Probing the light hole/heavy hole switching with correlated magneto-optical spectroscopy and chemical analysis on a single quantum dot.

A whole series of complementary studies have been performed on the same single nanowire containing a quantum dot: cathodoluminescence spectroscopy and imaging, micro-photoluminescence spectroscopy under magnetic field and as a function of temperature, and energy-dispersive x-ray spectrometry and imaging. The ZnTe nanowire was deposited on a Si3N4 membrane with Ti/Al patterns. The complete set of data shows that the CdTe quantum dot features the heavy-hole state as a ground state, although the compressive mismatch strain promotes a light-hole ground state as soon as the aspect ratio is larger than unity (elongated dot). A numerical calculation of the whole structure shows that the transition from the heavy-hole to the light-hole configuration is pushed toward values of the aspect ratio much larger than unity by the presence of a (Zn, Mg)Te shell, and that the effect is further enhanced by a small valence band offset between the semiconductors in the dot and around it.

Quantitative Reconstructions of 3D Chemical Nanostructures in Nanowires.

Energy dispersive X-ray spectrometry is used to extract a quantitative 3D composition profile of heterostructured nanowires. The analysis of hypermaps recorded along a limited number of projections, with a preliminary calibration of the signal associated with each element, is compared to the intensity profiles calculated for a model structure with successive shells of circular, elliptic, or faceted cross sections. This discrete tomographic technique is applied to II-VI nanowires grown by molecular beam epitaxy, incorporating ZnTe and CdTe and their alloys with Mn and Mg, with typical size down to a few nanometers and Mn or Mg content as low as 10%.

Structure and morphology in diffusion-driven growth of nanowires: the case of ZnTe.

Gold-catalyzed ZnTe nanowires were grown at low temperature by molecular beam epitaxy on a ZnTe(111) B buffer layer, under different II/VI flux ratios, including with CdTe insertions. High-resolution electron microscopy and energy-dispersive X-ray spectroscopy (EDX) gave information about the crystal structure, polarity, and growth mechanisms. We observe, under stoichiometric conditions, the simultaneous presence of zinc-blende and wurtzite nanowires spread homogeneously on the same sample. Wurtzite nanowires are cylinder-shaped with a pyramidal-structured base. Zinc-blende nanowires are cone-shaped with a crater at their base. Both nanowires and substrate show a Te-ended polarity. Te-rich conditions favor zinc-blende nanowires, while Zn-rich suppress nanowire growth. Using a diffusion-driven growth model, we present a criterion for the existence of a crater or a pyramid at the base of the nanowires. The difference in nanowire morphology indicates lateral growth only for zinc-blende nanowires. The role of the direct impinging flux on the nanowire's sidewall is discussed.

Biomonitoring of DNA damage and cytotoxicity in individuals exposed to cone beam computed tomography.

OBJECTIVES: The aim of the present study was to evaluate DNA damage (micronucleus) and cellular death (pyknosis, karyolysis and karyorrhexis) in exfoliated buccal mucosa cells from adults following cone beam CT exposure. METHODS: A total of 19 healthy adults (10 men and 9 women) submitted to cone beam CT were included. RESULTS: No significant statistically differences (P > 0.05) in micronucleus frequency were seen before and after cone beam CT exposure. In contrast, the tomography was able to increase other nuclear alterations closely related to cytotoxicity such as karyorrhexis, pyknosis and karyolysis (P < 0.05). CONCLUSION: In summary, these data indicate that cone beam CT may not be a factor that induces chromosomal damage, but it is able to promote cytotoxicity.

[Possibility of prenatal diagnosis of progressive muscular dystrophy: evaluation of creatine kinase activity in serum and the capping of lymphocytes]. / Possibilita' di diagnosi prenatale di distrofia muscolare progressive: valutazione dell'attivita' creatina-chinasica del siero e del "capping" dei linfociti.

Duchenne muscular dystrophy is a severe inherited disease. The pathogenesis is unknown. Duchenne dystrophy is characterized by a large number of membrane abnormalities, which are manifested by a leakage of muscle enzymes, such as creatine kinase (CK), and a reduction in cap formation in lymphocytes. In the present study serum CK and percentage lymphocyte capping in 8 patients with progressive muscular dystrophy, 6 with different myopathies and normal controls are investigated. Reduced antibody-induced redistribution of membrane antigens of B and T lymphocytes and high serum CK activity is found in boys with Duchenne dystrophy if compared with normal subjects and no correlation exists between the two parameters. Our data indicate that the determination of fetal serum CK activity associated with fetal lymphocyte capping may have diagnostic value in antenatal detection of Duchenne dystrophy.