Single-walled Carbon Nanotube Field-effect Transistors Research Articles

Controlling the electronic properties of SWCNT FETs via modification of the substrate surface prior to atomic layer deposition of 10 nm thick Al2O3 film

We demonstrate the controllability of the electronic transport properties of single-walled carbon nanotube (SWCNT) field effect transistors (FETs) via the use of 10 nm thick atomic-layer-deposited aluminum oxide (Al2O3) gate dielectric films, where the substrate surfaces were modified with differently functionalized self-assembled monolayers (SAMs) prior to their growth, namely SAMs with hydrophobic (−CH3) or hydrophilic (−OH) groups. Al2O3 grown on a hydrophilic surface causes the SWCNT FETs to keep their intrinsic p-type transfer characteristics by alleviating the electron-doping effect originating from defects in the Al2O3 film. However, the SAM with methyl groups increases the defect density of the Al2O3 film, enhancing the n-type transfer characteristics and inducing ambipolar to n-type behavior in the SWCNT FETs. In this work, we find clues about the distribution of charged defects in the Al2O3 film, which strongly influences the transfer characteristics of the SWCNT FETs, by measuring the thickness-dependent flat band voltages.

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-Throughput Peptide Epitope Mapping Using Carbon Nanotube Field-Effect Transistors

Label-free and real-time detection technologies can dramatically reduce the time and cost of pharmaceutical testing and development. However, to reach their full promise, these technologies need to be adaptable to high-throughput automation. To demonstrate the potential of single-walled carbon nanotube field-effect transistors (SWCNT-FETs) for high-throughput peptide-based assays, we have designed circuits arranged in an 8 × 12 (96-well) format that are accessible to standard multichannel pipettors. We performed epitope mapping of two HIV-1 gp160 antibodies using an overlapping gp160 15-mer peptide library coated onto nonfunctionalized SWCNTs. The 15-mer peptides did not require a linker to adhere to the non-functionalized SWCNTs, and binding data was obtained in real time for all 96 circuits. Despite some sequence differences in the HIV strains used to generate these antibodies and the overlapping peptide library, respectively, our results using these antibodies are in good agreement with known data, indicating that peptides immobilized onto SWCNT are accessible and that linear epitope mapping can be performed in minutes using SWCNT-FET.

Rapid and label-free detection of H5N1 virus using carbon nanotube network field effect transistor

DNA hybridization-based detection techniques are widely used in genetics, medicine, and drug discovery. However, the current techniques are usually based on labels and reagents that are time consuming and complex to implement. In this study, we report a label-free DNA sensor based on single-walled carbon nanotube field effect transistor (SWCNTFET) for selective DNA hybridization detection of H5N1 virus. A network of single-walled carbon nanotubes (SWCNTs) acts as the conductor channel. Probe DNA sequences were adsorbed onto SWCNTs. The developed DNA sensor can effectively detect full-complementary DNA with concentration as low as 1.25 pM. The sensitivity of the DNA sensor reached approximately 0.28 nM/nA. The effect of the parameters, including DNA probe concentration, its complementary concentration, mismatched sequence, and hybridization time, on the sensor response was also studied. The results showed the potential application of the DNA sensor for medical, environmental, and epidemic detection.

Study on the large-scale assembly and fabrication method for SWCNTs nano device

The large-scale assembly and fabrication method for single-walled carbon nanotube (SWCNT) nano devices was implemented. Assembly of SWCNT field effect transistor (FET) was realized by floating potential dielectrophoresis approach. The simulation of floating potential distribution of the chip was performed by comsol multiphysics coupling software. Six hundred devices were assembled on the area of less than one square centimeter. The fabricated devices were characterized by atomic force microscopy and scanning electron microscopy. The experimental results showed that large-scale assembly had been realized, and the success rate of ideal assembly for SWCNT FET had been assessed.

Detecting Lyme disease using antibody-functionalized single-walled carbon nanotube transistors

We examined the potential of antibody-functionalized single-walled carbon nanotube (SWNT) field-effect transistors (FETs) to use as a fast and accurate sensor for a Lyme disease antigen. Biosensors were fabricated on oxidized silicon wafers using chemical vapor deposition grown carbon nanotubes that were functionalized using diazonium salts. Attachment of Borrelia burgdorferi (Lyme) flagellar antibodies to the nanotubes was verified by atomic force microscopy and electronic measurements. A reproducible shift in the turn-off voltage of the semiconducting SWNT FETs was seen upon incubation with B. burgdorferi flagellar antigen, indicative of the nanotube FET being locally gated by the residues of flagellar protein bound to the antibody. This sensor effectively detected antigen in buffer at concentrations as low as 1ng/ml, and the response varied strongly over a concentration range coinciding with levels of clinical interest. Generalizable binding chemistry gives this biosensing platform the potential to be expanded to monitor other relevant antigens, enabling a multiple vector sensor for Lyme disease. The speed and sensitivity of this biosensor make it an ideal candidate for development as a medical diagnostic test.

