Imperial College London

ProfessorCeciliaMattevi

Faculty of EngineeringDepartment of Materials

Professor of Materials Science
 
 
 
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Contact

 

+44 (0)20 7594 0833c.mattevi

 
 
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Location

 

2.11Royal School of MinesSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
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83 results found

Tagliaferri S, Nagaraju G, Sokolikova M, Quintin-Baxendale R, Mattevi Cet al., 2024, 3D printing of layered vanadium disulfide for water-in-salt electrolyte zinc-ion batteries., Nanoscale Horiz

Miniaturized aqueous zinc ion batteries are attractive energy storage devices for wearable electronics, owing to their safety and low cost. Layered vanadium disulfide (VS2) has demonstrated competitive charge storage capability for aqueous zinc ion batteries, as a result of its multivalent states and large interlayer spacing. However, VS2 electrodes are affected by quick oxide conversion, and they present predefined geometries and aspect ratios, which hinders their integration in wearables devices. Here, we demonstrate the formulation of a suitable ink for extrusion-based 3D printing (direct ink writing) based on micro flowers of layered VS2 obtained using a scalable hydrothermal process. 3D printed architectures of arbitrary design present electrochemically active, porous and micron-sized struts with tuneable mass loading. These were used as cathodes for aqueous zinc-ion battery electrodes. The 3D printed VS2 cathodes were assembled with carbon/zinc foil anodes to form full cells of zinc-ion, demonstrating a capacity of ∼1.98 mA h cm-2 with an operating voltage of 1.5 V. Upon cycling a capacity retention of around 65% was achieved after ∼100 cycles. The choice of the electrolyte (a water-in-salt electrolyte) and the design of the pre-processing of the 3D printed cathode ensured improved stability against dissolution and swift oxidation, notorious challenges for VS2 in an aqueous environment. This works paves the way towards programmable manufacturing of miniaturized aqueous batteries and the materials processing approach can be applied to different materials and battery systems to improve stability.

Journal article

Panagiotopoulos A, Nagaraju G, Tagliaferri S, Grotta C, Sherrell PC, Sokolikova M, Cheng G, Iacoviello F, Sharda K, Mattevi Cet al., 2023, 3D printed inks of two-dimensional semimetallic MoS<sub>2</sub>/TiS<sub>2</sub> nanosheets for conductive-additive-free symmetric supercapacitors, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 11, Pages: 16190-16200, ISSN: 2050-7488

Journal article

Sokolikova MS, Cheng G, Och M, Palczynski P, El Hajraoui K, Ramasse QM, Mattevi Cet al., 2023, Tuning the 1T′/2H phases in W<sub><i>x</i></sub>Mo<sub>1-<i>x</i></sub>Se<sub>2</sub> nanosheets, NANOSCALE, Vol: 15, Pages: 2714-2725, ISSN: 2040-3364

Journal article

Och M, Anastasiou K, Leontis I, Zemignani GZ, Palczynski P, Mostaed A, Sokolikova MS, Alexeev EM, Bai H, Tartakovskii A, Lischner J, Nellist PD, Russo S, Mattevi Cet al., 2022, Synthesis of mono- and few-layered n-type WSe<sub>2</sub> from solid state inorganic precursors, NANOSCALE, Vol: 14, Pages: 15651-15662, ISSN: 2040-3364

Journal article

Rubio N, Suter T, Rana Z, Clancy AJ, Masuda S, Au H, Coulter G, Sirisinudomkit P, McMillan PF, Howard CA, Mattevi C, Brett DJL, Shaffer MSPet al., 2022, Platinum deposition on functionalised graphene for corrosion resistant oxygen reduction electrodes, JOURNAL OF MATERIALS CHEMISTRY A, Vol: 10, Pages: 20121-20127, ISSN: 2050-7488

Journal article

Guo Z, Cheng G, Xu Z, Xie F, Hu Y-S, Mattevi C, Titirici M-M, Ribadeneyra MCet al., 2022, Sodium Dual-Ion Batteries with Concentrated Electrolytes, CHEMSUSCHEM, ISSN: 1864-5631

Journal article

Nagaraju G, Tagliaferri S, Panagiotopoulos A, Och M, Quintin-Baxendale R, Mattevi Cet al., 2022, Durable Zn-ion hybrid capacitors using 3D printed carbon composites., J Mater Chem A Mater, Vol: 10, Pages: 15665-15676, ISSN: 2050-7488

