This work presents for the first time the possibility of reducing and tuning the work function of field emission cathodes coated with metal oxides by changing the chemical composition of oxide coatings using an example of heat-treated CNT/NiO nanocomposite structures. These cathodes are formulated using carbon nanotube (CNT) arrays that are coated with ultrathin layers of nickel oxide (CNT/NiO) by atomic layer deposition (ALD). It was found that NiO at thicknesses of several nanometers grown on CNTs heat treated at a temperature of 350 °C can change its stoichiometric composition towards the formation of oxygen vacancies, since the Ni³⁺/Ni²⁺ peak area ratio increases and the position of the Ni–O peak binding energies shifts as observed using X-ray photoelectron spectroscopy (XPS). According to the secondary electron cut-off, the work function was 4.95 for pristine CNTs and it was found that the work function of deposited NiO layers on CNTs decreased after heat treatment. The decrease in work function occurs as a result of changes in the chemical composition of the oxide film. For the heat-treated CNT/NiO composites, the work function was 4.30 eV with a NiO layer thickness of 7.6 nm, which was less than that for a NiO thin film close to the stoichiometric composition, which had a work function of 4.48 eV. The field emission current–voltage characteristics showed that the fields for producing an emission current density of 10 μA cm⁻² were 5.54 V μm⁻¹ for pure nanotubes and 4.32 V μm⁻¹ and 4.19 V μm⁻¹ for NiO-coated CNTs (3.8 and 7.6 nm), respectively. The present study has shown that heat treatment of deposited thin NiO layers on field cathodes is a promising approach to improve the efficiency of field emission cathodes and is a new approach in vacuum nanoelectronics that allows tuning the work function of field emission cathodes.

中文翻译：

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通过改变氧化物的化学成分来降低和调节场发射纳米复合材料CNT/NiO阴极的功函数

这项工作首次提出了通过使用热处理的 CNT/NiO 纳米复合结构的例子改变氧化物涂层的化学成分来降低和调整涂有金属氧化物的场发射阴极的功函数的可能性。这些阴极采用碳纳米管 (CNT) 阵列配制，并通过原子层沉积 (ALD) 涂有超薄氧化镍 (CNT/NiO) 层。研究发现，在 350 °C 温度下热处理的 CNT 上生长的几纳米厚度的 NiO 可以改变其化学计量组成，从而形成氧空位，因为 Ni ³⁺ /Ni ²⁺峰面积比增加，并且位置使用 X 射线光电子能谱 (XPS) 观察到 Ni-O 峰结合能的变化。根据二次电子截止，原始CNT的功函数为4.95，并且发现热处理后在CNT上沉积的NiO层的功函数降低。功函数的降低是由于氧化膜化学成分的变化而发生的。对于热处理后的CNT/NiO复合材料，NiO层厚度为7.6 nm时，功函数为4.30 eV，小于接近化学计量组成的NiO薄膜的功函数4.48 eV。场发射电流-电压特性表明，产生10 μA cm ^-2发射电流密度的场对于纯纳米管为5.54 V μm ^-1 ，对于NiO涂覆的CNT为4.32 V μm ^-1和4.19 V μm ^-1 ( 3.8 和 7.6 nm），分别。目前的研究表明，场阴极上沉积的薄氧化镍层的热处理是提高场发射阴极效率的一种有前途的方法，并且是真空纳米电子学中的一种新方法，可以调节场发射阴极的功函数。