Dang Mo

Determination of the optical properties of sol-gel-derived BaxSr1-xTiO3 thin film by spectroscopic ellipsometry

The optical properties of amorphous and polycrystalline BaxSr1-xTiO3 (BST) thin films fabricated on Si(100) substrates by a sol-gel spin-coating technique were investigated by spectroscopic ellipsometry (SE). The spectrum of the extinction coefficient k was obtained by using the refractive index and structure parameters determined by SE in the photon energy range of 2.1-5.2 eV. A four-phase fitting model was employed to describe the optical properties of the BST thin films; the spectra of their optical constants and the band gap energy Eg were determined by means of optimization. In addition, the refractive index dispersion data related to the short-range-order structure of the films agreed well with the single-oscillation energy model. The dependence of the refractive index, k and Eg on annealing temperature were analysed. The variation of optical band gap energy with composition was investigated by changing the content of barium in the films.

Determination of the Optical Properties of Sol-Gel-Derived Pb(Zr x Ti (1 − x ) )O 3 Thin Films by Spectroscopic Ellipsometry

Optical properties of polycrystalline Pb(Zr x Ti (1 m x ) )O 3 (PZT) thin films with different Zr/Ti ratios deposited on Si(100) substrates by the sol-gel techniques have been investigated by spectroscopic ellipsometry (SE) in the UV-visible region. The measured SE spectra were fitted by a model consisting of air/roughness/PZT/substrate. The roughness was modeled using the Bruggeman effective medium approximation. The optical constants of the PZT films were parameterized using the Forouhi-Bloomer model. The refractive index n, extinction coefficient k and thickness of samples with different Zr/Ti ratios have been obtained by analyzing the SE spectra. The influence of Zr/Ti ratios on the optical properties was discussed. The optical band gap energies E g for these films were reported under the assumption of a direct band-to-band transition. It has been found that the refractive index, extinction coefficient and optical band gap energy of the films were functions of the film compositions. The refractive index of polycrystalline PZT films increase with increasing Ti content. On the other hand, the optical band gap energy of polycrystalline PZT films decreases with increasing Ti content.

Transmission of light through a class of quasiperiodic multilayers

We study the optical transmission through a class of 1D quasiperiodic lattices, for which the substitution rules are B-->BA, and A-->BAB. The transmission coefficient exist a rich structure as a function of the wavelength of light. The switch-like ( on-off-on-off .. ) transmission coefficient has been found around delta=(3/2)pi. And a possible application as the narrowband filters is suggested.

Ellipsometric spectra and fractional derivative spectrum analysis of polyaniline films

Abstract Ellipsometric spectra of polyaniline films were measured for the first time. The complex dielectric function and the refractive index in the UV—visible range of both insulating and conducting polyaniline were obtained. The spectral structure was analysed with emphasis on the evolution of the electronic structure from an insulating to a conducting polymer. The threshold energy and the broadening parameter as well as the dimension are determined by the fractional derivative spectrum technique which was previously proposed by X.-F. He and D. Mo ( Chin. Phys. Lett. , 3 (1986) 565).

Light-induced absorption in (CU,CE)-doped (KNa)0.1 (Sr0.6 Ba0.4)0.9 Nb2O6 crystal

Abstract (Cu,Ce)-doped (KNa)0.1(Sr0.6Ba0.4)0.9Nb2O6 [KNSBN:(Cu,Ce)] crystal was successfully grown and characterized by measuring its absorption and the light-induced absorption changes. KNSBN:(Cu,Ce) crystal exhibit strong intensity- and polarization-dependent absorption in the visible spectral range. Light-induced absorption coefficient of up to 0.5 cm−1 and 0.2 cm−1 are obtained for the extraordinary and ordinary probe beams, respectively. The results indicate that the two-center charge transport model is more appropriate for KNSBN.

Verification of GaAs/AlAs superlattice theory by spectroscopic ellipsometry

Short-period GaAs/AlAs superlattice samples were prepared according to the theoretical calculations by Xia and Chang. We measured the ellipsometric spectra of these samples, and then obtained the complex dielectric function spectra of the superlattices. A comparison between the experimental and theoretical curves of the dielectric function spectra is performed. The Xia-Chang theory of short-period GaAs/AlAs superlattices has been verified by our experimental results.

Branching Rules and Gap-Labeling Properties for a Class of One-Dimensional Quasilattices*

The gap-labeling properties of the energy spectrum for a class of one-dimensional quasilattices have been investigated. We have studied the branching rules on subbands of the hierarchical energy spectrum and obtained the integrated density of states (IDOS). It is analytically proved that IDOS has the form , where and are integers, . The characteristic number can be used to label the corresponding energy gap. This conclusion is similar to that of one-dimensional Fibonacci quasicrystals.

DIFFRACTION PATTERN FOR A CLASS OF ONE-DIMENSIONAL QUASI-CRYSTALS

We study the diffraction pattern and indexing problems for a class of 1D quasiperiodic lattices, for which the substitution rules are B double-line arrow pointing right BA and A double-line arrow pointing right BAB. The similarity property of diffraction pattern has been found. The numerical calculation is performed to prove the theoretical results.