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7 results on '"Cottam, Nathan D."'

1. Surface decoration of graphene with all-inorganic perovskite nanocrystals

Author

Cottam, Nathan D.

Subjects
QC501 Electricity and magnetism
Abstract

Recent progress in the synthesis of high stability inorganic caesium lead halide perovskite nanocrystals (NCs) with unique optical and electronic properties has led to their increasing use in optoelectronic applications, such as broadband photodetectors. These NCs are of particular interest for the UV range as they have the potential to extend the wavelength range of photodetectors based on traditional materials. The physical properties of these nanostructures, such as the dynamics of charge carriers on different timescales and their effect on the optical recombination of carriers, are crucial for functional applications, but not yet fully understood. This work reports on a slow (> 1 s) reversible quenching of the NC photoluminescence due to a light-induced Stark effect involving defects on the surface of the NCs and the redistribution of photoexcited carriers onto the NC surface. We also demonstrate a defect-assisted high photoconductive gain (10⁶ A/W) in the UV-Visible range for graphene transistors decorated with perovskite NCs, resulting from the charge transfer between the NCs and graphene. This is accompanied by a giant hysteresis of the graphene resistance that is strongly dependent on electrostatic gating and temperature. We summarise the properties of the perovskite/graphene transistor with 3 characteristic response times: optical (∼ 10 s); electrical (∼ 100 s); and magnetic (∼ 500 s). Our data are well described by a phenomenological macroscopic 'two-capacitor' model of the charge transfer from bound states in the NCs into the graphene layer, providing a useful tool for the design of high-photoresponsivity perovskite/graphene transistors. Finally, we investigate the prospects of using scalable additive manufacturing, specifically inkjet printing, of graphene (iGraphene) and other low-dimensional materials for development of fully printed optoelectronic devices compatible with a range of flexible and wearable substrates. We demonstrate a hybrid perovskite/iGraphene photodetector with responsivity ∼15 A/W and use iGraphene as Ohmic contacts to other 2D materials.

Published
2022

2. Universal mobility characteristics of graphene originating from electron/hole scattering by ionised impurities

Author

Gosling, Jonathan H., Makarovsky, Oleg, Wang, Feiran, Cottam, Nathan D, Greenaway, Mark T., Patanè, Amalia, Wildman, Ricky, Tuck, Christopher J., Turyanska, Lyudmila, and Fromhold, T. Mark

Subjects
Condensed Matter - Materials Science, 82
Abstract

Pristine graphene and graphene-based heterostructures exhibit exceptionally high electron mobility and conductance if their surface contains few electron-scattering impurities. Here, we reveal a universal connection between graphene's carrier mobility and the variation of its electrical conductance with carrier density. Our model of graphene conductivity is based on a convolution of carrier density and its uncertainty, which reproduces the observed universality. Taking a single conductance measurement as input, this model accurately predicts the full shape of the conductance versus carrier density curves for a wide range of reported graphene samples. We verify the convolution model by numerically solving the Boltzmann transport equation to analyse in detail the effects of charged impurity scattering on carrier mobility. In this model, we also include optical phonons, which relax high-energy charge carriers for small impurity densities. Our numerical and analytical results both capture the universality observed in experiment and provide a way to estimate all key transport parameters of graphene devices. Our results demonstrate how the carrier mobility can be predicted and controlled, thereby providing insights for engineering the properties of 2D materials and heterostructures., Comment: 20 pages, 4 figures

Published
2020

4. Magnetic and Electric Field Dependent Charge Transfer in Perovskite/Graphene Field Effect Transistors.

Author

Cottam, Nathan D., Austin, Jonathan S., Zhang, Chengxi, Patanè, Amalia, Escoffier, Walter, Goiran, Michel, Pierre, Mathieu, Coletti, Camilla, Mišeikis, Vaidotas, Turyanska, Lyudmila, and Makarovsky, Oleg

Subjects
FIELD-effect transistors, CHARGE transfer, MAGNETIC fields, ELECTRIC fields, GRAPHENE, PEROVSKITE
Abstract

Stable all‐inorganic CsPbX3 perovskite nanocrystals (PNCs) with high optical yield can be used in combination with graphene as photon sensors with high responsivity (up to 106 A W−1) in the VIS‐UV range. The performance of these perovskite/graphene field effect transistors (FET) is mediated by charge transfer processes at the perovskite – graphene interface. Here, the effects of high electric (up to 3000 kV cm−1) and magnetic (up to 60 T) fields applied perpendicular to the graphene plane on the charge transfer are reported. The authors demonstrate electric‐ and magnetic‐field dependent charge transfer and a slow (>100 s) charge dynamics. Magneto‐transport experiments in constant (≈0.005 T s−1) and pulsed (≈1000 T s−1) magnetic fields reveal pronounced hysteresis effects in the transfer characteristics of the FET. A magnetic time is used to explain and model differences in device behavior under fast (pulsed) and slowly (continuous) changing magnetic fields. The understanding of the dynamics of the charge transfer in perovskite/graphene heterostructures developed here is relevant for exploitation of these hybrid systems in electronics and optoelectronics, including ultrasensitive photon detectors and FETs for metrology. [ABSTRACT FROM AUTHOR]

