Preparation of SrMoO4 thin films on Si substrates by chemical solution deposition

doi:10.1016/j.jcrysgro.2007.11.154

Journal of Crystal Growth

Volume 310, Issue 4, 15 February 2008, Pages 789-793

https://doi.org/10.1016/j.jcrysgro.2007.11.154 Get rights and content

Abstract

Crystallized SrMoO₄ thin films were prepared on (1 0 0)-oriented Si substrates by chemical solution deposition (CSD) method. The effects of the processing parameters on the growth of the films were investigated. Dense scheelite-type SrMoO₄ thin films could be prepared when calcined between 350 and 800 °C. The absorption band related to vibration mode of MoO₄²⁻ tetrahedra in Fourier transform infrared (FT-IR) spectra of SrMoO₄ thin films annealed at 350–900 °C was observed that undoubtedly confirmed the appearance of SrMoO₄ phase. The results showed that CSD method could be used to prepare SrMoO₄ thin films at rather low temperatures.

Introduction

Scheelite-type materials possess attractive luminescence and interesting structural properties, and have been widely used as laser host materials and scintillators [1], [2], [3]. SrMoO₄ (SMO) is a kind of scheelite-type material, and has excellent properties of green luminescence at liquid-nitrogen temperature (−196 °C) which is ascribed to an electronic transition of charge transfer type in the molecular orbital scheme of the undisturbed anionic MoO₄²⁻ complex [4].

Lots of methods have been successfully used to synthesize the scheelite-type materials, such as combustion method [5] and solid-state reactions [6]. However, the main problem in the processing is the volatile characteristics of MoO₃ during high-temperature treatments. It is necessary to synthesize crystallized SMO films at lower temperatures. Electrochemical method is an alternative method [7], but this method can be only used to deposit RMoO₄ (R=Ca, Sr, Ba) on Mo substrates, which limits the RMoO₄ films preparation. Another choice is the chemical solution deposition (CSD) method. The CSD method is an efficient way to fabricate oxide thin films [8], [9], [10]. Using CSD method, films can be synthesized at low temperatures and the metal ions can be well mixed at the molecular scale resulting in the improvements of compositional homogeneity, which is very important for preparation of multicomponent oxides. Compared with vacuum deposition methods, such as pulsed laser deposition and sputtering deposition, the CSD approach is a nonvacuum method and requires less equipment, which is easier to be scaled up, especially for large-area films with compositional homogeneity.

This work is devoted to the preparation of crystalline SMO thin film on (1 0 0)-oriented Si substrates via CSD method, and particularly focuses on the effects of the heat treatment parameters on the growth of SMO thin films.

Section snippets

Experiments

Strontium acetate (Sr(OOCCH₃)₂·0.5H₂O, purity 99%) and ammonium para-molybdate ((NH₄)₆Mo₇O₂₄·4H₂O, purity 99%) were used as the metallic cations sources. Ethylene glycol (HOCH₂CH₂OH (EG), purity 99.5%) and acetic acid glacial (CH₃COOH (HOAc), purity 99.5%) were used as solvents. Citric acid monohydrate (HOC(COOH)(CH₂COOH)₂·H₂O (CA), purity 99.5%) was used as chelating agent.

The preparing process of SMO thin films is outlined in Fig. 1. First, the ammonium para-molybdate and citric acid

Results and discussion

Fig. 2(a) and (b) shows the XRD patterns of the SMO thin films pyrolyzed at 300 and 350 °C, respectively. It is seen that the SMO thin films pyrolyzed at 300 °C is amorphous, but when the treatment temperature is increased to 350 °C, the characteristic SMO phase appears with the main and large diffraction peaks corresponding to the SMO phase. The XRD results demonstrate that the crystallization temperature of the SMO thin films deposited on Si substrates is rather low compared with that of bulky

Conclusion

A simple method for preparing SMO thin films on (1 0 0)-oriented Si single crystal substrates is presented. The SMO thin films pyrolyzed at 300 °C is amorphous and transforms in crystalline product with scheelite-type structure at 350 °C or higher temperatures without undesirable phases. From FE-SEM observation, it can be concluded that the grain sizes of SMO thin films increase with the annealing temperature. However, some pores are found to exist in the films when temperature is above 900 °C,

Acknowledgments

This work was supported by the National Key Basic Research Program of China under contract no. 2006CB601005, the National Nature Science Foundation of China under contract no. 10474100, Anhui Province NSF Grant no. 070414162, Director's Fund of Hefei Institutes of Physical Science, Chinese Academy of Sciences, and Fund of Chinese Academy of Sciences for Excellent Graduates.

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Preparation of SrMoO4 thin films on Si substrates by chemical solution deposition

Abstract

Introduction

Section snippets

Experiments

Results and discussion

Conclusion

Acknowledgments

Opt. Mater.

Opt. Commun.

Inorg. Chem. Commun.

Catal. Today

J. Alloys Compd.

Physica C

Thin Solid Films

Preparation of SrMoO₄ thin films on Si substrates by chemical solution deposition