Control of nitrogen defects in carbon nanotubes for self-powered memristive systems
- Authors: Il’in O.I.1, Homlenko D.N.1, Khubezhov S.A.2, Rudyk N.N.1, Il’ina M.V.1
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Affiliations:
- Southern Federal University
- North Ossetian State University named after Kosta Levanovich Khetagurov
- Issue: Vol 18, No 4 (2023)
- Pages: 806-809
- Section: Conference proceedings
- URL: https://genescells.ru/2313-1829/article/view/623421
- DOI: https://doi.org/10.17816/gc623421
- ID: 623421
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Abstract
Recent studies show that the additional introduction of heteroatoms into the structure of CNTs makes it possible to change their electronic and physical properties [1]. Of great interest is the process of doping CNTs with nitrogen atoms [2]. The introduction of nitrogen defects into a lattice of carbon atoms makes it possible to modify the CNT structure up to the demonstration of anomalous properties that are not appropriate for this material [3]. It has been shown that multi-walled N-CNTs can exhibit memristive and piezoelectric properties [4].
The parameters of CNTs during synthesis can be controlled by the plasma enhanced chemical vapor deposition (PECVD) method. The addition of ammonia (NH3) to the carbonaceous gas in the PECVD process allows CNTs to be doped directly during growth. At the same time, the dopant concentration and the type of nitrogen defects have a significant effect on the properties of CNTs. The memristive properties of CNTs have already been sufficiently studied [5], however, for their application in self-powered systems, additional studies of the parameters of the piezoelectric module of N-CNTs are required. The aim of this work is to study the effect of ammonia flow on the concentration, type of nitrogen defects, and the value of the piezoelectric modulus during growth of CNTs by the PECVD.
Silicon (100) substrates were used as samples with films of a buffer (Mo, 100 nm) sublayer and a catalytic layer (Ni, 15 nm). CNTs were grown at a temperature of 550 °C in an atmosphere of acetylene (C2H2, 35 sccm) and NH3. The C2H2 flow was kept constant, while the NH3 flow was changed in the C2H2:NH3 ratio from 1:1 to 1:10.
Based on the obtained SEM images, it was found that with an increase in the ratio of C2H2:NH3 flowes, an increase in the density of nanotubes in the array were observed. This occurs due to more active growth of N-CNTs on small nickel catalytic centers due to the accelerated process of hydrogen desorption and its binding with ions in ammonia plasma, which leads to an increase in the growth rate of nanotubes on smaller catalytic centers. Thus, the area of the catalytic center is one of the limiting factors of the growth rate and allows one to control the aspect ratio and density of CNTs in the array. An analysis of the XPS spectra showed that with an increase in the ratio of C2H2:NH3 flows from 1:1 to 1:10, a nonlinear change in the concentration of the nitrogen dopant in N-CNTs from 8.4 to 12 at % is also observed. This led to a nonlinear change in the piezoelectric modulus of nanotubes from 8.7 to 20.6 pm/V and a change in their memristive properties. It has been established that an increase in the concentration of doping nitrogen leads to an increase in the piezoelectric modulus of N-CNTs, which is the source of the memristive effect. The obtained results can be used in the development of energy-efficient piezoelectric nanogenerators based on an array of vertically aligned N-CNTs for autonomous memristive systems.
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Full Text
Recent research indicates that heteroatoms can be introduced to the structure of carbon nanotubes (CNTs) to alter their electronic and physical properties [1]. One particularly interesting method is the process of nitrogen doping CNTs [2]. Introducing nitrogen defects into the carbon atom lattice can modify the CNT structure to display anomalous properties that are not typical of this material [3]. Multi-walled N-CNTs have been shown to exhibit memristive and piezoelectric properties [4].
The plasma enhanced chemical vapor deposition (PECVD) method can be employed to manipulate the parameters of CNTs during synthesis. Incorporation of ammonia (NH3) into the carbonaceous gas used in the PECVD process directly dopes CNTs during growth. The concentration of dopants and the type of nitrogen defects have a crucial impact on the properties of CNTs. The memristive properties of carbon nanotubes (CNTs) have been extensively studied [5], however, for their use in self-powered systems, further research on the piezoelectric modulus parameters of nitrogen-doped CNTs is necessary.