Rechargeable Zn-ion hybrid capacitors (ZHCs) have gained considerable attention towards future energy storage applications owing to their non-flammable nature, high abundance of raw materials and remarkable energy storage performance. However, the uncontrolled growth of dendrites, interfacial corrosion of Zn anodes and limited mass loading of cathode materials, hinders their practical applicability. Herein, we demonstrate ZHCs with enhanced capacity and durability using a synergistic combination of a hybrid-ion electrolyte and a high-mass loading three-dimensionally (3D) printed graphene-carbon nanotube (Gr-C) cathode. The hybrid electrolyte composed of NaCl and ZnSO4, features higher ionic conductivity and lower pH compared with pristine ZnSO4, which enable uniform plating/stripping of Zn2+ ions on Zn anode, as demonstrated by in situ electrochemical and ex situ ToF-SIMs characterizations. Additionally, the multi-layered 3D Gr-C composite electrodes in ZHCs enable higher energy storage performance due to their porous architectures, high ion accessibility and dual-ion charge storage contributions. As a result, the 3D Gr-C//Zn cell unveiled a maximum capacity of 0.84 mA h cm-2 at 3 mA cm-2 with a high life cycle (78.7% at 20 mA cm-2) compared to the pristine electrolyte-based ZHCs (0.72 mA h cm-2 and 14.8%). The rapid rate measurements that we propose along with benchmarked energy density (0.87 mW h cm-2) and power density (31.7 mW cm-2) of hybrid electrolyte-based 3D Gr-C//Zn, pave the way for the development of dendrite-free and highly durable 3D energy storage devices.

Journal article

Xu L, Ramadan S, Rosa BG, Zhang Y, Yin T, Torres E, Shaforost O, Panagiotopoulos A, Li B, Kerherve G, Kim DK, Mattevi C, Jiao LR, Petrov PK, Klein Net al., 2022, On-chip integrated graphene aptasensor with portable readout for fast and label-free COVID-19 detection in virus transport medium., Sens Diagn, Vol: 1, Pages: 719-730

Graphene field-effect transistor (GFET) biosensors exhibit high sensitivity due to a large surface-to-volume ratio and the high sensitivity of the Fermi level to the presence of charged biomolecules near the surface. For most reported GFET biosensors, bulky external reference electrodes are used which prevent their full-scale chip integration and contribute to higher costs per test. In this study, GFET arrays with on-chip integrated liquid electrodes were employed for COVID-19 detection and functionalized with either antibody or aptamer to selectively bind the spike proteins of SARS-CoV-2. In the case of the aptamer-functionalized GFET (aptasensor, Apt-GFET), the limit-of-detection (LOD) achieved was about 103 particles per mL for virus-like particles (VLPs) in clinical transport medium, outperforming the Ab-GFET biosensor counterpart. In addition, the aptasensor achieved a LOD of 160 aM for COVID-19 neutralizing antibodies in serum. The sensors were found to be highly selective, fast (sample-to-result within minutes), and stable (low device-to-device signal variation; relative standard deviations below 0.5%). A home-built portable readout electronic unit was employed for simultaneous real-time measurements of 12 GFETs per chip. Our successful demonstration of a portable GFET biosensing platform has high potential for infectious disease detection and other health-care applications.

Journal article

Shao F, Woo SY, Wu N, Schneider R, Mayne AJ, De Vasconcellos SM, Arora A, Carey BJ, Preuß JA, Bonnet N, Och M, Mattevi C, Watanabe K, Taniguchi T, Niu Z, Bratschitsch R, Tizei LHGet al., 2022, Substrate influence on transition metal dichalcogenide monolayer exciton absorption linewidth broadening, Physical Review Materials, Vol: 6

The excitonic states of transition metal dichalcogenide (TMD) monolayers are heavily influenced by their external dielectric environment and depend on the substrate used. In this work, various wide band gap dielectric materials, namely hexagonal boron nitride (h-BN) and amorphous silicon nitride (Si3N4), under different configurations as support or encapsulation material for WS2 monolayers, are investigated to disentangle the factors contributing to inhomogeneous broadening of exciton absorption lines in TMDs using electron energy loss spectroscopy in a scanning transmission electron microscope. In addition, monolayer roughness in each configuration was determined from tilt series of electron diffraction patterns by assessing the broadening of diffraction spots by comparison with simulations. From our experiments, the main factors that play a role in linewidth broadening can be classified, in increasing order of importance, by monolayer roughness, surface cleanliness, and substrate-induced charge trapping. Furthermore, because high-energy electrons are used as a probe, electron-beam-induced damage on bare TMD monolayers is also revealed to be responsible for irreversible linewidth increases. h-BN not only provides clean surfaces of TMD monolayers and minimal charge disorder, but can also protect the TMD from irradiation damage. This work provides a better understanding of the mechanisms by which h-BN remains, to date, the most compatible material for 2D material encapsulation, facilitating the realization of intrinsic material properties to their full potential.

