Electron Content Gradients Research Articles

TiO2 nanocrystalline layer as a bridge linking TiO2 sub-microspheres layer and substrates for high-efficiency dye-sensitized solar cells

TiO2 sub-microspheres possess high surface area and superior light scattering effect which contributes to the high photocurrent density (Jsc) and power conversion efficiency (η) of dye-sensitized solar cells (DSSCs). However, the poor interconnection between the TiO2 sub-microspheres with substrates (N0S4) restricts the electron transport and charge collection. In order to resolve this drawback, we adopted a nanocrystalline monolayer as bridges to contact between the sub-microspheres and substrates (N1S3). The improved contact provides more direct transport channels and increases the increased electron concentration gradient from the top electrode to the bottom electrode, which accelerates the electron transport and charge collection. The combined effects of the faster electron transport rate, less surface states and higher collection efficiency for the N1S3 based DSSC contribute to the higher Jsc and η compared to the N0S4 based DSSC. While the photoelectrodes of N2S2 and N3S1 are too thick of nanocrystalline layer to improve the performance of DSSCs due to the decreased dye loading, reduced light scattering ability and increased crystal boundaries. As a result, a higher η of 10.34% is achieved by introducing the nanocrystalline layer, whereas, only 9.17% is obtained for the photoelectrode without this bridge.

Ionospheric response to the extreme solar burst of October 28, 2003

Using GPS and GLONASS navigation systems, instantaneous observations of solar burst effects on the Earth’s ionosphere are made. These observations are carried out for both Northern and Southern hemispheres, including the ionosphere at polar and equatorial latitudes. It is shown that the rate of total electron content (TEC) change is agrees well with the time profiles of solar bursts. An experimental dependence of the electron content gradient on the elevation angle is obtained.

Spectra of electron oscillations in magnetoplasmadynamic thruster

The intensity and spectra of electron oscillations in magnetoplasmadynamic (MPD) thruster have been experimentally studied. Oscillatory regimes corresponding to various relations between the relative gradients of magnetic field, electron concentration, and residual gas pressure in the vacuum chamber of the experimental setup have been determined. Relationship between the regimes of excitation of electron oscillations, the formation of an azimuthal current, and a change in the plasma flow potential is revealed. Model notions about the instability of plasma flow on low- and high-frequency branches of electron oscillations are developed.

Self-Assembly of Cuprous Oxide Micro/Nanostructures by Photo-Reduction Method

This study used a photo-reduction method to investigate cuprous oxide (Cu2O) self-assembled micro/nanostructures, and design a test specimen with an electron concentration gradient distribution. It also observed the Cu2O reduction of the self-assembled structure with respect to electron density. SEM analysis was adopted to analyze the growth mechanism and growth model. The results showed that, its structure size increased with photo-reduction time, and as the reduction solution concentration increased, its structure crystallinity declined. The basic unit of a self-assembled microstructure was Cu2O at a diameter of 10~15nm, then these particles conglomerate in self-assembly to form various kinds of Cu2O micro/nanostructures with respect to reduction electron density, and primarily presented in the form of a cone or cube. In the process of continuous self-assembly, there were many micro-defects under the perfect crystal surface. Considering the growth rate, the final growth surface of the structure was (111) or (100).

Transformation of acoustic waves in upper atmosphere

The transformation of acoustic waves into electromagnetic oscillations in the plasma of the upper atmosphere is analyzed. It is demonstrated that acoustic oscillations in ionosphere in the presence of the gradients of gas temperature and electron concentration lead to plasma vortices that provide the generation of electromagnetic waves.

Adaptation of the average monthly ionospheric model to current conditions using the data on maximum usable frequencies at two-hop reference radio links

The accuracy in determining the maximum usable frequencies (MUF) of reference radio links has been estimated. A method for using the data on MUF, obtained at two-hop reference radio links, in order to specify the horizontal gradients of electron concentration in the ionosphere has been proposed. The results of the observations at a system of two reference radio links are used to assess the efficiency of such a specification. It has been indicated that the developed method makes it possible to specify the values of the ionospheric critical frequency simultaneously in two radio link regions. The application of two-hop radio links together with one-hop lines substantially broadens the number of reference radio stations that can be used to adapt the parameters of the average monthly ionospheric model to the current conditions.

