Carbon Nanotube Quantum Dots Research Articles

Quantum paraelectric varactors for radiofrequency measurements at millikelvin temperatures

Radiofrequency reflectometry can provide fast and sensitive electrical read-out of charge and spin qubits in quantum dot devices coupled to resonant circuits. In situ frequency tuning and impedance matching of the resonator circuit using voltage-tunable capacitors (varactors) is needed to optimize read-out sensitivity, but the performance of conventional semiconductor- and ferroelectric-based varactors degrades substantially in the millikelvin temperature range relevant for solid-state quantum devices. Here we show that strontium titanate and potassium tantalate, materials which can exhibit quantum paraelectric behaviour with large field-tunable permittivity at low temperatures, can be used to make varactors with perfect impedance matching and resonator frequency tuning at 6 mK. We characterize the varactors at 6 mK in terms of their capacitance tunability, dissipative losses and magnetic field insensitivity. We use the quantum paraelectric varactors to optimize the radiofrequency read-out of carbon nanotube quantum dot devices, achieving a charge sensitivity of 4.8 μe Hz−1/2 and a capacitance sensitivity of 0.04 aF Hz−1/2.

Enhancement of the photothermoelectric effect through synergistic modulation of multiple parameters

The performance of photothermoelectric materials is severely limited by various intrinsic parameters that are difficult to simultaneously modulate, thereby hindering their applications in the fields of photodetectors, solar cells, thermoelectric therapy and so on. In this study, we have prepared suspended films composed of carbon nanotube (CNT) and molybdenum disulfide quantum dots (MoS2 QDs), which demonstrate a remarkable maximum photothermal conversion efficiency of 2201 K·mm2·W−1. This outstanding performance is attributed to the formation of a heterojunction between CNT and MoS2 QDs. Furthermore, the light absorption, temperature coefficient of resistance, and Seebeck coefficient of this suspended film are simultaneously modulated in a direction conducive to enhancing the photothermoelectric effect. Consequently, we have fabricated CNT-CNT/MoS2 QDs p-n junction photodetectors to showcase the improved photoresponse performance. This study presents an innovative approach for modulating multiple intrinsic parameters of photothermoelectric materials, which offers valuable insights for enhancing the performance of corresponding photothermoelectric devices.

Optomechanical Coupling and Damping of a Carbon Nanotube Quantum Dot

Optomechanical Coupling and Damping of a Carbon Nanotube Quantum Dot

Independent and coherent transitions between antiferromagnetic states of few-molecule systems

Molecular spintronics is usually based on paramagnetic or ferromagnetic ($S$ \ensuremath{\ne} 0) species. Here, the authors study small ensembles of two molecular antiferromagnets, {Mn${}_{4}$} and {Co${}_{4}$}, bound to carbon nanotube quantum dots. The current through the quantum dots shows a random telegraph signal caused by transitions between nondegenerate ${S}_{t\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}t}$ = 0 states of individual molecular antiferromagnets. Statistical analysis shows that transitions between those states are independent in the case of {Co${}_{4}$} ensembles, while {Mn${}_{4}$} ensembles display long-lived coherent superposition involving multiple complexes.

One-Step Preparation of High Performance TiO2/CNT/CQD Nanocomposites Bactericidal Coating with Ultrasonic Radiation

As an environmental semiconductor material, TiO2 has important applications in the fields of environmental protection and water treatment. The preparation of P25 particles into nano-functional material films with a high specific surface area has always been a bottleneck limiting its large-scale application. In this paper, a one-step method of preparing TiO2 nanocomposites by doping carbon nanotube (CNT) and carbon quantum dots (CQD) with tetrabutyltitanate and P25 TiO2 under ultrasonic radiation is proposed to synthesize a novel antifouling material, which both eliminates the bacterium of Escherichia coli and shows good photoelectric properties, indicating a great value for the industrial promotion of TiO2/CNT. This mesoporous composite exhibits a high specific surface area of 78.07 M2/g (BET) and a tested pore width range within 10–120 nm. The surface morphology of this composite is characterized by TEM and the microstructure is characterized through XRD. This preparation method can fabricate P25 particles into a nano-functional material film with a high specific surface area at a very low cost.

