Single Electron Tunneling Effects Research Articles

Single electron tunneling and Coulomb blockade effect in HfAlO∕Au nanocrystals/HfAlO trilayer nonvolatile memory structure

Single electron tunneling and Coulomb blockade effect have been observed in the HfAlO∕Au nanocrystals/HfAlO trilayer floating gate nonvolatile memory structure. This trilayer floating gate memory structure exhibits a significant memory window, and resonant tunneling current peaks and Coulomb staircase are obtained at 20K low temperature. Compared to the ordinary single electron devices, this is the first time that a clear single electron tunneling oscillation has been observed in the floating gate memory structure. This resonant tunneling phenomenon in floating gate memory may open a door toward application as single electron device.

ハイブリッド型微細加工技術を用いた金ナノ粒子の単電子トンネル効果の観測

We would like to share our recent results from a research on the single electron tunneling effect in a double-barrier tunneling junction (DBTJ) structure. Single Au nanoparticles were trapped in a nanogap electrodes, whose gap size was precisely controlled using a combination of electron beam lithography and molecular ruler technique. Here, we introduce how the novel combination technique was utilized to obtain the nanogap electrode. We also introduce the size effect of Au particles on the single electron tunneling behavior as a Coulomb island. Finally, we introduce the relation between the geometrical and electrical properties of the DBTJ.

Single-electron tunneling phenomena on preformed gold clusters deposited on dithiol self-assembled monolayers

We report on detailed low temperature scanning tunneling spectroscopy measurements performed on preformed nanometer sized gold clusters. The clusters are deposited on Au(1 1 1) films that are coated with a self-assembled monolayer of 1,4-benzenedimethanethiol molecules, thereby creating a double barrier tunnel junction. In this configuration electrons can only move between the scanning tunneling microscope tip and the substrate through tunneling via the cluster. Due to the very small cluster size this results in pronounced single-electron tunneling effects. Anomalies in the I( V) curves measured above a single cluster can be consistently described in terms of charging of the double barrier junction for the majority of the particles. Both Coulomb blockade and Coulomb staircase with step widths in the 200–600 meV range were observed on various individual clusters. The results agree with the commonly used semiclassical theory of charging effects in a double barrier tunnel junction. Furthermore, for a limited number of clusters, additional conductance peaks are observed which are attributed to strong electron confinement inside the nanoscale clusters.

Fullerene-Like (IF) NbxMo1-xS2 Nanoparticles

IF-Mo1-xNbxS2 nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H2S. The IF-Mo1-xNbxS2 nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS2 within the MoS2 host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS2 host lattice. Very few Nb atoms, if any, are intercalated between the MoS2 layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS2 (whereas unsubstituted IF-MoS2 nanoparticles are semiconducting). Furthermore the IF-Mo1-xNbxS2 nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures.

Electrostatic electron piston pump with in‐plane gate transistors

AbstractWe have demonstrated an electron pump with in‐plane gate (IPG) transistors fabricated by focused ion beam (FIB) implantation on GaAs–Alx Ga1–x As modulation‐doped heterostructure with a two‐dimensional electron gas (2DEG). The maskless fabrication process does not require any alignment between the circuit elements including the sources, the drains and the gates of the IPG transistors. Although, the device is operating at low frequencies (tens of kHz), it is capable to produce a current more than one order of magnitude higher than other electron pumps based on Coulomb blockade and single electron tunneling effects. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Negative differential resistance in tunneling transport through C60 encapsulated double-walled carbon nanotubes

The authors report electric transport properties of resonance tunneling field-effect transistors fabricated using C60-filled metallic double-walled carbon nanotubes. The devices exhibit strong resonance tunneling characteristics and the distinct negative differential resistance with high peak-to-valley current ratio about 1300 is observed at room temperature. In particular, at high bias voltages, the tunneling current is completely dominated by the Coulomb oscillation peaks with uniform conductance at room temperature, reflecting a strong single-electron tunneling effect.

Self-assembled metallic nanoparticles for spin dependent single electron tunneling

The study of spin-dependent single electron tunneling requires the preparation of particles with a nanometric size. These particles need not be ferromagnetic if the electrodes are. In order to fulfill the requirements of single electron tunneling effect, the preparation conditions of nanoparticles were studied, mainly for Fe and Au particles. The structure of these particles was then studied by scanning probe microscopy and transmission electron microscopy, and compared to the results of transport measurements. Particles with a diameter of the order of a nanometer were prepared and their lateral arrangement was controlled by self-organization phenomena.

