TY - JOUR
T1 - Effects of the passivating coating on the properties of silicon nanocrystals
AU - Tit, Nacir
AU - Yamani, Zain H.
AU - Graham, John
AU - Ayesh, Ahmad
N1 - Funding Information:
This work started during the visit of one of us (N.T.) to the CENT-KFUPM (Saudi Arabia) in summer 2009 under a financial support provided by the CENT. Special thanks are due to Fabio Trani for his technical support. The authors are indebted to extend their thanks to Anane Alkarmi, Jim Chelikowsky, Serdar Ögüt, Ali Reshak and Bashar Issa for many fruitful discussions. Partial financial support from the side of UAE University was provided via the Research Affairs under grant number 08-02-2-11/09. This work is also supported by Emirates Foundation.
PY - 2010/12/1
Y1 - 2010/12/1
N2 - The effects of the hydrogen-coating of silicon nanocrystals (Si:H NCs) on the chemical and physical properties are theoretically investigated. The empirical tight-binding (TB) method, within the minimal sp3-basis set and second nearest-neighbor interaction scheme, is employed to calculate the electronic structures, oscillator strength (OS) and recombination rates (RR). The coating is found to induce numerous effects: (i) the full chemical passivation of the dangling bonds existing on the surface of the silicon NCs; (ii) the charge-carrier quantum-confinement (QC) enhancement, which yields direct bandgap character, distinguished with strong and fast photoluminescence (PL) emissions. In this perspective, based on the modeling of the PL data, the QC rules are derived and found to be power-low like, similar to the case of a single particle confined in a 3D box; and (iii) the enhancement of the optical properties (i.e., OS and RR). Furthermore, to deepen our understanding of the coating effects, we have considered the Si29NC under three different situations: (a) un-coated; (b) the surface-dangling bonds being partially hydrogenated and the rest being dimerized (i.e., Si29H24 NC); (c) all the surface-dangling bonds being fully hydrogenated (i.e., Si 29H36 NC). Using the density-functional-theory (DFT), the total energy calculation has confirmed that the occurrence of to hydrogenization is more probable than the dimerization (i.e., Si29H36 has lower energy and is, thus, more stable than Si29H24). On one hand, these results corroborate the experimental findings presenting the enhancement of the optical efficiency with the increasing hydrogen content. On the other hand, the atomic relaxation is also shown to further enhance the optical properties and this should in turn corroborate the results of the experimental heat treatment of Si:H NC films, recently reported in literature.
AB - The effects of the hydrogen-coating of silicon nanocrystals (Si:H NCs) on the chemical and physical properties are theoretically investigated. The empirical tight-binding (TB) method, within the minimal sp3-basis set and second nearest-neighbor interaction scheme, is employed to calculate the electronic structures, oscillator strength (OS) and recombination rates (RR). The coating is found to induce numerous effects: (i) the full chemical passivation of the dangling bonds existing on the surface of the silicon NCs; (ii) the charge-carrier quantum-confinement (QC) enhancement, which yields direct bandgap character, distinguished with strong and fast photoluminescence (PL) emissions. In this perspective, based on the modeling of the PL data, the QC rules are derived and found to be power-low like, similar to the case of a single particle confined in a 3D box; and (iii) the enhancement of the optical properties (i.e., OS and RR). Furthermore, to deepen our understanding of the coating effects, we have considered the Si29NC under three different situations: (a) un-coated; (b) the surface-dangling bonds being partially hydrogenated and the rest being dimerized (i.e., Si29H24 NC); (c) all the surface-dangling bonds being fully hydrogenated (i.e., Si 29H36 NC). Using the density-functional-theory (DFT), the total energy calculation has confirmed that the occurrence of to hydrogenization is more probable than the dimerization (i.e., Si29H36 has lower energy and is, thus, more stable than Si29H24). On one hand, these results corroborate the experimental findings presenting the enhancement of the optical efficiency with the increasing hydrogen content. On the other hand, the atomic relaxation is also shown to further enhance the optical properties and this should in turn corroborate the results of the experimental heat treatment of Si:H NC films, recently reported in literature.
KW - Electronic structure of quantum dots
KW - Optical properties of nanoparticles
KW - Photoluminescence
UR - http://www.scopus.com/inward/record.url?scp=77957828791&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=77957828791&partnerID=8YFLogxK
U2 - 10.1016/j.matchemphys.2010.07.044
DO - 10.1016/j.matchemphys.2010.07.044
M3 - Article
AN - SCOPUS:77957828791
SN - 0254-0584
VL - 124
SP - 927
EP - 935
JO - Materials Chemistry and Physics
JF - Materials Chemistry and Physics
IS - 2-3
ER -