We investigate if the functionality of spin crossover molecules is preserved when they are assembled into an interfacial device structure. Specifically, we prepare and investigate gold nanoparticle arrays, into which room-temperature spin crossover molecules are introduced, more precisely, [Fe(AcS-BPP)2](ClO4)2, where AcS-BPP = (S)-(4-{[2,6-(dipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)ethanethioate (in short, Fe(S-BPP)2). We combine three complementary experiments to characterize the molecule-nanoparticle structure in detail. Temperature-dependent Raman measurements provide direct evidence for a (partial) spin transition in the Fe(S-BPP)2-based arrays. This transition is qualitatively confirmed by magnetization measurements. Finally, charge transport measurements on the Fe(S-BPP)2-gold nanoparticle devices reveal a minimum in device resistance versus temperature, R(T), curves around 260-290 K. This is in contrast to similar networks containing passive molecules only that show monotonically decreasing R(T) characteristics. Backed by density functional theory calculations on single molecular conductance values for both spin states, we propose to relate the resistance minimum in R(T) to a spin transition under the hypothesis that (1) the molecular resistance of the high spin state is larger than that of the low spin state and (2) transport in the array is governed by a percolation model.

Charge transport in networks of nanoparticles linked by molecular spacers is investigated. Remarkably, in the regime where cotunneling dominates, the molecular signature of a device is strongly enhanced. We demonstrate that the resistance ratio of identical networks with different molecular spacers increases dramatically, from an initial value of 50 up to 10(5) , upon entering the cotunneling regime. Our work shows that intrinsic molecular properties can be amplified through nanoscale engineering.

Colloidal platelets of hydrotalcite, a layered double hydroxide, have been prepared by coprecipitation at pH 11-12 of magnesium nitrate and aluminum nitrate at two different magnesium to aluminum ratios. Changing the temperature and ionic strength during hydrothermal treatment, the platelets were tailored to different sizes and aspect ratios. Amino-modified polyisobutylene molecules were grafted onto the platelets following a convenient new route involving freeze-drying. Organic dispersions in toluene were prepared of the particles with the largest size and highest aspect ratio. The colloidal dispersions prepared in this way showed isotropic-nematic phase transitions above a limiting concentration in a matter of days. The number density at the transition and the width of the biphasic region were determined and compared to theory. The orientation of the platelets in nematic droplets (tactoids) and at the isotropic-nematic interface were analyzed by polarization microscopy. It was observed that sedimentation induces a nematic layer in samples that are below the limiting concentration for isotropic-nematic phase separation. No nematic phase was observed in the initial aqueous suspensions of the ungrafted particles.

This paper focuses on how the electron temperature and other plasma properties affect optical emission and CO2 conversion in a CO2 plasma. Such plasma-mediated reactions can enable efficient CO2 reuse. We study CO2 and CO plasmas generated by inductively-coupled radiofrequency power (30-300 W) at low pressures (6-400 Pa). By varying the argon admixture, we can study the effect of the electron temperature, Te, on the conversion and emission properties using optical emission spectroscopy, mass spectrometry and electrical probe measurements. Importantly, we can observe several parameters simultaneously: Te, CO2 conversion, chemiluminescence from CO2 and dissociation products and optical emission from several atomic and CO transitions and from the C2 Swan system. Based on these results, we establish a correlation between Te, the CO2 conversion and the optical emission spectra. A low Te enhances CO2 conversion and Swan band emission. In contrast with published studies, our results show that the CO2 and C2 vibrations are not in local equilibrium. This means that the vibrational temperatures of CO2 and C2 should differ.

Plasma technology, combined with activation on surfaces, is a novel way to convert CO2 using green electricity.

No abstract

The synergy between catalysis and plasma chemistry often enhances the yield of chemical reactions in plasma-driven reactors. In the case of CO 2 splitting into CO and O 2 , no positive synergistic effect was observed in earlier studies with plasma reactors, except for dielectric barrier discharges, that do not have a high yield and a high efficiency. Here, we demonstrate that introducing metal meshes into radio frequency-driven plasma reactors increases the relative reaction yield by 20%-50%, while supported metal oxide catalysts in the same setups have no effect. We attribute this to the double role of the metal mesh, which acts both as a catalyst for direct CO 2 dissociation as well as for oxygen recombination.

SummaryWe prepare and investigate two-dimensional (2D) single-layer arrays and multilayered networks of gold nanoparticles derivatized with conjugated hetero-aromatic molecules, i.e., S-(4-{[2,6-bipyrazol-1-yl)pyrid-4-yl]ethynyl}phenyl)thiolate (herein S-BPP), as capping ligands. These structures are fabricated by a combination of self-assembly and microcontact printing techniques, and are characterized by electron microscopy, UV–visible spectroscopy and Raman spectroscopy. Selective binding of the S-BPP molecules to the gold nanoparticles through Au–S bonds is found, with no evidence for the formation of N–Au bonds between the pyridine or pyrazole groups of BPP and the gold surface. Subtle, but significant shifts with temperature of specific Raman S-BPP modes are also observed. We attribute these to dynamic changes in the orientation and/or increased mobility of the molecules on the gold nanoparticle facets. As for their conductance, the temperature-dependence for S-BPP networks differs significantly from standard alkanethiol-capped networks, especially above 220 K. Relating the latter two observations, we propose that dynamic changes in the molecular layers effectively lower the molecular tunnel barrier for BPP-based arrays at higher temperatures.