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

Abstract

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 ...

WS2 Nano-petals and Nano-bristles Supported on Carbon Nanotubes for Electron Emission Applications

“…For the 10, 20, 30, 40, 50 and 60 min samples, the measured turn-on voltages are 34.8, 29.5, 23.2, 35.5, 35.6, and 37.6 V/μm respectively, demonstrating an improvement in field emission performance that peaks at the 30 min sample. We have to be careful in the comparison here as the same pristine CNTs were found to have a turn-on field of 5.6 V/μm in a large parallel plate capacitor setup 35 . As the tungsten probe tip emitters tend to be much more resistive and not subjected to uneven heights in the specimens 36 , our main comparison would be between the reference CNTs.…”

Single-Walled Carbon Nanotubes Coated by Fe2O3Nanoparticles with Enhanced Magnetic Properties

“…The obtained values of coercivity and remnant magnetization is better or comparable to the results obtained from modified sol-gel method, repulsive micro-emulsion, and hydrothermal methods. 2 To further study the effect of reducing the amount of Fe 2 O 3 nanoparticles, samples were prepared the same way but with smaller mass of Fe 2 O 3 . As expected, this resulted in diminished values of coercivity as well as saturation magnetization, and remnant magnetization.…”

“…Magnetically sensitive Fe 2 O 3 coated carbon nanotubes (CNTs) have been widely reported due to their unique promising features and applications. [1][2][3][4][5][6] Compared to conventionally used cooling fluids like oil and water, with respective thermal conductivities of 0.2 W/m-K and 0.6 W/m-K, single-walled CNTs (SWNTs) and Fe 2 O 3 exhibit a thermal conductivity value as high as 2000-6000 W/m-K and 300-600 W/m-K, respectively. 3 Consequently, it is possible to prepare composite fluids, commonly called 'nanofluids', consisting of SWNTs and Fe 2 O 3 for applications as coolant and/or lubricant.…”