1
|
Laser-induced graphene on cross-linked sodium alginate. NANOTECHNOLOGY 2023; 35:115103. [PMID: 38081076 DOI: 10.1088/1361-6528/ad143a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/25/2023] [Accepted: 12/10/2023] [Indexed: 12/30/2023]
Abstract
Laser-induced graphene (LIG) possesses desirable properties for numerous applications. However, LIG formation on biocompatible substrates is needed to further augment the integration of LIG-based technologies into nanobiotechnology. Here, LIG formation on cross-linked sodium alginate is reported. The LIG is systematically investigated, providing a comprehensive understanding of the physicochemical characteristics of the material. Raman spectroscopy, scanning electron microscopy with energy-dispersive x-ray analysis, x-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy techniques confirm the successful generation of oxidized graphene on the surface of cross-linked sodium alginate. The influence of laser parameters and the amount of crosslinker incorporated into the alginate substrate is explored, revealing that lower laser speed, higher resolution, and increased CaCl2content leads to LIG with lower electrical resistance. These findings could have significant implications for the fabrication of LIG on alginate with tailored conductive properties, but they could also play a guiding role for LIG formation on other biocompatible substrates.
Collapse
|
2
|
Three-dimensional printing of silica glass with sub-micrometer resolution. Nat Commun 2023; 14:3305. [PMID: 37280208 DOI: 10.1038/s41467-023-38996-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Accepted: 05/15/2023] [Indexed: 06/08/2023] Open
Abstract
Silica glass is a high-performance material used in many applications such as lenses, glassware, and fibers. However, modern additive manufacturing of micro-scale silica glass structures requires sintering of 3D-printed silica-nanoparticle-loaded composites at ~1200 °C, which causes substantial structural shrinkage and limits the choice of substrate materials. Here, 3D printing of solid silica glass with sub-micrometer resolution is demonstrated without the need of a sintering step. This is achieved by locally crosslinking hydrogen silsesquioxane to silica glass using nonlinear absorption of sub-picosecond laser pulses. The as-printed glass is optically transparent but shows a high ratio of 4-membered silicon-oxygen rings and photoluminescence. Optional annealing at 900 °C makes the glass indistinguishable from fused silica. The utility of the approach is demonstrated by 3D printing an optical microtoroid resonator, a luminescence source, and a suspended plate on an optical-fiber tip. This approach enables promising applications in fields such as photonics, medicine, and quantum-optics.
Collapse
|
3
|
Identification of Ubiquitously Present Polymeric Adlayers on 2D Transition Metal Dichalcogenides. ACS NANO 2023. [PMID: 37220885 DOI: 10.1021/acsnano.3c01649] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
The interest in 2D materials continues to grow across numerous scientific disciplines as compounds with unique electrical, optical, chemical, and thermal characteristics are being discovered. All these properties are governed by an all-surface nature and nanoscale confinement, which can easily be altered by extrinsic influences, such as defects, dopants or strain, adsorbed molecules, and contaminants. Here, we report on the ubiquitous presence of polymeric adlayers on top of layered transition metal dichalcogenides (TMDs). The atomically thin layers, not evident from common analytic methods, such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), or scanning electron microscopy (SEM), could be identified with highly resolved time-of-flight secondary ion mass spectrometry (TOF-SIMS). The layers consist of hydrocarbons, which preferentially adsorb to the hydrophobic van der Waals surfaces of TMDs, derived from the most common methods. Fingerprint fragmentation patterns enable us to identify certain polymers and link them to those used during preparation and storage of the TMDs. The ubiquitous presence of polymeric films on 2D materials has wide reaching implications for their investigation, processing, and applications. In this regard, we reveal the nature of polymeric residues after commonly used transfer procedures on MoS2 films and investigate several annealing procedures for their removal.
Collapse
|
4
|
Ultrafast and Resist-Free Nanopatterning of 2D Materials by Femtosecond Laser Irradiation. ACS NANO 2023; 17:8041-8052. [PMID: 37074334 PMCID: PMC10173691 DOI: 10.1021/acsnano.2c09501] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The performance of two-dimensional (2D) materials is promising for electronic, photonic, and sensing devices since they possess large surface-to-volume ratios, high mechanical strength, and broadband light sensitivity. While significant advances have been made in synthesizing and transferring 2D materials onto different substrates, there is still the need for scalable patterning of 2D materials with nanoscale precision. Conventional lithography methods require protective layers such as resist or metals that can contaminate or degrade the 2D materials and deteriorate the final device performance. Current resist-free patterning methods are limited in throughput and typically require custom-made equipment. To address these limitations, we demonstrate the noncontact and resist-free patterning of platinum diselenide (PtSe2), molybdenum disulfide (MoS2), and graphene layers with nanoscale precision at high processing speed while preserving the integrity of the surrounding material. We use a commercial, off-the-shelf two-photon 3D printer to directly write patterns in the 2D materials with features down to 100 nm at a maximum writing speed of 50 mm/s. We successfully remove a continuous film of 2D material from a 200 μm × 200 μm substrate area in less than 3 s. Since two-photon 3D printers are becoming increasingly available in research laboratories and industrial facilities, we expect this method to enable fast prototyping of devices based on 2D materials across various research areas.
Collapse
|
5
|
Field Effect Transistor Gas Sensors Based on Mechanically Exfoliated Van der Waals Materials. ACS APPLIED MATERIALS & INTERFACES 2023; 15:17335-17343. [PMID: 36972407 DOI: 10.1021/acsami.2c23086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
The high surface-to-volume ratio and flatness of mechanically exfoliated van der Waals (vdW) layered materials make them an ideal platform to investigate the Langmuir absorption model. In this work, we fabricated field effect transistor gas sensors, based on a variety of mechanically exfoliated vdW materials, and investigated their electrical field-dependent gas sensing properties. The good agreement between the experimentally extracted intrinsic parameters, such as equilibrium constant and adsorption energy, and theoretically predicted values suggests validity of the Langmuir absorption model for vdW materials. Moreover, we show that the device sensing behavior depends crucially on the availability of carriers, and giant sensitivities and strong selectivity can be achieved at the sensitivity singularity. Finally, we demonstrate that such features provide a fingerprint for different gases to quickly detect and differentiate between low concentrations of mixed hazardous gases using sensor arrays.
