<p dir="ltr">Broadly, the focus of this work is on efficient statistical estimation and optimization of data arising from experimental data, particularly motivated by nanomanufacturing experiments on the material tellurene. Tellurene is a novel material for transistors with reliable attributes that enhance the performance of electronics (e.g., nanochip). As a solution-grown product, two-dimensional (2D) tellurene can be manufactured through a scalable process at a low cost. There are three main throughlines to this work, data augmentation, optimization, and equality constraint, and three distinct methodological projects, each of which addresses a subset of these throughlines. For the first project, I apply transfer learning in the analysis of data from a new tellurene experiment (process B) using the established linear regression model from a prior experiment (process A) from a similar study to combine the information from both experiments. The key of this approach is to incorporate the total equivalent amounts (TEA) of a lurking variable (experimental process changes) in terms of an observed (base) factor that appears in both experimental designs into the prespecified linear regression model. The results of the experimental data are presented including the optimal PVP chain length for scaling up production through a larger autoclave size. For the second project, I develop a multi-armed bandit Bayesian optimization (BO) approach to incorporate the equality constraint that comes from a mixture experiment on tellurium nanoproduct and account for factors with categorical levels. A more complex optimization approach was necessitated by the experimenters’ use of a neural network regression model to estimate the response surface. Results are presented on synthetic data to validate the ability of BO to recover the optimal response and its efficiency is compared to Monte Carlo random sampling to understand the level of experimental design complexity at which BO begins to pay off. The third project examines the potential enhancement of parameter estimation by utilizing synthetic data generated through Generative Adversarial Networks (GANs) to augment experimental data coming from a mixture experiment with a small to moderate number of runs. Transfer learning shows high promise for aiding in tellurene experiments, BO’s value increases with the complexity of the experiment, and GANs performed poorly on smaller experiments introducing bias to parameter estimates.</p>

Tellurite glass is a material with advantageous optical properties, such as high transparency from visible to mid-infrared wavelengths, high nonlinearity, and high solubility of light-emitting rare earth dopants. Although tellurite has been investigated in fibers and in some waveguide studies, there is still much to explore about it in integrated photonics. Here, we use a hybrid platform that monolithically combines tellurite with commercially available silicon nitride chips. The platform leverages silicon nitride’s many advantages, including its low propagation losses, mature fabrication techniques with small feature sizes, and low cost for mass production, to enable the development of new on-chip tellurite glass light sources. This thesis aims to study the optical properties of distributed Bragg reflector cavities and explore their potential for lasing when the tellurite is doped with different rare earths, namely erbium and thulium. Chapter 1 provides an overview of the context of this work, introducing the materials and cavity used here. Chapter 2 introduces the basic theory behind waveguides and Bragg gratings, as well as rare earth rate equation gain models, coupled mode theory, and a laser model based on the shooting method. Chapter 3 discusses the design, fabrication, and characterization of passive properties of distributed Bragg reflector cavities using undoped tellurite. Chapters 4 and 5 present proof-of-concept laser demonstrations, by using tellurite doped with erbium and thulium, respectively. These lasers constitute the first demonstrations of distributed Bragg reflector lasers in this hybrid tellurite-silicon nitride platform. Chapter 6 combines the laser model introduced in Chapter 2 with the designs and results from Chapters 3–5 to investigate different routes to optimize the laser performances by studying how their efficiencies vary with different parameters, such as background loss, cavity and grating lengths, and rare earth concentration. Chapter 7 summarizes this work and provides insights into future research work. / Thesis / Doctor of Philosophy (PhD) / Integrated photonics is an emerging technology that revolves around tiny circuits on chips, similar to electronics, but using light instead of electricity. Photonic integrated circuits can help achieve faster and more power-efficient devices for a wide range of applications. In this work, we explore the potential of tellurite glass, a material that has promising optical properties, to achieve on-chip lasers. Lasers are one of the fundamental components in these light-driven circuits but are challenging to be realized on a chip-scale. We achieved compact lasers, which are more than ten times thinner than a strand of hair, a couple of centimeters long, and emit invisible (infrared) eye-safe light. These devices are compatible with volume production and there is much room for optimizing them. The lasers investigated here are highly promising for applications including imaging systems (LiDAR) for autonomous vehicles, augmented and virtual reality, data communications, and chemical and physical sensors.

