Growth and characterization of rare-earth monosulfides for cold cathode applications

We report the successful growth of bulk cubic lanthanum sulfide (LaS) and neodymium sulfide (NdS). Powder x-ray diffraction scans of the samples show the rocksalt phase with a lattice constant a0=5.857(2) Å and 5.694(2) Å for LaS and NdS, respectively. In Raman scattering, one observes the vibrational density of states (cubic symmetry) and identifies the longitudinal optical and transverse acoustic phonons at 261(284) and 100(92) cm−1 with LaS(NdS), respectively. These rare-earth monosulfides offer attractive alternatives to the commonly used cesiated surfaces to reach negative electron affinity at various III–V semiconductor surfaces.