Solid State Phenomena Vol. 185

Abstract: The wide-gap semiconductor ZnO with nanostructures such as nanoparticles, nanorods, nanowires has high potential for a variety of sensor applications. This paper reviews the recent developments of ZnO one dimentional nanostructures for future gas sensor applications. Presented first is the factors contributing to the high performances of gas sensors using such nanostructures. Then various fabrication methods of the ZnO nanostructures including vapor phase growth, solution growth, and template-assisted growth are introduced. The characterization and properties of the ZnO nanostructures-based gas sensors are described. The basic mechanisms for explaining the behaviors of the gas sensors are also discussed.

Abstract: Doherty and Chiu reported on the potential use of propagating stress waves for monitoring fatigue crack development in a series of hard-to-inspect weep holes in the wing spar of an aging aircraft. New experimental evidence showed an interesting scattering phenomenon at the defect and demonstrated the ability to use this phenomenon to monitor the development of an upward developing fatigue crack. It was found that a scattered field can be used to highlight the presence of a source of a secondary wave mode arising from the interaction of the incident wave field with the defect. A detailed investigation into these observations will contribute to the creation of new basic scientific understanding of this phenomenon with the potential development of a novel and optimised approach for quantitative inspection of hard-to-inspect regions in a structure.

Abstract: Bi₂Te₃ and its solid solution remain the state-of-the-art thermoelectric materials for refrigeration applications in microelectronics industry, such as dissipating the heat generated by various devices. The fabrication method and associated processing parameters are to be optimised to get desirable composition exhibiting better electrical and thermal transport properties. Carrier concentration and mobility are found to be crucial in achieving high thermoelectric cooling efficiency and energy conversion. In this paper, we present the fabrication and analysis of thermoelectric thin films deposited by RF-magnetron sputtering from n-type Bi₂Te_2.7Se_0.3 and p-type Bi_0.5Sb_1.5Te₃ targets on a silicon substrate. X-ray diffraction, Scanning electron microscopy combined with energy dispersive spectrometry, electrical resistivity, Seebeck coefficient and thermal diffusivity measurements were used for the thermoelectric thin films characterization. We studied the effect of sputtering process parameters, on the structural, electrical and thermal transport characteristics of films. The observed results demonstrate both n-and p-type doped Bi₂Te₃ films exhibit desirable properties and could be potential candidates for thermoelectric micro-cooler applications.

Abstract: Biopolymers play still a relatively minor role in the packaging material markets. For this to grow further there are problems to be solved, such as inadequate barrier properties and moisture sensitivity. Atomic layer deposition (ALD) is one potential solution. Atomic layer deposition is a layer-by-layer thin film deposition process based on self-limiting gas-solid reactions. It is well suited for producing pinhole free barrier coatings uniform in thickness at relatively mild process conditions. The purpose of this presentation is to summarize our recent work done concerning atomic layer deposition of thin aluminum oxide layers onto biopolymers.

Abstract: Nickel-tungsten (Ni-W) plating process exhibited fewer environmental hazards and lower health hazards than conventional chromium bath processes did, because they had the potential to be substituted for certain future applications. This study attempted to develop Ni-W alloy coatings with different weight percentages of tungsten to produce by using nickel-tungsten citrate electrolyte baths that are deposited by pulse current power source techniques. The composition of the ratio of tungsten/nickel was controlled by the change from ion mass transfer rates for the interface between cathodes and electrolytes that were caused by adjustment by charging the over potential or rest that was regulated by the on-off time during pulse and reverse-pulse current. In this study, the corrosion resistance and the composition of the coatings related to the operating parameters were also discussed through the analyses of the experimental design method. Results were found that Ni-W alloy compositions governed through regulation of pulse and pulse-reverse parameters. The frequencies of electric current, T_on and T_off with pulse duty cycles had great impact on chemical composition and surface morphology for the deposits. Results of the electrochemical tests indicated the pulse plated Ni-W metal alloy coatings in which the corrosion resistance was superior to that of the alloy deposited by the direct current technique.

Abstract: In the present work, a piezoelectric diaphragm pump was designed and investigated. The pump uses a piezoelectric diaphragm transducer as the driving component, and two check valves located at the inlet and outlet to control the flow direction. The displacement of the transducer was first measured statically and dynamically. Then the vibration of check valves and the effects of chamber depth were investigated. Finally the pump performance was characterized. Maximum flow rate of 200 mL/min and pressure head of 5 mH₂O can be achieved.

Abstract: Smoke detection with multiwalled carbon nanotubes (MWCNTs)/cement composites have been studied. Pellets of MWCNTs reinforced Portland cement have been casted with varying MWCNTs %. The DC transient studies depicted an increase in conductivity when exposed to smoke. Responsivity in the range 26-46% has been obtained under smoky environment based on MWCNTs % in the composites. Ionic conductivity increased with frequency at room temperature under ambient and smoky environments. In this paper, we also report fabrication technique of the pellets and the sensing mechanism is explained on the basis of ionic conductivity of the cementitious material in combination with the conductive carbon fibers present in the porous matrix of the cement.

Abstract: Nickel-titanium (NiTi) alloys are high-performance shape memory alloy actuator materials [1]. These alloys are metals possessing a memory, which can be triggered thermally or mechanically. Thin film of nickel-titanium shape memory alloy (SMA) is an excellent candidate for micro electric mechanical systems (MEMS). On the other hand, PZT is well known for its superior ferroelectric, dielectric and piezoelectric properties [2]. Integrating a ferroelectric (PZT) with ferroelastic (NiTi) material is technically interesting as the resulting heterostructure may then produce the properties associated with both of the materials and enhances the performance of MEMS based devices [3]. An important issue in the synthesis of NiTi/PZT hybrid heterostructure is the formation of appropriate crystalline phases of each material. The interdiffusions present at the interface of NiTi and PZT layer makes it difficult to obtain the optimal properties of both the components suitably at lower thickness values. With the miniaturization of active thin film devices, particularly for MEMS applications, it is desirable to obtain the best properties at lower thickness values. Therefore, in the present study, we have tried to lower the thickness of top NiTi films with the help of thin TiO_x buffer layer between PZT and NiTi films. As expected, the excellent structural, electrical and mechanical properties of the NiTi/PZT heterostructure were achieved at lower thickness values.

Abstract: This paper reports the investigation of a root cause of stain formation on the surfaces of diamond-like carbon (DLC) films. The DLC thin films are prepared using a radio-frequency plasma enhance chemical vapor deposition (RF-PECVD) technique with C₂H₄ as a carbon precursor gas. We have observed water spot-like stains on the DLC surfaces after treating the films with a dilute solution of dipropylene glycol monomethyl ether (DPGME). Low voltage-scanning electron microscopy (SEM) is employed to examine the thin layer of agglomerated stains on the surfaces. The results from capacitance-voltage (C-V) measurements show that as-deposited films inherit some trapped charge accumulations within the structure, thereby resulting in the pronounced shift in the flat-band voltage. These trapped charges make the films prone to surface stain formation. Post-annealing of the DLC films at 200 °C in N₂ for 1 h has proven to reduce the trapped charge density, and therefore prevent stain formation on the DLC films.