Dr. -Ing. C. V. S Kiran

Dr. -Ing. C. Venkata Sai KiranBetter Materials for a Better Tomorrow

Project Scientist, Center for Materials Characterization and Testing
International Advanced Research Center for Powder Metallurgy and New Materials (ARCI),
Hyderabad, Telangana, India

Research: Dr.-Ing. V.S.K. Chakravadhanula

Research Areas

In situ Transmission Electron Microscopy

    In situ Electron Microscopy is the emerging field of Electron Microscopy involving Electron Microscopy under dynamic conditions with various stimuli. Based on these stimuli used, a variety of techniques/method are divided and are termed as in situ TEM techniques. Research and Developmental activities in these fields are gaining increasing importance, as the demands from the synthesis and fabrication groups increase, requiring the dynamics of materials modifications during their processes, understanding the basics of the process, therby leading towards an efficient material, its process and its properties.

    As an example, the video below depicts in situ TEM in liquids towards understanding the growth of Ag within a AgNO3 solution using an Posseidon single tilt sample holder from Protochips Inc. More information: Link

AgNO3 Solution - Electron Beam
Video: Depicting the growth of Ag in a dilute AgNO3 solution inside a Posseidon Liquid TEM Sample Holder from Protochips Inc.
Video is 4 X speed.

Transmission Electron Microscopy of Battery Materials (Electrodes and Electrolytes)

    Research in the field of energy storage systems has gained huge importance in all sectors of  life. Batteries contribute towards the major systems of Energy strorage systems. Improving the cycling capabilities, energy storage capacities, safety and security are the primary aspects which need a deeper understanding of the individual components of the battery i.e., Electrodes and Electrolytes. Presently there is exploding research towards development of new battery chemistries, new nanostructures of the individual components towards meeting the energy storage demands of the world. Therby leading to huge demand for high spatial resolution characterization of such components not only in the as-prepared state but also during various stages of cycling or even after cycling. In all the aforementioned cases, TEM offers a good choice, towards acheiving high spatial resolution. But the expectations of the researchers towards TEM has also been increasing with the advances of in situ electron microscopy, towards understanding the morphological, structural and compositional changes during the process of charging and discharging. For this purpose, the effective dose of the individual components of the battery are pivotal, ignoring which leads to the analysis of electron beam modified components as components of the battery. Thus modifying the complete electrochemistry of the battery. Analysis of individual components of the battery, their beam stability and the critical electron dose under varying imaging techniques become the key parameter. Hence understanding the radiation damage (either Radiolysis, Knock-on-damage or sputtering and heating) leading to either crystallization, amorphization or removal of material remains pivotal.

    Understanding this thereby leads towards "Better Materials for a Bettery Battery thereby Better Energy Storage System for a Better Tomorrow".

In situ TEM studies of Battery Materials

    Research in the field of in situ energy storage systems has gained huge importance in the present decade where batteries, besides being pivotal, also needs improving in their cycling capabilities, energy storage capacities, safety and security which need a deeper understanding of the interfaces of the battery i.e., Anode-Electrolyte and Cathode-Electrolyte. Many research groups around the world try to understand this towards the development of new battery chemistries, new nanostructures of the individual components towards meeting the energy storage demands of the world.
    TEM, being a high spatial resolution characterization tool enables the understanding of the variations or modifications at the nano-scale. Together with in situ sample holders with continous imaging during any experiment, high spatial resolution involves higher electron doses, increasing the effective dose applied on the system that might lead to radiation damage. Towards understanding the morphological, structural and compositional changes during the process of charging and discharging during an in situ TEM electrochemical cycling experiements, electron microscopists might be misled towards studying the electron beam modified materials and their electrochemical cycling.
    Effectively the calculation of the critical dose of the individual components of the battery in separate experiments are pivotal. Ignoring this might leads to the analysis of electron beam modified components as components of the battery, thereby studying the electrochemistry of the electron beam modified battery. More information: Link

