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Abstract
Surface hydroxylation is the basis for material removal in chemical mechanical polishing (CMP) of monocrystalline silicon, diamond, and YAG crystals. Existing studies use experimental observations to investigate surface hydroxylation, but lack in-depth understanding of the hydroxylation process. In this paper, for the first time to the best of our knowledge, we analyze the surface hydroxylation process of YAG crystals in an aqueous solution using first-principle calculations. The presence of surface hydroxylation was verified by X-ray photoelectron spectroscopy (XPS) and thermogravimetric mass spectrometry (TGA-MS) detections. This study complements the existing research on the material removal mechanism of the CMP process of YAG crystals and provides theoretical support for the future improvement of the CMP technology.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
High-power solid-state lasers are increasingly important in industrial, military, medical and scientific research, etc. The laser crystal is the working substance of a solid-state laser, which converts the energy provided by the outside world into a highly parallel and monochromatic laser through an optical resonant cavity. The surface/sub-surface damage of laser crystal, including fractures, cracks, scratches, pits, corrosion, etc. causes localized energy accumulation and high temperature in the vicinity, resulting in a decrease in the laser damage threshold [1,2]. Ultra-smooth surface finish without surface/sub-surface damage is always pursued in the processing of laser crystals [3]. Y3Al5O12 (YAG) crystal is the primary host material used for laser crystals in high-power solid-state lasers. YAG crystal is characterized by high hardness and brittle nature, and satisfactory surface finish cannot be obtained using conventional processing methods such as grinding and mechanical polishing [4]. Chemical mechanical polishing (CMP) is widely used as a final treatment for many materials to obtain an ultra-smooth surface finish, in which chemical interactions that occur between abrasive particles and crystals play a dominant role in the removal of materials at the atomic level [5].
Researchers carried out CMP experiments on a variety of materials and investigated the chemical reactions occurring on the workpiece surface. Sabia and Stevens [6] used CeO2 abrasives to polish fused silica on a polyurethane pad and experimentally verified that a chemical reaction occurred at the particle/workpiece interface. Aida et al. [7] used a colloidal silica slurry for CMP of sapphire, GaN, and SiC substrates, and argued that oxidation occurred on the surfaces of GaN and SiC substrates. Wang et al. [8] carried out CMP of Si wafers in an alkaline slurry using alumina and ceria particles with hydrogen peroxide and speculated that the chemical reaction products were generated on the surfaces of both the particles and the workpiece. Some researchers explained the material removal mechanism in CMP at the atomic level and proposed that the chemical reactions are based on surface hydroxylation. Wen et al. [9] used ReaxFF reactive molecular dynamics simulations to investigate the process of the silica particle sliding on the Si substrate in the aqueous H2O2. The initial Si substrate undergoes surface hydroxylation to form Si-OH bonds. Subsequently, the Si-O-Si bridge bonds are formed at the particle/workpiece interface based on the Si-OH bonds and detach the Si atoms from the workpiece surface by particle sliding process. Thomas et al. [10] performed the CMP process on the diamond with colloidal silica slurry and polyurethane/polyester polishing cloth. C-OH bonds are formed on the diamond surface by surface hydroxylation, which continues to react with the Si atoms in particles to form C-O-Si bonds. The polishing mechanism is that the C atoms on the diamond surface were attached to the silica particles through C-O-Si bridge bonds and were pulled out with the movement of the particles. Chemical reactions based on surface hydroxylation play a key role in the material removal mechanism of the CMP process. Current methods for studying surface hydroxylation in CMP at the atomic scale are generally based on Newtonian mechanics and cannot analyze the electron behavior in the bonding process of hydroxyl groups (-OH) and workpiece surface atoms. Moreover, limited by the development of potential functions, methods based on Newtonian mechanics cannot accurately analyze the interactions between some atoms.
