Determination Of Surface Potential Research Articles

Compact analytical modeling of underlap gate stack graded channel junction accumulation mode junctionless FET in subthreshold regime

This paper presents the compact analytical model of underlap gate stack (GS) graded channel (GC) junction accumulation mode (JAM) junctionless (JL) FET. At first, a comparative analysis between the two different graded channel schemes and non-graded channel is performed based on ION, IOFF and ION/IOFF ratio. The scheme that yields the higher ION/IOFF ratio along with smaller IOFF, is adopted in the proposed JL FET for further analysis. The 2D analytical modeling of the GS-GC-JAM-JL FET deals with the determination of surface potential, threshold voltage, subthreshold drain current, DIBL and subthreshold swing. Results obtained from analytical model and simulations are compared and an excellent match is found. Thus the present paper establishes the outstanding ability of proposed underlap GS-GC-JAM-JL FET architecture to shield the short channel effects without sacrificing its performance, and therefore, proves it as a potential candidate for ultra-low power applications.

X‐ray Spectroscopic Determination of Electrostatic Potential and Material Composition for Spacecraft: Experimental Results

AbstractRemote surface potential determination for nearby objects in space is an enabling technology for a range of space mission concepts, from improved rendezvous capabilities to touchless debris remediation with the electrostatic tractor concept. One concept is to use a nearby servicing spacecraft which fires electrons at the target. These electrons generate bremsstrahlung X‐rays, and the resultant X‐ray spectrum can be used to determine the landing energy of the electrons. By knowing the initial energy of the electrons, such as those emitted from an electron gun, the relative potential of the target can be inferred. The use of electron‐induced X‐rays to determine the electrostatic potential of a surface has previously been investigated theoretically, but this work demonstrates it experimentally. Accuracy is found to correlate to the angle between the detector and the target, and investigation of this relationship is a topic of future work. The mean error in landing energy is found to be approximately 1%, and the mean error in estimated plate voltage is found to be within the uncertainty of the high voltage power supply. Material determination is successfully demonstrated, using characteristic X‐rays to identify elements that make up less than 0.5% by mass of the target sample. Several possible means of improving landing energy accuracy are discussed.

Nanoparticle Tracking of Adenovirus by Light Scattering and Fluorescence Detection.

The detailed characterization of biological nanoparticles is of paramount importance for various industrial sectors, as for production of viral therapeutics. More recently, technologies that allow real-time quantification with simultaneous sizing and determination of surface potentials of virus particles in solution have been developed. In this study, nanoparticle tracking analysis (NTA) was applied to determine the size and the zeta potential of human adenovirus type 5 (AdV5), one the most frequently used therapeutic/oncolytic agents and viral vectors. Virus aggregation was detected, and the kinetics of the dissolution of virus aggregates were studied in real time. In addition, advanced fluorescence detection of AdV5 was performed enabling the measurements in matrices and discrimination of viral subpopulations. It was shown that NTA is an efficient approach for investigating infectious viruses in a live viewing mode. Consequently, NTA provides a promising methodology for virus particle detection and analysis in real time beyond assays requiring nucleic acids or infectivity.

Influence of Sterilization and Preservation Procedures on the Integrity of Serum Protein-Coated Magnetic Nanoparticles.

Protein-coated magnetic nanoparticles are promising candidates for various medical applications. Prior to their application into a biological system, one has to guarantee that the particle dispersions are free from pathogens or any other microbiologic contamination. Furthermore, to find entrance into clinical routine, the nanoparticle dispersions have to be storable for several months. In this study, we tested several procedures for sterilization and preservation of nanoparticle containing liquids on their influence on the integrity of the protein coating on the surface of these particles. For this, samples were treated by freezing, autoclaving, lyophilization, and ultraviolet (UV) irradiation, and characterized by means of dynamic light scattering, determination of surface potential, and gel electrophoresis afterwards. We found that the UV sterilization followed by lyophilization under the addition of polyethylene glycol are the most promising procedures for the preparation of sterilized long-term durable protein-coated magnetic nanoparticles. Ongoing work is focused on the optimization of used protocols for UV sterilization and lyophilization for further improvement of the storage time.

Determination of surface potential of hollow fiber membranes by streaming potential method

Streaming potential method at tangential flow of solution has been proposed as a means of measuring the surface potential of hollow fiber membranes. Zeta potential and surface charge for polyacrylonitrile hollow fiber nanofiltration membranes have been measured. The measurements have been made on the membranes of different porosities obtained by partial drying of initially wet membranes. Porosity has been evaluted from the rate of pressure-driven filtration of a solution through membrane pores. An equation has been derived that allows for assessment of the effect of solution flow in the porous layer. It has been shown that more correct values of membrane surface potential can be calculated using this equation.

