Elastic Behavior of Nb₂O₅/Al₂O₃ Core–Shell Nanowires in Terms of Short-Range-Order Structures

Abstract

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 Al 2 O 3 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 Nb 2 O 5 NWs and the Nb 2 O 5 /Al 2 O 3 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 Nb 2 O 5 NWs with no shell are determined to have a Young's modulus of 67 ± 10 GPa, which agrees with the published data on Nb 2 O 5 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 Nb 2 O 5 core and about 160 GPa for the Al 2 O 3 shell. When allowing for a change in the Young's modulus of the Al 2 O 3 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 Al 2 O 3 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.

Super-flexibility in Freestanding Single-Crystal SrRuO3 Conductive Oxide Membranes

“…The results indicate that the defect concentration (e.g., dislocations) in the SrRuO 3 crystal grows rapidly with reduced thickness (Figures and S3). The presence of defects such as dislocations in the membranes may lead to local disorder of the crystal structure and thus increase the degrees of freedom of the crystal framework, which could be beneficial to the super-flexibility of freestanding SrRuO 3 membranes. − Therefore, the freestanding membranes are more likely to be deformed and even buckled under external force. From a microscopic point of view, large stress could induce structural transition accompanying a prominent distortion of the Ru–O bonds and Ru–O–Ru bond angles, , and this distortion may tolerate great structural deformation, which may contribute to the super-flexibility of freestanding SrRuO 3 membranes.…”

Structural evolution of low-dimensional metal oxide semiconductors under external stress

“…Modern technological pressure to develop miniature electronic devices with improved performance has led to the rapid expansion of research into low-dimensional metal oxide semiconductors (MOSs), which have been extensively applied in thin film transistors [1] , flat panel displays [2] , logical gates [3] , biosensing [4] , gas sensors [5−7] , smart windows [8,9] , and so on. MOS nanomaterials can also serve as nano-level interconnects and active components in optoelectronic devices and nano-electro-mechanical systems (NEMS) [5,10] .…”