Small Bias Voltage Research Articles

Switchable Silver Mirror Window without Bromide Ion

The reversible electrochemical switching mirrors between mirror state and transparent state using silver bromide ion complex have been greatly investigated for application to smart windows and mirrors.1,2 There are some advantages to reflect light and not to absorb one in the high reflective silver metal state from the viewpoint of the thermal management. However, there are also some drawbacks to use bromide ion. Silver bromide ion complex is poor solubility in the common solvents, which also required strong polar solvents such as DMSO. In addition, the silver bromide ion complex is light-sensitive and not suitable for many applications. Moreover, Br3 - ion as the redox couple of Br- ion has absorption in the visible wavelength region. Therefore, it was important to find the other systems where Ag may be deposited in a mirror form without the use of bromide ion. In the previous study, a mixed solvent of ionic liquid and acetonitrile has been employed instead of DMSO and silver bromide was not used. This novel reversible silver switching mirror window system is quite simple, stable and safe because the materials used in this system are citric acid as the electrolyte additive and Pd nanoparticles (NPs) as the catalyst which are plated as nuclei on the ITO electrode for facilitating Ag plating and dissolution.3 In this study, the non-bromide ion switchable silver mirror window was prepared and its performance was investigated.The window has the sandwiched structure between Pd NPs deposited on the ITO electrode and semitransparent silver mesh (0.15 mm diameter, 40 mesh size) as a counter electrode on the glass substrate through silicon rubber spacer with 1 mm thickness. Silver plating bath composed of 0.2 M silver nitrite and 80 mM citric acid as an additive dissolved in the mixture solvent of EMIMTFSI ionic liquid and acetonitrile. The window size was 3.0 x 3.0 cm2. The transmittance of the transparent state of the device was 39% at the wavelength of more than 400 nm, which was not very high because of low transmittance of 58% at the silver mesh counter electrode as shown in Fig.1(a). Our college emblem was seen through the transparent state of the window. When the voltage bias was applied at -0.3 V for 7 sec, silver was electroplated on the Pd NP deposited on ITO to become the mirror state as shown in Fig.1(b). When the voltage bias was reversed at +0.3 V for 13 sec, the plated silver was electrodissolved to return to the transparent state of the window. The small voltage bias and the short plating/dissolution time was achieved in the present window.The stability of the mirror state of the device at the open circuit was investigated. The device firstly shows the transparent state at the no bias condition for 3 sec, indicating the transmittance of 39% at the wavelength of 500 nm. When the voltage bias was applied at -0.3 V for 7 sec, the transmittance decreases to 1%. The device was then changed at the open circuit and the transmittance was monitored for 1 hr. The value of the transmittance keeps at 1% after 1 hr. Therefore, our window shows good memory effect because of no use of bromide ion. Thus, the window has superior potential for meeting requirements for practical applications including smart windows.

Chemiresistive detection of silver ions in aqueous media

Silver is used as a water disinfectant in hospital settings as well as in purifiers for potable water. Although there are no strict regulations on the concentration of silver in water, adverse effects such as argyria and respiratory tract irritation have been correlated to excess silver consumption. Based on this, the levels of silver in water are recommended to be maintained below 100 ppb to ensure safety for human consumption. In this work, we present a silver sensor for use in aqueous media that utilizes bathocuproine, a silver selective chromophore, adsorbed onto few-layer graphene (FLG) flake networks for the chemiresistive detection of silver. Complexation of silver to bathocuproine modulates the conductivity of the FLG film, which can be probed by applying a small voltage bias. The decrease in resistance of the film correlates with the concentration of silver in solution between 3 ppb and 1 ppm. Exposing the sensor to a lower pH resets the sensor, allowing it to be reused and reset multiple times. This sensor demonstrates a new pathway to chemiresistive cation sensing using known selective complexing agents adsorbed onto graphitic thin films. This concept can be expanded to the detection of other relevant analytes in domestic, industrial and environmental water sources.

