MODIFICATION OF ALUMINIUM OXIDES THROUGH ION IMPLANTATION OF TRANSITION AND NOBLE METALS

• Autor(a) principal: Marques, Carlos Pedro Gonçalves
• Data de Publicação: 2009
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/37033
• topic: sapphire; ion implantation; transition metals; noble metals; nanoparticles; plasmons; Domínio/Área Científica::Engenharia e Tecnologia::Outras Engenharias e Tecnologias

Sapphire (α-Al2O3) crystals were implanted at room temperature with 3d- and 4f-shell transition ions (Ni, Cu, Zn, Eu and Yb) and noble metal ions Ag and Au, with energies in the range of 100 keV to 300 keV. The implanted fluences varied from 11015 cm-2 to 1.81017 cm-2, yielding up to 28 at. % concentration. Subsequent furnace annealings were performed up to 1573 K in vacuum (110-4 Pa) or in air for one hour. Rutherford backscattering spectrometry (RBS) and RBS under channelling conditions (RBS-C), X-Ray Diffraction (XRD), Optical Absorption (OA) and Ion Beam Induced Luminescence (IBIL) were used to characterize the as implanted state as well as the systems created after annealing on what concerns their composition, depth profiles, phases present and their structure, etc. The latter experimental technique was successfully established in our laboratory during this work and the experimental setup is described. The implantation of high fluences allowed embedded metallic precipitates to form, epitaxially aligned with the matrix, and of 10 nm sized dimensions. Thermal annealing in air promoted the crystalline recovery of the host sapphire and the formation of spinel oxide phases of the 3d transition metals and sesquioxides of Eu and Yb. The band gaps of these compounds were estimated via Tauc plots. Silver and gold do not form compounds and tend to segregate to the surface, with the motion of the recrystallization front of sapphire. Thermal annealings in vacuum promoted the alignment and growth of metallic phases, along the fast diffusion c-plane, while the crystalline recovery is limited. The exception is Zn in which case ZnO is observed after annealing at 1173 K. Low melting point metals (Cu and Zn) start to evaporate around 1073 K. The crystalline recovery of the matrix impel the highly mobile metallic ions to the surface where evaporation results in up to 90 % losses, which are higher on samples with c-plane directed to the surface (m- and r-cut samples). The OA measurements in the UV region allowed inspecting the evolution of O vacancy defects (F-centres), while surface plasmon resonant (SPR) bands were measured mainly in the visible region. Detection of the SPR bands was used to probe the emergence (above a threshold fluence) of the precipitates and measure their sizes. This allows envisaging the possibility of using the SPR band to estimate the implanted fluences. Varying the processing conditions made possible changing the SPR band maximum by up to 80 nm. The optical activation of Eu or Yb doped sapphire was measured with IBIL, the maximum luminescence reached after annealing in air at 1573 K.