Two-dimensional materials skip the energy barrier by growing one row at a time

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December 6, 2018

The peptides in this highly ordered two-dimensional array avoid the expected nucleation barrier by assembling in a row-by-row fashion.PNNL

A new collaborative study led by a research team at the Department of Energy’s Pacific Northwest National Laboratory, University of California, Los Angeles and the University of Washington could provide engineers new design rules for creating microelectronics, membranes and tissues, and open up better production methods for new materials. At the same time, the research, published online Dec. 6 in the journal Science, helps uphold a scientific theory that has remained unproven for over a century.
Just as children follow a rule to line up single file after recess, some materials use an underlying rule to assemble on surfaces one row at a time, according to the study.
Nucleation — that first formation step — is pervasive in ordered structures across nature and technology, from cloud droplets to rock candy. Yet despite some predictions made in the 1870s by the American scientist J. Willard Gibbs, researchers are still debating how this basic process happens.
The new study verifies Gibbs’ theory for materials that form row by row. Led by UW graduate student Jiajun Chen, working at PNNL, the research uncovers the underlying mechanism, which fills in a fundamental knowledge gap and opens new pathways in materials science.
Chen used small protein fragments called peptides that show specificity, or unique belonging, to a material surface. The UCLA collaborators have been identifying and using such material-specific peptides as control agents to force nanomaterials to grow into certain shapes, such as those desired in catalytic reactions or semiconductor devices. The research team made the discovery while investigating how a particular peptide — one with a strong binding affinity for molybdenum disulfide — interacts with the material.
“It was complete serendipity,” said PNNL materials scientist James De Yoreo, co-corresponding author of the …

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