Enhanced field emission of vertically aligned core-shelled carbon nanotubes with molybdenum oxide encapsulation

Yu, Jun; Sow, Chorng Haur; Wee, Andrew Thye Shen; Chua, Daniel H. C.

doi:10.1063/1.3139289

Cited by 10 publications

(9 citation statements)

References 25 publications

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“…Details of the CNTs preparation process and the custom-designed metal-organic chemical vapor deposition (MOCVD) system have been reported in our previous work. 23 Tungsten Hexacarbonyl (W(CO) 6 , bought from SigmaAldrich Pte Ltd) powders were used as precursor for WO x deposition. First, the CNT substrates were placed at the center of the MOCVD reaction chamber with a base pressure of $10 À6 Torr attained prior to deposition.…”

Section: Methodsmentioning

confidence: 99%

Synthesis of Three-Dimensional Tungsten Oxide Cactus-Shaped Nanostructures Supported on Carbon Nanotubes Template

Choo

Niu

et al. 2011

Electrochem. Solid-State Lett.

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We report that three-dimensional cactus-shaped tungsten oxide WO x (x ¼ 2-3) nanostructures have been synthesized over a large area using a simple one-step metal-organic chemical vapor deposition (MOCVD) technique at unusually lower temperatures than previously reported, making use of vertically aligned carbon nanotubes (CNTs) as the base template in a core-shell configuration. Each WO 3 crystallite forms independently perpendicular to the CNT spine resulting in the cactus-like structures. The presence of these structures has been shown to lead to improved electron emission properties, where the turn-on field was lowered from pristine CNTs at 3.47-2.31 V lm À1 with an increase in the field enhancement factor from $1225 to $3985. The growth mechanism of the nanostructures is discussed.Among all the transition metal oxides, tungsten oxides WO x (x ¼ 2-3) have been extensively studied due to their wide range of unique material properties, which includes electrochromic, optochromic and gasochromic properties. 1-9 These unique properties make WO x highly flexible for applications such as electrochromic windows, 1,2 solar cells, 3 gas sensors, 4,5,9 and photocatalyst materials. 6 One way to control and enhance its unique materials properties is to modify its morphology and physical structure. Different structures and morphologies have been reported. For example, different WO x reported morphologies include nanoparticles, 10,11 nanoplates, 12 whiskers, 13 nanotubes, 14 and nanorods, 6,15 etc. excluding conventional thin and thick films.There are many advantages in obtaining these unique nanosized structures. For example, there is a significant increase in the surface area of the nanostructured WO x as compared with thin films, leading to an increase in the efficiency of WO x based sensors. In the recent few years, nanostructured WO x , especially WO x nanowires, has also found potential applications in field emission applications due to their unique high-aspect ratio structures, 16-18 with good robustness and longevity. 19,20 One of the most attractive features lies with the morphology of WO x , where it has the capability to form tree-like structures when physical growth methods, such as conventional thermal deposition, 11,21,22 are used. This was reported by Zhu et al. as early as 1999, 21 where unique structures could be obtained through heating a W foil partly covered by a SiO 2 plate in an Ar atmosphere at 1600 C. There were also reports of three-dimensional regular (3D) network of WO x nanowires obtained through thermal evaporation of W powders in the presence of oxygen at 1400-1500 C. 22 In this letter, we report a simple approach to obtain 3D WO x nanostructures at a much lower temperature process of 600 C (as compared to >1000 C for standard furnace process). The uniqueness lies in using highly conductive multiwalled carbon nanotubes (CNTs) as the base template for the WO x nanowires to first encapsulate around forming a core-shell structure. Subsequently, unique 3D cactus-shaped nanostructures can be obtained ...

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Section: Methodsmentioning

confidence: 99%

Synthesis of Three-Dimensional Tungsten Oxide Cactus-Shaped Nanostructures Supported on Carbon Nanotubes Template

Choo

Niu

et al. 2011

Electrochem. Solid-State Lett.

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“…Recent years, many efforts have been conducted to enhance the FE properties of CNT‐based emitters by attaching or decorating the CNTs with metals or metal oxides 8–16. One route is to cover CNTs with a thin (∼10 nm) layer of low work function and low resistivity materials such as Er, Ti, IrO 2 , and RuO 2 8–11, which combine the benefits of lowering effective work function of emitters and keeping the high field enhancement factor of CNTs.…”

Section: Introductionmentioning

confidence: 99%

“…One route is to cover CNTs with a thin (∼10 nm) layer of low work function and low resistivity materials such as Er, Ti, IrO 2 , and RuO 2 8–11, which combine the benefits of lowering effective work function of emitters and keeping the high field enhancement factor of CNTs. Another route is to cover or dope CNTs with wide bandgap oxides such as MgO, SiO 2 , MoOx, and ZnO 6, 12–16. Such oxides generally have negative or small positive electron affinity, which could decrease the effective work function of emitters.…”

Section: Introductionmentioning

confidence: 99%

Mechanical fabrication of carbon nanotube/TiO₂ nanoparticle composite films and their field‐emission properties

Guo

et al. 2011

Physica Status Solidi (a)

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A simple mechanical rubbing method for fabricating films of carbon nanotubes (CNTs) and CNTs‐based composite materials is presented, and films of CNTs, TiO2 nanoparticles, and CNTs‐TiO2 composite with different proportions are realized. The field emission (FE) properties of these films are systematically studied in comparison experiments. It is found that the TiO2 films show neglectable FE current in the electrical field up to 10 V/µm, and CNTs‐TiO2 composite films with an optimum proportion (7–10 wt.%) of TiO2 nanoparticles exhibit dramatically‐improved FE properties compared with pure CNT films, in lowering turn‐on filed to 1.3 V/µm (CNT films: 2.5 V/µm), suppressing the degradation of FE current, and increasing the FE uniformity and stability. The mechanisms responsible for such improvement are also discussed.