<p dir="ltr">The separation of tellurium from cadmium telluride is examined using a unique combination of mild, anhydrous chlorination and complexation of the subsequent tellurium tetrachloride with 3,5-di-<i>tert</i>-butylcatechol. The resulting tellurium complex, Te(dtbc)₂, is isolated in moderate yield and features a 10³ to 10⁴ reduction in cadmium content, as provided by XRF and ICP-MS analysis. Similar results were obtained from zinc telluride. A significant separation between Te, Se, and S was observed after treating a complex mixture of metal chalcogenides with this protocol. These three tunable steps can be applied for future applications of CdTe photovoltaic waste.</p><p dir="ltr">We report the synthesis and characterization of the first series of tellurium and selenium complexes featuring an η⁵-cyclopentadienyl ligand. Reaction of Ph₃TeX (X = Cl, S₂CNEt₂) with MCp^R (M = Li, K; R = H, Me₄, Me₅) results in high yields of [Cp][TePh₃] (<b>1</b>), [Cp^Me4][TePh₃] (<b>2</b>), and [Cp*][TePh₃] (<b>3</b>), respectively. Similarly, reaction of Ph₃SeCl with LiCp and KCp* furnishes [Cp][SePh₃] (<b>4</b>) and [Cp*][SePh₃] (<b>5</b>). Each was characterized by X-ray crystallography, revealing similar η⁵-coordination with little distortion from an idealized half-sandwich geometry, presumably from the remaining lone pair on tellurium and selenium. The Te–centroid distances are relatively long (<b>1</b>: 2.770(3), <b>2</b>: 2.746(1), and <b>3</b>: 2.733(1) Å), suggesting a mostly ionic interaction. Se–centroid distances (<b>4</b>: 2.748(3), <b>5</b>: 2.707(2), 2.730(2) Å) were found to be surprisingly similar despite its smaller atomic radius. Compounds <b>2</b>, <b>3</b>, and <b>5</b> display rapid decomposition at room temperature, extruding a phenylated cyclopentadiene and the and the respective diphenylchalcogenide. The nature of bonding within these complexes was investigated through DFT methods and found to be primarily ionic in nature.</p><p dir="ltr">Synthesis of homoleptic zirconium and hafnium dithiocarbamate via carbon disulfide insertion into zirconium and hafnium amides were investigated for their utility as soluble molecular precursors for chalcogenide perovskites and binary metal sulfides. Treating M(NEtR)₄ (M= Zr, Hf and R= Me, Et) with CS₂ resulted in quantitative yields of homoleptic Group IV dithiocarbamates. Zr(k²-S₂CNMeEt) (<b>1</b>), Zr(k²-S₂CNEt₂)₄ (<b>2</b>), and Hf(k²-S₂CNEt₂)₄(<b>4</b>), a rare example of a crystal of a homoleptic hafnium CS₂ inserted amide species, were characterized. A computational analysis confirmed assignments for IR spectroscopy.<b> </b>To exemplify the utility of the Group IV dithiocarbamates, a solution-phase nanoparticle synthesis was performed to obtain ZrS₃ via the thermal decomposition of Zr(S₂CNMeEt)₄</p><p dir="ltr">Chalcogenide perovskites have garnered interest for applications in semiconductor devices due to their excellent predicted optoelectronic properties and stability. However, high synthesis temperatures have historically made these materials incompatible with the creation of photovoltaic devices. Here, we demonstrate the solution processed synthesis of luminescent BaZrS₃ and BaHfS₃ chalcogenide perovskite films using single-phase molecular precursors at sulfurization temperatures of 575 °C and sulfurization times as short as one hour. These molecular precursor inks were synthesized using known carbon disulfide insertion chemistry to create Group 4 metal dithiocarbamates, and this chemistry was extended to create species, such as barium dithiocarboxylates, that have never been reported before. These findings, with added future research, have the potential to yield fully solution processed thin films of chalcogenide perovskites for various optoelectronic applications.</p><p dir="ltr">Np(IV) Lewis base adducts were prepared by ligand substitution of NpCl₄(DME)₂. Using acetonitrile and pyridine, NpCl₄(MeCN)₄ (<b>1</b>) and NpCl₄(pyr)₄ (<b>2</b>), were isolated, respectively. All species were fully characterized using spectroscopic and structural analyses.</p>

Silicon photonics (SiP) has become a cornerstone technology of the modern age by leveraging the mature fabrication processes and infrastructure of the microelectronics industry for the cost-effective and high-volume production of compact and power-efficient photonic integrated circuits (PICs). The impact that silicon (Si)-based PICs have had on data communications, particularly data center interconnection and optical transceiver technologies, has encouraged SiP chip development and their use in other applications such as artificial intelligence, biomedical sensing and engineering, displays for augmented/virtual reality, free-space communications, light detection and ranging, medical diagnostics, optical spectroscopy, and quantum computing and optics. To expand the functionality and improve the performance of SiP circuits for these surging applications, subwavelength grating (SWG) metamaterials have been thoroughly investigated and implemented in various passive integrated photonic components fabricated on the silicon-on-insulator (SOI) platform. SWG metamaterials are periodic structures composed of two materials with different permittivities that exhibit unnatural properties by using a period shorter than the guided wavelength of light propagating through them. The ability to synthesize the constituent SiP materials without any need to alter standard fabrication procedures enables precise, flexible control over the electromagnetic field and sophisticated selectively over anisotropy, dispersion, polarization, and the mode effective index in these metastructures. This provides significant benefits to SOI devices, such as low loss mode conversion and propagation, greater coupling efficiencies and alignment tolerances for fiber-chip interfaces, ultrabroadband operation in on-chip couplers, and improved sensitivities and limits of detection in integrated photonic sensors. Parallel to the rise of SiP technology is the development of other materials compatible with mature PIC fabrication methods both in the foundry (e.g., silicon nitride (Si3N4)) and outside the foundry (e.g., high-index oxide glasses such as aluminum oxide (Al2O3) and tellurium oxide (TeO2)). Si3N4 offsets the pitfalls of Si as a passive waveguiding material, providing lower scattering and polarization-dependent losses, optical transparency throughout the visible spectrum, increased tolerance to