+publisher:"Indian Institute of Science" +contributor:("Banerjee, Dipankar")

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Indian Institute of Science

1. Hazra, Gopal. Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow.

Degree: PhD, Faculty of Science, 2018, Indian Institute of Science

URL: http://etd.iisc.ac.in/handle/2005/3791

► Our Sun is a variable star. The magnetic fields in the Sun play an important role for the existence of a wide variety of phenomena… (more)

▼ Our Sun is a variable star. The magnetic fields in the Sun play an important role for the existence of a wide variety of phenomena on the Sun. Among those, sunspots are the slowly evolving features of the Sun but solar ares and coronal mass ejections are highly dynamic phenomena. Hence, the solar magnetic fields could affect the Earth directly or indirectly through the Sun's open magnetic flux, solar wind, solar are, coronal mass ejections and total solar irradiance variations. These large scale magnetic fields originate due to Magnetohydrodynamic dynamo process inside the solar convection zone converting the kinetic energy of the plasma motions into the magnetic energy. Currently the most promising model to understand the large scale magnetic fields of the Sun is the Flux Transport Dynamo (FTD) model. FTD models are mostly axisymmetric models, though the non-axisymmetric 3D FTD models are started to develop recently. In these models, we assume the total magnetic fields of the Sun consist of poloidal and toroidal components and solve the magnetic induction equation kinematicaly in the sense that velocity fields are invoked motivated from the observations. Differential rotation stretches the poloidal field to generate the toroidal field. When toroidal eld near the bottom of the convection zone become magnetically buoyant, it rises through the solar convection zone and pierce the surface to create bipolar sunspots. While rising through the solar convection zone, the Coriolis force keeps on acting on the flux tube, which introduces a tilt angle between bipolar sunspots. Since the sunspots are the dense region of magnetic fields, they diffuse away after emergence. The leading polarity sunspots (close to equator) from both the hemisphere cancel each other across the equator and trailing polarity sunspots migrate towards the pole to generate effective poloidal fields. This mechanism for generation of poloidal field from the decay of sunspots is known as Babcock-Leighton process. After the poloidal field is generated, the meridional flow carries this field to the pole and further to the bottom of the convection zone where differential rotation again acts on it to generate toroidal field. Hence the solar dynamo goes on by oscillation between the poloidal field and toroidal field, where they can sustain each other through a cyclic feedback process. Just like other physical models, FTD models have various assumptions and approximations to incorporate these different processes. Some of the assumptions are observationally verified and some of them are not. Considering the availability of observed data, many approximations have been made in these models on the theoretical basis. In this thesis, we present various studies leading to better understanding of the different processes and parameters of FTD models, which include magnetic buoyancy, meridional circulation and Babcock-Leighton process. In the introductory Chapter 1, we first present the observational features of the solar magnetic fields, theoretical background of the FTD… Advisors/Committee Members: Choudhuri, Arnab Rai (advisor), Banerjee, Dipankar (advisor).

Subjects/Keywords: Solar Cycle; Sunspots; Solar Magnetic Field; Dynamo Theory; Flux Transport Dynamo Model; Meridional Circulation; Solar Polar Field; Flux Transport Solar Dynamo; Solar Cycles; Sun’s Polar Magnetic Field; Dynamo Model; 3D Babcock-Leighton Solar Dynamo Model; Astrophysics

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APA (6^th Edition):

Hazra, G. (2018). Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/3791

Chicago Manual of Style (16^th Edition):

Hazra, Gopal. “Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/3791.

MLA Handbook (7^th Edition):

Hazra, Gopal. “Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow.” 2018. Web. 23 Jan 2021.

Vancouver:

Hazra G. Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/3791.

