Surface Potential Characteristics Research Articles

Insights into the design principles of JF-ED-VTFET for biosensing application

In this research article, we have designed a junction-free electrostatically doped vertical tunnel field-effect transistor (JF-ED-VTEFT) for label-free biosensing applications. We incorporated a nano-cavity within the gate-oxide layer near the source end of the FET to enable the detection of biomolecules based on the principle of dielectric modulation and without the requirement of external labeling. The proposed biosensor is thoroughly analyzed, considering various aspects such as electric field, energy band, transfer characteristics, and sensitivity parameters including energy band diagram, ON-current, ION/IOFF ratio, electrical analysis, and surface potential characteristics. The investigation of sensitivity encompasses practical challenges, such as different filling factors and step-profiles resulting from steric hindrance. In addition, the performance of the biosensor is evaluated by analyzing the temperature and scaling fluctuation in the integrated nanocavities. Additionally, values of biomolecules that are close to standard have been taken to validate the performance and provide insight into the sensitivity of the biosensor for detecting and analyzing the molecules.

Vertical plane depth‐resolved surface potential and carrier separation characteristics in flexible CZTSSe solar cells with over 12% efficiency

AbstractCu2ZnSn(S,Se)4 (CZTSSe) solar cells have resource distribution and economic advantages. The main cause of their low efficiency is carrier loss resulting from recombination of photo‐generated electron and hole. To overcome this, it is important to understand their electron‐hole behavior characteristics. To determine the carrier separation characteristics, we measured the surface potential and the local current in terms of the absorber depth. The elemental variation in the intragrains (IGs) and at the grain boundaries (GBs) caused a band edge shift and bandgap (Eg) change. At the absorber surface and subsurface, an upward Ec and Ev band bending structure was observed at the GBs, and the carrier separation was improved. At the absorber center, both upward Ec and Ev and downward Ec‐upward Ev band bending structures were observed at the GBs, and the carrier separation was degraded. To improve the carrier separation and suppress carrier recombination, an upward Ec and Ev band bending structure at the GBs is desirable.

Molecular dipole regulated surface potential and ferroelectric characteristics in nanoconfined P(VDF-TrFE) architectures

Molecular dipole orientation is crucial to efficiently utilize the piezo- and ferroelectric polarization in polymers. Modern electronic applications of these polymer demand switching of dipoles with low voltage, which requires the dipole orientation to be perpendicular to the substrate (edge-on) rather than parallel (face-on). The 0D, 1D and 2D confinement of polymer architectures into nanoparticles, nanofibers, and thin films is a vital approach to control dipole orientation in ferroelectrics. Our findings show that for 1D (d33 ∼ 18 ± 2.2 pm/V) and 2D nanostructures (d33 ∼ 15 ± 1.5 pm/V) of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)), the molecular dipoles are edge-on, whereas for 0D, the dipoles are face-on, which would govern the ferroelectric and piezoelectric behaviour of these confined structures. The subsequent observation concludes that altering the dipole orientation allows precise modulation of surface potential and work function. The work functions of the 0D, 1D and 2D nanostructures are 4.56 ± 0.03 eV, 4.93 ± 0.51 eV and 4.68 ± 0.18 eV, respectively. The tunability of surface potential opens up the possibility of utilizing these nanostructures in single-material triboelectric series. Density functional theory (DFT)-based computations substantially support these experimental findings. This study provides a thorough understanding of the effect of molecule dipole orientation on piezo- and ferroelectric properties of P(VDF-TrFE) nanostructures.

Promoted osteogenesis by corona discharge poling induced in electroactive piezoelectric bioceramics

