Periodic Reporting for period 1 - 2DvdWHs (Layer-by-layer Assembly of Two-dimensional Polymer/ Graphene Heterostructures as Wafer-scale Flexible Opto-electronics)
Berichtszeitraum: 2020-02-01 bis 2022-01-31
Two-dimensional (2D) materials have been of great importance in nature and in technology, owing to their astonishing properties, which are different from those of their bulk counterparts. As a structural analogue of graphene, 2D polymers (2DPs) are macromolecules as topologically planar, separable, monolayer (ML) sheets with covalent (strong) bonds and long-ranging internal periodicity, whose physical and chemical properties depend on their building blocks, linkages, and topographies. [4+4]-Photocycloaddition between neighboring anthracene pairs with a face-to-face stacked packing can afford the controlled lateral polymerization of suitable monomers both in single crystals and in Langmuir–Blodgett (LB) MLs on the air/water interface, resulting in the formation of 2DPs. However, it is still challenging to locally control [4+4]-photocycloaddition to form covalent 2D materials at the nanoscale and molecular level.
Tip-enhanced Raman spectroscopy (TERS) integrates nanoscale spatial resolution of scanning probe microscopy (SPM) with the chemical selectivity of Raman spectroscopy, and can simultaneously provide topographic and molecular information on samples in a label-free fashion. By means of field enhancement due to a combination of localized surface plasmon resonances and a lightning-rod effect at a metallic tip apex, TERS has shown single-molecule sensitivity and down to subnanometer spatial resolution for experiments carried out on special samples at cryogenic temperatures.
By means of TERS techniques, the fellow can
(a) manipulate and visualize photon–electron molecule interactions during plasmon-induced [4+4]-cycloaddition polymerization of anthracene-based monomers on Au(111) via TERS imaging in real-time and space;
(b) obtain a 2DP nanoribbon from certain locations in monomer 1 ML when sufficient hot carriers were generated;
(c) shed light on the nanolithography of 2DP monolayers by manipulating the plasmon-induced [4+4]-cycloaddition reaction.
The work carried out in this project can enhance innovation capacity in plasmon-induced chemical reactions (PICRs) and 2D organic monolayers:
(a) Catalysis mechanism: Understanding the interaction between incident light, hot carriers, and target molecules during PICRs at the nanoscale will help to recognize the reaction mechanisms and promote the chemical transformation of the plasmon-mediated photocatalysis, which in turn should provide insights into how to rationally design efficient plasmonic catalysts.
(b) Growth mechanism: The need to grow a 2D polymer in two directions rather than only in one is extremely important in planar polymerizations. Direct experimental evidence supported for a self-stimulating growth mechanism.
(c) Plasmon-induced nanolithography: Nanolithography can create nanoscale patterns on different media, e.g. on silicon wafers and molecular monolayers, used in various fields of technology from electronic to biomedical devices. The current plasmon-induced nanolithography is the potential to write new 2D patterns onto a molecular monolayer.
Tip-enhanced Raman spectroscopy (TERS) integrates nanoscale spatial resolution of scanning probe microscopy (SPM) with the chemical selectivity of Raman spectroscopy, and can simultaneously provide topographic and molecular information on samples in a label-free fashion. By means of field enhancement due to a combination of localized surface plasmon resonances and a lightning-rod effect at a metallic tip apex, TERS has shown single-molecule sensitivity and down to subnanometer spatial resolution for experiments carried out on special samples at cryogenic temperatures.
By means of TERS techniques, the fellow can
(a) manipulate and visualize photon–electron molecule interactions during plasmon-induced [4+4]-cycloaddition polymerization of anthracene-based monomers on Au(111) via TERS imaging in real-time and space;
(b) obtain a 2DP nanoribbon from certain locations in monomer 1 ML when sufficient hot carriers were generated;
(c) shed light on the nanolithography of 2DP monolayers by manipulating the plasmon-induced [4+4]-cycloaddition reaction.
