Joseph K. L. Lai

Recent advances in manganese oxide nanocrystals: Fabrication, characterization, and microstructure

Characterization, and Microstructure Zhiwen Chen,*,†,§ Zheng Jiao,*,†,‡ Dengyu Pan,‡ Zhen Li,† Minghong Wu,*,†,‡ Chan-Hung Shek, C. M. Lawrence Wu, and Joseph K. L. Lai †Shanghai Applied Radiation Institute and ‡Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, People’s Republic of China Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong

Transformation evolution and infrared absorption spectra of amorphous and crystalline NANO-Al2O3 powders

Abstract Amorphous and crystalline nano-Al 2 O 3 powders were prepared by direct oxidation and hydrolysis of pure aluminum, respectively. The results by XRD and DTA measurements revealed that after annealing at 1370 K, the evolution in the amorphous nano-Al 2 O 3 powder involved a low temperature relaxation followed by a simple γ- to α-Al 2 O 3 transition. On the other hand, the γ- to θ- to α-A 2 O 3 transitions occurred in crystalline nano-A 2 O 3 powder. The infrared absorption spectra (IR) for both nano-powders after annealing at different temperatures were measured. The IR spectrum of the amorphous nano-A 2 O 3 powder exhibited a very broad and smooth band, without any fine structure in the wave-number range from 400 to 1000 cm −1 . This is in contrast to that of crystalline nano-A 2 O 3 powder. The results mentioned above are discussed with reference to the structure relaxation of amorphous nano-A 2 O 3 powder and the concept of lattice distortion.

GROWTH KINETICS OF INTERMETALLIC COMPOUNDS IN CHIP SCALE PACKAGE SOLDER JOINT

Department of Electronic Engineering, and *Department of Physics and Materials Science,City University of Hong Kong, Hong Kong, People’s Republic of China(Received May 18, 2000)(Accepted in revised form August 18, 2000)Keywords: Solder joint; Intermetallic; Aging; Kinetics; FatigueIntroductionAs the trend in requirements of electronic packaging is toward higher I/O, greater performance, higherdensity, and lighter weight, the use of area array packaging technology is expected to increase. The typeof packaging, such as ball grid array (BGA), chip scale package (CSP), and Flip Chip, provides theultimate in high I/O-density and count with superior electrical performance, and very small size. Themechanical properties of solder joint are recognized as one of the critical factors that determine theirreliability and lifetime [1–5]. During soldering, the formation of intermetallic compounds (IMCs) atsolder/substrate interface is inevitable and ensures a good metallurgical bond. However, during storageand field service, the growth of IMCs will influence the strength of solder joints and result inmechanical failure of the joints [6–10]. Our recent research result shows that the fatigue lifetime ofsolder joint decreases linearly with the increasing square root of IMCs layer thickness [11]. Since theintermetallic is responsible for the solder joint failures, attention has to be paid to the effect of IMCsgrowth on the lifetime and reliability of microelectronic assemblies.This paper discusses the Ni-Sn/Cu-Sn IMCs layer growth kinetics in the joint soldered on platedAu/Ni FR-4 printed circuit board (PCB), which is one of the most commonly used substrate for finepitch area array packaging. The kinetic model describing and predicting the IMC thickness can be usedto estimate the solder joint reliability and lifetime, according the relationship of the IMC thickness withvibration fatigue failure and cyclic bend fatigue.Experimental ProceduresIn this experiment, the chip scale package CSP46-T.75 with Sn/Pb-eutectic solder ball was placed andsoldered on FR-4 printed circuit boards using a high-speed flexible mounter (CASIO YCM-5500V) anda 5-zone N

Recent advances in tin dioxide materials: some developments in thin films, nanowires, and nanorods.

Thin Films, Nanowires, and Nanorods Zhiwen Chen,*,†,§,∥ Dengyu Pan,‡,§ Zhen Li,†,§ Zheng Jiao,*,†,‡,§ Minghong Wu,*,†,‡,§ Chan-Hung Shek,* C. M. Lawrence Wu, and Joseph K. L. Lai †Shanghai Applied Radiation Institute, ‡Institute of Nanochemistry and Nanobiology, School of Environmental and Chemical Engineering, Shanghai University, Shanghai 200444, People’s Republic of China Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Hong Kong

Grain growth in nanocrystalline SnO2 prepared by sol-gel route

Abstract The isothermal grain growth of nanocrystalline SnO 2 , prepared by the sol-gel route was investigated at various temperatures between 500°C and 800°C. Grain growth data were analyzed using two different models. A conventional grain growth model for polycrystalline materials yields an extremely low activation energy of 47 kJ/mol, but large grain growth exponent n from 5 to 11. These values exceed the rational region deduced from conventional theory. An alternative model is based on the assumption that the ordering of the interface regions in nanocrystalline SnO 2 occurs simultaneously with grain growth by structural relaxation. This structural relaxation model describes the grain growth kinetics satisfactorily and also yields a low activation energy of 31 kJ/mol appropriate for the rearrangement of atoms.

