Note that the carboxylic acid in the starting materials
was changed from n-octanoic acid, which was used in the literature [28], to 2-ethylhexanoic acid according to Dr. Masayuki Kanehara’s kind suggestions because the use of n-octanoic acid led to the formation of ITO nanoflowers, instead of nanoparticles, with significantly broadened SPR peaks (Additional file 1: Figure S1). The proportion of the tin precursor in the reagents, i.e., [tin(II) 2-ethylhexanoate] / ([tin(II) 2-ethylhexanoate] + [indium acetate]), was set to be 10 mol.% because this dopant ratio generated ITO nanocrystals with relatively this website high free electron density and strong SPR in the NIR region [28]. In a typical reaction, indium acetate (1.08 mmol), tin(II) 2-ethylhexanoate (0.12 mmol), 2-ethylhexanoic acid (3.6 mmol), oleylamine (10 mmol), and ODE (10 ml) were loaded in a three-neck flask and stirred at 80°C under vacuum for 30 min to obtain a clear solution. The solution was heated at 150°C for 60 min under an argon atmosphere. The reaction SGC-CBP30 temperature was further raised to 280°C and stabilized for 2 h to generate ITO nanocrystals. The ITO nanocrystals were precipitated out by adding ethyl acetate, purified, and redispersed in C2Cl4. The hot-injection approach In a typical reaction, indium acetate (1.08 mmol), tin(II) 2-ethylhexanoate
(0.12 mmol), 2-ethylhexanoic acid (3.6 mmol), and ODE (10 ml) were loaded in a three-neck flask and stirred at 80°C under vacuum for 30 min. The solution was heated at 150°C under an argon atmosphere for 60 min
before raising the temperature to 290°C. A separate solution of ODE (5 ml) containing oleylamine (10 mmol) at 220°C was rapidly injected into the reaction flask. The reaction mixture was then kept at 290°C for 2 h to obtain ITO nanocrystals. Fourier transform infrared spectroscopy analysis FTIR spectra were recorded on a Bruker Thiazovivin Tensor 27 FTIR spectrophotometer at room temperature (Bruker AXS, Inc., Winooski, VT, USA). The samples were prepared by directly spotting hot aliquots onto CaF2 plates. Note that in many spectra shown in the paper, we used very thick films to maximize the absorption signals, which may cause saturation of intensities of some relatively strong PTK6 peaks. Powder X-ray diffraction analysis X-ray diffraction (XRD) measurements were performed on an X’Pert PRO system (PANalytical, Almelo, The Netherlands) operated at 40 keV and 40 mA with Cu KR radiation (λ = 1.5406 Å). Transmission electron microscopy analysis Transmission electron microscopy (TEM) images were recorded using a JEOL JEM 1230 microscope (JEOL Ltd., Akishima-shi, Japan) operated at 80 keV. High-resolution TEM (HRTEM) was performed on a Tecnai G2 F20 S-TWIN microscope (FEI, Hillsboro, OR, USA) operated at 200 keV.