M.M. Arafat

Gas Sensors Based on One Dimensional Nanostructured Metal-Oxides: A Review

Recently one dimensional (1-D) nanostructured metal-oxides have attracted much attention because of their potential applications in gas sensors. 1-D nanostructured metal-oxides provide high surface to volume ratio, while maintaining good chemical and thermal stabilities with minimal power consumption and low weight. In recent years, various processing routes have been developed for the synthesis of 1-D nanostructured metal-oxides such as hydrothermal, ultrasonic irradiation, electrospinning, anodization, sol-gel, molten-salt, carbothermal reduction, solid-state chemical reaction, thermal evaporation, vapor-phase transport, aerosol, RF sputtering, molecular beam epitaxy, chemical vapor deposition, gas-phase assisted nanocarving, UV lithography and dry plasma etching. A variety of sensor fabrication processing routes have also been developed. Depending on the materials, morphology and fabrication process the performance of the sensor towards a specific gas shows a varying degree of success. This article reviews and evaluates the performance of 1-D nanostructured metal-oxide gas sensors based on ZnO, SnO2, TiO2, In2O3, WOx, AgVO3, CdO, MoO3, CuO, TeO2 and Fe2O3. Advantages and disadvantages of each sensor are summarized, along with the associated sensing mechanism. Finally, the article concludes with some future directions of research.

Effects of reflow on the interfacial characteristics between Zn nanoparticles containing Sn‐3.8Ag‐0.7Cu solder and copper substrate

Purpose – The purpose of this paper is to investigate the effects of zinc (Zn) nanoparticles on the interfacial intermetallic compounds (IMCs) between Sn‐3.8Ag‐0.7Cu (SAC) solder and Cu substrate during multiple reflow.Design/methodology/approach – The nanocomposite solders were prepared by manually mixing of SAC solder paste with varying amounts of Zn nanoparticles. The solder pastes were reflowed on a hotplate at 250°C for 45 s for up to six times. The actual Zn content after reflow was analyzed by inductively coupled plasma‐optical emission spectroscopy (ICP‐OES). The wetting behavior of the solders was characterized by analyzing the contact angles and spreading rates according to the Japanese Industrial Standard (JIS 23198‐3, 2003). The interfacial microstructure of the solder joints were investigated by field emission scanning electron microscope (FESEM) and energy dispersive X‐ray spectroscopy (EDAX).Findings – It was found that upon the addition of 0.3 wt% Zn nanoparticles to the SAC solder, the gr...

A Selective Ultrahigh Responding High Temperature Ethanol Sensor Using TiO2 Nanoparticles

In this research work, the sensitivity of TiO2 nanoparticles towards C2H5OH, H2 and CH4 gases was investigated. The morphology and phase content of the particles was preserved during sensing tests by prior heat treatment of the samples at temperatures as high as 750 °C and 1000 °C. Field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis were employed to characterize the size, morphology and phase content of the particles. For sensor fabrication, a film of TiO2 was printed on a Au interdigitated alumina substrate. The sensing temperature was varied from 450 °C to 650 °C with varying concentrations of target gases. Results show that the sensor has ultrahigh response towards ethanol (C2H5OH) compared to hydrogen (H2) and methane (CH4). The optimum sensing temperature was found to be 600 °C. The response and recovery times of the sensor are 3 min and 15 min, respectively, for 20 ppm C2H5OH at the optimum operating temperature of 600 °C. It is proposed that the catalytic action of TiO2 with C2H5OH is the reason for the ultrahigh response of the sensor.

Interfacial reaction and dissolution behavior of Cu substrate in molten Sn-3.8Ag-0.7Cu in the presence of Mo nanoparticles

Purpose – In electronic packaging, when solid copper comes in contact with liquid solder alloy, the former dissolves and intermetallic compounds (IMCs) form at the solid‐liquid interface. The purpose of this paper is to study the effect of the presence of molybdenum nanoparticles on the dissolution of copper and the formation of interfacial IMC.Design/methodology/approach – Cu wire having a diameter of 250 μm is immersed in liquid composite solders at 250°C up to 15 min. Composite solder was prepared by adding various amount of Mo nanoparticles into the Sn‐3.8Ag‐0.7Cu (SAC) solder paste. The dissolution behavior of Cu substrate is studied for SAC and Mo nanoparticles added SAC solders. The IMCs and its microstructure between the solder and substrate are analyzed by using conventional scanning electron microscope (SEM) and field emission SEM. The elemental analysis was done by using energy‐dispersive X‐ray spectroscopy.Findings – Generally, the dissolution of the substrate increases with increasing immersi...