CMP is also used to process hard and brittle laser crystals, such as YAG crystals due to its excellent ability to produce ultra-smooth surfaces. McKay [11] polished YAG crystal using silica slur and obtained an ultra-smooth surface with a roughness of RMS 0.1 nm (range 40 µm × 40 µm). However, the material removal mechanism was not explained in the study. Zhang et al. [1,12] analyzed the reaction products during the CMP of YAG crystal using X-ray photoelectron spectroscopy (XPS) and deduced that the surface atoms of YAG crystal were pulled out through Si-O-M (metal atom) bridge bonds at the particle/workpiece interface. Mu et al. [13] investigated the material removal mechanism in the CMP process of YAG crystal with different slurry pH values. The material removal depends on the Si-O-Al and Si-O-Y bridge bonds when the slurry pH is less than 12. The material removal was by removing the reaction layer formed on the surface while the slurry pH is about 13. Previous researches show that Si-O-M bridge bonds were the basis for material removal in the CMP process of YAG crystal. The formation of bridge bonds depends on the hydroxylation of the crystal surface, that is, the hydroxyl group was connected to unsaturated coordination atoms on the crystal surface to form Al-OH and Y-OH structures. However, to the best of the authors’ knowledge, all existing analyses of the hydroxylation process on the surface of YAG crystals are inferred from experimental phenomena and surface composition detection, and lack theoretical analyses of the formation of hydroxyl groups and the atomic configurations of the hydroxylated surface.
Insufficient understanding of the CMP material removal mechanism limits the development of CMP technology for YAG crystals. In this paper, the adsorption behavior of water molecules on the YAG (111) surface was investigated using the first-principle calculations, and the surface hydroxylation process of YAG crystal in an aqueous solution was analyzed for the first time. The dissociation and adsorption behavior of H2O molecules, the transfer of electrons during the bonding of atoms, and the strength of chemical bonds were calculated. The occurrence of surface hydroxylation was confirmed by the analysis of the composition changes on the crystal surface using X-ray photoelectron spectroscopy (XPS) and thermogravimetric mass spectrometry (TGA-MS) methods. This work contributes to a further understanding of the surface modification and material removal mechanism of YAG crystal in the CMP process, and provides theoretical guidance for the development of CMP technology for YAG crystal.
2. Computational and experimental methods
2.1 Computational method
YAG crystal is a cubic crystal with a garnet structure, and its lattice constant is 12.0 Å [14]. The cubic cell contains 160 atoms, and the space group is Oh10-Ia3d. The O atoms occupy the 96(h) sites; the Y ions occupy 24(c) sites; each Y ion is dodecahedral coordinated to eight O atoms. There are two different sites of Al atoms. The Al(oct) atoms occupy the 16(a) sites with an octahedral point symmetry, and the Al(tet) atoms occupy the 24(d) sites with a tetrahedral point symmetry [15]. A full cubic cell with 160 atoms is used as the initial YAG model in the calculation (in Fig. 1(a)).
Fig. 1. YAG model in the calculation, (a) full cubic cell with 160 atoms, (b) (111) crystal face before relaxation and (c) (111) crystal face after relaxation.
The calculations are performed using the MS-CASTEP code based on density functional theory [16]. The electron density in space is calculated by the Kohn-Sham equation,
The exchange-correlation potential adopted the Perdew–Burke–Ernzerhof (PBE) functional of the generalized gradient approximation (GGA). The electron-ion interaction is described by the ultrasoft pseudopotential. We use a single k-point (the gamma point) [17] and an energy cutoff of 600 eV in the calculation. The optimal lattice constant of our YAG model is 12.25 Å which has a 2.08% error compared with the experimental value. For our initial YAG model, the Y-O bond lengths are 2.39 Å and 2.52 Å; the bond length of Al(tet)-O is 1.78 Å and that of Al(oct)-O is 1.94 Å.
The optimized model was cleaved along the (111) crystal face to construct a surface model of the YAG crystal. A vacuum layer with a thickness of 20 Å [18] was set to eliminate the effect of periodicity on the crystal surface atoms. Fix the atomic layer with a thickness of 7 Å at the bottom of the model to simulate the atoms of the bulk crystal. The atomic layer at the top of the model with a thickness of 2 Å is set as the surface atomic layer and relaxed. The atomic structures of the YAG surface before and after sufficient relaxation are shown in Fig. 1(b) and Fig. 1(c), where the thickness of the surface atomic layer is reduced to 1.65 Å due to the loss of coordination atomic constraints at the crystal surface. The energy of the system decreases from -49033.62 eV to -49040.51 eV during the relaxation process, and the energy change process is shown in Fig. 2.
As shown in Fig. 3(a) and Fig. 3(b), H2O molecules were respectively placed at two sites on the crystal surface. The optimized bond angle and bond length of the H2O molecule structure after relaxation are 104.45° and 0.98 Å respectively, which are similar to the ones used in the well-known TIP classical water models (104.52° and 0.96 Å) [19,20], shown in Fig. 3(c).
