Coulomb Blockade Oscillations Research Articles

Analytical Modelling and Performance Characterization of Single Electron Transistor

One important component of the present nanotechnology research field is single electron transistor (SET) which has unrealized quality to operate at breakneck speeds with ultralow power consumption. The single electron transistor is a novel nanoscale switching device that can regulate the motion of a single electron in addition to maintaining its scalability down to the atomic level. In this context, scalability refers to the ability of electronic device to function better as their dimensions get smaller. The basic device properties that this single electron transistor (SET) operates on "quantized current-voltage (I-V) characteristic," "single electron tunneling effect," and "Coulomb blockade," are also covered. This study presents some of the key SET-related topics, such as modelling and simulation methods. Simulation of Nanostructures Method (SIMON) is circuit simulator for tunneling device with just a single electron device based on Monte Carlo approach. It enables simulation of any kind of circuits with voltage source, junctions in tunnels and capacitors in quasi stationary mode and transient mode. The most significant feature of SET that is applied in the research work is Coulomb blockade oscillation, so at the conclusion of this paper, a number of simulations utilizing the SIMON simulator are shown. The simulation results show that for gate capacitance CG = 2af, C∑ = 3af, IBIAS = 2nA, tunnel barrier resistance RT > 4.1KΩ and operating temperature T=21K the model reflects real SET characteristic with maximum voltage gain.

Characteristics of the single-electron conduction properties of randomly distributed metal nanodot arrays

Multi-dot single-electron devices (SEDs) have been fabricated using very thin Fe films by vacuum deposition on thermally oxidized or sputter-deposited SiO2 substrates. Although the SEDs fabricated on the two substrates showed very different conductance, Coulomb blockade (CB) oscillation clearly appeared in certain Fe thickness ranges for both cases. The CB oscillation changed from complex to simple with increasing Fe thickness, indicating that the decrease of the number of dots contributed to the CB oscillation. While the simple CB monotonically disappeared by the drain voltage (V D), the complex CB was robust against V D because V D distributed over the array composed of plural dots. The CB property change from complex to simple appeared in different thickness ranges for the two substrates, but in similar conductance ranges. This demonstrates that the conductance influenced by the inter-dot distance is an important factor for the CB characteristics of randomly distributed multi-dot SEDs.

Transport Characteristics of Silicon Multi-Quantum-Dot Transistor Analyzed by Means of Experimental Parametrization Based on Single-Hole Tunneling Model.

The transport characteristics of a gate-all-around Si multiple-quantum-dot (QD) transistor were studied by means of experimental parametrization using theoretical models. The device was fabricated by using the e-beam lithographically patterned Si nanowire channel, in which the ultrasmall QDs were self-created along the Si nanowire due to its volumetric undulation. Owing to the large quantum-level spacings of the self-formed ultrasmall QDs, the device clearly exhibited both Coulomb blockade oscillation (CBO) and negative differential conductance (NDC) characteristics at room temperature. Furthermore, it was also observed that both CBO and NDC could evolve along the extended blockade region within wide gate and drain bias voltage ranges. By analyzing the experimental device parameters using the simple theoretical single-hole-tunneling models, the fabricated QD transistor was confirmed as comprising the double-dot system. Consequently, based on the analytical energy-band diagram, we found that the formation of ultrasmall QDs with imbalanced energetic natures (i.e., imbalanced quantum energy states and their imbalanced capacitive-coupling strengths between the two dots) could lead to effective CBO/NDC evolution in wide bias voltage ranges.

Single-electron transport in H2O@C60 single-molecule transistors

Single-molecule transistors (SMTs) based on fullerenes and their derivatives have been recognized as a long-sought platform for studying the single-electron transport properties. H2O@C60 is a combination of fullerene and H2O, a typical light molecule. Here we use the ‘molecular surgery’ technique to synthesize the H2O@C60 molecule and then construct the H2O@C60 SMTs, together with the C60 SMTs. Evidences for single-electron transport have been obtained in our measurements, including explicit Coulomb blockade and Coulomb oscillations. We then calculate the detailed parameters of the H2O@C60 and C60 SMTs using a capacitance model derived from the Coulomb diamond feature, which gives a capacitance ratio of 1:5.05:8.52 for the H2O@C60 SMT and 1:29.5:74.8 for the C60 SMT. Moreover, the gate efficiency factor α turns out to be 0.0686 in the H2O@C60 SMT, about ten times larger than that in the C60 SMT. We propose that the enhanced gate efficiency in H2O@C60 SMT may be induced by the closer attachment of molecular orbital electron clouds to the gate substrate due to polarization effects of H2O.

