Observation Of Coulomb Blockade Research Articles

Current–voltage characteristics of strained, highly underdoped LaSr x CuO4 thin films

The temperature dependence of resistance and of current–voltage characteristics are studied for two underdoped La1.952Sr0.048CuO4 films with different thickness and different degrees of built-in compressive strain. Strain induces an inhomogeneous superconducting (SC) state in the films, with two-step SC transition, consistent with the presence of SC islands coupled by the proximity effect. On further cooling, superfluid density is suppressed and global phase coherence is never reached. Instead, a reentrant increase of resistance appears, reaching several orders of magnitude in the thinner, more strongly strained film, and saturating at lowest temperatures. The saturation is accompanied by Coulomb blockade, which resembles the blockade reported for Josephson junction (JJ) arrays. However, increasing magnetic field quickly diminishes the influence of Coulomb blockade on transport, which is distinct from the behavior observed for JJ arrays. The observation of Coulomb blockade indicates that Cooper pairs survive in the insulating state, suggesting the local character of pairing.

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.

Observation of Coulomb blockade in nanostructured epitaxial bilayer graphene on SiC

We study electron transport in nanostructures patterned in bilayer graphene patches grown epitaxially on SiC as a function of doping, magnetic field, and temperature. Away from charge neutrality transport is only weakly modulated by changes in carrier concentration induced by a local side-gate. At low n-type doping close to charge neutrality, electron transport resembles that in exfoliated graphene nanoribbons and is well described by tunnelling of single electrons through a network of Coulomb-blockaded islands. Under the influence of an external magnetic field, Coulomb blockade resonances fluctuate around an average energy and the gap shrinks as a function of magnetic field. At charge neutrality, however, conduction is less insensitive to external magnetic fields. In this regime we also observe a stronger suppression of the conductance below T*, which we interpret as a sign of broken interlayer symmetry or strong fluctuations in the edge/potential disorder.

Coulomb blockade and plasmonic nanoantenna effect in back gated ZnO nanorod FET

Fabrication and characterization of ZnO nanorod field effect transistor (FET) is reported. Back-gated ZnO nanowire FETs were fabricated on SiO2 covered p-type Si substrate using lithographically patterned Ti/Au contacts. The ZnO nanorods were synthesized by chemical bath deposition method using the precursors zinc nitrate hexahydrate (Zn (NO3)2·6H2O) and hexamethylenetetramine (HMT) (C6H12N4). Fabricated FET has shown clear gate response. I–V characterization done on the fabricated FET has shown Coulomb blockade and plasmonic nanoantenna like effects. The observation of Coulomb blockade and plasmonic effect of the fabricated FET structure have been explained.

Superior Current Carrying Capacity of Boron Nitride Encapsulated Carbon Nanotubes with Zero-Dimensional Contacts.

We report fabrication and characterization of hexagonal boron nitride (hBN)-encapsulated carbon nanotube (CNT) field effect transistors, which are coupled to electrical leads via zero-dimensional contacts. Device quality is attested by the ohmic contacts and observation of Coulomb blockade with a single periodicity in small bandgap semiconducing nanotubes. Surprisingly, hBN-encapsulated CNT devices demonstrate significantly enhanced current carrying capacity; a single-walled CNT can sustain >180 μA current or, equivalently, a current density of ∼2 × 10(10) A/cm(2), which is a factor of 6-7 higher than devices supported on SiO2 substrates. Such dramatic enhancement of current carrying capacity arises from the high thermal conductivity of hBN and lower hBN-CNT interfacial thermal resistance and has implications for carbon electronic applications.

In-Vacuum Projection of Nanoparticles for On-Chip Tunneling Spectroscopy

Starting with a discussion of the percolation problem applied to the trapping of conducting nanoparticles between nanometer-spaced electrodes, we show that a good strategy to trap a single nanoparticle between the electrodes is to prepare chips with low coverage of nanoparticles to avoid percolating current paths. To increase the probability of trapping a single nanoparticle, we developed a new method where nanoparticles are projected in-vacuum on the chip, followed by a measure of the tunnel current, in a cycle that is repeated up to a few thousand times until a preset threshold value is reached. A plot of the tunneling current as a function of time allows discriminating between the two possible current paths, i.e., a single nanoparticle trapped between the electrodes or a percolating path across many nanoparticles. We applied the method to prepare chip circuits with single gold nanoparticles, as demonstrated by the observation of Coulomb blockade. Furthermore, we applied the method to trap single magnetite nanoparticles for the study of electric-field-induced switching from insulator to metal in single nanoparticles.

