Effect of ligand methylation on the spin-switching properties of surface-supported spin-crossover molecules

X-ray absorption spectroscopy investigations of the spin-state switching of spin-crossover (SCO) complexes adsorbed on a highly-oriented pyrolytic graphite (HOPG) surface have shown so far that HOPG is a promising candidate to realize applications such as spintronic devices because of the stability of SCO complexes on HOPG and the possibility of highly efficient thermal and light-induced spin-state switching. Herein, we present the spin switching of several Fe(II) SCO complexes adsorbed on an HOPG surface with particular emphasis on the thermally induced spin transition behaviour with respect to different structural modifications. The complexes of the type [Fe(bpz)2(L)] (bpz  =  dihydrobis(pyrazolyl)borate, L  =  1,10-phenanthroline, 2,2'-bipyridine) and their methylated derivatives exhibit SCO in the solid state with some differences regarding cooperative effects. However, in the vacuum-deposited thick films on quartz, complete and more gradual spin transition behavior is observable via UV/vis spectroscopy. In contrast to that, all complexes show large differences upon direct contact with HOPG. Whereas the unmodified complexes show thermal and light-induced SCO, the addition of e.g. two or four methyl groups leads to a partial or a complete loss of the SCO on the surface. The angle-dependent measurement of the N K-edge compared to calculations indicates that the complete SCO and HS-locked molecules on the surface exhibit a similar preferential orientation, whereas complexes undergoing an incomplete SCO exhibit a random orientation on the surface. These results are discussed in the light of molecule-substrate interactions

In Situ Investigations of Simultaneous Two-Layer Slot Die Coating of Component-Graded Anodes for Improved High-Energy Li-Ion Batteries

The use of thicker electrodes can contribute to a reduction in cell costs. However, the properties of the electrode must be kept in view to be able to meet the performance requirements. Herein, the possibility of simultaneous multilayer slot die coating is investigated to improve the electrode properties of medium- and high-capacity anodes. The stable coating window of the two-layer slot die coating process is investigated to produce property-graded multilayer electrodes. Electrodes with different styrene–butadiene rubber (SBR) gradients are investigated with regard to adhesive force and electrochemical performance. An increase in the adhesive force of up to 43.5% and an increase in the discharge capacity is observed

High-Speed Coating of Primer Layer for Li-Ion Battery Electrodes by Using Slot-Die Coating

A reduction of the inactive components can increase the energy density and reduce production cost of Li‐ion batteries. But an effective reduction of the binder amount also negatively affects the adhesion of the electrode. Herein, slot‐die coating of a primer layer for Li‐ion anodes is investigated. It is shown that the use of a primer layer with only 0.3 g m$^{-2}$ can increase the adhesive force by the factor of 5 as well as the cell performance for anodes with low binder content. The process limits for a stable, defect‐free primer coating are investigated at coating speeds of up to 550 m min$^{-1}$. The limits coincide both for a setup without vacuum box and with vacuum box with theory‐based equations. By using a vacuum box, the minimum wet film thickness can be reduced by half

Ultrafast Optically Induced Ferromagnetic State in an Elemental Antiferromagnet

We present evidence for an ultrafast optically induced ferromagnetic alignment of antiferromagnetic Mn in Co/Mn multilayers. We observe the transient ferromagnetic signal at the arrival of the pump pulse at the Mn L3 resonance using x-ray magnetic circular dichroism in reflectivity. The timescale of the effect is comparable to the duration of the excitation and occurs before the magnetization in Co is quenched. Theoretical calculations point to the imbalanced population of Mn unoccupied states caused by the Co interface for the emergence of this transient ferromagnetic state

Thermal and Light Induced Spin Crossover Characteristics of a Functional Iron II Complex at Submonolayer Coverage on HOPG

Studies on the spin state switching characteristics of surface bound thin films of spin crossover SCO complexes are of interest to harness the device utility of the SCO complexes. Molecule substrate interactions govern the SCO of surface bound films in direct contact with the underlying substrates. In this study, we elucidate the role of molecule substrate interactions on the thermal and light induced spin state switching characteristics of a functional SCO complex [Fe H2B pz 2 2COOC12H25 bipy] pz pyrazole, C12 bpy dodecyl[2,2 amp; 8242; bipyridine] 5 carboxylate deposited at a submonolayer coverage on a highly oriented pyrolytic graphite HOPG substrate. A spin state coexistence of 42 low spin LS and 58 high spin HS is observed for the 0.4 ML deposit of the complex at 40 K, in contrast to the complete spin state switching observed in the bulk and in SiOx bound 10 nm thick films. Cooling the sample to 10 K results in a decrease of the LS fraction to 36 , attributed to soft X ray induced excited spin state trapping SOXIESST . Illumination of the sample with a green light amp; 955; 520 nm at 10 K caused the LS to HS switching of the remaining 36 LS complexes, by a process termed light induced excited spin state trapping LIESST . The mixed spin state in the submonolayer coverage of [Fe H2B pz 2 2COOC12H25 bipy] highlights the role of molecule HOPG substrate interactions in tuning the thermal SCO characteristics of the complex. The 100 HS state obtained after light irradiation indicates the occurrence of efficient on surface light induced spin switching, encouraging the development of light addressable molecular devices based on SCO complexe