Journal article

Rubio N, Au H, Coulter GO, Guetaz L, Gebel G, Mattevi C, Shaffer MSPet al., 2021, Effect of graphene flake size on functionalisation: quantifying reaction extent and imaging locus with single Pt atom tags, Chemical Science, Vol: 12, Pages: 1-13, ISSN: 2041-6520

Here, the locus of functionalisation on graphene-related materials and the progress of the reaction is shown to depend strongly on the starting feedstock. Five characteristically different graphite sources were exfoliated and functionalized using a non-destructive chemical reduction method. These archetypical examples were compared via a model reaction, grafting dodecyl addends, evaluated with TGA-MS, XPS and Raman data. A general increase in grafting ratio (ranging from 1.1 wt% up to 25 wt%) and an improvement in grafting stoichiometry (C/R) were observed as flake radius decreased. Raman spectrum imaging of the functionalised natural flake graphite identified that grafting is directed towards flake edges. This behaviour was further corroborated, at atomistic resolution, by functionalising the graphene layers with bipyridine groups able to complex single platinum atoms. The distribution of these groups was then directly imaged using aberration-corrected HAADF-STEM. Platinum atoms were found to be homogeneously distributed across smaller graphenes; in contrast, a more heterogeneous distribution, with a predominance of edge grafting was observed for larger graphites. These observations show that grafting is directed towards flake edges, but not necessary at edge sites; the mechanism is attributed to the relative inaccessibility of the inner basal plane to reactive moieties, resulting in kinetically driven grafting nearer flake edges. This phenomenology may be relevant to a wide range of reactions on graphenes and other 2d materials.

Journal article

Tagliaferri S, Nagaraju G, Panagiotopoulos A, Och M, Cheng G, Iacoviello F, Mattevi Cet al., 2021, Aqueous inks of pristine graphene for 3D printed microsupercapacitors with high capacitance., ACS Nano, Vol: 15, Pages: 15342-15353, ISSN: 1936-0851

Three-dimensional (3D) printing is gaining importance as a sustainable route for the fabrication of high-performance energy storage devices. It enables the streamlined manufacture of devices with programmable geometry at different length scales down to micron-sized dimensions. Miniaturized energy storage devices are fundamental components for on-chip technologies to enable energy autonomy. In this work, we demonstrate 3D printed microsupercapacitor electrodes from aqueous inks of pristine graphene without the need of high temperature processing and functional additives. With an intrinsic electrical conductivity of ∼1370 S m-1 and rationally designed architectures, the symmetric microsupercapacitors exhibit an exceptional areal capacitance of 1.57 F cm-2 at 2 mA cm-2 which is retained over 72% after repeated voltage holding tests. The areal power density (0.968 mW cm-2) and areal energy density (51.2 μWh cm-2) outperform the ones of previously reported carbon-based supercapacitors which have been either 3D or inkjet printed. Moreover, a current collector-free interdigitated microsupercapacitor combined with a gel electrolyte provides electrochemical performance approaching the one of devices with liquid-like ion transport properties. Our studies provide a sustainable and low-cost approach to fabricate efficient energy storage devices with programmable geometry.

Journal article

Suter TAM, Clancy AJ, Rubio Carrero N, Heitzmann M, Guetaz L, Shearing PR, Mattevi C, Gebel G, Howard CA, Shaffer MSP, McMillan PF, Brett DJLet al., 2021, Scalable sacrificial templating to increase porosity and platinum utilisation in graphene-based polymer electrolyte fuel cell electrodes, Nanomaterials, Vol: 11, Pages: 1-13, ISSN: 2079-4991

Polymer electrolyte fuel cells hold great promise for a range of applications but require advances in durability for widespread commercial uptake. Corrosion of the carbon support is one of the main degradation pathways; hence, corrosion-resilient graphene has been widely suggested as an alternative to traditional carbon black. However, the performance of bulk graphene-based electrodes is typically lower than that of commercial carbon black due to their stacking effects. This article reports a simple, scalable and non-destructive method through which the pore structure and platinum utilisation of graphene-based membrane electrode assemblies can be significantly improved. Urea is incorporated into the catalyst ink before deposition, and is then simply removed from the catalyst layer after spraying by submerging the electrode in water. This additive hinders graphene restacking and increases porosity, resulting in a significant increase in Pt utilisation and current density. This technique does not require harsh template etching and it represents a pathway to significantly improve graphene-based electrodes by introducing hierarchical porosity using scalable liquid processes.

