Semiconducting Single-walled Carbon Nanotubes Research Articles

Spectral Sensitization of n- and p-Type Gallium Phosphide Single Crystals with Single-Walled Semiconducting Carbon Nanotubes.

The spectral sensitization of single-crystal p-GaP by semiconducting single-walled carbon nanotubes (s-SWCNT) via hole injection into the p-GaP valence band is reported. The results are compared to SWNCT sensitized n-type single-crystal substrates: TiO2, SnO2, and n-GaP. It was found that the sensitized photocurrents from CoMoCAT and HiPco s-SWCNTs were from a hole injection mechanism on all substrates, even when electron injection into the conduction band should be energetically favored. The results suggest an intrinsic p-type character of the s-SWCNTs surface films investigated in this work.

Charge Transport in Mixed Semiconducting Carbon Nanotube Networks with Tailored Mixing Ratios.

The ability to prepare uniform and dense networks of purely semiconducting single-walled carbon nanotubes (SWNTs) has enabled the design of various (opto-)electronic devices, especially field-effect transistors (FETs) with high carrier mobilities. Further optimization of these SWNT networks is desired to surpass established solution-processable semiconductors. The average diameter and diameter distribution of nanotubes in a dense network were found to influence the overall charge carrier mobility; e.g., networks with a broad range of SWNT diameters show inferior transport properties. Here, we investigate charge transport in FETs with nanotube networks comprising polymer-sorted small diameter (6,5) SWNTs (0.76 nm) and large diameter plasma torch SWNTs (1.17-1.55 nm) in defined mixing ratios. All transistors show balanced ambipolar transport with high on/off current ratios and negligible hysteresis. While the range of bandgaps in these networks creates a highly uneven energy landscape for charge carrier hopping, the extracted hole and electron mobilities vary nonlinearly with the network composition from the lowest mobility (15 cm2 V-1 s-1) for only (6,5) SWNT to the highest mobility (30 cm2 V-1 s-1) for only plasma torch SWNTs. A comparison to numerically simulated network mobilities shows that a superposition of thermally activated hopping across SWNT-SWNT junctions and diameter-dependent intratube transport is required to reproduce the experimental data. These results also emphasize the need for monochiral large diameter nanotubes for maximum carrier mobilities in random networks.

Selective synthesis of metallic and semi-conducting single-walled carbon nanotube by floating catalyst chemical vapour deposition

Selective synthesis of both metallic and semi-conducting single-walled carbon nanotubes (SWCNTs) has been performed using floating catalyst chemical vapour deposition (FC-CVD). It was observed that partial pressure of hydrogen determined the selectivity of SWCNTs being predominantly metallic at lower hydrogen concentration (20 vol%) and predominantly semiconducting at higher hydrogen concentration (80 vol%). The qualitative and quantitative analysis on type of SWCNTs was performed based on UV–vis-NIR, Raman spectra at different wavelengths and SWCNT-based field effect transistor device performance. Transmission electron microscopy was used to get diameter distribution of SWCNTs. Detailed analysis showed that the type of SWCNTs was decided at the nucleation stage that was governed by the collision frequency between hydrogen molecules and iron nanoparticles.

Electrochemical biosensor for methyl parathion based on single-walled carbon nanotube/glutaraldehyde crosslinked acetylcholinesterase-wrapped bovine serum albumin nanocomposites

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been demonstrated as an excellent material for transistors, miniaturized devices and sensors due to their high carrier mobility, stability, scattering-free ballistic transport of carriers etc. Herein, we have designed a biosensor to selectively detect methyl parathion (MP, organophosphorus pesticide) using glutaraldehyde (Glu) cross-linked with acetylcholinesterase (AChE) immobilized on s-SWCNTs wrapped with bovine serum albumin (BSA). The fabricated biosensor was characterized and confirmed by Fourier-transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV). In the presence of MP, the effective interaction between AChE and MP favours the accumulation of MP-AChE complex on the glassy carbon electrode (GCE) surface which reduces the electron transfer property. Based on this interaction, detection of various concentration of MP was demonstrated by SWV using BSA/AChE-Glu-s-SWCNTs composite modified electrode. The proposed biosensor exhibited a wide linear range (WLR) for MP target in 100 mM phosphate buffered saline solution (PBS) (pH 7.4) from 1 × 10−10 M to 5 × 10−6 M with a limit of detection (LOD) of 3.75 × 10−11 M. In addition, the BSA/AChE-Glu-s-SWCNTs/GCE biosensor showed good repeatability and reproducibility for MP detection. Moreover, the proposed biosensor showed better electrode stability when stored at 4 °C. This new electrochemical biosensor is also exhibited high selectivity and sensitivity for MP, which made it possible to test MP in real strawberry and apple juices. Furthermore, the BSA/AChE-Glu-s-SWCNTs/GCE offered a favourable electron transfer between the acetylthiocholine chloride (ATCl) and electrode interface than BSA/AChE-s-SWCNTs/GCE, s-SWCNTs/GCE and bare GCE.

