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We demonstrate that the observed (in-)stability of n-doped carbon nanotube films in air not only depends on the employed dopant but is also strongly affected by sample-specific factors, such as the film thickness and density. We show this for two typical dopants, polyethylenimine and a potassium crown ether complex, by preparing films of increasing thickness. We argue that reports on dopant stability cannot be properly assessed without knowledge of these sample-specific parameters, which explains some of the conflicting results in the literature. [ABSTRACT FROM AUTHOR]

We demonstrate an optically tunable mode-locked fiber laser using long-period fiber grating (LPFG) coated with multi-walled carbon nanotubes (CNTs). The multi-walled CNTs can absorb light to convert it into thermal energy, and the resonance wavelength of the grating can be easily turned by varying the external modulated light power. This multi-walled CNT coated LPFG-based all-optical fast and efficient spectrum tunable filter enables continuous tuning of the central wavelength of the laser by manipulating the loss of the mode-locked laser, ensuring the stability of the mode-locking state. In the absence of modulated light on multi-walled CNTs, the soliton laser could generate 890 fs pulses at 1546.7 nm with a spectrum bandwidth of 3.26 nm and a signal-to-noise ratio of 73.1 dB. Through adjustment of the pump power of the modulation light on multi-walled CNTs, the mode-locked fiber laser can be continuously tuned from 1546.71 to 1563.15 nm. The response time of the optically tunable system was measured to be in the order of hundreds of milliseconds. The presented optical tuning filter shows great potential in the fiber laser system, offering a repeatable, straightforward, and rapidly responsive laser tuning technique. [ABSTRACT FROM AUTHOR]

Solid-state refrigeration technology has been attracting tremendous attention in recent decades. Plastic crystal pentaerythritol (PE) is a crucial barocaloric material in the solid-state refrigeration field due to its high entropy. However, its refrigeration temperature range and extremely low thermal conductivity are far from meeting the requirements of practical application. Here, we systematically investigate the barocaloric effect (BCE) of composite PE and silicon frame [consisting of silicon nanotube and silicene architectures (SNT-Sil)] and analyze the effects of different silicon models on the BCE performance based on molecular dynamics simulations and statistical analysis. A colossal BCE of PE/silicon frame composite is observed, and refrigeration temperature can be altered to the room temperature range by alloying neopentane (PA) into the PE matrix. It is found that the composite PE0.8PA0.2/SNT-Sil and PE0.9PA0.1/SNT-Sil demonstrate excellent comprehensive refrigeration performance near room temperature (300–320 K), with large isothermal entropy change ΔS (654–842 J kg−1 K−1), adiabatic temperature ΔT (34–47 K), and thermal conductivity κ (4.0–4.2 W m−1 K−1). The microscopic mechanism is discussed through pressure induced changes in bonding, structural, and vibrational properties. Importantly, the plastic crystal/silicon framework is easy to deform and requires smaller input work in the barocaloric refrigeration process compared to other nanomaterials such as carbon framework. This work provides important guidance on improving plastic crystals with colossal comprehensive refrigeration performance for practical applications. [ABSTRACT FROM AUTHOR]

Carbon nanotubes are promising candidates for thermoelectric power generation because of their one-dimensionality mediated high Seebeck coefficient, high electrical conductivity with added advantages of flexibility, light weight, and scalability. We report the temperature-dependent thermoelectric properties of single-walled carbon nanotube (SWCNTs) films. The SWCNTs films exhibit p-type metallic conduction with high Seebeck coefficient (∼69.5 μVK−1) and moderate electrical conductivity (∼76 Scm−1). The films exhibit low thermal conductivity (∼0.1 Wm−1 K−1) due to phonon scattering at the interjunction region. The synergetic combination of thermoelectric properties resulted in a high figure-of-merit of ∼0.11 at 305 K. A flexible thermoelectric generator based on SWCNTs films mounted on a curved hot surface exhibited an output of 17 mV and 54 μA under a small temperature gradient of 10 K. The present work provides possible avenues for developing wearable SWCNTs based thermoelectric power generation modules for harvesting body heat. [ABSTRACT FROM AUTHOR]

A self-supported CNT sponge is composed of uniformly twisted CNTs with high aspect ratio that enables the large specific surface area and good carrier conduction to go beyond the conventional carbon-based materials, shedding light on its high electrochemical activity in salt water. Herein, we demonstrate the comparable performance of the CNT sponge as the electrode pair to the most commonly used Ag/AgCl for sensing underwater electric fields. The CNT sponge electrodes exhibit a high electrochemical reactivity in salt water with a low noise of ∼10 nV/rt(Hz)@100 Hz within a wide range of the electric field frequency (e.g., 10–105 Hz), while the frequency response approaches a constant magnitude across the same range of frequency. The performance of the CNT sponge electrodes in ocean electric field sensing is further verified by measuring the electrical signal response curve at various characteristic frequencies within a small water container, and also under a simulated source within the water pool. The high chemical stability and low costs of carbon-based CNT sponges pave the way to their potential applications. [ABSTRACT FROM AUTHOR]

The ultrabroadband photodetectors are considered to hold significant potential for applications in optical sensing and communication. In this study, we report an ultrabroadband fiber-integrated optical power sensor (FOPS) based on the photothermal effect of multi-walled carbon nanotubes (MWCNTs). The device consists of two main components: the U-shaped fiber (UF) and the photosensitive unit (PSU), wherein the PSU is comprised of polydimethylsiloxane (PDMS) doped with MWCNTs. Under illumination, the photothermal effect of MWCNTs causes a thermal expansion of the PDMS, resulting in compression deformation of UF and transmission spectrum blueshift. Experimental results demonstrate that the proposed device achieves an optical photodetection ranging from 405 nm to 7.767 μm with a responsivity of 0.484 nm/mW. The response time exhibits a rising edge of 13 s and a falling edge of 7 s. Additionally, the device has integrated light motion tracking capability, achieving a displacement resolution of incident light as 1.25 nm/mm. As the proposed FOPS has advantages of ultrabroad detection band and high responsivity, it is a promising design for light detection. [ABSTRACT FROM AUTHOR]

