Nanotube Thin Films Research Articles

A comprehensive study of spray coating technique parameters and chemical postdeposition treatments for transparent conducting SWCNT thin films

The demands for transparent conducting films (TCFs) are continuously increasing and the future of this industry is going toward large scale, cheap and mechanically stable electronics. This study shows a simple way to fabricate low-cost transparent conductive single-walled carbon nanotube (SWCNT) thin films by spray coating. The work employed here demonstrates that it is possible to fabricate highly efficient SWCNT TCFs without the use of expensive ultrasonic spray coating equipment. Highly conductive TCFs were prepared by dispersing SWCNTs in an N-Methyl-2-pyrrolidone (NMP) solution. The spray coated TCF properties were studied by the effect of spray gun carrier gas pressure, concentration, and volume sprayed onto the substrates. The prepared thin films were subjected to post treatments with nitric acid (HNO3) using different treatment methods and times in order to improve the electrical conductivity. To further investigate the effect of p-doping in SWCNT thin films, HNO3 treatments were combined with thionyl chloride (SOCl2). The experimental results indicated that spray coating is an effective method to obtain highly conductive films without any chemical treatment, resulting in 273 Ω/sq sheet resistance, at 84% in the visible range. Additionally, the optimized films treated with both HNO3 and HNO3/SOCl2 showed great improvements at 83%–85% in the visible range and in sheet resistances followed by 98 and 103 Ω/sq with very good FOM values (1.6 × 10−3 and 2 × 10−3, respectively).

Engineering microcracks in MWCNT/elastomer bilayers for high-performance stretchable sensor development

Stretchable strain sensors in motion detection, health monitoring, and human-machine interfaces are limited by device sensitivity, linearity, hysteresis, stability, and reproducibility in addition to stretchability. Engineering defect structures in sensing material is an effective approach in modulating the material's physical properties, particularly those associated with mechanical responses. Here, we demonstrate that bilayers of carbon nanotubes deposited on an elastomer substrate are mechanically coupled. The microcrack size, density, and distribution in the nanotube thin film can be engineered through uniaxial tensile training to exhibit highly tunable and stable piezoresistive responses with sensitivity, linearity, range, and reproducibility. These responses far exceeding those in uniform metallic films, patterned structures, and composites. In addition, numerical analyses performed on a two-dimensional network model of the cracked nanotube film provide quantitative explanations of how crack configuration, and evolvement under strain, lead to the significant enhancements in stretchable sensor performance using current bilayer structures.

Fabrication and research of bi-functional CuNi2S4 nanosheets decorated TiO2/CuNi2S4 heterojunction photoanode for photoelectrochemical water splitting

As a traditional n-type semiconductor, TiO2 has good UV absorption ability and stable physical and chemical properties. However, its wide band gap and low oxygen evolution reaction (OER) activity limit its application in the field of photoelectrochemical (PEC) water splitting. In this work, a type-II TiO2/CuNi2S4 heterojunction photoanode is successfully constructed, which expanded the light absorption range to visible and enhanced the OER activity. Firstly, TiO2 nanotubes (NTs) thin films are prepared on Ti substrates by two-step anodization, and then the bi-functional electrocatalytic material CuNi2S4 is grown on TiO2 NTs in the shape of nanosheets (NSs) in situ by solvothermal method. As a bi-functional electrocatalytic material, CuNi2S4 has good visible light absorption property as well as OER catalytic activity. Compared with TiO2, the IPCE value of TiO2/CuNi2S4 is 2.59% at 635 nm, and that of TiO2 is a mere 0.002%. The separation efficiency and injection efficiency increase from 2.49% and 31.52% to 3.61% and 87.77%, respectively. At 1.23 V vs. RHE, the maximum photocurrent density is 0.26 mA/cm2, which is 2.6 times than that of TiO2 (0.11 mA/cm2), and can be maintained at 0.25 mA/cm2 for at least 2 h under light illumination. Moreover, a hydrogen production rate of 4.21 μmol⋅cm−2⋅h−1 is achieved within 2 h. This work provides a new idea for the application of TiO2 in the field of PEC water splitting and the construction of efficient and stable photoelectronic devices.

