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November 2016

Say NO to sample preparation and say Hi to XRM

In my 2 years of Ph.D. journey, I have been stuck in 'one thing' from past 8 months. And today, the issue got resolved in less than 8 minutes! All thanks to the Zeiss Microscopy booth at MRS 2016. 

I shared the problem I am facing at the Zeiss Booth : 

Since, I am working on clay ceramic samples (you can imagine them as square bricks) for water filtration it's challenging to cut the sample for sample preparation as the cutter either distorts the pores or fills up the pores. So, micro-CT is an issue due to sample size restriction. Also, it's impossible to scan down the depth of the sample using electron microscopy. 

 They showed me the solution - Go with 3D X-ray Microscopy came the instant reply as the instrument is non-destructive and supports large samples to produce high contrast 3D stack of the sample up-to sub-micron resolution. 


I felt so grateful to be a part of MRS conference, it really provides a huge platform to resolve your research problems. 



EM11.6 : Why SNDM for Characterizing SiO2/SiC Interface Quality

In today's morning session of the symposium - SiC Power Electronics, Dr. Yasuo Cho from Tohoku University, Sendai, Japan stated significant key reasons for using Scanning Non Linear Dielectric Microscopy (SNDM)  to characterize SiO2 /SiC interface quality.

The properties of SNDM are - 

  1. It has high capacitance sensitivity. (10-22 f)
  2. It's applicability for wide range of materials and devices.
  3. It's excellent potential for semi conductor material characterization. 
  4. Quickly estimates time of trap density.

The above attributes makes SNDM a quick - sensitive- technique for characterizing interface quality.


ES1: Materials Science and Chemistry for Grid-Scale Energy Storage

Yi Cui, Stanford University

Reviving of Li Metal Anode Through Materials Design

Written by Armin VahidMohammadi

Although there is a great interest in battery systems beyond lithium, Li-ion batteries are the only systems that have shown reliable performance and scale-ability for different applications in the industry. Yi Cui from Stanford University discussed the current status of Li-ion batteries and the future roadmap of developing the next generation of these battery systems. During the past 20 years, different materials designs have helped increase the performance of Li batteries. Silicon is one of the most promising electrode materials for lithium ion batteries as it has a very high theoretical capacity; however, it suffers from very poor mechanical stability due to the high volume expansion in the charge and discharge. Si particles suffer from mechanical instability and they break after some cycles due to huge volume expansion in their structure. Making particles smaller (nanosized particles) was explained as a solution to somehow overcome this mechanical failure and maintain the electrical contact inside the electrode network. Cui said the main challenge of Li metal resides in the problem of finding a host for it and also its high chemical reactivity. Cui’s group designed a stable interface to create a host for Li metal. Cui also introduced Li-reduced graphene oxide (rGO) as a promising electrode for lithium batteries.

ES1: Materials Science and Chemistry for Grid-Scale Energy Storage

Zhaoxin Yu, The Pennsylvania State University

A Super High Conducting Solid-State Electrolyte for Room-Temperature Sodium-Ion Batteries

Written by Armin VahidMohammadi

Beyond a doubt, battery systems beyond lithium-ion are one of the hottest research areas due to limited resources of lithium metal in the world and many different safety issues that are associated with current lithium ion batteries. One of the most promising candidates for lithium is sodium (Na). In the last talk of the morning session of the ES1 symposium, Zhaoxin Yu from The Pennsylvania State University presented work on solid-state sodium-ion batteries. The study introduced sulfide Na-ion solid state batteries where the system uses an electrolyte containing a mixture of Na, phosphorous, arsenic, and sulfur. Their electrolyte with the composition of Na3P1-xAsxS4 is a pure ionic conductor. It was explained that the As-substitution is a main reason for improved performance in their system and he went over the mechanism that is existing behind this change in the composition. Two factors were explained to affect the ionic conductivity of the solid-state electrolyte. One of them was the lattice expansion, and the other one was the sulfur and phosphorous bonding with Na atom. In low concentrations the lattice expansion is the dominating factor that increases the conductivity and in higher concentrations the stronger bonding between the sulfur and Na is the parameter that results in a decrease in the ionic conductivity. They had studied the moisture stability of their material as well.

