Absorption and luminescence of hydrogen and oxygen passivated silicon quantum dots

Silicon (Si) quantum dots (QDs) passivated with oxygen and hydrogen of size 1 nm in diameter are prepared by wet chemical route and electrochemical route respectively. The optical measurements reveal the strong absorption feature around 4.7 eV and weak absorption at 3.4 eV for oxygen passivated Si QDs. Hydrogen passivated Si QDs of the same size show absorption at 4.9 eV. Both the oxygen and hydrogen passivated Si QDs show broad luminescence around 3.9 and 3.8 eV. Films of these QDs, when coated on crystalline silicon solar cells, show an increase in the efficiency of the solar cell by 12 %. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/2788

Nanometer-scale studies of Al–Ga interdiffusion and As precipitate coarsening in nonstoichiometric AlAs/GaAs superlattices

We have investigated the effects of post-growth annealing on Al–Ga interdiffusion and As precipitate coarsening in AlAs/GaAs superlattices grown by molecular-beam epitaxy at low temperatures. High-resolution x-ray diffraction spectra show a significant decrease in the number and intensity of satellite peaks for the ex situ annealed compared with the as-grown superlattices, a feature which is often attributed to a reduction in interface abruptness. However, our cross-sectional scanning tunneling microscopy images show significant variation in the apparent superlattice period of the ex situ annealed compared with the as-grown superlattices. For the as-grown superlattices, preferential As precipitation on the GaAs side of AlAs/GaAs interfaces is evident. In the ex situ annealed superlattices, a preference for As precipitates at the GaAs on AlAs interface is apparent, although the As precipitates are no longer restricted to the interface region. Thus, the apparent change in superlattice period is likely due to variations in As precipitate density, which may be influenced by AlAs–GaAs alloying at the AlAs/GaAs interfaces. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70551/2/APPLAB-75-26-4082-1.pd

Is prenatal screening for Down syndrome needed in young pregnant women?

Background: Down syndrome originally known as Mongoloid’s idiocy is the most common autosomal disorder. Down syndrome (DS) can be detected by prenatal diagnosis which includes the triple marker screening test and chromosomal analysis.Methods: The study population comprised of 100 pregnant females amongst the age group of 20-45 (32.10±4.86) years. Triple Marker Test was done followed by amniocentesis or CVS with karyotyping or FISH.Results: Risk of <1:250 was considered high risk whereas ≥1:250 was considered as low risk. 32/45 (71%) were false-positive for Trisomy 21 detected as high risk by TMT. But there was good sensitivity and specificity for Trisomy 18.Conclusions: It can be concluded that the triple marker test is indeed only a screening test for the DS and that it has to be confirmed with the help of chromosomal analysis. The higher maternal age is an important parameter in DS but nowadays, even ones with a lower maternal age can also have a child with DS. So, in general, now all women are recommended to go for biochemical screening during their pregnancy

A conversion electron Mossbauer spectroscopy study of ion beam mixing at Fe: polyethylene interface

The effects of ion beam induced atomic mixing at the Fe-Polyethylene interface have been investigated by means of conversion electron Mossbauer spectroscopy [CEMS]. It is shown that the as deposited and ion beam mixed composites exhibit distinctly different features. In particular, the ion beam mixed composite shows that presence of Fe2+ state in polyethylene matrix along with the Fe-C austenite like phase