In Honor of Professor Millie Dresselhaus for Her Lifelong Contribution and Impact to Materials Research
Written by Natalie Briggs, Xun Gong, and Aashutosh Mistry
To remember and honor Mildred Dresselhaus’s lifelong contribution and impact to materials research, MRS convened a special workshop covering the topics of carbon nanotubes, thermoelectrics, graphene and two-dimensional materials, and frontier topics. Each of the four sessions concluded with a panel discussion.
Panel Discussion on Carbon Nanotubes
Esko Kauppinen, Aalto University
Hui-Ming Cheng, Chinese Academy of Sciences
Annick Loiseau, Office National d’Etudes et Recherches Aérospatiales
Shigeo Maruyama, The University of Tokyo
Marcos Assunção Pimenta, Universidade Federal de Minas Gerais
Jin Zhang, Peking University
After the morning session on carbon nanotubes, the speakers assembled for a panel discussion where they were asked: What are the challenges, synthesis/characterization/applications of carbon nanotubes in the next 10 years?
Carbon nanotubes have attracted much attention since their discovery in the 1990s; however, they currently still lack widespread use due to multiple factors. In terms of single-walled carbon nanotubes, even though they are relatively easy to grow, it is much more difficult to control the chirality distribution of the product.
Furthermore, the characterization of these materials have proven to be difficult. Techniques such as Raman and TEM have variable ability to differentiate tubes of different diameters, often resulting in incongruous results. The use of multiple techniques to cross check the product is recommended, which adds another layer of complexity. It can be argued that a material with a complex set of properties will require equally a complex characterization and production process, which is partly why there currently is a slowing of nanotube-related applications. In this respect, the field of graphene has an advantage. The future will be closely linked to the collaboration between synthetic chemists and materials researchers.
Even with single chirality growth, applications are not necessarily guaranteed. There is the additional consideration of cost, for example in the case of semi-transparent films. In addition to improving the understanding of all three areas, it is important to also better summarize the last 25 years of work to improve knowledge transfer to students.
When the panelists were asked what gets them excited in the field, they responded:
- Crystallographic perspective and the ability to grow such intricate structures.
- Millie used to talk about the potential of double-walled carbon nanotubes. Two sheets of graphene provide another set of unique tunable properties. If we can control both walls of a carbon nanotube, there will be a new set of metallic and semiconducting combinations.
Panel Discussion on Thermoelectrics
Gang Chen, Massachusetts Institute of Technology
Joseph Heremans, The Ohio State University
Arun Majumdar, Stanford University
Zhifeng Ren, University of Houston
Jihui Yang, University of Washington
Mona Zebarjadi, University of Virginia
The field of thermoelectrics describes the intrinsic properties of materials to convert thermal energy to electrical. This opens up the possibility of a completely solid-state energy conversion system. Though being studied in-depth scientifically, such materials have traditionally experienced quite a block for commercial applications. During the panel discussion, waste heat recovery and cooling were proposed as the two categories where thermoelectric devices could potentially find a niche market. With stricter carbon emission standard and the looming greenhouse effect, the thermoelectric technology could become viable. One should keep in mind that the thermoelectric devices have to be developed differently for heating and cooling applications. For example, the temperature differences are hundreds of kelvins for wasted heat recovery, while for cooling applications, they are of the order of 10 K, resulting in very different second law (of thermodynamics) performance. Another proposed idea was to use thermoelectric for electronics cooling, given its miniaturized size and solid-state operationality (which matches well with the processor chips requiring cooling). One associated aspect where thermoelectric devices have to do better is system cost, especially given the fact that other competing electricity generation technologies (i.e., wind and solar) are much ahead in terms of commercialization. From the standpoint of fundamental investigations and scientific progress on thermoelectric materials, still, many questions remain unanswered. Essentially the interactions among electron and phonon transport in lower order materials (0D, 1D, and 2D) and how it affects the associated topological properties are still poorly explained. The panel discussion thus urged the researchers to thrust their focus on two very different aspects of thermoelectric materials: physics of lower order materials and commercialization of these devices.
Panel Discussion on Graphene and 2D Materials
Pablo Jarillo-Herrero, Massachusetts Institute of Technology
Eva Andre, Rutgers University
Tony Heinz, Stanford University
Philip Kim, Harvard University
Frank Koppens, ICFO–The Institute of Photonic Sciences
Paul McEuen, Cornell University
Two-dimensional, or atomically-thin materials have garnered interest over the past 10 years due to their potential for application in atomically thin and nanoscale devices that span a range of functionalities. While previous and ongoing work in the field of 2D materials focuses on sensing and communications or memory technology from 2D materials, little has been done in the way of using these materials in the context of actuation. In the first session in the afternoon, prior to the panel discussion on graphene and 2D materials, one of the speakers—Paul McEuen of Cornell University— aims to realize 2D materials for actuation technologies and ultimate incorporation in nanoscale robots. Recent progress from McEuen shows that a single layer of graphene can be deposited on 2 nm of glass, and by simply applying voltages (on the scale of 100 mV), these structures can be made to bend and twist. When the voltage source is removed, the structures return to their original state. McEuen hopes to use these structures and knowledge to develop new, nanoscale robots made from 2D materials.
This session on 2D materials in the special workshop highlighted several key areas in the field and advances that are to come, and a panel discussion with experts in the field provided both future outlook on the field of 2D materials as well as their strengths and roles in technology. A key focus of the panel discussion was the question of the “next big thing” in materials science and technology. Panel members suggest that materials creation and combination hold great promise, specifically within the realm of 2D materials. One area that requires increased focus is the interplay and communication between chemists and physicists or materials scientists in the 2D field. Collaboration and communication between these fields would provide beneficial networks and knowledge bases for the advancement of the 2D field. Specifically, chemists can aid this field through knowledge of surface science and bottom-up materials synthesis. Panelists also look forward to a future of self-assembled heterostructures as well as energy harvesting, and self-replicating robots.
Panel Discussion on Frontier Topics
Tomás Palacios and Evelyn Wang, Massachusetts Institute of Technology
Mansour Shayegan, Princeton University
Gregory Timp, University of Notre Dame
Kang L. Wang, University of California, Los Angeles
Nai-Chang Yeh, California Institute of Technology
During the last session of the day, panelists responded to the question of what key lessons they learned from working with Millie Dresselhaus:
- Always pay attention to detail
- Science is about passion, hard work, generosity, and calmness in the face of adversity
- Frontier technology requires the development of a combination of new materials and new physics, which needs the close collaboration of scientists and engineers.
- Only with strong background in basic knowledge such as chemistry, biology, math, and physics can more complex ideas be built upon
To wrap up the special Workshop, following are a few final comments made by panelists regarding frontier topics:
Majoranas are subatomic particles predicted over 80 years ago that were recently experimentally confirmed using nanoscale instrumentation. Microsoft along with many universities are using these new discoveries to construct qubits or a quantum bit, a unit of quantum information. This will be the first step toward the development of a quantum computer. Depending on the amount of funding and resources devoted, experts believe that it is conceivable that the first qubit can be constructed within the next 2 to 3 years.
On Differences Between Biological Systems and Solid-State Materials
We often refer to proteins as machines, but they should not be imaged as a rigid set of solid-state operators. Instead they are fluctuating molecules, and life being a system that makes sense of these fluctuations to move forward. Thus it seems incorrect to make the above comparison.