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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Evidence for single-electron tunneling in electron energy spectra of diamond tip field emitter
摘要： Field emission from microscale diamond tips was studied using electron energy spectroscopy. A processing at high emission currents was applied to modify the atomic surface structure of pristine diamond tips. Subsequently, staircase-like current-voltage characteristics were obtained which are typical for the single-electron tunneling occurring due to the Coulomb blockade effect in emitting carbon nanostructures formed on the surface of the diamond tips. Characteristic electron energy spectra consisted of several peaks, each corresponding to a certain charging state of the emitting nanostructure. The measured spectra were used to determine the parameters of the Coulomb blockade (e.g. charging energy) and reveal peculiar features of single-electron effects in field emission systems.
关键词： electron energy spectroscopy,Coulomb blockade,single-electron tunneling,field emission
更新于2025-09-23 15:21:21
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Controlled Quantum-Dot Formation in Atomically-Engineered Graphene Nanoribbons Field-Effect Transistors
摘要： Graphene nanoribbons (GNRs) have attracted a strong interest from researchers worldwide, as they constitute an emerging class of quantum-designed materials. The major challenges towards their exploitation in electronic applications include reliable contacting, complicated by their small size (< 50 nm), as well as the preservation of their physical properties upon device integration. In this combined experimental and theoretical study, we report on the quantum dot (QD) behavior of atomically precise GNRs integrated in a device geometry. The devices consist of a film of aligned 5-atoms wide GNRs (5-AGNRs) transferred onto graphene electrodes with a sub 5-nm nanogap. We demonstrate that the narrow-bandgap 5-AGNRs exhibit metal-like behavior at room temperature and single-electron transistor behavior for temperatures below 150 K. By performing spectroscopy of the molecular levels at 13 K, we obtain addition energies in the range of 200-300 meV. DFT calculations predict comparable addition energies and reveal the presence of two electronic states within the bandgap of infinite ribbons when the finite length of the 5-AGNRs is accounted for. By demonstrating the preservation of the 5-AGNRs molecular levels upon device integration, as demonstrated by transport spectroscopy, our study provides a critical step forward in the realisation of more exotic GNR-based nano-electronic devices.
关键词： graphene nanoribbons,Coulomb blockade,molecular spectroscopy,device integration,Raman spectroscopy
更新于2025-09-23 15:21:01
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Strong Quantum Confinement Effects in Nanometer Devices with Graphene Directly Grown on Insulator by Catalyst-free Chemical Vapor Deposition
摘要： Background: The understanding of electrical properties of defective graphene in nanometer regime has lagged behind. Objective: This report intends to characterize defective but practically useful graphene as nanometer devices. Method: A-few-layer-thick graphene was directly grown on SiO2 substrate by alcohol-chemical vapor deposition (alcohol-CVD) using ethanol as carbon source and without the use of any catalytic metal. The graphene film was delineated into nanometer structures by electron beam lithography to make the nanoscale devices. Results: The Raman spectra of the graphene sheet on SiO2 shows relatively large D peak, which means the graphene is defective and consists of nanograins with an estimated size of 17 nm. Modulation of the graphene resistance by the gate voltage Vg was studied at room temperature. The film shows only p-type conduction, with a sheet resistance of 3.7 kΩ/□ and field-effect mobility calculated to be 44 cm2/Vs. From the temperature dependence of the graphene sheet, it is found that the resistance increases only by 7% from room temperature to 10 K, indicating low potential barrier between the domains, even though the graphene film is as thin as 1.6 nm and defective. From the conductance (Id/Vd) contour plot measured at 10 K of these nanodevices, aperiodic Coulomb-blockade feature and transport with a large gap were observed. Conclusion: Correlation among narrowest constriction widths, the variation of the addition energies and transport gaps in disordered graphene nanostructures is evident. These graphene nanodevices may have promising application in various nanodevices like single-electron (or single-hole) transistor, single-molecule transistor, van-der-Waals stacked nanodevices, etc.
关键词： graphene nanometer devices,Graphene nanostructures,sheet resistance,Raman spectra,Coulomb blockade,alcohol chemical vapor deposition,electron beam lithography
更新于2025-09-23 15:21:01
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Orbital Tuning of Tunnel Coupling in InAs/InP Nanowire Quantum Dots
摘要： We report results on the control of barrier transparency in InAs/InP nanowire quantum dots via the electrostatic control of the device electron states. Recent works demonstrated that barrier transparency in this class of devices displays a general trend just depending on the total orbital energy of the trapped electrons. We show that a qualitatively different regime is observed at relatively low filling numbers, where tunneling rates are rather controlled by the axial configuration of the electron orbital. Transmission rates versus filling are further modified by acting on the radial configuration of the orbitals by means of electrostatic gating, and the barrier transparency for the various orbitals is found to evolve as expected from numerical simulations. The possibility to exploit this mechanism to achieve a controlled continuous tuning of the tunneling rate of an individual Coulomb blockade resonance is discussed.
关键词： quantum dot,InAs/InP,nanowire,Coulomb blockade,tunnel barrier,electron tunneling rate
更新于2025-09-23 15:19:57
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Single-electron current gain in a quantum dot with three leads
摘要： The conductance through a quantum dot (QD) between a source and a drain electrode is usually controlled electrostatically by a nearby gate electrode. A periodic modulation of the conductance versus gate voltage is observed, swapping between Coulomb blockade and single-electron tunneling. By controlling the Fermi level of a third (‘base’) lead attached to the QD, we were able to switch a single-electron current from source to drain, exceeding the single-electron current to or from the base lead. A simple model is presented revealing the role of ground- and excited states within the QD for this dynamic operation of a single-electron transistor.
