Number Of Charge Carriers Research Articles

Investigation of Anodic Bond Formation Process and Potential Use of the Results

Anodic bonding is a widely used process in research and industry for MEMS Applications. The main advantage is that it is a very reliable process, that results in a strong and hermetically sealed bond. The bonding process is also very stable to perform. These properties are due to the process sequence of heating the wafers, to be bonded, to a temperature in the range of 300 to 450°C. One of these two wafers has to be made of borosilicate glass (e.g., SCHOTT Borofloat33®). In such glasses, sodium ions (network modifier) are dissolved out of the glass network in the temperature range mentioned and thus become free and mobile. If now a negative voltage of typically 1000V is applied to the glass wafer, the free positively charged sodium ions will move away from the contact area of both wafers, the later bonding interface, under the influence of the electric field. This results in a displacement current, which decreases again after a maximum is reached, due to the limited available number of charge carriers (sodium ions). This ultimately leads to a depletion of the charge carriers in the glass. It is generally assumed that a linked effect occurs in the bond field, namely that oxygen ions migrate from the glass to the bond interface, where they cause the actual bond formation via anodic oxidation.Even though this basic concept of the anodic bonding corresponds to state of the knowledge of how the anodic bond is actually formed [1], it is difficult to prove in practice. In order to gain a deeper insight into the formation of anodic bonding and thus open up new applications and even wider utilization of anodic bonding, a first basic experiment was done as follows: A glass wafer was provided with a thin aluminum layer by a sputtering process and another glass wafer was anodically bonded to this aluminum layer. The typical bonding current (depletion and current drop) was observed and the resulting composite of two glass wafers with a very thin intermediate aluminum layer was examined and tested for bonding quality. First of all, it can be stated that bonding formation has taken place locally between the the 6" wafers. Unfortunately, particle contamination could not be completely avoided during processing leading to larger unbonded areas, especially in the center of the wafer. Nevertheless, the bonded areas allow for evaluation of bonding quality. The sputtered aluminum layer has a higher thickness in the center, due to the fact that the glass wafer was eccentrically rotated below a small sputter target. This inhomogeneity effect enables the characterization of different Aluminum layer thicknesses in one sample. The sputter time was set, that at the wafer center an untransparent Aluminum layer was deposited, while at the wafer edge just a few nanometers of aluminum forming a semitransparent layer. After the bonding experiment it was noticed that in all the bonded area the aluminum appears rather homogeneously transparent. According to that it can be concluded that the aluminum layer is oxidized during anodic bonding transforming into transparent Aluminum oxide. This finding is a clear confirmation of the general thesis, that during anodic bonding an anodic oxidation takes place at the bond interface. In further examinations the influence of the bonding parameters on this oxidation process will be investigated. It is expected that with higher temperature and bonding voltage the oxidation will be enhanced, ending up with an optically highly transparent layer of Aluminum oxide. This might be relevant for emerging optical applications requiring anodic bonding as reliable bonding process together with optical transparence for visual light. As blade tests have shown the bonding conditions in the first process are not yet optimal – the bonding strength was rather low, but darker spots in the crack opened area indicate a transfer of the aluminum oxide layer. By variating and improving bonding conditions, a deeper insight into the details of the oxidation process during anodic bonding will be available. So far it is known that easy to oxidize materials (Silicon and Aluminum) can be well anodically bonded while rather inert materials (Silicon Nitride) are hardly or not bondable with this procedure. For that reason, some materials like Platinum, Gold, and Titanium these predictions will be evaluated in practice. With this more profound knowledge it might be possible to predict the anodic bonding behavior of different materials in the future.Literature:[1] Lapadatu, A. C., & Jakobsen, H. (2015). Anodic bonding. In Handbook of Silicon Based MEMS Materials and Technologies (pp. 599-610). William Andrew Publishing. Figure 1

Tailoring the electrical conductivity of Poly(vinylidene fluoride) by blending with poly (3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS) and ionic liquids

