Periodic Reporting for period 4 - EvoluTEM (Illuminating Atomic Scale Processes in Liquids and Gases)
Période du rapport: 2021-10-01 au 2023-03-31
Nanomaterials have the potential to improve efficiencies, reduce costs and provide enhanced performance in a broad range of applications including optoelectronics, catalysis, functional and antibacterial coatings, bioanalysis, and targeted drug delivery. However, we are often prevented from exploiting their full potential by the difficulty of controlling growth, agglomeration and degradation at the atomic scale. The properties of nanocrystals are highly sensitive to their morphology, composition and elemental distribution. For example: the bandstructure and corresponding optical properties of quantum dots are highly sensitive to size and doping, and quantum yields can be improved by shelling; in catalysis, bimetallic nanoparticles often exhibit improved properties compared to monometallic systems, but the highest performance is only achieved by optimising alloying and elemental segregation. However, the difficulty of probing dynamic chemical processes occurring within a liquid or gas environment has limited progress in this area. Environmental-cell (e-cell) transmission electron microscopy (TEM) is the only technique with the potential to directly probe nanomaterial synthesis and degradation occurring in liquids and gases at atomic resolution with elemental sensitivity. In this project we are building new capability in atomic resolution environmental TEM imaging and analysis. We then apply this platform to synthesise new photonic nanomaterials with enhanced performance.
We have successfully demonstrated a new design of engineered graphene liquid cell with the use of hexagonal boron nitride (BN) as a spacer layer (Kelly et al, Nano Letters 2018). We have demonstrated that this makes possible atomic resolution TEM imaging and elemental analysis which is limited only by the capabilities of the microscope; previous cell designs have had reduced imaging capabilities due to the presence of the liquid environment and cell itself. We demonstrated that this new graphene liquid cell design is substantially more robust than previous designs – surviving many rounds of vacuum cycling and scanning TEM imaging at a high (200kV) accelerating voltage without losing all the liquid. This key paper provides the ideal experimental platform for development of more advanced graphene-enabled environmental cell designs, which is a key focus going forward.
Developing the graphene-BN liquid cell platform required us to develop a deeper understanding of the mechanical (bend/fold) properties of this system and this has been published (Rooney et al Nature Comms 2018). We have used knowledge gained in the realisation of this ‘graphene-BN heterostructure sandwich’ technology to aid the development of photonic and catalytically active nanomaterials. We have found that our ultrathin cells (10-100 nm liquid thickness) are ideally suited to the study of photoactive 2D materials and photonic/catalytically active nanoparticles (metals and nitrides).
Specifically we are using our developed ‘graphene-BN heterostructure sandwich’ approach to explore the synthesis and degradation of highly photoactive 2D materials that are unstable in air, resulted in several high impact publications. For example a study of degradation in 2D black phosophorus (Clark et al Nano Letters, 2018), with preceding work having established the control methodology in graphene-BN stacks (Clark et al 2D materials, 2019). We have also pioneered the investigation of the rapidly growing area of 2D monochalcogenide crystals; a family of air sensitive but highly optically 2D materials (e.g. InSe and GaSe). Our recent publications have reported optical properties in ultrathin InSe and GaSe achieved via encapsulation (Terry et al 2D materials, 2018), as well as the structure and evolution of point and extended defects (Hopkinson et al ACS Nano, 2019). Investigations of few layer silicates have demonstrated unusual flow properties (Mogg et al Nature Nanotechnology 2019). We have also demonstrated the synthesis of ultra thin metal layers in graphene oxide sandwiches, which were found to have high electrocatalytic performance (Su et al Nano Letters, 2019).
We are now investigating the potential to extend the liquid cell technology we have developed for gas phase investigations. Experiments regarding the fundamentals of gas flow in 2D nanochannels have yielded highly promising results (Keerthi et al Nature 2019). Existing gas phase environmental TEM imaging with commercial holders have demonstrated that elemental mapping can benefit the development of catalytic nanoparticles (Govender et al, Materials Characterisation, 2019, Stewart, ACS Catalysis 2019). However we believe our new graphene based technology can significantly extend capabilities.