Collapse
|
6
|
Functionalisation of Graphene Sensor Surfaces for the Specific Detection of Biomarkers. Angew Chem Int Ed Engl 2023; 62:e202219024. [PMID: 36935352 DOI: 10.1002/anie.202219024] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 03/16/2023] [Accepted: 03/16/2023] [Indexed: 03/21/2023]
Abstract
We report on a controllable and specific functionalisation route for graphene field-effect transistors (GFETs) for the recognition of small physiologically active molecules. Key element is the noncovalent functionalisation of the graphene surface with perylene bisimide (PBI) molecules directly on the growth substrate. This Functional Layer Transfer enables the homogeneous self-assembly of PBI molecules on graphene, onto which antibodies are subsequently immobilised. The sensor surface was characterised by atomic force microscopy, Raman spectroscopy and electrical measurements, showing superior performance over conventional functionalisation after transfer. Specific sensing of small molecules was realised by monitoring the electrical property changes of functionalised GFET devices upon the application of methamphetamine and cortisol. The concentration dependent electrical response of our sensors was determined down to a concentration of 300 ng/ml for methamphetamine.
Collapse
|
7
|
Stacking Polymorphism in PtSe 2 Drastically Affects Its Electromechanical Properties. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2201272. [PMID: 35652199 PMCID: PMC9353474 DOI: 10.1002/advs.202201272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/18/2022] [Revised: 04/28/2022] [Indexed: 06/15/2023]
Abstract
PtSe2 is one of the most promising materials for the next generation of piezoresistive sensors. However, the large-scale synthesis of homogeneous thin films with reproducible electromechanical properties is challenging due to polycrystallinity. It is shown that stacking phases other than the 1T phase become thermodynamically available at elevated temperatures that are common during synthesis. It is shown that these phases can make up a significant fraction in a polycrystalline thin film and discuss methods to characterize them, including their Seebeck coefficients. Lastly, their gauge factors, which vary strongly and heavily impact the performance of a nanoelectromechanical device are estimated.
Collapse
|
8
|
Probing the Impact of Tribolayers on Enhanced Wear Resistance Behavior of Carbon-Rich Molybdenum-Based Coatings. ACS APPLIED MATERIALS & INTERFACES 2022; 14:26148-26161. [PMID: 35635256 DOI: 10.1021/acsami.2c03043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Minimizing friction and wear is one of the continuing challenges in many mechanical industries. Recent research efforts have been focused on accelerating the antifriction and antiwear properties of hard coatings through the incorporation of self-lubricant materials or the development of new architectures. In this present study, carbon-rich MoC, MoCN, and multilayer MoC/MoCN coatings were deposited using reactive magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were used to evaluate their properties, which revealed the presence of ceramic cubic crystallites, covalent bonds between primary elements, and an excess of amorphous carbon (a-C) in all of the coatings. The multilayer architecture and possible segregation of a-C around the ceramic crystallites resulted in improved mechanical properties for all coatings, with MoC/MoCN coatings having a maximum hardness of 21 GPa and elastic modulus of 236 GPa. Friction and wear behavior are initially determined by the structural-composition-property relationships of the respective coatings; later, the tribological characteristics are altered depending on the nature of tribolayer on both mating surfaces at the contact interface. The highest wear resistance of multilayer MoC/MoCN coating (8.7 × 10-8 mm3/N m) and MoC coating (3.9 × 10-7 mm3/N m) was due to the dissipation of contact stress by the tribofilm consisting of carbon tribo products like graphitic sp2 carbon, diamond-like sp3 carbon, and pyrrolic-N. On the other hand, MoCN coating depicted a lower wear resistance due to the frequent termination of C-H bonds by N, which restricts the strong formation of tribofilms as well as poor mechanical properties.
Collapse
|
9
|
Two-Dimensional Platinum Diselenide Waveguide-Integrated Infrared Photodetectors. ACS PHOTONICS 2022; 9:859-867. [PMID: 35308407 PMCID: PMC8931762 DOI: 10.1021/acsphotonics.1c01517] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Indexed: 05/11/2023]
Abstract
Low-cost, easily integrable photodetectors (PDs) for silicon (Si) photonics are still a bottleneck for photonic-integrated circuits (PICs), especially for wavelengths above 1.8 μm. Multilayered platinum diselenide (PtSe2) is a semi-metallic two-dimensional (2D) material that can be synthesized below 450 °C. We integrate PtSe2-based PDs directly by conformal growth on Si waveguides. The PDs operate at 1550 nm wavelength with a maximum responsivity of 11 mA/W and response times below 8.4 μs. Fourier-transform IR spectroscopy in the wavelength range from 1.25 to 28 μm indicates the suitability of PtSe2 for PDs far into the IR wavelength range. Our PtSe2 PDs integrated by direct growth outperform PtSe2 PDs manufactured by standard 2D layer transfer. The combination of IR responsivity, chemical stability, selective and conformal growth at low temperatures, and the potential for high carrier mobility makes PtSe2 an attractive 2D material for optoelectronics and PICs.
Collapse
|
10
|
Abstract
To date, the scalable synthesis of elemental two-dimensional materials beyond graphene still remains elusive. Here, we introduce a versatile chemical vapor deposition (CVD) method to grow borophenes, as well as borophene heterostructures, by selectively using diborane originating from traceable byproducts of borazine. Specifically, metallic borophene polymorphs were successfully synthesized on Ir(111) and Cu(111) single-crystal substrates and conjointly with insulating hexagonal boron nitride (hBN) to form atomically precise lateral borophene-hBN interfaces or vertical van der Waals heterostructures. Thereby, borophene is protected from immediate oxidation by a single hBN overlayer. The ability to synthesize high-quality borophenes with large single-crystalline domains in the micrometer scale by a straight-forward CVD approach opens up opportunities for the study of their fundamental properties and for device incorporation.
Collapse
|
11
|
Cover Feature: Covalent Patterning of 2D MoS
2
(Chem. Eur. J. 52/2021). Chemistry 2021. [DOI: 10.1002/chem.202102909] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
12
|
Abstract
The development of an efficient method to patterning 2D MoS2 into a desired topographic structure is of particular importance to bridge the way towards the ultimate device. Herein, we demonstrate a patterning strategy by combining the electron beam lithography with the surface covalent functionalization. This strategy allows us to generate delicate MoS2 ribbon patterns with a minimum feature size of 2 μm in a high throughput rate. The patterned monolayer MoS2 domain consists of a spatially well‐defined heterophase homojunction and alternately distributed surface characteristics, which holds great interest for further exploration of MoS2 based devices.
Collapse
|
13
|
Covalent Bisfunctionalization of Two‐Dimensional Molybdenum Disulfide. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202103353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
14
|
Covalent Bisfunctionalization of Two-Dimensional Molybdenum Disulfide. Angew Chem Int Ed Engl 2021; 60:13484-13492. [PMID: 33768735 PMCID: PMC8251601 DOI: 10.1002/anie.202103353] [Citation(s) in RCA: 16] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Indexed: 12/02/2022]
Abstract
Covalent functionalization of two‐dimensional molybdenum disulfide (2D MoS2) holds great promise in developing robust organic‐MoS2 hybrid structures. Herein, for the first time, we demonstrate an approach to building up a bisfunctionalized MoS2 hybrid structure through successively reacting activated MoS2 with alkyl iodide and aryl diazonium salts. This approach can be utilized to modify both colloidal and substrate supported MoS2 nanosheets. We have discovered that compared to the adducts formed through the reactions of MoS2 with diazonium salts, those formed through the reactions of MoS2 with alkyl iodides display higher reactivity towards further reactions with electrophiles. We are convinced that our systematic study on the formation and reactivity of covalently functionalized MoS2 hybrids will provide some practical guidance on multi‐angle tailoring of the properties of 2D MoS2 for various potential applications.
