Experimental Material Physics (Zardo)Head of Research Unit Prof. Dr.Ilaria ZardoOverviewMembersPublicationsProjects & CollaborationsProjects & Collaborations OverviewMembersPublicationsProjects & Collaborations Projects & Collaborations 15 foundShow per page10 10 20 50 Ultra high precision electron beam lithography system for nanodevice and nanostructures definition Research Project | 6 Project MembersIn the last decades nano- and quantum-science have been steadily growing in large part also thanks to the availability of ever more advanced processing, manipulation, and imaging tech-niques. Specifically, nanofabrication has been the leading enabler of experiments and devices, in which quantum mechanics play a key role. The University of Basel is nationally and internationally recognized as a leader innanoscience and nanotechnology. It was the leading house of the National Center in Competence and Re-search (NCCR) on Nanoscience, which later became the Swiss Nanoscience Institute (SNI). The University of Basel is leading the NCCR SPIN for the realization of spin qubits in Silicon and is also co-leading the NCCR QSIT on Quantum Science and Technology (with ETHZ as Leading House). The present proposal to the SNF R'Equip scheme is a joint effort of six principal investigators (PIs) in the physics department of the University of Basel, who work on current topics in quantum- and nano-science. The PIs, who submit this proposal together, do research that relies on the availability of state-of-the-art fabrication tools, such as an electron beam lithography (EBL) system. The proposal makes the case for the purchase of an ultra-high precision EBL system that combines high resolution, tunable acceleration voltages, different write-field size, ultra-high precision alignment, proximity correction, and mechanical stability. This combination is unique and crucial for the University of Basel to stay at the forefront of nano-science and technology. The system will be installed in the new clean room shared between the University of Basel and the Department of Biosystem Science and Engineering of the ETH. Therefore, the purchased system will be available for the users of the clean-room. Phonon-ART / Uncovering Phonon Dynamics by Advanced Raman Techniques Research Project | 2 Project MembersIn many technologies, heat management becomes the bottleneck for the next generation development. Phonons are mechanical vibrations of the atomic lattice that are responsible for the transmission of heat in many relevant materials, like semiconductors, thus controlling them analogously to photons and electrons is indispensable. Advanced time-resolved Raman spectroscopies enable the extraction of relevant information such as phonon spectra, lifetimes, and relaxation times, all critical to understanding thermal transport through advanced materials. In this project we aim to apply these techniques to solve two important open questions: (i) how to engineer the temperature sensors of the future based on diamond-based materials; and (ii) understanding the underlying physical mechanism responsible for deviations from the macroscopic predictions for nanoscale system, such as hypersonic surface phononic crystals, critical to technological applications. For this purpose, I propose four main objectives to the project. First, implementing an ultrafast time-resolved spontaneous Raman method to access the timescale of the absolute phonon mode population. Second, implementing a time-resolved stimulated Raman spectroscopy technique to explore the coherence of selectively excited phonons. Third, extending this technique to a time-resolved coherent anti-Stokes Raman (CARS) spectroscopy to probe the population dephasing lifetime of the system and energy relaxation time. This project will significantly advance the field of ultrafast, nano, materials and thermal science and will extend European knowledge in two different directions: advancing the current metrology tools by means of a fully developed time-resolved CARS setup at University of Basel, and studying energy flow dynamics in novel materials that will impact both fundamental understanding and technological applications. QUSTEC PhD fellowship - Hydrodynamic thermal transport and non-linear effects in 2D materials by means of pump-probe experiments Research Project | 1 Project MembersThe understanding and manipulation of charge and heat transport has a crucial importance for technological applications, impacting e.g. thermal management applications down to the nanoscale. Recently, hydrodynamic transport has stirred excitement in the scientific community. The potential of the field extends from finding new fundamental physics to some truly novel applications. The goal of this project is to achieve control over heat and charge transport in the hydrodynamic regime. To tame the elusive character of hydrodynamic transport, a deep understanding of materials science and device engineering are needed just as well as novel computational transport models and experimental protocols. In the frame of this project, we will perform pump-probe inelastic light scattering experiments, which gives important information on the time scale of phonon dynamics. It allows a direct determination of the absolute phonon mode population and of its temporal evolution. We will also perform pump-probe experiments in a spatially resolved manner in order to measure the phonon mean free path and coherence length of (selectively) excited phonon modes. Pump-probe experiments will also be conducted on 2D layers integrated in devices consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. In this way, we will be able to probe the time evolution of coherent excitations. QUSTEC PhD fellowship Hsieh Research Project | 1 Project MembersPhonons are responsible of heat transport in condensed matter. The capability to control heat transport at the nanoscale is relevant for different technological applications ranging from thermoelectric to heat management. In particular, thermal management in nano-electronics and other nano-systems has become the bottleneck for device scaling and performances in electronics. Due to the wavelengths and mean free paths of phonons, thermal transport at the nanoscale can be significantly different from thermal transport at the macro scale. Furthermore, the progress in nanofabrication enables the design and fabrication of nanostructures that can control heat transport by means of interference effects, achieving coherent phonon transport, and allowing exciting experiments (see e.g. Nature 503 , 209 (2013)). In the frame of this project, we propose nanowires as platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring (i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices). Specifically, we want to explore superlattice nanowires and nanowires junctions. Both systems are ideal platforms for exploring phonons interference effects. We will perform pump-probe inelastic light scattering experiments, which gives important information on the time scale of phonon dynamics. It allows a direct determination of the absolute phonon mode population and of its temporal evolution. We will also perform pump-probe experiments in a spatially resolved manner in order to measure the phonon mean free path and coherence length of (selectively) excited phonon modes. Pump-probe experiments will also be conducted on nanostructures integrated in devices consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. In this way, we will be able to probe the time evolution of both coherent and incoherent excitations. Hydronics Research Project | 1 Project MembersHydrodynamic transport of heat or charge in solids is an exotic phenomenon, discovered more than 50 years ago for the case of coherent thermal transport ("second sound"), that has gained much prominence recently, due to its prediction and experimental observation in low-dimensional materials and