Plastic crystals PE (pentaerythritol) possess colossal barocaloric effect (BCE) that is promising for solid-state refrigeration; however, the high phase transition temperature (> 400 K) and low thermal conductivity (<0.5 W·m−1·K−1) greatly hinder its practical application at room temperature. Here, we propose to complex plastic crystal (PC) with carbon nanotube/graphene architectures (CNT-Gra) to form [PC/CNT-Gra] composites and investigate the BCE based on molecular dynamics simulations. It is found that phase transition temperature of molecular order to disorder can be tuned by alloying PA (neopentane) or NPG (neopentyl glycol) into PE imbedded in CNT-Gra architectures. Importantly, we find that PE0.8PA0.2/CNT-Gra and PE0.75NPG0.25/CNT-Gra demonstrate both giant isothermal entropy changes ΔS (∼200 J·kg−1·K−1) and adiabatic temperature change ΔT (∼18 K) at room temperature. The large BCE mainly comes from the order–disorder transition of PC molecules imbedded in CNT-Gra architectures through analysis of the dynamic process of the composites. Importantly, the thermal conductivity of these campsites is as high as ∼10 W·m−1·K−1, enabling efficient thermal exchange that is vital for improving cooling performance of the cyclic refrigeration process. This work provides important insights for designing PC-based composites with optimized comprehensive cooling performance for potential room temperature refrigeration. [ABSTRACT FROM AUTHOR]

Crack-based flexible strain sensor generally shows significantly high sensitivity due to crack propagation induced conductive path reduction during stretching. To quantitatively analyze the relationship among strain, crack density, and device sensitivity, an electro-mechanical mathematical model is developed for investigating the performance of a carbon nanotube-silicon oxide/polydimethylsiloxane (CNT-SiOx/PDMS) based crack strain sensor. Strength and energy criteria are used to predict the crack density for SiOx/PDMS under different strains. The results are utilized with the probability distribution based cellular automata method to determine the crack distribution for further electrical analysis, which is related to the conductive and non-conductive classification of elements. Finally, the potential distribution for whole elements is calculated, leading to the investigation of sensitivity toward the CNT-SiOx/PDMS based strain sensor. The maximum predicted crack density of the SiOx/PDMS can reach 41.36 × 10−3 μm−1 under 60% tensile strain with a deviation of 5.23% compared to the experimental data. Correspondingly, the maximum predicted sensitivity of the device can reach 512.81 at a SiOx thickness of 3.93 μm, with the deviation of 9.25%. Based on the predicted results, it can be concluded that crack density affects the distribution and quantity of conductive elements. When stress is applied to the device, the crack density increases, and the conductive elements located in the crack area undergo a disconnection process, resulting a significant reduction in the conductive path and a rapid increase in sensitivity for strain sensor. [ABSTRACT FROM AUTHOR]

Robust, nanoscale light-emitting devices are attractive for emerging photonic and quantum engineering applications. However, conventional approaches suffer from fabrication challenges or lack the potential to address individual nanostructures, such as quantum dots. In this paper, we present a device that can produce electrically driven light emission from a single quantum dot using a single carbon nanotube as the charge injection contact. The device has a metal-oxide-semiconductor capacitor structure and operates based on an unconventional mechanism of electroluminescence, which relies on the use of bipolar voltage pulses. The proposed device can be fabricated in a simple manner using conventional lithographic processes, offering a scalable approach toward the development of optoelectronic devices at the single dot level. [ABSTRACT FROM AUTHOR]

Vanadium chalcogenides have been extensively studied owing to the diverse crystallographic structures with various stoichiometric ratios. The metal-to-insulator transition (MIT) widely reported in vanadium chalcogenides is a rapid reversible phase transition that requires small energy, demonstrating potential applications in memory devices. In this work, two-dimensional (2D) vanadium telluride (VTe2) nanosheets are prepared by the chemical vapor deposition method. The synthesized VTe2 nanosheets exhibit volatile threshold switching (TS) behaviors due to the MIT phase transition, which can be further confirmed by the temperature dependent TS behaviors. The TS memristor demonstrates good stability and high reliability with up to 1000 continuous and repeatable writing/erasing operations. Furthermore, based on the TS behaviors, the fabricated memristor can be utilized to implement basic Boolean logic operations of "OR," "AND," and "NOT." This study not only demonstrates the TS behaviors in the 2D VTe2 nanosheets owing to the MIT phase transition but also shows the potential applications of the TS devices in Boolean logic operations. [ABSTRACT FROM AUTHOR]

Achieving exceptional water-repellency and reliable reversible adhesion is crucial for the development of wearable flexible electronics. However, simultaneously achieving these properties presents a significant challenge, as water-repellency requires maximizing the presence of air while robust adhesion necessitates enhancing the solid fraction. In this study, we present a flexible and transparent conductive patch that addresses this challenge by offering simultaneous robust superhydrophobicity and strong adhesion in both dry and wet conditions. The device incorporates a unique combination of overhang micropillars, microgrids and a percolating network of carbon nanotubes. The proposed patch demonstrates outstanding water repellency with a contact angle exceeding 150°, while delivering impressive dry adhesion (>200 kPa) and wet adhesion (>150 kPa) performance. Furthermore, the device exhibits tunable electrical conductivity and optical transmittance. [ABSTRACT FROM AUTHOR]

In the digital era, novel smart materials require digital design with the more increasing demand on computational performance, the smaller scale we approach. Nanocomposites present an ultimate challenge, where the morphology of filler particles and their interactions with polymer have to be addressed. For carbon nanotube (CNT)-like particles, computational efficiency would increase multifold if we were able to replace these complex interactions with an equivalent 1D geometry. Unfortunately, for thermal analysis, it results in a singularity of infinite temperature. In this study, relying on undocumented yet possibilities in Abaqus software, we develop a technique to overcome the singularity and apply it to an aligned-CNT nanocomposite. Digital twin is populated with 3D particle morphology obtained by electron tomography, and numerical simulations demonstrate close reproducibility of experimentally measured values for homogenized thermal conductivity. [ABSTRACT FROM AUTHOR]