Electronic transport properties of NbC(C)-C nanocomposites

We report the electronic transport properties of a composite system comprising zero dimensional superconducting NbC(C) nanocapsules and carbon nanofiber matrix. DC susceptibility measurements of the nanocomposite indicate that the critical temperature (T-C) of NbC nanocrystals is 10.7 K. The temperature dependence of electrical resistivity of the specimen pellet follows the Mott's T-1/4 law in a temperature range between T-C of NbC and 300 K, owing to a strong degree of structural disorder in the carbon matrix. Below the T-C of NbC, when the change of its electrostatic energy Delta E is far greater than the thermal energy, an electron will be localized on an isolated NbC nanocrystal at very low temperatures, leading to Coulomb Blockade. As a result, a collective behavior of the single-electron tunneling effect takes place in a three-dimensional granular superconductors' network composed of the NbC/carbon/NbC tunneling junctions. The superconducting gap of NbC crystals is not found in the current-voltage curves, due to the suppression of surface superconductivity through the contact between NbC and carbon shells.

走査型トンネル顕微鏡による低次元ナノ構造の創成と計測

Recent developments of fabrication, manipulation and characterization techniques at nanometer scale for low-dimensional nanostructures using scanning tunneling microscopy (STM) are reviewed. Firstly two reliable methods for metallic nanostructure formation using tip material transfer are introduced. Secondly STM-manipulation of Au nanoclusters grown on self-assembled monolayers is introduced, where single electron tunneling effect is clearly observable using tunneling spectroscopy. As a new type of STM manipulation, a reversible control method of surface periodic structures (phases) on Si(100) at low temperatures is introduced. Finally using a single atom deposition technique using a controlled point contact, fabrication of one-dimensional quantum well on a single dimer row of Si(100) surface is explained. Combining the fabrication and characterization capabilities of STM in various environments, STM can be a powerful tool for the exploration of nanotechnology and nanoscience.

SingleC59NMolecule as a Molecular Rectifier

We report a new kind of experimental realization of a molecular rectifier, which is based on a single azafullerene C59N molecule in a double-barrier tunnel junction via the single electron tunneling effect. An obvious rectifying effect is observed. The positive onset voltage is about 0.5-0.7 V, while the negative onset voltage is about 1.6-1.8 V. Theoretical analyses show that the half-occupied molecular orbital of the C59N molecule and the asymmetric shift of the molecular Fermi level when the molecule is charged are responsible for the molecular rectification.

Spin dependent transport in ferromagnet/superconductor/ferromagnet single electron transistor

Ferromagnetic single electron transistors with Al islands and orthogonal ferromagnetic leads (Co) are fabricated using e-beam lithography followed by shadow evaporation techniques. I–V characteristics exhibit typical single electron tunneling effects. Transport measurements performed in external magnetic field show that, when the two ferromagnetic leads are in antiparallel configuration, spin imbalance leads to a suppression of superconductivity.

Single-electron tunneling to insulator surfaces measured by frequency detection electrostatic force microscopy

Single-electron tunneling events between a metal probe and an insulator surface are measured by frequency detection electrostatic force microscopy. Single-electron tunneling events typically cause 1–10Hz shifts in the 300kHz resonance frequency of the oscillating force probe. The frequency shifts appear only within a sub-2nm tip–sample gap and their magnitude is roughly uniform under fixed experimental conditions. An electrostatic model of the probe–sample system yields results consistent with the measurements.

Fabrication and characterization of metal-semiconductor field-effect-transistor-type quantum devices

Quantum dot transistors and nanowire transistors are fabricated from a metal-semiconductor field-effect-transistor-type wafer and are characterized at low temperatures. Clear single-electron tunneling and various quantum effects, such as transport through excited states and negative differential resistance, are observed in our wire device. Our data suggest that the potential fluctuation of the heavily doped GaAs layer has a much larger characteristic length than interimpurity spacing, and that this is due to the low ionization rate (approximately 10%) of the dopant atoms at 4.2 K.