nanostructures. While in most materials internal scattering processes lead to diffusive transport, pronounced anisotropy, low-dimensionality, or reduced temperatures can lead to hydrodynamic transport. These include coherent propagation of transport excitations, vortices in the viscous hydrodynamic transport, peculiar dependence on temperature or magnetic field, friction, slip and super-linear dependence of conductance as a function of width. Recent observations of hydrodynamic effects in 2D materials (graphene or 2DEGs) and in anisotropic 3D materials (PdCoO, SrTiO 3 , WP 2 ) for both charge and heat are striking, deserve extensive microscopic understanding, and can lead to engineering novel devices. There are major open key questions addressed in this proposal: i. Theory and simulation : Several hydrodynamic transport regimes have been posited - from second sound and coherent transport waves to friction effects in nanostructures. Viscosities can now be predicted and provide a bridge between Boltzmann transport and Navier-Stokes hydrodynamics. ii. Materials science : To reach the hydrodynamic regime materials will have to be cleanly fabricated. There is no sufficient understanding of the role of defects or of the influence of substrates and boundaries on the emergence of the hydrodynamic regime. iii. Experimental physics : Certain hydrodynamic signatures are yet to be confirmed experimentally, others have been shown only once and need to be reproduced. Oftentimes, evidence of hydrodynamic transport has to be based on several different effects to be conclusive. Further, clean demonstrations need to be developed for the measurement of heat, which pose well-known methodological challenges. iv. Device engineering : Materials, for which a hydrodynamic transport regime is expected, often fall into the realm of future device applications for other reasons ( e.g. , topological protection, high electronic mobility, optoelectronic properties). It is unclear how future, scaled devices will either suffer from hydrodynamics, or can even exploit hydrodynamic transport for device functionality. These research questions motivate a synergetic approach combining these four areas of science by partnering of four research groups with leading expertise in all these areas. Furthermore, it is proposed to combine the study of hydrodynamic effects in both heat and charge transport to exploit obvious synergies, such as the important role of electron-phonon scattering. The project will create a theoretical framework to extract hydrodynamic parameters ( e.g. the viscosity of a phonon system) from first principles. Materials will be grown and patterned to explore the limitations of designable hydrodynamic systems. Then, materials will be designed by layering and patterning of geometries to control hydrodynamic effects. Experiments will measure second-sound (pump-probe laser spectroscopy), non-local dissipation (scanning thermal microscopy), and quantify thermal, electrical and thermoelectric conductance and magnetoconductance of samples as a function of their dimensions. Finally, basic functional demonstration using 2-terminal and 3-terminal devices will be made showing rectification and drag-effects for heat and charge pumps. QUSTEC PhD fellowship - Phonon interference effects in superlattice nanowires and nanowires junctions through thermal transport experiments Research Project | 2 Project MembersPhonons are responsible of heat transport in condensed matter. The capability to control heat transport at the nanoscale is relevant for different technological applications ranging from thermoelectric to heat management. In particular, thermal management in nano-electronics and other nano-systems has become the bottleneck for device scaling and performances in electronics. Due to the wavelengths and mean free paths of phonons, thermal transport at the nanoscale can be significantly different from thermal transport at the macro scale. Furthermore, the progress in nanofabrication enables the design and fabrication of nanostructures that can control heat transport by means of interference effects, achieving coherent phonon transport, and allowing exciting experiments (see e.g. Nature 503 , 209 (2013)). In the frame of this project, we propose nanowires as platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring (i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices). Specifically, we want to explore superlattice nanowires and nanowires junctions. Both systems are ideal platforms for exploring phonons interference effects. Thermal transport will be investigated measuring the thermal conductivity of the nanowires with the so-called thermal bridge method, consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. Thermal transport experiments at the nanoscale are extremely challenging since they require the measurement of heat flows that are quantified in temperature gradients. Phonon Interference in nanostructures Research Project | 1 Project MembersThe objective of this proposal is the realization of interference experiments with phonons, reaching the same level of complexity that can be achieved with electrons and photons. The investigation of phonon interference and different phonon transport regimes is of fundamental interest and is crucial for the manipulation of phonons. Therefore, we aim at exploring: * Phonon interference in nanowire superlattices ( Project A ) * Phonon transport in nanowire junctions ( Project B ) We propose to use nanowires as the platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring ( i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices) and they enable the growth of high quality nanowire junctions or networks. Phonon interference will be probed by means of inelastic light scattering and thermal transport experiments on nanowire superlattices and nanowire junctions. The complexity and diversity of the envisioned experiments, which are key for the success of the proposed research project, requires the broad experimental spectrum and technological expertise acquired by the applicant and available in the Nanophononics Group. This project will strengthen the understanding of the physics of phonons. Furthermore, since phonons are responsible of heat transport, this project will also have an impact on thermal management at the nanoscale. The main applicant, Prof. Dr. Ilaria Zardo, has recently been appointed in September 2015 tenure-track assistant professor in the Department of Physics at the University of Basel, where she is leading the Nanophononics group. In 2017 she was awarded an ERC Starting Grant by the European Research Council. She received in 2015 the Hertha-Sponer Prize, awarded to a female scientist for outstanding scientific work in the field of physics. In 2014 she successfully applied with the project "NEW: Nanostructures for Energetic Wisdom" to the Innovational Research Incentives Scheme Veni, which is a prestigious Talent Scheme of the Netherlands Organization for Scientific Research (NWO), meant for talented, creative researchers who are starting their own line of research. She has 10 years' experience in nanowire growth, spectroscopy on single nanostructures, with focus on inelastic light scattering experiments, and investigation of thermoelectric properties of semiconductor nanowires, expertise acquired in the Technische Universität München and the Technical University of Eindhoven. Quantum structures in nanowires: physical properties on demand by hydrogen irradiation Research Project | 1 Project MembersNanowires (NWs) are filamentary crystals with diameters of tens of nanometers and several microns in length. The great interest attracted by semiconductor NWs has been triggered by the growing demand for compact and powerful nanoscale devices, where NWs may act as both interconnects and functionalized components. A lot of emphasis in today research in NWs is put on the engineering of complex quantum