RESEARCH
RESEARCH
Research Strategy
Research Strategy
My laboratory program encompasses basic and translational research at the interface between chemistry and physics, with the aim of performing fundamental studies in the field of solar fuels. My group combines:
My laboratory program encompasses basic and translational research at the interface between chemistry and physics, with the aim of performing fundamental studies in the field of solar fuels. My group combines:
(i) state-of-the-art synthesis techniques to control light absorption and electric field enhancement within metal/semiconductor architecture with a nanometer resolution
(i) state-of-the-art synthesis techniques to control light absorption and electric field enhancement within metal/semiconductor architecture with a nanometer resolution
(ii) 3D electromagnetic simulations to map the light absorption and field-enhancement as a function of location and photon energy
(ii) 3D electromagnetic simulations to map the light absorption and field-enhancement as a function of location and photon energy
(iii) photoelectrochemical (water-splitting) and gas-phase photocatalytic experiments (plasmonic CO2 photoconversion)
(iii) photoelectrochemical (water-splitting) and gas-phase photocatalytic experiments (plasmonic CO2 photoconversion)
(iv) planned advanced X-Ray absorption studies under light irradiation (collaboration with Trieste, synchrotron lab) to experimentally identify where light is most absorbed in these heterostructures.
(iv) planned advanced X-Ray absorption studies under light irradiation (collaboration with Trieste, synchrotron lab) to experimentally identify where light is most absorbed in these heterostructures.
Influence of Geometrical Parameters Within Nanostructured Photocathodes for Water-Splitting
Influence of Geometrical Parameters Within Nanostructured Photocathodes for Water-Splitting
We are currently investigating how the location of catalyst influences the conversion efficiency of Si nanowire array photocathode in the context of H2 generation under solar irradiation.
We are currently investigating how the location of catalyst influences the conversion efficiency of Si nanowire array photocathode in the context of H2 generation under solar irradiation.
Field-Enhanced Photocatalysis at Nanoscale Gaps
Field-Enhanced Photocatalysis at Nanoscale Gaps
Overview. Plasmonic metal nanoparticles can increase reaction rates and product selectivity under light irradiation due to the enhanced E-fields generated under plasmonic excitation.(1) This proposal will investigate CO2 photomethanation at Rh and Ru nanocatalysts located within metal and Si sub-20 nm nanogaps that can produce very large E-fields. State-of-the-art nanostructuring approaches providing a sub-2 nm spatial resolution(2) will be used to investigate the influence of bulk absorption, surface E-field enhancement and exposed surface area. This proposal involves the groups of G. Bourret, expert in plasmonics and nanostructuring,(2) and O. Diwald, expert in photoexcitation studies and in-situ spectroscopy. Photocatalytic experiments will be performed using a home-made high-vacuum cell compatible with in-situ IR spectroscopy. Hot electron generation and light absorption will be investigated using three-dimensional electromagnetic numerical simulations (in-house) combined with state of the art X-ray absorption experiments performed under laser irradiation (collaborations).
Overview. Plasmonic metal nanoparticles can increase reaction rates and product selectivity under light irradiation due to the enhanced E-fields generated under plasmonic excitation.(1) This proposal will investigate CO2 photomethanation at Rh and Ru nanocatalysts located within metal and Si sub-20 nm nanogaps that can produce very large E-fields. State-of-the-art nanostructuring approaches providing a sub-2 nm spatial resolution(2) will be used to investigate the influence of bulk absorption, surface E-field enhancement and exposed surface area. This proposal involves the groups of G. Bourret, expert in plasmonics and nanostructuring,(2) and O. Diwald, expert in photoexcitation studies and in-situ spectroscopy. Photocatalytic experiments will be performed using a home-made high-vacuum cell compatible with in-situ IR spectroscopy. Hot electron generation and light absorption will be investigated using three-dimensional electromagnetic numerical simulations (in-house) combined with state of the art X-ray absorption experiments performed under laser irradiation (collaborations).
References.
(1) Zhang, Zhang, Su, Yang, Everitt, Liu Nat. Commun. 2017, 8, 14542
(2) Bourret et al. Nano Lett. 2018, 18, 7343; Nature Nanotechnology 2015, 10, 319; Adv. Mater. 2012 24, 6065
Synthesis of hybrid nanostructures
Synthesis of hybrid nanostructures
We are expert in the synthesis of metal/semiconductor nanowire architectures with various morphologies. We are using colloidal lithography, metal-assisted chemical etching, wet-chemical etching and templated electrochemical lithography approaches to control heterostructures with a sub-10 nm spatial resolution.
We are expert in the synthesis of metal/semiconductor nanowire architectures with various morphologies. We are using colloidal lithography, metal-assisted chemical etching, wet-chemical etching and templated electrochemical lithography approaches to control heterostructures with a sub-10 nm spatial resolution.
