Publications

Journal article

WANG T, Yao C, Gao R, Holicky M, Hu B, Wu S, Kim H, NING H, Torrisi F, Bakulin Aet al., 2024,

Ultrafast carrier and lattice cooling in Ti2CTx MXene thin films

, Nano Letters: a journal dedicated to nanoscience and nanotechnology, ISSN: 1530-6984

Metallic MXenes are promising two-dimensional materials for energy storage, (opto)electronics, and photonics due to their high electrical conductivity and strong light-matter interaction. Energy dissipation in MXenes is fundamental for photovoltaic and photothermal applications. Here we apply ultrafast laser spectroscopy across a broad time range (fs-μs) to study the cooling dynamics of electrons and lattice in emerging Ti2CTx thin films compared to widely studied Ti3C2Tx thin films. Carrier cooling time in Ti2CTx is persistently ~2.6 ps withouthot-phonon bottleneck. After hot carrier cooling is completed, the transient absorption (TA) spectra of Ti2CTx MXene can be well described by thermochromic effect. Heat dissipation in MXene thin films occurs over hundreds of nanoseconds with thermal diffusivity ~ 0.06 mm2s−1for Ti2CTx and ~ 0.02 mm2s−1for Ti3C2Tx, likely due to inefficient inter-flake heat transfer. Our results unravel the energy dissipation dynamics in Ti2CTx films, showcasing the potential applications in energy conversion.

Journal article

Yao C, Leahu G, Holicky M, Liu S, Fenech-Salerno B, Lai MC, Larciprete MC, Ducati C, Divitini G, Li Voti R, Sibilia C, Torrisi Fet al., 2024,

Thermally conductive hexagonal boron nitride/polymer composites for efficient heat transport

, Advanced Functional Materials, Vol: 34, ISSN: 1616-301X

Commercial thermally conductive dielectric materials used in electronic packaging typically exhibit thermal conductivities (κ) ranging from 0.8 to 4.2 W m−1 K−1. Hexagonal boron nitride (h-BN) flakes are promising thermally conductive materials for the thermal management of next-generation electronics. These electrically insulating yet thermally conducting h-BN flakes can be incorporated as thermal fillers to impart high κ to polymer-based composites. A cellulose-based composite embedded with few-layer h-BN (FLh-BN) flakes, achieving a κ ≈ 21.7 W m−1 K−1, prepared using a cost-effective and scalable procedure is demonstrated. This value is >5 times higher than the κ observed in composites embedded with bulk h-BN (Bh-BN, κ ≈ 4.5 W m−1 K−1), indicating the benefits of the superior κ of FLh-BN on the κ of h-BN polymer composites. When applied as a paste for thermal interface material (TIM), the FLh-BN composite can reduce the maximum temperature (Tmax) by 24.5 °C of a heating pad at a power density (h) of 2.48 W cm−2 compared to Bh-BN composites at the same h-BN loading. The results provide an effective approach to improve the κ of cellulose-based thermal pastes for TIMs and demonstrate their viability for heat dissipation in integrated circuits (ICs) and high-power electronic devices.

Journal article

Holicky M, Fenech-Salerno B, Cass A, Torrisi Fet al., 2024,

Fabrication of graphene field effect transistors on complex non-planar surfaces

, Applied Physics Letters, Vol: 125, ISSN: 0003-6951

Graphene field effect transistors (GFETs) are promising devices for biochemical sensing. Integrating GFETs ontocomplex non-planar surfaces could uncap their potential in emerging areas of wearable electronics, such as smartcontact lenses and microneedle sensing. However, the fabrication of GFETs on non-planar surfaces is challengingusing conventional lithography approaches. Here, we develop a combined spray coating and photolithography setupfor the scalable fabrication of GFETs on non-planar surfaces and demonstrate their application as integrated GFETs onmicroneedles. We optimize the setup to pattern ⇠67 µm long GFET channels across the microneedle tips. Graphene isdeposited between photo-patterned electrodes by spray coating a liquid-phase exfoliated graphene ink, while monitoringthe channel resistance to achieve the required conductivity. The successful formation of the GFET channels is confirmedby SEM and EDX mapping, and the GFETs are shown to modulate in solution. This demonstrates an approach for themanufacturing of graphene electronic devices on complex non-planar surfaces like microneedles and opens possibilitiesfor wearable GFET microneedle sensors for real-time monitoring of biomarkers.