structures in NWs, for they encode new functionalities and/or enhance existing performances. This project aims at developing unexplored strategies for embedding site-controlled quantum structures in III-V NWs and at finding fast and effective routes to engineer the physical properties of NWs. The pursued routes will involve mainly post-growth hydrogen implantation, thus allowing to achieve different NW properties on demand with no need to change and re-optimize NW growth conditions. Remarkably, the changes in the NW properties will be reversible, as hydrogen can be removed by thermal or laser annealing. Hydrogen is a ubiquitous, highly mobile, and reactive impurity able to passivate most deep and shallow defects purposely or accidentally embedded in semiconductor crystals, and it is present in most steps of semiconductor growth and device processing. In this project, controlled low-energy H + incorporation will be performed on single NWs and large NW arrays. Among all hydrogen effects, two striking effects well known for bulk samples will be investigated and engineered in the field of NWs: the band gap opening in InN and In-rich InGaN, and the passivation of N atoms in dilute nitrides III-N-V semiconductors such as GaAsN and GaPN. The unique growth environment offered by NWs will allow to benefit from a much greater flexibility with respect to conventional, planar, epitaxial growth, owing to the seamlessly enhanced ability of NWs to accommodate elastic strain and to host even lattice-mismatched material combinations. A variety of quantum structures in NWs will be achieved within this project, mostly but not only by using hydrogenation: quantum dots, quantum wires, quantum rings, quantum well tubes, and quantum wells. The structural characterization of the NWs will be coupled to optical spectroscopy techniques (inelastic light scattering and photoluminescence), also under intense magnetic fields and in a time-resolved regime. The experimental studies will be complemented by a robust theoretical support. In this way, a full picture of the electronic, optical, magnetic, and thermal properties of the quantum structures in NWs will be achieved and controllably tuned. The strength of the proposed approach will be proven by obtaining NWs with desired magnetic, photonic, and thermoelectric properties: in quantum rings and tubes, magnetic states that should appear due to the circular symmetry of their carrier wavefunction will be probed for the first time; in quantum dots deterministically positioned in NWs, single photon emission and enhanced light extraction will be achieved in prototypical light emitting devices; in NWs with embedded (non-)periodic superlattices of quantum dots and quantum wells, an enhancement of the thermoelectric power factor and thus of the thermoelectric figure of merit will be pursued. Moreover, potential uses in other fields, including photovoltaics and quantum sensing are envisioned. In this project, fundamental scientific investigation and technological applications will be strongly entangled and benefit from each other, as many advanced functionalities are deeply rooted in the way physical laws work in the nanoscale realm. Nano-photonics with van der Waals heterostructures Research Project | 3 Project MembersWe propose to create van der Waals heterostructures for nano-photonics applications, notably as congurable single photon sources. The project involves nano-materials development (pristine heterostructures and quantum dots) and nano-photonics experiments (single emitter characterization). PHONUIT Research Project | 1 Project MembersIn the last decades, the power to control photons and electrons paved the way for extraordinary technological developments in electronic and optoelectronic applications. The same degree of control is still lacking with quantized lattice vibrations, i.e. phonons. Phonons are the carriers of heat and sound. The understanding and ability to manipulate phonons as quantum particles in solids enable the control of coherent phonon transport, which is of fundamental interest and could also be exploited in applications. Logic operations can be realized with the manipulation of phonons both in their coherent and incoherent form in order to switch, amplify, and route signals, and to store information. If brought to a mature level, phononic devices can become complementary to the conventional electronics, opening new opportunities. I envision to realize each part of this technology exploiting phonons and to bring them together in an integrated circuit on chip: a phononic integrated circuit. The objective of the proposal is: A: the realization of coherent phonon source and detector; B: the realization of phonon computation with the use of thermal logic gates; C: the realization of phonon based quantum and thermal memories. To this end it is crucial to engineer nanoscale heterostructures with suitable interfaces, and to engineer the phonon spectrum and the interface thermal resistance. Phonons will be launched, probed and manipulated with a combination of pump-probe experiments and resistive thermal measurements on chip. The proposed research will be of great relevance for fundamental research as well as for technological applications in the field of sound and thermal management. 12 12 OverviewMembersPublicationsProjects & Collaborations
Projects & Collaborations 15 foundShow per page10 10 20 50 Ultra high precision electron beam lithography system for nanodevice and nanostructures definition Research Project | 6 Project MembersIn the last decades nano- and quantum-science have been steadily growing in large part also thanks to the availability of ever more advanced processing, manipulation, and imaging tech-niques. Specifically, nanofabrication has been the leading enabler of experiments and devices, in which quantum mechanics play a key role. The University of Basel is nationally and internationally recognized as a leader innanoscience and nanotechnology. It was the leading house of the National Center in Competence and Re-search (NCCR) on Nanoscience, which later became the Swiss Nanoscience Institute (SNI). The University of Basel is leading the NCCR SPIN for the realization of spin qubits in Silicon and is also co-leading the NCCR QSIT on Quantum Science and Technology (with ETHZ as Leading House). The present proposal to the SNF R'Equip scheme is a joint effort of six principal investigators (PIs) in the physics department of the University of Basel, who work on current topics in quantum- and nano-science. The PIs, who submit this proposal together, do research that relies on the availability of state-of-the-art fabrication tools, such as an electron beam lithography (EBL) system. The proposal makes the case for the purchase of an ultra-high precision EBL system that combines high resolution, tunable acceleration voltages, different write-field size, ultra-high precision alignment, proximity correction, and mechanical stability. This combination is unique and crucial for the University of Basel to stay at the forefront of nano-science and technology. The system will be installed in the new clean room shared between the University of Basel and the Department of Biosystem Science and Engineering of the ETH. Therefore, the purchased system will be available for the users of the clean-room. Phonon-ART / Uncovering Phonon Dynamics by Advanced Raman Techniques Research Project | 2 Project MembersIn many technologies, heat management becomes the bottleneck for the next generation development. Phonons are mechanical vibrations of the atomic lattice that are responsible for the transmission of heat in many relevant materials, like semiconductors, thus controlling them analogously to photons and electrons is indispensable. Advanced time-resolved Raman spectroscopies enable the extraction of relevant information such as phonon spectra, lifetimes, and relaxation times, all critical to understanding