Network Single-walled Carbon Nanotube Research Articles

Selective detection of chlorine at room temperature utilizing single-walled carbon nanotubes functionalized with platinum nanoparticles synthesized via ultraviolet irradiation

In this study, photoreduction by an ultraviolet (UV) irradiation method was applied to synthesizing platinum (Pt) nanoparticles into networked single-walled carbon nanotubes (SWCNTs). To investigate the growth behaviour of Pt nanoparticles, we systematically controlled the UV irradiation intensity and exposure time. These processing factors significantly influenced the formation behaviour of Pt nanoparticles regarding diameter and density. Utilizing the photoreduction process, the sidewalls of SWCNTs were uniformly functionalized with Pt nanoparticles synthesized under optimal UV conditions. For application as practical chlorine (Cl2) sensors, the sensing performances of Pt nanoparticle-functionalized SWCNTs for Cl2 were compared against the injection of other gases such as nitrogen dioxide, ammonia and carbon monoxide. The results indicate that UV irradiation is an effective way to functionalize the sidewalls of SWCNTs with catalytic Pt nanoparticles. In addition, the Cl2 selectivity and response of SWCNT-based gas sensors were enhanced by functionalization with catalytic Pt nanoparticles.

Multilevel non-volatile data storage utilizing common current hysteresis of networked single walled carbon nanotubes

The characteristic source-drain current hysteresis frequently observed in field-effect transistors with networked single walled carbon-nanotube (NSWNT) channels is problematic for the reliable switching and sensing performance of devices. But the two distinct current states of the hysteresis curve at a zero gate voltage can be useful for memory applications. In this work, we demonstrate a novel non-volatile transistor memory with solution-processed NSWNTs which are suitable for multilevel data programming and reading. A polymer passivation layer with a small amount of water employed on the top of the NSWNT channel serves as an efficient gate voltage dependent charge trapping and de-trapping site. A systematic investigation evidences that the water mixed in a polymer passivation solution is critical for reliable non-volatile memory operation. The optimized device is air-stable and temperature-resistive up to 80 °C and exhibits excellent non-volatile memory performance with an on/off current ratio greater than 10(4), a switching time less than 100 ms, data retention longer than 4000 s, and write/read endurance over 100 cycles. Furthermore, the gate voltage dependent charge injection mediated by water in the passivation layer allowed for multilevel operation of our memory in which 4 distinct current states were programmed repetitively and preserved over a long time period.

Field and temperature dependent electron transport properties of random network single walled and multi walled carbon nanotubes

Field and temperature dependent electron transport properties of random network single walled carbon nanotubes (SWCNTs) and multi walled carbon nanotubes (MWCNTs) were investigated and compared. The electrical characterizations of drop casted CNT samples were done by two probe measurements by varying temperatures from 80 K to 300 K in the field region 1–400 V cm−1. The charge transport mechanisms at low (<3.5 V) and high (>3.5 V) fields were analyzed from measured I–V characteristic curves at various temperatures (<300 K) with respect to applied field. At low field, the ohmic behavior was observed and at high field the charge transport appears to be Poole–Frenkel type in both types of CNTs network. Electron–electron and electron–phonon scatterings in the localized defect states dominate in SWCNTs, whereas in MWCNTs the delocalization of charge carriers as well as the scattering centers is responsible due to the presence of inner shells. Because of the different nature of chirality in random network, the SWCNTs displayed lower conduction when compared to MWCNTs. The variation in Poole–Frenkel co-efficient (β) (SWCNTs-0.193 × 10−22; MWCNTs-0.089 07 × 10−22 J V1/2 cm−1/2), activation energy (SWCNTs-90 meV; MWCNTs-60 meV for field of ) and trap energy levels (SWCNTs-109 meV; MWCNTs-37 meV) are discussed for both SWCNTs and MWCNTs.

