High-resolution detectors for soft X-ray spectroscopy

Resonant Inelastic X-ray Scattering (RIXS) is a modern soft X-ray spectroscopy technique used to investigate the structure of and excitations in materials. It requires high resolution spectrometers and a brilliant, tunable, X-ray source and therefore is carried out at spectrometers such as SAXES at the Swiss Light Source Light, a synchrotron at the Paul Scherrer Institut. SAXES uses a grating to disperse X-rays scattered from a sample across a position sensitive detector, a Charge-Coupled Device (CCD). It has been recognised that the spatial resolution of the CCD currently limits the spectrometer resolution and therefore the investigations described in this thesis focus on developing and testing methods of improving the detector resolution. Whilst this thesis addresses improving the resolution of the detector at SAXES specifically, the methods and results are applicable to other applications requiring high spatial resolution soft X-ray detection. After an introduction, Chapters 2 and 3 describe the importance of RIXS, operation of SAXES and background of soft X-ray detection in CCDs. A comparison of models that describe charge spreading in a CCD is in Chapter 4, and the best model is implemented in a simulation package that generates populations of soft X-ray events. Chapter 5 explores the resolution improvements possible through applying centroid algorithms to simulated X-ray events, and Chapter 6 begins by describing experimental work undertaken to verify simulation results. Due to the limitations of applying centroiding algorithms to the current SAXES camera, a small-area Electron Multiplying CCD (EM-CCD) is experimentally tested (Chapter 7). Results with the EM-CCD proved positive, therefore in Chapter 8 the spatial resolution achievable with a large area EM-CCD is verified for a future SAXES camera upgrade. Due to the successful results presented in this thesis, negotiations to develop a new camera system for SAXES are underway, and interest from other RIXS beamlines in the community may lead to the work also being applied elsewhere. The detection of soft X-rays with high spatial resolution is applicable to other future CCD and EM-CCD instruments, such as astronomical X-ray observatories

CCD QE in the Soft X-ray Range

e2v has previously provided back-illuminated CCDs for several solar observation projects, resulting in a number of key articles on CCD QE in the soft X-ray region. To update these, e2v has arranged for tests on X-ray optimised EMCCDs at a synchrotron. These have shown QE of at least 45% from 40 eV to 2000 eV, with Enhanced process devices having significantly higher QE than Basic process. The measured values were similar to data published from the SDO SXI mission, showing that the e2v process has been stable over many years. The soft X-ray QE measurements show a reasonable fit to the simple layer model for energies > 600 eV. For energies < 100 eV, measurements show slightly lower QE than the model prediction for both Basic and Enhanced processes. For energies 100 eV to 600 eV, measurements show a reasonable fit to the model for the Basic process, but less improvement from the Enhanced process than the model predicts. Comparing the ~80% typical QE for UV-optimised CCDs at 385 nm with the 45% QE measured at 120 eV in this study, there is a discrepancy in QE for two photon energies with the same absorption length measured on CCDs from the same back-thinning process (one type with AR coating, one type without)

Family consultation to reduce early hospital readmissions among patients with end stage kidney disease: A randomized controlled trial

Background and objectives The US Centers for Medicare and Medicaid Services have mandated reducing early (30-day) hospital readmissions to improve patient care and reduce costs. Patients with ESKD have elevated early readmission rates, due in part to complex medical regimens but also cognitive impairment, literacy difficulties, low social support, and mood problems. We developed a brief family consultation intervention to address these risk factors and tested whether it would reduce early readmissions. Design, setting, participants, & measurements One hundred twenty hospitalized adults with ESKD (mean age=58 years; 50% men; 86% black, 14% white) were recruited from an urban, inpatient nephrology unit. Patients were randomized to the family consultation (n=60) or treatment-as-usual control (n=60) condition. Family consultations, conducted before discharge at bedside or via telephone, educated the family about the patient’s cognitive and behavioral risk factors for readmission, particularly cognitive impairment, and how to compensate for them. Blinded medical record reviews were conducted 30 days later to determine readmission status (primary outcome) and any hospital return visit (readmission, emergency department, or observation; secondary outcome). Logistic regressions tested the effects of the consultation versus control on these outcomes. Results Primary analyses were intent-to-treat. The risk of a 30-day readmission after family consultation (n=12, 20%) was 0.54 compared with treatment-as-usual controls (n=19, 32%), although this effect was not statistically significant (odds ratio, 0.54; 95% confidence interval, 0.23 to 1.24; P=0.15). A similar magnitude, nonsignificant result was observed for any 30-day hospital return visit: family consultation (n=19, 32%) versus controls (n=28, 47%; odds ratio, 0.53; 95% confidence interval, 0.25 to 1.1; P=0.09). Per protocol analyses (excluding three patients who did not receive the assigned consultation) revealed similar results. Conclusions A brief consultation with family members about the patient’s cognitive and psychosocial risk factors had no significant effect on 30-day hospital readmission in patients with ESKD

