Abstract: A metal Cr film with a thickness of 150nm was deposited on the surface of diamond particles by DC magnetron sputtering. SEM studies have shown that the Cr film formed on the diamond surface is substantially uniform, but small metal aggregates are present. Auger depth analysis found that significant interfacial diffusion occurred between the Cr film and the diamond substrate during the coating process. The corresponding Auger linear analysis shows that a chemical reaction at the interface during the deposition process forms part of the Cr2C3 species. The sputter deposition power has a great influence on the interfacial diffusion reaction between the diamond particles and the metal Cr film. Increasing the sputtering power greatly promotes the diffusion of Cr, but has little effect on the diffusion of C element. The essence of the interface diffusion reaction is the collision injection of the charged Cr atoms with the diamond substrate.
Key words: magnetron sputtering; diamond; Cr; interfacial diffusion reaction; AES
CLC number: TG731 TG156.8 Document code: A
Article ID: 1001-4381 (2000) 01-0024-03
The Study of Interface Diffusion and Reaction between Cr and Diamond Deposited by Magnetron Sputtering Technigue
Abstract: A Cr layer with thickness of 150nm was successfully deposited on the surface of diamond particles using DC magnetron sputtering technique. The interface diffusion and reaction between Cr layer and diamond substrate have been studied using AES depth profile and line shape analyses. The results show The interface diffusion and reaction take place during the deposition of Cr layer. The Cr atoms diffuse into diamond substrate, and react with carbon atom in diamond to form carbide on the interface. The interface diffusion and reaction result from the impact of Cr atoms which keep An energy of 3~4eV. The interface diffusion and reaction can be promoted significant by raising the sputtering power.
Key words: sputtering; diamond; Cr; interface diffusion and reaction; AES
Diamond has many excellent properties [1, 2] and is mostly used in cutting tools. However, due to the high surface energy and chemical inertness of diamond, the combination of diamond and metal matrix is ​​weak, which affects the performance and life of diamond cutting tools. Surface metallization is an effective way to solve this problem. Among them, the metallized diamond obtained by magnetron sputtering coating has good bonding strength, but the interface physicochemical process in sputter deposition process is still not well understood [3, 4]. In this study, a 150 nm thick metal Cr layer was deposited on the surface of diamond particles by magnetron sputtering. The bonding state of Cr/diamond interface was studied by Auger electron spectroscopy.
1 Experimental method
The artificial diamond particles with a particle size of 40-50 mesh were placed in a rotating device, and a uniform Cr metal film was deposited on the surface of the diamond particles by Ar atmosphere DC magnetron sputtering. The thickness of the Cr layer was controlled to 150 nm. The degree of vacuum in the preparation chamber was better than 2 × 10 -4 Pa, and the partial pressure of Ar gas at the time of sputtering was 0.15 Pa. The deposition rate was 0.4 nm/s, and the purity of Cr target and Ar gas was 99.999%.
Auger electron spectroscopy was performed on a PHI-610/SAM scanning Auger electron spectrometer. Using a single-channel CMA energy analyzer, the energy resolution is 0.3%, the analysis voltage of the coaxial electron gun is 3.0kV, the incident angle of the electron beam is 60°, and the vacuum of the analysis chamber is better than 2×10-7Pa. The Ar ion gun sputtering rate was calibrated to 30 nm/min by thermal oxidation of SiO2. SEM experiments were performed on a CSM950 scanning electron microscope. The resolution of the secondary electron image is better than 5 nm.
2 Experimental results and discussion
2.1 Apparent morphology of Cr/diamond samples prepared by magnetron sputtering The SEM results of diamond particles before and after Cr plating show that the difference is significant. The surface of the diamond particles coated with Cr film is evenly distributed with many fine white spots. The energy spectrum analysis of the scanning electron microscope shows that the Cr content is obviously higher than that of the black region, indicating that some metals aggregate and form an island structure during the deposition of the Cr film.