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“…Size is also the primary defining factor of the field enhancement factor. 9 Smaller γ-Fe 2 O 3 nanoparticles provide sharper tips that increase the field enhancement factor and induce higher local field concentration, hence reducing the height of the tunneling barrier. Consequently, we can deduce that the modest 12.5% improvement in the field enhancement factor of our samples is due to the large size of the Fe 2 O 3 nanoparticles, the largest of which are of similar width to the diameter of the CNTs.…”

Section: Resultsmentioning

confidence: 99%

Dual-Functional Magnetic and Field Emission Properties of γ-Fe₂O₃Coated Carbon Nanotubes Core-Shell Structures

Loh

Chua

2014

ECS J. Solid State Sci. Technol.

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A γ-Fe 2 O 3 coated carbon nanotube (CNT) core-shell structure with dual magnetic and field emission properties was successfully fabricated by a simple one-step technique. The γ-Fe 2 O 3 shell is deposited on vertically aligned multi-walled CNTs by chemical vapor deposition using ferrocene as the precursor at process temperatures of 200, 400 and 600 • C. At 400 • C, the γ-Fe 2 O 3 shell formed a polycrystalline coating of polygonal nanoparticles on the CNTs. Enhanced field emission performance was observed with a threshold field of 4.7 Vμm −1 compared to pristine CNTs at 5.6 Vμm −1 . Magnetic measurements revealed that the γ-Fe 2 O 3 -CNT composites demonstrated ferrimagnetic behavior with high saturation magnetization of 52.3 emu/g and coercivity of 237 Oe at room temperature.Fabricating nanostructures that exhibit two or more different properties is highly desirable for simultaneous and efficient technological applications. This expansion of functionalities of a pre-existing material is also advantageous for scaling down of devices in the effort to maximize utilization and minimize cost. Such multi-functional nanostructures can be achieved by effectively combining two different kinds of materials into nanocomposites, thereby forming heterojunctions at the interface. There are several ways to fabricate multi-functional nanocomposites, one of which is through the configuration of a core-shell structure. In this configuration, the core material acts as the template and supplies the main properties of the resulting composite. The shell material imparts additional functionalities and can also enhance the properties of the core. For example, t-ZnO/SnO 2 core-shell nanostructures showed new luminescence properties induced by epitaxial interfaces, 1 and Fe 3 O 4 /TiO 2 core-shell nanotubes were reported to exhibit dual magnetic and electromagnetic wave absorption characteristics. 2 In the field of biotechnology, magnetic-fluorescent nanocomposites such as Co/CdSe, Fe 3 O 4 /CdTe and CoFe 2 O 4 /silica have been extensively studied for use in multimodal imaging applications. [3][4][5] Because it is possible to enhance or alter the properties of carbon nanotubes (CNTs) by modifying their surface, CNTs are promising building blocks for multi-functional nanocomposites. CNTs have, for example, been reported to exhibit enhanced optical absorption in the UV-visible region when encased in a CdS shell, 6 and have been used as imaging agents with near-infrared absorption and magnetic capabilities when combined with Fe 3 O 4 . 7 In addition, their unique morphology and remarkable properties such as high aspect ratio, structural integrity, and high chemical stability 8 make CNTs an ideal candidate for electron emitters in vacuum nanoelectronic devices. Field emission performance of CNTs has been widely reported to have improved through coating with wide bandgap materials such as MoO, SiO 2 and MgO, due to the formation of Schottky barriers. 9,10 If a suitable material for the coating is selected, additional functionalities can be ...

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Enhanced field emission of vertically aligned core-shelled carbon nanotubes with molybdenum oxide encapsulation

Cited by 10 publications

References 25 publications

Synthesis of Three-Dimensional Tungsten Oxide Cactus-Shaped Nanostructures Supported on Carbon Nanotubes Template

Synthesis of Three-Dimensional Tungsten Oxide Cactus-Shaped Nanostructures Supported on Carbon Nanotubes Template

Mechanical fabrication of carbon nanotube/TiO₂ nanoparticle composite films and their field‐emission properties

Dual-Functional Magnetic and Field Emission Properties of γ-Fe₂O₃Coated Carbon Nanotubes Core-Shell Structures

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Enhanced field emission of vertically aligned core-shelled carbon nanotubes with molybdenum oxide encapsulation

Cited by 10 publications

References 25 publications

Synthesis of Three-Dimensional Tungsten Oxide Cactus-Shaped Nanostructures Supported on Carbon Nanotubes Template

Synthesis of Three-Dimensional Tungsten Oxide Cactus-Shaped Nanostructures Supported on Carbon Nanotubes Template

Mechanical fabrication of carbon nanotube/TiO2 nanoparticle composite films and their field‐emission properties

Dual-Functional Magnetic and Field Emission Properties of γ-Fe2O3Coated Carbon Nanotubes Core-Shell Structures

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Product

Resources

About

Mechanical fabrication of carbon nanotube/TiO₂ nanoparticle composite films and their field‐emission properties

Dual-Functional Magnetic and Field Emission Properties of γ-Fe₂O₃Coated Carbon Nanotubes Core-Shell Structures