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

Guided mode resonance filters (GMRFs) are a promising new generation of reflective narrow band filters, that combine structural simplicity with high efficiency. However their intrinsic poor angular tolerance and huge area limit their use in real life applications. Cavity-resonator-integrated guided-mode resonance filters (CRIGFs) are a new class of reflective narrow band filters. They offer in theory narrow-band high-reflectivity with a much smaller footprint than GMRF. Here we demonstrate that for tightly focused incident beams adapted to the CRIGF size, we can obtain simultaneously high spectral selecitivity, high reflectivity, high angular acceptance with large alignment tolerances. We demonstrate experimentally reflectivity above 74%, angular acceptance greater than ±4.2° for a narrow-band (1.4 nm wide at 847 nm) CRIGF.

No abstract

CaF2:Er layers have been grown by molecular-beam epitaxy on (100)-oriented CaF2 substrates; the Er concentration ranges from 1% to 50% (mole fraction). The 1.54 μm emission observed under excitation around 800 nm was studied by photoluminescence. Up to 35% Er concentration the integrated emission increases monotonously, quenching appearing for higher doping levels. Photoluminescence results are discussed within the framework of previous studies of Er3+ emission in the near-infrared range (830–860 nm) in order to gain insight into the Er centers involved in the 1.54 μm emission.

We report the measurement of a polarization-independent guided-mode resonant filter with a Q factor of approximately 2200 functioning near normal incidence in the near infrared (850 nm). Besides this remarkable performance, we provide a detailed optical and structural characterization of the component, which points out the origins of the limitation of the experimental performance. We conclude that the defaults in question can be corrected by improving the lithography process, and we are confident that even greater performance will be obtained in future realizations.

Abstract-We report the first fabrication and laser operation of channel waveguides based on LaF 3 planar thin films grown by molecular beam epitaxy. To our knowledge, this is the lowest phonon energy dielectric material to have shown guided-wave laser operation to date. A full characterization, in terms of spectroscopy, laser results, and propagation losses, is given for the planar thin films upon which the channel waveguides are based. Two channel-fabrication methods are then described, the first involves ion milling and the second takes the novel approach of using a photo-definable polymer overlay. Laser operation in Nd-doped samples is demonstrated at 1.06, 1.05, and 1.3 m, and the potential for mid-infrared laser sources based on such guides is discussed.

CaF2:Er thin films grown by molecular beam epitaxy on CaF2 substrates have been characterized as optical waveguides. The characterization has been carried out by measuring the synchronous angles in attenuated total reflection experiments. It has been found that the incorporation of Er3+ ions to the CaF2 crystal produces an increase of the refractive index of the material giving rise to the formation of a steplike planar optical waveguide. The refractive index increase shows a linear dependence with Er3+ concentration up to 35 mol %, at which point saturation is observed. The obtained results compared well with previously reported data on the lattice parameter of CaF2:Er3+ bulk crystals and fluorescence quenching from Er3+ ions in these layers. The results of this work show that the preparation of CaF2:Er3+ layers on CaF2 substrates by molecular beam epitaxy is an ideal method to produce monomode active optical waveguides useful for optoelectronic devices.

Bismuth-Antimony alloys () is the first reported 3D Topological Insulator (TI). Among many TIs reported to the date, it remains the most promising for spintronic applications thanks to its large conductivity, its colossal spin Hall angle, and the possibility to build low current spin-orbit-torque (SOT) magnetoresistive random access memories (MRAM). Nevertheless, the 2D integration of TIs on industrial standards is lacking. In this work, we report the inte-