Space Weather and the Global Positioning System

Space Weather and the Global Positioning System

Variations in the midlatitude and equatorial ionosphere during the October 2003 magnetic storm

The October 2003 geomagnetic storm (often called the Halloween storm) was one of the largest storms (as measured by Dst) yet recorded. The storm‐induced synoptic‐scale changes in the ionosphere's plasma content and density can be viewed through space weather maps created by objective analysis algorithms. For this study, these maps, which specify the electron density in altitude, latitude, and longitude, are created by the ionospheric data assimilation three dimensional (IDA3D), a three‐dimensional variation algorithm of the ionospheric electron density. These maps, representing the average conditions in the ionosphere over a 15 min sampling time, show how dramatically the ionosphere changed during the Halloween storm. Following the southward turning of the interplanetary magnetic field, the dayside electron content is significantly reduced in the equatorial ionosphere between ±18° magnetic latitude and is enhanced poleward of this latitude. This is the expected behavior when the equatorial fountain is enhanced by a strong penetration electric field. In addition, the electron content is significantly increased in the dayside midlatitude ionosphere, which corresponds to a storm‐enhanced density (SED) plume. Above 40° magnetic latitude, the dayside plasma content is significantly reduced in the regions adjacent to the SED structure, which enhances the electron content gradient. Electron density maps in the altitude–magnetic latitude plane show an increase in the topside electron densities within an SED plume.

Ionospheric electron concentration imaging using GPS over the USA during the storm of July 2000

A new technique for ionospheric imaging is demonstrated during a severe geomagnetic storm of 15th July 2000. The three‐dimensional time‐dependent imaging algorithm is applied to multi‐directional ground‐based GPS data and yields spatial maps of electron concentration. This technique is demonstrated by showing a series of images of the mid‐latitude ionosphere over the USA during the storm of July 2000. A strong uplift in the height of the F‐layer is observed after 20 UT on 15th July, followed by a severe latitudinal electron concentration gradient. Independent verification of the images is provided by the ionosondes and incoherent scatter radar data. The GPS images reveal the large‐scale dynamics of the ionosphere during the disturbed conditions and show the potential of geophysical imaging for storm‐time ionospheric studies.

Dynasonde observations of electron concentration gradients above Troms ø

The Dynasonde is a digital ionosonde which measures the amplitude and phase of radio echoes reflected from the ionosphere. In addition to the frequency and virtual range of each echo, one parameter of particular interest is the direction of arrival which allows horizontal structures in the ionosphere to be studied. Under suitable ionospheric conditions, namely where structures or strong gradients are present in the electron concentration, echoes may be observed out to horizontal distances of several hundred kilometres. We describe an automated method for latitudinally mapping these gradients in F-region peak electron concentration using the Dynasonde. Good agreement is found when the results are compared with a co-located incoherent scatter radar lending credibility to observations of electron concentration gradients by a Dynasonde alone. This is significant for sites where no supporting instruments exist. Although Dynasondes account for only a small fraction of digital ionosondes in use today, the techniques described in this paper could be extended to other digital ionosondes with similar directional capabilities. The combination of routine soundings, and the worldwide distribution of such instruments, would provide a powerful means to monitor ionospheric structures on a regular basis.

