Hole doping and surface functionalization of single-walled carbon nanotube chemiresistive sensors for ultrasensitive and highly selective organophosphor vapor detection

We developed a chemiresistive sensor based on doped and functionalized semiconducting single-walled carbon nanotube (SWNT) networks for ultrasensitive and rapid detection of dimethyl methylphosphonate (DMMP) (simulant of nerve agent sarin) vapor. The semiconducting SWNT network was deposited between interdigitated electrodes and modified by solid organic acid tetrafluorohydroquinone (TFQ). The TFQ molecules could not only selectively bind DMMP onto the sidewalls of SWNTs via the strong hydrogen bonding interaction, but also tailor the electronic properties of SWNTs via heavy hole doping. This synergetic effect significantly improved the sensitivity of the devices, and enabled the sensors to easily detect DMMP at 20 parts-per-trillion (ppt) concentration with a response time of less than 2 min, without the need for pre-concentration of the analytes. This sensitivity is about five orders of magnitude higher than that of the unmodified SWNT chemiresistor, and also significantly higher than that of the functionalized SWNT chemiresistors previously reported. Moreover, the SWNT-TFQ sensors could be recovered when DMMP is replaced with referencing gas. The SWNT-TFQ sensors also show excellent selectivity toward DMMP over some interfering organic vapors. The response mechanism, i.e. charge transfer and dedoping was investigated.     

Incorporation of single-wall carbon nanotubes into an organic polymer monolithic stationary phase for mu-HPLC and capillary electrochromatography

Single-wall carbon nanotubes (SWNT) were incorporated into an organic polymer monolith containing vinylbenzyl chloride (VBC) and ethylene dimethacrylate (EDMA) to form a novel monolithic stationary phase for high-performance liquid chromatography (HPLC) and capillary electrochromatography (CEC). The retention behavior of neutral compounds on this poly(VBC-EDMA-SWNT) monolith was examined by separating a mixture of small organic molecules using micro-HPLC. The result indicated that incorporation of SWNT enhanced chromatographic retention of small neutral molecules in reversed-phase HPLC presumably because of their strongly hydrophobic characteristics. The stationary phase was formed inside a fused-silica capillary whose lumen was coated with covalently bound polyethyleneimine (PEI). The annular electroosmotic flow (EOF) generated by the PEI coating allowed peptide separation by CEC in the counterdirectional mode. Comparison of peptide separations on poly(VBC-EDMA-SWNT) and on poly(VBC-EDMA) with annular EOF generation revealed that the incorporation of SWNT into the monolithic stationary phase improved peak efficiency and influenced chromatographic retention. The structures of pretreated SWNT and poly(VBC-EDMA-SWNT) monolith were examined by high-resolution transmission electron microscopy, Raman spectroscopy, scanning electron microscopy, and multipoint BET nitrogen adsorption/desorption.     

Evaluation of SOCl2 doping effect on electrical conductivity of thin films of SWNTs and SWNT/PEDOT-PSS composites

Transparent conductive thin films of single-walled carbon nanotubes (SWNTs) and their nanocomposites with an organic conductive polymer, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) with different CNT loadings ranging from 20 to 90 wt% were prepared and doped by exposing them to thionyl chloride (SOCl2) vapors. After exposure to SOCl2 vapor for 1 h, the SWNT film showed about 15-18% increase of electrical conductivity, while on the other hand pristine polymer film showed a decrease of electrical conductivity. The SWNT-polymer composite films showed a drastic increase in conductivity by doping with SOCl2 vapor, most interestingly, the doping effect was much higher for composite films with less CNT weight fraction and it was linearly decreased with increasing CNT loading. For instance, composite film with 10% and 90% CNT loading demonstrated about 65% and 10% increase of electrical conductivity, respectively. The interaction of SOCl2 vapors on SWNTs and composite films is investigated by UV-visible absorption and Raman spectroscopy.     

