【作者】 张超；

【导师】 王继刚；

【作者基本信息】 东南大学 ， 材料科学与工程， 2022， 硕士

【摘要】 石墨相氮化碳（g-C₃N₄）因其不含金属组分且具有优异的物理化学稳定性和良好的热稳定性,已成为一种有前途的场发射阴极材料。但是,g-C₃N₄的场发射性能受其形貌、比表面积、缺陷和微/纳米结构等因素影响。一般来说,g-C₃N₄通常是在520-580°C的高温条件下加热富氮原料（如三聚氰胺、双氰胺、氰胺和尿素）制备。然而,该合成方法所制制得样品存在比表面积小、发射位点少等缺点,从而导致场发射性能较差。研究发现,构建多孔纳米结构的g-C₃N₄可以提高场增强因子,从而改善材料场发射性能。此外,将g-C₃N₄与Zn O复合,可以有效促进g-C₃N₄中电子的积累,在外加电场下,增加了电子发射的几率,从而增强场发射性能。而且,分散在g-C₃N₄之间的颗粒状Zn O,能够有效防止电场屏蔽效应,为体系提供更多有效的发射位点。本文的实验内容和主要结论有如下几点:（1）以三聚氰胺和盐酸溶液作为原料,经过水热处理获得超分子前驱体,然后将超分子前驱体进行高温缩聚,制备出形貌较为规则均匀的g-C3N4纳米片（ACN）)。实验结果表明,ACN的带隙有所提升,由BCN的2.7 e V提升至ACN-1.0的2.76 e V。此外,场发射测试结果表明,ACN-0.25、ACN-0.5以及ACN-1.0的开启电场强度(E_to)分别为1.51、0.59和0.78 V/μm,当外加电场分别为2.44、1.72和1.86 V/μm时,ACN-0.25、ACN-0.5以及ACN-1.0的最大场发射电流密度分别为1.69、3.04和2.72 m A/cm²,其中ACN-0.5样品具有最优异的场发射性能。ACN-0.5样品具有良好的场发射性能主要是因为纳米片边缘可以帮助削弱材料表面势垒,提高内部电子逸出概率,提升场发射电流密度。（2）以三聚氰胺、三聚氰酸和醋酸溶液作为原料,经过水热处理获得了柱状结构的超分子前驱体,通过对柱状超分子前驱体进行直接热缩聚,成功制备了氮化碳六棱柱（ACNH）,另外热缩聚三聚氰胺制备了体相氮化碳（BCNH）。本实验中,利用不同浓度的醋酸溶液（HAc:H₂O分别为1:3、1:1、3:1）,制备了ACNH-1、ACNH-2以及ACNH-3样品以及直接热缩聚三聚氰胺得到的对照组BCNH。实验结果表明,ACNH的禁带宽度有所提高,由BCNH的2.66 e V增加至ACNH-2的2.76 e V。场发射测试结果表明,ACNH-1、ACNH-2以及ACNH-3的开启电场强度(E_to)分别为1.36、0.47和0.7 V/μm,阈值电场强度(E_thr)分别为2.58、1.22和1.63 V/μm。其中ACNH-2的场发射性能最为优秀,当外加场强达到2.23 V/μm时,其最大发射电流密度达到3.13 m A/cm²。ACNH-2样品具有优异的场发射性能,主要是因为其一维介孔棱柱状结构相比于传统体相块状结构具有更大的长径比和比表面积,可以帮助提高场增强因子。（3）通过液相超声ACNH样品获得对应氮化碳胶体,将其与二水合醋酸锌作为原料,通过水热法成功制备了不同复合比例的ACNH/Zn O复合产物,分别为ACNH/Zn O-4%、ACNH/Zn O-7%和ACNH/Zn O-10%与不含Zn O的对比样ACNH-T。实验结果表明,水热后样品形貌基本仍保持棱柱状,产物中Zn O在ACNH表面与其紧密接触并且呈颗粒状。场发射测试结果表明,ACNH-T、ACNH/Zn O-4%以及ACNH/Zn O-7%的开启电场强度(E_to)分别为1.49、0.86和0.72 V/μm,相比于ACNH-T,ACNH/Zn O复合样品的场发射性能更加优异。更多还原