thermal transport through advanced materials. In this project we aim to apply these techniques to solve two important open questions: (i) how to engineer the temperature sensors of the future based on diamond-based materials; and (ii) understanding the underlying physical mechanism responsible for deviations from the macroscopic predictions for nanoscale system, such as hypersonic surface phononic crystals, critical to technological applications. For this purpose, I propose four main objectives to the project. First, implementing an ultrafast time-resolved spontaneous Raman method to access the timescale of the absolute phonon mode population. Second, implementing a time-resolved stimulated Raman spectroscopy technique to explore the coherence of selectively excited phonons. Third, extending this technique to a time-resolved coherent anti-Stokes Raman (CARS) spectroscopy to probe the population dephasing lifetime of the system and energy relaxation time. This project will significantly advance the field of ultrafast, nano, materials and thermal science and will extend European knowledge in two different directions: advancing the current metrology tools by means of a fully developed time-resolved CARS setup at University of Basel, and studying energy flow dynamics in novel materials that will impact both fundamental understanding and technological applications. QUSTEC PhD fellowship - Hydrodynamic thermal transport and non-linear effects in 2D materials by means of pump-probe experiments Research Project | 1 Project MembersThe understanding and manipulation of charge and heat transport has a crucial importance for technological applications, impacting e.g. thermal management applications down to the nanoscale. Recently, hydrodynamic transport has stirred excitement in the scientific community. The potential of the field extends from finding new fundamental physics to some truly novel applications. The goal of this project is to achieve control over heat and charge transport in the hydrodynamic regime. To tame the elusive character of hydrodynamic transport, a deep understanding of materials science and device engineering are needed just as well as novel computational transport models and experimental protocols. In the frame of this project, we will perform pump-probe inelastic light scattering experiments, which gives important information on the time scale of phonon dynamics. It allows a direct determination of the absolute phonon mode population and of its temporal evolution. We will also perform pump-probe experiments in a spatially resolved manner in order to measure the phonon mean free path and coherence length of (selectively) excited phonon modes. Pump-probe experiments will also be conducted on 2D layers integrated in devices consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. In this way, we will be able to probe the time evolution of coherent excitations. QUSTEC PhD fellowship Hsieh Research Project | 1 Project MembersPhonons are responsible of heat transport in condensed matter. The capability to control heat transport at the nanoscale is relevant for different technological applications ranging from thermoelectric to heat management. In particular, thermal management in nano-electronics and other nano-systems has become the bottleneck for device scaling and performances in electronics. Due to the wavelengths and mean free paths of phonons, thermal transport at the nanoscale can be significantly different from thermal transport at the macro scale. Furthermore, the progress in nanofabrication enables the design and fabrication of nanostructures that can control heat transport by means of interference effects, achieving coherent phonon transport, and allowing exciting experiments (see e.g. Nature 503 , 209 (2013)). In the frame of this project, we propose nanowires as platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring (i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices). Specifically, we want to explore superlattice nanowires and nanowires junctions. Both systems are ideal platforms for exploring phonons interference effects. We will perform pump-probe inelastic light scattering experiments, which gives important information on the time scale of phonon dynamics. It allows a direct determination of the absolute phonon mode population and of its temporal evolution. We will also perform pump-probe experiments in a spatially resolved manner in order to measure the phonon mean free path and coherence length of (selectively) excited phonon modes. Pump-probe experiments will also be conducted on nanostructures integrated in devices consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. In this way, we will be able to probe the time evolution of both coherent and incoherent excitations. Hydronics Research Project | 1 Project MembersHydrodynamic transport of heat or charge in solids is an exotic phenomenon, discovered more than 50 years ago for the case of coherent thermal transport ("second sound"), that has gained much prominence recently, due to its prediction and experimental observation in low-dimensional materials and nanostructures. While in most materials internal scattering processes lead to diffusive transport, pronounced anisotropy, low-dimensionality, or reduced temperatures can lead to hydrodynamic transport. These include coherent propagation of transport excitations, vortices in the viscous hydrodynamic transport, peculiar dependence on temperature or magnetic field, friction, slip and super-linear dependence of conductance as a function of width. Recent observations of hydrodynamic effects in 2D materials (graphene or 2DEGs) and in anisotropic 3D materials (PdCoO, SrTiO 3 , WP 2 ) for both charge and heat are striking, deserve extensive microscopic understanding, and can lead to engineering novel devices. There are major open key questions addressed in this proposal: i. Theory and simulation : Several hydrodynamic transport regimes have been posited - from second sound and coherent transport waves to friction effects in nanostructures. Viscosities can now be predicted and provide a bridge between Boltzmann transport and Navier-Stokes hydrodynamics. ii. Materials science : To reach the hydrodynamic regime materials will have to be cleanly fabricated. There is no sufficient understanding of the role of defects or of the influence of substrates and boundaries on the emergence of the hydrodynamic regime. iii. Experimental physics : Certain hydrodynamic signatures are yet to be confirmed experimentally, others have been shown only once and need to be reproduced. Oftentimes, evidence of hydrodynamic transport has to be based on several different effects to be conclusive. Further, clean demonstrations need to be developed for the measurement of heat, which pose well-known methodological challenges. iv. Device engineering : Materials, for which a hydrodynamic transport regime is expected, often fall into the realm of future device applications for other reasons ( e.g. , topological protection, high electronic mobility, optoelectronic properties). It is unclear how future, scaled devices will either suffer from hydrodynamics, or can even exploit hydrodynamic transport for device functionality. These research questions motivate a synergetic approach combining these four areas of science by partnering of four research groups with leading expertise in all these areas. Furthermore, it is proposed to combine the study of hydrodynamic effects in both heat and charge transport to exploit obvious synergies, such as the important role of electron-phonon scattering. The project will create a theoretical framework to extract hydrodynamic parameters ( e.g. the viscosity of a phonon system) from first principles. Materials will be grown and patterned to explore the limitations of designable hydrodynamic systems. Then, materials will be designed by layering and patterning of geometries to control