fabrication error, and better handling of high-power optical signals. Meanwhile, Al2O3 and TeO2 both serve as excellent host materials for rare-earth ions, and TeO2 possesses strong nonlinear optical properties. Using a single-step post-fabrication thin film deposition process, these materials can be monolithically integrated onto Si PICs at a wafer scale, enabling the realization of complementary-metal-oxide-semiconductor (CMOS)-compatible, hybrid SiP devices for linear, nonlinear, and active functionalities in integrated optics. While SWG metamaterials have widely impacted the design space and applicability of integrated photonic devices in SOI, they have not yet made their mark in other material systems outside of Si. Furthermore, demonstrations of their capabilities in active processes, including optical amplification, are still missing. In this thesis, we present a process for developing various SWG metamaterial-engineered integrated photonic devices in different material systems both within and beyond SOI. The demonstrations in this thesis emphasize the benefits of SWG metamaterials in these devices and realize their potential for enhancing functionality in applications such as sensing and optical amplification. The objective of the thesis is to highlight the prospects of SWG metamaterial implementation in different media used in integrated optics. This is accomplished by experimentally demonstrating SWG metamaterial waveguides, ring resonators and other components composed of different hybrid core-cladding material systems, including Si-TeO2 and Si3N4-Al2O3. Chapter 1 introduces the background and motivation for integrated optics and SWG metamaterials and provides an overview and comparison of the different materials explored in this work. Chapter 2 presents an initial experimental demonstration of TeO2-coated SOI SWG metamaterial waveguides and mode converters. It also details the design of fishbone-style SWG waveguides aimed at lowering loss and enhancing mode overlap with the active TeO2 cladding material in the hybrid SiP platform. Chapter 3 details an open-access Canadian foundry process for rapid prototyping of Si3N4 PICs, emphasizing the Si3N4 material and waveguide fabrication methods, as well as the design and characterization of various integrated photonic components included in a process design kit. The platform is compared against other Si3N4 foundries, and plans for further development are also discussed. Chapter 4 reports the first demonstration of SWG metamaterial waveguides and ring resonators fabricated using a Si3N4 foundry platform. The measured devices have a propagation loss of ∼1.5 dB/cm, an internal quality factor of 2.11·10^5, and a bulk sensitivity of ∼285 nm/RIU in the C-band, showcasing competitive metrics with conventional Si3N4 waveguides and SWG ring resonators and sensors reported in SOI. Chapter 5 presents work towards an SWG metamaterial-engineered waveguide amplifier. The fabricated device, based in Si3N4 and functionalized by an atomic layer deposited, erbium-doped Al2O3 thin film cladding, exhibited a signal enhancement of ∼8.6 dB, highlighting its potential for on-chip optical amplification. Methods to reduce the loss within the material system are proposed to achieve net gain in future devices. Chapter 6 summarizes the thesis and discusses pathways for optimizing the current devices as well as avenues for exploring new and intriguing materials and devices for future applications in integrated photonics. / Thesis / Doctor of Philosophy (PhD)

A primeira parte desta tese aborda estudos sobre a reatividade de compostos de telúrio eletrofílicos, principalmente tetracloreto de telúrio e tricloretos aromáticos de telúrio. Novos aspectos da reatividade de TeCl4 frente a alcinos e algumas acetofenonas foram observados e, a partir da elucidação estrutural dos compostos obtidos, por cristalografia, uma racionalização mecanística foi proposta para cada caso. As proposições apresentadas encontraram respaldo com a detecção de intermediários transientes por estudos de espectrometria de massas com ionização por electron-spray (ESI-MS/MS). Além de novos aspectos da química do Telúrio, os compostos preparados encontraram aplicação como potentes e seletivos inibidores de cisteíno proteases. Com esta aplicação estabelecida, foram sintetizadas ambos os enantiômeros de uma telurana e a atividade inibitória destas frente a Catepsina B mostrou dependência da estereoquímica devido a dependência estereoquímica da interação entre a enzima e o inibidor. A segunda parte deste trabalho trata do desenvolvimento da reação de abertura de anel de aziridinas por reagentes organometálicos de cobre derivados de teluretos vinílicos e arílicos que resultaram em derivados de aminas homoalílicas ou homobenzílicas. Em seguida, a reatividade de aziridinas alílicas foi estudada frente a uma série de reagentes organometálicos de lítio, magnésio, cobre e zinco que mostraram influenciar a regio- e estereosseletividades das reações de abertura. / The first part of this thesis deals with the study of the reactivity of electrophilic tellurium compounds, mainly tellurium tetrachloride and aromatic tellurium trichlorides. New aspects of the reactivity of TeCl4 towards alkynes and some acetophenones were disclosed. A mechanistic rationale for each of the processes studied was possible by the determination of the stereochemistry for each product by monocrystal X-ray diffraction analysis. The proposition of the formation of cationic intermediates in the addition reaction of TeCl4 to alkynes was corroborated by the detection and characterization of transient intermediates by ESI-MS/MS experiments. Besides the new aspects of the Tellurium chemistry found, the prepared compounds showed a high and selective activity as inhibitors of cysteine proteases. A pair of enantiomers of a tellurane showed different activities against Human Catepsin B due to a stereochemical dependence in the enzyme/inhibitor interaction. The second part of the present work deals with the development of the ring opening reaction of aziridines by organometallic reagents of copper prepared from vinylic and arylic tellurides. These reactions led to homoallylic and homobenzylic amine derivatives. Finally, the reactivity of 2-alkenyl aziridines was studied towards a series of organometallic reagents of lithium, magnesium, copper and zinc which biased the regio- and stereoselectivities of the ring opening reactions.

