Browsing by Author "Liu, RG"

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Charge transfer process in Tl2Ba2Ca2Cu3O10 and Tl2Ba2CaCu2O8 thin films probed by polarized X-ray absorption spectroscopy
(1997-09-26)
Chen, JM
;
Liu, RG
;
Liu, RS
;
Lin, HC
;
Uen, TM
We report high-resolution polarized O 1s X-ray absorption spectra of highly c-axis-oriented Tl2Ba2Ca2Cu3O10 (Tl-2223) and Tl2Ba2CaCu2O8 (Tl-2212) superconducting thin films. Near the O Is edge, the low-energy pre-edge peak at 528.3 eV has mainly O 2p(xy) symmetry, while the pre-edge peak at 529.4 eV has predominantly O 2p, character. The spectral weight of the pre-edge peak at 528.3 eV, originating from the CuO2 planes, increases similar to 60% from the Tl-2212 to Tl-2223 thin films. Conversely, the high-energy pre-edge peak at 530.3 eV, originating from the TlO planes, is lower in spectral intensity by similar to 30% in Tl-2223 as compared to the Tl-2212 thin film. The experimental results clearly demonstrate the pictures of the self doping due to the charge transfer from the CuO2 layers to the TlO layers. (C) 1997 Published by Elsevier Science B.V.
Focus latitude enhancement of symmetrical phase mask design for deep submicron contact hole patterning
(2001-11-01)
Chou, SY
;
Lou, JC
;
Chen, LJ
;
Shiu, LH
;
Liu, RG
The mechanism of focus latitude enhancement for contact/via hole printing is explained by approximating the axis intensity distribution of an image as a series of cosine functions to characterize the interference between each pair of diffraction beams. It is found that a phase-shifting mask (PSM) with symmetrical assist features improves the depth of focus (DOF) by introducing destructive interference to counterbalance the intensity fluctuation from constructive interference as defocus. A simple formula was derived to represent the capability of focus latitude enlargement. It shows that the extent of enhancement depends on the exposure wavelength and numerical aperture of a projection lens only. Increasing the degree of partial coherence degrades the focal range enlargement because a larger illumination angle elongates the destructive interference pattern in the optical-axis direction to weaken its ability for intensity compensation. On the other hand, the lack of constructive interference in dense hole imaging fails the mask pattern transfer, which limits the application of the phase-shifting method to pattern pitch greater than root2lambda/NA. A tiny amount of spherical aberration results in prominent asymmetrical defocus behavior because the wave deformation in the projection lens shifts the distribution of constructive and destructive interference patterns to opposite defocus directions. The printing characteristics of 0.17 mum contact using an 18% transmission, rim-type attenuated phase-shifting mask are investigated to corroborate our analysis of defocus behavior. The dependence of depth of focus on pattern duty is stressed to elucidate the difference in mechanisms of focus latitude improvements for a sparse hole and periodic dense hole. (C) 2001 American Vacuum Society.
Polarized X-ray absorption studies in double-thallium-layer superconducting
(1998-04-01)
Chen, JM
;
Liu, RG
;
Liu, RS
;
Lin, HC
;
Uen, TM
Polarization-dependent O Is X-ray absorption spectra of highly c-axis-oriented Tl2Ba2Ca2Cu3O10 (Tl-2223) and TI2Ba2CaCu2O8 (Tl-2212) superconducting thin films have been measured by using synchrotron radiation. Near the O Is absorption edge, three distinct pre-edge peaks for both systems were clearly revealed. The low-energy pre-edge peak at 528.3 eV has mainly O 2p(xy) symmetry, while the pre-edge peak at 529.4 eV has predominantly O 2p(z) character. The spectral weight of the pre-edge peak at 528.3 eV, originating from the CuO2 planes, increase about 60% from the Tl-2212 to Tl-2223 thin films. Conversely, the high-energy pre-edge peak at 530.3 eV, originating from the TIO planes, is lower in, spectral intensity by similar to 30% in Tl-2223 as compared to the Tl-2212 thin film. The experimental results clearly demonstrates the pictures of the self doping due to the charge transfer from the CuO2 layers to the TlO layers.
Preparation and electronic properties of YBa2Cu3Ox films with controlled oxygen stoichiometries
(1998-08-01)
Wu, KH
;
Hsieh, MC
;
Chen, SP
;
Chao, SC
;
Juang, JY
We describe a novel technique capable of controlling the oxygen content of YBa2Cu3Ox (YBCO) films in a precise and reversible manner. The temperature dependence of resistivity and the distinct two-plateau behavior in critical temperature T-CO versus oxygen content plot of these films are consistent with those observed in the bulk and single crystals of YBCO. The O 1s and Cu 2p absorption spectra of these films were measured by polarization-dependent X-ray absorption spectroscopy (XAS). The intensity variations of the pre-edge peaks as a function of oxygen content are discussed. We also used these films to systematically study the electron-phonon coupling strength and the position of Fermi level by using a femtosecond pump-probe technique. A clear sign-reversal of the transient reflectivity, which was consistently explained by the thermomodulation model, was observed. Both of these optical measurements support the idea that the electronic structure of YBCO cuprates is based on the charge transfer model with hybridization between the Cu and O sites.