Breakthrough Computational Models for Nanofluidics, NEMS

Molecular and Electronic Nanostructures Co-chair Narayana Aluru recently reported on two important new findings in areas of nanoscale research. The papers involve innovative computational methods for analysis and design in the areas of nanoelectromechanical systems (NEMS) and in nanofluidics.

In the area of nanofluidics Aluru and his collaborators made the counter-intuitive discovery that on a graphite surface for low surface coverage, longer molecules diffuse faster compared to shorter molecules, giving scientists and others working in areas such as nanomanufacturing new insight into how molecules behave on very small surfaces.

In a paper published in Chemical Physics Letters this year called Surface diffusion of n-alkanes: Mechanisms and anomalous behavior, Aluru and his collaborator, Jae Park, reported on using molecular dynamics simulations to report this novel finding that has implications for applications such as deposition of polymers on surfaces, an important topic in manufacturing at the nanoscale.

"In the area of nanofluidics, one of our goals is to understand how fluids behave when you have tiny spaces or surfaces," Aluru said. "Diffusion is an important physical mechanism and understanding how a single molecule or a few molecules diffuse on a surface is a critical question in nanofluidics."

To read the paper, click here.

Aluru also reported recently on the development of new multiscale algorithms that seamlessly combine heterogeneous quantum-mechanical models with semi-classical and classical models for electrostatic and mechanical analysis of NEMS.

Published in Physical Review B earlier this year, Aluru and his collaborator, Yang Xu, related their discovery in a paper titled Multiscale electrostatic analysis of silicon nanoelectromechanical systems (NEMS) via heterogeneous quantum models.

Aluru said these new computational tools provide the accuracy capabilities of quantum mechanical analyses (without that method's computational limitation to small structures) and the speed of classical/semi-classical theories (with a degree of accuracy that these theories lack when applied to small structures).

"Quantum mechanical analysis is usually quite accurate but limited to very small structures," Aluru said. "If you want to apply those to large structures it becomes impossible computationally. On the other hand, classical and semi-classical theories are very fast but when you start applying them to smaller structures you can lose the accuracy. So you have a theory which is fast but can be inaccurate and you have something that is accurate but not practical."

Aluru said their theory combines the best aspects of both models.

"We have developed this theory where you can mix these length scales and you will get the accuracy and the speed," he said. "This multiscale method is the first one developed for NEMS. What this means is now that we have these tools we should be able to understand the physics of NEMS devices in detail that we haven't been able to before."