In order to tailor dielectric response and electrical conductivity, novel polymer blends based on poly(vinylidene fluoride (PVDF) and different fillers composed by poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and PEDOT:PSS/ionic liquids (ILs): PEDOT:PSS/N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]) and PEDOT:PSS/N-ethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([C2mpyr][TFSI]), with different PEDOT:PSS/IL contents (10, 20 and 40 wt%) were prepared through solvent casting. The morphological, physical-chemical and thermal properties of the polymer blends were evaluated, together with the influence of PEDOT:PSS/IL on the PVDF crystallization kinetics, dielectric and electrical conductivity.The incorporation of PEDOT:PSS/IL in the polymer matrix lead to a decrease of the PVDF spherulites. Furthermore, it was detected that both PEDOT:PSS and IL act as nucleation agents, promoting the homogeneous crystallization of PVDF as well as the crystallization into its b and g polar phases. The electrical conductivity formalism revealed significant contributions of PEDOT:PSS/IL to the electrical conductivity behavior of the blends, being thermally activated and described by the charge transport mechanism. Further, the dc conductivity increases due to the higher number of charge carriers of the PEDOT:PSS/IL content.The tailorable electrical characteristics of the PVDF/PEDOT:PSS-IL blends demonstrate their potential for applications in areas such as ionic actuators and battery devices.

Luminescence in Anion-Deficient Hafnia Nanotubes.

Hafnia-based nanostructures and other high-k dielectrics are promising wide-gap materials for developing new opto- and nanoelectronic devices. They possess a unique combination of physical and chemical properties, such as insensitivity to electrical and optical degradation, radiation damage stability, a high specific surface area, and an increased concentration of the appropriate active electron-hole centers. The present paper aims to investigate the structural, optical, and luminescent properties of anodized non-stoichiometric HfO2 nanotubes. As-grown amorphous hafnia nanotubes and nanotubes annealed at 700 °C with a monoclinic crystal lattice served as samples. It has been shown that the bandgap Eg for direct allowed transitions amounts to 5.65 ± 0.05 eV for amorphous and 5.51 ± 0.05 eV for monoclinic nanotubes. For the first time, we have studied the features of intrinsic cathodoluminescence and photoluminescence in the obtained nanotubular HfO2 structures with an atomic deficiency in the anion sublattice at temperatures of 10 and 300 K. A broad emission band with a maximum of 2.3-2.4 eV has been revealed. We have also conducted an analysis of the kinetic dependencies of the observed photoluminescence for synthesized HfO2 samples in the millisecond range at room temperature. It showed that there are several types of optically active capture and emission centers based on vacancy states in the O3f and O4f positions with different coordination numbers and a varied number of localized charge carriers (V0, V-, and V2-). The uncovered regularities can be used to optimize the functional characteristics of developed-surface luminescent media based on nanotubular and nanoporous modifications of hafnia.

The evolution of penta-graphene thermoelectrics: External fields as a key enabler for High-Performance devices

The tight-binding model is used in this study to examine the electronic and thermal properties of penta-Graphene (PG). To analyze these properties, approaches including the Kubo formula, linear response theory, and Green's function method are applied. The obtained numerical results show that by introducing bias voltage U, external magnetic field Π, and electron doping μ, significant modifications in electrical conductivity, magnetic susceptibility, and thermoelectric properties including power factor PF(T), Seebeck coefficients S(T), and figure of merit ZT(T) are observed. The band structure and density of states (DOS) of PG structure can be significantly altered by applying a bias voltage or an external magnetic field. The wide band gap of PG exhibited a marked reduction with the application of these external fields, displaying greater sensitivity to Π compared to U. Thermal properties of PG, including electrical conductivity σ(T), exhibit a peak as a function of temperature, which its peak position depends on the external fields and μ. Below the peak, σ(T) increases significantly with increasing external fields and μ, due to the reduced band gap and increased number of excited charge carriers, respectively. σ(T) demonstrates greater sensitivity to μ compared to Π, and both parameters have a more pronounced effect than bias voltage U. The magnetic field and bias voltage shift the peak position of the power factor PF(T) in opposite directions. Through tuning of the external fields, which alters the electronic structure of PG, the ZT(T) can be enhanced and its rate of increase is more dependent on bias voltage than on magnetic field.

