical parameters of dimethyl and di-iso-propyl dithiocarbamate complexes of palladium(II)

The standard molar enthalpy of formation of crystalline dialkyldithiocarbamate chelates, [Pd(S₂CNR₂)₂], with R=CH₃ and i-C₃H₇, was determined through reaction-solution calorimetry in 1,2-dichloroethane, at 298 K. Using the standard molar enthalpies of formation of the gaseous chelates, the homolytic (526±18 and 666±10) and heterolytic (2693±18 and 2957±10 kJ mol^-1) mean enthalpies of palladium-sulphur bond dissociation were calculated. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermochemical Properties of Palladium(II) Chelates Involving Dialkyldithiocarbamates

The standard molar enthalpies of formation of crystalline dialkyldithiocarbamates chelates, [Pd(S₂CNR₂)₂], with R=C₂H₅, n-C₃H₇, n-C₄H₉ and i-C₄H₉, were determined through reaction-solution calorimetry in acetone, at 298.15 K. From the standard molar enthalpies of formation of the gaseous chelates, the homolytic (172.4±3.8, 182.5±3.2,150.9±3.1 and 162.6±3.1 kJ mol⁻¹) and heterolytic (745.0±3.8, 803.7±3.3,834.3±3.1 and 735.2±3.0 kJ mol⁻¹) mean palladium-sulphur bond-dissociation enthalpies were calculated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Band-gap fluctuations in amorphous semiconductors

The exponential absorption tails of amorphous semiconductors are described by integrating the band-to-band absorption over an exponential distribution of band-gap. This requires that the tail states are derived from the band states, and are therefore not highly localised. We show that the fluctuations required by the absorption predict the principal features of the intrinsic 1.4eV luminescence of a-Si:H. The origin of the fluctuations is attributed to ‘frozen’ phonons which constitute the amorphous short-range disorder.     

Thermochemistry of piperidine adducts of some bivalent transition metal bromides

The adducts [MBr₂(pipd) _n ] (where M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), or Zn(II); pipd = piperidine; n = 1/2, 1, or 3/4) were synthesized and characterized by melting points, elemental analysis, thermal studies, and IR and electronic spectroscopy. From calorimetric studies in solution, the standard enthalpies of formation and several other thermochemical parameters of them were determined. The mean standard enthalpies of the metal–nitrogen bonds were calculated, as well as the enthalpies of the adduct formation in the gaseous phase. Using the values obtained for the enthalpies of reaction, the acidity order of the salts is obtained: FeBr₂ > MnBr₂ and CoBr₂ > NiBr₂. Comparing with pyridine adducts, the ligand piperidine is more basic than the ligand pyridine: pipd > py.     

Thermochemistry of some adducts of Indium(III) chloride with neutral donors

The [InCl₃(L) _n ] (where L is 2,2′-bipyridine (bipy), 2,2′-bipyridine N,N′-dioxide (bipyNO), N,N-dimethylacetamide (dma), urea (u), thiourea (tu) or 1,1,3,3-tetramethylthiourea (tmtu); n = 1.5, 3 or 4) were synthesized and characterized by melting points, elemental analysis, thermal analysis and IR spectroscopy. The enthalpies of dissolution of the adducts, Indium(III) chloride and ligands in 1.2 M aqueous HCl were measured and by using thermochemical cycles, the following thermochemical parameters for the adducts have been determined: the standard enthalpies for the Lewis acid/base reactions (Δ_r H ^θ), the standard enthalpies of formation (Δ_f H ^θ), the lattice standard enthalpies (Δ_M H ^θ), and the standard enthalpies of decomposition (Δ_D H ^θ).     

Metal-sensitive and thermostable trypsin from the crevalle jack (<Emphasis Type="Italic">Caranx hippos</Emphasis>) pyloric caeca: purification and characterization

Background

Over the past decades, the economic development and world population growth has led to increased for food demand. Increasing the fish production is considered one of the alternatives to meet the increased food demand, but the processing of fish leads to by-products such as skin, bones and viscera, a source of environmental contamination. Fish viscera have been reported as an important source of digestive proteases with interesting characteristics for biotechnological processes. Thus, the aim of this study was to purify and to characterize a trypsin from the processing by-products of crevalle jack (Caranx hippos) fish.

Results

A 27.5 kDa trypsin with N-terminal amino acid sequence IVGGFECTPHVFAYQ was easily purified from the pyloric caeca of the crevalle jack. Its physicochemical and kinetic properties were evaluated using N-α-benzoyl-_DL-arginine-p-nitroanilide (BApNA) as substrate. In addition, the effects of various metal ions and specific protease inhibitors on trypsin activity were determined. Optimum pH and temperature were 8.0 and 50°C, respectively. After incubation at 50°C for 30 min the enzyme lost only 20% of its activity. K _m , k_cat, and k _cat /K _m values using BApNA as substrate were 0.689 mM, 6.9 s^-1, and 10 s^-1 mM^-1, respectively. High inhibition of trypsin activity was observed after incubation with Cd²⁺, Al³⁺, Zn²⁺, Cu²⁺, Pb²⁺, and Hg²⁺ at 1 mM, revealing high sensitivity of the enzyme to metal ions.

Conclusions

Extraction of a thermostable trypsin from by-products of the fishery industry confirms the potential of these materials as an alternative source of these biomolecules. Furthermore, the results suggest that this trypsin-like enzyme presents interesting biotechnological properties for industrial applications.