The work carried out in this project can enhance innovation capacity in plasmon-induced chemical reactions (PICRs) and 2D organic monolayers:
(a) Catalysis mechanism: Understanding the interaction between incident light, hot carriers, and target molecules during PICRs at the nanoscale will help to recognize the reaction mechanisms and promote the chemical transformation of the plasmon-mediated photocatalysis, which in turn should provide insights into how to rationally design efficient plasmonic catalysts.
(b) Growth mechanism: The need to grow a 2D polymer in two directions rather than only in one is extremely important in planar polymerizations. Direct experimental evidence supported for a self-stimulating growth mechanism.
(c) Plasmon-induced nanolithography: Nanolithography can create nanoscale patterns on different media, e.g. on silicon wafers and molecular monolayers, used in various fields of technology from electronic to biomedical devices. The current plasmon-induced nanolithography is the potential to write new 2D patterns onto a molecular monolayer.
In this project, the fellow studied a plasmon-induced [4+4]-cycloaddition in-situ, using 2D arrays of anthracene-based monomers deposited on Au(111) using TERS imaging and density functional theory (DFT) calculations. This work extended the mechanistic understanding of PICRs and shows a way for localized design at the nanometer scale and molecular level of covalent 2D materials.
The works carried out and overview of the progress:
(a) Amphiphilic monomers 1 and 2 with the same anthracene-based backbone but different substituents were utilized for forming the corresponding 2DPs exciting both by UV laser irradiation (365 nm, 3.40 eV) and hot carriers (EF + 1.96 eV). These monomers exhibit an antiparallel packing of the anthracene blades that are perfectly positioned for [4+4]-photocycloaddition to form 2DPs (Fig. 1).
(b) The monomer MLs were prepared at an air/water interface on a LB trough, which allowed for the controllable transfer of those MLs onto Au(111) with physisorbed molecule/substrate interactions. The same TER spectral features of the plasmon-induced 2DPs as those produced by UV light irradiation were found. However, the different substituent and spatial effects from their molecular structures were shown to affect the catalytic activity of the hot carriers.
(c) TERS imaging observed the in-plane polymerization within individual map pixels (3.125 × 3.125 nm2) and resolved single 2DP 1 growth areas with ~3.7 nm spatial resolution. Combined with DFT calculations, the fellow proposed that the 2D polymerization is initiated from the formation of transient negative ion and triplet excited states, and that hot electron transfer occurs from Au(111) to the MLs through an inelastic tunneling process.
(d) Applying hot carriers to these MLs in consecutive scans supports the view that initially formed areas with polymer triggers further polymer growth in their direct proximity, which would be the characteristics of a self-stimulating growth mechanism.
The fellow has popularized his academic publications on Twitter (https://twitter.com/ChemistryNews/status/1419960772998754308; https://twitter.com/nanotrac/status/1419978389134483460) Facebok (https://www.facebook.com/permalink.php?story_fbid=2979314989001972&id=1658850487715102) and WeChat (http://m.nanoer.net/main/view?id=34084) to increase the public understanding of the scientific results, promote the work to the general public, connect the general public with the scientific community, make the proposed research understandable and attractive to the public, and promote the impact of the MSCA action.
The works carried out and overview of the progress:
(a) Amphiphilic monomers 1 and 2 with the same anthracene-based backbone but different substituents were utilized for forming the corresponding 2DPs exciting both by UV laser irradiation (365 nm, 3.40 eV) and hot carriers (EF + 1.96 eV). These monomers exhibit an antiparallel packing of the anthracene blades that are perfectly positioned for [4+4]-photocycloaddition to form 2DPs (Fig. 1).
(b) The monomer MLs were prepared at an air/water interface on a LB trough, which allowed for the controllable transfer of those MLs onto Au(111) with physisorbed molecule/substrate interactions. The same TER spectral features of the plasmon-induced 2DPs as those produced by UV light irradiation were found. However, the different substituent and spatial effects from their molecular structures were shown to affect the catalytic activity of the hot carriers.