Mapping Charge Transport by Electroluminescence in Chirality-Selected Carbon Nanotube Networks

We demonstrate random network single-walled carbon nanotube (SWNT) field-effect transistors (FETs) in bottom contact/top gate geometry with only five different semiconducting nanotube species that were selected by dispersion with poly(9,9-dioctylfluorene) in toluene. These FETs are highly ambipolar with balanced hole and electron mobilities and emit near-infrared light with narrow peak widths (<40 meV) and good efficiency. We spatially resolve the electroluminescence from the channel region during a gate voltage sweep and can thus trace charge transport paths through the SWNT thin film. A shift of emission intensity to large diameter nanotubes and gate-voltage-dependent photoluminescence quenching of the different nanotube species indicates excitation transfer within the network and preferential charge accumulation on small band gap nanotubes. Apart from applications as near-infrared emitters with selectable emission wavelengths and narrow line widths, these devices will help to understand and model charge transport in realistic carbon nanotube networks.

High-performance carbon nanotube network transistors fabricated using a hole punching technique

We develop a unique approach for fabricating high-performance carbon nanotube network transistors based on lithographic density control via a hole punching technique. In an as-grown dense network of single-walled carbon nanotubes (SWNTs), approximately two-thirds of the tubes are semiconducting and one-third are metallic, leading to a poor on/off ratio ( 10 000, with a high yield (>85%) and a large carrier mobility (20 cm2 V−1 s−1). The on current degradation is not severe, unlike the degradation in networks prepared with a homogeneous density. The hole punching technique introduced here may be applied to network SWNT field effect transistor applications and provide new opportunities for controlling the properties of one-dimensional nanostructured percolating systems.

Photonic Responses of Devices Based on Horizontally Aligned and Network Single-Walled Carbon Nanotubes and the Effect of Environmental Gas on Device Performance

Combining bottom-up with top-down method, devices based on horizontally aligned and network single-walled carbon nanotubes (SWCNTs) are fabricated for infrared (IR) detecting applications. Instead of thermal effect, quantum effect plays a dominant role in the sensing process. Under 0.3 mW/mm2 IR lamp illumination at 78 K in vacuum, the aligned device has a conductance increase as large as 68%, while the conductance of the network device increases 12%. Both devices perform much better than the SWCNT-polymer nanocomposites. Interestingly, at room temperature in the air, the photoresponse of the aligned device decreases compared to that in vacuum, while the network device performance boosts. We also test the devices in ambient argon, helium and nitrogen, respectively, similar results are achieved. Intertube junctions are considered to be responsible for the different behaviors. Our findings may pave a way for the design, fabrication, and packaging of low-cost and high-performance SWCNT-based IR sensors.

Network single-walled carbon nanotube biosensors for fast and highly sensitive detection ofproteins

Detection of proteins is powerfully assayed in the diagnosis of diseases. A strategy for thedevelopment of an ultrahigh sensitivity biosensor based on a network single-walled carbonnanotube (SWNT) field-effect transistor (FET) has been demonstrated. MetallicSWNTs (m-SWNTs) in the network nanotube FET were selectively removed orcut via a carefully controlled procedure of electrical break-down (BD), and leftnon-conducting m-SWNTs which magnified the Schottky barrier (SB) area. Thisnanotube FET exhibited ultrahigh sensitivity and fast response to biomolecules. Thelowest detection limit of 0.5 pM was achieved by exploiting streptavidin (SA) or abiotin/SA pair as the research model, and BD-treated nanotube biosensors had a2 × 104-fold lower minimum detectable concentration than the device without BD treatment. Theresponse time is in the range of 0.3–3 min.

Doping-free fabrication of n-type random network single-walled carbon nanotube field effect transistor with yttrium contacts

This work reports the realization of high performance n-type random network single-walled carbon nanotube (rn-SWCNT) field effect transistor (FET) by means of contact engineering, where a low work function metal, Yttrium (Y), is used as the source and drain contacts. The presence of crossed metallic ( m-) and semiconducting ( s-) SWCNT junctions in the channel of rn-SWCNT FETs, which form p-type rectifying Schottky barrier, is believed to introduce non-negligible hole current in the fabricated FETs and lead to undesirable ambipolar characteristic. By means of soaking in 2,4,6-triphenylpyrylium tetrafluoroborate (2,4,6-TPPT), we have successfully converted the ambipolar rn-SWCNT FETs to highly unipolar n-type devices by selectively removing the m-SWCNTs in the FET channel. The best characteristics of our unipolar n-type rn-SWCNT FETs are as follows: on/off current ratio up to ∼10 5, mobility as high as 25 cm 2 V −1 s −1, and transconductance of 0.12 μS/μm; they have demonstrated air-stable n-type characteristics and are also more reproducibility than individual SWCNT FETs.

