219 research outputs found
First-principles investigations of transition metal hyperdoped silicon and germanium for intermediate band engineering
No full textSilicon is the dominant material in the semiconductor industry, massively used in transistors, rectifiers, microchips, and other solid-state electronic devices. On top of that, its optoelectronic properties are largely utilized in photovoltaics, photodiodes, and photodetectors. However, in many optoelectronic devices silicon is limited by its band gap of 1.12 eV (_ = 1,110 nm) which precludes absorption of low energy infrared photons. For example, current photovoltaic devices suffer energy loss to a great extent due to non-absorption of a large portion of the incoming solar spectrum. Additionally, if the photoresponse of silicon could be extended to the infrared, silicon could be used to replace more expensive germanium based detectors.
My thesis research focuses on defect engineering of silicon to extend the photoresponse to the infrared regime. Recently, introducing defects at large concentrations several orders of magnitude larger than the equilibrium solubility limit has emerged as an approach to engineering the optical response of silicon. Specifically my thesis research addresses three aspects of hyperdoped semiconductors, which are as follows. (i) Carrying out first-principles investigations of gold hyperdoped silicon to provide detailed insights into recent extensive experimental investigations. This analysis helps to reveal the origins of the sub band gap optical response observed in this system, as well as to provide insights into the metastability and atomic scale mechanism of the loss of optical response upon thermal annealing. (ii) Moving beyond gold to consider alternative suitable transition metal dopants. It is of interest to identify candidate dopants that enhance optical absorption, and have sufficient solubility in silicon to remain dissolved in the semiconductor at high concentration and/or can become kinetically trapped to mitigate metastability. (iii) Using the insights gained from gold (Au) hyperdoped silicon systems, which have been extensively studied, to extend defect analysis towards gold hyperdoped germanium. This work involves carrying out high-accuracy first-principles modeling of candidate dopant defects in silicon, and assessing their promise for sub band gap absorption.
For gold hyperdoped silicon, first-principles density functional theory is used to first establish the origins of sub band gap optical absorption. While the experimentally synthesized systems likely contain a distribution of gold-related defects, experiments and the electronic structure analysis presented here strongly suggest that substitutional gold is responsible for the optical response. Unfortunately, the experimentally realized system optically deactivates upon thermal treatment. To understand the deactivation, I propose a mechanism for the evolution of atomic structure during thermal relaxation using simulations of energy barrier calculations, diffusion, and defect reactions. The dissociative mechanism, in which diffusion occurs by exchange of substitutional and interstitial sites via vacancy formation and annihilation, is identified as the likely path for deactivation. Further, the experimentally observed lattice contraction is explained by the presence of vacancies and gold-vacancy complexes in excess concentrations. The presence of these vacancies is attributed to the minimization of the strain that arises from the large volume of gold incorporated into silicon.
Towards the goal of identifying candidate hyperdoped materials for advanced optoelectronic devices such as intermediate band photovoltaics, I have carried out a systematic study of transition metal dopants in silicon in search for better dopants. To find other possible candidate dopants that could exhibit infrared absorption and, possibly, better solubility in silicon, I have assessed alternative transition metals such as Mn, Fe, Co, Ni, Cu and Ag using the optical design rules learned from prior investigations of chalcogen hyperdoped silicon. As the gold doped silicon study shows that not only the optical absorption but the (meta)stability of the system is also important, I have included an analysis of solubility and diffusion in silicon. This investigation also provided an opportunity to reassess the properties of transition metal defects in silicon, which had been studied extensively several decades ago, now using modern first-principles methods. As part of this analysis I have summarized their magnetic and electronic structure using density of states, orbital hybridization analysis, and band diagrams. Finally, I have extended the analysis of gold hyperdoped silicon to gold hyperdoped germanium. The relationship between measured carrier decay dynamics and some possible defect configurations are proposed in conjunction with recent experimentally achieved high
concentrations of gold and demonstrated optical response in germanium.Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2021-12-01The student, Naheed Ferdous, accepted the attached license on 2019-10-24 at 14:40.The student, Naheed Ferdous, submitted this Dissertation for approval on 2019-10-24 at 15:00.This Dissertation was approved for publication on 2019-10-31 at 15:49.DSpace SAF Submission Ingestion Package generated from Vireo submission #14517 on 2020-02-28 at 17:21:15Made available in DSpace on 2020-03-02T22:12:13Z (GMT). No. of bitstreams: 4
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Previous issue date: 2019-10-31Embargo set by: Seth Robbins for item 113871
Lift date: 2022-03-02T22:12:26Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113871
Lift date: 2022-03-02T22:15:21Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 113871
Lift date: 2022-03-02T22:18:25Z
Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD systemU of I Only Restriction Lifted for Item 113871 on 2022-03-03T10:15:13Z
Comparison of performance of shell-and-tube heat exchangers with conventional segmental baffles and continuous helical baffle
No full textProject Report on “Financial Performance Evaluation of Commercial Banks in Bangladesh”
No full textThe general objective of this study is to evaluate the financial performance of the commercial banks and the Islamic banks in context of Bangladesh. The author tries to critically compare the pros and cons across the commercial and Islamic banks in the country in this report
Representation Of Women In Parliament Of Bangladesh: Is It Hopeful?