Effect of Low-Temperature Diffusion Annealing on the Properties of PbSnTe〈In〉 Epilayers

A procedure was proposed for low-temperature vapor-phase In doping of Pb_{1 – x} Sn _x Te films grown by molecular-beam epitaxy on BaF₂ substrates. Diffusion annealing was carried out in a hydrogen atmosphere in the presence of a vapor source identical in composition to the film and a dopant source at temperatures which were, in most cases, no higher than the growth temperature (300–460°C). The effect of diffusion annealing on the composition, transport properties, and homogeneity of both undoped and In doped films was examined. The results suggest that indium is transported in the vapor phase in the form of indium tellurides resulting from the reaction between Te vapor and liquid In.     

Fluorine doped gallium tin oxide composite films as transparent conductive oxides on polyethylene terephthalate film prepared by electron cyclotron resonance metal organic chemical vapor deposition

The undoped and fluorine doped gallium tin oxide composite films are prepared by an electron cyclotron resonance metal organic chemical vapor deposition. Characteristics of structural, optical and electrical properties of the fluorine doped gallium tin oxide composite thin films are investigated. The four point probe method, atomic force microscopy and X-ray photoelectron spectroscopy are employed to characterize the composite thin films. UV-visible, X-ray diffraction, scanning electron microscope and Hall measurement performed on fluorine doped gallium tin oxide composite are films deposited on polyethylene terephthalate substrates. The diffraction pattern shows the presence of tetragonal structure with (112) special orientation for fluorine doped gallium tin oxide composite films. The doped composite film on F/Ga + Sn mole ratio of 0.35 is observed the lowest electrical resistivity of 3.35 × 10^− 4 Ω cm.     

Screen-printed single-walled carbon nanotube networks and their use for dimethyl methylphosphonate detection

Single-walled carbon nanotube (SWNT) films were prepared on silicon/silica substrates by screen-printed technique at a wafer scale, and their sensing properties to dimethyl methylphosphonate (DMMP) were studied. The SWNT networks were characterized by field-emission scanning electron microscope. The resistance responses to different concentrations of DMMP vapors were investigated at room temperature. The results showed that the resistance changes of the screen-printed SWNT films increased rapidly in varying concentrations ranging from 20 to 200?ppm. The sensor exhibited high resistance responses, good reproducibility and excellent long-term stability for DMMP vapor detection. The screen-printed SWNT networks would be potentially extended to large-scale, low cost and simple manufacturing sensor applications.     

液相电沉积类金刚石薄膜的相关物理化学问题

利用液相电沉积技术制备了含氢类金刚石薄膜(ＤＬＣ);讨论了应用电位和沉积碳源对沉积过程和薄膜结构的影响;结果表明有高介电常数、低粘度、分子中甲基基团直接与极性基团键合的有机液体是合适的沉积碳源;通过增加沉积电位将有利于薄膜中ｓｐ^３碳的生长;最后,作者提出了液相沉积类金刚石薄膜的反应机理－极化－反应机制,在电场的作用下,有机分子被极化并在电极表面反应生成ＤＬＣ薄膜和其他产物．     

Dimethyl methylphosphonate detection with a single-walled carbon nanotube capacitive sensor fabricated by airbrush technique

Single-walled carbon nanotube (SWNT) films were prepared on interdigitated electrodes by airbrush technique, and their sensing properties to dimethyl methylphosphonate (DMMP) were studied. The SWNT films were characterized by field-emission scanning electron microscope. The response to different concentrations of DMMP vapors were investigated at room temperature. The results showed that the capacitance of airbrush SWNT sensor decreased rapidly in varying concentrations ranging from 12 to 60 mg/m³ (2.4–12 ppm). The capacitance sensitivity was about 12.5 % when exposed to 12 mg/m³ DMMP vapor. The capacitance sensitivity was higher when the initial capacitance and loss tangent were higher and the SWNT film was denser. It was found that the capacitance sensitivity was nearly 10 times to the resistance sensitivity. The airbrush SWNT sensor exhibited highly and fast capacitance response, good repeatability and selectivity for DMMP vapor.     

