Rectification Direction Research Articles

Controlling stacking order and charge transport in π-stacks of aromatic molecules based on surface assembly.

Here, we report a facile procedure based on surface self-assembly for controlling the π-π stacking order and relevant rectified charge transport properties in stacks of aromatic molecules on a single-molecule scale. A high rectification ratio of 10 was achieved and the rectification direction was uniquely determined by the controlled stacking order of the aromatic molecules on the graphene layers of HOPG.

Model of self assembled monolayer based molecular diodes made of ferrocenyl-alkanethiols

There has been significant work investigating the use of self assembled monolayers (SAMs) made of ferrocenyl terminated alkanethiols for realizing molecular diodes, leading to remarkably large forward-to-reverse current rectification ratios. In this study, we use a multiband barrier tunneling model to examine the electrical properties of SAM-based molecular diodes made of HSC9Fc, HSC11Fc, and HSCiFcC13−i (0 ≤ i ≤ 13). Using our simple physical model, we reproduce the experimental data of charge transport across various ferrocenyl substituted alkanethiols performed by Nijhuis, Reus, and Whitesides [J. Am. Chem. Soc. 132, 18386–184016 (2010)] and Yuan et al. [Nat. Commun. 6, 6324 (2015)]. Especially, the model allows predicting the rectification direction in HSCiFcC13−i (0 ≤ i ≤ 13) based molecular diodes depending on the position of the ferrocenyl (Fc) moiety within the molecules. We show that the asymmetry of the barrier length at both sides of the Highest Occupied Molecular Orbital of the ferrocenyl moiety strongly contributes to the rectifying properties of ferrocenyl-alkanethiol based molecular junctions. Furthermore, our results reveal that bound and quasi-bound states play an important role in the charge transport.

Biomimetic Nanofluidic Diode Composed of Dual Amphoteric Channels Maintains Rectification Direction over a Wide pH Range.

pH-gated ion channels in cell membranes play important roles in the cell's physiological activities. Many artificial nanochannels have been fabricated to mimic the natural phenomenon of pH-gated ion transport. However, these nanochannels show pH sensitivity only within certain pH ranges. Wide-range pH sensitivity has not yet been achieved. Herein, for the first time, we provide a versatile strategy to increase the pH-sensitive range by using dual amphoteric nanochannels. In particular, amphoteric polymeric nanochannels with carboxyl groups derived from a block copolymer (BCP) precursor and nanochannels with hydroxyl groups made from anodic alumina oxide (AAO) were used. Due to a synergistic effect, the hybrid nanochannels exhibit nanofluidic diode properties with single rectification direction over a wide pH range. The novel strategy presented here is a scalable, low-cost, and robust alternative for the construction of large-area membranes for nanofluidic applications, such as the separation of biomolecules.

Biomimetic Nanofluidic Diode Composed of Dual Amphoteric Channels Maintains Rectification Direction over a Wide pH Range

AbstractpH‐gated ion channels in cell membranes play important roles in the cell's physiological activities. Many artificial nanochannels have been fabricated to mimic the natural phenomenon of pH‐gated ion transport. However, these nanochannels show pH sensitivity only within certain pH ranges. Wide‐range pH sensitivity has not yet been achieved. Herein, for the first time, we provide a versatile strategy to increase the pH‐sensitive range by using dual amphoteric nanochannels. In particular, amphoteric polymeric nanochannels with carboxyl groups derived from a block copolymer (BCP) precursor and nanochannels with hydroxyl groups made from anodic alumina oxide (AAO) were used. Due to a synergistic effect, the hybrid nanochannels exhibit nanofluidic diode properties with single rectification direction over a wide pH range. The novel strategy presented here is a scalable, low‐cost, and robust alternative for the construction of large‐area membranes for nanofluidic applications, such as the separation of biomolecules.

Effects of Asymmetric Local Joule Heating on Silicon Nanowire-Based Devices and Their Applications

With rapid advancement of semiconductor manufacturing and measurement techniques, silicon nanowires (Si NWs) have been produced by several methods and successfully incorporated in solar cells, light emitting diodes and photodetectors due to their unique properties, such as high surface-to-volume ratio, quantum confinement effect and high crystal quality. In this study, silicon nanowires were fabricated by metal assisted–chemical etching (MacEtch) combined with nanosphere lithography (NSL) and subsequently used as building blocks for parallel silicon nanowire-based devices using alternating current (AC) or direct current (DC) dielectrophoresis alignment across Pt electrodes. The role of Si NWs/Pt metal contacts and its effect on electrical and photosensing properties of the devices were investigated.The results show that the devices exhibited rectifying current-voltage characteristics randomly after the strong AC electric field was applied across electrodes for NWs alignment. On the other hand, the rectifying behavior of the devices can be observed as the devices were measured in the wide voltage range after the weak DC electric field was applied across electrodes for NWs alignment, and furthermore the rectification direction can be controlled by the voltage sweep direction. This phenomenon can be associated with the increased Schottky barrier height on the high-temperature anode side as the asymmetric Joule heating effect occurs instantly in the electrical measurement process. The photosensing properties of the rectifying device were further investigated. By utilizing the increased Schottky barrier height in reverse-biased mode under white light illumination, the high speed and high photoresponse can be achieved due to the efficient electron-hole separation by strong built-in electric field in the depletion region.

