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Hughes, G.

Publications and source records attributed to Hughes, G..

Growth chemistry of cobalt nitride by plasma enhanced atomic layer deposition

State-of-the-art atomic layer deposition (ALD) and photoemission characterisation are applied to grow and characterise cobalt nitride, a material that has applications in renewable energy and semiconductor technologies. The growth process is characterised using an in situ cycle-by-cycle methodology to identify the main factors which underpin optimal material growth. The role of co-reactant dosing and substrate temperature is analysed in detail to demonstrate the impact these parameters have on the overall composition of the film. The in situ approach, combined with high-energy synchrotron-based photoemission studies of the resulting films, enables understanding of the bulk chemical properties without need for physical removal of material by sputtering. The results provide an insight into optimising plasma assisted ALD processes for deposition of cobalt nitride, and strategies for minimizing carbon incorporation into the film from the precursor ligands.

36 MATERIALS SCIENCE↗

Multiwavelength Observations of the Blazar VER J0521+211 during an Elevated TeV Gamma-Ray State

We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 ± 0.4) × 10 –7 photons m –2 s –1 , or ~37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when the flux was higher. Using the gamma-ray spectrum and four models of the extragalactic background light (EBL), a conservative 95% confidence upper limit on the redshift of the source was found to be z ≤ 0.31. Unlike the gamma-ray and X-ray bands, the optical flux did not increase significantly during the studied period compared to the archival low-state flux. The spectral variability from optical to X-ray bands suggests that the synchrotron peak of the spectral energy distribution (SED) may become broader during flaring states, which can be adequately described with a one-zone synchrotron self-Compton model varying the high-energy end of the underlying particle spectrum. The synchrotron peak frequency of the SED and the radio morphology of the jet from the MOJAVE program are consistent with the source being an intermediate-frequency-peaked BL Lac object.

79 ASTRONOMY AND ASTROPHYSICS↗

Detection of the Crab Nebula with the 9.7 m prototype Schwarzschild-Couder telescope

The Schwarzschild-Couder Telescope (SCT) is a telescope concept proposed for the Cherenkov Telescope Array. It employs a dual-mirror optical design to remove comatic aberrations over an 8° field of view, and a high-density silicon photomultiplier camera (with a pixel resolution of 4 arcmin) to record Cherenkov emission from cosmic ray and gamma-ray initiated particle cascades in the atmosphere. Additionally, the prototype SCT (pSCT), comprising a 9.7 m diameter primary mirror and a partially instrumented camera with 1536 pixels, has been constructed at the Fred Lawrence Whipple Observatory. The telescope was inaugurated in January 2019, with commissioning continuing throughout 2019. We describe the first campaign of observations with the pSCT, conducted in January and February of 2020, and demonstrate the detection of gamma-ray emission from the Crab Nebula with a statistical significance of 8.6σ.

79 ASTRONOMY AND ASTROPHYSICS↗

Very High Energy Outburst of Markarian 501 in May 2009

The very high energy (VHE; E great than 100 GeV) blazar Markarian 501 was observed between April 17 and May 5 (MJD 5493854956), 2009, as part of an extensive multi-wavelength campaign from radio to VHE. Strong VHE -ray activity was detected on May 1st with Whipple and VERITAS, when the flux (E greater than 400 GeV) increased to 10 times the pre-flare baseline flux (3.9 x 10(exp -11 ph cm(exp -2 S(exp -1), reaching five times the flux of the Crab Nebula. This coincided with a decrease in the optical polarization and a rotation of the polarization angle by 15deg. This VHE flare showed a fast flux variation with an increase of a factor approximately 4 in 25 min, and a falling time of approximately 50 min. We present the observations of the quiescent state previous to the flare and of the high state after the flare, focusing on the flux and spectral variability from Whipple, VERITAS, Fermi-LAT, RXTE, and Swift combined with optical and radio data.

BL Lacertae objects: individual: Mrk 501 / gamma r↗

Stable vacuum UV CCD detectors designed for space flight experiments

Thinned, backside-illuminated, p-channel CCD images are under development which can exploit the surface potential in VUV applications, yielding enhanced quantum efficiency to wavelengths as short as 1100 A. The current goal is production of large-format, 5-micron pixel imagers for spectrographic and imaging VUV spaceflight experiments. Model predictions of the effect of device design on quantum efficiency, well capacity, and crosstalk are presented for such 5-micron-approaching pixel sizes.

Socker, Dennis G.↗