Journal article

Yong S, Yao C, Hillier N, Kim H, Holicky M, Liu S, Doherty R, Torrisi F, Beeby Set al., 2024,

Ti3C2 MXene as additive for low‐cost textile supercapacitors with enhanced electrical performance

, Advanced Materials Technologies, Vol: 9, ISSN: 2365-709X

Textile-based energy storage components are paramount for establishing invisible electronic textiles that do not require conventional rigid batteries. A novel and scalable fabrication method is reported for introducing MXene (Ti3C2Tx) into activated carbon (AC) supercapacitors to enhance electrochemical performance. Supercapacitors are prepared within a single layer of textile with a phase-inverted polymer membrane fabricated within the textile yarn structure to form a porous, flexible, and mechanically durable separator. MXene is introduced in two different forms: 1) A multilayer MXene (m-MXene)powder is mechanically mixed with an AC slurry and deposited onto the textile. 2) Delaminated MXene (d-Mxene) nanosheets are spray-coated onto the surface of spray coated AC electrode. With an organic electrolyte, 1 M tetraethylammonium tetrafluoroborate in dimethyl sulfoxide, these supercapacitors are electrochemically stable between +/− 2.6 V and demonstrate a maximum areal capacitance of 148.7 mF cm−2, an energy density of 0.921 mWh cm−2, and a power density of 1.01 mW cm−2. The addition of MXenes improves the areal capacitance and by combining both approaches an improvement of 220% is achieved compared with identical supercapacitors with standard AC electrodes. The novelty of this work is to develop a scalable and straightforward solution processing method for introducing MXene into carbon supercapacitor electrodes enabling high-performance textile-based energy storage devices.

Journal article

Yong S, Yao C, Hillier N, Kim H, Holicky M, Liu S, Doherty R, Torrisi F, Stephen Bet al., 2024,

Ti3C2 MXene as additive for low-cost textile supercapacitors with enhanced electrical performance

, Advanced Materials Technologies, Vol: 9, ISSN: 2365-709X

Textile-based energy storage components are paramount for establishing invisible electronic textiles that do not require conventional rigid batteries. A novel and scalable fabrication method is reported for introducing MXene (Ti3C2Tx) into activated carbon (AC) supercapacitors to enhance electrochemical performance. Supercapacitors are prepared within a single layer of textile with a phase-inverted polymer membrane fabricated within the textile yarn structure to form a porous, flexible, and mechanically durable separator. MXene is introduced in two different forms: 1) A multilayer MXene (m-MXene)powder is mechanically mixed with an AC slurry and deposited onto the textile. 2) Delaminated MXene (d-Mxene) nanosheets are spray-coated onto the surface of spray coated AC electrode. With an organic electrolyte, 1 M tetraethylammonium tetrafluoroborate in dimethyl sulfoxide, these supercapacitors are electrochemically stable between +/− 2.6 V and demonstrate a maximum areal capacitance of 148.7 mF cm−2, an energy density of 0.921 mWh cm−2, and a power density of 1.01 mW cm−2. The addition of MXenes improves the areal capacitance and by combining both approaches an improvement of 220% is achieved compared with identical supercapacitors with standard AC electrodes. The novelty of this work is to develop a scalable and straightforward solution processing method for introducing MXene into carbon supercapacitor electrodes enabling high-performance textile-based energy storage devices.

