Tuning Phase Transitions in 1T-TaS₂ via the Substrate

Abstract

Phase transitions in 2D materials can lead to massive changes in electronic properties that enable novel electronic devices. Tantalum disulfide (TaS), specifically the "1T" phase (1T-TaS), exhibits a phase transition based on the formation of commensurate charge density waves (CCDW) at 180 K. In this work, we investigate the impact of substrate choice on the phase transitions in ultrathin 1T-TaS. Doping and charge transfer from the substrate has little impact on CDW phase transitions. On the contrary, we demonstrated that substrate surface roughness is a primary extrinsic factor in CCDW transition temperature and hysteresis, where higher roughness leads to smaller transition hysteresis. Such roughness can be simulated via surface texturing of SiO/Si substrates, which controllably and reproducibly induces periodic strain in the 1T-TaS and thereby enables the potential for engineering CDW phase transitions.

Chemical Growth of 1T‐TaS2 Monolayer and Thin Films: Robust Charge Density Wave Transitions and High Bolometric Responsivity

“…As the thickness decreases, the phase transition temperature in 1 T ‐TaS 2 sheets shows a slight increase trend for warming process and decrease trend for cooling process (Figure e). The layer‐dependent CDW transition temperature has reported for 1T‐TaS 2 and other 2D materials, which is sensitive to the sample quality. Another observed signature is that larger NCCDW–CCDW hysteresis was observed in the thinner 1 T ‐TaS 2 flakes (Figure e), which may have resulted from the larger NC–C phase transition barrier in thinner 1 T ‐TaS 2 flakes due to the enhanced pinning of nucleated domain walls …”

Recent Advances in Two-Dimensional Materials with Charge Density Waves: Synthesis, Characterization and Applications

“…Substrates can steer to modification of the band gap [96], along with indirect-to-direct band gap [97], modulation in the optical band gap and introduction of magnetism [98]. R. Zhao et al reported tuning the phase transitions in 1T-TaS2 on different substrates [99], revealing that doping and charge transfer from the substrate have a minimal effect on CDW phase transitions, but substrate surface roughness is a predominant external factor on C-CDW transition temperature and hysteresis.…”

Friction anomalies at first-order transition spinodals: 1T-TaS2

“…In this layer compound a well known first-order, hysteretic transition of joint structural and electronic nature takes place between a low-temperature commensurate charge-density-wave (CCDW) 13 13 phase, [6,7] believed to be Mott insulating [8,9], and a nearly commensurate charge-density-wave (NCCDW) phase, metallic and even superconducting under pressure [7] and alloying with 1T-TaSe 2 [10]. Notably, 1T-TaS 2 has been subject to very intense studies over the last decade, in connection with transient or hidden metastable phases under high excitation, [11][12][13] with the unusual substrate, thickness, and disorder dependence of its transitions [14][15][16][17], and with a spin liquid in the CCDW phase [18][19][20]. While insensitive to these electronic excitations, the present frictional study sheds fresh light on the thermodynamic nature of the important CCDW-NCCDW transformation.…”