Solid-state synthesis of luminescent silicon nitride nanocrystals

Mita Dasog, Jonathan G. C. Veinot
2012 Chemical Communications  
Experimental 1. Materials: Tetraethoxysilane (TEOS, 99%, Sigma-Aldrich), urea (CO(NH 2 ) 2 , 98%, Fisher), sodium hydroxide (NaOH, 97%, Caledon), magnesium powder (Mg, 99%, BDH), toluene (ACS grade, BDH), ethanol (ACS grade, Sigma-Aldrich), hydrofluoric acid (HF, 49%, J. T. Baker) were used as received. Synthesis of the (SiO 2 ) n sol-gel polymer: The silica sol-gel was synthesized via a base catalyzed method. Briefly, TEOS (5 mL, 22.5 mmol) was stirred with ethanol (10 mL), deionized water (20
more » ... deionized water (20 mL) and NaOH solution (10 M, 0.5 mL) for 3 days. The white precipitate was collected by vacuum filtration and washed with deionized water multiple times (4 × 25 mL). The solid was transferred to an oven and was kept there for 24 hours at 100 o C to drive off any residual water and ethanol (yield 92%) Synthesis, Purification and Isolation of Freestanding Si 3 N 4 NCs: Silica sol-gel polymer (1.00 g, 17 mmol w.r.t Si content), urea (0.90 g, 15 mmol) and magnesium powder (0.82 g, 34 mmol) were mixed manually with a mortar and pestle and thermally processed at 500 o C for 3 hours under 5% H 2 /95% Ar atmosphere. The resulting grey/black powder (1.62 g) was treated with concentrated hydrochloric acid (5 mL) for 30 min to remove reaction byproducts. The grey/white precipitate (0.65 g) was isolated by vacuum filtration. The solid was washed with deionized water until the washings had a neutral pH (ca. 7). This was followed by washing with ethanol (20 mL) and acetone (3 × 20 mL) and was air dried to yield crude, silica contaminated Si 3 N 4 nanocrystals. Electronic Supplementary Material (ESI) for Chemical Communications This journal is The solid obtained from the HCl extraction was treated with hydrofluoric acid to remove SiO 2 impurities. In a typical etching procedure, 100 mg of the sample was transferred to a Teflon test tube and 1:1:1 solution of 49% HF (aq) : H 2 O : ethanol (10 mL) was added. The mixture was stirred for 60 min followed by extraction into 10 mL toluene. The freestanding nanocrystals were washed multiple times with toluene by centrifugation at 32000 rpm. Characterization: Fourier Transformation Infrared Spectroscopy (FTIR) was performed on Nicolet Magna 750 IR spectrometer. X-ray powder diffraction (XRD) patterns were collected using an INEL XRG 3000 X-Ray diffractometer with CuK α radiation (λ = 1.54 Å). Thermogravimetric analysis (TGA) was performed on PerkinElmer Pyris 1 using a platinum sample pan at a heating rate of 18 o C/min in air. XPS analysis was performed using a Kratos Axis Ultra instrument operating in energy spectrum mode at 210 W. The base pressure and operating chamber pressure were maintained at 10 -7 Pa. A monochromatic Al K α source (λ = 8.34 Å) was used to irradiate the samples, and the spectra were obtained with an electron takeoff angle of 90°. To minimize sample charging, the charge neutralizer filament was used when required. Survey spectra were collected using an elliptical spot with major and minor axis lengths of 2 and 1 mm, respectively, and 160 eV pass energy with a step of 0.33 eV. CasaXPS software (Vamas) was used to interpret high-resolution (HR) spectra. All of the spectra were internally calibrated to the C 1s emission (284.8 eV). After calibration, the background was subtracted using a Shirley-type background to remove most of the extrinsic loss structure. The full width half maxima (fwhm)
doi:10.1039/c2cc16971a pmid:22430493 fatcat:vgmgfvfacjajliajd5ywlc7n44