Structural and chemical characterization of semiconductor nanowires using a hard X-ray nanoprobe

Orateur : Manh-Hung CHU (ESRF)

Much effort has been devoted to the investigation of dilute magnetic semiconductors in recent years due to their potential applications in spintronics nanodevices[1]. In particular, Co-doped ZnO nanowires (NWs) offer unique advantages owing to the large aspect ratio and theoretically predicted room temperature ferromagnetism [2]. Cobalt is known to be optically active in semiconductors through the Co 3d intra-shell transition, thus Co doped ZnO NWs could also provide promising optical properties for future optoelectronic nanodevices [3]. However, doping of NWs with transition metals during growth remains a challenge [4]. Due to the self-organized growth mechanisms, the NWs are sensitive to changes in the growth conditions. Up to date, ion implantation process has proven to be an effective way for doping with Co in a controlled manner ZnO NWs [5]. However, this process generally produces unwanted structural defects in the NWs, a post-implantation thermal annealing is therefore often used to restore the crystal structure [5]. Determining the doping homogeneity and the structural order in individual implanted NWs is crucial to understand their behavior in the spintronics and optoelectronics nanodevices. Here we show that Co atoms are homogeneously distributed along the NWs by using X-ray fluorescence [6]. The high structural order of the single Co:ZnO NWs with post-implantation thermal annealing is observed by the X-ray absorption [7]. In addition, the unavoidable atomic lattice distortions generated only by the ion implantation process was also studied. The results show that ion implantation-induced damage prevents a high degree of local structural order around Co and Zn atoms along single NWs. In particular, by extended X-ray absorption fine structure, our findings reveal a significant increase of the Debye-Waller factor and an expansion of the lattice along the as-implanted NWs[8]. The large range order studied by nano-X-ray diffraction also confirms an expansion of c lattice constant along the as-implanted NWs [9]. Once more, our X-ray absorption spectroscopy and diffraction data analysis supports the good recovery of the implantation-induced damage of the ZnO host lattice through the post thermal annealing. References [1] H. Ohno, Science 281, 951 (1998). [2] Y. W. Heo, D. Norton, L. Tien, Y. Kwon, B. Kang, F. Ren, S. Pearton, and J. Laroche, Mater. Sci. Eng. R 47, 1, (2004). [3] S. Müller. M. Zhou, Q. Li, and C. Ronning, Nanotechnology 20, 135704, (2009). [4] D. E. Perea, E. R. Hemesath, E. J. Schwalbach, J. L. Lensch-Falk, P. W. Woorhees, and L. J. Lauhon, Nature Nanotechnology 4, 315 (2009). [5] C. Ronning, C. Borschel, S. Geburt, and R. Niepelt, Mater. Sci. Eng.R 70, 30 (2010). [6] M. H. Chu, J. Segura-Ruiz, G. Martínez-Criado, P. Cloetens, I. Snigireva, S. Geburt, and C. Ronning, Phys. Status Solidi RRL 5, 283 (2011) [7] J. Segura-Ruiz, G. Martínez-Criado, M. H. Chu, S. Geburt, and C. Ronning, Nano Lett. 11, 5322 (2011). [8] M. H. Chu, J. Segura-Ruiz, G. Martínez-Criado, S. Geburt, and C. Ronning, Appl. Phys. Lett. 103, 141911 (2013). [9] M. H. Chu, J. Segura-Ruiz, G. Martínez-Criado, S. Geburt, and C. Ronning, Phys. Status Solidi a (accepted).

Télécharger dans mon agenda