2.2 Interface diffusion during the preparation of Cr/diamond samples Figure 1 shows the Auger depth profile of Cr/diamond samples. It can be seen that the thickness of the metal Cr film is about 150 nm, and the interfacial layer width with diamond is about 65 nm, which is much wider than the interface layer produced by the evaporation coating, indicating that interfacial diffusion occurs between Cr/diamond. This is due to the high energy Cr atoms bombarding the diamond surface during the sputter deposition process and creating a partial "injection" effect that causes the metal Cr to diffuse toward the diamond substrate.
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Fig.1 Auger depth profile analysis of Cr/diamond original sample Fig.1 The AES depth profile spectrum of
Un-annealed Cr/diamond particle
The oxygen of the surface layer is mainly derived from the surface adsorption and the natural oxide layer of Cr, and thus the content is high. Since the Cr layer prepared on the surface of the diamond particles is thin and has many structural defects, part of the adsorbed oxygen on the surface can diffuse into the inside of the film layer, and during the deposition of the metal Cr film, residual oxygen or water vapor exists in the vacuum. Therefore, a small amount of residual oxygen can also be generated in the film layer. This oxygen content is low and does not substantially vary with the depth of the film. In the depth profile, although a diffusion of the interface occurs and a wide interfacial diffusion layer is formed, a stoichiometric carbide layer is not formed.
2.3 Interfacial reaction products of Cr/diamond original samples The Auger linear analysis can study the chemical state of each element in the film layer, so as to infer the interface chemical reaction and determine the species generated by the interfacial reaction [5-7].
Figure 2 shows the C KLL Auger line profile of the original sample, where the peak of the diamond standard is at 269.1 eV and the Ausch peak of the carbide is three at 249.6 eV, 257.9 eV and 267.0 eV. The Auger peak of the sample surface C is located at 260.0 eV, and the shape is very similar to that of the diamond standard, and there is no sign of peak shape superposition. The carbon peak of the surface is mainly caused by the adsorbed C contamination (the diamond is graphitized due to the sputtering of Ar+, so the diamond standard shown is actually graphitized diamond). .gif)
Fig. 2 C KLL line spectrum at different depths of the original sample Fig.2 The line shape of C KLL in various
Depth of Cr/diamond deposited sample
At the Cr/diamond interface near the Cr layer (sputtering for 3.5 min), there is a significant difference between the Au strike line and the surface of C. Two weak peaks appeared at 249.6eV and 257.9eV, and their peak shape and peak position were in good agreement with the carbide; the peak at 267.0eV showed the characteristics of carbide and elemental carbon superposition peak, among which carbide The relative content is higher. After 4.2 min of sputtering, the Aus-line shape of carbon is closer to the diamond standard, but there are small protrusions at the positions of 249.6 eV and 257.9 eV, and the position of the peak larger than 260 eV is also slightly higher than the kinetic energy, reflecting the characteristics of carbide. This indicates that the peak is still a composite peak of carbide and elemental carbon, but the relative proportion of elemental carbon is much higher than that of carbide. After 5.2 min of sputtering, the Auger peak shape of carbon is closer to diamond in position and shape than the peak after sputtering for 4.2 min, which proves that the proportion of elemental carbon is dominant. Although the diamond body has not yet reached this point, no carbides are present. In the interfacial layer, carbides are mainly derived from interfacial chemical reactions, while elemental carbon is produced by the diffusion of diamond substrates.
It can be seen that during the preparation of the original Cr/diamond sample, a relatively obvious interfacial diffusion occurs, but the degree of chemical reaction is small. In the interface region, when the content of Cr is high, carbon is mainly present in the form of metal carbides, and when the Cr content is low, C is mainly present in elemental form.