Coulomb-blockade oscillation in CdS, ZnS and CdS/ZnS core-shell quantum dots

CdS, ZnS and core–shell CdS/ZnS quantum dots (QDs) with different ratio concentration of core to shell (1:1, 1:2, 1:3, 1:4, 1:5) were synthesized and their structural, optical and electrical properties were studied with respect to the increase shell thickness. XRD exhibits the wurtzite structure of CdS QDs along with the cubic trace of ZnS. HRTEM images exhibit spherical shaped particle morphology for both CdS and CdS/ZnS core–shell QDs. The optical properties show a defect control mechanism in carrier transport. Enhancing shell thickness introduces higher defect density, defect induced crystal strain and charge separation which leads to quantum mechanical tunneling in determination of conduction mechanism through QDs. The current-voltage (I-V) characteristics of the QD devices shows an oscillatory behavior which may be attributed to coulomb-blockade oscillations because of quantum structure of QDs. Room temperature quantum oscillation behavior has been studied systematically for the synthesized semiconductor core/shell QDs which is the major finding of the present work. Mullen’s two tunnel junction model has been used for the QD devices, which is in agreement with the observed coulomb oscillations for R1 ≪ R2 and C1 ≪ C2, originated from defect induced surface and interface of core/shell structure. The present experimental results may contribute towards study and development of futuristic quantum oscillatory nanoscale devices.

Synthesis of Self-Assembled Single Atomic Layer Gold Crystals-Goldene.

We report, for the first time, a technique to synthesize free-standing, one-atom thick 2D gold crystals (namely, goldene) and self-assembled 2D periodic arrays of goldene. High-resolution transmission electron microscopy (HRTEM) imaging of goldene revealed herringbone and honeycomb lattices, which are primarily gold surface features due to its reconstruction. Imaging of these surface-only features by a nonsurface characterization technique such as HRTEM is an unequivocal proof of the absence of three-dimensionality in goldene. Atomic force microscopy confirmed 1-2 Å thickness of goldene. High-resolution X-ray photoelectron spectroscopy (HR-XPS), selective area electron diffraction, and energy-dispersive X-ray spectroscopy confirmed the chemical identity of goldene. We discovered the phenomenon of electric field-induced self-assembly of goldene supracrystals with a herringbone structure and developed an electric field printing (e-print) technique for goldene arrays. Goldene showed a semiconductor response with a knee voltage of ∼3.2 V, and I/V spectroscopy revealed periodic room temperature Coulomb blockade oscillations. These observations are consistent with the theoretical calculations reported in the literature predicting enhanced Coulombic interactions between gold valence electrons and the nucleus in stable 2D gold. Goldene exhibited multiple, intense, and well-resolved optical absorption peaks and several fine bands across the UV-vis region, and we calculated its optical band gap to be 3.59 eV. Magnetic force microscopy measurements of goldene periodic arrays showed a ∼5 mV peak amplitude confirming its ferromagnetism. Optical and magnetic properties of goldene are consistent with those reported in the literature for 2D planar gold clusters with less than 12 atoms.

Demonstration and operation of quantum harmonic oscillators in an AlGaAs-GaAs heterostructure

The quantum harmonic oscillator (QHO), one of the most important and ubiquitous model systems in quantum mechanics, features equally spaced energy levels or eigenstates. Here we present a new class of nearly ideal QHOs formed by hydrogenic substitutional dopants in an AlGaAs/GaAs heterostructure. On the basis of model calculations, we demonstrate that, when a δ-doping Si donor substitutes the Ga/Al lattice site close to AlGaAs/GaAs heterointerface, a hydrogenic Si QHO, characterized by a restoring Coulomb force producing square law harmonic potential, is formed. This gives rise to QHO states with energy spacing of ∼8–9 meV. We experimentally confirm this proposal by utilizing gate tuning and measuring QHO states using an aluminum single-electron transistor (SET). A sharp and fast oscillation with period of ∼7–8 mV appears in addition to the regular Coulomb blockade (CB) oscillation with much larger period, for positive gate biases above 0.5 V. The observation of fast oscillation and its behavior is quantitatively consistent with our theoretical result, manifesting the harmonic motion of electrons from the QHO. Our results might establish a general principle to design, construct and manipulate QHOs in semiconductor heterostructures, opening future possibilities for their quantum applications.

Superconducting Proximity in Intrinsic Magnetic Topological Insulator MnBi2Te4-NbN Hybrid Device Modulated by Coulomb Blockade Effect.

The combination of nontrivial topology, magnetism, and superconductivity could offer the potential to realize exotic excitations of quasiparticles. MnBi2Te4, as an intrinsic magnetic topological insulator, may be a good platform to create Majorana fermions if coupled to an s-wave superconductor. Here, we report the transport properties of a MnBi2Te4-NbN hybrid device. This device exhibits clear Coulomb blockade oscillations. We observe a large zero-bias conductance peak that exists over considerable changes in gate voltage, magnetic field, and temperature, which is interpreted as a not fully developed supercurrent. The zero-bias peak shows a nonmonotonic evolution with a magnetic field and an abrupt π phase shift with changing temperature. Zero-energy bound states and a topological phase transition may exist in this hybrid system. Our results provide the first experimental investigation into the properties of the intrinsic magnetic topological insulator/superconductor hybrid structures modulated by the Coulomb blockade effect.

