Csiszár Gábor, Lawitzki Robert, Everett Christopher, Schmitz Guido
Department of Materials Physics, Institute for Materials Science, University of Stuttgart, Stuttgart 70569, Germany.
Department of Functional Materials, Faculty of Physics, Technical University Munich, Garching 85747, Germany.
ACS Appl Mater Interfaces. 2021 May 26;13(20):24238-24249. doi: 10.1021/acsami.1c02936. Epub 2021 May 14.
Single-crystalline niobium pentoxide nanowires (NWs) of length 10-15 μm and diameter 100-200 nm are synthesized by thermal oxidation of niobium substrates in a mild vacuum (3-10 mbar). Amorphous AlO shells of varying thicknesses (10, 30, 40, and 50 nm) are deposited on top of the wires using atomic layer deposition. Bending tests of the uncoated NbO NWs and the NbO/AlO core-shell NWs are carried out inside a scanning electron microscope using a micromanipulator with a force measurement tip. The experimental deflection curves are modeled with Euler-Bernoulli (E-B) beam theory, and the Young's modulus is manipulated to determine the best fit. The NbO NWs with no shell are determined to have a Young's modulus of 67 ± 10 GPa, which agrees with the published data on NbO thin films. For core-shell NWs, only small deflections of the wires with 10 and 30 nm thick shells can be fitted with the E-B model when utilizing constant Young's modulus values of 67 GPa for the NbO core and about 160 GPa for the AlO shell. When allowing for a change in the Young's modulus of the AlO shell, the Young's modulus is determined to be at 120 ± 10 GPa for 10 nm and 145 ± 12 GPa for 30 nm at the highest applied load. For thicknesses of 40 nm and 50 nm, we observed a reduced but constant 120 ± 11 and 111 ± 10 GPa, respectively. Such behavior may result from structural disordering of the amorphous AlO through reducing fractions of the densely packed polyhedra, while the fractions of the loosely packed polyhedra increase as a result of the increasing strain or the fabrication process. The increased disorder is associated with increased average interatomic spacing. Thus, the atomic bonding force and also the Young's modulus decrease.
通过在适度真空（3 - 10毫巴）中对铌衬底进行热氧化，合成了长度为10 - 15微米、直径为100 - 200纳米的单晶五氧化二铌纳米线（NWs）。使用原子层沉积法在这些纳米线顶部沉积了不同厚度（10、30、40和50纳米）的非晶态AlO壳层。使用带有力测量尖端的微操纵器在扫描电子显微镜内对未涂层的NbO NWs和NbO/AlO核壳NWs进行弯曲测试。实验挠度曲线采用欧拉 - 伯努利（E - B）梁理论进行建模，并通过调整杨氏模量来确定最佳拟合。确定无壳的NbO NWs的杨氏模量为67±10吉帕，这与已发表的关于NbO薄膜的数据一致。对于核壳NWs，当对NbO核使用67吉帕的恒定杨氏模量值，对AlO壳使用约160吉帕的恒定杨氏模量值时，只有10纳米和30纳米厚壳层的纳米线的小挠度可以用E - B模型拟合。当考虑AlO壳层杨氏模量的变化时，在最高施加负载下，确定10纳米厚壳层的杨氏模量为120±10吉帕，30纳米厚壳层的杨氏模量为145±12吉帕。对于40纳米和50纳米的厚度，我们分别观察到降低但恒定的120±11吉帕和111±10吉帕。这种行为可能是由于非晶态AlO的结构无序，通过减少密集堆积多面体的比例，而松散堆积多面体的比例由于应变增加或制造过程而增加。无序度的增加与平均原子间距的增加相关。因此，原子键合力以及杨氏模量降低。
