The magnetron sputtered La0.7Sr0.3MnO3 films were implanted with different doses (5 ′ 1015 ions×cm?2 and 5 ′ 1016 ions×cm-2) of Al ions at different negative pulsed voltages (30 kV and 50 kV) by plasma based ion implantation and then annealed at 973 K for 1 h in air. The microstructure, surface morphologies, surface roughness, metal-insulator transition and room temperature emittance properties of the post-implantation annealed films were investigated and compared with those of the La0.7Sr0.3MnO3 film annealed at 973 K for 1 h in air. The results indicate that the post- implantation annealed films show single perovskite phase and obvious (100) preferred orientation growth. The Mn-O bond length, surface roughness and metal-insulator transition temperature (TMI) of the films can be effectively adjusted by changing implantation voltage or implantation dose of Al ions. However, the change of implantation parameters just has a small effect on room temperature emittance of the films. Compared with the annealed film, the post-implantation annealed films have shorter Mn-O bond length and lower room temperature emittance. The TMI of the films implanted at low voltage is lower than that of the annealed film, which mainly results from the degradation of oxidization during annealing process and the part displacement of Mn3+-O2+- Mn4+ double exchange channels by Al3+-O2?-Mn4+. The post-implanted annealed film implanted at 50 kV/5 ′ 1016 ions×cm-2 has a higher TMI than the annealed film, which is 247 K. The increase of TMI of the film implanted with high dose of Al ions at high voltage can be attributed to the improvement of microstructure.
ABO3 type perovskite manganites La1−xMxMnO3 (M = Ca, Sr or Ba) with appropriate doping concentration (x) have a variable emittance property based on the metal-insulator transition [
The modification effect of ion implantation strongly depends on the kind of implanted ions. Aluminum has a low density and is easy to be oxidized. Thus implanting with aluminum cannot obviously increase the volume density but potentially improves oxygen content of La1−xMxMnO3. Meanwhile, this treatment also affects the double exchange interaction. It means that the structure, composition and TMI of La1−xMxMnO3 will change, which will result in different emittance properties. Up to now, the investigation on microstructure and properties especially the emittance property of La1−xMxMnO3 implanted with aluminum is very little. Therefore, In this work, the La0.7Sr0.3MnO3 films were implanted with aluminum at various negative pulsed voltages and implantation doses by plasma based ion implantation and post-implantation annealed in air. The structure, surface state, metal-insulator transition and room temperature emittance property of the modified films have been studied.
The La0.7Sr0.3MnO3 films were deposited on Si(100) by DC magnetron sputtering from a La0.7Sr0.3MnO3 ceramic target. During deposition process, the Si substrate was kept at 853 K. The deposition was carried out in Ar (75 vol %) + O2 (25 vol %) ambience at a total pressure of 0.5 Pa. The thickness of the films was about 700 - 750 nm. After deposition, the films were implanted with aluminum at negative pulsed voltages and then were annealed in air. The treatment parameters are shown in
The phase structure of the films was confirmed by Glance angle X-ray diffraction (GXRD) using Cu Kα radiation and 5˚ angle. The surface morphologies and mean roughness of the films were studied by atomic force microscope (AFM). The bond structure and IR reflectance spectra at room temperature of the films were examined using Fourier transform infrared spectroscopy (FTIR). The resistivity was measured as a function of the temperature using the standard four-probe method between 10K and 325 K in zero field.
Film | Implantation voltage (V) | Implantation dose (ions×cm−2) | Annealing treatment |
---|---|---|---|
1 | - | - | Annealing at 973 K for 1 h in air |
2 | 30 | 5 × 1015 | |
3 | 50 | 5 × 1015 | |
4 | 50 | 5 × 1016 |
post-implantation annealed films due to low Al concentration. However, the treatment of implanting with Al and post-implantation annealing makes the phase structure of the films quite different from that of the annealed film. The annealed film has a phase structure similar to that of the corresponding bulk with same composition. The post-implantation annealed films show quite obvious (100) preferred orientation growth and the degree of preferred orientation depends on the implantation voltage and implantation dose. By comparison, the post-implan- tation annealed film implanted at 30 kV/5 ´ 1015 ions×cm−2 has the highest degree of (100) preferred orientation.
The higher the stretching vibration frequency of Mn-O bond is, the shorter the length of Mn-O bond is. It implies that the Mn-O bond length of the post-implantation annealed films is shorter than that of the annealed film and can be adjusted by changing the implantation voltage and implantation dose. The shortening of Mn-O bond can enhance the double exchange interaction, which is propitious to the increase of metal-insulator transition temperature.
The AFM surface morphologies of the post-implantation annealed and annealed films are shown in
In order to understand the effect of the treatment of implanting with Al and post-implantation annealing on the transport property of the films, the temperature dependence of resistivity of the films was measured. But the
measurement of the post-implantation annealed film implanted at 50 kV/5 × 1015 ions×cm−2 failed due to high resistance over the range of the used instrument, which indicates that this film is insulation state in the measuring temperature range. The temperature dependence of resistivity of the other three films is shown in
reflectance is small for the post-implantation annealed films. As these films are nontransparent, the emittance of them can be evaluated based on their reflectance as per the followed formula [
The post-implantation annealed La0.7Sr0.3MnO3 films exhibit single perovskite phase and obvious (100) preferred orientation growth. The degree of (100) preferred orientation, Mn-O bond length, surface roughness and metal-insulator transition temperature of these films can be adjusted by changing the implantation voltage and implantation dose of Al. Compared with the annealed film, the post-implantation annealed films have shorter Mn-O bond length and lower room temperature emittance. However, the TMI change tendency of the post- implantation annealed films strongly depends on the implantation voltage and implantation dose. The post- implantation annealed films implanted with Al at low voltage or low dose have lower TMI than the annealed film due to the degradation of oxidation degree and the part displacement of Mn3+-O2−-Mn4+ by Al3+-O2--Mn4+. The post-implantation annealed film implanted with Al at 50 kV/5 × 1016 ions×cm−2 has higher TMI than the annealed film because the improvement of microstructure of the film promotes metal-insulator transition. The changes of implantation voltage and implantation dose have only a small effect on the room temperature emittance of the post-implantation annealed films. By comparison, the modified La0.7Sr0.3MnO3 films with (100) preferred orientation have relatively lower emittance at room temperature.
This work is supported by the Natural Science Foundation of China (Project No.: 51101051), Natural Science Foundation of Jiangsu Province (Project No.: BK2011250), Jiangsu Province Postdoctoral Science Foundation funded project (Project No.: 1101017C), China Scholarship Council and Outstanding innovative talents support plan of Hohai University.
Shaoqun Jiang,Gang Wang,Xinxin Ma,Xinxin Ma,Guangze Tang, (2015) Characteristics of La0.7Sr0.3MnO3 Films Modified by Aluminum Ions Implantation and Post-Implantation Annealing. Journal of Materials Science and Chemical Engineering,03,22-28. doi: 10.4236/msce.2015.31004