Communication Cite This: Chem. Mater. XXXX, XXX, XXX−XXX
pubs.acs.org/cm
Facile Synthesis of Uniform Sn1−xGex Alloy Nanocrystals with Tunable Bandgap Qi Yang,† Xixia Zhao,† Xiaotong Wu, Mingrui Li, Qian Di, Xiaokun Fan, Jichao Zhu, Xing Song, Qian Li, and Zewei Quan* Department of Chemistry, Southern University of Science and Technology (SUSTech), Shenzhen, Guangdong 518055, P. R. China
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S Supporting Information *
S
compared with previously reported methods to synthesize phase pure Sn1−xGex alloy NCs (above 300 °C).11,12 Synthesis of Sn1−xGex Alloy NCs. A new strategy utilizing Sn NCs as the template is developed to synthesize a series of uniform Sn1−xGex alloy NCs. First, spherical Sn NCs with good size uniformity were synthesized according to a reported procedure,40 in which SnCl2 was reduced in the presence of W(CO)6, oleylamine (OAm), 1-octadecene (ODE), and hexamethyldisilazane (HMDS) at 210 °C for 10 min. The average size of Sn NCs is 11.0 ± 1.3 nm based on the statistics by collecting over 500 particles (Figure S1a), and the tetragonal structure of Sn NCs is confirmed by the X-ray diffraction (XRD) pattern, as shown in Figure S2. Sn1−xGex alloy NCs with different ratios were synthesized by injecting a GeI2-TOP precursor solution to the crude solution of Sn NCs at room temperature, followed by heating the mixture at varied temperature and time (refer to the Experimental Section in Supporting Information for details). Figure 1a,b shows the transmission electron microscopy (TEM) images of asprepared Sn0.18Ge0.82 alloy NCs, showing that the morphology and size of starting Sn NCs are well maintained during the alloying process, as shown in Figure S1. The observed interplanar spacing of about 3.28 Å in Figure 1c should be ascribed to the (111) d-spacing of cubic Sn0.18Ge0.82 alloy NCs. This result is consistent with the XRD measurement (Figure 2b), which clearly shows the pure phase of Sn0.18Ge0.82 alloy NCs. Figure 1d−f and Figure S3 show the EDS elemental mapping results of Sn0.18Ge0.82 alloy NCs, confirming the uniform distributions of Sn and Ge elements over the entire alloy NCs, which is discussed below. Structure Evolution from Sn NCs to Sn1−xGex Alloy NCs. To clarify the formation mechanism of Sn1−xGex alloy NCs, their structural transformations were investigated in detail by the ex situ XRD. Figure 2a shows the XRD patterns of samples that are collected as soon as the reaction temperature reaches different temperatures from 60 to 180 °C during the heating process (∼10 °C/min). When the temperature is raised to 90 °C, one broad diffraction peak centered at ∼26° appears besides the diffraction peaks from Sn NCs, implying that the Sn1−xGex alloy nanoparticles with poor crystallinity may be formed at this stage. With continuously increasing reaction temperature to 180 °C, the peak intensities from tetragonal Sn NCs gradually decrease, while those from
ince Ge possesses a series of advantages such as narrow bandgap (0.7 eV at 300 K),1 large Bohr radius (∼24 nm), and good near-infrared-emitting property,2−4 it has been highly attractive for photonics,5 photodetectors,6 biomedical imaging,7 and solar cells8 in the past decades.9 By introducing Sn into the Ge crystal to form Sn1−xGex alloy nanocrystals (NCs), it can exhibit a tunable bandgap in the near-infrared region through regulating their composition and size due to the quantum confinement effect.10−12 For instance, Sn1−xGex alloy quantum dots with different sizes (1−12 nm) have been investigated and can exhibit tunable bandgaps of 0.72−2.16 eV.10,13,14 However, high crystallization temperature of Ge (above 300 °C)15−17 and large lattice mismatch (∼14%),12 as well as low solubility (
