The picture at right is a rendering of a hydrogen terminated silicon [111] surface, showing a single hydrogen atom bonded to each surface silicon atom and projecting perpendicular to the surface. In the simulation below, the view can be scrolled to show the various crystal orientations. A monohydride step is visible in the simulation directed along [011]. The relatively slow etch rates of surface and step monohydride silicon atoms compared to dihydride and trihydride silicon surface atoms is what leads to flattening of silicon [111] surfaces treated with NH4F.
