Periodic Reporting for period 1 - 2D_PHOT (Two Dimensional Materials for Photonic Devices)
Reporting period: 2020-03-16 to 2022-03-15
European commission, recently, have proposed a set of measures for achieving technological leadership in semiconductor technologies and applications. Chips are strategic assets for key industrial value chains and semiconductors are also at the centre of strong geopolitical interests, conditioning countries capacity to act and drive digital. Manufacturing these optoelectronic devices at an industrial scale raises concerns at technological, economic, environmental and political levels. Scientific research focuses on new-generation semiconductors to generate inexpensive and highly efficient photodetectors and photonic devices. This is where this Marie Skłodowska Curie Action (MSCA) project, entitled “Two Dimensional Materials for Photonic Devices (2D_PHOT)” focus on. The project has had a clear perspective regarding this scenario, searching for alternatives to typical material for photovoltaics designing flexible devices based on two dimensional materials. In this context two-dimensional transition metal dichalcogenides (TMDCs), such as MoS2 or MoSe2, appear promising since these materials feature long-term stability and have direct band gap as monolayers, and can be used in electronics as transistors and in optics as emitters and detectors.
The work on TMDCs monolayers is an emerging research and development field since the discovery of the direct bandgap and their potential applications in electronics and valley physics TMDCs are often combined with other 2D materials like graphene and hexagonal boron nitride to make van der Waals heterostructure. These heterostructures need to be optimized to be possibly used as building blocks for a plenty of different devices such as transistors, solar cells, LEDs, photodetectors, fuel cells, photocatalytic or chemical and biosensing devices. However, for photovoltaics, limited thickness absorption constitutes a general challenge for these two-dimensional materials.
The project roadmap included the design, fabrication and characterization of photonic/plasmonic nanostructured based on transition metal dichalcogenides to overcome this limitation integrating photonic design. So, the obtained results have shown that the fabricated nanostructures increase the absorption performance of these TMDCs materials, but also are useful for the designed optical devices as polarizers or transparent electrodes.
The work on TMDCs monolayers is an emerging research and development field since the discovery of the direct bandgap and their potential applications in electronics and valley physics TMDCs are often combined with other 2D materials like graphene and hexagonal boron nitride to make van der Waals heterostructure. These heterostructures need to be optimized to be possibly used as building blocks for a plenty of different devices such as transistors, solar cells, LEDs, photodetectors, fuel cells, photocatalytic or chemical and biosensing devices. However, for photovoltaics, limited thickness absorption constitutes a general challenge for these two-dimensional materials.
The project roadmap included the design, fabrication and characterization of photonic/plasmonic nanostructured based on transition metal dichalcogenides to overcome this limitation integrating photonic design. So, the obtained results have shown that the fabricated nanostructures increase the absorption performance of these TMDCs materials, but also are useful for the designed optical devices as polarizers or transparent electrodes.
In the framework of 2D_PHOT, great effort was invested in controlling the nanostructuring of MoSe2. Our results show that it is possible to modify a regular thin film and fabricate a super-absorber photonic crystal through of the simple, safe and fast method of laser ablation. We optimized, in this project, the parameters used on laser patterning lithography for different transition metal dichalcogenides in order to avoid surface debris and excessive heat which modifies the chemical structure of the sample.
So, we have fabricated a squared array of holes in a MoSe2 thin film over a Mo metallic foil substrate. This array has a lattice period of 450 nm and a diameter of the holes of 360 nm to optimize the absorption in a broadband range in the visible and near infrared (450 nm to 850 nm).
Integrating the absorbing experimental results of our fabricated photonic nanostructure, we notice an absorption around 90% that corresponds an enhancement over flat reference of 42%. This device is robust with the angle incidence and the spectral features are in excellent agreement with computational calculations based on finite difference time domain method.
In other part of the project selected nanostructures were designed for extraordinary transmission in continuous metallic thin films based on TMDC/metal /TMDC. We made a study for different materials and geometrical configurations obtaining maximum values of transmission around 90%. The region of the transmission can be tuned by modifying their geometric parameters can be used in the telecommunications range. These configurations show high transmission independently of the angle of incidence up to 70º. And introducing a SiO2 layer between the TMDC and metal can be obtained a broadband range for transmission. Also, a period of nanostructured lines can be suitable as a polarizer in the infrared range. Finally, as a proof of concept, we fabricated and measured a system composed of PDMS-MoS2-Au-MoS2-PDMS obtaining values of transmission of 60% in a broadband range of wavelengths in the near infrared and peaks of 70% of transmission for a 30 nm thick gold layer and a sheet resistance of 5 Ω/sq.