In this paper, we report a method to estimate the average length of bundles in a randomly oriented network of single-walled carbon nanotubes (SWCNTs) by analyzing the dependence of its sheet resistance on the distance between contacts. We propose an analytical model to verify the method and find the model's limitations using Monte Carlo simulations. Then, we apply the proposed approach to experimental results acquired from 95% (at 550 nm wavelength) transparent SWCNT films. The proposed method to estimate the average SWCNT bundle length can be used in situ and does not require any specific sample preparation step that can distort the SWCNT network. [ABSTRACT FROM AUTHOR]

Carbon nanotube films are a promising class of materials for bolometric photodetectors due to a unique combination of extremely thin (nm-sized) free-standing form factor with small thermal capacity and intriguing electronic and optical properties, thereby, ensuring high sensitivity and high speed of operation. Nevertheless, the key parameter for bolometric sensor material—the temperature coefficient of resistance (TCR)—is unacceptably low limiting the application of the carbon nanotube films. Here, we examine the plasma treatment of single-walled carbon nanotube (SWCNT) films as the effective method for the TCR enhancement. We study the effect of different plasma gases (oxygen, nitrogen, and hydrogen) on the conductivity of treated films. Also, we investigate the effect of defectiveness, length, and bundling degree of the SWCNTs on TCR. The optimized procedure allows to increase the TCR up to 1.7% K−1 by modulus at 100 K and to 0.8% K−1 at 300 K. The bolometer prototypes based on the plasma-treated SWCNT films demonstrate high sensitivity over a wide IR range (∼21 V/W), a short response time (∼1 ms), and low noise equivalent power (∼8 × 10−9 W Hz−1/2) at the temperature of 100 K. [ABSTRACT FROM AUTHOR]

Far-ultraviolet-C (UVC) light is an efficient and safe germicide because the wavelength band eradicates viruses but is harmless to human cells. In this study, electron-beam-pumped AlGaN emitters have been introduced as an alternative to far-UVC light emitting diodes which are limited by certain drawbacks, such as low conductivity and light absorption of the p-layer and side emission due to polarization at short wavelengths. We demonstrate a highly efficient far-UVC AlGaN emitter using a carbon nanotube-based cold cathode electron beam (C-beam). To maximize light emission, materials were grown via novel in situ lateral polarity engineering epitaxy. The C-beam enables the large-area emission of up to 528 mm2, and the maximum power conversion efficiency is 0.5% at 232 nm. [ABSTRACT FROM AUTHOR]

Nanostructured surfaces enhance ion yields in matrix-assisted laser desorption–ionization mass spectrometry (MALDI-MS). The spike protein complex, S1, is one fingerprint signature of Sars-CoV-2 with a mass of 75 kDa. Here, we show that MALDI-MS yields of Sars-CoV-2 spike protein ions in the 100 kDa range are enhanced 50-fold when the matrix–analyte solution is placed on substrates that are coated with a dense forest of multi-walled carbon nanotubes, compared to yields from uncoated substrates. Nanostructured substrates can support the development of mass spectrometry techniques for sensitive pathogen detection and environmental monitoring. [ABSTRACT FROM AUTHOR]

This paper demonstrates an elastic (i.e., both flexible and stretchable) pixel matrix based on the patterned films of single-walled carbon nanotubes, which were obtained using optical lithography and plasma etching. The proposed elastic electrodes maintain their initial resistivity at 10% stretching. We also demonstrate an application of the elastic pixel matrix to an array of III–V semiconductor nanowires encapsulated into the elastic polymer matrix, which paves the way for highly deformable inorganic light-emitting or photodetector devices. [ABSTRACT FROM AUTHOR]

Low temperature Carbon Nano-tubes (CNTs) growth technology is developed in this work with the insert of Al (Aluminum) between Ni (Nickel) and Ti (Titanium) as the reactant. The optimized Al thicknesses are also investigated. CNTs growth at the low temperature below 400 °C is the key factor for the back end of line compatible process integration. In this work, we grow the CNTs by thermal chemical vapor deposition process at 350 and 400 °C. The low ratio of peak ID/IG in Raman spectra and scanning electron microscope images proves the CNTs material quality. On the other hand, the high thermal conductivity (k) value of ∼50 W m − 1 K − 1 is also demonstrated. Both high material quality and k value on our low temperature grown CNTs show promising opportunities for the integration of semiconductor three dimensional packages and power-via related applications. [ABSTRACT FROM AUTHOR]

Plastic crystal neopentylglycol (NPG, C5H12O2) has become an important candidate material in the future solid-state refrigeration field due to its huge colossal barocaloric effects near room temperature. However, NPG encounters significant shortcomings in practical cooling process that hinders its further application. Here, we systematically investigate the effect of defects and substituting a small amount of additional alien molecules on the barocaloric performance of NPG plastic crystals. It is found that low concentration of defects and substitution moderately affect the isothermal entropy, adiabatic temperature, and thermal hysteresis of NPG. Importantly, the substituted carbon nanotubes significantly enhance the thermal conductivity by more than one order of magnitude, arising from structural-modification enhanced acoustic phonons. Using dimensionless variable, we define the comprehensive cooling performance that represents the most promising working materials for barocaloric refrigeration. The present work provides important guidance on improving the barocaloric performance of NPG as prototypical plastic crystals for practical cooling applications. [ABSTRACT FROM AUTHOR]