hydrodynamic effects. Experiments will measure second-sound (pump-probe laser spectroscopy), non-local dissipation (scanning thermal microscopy), and quantify thermal, electrical and thermoelectric conductance and magnetoconductance of samples as a function of their dimensions. Finally, basic functional demonstration using 2-terminal and 3-terminal devices will be made showing rectification and drag-effects for heat and charge pumps. QUSTEC PhD fellowship - Phonon interference effects in superlattice nanowires and nanowires junctions through thermal transport experiments Research Project | 2 Project MembersPhonons are responsible of heat transport in condensed matter. The capability to control heat transport at the nanoscale is relevant for different technological applications ranging from thermoelectric to heat management. In particular, thermal management in nano-electronics and other nano-systems has become the bottleneck for device scaling and performances in electronics. Due to the wavelengths and mean free paths of phonons, thermal transport at the nanoscale can be significantly different from thermal transport at the macro scale. Furthermore, the progress in nanofabrication enables the design and fabrication of nanostructures that can control heat transport by means of interference effects, achieving coherent phonon transport, and allowing exciting experiments (see e.g. Nature 503 , 209 (2013)). In the frame of this project, we propose nanowires as platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring (i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices). Specifically, we want to explore superlattice nanowires and nanowires junctions. Both systems are ideal platforms for exploring phonons interference effects. Thermal transport will be investigated measuring the thermal conductivity of the nanowires with the so-called thermal bridge method, consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. Thermal transport experiments at the nanoscale are extremely challenging since they require the measurement of heat flows that are quantified in temperature gradients. Phonon Interference in nanostructures Research Project | 1 Project MembersThe objective of this proposal is the realization of interference experiments with phonons, reaching the same level of complexity that can be achieved with electrons and photons. The investigation of phonon interference and different phonon transport regimes is of fundamental interest and is crucial for the manipulation of phonons. Therefore, we aim at exploring: * Phonon interference in nanowire superlattices ( Project A ) * Phonon transport in nanowire junctions ( Project B ) We propose to use nanowires as the platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring ( i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices) and they enable the growth of high quality nanowire junctions or networks. Phonon interference will be probed by means of inelastic light scattering and thermal transport experiments on nanowire superlattices and nanowire junctions. The complexity and diversity of the envisioned experiments, which are key for the success of the proposed research project, requires the broad experimental spectrum and technological expertise acquired by the applicant and available in the Nanophononics Group. This project will strengthen the understanding of the physics of phonons. Furthermore, since phonons are responsible of heat transport, this project will also have an impact on thermal management at the nanoscale. The main applicant, Prof. Dr. Ilaria Zardo, has recently been appointed in September 2015 tenure-track assistant professor in the Department of Physics at the University of Basel, where she is leading the Nanophononics group. In 2017 she was awarded an ERC Starting Grant by the European Research Council. She received in 2015 the Hertha-Sponer Prize, awarded to a female scientist for outstanding scientific work in the field of physics. In 2014 she successfully applied with the project "NEW: Nanostructures for Energetic Wisdom" to the Innovational Research Incentives Scheme Veni, which is a prestigious Talent Scheme of the Netherlands Organization for Scientific Research (NWO), meant for talented, creative researchers who are starting their own line of research. She has 10 years' experience in nanowire growth, spectroscopy on single nanostructures, with focus on inelastic light scattering experiments, and investigation of thermoelectric properties of semiconductor nanowires, expertise acquired in the Technische Universität München and the Technical University of Eindhoven. Quantum structures in nanowires: physical properties on demand by hydrogen irradiation Research Project | 1 Project MembersNanowires (NWs) are filamentary crystals with diameters of tens of nanometers and several microns in length. The great interest attracted by semiconductor NWs has been triggered by the growing demand for compact and powerful nanoscale devices, where NWs may act as both interconnects and functionalized components. A lot of emphasis in today research in NWs is put on the engineering of complex quantum structures in NWs, for they encode new functionalities and/or enhance existing performances. This project aims at developing unexplored strategies for embedding site-controlled quantum structures in III-V NWs and at finding fast and effective routes to engineer the physical properties of NWs. The pursued routes will involve mainly post-growth hydrogen implantation, thus allowing to achieve different NW properties on demand with no need to change and re-optimize NW growth conditions. Remarkably, the changes in the NW properties will be reversible, as hydrogen can be removed by thermal or laser annealing. Hydrogen is a ubiquitous, highly mobile, and reactive impurity able to passivate most deep and shallow defects purposely or accidentally embedded in semiconductor crystals, and it is present in most steps of semiconductor growth and device processing. In this project, controlled low-energy H + incorporation will be performed on single NWs and large NW arrays. Among all hydrogen effects, two striking effects well known for bulk samples will be investigated and engineered in the field of NWs: the band gap opening in InN and In-rich InGaN, and the passivation of N atoms in dilute nitrides III-N-V semiconductors such as GaAsN and GaPN. The unique growth environment offered by NWs will allow to benefit from a much greater flexibility with respect to conventional, planar, epitaxial growth, owing to the seamlessly enhanced ability of NWs to accommodate elastic strain and to host even lattice-mismatched material combinations. A variety of quantum structures in NWs will be achieved within this project, mostly but not only by using hydrogenation: quantum dots, quantum wires, quantum rings, quantum well tubes, and quantum wells. The structural characterization of the NWs will be coupled to optical spectroscopy techniques (inelastic light scattering and photoluminescence), also under intense magnetic fields and in a time-resolved regime. The experimental studies will be complemented by a robust theoretical support. In this way, a full picture of the electronic, optical, magnetic, and thermal properties of the quantum structures in NWs will be achieved and controllably tuned. The strength of the proposed approach will be proven by obtaining NWs with desired magnetic, photonic, and thermoelectric properties: in quantum rings and tubes, magnetic states that should appear due to the circular symmetry of their carrier wavefunction will be probed for the first time; in quantum dots deterministically positioned in NWs, single photon emission and enhanced light extraction will be achieved in prototypical light emitting devices; in NWs with embedded (non-)periodic superlattices of quantum dots and quantum wells, an enhancement of the thermoelectric power factor and thus of the thermoelectric