Council of Science Editors:

Hazra G. Understanding the Behavior of the Sun's Large Scale Magnetic Field and Its Relation with the Meridional Flow. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/3791

Indian Institute of Science

2. Kantibhai, Agrawal Priyanka. Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834.

Degree: PhD, Engineering, 2018, Indian Institute of Science

URL: http://etd.iisc.ac.in/handle/2005/4036

► IMI 834 is a near- Ti alloy used in high temperature applications such as compressor discs and blades of aero engines. Titanium alloys including IMI… (more)

▼ IMI 834 is a near- Ti alloy used in high temperature applications such as compressor discs and blades of aero engines. Titanium alloys including IMI 834 are known to exhibit dynamic strain aging (DSA) over the temperature range of 623-773K. However, the interplay between DSA and creep has not been previously studied in detail in titanium alloys. The objective of the present study is to probe creep mechanisms and phenomenology at intermediate temperatures in IMI 834 where DSA is expected to play a prominent role. Coupons of IMI834, cut from a hot rolled rod, were heat treated to obtain a microstructure of 80% equated , 15% of lamellar and 5% . The heat treatment was optimized to ensure Si retention in the solution as it is known to affect DSA in titanium alloys. Constant strain rate tests carried out in tension over a range of temperatures and strain rates identified the DSA regime in the temperature range of 623-823K as determined by serrated behavior in stress-strain curves and negative strain rate sensitivity. The dislocation structure in this domain is dominated by jogged screw dislocations in slip bands. Strain accumulation is shown to depend on conservative jog glide along the length of screw dislocations due to line tension forces. We have tried to predict this domain of DSA using Friedel’s model for breakaway stress, i.e. the stress required to break free the dislocations from solute atmosphere, using estimates of solute concentration accumulating at the edge jogs on arrest during thermally activated glide of the jogs at static solute obstacles. There is a good agreement between model and experimental data showing a DSA peak in the temperature range of 673-723K. The solute species responsible for DSA is estimated to be Si and C, but dominated by C in this temperature and strain rate regime. Creep behavior of the alloy was explored over similar temperature regime in tension. Over this temperature range, especially at lower temperatures, very low strain rates below the resolution limits of the strain gauge were reached before the onset of steady state and therefore current work is primarily focused on primary creep behavior. Different types of primary creep behavior were observed with temperature and stress. Anomalous primary creep behavior has been observed in the form of an abrupt decrease in strain rate beyond certain critical strains, as well as in a stress insensitivity of instantaneous strain rates on loading at 673K. At higher temperatures of 773K, conventional behavior showed strain rates approaching a steady state value. Dislocation structure in primary creep was again dominated by jogged screw dislocations. At the strain rates associated with creep, our model shows that transitions occur in jog glide from solute breakaway controlled glide to solute drag controlled glide and then again to thermally activated glide over static solutes with increasing temperature. However, in contrast to high strain rate behavior, Si solutes dominates the mechanisms of jog glide in creep. The work of this thesis… Advisors/Committee Members: Banerjee, Dipankar (advisor).

Subjects/Keywords: Dynamic Strain Aging (DSA); IMI 834; Steady State Creep Models; α-Titanium; Creep; Near-α Ti Alloy; Friedel’s Model; Titanium Alloys; Portevin-Le Chatelier (PLC) Effect; Materials Engineering

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APA (6^th Edition):

Kantibhai, A. P. (2018). Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/4036

Chicago Manual of Style (16^th Edition):

Kantibhai, Agrawal Priyanka. “Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/4036.

MLA Handbook (7^th Edition):

Kantibhai, Agrawal Priyanka. “Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834.” 2018. Web. 23 Jan 2021.

Vancouver:

Kantibhai AP. Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/4036.