Laser-produced plasma sources of short-wavelength (1–20-nm) radiation are actively used nowadays in numerous applications, including water-window microscopy and extreme ultra-violet lithography. Suppression of laser-plasma debris (responsible for damaging optics) is crucial for the lifetime prolongation of optical systems operated with the short-wavelength radiation. Here, we examine the capability of single-walled carbon nanotube (SWCNT)-based membranes to decrease an InSn plasma flux containing both ions and atoms. Faraday cup measurements show that 40- and 90-nm-thick SWCNT membranes reduce the total charge transition by 20 and 130 times, respectively. The ion analyzer measurements demonstrate that ions pass through the membrane mainly due to the collisionless (ballistic) mechanism. Using scanning electron microscopy, we estimate a decrease in a plasma (ions + atoms) flux to be of 18 and 140 times for 40- and 90-nm-thick SWCNT-based membranes, respectively. The average plasma flux attenuation coefficient of SWCNT membranes is calculated as k = 0.063 nm − 1 . [ABSTRACT FROM AUTHOR]

Adding a functionalized interlayer is one of the effective means to solve the problem of capacity attenuation caused by the shuttle of polysulfides in lithium–sulfur (Li–S) batteries. Moreover, the interlayer has the potential to take on more roles, such as having good mechanical flexibility to ensure high safety and flame-retardant property to improve the high temperature performance of the battery. Thus, in this work, an MXene/Co3O4–CNT film interlayer that is capable of dual chemisorption to polysulfides with good mechanical strength and flame retardancy has been investigated. The resultant Li–S battery assembled with this interlayer exhibits a high discharge capacity of 1569.5 mA h g−1, an excellent charge–discharge stability over 600 cycles, and a high temperature stability of the electrochemical performance. [ABSTRACT FROM AUTHOR]

The output performance of triboelectric nanogenerators (TENGs) is fatally determined by the capacitive capability of triboelectric electrodes. One promising solution is embedding conductive fillers in triboelectric polymers, typically carbon nanotubes (CNTs) in polydimethylsiloxane (PDMS). Each CNT will serve as a capacitor in the PDMS matrix to store electric energy through polarization. However, the CNTs are easily cross-linked with each other, which makes the triboelectric materials conductive or semi-conductive. The output voltage will be limited due to current leaks through conducting or tunneling, and thus, suppress the energy harvesting efficiency of TENGs. Here, we propose to use an insulation layer to wrap CNTs to avoid direct-contact between CNTs and improve the overall performance of TENGs. Our results show that the leakage current has been significantly suppressed and the output performance of TENGs has been dramatically improved. This work provides a material design idea, which is expected to become a universal method to improve the output performance of TENGs. [ABSTRACT FROM AUTHOR]

We examine if the bundling of semiconducting carbon nanotubes (CNTs) can increase the transconductance and on-state current density of field effect transistors (FETs) made from arrays of aligned, polymer-wrapped CNTs. Arrays with packing density ranging from 20 to 50 bundles μm−1 are created via tangential flow interfacial self-assembly, and the transconductance and saturated on-state current density of FETs with either (i) strong ionic gel gates or (ii) weak 15 nm SiO2 back gates are measured vs the degree of bundling. Both transconductance and on-state current significantly increase as median bundle height increases from 2 to 4 nm, but only when the strongly coupled ionic gel gate is used. Such devices tested at −0.6 V drain voltage achieve transconductance as high as 50 μS per bundle and 2 mS μm−1 and on-state current as high as 1.7 mA μm−1. At low drain voltages, the off-current also increases with bundling, but on/off ratios of ∼105 are still possible if the largest (95th percentile) bundles in an array are limited to ∼5 nm in size. Radio frequency devices with strong, wraparound dielectric gates may benefit from increased device performance by using moderately bundled as opposed to individualized CNTs in arrays. [ABSTRACT FROM AUTHOR]

As one of the most promising lithium primary batteries, lithium/fluorinated carbon (Li/CFx) batteries are irreplaceable in military, aerospace, medical, and other markets due to their advantages such as the high energy density, long shelf life, and wide operating temperature. However, it is difficult to enable CFx cathode materials to achieve simultaneously high-capacity and excellent rate-capability. Moreover, the high-temperature direct F2 fluorination method for the commercial CFx material preparation is hazardous, eco-unfriendly, and costly. Herein, we developed an efficient, safe, and cost-effective synthesis approach, in which plasma fluorinated multi-walled carbon nanotubes (PFCNTs) were synthesized by using CF4 plasma as a fluorine source under a low fluorination temperature (300 °C) within excessively short time (110 min). The plasma not only induced ionization of CF4 gas through the electron impact reaction but also promoted the diffusion of fluorine-containing ions in multi-walled carbon nanotubes. The PFCNT possessed un-fluorinated graphitic inner layers, electrochemically active semi-ionic C–F bonds, and few inactive C–F2 and conductive sp2 C=C bonds, endowing it excellent electronic and electrochemical properties. PFCNTs exhibited a high specific capacity of 819.3 mAh/g with an energy density of 2050 Wh/kg. Furthermore, a Li/PFCNT coin cell delivered a capacity of 527.4 mAh/g and a maximum power density of 58 206 W/kg at an ultrahigh current density of 30 A/g. The underling fluorination mechanism was also analyzed by combining with the plasma diagnostic tool of optic emission spectroscopy. [ABSTRACT FROM AUTHOR]

Conventional wet electrodes, such as a silver/silver chloride electrode, are limited for electroencephalogram (EEG) sensors directly attached to the scalp with existing hair due to their incomplete contact and increased impedance. In this study, an all-solution-processed trapezoidal electrode array is demonstrated for highly sensitive and reliable detection of EEG signals even when in direct contact with the scalp. The proposed noninvasive EEG sensors based on nanocomposites consisting of single-wall carbon nanotube random networks incorporated into a gelatin matrix exhibited a relatively low contact impedance of 11.16 × 102 Ω and a high sensitivity of 14.81 dB regardless of existing hair for real-time EEG recording without conductive gels or electrolytes. Furthermore, the origin of such advances induced by the soft and conductive electrode array is investigated by analyzing the effective contact area and signal-to-noise ratio on different scalp positions from 20 different subjects. A trapezoidal EEG electrode penetrates the dense hair and bypasses the hair shaft owing to its deformable shape induced by the soft and flexible nanocomposite film. [ABSTRACT FROM AUTHOR]

