Electron Mobility Research Articles

Interface engineering of the dz2 electrons mobility for single atom catalytic activity and selectivity

Transition metal singlet embedded in nitrogen-doped carbon material (M-N-C) has been demonstrated as a promising electrochemical oxygen reduction reaction (ORR) catalyst; however, the unsatisfying activity and production selectivity have hampered its widespread applications in energy storage and conversion technologies. Herein, interface engineering by facilitating M-N-C catalysts (M from 3d to 4d electron-containing elements) with MXene has been utilized to regulate their ORR performance. It is found that the charge transfer occurring within the interface not only tunes the electron occupancy of the 3d/4d orbitals of the metal site, but also delocalizes the population of the dz2 states. This alternation enhances the mobility of the electrons and promotes the 4e catalytic process thermodynamically. Meanwhile, the formation of ∗HOOH, the key reaction intermediate for 2e reaction, is hindered due to the alleviation of the binding capacity, which is beneficial to improve production selectivity. This study provides foundational understanding for the ORR catalytic mechanism at the atomic level and opens up new avenues for designing high-demanded electrocatalysts.

N-Type Doping Effect of Anthracene-Based Cationic Dyes in Organic Electronics.

n-Type doping for improving the electrical characteristics and air stability of n-type organic semiconductors (OSCs) is important for realizing advanced future electronics. Herein, we report a selection method for an effective n-type dopant with an optimized structure and thickness based on anthracene cationic dyes with high miscibility induced by a molecular structure similar to that of OSCs. Among the doped OSCs evaluated, rhodamine B (RhoB)-doped OSC exhibits the highest density, a smallest roughness of 2.69 nm, a phase deviation of 0.85° according to atomic force microscopy measurements, and the highest electron mobility (μ), showing its high miscibility. Surface doping of RhoB affords the lowest contact resistance of 2.01 × 105 Ω cm compared to bulk and contact doping, resulting in an effective doping structure. The RhoB-doped OSC retains 81.63% of the original μ value of 6.13 × 10-2 cm2 V-1 s-1 after 15 days, whereas pristine OSC shows a lower μ of 2.33 × 10-2 cm2 V-1 s-1 and maintains only 4.41% of the original value after 15 days. Our findings demonstrate that this methodology is effective for the selection of a high-performance n-type dopant for OSCs toward the development of high-performance and air-stable n-type organic electronics.

Simulation-based optimization of barrier and spacer layers in InAlN/GaN HEMTs for improved 2DEG density

In this study, we utilize Nextnano device simulation software to systematically investigate the dependence of 2-DEG (two-dimensional electron gas) density on the barrier and spacer Layers in InAlN/GaN high electron mobility transistors (HEMTs). By simulating a range of barrier thicknesses, In mole fractions, and spacer layer thicknesses, we reveal the intricate ways in which these parameters influence device performance. Our simulations demonstrate that precise control of the InAlN barrier thickness and In mole fraction, along with the AlN spacer thickness, is crucial for optimizing 2DEG density and, consequently, the overall electrical properties of the HEMTs. Notably, our results highlight that an InAlN barrier thickness below 12 nm, coupled with an optimized In mole fraction and a finely tuned AlN spacer thickness close to 1 nm, significantly enhances 2DEG density without compromising mobility. These insights provide a detailed understanding of the material and structural dependencies critical for the design and development of high-performance InAlN/GaN HEMTs. Our study includes detailed calculations of the device's I–V characteristics. Notably, the highest peak output current is observed at a 1 nm AlN spacer thickness, reaching 0.91 A/mm. Our findings highlight a noteworthy agreement between the results derived from our computational simulations and experimental measurements.

UV-random lasing of ZnO films decorated with Au nanoparticles and modification of lasing threshold by surface plasmon effect

Threshold energy values for random lasing action are determined from spectral and temporal coherence studies in systems with incoherent feedback. Zinc oxide films with and without their surface having been decorated with gold nanoparticles stand simultaneously for the active and the scattering medium, whereas pumping is carried out by a conventional laser system operating at the picosecond pulse regime. The influence of the gold surface on both the threshold and the intensity of the optical response is investigated. Whenever localized surface plasmon resonances are supported, electron mobility at the gold boundaries facilitates reinsertion of the trapped electrons into shallow defect levels to the conduction band. In consequence the characteristic visible emission from ZnO (green) due to transitions from such levels is suppressed, thus lowering the pumping threshold prerequisite for random lasing emission. The tunning of the random lasing threshold is achievable by means of control on the morphology and size effects of the gold nanoparticles. This contribution shows that specific post-thermal treatments could be exploited to adjust the lasing properties of novel metal decorated systems, which already feature random lasing before decoration. In principle, the extension of the decoration should be rather small to minimize response losses due to screening side effects of the metal phase, which obtrudes direct contact of the pumping photons with the semiconductor system.