Enhancing surface production of negative ions using nitrogen doped diamond in a deuterium plasma

The production of negative ions is of significant interest for applications including mass spectrometry, particle acceleration, material surface processing, and neutral beam injection for magnetic confinement fusion. Methods to improve the efficiency of the surface production of negative ions, without the use of low work function metals, are of interest for mitigating the complex engineering challenges these materials introduce. In this study we investigate the production of negative ions by doping diamond with nitrogen. Negatively biased (−20 V or −130 V), nitrogen doped micro-crystalline diamond films are introduced to a low pressure deuterium plasma (helicon source operated in capacitive mode, 2 Pa, 26 W) and negative ion energy distribution functions are measured via mass spectrometry with respect to the surface temperature (30 °C to 750 °C) and dopant concentration. The results suggest that nitrogen doping has little influence on the yield when the sample is biased at −130 V, but when a relatively small bias voltage of −20 V is applied the yield is increased by a factor of 2 above that of un-doped diamond when its temperature reaches 550 °C. The doping of diamond with nitrogen is a new method for controlling the surface production of negative ions, which continues to be of significant interest for a wide variety of practical applications.

Photon-assisted resonant Andreev reflections: Yu-Shiba-Rusinov and Majorana states

Photon-assisted tunneling frequently provides detailed information on the underlying charge-transfer process. In particular, the Tien-Gordon approach and its extensions predict that the sideband spacing in bias voltage is a direct fingerprint of the number of electrons transferred in a single tunneling event. Here, we analyze photon-assisted tunneling into subgap states in superconductors in the limit of small temperatures and bias voltages where tunneling is dominated by resonant Andreev processes and does not conform to the predictions of simple Tien-Gordon theory. Our analysis is based on a systematic Keldysh calculation of the subgap conductance and provides a detailed analytical understanding of photon-assisted tunneling into subgap states, in excellent agreement with a recent experiment. We focus on tunneling from superconducting electrodes and into Yu-Shiba-Rusinov states associated with magnetic impurities or adatoms, but we also explicitly extend our results to include normal-metal electrodes or other types of subgap states in superconductors. In particular, we argue that photon-assisted Andreev reflections provide a high-accuracy method to measure small, but nonzero energies of subgap states which can be important for distinguishing conventional subgap states from Majorana bound states.

First-principles study on strain-modulated negative differential resistance effect of in-plane device based on heterostructure tellurene

We built an in-plane device using the semiconductor and metal phases of monolayer tellurene and investigated its transport properties by the Keldysh nonequilibrium Green’s function method combined with density functional theory simulations. An obvious negative differential resistance (NDR) effect is found in the current-voltage curve of the in-plane device based on group-VI two-dimensional material for the first time, which can be explained by analyzing the transmission spectra and the electronic structure of the device. Further, the transport properties of the device under uniaxial and biaxial strains were also investigated. It is found that the local peak current of the device at small bias voltage exhibits a perfect exponential change with the x-axis strain, and the peak-to-valley ratio can be improved at most 602% by the strain. Our studies provide important support for the applications of tellurene in in-plane devices.

Study of the Electrical Properties of Cu₂ZnSnS₄ (CZTS) Thin Film Using Atomic Force Microscopy (AFM) Techniques.

CZTS is a compound semiconductor made from elements which are plainly available and nonpoisonous having favorable optoelectronic properties for thin film solar cell (TFSC) applications. In this study, Cu-poor CZTS thin film was fabricated on soda lime glass (SLG)/Mo-deposited substrate using cosputtering followed by post sulfurization in H₂S atmosphere. Local electrical transport study was carried out by using conductive atomic force microscopy (C-AFM) for small bias voltage (100 mV). Here we observed that most of the dark current (Idark) flow through grain boundaries (GBs) than grain interiors. The positive high current about 3.4 nA and sharp C-AFM signal at the GBs, dips to the zero (0) value at the grain interior. Local surface potential (Vsurface) study was carried out using kelvin probe force microscopy (KPFM), which showed that the positive Vsurface potential about 175 mV in the vicinity of GBs in a Cu-poor CZTS sample. On the basis of these results we inferred a potential landscape (VL) around the GBs. All result shows that due to variation in elemental composition which creates Cu-deficit or CuZn anti site defects at GBs, leads reduced effective band gap (Eeff) than the bulk towards grain inner to GBs.[-2pt].

