Single-walled Carbon Nanotube Films Research Articles

Effective doping of single-walled carbon nanotube films with bromine under ultrasound

Carbon nanomaterials such as graphene and carbon nanotubes (CNTs) have attracted considerable interest from the scientific community over the past decades. Due to the extraordinary properties they are envisioned to play a key role in a wide spectrum of applications in the upcoming future. An interesting property of carbon nanostructures is the sensitivity of their electronic properties to a range of chemical stimuli. Consequently, their capabilities for charge propagation may be significantly enhanced upon appropriate combination with a chemical compound, which can affect the Fermi level of the material. In this work, the impact of addition of bromine to single-walled CNT (SWCNT) films on their electrical and thermoelectric properties was investigated. The experimental results revealed that thermoelectric capabilities of the material may be enhanced by two orders of magnitude by sonication-assisted introduction of Br2 into a SWCNT network. Conducted computations unravelled how the dopant affects the electronic properties of the SWCNT host and its charge transport properties.

Understanding the solvent effects on polarity switching and thermoelectric properties changing of solution-processable n-type single-walled carbon nanotube films

Developing high performance solution-processable n-type thermoelectric materials is challenging. In this paper, we report that single-walled carbon nanotubes (SWCNTs) prepared in dimethyl sulfoxide (DMSO) (SWCNTs/DMSO) exhibit a high n-type electrical conductivity of 2298 S/cm at room temperature, which is superior to that of previously reported n-type solution-processable SWCNTs. The maximum n-type electrical conductivity was 3490 S/cm at 373 K. The great electrical conductivity results in a high n-type power factor of 195 μW/m-K2 for SWCNTs/DMSO films at 373 K which is larger than most of the n-type solution-processable SWCNTs. The theoretical calculation indicates that the wrapping morphology of the surfactant on SWCNTs is strongly affected by different solvent polarities which lead to different packing densities of the SWCNT films as demonstrated in the scanning electron microscope images, subsequently affecting the n-type doping efficiency and the n-type electrical conductivity. The electrical conductivity affected by the mixed p- and n-type carriers in the film were discussed. A full SWCNT thermoelectric generator has been fabricated to show the heat-to-electricity conversion ability of the materials. This work reveals a potential method to prepare highly conductive n-type SWCNTs by choosing the proper solvent for optimized thermoelectric performance.

Single‐Walled Carbon Nanotube Thin Film for Flexible and Highly Responsive Perovskite Photodetector

AbstractMetal–halide perovskites have recently shown tremendous progress in flexible photodetector applications owing to their great optical and electronic properties. However, apart from charge generating material, the high performance device requires a reasonable choice of electrodes for efficient carrier management as well. For example, the widespread use of gold and silver electrodes often results in perovskite device degradation while being expensive. Here, low‐cost and chemically inert single‐walled carbon nanotube (SWCNT) thin films are employed as electrodes to create highly responsive and flexible photodetector based on cesium lead tribromide (CsPbBr3) microcrystals. Direct growth of the perovskite on SWCNT forms excellent contact between the components leading to the state‐of‐the‐art responsivity for flexible perovskite photodetectors 1321 A W−1 at 5 V and under illumination intensity 1 mW cm−2 at 505 nm wavelength. The advanced properties of SWCNT films realized on a flexible substrate allow for robust operation over 104 cycles of device bending along with all parameters stability at ambient conditions for at least 1.5 months. The proposed design reveals the potential of SWCNT thin film electrodes for high performance perovskite flexible devices.

Tunable photo-patterning of organic color-centers

Organic color-centers (OCCs) in single-walled carbon nanotubes (SWCNTs) have been intensively investigated for quantum technologies, bio- and chemical sensing, bioimaging. The precise localization of OCCs at a scalable manner will bring about a revolution into next generation optoelectronics, which, however, remains a great challenge till now. Here, a scalable, low cost and universal photo-patterning strategy is developed to implant OCCs at desired locations on (6,5)-chirality SWCNT films by combining optically active diazonium chemistry and micro-contact printing methods. Notably, the patterns can be tunable by changing the solvents used for the patterning chemistry, affording control over the weight of diazonium salts at different regions. A systematic investigation reveals that the solvent properties (polarity and vapor pressure), the volume and concentration of ink used, the patterning methods, and the concentration of MeODz all contribute to the tunable patterning. This spatial accurate and solvent tunable photo-patterning technique is simple, scalable, and amenable to the integration of other color center chemistries and 2D transition metal dichalcogenides for the next-generation chip-integrated nanoelectronics and optoelectronics with high device uniformity and manipulability at molecular level.