Performance Evaluation of 32-nm CNT-OPAMPs in Analog Circuits: Design and Comparison of Leapfrog Filters

In this paper, we have presented the design and characteristic performance evaluation of a 6-order Leapfrog Filter. First we designed the filter by using Silicon-based CMOS Operational Amplifiers (Si-OPAMPs). Then we designed the filter with Carbon Nanotube-based Operational Amplifiers (CNT-OPAMPs) using a benchmark nine-transistor Operational Amplifier (OPAMP) model with single-walled Carbon Nanotube Field-Effect Transistors (SW-CNTFETs) as primary building-blocks for 32nm technology. We compared the performance between the two and achieved higher phase margin, improved power dissipation, and significantly higher input resistance for the CNT-OPAMP based filter. Then we further evaluated the performance of the CNT-OPAMP based filter by changing the number of SWNTs used in the intrinsic channel region of the CNTFET, keeping all other design parameters the same. Our simulation-based assessment has shown a satisfactory superiority for CNT-OPAMP filter design in comparison with Si-based CMOS filter design. The results obtained suggest that the CNT-OPAMP has a promising potential for low-power, high-speed applications in both analog and mixed-signal nanoelectronic circuits.

Single Molecule Dynamic Transduction by Carbon Nanotube Circuits

Nanoscale electronic devices like field-effect transistors (FETs) have long promised to provide sensitive, label-free detection of biomolecules. In particular, single-walled carbon nanotubes (SWNTs) have the requisite sensitivity to detect single molecule events, and have sufficient bandwidth to directly monitor single molecule dynamics in real time. Recent measurements have demonstrated this premise by monitoring the dynamic, single-molecule processivity of three different enzymes: lysozyme, protein kinase A, and the Klenow Fragment of polymerase I. Initial successes in each case indicated the generality and attractiveness of SWNT FETs as a new tool to complement other single molecule techniques. However, further generalization of the SWNT FET technique demands reliable design rules that can predict the success and applicability of these devices. Here, we address this need by focusing on the transduction mechanisms that link enzyme processivity to electrical signal generation in a SWNT FET. Using ten different lysozyme variants synthesized by mutagenesis, we systematically dissect the enzyme-SWNT interaction in order to understand this transduction. The data prove that mechanical displacements of charged functionalities near the SWNT attachment site are the primary sources of transduction, and that the resulting devices are sensitive enough to track the motions of just one charged amino acid. The purposeful incorporation of a charged group at a particular location allows the device to be designed to have sensitivity to particular chemical activities or allosterically-driven mechanical motions. The findings provide rules for the creation of similarly effective nanocircuits using a wide range of enzymes or proteins.

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.

The selective removal of metallic carbon nanotubes from As-grown arrays on insulating substrates

We present a method of selectively removing metallic single-walled carbon nanotubes (SWCNTs) from as-grown arrays on quartz substrates. The process utilizes an external silicon piece as a temporary global top gate to increase the resistance of the semiconducting SWCNTs while current is passed through the metallic SWCNTs, causing electrical breakdown through joule heating. The resulting SWCNT field-effect transistors (FETs) consistently produce on/off current ratios greater than 1000. Additionally, we find that the high frequency parasitic losses between 1 GHz and 6 GHz on the completed SWCNT FETs are significantly lower than on comparable SWCNT FETs fabricated on silicon substrates.

Single-walled carbon nanotube field-effect transistors with graphene oxide passivation for fast, sensitive, and selective proteindetection

We report a novel technique to design an insulating membrane with attachment sites on top of single-walled carbon nanotubes (SWNTs) for achieving high sensitivity and selectivity in an SWNT field-effect transistor (FET) biosensor. Because electronic properties of SWNTs are extremely sensitive to the surface state, direct immobilization of proteins or DNAs onto SWNTs will generate surface defects through chemical reactions or physical adsorption, resulting in degradation of performance and instability of SWNT-FET biosensor devices. Here we demonstrate fabrication of novel FET biosensor devices using SWNTs as semiconducting channels, and a monolayer of graphene oxide (GO) membrane covered on the SWNTs as a passivating layer to avoid direct attachment of biomaterials on SWNTs, thereby preserving intrinsic electrical properties of SWNTs. Gold nanoparticles (Au NPs) are decorated on the GO layer for the covalent attachment of biotin, which is then used to selectively detect the target avidin. The passivation with GO layers can effectively lead to enhanced sensitivity of biosensor devices through increasing the on/off ratio of FET sensors.

