Molybdenum Disulfide Sees the Light

Plasmonics combined with MoS2 could lead to the material being useful in LED applications

2 min read
Molybdenum Disulfide Sees the Light
Illustration: Northwestern University

Roughly two years ago, researchers at MIT started to look at the potential of molybdenum disulfide (MoS2) for photovoltaic applications. The results were somewhat mixed. They saw relatively low conversion efficiency numbers, but were encouraged by the discovery that placing just three sheets of MoS2 into a one-nanometer-thick stack makes it possible to absorb up to 10 percent of incident sunlight. That’s an order of magnitude higher than gallium arsenide and silicon.

While that was indeed an encouraging development, it was far from enough to make anyone start clamoring for MoS2 to replace silicon in photovoltaics or other photonics uses.

Now researchers at Northwestern University have employed plasmonics in combination with MoS2, boosting its ability to absorb light as well as its photolumiscence.

Applying plasmonic nanostructures to photovoltaics is not new. Back in 2012, researchers at Princeton University developed a plasmonic nanostructure that, if incorporated in solar cells, would let them absorb 96 percent of the light that hit them and increase their conversion efficiency by 175 percent. 

Plasmonics exploits oscillations in the density of electrons that are generated when photons hit a metal surface. In addition to its use in photovoltaics, plasmonics has a number of other potential applications, including transmitting data on computer chips and producing high-resolution lithography.

In research published in the journal Nano Letters,  the Northwestern team used plasmonic silver nanodisc arrays that significantly increased the photoluminescence of the MoS2.

“We have known that these plasmonic nanostructures have the ability to attract and trap light in a small volume,” said Serkan Butun, a postdoctoral researcher, in a press release. “Now we’ve shown that placing silver nanodiscs over the material results in twelve times more light emission.”

This twelve-fold increase in light emissions is caused by the plasmonic resonance coupling to both the excitation and emission fields. This increases the interaction of light and matter at the nanoscale.

The researchers believe that this enhanced light emission could lead to MoS2 being used in light emitting diode applications.

“This is a huge step, but it’s not the end of the story,” said Koray Aydin, who led the research, in a press release. “There might be ways to enhance light emission even further. But, so far, we have successfully shown that it’s indeed possible to increase light emission from a very thin material.”

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3D-Stacked CMOS Takes Moore’s Law to New Heights

When transistors can’t get any smaller, the only direction is up

10 min read
An image of stacked squares with yellow flat bars through them.
Emily Cooper

Perhaps the most far-reaching technological achievement over the last 50 years has been the steady march toward ever smaller transistors, fitting them more tightly together, and reducing their power consumption. And yet, ever since the two of us started our careers at Intel more than 20 years ago, we’ve been hearing the alarms that the descent into the infinitesimal was about to end. Yet year after year, brilliant new innovations continue to propel the semiconductor industry further.

Along this journey, we engineers had to change the transistor’s architecture as we continued to scale down area and power consumption while boosting performance. The “planar” transistor designs that took us through the last half of the 20th century gave way to 3D fin-shaped devices by the first half of the 2010s. Now, these too have an end date in sight, with a new gate-all-around (GAA) structure rolling into production soon. But we have to look even further ahead because our ability to scale down even this new transistor architecture, which we call RibbonFET, has its limits.

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