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Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and atomic force microscopy (AFM) were employed to investigate the detailed surface bonding structure and morphology of polyethyleneimine (PEI) layers coated on a SiO 2 substrate in concentrations of 0.5 10.0 mass%. With an increase in the PEI concentration, the CN bonds corresponding to the imine group (NH) became dominant in the PEI layers, implying a characteristic feature to verify the immobilization of PEI on the SiO 2 surface. The thickness of PEI layer calculated using AR-XPS gradually increased with increasing PEI concentration up to a maximum 5 mass%, above which it became saturated. AFM results showed that an increase in PEI concentration led to a decrease in the root mean square (RMS) roughness of PEI layers. Such a saturation tendency of PEI thickness combined with the strongly dependence of the surface morphology behavior of PEI layers on the PEI concentration indicated that SiO 2 surface was fully covered by monolayer PEI with a smooth surface morphology at PEI concentration in excess of 5 mass%.

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