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三维(3D)石墨烯材料具有优异的电子发射性能与机械稳定性, 在高电流密度场发射器件领域展现出显著优势. 本文通过飞秒激光一步法原位制备氧化铜修饰三维石墨烯复合材料(LIG/CuO), 实现了软木碳化与铜氧化的同步调控. 利用铜盐浸润与抗坏血酸还原构建浅层富铜前驱体, 经激光辐照同步诱导纤维素碳化为少层石墨烯和Cu向CuO转变, 形成CuO纳米颗粒(30—80 nm)包覆的微晶石墨烯三维纤维网络. 该结构展现出卓越场发射性能, 制备的纯LIG阈值电场值为~2.12 V/μm, 场增强因子~8223; 优化的CuO 负载量后, LIG/CuO-5阈值电场值减至1.57 V/μm, 场增强因子达~8823, 并在2.89 V/μm下实现了22.71 mA/cm²超高电流密度的电子发射. 密度泛函理论(DFT)计算揭示异质结界面电子从CuO向石墨烯转移, 使石墨烯功函数从4.833 eV降至4.677 eV, 同时CuO表面能带弯曲协同降低隧穿势垒. 此外, CuO纳米颗粒的局域电场增强效应与优化分布密度协同使有效发射点密度提升.Three-dimensional (3D) graphene materials have excellent electronic emission performance and mechanical stability, showing significant advantages in the field of high current density field emitters. In this study, copper oxide modified three-dimensional graphene composites (LIG/CuO) are prepared in situ by a femtosecond laser one-step method, which realizes the simultaneous regulation of cork carbonization and copper oxidation. Shallow copper-rich precursors are constructed by copper salt infiltration and ascorbic acid reduction. Laser irradiation is used to synchronously induce the carbonization of cellulose into few-layer graphene and the transformation of Cu into CuO, forming a three-dimensional fiber network of microcrystalline graphene coated with CuO nanoparticles (30—80 nm). The structure exhibits excellent field emission performance: the threshold field of preparing pure laser- induced graphene (LIG) is ~2.12 V/μm and the field enhancement factor is ~8223. After optimizing CuO loading, the threshold field of LIG/CuO-5 is reduced to 1.57 V/μm, the field enhancement factor rises up to ~8823, and the ultra-high current density of 22.71 mA/cm2 is achieved at 2.89 V/μm. The density functional theory (DFT) calculations show that the electrons at the heterojunction interface transfer from CuO to graphene, which reduces the work function of graphene from 4.833 eV to 4.677 eV, and the band bending of CuO surface synergistically reduces the tunneling barrier. In addition, the local electric field enhancement effect of CuO nanoparticles and the optimized distribution density synergistically increase the effective emission point density. The performance improvement is mainly attributed to three synergistic effects: (Ⅰ) the three-dimensional porous graphene network provides abundant tip emission sites; (Ⅱ) the introduction of CuO nanoparticles reduces the work function of the composite material from 4.833 eV to 4.667 eV, effectively reducing the electron escape barrier; (Ⅲ) the heterojunction interface forms a directional electron migration channel under a positive bias electric field, combined with the excellent conductivity of LIG, which significantly improves the electron tunneling efficiency.
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Keywords:
- laser-induced graphene /
- cuo nanoparticles /
- composite cathode /
- field emission
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图 1 激光辐照制备LIG/CuO示意图
Fig. 1. Flow diagram of LIG/CuO preparation by laser irradiation.
图 2 不同样品的场发射电镜照片 (a1) LIG(截面图); (a2) LIG/CuO-5(截面图); (b1), (b2) LIG; (c1), (c2) LIG/CuAc-5; (d1), (d2) LIG/CuO-2.5; (e1), (e2) LIG/CuO-5; (f1), (f2) LIG/CuO-10; (g) LIG/CuO-5的元素分布图
Fig. 2. Field emission electron microscopy images of different samples: (a1) LIG (cross section); (a2) LIG/CuO-5 (cross section); (b1), (b2) LIG; (c1), (c2) LIG/CuAc-5; (d1), (d2) LIG/CuO-2.5; (e1), (e2) LIG/CuO-5; (f1), (f2) LIG/CuO-10; (g) mapping images of LIG/CuO-5.
图 3 样品的TEM照片 (a) LIG; (b), (c) LIG/CuO-5
Fig. 3. TEM images of samples: (a) LIG; (b), (c) LIG/CuO-5.
图 4 样品LIG和LIG/CuO-5的(a) Raman谱图和(b) FTIR谱图
Fig. 4. Raman spectra (a) and FTIR spectra (b) of LIG and LIG/CuO-5.
图 5 (a) LIG/CuO-5的XPS图谱全谱; (b) C 1s, (c) O 1s, (d) Cu 2p的高分辨XPS光谱
Fig. 5. (a) Survey XPS spectrum of the LIG/CuO-5; high-resolution XPS spectra of C 1s (b), O 1s (c) and Cu 2p (d).
图 6 (a) 构建的LIG, CuO和LIG/CuO 3D模型和计算得到的功函数; (b) LIG, CuO和 LIG/CuO 的分波态密度(PDOS)图(灰色虚线为费米能级)
Fig. 6. (a) LIG, CuO and LIG/CuO 3D models and the calculated work functions; (b) the partial density of states (PDOS) of LIG, CuO and LIG/CuO (the gray dotted line is the Fermi level).
图 7 (a)样品LIG, LIG/CuAc-5, LIG/CuO-2.5, LIG/CuO-5和LIG/CuO-10的J-E曲线; (b)相应的F-N曲线; (c)样品相对应的开启阈值(Eth)和场增减因子(β)关系曲线; (d)样品LIG和LIG/CuO-5场发射稳定性曲线
Fig. 7. (a) J-E plots of LIG, LIG/CuAc-5, LIG/CuO-2.5, LIG/CuO-5 and LIG/CuO-10; (b) F-N plots; (c) relationship plots of Eth and β versus the samples; (d) stability plots of LIG and LIG/CuO-5.
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