Dominant aim of the paper was to verify the existence of the SimHn clusters in a-Si:H layers. Thin layers were deposited by plasma-enhanced chemical vapor deposition (PECVD) on both glass and crystalline silicon substrates. Their IR and structural properties were investigated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction at grazing incidence angle (XRDGI). We have found that the layer probably consists of larger structurally ordered parts corresponding to SimHn clusters and separated groups of (Si-H-x)(N). The ordered parts could be identified as some of SimHn clusters ranging from (10, 16) to (84, 64) represented by corresponding vibration frequencies in three following IR regions: 600-750, 830-900 and 2080-2180 cm(-1). XRDGI measurement indicates that diffraction maximum at around 2 Theta = 28 degrees can be attributed to an existing SimHn cluster. (c) 2006 Elsevier B.V. All rights reserved.