Random Charge Fluctuations Research Articles

Single-hole pump in germanium

Single-charge pumps are the main candidates for quantum-based standards of the unit ampere because they can generate accurate and quantized electric currents. In order to approach the metrological requirements in terms of both accuracy and speed of operation, in the past decade there has been a focus on semiconductor-based devices. The use of a variety of semiconductor materials enables the universality of charge pump devices to be tested, a highly desirable demonstration for metrology, with GaAs and Si pumps at the forefront of these tests. Here, we show that pumping can be achieved in a yet unexplored semiconductor, i.e. germanium. We realise a single-hole pump with a tunable-barrier quantum dot electrostatically defined at a Ge/SiGe heterostructure interface. We observe quantized current plateaux by driving the system with a single sinusoidal drive up to a frequency of 100 MHz. The operation of the prototype was affected by accidental formation of multiple dots, probably due to disorder potential, and random charge fluctuations. We suggest straightforward refinements of the fabrication process to improve pump characteristics in future experiments.

Melting of strongly coupled, negatively charged, two‐dimensional dust cluster: The role of charge fluctuation amplitude

AbstractStructural and melting characteristics are investigated for negatively charged dust particles in the presence of a two‐dimensional electrostatic parabolic confinement potential. For a restricted number of dust particles that are subject to the permanent flow of electrons and ions, numerical simulation is conducted taking into account the random charge fluctuation. The amplitude of the charge fluctuation affects the ground‐state configuration and melting characteristics of a finite number of particles interacting through Coulomb potential. The melting temperature decreases when the amplitude of the charge fluctuation increases as a result of particles' strong repulsive interaction.

Random dust charge fluctuations in the near‐Enceladus plasma

AbstractStochastic dust charge fluctuations have been studied in the light of Cassini data on the near‐Enceladus plasma environment. Estimates of fluctuation time scales showed that this process can be of importance for the grains emanating from the icy moon. The analytical modeling predicts that in the dust‐loaded Enceladus plasma a majority of the grains acquires fluctuating negative charges, but there might appear a minority of positively charged particles. The probability of this effect mostly depends on the ratio of the dust/plasma number densities. Our findings appear to be supported by the available Cassini Plasma Spectrometer measurements of the charged grain distributions during E3 and E5 plume flybys. The theoretical results can also provide new insights into the intricate process of particle dynamics in the inner magnetosphere.

(Invited) Random Telegraph Noise: From a Device Physicist's Dream to a Designer's Nightmare

An overview is given on Random Telegraph Noise (RTN) in MOS-based devices. First, the basic properties and physics are briefly outlined, emphasizing the stochastic nature of its main parameters: the capture and emission time constant, while its amplitude is fixed and specific for each trap. Different techniques exist to characterize RTN in MOS devices, either by time or frequency domain measurements. A distinction can also be made between dynamic equilibrium methods like noise spectroscopy or transient measurements, based on a Deep-Level Transient Spectroscopy approach. While single-device based RTN measurements are still of high value, for modern circuit applications, techniques are being developed allowing a fast assessment of RTN in a large number of transistors. The scaling of CMOS technologies to the 32 nm and below raises the issue of variability induced either by random dopant fluctuations or in general, by random charge fluctuations, both spatially and in time. As will be seen, the presence of traps responsible for RTN brings about an additional source of variability which may become dominant in future memories. Finally, it will be shown that RTN is not only a fundamental component of 1/f noise but the same oxide traps are also largely responsible for the Bias Temperature Instability (BTI) in scaled MOSFETs. This leads to a self-consistent model for BTI and a stochastic approach towards the reliability prediction of deep submicron CMOS technologies.

Modeling the interaction between two dimensional strongly coupled confined dust clusters

Numerical simulations based on the Monte Carlo method are conducted to investigate ground-state configurations and phase transitions of strongly coupled dust particles. The interaction between negatively charged dust particles is modeled by three different potentials, namely, Coulomb, Yukawa, and logarithmic. The effect of random charge fluctuation is taken into account for a dominant charging process by particles collection and in the presence of two dimensional parabolic confinement potential. Structural arrangement and phase transition are found to be dependent on the potential interaction and the charge fluctuation. The changes in the melting temperature, when the charge fluctuation is taken into account, are particularly noticeable for systems with particles interacting through logarithmic potential.