ES2: Materials Challenges for Flow-Based Energy Conversion and Storage

Yury Gogotsi, Drexel University

Flowable Capacitive and Pseudocapacitive Energy Storage

Written by Armin VahidMohammadi

Flowable energy storage devices have recently attracted a lot of attention because of the different advantages they can provide in large-scale energy storage and water deionization. Yury Gogotsi from Drexel University shed light on important aspects of the materials challenges for future flowable energy storage devices. He first summarized how energy is stored in batteries and supercapacitors by explaining the mechanisms of charge storage in electric double layer capacitors (EDLCs), pseudocapacitors, and batteries. Materials with pseudocapacitive properties are promising because the charge storage process happens fast enough in them that it is not diffusion-limited anymore. Gogotsi explained how this technology can be used in flowable applications and provide significant improvements. Flowable slurry of carbon suspended in a liquid electrolyte was given as an example to discuss the different effecting parameters in a flowable energy storage system. Gogotsi mentioned how we should move from the conventional electrode types to the suspension type electrodes. Some challenges in this field were also mentioned such as conductivity of slurry, loading of the material, dispersion, stability, rheological behavior, and electrochemical cell design. Gogotsi mainly focused on materials development for flow-based capacitive and pseudocapacitive systems. In the last part of his talk, he introduced their group’s findings on the application of two-dimensional (2D) transition metal carbides (MXenes) for flowable energy storage applications. MXenes, which were discovered back in 2011 at Drexel University, are a new family of 2D materials that exhibit very interesting and promising properties for different energy storage systems such as supercapacitors and batteries. He showed their preliminary results on excellent conductivity and the flow ability of MXene suspensions even with high loading of MXene flakes.

ES2: Materials Challenges for Flow-Based Energy Conversion and Storage

Bryan Byles, Drexel University

Tunnel Structured Manganese Oxides as Electrode Materials for Hybrid Capacitive Deionization

Written by Armin VahidMohammadi

Bryan Byles from Drexel University explained the research group’s work on capacitive deionization using tunnels structured manganese oxides. In their research, at first and through performing XRD analysis, uniform tunneled structure was assumed; however, when they performed TEM studies, it was observed that it is not always the case for different manganese oxides. In this research, activated carbon was used as counter electrode and manganese oxide with different structures was used as the working electrode for the purpose of capacitive deionization. To confirm the change in the ion concentration, they had used a conductivity probe to measure the conductivity of the solutions before and after test, which from that, the concentration of ions can be found out. Byles mentions that the ion-removal step was done for 15 min at +1.2 V, and the ion-release step was carried out for 15 min at -1.2 V. It was shown that the ion-removal capacitance they were achieving at the beginning was further maintained through several cycles. Among different structures studied, alpha manganese oxide had shown the highest capacitive in potassium chloride (KCl) solution. From their different electrode structure and various experiments, it was concluded that electrodes with smaller tunnels in their structure have preference for adsorption of smaller ions and larger ions have preference for larger ions. Byles concluded his talk by pointing out that through investigating three different types of manganese oxide, the researchers were able to find out the size relation of tunnels in the structure of their electrode and ions. It can be easily concluded that the crystal structure engineering is a key parameter to improve materials performance for capacitive deionization.

ES3: Perovskite Solar Cell Research from Material Properties to Photovoltaic Function

Photon Recycling in Perovskite

Written by Xiwen Gong

Photon recycling describes the process whereby photons generated through radiative recombination of light absorbers are re-absorbed by themselves, instead of being emitted out of the solar cell. This process tends to happen when there is fast radiative recombination and slow nonradiative recombination. Recently, photo recycling has been observed in lead halide perovskite, and is drawing increasing attention from the photovoltaic field.

Johannes Richter from the University of Cambridge mentioned in his talk that photon recycling is crucial to boost open circuit voltage (Voc), leading to a promising pathway to approach the Shockley-Queisser limit in perovskite solar cell devices. The photoluminescence peak shows redshift when the excitation spot was moved farther away from the collection position. Meanwhile, the redshifted luminescence shows longer lifetime, compared to that with shorter wavelength. This phenomenon indicates photon recycling might happen so that photon intensity was maintained at large distance and long timescale.

