scholarly journals Direct 3D observation and unravelling of electroconvection phenomena during concentration polarization at ion-exchange membranes

2021 ◽  
Author(s):  
Matthias Wessling
Keyword(s):  
Velocity Field ◽  
Current Density ◽  
Concentration Polarization ◽  
Decisive Role ◽  
Spatial Spectrum ◽  
Mean Square ◽  
Experimental Proof ◽  
Time Resolved ◽  
Spatio Temporal ◽  
Spatial Spectra

A decade ago, two-dimensional microscopic flow visualization proved the theoretically predicted existence of electroconvection roles as well as their decisive role in destabilizing the concentration polarization layer at ion-selective fluid/membrane interfaces. Electroconvection induces chaotic flow vortices injecting volume having bulk concentration into the ion-depleted diffusion layer at the interface. Experimental quantification of these important flow patterns have so far only been carried out in 2D. Numerical direct simulations suggest 3D features, yet experimental proof is lacking. 3D simulations are also limited in covering extended spacial and temporal scales.This study presents a new comprehensive experimental method for the time-resolved recording of the 3D electroconvective velocity field near a cation-exchange membrane. For the first time, the spatio-temporal velocity field can be visualized in 3D at multiples of the overlimiting current density. In contrast to today’s simulations, these experiments cover length and time scales typical for actual electrodialytic membrane processes.We visualize coherent vortex structures and reveal the changes in the velocity field and its statistics during the transition from vortex rolls to vortex rings with increasing current density. The transition is characterized by changes in the rotational direction, mean square velocity, and temporal energy spectrum with only little influence on the spatial spectrum. These findings indicate a more significant impact of EC’s structural change on the mean square velocities and temporal spectra than on the spatial spectra. This knowledge is a prerequisite for engineering ion-selective surfaces that will enable the operation of electrically driven processes beyond the diffusion-limited Nernst regime.

DISCRIMINATION OF PHOTONS PRODUCED BY CLASSICAL AND QUANTUM-MECHANICAL SOURCES

1991 ◽  
Vol 06 (05) ◽  
pp. 749-753
Author(s):  
THOMAS LIPPERT ◽  
SREE RAM VALLURI ◽  
NORBERT GRÜN ◽  
WERNER SCHEID
Keyword(s):  
Root Mean Square ◽  
Current Density ◽  
Heavy Ion ◽  
Relativistic Heavy Ion Collisions ◽  
Quantum Mechanical ◽  
Mean Square ◽  
Mean Square Deviation ◽  
Experimental Proof ◽  
Ion Collisions ◽  
The Mean

In this note we suggest an experimental proof for testing whether the photon production by bremsstrahlung in relativistic heavy ion collisions can be described in terms of a classical nuclear current density or not. We propose to measure not only the mean number of photons with a given energy, but also the corresponding root mean square deviation of it. A classical description of the current density is possible if the squared deviation is equal to the mean number of photons.

Electron-beam damage of oxides at high current densities

1989 ◽  
Vol 47 ◽  
pp. 634-635
Author(s):  
M. R. McCartney ◽  
J. K. Weiss ◽  
David J. Smith
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Current Density ◽  
Transition Metal Oxides ◽  
Time Resolved ◽  
Rapid Acquisition ◽  
Resolution Electron ◽  
Current Densities ◽  
Electron Stimulated Desorption ◽  
Channel Analyzer

It is well-known that electron-beam irradiation within the electron microscope can induce a variety of surface reactions. In the particular case of maximally-valent transition-metal oxides (TMO), which are susceptible to electron-stimulated desorption (ESD) of oxygen, it is apparent that the final reduced product depends, amongst other things, upon the ionicity of the original oxide, the energy and current density of the incident electrons, and the residual microscope vacuum. For example, when TMO are irradiated in a high-resolution electron microscope (HREM) at current densities of 5-50 A/cm2, epitaxial layers of the monoxide phase are found. In contrast, when these oxides are exposed to the extreme current density probe of an EM equipped with a field emission gun (FEG), the irradiated area has been reported to develop either holes or regions almost completely depleted of oxygen. ’ In this paper, we describe the responses of three TMO (WO3, V2O5 and TiO2) when irradiated by the focussed probe of a Philips 400ST FEG TEM, also equipped with a Gatan 666 Parallel Electron Energy Loss Spectrometer (P-EELS). The multi-channel analyzer of the spectrometer was modified to take advantage of the extremely rapid acquisition capabilities of the P-EELS to obtain time-resolved spectra of the oxides during the irradiation period. After irradiation, the specimens were immediately removed to a JEM-4000EX HREM for imaging of the damaged regions.

scholarly journals A data reduction and compression description for high throughput time-resolved electron microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Abhik Datta ◽  
Kian Fong Ng ◽  
Deepan Balakrishnan ◽  
Melissa Ding ◽  
See Wee Chee ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Temporal Resolution ◽  
Data Reduction ◽  
Accurate Estimation ◽  
Data Streaming ◽  
Compression Scheme ◽  
Raw Data ◽  
Time Resolved ◽  
Detection And Counting ◽  
Spatio Temporal

AbstractFast, direct electron detectors have significantly improved the spatio-temporal resolution of electron microscopy movies. Preserving both spatial and temporal resolution in extended observations, however, requires storing prohibitively large amounts of data. Here, we describe an efficient and flexible data reduction and compression scheme (ReCoDe) that retains both spatial and temporal resolution by preserving individual electron events. Running ReCoDe on a workstation we demonstrate on-the-fly reduction and compression of raw data streaming off a detector at 3 GB/s, for hours of uninterrupted data collection. The output was 100-fold smaller than the raw data and saved directly onto network-attached storage drives over a 10 GbE connection. We discuss calibration techniques that support electron detection and counting (e.g., estimate electron backscattering rates, false positive rates, and data compressibility), and novel data analysis methods enabled by ReCoDe (e.g., recalibration of data post acquisition, and accurate estimation of coincidence loss).