Characterization of Charge Separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) Ion Source for Mass Spectrometry

An initial investigation into the effects of charge separation in the Array of Micromachined UltraSonic Electrospray (AMUSE) ion source is reported to gain understanding of ionization mechanisms and to improve analyte ionization efficiency and operation stability. In RF-only mode, AMUSE ejects, on average, an equal number of slightly positive and slightly negative charged droplets due to random charge fluctuations, providing inefficient analyte ionization. Charge separation at the nozzle orifice is achieved by the application of an external electric field. By bringing the counter electrode close to the nozzle array, strong electric fields can be applied at relatively low DC potentials. It has been demonstrated, through a number of electrode/electrical potential configurations, that increasing charge separation leads to improvement in signal abundance, signal-to-noise ratio, and signal stability.

Random charge fluctuation effect on strongly correlated dust particles confined in two dimensions

Random charge fluctuation effect is investigated for positively charged strongly coupled dust particles. The dust particles are moving in two dimensions and are confined by a parabolic potential. Using the Monte Carlo method, the effect of charge fluctuation is investigated for a finite number of particles interacting through a screened Yukawa potential. It is found that the charge fluctuation corresponds to an additional heating of the system giving rise to a change on the background configurations as well as on the melting characteristics.

Finite coulomb crystal formation

Dust particles immersed within a plasma environment, such as those found in planetary rings or comets, will acquire an electric charge. If the ratio of the inter-particle potential energy to average kinetic energy is large enough the particles will form either a “liquid” structure with short-range ordering or a crystalline structure with long-range ordering. Since their discovery in laboratory environments in 1994, such crystals have been the subject of a variety of experimental, theoretical and numerical investigations. Most numerical and theoretical investigations have examined infinite systems assuming periodic boundary conditions. Since experimentally observed crystals can be comprised of a few hundred particles, this often leads to discrepancies between predicted theoretical results and experimental data. In addition, recent studies have concentrated on the importance of random charge variations between individual dust particles, but very little on the importance of size variations between the grains. Such size variations naturally lead to inter-grain charge variations which can easily become more important than those due to random charge fluctuations (which are typically less than one percent). Although such size variations can be largely eliminated experimentally by introducing mono-dispersive particles, many laboratory systems and all astrophysical environments contain significant size distributions. This study utilizes a program to find the equilibrium positions of a dusty plasma system as well as a modified Barnes–Hut code to model the dynamic behavior of such systems. It is shown that in terms of inter-particle spacing and ordering, finite systems are significantly different than infinite ones, particularly for the most-highly ordered states.

Dust diffusion across a magnetic field due to random charge fluctuations

Dust particle diffusion across a magnetic field due to random charge fluctuations is reconsidered. Previously it was suggested that this mechanism could be one of the most effective processes which transport particles in the inner Jovian magnetosphere [G. E. Morfill, E. Grün, and T. V. Johnson, Planet Space Sci. 28, 1087 (1980)]. A general expression for the diffusion constant is derived using the stochastic equation of dust particle motion and known properties of random charge fluctuations. The dependence of the diffusion constant on magnetic-field strength and fluctuation amplitude is discussed. Numerical evaluation for conditions typical for the inner Jovian magnetosphere is presented.

Effect of Stochastic Grain Charge Fluctuation on the Kinetic Energy of the Particles in Dusty Plasma

Random charge fluctuations are always present in dusty plasmas due to the discrete nature of currents charging the dust particles. These fluctuations can be a reason of the heating of dust particle systems. In this paper we show by analytical evaluations and numerical simulation that charge fluctuations provide an effective source of energy and can heat the dust particles up to several eV, in conditions close to experimental ones.

Charge-fluctuation-induced heating of dust particles in a plasma.

Random charge fluctuations are always present in dusty plasmas due to the discrete nature of currents charging the dust particle. These fluctuations can be a reason for the heating of the dust particle system. Such unexpected heating leading to the melting of the dust crystals was observed recently in several experiments. In this paper we show by analytical evaluations and numerical simulation that charge fluctuations provide an effective source of energy and can heat the dust particles up to several eV, in conditions close to experimental ones.

