Periodic Reporting for period 4 - FUTURE-PRINT (Tuneable 2D Nanosheet Networks for Printed Electronics)
Période du rapport: 2021-05-01 au 2023-01-31
Printed electronics are becoming increasingly relevant and will require cheap, mass-produced devices. It is thought that 2D-material based devices can surpass the state of the art in the near future. To achieve this, we will need to develop 2D inks and printing methods and learn to fabricate printed devices. The development of high performance printed devices will enable a range of technologies. For example they will transform the field of wearable health monitors by allowing sensing, data management, power and communications to be handled locally. This will allow a range of developments from gait analysis sensor arrays to heart monitors for agricultural animals.
The objective of this project is to solve these problems to the point where we can routinely print a range of devices using predominately 2D nanosheets. Solving these problems will lead to cheaper printed electronics with higher performance than is currently available. Such capabilities will enable future technologies such as the internet of things.
The objective of this project is to solve these problems to the point where we can routinely print a range of devices using predominately 2D nanosheets. Solving these problems will lead to cheaper printed electronics with higher performance than is currently available. Such capabilities will enable future technologies such as the internet of things.
This project has produced a range of new 2D materials in the form of inks including TiS2, Co(OH)2, Zn(OH)2, GeS, talc, BiOCl, FeS2, SnP3, RedP, Fe2O3 and described the nanosheet exfoliation mechanism. We developed new methods to characterize the nanosheets and measure their size.
We demonstrated a number of methods to print the resultant inks including: inkjet printing, spray coating, aerosol jet printing, vacuum filtration, slurry coating and Langmuir-Schaeffer deposition. Detailed film characterization (SEM, AFM, optical spectroscopy, XRD) was done on these films. We also developed a new characterization method using SEM and FIB to generate 3D images of nanosheet networks allowing a quantitative analysis of morphological factors such as porosity, tortuosity and nanosheet alignment.
We learned to print complex materials such as polymer/nanosheet composites and nano:nano composites which we showed to yield very high performance printed electrochemical devices e.g. battery electrodes.
We performed comprehensive electrical testing on our networks, for example measuring both conductivity and carrier mobility and how conduction depends on network morphology. We developed a theoretical model describing the relationship between nanosheet size and network conductivity and which allows the junction resistance to be extracted from data. This allowed us to quantify junction resistances for networks of graphene, WS2, WSe2, MoS2, obtaining values from 10 kOhm for graphene to 1 GOhm for the semiconducting nanosheets.
We also made printed devices consisting of only graphene nanosheet networks. These were predominantly piezo resistive sensing devices. we were able to optimize printing methods, produce very high sensitivity sensors and to quantify the sensing mechanism.
In addition, silver nanoplatelet inks were deposited via aerosol jet to yield highly conductive patterns which perform extremely well as EMI shields, transparent conductors and electrodes.
We showed that vertically stacked printed networks of conductive/insulating/conductive materials could be used as printed capacitors. We investigated a number of materials in the conductor/insulator/conductor structure using silver nanoplatelets as conductors and boron nitride and BiOCl nanosheets as insulators. We developed this theme of stacked films to produce hetero stacks including semiconducting 2D materials. We first produced heterostacks of ITO, WS2 and carbon nanotubes. We showed that these structures displayed ohmic or diode behaviour depending on the doping state of the WS2. We developed this work further printing more stacks consisting of ITO/PEDOT:PSS/ WSe2/ ZnO/Aluminium. These stacks were found to act as high performance diodes with vet high rectification ratio >10,000 and sensitive light detection performance.
Most importantly, we used printed stacks as electronic devices. Using electrolytic gating, we demonstrated all-printed, vertically stacked transistors with graphene source, drain, and gate electrodes, channels fabricated from MoS2, Ws2, MoSe2 or WSe2, and a boron nitride (BN) separator, all formed from printed networks of nanosheet. The porous interior of the BN network was filled with an ionic liquid that allows electrolytic gating in a solid-like structure. Nanosheet network transistors displayed on/off ratios of up to 10000, and mobilities of >0.1 square centimeters per volt per second. Collaborating with researchers in France, we developed novel chemical functionalization strategies which reduced junction resistance by a factor of 10, leading to a proportional mobility enhancement.
While this work was the first demonstration of printed nanosheet transistors, and a major breakthrough, the achieved mobilities were low. We used the work described above to quantify junction resistances to produce better nanosheet networks with lower junction resistance and higher mobility. This involved developing electrochemical exfoliation methods to produce high aspect ratio nanosheets which tend to form low resistance junctions as well as perfecting Langmuir Schaefer deposition methods which tend to yield highly aligned networks with overlapping nanosheets. We also developed a new method, based on impedance spectroscopy, to directly measure junction resistance. we found that the combination of high aspect ratio nanosheets and aligned films gave junction resistances of ~MOhm, much lower then the GOhm values described above. this allowed us to produce transistors based on MoS2 and WS2 networks, with mobilities above 10 cm2/Vs, close to the global state-of-the-art for printed transistors.
This project has yielded 31 papers in international journals, including high impact journals such as science and nature energy. Are paper on printed nanosheet transistors which appeared in science has been cited over 300 times. We have reported the results obtained in this project are many many conferences, with over 30 invited talks given on this topic. We have submitted 2 patent applications on printed device formation and the production of piezoresistive sensors. 1 of my postdocs has set up a spin out company to develop these printed sensors.