Direct Solution Deposition of Large-Area Non-Solvated Fullerene Single-Crystal Films for High-Performance n-Type Field-Effect Transistors.

Fullerene (C60) crystals have attracted considerable attention in the field of optoelectronic devices owing to their excellent performance as n-type semiconductor material. However, a challenge still remains unbeaten as to the continuous crystallization of non-solvated C60 single-crystal films with high coverage and uniform alignment using low-cost solution techniques. Here, a facile bar coating method is used to prepare ribbon-shaped non-solvated C60 crystals with a large area (up to centimeters) and high coverage (>95%) by precisely controlling the crystallization process from specific solvents. Benefiting from the non-solvated crystalline structure, well-distributed thickness, uniform morphological alignment, and crystallographic orientation, organic field-effect transistors fabricated from the C60 single-crystal films exhibit a high average electron mobility of 2.28cm2V-1s-1, along with the coefficient of variance (CV) as small as 13.6%. This efficient manufacturing method will lay a strong foundation for C60 single-crystal films to fit into the future high-performance integrated optoelectronic application.

Endless Dirac nodal lines and high mobility in kagome semimetal Ni3In2Se2 : a theoretical and experimental study

Kagome-lattice crystal is crucial in quantum materials research, exhibiting unique transport properties due to its rich band structure and the presence of nodal lines and rings. Here, we investigate the electronic transport properties and perform first-principles calculations for Ni3In2Se2kagome topological semimetal. First-principles calculations of the band structure without the inclusion of spin-orbit coupling (SOC) shows that three bands are crossing the Fermi level (EF), indicating the semi-metallic nature. With SOC, the band structure reveals a gap opening of the order of 10 meV.Z2index calculations suggest the topologically nontrivial natures (ν0;ν1ν2ν3) = (1;111) both without and with SOC. Our detailed calculations also indicate six endless Dirac nodal lines and two nodal rings with aπ-Berry phase in the absence of SOC. The temperature-dependent resistivity is dominated by two scattering mechanisms:s-dinterband scattering occurs below 50 K, while electron-phonon (e-p) scattering is observed above 50 K. The magnetoresistance (MR) curve aligns with the theory of extended Kohler's rule, suggesting multiple scattering origins and temperature-dependent carrier densities. A maximum MR of 120% at 2 K and 9 T, with a maximum estimated mobility of approximately 3000 cm2V-1s-1are observed. Ni3In2Se2is an electron-hole compensated topological semimetal, as we have carrier density of electron (ne) and hole (nh) arene≈nh, estimated from Hall effect data fitted to a two-band model. Consequently, there is an increase in the mobility of electrons and holes, leading to a higher carrier mobility and a comparatively higher MR. The quantum interference effect leading to the two dimensional (2D) weak antilocalization effect (-σxx∝ln(B)) manifests as the diffusion of nodal line fermions in the 2D poloidal plane and the associated encircling Berry flux of nodal-line fermions.

Supramolecular Cucurbit[5]uril Modulates the Buried SnO2/Perovskite Interface for Efficient and Stable Perovskite Solar Cells

AbstractReducing non‐radiative recombination caused by defects at buried interfaces is crucial to the development of efficient and stable perovskite solar cells (PSCs). Herein, supramolecular cucurbit[5]uril (CB[5]) is introduced into the SnO2 layer, where it engages in host–guest interactions to suppress oxygen vacancies in SnO2, prevent particle aggregation, and enhance the electron mobility of SnO2. By serving as a bridging agent at the buried interface between SnO2 and the perovskite layer, CB[5] reduces the defect density and improves the carrier extraction efficiency. It also reduces the surface energy of the SnO2 substrate, facilitates the formation of large grains in the perovskite film, alleviates residual lattice stresses, and enhances the film quality. Consequently, the PSC with CB[5] shows a champion power conversion efficiency of 24.83%. Moreover, an unencapsulated device incorporating CB[5] retains more than 87% of its initial PCE under continuous illumination at the maximum power point tracking for 1000 h. This study pioneers the utilization of cucurbiturils in PSCs and provides insights into how supramolecular compounds can regulate buried interfaces.