Brightening of Long, Polymer-Wrapped Carbon Nanotubes By Large Scale sp3 Functionalization

Networks of long, polymer-sorted semiconducting single-walled carbon nanotubes (SWNTs) show excellent transport of both electrons and holes and are thus perfectly suited for electrically-driven light emission in the near-infrared (NIR) [1,2]. So far, their application in near-infrared light-emitting devices has been hampered by their low photoluminescence quantum yield (PLQY) and strong self-absorption owing to their small Stokes shift. In recent years, the controlled introduction of a low density of sp3 defects as exciton trapping sites was shown to lead to red-shifted emission with longer exciton lifetimes and improved PLQYs. However, due to the polarity of the employed diazonium salt reagent, this approach was limited to aqueous dispersions of SWNTs with often short tube lengths and the undesired presence of stabilizers. Here, we present a novel route to sp3 functionalization with diazonium salts in organic, non-halogenated solvents, thereby making it compatible with polymer-wrapped long SWNTs produced by shear force mixing. As a result of the low density of exciton quenching sites on shear mixed SWNTs [3], the excitons are efficiently channeled to the emissive defect sites, leading to absolute PLQYs of 4 % for functionalized (6,5) SWNT dispersions in toluene. This new method paves the way toward the large scale production of high-quality sp3 functionalized SWNTs and hence also thin films for optoelectronic devices with narrowband near-infrared emission. [1] Rother et al., ACS Appl. Mater. Interfaces 2016, 8, 5571-5579. [2] Brohmann et al., J. Phys. Chem. C 2018, 122, 19886-19896. [3] Graf et al., Carbon 2016, 105, 593-599. Figure 1

The Impact of Exposed Surface Area on the Response of SWCNT Optical Sensors

Due to their distinct and advantageous fluorescence properties, semiconducting single-walled carbon nanotubes (SWCNTs) are being applied to a variety of optical sensing applications. Limitations in solubility and biocompatibility have been overcome by non-covalently functionalizing the surface of the SWCNT with wrappings using techniques that retain its inherent fluorescence. Though wrappings based on surfactants and single-stranded DNA (ssDNA) have been extensively studied for this purpose, they are limited by factors such as lack of selectivity and lower fluorescence quantum yield, respectively. In this study, we take advantage of the higher fluorescence emission of surfactant-coated SWCNTs and focus on new approaches that can tune their selectivity as sensors. Through the concomitant monitoring of both the fluorescence intensity and wavelength position of emission peaks, we demonstrate the ability to increase the selectivity of sensors based on surfactant-suspended SWCNTs while retaining their higher fluorescence intensity. These results provide not only a promising avenue for rationally designing SWCNT sensors, but also insight on the mechanisms governing the selectivity of existing SWCNT-based optical sensors.

Charge Transport in Mixed Semiconducting SWCNT Networks with Tailored Diameter Distributions

The recent availability of purely semiconducting single-walled carbon nanotubes (SWCNTs) and the ability to prepare dense and uniform SWCNT networks from dispersion has led to promising applications in optoelectronics, e.g. in field-effect transistors (FETs), light-emitting diodes, notch filters and solar cells. Further optimization and controlled tuning of nanotube networks is desirable to establish them as competitive semiconducting materials. The impact of the SWCNT network composition on the overall charge transport was demonstrated recently [1]. The uneven energy landscape of networks with a broad tube diameter and thus bandgap distribution results in inferior transport properties. Contrary to common belief, the charge transport in networks is not solely determined by tube-tube junctions but intra-nanotube transport also has a significant impact on the overall network mobility. Here, we examine this hypothesis in a detailed charge transport study of FETs with SWCNT networks consisting of polymer-sorted small diameter (6,5) SWCNTs (0.76 nm) and large diameter plasma torch SWCNTs (1.2-1.5 nm) with different but controlled mixing ratios. All FETs showed balanced ambipolar transport with low off-currents and negligible hysteresis. The extracted mobilities varied characteristically with network composition. The obtained experimental data are compared to results from numerically simulated networks with analogous SWCNT compositions. The employed random resistor network model was recently shown to adequately describe the carrier density-dependent mobility in SWCNT networks [2]. [1] M Brohmann et al., J. Phys Chem. C 122, 19886-19896 (2018) [2] S. P. Schießl et al., Phys. Rev. Mater. 1, 046003 (2017) Figure 1