Double coupled electron shuttle

A nano-shuttle consisting of two metallic islands connected in series and integrated between two contacts is studied. We evaluate the electron transport through the system in the presence of a source-drain voltage with and without an RF excitation. We evaluate the response of the system in terms of the net direct current generated by the mechanical motion of the oscillators. An introduction to the charge stability diagram is given in terms of electrochemical potentials and mechanical displacements. The low capacitance of the islands allows the observation of Coulomb blockade even at room temperature. Using radio frequency excitations, the nonlinear dynamics of the system is studied. The oscillators can be tuned to unstable regions where mechanically assisted transfer of electrons can further increase the amplitude of motion, resulting of a net energy being pumped into the system. The instabilities can be exploited to parametrically amplify the response to an excitation, suggesting a practical scheme for detection of mechanical motion of nanoscale objects.

Observation of Coulomb blockade and ballistic tunneling in graphene single electron transistor

A square graphene single electron transistor (SET) was defined with two side gates, and its transport was studied at low temperature at T = 2 K. At zero magnetic field, Coulomb blockade oscillations were clearly observed near the Dirac point of this device. At high magnetic field, in the quantum Hall regime, we observed ballistic tunneling of the carriers through the graphene SET, contrary to the Coulomb blockades observed while approaching the vicinity of the Dirac point.

CHARACTERIZATION OF CONDUCTION MECHANISMS RELEVANT TO DEVICE PERFORMANCE IN NANOPERFORATED GRAPHENE

We have recently reported on the synthesis and characterization of a new form of nanostructured graphene that we call "nanoperforated graphene". Nanoperforated graphene is fabricated by etching a periodic array of nanoscale holes into atomic membranes of graphene to create an ultrathin superlattice-like structure. Nanoperforated graphene demonstrates semiconductor-like behavior and we have realized room-temperature field-induced conductance modulation as high as 450 (compared with < 10 for unpatterned graphene) with field-effect mobilities of ~ 1 cm2V-1s-1. Here, we discuss the conduction mechanisms in nanoperforated graphene and the relevance of this new material for field-effect transistor devices. In nanoperforated graphene with 15 nm nanoconstrictions, we observe that the low-bias mobility is independent of temperature, consistent with elastic scattering-limited conduction. At low temperatures, a transport gap limits conduction in the sub-threshold regime and affects the threshold voltage for band conduction. We show that the high-bias electrical characteristics of nanoperforated graphene are similar to "artificial solids," a class of materials made of 2D arrays of Coulomb islands, consistent with observed Coulomb Blockade features in the sub-threshold regime. Currently, the device characteristics of the nanopatterned graphene material are found to be suitable for large-area, thin-film transistor applications. Future higher-performance applications are expected.

Hydrogen silsesquioxane electron beam lithography for ultra-small single electron transistors in silicon on insulator

A process for the fabrication of ultra-small silicon single electron transistors with 10 nm constrictions and 40 nm island diameters based on electron beam lithography with hydrogen silsesquioxane negative resist and reactive ion etching of a thin silicon on insulator device layer is presented. The observed Coulomb blockade at room temperature indicates that even at this size small dopant clusters are formed in highly doped material and act as effective islands in a multi-junction device.

Fabrication of vertically aligned carbon nanotubes for spintronic device applications

We report on the observation of coulomb blockade and coulomb staircase at room temperature in multiwalled carbon nanotube (MWCNT) based heterostructures. The hybrid structure consists of nickel ferromagnets separated by vertically aligned MWCNTs. The MWCNTs were grown vertically on a nickel substrate by a double plasma hot filament chemical vapour deposition technique. Deposition of ferromagnetic nickel nanoparticles on the top of MWCNTs was achieved for the first time using the laser chemical vapour deposition method. The fabrication technique is unique in that it is formed of many individual ferromagnetic tunnel junctions integrated into a single system. A well defined coulomb blockade and coulomb staircase was displayed in current–voltage characteristics obtained by scanning tunnelling spectroscopy. The capacitance (1. 6 × 10−18 F) in the system is determined from the spacing ΔV between peaks in the dI/dV curves.

Coulomb blockade behavior in individual multiwalled carbon nanotubes

In this study, the transport characteristics of multiwalled carbon nanotubes were measured at low temperatures using the multiple-probe technique. Cr metal was used as the electrode material and good Ohmic contact to the tube was obtained. Measurements using two- and four-probe techniques showed Coulomb oscillation with nearly the same period, indicating that the local islands formed inside the nanotube. Our experiments and simulation results suggested that the local barriers existing between electrodes divided our tube into a chain of weakly coupled islands and were responsible for the observed Coulomb blockade behaviors.

Defect Effect on Electrical Transport of Multiwalled Carbon Nanotubes

The low-temperature transport properties of individual multiwalled carbon nanotubes are investigated at low temperatures using the multiple-probe technique. A low-ohmic contact between an electrode and a tube is prepared to prevent the influence of contact. Measurements using two- and four-probe techniques show Coulomb oscillations with nearly the same periods, indicating that the tunneling barriers are inside the tubes between each pair of electrodes. The experiment and the theoretical simulation suggest the existence of local barriers being responsible for the formation of a chain of weakly coupled islands and for the observed Coulomb blockade characteristics.

