PdO, widely used in catalysis in powder form for decades, has been predicted recently to be a Dirac semimetal. Synthesis of high-quality single crystals of this material is thus of great interest. Here, by using ozone-assisted molecular beam epitaxy, PdO thin films were grown on a MgO (001) substrate. X-ray diffraction and transmission electron microscopy indicate the film is $a/b$ axis oriented, with the $c$ axis lying in plane. Fully oxygenated PdO films have a low density of holelike carriers, and are insulating at the lowest temperatures. Our density functional theory calculations using the Heyd-Scuseria-Ernzerhof exchange-correlation functional suggest a ∼1.0 eV band gap at the $M$ point, where the gap can be reduced by tensile strain along the $c$ axis and the bands begin to invert when the tensile strain is as high as 18%. Although tensile strain of this magnitude is experimentally not viable using epitaxy, electrons can be doped by oxygen reduction. Our results emphasize the need for careful consideration of electron correlation effects and stoichiometry in ab initio modeling of topological semimetals involving transition metal oxides.

中文翻译：

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PdO在MgO（001）上的分子束外延

数十年来，以粉末形式广泛用于催化的PdO最近被预测为狄拉克半金属。因此，这种材料的高质量单晶的合成引起了极大的兴趣。在这里，通过使用臭氧辅助分子束外延，在MgO（001）衬底上生长了PdO薄膜。X射线衍射和透射电子显微镜表明该膜是$\mathrm{一种}/b$ 面向轴，带有 $C$轴位于平面上。完全氧化的PdO膜具有低密度的孔状载体，并在最低温度下绝缘。我们使用Heyd-Scuseria-Ernzerhof交换相关函数进行的密度泛函理论计算表明，在$\mathrm{中号}$ 点，沿拉应力可以减小间隙 $C$当拉伸应变高达18％时，带开始反转。尽管使用外延在实验上无法达到这种强度的拉伸应变，但是可以通过氧还原来掺杂电子。我们的结果强调，在涉及过渡金属氧化物的拓扑半金属的从头算建模中，需要仔细考虑电子相关效应和化学计量。