Open loop Kelvin probe force microscopy with single and multi-frequency excitation

Conventional Kelvin probe force microscopy (KPFM) relies on closed loop (CL) bias feedback for the determination of surface potential (SP). However, SP measured by CL-KPFM has been shown to be strongly influenced by the choice of measurement parameters due to non-electrostatic contributions to the input signal of the bias feedback loop. This often leads to systematic errors of several hundred mV and can also result in topographical crosstalk. Here, open loop (OL)-KPFM modes are investigated as a means of obtaining a quantitative, crosstalk free measurement of the SP of graphene grown on Cu foil, and are directly contrasted with CL-KPFM. OL-KPFM operation is demonstrated in both single and multi-frequency excitation regimes, yielding quantitative SP measurements. The SP difference between single and multilayer graphene structures using OL-KPFM was found to be 63 ± 11 mV, consistent with values previously reported by CL-KPFM. Furthermore, the same relative potential difference between Al2O3-coated graphene and Al2O3-coated Cu was observed using both CL and OL techniques. We observed an offset of 55 mV between absolute SP values obtained by OL and CL techniques, which is attributed to the influence of non-electrostatic contributions to the input of the bias feedback used in CL-KPFM.

Combined Determination of Specific Surface Area and Surface Charge Properties of Charged Particles from a Single Experiment

Specific surface area and surface charge properties such as surface potential, surface charge density, electrostatic field strength at surface, and surface charge number are important characteristics of charged particles in soil and the environment. Currently there is not a theory or method that could give a combined determination for those parameters from a single experiment. In this paper, an approach is described that employs cation exchange experiments to develop data that can be interpreted using newly a derived set of theoretically-based equations. First we give two modifications, respectively, for the nonlinear Poisson-Boltzmann equation and for the cation exchange equilibrium equation. Second, from the modified Poisson-Boltzmann equation, new equations for describing cation exchange equilibrium as considering the cationic hydration effect were obtained. Finally, the theory for the combined determination of the five surface properties through a single experiment of cation exchange equilibrium was established. In the experimental study, the three constant parameters in the theory have been calibrated through a standard sample, illite, and the calibrated variables can be directly applied to any other materials determination for a given electrolyte system. In addition, Na/Ca exchange equilibrium for three different soils were determined, and then the five surface properties were calculated. The application of the new theory showed that this new method could give reliable determination results of the five surface properties for both permanently and variably charged materials. For the specific surface area determination, the new method could be used in both swelling and nonswelling materials. For the surface potential determination, this method could give the surface potential values under different electrolyte composition and concentration conditions.

Accurate surface potential determination in Schottky diodes by the use of a correlated current and capacitance voltage measurements. Application to n-InP

Based on current voltage (I—Vg) and capacitance voltage (C—Vg) measurements, a reliable procedure is proposed to determine the effective surface potential Vd(Vg) in Schottky diodes. In the framework of thermionic emission, our analysis includes both the effect of the series resistance and the ideality factor, even voltage dependent. This technique is applied to n-type indium phosphide (n-InP) Schottky diodes with and without an interfacial layer and allows us to provide an interpretation of the observed peak on the C—Vg measurements. The study clearly shows that the depletion width and the flat band barrier height deduced from C—Vg, which are important parameters directly related to the surface potential in the semiconductor, should be estimated within our approach to obtain more reliable information.

Analytical solution of Poisson–Boltzmann equation for interacting plates of arbitrary potentials and same sign

Efficient calculation of electrostatic interactions in colloidal systems is becoming more important with the advent of such probing techniques as atomic force microscopy. Such practice requires solving the nonlinear Poisson–Boltzmann equation (PBE). Unfortunately, explicit analytical solutions are available only for the weakly charged surfaces. Analysis of arbitrarily charged surfaces is possible only through cumbersome numerical computations. A compact analytical solution of the one-dimensional PBE is presented for two plates interacting in symmetrical electrolytes. The plates can have arbitrary surface potentials at infinite separation as long they have the same sign. Such a condition covers a majority of the colloidal systems encountered. The solution leads to a simple relationship which permits determination of surface potentials, surface charge densities, and electrostatic pressures as a function of plate separation H for different charging scenarios. An analytical expression is also presented for the potential profile between the plates for a given separation. Comparison of these potential profiles with those obtained by numerical analysis shows the validity of the proposed solution.

Determination of Clay Surface Potential: A More Reliable Approach

Surface electrical potential is an important parameter in soil electrochemistry. Currently there are several methods that can be used to estimate the surface potential, but they all have their limitations. Thus a noninvasive, more reliable, and widely applicable method is needed. In this research, a new method for the determination of surface potential was developed. The new method not only provides a more reliable determination for the surface potential, but also can be widely applied to any charged materials under any conditions of pH, temperature, and electrolyte concentration. The new method was used to determine the surface potentials of 36 different montmorillonites. Results showed that the average surface potential obtained by the new method was 5.4 times higher than the average zeta potential from electrophoresis experiments. Under the same experimental conditions, the estimated swelling pressures based on the surface potentials from the new method matched the experimental data very well for the montmorillonite/aqueous solutions, while the predicted values based on the zeta potential deviated from the experimental data, indicating that the new approach provides a more reliable prediction of surface potential than the zeta potential approach.

