Thermal manipulation of plasmons in atomically thin films

July 21, 2020

Surface plasmons in graphene have been widely studied in the past decade due to their very appealing properties, such as the strong tunability of its optical properties through electrical gating and the relatively high plasmon lifetime. However, these exceptional properties are limited to lower frequencies ranging from the mid-infrared (mid-IR) to the terahertz (THz) spectral regions. Additionally, electrical tunability of graphene cannot be achieved in an ultrafast manner, what poses an obstacle for its application in high-speed technological devices that are becoming increasingly important.

In a new paper published in Light Science & Application, a team from ICFO-Institut de Ciencies Fotoniques (Barcelona, Spain) has proposed an all-optical technique to modulate the plasmonic response of graphene- and/or thin-metal-based systems in an ultrafast manner, in a spectrum ranging from mid-infrared to visible (vis-NIR) frequencies. They propose a pump-probe setup where an ultrafast and very intense pump beam is used to heat the electrons of the graphene. Based on the low heat capacity of this 2D material -meaning that a small amount of energy absorbed by this material can induce a large increase in the temperature of its electrons- and on the strong dependence of graphene's conductivity with its electronic temperature, the optical properties of the system will be modulated by the electronic temperature increase, and this can be measured by the probe beam.

Interestingly, this technique can be used to all-optically excite plasmons not only in the graphene sheet, but also in a thin metallic layer placed nearby it. Following a previous work by the same group, they propose to do so by engineering a pump beam such that its wave-front intensity varies spatially in a periodic manner. As such, the electronic temperature in graphene (and subsequently its conductivity) also varies locally in the surface of the sheet, acting as an effective grating that scatters the probe beam and couples it into plasmons. Depending on the wavelength of the probe beam and the presence of a metallic thin film nearby the graphene sheet, this technique can be used to excite either graphene plasmons (mid-IR), metallic plasmons (vis-NIR) or hybrid acoustic plasmons (THz). "In this way, one can excite and manipulate plasmons in a wide spectral range without the need for lateral patterning or using external devices, like SNOM tips, to couple propagating light into plasmons" the authors added.

On a different note, the authors propose to employ nanoscale photothermal effects in order to achieve ultrafast modulation of light. They envision a structure composed of a thin metallic grating on top of a graphene sheet doped to some Fermi level. Then, by increasing the temperature of the graphene electrons via a pump beam, the chemical potential of graphene will decrease, and the interband transitions in graphene will become significant at lower energies, and will quench the plasmonic peak measured by the reflection of a probe beam. "The temperature of graphene electrons can achieve several thousands of Kelvins, resulting in a damping of the reflection peak up to 70%", the authors claim. A similar effect can be observed in graphene acoustic plasmons, but in this case the reason for the quenching is the increasing of the graphene inelastic losses with the electronic temperature. "In both cases, the modulation of the optical response is ultrafast, unlike alternative ways to modulate the response, such as electrically changing the Fermi level of graphene", the authors added.

"Our study opens a promising avenue toward the active photothermal manipulation of the optical response in atomically thin materials with potential applications in ultrafast light modulation", the authors conclude.
-end-


Light Publishing Center, Changchun Institute of Optics, Fine Mechanics And Physics, Chinese Academy

Related Graphene Articles from Brightsurf:

How to stack graphene up to four layers
IBS research team reports a novel method to grow multi-layered, single-crystalline graphene with a selected stacking order in a wafer scale.

Graphene-Adsorbate van der Waals bonding memory inspires 'smart' graphene sensors
Electric field modulation of the graphene-adsorbate interaction induces unique van der Waals (vdW) bonding which were previously assumed to be randomized by thermal energy after the electric field is turned off.

Graphene: It is all about the toppings
The way graphene interacts with other materials depends on how these materials are brought into contact with the graphene.

Discovery of graphene switch
Researchers at Japan Advanced Institute of Science and Technology (JAIST) successfully developed the special in-situ transmission electron microscope technique to measure the current-voltage curve of graphene nanoribbon (GNR) with observing the edge structure and found that the electrical conductance of narrow GNRs with a zigzag edge structure abruptly increased above the critical bias voltage, indicating that which they are expected to be applied to switching devices, which are the smallest in the world.

New 'brick' for nanotechnology: Graphene Nanomesh
Researchers at Japan advanced institute of science and technology (JAIST) successfully fabricated suspended graphene nanomesh (GNM) by using the focused helium ion beam technology.

Flatter graphene, faster electrons
Scientists from the Swiss Nanoscience Institute and the Department of Physics at the University of Basel developed a technique to flatten corrugations in graphene layers.

Graphene Flagship publishes handbook of graphene manufacturing
The EU-funded research project Graphene Flagship has published a comprehensive guide explaining how to produce and process graphene and related materials (GRMs).

How to induce magnetism in graphene
Graphene, a two-dimensional structure made of carbon, is a material with excellent mechani-cal, electronic and optical properties.

Graphene: The more you bend it, the softer it gets
New research by engineers at the University of Illinois combines atomic-scale experimentation with computer modeling to determine how much energy it takes to bend multilayer graphene -- a question that has eluded scientists since graphene was first isolated.

How do you know it's perfect graphene?
Scientists at the US Department of Energy's Ames Laboratory have discovered an indicator that reliably demonstrates a sample's high quality, and it was one that was hiding in plain sight for decades.

Read More: Graphene News and Graphene Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.