User Facilities for X-Ray and Neutron Absorption Spectroscopy - A survey of analyzing material properties when other syntheses don’t provide results!

At the Spring MRS 2019 conference, some of the U.S. Department of Energy’s laboratories held tutorials on their state-of-the-art nanoscale science research centers and user facilities. The Center of Nanophase Materials Sciences (CNMS) at Oak Ridge National Laboratory and the Center for Nanoscale Materials (CNM) at Argonne National Laboratory were prominently featured, with studies that included material local distortions, chemical short range bordering, nanostructuring, and crystallographic phase transitions.

The main tutorial, the ‘Mini X-Ray and Neutron School on In Situ Materials Research’, featured researcher Katharine L. Page (ORNL), where user facilities assessed data via constructing a pair distortion function (PDF), an atomic-level scattering technique, after detection. Chemical short range order via PDF can infer material substitution effects, chemical clustering, ion-specific local environments, and vacancy ordering. Nanomaterial structuring information based on a PDF can also be determined: finite size/shape effects, surface/interface structure, nanostructure polymorphs, and growth/transformation. Such a technique is also transferrable to amorphous structures, where an understanding of oxide liquids, for instance, is essential in nuclear meltdown scenarios, evolution of planetary bodies, glass formation, and crystal nucleation.

Researchers are encouraged to pursue PDF studies if they have already modeled many material parameters possible while in reciprocal space, and if they suspect local material structure may differ from the long-range structure. Evidence of a distinct local structure may be available if one finds signatures of disorder through complementary methods, or if an average structure model fails to explain observed material properties.

The user facilities for such nanoscale science research centers are as follows:

• Center for Nanophase Materials Science at Oak Ridge National Laboratory (cnms.ornl.gov)
• Center for Nanoscale Materials (CNM) at Argonne National Laboratory (anl.gov/cnm)
• Center for Functional Nanomaterials (CFN) at Brookhaven National Laboratory (bnl.gov/cfn)
• Center for Integrated Nanotechnologies (CINT) and Los Alamos and Sandia National Laboratories (cint.lanl.gov)
• The Molecular Foundry (TMF) at Lawrence Berkeley National Laboratory (foundry.lbl.gov)

MRS Frontiers: Materials for Quantum, Biology, Sustainability, & Artificial Intelligence

This 2019 MRS Spring Meeting featured a grandiose reception for attendees, concerning what would be the new topical areas of interest for future scientific meetings. While some seminal works in Quantum Information Technologies, Artificial Intelligence, Biomaterials (for example), and Materials for Sustainability have driven pop science intrigue, there is no doubt as to their research prominence, application, and concern for implementation based on where strategic materials advances could bring these fields into a more palatable reality.

The networking reception itself was a very successful addition to the Meeting, collecting feedback and constructing working groups for where these topical areas are poised to inspire research presentations and publications, as well as secure collaborations for new research initiatives, grant applications, and establishing benchmarks for funding priorities.

MRS, from grassroots initiatives of supporting higher level lobbying for initiatives pertinent to materials researchers, features political proceeds newsletters and the Materials Voice - a support feature for US constituents to e-mail their congressional representatives about specific policy concerns that are of vital importance to the materials research community. MRS, with the addition of other professional scientific organizations, features the National Photonics Initiative and National Quantum Initiative as a means for researchers to follow, at high level, the impending frontiers of research.

The MRS Frontiers Reception: Building Communities event was supported in part by ASU, ASM, LANL, ReACT, NSF, and Symposium ES13.

Material Structural Considerations for Energy Applications: How adapting a chemical synthesis at nanoscale drives improved performance

At the MRS Symposium for Energy Materials, materials for developing Concentrated Solar Power (CSP) technologies was for another year, a hot topic. CSP demands differ from those materials needed for driving photovoltaics - rather than certain semiconductor media or perovskites, this symposia examined materials that absorb the sun’s energy to transfer to a conventional Rankine- or Brayton-cycle thermodynamic process, using mechanical work to generate electricity as an intermediary.

