Search

100 [micro]m thick films of CdTe were grown on semi-insulating (100) GaAs substrates by Physical Vapor Transport (PVT) in a modified Molecular Beam Epitaxy facility. The grown layers were highly oriented as revealed from X-ray pole figure measurements. Temperature- and intensity-dependent photoluminescence measurements were taken before and after the chemical removal of the substrate to determine the effect of the GaAs substrate and to estimate the crystallographic quality of the layers. Current-voltage characteristics were performed to obtain the resistitivity of the layers with [10.sup.8] [OMEGA]cm. Index Terms--CdTe, MBE, photoluminescence, radiation detector, thick films, x-ray diffraction.

EIGER is a single-photon-counting hybrid pixel detector developed at the Paul Scherrer Institut, Switzerland. It is designed for applications at synchrotron light sources with photon energies above 5 keV. Features of EIGER include a small pixel size (75 µm × 75 µm), a high frame rate (up to 23 kHz), a small dead-time between frames (down to 3 µs) and a dynamic range up to 32-bit. In this article, the use of EIGER as a detector for electrons in low-energy electron microscopy (LEEM) and photoemission electron microscopy (PEEM) is reported. It is demonstrated that, with only a minimal modification to the sensitive part of the detector, EIGER is able to detect electrons emitted or reflected by the sample and accelerated to 8-20 keV. The imaging capabilities are shown to be superior to the standard microchannel plate detector for these types of applications. This is due to the much higher signal-to-noise ratio, better homogeneity and improved dynamic range. In addition, the operation of the EIGER detector is not affected by radiation damage from electrons in the present energy range and guarantees more stable performance over time. To benchmark the detector capabilities, LEEM experiments are performed on selected surfaces and the magnetic and electronic properties of individual iron nanoparticles with sizes ranging from 8 to 22 nm are detected using the PEEM endstation at the Surface/Interface Microscopy (SIM) beamline of the Swiss Light Source. [ABSTRACT FROM AUTHOR]

JUNGFRAU (adJUstiNg Gain detector FoR the Aramis User station) is a two-dimensional hybrid pixel detector for photon science applications at free-electron lasers and synchrotron light sources. The JUNGFRAU 0.4 prototype presented here is specifically geared towards low-noise performance and hence soft X-ray detection. The design, geometry and readout architecture of JUNGFRAU 0.4 correspond to those of other JUNGFRAU pixel detectors, which are charge-integrating detectors with 75 µm × 75 µm pixels. Main characteristics of JUNGFRAU 0.4 are its fixed gain and r.m.s. noise of as low as 27 e− electronic noise charge (<100 eV) with no active cooling. The 48 × 48 pixels JUNGFRAU 0.4 prototype can be combined with a charge-sharing suppression mask directly placed on the sensor, which keeps photons from hitting the charge-sharing regions of the pixels. The mask consists of a 150 µm tungsten sheet, in which 28 µm-diameter holes are laser-drilled. The mask is aligned with the pixels. The noise and gain characterization, and single-photon detection as low as 1.2 keV are shown. The performance of JUNGFRAU 0.4 without the mask and also in the charge-sharing suppression configuration (with the mask, with a `software mask' or a `cluster finding' algorithm) is tested, compared and evaluated, in particular with respect to the removal of the charge-sharing contribution in the spectra, the detection efficiency and the photon rate capability. Energy-dispersive and imaging experiments with fluorescence X-ray irradiation from an X-ray tube and a synchrotron light source are successfully demonstrated with an r.m.s. energy resolution of 20% (no mask) and 14% (with the mask) at 1.2 keV and of 5% at 13.3 keV. The performance evaluation of the JUNGFRAU 0.4 prototype suggests that this detection system could be the starting point for a future detector development effort for either applications in the soft X-ray energy regime or for an energy-dispersive detection system. [ABSTRACT FROM AUTHOR]