Effects of Metallic Nanoparticles on Interfacial Intermetallic Compounds in Tin-Based Solders for Microelectronic Packaging

Tin (Sn)-based solders have established themselves as the main alternative to the traditional lead (Pb)-based solders in many applications. However, the reliability of the Sn-based solders continues to be a concern. In order to make Sn-based solders microstructurally more stable and hence more reliable, researchers are showing great interest in investigating the effects of the incorporation of different nanoparticles into them. This paper gives an overview of the influence of metallic nanoparticles on the characteristics of interfacial intermetallic compounds (IMCs) in Sn-based solder joints on copper substrates during reflow and thermal aging. Nanocomposite solders were prepared by mechanically blending nanoparticles of nickel (Ni), cobalt (Co), zinc (Zn), molybdenum (Mo), manganese (Mn) and titanium (Ti) with Sn-3.8Ag-0.7Cu and Sn-3.5Ag solder pastes. The composite solders were then reflowed and their wetting characteristics and interfacial microstructural evolution were investigated. Through the paste mixing route, Ni, Co, Zn and Mo nanoparticles alter the morphology and thickness of the IMCs in beneficial ways for the performance of solder joints. The thickness of Cu3Sn IMC is decreased with the addition of Ni, Co and Zn nanoparticles. The thickness of total IMC layer is decreased with the addition of Zn and Mo nanoparticles in the solder. The metallic nanoparticles can be divided into two groups. Ni, Co, and Zn nanoparticles undergo reactive dissolution during solder reflow, causing in situ alloying and therefore offering an alternative route of alloy additions to solders. Mo nanoparticles remain intact during reflow and impart their influence as discrete particles. Mechanisms of interactions between different types of metallic nanoparticles and solder are discussed.

Effects of Mn nanoparticles on wettability and intermetallic compounds in between Sn-3.8Ag-0.7Cu and Cu substrate during multiple reflow

In this research, the effects of Mn nanoparticles on wettability and interfacial intermetallic compounds in between Sn-3.8Ag-0.7Cu (SAC) solder and copper (Cu) substrate was investigated. The nanocomposite solders were fabricated by mechanical mixing of SAC solder paste with Mn nanoparticles. The melting characteristic of the solders was characterized by differential scanning calorimeter (DSC). The solder pastes were reflowed in a reflow oven at 250°C for 60 seconds. The spreading rate and contact angle of the solders was calculated to measure the wettability. The solder joints were characterized by field emission scanning electron microscope (FESEM) and energy dispersive X-Ray (EDX). It was found that with the addition of Mn nanoparticles the total IMC thickness decreased after first and six times reflow. The Cu3Sn layer was not affected with the addition of Mn nanoparticles. However, some probable mechanism is suggested to explain the effect of Mn nanoparticles on SAC solder.

Reflow behavior of Mo nanoparticle added Sn-3.8Ag-0.7 Cu solder

This work investigates the reflow behavior of lead-free Sn-3.8Ag-0.7Cu solder on Cu substrate in the presence of Mo nanoparticles up to 0.1 wt%. Solders were reflowed in a reflow oven up to six times. The melting behavior of the composite solder was investigated by differential scanning calorimeter. The spreading rate and wetting angle were evaluated to measure the solderability of the composite solder on Cu substrate. It is found that during multiple reflow the interfacial IMC thickness and scallop diameter decreased with the addition of Mo nanoparticles. The presence of Mo nanoparticles was found to hinder the formation of rod shaped Cu6Sn5 IMC during multiple reflow cycles. Investigation on the top surface of interfacial IMC shows that Mo nanoparticles does not dissolve into the solder and imparts their effects on interfacial IMC as particles.

Developments in Semiconducting Oxide-Based Gas-Sensing Materials

Semiconducting metal oxides are very promising gas sensor materials because of their high sensitivity toward many target gases in conjunction with easy fabrication methods, low cost and high compatibility with other parts and processes. Increasing the surface-to-volume ratio is one of the attractive techniques for improving the performance of gas sensors. For this reason, the dimensionality of sensing material has evolved from thick film to thin film technology and more recently to one-dimensional (1-D) nanostructures. This chapter reviews the recent development of semiconducting metal oxides having 1-D nanostructure for gas-sensing applications. At the beginning of this chapter, a brief mechanism of gas sensing is presented for semiconducting metal oxides. After this, the evaluation of dimensionality in gas-sensing materials is discussed briefly. The focus of this chapter is the modification of 1-D nanostructures by different techniques such as producing hollow or porous nanostructures, applying coating, loading nanoparticles, doping or by using mixed oxides. All these recent modifications in gas-sensing materials show some better performance compared with their counterparts. Finally, this chapter is concluded with summary of some major findings and future research directions.