Effect of oxygen deficiency on the Raman spectra and hyperfine interactions of nanometer SnO2

Abstract The Raman and Mossbauer spectra of nano-SnO2 specimens with crystallite size 3–16 nm were measured at room temperature. Specimens were annealed at different temperatures in oxygen atmosphere and vacuum respectively. Both the Raman and Mossbauer spectra of the specimens consist of crystalline and interface (or surface) components. The effects of oxygen deficiency on the Raman spectra are presented and correlated with the changes of the Sn-O bond properties, which were obtained from the corresponding Mossbauer spectra.

Nanomicrostructure, chemical stability and abnormal transformation in ultrafine particles of oxidized tin

Abstract Ultrafine oxidized tin particles with particle size about 6 nm have been prepared by inert gas condensation deposition under low oxygen pressure. The nanostructure, hyperfine parameters, and chemical stability of the particles have been studied by means of TEM, XRD and Mossbauer spectra analysis. The results show that the nanostructure of particles can be divided into a crystalline component and a disordered component. Nano-powders have high chemical activity and can be oxidized into stable SnO 2 compounds at ambient temperature. XRD measurements indicate that post-annealing at temperatures of 300–600 °C for 2 h in air produced orthorhombic and tetragonal SnO 2 phases. Orthorhombic SnO 2 phase may be an intermediate phase during the transformation of disordered SnO 2 to tetragonal SnO 2 (rutile) which is the high temperature stable phase under oxygen deficiency conditions.

Effect of solution treatment on the transformation behaviour of cold-rolled duplex stainless steels

Abstract The transformation kinetics of the γ → α transition in duplex stainless steels (Feroplug materials) within the solution treatment temperature range of 1050–1250 °C and the accompanying ageing behaviour have been studied by the use of optical/scanning electron microscopy, an image analyzer and magnetic measurements. Increasing the solution treatment temperature increases the amount of ferrite and reduces the anisotropy in the morphology of the ferrite phase in the matrix. In addition, an increase in the ferrite content leads to less chromium and more nickel within the ferrite phase. Ageing at 600 °C and 700 °C showed that the starting time of ferrite transformation (decomposition) is independent of the solution treatment temperature. The main influence of solution treatment temperature is on the overall time required for completion of transformation and the morphology of the secondary austenite ( γ 2 ) formed during transformation. A higher solution treatment temperature produces a ferrite phase of lower chromium content, this increases the time required for the α → γ 2 + σ transformation and produces needle-shaped intragranular γ 2 .

Hierarchical mesoporous MnO2 superstructures synthesized by soft-interface method and their catalytic performances

To obtain a highly efficient and stable heterogeneous catalyst in catalytic wet hydrogen peroxide oxidation, we have successfully synthesized hierarchical mesoporous manganese dioxide (MnO2) superstructures by a facile and environmental friendly method on a soft-interface between CH2Cl2 and H2O without templates. The main crystal phase of as-prepared MnO2 was proved to be ε-MnO2 by X-ray diffraction techniques. The structure characterizations indicated that the hierarchical MnO2 superstructures were composed of urchin-like MnO2 hollow submicrospheres assembled by one-dimension nanorods building blocks with rich mesoporosity. The nitrogen sorption analysis confirmed that the as-synthesized MnO2 has an average pore diameter of 5.87 nm, mesoporous volume of 0.451 cm(3) g(-1), and specific surface area of 219.3 m(2) g(-1). Further investigations revealed that a possible formation mechanism of this unique hierarchical superstructure depended upon the synthesis conditions. The catalytic performances of the hierarchical mesoporous MnO2 superstructures were evaluated in catalytic degradation of methylene blue in the presence of H2O2 at neutral pH, which demonstrated highly efficient catalytic degradation of the organic pollutant methylene blue using hierarchical mesoporous MnO2 superstructures as catalyst at room temperature.

Assembling tin dioxide quantum dots to graphene nanosheets by a facile ultrasonic route.

Nanocomposites have significant potential in the development of advanced materials for numerous applications. Tin dioxide (SnO2) is a functional material with wide-ranging prospects because of its high electronic mobility and wide band gap. Graphene as the basic plane of graphite is a single atomic layer two-dimensional sp(2) hybridized carbon material. Both have excellent physical and chemical properties. Here, SnO2 quantum dots/graphene composites have been successfully fabricated by a facile ultrasonic method. The experimental investigations indicated that the graphene was exfoliated and decorated with SnO2 quantum dots, which was dispersed uniformly on both sides of the graphene. The size distribution of SnO2 quantum dots was estimated to be ranging from 4 to 6 nm and their average size was calculated to be about 4.8 ± 0.2 nm. This facile ultrasonic route demonstrated that the loading of SnO2 quantum dots was an effective way to prevent graphene nanosheets from being restacked during the reduction. During the calcination process, the graphene nanosheets distributed between SnO2 nanoparticles have also prevented the agglomeration of SnO2 nanoparticles, which were beneficial to the formation of SnO2 quantum dots.