A primeira parte desta tese aborda estudos sobre a reatividade de compostos de telúrio eletrofílicos, principalmente tetracloreto de telúrio e tricloretos aromáticos de telúrio. Novos aspectos da reatividade de TeCl4 frente a alcinos e algumas acetofenonas foram observados e, a partir da elucidação estrutural dos compostos obtidos, por cristalografia, uma racionalização mecanística foi proposta para cada caso. As proposições apresentadas encontraram respaldo com a detecção de intermediários transientes por estudos de espectrometria de massas com ionização por electron-spray (ESI-MS/MS). Além de novos aspectos da química do Telúrio, os compostos preparados encontraram aplicação como potentes e seletivos inibidores de cisteíno proteases. Com esta aplicação estabelecida, foram sintetizadas ambos os enantiômeros de uma telurana e a atividade inibitória destas frente a Catepsina B mostrou dependência da estereoquímica devido a dependência estereoquímica da interação entre a enzima e o inibidor. A segunda parte deste trabalho trata do desenvolvimento da reação de abertura de anel de aziridinas por reagentes organometálicos de cobre derivados de teluretos vinílicos e arílicos que resultaram em derivados de aminas homoalílicas ou homobenzílicas. Em seguida, a reatividade de aziridinas alílicas foi estudada frente a uma série de reagentes organometálicos de lítio, magnésio, cobre e zinco que mostraram influenciar a regio- e estereosseletividades das reações de abertura. / The first part of this thesis deals with the study of the reactivity of electrophilic tellurium compounds, mainly tellurium tetrachloride and aromatic tellurium trichlorides. New aspects of the reactivity of TeCl4 towards alkynes and some acetophenones were disclosed. A mechanistic rationale for each of the processes studied was possible by the determination of the stereochemistry for each product by monocrystal X-ray diffraction analysis. The proposition of the formation of cationic intermediates in the addition reaction of TeCl4 to alkynes was corroborated by the detection and characterization of transient intermediates by ESI-MS/MS experiments. Besides the new aspects of the Tellurium chemistry found, the prepared compounds showed a high and selective activity as inhibitors of cysteine proteases. A pair of enantiomers of a tellurane showed different activities against Human Catepsin B due to a stereochemical dependence in the enzyme/inhibitor interaction. The second part of the present work deals with the development of the ring opening reaction of aziridines by organometallic reagents of copper prepared from vinylic and arylic tellurides. These reactions led to homoallylic and homobenzylic amine derivatives. Finally, the reactivity of 2-alkenyl aziridines was studied towards a series of organometallic reagents of lithium, magnesium, copper and zinc which biased the regio- and stereoselectivities of the ring opening reactions.

The CdTe family members (in particular CdZnTe) remain the substrate of choice for epitaxial growth of HgCdTe for use in high performance infrared (IR) detectors and focal plane arrays. This is the case despite advances in the use of alternate substrate technologies such as buffered GaAs and GaAs on Si; these technologies, to date, have not reproducibly demonstrated device performance comparable to the arrays made in HgCdTe grown on CdZnTe and CdTe. The quality of CdTe family materials has improved significantly over the past several years and so the quality and reproducibility of IR detectors has improved along with them. It is clear, however, that CdTe family substrates still have a significant impact on the performance of HgCdTe devices and that further research is required to reduce the effects of substrate on these devices. Unlike silicon or gallium arsenide, it is very difficult to grow the large area single crystals of CdZnTe due to thermodynamic limitations. It has the lowest thermal conductivity among all semiconductors that makes it difficult to obtain planar solid-liquid interface, which is desirable for the growth of large area single crystals of CdZnTe. Due to its high ionicity and weak bonding, defects are easily incorporated during the growth. Also, it is well established that both the structural defects and impurity content of Hg1-xCdxTe epitaxial layers are strongly influenced by the quality of the substrates used in the epitaxial growth process. A substrate of poor structural quality will result in a poor substrate/layer interface from which defects will propagate into the epilayer. It is known that our focal plane arrays (FPAs) are backside illuminated, with the device connected to underlying silicon multiplexer, using a matrix of indium bumps. Thus the substrate should have high IR transmission to pass the radiation on to the detector for collection. High IR transmission requires chemically and electrically homogeneous crystals free from extraneous second phase particles. This objective is one of the most difficult thermodynamic and technological problems in the growth of CdTe and related alloys. The bulk CdZnTe crystals grown from melt suffer from the inherent disadvantage of accommodating tellurium precipitates because of high growth temperature and phase diagram limitations. These tellurium (Te) precipitates condense as cadmium vacancies and Te interstitials during the cooling process, which contribute to intrinsic point defects. Although extensive efforts have been made in the area of