Oxygen-defect rich SnO2-based homogenous composites for fast response and recovery hydrogen sensor

As a kind of green energy, hydrogen (H2) has been widely concerned and applied by people. One of the biggest challenges for sensing applications is the quick detection of hydrogen leaks or their release in various conditions, particularly in large electric vehicle batteries. This study successfully constructed a quick response and recovery hydrogen sensor based on the In2O3-SnO2 heterojunction. The response and recovery time of the In2O3-SnO2 hydrogen sensor is 1.1/1.9 s to 50 ppm H2. This is reduced to 11.0 %/9.5 % compared to the SnO2 hydrogen sensor. This sensor's remarkable gas detecting properties are mainly attributed to the In2O3-SnO2 heterojunction creation, crystal structure modification, and increased specific surface area (92.9 m2/g). Homogenous In2O3-SnO2 nanocomposites contain more oxygen defects, which is the primary factor enhancing the sensor's ability to detect gases. Firstly, indium ions are incorporated in the lattice of SnO2 results in lattice distortion and enhances the presence of oxygen deficiency in the composites, which plays a pivotal role in achieving rapid response and recovery of the sensor. Secondly, In2O3-SnO2 heterostructures promote rapid adsorption of oxygen molecules and target gases by facilitating effective electron mobility on their surface. The quicker response and recovery times of hydrogen sensors based on In2O3-SnO2 heterojunctions are observed. This innovative approach to creating fast-responding gas sensors highlights the promise of heterojunction-based hydrogen sensors for real-time H2 monitoring and opens up new research directions.

Single-Layer InGeS: Robust direct Bandgap, super high electron Mobility, long-lived Carriers, and Ohmic contact for Next-Generation Field-Effect transistors

Two-dimensional (2D) materials holding appropriate bandgaps, high carrier mobility, and long carrier lifetime require to be urgently explored as electronic devices such as field effect transistors (FETs) become more and more miniaturized. Herein, single-layer (SL) InGeS is thoroughly investigated using first-principles calculations. Theoretical results confirm SL InGeS has nice thermal and dynamical stability at 300 K. SL InGeS holds a direct bandgap of 1.28 eV by HSE06, and its electrons and holes are inherently located at different atomic regions. In the visible range, SL InGeS displays a maximum optical absorption of ∼ 5 × 105 cm−1, surpassing that of most known 2D materials. Furthermore, SL InGeS possesses high electron mobility (∼11100 cm2 V−1 s−1) and relatively low hole mobility (∼1000 cm2 V−1 s−1), and its carrier lifetime is as long as 4.99 ns. In addition, an Ohmic contact is designed in the graphene/InGeS heterojunction, implying small current resistance. In brief, all these scientific findings promise SL InGeS is a hopeful candidate in ultrathin FET devices.

Synthesis and characterization of zinc ferrite nanoparticles@GO for the photocatalytic degradation of Methylene Blue dye under visible light

