Memristors with Monolayer Graphene Electrodes Grown Directly on Sapphire Wafers.

The development of the memristor has generated significant interest due to its non-volatility, simple structure, and low power consumption. Memristors based on graphene offer atomic monolayer thickness, flexibility, and uniformity and have attracted attention as a promising alternative to contemporary field-effect transistor (FET) technology in applications such as logic and memory devices, achieving higher integration density and lower power consumption. The use of graphene as electrodes in memristors could also increase robustness against degradation mechanisms, including oxygen vacancy diffusion to the electrode and unwanted metal ion diffusion.

Two-Step Synthesis of Bismuth-Based Hybrid Halide Perovskite Thin-Films.

Lead halide perovskites have been revolutionary in the last decade in many optoelectronic sectors. Their bismuth-based counterparts have been considered a good alternative thanks to their composition of earth-abundant elements, good chemical stability, and low toxicity. Moreover, their electronic structure is in a quasi-zero-dimensional (0D) configuration, and they have recently been explored for use beyond optoelectronics.

Bright and Efficient Sensitized Near-Infrared Photoluminescence from an Organic Neodymium-Containing Composite Material System.

Intense organic neodymium (Nd) emission is obtained with near-infrared (NIR) emission equivalent in intensity to that of an organic semiconductor emitting material. The advantage of Nd emission is its narrow line width and NIR emission, which is enhanced by ∼3000 times at low excitation power through an efficient sensitization effect from a composite organic sensitizer. This performance is optimized at high concentrations of Nd ions, and the organic perfluorinated system provides the ion excitations with a quantum efficiency of ∼40%.

Manipulation of Molecular Vibrations on Condensing Er State Densities for 1.5 μm Application.

Vibrational modes of chemical bonds in organic erbium (Er) materials play an important role in determining the efficiency of the 1.5 μm Er emission. This work studies the energy coupling of the Er intra-4f transitions and vibrational modes.

Experimental Studies on the Dynamic Memcapacitance Modulation of the ReO@ReS Composite Material-Based Diode.

In this study, both memcapacitive and memristive characteristics in the composite material based on the rhenium disulfide (ReS) rich in rhenium (VI) oxide (ReO) surface overlayer (ReO@ReS) and in the indium tin oxide (ITO)/ReO@ReS/aluminum (Al) device configuration is presented. Comprehensive experimental analysis of the ReO@ReS material properties' dependence on the memcapacitor electrical characteristics was carried out by standard as well as frequency-dependent current-voltage, capacitance-voltage, and conductance-voltage studies. Furthermore, determination of the charge carrier conduction model, charge carrier mobility, density of the trap states, density of the available charge carrier, free-carrier concentration, effective density of states in the conduction band, activation energy of the carrier transport, as well as ion hopping was successfully conducted for the ReO@ReS based on the experimental data.

Fitting the magnetoresponses of the OLED using polaron pair model to obtain spin-pair dynamics and local hyperfine fields.

Organic light-emitting diode (OLED) displays a sign reversal magnetic field effect (MFE) when the applied magnetic field range is reduced to the sub-milliTesla range and the Polaron Pair Model has been successful in explaining the ultra-small MFE. Here, we obtained high resolution (~ 1 µT) magnetoconductance (MC) and magnetoelectroluminescence (MEL) of a tris-(8-hydroxyquinoline)aluminium-based (Alq) OLED within the magnetic field range of ± 500 µT with the earth magnetic field components cancelled. A clear "W" shaped MC with a dip position of ± 250 µT and a monotonic MEL were observed.

Modelling and fitting the Polaron Pair Magnetoconductance model to obtain a realistic local hyperfine field in Tris-(8-hydroxyquinoline)aluminium based diodes.

The Polaron Pair (PP) model has been successfully applied to magnetoconductance (MC) in organic semiconductor devices under ultra-small magnetic fields (USMFE). We report µT resolution MC measurements carried out with high sensitivity (better than 10) on the common organic semiconductor tris-(8-hydroxyquinoline)aluminium in the range ±500 µT displaying clear minima at ~±240 µT. Unlike traditional approaches, where device MC is simply evaluated using the PP model using nominal parameters for microscopic quantities such as the local hyperfine magnetic field, we have carried out actual fitting of the PP MC model to the experimentally obtained data.

