Cathodoluminescence Spectroscopy: An Accurate Technique for the Characterization of the Fabrication Technology of GaAlAs/GaAs Heterojunction Bipolar Transistors

Cathodoluminescence (CL) spectroscopy and imaging performed at low temperature have been used to qualify the heterojunction bipolar transistor fabrication technology, particularly the etching and ion implantation steps. CL has been used to optimize low defect technological processes. The protection of the active region during the insulation process has been optimized. The best result is obtained when using a bilayer of silicon nitride and photoresist. In order to minimize it, the damage induced by the etching process has also been studied. The best result is obtained when combining Ar ion beam etching and chemical etching. The possibilities to perform localized spectroscopy, to visualize the different emitting regions and to achieve semiquantitative signal analysis, makes CL a powerful microcharacterization method

Human MLH1 Protein Participates in Genomic Damage Checkpoint Signaling in Response to DNA Interstrand Crosslinks, while MSH2 Functions in DNA Repair

DNA interstrand crosslinks (ICLs) are among the most toxic types of damage to a cell. For this reason, many ICL-inducing agents are effective therapeutic agents. For example, cisplatin and nitrogen mustards are used for treating cancer and psoralen plus UVA (PUVA) is useful for treating psoriasis. However, repair mechanisms for ICLs in the human genome are not clearly defined. Previously, we have shown that MSH2, the common subunit of the human MutSα and MutSβ mismatch recognition complexes, plays a role in the error-free repair of psoralen ICLs. We hypothesized that MLH1, the common subunit of human MutL complexes, is also involved in the cellular response to psoralen ICLs. Surprisingly, we instead found that MLH1-deficient human cells are more resistant to psoralen ICLs, in contrast to the sensitivity to these lesions displayed by MSH2-deficient cells. Apoptosis was not as efficiently induced by psoralen ICLs in MLH1-deficient cells as in MLH1-proficient cells as determined by caspase-3/7 activity and binding of annexin V. Strikingly, CHK2 phosphorylation was undetectable in MLH1-deficient cells, and phosphorylation of CHK1 was reduced after PUVA treatment, indicating that MLH1 is involved in signaling psoralen ICL-induced checkpoint activation. Psoralen ICLs can result in mutations near the crosslinked sites; however, MLH1 function was not required for the mutagenic repair of these lesions, and so its signaling function appears to have a role in maintaining genomic stability following exposure to ICL-induced DNA damage. Distinguishing the genetic status of MMR-deficient tumors as MSH2-deficient or MLH1-deficient is thus potentially important in predicting the efficacy of treatment with psoralen and perhaps with other ICL-inducing agents

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

VARIATION AVEC LA TEMPÉRATURE DE LA BANDE INTERDITE DU CHAMP CRISTALLIN ET DU COUPLAGE SPIN-ORBITE EN CENTRE DE ZONE DE AgGaSe2 ET AgGaTe2

Les composés ternaires à structure chalcopyrite possèdent trois bandes de valence en centre de zone auxquelles correspondent trois transitions (A, B et C) avec la bande de conduction. Des mesures de réflectivité simple et modulée en longueur d'onde sur AgGaSe2 et AgGaTe2 nous ont permis de déterminer la variation des énergies de ces trois transitions entre la température de l'hélium liquide et la température ambiante. La cathodoluminescence nous a permis de vérifier que la transition A correspond à la bande interdite pour AgGaTe2 et de préciser son énergie. Pour AgGaSe2, la largeur de la bande interdite croît avec la température entre 5 et 95 K et décroît aux températures supérieures avec un coefficient très faible (- 1,2 x 10-4 eV/K). AgGaTe2 présente un comportement moins anormal. Cependant le coefficient de température au-dessus de 100 K est également faible (~ -2 x 10-4 eV/K). Nous avons calculé l'énergie du champ cristallin ƊCF et le couplage spin-orbite ƊSO à partir des énergies des trois transitions à l'aide du modèle quasi cubique. Dans les deux cas | ƊCF | est une fonction décroissante et ƊSO une fonction croissante de la température. Nous attribuons la variation de ƊSO à une diminution avec la température du coefficient d'hybridation des électrons de type p de la bande de valence avec les électrons 4d de l'argent. Ceci permet d'expliquer qualitativement la variation anormale de la bande interdite de ces composés en supposant que la différence de bande interdite binaire-ternaire équivalent est proportionnelle au coefficient d'hybridation α.The ternary compounds with chalcopyrite structure have three valence bands in the center of the Brillouin zone. Therefore there are three transitions (A, B and C) from the valence bands to the conduction band. Reflectivity measurements performed on AgGaSe2 and AgGaTe2 (wavelength modulated or not) allowed us to determine the energy variation of these transitions between liquid helium and room temperatures. For AgGaTe2, cathodoluminescence measurements have established that the A transition corresponds to the band gap. For AgGaSe2, the band Sap increases with temperature between 5 and 95 K and decreases for higher temperatures with a very weak coefficient (- 1.2 x 10-4 eV/K). The behaviour of AgGaTe2 is less abnormal. However the temperature coefficient above 100 K is also weak (~ 2 x 10-4 eV/K). The crystal field energy ƊCF and the spin-orbit splitting ƊSO have been calculated from the energies of the three transitions using the quasi cubic model. In both cases | ƊCF | decreases while ƊSO increases with temperature. The spin-orbit variation is ascribed to a decrease along with temperature of the hybridization coefficient of the valence band p-type electrons with the 4d electrons of silver. This can explain qualitatively the anomalous variation of the band gap of these compounds assuming that the difference of the band gap between equivalent binary and ternary compounds is proportional to the hybridization coefficient α