Luminescence properties of ultrasmall amorphous Si nanoparticles with sizes smaller than 2 nm

Using electrochemical etching of amorphous Si films deposited on metal molybdenum and subsequent ultrasonic treatment in water and chloroform solutions, we have fabricated the suspensions of amorphous Si nanoparticles with a size range of 1–3 nm (the probable size is at 1.7 nm with a Gaussian fitting), which are uniformly dispersed in the solvents. We examined the photoluminescence (PL) spectra of the two kinds of suspensions and found that for the chloroform suspension, the PL spectrum lasts to blueshift as the excitation wavelength decreases. For the water suspension, the PL spectrum initially shows blueshift with decreasing excitation wavelength and then remains unchanged in peak position when the excitation wavelength is below 320 nm. We attribute this difference to different surface bonding structures of amorphous Si nanoparticles, induced by the solvents. This work indicates that the surface structure has a large influence on the PL properties of Si nanoparticles with sizes smaller than 2 nm.