Single phase polycrystalline pellets of CuMO2 (M = Al, Cr, Y) semiconductors with delafossite structure were prepared
by sol-gel method and solid state reaction, respectively. The XRD results shows that structure can be indexed as
3R-CuAlO2 (JCPDF No. 35-1401), 3R-CuCrO2 (JCPDF No. 89-6744) and 2H-CuYO2 (JCPDF No. 76-1422),
respectively. The conductivities of CuMO2 are thermally activated in the measured temperature range with the activation
energy EA about 0.24eV, 0.34eV and 0.25eV, respectively. The conductivities of CuMO2 decrease monotonously with
the increase of radius of M cation. This phenomenon coincides with the previous theoretical studies that the hole
conduction path of CuMO2 was predominantly in the Cu-ions layers, and the Cu-Cu spacing (or α-axis length) was
governed by the M cation size, which modifies the wave function overlap between Cu-ions and results in decrease of the
conductivities. The room temperature ozone sensing properties of CuMO2 (M = Al, Cr, Y) polycrystalline pellets were
studied. Ozone-purified air-ozone circles were used to measure the ozone gas sensing properties of all the specimens,
which are similar to the practical measurement environments. The relative humidity of the environment was controlled
around 60 RH% ± 5 RH%. The temperature was controlled around 300K ± 0.5K. Except for CuYO2 pellets, CuAlO2 and
CuCrO2 pellets show reversible responds to ozone gas at room temperature. The room temperature ozone sensing
properties of CuCrO2 film prepared by pulsed laser deposition was also studied. The response time of CuCrO2 film is
about 3.5 min to 90% of the final value and the recovery time is about 2 min to 10% of the steady state signal under
ozone concentration of 600 ppm. Though the performance is not yet sufficiently high for practical use, the delafossites
CuMO2 (M = Al and Cr), as parent compounds of room temperature ozone sensing materials, are recommendable for
further studies on the improvement of ozone sensing properties.
Strong room temperature ultraviolet emission is observed in highly oriented ZnO microcrystallite films prepared on (001) sapphire substrates by pulsed laser deposition method (PLD). The influences of substrate temperature, distance between the target and the substrate, oxygen pressure, and laser energy density on structural and optical properties were systemically studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) and room temperature photoluminescence (PL) measurements. The XRD as well as the SEM results showed that all the four experiment parameters had obvious effects on the structure and micrograph of the derived ZnO films. From the room temperature photoluminescence spectra, all the derived samples have a strong ultraviolet (UV) emission about 376nm, and the visible emission is depressed greatly. Additionally, the results showed that the processing parameters could obviously affect the PL properties and the reasons were also discussed. From our results, the UV PL intensity is strongly depending both on the crystallinity and the stoichiometry of the ZnO films.
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