figure of merit will be pursued. Moreover, potential uses in other fields, including photovoltaics and quantum sensing are envisioned. In this project, fundamental scientific investigation and technological applications will be strongly entangled and benefit from each other, as many advanced functionalities are deeply rooted in the way physical laws work in the nanoscale realm. Nano-photonics with van der Waals heterostructures Research Project | 3 Project MembersWe propose to create van der Waals heterostructures for nano-photonics applications, notably as congurable single photon sources. The project involves nano-materials development (pristine heterostructures and quantum dots) and nano-photonics experiments (single emitter characterization). PHONUIT Research Project | 1 Project MembersIn the last decades, the power to control photons and electrons paved the way for extraordinary technological developments in electronic and optoelectronic applications. The same degree of control is still lacking with quantized lattice vibrations, i.e. phonons. Phonons are the carriers of heat and sound. The understanding and ability to manipulate phonons as quantum particles in solids enable the control of coherent phonon transport, which is of fundamental interest and could also be exploited in applications. Logic operations can be realized with the manipulation of phonons both in their coherent and incoherent form in order to switch, amplify, and route signals, and to store information. If brought to a mature level, phononic devices can become complementary to the conventional electronics, opening new opportunities. I envision to realize each part of this technology exploiting phonons and to bring them together in an integrated circuit on chip: a phononic integrated circuit. The objective of the proposal is: A: the realization of coherent phonon source and detector; B: the realization of phonon computation with the use of thermal logic gates; C: the realization of phonon based quantum and thermal memories. To this end it is crucial to engineer nanoscale heterostructures with suitable interfaces, and to engineer the phonon spectrum and the interface thermal resistance. Phonons will be launched, probed and manipulated with a combination of pump-probe experiments and resistive thermal measurements on chip. The proposed research will be of great relevance for fundamental research as well as for technological applications in the field of sound and thermal management. 12 12
Ultra high precision electron beam lithography system for nanodevice and nanostructures definition Research Project | 6 Project MembersIn the last decades nano- and quantum-science have been steadily growing in large part also thanks to the availability of ever more advanced processing, manipulation, and imaging tech-niques. Specifically, nanofabrication has been the leading enabler of experiments and devices, in which quantum mechanics play a key role. The University of Basel is nationally and internationally recognized as a leader innanoscience and nanotechnology. It was the leading house of the National Center in Competence and Re-search (NCCR) on Nanoscience, which later became the Swiss Nanoscience Institute (SNI). The University of Basel is leading the NCCR SPIN for the realization of spin qubits in Silicon and is also co-leading the NCCR QSIT on Quantum Science and Technology (with ETHZ as Leading House). The present proposal to the SNF R'Equip scheme is a joint effort of six principal investigators (PIs) in the physics department of the University of Basel, who work on current topics in quantum- and nano-science. The PIs, who submit this proposal together, do research that relies on the availability of state-of-the-art fabrication tools, such as an electron beam lithography (EBL) system. The proposal makes the case for the purchase of an ultra-high precision EBL system that combines high resolution, tunable acceleration voltages, different write-field size, ultra-high precision alignment, proximity correction, and mechanical stability. This combination is unique and crucial for the University of Basel to stay at the forefront of nano-science and technology. The system will be installed in the new clean room shared between the University of Basel and the Department of Biosystem Science and Engineering of the ETH. Therefore, the purchased system will be available for the users of the clean-room.
Phonon-ART / Uncovering Phonon Dynamics by Advanced Raman Techniques Research Project | 2 Project MembersIn many technologies, heat management becomes the bottleneck for the next generation development. Phonons are mechanical vibrations of the atomic lattice that are responsible for the transmission of heat in many relevant materials, like semiconductors, thus controlling them analogously to photons and electrons is indispensable. Advanced time-resolved Raman spectroscopies enable the extraction of relevant information such as phonon spectra, lifetimes, and relaxation times, all critical to understanding thermal transport through advanced materials. In this project we aim to apply these techniques to solve two important open questions: (i) how to engineer the temperature sensors of the future based on diamond-based materials; and (ii) understanding the underlying physical mechanism responsible for deviations from the macroscopic predictions for nanoscale system, such as hypersonic surface phononic crystals, critical to technological applications. For this purpose, I propose four main objectives to the project. First, implementing an ultrafast time-resolved spontaneous Raman method to access the timescale of the absolute phonon mode population. Second, implementing a time-resolved stimulated Raman spectroscopy technique to explore the coherence of selectively excited phonons. Third, extending this technique to a time-resolved coherent anti-Stokes Raman (CARS) spectroscopy to probe the population dephasing lifetime of the system and energy relaxation time. This project will significantly advance the field of ultrafast, nano, materials and thermal science and will extend European knowledge in two different directions: advancing the current metrology tools by means of a fully developed time-resolved CARS setup at University of Basel, and studying energy flow dynamics in novel materials that will impact both fundamental understanding and technological applications.
QUSTEC PhD fellowship - Hydrodynamic thermal transport and non-linear effects in 2D materials by means of pump-probe experiments Research Project | 1 Project MembersThe understanding and manipulation of charge and heat transport has a crucial importance for technological applications, impacting e.g. thermal management applications down to the nanoscale. Recently, hydrodynamic transport has stirred excitement in the scientific community. The potential of the field extends from finding new fundamental physics to some truly novel applications. The goal of this project is to achieve control over heat and charge transport in the hydrodynamic regime. To tame the elusive character of hydrodynamic transport, a deep understanding of materials science and device engineering are needed just as well as novel computational transport models and experimental protocols. In the frame of this project, we will perform pump-probe inelastic light scattering experiments, which gives important information on the time scale of phonon dynamics. It allows a direct determination of the absolute phonon mode population and of its temporal evolution. We will also perform pump-probe experiments in a spatially resolved manner in order to measure the phonon mean free path and coherence length of (selectively) excited phonon modes. Pump-probe experiments will also be conducted on 2D layers integrated in devices consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. In this way, we will be able to probe the time evolution of coherent excitations.
