Arturo Martinez

Evolution of the amount of InAs in wetting layers in an InAs/GaAs quantum-dot system studied by reflectance difference spectroscopy

The wetting layer (WL) in InAs/GaAs quantum-dot systems has been studied by reflectance difference spectroscopy (RDS). Two structures related to the heavy-hole (HH) and light-hole (LH) related transitions in the WL have been observed. On the basis of a calculation model that takes into account the segregation effect and exciton binding energies, the amount of InAs in the WL (t(WL)) and its segregation coefficient ( R) have been determined from the HH and LH transition energies. The evolutions of tWL and R exhibit a close relation to the growth modes. Before the formation of InAs dots, t(WL) increases linearly from similar to 1 to similar to 1.6 monolayer (ML), while R increases almost linearly from similar to 0.8 to similar to 0.85. After the onset of dot formation, t(WL) is saturated at similar to 1.6 ML and R decreases slightly from 0.85 to 0.825. The variation of tWL can be interpreted by using an equilibrium model. Different variations of in-plane optical anisotropy before and after dot formation have been observed.

Phase behaviour of symmetric binary mixtures with partially miscible components in slit-like pores. Application of the fundamental measure density functional approach

We investigate adsorption in slit-like pores of model symmetric binary mixtures exhibiting demixing in bulk phase, by using a density functional approach. Our focus is on the evaluation of the first-order phase transitions in adsorbed fluids and the lines separating mixed and demixed phases. The scenario for phase transitions is sensitive to the pore width and to the energy of adsorption. Both these parameters can change the phase diagrams of the confined fluid. In particular, for relatively wide pores and for strong wall–fluid interactions, the demixing line can precede the first-order transition. Moreover, a competition between layering transitions and demixing within particular layers also leads to further enrichment of the phase diagram.

Phase behavior of symmetric binary mixture with partially miscible components in slitlike pores: Density functional approach

We investigate adsorption of a model symmetric binary mixture, exhibiting demixing in a bulk phase, in slitlike pores by using a density functional approach. Our focus is on the evaluation of the first-order phase transitions between adsorbed phases and lines delimiting mixed and demixed adsorbed phases. The scenario for phase changes is sensitive to the pore width and to the energy of adsorption. Both these parameters can qualitatively change the phase behavior of the confined fluid. In particular, for relatively wide pores and for strong wall–fluid interactions, a demixing line can precede the first-order transition. Moreover, a competition between layering type behavior and demixing within particular layers also can lead to further complications of the phase diagram, reflected by the presence of consecutive branches, describing the equilibrium between different adsorbed phases.

Phase diagrams for a binary mixture confined in narrow slitlike pores with energetically heterogeneous walls from a lattice mean-field approach

We investigate the phase behaviour of binary symmetric lattice fluid, exhibiting partial demixing in slitlike pores with heterogeneous walls. The calculations are carried out assuming a cubic lattice with vacancies and a model for heterogeneity similar to that of Rocken and Tarazona (1996 J. Chem. Phys. 105 2034). We concentrate on the effects of surface heterogeneity on the scenarios for the phase transformations. It is shown that for wide enough pores a step-wise condensation occurs between demixed phases. For narrower pores the λ-line may cross the boundaries of the bridge phase and multiple critical end points appear. In such cases, at low temperatures the bridge phase formation occurs between demixed phases, at intermediate temperature it involves mixed and demixed phases and finally it becomes a transition between two demixed phases again.

Properties of Transparent Zinc‐Tin Oxide Conducting Films Prepared by Chemical Spray Pyrolysis

In this work we have prepared thin films of zinc‐tin oxide by the chemical spray pyrolysis method. The structural, electrical and optical properties were studied for all films as a function of the zinc content in the starting solution, yielding values of electrical resistivity (ρ), Hall mobility (μ), carrier concentration (n), and optical transmission (T) suitable for optoelectronic applications, e.g. our optimal values were ρ = 3.56×10−2 Ω cm and T = 0.77.