Journal article

Tagliaferri S, Panagiotopoulos A, Mattevi C, 2021, Direct ink writing of energy materials, Materials Advance, Vol: 2, Pages: 540-563, ISSN: 2633-5409

3D printing is a promising technique for the sustainable fabrication of energy devices with arbitrary architectures. Extrusion-based 3D printing, called Direct Ink Writing, are increasingly used for the manufacturing of batteries, supercapacitors and catalytic systems. In order to obtain me-chanically stable and functional devices, inks formulation must meet stringent criteria for printability, that are usually expressed in terms of rheological properties. Inks are rheologically complex fluids, in which the electroactive materials are mixed with additives and solvents to form an extrudable and self-standing paste. The ink formulation process plays a key role in tuning the rheology and the functional properties of the printed device. In this review, inks formulation, rheological characteristics and device performance are critically discussed, providing insights into the rheology-printability and formulation- functional properties relationships. The main strategies that have been proposed to obtain printable inks from energy materials are reviewed. The role played by the different ink components to achieve the target rheology is contextualized and the integration of different inks into an all-printed device is discussed. Finally, an outlook on the future challenges and opportunities for the DYW of energy materials is provided with the view that general formulations which do necessitate thermal post processing could widen the opportunities of this manufacturing technique enabling the use for large scale production of energy devices.

Journal article

Och M, Martin M-B, Dlubak B, Seneor P, Mattevi Cet al., 2021, Synthesis of emerging 2D layered magnetic materials., Nanoscale, Vol: 13, Pages: 2157-2180, ISSN: 2040-3364

van der Waals atomically thin magnetic materials have been recently discovered. They have attracted enormous attention as they present unique magnetic properties, holding potential to tailor spin-based device properties and enable next generation data storage and communication devices. To fully understand the magnetism in two-dimensions, the synthesis of 2D materials over large areas with precise thickness control has to be accomplished. Here, we review the recent advancements in the synthesis of these materials spanning from metal halides, transition metal dichalcogenides, metal phosphosulphides, to ternary metal tellurides. We initially discuss the emerging device concepts based on magnetic van der Waals materials including what has been achieved with graphene. We then review the state of the art of the synthesis of these materials and we discuss the potential routes to achieve the synthesis of wafer-scale atomically thin magnetic materials. We discuss the synthetic achievements in relation to the structural characteristics of the materials and we scrutinise the physical properties of the precursors in relation to the synthesis conditions. We highlight the challenges related to the synthesis of 2D magnets and we provide a perspective for possible advancement of available synthesis methods to respond to the need for scalable production and high materials quality.

Journal article

Asaithambi A, Kozubek R, Prinz GM, Reale F, Pollmann E, Ney M, Mattevi C, Schleberger M, Lorke Aet al., 2021, Laser- and Ion-Induced Defect Engineering in WS<inf>2</inf> Monolayers, Physica Status Solidi - Rapid Research Letters, Vol: 15, ISSN: 1862-6254

Tungsten disulfide is one of the prominent transition metal dichalcogenide materials, which shows a transition from an indirect to a direct bandgap as the layer thickness is reduced down to a monolayer. To use (Formula presented.) monolayers in devices, detailed knowledge about the luminescence properties regarding not only the excitonic but also the defect-induced contributions is needed. Herein, (Formula presented.) monolayers are irradiated with (Formula presented.) ions with different fluences to create different defect densities. Apart from the excitonic contributions, two additional emission bands are observed at low temperatures. These bands can be reduced or even suppressed, if the flakes are exposed to laser light with powers up to 1.5 mW. Increasing the temperature up to room temperature leads to recovery of this emission, so that the luminescence properties can be modified using laser excitation and temperature. The defect bands emerging after ion irradiation are attributed to vacancy defects together with physisorbed adsorbates at different defect sites.

Journal article

Wakamura T, Wu NJ, Chepelianskii AD, Gueron S, Och M, Ferrier M, Taniguchi T, Watanabe K, Mattevi C, Bouchiat Het al., 2020, Spin-orbit-enhanced robustness of supercurrent in graphene/WS2Josephson junctions, Physical Review Letters, Vol: 125, ISSN: 0031-9007

We demonstrate the enhanced robustness of the supercurrent through graphene-based Josephson junctions in which strong spin-orbit interactions (SOIs) are induced. We compare the persistence of a supercurrent at high out-of-plane magnetic fields between Josephson junctions with graphene on hexagonal boron-nitride and graphene on WS2, where strong SOIs are induced via the proximity effect. We find that in the shortest junctions both systems display signatures of induced superconductivity, characterized by a suppressed differential resistance at a low current, in magnetic fields up to 1 T. In longer junctions, however, only graphene on WS2 exhibits induced superconductivity features in such high magnetic fields, and they even persist up to 7 T. We argue that these robust superconducting signatures arise from quasiballistic edge states stabilized by the strong SOIs induced in graphene by WS2.

