Discovering how individual atoms contribute to the melting of membranes
Written by Allie Arp
Photo by Arlie Yruma
The project, titled “Local Atomic-level Thermodynamic Probe for Nanoscience of 2D Membranes: Synthesis, NMR and Nanocalorimetry Study,” is built upon previous research Allen and group have conducted, with a twist. This twist is the inclusion of the nuclear magnetic resonance (NMR) technique into the calorimetry study of small material.
In nanoscience, small changes in the structure of 2D AgSCn membranes can create big differences in their melting temperature, in some cases a change in more than 120°F. These changes are large with respect to other 2D membranes such as the lipid membranes that form the outer layer of biological cells. In the case of human survival, the body temperature is limited to a narrow range between 60°F and 105°F.
“This research is venturing out there a little beyond our comfort zone.” said Allen, an emeritus professor in the materials science and engineering department.
Besides NMR, Allen’s group employs nanocalorimetry in their research. Nanocalorimetry was invented by Allen’s group and has the capability of measuring small material. It can measure single-layer membranes less than two nanometers thick as well as nanometer size magic number metal clusters.
NMR adds new possibilities for research at a very small scale. While nanocalorimetry can determine average thermodynamic values, it is blind to depth perception. NMR has the ability to distinguish one atom from another and is based on the same physics as the common medical technology, MRI. MRI scans allow doctors to distinguish between bone and muscle tissue based on the different molecular environment. However, NMR used in this research uses the chemical shift of carbon atoms to distinguish, on the microscopic atomic level, one atom from another, allowing its location within the crystal to be identified.
Allen and his group, along with Andre Schleife, materials science and engineering professor at Illinois, plan to construct an energy landscape map of material using this experimental process of combining calorimetry with NMR and computational material science. The model produced by the team will allow for researchers to predict the outcome of a combination of elements within the membrane prior to combining them. Modelling would save time, research dollars and open up new pathways, which may be difficult to do experimentally.
“People ask ‘Who works in nanometers?’ ” Allen said. “Those of us who work in nanoelectronics have always been dealing on the nanometers scale. We scale devices down to nanometer-size to make things faster, and faster is everything!”
One common example of nanometer use is in modern electronics. As components of electronic devices get smaller, materials that make electrical contacts to the transistor become unusable as small sizes. In another example, according to textbooks, the element Indium melts at 156°C. However, through lab work, Allen and his group discovered that if the size of indium is decreased down to two nanometers, it melts at room temperature, 20°C.
“Our goal is to connect the reading signatures of individual atoms with our work in heat (calorimetry) measurements,” Allen said. “This has never been done systematically before to our knowledge, connecting NMR with calorimetry, and will be a new breakthrough.”
The new research is based upon a recent breakthrough by Allen’s former student, Zichao Ye, who won the Materials Research Society Graduate Student Silver Award for this research in 2017.
In addition to the research aspect, each NSF proposal includes a “Broader Impact” component that helps bring science to a larger audience. For the last five years, Allen, his wife Joy, and several students have traveled to Browning, Montana, to give groups of middle and high-school students on the Blackfeet Reservation a hands-on science experience focusing on building solar and wind energy kits as part of a science camp.
For Allen, the experience is as personally rewarding for him as it is for the students.
“Going into a community that is culturally different allows us to rethink what we are doing here,” Allen said. “It teaches us something new and moves us out of our comfortable trenches. It is refreshing.”
The community college on the Blackfeet Reservation is unique because it offers pre-engineering and nursing programs. One of the goals of Blackfeet Community College is to encourage more Native American interest in the sciences. It recently opened a new math and sciences building to attract more students.