Council of Science Editors:

Kantibhai AP. Dynamic Strain Aging and Creep in near-α Ti Alloy, IMI834. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/4036

Indian Institute of Science

3. Nair, Shanoob Balachandran. Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys.

Degree: PhD, Faculty of Engineering, 2017, Indian Institute of Science

URL: http://etd.iisc.ac.in/handle/2005/2678

► The properties of titanium alloys are based on alloy compositions and microstructures that consist of mixtures of the two allotropic modifications of titanium, the low… (more)

▼ The properties of titanium alloys are based on alloy compositions and microstructures that consist of mixtures of the two allotropic modifications of titanium, the low temperature α (hcp) and the high temperature β (bcc) phases. This thesis deals with the hot working behaviour of three commercial titanium alloy compositions designated IMI834, Ti17 and Ti5553 with a focus and detailed analysis of the Ti5553 alloy. These alloys represent the differing uses of titanium alloys in the aerospace industry. IMI834 is a near α alloy used in high temperature creep resistant applications as compressor discs and blades in aeroengines. Ti17 is a high strength alloy α+β used at intermediate temperatures in fan and compressor discs of aeroengines, while Ti5553 is a high strength-high toughness metastable β alloy used in the undercarriages of aircraft. The three alloys have widely differing β transus temperatures (related to α phase stability) and compositions. Titanium alloys are vacuum arc melted and thermomechanically processed. This process involves ingot breakdown in β (bcc) phase, and subsequent thermomechanical processing in two-phase α+β (hcp+bcc) region at temperatures that typically involve volume fractions of α in lath or plate form ranging from 15% to about 30%. The thermomechanical processing breaks down lath α to spheroidal particles, a process known as globularisation. Chapter I of this thesis reviews the current understanding of the hot working of titanium alloys and microstructure evolution during the hot working process. Chapter II summarises the main experimental techniques used: the hot compression test, and subsequent microstructure and microtexture analysis by scanning electron microscopy and related electron back scattered diffraction techniques (EBSD), transmission electron microscopy and related precession electron diffraction techniques (PED) for orientation imaging. The starting structure in the α+β domain of hot work is generally not a random distribution of the 12 variant Burgers Orientation Relationship (BOR) between the α and β phases, (11̅0)β || (0001)α and <111>β || <112̅0>α . A variety of morphologies and distributions ranging from the typical colony structures of near α and α+β alloys to the fine distributions of variants arranged in a triangular fashion are observed with specific growth directions and habit planes. Chapter III describes a quantitative evaluation of α distribution that are typical of some of the starting structures for the hot working conditions used in this thesis, specifically in the Ti5553 alloy. For this purpose, a Matlab based script has been developed to measure the spatially correlated misorientation distribution. It was found that experimental spatially correlated misorientation distribution varies significantly from a random frequency for both pair and triplet wise distribution of α laths. The analysis of these structures by established techniques of analysis of self-accommodated structures based on strain energy minimisation shows that the observed variant… Advisors/Committee Members: Banerjee, Dipankar (advisor).

Subjects/Keywords: Titanium Alloys; Titanium Alloys Microstructure; Titanium Alloys Microtexture; Microstructure Evolution; Ti5553 Alloy; Materials Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Nair, S. B. (2017). Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/2678

Chicago Manual of Style (16^th Edition):

Nair, Shanoob Balachandran. “Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys.” 2017. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/2678.

MLA Handbook (7^th Edition):

Nair, Shanoob Balachandran. “Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys.” 2017. Web. 23 Jan 2021.

Vancouver:

Nair SB. Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2017. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/2678.

Council of Science Editors:

Nair SB. Effect of Thermomechanical Processing on Microstructure And Microtexture Evolution in Titanium Alloys. [Doctoral Dissertation]. Indian Institute of Science; 2017. Available from: http://etd.iisc.ac.in/handle/2005/2678

Indian Institute of Science

4. Tiwary, Chandra Sekhar. Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys.

Degree: PhD, Faculty of Engineering, 2018, Indian Institute of Science

URL: http://etd.iisc.ac.in/handle/2005/2991

► The thesis introduces a novel alloy system based on submicron distributions of intermetallic phases realised through eutectic solidification in the ternary system Ni-Al-Zr. Various compositions… (more)