Design and characterisation of the new CIS115 sensor for JANUS, the high resolution camera on JUICE

JUICE, the Jupiter Icy Moon Explorer, is a European Space Agency L-class mission destined for the Jovian system. Due for launch in 2022, it will begin a science phase after its transit to Jupiter that will include detailed investigations of three of the Galilean moons: Ganymede, Callisto and Europa. JUICE will carry payloads to characterise the Jovian environments, divided into in situ, geophysical and remote sensing packages. A key instrument in the remote sensing package is JANUS, an optical camera operating over a wavelength range of 350 nm to 1064 nm. JANUS will be used to study the external layers of Jupiter’s atmosphere, the ring system and the planetary bodies. To achieve the science goals, resolutions of better than 5 m per pixel are required for the highest resolution observations during the 200 km altitude orbit of Ganymede, whilst the system is operated with a signal to noise ratio of better than 100. Jupiter’s magnetic field is a dominant object in the solar system, trapping electrons and other charged particles leading to the radiation environment around Jupiter being very hostile, especially in the regions closest to Jupiter in the Ganymede orbit. The radiation tolerance of the focal plane detector in JANUS is therefore a major concern and radiation testing is vital to confirm its expected performance after irradiation will meet requirements set by the science goals. JANUS will be using a detector from e2v technologies plc, the CMOS Imaging Sensor 115 (CIS115), which is a device manufactured using 0.18 μm Imaging CMOS Process with a 2000 by 1504 pixel array each 7 μm square. The pixels have a 4T pinned photodiode pixel architecture, and the array is read out through four differential analogue outputs. This paper describes the preliminary characterisation of the CIS115, and results obtained with the CIS107 precursor sensor

The use of EM-CCDs on high resolution soft x-ray spectrometers

Charge-Coupled Devices (CCDs) have been traditionally used on high resolution soft X-ray spectrometers, but with their ability to increase the signal level in the detector before the readout noise of the system is added, Electron-Multiplying CCDs (EM-CCDs) have the potential to offer many advantages in soft X-ray detection. Through this signal multiplication an EM-CCD has advantages over conventioanl CCDs of increased signal, suppressed noise, faster readout speeds for the same equivalent readout noise and an increased inmmunity to Electro-Magnetic Intereference. This paper will look at present and future spacel applications for high resolution soft X-ray spectrometers and assess the advantages and disadvantage of using EM-CCDs in these applications

High-resolution soft x-ray spectrometry using the electron-multiplying charge-coupled device (EM-CCD)

The Electron-Multiplying Charge-Coupled Device (EM-CCD) shares a similar structure to the CCD except for the inclusion of a gain register that multiplies signal before the addition of read-noise, offering sub-electron effective readnoise at high frame-rates. EM-CCDs were proposed for the dispersive spectrometer on the International X-ray Observatory (IXO) to bring sub-300 eV X-rays above the noise, increasing the science yield. The high-speed, low-noise performance of the EMCCD brought added advantages of reduced dark current and stray-light per frame, reducing cooling and filtering requirements. To increase grating efficiency, several diffracted spectral orders were co-located so the inherent energy resolution of the detector was required for order separation. Although the spectral resolution of the EM-CCD is degraded by the gain process, it was shown that the EM-CCD could achieve the required separation. The RIXS spectrometer at the Advanced Resonant Spectroscopy beamline (ADRESS) of the Swiss Light Source (SLS) at the Paul Scherrer Institute currently uses a CCD, with charge spreading between pixels limiting the spatial resolution to 24 μm (FWHM). Through improving the spatial resolution below 5 μm alongside upgrading the grating, a factor of two energy resolution improvement could theoretically be made. With the high-speed, low-noise performance of the EM-CCD, photon-counting modes could allow the use of centroiding techniques to improve the resolution. Using various centroiding techniques, a spatial resolution of 2 μm (FWHM) has been achieved experimentally, demonstrating the benefits of this detector technology for soft X-ray spectrometry. This paper summarises the use of EM-CCDs from our first investigations for IXO through to our latest developments in ground-based testing for synchrotron-research and looks beyond to future possibilities