QUSTEC PhD fellowship Hsieh Research Project | 1 Project MembersPhonons are responsible of heat transport in condensed matter. The capability to control heat transport at the nanoscale is relevant for different technological applications ranging from thermoelectric to heat management. In particular, thermal management in nano-electronics and other nano-systems has become the bottleneck for device scaling and performances in electronics. Due to the wavelengths and mean free paths of phonons, thermal transport at the nanoscale can be significantly different from thermal transport at the macro scale. Furthermore, the progress in nanofabrication enables the design and fabrication of nanostructures that can control heat transport by means of interference effects, achieving coherent phonon transport, and allowing exciting experiments (see e.g. Nature 503 , 209 (2013)). In the frame of this project, we propose nanowires as platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring (i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices). Specifically, we want to explore superlattice nanowires and nanowires junctions. Both systems are ideal platforms for exploring phonons interference effects. We will perform pump-probe inelastic light scattering experiments, which gives important information on the time scale of phonon dynamics. It allows a direct determination of the absolute phonon mode population and of its temporal evolution. We will also perform pump-probe experiments in a spatially resolved manner in order to measure the phonon mean free path and coherence length of (selectively) excited phonon modes. Pump-probe experiments will also be conducted on nanostructures integrated in devices consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. In this way, we will be able to probe the time evolution of both coherent and incoherent excitations.
Hydronics Research Project | 1 Project MembersHydrodynamic transport of heat or charge in solids is an exotic phenomenon, discovered more than 50 years ago for the case of coherent thermal transport ("second sound"), that has gained much prominence recently, due to its prediction and experimental observation in low-dimensional materials and nanostructures. While in most materials internal scattering processes lead to diffusive transport, pronounced anisotropy, low-dimensionality, or reduced temperatures can lead to hydrodynamic transport. These include coherent propagation of transport excitations, vortices in the viscous hydrodynamic transport, peculiar dependence on temperature or magnetic field, friction, slip and super-linear dependence of conductance as a function of width. Recent observations of hydrodynamic effects in 2D materials (graphene or 2DEGs) and in anisotropic 3D materials (PdCoO, SrTiO 3 , WP 2 ) for both charge and heat are striking, deserve extensive microscopic understanding, and can lead to engineering novel devices. There are major open key questions addressed in this proposal: i. Theory and simulation : Several hydrodynamic transport regimes have been posited - from second sound and coherent transport waves to friction effects in nanostructures. Viscosities can now be predicted and provide a bridge between Boltzmann transport and Navier-Stokes hydrodynamics. ii. Materials science : To reach the hydrodynamic regime materials will have to be cleanly fabricated. There is no sufficient understanding of the role of defects or of the influence of substrates and boundaries on the emergence of the hydrodynamic regime. iii. Experimental physics : Certain hydrodynamic signatures are yet to be confirmed experimentally, others have been shown only once and need to be reproduced. Oftentimes, evidence of hydrodynamic transport has to be based on several different effects to be conclusive. Further, clean demonstrations need to be developed for the measurement of heat, which pose well-known methodological challenges. iv. Device engineering : Materials, for which a hydrodynamic transport regime is expected, often fall into the realm of future device applications for other reasons ( e.g. , topological protection, high electronic mobility, optoelectronic properties). It is unclear how future, scaled devices will either suffer from hydrodynamics, or can even exploit hydrodynamic transport for device functionality. These research questions motivate a synergetic approach combining these four areas of science by partnering of four research groups with leading expertise in all these areas. Furthermore, it is proposed to combine the study of hydrodynamic effects in both heat and charge transport to exploit obvious synergies, such as the important role of electron-phonon scattering. The project will create a theoretical framework to extract hydrodynamic parameters ( e.g. the viscosity of a phonon system) from first principles. Materials will be grown and patterned to explore the limitations of designable hydrodynamic systems. Then, materials will be designed by layering and patterning of geometries to control hydrodynamic effects. Experiments will measure second-sound (pump-probe laser spectroscopy), non-local dissipation (scanning thermal microscopy), and quantify thermal, electrical and thermoelectric conductance and magnetoconductance of samples as a function of their dimensions. Finally, basic functional demonstration using 2-terminal and 3-terminal devices will be made showing rectification and drag-effects for heat and charge pumps.
QUSTEC PhD fellowship - Phonon interference effects in superlattice nanowires and nanowires junctions through thermal transport experiments Research Project | 2 Project MembersPhonons are responsible of heat transport in condensed matter. The capability to control heat transport at the nanoscale is relevant for different technological applications ranging from thermoelectric to heat management. In particular, thermal management in nano-electronics and other nano-systems has become the bottleneck for device scaling and performances in electronics. Due to the wavelengths and mean free paths of phonons, thermal transport at the nanoscale can be significantly different from thermal transport at the macro scale. Furthermore, the progress in nanofabrication enables the design and fabrication of nanostructures that can control heat transport by means of interference effects, achieving coherent phonon transport, and allowing exciting experiments (see e.g. Nature 503 , 209 (2013)). In the frame of this project, we propose nanowires as platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring (i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices). Specifically, we want to explore superlattice nanowires and nanowires junctions. Both systems are ideal platforms for exploring phonons interference effects. Thermal transport will be investigated measuring the thermal conductivity of the nanowires with the so-called thermal bridge method, consisting of suspended SiNx membranes with implemented metallic coils, which can be used both as heaters and thermometers. Thermal transport experiments at the nanoscale are extremely challenging since they require the measurement of heat flows that are quantified in temperature gradients.
