Rapid, Low Temperature Synthesis of Germanium Nanowires from. Oligosilylgermane Precursors

Transcription

1 Supporting Information Rapid, Low Temperature Synthesis of Germanium Nanowires from Oligosilylgermane Precursors Mohammad Aghazadeh Meshgi a, Subhajit Biswas b,c, David McNulty b,, Colm O'Dwyer b, Giuseppe Alessio Verni b,c, John O Connell b,c, Fionán Davitt b,c, Ilse Letofsky-Papst d, Peter Poelt d, Justin D. Holmes b,c,* and Christoph Marschner a,* a Institute of Inorganic Chemistry, Graz University of Technology, Stremayrgasse 9, Graz, Austria. b Department of Chemistry and the Tyndall National Institute, University College Cork, Cork, Ireland. c AMBER@CRANN, Trinity College Dublin, Dublin 2, Ireland. d Institute of Electron Microscopy and Nanoanalysis, Graz University of Technology, Steyrergasse 17, Graz, Austria. Raman spectroscopy and XRD analysis of indium incorporation in the structure of Ge nanowires Besides EDX analysis, XRD and Raman spectroscopy were used to determine the incorporation of indium atoms in the structure of Ge nanowires. Figure S9 displays the Raman spectra of Ge nanowires samples grown under different reaction conditions. The yellow line with a peak at 300 cm -1 relates to a Ge micropowder, used as a bulk Ge reference, having the same frequency as bulk Ge reported elsewhere 1. In comparison to the Raman spectrum of the Ge micropowder, the Raman spectra of the Ge nanowires were red-shifted. This red shift can either be the effect of a dopant 2 or defects 3 in the structure of the Ge nanowires. As the purple line, which relates to the sample with the minimum amount of S1

2 crystalline defects (Figure 4),,displays a red shift, it can be concluded that In incorporation in the structure of the nanowires can partially cause the red shift in the Raman spectra. Figure S10 displays XRD spectrum of a nanowire sample with the minimum amount of the crystalline defects (Figure 4) with 0.9± 0.1 at% In incorporation. The red XRD pattern relates to the Ge micropowder used as bulk Ge reference, with a diamond cubic crystal structure. A small shift was observed between the XRD patterns of Ge nanowires (blue line) and that bulk Ge (red line). This small shift in the XRD patterns can be explained by Vegard s law and In incorporation into the structure of Ge nanowires. Ge with a cubic crystal structure has a lattice constant of 5.66 Å 4 and In with a tetragonal crystal structure has lattice constants of a = b = 3.25 Å, c = 4.94 Å. Equation S1 depicts the lattice spacing of Ge doped with 1 percent of indium according to Vegard s law which is approximately 5.63 Å. 5,6.. = (S1) Calculation of the interplanar d spacing of the (220) lattice plane of the Ge nanowires from XRD spectrum resulted in a lattice constant of 5.61 Å. This experimentally driven lattice constant of the Ge nanowires form XRD data is very close to the lattice constant of Ge doped with 1 at% of indium, which was obtained by Vegard s law with the value of 5.63 Å. This finding from XRD analysis further suggests the presence of incorporated In atoms in the Ge diamond cubic lattice. S2

3 Figure S1. 29 Si{ 1 H} NMR spectrum of precursor 1 in C 6 D 6. S3

4 Figure S2. 13 C{ 1 H} NMR spectrum of precursor 1 in C 6 D 6. S4

5 Figure S3. 1 H NMR spectrum of precursor 1 in C 6 D 6. S5

6 Figure S4. 29 Si{ 1 H} NMR spectrum of precursor 2 in C 6 D 6. S6

7 Figure S5. 13 C{ 1 H} NMR spectrum of precursor 2 in C 6 D 6. S7

8 Figure S6. 1 H NMR spectrum of precursor 2 in C 6 D 6. S8

9 (a) (b) Figure S7. SEM images of Ge nanowires synthesized with precursor 1 in the presence of TOPO (a) in n-hexadecane at 300 C and (b) in squalane at 380 C. S9