Disordered mesoporous silica low-k thin films prepared by vapor deposition into a triblock copolymer template film

Mesoporous silica films have been prepared by a vapor phase method using tetraethoxysilane (TEOS) in a batch reactor and in a continuous flow reactor. The TEOS molecules penetrated into a triblock copolymer films and then a triblock copolymer/silica composite structure was formed. A two dimensional grazing-incidence small angle X-ray scattering pattern and field emission scanning electron microscopy images of the films indicated that the films possess ordered and disordered regions. The tortuous pore channels in the wormhole-like disordered structure run parallel to the film surface. The mesostructured triblock copolymer/silica composite films were treated with a trimethylethoxysilane (TMES) vapor before and after calcination. The vapor infiltration treatments effectively improved mechanical strength and hydrothermal stability of the films. The dielectric constant of the TMES-treated mesoporous silica films was reduced into the 1.5–1.7 range.     

Aroused problems in the deposition of diamond-like carbon films by using the liquid phase electrodeposition technique

Hydrogenated diamond-like carbon (DLC) films were prepared by using liquid phase electrodeposition technique. The effects of the applied potential and the carbon sources on the deposition process and film structures were studied. It has been found that the organic liquids with high dielectric constants, small viscosities and the methyl group bonding to the polar group are appropriate carbon sources. The increasing of potential improves the formation of sp³ carbon during the deposition process. In a high electric field, organic molecules are polarized and reacted on the surface of the electrode, turning out DLC and other products. It is believed that the reaction follows a polarization-reaction mechanism.     

Superfast-response and ultrahigh-power-density electromechanical actuators based on hierarchal carbon nanotube electrodes and chitosan

Here we report a novel single-walled carbon nanotube (SWNT) based bimorph electromechanical actuator, which consists of unique as-grown SWNT films as double electrode layers separated by a chitosan electrolyte layer consisting of an ionic liquid. By taking advantage of the special hierarchical structure and the outstanding electrical and mechanical properties of the SWNT film electrodes, our actuators show orders-of-magnitude improvements in many aspects compared to previous ionic electroactive polymer (i-EAP) actuators, including superfast response (19 ms), quite wide available frequency range (dozens to hundreds of Hz), incredible large stress generating rate (1080 MPa/s), and ultrahigh mechanical output power density (244 W/kg). These remarkable achievements together with their facile fabrication, low driving voltage, flexibility, and long durability enable the SWNT-based actuators many applications such as artificial muscles for biomimetic flying insects or robots and flexible deployable reflectors.     

Phase behavior and shear alignment in SWNT-surfactant dispersions

The effect of single-walled carbon nanotubes (SWNT) on the phase behavior of the cationic surfactant cetyltrimethylammonium bromide (CTAB) in aqueous solutions is investigated at room temperature. Small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM) are used for characterization of bulk dispersions and nanometrically thin films. Additional carbonaceous additives (fullerenes, multi-walled carbon nanotubes, and carbon black) serve as reference systems. It is found that dispersions of carbonaceous additive (excluding fullerenes) at intermediate surfactant concentrations (below the liquid-crystalline region of the native surfactant) induce demixing and macroscopic phase separation in otherwise homogeneous solutions of CTAB. Two coexisting liquid phases of similar CTAB concentrations are observed, with the carbonaceous species residing within the lower phase. At high CTAB concentrations (liquid-crystal region) the SWNTs are found to incorporate into the ordered lyotropic liquid-crystalline phase while preserving the native d-spacing. Investigation of nanometrically thin films at intermediate surfactant concentrations under external shear reveals shear-induced structure (SIS) in the presence of minute amounts of SWNTs. The effect is found to be exclusive to SWNT and does not occur in dispersions of other carbonaceous additives.     

Reversible light-controlled conductance switching of azobenzene-based metal/polymer nanocomposites

We present a new concept of light-controlled conductance switching based on metal/polymer nanocomposites with dissolved chromophores that do not have intrinsic current switching ability. Photoswitchable metal/PMMA nanocomposites were prepared by physical vapor deposition of Au and Pt clusters, respectively, onto spin-coated thin poly(methylmethacrylate) films doped with azo-dye molecules. High dye concentrations were achieved by functionalizing the azo groups with tails and branches, thus enhancing solubility. The composites show completely reversible optical switching of the absorption bands upon alternating irradiation with UV and blue light. We also demonstrate reversible light-controlled conductance switching. This is attributed to changes in the metal cluster separation upon isomerization based on model experiments where analogous conductance changes were induced by swelling of the composite films in organic vapors and by tensile stress.     

