We generalize a simple model for superlattices to include the effect of differential capacitance. It is shown that the model always has a stable steady-state solution （SSS） if all differential capacitances are posit...We generalize a simple model for superlattices to include the effect of differential capacitance. It is shown that the model always has a stable steady-state solution （SSS） if all differential capacitances are positive. On the other hand, when negative differential capacitance is included, the model can have no stable SSS and be in a self-sustained current oscillation behavior. Therefore, we find a possible minimum toy model with both negative differential resistance and negative differential capacitance which can include the phenomena of both self-sustained current oscillation and I-V oscillation of stable SSSs.展开更多
Differential capacitance is derived based upon energy,charge or current considerations,and determined when it may go negative or positive.These alternative views of differential capacitances are analyzed,and the relat...Differential capacitance is derived based upon energy,charge or current considerations,and determined when it may go negative or positive.These alternative views of differential capacitances are analyzed,and the relationships between them are shown.Because of recent interest in obtaining negative capacitance for reducing the subthreshold voltage swing in field effect type of devices,using ferroelectric materials characterized by permittivity,these concepts are now of paramount interest to the research community.For completeness,differential capacitance is related to the static capacitance,and conditions when the differential capacitance may go negative in relation to the static capacitance are shown.展开更多
In this paper,it is shown that for stable,steady state operation of devices typical of microwave and millimeter wave electronics,no negative differential capacitance is possible with conventional thinking.However,it m...In this paper,it is shown that for stable,steady state operation of devices typical of microwave and millimeter wave electronics,no negative differential capacitance is possible with conventional thinking.However,it may be possible,with strain engineering of materials,to obtain some if not all elements of the differential capacitance tensor which are negative.Rigorous derivations are provided based upon analyzing the physics using thermodynamic phenomenological free energy.It should be emphasized that,even with strain engineering,and possible discovery of some negative capacitive elements,stable operation will not be obtained because the thermodynamics precludes it.展开更多
Based on micro-displacement measurement principles of the spherical differential capacitance sensor, the relationship between the capacitance variation and the micro-displacement of each pair of detecting electrodes f...Based on micro-displacement measurement principles of the spherical differential capacitance sensor, the relationship between the capacitance variation and the micro-displacement of each pair of detecting electrodes for the superconducting gyroscope （SCG） with eight detecting electrodes is analyzed. The model of the SCG rotor drift is established through dimensionless processing, linearization within micro-displacement and the least-square approach. Both the measurement scheme of the SCG rotor drift based on the model and its parameter relationship are presented. To guarantee the potential of the suspension rotor to be zero, the distributing scheme of four pairs of detecting electrodes is presented. The scheme can measure the magnitude and the direction of the rotor drift. The negative factors for affecting the measurement precision of .the SCG rotor drift and simulation results of the total effects are given. Simulation results show that the distributing capacitance of these differential capacitance sensors, the zero potential of the rotor and the model error are the major negative factors. The methods for eliminating those negative factors and the application range of the model are given. The model ensures the relationship between the output voltage and the rotor drift be linear.展开更多
In order to understand the electric interfacial behavior, mean field based electric double layer （EDL） theory has been continuously developed over the past 150 years. In this article, we briefly review the developme...In order to understand the electric interfacial behavior, mean field based electric double layer （EDL） theory has been continuously developed over the past 150 years. In this article, we briefly review the development of the EDL model, from the dimensionless Gouy-Chapman model to the symmetric Bikerman-Freise model, and finally toward size-asymmetric mean field theory models. We provide the general derivations within the framework of Helmholtz free energy of the lattice- gas model, and it can be seen that the above-mentioned models are consistent in the sense that the interconversi0n among them can be achieved by reducing the basic assumptions.展开更多