Exciton Controlled-NOT Gate Using Coupled Quantum Dots in Carbon Nanotube

A four-level system is a prerequisite for the controlled-NOT (CNOT) gate and is realized with excitons confined in the coupled quantum dots (QDs). The coupled QDs are fabricated by chemically bonding the collagen model peptides to a single-walled carbon nanotube. An interdot exciton–exciton interaction and an exciton four-level system based on it are confirmed through photoluminescence measurements. Rabi oscillations of the exciton populations are observed, which allow the manipulations of the exciton four-level system with designed laser-pulse sequences. The tests on whether the exciton four-level system operates as a CNOT gate are conducted, and the quantum process fidelity is estimated to be approximately 0.7–0.8. The SWAP operation is also demonstrated by employing the CNOT gate three times.

Impact of Kondo correlations and spin–orbit coupling on spin-polarized transport in carbon nanotube quantum dot

Spin polarized transport through a quantum dot coupled to ferromagnetic electrodes with noncollinear magnetizations is discussed in terms of nonequilibrium Green functions formalism in the finite-U slave boson mean field approximation. The difference of orientations of the magnetizations of electrodes opens off-diagonal spin–orbital transmission and apart from spin currents of longitudinal polarization also spin-flip currents appear. We also study equilibrium pure spin current at zero bias and discuss its dependence on magnetization orientation, spin–orbit coupling strength and gate voltage. Impact of these factors on tunneling magnetoresistance (TMR) is also undertaken. In general spin–orbit coupling weakens TMR, but it can change its sign.

Phonon-Induced Pairing in Quantum Dot Quantum Simulator.

Quantum simulations can provide new insights into the physics of strongly correlated electronic systems. A well-studied system, but still open in many regards, is the Hubbard-Holstein Hamiltonian, where electronic repulsion is in competition with attraction generated by the electron-phonon coupling. In this context, we study the behavior of four quantum dots in a suspended carbon nanotube and coupled to its flexural degrees of freedom. The system is described by a Hamiltonian of the Hubbard-Holstein class, where electrons on different sites interact with the same phonon. We find that the system presents a transition from the Mott insulating state to a polaronic state, with the appearance of pairing correlations and the breaking of the translational symmetry. These findings will motivate further theoretical and experimental efforts to employ nanoelectromechanical systems to simulate strongly correlated systems with electron-phonon interactions.

Nanomaterials: Applications in Electronics

Nanotechnology is steadily transgressing from the laboratory to the commercial sphere and is enhancing products in a variety of sectors. Nanotechnology R&D has evolved from foundational discoveries aimed at understanding and exploiting nanoscale behaviour to an enabling technology. Nanomaterials are materials which are sized between 1 to 100 nm. Due to the basic characteristics of nanomaterials such as optical properties, reflection, transmission, absorption, and light emission, which are different from those of bulk materials, nanomaterials are useful in a variety of applications in different fields. In this paper the different types of nanomaterials have been outlined based upon their dimensions and applications in the field of electronics such as Quantum dots (QD’s) in solar cells and Carbon Nanotubes and graphene in FETs.

Vacuum-field-induced THz transport gap in a carbon nanotube quantum dot

The control of light-matter interaction at the most elementary level has become an important resource for quantum technologies. Implementing such interfaces in the THz range remains an outstanding problem. Here, we couple a single electron trapped in a carbon nanotube quantum dot to a THz resonator. The resulting light-matter interaction reaches the deep strong coupling regime that induces a THz energy gap in the carbon nanotube solely by the vacuum fluctuations of the THz resonator. This is directly confirmed by transport measurements. Such a phenomenon which is the exact counterpart of inhibition of spontaneous emission in atomic physics opens the path to the readout of non-classical states of light using electrical current. This would be a particularly useful resource and perspective for THz quantum optics.

Dual-Tunable Memristor Based on Carbon Nanotubes and Graphene Quantum Dots.

