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Musfeldt Group Published in 2D Materials

The Musfeldt group published their work “Exploring few and single layer CrPS4 with near-field infrared spectroscopy” in 2D Materials. First author is Sabine Neal, UT chemistry alum.

“We combine synchrotron-based near-field infrared spectroscopy and first principles lattice dynamics calculations to explore the vibrational response of CrPS4 in bulk, few-, and single-layer form,” Neal said. “Analysis of the mode pattern reveals a C2 polar + chiral space group, no symmetry crossover as a function of layer number, and a series of non-monotonic frequency shifts in which modes with significant intralayer character harden on approach to the ultra-thin limit whereas those containing interlayer motion or more complicated displacement patterns soften and show inflection points or steps.”

This is different from MnPS3 where phonons shift as 1/size2 and are sensitive to the three-fold rotation about the metal center that drives the symmetry crossover. “We discuss these differences as well as implications for properties such as electric polarization in terms of presence or absence of the P–P dimer and other aspects of local structure, sheet density, and size of the van der Waals gap,” Neal said.

Figure 1. (a) Crystal structure of CrPS4 at 300 K [23]. The sheet thickness and size of the van der Waals gap are indicated. (b) Schematic of the near-field infrared technique in which an atomic force microscope (AFM) cantilever tip directs light to the sample surface. (c) High resolution AFM image of exfoliated CrPS4. (d) Schematic diagram of the symmetry subgroup relationships as they pertain to the presence or absence of a phosphorus dimer.