As the photon recycling and normal carrier diffusion process occurs simultaneously, it is complicated to distinguish one from another by simply measuring transient photoluminescence from the sample surface. Takumi Yamada from Tokyo University proposed to solve this problem by exciting the perovskite confocal two-photon source: the excitation depth is dramatically enhanced and tunable by changing the focus length. By comparing the photoluminescent lifetimes at different excitation depths, the researchers were able to obtain the kinetics from phonon recycling and diffusion separately.

EM10: Emerging Materials and Technologies for Nonvolatile Memories

Suhas Somnath, Oak Ridge National Laboratory 

Scanning Probe Microscopy Techniques for Ultrafast Probing of Ferroelectric and Multiferroic Materials

Written by Vineet Venugopal

Oak Ridge National lab has for many years led innovation in piezoforce microscopy introducing ever more sophisticated techniques to extricate information from atomic force imaging of ferroelectric materials. Suhas Somnath introduced a new mode of imaging termed “general mode voltage spectroscopy” or G-mode. This mode captures raw information from the cantilever in a wide bandwidth with sampling rates as high as 100 Mhz. This means that a surface that would have taken several hours with the currently popular mode (band excitation) can now be imaged in a few minutes. Furthermore, as many as 10000 loops per second can be measured on a sample spot. Altogether this method is 3500x faster than band excitation. Relevant materials data such as local strains are extracted from the raw data using suitable filters. This method is particularly exciting for data science-based methods of the future.

TC4: Advances in Spatial, Energy and Time Resolution in Electron Microscopy

R.J. Miller, Max Planck Institute for the Structure and Dynamics of Matter, Hamburg Centre for Ultrafast Imaging, University of Toronto

Mapping Atomic Motions with Ultrabright Electrons—Realization of the Chemists’ Gedanken Experiment

Written by Yuanyuan Zhu

One of the “holy grails” in chemistry and materials science has been the capability of making direct observation of the atomic motions driving chemical processes. Extraordinary space-time resolution - relevant timescales in the 10-100 femtosecond and atomic imaging requiring Å or sub-Å

resolution - needs to be achieved to capture the motion of atoms. Here, R.J. Miller, director of the Atomically Resolved Dynamics Department of the Max Planck Institute for the Structure and Dynamics of Matter and professor of chemistry and physics at the University of Toronto presented an excellent overview on the global competition and progress in ultrafast atomic imaging. His research is focused on understanding molecular reaction dynamics on the fastest possible time scales, with an overall objective of bringing new insight into the structure-function correlation to chemical and biological processes. In particular, Miller reported the development of some of the world’s brightest electron sources in his laboratory, which can literally light up atomic motions on the femtosecond timescale to directly resolve this structure-function correlation and to provide the most fundamental (atomic) basis for understanding chemical and biological processes.

NM2: 2D Layers and Heterostructures beyond Graphene—Theory, Preparation, Properties and Devices

Mauricio Terrones, The Pennsylvania State University

Defect Engineering in 2-Dimensional Materials—Graphene, Doped-Graphene and Beyond

Written by Yuanyuan Zhu

Mauricio Terrones at The Pennsylvania State University presented an overview on one of the most important current topics in the research area of two-dimensional (2D) functional nanomaterials on their defect engineering. Terrones’ research group concentrates on challenging synthesis of high-quality graphene and doped graphene on copper substrates by chemical vapor deposition. With the combined capability of both synthesis and characterization, the research team was able to study the correlation between deposition condition and defects type and density in graphene and nitrogen-doped graphene, as well as assemble 2D chalcogenides with different heterogeneous structures. Using scanning tunneling microscopy, Raman spectroscopy, and density functional theory calculations, the researchers suggested that the structural origin for doped graphene working as highly sensitive gas sensors could stem from promoted charge transfer because of band structure modification with the presence of nitrogen dopants. Despite the continuous progress in recent research, fabrication of the 2D electron device with well-controlled defects remains a challenge.