Single-walled Carbon Nanotube Devices Research Articles

Novel pyrenehexafluoroisopropanol derivative-decorated single-walled carbon nanotubes for detection of nerve agents by strong hydrogen-bonding interaction

Fabrication of hybridized single-walled carbon nanotube (SWNT) device based on novel sensing material N-4-Hexafluoroisopropanolphenyl-1-pyrenebutyramide (HFIPP) via facile approach has been reported for the first time. Considered that strong hydrogen-bonding can be formed between HFIPP and dimethyl methylphosphonate (DMMP) (simulant of nerve agent sarin), the HFIPP-decorated SWNT device has been employed to detect DMMP. The detection limit achieved with our sensor is as low as 50 ppb; moreover, the response and reproducibility can be presented clearly even at very low concentration of DMMP. Excellent sensitivity and selectivity of the hybridized SWNT-HFIPP device suggest that it has great potential application for detecting explosives and nerve agents. In order to investigate sensing mechanism of SWNT-HFIPP for DMMP, control electrical and fluorescent experiments have been carried out and discussed in the present paper.

Diode properties of nanotube networks

Single-walled carbon nanotubes (SWCNT) were prepared using iron catalysts deposited by indirect evaporation on silicon substrate covered with 500 nm-thick thermal oxide. Diode SWCNT devices have been fabricated using Au and Al, as the asymmetric metal contacts, and a random network of metallic and semiconducting nanotubes as the device channel. No effort was made to align the SWCNTs or to eliminate metallic nanotubes in our devices. Asymmetric voltage–current behavior was seen. Current rectification was observed in the source–drain bias range of − 3 V to + 3 V. Rectification was somewhat surprising since, although metallic tubes are in the minority (∼ 1/3), they could potentially act as shunts and mask the electric properties of the semiconducting majority. No correlation between electrode spacing and current rectification was observed. The lowest leakage current measured was 1% of the maximum current carrying capacity. Maximum forward-biased current capacities range between 8 μA and 841 μA.

Dip-Pen Nanolithography of Electrical Contacts to Single-Walled Carbon Nanotubes

This paper discusses a method for the direct patterning of Au electrodes at nanoscale resolution using dip-pen nanolithography, with proof-of-concept demonstrated by creating single-walled carbon nanotube devices. This technique enables insight into three key concepts at the nanoscale: using dip-pen nanolithography as an alternative to electron-beam lithography for writing contacts to carbon nanotubes, understanding the integrity of contacts and devices patterned with this technique, and on a more fundamental level, providing a facile method to compare and understand electrical and Raman spectroscopy data from the same isolated carbon nanotube. Electrical contacts to individual and small bundle single-walled carbon nanotubes were masked by an alkylthiol that was deposited via dip-pen nanolithography on a thin film of Au evaporated onto spin-cast, nonpercolating, and highly isolated single-walled carbon nanotubes. A wet Au etching step was used to form the individual devices. The electrical characteristics for three different single-walled carbon nanotube devices are reported: semimetallic, semiconducting, and metallic. Raman analysis on representative devices corroborates the results from AFM imaging and electrical testing. This work demonstrates a technique for making electrical contact to nanostructures of interest and provides a platform for directly corroborating electrical and optical measurements. The merits of using dip-pen nanolithography include flexible device configuration (such as varying the channel length and the number, size, and orientation of contacts), targeted patterning of individual devices with imaging and writing conducted in the same instrument under ambient conditions, and negligible damage to single-walled carbon nanotubes during the fabrication process.

Oriented Immobilization of Antibody Fragments on Ni-Decorated Single-Walled Carbon Nanotube Devices

We herein demonstrate that Ni-decorated single-walled carbon nanotube field effect transistors (SWNT-FETs) combined with antibody fragments can be used as effective biosensing platforms. Nanoscales Ni particles 20 to 60 nm in diameter were formed on the sidewalls of SWNT-FETs using an electrochemical method. Carcinoembryonic antigen (CEA)-binding single chain variable fragments (scFvs) with a hexahistidine tag [(his)(6)] were synthesized using genetic engineering, and ordered immobilization of anti-CEA ScFvs on Ni nanoparticles was achieved by exploiting the specific interaction between hexahistidine and Ni. Whereas randomly oriented anti-CEA scFvs did not impart a noticeable change of conductance upon addition of CEA, a clear increase in conductance was observed using Ni-decorated SWNT-FETs functionalized with engineered scFvs.