purification of the CdZnTe crystals by using 6N pure starting materials, still the high temperature melt growth leads to impurity pickup during the crystal growth process. This deviation in the stoichiometry, especially due to free carriers, impurities and second phase tellurium precipitates, play the major role in reducing the infrared transmission through the CdZnTe substrate material. Also they affect the device performance when used for detector applications. In this context a thorough investigation of the non-stoichiometry of the CdZnTe material is mandatory to improve the material quality. It is my endeavor in this respect to present in this thesis “optical and structural investigations of defects in CdZnTe (Zn~4%) crystals”. The present thesis has been organized into six chapters. Chapter 1: It presents an up to date comprehensive review of the defects in CdTe binary and CdZnTe ternary compound semiconductors. It includes an introduction to the ternary II-VI cadmium zinc telluride with potential device applications. Issues related to CdTe based substrates for infrared (IR) applications have been discussed. Growth as well as several material aspects like crystal structure, band structure, mechanical, thermal, optical and dielectric properties have been discussed in details. The chapter ends with the motivation and scope for the present thesis. Chapter 2 : Te precipitates were identified and characterized in CdZnTe (Zn ~ 4%) crystals using various physical characterization techniques and the results are presented in Chapter 2. X-ray diffraction rocking curve measurements were carried out on a series of samples to assess the overall crystalline quality of the as grown CdZnTe crystals, in conjunction with Fourier transform infrared (FTIR) absorption spectroscopy measurements to identify the presence of Te precipitates. Further, the CdZnTe samples having Te precipitates were systematically characterized using micro-Raman imaging technique. CdZnTe wafers grown in three and six zone furnaces using quartz and/or pyrolytic boron nitride (PBN) crucibles have been subjected to micro-Raman imaging to quantify and understand the nature of Te precipitates. It is well known that for the normal phase of Te precipitates, the Raman modes appear centered around 121 (A1), 141(E) /TO (CdTe) cm -1and a weak mode around 92 (E) cm -1 in CdZnTe indicating the presence of trigonal lattice of Te. Using the micro-Raman maps and taking the spatial distribution of the area ratio of 121 to 141 cm-1 Raman modes, the size and distribution of Te precipitates were estimated. A substantial reduction in Te precipitate size and an improvement in the IR transmission in the 2.2 – 5 µm IR window was observed in the CdZnTe crystals subjected to post growth annealing under Cd+Zn vapors at 650 oC for 6 hrs. Also it is shown that the samples grown in pyrolytic boron nitride (PBN) crucibles have shown an overall improvement in the crystalline quality and reduction in the Te precipitate size as compared to the samples grown in quartz crucibles. The possible reasons for these observations have been discussed in chapter 2. The presence of Te precipitates under high pressure phase was detected by the blueshift of the Raman bands that appear at 121 (A1) cm-1for a normal Te phase, indicating that these micro-Raman maps are basically the distribution of Te precipitates in different phases. NIR microscopy imaging has been carried out to further substantiate the presence of Te precipitates under high pressure phase and that of larger Te precipitates. The significance of micro-Raman imaging lies in quantifying and demonstrating the high pressure phase of Te precipitates in CdZnTe crystals in a non-destructive way. Also it is shown that the presence of Te precipitates lead to loss of useful signal in the 2.2 – 6 µm wavelength regions and hence are “deleterious” for substrate applications of CdZnTe crystals required for the growth and fabrication of HgCdTe detectors. Chapter 3: The effects of annealing and hydrogenation on the low temperature photoluminescence (PL) spectra of CdZnTe (Zn ~ 4%) crystals are reported in this chapter. It is shown that annealing at 600 oC for 12 hrs under Cd vapors has resulted in the disappearance of both C-A and DAP recombination features (attributed to singly ionized cadmium vacancy acceptors) observed in the 1.5 – 1.6 eV band edge region in the low temperature PL spectra of CdZnTe, confirming the origination of these bands from Cd vacancy defects. The presence of copper impurity has been identified by the appearance of the 1.616 (AoX) eV energy peak attributed to exciton bound to the neutral copper acceptor and the 1.469 eV band attributed to copper acceptor in the donor acceptor pair (DAP) recombinations. It is shown that, only annealing under Cd+Zn vapors at 650 oC for 6 hrs has resulted in the passivation of the 1.469 eV band and the mechanism has been explained invoking the Hume-Rothery rule. Passivation of the 1.469 eV band is significant, since CdZnTe substrate copper contamination was found to degrade HgCdTe epitaxial layer and hence the performance of HgCdTe infrared (IR) detectors. Also it shown that vacuum annealing has resulted in the introduction of a new defect band around 0.85 eV in the low temperature PL spectra of CdZnTe possibly due to the loss of Cd and/or Zn. Further, the effects of hydrogenation in passivating the defect bands observed in the low temperature PL spectra of the control CdZnTe