Double gate operation of metal nanodot array based single electron device

Multidot single-electron devices (SEDs) can enable new types of computing technologies, such as those that are reconfigurable and reservoir-computing. A self-assembled metal nanodot array film that is attached to multiple gates is a candidate for use in such SEDs for achieving high functionality. However, the single-electron properties of such a film have not yet been investigated in conjunction with optimally controlled multiple gates because of the structural complexity of incorporating many nanodots. In this study, Fe nanodot-array-based double-gate SEDs were fabricated by vacuum deposition, and their single-electron properties (modulated by the top- and bottom-gate voltages; VT and VB, respectively) were investigated. The phase of the Coulomb blockade oscillation systematically shifted with VT, indicating that the charge state of the single dot was controlled by both the gate voltages despite the metallic random multidot structure. This result demonstrates that the Coulomb blockade oscillation (originating from the dot in the multidot array) can be modulated by the two gates. The top and bottom gates affected the electronic state of the dot unevenly owing to the geometrical effect caused by the following: (1) vertically asymmetric dot shape and (2) variation of the dot size (including the surrounding dots). This is a characteristic feature of a nanodot array that uses self-assembled metal dots; for example, prepared by vacuum deposition. Such variations derived from a randomly distributed nanodot array will be useful in enhancing the functionality of multidot devices.

Comment on "Coulomb Blockade and Bloch Oscillations in Superconducting Ti Nanowires".

Comment on "Coulomb Blockade and Bloch Oscillations in Superconducting Ti Nanowires".

Investigations of Optical Coulomb Blockade Oscillations in Plasmonic Nanoparticle Dimers

The exploration of Coulomb blockade oscillations in plasmonic nanoparticle dimers is the subject of this study. When two metal nanoparticles are brought together at the end of their journey, tunnelling current prevents an infinite connection dipolar plasmon and an infinite amplification in the electric fields throughout the hot spot in between nanoparticles from occurring. One way to think about single-electron tunnelling through some kind of quantum dot is to think about Coulomb blockage oscillations in conductance. The electron transport between the dot and source is considered. The model of study is the linear conductance skilled at describing the basic physics of electronic states in the quantum dot. The linear conductance through the dot is defined as G = lim ⟶ 0 I / V in the limit of infinity of small bias voltage. We discuss the classical and quantum metallic Coulomb blockade oscillations. Numerically, the linear conductance was plotted as a function gate voltage. The Coulomb blockade oscillation occurs as gate voltage varies. In the valleys, the conductance falls exponentially as a function gate voltage. As a result of our study, the conductance is constant at high temperature and does not show oscillation in both positive and negative gate voltages. At low temperature, conductance shows oscillation in both positive and negative gate voltages.

Shell Induced Optical Properties and Coulomb-Blockade Oscillation in Cds/Zns Core-Shell Quantum Dots

Shell Induced Optical Properties and Coulomb-Blockade Oscillation in Cds/Zns Core-Shell Quantum Dots

Reconfigurable Multivalue Logic Functions of a Silicon Ellipsoidal Quantum-Dot Transistor Operating at Room Temperature.

Reconfigurable multivalue logic functions, which can perform the versatile arithmetic computation of weighted electronic data information, are demonstrated at room temperature on an all-around-gate silicon ellipsoidal quantum-dot transistor. The large single-hole transport energy of the silicon quantum ellipsoid allows the stable M-shaped Coulomb blockade oscillation characteristics at room temperature, and the all-around-gate structure of the fabricated transistor enables us to perform the precise self-control of the energetic Coulomb blockade conditions by changing the applied bias voltage. Such a self-controllability of the M-shaped Coulomb blockade oscillation characteristics provides a great advantage to choose multiple operation points for the reconfigurable multivalue logic functions. Consequently, the weighted data states (e.g., tri-value and quattro-value) are effectively demonstrated by utilizing only the device physics in the all-around-gate silicon ellipsoidal quantum-dot transistor. These findings are of great benefit for the practical application of the silicon quantum device at an elevated temperature for future nanoelectronic information technology.

Coulomb blockade oscillations of heat conductance in the charge Kondo regime

We develop a method of theoretically investigating the charge, energy and heat transport in the presence of the charge Kondo correlations. The Coulomb blockade oscillations of heat conductance in the single electron transistor exhibiting the charge Kondo effects are investigated. We explore the Wiedemann Franz ratio in both charge-single channel and charge-two channel Kondo regime. The close connections of our findings with the recent experiments on multi-channel charge Kondo effects are discussed.

