Dry-printed carbon nanotube film based electrochemical immunosensor for total testosterone detection

Single-walled carbon nanotube (CNT) film is a transparent, conductive, and flexible material that exhibits uniform physical and electronic properties1. Several promising optoelectronic and photovoltaic device applications of these films have recently been demonstrated2. However, in previous works, the properties of the junction between the CNT film and the semiconductor substrate (typically Si) have not been properly characterized2. Here, we analyze the interface and transport properties of the junction between the CNT film and Si substrates by fabricating metal-semiconductor (MS) and metal-insulator-semiconductor (MIS) structures, where the CNT film acts as the metal and Si is the semiconductor. Our results help to better understand the electrical properties of the CNT film-Si contacts and to improve the design of optoelectronic and photovoltaic devices which use CNT films as transparent conductive electrodes. Device fabrication begins by preparing CNT films using a vacuum filtration approach1,3 (Fig. 1a) and opening windows in SiO 2 layers on 1015–1016 cm−3 doped n- and p-type Si substrates (Figs. 1c and 1d). For MIS structures, a thin oxide layer is then thermally grown on the exposed Si areas (Fig. 1d2). Next, the CNT films are deposited over both MS and MIS samples (Figs. 1d) and then patterned by O 2 plasma etching3 to form individual devices (Figs. 1e). Finally, metallic rings are deposited on the films for electrical probing (Figs. 1e). For comparison, control samples in which CNT film is replaced with a Ti/Au layer (10/90 nm) have also been fabricated and characterized. An optical image of a CNT film-Si MS structure is shown in Fig. 1b.

The different post treatments of carbon nanotube (CNT) films were studied to investigate the effects of their crystalline perfection on lithium-ion battery performance. The crystal structures of the CNT films were differently developed by heat and acid-heat treatments. The treated CNT films were prepared as an anode electrode for use in flexible lithium ion batteries. This free-standing electrode did not contain a polymeric binder, conducting carbon powder and current collector. The electrochemical performance of the electrodes made with differently treated CNT films was evaluated via charge-discharge test, cyclic voltammetry and impedance measurement. The heat treated CNT films showed a higher capacity (250 mAh/g at a 0.5C rate) due to the increase of their crystalline perfection compared to the raw CNT films. In addition, the CNT film electrodes exhibited a good capacity retention at a high charging rate. This result suggested that the CNT film electrodes performed well without some components within cells. Eventually, the CNT films might be utilized for bendable lithium-ion batteries due to their flexibility and high electrical conductivity. The CNT films would be a potential electrode material for a specific thin/bendable lithium-ion battery that does not need a high capacity.

Functionalized carbon nanotube films by thiol-ene click reaction

Summary form only given. The effect of surface treatment by hydrogen plasma treatment on the uniformity field emission from carbon nanotube (CNT) film will be studied. The CNT film was prepared by using thermal vapour deposition (CVD) on Ni-Cr/Si. The surface of as-grown CNT film will be treated by reactive ion etch (RIE) system in hydrogen plasma. In order to compare the microstructure of untreated CNT film with treated CNT film, scanning electron microscopy and transmission electron microscopy will be employed. The I-V characteristics and uniformity of field emission of both the untreated and treated CNT film will be measured in ultra-high vacuum by using transparent anode technique. The I-V and uniformity of field emission of the CNT film will be compared before and after hydrogen plasma treatment. The mechanism for the observed effect will be investigated.