crystals are discussed. Using micro-Raman imaging technique, it is shown that hydrogenation has resulted in the reduction in size and restoration of normal phase for Te precipitates, which otherwise were present under high pressure phase in CdZnTe crystals. It is shown that the net effect of hydrogenation is to improve the quality of CdZnTe crystals at low temperature (50 oC) as compared to the high Cd+Zn annealing temperature (650 oC) whose effect is only to reduce the size of Te precipitates. To further substantiate this an analysis of the temperature dependent resonance micro-Raman spectra recorded with 633 and 488 nm lasers has been made and it is shown that appearance of the multiple orders (up to 4 orders) of the CdTe like LO phonon modes and emergence of the ZnTe like LO phonon mode are clear indications of the improved quality of the hydrogenated CdZnTe crystals. Chapter 4: Manifestation of Fe2+and Fe3+charge states of Fe in undoped CdZnTe (Zn ~ 4 %) crystals grown in quartz crucibles by asymmetrical Bridgemann method and their respective optical and magnetic behaviors have been discussed in this chapter. Fe2+being optically active shows absorption around 2295 cm-1in the low temperature (T = 3 K) FTIR spectra, while Fe3+being magnetically active exhibits coexistence of para and ferromagnetic phases, as identified by low temperature electron spin resonance and supported independently by low temperature SQUID and AC susceptibility measurements. In the paramagnetic phase (TC ~ 4.8 K) the inverse of ac susceptibility follows the Curie-Weiss law. In the ferromagnetic phase (TC ~ 4.8 K) the thermal evolution of magnetization follows the well known Bloch’s T3/2 law. This is further supported by the appearance of hysteresis in the SQUID measurements at 2K below TC. Small coercive field of 10 Oe as estimated in the hysteresis suggests that the magnetic anisotropy is very small in these systems. Chapter 5: In this chapter, details of the indigenously developed laser beam induced current (LBIC) instrumentation have been presented. These include instrumental arrangement of the micro-mechanical system for raster scanning of defects in semicoductors and fabrication details of continuous flow liquid helium cryostat for low temperature LBIC measurements. Preliminary LBIC data recorded using this system have been shown to demonstrate the operability of the system. Chapter 6: This chapter includes a brief write-up summarizing the results and draws the attention for the possible future work. Appendix A: Here C++ programs for LBIC measurements are presented. Appendix B: Here the CAD diagrams for the full cross sectional view of the liquid helium cryostat consisting of “assembly liquid helium cryostat” and “part liquid helium cryostat” are attached.

The current research project investigated the anoxygenic phototrophic and metal(loid) transforming bacteria of hypersaline and deep ocean hydrothermal environments. The East German Creek brine springs, an unusual flowing hypersaline system, was enumerated using classical techniques. Subterranean sulfide supported purple sulfur and nonsulfur bacteria, but at the highly oxygenated surface, aerobic anoxygenic phototrophs (AAP) were numerically dominant (up to 16-36% of cultivable bacteria). Strains (EG8, EG13, EG17, EG19) with unusual phylogenetic affiliation and novel photosynthetic and metal(loid) reducing traits were described taxonomically. Chromocurvus halotolerans gen. nov., sp. nov. was proposed as a second example of a gammaproteobacterial AAP. It exhibited bent rod-shaped cells, unusual among AAP. Facultatively anaerobic Charonomicrobium ambiphototrophicum gen. nov., sp. nov. was capable of both aerobic and anaerobic anoxygenic photosynthesis, and incapable of photoautotrophy, distinguishing it from both AAP and purple nonsulfur bacteria. Roseovarius vanadiphilum sp. nov. surprisingly produced 4.5 times more biomass and 2 times more bacteriochlorophyll (BChl) at extremely high NaVO3 concentration (7.5 g/l) than in metal-free medium. A second novel metabolic mode, anaerobic respiration on the toxic metalloid tellurate, was described for a relative of non-phototrophic Shewanella frigidimarina (ER-Te-48), from deep ocean hydrothermal vent Paralvinella worms at Explorer Ridge in the Pacific Ocean. Other strains respired on SeO32- (ER-Se-17L), VO3- (ER-V-6), and VO43- (AV-V-25). These organisms provided the first examples of anaerobic respiration on Te, Se and V at hydrothermal vents. High level resistance of AAP to metal(loid)s prompted investigation of the influence of TeO32- on photosynthetic pigment production in species including Erythromicrobium ramosum (from a terrestrial hydrothermal system) and Erythrobacter litoralis (from a hypersaline supralittoral system). Tellurite enhanced photosynthetic pigment production up to 3.4 times, consistent with an antioxidant carotenoid-based defense mechanism. However, in E. litoralis BChl precursors such as Mg protoporphyrin or its monomethyl ester also accumulated, indicating biosynthetic pathway interruption. In hydrothermal and hypersaline ecosystems, largely devoid of eukaryotic phototrophs but often enriched in metal(loid)s, AAP and metal(loid) reducers are key modulators of nutrient and toxin availability. The presented results on their ecology, physiology and biochemistry have important implications for theoretical understanding of extreme environments and hold potential for biotechnological applications.