Rapid bone reconstruction and regeneration process is still a problem to be solved in the clinical orthopedic treatment. In vivo electric stimulation (ES) shows great promise in repair and regeneration of damaged tissues, and the piezoelectric characteristic of nature bone tissue make the electrical activity piezoelectricity biomaterials feasible and attractive in bone regeneration. Herein, we prepared a biocompatible lead-free piezoelectric ceramic K0.5Na0.5NbO3 (KNN) via solid phase sintering, which possesses wireless ES capability through corona discharge poling. Compared with the traditional piezoelectric ceramic polarization methods, corona discharge poling is a non-contact and biologically safer electrical poling method without electrodes or insulating liquids. The results of piezoelectricity, the water contact angle, the protein adsorption, surface potential characteristics of KNN ceramics and bone mesenchymal stem cells (BMSCs) behavior on ceramics, showed that after corona discharge poling the surface of KNN piezoelectric ceramic became hydrophilic, and positively charged, and the electrostatic effect formed by these charges promoted protein adsorption and BMSCs attachment and proliferation, which further promoted osteogenic differentiation. In conclusion, we used the corona discharge to polarize KNN piezoelectric ceramics and excellent biocompatibility of the ceramics was maintained after poling. Meanwhile, our work demonstrated the potential application of piezoelectric bio-ceramic materials in bone regeneration.

Morphology, Surface Potential, and Surface Groups Characteristics of the Montmorillonite/Bacteria Complex

Morphology, Surface Potential, and Surface Groups Characteristics of the Montmorillonite/Bacteria Complex

Study on the Force Model of Squeezed Branch Piles Based on Surface Potential Characteristics

Squeezed branch piles, which boast the advantages of great bearing capacity, small settlement, and good stability, are an important infrastructure in the foundation of buildings, and their safety state is related to the safety of the entire structure. As a non-destructive testing method, surface potential can be used to effectively evaluate the damaged state of a pile foundation without destroying its stability. On this basis, in this study, the characteristics of surface potential change during settlement and deformation of squeezed branch piles under graded loading were tested and analyzed with the aid of a self-made loading system of reaction beams and an LB-IV multi-channel potential data acquisition system. The results show that: Under graded loading, squeezed branch piles can produce surface potential signals whose intensity can well reflect the settlement and local failure characteristics of the pile foundation; The potential signals change in advance of load; and they fluctuate violently before local fracturing of squeezed branch piles. The unstable fluctuation of the potential signal can be regarded as a precursor to the fracturing of squeezed branch piles. The research results have positive theoretical significance and important application value for assessing the stability of both branch piles and their stress states on site and monitoring and forecasting the disaster of pile foundation instability.

Poisson-Schrödinger simulation and analytical modeling of inversion charge in FDSOI MOSFET down to 0 K – Towards compact modeling for cryo CMOS application

Poisson-Schrödinger (PS) simulations and an analytical charge model for a back biased FDSOI structure operated at deep cryogenic temperatures have been developed. PS simulations have been conducted down to 0 K, where metallic statistics applies, by replacing the F0 Fermi integral by a Heaviside function. Considering, as a first approximation, two separated channels for front and back interface, a set of implicit equations has been established based on a single subband scheme within the Airy approach, providing a good description of surface potential, inversion charge and capacitance characteristics of FDSOI structures operated at very low temperature and for various back biases and silicon thicknesses. This analytical charge model is a first step towards a compact model of FDSOI MOSFET for circuit design at cryogenic condition.

Enhancement of the molecular orientation of TPBi in coevaporated films of UGH‐2 host molecules

In this study, we investigated the spontaneous orientation polarization (SOP) in coevaporated films of polar and nonpolar molecules. SOP has been commonly observed in the evaporated films of organic light‐emitting diode materials, and it influences the device performances. However, the mechanism of the SOP formation is yet to be clarified. Herein, we characterized the molecular orientation of polar molecules of 1,3,5‐tris (1phenyl‐1H‐benzimidazol‐2‐yl) benzene (TPBi) in coevaporated films with nonpolar molecules of 1,4‐bis‐(triphenylsilyl) benzene (UGH‐2) or 4,4′‐bis (N‐carbazolyl)‐1,1′‐biphenyl (CBP). We measured the surface potential characteristics of the coevaporated films. We found that the molecular orientation of TPBi in both UGH‐2 and CBP hosts was enhanced, though the apparent enhancement factor was small in the UGH‐2 host. The enhancement of the molecular orientation is attributed to the reduction of the electrostatic interaction between polar molecules (TPBi), which deteriorates SOP as previously reported. In addition, our results suggest that the SOP of TPBi is robust even in the UGH‐2 host, in contrast to the random orientation of Ir complexes in the UGH‐2 host. Considering a polyhedral shape of Ir complexes, the robust SOP of TPBi in the host molecules with a weak van der Waals interaction, such as UGH‐2, is possibly due to its disk‐like molecular shape.