【Abstract】 Graphitic phase carbon nitride（g-C₃N₄）has become an emerging and promising field emission cathode material due to its absence of metal components,excellent physicochemical stability and good thermal stability.g-C₃N₄’s field emission performance is influenced by its morphology,specific surface area,defects and micro/nanostructure.In general,g-C₃N₄ is prepared by thermal polycondensation of nitrogen-rich raw materials（e.g.melamine,dicyandiamide,cyanamide and urea）at high temperatures of 520-580°C.This synthetic method usually results in a small specific surface area and few emission sites for the produced samples,which leads to poor field emission performance.The construction of porous nanostructures can increase the sample field enhancement factor and thus improve the field emission performance.In addition,compounding g-C₃N₄ with Zn O can effectively promote the accumulation of electrons in g-C₃N₄,which increases the chance of electron emission under the applied electric field,thus enhancing the field emission performance.The granular Zn O dispersed between g-C₃N₄ can effectively prevent the electric field shielding effect and provide more effective emission sites for the system.The experimental content and main conclusions of this paper are as follows:（1）Supramolecular precursors were obtained by hydrothermal treatment using melamine and hydrochloric acid solutions as raw materials.Carbon nitride nanosheets（ACN）with a more regular and homogeneous morphology were prepared by direct thermal polycondensation of the supramolecular precursors,and bulk phase carbon nitride（BCN）was also prepared by thermal polycondensation of melamine.In this experiment,ACN-0.25,ACN-0.5 and ACN-1.0samples were prepared using hydrochloric acid solutions at concentrations of 0.25,0.5 and 1.0mol/L,respectively,as well as bulk-phase carbon nitride（BCN）obtained by direct heat-condensation of melamine.The experimental results show that the band gap of ACN has increased from 2.7 e V for BCN to 2.76 e V for ACN-1.0.In addition,the field emission test results show that the electric field strengths（Eto）of ACN-0.25,ACN-0.5 and ACN-1.0 are 1.51,0.59 and 0.78 V/μm,respectively,when the applied electric field is 2.44,1.72 and 1.86 V/μm,respectively.The maximum field emission current densities of ACN-0.25,ACN-0.5 and ACN-1.0 were 1.69,3.04 and 2.72 m A/cm2 when the applied electric field was 2.44,1.72 and 1.86V/μm,respectively,with the ACN-0.5 sample having the best field emission performance.The good field emission performance of the ACN-0.5 sample is mainly due to the fact that the edges of the nanosheets can weaken the potential barrier on the surface of the material,which increases the probability of internal electron escape and the field emission current density.（2）Supramolecular precursors with a columnar structure were obtained by hydrothermal treatment using melamine,melinic acid and acetic acid solutions as raw materials,and carbon nitride hexagonal prisms（ACNH）were successfully prepared by direct thermal polycondensation of the columnar supramolecular precursors,in addition to the preparation of bulk phase carbon nitride（BCNH）by thermal polycondensation of melamine.In this experiment,ACNH-1,ACNH-2 and ACNH-3 samples were prepared using different concentrations of acetic acid solutions（HAc:H2O 1:3,1:1 and 3:1,respectively）,as well as the control BCNH obtained by direct heat-condensation of melamine.The results of the field emission tests showed that ACNH-1,ACNH-2 and ACNH-3 had an electric field strength（Eto）of 1.36,0.47 and 0.7 V/μm,respectively,and a threshold electric field strength（Ethr）of 2.58,1.22 and 1.63 V/μm,respectively.The excellent field emission performance of the ACNH-2sample is mainly due to its one-dimensional mesoporous prismatic structure,which has a larger aspect ratio and specific surface area compared to the conventional bulk structure,which can help to improve the field enhancement factor.（3）The corresponding carbon nitride colloids were obtained by liquid phase sonication of ACNH samples,which were used as raw materials for the hydrothermal preparation of ACNH/Zn O composite products with different composite ratios,ACNH/Zn O-4%,ACNH/Zn O-7%and ACNH/Zn O-10%,respectively,and a comparison sample ACNH-T without Zn O.The results show that the shape of the samples remained essentially prismatic after hydrothermal treatment,with Zn O in close contact with the surface of ACNH and in granular form.The results of the field emission tests show that the electric field strengths(E_to)of ACNH-T,ACNH/Zn O-4%and ACNH/Zn O-7%are 1.49,0.86 and 0.72 V/μm respectively,which are superior to those of ACNH-T.更多还原