Mrk 421, Mrk 501, and 1ES 1426+428 at 100 GeV with the CELESTE Cherenkov Telescope

We have measured the gamma-ray fluxes of the blazars Mrk 421 and Mrk 501 in the energy range between 50 and 350 GeV (1.2 to 8.3 x 10^25 Hz). The detector, called CELESTE, used first 40, then 53 heliostats of the former solar facility "Themis" in the French Pyrenees to collect Cherenkov light generated in atmospheric particle cascades. The signal from Mrk 421 is often strong. We compare its flux with previously published multi-wavelength studies and infer that we are straddling the high energy peak of the spectral energy distribution. The signal from Mrk 501 in 2000 was weak (3.4 sigma). We obtain an upper limit on the flux from 1ES 1426+428 of less than half that of the Crab flux near 100 GeV. The data analysis and understanding of systematic biases have improved compared to previous work, increasing the detector's sensitivity.Comment: 15 pages, 14 figures, accepted to A&A (July 2006) August 19 -- corrected error in author lis

The First VERITAS Telescope

The first atmospheric Cherenkov telescope of VERITAS (the Very Energetic Radiation Imaging Telescope Array System) has been in operation since February 2005. We present here a technical description of the instrument and a summary of its performance. The calibration methods are described, along with the results of Monte Carlo simulations of the telescope and comparisons between real and simulated data. The analysis of TeV $\gamma$-ray observations of the Crab Nebula, including the reconstructed energy spectrum, is shown to give results consistent with earlier measurements. The telescope is operating as expected and has met or exceeded all design specifications.Comment: Accepted by Astroparticle Physic

Growth by the heat exchanger method of NaBiW2O8 and Na5B2P3O13 crystals

In this paper, we present the results of our attempt to grow NaBiW2O8 (NBW) and Na5B2P3O13 (NBP) crystals by the heat exchanger method (HEM). This method is slightly different from the Bridgman technique: the crucible is kept fixed in the setup and the center of the crucible bottom is cooled by a variable helium gas flow. It allows very good control of the growth rate and minimizes parasitic crystallization at the crucible walls. First experiments for growing these two materials by the HEM technique have shown very promising results with single-crystal sizes of few cubic centimetres.

Вплив товщини пластини та кількості сіток трафаретного друку на Al-BSF у кристалічних кремнієвих сонячних елементах

У роботі були проведені експериментальні дослідження процесу легування алюмінієвих (Al) паст, надрукованих трафаретним друком на кремнієвих поверхнях для сонячних елементів. Досліджений вплив товщини пластини та кількості сіток трафаретного друку на властивості поля задньої поверхні Al (Al-BSF) кремнієвих сонячних елементів Чохральського (Cz-Si). Використовувалися екрани з різною кількістю сіток (150, 200 і 400 меш) для друку різної кількості пасти Al (7, 9,4 та 12 мг/см2). Швидкий термічний відпал (RTP) при 750 °C і 800 °C протягом 60 с був застосований для формування ALBSF. SEM показав утворення шорсткої поверхні з шаром легуючого шару товщиною 4,31 мкм на об’ємній кремнієвій пластині. Аналіз ECV та SIMS показав, що пікова температура відпалу 750 °C і кількість пасти Al 12 мг/см2 підходять для створення оптимального Al-BSF. Ця робота виявила, що на властивості Al-BSF сильно впливає кількість меш, яка використовується для трафаретного друку пасти Al. Однак не було помічено монотонного зв’язку з товщиною пластини. Маска з 150 меш дозволила отримати високі концентрації Al на поверхні, максимальну глибину дифузії та більший середній час життя носіїв заряду.In this study, experiments on the alloying process from screen-printed aluminum (Al) pastes on silicon surfaces for solar cell applications were conducted. We investigated the effect of wafer thickness and screen-printing mesh counts on the Al back surface field (Al-BSF) properties of Czochralski silicon (Cz-Si) solar cells Screens with different mesh counts (150, 200 and 400 mesh) were used to print variable amounts of Al paste (7, 9.4 and 12 mg/cm2). Rapid thermal annealing (RTP) annealing processes of 750 °C and 800 °C for 60 s were applied to form AL-BSF. SEM micrographs showed the formation of a rough surface with 4.31 µm alloying layer over bulk Si wafer. ECV and SIMS analysis showed that an annealing peak temperature of 750 °C and an amount of Al paste of 12 mg/cm2 are suitable for the creation of an optimal Al-BSF. This work revealed that Al-BSF properties are strongly affected by the mesh counts used in screen-printing of Al paste. However, no monotonic relationship was noticed with the wafer thickness. The mask with 150 meshes allowed to obtain high Al concentrations at the surface, maximum diffusion depth and longer average lifetimes of charge carriers

Aluminium-induced crystallization of amorphous silicon films deposited by DC magnetron sputtering on glasses

Amorphous silicon (a-Si) and hydrogenated amorphous silicon (a-Si:H) films were deposited by DC magnetron sputtering technique with argon and hydrogen plasma mixture on Al deposited by thermal evaporation on glass substrates. The a-Si/Al and a-Si:H/Al thin films were annealed at different temperatures ranging from 250 to 550 °C during 4 h in vacuum-sealed bulb. The effects of annealing temperature on optical, structural and morphological properties of as-grown as well as the vacuum-annealed a-Si/Al and a-Si:H/Al thin films are presented in this contribution. The averaged transmittance of a-Si:H/Al film increases upon increasing the annealing temperature. XRD measurements clearly evidence that crystallization is initiated at 450 °C. The number and intensity of diffraction peaks appearing in the diffraction patterns are more important in a-Si:H/Al than that in a-Si/Al layers. Results show that a-Si:H films deposited on Al/glass crystallize above 450 °C and present better crystallization than the a-Si layers. The presence of hydrogen induces an improvement of structural properties of poly-Si prepared by aluminium-induced crystallization (AIC