Effect of anti-reflecting layers on device performance of SWCNTs/Si hetero-junction hybrid solar cells

Single wall carbon nano-tubes/Silicon (SWCNTs-Si) solar cells have the ability of being an ideal substitute to the expensive crystalline based Silicon solar cells because of promising cell efficiency and cost effectiveness. Single wall carbon nanotubes (SWCNTs) thin films are deposited on n-type silicon substrate to obtain heterojunction solar cells. To enhance the performance of these heterojunction solar cells Molybdenum Oxide and Tin Chloride are deposited on SWCNTs/Si substrates respectively. It has been confirmed from Raman spectroscopy that the doping of MoOx has enhanced p type behaviour of SWCNTs, MoOx layer acts as an anti-reflection layer and protects the n-Si and SWCNTs interface from deposition of oxides. While on the other hand SnCl2 acts as antireflection layer, enhances p-type doping of SWCNTs and suppression of recombination. Three hybrid heterojunction solar cells were fabricated by using MoOx on SWCNTs/Si, SnCl2 on SWCNTs/Si and both MoOx and SnCl2 on SWCNTs/Si, respectively. For structural analysis we have performed X-Ray diffraction (XRD) and Raman analysis. Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) are performed for surface analysis which confirms the smooth protected layers of MoOx and SnCl2; furthermore confirmed the presence of deposited metal oxide MoOx and SnCl2. Optical properties such as reflectance of thin films studies by UV visible spectroscopy. Maximum efficiency of 8.2% has been obtained by using both MoOx and SnCl2 on SWCNTs/Si solar cell.

Controlled Formation of Honey Carbon Nanotube Thin Films by Tailoring the Ratio of Admixture Concentration and Annealing Time.

Controlled Formation of Honey Carbon Nanotube Thin Films by Tailoring the Ratio of Admixture Concentration and Annealing Time.

Single-Walled Carbon Nanotube (SWCNT) thin films via automatic spray coating and nitric acid vapor treatment

In the realm of optoelectronics to produce thin film, SWCNT (Single-Walled Carbon Nanotube) is a promising alternative to Indium Tin Oxide (ITO). However, it is still challenging to manufacture SWCNT thin film that is low-cost, homogenous and has minimal sheet resistance. In this work, SWCNT thin films were deposited by using the automated spray coating method. To enhance the film quality and optoelectronic characteristics, post-deposition treatment through nitric acid vapor was carried out. The optimized SWCNT thin films exhibited optical transparency in the range of 60.4% at 800 nm and sheet resistance of 6.6 Ω/square. The sheet resistance of our fabricated SWCNT thin films was lower than the value of ITO films (10 Ω/square), putting forth evidence which suggests the potential of SWCNTs as an alternative to ITO.

P‐153: Late‐News Poster: Temporal Photo‐Response Analysis of Inkjet‐Printed Transparent Single‐Walled Carbon Nanotube Thin‐Film Transistors

We demonstrated the temporal photo‐response of transparent and flexible carbon nanotube thin‐film transistors. Fabricated carbon nanotube thin film transistors showed exponential degradation with light illumination and linear recovery after light off. The result indicates that the principal mechanism of photo‐response in carbon nanotube transistors is photo‐desorption of oxygen molecules.

