A greenhouse gas silicon microchip sensor using a conducting composite with single walled carbon nanotubes

Molecular simulations were performed to investigate the adsorption and diffusion properties of methane and carbon dioxide in carbon nanotubes (CNTs) with preadsorbed water at 300 K and pressures up to 40 bar. Our results show that, at low pressures, a high uptake of methane and carbon dioxide is obtained in relatively small pores, and the presence of water enhances the adsorption of carbon dioxide in CNTs with large diameters. The effect of the preadsorbed water is more pronounced on the mobility of methane than that of carbon dioxide. Importantly, at high water contents, we see that the mobility of methane is a nonmonotonic function of the nanotube diameter. This is probably due to the splitting of the water clusters in the small pores which may lead to a faster diffusion process. Simulations were also performed for the methane/carbon dioxide mixture in CNTs with preadsorbed water. Here, the overall adsorption and diffusion properties are similar to those observed for the methane/water and carbon dioxide/water mixtures in CNTs. The adsorption selectivity of carbon dioxide over methane increases with water content which may be because of the relatively stronger water-carbon dioxide interactions. A significant result is that the mobility of methane in the CNTs decreases with decreasing bulk mole fraction of methane. In general, this decrease is more pronounced at higher loadings of methane and lower water contents. However, the presence of methane has less effect on the diffusion properties of carbon dioxide in the CNTs. These results may be explained by the preferential adsorption of carbon dioxide over methane in the CNTs. Furthermore, these simulated adsorption isotherms and diffusivity results are in reasonable agreement with the theoretical predictions based on the ideal adsorbed solution theory and the Krishna and Paschek approach, respectively.

Summary form given only. As carbon nanotubes (CNTs) are becoming the most promising material for nanoelectronic devices, interests on their high-frequency properties are being further increased. Recently, many active researches characterizing single-wall or multi-wall CNTs have been reported. Here, we fabricate the device with a bundle of single-wall CNT (SWCNT) captured between two signal electrodes of a coplanar waveguide (CPW), and report its radio-frequency (RF) characterization and equivalent circuit modeling. The article shows an SEM image of the SWCNT bundle captured between two signal electrodes of the CPW with the gap of 700 nm. First of all, the CPW for GSG measurement was fabricated on the high resistivity Si wafer by photolithography and lift-off process. Further electron beam lithography made the CPW has sharp signal electrodes to alleviate the drastic impedance mismatching with the SWCNT and to minimize the parasitic capacitance between two signal electrodes. The bundle of SWCNTs was captured between two signal electrodes of the CPW by dielectrophoresis alignment. Then, we made the ohmic contact between the SWCNT and the CPW by using Au electroplating and subsequent thermal annealing. This electroplating process does not require one more step of lithography. The article shows the measured transmission (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">21</sub> ) and reflection (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ) characteristics of the CPWs with/without SWCNT at frequencies of 0.1 ~ 40 GHz. The transmission of the CPW with SWCNT is 1 dB larger than that of the CPW without SWCNT at 10 GHz. The difference denotes the amount of the transmission through SWCNT, and it is added to the transmission through the parasitic capacitance between two signal electrodes of the open CPW. The reflection of the CPW with SWCNT is maximum 1.7 dB smaller than that of the CPW without SWCNT at 38 GHz. Figure 3 shows the equivalent circuit model of the CPW combined with SWCNT. The parasitic parameter values of the open CPW were extracted from the measurement data of the CPW without SWCNT by ADS optimization. The parasitic values are follows; L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 0.006 nH, L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> = 0.005 nH, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , = 8 Omega, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> = 10.7 Omega, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 0.04 pF, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> = 0.05 pF, and C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> = 0.07 fF. Then, we extracted the other parameter values (due to SWCNT) from the measurement data of the CPW with SWCNT, keeping the parasitic values of the open CPW. The values are follows; R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> = 4.1 kOmega, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">el</sub> = 0.9 fF, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CNT</sub> = 1.04 kOmega, and L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> = 1.2 nH. We completed the total equivalent circuit model of the CPW with SWCNT by using ADS optimization since the de-embedding of CPW pads may result in overestimation due to contact resistance. The article shows the magnitude and phase of the impedance (Z) obtained from the measurement and from the equivalent circuit of the CPW with SWCNT. The measured data are consistent with the modeled data within a reasonable accuracy. In summary, we have captured SWCNT between two signal electrodes of the CPW and presented its high-frequency characterization. From the de-embedding process using the equivalent circuit, we successfully obtain the resistance (R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CNT</sub> = 1 -04 kOmega) and the inductance (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> = 1.2 nH) of the SWCNT bundle.

