Tham khảo tài liệu 'properties and applications of silicon carbide part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 172 Properties and Applications of Silicon Carbide The Ni-Si equilibrium phase diagram Nash Nash 1992 predicts six stable intermetallic compounds Ni3Si Ni31Si12 Ni2Si Ni3Si2 NiSi and NiSi2. Only three of compounds melt congruently namely Ni31Si12 Ni2Si and NiSi. The others form via the peritectic reaction. The synthesis method of the nickel silicides in Ni-Si system includes conventional melting and casting and solid state reaction between Ni and Si the latter of which has been realised in two different ways thin films and bulk diffusion couples. Other techniques such as ion beam mixing Hsu Liang 2005 and mechanical alloying Lee et al. 2001 can also be used. In the case of thin film reactions Ottaviani 1979 Zheng et al 1983 Chen et al 1985 Lee et al 2000 Yoon et al 2003 the formation of the compounds depends on the relative amounts of the Ni and Si available for the reactions the annealing temperature the atmosphere and impurities contained in the layers. Important characteristics include sequential appearance of phases . one compound is formed first and the second starts to form later on and the absence of certain phases. Ni2Si is always the first phase to form and Ni3Si2 is always absent in thin film experiments. After one of the elements is consumed the next compound is richer in the remaining element. Binding energy eV Fig. 1. Normalized XPS core level spectra from different silicides. Surface silicides were prepared by means of thin film solid-state reactions controlling the heating procedure in vacuum and the right sample preparation. Cao et al. 2009 XPS X-ray photoelectron spectroscopy can be used as a fingerprint for correct phase identification at the surface. The XPS core level spectra of Ni 2p3 2 in different silicides are shown in Fig. 1. In comparison to the Ni 2p3 2 peak eV representing the metal the core level shift AEc are eV for Ni3Si eV for Ni31Si12 eV for Ni2Si eV for NiSi and eV for NiSi2 respectively. With higher .