Collapse
|
15
|
Slippery polymer monoliths: Surface functionalization with ordered MoS2 microparticle arrays. Colloids Surf A Physicochem Eng Asp 2021. [DOI: 10.1016/j.colsurfa.2021.126363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
|
16
|
Hydrogenation of diamond nanowire surfaces for effective electrostatic charge storage. NANOSCALE 2021; 13:7308-7321. [PMID: 33889909 DOI: 10.1039/d1nr00189b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
We report a novel versatile method for writing charged areas on diamond nanowire (DNW) surfaces using an atomic force microscopy (AFM) tip. Transmission electron microscopy (TEM) investigations revealed the existence of abundant plate-like diamond aggregates, which were encased in layers of graphite, forming nano-sized diamond-graphite composites (DGCs) on DNW surfaces. These DGCs are the main feature, acting as charge-trapping centers and storing electrostatic charge. A hydrogenation process has been observed effectively enhancing the charge-trapping properties of these DNW materials. The effective charge trapping properties with hydrogenation are ascribed to the disintegration of the DGCs into smaller pieces, with an overall increase in the metallic nanographitic phase fractions in a dielectric diamond matrix. Moreover, the written charge on the surface can be easily modified, re-written, or completely erased, enabling application in diamond-based re-writable electronic devices. However, excessive hydrogenation degrades the charge-trapping properties, which is attributed to the etching of the DGCs from the surface. This study demonstrates the potential importance of a simple hydrogenation process in effective electrostatic charge trapping and storage for diamond related nanocarbon materials and the role of DGCs to further enhance it.
Collapse
|
17
|
Synthesis and characterisation of thin-film platinum disulfide and platinum sulfide. NANOSCALE 2021; 13:7403-7411. [PMID: 33889876 DOI: 10.1039/d0nr06197b] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Group-10 transition metal dichalcogenides (TMDs) are rising in prominence within the highly innovative field of 2D materials. While PtS2 has been investigated for potential electronic applications, due to its high charge-carrier mobility and strongly layer-dependent bandgap, it has proven to be one of the more difficult TMDs to synthesise. In contrast to most TMDs, Pt has a significantly more stable monosulfide, the non-layered PtS. The existence of two stable platinum sulfides, sometimes within the same sample, has resulted in much confusion between the materials in the literature. Neither of these Pt sulfides have been thoroughly characterised as-of-yet. Here we utilise time-efficient, scalable methods to synthesise high-quality thin films of both Pt sulfides on a variety of substrates. The competing nature of the sulfides and limited thermal stability of these materials is demonstrated. We report peak-fitted X-ray photoelectron spectra, and Raman spectra using a variety of laser wavelengths, for both materials. This systematic characterisation provides a guide to differentiate between the sulfides using relatively simple methods which is essential to enable future work on these interesting materials.
Collapse
|
18
|
Large-area integration of two-dimensional materials and their heterostructures by wafer bonding. Nat Commun 2021; 12:917. [PMID: 33568669 PMCID: PMC7876008 DOI: 10.1038/s41467-021-21136-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 01/14/2021] [Indexed: 01/31/2023] Open
Abstract
Integrating two-dimensional (2D) materials into semiconductor manufacturing lines is essential to exploit their material properties in a wide range of application areas. However, current approaches are not compatible with high-volume manufacturing on wafer level. Here, we report a generic methodology for large-area integration of 2D materials by adhesive wafer bonding. Our approach avoids manual handling and uses equipment, processes, and materials that are readily available in large-scale semiconductor manufacturing lines. We demonstrate the transfer of CVD graphene from copper foils (100-mm diameter) and molybdenum disulfide (MoS2) from SiO2/Si chips (centimeter-sized) to silicon wafers (100-mm diameter). Furthermore, we stack graphene with CVD hexagonal boron nitride and MoS2 layers to heterostructures, and fabricate encapsulated field-effect graphene devices, with high carrier mobilities of up to [Formula: see text]. Thus, our approach is suited for backend of the line integration of 2D materials on top of integrated circuits, with potential to accelerate progress in electronics, photonics, and sensing.
Collapse
|
19
|
Electronic and structural characterisation of polycrystalline platinum disulfide thin films. RSC Adv 2020; 10:42001-42007. [PMID: 35516737 PMCID: PMC9057923 DOI: 10.1039/d0ra07405e] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2020] [Accepted: 11/02/2020] [Indexed: 12/15/2022] Open
Abstract
We employ a combination of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) to investigate the properties of layered PtS2, synthesised via thermally assisted conversion (TAC) of a metallic Pt thin film. STM measurements reveal the 1T crystal structure of PtS2, and the lattice constant is determined to be 3.58 ± 0.03 Å. STS allowed the electronic structure of individual PtS2 crystallites to be directly probed and a bandgap of ∼1.03 eV was determined for a 3.8 nm thick flake at liquid nitrogen temperature. These findings substantially expand understanding of the atomic and electronic structure of PtS2 and indicate that STM is a powerful tool capable of locally probing non-uniform polycrystalline films, such as those produced by TAC. Prior to STM/STS measurements the quality of synthesised TAC PtS2 was analysed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. These results are of relevance to applications-focussed studies centred on PtS2 and may inform future efforts to optimise the synthesis conditions for thin film PtS2. Semiconducting thin-film polycrystalline PtS2 is characterised by atomically resolved scanning tunnelling microscopy and spectroscopy.![]()
Collapse
|
20
|
Low-temperature synthesis and electrocatalytic application of large-area PtTe 2 thin films. NANOTECHNOLOGY 2020; 31:375601. [PMID: 32498057 DOI: 10.1088/1361-6528/ab9973] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The synthesis of transition metal dichalcogenides (TMDs) has been a primary focus for 2D nanomaterial research over the last 10 years, however, only a small fraction of this research has been concentrated on transition metal ditellurides. In particular, nanoscale platinum ditelluride (PtTe2) has rarely been investigated, despite its potential applications in catalysis, photonics and spintronics. Of the reports published, the majority examine mechanically-exfoliated flakes from chemical vapor transport (CVT) grown crystals. This method produces high quality-crystals, ideal for fundamental studies. However, it is very resource intensive and difficult to scale up meaning there are significant obstacles to implementation in large-scale applications. In this report, the synthesis of thin films of PtTe2 through the reaction of solid-phase precursor films is described. This offers a production method for large-area, thickness-controlled PtTe2, potentially suitable for a number of applications. These polycrystalline PtTe2 films were grown at temperatures as low as 450 °C, significantly below the typical temperatures used in the CVT synthesis methods. Adjusting the growth parameters allowed the surface coverage and morphology of the films to be controlled. Analysis with scanning electron- and scanning tunneling microscopy indicated grain sizes of above 1 µm could be achieved, comparing favorably with typical values of ∼50 nm for polycrystalline films. To investigate their potential applicability, these films were examined as electrocatalysts for the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR). The films showed promising catalytic behavior, however, the PtTe2 was found to undergo chemical transformation to a substoichiometric chalcogenide compound under ORR conditions. This study shows while PtTe2 is stable and highly useful for in HER, this property does not apply to ORR, which undergoes a fundamentally different mechanism. This study broadens our knowledge on the electrocatalysis of TMDs.
