Development of CCD and EM-CCD Technology for High Resolution X-Ray Spectrometry

This thesis discusses the development of Charge-Couple Device (CCD) and Electron Multiplying CCD (EM-CCD) technology for high resolution X-ray spectroscopy. Of particular interest is the spectral resolution performance of the devices alongside the optimisation of the quantum efficiency through the use of back-illuminated CCDs, thin filter technology and improved passivation techniques. The early chapters (1 through 5) focus on the background and theory that is required to understand the purpose of the work in this thesis and how semiconductors can be used as the detector of high resolution X-ray spectrometers. Chapter 6 focuses on the soft X-ray performance of three different types of conventional CCD using the PTB beamline at BESSY II. The results show that there is degradation in spectral resolution in all three devices below 500 eV due to incomplete charge collection and X-ray peak asymmetry. The Hamamatsu device is shown to degrade faster than the CCD30-11 variants and this is attributed to the thickness of the active silicon (>50 μm) in the device and also its thicker dead-layer (~75 nm) which is found by evaluating the device's soft X-ray QE). The charge loss at the back-surface generation/recombination centres is also investigated and is found to be higher in the Hamamatsu device, again due to its thicker dead-layer. Chapter 7 is an investigation of the Modified Fano Factor which aims to describe the spectral resolution degradation that is expected when an EM-CCD is used to directly detect soft X-rays. The factor is predicted analytically, modelled and then verified experimentally allowing EM-CCD performance over the soft X-ray range to be predicted with high levels of confidence. Chapter 8 is a detailed look into work completed for the phase 0 study of the off plane X-ray grating spectrometer on the International X-ray Observatory. The work includes a detailed contamination study, effective area analysis, the pointing knowledge requirement and the use of filters to minimise optical background

Developing a high-resolution x-ray imager using electron-multiplying (EM) CCDs

Applications at synchrotron facilities such as macromolecular crystallography and high energy X-ray diffraction require high resolution imaging detectors with high dynamic range and large surface area. Current systems can be split into two main categories: hybrid pixel detectors and scintillator-coupled Charge-Coupled Devices (CCDs). Whilst both have limitations, CCD-based systems (coupled to fibre-optics to increase imaging area) are often used in these applications due to their small pixels and the high resolution. Electron-Multiplication CCDs (EM-CCDs) are able to suppress the readout noise associated with increased readout speed offering a low noise, high speed detector solution. A previous pilot study using a small-area (8 mm × 8 mm) scintillator-coupled EM-CCD found that through high frame-rates, low noise and novel uses of photon-counting, resolution could be improved from over 80 μm to 25 μm at 2 fps. To further improve this detector system, high speed readout electronics can be used alongside a fibre-optic taper and EM-CCD to create a “best of both worlds” solution consisting of the high resolution of a CCD, along with the low noise, high speed (high dynamic range) and large effective area of pixel detectors. This paper details the developments in the study and discusses the latest results and their implication on the system design

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

A study of electron-multiplying CCDs for use on the International X-ray Observatory off-plane x-ray grating spectrometer

CCDs are regularly used as imaging and spectroscopic devices on space telescopes at X-ray energies due to their high quantum efficiency and linearity across the energy range. The International X-ray Observatory's X-ray Grating Spectrometer will also look to make use of these devices across the energy band of 0.3 keV to 1 keV. At these energies, when photon counting, the charge generated in the silicon is close to the noise of the system. In order to be able to detect these low energy X-ray events, the system noise of the detector has to be minimised to have a sufficient signal-to-noise-ratio. By using an EM-CCD instead of a conventional CCD, any charge that is collected in the device can be multiplied before it is read out and as long as the EM-CCD is cool enough to adequately suppress the dark current, the signal-to-noise ratio of the device can be significantly increased, allowing soft X-ray events to be more easily detected. This paper will look into the use of EM-CCDs for the detection of low energy X-rays, in particular the effect that using these devices will have on the signal to noise ratio as well as any degradation in resolution and FWHM that may occur due to the additional shot noise on the signal caused by the charge packet amplification process

