In situ trap properties in CCDs: the donor level of the silicon divacancy

The silicon divacancy is one of the main defects of concern in radiation damage studies of Charge-Coupled Devices (CCDs) and, being immobile at room temperature, the defect is accessible to a variety of characterisation techniques. As such, there is a large amount of (often conflicting) information in the literature regarding this defect. Here we study the donor level of the divacancy, one of three energy levels which lie between the silicon valence and conduction bands. The donor level of the divacancy acts as a trap for holes in silicon and therefore can be studied through the use of a p-channel CCD. The method of trap-pumping, linked closely to the process of pocket-pumping, has been demonstrated in the literature over the last two years to allow for in-situ analysis of defects in the silicon of CCDs. However, most work so far has been a demonstartion [sic] of the techinique [sic]. We begin here to use the technique for detailed studies of a specific defect centre in silicon, the donor level of the divacancy. The trap density post-irradiation can be found, and each instance of the trap identified independently of all others. Through the study of the trap response at different clocking frequencies one can measure directly the defect emission time constant, and through tracking this at different temperatures, it is possible to use Shockley-Read-Hall theory to calculate the trap energy level and cross-section. A large population of traps, all with parameters consistent with the donor level of the divacancy, has been studied, leading to a measure of the distribution of properties. The emission time constant, energy level and cross-section are found to have relatively large spreads, significantly beyond the small uncertainty in the measurement technique. This spread has major implications on the correction of charge transfer inefficiency effects in space applications in which high precision is required

Charge transfer efficiency in a p-channel CCD irradiated cryogenically and the impact of room temperature annealing

It is important to understand the impact of the space radiation environment on detector performance, thereby ensuring that the optimal operating conditions are selected for use in flight. The best way to achieve this is by irradiating the device using appropriate mission operating conditions, i.e. holding the device at mission operating temperature with the device powered and clocking. This paper describes the Charge Transfer Efficiency (CTE) measurements made using an e2v technologies p-channel CCD204 irradiated using protons to the 10 MeV equivalent fluence of 1.24×109 protons.cm-2 at 153 K. The device was held at 153 K for a period of 7 days after the irradiation before being allowed up to room temperature where it was held at rest, i.e. unbiased, for twenty six hours to anneal before being cooled back to 153 K for further testing, this was followed by a further one week and three weeks of room temperature annealing each separated by further testing. A comparison to results from a previous room temperature irradiation of an n-channel CCD204 is made using assumptions of a factor of two worse CTE when irradiated under cryogenic conditions which indicate that p-channel CCDs offer improved tolerance to radiation damage when irradiated under cryogenic conditions

Development of EM-CCD-based X-ray detector for synchrotron applications

A high speed, low noise camera system for crystallography and X-ray imaging applications is developed and successfully demonstrated. By coupling an electron-multiplying (EM)-CCD to a 3:1 fibre-optic taper and a CsI(Tl) scintillator, it was possible to detect hard X-rays. This novel approach to hard X-ray imaging takes advantage of sub-electron equivalent readout noise performance at high pixel readout frequencies of EM-CCD detectors with the increase in the imaging area that is offered through the use of a fibre-optic taper. Compared with the industry state of the art, based on CCD camera systems, a high frame rate for a full-frame readout (50 ms) and a lower readout noise (<1 electron root mean square) across a range of X-ray energies (6–18 keV) were achieved

Grand Rounds for Dental Students: An Exploration

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153609/1/jddj002203372015795tb05910x.pd

Modelling charge storage in Euclid CCD structures

The primary aim of ESA's proposed Euclid mission is to observe the distribution of galaxies and galaxy clusters, enabling the mapping of the dark architecture of the universe [1]. This requires a high performance detector, designed to endure a harsh radiation environment. The e2v CCD204 image sensor was redesigned for use on the Euclid mission [2]. The resulting e2v CCD273 has a narrower serial register electrode and transfer channel compared to its predecessor, causing a reduction in the size of charge packets stored, thus reducing the number of traps encountered by the signal electrons during charge transfer and improving the serial Charge Transfer Efficiency (CTE) under irradiation [3]. The proposed Euclid CCD has been modelled using the Silvaco TCAD software [4], to test preliminary calculations for the Full Well Capacity (FWC) and the channel potential of the device and provide indications of the volume occupied by varying signals. These results are essential for the realisation of the mission objectives and for radiation damage studies, with the aim of producing empirically derived formulae to approximate signal-volume characteristics in the devices. These formulae will be used in the radiation damage (charge trapping) models. The Silvaco simulations have been tested against real devices to compare the experimental measurements to those predicted in the models. Using these results, the implications of this study on the Euclid mission can be investigated in more detail