Fig. 3. H2O molecules adsorbed on the surface of YAG crystal, (a) Home view, (b) Top view, (c) H2O molecule.
2.2 Experimental method
The surface composition of YAG crystal in an aqueous solution was analyzed by XPS and TGA-MS. The samples used in this study were Φ15 mm × 1 mm (1 1 1)-oriented YAG crystals which were polished with diamond sandpaper with 1 µm particles for 30 min to remove impurities and oxide layer on the surface and expose the internal atoms. Sample 1 was protected by nitrogen gas to isolate it from H2O molecules in the air, and sample 2 was immersed in deionized water for 30 min to simulate the aqueous environment of the CMP process. After preparing the samples, they were immediately transferred to the XPS chamber for vacuum processing.
The XPS detection was performed on the X-ray photoelectron spectrometer (ESCALAB 250Xi, ThermoFisher, UK). The chamber was operated at a vacuum of 2 × 10−9 mbar (with the X-ray source turned on) using a monochromatic Al kα (1486.6 eV) light source with a resolution of ≤0.45 eV. The passage energies of the high-resolution spectrum and the full spectrum were 20 eV and 100 eV, respectively, with scan steps of 0.05 eV and 1 eV. The beam spot size was 500 µm, the scanning mode was CAE, and the lensing mode was Standard. The C-1s (284.8 eV) was used as a standard to determine the true binding energy of the sample by deducting the effect of charging effect.
YAG crystal immersed in deionized water was ground into powder and dried at 100 degrees Celsius for 60 min and then subjected to thermogravimetric analysis. TGA-MS was carried out on the thermogravimetric analyzer (Thermo plus EV2 / Thermo mass photo, Rigaku, Japan). The test temperature was 30 °C ∼ 600 °C, and the heating duration was 132 min. The gas flow rate was 300 ml/min. MS detection range was m/z:1-400, and MS signal acquisition was 1s.
3. Results and discussions
3.1 Formation of surface hydroxylation
The unsaturated coordinated Al and Y atoms on the surface of the YAG crystal provide strong Lewis acid (electron acceptor) sites for the adsorption of H2O molecules [21]. The geometric optimization of the H2O molecules produced two different states: the dissociated state and the metastable state. As shown in Fig. 4(a), after relaxation, the H2O molecule at site 1 behaves in a dissociated state. The dissociated H(2) atom forms a hydroxyl group with the O(2) atom on the crystal surface. The H(1) and O(1) atoms of the H2O molecule form another hydroxyl group. From Fig. 4(b) to (d), it can be seen that the electron density between the H(2) atom and the O(1) atom is 0, indicating that the H(2) atom is wholly dissociated from the H2O molecule. There are electrons distributed between the hydroxyl group -O(1)H(1) and both the unsaturated coordinated Al(1) and Y(1) atoms on the crystal surface, representing the formation of chemical bonds. In Fig. 5, the red area indicates an increase in electron density, and the blue area indicates a decrease in electron density. When the hydroxyl group -O(1)H(1) dissociated from the H2O molecule is adsorbed on the crystal surface, the electron density between the hydroxyl group and the surface Al(1) atom and Y(1) atoms increase significantly, indicating that hydroxylation occurs on the crystal surface and Al-OH and Y-OH chemical bonds are formed.
Fig. 4. H2O molecule adsorbed on site 1, (a) H2O dissociated into a hydroxyl group -O(1)H(1) and an H(1) atom, and electron density of (b) hydroxyl group -O(1)H(1) and H(1) atom, (c) hydroxyl group -O(1)H(1) and surface atom Y(1), and (d) hydroxyl group -O(1)H(1)and surface atom Al(1).
Fig. 5. electron density difference between hydroxyl group -O(1)H(1) and surface atoms of (a) Al(1) and (b) Y(1).
Figure 6 shows the partial density of states (PDOS) of O(1) atom, Al(1) atom and Y(1) atom in the case of hydroxyl groups bonding with surface atoms. The PDOS of O-2s orbital has obvious overlapping peaks in the energy range of -21.70 eV∼-19.59 eV with those of the Al-3s, Al-3p, Y-4d and Y-5s orbitals, respectively. Meanwhile, the PDOS of O-2p orbital shows several overlapping peaks in the energy range of -10.22eV∼-2.77 eV with those of the Al-3s, Al-3p, Y-4p, Y-4d and Y-5s orbitals, respectively. It indicated that the O atom and its neighboring Al and Y atoms undergo orbital hybridization, i.e., O(1)-Al(1) and O(1)-Y(1) covalent bonds were formed.
