X-Ray microcalorimeter detectors - Technology developments for high energy astrophysics space missions

Improvements in the design, fabrication, and performance of astronomical detectors has ushered in the so-called era of multi messenger astrophysics, in which several different signals (electromagnetic waves, gravitational waves, neutrinos, cosmic rays) are processed to obtain detailed descriptions of their sources. Soft x-ray instrumentation has been developed in the last decades and used on board numerous space missions. This has allowed a deep understanding of several physical phenomena taking place in astrophysical sources of different scales from normal stars to galaxy clusters and huge black holes. On the other hand, imaging and spectral capabilities in the the hard x-rays are still lagging behind with high potentials of discovery area. Modern cryogenic microcalorimeters have two orders of magnitude or more better energy resolution with respect to CCD detectors at the same energy in the whole X-ray band. This significant improvement will permit important progress in high energy astrophysics thanks to the data that will be provided by future missions adopting this detector technology such as the ESA L2 mission Athena, the JAXA/NASA mission XRISM, both under development, or the NASA LYNX mission presently under investigation. The JAXA/NASA mission Hitomi, launched in 2016 and failed before starting normal operation, has already given a hint of the high potential of such detectors. Due to their very high sensitivity, X-ray cryogenic microcalorimeters need to be shielded from out of band radiation by the use of efficient thin filters. These microcalorimeters work by measuring the temperature increase caused by a photon that hits an X-ray absorber. In neutron transmutation doped germanium (NTD Ge) devices the temperature increase in the absorber is measured by a semiconductor thermometer made of germanium doped by the neutron transmutation doping technique. They are characterized by relatively low specific heat and low sensitivity to external magnetic fields. These characteristics make them promising detectors for hard X-ray detectors for space and laboratory applications. Research groups of the the X-ray Astronomy Calibration and Testing (XACT) Laboratory of the Osservatorio Astronomico di Palermo – Istituto Nazionale di Astrofisica (INAF-OAPA), and of the Dipartimento di Fisica e Chimica “Emilio Segrè” (DiFC) of the Università di Palermo have already developed experience related to the design, fabrication and testing of NTD Ge microcalorimeters. Furthermore, the research group has participated for many years in the design and development of filters for x-ray detectors in different space missions. This thesis concerns the development of materials and technologies for high energy microcalorimeters. In particular its aim is to design and fabricate thick bismuth absorbers for NTD germanium microcalorimeter arrays to extend their detection band toward hard X-ray energies. Filters for shielding microcalorimeters from different background radiation arriving on the detectors were also studied. The design and fabrication of thick bismuth absorbers for hard x-rays detection (20 keV ≤ E ≤ 100 keV) is part of an ongoing effort to develop arrays of NTD Ge microcalorimeters by planar technologies for astrophysical applications. One potential application of such detectors is in the high spectral resolution (∆E ~ 50 eV) investigation of the hard X-ray emission from the solar corona, which is the goal of a stratospheric balloon borne experiment concept named MIcrocalorimeters STratospheric ExpeRiment for solar hard X rays (MISTERX) presently under study at INAF-OAPA. The characterization activity of filters for microcalorimeters in also related to the implementation of the European Space Agency high energy mission named Athena (Advanced Telescopes for High Energy Astrophysics). This thesis describes the design, fabrication, and characterization of the bismuth absorbers, as well as the characterization of filters for Athena. Chapter one summarizes the working principles of NTD Ge microcalorimeters and their applications. Chapter 2 describes the design of the bismuth absorber array on suitable substrates. Chapter 3 focuses on the electroplating process for the bismuth layer deposition, with details about the design and fabrication of the microlithographic mask for the array patterning, and about the development of the microlithographic process for the array fabrication on the chosen substrates. The fabrication of 4 x 4 absorber arrays is also described. Chapter 4 reports on the characterization activity of deposited bismuth layers by different techniques; their morphology was investigated by scanning electron microscopy. The electrochemical impedance spectroscopy technique was used to increase grown layer quality. Fabricated arrays were also characterized. Chapter 5 describes the characterization activity for different filter prototype samples developed for Athena. Mechanical robustness, radio frequency attenuation and radiation damage caused by protons were evaluated. Radiation damage effects at different doses were in particular investigated on silicon nitride filters by scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-Vis-IR spectroscopy and x-ray attenuation measurements. Details on both technical detector requirements and different sensor types are given in the Appendix

Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

AMSAHTS 1990: Advances in Materials Science and Applications of High Temperature Superconductors

This publication is comprised of abstracts for oral and poster presentations scheduled for AMSAHTS '90. The conference focused on understanding high temperature superconductivity with special emphasis on materials issues and applications. AMSAHTS 90, highlighted the state of the art in fundamental understanding of the nature of high-Tc superconductivity (HTSC) as well as the chemistry, structure, properties, processing and stability of HTSC oxides. As a special feature of the conference, space applications of HTSC were discussed by NASA and Navy specialists

Proceedings of the 4th International Conference and Exhibition: World Congress on Superconductivity, Volume 2