Probing the depletion region of a two-dimensional electron system in high magnetic fields

To investigate a two-dimensional electron system (2DES) in high magnetic fields and at temperatures below 0.1 K, a metal single-electron transistor (SET) was fabricated as a local electrometer on top of a GaAs/AlGaAs heterostructure containing the 2DES. Probing the bulk of the 2DES, the chemical potential variations of the 2DES versus magnetic field were directly measured and relaxation phenomena on a long time scale were observed within quantum Hall plateau regimes of low Landau-level filling factors. To probe the depletion region of the 2DES, a gate electrode was used to redefine the 2DES edge close to the SET by electrostatical depletion. For a 5 μm distance of the gate electrode's edge to the SET island, the electron concentration under the SET island is only homogeneously reduced by few percent due to the negative voltage applied to the gate electrode. But for a 0.9 μm distance, the SET detects a steep electron concentration gradient, indicating that with increasing the depletion voltage, the 2DES edge is indeed shifted towards the SET. By this approach we mapped out the screening properties and the electrostatic potential variations within the depletion region of the 2DES for magnetic fields corresponding to Landau-level filling factors between ν=1 and ν=4. Compressible and incompressible strips are resolved.

The effect of the mid-latitude ionospheric trough on whistler mode ducting during magnetic storms

Whistler-mode signals observed at Faraday, Antarctica (65° S, 64° W, Λ=50.8°) show anomalous changes in group delay and Doppler shift with time during the main phase of intense geomagnetic activity. These changes are interpreted as the effect of refracting signals into and out of ducts near L=2.5 by electron concentration gradients associated with edges of the mid-latitude ionospheric trough. The refraction region is observed to propagate equatorwards at velocities in the range 20–85 ms −1 during periods of high geomagnetic activity ( K p ≥ 5), which is in good agreement with typical trough velocities. Model estimates of the time that the trough edges come into view from Faraday show a good correlation with the observed start times of the anomalous features. Whistler-mode signals observed at Dunedin, New Zealand (46° S, 171° E, Λ=52.5°) that have propagated at an average L-shell of 2.2 (Λ=47.6°) do not show such trough-related changes in group delay. These observations are consistent with a lower occurrence of the trough at lower invariant latitudes.

The sunspot cycle and “auroral” F layer irregularities

The use of the word “aurora” for many different observations at high latitudes has limited the concepts involved; this is particularly true for F region irregularities. Observations setting the position of the auroral oval (Starkov and Fel'dshtein, 1970) were made using primarily the 555.7‐nm green line, which is emitted predominantly at E layer heights. These observations have shown that the change in position of the auroral oval for low values of Kp as a function of sunspot cycle is of the order of 1° to 2° between sunspot maximum and sunspot minimum. However, irregularities in the F region show much larger solar cycle variations in the locations of the equatorward boundary, typically 10°. A review of scintillation data indicates that at a given auroral latitude, the scintillation activity increases with sunspot number. In addition, for a constant scintillation intensity, the equatorward boundary moves to lower latitudes as sunspot maximum is approached. We review existing spread F studies and show that for quiet geomagnetic conditions, there is lower occurrence during years of low sunspot numbers than during years of high sunspot numbers. However, the spread F index, related to Δ ƒ/ƒ0F2, is higher during years of low sunspot number than during years of high sunspot number. We demonstrate that this apparent dichotomy can be reconciled by using a new method of normalizing the spread F index by the maximum electron concentration of the F layer. We briefly discuss the possible explanations for the observed solar cycle variations of irregularity occurrence in terms of the absolute values and gradients of electron concentration and the E region conductivity.

Transionospheric radiosounding

This paper presents a method for making diagnostics of the ionosphere-transionospheric radiosounding (TIS). History, equipment, methodology, and new scientific results are described. The use of this type of sounding for applied purposes is considered: for N( h) profile determination, for calculation of MUF for radio communication, for estimation of horizontal gradients of electron concentration, and for measurement of cut-off frequency of transionospheric radio propagation. It is stressed that transionospheric sounding is the final link of the radiosounding system. In combination with ground-based and topside soundings, the TIS method forms a closed system of ionospheric radiosounding diagnostics.

