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1.
Artigo em Inglês | MEDLINE | ID: mdl-32057228

RESUMO

Direct growth of vertically-oriented graphene (VG) nanowalls on soda-lime glass has practical significance in extending the application of graphene to daily-life related areas, such as gas sensors and conductive electrodes, via combining their complementary properties and applications. However, low temperature deposition derived VG films (e.g. on glass) usually present relative low conductivity and optical transparency. To tackle this issue, an ethanol-precursor-based, radio-frequency plasma enhanced chemical vapor deposition (rf-PECVD) route for the synthesis of VG-nanowalls is developed in this research, around the softening temperature of soda-lime glass (~600 ℃) templates. The average sheet resistance ~2.4 kΩ·sq-1 (at transmittance ~81.6%) is only one-half of that achieved by a traditional methane-precursor-based PECVD route. Based on the highly conductive and optical transparent VG/glass, as well its scalable size up to 25-inch scale, high-performance reversible thermochromic devices were successfully constructed with VG/glass as transparent heaters. Hereby, this work should propel the scalable synthesis and applications of highly conductive VG films on glass in next-generation transparent electronics and switchable windows.

2.
Small ; 16(4): e1905485, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31894647

RESUMO

Direct growth of graphene on glass can bring an innovative revolution by coupling the complementary properties of traditional glass and modern graphene (such as transparency and conductivity), offering brand new daily-life related applications. However, preparation of high-quality graphene on nonmetallic glass is still challenging. Herein, the direct route of low sheet resistance graphene on glass is reported by using in situ-introduced water as a mild etchant and methane as a carbon precursor via chemical vapor deposition. The derived graphene features with large domain sizes and few amorphous carbon impurities. Intriguingly, the sheet resistance of graphene on glass is dramatically lowered down to ≈1170 Ω sq-1 at the optical transmittance ≈93%, ≈20% of that derived without the water etchant. Based on the highly conductive and optical transparent graphene on glass, a see-through thermochromic display is thus fabricated with transparent graphene glass as a heater. This work can motivate further investigations of the direct synthesis of high-quality graphene on functional glass and its versatile applications in transparent electronic devices or displays.

3.
Small ; 16(5): e1907115, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31943829

RESUMO

Since the advent of monolayered 2D transition metal carbide and nitrides (MXenes) in 2011, the number of different monolayer systems and the study thereof have been on the rise. Mo2 Ti2 C3 is one of the least studied MXenes and new insights to this material are of value to the field. Here, the stability of Mo2 Ti2 C3 under electron irradiation is investigated. A transmission electron microscope (TEM) is used to study the structural and elemental changes in situ. It is found that Mo2 Ti2 C3 is reasonably stable for the first 2 min of irradiation. However, structural changes occur thereafter, which trigger increasingly rapid and significant rearrangement. This results in the formation of pores and two new nanomaterials, namely, N-doped graphene membranes and Mo nanoribbons. The study provides insight into the stability of Mo2 Ti2 C3 monolayers against electron irradiation, which will allow for reliable future study of the material using TEM. Furthermore, these findings will facilitate further research in the rapidly growing field of electron beam driven chemistry and engineering of nanomaterials.

4.
Adv Mater ; 32(1): e1903266, 2020 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-31583792

RESUMO

Grain boundaries produced during material synthesis affect both the intrinsic properties of materials and their potential for high-end applications. This effect is commonly observed in graphene film grown using chemical vapor deposition and therefore caused intense interest in controlled growth of grain-boundary-free graphene single crystals in the past ten years. The main methods for enlarging graphene domain size and reducing graphene grain boundary density are classified into single-seed and multiseed approaches, wherein reduction of nucleation density and alignment of nucleation orientation are respectively realized in the nucleation stage. On this basis, detailed synthesis strategies, corresponding mechanisms, and key parameters in the representative methods of these two approaches are separately reviewed, with the aim of providing comprehensive knowledge and a snapshot of the latest status of controlled growth of single-crystal graphene films. Finally, perspectives on opportunities and challenges in synthesizing large-area single-crystal graphene films are discussed.