Carbon nanotubes (CNT) are nano-scale tubular structures which consist of seamless cylindrical shells of graphitic sheets. They were first found by professor Sumio Iijima in the arcdischarge soot between graphite electrodes in 1991 [1]. As a newly discovered carbon allotrope, CNTs have drawn worldwide attentions by their unique electrical, mechanical, and thermal properties. Seven years after their discovery, CNTs were synthesized in the form of arrays by chemical vapor deposition (CVD) [2,3]. For the first time in the history, billions of CNTs were aligned in the vertical direction on a substrate, and their growth position can be controlled by catalyst pattern design [3]. In 2002, we discovered a new type of CNT array, which is named the super-aligned CNT array. This kind of array was composed of clean, straight and defectfree CNTs, and there exist strong Van de Waals forces between adjacent nanotubes. Due to this unique feature, when one picks a strand of CNTs by tweezers or adhesive tapes, continuous long yarns or films can be simply pulled out from the array [4], as shown in figure 1. This discovery had enabled us to produce macroscopic materials with pure CNTs with a quick and easy dry spin process, as shown in figure 2. In 2005, we scaled up the substrate size of the CNT arrays from 1 inch to 4 inches, which could provide CNT films as wide as 10 cm [5]. Figure 1. The mechanism of dry spinning CNT yarns and films from super-aligned CNT arrays. The CNT yarns and films are composed of sparse parallel CNTs along the pulling direction. With the large percent of the vacancy between CNTs, the as drawn films can have transparency up to 90%. Therefore, CNT films can be used as a new type of transparent conductive film which have potential applications in liquid crystal displays and touch panels. The CNT films also have superb flexibility which is desired in flexible IT products. Figure 2. a) Spinning CNT film. b) A SEM image of the CNT film. c) A CNT film shrink into a fiber when passing through a drop of ethanol. d) A SEM image of the CNT fiber.

We describe new transfer method of carbon nanotube (CNT) film onto the poly-dimethysiloxane (PDMS) based on the poor adhesion between Si wafer and Au layer. To combine the CNT film with the polymer-MEMS field, it is required to transfer CNT film onto the polymer substrates. CNT film was fabricated by vacuum filtration method and was transferred onto the Au-deposited Si wafer. Using photolithography process, CNT film was patterned and PDMS is pouring and curing on the wafer. After peeling off the PDMS, patterned CNT film was transferred which was embedded into the PDMS. The possibility of embedded CNT film in the micro system was demonstrated in the application of electro-thermal actuator.

A carbon nanotube (CNT) film on a substrate is characterized at millimeter waves (220 GHz−330 GHz) by metal rectangular waveguide scattering parameters (S-parameters) measurements. The anisotropy of the CNT film is investigated for different orientations of the on-substrate CNT film. The standard Nicolson–Ross–Weir (NRW) approach has been adopted to extract the complex permittivity (εr=ε′-jε″) and permeability (μr=μ′-jμ″) of the on-substrate CNT film from the measured S-parameters. The effective medium theory is then applied to remove the impact of the substrate and characterize the intrinsic CNT film. The observed frequency independent and anisotropic behaviors of the CNT film are very promising indicators that this material could be invaluable for a range of millimeter-wave applications.

Due to their unusual electrical conductivity, carbon nanotubes as the ideal candidates for making future electronic components have extensive application potentiality. In order to meet the requirements in space electronic components for carbon nanotubes, effect of 170 keV proton irradiation on structure and electrical conductivity of multi-walled carbon nanotubes (MWCNTs) film is investigated in this paper. Surface morphologies and microstructure of the carbon nanotube films are examined by scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy, respectively. Electrical conductivities of the carbon nanotube films before and after 170 keV proton irradiation are measured using four-point probe technique. SEM analysis reveals that when proton irradiation fluence is greater than 51015 p/cm2, the surface of the carbon nanotube film becomes rough and loose, and obvious bending, shrinkage, and entanglement of nanotubes are observed. Moreover, the shrinkage phenomenon of MWCNTs caused by proton irradiation is found the first time so far as we know. Based on Raman and XPS analyses, it is confirmed that 170 keV protons can improve the ordered structure of the MWCNTs, and irradiation fluence plays a key role in reducing the disorder in the MWCNTs. Improvement of the irradiated MWCNTs by 170 keV protons can be attributed to restructuring of defect sites induced by knock-on atom displacements. On the other hand, carbon impurities on surface of the MWCNT film are reduced due to the effect of sputtering by the 170 keV proton irradiation, which is also helpful to the improvement of the structure of carbon nanotubes. EPR spectra show that the electrons delocalized over carbon nanotubes decrease with increasing irradiation fluence, implying that the carbon nanotube film is not sensitive to ionizing radiation induced by the 170 keV protons, and the electrical conductivities of the MWCNTs films may be decreased. Four-point probe technical analysis shows that with increasing irradiation fluence, electrical properties of the carbon nanotubes film deteriorate, which can be attributed to the changes in electronic properties and morphology of the MWCNT films induced by 170 keV protons. Acquired results could be beneficial to tailoring of structure and properties for the carbon nanotubes film irradiated by protons to develop nanoelectronics of radiation-resistant systems.

