Effects of Dimensionality on the Charge-Density Wave Phases of Transition-Metal Dichalcogenides

We investigate the effects of dimensionality on the electronic properties of the transition-metal dichalcogenides \textit{2H}-TaSe$_{\mathrm{2}}$, \textit{1T}-TaSe$_{\mathrm{2}}$, and \textit{1T}-TaS$_{\mathrm{2}}$. In bulk, these materials exhibit various commensurate and incommensurate charge-density wave (CDW) phase transitions that are currently attracting interest for possible CDW field-effect device applications. We explore the evolution of the CDW groundstate properties as the materials approach a few monolayers, achieved via mechanical exfoliation of bulk single-crystals. Raman spectroscopy of \textit{2H}-TaSe$_{\mathrm{2}}$ and \textit{1T}-TaSe$_{\mathrm{2}}$, and \textit{1T}-TaS$_{\mathrm{2}}$, carried out over a wide-range of temperatures, was used as probe of the change in the lattice dynamics from the bulk to the single-layer phases of these materials. The effect of dimensionality on the CDW transition temperatures will be presented.