Investigation On The Modifiction Of Thermoelectric Properties For Ca₃Co₄O₉and SrTiO₃Thin Films By Ion Implantation

With the development of modern society, human beings are forced to develop the newenergy conversion techniques due to the increasingly energy crisis and serious environmentalproblems. Thermoelectric materials can convert heat energy into electrical energy directlywithout any environmental pollutions. The current invistigation results show thatthermoelectric energy conversion technique is unlikely to replace the traditional powergeneration techniques, but it can provide an efficiency supplement to the traditionaltechniques. Especially, the thermoelectric devices are able to convert waste heat to electricalenergy. In this context, the energy utilization efficiency will be improved.A major challenge in the implementation of thermoelectric power generation is the lowenergy conversion effciency. Doping is one of the most important methods for improving theperformance of the thermoelectric materials. However, the preparation of dopedthermoelectric oxide thin films are very complex or requires on expensive equepment, so it isdifficult to industrial production. The ion beam injection technique has been used in theproduction of semiconductor sucessfully. If this technique can be applied to the dopingprocess of thermoelectric oxide thin films, there are several advantanges over the traditionapproaches, such as simplification doping process, adaptability to industrial production and soon. Therfore, in order to find a simple and easy industrial doping method, two typicalthermoelectric oxide thin films, p-type Ca3Co4O9and n-type SrTiO3, were modified by ionimplantion and their thermoelectric properties were investigated carefully..The concrete works of this paper is as follows:1) High quality c-axis oriented Ca3Co4O9thin films have been epitaxially grown on (0001)Al2O3single crystal substrates using pulsed laser deposition (PLD), and different doses ofNb ions were injected into the films using an ion beam injection technique. The resistivityand Seebeck coefficient of the films were measured in the temperature range175-380K.The results demonstrated that the power factor of the films were modified with the dopingof Nb. When the injected Nb concentration was3.65×1019/cm3, the power factor of thefilm reached0.10mW/m K2at room temperature, and it appproached a maximum value of0.17mW m-1K-2at380K.2) A nanoscale NbNxsecond phase were generated in the films with the heat treament in pureN2after Nb ion implantion. The resistivity and Seebeck coefficient of the films weremeasured in the temperature range175-380K. The results indicated that the power factorof the films increases when implanted with appropriate quantities of Nb. When theinjected Nb concentration was1.46×1020/cm3, the power factor of the film reached0.17mW m-1K-2at room temperature, which is nearly twice as large as that for pure Ca3Co4O9film. A maximum value of0.22mW m-1K-2was obtained at380K. NbNxsecond phasedoped Ca3Co4O9film has a better thermoelectric perforemance than Nb doped Ca3Co4O9film.3) High quality c-axis oriented SrTiO3epitaxial thin films have been grown on (001) LaAlO3single crystal substrates using PLD, and different doses of Nb ions were implanted intothe films using an ion beam injection technique. The resistivity and Seebeck coefficient ofthe films were measured in the temperature range50-380K. The results demonstrated thatthe power factor of the films were modified with doping of Nb. When the injected Nbconcentration was8.66×1020/cm3, the power factor of the film reached1.1mW m-1K-2atroom temperature and it appproached a maximum value of2.0mW m-1K-2at380K.