Paper Outlines First Observation of Nano-scale Phenomenon


Toby Weber

The defining characteristic of nanotechnology, where devices and their features are measured in billionths of a meter, is size. But size isn’t the only thing that sets the nano-realm apart. Materials and devices can behave differently – startlingly differently even – at the nano-scale than they do when in larger forms.

Pradeep Sharma, chair and professor of mechanical engineering, has recently co-authored a paper that outlines one such phenomenon and provides a likely explanation for it.

The paper, which was published in a recent issue of the journal Nature Communications, involves a new breed of capacitor built out of nanowires. These devices were constructed in the lab of Rice University’s Pulickel Ajayan and Jun Lou, who led the project represented in the article.

Capacitors are energy storage devices widely used in electronics. While they have the ability to discharge energy very rapidly, their total energy storage ability is typically low.

It’s well known, though, that as capacitors are made smaller, their capacitance, or ability to store an electronic charge, increases per unit area.

So while researchers expected these nanowire devices to have high capacitance, they were surprised to find them storing far more energy than predicted. “The capacitance was almost fifty times larger than it should have been. At that point the question became why,” said Sharma.

Professors Ajayan and Lou approached Sharma, an expert in theoretical and computational modeling of the nanomaterials, to help interpret these experimental results. After detailed quantum mechanical modeling, Sharma and his students realized this higher-than-expected capacitance was a consequence of so-called negative quantum capacitance arising from the interface of the different materials in the nanowires, specifically a metal and a dielectric material.

When compared to classical capacitance, quantum capacitance adds up in such a way that its contribution is very small and usually neglected. On the nanoscale, however, quantum capacitance’s is quite influential. Usually, quantum capacitance is positive. The notable element in this study is that the results can only be explained by invoking the concept of negative quantum capacitance. By combining with classical capacitance, this negative capacitance actually produces the larger-than-expected results.

With the existence of negative quantum capacitance now confirmed, Sharma said that by tailoring the metal-dielectric interface researchers could leverage the phenomenon to create nano-devices with dramatically higher energy capacity.


Department/Academic Programs: 

Related News Stories

Non-Invasive Eye-Movement Sensors Developed by UH's Ryou

Jae-Hyun Ryou, Ph.D., an Associate Professor of the Mechanical Engineering Department at the University of Houston's Cullen College of Engineering, is the lead author for a new research article describing eye-movement sensors that can record data by less obstructive methods than previously thought.

23 honored with 2020-21 Faculty and Student Excellence Awards

The W.T. Kittinger Teaching Excellence Award is traditionally the highest teaching award given in the College. It recognizes outstanding teaching and service to students. This year's recipient is Di Yang of Mechanical Engineering.

The Cullen College of Engineering at the University of Houston and Dr. Joseph W. Tedesco, Ph.D., P.E., the Elizabeth D. Rockwell Endowed Chair and Dean, are pleased to share the 2020-21 Faculty and Student Excellence Award winners.

The initial announcement was made during the virtual Spring 2021 State of the College Address on May 4.

21 Cullen College students receive SURF opportunities

A group of 21 students from the Cullen College of Engineering have been selected for the University of Houston's Summer Undergraduate Research Fellowships.

The Cullen College of Engineering is proud to announce that 21 undergraduate students have been selected for the University of Houston's Summer Undergraduate Research Fellowship (SURF), according to the Honors College.

Upcoming Events / Seminars