A peptide receptor-based bioelectronic nose for the real-time determination of seafood quality

We herein report a peptide receptor-based bioelectronic nose (PRBN) that can determine the quality of seafood in real-time through measuring the amount of trimethylamine (TMA) generated from spoiled seafood. The PRBN was developed using single walled-carbon nanotube field-effect transistors (SWNT-FETs) functionalized with olfactory receptor-derived peptides (ORPs) which can recognize TMA and it allowed us to sensitively and selectively detect TMA in real-time at concentrations as low as 10fM. Utilizing these properties, we were able to not only determine the quality of three kinds of seafood (oyster, shrimp, and lobster), but were also able to distinguish spoiled seafood from other types of spoiled foods without any pretreatment processes. Especially, the use of small synthetic peptide rather than the whole protein allowed PRBNs to be simply manufactured through a single-step process and to be reused with high reproducibility due to no requirement of lipid bilayers. Furthermore, the PRBN was produced on a portable scale making it effectively useful for the food industry where the on-site measurement of seafood quality is required.

Radiation Effects in Carbon Nanoelectronics

We experimentally investigate the effects of Co-60 irradiation on the electrical properties of single-walled carbon nanotube and graphene field-effect transistors. We observe significant differences in the radiation response of devices depending on their irradiation environment, and confirm that, under controlled conditions, standard dielectric hardening approaches are applicable to carbon nanoelectronics devices.

Study on dual-lateral-gate suspended-body single-walled carbon nanotube field-effect transistors

Self-aligned suspended-body single-walled (SW) carbon nanotube field-effect transistors (CNFETs) with dual lateral gates have been demonstrated. Two independent lateral gates are symmetrically placed less than 100nm away from the CNT channel. The operations of the suspended-body SWCNFETs in single-gate (SG) mode and dual-gate (DG) mode are analyzed in detail. In SG mode, strong controllability of the primary gate and the tuning effect of the second gate have been observed. Tunable threshold voltage and transconductance with constant subthreshold swings are the typical effects in the suspended-body CNFETs. Compared to SG mode, superior characteristics have been obtained in DG mode: remarkably improved subthreshold slope (from 130mV/decade to 86mV/decade), three time larger on-current and four times larger transconductance. The dual-lateral-gate suspended-body CNFETs are of great interest for complementary metal–oxide–semiconductor (CMOS) and nano-electro-mechanical-systems (NEMS) devices, such as tunable/switchable resonators for sensing and radio-frequency applications.

Self-aligned lateral dual-gate suspended-body single-walled carbon nanotube field-effect transistors

Self-aligned lateral dual-gate suspended-body single-walled carbon nanotube (CNT) field-effect transistors (CNFETs) have been demonstrated. A nano-precision assembly method using resist-assisted ac-dielectrophoresis is applied. Superior I-V characteristics controlled by two independent lateral gates spaced sub-100 nm away from the CNT body are experimentally observed and studied. The dual-gate operation mode effectively boosts the device performance: 34% smaller subthreshold slope, three times larger on-current, and four times higher transconductance. The proposed dual-gate suspended-body CNFETs hold promise for bottom-up fabrication of advanced complementary metal-oxide-semiconductor circuits and nano-electro-mechanical systems devices, such as tunable/switchable resonators for sensing and radio-frequency applications.

Single-molecule dynamics of lysozyme processing distinguishes linear and cross-linked peptidoglycan substrates.

The dynamic processivity of individual T4 lysozyme molecules was monitored in the presence of either linear or cross-linked peptidoglycan substrates. Single-molecule monitoring was accomplished using a novel electronic technique in which lysozyme molecules were tethered to single-walled carbon nanotube field-effect transistors through pyrene linker molecules. The substrate-driven hinge-bending motions of lysozyme induced dynamic electronic signals in the underlying transistor, allowing long-term monitoring of the same molecule without the limitations of optical quenching or bleaching. For both substrates, lysozyme exhibited processive low turnover rates of 20-50 s(-1) and rapid (200-400 s(-1)) nonproductive motions. The latter nonproductive binding events occupied 43% of the enzyme's time in the presence of the cross-linked peptidoglycan but only 7% with the linear substrate. Furthermore, lysozyme catalyzed the hydrolysis of glycosidic bonds to the end of the linear substrate but appeared to sidestep the peptide cross-links to zigzag through the wild-type substrate.

