TY - JOUR
T1 - Investigation of the effect of in situ annealing of FePt nanodots under high vacuum on the chemical states of Fe and Pt by x-ray photoelectron spectroscopy
AU - Murugesan, M.
AU - Bea, J. C.
AU - Yin, C. K.
AU - Nohira, H.
AU - Ikenaga, E.
AU - Hattori, T.
AU - Nishijima, M.
AU - Fukushima, T.
AU - Tanaka, T.
AU - Miyao, M.
AU - Koyanagi, M.
N1 - Funding Information:
This work was performed at Venture Business Laboratory, Tohoku University, and supported by Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Agency (JST). The authors would like to thank Professor K. Hirose of Institute of Space and Astronautical Science, Professor S. Samukawa of Institute of Fluid Science, Tohoku University, and Professor S. Kono of IMRAM, Tohoku University for their fruitful discussions and collaborations. FIG. 1. Cross-sectional schematic view of samples for XPS analysis. θ is the photoelectron take-off angle and d is the information depth. FIG. 2. Cross-sectional HRTEM images of 10 nm thick FePt nanodot films in situ annealed at different temperatures. FIG. 3. (a) Pt 4 f core level XP spectra measured at θ = 10 ° obtained with 10 nm thick FePt nanodot films in situ annealed at different temperatures. (b) Pt 4 f core level XP spectra measured at θ = 80 ° obtained with 10 nm thick FePt nanodot films in situ annealed at different temperatures. FIG. 4. (a) Fe 3 p core level XP spectra measured at θ = 10 ° obtained with 10 nm thick FePt nanodot films in situ annealed at different temperatures. (b) Fe 3 p core level XP spectra measured at θ = 80 ° obtained with 10 nm thick FePt nanodot films in situ annealed at different temperatures. FIG. 5. Fe 2 p core level XP spectra measured at θ = 10 ° and 80 ° obtained with 10 nm thick FePt nanodot films in situ annealed at different temperatures. FIG. 6. Valence band XP spectra measured at various θ values obtained with 10 nm thick FePt nanodot films in situ annealed at different temperatures.
PY - 2008
Y1 - 2008
N2 - The chemical states of Fe and Pt in in situ annealed L 10 structured FePt nanodots formed by self-assembled nanodot deposition method have been systematically investigated by angle resolved x-ray photoelectron spectroscopy. From the Fe3p and the Pt4f core level x-ray photoelectron (XP) spectra, it is evident that both the Fe and Pt of the nanodots were oxidized in the as-grown state. After the in situ annealing under high vacuum, a peak corresponding to metallic Fe begins to appear, and subsequently the metallic peak fraction increased with the increase in the annealing temperature. In line with this, the peak fraction of the respective oxides is drastically decreased. Irrespective of the annealing temperatures, it is inferred from the intensity of the XP spectrum that the Fe atom of the FePt nanodots is highly prone to oxidation than the Pt atom. Nevertheless, the valence band spectra of the as-grown FePt nanodot film clearly depict the presence of metallic Fe-Pt alloy. We would like to explain the results of the core level and valence band XP spectra as follows: only the peripheral Fe and Pt atoms of the as-formed FePt nanodots are bonded to the oxygen of the cosputtered SiO2 matrix, whereas the metallic core of the as-formed FePt nanodots is always preserved. The very good vacuum ambient during postannealing highly promotes the dissociation of oxygen from the metal oxides via reduction reaction. This results into an increase in the fraction of metallic Fe and Pt at the periphery of FePt nanodots and the formation of high quality SiO2 matrix after annealing. Similar results were also observed for the monatomic W as well as Pt nanodots embedded in SiO2 matrix. Hence, this simple, rather effective method of in situ annealing of metal dots dispersed in an insulating matrix can be readily employed in the fabrication of high-density nanodot memory devices.
AB - The chemical states of Fe and Pt in in situ annealed L 10 structured FePt nanodots formed by self-assembled nanodot deposition method have been systematically investigated by angle resolved x-ray photoelectron spectroscopy. From the Fe3p and the Pt4f core level x-ray photoelectron (XP) spectra, it is evident that both the Fe and Pt of the nanodots were oxidized in the as-grown state. After the in situ annealing under high vacuum, a peak corresponding to metallic Fe begins to appear, and subsequently the metallic peak fraction increased with the increase in the annealing temperature. In line with this, the peak fraction of the respective oxides is drastically decreased. Irrespective of the annealing temperatures, it is inferred from the intensity of the XP spectrum that the Fe atom of the FePt nanodots is highly prone to oxidation than the Pt atom. Nevertheless, the valence band spectra of the as-grown FePt nanodot film clearly depict the presence of metallic Fe-Pt alloy. We would like to explain the results of the core level and valence band XP spectra as follows: only the peripheral Fe and Pt atoms of the as-formed FePt nanodots are bonded to the oxygen of the cosputtered SiO2 matrix, whereas the metallic core of the as-formed FePt nanodots is always preserved. The very good vacuum ambient during postannealing highly promotes the dissociation of oxygen from the metal oxides via reduction reaction. This results into an increase in the fraction of metallic Fe and Pt at the periphery of FePt nanodots and the formation of high quality SiO2 matrix after annealing. Similar results were also observed for the monatomic W as well as Pt nanodots embedded in SiO2 matrix. Hence, this simple, rather effective method of in situ annealing of metal dots dispersed in an insulating matrix can be readily employed in the fabrication of high-density nanodot memory devices.
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U2 - 10.1063/1.2973665
DO - 10.1063/1.2973665
M3 - Article
AN - SCOPUS:54049098325
SN - 0021-8979
VL - 104
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 7
M1 - 074316
ER -