An Electrically Modulated Single-Color/Dual-Color Imaging Photodetector.

An electrically modulated single-/dual-color imaging photodetector with fast response speed is developed based on a small molecule (COi 8DFIC)/perovskite (CH3 NH3 PbBr3 ) hybrid film. Owing to the type-I heterojunction, the device can facilely transform dual-color images to single-color images by applying a small bias voltage. The photodetector exhibits two distinct cut-off wavelengths at ≈544 nm (visible region) and ≈920 nm (near-infrared region), respectively, without any power supply. Its two peak responsivities are 0.16 A W-1 at ≈525 nm and 0.041 A W-1 at ≈860 nm with a fast response speed (≈102 ns). Under 0.6 V bias, the photodetector can operate in a single-color mode with a peak responsivity of 0.09 A W-1 at ≈475 nm, showing a fast response speed (≈102 ns). A physical model based on band energy theory is developed to illustrate the origin of the tunable single-/dual-color photodetection. This work will stimulate new approaches for developing solution-processed multifunctional photodetectors for imaging photodetection in complex circumstances.

Interfacial effects on leakage currents in Cu/\u03b1-cristobalite/Cu junctions

As the miniaturization trend of integrated circuit continues, the leakage currents flow through the dielectric films insulating the interconnects become a critical issue. However, quantum transport through the mainstream on-chip interfaces between interconnects and dielectrics has not been addressed from first principles yet. Here, using first-principles calculations based on density functional theory and nonequilibrium Green’s function formalism, we investigate the interfacial-dependent leakage currents in the Cu/α-cristobalite/Cu junctions. Our results show that the oxygen-rich interfaces form the lowest-leakage-current junction under small bias voltages, followed by the silicon-rich and oxygen-poor ones. This feature is attributed to their transmission spectra, related to their density of states and charge distributions. However, the oxygen-poor interfacial junction may conversely have a better dielectric strength than others, as its transmission gap, from −2.8 to 3.5 eV, is more symmetry respect to the Fermi level than others.

Nonlinear Thermoelectricity with Electron-Hole Symmetric Systems.

In the linear regime, thermoelectric effects between two conductors are possible only in the presence of an explicit breaking of the electron-hole symmetry. We consider a tunnel junction between two electrodes and show that this condition is no longer required outside the linear regime. In particular, we demonstrate that a thermally biased junction can display an absolute negative conductance, and hence thermoelectric power, at a small but finite voltage bias, provided that the density of states of one of the electrodes is gapped and the other is monotonically decreasing. We consider a prototype system that fulfills these requirements, namely, a tunnel junction between two different superconductors where the Josephson contribution is suppressed. We discuss this nonlinear thermoelectric effect based on the spontaneous breaking of electron-hole symmetry in the system, characterize its main figures of merit, and discuss some possible applications.

Electronic transport decay rule for junction of oligophenylene molecules sandwiched between phosphorene nanoribbons

We study the influence of electrodes on the exponential transport rule for the junction of oligophenylene-linked and oligoacene-linked molecules between two zigzag phosphorene nanoribbons (ZPNRs), where molecules consisting of one, two and three benzene rings are considered, respectively. We find by ab initio calculations that the amplitude of current through the junction is dependent on both the molecular length and the molecule–ZPNR coupling manner. In specification, the current through the single-bond coupled junction with the molecular plane perpendicular to the ZPNRs is almost two times that with parallel configuration due to the greater number of transport channels provided by the p y orbital in the former case. In contrast, the current of the junction with double-bond coupling is nearly two orders of magnitude larger because of the stronger coupling strength. Nevertheless, in any case the ZPNR–electrode junction, like metal–electrode junctions, also obeys the exponential decaying rule in transport with the variation of molecular length. Importantly, the relationship between the resistance and the molecular length, regardless of the coupling details, can be fitted by a linear line in the semilog coordinate but with different slopes determined by the coupling manner. This indicates that the exponential rule of transport under small bias voltages is electrode-material-independent for molecular junctions with any electrode. But the value of the decaying factor, importantly, is heavily dependent not only on the molecule itself but also on the electrode materials as well as the molecule–electrode coupling method.