Development of a Novel Composite Material with Carbon Nanotubes Assisted by Self-Assembled Peptides Designed in Conjunction with β-Sheet Formation

Band Engineering of Carbon Nanotubes for Device Applications

Carbon nanotubes (CNTs) offer tremendous promise as emerging materials for sensing applications. However, we still lack a systematic approach for realization of functional nanodevices based on carbon nanotubes. An approach that produces carbon nanotubes with a conventional complementary metal oxide semiconductor (CMOS) technology will address such challenges. A simple methodology for integrating single-walled carbon nanotubes (SWNTs) onto CMOS integrated circuits is presented. The SWNTs are incorporated onto a CMOS chip between electrodes made with available metal layers from the CMOS process. For proof of concept, assembly of SWNTs serving as feedback resistors of a two-stage Miller compensated operational amplifier utilizing dielectrophoretic (DEP) assembly is demonstrated. The measured electrical properties from the integrated SWNTs yield ohmic behavior with a two-terminal resistance of ~37.5 KΩ. The measured small signal ac gain (about −2) from the inverting amplifier confirmed successful integration of CNTs onto the CMOS circuitry. Furthermore, the temperature response of the SWNTs integrated onto CMOS circuitry exhibited a temperature coefficient of resistance (TCR) of −0.4%/°C. Bare SWNTs were reported sensitive to various chemicals, and functionalization of SWNTs with biomolecular complexes further enhances their specificity and sensitivity. After decorating ss-DNA on SWNTs, the sensing response of the gas sensor is enhanced (up to ~300 and ~250% for methanol vapor and isopropanol alcohol vapor, respectively) compared with bare SWNTs. This methodology for integrating SWNTs onto CMOS technology is versatile, high yield, and paves the way to the realization of novel miniature CNT-based sensor systems.

We report the modification of gold and graphite electrodes with commercially available carbon nanotubes for immobilization of Desulfovibrio fructosovorans [NiFe] hydrogenase, for hydrogen evolution or consumption. Multiwalled carbon nanotubes, single-walled carbon nanotubes (SWCNs), and amine-modified and carboxyl-functionalized SWCNs were used and compared throughout. Two separate methods were performed: covalent attachment of oriented hydrogenase by controlled architecture of carbon nanotubes at gold electrodes, and adsorption of hydrogenase at carbon-nanotube-coated pyrolytic graphite electrodes. In the case of self-assembled carbon nanotubes at gold electrodes, hydrogenase orientation based on electrostatic interaction with the electrode surface was found to control the electrocatalytic process for H(2) oxidation. In the case of carbon nanotube coatings on pyrolytic graphite electrodes, catalysis was controlled more by the geometry of the nanotubes than by the orientation of the enzyme. Noticeably, shortened SWCNs were demonstrated to allow direct electron transfer and generate high and quite stable current densities for H(2) oxidation via adsorbed hydrogenase, despite having many carboxylic surface functions that could yield unfavorable hydrogenase orientation for direct electron transfer. This result is attributable to the high degree of oxygenated surface functions in addition to the length of shortened SWCNs that yields highly divided materials.