Collapse
|
21
|
Effect of localized helium ion irradiation on the performance of synthetic monolayer MoS 2 field-effect transistors. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2020; 11:1329-1335. [PMID: 32953377 PMCID: PMC7476591 DOI: 10.3762/bjnano.11.117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 08/19/2020] [Indexed: 05/31/2023]
Abstract
Helium ion irradiation is a known method of tuning the electrical conductivity and charge carrier mobility of novel two-dimensional semiconductors. Here, we report a systematic study of the electrical performance of chemically synthesized monolayer molybdenum disulfide (MoS2) field-effect transistors irradiated with a focused helium ion beam as a function of increasing areal irradiation coverage. We determine an optimal coverage range of approx. 10%, which allows for the improvement of both the carrier mobility in the transistor channel and the electrical conductance of the MoS2, due to doping with ion beam-created sulfur vacancies. Larger areal irradiations introduce a higher concentration of scattering centers, hampering the electrical performance of the device. In addition, we find that irradiating the electrode-channel interface has a deleterious impact on charge transport when contrasted with irradiations confined only to the transistor channel.
Collapse
|
22
|
Titelbild: Site‐Selective Oxidation of Monolayered Liquid‐Exfoliated WS
2
by Shielding the Basal Plane through Adsorption of a Facial Amphiphile (Angew. Chem. 33/2020). Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202007849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
23
|
Site-Selective Oxidation of Monolayered Liquid-Exfoliated WS 2 by Shielding the Basal Plane through Adsorption of a Facial Amphiphile. Angew Chem Int Ed Engl 2020; 59:13785-13792. [PMID: 32449582 PMCID: PMC7496821 DOI: 10.1002/anie.202005730] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Indexed: 12/31/2022]
Abstract
In recent years, various functionalization strategies for transition‐metal dichalcogenides have been explored to tailor the properties of materials and to provide anchor points for the fabrication of hybrid structures. Herein, new insights into the role of the surfactant in functionalization reactions are described. Using the spontaneous reaction of WS2 with chloroauric acid as a model reaction, the regioselective formation of gold nanoparticles on WS2 is shown to be heavily dependent on the surfactant employed. A simple model is developed to explain the role of the chosen surfactant in this heterogeneous functionalization reaction. The surfactant coverage is identified as the crucial element that governs the dominant reaction pathway and therefore can severely alter the reaction outcome. This study shows the general importance of the surfactant choice and how detrimental or beneficial a certain surfactant can be to the desired functionalization.
Collapse
|
24
|
Cover Picture: Site‐Selective Oxidation of Monolayered Liquid‐Exfoliated WS
2
by Shielding the Basal Plane through Adsorption of a Facial Amphiphile (Angew. Chem. Int. Ed. 33/2020). Angew Chem Int Ed Engl 2020. [DOI: 10.1002/anie.202007849] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
25
|
Rapid and Large-Area Visualization of Grain Boundaries in MoS 2 on SiO 2 Using Vapor Hydrofluoric Acid. ACS APPLIED MATERIALS & INTERFACES 2020; 12:34049-34057. [PMID: 32618182 PMCID: PMC7393636 DOI: 10.1021/acsami.0c06910] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 07/03/2020] [Indexed: 06/11/2023]
Abstract
Grain boundaries in two-dimensional (2D) material layers have an impact on their electrical, optoelectronic, and mechanical properties. Therefore, the availability of simple large-area characterization approaches that can directly visualize grains and grain boundaries in 2D materials such as molybdenum disulfide (MoS2) is critical. Previous approaches for visualizing grains and grain boundaries in MoS2 are typically based on atomic resolution microscopy or optical imaging techniques (i.e., Raman spectroscopy or photoluminescence), which are complex or limited to the characterization of small, micrometer-sized areas. Here, we show a simple approach for an efficient large-area visualization of the grain boundaries in continuous chemical vapor-deposited films and domains of MoS2 that are grown on a silicon dioxide (SiO2) substrate. In our approach, the MoS2 layer on a SiO2/Si substrate is exposed to vapor hydrofluoric acid (VHF), resulting in the differential etching of SiO2 at the MoS2 grain boundaries and SiO2 underneath the MoS2 grains as a result of VHF diffusing through the defects in the MoS2 layer at the grain boundaries. The location of the grain boundaries can be seen by the resulting SiO2 pattern using optical microscopy, scanning electron microscopy, or Raman spectroscopy. This method allows for a simple and rapid evaluation of grain sizes in 2D material films over large areas, thereby potentially facilitating the optimization of synthesis processes and advancing applications of 2D materials in science and technology.
Collapse
|
26
|
Site‐Selective Oxidation of Monolayered Liquid‐Exfoliated WS
2
by Shielding the Basal Plane through Adsorption of a Facial Amphiphile. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202005730] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
|
27
|
Low-Humidity Sensing Properties of Multi-Layered Graphene Grown by Chemical Vapor Deposition. SENSORS 2020; 20:s20113174. [PMID: 32503202 PMCID: PMC7313702 DOI: 10.3390/s20113174] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/28/2020] [Revised: 05/27/2020] [Accepted: 06/01/2020] [Indexed: 11/23/2022]
Abstract
Humidity sensing is fundamental in some applications, as humidity can be a strong interferent in the detection of analytes under environmental conditions. Ideally, materials sensitive or insensitive towards humidity are strongly needed for the sensors used in the first or second case, respectively. We present here the sensing properties of multi-layered graphene (MLG) upon exposure to different levels of relative humidity. We synthesize MLG by chemical vapor deposition, as shown by Raman spectroscopy, Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Through an MLG-based resistor, we show that MLG is scarcely sensitive to humidity in the range 30%–70%, determining current variations in the range of 0.005%/%relative humidity (RH) well below the variation induced by other analytes. These findings, due to the morphological properties of MLG, suggest that defective MLG is the ideal sensing material to implement in gas sensors operating both at room temperature and humid conditions.