(c) TERS imaging observed the in-plane polymerization within individual map pixels (3.125 × 3.125 nm2) and resolved single 2DP 1 growth areas with ~3.7 nm spatial resolution. Combined with DFT calculations, the fellow proposed that the 2D polymerization is initiated from the formation of transient negative ion and triplet excited states, and that hot electron transfer occurs from Au(111) to the MLs through an inelastic tunneling process.
(d) Applying hot carriers to these MLs in consecutive scans supports the view that initially formed areas with polymer triggers further polymer growth in their direct proximity, which would be the characteristics of a self-stimulating growth mechanism.
The fellow has popularized his academic publications on Twitter (https://twitter.com/ChemistryNews/status/1419960772998754308; https://twitter.com/nanotrac/status/1419978389134483460) Facebok (https://www.facebook.com/permalink.php?story_fbid=2979314989001972&id=1658850487715102) and WeChat (http://m.nanoer.net/main/view?id=34084) to increase the public understanding of the scientific results, promote the work to the general public, connect the general public with the scientific community, make the proposed research understandable and attractive to the public, and promote the impact of the MSCA action.
Progress beyond the state of the art:
With travel restricted during the COVID-19 pandemic, the fellow had to adjust the project. The updated idea for the project switched to fabricating 2D organic/inorganic vdWHs nanodevices by using a mechanical exfoliation method. Since the 2DP based on the [2 + 2]-cycloaddition is reversible at around 150 °C, the prepared vertical nanotransistors are the new generation of 2D vdWHs with tunable optical bandgaps. To the best of our knowledge, these are the first 2D organic/inorganic field-effect tunneling transistors that integrated 2DPs with Gr with flexible properties based on their unique interlayer interactions.
Expected results:
The corresponding results are expected to contribute to a new paper in Nature Communications.
Potential impacts:
Since 2DPs offer great flexibility in composition, porosity, modifiability, and other physicochemical properties, which enable their applications in optoelectronic devices, membrane separation, surface catalysis, and molecular sensing. Consequently, 2DPs can be the ideal candidate to integrate with Gr through layer-by-layer assembly, which will lead to a new generation vdWHs with tunable and customized opto-electronic properties for engineering devices for the future technologies. Additionally, by combining the tape exfoliation method with polymer transfer techniques together, not only the properties, orders, and numbers of individual 2D monolayers but also the atomic layer precise can be controlled and realized easily. This vertical layer-by-layer strategy can also be extended to other 2D materials (e.g. transition metal dichalcogenides (TMDCs) and hexagonal boron nitride (hBN)) and monomer systems.
With travel restricted during the COVID-19 pandemic, the fellow had to adjust the project. The updated idea for the project switched to fabricating 2D organic/inorganic vdWHs nanodevices by using a mechanical exfoliation method. Since the 2DP based on the [2 + 2]-cycloaddition is reversible at around 150 °C, the prepared vertical nanotransistors are the new generation of 2D vdWHs with tunable optical bandgaps. To the best of our knowledge, these are the first 2D organic/inorganic field-effect tunneling transistors that integrated 2DPs with Gr with flexible properties based on their unique interlayer interactions.
Expected results:
The corresponding results are expected to contribute to a new paper in Nature Communications.
Potential impacts:
Since 2DPs offer great flexibility in composition, porosity, modifiability, and other physicochemical properties, which enable their applications in optoelectronic devices, membrane separation, surface catalysis, and molecular sensing. Consequently, 2DPs can be the ideal candidate to integrate with Gr through layer-by-layer assembly, which will lead to a new generation vdWHs with tunable and customized opto-electronic properties for engineering devices for the future technologies. Additionally, by combining the tape exfoliation method with polymer transfer techniques together, not only the properties, orders, and numbers of individual 2D monolayers but also the atomic layer precise can be controlled and realized easily. This vertical layer-by-layer strategy can also be extended to other 2D materials (e.g. transition metal dichalcogenides (TMDCs) and hexagonal boron nitride (hBN)) and monomer systems.