Potential Barrier Structure Research Articles

Internal friction in nb-v-o alloys

The logarithmic decrement, δ, was measured in Nb-V-O alloys with the V content of 0.5, 1.0, 1.9, 7, 12, 20 and 50 at.% using a low frequency ( f= 3-7 Hz) inverse torsion pendulum in the temperature range from 20 to 800°C. The complex oxygen atom Snoek peaks were analysed with the help of a computer and individual Debye form constituent peaks- jwere extracted. The parameters of these peaks were used to derive information of two sorts: (a) distribution of oxygen atoms over octahedral interstices which differ in the number jof V atoms in the nearest neighbour lattice sites (static parameter) and (b) the potential barriers for oxygen atoms diffusing from j-positions (dynamic parameter). The first was used to evaluate the binding energies of oxygen with vanadium atoms in jV-O complexes, the second made understandable the structure of potential barriers for diffusion of the oxygen atoms from positions j. The differences between measurements of static and dynamic characteristics are discussed.

Enhancement of electron-wave reflection by superlattices with multiple stacks of multiquantum barriers

We report a superlattice (SL) with multiple stacks of multiquantum barriers (MQB), which can reflect electrons more effectively than with a single stack of MQB. The reflectivities are calculated and compared with one another for a variety of potential barrier structures. The multistack SL has a wider energy spectrum within which electrons are reflected. Four types of n-GaAs/i-barrier/n-GaAs diodes were fabricated to confirm the calculated results. The current-voltage characteristics measured at 77 K for these diodes show that the turn-on voltage increases with the number of stacks of MQBs in the SL. This is in agreement with our calculated results.

ＳＴＭにおける共鳴トンネル効果とその負性抵抗特性

In the analysis of scanning tunneling microscopy (STM), a one-dimensional model is used to predict the tunneling spectrum of a quantum well structure. Investigations of the current-voltage characteristics for the double potential barrier structure are presented for a heterostructure (GaAs/AlAs/GaAs) -vacuum-STM tip (GaAs) system. The dependences of resonant tunneling current-voltage characteristics on the double-barrier structures are shown for the peak voltage of negative resistance and the shape of negative resistance.

Finite-element calculation of the transmission probability and the resonant-tunneling lifetime through arbitrary potential barriers

A numerical method for the calculation of the transmission probability through a potential barrier or structure and of the lifetime of a resonant state in a double- or multiple-barrier structure is presented. This method is based on a combination of the finite-element method and the analytical approach. A generalized boundary condition of the heterointerface is introduced by use of the interface matrix, and thus the method is applicable to the potential barriers made of arbitrary semiconductors. The validity of the method is confirmed by calculating the transmission probability of rectangular potential barriers and double barrier structures. Numerical results on sinusoidal barriers and voltage-applied barriers are also presented. >

Hopping ionic conductivity in Ce-dopedSrF2. I. Ionic thermocurrent results

In this paper we present ionic thermocurrent (ITC) results obtained for ${\mathrm{Sr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ single crystals (0.0001<x<0.4). From the dipolar relaxation peak in the ITC recordings the concentration of ${\mathrm{Ce}}^{3+}$-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ dipolar complexes has been determined. We conclude that only isolated dipoles contribute significantly to the dipolar relaxation peak and that the dipoles are randomly distributed over the ${\mathrm{SrF}}_{2}$ lattice. We find that in the dilutely doped crystals (x<0.005) interstitial ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ions dissociated from ${\mathrm{Ce}}^{3+}$-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ dipolar complexes are responsible for an Arrhenius-type ionic conductivity. The position of the so-called high-temperature peak, observed in the ITC recordings, is directly proportional to the activation energy, from which the association energy of ${R}^{3+}$-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ dipolar complexes has been obtained (R=La, Ce, Pr, Nd, Eu, Sm, Gd, Er, Dy, Yb, Lu, or Y in ${\mathrm{SrF}}_{2}$ or La, Eu, Gd, or Yb in ${\mathrm{BaF}}_{2}$). At higher doping concentrations non-Arrhenius-type ionic conductivity, caused by hopping of interstitial ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ions in the random potential energy barrier structure of the heavily doped fluorite lattice, is observed. In addition, results obtained from quenching experiments performed on ${\mathrm{Sr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{La}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ are presented.

Hopping ionic conductivity in Ce-doped SrF2. II. Results obtained from impedance measurements.

The complex dielectric constant of ${\mathrm{Sr}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{F}}_{2+\mathrm{x}}$ single crystals has been measured at frequencies between 90 Hz and 30 kHz with the temperature ranging from 100 to 550 K and 0.0001lxl0.40. We have paid special attention to the frequency and temperature dependence of the ionic conductivity. For Ce concentrations lower than 0.5 mol?frequency-independent Arrhenius-type ionic conductivity has been observed, which is attributed to the mobility of interstitial ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ions dissociated from ${\mathrm{Ce}}^{3+}$-${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ dipolar complexes present in the crystals. At higher Ce concentration an increase of the ionic conductivity by several orders of magnitude has been observed; in addition the ionic conductivity depends upon the frequency. Employing a model in which the mobility of the interstitial ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ions is relatively large in the vicinity of the Ce impurities and the ${\mathrm{Ce}}^{3+}$ ions are randomly distributed over the ${\mathrm{SrF}}_{2}$ lattice the results have been interpreted. Essential in the interpretation is the random potential energy barrier structure in the crystals experienced by a hopping interstitial ${\mathrm{F}}^{\mathrm{\ensuremath{-}}}$ ion.

Calculation of transmission tunneling current across arbitrary potential barriers

This paper presents a simple method for accurately calculating quantum mechanical transmission probability and current across arbitrary potential barriers by using the multistep potential approximation. This method is applicable to various potential barriers and wells, including continuous variations of potential energy and electron effective mass. Various potential barrier structures and a hot-electron transistor are analyzed to show the feasibility of this method.

Potential Barrier and Molecular Structure of Methyl Mercaptan from its Microwave Spectra

The microwave spectrum of normal methyl mercaptan has been studied in the frequency range from 14 to 29 kMc/sec. The potential barrier height hindering internal rotation has been determined as 444±10 cm -1 from the analysis of the lines corresponding to the transitions involving both over-all and internal rotations. The fine structures of J =1←0, K =0←0 lines of the various isotopic species have also been analysed and discussed. The molecular structure of methyl mercaptan has been calculated to be d SH =1.336±0.01 A, d CS =1.819±0.005 A, d C H =1.091±0.01 A, \(\angle\)CSH=96°30'±1°, \(\angle\)HCH=109°45'±30' and the angle between CS bond and methyl axis, θ=2^°0'±30'.