Mixed Ionic‐Electronic Conduction Enables Halide‐Perovskite Electroluminescent Photodetector

AbstractLight emission and detection are the two fundamental features of optoelectronic communication systems. Until now, both functions have been realized with a p–n diode, which is used in a wide range of applications. However, due to the competing dynamics of carrier injection and photocarrier collection, in such devices, electroluminescence and photodetection are realized separately by switching the direction of the applied electrical bias. Here, mobile ions in halide perovskites are benefited from to demonstrate electroluminescence and photodetection simultaneously, without switching the direction of the applied electrical bias. The electroluminescent photodetector consists of a CsPbBr3 microwire integrated with electrodes made of a single‐walled carbon nanotube thin film, providing Schottky barriers at the interfaces. The dual functionality stems from the modulation of these barriers by mobile ions in cooperation with photogenerated charge carriers. Furthermore, such complex charge dynamics additionally result in a novel effect: light‐enhanced electroluminescence. The new optoelectronic phenomena demonstrated in the simple lateral device design will expand the applications of mixed ionic‐electronic conductors toward cheap and efficient multifunctional optoelectronic devices able to simultaneously generate and receive optical data.

Towards sustainable transparent flexible heaters: Integration of a BNNT interlayer using green solvent substitution

Processing materials in electronics with non-toxic, green solvents can provide environmental benefits while reducing manufacturing health and safety challenges. Unfortunately, green solvents are often unable to provide comparable solubilizing characteristics and present challenges in printing and film formation compared to conventional organic solvents. Therefore, green materials are often developed in parallel to their processing method for successful implementation. In this study, we report on the use of a polyvinyl butyral (PVB) and ethanol solution as a replacement for poly (3-hexylthiophene-2,5-diyl) (P3HT) and chloroform and its’ first demonstration in boron nitride nanotube (BNNT) thin film interlayers for improved thermal and mechanical performance in silver microgrid transparent heaters. Using PVB/ethanol led to comparable thin films of BNNT, achieving a clear tube network formation across the substrate surface and resulting in near identical optical transparency and surface energy measurements compared to the P3HT/chloroform system. Silver microgrids printed on BNNT-coated polyethylene terephthalate (PET) with PVB as dispersant exhibited a similar conductive performance to the microgrids printed on BNNT-coated PET with P3HT, providing the same level of mechanical endurance and maintaining thermal performance metrics upon applied voltage. The PVB and ethanol system presents an exemplary green material combination for the novel deposition of BNNT thin film interlayers for integration into transparent heaters.

Near‐Intrinsic Photo‐ and Electroluminescence from Single‐Walled Carbon Nanotube Thin Films on BCB‐Passivated Surfaces

AbstractTheir outstanding electrical and optical properties make semiconducting single‐walled carbon nanotubes (SWCNTs) highly suitable for charge transport and emissive layers in near‐infrared optoelectronic devices. However, the luminescence spectra of SWCNT thin films on commonly used glass and Si/SiO2 substrates are often compromised by broadening of the main excitonic emission and unwanted low‐energy sidebands. Surface passivation with a commercially available, low dielectric constant, cross‐linked bis‐benzocyclobutene‐based polymer (BCB) enhances the emission properties of SWCNTs to the same level as hexagonal boron nitride (h‐BN) flakes do. The presence of BCB suppresses sideband emission, especially from the Y1 band, which is attributed to defects introduced by the interaction of the nanotube lattice with oxygen‐containing terminal groups of the substrate surface. The facile and reproducible deposition of homogeneous BCB films over large areas combined with their resistance against common solvents and chemicals employed during photolithography make them compatible with standard semiconductor device fabrication. Utilizing this approach, light‐emitting (6,5) SWCNT network field‐effect transistors are fabricated on BCB‐treated glass substrates with excellent electrical characteristics and near‐intrinsic electroluminescence. Hence, passivation with BCB is proposed as a standard treatment for substrates used for spectroscopic investigations of and optoelectronic devices with SWCNTs and other low‐dimensional emitters.