We demonstrated a number of methods to print the resultant inks including: inkjet printing, spray coating, aerosol jet printing, vacuum filtration, slurry coating and Langmuir-Schaeffer deposition. Detailed film characterization (SEM, AFM, optical spectroscopy, XRD) was done on these films. We also developed a new characterization method using SEM and FIB to generate 3D images of nanosheet networks allowing a quantitative analysis of morphological factors such as porosity, tortuosity and nanosheet alignment.
We learned to print complex materials such as polymer/nanosheet composites and nano:nano composites which we showed to yield very high performance printed electrochemical devices e.g. battery electrodes.
We performed comprehensive electrical testing on our networks, for example measuring both conductivity and carrier mobility and how conduction depends on network morphology. We developed a theoretical model describing the relationship between nanosheet size and network conductivity and which allows the junction resistance to be extracted from data. This allowed us to quantify junction resistances for networks of graphene, WS2, WSe2, MoS2, obtaining values from 10 kOhm for graphene to 1 GOhm for the semiconducting nanosheets.
We also made printed devices consisting of only graphene nanosheet networks. These were predominantly piezo resistive sensing devices. we were able to optimize printing methods, produce very high sensitivity sensors and to quantify the sensing mechanism.
In addition, silver nanoplatelet inks were deposited via aerosol jet to yield highly conductive patterns which perform extremely well as EMI shields, transparent conductors and electrodes.
We showed that vertically stacked printed networks of conductive/insulating/conductive materials could be used as printed capacitors. We investigated a number of materials in the conductor/insulator/conductor structure using silver nanoplatelets as conductors and boron nitride and BiOCl nanosheets as insulators. We developed this theme of stacked films to produce hetero stacks including semiconducting 2D materials. We first produced heterostacks of ITO, WS2 and carbon nanotubes. We showed that these structures displayed ohmic or diode behaviour depending on the doping state of the WS2. We developed this work further printing more stacks consisting of ITO/PEDOT:PSS/ WSe2/ ZnO/Aluminium. These stacks were found to act as high performance diodes with vet high rectification ratio >10,000 and sensitive light detection performance.
Most importantly, we used printed stacks as electronic devices. Using electrolytic gating, we demonstrated all-printed, vertically stacked transistors with graphene source, drain, and gate electrodes, channels fabricated from MoS2, Ws2, MoSe2 or WSe2, and a boron nitride (BN) separator, all formed from printed networks of nanosheet. The porous interior of the BN network was filled with an ionic liquid that allows electrolytic gating in a solid-like structure. Nanosheet network transistors displayed on/off ratios of up to 10000, and mobilities of >0.1 square centimeters per volt per second. Collaborating with researchers in France, we developed novel chemical functionalization strategies which reduced junction resistance by a factor of 10, leading to a proportional mobility enhancement.
While this work was the first demonstration of printed nanosheet transistors, and a major breakthrough, the achieved mobilities were low. We used the work described above to quantify junction resistances to produce better nanosheet networks with lower junction resistance and higher mobility. This involved developing electrochemical exfoliation methods to produce high aspect ratio nanosheets which tend to form low resistance junctions as well as perfecting Langmuir Schaefer deposition methods which tend to yield highly aligned networks with overlapping nanosheets. We also developed a new method, based on impedance spectroscopy, to directly measure junction resistance. we found that the combination of high aspect ratio nanosheets and aligned films gave junction resistances of ~MOhm, much lower then the GOhm values described above. this allowed us to produce transistors based on MoS2 and WS2 networks, with mobilities above 10 cm2/Vs, close to the global state-of-the-art for printed transistors.
This project has yielded 31 papers in international journals, including high impact journals such as science and nature energy. Are paper on printed nanosheet transistors which appeared in science has been cited over 300 times. We have reported the results obtained in this project are many many conferences, with over 30 invited talks given on this topic. We have submitted 2 patent applications on printed device formation and the production of piezoresistive sensors. 1 of my postdocs has set up a spin out company to develop these printed sensors.
Beyond state-of-the-art results demonstrating this project include:
a large range (>10) of new 2D materials;
development of various high performance printing methods (e.g. aerosol jet printing and Langmuir-Shaffer deposition);
the first all printed 2D transistor in 2017, followed in 2022 by the first flexible printed 2D transistor with mobility >10 cm2/Vs;
extremely high conductivity printed films from silver nanoplatelets;
the first explanation for sensing mechanism in piezo resistive nanosheet sensors;
new methods for the measurement of inter-nanosheet junction resistance;
demonstration of SEM/FIB for 3D imaging of nanosheet networks.
a large range (>10) of new 2D materials;
development of various high performance printing methods (e.g. aerosol jet printing and Langmuir-Shaffer deposition);
the first all printed 2D transistor in 2017, followed in 2022 by the first flexible printed 2D transistor with mobility >10 cm2/Vs;
extremely high conductivity printed films from silver nanoplatelets;
the first explanation for sensing mechanism in piezo resistive nanosheet sensors;
new methods for the measurement of inter-nanosheet junction resistance;
demonstration of SEM/FIB for 3D imaging of nanosheet networks.