The current research project investigated the anoxygenic phototrophic and metal(loid) transforming bacteria of hypersaline and deep ocean hydrothermal environments. The East German Creek brine springs, an unusual flowing hypersaline system, was enumerated using classical techniques. Subterranean sulfide supported purple sulfur and nonsulfur bacteria, but at the highly oxygenated surface, aerobic anoxygenic phototrophs (AAP) were numerically dominant (up to 16-36% of cultivable bacteria). Strains (EG8, EG13, EG17, EG19) with unusual phylogenetic affiliation and novel photosynthetic and metal(loid) reducing traits were described taxonomically. Chromocurvus halotolerans gen. nov., sp. nov. was proposed as a second example of a gammaproteobacterial AAP. It exhibited bent rod-shaped cells, unusual among AAP. Facultatively anaerobic Charonomicrobium ambiphototrophicum gen. nov., sp. nov. was capable of both aerobic and anaerobic anoxygenic photosynthesis, and incapable of photoautotrophy, distinguishing it from both AAP and purple nonsulfur bacteria. Roseovarius vanadiphilum sp. nov. surprisingly produced 4.5 times more biomass and 2 times more bacteriochlorophyll (BChl) at extremely high NaVO3 concentration (7.5 g/l) than in metal-free medium. A second novel metabolic mode, anaerobic respiration on the toxic metalloid tellurate, was described for a relative of non-phototrophic Shewanella frigidimarina (ER-Te-48), from deep ocean hydrothermal vent Paralvinella worms at Explorer Ridge in the Pacific Ocean. Other strains respired on SeO32- (ER-Se-17L), VO3- (ER-V-6), and VO43- (AV-V-25). These organisms provided the first examples of anaerobic respiration on Te, Se and V at hydrothermal vents. High level resistance of AAP to metal(loid)s prompted investigation of the influence of TeO32- on photosynthetic pigment production in species including Erythromicrobium ramosum (from a terrestrial hydrothermal system) and Erythrobacter litoralis (from a hypersaline supralittoral system). Tellurite enhanced photosynthetic pigment production up to 3.4 times, consistent with an antioxidant carotenoid-based defense mechanism. However, in E. litoralis BChl precursors such as Mg protoporphyrin or its monomethyl ester also accumulated, indicating biosynthetic pathway interruption. In hydrothermal and hypersaline ecosystems, largely devoid of eukaryotic phototrophs but often enriched in metal(loid)s, AAP and metal(loid) reducers are key modulators of nutrient and toxin availability. The presented results on their ecology, physiology and biochemistry have important implications for theoretical understanding of extreme environments and hold potential for biotechnological applications.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Memory is considered to be a process that has several stages, including acquisition, consolidation and retrieval. Memory impairment occurs when important synapses are modified. Alzheimer s disease (DA) is the most common cause of dementia. DA is characterized by cognitive damage, accumulation of the pathogenic amyloid-β (Aβ) peptide, and cholinergic dysfunction. Moreover, oxidative stress is associated with DA. Therapies used for dementia are still palliative rather than curative. Consequently, new therapies are urgently required. Biological effects of tellurium compounds have been studied, leading to a set of interesting and promising applications. Accordingly, 2-phenylethinyl-butyltellurium (PEBT), an organotellurium compound, has been reported as antioxidant. The purpose of this study was to characterize PEBT as a promising alternative for memory improvement and prevention of cognitive deficits, using experimental models of DA in mice. Initially, the present study was conducted to evaluate the effect of a single oral administration (p.o.) of PEBT at a dose of 10 mg/kg on memory, employing the step-down inhibitory avoidance task. PEBT administered 1 h before training, immediately after training or 1 h before the test session of the step-down inhibitory avoidance task increased the step-down latency time in comparison to the control mice, improving acquisition, consolidation, and retrieval of memory, respectively. The glutamate uptake, but not glutamate release, by cerebral cortex and hippocampal slices of mice was inhibited after 1 h of treatment with PEBT. After 24 h of PEBT exposure, the inhibition of cerebral cortex glutamate uptake disappeared. The improvement of memory by PEBT seems most likely to be mediated through an interaction with the amino acid transporters of the glutamatergic system. Thereafter, a subchronic PEBT treatment (1 mg/kg, p.o., for 10 days) after injection of Aβ(25-35) (3 nmol/3 μl/per site, intracerebroventricular) reversed Aβ-induced learning and memory deficits in the Morris water maze and step-down inhibitory avoidance tasks. In addition, PEBT (10 mg/kg, p.o.), administered 30 min before scopolamine (1 mg/kg, intraperitoneal), ameliorated memory deficit induced by this amnesic agent in the Morris water maze. Further, scopolamine was given 30 min before training and test or immediately post-training of step-down inhibitory avoidance task, inducing damage on acquisition, retrieval, and consolidation of memory, respectively. PEBT, administered 