Nanocarbon materials have the advantages of biocompatibility, thermal stability and chemical stability and have shown excellent electrical properties in electronic devices. In this study, Al/MWCNT:GQD/ITO memristors with rewritable nonvolatile properties were prepared based on composites consisting of multiwalled carbon nanotubes (MWCNTs) and graphene quantum dots (GQDs). The switching current ratio of such a device can be tuned in two ways. Due to the ultraviolet light sensitivity of GQDs, when the dielectric material is illuminated by ultraviolet light, the charge capture ability of the GQDs decreases with an increasing duration of illumination, and the switching current ratio of the device also decreases with an increasing illumination duration (103–10). By exploiting the charge capture characteristics of GQDs, the trap capture level can be increased by increasing the content of GQDs in the dielectric layer. The switching current ratio of the device increases with increasing GQD content (10–103). The device can be programmed and erased more than 100 times; the programmable switching state can withstand 105 read pulses, and the retention time is more than 104 s. This memristor has a simple structure, low power consumption, and enormous application potential for data storage, artificial intelligence, image processing, artificial neural networks, and other applications.

Effects of Three Carbonaceous Nanomaterials on the Developmental Toxicity, Oxidative Stress, and Metabolic Profile in Zebrafish

As an important part of artificial nanomaterials, carbonaceous nanomaterials (CNMs) are widely applied in a plenty of areas such as energy, manufacturing and pharmaceutical industries. In the present study, the developmental toxicity, induced by three typical CNMs including graphene oxide (GO), carbon nanotube (CNT) and graphene oxide quantum dot (GOQD) was investigated in the typical model animal, zebrafish larva. The induced sub-acute toxicity at the low concentration of GO, CNT and GOQD was investigated in adult zebrafish, either. Moreover, the molecular mechanisms at the level of metabolomics were also explored. The results showed that there was a significant increase in reactive oxygen species (ROS), and mitochondrial membrane damage was caused by GO, CNT and GOQD in zebrafish larva. However, there was no significant developmental toxicity on zebrafish larva. The toxicity order in terms of the ROS increase and mitochondrial membrane damage was GOQD > CNT > GO. The chronic exposure at the typical environment-associated concentration (0.01 mg·L-1) of CNMs can induce gill and kidney cell senescence of adult zebrafish. Meanwhile, it can also inhibit total superoxide dismutase (T-SOD) activity in adult zebrafish in the subacute toxicity test (21 d) at the concentration of 0.01 mg·L-1. The metabolomics research revealed that the toxicity order at the environment-associated concentration acting on adult zebrafish was GOQD > CNT > GO; and it showed that fatty acids and proline turbulence may be responsible for one of the molecular mechanisms of T-SOD inhibition in adult zebrafish. This work can supply rationale to evaluate the potential risk of ecosystems and human health induced by the three typical CNMs.

Metallic carbon nanotube quantum dots with broken symmetries as a platform for tunable terahertz detection

Generating and detecting radiation in the technologically relevant range of the so-called terahertz gap (0.1–10 THz) is challenging because of a lack of efficient sources and detectors. Quantum dots in carbon nanotubes have shown great potential to build sensitive terahertz detectors, usually based on photon-assisted tunneling. A recently reported mechanism combining resonant quantum dot transitions and tunneling barrier asymmetries results in a narrow linewidth photocurrent response with a large signal-to-noise ratio under weak THz radiation. That device was sensitive to one frequency, corresponding to transitions between equidistant quantized states. In this work we show, using numerical simulations together with scanning tunneling spectroscopy studies of a defect-induced metallic zigzag single-walled carbon nanotube quantum dot, that breaking simultaneously various symmetries in metallic nanotube quantum dots of arbitrary chirality strongly relaxes the selection rules in the electric dipole approximation and removes energy degeneracies. This leads to a richer set of allowed optical transitions spanning frequencies from 1 THz to several tens of THz, for a ∼10 nm quantum dot. Based on these findings, we propose a terahertz detector device based on a metallic single-walled carbon nanotube quantum dot defined by artificial defects. Depending on its length and contacts transparency, the operating regimes range from a high-resolution gate-tunable terahertz sensor to a broadband terahertz detector. Our calculations indicate that the device is largely unaffected by temperatures up to 100 K, making carbon nanotube quantum dots with broken symmetries a promising platform to design tunable terahertz detectors that could operate at liquid nitrogen temperatures.

