Individual Semiconducting Carbon Nanotubes Research Articles

Single-particle states spectroscopy in individual carbon nanotubes with an aid of tunneling contacts

Recent studies have demonstrated that the band structure of a carbon nanotube (CNT) depends not only on its geometry but also on various factors such as atmosphere chemical composition and dielectric environment. Systematic studies of these effects require an efficient tool for an in situ investigation of a CNT band structure. In this work, we fabricate tunneling contacts to individual semiconducting carbon nanotubes through a thin layer of alumina and perform tunneling spectroscopy measurements. We use field-effect transistor configuration with four probe contacts (two tunnel and two ohmic) and bottom gates. Bandgap values extracted from tunneling measurements match the values estimated from the diameter value within the zone-folding approximation. We also observe the splitting of Van-Hove singularities of the density of states under an axial magnetic field.

Reconfigurable Tunneling Transistors Heterostructured by an Individual Carbon Nanotube and MoS2

Low-dimensional semiconductors have shown great potential in switches for their atomically thin geometries and unique properties. It is significant to achieve new tunneling transistors by the efficient stacking methodology with low-dimensional building blocks. Here, we report a one-dimensional (1D)-two-dimensional (2D) mixed-dimensional van der Waals (vdW) heterostructure, which was efficiently fabricated by stacking an individual semiconducting carbon nanotube (CNT) and 2D MoS2. The CNT-MoS2 heterostructure shows specific reconfigurable electrical transport behaviors and can be set as a nn junction, pn diode, and band-to-band tunneling (BTBT) transistor by gate voltage. The transport properties, especially BTBT, could be attributed to the electron transfer from MoS2 to CNT through the ideal vdW interface and the 1D nature of the CNT. The progress suggests a new solution for tunneling transistors by making 1D-2D heterostructures from the rich library of low-dimensional nanomaterials. Furthermore, the reconfigurable functions and nanoscaled junction show that it is prospective to apply CNT-MoS2 heterostructures in future nanoelectronics and nano-optoelectronics.

(Invited) Thermal Exciton Radiation of Macroscopic Semiconducting Carbon Nanotube Membranes

Individual semiconducting carbon nanotubes at high temperature more than ~1000 K show narrowband near infrared thermal radiation owing to exciton resonances [1], which may be useful in thermophotovoltaic energy harvesting. However, it still remains to be clarified whether macroscopic membranes consisting of semiconducting carbon nanotubes can also show narrowband thermal exciton radiation. Our recent progress on the study of thermal radiation properties of macroscopic membranes of chirality-separated [2] semiconducting carbon nanotubes will be discussed. [1] T. Nishihara, A. Takakura, Y. Miyauchi, and K. Itami, Nat. Commun. 9, 3144 (2018). [2] H. Liu, D. Nishide, T. Tanaka, and H. Kataura, Nat. Commun. 2, 309 (2011).

Optically Triggered Melting of DNA on Individual Semiconducting Carbon Nanotubes

AbstractOptical excitation of nanostructures is known to induce local heating, a phenomenon that has been intensely exploited for drug release, gene delivery, cancer thermotherapy, and energy harvesting. However, the effect is typically small requiring collective heating of a large concentration or aggregates of particles. Herein, we show that optical excitation of individual semiconducting single‐walled carbon nanotubes triggers strongly localized heating adequate to melt non‐covalently attached double‐stranded oligonucleotides in solution. In contrast to conventional thermal dehybridization, this optically triggered DNA melting occurs at a solution temperature that is 22 °C lower than the DNA melting temperature. This unexpectedly large localized optical heating effect provides important new insights to design selective optical nanoheaters at the single particle level.

Optically Triggered Melting of DNA on Individual Semiconducting Carbon Nanotubes.

Optical excitation of nanostructures is known to induce local heating, a phenomenon that has been intensely exploited for drug release, gene delivery, cancer thermotherapy, and energy harvesting. However, the effect is typically small requiring collective heating of a large concentration or aggregates of particles. Herein, we show that optical excitation of individual semiconducting single-walled carbon nanotubes triggers strongly localized heating adequate to melt non-covalently attached double-stranded oligonucleotides in solution. In contrast to conventional thermal dehybridization, this optically triggered DNA melting occurs at a solution temperature that is 22 °C lower than the DNA melting temperature. This unexpectedly large localized optical heating effect provides important new insights to design selective optical nanoheaters at the single particle level.

Analysis of random telegraph noise observed in semiconducting carbon nanotube quantum dots

We have investigated random telegraph noise (RTN) observed in individual semiconducting carbon nanotubes (CNTs) in Coulomb-blockade regime. RTN characteristics are studied as a function of gate-voltage and drain–source voltage. Our results are explained by the capture and emission of carriers by charge traps in the vicinity of CNTs. Because of the large RTN amplitude, often greater than ∼50% of the total current, RTN measurements can be developed into an effective tool to estimate the trap energy and the location of the trap in CNT quantum dot devices.

Electrical power dissipation in semiconducting carbon nanotubes on single crystal quartz and amorphous SiO2

Heat dissipation in electrically biased individual semiconducting carbon nanotubes (CNTs) on single crystal quartz and amorphous SiO2 is examined with temperature profiles obtained by spatially resolved Raman spectroscopy. Despite the differences in phonon velocities, thermal conductivity, and van der Waals interactions with CNTs, on average, heat dissipation into single crystal quartz and amorphous SiO2 is found to be similar. Large temperature gradients and local hot spots often observed underscore the complexity of CNT temperature profiles and may be accountable for the similarities observed.