Development and Characterization of a New Solid Polymer Electrolyte for Supercapacitor Device

In this study, solid polymer electrolytes (SPEs) are based on methylcellulose (MC) used as a polymer host and sodium iodide (NaI) as a dopant. The SPE films are developed using different contents of ethyl carbonate (EC) as a plasticizer to enhance their properties via a solution casting method. The surface morphology of SPE films is shown using polarized optical microscopy (POM), which indicates the existence of amorphous patches due to the plasticizing effect of EC. The creation of a complex between MC, NaI, and EC was confirmed by Fourier transform infrared (FTIR) spectra. A tiny amount of EC applied to the MC-NaI polymer salt matrix increases the number of charge carriers and improves ionic conductivity. The ionic conductivity of the generated polymer electrolytes is examined using electrochemical impedance spectroscopy (EIS). The high-ion conducting PE of 5.06 × 10−3 S·cm−1 was found with the mixture MC + 50 wt% NaI + 10 wt% EC (room temperature). The linear speed voltammetry (LSV) test shows that the optimized polymer electrolyte can withstand decomposition up to 2.5 V. The optimized sample transmission numbers were calculated using a TNM (transference number measurement) approach, and the results show that 99% of the ions contribute to the conductivity, compared to only 1% of the electrons. A solid-state electrical double-layer capacitor (EDLC) was fabricated using the highest ion-conductive polymer electrolyte and graphene oxide (GO)-based electrodes. The galvanostatic charge-discharge (GCD) technique was performed, and the GCD graph shows the behavior of an ideal capacitor with a less Faradic process and a low ESR value. The GO-based cell’s columbic efficiency is 100%, and the system delivers the charge for a long duration. The EDLC cell demonstrates outstanding cyclability. The specific capacitance of the EDLC cell incorporated with MC + 50 wt. % NaI + 10 wt. % EC was found to be 154.66 F/g.

Combined density functional theory and molecular dynamics analyses on Lithium/Sodium ion interaction and diffusion in gel polymer electrolytes with poly-vinylidene fluoride scaffold, propylene carbonate/Ionic Liquid solvent, and perchlorate salt

Choice of a proper electrolyte is very crucial to enhance the overall performance of a metal-ion battery. In this work, dispersion corrected density functional theory and classical molecular dynamics simulations are carried out to explore the metal ion (Li+ and Na+) interaction and diffusion through polyvinylidene fluoride (PVDF)-based gel polymer electrolytes. Four types of polymer/solvent/salt electrolyte systems are investigated considering PVDF scaffold for each case, and conventionally used propylene carbonate and rarely used, albeit cheaper, ionic liquid [BMIM][ClO4] as solvent, along with metal perchlorate salts LiClO4 and NaClO4. Inter-unit interactions within the electrolyte clusters, electrolyte uptake, and electrochemical stability of the electrolytes are explained by gas-phase DFT analyses, considering the polymer/solvent/salt components in 1:1:1 molecular ratio. Diffusion of the ions and ionic conductivity of the electrolytes are explored by MD simulation referring to two different size and time scales. From the DFT-based non-bonding interaction analyses, metal ions are found to exhibit strong non-covalent interactions with the adjacent O and F atoms, where the O atoms are parts of PC and [ClO4]- ions, and F atoms are from the PVDF chains. [BMIM]+, [ClO4]-, and PVDF are found to interact through weak van der Waals type hydrogen bonds. Both DFT and MD calculations suggest that, Li+ and Na+ ions are primarily coordinated with [ClO4]- ions. Dynamics studies confirm that for PVDF/IL/salt, total ionic conductivity is predominated by [BMIM]+ and [ClO4]-, exhibiting lower metal ion diffusivity as compared to PC-containing electrolytes. For both Li- and Na-ion systems, owing to the availability of higher number of charge carriers, electrolytes containing ILs show higher ionic conductivity compared to those containing PC as the solvent.