Ions in the bulk of solvent-free ionic liquids bind into ion pairs and clusters.The competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,...Ions in the bulk of solvent-free ionic liquids bind into ion pairs and clusters.The competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,determines the portion of free ions in the electrical double layer.We present the simplest possible mean-field theory to study this effect."Cracking"of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid.The predictions from the theory are verified and further explored by molecular dynamics simulations.A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape,despite the low concentration of free charge carriers,because the dielectric response reduces the threshold concentration for the bell-to camelshape transition.The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer.But in spite of the simplicity of the model,its findings demonstrate a clear physical effect:a preference to be a charged monopole rather than a dipole(or higher order multipole)in strong electric field.展开更多
Gold nanoparticles were immobilized onto the electrode surface by simple self-assembly technique. Interestingly, the ensembles of these nanoparticles exhibit quantized charging behaviors in aqueous solution. Possible ...Gold nanoparticles were immobilized onto the electrode surface by simple self-assembly technique. Interestingly, the ensembles of these nanoparticles exhibit quantized charging behaviors in aqueous solution. Possible mechanism for such behaviors was proposed.展开更多
Differential capacitive detection has been widely used in the displacement measurement of the proof mass of vibratory gyroscopes, but it did not achieve high resolutions in angle detection of rotational gyroscopes due...Differential capacitive detection has been widely used in the displacement measurement of the proof mass of vibratory gyroscopes, but it did not achieve high resolutions in angle detection of rotational gyroscopes due to restrictions in structure, theory, and interface circuitry. In this paper, a differential capacitive detection structure is presented to measure the tilt angle of the rotor of a novel rotational gyroscope. A mathematical model is built to study how the structure's capacitance changes with the rotor tilt angles. The relationship between differential capacitance and structural parameters is analyzed, and preliminarily optimized size parameters are adopted. A lownoise readout interface circuit is designed to convert differential capacitance changes to voltage signals. Rate table test results of the gyroscope show that the smallest resolvable tilt angle of the rotor is less than 0.47(0.00013?),and the nonlinearity of the angle detection structure is 0.33%, which can be further improved. The results indicate that the proposed detection structure and the circuitry are helpful for a high accuracy of the gyroscope.展开更多
基金The project supported by National Natural Science Foundation of China under Grant No. 10347101 and the Grant from Beijing Normal University
文摘We generalize a simple model for superlattices to include the effect of differential capacitance. It is shown that the model always has a stable steady-state solution （SSS） if all differential capacitances are positive. On the other hand, when negative differential capacitance is included, the model can have no stable SSS and be in a self-sustained current oscillation behavior. Therefore, we find a possible minimum toy model with both negative differential resistance and negative differential capacitance which can include the phenomena of both self-sustained current oscillation and I-V oscillation of stable SSSs.
文摘Differential capacitance is derived based upon energy,charge or current considerations,and determined when it may go negative or positive.These alternative views of differential capacitances are analyzed,and the relationships between them are shown.Because of recent interest in obtaining negative capacitance for reducing the subthreshold voltage swing in field effect type of devices,using ferroelectric materials characterized by permittivity,these concepts are now of paramount interest to the research community.For completeness,differential capacitance is related to the static capacitance,and conditions when the differential capacitance may go negative in relation to the static capacitance are shown.
文摘In this paper,it is shown that for stable,steady state operation of devices typical of microwave and millimeter wave electronics,no negative differential capacitance is possible with conventional thinking.However,it may be possible,with strain engineering of materials,to obtain some if not all elements of the differential capacitance tensor which are negative.Rigorous derivations are provided based upon analyzing the physics using thermodynamic phenomenological free energy.It should be emphasized that,even with strain engineering,and possible discovery of some negative capacitive elements,stable operation will not be obtained because the thermodynamics precludes it.
