Influence of the temperature on the carrier capture into self-assembled InAs/GaAs quantum dots

Photoluminescence (PL) spectroscopy and atomic-force microscopy (AFM) were used to investigate the size evolution of InAs quantum dots on GaAs(001) as a function of the amount of InAs material. Different families of islands were observed in the AFM images and unambiguously identified in the PL spectra, together with the signal of the wetting layer. PL measurements carried out at low and intermediate temperatures showed a thermal carrier redistribution among dots belonging to different families. The physical origin of this behavior is explained in terms of the different temperature dependence of the carrier-capture rate into the quantum dots. At high temperatures, an enhancement of the total PL-integrated intensity of the largest-sized quantum dots was attributed to the increase of diffusivity of the photogenerated carriers inside the wetting layer. (C) 2003 American Institute of Physics.931016279628

Searching for molecular markers in head and neck squamous cell carcinomas (HNSCC) by statistical and bioinformatic analysis of larynx-derived SAGE libraries

Background: Head and neck squamous cell carcinoma (HNSCC) is one of the most common malignancies in humans. The average 5-year survival rate is one of the lowest among aggressive cancers, showing no significant improvement in recent years. When detected early, HNSCC has a good prognosis, but most patients present metastatic disease at the time of diagnosis, which significantly reduces survival rate. Despite extensive research, no molecular markers are currently available for diagnostic or prognostic purposes. Methods: Aiming to identify differentially-expressed genes involved in laryngeal squamous cell carcinoma (LSCC) development and progression, we generated individual Serial Analysis of Gene Expression (SAGE) libraries from a metastatic and non-metastatic larynx carcinoma, as well as from a normal larynx mucosa sample. Approximately 54,000 unique tags were sequenced in three libraries. Results: Statistical data analysis identified a subset of 1,216 differentially expressed tags between tumor and normal libraries, and 894 differentially expressed tags between metastatic and non-metastatic carcinomas. Three genes displaying differential regulation, one down-regulated (KRT31) and two up-regulated (BST2, MFAP2), as well as one with a non-significant differential expression pattern (GNA15) in our SAGE data were selected for real-time polymerase chain reaction (PCR) in a set of HNSCC samples. Consistent with our statistical analysis, quantitative PCR confirmed the upregulation of BST2 and MFAP2 and the downregulation of KRT31 when samples of HNSCC were compared to tumor-free surgical margins. As expected, GNA15 presented a non-significant differential expression pattern when tumor samples were compared to normal tissues. Conclusion: To the best of our knowledge, this is the first study reporting SAGE data in head and neck squamous cell tumors. Statistical analysis was effective in identifying differentially expressed genes reportedly involved in cancer development. The differential expression of a subset of genes was confirmed in additional larynx carcinoma samples and in carcinomas from a distinct head and neck subsite. This result suggests the existence of potential common biomarkers for prognosis and targeted-therapy development in this heterogeneous type of tumor.Fundação de Amparo a Pesquisa do Estado de São Paulo/FAPESP [05/51467-0]; [04/12054-9]; [07/50894-7]Ludwig Institute for Cancer ResearchConselho Nacional de Pesquisas/CNPqCoordenacao de Aperfeicoamento do Pessoal do Ensino Superior/CAPE

Band-edge modifications due to photogenerated carriers in single p-type delta-doped GaAs layers

The photogenerated carrier-induced band-edge modifications of beryllium single delta-doped GaAs layers com comprising a two-dimensional hole gas (2DHG) were investigated by means of photoluminescence, selective photoluminescence, and photoluminescence excitation spectroscopies. The results show direct evidence for a photoinduced electron confinement effect, which strongly enhances the radiative-recombination probability between electrons and holes of the 2DHG at low temperatures,5974634463

Band-edge Modifications Due To Photogenerated Carriers In Single P-type δ-doped Gaas Layers

The photogenerated carrier-induced band-edge modifications of beryllium single δ-doped GaAs layers comprising a two-dimensional hole gas (2DHG) were investigated by means of photoluminescence, selective photoluminescence, and photoluminescence excitation spectroscopies. The results show direct evidence for a photoinduced electron confinement effect, which strongly enhances the radiative-recombination probability between electrons and holes of the 2DHG at low temperatures. © 1999 The American Physical Society.59746344637Schubert, E.F., (1994) Epitaxial Microstructures, 40, p. 1. , edited by A. C. Gossard, Semiconductors and Semimetals Academic, New YorkEnderlein, R., Sipahi, G.M., Scolfaro, L.M.R., Leite, J.R., Diaz, I.F.L., (1994) Mater. Sci. Eng., B, 35, p. 396Sipahi, G.M., Enderlein, R., Scolfaro, L.M.R., Leite, J.R., (1996) Phys. Rev. B, 53, p. 9930Buyanova, I.A., Chen, W.M., Henry, A., Ni, W.-X., Hansson, G.V., Monemar, B., (1996) Phys. Rev. B, 53, p. 9587Sipahi, G.M., Enderlein, R., Scolfaro, L.M.R., Leite, J.R., Da Silva, E.C.F., Levine, A., (1998) Phys. Rev. B, 57, p. 9168Gilinsky, A.M., Zhuravlev, K.S., Lubyshev, D.I., Migal, V.P., Preobrashenskii, V.V., Semiagin, B.R., (1991) Superlattices Microstruct., 10, p. 399Estimated from Hall measurements on molecular beam epitaxy grown bulk GaAsAshen, D.J., Dean, P.J., Hurle, D.T.J., Mullin, J.B., White, A.M., Greene, P.D., (1975) J. Phys. Chem. Solids, 36, p. 1041Richards, D., Wagner, J., Schneider, H., Hendorfer, G., Maier, M., Fischer, A., Ploog, K., (1993) Phys. Rev. B, 47, p. 962