Electron current density

The electron current density J has units of A/cm and in a semiconductor results from drift and diffusion. In the absence of concentration gradients, equation 7 reduces to Ohm s law, = nqp E = [Pg.346]

HBT Device Characteristics. The HBT consists of two back-to-back n—p diodes. In the most typical configuration the emitter—base diode is forward biased, with the coUector-base diode reverse biased. Because the current ia a forward-biased n—p diode is exponentiaUy dependent on the bias, smaU changes ia the emitter-base voltage result ia large changes ia the emitter current. The current across the emitter-base junction is a combination of the electrons iajected iato the base and the holes iajected iato the emitter. If the diode was semi-infinite to each side, the electron current density,/, could be expressed as foUows (44), where q is the electron charge, Vis the bias across the diode, kT... 

Similarly to Eq. (2.6), fCis a proportionality constant containing fixed operating conditions, for example incident electron current density, transmission of the analyzer at the kinetic energy Ea, efficiency of the detector at the kinetic energy Ea, and the probability of the Auger transition XYZ. 

The electron current density may then be found from Eq. (1-137). 

When a probe is inserted into a plasma, it will experience electrons and ions colliding with its tip. Due to the high mean speed of electrons, the flow of electrons is higher than the flow of ions. Consequently, the tip will charge up negatively until the electrons are repelled, and the net current then is zero. The probe potential then is the floating potential, Vfl. The electron current density Je then balances the ion current density 7,. At potentials lower than Vfl the ion current cannot increase further—in fact, only ions are collected from the plasma—and the ion saturation current /,s is measured. The plasma potential Vpi is defined as the potential at which all electrons arriving near the probe are collected and the probe current equals the electron current. Note that the plasma assumes the plasma potential in the absence of a probe hence probe perturbation at Vpi is... 

Theoretical calculation of NMR chemical shifts is usually done by first considering the electronic current density which is induced by the external magnetic field. Once this current has been calculated the chemical shift can be obtained by application of the Biot-Savard law, which describes the magnetic field created by it. The strength of this field at the position of an atom represents the NMR chemical shielding of this atom. 

When the electronic current density j(r) has been calculated, the Biot-Savart law for the induced magnetic field reads ... 

Electron current density (je), 22 243 in silicon-based semiconductors, 22 238 Electron cyclotron resonance (ECR),... 

On the other hand, the estimate of the Breit interaction energy is, in all cases, quite satisfactory in any atomic or ionic superposition model. The reason for this has already been discussed the Breit interaction energy arises due to electron current density in the neighbourhood of the nuclei, which is dominated by the core electrons and is apparently insensitive to the valence electron environment. 

The second major mechanism of VCD is the production of vibrationally generated electronic current density by the vibrational motion of a local oscillator. Usually, such currents are induced in molecular rings, or fragments of rings, and the local oscillator may either be attached to the ring or contained in it. The resulting VCD per oscillator is biased and monosignate. 

In their first paper, Lepage et al. [37] demonstrated that the appearance of the CO electronic state derives exclusively from the electron-induced fragmentation of condensed methanol molecules. Assuming a uniform electron current density within the electron beam, it can also be shown that for induced CO concentrations below 2%, an effective cross section for CO production Cp can be calculated via the formula... 

All these arguments can be applied to the electrons making n—tp and p n crossings and giving rise to electron current densities. The net electron current density is given by an expression similar to (7.63), i.e.,... 

In this equation, cx[ is the concentration of M"+ at a distance x from the x = 0 plane at a time t after the switching on of the constant electronation current density, c° is the bulk concentration of M"+, and the other terms have their usual significance. 

The most significant effect of a convective-diffusive transport mechanism is to counteract the tendency of the electronation-current density to reduce the interfacial concentration of electron acceptors to zero. Further, since the interfacial concentration of electron acceptors then remains at a value above that given by the diffusion-based equations, a transition time, indicated by a rapid potential variation, need not be attained. 

Electronic Current Density in the Presence of Static Electric and Magnetic Fields. 

McCoy, M. A. and Wyss, D. F., Spatial localization of ligand binding sites from electron current density surfaces calculated from NMR chemical shift perturbations. JAm Chem Soc, 2002,... 

In a typical EEL spectrum, the count rate Ia (area under the excitation edge after background subtraction, for element A) is a product of the incident electron current density, J0, the number of atoms Na of element A per unit area, and oa> the total ionization cross-section per atom for the excitation of the appropriate inner-shell by the incident electrons. However, to preserve good energy resolution, an aperture is placed after the specimen which limits scattering to angles less than P and hence only a fraction of the core loss signal Ia(P) is measured. Moreover, in most... 

To obtain quantitative expressions for the corrosion current and the corrosion potential, one has to substitute the proper expression for the metal-dissolution- and electronation-current densities. If no oxide films form on the surface of the corroding metal and neither of the current densities is controlled by mass transport, i.e., there is no concentration overpotential, one can insert the Butler-Volmer expression for the deelectronation- and electronation-current densities. Thus,... 

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