Journal article

Rider MS, Sokolikova M, Hanham SM, Navarro-Cia M, Haynes P, Lee D, Daniele M, Guidi MC, Mattevi C, Lupi S, Giannini Vet al., 2020, Experimental signature of a topological quantum dot, Nanoscale, ISSN: 2040-3364

Topological insulators (TIs) present a neoteric class of materials, whichsupport delocalised, conducting surface states despite an insulating bulk. Dueto their intriguing electronic properties, their optical properties havereceived relatively less attention. Even less well studied is their behaviourin the nanoregime, with most studies thus far focusing on bulk samples - inpart due to the technical challenges of synthesizing TI nanostructures. Westudy topological insulator nanoparticles (TINPs), for which quantum effectsdominate the behaviour of the surface states and quantum confinement results ina discretized Dirac cone, whose energy levels can be tuned with thenanoparticle size. The presence of these discretized energy levels in turnleads to a new electron-mediated phonon-light coupling in the THz range. Wepresent the experimental realisation of Bi$_2$Te$_3$ TINPs and strong evidenceof this new quantum phenomenon, remarkably observed at room temperature. Thissystem can be considered a topological quantum dot, with applications to roomtemperature THz quantum optics and quantum information technologies.

Journal article

Song W, Stein Scholtis E, sherrel P, deana T, Ngiam J, Lischner J, Fearn S, Bemmer V, Mattevi C, Klein N, Xie F, riley Jet al., 2020, Electronic Structure Influences on the Formation of the Solid Electrolyte Interphase, Energy and Environmental Science, ISSN: 1754-5692

Journal article

Weiss C, Carriere M, Fusco L, Capua I, Regla-Nava JA, Pasquali M, Scott JA, Vitale F, Unal MA, Mattevi C, Bedognetti D, Merkoçi A, Tasciotti E, Yilmazer A, Gogotsi Y, Stellacci F, Delogu LGet al., 2020, Toward nanotechnology-enabled approaches against the COVID-19 pandemic, ACS Nano, Vol: 14, Pages: 6383-6406, ISSN: 1936-0851

The COVID-19 outbreak has fueled a global demand for effective diagnosis and treatment as well as mitigation of the spread of infection, all through large-scale approaches such as specific alternative antiviral methods and classical disinfection protocols. Based on an abundance of engineered materials identifiable by their useful physicochemical properties through versatile chemical functionalization, nanotechnology offers a number of approaches to cope with this emergency. Here, through a multidisciplinary Perspective encompassing diverse fields such as virology, biology, medicine, engineering, chemistry, materials science, and computational science, we outline how nanotechnology-based strategies can support the fight against COVID-19, as well as infectious diseases in general, including future pandemics. Considering what we know so far about the life cycle of the virus, we envision key steps where nanotechnology could counter the disease. First, nanoparticles (NPs) can offer alternative methods to classical disinfection protocols used in healthcare settings, thanks to their intrinsic antipathogenic properties and/or their ability to inactivate viruses, bacteria, fungi, or yeasts either photothermally or via photocatalysis-induced reactive oxygen species (ROS) generation. Nanotechnology tools to inactivate SARS-CoV-2 in patients could also be explored. In this case, nanomaterials could be used to deliver drugs to the pulmonary system to inhibit interaction between angiotensin-converting enzyme 2 (ACE2) receptors and viral S protein. Moreover, the concept of "nanoimmunity by design" can help us to design materials for immune modulation, either stimulating or suppressing the immune response, which would find applications in the context of vaccine development for SARS-CoV-2 or in counteracting the cytokine storm, respectively. In addition to disease prevention and therapeutic potential, nanotechnology has important roles in diagnostics, with potential to sup

Journal article

Sokolikova MS, Mattevi C, 2020, Direct synthesis of metastable phases of 2D transition metal dichalcogenides, Chemical Society Reviews, Vol: 49, Pages: 3952-3980, ISSN: 0306-0012