Collapse
|
28
|
Cover Feature: Defect Engineering of Two‐Dimensional Molybdenum Disulfide (Chem. Eur. J. 29/2020). Chemistry 2020. [DOI: 10.1002/chem.202001486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
|
29
|
Abstract
Two‐dimensional (2D) molybdenum disulfide (MoS2) holds great promise in electronic and optoelectronic applications owing to its unique structure and intriguing properties. The intrinsic defects such as sulfur vacancies (SVs) of MoS2 nanosheets are found to be detrimental to the device efficiency. To mitigate this problem, functionalization of 2D MoS2 using thiols has emerged as one of the key strategies for engineering defects. Herein, we demonstrate an approach to controllably engineer the SVs of chemically exfoliated MoS2 nanosheets using a series of substituted thiophenols in solution. The degree of functionalization can be tuned by varying the electron‐withdrawing strength of substituents in thiophenols. We find that the intensity of 2LA(M) peak normalized to A1g peak strongly correlates to the degree of functionalization. Our results provide a spectroscopic indicator to monitor and quantify the defect engineering process. This method of MoS2 defect functionalization in solution also benefits the further exploration of defect‐free MoS2 for a wide range of applications.
Collapse
|
30
|
Calibration of Nonstationary Gas Sensors Based on Two-Dimensional Materials. ACS OMEGA 2020; 5:5959-5963. [PMID: 32226876 PMCID: PMC7098003 DOI: 10.1021/acsomega.9b04325] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Accepted: 02/21/2020] [Indexed: 05/24/2023]
Abstract
Two-dimensional materials (2DMs) have high potential in gas sensing, due to their large surface-to-volume ratio. However, most sensors based on 2DMs suffer from the lack of a steady state during gas exposure, hampering sensor calibration. Here, we demonstrate that analysis of the time differential of the signal output enables the calibration of chemiresistors based on platinum or tungsten diselenide (PtSe2, WSe2) and molybdenum disulfide (MoS2), which present nonstationary behavior. 2DMs are synthesized by thermally assisted conversion of predeposited metals on a silicon/silicon dioxide substrate and therefore are integrable with standard complementary metal-oxide semiconductor (CMOS) technology. We analyze the behavior of the sensors at room temperature toward nitrogen dioxide (NO2) in a narrow range from 0.1 to 1 ppm. This study overcomes the problem of the absence of steady-state signals in 2DM gas sensors and thus facilitates their usage in this highly important application.
Collapse
|
31
|
Insights into Multilevel Resistive Switching in Monolayer MoS 2. ACS APPLIED MATERIALS & INTERFACES 2020; 12:6022-6029. [PMID: 31920069 DOI: 10.1021/acsami.9b15677] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The advent of two-dimensional materials has opened a plethora of opportunities in accessing ultrascaled device dimensions for future logic and memory applications. In this work, we demonstrate that a single layer of large-area chemical vapor deposition-grown molybdenum disulfide (MoS2) sandwiched between two metal electrodes can be tuned to show multilevel nonvolatile resistive memory states with resistance values separated by 5 orders of magnitude. The switching process is unipolar and thermochemically driven requiring significant Joule heating in the reset process. Temperature-dependent electrical measurements coupled with semiclassical charge transport models suggest that the transport in these devices varies significantly in the initial (pristine) state, high resistance state, and low resistance state. In the initial state, the transport is a one-step direct tunneling (at low voltage biases) and Fowler Nordeim tunneling (at higher bias) with an effective barrier height of 0.33 eV, which closely matches the Schottky barrier at the MoS2/Au interface. In the high resistive state, trap-assisted tunneling provides a reasonable fit to experimental data for a trap height of 0.82 eV. Density functional theory calculations suggest the possibility of single- and double-sulfur vacancies as the microscopic origins of these trap sites. The temperature-dependent behavior of the set and reset process are explained by invoking the probability of defect (sulfur vacancy) creation and mobility of sulfur ions. Finally, conductive atomic force microscopy measurements confirm that the multifilamentary resistive memory effects are inherent to a single-crystalline MoS2 triangle and not necessarily dependent on grain boundaries. The insights suggested in this work are envisioned to open up possibilities for ultrascaled, multistate, resistive memories for next-generation digital memory and neuromorphic applications.
Collapse
|
32
|
Crystal-structure of active layers of small molecule organic photovoltaics before and after solvent vapor annealing. Z KRIST-CRYST MATER 2020. [DOI: 10.1515/zkri-2019-0055] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Abstract
It is demonstrated by a detailed structural analysis that the crystallinity and the efficiency of small molecule based organic photovoltaics can be tuned by solvent vapor annealing (SVA). Blends made of the small molecule donor 2,2′-[(3,3′″,3″″,4′-tetraoctyl[2,2′:5′,2″:5″,2′″:5′″,2″″-quinquethiophene]-5,5″″-diyl)bis[(Z)-methylidyne(3-ethyl-4-oxo-5,2-thiazolidinediylidene)]]bis-propanedinitrile (DRCN5T) and the acceptor [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were annealed using solvent vapors with either a high solubility for the donor (tetrahydrofuran), the acceptor (carbon disulfide) or both (chloroform). The samples were analyzed by grazing-incidence wide-angle X-ray scattering (GIWAXS), electron diffraction, X-ray pole figures, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). A phase separation of DRCN5T and PC71BM is induced by SVA leading to a crystallization of DRCN5T and the formation of a DRCN5T enriched layer. The DRCN5T crystallites possess the two dimensional oblique crystal system with the lattice parameters a = 19.2 Å, c = 27.1 Å, and β = 111.1° for the chloroform case. No major differences in the crystal structure for the other solvent vapors were observed. However, the solvent choice strongly influences the size of the DRCN5T enriched layer. Missing periodicity in the [010]-direction leads to the extinction of all Bragg reflections with k ≠ 0. The annealed samples are randomly orientated with respect to the normal of the substrate (fiber texture).