5.
Nat Commun ; 10(1): 5013, 2019 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-31676774

RESUMO

For atomically thin two-dimensional materials, interfacial effects may dominate the entire response of devices, because most of the atoms are in the interface/surface. Graphene/sapphire has great application in electronic devices and semiconductor thin-film growth, but the nature of this interface is largely unknown. Here we find that the sapphire surface has a strong interaction with some of the carbon atoms in graphene to form a C-O-Al configuration, indicating that the interface interaction is no longer a simple van der Waals interaction. In addition, the structural relaxation of sapphire near the interface is significantly suppressed and very different from that of a bare sapphire surface. Such an interfacial C-O-Al bond is formed during graphene growth at high temperature. Our study provides valuable insights into understanding the electronic structures of graphene on sapphire and remote control of epitaxy growth of thin films by using a graphene-sapphire substrate.

6.
ACS Nano ; 13(11): 13235-13243, 2019 Nov 26.
Artigo em Inglês | MEDLINE | ID: mdl-31652045

RESUMO

Lithium-sulfur (Li-S) batteries are recognized as one of the most promising energy storage systems due to the high energy density and cost effectiveness. However, their practical implementation has still been handicapped due to notorious lithium polysulfide (LiPS) shuttle and depressed sulfur redox kinetics. It is therefore desirable to exploit key mediators synergizing electrical conductivity and electrocatalytic activity for the cathode. Herein, we report the employment of atmospheric pressure chemical vapor deposition to harness the efficient and controllable synthesis of metallic VTe2 over particulated MgO substrates, which has scarcely been demonstrated by conventional wet-chemical synthetic routes thus far. The thus-derived VTe2@MgO heterostructure as an efficient promotor enables effective regulation of LiPSs with respect to polysulfide capture/conversion and Li2S decomposition. As a result, a S/VTe2@MgO cathode with a sulfur loading of 1.6 mg cm-2 harvests long-term cyclability with a negligible capacity decay of 0.055% per cycle over 1000 cycles at 1.0 C. Even at a sulfur loading of 6.9 mg cm-2, the cathode still delivers electrochemical performances that can rival the state-of-the-art high-loading counterparts. Our work might offer a feasible solution for developing heterostructured promotors with multifunctionality and electrocatalytic activity for high-performance Li-S batteries.

7.
Nat Commun ; 10(1): 4913, 2019 10 29.
Artigo em Inglês | MEDLINE | ID: mdl-31664025

RESUMO

Wearable and portable self-powered units have stimulated considerable attention in both the scientific and technological realms. However, their innovative development is still limited by inefficient bulky connections between functional modules, incompatible energy storage systems with poor cycling stability, and real safety concerns. Herein, we demonstrate a flexible solar-charging integrated unit based on the design of printed magnesium ion aqueous asymmetric supercapacitors. This power unit exhibits excellent mechanical robustness, high photo-charging cycling stability (98.7% capacitance retention after 100 cycles), excellent overall energy conversion and storage efficiency (ηoverall = 17.57%), and outstanding input current tolerance. In addition, the Mg ion quasi-solid-state asymmetric supercapacitors show high energy density up to 13.1 mWh cm-3 via pseudocapacitive ion storage as investigated by an operando X-ray diffraction technique. The findings pave a practical route toward the design of future self-powered systems affording favorable safety, long life, and high energy.