Low-dimensional semiconductors have been considered excellent materials to construct photodetectors for infrared detection with an easy process and excellent compatibility but suffer from low detectivity mainly owing to the poor light absorption of the ultra-thin body. Here, we demonstrate a thin film transistor (TFT) based short-wave infrared photodetector consisting of a carbon nanotube (CNT) TFT gated by a PbS colloidal quantum dots (CQDs) based heterojunction. The thick PbS CQDs' film efficiently absorbs infrared light and then excites and separates electron–hole pairs to generate a photovoltage at the pn heterojunction of the PbS CQDs/ZnO film. The photovoltage is further amplified and transduced in situ by the CNT TFT under the heterojunction, and then the detector featured a specific detectivity of 5.6 × 1013 Jones under 1300 nm illumination and a fast response of the sub-ms level (0.57 ms). The CQDs based heterojunction gating TFT represents a universal architecture for highly sensitive low-dimensional semiconductor based infrared photodetectors, competitive with state-of-the-art epitaxial semiconductors and enabling monolithic integration technology. [ABSTRACT FROM AUTHOR]

Surface graphitization as a result of Joule heating by a field-emission (FE) current is revealed for needlelike diamond nanotips. The apex temperature and electrical resistance of the diamond needles during FE were measured by electron spectroscopy. Transmission electron microscopy indicated that the diamond structure in the near-surface layer was transformed into well-ordered graphene layers after FE with currents of up to 30 μA. The resulting structure can be viewed as a multi-walled carbon nanotube (MWCNT) having a diamond core. Thus, the observed FE behavior exhibited by the graphitized diamond needles is qualitatively similar to that of MWCNTs. On the other hand, due to its outstanding thermal conductivity, the diamond core ensures an efficient Joule heat dissipation, which provides better emission stability and higher currents, up to at least 225 μA. It makes these graphitized diamond needles promising candidates for high-brightness point electron sources required for various applications, e.g., in electron microscopy or scanning electron lithography. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that the band structure of a carbon nanotube (CNT) depends not only on its geometry but also on various factors such as atmosphere chemical composition and dielectric environment. Systematic studies of these effects require an efficient tool for an in situ investigation of a CNT band structure. In this work, we fabricate tunneling contacts to individual semiconducting carbon nanotubes through a thin layer of alumina and perform tunneling spectroscopy measurements. We use field-effect transistor configuration with four probe contacts (two tunnel and two ohmic) and bottom gates. Bandgap values extracted from tunneling measurements match the values estimated from the diameter value within the zone-folding approximation. We also observe the splitting of Van-Hove singularities of the density of states under an axial magnetic field. [ABSTRACT FROM AUTHOR]

The flexoelectric effect corresponds to the linear variation of the electric polarization of a material subjected to a strain gradient (i.e., during its mechanical bending). Unlike piezoelectricity, it also exists in non-centrosymmetric materials. Furthermore, due to the gradient term, its magnitude can increase as the size of the system decreases. Thanks to this effect, nanoscale systems could be used to harvest thermal vibration energy to power a microdevice. These could be multi-wall carbon nanotubes since they are known to bend easily in an elastic manner. However, it is very challenging to experimentally measure the flexoelectric behavior of a single multi-wall carbon nanotube due to its small size (less than 50 nm in diameter), to the low level of induced charges, and to the need to vary the imposed stress. To progress in this direction, a six-degree-of-freedom robot with a fiber tip is used inside a dual-beam microscope to pick up few single carbon nanotubes from a tangle and connect them to the fiber tip. After ion-soldering the two tips, each carbon nanotube is dynamically bent several times while monitoring the brightness of the bending area and its effective radius of curvature. This allowed us to demonstrate qualitatively the flexoelectric effect at the level of a single multi-wall carbon nanotube. [ABSTRACT FROM AUTHOR]

Covalent organic frameworks (COFs) with redox-active moieties are potential capacitive energy storage materials. However, their performance is limited by their poor electrical conductivity and sluggish ion diffusion in their nanopores. Herein, we report coaxial one-dimensional van der Waals heterostructures (vdWHs) comprised of a carbon nanotube (CNT) core and a pyrene–pyridine COF shell synthesized by an in situ wrapping method. The coaxial structure allows efficient electronic interaction between the CNT core and COF shell and improves the electrical conductivity significantly. It also improves electrolyte ion accesses to redox-active pyridine groups in the COF, resulting in excellent capacitive energy storage performance with a high specific capacitance of ∼360 F g−1, an excellent rate capability of ∼80%, and a good stability of 92% capacitance retention after 20 000 charge/discharge cycles. Our strategy opens the door to create other multi-dimensional vdWHs for various potential applications. [ABSTRACT FROM AUTHOR]

Detection and analysis of volatile organic compounds' (VOCs) biomarkers lead to improvement in healthcare diagnosis and other applications such as chemical threat detection and food quality control. Here, we report on tri-molybdenum phosphide (Mo3P) and multiwalled carbon nanotube (MWCNT) junction-based vapor quantum resistive sensors (vQRSs), which exhibit more than one order of magnitude higher sensitivity and superior selectivity for biomarkers in comparison to pristine MWCNT junctions based vQRSs. Transmission electron microscope/scanning tunneling electron microscope with energy dispersive x-ray spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy studies reveal the crystallinity and the presence of Mo and P elements in the network. The presence of Mo3P clearly enhanced the performance of vQRS as evidenced in sensitivity and selectivity studies. The vQRSs are stable over extended periods of time and are reproducible, making them a potential candidate for sensing related applications. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotubes (SWCNTs) are attractive materials for next-generation energy-harvesting technologies, including thermoelectric generators, due to their tunable opto-electronic properties and high charge carrier mobilities. Controlling the Fermi level within these unique 1D nanomaterials is often afforded by charge transfer interactions between SWCNTs and electron or hole accepting species. Conventional methods to dope SWCNT networks typically involve the diffusion of molecular redox dopant species into solid-state thin films, but solution-phase doping could potentially provide routes and/or benefits for charge carrier transport, scalability, and stability. Here, we develop a methodology for solution-phase doping of polymer-wrapped, highly enriched semiconducting SWCNTs using a p-type charge transfer dopant, F4TCNQ. This allows doped SWCNT inks to be cast into thin films without the need for additional post-deposition doping treatments. We demonstrate that the introduction of the dopant at varying stages of the SWCNT dispersion process impacts the ultimate thermoelectric performance and observe that the dopant alters the polymer selectivity for semiconducting vs metallic SWCNTs. In contrast to dense semiconducting polymer films, where solution-phase doping typically leads to disrupted morphologies and poorer TE performance than solid-state doping, thin films of solution-doped s-SWCNTs perform similarly to their solid-state doped counterparts. Interestingly, our results also suggest that solution-phase F4TCNQ doping leads to fully ionized and dimerized F4TCNQ anions in solid-state films that are not observed in films doped with F4TCNQ after deposition. Our results provide a framework for the application of solution-phase doping to a broad array of high-performance SWCNT-based thermoelectric materials and devices that may require high-throughput deposition techniques. [ABSTRACT FROM AUTHOR]