Effects of multiple cations and sintering temperature on microstructure and dielectric properties in Na1/2Ln1/2Cu3Ti4O12 (Ln = Sm and Eu) ceramic materials

Na1/2Eu1/2Cu3Ti4O12 and Na1/2Sm1/2Cu3Ti4O12 dielectric ceramics were synthesized at different sintering temperatures (950, 975 and 1000 °C) by a solid-state reaction method. Phase structure, cation valence state, and dielectric properties of all sintered ceramics were systematically investigated. When the preparation temperature was changed, the Cu+ ion concentration of (Na+, Eu3+) co-doped ceramics changed faster than that of (Na+, Sm3+) co-doped ceramics. Abnormally high dielectric constants of ~ 3.17 × 104 and ~ 1.06 × 104 (at 10 Hz and 303 K) were achieved in Na1/2Sm1/2Cu3Ti4O12 and Na1/2Eu1/2Cu3Ti4O12 ceramics prepared at 950 °C, respectively. However, Na1/2Sm1/2Cu3Ti4O12 and Na1/2Eu1/2Cu3Ti4O12 prepared in high sintering temperature (1000 °C) exhibited a good frequency stability of dielectric permittivity. It was demonstrated that an increasing number of charge carriers induced by the increase of sintering temperature could lead to a competitive coexistence of two polarization mechanisms (surface barrier layer capacitor and internal barrier layer capacitor), further changing the dielectric properties of CaCu3Ti4O12-based ceramics.

Investigating Theoretical Frameworks: Comprehending the Relationship between σ, n, and μ in MnO2 Dispersed Films.

Solid polymer electrolytes (SPEs) made from a polymer-salt matrix show great potential for use in various applications, such as batteries, fuel cells, supercapacitors, solar cells, and electrochromic devices. Research on various theoretical and experimental aspects of these SPEs is highly pursued worldwide. However, due to the lack of direct experimental techniques for the measurement of the number of charge carriers (n) and their mobility (μ), reports on their correlation with conductivity (σ) and their exact theoretical justification are rare in literature studies. This paper is an attempt toward the search for the well-established theoretical formulation for n and μ that can justify the experimental results. In a previous attempt, it could only be demonstrated that the available theoretical bases show different values, but we could not come to any concrete conclusion. This research involves the use of three theoretical models, namely, the Rice and Roth model, the Trukhan model, and the Schutt and Gerdes model. The purpose of this study is to analyze the varying conductivity levels by calculating the concentration and mobility of charge carriers. To obtain the required parameters, impedance spectroscopy data were used. The Trukhan model was used to determine the precise value of the diffusion coefficient. By utilizing the dielectric tangent loss, the concentration of charge carriers and ion mobility were calculated. The Schutt and Gerdes (S&G) model was also used; this model is based on the dielectric constant and the relaxation frequency, which were derived from the EIS data. Finally, the Rice and Roth model was also employed, which is known for the ion transport in "super" ionic conductors. This was employed on the temperature-dependent impedance data for three different compositions of the films. A correlation is established between n and μ with σ using all three models. However, the Trukhan model is the most suitable for explaining the behavior of our system.

Enhancing Light Harvesting in Dye-Sensitized Solar Cells through Mesoporous Silica Nanoparticle-Mediated Diffuse Scattering Back Reflectors

Dye-sensitized solar cells (DSSCs) hold unique promise in solar photovoltaics owing to their low-cost fabrication and high efficiency in ambient conditions. However, to improve their commercial viability, effective, and low-cost methods must be employed to enhance their light harvesting capabilities, and hence photovoltaic (PV) performance. Improving the absorption of incoming light is a critical strategy for maximizing solar cell efficiency while overcoming material limitations. Mesoporous silica nanoparticles (MSNs) were employed herein as a reflective layer on the back of transparent counter electrodes. Chemically synthesized MSNs were applied to DSSCs via bar coating as a facile fabrication step compatible with roll-to-roll manufacturing. The MSNs diffusely scatter the unused incident light transmitted through the DSSCs back into the photoactive layers, increasing the absorption of light by N719 dye molecules. This resulted in a 20% increase in power conversion efficiency (PCE), from 5.57% in a standard cell to 6.68% with the addition of MSNs. The improved performance is attributed to an increase in photon absorption which led to the generation of a higher number of charge carriers, thus increasing the current density in DSSCs. These results were corroborated with electrochemical impedance spectroscopy (EIS), which showed improved charge transport kinetics. The use of MSNs as reflectors proved to be an effective practical method for enhancing the performance of thin film solar cells. Due to silica’s abundance and biocompatibility, MSNs are an attractive material for meeting the low-cost and non-toxic requirements for commercially viable integrated PVs.