关键词： electronic wavefunction,coulomb blockade,single-electron tunneling,quantum dot excitations
更新于2025-09-23 15:19:57
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Single Photon Emission from a Plasmonic Light Source Driven by a Local Field-Induced Coulomb Blockade
摘要： A hallmark of quantum control is the ability to manipulate quantum emission at the nanoscale. Through scanning tunneling microscopy induced luminescence (STML) we are able to generate plasmonic light originating from inelastic tunneling processes that occur in the vacuum between a tip and a few-nanometer thick molecular film of C60 deposited on Ag(111). Single photon emission, not of molecular excitonic origin, occurs with a 1/e recovery time of a tenth of a nanosecond or less, as shown through Hanbury Brown and Twiss photon intensity interferometry. Tight-binding calculations of the electronic structure for the combined Ag-C60-tip system results in good agreement with experiment. The tunneling happens through electric field induced split-off states below the C60 LUMO band, which leads to a Coulomb blockade effect and single photon emission. The use of split-off states is shown to be a general technique that has special relevance for narrowband materials with a large bandgap.
关键词： STM induced luminescence,antibunching,Coulomb blockade,plasmon,split-off states
更新于2025-09-23 15:19:57
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Single-electron pumping in a ZnO single-nanobelt quantum dot transistor
摘要： Diluted magnetic semiconductors (DMSs) have traditionally been employed to implement spin-based quantum computing and quantum information processing. However, their low Curie temperature is a major hurdle in their use in this field, which creates the necessity for wide bandgap DMSs operating at room temperature. In view of this, a single-electron transistor (SET) with a global back-gate was built using a wide bandgap ZnO nanobelt (NB). Clear Coulomb oscillations were observed at 4.2 K. The periodicity of the Coulomb diamonds indicates that the Coulomb oscillations arise from single quantum dots of uniform size, whereas quasi-periodic Coulomb diamonds correspond to the contribution of multi-dots present in the ZnO NB. By applying an AC signal to the global back-gate across a Coulomb peak with varying frequencies, single-electron pumping was observed; the increase in current was equal to the production of electron charge and frequency. The current accuracy of about 1% for both single- and double-electron pumping was achieved at a high frequency of 25 MHz. This accurate single-electron pumping makes the ZnO NB SET suitable for single-spin injection and detection, which has great potential for applications in quantum information technology.
关键词： single-electron pumping,ZnO nanobelt,Coulomb blockade,quantum dot transistor
更新于2025-09-23 15:19:57
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Scenarios of local spectral property and multifunctional spin selecting for a triple quantum dot molecule: How do the bonding and antibonding orbitals contribute to the spin currents?
摘要： Molecular electronic device is considered as a promising candidate for next generation electronic component, where the basic challenge involves understanding the charge and spin transports through molecular objects. In this paper, with the help of the sophisticated numerical renormalization group technique, we study theoretically the spin selective transport in a parallel triple quantum dot molecular device pierced by a local magnetic field along z axis. Based on simplified parameters of real molecular system, we find such device acts as a multi-functional spin selector when the inter-molecule tunneling couplings are asymmetric, including two 100% polarized spin-up summits, and one 100% spin-down summit in the linear conductance. We show in detail the local density of states for the bonding and anti-boding orbitals, and attribute the spin selection to the orbital polarized Coulomb blockade effect. We demonstrate our numerical results are consistent with those estimated by the analytical techniques, including the Friedel sum rule and the energy level crossings of the isolated orbitals.
关键词： Coulomb blockade effect,Multifunctional spin selector,Triple quantum dot molecule,Numerical renormalization group technique,Molecular electronics device
更新于2025-09-12 10:27:22
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Fabrication and characterization of quantum dot devices based on tetralayer graphene/hexagonal boron nitride heterostructures
摘要： We report on low temperature carrier transport property of quantum dot devices based on hexagonal boron nitride-encapsulated tetralayer graphene heterostructures. In the device with single dot geometry, we demonstrate a stochastic Coulomb blockade, suggesting formation of multiple dots coupled each other in series/parallel. Under a perpendicular magnetic field, the overlapping Coulomb diamonds are lifted at zero bias voltage and the charging energy is decreased. These imply the suppression of multiple dots behavior. Our results pave a way toward the investigation of interlayer correlation on single electron transport in few-layer graphene quantum dots.
关键词： magnetic field,hexagonal boron nitride,Coulomb blockade,tetralayer graphene,quantum dot
更新于2025-09-12 10:27:22
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Quantitative comparison of Anderson impurity solvers applied to transport in quantum dots
摘要： We study the single impurity Anderson model (SIAM) using the equations of motion method (EOM), the non-crossing approximation (NCA), the one-crossing approximation (OCA), and Wilson’s numerical renormalization group (NRG). We calculate the density of states and the linear conductance focusing on their dependence on the chemical potential and on the temperature paying special attention to the Kondo and Coulomb blockade regimes for a large range of model parameters. We report that some standard approximations based on the EOM technique display a rather unexpected poor behavior in the Coulomb blockade regime even at high temperatures. Our study offers a critical comparison between the different methods as well as a detailed compilation of the shortcomings and limitations due the approximations involved in each technique, thus allowing for a cost-benefit analysis of the different solvers that considers both numerical precision and computational performance.
关键词： transport,Anderson impurity solvers,quantum dots,Coulomb blockade,Kondo effect
更新于2025-09-12 10:27:22