Supporting Information File. Solution-based synthesis of GeTe octahedra at low temperature

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1 Supporting Information File Solution-based synthesis of GeTe octahedra at low temperature Stephan Schulz, a * Stefan Heimann, a Kevin Kaiser, a Oleg Prymak, a Wilfried Assenmacher, b Jörg Thomas Brüggemann, c Bert Mallick, c Anja Verena Mudring c,d a Institute of Inorganic Chemistry and Center for Nanointegration Duisburg-Essen (CENIDE), University of Duisburg-Essen, Universitätsstr. 5-7, D Essen, Germany. b Institute of Inorganic Chemistry, University of Bonn, Römerstr. 164, D Bonn, Germany. Inorganic Chemistry III Materials Engineering and Characterization, Ruhr-University Bochum, Bochum, Germany. d Materials Science and Engineering, Iowa State University, Ames, IA 50010, USA. S1

2 In situ NMR Characterization Figure S1. In situ NMR spectroscopy study on the reaction of GeCl 2 dioxane and Te(SiEt 3 ) 2 in C 6 D 6 : 1 H NMR spectra: a) Et 3 SiCl; b) GeCl 2 dioxane + Te(SiEt 3 ) 2 ; c) Te(SiEt 3 ) 2. Figure S2. In situ NMR spectroscopy study on the reaction of Te(SiEt 3 ) 2 and oleylamine in C 6 D 6 : 1 H NMR spectra: a) oleylamine; b) oleyln(h)siet 3 ; c) Te(SiEt 3 ) 2 + oleylamine in C 6 D 6. S2

3 Thermogravimetry Figure S3. TGA/DTA experiment of GeTe octahedra in Ar-atmosphere (DTA black curve; TGA red curve). S3

4 Powder X-Ray Diffraction The texture coefficient (TC) was calculated using the relationship defined by Barret and Massalski TC (hkl) = I (hkl) /I 0(hkl) / [n -1 (I (hkl) /I 0(hkl) )] (1) where I is the intensity of the diffraction peaks, I (hkl) and I 0(hkl) are the intensities of the (hkl) plane in the diffractograms, measured for the nanocrystalline sample GeTe and the microcrystalline GeTe sample (without texture, JCPDS No [1] ), respectively; n is the number of selected diffraction peaks (here n = 11), and h, k, and l are the Miller indices of the individual crystallographic planes. The summation in the denominator was taken for the 11 hkl-planes (see table S4). The background was subtracted. [1] Grier, D., McCarthy, G., Seidler, D., Boudjouk, P., North Dakota State Univ., Fargo, ND, USA., ICDD Grant-in- Aid (1993) Table S1. Lattice spacing (d) and calculated texture coefficients (TC) for different hkl of the investigated GeTe nanoparticles. The defined FWHMs were used for the Williamson-Hall plot. hkl 2θ / d / Å FWHM / TC (hkl) * * * The found d-values are in a good agreement with our TEM results as well as those reported by Kim et al. [1] In the table only that FWHM- and TC-values presented, which were taken for the calculation. [1] Kim, M. H.; Gupta, G.; Kim, J. RSC Adv. 2013, 3, S4

5 Figure S4. Williamson-Hall plot of B*cosθ and sinθ: Crystallite size D hkl and microstrain ε contributions to the peak broadening in diffractogram presented in Fig. 5 (intercept Kλ/D hkl and slope η). The average crystallite size (D hkl ) of the GeTe nanoparticles was calculated by means of the Rietveld refinement using Debye-Scherrer s formula: D hkl = Kλ/(FWHM*cosθ) where K is shape factor (0.89), λ is wavelength of Cukα radiation (1.54 Å), and FWHM is Full width at half maximum of the diffraction peaks. The microstrain (ε) induced in GeTee nanoparticles due to crystal distortion was calculated by means of the Rietveld refinement using the formula: ε= FWHM/4tanθ The instrumental correction was taken into account. The crystallite size and microstrain contribute to the peak broadening and can be distinguished by the Williamson-Hall plot (W-H) of B*cosθ and sinθ (see Fig. S5).This W-H plot shows, the larger the intercept (H=Kλ/D hkl ), the smaller the crystallite size (D hkl ), the larger the slope (η), the larger the microstrain (ε hkl ). In the case of the produced GeTe nanoparticles we have both effects. S5

6 TEM Characterization It was possible to tilt crystals in orientations of main zone axes and to determine the growth direction and indices of the crystal faces. All main zone axis orientations <100>, <111> and <110> of the pseudo cubic face centered GeTe were obtained. Figure S5 shows a GeTe octahedron along the pseudo 4fold axis and figure S6 is perpendicular to a triangular crystal face. Figure S8 shows the crystal with an edge parallel to the incident electron beam. S6

7 a) b) 293,3 pm 293,3 pm c) d) e) f) Figure S5. a) TEM bright field image of a GeTe crystal in zone axis orientation; b) Fourier-filtered HRTEM image with marked lattice fringes; c) Electron diffraction pattern with indices and zone axis for GeTe in rhombohedral setting (R-3m; a: 5.98 Å, α:88.3 ); d) Electron diffraction pattern with indices and zone axis for GeTe in hexagonal setting (R-3mH; a: 8.35, c: Å); e) HRTEM image without further processing; f) Diffractogramm (Fourier transform) of the HRTEM image (e)). S7

8 a) b) c) d) e) f) Figure S6. a) TEM bright field image of a GeTe crystal in zone axis orientation; b) Fourier-filtered HRTEM image with marked lattice fringes; c) Electron diffraction pattern with indices and zone axis for GeTe in rhombohedral setting (R-3m; a: 5.98 Å, α:88.3 ); d) Electron diffraction pattern with indices and zone axis for GeTe in hexagonal setting (R-3mH; a: 8.35, c: Å); e) HRTEM image without further processing; f) Diffractogramm (Fourier transform) of the HRTEM image (e)). S8

9 a) b) c) d) e) f) Figure S7. a) TEM bright field image of a GeTe crystal in zone axis orientation; b) Fourier-filtered HRTEM image with marked lattice fringes; c) Electron diffraction pattern with indices and zone axis for GeTe in rhombohedral setting (R-3m; a: 5.98 Å, α:88.3 ); d) Electron diffraction pattern with indices and zone axis for GeTe in hexagonal setting (R-3mH; a: 8.35, c: Å); e) HRTEM image without further processing; f) Diffractogramm (Fourier transform) of the HRTEM image (e)). S9

10 a) b) c) d) e) f) 7 Figure S8. a) TEM bright field image of a GeTe crystal in zone axis orientation; b) Fourier-filtered HRTEM image with marked lattice fringes; c) Electron diffraction pattern with indices and zone axis for GeTe in rhombohedral setting (R-3m; a: 5.98 Å, α:88.3 ); d) Electron diffraction pattern with indices and zone axis for GeTe in hexagonal setting (R-3mH; a: 8.35, c: Å); e) HRTEM image without further processing; f) Diffractogramm (Fourier transform) of the HRTEM image (e)). S10