Effects of Mode of Preparation of Titanium Dioxide Nanotube Arrays on Their Photocatalytic Properties: Application to p-Nitroaniline Degradation

The aim of this study was to investigate the photoactivity of dioxide titanium (TiO2) nanotube films depending on different structure factors including pore size, tube length, tube wall thickness and crystallinity. Aqueous p-nitroaniline was used as a probe to assess the photocatalytic activity of titanium dioxide nanotube layers under UV irradiations. Self-organized titanium dioxide nanotube thin films were prepared by electrochemical anodization of titanium (Ti) foils and Ti thin films sputtered onto silicon (Si). The amorphous as-formed titanium nanotube layers were then annealed at different temperatures ranging from 450 to 900 °C in order to form crystalline phases. The structure and the morphology of the films were characterized by surface analysis techniques and scanning electron microscopy, respectively. The photocatalytic activity of the resulting TiO2 thin films was evaluated by monitoring the UV degradation of p-nitroaniline by UV spectrophotometry and by determining nitrification yields of by ion chromatography. The highest photocatalytic activity was exhibited for titanium nanotubes annealed at 450 °C. The presence of rutile -obtained for an annealing temperature of 900 °C—appeared to reduce the photodegradation yield of p-nitroaniline. Finally, the TiO2 nanotubes obtained from Ti foils revealed the most efficient photocatalytic properties.

Acid-modified CNT/Zinc Oxide nanowires based high performance broadband photodetector

In this study, the authors have reported the impact of post-treatment via exposure to acid on single walled carbon nanotubes (SWNTs) thin film (TF) based SWNT/ZnO Nanowire (NW) broad band photodetector. The ZnO NWs were deposited on SWNT (with and without acid-treated) using a simple catalytic free process called glancing angle deposition (GLAD) technique. Acid-treated SWNT samples warranted the growth of high quality ZnO NWs over them. On fabricating photodetectors with the acid-treated ZnO NW/SWNT TF heterostructure (HS) gave better device performance as compared to the as-deposited ZnO NW/SWNT TF HS (without acid-treatment) sample. The acid-treated device showed a large responsivity (85.45 A/W), specific detectivity (0.859 × 1012 Jones) and with a low noise equivalent power of 3.9101 pW values. Moreover, the oxygen adsorption–desorption mechanism in SWNTs impacted the electrical resistance of the nanotubes which affected nanotube conductivity. The acid-treatment favoured relatively faster charge separation at the ZnO NW/SWNT heterojunction thus providing a fast device response (trise = 0.11 s, tfall = 0.39 s at + 5 V). The fabricated acid-treated device showed good broad band detection (250 nm-750 nm) which was explained with respect to the optical absorption profile of the sample.

Fully solution-processed carbon nanotubes thin film transistors and PMOS inverters on glass substrate

We report fully solution-processed thin film transistors and PMOS inverters fabricated on glass substrates using single-walled carbon nanotubes (SWCNTs) as active semiconducting material. All the electrodes (gate, source, and drain) were inkjet-printed using silver (Ag) as conductive ink. Spin coated poly-4-vinylphenol dielectric was optimized in terms of thickness and heating conditions for solution-processed SWCNTs thin film transistors to achieve a mobility equal to 0.81 cm2 V−1s−1. We will show that, hole traps at the dielectric-semiconductor interface are responsible for the hysteresis in the transfer curve, and controlled by the different sweep rate of the gate field. Drain-current transients under different bias conditions were studied and the increase in current occurs due to slow polarizations of residual dipolar groups in the dielectric. The adopted technology has been exploited to fabricate a PMOS inverter and studied for high gain and noise margin values at the supply voltage, V DD = −40 V.

Study of gate induced sensitivity amplification in carbon nanotube thin film transistor based ammonia sensor

Gas sensors based on carbon nanotube thin film transistors (CNT TFT) have been widely investigated in the past. However, studies on the active sensing properties i.e. effects of gate induced variations in sensing of such devices are deficient. In this work the effects of gate voltage on the ammonia sensing properties of a single wall CNT TFT are investigated. It is observed that under the influence of a gate field, the device sensitivity and detection limit (LOD) can be improved by more than 11 and 6 times respectively. The amplification of sensor response is found to occur for both the gate polarities and this is attributed to a combination of two phenomena. Firstly, ab-initio Molecular dynamics (MD) based adsorption studies of ammonia molecules to a CNT device indicate that the introduction of a gate field leads to an increase in the adsorption energy of ammonia to the device especially for a positive gate which is directly relatable to the observed amplification in sensing. Additionally, in the negative gate regime, a reversible increase of the contact resistance induced by ammonia exposure is thought to be the primary contributing factor in increasing the responsivity of the sensor. This is also thought to contribute to improving the sensor selectivity at negative gate.

