A Combined Top‐Down/Bottom‐Up Approach for the Nanoscale Patterning of Spin‐Crossover Coordination Polymers

Abstract

Molecular spin-crossover complexes of 3d 4 -3d 7 transitionmetal ions have been the focus of many researchers' work because of their fascinating properties associated with the bistability of their electronic states (high spin (HS) or low spin (LS)). [1] Although the origin of the spin-crossover phenomenon is purely molecular, the macroscopic behavior of these systems in the solid state is strongly determined by the interactions, of mainly elastic origin, between the transition-metal ions.[2]Recently, remarkable progress has been made in the area of spin-crossover complexes with infinite one-, two-, or three-dimensional (1D, 2D, 3D) networks, the so-called coordination polymers.[3] The purpose of this approach was the enhancement and fine tuning of cooperative properties by the strong covalent links between the metallic centers in the polymers.[4]Indeed, a number of highly cooperative polymer systems have been reported in the recent literature that display hysteretic behavior (thermal and piezo), in some cases even at room temperature. In addition to this, we have recently demonstrated that 3D coordination polymers represent an attractive platform for growth of surface thin films with spin-crossover properties. [5] In fact, the 3D network structure allows the sequential assembly, via stepwise adsorption reactions, of multilayer films based entirely on intra-and interlayer coordination bonds. These films have opened up possibilities for investigating size-reduction effects, optical and dielectric properties, and device applications of spin-crossover materials.[6]A further step in this direction is the generation of microand nanometer-sized lateral patterns. In fact, the multilayer sequential assembly (MSA) process (also called directed assembly or layer-by-layer assembly in the literature [7] ) has become increasingly popular not only for fabricating thin films but also many efforts have been devoted to generating distinct patterns of the multilayer films. Various lithographic and nonlithographic methods-such as deposition on chemically patterned surfaces, inkjet printing, lift-off processes, etching, direct photopatterning, and microcontact printing-have been explored with this aim.[8] Each method has, of course, different merits, but the lift-off process remains an industry standard owing to its simplicity and reliability. Furthermore, when combined with electron-beam lithography (EBL), it allows patterns to be obtained in a wide size range down to the sub-10 nm limit, [9] and the alignment of the patterns is also possible with respect to structures that may already exist on the substrate. In this Communication, we report on a process for nanoand microscale assembly of the 3D spin-crossover coordination polymer Fe(pyrazine)[Pt(CN) 4 ] (1) (Scheme 1) by using a combination of top-down (lift-off) and bottom-up (MSA) methods. We call attention to the 3D polymer nature of this system, which is the key aspect for 1) obtaining room-temperature hysteresis, 2) assembling multilayers, and 3) performing COMMUNICATION

Light‐Induced Stored Information in Nanoparticles

“…[14] With regard to the bottom-up approach, classically this has been achieved by well-established step-by-step combination of reactants and, indeed, has resulted in many mononuclear, dinuclear and polynuclear materials with interesting magnetic properties Ϫ including those features required for potential integration into devices (i.e., room-temperature transitions, hysteresis loops).…”

Effect of texture alteration by thin film fabrication on the spin crossover of [Fe(3-Br-phen)2(NCS)2]·0.5CH3OH

“…Thus, reducing particle size results in reducing cooperative effects as predicted by a recent theoretical model for SCO nanoparticles [4] and noted for [Fe(pz)Pt(CN) 4 ] (pz = pyrazine) [5]. This result is particularly attractive in the frame of the current miniaturization of SCO molecular units at the nanometre scale [5][6][7][8][9], in view of their potential use in information storage devices thanks to micro and nanopatterning [10,11]. Nevertheless, exact role of effect of size reduction or shape deterioration on SCO properties Raman spectra of (1) and thin film (2) on quartz, at room temperature (100-4000 cm -1 ).…”

Density functional theory calculations and vibrational spectroscopy on iron spin-crossover compounds

“…This effect has been explained by solvent effects, but needs evidently more investigation. Recently it was possible to obtain micro-and nanometer-sized patterns of [Fe(pyrazine) 6 ][Pt(CN) 4 ] by using a PMMA photo resist mask as a barrier for the assembly of the multilayer film on gold surface [54]. On the basis of the observed Raman pattern one-and two-mode behaviour has been established [55].…”