Journal article

Liu W, Zhang H, Liang S, Wang T, He S, Hu Y, Zhang R, Ning H, Ren J, Bakulin A, Gao F, Yuan J, Zou Yet al., 2023,

The Synthesis of a Multiple D-A Conjugated Macrocycle and Its Application in Organic Photovoltaic

, ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, Vol: 62, ISSN: 1433-7851

Cite

Journal article

Zhang X, Tan W, Carey T, Wen B, He D, Arbab A, Groombridge A, Smail F, de La Verpilliere J, Yao C, Wang Y, Wei X, Liu H, Xie S, Torrisi F, De Volder M, Zhou W, Boies Aet al., 2023,

Enhanced composite thermal conductivity by percolated networks of in-situ confined-grown carbon nanotubes

, Nano Research, Vol: 16, Pages: 12821-12829, ISSN: 1998-0000

Despite the ever-increasing demand of nanofillers for thermal enhancement of polymer composites with higher thermal conductivity and irregular geometry, nanomaterials like carbon nanotubes (CNTs) have been constrained by the nonuniform dispersion and difficulty in constructing effective three-dimensional (3D) conduction network with low loading and desired isotropic or anisotropic (specific preferred heat conduction) performances. Herein, we illustrated the in-situ construction of CNT based 3D heat conduction networks with different directional performances. First, to in-situ construct an isotropic percolated conduction network, with spherical cores as support materials, we developed a confined-growth technique for CNT-core sea urchin (CNTSU) materials. With 21.0 wt.% CNTSU loading, the thermal conductivity of composites reached 1.43 ± 0.13 W/(m·K). Secondly, with aligned hexagonal boron nitride (hBN) as an anisotropic support, we constructed CNT-hBN aligned networks by in-situ CNT growth, which improved the utilization efficiency of high density hBN and reduced the thermal interface resistance between matrix and fillers. With ~ 8.5 wt.% loading, the composites possess thermal conductivity up to 0.86 ± 0.14 W/(m·K), 374% of that for neat matrix. Due to the uniformity of CNTs in hBN network, the synergistic thermal enhancement from one-dimensional (1D) + two-dimensional (2D) hybrid materials becomes more distinct. Based on the detailed experimental evidence, the importance of purposeful production of a uniformly interconnected heat conduction 3D network with desired directional performance can be observed, particularly compared with the traditional direct-mixing method. This study opens new possibilities for the preparation of high-power-density electronics packaging and interfacial materials when both directional thermal performance and complex composite geometry are simultaneously required.

Journal article

Zhang J, Qin J, Cai W, Tang Y, Zhang H, Wang T, Bakulin A, Hu B, Liu X-K, Gao Fet al., 2023,

Transport layer engineering toward lower threshold for perovskite lasers

, Advanced Materials, Vol: 35, ISSN: 0935-9648

Charge-transport layers are essential for achieving electrically pumped perovskite lasers. However, their role in perovskite lasing is not fully understood. Here, the role of charge-transport layers on the lasing actions of perovskite films is explored by investigating the amplified spontaneous emission (ASE) thresholds. A largely reduced ASE threshold and enhanced ASE intensity is demonstrated by introducing an additional hole transport layer poly(triaryl amine) (PTAA). It is shown that the key role of the PTAA layer is to accelerate the hot-carrier cooling process by extracting holes in perovskites. With reduced hot holes, the Auger recombination loss is largely suppressed, resulting in decreased ASE threshold. This argument is further supported by the fact that the ASE threshold can be further reduced from 25.7 to 7.2 µJ cm−2 upon switching the pumping wavelength from 400 to 500 nm to directly avoid excess hot-hole generation. This work exemplifies how to further reduce the ASE threshold with transport layer engineering through hot-hole manipulation. This is critical to maintaining the excellent gain properties of perovskites when integrating them into electrical devices, paving the way for electrically pumped perovskite lasers.