Effect of a Silicon Oxide Substrate on the Electronic Properties and the Electrical Conductivity of Mono- and Bilayer Films of Armchair Single-Wall Carbon Nanotubes: a Quantum-Mechanical Study

Effect of a Silicon Oxide Substrate on the Electronic Properties and the Electrical Conductivity of Mono- and Bilayer Films of Armchair Single-Wall Carbon Nanotubes: a Quantum-Mechanical Study

Saturable absorption and nonlinear refraction in free-standing carbon nanotube film: Theory and experiment

The nonlinear absorption and refraction of free-standing films made of single-walled carbon nanotubes (SWNTs) have been investigated experimentally and theoretically. By solving the quantum kinetic equations that take into account both the intra- and interband transitions, we obtain the analytical expression for the SWNT nonlinear conductivity. The nonlinear absorption coefficient and saturation intensity of the film comprising randomly orientated SWNTs have been calculated in a broad spectral range spanning over M11, S11, and S22 absorption bands. The effects of the laser pulse duration and dynamic Burstein−Moss shift on the saturation intensity have been revealed. We demonstrate in the experiment that, under irradiation with femtosecond laser pulses, the absorption modulation depth of SWNT film at resonance wavelength 1375 nm is as high as 30%. The observed saturation intensity minimum is red-shifted with respect to the absorption maximum due to the dynamic Burstein−Moss shift. The saturation intensity within the S22 band is 26−fold lower than that out of the band at 795 nm. The closed-aperture z-scan measurements reveal the negative nonlinear refractive index n2 = −3.1 × 10−12 cm2/W at 795 nm.

Revealing the effect of electrocatalytic performance boost during hydrogen evolution reaction on free-standing SWCNT film electrode

Large-scale sustainable hydrogen production by water electrolysis requires a highly active yet low-cost hydrogen evolution reaction (HER) electrocatalyst. Conductive carbon nanomaterials with high surface areas are promising candidates for this purpose. In this contribution, single-walled carbon nanotubes (SWCNTs) are assembled into free-standing films and directly used as HER electrodes. During the initial 20 h of electrocatalytic performance in galvanostatic conditions, the films undergo activation, which results in a gradual overpotential decrease to the value of 225 mV. Transient physicochemical properties of the films at various activation stages are characterized to reveal the material features responsible for the activity boost. Results indicate that partial oxidation of iron nanoparticles encapsulated in SWCNTs is the major contributor to the activity enhancement. Furthermore, besides high activity, the material, composed of only earth-abundant elements, possesses exceptional performance stability, with no activity loss for 200 h of galvanostatic performance at − 10 mA cm−2. In conclusion, the work presents the strategy of engineering a highly active HER electrode composed of widely available elements and provides new insights into the origins of electrocatalytic performance of SWCNT-based materials in alkaline HER.

Indentation behavior of suspended single-walled carbon nanotube films

Suspended thin film carbon nanotubes with suitable mechanical strength are in high demand for applications such as sensors, particle filters, or thermoacoustic speakers. However, researchers working on the production and development of applications for thin films have found difficulty in evaluating their mechanical strength. This research shows the nano-indentation behavior of thin (<26 nm thickness) single-walled carbon nanotube suspended films, to evaluate their mechanical strength. Indentation tests, scanning electron microscopy, and Raman, infrared, reflection spectroscopy showed that the high crystallinity of carbon nanotubes and film thickness uniformity are important for achieving high mechanical strength.