The hydrolysis reaction of the H2O molecule occurred due to the unsaturated coordination atoms, and the hydroxyl group of the hydrolysis product formed covalent bonds with the surface atoms of the YAG crystal, realizing part of the surface hydroxylation. Simultaneously, the H(2) atom dissociated from the H2O molecule adsorbed on the near-neighboring surface unsaturated coordination O(2) atom to form a new hydroxyl group. As shown in Fig. 7, a significant number of electrons are distributed between the H(2) and O(2) atoms. The PDOS of H-1s orbital and O-2s, O-2p orbitals have multiple overlapping peaks in the energy range of -21.19 eV ∼ -18.09 eV, -8.74 eV ∼ -4.54 eV, and 1.09 eV ∼ 15.32 eV, indicating that H(2) atom formed covalent bonds with surface O(2) atom when adsorbed on the crystal surface.
3.2 Adsorption of metastable state H2O molecule
Figure 8(a) shows the molecular configuration of the H2O molecule at site 2 adsorbed on the crystal surface. Figure 8(b) shows the electron density distribution inside the H2O molecule, which shows that there are still shared electrons between the H and O atoms, indicating that the H2O molecule at site 2 has not dissociated. The bond length of the H-O bonds elongated from 0.98 Å to 1.00 Å, showing that the water molecule was adsorbed on the crystal surface in a metastable state. Figure 8(c) shows that after the H2O molecule was adsorbed on the crystal surface, there was significant distribution of electrons between the O(3) atom and the unsaturated coordination Al(2) atom, forming an Al-O chemical bond. Figure 8(d) shows the differential electron density of H2O molecules after adsorption. The electron density around the H(3), H(4) atoms in the H2O molecule decreased, and the electron density between the O(3) and Al(2) atoms increased after adsorption. It indicates that some electrons in the H2O molecule were transferred to the crystal surface, resulting in weaker H-O bonds in the H2O molecule, making the H-O bond length longer and enhancing the adsorption of the H2O molecule. Figure 9 shows the PDOS of O(3) atom in the H2O molecule at site 2 and its neighboring Al(2) atom on the crystal surface. The PDOS of O-2s, O-2p orbitals and Al-3s, Al-3p orbitals showed multiple overlapping peaks in the energy range of -26.07 eV∼-24.42 eV, -11.65 eV∼-10.20 eV, -8.73 eV∼-4.18 eV and 0.14 eV∼15.59 eV, indicating the covalence of O-Al bonds.
Fig. 8. H2O molecule adsorbed on site 2, (a) molecular configuration, (b) electron density of H2O molecule, (c) electron density of H2O-Al(2) and (d) electron density difference of H2O-Al(2).
The bonding strength of the hydroxyl groups and H2O molecules to the crystal surface atoms can be analyzed based on the populations and lengths of chemical bonds. The properties of chemical bonds between hydroxyl groups, H2O molecules and the crystal surface atoms are listed in Table 1. Each hydroxyl group forms chemical bonds with two neighboring surface metal atoms (Al, Y), while the H2O molecule forms a chemical bond with one surface metal atom. The bonding strength of the hydroxyl group to the surface atoms is greater than that of the H2O molecule in the metastable state to the surface atoms. Therefore, it can be concluded that hydroxylation is the main form of surface modification of YAG crystals in an aqueous solution.
Table 1. Populations and lengths of chemical bonds between H2O molecules and crystal surface
In summary, H2O molecules are adsorbed on the surface of YAG crystal in two states: dissociated state and metastable state. The dissociated state forms a hydroxyl group and an H atom. The hydroxyl group will bond with the Al and Y atoms on the crystal surface, while the dissociated H atom will combine with the O atom on the crystal surface to form a new hydroxyl group, resulting in the surface hydroxylation of the YAG crystal. H2O molecules in the metastable state also form chemical bonds with crystal surface atoms to enhance the adsorption, but the bonding strength is relatively weak compared to that of hydroxyl groups.
