Abstract
We applied angle-dependent transmission infrared spectroscopy for determination of the molecular orientation of a decyl monolayer chemically bonded to the Si(111) surface. The peak intensities for CH2 symmetric and antisymmetric stretching modes show similar variations as a function of incident angle. CH3 antisymmetric in-plane stretching mode shows a prominent increase in proportion to incident angle, but CH3 out-of-plane stretching mode decreases. By analyzing these experimental data, we estimated the orientation angles of dynamic dipole moments for these modes. We have evaluated the tilt angle of a carbon framework from the surface normal to be 27–30°, when the multireflection in a Si wafer is taken into account. However, without considering multireflection, the tilt angle becomes 15–20°. We conclude that the multireflection in the Si substrate should be considered in the analysis of angle dependent transmission IR spectra.