Amorphous cobalt borate nanosheets grown on MoS2 nanosheet for simultaneously improving the flame retardancy and mechanical properties of polyacrylonitrile composite fiber

It is a great challenge to achieve efficient flame retardance with no mechanical deterioration to polymers. In this study, novel sandwich-like cobalt borate nanosheets-molybdenum disulfide (CoBi-MoS2) hybrids are synthesized by a facile aqueous-phase synthesis approach at room-temperature, and employed as nanofillers for PAN fiber. The amorphous CoBi nanosheet with surface Lewis pairs and potential flame-retardant characteristics acts as interfacial compatibilizer and cooperative flame-retardant, enabling simultaneous improvement in both flame-retardant and mechanical properties of 2 wt% CoBi-MoS2/PAN composite fiber. Compared with pure PAN fiber, the peak heat release rate, peak smoke production rate and peak CO production rate of 2 wt% CoBi-MoS2/PAN composite fiber are decreased by 46.2%, 45.7% and 62.9%, respectively. The gaseous and condensed phase analysis reveals that the catalytic redox activity, cross-linked charring and physical barrier effect of the CoBi-MoS2 are responsible for the flame-retardant enhancements of PAN composite fiber. Simultaneously, the 2 wt% CoBi-MoS2/PAN composite fiber exhibits a 58.7% and 49.1% improvement in tensile strength and elongation at break compared to pure PAN fiber.

Influence of intermolecular interactions on the formation of spontaneous orientation polarization in organic semiconducting films

AbstractSpontaneous orientation polarization (SOP) has been frequently observed in the evaporated films of organic light‐emitting diode materials. Because SOP modifies the charge injection and the accumulation properties of the device, understanding and controlling SOP is crucial in optimizing the performance of the device. In this study, we investigated the dominant factors for SOP formation by focusing on intermolecular interactions. We examined the giant surface potential characteristics of coevaporated films incorporating 1,3,5‐tris(1‐phenyl‐1H‐benzimidazol‐2‐yl)benzene (TPBi) that is a typical polar molecule exhibiting SOP. In the coevaporated films of TPBi and nonpolar molecules such as 4,4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl and 4,4′,4″‐tris (carbazol‐9‐yl)triphenylamine, the orientation degree of the permanent dipole moment (PDM) of TPBi is significantly enhanced with diluted TPBi density, though the enhancement is weak on the film with N,N′‐bis(1‐naphthyl)‐N,N′‐diphenyl‐1,1′‐biphenyl‐4,4′‐diamine. The results indicate that the PDM interaction between polar molecules results as a negative factor for SOP formation. Furthermore, we found that SOP formation is suppressed by the surface treatment of the self‐assembled monolayer on the gold substrate, indicating a positive effect of the van der Waals interaction between the molecule and the substrate surface.

Analytical Modeling of Ion Sensitive Broken Gate TFET for pH Sensing Applications

In this letter, structural modification of a conventional tunnel field effect transistor (TFET) device is presented to act as an effective pH sensor. The change in hydrogen ion concentration in the aqueous solution is to be detected by the present broken gate (BG) TFET based pH sensor with its semiconducting material being modified as the electrolytic region. The chemical reactions at the interface of the gate dielectric and the electrolyte generate a surface charge density, making the device sensitive to pH. An analytical model of the BG TFET is developed here to capture the impact of pH variations on surface potential and drain current characteristics of the device. The sensitivity of the device is then investigated by extracting the threshold voltage shift as the pH values of the injected solution are varied. The accuracy of the analytical results is further corroborated by ATLAS simulator extracted data.