3.3 Detection of surface composition
The change of surface composition before and after immersion in deionized water was analyzed by XPS to study the surface hydroxylation process of YAG crystals in an aqueous solution. Figure 10 illustrates the XPS spectra of O-1s. The O1s spectra of YAG crystal without immersion in deionized water can be decomposed into two peaks: at 530.30 eV and 531.35 eV, corresponding to Al-O and Y-O bonds respectively [22,23], as shown in Fig. 10(a). After being immersed in deionized water, the XPS spectra of YAG crystals changed significantly, indicating that new structures were generated on the crystal surface. As shown in Fig. 10(b), a new peak appears at 532.15 eV, representing the formation of O-H bonds [24].
Fig. 10. High-resolution XPS spectra of O-1s on the surface of YAG crystals, (a) not immersed in deionized water, (b) immersed in deionized water.
The bonding of hydroxyl groups to metal atoms (Al, Y) on the crystal surface is analyzed by XPS spectra of Al-2p and Y-3d, shown in Fig. 11. Figure 11(a) and Fig. 11(b) show the high-resolution XPS spectra of the Al-2p before and after the YAG crystals immersed in deionized water. After immersion, a new peak appears at 74.20 eV, representing the bonding of the hydroxyl group to the Al atoms on the crystal surface [21]. Figure 11(c) and Fig. 11(d) show the high-resolution XPS spectra of the Y-3d in the YAG crystal. The Y-3d orbitals of the YAG crystal split into Y-3d3/2 and Y-3d5/2 with a binding energy difference of 2 eV, so two peaks with an area ratio of 2:3 and binding energies of 159.40 eV and 157.40 eV are evident in the XPS spectra. After immersion, two peaks of the Y-OH bond appeared: The Y-OH (Y-3d3/2) peak with a binding energy of 159.80 eV and the Y-OH (Y-3d5/2) peak with a binding energy of 157.80 eV. Their binding energy difference and area ratio were consistent with the two splitting peaks of Y-3d spectra. The XPS results of the surface composition of YAG crystals before and after immersion in deionized water show that hydroxyl groups exist on the crystal surface and form chemical bonds with the surface atoms, i.e., the formation of surface hydroxylation.
Fig. 11. High-resolution XPS spectra of Al-2p (a) not immersed in deionized water, (b) immersed in deionized water, and Y-3d (c) not immersed in deionized water, (d) immersed in deionized water.
The presence of hydroxyl groups and metastable H2O molecules adsorbed on the crystal surface can be further verified by the phenomenon of thermal weight loss at different temperature stages due to the different adsorption strength of hydroxyl groups and H2O molecules. The adsorbed metastable H2O molecules typically detaches from the crystal surface in the temperature range of 20 °C∼200 °C, which is called dehydration phenomenon. Hydroxyl groups are condensed into H2O molecules and detached in the temperature range of 200 °C∼800 °C, which is called dehydroxylation phenomenon. The dehydration and dehydroxylation phenomena of YAG crystal were investigated by TGA-MS (Fig. 12). The thermogravimetric (TG) and derivative thermogravimetric (DTG) curves reveal three weight losses at 180 °C, 290 °C and 410 °C. The smooth MS profile of released H2O (m/z = 18) shows three peaks at the temperatures where weight losses occur, which are attributed to dehydration and dehydroxylation. The elimination of the adsorbed H2O molecules occurred at 180 °C, and the dehydroxylation of Al-OH and Y-OH occurred at 290 °C and 410 °C respectively [25–29]. TGA-MS provides further evidence of surface hydroxylation.
Fig. 12. TG-DTG curves and of YAG crystal after immersed in deionized water and MS profiles of gaseous product.
4. Conclusion
Surface hydroxylation is the basis of the material removal mechanism in the CMP process of YAG crystal, but it has not been sufficiently investigated in existing research. In this work, the surface hydroxylation of YAG crystal in an aqueous solution is explained using the first-principle calculations, revealing the different states of H2O molecules and the bonding of hydroxyl groups to surface atoms. XPS spectra and TGA-MS were used to detect changes in crystal surface composition to verify the formation of surface hydroxylation. The conclusions are listed as follows:
- 1) The H2O molecules adsorbed on the surface of YAG crystals exist in two states: dissociated state and metastable state. The H2O molecules in the dissociated state divide into a hydroxyl group and an H atom. The length of the H-O bond of the H2O molecule in the metastable state is elongated from 0.98 Å to 1.00 Å.
