Laboratory for Surface Modification (LSM)

Seminars Archives

August 2017 | September 2017 | October 2017

Thursday, September 07, 2017

Nan Yao
Princeton University
12:00 Noon CHEM 260
Thursday, September 14, 2017
Tetrahedral Transition Metal Chalcogenides as Functional Inorganic Materials
Efrain Rodriquez
Chemistry and Biochemistry
University of Maryland
12:00 Noon CHEM 260

Transition metal dichalcogenides (TMDs) have resurfaced as functional inorganic materials for their diverse applications including transistor-type devices, sensors, and hydrogen evolution catalysis. We present a more recent category of layered materials we term tetrahedral transition metal chalcogenides (TTMCs) that display different functional behavior from TMDs. These layered TTMCs are built of square metal lattices with electron rich transition metals such as Fe(II) and Co(II) in tetrahedral coordination. Due to the weak van der Waals interactions that hold the chalcogenide layers together, intercalation chemistry in aqueous solutions can be utilized to prepare new phases with interesting magnetic and electronic properties including ferromagnetism and superconductivity. Our group’s strategy has been to incorporate guest species into the TTMC hosts to tune the physical properties. We construct a simple bonding model to interpret the electronic structure of the square metal lattice in TTMCs, and use it to predict the properties of future phases. Furthermore, we demonstrate that these layered metal chalcogenides could be made into novel two-dimensional (2D) materials either as single layers or as heterostructures with other 2D motifs.
Thursday, September 21, 2017
Wetting In Color Kit (WICK)
Joanna Aizenberg
Harvard University
12:00 Noon CHEM 260

“Colorimetric litmus tests such as pH paper have enjoyed wide commercial success due to their inexpensive production and exceptional ease of use. Many such techniques operate based on a chemical tag whose optical absorption or fluorescence spectrum changes in response to a specific analyte. Specificity is an advantage in this case, but limits the variety of substances for which such a sensor can be used. On the other hand, the use of structural color has no inherent specific chemical requirements. Thus, tunable structural color carries the potential for broad applicability in colorimetric sensing.

We developed a technique for patterning multiple chemical functionalities throughout the inner surfaces of a highly ordered iridescent 3D photonic crystal, generating complex wettability patterns. When immersed in a liquid, the pores are selectively infiltrated in a unique spatial pattern, creating an optical fingerprint of that liquid through the color contrast between wetted and non-wetted regions. Using this platform, we have illustrated multilevel encryption, with selective decoding by specific liquids. A remarkable selectivity of wetting, combined with the easily detectable optical response, allow us to also exploit this system as a colorimetric indicator for liquids. Moreover, by functionalizing the surfaces with an environment-sensitive groups and observing the changes in the wetting behavior, we can follow the history of the exposure of the material to a certain stimulus. WICK may find applications in a broad range of technologies, including a convenient and direct method for liquid detection and encryption, or as a tag for low-cost monitoring of tampering or material aging.”
Thursday, September 28, 2017
Advanced Nanostructures for Electrocatalytic Applications
Chao Wang
Chemical and Biomolecular Engineering
John Hopkins University
12:00 Noon CHEM 260

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