Journal article

Carwithen BP, Hopper TR, Ge Z, Mondal N, Wang T, Mazlumian R, Zheng X, Krieg F, Montanarella F, Nedelcu G, Kroll M, Siguan MA, Frost JM, Leo K, Vaynzof Y, Bodnarchuk MI, Kovalenko MV, Bakulin AAet al., 2023,

Confinement and exciton binding energy effects on hot carrier cooling in lead halide perovskite nanomaterials

, ACS Nano, Vol: 17, Pages: 6638-6648, ISSN: 1936-0851

The relaxation of the above-gap (“hot”) carriers in lead halide perovskites (LHPs) is important for applications in photovoltaics and offers insights into carrier–carrier and carrier–phonon interactions. However, the role of quantum confinement in the hot carrier dynamics of nanosystems is still disputed. Here, we devise a single approach, ultrafast pump–push–probe spectroscopy, to study carrier cooling in six different size-controlled LHP nanomaterials. In cuboidal nanocrystals, we observe only a weak size effect on the cooling dynamics. In contrast, two-dimensional systems show suppression of the hot phonon bottleneck effect common in bulk perovskites. The proposed kinetic model describes the intrinsic and density-dependent cooling times accurately in all studied perovskite systems using only carrier–carrier, carrier–phonon, and excitonic coupling constants. This highlights the impact of exciton formation on carrier cooling and promotes dimensional confinement as a tool for engineering carrier–phonon and carrier–carrier interactions in LHP optoelectronic materials.

Journal article

Wang T, Hopper T, Mondal N, Liu S, Yao C, Zheng X, Torrisi F, Bakulin Aet al., 2023,

Hot carrier cooling and trapping in atomically thin WS₂ probed by three-pulse femtosecond spectroscopy

, ACS Nano, Vol: 17, Pages: 6330-6340, ISSN: 1936-0851

Transition metal dichalcogenides (TMDs) have shown outstanding semiconducting properties which make them promising materials for next-generation optoelectronic and electronic devices. These properties are imparted by fundamental carrier–carrier and carrier–phonon interactions that are foundational to hot carrier cooling. Recent transient absorption studies have reported ultrafast time scales for carrier cooling in TMDs that can be slowed at high excitation densities via a hot-phonon bottleneck (HPB) and discussed these findings in the light of optoelectronic applications. However, quantitative descriptions of the HPB in TMDs, including details of the electron–lattice coupling and how cooling is affected by the redistribution of energy between carriers, are still lacking. Here, we use femtosecond pump–push–probe spectroscopy as a single approach to systematically characterize the scattering of hot carriers with optical phonons, cold carriers, and defects in a benchmark TMD monolayer of polycrystalline WS2. By controlling the interband pump and intraband push excitations, we observe, in real-time (i) an extremely rapid “intrinsic” cooling rate of ∼18 ± 2.7 eV/ps, which can be slowed with increasing hot carrier density, (ii) the deprecation of this HPB at elevated cold carrier densities, exposing a previously undisclosed role of the carrier–carrier interactions in mediating cooling, and (iii) the interception of high energy hot carriers on the subpicosecond time scale by lattice defects, which may account for the lower photoluminescence yield of TMDs when excited above band gap.

Journal article

Fenech-Salerno B, Holicky M, Yao C, Cass A, Torrisi Fet al., 2023,

A sprayed graphene transistor platform for rapid and low-cost chemical sensing

, Nanoscale, Vol: 15, Pages: 3243-3254, ISSN: 2040-3364

We demonstrate a novel and versatile sensing platform, based on electrolyte-gated graphene field-effect transistors, for easy, low-cost and scalable production of chemical sensor test strips. The Lab-on-PCB platform is enabled by low-boiling, low-surface-tension sprayable graphene ink deposited on a substrate manufactured using a commercial printed circuit board process. We demonstrate the versatility of the platform by sensing pH and Na+ concentrations in an aqueous solution, achieving a sensitivity of 143 ± 4 μA per pH and 131 ± 5 μA per log10Na+, respectively, in line with state-of-the-art graphene chemical sensing performance.

