(Nanowerk News)来自NUST MISIS无机纳米材料实验室的科学家和他们的国际同事已经证明，通过拉伸碳纳米管，可以改变其结构和导电性能。
“纳米管是一个折叠的石墨烯层，它的基础是一个正六边形网格，顶点是碳原子。”如果将纳米管中的一个碳键旋转90度，就会形成一个五边形和一个七边形而不是六边形，在这种情况下就会形成所谓的石威尔士缺陷。在一定条件下，这种缺陷可能发生在结构中。早在90年代末,这是预测,这个缺陷的迁移沿墙的高度激烈的纳米管的应用机械应力可能导致其结构的变化——一个连续的纳米管的手性的变化,从而导致其电子特性的变化。自然与数学科学博士、NUST MISIS无机纳米材料实验室“纳米结构理论材料科学”基础设施项目负责人、副教授Pavel Sorokin说。
“我们负责在NUST MISIS实验室的一台超级计算机上对这一过程进行理论建模，并为实验部分的工作开发新材料。我们很高兴模拟结果[支持]实验数据”，研究工作的合著者，物理和数学科学的候选人，NUST MISIS无机纳米材料实验室的研究员Dmitry Kvashnin补充道。
Deformation of nanotubes to control conductivity
(Nanowerk News) Scientists from the NUST MISIS Laboratory of Inorganic Nanomaterials together with their international colleagues have proved it possible to change the structural and conductive properties of carbon nanotubes by stretching them.
This can potentially expand nanotubes' application into electronics and high-precision sensors such as microprocessors and high-precision detectors. The research article has been published in Ultramicroscopy ("Chirality transitions and transport properties of individual few-walled carbon nanotubes as revealed by in situ TEM probing").
Carbon nanotubes can be represented as a sheet of graphene rolled in a special way. There are different ways of 'folding' it, which leads to the graphene edges interconnecting at different angles, forming either armchair, zigzag or chiral nanotubes (Fig.1).
Nanotubes are considered to be promising materials for use in electronics and sensors because they have high electrical conductivity, which would work well in things like microprocessors and high-precision detectors.
However, when producing carbon nanotubes it is hard to control their conductivity. Nanotubes with metallic and semiconducting properties can grow into a single array while microprocessor-based electronics require semiconducting nanotubes that have the same characteristics.
Scientists from the NUST MISIS Laboratory of Inorganic Nanomaterials jointly with a research team from Japan, China and Australia, led by Professor Dmitri Golberg, have proposed a method that allows for the modification of the structure of ready-made nanotubes and thus changes their conductive properties.
"The basis of the nanotube – a folded layer of graphene – is a grid of regular hexagons, the vertices of which are carbon atoms. If one of the carbon bonds in the nanotube is rotated by 90 degrees, a pentagon and a heptagon are formed at this [junction] instead of a hexagon, and a so-called Stone-Wales defect is obtained in this case. Such a defect can occur in the structure under certain conditions. Back in the late 90s, it was predicted that the migration of this defect along the walls of a highly heated nanotube with the application of mechanical stress could lead to a change in its structure - a sequential change in the chirality of the nanotube, which leads to a change in its electronic properties. No experimental evidence for this hypothesis has previously been obtained, but our research paper has presented convincing proof of it", said Associate Professor Pavel Sorokin, Doctor of Physical & Mathematical Sciences and head of the 'Theoretical Materials Science of Nanostructures' infrastructure project at the NUST MISIS Laboratory of Inorganic Nanomaterials.
Scientists from the NUST MISIS Laboratory of Inorganic Nanomaterials have conducted simulations of the experiment at the atomic level. At first, the nanotubes were lengthened to form the first structural defect consisting of two pentagons and two heptagons (a Stone-Wales defect, Fig.2a), where the prolonged lengthening of the tube began tospread to the sides, rearranging other carbon bonds (Fig.2b). It was at this stage that the structure of the nanotubes changed. With further stretching, more and more Stone-Wales defects began to form, eventually leading to a change in the nanotubes' conductivity (Fig. 2).
"We were responsible for the theoretical modeling of the process on a supercomputer in the NUST MISIS Laboratory for Modeling and Development of New Materials for the experimental part of the work. We are glad that the simulation results [support] the experimental data", added Dmitry Kvashnin, co-author of the research work, Candidate of Physical & Mathematical Sciences and a researcher at the NUST MISIS Laboratory of Inorganic Nanomaterials.
The proposed technology is capable of helping in the transformation of metallic nanotubes' structure for their further application in semiconductor electronics and sensors such as microprocessors and ultrasensitive detectors.