Long-Lived Free Charge Carriers at Heterojunctions between Semiconducting Single-Walled Carbon Nanotubes and Perylene Diimide Electron Acceptors

Semiconducting single-walled carbon nanotubes (s-SWCNTs) have been thoroughly investigated as the components of various photovoltaic cells due to several advantages such as spectral tunability, absence of charge-transfer (CT) states, giant aspect ratio, chemical robustness, and hydrophobicity. In the previous study, it was reported that the heterojunctions between s-SWCNTs and perylene diimide (PDI)-based electron acceptors yield long-lived charge separated states whose lifetimes are more than 1.5 µs. Besides the potential of PDI-based electron acceptors to substitute fullerene-based electron acceptors, this work noted the significance of the molecular geometries of PDI-based electron acceptors which result in molecular aggregation and the associated charge delocalization in the acceptor phase. However, the true characteristics of the long-lived charge carriers for these heterojunctions have not been revealed yet. For instance, the degree to which the charge carriers generated at these heterojunctions are free or trapped was not yet clear. Moreover, it was not determined whether the charge recombination process from these heterojunctions is monomolecular-like or bimolecular-like. In this study, we explored the nature of charge carriers for the heterojunctions between (6,5) s-SWCNTs and two different PDI-based electron acceptors by combining two effective spectroscopic techniques: transient absorption (TA) and time-resolved microwave conductivity (TRMC). Two PDI-based electron acceptors, hPDI2-pyr-hPDI2 and Trip-hPDI2, were synthesized and coated on (6,5) s-SWCNT films to form donor-acceptor heterojunctions. TA and TRMC studies reveal that the dynamics of the charge-separated states across the (6,5) s-SWCNT/PDI-based acceptor heterojunctions remain similar over three orders of magnitude in absorbed photon flux. This fluence independence of the heterojunctions indicates that the charge carriers recombine ‘pseudo’-monomolecularly. Moreover, the charge recombination kinetics from TA and TRMC studies are well-matched, indicating that most of the generated charge carriers are free, not trapped. The unconventionally strong suppression of bimolecular charge recombination from these heterojunctions, supported by fluence independence of charge recombination dynamics, may be attributed to the high carrier mobility and good charge delocalization in both (6,5) s-SWCNTs and PDI-based acceptors. These factors can also be regarded as the origin of high free charge carrier generation in these heterojunctions. These photophysical studies provide the fundamental understandings of the charge generation process in s-SWCNT-based heterojunctions and how different electron acceptor materials can impact the nature of charge generation with respect to the heterojunction energetics and molecular orientations. The results can inform rational design strategies for s-SWCNT-based optoelectronic applications.

Single-Walled Carbon Nanotube-Clostridium Ljungdahlii hybrid for Carbon Dioxide Fixation to Value-Added Chemicals

Direct electricity-powdered production of value-added carbon organic compoundsfrom CO2 and H2O, a process that mimics natural Wood–Ljungdahl pathway (WLP), is of fundamental and practical interestfor renewable energy applications. The process depends on electrotrophy, the ability of some microorganisms to use electrons derived from an electrode as the sole energy source to reduce carbon dioxide. In this work, an acetogenic microorganism Clostridium ljungdahliiis immobilizedon carbon felt (CF) andhighly enriched semiconducting single-walled carbon nanotube (SWCNT) scaffolds under different conditions (physical soaking and growth under electrochemical bias). As a proof of principle, we demonstrate that this conductive carbon-bacteria system can utilize electrical current to fix CO2 under to multiple chemical targets, such as acetate and ethanol. The porous structure of the hybrid electrode provides the large surface area needed for high bacteria loading and excellent diffusion kinetics, while the s-SWCNTs appear to facilitate unique modes of bacterial adsorption and strong interfacial interactions. As such, the hybrid system enables low overpotential (η < 200 mV) and high Faradaic efficiency (> 90%). With the SWCNT modification and bacteria electrochemical growth, the hybrid electrode exhibited much higher performance on acetate production due to the enhanced bacteria-electrode interface quality for charge transfer. I will also discuss our efforts to understand the biochemicalpathways and possible underlying charge transfer mechanisms of CO2reduction of this SWCNT-Clostridium ljungdahliisystem. These results suggest a potential route for using SWCNTs to facilitate efficient microbial electrochemical biofilm formation and energy storage, furthering the potential applicability in bioelectrochemical systems.