The precise control of carbon nanotube structures plays a crucial role in understanding their intrinsic transport as well as in utilizing them for energy harvesting applications. In this paper, we elucidate that slight differences in the purity and diameter distribution of semiconducting single-walled carbon nanotubes (sc-SWCNTs) lead to the significant modulation of thermoelectric transport in their networks. Conducting polymers examined here enable the sorting of the sc-SWCNTs with desired purity and diameter distribution, as well as fixed solid state morphology. Particularly, the approximately tenfold enhancement of thermoelectric power factors is achieved by improving sc-SWCNT purity from 94% to 99% and increasing mean diameters from 1.0 to 1.2 nm. This work provides a rational design for boosting the thermoelectric properties of sc-SWCNT networks. [ABSTRACT FROM AUTHOR]

The p-type properties of carbon nanotubes (CNTs) in organic thermoelectric devices need urgent improvement for large-scale, low-grade thermal energy applications. Here, we present a suitable approach to significantly enhance the power factor (PF) by increasing the electrical conductivity through the low-temperature calcination-induced pyrolysis of the insulating γ-cyclodextrin polymer (PγCyD), which is used as a solubilizer of film-like CNTs. The low-temperature calcination method, which can be used to realize good electrical contact between CNT bundles, shows enhancement behavior as a universal phenomenon for not only PγCyD but also other commonly used polymers for CNT films. To moderate the calcination temperature, the Pd catalyst was added, and the optimal temperature was reduced from 340 °C to 250 °C. Consequently, the PF value of the CNT film was 570 μW m−1 K−2, which was found to be more than twice that of the original CNT film. In addition, we demonstrated the energy harvesting capability of a thermoelectric generator based on this p-type CNT film; a thermoelectric generator with 10 p-type thermoelectric elements showed a maximum power output of 10.3 μW with a temperature difference of 75 °C, which is comparable to the maximum power output of some of the best single-component organic thermoelectric devices demonstrated to date. This outstanding output power shows that easy-to-handle CNT films with low-temperature heat treatment can open new avenues for the development of thermoelectric generators. [ABSTRACT FROM AUTHOR]

The low-frequency noise is of special interest for carbon nanotubes devices, which are building blocks for a variety of sensors, including radio frequency and terahertz detectors. We studied noise in as-fabricated and aged carbon nanotube networks (CNNs) field-effect transistors. Contrary to the majority of previous publications, as-fabricated devices demonstrated the superposition of generation-recombination (GR) and 1/f noise spectra at a low-frequency range. Although all the devices revealed identical current–voltage characteristics, GR noise was different for different transistors. This effect is explained by the different properties and concentrations of trap levels responsible for the noise. Unexpectedly, exposure of these devices to the atmosphere reduced both the resistance and GR noise due to nanotube's p-doping by adsorbed water molecules from the ambient atmosphere. The presence of the generation recombination noise and its dependences on the environment provides the basis for selective gas sensing based on the noise measurements. Our study reveals the noise properties of CNNs that need to be considered when developing carbon nanotubes-based selective gas sensors. [ABSTRACT FROM AUTHOR]

We present a method to dissolve carbon nanotubes that simultaneously allows to prepare n-doped films. These films are composed of thinner bundles of longer tubes when compared to films prepared using surfactants and sonication. Their negative Seebeck coefficient and high electrical conductivity make them good candidates for thermoelectric applications. We investigate their stability in air by aging them at elevated temperatures, showing stabilities over 500 h, which is further improved by the use of crown ethers. Finally, we demonstrate the usefulness of the prepared materials by fabricating an organic thermoelectric generator comprising 40 legs. [ABSTRACT FROM AUTHOR]

Long single-wall carbon nanotubes (SWCNTs) with a controlled conductivity type or chirality are interesting for fundamental study and are promising in many different technological applications, such as nanoelectronics, optoelectronics, and also upon utilizing them as nanoscale reactors to produce nanomaterials. In this study, the long aligned large diameter SWCNTs and the large diameter nanotube dense networks were synthesized via a vapor-phase epitaxial re-growth method. The nanotubes were re-grown on ST (stable temperature)-cut quartz substrates from short SWCNT seeds using the mixture of ethanol and acetylene as a precursor. The efficient nanotube re-growth was achieved using unsorted SWCNTs with diameters of 1.2–2.0 nm and semiconducting SWCNTs, sorted by an aqueous two-phase extraction method, as seeds. According to our study, the re-grown nanotubes in an array have an average length of 5.5 μm, while the individual re-grown nanotubes can reach up to 20–30 μm. The extensive optical study confirms the preservation of SWCNTs diameter during the re-growth and signifies the high quality of produced nanotubes. We demonstrate the SWCNT chirality selective efficiency of the re-growth, which leads to predominance of the metallic nanotubes. [ABSTRACT FROM AUTHOR]

