Controlled Nanoplatelet Deposition of 2D Chromium Trihalide Solid Solutions

Abstract

The two-dimensional (2D) chromium trihalides CrCl 3 , CrBr 3 , and CrI 3 are most famous for their exotic magnetic properties when their crystals get downscaled to nanometer dimensions. One way to tune the properties of such materials and to further increase their potential utility, e.g., in spintronics, is the formation of solid solutions. Here, we present a detailed theoretical and experimental study on the synthesis and nanoplatelet growth of CrBr x Cl 3−x and CrBr x I 3−x solid solutions. Phase pure powder was obtained by tempering the respective parent compounds at 600 and 550 °C, using additional iodine in the case of CrBr x I 3−x . The dominant stacking order changes at x = 1.8 for CrBr x Cl 3−x while remaining similar to CrI 3 for the whole CrBr x I 3−x series. A consecutive chemical vapor transport from 575 → 525 °C for 2 h (CrBr x Cl 3−x ) or 600 → 550 °C for 3 h with 0.1 mmol additional iodine (CrBr x I 3−x ) resulted in the deposition of high-quality nanoplatelets on a substrate with only several nanometers in height. The composition can be controlled by the choice of the starting material, since only small shifts in the anion ratio occur during the transport. The deposited CrBr x Cl 3−x nanoplatelets can then be easily delaminated by ultrasonication in ethanol to reduce the height even further to few-layer dimensions. These nanoplatelets could potentially be used to investigate the property changes (e.g., in terms of magnetic response) for the downscaling of these solid solutions. We further demonstrate the quality of the deposited material by transmission electron microscopy, selected area electron diffraction, and X-ray photoelectron spectroscopy. Raman spectroscopy of the solid solution series reveals a complex evolution of vibrational modes. Photoluminescence measurements on solid solution samples show emission peaks in the near-infrared energy range with the specific energy and intensity being composition and temperature dependent.

Structural and Magnetic Transitions Caused by Dimer Formation in the CrCl3–MoCl3 Solid Solution

“…However, even with this space group some of the observed reflections stay unindexed with the assumption of a rhombohedral centering but should be systematically extinct. A similar behavior has been observed in a previous study in the case of pure CrBr 3 and CrCl 3 –CrBr 3 solid solution samples with high Br content, but there the respective reflections were of rather low intensity and could possibly be explained by symmetry-breaking stacking faults, while in the present case the respective reflections show much higher intensities, making a different space group more likely. For this reason, we assume that these intermediate samples crystallize in a hexagonal primitive Bravais lattice (hP).…”

“…The most obvious, abrupt changes in the diffraction patterns occur at about x = 0.75 and 0.30 as well as between the pattern of pure MoCl 3 and the sample with the lowest investigated Cr content of x = 0.08 (Figure a,b). As known from other 2D TMTH solid solution series, such phase transitions can be caused by a simple change in the stacking order of the individual 2D layers, as in the case of the CrCl 3 –CrBr 3 solid solution series . For the 2D TMTH, two dominant stacking variants are known for the bulk material, namely the RhBr 3 type (space group C 2/ m ) and the BiI 3 type (space group R -3).…”

“…This hints to a connection between the phase transformation and the formation of dimer clusters within the individual 2D layers. The further calculated ratio is a measure for the distortion of the hexagonal cation arrangement inside the 2D honeycomb layers . It is 1.0 for ideally undistorted arrangement and deviates from 1.0 in the case of distortion like in the case of MoCl 3 .…”

“…The results for the most important parameters are displayed in Figure , while the results for all lattice parameters including the error bars can be found in Table S3 and Figure S3. Since not all lattice parameters correspond to the same interatomic distances for the monoclinic and hexagonal structures in their respective setting, the values of b (and further also c and β in Figure S3) for the samples assigned to hP were artificially calculated to correspond to the same distances in the lattice as for the monoclinic ones to ensure a simple comparability between the phases by Vegard’s law …”

Trendbericht Festkörperchemie und Materialforschung 2024

“…Insbesondere die starke Anisotropie sowie die Abhängigkeit der magnetischen Ordnung von der Schichtenzahl könnten für die Anwendung in der Spintronic relevant sein (Abbildung 11). 65) Albert und Kolleg:innen haben in temperaturabhängigen Messungen an Einkristallen die anisotropen magnetischen Eigenschaften der αund β-Phase von MnB bestimmt. α-MnB weist dabei entlang der c-Achse eine Verkippung der Spins und eine klassische ferromagnetische Kopplung auf.…”