Comparison of Back-Thinned Detector Ultraviolet Quantum Efficiency for Two Commercially Available Passivation Treatments

Back-thinned silicon detectors offer a high response over a very broad spectrum for direct detection by providing an efficient optical path into the sensing silicon avoiding front face structures manufactured from metal, polysilicon, nitrides, and oxides that may absorb the incident light before reaching the sensing silicon. We have tested two CCDs with different back-surface shallow p+ implant thicknesses (basic and enhanced) at the M4 line (wavelength between 40 and 400 nm) at Physikalisch-Technische Bundesanstalt (PTB)’s Metrology Light Source in Berlin. This characterization in the ultraviolet spectral range extends the soft X-ray quantum efficiency (QE) data set previously acquired with the exact same devices. Due to the short absorption depth and the scope for many types of interactions of the device materials with ultraviolet photons, QE measurement and stability of the device against extended exposure in the UV are of ongoing interest. Therefore, QE measurements have been carried out before and after exposures to quantify any change in behavior. To allow characterization of the passivation processes only, the devices have no antireflection coating. The measured QE of the standard back-thinned CCD is below 10% between 70 and 370 nm. An average additional 5% efficiency is achieved in the enhanced device within the same range. At the limits of the measured spectrum, toward soft X-rays or toward the visible range, the QE increases and the difference between the standard and the enhanced process is reduced as the photon absorption length increases beyond the immediate back-surface. The measured QE after long high-flux exposures at 200 nm shows remarkable improvement

A Novel TLR4-Mediated Signaling Pathway Leading to IL-6 Responses in Human Bladder Epithelial Cells

The vigorous cytokine response of immune cells to Gram-negative bacteria is primarily mediated by a recognition molecule, Toll-like receptor 4 (TLR4), which recognizes lipopolysaccharide (LPS) and initiates a series of intracellular NF-κB–associated signaling events. Recently, bladder epithelial cells (BECs) were reported to express TLR4 and to evoke a vigorous cytokine response upon exposure to LPS. We examined intracellular signaling events in human BECs leading to the production of IL-6, a major urinary cytokine, following activation by Escherichia coli and isolated LPS. We observed that in addition to the classical NF-κB–associated pathway, TLR4 triggers a distinct and more rapid signaling response involving, sequentially, Ca(2+), adenylyl cyclase 3–generated cAMP, and a transcriptional factor, cAMP response element–binding protein. This capacity of BECs to mobilize secondary messengers and evoke a more rapid IL-6 response might be critical in their role as first responders to microbial challenge in the urinary tract

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

Evaluation of sensors for the detection of energy resolved very soft x-ray fluorescence

Energy-dispersive imaging spectroscopy of X-ray emission from the Earth’s aurorae promises to further knowledge in the field of aeronomy. Time- and spatially-resolved observations of fluorescence from the dominant atmospheric components require the detection of X-rays as soft as 390 eV with a resolution of no more than 100 eV at these energies. The Auroral X-ray Imaging Spectrometer (AXIS) instrument of the Disturbed and quiet time Ionosphere-thermosphere System at High Altitudes (DISHA) mission is expected to perform these observations. The baseline instrument design has suggested the use of an electron-multiplying charge-coupled device (EMCCD). The EMCCD’s electron-multiplying register can reduce the effective readout noise and enable the detection of signals as small as a single photoelectron. For the detection of soft X-rays, however, the noise penalty from the EM register’s stochastic process degrades energy resolution. Emerging CMOS image sensors (CIS), particularly the Teledyne e2v CIS221-X test device, with back illumination, full depletion (with 36 μm thickness), large pixel sizes (40 μm), and low readout noise (3 e- rms effective) are expected to achieve the required performance without the effects of the EM register. Simple models for X-ray event sensitivity, detectability, and resolution, indicate that candidate CIS equal or better EMCCD performance. Furthermore, CIS offer other advantages including lower power consumption, higher operating temperature, and increased radiation hardness. However, these sensors introduce other behaviors that may impact their apparent benefits, which initial experimental testing and analyses are working to understand