The preparation of mass producible, highly-cycling stable Si/C anode materials with nano-sized silicon crystals embedded in highly amorphous silicon matrix
AbstractAmorphous silicon films were prepared by dc reactive magnetron sputtering under conditions approaching the phase transition to microcrystallinity. Using TEM imaging these films were found to contain clusters of 5 to 50 nm sized Si crystallites embedded in an amorphous silicon matrix. Photocapacitance and transient photocurrent sub-band-gap optical spectra of this material appear to consist of a superposition of a spectrum typical of amorphous silicon together with an optical transition, with a threshold near 1. 1eV, that exhibits a very large optical cross section. This transition arises from valence band electrons being optically inserted into empty levels lying within the amorphous silicon mobility gap. Using modulated photocurrent methods we have determined that these states also dominate the electron deep trapping in this material. We argue that these states arise from defects at the crystalline-amorphous boundary.
Amorphous silicon/carbon (Si/C) layers coated on graphitized carbon black (GCB) particles in porous microspheres (PMs) exhibited an improved electrochemical performance.
High-resolution transmission electron microscopy (HRTEM) is used to reveal fine structures of amorphous silicon induced by Vickers indentation and its interface with unindented silicon matrix. Deformation microtwins at the interface and continuous transition from lattice structure of crystal into amorphous structure at the interface are observed. Within the amorphous silicon near the periphery of the indented region, there are many clusters characterized by distorted silicon lattice. A possible mechanism of lattice-distortion-induced amorphization at the periphery of indented silicon is suggested. All the indentations are performed at ambient temperature.
This paper presents the results of PL spectrum studies for Si nano-crystallites embedded
in amorphous silicon matrix. Investigated layers were deposited by the hot-wire CVD method on
glass substrates at the wafer temperature 300°C and different filament temperatures from the range
1650-1950°C. It was shown that variation of temperatures of filament (hot-wire) allows to produce
the films with desirable parameters. Using of X-ray diffraction and photoluminescence methods the
correlation between some photoluminescence bands and the sizes of Si nano-crystallites as well as
the amorphous phase volume was shown. The nature of light emission is discussed.
Nanosilicon Crystallite Embedded into Amorphous Silicon Matrix: Polymorphous SiliconThin Film, Obtained by Plasma Enhanced Chemical Vapor Deposition