- 2) The dissociated hydroxyl group is attached to both the neighboring unsaturated coordination Al and Y atoms on the crystal surface, forming Al-OH and Y-OH bonds. The H atom is connected to the unsaturated coordination O atom on the crystal surface, forming a new hydroxyl group.
- 3) Some electrons of H2O molecules in the metastable state are transferred to the crystal surface, so the H2O molecules form chemical bonds with unsaturated coordination atoms on the crystal surface, which strengthens the adsorption of H2O molecules to the crystal surface.
It is generally believed that after surface hydroxylation, the atoms on the crystal surface attach to the particles via hydroxyl groups and are pulled out with the movement of the particles, resulting in the material removal. We will investigate the chemical reactions and mechanical interactions at the interface between the particles and the crystal in the following work. This paper clearly explains the surface hydroxylation process of the YAG crystal and provides theoretical guidance for future improvement in the CMP technology of YAG crystals.
Funding
National Key Research and Development Program of China (2022YFB3605902); Science Fund for Creative Research Groups (51621064).
Acknowledgments
The authors would like to appreciate the financial support from National Key R&D Program of China (No.2022YFB3605902) and Science Fund for Creative Research Groups of NSFC (No.51621064).
Disclosures
The authors declare that there are no conflicts of interest related to this article.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. Z. Zhang, Z. Jin, J. Guo, X. Han, Q. Mu, and X. Zhu, “A novel chemical mechanical polishing slurry for yttrium aluminum garnet crystal,” Appl. Surf. Sci. 496, 143601 (2019). [CrossRef]
2. D. W. Camp, M. R. Kozlowski, L. M. Sheehan, M. A. Nichols, M. Dovik, R. G. Raether, and I. M. Thomas, “Subsurface damage and polishing compound affect the 355-nm laser damage threshold of fused silica surfaces,” Proc. SPIE 3244, 356–364 (1998). [CrossRef]
3. X. Han, Z. Jin, Q. Mu, L. Niu, and P. Zhou, “Internal stress and deformation analysis of ultra-thin plate-shaped optical parts in thinning process,” Opt. Express 27(19), 27202–27214 (2019). [CrossRef]
4. C. Li, X. Li, Y. Wu, F. Zhang, and H. Huang, “Deformation mechanism and force modelling of the grinding of YAG single crystals,” Int. J. Mach. Tool. Manu. 143, 23–37 (2019). [CrossRef]
5. X. Han, Z. Jin, Q. Mu, Y. Yan, and P. Zhou, “Morphological characteristics and formation mechanism of latent scratches in chemical mechanical polishing,” J. Mater. Process. Technol. 307, 117689 (2022). [CrossRef]
6. R. Sabia and H. J. Stevens, “Performance characterization of cerium oxide abrasives for chemical-mechanical polishing of glass,” Mach. Sci. Technol. 4(2), 235–251 (2000). [CrossRef]
7. H. Aida, T. Doi, H. Takeda, H. Katakura, S. W. Kim, K. Koyama, and M. Uneda, “Ultraprecision CMP for sapphire, GaN, and SiC for advanced optoelectronics materials,” Curr. Appl. Phys. 12, S41–S46 (2012). [CrossRef]
8. Y. G. Wang, L. C. Zhang, and A. Biddut, “Chemical effect on the material removal rate in the CMP of silicon wafers,” Wear 270(3-4), 312–316 (2011). [CrossRef]
9. J. Wen, T. Ma, W. Zhang, A. C. von Duin, and X. Lu, “Atomistic mechanisms of Si chemical mechanical polishing in aqueous H2O2: ReaxFF reactive molecular dynamics simulations,” Comput. Mater. Sci. 131, 230–238 (2017). [CrossRef]
10. E. L. Thomas, G. W. Nelson, S. Mandal, J. S. Foord, and O. A. Williams, “Chemical mechanical polishing of thin film diamond,” Carbon 68, 473–479 (2014). [CrossRef]
11. J. M. N. Mc Kay, “Chemical Mechanical Polishing and Direct Bonding of YAG and Y2O3,” Ph.D. dissertation (University of California, Los Angeles, 2016).