Collapse
|
33
|
Sub-millimeter size high mobility single crystal MoSe2 monolayers synthesized by NaCl-assisted chemical vapor deposition. RSC Adv 2020; 10:1580-1587. [PMID: 35494696 PMCID: PMC9048230 DOI: 10.1039/c9ra09103c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Accepted: 12/26/2019] [Indexed: 01/11/2023] Open
Abstract
Monolayer MoSe2 is a transition metal dichalcogenide with a narrow bandgap, high optical absorbance and large spin-splitting energy, giving it great promise for applications in the field of optoelectronics. Producing monolayer MoSe2 films in a reliable and scalable manner is still a challenging task as conventional chemical vapor deposition (CVD) or exfoliation based techniques are limited due to the small domains/nanosheet sizes obtained. Here, based on NaCl assisted CVD, we demonstrate the simple and stable synthesis of sub-millimeter size single-crystal MoSe2 monolayers with mobilities ranging from 38 to 8 cm2 V−1 s−1. The average mobility is 12 cm2 V−1 s−1. We further determine that the optical responsivity of monolayer MoSe2 is 42 mA W−1, with an external quantum efficiency of 8.22%. Sub-millimeter single crystal MoSe2 monolayers with a mobility of 38 cm2 V−1 s−1 and responsivity of 42 mA W−1 were synthesized by NaCl-assisted chemical vapor deposition.![]()
Collapse
|
34
|
Nanoelectromechanical Sensors Based on Suspended 2D Materials. RESEARCH (WASHINGTON, D.C.) 2020; 2020:8748602. [PMID: 32766550 PMCID: PMC7388062 DOI: 10.34133/2020/8748602] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Accepted: 04/23/2020] [Indexed: 01/09/2023]
Abstract
The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.
Collapse
|
35
|
Abstract
Two-dimensional (2D) layered semiconductors have recently emerged as attractive building blocks for next-generation low-power nonvolatile memories. However, challenges remain in the controllable fabrication of bipolar resistive switching circuit components from these materials. Here, the experimental realization of lateral memtransistors from monolayer single-crystal molybdenum disulfide (MoS2) utilizing a focused helium ion beam is reported. Site-specific irradiation with the focused probe of a helium ion microscope creates a nanometer-scale defect-rich region, bisecting the MoS2 lattice. The reversible drift of these defects in the applied electric field modulates the resistance of the channel, enabling versatile memristive functionality. The device can reliably retain its resistance ratios and set/reset biases for 1180 switching cycles. Long-term potentiation and depression with sharp habituation are demonstrated. This work establishes the feasibility of ion irradiation for controllable fabrication of 2D memristive devices with promising key performance parameters, such as low power consumption. The applicability of these devices for synaptic emulation may address the demands of future neuromorphic architectures.
Collapse
|
36
|
Ultrafast Carrier Dynamics and Bandgap Renormalization in Layered PtSe 2. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2019; 15:e1902728. [PMID: 31276302 DOI: 10.1002/smll.201902728] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Indexed: 06/09/2023]
Abstract
Carrier interactions in 2D nanostructures are of central importance not only in condensed-matter physics but also for a wide range of optoelectronic and photonic applications. Here, new insights into the behavior of photoinduced carriers in layered platinum diselenide (PtSe2 ) through ultrafast time-resolved pump-probe and nonlinear optical measurements are presented. The measurements reveal the temporal evolution of carrier relaxation, chemical potential and bandgap renormalization in PtSe2 . These results imply that few-layer PtSe2 has a semiconductor-like carrier relaxation instead of a metal-like one. The relaxation follows a triple-exponential decay process and exhibits thickness-dependent relaxation times. This occurs along with a band-filling effect, which can be controlled based on the number of layers and may be applied in saturable absorption for generating ultrafast laser pulses. The findings may provide means to study many-body physics in 2D materials as well as potentially leading to applications in the field of optoelectronics and ultrafast photonics.
Collapse
|
37
|
Abstract
Porous single-layer molybdenum disulfide (MoS2) is a promising material for applications such as DNA sequencing and water desalination. In this work, we introduce irradiation with highly charged ions (HCIs) as a new technique to fabricate well-defined pores in MoS2. Surprisingly, we find a linear increase of the pore creation efficiency over a broad range of potential energies. Comparison to atomistic simulations reveals the critical role of energy deposition from the ion to the material through electronic excitation in the defect creation process and suggests an enrichment in molybdenum in the vicinity of the pore edges at least for ions with low potential energies. Analysis of the irradiated samples with atomic resolution scanning transmission electron microscopy reveals a clear dependence of the pore size on the potential energy of the projectiles, establishing irradiation with highly charged ions as an effective method to create pores with narrow size distributions and radii between ca. 0.3 and 3 nm.
Collapse
|
38
|
Optimized single-layer MoS 2 field-effect transistors by non-covalent functionalisation. NANOSCALE 2018; 10:17557-17566. [PMID: 30226520 DOI: 10.1039/c8nr02134a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Field-effect transistors (FETs) with non-covalently functionalised molybdenum disulfide (MoS2) channels grown by chemical vapour deposition (CVD) on SiO2 are reported. The dangling-bond-free surface of MoS2 was functionalised with a perylene bisimide derivative to allow for the deposition of Al2O3 dielectric. This allowed the fabrication of top-gated, fully encapsulated MoS2 FETs. Furthermore, by the definition of vertical contacts on MoS2, devices, in which the channel area was never exposed to polymers, were fabricated. The MoS2 FETs showed some of the highest mobilities for transistors fabricated on SiO2 with Al2O3 as the top-gate dielectric reported so far. Thus, gate-stack engineering using innovative chemistry is a promising approach for the fabrication of reliable electronic devices based on 2D materials.
Collapse
|
39
|
In Situ Formed Protective Barrier Enabled by Sulfur@Titanium Carbide (MXene) Ink for Achieving High-Capacity, Long Lifetime Li-S Batteries. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2018; 5:1800502. [PMID: 30250792 PMCID: PMC6145260 DOI: 10.1002/advs.201800502] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Revised: 04/23/2018] [Indexed: 05/22/2023]
Abstract
Sulfur (S) is an attractive cathode material with advantages including high theoretical capacity and low cost. However, issues such as the lithium polysulfide shuttle effect and its insulating properties greatly limit the future applications of lithium-sulfur (Li-S) batteries. Here, a viscous aqueous ink with nanoscale S uniformly decorated on the polar, metallically conductive titanium carbide MXene nanosheets (S@Ti3C2T x ) is reported to address these issues. Importantly, it is observed that the conductive Ti3C2T x mediator efficiently chemisorbs the soluble polysulfides and converts them into thiosulfate/sulfate. The in situ formed sulfate complex layer acts as a thick protective barrier, which significantly retards the shuttling of polysulfides upon cycling and improves the sulfur utilization. Consequently, the binder-free, robust, highly electrically conductive composite film exhibits outstanding electrochemical performance, including high capacities (1244-1350 mAh g-1), excellent rate handling, and impressive cycling stability (0.035-0.048% capacity loss per cycle), surpassing the best MXene-S batteries known. The fabrication of a pouch cell based on the freestanding S@Ti3C2T x film is also reported. The prototype device showcases high capacities and excellent mechanical flexibility. Considering the broad family of MXenes and their unique roles in immobilizing the polysulfides, various S@MXene composites can be similarly fabricated with promising Li+ storage capability and long lifetime performance.