The different polymorphic phases of transition metal dichalcogenides (TMDs) have attracted enormous interest in the last decade. The metastable metallic and small band gap phases of group VI TMDs displayed leading performance for electrocatalytic hydrogen evolution, high volumetric capacitance and some of them exhibit large gap quantum spin Hall (QSH) insulating behaviour. Metastable 1T(1T′) phases require higher formation energy, as compared to the thermodynamically stable 2H phase, thus in standard chemical vapour deposition and vapour transport processes the materials normally grow in the 2H phases. Only destabilization of their 2H phase via external means, such as charge transfer or high electric field, allows the conversion of the crystal structure into the 1T(1T′) phase. Bottom-up synthesis of materials in the 1T(1T′) phases in measurable quantities would broaden their prospective applications and practical utilization. There is an emerging evidence that some of these 1T(1T′) phases can be directly synthesized via bottom-up vapour- and liquid-phase methods. This review will provide an overview of the synthesis strategies which have been designed to achieve the crystal phase control in TMDs, and the chemical mechanisms that can drive the synthesis of metastable phases. We will provide a critical comparison between growth pathways in vapour- and liquid-phase synthesis techniques. Morphological and chemical characteristics of synthesized materials will be described along with their ability to act as electrocatalysts for the hydrogen evolution reaction from water. Phase stability and reversibility will be discussed and new potential applications will be introduced. This review aims at providing insights into the fundamental understanding of the favourable synthetic conditions for the stabilization of metastable TMD crystals and at stimulating future advancements in the field of large-scale synthesis of materials with crystal phase control.

Journal article

Au H, Rubio N, Buckley DJ, Mattevi C, Shaffer MSPet al., 2020, Thermal decomposition of ternary sodium graphite intercalation compounds, Chemistry: A European Journal, Vol: 26, Pages: 6545-6553, ISSN: 0947-6539

Graphite intercalation compounds (GICs) are often used to produce exfoliated or functionalised graphene related materials (GRMs) in a specific solvent. This study explores the formation of the Na-tetrahydrofuran (THF)-GIC and a new ternary system based on dimethylacetamide (DMAc). Detailed comparisons of in situ temperature dependent XRD with TGA-MS and Raman measurements reveal a series of dynamic transformations during heating. Surprisingly, the bulk of the intercalation compound is stable under ambient conditions, trapped between the graphene sheets. The heating process drives a reorganisation of the solvent and Na molecules, then an evaporation of the solvent; however, the solvent loss is arrested by restacking of the graphene layers, leading to trapped solvent bubbles. Eventually, the bubbles rupture, releasing the remaining solvent and creating expanded graphite. These trapped dopants may provide useful property enhancements, but also potentially confound measurements of grafting efficiency in liquid-phase covalent functionalization experiments on 2D materials.

Journal article

Zatko V, Galbiati M, Dubois SM-M, Och M, Palczynski P, Mattevi C, Brus P, Bezencenet O, Martin M-B, Servet B, Charlier J-C, Godel F, Vecchiola A, Bouzehouane K, Collin S, Petroff F, Dlubak B, Seneor Pet al., 2019, Band-structure spin-filtering in vertical spin valves based on chemical vapor deposited WS2., ACS Nano, Vol: 13, Pages: 14468-14476, ISSN: 1936-0851

We report on spin transport in WS2-based 2D-magnetic tunnel junctions (2D-MTJs), unveiling a band structure spin filtering effect specific to the transition metal dichalcogenides (TMDCs) family. WS2 mono-, bi-, and trilayers are derived by a chemical vapor deposition process and further characterized by Raman spectroscopy, atomic force microscopy (AFM), and photoluminescence spectroscopy. The WS2 layers are then integrated in complete Co/Al2O3/WS2/Co MTJ hybrid spin-valve structures. We make use of a tunnel Co/Al2O3 spin analyzer to probe the extracted spin-polarized current from the WS2/Co interface and its evolution as a function of WS2 layer thicknesses. For monolayer WS2, our technological approach enables the extraction of the largest spin signal reported for a TMDC-based spin valve, corresponding to a spin polarization of PCo/WS2 = 12%. Interestingly, for bi- and trilayer WS2, the spin signal is reversed, which indicates a switch in the mechanism of interfacial spin extraction. With the support of ab initio calculations, we propose a model to address the experimentally measured inversion of the spin polarization based on the change in the WS2 band structure while going from monolayer (direct bandgap) to bilayer (indirect bandgap). These experiments illustrate the rich potential of the families of semiconducting 2D materials for the control of spin currents in 2D-MTJs.