Conference paper

Torrisi F, 2023,

Two-Dimensional Material Inks and Composites for Printed and Wearable Electronics

, Pages: 233-234

Wearable electronics play a primary technology to enable remote healthcare provision, which is highly important in a post-pandemic society. Graphene and related 2 D materials (GRMs) hold a great potential for wearable electronics for their novel electrical and optical properties. I will give a brief overview on the development of high-yield, cost-effective and large-scale production techniques for GRM-based inks, and the portfolio of reproducible deposition processes enabling GRM-based printable devices on flexible and textile substrates. Then I will show how careful tuning of the flakes-substrate surface interaction and GRM deposition process enables hybrid heterojunctions from 2D materials, achieving mobility >100 cm2 V-1s-1 at room temperature. Finally, I will demonstrate how unveiling of the electronic transport in printed networks of 2D materials paves the way to high-performance inkjet printed integrated circuits of 2 D material semiconductors, such as MoS2

Abstract
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Journal article

Latham KG, Edathil AA, Rezaei B, Liu S, Nguyen S, Keller SS, Torrisi F, Greenhalgh ES, Titirici M-Met al., 2022,

Challenges and opportunities in free-standing supercapacitors research

, APL Materials, Vol: 10, Pages: 1-14, ISSN: 2166-532X

The design of commercial supercapacitors has remained largely unchanged since the 1970s, comprising powdered electrodes housed in rigid metal cylinders or pouches. To power the next generation of integrated technologies, an evolution in supercapacitor materials and design is needed to create multifunctional materials that allow energy storage while imparting additional material properties (e.g., flexibility and strength). Conductive free-standing electrodes produced from fibers or 3D printed materials offer this opportunity as their intrinsic mechanical properties can be transferred to the supercapacitor. Additionally, their conductive nature allows for the removal of binders, conductive agents, and current collectors from the supercapacitor devices, lowering their economic and environmental cost. In this Perspective, we summarize the recent progress on free-standing supercapacitors from new methods to create free-standing electrodes to novel applications for these devices, together with a detailed discussion and analysis on their electrochemical performance and physicochemical and mechanical properties. Furthermore, the potential directions and prospects of future research in developing free-standing supercapacitors are proposed.

Journal article

Kim H, Arbab A, Fenech Salerno B, Yao C, MacPherson R, Kim JM, Torrisi Fet al., 2022,

Barium titanate-enhanced hexagonal boron nitride inks for printable high-performance dielectrics

, Nanotechnology, Vol: 33, Pages: 1-8, ISSN: 0957-4484

Printed electronics have been attracting significant interest for their potential to enable flexible and wearable electronic applications. Together with printable semiconductors, solution processed dielectric inks are key in enabling low-power and high-performance printed electronics. In the quest for suitable dielectrics inks, two-dimensional materials such as hexagonal boron nitride (h-BN) have emerged in the form of printable dielectrics. In this work, we report barium titanate (BaTiO3) nanoparticles as an effective additive for inkjet-printable h-BN inks. The resulting inkjet printed h-BN/BaTiO3 thin films reach a dielectric constant (εr) of ~ 16 by adding 10% of BaTiO3 nanoparticles (in their volume fraction to the exfoliated h-BN flakes) in water-based inks. This result enabled all-inkjet printed flexible capacitors with C ~ 10.39 nF cm-2, paving the way to future low power, printed and flexible electronics.