12. Z. Zhang, Z. Jin, and J. Guo, “The effect of the interface reaction mode on chemical mechanical polishing,” CIRP J. Manuf. Sci. Tec. 31, 539–547 (2020). [CrossRef]
13. Q. Mu, Z. Jin, X. Han, Y. Yan, Y. Zhang, and P. Zhou, “Effects of slurry pH on chemical and mechanical actions during chemical mechanical polishing of YAG,” Appl. Surf. Sci. 563, 150359 (2021). [CrossRef]
14. F. Euler and J. A. Bruce, “Oxygen coordinates of compounds with garnet structure,” Acta Crystallogr. 19(6), 971–978 (1965). [CrossRef]
15. J. Chen, T. C. Lu, Y. Xu, A. G. Xu, and D. Q. Chen, “Ab initio study of a charged vacancy in yttrium aluminum garnet (Y3Al5O12),” J. Phys.: Condens. Matter 20(32), 325212 (2008). [CrossRef]
16. L. B. Shi, C. Y. Xu, and H. K. Yuan, “A CASTEP study on magnetic properties of C-doped ZnO crystal,” Phys. B 406(17), 3187–3191 (2011). [CrossRef]
17. B. C. Shih, D. B. Jochym, K. Refson, and J. R. Yates, “Large scale CASTEP calculations to interpret solid-state NMR and Vibrational Spectroscopy experiments,” Tech. Rep. eCSE04-010 (archer.ac.uk, 4th eCSE call).
18. K. Yuge, A. Seko, A. Kuwabara, F. Oba, and I. Tanaka, “Ordering and segregation of a Cu75 Pt25(111) surface: A first-principles cluster expansion study,” Phys. Rev. B 76(4), 045407 (2007). [CrossRef]
19. M. Allesch, “A first principles simulation of rigid water,” J. Chem. Phys. 120(11), 5192–5198 (2004). [CrossRef]
20. M. W. Mahoney and W. L. Jorgensen, “A five-site model for liquid water and the reproduction of the density anomaly by rigid, nonpolarizable potential functions,” J. Chem. Phys. 112(20), 8910–8922 (2000). [CrossRef]
21. K. C. Hass, W. F. Schneider, A. Curioni, and W. Andreoni, “The chemistry of water on alumina surfaces: Reaction dynamics from first principles,” Science 282(5387), 265–268 (1998). [CrossRef]
22. X. Guo, Y. Q. Sun, and K. Cui, “Darkening of zirconia: a problem arising from oxygen sensors in practice,” Sens. Actuators, B 31(3), 139–145 (1996). [CrossRef]
23. C. D. Wagner, D. E. Passoja, H. F. Hillery, T. G. Kinisky, H. A. Six, W. T. Jansen, and J. A. Taylor, “Auger and photoelectron line energy relationships in aluminum–oxygen and silicon–oxygen compounds,” J. Vac. Sci. Technol. 21(4), 933–944 (1982). [CrossRef]
24. D. A. Pawlak, K. Woźniak, Z. Frukacz, T. L. Barr, D. Fiorentino, and S. Seal, “ESCA studies of yttrium aluminum garnets,” J. Phys. Chem. B 103(9), 1454–1461 (1999). [CrossRef]
25. M. Aghazadeh, T. Yousefi, and M. Ghaemi, “Low-temperature electrochemical synthesis and characterization of ultrafine Y(OH)3 and Y2O3 nanoparticles,” J. Rare Earths 30(3), 236–240 (2012). [CrossRef]
26. D. Y. Kang, J. Zang, E. R. Wright, A. L. McCanna, C. W. Jones, and S. Nair, “Dehydration, dehydroxylation, and rehydroxylation of single-walled aluminosilicate nanotubes,” ACS Nano 4(8), 4897–4907 (2010). [CrossRef]
27. V. M. Bermudez, “Investigation of the interaction of γ-Al2O3 with aqueous solutions of dimethyl methylphosphonate using infrared multiple internal reflection spectroscopy,” Langmuir 29(5), 1483–1489 (2013). [CrossRef]
28. R. L. Frost, J. T. Kloprogge, S. C. Russell, and J. Szetu, “Dehydroxylation of aluminum (Oxo) hydroxides using infrared emission spectroscopy. Part II: Boehmite,” Appl. Spectrosc. 53(5), 572–582 (1999). [CrossRef]
29. D. Madej, “Examination of dehydration and dehydroxylation of synthetic layered (oxy) hydroxides through thermal analysis (TG-DSC-EGA-MS) and a discussion to the second Pauling’s rule,” Inorg. Chim. Acta 482, 402–410 (2018). [CrossRef]