Flexible Perovskite CsPbBr3 Light Emitting Devices Integrated with GaP Nanowire Arrays in Highly Transparent and Durable Functionalized Silicones.

The architecture of transparent contacts is of utmost importance for creation of efficient flexible light-emitting devices (LEDs) and other deformable electronic devices. We successfully combined the newly synthesized transparent and durable silicone rubbers and the semiconductor materials with original fabrication methods to design LEDs and demonstrate their significant flexibility. We developed electrodes based on a composite GaP nanowire-phenylethyl-functionalized silicone rubber membrane, improved with single-walled carbon nanotube films for a hybrid poly(ethylene oxide)-metal-halide perovskite (CsPbBr3) flexible green LED. The proposed approach provides a novel platform for fabrication of flexible hybrid optoelectronic devices.

Red GaPAs/GaP Nanowire-Based Flexible Light-Emitting Diodes.

We demonstrate flexible red light-emitting diodes based on axial GaPAs/GaP heterostructured nanowires embedded in polydimethylsiloxane membranes with transparent electrodes involving single-walled carbon nanotubes. The GaPAs/GaP axial nanowire arrays were grown by molecular beam epitaxy, encapsulated into a polydimethylsiloxane film, and then released from the growth substrate. The fabricated free-standing membrane of light-emitting diodes with contacts of single-walled carbon nanotube films has the main electroluminescence line at 670 nm. Membrane-based light-emitting diodes (LEDs) were compared with GaPAs/GaP NW array LED devices processed directly on Si growth substrate revealing similar electroluminescence properties. Demonstrated membrane-based red LEDs are opening an avenue for flexible full color inorganic devices.

Air stability of n-type single-walled carbon nanotube films with anionic surfactants investigated using molecular dynamics

The semiconducting property and air-stability of n-type single-walled carbon nanotube (SWCNT) are important for manufacturing all-carbon thermoelectric generators. We fabricated n-type SWCNT films with different anionic surfactants via drop-casting followed by heat treatment. Among the surfactants used (sodium dodecyl sulfate (SDS), sodium cholate (SC), and sodium dodecylbenzene sulfonate (SDBS)), the SWCNT films with SDBS surfactants exhibited an n-type Seebeck coefficient for 35 days. Structural analyses of the films showed that the SWCNT bundles and SDBS surfactants were homogeneously mixed. To investigate the mechanism behind the air-stability of the n-type property in SWCNT films, molecular dynamics (MD) calculations were performed. The MD calculations revealed that the adsorbability of SDBS molecules to SWCNT was higher than that of the other surfactants, which was consistent with the results of structural analyses. The sodium atoms in the vicinity of the SWCNT surface were vital in imparting n-type properties to the SWCNT. The SWCNT films with SDBS surfactants exhibited n-type properties for a long period of time because the surfactant molecules homogeneously covered the SWCNT surface, which enhanced the transfer of electrons from the sodium atoms to the SWCNT. The findings will aid toward further improving the air-stability of n-type SWCNT films using new surfactants.

Rapid annealing and cooling induced surface cleaning of semiconducting carbon nanotubes for high-performance thin-film transistors

Semiconducting single-walled carbon nanotube (s-SWCNT) films require high-quality preparation and optimization for use in carbon-based electronic devices. Tremendous progress has been made in s-SWCNTs sorting technology with conjugated polymers to obtain high-purity s-SWCNT films. However, one drawback of this technology is residual polymer wrapping on s-SWCNT surfaces. These residual polymers have poor conductivity, impeding the charge transport between the nanotube-electrode and the nanotube-nanotube. To address this issue, a rapid annealing and cooling method was developed for cleaning the s-SWCNT films, which can thoroughly remove the wrapped polymers from the surfaces of s-SWCNTs, effectively reducing the contact resistance between the nanotube-metal electrode and the nanotube-nanotube. Our results show that thin-film transistors made of cleaned s-SWCNTs exhibited improved performance when compared with pristine s-SWCNT films rinsed with an organic solvent. The contact resistance between the s-SWCNTs and the electrode was reduced by 700%, while the on–state current density of the CNT-TFTs increased by nearly 600%. These results thus demonstrated the effectiveness of our developed method for removing polymers from the surfaces of s-SWCNTs, which is essential for the further development of carbon nanotube electronic devices and circuits.