▼ The thesis introduces a novel alloy system based on submicron distributions of intermetallic phases realised through eutectic solidification in the ternary system Ni-Al-Zr. Various compositions in this system comprising of intermetallic phases distributed in different eutectic structures show ultra-high strength at temperatures upto 700°C combined with reasonable tensile plasticity, exceptional oxidation resistance and high temperature structural stability. Intermetallics have long been used in high temperature alloys systems such as in the classical Ni-base superalloys that derive their strength from nanoscale dispersions of the aluminide, Ni3Al(γ’) in a matrix of disordered fcc Ni (γ), alloyed with expensive, high density refractory elements such as Re and Ru. The high temperature applications of intermetallics derive from their strength retention to high temperatures, creep resistance enabled by low diffusion rates, and attractive oxidation resistance based on high concentration of elements such as Al that forms stable oxides. Several decades of effort on the development of new generation of intermetallic alloys through the 80’s and 90’s have gone unrewarded, with the exception of TiAl based alloys that are now used in recent generation aircraft engines. The promise of intermetallics as high temperature candidate materials is limited by their poor ductility or toughness arising from several intrinsic properties such as low grain boundary cohesive strength (in the case of Ni3Al) or an insufficient number of slip systems (as in NiAl) or extrinsic effects such as embrittlement by hydrogen (Fe3Al) that derive fundamentally from the existence of directionality in bonding. However, low ductility or toughness can often be alleviated by limiting the length scale for slip. We have therefore examined the possibility of combining intermetallics in the form of eutectic structures, potentially limiting slip lengths within each intermetallic constituent. Eutectic structures in binary systems limit the choice of intermetallic combinations so that finding such combinations with engineering potential is difficult. On the other hand combinations of three elements or more would enable a significantly larger set of permutations of eutectic intermetallics, provided the constituent binary phase diagrams contain either eutectic or peritectic reactions involving intermetallic phases, as well as intermediate intermetallic phases. The ternary Ni-Al-Zr system met our criterion in several ways. The Ni-Al binary phase diagram shows a peritectic reaction from liquid and NiAl (Pm 3m, B2 with a lattice parameter of 0.288nm) to form Ni3Al (Pm 3m, L12 with a lattice parameter of 0.356 nm), intermetallics that have been extensively investigated in earlier literature. The Ni-Zr system shows a peritectic reaction between liquid and the Ni7Zr2 (C12/m1 with a lattice parameters a=0.469nm, b=0.823nm, c=1.219nm) phase to form the intermetallic Ni5Zr (F 43m with a lattice parameter of 0.670nm). Further the NiAl and Ni7Zr2 are both intermediate phases… Advisors/Committee Members: Chattopadhyay, K (advisor), Banerjee, Dipankar (advisor).

Subjects/Keywords: Intermetallic Alloys; Nickel-Aluminium-Zirconium Eutectic Alloys; Ni-Al-Zr Alloys; Ternary Alloys; Intermetallic Eutectic Composites; Metallurgy

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Tiwary, C. S. (2018). Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/2991

Chicago Manual of Style (16^th Edition):

Tiwary, Chandra Sekhar. “Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/2991.

MLA Handbook (7^th Edition):

Tiwary, Chandra Sekhar. “Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys.” 2018. Web. 23 Jan 2021.

Vancouver:

Tiwary CS. Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/2991.

Council of Science Editors:

Tiwary CS. Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/2991

Indian Institute of Science

5. Vinay, K S. Microstructural Evolution of Directionally Solidified Ni-Al-Re/Ru Alloys.

Degree: MSc Engg, Engineering, 2018, Indian Institute of Science

URL: http://etd.iisc.ac.in/handle/2005/4056

► Nickel based superalloys are high temperature materials which find application as blade and disc components of jet engines due to their ability to retain their… (more)

