Compared with the OA-OAm- based hot injection obtained materials, the addition of trioctylphoshone one in the work of Qing Shen is more efficient, leading to lower defect and thus near 100% absolute photoluminescence quantum yield for CsPbI3.
MRS Fall meetings are indeed in a great city, and I think that's what makes MRS fall meetings a little bit different than other materials-related conferences throughout the year. Boston is a city full of energy and places to discover. Yes, the weather is a little bit chilly at this time of the year in Boston, and this might make it difficult for most of the attendees to go around the city and explore it when they are done with the conference. However, despite the cold weather, there are still lots of nice places, restaurants, and activities that one can go or do in Boston. Notably, the streets around the conference venue are great. The Prudential Center, shops and restaurants in Newbury street, and all other nice places that are located close to the Hynes Convention Center provide an excellent experience for all MRS attendees and visitors. Don't forget to explore Boston next time you are in MRS - or if you are spending a couple of more days here before you head back. It's an impressive city.
It's a bit bittersweet — the Fall Meeting is almost over. The sessions are still ongoing. I especially enjoyed the BM04 and BM09 sessions.
The venue was excellent and and the poster sessions were definitely very informative for me. Thanks to the caterers for the excellent food and coffee!
See y'all next Spring in Phoenix! In the meantime, if you would like to get the updates from MRS, please follow @Materials_MRS on twitter.
The last invited talk of symposium EP03 of 2018 MRS Fall meeting was about 2D transition metal carbides and nitrides and their applications. Dr. Anasori from Drexel University talked about the structure and composition of these novel family of materials and concluded his talk with some of their applications in wireless communication and gas-sensing devices. The family of 2D MXenes now invloves more than 30 experimentally made compositions where each of them has their own properties. MXenes are probably the least studied 2D materials, and there is a lot of room to explore these materials.
The Fall meeting of MRS had many different talks on MXenes, which shows the growing interest in the research community to work on these novel 2D materials. Among these talks, were two invited talks by Prof. Yury Gogotsi from Drexel University who talked about the electrochemical applications of MXenes and their promising performances in energy storage devices.
If you are interested in MXenes, a quick search in Google Scholar will give you a good perspective on how different groups around the world are applying these 2D materials in their researchs.
Giulia Galli, The University of Chicago and Argonne National Laboratory
The Long and Winding Road: Predicting Material Properties Through Theory and Computation
Written by Ashley White
Galli’s Thursday evening Materials Theory Award talk was centered around three scientific examples, or “short stories,” as she called them. The stories had a common thread of the relationship between structure and function, and how we can understand, predict, and eventually control this relationship to design an optimal material. This approach was discussed in the context of optimal materials to absorb light in photo-electrochemical cells, optimal nanostructured materials for solar cells and electronic devices, and defects in semiconductors for quantum information devices.
In her first story on photo-electrochemical cells, Galli emphasized the importance of understanding, first and foremost, the interface between the electrode and water, as well as the band offsets, which control how charge travels in the system. Galli discussed two examples—silicon surfaces and tungsten oxide. In computing the absolute positions of the bands of liquid water and the band offsets between liquid water and the solids, Galli found that: (1) the solid-liquid interaction is not negligible; (2) multiple combined effects are present; and (3) surface functionalization can be tailored to optimize the photoabsorbent properties. In particular, she emphasized that understanding the electronic structure of solvated surfaces at finite temperature is critical for optimizing the materials system. Overall, she cautioned that studying the intrinsic properties of a material is insufficient, and in some cases misleads one away from predicting the optimal material.
Galli’s second story focused on electronic transport properties in nanoparticles, which may be enhanced through the use of inorganic ligands. In this example, she emphasized the importance of closely and iteratively incorporating experiment with simulations. To develop a structural motif for their models, Galli’s group had to work closely with experimentalists to refine and validate their calculations. Only after the model was validated by experiment could they use it as an input for further molecular dynamics simulations to successfully predict the electronic properties of their materials.
Galli’s third story was about manipulating defects in semiconductor materials for quantum information science. In this case, Galli explained, it is important to understand not only the electronic structure but also the spin decoherence, since it is related to interconnections between defects. Through a combination of approaches, including coupling the electronic structure calculation to the spin Hamiltonian, Galli was able to get excellent agreement between theory and experimental results for di-vacancy in silicon carbide—an approach which can now be extended to other systems as well.
An overarching challenge and goal for the future, Galli said, is to solve the “inverse problem” of being able to design new materials with pre-determined properties based on theoretical and computational information. In closing, Galli dedicated her talk and her award to Alessandro De Vita, a professor of physics and materials science at King’s College London and a collaborator of Galli’s, who passed away unexpectedly in October.
The Materials Theory Award, endowed by Toh-Ming Lu and Gwo Ching Wang, recognizes exceptional advances made by materials theory to the fundamental understanding of the structure and behavior of materials. Galli received the award “for the development of advanced first-principles simulation methods and their application to the understanding, prediction and design of complex nanostructured materials.”
