NER: Chemical Vapor Deposition of Carbon Nanotube/Diamond Composites

项目摘要这个纳米规模的探索性研究项目的目标是利用化学气相沉积方法生长碳纳米管和金刚石的复合膜，广泛地表征这些膜，并通过详细的分子过程模拟在原子水平上了解膜的生长过程。碳纳米管(CNT)和钻石具有各自独特的特性，但在某种程度上也具有互补性，因此由这些组件制成的复合材料应该具有真正独特的特性。据预测，碳纳米管具有极高的杨氏模量值，同时还能够承受轴向的大应变。已经证明，使用原子力显微镜的尖端，多壁碳纳米管可以在不引起任何明显骨折的情况下通过大角度重复弯曲。另一方面，钻石是已知的最坚硬的材料，具有最高的室温导热系数。其他性能包括非常低的摩擦系数、良好的电阻率和光学透明度，以及适当掺杂时的一些优异的半导体性能。最近的研究表明，多晶金刚石可以很容易地以薄膜的形式沉积在各种衬底上。这种金刚石薄膜主要用于耐磨涂层和散热装置，尽管薄膜的脆性极大地限制了纯金刚石薄膜的使用。为了在解决脆性问题的同时充分利用金刚石的良好性能，研制了一种既要有极高的硬度又要有优异的韧性的碳纳米管/金刚石复合材料。合成方法是化学气相沉积(CVD)，目前用于在类似条件下沉积金刚石和碳纳米管。通过对工艺条件的精心选择，可以制备出致密、界面牢固的碳纳米管/金刚石薄膜，该薄膜可以通过改变反应器参数来控制和优化。沉积实验是在现有的CVD反应器中进行的，该反应器进行了轻微的修改，以允许在同一晶片上沉积碳纳米管和金刚石。在初始碳纳米管薄膜形成后，使用热丝CVD(HF-CVD)沉积金刚石。用高分辨电子显微镜对复合膜的结构特性进行了表征。研究了衬底和催化剂对碳纳米管和金刚石生长的影响，以及界面应力和膜内应力。用原子力显微镜研究了该复合材料的力学性能。相辅相成的建模和模拟工作提供了对基本现象的理解，提供了对补救措施和潜在的工艺改进的见解。广泛的影响这项工作为大学生提供了纳米技术方面的教育和经验。这项研究的结果通过会议和档案期刊出版物广泛传播。如果这种薄膜合成的努力取得成功，新兴纳米技术产业的技术转移将具有巨大的潜力。来自代表性不足群体的学生的参与通过招生努力和大学的正式激增计划来促进。该项目所需的设施升级改善了基础设施，提高了在纳米材料领域进行研究的能力。

PROJECT SUMMARY The objectives of this nanoscale exploratory research project are the growth of composite films of carbon nanotubes and diamond using chemical-vapor deposition, to extensively characterize these films, and to understand the film-growth process at the atomistic level through detailed simulations of the molecular processes. Carbon nanotubes (CNT) and diamond have properties that are individually exceptional but also complementary in a fashion such that a composite material made of these components should have truly unique properties. CNT are predicted to have extremely high values of Young's modulus while also being able to sustain large strain in the axial direction. It has been demonstrated that, using the tip of an AFM, multiwalled CNT can be bent repeatedly through large angles without causing any apparent fracture. On the other hand, diamond is the hardest known material and has the highest room-temperature thermal conductivity. Other properties include a very low coefficient of friction, good resistivity and optical transparency, and some superior semiconducting properties when appropriately doped. Recent research has shown that polycrystalline diamond can be readily deposited as a film on various substrates. Such diamond films have found applications primarily as wear-resistant coatings and heat-spreading devices, though film brittleness significantly limits the use of pure diamond films. In order to capitalize on the favorable properties of diamond while addressing the brittleness problem, a CNT/diamond composite material is manufactured that should have extreme hardness combined with outstanding toughness. The synthesis method is chemical vapor deposition (CVD) which is currently used to deposit both diamond and CNT under similar conditions. By careful selection of process conditions, a dense CNT/diamond film with a strong interface is produced that can be controlled and optimized by variation of reactor parameters. Deposition experiments are conducted in an existing CVD reactor, which is slightly modified to allow for CNT and diamond deposition on the same wafer. After the initial CNT film is generated, diamond is deposited using hot-filament CVD (HF-CVD). The structural properties of the composite films are characterized by high-resolution transmission electron microscopy. The roles of the substrate and catalyst on the growth of CNT and diamond, and the interface and internal film stresses are investigated. The mechanical properties of the composite are studied with atomic-force microscopy using a diamond-tipped probe. A complementary modeling and simulation effort provides understanding of the fundamental phenomena offers insight into remedial measures and potential process improvement.Broader impactThis work provides education and experience for university students in nanotechnology. Results obtained in this study are widely disseminated through conferences and archival journal publications. Should this effort at film synthesis be successful, a great potential for technology transfer with the emerging nanotechnology industry will be present. The involvement of students from under-represented groups is promoted through recruiting efforts, as well as through the university's formal SURGE program. Facility upgrades required for this project improve the infrastructure and enhance the ability to conduct research in the area of nanomaterials .