Chumak Maksim A, Popov Eugeni O, Filippov Sergei V, Kolosko Anatoly G, Kirilenko Demid A, Bert Nikolay A, Zhizhin Evgeniy V, Koroleva Alexandra V, Yezhov Ilya S, Maximov Maxim Yu
Ioffe Institute, Saint Petersburg 19402, Russia.
St. Petersburg University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
Nanoscale. 2024 May 30;16(21):10398-10413. doi: 10.1039/d4nr00908h.
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 Ni/Ni 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 were 5.54 V μm for pure nanotubes and 4.32 V μm and 4.19 V μm 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.
这项工作首次通过以经过热处理的碳纳米管/氧化镍（CNT/NiO）纳米复合结构为例，改变氧化物涂层的化学成分，展示了降低和调节涂覆金属氧化物的场发射阴极功函数的可能性。这些阴极是通过原子层沉积（ALD）在碳纳米管（CNT）阵列上涂覆超薄氧化镍层（CNT/NiO）制成的。研究发现，在350℃温度下热处理的碳纳米管上生长的厚度为几纳米的氧化镍，其化学计量组成会朝着形成氧空位的方向变化，因为使用X射线光电子能谱（XPS）观察到镍/镍峰面积比增加，且镍-氧峰结合能的位置发生了偏移。根据二次电子截止情况，原始碳纳米管的功函数为4.95，并且发现热处理后碳纳米管上沉积的氧化镍层的功函数降低。功函数的降低是由于氧化膜化学成分的变化导致的。对于经过热处理的CNT/NiO复合材料，当氧化镍层厚度为7.6nm时，功函数为4.30eV，这低于接近化学计量组成的氧化镍薄膜的功函数4.48eV。场发射电流-电压特性表明，对于纯纳米管，产生10μA cm发射电流密度所需的场强为5.54V/μm，对于涂覆氧化镍的碳纳米管（3.8nm和7.6nm），分别为4.32V/μm和4.19V/μm。本研究表明，在场阴极上对沉积的薄氧化镍层进行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，它能够调节场发射阴极的功函数。
