arXiv subjects

Sreejith Nair

Publications and source records attributed to Sreejith Nair.

21 records · Page 2Linked to original sources

arXiv2023

Mending Cracks in Rutile TiO$_{2}$ with Electron Beam

Restructuring of rutile TiO$_{2}$ under electron beam irradiation driven by radiolysis was observed and analyzed using a combination of atomic-resolution imaging and electron energy loss spectroscopy (EELS) in scanning transmission electron microscopy (STEM). It was determined that a high-energy (80-300 keV) electron beam at high doses ($\gtrapprox 10^7 \ e/nm^2$) can constructively restructure rutile TiO$_{2}$ with an efficiency of $6\times 10^{-6}$. These observations were realized using rutile TiO$_{2}$ samples with atomically sharp nanometer-wide cracks. Based on atomic-resolution STEM imaging and quantitative EELS analysis, we propose a $"$ 2-step $"$ rolling model of the octahedral building blocks of the crystal to account for observed radiolysis-driven atomic migration.

cond-mat.mtrl-sci↗

arXiv2021

Solid Source Metal-Organic Molecular Beam Epitaxy of Epitaxial RuO2

A seemingly simple oxide with a rutile structure, RuO2 has been shown to possess several intriguing properties ranging from strain-stabilized superconductivity to a strong catalytic activity. Much interest has arisen surrounding the controlled synthesis of RuO2 films but, unfortunately, utilizing atomically-controlled deposition techniques like molecular beam epitaxy (MBE) has been difficult due to the ultra-low vapor pressure and low oxidation potential of Ru. Here, we demonstrate the growth of epitaxial, single-crystalline RuO2 films on different substrate orientations using the novel solid-source metal-organic (MO) MBE. This approach circumvents these issues by supplying Ru using a pre-oxidized solid metal-organic precursor containing Ru. High-quality epitaxial RuO2 films with bulk-like room-temperature resistivity of 55 micro-ohm-cm were obtained at a substrate temperature as low as 300 C. By combining X-ray diffraction, transmission electron microscopy, and electrical measurements, we discuss the effect of substrate temperature, orientation, film thickness, and strain on the structure and electrical properties of these films. Our results illustrating the use of novel solid-source MOMBE approach paves the way to the atomic-layer controlled synthesis of complex oxides of stubborn metals, which are not only difficult to evaporate but also hard to oxidize.

cond-mat.mtrl-sci↗

arXiv2021

The Black hole Black string phase transition in Einstein-Gauss-Bonnet gravity

We investigate the presence of a black hole black string phase transition in Einstein Gauss Bonnet (EGB) gravity in the large dimension limit. The merger point is the static spacetime connecting the black string phase with the black hole phase. We consider several ranges of the Gauss-Bonnet parameter. We find that there is a range when the Gauss-Bonnet corrections are subordinate to the Einstein gravity terms in the large dimension limit, and yet the merger point geometry does not approach a black hole away from the neck. We cannot rule out a topology changing phase transition as argued by Kol. However as the merger point geometry does not approach the black hole geometry asymptotically it is not obvious that the transition is directly to a black hole phase. We also demonstrate that for another range of the Gauss-Bonnet parameter, the merger point geometry approaches the black hole geometry asymptotically when a certain parameter depending on the Gauss-Bonnet parameter $α$ and on the parameters in the Einstein-Gauss-Bonnet black hole metric is small enough.

gr-qc↗