8.
Small ; : e1902844, 2019 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-31490630

RESUMO

Bilayer or few-layer 2D materials showing novel electrical properties in electronic device applications have aroused increasing interest in recent years. Obtaining a comprehensive understanding of interlayer contact conductance still remains a challenge, but is significant for improving the performance of bilayer or few-layer 2D electronic devices. Here, conductive atomic force microscope (C-AFM) experiments are reported to explore the interlayer contact conductance between bilayer graphene (BLG) with various twisted stacking structures fabricated by the chemical vapor deposition (CVD) method. The current maps show that the interlayer contact conductance between BLG strongly depends on the twist angle. The interlayer contact conductance of 0° AB-stacking bilayer graphene (AB-BLG) is ≈4 times as large as that of 30° twisted bilayer graphene (t-BLG), which indicates that the twist angle-dependent interlayer contact conductance originates from the coupling-decoupling transitions. Moreover, the moiré superlattice-level current images of t-BLG show modulations of local interlayer contact conductance. Density functional theory calculations together with a theoretical model reproduce the C-AFM current map and show that the modulation is mainly attributed to the overall contribution of local interfacial carrier density and tunneling barrier.

9.
Adv Mater ; 31(43): e1902978, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31502709

RESUMO

Contamination is a major concern in surface and interface technologies. Given that graphene is a 2D monolayer material with an extremely large surface area, surface contamination may seriously degrade its intrinsic properties and strongly hinder its applicability in surface and interfacial regions. However, large-scale and facile treatment methods for producing clean graphene films that preserve its excellent properties have not yet been achieved. Herein, an efficient postgrowth treatment method for selectively removing surface contamination to achieve a large-area superclean graphene surface is reported. The as-obtained superclean graphene, with surface cleanness exceeding 99%, can be transferred to dielectric substrates with significantly reduced polymer residues, yielding ultrahigh carrier mobility of 500 000 cm2 V-1 s-1 and low contact resistance of 118 Ω µm. The successful removal of contamination is enabled by the strong adhesive force of the activated-carbon-based lint roller on graphene contaminants.

10.
Sci Adv ; 5(8): eaaw8337, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31448331

RESUMO

Directly incorporating heteroatoms into the hexagonal lattice of graphene during growth has been widely used to tune its electrical properties with superior doping stability, uniformity, and scalability. However the introduction of scattering centers limits this technique because of reduced carrier mobilities and conductivities of the resulting material. Here, we demonstrate a rapid growth of graphitic nitrogen cluster-doped monolayer graphene single crystals on Cu foil with remarkable carrier mobility of 13,000 cm2 V-1 s-1 and a greatly reduced sheet resistance of only 130 ohms square-1. The exceedingly large carrier mobility with high n-doping level was realized by (i) incorporation of nitrogen-terminated carbon clusters to suppress the carrier scattering and (ii) elimination of all defective pyridinic nitrogen centers by oxygen etching. Our study opens up an avenue for the growth of high-mobility/conductivity doped graphene with tunable work functions for scalable graphene-based electronic and device applications.

11.
ACS Nano ; 13(9): 10272-10278, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31430126

RESUMO

High-quality graphene film grown on dielectric substrates by a direct chemical vapor deposition (CVD) method promotes the application of high-performance graphene-based devices in large scale. However, due to the noncatalytic feature of insulating substrates, the production of graphene film on them always has a low growth rate and is time-consuming (typically hours to days), which restricts real potential applications. Here, by employing a local-fluorine-supply method, we have pushed the massive fabrication of a graphene film on a wafer-scale insulating substrate to a short time of just 5 min without involving any metal catalyst. The highly enhanced domain growth rate (∼37 nm min-1) and the quick nucleation rate (∼1200 nuclei min-1 cm-2) both account for this high productivity of graphene film. Further first-principles calculation demonstrates that the released fluorine from the fluoride substrate at high temperature can rapidly react with CH4 to form a more active carbon feedstock, CH3F, and the presence of CH3F molecules in the gas phase much lowers the barrier of carbon attachment, providing sufficient carbon feedstock for graphene CVD growth. Our approach presents a potential route to accomplish exceptionally large-scale and high-quality graphene films on insulating substrates, i.e., SiO2, SiO2/Si, fiber, etc., at low cost for industry-level applications.