(Invited) Thermo-Excitonic Properties of Semiconducting Single-Walled Carbon Nanotubes

Because of the large binding energy of one-dimensional excitons on the order of 0.5 eV, excitons are stable in semiconducting single-walled carbon nanotubes (SWNTs) even at high temperatures more than 1000 K. This unique exciton property, with the very high intrinsic thermal stability of the materials, enables thermal generation of excitons in semiconducting SWNTs; this results in thermal radiation with very narrow spectral bandwidth even at 1000-2000 K [1]. We will report our recent progress in the study on the thermal exciton radiation from SWNTs. [1] T. Nishihara, A. Takakura, Y. Miyauchi, and K. Itami, Nat. Commun. 9, 3144 (2018).

Ballistic transport in bent-shaped carbon nanotubes

We report theoretical investigations of ballistic quantum transport properties of smoothly bent semiconducting single-walled carbon nanotubes (SWCNTs). The SWCNT is doped into NxN and PxP forms where N and P stand for N-type and P-type doping, x takes N-type, P-type or intrinsic I-type. Our calculation is based on a state-of-the-art non-equilibrium Green's function approach combined with density functional theory. The smooth bent induces a small electron redistribution on the SWCNT arc, which leads to rich and major transport differences between the NxN and PxP tubes. Conductance G of NNN tubes does not change with the bending angle β, while G of PPP tubes decreases with it. G of NPN and PNP tubes increases with β, while that of the PNP tubes varies with it in an oscillatory manner. The bent induced transport phenomena can be well understood by analyzing the microscopic physics of the electronic density distribution and quantum interferences between scattering states which traverse different paths along the bent-shaped tubes. The predicted conductance versus bent angle is useful for estimating how a flexible system may behave when strained and/or bent.

High‐Performance Partially Printed Hybrid CMOS Inverters Based on Indium‐Zinc‐Oxide and Chirality Enriched Carbon Nanotube Thin‐Film Transistors

AbstractComplementary metal–oxide‐semiconductor (CMOS) inverters with low power consumption and high noise immunity are essential for realizing practical applications of printed logic gates and circuits. However, the performance of existing printed CMOS inverters is still unsatisfactory because p‐type and n‐type transistors do not match well. This work demonstrates novel low‐voltage and high‐performance CMOS inverters using partially printed thin‐film transistors (TFTs) on 50 nm HfO2/Si substrates based on n‐type indium zinc oxides (IZOs) and p‐type chirality enriched (9,8) semiconducting single‐walled carbon nanotubes (SWCNTs). The high‐k dielectric materials grown using atomic layer deposition and (9,8) SWCNTs with relatively large band gaps help to match the characteristics of p‐type and n‐type transistors—the IZO and SWCNT TFTs exhibit similar mobility on/off ratio, small hysteresis, and low sub‐threshold swing at low operating voltages. The hybrid CMOS inverters demonstrate excellent performance with the highest voltage gain up to 45, the largest noise margin of 83% at 1/2 Vdd, and the lowest static power consumption of 0.4 µW at Vdd of 2 V among recently reported printed CMOS inverters under relatively low annealing temperatures (300 °C). The strategies demonstrated here can be considered as general approaches to realize a new generation of high‐performance printed logic gates and circuits.

Controllable Growth of (n, n −1) Family of Semiconducting Carbon Nanotubes

Summary Semiconducting single-walled carbon nanotubes (SWNTs) with controlled chirality (n, m) and band gaps are expected to create a new era of electronics. Here, we report a rational design to enable SWNTs’ near-equilibrium nucleation and then grow a new family of semiconducting SWNTs: (n, n − 1) carbon nanotubes. No metallic SWNTs were observed in ∼100 samples by reflection optical spectral measurements. Combined with catalyst controlling, we have successfully synthesized both large-diameter (>2 nm) (n, n − 1) SWNTs and single-chirality (10, 9) SWNTs with abundances of 88% and >80%, respectively. Theoretical analysis indicates that the chirality of (n, n) tubes tends to change to (n, n − 1) by kinetically incorporating an energetically preferred pentagon-heptagon pair in the tube wall. This strategy opens up a new route for the growth of SWNT families beyond catalyst design.

