  Here, we demonstrate an approach that provides a precise control of the
dimension of InAs from one-dimensional nanowires to wafer-scale free-standing
two-dimensional nanosheets, which have a high degree of crystallinity and
outstanding electrical and optical properties, using molecular-beam epitaxy by
controlling catalyst alloy segregation. In our approach, two-dimensional InAs
nanosheets can be obtained directly from one-dimensional InAs nanowires by
silver-indium alloy segregation, which is much easier than all previously
reported method, such as traditional buffering technique and select area
epitaxial growth. Detailed transmission electron microscopy investigations
provide a solid evidence that the catalyst alloy segregation is the origination
of the InAs dimensional transformation from one-dimensional nanowires to
two-dimensional nanosheets, and even to three-dimensional complex crosses.
Using this method, we find that the wafer-scale free-standing InAs nanosheets
can be grown on various substrates including Si, MgO, sapphire and GaAs etc.
The InAs nanosheets grown at high temperature are pure phase single crystals
and have a high electron mobility and a long time-resolved THz kinetics
lifetime. Our work will open up a conceptually new and general technology route
toward the effective controlling the dimension of the low-dimensional III-V
semiconductors. It may also enable the low-cost fabrication of free-standing
nanosheet-based devices on an industrial scale.