(Invited) Application of Machine Learning in Carbon Nanotube-Based Biosensors

Among electrochemical sensors, electrolyte-gated field-effect transistor (FET) with semiconducting single-walled carbon nanotubes (SWCNTs) is one of the most promising choices for the ultrasensitive biosensors. The biosensing is typically based on the recognition of analytes with capture probes (antibody, aptamer, receptor, enzyme, etc.) attached to SWCNTs. While the capture probes improve the chemical sensitivity and selectivity, the stability of the nanotube-based biosensors is limited by the activity of the capture probes. Another approach involves sensor arrays with different metal nanoparticles/self-assembled monolayers on the SWCNTs that act as nonspecific receptors. These sensor arrays can be trained with machine learning algorithms to distinguish analytes.When analytes bind to the sensor surface and interact with the semiconducting SWCNTs, they can cause modulations of the number of charge carriers in the FET channel, changing the device conductance, and eventually result in change in the FET characteristics, i.e., measured source-drain current vs. applied gate voltage. Rich information regarding the biorecognition process, sensing mechanism and sensing performances can be extracted from the changes in FET transfer characteristics. We proposed 11 features that can be selected to accurately describe the changes in FET transfer curves, including (1) relative change in transconductance, (2) threshold voltage (Vth) shift, (3, 10) relative change in conductance at ±0.6 Vg, (4-9) change in overall conductance normalized to conductance at Vth, and (11) the relative change in minimum conductance (see figure below). The transfer characteristics were extracted as distinct features for model training using established machine learning algorithms.We fabricated SWCNT-FET array functionalized with gold nanoparticles and different self-assembled monolayers (dodecanethiol and lipoic acid) for the sensing of nonmalignant and malignant cells, which were classified by linear discriminant analysis.[1] We have also demonstrated that the SWCNT-FET sensor array could be used for the screening of cell behaviors, and that live/dead mouse B16 melanoma cells could be successfully classified with machine learning.[2] [1] Silva, G. O.; Michael, Z. P.; Bian, L.; Shurin, G. V.; Mulato, M.; Shurin, M. R.; Star, A., Nanoelectronic Discrimination of Nonmalignant and Malignant Cells Using Nanotube Field-Effect Transistors. ACS Sens. 2017, 2, 1128–1132.[2] Liu, Z. R.; Shurin, G. V.; Bian, L.; White, D. L.; Shurin, M. R.; Star, A., A Carbon Nanotube Sensor Array for the Label-Free Discrimination of Live and Dead Cells with Machine Learning. Anal. Chem. 2022, 94, 3565-3573. Figure 1

Charge transport properties of interstitially doped graphene: a first-principles study

The role of interstitial atomic doping on transport properties of graphene was systematically studied using first-principles density functional theory (DFT). The study revealed that interstitial Au doping results in a p-type transfer of holes to graphene as the dopant concentration increases to 25%, with the Dirac point shifting to the Fermi level and localised states of atomic dopants appearing at the Fermi level and at energy of −1 eV. Ca, Ag and Al interstitial doping induces an n-type transfer of electrons to graphene with the Dirac point moving away from the Fermi level and localised states appearing at the Fermi level and at energy levels of ∼2 eV for Ca, around −3.5 eV for Ag, −3.5 eV and ∼1.6 eV for Al. As the dopant concentration increases further to 50%, the number of holes (or electrons) decreases for all dopants, except for Ca, as the localised state at the Fermi level disappears, and the Dirac point returns towards the Fermi level. Our research provides insights into how to reconcile the localised state and the number of charge carriers that play a significant role in the transport properties of interstitial doped graphene.

