Selective substitution induced anomalous phonon stiffening within quasi-one-dimensional P—P chains in SiP2

Unraveling High Thermal Conductivity with In-Plane Anisotropy Observed in Suspended SiP2

“…To select the most suitable Raman vibration mode as the thermometer, we measured temperature-dependent Raman spectra from 100 to 370 K. Figure 2a,b presents the temperature-dependent Raman spectra in the range of 280− 530 cm −1 with the incident laser polarized perpendicular and parallel to the b-axis direction, respectively, which shows five obvious Raman peaks that are assigned as A g 4 (305), B 1g 3 (399), A g 5 (433), A g 6 (467), and A g 7 (494 cm −1 ), based on the lattice vibration symmetry. 20 The Lorentzian function is then used to best fit each Raman spectrum, and the peak positions of the Raman vibration modes mentioned above are extracted and plotted in Figure 2c. The vibration frequencies decrease obviously with an increase in temperature, suggesting that the phonon vibration modes are extremely sensitive to temperature.…”

“…Importantly, bonded P 2 atoms form quasi-1D P–P chains (yellow dashed circle) along the b axis. Due to these quasi-1D P–P chains embedded in the 2D lattice, SiP 2 exhibits interesting physical properties, including anisotropic optical spectra, anisotropic exciton–phonon interactions, and hybrid-dimensional excitonic states . The low-symmetric lattice structure always leads to anisotropic phonon dispersion and affects phonon and heat transport .…”

“…Obviously, the Raman peak position of the B 1g 3 mode is relatively sensitive to temperature changes, most likely because the B 1g 3 mode is more sensitive to the thermal expansion-induced "volume-change" shift, 34,35 considering that the B 1g 3 mode is the vibration mode where only P atoms in P−P chains are involved and vibrate along the P−P chain direction. 20 Hence, we chose the B 1g 3 mode as the thermometer for temperature-dependent quantitative analysis and the following thermal conductivity analysis.…”

“…On the other hand, the magnitude of the Raman redshift in a certain temperature variation range matters as well because the more sensitive the Raman peak position is to the temperature variation, the more accurately the temperature can be calibrated by the Raman peak. Obviously, the Raman peak position of the B 1g 3 mode is relatively sensitive to temperature changes, most likely because the B 1g 3 mode is more sensitive to the thermal expansion-induced “volume-change” shift, , considering that the B 1g 3 mode is the vibration mode where only P atoms in P–P chains are involved and vibrate along the P–P chain direction . Hence, we chose the B 1g 3 mode as the thermometer for temperature-dependent quantitative analysis and the following thermal conductivity analysis.…”

“…By this means, heat generation and dissipation can thus be properly regulated to prevent devices from heat-induced performance degradation. , Therefore, exploring emerging anisotropic 2D materials with high thermal conductivity would be helpful for addressing heat-related challenges and enhancing device performance. Since the layered semiconductor SiP 2 exhibits typical in-plane anisotropy embedded quasi-one-dimensional (1D) P–P chains along the b -axis direction of the crystal lattice, its low-symmetric lattice and the corresponding anisotropic properties have been demonstrated − in polarized optoelectronic applications and as a dielectric for novel nanodevices . With these promising characteristics, heat dissipation in SiP 2 -based nanodevices has attracted much attention.…”