Motion Of Charge Carriers Research Articles

Effect of Fe2O3 Nanoparticles Dust on the D.C Plasma Characteristics with Mirror Magnetron

In this paper, the effect of iron oxide nanoparticles dust (Fe2O3 NPs) on the parameters of DC electric discharge plasma under vacuum in argon gas was studied with the presence of a mirror magnetron behind the electrodes (cathode and anode) at constant pressure and with different amounts of Fe2O3 nanoparticles. Calculations presented a reduction of the plasma emission intensity with the NPs content. Both the plasma density (calculated by Stark's broadening method) and the mean electron temperature (calculated using Boltzmann's equation) decreased with increasing the Fe2O3 nanoparticles dust content, which indicates clearly the effect of dust density on restricting the movement of charge carriers, which in turn reduces inelastic plasma collisions.

Enhanced pollutant photodegradation over nanoporous titanium-vanadium oxides with improved interfacial interactions

This study addressed the separation problem of colloidal catalytic powder from its solution and pore blockage of traditional metallic oxides by fabricating nanoporous composites of titanium (Ti)-vanadium (V) oxide via magnetron sputtering, electrochemical anodization, and annealing processes. The effect of V-deposited loading on the composite semiconductors was investigated by varying V sputtering power (20–250 W) to correlate their physicochemical properties to the photodegradation performance of methylene blue. The obtained semiconductors revealed circular and elliptical pores (14–23 nm) and formed different metallic and metallic oxide crystalline phases. Within the nanoporous composite layer, V ions substituted Ti4+, leading to Ti3+ formation accompanied by decreased band gap values and higher visible-light absorption. Thus, the band gap of TiO2 was 3.15 eV, while that of Ti-V oxide with the maximum V content (at 250 W) was 2.47 eV. The interfacial separators between clusters in the mentioned composite created traps disrupting the charge carrier movements between crystallites, thereby decreasing the photoactivity. In contrast, the composite prepared with the minimum V content showed approximately 90% degradation efficiency under solar-simulated irradiation resulting from the homogeneous V dispersion and the lower recombination possibility, owing to its p-n heterojunction constituent. The nanoporous photocatalyst layers with their novel synthesis approach and outstanding performance can be applied in other environmental remediation applications.

Tandem internal electric fields in intralayer/interlayer carbon nitride homojunction with a directed flow of photo-excited electrons for photocatalysis

Photocatalytic hydrogen production is a green technology while significantly impeded by the sluggish and uncontrolled charge dynamics for less electron accumulation on catalyst surface. Herein, we proposed an effective strategy of epitaxial growth of a van der Waals (VDW) homojunction on an intralayer homojunction of carbon nitride for a controlled charge flow. Experimental and simulation collectively disclosed a tandem internal electric field (IEF) in the integrated hybrid, stringing a lateral IEF along the intralayer homojunction with a vertical IEF within the VDW homojunction. The planar IEF dominates laterally dispersive movement of charge carriers for their efficient separations and mobilities, meanwhile the vertical IEF induces an oriented accumulation of the dispersive hot electrons to the catalyst surface for intensified hydrogen reduction. The tandem IEF renders the hydrogen evolution rate at 3.5-fold higher than in-planar homojunction, and 6.3 times higher than g-C3N4 benchmark. This work realizes charge-directing dynamics for robust photocatalysis.

Effect of nonequivalent doping on dielectric and microwave absorbing properties of LaFeO3-based ceramics

Development of microwave absorption materials (MAMs) with thin thickness, high oxidation resistance and tunable effective absorbing bandwidth (EAB) is particularly urgent for practical applications but remains a great challenge. In this work, a series of novel MAMs, (La1-xSrx)FeO3/Al2O3 pseudo-binary composites were synthesized, and their electromagnetic parameters, microwave absorbing capacity and related mechanisms were revealed systematically. Attributed to appropriate attenuation coefficients and superior impedance matching, the equilibrium phase in (La0.3Sr0.7)FeO3/Al2O3 pseudo-binary composite presents the best electromagnetic wave absorption property, in which RLmin = −38dB, effective absorption bandwidth (EAB: RL＜-10 dB) is up to 2.78 GHz with a thickness of 1.5 mm and its tunable EAB is 13.22 GHz when thickness ranged from 1 mm to 3 mm, indicating its is a superior MAM. The excellent microwave absorbing properties of (La0.3Sr0.7)FeO3/Al2O3 pseudo-binary composite is derived from space charge polarization caused by plenty of heterogeneous interfaces, dipole polarization introduced by doping, and conductive loss originating from directional movement of charge carriers.

