Dr. -Ing. C. Venkata Sai KiranBetter Materials for a Better Tomorrow
Vikram Sarabhai Space Centre (VSSC),
Indian Space Research Organization (ISRO)
Thiruvananthapuram, Kerala, India.
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
Transmission Electron Microscopy of Battery Materials (Electrodes and Electrolytes)
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.
Electron Microscopy of Ayurvedic medicines prepared by herbal routes.
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
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.
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.
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
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.
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.
Electron Microscopy of Nanocomposites
and Characterization of Nanocomposite Materials through vapor-phase
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
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|Copyright Â© 2016 Dr. -Ing.
C.V. S. Kiran