Temperature-dependent single-electron tunneling effect in lightly and heavily doped GaN nanowires

We studied the electrical transport properties of GaN nanowires with two different doping levels. Measurements taken at various temperatures demonstrate that the electrical transport depends mainly on the single-electron tunneling effect up to a relatively high temperature of $\ensuremath{\sim}150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The aperiodic oscillations which we observed were attributed to single-electron tunneling through multiple quantum dots within the nanowire, which originated from various defects and the inhomogeneous distribution of the dopants.

Electron counting of single-electron tunneling current

Single-electron tunneling through a quantum dot is detected by means of a radio-frequency single-electron transistor. Poisson statistics of single-electron tunneling events are observed from frequency domain measurements, and individual tunneling events are detected in the time-domain measurements. Counting tunneling events gives an accurate current measurement in the saturated current regime, where electrons tunnel into the dot only from one electrode and tunnel out of the dot only to the other electrode.

Modeling and experimental investigation of cantilever dynamics in force detected single electron tunneling

The dynamic response of a voltage biased oscillating cantilever probe is investigated through experimental and theoretical analysis as it approaches a dielectric surface. When the tip reaches the appropriate gap single electron tunneling events are detected between the metallic tip and the surface. The tunneling events cause a decrease of the electrostatic force and force gradient acting between tip and sample. The change in the electrostatic force is detected as an abrupt decrease of the cantilever oscillation amplitude. Additionally, due to the nonlinear interaction between tip and sample, the cantilever oscillation amplitude in very close proximity of the sample can have multiple values. Typically, as the tip-sample gap is reduced, a transition between two stable cantilever oscillation modes is detected as an abrupt increase in the oscillation amplitude. If this transition occurs at a gap larger than the tunneling gap, no tunneling event is detected. A theoretical model that includes both the electrostatic and mechanical effects has been developed to investigate the cantilever response in close proximity of the sample. The model, which includes the effects of the single electron tunneling events, is in good agreement with the measurements.

Periodic tunnel-current oscillations in metal droplets

We have observed strong current oscillations in a metal droplet system by point-contact tunneling with a scanning tunneling microscope at 77 K. The oscillations have a periodicity equal to the single-electron charging voltage, e/C=28 mV, where C is the metal droplet capacitance. The current oscillations are large in magnitude, robust, and insensitive to tip position. A simple model of the system based on a self-biased single-electron transistor suggests the contribution of multidroplet single-electron tunneling effects.

Octanedithiol layer as tunneling barrier

Au deposited octanedithiol/Au(111) samples provide homogeneous Au nanoclusters, well defined tunneling barriers and atomically flat substrate, which enables us to observe single electron tunneling effects and the kinetic energy shifts of the photoelectrons on the same sample in tunneling spectroscopy and photoelectron spectroscopy, respectively. Through the manipulation technique and the observation of Coulomb staircase by tunneling microscopy and spectroscopy, it is shown that this system provides the uniform resistance (∼140 MΩ) between clusters and Au(111) surface.

Single-electron tunneling to insulator surfaces detected by electrostatic force

The detection of single-electron tunneling events between a metallic scanning probe tip and an insulating surface is demonstrated by an electrostatic force method. When a voltage-biased oscillating atomic force microscopy tip is placed within tunneling range of the surface of an insulator, single-electron tunneling events are observed between the tip and electronic states at the surface. The events cause an abrupt reduction in cantilever oscillation amplitude, due to the instantaneous reduction of the force gradient at the tip. In most cases, only a single electron tunnels to or from the surface. Experimental data show that no physical contact is made during the tunneling events.

Consistent size dependency of core-level binding energy shifts and single-electron tunneling effects in supported gold nanoclusters

Uniform Au-clusters supported on well-defined substrate [octanedithiol/Au(111)] were analyzed by tunneling and x-ray photoelectron spectroscopy. Single-electron tunneling effect and the binding-energy shift observed in these spectroscopies exhibit the consistent cluster-size dependency. Au $4f$ core-level shift of the supported clusters can be well explained by the charging energy ${e}^{2}/2C,$ where C is the capacitance between a cluster and its surroundings. The main contributions to this C are the self-capacitance of the cluster, the dielectric constant of the octanedithiol layer $(\ensuremath{\epsilon}\ensuremath{\sim}3)$ and the effect of the substrate. The other possible contributions are attributed to the effect of nearest-neighbor clusters and the electron spillout from the cluster and substrate due to the coupling between the molecular orbital and the conducting electrons.