Logic circuits based on individual semiconducting and metallic carbon-nanotubedevices

Nanoscale transistors employing an individual semiconducting carbon nanotube as thechannel hold great potential for logic circuits with large integration densities that can bemanufactured on glass or plastic substrates. Carbon nanotubes are usually produced as amixture of semiconducting and metallic nanotubes. Since only semiconductingnanotubes yield transistors, the metallic nanotubes are typically not utilized.However, integrated circuits often require not only transistors, but also resistiveload devices. Here we show that many of the metallic carbon nanotubes thatare deposited on the substrate along with the semiconducting nanotubes can beconveniently utilized as load resistors with favorable characteristics for the design ofintegrated circuits. We also demonstrate the fabrication of arrays of transistorsand resistors, each based on an individual semiconducting or metallic carbonnanotube, and their integration on glass substrates into logic circuits with switchingfrequencies of up to 500 kHz using a custom-designed metal interconnect layer.

Highly Reliable Carbon Nanotube Transistors with Patterned Gates and Molecular Gate Dielectric

The prospect of realizing nanoscale transistors using individual semiconducting carbon nanotubes offers enormous potential, both as an alternative to silicon technology beyond conventional scaling limits and as a way to implement high-speed devices and circuits on flexible substrates. A significant challenge is the realization of low-voltage nanotube transistors with individually addressable gate electrodes that display large transconductance, steep subthreshold swing, and large on/off ratio. Their integration into circuits with large signal gain and good stability still needs to be demonstrated. Here, we demonstrate that these important goals can be achieved with the help of a bottom-gate device structure that combines patterned metal gates with a thin gate dielectric based on a molecular self-assembled monolayer. The obtained transistors operate with a gate-source voltage of 1 V and have a transconductance of 5 microS, a subthreshold swing of 68 mV/decade, and an on/off ratio of 10(7). To verify the excellent operational and shelf life stability, we show that the device performance does not degrade during 10,000 switching cycles and during storage under ambient conditions for more than 300 days. We also demonstrate that the device structure allows the implementation of unipolar logic circuits with good switching characteristics.

Origins of1∕fnoise in individual semiconducting carbon nanotube field-effect transistors

The temperature dependence of $1∕f$ noise in individual semiconducting carbon nanotube (CNT) field-effect transistors is used to estimate the distribution of activation energies of the fluctuators $D(E)$ responsible for the noise. $D(E)$ shows a rise at low energy with no characteristic energy scale, and a broad peak at $\ensuremath{\sim}0.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The peak, responsible for the majority of noise at room temperature, cannot be due to electronic excitations, carrier number fluctuations, or structural fluctuations of the CNT, and likely results from the motion of defects in the dielectric or at the CNT-dielectric interface, or very strongly physisorbed species (binding energy $\ensuremath{\sim}0.4\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$) on the CNT or dielectric surface.

Effects of Chirality and Diameter on Electron Transport Properties in Individual Semiconducting Carbon Nanotubes

AbstractWe report on the effects of chirality and diameter on the electron transport properties in individual semiconducting, single wall carbon nanotubes. The Boltzmann transport equation is solved indirectly by the Ensemble Monte Carlo method and directly by Rode's iterative technique. Results show considerable effects of chirality and group on band structure and transport properties of tubes with small diameters. However the effects of chirality and group become negligible for tubes with large diameters. Diameter affects these properties more strongly than either chirality or group.

Hooge’s constant for carbon nanotube field effect transistors

The 1∕f noise in individual semiconducting carbon nanotubes (s-CNT) in a field effect transistor configuration has been measured in ultrahigh vacuum and following exposure to air. The amplitude of the normalized current spectral noise density is independent of source-drain current and inversely proportional to gate voltage, to channel length, and therefore to carrier number, indicating that the noise is due to mobility rather than number fluctuations. Hooge’s constant for s-CNT is found to be (9.3±0.4)×10−3 The magnitude of the 1∕f noise is substantially decreased by exposing the devices to air.

Photoconductivity Spectra of Single-Carbon Nanotubes: Implications on the Nature of Their Excited States

We have measured the photoconductivity excitation spectra of individual semiconducting carbon nanotubes incorporated as the channel of field-effect transistors. In addition to the pronounced resonance that correlates with the second van Hove transition (E(22)) in semiconducting carbon nanotubes, a weaker sideband at about 200 meV higher energy is observed. Electronic structure calculations that include electron-phonon coupling indicate that the spectra originate from the simultaneous excitation of an exciton (main resonance) and a C-C bond stretching phonon (sideband). The spectral features are not compatible with an interband interpretation of the excitation involved.

Photoelectronic transport imaging of individual semiconducting carbon nanotubes

Photoconductivity in individual semiconducting single-wall carbon nanotubes was investigated using a confocal scanning optical microscope. The magnitude of the photocurrent was found to increase linearly with the laser intensity, and to be maximum for parallel orientation between the light polarization and the tube axis. Larger currents were obtained upon illuminating the tubes at 514.5 nm in comparison to those at 647.1 nm, consistent with the semiconducting tubes having a resonant absorption energy at the former wavelength. Moreover, the determination of the photoresponse as a function of position along single nanotubes has proven to be a useful tool to monitor local electronic structure effects.

Chemical profiling of single nanotubes: Intramolecular p–n–p junctions and on-tube single-electron transistors

Electrical transport properties of intramolecular p–n–p junctions formed on individual semiconducting carbon nanotubes are reported. Chemical dopant “profiling” along the length of a nanotube divides the nanotube into two p-doped sections and a central n-doped section. The double p–n junctions formed on the nanotube dictate the electrical characteristics of the system. Well-defined and highly reproducible single-electron transistors with much smaller size than the geometrical length of the nanotube are obtained.