Human exposure to airborne carbon nanotubes (CNT) is increasing because of their applications in different sectors; therefore, they constitute a biological hazard. Consequently, developing studies on CNT toxicity become a necessity. CNTs can have different properties in term of length, size and charge. Here, we compared the cellular effect of multiwall (MWCNTs) and single wall CNTs (SWCNTs). MWCNTs consist of multiple layers of graphene, while SWCNTs are monolayers. The effects of MWCNTs and SWCNTs were evaluated by the water‐soluble tetrazolium salt cell proliferation assay on NR8383 cells, rat alveolar macrophage cell line (NR8383). After 24 hours of exposure, MWCNTs showed higher toxicity (50% inhibitory concentration [IC50] = 3.2 cm2/cm2) than SWCNTs (IC50 = 44 cm2/cm2). Only SWCNTs have induced NR8383 cells apoptosis as assayed by flow cytometry using the annexin V/IP staining test. The expression of genes involved in oxidative burst (Ncf1), inflammation (Nfκb, Tnf‐α, Il‐6 and Il‐1β), mitochondrial damage (Opa) and apoptotic balance (Pdcd4, Bcl‐2 and Casp‐8) was determined. We found that MWCNT exposure predominantly induce inflammation, while SWCNTs induce apoptosis and impaired mitochondrial function. Our results clearly suggest that MWCNTs are ideal candidates for acute inflammation induction. In vivo studies are required to confirm this hypothesis. However, we conclude that toxicity of CNTs is dependent on their physical and chemical characteristics.

With clean fuels increasingly used for transportation due to environmental concerns and limited supply of fossil fuels, hydrogen is attracting more attention as a clean fuel free from carbon dioxide and other greenhouse gas emissions. Analysis of hydrogen diffusion in single-walled carbon nanotube was performed with molecular dynamic simulation. The carbon nanotube is chosen because of a well-known fact that it is an excellent adsorption material with high surface volume ratio. In this paper, diffusivity rate are simulated to study the interaction of molecular and atomic hydrogen with single-walled carbon nanotubes. The adsorption energy and repulsive energy are analyzed to explore the nanotube structure after desorption and the mechanism of desorption. Electric charge density is also studied in order to understand better the process of hydrogen adsorption in CNT. A background of the hydrogen storage problem with carbon nanotubes is provided and the issues to be resolved have been highlighted. Future directions to address these challenges have also been suggested. We make a case that molecular simulation studies can identify the most promising structures and compositions to maximize hydrogen storage.

Comparative analysis of single-walled and multi-walled carbon nanotubes for electrochemical sensing of glucose on gold printed circuit boards

The adsorption of carbon dioxide in the presence of water in single-walled carbon nanotubes is studied using Monte Carlo simulation, at 300, 325, and 350 K. We also investigate the influence of the diameter and chirality of the nanotubes on the adsorption isotherms of CO2. It is observed that increasing the nanotube diameter from 1.36 nm (10, 10) to 2.03 nm (15, 15) leads to enhanced CO2 capacity, while change in chirality has little effect on the adsorption capacity of carbon nanotubes. Our results show that the influence of preadsorbed water on CO2 adsorption is dependent on both the effects of excluded volume and H2O–CO2 interactions. The maximum adsorbed amount of CO2 decreases linearly with the loading of water, and drops more rapidly in narrower nanotubes. The structure of water in hydrophobic nanopores is in the form of hydrogen-bonded clusters, and its adsorption does not affect the arrangement and orientation of CO2 molecules (i.e., it does not affect the mechanism of CO2 adsorption). The average size of water clusters coexisting with CO2 depends strongly on the adsorbed amount of CO2; however, it is shown that splitting large water clusters into smaller ones can lead to significant enhancement of CO2 adsorption, due to the resulting stronger water–CO2 interaction. The maximum percentage increase in the excess adsorption of CO2 is as high as 53.4% when a single cluster is split into multiple smaller clusters. This finding demonstrates that the efficiency of CO2 capture from flue gas can be significantly improved by controlling the structure of coexisting water in carbon nanotubes.