Development of poly (methyl methacrylate)-supported transfer technique of single-wall carbon nanotube conductive films for flexible devices

We propose a transfer technique of single-wall carbon nanotube (SWCNT) films to be applied to a wide variety of flexible electronic devices. SWCNT films were first heat-treated in advance to remove solvents and dispersants in the films on high heat-resistant Cu substrates and were then poly (methyl methacrylate)-supported transferred onto low heat-resistant polyethylene terephthalate and paper substrates. We characterized the flexibility and electrical properties of the films transferred by this technique. The transferred films showed high flexibility and high electrical conductivity (8.4 × 104 ∼ 1.1 × 105 S/m). X-ray photoelectron spectroscopy measurements revealed that the transferred films were free from Fe residues. Although a slight amount of the Cu residues existed, it was found that the residues did not contributed to the electrical conduction. By using this technique, we enabled to fabricate highly flexible and highly electrical conductive SWCNT films on flexible substrates with low heat resistance, which provide further potential for the application of these films to flexible electronic devices.

In Silico Study of the Influence of Various Substrates on the Electronic Properties and Electrical Conductivity of Mono- and Bilayer Films of Armchair Single-Walled Carbon Nanotubes

We investigate electronic and electro-physical properties of mono- and bilayer armchair single-walled carbon nanotube (SWCNT) films located on substrates of different types, including substrates in the form of crystalline silicon dioxide (SiO2) films with P42/mnm and P3121 space symmetry groups. The SWCNT films interact with substrate only by van der Waals forces. The densities of electronic states (DOS) and the electron transmission functions are calculated for SWCNT films with various substrates. The electrical conductivity of SWCNT films is calculated based on the electron transmission function. It is found that the substrate plays an important role in the formation of DOS of the SWCNT films, and the surface topology determines the degree and nature of the mutual influence of the nanotube and the substrate. It is shown that the substrate affects the electronic properties of monolayer films, changing the electrical resistance value from 2% to 17%. However, the substrate has practically no effect on the electrical conductivity and resistance of the bilayer film in both directions of current transfer. In this case, the values of the resistances of the bilayer film in both directions of current transfer approach the value of ~6.4 kΩ, which is the lowest for individual SWCNT.

Carbon Nanotube Far Infrared Detectors with High Responsivity and Superior Polarization Selectivity Based on Engineered Optical Antennas.

Single-wall carbon nanotube (SWCNT) thin films are promising for sensitive uncooled infrared detection based on the photothermoelectric effect. The SWCNT film is usually shaped into a belt and diversely doped to form a p-n junction at the center. Under the illumination of a focused incident light, the temperature gradient from the junction to the contacts leads to photoresponse. When the SWCNTs are aligned in one direction, the photoresponse becomes polarization selective. Although a typical bowtie antenna can improve the responsivity and polarization extinction ratio by deep-subwavelength light focusing, the absolute absorptance of the junction region is only 0.6%. In this work, the antenna was engineered for a higher light coupling efficiency. By integrating a bottom metal plane at a specific distance from the SWCNT film and optimizing the antenna geometries, we achieved ultra-efficient impedance matching between the antenna and the SWCNTs, thus the absorptance of the junction region was further enhanced by 21.3 times and reached 13.5%, which is more than 3 orders of magnitude higher than that of the device without the engineered antenna. The peak responsivity was further enhanced by 19.9 times and responsivity reached 1500 V/W at 1 THz. The resonant frequency can be tuned by changing the size of the antenna. Over the frequency range of 0.5 THz to 1.5 THz, the peak responsivity was further enhanced by 8.1 to 19.9 times, and the polarization extinction ratio was enhanced by 2.7 to 22.3 times. The highest polarization extinction ratio reached 3.04 × 105 at 0.5 THz. The results are based on the numerical simulations of the light and the thermal fields.

