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Dielectric and p-type Characteristics of Li-doped ZnO Thin Films
Guojie Li,최병춘 한국물리학회 2014 새물리 Vol.64 No.7
We report the structural, dielectric and electronic properties of Zn1−xLixO (x = 0.1, 0.05, 0.10) thin films prepared on Pt(111)/Ti/SiO2/Si substrates by using pulsed laser deposition (PLD). Xray diffraction (XRD) analyses revealed that all of films had a single phase as the Zn-O bond length gradually increased with increasing Li content at first and then decreased after a certain threshold. 5-at% and 10-at% Li-doped ZnO thin films show p-type behavior based on Hall-effect measurements. The existence of defects, such as Lii (interstitial Li) and LiZn (substitutional Li at the Zn site), should be considered in the host materials. The relationship between the defects and the Li concentration is consistent with the dielectric results. The stabilization of p-type thin films as to the behavior of defects is also discussed theoretically.
Structural, Morphological, and Optical Studies on Li-doped ZnO Thin Films Deposited by Using PLD
Guojie Li,S. Sambasivam,Saes Byul Kim,박성욱,정중현,전병억,최병춘 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.4
We report the structural and the optical properties of Zn_(1−x)Li_xO (x = 0.0, 0.02, 0.08, 0.12, 0.18) nanocrystalline thin films deposited on ?Al_2O_3 substrates by using pulsed laser deposition. X-ray diffraction (XRD) analysis revealed that all the films were single phase and had a hexagonal wurtzite structure. The lattice constant increased gradually with increasing Li content. Atomic force microscopy (AFM) showed that the grain size of the films was approximately 20 ?30 nm. Optical absorption studies in the wavelength range 200 ?900 nm revealed an increase in the band gap of the Li-doped ZnO films from 3.19 to 3.41 eV. Photoluminescence (PL) spectroscopy of these films was carried out. The luminescence observed was attributed to defects in the nanocrystalline Li-doped ZnO films, and the PL intensity decreased with increasing Li content.
Jun, Byeong-Eog,Kim, Sas Byul,Li, Guojie,Chun Choi, Byung,Kee Moon, Byung,Hyun Jeong, Jung Royal Swedish Academy of Sciences 2010 Physica scripta Vol.2010 No.t139
<P>Alkaline niobate <I>A</I>NbO<SUB>3</SUB> (<I>A</I>=K, Li and Na) ceramics were fabricated into the composites of K<SUB>0.5</SUB>Na<SUB>0.5</SUB>NbO<SUB>3</SUB> (KNN) and NaK<SUB>2</SUB>Li<SUB>2</SUB>Nb<SUB>5</SUB>O<SUB>15</SUB> (NKLN) phases. The NKLN phase was composed of completely filled tetragonal tungsten-bronze and LiNbO<SUB>3</SUB> structures. The (1−<I>x</I>)KNN–(<I>x</I>/5)NKLN composite ceramics displayed alloy effects with changing <I>x</I>. The NKLN phase was expected to be solidified into the KNN phase through the liquidus–solidus curve of the (1−<I>x</I>)KNN–(<I>x</I>/5)NKLN composite ceramics. The (1−<I>x</I>)KNN–(<I>x</I>/5)NKLN composite ceramics showed the ferroelectric distortions with orthorhombic symmetry. We discussed the ferroelectric and dielectric properties of the (1−<I>x</I>)KNN–(<I>x</I>/5)NKLN composite ceramics.</P>
박진영,박병락,Li Zhan,Weixiao Du,Baozhen Shan,Guojie Liu,황운봉 한국물리학회 2019 Current Applied Physics Vol.19 No.4
This work presents a facile fabrication method for vertical polymerised structures with a tuned superhydrophobic surface on an aluminium alloy. This method includes vertically polymerising heptadecafluoro- 1,1,2,2-tetra-hydrodecyltrichlorosilane (HDFS), which is used for self-assembled monolayer (SAM) coatings, wherein vertical polymerisation is normally considered a process defect. For fabricating the base structure, aluminium hydroxide was generated to form a nanostructure. HDFS was coated as an SAM and microflake fabrication was carried out on this surface for various lengths of time. Microflakes were fabricated by vertical polymerisation of HDFS through this process. Samples coated for 10–30 min showed the water contact angle (θC) of>168.3° and the lowest water sliding angle (θS) of<11.8°. After 30 min, the water droplet clung to the microstructure that increased in size beyond 1 μm, thereby increasing of θS. This micro/nano dual-scale-flake surface was achieved without any hazardous etching processes and can be facilely applied in various industrial fields that require superhydrophobic surfaces.
Damping for Wind Turbine Electrically Excited Synchronous Generators
Wang Tianyu,Li Guojie,Zhang Yu,Fang Chen 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.4
The electrically excited synchronous generator (EESG) is applied in wind turbine systems recently. In an EESG control system, electrical torque is affected by stator flux and rotor current. So the control system is more complicated than that of the permanent-magnet synchronous generator (PMSG). Thus, the higher demanding of the control system is required especially in case of wind turbine mechanical resonance. In this paper, the mechanism of rotor speed resonant phenomenon is introduced from the viewpoint of mechanics firstly, and the characteristics of an effective damping torque are illustrated through system eigenvalues analysis. Considering the variables are tightly coupled, the four-order small signal equation for torque is derived considering stator and rotor control systems with regulators, and the bode plot of the closed loop transfer function is analyzed. According to the four-order mathematical equation, the stator flux, stator current, and electrical torque responses are derived by torque reference step and ramp in MATLAB from a pure mathematical deduction, which is identical with the responses in PSCAD/EMTDC simulation results. At last, the simulation studies are carried out in PSCAD software package to verify the resonant damping control strategy used in the EESG wind turbine system.
Damping for Wind Turbine Electrically Excited Synchronous Generators
Tianyu, Wang,Guojie, Li,Yu, Zhang,Chen, Fang The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.4
The electrically excited synchronous generator (EESG) is applied in wind turbine systems recently. In an EESG control system, electrical torque is affected by stator flux and rotor current. So the control system is more complicated than that of the permanent-magnet synchronous generator (PMSG). Thus, the higher demanding of the control system is required especially in case of wind turbine mechanical resonance. In this paper, the mechanism of rotor speed resonant phenomenon is introduced from the viewpoint of mechanics firstly, and the characteristics of an effective damping torque are illustrated through system eigenvalues analysis. Considering the variables are tightly coupled, the four-order small signal equation for torque is derived considering stator and rotor control systems with regulators, and the bode plot of the closed loop transfer function is analyzed. According to the four-order mathematical equation, the stator flux, stator current, and electrical torque responses are derived by torque reference step and ramp in MATLAB from a pure mathematical deduction, which is identical with the responses in PSCAD/EMTDC simulation results. At last, the simulation studies are carried out in PSCAD software package to verify the resonant damping control strategy used in the EESG wind turbine system.