Growth, cathodoluminescence and field emission of ZnS tetrapod tree-like heterostructures

We report the growth mechanism, cathodolumirteseenee and field emission of dual phase ZnS tetrapod tree-like heterostructures. This novel heterostructures consist of two phases: zinc blende for the trunk and hexagonal wurtzite for the branch. Direct evidence is presented for the polarity induced growth of tetrapod ZnS trees through high-resolution electron microscopy study, demonstrating that Zn-terminated ZnS (111)/(0001) polar surface is chemically active and S-terminated (1̄1̄1̄)/(0001̄) polar surface is inert in the growth of tetrapod ZnS trees. Two strong UV emissions centered at 3.68 and 3.83 e V have been observed at room temperature, which are attributed to the bandgap emissions from the zinc blende trunk and hexagonal wurtzite branch, indicating that such structures can be used as unique electromechanical and optoelectronic components in potential light sources, laser and light emitting display devices. In addition, the low turn-on field (2.66 μm^-1), high field-enhancement factor (over 2600), large current density (over 30 mAcm ^-2 at a macroscopic field of 4.33 Vμm^-1) and small fluctuation (∼1 %) further indicate the availability of ZnS tetrapod tree-like heterostructures for field emission panel display. This excellent field-emission property is attributed to the specific crystallographic feature with high crystallinity and cone-shape patterned branch with nanometer-sized tips. Such a structure may optimize the FE properties and make a promising field emitter.