S. Wannaparhun et al /Applied Surface Science 185(2002)183-196 3. 2. Mullite For reference, we also analyze mullite. Detailed Al(2p), Si(2p), and O(ls) XPS spectra are shown in part(b)of Figs. 3, 5 and 8. For a pure mullite sample, all signals are supposed to be from the mullite phase Using peakfit software, a single deconvoluted peak is obtained in all XPS spectra. This indicates th sence of a single phase in the as-received mullite. I (b) Fig. 7b, the deconvoluted Al(2p) at a BE of 74.9eV close to that of Al(2p)in a pure mullite(74.8eV [51). In Fig. 6b, the deconvoluted Si(2p) spectrum indicates a Be of 102.8 eV, which is consistent with a pure aluminosilicate (102.8eV [51)). The shape of the Si(2p)spectrum is symmetric and indicates no shoulder on either side of the spectra as compared 11511010510095 to the as-received alumina. The deconvoluted o(ls) spectrum in Fig. 9b, the BE of 531.7 eV indicates the B E(ev oxygen environment in mullite only (531.6eV Fig. 6. Deconvoluted Si(2p)XPS spectrum of the as-received:(a) 51) lumina matrix;(b) mullite(I: aluminum oxide; 2: aluminosili- The surface si/al ratio of the as-received calculated from the XPs survey scan is close theoretical value of 0.33(based on the mullin mical formula of 3Al2O32SiO2). A slight discrepancy survey scan. The presence of Si(2p) line indicates a in the ratio might come from the peak deconvoluting ery small amount of silicon in aluminosilicate form. procedure or the presence of any surface contaminan To confirm the XPS results, a thin specimen of the as- However, the as-received mullite spectra are very received composite was analyzed using TEM(Fig. 7). consistent with the literature It is worth indicated the presence of silicon in the matrix 3.3. Nextel-720 fiber region of the as-received composite. The preser of gallium ( Ga) was from the TEM sample 3.3.1. XPS Al(2p) preparation using FIB. Source of silicon might be In Fig. 10a, the deconvoluted Al(2p) spectrum from the sol-gel matrix binders during processing. revealed two peaks at 73.5 and 74.2 eV, respectively Thus, we are able to identify not only the foreign phase ( Table 1). The main peak at 74.2 eV with 85.0%o area is in the matrix but also its chemistry. consistent with aluminosilicate (74.6eV 51]).A small peak at 73.5 eV with 15.0% area correspond 3.1.1.3. XPS O(Is). XPS O(1s) spectrum(Fig. &a) to Al2O3 (73.9eV [51])only. According to the litera- indicates an asymmetric feature on its left-hand ture, the fiber was composed of around 60% mullite shoulder. The deconvoluted peaks derived from the and 40%0 a-Al2O3 by mole percent. Based on this spectrum(Fig. 9a) show two peaks at 530.26eV information, the Al(2p) signal of 85.0% would be (aluminum oxide, 89.1% area) and 531.66 eV attributed to the mullite phase and around 15.0%o were (aluminosilicate, 10.9% area), respectively (Table 1). that of the a-Al2O3. Please note that the difference Therefore, it can be concluded that the deconvoluted between the compositional information from the lit O(1s)spectrum was consistent with both Al(2p) and erature and the XPS analysis can be attributed to many Si(2p)spectra. This confirms that the alumina matrix factors. One is that the compositional information was composed of a Si-containing phase, which was an obtained from any XPS analysis is only from the surface region only, while the composition ofsurvey scan. The presence of Si(2p3 ) line indicates a very small amount of silicon in aluminosilicate form. To confirm the XPS results, a thin specimen of the as￾received composite was analyzed using TEM (Fig. 7). It is worthy to note that the EDS analysis also indicated the presence of silicon in the matrix region of the as-received composite. The presence of gallium (Ga) was from the TEM sample preparation using FIB. Source of silicon might be from the sol–gel matrix binders during processing. Thus, we are able to identify not only the foreign phase in the matrix but also its chemistry. 3.1.1.3. XPS O(1s). XPS O(1s) spectrum (Fig. 8a) indicates an asymmetric feature on its left-hand shoulder. The deconvoluted peaks derived from the spectrum (Fig. 9a) show two peaks at 530.26 eV (aluminum oxide, 89.1% area) and 531.66 eV (aluminosilicate, 10.9% area), respectively (Table 1). Therefore, it can be concluded that the deconvoluted O(1s) spectrum was consistent with both Al(2p) and Si(2p3 ) spectra. This confirms that the alumina matrix was composed of a Si-containing phase, which was an aluminosilicate. 3.2. Mullite For reference, we also analyze mullite. Detailed Al(2p), Si(2p3 ), and O(1s) XPS spectra are shown in part (b) of Figs. 3, 5 and 8. For a pure mullite sample, all signals are supposed to be from the mullite phase. Using peakfit software, a single deconvoluted peak is obtained in all XPS spectra. This indicates the pre￾sence of a single phase in the as-received mullite. In Fig. 7b, the deconvoluted Al(2p) at a BE of 74.9 eV is close to that of Al(2p) in a pure mullite (74.8 eV [51]). In Fig. 6b, the deconvoluted Si(2p) spectrum indicates a BE of 102.8 eV, which is consistent with a pure aluminosilicate (102.8 eV [51]). The shape of the Si(2p3 ) spectrum is symmetric and indicates no shoulder on either side of the spectra as compared to the as-received alumina. The deconvoluted O(1s) spectrum in Fig. 9b, the BE of 531.7 eV indicates the oxygen environment in mullite only (531.6 eV [51]). The surface Si/Al ratio of the as-received mullite calculated from the XPS survey scan is close to the theoretical value of 0.33 (based on the mullite che￾mical formula of 3Al2O32SiO2). A slight discrepancy in the ratio might come from the peak deconvoluting procedure or the presence of any surface contaminant. However, the as-received mullite spectra are very consistent with the literature. 3.3. Nextel-720 fiber 3.3.1. XPS Al(2p) In Fig. 10a, the deconvoluted Al(2p) spectrum revealed two peaks at 73.5 and 74.2 eV, respectively (Table 1). The main peak at 74.2 eV with 85.0% area is consistent with aluminosilicate (74.6 eV [51]). A small peak at 73.5 eV with 15.0% area corresponds to Al2O3 (73.9 eV [51]) only. According to the litera￾ture, the fiber was composed of around 60% mullite and 40% a-Al2O3 by mole percent. Based on this information, the Al(2p) signal of 85.0% would be attributed to the mullite phase and around 15.0% were that of the a-Al2O3. Please note that the difference between the compositional information from the lit￾erature and the XPS analysis can be attributed to many factors. One is that the compositional information obtained from any XPS analysis is only from the surface region only, while the composition of Fig. 6. Deconvoluted Si(2p3 ) XPS spectrum of the as-received: (a) alumina matrix; (b) mullite (1: aluminum oxide; 2: aluminosili￾cate). 188 S. Wannaparhun et al. / Applied Surface Science 185 (2002) 183–196