Gold Sputtering at the Interfaces: An Easily Operated Strategy for Enhancing the Energy Storage Capability of Laminated Polymer Dielectrics

Polymers with excellent dielectric properties are strongly desired for pulsed power film capacitors. However, the adverse coupling between the dielectric constant and breakdown strength greatly limits the energy storage capability of polymers. In this work, we report an easily operated method to solve this problem via sputtering the interface of bilayer polymer films with ultralow content of gold nanoparticles. Interestingly, the gold nanoparticles can effectively block the movement of charge carriers because of the Coulomb blocking effect, yielding significantly enhanced breakdown strength. Meanwhile, the gold nanoparticles can act as electrodes to form numerous equivalent microcapacitors, resulting in an obviously enhanced dielectric constant. Impressively, the polymer film with merely 0.01 vol % gold nanoparticles exhibits an obvious dielectric constant and breakdown strength, which are 129 and 131% that of the pristine polymer film, respectively. Consequently, a high energy density which is 176% of that of the pristine polymer film is achieved, and a high efficiency of 79.2% is maintained. Moreover, this process can be well combined with the production process of commercial dielectric polymer films, which is beneficial for mass production. This work offers an easily operated way to improve the dielectric capacitive energy storage properties of polymers, which could also be applicable to other materials, such as ceramics and composites.

Inhomogeneous magnetic fields interacting with spinful states in a double quantum dot: Evidence for a staggered spin-orbit interaction

The coupling of the spin and the motion of charge carriers is an important ingredient for the manipulation of the spin degree of freedom and for the emergence of topological matter. Creating domain walls in the spin-orbit interaction at the nanoscale may turn out to be a crucial resource for engineering topological excitations suitable for universal topological quantum computing or for new schemes for spin quantum bits. Realizing this in natural platforms remains a challenge. Using circuit quantum electrodynamics magnetospectroscopy, we investigate the spinful states of a double quantum dot made in a single wall carbon nanotube with lithographically patterned magnetically textured gates. While a full understanding of the behavior of our magnetic textures would be helpful, the experimental signals are consistent with a change of the spin-orbital structure of the states above each gate. The coherence of the data, backed up by extensive theoretical modeling and a control device, points towards the existence of a synthetic staggered spin-orbit interaction in our device.

Impurity level substitution of Cr and Ni in CaBaCo4O7 – a dielectric study

The fascinating physical characteristics of the 114-cobaltate, CaBaCo4O7, like alternate stacking of two-dimensional layers of CoO4 tetrahedra in triangular and kagomé patterns, geometrical frustration, and magnetoelectric coupling have attracted several studies in the magneto-structural and dielectric sectors. But the study of electrical conduction dynamics remains practically unknown. Here we have presented dc conduction studies and ac dielectric spectroscopy intending to understand the charge conduction and charge carrier relaxation dynamics of CaBaCo4O7, along with two chemically substituted derivatives – CaBaCo3.96Cr0.04O7 and CaBaCo3.96Ni0.04O7, of impurity level (1%) substitutions. We observe that dc conduction at low temperatures is mediated by variable range polaron hopping, while the ac conduction study points out small-polaron-tunneling across strongly localized states. Electric modulus obeys the Havriliak-Negami equation, with parameters α and γ significantly less than unity, indicating strong distribution in relaxation times; and its non-exponential nature, pointing out the cooperative motion of charge carriers. Imaginary electric modulus is not scaled to a single master curve for the three samples, signifying differences in charge relaxation dynamics.

