ORCID Profile
0000-0003-2356-5816
Current Organisation
University of Nottingham
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Publisher: IOP Publishing
Date: 19-03-2021
Abstract: Monolayers of hexagonal boron nitride (hBN) are grown on graphite substrates using high-temperature molecular beam epitaxy (HT-MBE). The hBN monolayers are observed to grow predominantly from step edges on the graphite surface and exhibit a strong dependence of the morphology, including the dominant crystallographic edge, of the hBN monolayers, on the growth temperature, as well as systematic variations in growth rate and coverage, and significant differences in the growth at monolayer and multilayer graphite steps. At graphite monolayer steps hBN grows laterally across the surface on the lower terrace, but hBN growth on the upper side of the graphite step is more limited and is nucleated by three-dimensional clusters. Multilayer graphite steps exhibit a much higher density of non-planar hBN aggregates and growth on both the upper and lower terraces occurs. The results show that the hBN monolayer growth edge type, hBN island shape and the presence of hBN aggregates can be controlled in HT-MBE, with the highest quality layers grown at a substrate temperature of about 1390 °C. Sequential HT-MBE growth of hBN, graphene (G) and a second cycle of hBN growth results in the formation of monolayer thick lateral hBN–G–hBN heterostructures, in which a strip of G is embedded between monolayers of hBN.
Publisher: IOP Publishing
Date: 23-12-2023
Abstract: Epitaxial graphene on SiC is the most promising substrate for the next generation 2D electronics, due to the possibility to fabricate 2D heterostructures directly on it, opening the door to the use of all technological processes developed for silicon electronics. To obtain a suitable material for large scale applications, it is essential to achieve perfect control of size, quality, growth rate and thickness. Here we show that this control on epitaxial graphene can be achieved by exploiting the face-to-face annealing of SiC in ultra-high vacuum. With this method, Si atoms trapped in the narrow space between two SiC wafers at high temperatures contribute to the reduction of the Si sublimation rate, allowing to achieve smooth and virtually defect free single graphene layers. We analyse the products obtained on both on-axis and off-axis 4H-SiC substrates in a wide range of temperatures (1300 °C–1500 °C), determining the growth law with the help of x-ray photoelectron spectroscopy (XPS). Our epitaxial graphene on SiC has terrace widths up to 10 μ m (on-axis) and 500 nm (off-axis) as demonstrated by atomic force microscopy and scanning tunnelling microscopy, while XPS and Raman spectroscopy confirm high purity and crystalline quality.
Publisher: Elsevier BV
Date: 10-2019
Publisher: Wiley
Date: 08-07-2019
Publisher: Wiley
Date: 03-10-2021
Abstract: Geometrical structuring of monolithic metal‐organic frameworks (MOFs) components is required for their practical implementation in many areas, including electronic devices, gas storage/separation, catalysis, energy storage as well as bio‐medical applications. Despite progress in structuring MOFs, an approach for the precise patterning of MOF functional geometries in the millimeter‐ to micro‐meter depth is lacking. Here, a facile and flexible concept for the microfabrication of complex MOF patterns on large surfaces is reported. The method relies on the engineering of easily‐writable sheets of precursor metal oxide nanoparticles. The gas‐phase conversion of these patterned ceramic nanoparticle sheets results in monolithic MOF objects with arbitrarily shaped geometries and thicknesses of up to hundreds of micrometers. The writing of complex patterns of zeolitic imidazolate framework‐8 (ZIF‐8) is demonstrated by a variety of approaches including ion beam, laser, and hand writing. Nanometer‐scale patterns are achieved by focused ion beam (FIB). Artless handwritings are obtained by using a pen in a similar fashion to writing on a paper. The pure ZIF‐8 composition of the resulting patterns is confirmed by a series of physical and chemical characterization. This facile MOF precursor‐writing approach provides novel opportunities for the design of MOF‐based devices with applications ranging from micro‐fluidics to renewable energy systems.
