Laser-Induced Reactivity of NH3\mathsf{_3} on GaAs Surface

We have studied the reactivity of NH$_3$ on GaAs (100) surface irradiated by 280 nm laser beam at low fluence ($<$ 50 mJ cm$^{-2}$ per pulse) in an experimental set-up which allows a very sensitive characterization of the surface state using mass spectrometry. Thanks to this analysis technique we could follow desorbed NH$_x$ $(x = 2,~3)$ species during the laser treatment; this phase achieved, GaN$^+$ could be identified as an evidence of N fixation using laser desorption mass spectrometry of the treated surface. This characterization mode demonstrates the fluence and laser shot number dependencies on laser treatment efficiency. At 280 nm the N fixation is maximum for laser fluence of about 25 mJ cm$^{-2}$ (per pulse). Still even in the best nitridation conditions, the process appears to be of little efficiency, since it leads to the formation of less than one monolayer of GaN. These results combined with a numerical model of GaAs laser heating give evidence for the laser-induced nitridation to be thermally assisted.Nous avons étudié la réactivité de NH$_3$ sur la surface d'un échantillon de GaAs irradié par un faisceau laser UV (280 nm) de faible fluence ($<$ 50 mJ cm$^{-2}$). Les expériences ont été menées dans un dispositif expérimental utilisant la spectrométrie de masse et permettant une caractérisation présise de l'état de la surface. Grâce à cette technique d'analyse nous avons pu suivre les espèces NH$_x^+$ $(x = 2,~3)$ désorbées pendant le traitement laser, cette étape terminée, nous avons détecté, par la spectrométrie de masse associée à la désorption laser, les ions GaN$^+$ émis depuis la surface traitée, ils indiquent que la nitruration de GaAs s'est bien produite pendant le traitement. Cette technique de caractérisation nous a permis d'étudier l'influence de la fluence et du nombre de tirs laser sur l'efficacité du traitement. À 280 nm l'efficacité de la nitruration assistée par laser du GaAs est maximum pour une fluence laser proche de 25 mJ cm$^{-2}$ (par tir). Cependant même dans les conditions optimales de nitruration, le processus apparaît peu efficace puisqu'il conduit à la formation de moins d'une monocouche de GaN. Ces résultats expérimentaux couplés à un modèle numérique du chauffage laser de GaAs ont montré que le laser produit, pour les réactions de surface, des effets essentiellement thermiques proches de ceux obtenus par un chauffage conventionnel, lent, du substrat de GaAs

Opportunistic infections and AIDS malignancies early after initiating combination antiretroviral therapy in high-income countries

Background: There is little information on the incidence of AIDS-defining events which have been reported in the literature to be associated with immune reconstitution inflammatory syndrome (IRIS) after combined antiretroviral therapy (cART) initiation. These events include tuberculosis, mycobacterium avium complex (MAC), cytomegalovirus (CMV) retinitis, progressive multifocal leukoencephalopathy (PML), herpes simplex virus (HSV), Kaposi sarcoma, non-Hodgkin lymphoma (NHL), cryptococcosis and candidiasis. Methods: We identified individuals in the HIV-CAUSAL Collaboration, which includes data from six European countries and the US, who were HIV-positive between 1996 and 2013, antiretroviral therapy naive, aged at least 18 years, hadCD4+ cell count and HIV-RNA measurements and had been AIDS-free for at least 1 month between those measurements and the start of follow-up. For each AIDS-defining event, we estimated the hazard ratio for no cART versus less than 3 and at least 3 months since cART initiation, adjusting for time-varying CD4+ cell count and HIV-RNA via inverse probability weighting. Results: Out of 96 562 eligible individuals (78% men) with median (interquantile range) follow-up of 31 [13,65] months, 55 144 initiated cART. The number of cases varied between 898 for tuberculosis and 113 for PML. Compared with non-cART initiation, the hazard ratio (95% confidence intervals) up to 3 months after cART initiation were 1.21 (0.90-1.63) for tuberculosis, 2.61 (1.05-6.49) for MAC, 1.17 (0.34-4.08) for CMV retinitis, 1.18 (0.62-2.26) for PML, 1.21 (0.83-1.75) for HSV, 1.18 (0.87-1.58) for Kaposi sarcoma, 1.56 (0.82-2.95) for NHL, 1.11 (0.56-2.18) for cryptococcosis and 0.77 (0.40-1.49) for candidiasis. Conclusion: With the potential exception of mycobacterial infections, unmasking IRIS does not appear to be a common complication of cART initiation in high-income countries. © 2014 Wolters Kluwer Health | Lippincott Williams &amp; Wilkins

Opportunistic infections and AIDS malignancies early after initiating combination antiretroviral therapy in high-income countries

Background: There is little information on the incidence of AIDS-defining events which have been reported in the literature to be associated with immune reconstitution inflammatory syndrome (IRIS) after combined antiretroviral therapy (cART) initiation. These events include tuberculosis, mycobacterium avium complex (MAC), cytomegalovirus (CMV) retinitis, progressive multifocal leukoencephalopathy (PML), herpes simplex virus (HSV), Kaposi sarcoma, non-Hodgkin lymphoma (NHL), cryptococcosis and candidiasis. Methods: We identified individuals in the HIV-CAUSAL Collaboration, which includes data from six European countries and the US, who were HIV-positive between 1996 and 2013, antiretroviral therapy naive, aged at least 18 years, hadCD4+ cell count and HIV-RNA measurements and had been AIDS-free for at least 1 month between those measurements and the start of follow-up. For each AIDS-defining event, we estimated the hazard ratio for no cART versus less than 3 and at least 3 months since cART initiation, adjusting for time-varying CD4+ cell count and HIV-RNA via inverse probability weighting. Results: Out of 96 562 eligible individuals (78% men) with median (interquantile range) follow-up of 31 [13,65] months, 55 144 initiated cART. The number of cases varied between 898 for tuberculosis and 113 for PML. Compared with non-cART initiation, the hazard ratio (95% confidence intervals) up to 3 months after cART initiation were 1.21 (0.90-1.63) for tuberculosis, 2.61 (1.05-6.49) for MAC, 1.17 (0.34-4.08) for CMV retinitis, 1.18 (0.62-2.26) for PML, 1.21 (0.83-1.75) for HSV, 1.18 (0.87-1.58) for Kaposi sarcoma, 1.56 (0.82-2.95) for NHL, 1.11 (0.56-2.18) for cryptococcosis and 0.77 (0.40-1.49) for candidiasis. Conclusion: With the potential exception of mycobacterial infections, unmasking IRIS does not appear to be a common complication of cART initiation in high-income countries