Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Photoluminescence from Silicon nanoparticles embedded in ammonium
  silicon hexafluoride   Silicon (Si) nanoparticles (NPs) were synthesized by transforming Si wafer
surface to ammonium silicon hexafluoride (ASH) or (NH4)2SiF6 under acid vapor
treatment. Si-NPs are embedded within the polycrystalline (ASH) layer formed on
the Si surface exhibit a strong green-orange photoluminescence (PL). Difference
measurements revealed a major double component spectra consisting of a broad
band associated with the ASH-Si wafer interfacial porous oxide layer and a high
energy band attributable to Si-NPs embedded in the ASH. The origin of the
latter emission can be explained in terms of quantum/spatial confinement
effects probably mediated by oxygen related defects in or around Si-NPs.
Although Si-NPs are derived from the interface they are much smaller in size
than those embedded within the interfacial porous oxide layer (SiOx, 1 < x <
2). Transmission electron microscopy (TEM) combined with Raman scattering and
Fourier transformed infrared (FTIR) analysis confirmed the presence of Si-NPs
and Si-O bondings pointing to the role of oxygen related defects. The presence
of oxygen of up to 4.5 at.% in the (NH4)2SiF6 layer was confirmed by energy
dispersive spectroscopy (EDS) analysis.

3
The categories of this paper are: physics
32
The categories of this paper are: atom-ph
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
37
The categories of this paper are: supr-con
34
The categories of this paper are: chem-ph
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
13
The categories of this paper are: quant-ph
35
The categories of this paper are: mtrl-th
31
The categories of this paper are: ao-sci
18
The categories of this paper are: econ
19
The categories of this paper are: eess
6
The categories of this paper are: astro-ph
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas