Periodic Reporting for period 2 - DiSeTCom (Dirac Semimetals based Terahertz Components)
Periodo di rendicontazione: 2021-10-01 al 2023-12-31
DiSeTCom brings together experimentalists and theoreticians working in synergy to proof the concept and to build prototypes of components for THz photonics. Being based on 2D Dirac semimetals (graphene, silicene, germanene) and metamaterials paradigm, these components are capable to outperform the existing ones in terms tunability in integrated solutions. The project relied on solid theoretical background that has enabled finding of the constituent parameters of 2D semimetals with account for defects, doping, stacking, strain and biasing using ab initio and tight binding approaches. The advanced nanoelectromagnetics techniques were employed to reveal physical phenomena underlying the response of both individual Dirac semimetal based metaatoms and their arrays in the THz spectral range. From the experimental side, the DiSeTCom aimed at development of feasible and handy techniques for fabrication of metasurfaces based on Dirac semimetals that should lead to prototype of THz components with unprecedented performance. Robust design and sensitivity analysis has allowed us to address the innovation objectives of the project contributing to the European technological leadership through multisectorial and international cooperation supported by knowledge sharing. In the course of the project implementation special attention was paid to the personalized training of ESRs in topics and skills needed to succeed in their research carrier in photonics, nanofabrication and 2D materials domains.
123 person-months secondments have been executed, and the principal objectives of the project reached.
More than 80 articles, 33 of which involved two or more project teams, were published in high-impact international journals. Many other articles are in preparation or submitted.
Our scientific results include:
- The formation of silicene on graphene grown on graphitized 4H-SiC(0001) and on highly oriented pyrolytic graphite (HOPG) as template substrate was investigated. Synthesis route consists of evaporating silicon under ultrahigh vacuum conditions (UHV) keeping the substrate at room temperature. In the same experimental chamber, the samples were characterized with STM, STS and XPS. From the experiments and theoretical calculations, we observed three different stable configurations on HOPG: (i) formation silicene nanosheets, (ii) 3D clusters, and (iii) Si 2D nanosheets intercalated below the first top layer of carbon atoms
- The morphology of the Dirac meta-atoms was studied by combining SEM and optical microscopy techniques. This allowed us to reveal the dependence of the carbon shell thickness, roughness and porosity on the synthesis parameters. The continuity of the Dirac semimetals shells was investigated by using STM, AFM and HRTEM measurements. The electrical conductivity of the deposited shells was compared with that obtained for plane samples.
- We showed that smooth electron waveguides in tilted Dirac materials can be used to manipulate the degree of valley polarization of quasiparticles travelling along a particular direction of the channel. We examine the particular case of the hyperbolic secant potential to model realistic top-gated structures for valleytronic applications.
- We studied theoretically optical properties of emerging two‐dimensional (2D) materials and metamaterials with tilted Dirac cones in the electronic band structure and developed an optical recipe to fully characterize the tilt and Fermi velocity anisotropy of any 2D tilted Dirac cone solely from its absorption spectrum. We expect this work to encourage Dirac cone engineering as a major route to create gate-tunable thin-film polarizers.
- We have developed and characterized triboelectric nanogenerators consisting of triboelectric layers obtained from composite materials of (1) bamboo+starch and (2) bamboo+starch+graphene water suspensions. We observed that the addition of graphene improves the power density generation.
- The efficient ultra-thin electromagnetic absorber based on an array of multi-layered graphene hemispheres was fabricated by combining 3D ink-jet printing, electroplating and chemical vapor deposition processes. These submicron thick metasurfaces demonstrate almost perfect absorption, > 95%, in very broad frequency range. They are also robust against macroscopic structural defects, i.e. their electromagnetic properties remain the same when structure comprises up to 40% of randomly distributed holes and other geometrical imperfectness.
Dissemination:
more than 40 actions, including newspaper interviews, popular books, and dissemination at schools
Exploitation:
the following studies have been identified as under-development innovations with possible industrial/medical/societal/technological applications:
- Prototypes of tunable and ultrathin (less than 1 micron thick) THz lens and filters that outperform existing ones in terms of footprint
- The broadband absorbing graphene structures with extraordinarily aging and wear resistance that open a way for hostile environment applications
- The Si3N4 membrane enhanced with pyrolyzed graphitic 20 nm thick PyC film open new opportunities for design of novel ultrabroad band bolometric radiation detectors
- The C-shaped polymer metasurfaces with extraordinary focus performance capable to maintain focusiong ability when subjected to bending
- Graphene-enhanced THz grating fabricated by femtosecond micromachined SiO2 substrate
- The negligible influence of the grain size on the performance of the graphene-based metasurfaceces and metamaterials was demonstrated
More than 80 articles, 33 of which involved two or more project teams, were published in high-impact international journals. Many other articles are in preparation or submitted.
Our scientific results include:
- The formation of silicene on graphene grown on graphitized 4H-SiC(0001) and on highly oriented pyrolytic graphite (HOPG) as template substrate was investigated. Synthesis route consists of evaporating silicon under ultrahigh vacuum conditions (UHV) keeping the substrate at room temperature. In the same experimental chamber, the samples were characterized with STM, STS and XPS. From the experiments and theoretical calculations, we observed three different stable configurations on HOPG: (i) formation silicene nanosheets, (ii) 3D clusters, and (iii) Si 2D nanosheets intercalated below the first top layer of carbon atoms
- The morphology of the Dirac meta-atoms was studied by combining SEM and optical microscopy techniques. This allowed us to reveal the dependence of the carbon shell thickness, roughness and porosity on the synthesis parameters. The continuity of the Dirac semimetals shells was investigated by using STM, AFM and HRTEM measurements. The electrical conductivity of the deposited shells was compared with that obtained for plane samples.
- We showed that smooth electron waveguides in tilted Dirac materials can be used to manipulate the degree of valley polarization of quasiparticles travelling along a particular direction of the channel. We examine the particular case of the hyperbolic secant potential to model realistic top-gated structures for valleytronic applications.
- We studied theoretically optical properties of emerging two‐dimensional (2D) materials and metamaterials with tilted Dirac cones in the electronic band structure and developed an optical recipe to fully characterize the tilt and Fermi velocity anisotropy of any 2D tilted Dirac cone solely from its absorption spectrum. We expect this work to encourage Dirac cone engineering as a major route to create gate-tunable thin-film polarizers.
- We have developed and characterized triboelectric nanogenerators consisting of triboelectric layers obtained from composite materials of (1) bamboo+starch and (2) bamboo+starch+graphene water suspensions. We observed that the addition of graphene improves the power density generation.
- The efficient ultra-thin electromagnetic absorber based on an array of multi-layered graphene hemispheres was fabricated by combining 3D ink-jet printing, electroplating and chemical vapor deposition processes. These submicron thick metasurfaces demonstrate almost perfect absorption, > 95%, in very broad frequency range. They are also robust against macroscopic structural defects, i.e. their electromagnetic properties remain the same when structure comprises up to 40% of randomly distributed holes and other geometrical imperfectness.
Dissemination:
more than 40 actions, including newspaper interviews, popular books, and dissemination at schools
Exploitation:
the following studies have been identified as under-development innovations with possible industrial/medical/societal/technological applications:
- Prototypes of tunable and ultrathin (less than 1 micron thick) THz lens and filters that outperform existing ones in terms of footprint
- The broadband absorbing graphene structures with extraordinarily aging and wear resistance that open a way for hostile environment applications
- The Si3N4 membrane enhanced with pyrolyzed graphitic 20 nm thick PyC film open new opportunities for design of novel ultrabroad band bolometric radiation detectors
- The C-shaped polymer metasurfaces with extraordinary focus performance capable to maintain focusiong ability when subjected to bending
- Graphene-enhanced THz grating fabricated by femtosecond micromachined SiO2 substrate
- The negligible influence of the grain size on the performance of the graphene-based metasurfaceces and metamaterials was demonstrated
The fabricated metasurfaces showed record high microwave and THz absorption for structures of submicron thickness. The ab-initio numerical tools used in the project were modified to reveal the electronic and optical properties of a Dirac semimetal including graphene and silicene. Potential impact of our studies concerns the development of the novel ultrathin flexible THz and microwave absorbers for security, medicine and environmental applications.
We demonstrated that replacing flat substrate with 3D structured one can increase the THz absorptance from 50% to 80-90%. The presence of an additional graphene layer in the system makes it possible to significantly change the dispersion of the electromagnetic response and increase the overall absorption level, at low frequencies in particular.
The fabricated structured graphene films showed outstanding THz performance in terms of the absorbance and bandwidth. They are the best candidates for fabrication ultra-thin and ultra-light THz components. Our experiments and numerical simulations showed that these structures are tolerant with respect to the fabrication defects and doping level of graphene and suit well requirements for scaled fabrication of THz passive components including attenuators, filters and polarizers.
A simple versatile tool for the design and fabrication of graphene-enhanced passive devices based on the laser micromachining of graphene enhanced gold-plated dielectric substrates was proposed and tested in THz frequency range. The fabricated metasurface demonstrated almost perfect absorption in the broad THz range spanning over more than one decade from 100 GHz. The obtained transmittivity is four times lower than that achievable in the flat free standing graphene sheet of the same conductivity.
We demonstrated that replacing flat substrate with 3D structured one can increase the THz absorptance from 50% to 80-90%. The presence of an additional graphene layer in the system makes it possible to significantly change the dispersion of the electromagnetic response and increase the overall absorption level, at low frequencies in particular.
The fabricated structured graphene films showed outstanding THz performance in terms of the absorbance and bandwidth. They are the best candidates for fabrication ultra-thin and ultra-light THz components. Our experiments and numerical simulations showed that these structures are tolerant with respect to the fabrication defects and doping level of graphene and suit well requirements for scaled fabrication of THz passive components including attenuators, filters and polarizers.
A simple versatile tool for the design and fabrication of graphene-enhanced passive devices based on the laser micromachining of graphene enhanced gold-plated dielectric substrates was proposed and tested in THz frequency range. The fabricated metasurface demonstrated almost perfect absorption in the broad THz range spanning over more than one decade from 100 GHz. The obtained transmittivity is four times lower than that achievable in the flat free standing graphene sheet of the same conductivity.