Halim Joseph, Persson Ingemar, Moon Eun Ju, Kühne Philipp, Darakchieva Vanya, Persson Per O Å, Eklund Per, Rosen Johanna, Barsoum Michel W
Department of Physics, Chemistry and Biology (IFM), Thin Film Physics Division, Linköping University, SE-58183 Linköping, Sweden.
J Phys Condens Matter. 2019 Apr 24;31(16):165301. doi: 10.1088/1361-648X/ab00a2. Epub 2019 Jan 22.
Two-dimensional (2D) transition metal carbides and/or nitrides (MXenes) are a new class of 2D materials, with extensive opportunities for property tailoring due to the numerous possibilities for varying chemistries and surface terminations. Here, TiAlC and NbAlC MAX phase epitaxial thin films were deposited on sapphire substrates by physical vapor deposition. The films were then etched in LiF/HCl solutions, yielding Li-intercalated, 2D TiCT and NbCT films, whose terminations, transport and optical properties were characterized. The former exhibits metallic conductivity, with weak localization below 50 K. In contrast, the Nb-based film exhibits an increase in resistivity with decreasing temperature from RT down to 40 K consistent with variable range hopping transport. The optical properties of both films were determined from spectroscopic ellipsometry in the 0.75 to 3.50 eV range. The results for TiCT films confirm the metallic behavior. In contrast, no evidence of metallic behavior is observed for the NbCT film. The present work therefore demonstrates that one fruitful approach to alter the electronic and optical properties of MXenes is to change the nature of the transition metal.
二维（2D）过渡金属碳化物和/或氮化物（MXenes）是一类新型二维材料，由于其化学组成和表面端基具有多种变化可能性，因而在性能剪裁方面拥有广泛的机会。在此，通过物理气相沉积法在蓝宝石衬底上沉积了TiAlC和NbAlC MAX相外延薄膜。然后将这些薄膜在LiF/HCl溶液中蚀刻，得到锂插层的二维TiCT和NbCT薄膜，并对其端基、输运和光学性质进行了表征。前者表现出金属导电性，在50 K以下存在弱局域化现象。相比之下，基于Nb的薄膜在从室温降至40 K的过程中，电阻率随温度降低而增加，这与变程跳跃输运一致。通过光谱椭偏仪在0.75至3.50 eV范围内测定了两种薄膜的光学性质。TiCT薄膜的结果证实了其金属行为。相比之下，未观察到NbCT薄膜有金属行为的迹象。因此，本工作表明，改变MXenes电子和光学性质的一种有效方法是改变过渡金属的性质。