10 (a) (b) Figure S8. (a) STEM image in HAADF mode and EDX single point analysis from an individual Ge nanowire, synthesized from precursor 1 and displaying 1.8 at.% In incorporation. (b) EDX spectrum from several Ge nanowires synthesized from precursor 1, again highlighting the incorporation of In atoms within the structure of the nanowires. Fe, Co, Cu and carbon peaks observed were from the TEM grid. S10

11 In Ge Figure S9. EDX mapping of a Ge nanowire displayed a homogenous distribution of indium atoms within its Ge structure.. S11

12 Figure S10. Raman spectra of Ge nanowires. Yellow line: Ge micropowder used as a bulk Ge reference. Red line: Ge nanowires synthesized with precursor 1 at 300 C. Green line: Ge nanowires synthesized with precursor 1 at 350 C. Blue line: Ge nanowires synthesized with precursor 1 at 180 C. Purple line: Ge nanowires synthesized with precursor 2 at 350 C. In comparison to the spectrum of the Ge reference, a small shift toward shorter wavelengths was observed for the spectra of the Ge nanowires. The samples synthesized using precursor 2 at 350 C, with the minimum amount of crystalline defects and 0.9 ± 0.1 at% indium incorporation, had the highest intensity (purple line). S12

13 Figure S11. XRD spectrum of the sample with highest degree of straight and single crystalline nanowires prepared with precursor 2 at 350 C. Red peaks relate to a Ge micropowder considered as a bulk Ge reference. A small mismatch between the spectra of the Ge nanowires and the Ge reference arises from the Ge lattice change because of indium atoms incorporation into the structure of the Ge nanowires. S13

14 Figure S Si{ 1 H} NMR spectrum from the decomposition of precursor 1 in the presence of TOPO at 180 C (with D 2 O lock). The peak at 6.9 ppm corresponds to hexamethyldisiloxane. S14

15 Figure S Si{ 1 H} NMR spectrum from the decomposition of precursor 1 in the presence of OA at 300 C. The peak at 6.9 ppm relates to hexamethyldisiloxane whereas the peak at 1.6 ppm relates to trimethylsilyloleylamine compound (with D 2 O lock). S15

16 Figure S Si{ 1 H} INEPT NMR spectrum from the reaction of chlorotrimethylsilane with OA. Peaks at 6.9, 4.9 and 1.6 ppm belong to hexamethyldisiloxane, bis(trimethylsilyl)oleylamine and trimethylsilyloleylamine, repectively (with D 2 O lock). S16

17 Figure S15. SEM images showing the product from the decomposition of precursor 1 in the presence of a OA and TOPO mixture at 350 C. S17

18 References (1) Majumdar, D.; Biswas, S.; Ghoshal, T.; Holmes, J. D.; Singha, A. Probing Thermal Flux in Twinned Ge Nanowires through Raman Spectroscopy. ACS Appl. Mater. Interfaces 2015, 7, (2) Fukata, N.; Sato, K.; Mitome, M.; Bando, Y.; Sekiguchi, T.; Kirkham, M.; Hong, J.; Wang, Z. L.; Snyder, R. L. Doping and Raman Characterization of Boron and Phosphorus Atoms in Germanium Nanowires. ACS Nano 2010, 4, (3) Biswas, S.; Singha, A.; Morris, M. A.; Holmes, J. D. Inherent Control of Growth, Morphology, and Defect Formation in Germanium Nanowires. Nano Lett. 2012, 12, (4) Crystallography Open Database. (5) Vegard, L. XV. Die Röntgenstrahlen im Dienste der Erforschung der Materie. Z. Kristallogr. 1928, 67, (6) Vegard, L. Die Konstitution der Mischkristalle und die Raumfüllung der Atome. Z. Physik 1921, 5, S18