Janus Reversal and Coulomb Blockade in Ferrocene-Perylenebisimide and N,N,N',N'-Tetramethyl-para-phenylenediamine-Perylenebisimide D-σ-A Rectifiers.

Sandwiches "EGaIn|Ga2O3|LB monolayer of 2|Au" and "EGaIn|Ga2O3|LB monolayer of 3|Au" rectify. They are formed from a Langmuir-Blodgett (LB) monolayer of 2 or 3 transferred onto thermally evaporated gold. Molecules 2 and 3 are of the donor-sigma-acceptor (D-σ-A) type and have the same perylenebisimide (PBI) acceptor as previously studied molecule 1. Molecule 1 has the weak donor pyrene, 2 has the good donor ferrocene, and 3 has the very strong donor N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). All three molecules have a long swallowtail ending in a thioacetyl group, which ensures slow chemisorption onto the Au electrode. These molecules were contacted directly by a gallium indium eutectic (EGaIn) drop, covered by a defective oxide Ga2O3 layer. As before for 1, the direction of rectification for 2 is bias-dependent. In the ±1.0 V range, the rectification is at positive V, with a rectification ratio (RR) that is initially greater than 5 and then decreases on successive scans to 2, while the currents decrease by as much as 2 orders of magnitude. In the ±2.5 V range, the rectification direction for 2 reverses, while upon repeated scanning the rectification ratio (in the negative direction) increases and the currents decrease. For molecule 3, both directions have a charge-trapped state (Coulomb blockade) leading to Voffset in both biases, but at high potentials rectification set is, with large RR (up to 2,800) at ±2.5 V.

Biomimetic heterogeneous multiple ion channels: a honeycomb structure composite film generated by breath figures.

We design a novel type of artificial multiple nanochannel system with remarkable ion rectification behavior via a facile breath figure (BF) method. Notably, even though the charge polarity in the channel wall reverses under different pH values, this nanofluidic device displays the same ionic rectification direction. Compared with traditional nanochannels, this composite multiple ion channel device can be more easily obtained and has directional ionic rectification advantages, which can be applied in many fields.

Microstructure, ferroelectric and dielectric properties of sandwich structure for Na0.5Bi0.5TiO3 thin film modified with aliovalent substitution

Na0.5Bi0.5TiO3 (NBT)-based sandwich structure composed of Na0.5Bi0.5Ti0.98Nb0.02O3 (NBTNb) middle film and Na0.5Bi0.5Ti0.98Mn0.02O3 (NBTMn) buffer layer was fabricated on indium tin oxide/glass substrate via chemical solution deposition. X-ray diffraction measurement reveals the multilayered film can be crystallized into a phase-pure perovskite structure. The significant diode-like rectification effect as well as the switching of rectification direction are observed. A well-defined polarization–electric field hysteresis loop exhibits a large remanent polarization (Pr) of 25μC/cm2. The dielectric tunability increases monotonously with the increasing of applied voltage and tends to be saturated with a maximum value of 28% at ±20V. These results suggest that NBTNb thin film sandwiched by NBTMn buffer layer can effectively improve the electrical performances of NBT-based ferroelectric thin film.

Rectification Properties of Low Aspect Ratio TEM Drilled Nanopores

Nanopores have garnered much scientific interest due for their applications in modeling biological systems and as use for biosensors. Their size creates a system in which transported ions must interact with the pore walls. These nanoscale effects have led to the devolvement of ion controlling devices such as diodes and transistors with a broad range of applications. Past studies of ionic diodes have mainly focused on lateral dimension dependencies on rectification while keeping the length in the micrometer range. The ability to shorten nanopore diodes while retaining their rectification abilities has important applications to the production of ionic circuits, artificial cells, and lab-on-a-chip systems. We look at the rectification abilities of 30 nm long nanopores drilled by the transmission electron microscope (TEM) into a Silicon Nitride membrane between ±1V at 10 mM, 100 mM, and 1 M KCl. We perform current-voltage (I-V) measurements on single nanopores in 3 states: as-prepared by TEM, one side evaporated with 8 nm thick layer of gold, and after modifying the gold layer with thiols. In the two modified states, the pores show rectification at all concentrations. The rectification direction indicates that the pores rectify as if conical rather than cylindrical indicating the double conical nature of TEM drilled nanopores plays a significant role at the nanometer scale. Additionally, with only gold, the rectification and current magnitudes are enhanced due to nonlinear kinetic flow near one of the pore openings. The recorded current-voltage curves exhibit three regimes with ohmic, limiting and overlimiting currents, previously observed in nanofluidic large-aspect ratio channels. Rectification in nanometer long pores would be of significant importance to the future development and miniaturization of ionic nanoscale systems.

