scholarly journals The Ultimate Ballistic Drift Velocity in Carbon Nanotubes

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Mohammad Taghi Ahmadi ◽  
Razali Ismail ◽  
Michael L. P. Tan ◽  
Vijay K. Arora
Keyword(s):  
Energy Spectrum ◽  
Electric Field ◽  
Carrier Concentration ◽  
Drift Velocity ◽  
Mean Free Path ◽  
High Electric Field ◽  
Fermi Velocity ◽  
Zero Field ◽  
Saturation Velocity ◽  
The Mean

The carriers in a carbon nanotube (CNT), like in any quasi-1-dimensional (Q1D) nanostructure, have analog energy spectrum only in the quasifree direction; while the other two Cartesian directions are quantum-confined leading to a digital (quantized) energy spectrum. We report the salient features of the mobility and saturation velocity controlling the charge transport in a semiconducting single-walled CNT (SWCNT) channel. The ultimate drift velocity in SWCNT due to the high-electric-field streaming is based on the asymmetrical distribution function that converts randomness in zero-field to a stream-lined one in a very high electric field. Specifically, we show that a higher mobility in an SWCNT does not necessarily lead to a higher saturation velocity that is limited by the mean intrinsic velocity depending upon the band parameters. The intrinsic velocity is found to be appropriate thermal velocity in the nondegenerate regime, increasing with the temperature, but independent of carrier concentration. However, this intrinsic velocity is the Fermi velocity that is independent of temperature, but depends strongly on carrier concentration. The velocity that saturates in a high electric field can be lower than the intrinsic velocity due to onset of a quantum emission. In an SWCNT, the mobility may also become ballistic if the length of the channel is comparable or less than the mean free path.

scholarly journals Analytical Study of Drift Velocity in Low Dimensional Devices

2014 ◽  
Vol 4 (2) ◽  
Author(s):  
Mohammad T. Ahmadi ◽  
Ismail Saad ◽  
Munawar A.Riadi ◽  
Razali Ismail ◽  
Vijay K.Arora
Keyword(s):  
Carrier Concentration ◽  
Drift Velocity ◽  
Analytical Study ◽  
Quantum Limit ◽  
Fermi Velocity ◽  
Zero Field ◽  
New Device ◽  
Effect Transistor ◽  
Low Dimensional ◽  
Very High

Understanding of quantum limit in low dimensional devices helps to develop the new device types same as Carbon Nanotube Field Effect Transistor (CNTFET) and Naonowire. For each dimensionality the limitations on carrier drift velocity due to the high-field streaming of otherwise randomly velocity vector in equilibrium is reported. The results are based on the asymmetrical distribution function that converts randomness in zero-field to streamlined one in a very high electric field. The ultimate drift velocity for all dimensions is found to be appropriate thermal velocity for a nondegenerately doped sample of silicon, increasing with the temperature, but independent of carrier concentration. However, the ultimate drift velocity is the Fermi velocity for degenerately doped silicon increasing with carrier concentration but independent of the temperature.

scholarly journals Experimental and theoretical studies of the behaviour of slow electrons in air. I

1949 ◽  
Vol 196 (1046) ◽  
pp. 402-426 ◽  
Keyword(s):  
Drift Velocity ◽  
Mean Free Path ◽  
Free Electrons ◽  
Direct Measurements ◽  
Electronic Motion ◽  
The Mean ◽  
Gas Molecules ◽  
Slow Electrons ◽  
Experimental And Theoretical Studies ◽  
Unit Pressure

This paper is an account of an experimental investigation of the motions of free electrons in air by the method developed by Townsend. An improved form of apparatus is described with the appropriate theory. The following parameters of the electronic motion were determined as functions of the ratio Z/p of the electric field strength Z to the gas pressure p : Townsend’s energy factor k r the drift velocity W , the mean free path at unit pressure L and the mean proportion n of its energy lost in collisions with gas molecules. The experimental data are given in the form of tables and curves. The drift velocity W is found by a new procedure based on the Hall effect and by comparing the velocities W so obtained with the direct measurements of W by Nielsen & Bradbury it is seen that the velocities of agitation are distributed approximately according to Druyvesteyn’s law when Z/p exceeds 0.5. Bailey’s factor G , which is of importance in ionospheric studies, is obtained from the experimental dependence of η on k r . Theoretical formulae are derived for k r and W in terms of L, G and Z/p . The theory of the new method for measuring W is given in an appendix.

