我的Nature Materials论文：一种碳的一维同素异形体

作者：wulishi8（三秋）

   我的Nature Materials论文在今天刚刚上线，因此来写个关于碳材料的小故事。我的论文链接，欢迎大家去围观：http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4617.html

就像奥运会的口号一样，“更快、更高、更强”。科学研究也往往向极端的方向演化：大到宇宙，小到夸克、原子。在二维材料的研究中，科学家往往对制备更大更薄的单晶样品感兴趣。具体到碳链的研究上，因为其本身的一维结构限制，就意味着研究的目标只剩下了在长度上的突破，即，制备更长的碳链。

图1是论文中的Figure1。

众所周知，碳原子因为其独特的4电子结构，使得其区别于其他元素，拥有多种同素异形体（碳原子的神奇之处还在于它是创造了生命必不可少的主要元素，组成各类蛋白质。。。）。这些碳的同素异形体的导电性能从导体、半导体、半金属，一直延伸到绝缘体，见图2（Hirsch.Nature Mater. 2010）。如：sp3杂化形成的金刚石是绝缘体；sp2杂化形成的石墨、石墨烯（2010年诺贝尔奖物理奖），是良导体；区于sp3和sp2之间的，如碳纳米管和富勒烯（如C60，C70等等，1996年诺贝尔奖化学奖），是半导体/金属型和半导体。最后，单三键形成的sp杂化的碳链，则是能带随着其长度可调的半导体。

图2：各类碳的同素异形体

然而，碳链是这类众多碳的同素异形体中，最不为人知的一个。最主要的原因是：它的结构极不稳定，难以存在于常温常压下，且相互之间容易产生cross-link反应。石墨烯在2004年被剥离出来之前，也被广泛地认为单原子层的石墨烯不存在，因为其热力学的不稳定性。然而，现在大家都知道，不仅石墨烯单原子层可以稳定存在，并且其他各类金属，有机物，无机物的单原子层也可以被制备和发现，如：2016年3月刚刚实现的硼单原子层，14年的铁单原子层，目前热门的各类TMDs材料，黑磷，等等。

碳链的存在和发现一直存在着很大的争议（Smith,et al. Science 1981, 1982）。它的发现可以追溯到上个世纪60年代，苏联科学家号称在陨石中发现了一维的碳链结构，并将其命名为carbyne（Kasatochkin,et al. Dokl. Akad. Nauk SSSR 1967）。之后对于碳链的研究，大致可以分为几类：

1) 在自然中寻找和发现，包含宇宙中，陨石中，火山岩中，等等。

2) 实验室中模拟高温高压环境制备碳链（如：Heath,et al. J. Am. Chem. Soc. 1987）；

3) 利用自下而上的化学方法，从短到长，制备碳链（如：Chalifouxet al. Nature Chemistry 2010）；

4) 在碳管中制备碳链（如：ZhaoPRL2003以及我的NatureMaterials论文）。

Smalley,Curl和Kroto因为他们对于富勒烯的研究而获得1996年的诺贝尔奖化学奖。然而他们研究的起因是，Curl一直在从事对于碳链的研究。他开始是利用光谱方法来研究宇宙中存在的短碳链，然而这种方法不仅费时费力，并且相当昂贵。他听说了Smalley实验室有一台最新设计的激光沉积系统，配备有先进的massspectrometer，可以模仿宇宙中的高温环境同时测试产物的mass，因此他想利用同样的系统来模拟宇宙中的极端环境来人工制备碳链。由此，偶然而必然地带来了C60的神奇发现（Kroto,et al. Nature 1985）。其实，他们也成功地利用这台设备制备出了各种长度的短碳链（Heath,et al. J. Am. Chem. Soc. 1987）。

碳链的化学法制备，最早可以追溯到1885年，Baeyer利用化学法，初步尝试制备短碳链。Baeyer由于他在有机化学中的整体贡献，而获得了1905年的诺贝尔奖化学奖。经过一百多年的发展，利用自下而上的方法，获得了最长包含44个碳原子的碳链（Chalifouxet al. Nature Chemistry 2010）。

在碳管中制备碳链，源于碳管的研究兴起，启发于C60@碳纳米管的peapod结构的成功制备。利用碳管的保护，来达到制备长碳链的目的。最开始是由赵新洛教授利用电弧法直接制备得到了存在于多壁碳纳米管中的长直碳链（Zhao,et al. Physical Review Letters 2003）。之后Shinohara教授组对于短碳链填充到碳纳米管中进行了广泛的研究。我的这篇NM论文的意义在于：利用后处理的方法，在双壁碳纳米管中直接大量制备微米级别的碳链（包含几千个碳原子），并且利用TEM和近场拉曼直接观测到了碳链的长度和拉曼峰；另外，还研究了碳链和碳管之间的相互作用。不久之后，还将有几篇论文专注于：碳链和碳管之间的电荷传递，碳链的能级，碳链对于碳管荧光光谱增强的研究，等等。届时再一一介绍。

