The quality of polydihydrosilane liquid films is a key factor in the fabrication of solution-processed silicon films. This study investigates the stability of polydihydrosilane liquid films with a thickness L of similar to 40 nm on solid substrates by a comparison between the observed optical microscope images and the values of the Hamaker constant A(ALS) for the air/liquid (polydihydrosilane)/solid substrate systems. A(ALS) values for a series of SiO2-based substrates were determined by adopting a simple spectrum method. We found that the micrographs of the polydihydrosilane films provide direct evidence of stability in accordance with the sign of A(ALS): a stable liquid film with A(ALS) > 0 showed a continuous figure, while an unstable film with A(ALS) < 0 exhibited an array of dots caused by the rupture of the film. The array of dots in the unstable liquid films has a slight orderly distribution with a period A that is in accord with the characteristic wavelength of the undulation related to the spinodal-like decomposition in van der Waals unstable liquid. (C) 2012 Elsevier B.V. All rights reserved.