Size- and temperature-dependent Young's modulus of SiC nanowires determined by a laser-Doppler vibration measurement

Abstract

Young's modulus of Fe-catalyzed silicon carbide (SiC) nanowires was measured in the temperature range of 300–575 K by the use of a laser Doppler vibrometer. The nanowires have a face-centered cubic structure grown along the [111] direction and exhibit different cross-sectional geometries, including circle, rectangle, hexagon, ellipse, trapezoid, and triangle. When the effective diameters of the nanowires decrease from 200 to 55 nm, their room-temperature Young's modulus decreases from ∼550 GPa (the bulk value) to ∼460 GPa, i.e., a reduction of ∼16%, and their temperature coefficient of Young's modulus varies from −47.4 ± 1.7 ppm/K (the bulk value) to −78.1 ± 5.9 ppm/K, i.e., a change of ∼65%. The size and temperature dependency of the modulus would greatly benefit the design and fabrication of high-temperature mechanical sensors based on SiC nanostructures.

Young's Modulus and Thermal Stability of Individual Sb2O3 Nanowires at Elevated Temperatures

“…Note that the cross‐sectional profile was obtained after the TEM characterization, by fracturing the nanowire cantilever near the frame edge by a W tip under the optical microscope and then acquiring at an angle of ≈5° deviated from its axial direction. [ 17,18 ] High‐resolution TEM analysis further revealed that, after the test at elevated temperatures, the edge of the nanowire changed to an amorphous structure, while the core still had a crystalline structure, as shown in Figure 2i. This suggests a crystalline–amorphous transition might initiate at the surface, and then extend into the core.…”

“…Note that α ( T ) is considered the same as the bulk value of 21 ppm K −1 . [ 27 ] The TCE value is much greater than the corresponding value of −(47.4–78.1) ppm K −1 for SiC nanowires with diameters of 55 to 200 nm, [ 17 ] slightly greater than the value of −108.7 ppm K −1 for ZnO nanowires with diameters of 101 to 350 nm, [ 16 ] and significantly smaller than the value of (410–449) ppm K −1 for metal Ag microwhiskers. [ 28 ]…”

“…Through the window, the thermally vibrational spectra of the nanowire cantilever could be detected by a laser Doppler vibrometer (LDV; Polytec MSA‐ 500; wavelength λ = 633 nm; 500 μW power; objective: Mitutoyo M Plan APO Plan 50×). According to the Euler–Bernoulli beam theory, Young's modulus, , of the nanowire cantilever can be derived from [ 17,20,21 ] where f n ( T ), L ( T ), I ( T ), A ( T ), and ρ(T) are the resonant frequencies, suspended length, area moment of inertia, cross‐sectional area, and density of the nanowire at temperature T , respectively; and β n (=1.875, 4.694, 7.855, … for n = 1, 2, 3, …) are the constants satisfying the transcendental equation, cos β n cosh β n + 1 = 0. Note that the L , I , A values at RT could be determined by the size and morphology of the nanowire cantilever examined by SEM (JEOL JSM‐7800 F and Nova NanoSEM230) and TEM (FEI Tecnai F20 operated at 200 kV) before and after the test.…”

“…Note that the L , I , A values at RT could be determined by the size and morphology of the nanowire cantilever examined by SEM (JEOL JSM‐7800 F and Nova NanoSEM230) and TEM (FEI Tecnai F20 operated at 200 kV) before and after the test. As a result, the temperature coefficient of Young's modulus, TCE = (∂ E /∂ T )/ E , of the nanowire could be estimated by [ 17 ] where α ( T ) and TCF are the thermal expansion coefficient and temperature coefficient of the resonant frequency of the nanowire.…”

“…[ 15 ] In our previous work, we reported the development of a laser‐Doppler vibration testing approach for real‐time measurement of the resonant frequency variation of cantilevered nanowires with the change of environmental temperature, which provided a facile route to measure the temperature‐dependence of Young's modulus of nanowires. [ 16,17 ] In this study, we would use the vibrometry approach to measure the resonant frequencies of Sb 2 O 3 nanowire cantilevers within the temperature range of from RT to 650 K, which enabled the testing of the temperature dependence of Young's modulus and thermal stability of Sb 2 O 3 nanowires up to their melting/sublimation point.…”