Multifunctionality in Janus CrMCN4 (M = Si/Ge) Monolayers: Valleytronic Physics, Piezoelectric Response, and Photocatalytic Potential
First-principles calculations show that CrSiCN4 and CrGeCN4 monolayers are direct-gap semiconductors whose properties can be tuned by composition and strain. These materials exhibit tunable electronic, spin, valleytronic, and piezoelectric characteristics. Strain engineering significantly modifies the band gap and drives transitions between direct and indirect states, while the Janus asymmetry enables a built-in electric field for photocatalytic applications.