Electronic properties of atomic layer deposition films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy
Electronic properties of atomic layer deposition films, anatase and rutile TiO2 studied by resonant photoemission spectroscopy
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DOI：
10.1088/0022-3727/49/27/275304
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发表时间：
2016-07-13
影响因子：
3.4
通讯作者：
Schmeisser, D.
中科院分区：
文献类型：
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作者：
Das, C.;Richter, M.;Schmeisser, D.
以异丙醇钛为前驱体，采用原子层沉积(ALD)法在250℃下制备了二氧化钛薄膜，并用共振光电子能谱(ResPES)对薄膜进行了分析。我们报道了Ti2p和O1s的芯能级，价带(VB)谱和X射线吸收谱(XAS)数据，以及O1s和Ti3p吸收边的共振光电子能谱(ResPES)分布。我们确定了元素丰度、VB极大值的位置、VB和导带(CB)中的偏态密度(PDOS)，并以能带方案收集了这些数据。此外，我们还分析了带隙状态以及由极化子和电荷转移激发引起的本征态。发现这些态在共振激发时会引起多次俄歇衰变过程。我们识别了其中的几个过程，并定量地确定了它们对俄歇信号的相对贡献。由于我们的ResPES数据可以定量分析这些缺陷状态，我们确定了PDOS在VB和CB中的相对丰度以及电荷中性水平。用与TiO2ALD层相同的方法分析了TiO2的锐钛矿型和金红石型。比较了TiO2AlD层与锐钛矿型和金红石型TiO2AlD层的电子性质。在我们的比较研究中，我们发现ALD具有不同于锐钛矿和金红石的独特的电子结构。然而，电子结构的许多细节是可比较的，我们受益于我们的光谱数据和我们仔细的分析来找到这些差异。这可以归因于与锐钛矿型和金红石型相比，ALD薄膜的O2P和Ti3d4s态的杂化程度更高。
The TiO2 films are prepared by atomic layer deposition (ALD) method using titanium isopropoxide precursors at 250 degrees C and analyzed using resonant photoemission spectroscopy (resPES). We report on the Ti2p and O1s core levels, on the valence band (VB) spectra and x-ray absorption spectroscopy (XAS) data, and on the resonant photoelectron spectroscopy (resPES) profiles at the O1s and the Ti3p absorption edges. We determine the elemental abundance, the position of the VB maxima, the partial density of states (PDOS) in the VB and in the conduction band (CB) and collect these data in a band scheme. In addition, we analyze the band-gap states as well as the intrinsic states due to polarons and charge-transfer excitations. These states are found to cause multiple Auger decay processes upon resonant excitation. We identify several of these processes and determine their relative contribution to the Auger signal quantitatively. As our resPES data allow a quantitative analysis of these defect states, we determine the relative abundance of the PDOS in the VB and in CB and also the charge neutrality level.The anatase and rutile polymorphs of TiO2 are analyzed in the same way as the TiO2 ALD layer. The electronic properties of the TiO2 ALD layer are compared with the anatase and rutile polymorphs of TiO2. In our comparative study, we find that ALD has its own characteristic electronic structure that is distinct from that of anatase and rutile. However, many details of the electronic structure are comparable and we benefit from our spectroscopic data and our careful analysis to find these differences. These can be attributed to a stronger hybridization of the O2p and Ti3d4s states for the ALD films when compared to the anatase and rutile polymorphs.