Due to rising environmental pollution, there has been a growing focus on photo degradation catalysts for pollution removal. Under visible light irradiation, methylene blue dye (MB) photocatalytic degradation has been studied using Zinc ferrite nanoparticles (ZnFe2O4 NPs) and Zinc ferrite nanoparticles/graphene oxide (ZnFe2O4/GO). Methylene blue dye is a carcinogenic pollutant that poses risks to both humans and marine life. The synthesis of ZnFe2O4/GO was achieved by the biotemplating method. Synthesized nanoparticles were loaded on graphene oxide (GO) in different ratios (Zn1:GO1, Zn1:GO3, and Zn1:GO5). Nanocomposite characterization was done utilizing Raman Spectroscopy analysis, FT–IR, XRD, BET, FE-SEM–EDX, XPS, and TEM. The confirmation of the cubic spinel structure of ZnFe2O4 NPs has been validated uniformly distributed on the surface of the GO sheets. The vigorous interaction between ZnFe2O4 NPs and graphene sheets facilitates rapid electron mobility, enhancing electron separation and holes in photocatalytic applications. The aforementioned parameters are crucial in MB’s photocatalytic degradation performance. Photocatalytic degradation processes depend on pH solution, initial dye concentration, and catalyst dosage. The outcomes demonstrated that augmenting the proportion of graphene oxide amplified MB photo degradation. Under the optimum conditions of 1 g/L dose, pH 8, 10 mg/L initial dye concentration, and 180-min irradiation time, the degradation ratio increased to 51.17 %, 59.70 %, 89.49 %, and 97.38 % using ZnFe2O4, Zn1:GO1, Zn1:GO3, and Zn1:GO5, respectively. Based on the photo degradation process, GO exhibited superior photocatalytic performance at the highest concentration. The kinetics data showed that the photo degradation reaction adheres to the pseudo-second-order. The study indicated that the eco-friendly, non-toxic photocatalyst ZnFe2O4/GO can be used as an effective potential substance for water treatment as well as the elimination of hazardous organic dyes from aqueous solutions.

Bulk photovoltaic effect and high mobility in the polar 2D semiconductor SnP2Se6.

The growth of layered 2D compounds is a key ingredient in finding new phenomena in quantum materials, optoelectronics, and energy conversion. Here, we report SnP2Se6, a van der Waals chiral (R3 space group) semiconductor with an indirect bandgap of 1.36 to 1.41 electron volts. Exfoliated SnP2Se6 flakes are integrated into high-performance field-effect transistors with electron mobilities >100 cm2/Vs and on/off ratios >106 at room temperature. Upon excitation at a wavelength of 515.6 nanometer, SnP2Se6 phototransistors show high gain (>4 × 104) at low intensity (≈10-6 W/cm2) and fast photoresponse (< 5 microsecond) with concurrent gain of ≈52.9 at high intensity (≈56.6 mW/cm2) at a gate voltage of 60 V across 300-nm-thick SiO2 dielectric layer. The combination of high carrier mobility and the non-centrosymmetric crystal structure results in a strong intrinsic bulk photovoltaic effect; under local excitation at normal incidence at 532 nm, short circuit currents exceed 8 mA/cm2 at 20.6 W/cm2.

A novel method to determine bias-dependent source and drain parasitic series resistances in AlGaN/GaN high electron mobility transistors

The AlGaN/GaN high electron mobility transistors (HEMTs) with T-gate that suitable for high frequency applications were fabricated. A novel method to extract the bias-dependent source and drain parasitic series resistances (Rs and Rd) of AlGaN/GaN HEMTs is proposed. By analyzing the distributed capacitance and current generator network in the velocity saturated regions of the AlGaN/GaN HEMTs, a new restriction relationship between small-signal equivalent circuit elements is found. The Rs and Rd can be determined under active bias through wideband S-parameter measurements, which can better reflect the physical mechanism of AlGaN/GaN HEMTs under normal operation. The S-parameters and extrinsic transconductance calculated based the small-signal equivalent circuit element values extracted by the method proposed in this paper are very consistent with the experimental values, which reflects the accuracy of this element extraction method. In this paper, the physical mechanism that causes Rs and Rd to vary with bias voltage is also studied. This study has a deeper insight into the bias-dependence of Rs and Rd, which modifies the understanding for physical mechanisms of AlGaN/GaN HEMTs. The research results provide new ideas for establishing small-signal equivalent circuit models containing more physical effects and is of great significance to GaN-based integrated circuit design.

Enhanced electrical performance in graphene field-effect transistors through post-annealing of high-k HfLaO gate dielectrics