Publisher: IOP Publishing
Date: 15-02-2021
Abstract: The potential of transition metal dichalcogenides such as MoS 2 for energy storage has been significantly limited so far by the lack of conductivity and structural stability. Employing highly conductive, graphitic materials in combination with transition metal dichalcogenides can address this gap. Here, we explore the use of a layered electrode structure for solid-state supercapacitors, made of MoS 2 and epitaxial graphene (EG) on cubic silicon carbide for on-silicon energy storage. We show that the energy storage of the solid-state supercapacitors can be significantly increased by creating layered MoS 2 /graphene electrodes, yielding a substantial improvement as compared to electrodes using either EG or MoS 2 alone. We conclude that the conductivity of EG and the growth morphology of MoS 2 on graphene play an enabling role in the successful use of transition metal dichalcogenides for on-chip energy storage.
Publisher: American Chemical Society (ACS)
Date: 31-07-2018
Publisher: Wiley
Date: 04-09-2018
Abstract: This work demonstrates the effect of oxygen vacancies in SnO
Publisher: IOP Publishing
Date: 29-06-2023
Abstract: Integration of graphene and hexagonal boron nitride (hBN) in lateral heterostructures has provided a route to broadly engineer the material properties by quantum confinement of electrons or introduction of novel electronic and magnetic states at the interface. In this work we demonstrate lateral heteroepitaxial growth of graphene nanoribbons (GNRs) passivated by hBN using high-temperature molecular beam epitaxy (HT-MBE) to grow graphene in oriented hBN trenches formed ex-situ by catalytic nanoparticle etching. High-resolution atomic force microscopy (AFM) reveals that GNRs grow epitaxially from the etched hBN edges, and merge to form a GNR network passivated by hBN. Using conductive AFM we probe the nanoscale electrical properties of the nanoribbons and observe quasiparticle interference patterns caused by intervalley scattering at the graphene/hBN interface, which carries implications for the potential transport characteristics of hBN passivated GNR devices.
Publisher: IOP Publishing
Date: 15-05-2020
Abstract: Integration of graphene and hexagonal boron nitride (hBN) into lateral heterostructures has drawn focus due to the ability to broadly engineer the material properties. Hybrid monolayers with tuneable bandgaps have been reported, while the interface itself possesses unique electronic and magnetic qualities. Herein, we demonstrate lateral heteroepitaxial growth of graphene and hBN by sequential growth using high-temperature molecular beam epitaxy (MBE) on highly oriented pyrolytic graphite (HOPG). We find, using scanning probe microscopy, that graphene growth nucleates at hBN step edges and grows across the surface to form nanoribbons with a controlled width that is highly uniform across the surface. The graphene nanoribbons grow conformally from the armchair edges of hexagonal hBN islands forming multiply connected regions with the growth front alternating from armchair to zigzag in regions nucleated close to the vertices of hexagonal hBN islands. Images with lattice resolution confirm a lateral epitaxial alignment between the hBN and graphene nanoribbons, while the presence of a moiré pattern within the ribbons indicates that some strain relief occurs at the lateral heterojunction. These results demonstrate that high temperature MBE is a viable route towards integrating graphene and hBN in lateral heterostructures.
Publisher: Wiley
Date: 21-07-2022
Abstract: The family of van der Waals (vdW) materials is large and erse with applications ranging from electronics and optoelectronics to catalysis and chemical storage. However, despite intensive research, there remains significant knowledge‐gaps pertaining to their properties and interactions. One such gap is the interaction between these materials and hydrogen, a potentially vital future energy vector and ubiquitous processing gas in the semiconductor industry. This work reports on the interaction of hydrogen with the vdW semiconductor SnS 2 , where molecular hydrogen (H 2 ) and H‐ions induce a controlled chemical conversion into semiconducting‐SnS or to β‐Sn. This hydrogen‐driven reaction is facilitated by the different oxidation states of Sn and is successfully applied to form SnS 2 /SnS heterostructures with uniform layers, atomically flat interfaces and well‐aligned crystallographic axes. This approach is scalable and offers a route for engineering materials at the nanoscale for semiconductor technologies based on the earth‐abundant elements Sn and S, a promising result for a wide range of potential applications.
