ABSOLUTE SURFACE-DENSITY OF THE AMINE GROUP OF THE AMINOSILYLATED THIN-LAYERS - ULTRAVIOLET-VISIBLE SPECTROSCOPY, 2ND-HARMONIC-GENERATION, AND SYNCHROTRON-RADIATION PHOTOELECTRON-SPECTROSCOPY STUDY
Jh. Moon et al., ABSOLUTE SURFACE-DENSITY OF THE AMINE GROUP OF THE AMINOSILYLATED THIN-LAYERS - ULTRAVIOLET-VISIBLE SPECTROSCOPY, 2ND-HARMONIC-GENERATION, AND SYNCHROTRON-RADIATION PHOTOELECTRON-SPECTROSCOPY STUDY, Langmuir, 13(16), 1997, pp. 4305-4310
The surface of a fused silica and oxidized silicon wafer (SiO2/Si(100)
) was treated with (3-aminopropyl)triethoxysilane (1), (3-aminopropyl)
diethoxymethylsilane (2), and (3-aminopropyl)ethoxydimethylsilane (3)
for 72 h in solution. Thickness of the aminosilylated film out of 1 in
creases rapidly, and it turns out to be around 100 A in 72 h. Rather s
low increase of the thickness is observed for 2, which produces the la
yers of 8 and 14 Angstrom in 10 and 72 h, respectively. The reagent 3
produces the monolayers of constant thickness 7-8 Angstrom during the
whale span of the reaction. The aminosilane layer was allowed to react
with 4-nitrobenzaldehyde to form an imine, and absorbance (A(surf)) o
f the imine was recorded by UV-vis spectroscopy. The imine was hydroly
zed in a known volume of water to produce 4-nitrobenzaldehyde, and sub
sequently its absorbance was measured. Thus observed number of the ald
ehyde molecules is equivalent to the number of the imine molecules on
the surface. With the known surface area of the substrates, the absolu
te surface density of the imine, that is, the reactive amine group on
the surface, was calculated. At an early stage of the aminosilylation
with 2, a surface density of 3.9 amine groups per 100 Angstrom(2) was
measured. A relatively low value was observed for 3. It is also observ
ed that 1 produces a multilayer with rough surface morphology, of whic
h surface density increases sharply by the reaction time. Tilt angle o
f the imine was estimated from the A(surf) and the absolute surface de
nsity. The angles vary among 23-47 degrees depending on the reaction c
ondition. Second harmonic generation of a laser light of 1064 nm was o
bserved for the imine-formed substrates. X-ray photoelectron spectrosc
opy utilizing a synchrotron radiation source, in particular for the N(
1s) binding energy region, confirmed the chemical transformation. Also
, it is observed that the nitro group of the imine is cleaved by X-ray
s.