12.
Angew Chem Int Ed Engl ; 58(41): 14446-14451, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31286615

RESUMO

Contamination commonly observed on the graphene surface is detrimental to its excellent properties and strongly hinders its application. It is still a great challenge to produce large-area clean graphene film in a low-cost manner. Herein, we demonstrate a facile and scalable chemical vapor deposition approach to synthesize meter-sized samples of superclean graphene with an average cleanness of 99 %, relying on the weak oxidizing ability of CO2 to etch away the intrinsic contamination, i.e., amorphous carbon. Remarkably, the elimination of amorphous carbon enables a significant reduction of polymer residues in the transfer of graphene films and the fabrication of graphene-based devices and promises strongly enhanced electrical and optical properties of graphene. The facile synthesis of large-area superclean graphene would open the pathway for both fundamental research and industrial applications of graphene, where a clean surface is highly needed.

13.
Nat Commun ; 10(1): 3457, 2019 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-31358759

RESUMO

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

14.
ACS Nano ; 13(7): 7517-7526, 2019 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-31150583

RESUMO

Mass production of graphene powders affording high quality and environmental benignancy serves as a prerequisite for the practical usage of graphene in multiple energy storage applications. Herein, we exploit a salt-templated CVD approach to harness the direct synthesis of nitrogen-doped graphene (NG) nanosheets and related ink dispersions in a scalable, safe, efficient, and green fashion. Thus-fabricated NG accompanying large productivity, excellent electrical conductivity, and favorable solution processability possesses implications in printable energy storage devices. With the NG-based ink in hand, self-standing 3D architectures with programmable patterns can be directly printed over a myriad of substrates. Accordingly, both electrode preparation for flexible supercapacitors and separator modification in Li-S batteries can be enabled via printing by employing our NG-based composite inks. This work thus represents a practical route for mass production of graphene inks with cost-effectiveness and eco-friendliness for emerging energy storage technology.

15.
J Am Chem Soc ; 141(19): 7670-7674, 2019 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-31058498

RESUMO

Chemical vapor deposition (CVD) enables the large-scale growth of high-quality graphene film and exhibits considerable potential for the industrial production of graphene. However, CVD-grown graphene film contains surface contamination, which in turn hinders its potential applications, for example, in electrical and optoelectronic devices and in graphene-membrane-based applications. To solve this issue, we demonstrated a modified gas-phase reaction to achieve the large-scale growth of contamination-free graphene film, i.e., superclean graphene, using a metal-containing molecule, copper(II) acetate, Cu(OAc)2, as the carbon source. During high-temperature CVD, the Cu-containing carbon source significantly increased the Cu content in the gas phase, which in turn suppressed the formation of contamination on the graphene surface by ensuring sufficient decomposition of the carbon feedstock. The as-received graphene with a surface cleanness of about 99% showed enhanced optical and electrical properties. This study opens a new avenue for improving graphene quality with respect to surface cleanness and provides new insight into the mechanism of graphene growth through the gas-phase reaction pathway.

16.
Adv Mater ; 31(29): e1901624, 2019 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-31140651

RESUMO

For III-nitride-based devices, such as high-brightness light-emitting diodes (LEDs), the poor heat dissipation of the sapphire substrate is deleterious to the energy efficiency and restricts many of their applications. Herein, the role of vertically oriented graphene (VG) nanowalls as a buffer layer for improving the heat dissipation in AlN films on sapphire substrates is studied. It is found that VG nanowalls can effectively enhance the heat dissipation between an AlN film and a sapphire substrate in the longitudinal direction because of their unique vertical structure and good thermal conductivity. Thus, an LED fabricated on a VG-sapphire substrate shows a 37% improved light output power under a high injection current (350 mA) with an effective 3.8% temperature reduction. Moreover, the introduction of VG nanowalls does not degrade the quality of the AlN film, but instead promotes AlN nucleation and significantly reduces the epilayer strain that is generated during the cooling process. These findings suggest that the VG nanowalls can be a good buffer layer candidate in III-nitride semiconductor devices, especially for improving the heat dissipation in high-brightness LEDs.

