Page 7 - CEMS Newsletter Fall 2023

FACULTY NEWS
Faculty promotions
Newly-promoted faculty share research updates.
Effective Fall semester 2023, Xiang Cheng and David Flannigan were promoted to the rank of professor. They share their research updates below.
David Flannigan
Flannigan’s research focuses on the development and application of advanced transmission electron microscopy technologies and instrumentation. He is one
of the pioneers of ultrafast electron microscopy, or UEM, which aims to increase the time resolution of electron microscopes by ten orders of magnitude to the femtosecond scale. Flannigan’s team
Xiang Cheng
Xiang Cheng
uses ultrashort-pulsed lasers
that they interface with
electron microscopes to gain high-precision control
over the electron beam. With this high level of control, they were the first to directly image coherent strain waves, called phonons, moving through materials. This required reaching combined nanometer (10-9 meters)
and picosecond (10-12 seconds) resolutions with UEM. They are now expanding the application space of this instrumentation. For example, they have recently directly imaged ultrafast phase transformations in ferroelectric- dielectric superlattice structures, and they have demonstrated that using a pulsed electron beam can reduce the damage done to specimens during inspection. This latter discovery has generated a great deal of attention from both academia and industry – several groups are now working to apply the method to a wide range of materials, including biological specimens, which are especially prone to electron-beam damage. Indeed, such pulsed-beam capabilities are now being included in commercial aberration-corrected electron microscopes.
The Cheng group studies soft matter physics, biophysics and fluid mechanics. Their research is driven by fundamental questions in statistical and biological physics, as well as engineering issues related to the design and processing
of soft and bio-materials.
They employ state-of-the-art imaging techniques including high-speed photography, confocal microscopy and digital holographic microscopy to image fluid flow at small spatial
David Flannigan
scales and fast time scales. By integrating the concepts from transport phenomena, statistical and thermal physics, colloidal and interfacial science, rheology and biochemical engineering, the Cheng group develops quantitative understandings of the intriguing flow behaviors of soft matter and bio-materials under both equilibrium and non-equilibrium conditions. Specifically, the Cheng group focuses on three research topics. (i) Locomotion of microorganism. The locomotion of microorganisms in fluid media plays a central role in many biological phenomena. The research at the Cheng group is to understand
the physical principles and resolve the microscopic
flow structures governing the locomotion of various microorganisms. (ii) Collective dynamics of active fluids. Active fluids are dispersions of self-propelled particles with examples including flocking animals, suspensions of motile bacteria, and assays of motor-driven cytoskeletal filaments. The group’s research aims to reveal the emergent collective dynamics in these nonequilibrium systems. (iii) Drop impact. The group studies the dynamics of drop impact and helps to improve industrial practices in printing and coating.
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