▼ Nickel based superalloys are high temperature materials which find application as blade and disc components of jet engines due to their ability to retain their mechanical properties at temperatures close to 0.8 of their melting point. The modern day nickel based superalloys are multicomponent alloys, containing up to 12 alloying elements which are added in balanced proportions to achieve high temperature strength and microstructural stability, Re and Ru have been the recent additions made to superalloy compositions in the last two decades. But the roles of Re and Ru in terms of partitioning among the phases γ and γ’ and its effects on mechanical properties are still not clear. Hence an effort was made to study their effects under constrains of constant volume fractions of γ’ and misfit between γ and γ’, to isolate effects that result purely due to composition. Three model alloy systems (two ternary and one quaternary) of the type Ni-Al-xRe, Ni-Al-yRu and Ni-Al-xRe-yRu, x=2.5/4 and y=2.5/6 with minor additions of 1.4 Hf and 0.07 C for reasons of castability were synthesized by investment casting. This thesis deals with the solidification related aspects of these alloys. Chapter 1 deals with a brief overview of Ni based superalloys in terms of their physical metallurgy, processing, microstructure and the effects of Re and Ru studied in literature. These are summarized and the objective of thesis laid out. The experimental details of the techniques employed for studying the cast structure such as optical microscopy, scanning electron microscopy, electron probe microanalysis and differential scanning calorimetry are discussed in Chapter 2 In Chapter 3, the experimental results concerning microstructure, chemistries (local and global), differential scanning calorimetry and supporting Thermo-Calc based simulations are presented. The composition of the directionally solidified alloys were estimated using quantitative EPMA spot analysis after homogenizing them to the best possible extent. The cooling rates experienced by the bottom, middle and tip sections (25mm, 150mm and 295mm respectively from chill plate) of the model alloys during casting was estimated using ProCASTTM simulations. The simulations show the cooling rates to vary from 12.5 K/min to 6 K/min, corresponding to the range of thermal gradients 3000 K/m to 1500 K/m from bottom to tip sections. These estimations were performed assuming a constant withdrawal velocity of 24 cm/hr. The morphological evolution of cast structure from bottom to tip section of the alloys was studied at a coarse scale with the aid of optical microscopy. A tendency towards increased branching of dendrites to form well developed tertiary arms is observed on moving from bottom to tip sections. Quantitative measurement of primary and secondary arm spacings (PDAS and SDAS) indicate that PDAS values increase from bottom to middle section and then saturates, whereas the SDAS values show an increase from bottom to tip sections. Also, the PDAS and SDAS values of MA-3 were observed to be… Advisors/Committee Members: Banerjee, Dipankar (advisor).

Subjects/Keywords: Nickel Based Superalloys; Solidification Alloys; Alloy Composition; Ni-Based Superalloys; Ni-Al-Re/Ru Alloys; Materials Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Vinay, K. S. (2018). Microstructural Evolution of Directionally Solidified Ni-Al-Re/Ru Alloys. (Masters Thesis). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/4056

Chicago Manual of Style (16^th Edition):

Vinay, K S. “Microstructural Evolution of Directionally Solidified Ni-Al-Re/Ru Alloys.” 2018. Masters Thesis, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/4056.

MLA Handbook (7^th Edition):

Vinay, K S. “Microstructural Evolution of Directionally Solidified Ni-Al-Re/Ru Alloys.” 2018. Web. 23 Jan 2021.

Vancouver:

Vinay KS. Microstructural Evolution of Directionally Solidified Ni-Al-Re/Ru Alloys. [Internet] [Masters thesis]. Indian Institute of Science; 2018. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/4056.

Council of Science Editors:

Vinay KS. Microstructural Evolution of Directionally Solidified Ni-Al-Re/Ru Alloys. [Masters Thesis]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/4056

Indian Institute of Science

6. Yaddanapudi, G R Krishna. Effect of Process Parameters on the Growth of N-Polar GaN on Sapphire by MOCVD.

Degree: PhD, Faculty of Engineering, 2017, Indian Institute of Science

URL: http://etd.iisc.ac.in/handle/2005/2662

► Group III-Nitrides (GaN, InN & AlN) are considered one of the most important class of semiconducting materials after Si and GaAs. The excellent optical and… (more)