Signatures of topological ground state degeneracy in Majorana islands

We consider a mesoscopic superconducting island hosting multiple pairs of Majorana zero-energy modes. The Majorana island consists of multiple p-wave wires connected together by a trivial (s-wave) superconducting backbone and is characterized by an overall charging energy $E_C$; the wires are coupled to normal-metal leads via tunnel junctions. We calculate the average charge on the island as well as non-local conductance matrix as a function of a p-wave pairing gap $\Delta_P$, charging energy $E_C$ and dimensionless junction conductances $g_i$. We find that the presence of a topological ground-state degeneracy in the island dramatically enhances charge fluctuations and leads to the suppression of Coulomb blockade effects. In contrast with conventional (s-wave) mesoscopic superconducting islands, we find that Coulomb blockade oscillations of conductance are suppressed in Majorana islands regardless of the ratio $E_C/\Delta_P$ or the magnitude of the conductances $g_i$. We also discuss our findings in relation to the so-called topological Kondo effect.

Mesoscopic capacitance oscillations due to quantum dynamic coherence in an interacting quantum capacitor

We have measured the electrochemical capacitance in a quantum coherent capacitor consisting of a quantum dot connected to an electron reservoir by a gate tunable quantum point contact and Coulomb coupled to a gate. The results show that for a weak transparent channel, the capacitance exhibits sharp Coulomb blockade oscillations with gate voltage related to the oscillations of the dot density of states, which is almost independent of the applied magnetic field. As the transmitting channel becomes more transparent, the capacitance oscillations decrease in magnitude reflecting the broadening of the resonances. Remarkably, we find that the capacitance oscillation persists even for a fully transparent quantum channel. From the magnetic field and temperature dependence, we conclude that such a capacitance oscillation is a mesoscopic coherent effect that arises due to the interference of electrons in a nearly open dot.

Robust subgap edge conduction in bilayer graphene with disordered edge termination

The subgap transport in electrostatically gapped bilayer graphene (BLG) is explored by adopting ultrashort constrictions of BLG. We confirmed the emergence of the edge conducting channels, with a residual conductance of $\ensuremath{\sim}2{e}^{2}/h$ per edge of realistic disorder. Transport along the edge state exhibits either Coulomb blockade oscillations or Fabry-Perot interference, depending on the interfacial transparency between the reservoirs and the edge channel. Both residual conductance and band-gap dependence of the penetration range of the edge state from a constriction edge coincide well with the behavior of the theoretically predicted robust edge conducting channel, which forms irrespective of the degree of edge disorder.

Electrical monitoring of photoisomerization of block copolymers intercalated into graphene sheets

Insulating polymers have received little attention in electronic applications. Here, we synthesize a photoresponsive, amphiphilic block copolymer (PEO-b-PVBO) and further control the chain growth of the block segment (PVBO) to obtain different degrees of polymerization (DPs). The benzylidene oxazolone moiety in PEO-b-PVBO facilitated chain-conformational changes due to photoisomerization under visible/ultraviolet (UV) light illumination. Intercalation of the photoresponsive but electrically insulating PEO-b-PVBO into graphene sheets enabled electrical monitoring of the conformational change of the block copolymer at the molecular level. The current change at the microampere level was proportional to the DP of PVBO, demonstrating that the PEO-b-PVBO-intercalated graphene nanohybrid (PGNH) can be used in UV sensors. Additionally, discrete signals at the nanoampere level were separated from the first derivative of the time-dependent current using the fast Fourier transform (FFT). Analysis of the harmonic frequencies using the FFT revealed that the PGNH afforded sawtooth-type current flow mediated by Coulomb blockade oscillation.

High dynamic resistance elements based on a Josephson junction array.

A chain of superconductor–insulator–superconductor junctions based on Al–AlOx–Al nanostructures and fabricated using conventional lift-off lithography techniques was measured at ultra-low temperatures. At zero magnetic field, the low current bias dynamic resistance can reach values of ≈1011 Ω. It was demonstrated that the system can provide a decent quality current biasing circuit, enabling the observation of Coulomb blockade and Bloch oscillations in ultra-narrow Ti nanowires associated with the quantum phase-slip effect.

Quantum anti-dot formed with an airbridge gate in the quantum Hall regime

We demonstrate a quantum antidot (QAD) formed with an airbridge gate on an AlGaAs/GaAs heterostructure, where a sub-micron pillar-shaped surface gate is biased via the bridge. We study transport through the QAD in the two regimes; one with a fully depleted region and the other with a partially depleted region at the center of the QAD. While standard Coulomb blockade (CB) oscillations with discrete levels are observed in the fully depleted region, short-period CB oscillations and more complicated patterns with multiple QADs are seen in the partially depleted region. The device is promising for investigating the few-particle regime.