Diffusion doping of cobalt in rod-shape anatase TiO\u3csub\u3e2\u3c/sub\u3e nanocrystals leads to antiferromagnetism†

Cobalt(II) ions were adsorbed to the surface of rod-shape anatase TiO2 nanocrystals and subsequently heated to promote ion diffusion into the nanocrystal. After removal of any remaining surface bound cobalt, a sample consisting of strictly cobalt-doped TiO2 was obtained and characterized with powder Xray diffraction, transmission electron microscopy, UV-visible spectroscopy, fluorescence spectroscopy, X-ray photoelectron spectroscopy, SQUID magnetometry, and inductively-coupled plasma atomic emission spectroscopy. The nanocrystal morphology was unchanged in the process and no new crystal phases were detected. The concentration of cobalt in the doped samples linearly correlates with the initial loading of cobalt(II) ions on the nanocrystal surface. Thin films of the cobalt doped TiO2 nanocrystals were prepared on indium-tin oxide coated glass substrate, and the electrical conductivity increased with the concentration of doped cobalt. Magnetic measurements of the cobalt-doped TiO2 nanocrystals reveal paramagnetic behavior at room temperature, and antiferromagnetic interactions between Co ions at low temperatures. Antiferromagnetism is atypical for cobalt-doped TiO2 nanocrystals, and is proposed to arise from interstitial doping that may be favored by the diffusional doping mechanism

Quantitative Control in Single Atom Doping for Solotronic TiO2 Nanocrystals

Doping is a powerful and effective way to alter the electronic, optical, and structural properties of an intrinsic semiconductor. However, the precise control over the dopant concentration in semiconductor nanocrystals is a major challenge. In the extreme case, a single impurity atom in the nanocrystal gives rise to \u27solotronic\u27 nanocrystals that are predicted to behave as quantum information storage devices with high precision, efficiency, and fidelity. The study of solotronic nanocrystals has the potentiality to open a new avenue for quantum information storage and processing. In our group, we developed a unique method to control the thermodynamic ion diffusion of cobalt into TiO2 nanocrystals. The result demonstrates homogeneous cobalt ions doping with unprecedented control. The control over the doping process is convincing toward single metal ion doping. In this presentation, synthesize, characterization, quantitative control doping, and the properties of cobalt-doped nanocrystals will be presented