Surface potential determination in planar lipid bilayers: A simplification of the conductance-ratio method

One of the methods available for the measurement of surface potentials of planar lipid bilayers uses the conductance ratio between a charged and a neutral bilayer doped with ionophores to calculate the surface potential of the charged bilayer. We have devised a simplification of that method which does not require the use of an electrically neutral bilayer as control. The conductance of the charged bilayer is measured before and after the addition of divalent cations (Ba 2+) to the bathing solution. Ba 2+ ions screen fixed surface charges, decreasing the surface potential. If the membrane is negatively charged the screening has the effect of decreasing the membrane conductance to cations. The resulting conductance ratio is used to calculate the surface potential change, which is fed into an iterative computer program. The program generates pairs of surface potential values and calculates the surface charge density for the two conditions. Since the surface charge density remains constant during this procedure, there is only one pair of surface potentials that satisfies the condition of constant charge density. Applying this method to experimental data from McLaughlin et al. [McLaughlin, S.G.A., Szabo, G. and Eisenman, G., Divalent ions and the surface potential of charged phospholipid membranes, J. Gen. Physiol., 58 (1971) 667–687.] we have found very similar results. We have also successfully used this method to determine the effect of palmitic acid on the surface potential of asolectin membranes.

Determination of surface potentials from the electrode potentials of a single-crystal electrode

Determination of surface potentials Ψ 0 at the metal oxide/aqueous solution interface from measured electrode potentials of a metal oxide single-crystal electrode (SCrE) is described. The proposed method is based on the surface complexation model and evaluates the surface potential at the isoelectric point, i.e., at pH iep. This value is used for calculation of Ψ 0 values from the measured electrode potentials. Both 1-p K and 2-p K models produced the same result so that the procedure does not depend on the assumed mechanism of the surface charging. It is proposed to determine the pristine point of zero charge pH eln and the isoelectric point pH iep, and use these data to set the scale of surface potentials. The value of pH eln can be obtained at a sufficiently low ionic strength where pH pzc coincides with pH iep. The method is demonstrated on the example of the anatase single-crystal electrode. From the shifts of pH iep and pH pzc with respect to the pristine point of zero charge pH eln it was concluded that Cl − ions exhibit higher affinity for association with positively charged surface groups than ClO − 4 ions. Also, preferential surface association of Na + cations compared to both anions was detected. The slopes of the Ψ 0 ( pH ) functions were found to be significantly lower in magnitude with respect to the Nernst equation, which is due to the high degree of counterion association at the surface caused by their relatively high concentration.

Intermittent Bias Application in Kelvin Probe Force Microscopy for Accurate Determination of Surface Potential

We propose an intermittent bias application method in Kelvin probe force microscopy (KFM) to suppress electrostatic force variation due to an oscillatory motion of a KFM tip. In this method, spiky biases, instead of the bias in a sinusoidal waveform, which is used in conventional KFM, are intermittently applied to generate electrostatic force at exact moments when the tip approaches the closest position to a sample surface. The observed potential distribution around self-assembled InAs quantum dots indicates that the intermittent bias application method improved the quality of the potential images and that the achieved spatial resolution was estimated to be better than 10 nm.

Sample-and-Hold Operation in Kelvin Probe Force Microscopy

To achieve a more accurate determination of surface potential in Kelvin probe force microscopy (KFM), we have proposed and demonstrated a sample-and-hold operation of KFM (SH-KFM), in which a sample-and-hold (S/H) circuit is inserted between an optical deflection sensor and a lock-in amplifier, to sample the deflection signal at a tapping frequency. Owing to the sampling operation, the cantilever bending due to the electrostatic force can be extracted at a desired phase in the tapping oscillation by intentional tuning of a time delay for sampling. We performed SH-KFM measurements on InAs quantum dots, and successfully observed a very clear site dependence of the potential with a large contrast. The results also indicated that the spatial resolution in the potential images was estimated to be better than 10 nm, and that the amplitude of an ac modulation bias in KFM could be reduced to 10 mVp–p without any remarkable degradation of the potential images.

