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A Comparative Study of Boron and Phosphorus Doping Effects in SiC: H Films Prepared by ECR-CVD

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Journal of Materials Science & Technology 1998年第1期14卷 65-71页

作者： S.F. Yoon (school of Electrical and Electronic Engineering, nanyang technological university, nanyang Avenue,singapore 639798, Rep. of singapore) school of Electrical and Electronic Engineering Nanyang Technological University Nanyang Avenue Singapore 639798 Singapore

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) technique from a mixture of methane, silane and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the microwave power on the deposition rate and optical bandgap were investigated, and variations in the photoand dark-conductivities and activation energy were studied in conjunction with film analysis using the Raman scattering technique. In the case of boron-doped samples, the conductivity increased rapidly to a maximum, followed by rapid reduction at high microwave power. The ratio of the photo- to dark-conductivity (σph/σd) peaked at microwave power of ~600 W. Under conditions of high microwave power, Raman scattering analysis showed evidence of the formation and increase in the silicon microcrystalline and diamond-like phases in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the *** the case of phosphorusdoped SiC:H samples, it was found that increase in the microwave power has the effect of enhancing the formation of the silicon microcrystalline phase in the films which occurred in correspondence to a rapid increase in the conductivity and reduction in the activation energy The conductivity increase stabilised in samples deposited at microwave power exceeding 500 W probably as a result of dopant saturation. Results from Raman scattering measurements also showed that phosphorus doping had the effect of enhancing the formation of the silicon microcrystals in the film whereas the presence of boron had the effect of preserving the amorphous structure.

关键词： ECR A Comparative Study of Boron and Phosphorus Doping Effects in SiC H Films Prepared by ECR-CVD

Optical and Structural Properties of In_(0.52)Al_(0.48)As/InP Structures Grown at Very High Arsenic Overpressures by Molecular Beam Epitaxy

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Journal of Materials Science & Technology 1998年第3期14卷 231-235页

作者： S.F. Yoon(school of Electrical and Electronic Engineering, nanyang technological university, nanyang Avenue,singapore 639798, Rep. of singapore school of Electrical and Electronic Engineering Nanyang Technological University Nanyang Avenue Singapore 639798 Singapore

Growth of ln0.52Al0.48As epitaxial layers on lnP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressures (V/III flux ratios from 30 to 300) has been carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) shows a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 result in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room temperature Raman scattering measurements show a narrowing in the lnAs-like and AlAs-like longitudinal-optic (LO)phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectra taken at increasing temperatures show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep lying centres. This effect is more prominent in samples grown at lower V/III flux ratios. Hall effect measurements show a gradual reduction in the mobility in correspondence to an increase in the electron concentration as the flux ratio is increased.

关键词： As/InP Structures Grown at Very High Arsenic Overpressures by Molecular Beam Epitaxy InP Optical and Structural Properties of In Al

Characteristics of In_(0.52)Al_(0.48)As Grown on InP(100) Substrates by Molecular Beam Epitaxy: Growth Optimisation and Effects of Si Doping

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Journal of Materials Science & Technology 1997年第2期13卷 91-98页

作者： S.F.Yoon(school of Electrical and Electronic Engineering, nanyang technological university, Nanyng Avenue,singapore 639798, Rep. of singapore) school of Electrical and Electronic Engineering Nanyang Technological University Nanyang Avenue Singapore 639798 Singapore

Growth of In0.52Al0.48As epilayers on InP (100) substrates by molecular beam epitaxy at a wide range of substrate tempreatures (470~550℃) and at different Si doping levels has been carried out. Low temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) analyses shaw a strong dependence of the PL and XRD linewidths, XRD intensity ratio (Lepi/Isub), and lattice-mismatch on the substrate temperature. The X-ray diffraction peaks of samples grown at law temperatures show a composition of smaller peaks, indicating the presence of disorder due to alloy clustering. Raman scattering measurements of the same samples show an additional higher energy mode at 273 cm-1 in addition to the InAs-like and AlAs-like longitudinal-optic (LO) phonon modes. Samples doped with Si show an inverted S-shaped dependence of the PL peak energy variation with the temperature which weakens at high doping levels due to a possible reduction in the donor binding energy. Supported be observations of a reduction in both the AlAs-like and InAs-like LO phonon frequencies and a broadening of the LO phonon line shape as the doping level is increased, the PL intensity also shows in increasing degrees at higher doping levels, a temperature dependence which is characteristic of disordered and amorphous materials.

关键词： As Grown on InP Characteristics of In Growth Optimisation and Effects of Si Doping Substrates by Molecular Beam Epitaxy InP Al Si

Development and optimisation of electrode materials in solid oxide fuel cells

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电池 2002年第3期32卷 133-137页

作者： JIANG San ping(Fuel Cell Strategic Research Programme, school of Mechanical and Production Engineering,nanyang technological university, nanyang Avenue, singapore 639798) Fuel Cell Strategic Research Programme School of Mechanical and Production Engineering Nanyang Technological University 新加坡 639798

Solid oxide fuel cell (SOFC) is an all solid electrochemical device to convert fuels such as hydrogen and natural gas to electricity with high efficiency and very low greenhouse gas emission compared to traditional thermal power generation plants. Moreover, the reliability and efficiency of SOFC is critically dependent on the performance and stability of its components including anode, cathode and electrolyte. This in turn is largely dependent on the material selection and the fabrication processes. In this paper, specific examples are given to demonstrate strategy and process in the development and optimisation of electrode materials such as Ni/Y 2O 3 ZrO 2 cermet anodes and (LaSr)MnO 3 based cathodes. The results also demonstrate the importance of fabrication processes and that the understanding of the electrode process plays a very important role in the optimisation process of electrode materials.