Collapse
|
40
|
Abstract
The optical response of metallic nanohelices is mainly governed by a longitudinal localised surface plasmon resonance (LSPR) which arises due to the helical anisotropy of the system. Up to now, experimental studies have predominantly addressed the far-field response, despite the fact that the LSPR being of broad interest for converting incoming light into strongly enhanced (chiral) optical near-fields. Here, we demonstrate the control and spatial reproducibility of the plasmon-induced electromagnetic near-field around metallic nanohelices via surface-enhanced Raman scattering. We discuss how the near-field intensity of these nanostructures can be custom-tailored through both the nanoscaled helical structure and the electronic properties of the constituting metals. Our experiments, which employ graphene as an accurate probing material, are in quantitative agreement with corresponding numerical simulations. The findings demonstrate metallic nanohelices as reference nanostructured surfaces able to provide and fine-tune optical fields for fundamental studies as well as sensing or (chiro-optical) imaging applications.
Collapse
|
41
|
Highly Sensitive Electromechanical Piezoresistive Pressure Sensors Based on Large-Area Layered PtSe 2 Films. NANO LETTERS 2018; 18:3738-3745. [PMID: 29768010 PMCID: PMC6014683 DOI: 10.1021/acs.nanolett.8b00928] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 04/23/2018] [Indexed: 05/23/2023]
Abstract
Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe2), an exciting and unexplored 2D transition metal dichalcogenide material, is particularly interesting because its low temperature growth process is scalable and compatible with silicon technology. Here, we report the potential of thin PtSe2 films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe2 films grown by thermally assisted conversion of platinum at a complementary metal-oxide-semiconductor (CMOS)-compatible temperature of 400 °C. We report high negative gauge factors of up to -85 obtained experimentally from PtSe2 strain gauges in a bending cantilever beam setup. Integrated NEMS piezoresistive pressure sensors with freestanding PMMA/PtSe2 membranes confirm the negative gauge factor and exhibit very high sensitivity, outperforming previously reported values by orders of magnitude. We employ density functional theory calculations to understand the origin of the measured negative gauge factor. Our results suggest PtSe2 as a very promising candidate for future NEMS applications, including integration into CMOS production lines.
Collapse
|
42
|
Abstract
Platinum diselenide (PtSe2) is a group-10 transition metal dichalcogenide (TMD) that has unique electronic properties, in particular a semimetal-to-semiconductor transition when going from bulk to monolayer form. We report on vertical hybrid Schottky barrier diodes (SBDs) of two-dimensional (2D) PtSe2 thin films on crystalline n-type silicon. The diodes have been fabricated by transferring large-scale layered PtSe2 films, synthesized by thermally assisted conversion of predeposited Pt films at back-end-of-the-line CMOS compatible temperatures, onto SiO2/Si substrates. The diodes exhibit obvious rectifying behavior with a photoresponse under illumination. Spectral response analysis reveals a maximum responsivity of 490 mA/W at photon energies above the Si bandgap and relatively weak responsivity, in the range of 0.1-1.5 mA/W, at photon energies below the Si bandgap. In particular, the photoresponsivity of PtSe2 in infrared allows PtSe2 to be utilized as an absorber of infrared light with tunable sensitivity. The results of our study indicate that PtSe2 is a promising option for the development of infrared absorbers and detectors for optoelectronics applications with low-temperature processing conditions.
Collapse
|
43
|
Oxide-mediated recovery of field-effect mobility in plasma-treated MoS 2. SCIENCE ADVANCES 2018; 4:eaao5031. [PMID: 29511736 PMCID: PMC5837433 DOI: 10.1126/sciadv.aao5031] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 01/24/2018] [Indexed: 05/22/2023]
Abstract
Precise tunability of electronic properties of two-dimensional (2D) nanomaterials is a key goal of current research in this field of materials science. Chemical modification of layered transition metal dichalcogenides leads to the creation of heterostructures of low-dimensional variants of these materials. In particular, the effect of oxygen-containing plasma treatment on molybdenum disulfide (MoS2) has long been thought to be detrimental to the electrical performance of the material. We show that the mobility and conductivity of MoS2 can be precisely controlled and improved by systematic exposure to oxygen/argon plasma and characterize the material using advanced spectroscopy and microscopy. Through complementary theoretical modeling, which confirms conductivity enhancement, we infer the role of a transient 2D substoichiometric phase of molybdenum trioxide (2D-MoO x ) in modulating the electronic behavior of the material. Deduction of the beneficial role of MoO x will serve to open the field to new approaches with regard to the tunability of 2D semiconductors by their low-dimensional oxides in nano-modified heterostructures.
Collapse
|
44
|
Induction of Chirality in Two-Dimensional Nanomaterials: Chiral 2D MoS 2 Nanostructures. ACS NANO 2018; 12:954-964. [PMID: 29338193 DOI: 10.1021/acsnano.7b06691] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Two-dimensional (2D) nanomaterials have been intensively investigated due to their interesting properties and range of potential applications. Although most research has focused on graphene, atomic layered transition metal dichalcogenides (TMDs) and particularly MoS2 have gathered much deserved attention recently. Here, we report the induction of chirality into 2D chiral nanomaterials by carrying out liquid exfoliation of MoS2 in the presence of chiral ligands (cysteine and penicillamine) in water. This processing resulted in exfoliated chiral 2D MoS2 nanosheets showing strong circular dichroism signals, which were far past the onset of the original chiral ligand signals. Using theoretical modeling, we demonstrated that the chiral nature of MoS2 nanosheets is related to the presence of chiral ligands causing preferential folding of the MoS2 sheets. There was an excellent match between the theoretically calculated and experimental spectra. We believe that, due to their high aspect ratio planar morphology, chiral 2D nanomaterials could offer great opportunities for the development of chiroptical sensors, materials, and devices for valleytronics and other potential applications. In addition, chirality plays a key role in many chemical and biological systems, with chiral molecules and materials critical for the further development of biopharmaceuticals and fine chemicals, and this research therefore should have a strong impact on relevant areas of science and technology such as nanobiotechnology, nanomedicine, and nanotoxicology.
Collapse
|
45
|
Atmospheric pulsed laser deposition and thermal annealing of plasmonic silver nanoparticle films. NANOTECHNOLOGY 2017; 28:445601. [PMID: 28884710 DOI: 10.1088/1361-6528/aa8b32] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A new method for pulsed laser deposition of plasmonic silver nanoparticle (NP) films in flowing gas at atmospheric pressure is described. The ablation was done using an excimer laser at 248 nm. Fast optical imaging shows that the ablation plume is captured by the flowing gas, and is expected to form a NP aerosol, which is carried 5-20 mm to the substrate. The dependence of the deposition rate on laser fluence, gas flow velocity, and target-substrate distance was investigated using electron microscopy and absorption spectroscopy of the deposited films. The NP films were annealed in argon and hydrogen at 400 °C, and in air for temperatures in the range 200 °C-900 °C, leading to strong enhancement, and narrowing of the surface plasmon resonance. The films were used for surface enhanced Raman spectroscopy of a 10-5 molar solution of Rhodamine 6G; films annealed in air at 400 °C were five times more sensitive than the as-deposited films.