Erratum: Dynamical properties of random charge fluctuations in a dusty plasma with different charging mechanisms [Phys. Rev. E59, 6017 (1999)

Erratum: Dynamical properties of random charge fluctuations in a dusty plasma with different charging mechanisms [Phys. Rev. E<b>59</b>, 6017 (1999)

Dynamical properties of random charge fluctuations in a dusty plasma with different charging mechanisms.

A dust particle in a plasma acquires electric charge by collecting electrons and ions, and sometimes by emitting electrons. The charging currents consist of discrete charges, causing the charge to fluctuate around an equilibrium value. We developed a model yielding a general expression for the charge fluctuations' temporal autocorrelation function. Both the magnitude and characteristic time of fluctuations can be obtained, knowing the specific form of charging currents. Numerical results are presented for different charging mechanisms, including charging by thermionic and photoelectric emission. It is shown that for all charging mechanisms the amplitude of fluctuations varies as DeltaZ = alpha square root [</Z/>], where <Z> is the equilibrium dust grain charge in units of electron charges.

Noise of junction devices.

The conduction and noise mechanisms and the relevant models are quite different and more complex for bipolar than for unipolar media and devices. A new general approach to p-n junction noise, which ascribes its origin to the charge fluctuations of the defect centers, is proposed. For the single defect the relaxation time, the Langevin noise sources, and the modulation of the generation-recombination (GR) current across the neighboring defects, are computed according to a previous model by means of the Shockley-Read-Hall theory, the Schottky theorem, and the Poisson equation. The interactions of the charge and current fluctuations of the single defect with the output short-circuit currents are then expressed by means of proper charge and current coupling coefficients. In their turn, these are computed in closed general form for a long junction, for both neutral and space-charge regions, by means of continuity and Poisson equations and using a new method which reduces the noise coupling problems from three to one dimension. In this way, a general expression of the noise spectrum of the junction, which holds good for any doping and bias voltage and for any frequency up to the reciprocal of the lifetime of the carrier, is obtained.It contains two contributions. One of them, for reverse bias and high frequency, leads to two-thirds shot noise whereas, in most other cases, it gives a full shot noise. The other excess term, deriving from the GR current modulation, for equal relaxation time \ensuremath{\tau} of the defects, produces a GR noise, whereas, for dispersed \ensuremath{\tau}'s, it yields a 1/${f}^{\ensuremath{\gamma}}$ noise with \ensuremath{\gamma}\ensuremath{\simeq}1 down to the lowest measurable frequency f. For zero-bias voltage, according to Nyquist's theorem, the two terms give the thermal noise. According to a recent model, even for the p-n junctions the 1/${f}^{\ensuremath{\gamma}}$ noise originates from the fact that the excess term is the superimposition of Lorentzian spectra proportional to ${\ensuremath{\tau}}^{1+\ensuremath{\nu}}$ with \ensuremath{\nu}&gt;0 so that a very small fraction of defects with dispersed \ensuremath{\tau} may be sufficient to generate itself. Finally, the new charge coupling coefficients and the continuity equations allow us to compute the fluctuation of the output current in the time domain due to the random burst charge fluctuations of each single-energy-level defect and, thus, to account for the burst noise, too. By accounting for all types of noise in the junction devices, the new unified approach appears to be a general and exhaustive model.

Dust in jupiter's magnetosphere: Physical processes

The physical processes acting on charged microscopic dust grains in the Jovian magnetosphere are examined. Such small dust grains are believed to be injected continuously into the magnetosphere via volcanic activity on Io. It is shown that electromagnetic forces dominate the dust particle dynamics, and that these particles behave adiabatically, in the sense that the guiding centre approximation to their motion applies. Based on this fact, the diffusion across field lines, caused by random charge fluctuations of the dust grains, can be determined. This diffusion is the major cross field transport mechanism and determines the dispersion of dust grains from Io throughout the inner Jovian magnetosphere. Other physical processes (radiation pressure drag, Coulomb drag, sputtering) are also examined regarding their importance for particle transport.