Investigation on Sb distribution for InSb/InAs sub-monolayer heterostructure using TEM techniques.

InSb/InAs sub-monolayer (SML) nanostructures such as SML quantum dots offer sharper emission spectra, a better modal gain and a larger modulation bandwidth compared to its Stranski-Krastanov counterpart. In this work, the Sb distribution of SML InSb layers grown by migration enhanced epitaxy has been analyzed by transmission electron microscopy (TEM) techniques. The analysis of the material by diffraction contrast in 002 dark field conditions and by atomic column resolved high angle annular dark field-scanning TEM reveal the presence of a low Sb content InSbAs continuous layer with scarce Sb-rich InSbAs agglomerates. The intensity profiles obtained by both techniques point to Sb segregation during growth. This segregation has been quantified using the Muraki segregation model obtaining a high segregation coefficient R of 0.81 towards the growth direction. The formation of a continuous InSbAs wetting layer as a result of a SML deposition of Sb on the InAs surface is discussed.

Structural characterization of bulk and nanoparticle lead halide perovskite thin films by (S)TEM techniques.

Lead halide (APbX3) perovskites, in polycrystalline thin films but also perovskite nanoparticles (NPs) has demonstrated excellent performance to implement a new generation of photovoltaic and photonic devices. The structural characterization of APbX3 thin films using (scanning) transmission electron microscopy ((S)TEM) techniques can provide valuable information that can be used to understand and model their optoelectronic performance and device properties. However, since APbX3 perovskites are soft materials, their characterization using (S)TEM is challenging. Here, we study and compare the structural properties of two different metal halide APbX3 perovskite thin films: bulk CH3NH3PbI3 prepared by spin-coating of the precursors in solution and CsPbBr3 colloidal NPs synthetized and deposited by doctor blading. Both specimen preparation methods and working conditions for analysis by (S)TEM are properly optimized. We show that CH3NH3PbI3 thin films grown by a one-step method are composed of independent grains with random orientations. The growth method results in the formation of tetragonal perovskite thin films with good adherence to an underlying TiO2 layer, which is characterized by a photoluminescence (PL) emission band centered at 775 nm. The perovskite thin films based on CsPbBr3 colloidal NPs, which are used as the building blocks of the film, are preserved by the deposition process, even if small gaps are observed between adjacent NPs. The crystal structure of CsPbBr3 NPs is cubic, which is beneficial for optical properties due to its optimal band gap. The absorption and PL spectra measured in both the thin film and the colloidal solution of CsPbBr3 NPs are very similar, indicating a good homogeneity of the thin films and the absence of aggregation of NPs. However, a particular care was required to avoid long electron irradiation times during our structural studies, even at a low voltage of 80 kV, as the material was observed to decompose through Pb segregation.

[Effectiveness of partial splenectomy in the treatment of hereditary spherocytosis]. / Efectividad de la esplenectomía parcial en el tratamiento de la esferocitosis hereditaria.

OBJECTIVES: To evaluate the hematological and clinical response to partial splenectomy in a group of children with hereditary spherocytosis. MATERIAL AND METHODS: We analyzed the main hematological and clinical features in 13 patients with hereditary spherocytosis submitted to partial splenectomy. The diagnosis of the disease and the hematological studies was made according to standard methods. To establish the inheritance pattern we also studied both parents. During the surgical procedure the upper two thirds of the spleen were removed and the lower pole was preserved. We use prophylactic penicillin (250 mg twice a day) during 3 years. RESULTS: The diagnosis of the disease was made during the first year of life in 11 patients, 76.9% had neonatal hyperbilirrubinemia, 53.8% showed hepatomegaly and in 69.2% we observed splenomegaly. 84.6% received blood transfusion. The hemoglobin level was significantly increased (p = 0.04) and the reticulocytes significantly diminished (p = 0.01) after splenectomy. No hemolytic crises, blood cell transfusion requirement neither infection was observed after surgery. CONCLUSIONS: Although the number of patients and the post-surgical follow-up is reduced, the hematological recovery observed in our cases suggest that partial splenectomy is a beneficial surgical procedure for the treatment of the typical and severe form of hereditary spherocytosis.