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Zhenyu Zhang's blog

P as the Optimal Inhibitor for Suppressing Surface Electromigration and Electrical Breakdown at the Source

Based on an extensive search across the periodic table utilizing first-principles density functional theory, we discover phosphorus to be an optimal surface electromigration inhibitor on the technologically important Cu(111) surface-the dominant diffusion pathway in modern nanoelectronics interconnects. Unrecognized thus far, such an inhibitor is characterized by energetically favoring (and binding strongly at) the kink sites of step edges.

Bridging the gap with a "stepping stone" for more solar energy

Converting the abundant energy from the sun into a form convenient for human use has been a long standing dream for sustainable generation of environmentally clean energy.  With the seminal discovery of water splitting by Fujishima and Honda in the early 1970s [1], titanium dioxide (TiO2), an inexpensive white pigment widely used in our daily life, emerged as the premier photocatalysts for enabling solar energy utilization. However, because of its wide intrinsic band gap, TiO2 can absorb only ultraviolet light. This results in less than 1% efficiency for solar energy conversion. Reducing the band gap of TiO2 is the main avenue for boosting the conversion efficiency. In a recent paper to appear in Phys Rev. Lett. [2], Zhu et

A strained film grown on a vicinal substrate: Steps bunch or not to bunch?

When a strained film is grown on a vicinal substrate, the steps advance like a train when the deposited atoms have sufficient mobility to reach the step edges. However, as the steps advance, the strain-induced force monopoles associated with the steps cause the steps to attract to each other (J. Tersoff, PRL 74, 4962, (1995)), resulting in a thermodynamic instability of the steps in the form of step bunching (J. Tersoff, et al., PRL 75, 2730 (1995)).

A "cool" way to remove hydrogen...and possibly a faster way to grow better crystals?

In growth of essentially every compound material such as GaN, one element always diffuses faster than the other(s) at the growth front. To grow good-quality materials, even the most sluggish element has to be sufficiently mobile, forcing materials growers to go to higher growth temperatures.

No need to worry about gravity at the atomic-/nano-scale

When a metal is grown onto a substrate of itself (homoepitaxy), the growth front is typically smooth, or at most is roughened by the formation of shallow hills (called surface mounds). The underlying reason for the roughening has been recognized to be of kinetic nature: Atoms landed on an upper terrace do not have enough time to overcome the "road blocks" provided by the steps and fill all the valleys (known as the Villian instability).

Quantum Stability of Metallic Thin Films and Nanostructures

When a metal system shrinks its dimension(s), the conduction electrons inside the metal feel the squeezing, and are forced into (discrete) quantum states. Such confined motion of the conduction electrons may influence the global or local stability of the low dimensional systems, and in the case of a thin film on a foreign substrate this "quantum energy" of electronic origin can easily overwhelm the strain effects in definging the film stability, thereby severely influencing the preferred growth mode (see, e.g., Suo and Zhang, Phys. Rev. B 58, 5116 (1998)).

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