Analytical Model for Photocurrent–Voltage and Impedance Response of Illuminated Semiconductor/Electrolyte Interface under Small Voltage Bias

Semiconductor/electrolyte interfaces attract intense interest to convert solar energy to chemical fuels. Although many analytical models describing the photocurrent–voltage response of these device...

Field-induced p-n transition in yttria-stabilized zirconia

Oxide ion conducting yttria-stabilised zirconia ceramics show the onset of electronic conduction under a small bias voltage. Compositions with a high yttria content undergo a transition from p-type to n-type behavior at voltages in the range 2.4 to 10 V, which also depends on oxygen partial pressure. Surface reactions have a direct influence on bulk electronic conductivities, with possible implications for voltage-induced flash phenomena and resistive switching.

Coherent spin transport through a six-coordinate FeN6 spin-crossover complex with two different spin configurations

Due to the magnetic bistability, single-molecule spin-crossover (SCO) complexes have been considered to be the most promising building blocks for molecular spintronic devices. Here, we explore the SCO behavior and coherent spin transport properties of a six-coordinate FeN $_6$ complex with the low-spin (LS) and high-spin (HS) states by performing extensive first-principles calculations combined with non-equilibrium Green's function technique. Theoretical results show that the LS $\leftrightarrow$ HS spin transition via changing the metal-ligand bond lengths can be realized by external stimuli, such as under light radiation in experiments. According to the calculated zero-bias transmission coefficients and density of states as well as the $I$ - $V$ curves under small bias voltages of FeN $_6$ SCO complex with the LS and HS states sandwiched between two Au electrodes, we find that the examined molecular junction can act as a molecular switch, tuning from the OFF (LS) state to the ON (HS) state. Moreover, the spin-down electrons govern the current of the HS molecular junction, and this observed perfect spin-filtering effect is not sensitive to the detailed anchoring structure. These theoretical findings highlight this examined six-coordinate FeN $_6$ SCO complex for potential applications in molecular spintronics.

Electrical tuning of a terahertz quantum cascade laser based on detuned intersubband absorption

A mechanism to electrically tune the frequency of terahertz quantum cascade lasers (QCLs) is developed that allows for tuning, while the QCL is operated close to its peak bias and temperature. Two optically coupled but electrically isolated cavities are used in which the bias of a control cavity tunes the resonant-mode of the coupled QCL cavity independent of the QCL's operating bias. Approximately 4 GHz electrical tuning is realized for a 3.6 THz distributed-feedback QCL operating in pulsed mode at 58 K in a Stirling cooler. The single-mode QCL emits near-constant peak-power in the range of 5−5.3 mW through the tuning range and radiates in a narrow single-lobed beam with a far-field divergence of ∼4°×11°. The superlattice structure of the QCL is designed to implement a low-voltage intersubband absorption transition that is detuned from that of its gain transition, the strength of which could be controlled sensitively with applied voltage utilizing resonant-tunneling injection of electrons in the absorption subband. The tuning is realized by the application of small bias voltages (∼6−7 V) and requires a narrow bias range (∼1 V, ∼40 A/cm2) to traverse across the entire tuning range, and the method should be generally applicable to all intersubband lasers including mid-infrared QCLs.

Three‐level dual‐buck voltage balancer with active output voltagesbalancing

This study proposes a three-level dual-buck voltage balancer, which consists of two three-level buck circuits. It can split a DC input voltage source into two DC output voltage sources. The DC output voltage sources may have the same levels or different levels based on applications, while the sum of the two output voltages is always equal to the input voltage level. To achieve three-level states, a control strategy of introducing an extra freewheeling time is presented by adding a small extra DC bias voltage in the control loop. The operation principles are analysed in detail. In addition, the small-signal model is also given to design parameters. Finally, a prototype was built and tested based on a single output voltage loop in the lab. The experimental results had verified the balancer has a good ability for operating in three-level states and balancing output voltages.

