Belotcerkovtceva Daria, Maciel Renan P, Berggren Elin, Maddu Ramu, Sarkar Tapati, Kvashnin Yaroslav O, Thonig Danny, Lindblad Andreas, Eriksson Olle, Kamalakar M Venkata
Department of Physics and Astronomy, Uppsala University, P.O. Box 516, SE-751 20 Uppsala, Sweden.
Department of Materials Science and Engineering, Uppsala University, P.O. Box 35, SE-751 03 Uppsala, Sweden.
ACS Appl Mater Interfaces. 2022 Aug 10;14(31):36209-36216. doi: 10.1021/acsami.2c06626. Epub 2022 Jul 22.
Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced p-type doping in graphene, in sharp contrast to TiO, the AlO/graphene interface shows the presence of appreciable sp defects. Electronic structure calculations disclose that significant p-type doping occurs due to a combination of sp bonds formed between C and O atoms at the interface and possible slightly off-stoichiometric defects of the aluminum oxide layer. Furthermore, the sp hybridization at the AlO/graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spin-lifetimes in AlO barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.
金属氧化物与石墨烯的附着对于石墨烯纳米电子学和自旋电子学界面具有根本重要性。在这类器件中，氧化钛和氧化铝是两种广泛使用的隧道势垒，它们提供了最佳的界面电阻以及决定输运参数和器件性能的独特界面条件。在此，我们通过电输运测量、拉曼光谱和光电子能谱，并结合此类界面的第一性原理电子结构计算，揭示了这些金属氧化物与石墨烯界面方式的根本差异。虽然这两种氧化层都会在石墨烯中引起表面电荷转移诱导的p型掺杂，但与TiO形成鲜明对比的是，AlO/石墨烯界面存在明显的sp缺陷。电子结构计算表明，显著的p型掺杂是由于界面处C和O原子之间形成的sp键以及氧化铝层可能存在的轻微非化学计量缺陷共同作用的结果。此外，AlO/石墨烯界面处的sp杂化导致不饱和键具有独特的磁矩，这不仅解释了在AlO势垒石墨烯自旋电子器件中广泛观察到的低自旋寿命，还为新型混合电阻开关和自旋阀提供了可能性。