탄소나노튜브 대면적 어셈블리를 통한 고감도-고선택성 과산화수소 센서 개발

탄소나노튜브 대면적 어셈블리를 통한 고감도-고선택성 과산화수소 센서 개발

Self-optimizing iron phosphorus oxide for stable hydrogen evolution at high current

Electrocatalytic water splitting have demonstrated an established methodology to generate hydrogen of high purity, attracting lots of attention from industry. However, deficient supplies or poor electrochemical stability of catalysts contributes to unsatisfactory electrocatalytic hydrogen production, particularly while maintaining high current densities. Herein, we develop a robust catalyst by directly phosphating raw single-walled carbon nanotube films which can be self-optimized into O-FePx-SWCNT, P-Fe2O3-SWCNT or P-FeOOH-SWCNT catalysts, depending on the selected electrolytes with different pH values. The electrochemical measurements reveal the excellent electrocatalytic performance of catalytic films in a wide pH range. Notably, there is no observable degradation, even following one-week of continuous electrolysis process, which reached an elevated current density of 125 mA/cm2 at neutral conditions. In order to manifest its cogent applications, the catalyst is employed to stably electrolyze lake water, further indicating potential hydrogen production in inland areas. Our work confirms the feasibility of using structural self-optimization engineering to develop desirable electrocatalysts, providing flexible catalytic films for practical applications and answering the long-standing controversial question about active sites based on X-ray absorption fine structure (XAFS), operando synchrotron radiation Fourier transform infrared (SR-FTIR) spectroscopy and theoretical calculations, which will significantly contribute to the advancement of HER-related basic and applied research.

Band structure dependent electronic localization in macroscopic films of single-chirality single-wall carbon nanotubes

Significant understanding has been achieved over the last few decades regarding chirality-dependent properties of single-wall carbon nanotubes (SWCNTs), primarily through single-tube studies. However, macroscopic manifestations of chirality dependence have been limited, especially in electronic transport, despite the fact that such distinct behaviors are needed for many applications of SWCNT-based devices. In addition, developing reliable transport theory is challenging since a description of localization phenomena in an assembly of nanoobjects requires precise knowledge of disorder on multiple spatial scales, particularly if the ensemble is heterogeneous. Here, we report an observation of pronounced chirality-dependent electronic localization in temperature and magnetic field dependent conductivity measurements on macroscopic films of single-chirality SWCNTs. The samples included large-gap semiconducting (6,5) and (10,3) films, narrow-gap semiconducting (7,4) and (8,5) films, and armchair metallic (6,6) films. Experimental data and theoretical calculations revealed Mott variable-range-hopping dominated transport in all samples, while localization lengths fall into three distinct categories depending on their band gaps. Armchair films have the largest localization length. Our detailed analyses on electronic transport properties of single-chirality SWCNT films provide significant new insight into electronic transport in ensembles of nanoobjects, offering foundations for designing and deploying macroscopic SWCNT solid-state devices.

Sensing Organophosphorus Compounds with SWCNT Films.

Promising electrical properties of single-walled carbon nanotubes (SWCNTs) open a spectrum of applications for this material. As the SWCNT electronic characteristics respond well to the presence of various analytes, this makes them highly sensitive sensors. In this contribution, selected organophosphorus compounds were detected by studying their impact on the electronic properties of the nanocarbon network. The goal was to untangle the n-doping mechanism behind the beneficial effect of organic phosphine derivatives on the electrical conductivity of SWCNT networks. The highest sensitivity was obtained in the case of the application of 1,6-Bis(diphenylphoshpino)hexane. Consequently, free-standing SWCNT films experienced a four-fold improvement to the electrical conductivity from 272 ± 21 to 1010 ± 44 S/cm and an order of magnitude increase in the power factor. This was ascribed to the beneficial action of electron-rich phenyl moieties linked with a long alkyl chain, making the dopant interact well with SWCNTs.

Specular Reflectometry Studies of Alcohol-Induced Densification for Thin Films of Single-Walled Carbon Nanotubes

Specular Reflectometry Studies of Alcohol-Induced Densification for Thin Films of Single-Walled Carbon Nanotubes