Detection of Lectins using Glyco-Functionalized Nanosensors

ABSTRACTWe have used single-walled carbon nanotube field-effect transistor (SWNT-FET) and chemically converted graphene field-effect transistor (CCG-FET) devices to probe the interactions between carbohydrates and their recognition lectins. Porphyrin- and pyrene-based glycoconjugates were used as receptor molecules and the target lectins were two bacterial lectins that present different carbohydrate preference, namely PA-IL, PA-IIL from Pseudomonas aeruginosa and a plant lectin Concanavalin A. The specific binding between lectin and carbohydrate can be transduced to the change in FET device conductance. An initial study with SWNT-FET noncovalently functionalized with porphyrin-based glycoconjugates showed both good selectivity and sensitivity. To compare SWNT and CCG performance, pyrene- and porphyrin-based glycoconjugates were functionalized noncovalently on the surface of CCG-FET and SWNT-FET devices, which were then treated with non-specific and specific lectins. The responses were compared and rationalized using computer-aided models of carbon nanostructure/glycoconjugate interactions. Fluorescence microscopy, atomic force microscopy, UV-vis-NIR spectroscopy and Isothermal titration microcalorimetry (ITC) measurements were used to confirm the electrical results.

Specific Binding of Alzheimer's Aβ Peptide Fibrils to Single-Walled Carbon Nanotubes

Amyloids constitute a class of protein and protein fragments believed to be involved in the pathologies associated with Alzheimer's, Parkinson's and Creutzfeldt-Jakob diseases. These proteins can self-assemble into unique fibrillar structures that are resistant to normal protein degradation. Interesting recent developments in the study of amyloid fibrils demonstrate that they bind carbon allotropes. In this study using single-walled carbon nanotube field-effect transistors (SWCNT-FETs), we show that the fibrillar form of Alzheimer's amyloid β (1–40) and (1–42) peptides specifically bind non-functionalized SWCNT in a saturable manner. Both peptides exhibited near identical binding curves with half-maximal binding concentrations of approximately 12 μg/ml. Binding of the peptides to SWCNTs was diminished by including dimethyl sulphoxide (DMSO) at concentrations that inhibits fibril formation. Lastly a monoclonal antibody (BAM-10), which binds to the N-terminal region of Alzheimer's amyloid fibrils, recognizes the amyloid peptides adhering to SWCNTs in the absence of DMSO, but not in the presence of 75% DMSO. Taken together, these results suggest that the fibrillar form of the Alzheimer's amyloid peptides are specifically binding to SWCNTs.

Single-Walled Carbon Nanotube-Based Gas Sensors for NO2 Detection

An efficient method for nitrogen dioxide (NO2) gas detection in single-walled carbon nanotubes (SWCNTs) ordered using dielectrophoretical (DEP) technology after dispersion in sodium dodecyl sulfate (SDS) surfactant solution. Atom force microscopy (AFM) and scanning electron microscopy (SEM) images revealed that SWCNTs were assembled between the microelectrodes. SWCNTs were affected by the electrophoretic force which was carried out by the related theoretical analysis in a nonuniform electric field. SWCNT field effect transistors (SWCNT-FETs) geometry was obtained. The electrical performance of NO2 gas sensor with SWCNT-FETs structure was tested before and after NO2 at room temperature. Experimental results that the efficient assembly of SWCNTs were obtained when the applied alternating current voltage has a frequency of 2 MHz and an amplitude of 10 V. SWCNTs-based gas sensor had high sensitivity to NO2, and the electrical conductance of NO2 gas sensor reduced two times. SWCNTs surface gas molecules were washed out by means of ultraviolet ray irradiation in 10 minutes. NO2 gas sensor could be duplicated. Meanwhile, it also provided an effective method of assembly and manufacture for other one-dimensional nanomaterials assembly of nanoelectronic devices.

Resist-assisted assembly of single-walled carbon nanotube devices with nanoscale precision

We report a novel resist-assisted dielectrophoresis method for single-walled carbon nanotube (SWCNT) assembly. It provides nanoscale control of the location, density, orientation and shape of individual SWCNTs. Sub-50nm accuracy and a yield higher than 85% have been achieved. Using the method, we demonstrate suspended-body SWCNT field-effect transistors (FETs) with back-gate and sub-100nm air-gap lateral-gate configurations. The suspended-body SWCNT FETs show excellent electrical characteristics with Ion/Ioff∼107, ultra-low off currents ∼10−14A and small subthreshold swings. The technique contributes to the ultimate solution for bottom-up fabrication of a broad field of CNT-based devices, such as: complementary metal–oxide-semiconductor and nano-electrical–mechanical-system devices for sensing and radio-frequency applications. Moreover, the versatile method could be applied to the assembly of many other promising materials, such as: nanowires and graphene flakes.