TY - JOUR
T1 - Genesis and Propagation of Fractal Structures during Photoelectrochemical Etching of n-Silicon
AU - Richter, Matthias H.
AU - Lublow, Michael
AU - Papadantonakis, Kimberly M.
AU - Lewis, Nathan S.
AU - Lewerenz, Hans Joachim
N1 - Funding Information:
This work was supported through the Office of Science of the U.S. Department of Energy (DOE) under award no. DE-SC0004993 to the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub. H.J.L. was supported by DFG project Le1192-4. Research was in part carried out at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. Dedicated to the memory of Hans-Joachim Lewerenz.
PY - 2020/4/8
Y1 - 2020/4/8
N2 - The genesis, propagation, and dimensions of fractal-etch patterns that form anodically on front- or back-illuminated n-Si(100) photoelectrodes in contact with 11.9 M NH4F (aqueous) have been investigated during either a linear potential sweep or a constant potential hold (E = +6.0 V versus Ag/AgCl). Optical images collected in situ during electrochemical experiments revealed the location and underlying mechanism of initiation and propagation of the structures on the surface. X-ray photoelectron spectroscopic (XPS) data collected for samples emersed from the electrolyte at varied times provided detailed information about the chemistry of the surface during fractal etching. The fractal structure was strongly influenced by the orientation of the crystalline Si sample. The etch patterns were initially generated at points along the circumference of bubbles that formed upon immersion of n-Si(100) samples in the electrolyte, most likely due to the electrochemical and electronic isolation of areas beneath bubbles. XPS data showed the presence of a tensile-stressed silicon surface throughout the etching process as well as the presence of SiOxFy on the surface. The two-dimensional fractal dimension, Df,2D, of the patterns increased with etching time to a maximum observed value of Df,2D = 1.82. Promotion of fractal etching near etch masks that electrochemically and electronically isolated areas of the photoelectrode surface enabled the selective placement of highly branched structures at desired locations on an electrode surface.
AB - The genesis, propagation, and dimensions of fractal-etch patterns that form anodically on front- or back-illuminated n-Si(100) photoelectrodes in contact with 11.9 M NH4F (aqueous) have been investigated during either a linear potential sweep or a constant potential hold (E = +6.0 V versus Ag/AgCl). Optical images collected in situ during electrochemical experiments revealed the location and underlying mechanism of initiation and propagation of the structures on the surface. X-ray photoelectron spectroscopic (XPS) data collected for samples emersed from the electrolyte at varied times provided detailed information about the chemistry of the surface during fractal etching. The fractal structure was strongly influenced by the orientation of the crystalline Si sample. The etch patterns were initially generated at points along the circumference of bubbles that formed upon immersion of n-Si(100) samples in the electrolyte, most likely due to the electrochemical and electronic isolation of areas beneath bubbles. XPS data showed the presence of a tensile-stressed silicon surface throughout the etching process as well as the presence of SiOxFy on the surface. The two-dimensional fractal dimension, Df,2D, of the patterns increased with etching time to a maximum observed value of Df,2D = 1.82. Promotion of fractal etching near etch masks that electrochemically and electronically isolated areas of the photoelectrode surface enabled the selective placement of highly branched structures at desired locations on an electrode surface.
KW - fractal structures
KW - photoelectrochemistry
KW - photoelectron spectroscopy
KW - silicon
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U2 - 10.1021/acsami.9b22900
DO - 10.1021/acsami.9b22900
M3 - Article
C2 - 32176476
AN - SCOPUS:85083085266
VL - 12
SP - 17018
EP - 17028
JO - ACS applied materials & interfaces
JF - ACS applied materials & interfaces
SN - 1944-8244
IS - 14
ER -