Optimization of single-walled carbon nanotube growth and study of the hysteresis of random network carbon nanotube thin film transistors

Random network single-walled carbon nanotube (SWNT)-based thin film transistors show excellent properties in sensors, electronic circuits, and flexible devices. However, they exhibit a significant amount of hysteresis behavior, which should be solved prior to use in industrial applications. This paper provides optimum conditions for the growth of random network SWNTs and reveals that the observed hysteresis behavior originates from the charge exchange between the SWNTs and the dielectric layer rather than from changes in the intrinsic properties of the SWNTs. This was proven by studying the conditions of stepwise gate sweep experiments and time measurements. This paper also shows that top gate SWNT thin film transistors (TFTs) with an SU-8 dielectric layer could provide a practical solution to the hysteresis problem for SWNT TFTs in electronic circuit applications.

Thin film transistors using preferentially grown semiconducting single-walledcarbon nanotube networks by water-assisted plasma-enhanced chemical vapordeposition

Nearly perfect semiconducting single-walled carbon nanotube random network thin filmtransistors were fabricated and their reproducible transport properties were investigated.The networked single-walled carbon nanotubes were directly grown by water-assistedplasma-enhanced chemical vapor deposition. Optical analysis confirmed that the nanotubeswere mostly semiconductors without clear metallic resonances in both the Raman and theUV–vis–IR spectroscopy. The transistors made by the nanotube networks whose densitywas much larger than the percolation threshold also showed no metallic paths.Estimation based on the conductance change of semiconducting nanotubes in theSWNT network due to applied gate voltage difference (conductance difference foron and off state) indicated a preferential growth of semiconducting nanotubeswith an advantage of water-assisted PECVD. The nanotube transistors showed10−5 ofon/off ratioand ∼8 cm2 V−1 s−1 of field effect mobility.

Deposition of silver nanoparticles on single wall carbon nanotubes via a self assembled block copolymer micelles

We demonstrate a facile route to decorate the surface of networked single walled carbon nanotubes (SWNTs) with silver nanoparticles (Ag NPs). The method is based on utilization of either spherical poly(styrene- b-4vinylpyridine) (PS- b-P4VP) or cylindrical poly(styrene- b-acrylic acid) (PS- b-PAA) copolymer micelles capable of stabilizing nanotubes in solution and subsequently forming a thin and uniform block copolymer/SWNTs composite film upon spin coating. The selective doping of silver acetate into either P4VP or PAA domains in a thin composite film, followed by thermal treatment, results in the formation of Ag NPs in the cores of micelles. Further heat treatment at 500 °C sufficiently high for degrading both block copolymers allows us to fabricate a thin SWNTs network in which Ag NPs are efficiently deposited on the surface of nanotubes. A sharp surface plasmon absorption band around 400 nm of the networked SWNTs with Ag NPs confirms the presence of Ag NPs with narrow distribution in their size.

Distinguishing self-gated rectification action from ordinary diode rectification in back-gated carbon nanotube devices

Self-gating leading to rectification action is frequently observed in two-terminal devices built from individual or networked single-walled carbon nanotubes (SWCNTs) on oxidized Si substrates. The current-voltage (I-V) curves of these SWCNT devices remain unaltered when switching the measurement probes. For ordinary diodes, the I-V curves are symmetric about the origin of the coordinates when exchanging the probes. Numerical simulations suggest that the self-gated rectification action should result from the floating semiconducting substrate which acts as a back gate. Self-gating effect is clearly not unique for SWCNT devices. As expected, it is absent for devices fabricated on insulating substrates.