In agricultural systems, soil carbon dioxide emissions and physical properties are thought to depend largely on management practices. This field study was carried out in a semi-arid region of eastern Tunisia to evaluate the effects of tillage management on soil carbon dioxide emissions and related physical properties; bulk density (BD), penetration resistance (PR), total porosity (TP) and air-filled porosity (AFP). Tillage management treatments included plowing with a moldboard plow or a disk plow to different depths, described here as shallow (10 cm), medium (15 cm) and deep (25 cm). No-tillage was also considered as a control plot. Correlation analysis was used to explore how soil carbon dioxide emissions (CO2) were related to the other studied properties. The results showed higher carbon dioxide (CO2) emissions (p < .05) from tilled soil compared to no-till (NT), regardless of the tillage management. No significant differences in carbon dioxide (CO2) emissions were found between moldboard and disk plow tillage at the same tillage depth. Soil carbon dioxide release was the highest after deep tillage (moldboard = 0.101 t ha−1 and disk plow = 0.107 t ha−1) suggesting that deeper tillage to 25 cm promoted higher carbon dioxide (CO2) emissions. Significant differences with tillage were observed in bulk density (BD) and penetration resistance (PR) compared to no-tillage. Correlations of carbon dioxide emissions to soil physical properties across all the tillage treatments indicated significant negative relationships between carbon dioxide (CO2) emissions and soil bulk density (BD) and penetration resistance (PR) and significant positive relationships between carbon dioxide (CO2) and total porosity (TP) and air-filled porosity (WFP) suggesting that these soil attributes are important controlling factors of carbon dioxide (CO2) emissions.

This study investigated the genotoxic effects of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs) on Chlorella vulgaris under controlled laboratory conditions. SWCNTs (1–2 nm diameter) and MWCNTs (10–20 nm diameter) were used, and toxicity assessments followed the OECD standardized protocol. DNA damage in exposed algal cells was evaluated using the Comet Assay (CAM), observed under a fluorescence microscope, and analyzed with CASP software. The specific growth rate of C. vulgaris increased at concentrations up to 12.5 mg/L for both types of carbon nanotubes but declined at higher concentrations. Chlorophyll content decreased progressively with increasing SWCNT concentrations and exposure duration. Comet Assay results were statistically significant (p < 0.05), confirming notable genotoxic effects. Both SWCNTs and MWCNTs caused reductions in cell number and chlorophyll concentration, with SWCNTs demonstrating a greater impact. Nuclear structural changes were observed in all treatments, but more pronounced damage was associated with SWCNT exposure. Tail moment (TM) values showed significant differences between CNT-treated samples and controls across various concentrations, indicating a concentration-dependent toxicity. These findings suggest that carbon nanotubes, particularly SWCNTs, can significantly affect algal health and genetic integrity, highlighting the need for careful environmental risk assessments of nanomaterials.

