In this research, we have investigated the unintended graphene nucleation problem and its damaging effects on monolayer graphene synthesis in low-pressure chemical vapor deposition (LPCVD) process. This problem is the growth of graphene on the copper surface with no carbon feedstock. A new source of undesired carbon species was identified which has not been addressed so far. The hydrogen-rich heating stage was diagnosed as the onset of the unintended nucleation for the first time owing to the determinant catalytic role of hydrogen in this stage. It was found out that this problem leads to uncontrollable growth of multilayer graphene, growth of defective graphene film and also inhibition of the reliable synthesis of monolayer graphene. We managed to grow enhanced-quality monolayer graphene by developing some innovative solutions to the problem containing a general solution based on the hydrogen effects in the heating stage. The results reveal a significant decrease in the unintended nucleation density from ~ 2000 to almost zero domains per 100 × 100 µm2 copper area. Furthermore, Raman, HRTEM and SAED analysis confirm the defect-free growth of monolayer graphene after employing the solutions. These findings could pave the way for the reliable synthesis of high-quality monolayer graphene as well as large-sized graphene domains.

中文翻译：

---

在 LPCVD 过程中没有预期碳前体的石墨烯生长：原因、解决方案和影响

在这项研究中，我们研究了在低压化学气相沉积 (LPCVD) 工艺中意外的石墨烯成核问题及其对单层石墨烯合成的破坏性影响。这个问题是在没有碳原料的情况下，石墨烯在铜表面上的生长。一种新的不需要的碳物质来源已被确定，目前尚未解决。由于氢在该阶段的决定性催化作用，富氢加热阶段首次被诊断为意外成核的开始。研究发现，该问题导致多层石墨烯的生长不可控，石墨烯薄膜的生长有缺陷，也阻碍了单层石墨烯的可靠合成。我们通过开发一些创新的解决方案来解决问题，其中包含基于加热阶段氢效应的通用解决方案，从而成功地生长出质量更高的单层石墨烯。结果表明，每 100 × 100 µm2 铜面积的非预期成核密度从约 2000 个域显着降低到几乎为零。此外，拉曼、HRTEM 和 SAED 分析证实了使用该溶液后单层石墨烯的无缺陷生长。这些发现可以为可靠合成高质量的单层石墨烯以及大尺寸石墨烯域铺平道路。HRTEM 和 SAED 分析证实了使用该溶液后单层石墨烯的无缺陷生长。这些发现可以为可靠合成高质量的单层石墨烯以及大尺寸石墨烯域铺平道路。HRTEM 和 SAED 分析证实了使用该溶液后单层石墨烯的无缺陷生长。这些发现可以为可靠合成高质量的单层石墨烯以及大尺寸石墨烯域铺平道路。