In situ TEM studies of Memristive Materials

    Memristors are nanoscale resistive switching devices. Memristors have been of huge interest for memory, logic and neuromorphic applications in the recent times. Generally, their switching effects in dielectric-based devices are assumed to be caused by conducting filament formation across the electrodes. But the nature of the filaments, their growth mechanisms and dynamics are in huge debate, which demand in situ high spatial resolution characterization techniques. In situ transmission electron microscopy with its imaging, structural and compositional analysis at the nanoscale is an optimum technique to understand the growth mechanisms and dynamics. Through systematic ex situ and in situ TEM studies on nanoscale devices under various programming conditions, the underlying mechanisms can be identified. The results obtained through  deserves particular attention for continued device optimization.
Indexing, mapping and evaluating the Indian Electron Microscopes and Facilities

Based on the understanding of various EM facilities around the world and the experience gained in establishing collaboration, I myself initiated a project on the evaluation of EM characterization facilities in India in a view to enhance the future perspective and dream of establishing state-of-the-art characterization facility for India. This report will be published and would aid towards this dream. In the google map above you find all the FEI TEM's-Blue Color, JEOL TEM's-Green Color and Hitachi TEM's-Brown Color. The EMSI zonal headquarters are also available, but one has to open the flap out and select EM Soceities and unselect the TEM.
Traditional Indian Materials: Correlating known properties with the morphology, structure and chemical composition
Indian rich traditions have a variety of cultural heritage. Traditionally there have been a healthy era of non-processed (traditionally-processed) materials, used in day to day activities. Many of these materials have been used even today in villages, because of the knowledge given by the ancestors. Unfortunately less scientific evidenceexists . An effort is here made to correlate the known functionality or the properties with a scientific understanding by studying the morphology, structure and chemical compositon of the corresponding materials.
Transmission Electron Microscopy of Ayurvedic medicines prepared by herbal routes.

    Ayurvedic medicines are nano-/micro- materials made by all-green technologies and are the Traditional Indian Medicine. Actual prepration strategies and recepies are mentioned in the vedas. This alternate medicine has proved to be very helpful in treating diseases. But characterization of such materials involves high resolution techniques in addition to bulk characterization techniques. Morphology, Structure and Compositional analysis is pivotal towards the establishment of standards for the Ayurvedic medicines or "Bhasmas".

TEM studies of the ternary Ti36Al62Nb2 alloy

    Al-rich Ti-Al alloys attracted some attention during the past years due to the possibility of their application as light-weight, high-performance materials at elevated temperatures. The effect of the addition of Nb to Al-rich Ti-Al alloys has been studied for Ti36Al62Nb2 by a combined approach of transmission electron microscopy (TEM) techniques for unraveling the structure and composition at the nanoscale. Structural analyses on as-cast ternary alloys revealed the presence of h-TiAl2-, Ti3Al5- and ?-TiAl-type phases. After heat treatment, phase transformations like the replacement of the metastable h-TiAl2-type by the stable r-TiAl2-type were identified. Additionally, changes of the microstructural features like the formation of interfaces with different orientation relationships are apparent. The orientation and interfacial relationships involved are compared to those of binary Ti-Al alloys rich in Al. More information: Link

Electron Tomography of Nanocomposite Materials

    Unlike the case of polymers, in the case of Ag nanoparticles on TiO2, segregation of the clusters on the surface also provides a fast pathway for Ostwald ripening without any restrictions by elastic distortions at least for those clusters which are in direct contact with the surface.

    3D electron tomography was employed on the TiO2 based nanocomposite thin ?lms to explain the two step model for the particle size distribution. First step involved the formation of small nanoparticles during vacuum phase deposition or on the growing surface. Second step after the deposition process involved the formation of larger particles through particle coarsening by Ostwald ripening and surface segregation. More information: Link

Ag-TiO2 Tilt Series Ag-TiO2 Visualization
Video: showing the acquired tilt-series with a single-tilt Tomography sample holder
Video: showing the visualization of the reconstructed volume where TiO2 is transparant and Ag has been given golden color.

In situ TEM heating of oxide-based Nanocomposites

   A study involving the in situ heating of the TiO2 based nanocomposites in the TEM con?rms the absence of the formation of TiO unlike the SHI irradiation. Changes of the microstructure of the nanocomposite ?lm upon annealing allowed demonstrating the absence of the formation of TiO but rather only the crystallization of the TiO2.