Interconnected CuO nanoplates as a highly efficient electrocatalyst for oxygen evolution reaction

In this present work, we successfully develop copper oxide (CuO) nanoplates using a facile precipitation process without utilizing any convoluted equipment and high-cost raw materials. The X-ray diffraction (XRD), Raman, and the energy dispersive X-ray (EDX) analysis revealed the formation of pure phase CuO powder. The sample exhibits an interconnected nanoplates-like structure, which facilitates the fast movement of charge carriers throughout the sample. For the sample, a moderate overpotential (492 mV vs SCE) is sufficient to achieve a current density of 10 mA/cm2. It exhibits a low Tafel slope of 69.5 mV dec−1 and achieved long-term stability over 5000 cyclic voltammetry (CV) cycles.

Direct Tracking of Charge Carrier Drift and Extraction from Perovskite Solar Cells by Means of Transient Electroabsorption Spectroscopy.

The best perovskite solar cells currently demonstrate more than 25% efficiencies, yet many fundamental processes that determine the operation of these devices are still not fully understood. In particular, even though the device performance strongly depends on charge carrier transport across the perovskite layer to selective electrodes, information about this process is still very controversial. Here, we investigate charge carrier motion and extraction from an archetypical CH3NH3PbI3 (MAPI) perovskite solar cell. We use the ultrafast electric-field-modulated transient absorption technique, which allows us to evaluate the electric field dynamics from the time-resolved electroabsorption spectra and to visualize the motion of charge carriers with subpicosecond time resolution. We demonstrate that photogenerated holes drift across the mesoporous TiO2/perovskite layer during hundreds of picoseconds. On the other hand, their extraction into the spiro-OMeTAD hole transporting layer lasts for more than 1 nanosecond, suggesting that the hole extraction is limited by the perovskite/spiro-OMeTAD interface rather than by the hole transport through the perovskite layer. Additionally, we use the ultrafast time-resolved fluorescence technique that reveals fluorescence decay during tens of picoseconds, which we attribute to the spatial separation of electrons and holes.

Revisiting thermal charge carrier refractive noise in semiconductor optics for gravitational-wave interferometers

The test masses in next-generation gravitational-wave interferometers may have a semiconductor substrate, most likely silicon. The stochastic motion of charge carriers within the semiconductor will cause random fluctuations in the material's index of refraction, introducing a noise source called thermal charge carrier refractive (TCCR) noise. TCCR noise was previously studied in 2020 by Bruns et al., using a Langevin force approach. Here we compute the power spectral density of TCCR noise by both using the fluctuation-dissipation theorem and accounting for previously neglected effects of the standing wave of laser light produced by reflections along the direction of beam propagation. We quantify our results with parameters from Einstein Telescope, and we show that at temperatures of 10 K the amplitude of TCCR noise is up to a factor of $\sqrt{2}$ times greater than what was previously claimed. From 77 K to 300 K the amplitude is around 5 to 7 orders of magnitude lower than previously claimed when we choose to neglect the standing wave, and is up to a factor of 6 times lower if the standing wave is included. Despite these differences, we still conclude like Bruns et al. that TCCR noise should not be a limiting noise source for next-generation gravitational-wave interferometers.

Dielectric and bipolar resistive switching properties of Ag doped As–S–Se chalcogenide for non-volatile memory applications

In this study, dielectric and bipolar resistive switching properties of the chalcogenide from the Ag–As40S30Se30 system were investigated for potential application in non-volatile memory devices. Preparation of the glasses was done with the use of melt-quenching technique. Current–voltage (I–V) characteristics were determined at different temperatures, and stability of the Ag/chalcogenide sample/Ag structure through constant value of memory window was noticed. Namely, it was observed that a bipolar resistive switching effect is present in the prepared samples with noticeable transitions between high-resistance and low-resistance states when the voltage polarity was changed. Temperature dependent I–V measurements indicated that resistive switching voltage decreases as temperature increases suggesting thermally activated motion of charge carriers. The conduction model fitting results suggested that the Ohmic and space-charge limited current conduction are responsible for resistive switch. Based on the analysis of the obtained results, resistive switching mechanism was explained by using filamentary conduction. In addition, study of dielectrical properties indicated presence of space charge polarization. The presented results show that the synthesized material has properties that suggest them for potential application in non-volatile memory devices.