Synthesis and Application of Nanocomposite Reinforced with Decorated Multi Walled Carbon Nanotube with Luminescence Quantum Dots

Amidst the COVID-19 pandemic, environmental problems such as energy crisis, global warming, and contamination from pathogenic micro-organisms are still prevailed and strongly demanded progress in high-performance energy storing and anti-microbial materials. The nanocomposites are materials that have earned large interest owing to their promising applications for countering global issues related to sustainable energy and a flourishing environment. Here, polypyrrole coated hybrid nanocomposites of multi-walled carbon nanotube and cadmium sulfide quantum dots named MCP were synthesized using facile and low-cost in-situ oxidative polymerization method. Characterization techniques confirmed the synthesis. Electrochemical studies showed that the nanocomposite 1-MCP showed an impressively higher super capacitance behavior in comparison to f-MWCNT, 7-MCP and 5-MCP. The improved performance of the nanocomposites was attributed mainly to the good conductivity of carbon nanotubes and polypyrrole, high surface area, and stability of the carbon nanotubes and the high electrocatalytic activity of the cadmium sulfide quantum dots. Owing to the synergistic effect of MWCNT, CdS, and PPy the synthesized ternary nanocomposite also inhibited the growth and multiplication of tested bacteria such as S. aureus, and E. coli completely within 24 h. On the whole, the assimilated nanocomposite MCP opens promising aspects for the development of upcoming energy storage devices and as an antibacterial agent.

Kondo effects in small-bandgap carbon nanotube quantum dots.

We study the magnetoconductance of small-bandgap carbon nanotube quantum dots in the presence of spin–orbit coupling in the strong-correlations regime. A finite-U slave-boson mean-field approach is used to study many-body effects. Different degeneracies are restored in a magnetic field and Kondo effects of different symmetries arise, including SU(3) effects of different types. Full spin–orbital degeneracy might be recovered at zero field and, correspondingly, the SU(4) Kondo effect sets in. We point out the possibility of the occurrence of electron–hole Kondo effects in slanting magnetic fields, which we predict to occur in magnetic fields with an orientation close to perpendicular. When the field approaches a transverse orientation a crossover from SU(2) or SU(3) symmetry into SU(4) is observed.

CFD Study Based on Effect of Employing the Single-Walled Carbon Nanotube (SWCNT) and Graphene Quantum Dots (GQD) Nanoparticles and a Particular Fin Configuration on the Thermal Performance in the Shell and Tube Heat Exchanger

In this research, the thermal attributes of shell and finned tube heat exchanger such as thermal efficiency, pressure drop, heat transfer rate and average temperature in the tube side of heat exchanger with using the different volume concentration of nanoparticles (SWCNT and Graphene quantum dot) at the various Reynolds number by applying either fin blades and without fin blades have been conducted numerically. In this heat exchanger the hot fluid or nanofluid flows in the tube section and cold fluid or pure water moves in the shell side. As regarding to results obtained the majority of thermal characteristics like heat transfer rate, pressure drop and effectiveness enhanced with augmentation of Reynolds number and increasing of volume concentration of nanofluids to 1% volumetric of working fluid whereas at the higher volume concentrations of nanoparticles (upper from 1% volumetric) the thermal properties of heat exchanger decreased generally. Also pressure drop intensifies with increment of Reynolds number and volume concentration of nanoparticles that at higher Reynolds number the effects of nanoparticles on the pressure drop were more noticeable. The average temperature of heat exchanger in the end section of inside tubes increased with augmentation of Reynolds number and nanoparticles. Finally, according to the results obtained in this study, most impression on the thermal attributes enhancement was found by employing of finned tubes compared to other factor which this factor increased heat transfer rate of heat exchanger by almost 188% also the effects of nanoparticles at the high levels of volume concentration especially for 5% of SWCNT nanoparticle on the pressure drop obtained about 80% compared to the base fluid.

