ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
After ex situ etching with various solutions of hydrofluoric acid (HF) and ammonium fluoride (NH4F) Si(111) samples are transferred into ultrahigh vacuum with an ultrafast load-lock and characterized by scanning tunneling microscopy (STM): Concentrated HF selectively removes any surface oxide and, thus chemically prepares the initially burried, isotropically rough Si/SiO2 interface while highly buffered HF (i.e., NH4F) attacks bulk silicon anisotropically. After a rapid homogenization of the chemical surface termination (HF: various hydrides, fluorine, ...) towards a perfect, unreconstructed monohydride phase, Si(111)-(1×1):H, NH4F etching leads to a time-dependent transformation of isotropic roughness into a pattern of triangular etch defects with monohydride steps perpendicular to 〈2¯11(approximately-greater-than) due to a preferential removal of lower-coordinated atomic defect sites. A predominant atomic step structure due to sample miscut (vicinal surfaces with azimuth ≠〈2¯11(approximately-greater-than)) can oppose the anisotropic NH4F etching: At low step density (small polar angle of miscut) a meandering of atomic steps with straight monohydride portions is observed while at high step density strong step-step interaction counterbalances anisotropic removal and forces an etching by a homogeneous flow of (nonmonohydride) steps along the macroscopic misorientation. Local findings obtained with STM are compared to macroscopically averaged results from a simultaneous quantitative analysis of low-energy electron diffraction profiles.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.353845
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