Since their discovered in 1991, carbon nanotubes have demonstrated many remarkable mechanical, electrical and thermal properties, showing promising potentials in many fields. Carbon nano tubes have attracted world-wide attentions during the years, many research work have been performed during the years. At Tsinghua University, we have reported previously two kinds of research work on laser processing of canbon nanotubes: (1) Connection of macro-sized double-walled carbon nanotube strands by laser irradiation; (2) Light emission from multiwalled carbon nanotubes under CW CO2 laser irradiation. This work is a continuous effort in the research area, which focuses on the structure modification of carbon nano tube powder and film by laser shock peening process. A Q-switched nano second Nd:YAG laser pulse induces a shock wave on metal surface with very high pressure (up to Giga or even tens of Giga pascal), which produces normally plastic deformation and a few hundred MPa of the residual compressive stress on the surface of materials, enhancing the anti-fatigue properties of metals and extending the fatigue life of the processed components. We used laser shock peening to process the carbon nanotube powder and carbon nanotube film to explore the possible structure modification. Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), and Micro Raman Spectrum were used to analyze the morphology and spectrum to identify the structure modification of the carbon nanotube powder and film after laser shock peening process and then to establish the relationship between the process parameters and the structure modification. The research impact and potential applications were discussed based on the research.Since their discovered in 1991, carbon nanotubes have demonstrated many remarkable mechanical, electrical and thermal properties, showing promising potentials in many fields. Carbon nano tubes have attracted world-wide attentions during the years, many research work have been performed during the years. At Tsinghua University, we have reported previously two kinds of research work on laser processing of canbon nanotubes: (1) Connection of macro-sized double-walled carbon nanotube strands by laser irradiation; (2) Light emission from multiwalled carbon nanotubes under CW CO2 laser irradiation. This work is a continuous effort in the research area, which focuses on the structure modification of carbon nano tube powder and film by laser shock peening process. A Q-switched nano second Nd:YAG laser pulse induces a shock wave on metal surface with very high pressure (up to Giga or even tens of Giga pascal), which produces normally plastic deformation and a few hundred MPa of the residual compressive stress on t...

We demonstrate the Schottky behavior of single-walled carbon nanotube (CNT) film contacts on GaAs by fabricating and characterizing metal-semiconductor-metal (MSM) photodetectors with CNT film electrodes. We extract the Schottky barrier height of CNT film contacts on GaAs by measuring the dark I-V characteristics as a function of temperature. The results show that at temperatures above ∼260 K, thermionic emission of electrons with a barrier height of ∼0.54 eV is the dominant transport mechanism in CNT film–GaAs junctions, whereas at lower temperatures, tunneling begins to dominate suggested by the weak dependence of current on temperature. Assuming an ideal MS diode, this barrier height corresponds to a CNT film workfunction of ∼4.6 eV, which is in excellent agreement with the previously reported values. Furthermore, we characterize the effect of device geometry on the dark current and find that dark currents of the MSM devices scale rationally with device geometry, such as the device active area, finger width, and finger spacing. Finally, we compare the dark and photocurrent of the CNT film-based MSM photodetectors with standard metal-based MSMs. We find that MSM devices with CNT film electrodes exhibit a higher photocurrent-to-dark current ratio while maintaining a comparable responsivity relative to metal control devices. These results not only provide valuable information about the fundamental properties of the CNT film–GaAs interface but also open up the possibility of integrating CNT films as transparent and conductive Schottky electrodes in conventional semiconductor electronic and optoelectronic devices.

