标题: 氧化钯奈米薄片之成长机制与光电特性之研究
Growth and Photoelectrical Properties of Reactive Sputtered PdO Nanoflakes
作者: 黄建融
Huang, Chien-Jung
潘扶民
Pan, Fu-Ming
材料科学与工程学系
关键字: 氧化钯;奈米薄片;反应性溅镀;核壳;光电性质;成长机制;PdO;nanoflake;sputter;core-shell;photoelectrical;growth mechanism
公开日期: 2010
摘要: 于本论文中,我们利用反应性溅镀法成长氧化钯薄膜并且研究期成长机制与光电特性,包含场发射、光感应与光催化反应。当氧化钯成长于白金基板上时,此氧化钯具有片状之形貌。此奈米薄片具有核壳结构,其结构为一层氧化钯包覆一颗单晶钯。我们将此被氧化钯层包覆之奈米薄片的成因归咎于氧化钯与白金基材之间晶格不匹配产生之介面压应力所形成。测试此奈米薄片之场发射特性并发现其场强因子约为791。氧化钯薄片亦成长于二氧化矽基板上并研究其光感应特性。于室温下所成长之氧化钯薄膜亦具有奈米薄片结构并垂直站立于二氧化矽基板上。于400 oC下退火后,此奈米薄片具有单晶结构。于400 oC下退火后之氧化钯薄膜之能隙坐落于红光区(约2.06 eV),并且于紫外光(365 nm)照射下展现极佳之光敏感度。造成此高之光敏感度乃由于此薄膜具有极佳之结晶性,因此减少电子电洞对覆合中心。此外,此薄膜亦具有较低电阻,因此具有较高之载子传输效率。于紫外光起始照射时,电流密度有些许下降之趋势,此为O2-离子吸附于此400 oC退火后之氧化钯薄片上所造成。
我们亦制备了PdO/TiO2异质结构以探讨其光催化分解亚甲基蓝特性。于紫外光-可见光照射下,相较于纯TiO2奈米球,PdO/TiO2异质结构对于亚甲基蓝具有两倍之光触媒活性。此提高之光触媒活性乃归功于此两半导体氧化物异质接合所形成之位能障。此对于亚甲基蓝分解之光触媒反应机制亦于本文中探讨。于可见光照射下,虽然PdO仍可被激发,但此PdO/TiO2异质结构对于亚甲基蓝仅有微弱之触媒活性。我们将其归因于此异质结构中非平衡之光激发载子的次费米能阶不匹配所造成。而表面分解亚甲基蓝反应的氧化还原电位不匹配亦是其因素之一。
In the thesis, we deposited palladium oxide nanoflake thin films by reactive sputter deposition (RSD) and various properties were studied including electron field emission, photoconduction and photocatalysis. The PdO thin film RSD-deposited on the Pt substrate had a flake-like morphology. The nanosized flake had a core-shell structure with a single Pd grain encapsulated by a crystalline PdO surface layer. The formation of the PdO capped nanoflakes was a result of a large interfacial stress built up between PdO and Pt due to lattice mismatch. Field emission characteristics of the nanoflakes were studied and a field enhancement factor of 791 was obtained.
PdO nanoflakes were also deposited on a SiO2 substrate by reactive sputter deposition and photoconduction characteristics of the thin films were examined. PdO thin films deposited at 25 oC is composed of bowed nanoflakes standing on the SiO2 substrate, which have a single-crystalline structure after thermal anneal at 400 oC. The 400 oC-annealed nanoflake thin film has a bandgap energy in the red-light range (~2.06 eV), and exhibits a very sensitive photoresponse upon UV (365 nm) illumination. The high photoresponse sensitivity of the 400 oC-annealed nanoflake thin film is ascribed to a lower density of recombination centers and traps due to an excellent crystallinity and a high carrier extraction efficiency due to a low electrical resistivity. A slight decrease in the photocurrent density during the initial stage of the UV illumination is attributed to adsorption of O2- anions on the 400oC-annealed nanoflakes.
We deposited PdO nanoflakes by RSD on TiO2 nanoparticles dispered on the SiO2 substrate for the study of photocatalytic decomposition of methylene blue (MB) molecules. The PdO/TiO2 heterostructure has a photocatalytic activity toward MB decomposition under UV-vis light illumination as larege as twice that of bare TiO2 nanoparticles. The enhancement of the photocatlaytic activity is ascribed to the fast photogenerated carrier separation resulting from the potential barrier formed at the heterojunction between the two semiconductor oxides. A photocatalytic reaction mechanism for the MB decomposition is proposed. The PdO/TiO2 heterostructure exhibits little photocatalytic activity toward the MB decomposition under visible light illumination even thoung PdO can be photoexcited by visible light. We ascribe the photocatalytic inactivity to the mismatch between quasi-Fermi levels of nonequlibrium photogenerated carriers in the heterostructure and the redox potential of primary surface reactions leading to the MB decompostion.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079418821
http://hdl.handle.net/11536/40793
显示于类别:Thesis


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