Nanostructuring of Si via metal-assisted chemical etching (MACE)
Nanostructuring of Si via metal-assisted chemical etching (MACE)
We have a strong expertise in the synthesis of silicon nanowire arrays using a combination of metal-assisted chemical etching (MACE) and colloidal lithography. Colloidal lithography is based on the formation of hexagonal close-packed polymeric sphere monolayers at the surface of the silicon substrate via self-assembly (done in collaboration with Prof. Vogel, FAU Erlangen). The spheres can be shrinked down with oxygen plasma, which after deposition of gold and lift-off yields a gold nanohole array, which is used as a catalytic mesh pattern for MACE. MACE is a low-cost, solution-based and high-throughput technique to nanostructure silicon using such a metal pattern to anistropically etch silicon in an HF/H2O2 solution. The preferential reduction of the H2O2 at the metal surface injects holes through the metal/silicon junction that oxidizes silicon, which dissolves in HF. Due to van der Waals interaction, the metal film drills through the silicon and forms silicon micro/nanowires.
We have a strong expertise in the synthesis of silicon nanowire arrays using a combination of metal-assisted chemical etching (MACE) and colloidal lithography. Colloidal lithography is based on the formation of hexagonal close-packed polymeric sphere monolayers at the surface of the silicon substrate via self-assembly (done in collaboration with Prof. Vogel, FAU Erlangen). The spheres can be shrinked down with oxygen plasma, which after deposition of gold and lift-off yields a gold nanohole array, which is used as a catalytic mesh pattern for MACE. MACE is a low-cost, solution-based and high-throughput technique to nanostructure silicon using such a metal pattern to anistropically etch silicon in an HF/H2O2 solution. The preferential reduction of the H2O2 at the metal surface injects holes through the metal/silicon junction that oxidizes silicon, which dissolves in HF. Due to van der Waals interaction, the metal film drills through the silicon and forms silicon micro/nanowires.
Electrochemical templated syntheses of metal-semiconductor nanowires
Electrochemical templated syntheses of metal-semiconductor nanowires
We have developed further concepts used to control metal arrays within porous alumina membranes based on electrochemical approaches. The three-dimensional electrochemical axial lithography (3DEAL) can be used to pattern pre-synthesized silicon nanowire arrays with metal structures with a sub-10 nm spatial resolution.
We have developed further concepts used to control metal arrays within porous alumina membranes based on electrochemical approaches. The three-dimensional electrochemical axial lithography (3DEAL) can be used to pattern pre-synthesized silicon nanowire arrays with metal structures with a sub-10 nm spatial resolution.
Surface-Enhanced Raman Spectroscopy
Surface-Enhanced Raman Spectroscopy
Under light irradiation, metal nanostructures can sustain localized surface plasmon resonances (LSPRs) due to the oscillation of the metal surface free electrons under the incident electric field. At the LSPR, light absorption and scattering are largely increased and the near-electric field can be enhanced by a few orders of magnitude. This effect can be used to enhance Raman scattering since the local field enhancement enhances both the incident laser excitation and the scattered photons. This leads to the so-called surface-enhanced Raman scattering, or SERS. The SERS enhancement scales roughly as E4, thus leading to a dramatic enhancement of the sensitivity of Raman spectroscopy. In collaboration with the group of Maurizio Musso, we are investigated various SERS substrates.
Under light irradiation, metal nanostructures can sustain localized surface plasmon resonances (LSPRs) due to the oscillation of the metal surface free electrons under the incident electric field. At the LSPR, light absorption and scattering are largely increased and the near-electric field can be enhanced by a few orders of magnitude. This effect can be used to enhance Raman scattering since the local field enhancement enhances both the incident laser excitation and the scattered photons. This leads to the so-called surface-enhanced Raman scattering, or SERS. The SERS enhancement scales roughly as E4, thus leading to a dramatic enhancement of the sensitivity of Raman spectroscopy. In collaboration with the group of Maurizio Musso, we are investigated various SERS substrates.
SERS
Mass-Produced SERS substrates
Metal nanoring/Si nanowire arrays
Controlling light absorption at the nanoscale
Controlling light absorption at the nanoscale
Silicon nanowire arrays have a rich interaction with light. Using the architectural control afforded by MACE, we can control light absorption at the macroscale and the nanoscale.
Silicon nanowire arrays have a rich interaction with light. Using the architectural control afforded by MACE, we can control light absorption at the macroscale and the nanoscale.
Electromagnetic simulations
Electromagnetic simulations
We perform three-dimensional electromagnetic simulations based on the finite-difference time domain (FDTD) methods. This allows us to estimate the enhancement of the electric field at the nanostructure surface and to predict light absorption and scattering spectrum.
We perform three-dimensional electromagnetic simulations based on the finite-difference time domain (FDTD) methods. This allows us to estimate the enhancement of the electric field at the nanostructure surface and to predict light absorption and scattering spectrum.
