CHINESE JOURNAL OF PHYSICS VOL. 49 , NO. 1 FEBRUARY 2011 Polarization Dependent Raman Active Modes Study of the Mo 1−x W x S 2 Mixed Layered Crystals Dumitru O. Dumcenco, 1 Yu-Chen Su, 1 Yi-Ping Wang, 1 Kuei-Yu Chen, 1 Ying-Sheng Huang, 1, ∗ Ching-Hwa Ho, 1 and Kwong-Kau Tiong 2 1 Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan 2 Department of Electrical Engineering, National Taiwan Ocean University, Keelung 202, Taiwan (Received April 12, 2010) A systematic study of a series of Mo 1-x W x S 2 mixed-layered crystals with 0 ≤ x ≤ 1 grown by the chemical vapor transport method was conducted by using Raman scattering measurements. The composition of the samples was determined by X-ray photoelectron spectroscopy. Measurements in the basal plane revealed two dominant first-order Raman- active modes A 1g and E 1 2g as well as several second-order modes in the range of 250–450 cm -1 . The E 1g mode was observed in the edge plane of thick samples. For all the Mo 1-x W x S 2 samples, the peaks corresponding to the A 1g mode showed one-mode behavior, whereas the peaks corresponding to the E 1 2g mode exhibited two-mode behavior. These results can be explained on the basis of the atomic displacements for each mode. In the case of the A 1g mode, only sulfur atoms vibrate, and this results in the one-mode behavior. In contrast, in the case of the E 1 2g mode, metal atoms and sulfur atoms vibrate together, and the resulting mass difference between the vibrating Mo and W cations results in the two-mode behavior of the peaks corresponding to the E 1 2g mode. PACS numbers: 63.20.-e; 63.22.-m; 78.20.-e; 78.30.-j I. INTRODUCTION Layered semiconductors with the chemical formula TX 2 (T = Mo, W; X = S, Se, Te) have a two-dimensional layered-type structure that causes most of their physical properties to be anisotropic [1–4]. Layered TX 2 materials have also been extensively investigated because of their potential practical applications, e.g., in manufacturing efficient electrodes for photoelectrochemical solar cells [5–7], for use as catalysts in industrial applications and as solid-state lubricants [11–13], and in manufacturing secondary batteries [8–10]. Over the last two decades, several papers have been published on the preparation of Mo 1−x W x S 2 compounds directly from the constituent elements and their characterization [14, 15]; papers have also been published on nanotubes and related structures [16–18]. By performing piezoreflectance measurements in the vicinity of the direct band-edge, it has been found that the transition energies of the Mo 1−x W x S 2 compounds [15] vary smoothly with the tungsten content x. In this paper, we performed a systematic Raman scattering study of a series of http://PSROC.phys.ntu.edu.tw/cjp 270 c ⃝ 2011 THE PHYSICAL SOCIETY OF THE REPUBLIC OF CHINA