Targeting of immunosuppressive myeloid cells from glioblastoma patients by modulation of size and surface charge of lipid nanocapsules

BackgroundMyeloid derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs) are two of the major players involved in the inhibition of anti-tumor immune response in cancer patients, leading to poor prognosis. Selective targeting of myeloid cells has therefore become an attractive therapeutic strategy to relieve immunosuppression and, in this frame, we previously demonstrated that lipid nanocapsules (LNCs) loaded with lauroyl-modified gemcitabine efficiently target monocytic MDSCs in melanoma patients. In this study, we investigated the impact of the physico-chemical characteristics of LNCs, namely size and surface potential, towards immunosuppressive cell targeting. We exploited myeloid cells isolated from glioblastoma patients, which play a relevant role in the immunosuppression, to demonstrate that tailored nanosystems can target not only tumor cells but also tumor-promoting cells, thus constituting an efficient system that could be used to inhibit their function.ResultsThe incorporation of different LNC formulations with a size of 100 nm, carrying overall positive, neutral or negative charge, was evaluated on leukocytes and tumor-infiltrating cells freshly isolated from glioblastoma patients. We observed that the maximum LNC uptake was obtained in monocytes with neutral 100 nm LNCs, while positively charged 100 nm LNCs were more effective on macrophages and tumor cells, maintaining at low level the incorporation by T cells. The mechanism of uptake was elucidated, demonstrating that LNCs are incorporated mainly by caveolae-mediated endocytosis.ConclusionsWe demonstrated that LNCs can be directed towards immunosuppressive cells by simply modulating their size and charge thus providing a novel approach to exploit nanosystems for anticancer treatment in the frame of immunotherapy.

Performance Assessment of a Cavity on Source ChargePlasmaTFET-based Biosensor

The promising candidate for designing a highly sensitive biosensor is the tunneling field effect transistor (TFET). In this work, for the first time the performance analysis of a cavity on source charge plasma tunneling field effect transistor (CS-CPTFET) based lable-free biosensor has been proposed. To design the device,charge plasma concept is adapted, where suitable metal workfunctions have been used to create the source and drain regions. The charge plasma technique reduces random dopant fluctuation, thermal budget and steps required for the fabrication. The significant advantage of the proposed device includes the creation of abrupt doping profile at the tunneling junction (source-channel).The achievement of abrupt doping profile at the tunneling junction is responsible for the enhanced sensitivity and suppression of negative conduction (ambipolar) since the cavity is created in the source oxide region of CS-CPTFET biosensor. The response of the proposed biosensor for various biomolecules has been analyzed in terms of band energy variation, electric field, surface potential and transfer characteristics by using Silvaco ATLAS device simulator. Various biomolecules such as uricase (k = 1.54), Glucose oxidase (k = 3.46), APTES (k = 3.57), bacteriophage T7 (k = 6.3), keratin (k = 8) and gelatin (k = 12) have been considered for examining the performance of proposed biosensor.

Experimental study on characteristics of surface potential and current induced by stress on coal mine sandstone roof

Rocks generate voltage and current when subjected to load. Hence, the study of their characteristics is critical to the prevention and management of mine dynamic disasters and their secondary impacts. To investigate the characteristics of surface potential and current induced by stress on coal mine sandstone roof, an experimental scheme for determining the mechanical–electrical characteristics of rocks is constructed. The aforementioned system tests the evolution rules of current and voltage generated by the coal mine sandstone roof at different loading rates; the formation mechanism and coupling rules with mechanical properties of sandstone are also analysed. Experimental results show that although loading rates may differ, the variations of pressure stimulated current (PSC) and pressure stimulated voltage (PSV) curves are similar. Throughout the loading process, the PSC is divided into three stages: rapid growth, slow growth, and peak; on the other hand, the PSV curve exhibits a ‘double peak’ characteristic. The loading rate changes the current and voltage growth rates and peak values. When combined with mechanical properties, it can be observed that the PSC is related to the effective elastic modulus, whereas the PSV is related to micro-crack and macro-crack events in rocks. The current and voltage generated by the coal mine sandstone roof subjected to load are consistent with stress. The mechanical–electrical properties of sandstone indicate that the change processes in the PSC and PSV result from the coupling effects of various mechanisms. In the compaction stage, these are mainly caused by the piezoelectric effect of sandstone. In the elastic–plastic deformation stage, they are primarily generated by the electric dipoles formed by micro-cracks. In the sandstone fracture deformation stage, the change processes are mainly caused by the crack tip discharge. This study provide an experimental basis and practical results that reflect the microscale process and electrical precursors of sandstone fracturing.