关键词：固体氧化物燃料电池电极材料电极优化

A Hybrid Low Temperature Surface Alloying Process for Austenitic Stainless Steels

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材料热处理学报 2004年第5期25卷 307-310页

作者： Y.Sun schoolofMaterialsEngineering NanyangTechnologicalUniversitySingapore639798

This paper describes a novel, hybrid process developed to engineer the surfaces of austenitic stainless steels at temperatures below 450°C for the improvement in wear and corrosion resistance. The process is carried out in the plasma of a glow discharge containing both nitrogen and carbon reactive species, and facilitates the incorporation of both nitrogen and carbon into the austenite surface to form a dual-layer structure comprising a nitrogen-rich layer on top of a carbon-rich layer. Both layers can be precipitation-free at sufficiently low processing temperatures, and contain nitrogen and carbon respectively in supersaturated fee austenite solid solutions. The resultant hybrid structure offers several advantages over the conventional low temperature nitriding and the newly developed carburizing processes in terms of mechanical and chemical properties, including higher surface hardness, a hardness gradient from the surface towards the layer-core interface, uniform layer thickness, and much enhanced corrosion resistance. This paper discusses the main features of this hybrid process and the various structural and properties characteristics of the resultant engineered surfaces.

关键词：奥氏体不锈钢表面铸合等离子体渗氮等离子体渗碳磨损腐蚀

Rational points and zeta functions of some curves over finite fields

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Science China Mathematics 2010年第11期53卷 2855-2863页

作者： WANG Long1, & LUO JinQuan2,3 1Department of mathematical sciences, Tsinghua university, Beijing 100084, China 2school of mathematical sciences, Yangzhou university, Yangzhou 225002, China 3Division of mathematical sciences, school of physical and mathematical sciences, nanyang Technology university, 637371, singapore Department of mathematical sciences Tsinghua University Beijing China school of mathematical sciences Yangzhou University Yangzhou China Division of mathematical sciences School of Physical and Mathematical Sciences Nanyang Technology University Singapore Singapore

In this paper we study the number of rational points on some curves over finite fields. Moreover, zeta functions of the associated function fields are evaluated explicitly.

关键词： exponential sum rational point rational place zeta function

Complete solving of explicit evaluation of Gauss sums in the index 2 case

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Science China Mathematics 2010年第9期53卷 2525-2542页

作者： YANG Jing1,2 & XIA LingLi3,1Department of mathematical sciences,Tsinghua university,Beijing 100084,China 2Division of mathematical sciences,school of physical and mathematical sciences,nanyang technological university,637371,singapore 3Basic Courses Department,Beijing Union university,Beijing 100101,China Department of mathematical sciences Tsinghua University Beijing China Division of mathematical sciences School of Physical and Mathematical Sciences Nanyang Technological University Nanyang Singapore Basic Courses Department Beijing Union University Beijing China

Let p be a prime number,N be a positive integer such that gcd(N,p) = 1,q = pf where f is the multiplicative order of p modulo *** χ be a primitive multiplicative character of order N over finite field *** paper studies the problem of explicit evaluation of Gauss sums G(χ) in the "index 2 case"(i.e.[(Z/NZ):] = 2).Firstly,the classification of the Gauss sums in the index 2 case is ***,the explicit evaluation of Gauss sums G(χλ)(1 λ N-1) in the index 2 case with order N being general even integer(i.e.N = 2r·N0,where r,N0 are positive integers and N0 3 is odd) is ***,combining with the researches before,the problem of explicit evaluation of Gauss sums in the index 2 case is completely solved.

关键词： Gauss sum Stickelberger’s theorem Stickelberger congruence Davenport-Hasse lifting formula Davenport-Hasse product formula

Revisited Vanoni-Brooks sidewall correction

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International Journal of Sediment Research 2011年第4期26卷 524-528页

作者： Nian-Sheng CHENG 1 Assoc.Prof,school of Civil and Environmental Engineering,nanyang technological university,nanyang Avenue,singapore 639798. Assoc. Prof. School of Civil and Environmental Engineering Nanyang Technological University Nanyang Avenue Singapore 639798

The evaluation of the sidewall friction could be inconvenient in the implement of the Vanoni-Brooks sidewall correction *** the Colebrook-White equation and Nikuradse’s pipe friction data,two explicit formulae are developed in this note for finding the sidewall friction *** are applicable for various sidewalls that are either hydrodynamically-smooth or rough,or in the transitional regime.

关键词： Sidewall correction Friction factor Open channel flow Pipe flow Sediment transport

Scour and Scour Countermeasures at Bridge Sites

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Transactions of Tianjin university 2008年第4期14卷 289-295页

作者： CHIEW Yee-Meng school of Civil and Environmental Engineering Nanyang Technological University

This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer's ability to propose devices for effective scour *** summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour.

关键词： abutment scour pier scour river engineering scour countermeasure riprap protection sediment transport