Integration of carbon nanotubes as hole transport electrode in polymer/fullerene bulk heterojunction solar cells

Transparent and conductive single-walled carbon nanotube (SWNT) thin films were fabricated onto glass substrates and their optical and electrical properties were evaluated. Particular attention was given to the dependence of the conductivity and optical transparency on the thickness of the films. Furthermore, the SWNT thin films were integrated in organic photovoltaic devices as the hole transport electrode. The best photovoltaic performance was observed for the devices utilizing 80 nm SWNT films with a sheet resistance of 362 Ω/sq, and a transmittance of 64% at 520 nm. The experiments reveal that SWNTs films can be used as transparent electrodes for efficient, flexible organic photovoltaic devices.     

Charge-transfer interaction in single-walled carbon nanotubes with tetrathiafulvalene and their applications

We observed that single-walled carbon nanotube (SWNT) was aligned in the presence of TTF This alignment was induced by a specific interaction between SWNT and tetrathiafulvalene (TTF), a well-known organic donor. The interaction between the two molecules can be explained by a charge-transfer, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The binding energies of S (2P1/2) and S (2P3/2) were shifted from 163.0 eV and 164.1 eV to 163.9 eV and 165.1 eV, respectively. In Raman spectra of the SWNT-TTF, three peaks of SWNT in radial breathing mode were also upshifted by 4-5 cm(-1). The charge-transfer interaction also contributed in modifying the electronic structure of SWNT and furthermore enhanced the electrical conductivity of SWNT. A more conductive thin film was fabricated using the SWNT-TTF Four-probe measurement revealed that the surface resistance of the SWNT-TTF film was reduced to 4.359 omega at room temperature while that of SWNT film was 6.894 omega. These results enable carbon nanotubes to be utilized more for practically for industrial applications in fabricating peculiar nano-sized building blocks.     

Synthesis of diamond films by pulsed liquid injection chemical vapor deposition using a mixture of acetone and water as precursor

A chemical vapor deposition reactor based on the flash evaporation of an organic liquid precursor was used to grow diamond films on Si substrates. An effective pulsed liquid injection mechanism consisting of an injector, normally used for fuel injection in internal combustion engines, injects micro-doses of the precursor to the evaporation zone at 280 °C and is instantly evaporated. The resulting vapor mixture is transported by a carrier gas to the high-temperature reaction chamber where the diamond nucleates and grows on the substrate surface at temperatures ranging from 750 to 850 °C. The injection frequency, opening time, number of pulses and other injector parameters are controlled by a computer-driven system. The diamond film morphology and structure were characterized by scanning electron microscopy and Raman spectroscopy. The as-deposited diamond films show a ball-shaped morphology with a grain size that varies from 100 to 400 nm, as well as the characteristic diamond Raman band at 1332 cm^− 1. The effects of the experimental parameters and operation principle on the diamond films quality are analyzed and discussed in terms of crystallinity, composition, structure, and morphology.     

Effects of Ni doping on photocatalytic activity of TiO<Subscript>2</Subscript> thin films prepared by liquid phase deposition technique

The TiO₂ thin films doped by Ni uniformly and non-uniformly were prepared on glass substrate from an aqueous solution of ammonium hexa-fluoro titanate and NiF₂ by liquid phase deposition technique. The addition of boric acid as an F ⁻ scavenger will shift the equilibrium to one side and thereby deposition of the film is progressed. The rate of the reaction and the nature of deposition depend on growing time and temperature. The resultant films were characterized by XRD, EDAX, UV and SEM. The result shows that the deposited films have amorphous background, which becomes crystalline at 500°C. The EDAX data confirms the existence of Ni atoms in TiO₂ matrix. XRD analysis reveals the peaks corresponding to Ni but no peak of crystalline NiO was found. The transmittance spectra of Ni uniformly and non-uniformly doped TiO₂ thin films show ‘blue shift and red shift’, respectively. Ni-doped TiO₂ thin films can be used as photocatalyst for the photodegradation of methyl orange dye. It was found that, organic dye undergoes degradation efficiently in presence of non-uniformly Ni-doped TiO₂ thin films when compared to uniformly doped films and pure TiO₂ films under visible light. The photocatalytic activity increases with increase in the concentration of Ni in case of nonuniformly doped thin films but decreases with the concentration when uniformly doped thin films were used.     