The Performance of Composite Nanoparticles Based on Fe3O4@SiO2/PLGA/PFOB in Magnetic Resonance Imaging and Photoacoustic Imaging

Polylactic acid glycolic acid (PLGA), a polymer material, is used as a shell and perfluorooctane (PFOB) as the core. Fe3O4@SiO2 nanoparticles are distributed in the shell to prepare a magnetic phase change multifunctional nano emulsion contrast agent (Fe3O4@SiO2/PLGA/PFOB). The ultrasound, magnetic resonance imaging and CT imaging effects of the contrast agent on normal rat liver parenchyma are investigated. Methods: Single emulsification method is used to prepare Fe3O4@SiO2-loaded polymer Fe3O4@SiO2/PLGA/PFOB nanoparticles encapsulated with PLGA. In addition, polymer Fe3O4@SiO2/PLGA nanoparticles loaded with Fe3O4@SiO2 nanoparticles, PLGA@PFOB nanoparticles coated with PLGA and blank PLGA nanoparticles are prepared as experimental control group. Its surface morphology, internal structure, particle size, potential and other general characteristics are tested. RAW264.7 mouse mononuclear macrophages are cultured in vitro. Prussian blue staining is used to observe macrophage phagocytosis after Fe3O4@SiO2/PLGA/PFOB contrast agent is added to incubate for 3 hours. MTT method is used to detect the effect of contrast agent on cell activity. The macrophage suspension engulfed with Fe3O4-PFOB is examined by ultrasound, magnetic resonance and CT. The results showed that Fe3O4@SiO2/PLGA/PFOB is brown emulsion after being dissolved in double distilled water. Under the light microscope and scanning electron microscope, Fe3O4@SiO2/PLGA/PFOB is spherical, with regular shape, uniform size, good dispersity and smooth surface. Macrophages are dependent on the phagocytosis of the contrast medium without affecting the activity of macrophages. Moreover, in vitro imaging experiments, compared with the control group, macrophages phagocytized by Fe3O4@SiO2/PLGA/PFOB have obvious enhancement effects in ultrasound, magnetic resonance and CT imaging. In conclusion, Fe3O4@SiO2/PLGA/PFOB has good stability in vivo, can be engulfed by liver macrophages, and can enhance ultrasound, magnetic resonance and CT imaging of liver parenchyma. It is a safe and effective multifunctional ultrasound contrast agent.

Understanding the influence of nano micro filler on electrical and mechanical behaviour of epoxy nanocomposites

The study of epoxy nano micro composites clearly indicates that the material has better dielectric properties with a good discharge resistance and less surface charge accumulation on its surface. The impact of high-frequency AC voltage and the percentage of ripple content in DC voltage on corona inception caused by water droplets was analyzed. Under a high frequency, the variation in the shape of the water droplet is the same as that under 50 Hz AC voltage. The UHF signal radiated due to water droplet initiated discharges have signal bandwidth in the range of 300 MHz-3 GHz. The influence of corona discharge on surface properties of the material, its variation to contact angle and water droplet initiated corona activity under AC voltage was analyzed. The surface potential characteristics were altered with corona-aged specimen. The impact of an ion-trapping particle on nanocomposites clearly exhibits its characteristics through surface potential studies. Water diffusion into the insulating materials varies with the type of filler material. The temperatures measured during arcing, analyzed through laser-induced breakdown spectroscopy (LIBS), were correlated with the hardness of the material. In addition, the mechanical properties, especially storage modulus and tan δ, were analyzed through dynamic mechanical analysis (DMA) studies.

Experimental study on variation laws of coal surface potential during gas adsorption

ABSTRACT In this study, we designed an experimental system of surface potential during coal adsorption of gas to examine the characteristics of surface potential in this process. The results suggested that surface potential was generated in this process and that it was enhanced with the passage of time. In adsorption cycles, the higher the pressure, the greater the surface potential signals, and they increase exponentially. Thereby, research on surface potential during gas adsorption on coal holds great theoretical significance for understanding the physical properties of coal.