Improving the Performance and Uniformity of Carbon-Nanotube-Network-Based Photodiodes via Yttrium Oxide Coating and Decoating.

Semiconducting single-walled carbon nanotube thin films can be obtained by conjugated polymer wrapping sorting technique followed by solution deposition and can be utilized as channel materials of field-effect transistors and absorbing layers of photodiodes. However, after the deposition process, there are still polymer molecules wrapping around nanotubes, remaining between nanotubes, and remaining on the thin-film surface, which will cause large nanotube-electrode resistance and tube-tube resistance. Here, we demonstrate an yttrium oxide coating-and-decoating technique that can remove polymers only around electrodes and thus improve the performance of photodiodes without inducing new defects in the device channel. After the treatment of only the contact area, the average short-circuit current of a photodiode increases from 9.1 to 10.7 nA, whereas the average open-circuit voltage increases from 0.25 to 0.30 V. This method also improves device uniformity significantly.

Environment Effects on the Charge States of Metallic and Semiconducting SWCNTs during Their Separation by the Electric-Field Induced Layer Formation Method

The mechanism of separating metallic (m-) and semiconducting (s-) single-walled carbon nanotubes (SWCNTs) by electric-field induced layer formation (ELF) was investigated, by examining effects from the environmental conditions, that is, the pH and surfactant concentration on the separation process. Time course analysis showed that the pH and surfactant concentration in the cell become inhomogeneous during the ELF separation process. The ζ potential measurements revealed that the s-SWCNTs are much more negatively charged than m-SWCNTs in the specific pH range. The mechanism of ELF separation of m- and s-SWCNTs by forming layers is attributed to the dynamic changing/balancing of the electrophoretic and electroosmotic forces acting on the SWCNTs. The applicability of various surfactants for the ELF method was also discussed in terms of the surfactant types and the molecular structures.

Thermal management for purification of aligned arrays of single-walled carbon nanotubes based on thermocapillary flow by pulsed heating

Semiconducting single-walled carbon nanotube (s-SWNT) arrays attract much attention due to the ideal configuration for high performance electronics. A recent approach based on the nanoscale thermocapillary flow enabled the achievement of aligned arrays of highly purified s-SWNTs by removing the metallic SWNTs (m-SWNTs) in as-grown arrays by direct pulsed current injection. Thermal management of this process is critically important since the cumulative heating from the m-SWNT array yields a high temperature increase to cause the difficult control of thermocapillary flow. In this paper, an analytical heat transfer model combining a two-dimensional transient thermal model and a three-dimensional steady state thermal model is established for predicting the temperature increase of the SWNT array under a pulsed current injection with a period step function. The analytical predictions agree well with three-dimensional finite element analysis. Effects of parameters (such as duty cycle, period, spacing, etc.) on the temperature distributions and the maximum temperature increase are investigated systematically. These results can help guide the purification process to reduce the adverse thermal effects to obtain highly purified s-SWNTs.

Radical Polymers Alter the Carrier Properties of Semiconducting Carbon Nanotubes

Radical polymers are composed of nonconjugated macromolecular backbones and pendant groups that bear stable open-shell sites; these functional macromolecules have been utilized in myriad electrochemical, optoelectronic, and thermoelectric devices to date. Here, we combine radical polymers with semiconducting single-walled carbon nanotubes (SWCNTs) to form composite materials using a scalable fabrication process. Importantly, we are able to tune the charge carrier characteristics of the SWCNTs by controlling the macromolecular architecture of the radical polymer used to form the composite. This is a critical handle as creating stable, electron-transporting (i.e., n-type) SWCNT thin films using scalable processes is a long-sought goal in the field. Specifically, hole-transporting (i.e., p-type) SWCNT thin films were deposited using a simple drop-casting methodology. Then, a radical polymer thin film was coated on top of the SWCNT thin film in order to create a composite system. Three different radical polymer chemistries were evaluated in terms of their ability to manipulate the optoelectronic properties of the composite systems relative to the pristine SWCNT thin films. Two of the three radical polymer chemistries, poly(2,2,6,6-tetramethylpiperidinyloxy methacrylate) (PTMA) and poly(2,3-bis(2′,2′,6′,6′-tetramethylpiperidinyl-N-oxyl-4′-oxycarbonyl)-5-norbornene) (PTNB), contained different macromolecular backbones but shared the same nitroxide radical open-shell chemistry. Instead, the third radical polymer, poly(2,6-ditert-butyl-4-((3,5-ditert-butyl-4-phenoxyl)(4-vinylphenyl)methylene)cyclohexa-2,5-dienone) (PGSt), was based upon the galvinoxyl styrene radical. Neither of the nitroxide-based radical polymers demonstrated any significant electrochemical interaction with the SWCNT thin films. Conversely, the addition of the galvinoxyl styrene-based radical polymer converted the SWCNT thin films from ones that were unipolar p-type materials to a system that allowed for both hole and electron transport (i.e., ambipolar behavior was observed) when the thin films were incorporated into organic field-effect transistor (OFET) test bed devices. In these ambipolar systems, the hole mobility and electron mobility values were determined to be 0.07 and 0.24 cm2 V–1 s–1, respectively. A combination of ultraviolet–visible–near-infrared (UV–vis–NIR) light absorption and Raman spectroscopy revealed the means by which this doping occurred. This provides for a foundational underpinning for the observed behavior, and this work also demonstrates a straightforward and scalable means by which to apply these functional open-shell macromolecules in flexible and printed electronic devices.

