Unique structure and surface-related elastic modulus of alumina nanobelts

Abstract

Single-crystalline α-AlO nanobelts were synthesized by high-temperature chemical vapor deposition in a high-purity H atmosphere. The crystalline planes for the upper and side surfaces of the nanobelts were [Formula: see text] and [Formula: see text] and the orientations along height, length and width directions were [Formula: see text] [Formula: see text] and [Formula: see text] respectively. The formation of such a unique structure was dependent on the strong reducing atmosphere used in the growth process, and the deactivation of the [Formula: see text] plane by hydrogen could be the primary cause. The elastic modulus of the nanobelts was measured using a thermal resonance method. The moduli for the nanobelts were about 320 GPa for thicknesses above 40 nm, and slightly increased to 356 GPa as the thickness decreased to 31 nm. The slightly low modulus values compared to the theoretical value of 371 GPa is attributed to oxygen vacancies within the nanobelts, while the increase in modulus with decreased thickness comes from the stiffening effect caused by surface relaxation.

The Mechanical Properties of Nanowires

“…Figure 15 shows a SEM images of Al 2 O 3 NW cantilevers of different resonating lengths and the corresponding frequency spectra. [164] The ratios of the measured resonant frequencies for the 4 resonating lengths are1: 6.23: 17 (13) are smaller than 2%. This indicates that the NW cantilevers were well-clamped and should have highly uniform cross-sections.…”

“…If a NW cantilever is well clamped and its dimensional inaccuracy can be neglected, the ratios of the measured resonant frequencies should be constant, defined as,160 $f_1:f_2:f_3:f_4\cdots =1:6.265:17.554:34.402\cdots \hspace{0.17em}$where f i ( i = 1, 2, 3, 4…) is the resonant frequency of i th vibration mode of the NW cantilever. Figure 15 shows a SEM images of Al 2 O 3 NW cantilevers of different resonating lengths and the corresponding frequency spectra 164. The ratios of the measured resonant frequencies for the 4 resonating lengths are1: 6.23: 17.33: 33.81,1: 6.22: 17.31: 33.95,1: 6.20: 17.26: 34.08 and1: 6.12: 17.25, respectively.…”

“…Owing to its simplicity and efficiency in operation, the resonant vibration testing was widely used to determine the elastic modulus of NWs including Si,154, 166 Ge,167 Co,168 W,161, 169 SiC,170 GaN,99, 171 Ag 2 Ga,154 BN,172 ZnO,149, 165, 173, 174 WO 3 ,175 In 2 O 3 ,168 Sb 2 O 3 ,176 Al 2 O 3 ,164 amorphous SiO 2 ,177 metallic glasses 153. In particular, the use of SLDV not only significantly increases the detection resolution of a NW specimen's vibrational spectra, but also eliminates the issues relating to clamping and dimensional non‐uniformity 154, 161, 164.…”

“…In a SLDV test that is capable of detecting thermally driven vibration, the self-adhesion between a NW and a substrate is usually sufficiently strong to hold the NW in place. [160,164] However, if an external excitation source is required, than such clamping may not be sufficient. [165] By examining the ratios of resonant frequencies of a NW cantilever, the effect of clamping or geometric uniformity on testing accuracy can be precisely determined if SLDV is used.…”

The effect of surface texture on the kinetic friction of a nanowire on a substrate

“…For a NW with a thickness of t , if t  >  t c , the NW will span over the groove, and if t  >  t c , the NW will be in contact with the bottom of the grooves. Substituting the typical parameters of the narrow grooves and NWs used in the tests, w g  = 1.2 μm, h g  = 60 , φ  =  π /4, E  = 310 nm GPa47 and γ = 1 mJ/m 2 (see Appendix 1) into Equation (2), we obtained t c  ≈ 10 nm, which is significantly smaller than the NW thickness used in our tests. This indicates that the NWs being tested would be unable to conform to the grooves during sliding.…”