JUNGFRAU (adJUstiNg Gain detector FoR the Aramis User station) is a two-dimensional hybrid pixel detector for photon science applications in free electron lasers, particularly SwissFEL, and synchrotron light sources. JUNGFRAU is an automatic gain switching, charge-integrating detector which covers a dynamic range of more than 104 photons of an energy of 12 keV with a good linearity, uniformity of response, and spatial resolving power. The JUNGFRAU 1.0 application-specific integrated circuit (ASIC) features a 256 x 256 pixel matrix of 75 x 75 µm² pixels and is bump-bonded to a 320 µm thick Si sensor. Modules of 2 x 4 chips cover an area of about 4 x 8 cm². Readout rates in excess of 2 kHz enable linear count rate capabilities of 20 MHz (at 12 keV) and 50 MHz (at 5 keV). The tolerance of JUNGFRAU to radiation is a key issue to guarantee several years of operation at free electron lasers and synchrotrons. The radiation hardness of JUNGFRAU 1.0 is tested with synchrotron radiation up to 10 MGy of delivered dose. The effect of radiation-induced changes on the noise, baseline, gain, and gain switching is evaluated post-irradiation for both the ASIC and the hybridized assembly. The bare JUNGFRAU 1.0 chip can withstand doses as high as 10 MGy with minor changes to its noise and a reduction in the preamplifier gain. The hybridized assembly, in particular the sensor, is affected by the photon irradiation which mainly shows as an increase in the leakage current. Self-healing of the system is investigated during a period of 11 weeks after the delivery of the radiation dose. Annealing radiation-induced changes by bake-out at 100 °C is investigated. It is concluded that the JUNGFRAU 1.0 pixel is sufficiently radiation-hard for its envisioned applications at SwissFEL and synchrotron beam lines. [ABSTRACT FROM AUTHOR]

The SLS detectors group has a longstanding history in the development of hybrid X-ray detectors for synchrotrons [1]. Hybrid detectors consist of a sensor (usually silicon) absorbing the photons and front-end electronics transforming the charge into a measurable signal. The two parts are distinct and can therefore be optimized separately, depending on the application. The group has the know-how to design sensors and Read-Out Chips (ROC) in-house, assemble the detectors with a high yield for a large number of channels (both wire- and bump-bonding), and develop data acquisition systems and software. The detectors must provide high-quality data and be reliable for the daily user operation at the beamlines. They are normally developed to target specific applications, and particular effort is put into the integration of the systems at the beamlines and on their reliability. The detector group works in close connection with the beamline scientists of the SLS as early as the development phase and then later to train them in operating the detectors in an optimized way and in supporting the final users. [ABSTRACT FROM AUTHOR]

With the continual drive towards bigger, better, and brighter light sources, whole new areas of scientific research are possible that would have been unimaginable or even were believed impossible before. For example, imaging of single bioparticles has been demonstrated at Free Electron Lasers (FELs) [1], and synchrotron beamlines can now be used to study real-time changes in samples on a timescale of milliseconds. [ABSTRACT FROM AUTHOR]

Eiger is the next-generation single-photon-counting pixel detector following the widely used Pilatus detector. Its smaller pixel size of 75 µm × 75 µm, higher frame rate of up to 22 kHz, and practically zero dead-time (∼4 µs) between exposures will further various measurement methods at synchrotron sources. In this article Eiger's suitability for X-ray photon correlation spectroscopy (XPCS) is demonstrated. By exploiting its high frame rate, complementary small-angle X-ray scattering (SAXS) and XPCS data are collected in parallel to determine both the structure factor and collective diffusion coefficient of a nano-colloid suspension. For the first time, correlation times on the submillisecond time scale are accessible with a large-area pixel detector. [ABSTRACT FROM AUTHOR]

