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Photoluminescent porous layers were formed on highly resistive p-type silicon by metal-assisted chemical etching using Na2S2O8 as an oxidizing agent. A thin layer of Ag was deposited on the (100) Si surface prior to immersion in a solution of HF and Na2S2O8. The morphology of the porous silicon (PS) layer formed by this method as a function of etching time was investigated by scanning electron microscopy (SEM). It shows that the surface is porous and the thickness of PS layer increases with etching time and is not limited as observed with the electrochemical method. Energy-dispersive X-ray (EDX) was used to analyse the chemical composition of PS layers. The EDX spectra show that the metal is not present on the PS surface after etching. Photoluminescence (PL) from metal-assisted chemically etched layers was measured using a He-Cd laser ...
A light-emitting layer has been made on highly resistive n-type silicon (6.4 kcm) using photochemical etching in a mixture of HF with H2O2. The morphology of the porous films grown after exposure to a He-Ne laser (633 nm) at normal incidence was analysed by Atomic Force Microscopy (AFM). The results show that the film obtained are porous and the morphology of the porous layer obtained are shown to be similar to that obtained by the electrochemical method on highly doped silicon. Furthermore, excitation of the porous silicon layer formed on highly resistive silicon samples under He-Cd laser (325 nm) irradiation shows that the PL intensity increases with increasing etching time. The maximum PL spectrum peaked at 636 nm with a FWHM of about 0.3 eV. Finally, the quantum confinement effect has been invoked to explain the bright, visible, ro...
The high-affinity receptor for human granulocyte/macrophage colony-stimulating factor (hGM-CSF) is composed of two subunits, alpha and beta. The alpha subunit binds GM-CSF with low affinity, whereas the beta subunit does not bind GM-CSF by itself. The alpha and beta subunits together form the high-affinity GM-CSF receptor. The beta subunit has extensive sequence homology with the mouse interleukin 3 (IL-3) receptor (AIC2A) and its homologue (AIC2B) that does not bind IL-3 or other cytokines including GM-CSF. To examine the function of these receptor components, we expressed the alpha subunit of the hGM-CSF receptor with the human beta subunit or the mouse AIC2A or AIC2B in a mouse IL-3-dependent pro-B-cell line, Ba/F3, and in a mouse IL-2-dependent T-cell line, CTLL2. Coexpression of the alpha and beta subunits in Ba/F3 and CTLL2 cells...
Erythropoietin (Epo) is a cytokine which specifically regulates differentiation and proliferation of erythroid progenitor cells. We report here that Epo receptor expressed in interleukin 3-dependent lymphoid Ba/F3 cells transmits both differentiation and growth signals. Epo stimulation of these cells leads to activation of transcription and/or translation of the erythroid-specific transcription factors GATA-1 and SCL, followed by the accumulation of both alpha- and beta-globin chains. These results suggest that expression and activation of the Epo receptor regulates erythroid-specific gene expression and might play a role in determining a cell lineage in vivo and that GATA-1 and SCL may exert their effects after Epo binds to its receptor. It was further found that chimeric receptors composed of extracellular domains of Epo receptor and...
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