Label-free detection of DNA hybridization using pyrene-functionalized single-walled carbon nanotubes: effect of chemical structures of pyrene molecules on DNA sensing performance

We investigate the effect of functional groups of pyrene molecules on the electrical sensing performance of single-walled carbon nanotubes (SWNTs) based DNA biosensor, in which pyrenes with three different functional groups of carboxylic acid (Py-COOH), aldehyde (Py-CHO) and amine (Py-NH2) are used as linker molecules to immobilize DNA on the SWNT films. UV/Visible absorption spectra results show that all of the pyrene molecules are successfully immobilized on the SWNT surface via pi-pi stacking interaction. Based on fluorescence analysis, we show that the amide bonding of amine terminated DNA via pyrene containing carboxylic groups is the most efficient to immobilize DNA on the nanotube film. The electrical detection results show that the conductance of Py-COOH modified SWNT film is increased upon DNA immobilization, followed by further increase after hybridization of target DNAs. It indicates that the pyrene molecules with carboxylic acid groups play an important role to achieve highly efficient label-free detection by nondestructive and specific immobilization of DNAs.     

Single-walled carbon nanotubes used as stationary phase in GC

Single-walled carbon nanotubes (SWNTs) have high surface area, high adsorption ability, and nanoscale interactions. In this study, capillary columns including SWNTs, ionic liquid (IL), and IL + SWNTs for GC were prepared. The separation results showed that SWNTs possessed a wide selectivity toward alkanes, alcohols, aromatic compounds, and ketones, and a SWNT capillary column was a very useful GC column for the separation of gas samples. Coating the IL stationary phase on the SWNT capillary column, the SWNTs were able to improve chromatographic characteristic of ionic liquid. Comparing the IL coated on three graphite carbon black capillary columns, which were prepared by dynamic coating, static coating, and chemical bonding the Carbopack C with on SWNTs capillary column, the capacity factors were much higher on the SWNT column. The SEM showed that SWNTs could be bonded to the inner surface of capillary tubing, and most of them were linked end-to-end to form a layer of network structure of skeletons resulting in a high surface area, which increased the interactions between stationary phase and analytes. This is the first single-wall carbon nanotubes bonded to the fused-silica capillary tubing. In the first approach, SWNTs assist ionic liquid with enhanced chromatographic characteristic in GC. This work indicates that SWNTs make it possible to extend the application range on the newly prepared chromatographic stationary phases for GC.     

Photovoltaic device performance of single-walled carbon nanotube and polyaniline films on n-Si: device structure analysis

In this paper, we explore the use of two organic materials that have been touted for use as photovoltaic (PV) materials: inherently conducting polymers (ICPs) and carbon nanotubes (CNTs). Due to these materials' attractive features, such as environmental stability and tunable electrical properties, our focus here is to evaluate the use of polyaniline (PANI) and single wall carbon nanotube (SWNT) films in heterojunction diode devices. The devices are characterized by electron microscopy (film morphology), current-voltage characteristics (photovoltaic behavior), and UV/visible/NIR spectroscopy (light absorption). We have found that both PANI and SWNT can be utilized as photovoltaic materials in a simple bilayer configuration with n-type Silicon: n-Si/PANI and n-Si/SWNT. It was our aim to determine how photovoltaic performance was affected utilizing both PANI and SWNT layers in multilayer devices: n-Si/PANI/SWNT and n-Si/SWNT/PANI. The short-circuit current density increased from 4.91 mA/cm(2) (n-Si/PANI) to 12.41 mA/cm(2) (n-Si/PANI/SWNT), while an increase in power conversion efficiency by ~91% was also observed. In the case of n-Si/SWNT/PANI and its corresponding device control (n-Si/SWNT), the short-circuit current density was decreased by an order of magnitude. The characteristics of the device were affected by the architecture and the findings have been attributed to the more effective transport of holes from the PANI to SWNT and less effective transport of holes from PANI to SWNT in the respective multilayer devices.