MYTHEN 3 is a new single-photon-counting readout chip being developed by the SLS detector group in 110 nm UMC technology. It will equip a 60 k-channel, 50 μ m pitch microstrip detector optimized for powder diffraction experiments. Every readout channel features an amplifier and a shaper with variable gain and shaping time. The shaper output is fed to three independent discriminators, each one having a dedicated threshold, trim bit set and enable signal. The outputs of the three discriminators are processed by the counting logic section which, according to the mode of operation selected, generates the hits for the three following 24-bit counters. Several operation modes are foreseen: dual polarity, energy-windowing, count rate improvement, charge sharing suppression and pump with multiple probe time slots. The first 64-channel prototype has been tested in the lab, with fluorescence X-rays and with a synchrotron beam to characterize its noise and count rate capability. Based on the results obtained from the first chip a second 64-channel prototype has been developed and sent to production. The architecture of the chip and characterization results of the first chip will be presented. • New microstrip photon counting readout chip with three thresholds and counters. • Very fast frame rates allow for sub-ms time resolved studies. • Low threshold dispersion and reduced noise improve fluorescence suppression. • Fast shaping times allow for experiments at higher intensities. [ABSTRACT FROM AUTHOR]

Abstract: The AGIPD (Adaptive Gain Integrating Pixel Detector) is a detector under development, to be used in the European X-ray Free-Electron Laser (XFEL). The constraints imposed by the XFEL source are discussed, and the solutions implemented to cope with them are explained. The present status of the project is reported, along with results achieved in terms of noise, memory depth, and radiation tolerance. [Copyright &y& Elsevier]

Hybrid pixel detectors have become indispensable at synchrotron and X-ray free-electron laser facilities thanks to their large dynamic range, high frame rate, low noise, and large area. However, at energies below 3 keV, the detector performance is often limited because of the poor quantum efficiency of the sensor and the difficulty in achieving single-photon resolution due to the low signal-to-noise ratio. In this paper, we address the quantum efficiency of silicon sensors by refining the design of the entrance window, mainly by passivating the silicon surface and optimizing the dopant profile of the n + region. We present the measurement of the quantum efficiency in the soft X-ray energy range for silicon sensors with several process variations in the fabrication of planar sensors with thin entrance windows. The quantum efficiency for 250 eV photons is increased from almost 0.5% for a standard sensor to up to 62% as a consequence of these developments, comparable to the quantum efficiency of backside-illuminated scientific CMOS sensors. Finally, we discuss the influence of the various process parameters on quantum efficiency and present a strategy for further improvement.

Chromium compensated GaAs or GaAs:Cr sensors provided by the Tomsk State University (Russia) were characterized using the low noise, charge integrating readout chip JUNGFRAU with a pixel pitch of 75 × 75 µm 2 regarding its application as an X-ray detector at synchrotrons sources or FELs. Sensor properties such as dark current, resistivity, noise performance, spectral resolution capability and charge transport properties were measured and compared with results from a previous batch of GaAs:Cr sensors which were produced from wafers obtained from a different supplier. The properties of the sample from the later batch of sensors from 2017 show a resistivity of 1.69 × 10 9 Ω/cm, which is 47% higher compared to the previous batch from 2016. Moreover, its noise performance is 14% lower with a value of (101.65 ± 0.04) e - ENC and the resolution of a monochromatic 60 keV photo peak is significantly improved by 38% to a FWHM of 4.3%. Likely, this is due to improvements in charge collection, lower noise, and more homogeneous effective pixel size. In a previous work, a hole lifetime of 1.4 ns for GaAs:Cr sensors was determined for the sensors of the 2016 sensor batch, explaining the so-called "crater effect" which describes the occurrence of negative signals in the pixels around a pixel with a photon hit due to the missing hole contribution to the overall signal causing an incomplete signal induction. In this publication, the "crater effect" is further elaborated by measuring GaAs:Cr sensors using the sensors from 2017. The hole lifetime of these sensors was 2.5 ns. A focused photon beam was used to illuminate well defined positions along the pixels in order to corroborate the findings from the previous work and to further characterize the consequences of the "crater effect" on the detector operation.