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首页> 外文期刊>The journal of physical chemistry, C. Nanomaterials and interfaces >LEED and DFT Study of the Quasihexagonal TiO2 Structure on Cu(001)
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LEED and DFT Study of the Quasihexagonal TiO2 Structure on Cu(001)

机译：Cu（001）上准六方TiO2结构的LEED和DFT研究

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Reactive deposition of Ti on the Cu(001) surface saturated with chemisorbed oxygen results in the formation of an ordered ultrathin film with a slightly distorted hexagonal (quasihexagonal) unit cell. We find that, under appropriate substrate temperature, evaporation rates, and O2 pressure, it is possible to cover the whole substrate surface with the TiO2 quasihexagonal phase. An O-Ti-O trilayer model for the (quasi) hexagonal structure is consistent with angle scanned XPD data relative to the Ti 2p signal and with the LEED I-V experimental intensity curves. From a careful inspection of the LEED pattern, we derive a distortion of the hexagonal unit cell corresponding to a p(2 x 7) coincidence mesh with the substrate. The p(2 x 7) coincidence was used to model XPD data. For the analysis of LEED-IV data and for DFT calculation, the p(2 x 7) was approximated by a c(2 x 6) coincidence mesh. The c(2 x 6) approximation is very close to a p(2 x 7) in terms of lattice parameters but contains a reduced number of nonequivalent atoms. From LEED-IV analysis and DFT calculations, we derive the registry between the c(2 x 6) titanium oxide mesh and the substrate. We find that interfacial O atoms located at the corners and at the center of the unit mesh sit on top of the Cu atoms at the interface. The comparison of the DFT calculations performed for the free-standing O-Ti-O trilayer with a regular hexagonal unit cell and for the trilayer on Cu with a c(2 x 6) coincidence mesh indicates that the strain energy is more than compensated by the interaction with the substrate. The values of the interlayer spacing and the registry of the oxide film derived from the DFT calculations are in good agreement with the experimental results. The DFT calculations indicate that the bonding at the interface is characterized by a direct Cu-O interaction with overlap between the O 2p and the Cu 4sp states. The calculations indicate that, because of an upshift of the O 2p bands and a downshift of the Ti 4s states, the TiO2 film loses its insulator character and the electron states close to the Fermi level are dominated by the contribution from the Ti 3d orbitals.
机译：Ti在化学吸附的氧饱和的Cu（001）表面上的反应性沉积导致形成有序的超薄膜，该薄膜具有略微扭曲的六边形（准六边形）晶胞。我们发现，在适当的基板温度，蒸发速率和O2压力下，可以用TiO2准六方相覆盖整个基板表面。用于（近似）六边形结构的O-Ti-O三层模型与相对于Ti 2p信号的角度扫描XPD数据以及LEED I-V实验强度曲线一致。从对LEED图案的仔细检查中，我们得出六角形晶胞的变形，该变形对应于与基板的p（2 x 7）符合网格。 p（2 x 7）巧合用于对XPD数据进行建模。对于LEED-IV数据分析和DFT计算，p（2 x 7）由c（2 x 6）符合网格近似。就晶格参数而言，c（2 x 6）近似值非常接近p（2 x 7），但包含的非等价原子数减少了。从LEED-IV分析和DFT计算，我们得出c（2 x 6）氧化钛网与基材之间的注册表。我们发现位于单元网格的角和中心的界面O原子位于界面处Cu原子的顶部。对具有正六边形晶胞的独立O-Ti-O三层和具有ac（2 x 6）重合网格的Cu上的三层进行的DFT计算的比较表明，应变能大于通过与底物的相互作用。由DFT计算得出的层间间距和氧化膜的配准值与实验结果非常吻合。 DFT计算表明，界面处的键合以Cu-O直接相互作用为特征，且O 2p和Cu 4sp状态之间存在重叠。计算表明，由于O 2p带的上移和Ti 4s态的下移，TiO2薄膜失去了绝缘体特性，接近费米能级的电子态受Ti 3d轨道的贡献支配。

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