Rectification inversion in oxygen substituted graphyne-graphene-based heterojunctions.

Current rectification is found in oxygen-substituted zigzag graphyne nanoribbon/hydrogen-terminated zigzag graphene nanoribbon heterostructure junctions, from the application of nonequilibrium Green's function formalism combined with density functional theory. This behavior could be tuned by varying the number and location of oxygen atoms in the zigzag graphyne nanoribbon parts, and the rectification direction could be reversed due to the parity limitation tunneling effect. Moreover, an obvious negative differential resistance behavior is found and may be explained by two different mechanisms.

Field induced rectification and memristive behavior of TlGaSe2 layered semiconductor

We report the internal electric field induced rectification in TlGaSe2 layered semiconductor. This built-in internal electric field was imprinted into the TlGaSe2 sample prior to the measurements while cooling the samples under the external electric field. We employ various pairs of metallic electrodes (In-In, Au-In, Au-Cu), which are deposited on a smooth mirror-like surfaces of TlGaSe2 crystal, respectively, and used to measure the current flow in two directions, parallel and perpendicular to the plane of layers. The current–voltage (I–V) characteristics were measured on the samples with imprinted internal electric field. The diode-like I–V characteristics was observed with the rectification polarity coinciding with the direction of the imprinted electric field. This effect was observed in both directions parallel and perpendicular to the plane of layers. Our results support that near the metal-TlGaSe2 interface the barrier is formed after the pretreatment of the sample in the electric field. So, the diode with a controlled rectification direction, which is achieved by changing the polarization direction using an external bias, is fabricated. The field induced motion of the charge, which piles up under the respective contact that forms a barrier is assumed. The memristive behavior with characteristic pinched hysteresis loop is also observed.

Photocurrent from a carbon nanotube diode with split-gate and asymmetric contact geometry

We fabricated a Ti/Pd asymmetrically contacted single carbon nanotube (CNT) field-effect transistor (FET) with split-gates. Transfer characteristics can be explained if the Schottky barrier for electrons is lower at the Pd contact than it is at the Ti contact. Strong rectification is observed when the gates are unbiased, and the rectification direction can be inverted with the appropriate gate bias. When operated as an FET the device has an on/off ratio of 1 × 107. Under illumination, photocurrent can only be observed with opposite split-gate bias. Open circuit voltage (VOC) and short circuit current (ISC) increase with increasing opposite polarity split-gate bias, representing the first demonstration of the modulation of VOC and ISC in an asymmetric contact CNT FET.

Enhanced rectifying performance by asymmetrical gate voltage for BDC20 molecular devices

By applying the asymmetrical gate voltage on the 1,4-bis (fullero[c]pyrrolidin-1-yl) benzene BDC20 molecule, we investigate theoretically its electronic transport properties using the density functional theory and nonequilibrium Green's function formalism for a unimolecule device with metal electrodes. Interestingly, the rectifying characteristic with very high rectification ratio, 91.7 and 24.0, can be obtained when the gate voltage is asymmetrically applied on the BDC20 molecular device. The rectification direction can be tuned by the different gate voltage applying regions. The rectification behavior is understood in terms of the evolution of the transmission spectrum and projected density of states spectrum with applied bias combined with molecular projected self-consistent Hamiltonian states analyses. Our finding implies that to realize and greatly promote rectifying performance of the BDC20 molecule the variable gate voltage applying position might be a key issue.

PH-regulated ionic current rectification in conical nanopores functionalized with polyelectrolyte brushes

Mimicking biological ion channels capable of pH-regulated ionic transport, synthetic nanopores functionalized with pH-tunable polyelectrolyte (PE) brushes have been considered as versatile tools for active transport control of ions, fluids, and bioparticles on the nanoscale. The ionic current rectification (ICR) phenomenon through a conical nanopore functionalized with PE brushes whose charge highly depends upon the local solution properties (i.e., pH and background salt concentration) is studied theoretically for the first time. The results show that the rectification magnitude, as well as the preferential rectification direction, is sensitive to the pH stimulus. The bulk concentration of the background salt can also significantly influence the charge of the PE brushes and accordingly affect the ICR phenomenon. The obtained results provide an insightful understanding of the pH-regulated ICR and guidelines for designing nanopores functionalized with PE brushes for pH-tunable applications.