Field-induced SU(4) to SU(2) Kondo crossover in a half-filling nanotube dot: Spectral and finite-temperature properties

We study finite-temperature properties of the Kondo effect in a carbon nanotube (CNT) quantum dot using the Wilson numerical renormalization group (NRG). In the absence of magnetic fields, four degenerate energy levels of the CNT consisting of spin and orbital degrees of freedom give rise to the SU(4) Kondo effect. We revisit the universal scaling behavior of the SU(4) conductance for quarter- and half-filling in a wide temperature range. We find that the filling dependence of the universal scaling behavior at low temperatures $T$ can be explained clearly with an extended Fermi-liquid theory. This theory clarifies that a $T^{2}$ coefficient of conductance becomes zero at quarter-filling whereas the coefficient at half-filling is finite. We also study a field-induced crossover from the SU(4) to SU(2) Kondo state observed at the half-filled CNT dot. The crossover is caused by the matching of the spin and orbital Zeeman splittings, which lock two levels among the four at the Fermi level even in magnetic fields $B$. We find that the conductance shows the SU($4$) scaling behavior at $\mu_{B}B<k_{B}T_{K}^{\mathrm{SU(4)}}$ and it exhibits the SU($2$) universality at $\mu_{B}B\gg k_{B}T_{K}^{\mathrm{SU(4)}}$, where $T_{K}^{\mathrm{SU(4)}}$ is the SU($4$) Kondo temperature. To clarify how the excited states evolve along the SU(4) to SU(2) crossover, we also calculate the spectral function. The results show that the Kondo resonance width of the two states locked at the Fermi level becomes sharper with increasing fields. The spectral peaks of the other two levels moving away from the Fermi level merge with atomic limit peaks for $\mu_{B}B \gtrsim k_{B}T_{K}^{\mathrm{SU(4)}}$.

Ultrasound-assisted microwave synthesis of CdS/MWCNTs QDs: A material for photocatalytic and corrosion inhibition activity

Semiconductor CdS/Multiwalled carbon nanotube quantum dots with crystallite size of 2–3 nm have been successfully synthesized by an ultrasound-assisted microwave method. The sap of opunica ficus-indica fruit is used as natural capping agent to enhance the quantum dot’s stability. The synthesized CdS/MWCNTs QDs were characterized by XRD, UV–Visible, FT-IR, HR-TEM, DLS, TGA, DTA and XRF. The photocatalytic activity of the QDs was tested for the degradation of dye, pararosaniline under simulated Ultra-violet radiation. The degradation rate was found up to 99.19% within 150 Min. The influence of QDs as corrosion inhibition on zinc plate in three aerated electrolytes solutions namely NaCl, HCl and KOH was studied by Tafel polarization technique. The result showed that corrosion resistance succeeded due to CdS/MWCNTs QDs coating over Zn surface.

Quantum capacitance mediated carbon nanotube optomechanics

Cavity optomechanics allows the characterization of a vibration mode, its cooling and quantum manipulation using electromagnetic fields. Regarding nanomechanical as well as electronic properties, single wall carbon nanotubes are a prototypical experimental system. At cryogenic temperatures, as high quality factor vibrational resonators, they display strong interaction between motion and single-electron tunneling. Here, we demonstrate large optomechanical coupling of a suspended carbon nanotube quantum dot and a microwave cavity, amplified by several orders of magnitude via the nonlinearity of Coulomb blockade. From an optomechanically induced transparency (OMIT) experiment, we obtain a single photon coupling of up to g0 = 2π ⋅ 95 Hz. This indicates that normal mode splitting and full optomechanical control of the carbon nanotube vibration in the quantum limit is reachable in the near future. Mechanical manipulation and characterization via the microwave field can be complemented by the manifold physics of quantum-confined single electron devices.

Counting statistics of dark-state transport through a carbon nanotube quantum dot

In a recent experiment [A. Donarini et al., Nat Comms 10, 381 (2019)], electronic transport through a carbon nanotube quantum dot was observed to be suppressed by the formation of a quantum-coherent ``dark state''. In this paper we consider theoretically the counting statistics and waiting-time distribution of this dark-state-limited transport. We show that the statistics are characterised by giant super-Poissonian Fano factors and long-tailed waiting-time distributions, both of which are signatures of the bistability and extreme electron bunching caused by the dark state.