Cyril Koughia

Springer Handbook of Electronic and Photonic Materials

The Springer Handbook of Electronic and Photonic Materials has been prepared to give a broad coverage of a wide range of electronic and photonic materials, starting from fundamentals and building up to advanced topics and applications. Its wide coverage with clear illustrations and applications, its chapter sequencing and logical flow, make it very different than other electronic materials handbooks. Each chapter has been prepared either by experts in the field or instructors who have been teaching the subject at a university or in corporate laboratories. The handbook provides an accessible treatment of the material by developing the subject matter in easy steps and in a logical flow. Wherever possible, the sections have been logically sequenced to allow a partial coverage at the beginning of the chapter for those who only need a quick overview of the subject. Additional valuable features include the practical applications used as examples, details on experimental techniques, useful tables that summarize equations, and, most importantly, properties of various materials. The handbook also has an extensive glossary at the end being helpful to those readers whose background may not be directly in the field. Key Topics Fundamental Electronic, Optical and Magnetic Properties Materials Growth and Characterization Materials for Electronics Materials for Optoelectronics and Photonics Novel Materials Selected Applications Features Contains over 600 two-color illustrations Includes over 100 comprehensive tables summarizing equations, experimental techniques and properties of various materials Emphasizes physical concepts over extensive mathematical derivations Parts and chapters with summaries, detailed index and fully searchable CD-ROM guarantee quick access to data and links to other sources Delivers a wealth of up-to-date references Incorporates a detailed Glossary of Terms

Spatially resolved measurement of high doses in microbeam radiation therapy using samarium doped fluorophosphate glasses

The measurement of spatially resolved high doses in microbeam radiation therapy has always been a challenging task, where a combination of high dose response and high spatial resolution (microns) is required for synchrotron radiation peaked around 50 keV. The x-ray induced Sm3+ → Sm2+ valence conversion in Sm3+ doped fluorophosphates glasses has been tested for use in x-ray dosimetry for microbeam radiation therapy. The conversion efficiency depends almost linearly on the dose of irradiation up to ∼5 Gy and saturates at doses exceeding ∼80 Gy. The conversion shows strong correlation with x-ray induced absorbance of the glass which is related to the formation of phosphorus-oxygen hole centers. When irradiated through a microslit collimator, a good spatial resolution and high “peak-to-valley” contrast have been observed by means of confocal photoluminescence microscopy.

X-ray induced Sm3+ to Sm2+ conversion in fluorophosphate and fluoroaluminate glasses for the monitoring of high-doses in microbeam radiation therapy

Fluorophosphate and fluoroaluminate glasses doped with trivalent samarium were evaluated as sensors of x-ray radiation for microbeam radiation therapy at the Canadian Light Source using the conversion of trivalent Sm3+ to the divalent form Sm2+. Both types of glasses show similar conversion rates and may be used as a linear sensor up to ∼150 Gy and as a nonlinear sensor up to ∼2400 Gy, where saturation is reached. Experiments with a multi-slit collimator show high spatial resolution of the conversion pattern; the pattern was acquired by a confocal fluorescence microscopy technique. The effects of previous x-ray exposure may be erased by annealing at temperatures exceeding the glass transition temperature Tg while annealing at TA < Tg enhances the Sm conversion. This enhancement is explained by a thermally stimulated relaxation of host glass ionic matrix surrounding x-ray induced Sm2+ ions. In addition, some of the Sm3+-doped glasses were codoped with Eu2+-ions but the results show that there is no marked ...

Excitation diffusion in GeGaSe and GeGaS glasses heavily doped with Er 3

Using the photoluminescence from GeGaSe:Er to pump GeGaS:Er, we examine the efficiency of light trapping. By measuring the photoluminescence decay time in powdered materials with varying particle size, we are able to exclude the influence of light trapping and to pinpoint the effect of self-quenching. The critical concentrations of Er for efficient self-quenching are determined by fitting experimental data to existing models. These values are found to be much larger than the concentrations inducing the formation of Er-clusters.

Optically erasable samarium-doped fluorophosphate glasses for high-dose measurements in microbeam radiation therapy

Previous work has demonstrated that fluorophosphate (FP) glasses doped with trivalent samarium (Sm3+) can be used as a dosimetric detector in microbeam radiation therapy (MRT) to measure high radiation doses and large dose variations with a resolution in the micrometer range. The present work addresses the use of intense optical radiation at 405 nm to erase the recorded dose information in Sm3+-doped FP glass plates and examines the underlying physics. We have evaluated both the conversion and optical erasure of Sm3+-doped FP glasses using synchrotron-generated high-dose x-rays at the Canadian Light Source. The Sm-ion valency conversion is accompanied by the appearance of x-ray induced optical absorbance due to the trapping of holes and electrons into phosphorus-oxygen hole (POHC) and electron (POEC) capture centers. Nearly complete Sm2+ to Sm3+ reconversion (erasure) may be achieved by intense optical illumination. Combined analysis of absorbance and electron spin resonance measurements indicates that th...