Label-free electrical quantification of amplified nucleic acids through nanofluidic diodes

A label-free method of quantifying nucleic acids in polymerase chain reaction (PCR) is described and could be the basis for miniaturized devices that can amplify and detect target nucleic acids in real time. The method takes advantage of ionic current rectification effect discovered in nanofluidic channels exhibiting a broken symmetry in electrochemical potential – nanofluidic diodes. Nanofluidic diodes are prototyped here on nanopipettes readily pulled from individual thin-walled glass capillaries for a proof of concept demonstration yet the basic concept would be applicable to ionic rectifiers constructed through other means. When a nanopipette modified in the tip region with cationic polyelectrolytes is presented with an unpurified PCR product, the tip surface electrostatically interacts with the amplicons and modulates its ionic rectification direction in response to the intrinsic charge of those adsorbed. Modulations are gradual and correlate well with the mass concentration of the amplicons above 2.5ng/μL, rather than their sizes, with adequate discrimination against the background. Moreover, the tip surface, following a measurement, is regenerated through a layer-by-layer assembly of cationic polyelectrolytes and amplicons. The regenerated tips are capable of measuring distinct mass concentrations without signs of noticeable degradation in sensitivity. Further, the tips are shown capable of reproducing the amplification curve of real-time PCR through sequential steps of surface regeneration and simple electrical readout during the intermediate reaction stages. This suggests that nanopipettes as nanofluidic diodes are at a capacity to be employed for monitoring the PCR progress.

Efficient phase-tunable Josephson thermal rectifier

Josephson tunnel junctions are proposed as efficient phase-tunable thermal rectifiers. The latter exploit the strong temperature dependence of the superconducting density of states and phase-dependence of heat currents flowing through Josephson junctions to operate. Remarkably, large heat rectification coefficients up to 800% can potentially be achieved using conventional materials and standard fabrication methods. In addition, these devices allow for the in-situ fine tuning of the thermal rectification magnitude and direction.

Rectification direction inversion in a phosphododecamolybdic acid/single-walled carbon nanotube junction

We report the inversion of current rectification direction in a phosphododecamolybdic acid (PMo12)/single-walled carbon nanotube (SWNT) nanoscale junction resulted from a change in the particle size or chirality of the SWNTs. Results of Kelvin probe force microscopy (KPFM) studies demonstrated that the charge distribution of PMo12/SWNT in semiconducting SWNTs was opposite to that of metallic SWNTs, owing to differences in the efficiency of charging from the SWNTs to PMo12. The mechanism of the inversion of rectification direction involves combination of the usual p–n junction and current–voltage (I–V) drift induced by the dipole moment at the PMo12/SWNT interface.

Effect of iodine doping of phthalocyanine on the photocurrent generation in a phthalocyanine/C60 heterojunction

Photocurrent generation in an indium–tin oxide (ITO)/iodine-doped Ni-phthalocyanine (NiPc-Ix)/C60/In/Al heterojunction device with x~1 was studied. By keeping the device in air after preparation, the device slowly reached a stationary state in which the sign of the photocurrent is opposite to that of a non-doped ITO/NiPc/C60/In/Al device although the rectification direction for the dark current is the same. By a simulation of incident photon-to-current conversion efficiency spectra and a measurement of internal electric field by electroabsorption spectroscopy, it was elucidated that, in the doped device, the band bending near the phthalocyanine/C60 interface is absent and the photocurrent is generated by a weak Schottky barrier at the C60/In interface. It is also shown that the C60 film encapsulates the doped iodine into the NiPc-Ix layer to stabilize the doping level and prevent the reaction of iodine with In.

Rectifying and negative differential resistance behaviors of a functionalized Tour wire: The position effects of functional groups

Based on Tour wire, we construct four D-π-A molecular devices with different positional functional groups, in an attempt to explore the position effects of functional groups on their electronic transport properties and to show that some interesting physical phenomena can emerge by only varying the position of functional groups. The first-principles calculations demonstrate that the position of functional groups can affect the rectifying behaviors (rectification direction and ratio) significantly and determines whether or not the negative differential resistance (NDR) can be observed as well as the physical origin of the NDR phenomenon.

Scan-Rate-Dependent Ion Current Rectification and Rectification Inversion in Charged Conical Nanopores

Herein we report a theoretical study of diode-like behavior of negatively charged (e.g., glass or silica) nanopores at different potential scan rates (1-1000 V·s(-1)). Finite element simulations were used to determine current-voltage characteristics of conical nanopores at various electrolyte concentrations. This study demonstrates that significant changes in rectification behavior can be observed at high scan rates because the mass transport of ionic species appears sluggish on the time scale of the voltage scan. In particular, it explains the influence of the potential scan rate on the nanopore rectifying properties in the cases of classical rectification, rectification inversion, and the "transition" rectification domain where the rectification direction in the nanopore could be modulated according to the applied scan rate.