Ionic liquids enable efficient gating of materials with nanoscale morphology due to the formation of a nanoscale double layer that can also follow strongly vaulted surfaces. On carbon nanotubes, this can lead to the formation of a cylindrical gate layer, allowing an ideal control of the drain current even at small gate voltages. In this work, we apply ionic liquid gating to chirality-sorted (9, 8) carbon nanotubes bridging metallic electrodes with gap sizes of 20 nm and 10 nm. The single-tube devices exhibit diameter-normalized current densities of up to 2.57 mA/μm, on-off ratios up to 104, and a subthreshold swing down to 100 mV/dec. Measurements after long vacuum storage indicate that the hysteresis of ionic liquid gated devices depends not only on the gate voltage sweep rate and the polarization dynamics but also on charge traps in the vicinity of the carbon nanotube, which, in turn, might act as trap states for the ionic liquid ions. The ambipolar transfer characteristics are compared with calculations based on the Landauer–Büttiker formalism. Qualitative agreement is demonstrated, and the possible reasons for quantitative deviations and possible improvements to the model are discussed. Besides being of fundamental interest, the results have potential relevance for biosensing applications employing high-density device arrays. [ABSTRACT FROM AUTHOR]

We report the observation of Coulomb blockade in electron field emission (FE) from single-wall carbon nanotubes (SWCNTs), which is manifested as pronounced steps in the FE current–voltage curves and oscillatory variations in the energy distribution of emitted electrons. The appearance of the Coulomb blockade is explained by the formation of nanoscale protrusions at the apexes of SWCNTs due to the electric field-assisted surface diffusion of adsorbates and carbon adatoms. The proposed adsorbate-assisted FE mechanism is substantially different from the well-known resonant tunneling associated with discrete electronic states of adsorbed atoms. The simulations based on the Coulomb blockade theory are in excellent agreement with the experimental results. The SWCNT field emitters controlled by the Coulomb blockade effect are expected to be used to develop on-demand coherent single-electron sources for advanced vacuum nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Conductive carbon fillers were commonly used to mix with polydimethylsiloxane to improve the output performance of polydimethylsiloxane-based triboelectric nanogenerators. In this work, we focused on the mechanism underlying the unpredictable output performance influenced by adding conductive fillers. We selected multiwall carbon nanotubes as conductive fillers and investigated their electronegative performance in triboelectric nanogenerators. An optimized performance was achieved when the weight concentration of carbon nanotubes was about 0.4%. The open-circuit voltage can reach up to 720 V, the short-circuit current was about 18.28 μ A , and a power density of 4.65 mW (11.62 W / m 2 ) was obtained at the load resistance of 55.15 M Ω and a stimulus frequency of 2.0 Hz. The attractive performance was attributed to the appropriate balance of the capacitive effect and the leakage effect of carbon nanotubes to triboelectric charges. A model based on alternative current impedance analysis has been proposed, which may be helpful for future triboelectric nanogenerator design and investigation. [ABSTRACT FROM AUTHOR]

Understanding the relationships between the thermal conductivity and carrier density in thin films is of great importance for the thermal management of flexible thin film electronics. Here, we report a robust measurement technique to tune the carrier density in thin films and to evaluate their cross-plane thermal conductivities simultaneously. We employed the time-domain thermoreflectance method using an Au transducer and evaluated the thin film thermal conductivity in situ using electrolyte gating with an ionic gel. The robust measurement technique proposed in this study elucidated the relationships among the above-mentioned parameters in semiconducting single-walled carbon nanotubes. [ABSTRACT FROM AUTHOR]

A complex quantum dot circuit based on a clean and suspended carbon nanotube embedded in a circuit quantum electrodynamic (cQED) architecture is a very attractive platform to investigate a large spectrum of physics phenomena ranging from qubit physics to nanomechanics. We demonstrate a carbon nanotube transfer process allowing us to integrate clean carbon nanotubes into complex quantum dot circuits inside a cQED platform. This technique is compatible with various contacting materials such as superconductors or ferromagnets. This makes it suitable for hybrid quantum devices. Our results are based on eight different devices demonstrating the robustness of this technique. [ABSTRACT FROM AUTHOR]

We theoretically report an explicit and robust scheme, 2N-rule, for systematically searching topological phases in carbon nanotubes (CNTs) of all diameters. By investigating the topological Zak phase based on both analytical model and first-principles approaches, such a 2N-rule of insulating CNT(n,0) is generally established: when n = 2 N , where N is an integer (an even n), it is a topological insulator; otherwise, it is a normal insulator. For finite-length topological CNTs, topologically protected quantum modes naturally occur at the tube ends, which hold significant robustness against external environment perturbations, taking advantage over fragile edge states in conventional systems. The topological CNTs can provide a platform for potential applications in reliable carbon nanoelectronics as well as exploring fundamental science of one-dimensional topological materials. [ABSTRACT FROM AUTHOR]

Single-walled carbon nanotube (SWNT) has attracted widespread attention for its unique one-dimensional atomic structure and outstanding physical and chemical properties. For both fundamental research and practical applications, it is critical to figure out the chirality of SWNT because the electronic band structure and the consequent electrical and optical properties are determined by its chirality. Here, we found that the chirality of SWNT on an insulating hexagonal boron nitride (h-BN) substrate can be obtained in a quick and concise manner through measuring the aligning direction and the diameter of SWNT. Additionally, Rayleigh scattering spectroscopy is conducted to confirm the obtained chirality. The developed technique for direct detection of chirality of SWNT on an insulating h-BN substrate could advance the study of chirality-dependent functional SWNT devices and the applications of SWNT related to chirality. [ABSTRACT FROM AUTHOR]