Coulomb blockade oscillation in a multiwalled carbon nanotube with internanotube tunnel junctions

Internanotube charge transport in a multiwalled carbon nanotube (MWNT) was investigated. We directly measured electrical transport from the outer nanotube to the inner nanotubes in a MWNT with two electrodes. The outer nanotubes between the two electrodes were disconnected, leaving the innermost nanotube, so that the current flows into the innermost nanotube via the internanotube junctions. The transport properties of this device clearly showed Coulomb blockade oscillation with a charging energy of 15 meV at 4.2 K. The observed Coulomb blockade oscillation was nonperiodic to the gate voltage, indicating that the multiple internanotube tunnel junctions were formed underneath the electrodes.

Observation of peak splitting in the Coulomb blockade regime of a carbon nanotube rope

Abstract Electronic transport measurements have been carried out on a single-walled carbon nanotube (SWCN) rope contacted to a 4-probe Au/Pd electrode in the Coulomb blockade regime. With varying substrate backgate voltage, the observed Coulomb blockade peaks exhibit interesting three-way splitting. We find that this peak splitting can be attributed to a contribution from resonant tunnelling through discrete energy levels of a finite length metallic SWCN within the rope. We also consider the role that interactions between `quantum dot' (Q-dot) regions within the rope can play in causing the peak splitting.

Study on spin dependent tunneling and Coulomb blockade in granular systems with restricted tunneling paths

We describe the microfabrication process of a granular nanobridge structure consisting of electrodes separated by a nanometer-sized gap in which a thin insulating Co–Al–O granular film is filled, and discuss the observed Coulomb blockade with a clear threshold voltage ( V th) and the enhanced tunnel magnetoresistance of about 30% at a voltage slightly above V th. Recent results of our scanning tunneling microscopy studies to clarify the topographic features and single electron tunneling phenomena on the surface of Co–Al–O granular films are also presented.

Coulomb blockade and coherent single-cooper-pair tunneling in single Josephson junctions.

We have measured the current-voltage characteristics of small-capacitance single Josephson junctions at low temperatures ( T< or =0.04 K), where the strength of the coupling between the single junction and the electromagnetic environment was controlled with one-dimensional arrays of dc SQUIDs. We have clearly observed Coulomb blockade of Cooper-pair tunneling and even a region of negative differential resistance, when the zero-bias resistance of the SQUID arrays is much higher than the quantum resistance h/e(2) approximately 26 kOmega. The negative differential resistance is evidence of coherent single-Cooper-pair tunneling in the single Josephson junction.

Coulomb Blockade Related to an Anti-localization Effect in External Environment in an Array of Single Tunnel Junctions/Carbon Nanotubes

We report on Coulomb blockade caused by a high-impedance external electromagnetic environment (EME) related to a localization effect in a single tunnel junctions/Carbon nanotubes system. Observed Coulomb blockade, supported by a linear temperature dependence of zero bias conductance, mathematically follows phase correlation theory, which explains the roles of EME and implies that tunneling of electrons is suppressed by transferring the energy to its EME with a total impedance Zt(ω) higher than quantum resistance. Our high Zt(ω), however, is strongly associated with anti-localization effect without any energy dissipation but actually contributes to Coulomb blockade, because its phase modulation by magnetic field modulates also Coulomb blockade. Is the energy transfer to such high impedance EME actually indispensable for Coulomb blockade?

Coulomb blockade related to a localization effect in a single tunnel-junction/carbon-nanotube system

We report on Coulomb blockade caused by the high impedance external electromagnetic environment (EME) related to a localization effect in a single tunnel-junction/carbon-nanotube system. Observed Coulomb blockade, supported by a linear temperature dependence of zero-bias conductance, mathematically follows phase correlation theory, which explains the roles of EME and implies that tunneling of electrons is suppressed by transferring the energy to its EME with a total impedance ${Z}_{t}(\ensuremath{\omega})$ higher than quantum resistance. Our high ${Z}_{t}(\ensuremath{\omega}),$ however, is strongly associated with the antilocalization effect without any energy dissipation but actually contributes to Coulomb blockade, because its phase modulation by magnetic field modulates also Coulomb blockade. Is the energy transfer to such high impedance EME actually indispensable for Coulomb blockade?

Coulomb blockade in low-mobility nanometer size Si MOSFET’s

We investigate coherent transport in Si:MOSFETs with nominal gate lengths 50 to 100nm and various widths at very low temperature. Independent of the geometry, localized states appear when G=e^{2}/h and transport is dominated by resonant tunnelling through a single quantum dot formed by an impurity potential. We find that the typical size of the relevant impurity quantum dot is comparable to the channel length and that the periodicity of the observed Coulomb blockade oscillations is roughly inversely proportional to the channel length. The spectrum of resonances and the nonlinear I-V curves allow to measure the charging energy and the mean level energy spacing for electrons in the localized state. Furthermore, we find that in the dielectric regime, the variance var(lng) of the logarithmic conductance lng is proportional to its average value <lng> consistent with one-electron scaling models.