Browsing by Author "Liang, C. W."

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Electrically controllable spontaneous magnetism in nanoscale mixed phase multiferroics
(2011-03-01)
He, Q.
;
Chu, Y. -H.
;
Heron, J. T.
;
Yang, S. Y.
;
Liang, W. I.
Magnetoelectrics and multiferroics present exciting opportunities for electric-field control of magnetism. However, there are few room-temperature ferromagnetic-ferroelectrics. Among the various types of multiferroics the bismuth ferrite system has received much attention primarily because both the ferroelectric and the antiferromagnetic orders are quite robust at room temperature. Here we demonstrate the emergence of an enhanced spontaneous magnetization in a strain-driven rhombohedral and super-tetragonal mixed phase of BiFeO(3). Using X-ray magnetic circular dichroism-based photoemission electron microscopy coupled with macroscopic magnetic measurements, we find that the spontaneous magnetization of the rhombohedral phase is significantly enhanced above the canted antiferromagnetic moment in the bulk phase, as a consequence of a piezomagnetic coupling to the adjacent tetragonal-like phase and the epitaxial constraint. Reversible electric-field control and manipulation of this magnetic moment at room temperature is also shown.
New Observations on the Physical Mechanism of Vth-Variation in Nanoscale CMOS Devices After Long Term Stress
(2011)
Hsieh, E. R.
;
Chung, Steve S.
;
Tsai, C. H.
;
Huang, R. M.
;
Tsai, C. T.
A new effect, called random trap fluctuation(RTF), is proposed to study the impact of hot carrier stress on the device variability. It was found that not only the popular random dopant fluctuation (RDF), but also the traps, caused by the HC stress or FN-stress, induce the V(th) variation. After the FN stress, it was found that Vth variation is worse in pMOSFETs due to stress-induced interface traps. While, under the HC stress, different Vth variations were found for nMOSFETs and pMOSFETs. The Vth variation is enhanced in pMOSFETs due to RTF and reduced in nMOSFET as a result of the Trap Blocking Effect (TBE). RTF in pMOSFET might be the dominant factor of CMOS reliability for future generations.
Ultrafast Dynamics of BiFeO(3) Thin Films Studied by Dual-Color Femtosecond Spectroscopy
(2011-01-01)
Chen, L. Y.
;
Yang, J. C.
;
Shih, H. C.
;
Liang, C. W.
;
Wu, T. -Y.
The ultrafast dynamics in (100)-oriented BiFeO(3) thin films were studied from 20 K to 300 K by using the dual-color femtosecond pump-probe spectroscopy, which were performed by the 400 nm (3.1 eV) pump pulses above the energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap of 2.67 eV. From the temperature-dependent transient reflectivity changes (Delta R/R), the anomalous changes were clearly observed below 200 K caused by magnons. Thus, the femtosecond pump-probe spectroscopy could unambiguously reveal the magnetization dynamics in BiFeO(3) with strong magnetoelectric coupling.
Ultrafast Dynamics of BiFeO3 Thin Films Studied by Dual-Color Femtosecond Spectroscopy
(2011-01-01)
Chen, L. Y.
;
Yang, J. C.
;
Shih, H. C.
;
Liang, C. W.
;
Wu, T. -Y.
The ultrafast dynamics in (100)-oriented BiFeO3 thin films were studied from 20 K to 300 K by using the dual-color femtosecond pump-probe spectroscopy, which were performed by the 400 nm (3.1 eV) pump pulses above the energy gap of 2.67 eV and the 800 nm (1.55 eV) probe pulses below the energy gap of 2.67 eV. From the temperature-dependent transient reflectivity changes (Delta R/R), the anomalous changes were clearly observed below 200 K caused by magnons. Thus, the femtosecond pump-probe spectroscopy could unambiguously reveal the magnetization dynamics in BiFeO3 with strong magnetoelectric coupling.