For all dynamic experiments the realisation of high speed imaging and maximising the information obtained for a particular electron dose is critical. We have taken advantage of the high speed camera available in national facilities to reveal the mechanism of oxidation of aluminium (Nguyen et al ASC Applied Materials and Interfaces, 2018). To achieve 3D elemental mapping of beam sensitive nanoparticles we have applied the Nobel prize winning approach of single particle reconstruction to spectroscopy TEM data for the first time, revealing a unprecedented surface chemistry information (Wang et al Nano Letters, 2018).
Developing the graphene-BN liquid cell platform required us to develop a deeper understanding of the mechanical (bend/fold) properties of this system and this has been published (Rooney et al Nature Comms 2018). We have used knowledge gained in the realisation of this ‘graphene-BN heterostructure sandwich’ technology to aid the development of photonic and catalytically active nanomaterials. We have found that our ultrathin cells (10-100 nm liquid thickness) are ideally suited to the study of photoactive 2D materials and photonic/catalytically active nanoparticles (metals and nitrides).
Specifically we are using our developed ‘graphene-BN heterostructure sandwich’ approach to explore the synthesis and degradation of highly photoactive 2D materials that are unstable in air, resulted in several high impact publications. For example a study of degradation in 2D black phosophorus (Clark et al Nano Letters, 2018), with preceding work having established the control methodology in graphene-BN stacks (Clark et al 2D materials, 2019). We have also pioneered the investigation of the rapidly growing area of 2D monochalcogenide crystals; a family of air sensitive but highly optically 2D materials (e.g. InSe and GaSe). Our recent publications have reported optical properties in ultrathin InSe and GaSe achieved via encapsulation (Terry et al 2D materials, 2018), as well as the structure and evolution of point and extended defects (Hopkinson et al ACS Nano, 2019). Investigations of few layer silicates have demonstrated unusual flow properties (Mogg et al Nature Nanotechnology 2019). We have also demonstrated the synthesis of ultra thin metal layers in graphene oxide sandwiches, which were found to have high electrocatalytic performance (Su et al Nano Letters, 2019).
We are now investigating the potential to extend the liquid cell technology we have developed for gas phase investigations. Experiments regarding the fundamentals of gas flow in 2D nanochannels have yielded highly promising results (Keerthi et al Nature 2019). Existing gas phase environmental TEM imaging with commercial holders have demonstrated that elemental mapping can benefit the development of catalytic nanoparticles (Govender et al, Materials Characterisation, 2019, Stewart, ACS Catalysis 2019). However we believe our new graphene based technology can significantly extend capabilities.
For all dynamic experiments the realisation of high speed imaging and maximising the information obtained for a particular electron dose is critical. We have taken advantage of the high speed camera available in national facilities to reveal the mechanism of oxidation of aluminium (Nguyen et al ASC Applied Materials and Interfaces, 2018). To achieve 3D elemental mapping of beam sensitive nanoparticles we have applied the Nobel prize winning approach of single particle reconstruction to spectroscopy TEM data for the first time, revealing a unprecedented surface chemistry information (Wang et al Nano Letters, 2018).
Our new engineered graphene liquid cells have enabled us to go beyond simply imaging in liquid to allow us to perform the first dynamic reactions in graphene liquid cells. We have performed a plethora of nanomaterials synthesis and degradation reactions with several papers in the final stages of writing and manuscript submission. Using our newly acquired skills we are just beginning the stage of in situ electrochemical testing. Following the success of gas flow testing (Keerthi et al Nature 2019,) this is another exciting area of current TEM experiments, which is expected to yield several high impact publications in the next 12 months. We are also extending our nanoparticle work to achieve better time resolution while maintaining elemental sensitivity. Finally current work has demonstrated exciting results on synthesis and degradation of magnetic 2D crystals which likely to yield several good publications before the end of the project.