▼ Group III-Nitrides (GaN, InN & AlN) are considered one of the most important class of semiconducting materials after Si and GaAs. The excellent optical and electrical properties of these nitrides result in numerous applications in lighting, lasers, and high-power/high-frequency devices. Due to the lack of cheap bulk III- Nitride substrates, GaN based devices have been developed on foreign substrates like Si, sapphire and SiC. These technologies have been predominantly developed on the so called Ga-polarity epitaxial stacks with growth in the [0001] direction of GaN. It is this orientation that grows most easily on sapphire by metal organic chemical vapor deposition (MOCVD), the most common combination of substrate and deposition method used thus far. The opposite [000¯1] or N-polar orientation, very different in properties due to the lack of an inversion centre, offers several ad- vantages that could be exploited for better electronic and optoelectronic devices. However, its growth is more challenging and needs better understanding. The aim of the work reported in this dissertation was a systematic investigation of the relation between the various growth parameters which control polarity, surface roughness and mosaicity of GaN on non-miscut sapphire (0001) wafers for power electronics and lighting applications, with emphasis on the realization of N-polar epitaxial layers. GaN is grown on sapphire (0001) in a two-step process, which involves the deposition of a thin low temperature GaN nucleation layer (NL) on surface modified sapphire followed by the growth of high temperature device quality GaN epitaxial layer. The processing technique used is MOCVD. Various processing methods for synthesis of GaN layers are described with particular em- phasis on MOCVD method. The effect of ex situ cleaning followed by an in situ cleaning on the surface morphology of sapphire (0001) wafers is discussed. The characterization tools used in this dissertation for studying the chemical bond nature of nitrided sapphire surface and microstructural evolution (morphological and structural) of GaN layers are described in detail. The effect of nitridation temperature (TN) on structural transformation of non- miscut sapphire (0001) surface has been explored. The structural evolution of nitrided layers at different stages of their process like as grown stage and thermal annealing stage is investigated systematically. The chemical bond environment information of the nitrided layers have been examined by x-ray photoelectron spectroscopy (XPS). It is found that high temperature nitridation (TN ≥ 800 °C) results in an Al-N tetrahedral bond environment on sapphire surface. In contrast, low temperature nitridation (TN = 530 °C) results in a complex Al-O-N environment on sapphire surfaces. Microstructural evolution of low temperature GaN NLs has been studied at every stage of processing by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Surface roughness evolution and island size distribution of NLs measured from AFM… Advisors/Committee Members: Banerjee, Dipankar (advisor), Raghavan, Srinivasan (advisor).

Subjects/Keywords: Semiconductors; Nitrides; Gallium Nitride; N-Polar Gallium Nitride; Metal Organic Chemical Vapor Deposition (MOCVD); Galllium Nitride Growth; High Temperature Gallium Nitride; Low Temperature Gallium Nitride; GaN; Materials Engineering

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Yaddanapudi, G. R. K. (2017). Effect of Process Parameters on the Growth of N-Polar GaN on Sapphire by MOCVD. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/2662

Chicago Manual of Style (16^th Edition):

Yaddanapudi, G R Krishna. “Effect of Process Parameters on the Growth of N-Polar GaN on Sapphire by MOCVD.” 2017. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/2662.

MLA Handbook (7^th Edition):

Yaddanapudi, G R Krishna. “Effect of Process Parameters on the Growth of N-Polar GaN on Sapphire by MOCVD.” 2017. Web. 23 Jan 2021.

Vancouver:

Yaddanapudi GRK. Effect of Process Parameters on the Growth of N-Polar GaN on Sapphire by MOCVD. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2017. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/2662.

Council of Science Editors:

Yaddanapudi GRK. Effect of Process Parameters on the Growth of N-Polar GaN on Sapphire by MOCVD. [Doctoral Dissertation]. Indian Institute of Science; 2017. Available from: http://etd.iisc.ac.in/handle/2005/2662

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