Browsing by Author "Radhakrishnan, Sruthi"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Chemical Modification of 2D materials and the ensuing properties(2017-11-22) Radhakrishnan, Sruthi; Ajayan, Pulickel M.Functionalization of nanomaterials is a definitive strategy to modulate them to achieve desired properties. Any functionalization introduces defects in the 2D lattice, which affect the properties of these layered materials. This thesis focuses on the effects of fluorination on the structure and properties of atomically thin-layered materials and a variety of applications of these materials in the fields from medicine to energy will be covered in this thesis. The first chapter gives an overview of nanomaterials in general, focusing more on 2D materials, their functionalization and their unique properties. To tailor to the rest of the chapters, a brief discussion about fluorinated graphene - the strategies of fluorination developed, their advantages and limitations; the structural defects introduced by fluorination and its influence on the conversion of a zero-bandgap material to a semi-conductor and the collective magnetism induced by point defects is discussed. The second chapter talks about fluoro-graphene quantum dots focusing on my work and its application in MRI and why it could potentially push the limits of MRI. FGO being a metal free agent has less contrast compared to conventional agents. Therefore, the third chapter gives a perspective on the enhancement of MRI contrast by formation of FGO-Iron oxide composite, as well as using it as utilizing the fluorescence of FGO in cellular imaging. The fourth chapter opens with the motivation from structural and functional changes in fluoro-graphene to explore fluorine functionalization in other 2D materials like h-BN, MoS2 and WS2. The new technique developed for functionalization will be compared with the existing techniques discussed in the first chapter, and point out the advantages of the method in terms of scalability, controllability etc. The modification of electronic band structure of h-BN to a wide bandgap semiconductor via introduction of defect levels will be described in detail along with the band structure calculations using DFT. An analysis of the origin of unconventional magnetic behavior induced by fluorination and room temperature ferromagnetism will be followed by its application as a magnetic semiconductor. The fifth chapter would be an extension of the fourth chapter, a discussion of the optical properties of FBN quantum dots and its modulation with the amount of fluorination will be followed by its application in biological detection. Moving on to the sixth chapter, it explores the effect of fluorination on other 2D materials like WS2 and its consequent exfoliation and transformation. With an interest in the changes in tribological properties of TMDs like WS2 with doping and gating this chapter will also study the measurement of friction in f-WS2 using AFM. The chapter closes with a study on the magnetic properties. The seventh chapter summarizes the main findings of the thesis and reviews the scope for further studies.Item Fluorinated h-BN as a magnetic semiconductor(American Association for the Advancement of Science, 2017) Radhakrishnan, Sruthi; Das, Deya; Samanta, Atanu; de los Reyes, Carlos A.; Deng, Liangzi; Alemany, Lawrence B.; Weldeghiorghis, Thomas K.; Khabashesku, Valery N.; Kochat, Vidya; Jin, Zehua; Sudeep, Parambath M.; Martí, Angel A.; Chu, Ching-Wu; Roy, Ajit; Tiwary, Chandra Sekhar; Singh, Abhishek K.; Ajayan, Pulickel M.We report the fluorination of electrically insulating hexagonal boron nitride (h-BN) and the subsequent modification of its electronic band structure to a wide bandgap semiconductor via introduction of defect levels. The electrophilic nature of fluorine causes changes in the charge distribution around neighboring nitrogen atoms in h-BN, leading to room temperature weak ferromagnetism. The observations are further supported by theoretical calculations considering various possible configurations of fluorinated h-BN structure and their energy states. This unconventional magnetic semiconductor material could spur studies of stable two-dimensional magnetic semiconductors. Although the high thermal and chemical stability of h-BN have found a variety of uses, this chemical functionalization approach expands its functionality to electronic and magnetic devices.Item High hardness in the biocompatible intermetallic compound β-Ti3Au(AAAS, 2016) Svanidze, Eteri; Besara, Tiglet; Ozaydin, M. Fevsi; Tiwary, Chandra Sekhar; Wang, Jiakui K.; Radhakrishnan, Sruthi; Mani, Sendurai; Xin, Yan; Han, Ke; Liang, Hong; Siegrist, Theo; Ajayan, Pulickel M.; Morosan, E.The search for new hard materials is often challenging, but strongly motivated by the vast application potential such materials hold. Ti3Au exhibits high hardness values (about four times those of pure Ti and most steel alloys), reduced coefficient of friction and wear rates, and biocompatibility, all of which are optimal traits for orthopedic, dental, and prosthetic applications. In addition, the ability of this compound to adhere to ceramic parts can reduce both the weight and the cost of medical components. The fourfold increase in the hardness of Ti3Au compared to other Ti–Au alloys and compounds can be attributed to the elevated valence electron density, the reduced bond length, and the pseudogap formation. Understanding the origin of hardness in this intermetallic compound provides an avenue toward designing superior biocompatible, hard materials.Item Metal-Free Dual Modal Contrast Agents Based on Fluorographene Quantum Dots(Wiley, 2016) Radhakrishnan, Sruthi; Samanta, Atanu; Sudeep, Parambath M.; Maldonado, Kiersten L.; Mani, Sendurai A.; Acharya, Ghanashyam; Tiwary, Chandra Sekhar; Singh, Abhishek K.; Ajayan, Pulickel M.Fluorographene quantum dots prepared from fluorinated graphene oxide (FGO) show a linear dependence of the magnetization on the applied field. This is further supported by DFT calculations taking into account a few possible systems of functionalized graphene quantum dots. The inherent magnetism, high concentration of fluorine and cyto-compatibility of these quantum dots promise potential application as a dual modal agent for proton and 19F based Magnetic Resonance Imaging which is investigated here. A metal free dual modal contrast agent would bring about a great change in the efficiency and resolution of this widely used imaging tool.