Single-walled carbon nanotube (SWCNT) thin film for optoelectronics device prepared by spray coating technique.

CNT is a novel material with exceptional properties. SWCNT thin films have been used in many different applications. To fabricate the SWCNT film, various methodologies have been introduced, however, the problem of fabricating uniform SWCNT thin film remains unsolved. Spray coating technique (SCT) is the most effective method for producing a uniform SWCNT thin film. The CNT thin films were deposited on glass substrates via SCT with different nozzle distances (from 2.5 cm to 12.5 cm). The morphological, topological, electrical and optical properties of CNT thin films were characterized using appropriate techniques. The electrical analysis depicted that the sheet resistance of thin films reduced from 40220 Ω/sq. to 1330 Ω/sq. as the spray nozzle distance was increased from 2.5 cm to 10 cm sheet resistance reached 2133 Ω/sq. for 12.5 cm which confirmed the concentration of CNT was highest at 10 cm nozzle distance. The optical analysis of the CNT thin films gave transmittance values in percentage of 64%, 60%, 52%, 43%, and 46%, respectively for the nozzle distance of 2.5 cm, 5 cm, 7.5 cm, 10 cm, and 12.5 cm. Transmittance percentage decreased from 2.5 cm to 10 cm nozzle distance, indicative of an uniform film coverage of CNT layer. The findings of this study could be a platform for producing an optimized CNT thin film using a SCT for optoelectronic devices.

Tunable THz flat zone plate based on stretchable single-walled carbon nanotube thin film

Tunable optoelectronics have attracted a lot of attention in recent years because of their variety of applications in next-generation devices. Among the potential uses for tuning optical elements, those allowing consistent parameter control stand out. We present an approach for the creation of mechanically tunable zone plate lenses in the THz range. Our devices comprise single-walled carbon nanotube (SWCNT) thin films of predetermined design integrated with stretchable polymer films. These offer high-performance and in situ tunability of focal length up to 50%. We studied the focusing properties of our lenses using the backward-wave oscillator THz imaging technique, supported by numerical simulations based on the finite element frequency domain method. Our approach may further enable the integration of SWCNT films into photonic and optoelectronic applications and could be of use for the creation of a variety of flexible and stretchable THz optical elements.

Ultrafast Optomechanical Terahertz Modulators Based on Stretchable Carbon Nanotube Thin Films

For terahertz wave applications, tunable and rapid modulation is highly required. When studied by means of optical pump–terahertz probe spectroscopy, single-walled carbon nanotube (SWCNT) thin films demonstrated ultrafast carrier recombination lifetimes with a high relative change in the signal under optical excitation, making them promising candidates for high-speed modulators. Here, combination of SWCNT thin films and stretchable substrates facilitated studies of the SWCNT mechanical properties under strain and enabled the development of a new type of an optomechanical modulator. By applying a certain strain to the SWCNT films, the effective sheet conductance and therefore modulation depth can be fine-tuned to optimize the designed modulator. Modulators exhibited a photoconductivity change of approximately 2 times of magnitude under the strain because of the structural modification in the SWCNT network. Stretching was used to control the terahertz signal with a modulation depth of around 100% without strain and 65% at a high strain operation of 40%. The sensitivity of modulators to beam polarization is also shown, which might also come in handy for the design of a stretchable polarizer. Our results give a fundamental grounding for the design of high-sensitivity stretchable devices based on SWCNT films.

