Division of Chemical and Biomolecular Engineering, School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore 639798, Singapore.
Phys Chem Chem Phys. 2011 Jun 28;13(24):11663-70. doi: 10.1039/c1cp20228f. Epub 2011 May 19.
We apply DFT calculations to evaluate the electronic properties of germanium nanowires (GeNWs) upon adsorption of water molecules and reveal the possible causes of the experimentally observed electrical hysteresis in GeNWs based electronic devices. We show that the absorption of water molecules on the GeNW surface would lead to the formation of hydroxyl passivated GeNWs (OH-GeNWs). The first step of the formation mechanism is physisorption of water molecules toward a Ge atom then followed by dissociation of water molecules to form OH-GeNWs, consistent with experimental observation of reversible and irreversible electrical hystereses. More importantly, we also predict that the effective masses of OH-GeNWs depend strongly on their growth orientation and depend nonlinearly on the OH coverage percentage. We propose that the electrical hysteresis phenomenon observed in experiment can be attributed to the formation of OH-GeNWs with different OH coverage percentages, along with different alignments of the OH groups on the GeNW surface, and also the presence of surface trap state defects, during the different stages of I-V measurement.
我们应用密度泛函理论（DFT）计算来评估锗纳米线（GeNWs）在吸附水分子后的电子性质，并揭示实验观测到的基于 GeNWs 的电子器件中电滞后现象的可能原因。我们表明，水分子在 GeNW 表面的吸附会导致形成羟基钝化的 GeNWs（OH-GeNWs）。形成机制的第一步是水分子朝着 Ge 原子的物理吸附，然后水分子解离形成 OH-GeNWs，这与实验观测到的可逆和不可逆电滞后现象一致。更重要的是，我们还预测，OH-GeNWs 的有效质量强烈依赖于其生长方向，并与 OH 覆盖率呈非线性关系。我们提出，实验中观察到的电滞后现象可归因于在不同的 I-V 测量阶段，形成具有不同 OH 覆盖率、不同 OH 基团在 GeNW 表面排列方式以及表面陷阱态缺陷的 OH-GeNWs。
