  Black phosphorus (BP) analogous tin(II) sulfide (SnS) has recently emerged as
an attractive building block for electronic devices due to its highly
anisotropic response. Two-dimensional (2D) SnS has shown to exhibit in-plane
anisotropy in optical and electrical properties. However, the limitations in
growing ultrasmall structures of SnS hinder the experimental exploration of
anisotropic behavior in low dimension. Here, we present an elegant approach of
synthesizing highly crystalline nanometer-sized SnS sheets. Ultrasmall SnS
exhibits two distinct valleys along armchair and zig-zag directions due to
in-plane structural anisotropy like bulk SnS. We show that in such SnS
nanosheet dots, the band gaps corresponding to two valleys are increased due to
quantum confinement effect. We particularly observe that SnS quantum dots (QDs)
show excitation energy dependent photoluminescence (PL), which originates from
the two nondegenerate valleys. Our work may open up an avenue to show the
potential of SnS QDs for new functionalities in electronics and
optoelectronics.