Advances in this field have previously encouraged researchers to develop inorganic materials that exhibit spectral-selectivity, or a sensitivity to absorptance at specific solar wavelengths and reflectance at higher infrared wavelengths, to prohibit events of waste heat occurring based on re-radiative emissivity. However, with materials that can survive at higher working temperatures, this material feature isn’t as prudent as general absorptivity. Tailoring the structural properties of nano-materials can support improved light-trapping capabilities, where nanostructures trap light of very short wavelengths.

A research encouragement was in comparisons to the nanostructure of Surrey NanoSystems’ VantaBlack, that absorbs up to 99.96% of visible light based on a nano-needle structure. Researchers at the University of California, San Diego have shown a comparable nanomaterial structuring feasibility from a simplified chemical synthesis. As a cost-effective means of upscaling the process to large CSP power plants, such as the Crescent Dunes CSP Plant in Nevada, researchers are poised to explore how such a process can be further stabilized for longer survivability to ensure such a method can be commercially viable.

My MRS Experience

Blogging for 2019 MRS Spring Conference has been an educational experience for me. I had to learn how to balance taking notes for various talks, summarizing the developments succinctly without missing out on the important details, and trying to communicate scientific research without using too much jargon so that people outside of the field can understand it. Additionally, the beautiful city of Phoenix, Arizona has been punishing in its heat so going outside for a short walk in between sessions feels like running a marathon. Nevertheless, the place has been so welcoming, the Phoenix Convention Center was an excellent location to host so many people. 

The various talks, symposia and outreach activities really motivated me to go back to the laboratory and work hard on my research. My goal was to learn more about thermoelectric behavior, the basics of organic thermoelectrics and their applications in flexible devices. Talks by researchers like Prof. Gang Chen, Prof. Yi Cui, and Prof. Joseph Wang were very enlightening in terms of understanding where materials research is going and what future scientists like me should focus on. Moreover, talks by Prof. Graeve during the Women in MSE Breakfast and by Dr. Arenberg during the Symposium X session on The James Webb Space Telescope helped me understand the breadth of materials science, as well as my role in this community as a woman, an engineer, and a minority. 

Overall, this has been an excellent experience. I feel honored to have been able to write about it, and am thankful to Ms. Judy Meiksin for this opportunity. Moreover, I had a great experience presenting my own research on flexible electronics (the last presentation on the last day, so I like to pretend I got to close the MRS Conference) and look forward to attending this conference in the coming years. 

Material Considerations for the Hubble Successor: Development of the James Webb Space Telescope

Presented at the MRS Symposium X by Jonathan Arenberg, Ph.D., Northrup Grumman

As a successor to the Hubble and Spitzer space telescope, the James Webb Space Telescope (JWST) originated in design from the 1990s, developed by NASA in collaboration with the Canadian and European Space Agencies and contracted by Northrup Grumman - it is named after the 2nd NASA administrator. With a projected launch date of 2021, its main mission feature is detecting the first luminous objects in the universe, from the beginning of time (only millions of years after the Big Bang). According to Arenberg, “The [JWST] will take the Universe’s ‘baby pictures’, and understand the development of elegant galaxies.” Major breakthroughs of more reliable, low-cost materials that function in exo-planetary conditions have been pivotal to enabling cost and design targets.

JWST is more than seven times the size of the Hubble’s area - its primary mirror alone is about 6.5 meters in diameter! Certain material considerations include those that can maintain structural integrity under varying temperatures; a telescope can experience near-cryogenic temperatures at a cold side and up to 700ºC on the hot side.

To observe faint signatures of the earliest galaxies, large telescopes enabling high detector resolutions are necessary. Early stars in the universe are hydrogen burning, and emit visible light. Over time however, this energy is ‘red-shifted’, and in our modern era, can only be detected in the infrared spectrum. Essentially, NASA’s scientists engage in a sort of forensics mission - with an understanding of the earliest material traces that could conceivably be detected, clues about the early universe are unraveled based on tracking specific functional phenomenology.

Arenberg remarked, “Science wants to answer pivotal questions, such as ‘How did the Universe start?’ ‘How does the Universe work?’ ‘Are we alone?’ JWST will give humanity its first look at the first stars and galaxies in the universe - essentially, the beginning of everything. Working on [such a project has been] the job of a lifetime.”