An interfacial toughening strategy for high stability 2D/3D perovskite X-ray detectors with a carbon nanotube thin film electrode.

Single-crystalline metal halide perovskite materials hold great promise for developing next-generation low-dose X-ray detection. To bring this new technology into reality, it is important to improve the durability of perovksite detectors by suppressing the well-known corrosion and ion diffusion problems at the perovskite/electrode interface. For imaging application, it is also imperative to develop new assembling approaches to realise non-planar interconnection between thick perovskite crystals and thin-film transistor (TFT) backplanes. Herein, a flexible and mechanically robust carbon nanotube (CNT) film was proposed to replace noble metal electrodes. The proposed CNT film, whose binder contains a carboxyl group, can form solid contact with a phenethylamine-based two-dimensional (2D) perovskite via amide coupling, thus toughening the perovskite-electrode interface. The resulting CNT/2D-3D perovskite detector shows an applaudable low dark current, high sensitivity, a low dose detection limit and excellent stability, retaining 98% of its initial sensitivity after storage for three months. Moreover, the flexible CNT films are also beneficial for making non-planar interconnection between thick perovskite crystals and TFT backplanes. The proposed flexible CNT thin film electrode thus provides a facile route towards realising a low-dose, high-resolution and highly stable perovskite X-ray detector.

Large area roll-to-roll printed semiconducting carbon nanotube thin films for flexible carbon-based electronics.

A universal roll-to-roll (R2R) printing approach was developed to construct large area (8 cm × 14 cm) semiconducting single-walled carbon nanotube (sc-SWCNT) thin films on flexible substrates (such as polyethylene terephthalate (PET), paper, and Al foils) at a printing speed of 8 m min-1 using highly concentrated sc-SWCNT inks and crosslinked poly-4-vinylphenol (c-PVP) as the adhesion layer. Bottom-gated and top-gated flexible printed p-type TFTs based on R2R printed sc-SWCNT thin films exhibited good electrical properties with a carrier mobility of ∼11.9 cm2 V-1 s-1, Ion/Ioff ratios of ∼106, small hysteresis, and a subthreshold swing (SS) of 70-80 mV dec-1 at low gate operating voltages (±1 V), and excellent mechanical flexibility. Furthermore, the flexible printed complementary metal oxide semiconductor (CMOS) inverters demonstrated rail-to-rail voltage output characteristics under an operating voltage as low as VDD = -0.2 V, a voltage gain of 10.8 at VDD = -0.8 V, and power consumption as low as 0.056 nW at VDD = -0.2 V. To the best of our knowledge, the electrical properties of the printed SWCNT TFTs (such as Ion/Ioff ratio, mobility, operating voltage, and mechanical flexibility) and printed CMOS inverters based on the R2R printed sc-SWCNT active layer in this work are excellent compared to those of R2R printed SWCNT TFTs reported in the literature. Consequently, the universal R2R printing method reported in this work could promote the development of fully printed low-cost, large-area, high-output, and flexible carbon-based electronics.

Areal Density Control of Liquid-Supported Carbon Nanotube Thin Films.

Carbon nanotube (CNT) films have extensive applications due to their excellent electrical, mechanical, and thermal properties. A grand challenge is controlling areal density of CNT films to accommodate various applications. Here, a method based on the Marangoni effect is used to fabricate liquid-supported CNT films with tunable areal density, scalable area, and transferability to arbitrary substrates. By adjusting the viscosity and surface tension of the base liquid media, the Marangoni flow area of surfactant-assisted single-walled CNT (SWCNT) dispersion on the surface of base media was controllable and sparse or dense SWCNT films can be easily obtained. The thickness of the films is controlled by changing the concentration of the SWCNT dispersion. These SWCNT-based transparent-conductive films have widely controllable transmittance and conductivity and exhibit great photoelectric properties (T ∼ 82.4%, Rs ∼ 407 Ω/sq).