Comprehensive Evaluation of Surface Potential Characteristics on Mesenchymal Stem Cells' Osteogenic Differentiation.

The surface electric potential of biomaterials has been extensively proven to play a critical role in stem cells' fate. However, there are ambiguous reports on the relation of stem cells' osteogenic capacity to surface potential characteristics (potential polarity and intensity). To address this, we adopted a surface with a wide potential range and both positive/negative polarity in a comprehensive view to get insight into surface potential-regulating cellular osteogenic differentiation. Tb xDy1- xFe2 alloy/poly(vinylidene fluoride-trifluoroethylene) magnetoelectric films were prepared, and the film could provide controllable surface potential characteristics with positive or negative polarity and potential (ϕME) intensity variation from 0 to ±120 mV as well as keep the surface chemical composition and microstructure unchanged. Cell culture results showed that osteogenic differentiation of mesenchymal stem cells on both positive and negative potential films was obviously upregulated when the /ϕME/ intensities were set from 0-55 mV. Differently, the highest upregulated osteogenic differentiation on the positive potential films corresponded to the /ϕME/ intensity from 35-55 mV and was better than that on the negative potential films whereas the highest on the negative potential films corresponded to the /ϕME/ intensity from 0-35 mV and was better than that on the positive potential films. This fact could illustrate why previous reports appeared ambiguously; i.e., the comparative result in osteogenic differentiation between the positive and negative potential films strongly depends on the selection of surface potential intensity. On the basis of assaying of the exposed functional sites (RGD and PHSRN) of the adsorbed fibronectin (FN) and the expression of cellular integrin α5 and β1 subunits, the difference in the behavior between the positive and negative potential films was attributed to the distinct conformation of adsorbed fibronectin (FN) and the opposite changing trend with /ϕME/ for the two films, which triggers the osteogenesis-related FAK/ERK signaling pathway to a different extent. This study could provide new cognition for the in-depth understanding of the regulation mechanism underlying surface potential characteristics in cell behaviors.

Surface Potential and Breakdown Characteristics of Epoxy/AlN Nanocomposites Under DC and Pulse Voltages

In dc high-temperature superconducting fault-current-limiter (HTSFCL) operation, epoxy resin used as the current lead insulation withstands dc voltage. In the case of lightning stroke or line fault, HTSFCL needs to withstand the additional pulse voltage, which is several times greater than that of the dc voltage, and the polarity may be different from that of the dc voltage. It intensifies the electric field distortion, induces partial discharge, and causes insulation failure. To improve the insulation properties of the current lead, the epoxy/aluminum nitride (AlN) nanocomposites with the filler content of AIN nanoparticles of 0, 1, 3, and 5 wt% were prepared. The trap distribution of the sample was acquired to clarify the effects of AlN content on the surface potential behaviors. The results show that the amplitude and the polarity of the pulse voltage can affect the surface charge accumulation of the sample under dc voltage. Moreover, the addition of AlN nanoparticles improves the breakdown voltage of the sample in LN 2 under dc and pulse voltages.

Low-temperature oxygen plasma treatment of single-layer molybdenum disulfide

Two-dimensional (2D) molybdenum disulfide (MoS2) is considered a promising candidate for next-generation electronic devices because of its non-zero band-gap, mechanical flexibility, and optical transparency. In this study, the structural, mechanical, and surface potential characteristics of single-layer MoS2 films subjected to oxygen plasma treatment were investigated. Comparison of the Raman spectra of single-layer MoS2 films before and after plasma treatment revealed that plasma treatment caused mechanical stripping. The difference between and A1g peaks and the position of the longitudinal acoustic mode changed considerably following oxygen plasma treatment. Atomic force microscopy was used to explore the changes of the structure, mechanical behavior, and surface potential of the MoS2 films induced by plasma treatment. Root mean square values were used to analyze the changes of surface roughness, adhesion, and surface potential of the MoS2 films induced by oxygen plasma treatment. The root mean square roughness of the films first increased and then decreased with increasing plasma treatment duration. The defect content of the MoS2 films was increased by oxygen plasma treatment and the surface potential decreased considerably. These finding could be important for producing two-dimensional dichalcogenide-based electrical and optoelectronic devices.