FLOTEing Semiconductors

Runqiao Song from North Carolina State University (go Wolfpack!) presented her research titled "Determining the Thermomechanical Properties of Polymer Semiconductors Supported on Elastomers" as a part of the second half of the morning session in Symposium EP04.13: Soft Electronics—Manufacturing and Design I. This research was carried out in collaboration with Harry Schrick, Nrup Balar, Salma Siddika, with PI Prof. Brendan O'Connor, all at North Carolina State University as well. 

Song's research focused on creating a new method, titled Film Laminated on Thin Elastomer (FLOTE) method to measure the mechanical and viscoelastic properties of organic semiconductors. This is important because various applications of these materials such as flexible displays need accurate measurements of the materials' mechanical properties. Current techniques such as bulk measurement methods using a Load Frame fail to take into account the thin film processing techniques since they require large amounts of bulk materials, whereas other thin film measurement methods such as Film-On-Water cannot show compression characterization and do not allow for temperature control to measure viscoelastic properties. The FLOTE method presents many advantages such as being sensitive to thin film processing, temperature control, ability to study substrate dependence of mechanical properties of thin films, study of cyclic loading with compression, and capability to carry out dynamic mechanical analysis (DMA) for viscoelastic properties of organic semiconductors. By using a thin film P3HT supported on a thin polydimethylsiloxane (PDMS) substrate, Song was able to use FLOAT and DMA to analyse the entire stress-strain behavior, fatigue behavior, and viscoelastic behavior with good correlation, supported by finite element analysis. They determined that the glass transition temperature of P3HT was 30 degrees Celcius, with a glassy behavior of the polymer below this. 

Hence, Song and colleagues were able to develop a mechanical probing method that was versatile and efficient for analyzing thin films. 

Haute Couture with Carbon Nanotube Bracelets

Kyung Tae Park from Korea Institute of Science and Technology and Seoul National University presented a very interesting and engaging talk titled "Carbon Nanotube Based Thermoelectric Bracelet Fabricated by Direct Printing on a Flexible Cable" as a part of symposium EP13: Thermoelectrics - Materials, Methods and Devices on the last day of the 2019 MRS Spring Conference. This was an intriguing application of carbon nanotube (CNT) based thermoelectric (TE) wearable devices, taking into account the various requirements for wearables. 

Park started with how there are certain requirements that wearable TE devices have to meet in order to perform well and also be comfortable. These include good TE performance, a preference of out-of-plane architecture over in-plane especially for body heat harvesting where the temperature gradient is also out-of-plane, lightweight, flexible, and conformable. Various materials have been investigated for this application but they all have their pros and cons. Inorganic semiconductors have the highest power factors but are brittle and toxic, conducting polymers are flexible and lightweight but have low power factors and are difficult to obtain in the n-type form. Hence, Park used doped CNTs which are flexible, lightweight, stable, and have power factors that are better than conducting polymers but lower than inorganic semiconductors. By creating p-type CNTs doped with polyacrylic acid and n-type CNTs doped with polyethyleneimine, they were able to create a viscous printing ink that was further deposited on a 3D cable that could be worn for energy harvesting applications. The reported output voltage was 41.4 milliVolts and the bracelet showed very little change in its resistance even after undergoing 3500 bending and unbending cycles. 

To read more about this research, please click here. 

The Two Charge Transfer States Solution

Bharati Neelamraju, a PhD student from The University of Arizona presented her work on organic semiconductors (OSCs) titled "Doping in Organic Thermoelectrics—The Tale of Two Charge Transfer States" as a part of EP13: Thermoelectrics - Materials, Methods and Devices. This research was carried out in collaboration with Kristen Watts, Erin Ratcliff, and Jeanne Pemberton, also from The University of Arizona. 