Nonlocal and cascaded effects in nonlinear graphene nanoplasmonics.

The ability of plasmons to focus light on nanometer length scales opens a wide range of enticing applications in optics and photonics, among which the enhancement of nonlinear light-matter interactions for all-optical modulation and spectral diversification emerges as a prominent theme. However, the subwavelength plasmonic near-field enhancement in good plasmonic materials such as noble metals is hindered by large ohmic losses, while conventional phase-matching of fields in bulk nonlinear crystals is not suitable for realizing nonlinear optical phenomena on the nanoscale. In contrast, anharmonic electron motion of free charge carriers in highly-doped graphene, which supports long-lived, highly-confined, and actively-tunable plasmons, renders the carbon monolayer an excellent platform for both plasmonics and nonlinear optics. Here we theoretically explore the enhancement in nonlinear response that can be achieved by interfacing multiple graphene nanostructures in close proximity to trigger nonlocal effects associated with large gradients in the electromagnetic near field. Focusing on second- and third-harmonic generation, we introduce a semianalytical formalism to describe interacting graphene nanoribbons with independent width, location, and electrical doping, so as to realize configurations in which plasmonic resonances may simultaneously enhance both the fundamental optical excitation frequency and harmonic intermediary and/or output frequencies. Our findings reveal the importance of both passive and active tuning in the design of atomically-thin nanostructures for nonlinear optical applications, and in particular emphasize the role played by nonlocal effects in generating an even-ordered nonlinear response that may contribute to other nonlinear optical processes through a cascaded interaction. We anticipate that our findings can aid in the design of actively-tunable nonlinear plasmonic resonators and metasurfaces.

An investigation into the hybrid architecture of Mn-Co nanoferrites incorporated into a polyaniline matrix for photoresponse studies.

In this study, an enhanced photoresponse was observed in the Mn-Co Nanoferrites (MCFs)-Polyaniline (PANI) nanohybrid architecture due to the formation of interface between PANI and MCFs, which provided a conduction pathway for the movement of charge carriers, and these interfaces were observed in a high-resolution transmission electron micrograph (HR-TEM). X-ray photoelectron spectroscopy (XPS) suggests that the carbon (C 1s) of the MCF-PANI nanohybrid shows peaks at 287.80 eV for CO, 286.17 eV for C-O, 285.24 eV for C-N, 284.50 eV for the sp3 hybridized carbon (C-C/C-H) and 283.84 eV for the sp2 hybridized carbon (CC). Current-voltage (I-V) curves reveal an ohmic nature of the MCF-PANI nanohybrid photodetector device. The photoresponse measurements were analyzed using the trap depth concept, demonstrating that the conductive polymer increases the photoconduction mechanism efficiency of MCFs. The constructed photodetector device exhibits a high photoresponsivity of 22.69 A W-1, a remarkable detectivity of 1.36 × 1012 cm Hz1/2 W-1 and a fast rise/decay time of 0.7/0.8 s. The excellent performance of the as-fabricated photodetector device could be explained by the intimate interaction between MCFs and PANI at their interface.

Nanocomposites of Cu2O with plasmonic metals (Au, Ag): design, synthesis, and photocatalytic applications.

Metal-semiconductor nanocomposites have been utilized in a multitude of applications in a wide array of fields, prompting substantial interest from different scientific sectors. Of particular interest are semiconductors paired with plasmonic metals due to the unique optical properties that arise from the individual interactions of these materials with light and the intercomponent movement of charge carriers in their heterostructure. This review focuses on the pairing of Cu2O semiconductor with strongly plasmonic metals, particularly Au and Ag. The design and synthesis of Au-Cu2O and Ag-Cu2O nanostructures, along with ternary nanostructures composed of the three components, are described, with in-depth discussion on the synthesis techniques and tunable parameters. The effects of compositing on the optical and electronic properties of the nanocomposites in the context of photocatalysis are discussed as well. Concluding remarks and potential areas for exploration are presented in the last section.

