Browsing by Author "Peng, CH"

Now showing 1 - 10 of 10

A self-propagating high-temperature synthesis method for Ni-ferrite powder synthesis
(2004-03-25)
Peng, CH
;
Hwang, CC
;
Hong, CK
;
Chen, SY
;
材料科學與工程學系
Ni-ferrite (NiFe2O4) powder was synthesized by a self-propagating high-temperature synthesis (SHS) process using Fe, Fe2O3 and various Ni-containing species (Ni-CSs) as reactants. The reactants were thoroughly mixed and pressed into a cylindrical compact. The compact was ignited by electrical heating under oxygen partial pressures varying between 0.02 and 1.5 MPa. The effects of the type of Ni-containing species, the reactant composition, the oxygen pressure on the combustion temperature, and the product conversion were investigated. X-ray diffraction (XRD) analysis showed that oxygen pressure promoted product conversion. Among several Ni-containing species tested, Ni2O3 was found to give the highest conversion. The product conversion increased with increasing iron content and then decreased with further increase in iron content. Scanning electron microscope (SEM) observations showed that the product synthesized is mostly in the form of agglomerated fine particles with submicron size (0.1-0.5 mum). Hysteresis behavior analysis showed that the product as synthesized possessed better soft magnetic properties when compared with commercial Ni-ferrite prepared by the solid reaction method. (C) 2004 Elsevier B.V. All rights reserved.
Combustion synthesis of Ni-Zn ferrite powder - influence of oxygen balance value
(2005-01-01)
Hwang, CC
;
Tsai, JS
;
Huang, TH
;
Peng, CH
;
Chen, SY
In this study, Ni0.5Zn0.5FC2O4 powder was synthesized via an exothermic reaction between nitrates [Ni(NO3)(2).6H(2)O, Zn(NO3)(2).6H(2)O, Fe(NO3)(3).9H(2)O, and NH4NO3] and glycine [NH2CH2COOH]. By adjusting the glycine-to-nitrates ratio, the oxygen balance (OB) values of the reactant mixtures can be varied in which the combustion phenomena is altered and thereby the as-synthesized products with different characteristics are obtained. An interpretation based on the measurement of maximum combustion temperature (T-c) and the amounts of gas evolved during reaction for various OB values has been proposed regarding the nature of combustion and its correlation with the characteristics of as-synthesized products. After instrumental analyses, it is shown that the as-synthesized powders are nanoscale crystallites with a large specific surface area and they inherit a superparamagnetic behavior. (C) 2004 Elsevier Inc. All rights reserved.
Effect of annealing atmosphere on physical characteristics and photoluminescence properties of nitrogen-implanted ZnO thin films
(2005-11-15)
Yang, CC
;
Lin, CC
;
Peng, CH
;
Chen, SY
;
材料科學與工程學系
ZnO films were pre-treated with nitrogen implantation in the range from 5 x 10(12) to 5 x 10(15) cm(-2). Effect of nitrogen concentration on structural crystallinity and photoluminescence properties of nitrogen-implanted ZnO films under different atmospheres and annealing treatments was investigated. It was found that there exists a solubility issue of nitrogen in ZnO films at 850 degrees C via secondary ion mass spectrometry (SIMS). It was found that the peak intensity of near band-edge (NBE) emission remarkably decreases with the increase of concentration of implanted nitrogen if annealed in nitrogen atmosphere due to the increased oxygen vacancies. However, when the ZnO was implanted with 5 x 10(12) cm(-2) and annealed in oxygen atmosphere, the optical properties are improved probably because the effective incorporation of O atom diminishes those donor levels (oxygen vacancies) and the crystallinity is also improved due to implanted nitrogen. However, excess nitrogen would reduce the crystallinity and promote the formation of the deep-level emission due to high amount of intrinsic and structure defects. (c) 2005 Elsevier B.V. All rights reserved.
Electromagnetic wave absorption behavior of NiZn-ferrite prepared via hydrothermal method
(2005)
Peng, CH
;
Wang, HW
;
Kan, SW
;
Chen, SY
;
材料科學與工程學系
Ni0.5Zn0.5Fe2O4 ferrite powders were synthesized by a hydrothermal method. The nanoparticles of these materials were mixed with a thermal-plastic polyurethane (TPU) polymer in order to form a suitable composite for electromagnetic wave absorber in a frequency range from 2.0 to 15.0 GHz. The effect of particle size on the reflection loss was investigated by comparing nanosized and microsized powders. The reflection loss as a function of frequency (f), thickness of the absorber(d), the real and imaginary part of permittivity (epsilon' / epsilon") and the real and imaginary part of permeability (mu'/mu") were obtained by calculation using the Bruggeman effective medium theory. The effect of Co2+, Cu2+, and Mg2+ on the reflection loss was also studied.
Low temperature (850 degrees C) two-step N2O annealed thin gate oxides
(1996)
Lai, CS
;
Lee, CL
;
Lei, TF
;
Chao, TS
;
Peng, CH
The electrical characteristics of thin gate dielectrics prepared by low temperature (850 degrees C) two-step N2O nitridation (LTN) process are presented. The gate oxides were grown by wet oxidation at 800 degrees C and then annealed in N2O at 850 degrees C. The oxide with N2O anneal, even for low temperature (850 degrees C), had nitrogen incorporation at oxide/silicon interface. The charge trapping phenomena and interface-state generation (Delta D-itm) induced by constant current stressing were reduced and charge-to-breakdown (Q(bd)) under constant current stressing was increased. This LTN oxynitride was used as gate dielectric for N-channel MOSFET, whose hot-carrier immunity was shown improved and reverse short channel effect (RSCE) was suppressed.
