Anomalous Temperature-Dependent Raman Scattering of Vapor-Deposited Two-Dimensional Bi Thin Films

As a topological material, bismuth (Bi) shows unique physical properties when its thickness is reduced to two dimensions. Here, single crystal, high stability, and continuous Bi thin films are successfully synthesized through vapor deposition method. We further investigate its temperature-dependent Raman spectroscopy behavior ranging from 80 to 513 K. The first-order temperature coefficients of E-g and A(1g) Raman modes are estimated to be -0.0133 and -0.0253 cm(-1)/K, respectively. A physical model is used to analyze the observed nonlinear temperature-dependent Raman shifts, including the thermal expansion and three- and four-phonon anharmonic effects. The full width at half maximum of A(1g) mode has an abnormal behavior at about 193 K, implying a phase transition near 193 K. This research promotes the deep exploration of the basic physical properties of Bi thin films and provides properties of Bi thin films, which is crucial for developing thermal and electronic applications of Bi-based devices. the fundamental information about the thermal