Efficient Carbon Nanotube Photodiodes

A single photon absorbed in a single-walled carbon nanotube device can generate multiple unbound particles carrying an electric charge. Gabor et al. (p. [1367][1]) report that in such a device at low temperatures, excitation with light of increasing energy leads to well-defined stepwise increases in current. Interestingly, because of the unique band structure of carbon nanotubes, this behavior is analogous to particle-antiparticle creation commonly observed in high-energy particle physics. These observations point to the promise of investigations in other nanoscale carbon systems, such as graphene, and could lead to numerous applications, including highly sensitive photon detection and ultra-efficient photovoltaics. [1]: /lookup/doi/10.1126/science.1176112

Extremely Efficient Multiple Electron-Hole Pair Generation in Carbon Nanotube Photodiodes

We observed highly efficient generation of electron-hole pairs due to impact excitation in single-walled carbon nanotube p-n junction photodiodes. Optical excitation into the second electronic subband E22 leads to striking photocurrent steps in the device I-V(SD) characteristics that occur at voltage intervals of the band-gap energy E(GAP)/e. Spatially and spectrally resolved photocurrent combined with temperature-dependent studies suggest that these steps result from efficient generation of multiple electron-hole pairs from a single hot E22 carrier. This process is both of fundamental interest and relevant for applications in future ultra-efficient photovoltaic devices.

Noncovalent Functionalization of Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWNTs) have attracted much attention on account of their potential to be transformed into new materials that can be employed to address a wide range of applications. The insolubility of the SWNTs in most solvents and the difficulties of handling these highly intractable carbon nanostructures, however, are restricting their real-life applications at the present time. To improve upon the properties of the SWNTs, low-cost and industrially feasible approaches to their modifications are constantly being sought by chemists and materials scientists. Together, they have shown that noncovalent functionalization of the SWNTs can do much to preserve the desired properties of the SWNTs while remarkably improving their solubilities. This Account describes recent advances in the design, synthesis, and characterization of SWNT hybrids and evaluates applications of these new hybrid materials based on noncovalently functionalized SWNTs. Their solubilization enables the characterization of these hybrids as well as the investigation of the properties of the SWNTs using solution-based techniques. Cognizant of the structural properties of the functional molecules on the SWNTs, we present some of the recent work carried out by ourselves and others under the umbrella of the following three subtopics: (i) aromatic small-molecule-based noncovalent functionalization, (ii) biomacromolecule-based noncovalent functionalization, and (iii) polymer-based noncovalent functionalization. Several examples for the applications of noncovalently functionalized SWNT hybrids in the fabrication of field-effect transistor (FET) devices, chemical sensors, molecular switch tunnel junctions (MSTJs), and photovoltaic devices are highlighted and discussed. The blossoming of new methods for the noncovalent functionalization of the SWNTs promises a new generation of SWNT hybrid-based integrated multifunctional sensors and devices, an outcome which is essential for the development of carbon nanotube chemistry that interfaces with physics, materials, biology, and medical science.

Incorporation of Single-Walled Carbon Nanotubes into Functional Sensor Applications

Due to their extreme sensitivity to surface adsorption events, there has been great interest in incorporating single walled carbon nanotubes (SWNTs) into sensing devices. However, a practical sensor needs to have selective response in addition to sensitivity. Therefore, recent efforts have focused on efforts to increase selectivity in SWNT sensors. This manuscript article presents recent progress toward incorporation of SWNTs into enhanced sensor and electronic applications. SWNTs are a nanometer-scale material with properties that have made them the focus of research for a variety of electronic applications. Particularly, SWNT gas sensors have received significant interest of late. Electrical transducers based on monitoring the change in conductance or threshold voltage of SWNT devices upon exposure to an analyte have the advantage of being small, simple and low power devices.

Toward surround gates on vertical single-walled carbon nanotube devices

The one-dimensional, cylindrical nature of single-walled carbon nanotubes (SWCNTs) suggests that the ideal gating geometry for nanotube field-effect transistors (FETs) is a surround gate (SG). Using vertical SWCNTs templated in porous anodic alumina, SGs are formed using top-down processes for the dielectric/metal depositions and definition of the channel length. Surround gates allow aggressive scaling of the channel to 25% of the length attainable with a bottom-gate geometry without incurring short-channel effects. The process demonstrated here for forming SGs on vertical SWCNTs is amenable for large-scale fabrication of multinanotube FETs.