Features of the longitudinal and transverse tensoresistances of low-resistance n-Si

Features of longitudinal and transverse tensoresistances and the tenso-Hall effect in low-resistance n-Si crystals doped with phosphorus, antimony, and arsenic were studied. The impurity-specific mechanisms which lead to changes in the number of charge carriers (“incomplete ionization” and deactivation of impurities), as well as a change in the efficiency of the scattering on impurity density fluctuations were considered to explain the tensoresistive peculiarities. It is supposed that the dominant factor determining the efficiency of scattering on impurity density fluctuations is the value of the lattice strain introduced by the impurity itself. An increase in the transverse tensoresistance with pressure increasing revealed in n-Si samples doped with phosphorus and antimony was explained by the fluctuations of impurity density. For these samples, a maximum and instabilities on dependencies of the tenso-Hall effect are observed at 4.2 K. An increase in the measurement temperature, the manifestation of instabilities is weakened.

Effect of Rubidium Fluoride on Grain Sintering and Optoelectronic Properties of Nanostructured CuInSe2 Thin Films Obtained by Solution Processing

Chalcopyrite CuInSe2 (CISe) and Cu(In, Ga)(S, Se)2 (CIGS) absorber layers, have emerged as promising alternatives in the solar cell field due to their unique properties such as power conversion efficiencies (PCEs) above 20 %, direct bandgap, and high absorption coefficient. This enables the making of high-quality PV devices with absorbers from 2 μm thick, significantly reducing the use of raw materials. Additionally, the CISe absorber layer is a desirable material for Perovskite/CIS tandem configuration with a narrow band gap at the bottom that has demonstrated PCEs close to 25 %, and potential applications in lightweight and/or flexible substrates. Recently, the addition of alkali elements such as sodium, potassium, rubidium, and cesium via post-deposition techniques (PDTs) has demonstrated an improvement in CIGS-based solar cells’ performance. In this study, 10, 20, and 30 nm thick layers of rubidium fluoride were post-deposited on CISe-films made by solution processing techniques and then selenized under a selenium-argon atmosphere to improve the CISe photoelectronic properties such as the number of charge carriers collected and grain growth, critical characteristics to ensure useful photovoltaic devices. Thus, the effect of rubidium fluorine on CISe-based solar cells was analyzed using several characterization techniques. According to the results, thin films made by an amine-thiol mixture with uniform atomic composition were obtained. The crystallinity and grain growth improved with an increase in rubidium fluoride addition. Moreover, with 10 nm of rubidium fluoride, an improvement in the lifetime of the charge carrier, photoluminescence intensity, and the number of carriers collected by the solar cells was obtained.

Study of the structural, optical, and electrical properties of polyethylene oxide/ polyvinylidene fluoride (PEO/PVDF) blend dispersed with silver oxide (Ag2O) nanoparticles as an advanced multifunctional matrix for flexible electronic devices

The present study describes the preparation and characterization of new nanocomposite films based on a polyethylene oxide/polyvinylidene fluoride (PEO/PVDF) blend, doped with varying weight percentages of silver oxide (Ag2O) nanoparticles using the solution casting process. The films were analyzed using a variety of analytical techniques to understand their properties. The X-ray diffraction analysis revealed the complex formation between PEO/PVDF and Ag2O, indicating that the dopant was interacting with the polymer blend. Fourier transform infrared (FT-IR) analysis showed variations in the spectra with increasing dopant concentration, further confirming the interaction between the dopant and the polymer blend. UV–Vis analysis showed a decrease in the magnitude of the optical band gap (Eg) with an increase in the concentration of Ag2O, indicating an improvement in the optical properties of the films. Scanning electron microscope (SEM) images showed a change in the surface morphology of the films with the addition of Ag2O. The introduction of Ag2O into the PEO/PVDF blend resulted in an increase in the conductivity of the films at room temperature, which can be attributed to the increase in the number of mobile charge carriers and their mobility. Additionally, the dielectric analysis showed a significant dielectric dispersion in the frequency range investigated, which became stronger with increasing amounts of Ag2O in the film. The study suggests that the new nanocomposite films have improved optical and electrical properties, making them suitable for applications in optical devices and dielectric applications.