Motoyuki Karita, Shizuoka University
Structural Changes in Carbon Nanotube Yarn Exposed to Actual Space Environment
Written by Tianyu Liu
Have you dreamed of taking an elevator from Earth to the Universe for space traveling? This fictitious idea might come true. Materials researchers have proposed to use carbon nanotubes (CNTs) to make the elevator ropes, due to the excellent mechanical robustness of CNT. However, the high-energy radiations in the Universe might compromise the structural integrity of CNTs and, thus, the safety of the elevators. Motoyuki Karita from Shizuoka University, Japan, studied the degrading process of multiwalled CNTs when exposed to the actual space environment. The researchers attached a piece of CNT-yarn mat on the outside wall of an international space station, and monitored the structural change during two years. In the meantime, on Earth, Karita and co-workers performed comparison tests by irradiating three pieces of the same CNT mats with atomic oxygen (AO), electron beam, and ultraviolet light. The CNT mat in the space experienced significant deterioration in mechanical strength, similar to the AO-irradiation case performed on Earth. Karita’s study reveals that the atomic oxygen atoms are the most corrosive species to CNTs, and protective coating of CNTs is indispensable to ensure the reliably of CNT-elevators.
Naomi S. Ginsberg, University of California, Berkeley
Functional Imaging of Energy Flow in Materials at the Nanoscale
Written by Daniel Gregory
Naomi S. Ginsberg of the University of California, Berkeley is developing techniques for ultrafast measurements of energy propagation in solids. She began by asking the simple question about which trajectory do energy carriers in a polymer or other material travel through the system? Short lifetimes and small distances have made this a challenging question to answer, requiring high sensitivity for carrier tracking, a high temporal and three-dimensional (3D) spatial resolution, and no restricting phenomena to make the technique applicable in a wide range of 3D semiconductors. The result was a combination of transient absorption spectroscopy and scanning electron microscopy, using interferometric scattering microscopy as a probe. Ginsberg explained how to read the results of the system before demonstrating several videos of the technique. Of particular note was the ability to see grain boundaries within polycrystalline materials, where it was determined that excitons traveled deeper into the film upon reaching a grain boundary. Ginsberg concluded with a demonstrated observation of parallel light and heat transport viewed orthogonally in the same system, and planned future work on using the technique to observe lithium ion transport.
Mark Hersam, Northwestern University
Nanostructured Graphene-Coated Cathodes for High-Performance Lithium-Ion Batteries
Written by Tianyu Liu
Spinel lithium manganese oxide (LMO) is a high-performance and low-cost cathode material of Li-ion batteries. Unfortunately, the practicability of LMO is greatly hindered by its poor structure stability due to the disproportion reaction of Mn3+ ions that yields soluble Mn2+ ions. Mark Hersam from Northwestern University demonstrated that graphene-coating was effective to suppress the dissolution of LMO and improve its lifetime. Hersam’s research team first synthesized single-layer graphene films by chemical vapor deposition and then transferred them onto LMO nanoparticles. Using molecular simulation, Hersam showed that the graphene surface layers blocked the Mn2+ diffusion from LMO to electrolytes, which minimized the likelihood of the Mn2+ generation. Additionally, the structural defects of the graphene allowed the Li+ conduction needed for battery functioning. The resulting graphene-coated LMO cathodes concurrently resolved multiple problems that plagued nanoparticle-based lithium-ion battery electrodes including poor cycling stability, low packing density, and high additive content.
Jin-Kyung Kim, Sungkyunkwan University
Negative Poisson’s Ratio of a Natural Nanocomposite Studied by In Situ TEM Mechanical Testing
Written by Hortense Le Ferrand
Limpets are small conical molluscs that scratch algae at the surface of rocks using small teeth, which are among the strongest biological materials. Instead of being straight as human molars, limpet’s teeth are curved in a sickle-like shape, to reduce the stress concentration at the tip. Using focus-ion beam (FIB) to cut thin slices and transmission electron microscopy (TEM), Jin-Kyung Kim and his colleagues could determine the graded microstructure of the tooth. In the interior part of the sickle, called the leading part, nanorods of goethite, a mineral rich in iron, are clustered into random orientations in an amorphous hydrated matrix rich in silica. In the outer part, however, goethite is under the form of larger diamond-shaped crystals.
Another particularity of this biomaterial is a negative Poisson ratio: When the material is strained, its volume increases both in the longitudinal and transverse direction. This behavior, called auxetic, arises from the rotation of the nanocrystals during stretching, as observed directly by in situ TEM mechanical testing. Furthermore, cracking occurs in a brittle fashion in the leading part, whereas crack arrest, bifurcation, and microcracking are observed in the trailing part of the tooth. As a conclusion, limpets have teeth that are strong, auxetic, and wear-resistant in the grinding interior, and softer but tougher on the outer part.
Brian W. Sheldon, Brown University
Fracture Toughness Improvements and Lithium Metal Penetration in Nanocomposite Ceramic Electrolytes
Written by Arundhati Sengupta
Ceramic solid electrolytes have low toughness and face challenges for use in lithium batteries owing to Li infiltration/penetration (short-circuiting) through these electrolytes. Brian Sheldon of Brown University talks about ways to overcome the challenges. According to a recent work carried out by Sheldon and co-workers, the onset of Li infiltration was found to depend on surface morphology (defect size and density) of the solid electrolyte used. Sheldon says that spark plasma sintering (SPS) of the solid electrolytes can help achieve significant improvement in their fracture toughness. Use of suitable nanoscale additives (reinforcements) such as graphene to composite with the solid electrolytes can also help improve the toughness by building “ductile-type behavior.” As an example, he discussed Li1.3Al0.4Ti1.6(PO4)3 (LATP) solid electrolyte reinforced with reduced graphene oxide (rGO). Significant toughening was observed even with a low rGO volume fraction (1%) in LATP-rGO composite. Furthermore, in describing the mechanism of electrolyte fracture by Li infiltration (involving propagation of surface flaws), Sheldon points out that the parameter KIC referred to as the fracture toughness is not actually a true indicator of the same and requires further investigation.