Sai Rama Krishna Malladi

Carbonaceous Chondrites have special significance in the stellar evolution and in particular in the evolution of life on earth. The carbonaceous meteorite that fell in Mukundpura village, Jaipur, Rajasthan on 6th June 2017 is one such rare CM2 carbonaceous meteorite. We carried out high resolution scanning and transmission electron microscopic studies on typical thin sections, showing abundant grains of iridium, pentlandite, and more interestingly crystalline carbon. These crystallite carbon grains resemble nanodiamond like signature in the freshest Mukundpura meteorite. The high-resolution Raman spectroscopic measurements are carried out on the crystalline carbon grains, showing well resolved three distinct peaks with a vibrational mode at 1315 cm-1, with the onset of a weak vibrational mode at 1150 cm-1, substantiating the observation of nanocrystalline diamond in Mukundpura meteorite. The broad peak centered at 1360 cm-1 and 1575 cm-1 (as an average), suggest the presence of graphitic carbon as well together with apparent presence of nanocrystalline diamond. The average size of nanocrystalline diamond is ~ 3-5 nm. High iridium content in this meteorite supports the meteoric impact related iridium anomaly in geological stratigraphic boundaries (e.g. Cretaceous-Tertiary boundary) that has caused mass extinction of flora and fauna.

Real-time in situ monitoring during chemical synthesis can provide vital clues for tracking nanoparticle synthesis, potentially leading to application-optimized reaction products with high yield and reproducibility. In this article, we demonstrate a homemade extinction spectroscopy platform that can track nanoparticle synthesis and chemical reactions with sub-ms time resolution. In the first part of the paper, we provide the various steps required for building and aligning the optical platform that can perform in situ extinction measurements. Subsequently, we employ the platform to study the growth of anisotropic gold bipyramids and nanorods. We show that adjusting the reaction temperature can significantly alter the synthesis rate. Thereafter, we use this system to track the photo-degradation of methylene blue dye using CeO2 nanoparticles and to track pH changes in solution. Finally, we have detailed the potential pitfalls that can arise while using the system and potential avenues for addressing them. In addition to the examples demonstrated here, the established platform can be used to study other reactions, including drug synthesis, protein aggregation, phase separation, and sol-gel synthesis by choosing an appropriate wavelength range of operation. The information extracted from this analysis can be used to modify the reaction conditions in real-time to obtain a pre-determined synthesis product, thereby making synthesis processes efficient and convenient.

Using in situ correlative micro-spectroscopy techniques, we study the temperature-directed shape change of anisotropic gold bipyramids (AuNBP), leading to localized plasmon resonance tunability of more than 250 nm.

Liquid cell transmission electron microscopy (LCTEM) is a powerful technique for investigating crystallisation dynamics with nanometre spatial resolution. However, probing phenomena occurring in liquids while mixing two precursor solutions has proven extremely challenging, requiring sophisticated liquid cell designs. Here, we demonstrate that introducing and withdrawing solvents in sequence makes it possible to maintain optimal imaging conditions while mixing liquids in a commercial liquid cell. We succeeded in visualising a fast nanoscale crystallisation mechanism when an organic molecule of R-BINOL-CN dissolved in chloroform interacts with methanol. The scanning transmission electron microscopy images recorded in real-time during the interaction of the two volatile solvents reveal the formation of chain-like structures of R-BINOL-CN particles, whereas they coalesce to form single large particles when methanol is absent. Our approach of mixing liquids establishes a platform for novel LCTEM studies of a wide range of electron-beam-sensitive materials, including drug molecules, polymers and molecular amphiphiles.

Liquid cell transmission electron microscopy (LCTEM) is a powerful technique for revealing crystallisation dynamics with nm spatial resolution. However, the study of liquids while mixing precursor solutions is extremely challenging. Here, we show how the antisolvent-driven crystallisation of an organic crystal, a widely-employed precipitation route in the pharmaceutical industry, can be visualised directly in a commercially-available liquid cell by flushing the antisolvent past a thin layer of solvent while recording scanning transmission electron microscopy (STEM) images in real-time. Our results reveal particles forming chain-like structures during antisolvent-mediated growth, whereas they coalesce to form single large particles in the absence of an antisolvent. Our approach of mixing the liquids in sequence and using STEM mode to record images with precise electron dose control establishes a platform for novel LCTEM studies of a wide range of electron-beam-sensitive materials, including drug molecules, polymers and molecular amphiphiles that are created during reagent mixing.

In this study, the ability of ozone to oxidise toluene present in low levels into CO and CO₂ was studied. The catalytic ozonation of toluene was carried out in a micro-fixed bed reactor. The oxidation was done in two steps: toluene adsorption on the catalyst followed by sequential ozone desorption. Toluene breakdown by ozone at low temperature and atmospheric pressure was achieved using γ-Al₂O₃ supported transition metal oxides impregnated with a reduced noble metal. The catalyst Ag–CoO_x/γ-Al₂O₃ efficiently oxidised and transformed toluene into products (52.4% CO_x yield). This catalyst has a high surface area, more acidic sites, and lattice oxygens for better toluene oxidation. The addition of Ag to the CoO_x/γ-Al₂O₃ catalyst surface improved toluene adsorption on the catalyst surface, resulting in improved product yield, selectivity, and carbon balance.

We use off-axis electron holography to measure the electrostatic charge density distributions on graphene-based nanogap devices that have thicknesses of between one and ten monolayers and separations of between 8 and 58 nm with a precision better than a single unit charge. Our experimental measurements, which are compared with finite element simulations, show that the graphene tips, which have thicknesses of a single monolayer at their ends, exhibit charge accumulation along their edges. The results are relevant for both fundamental research on graphene electrostatics and applications of graphene nanogaps to single nucleotide detection in DNA sequencing, single molecule electronics, plasmonic antennae and cold field emission sources.