Microwave absorbing materials using Ag-NiZn ferrite core-shell nanopowders as fillers
(2004-12-01)
Peng, CH
;
Wang, HW
;
Kan, SW
;
Shen, MZ
;
Wei, YM
Silver nanoparticles coated with Ni0.5Zn0.5Fe2O4 spinel ferrites, forming a core-shell structure, were synthesized by utilizing hydrothermal method at different ferrite/silver ratio (ferrite/silver = 6/1, 4/1, 2/1, 1/1, 1/6) and introduced into polyurethane matrix to be a microwave absorber. The complex permittivity (epsilon', epsilon") and permeability (mu', mu") of absorbing composite materials consisted of ferrite/silver core-shell nanopowders and polyurethane were measured in the frequency range of 2-15 GHz. The reflection loss and matching frequency were calculated from measured data using theory of the absorbing wall for different ferrite/silver ratios. It was found that the matching frequency for reflection loss exceeded a satisfactory -25dB at 9.0 GHz for using NiZn ferrite as a filler shifts to higher frequencies (10.9-13.7 GHz) as the ferrite/silver ratio of core-shell nano-filler decreased from 6/1 to 2/1. The present result demonstrates that microwave absorbers using ferrite/silver core-shell filler can be fabricated for the applications over 9 GHz, with reflection loss more than-25 dB for specific frequencies, by controlling the ferrite/silver ratio of the core-shell nano-fillers in the composites. (C) 2004 Elsevier B.V. All rights reserved.
Microwave-absorbing characteristics for the composites of thermal-plastic polyurethane (TPU)-bonded NiZn-ferrites prepared by combustion synthesis method
(2005-02-25)
Peng, CH
;
Hwang, CC
;
Wan, J
;
Tsai, JS
;
Chen, SY
NiZn ferrite with the chemical formula Ni0.5-xZn0.5-xM2xFe2O4 (M = Co, Cu, or Mg, and x = 0 or 0.05) was synthesized by a combustion synthesis method using metal nitrates and urea ((NH2)(2)CO) as reactants. The narrocrystallite of these materials were mixed with a thermal-plastic polyurethane (TPU) elastomer to be converted into a microwave-absorbing composite. The complex relative permittivity (epsilon(r) = epsilon'-jepsilon") and permeability (mu(r)=mu'-jmu") of the absorber were measured in a frequency range of 2-12GHz. The reflection loss (R.L.), matching frequency (f(m)) and matching thickness (d(m)) were calculated using the theory of the absorbing wall. Effects of both the particle size of ferrite and the dopant presented in the ferrite on the electromagnetic properties and microwave-absorbing characteristics were investigated. It was found that nanoparticles around 40 nm exhibit higher reflection loss than both those obtained from micro-sized powders and those with size less than 25 nm. Also, it was shown that the Co-doped, Mg-doped, and Cu-doped NiZn ferrite-TPU composites could be designed to be more negative than -20 dB, in a frequency range of 2-12 GHz, to become promising materials for microwave-absorbing application. These doped ferrite-containing composites have more effective microwave-absorbing characteristics compared to undoped one. (C) 2004 Elsevier B.V. All rights reserved.
Preparation and characterization of YBa2Cu3O7-x superconductor by means of a novel method combining sol-gel and combustion synthesis techniques
(2004-06-15)
Peng, CH
;
Hwang, CC
;
Hong, CK
;
Chen, SY
;
材料科學與工程學系
The electromagnetic wave absorbing characteristics of MnZn ferrite-TPU composite materials
(2005)
Peng, CH
;
Wang, HW
;
La, YT
;
Chen, SY
;
材料科學與工程學系
The complex permeability and permittivity (mu(r)*and epsilon(r)*) were investigated for MnZn ferrite-TPU (thermal-plastic polyurethane) composite with ferrite weight percentage varying from 66.7%-88.9%. Fine ferrite powders doped with Mg, Co, and Cu prepared by the citrate gel route were used as fillers. The effective complex permeability and permittivity specta in composites with various ferrite weight percentage were calculated using the Bruggeman effective medium theory. It was found that the dopant content and ferrite/TPU ratio influences the microwave-absorbing characteristics. The results show that the absorbers with (Mg, Co, Cu) doped ferrite have excellent electromagnetic absorption. The reflection loss more than 20dB at the frequencies below 3 GHz can be achieved by controlling the ferrite content and doped elements in the ferrite-TPU composites.
Tunable growth of ZnO nanorods synthesized in aqueous solutions at low temperatures
(2006-01-01)
Hsiao, CS
;
Peng, CH
;
Chen, SY
;
Liou, SC
;
材料科學與工程學系
Highly arrayed ZnO nanorods were fabricated on the Si substrate buffered with patterned ZnO film (ZnOf/Si) via wet-chemical process. The growth behavior and morphology of single-crystal ZnO nanorods (ZNs) were investigated in terms of the annealing temperatures of the sputtered ZnO film. We found that the growth morphology of ZnO nanorods is strongly dominated by the grain size of the ZnO film on the Si substrate. The ZnOf/Si substrate was annealed at above a critical temperature to promote the crystallization of ZnO phase, and high-resolution transmission electron microscopy demonstrated that both ZNs and ZnOf on Si substrate are coherent. Furthermore, the ZNs seem to nucleate from the concave tip near the grain boundary between two ZnO grains in the ZnO film because of higher surface energy. However, a higher annealing temperature may lead to the formation of a larger ZnO crystal due to the coplanar coalescence behavior of several individual ZnO nanorods. (c) 2006 American Vacuum Society.