最后，做个广告，欢迎大家加入我2016年3月份新创建的“碳纳米管与拉曼光谱”qq群（扫下面的二维码或群号：378577988，加群链接：http://jq.qq.com/?_wv=1027&k=27MdYPT），一起分享各类资源和讯息，目前有500余群友，很多好的共享资源（如科学家的PPT，各类书籍，经典文献，群友分享，实用工具软件，等等）。

另外，也欢迎加入我们为了探索新型科学交流而创办的qq群： 点击链接加入群【CVD、碳材料与器件】：http://jq.qq.com/?_wv=1027&k=2BwyfHY230458205，几乎每个月都会安排qq在线专业报告，目前有近一千群友。

下面是英文的宣传文章，以供参考(https://www.sciencedaily.com/releases/2016/04/160404134046.htm 或 http://medienportal.univie.ac.at/presse/aktuelle-pressemeldungen/detailansicht/artikel/unraveling-truly-one-dimensional-carbon-solids/)。

Unravelingtruly one dimensional carbon solids

Direct proof of stable ultra-long 1D carbonchains as a route to carbyne

Elementalcarbon appears in many different forms, including diamond and graphite. Theirunique structural, electrical and optical properties have a broad range ofpotential applications in composite materials and nanoelectronics. Within the“carbon family”, only carbyne, the truly one-dimensional form of carbon, hasnot yet been synthesized; although studied for the last 50 years, its extremeinstability in ambient conditions has rendered the final experimental proof ofits existence elusive. In an international collaboration, researchers at theUniversity of Vienna, led by Thomas Pichler, have succeeded in developing anovel route for the bulk production of carbon chains composed of more than6,000 carbon atoms, using thin double-walled carbon nanotubes as protectivehosts for the chains. These findings represent an elegant forerunner towardsthe final goal of carbyne’s bulk production and will be published in NatureMaterials.

Evenin its elemental form, the high bond versatility of carbon allows for manydifferent well-known materials, including diamond and graphite. A single layerof graphite, termed graphene, can then be rolled or folded into carbonnanotubes or fullerenes, respectively. To date, Nobel prizes have been awardedfor both graphene (2010) and fullerenes (1996). Although the existence ofcarbyne, an infinitely long carbon chain, was proposed in 1885 by Adolf vonBaeyer (Nobel laureate for his overall contributions in organic chemistry,1905), scientists have not yet been able to synthesize this material. VonBaeyer even suggested that carbyne would remain elusive as its high reactivitywould always lead to its immediate destruction. Nevertheless, carbon chains ofincreasing length have been successfully synthesized over the last 50 years,with a record of around 100 carbon atoms (2003). This record has now beenbroken by more than one order of magnitude, with the demonstration ofmicrometer length-scale chains.

The new record
Researchers from the University of Vienna, led by Thomas Pichler, havepresented a novel approach to grow and stabilize carbon chains with a recordlength of 6,000 carbon atoms, improving the previous record by more than oneorder of magnitude. They use the confined space inside a double-walled carbonnanotube as a nano-reactor to grow ultra-long carbon chains on a bulk scale. Incollaboration with the groups of Kazu Suenaga at the AIST Tsukuba in Japan,Lukas Novotny at the ETH Zürich in Switzerland and Angel Rubio at the MPIHamburg in Germany and UPV/EHU San Sebastian in Spain, the existence of thechains has been unambiguously confirmed by using a multitude of sophisticated,complementary methods. These are temperature dependent near- and far-fieldRaman spectroscopy with different lasers (for the investigation of electronicand vibrational properties), high resolution transmission electron spectroscopy(for the direct observation of carbyne inside the carbon nanotubes) and x-rayscattering (for the confirmation of bulk chain growth).

The researchers present their study in the latest edition of "NatureMaterials". "The direct experimental proof of confined ultra-longlinear carbon chains, which are more than an order of magnitude longer than thelongest proven chains so far, can be seen as a promising step towards the finalgoal of unraveling the “holy grail” of carbon allotropes, carbyne”, explainsthe lead author, Lei Shi.

Application potential
Carbyne is very stable inside double-walled carbon nanotubes. This propertyis crucial for its eventual application in future materials and devices.According to theoretical models, carbyne’s mechanical properties exceed allknown materials, outperforming both graphene and diamond. Carbyne’s electricalproperties suggest novel nanoelectronic applications in quantum spin transportand magnetic semiconductors.

The work was supported by FWF and the EU.

Publication in "Nature Materials":
"Confined linear carbon chains as a route to bulk carbyne": LeiShi, Philip Rohringer, Kazu Suenaga, Yoshiko Niimi,Jani Kotakoski, Jannik C.Meyer, Herwig Peterlik, Marius Wanko, Seymur Cahangirov, Angel Rubio, ZacharyJ. Lapin, Lukas Novotny, Paola Ayala, Thomas Pichler, Nature Materials,2016

http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4617.html
http://dx.doi.org/10.1038/NMAT4617