Jian-Biao Chen

Enhanced field emission from hydrogenated TiO2 nanotube arrays

The field emission (FE) properties of TiO(2) nanotube arrays (TNAs) synthesized by anodization are dramatically improved after hydrogenation at various temperatures in a range of 400-550 °C. Compared with pristine TNAs, the turn-on fields of hydrogenated TNAs (H:TNAs) are significantly decreased from 18.23 to 1.75 V μm(-1), and closely related to hydrogenation temperature. Importantly, the optimized sample of H:TNAs prepared at 550 °C shows excellent FE performances involving both a low turn-on field of 1.75 V μm(-1), a high current density of 4.0 mA cm(-2) at 4.50V μm(-1), and a remarkable FE stability over 480 min. The substantially enhanced FE properties can be attributed to the combination of a typical tubular morphology, a reduced work function and the improved conductivity of H:TNAs.

Enhancement of the Field Emission from the TiO2 Nanotube Arrays by Reducing in a NaBH4 Solution

A mass of oxygen vacancies are successfully introduced into TiO2 nanotube arrays using low-cost NaBH4 as a reductant in a liquid-phase environment. By controlling and adjusting the reduction time over the range of 0-24 h, the doping concentration of the oxygen vacancy is controllable and eventually reaches saturation. Meanwhile, the thermal stability of oxygen vacancies is also investigated, indicating that part of the oxygen vacancies remain stable up to 250 °C. In addition, this liquid-phase reduction strategy significantly lowers the requirements of instruments and cost. More interesting, reduced TiO2 nanotube arrays show drastically enhanced field emission performances including substantially decreased turn-on field from 25.01 to 2.65 V/μm, a high current density of 3.5 mA/cm(2) at 7.2 V/μm, and an excellent field emission stability and repeatability. These results are attributed to the oxygen vacancies obtained by reducing in NaBH4 solution, resulting in a reduced effective work function and an increased conductivity.

Low-temperature liquid phase reduced TiO2 nanotube arrays: synergy of morphology manipulation and oxygen vacancy doping for enhancement of field emission.

The partially reduced TiO(2) nanotube arrays (TNAs) are prepared via an uncomplicated and low-cost liquid phase reduction strategy using NaBH(4) as the reducing agent. By controlling and adjusting the reduction temperatures from 30 to 90 °C, the reduction treatment can not only change their surface morphology but also introduce oxygen vacancies into them, resulting in an optimized morphology, elevated Fermi-level, reduced effective work function and improved conductivity of the TNAs. Meanwhile, the thermal and long-term stability of oxygen vacancy are also investigated, indicating that the oxygen vacancies retain long-term stability from room temperature up to 150 °C. More interesting, partially reduced TNAs show drastically enhanced field emission (FE) performances including substantially decreased turn-on field from 18.86 to 1.53 V μm(-1), a high current density of 4.00 mA cm(-2) at 4.52 V μm(-1), and an excellent FE stability and repeatability. These very promising results are attributed to the combination of the optimized morphology and introduced oxygen vacancies, which can increase FE sites, reduce effective work function and increase conductivity.

Enhanced field emission from hydrogenated SnO2 nanoparticles embedded in TiO2 film on fluorinated tin oxide substrate

Hydrogenated SnO2 nanoparticles (H:SNPs) were prepared on fluorinated tin oxide covered glass using reduction and hydrogenation technologies with TiO2 sol. By adjusting the hydrogenated temperature over the range of 400–550 °C, the H:SNPs were uniformly embedded in the TiO2 film, exhibiting the ability to precisely control their density and size using this method. Simultaneously, their band structures were modified, resulting in a reduced work function and an increased electrical conductivity. Hence, the optimized H:SNPs prepared at 500 °C showed excellent field emission (FE) performances, with both a low turn-on field of 3.81 V/μm and remarkable FE stability over a 480-min period.

Field emission property of carbon-doped TiO2 nanotube arrays with controllable doping content of carbon

To achieve an optimum cold cathode emitter, well-aligned TiO2/Ti nanotube arrays (TNAs) were synthesized by anodic oxidation and doped with carbon by pyrolysis of C2H2 at 550 °C. By controlling the carbon doping content, the field emission (FE) properties of carbon-doped TiO2/Ti nanotube arrays (C-TNAs) were optimized. Compared with the high turn-on field of 19.19 V/μm from pure TNAs, the turn-on field of C-TNAs was decreased to 11.60, 6.35, 4.10, and 5.77 V/μm when the doping content of carbon was increased to 0.62, 0.82, 1.81, and 3.31 at. %, respectively. Obviously, the FE properties of TNAs were dramatically improved and optimized by adjusting the carbon doping content, which can be attributed to the typical tubular morphology, an enhanced conductivity, and a reduced work function.

Enhanced field emission properties from oxygen-deficient α-Fe2O3 nanorod arrays

Hydrothermally grown FeOOH nanorods were successfully transformed into oxygen-deficient α-Fe2O3 nanorod arrays (HNAs) with a pure phase by annealing in an Ar atmosphere at the temperatures of 300–550 °C. It was found that the oxygen-deficient HNAs exhibited an increased oxygen vacancy (Fe2+ site) concentration with the increase in annealing temperature. On the basis of the experimental results, a possible mechanism for the formation of the oxygen-deficient HNAs is hypothesized. In particular, the turn-on field of oxygen-deficient HNAs can be optimized to 1.45 V/μm, which is much smaller than that of pristine HNAs. The emission current density can reach 3.37 mA/cm2 at 4.86 V/μm for the oxygen-deficient HNAs. Such excellent field emissions properties are the best performances reported till date for a pristine α-Fe2O3 field emitter and are mainly attributed to the increased conductivity and decreased work function resulting from the introduced oxygen vacancies.

Fabrication and field emission of carbon nanotubes/TiO2/Ti composite nanostructures

Well-aligned TiO2/Ti nanotube arrays were fabricated by anodic oxidation, then carbon nanotubes (CNTs) were grown into TiO2/Ti nanotube arrays to form CNTs/TiO2/Ti composite nanostructures by catalytic chemical-vapor deposition for different deposition times. The morphology and quality of samples were assessed by field-emission scanning-electron microscopy and Raman spectroscopy. The field emission (FE) results indicate that the FE properties of CNTs/TiO2/Ti composite nanostructures were dramatically improved compared with bare TiO2/Ti nanotube arrays, and when the growth time of CNTs was 60 min, the composite nanostructures possessed the lowest turn-on field of 1.3 V/μm, the highest emission-current density of 10 mA/cm2 was easily gained at 5.6 V/μm, and there was good FE stability.Well-aligned TiO2/Ti nanotube arrays were fabricated by anodic oxidation, then carbon nanotubes (CNTs) were grown into TiO2/Ti nanotube arrays to form CNTs/TiO2/Ti composite nanostructures by catalytic chemical-vapor deposition for different deposition times. The morphology and quality of samples were assessed by field-emission scanning-electron microscopy and Raman spectroscopy. The field emission (FE) results indicate that the FE properties of CNTs/TiO2/Ti composite nanostructures were dramatically improved compared with bare TiO2/Ti nanotube arrays, and when the growth time of CNTs was 60 min, the composite nanostructures possessed the lowest turn-on field of 1.3 V/μm, the highest emission-current density of 10 mA/cm2 was easily gained at 5.6 V/μm, and there was good FE stability.