Journal article

Spanu A, Mascia A, Baldazzi G, Fenech Salerno B, Torrisi F, Viola G, Bonfiglio A, Cosseddu P, Pani Det al., 2022,

Parylene C-based, breathable tattoo electrode for high-quality biopotential measurements

, Frontiers in Bioengineering and Biotechnology, Vol: 10, Pages: 1-15, ISSN: 2296-4185

A breathable tattoo electrode for bio-potential recording based on a Parylene C nanofilm is presented in this study. The proposed approach allows for the fabrication of micro-perforated epidermal submicrometer-thick electrodes that conjugate the unobtrusiveness of Parylene C nanofilms and the very important feature of breathability. The electrodes were fully validated for electrocardiography (ECG) measurements showing performance comparable to that of conventional disposable gelled Ag/AgCl electrodes, with no visible negative effect on the skin even many hours after their application. This result introduces interesting perspectives in the field of epidermal electronics, particularly in applications where critical on-body measurements are involved.

Journal article

Piatti E, Arbab A, Galanti F, Carey T, Anzi L, Spurling D, Roy A, Zhussupbekova A, Patel K, Kim JM, Daghero D, Sordan R, Nicolosi V, Gonnelli R, Torrisi Fet al., 2021,

Charge transport mechanisms in inkjet-printed thin-film transistors based on two-dimensional materials

, Nature Electronics, Vol: 4, Pages: 893-905, ISSN: 2520-1131

Printed electronics using inks based on graphene and other two-dimensional materials can be used to create large-scale, flexible, and wearable devices. However, the complexity of the ink formulations, and the polycrystalline nature of the resulting thin films, have made it difficult to examine charge transport in such devices. Here we report the charge transport mechanisms of surfactant- and solvent-free inkjet-printed thin-film devices based on few-layer graphene (semi-metal), molybdenum disulfide (MoS2, semiconductor) and titanium carbide MXene (Ti3C2, metal) by investigating the temperature, gate and magnetic field dependencies of their electrical conductivity. We find that charge transport in printed few-layer MXene and MoS2 devices is dominated by the intrinsic transport mechanism of the constituent flakes: MXene exhibits a weakly-localized 2D metallic behaviour at any temperature, whereas MoS2 behaves as an insulator with a crossover from 3D-Mott variable-range hopping to nearest-neighbour hopping around 200 K. Charge transport in printed few-layer graphene devices is dominated by the transport mechanism between different flakes, which exhibit 3D-Mott variable range hopping conduction at any temperature.

Journal article

Kafourou P, Nugraha MI, Nikitaras A, Tan L, Firdaus Y, Aniés F, Eisner F, Ding B, Wenzel J, Holicky M, Tsetseris L, Anthopoulos TD, Heeney Met al., 2021,

Near-IR absorbing molecular semiconductors incorporating cyanated benzothiadiazole acceptors for high performance semi-transparent n-type organic field-effect transistors

, ACS Materials Letters, Vol: 4, Pages: 165-174, ISSN: 2639-4979

Small band gap molecular semiconductors are of interest for the development of transparent electronics. Here we report two near-infrared (NIR), n-type small molecule semiconductors, based upon an acceptor-donor-acceptor (A-D-A) approach. We show that the inclusion of molecular spacers between the strong electron accepting end group, 2,1,3-benzothiadiazole-4,5,6-tricarbonitrile, and the donor core affords semiconductors with very low band gaps down to 1 eV. Both materials were synthesised by a one-pot, sixfold nucleophilic displacement of a fluorinated precursor by cyanide. Significant differences in solid-state ordering and charge carrier mobility are observed depending on the nature of the spacer, with a thiophene spacer resulting in solution processed organic field-effect transistors (OFETs) exhibiting excellent electron mobility up to 1.1 cm2 V-1s-1. The use of silver nanowires as the gate electrodes enables the fabrication of semi-transparent OFET device with average visible transmission of 71% in the optical spectrum.

