Near-field plasmonics served as a support system to explore single-molecule spectroscopy, quantum information processing, and cavity quantum electrodynamics whose study critically requires control over light, heat, and charge at the nanoscale level.
Study: Nanoheating and Nanoconduction with Near-Field Plasmonics: Prospects for Harnessing the Moiré and Seebeck Effects in Ultrathin Films. Image Credit: Yurchanka Siarhei/Shutterstock.com
Nanoresonators and near-field transducers (NFTs) allow the sub-diffraction of light below the classical diffraction limit via the coupling of photon-plasmonic modes. An article published in the journal Advanced Optical Materials theoretically demonstrated the possibility of modulating the light, heat, and current by utilizing the NFT when incident on layers of black phosphorous (BP).
Furthermore, the moiré physics of two films with relative rotations and the Seebeck effect was investigated for which the temperature gradients were induced by an electrical voltage. The results revealed these methods could regulate the temperature distribution effectively with values between 101 and 102 Kelvin, which is critical in many nanodevices. In addition, the directional flow of current was manipulated, helping in electrical switching and output steering of energy.
Moiré and Seebeck Effect
Nanoplasmonics is an up-and-coming research topic and is a convenient approach to producing noisy intermediate-scale quantum (NISQ) devices at room temperature. It leverages its ultrafast dynamics and plasmonically coupled quantum emitter’s low decoherence rates. These characteristics are prerequisites for fabricating quantum networks, including logic gates, memories, and many more.
The moiré effect is a physical phenomenon of linear optics. Moiré patterns arise from the superposition of two (or more) similar but slightly offset templates over flat (or curved) surfaces in which one (or more) is rotated, translated, or subjected to any form of altercation from the initial position. This results in a series of periodic dark/bright fringes whose characteristics are determined by the period, orientation, and shape of the patterned samples.
When two arrays of similar periods are superposed, the period of the resultant pattern acts like a magnifier of the original period. The Moiré effect has been used in different areas, including microscopy, cryptography, profilometry, and material stress evaluation.
Recently, moiré superlattices formed because of the peculiar stacking sequence between neighboring layers in 2D heterojunctions represent a regular modulation of interlayer interactions and contribute to an extra degree of freedom for manipulating the electronic structure of 2D materials.
The Seebeck effect induces voltage and produces electric current due to a temperature gradient. This effect is commonly used in devices for biosensing and solar energy harvesting at the industrial level to investigate this effect on the nanoscale.
Moiré and Seebeck Effects in Ultrathin Films
The advancements in cancer treatments, data storage devices, and photovoltaic and solar cell technology will require the manipulation of heat and current at the nanoscale level. In the present work, two methods were reported to tune current and heat in ultrathin films using Seebeck or Moiré effects that were executed via near-field plasmonics.
Owing to the outstanding optical and thermal conductivities, ultrathin films, and transition metal dichalcogenides (TMDCs) were considered substrates of interest with several applications in thermoelectric and optoelectronic nanodevices. Recently, BP and single atomic layer phosphorene were considered as materials for these nanodevices.
Here, thin-film BP was measured to have Seebeck coefficients between 102 and 103 microvolts per kelvin and was comparable to TMDCs that could convert heat fluxes to electrical current. Besides the Seebeck effect, the Moiré effect was also investigated in terms of dispersing light, heat, and current.
The studies conducted in the present work examined how the Moiré effect was harnessed to control nanoheating and subsequent conversion to electric currents in two overlapping ultrathin films. In particular, the current work focused on ultrathin films of BP with a few atomic layers based on previous reports and an understanding of the benefits of BP for emerging technologies and the high degree of tunability of its optical and electrical properties.
The changes in the spatial distribution of current and temperature observed in the present work originated from intrinsic anisotropy of BP films, along with their strong thermoelectric response manifested due to extreme temperature gradients that were realized via nanoheating with NFTs.
To summarize, the potential of NFT in controlling the conduction of charges at the nanoscale level and nanoheating via the Seebeck and Moiré effects were reported. Additionally, the Peltier effect was studied for Onsager reciprocity and anisotropic Seebeck coefficients using a few-layer BP at high temperatures.
In addition to alterations in the spatial distribution of current and temperature, the maximum values of each may be tuned based on the experimental requirements. Moreover, the possibility of steering directional output from the ultrathin films using the Moiré effect was demonstrated.
Unlike previously used nanoresonators for manipulating heat on the nanoscale, the use of NFT was emphasized to be unintegrated with the media. The present work also highlighted that BP could degrade even at room temperature, altering the Peltier and Seebeck response. Besides BP, other two-dimensional (2D) materials with similar electrical and thermal conductivity parameters were anticipated to be interesting candidates for further investigation.
Bello, F. D., Clarke, D. D. A., Tarasenko, I., Donegan, J. F., Hess, O. (2022). Nanoheating and Nanoconduction with Near-Field Plasmonics: Prospects for Harnessing the Moiré and Seebeck Effects in Ultrathin Films. Advanced Optical Material. https://onlinelibrary.wiley.com/doi/10.1002/adom.202201358