Finally, we developed a nanostructure to enhance the photoluminescence intensity of two-dimensional monolayers of transition metal dichalcogenides based on plasmonic supercrystal arrays. These plasmonic supercrystal arrays are deposited on top the monolayers by means of a template-assisted assembly of gold nanospheres with patterned polydimethylsiloxane molds (PDMS). These supercrystals arrays consist on square arrays of hexagonally packed gold nanoparticles (50 nm of diameter) which exhibit well-defined surface lattice resonance modes that can be tuned from the visible through the near-infrared by simple variation of the lattice parameter. This tunability can be used to enhance the photoluminescence emission of different transition metal dichalcogenides monolayers. So, as proof of concept, the photoluminescence signal of the monolayer MoS2 and MoSe2 can be significantly enhanced up to 5-6-fold coupling the frequency of the surface lattice resonance of the plasmonic supercrystal to the frequency emission of the transition metal dichalcogenides monolayer. These systems could be suitable for mechanisms of plasmon-resonance driven generation and injection of hot electrons for current generation.
The dissemination of the project results was carried out in different ways: At the educational outreach level, we participated in a workshop within the framework of the European Researchers Night in the Altice Forum of Braga. On the other hand, some of the results obtained during the project have been presented in conferences and symposia, have been submitted for publication, or are currently under preparation.
So, we have fabricated a squared array of holes in a MoSe2 thin film over a Mo metallic foil substrate. This array has a lattice period of 450 nm and a diameter of the holes of 360 nm to optimize the absorption in a broadband range in the visible and near infrared (450 nm to 850 nm).
Integrating the absorbing experimental results of our fabricated photonic nanostructure, we notice an absorption around 90% that corresponds an enhancement over flat reference of 42%. This device is robust with the angle incidence and the spectral features are in excellent agreement with computational calculations based on finite difference time domain method.
In other part of the project selected nanostructures were designed for extraordinary transmission in continuous metallic thin films based on TMDC/metal /TMDC. We made a study for different materials and geometrical configurations obtaining maximum values of transmission around 90%. The region of the transmission can be tuned by modifying their geometric parameters can be used in the telecommunications range. These configurations show high transmission independently of the angle of incidence up to 70º. And introducing a SiO2 layer between the TMDC and metal can be obtained a broadband range for transmission. Also, a period of nanostructured lines can be suitable as a polarizer in the infrared range. Finally, as a proof of concept, we fabricated and measured a system composed of PDMS-MoS2-Au-MoS2-PDMS obtaining values of transmission of 60% in a broadband range of wavelengths in the near infrared and peaks of 70% of transmission for a 30 nm thick gold layer and a sheet resistance of 5 Ω/sq.
Finally, we developed a nanostructure to enhance the photoluminescence intensity of two-dimensional monolayers of transition metal dichalcogenides based on plasmonic supercrystal arrays. These plasmonic supercrystal arrays are deposited on top the monolayers by means of a template-assisted assembly of gold nanospheres with patterned polydimethylsiloxane molds (PDMS). These supercrystals arrays consist on square arrays of hexagonally packed gold nanoparticles (50 nm of diameter) which exhibit well-defined surface lattice resonance modes that can be tuned from the visible through the near-infrared by simple variation of the lattice parameter. This tunability can be used to enhance the photoluminescence emission of different transition metal dichalcogenides monolayers. So, as proof of concept, the photoluminescence signal of the monolayer MoS2 and MoSe2 can be significantly enhanced up to 5-6-fold coupling the frequency of the surface lattice resonance of the plasmonic supercrystal to the frequency emission of the transition metal dichalcogenides monolayer. These systems could be suitable for mechanisms of plasmon-resonance driven generation and injection of hot electrons for current generation.
The dissemination of the project results was carried out in different ways: At the educational outreach level, we participated in a workshop within the framework of the European Researchers Night in the Altice Forum of Braga. On the other hand, some of the results obtained during the project have been presented in conferences and symposia, have been submitted for publication, or are currently under preparation.
We would like to point out that the nanostructuration of TMDC thin films studied and developed in the project 2D_PHOT overcame the low absorption due to the limitation thickness, having direct impact in the photovoltaic technology. Also other research and technological areas can profit from its implementation could be high-sensitivity detection, photo-catalysis, etc. All these areas would very much profit from the knowledge gained in the project understanding plasmonic and photonic interactions involving high dielectric TMDC and metals nanostructures.
Also we have achieved a high efficient transparent electrode with a low sheet resistance. These attempts involve several benefits for solar tandem cell and photonic devices suitable to be used as a polarizer in the infrared range and in telecommunications.
Finally, an enhancement of the photoluminescence of these devices have been get interacting with metallic nanoparticles and incorporating plasmonic effects to these semiconducting materials making suitable for fabricating optoelectronic emitters.
From the socio-economical point of view, 2D_PHOT has contributed, to enhance the efficiency of photonic and optoelectronic devices in the network of developing semiconducting chips.
Also we have achieved a high efficient transparent electrode with a low sheet resistance. These attempts involve several benefits for solar tandem cell and photonic devices suitable to be used as a polarizer in the infrared range and in telecommunications.
Finally, an enhancement of the photoluminescence of these devices have been get interacting with metallic nanoparticles and incorporating plasmonic effects to these semiconducting materials making suitable for fabricating optoelectronic emitters.
From the socio-economical point of view, 2D_PHOT has contributed, to enhance the efficiency of photonic and optoelectronic devices in the network of developing semiconducting chips.