Journal article

Bohm S, Ingle A, Bohm M, Fenech Salerno B, Wu S, Torrisi Fet al., 2021,

Graphene production by cracking

, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 379, Pages: 1-14, ISSN: 1364-503X

n recent years, graphene has found its use in numerous industrial applications due to its unique properties. While its impermeable and conductive nature can replace currently used anticorrosive toxic pigments in coating systems, due to its large strength to weight ratio, graphene can be an important component as a next-generation additive for automotive, aerospace & construction applications. The current bottlenecks in using graphene & graphene oxide and other 2D materials are the availability of cost-effective, high-quality materials and their effective incorporation (functionalisation and dispersion)into the product matrices. On overcoming these factors, graphene may attract significant demands in terms of volume consumption. Graphene can be produced on industrial scales and cost-effective top-down routes such as chemical, electro chemical, and/or high-pressure mechanical exfoliation. Graphene depending on end applications can be chemically tuned and modified via functionalisation so that easy incorporation into product matrices is possible. This paper discusses different production methods and their impact on the quality of graphene produced in terms of energy input. Graphene with an average thickness below five layers were produced by both methods with varied defects. However, a higher yield of graphene with a lower number of layers was produced by the high-pressure exfoliation route.

Journal article

Seyedin S, Carey T, Arbab A, Eskandarian L, Bohm S, Kim JM, Torrisi Fet al., 2021,

Fibre electronics: towards scaled-up manufacturing of integrated e-textile systems

, Nanoscale, Vol: 13, Pages: 12818-12847, ISSN: 2040-3364

The quest for a close human interaction with electronic devices for healthcare, safety, energy and security has driven giant leaps in portable and wearable technologies in recent years. Electronic textiles (e-textiles) are emerging as key enablers of wearable devices. Unlike conventional heavy, rigid, and hard-to-wear gadgets, e-textiles can lead to lightweight, flexible, soft, and breathable devices, which can be worn like everyday clothes. A new generation of fibre-based electronics is emerging which can be made into wearable e-textiles. A suite of start-of-the-art functional materials have been used to develop novel fibre-based devices (FBDs), which have shown excellent potential in creating wearable e-textiles. Recent research in this area has led to the development of fibre-based electronic, optoelectronic, energy harvesting, energy storage, and sensing devices, which have also been integrated into multifunctional e-textile systems. Here we review the key technological advancements in FBDs and provide an updated critical evaluation of the status of the research in this field. Focusing on various aspects of materials development, device fabrication, fibre processing, textile integration, and scaled-up manufacturing we discuss current limitations and present an outlook on how to address the future development of this field. The critical analysis of key challenges and existing opportunities in fibre electronics aims to define a roadmap for future applications in this area.

Journal article

Hui F, Liu P, Hodge S, Carey T, Wen C, Torrisi F, Galhena T, Tomarchio F, Lin Y, Moreno E, Roldan J, Koren E, Ferrari A, Lanza Met al., 2021,

In-situ observation of low-power nano-synaptic response in graphene oxide using conductive atomic force microscopy

, Small, Vol: 17, ISSN: 1613-6810

Multiple studies have reported the observation of electro-synaptic response in different metal/insulator/metal devices; however, most of them analysed large (>1 µm2) devices that do not meet the integration density required by the industry (1010 devices/mm2). Some studies employed a scanning tunnelling microscope (STM) to explore nano-synaptic response in different materials, but in this setup there is a nanogap between the insulator and one of the metallic electrodes (i.e. the STM tip), which is not present in real devices. Here we show how to use a conductive atomic force microscope (CAFM) to explore the presence and quality of nano-synaptic response in confined areas <500 nm2. For this study, we selected graphene oxide (GO) due to its easy fabrication and excellent electrical properties. Our experiments indicate that metal/GO/metal nano-synapses exhibit potentiation and paired pulse facilitation with low write current levels <1 µA (i.e. power consumption ~3 μW), controllable excitatory post-synaptic currents and long-term potentiation and depression. Our results provide a new method to explore nano-synaptic plasticity at the nanoscale, and point GO as an important candidate material for the fabrication of ultra-small (<500 nm2) electronic synapses fulfilling the integration density requirements of neuromorphic systems.

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Ultrafast carrier and lattice cooling in Ti2CTx MXene thin films

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