Preparation And Characterization Of CuAlO₂Transparent Conductive Oxides

Unique transparent and conducting properties of transparent conducting oxides（TCO） lead them for numerous optoelectronic applications, such as solar cell, LCD,gas sensors, thermal conductive glass etc. However, almost all of the well-knownTCOs have n-type conductivity; the lack of p-type TCOs severely limits the potentialapplications of these materials to design p-n junction devices. CuAlO₂is known as atransparent oxide material that exhibits p-type conductivity designed based on thetheory of valence band modification. Recently, many efforts have been done toimprove its photoelectric properties and related performances due to the advantage ofnative p-type conductivity and transmittance in infrared region. Furthermore, the mostpromising gas sensitive materials require operation at high temperatures of200⁴50℃, but CuAlO₂is found to be sensitive to ozone gas at room temperature.In this thesis, Cr doped CuAlO₂transparent conductive thin films have beensuccessfully prepared with a dual-layer process combing the advantages of bothmagnetron sputtering and sol-gel. We studied its electric conductivity andtransmittance in the infrared region. In addition, CuAlO₂thin films with different Cocontent were synthesized by solid-state reaction from Cu₂O and Al₂O₃powder.Magnetic properties of Co doped CuAlO₂thin films have been further investigated.Finally, one-dimensional nanofibers Cu-Al-O were prepared by electrostatic spinningmethod, meanwhile its ozone gas sensitive properties were discussed. The maincontent and results are as follows:（1） We deposited300nm of Cu₂O film on Si substrate using magnetronsputtering firstly, and then a layer of Al （NO₃）₃colloid was sequentially spinned. The CuAlO₂films are crystallized at high temperature. Our results indicate that the bestannealing temperature is900℃. Based on the same recipe, Cr dopedCuAlO₂（0%-7%） thin films have been prepared and its transmittance in the infrared region hasalso been studied. With the varation of Cr content from0%to7%, the transmittancein infrared region and the conductivity of the thin films have significant changes. Thebest conductivity of CuAl_0.97Cr_0.03O₂shows transmittance of about70%in range of2500-4500nm.（2） We synthesized thin films of CuAl_1-xCo_xO₂（x=0.00-0.07） on a sapphiresubstrate using a spin-on technique assisted by proper EC and terpineol solvent at1150°C. The samples are all single-phase delafossite CuAlO₂.The analysis suggeststhat Co is present in the+2oxidation state in the Co-doped CuAlO₂matrix and Coions substitute for the Al site. The pristine CuAlO₂sample shows diamagnetism andCo-doped CuAlO₂samples show ferromagnetic at RT. The best doping quantity is5%.The CuAl_0.95Co_0.05O₂film has the most saturated magnetic moment which is0.110emu/g, and its corresponding remanent magnetization is0.019emu/g.（3） One-dimensional nanofibers Cu-Al-O are fabricated by electrostatic spinningmethod. The influence of annealing temperature on lattice structure and surfacetopography is discussed in great details. It is found that the CuAlO₂formingtemperature is above1100℃, which leads to pretty uniform diameter fibers.Moreover, gas sensor was made using one-dimensional nanofibers Cu-Al-O and itsgas sensitive properties were detected. The sample performs obvious response toozone gas at room temperature. The response time and recovery time are short as2.74s and15.15s, respectively. Both response and recovery time reduce along withozone concentration increase. This study demonstrates the feasibility of developing aninexpensive ozone sensor by virtues of Cu-Al-O one-dimensional nanofiber.