Synthesis and Dielectric Properties of MgO:ZnO Composites

The dielectric properties of the fabricated composites MgO:ZnO with various mixing ratios (100,75:25,50:50,25:75, and 100 wt. %)were investigated. The structure analysis was conducted using X-ray diffraction. The structure phase, crystallite size and purity of the fabricated MgO:ZnO composites were confirmed using X-ray diffraction spectra. The results declared that the diffraction spectrum of 100%MgO composite samples were compatible with cubic structure along the plane (200) while the structures of residual composite's samples were compatible with hexagonal structures. The crystal size of the most pronounced plane (101) for crystal growth was changed from 30.4 nm to 53.2 nm by increasing ZnO ratio from 25 to 100wt%. The dielectric properties were studied as function of frequency over the range (50Hz-10MHz). The a.c conductivity σa.c(ω) showed power low dependence for the full frequency range except for the composites samples of 0 and 75 %wt. ZnO which showed d.c region in the low frequency range. The exponent (s) values which represents the slope of ln σa.c(ω) and ln(ω) changed in non-regular manner by increasing the ZnO ratio. The dielectric constant ε1 and the dielectric loss ε2 increased with the increase of the ZnO ratio up to 75% ZnO and then decreased with further increase of ZnO ratio. The dielectric loss peaks observed in the plot diagram of ε2 against ln(ω) is found to shift towards the high-frequency side which indicates the decrease of relaxation time and prompt movement of charge carriers .The polarizability values (α) estimated from the COLE –COLE diagram increased from 0.112 to 0.467 when the ratio of ZnO changed from 0 to 50wt.% which referred to reduction of the intermolecular forces. While (α) reduced drastically at 75wt.% ZnO which referred to the growing of the intermolecular forces.

Improve the efficiency of organic light-emitting diodes using a novel hole injection layer with triple-layer gradually doped structure

In this study, we reported the fabrication of an organic light-emitting diodes (OLED) using the metal oxide Nb-doped ZnO (NZO) and the common hole transport layer of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) to form a novel hole injection layer with gradually-doped triple-layer structure (HITL). The comparison between the stepwise doped double-layer and uniformly doped device showed that the HITL structure could effectively improve the current efficiency of the OLED device. The results of both current density-voltage measurement by hole-only device (HOD) and the UV photoelectron spectroscopy (UPS) confirmed that the highest occupied molecular orbital (HOMO) energy level could help to improve the hole injection performance. In addition, the non-destructive analysis method of capacitance-voltage was used to observe the movement of charge carriers during the operation of the device. The comparison study indicated that by the stepwise doped double-layer injection layer, the influence of the doping gradient on the carrier injection was confirmed, and a smaller doping gradient was found to show the better performance of carrier injection. Based on the results obtained from this study, the maximum luminance and current efficiency of OLED device with HITL was found to be enhanced by approximately 2.48 times and 32.6% respectively when compared with the device without hole injection layer. Various measurements carried out in this study showed that the HITL structure could effectively improve the characteristics of hole carriers, and thereby the better charge balance effect and a more stable current efficiency performance could be achieved by reducing the current efficiency roll-off effect. • In this study, we demonstrated the performances of Alq 3 -based OLED using a novel hole injection layer with triple-layer gradually-doped structure (HITL). • The HITL structure can effectively improve the characteristics of hole carriers, thereby obtaining a better charge balance effect, reducing the efficiency roll-off effect, and obtaining a more stable efficiency performance. • Compared with the double-layer stepwise doped injection layer, the influence of the doping gradient on the carrier transport is confirmed, and a smaller doping gradient has a better performance of carrier injection and transport.

