Strain distribution in epitaxial SrTiO3 thin films

Abstract

The lattice strain distributions of epitaxial SrTiO 3 films deposited on LaAlO 3 were investigated by in situ x-ray diffraction at the temperature range of 25-300 K, grazing incident x-ray diffraction, and high resolution x-ray diffraction. The nearly linear temperature dependence of the out-of-plane lattice constant of SrTiO 3 was observed in the measured temperature range. The depth distribution of the lattice strain at room temperature for SrTiO 3 films includes the surface layer, strained layer, and interface layer. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2424282͔ SrTiO 3 ͑STO͒ is an incipient ferroelectric material in perovskite structure, which has been extensively studied for its application in tunable microwave devices for having a large and variable dielectric constant. 1,2 STO is also a perfect prototype to investigate phase transition, 3 especially to understand the surface and interface structural configuration for the perovskite films grown on it. 4 Although ferroelectric properties were only reported through oxygen isotope exchange ͑ST 18 O͒, 3,5 and cation substitution, 6,7 recent theories and experiments validate the existence of ferroeletricity in STO thin films under strain. [8][9][10] He et al. [11][12][13] systematically studied the structural phase transition of STO thin films under strain. Devonshire 14 predicted the shift of the ferroelectric phase transition temperature ͑T c ͒ for STO thin films due to the biaxial strain. Haeni et al. 10 reported that the room temperature ferroelectricity appears for the tensile strained STO thin films on DyScO 3 substrates, although STO crystal is incipient ferroelectric. There is little work on the observation of distribution of lattice strain along the normal of sample surface for STO thin films.In this letter, the distribution of the lattice strain of the epitaxial STO films grown on LaAlO 3 ͑LAO͒ ͑001͒ substrate by laser molecular beam epitaxy ͑MBE͒ deposition ͑L-MBE͒ is investigated. The temperature dependence of the c-direction lattice constant ͑c-T curve͒ is nearly linear, which is different from that of the bulk. The depth dependence of the lattice strain is not homogeneous, which may be due to the competition between the elastic restore and the lattice mismatch between STO film and LAO substrate.STO films were grown on LAO ͑001͒ single crystal substrate in a L-MBE system. The technique was used to deposit STO on Si in our previous studies. 15,16 Briefly, a single crystal STO target was used to grow STO film. A KrF excimer laser was used in a repetition rate of 2 Hz. The substrate was heated to 770°C. The film thicknesses were 80, 150, and 280 nm from the measurement of a Dektax 3 ST surface profile. X-ray diffraction ͑XRD͒ ͑Cu K␣ radiation͒ analysis was performed using the /2 scan mode on a Rigaku Dmax-rB and a Bruker Advanced D8 X-ray diffractometer. The depth dependence of strain, which is related to the film thickness, was determined by grazing incident x-ray diffraction ͑surface x-ray diffraction͒, which was carried out on Be...

Variation in structure and photoluminescence in SrTiO3 film buffered by SrRuO3

“…3, the temperature dependence of the out of plane lattice parameter of c is deduced according to the reflection position at low temperature. A nearly linear behavior between c and T are shown, which is very similar to that of STO on LAO [15].…”

“…We believe that the blue-light emission may relate to the detailed structure properties. To recognize the structure effects on the blue-light emission, PL measurements are performed on the STO single crystal, and also the STO film epitaxed on LAO, which we have characterized in structure [15]. It is shown that the blue-light emission disappears in these two cases.…”

Effects of substrate on structure and the magnetic properties of (001)-textured FePt films grown at low temperature

“…We ignore the depth dependence of the inplane lattice parameter although we have shown that the inplane parameter of the film varies slightly with the depth of the film in our previous studies on Co/Cu multilayers 12 and SrTiO3/LaAlO3 systems. 13 The ordering parameters S, defined by Endo et al, 14 are calculated to be 0.40, 0.80, and 0.66 for FP film on LAO, STO, and MgO, based on the above measurements, individually. We then define the tetragonal distortion as: 15,16 a) Author to whom correspondence should be addressed.…”

Surface structure for Au on (001) SrTiO3

“…Because of having particular properties different from the bulk, great attention has been focused on the bulk STO [2,3] and the strained STO thin films recent years [4,5]. Many reconstructions of STO surfaces have been reported, depending on the preparation procedures, temperature, pressure and chemical environments [6].…”