The quasi‐static tensile properties of carbon nanotube (CNT) films have been extensively investigated, yet research on their impact tensile properties at high strain rates remains scarce. In this article, CNT films prepared by floating catalyst chemical vapor deposition (FCCVD) method were densely arranged by chlorosulfuric acid (CSA) under wet stretching. The Instron 3365 and miniaturized split Hopkinson tension bar (SHTB) were used to conduct tensile testing at different strain rates. The findings reveal that CSA wet‐stretching markedly enhances the density and orientation of CNT films, resulting in significant improvements in tensile properties with a notable strain rate effect. Specifically, when immersed for 60 s under a draft ratio of 40% and a strain rate of 1900 s−1, the densified CNT films exhibit maximum stress and energy absorption values of 777.44 MPa and 54.79 MJ/m3, respectively, achieving a 637.1% and 425.7% increase compared with the original film. This research provides a convenient and feasible strategy to prepare CNT films with high energy absorption tolerance across various strain rates, thus expanding the practical application potential of CNT films.Highlights The study innovates a posttreatment way to produce superior FCCVD CNT films. CSA treatment and wet stretching enhance CNT films' mechanical properties. Dynamic fracture strength boosts over 600% and energy absorption raises over 400%. CSA can purify FCCVD‐prepared CNT films, greatly improving their properties. The Prep can be effectively integrated with the direct spinning process.

Enhanced field emission properties of carbon nanotube films using densification technique

Developing strong and tough carbon nanotube films by a proper dispersing strategy and enhanced interfacial interactions

Field emission property of Ga-doped carbon nanotube (CNT) film has been studied and compared with those of un-doped, N-doped as well as B and N co-doped CNT films. It is found that the Ga-doped CNT film exhibits superior field emission property to the other films. The turn-on field for Ga-doped CNT film is well below 1.0 V/μm, lower than those for un-doped (2.22 V/μm), N-doped (1.1 V/μm), B and N co-doped (4.4 V/μm) CNT films. Its current density reaches 5000 μA/cm2at 2.6 V/μm which is well above those for un-doped (1400 μA/cm2), N-doped (3000 μA/cm2) as well as B and N co-doped (2) CNT films at applied electric field of 5.7 V/μm. First principles calculations were carried out to obtain the binding energy and electronic nature altering of a CNT by Ga doping. It is shown that Ga-doped CNT (8,0) alters from semiconductor to intrinsic metal and a binding energy of 2.7527 eV is obtained. The field emission property can not simply be explained by the defect concentration, but can be understood by significant altering in the local density of states near the Fermi level introduced by dopants.

In last decade, organic solar cell (OSC) has attracted many attentions due to its special advantages such as low cost, easy large scale fabrication and high flexibility. However, the stylish OSC anode Indium Tin Oxide (ITO) is not flexible and would undergo breakdown on bending of flexible substrates. What’s more, ITO is costly since the limited indium in the nature. Recently, carbon nanotubes (CNTs) film shows potential to alternate ITO as high performance flexible anode since its ability to surmount these constrains and similar work function with ITO. Nevertheless the conductivity and transparence of CNTs film are still far below its counterpart. Additionally, a dependable model of OSC with CNTs film anode is not well established. In this paper, transparent conductive CNTs film is prepared on glass and plastic substrates at first. A facile filtration and pressing fabrication method is introduced. Our empirical model shows that dimension of CNTs bundles has significant effect on CNT network performance. FTIR shows the post-treatment effect on CNTs film. The OSC with high performance CNTs film anode shows similar efficiency compared with regular OSC with ITO anode.