IonMonger 2.0: software for free, fast and versatile simulation of current, voltage and impedance response of planar perovskite solar cells

The second generation of the open-source MATLAB-based software tool IonMonger, for solving drift–diffusion models of charge transport in planar perovskite solar cells, is presented here. This version is based upon a generalisation of the original drift–diffusion model of charge carrier and ion motion in the perosvkite cell, as described in Courtier (J Comput Electron 18:1435–1449, 2019). The generalised model has the flexibility to capture (1) non-Boltzmann statistics of charge carriers in the transport layers, (2) steric effects for the ions in the perovskite layer, (3) generation of charge carriers from light made up of a spectrum of different wavelengths and, (4) Auger recombination. The updated software is significantly more stable than the original version and also adds the ability to simulate impedance spectroscopy measurements as well as transient voltage and/or illumination protocols. In addition, it is fully backwards compatible with the original version and displays improved performance through refinement of the underlying numerical methods. Furthermore, the software has been made accessible to a wider user base by the addition of IonMonger Lite, a version that leverages MATLAB’s live scripts and eliminates the need for a detailed knowledge of MATLAB’s syntax.

2D hexagonal yttrium doped SnO2 nanoplatelets for photocatalytic degradation

In this study, simple morphological and structural evolutions of two-dimensional hexagonal nanoplatelets were investigated. XRD analysis of SnO2 and SnO2:Y has revealed a tetragonal structure and photoluminescence spectra exhibited a visible emission broadband peak around 464 nm and 528 nm. The photoluminescence spectra of SnO2:Y (7 wt.%) confirm the increased charge separation, which inhibits electron–hole recombination. Raman spectra validated the presence of oxygen vacancies in SnO2:Y (7 wt.%) nanoplatelets. It has been shown that hexagonal SnO2:Y (7 wt.%) nanoplatelets perform better in photocatalytic degradation than conventional spherical nanoparticles. EIS measurements were performed to investigate the charge carrier movement of SnO2 and SnO2:Y nanoparticles. Our study is the first to illustrate the two-dimensional morphology of SnO2:Y (7 wt.%) hexagonal nanoplatelets and their application as a photocatalytic material.

Charge carrier motion and effect of fixed oxide charge in a microstructured silicon radiation detector

Signal formation in a microstructured semiconductor neutron detector is more complex than in planar diode geometry. Three-dimensional microstructures are laterally smaller than the ionization cloud length, and the electric fields may be weak enough to exhibit plasma time effects. This work is the first detailed treatment of charge carrier motion in these complex semiconductor devices to replicate the time profile and signal magnitude. Simulations were performed using COMSOL Multiphysics to investigate various parameters that affect the propagation of the charge cloud. It was observed that the size of the simulated three-dimensional structure had an impact on the induced current pulse, indicating the importance of simulation geometry optimization to accurately simulate charge cloud expansion. COMSOL Multiphysics was used to replicate accurate charge creation profiles using energy deposition information imported from radiation transport codes. A detailed simulation methodology is presented to benchmark preamplifier event pulses along with complexities in modeling the charge carrier motion along the etched microstructured trenches with Si–SiO2 boundary conditions, including fixed oxide charge and interface trapping.

Laser-Shock-Driven In Situ Evolution of Atomic Defect and Piezoelectricity in Graphitic Carbon Nitride for the Ionization in Mass Spectrometry.

Nanostructures─coupled with mass spectrometry─have been intensively investigated to improve the detection sensitivity and reproducibility of small biomolecules in laser desorption/ionization mass spectrometry (LDI-MS). However, the impact of laser-induced shock wave on the ionization of the nanostructures has rarely been reported. Herein, we systematically elucidate the laser shock wave effect on the ionization in terms of the in situ development of atomic defects and piezoelectricity in two-dimensional graphitic carbon nitride nanosheets (g-C3N4 NS) by short laser pulses. The mass analysis results of immunosuppressive drugs verify the enhanced LDI-MS performance, structurally originating from anisotropic lattice distortions in g-C3N4 NS, i.e., in-plane extension (contraction) and out-of-plane contraction (extension) that modulate the charge carrier motion. Along with the experimental investigations, density functional theory calculations on Mulliken charges and dipole moments demonstrate the contribution of defect and piezoelectricity to the ionization. The results of this study provide a mechanistic understanding of the underlying ionization processes, which is crucial for revealing the full potential of laser shock waves in LDI-MS.