Carbon nanotube(CNT), which was discovered by Ijima, has been used wisely in various fields of materials due to their high-quality properties such as superior electrical conductivity, chemical stability and so on. Carbon nanotubes could be divided into two kinds, single-walled carbon nanotubes(SWCNTs) and multi-walled carbon nanotubes(MWCNTs). This classification is depending on carbon nanotubes' internal structure. Additionally, with further research, single-walled carbon nanotubes could be separate into metallic SWCNTs and semiconducting SWCNTs. One of the separation methods is using agarose gel electrophoresis, which was discovered by Tanaka. Based on the above method, researcher Kataura developed column separation of SWCNTs by using agarose gel without electricity. Although carbon nanotubes have been well-known for their properties, they can not exhibit them under normal conditions due to the agglutination that caused by intermolecular interaction. Therefore, to make carbon nanotubes exhibit their useful properties, technology of dispersing agglutinate carbon nanotubes is required. There are two major methods widely used to disperse CNTs currently. The first one is chemical dispersion. Increase carboxylic acid into strong acid-treated CNTs and use ultrasonic irradiation. However, excessive acid can cause damage to structure of CNTs which will make CNTs lose their original properties. Besides chemical dispersion, physical dispersion is a simple method which use ultrasonic irradiation to loosen agglutinate CNTs directly. However, in this method, re-agglutination is tend to occur, and excessive ultrasonic irradiation will also cause damage to the structure of CNTs. We have succeeded in developing CNTs' conductive composite resin with the method of dispersing CNTs by aromatic compounds.However, these resins developed by us have some shortages, such as lacking in conductivity. Although this degree of conductivity seems to reach the standard of touch screen, liquid crystal display's standard has not been reached yet. In our research, to increase the conductivity of risen, we tried to choose different kinds of CNTs, and consider that the metallic SWCNT would exhibit better conductivity than the CNT which was not separated.To test and verify if composite resin developed by metallic SWCNT could exhibit significant conductivity, we did a comparative experiment among metallic SWCNT, semiconducting SWCNT, and SWCNT without separation. Using these three types of SWCNT to develop composite resin, and then compared their conductivity.The result of the experiment above was unexpected, which showed semiconducting SWCNT's composite resin has the highest conductivity while metallic SWCNT has the worst conductivity. The prediction of this experiment's result was metallic SWCNT will exhibit the most significant conductivity because metal's conductivity is better than semiconductor under the normal condition. Through the inspection，we had a presumption that the effect of electron hopping lead to the highest conductivity of semiconducting SWCNT. Effect of electron hopping can occur in the field of semiconductor, the mechanism is that the electrons might leave their electron orbit because of external energy such as heat. In our experiment, phenylethyl alcohol was used as dispersion medium to disperse SWCNTs. Adding it to agglutinated SWCNTs will cause gaps between SWCNTs' molecules, electrons could change their orbits because of these gaps. During this effect, the movement of electrons will inflect the conductivity of the material. As a result, it was possible that semiconducting SWCNT exhibit high conductivity because of the effect of electron hopping which cause the movement of electron.

A metallic single-walled carbon nanotube (SWCNT) has been proposed as a highly sensitive temperature sensor with consideration of self-heating induced scattering. This sensor can be implemented to sense temperature spanning from 20º C to 400º C with high temperature coefficient of resistivity (TCR) ranging from 0.0035/ºC to 0.009/ ºC. Important aspect of this work is consideration of self-heating in SWCNT which was not considered in earlier carbon nanotube based temperature sensors. We have studied a metallic SWCNT over a silicon dioxide substrate and in between two metal contacts. Bias voltage of 0.1V has been applied in between these two contacts. For resistivity calculation, we have utilized one-dimensional semi-classical transport model assuming SWCNT is perfectly conducting. The heat flow equation has been solved assuming steady state flow of heat. We have also assumed that contact and substrate are in thermal equilibrium with the surroundings. Since self-heating significantly affects electro-thermal transport, incorporation of this phenomenon enables to design and model ambient temperature sensor accurately. We have studied CNT sensor with different lengths and chiralities. The results show that resistances of longest (3μm) and thinnest (9, 0) CNTs increase rapidly with temperature. For a 3μm long metallic SWCNT with chirality index (9, 0), TCR has the maximum value (~0.009/ ºC).

This study performs a series of Molecular Dynamics (MD) and Molec- ular Statics (MS) simulations to investigate the mechanical properties of single- walled carbon nanotubes (SWCNTs) under a uniaxial tensile strain. The simula- tions focus specifically on the effects of the nanotube helicity, the nanotube diame- ter and the percentage of vacancy defects on the bond length, bond angle and tensile strength of zigzag and armchair SWCNTs. In this study, a good agreement is ob- served between the MD and MS simulation results for the stress-strain response of the SWCNTs in both the elastic and the plastic deformation regimes. The MS simulations reveal that in the plastic deformation regime, the tensile strength of the armchair and zigzag SWCNTs increases with an increasing wrapping angle. In addition, it is shown that the tensile strength reduces significantly at larger val- ues of the nanotube diameter. Moreover, it is observed that the tensile strength of both SWCNTs reduces as the percentage of defects within the nanotube structure increases. Finally, it is found that the results obtained from the molecular statics method are relatively insensitive to instabilities in the atomic structure, particularly in the absence of thermal fluctuations, and are in good agreement with the predic- tions obtained from the molecular dynamics method.