Mean free path

About: Mean free path is a research topic. Over the lifetime, 4412 publications have been published within this topic receiving 114418 citations.

Transport processes of electrons in MNOS structures

Abstract: The transport processes of electrons in MNOS structures, especially in the SiO2 layer and the surface region of the Si substrate, have been investigated using p‐channel MNOS transistors with a relatively thick SiO2 layer to avoid the complexity of two‐carrier transport in the system. An induced junction technique utilizing the electron and hole separation properties of the transistor structure was used as a means of analysis. Theoretical derivation of the carrier multiplication factor, i.e., the number of electron‐hole pairs produced by an electron entering the Si from the SiO2, is calculated. It is experimentally shown that an electron entering the Si from the SiO2 produces approximately one electron‐hole pair in the low negative gate bias voltage range up to a critical voltage, and above this critical voltage the multiplication factor increases with increasing gate bias voltage. The former observation is in good agreement with the prediction of the theory, considering cascaded impact ionization of an electron with high energy in Si. The latter fact reveals that electrons in SiO2 become hot in the high voltage range. The critical voltage coincides with the value theoretically estimated using an LO phonon energy of 0.153 eV and an electron‐phonon scattering length of 1.74 A in SiO2. The mean free path of the electrons between scatterings by defects or other scattering centers in SiO2 is estimated to be about 30 A by analyzing gate bias dependence of the multiplication phenomena.

Transmission of a pulsed thin light beam through thick turbid media: experimental results

Abstract: Experimental results of light pulse transmission through thick turbid media are presented. Measurements have been carried out on polystyrene latex spheres by using a picosecond thin laser beam and a streak camera system. The results show that the shape of the received pulse depends mostly on the transport mean free path and on the absorption coefficient of the medium, indicating that both the absorption coefficient and the asymmetry factor of the scattering function can be obtained from the pulse shape. The results also show that a detectable amount of received photons follows trajectories near the source receiver line even for large values of optical depth, indicating the potential of a time-gated scanning imaging system to detect absorbing structures inside thick turbid media.

When do particles follow field lines

Abstract: [1] We examine charged particle transport perpendicular to the large scale magnetic field. We find that the limit of an infinite parallel mean free path of particles diffusing along the large scale magnetic field is a necessary condition for which the diffusive spread of the magnetic field lines leads to a proportional spread of the particles. When it occurs this requires that parallel mean free path is well in excess of the smaller of the system size and the turbulence ultrascale. However, there are alternative situations in which particles may diffuse, but field lines do not. In the latter cases the asymptotic behavior is that which persists after the parallel mean free path exceeds some multiple of the correlation scales. This phenomenon of diffusing particles/non-diffusing field lines is typically determined by the 2D turbulence spectrum, where the diffusion coefficient of the magnetic field due to 2D turbulence can diverge if the spectrum of the 2D fluctuations is not well behaved at small wave numbers. We also show that the classical relation between parallel and perpendicular diffusion for high energy particles is consistent with the field line random walk description of particle diffusion.

Relaxation of electronic excitations in CaF2 nanoparticles

Abstract: The luminescence properties of CaF2 nanoparticles with various sizes (20–140 nm) are studied upon the excitation by VUV and x-ray quanta in order to reveal the influence of ratio of mean free path and thermalization length of charge carriers and nanoparticle size on the self-trapped exciton luminescence. The luminescence intensity for exciting quantum energies corresponding to optical creation of exciton and to the range of electronic excitation multiplication is not so sensitive to nanoparticle size as for quanta with energy of Eg < hν < 2Eg. The dependences of luminescence intensity on nanoparticle size at the excitation by quanta of various energies are discussed in terms of electron-phonon and electron-electron scattering lengths and energy losses on surface defects.