Tuning a sign of magnetoelectric coupling in paramagnetic NH2(CH3)2Al1-xCrx(SO4)2 × 6H2O crystals by metal ion substitution.

Hybrid organometallic systems offer a wide range of functionalities, including magnetoelectric (ME) interactions. However, the ability to design on-demand ME coupling remains challenging despite a variety of host-guest configurations and ME phases coexistence possibilities. Here, we report the effect of metal-ion substitution on the magnetic and electric properties in the paramagnetic ferroelectric NH2(CH3)2Al1-x Cr x (SO4)2 × 6H2O. Doing so we are able to induce and even tune a sign of the ME interactions, in the paramagnetic ferroelectric (FE) state. Both studied samples with x = 0.065 and x = 0.2 become paramagnetic, contrary to the initial diamagnetic compound. Due to the isomorphous substitution with Cr the ferroelectric phase transition temperature (T c ) increases nonlinearly, with the shift being larger for the 6.5% of Cr. A magnetic field applied along the polar c axis increases ferroelectricity for the x = 0.065 sample and shifts T c to higher values, while inverse effects are observed for x = 0.2. The ME coupling coefficient αME = 1.7 ns/m found for a crystal with Cr content of x = 0.2 is among the highest reported up to now. The observed sign change of αME with a small change in Cr content paves the way for ME coupling engineering.

High conductivity organic thin films for spintronics: the interface resistance bottleneck.

Highly electrochemically doped poly(2,5-bis(3-dodecyl-2-yl)-thieno[3,2-b]thiophene (pBTTT) thin films exhibiting remarkably high conductivities values reaching 3000-5000 Ω(-1) cm(-1) are investigated. Experimental evidence of delocalized transport properties of this material at the onset of metallicity makes it an ideal candidate for spin valve device integration. Nevertheless, the interface resistance between the polymer and metallic electrodes is orders of magnitudes larger than the expected spin resistance of the active channel. This prevents the collection of a spin current. This finding can explain the lack of success in making lateral organic spin valves reported in the literature, especially the related absence of spin signals in non-local spin valve and Hanle current measurements in organic thin films.

Conductivity in organic semiconductors hybridized with the vacuum field.

Much effort over the past decades has been focused on improving carrier mobility in organic thin-film transistors by optimizing the organization of the material or the device architecture. Here we take a different path to solving this problem, by injecting carriers into states that are hybridized to the vacuum electromagnetic field. To test this idea, organic semiconductors were strongly coupled to plasmonic modes to form coherent states that can extend over as many as 10(5) molecules and should thereby favour conductivity. Experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility. A theoretical quantum model confirms the delocalization of the wavefunctions of the hybridized states and its effect on the conductivity. Our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.

Heteronanojunctions with atomic size control using a lab-on-chip electrochemical approach with integrated microfluidics.

A versatile tool for electrochemical fabrication of heteronanojunctions with nanocontacts made of a few atoms and nanogaps of molecular spacing is presented. By integrating microfluidic circuitry in a lab-on-chip approach, we keep control of the electrochemical environment in the vicinity of the nanojunction and add new versatility for exchanging and controlling the junction's medium. Nanocontacts made of various materials by successive local controlled depositions are demonstrated, with electrical properties revealing sizes reaching a few atoms only. Investigations on benchmark molecular electronics material, trapped between electrodes, reveal the possibility to create nanogaps of size matching those of molecules. We illustrate the interest of a microfluidic approach by showing that exposure of a fabricated molecular junction to controlled high solvent flows can be used as a reliability criterion for the presence of molecular entities in a gap.

Nanotrench for nano and microparticle electrical interconnects.

We present a simple and versatile patterning procedure for the reliable and reproducible fabrication of high aspect ratio (10(4)) electrical interconnects that have separation distances down to 20 nm and lengths of several hundreds of microns. The process uses standard optical lithography techniques and allows parallel processing of many junctions, making it easily scalable and industrially relevant. We demonstrate the suitability of these nanotrenches as electrical interconnects for addressing micro and nanoparticles by realizing several circuits with integrated species. Furthermore, low impedance metal-metal low contacts are shown to be obtained when trapping a single metal-coated microsphere in the gap, emphasizing the intrinsic good electrical conductivity of the interconnects, even though a wet process is used. Highly resistive magnetite-based nanoparticles networks also demonstrate the advantage of the high aspect ratio of the nanotrenches for providing access to electrical properties of highly resistive materials, with leakage current levels below 1 pA.