Collapse
|
46
|
Transparent, Flexible, and Conductive 2D Titanium Carbide (MXene) Films with High Volumetric Capacitance. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2017; 29:1702678. [PMID: 28741695 DOI: 10.1002/adma.201702678] [Citation(s) in RCA: 292] [Impact Index Per Article: 41.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2017] [Revised: 06/11/2017] [Indexed: 05/21/2023]
Abstract
2D transition-metal carbides and nitrides, known as MXenes, have displayed promising properties in numerous applications, such as energy storage, electromagnetic interference shielding, and catalysis. Titanium carbide MXene (Ti3 C2 Tx ), in particular, has shown significant energy-storage capability. However, previously, only micrometer-thick, nontransparent films were studied. Here, highly transparent and conductive Ti3 C2 Tx films and their application as transparent, solid-state supercapacitors are reported. Transparent films are fabricated via spin-casting of Ti3 C2 Tx nanosheet colloidal solutions, followed by vacuum annealing at 200 °C. Films with transmittance of 93% (≈4 nm) and 29% (≈88 nm) demonstrate DC conductivity of ≈5736 and ≈9880 S cm-1 , respectively. Such highly transparent, conductive Ti3 C2 Tx films display impressive volumetric capacitance (676 F cm-3 ) combined with fast response. Transparent solid-state, asymmetric supercapacitors (72% transmittance) based on Ti3 C2 Tx and single-walled carbon nanotube (SWCNT) films are also fabricated. These electrodes exhibit high capacitance (1.6 mF cm-2 ) and energy density (0.05 µW h cm-2 ), and long lifetime (no capacitance decay over 20 000 cycles), exceeding that of graphene or SWCNT-based transparent supercapacitor devices. Collectively, the Ti3 C2 Tx films are among the state-of-the-art for future transparent, conductive, capacitive electrodes, and translate into technologically viable devices for next-generation wearable, portable electronics.
Collapse
|
47
|
Enabling Flexible Heterostructures for Li-Ion Battery Anodes Based on Nanotube and Liquid-Phase Exfoliated 2D Gallium Chalcogenide Nanosheet Colloidal Solutions. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2017; 13:1701677. [PMID: 28692755 DOI: 10.1002/smll.201701677] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2017] [Indexed: 05/23/2023]
Abstract
2D metal chalcogenide (MC) nanosheets (NS) have displayed high capacities as lithium-ion battery (LiB) anodes. Nevertheless, their complicated synthesis routes coupled with low electronic conductivity greatly limit them as promising LiB electrode material. Here, this work reports a facile single-walled carbon nanotube (SWCNT) percolating strategy for efficiently maximizing the electrochemical performances of gallium chalcogenide (GaX, X = S or Se). Multiscaled flexible GaX NS/SWCNT heterostructures with abundant voids for Li+ diffusion are fabricated by embedding the liquid-exfoliated GaX NS matrix within a SWCNT-percolated network; the latter improves the electron transport and ion diffusion kinetics as well as maintains the mechanical flexibility. Consequently, high capacities (i.e., 838 mAh g-1 per gallium (II) sulfide (GaS) NS/SWCNT mass and 1107 mAh g-1 per GaS mass; the latter is close to the theoretical value) and good rate capabilities are achieved, which can be majorly attributed to the alloying processes of disordered Ga formed after the first irreversible GaX conversion reaction, as monitored by in situ X-ray diffraction. The presented approach, colloidal solution processing of SWCNT and liquid-exfoliated MC NS to produce flexible paper-based electrode, could be generalized for wearable energy storage devices with promising performances.
Collapse
|
48
|
Lithium Titanate/Carbon Nanotubes Composites Processed by Ultrasound Irradiation as Anodes for Lithium Ion Batteries. Sci Rep 2017; 7:7614. [PMID: 28790388 PMCID: PMC5548767 DOI: 10.1038/s41598-017-06908-3] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2017] [Accepted: 06/20/2017] [Indexed: 11/09/2022] Open
Abstract
In this work, lithium titanate nanoparticles (nLTO)/single wall carbon nanotubes (SWCNT) composite electrodes are prepared by the combination of an ultrasound irradiation and ultrasonic spray deposition methods. It was found that a mass fraction of 15% carbon nanotubes optimizes the electrochemical performance of nLTO electrodes. These present capacities as high as 173, 130, 110 and 70 mAh.g-1 at 0.1C, 1C, 10C and 100C, respectively. Moreover, after 1000 cycles at 1C, the nLTO/SWCNT composites present a capacity loss of just 9% and a Coulombic efficiency of 99.8%. Therefore, the presented methodology might be extended to other suitable active materials in order to manufacture binder free electrodes with optimal energy storage capabilities.
Collapse
|
49
|
All-printed thin-film transistors from networks of liquid-exfoliated nanosheets. Science 2017; 356:69-73. [DOI: 10.1126/science.aal4062] [Citation(s) in RCA: 305] [Impact Index Per Article: 43.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2016] [Accepted: 03/13/2017] [Indexed: 01/18/2023]
|
50
|
Hot-Volumes as Uniform and Reproducible SERS-Detection Enhancers in Weakly-Coupled Metallic Nanohelices. Sci Rep 2017; 7:45548. [PMID: 28358022 PMCID: PMC5372087 DOI: 10.1038/srep45548] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 02/27/2017] [Indexed: 11/09/2022] Open
Abstract
Reproducible and enhanced optical detection of molecules in low concentrations demands simultaneously intense and homogeneous electric fields acting as robust signal amplifiers. To generate such sophisticated optical near-fields, different plasmonic nanostructures were investigated in recent years. These, however, exhibit either high enhancement factor (EF) or spatial homogeneity but not both. Small interparticle gaps or sharp nanostructures show enormous EFs but no near-field homogeneity. Meanwhile, approaches using rounded and separated monomers create uniform near-fields with moderate EFs. Here, guided by numerical simulations, we show how arrays of weakly-coupled Ag nanohelices achieve both homogeneous and strong near-field enhancements, reaching even the limit forreproducible detection of individual molecules. The unique near-field distribution of a single nanohelix consists of broad hot-spots, merging with those from neighbouring nanohelices in specific array configurations and generating a wide and uniform detection zone ("hot-volume"). We experimentally assessed these nanostructures via surface-enhanced Raman spectroscopy, obtaining a corresponding EF of ~107 and a relative standard deviation <10%. These values demonstrate arrays of nanohelices as state-of-the-art substrates for reproducible optical detection as well as compelling nanostructures for related fields such as near-field imaging.
Collapse
|