Lasek Kinga, Ghorbani-Asl Mahdi, Pathirage Vimukthi, Krasheninnikov Arkady V, Batzill Matthias
Department of Physics, University of South Florida, Tampa, Florida 33620, United States.
Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, 01328 Dresden, Germany.
ACS Nano. 2022 Jun 28;16(6):9908-9919. doi: 10.1021/acsnano.2c04303. Epub 2022 Jun 2.
The platinum-tellurium phase diagram exhibits various (meta)stable van der Waals (vdW) materials that can be constructed by stacking PtTe and PtTe layers. Monophase PtTe, being the thermodynamically most stable compound, can readily be grown as thin films. Obtaining the other phases (PtTe, PtTe, PtTe), especially in their ultimate thin form, is significantly more challenging. We show that PtTe thin films can be transformed by vacuum annealing-induced Te-loss into PtTe- and PtTe-bilayers. These transformations are characterized by scanning tunneling microscopy and X-ray and angle resolved photoemission spectroscopy. Once PtTe is formed, it is thermally stable up to 350°C. To transform PtTe into PtTe, a higher annealing temperature of 400°C is required. The experiments combined with density functional theory calculations provide insights into these transformation mechanisms and show that a combination of the thermodynamic preference of PtTe over a phase segregation into PtTe and PtTe and an increase in the Te-vacancy formation energy for PtTe compared to the starting PtTe material is critical to stabilize the PtTe bilayer. To desorb more tellurium from PtTe and transform the material into PtTe, a higher Te-vacancy formation energy has to be overcome by raising the temperature. Interestingly, bilayer PtTe can be retellurized by exposure to Te-vapor. This causes the selective transformation of the topmost PtTe layer into two layers of PtTe, and consequently the synthesis of e PtTe. Thus, all known Pt-telluride vdW compounds can be obtained in their ultrathin form by carefully controlling the stoichiometry of the material.
铂 - 碲相图展示了各种（亚）稳定的范德华（vdW）材料，这些材料可通过堆叠PtTe和PtTe层构建而成。单相PtTe作为热力学上最稳定的化合物，很容易生长成薄膜。而获得其他相（PtTe、PtTe、PtTe），尤其是它们的极薄形式，则具有更大的挑战性。我们表明，PtTe薄膜可通过真空退火诱导的碲损失转变为PtTe - 和PtTe - 双层。这些转变通过扫描隧道显微镜、X射线和角分辨光电子能谱进行表征。一旦形成PtTe，它在高达350°C时是热稳定的。要将PtTe转变为PtTe，则需要400°C的更高退火温度。这些实验与密度泛函理论计算相结合，深入了解了这些转变机制，并表明PtTe相对于相分离成PtTe和PtTe的热力学偏好以及与起始PtTe材料相比PtTe中碲空位形成能的增加，对于稳定PtTe双层至关重要。为了从PtTe中解吸出更多碲并将材料转变为PtTe，必须通过提高温度来克服更高的碲空位形成能。有趣的是，双层PtTe可通过暴露于碲蒸气中重新碲化。这会导致最顶层的PtTe层选择性地转变为两层PtTe，从而合成e PtTe。因此，通过仔细控制材料的化学计量比，可以获得所有已知的铂 - 碲化物vdW化合物的超薄形式。
