The first reactions involving tin(IV) phenyl thiolate were carried out at the University of Bath by Dr. T. G. Hibbert. A solution of 0.5 g tin(IV) phenyl thiolate in 20 ml toluene was used to create a mist, which was transported to the CVD reactor in a 1 dm^min"’ stream of nitrogen. The reaction was carried out until the entire precursor was expended. The coater temperature during reaction was 300 °C. The substrate used was carbon-doped silica coated glass, and no hydrogen sulfide was admitted to the system. The resulting films were yellow in colour. These were investigated by X-ray diffraction and Raman microscopy. The X-ray diffraction pattern of the film deposited at 400 °C is shown in Figure 5.1 and the Raman spectrum of the same film is given in Figure 5.2.
ro c 3 o o 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 2 theta / degrees
Figure 5.1 X-ray diffraction pattern o f the film deposited from tin(IV ) phenyl thiolate at 400 °C.
Both Figure 5.1 and Figure 5.2 bear no resemblance to any of the tin sulfide reference X-ray diffraction patterns and Raman patterns in Figures 2.4 and 2.6 respectively. Comparison with Figures 2.5 and 2.7 showed that both the X-ray diffraction and Raman data were consistent with the film being tin(II) tin(IV) oxide (8 0 3 0 4).
M
I
C0 50 100 150 200 250 300 350 400
Wavenumber/cm-1
Figure 5.2 R am an spectrum o f the film deposited from tin(IV ) phenyl thiolate at 400 °C.
F u rth e r re a c tio n s w ere c a rrie d ou t at U n iv e rsity C o lle g e , u sin g tin (IV ) p h enyl th io la te and h y d ro g e n su lfid e. M an y o f th ese w ere su cc essfu l. T h e full d e ta ils o f all re actio n s e a rn e d o u t an d the visual a p p e ara n ces o f the re su ltin g film s are liste d in T a b le 5.1.
Table 5.1 R eaction conditions for the CVD reaction o f tin(IV ) phenyl thiolate.
C o a te r te m p e ra tu re
r c )
S o lv e n t H y d ro g e n su lfid e
(dm ^m in'*)
V isu al ap p e ara n ce
400 A cetone 0.2 Thin, yellow
405 H exane 0.4 t Thin, yellow
448 H exane 0.4 t Y ello w
454 CHCI3 0.2 Grey & brown
502 H exane 0.4 t Thin, grey
550 H exane 0 Grey
550 A cetone 0.4 t Grey
550 CHCI3 0 Thin, brown
550 CHCI3 0.2 Grey
F o r the re a c tio n s m a rk e d t , h y d ro g e n su lfid e flo w e d th ro u g h th e re a c tio n so lu tio n w hile the m ist w as b ein g created . In the c a se o f all o th e r re a c tio n s, h y d ro g e n su lfid e d id not m eet the p re c u rso r until im m e d ia te ly p rio r to the re actio n c h a m b e r. In th e case o f the re actio n s m a rk e d t , it is p o ssib le that a sm all a m o u n t o f re a c tio n o c c u rre d in the flask
where the aerosol was created. Tliis may account for some o f the differences in reaction product.
Tlie films were too thin for investigation by X-ray diffraction.
5.2.1.1 Raman microscopy
Raman microscopy was carried out on all films. It was noted that in many cases the films were not o f a single phase. Figure 5.3 shows the Raman spectra of films deposited at 450 and 500 °C with a hydrogen sulfide flow of 0.4 dm^min'\
<0 c m 50 100 150 200 250 300 350 400 0 W a v e n u m b e r / cm-1
Figure 5.3 Raman spectra of films deposited from tin(lV) phenyl thiolate with 0.4 dm min hydrogen sulfide at (a) 450 and (b) 500 °C.
This shows that at 450 °C tin(IV) sulfide is the predominant phase formed, while at 500 °C a mixture is seen. At this higher temperature, the major phase is tin(II) sulfide, however a small band is observed at 310 c m '\ This could be due to the major peaks of both tin(IV) sulfide and mixed valent Sn2S3.
Figure 5.4 shows the Raman spectra o f films deposited at 400 and 450 °C with a 0.2 dm^min'^ flow of hydrogen sulfide. In these reactions hydrogen sulfide did not meet the tin(IV) phenyl thiolate until the reaction chamber, so there was no chance o f the solution reacting prior to aerosol creation.
(/) c £ c 150 200 250 300 350 400 0 50 100 Wavenumber / cm-1
Figure 5.4 Raman spectra of films deposited from tin(lV) phenyl thiolate with 0.2 dm^min * at (a) 400 and (b) 450 °C.
Figure 5.4 shows the same trend, of tin sulfides o f lower oxidation states being available at higher temperatures. At 400 °C a mixture of tin(IV) sulfide and mixed valent tin(II) tin(IV) trisulfide is observed, while at 450 °C a mixture o f tin(II) tin(IV) trisulfide and tin(II) sulfide is seen. A significant difference between Figures 5.3 and 5.4 is that mixed valent tin sulfide is more prominent when there was no pre-reaction of the precursor with H2S in the round-bottomed flask.
5.2.1.2 Energy dispersive analysis by X-rays
All films analysed were found to contain tin and sulfur. As the films were very thin much of the excitation volume contained glass. Some of the films were deposited on tin oxide / silica coated glass, so the tin in the undercoating interfered with the result. Other films, which were deposited on silica coated glass, were so thin that the calcium content in the underlying glass also interfered with the tin signal, but the tin to sulfur ratio was approximately 1:1.
5.2.1.3 Scanning electron microscopy
The SEM image of the film deposited from tin(IV) phenyl thiolate with hydrogen sulfide at 500 °C from a hexane solution is shown in Figure 5.5. The substrate was tin oxide / silica coated glass. Small particles are observed, in discreet clusters.
Figure 5.5 SEM im age o f a film deposited from tin(IV) phenyl thiolate with hydrogen sulHde at 500 °C.