Endohedral Fullerene Fe@C28 Adsorbed on Au(111) Surface as a High-Efficiency Spin Filter: A Theoretical Study.

We present a theoretical study on the adsorption and spin transport properties of magnetic Fe@C28 using Ab initio calculations based on spin density functional theory and non-equilibrium Green’s function techniques. Fe@C28 tends to adsorb on the bridge sites in the manner of C–C bonds, and the spin-resolved transmission spectra of Fe@C28 molecular junctions exhibit robust transport spin polarization (TSP). Under small bias voltage, the transport properties of Fe@C28 are mainly determined by the spin-down channel and exhibit a large spin polarization. When compressing the right electrode, the TSP is decreased, but high spin filter efficiency (SFE) is still maintained. These theoretical results indicate that Fe@C28 with a large magnetic moment has potential applications in molecular spintronics.

Electrically tunable temporal imaging in a graphene-based waveguide

We propose an electrically tunable temporal imaging system (TIS) based on four-wave mixing in a dispersion engineered graphene-based waveguide, which could realize a magnification factor of 1000× for a signal consisting of two 100-fs-wide pulses separated by 500 fs and a large working bandwidth of about 700 nm. The TIS was analyzed by solving the couple-mode equations in detail. It was demonstrated that the working wavelength range could be tuned via a small disturbed bias voltage applied to the graphene layer without changing the geometric structure of the waveguide. These results provide attractive insights for potential applications in integrated optics and optical communications.

Current Transport Mechanism in p-InSb–n-CdTe Heterojunction

Based on the analysis of the forward current-voltage characteristics of the p-InSb–n-CdTe heterojunction fabricated by a method of pulsed laser deposition, the existence of two charge injection mechanisms was experimentally confirmed. At relatively small external bias voltages (0.03 V < U < 0.15 V), the current is in a satisfactory agreement with the expression I ~ exp(qU/ηkT) with the ideality factor η = 1. Above 0.18 V, the current-voltage characteristic obeys the law I ~ U3/2 followed by an attainment to the linear section (the cut-off voltage of current is 0.47 V). A theoretical model of current transport is given taking into account the peculiarities of the heterojunction band discontinuity, leading to the origination of inversion layer near the interface.

Capacitance and impedance spectroscopy studies of polymer light emitting diodes based on MEH-PPV:BT blends

Light emitting polymer poly [2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) is blended with a wide bandgap electron transport material benzothiadiazole (BT) and its effect on the electronic properties has been studied by capacitance and impedance spectroscopy (IS) in PLEDs. The impedance data is fitted using equivalent circuit models and the minimum parallel resistance (Rp) at zero bias have been obtained for 1:3 ratio of MEH-PPV:BT blended devices. The negative capacitance (NC) shows the occurrence of the trap-assisted non-radiative recombination mechanism at low frequencies in the unblended MEH-PPV PLEDs. Further, this behavior is seen to be reduced in PLEDs with MEH-PPV:BT blends. This clearly suggests that the blending of MEH-PPV and BT at different weight ratios results in the suppression of trap-assisted recombination. This can be attributed to the elimination of trap states due to the dilution of semiconductor material on account of the addition of wide bandgap host material. Moreover, the blended devices have shown a significant improvement in the conductivity at small bias voltages.

Effect of Pd concentration on the structural, morphological and photodiode properties of TiO2 nanoparticles

In this work, intrinsic and doped TiO2 nanoparticles with different Palladium (Pd) concentrations were successfully synthesized via solvothermal method. The structural, morphological and optical properties of the as-synthesized nanoparticles are investigated. Photodiode properties of the as-synthesized nanoparticles based spin coated films are also investigated. A p-n and p-i-n heterojunction structures are fabricated on ITO coated glass and studied for small (± 5 V) bias voltage. From the IV characterization, responsivity, sensitivity, external quantum efficiency and switch current ratio is evaluated for both the heterostructures. Results showed that the proposed p-i-n photodiode attain good stability and quick response as compared to the conventional p-n photodiode. Hall measurement confirmed that heavily Pd doped TiO2 nanoparticles is an efficient p-type material for fabrication of thin film photo-devices.