An approach to the method for determination of surface potential on solid/liquid interface: theory

The electrochemical properties on solid particle surfaces in an aqueous system have found wide application in many fields. However, for some of them there are no reliable methods of determination. What is particularly worth mentioning is the surface potentials of solid particles. Though this is a most important property and a most basic parameter in colloid interface electrochemistry, no reliable method for its determination is available yet. In the present paper, based on the diffuse double-layer theory, mathematical relations are constructed between the average concentration of ions positively adsorbed in the diffuse double layer and the surface potential of solid particles, thus transforming the determination of surface potential of solid particles into that of the average concentration of ions in the diffuse double layer, and then by applying the standard relationships of Gouy–Chapman theory, the mathematical relations of the average concentration of ions in the diffuse double layer with surface charge density, electrical field strength at surface, and specific surface area of solid particles are constructed.

An approach to the method for determination of surface potential on solid/liquid interface: theory

The electrochemical properties on solid particle surfaces in an aqueous system have found wide application in many fields. However, for some of them there are no reliable methods of determination. What is particularly worth mentioning is the surface potentials of solid particles. Though this is a most important property and a most basic parameter in colloid interface electrochemistry, no reliable method for its determination is available yet. In the present paper, based on the diffuse double-layer theory, mathematical relations are constructed between the average concentration of ions positively adsorbed in the diffuse double layer and the surface potential of solid particles, thus transforming the determination of surface potential of solid particles into that of the average concentration of ions in the diffuse double layer, and then by applying the standard relationships of Gouy–Chapman theory, the mathematical relations of the average concentration of ions in the diffuse double layer with surface charge density, electrical field strength at surface, and specific surface area of solid particles are constructed.

Bulk generation lifetime studies in semiconductor structures with nonuniform distribution of electrically active defects in silicon

A method for investigation of bulk generation lifetime of minority carriers τ g and their profiles in semiconductor of electron devices has been developed. It is based on combined application of dynamic unsteady-state current–voltage characteristics (DUCVC) and high-frequency capacitance–voltage characteristics (HFCVC) of metal–insulator–semiconductor (MIS) structures.The main advantage of DUCVC over other methods consists in higher sensitivity to registration of generation processes, possibility of direct determination of surface potential in MIS structures and experimental simplicity. Combined application of two kinds of stated characteristics eliminates doping concentration N d from τ g analysis in case of constant N d value in semiconductor. Thus the accuracy of τ g determination increases. If the doping concentration is constant and known, τ g is obtained only from DUCVC analysis. Bulk generation lifetime profiles have been investigated in Si–SiO 2 structures after formation of an internal getter near subsurface region of silicon. Effect of hydrogen annealings on formation of defect-free zone in silicon was investigated. Nonuniform distribution of electrically active defects (EAD) in silicon has been revealed.

Correlating surface forces with surface reactivity of gypsum crystals by atomic force microscopy. Comparison with rheological properties of plaster

Atomic Force Microscopy (AFM) was used to image the surface reactivity as well as to characterize quantitatively the surface forces between two gypsum (CaSO4, 2H2O) crystals. Measurements on different crystal faces, which vary in morphology, structure, hydrophilicity, surface charge, were performed in both air and ionic solutions. In ionic solutions, varying the experimental parameters, the ionic nature and the concentration as well as the duration of the contact leads to the conclusion that the adhesion occurs whatever the orientation of faces. Nevertheless, the magnitude of the adhesion of a physical nature (Van der Waals and ionic correlation) depends on the surface charge density of each face while its increase is related to the growth of the contact area between the two crystals. In air, the systematic determination of surface potential with respect to the orientation of crystalline faces, the relative humidity and the duration and the area of contact between gypsum crystals suggests three types of physical forces: the Van der Waals forces, the electrostatic and capillary forces. In addition, the reactivity study displayed a reactive process of matter transfer, which is added to the surface forces to ensure the adhesion. Correlation between AFM results related to the micrometer scale and rheological measurements, performed on plaster (CaSO4, 0.5H2O) suspensions (pastes) and on macroscopic hardened plaster beams, is also demonstrated.

New Method for Determination of Surface Potential of Microscopic Particles by Second Harmonic Generation

A new noninvasive method for determining the surface electrostatic potential and surface charge density of microscopic particles using second harmonic generation (SHG) is described. The surface electrostatic properties of 1.05 μm polystyrene sulfate spheres in aqueous solution and that of 0.22 μm oil droplets in aqueous emulsions are obtained. Comparisons of the surface potentials obtained from SHG with the zeta potential obtained from electrophoresis are in excellent agreement with theoretical predictions.

Surface potential determination in irradiated MOS transistors combining current-voltage and charge pumping measurements

A method combining charge pumping and current-voltage measurements is presented for determining the surface potential versus gate voltage relationship in irradiated MOS transistors. This technique uses parameter optimization and simple numerical equations. It can be applied even for a high interface state density and for a non-uniform distribution in the silicon bandgap. This makes the method attractive for all studies concerning interface trap characterization or accurate modeling of MOS transistors in subthreshold regime. In this study, this new approach is applied to n-channel transistors irradiated up to 10 Mrad (SiO/sub 2/).