Abstract
In this study, single groove nanoscratch experiments using a friction force microscope (FFM) with a monocrystalline diamond tip were conducted on a c-plane sapphire wafer to analyze the ductile-regime removal and deformation mechanism including the anisotropy. Various characteristics, such as scratch force, depth, and specific energy for each representative scratch direction on the c-plane of sapphire, were manifested by the FFM, and the results of the specific scratch energy showed a trend of six-fold symmetry on taking lower values than those of the other scratch directions when the scratch directions correspond to the basal slip directions as . Since this can be due to the effect of most probably basal slip or less probably basal twinning on the c-plane, a molecular dynamics (MD) simulation of zinc, which is one of the hexagonal close-packed (hcp) crystals with similar slip/twining systems, was attempted to clarify the phenomena. The comparison results between the nanoscratch experiment and the MD simulation revealed that both the specific scratch energy and the burr height were minimized when scratched in the direction of the basal slip. Therefore, it was found that both the machining efficiency and the accuracy could be improved by scratching in the direction of the basal slip in the single groove nanoscratch of c-plane sapphire.
Highlights
Single crystal sapphire (α-Al2 O3 ) is widely used in various industries due to superior physical, chemical and optical properties, namely c-plane sapphire substrates are widely used to grow group III-V and II-VI element-based semiconductor compounds such as GaN for blue LEDs and laser diodes [1,2]
In order to clarify the ductile-regime machining mechanism of c-plane sapphire including its anisotropy, in order to clarify the scratch direction that is efficient for material removal rate and/or machined surface accuracy—because they have already not been clarified—a series of single groove nanoscratch experiments using a friction force microscope (FFM) with a monocrystalline diamond tip was conducted on c-plane sapphire wafer substrate
Molecular dynamics (MD) simulation was applied to zinc (Zn), one of the hexagonal close-packed crystals with a similar slip/twinning system, to compare with the experimental results and to clarify the similarity with the deformation mechanism of hcp crystals as well as the ductile-regime machining mechanism of c-plane sapphire wafer through single groove nanoscratch
Summary
Single crystal sapphire (α-Al2 O3 ) is widely used in various industries due to superior physical, chemical and optical properties, namely c-plane sapphire substrates are widely used to grow group III-V and II-VI element-based semiconductor compounds such as GaN for blue LEDs and laser diodes [1,2]. Nanomaterials 2021, 11, 1739 focused on the machining anisotropy of monocrystalline sapphire in the ductile-regime by nanoscratch or similar methods which have clarified the effect of the tool rake angle [16] and the slip/twinning systems [17] on the deformation states—even though it is important to clarify the deformation and removal mechanisms including the anisotropy, which are concerned with the machining efficiency and machined surface and sub-surface qualities. In order to clarify the ductile-regime machining mechanism of c-plane sapphire including its anisotropy, in order to clarify the scratch direction that is efficient for material removal rate and/or machined surface accuracy—because they have already not been clarified—a series of single groove nanoscratch experiments using a friction force microscope (FFM) with a monocrystalline diamond tip was conducted on c-plane sapphire wafer substrate. Molecular dynamics (MD) simulation was applied to zinc (Zn), one of the hexagonal close-packed (hcp) crystals with a similar slip/twinning system, to compare with the experimental results and to clarify the similarity with the deformation mechanism of hcp crystals as well as the ductile-regime machining mechanism of c-plane sapphire wafer through single groove nanoscratch
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