Direct measurement of charge transport through helical poly(ethyl propiolate) nanorodswired into gaps in single walled carbon nanotubes

We report the direct measurement of electrical transport through rod-like polymer molecules,of poly(ethyl propiolate) (PEP), utilizing single walled carbon nanotubes (SWNTs) aselectrodes. The electrical properties of the devices were measured (i) before cutting aSWNT, (ii) when a SWNT was cut and (iii) after PEP deposition into the nanoscale gap ina cut SWNT. The gate-dependent electrical properties showed a reduction in current fromIon = 2.4 × 10−7 A for SWNTdevices to Ion = 3.6 × 10−9 A for PEP bridge devices, both with the ON/OFF ratio of104. Similarly, metallic SWNT devices showed a reduction in current from a few hundreds ofµA fora SWNT device to a few nA for a PEP–SWNT structure. The current density of a single PEP moleculeis 105–106 A cm−2, which is relatively high, indicating that the PEP molecule can carry significant current.Use of SWNT electrodes was seen to be an effective method of contacting PEP nanorods tofacilitate electrical measurements.

A Comparative Study of Poly(3-octylthiophene) and Poly(3-hexylthiophene) Solar Cells Blended with Single Walled Carbon Nanotubes

Poly(3-hexylthiophene) (P3HT):single walled carbon nanotube (SWNT) and poly(3-octylthiophene) (P3OT):SWNT thin films and bulk heterojunction solar cells were fabricated with 0, 1, and 2 wt % of SWNTs. The current density in P3HT is found to be higher than that of P3OT by an order of magnitude at 5 V. Hole mobility in P3HT is found to be higher than in P3OT. Photoluminescence measurements show that the nature of electronic interaction of SWNTs with P3OT and P3HT is not same. For P3OT:SWNT (1 wt %) devices, a ∼3 times increase in the short circuit current density Jsc was obtained compared to pristine P3OT device. For P3HT:SWNT devices, no such improvement was found. The open circuit voltage Voc of P3HT:SWNT (1 wt %) solar cell was found to be 0.82 V while 1.2 V was obtained for P3OT:SWNT (1 wt %) solar cell. This is higher than 0.98 V previously reported for similar solar cells. It is found that the Voc decreases with increase in SWNT content due to the SWNTs acting as shunt paths between anode and cathode.

Transition between Particle Nature and Wave Nature in Single-Walled Carbon Nanotube Device

A convertible transistor that can operate as a resonant-tunneling transistor (RTT) and also as a single-hole transistor (SHT) using single-walled carbon nanotube (SWNT) is fabricated. The transition between RTT and SHT is achieved by modulating the coupling strength between the electrode and the quantum island using gate voltage change. Schottky barriers at the contact between the SWNT and the electrodes act as tunneling barriers. The thicknesses of the tunneling barriers are modulated by the gate voltage change, and the strength of the coupling between the electrode and quantum island is also changed. The characteristics of the convertible transistor can be observed up to 100 K.

Nanoelectromechanics of suspended carbon nanotubes

We discuss different types of measurements targetting the interplay of mechanical motion with electrical transport in suspended single-wall carbon nanotube devices. In driven resonator experiments, the transversal acoustical vibration mode is detected and identified at room temperature using ac down-mixing techniques. In contrast, low-temperature transport spectroscopy enables the observation of the longitudinal acoustic mode in the quantum limit in single electron tunnelling. This vibrational excitation can also be observed in higher order tunnelling current for appropriate electronic coupling to the leads. Experimental roads towards the quantum limit of the transversal vibration mode—as ultimate quantum-limited beam resonator—are explored, e.g. extending both abovementioned measurement techniques.

Reversible Metal−Insulator Transitions in Metallic Single-Walled Carbon Nanotubes

We report on reversible metal to insulator transitions in metallic single-walled carbon nanotube devices induced by repeated electron irradiation of a nanotube segment. The transition from a low-resistive, metallic state to a high-resistive, insulating state by 3 orders of magnitude was monitored by electron transport measurements. Application of a large voltage bias leads to a transition back to the original metallic state. Both states are stable in time, and transitions are fully reversible and reproducible. The data is evidence for a local perturbation of the nanotube electronic system by removable trapped charges in the underneath substrate and excludes structural damage of the nanotube. The result has implications for using electron-beam lithography in nanotube device fabrication.

