TY - JOUR
T1 - Anion F--induced etching of silicon nanowires with diverse doping levels, surface crystalline orientations, and porosity
AU - Liu, Junjun
AU - Huang, Zhifeng
N1 - We gratefully acknowledge Yuk-Kuen Wu for her technical assistance in XPS, Dr. Billy King-Fai Lee and Prof. Kok-Wai Cheah (Physics, HKBU) for their technical support in PL, and Benson Siu-Cheong Leung (Physics, HKBU) for his technical assistance in TEM (funded by Grant SEG_HKBU06). This work was supported by Grants NSFC/21203010 and ECS/ RGC/HKBU-204412 (J.J.).
PY - 2014/8/7
Y1 - 2014/8/7
N2 - 40% aqueous NH4F can passivate Si wafers with H-termination but unexpectedly etch silicon nanowires (SiNWs), attributed to the surface F-termination caused by the nucleophilic attack of F- anions to Si atoms. The grafted Si-F bonds with strong dipole moment significantly polarize and weaken Si back bonds, and the polarized back bonds tend to be vulnerably attacked by F- anions, resulting in the etching of SiNWs. The F-termination is confirmed by ATR-FTIR, XPS, and PL spectroscopy. The etching rate in terms of the NW length is evaluated on SiNWs with diverse doping levels, surface crystalline orientations, and porosity, which could be explained by three factors including the doping level, atomic ratio F1s/Si 2p, and the stoichiometric x of the surface termination Si-F x. NH4F dissolves surface oxides and then commences to etch SiNWs. As comparison, mesoporous SiNWs (mpSiNWs) have porosified surfaces not fully passivated by native oxides, leading to the simultaneous etching of oxides and Si skeletons. This work contributes to understanding the difference in surface reactions between bulky Si and one-dimensional SiNWs, and to providing useful information about surface processing and modification of SiNW-based nanoelectronic devices.
AB - 40% aqueous NH4F can passivate Si wafers with H-termination but unexpectedly etch silicon nanowires (SiNWs), attributed to the surface F-termination caused by the nucleophilic attack of F- anions to Si atoms. The grafted Si-F bonds with strong dipole moment significantly polarize and weaken Si back bonds, and the polarized back bonds tend to be vulnerably attacked by F- anions, resulting in the etching of SiNWs. The F-termination is confirmed by ATR-FTIR, XPS, and PL spectroscopy. The etching rate in terms of the NW length is evaluated on SiNWs with diverse doping levels, surface crystalline orientations, and porosity, which could be explained by three factors including the doping level, atomic ratio F1s/Si 2p, and the stoichiometric x of the surface termination Si-F x. NH4F dissolves surface oxides and then commences to etch SiNWs. As comparison, mesoporous SiNWs (mpSiNWs) have porosified surfaces not fully passivated by native oxides, leading to the simultaneous etching of oxides and Si skeletons. This work contributes to understanding the difference in surface reactions between bulky Si and one-dimensional SiNWs, and to providing useful information about surface processing and modification of SiNW-based nanoelectronic devices.
UR - http://www.scopus.com/inward/record.url?scp=84905860815&partnerID=8YFLogxK
U2 - 10.1021/jp506131d
DO - 10.1021/jp506131d
M3 - Journal article
AN - SCOPUS:84905860815
SN - 1932-7447
VL - 118
SP - 17870
EP - 17877
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 31
ER -