Thermal Functionalization of Hydrogen-Terminated Porous Silicon Surfaces with Terminal Alkenes and Aldehydes
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907 cm 1031 cm -1
a
Intensity (A. U.)
-1
2920 cm
-1
1467 cm
-1
b 2922 cm
1740 cm
-1
2242 cm
-1
1065 cm
-1
-1
c
3500
3000
2500
2000
1500
1000
-1
Wavenumbers (cm ) Figure 1: DRIFT spectra of a) hydrogen-terminated PSi and of modified PSi surfaces modified with b) 1decene and c) ethyl undecylenate.
F11.4.2
in all freshly etched samples and is due to interstitial oxygen within the bulk silicon lattice (Fig. 1a). After derivatization with 1-decene, additional peaks appear due to C-Hx stretching vibrations at 2920 cm-1 and CH2 deformation mode at 1467 cm-1 (Fig. 1b). No increase of the peak intensity at 1031 cm-1 was observed, which is compatible with the chemical composition of the organic molecule and with a chemical process occuring without any surface oxidation. Figure 1c exhibits the spectrum of the PSi surface modified with ethyl undecylenate. An intense peak at 1740 cm-1 due to the carbonyl stretching mode and a peak at 1065 cm-1 assigned to the C-O stretching mode of the ester along with Si-O-Si vibrations as confirmed by the prensence of the Si-H stretching band at 2242 cm-1, have been observed. The peak at 2242 cm-1 results most likely from a partial oxidation of the surface induced by traces of water present in the chemical reagent. X-ray photoelectron spectroscopy was used to evaluate the elemental composition of the surface before and after derivatization. The spectrum of the as-anodized surface (Fig. 2a) exhibits main peaks due to silicon 2p and 2s at 99 and 151 eV, respectively, and small peaks (F1s, O1s and C1s) associated with small fractions of the etching solution, which has reacted with the PSi surface during the preparation, and physisorbed chemicals. After reaction with 1decene at 115°C for 16 hours, a large increase of the carbon content was observed (Fig. 2b). The presence of a small oxygen peak is not associated with surface oxidation, as the silicon peak in high-resolution XPS did not show any shift to higher binding energy due to the formation of silicon-oxygen bonds. Figure 2c corresponds to the PSi surface modified with ethyl undecylenate. An increase of both carbon and oxygen signals was observed. However, the oxygen signal is much higher than expected and is not correlated with the monolayer elemental composition. The presence of an intense silicon peak at 103 eV in high-resolution XPS indicates there has been a partial oxidation of the surface and this corroborates the infrared results obtained for the ethyl undecylenate.
F1s
C1s
O1s
Intensity (A. U.)
a
b
c
1200
1000
800
600
400
200
0
Binding Energy (eV) Figure 2: XPS survey of a) hydrogen-terminated PSi and of PSi surfaces modified with b) 1-decene and c) ethyl undecylenate.
The modified surfaces with 1-decene, octyl and decyl aldehydes retain 40 to 80% of the intensity of the original PL (Fig. 3). The functionalized samples exhibit an orange-red F11.4.3
PL Intensity (A. U.)
photoluminescence comparable to the H-terminated sample, which is characteristic of 70 % porosity. The PL peak shape and
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