Recognizing and distinguishing the dynamic characteristics of scanning tunneling microscopy (STM) system is fatal for studying STM image. In this paper, a method for analyzing system’s characteristics by using a damped harmonic oscillator model is presented. The model is driven by random force and all of its properties are described by damping and periodic. For the general solution of such harmonic oscillator’s Langevin equation is deduced and the auto-correlation function (ACF) is obtained for fitting curve. It is shown that damping and periodic property of the two curves have a good agreement by comparing the fitting curve with the auto-correlation curve of time series dates which are acquired by STM. It could be concluded that the damped harmonic oscillator model and auto-correlation method are feasible for analyzing the dynamic characteristics of STM system.
Fe 3 F 4 with the spinel structure was designed, and its electric and magnetic properties were calculated in system based on density function theories. And then they were compared with those of Fe 3 O 4. From our calculation, Fe 3 F 4 is a kind of new stable approximate half-metal material because its spin-polarization at fermi level is about 95%, which is near to 100%. The steady constant of crystal lattice is 0.643 nm. The energy distance between the top of the up-spin valence band and the fermi level is about 2.05 eV, which is much larger than 0.6 eV of Fe 3 O 4. In the other hand, the resistivity of Fe 3 F 4 is lower than that of Fe 3 O 4. The molecular magnetic moments 10.68μB of Fe 3 F 4 are evidently higher than 4.0μB of Fe 3 O 4. This shows that there is stronger spin-correlation scattering on transmitted carriers in Fe 3 F 4 than in Fe 3 O 4 so that Fe 3 F 4 may have higher magnetoresistance than Fe 3 O 4. Extremely localization of 3d-electrons caused by hybrid orbits of F2p and Fe3d orbits is the mechanism of the distribution of electronic charges and magnetic moments of Fe 3 F 4.
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