17.
Nat Mater ; 18(6): 520-524, 2019 06.
Artigo em Inglês | MEDLINE | ID: mdl-31114064
18.
Nanomaterials (Basel) ; 9(4)2019 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-30959885

RESUMO

Transparent heating devices are widely used in daily life-related applications that can be achieved by various heating materials with suitable resistances. Herein, high-performance vertically-oriented graphene (VG) films are directly grown on soda-lime glass by a radio-frequency (rf) plasma-enhanced chemical vapor deposition (PECVD) method, giving reasonable resistances for electrothermal heating. The optical and electrical properties of VG films are found to be tunable by optimizing the growth parameters such as growth time, carrier gas flow, etc. The electrothermal performances of the derived materials with different resistances are thus studied systematically. Specifically, the VG film on glass with a transmittance of ~73% at 550 nm and a sheet resistance of ~3.9 KΩ/□ is fabricated into a heating device, presenting a saturated temperature up to 55 °C by applying 80 V for 3 min. The VG film on the glass at a transmittance of ~43% and a sheet resistance of 0.76 KΩ/□ exhibits a highly steady temperature increase up to ~108 °C with a maximum heating rate of ~2.6 °C/s under a voltage of 60 V. Briefly, the tunable sheet resistance, good adhesion of VG to the growth substrate, relative high heating efficiency, and large heating temperature range make VG films on glass decent candidates for electrothermal related applications in defrosting and defogging devices.

19.
Adv Mater ; 31(23): e1807345, 2019 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30993771

RESUMO

The growth of single-crystal III-nitride films with a low stress and dislocation density is crucial for the semiconductor industry. In particular, AlN-derived deep-ultraviolet light-emitting diodes (DUV-LEDs) have important applications in microelectronic technologies and environmental sciences but are still limited by large lattice and thermal mismatches between the epilayer and substrate. Here, the quasi-van der Waals epitaxial (QvdWE) growth of high-quality AlN films on graphene/sapphire substrates is reported and their application in high-performance DUV-LEDs is demonstrated. Guided by density functional theory calculations, it is found that pyrrolic nitrogen in graphene introduced by a plasma treatment greatly facilitates the AlN nucleation and enables fast growth of a mirror-smooth single-crystal film in a very short time of ≈0.5 h (≈50% decrease compared with the conventional process), thus leading to a largely reduced cost. Additionally, graphene effectively releases the biaxial stress (0.11 GPa) and reduces the dislocation density in the epilayer. The as-fabricated DUV-LED shows a low turn-on voltage, good reliability, and high output power. This study may provide a revolutionary technology for the epitaxial growth of AlN films and provide opportunities for scalable applications of graphene films.

20.
Nat Commun ; 10(1): 1912, 2019 04 23.
Artigo em Inglês | MEDLINE | ID: mdl-31015405

RESUMO

Impurities produced during the synthesis process of a material pose detrimental impacts upon the intrinsic properties and device performances of the as-obtained product. This effect is especially pronounced in graphene, where surface contamination has long been a critical, unresolved issue, given graphene's two-dimensionality. Here we report the origins of surface contamination of graphene, which is primarily rooted in chemical vapour deposition production at elevated temperatures, rather than during transfer and storage. In turn, we demonstrate a design of Cu substrate architecture towards the scalable production of super-clean graphene (>99% clean regions). The readily available, super-clean graphene sheets contribute to an enhancement in the optical transparency and thermal conductivity, an exceptionally lower-level of electrical contact resistance and intrinsically hydrophilic nature. This work not only opens up frontiers for graphene growth but also provides exciting opportunities for the utilization of as-obtained super-clean graphene films for advanced applications.

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