Optical and Vibrational Studies of Partially Edge-Terminated Vertically Aligned Nanocrystalline MoS2 Thin Films

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• 作者：Anand P. S. Gaur ; Satyaprakash Sahoo ; Majid Ahmadi ; Maxime J.-F. Guinel ; Sanjeev K. Gupta ; Ravindra Pandey ; Sandwip K. Dey ; Ram S. Katiyar
• 刊名：Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：December 12, 2013
• 年：2013
• 卷：117
• 期：49
• 页码：26262-26268
• 全文大小：489K
• 年卷期：v.117,no.49(December 12, 2013)
• ISSN：1932-7455

文摘

We report the optical and vibrational properties of nanocrystalline MoS₂ thin films, which are comprised of stripe-like partially edge-terminated vertically aligned (ETVA) nano-size crystals dispersed in 001 oriented regions, grown on large insulating substrates. From high-resolution transmission electron microscopy experiments, the average grain size of ETVA MoS₂ layers was found to be 5 nm and consist of three to five monolayers. The ETVA and flat nanocrystalline regions were in equivalent proportions in the films. The films were highly transparent (80%), but the transmittance decreased as the energy of the incident light approached the band gap. Additionally, weak excitonic peaks were observed in both the absorption and transmission spectra. The room-temperature Raman study showed that the line shape for both E_k">2g^k">1 and A_1g modes was significantly broader, and few additional Raman modes were observed in comparison to bulk MoS₂. The broadening in the line shape of the A_1g mode was analyzed using the phonon-confinement model, and the calculated grain size was in good agreement with transmission electron microscopy measurements. Moreover, the temperature coefficient of the A_1g mode was determined from the temperature-dependent Raman studies.