Phonon Interference in nanostructures Research Project | 1 Project MembersThe objective of this proposal is the realization of interference experiments with phonons, reaching the same level of complexity that can be achieved with electrons and photons. The investigation of phonon interference and different phonon transport regimes is of fundamental interest and is crucial for the manipulation of phonons. Therefore, we aim at exploring: * Phonon interference in nanowire superlattices ( Project A ) * Phonon transport in nanowire junctions ( Project B ) We propose to use nanowires as the platform for investigating and designing the phonon interference effects because they offer unique possibilities in terms of heterostructuring ( i.e. combining materials that cannot be joined in 2D because of lattice mismatch and realizing crystal phase superlattices) and they enable the growth of high quality nanowire junctions or networks. Phonon interference will be probed by means of inelastic light scattering and thermal transport experiments on nanowire superlattices and nanowire junctions. The complexity and diversity of the envisioned experiments, which are key for the success of the proposed research project, requires the broad experimental spectrum and technological expertise acquired by the applicant and available in the Nanophononics Group. This project will strengthen the understanding of the physics of phonons. Furthermore, since phonons are responsible of heat transport, this project will also have an impact on thermal management at the nanoscale. The main applicant, Prof. Dr. Ilaria Zardo, has recently been appointed in September 2015 tenure-track assistant professor in the Department of Physics at the University of Basel, where she is leading the Nanophononics group. In 2017 she was awarded an ERC Starting Grant by the European Research Council. She received in 2015 the Hertha-Sponer Prize, awarded to a female scientist for outstanding scientific work in the field of physics. In 2014 she successfully applied with the project "NEW: Nanostructures for Energetic Wisdom" to the Innovational Research Incentives Scheme Veni, which is a prestigious Talent Scheme of the Netherlands Organization for Scientific Research (NWO), meant for talented, creative researchers who are starting their own line of research. She has 10 years' experience in nanowire growth, spectroscopy on single nanostructures, with focus on inelastic light scattering experiments, and investigation of thermoelectric properties of semiconductor nanowires, expertise acquired in the Technische Universität München and the Technical University of Eindhoven.
Quantum structures in nanowires: physical properties on demand by hydrogen irradiation Research Project | 1 Project MembersNanowires (NWs) are filamentary crystals with diameters of tens of nanometers and several microns in length. The great interest attracted by semiconductor NWs has been triggered by the growing demand for compact and powerful nanoscale devices, where NWs may act as both interconnects and functionalized components. A lot of emphasis in today research in NWs is put on the engineering of complex quantum structures in NWs, for they encode new functionalities and/or enhance existing performances. This project aims at developing unexplored strategies for embedding site-controlled quantum structures in III-V NWs and at finding fast and effective routes to engineer the physical properties of NWs. The pursued routes will involve mainly post-growth hydrogen implantation, thus allowing to achieve different NW properties on demand with no need to change and re-optimize NW growth conditions. Remarkably, the changes in the NW properties will be reversible, as hydrogen can be removed by thermal or laser annealing. Hydrogen is a ubiquitous, highly mobile, and reactive impurity able to passivate most deep and shallow defects purposely or accidentally embedded in semiconductor crystals, and it is present in most steps of semiconductor growth and device processing. In this project, controlled low-energy H + incorporation will be performed on single NWs and large NW arrays. Among all hydrogen effects, two striking effects well known for bulk samples will be investigated and engineered in the field of NWs: the band gap opening in InN and In-rich InGaN, and the passivation of N atoms in dilute nitrides III-N-V semiconductors such as GaAsN and GaPN. The unique growth environment offered by NWs will allow to benefit from a much greater flexibility with respect to conventional, planar, epitaxial growth, owing to the seamlessly enhanced ability of NWs to accommodate elastic strain and to host even lattice-mismatched material combinations. A variety of quantum structures in NWs will be achieved within this project, mostly but not only by using hydrogenation: quantum dots, quantum wires, quantum rings, quantum well tubes, and quantum wells. The structural characterization of the NWs will be coupled to optical spectroscopy techniques (inelastic light scattering and photoluminescence), also under intense magnetic fields and in a time-resolved regime. The experimental studies will be complemented by a robust theoretical support. In this way, a full picture of the electronic, optical, magnetic, and thermal properties of the quantum structures in NWs will be achieved and controllably tuned. The strength of the proposed approach will be proven by obtaining NWs with desired magnetic, photonic, and thermoelectric properties: in quantum rings and tubes, magnetic states that should appear due to the circular symmetry of their carrier wavefunction will be probed for the first time; in quantum dots deterministically positioned in NWs, single photon emission and enhanced light extraction will be achieved in prototypical light emitting devices; in NWs with embedded (non-)periodic superlattices of quantum dots and quantum wells, an enhancement of the thermoelectric power factor and thus of the thermoelectric figure of merit will be pursued. Moreover, potential uses in other fields, including photovoltaics and quantum sensing are envisioned. In this project, fundamental scientific investigation and technological applications will be strongly entangled and benefit from each other, as many advanced functionalities are deeply rooted in the way physical laws work in the nanoscale realm.
Nano-photonics with van der Waals heterostructures Research Project | 3 Project MembersWe propose to create van der Waals heterostructures for nano-photonics applications, notably as congurable single photon sources. The project involves nano-materials development (pristine heterostructures and quantum dots) and nano-photonics experiments (single emitter characterization).
PHONUIT Research Project | 1 Project MembersIn the last decades, the power to control photons and electrons paved the way for extraordinary technological developments in electronic and optoelectronic applications. The same degree of control is still lacking with quantized lattice vibrations, i.e. phonons. Phonons are the carriers of heat and sound. The understanding and ability to manipulate phonons as quantum particles in solids enable the control of coherent phonon transport, which is of fundamental interest and could also be exploited in applications. Logic operations can be realized with the manipulation of phonons both in their coherent and incoherent form in order to switch, amplify, and route signals, and to store information. If brought to a mature level, phononic devices can become complementary to the conventional electronics, opening new opportunities. I envision to realize each part of this technology exploiting phonons and to bring them together in an integrated circuit on chip: a phononic integrated circuit. The objective of the proposal is: A: the realization of coherent phonon source and detector; B: the realization of phonon computation with the use of thermal logic gates; C: the realization of phonon based quantum and thermal memories. To this end it is crucial to engineer nanoscale heterostructures with suitable interfaces, and to engineer the phonon spectrum and the interface thermal resistance. Phonons will be launched, probed and manipulated with a combination of pump-probe experiments and resistive thermal measurements on chip. The proposed research will be of great relevance for fundamental research as well as for technological applications in the field of sound and thermal management.