Neelamraju's research focuses on studying the change in electrical conductivity as dopants interact with their OCS hosts. This is especially important because improving the performance of thermoelectric devices relies critically on enhancing and understanding their electrical conductivities, especially when a dopant is added. Neelamraju studied the system of regiregular (rr) and regioirregular (ri) P3HT that is doped with F4TCNQ which is a p-type dopant. Additionally, she studied the two types of charge transfer states that occur in doped systems: (i) Integral charge transfer (ICT) where one electron is transferred. This is an ideal charge transfer state and is preferable since it results in a completely free charge carrier, and (ii) Partial charge transfer (CPX) where less than one electron is available, and instead there is a hybridization of the molecular orbitals. This results in the electron being in a trapped state, and hence is not a preferable state. Neelamraju observed that for the P3HT-F4TCNQ system, there is a movement between the ICT and CPX states, in case of the rr-P3HT. This is directly correlated to the microstructure of the system, and hence changing this can change the charge transfer state. When it comes to ri-P3HT which is completely amorphous, the CPX state is dominant at high dopant mole ratios. This was an interesting observation, and the research group is still studying the reasons for this observation and how to further characterize it. They are also trying to understand if there is a direct correlation between the microstructures and charge transfer states even in the case of ri-P3HT-F4TCNQ systems. 

Modifying Polymers to Improve Thermoelectric Performance

Dr. Suhao Wang from Linkoping University presented a very interesting talk on improving the performance of n-type organic thermoelectrics (TEs) titled "The Role of Polymer Structure on N-Type Organic Thermoelectrics" as a part of EP13: Thermoelectrics - Materials, Methods and Devices. 

While p-type organic materials for TE applications have been extensively explored and show a good electrical conductivity of 1000 S/cm in case of PEDOT:PSS, when it comes to n-type organic TEs, it is difficult to achieve good performance. Materials like naphthalenediimide–bithiophene copolymer P(NDI2OD-T2), which has a high electron mobility polymer and has been used as active layers for OFET/OSC devices, can only be doped to a conductivity of 0.003 S/cm, regardless of the doping conditions and dopant used. Dr. Wang's research focused on understanding the reasons for this performance, as well as understanding how planarity within the polymer chain can affect its performance as an n-type material. They observed that in the planar polymer BBL₈ which has a more planar structure, the polymer is double-stranded and its donor-acceptor (D-A) characteristics extend over three repeating units rather than just one, as is the case in P(NDI2OD-T2). Hence, BBL₈ exhibits electrical conductivity that is three times higher. Using this principle, Dr. Wang and his collaborators synthesized a new type of P(NDI2OD-T2) polymer with Tz2 that has a much better D-A performance due to its planarized structure. Hence, by increasing the backbone planarity they were able to improve the D-A characteristics. 

To read more about this research work, please click here. 

Using Less to Cool More

As a part of the evening session of Symposium QN05 : Emerging Thermal Materials—From Nanoscale to Multiscale Thermal Transport, Energy Conversion, Storage and Thermal Management, Amin Nozariasbmarz, a PhD student at The Pennsylvania State University presented his research on optimizing the performance of thermoelectric (TE) coolers (TECs) and generators (TEGs), titled "Efficient Thermoelectric Materials and Module Design for Wearable Applications".

Amin started the talk by illustrating the basics of TE devices. These are solid state devices that take the advantage of the Seebeck effect to generate electricity from an applied temperature gradient or are capable to moving heat away from an area (refrigeration) by taking advantage of the Peltier effect. In this way, wearable applications of TEs can include both TECs and TEGs. However, it is important to note that unlike commercial applications of TE devices where the temperature gradients encountered are quite high, when it comes to wearable applications for the human body, the temperature gradients expected are quite low (between 1-3 degrees C, usually). 

Amin's analysis took into account that there are two ways to improve performance of TE devices: (i) improving the material's intrinsic thermoelectric properties and (ii) improving the device design. By focusing on the latter, Amin and his colleagues were able to posit that for low thermal gradient applications, optimizing the fill factor and aspect ratio of the TE module is a good way to improve overall TE module performance. The fill factor refers to the ratio of surface area of the TE legs to that of the module, whereas the aspect ratio refers to the ratio of the length of the leg to its width. In commercial devices, the fill factor is usually 20% or more, but using their analytical modelling, Amin was able to conclude that for wearable applications, the fill factor should be lower to about 10-15% to get the maximum cooling power in case of TECs, or maximum power generation in case of TEGs. In this way they were able to demonstrate the possibility of creating TECs with twice the cooling power and eight times more cooling compared to commercial TECs at the same applied voltages. This is great news for thermoelectrics researchers who are trying to use less material to create more conformable and lightweight wearable TECs and TEGs. 

To know more about this research work, please click here.