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1.
Nanotechnology ; 30(23): 235301, 2019 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-30769339

RESUMO

One-dimensional (1D) and three-dimensional (3D) residue-free metal oxide patterns are directly fabricated over large areas using liquid transfer imprint lithography (LTIL) with an ultraviolet-curable metal oxide precursor resist. A 1D line or pillar array of metal oxides nano-patterns without a residual layer is formed by LTIL and annealing processes. A 3D layer-by-layer nanomesh structure is successfully constructed by repeating the LTIL method without a complex etching process. In addition, it is possible to form a hierarchical structure in which zinc oxide nanowires are selectively grown on a desired zinc oxide (ZnO) seed pattern formed by LTIL via a hydrothermal method. Unlike the pattern fabricated by the conventional nanoimprint lithography method, in the case of the pattern formed by LTIL the residues accumulated between the patterns during the patterning procedure can be removed, and thus it is possible to easily form various types of nanostructures.

2.
Nat Commun ; 10(1): 987, 2019 02 25.
Artigo em Inglês | MEDLINE | ID: mdl-30804336

RESUMO

The original version of this Article contained an error in the spelling of the author Matthew Holwill, which was incorrectly given as Mathew Holwill. This has now been corrected in both the PDF and HTML versions of the Article.

3.
Nat Commun ; 10(1): 230, 2019 01 16.
Artigo em Inglês | MEDLINE | ID: mdl-30651554

RESUMO

Despite a rich choice of two-dimensional materials, which exists these days, heterostructures, both vertical (van der Waals) and in-plane, offer an unprecedented control over the properties and functionalities of the resulted structures. Thus, planar heterostructures allow p-n junctions between different two-dimensional semiconductors and graphene nanoribbons with well-defined edges; and vertical heterostructures resulted in the observation of superconductivity in purely carbon-based systems and realisation of vertical tunnelling transistors. Here we demonstrate simultaneous use of in-plane and van der Waals heterostructures to build vertical single electron tunnelling transistors. We grow graphene quantum dots inside the matrix of hexagonal boron nitride, which allows a dramatic reduction of the number of localised states along the perimeter of the quantum dots. The use of hexagonal boron nitride tunnel barriers as contacts to the graphene quantum dots make our transistors reproducible and not dependent on the localised states, opening even larger flexibility when designing future devices.

4.
ACS Nano ; 12(11): 10764-10771, 2018 Nov 27.
Artigo em Inglês | MEDLINE | ID: mdl-30335961

RESUMO

Hexagonal boron nitride (h-BN) and graphene have emerged as promising materials for proton exchange membranes because of their high proton conductivity and chemical stability. However, the defects and grain boundaries generated during the growth and transfer of two-dimensional materials limit their practical applicability. Here, we report the fabrication of membrane electrode assemblies using large-area single-oriented AA'-stacked trilayer h-BN (3L-BN), which exhibits very few defects during the growth and transfer, as a proton exchange membrane for use in fuel cell systems. The fuel cell based on AA'-stacked 3L-BN showed a H2 permeation current density as low as 2.69 mA cm-2 and an open circuit voltage (OCV) as high as 0.958 V; this performance is much superior to those for cells based on Nafion (3.7 mA cm-2 and 0.942 V, respectively) and single-layer h-BN (10.08 mA cm-2 and 0.894 V, respectively). Furthermore, the fuel cell with the AA'-stacked 3L-BN membrane almost maintained its original performance (OCV, maximum power density, and H2 permeation current density) even after 100 h of an accelerated stress test at 30% RH and 90 °C, while the fuel cells with the Nafion and single-layer BN membranes exhibited severely deteriorated performances. The stability of the cell based on the AA'-stacked 3L-BN membrane was better because the membrane prevented gas crossover and suppressed the generation of reactive radicals during cell operation.

5.
J Am Chem Soc ; 139(27): 9392-9400, 2017 07 12.
Artigo em Inglês | MEDLINE | ID: mdl-28633527

RESUMO

Atomically thin molybdenum disulfide (MoS2), a direct-band-gap semiconductor, is promising for applications in electronics and optoelectronics, but the scalable synthesis of highly crystalline film remains challenging. Here we report the successful epitaxial growth of a continuous, uniform, highly crystalline monolayer MoS2 film on hexagonal boron nitride (h-BN) by molecular beam epitaxy. Atomic force microscopy and electron microscopy studies reveal that MoS2 grown on h-BN primarily consists of two types of nucleation grains (0° aligned and 60° antialigned domains). By adopting a high growth temperature and ultralow precursor flux, the formation of 60° antialigned grains is largely suppressed. The resulting perfectly aligned grains merge seamlessly into a highly crystalline film. Large-scale monolayer MoS2 film can be grown on a 2 in. h-BN/sapphire wafer, for which surface morphology and Raman mapping confirm good spatial uniformity. Our study represents a significant step in the scalable synthesis of highly crystalline MoS2 films on atomically flat surfaces and paves the way to large-scale applications.

6.
ACS Nano ; 10(9): 8973-9, 2016 09 27.
Artigo em Inglês | MEDLINE | ID: mdl-27563804

RESUMO

Transition metal dichalcogenides (TMDs) have recently received increasing attention because of their potential applications in semiconducting and optoelectronic devices exhibiting large optical absorptions in the visible range. However, some studies have reported that the grain boundaries of TMDs can be easily degraded by the presence of oxygen in water and by UV irradiation, ozone, and heating under ambient conditions. We herein demonstrate the photodegradation of WSe2 and MoSe2 by laser exposure (532 nm) and the subsequent prevention of this photodegradation by encapsulation with hexagonal boron nitride (h-BN) layers. The photodegradation was monitored by variation in peak intensities in the Raman and photoluminescence spectra. The rapid photodegradation of WSe2 under air occurred at a laser power of ≥0.5 mW and was not observed to any extent at ≤0.1 mW. However, in the presence of a water droplet, the photodegradation of WSe2 was accelerated and took place even at 0.1 mW. We examined the encapsulation of WSe2 with h-BN and found that this prevented photodegradation. However, a single layer of h-BN was not sufficient to fully prevent this photodegradation, and so a triple layer of h-BN was employed. We also demonstrated that the photodegradation of MoSe2 was prevented by encapsulation with h-BN layers. On the basis of X-ray photoelectron spectroscopy and scanning photoemission microscopy data, we determined that this degradation was caused by the photoinduced oxidation of TMDs. These results can be used to develop a general strategy for improving the stability of 2D materials in practical applications.

7.
Nano Lett ; 16(5): 3360-6, 2016 05 11.
Artigo em Inglês | MEDLINE | ID: mdl-27120101

RESUMO

Large-scale growth of high-quality hexagonal boron nitride has been a challenge in two-dimensional-material-based electronics. Herein, we present wafer-scale and wrinkle-free epitaxial growth of multilayer hexagonal boron nitride on a sapphire substrate by using high-temperature and low-pressure chemical vapor deposition. Microscopic and spectroscopic investigations and theoretical calculations reveal that synthesized hexagonal boron nitride has a single rotational orientation with AA' stacking order. A facile method for transferring hexagonal boron nitride onto other target substrates was developed, which provides the opportunity for using hexagonal boron nitride as a substrate in practical electronic circuits. A graphene field effect transistor fabricated on our hexagonal boron nitride sheets shows clear quantum oscillation and highly improved carrier mobility because the ultraflatness of the hexagonal boron nitride surface can reduce the substrate-induced degradation of the carrier mobility of two-dimensional materials.

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