标题: | 以阳极氧化铝奈米孔洞为模板辅助合成垂直准直奈米碳管阵列 Anodic aluminum oxide template assisted growth of vertically aligned carbon nanotube arrays |
作者: | 张峻恺 Jun-Kai Chang 郭正次 Cheng-Tzu Kuo 材料科学与工程学系 |
关键字: | 奈米碳管;阳极氧化铝奈米孔洞;石墨;场发射;电浆;化学气相沉积法;密度控制;非晶质碳;carbon nanotubes;AAO;graphite;field emisssion;plasma;CVD;density control;amorphous carbon |
公开日期: | 2003 |
摘要: | 自从1991年发现奈米碳管以来,专家学者经过十余年的研究,虽然对其比以往了解得多,但在应用方面仍有许多问题尚待克服。其中,场发射显示器一直是众人认为最有潜力实现的碳管商品,其所需要的基板便是拥有高度准直的奈米碳管阵列。时至今日,场发射显示器的商品依旧是只闻其声,不闻其人,其中极重要的一环即是无法有效的控制奈米碳管的生长,包括准直性、长度以及密度。本实验已成功的制造出规则排列的阳极氧化铝奈米孔洞,并利用电镀法沉积触媒于孔洞内,再以此为模板,进行以氢气与甲烷为反应气体的电子回旋共振化学气相沉积法来合成奈米碳管阵列。由于模版的作用再加上合成的参数中允许加入偏压,如此合成的奈米碳管具有极佳的准直性。值得注意的是,由于电子回旋共振化学气相沉积法拥有较低的合成速率,碳管的长度可以经由合成的时间来做细微的控制;相较于文献上类似的做法,本实验可以合成均匀长度之碳管,且拥有良好的石墨化结构。在密度的控制上,利用改变反应气体的流量比例,造成特定量的非晶质碳沉积在孔洞上,某些尚未长出洞口的碳管因得不到成长所需碳源而停止生长,经过如此非晶质碳与成长碳管之竞争反应,即可达成密度控制的目的。另一方面,碳管阵列的场发射特性亦为吾人所关注的焦点,此一性质为碳管做为场发射源的首要考量。针对不同长度及密度的碳管,我们皆加以量测其场发射效应;在长度方面,我们发现在相同的密度下,最长的碳管拥有最佳的场发射效应。而在不同密度方面,由于屏蔽效应,最密的碳管反而拥有较差的场发射表现,但额外必须考虑的是,因为利用反应气体浓度的改变为控制的条件,当碳源气体变多,使得非晶质碳不但容易在奈米孔洞内沉积,长出孔洞表面的碳管上也容易被其覆盖,间接的驱动触媒的毒化现象,密度低的碳管同时也具有较短的长度,由此,我们也得到了一个在长度及密度恰好时的最佳场发射特性,场发射增强因子,也在这些量测中被一一的计算出来。其它,我们也做了许多定性与定量的分析,包括各种的电子显微镜影像、拉曼光谱、欧杰电子光谱,也将在以下的文章中详述。 In order to utilize the excellent field emission properties as specific applications, ordered carbon nanotubes (CNTs) arrays with controllable length and density has become an important issue. Highly CNTs have been successfully grown in vertical channels of the anodic aluminum oxide (AAO) template by microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD). Nanoporous AAO templates with hexagonal pore pattern were prepared by the two-step anodization of Al films. Following the electroplating of Co catalyst into the pore bottom, multiwalled CNTs were synthesized in the ECR-CVD system using a gas mixture of CH4 and H2. The microstructure of the CNTs was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The CNTs with a very high packing density and a uniform size distribution are well-graphitized, and Co particles embedded at their tips implies the tip growth mechanism. The segments of CNTs stretching out of the AAO nanopores still maintain relatively good alignment, and have a very slow growth rate, which allows us to obtain reproducible tube length by tuning the growth time. Field emission measurements of the CNTs showed derivable electron emission properties, attributed to their uniformity in size, good alignment, and good graphitization properties. Moreover, a simple method was proposed to control the tube number density of the Co-catalyzed CNTs on AAO template, which was realized by in situ regulating the flow rate ratio of CH4/H2 precursor gases during the CNT growth. The amorphous carbon byproduct of CNT growth was employed to confine the CNT outgrowth from AAO nanopores. There was a competition reaction between the CNT growth and the amorphous carbon deposition. It was found that the number of CNTs escaped from the AAO nanopores decreases linearly following the increase of the CH4 concentration. The field emission of the AAO assisted CNTs can be optimized by tuning the tube number density. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT009118502 http://hdl.handle.net/11536/50713 |
显示于类别: | Thesis |
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