The noise performance of electron-multiplying charge-coupled devices at X-ray energies

Electron-multiplying charge-coupled devices (EMCCDs) are used in low-light-level (L3) applications for detecting optical, ultraviolet, and near-infrared photons (10–1100 nm). The on-chip gain process is able to increase the detectability of any signal collected by the device through the multiplication of the signal before the output node. Thus, the effective readout noise can be reduced to subelectron levels, allowing the detection of single photons. However, this gain process introduces an additional noise component due to the stochastic nature of the multiplication. In optical applications, this additional noise has been characterized. The broadening of the detected peak is described by the excess noise factor. This factor tends to a value of √2 at high gain (>100x). In X-ray applications, the situation is improved by the effect that Fano factor f has on the shot noise associated with X-ray photon detection (f ≈ 0.12 at X-ray energies). In this paper, the effect of the detection of X-ray photons in silicon is assessed both analytically and through a Monte Carlo model of the gain amplification process. The excess noise on the signal is predicted (termed the modified Fano factor) for photon detection in an EM-CCD at X-ray energies. A hypothesis is made that the modified Fano factor should tend to 1.115 at high levels of gain (>10x). In order to validate the predictions made, measurements were taken using an 55 Fe source with Mn k-alpha X-ray energy of 5898 eV. These measurements allowed the hypothesis to be verified

Row Widths for Full Season Soybeans in Kentucky

Soybean yields in Kentucky have increased steadily in the past 20 years as a result of improved varieties and production practices. To achieve even higher yields new varieties and better production practices need to be developed and tested. One possibility for increasing soybean yields is to plant in narrow rows using varieties which respond to this practice. Although previous research in Kentucky has not shown a yield advantage for full season soybeans planted in narrow rows, researchers in other states have recently shown increases in yield with narrowing row widths. A number of new varieties have also been developed specifically for narrow row plantings. These varieties are shorter, lodge less, and have a high yield potential. This study was designed to answer the question: Will narrow row widths provide higher yields for these soybean varieties when grown under full season conditions in Kentucky

Performance Testing of a Novel Off-plane Reflection Grating and Silicon Pore Optic Spectrograph at PANTER

An X-ray spectrograph consisting of radially ruled off-plane reflection gratings and silicon pore optics was tested at the Max Planck Institute for extraterrestrial Physics PANTER X-ray test facility. The silicon pore optic (SPO) stack used is a test module for the Arcus small explorer mission, which will also feature aligned off-plane reflection gratings. This test is the first time two off-plane gratings were actively aligned to each other and with a SPO to produce an overlapped spectrum. The gratings were aligned using an active alignment module which allows for the independent manipulation of subsequent gratings to a reference grating in three degrees of freedom using picomotor actuators which are controllable external to the test chamber. We report the line spread functions of the spectrograph and the actively aligned gratings, and plans for future development.Comment: Draft Version March 19, 201

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

The noise performance of electron-multiplying charge-coupled devices at soft X-ray energy values

The use of electron-multiplying charge-coupled devices (CCDs) for high-resolution soft X-ray spectroscopy has been proposed in previous studies, and the analysis that followed experimentally identified and verified a modified Fano factor for X-ray detection using an 55Fe X-ray source. However, further experiments with soft X-rays at 1000 eV were less successful, attributed to excessive split events. More recently, through the use of deep-depletion e2v CCD220 and on-chip binning, it has been possible to greatly reduce the number of split events, allowing the result for the modified Fano factor at soft X-ray energy values to be verified. This paper looks at the earlier attempt to verify the modified Fano factor at 1000 eV with e2v CCD97 and shows the issues created by splitting of the charge cloud between pixels. It then compares these earlier results with new data collected using e2v CCD220, investigating how split-event reduction allows the modified Fano factor to be verified for low-energy X-rays