Nowadays, strength monitoring of concrete structures by the nondestructive method has gained more attention. Strength monitoring is not only important to determine the readiness of structures for service, but also to ensure the safety of the structure itself during the construction. The main goal of in-situ monitoring the strength gain in concrete is to obtain reliable information about the quality of concrete which can be further used to assess construction schedule and process of concrete structures, such as determining the optimal traffic opening time. The current methods are unreliable, inefficient, costly and partially destructive. To address these challenges, this paper aims to investigate the feasibility of employing polymer based piezoelectric sensors to characterize the in-situ compressive strength gain of concrete at the early ages. The pitch-catch approach was considered for the active sensing approach. In this approach, a piezoelectric transducer acts an actuator to propagates the Lamb waves while another piezoelectric device works as a sensor to detect the signal. A PVDF sensor was fabricated using electrospinning method, and a commercial PZT transducer was used to generate the Lamb waves. The developed piezoelectric-based set-up has shown a promising technique for strength development of cementitious materials at early ages.
Zinc oxide (ZnO) is an earth abundant wide bandgap semiconductor of great interest in the recent years. ZnO has many unique properties, such as non-toxic, large direct bandgap, high exciton binding energy, high transparency in visible and infrared spectrum, large Seebeck coefficient, high thermal stability, high electron diffusivity, high electron mobility, and availability of various nanostructures, making it a promising material for many applications. The growth techniques of ZnO is reviewed in this work, including sputtering, PLD, MOCVD and MBE techniques, focusing on the crystalline quality, electrical and optical properties. The problem with p-type doping ZnO is also discussed, and the method to improve p-type doping efficiency is reviewed. This paper also summarizes the current state of art of ZnO in thermoelectric and photovoltaic applications, including the key parameters, different device structures, and future development.
ZnO-based materials show promise in energy harvesting applications, such as piezoelectric, photovoltaic and thermoelectric. In this work, ZnO-based vertical Schottky barrier solar cells were fabricated by MOCVD de- position of ZnO thin films on ITO back ohmic contact, while Ag served as the top Schottky contact. Various rapid thermal annealing conditions were studied to modify the carrier density and crystal quality. Greater than 200 nm thick ZnO films formed polycrystalline crystal structure, and were used to demonstrate Schottky solar cells. I-V characterizations of the devices showed photovoltaic performance, but but need further development. This is the first demonstration of vertical Schottky barrier solar cell based on wide bandgap ZnO film. Thin film and bulk ZnO grown by MOCVD or melt growth were also investigated in regards to their room- temperature thermoelectric properties. The Seebeck coefficient of bulk ZnO was found to be much larger than that of thin film ZnO at room temperature due to the higher crystal quality in bulk materials. The Seebeck coefficients decrease while the carrier concentration increases due to the crystal defects caused by the charge carriers. The co-doped bulk Zn0:96Ga0:02Al0:02O showed enhanced power factors, lower thermal conductivities and promising ZT values in the whole temperature range (300-1300 K).
The wide-bandgap semiconductor ZnO has gained major interest in research community for its unique properties and wide range of applications. In this review article, we present synthesis techniques and a few emerging applications for ZnO. Common techniques for growing ZnO films are discussed briefly, and a detailed discussion of MOCVD growth of ZnO is provided citing previous experimental reports on this technique by our group and others. A few important and distinctive uses of ZnO are discussed for various applications focusing on the current limitations of ZnO to realize its feasibility in these applications.
Conference Committee Involvement (1)
Sixteenth International Conference on Solid State Lighting and LED-based Illumination Systems
9 August 2017 | San Diego, California, United States