Bistable spin-crossover (SCO) complexes that undergo abrupt and hysteretic (ΔT 1/2 ) spin-state switching are desirable for molecule-based switching and memory applications. In this study, we report on structural facets governing hysteretic SCO in a set of iron(II)-2,6-bis62 K -is observed for 1, whereas 2 undergoes above-room-temperature lattice-solvent content-dependent SCO -T 1/2 = 331 K; ΔT 1/2 = 43 K. Variable-temperature single-crystal X-ray diffraction studies of the complexes revealed pronounced molecular reorganizations -from the Jahn-Teller-distorted HS state to the less distorted LS state -and conformation switching of the ethyl group of the COOEt substituent upon SCO. Consequently, we propose that the large structural reorganizations rendered SCO hysteretic in 1 and 2. Such insights shedding light on the molecular origin of thermal hysteresis might enable the design of technologically relevant molecule-based switching and memory elements.
The preparation of two-dimensional transition metal dichalcogenides on an industrially relevant scale will rely heavily on bottom-up methods such as chemical vapour deposition. In order to obtain sufficiently large quantities of high-quality material, a knowledge-based optimization strategy for the synthesis process must be developed. A major problem that has not yet been considered is the degradation of materials by etching during synthesis due to the high growth temperatures. To address this problem, we introduce a mathematical model that accounts for both growth and, for the first time, etching to describe the synthesis of two-dimensional transition metal dichalcogenides. We consider several experimental observations that lead to a differential equation based on several terms corresponding to different supply mechanisms, describing the time-dependent change in flake size. By solving this equation and fitting two independently obtained experimental data sets, we find that the flake area is the leading term in our model. We show that the differential equation can be solved analytically when only this term is considered, and that this solution provides a general description of complex growth and shrinkage phenomena. Physically, the dominance suggests that the supply of material via the flake itself contributes most to its net growth. This finding also implies a predominant interplay between insertion and release of atoms and their motion in the form of a highly dynamic process within the flake. In contrast to previous assumptions, we show that the flake edges do not play an important role in the actual size change of the two-dimensional transition metal dichalcogenide flakes during chemical vapour deposition.
Controlled heating experiments in an inert environment have been performed on WS2 monolayers, in order to clarify the conflicting reports on the high-temperature photoluminescent response of 2D TMDs. We find...
We describe a setup for the analysis of secondary ions and neutrals emitted from solid surfaces and two-dimensional materials during irradiation with highly charged ions. The ultra-high-vacuum setup consists of an electron beam ion source to produce bunches of ions with various charge states q (e.g. Xe 1+ -Xe 46+ ) and thus potential energies, a deceleration/acceleration section to tune the kinetic energy of the ions in the range of 5 keV to 20 x q keV, a sample stage for laser-cleaning and positioning of freestanding as well as supported samples, a pulsed excimer laser for postionization of sputtered neutrals, and a reflectron type time-of-flight mass spectrometer enabling us to analyze mass and velocity distributions of the emitted particles. With our setup, contributions from potential and kinetic energy deposition can be studied independently of each other. Charge dependent experiments conducted at a constant kinetic energy show a clear threshold for the emission of secondary ions from SrTiO 3 . Data taken with the same projectile charge state, but at a different kinetic energy, reveals a difference in the ratio of emitted particles from MoS 2 . In addition, first results are presented, demonstrating how velocity distributions can be measured with the new setup.
Bistable spin‐state switching near room temperature: Two mononuclear iron(II) complexes showing technologically relevant abrupt and wide hysteretic, bistable spin‐state switching characteristics in the vicinity of room temperature are reported. The large structural reorganizations from the Jahn–Teller‐distorted high‐spin state to the less distorted low‐spin state and ethyl group conformational switching are proposed as the main contributing factors rendering the switching hysteretic. More information can be found in the Research Article by M. Schleberger, H. Wende, S. K. Kuppusamy, M. Ruben, et al. (DOI: 10.1002/chem.202103853).
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