Figure 3 shows the Auger line spectrum of Cr LM23M4. The Auger peak position of each standard is shown in the figure. The Auger peak shape of Cr at the surface is wider, and its Auger line shape is different from any standard. It is not possible to speculate on the specific species of this peak and can only be considered as a mixture of multiple substances. However, the peak shape and the oxide are much different, indicating that the surface Cr does not mainly exist in the state of oxide, and a large amount of oxygen on the surface mainly comes from the adsorption of adsorption. After 3.5 min of sputtering, the Auger peak shape of the sample is very similar to that of the metal Cr, that is, Cr is mostly present in elemental form. After 4.2 min of sputtering, the peak shape of the sample was significantly different from that of elemental Cr. The peak position was low and there were small protrusions at 480 eV, indicating that the peak is a superposition peak of metal and carbide. After 5.5 min of sputtering, the small peak at 480 eV of the sample was more obvious, and the peak near 485 eV continued to move to Auger's low kinetic energy and the peak shape became wider, indicating that the carbide content was greatly increased. The depth at this time is close to the diamond body, and the content of C is very high, but Cr is not completely converted into metal carbide, which indicates that although the sample has undergone a relatively significant interface diffusion, the interface reaction is lighter. .gif)
Fig. 3 Cr LM23M4 line spectrum at different depths of the original sample Fig.3 The line shape of Cr LM23M4 in
Various depth of Cr/diamond deposited sample
Figure 4 shows the LM1M4 Auger line spectrum of Cr. The Auger line shape of the metal element and the carbide in this energy segment is very close. It can be seen that the Auger shape of the sample is different from that of the oxide, so that the oxide content of Cr in the sample is small. Figure 5 is an MVV Auger line spectrum of Cr. In this energy segment, the oxide is much stronger than the Auger transition of carbide and metal element, so the peak shape and peak intensity of the sample at this time do not reflect the amount of each species. It can be seen from the figure that the Auger peak of the sample is between oxide and carbide and has a broad peak shape, indicating that the two compounds are present at the same time. From this figure, it can be concluded that a small amount of metal oxide is always present in the metal plating film and in the interface region. \
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It can be seen that the magnetron sputtering method makes the Cr/diamond have obvious interface diffusion and weak interfacial chemical reaction. The driving force of the interface diffusion reaction is mainly the kinetic energy of the deposited atomic Cr.
2.4 Effect of sputtering power on interfacial diffusion reaction In the depth profile of samples coated with different sputtering powers, the relationship between the depth of the 1:1 mixture layer and the interface width and sputtering power is shown in the following table. It can be seen that with the increase of sputtering power, the interface width of Cr/diamond increases correspondingly, which indicates that increasing the sputtering power can promote the interface diffusion between Cr/diamond; the proportional point becomes deeper, indicating that the diffusion of Cr is strengthened. .jpg)
From the surface of the Cr film to the diamond body, the 1:1 point and the end point depth of the interface layer gradually deepen with the increase of power, and the depth of the former is faster than the latter with the increase of power, indicating that the power has a greater influence on the diffusion of Cr. This is because increasing the sputtering power can produce two effects. First, the substrate temperature is raised, and the rate of diffusion between Cr/diamonds is accelerated, but the effect is not significant, so that it actually causes the diffusion between solid molecules to be negligible; second, the "injection" effect is enhanced. It is the main reason why the power layer increases the interface layer. The increase of sputtering power increases the kinetic energy of the particles emitted by the target, so that the particles can travel longer distances in the substrate by overcoming more intermolecular forces, and the macroscopically appears to increase the interface width and the interface into the substrate. Advance. Since this phenomenon depends on the kinetic energy of the sputter deposited atoms, the promotion effect on the diffusion of C atoms is small. At the same time, Cr with higher energy can react with carbon atoms in the diamond to form metal carbides at the interface.
3 Conclusion
A 150 nm thick Cr metal film was deposited on the surface of the diamond particles by magnetron sputtering. A significant interfacial diffusion reaction occurred in the coating, and Cr2C3 metal carbide was formed at the interface. The source of the interfacial diffusion reaction is the high kinetic energy of the sputter deposited atoms. Increasing the sputter deposition power can greatly promote the diffusion of Cr, thereby enhancing the interfacial diffusion reaction.
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