Nav: Home

Unveiling the electron's motion in a carbon nanocoil

May 15, 2016

Carbon nanocoils (CNCs) are an exotic class of low-dimensional nanocarbons whose helical shape may make them suitable for applications such as microwave absorbers and various mechanical components such as springs. Typical thicknesses and coil diameters of CNCs fall within the ranges of 100-400 nm and 400-1000 nm, respectively, and their full lengths are much larger, on the order of several tens of micrometers. Despite earlier pioneering work, the relationships between the geometric shape of natural CNCs and their mechanical and electrical properties, particularly the electrical resistivity, are not well understood.

Now, researchers at Toyohashi Tech, University of Yamanashi, National Institute of Technology, Gifu College, and Tokai Carbon Co., Ltd. have established that the resistivity of CNCs increases with coil diameter. This required the development of a precise resistivity measurement method, using a focused ion beam (FIB) and nanomanipulator technique to select a sample CNC with the desired coil geometry and then make firm electrical connections to the instrument's electrodes. All the resistivity data obtained with CNCs were well fitted by a curve predicted by a theory known as variable range-hopping (VRH), which is suitable for disordered materials at low temperatures.

The research shows that the interior of the nanocoil contains material that affects its electrical properties. The scientists examined 15 individual CNCs, and three CNCs that had been artificially-graphitized to give them lower resistivity (G-CNCs). Although the resistivity of the CNCs increased with coil diameter, it was almost unchanged for the G-CNCs. As a consequence, for the CNCs with the largest diameters, the resistivity was almost two orders of magnitude larger than that of the graphitized versions. This large discrepancy in the resistivity between CNCs and G-CNCs indicates a significant structural complexity inside the CNCs. Our results imply that the interior of CNCs with large coil diameter is filled with a highly-disordered carbon network that consists of many small regions (known as sp2 domains) embedded in a sea of amorphous carbon. To verify this theory, the temperature dependence of the resistivity between 4 K and 280 K was examined. The resistivity data obeyed two different versions of the VRH theory; the regime in the temperature range of 50-280 K was found to be the so-called Mott-VRH version, while that in the range of 4-20 K was the Efros-Shklovskii-VRH version. Interestingly, the resistivity curves shifted smoothly between regimes as the coil diameter was changed.

"We found this behavior three years ago. Owing to the efforts of two students, we included the resistivity data for G-CNCs and straight carbon nanofibers (CNFs), and compared them to the data for the CNCs", explains Associate Professor Yoshiyuki Suda, "I am so glad that Prof. Hiroyuki Shima and Dr. Tamio Iida joined this study. We obtained the low-temperature measurement data and discussed it using the VRH theory. Eventually, we came to the conclusion that this behavior is a unique phenomenon for CNCs and can be fitted by VRH."

The first author, Master's course student Yasushi Nakamura, commented on how they went beyond the CNC resistivity measurements of other groups. "It was a long and challenging task. I had to prepare many single CNC samples using a focused ion-beam apparatus. Our finding was achieved by establishing a precise measurement system using a scanning electron microscope and acquiring resistivity data for many single CNCs."

The group's present results on resistivity are in qualitative agreement with their previous findings on the mechanical properties of CNCs: Tensile load experiments showed that their shear modulus increases with coil diameter. The positive correlation between the shear modulus and coil diameter is possibly caused by the fact that in large-diameter CNCs, the population of sp2 domains, which are fragile against shear stress, is reduced in comparison to small-diameter CNCs.

These results imply that, with nanocoils, the resistance as well as the inductance are defined by geometric factors. In particular, coil diameter, pitch, and length are important. The correlation found can be used to improve control over the peak frequency of electromagnetic wave absorption, in which a particular range of frequencies (~GHz) is absorbed, dependent on the impedance properties.

These findings pave the way for CNC-based nanodevices, ranging from electromagnetic wave absorbers to nano-solenoids and extra-sensitive mechanical springs.
Funding agency: This work was partly supported by JSPS KAKENHI Grant Numbers 24360108, 25390147, and 15K13946, and the Toyota Physical and Chemical Research Institute.

Reference: Yasushi Nakamura, Yoshiyuki Suda, Ryuji Kunimoto, Tamio Iida, Hirofumi Takikawa, Hitoshi Ue, and Hiroyuki Shima (2016). Precise measurement of single carbon nanocoils using focused ion beam technique, Applied Physics Letters, 108, 153108. 10.1063/1.4945724

Further information

Toyohashi University of Technology
1-1 Hibarigaoka, Tempaku
Toyohashi, Aichi Prefecture, 441-8580, JAPAN

Inquiries: Committee for Public Relations

Toyohashi University of Technology, which was founded in 1976 as a National University of Japan, is a leading research institute in the fields of mechanical engineering, advanced electronics, information sciences, life sciences, and architecture.


Toyohashi University of Technology

Related Data Articles:

Storing data in music
Researchers at ETH Zurich have developed a technique for embedding data in music and transmitting it to a smartphone.
Life data economics: calling for new models to assess the value of human data
After the collapse of the blockchain bubble a number of research organisations are developing platforms to enable individual ownership of life data and establish the data valuation and pricing models.
Geoscience data group urges all scientific disciplines to make data open and accessible
Institutions, science funders, data repositories, publishers, researchers and scientific societies from all scientific disciplines must work together to ensure all scientific data are easy to find, access and use, according to a new commentary in Nature by members of the Enabling FAIR Data Steering Committee.
Democratizing data science
MIT researchers are hoping to advance the democratization of data science with a new tool for nonstatisticians that automatically generates models for analyzing raw data.
Getting the most out of atmospheric data analysis
An international team including researchers from Kanazawa University used a new approach to analyze an atmospheric data set spanning 18 years for the investigation of new-particle formation.
More Data News and Data Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Erasing The Stigma
Many of us either cope with mental illness or know someone who does. But we still have a hard time talking about it. This hour, TED speakers explore ways to push past — and even erase — the stigma. Guests include musician and comedian Jordan Raskopoulos, neuroscientist and psychiatrist Thomas Insel, psychiatrist Dixon Chibanda, anxiety and depression researcher Olivia Remes, and entrepreneur Sangu Delle.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...