The apex-field enhancement factor (aFEF) is regarded as a meaningful parameter to characterize field electron emission (FE) devices. If experimentally extracted from orthodox current–voltage characteristics, this parameter reliably quantifies how much the emitter's sharp tip locally magnifies the applied external electrostatic field. Many experimental works have reported FE from arrays of carbon nanotubes with fixed spacing (c) between nearest-neighbor emitters, fixed apex-radii (r), and various height (h) and claimed the existence of an aspect ratio (h/r) at which a local maximum effective aFEF is achieved. Hereafter, it is shown that those results are not consistent with simulations using basic electrostatics for both finite or infinite regular square arrays of emitters. Quite interestingly, our results show that the aFEF (γa), for an emitter in an infinity regular array, simply saturates at γs for h ≳ 0.7 c. Additionally, we found a universal behavior in which γa scales as γ a ∼ γ s (h / c) 0.84 , when h ≲ 0.7 c , for h / r ≳ 50. These results provide a practical rule for the design of large arrays of field emitters, which can be used to build FE nanoelectromechanical resonators with both mechanical strength and reduced Joule losses. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNTs) can be used in many different applications. Field emission (FE) measurements were used together with Raman spectroscopy to show a correlation between the microstructure and field emission parameters. However, field emission characterization does not suffer from fluorescence noise present in Raman spectroscopy. In this study, Raman spectroscopy is used to characterize vertically aligned CNT forest samples based on their D/G band intensity ratio (ID/IG), and FE properties such as the threshold electric field, enhancement coefficient, and anode to CNT tip separation (ATS) at the outset of emission have been obtained. A relationship between ATS at first emission and the enhancement factor, and, subsequently, a relationship between ATS and the ID/IG are shown. Based on the findings, it is shown that a higher enhancement factor (∼3070) results when a lower ID/IG is present (0.45), with initial emissions at larger distances (∼47 μm). For the samples studied, the morphology of the CNT tips did not play an important role; therefore, the field enhancement factor (β) could be directly related to the carbon nanotube structural properties such as breaks in the lattice or amorphous carbon content. Thus, this work presents FE as a complementary tool to evaluate the quality of CNT samples, with the advantages of a larger probe size and an averaging over the whole nanotube length. Correspondingly, one can find the best field emitter CNT according to its ID/IG. [ABSTRACT FROM AUTHOR]

Though thermophotovoltaic (TPV) systems have been studied for many decades, the demonstrated conversion efficiencies have remained far lower than the theoretical maximum. Here, in this work, we investigate the reason for low efficiency, especially in TPV systems employing selective thermal emitters, and determine design pathways toward high efficiency. We model both the optical and optoelectronic components of the TPV system and study the influence of the emitter selectivity on the optimum bandgap of the photovoltaic cell, heat sink requirements, and maximum conversion efficiency for any given emitter temperature from 1000 to 2000 K. Our calculations suggest that thermal emitters with at least 20 dB suppression of sub-bandgap emission and an emission enhancement of 100× can push the overall efficiency to 70% of Carnot's limit. Furthermore, we show that such an extreme requirement on suppression is at the performance limits for resonant thermal emitters employing refractory plasmonic materials such as Mo, W, Ta, TiN, and carbon nanotubes. [ABSTRACT FROM AUTHOR]

Recent studies on fluid-coupled nanoresonators (represented by argon-filled carbon nanotubes or CNTs) have shown nonintuitive variation of the fluid dissipation (Dflu) with fluid density ( ρ * ) at high-frequency oscillations. In this letter, we propose a physical mechanism that can explain such a behavior. We identify that argon atoms are in the disordered (ordered) state within the CNTs at small (large) ρ * . For low-frequency oscillations, i.e., for oscillations with large characteristic excitation time scales, the argon atoms, at both large and small ρ * , have enough time to dissipate all the energy added from the imposed oscillations. But for high-frequency oscillations, i.e., for oscillations with small characteristic excitation time scales, while the argon atoms in the disordered state (low density) can dissipate all the energy in that small time, those in the ordered state (high density) cannot dissipate all the energy (and hence stores some energy) in that time. This explains the nonmonotonic density-dependence of Dflu in argon-filled CNTs at high frequency. We also explain this nonmonotonic density-dependence of Dflu from the corresponding Deborah number (De). De represents the ratio of the fluid relaxation to the excitation time scales. The relaxation time of CNT-confined argon increases with ρ * . Therefore, for a large-frequency (or a small excitation time) oscillation, De becomes large and the fluid starts losing its fluidity and shows solidlike ("elastic") characteristics. This viscoelastic behavior ensures a partial storage (without dissipation) of the imposed oscillation, which in turn explains the nonmonotonic variation of Dflu with ρ * for large-frequency oscillations. [ABSTRACT FROM AUTHOR]

Double-walled carbon nanotubes have many advantages over their singled-walled counterparts such as higher mechanical strength and thermal stability. They can be synthesized by well-established methods like arc-discharge, chemical vapor deposition, and the annealing of molecules and nanocompounds encapsulated in single-walled carbon nanotubes. However, the material grown with these methods does not necessarily have a homogeneous morphology across an entire sample. Aiming at a controllable structure, we have decomposed molecules encapsulated in the hollow core of known diameter nanotubes via in situ laser annealing while simultaneously monitoring the Raman spectral response of the material. Our results show that thin inner tubes can be synthesized inside their single-walled hosts. We have also observed that monitoring the laser wavelength and power and choosing the host's diameter, the chirality of the inner tubes can be tailored in a controlled manner. Interestingly, linear carbon chains, as a one-dimensional allotrope of carbon, were formed as well. The dynamic of the chains annealed at higher power indicates the decomposition of the longer into shorter ones. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) spectroscopy with unparalleled sensitivity for fingerprint detection of aromatic dyes is demonstrated by loading highly dense Au@Ag core/shell nanoparticles (NPs) on carbon nanotubes (CNTs). The Raman spectrum of crystal violet molecules adsorbed on the optimal CNT/Au@Ag NPs (8.4% Au and 8.6% Ag) can be distinguished as low as 10−14 M, achieving ultralow SERS detection. Besides electromagnetic enhancement originating from the Au@Ag core-shell, the strong electron-phonon coupling effect in CNTs is highlighted by the formation of more defects via doping bimetallic NPs, further improving SERS activity. Thus, this finding will offer a strategy for boosting SERS performance in widespread applications. [ABSTRACT FROM AUTHOR]