Simultaneous VHF and UHF radar observations of the mesosphere at Arecibo during a solar flare: A check on the gradient‐mixing hypothesis

Simultaneous UHF and VHF radar observations of the 60–90 km mesosphere at Arecibo were made during the occurrence of a January 1981 type 4 solar X ray flare. The observations involved use of the UHF incoherent scatter technique at 430 MHz and the VHF turbulent scatter technique at 46.8 MHz. These observations provided a unique opportunity to test the basic premises of the turbulent gradient mixing hypothesis. UHF measurements show that enhanced electron concentration gradients were established with the flare onset. Two turbulent layers were observed with the 46.8 MHz radar before, during and after the flare. Enhanced scattering from both layers peaked within 3–6 min of the beginning of the flare. Only a slight variability in Doppler width of VHF returns from both layers was observed over the pre‐ to post flare period indicating that the power dissipation associated with turbulence remained essentially constant. We find that almost all the enhancement of VHF signals can be attributed to the flare induced increase in electron concentration gradients. We also conclude that the observed delay of 3–6 min between flare onset and the peak of VHF returns is related to an eddy overturning time required for mixing‐in of gradients to the Bragg scale.

The theory of radio windows in planetary magnetospheres

The theory of radio windows given in two previous papers for a stratified cold plasma is extended to apply in a warm plasma. It is used to investigate one suggested mechanism for the production of non-thermal continuum radiation in magnetospheric cavities. The source is a plasma wave that enters a region where there is a gradient of electron concentration and there undergoes partial linear mode conversion to give ordinary and extraordinary electromagnetic waves and a reflected plasma wave. This theory is needed particularly for the plasmapause and magnetopause where the concentration gradients may be large. It is therefore necessary to use a full-wave integration of the governing differential equations. These are derived for a warm plasma. When they are integrated, the problem of numerical swamping is severe and is dealt with by a special method. Some typical results are presented and discussed.

The theory of radio windows in the ionosphere and magnetosphere—II

A theory of radio windows in a previous paper was based on the approximations of ray theory and does not apply for a plasma in which the gradient of electron concentration is too great. Observations have shown that large gradients are often of interest and to deal with this a theory is given that uses a full wave integration of the governing differential equations. It applies only in a cold plasma. The source of the waves is a Z mode wave that arises from a plasma wave. After partial penetration of the window it gives two emergent waves, ordinary and extraordinary, whose amplitudes are calculated. The gradient of electron concentration and the effective electron collision frequency are assumed to be independent of the coordinates. At one level the refractive index for the Z mode is very large. To deal with this a standard method is used in which part of the path of integration is a contour in complex space. A possible extension to deal with still greater gradients is briefly reviewed.

Doppler Shift of Radio Signals Transmitted between Orbiting Satellites

A general expression, applicable at VHF and above, is derived for the Doppler shift of radio signals transmitted between two satellites embedded in the ionosphere. The Doppler shift is made up of several contributions which depend on (a) the rate of change of the free space path between the satellites, (b) the components, perpendicular to the line of sight between the satellites, of both the mean velocity of the satellites and the electron concentration gradients, (c) the moment of the perpendicular electron concentration gradients and the deviations from the mean of the individual satellite perpendicular velocities, (d) the velocity components along the line of sight between the satellites, and the electron concentration values at each satellite, and (e) changes occurring in the ionosphere with time.

On the theory of Debye averaging in the C-V profiling of semiconductors

We discuss the nature of the Debye averaging that takes place in the C-V profiling of highly non-uniform electron distributions in semiconductors. It is shown that the averaging process preserves the moment of the electron distribution. This property can be used to extract certain quantitative details about the electron distribution that appear to have been obliterated by the averaging, without a need to reconstruct the entire true electron distribution. As an example, the extraction of the steepness of a diffusion gradient is discussed. In the limit of a weak electron concentration gradient, the width of the Debye averaging is shown to be such that the RMS averaging distance is (2)L D , where L D is the Debye length.

Non-linear electrical effect in graded-electron concentration silicon

Abstract A gradient of carrier concentration in semiconductors can create a double-frequency internal electric field which is parallel to this gradient and perpendicular to the applied a.c. field. This warm-carrier effect was measured in silicon specimens with a gradient of electron concentration, at 77 and 300 K, under applied fields from 1 to 10 V m-1 and within the frequency range of 0.3–20 kHz. A comparison between experimental data and a theoretical model is discussed.