Large oscillating nonlocal voltage in multiterminal single-wall carbon nanotube devices

We report on the observation of a nonlocal voltage in a ballistic (quasi)-one-dimensional conductor, realized by a single-wall carbon nanotube with four contacts. The contacts divide the tube into three quantum dots, which we control by the back-gate voltage ${V}_{g}$. We measure a large oscillating nonlocal voltage ${V}_{\mathrm{nl}}$ as a function of ${V}_{g}$. Though a resistor model that includes the impedance of the voltmeter can account for a nonlocal voltage including change of sign, it fails to describe the magnitude properly. The large amplitude of ${V}_{\mathrm{nl}}$ is due to quantum interference effects and can be understood within the scattering approach of electron transport.

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.

Simultaneous Spectroscopic and Solid-State Electronic Measurement of Single-Walled Carbon Nanotube Devices

We describe simultaneous spectroscopic and solid-state electronic operation of a single-walled carbon nanotube (SWNT) thin film device under the influence of NH3 and NO2 gases. Using this simultaneous approach we show that both the optical absorbance and network conductance show a shared time dependency upon exposure to NH3 or NO2 gas. We show that the device behavior is dominated by gas adsorption on the SWNT network, and we explore the role of network density in regards to device behavior under gas exposure. Last, we provide evidence to suggest that the device sensitivity toward a particular analyte can be tuned by simply varying the density of the SWNT network.

High temperature resistance of small diameter, metallic single-walled carbon nanotube devices

The effects of high temperature cycling on the resistance of metallic single-walled carbon nanotube (SWCNT) devices is measured in situ. Individual, small-diameter SWCNTs contacted by palladium or titanium electrodes were measured from room temperature up to 1000K in ultrahigh vacuum. Upon the first thermal cycling, the device resistances fluctuate and generally decrease. Pd-contacted devices typically become stable by 450K, whereas Ti-contacted devices require higher treatments above 600K. Once these temperatures have been exceeded, subsequent thermal cycling has minimal effects. Heat-treated devices exhibit linear temperature dependences, with Pd and Ti contacts producing average temperature coefficients of −3×10−4∕K and 1.1×10−3∕K, respectively.

Radio frequency analog electronics based on carbon nanotube transistors

The potential to exploit single-walled carbon nanotubes (SWNTs) in advanced electronics represents a continuing, major source of interest in these materials. However, scalable integration of SWNTs into circuits is challenging because of difficulties in controlling the geometries, spatial positions, and electronic properties of individual tubes. We have implemented solutions to some of these challenges to yield radio frequency (RF) SWNT analog electronic devices, such as narrow band amplifiers operating in the VHF frequency band with power gains as high as 14 dB. As a demonstration, we fabricated nanotube transistor radios, in which SWNT devices provide all of the key functions, including resonant antennas, fixed RF amplifiers, RF mixers, and audio amplifiers. These results represent important first steps to practical implementation of SWNTs in high-speed analog circuits. Comparison studies indicate certain performance advantages over silicon and capabilities that complement those in existing compound semiconductor technologies.

Chemically Assisted Directed Assembly of Carbon Nanotubes for the Fabrication of Large-Scale Device Arrays

We report the directed assembly of single-walled carbon nanotubes (SWCNTs) at lithographically defined positions on gate oxide surfaces, allowing for the high yield ( approximately 90%) and parallel fabrication of SWCNT device arrays. SWCNTs were first chemically functionalized through diazonium chemistry with a hydroxamic acid end group that both renders the SWCNTs water-soluble and discriminately binds the SWCNTs to basic metal oxide surfaces (i.e., hafnium oxide (HfO2)). The functionalized SWCNTs are then assembled from an aqueous solution into narrow trenches etched into SiO2 films with HfO2 at the bottom. The side walls of the patterned trenches induce alignment of the SWCNTs along the length of the trenches. Heating the structures to 600 degrees C removes the organic moieties, leaving pristine SWCNTs as evidenced by Raman spectroscopy and electrical measurements. Palladium source-drain electrodes deposited perpendicular to the trench length readily contact the ends of the aligned SWCNTs. The resultant devices exhibit the electrical performance expected for SWCNT devices, with no performance deterioration as a result of the placement process. This technique allows for the directed assembly and alignment of SWCNTs over a large area and results in a high yield of working devices, presenting a promising path toward large-scale SWCNT device integration.