This document contains papers presented at the 4th International Conference Exhibition: World Congress on Superconductivity held June 27-July 1, 1994 in Orlando, Florida. These documents encompass research, technology, applications, funding, political, and social aspects of superconductivity. The areas covered included: high-temperature materials; thin films; C-60 based superconductors; persistent magnetic fields and shielding; fabrication methodology; space applications; physical applications; performance characterization; device applications; weak link effects and flux motion; accelerator technology; superconductivity energy; storage; future research and development directions; medical applications; granular superconductors; wire fabrication technology; computer applications; technical and commercial challenges; and power and energy applications

Scaling up Electronic Spin Qubits into a Three-Dimensional Metal-Organic Framework

Practical implementation of highly coherent molecular spin qubits for challenging technological applications, such as quantum information processing or quantum sensing, requires precise organization of electronic qubit molecular components into extended frameworks. Realization of spatial control over qubit–qubit distances can be achieved by coordination chemistry approaches through an appropriate choice of the molecular building blocks. However, translating single qubit molecular building units into extended arrays does not guarantee a priori retention of long quantum coherence and spin–lattice relaxation times due to the introduced modifications over qubit–qubit reciprocal distances and molecular crystal lattice phonon structure. In this work, we report the preparation of a three-dimensional (3D) metal–organic framework (MOF) based on vanadyl qubits, [VO­(TCPP-Zn2-bpy)] (TCPP = tetracarboxylphenylporphyrinate; bpy = 4,4′-bipyridyl) (1), and the investigation of how such structural modifications influence qubits’ performances. This has been done through a multitechnique approach where the structure and properties of a representative molecular building block of formula [VO­(TPP)] (TPP = tetraphenylporphyrinate) (2) have been compared with those of the 3D MOF 1. Pulsed electron paramagnetic resonance measurements on magnetically diluted samples in titanyl isostructural analogues revealed that coherence times are retained almost unchanged for 1 with respect to 2 up to room temperature, while the temperature dependence of the spin–lattice relaxation time revealed insights into the role of low-energy vibrations, detected through terahertz spectroscopy, on the spin dynamics

Influence of Material and Geometry on the Performance of Superconducting Nanowire Single-Photon Detectors

Superconducting Nanowire Single-Photon Detectors offer the capability to detect electromagnetic waves on a single photon level in a wavelength range that far exceeds that of alternative detector types. However, above a certain threshold wavelength, the efficiency of those detectors decreases stronlgy, leading to a poor performance in the far-infrared range. Influences on this threshold are studied and approaches for improvement are verified experimentally by measurement of the device performance

Implementation of a High-Frequency Circuit into a Scanning Tunneling Microscope

Tunneling across superconducting junctions is associated with a variety of different processes that transfer single electrons, Cooper pairs, or even larger amounts of electrons by multiple Andreev reflections. Resonances inside the superconducting energy gap, like e.g. induced by magnetic adatoms, add resonant Andreev reflections to the variety of tunneling processes. We have successfully established two spectroscopic methods to study the nature of tunneling processes in superconductors. In the first approach, we complement the capabilities of a scanning tunneling microscope by introducing high-frequencies (HF) up to 40 GHz into the tunnel junction. The charge carriers involved in the tunneling process can exchange energy with the radiated HF field which leads to photon-assisted tunneling. Based on the theory of Tien und Gordon it is predicted that the sideband spacing in the bias voltage is a direct fingerprint of the number of electrons transferred in a single tunneling event. Here we have used photon-assisted tunneling to study superconducting tunnel junctions that exhibit Yu-Shiba-Rusinov states (YSR) induced by magnetic Mn adatoms on Pb(111). By exploiting the tunability of the junction conductivity we could specifically obtain insights into the contributions of single-electron tunneling and resonant Andreev processes to the YSR states. While the simple Tien-Gordon description is sufficient to describe single-electron tunneling and Cooper pair tunneling into the pure substrate, we show that the description breaks down for resonant Andreev reflections. We developed an improved theoretical model based on rate equations and the ac modulation of the bias voltage. Our model is in excellent agreement with our data. In a second spectroscopic approach, we investigate Cooper pair tunneling in current-biased Josephson junctions. We show that the critical current is strongly reduced by magnetic impurities, which reflects a reduced superconducting order parameter in the vicinity of the magnetic adatom. Our results of photon-assisted tunneling and Josephson spectroscopy show that we have established two powerful methods for the investigation of superconducting tunneling processes at the atomic scale. These methods could be particularly informative for the investigation of unconventional and topological superconductors

Ultraviolet-visible nanophotonic devices

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Sciences of Bilkent University, 2010.Thesis (Ph. D.) -- Bilkent University, 2010.Includes bibliographical references leaves 130-141.Recently in semiconductor market, III-Nitride materials and devices are of much interest due to their mechanical strength, radiation resistance, working in the spectrum from visible down to the deep ultraviolet region and solar-blind device applications. These properties made them strongest candidates for space telecommunication, white light generation, high power lasers and laser pumping light emitting diodes. Since, like other semiconductors, there have been material quality related issues, ongoing research efforts are concentrated on growing high quality crystals and making low p-type ohmic contact. Also, in light emitting device applications, similar to the visible and infrared spectrum components, there are challenging issues like high extraction efficiency and controlled radiation. In this thesis, we worked on growth and characterizations of high quality (In,Al)GaN based semiconductors, fabricating high performance photodiodes and light emitting diodes. We studied different surface modifications and possibilities of obtaining light emitting diode pumped organic/inorganic hybrid laser sourcesBütün, BayramPh.D