High-k gate dielectrics have attracted a great deal of attention in the investigation of transistors due to their unique properties such as superior gate controllability. However, their integration into graphene field-effect transistors (GFETs) remains problematic and the physical mechanisms governing the performance of these devices are still not fully understood. In this study, the effects of post-annealing on GFETs utilizing the high-k HfLaO ternary oxide as the gate dielectric were comprehensively investigated. The HfLaO film was deposited on top of graphene by magnetron sputtering, and the device performance with various post-annealing temperatures was conducted. It was found that post-annealing temperature can effectively increase the dielectric constant through balancing the oxygen-vacancy defects and moisture absorption. Both the surface morphology of HfLaO and performance of GFETs were investigated, and the fabricated GFETs exhibit notable electrical performance enhancements. Specifically, GFETs with a 200 °C post-annealed HfLaO gate dielectric demonstrate the optimal device performance, featuring a minimal Dirac point voltage (VDirac) of 1.1 V and a minimal hysteresis (ΔVDirac) of 0.5 V. The extracted hole and electron mobilities are 4012 and 1366 cm2/V · s, respectively, nearly one order of magnitude higher than that of GFETs with as-deposited HfLaO. This work outperforms other existing GFETs utilizing high-k gate dielectric and chemical vapor deposition grown graphene in terms of both carrier mobility and on–off ratio. It is also noted that the excessive post-annealing temperature can negatively impact the GFET performance through introducing oxygen vacancies, increasing the surface roughness, lowering the breakdown voltage, and inducing recrystallization.

Regulating coordinatively unsaturated Co active sites in TA@ZIF-L(Co) via tannic acid for efficient photoelectrochemical water oxidation

Metal-organic frameworks (MOFs) as a cocatalyst can enhance the photoelectrochemical (PEC) water oxidation performance to a certain extent, but still suffer from deficient exposure of active sites and low electron mobility. In this work, 2D Leaf-like zeolitic imidazolate frameworks (ZIF-L) were selected as a precursor for the generation of defective structures by tannic acid (TA) functionalization-assisted etching, and then coupling it with BiVO4 to prepare a novel and highly efficient TA@ZIF-L(Co)/BiVO4 photoanode by a simple impregnation method. The photocurrent density of TA@ZIF-L(Co)/BiVO4 composite photoanode achieves 4.21 mA cm−2 at 1.23 VRHE under AM 1.5 G illumination, which is superior to that of ZIF-L(Co)/BiVO4, and three times that of the bare BiVO4, with a charge injection efficiency of up to 80 %, and its stability is also remarkably improved. Experimental results and DFT calculations showed that the introduction of TA not only improved the light absorption efficiency, but also exposed more active sites, increased the electron density of the coordinatively unsaturated Co active sites, and enhanced the polarized electric field on the surface, thus accelerating electron mobility. This work demonstrates that TA as a surface modifier has great potential to activate metal sites and change the electronic environment of MOFs for BiVO4-based photoanode in PEC water oxidation, providing valuable insights into the rational design of photoanodes.

Electrochemical Synthesis of Urea from Carbon Dioxide and Nitrite at Cobalt Phthalocyanine-Ion Liquid Electrodes

Electrochemical coreduction of carbon dioxide and nitrogen oxyanion/oxide pollutants are attractive processes for simultaneous environmental remediation and sustainable production of urea. The development of suitable technology requires catalysts and electrodes that provide higher efficiencies by decreasing the overpotential required and increasing the faradaic efficiency. Electrode design is a key element in this process through which the environment of the catalyst can be manipulated to optimize activity and selectivity. Here, ionic liquids have been used to control the coreduction of carbon dioxide and nitrite at a cobalt phthalocyanine catalyst. Increasing the hydrophobicity of the catalyst layer with a mixture of 1-butylpyridinium hexafluorophosphate and trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide was found to increase the faradaic efficiency for urea formation to 27% at the lowest overpotential (−0.064 V vs RHE), from 3% for a Nafion binder. Modulation of the electronic structure, arrangement (aggregation vs adsorption on the carbon support) and/or mobility (via solubilization) of the CoPc catalyst appear to play a role in determining the rate and faradaic efficiency of urea production. Combining the CoPc catalyst with a carbon supported Cu cocatalyst increased the rate of urea production by 195% at –0.064 V.

Novel indium phosphide charged particle detector characterization with a 120 GeV proton beam

Thin film detectors which incorporate semiconductor materials other than silicon have the potential to build upon their unique material properties and offer advantages such as faster response times, operation at room temperature, and radiation hardness. To explore the possibility, promising candidate materials were selected, and particle tracking detectors were fabricated. An indium phosphide detector with a metal-intrinsic-metal structure has been fabricated for particle tracking. The detector was tested using radioactive sources and a high energy proton beam at Fermi National Accelerator Laboratory. In addition to its simplistic design and fabrication process, the indium phosphide particle detector showed a very fast response time of hundreds of picoseconds for the 120 GeV protons, which are comparable to the ultra-fast silicon detectors. This fast-timing response is attributed to the high electron mobility of indium phosphide. Such material properties can be leveraged to build novel detectors with superlative performance.