文摘Based on micro-displacement measurement principles of the spherical differential capacitance sensor, the relationship between the capacitance variation and the micro-displacement of each pair of detecting electrodes for the superconducting gyroscope （SCG） with eight detecting electrodes is analyzed. The model of the SCG rotor drift is established through dimensionless processing, linearization within micro-displacement and the least-square approach. Both the measurement scheme of the SCG rotor drift based on the model and its parameter relationship are presented. To guarantee the potential of the suspension rotor to be zero, the distributing scheme of four pairs of detecting electrodes is presented. The scheme can measure the magnitude and the direction of the rotor drift. The negative factors for affecting the measurement precision of .the SCG rotor drift and simulation results of the total effects are given. Simulation results show that the distributing capacitance of these differential capacitance sensors, the zero potential of the rotor and the model error are the major negative factors. The methods for eliminating those negative factors and the application range of the model are given. The model ensures the relationship between the output voltage and the rotor drift be linear.
基金supported by the National Natural Science Foundation of China(Grant Nos.21421001,21373118,and 21203100)the Natural Science Foundation of Tianjin,China(Grant No.13JCQNJC06700)+1 种基金the MOE Innovation Team of China(Grant No.IRT13022)NFFTBS(Grant No.J1103306)
文摘In order to understand the electric interfacial behavior, mean field based electric double layer （EDL） theory has been continuously developed over the past 150 years. In this article, we briefly review the development of the EDL model, from the dimensionless Gouy-Chapman model to the symmetric Bikerman-Freise model, and finally toward size-asymmetric mean field theory models. We provide the general derivations within the framework of Helmholtz free energy of the lattice- gas model, and it can be seen that the above-mentioned models are consistent in the sense that the interconversi0n among them can be achieved by reducing the basic assumptions.
基金funding support from the National Natural Science Foundation of China(51876072)financial support from National Natural Science Foundation of China(21802170)+2 种基金supported through a studentship of the Centre for Doctoral Training on Theory and Simulation of Materials at Imperial College London,funded by the EPSRC(EP/L015579/1)the funding from the Thomas Young Centre under grant number TYC-101funding from the Leverhulme Trust(Grant No.RPG2016-223)
文摘Ions in the bulk of solvent-free ionic liquids bind into ion pairs and clusters.The competition between the propensity of ions to stay in a bound state,and the reduction of the energy when unbinding in electric field,determines the portion of free ions in the electrical double layer.We present the simplest possible mean-field theory to study this effect."Cracking"of ion pairs into free ions in electric field is accompanied by the change of the dielectric response of the ionic liquid.The predictions from the theory are verified and further explored by molecular dynamics simulations.A particular finding of the theory is that the differential capacitance vs potential curve displays a bell shape,despite the low concentration of free charge carriers,because the dielectric response reduces the threshold concentration for the bell-to camelshape transition.The presented theory does not take into account overscreening and oscillating charge distributions in the electrical double layer.But in spite of the simplicity of the model,its findings demonstrate a clear physical effect:a preference to be a charged monopole rather than a dipole(or higher order multipole)in strong electric field.
文摘Gold nanoparticles were immobilized onto the electrode surface by simple self-assembly technique. Interestingly, the ensembles of these nanoparticles exhibit quantized charging behaviors in aqueous solution. Possible mechanism for such behaviors was proposed.
基金Project supported by the National Natural Basic Research Program(973)of China(No.2012CB934104)the National Natural Science Foundation of China(No.61071037)the Natural Science Foundation of Heilongjiang Province,China(No.F201418)
文摘Differential capacitive detection has been widely used in the displacement measurement of the proof mass of vibratory gyroscopes, but it did not achieve high resolutions in angle detection of rotational gyroscopes due to restrictions in structure, theory, and interface circuitry. In this paper, a differential capacitive detection structure is presented to measure the tilt angle of the rotor of a novel rotational gyroscope. A mathematical model is built to study how the structure's capacitance changes with the rotor tilt angles. The relationship between differential capacitance and structural parameters is analyzed, and preliminarily optimized size parameters are adopted. A lownoise readout interface circuit is designed to convert differential capacitance changes to voltage signals. Rate table test results of the gyroscope show that the smallest resolvable tilt angle of the rotor is less than 0.47(0.00013?),and the nonlinearity of the angle detection structure is 0.33%, which can be further improved. The results indicate that the proposed detection structure and the circuitry are helpful for a high accuracy of the gyroscope.