Spatio-Temporal Current Density Reconstruction from EEG-/MEG-Data

2003 ◽  
pp. 472-482
Author(s):  
Alfred K. Louis ◽  
Uwe Schmitt ◽  
Felix Darvas ◽  
Helmut Büchner ◽  
Manfred Fuchs
Keyword(s):  
Current Density ◽  
Spatio Temporal

scholarly journals Characterization of thin CdTe solar cells with a CdSeTe front layer

MRS Advances ◽  
2019 ◽  
Vol 4 (37) ◽  
pp. 2053-2062
Author(s):  
Alexandra M. Bothwell ◽  
Jennifer A. Drayton ◽  
Pascal M. Jundt ◽  
James R. Sites
Keyword(s):  
Current Density ◽  
Fill Factor ◽  
Alloy Layer ◽  
Time Resolved ◽  
Loss Analysis ◽  
Cdte Solar Cells ◽  
Close Space Sublimation ◽  
Device Structures ◽  
Electroluminescence Intensity ◽  
Time Resolved Photoluminescence

ABSTRACTThin CdTe photovoltaic device efficiencies show significant improvement with the incorporation of a CdSeTe alloy layer deposited between a MgZnO emitter and CdTe absorber. CdTe and CdSeTe/CdTe devices fabricated by close-space sublimation with a total absorber thickness of 1.5 µm are studied using microscopy measurements and show minimal diffusion of Se into the CdTe. Current loss analysis shows that the CdSeTe layer is the primary absorber in the CdSeTe/CdTe structure, and fill factor loss analysis shows that ideality-factor reduction is the dominant mechanism of fill factor loss. Improvement in the CdSeTe/CdTe absorber quality compared to CdTe is also reflected in spectral and time-resolved photoluminescence measurements. Current density vs. voltage measurements show an increase in current density of up to 2 mA/cm2 with the addition of CdSeTe due to a band gap shift from 1.5 to 1.42 eV for CdTe and CdSeTe/CdTe absorbers respectively. Voltage deficit is lower with the incorporation of the CdSeTe layer, corroborated by improved electroluminescence intensity. The addition of CdSeTe into CdTe device structures has increased device efficiencies from 14.7% to 15.6% for absorbers with a total thickness less than two microns.

Unified Analysis of the Metal Vapour Arc

1973 ◽  
Vol 28 (3-4) ◽  
pp. 417-428 ◽  
Author(s):  
G. Ecker
Keyword(s):  
Space Charge ◽  
Electron Temperature ◽  
Current Density ◽  
Space Charge Region ◽  
Decisive Role ◽  
Emission Current Density ◽  
Mean Free Path ◽  
Vacuum Arc ◽  
Metal Vapour ◽  
Cathode Drop

Abstractfor given values of the total current density j and the cathode spot surface temperature T a unified and consistent calculation of the cathode drop, Uc , the electron temperature in the ionization region T _- the electron emission current density je , the ion current density j+ , and the extension of the space charge region lsp are presented.We find that the counter diffusion of plasma electrons into the space charge region plays a decisive role. It causes an effective space charge region extension lsp of a few plasma electron Debey lengths which in general is much less than the ion mean-free-path commonly used. Without the effect of the counter diffusing electrons, the theoretical results deviate from the experimental data by orders of magnitude.For the example of a Cu metal vapour-or vacuum arc the cathode drop is found to be approximately Uc = 15 [V], the electron temperature about T- =25000 [°K] and the ratio j+/j= 0.5.Since the analysis allows for multiple ionization the presence of multiply charged ions in the spot area can be calculated.The results of this investigation justify within the E-areas the approximations used in the analysis for the copper arc in an earlier investigation 1. Outside these E-areas a recalculation with the new results derived here may cause markable changes.

scholarly journals Structural, Optical and Electrical Characterizations of Midwave Infrared Ga-Free Type-II InAs/InAsSb Superlattice Barrier Photodetector

Photonics ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 76
Author(s):  
U. Zavala-Moran ◽  
M. Bouschet ◽  
J. Perez ◽  
R. Alchaar ◽  
S. Bernhardt ◽  
...  
Keyword(s):  
Current Density ◽  
Dark Current ◽  
Spectral Response ◽  
Minority Carrier Lifetime ◽  
Peak Position ◽  
Type Ii ◽  
Dark Current Density ◽  
Time Resolved ◽  
Midwave Infrared ◽  
Electrical Characterizations

In this paper, a full set of structural, optical and electrical characterizations performed on midwave infrared barrier detectors based on a Ga-free InAs/InAsSb type-II superlattice, grown by molecular beam epitaxy (MBE) on a GaSb substrate, are reported and analyzed. a Minority carrier lifetime value equal to 1 µs at 80 K, carried out on dedicated structure showing photoluminescence peak position at 4.9 µm, is extracted from a time resolved photoluminescence measurement. Dark current density as low as 3.2 × 10−5 A/cm2 at 150 K is reported on the corresponding device exhibiting a 50% cut-off wavelength around 5 µm. A performance analysis through normalized spectral response and dark current density-voltage characteristics was performed to determine both the operating bias and the different dark current regimes.

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