Ultrafast terahertz photoresponse of single and double-walled carbon nanotubes: Optical pump-terahertz probe spectroscopy

Photocarrier excitation in conventional semiconductors enhances the conductivity due to increased intraband absorption of terahertz (THz) radiation. We report frequency dependent photoconductivity in terahertz range after 800 nm optical pump excitation in (6,5) semiconducting single-walled carbon nanotubes (SWCNT) and double-walled carbon nanotubes (DWCNT) containing both metallic and semiconducting tubes. The real and imaginary parts of photoconductivity (Δσ(ω)) show non-Drude behavior. In SWCNT, the real part ΔσRe(ω) is positive for low frequency and negative on the high-frequency side of the terahertz spectra. In contrast, DWCNTs show negative ΔσRe(ω) on low frequency and positive on the high-frequency side. This contrasting behavior is explained using Boltzmann transport theory, where the carrier scattering rate is energy dependent. Taking the scattering rate to be dominated by short-range disorder scattering, we show that the Boltzmann transport model captures the unique experimental features of Δσ(ω), for SWCNT as well as DWCNT. Both the semiconducting and metallic nanotubes in DWCNT are shown to contribute to the observed photoconductivity.

Tiny nano-scale junction built on B/N doped single carbon nanotube

The characteristic sizes of carbon nanotube (CNT)-based devices are constantly being reduced. However, this continuing miniaturization is still facing many problems and requires innovative ideas and structures. By regular doping of boron and nitrogen atoms in a semiconducting single-wall carbon nanotube (SWCNT), we have constructed a nano-scale junction with rectifying characteristics. The I–V curve of our junction resembles the I–V curve of an ideal diode with a p-n junction. This junction channel is about 0.6 nm wide and 3.4 nm long, and the footprint is 5.1 nm long. Under a 0.5 V bias, the junction has a leakage current of −8.8 × 10−3 μA, a rectifying ratio Ion/Ioff of 0.716 × 103, and a current density of 10.52 mA μm−1. Our study also shows how different dopant distributions influence the I–V curve. Such a regular nano-scale doping method is effective and important, compared with the traditional random doping method.

Dopamine sensing by boron and nitrogen co-doped single-walled carbon nanotubes: A first-principles study

Dopamine (DA) is a catecholamine neurotransmitter that can cause some nervous system disorders, leading to Parkinson's disease. Thus, the development of a dopamine sensor is important for the diagnosis of these disorders. Here, we studied the adsorption of DA on semiconducting single-walled carbon nanotubes (SWNTs), including pure, and B,N co-doped (6,5) SWNTs, via DFT calculations. Our results indicated that DA can form multiple molecular interactions with pure (6,5) SWNT. However, these interactions have limited effects on the electronic properties; therefore, the band gap and conductivity of pure (6,5) SWNT did not change significantly after DA adsorption. On the other hand, regarding the adsorption of DA on a B,N co-doped (6,5) SWNT, we found that not only stronger molecular interactions such as C-H⋯π interactions were established but also an NDAB dative bond between DA and the SWNT was formed, altering the electronic properties of this SWNT. These cooperative interactions after DA adsorption caused much more pronounced changes in the band gaps and conductivities of B,N co-doped (6,5) SWNTs than in those of pure (6,5) SWNT. Our results demonstrated that the sensitivity of a pure (6,5) SWNT to detect dopamine was enhanced in the B,N co-doped (6,5) SWNT.