Progress in electron energy modeling for plasma flows and discharges

A novel formulation of the electron energy relaxation terms is presented here, which is applicable to plasma flows and discharges wherein the electron temperature could be higher or lower than the gas temperature. It is demonstrated that the electron energy losses due to inelastic collisions can be expressed as a function of only two species-dependent parameters: the reduced electric field and the reduced electron mobility. This formulation is advantageous over previous ones, being simpler to implement and more accurate when experimental data of the reduced electric field and reduced mobility are available. Curve fits to empirical data of these two properties are outlined here for all important air molecular species. The approach accounts for all inelastic electron energy relaxation processes without needing individual cross sections or rates, reducing potential errors associated with independently handling each process. Several test cases are presented to validate the proposed electron energy source terms including reentry plasma flows for which the electron temperature is less than the gas temperature, as well as discharges in which the electron temperature reaches values in excess of 30 eV. In all cases, the agreement with experimental data is observed to be very good to excellent, significantly surpassing prior electron energy models for plasma flows.

Ultra-high electron mobility in Sn-doped two-dimensional Ga2O3 modified by biaxial strain and electric field

2D Ga2O3 exhibits overwhelming advantages over its bulk counterpart, whereas manipulating the carriers is rare. We report strain-dependent electronic structures and transport properties of Sn-doped 2D Ga2O3 using first-principles calculations with deformation potential theory. The band gaps are tunable from 2.23 eV to 1.20 eV due to the strain-mediated σ* anti-bonding and π bonding state variations. Specifically, ultra-high electron mobility of 22579.32 cm2V−1s−1 is predicated under 8% tensile. Further electric field modulations suggest the retaining of band gap and effective mass. These results highlight its property manipulations and nanoscale electronic applications.

Influence of fixed charges and trapped electrons on free electron mobility at 4H-SiC(0001)/SiO2 interfaces with gate oxides annealed in NO or POCl3

Free electron mobility (μ free) in 4H-SiC(0001) MOSFETs with gate oxides annealed in NO or POCl3 was calculated in a wide range of effective normal field (E eff) from 0.02 to 2 MV cm−1, taking account of scattering by fixed charges and trapped electrons. The present calculation indicates that the Hall mobility in the high-E eff region experimentally obtained for NO-annealed MOSFETs (14 cm2 V−1 s−1 at 1.1 MV cm−1) is much lower than that for POCl3-annealed MOSFETs (41 cm2 V−1 s−1) due to severe Coulomb scattering by electrons trapped at a very high density of interface states.

Therapeutic Voyage of Graphene-based Biosensor

: The study of carbon-based materials and nanoparticles is currently an exciting field of study in the domain of material science. One of the most prominent of these materials is graphene, along with its related components graphene oxide and reduced graphene oxide. A single-layer, twodimensional nanomaterial called graphene (GN) is employed in many different industries, such as electronics and biology. Graphene is a remarkable two-dimensional substance that has earned the title of "wonder material." Its remarkable electrical, optical, thermal, and mechanical qualities have attracted significant attention. Graphene's intriguing characteristics have led to its integration into numerous biosensing applications. Graphene possesses remarkable chemical, electrical, and physical qualities. The distinctive properties of graphene, particularly its electrical conductivity, large surface area, and significant electron mobility, are focusing more attention on applications in biomedicine that facilitate easier health monitoring. Biosensors with high sensitivity and precision can enhance patient care, and offer an opportunity for an early illness diagnosis and clinical pathogen identification. Additionally, a wide range of biological molecules, including glucose, hydrogen peroxide, cholesterol, dopamine, etc., can be detected using graphene-based biosensors. This study evaluates contemporary developments regarding graphene-based biosensors and their prospects and difficulties in this rapidly developing profession in the coming era. Graphene-based nanomaterials are appropriate to be employed in various biological and sensory contexts, including medicine and gene transfer, because of their unusual topologies and extraordinary properties. Graphene's outstanding characteristics enable biosensing applications to obtain the appropriate sensitivity, selectivity, and repeatability for a range of targets.