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Hongtao Yuan researches electronic and optoelectronic behavior at material interfaces. His Nanjing University profile describes electric-field control of charge, spin and orbital behavior in low-dimensional systems and records his earlier Stanford work with Yi Cui and Harold Hwang.^[ref]

He also coauthored the indium tin oxide study of band nonparabolicity.^[ref] A basic experimental distinction in this field is between changing the number of carriers electrically and changing a material's chemical composition. Both can alter conductivity, but their structural effects and reversibility need not be the same. Comparing transport and optical response helps identify what has changed beyond a single resistance value.

By Xiaoge Liu, Junghyun Park, Ju-Hyung Kang, Hongtao Yuan, Yi Cui, Harold Hwang and Mark Brongersma. Applied Physics Letters 105, 181117 (2014). Figure 3: Hall measurements, carrier density, optical plasma frequency and mobility. Byline corroborated by Stanford SIMES: simes.stanford.edu/publications/quantum?page=21

Yi Cui develops nanomaterials and methods for studying their structure and behavior, with applications including lithium-ion batteries, catalysis and environmental technologies. His Stanford research description identifies this combination of material design and characterization.^[ref] He also coauthored the indium tin oxide study cited here.^[ref]

A useful geometric motivation for nanoscale design is that a sphere's surface-area-to-volume ratio is $3/r$. Reducing its radius tenfold increases that ratio tenfold, changing how much material lies near an interface. In an electrode, small dimensions can also shorten transport distances, while a greater exposed surface can increase unwanted reactions. Useful material design must therefore test the complete device behavior rather than assuming smaller features improve every property.