Publisher: Elsevier BV
Date: 12-2018
Publisher: Wiley
Date: 13-10-2021
Abstract: Layered molybdenum disulphide (MoS 2 ) crystals in combination with graphene create the opportunity for the development of heterostructures with tailored surface and structural properties for energy storage applications. Herein, 2D heterostructures are developed by growing MoS 2 on epitaxial and self‐standing nanoporous graphene (NPG) using chemical vapor deposition (CVD). The effect of substrate as well as different CVD growth parameters such as temperature, amount of sulfur and MoO 3 precursors, and argon flow on the growth of MoS 2 is systematically investigated. Interestingly, various structures of MoS 2 such as monolayer triangular islands, spirals, standing sheets, and irregular stacked multilayered MoS 2 are successfully developed. The growth mechanism is proposed using different advanced characterization techniques. The formation of a continuous wetting layer with grain boundaries over the surface prior to formation of any other structures is detected. As a proof of principle, MoS 2 /NPG is employed for the first time as anode material in potassium ion battery. The electrode delivers a specific capacity of 389 mAh g −1 with over 98% stability after 200 cycles. The porous structures clearly facilitate the ion transport which is beneficial for the ion battery. These encouraging results open new opportunities to develop hierarchical heterostructures of 2D‐materials for next‐generation energy storage technologies.
Publisher: Springer Science and Business Media LLC
Date: 15-10-2020
DOI: 10.1038/S41598-020-74024-W
Abstract: Van der Waals heterostructures of monolayer transition metal dichalcogenides (TMDs) and graphene have attracted keen scientific interest due to the complementary properties of the materials, which have wide reaching technological applications. Direct growth of uniform, large area TMDs on graphene substrates by chemical vapor deposition (CVD) is limited by slow lateral growth rates, which result in a tendency for non-uniform multilayer growth. In this work, monolayer and few-layer WS 2 was grown on epitaxial graphene on SiC by sulfurization of WO 3 − x thin films deposited directly onto the substrate. Using this method, WS 2 growth was achieved at temperatures as low as 700 °C – significantly less than the temperature required for conventional CVD. Achieving long-range uniformity remains a challenge, but this process could provide a route to synthesize a broad range of TMD/graphene van der Waals heterostructures with novel properties and functionality not accessible by conventional CVD growth.
Publisher: American Chemical Society (ACS)
Date: 22-05-2019
DOI: 10.1021/ACS.LANGMUIR.8B04233
Abstract: The surface-assisted reaction of rationally designed organic precursors is an emerging approach toward fabricating atomically precise nanostructures. Recently, on-surface decarboxylation has attracted attention due to its volatile by-products, which tend to leave the surface during the reaction means only the desired products are retained on the surface. However, in addition to acting as the reactive site, the carboxylic acid groups play a vital role in the adsorption configuration of small-molecule molecular precursors and therefore in the reaction pathways. Here, scanning tunnelling microscopy (STM), synchrotron radiation photoelectron spectroscopy (SRPES), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy have been employed to characterize the monodeprotonated, fully deprotonated, and decarboxylated products of isophthalic acid (IPA) on Cu(111). IPA is partially reacted (monodeprotonated) upon adsorption on Cu(111) at room temperature. Angular-dependent X-ray photoelectron spectroscopy reveals that IPA initially anchors to the surface via the carboxylate group. After annealing, the molecule fully deprotonates and reorients so that it anchors to the surface via both carboxylate groups in a bipodal configuration. NEXAFS confirms that the molecule is tilted upon adsorption and after full deprotonation. Following decarboxylation, the flat-lying molecule forms into oligomeric motifs on the surface. This work demonstrates the importance of molecular adsorption geometry for on-surface reactions.
Publisher: Royal Society of Chemistry (RSC)
Date: 2020
DOI: 10.1039/D0TC02848G
Abstract: Graphene-protected Cu nanoislands as VOC plasmonic sensors.
Publisher: Informa UK Limited
Date: 13-04-2023
Publisher: Wiley
Date: 05-10-2023
Publisher: Elsevier BV
Date: 06-2021
Publisher: American Chemical Society (ACS)
Date: 12-08-2022
Location: United Kingdom of Great Britain and Northern Ireland
Start Date: 2021
End Date: 2024
Funder: Engineering and Physical Sciences Research Council
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