Corona Poling Induced Phase Transition to Highly Polar Phase in P(VDF-TrFE-CFE) Dielectric and Charge Transport of Organic Field-Effect Transistors.

Increasing the number of charge carriers flowing through the charge transport channel to improve the electrical performance of organic field-effect transistors (OFETs) is important because it leads to a low driving voltage and a high drain current value. This paper proposes a new strategy, the corona poling process, to enhance the electrical performance of OFETs using an external electric field when forming a dielectric film using a PVDF-based high-k dielectric terpolymer, P(VDF-TrFE-CFE). A corona poling process was applied to align the dipoles with high-k dielectric molecules and improve the capacitance, thereby increasing the number of charge carriers. Through this process, by observing the phase transition of a PVDF dielectric through a corona poling process in the GIWAXS data, the phase transition through an external electric field was thoroughly revealed for the first time. As a result, the capacitance of high-k dielectric films can be improved, and the amount of charge carriers can be increased by a simple corona poling process. In addition, to reduce the effect of deep trap sites caused by the dipole alignment, a thin low-k dielectric, polystyrene (PS), was introduced between the active and high-k dielectric layers to provide trap site passivation, thereby increasing the electrical performance of the OFET. Therefore, through this strategy, using a diketopyrrolopyrrole (DPP)-based donor-acceptor (D-A) copolymer as an active material of OFET, the average saturation region hole mobility was improved from 0.34 to 0.60 cm2/Vs. Thus, the electrical performances of the OFETs were improved by enhancing the capacitance through the corona poling process and reducing the charge carrier trap sites introduced by the high-k and low-k bi-layer dielectric layer. Importantly, this work offers a new strategy for the post-treatment to improve electrical performance of organic devices.

Effect of addition of polyether amine and TiO2 nanofibers on the properties of PEO based sodium ion conducting composites

Sodium ion conducting polymer composite films have been prepared using the blend of poly (ethylene oxide) and polyetheramine (JEFFAMINE ED2003) in which sodium trifluoromethane sulfonate (NaTf) salt and varying amounts of inorganic filler (TiO2 nanofibers) have been added. The effect of TiO2 nanofibers addition has been seen in terms of improved ionic conductivity and electrochemical stability of the nanocomposite film. Highest ionic conductivity of ∼3.5 × 10⁻⁵ Scm⁻1 (at room temperature) along with an electrochemical stability up to ∼2.6 V has been obtained for PEO-Jeffamine blend based solid polymer electrolyte (SPE) with 10 wt% of NaTf salt and a small amount (0.2 wt%) of TiO2 nanofibers. A non monotonic variation in the room temperature ionic conductivity and intensity of XRD peaks has been seen for composite films with increasing concentration of TiO2 nanofibers. Uniform distribution of salt (Na, F and S) and TiO2 nanofibers in the prepared composite film has been obtained in the elemental mapping. FTIR results have given evidence of interaction between the blended polymers, salt and TiO2. The wavelength and duration of exposure of UV radiation have altered the electrical properties of film. Increase in the number of ionic charge carriers has been attained on exposure to UV radiation.

Nanoscale Confinement Effects on Ionic Conductivity of Solid Polymer Electrolytes: The Interplay between Diffusion and Dissociation.