Journal article

Chong JY, Wang B, Sherrell PC, Pesci FM, Mattevi C, Li Ket al., 2019, Fabrication of graphene‐covered micro‐tubes for process intensification, Advanced Engineering Materials, Vol: 21, Pages: 1-6, ISSN: 1438-1656

Graphene is known for its high surface‐area‐to‐mass ratio. However, for graphene to be used in engineering processes such as catalytic reactors or heat exchangers, high surface‐area‐to‐volume ratio is essential. Currently, graphene is only prepared in sheet form, which limits its surface‐area‐to‐volume ratio to around 200 m2 m−3. In this study, we propose and demonstrate a technique based on chemical vapour deposition (CVD) to realise graphene on a copper‐based micro‐tubular substrate to not only substantially increase its surface‐area‐to‐volume ratio to a value over 2000 m2 m−3, but also to eliminate maldistribution of flows commonly unavoidable in flat‐sheet configurations. Our approach uses a dual‐layer micro‐tubular substrate fabricated by a phase‐inversion facilitated co‐extrusion technique. In the substrate, a thin copper outer layer is employed to enable the CVD growth of graphene, and an inner Cu‐Fe layer is adopted to provide a strong mechanical support. Our study shows that this approach is feasible to produce graphene with a very high surface‐area‐to‐volume ratio for possible practical applications in catalytic reactors or heat exchangers, though problems such as the inter‐diffusion between the two metal layers and defects in graphene need to be further addressed. To the best of our knowledge, this study is the first attempt to prepare graphene with high surface‐area‐to‐volume ratio by a CVD route.

Journal article

Sherrell PC, Palczynski P, Sokolikova MS, Reale F, Pesci FM, Och M, Mattevi Cet al., 2019, Large-area CVD MoS2/WS2 heterojunctions as a photoelectrocatalyst for salt water oxidation, ACS Applied Energy Materials, Vol: 2, Pages: 5877-5882, ISSN: 2574-0962

Splitting salt water via sunlight into molecular oxygen and hydrogen for use as fuel or as an energy carrier is a clear pathway toward renewable energy. Monolayer MoS2 and WS2 are promising materials for the energetically demanding water oxidation reaction, absorbing ∼10% of incident light in the visible spectrum and possessing chemical stability and band edges more positive than the oxidation potential of water. A heterostructure of MoS2/WS2 forms a type-II heterojunction, supporting fast separation of the photogenerated charge carriers across the junction. Here, we show the role played by defects in determining the efficiency of the photon-driven oxidation process. By reducing the defects in this material system, it is possible to obtain an incident photon-to-current conversion efficiency (IPCE) of ∼1.6% and a visible-light-driven photocurrent density of 1.7 mA/cm2 for water oxidation. The efficiency is one order of magnitude higher than that of photoelectrocatalytic hydrogen reduction and water oxidation supported by liquid-phase exfoliated transition-metal dichalcogenides (TMDs). This result has been achieved with chemically vapor deposited (CVD) MoS2/WS2 heterojunctions, in the form of 100 μm large flakes assembled to form thin films. The large flakes sizes, compared to liquid-phase exfoliated materials (normally <5 μm), and thus the low edge flake density, and the flakes’ atomically sharp and clean interfaces between the flakes are responsible for reducing charge carrier recombination. These results show a general approach to the scalable synthesis of high-crystal-quality low-dimensional semiconductor photoelectrodes for solar energy conversion systems. It also shows the uniqueness of the CVD synthesis process of these materials, which can lead to high quality materials without the need of any postsynthesis treatments.

Journal article

Wakamura T, Reale F, Palczynski P, Zhao MQ, Johnson ATC, Gueron S, Mattevi C, Ouerghi A, Bouchiat Het al., 2019, Spin-orbit interaction induced in graphene by transition metal dichalcogenides, Physical review B: Condensed matter and materials physics, Vol: 99, ISSN: 1098-0121

We report a systematic study on strong enhancement of spin-orbit interaction (SOI) in grapheneinduced by transition-metal dichalcogenides (TMDs). Low temperature magnetotoransport mea-surements of graphene proximitized to different TMDs (monolayer and bulk WSe2, WS2and mono-layer MoS2) all exhibit weak antilocalization peaks, a signature of strong SOI induced in graphene.The amplitudes of the induced SOI are different for different materials and thickness, and we findthat monolayer WSe2and WS2can induce much stronger SOI than bulk WSe2, WS2and mono-layer MoS2. The estimated spin-orbit (SO) scattering strength for graphene/monolayer WSe2andgraphene/monolayer WS2reachesª10 meV whereas for graphene/bulk WSe2, graphene/bulk WS2and graphene/monolayer MoS2it is around 1 meV or less. We also discuss the symmetry and typeof the induced SOI in detail, especially focusing on the identification of intrinsic (Kane-Mele) andvalley-Zeeman (VZ) SOI by determining the dominant spin relaxation mechanism. Our findingspave the way for realizing the quantum spin Hall (QSH) state in graphene.