ESR study of samarium doped fluorophosphate glasses for high-dose, high-resolution dosimetry

We have studied the effect of samarium doping concentration and thermal annealing on X-ray induced defect centers, including phosphorus-oxygen hole and electron centers (POHC and POEC), in Sm3+-doped fluorophosphate glasses towards developing a potential high-dose, high-resolution detector for microbeam radiation therapy. ESR measurements show that defect center formation is suppressed by increasing the Sm-dopant concentration with POECs more strongly influenced than POHCs. This can be explained by a model based on the competition between defect center formations and Sm3+ ⇆ Sm2+ interconversion. Thermal annealing at increasing moderate temperatures (TA = 100−300 °C) reduces the POHC related ESR and induced absorbance bands while those of POEC continue to survive. ESR measurements over a wider range show the trace of a very broad ESR signal in samples containing Sm2+ ions including those annealed at temperatures between 350 °C and glass transition temperature (Tg ≈ 460 °C). Finally, thermal annealing at 550 °C (> Tg) totally erases all the ESR signals and restores the sample to its original unirradiated state.

Active pixel image sensor for large-area medical imaging

The most widely used pixel architecture is a passive pixel sensor (PPS) where the pixel consists of a detector and an a-Si:H thin-film transistor readout switch. While the PPS has the advantage of being compact and amenable towards high-resolution imaging, the data line capacitance, resistance, and the column charge amplifiers add a large noise component to the PPS that reduces the minimum readable sensor input signal. Building upon previous research into active pixel sensor (APS) based amplified pixel readout circuits, this work investiates a current-mediated APS (C-APS) x-ray detection array for diagnostic medical imaging applications. Preliminary tests indicate linear performance, and a programmable circuits gain via choice of supply voltage and sampling time. In addition, the performance of C-APS amplified pixels is measured from both, a-Si TFT metastability and noise performance perspectives. Theory and measurements indicate that the C-APS pixel architecture is promising for diagnostic medical imaging modalities including low noise, real-time fluoroscopy.

Electrical Conduction in Metals and Semiconductors

Electrical transport through materials is a large and complex field, and in this chapter we cover only a few aspects that are relevant to practical applications. We start with a review of the semi-classical approach that leads to the concepts of drift velocity, mobility and conductivity, from which Matthiessen’s Rule is derived. A more general approach based on the Boltzmann transport equation is also discussed. We review the conductivity of metals and include a useful collection of experimental data. The conductivity of nonuniform materials such as alloys, polycrystalline materials, composites and thin films is discussed in the context of Nordheim’s rule for alloys, effective medium theories for inhomogeneous materials, and theories of scattering for thin films. We also discuss some interesting aspects of conduction in the presence of a magnetic field (the Hall effect). We present a simplified analysis of charge transport in semiconductors in a high electric field, including a modern avalanche theory (the theory of lucky drift). The properties of low-dimensional systems are briefly reviewed, including the quantum Hall effect.

Optical Properties of Electronic Materials: Fundamentals and Characterization

Light interacts with materials in a variety of ways; this chapter focuses on refraction and absorption. Refraction is characterized by a material’s refractive index. We discuss some of the most useful models for the frequency dependence of the refractive index, such as those due to Cauchy, Sellmeier, Gladstone–Dale, and Wemple–DiDominico. Examples are given of the applicability of the models to actual materials. We present various mechanisms of light absorption, including absorption by free carriers, phonons, excitons and impurities. Special attention is paid to fundamental and excitonic absorption in disordered semiconductors and to absorption by rare earth, trivalent ions due to their importance in modern photonics. We also discuss the effect of an external electric field on absorption, and the Faraday effect. Practical techniques for determining the optical parameters of thin films are outlined. Finally, we present a short technical classification of optical glasses and materials.

Thermally Induced Nanostructures in Samarium-Doped Glass Ceramics for X-Ray Sensor Applications

There is much interest in various glass-ceramics doped with rare-earth (RE) metals for x-ray storage phosphor and/or x-ray scintillator applications for potential use in high resolution x-ray imaging. The phosphor and scintillator properties of these glass ceramics depend on the formation of RE embedded nanocrystals in their structure. The heat treatment and annealing of the starting RE-doped glasses is critically important to the formation and control of the glass ceramic nanocrystals. We have studied the thermal and photoluminescence properties of Sm-doped fluorochlorozirconate glass ceramics. We selected useful host compositions and appropriate heat treatment and annealing procedures needed to grow the required RE-doped nanocrystals in a glass matrix for sensor applications.