No full textThe poor representation of women in nearly each policy-making facet of life is a universal matter. In the entire world, women are represented in government in poor ratio to their entire populace. A component of representative democracy is that irrespective of gender, all people have equal prospects to partake in the political arena. In elective points, better representation of women of power is a matter of fairness and parity. Yet, representation of women in many parliaments is often limited. Democracy cannot embellish without a rational representation of women in the parliament, which is the most influential organization of democratic states. The analytical structure of this study undertakes that the presence of women in parliament does not inevitably turn into the functional picture rather it is a result of organizational, sociological and institutional facets. This has failed to make an effective impact on the representation of women in Parliament in a particular political situation. Therefore, the issues that impede or enable women’s representation in elective points differ with the issue of socioeconomic progress, culture and the form of political arrangement. The author has taken a modest endeavor to disclose about the significant matters linked to women’s poor representation in Bangladesh Parliament
Optimization of hormonal dose during masculinization of tilapia (Oreochromis niloticus) fry
No full textThe experiment was conducted to optimize the dose of 17α-methyl testosterone (MT) during masculinization of tilapia
(Oreochromis niloticus) fry. Five treatments were designed with various doses of hormone to find out the most
effective one. The treatments were designated as T1 (0 mg MT/kg), T2 (40 mg MT/kg), T3 (50 mg MT/kg), T4 (60 mg
MT/kg) and T5 (70 mg MT/kg). MT was administered orally by using nursery feed and Ethanol (as hormone carrier
solvents) diet to tilapia fry for 28 days in hapa. After completion of the trial period of 28 days nursing of the
experimental fry was continued for further 2 months with commercial feed. At the end of experiment the sex ratio was
determined by examining gonad after dissecting the fish. Growth performance was monitored by recording the
morphometric characteristics i.e. weight gain (g), average daily weight gain (g). The analysis of growth data showed
significant variation in weight, % weight gain, SGR (% /day) of fish among the different treatments. SGR increases
with the increase of hormone dose. The present study demonstrated that all MT receiving treatments showed a
significantly (p<0.01) higher male proportion (94.28%) than control (48.57%). The dose of 60 mg MT/kg of feed
resulted in maximum male population (94.28%). The result indicated that the optimum dose of MT hormone was 60
mg /kg with a feeding period of 28 days after hatching
Przedsiębiorczość w turystyce opartej na społecznościach lokalnych Sri Lanki
No full textThis study is focused on entrepreneurship in community-based tourism (CBT) in Sri Lanka. It examines the effect of entrepreneurial competences and orientation towards the performance of homestays although the majority are not successful. Recent research has revealed that homestay tourism is not effective, nonetheless it has been identified as the sector for the development for entrepreneurs and can make a considerable contribution to the Sri Lankan economy. The purpose of this study is to enhance CBT by showing how to develop productive entrepreneurs in this sector. Resource based view (RBV) theory is the basis – 645 registered homestay units operate as a CBT practice and the study sample was 252 entrepreneurs. Structural equation modelling (SEM) was used to analyze the data. From the findings of the study, both entrepreneurial competences and orientation significantly affect entrepreneur performance in CBT. This study will help expand CBT for successful entrepreneurs emerging from the tourism sector.Artykuł jest poświęcony zagadnieniu przedsiębiorczości w turystyce opartej na społecznościach lokalnych (CBT – community-based tourism) Sri Lanki. Autorzy omówili znaczenie kompetencji przedsiębiorczych oraz orientacji na jakość w przypadku pobytów oferowanych w domach rodzin goszczących, choć w większości z nich nie jest ona zadowalająca. Wprawdzie najnowsze badania wykazały, że turystyka oparta na takich pobytach nie jest efektywna, ale mimo to została ona uznana za sektor rozwojowy dla przedsiębiorców, który może wnosić znaczący wkład w gospodarkę Sri Lanki. Celem pracy jest wzmocnienie pozycji CBT poprzez pokazanie jak można stać się produktywnym przedsiębiorcą w tym sektorze. Podstawą do rozważań jest teoria podejścia zasobowego (resource-based view – RBV) – w ramach CBT zarejestrowanych jest 645 jednostek świadczących usługę pobytów domowych. Próba badawcza objęła 252 przedsiębiorców. Do analizy danych zastosowano modele równań strukturalnych (structural equation modeling – SEM). Wyniki badań świadczą o tym, że zarówno kompetencje, jak i orientacja przedsiębiorcza znacząco wpływają na działanie przedsiębiorcy CBT. Opisywane badanie pomoże rozwinąć turystykę opartą na społeczności lokalnej jako część krajowego sektora turystycznego
Roundness and taper of holes during drilling composites of various thickness by HSS drill bit under dry condition
No full text
Enhanced IEEE 802.11 by integrating multiuser dynamic OFDMA
No full textThis thesis was scanned from the print manuscript for digital preservation and is copyright the author.
Researchers can access this thesis by asking their local university, institution or public library to
make a request on their behalf. Monash staff and postgraduate students can use the link in the References field
FoxO1–Dio2 signaling axis governs cardiomyocyte thyroid hormone metabolism and hypertrophic growth
No full textForkhead box O (FoxO) proteins and thyroid hormone (TH) have well established roles in cardiovascular morphogenesis and remodeling. However, specific role(s) of individual FoxO family members in stress-induced growth and remodeling of cardiomyocytes remains unknown. Here, we report that FoxO1, but not FoxO3, activity is essential for reciprocal regulation of types II and III iodothyronine deiodinases (Dio2 and Dio3, respectively), key enzymes involved in intracellular TH metabolism. We further show that Dio2 is a direct transcriptional target of FoxO1, and the FoxO1–Dio2 axis governs TH-induced hypertrophic growth of neonatal cardiomyocytes in vitro and in vivo. Utilizing transverse aortic constriction as a model of hemodynamic stress in wild-type and cardiomyocyte-restricted FoxO1 knockout mice, we unveil an essential role for the FoxO1–Dio2 axis in afterload-induced pathological cardiac remodeling and activation of TRα1. These findings demonstrate a previously unrecognized FoxO1–Dio2 signaling axis in stress-induced cardiomyocyte growth and remodeling and intracellular TH homeostasis
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