Fig: In–situ heating of the 11 % MVF Au–TiO2 nanocomposites at (a) room temperature (b) 100 C(c) 200 C, (d) 300 C, (e) 400 C and (f) 500 C (total time 3 hrs).
Particle Size Distribution Au-TiO2 nanocomposites
Fig: Particle size distribution of the Au–TiO2 nanocomposite in the above figure at (a) room temperature (b) 100 C (c) 200 C, (d) 300 C, (e) 400 C and (f) 500 C (total time 3 hrs).

Swift Heavy Ion Irradiation of Noble-metal based Nanocomposite Materials

   Tuning the optical properties of nanocomposites can be achieved by using swift heavy ion irradiation (SHI) of the nanocomposites. The SHI beamlines from both the Hahn–Meitner–Institute in Berlin, Germany and the Inter University Accelerator Center in New–Delhi, India, were employed in this work. The TiO phase formation on SHI irradiation with increasing ?uence was understood by the interaction of two different counteracting mechanisms, where at lower ?uences, the tendency towards the formation of TiO existed with the larger unaffected areas and at higher ?uences, the destruction of the evolved TiO phase into fragments was evident. This served as an evidence for the counter play between "hit" and "no–hit", "single–hit" and "multiple–hit" processes. More information: Link

TiO + SAED + Simulated
Fig: Brightfield TEM image of the TiO crystal formed at the fluence of 3 X 1012 ions/cm2 with the associated experimental (center) and simulated (right) SAED patterns showing clearly the single crystalline nature in the zone axis of [2 1 1]. SAED pattern simulations were done using the the software JEMS.

SHI irradiation of Ag nanoparticles embedded in PTFE matrix shows a marginal dissolution of Ag nanoparticles along with a slight agglomeration of nanoparticles. At higher ?uences, carbon rich areas were observed, which were as a result of the carbonization along the ion tracks.

Fig: SHI irradiation induced changes in the PTFE matrix of the nanocomposite along the ion tracks.

    Enhancement of the silver ion release after SHI irradiation at a fluence was observed to the fact that the ion trajectories after irradiation provide better silver ion release.

SHI Ion release
Fig: Enhanced release of silver ions after SHI irradiation at a fluence of 11013 ions/cm2 when compared to the pristine sample.

Transmission Electron Microscopy of Nanocomposites

Synthesis and Characterization of Nanocomposite Materials through vapor-phase deposition methods

   Nanocomposite thin film coatings with a wide range of metal volume fractions were prepared by co–sputtering of TiO2/Teflon and Ag/Au/Cu from two different magnetron sources simultaneously in a home made deposition chamber under high vacuum conditions. Two different types of host materials a polymeric (PTFE) and a ceramic (TiO2) were studied in this work. Morphology, optical and antibacterial properties of these nanocomposites were examined. The formation of metallic nanoparticles upon vapor phase co–deposition of a metal and a dielectric matrix component can be understood in terms of the high cohesive energy of the metal and the low metal-matrix interaction energy which lead to high metal atom mobility on the growing composite surface and metal aggregation whenever metal atoms encounter each other or a metal cluster.  

    In addition, efforts towards tuning of the double plasmon resonances by tailoring the dielectric separation were carried out. Bimetallic nanocomposites based on sandwich geometry in polymer system, the changes in the particle plasmon spectra of sandwiched Au nanoclusters as a result of the presence of Ag nanoclusters in their vicinity and vice versa was studied. Also, the optimum dielectric barrier thickness for the observation of equal intensity double plasmon resonance was reported. Functionality of the nanocomposites in terms of the antibacterial properties was studied. Cultures of B.megaterium, S.aureus, S.epidermidis and E.coli were used to study the effect on the Ag–TiO2 nanocomposites. Additionally, silver ion release studies were carried out at dfferent MVFs by using X-ray photoelectron and UV-Vis/NIR spectroscopies. More Information: Link

Dr. -Ing. C. V. S Kiran

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