“…20 The mentioned research on VO 2 -based core-shell nanostructures represents examples of a huge endeavor to develop analogous structures of a vast range of materials, and representative recent work on hollow nanospheres-which will be shown below to have the most interesting properties for the case of VO 2 -has been presented for a multitude of other oxides including MgO, 21 SiO 2 , 22 c-MnO 2 , 23 NiO, 24 ZnO, 25 In 2 O 3 , 26,27 and SnO 2 . 28,29 Other recent investigations embrace hollow nanospheres of sulfides, [30][31][32] selenides, 33 phosphates, 34 carbides, 35 and metals in elemental 36,37 and composite 38,39 form.…”