Journal article

Sokolikova MS, Sherrell PC, Palczynski P, Bemmer VL, Mattevi Cet al., 2019, Direct solution-phase synthesis of 1T’ WSe2 nanosheets, Nature Communications, Vol: 10, Pages: 1-8, ISSN: 2041-1723

Crystal phase control in layered transition metal dichalcogenides is central for exploiting their different electronic properties. Access to metastable crystal phases is limited as their direct synthesis is challenging, restricting the spectrum of reachable materials. Here, we demonstrate the solution phase synthesis of the metastable distorted octahedrally coordinated structure (1T’ phase) of WSe2 nanosheets. We design a kinetically-controlled regime of colloidal synthesis to enable the formation of the metastable phase. 1T’ WSe2 branched few-layered nanosheets are produced in high yield and in a reproducible and controlled manner. The 1T’ phase is fully convertible into the semiconducting 2H phase upon thermal annealing at 400 °C. The 1T’ WSe2 nanosheets demonstrate a metallic nature exhibited by an enhanced electrocatalytic activity for hydrogen evolution reaction as compared to the 2H WSe2 nanosheets and comparable to other 1T’ phases. This synthesis design can potentially be extended to different materials providing direct access of metastable phases.

Journal article

Jia J, White ER, Clancy AJ, Rubio N, Suter T, Miller TS, McColl K, McMillan PF, Brázdová V, Corà F, Howard CA, Law RV, Mattevi C, Shaffer MSPet al., 2018, Fast exfoliation and functionalisation of two-dimensional crystalline carbon nitride by framework charging, Angewandte Chemie, Vol: 57, Pages: 12656-12660, ISSN: 1521-3757

Two-dimensional (2D) layered graphitic carbon nitride (gCN) nanosheets offer intriguing electronic and chemical properties. However, the exfoliation and functionalisation of gCN for specific applications remain challenging. We report a scalable one-pot reductive method to produce solutions of single- and few-layer 2D gCN nanosheets with excellent stability in a high mass yield (35 %) from polytriazine imide. High-resolution imaging confirmed the intact crystalline structure and identified an AB stacking for gCN layers. The charge allows deliberate organic functionalisation of dissolved gCN, providing a general route to adjust their properties.

Journal article

Sherrell PC, Sharda K, Grotta C, Ranalli J, Sokolikova MS, Pesci FM, Palczynski P, Bemmer VL, Mattevi Cet al., 2018, Thickness dependant characterization of chemically exfoliated TiS2 nanosheets, ACS Omega, Vol: 3, Pages: 8655-8662, ISSN: 2470-1343

Monolayer TiS2 is the lightest member of the transition metal dichalcogenides family with promising application in energy storage and conversion systems. Use of TiS2 has been limited by the lack of rapid characterisation of layer number via Raman spectroscopy and its easy oxidation in wet environment. Here, we demonstrate layer number dependent Raman modes for TiS2. 1T-TiS2 presents two characteristics Raman active modes, A1g (out-of-plane) and Eg (in-plane). We identified a characteristic peak frequency shift of the Eg mode with the layer number and an unexplored Raman mode at 372 cm-1 whose intensity changes relative to the A1g mode with the thickness of TiS2 sheets. These two characteristic features of the Raman spectra allow the determination of layer numbers between 1 and 5 in exfoliated TiS2. Further, we develop a method to produce oxidation-resistant inks of micron sized mono- and few-layered TiS2 nanosheets at concentrations up to 1 mg/mL .These TiS2 inks can be deposited to form thin films with controllable thickness and nanosheet density over cm2 areas. This opens up pathways for a wider utilization of exofliated TiS2 towards a range of applications.

Journal article

Mattevi C, 2018, Electronic band structure of Two-DimensionalWS2/Graphene van derWaals Heterostructure, Physical Review B, ISSN: 2469-9950

Journal article

Henck H, Ben Aziz Z, Pierucci D, Laourine F, Reale F, Palczynski P, Chaste J, Silly MG, Bertran F, Le Fevre P, Lhuillier E, Wakamura T, Mattevi C, Rault JE, Calandra M, Ouerghi Aet al., 2018, Electronic band structure of two-dimensional WS2/Graphene van der Waals heterostructures, Physical Review B, Vol: 97, Pages: 155421 – 1-155421 – 8, ISSN: 2469-9950

Combining single-layer two-dimensional semiconducting transition metal dichalcogenides (TMDs)with graphene layer in van der Waals heterostructuresoffers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single layer WS2on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements(ARPES)and Density Functional Theory(DFT)calculations. The results show good electronic properties as well as well-defined band arising from the strong splitting of the single layer WS2valence band at K points, with a maximum splitting of 0.44 eV.By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is closeto the calculations forsuspended single layer WS2. .Our results provide an important reference for future studies of electronic properties of WS2and its applications in valleytronic devices.

Journal article

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