Solid polymer electrolytes (SPEs) are attractive for next-generation lithium metal batteries but still suffer from low ionic conductivity. Nanostructured materials offer design concepts for SPEs with better performance. Using molecular dynamics simulation, we examine SPEs under nanoscale confinement, which has been demonstrated to accelerate the transport of neutral molecules such as water. Our results show that while ion diffusion indeed accelerates by more than 2 orders of magnitude as the channel diameter decreases from 15 to 2 nm, the ionic conductivity does not increase significantly in parallel. Instead, the ionic conductivity shows a nonmonotonic variation, with an optimal value above, but on the same order as, its bulk counterparts. This trend is due to enhanced ion association with decreasing channel size, which reduces the number of effective charge carriers. This effect competes with accelerated ion diffusion, leading to the nonmonotonicity in ion conductivity.

Photocatalytic effects on Au@TiO2 confined in BMIm.NTf2 ionic liquid for hydrogen evolution reactions

We report a photocatalytic device based on gold nanoparticles (AuNPs/TiO2) coated with an ionic liquid (IL) as a very active, stable, and versatile system for hydrogen evolution reactions (HERs) via methanol photo reforming (MPR) and photocatalytic water-splitting (WSR) reaction. The devices prepared by magnetron sputtering yield hybrid materials with direct Au–TiO2 interactions that were subsequently coated with BMIm.NTf2 (IL@Au@TiO2). The IL presence critically enhances the photocatalytic performance given its interaction with the AuNPs and TiO2 surfaces by decreasing the flat band energy levels and the Schottky barrier thickness. The results show an increase in the number of charge carriers yielding a capacitor-like effect generated by interactions of IL and Au@TiO2 particles. Apparent quantum yield (AQY) up to 28.3% under UV irradiation (365 nm) and 22.9% at 405 nm irradiation were observed in the HER employing the as-prepared materials.

Dye degradation, antimicrobial activity, and molecular docking analysis of carbon sphere and graphene oxide–doped aluminum oxide

In this research work, pristine and various concentrations (2.4 wt%) of graphene oxide (GO)/carbon sphere (CS)–doped Al2O3 nanostructures (NSs) were synthesized with the chemical sol–gel method. Aluminum oxide (Al2O3) exhibits quick recombination of electrons and holes with a low specific surface to limit catalytic and antibacterial activities. Al2O3 doped with CS is good in wastewater treatment and reduces the size of NSs. The incorporation of graphene oxide (GO) into Al2O3 at different concentrations (2 and 4 wt%) enhances both the structural and chemical stabilities of the resulting material while concurrently decreasing the number of charge carriers and reducing the band gap energy. This modified Al2O3-GO composite exhibits promising potential for utilization in dye degradation and antibacterial activity. A series of characterizations were performed to investigate the structural, morphological, and optical properties. The NSs exhibited excellent catalytic activity (CA) against rhodamine B (RhB) dye in acidic, basic, and neutral media. The antimicrobial activity was tested against Escherichia coli. Pairs of electrons and holes are the primary building blocks for the production of reactive oxygen species (ROS), which causes bacteria to die. The significant inhibition zones against E. coli were calculated to be approximately 5.65 mm when compared to ciprofloxacin. Moreover, in silico investigations have revealed the possible inhibitory impact of produced nanomaterials (GO/CS-doped Al2O3) on DNA gyrase and FabI enzymes of fatty acid biosynthesis.

Orbital-resolved observation of singlet fission

Singlet fission1–13 may boost photovoltaic efficiency14–16 by transforming a singlet exciton into two triplet excitons and thereby doubling the number of excited charge carriers. The primary step of singlet fission is the ultrafast creation of the correlated triplet pair17. Whereas several mechanisms have been proposed to explain this step, none has emerged as a consensus. The challenge lies in tracking the transient excitonic states. Here we use time- and angle-resolved photoemission spectroscopy to observe the primary step of singlet fission in crystalline pentacene. Our results indicate a charge-transfer mediated mechanism with a hybridization of Frenkel and charge-transfer states in the lowest bright singlet exciton. We gained intimate knowledge about the localization and the orbital character of the exciton wave functions recorded in momentum maps. This allowed us to directly compare the localization of singlet and bitriplet excitons and decompose energetically overlapping states on the basis of their orbital character. Orbital- and localization-resolved many-body dynamics promise deep insights into the mechanics governing molecular systems18–20 and topological materials21–23.