A new deep SCUBA survey of gravitationally lensing clusters

We have conducted a new deep SCUBA survey, which has targetted 12 lensing galaxy clusters and one blank field. In this survey we have detected several sub-mJy sources after correcting for the gravitational lensing by the intervening clusters. We here present the preliminary results and point out two highlights.Comment: 4 pages, 2 figures, "Multiwavelength Cosmology" Mykonos, June 2003, conference proceeding

Trap pumping schemes for the Euclid CCD273 detector: characterisation of electrodes and defects

The VISible imager instrument (VIS) on board the Euclid mission will deliver high resolution shape measurements of galaxies down to very faint limits (R ~ 25 at 10σ) in a large part of the sky, in order to infer the distribution of dark matter in the Universe. To help mitigate radiation damage effects that will accumulate in the detectors over the mission lifetime, the properties of the radiation induced traps needs to be known with as high precision as possible. For this purpose the trap pumping method will be employed as part of the in-orbit calibration routines. Using trap pumping it is possible to identify and characterise single traps in a Charge-Coupled Device (CCD), thus providing information such as the density, emission time constants and sub-pixel positions of the traps in the detectors. This paper presents the trap pumping algorithms used for the radiation testing campaign of the CCD273 detectors, performed by the Centre for Electronic Imaging (CEI) at the Open University, that will be used for the VIS instrument. The CCD273 is a four-phase device with uneven phase widths, which complicates the trap pumping analysis. However, we find that by optimising the trap pumping algorithms and analysis routines, it is possible to obtain sub-pixel and even sub-phase positional information about the traps. Further, by comparing trap pumping data with simulations, it is possible to gain more information about the effective electrode widths of the device

Ground-state energy and entropy of the two-dimensional Edwards-Anderson spin-glass model with different bond distributions

We study the two-dimensional Edwards-Anderson spin-glass model using a parallel tempering Monte Carlo algorithm. The ground-state energy and entropy are calculated for different bond distributions. In particular, the entropy is obtained by using a thermodynamic integration technique and an appropriate reference state, which is determined with the method of high-temperature expansion. This strategy provide accurate values of this quantity for finite-size lattices. By extrapolating to the thermodynamic limit, the ground-state energy and entropy of the different versions of the spin-glass model are determined.Comment: 18 pages, 5 figure

Monte Carlo simulations of hyper-velocity particulate mechanics within silicon micropore optics

The focal planes of X-ray astronomy missions are at risk of particulate impacts from both micrometeoroids and orbital debris due to the open aperture of the narrow-angle incidence optics. Silicon micro-pore optics (sMPOs) have seen significant development due to their wide-angle observing capabilities and are planned for use in future X-ray space missions such as SMILE and THESEUS. Although previous space missions have seen sporadic and disruptive events in detectors which are attributed to particulate impacts, the number of particulates that can traverse the new sMPO and affect detector performance is not currently known, preventing the quantification of damage on focal planes. Work carried out on nested shell X-ray optics suggested that hyper-velocity particulates could scatter from the polished inner-mirrors and be focused on the focal plane of an instrument. By assuming that this basic scattering mechanic is present in sMPO, along with the natural clear path from space to the focal plane, the overall transmission rate of particulates through such an optic can be calculated using the Monte Carlo simulation methodology. By using the simulation presented here, along with known micrometeoroid flux models and so-called damage equations, the risk to focal planes of large-scale space missions due to hyper-velocity particulate impacts can for the first time be quantified. As such, the work presented here has many applications and uses across a wide range of fields

Properties of a Dilute Bose Gas near a Feshbach Resonance

In this paper, properties of a homogeneous Bose gas with a Feshbach resonance are studied in the dilute region at zero temperature. The stationary state contains condensations of atoms and molecules. The ratio of the molecule density to the atom density is $\pi na^3$. There are two types of excitations, molecular excitations and atomic excitations. Atomic excitations are gapless, consistent with the traditional theory of a dilute Bose gas. The molecular excitation energy is finite in the long wavelength limit as observed in recent experiments on $^{85}$Rb. In addition, the decay process of the condensate is studied. The coefficient of the three-body recombination rate is about 140 times larger than that of a Bose gas without a Feshbach resonance, in reasonably good agreement with the experiment on $^{23}$Na.Comment: 11 pages, 1 figure, comparison between the calculated three-body recombination rate and the experimental data for Na system has been adde