scholarly journals Структура призондового слоя в газоразрядной плазме при произвольной ориентации плоского зонда относительно электрического поля в плазме

2019 ◽  
Vol 89 (10) ◽  
pp. 1545
Author(s):  
O. Мурильо ◽  
А.С. Мустафаев ◽  
В.С. Сухомлинов
Keyword(s):  
Electric Field ◽  
Electron Energy ◽  
Exchange Process ◽  
Mean Free Path ◽  
Ionization Rate ◽  
Inert Gases ◽  
Mutual Orientation ◽  
Mean Velocity ◽  
Charge Exchange Process ◽  
The Mean

AbstractWe investigate the structure of the wall sheath of a gas discharge near a flat surface at a negative potential for high mean electron energy. It is shown that in the conditions where the mean energy of ions in the plasma is much lower than the mean electron energy, the parameters of the wall sheath weakly depend on the mutual orientation of the normal to the surface and the electric field in the plasma for an arbitrary ratio of the Debye radius to the ion mean free path relative to the resonant charge exchange process. It is found that for inert gases (He, Ar) for ratio E / P of the electric field to pressure exceeding 10 V/(cm Torr) in the plasma, the disregard of ionization in the perturbed wall sheath can lead to substantial errors in the calculation of its parameters. It is shown that the ionization leads to an increase in the electric field in the wall sheath and, as a consequence, to an increase in the mean velocity of ions at the boundary between the quasi-neutral presheath and the part of the perturbed wall sheath in which quasi-neutrality is substantially violated. The parameters of the wall sheath where quasi-neutrality is significantly violated depend on the ionization rate much less strongly than the corresponding parameters of the quasi-neutral presheath. We have determined the relation for concentration of charged particles in the unperturbed plasma from the ion saturation current considering the actual ion energy distribution function in the plasma as well as ionization in the presheath and the part of the perturbed wall sheath in which quasi-neutrality is violated significantly.

The electrical conductivity of thin wires

1950 ◽  
Vol 201 (1067) ◽  
pp. 545-560 ◽  
Keyword(s):  
Electrical Conductivity ◽  
Free Path ◽  
Mean Free Path ◽  
Fermi Velocity ◽  
Approximate Methods ◽  
Conduction Electrons ◽  
The Third ◽  
Thin Wires ◽  
Velocity Surface ◽  
The Mean

In the first part of this paper, simple approximate methods have been developed for evaluating the electrical conductivity of films and wires of a size comparable with the mean free path of the conduction electrons. In the second part, a rigorous theory has been given of the electrical conductivity of a thin wire, on the assumptions that the Fermi velocity surface is spherical and that the collisions of the electrons at the surface of the wire are inelastic. In the third part of the paper, this theory has been generalized to cover the case where the scattering is no longer inelastic. In the final part, Andrew’s recent experimental results for a thin mercury wire have been fitted to the theoretical curves obtained, and the mean free path evaluated.

An equation for the drift velocity of relativistic electrons scattered isotropically and a negative magneto-resistance effect

1990 ◽  
Vol 44 (1) ◽  
pp. 47-59 ◽  
Author(s):  
M. Nagata
Keyword(s):  
Momentum Transfer ◽  
Drift Velocity ◽  
Relativistic Equation ◽  
Mean Free Path ◽  
Electron Mass ◽  
Relativistic Electrons ◽  
Relativistic Case ◽  
The Mean ◽  
Magneto Resistance ◽  
Transfer Term

Previous work on non-relativistic electrons isotropically scattered by neutral atoms is extended to the relativistic case, and an equation is derived for the electron drift velocity. In the non-relativistic case the drift-velocity equation contains a corrected momentum-transfer term arising from the fact that the collision phenomenon is characterized by the mean free path rather than by the mean collision time. In the present work it is found that the time variation of the electron mass has a very complicated effect on the relativistic equation for the drift velocity. In addition, an unexpected theoretical result is obtained: a negative magneto-resistance effect in which the magneto-resistance decreases as the magnitude of a magnetic field imposed on the plasma increases. However, this effect is not a relativistic one but is rather due to the correction in the momentum-transfer term.

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