Laser-derived One-Pot Synthesis of Silicon Nanocrystals Terminated with Organic Monolayers

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1 Electronic Supplementary Information for: Laser-derived One-Pot Synthesis of Silicon Nanocrystals Terminated with Organic Monolayers N. Shirahata,*,a M. R. Linford, b S. Furumi, a L. Pei, b Y. Sakka, a R. J. Gates, b M. C. Asplund b a National Institute for Materials Science (NIMS), Sengen, Tsukuba, Ibaraki 35-47, Japan. SIRAATA.naoto@nims.go.jp b Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 8462 Experimental Details Synthesis of samples Synthesis of the organically-terminated silicon nanocrystals: A 2 ml of 1-octene was treated with sodium sulfate, and was then collected into Schlenk flask. Next, the Schlenk flask was subjected to freeze-pump-thaw (FPT) cycle on a grease-free vacuum line for at least 3 min by the use of Dewar flasks filled with liquid nitrogen in order to remove the dissolved oxygen. Finally, the oxygen-free 1-octene was stored under argon atmosphere until before use. These procedures were performed on a grease-free glass vacuum line at room temperature and atmospheric pressure. A hydrogen-terminated wafer of silicon was placed in the quartz cell, and purged several times with Ar gas. Next, the quartz cell was filled with the oxygen-free 1-octene for subsequent laser ablation in liquid environment. In the cell, the target silicon was ablated for 3 min by Nd:YAG pulsed laser (λ: 532 nm, power density: 1. J/cm 2, pulse duration: 4 6 ns, repetition rate: 1 z). After 3 min, the solvent was removed by rotary evaporation. The synthesized nanocrystals: 1 NMR (3 Mz, CDCl 3, 2ºC, TMS): δ 1.25 (s, 12Η), 1.1 (s, 2),.88 (s, 3). 13 C NMR (75 Mz, CDCl 3, 2ºC, TMS): δ 31.74, 29.7, 28.84, 22.64, Preparation of octane-terminated polycrystalline silicon particle (d >2 nm): Silicon powder (YAMAISIMETAL, Co. Ltd., No. 6) was used as a starting material. A 1 mg of the powder was treated for 15 min with an aqueous 1% F solution to generate the Si- terminated surface. The -terminated silicon particle was then washed with methanol, and was then filtrated with a polyvinylidene fluoride (PVDF) membrane filter (2 nm diameter pore size, Millipore) to collect only polycrystalline silicon particles larger than 2 nm in physical size. As a result, we removed the particles less than 2 nm. Prior to the thermal radical reaction, a 5 ml of 1-octene was treated with sodium sulfate, and was then collected into Schlenk flask. Next, the Schlenk flask was subjected to FPT cycle on a grease-free vacuum line for at least 3 min by the use of Dewar flasks filled with liquid nitrogen in order to remove the dissolved oxygen. Finally, the oxygen-free 1-octene was

2 stored under argon atmosphere until before use. To perform a thermal radical reaction, the -terminated silicon particle was added into a small three-necked flask with the 1-octene. The flask was fitted with a thermometer, an argon-gas inlet with oxygen and moisture filters, and a reflux condenser which the other side was connected to a glass-tube with liquid paraffin to avoid undesired aeration. Shortly thereafter, the bubbling of the solution with argon-gas was performed for at least 3 min. Subsequently, the solution was heated for 5 h at 12ºC under a flow of argon-gas. After the excess of 1-octene was removed under reduced pressure with heating in a water bath, the brownish product, i.e., octane-terminated polycrystalline silicon particle, was obtained, and used as a bulk silicon. Characterization Raman spectrum was collected using the nm line of an Ar ion laser beam in a backscattering geometry (BeamLok 26-RS/T64, Spectro-Physics, Mountain View, CA/Jobin Yvon, oriba, France). To acquire the Raman spectrum, polarized light from the laser was focused on the sample dropped on a gold-coated glass plate at room temperature. The RTEM and STEM micrographs of the sample were obtained using a JEM-21F with a.1 nm in resolution at a 2 kv of acceleration voltage in bright- and dark-field modes. 1 and 13 C NMR spectra were collected at 2ºC on a JEOL FT NMR system, operating at 3 Mz and 75 Mz, respectively. FTIR spectrum was examined at 1 cm 1 resolution with 256 scans using a Spectrum GX, Perkin-Elmer. For this measurement, a 3 μl of chloroform containing the sample was coated over the surface of KBr disk. Optical absorbance spectrum was recorded in dichloromethane for silicon derivatives at room temperature with a UV-visible spectrophotometer (U29, itachi Co., Japan) with a 1 nm of resolution. The PL spectrum was obtained with a Fluorescence Spectrophotometer Model F-7 (itachi igh-technologies, Japan), and the spectral resolution was 1 nm The absorption and PL spectra of the solvent, i.e., dichloromethane, were subtracted from each of the sample s spectra, respectively.

3 Supplementary Material (ESI) for Chemical Communications 2.Å () 3.1Å (111) 5nm nm 1nm Fig. S1. TEM images with corresponding to FFT analyses or SAED patterns of a sample prepared in 1-octene. In all the high resolution images, the single-crystalline nanocrystals overlap each other. The lattice fringe spacings of 3.1 Å and 2. Å are consistent with those of the (111) and the () planes in diamond-structured silicon, respectively. This image shows an area of overlap between different nanocrystals with (111) and () phase. EDX showed that these nanocrystals assemblages are composed of silicon. An SAED pattern of a 5 nm single crystal (see inset) taken from [1] direction. A typical STEM image in dark field mode of the nanocrystals. A histogram of size distribution of the nanocrystal s sample.

4 (A) C C C 2 (C 2 ) 4 C (B) ppm C 2 =C 2 -C 3 (g) (h) (h) (g) ppm Fig. S2. (A) 1 and (B) 13 C NMR spectra of 1-octene. Absorbance (arb unit) ν( C C 3 ) 2952, 2864 δ( C C 3 ) 1442, ν( C C , 2852 ν(si C δ( C C Wavelength (cm 1 ) δ(si C ν( O Si O Fig. S3. FTIR spectrum of silicon nanocrystals prepared in neat 1-octene with the assignment of the absorption peaks.

5 .7 Absorbance nm 283 nm Wavelength (nm) Fig. S4. Optical absorption spectrum of polycrystalline silicon particle (d>2 nm) terminated with octane monolayers.