30 min before scopolamine, improved consolidation and retrieval stages, but not acquisition. General locomotor and exploratory activities, evaluated in the open-field test, were similar in all mice. Finally, the antiapoptotic effect of PEBT was evaluated. Human retinal pigment epithelial cells (ARPE-19 cell line) were exposed to in vitro oxidative stress by 10 ng/ml tumor necrosis factor-α and 600 μM H2O2. One hour PEBT incubation at concentrations of 7.5 and 10 μM attenuated the apoptosis induced by oxidative stress. This effect lasted up to 6 hours after oxidative stress induction. PEBT (5 and 10 μM) inhibited oxidative stress-induced poly (ADP-ribose) polymerase (PARP) cleavage and restored extracellular-signal-related kinase (ERK) phosphorylation decreased by oxidative stress. The protective mechanism exerted by PEBT against oxidative stress may involve PARP cleavage, regulation of ERK pathway, as well as its known antioxidant properties. In conclusion, the finds of the present thesis point out the ameliorative effect of PEBT on memory stages (acquisition, consolidation and retrieval). Likewise, PEBT improved memory impairment in mice. These effects seem to be due to strengthen the physiological glutamatergic tonus by PEBT and the antiapoptotic effect of PEBT. Therefore, PEBT could be considered a candidate for the prevention of memory deficits such as those observed in DA. / memória inclui pelo menos três tipos de processamento relacionados entre si: aquisição, consolidação e evocação. A memória é afetada quando as sinapses encarregadas de fazer ou evocar memórias encontram-se alteradas. A doença de Alzheimer (DA) é a causa mais comum de demência. A DA é caracterizada por danos cognitivos, acúmulo de peptídeo β-amiloide (Aβ) e disfunção colinérgica. Além disso, o estresse oxidativo está associado à DA. Uma vez que ainda não há cura para a DA e as terapias atuais são apenas paliativas, torna-se importante a busca de novos compostos para melhorar danos cognitivos. Com o estudo dos efeitos biológicos de compostos de telúrio, muitas aplicações estão sendo descobertas. Neste sentido, o composto orgânico de telúrio 2-feniletinil-butiltelúrio (PEBT) apresenta efeito antioxidante. O objetivo deste estudo foi caracterizar o PEBT como uma alternativa promissora para a melhora e prevenção de danos cognitivos, usando modelos experimentais da DA em camundongos. Primeiramente, avaliou-se o efeito de uma única dose oral (p.o) de PEBT (10 mg/kg) na memória, utilizando a tarefa da esquiva inibitória. O tratamento com PEBT 1 h antes do treino, imediatamente após o treino ou 1 h antes do teste da esquiva inibitória aumentou a latência comparada com os animais controles, melhorando a aquisição, consolidação e evocação da memória, respectivamente. A captação de glutamato, mas não a liberação deste neurotrasmissor, foi inibida em córtex e hipocampo de camundongos após 1 h de tratamento com PEBT. Após 24 h, a inibição da captação de glutamato no córtex não foi mais evidenciada. A melhora da memória causada pelo PEBT parece ser mediada através da interação com os transportadores de glutamato. Além disso, o tratamento subcrônico com PEBT (1 mg/kg, p.o., por 10 dias) após a injeção de Aβ(25-35) (3 nmol/3 μl/per site, intracerebroventricular) reverteu o prejuízo no aprendizado e na memória causados por Aβ nas tarefas do labirinto aquático de Morris e na esquiva inibitória. O PEBT (10 mg/kg, p.o.), adminstrado 30 min antes da escopolamina (1 mg/kg, intraperitoneal), também protegeu do dano de memória causado por este agente anticolinérgico no labirinto aquático de Morris. Quando a escopolamina foi administrada 30 min antes do treino ou teste, ou imediatamente após o treino da esquiva inibitória houve dano na aquisição, evocação e consolidação da memória, respectivamente. O PEBT, administrado 30 min antes da escopolamina, protegeu do dano na consolidação e evocação da memória, mas não na aquisição. Não houve diferença nas atividades locomotora e exploratória dos animais tratados com o PEBT no teste do campo aberto. Finalmente, o efeito antiapoptótico do PEBT foi avaliado. Células do epitélio pigmentado da retina humana (linhagem ARPE-19) foram expostas ao estresse oxidativo induzido pelo fator de necrose tumoral-α (10 ng/ml) e H2O2 (600 μM). O PEBT (7.5 e 10 μM), quando pré-incubado por 1 h, protegeu contra a apoptose induzida pelo estresse oxidativo e este efeito permaneceu até 6 h após a indução. O PEBT (5 e 10 μM) inibiu a clivagem da poli(ADP-ribose) polimerase (PARP) induzida por estresse oxidativo e, também, restaurou a fosforilação da quinase regulada por sinal extracelular (ERK). O efeito protetor do PEBT contra o estresse oxidativo parece envolver a clivagem da PARP e a regulação da fosforilaçao de ERK, além de sua atividade antioxidante. Nesse sentido, os resultados apresentados nesta tese destacam o efeito do PEBT na melhora das três fases da memória, bem como em modelos de dano cognitivos em camundongos. Estes resultados parecem estar relacionados ao aumento do tônus glutamatérgico causado pelo PEBT e seu efeito antiapoptótico. Assim sendo, estes dados sugerem que o PEBT poderá, futuramente, ser considerado candidato para a prevenção de danos de memória, como aqueles observados na DA.