Published
2023
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5. Light-Induced Stark Effect and Reversible Photoluminescence Quenching in Inorganic Perovskite Nanocrystals

Author

Cottam, Nathan D., Zhang, Chengxi, Wildman, Joni L., Turyanska, Lyudmila, and Makarovsky, Oleg

Abstract

Inorganic perovskite nanocrystals (NCs) have demonstrated a number of unique optical and electronic properties for optoelectronic applications. However, the physical properties of these nanostructures, such as the dynamics of charge carriers on different timescales and their effect on the optical recombination of carriers, are not yet fully understood. This work reports on a slow (>1s) reversible quenching of the NC photoluminescence due to a light-induced Stark effect involving defects on the surface of the NCs and the redistribution of photoexcited carriers onto the NC surface. This phenomenon can influence the operation of optoelectronic devices based on these NCs, including hybrid photosensors based on graphene decorated with inorganic perovskite NCs, revealing their prospects and limitations.

Published
2021

6. Inter-Flake Quantum Transport of Electrons and Holes in Inkjet-Printed Graphene Devices

Author

Wang, Feiran, Gosling, Jonathan H, Trindade, Gustavo F, Rance, Graham A, Makarovsky, Oleg, Cottam, Nathan D, Kudrynskyi, Zakhar, Balanov, Alexander G, Greenaway, Mark T, Wildman, Ricky D., Hague, Richard, Tuck, Christopher, Fromhold, T. Mark, and Turyanska, Lyudmila

Subjects
percolation dynamics, inkjet printing, field effect transistor, graphene, Monte Carlo simulations
Abstract

© 2020 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH 2D materials have unique structural and electronic properties with potential for transformative device applications. However, such devices are usually bespoke structures made by sequential deposition of exfoliated 2D layers. There is a need for scalable manufacturing techniques capable of producing high-quality large-area devices comprising multiple 2D materials. Additive manufacturing with inks containing 2D material flakes is a promising solution. Inkjet-printed devices incorporating 2D materials have been demonstrated, however there is a need for greater understanding of quantum transport phenomena as well as their structural properties. Experimental and theoretical studies of inkjet-printed graphene structures are presented. Detailed electrical and structural characterization is reported and explained by comparison with transport modeling that include inter-flake quantum tunneling transport and percolation dynamics. The results reveal that the electrical properties are strongly influenced by the flakes packing fraction and by complex meandering electron trajectories, which traverse several printed layers. Controlling these trajectories is essential for printing high-quality devices that exploit the properties of 2D materials. Inkjet-printed graphene is used to make a field effect transistor and Ohmic contacts on an InSe phototransistor. This is the first time that inkjet-printed graphene has successfully replaced single layer graphene as a contact material for 2D metal chalcogenides.

Published
2021

7. Surface decoration of graphene with all-inorganic perovskite nanocrystals

Author

Cottam, Nathan D. and Cottam, Nathan D.

Abstract

Recent progress in the synthesis of high stability inorganic caesium lead halide perovskite nanocrystals (NCs) with unique optical and electronic properties has led to their increasing use in optoelectronic applications, such as broadband photodetectors. These NCs are of particular interest for the UV range as they have the potential to extend the wavelength range of photodetectors based on traditional materials. The physical properties of these nanostructures, such as the dynamics of charge carriers on different timescales and their effect on the optical recombination of carriers, are crucial for functional applications, but not yet fully understood. This work reports on a slow (> 1 s) reversible quenching of the NC photoluminescence due to a light-induced Stark effect involving defects on the surface of the NCs and the redistribution of photoexcited carriers onto the NC surface. We also demonstrate a defect-assisted high photoconductive gain (10^6 A/W) in the UV–Visible range for graphene transistors decorated with perovskite NCs, resulting from the charge transfer between the NCs and graphene. This is accompanied by a giant hysteresis of the graphene resistance that is strongly dependent on electrostatic gating and temperature. We summarise the properties of the perovskite/graphene transistor with 3 characteristic response times: optical (∼ 10 s); electrical (∼ 100 s); and magnetic (∼ 500 s). Our data are well described by a phenomenological macroscopic ‘two-capacitor’ model of the charge transfer from bound states in the NCs into the graphene layer, providing a useful tool for the design of high-photoresponsivity perovskite/graphene transistors. Finally, we investigate the prospects of using scalable additive manufacturing, specifically inkjet printing, of graphene (iGraphene) and other low-dimensional materials for development of fully printed optoelectronic devices compatible with a range of flexible and wearable substrates. We demonstrate a hybrid perovskite

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