This study aims to investigate the influence of ammonia flow on the concentration, type of nitrogen defects, and the value of the piezoelectric modulus during growth of CNTs using PECVD.
Silicon (100) substrates served as the sample materials and featured a buffer sublayer (Mo, 100 nm) and a catalytic layer (Ni, 15 nm). CNTs grew in an acetylene (C2H2, 35 sccm) and NH3 atmosphere at a temperature of 550 °C. The C2H2 flow rate remained constant, while the NH3 flow rate varied in the C2H2:NH3 ratios from 1:1 to 1:10.
Based on the SEM images obtained, an increase in the density of nanotubes in the array was observed with higher ratios of C2H2:NH3 flows. This is attributed to the more active growth of N-CNTs on small nickel catalytic centers, owing to the accelerated process of hydrogen desorption and its bonding with ions in ammonia plasma, resulting in accelerated growth rate of nanotubes on smaller catalytic centers. Thus, the size of the catalytic center limits the growth rate, enabling modulation of the aspect ratio and density of CNTs. An XPS spectra analysis reveals a non-linear increase in nitrogen dopant concentration in N-CNTs from 8.4 to 12% with augmented C2H2:NH3 flow ratio from 1:1 to 1:10. This resulted in a non-linear shift in the piezoelectric modulus of nanotubes from 8.7 to 20.6 pm/V and a corresponding alteration in their memristive properties. Increasing the concentration of doping nitrogen has been shown to elevate the piezoelectric modulus of N-CNTs, thus serving as the origin of the memristive effect. These findings can be applied to the creation of energy-efficient piezoelectric nanogenerators that use an arrangement of vertically aligned N-CNTs for autonomous memristive systems.
ADDITIONAL INFORMATION
Authors’ contribution. All authors made a substantial contribution to the conception of the work, acquisition, analysis, interpretation of data for the work, drafting and revising the work, final approval of the version to be published and agree to be accountable for all aspects of the work.
Funding sources. The reported studies were funded by the Russian Science Foundation grant No. 22-79-10163 at the Southern Federal University.
Competing interests. The authors declare that they have no competing interests.
About the authors
O. I. Il’in
Southern Federal University
Author for correspondence.
Email: oiilin@sfedu.ru
Russian Federation, Taganrog
D. N. Homlenko
Southern Federal University
Email: oiilin@sfedu.ru
Russian Federation, Taganrog
S. A. Khubezhov
North Ossetian State University named after Kosta Levanovich Khetagurov
Email: oiilin@sfedu.ru
Russian Federation, Vladikavkaz
N. N. Rudyk
Southern Federal University
Email: oiilin@sfedu.ru
Russian Federation, Taganrog
M. V. Il’ina
Southern Federal University
Email: oiilin@sfedu.ru
Russian Federation, Taganrog
References
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- Ayala P, Arenal R, Rümmeli M, et al. The doping of carbon nanotubes with nitrogen and their potential applications. Carbon. 2010;48(3):575–586. doi: 10.1016/j.carbon.2009.10.009
- Il’ina MV, Il’in OI, Guryanov AV, et al. Anomalous piezoelectricity and conductivity in aligned carbon nanotubes. J Mater Chem C. 2021;9:6014–6021. doi: 10.1039/D1TC00356A
- Il’ina MV, Il’in OI, Osotova OI, et al. Pyrrole-like defects as origin of piezoelectric effect in nitrogen-doped carbon nanotubes. Carbon. 2022;190(312):348–358. doi: 10.1016/j.carbon.2022.01.014
- Il’ina MV, Il’in OI, Blinov YF, et al. Memristive switching mechanism of vertically aligned carbon nanotubes. Carbon. 2017;123:514–524. doi: 10.1016/j.carbon.2017.07.090
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