Preparation of EuO films by sol-gel technique
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Preparation of EuO films by sol-gel technique Guanghua Yi and E. Batalla Department of Physics, Royal Military College, Kingston, Ontario, Canada, K7K 5L0 (Received 14 July 1995; accepted 26 April 1996)
EuO thin films with the cubic NaCl structure were fabricated by a sol-gel technique. The composition and crystal structure of the films were investigated as a function of firing temperature. The preparation of the stock solution and the coating and firing of the films are described. The firing of the gel film and the reduction of the Eu2 O3 phase are also discussed.
I. INTRODUCTION
The research on EuO is motivated by the fact that the compound is a ferromagnetic semiconductor and has very large magneto-optic effects at low temperatures.1 Hence, thin films of EuO have been used for magnetooptical recording models for several years.2 In recent years, EuSe films have been used to image magnetic flux in superconductors to study their critical current distribution at liquid helium temperatures.3 Since EuO is a similar compound with a higher Curie temperature (Tc 69 K as opposed to 4.5 K for EuSe), thin film EuO could also be used to measure the critical current in high-temperature superconducting films at liquid nitrogen temperatures. Almost all of the applications of EuO require the compound to be prepared in film form. Up to now, EuO films have been prepared using techniques such as electron beam evaporation of EuO slugs,4 simultaneous evaporation of Eu and Eu2 O3 ,5 reactive evaporation of Eu in an oxygen partial pressure, sputtering,6 and controlled oxidizing of an Eu metal film.7 Since Eu ions can assume two valence states, Eu11 and Eu31 , both EuO and Eu2 O3 are possible, and Eu2 O3 is thermodynamically favored to form even in a very low oxygen partial pressure. Therefore, these physical deposition techniques have the common feature that it is necessary to deposit the films in extremely high vacuum or in an accurately controlled oxygen partial pressure to obtain good quality films. Moreover, a pure EuO source is not easily manufactured, and it is difficult to stabilize the evaporation rates of Eu and Eu2 O3 simultaneously. In recent years, the fabrication of films by sol-gel techniques has become an important process tool.8 In sol-gel processing, a solution containing the required species is first prepared. The solution is then applied to a substrate to form a liquid layer. To obtain a continuous film, the liquid layer should be gelled to form a homogeneous solid film. The solid film is then dried and fired to displace unwanted components to form an amorphous inorganic film. On heating to high temperatures, the inorganic film will crystallize to become a ceramic film. 2470
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 10, Oct 1996
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In sol-gel processing of films, organic compounds are used as vehicles to prepare solutions containing metal ions. The amount of the organic compounds retained in the gelled films can be controlled
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