Continuous Tuning of Organic Phosphorescence by Diluting Triplet Diffusion at the Molecular Level.

Organic long-persistent phosphorescent materials are advantageous due to the cost-effectiveness and easy processability. The organic phosphorescence is achieved by the long-lived triplet excitons, and the challenges are recognized regarding the various nonradiative pathways to quench the emission lifetime. Taming long-lived phosphorescence is generally engaged with the charge-transfer or exciton diffusion in molecular stacking to stabilize triplet excitons or form a photoinduced ionized state.

High sensitization efficiency and energy transfer routes for population inversion at low pump intensity in Er organic complexes for IR amplification.

Organic erbium complexes have long been of interest due to their potential for using the strong absorption into the organic to sensitise the erbium emission. Despite this interest there is remarkably little quantitative information on how effective the approach is and the discussion of the energy transfer mechanism is generally vague. Here we accurately quantify the sensitisation as a function of excitation pump density and model it using a rate equation approach.

Room temperature synthesis of ReS through aqueous perrhenate sulfidation.

In this study, a direct sulfidation reaction of ammonium perrhenate (NHReO) leading to a synthesis of rhenium disulfide (ReS) is demonstrated. These findings reveal the first example of a simplistic bottom-up approach to the chemical synthesis of crystalline ReS. The reaction presented here takes place at room temperature, in an ambient and solvent-free environment and without the necessity of a catalyst.

Sensitization, energy transfer and infra-red emission decay modulation in Yb-doped NaYF nanoparticles with visible light through a perfluoroanthraquinone chromophore.

Infra-red emission (980 nm) of sub 10 nm Yb-doped NaYF nanoparticles has been sensitized through the excitation of 2-hydroxyperfluoroanthraquinone chromophore (1,2,3,4,5,6,7-heptafluro-8-hydroxyanthracene-9,10-dione) functionalizing the nanoparticle surface. The sensitization is achieved with a broad range of visible light excitation (400-600 nm). The overall near infra-red (NIR) emission intensity of Yb ions is increased by a factor 300 as a result of the broad and strong absorption of the chromophore compared with ytterbium's intrinsic absorption.

Carbon Nanotube-Quantum Dot Nanohybrids: Coupling with Single-Particle Control in Aqueous Solution.

A strategy is reported for the controlled assembly of organic-inorganic heterostructures consisting of individual single-walled carbon nanotubes (SWCNTs) selectively coupled to single semiconductor quantum dots (QDs). The assembly in aqueous solution was controlled towards the formation of monofunctionalized SWCNT-QD structures. Photoluminescence studies in solution, and on surfaces at the single nanohybrid level, showed evidence of electronic coupling between the two nanostructures.

Solution-Processable Carbon Nanoelectrodes for Single-Molecule Investigations.

Here we present a solution-based assembly method for producing molecular transport junctions employing metallic single-walled carbon nanotubes as nanoelectrodes. The molecular junction conductance of a series of oligophenyls was successfully measured, highlighting the potential of an all-carbon based approach for the fabrication of solution-processable single-molecule junctions for molecular electronics.

Synthesis, Characterization, and Application of Core-Shell Co0.16Fe2.84O4@NaYF4(Yb, Er) and Fe3O4@NaYF4(Yb, Tm) Nanoparticle as Trimodal (MRI, PET/SPECT, and Optical) Imaging Agents.

Multimodal nanoparticulate materials are described, offering magnetic, radionuclide, and fluorescent imaging capabilities to exploit the complementary advantages of magnetic resonance imaging (MRI), positron emission tomography/single-photon emission commuted tomography (PET/SPECT), and optical imaging. They comprise Fe3O4@NaYF4 core/shell nanoparticles (NPs) with different cation dopants in the shell or core, including Co0.16Fe2.

Concentration dependence of the up- and down-conversion emission colours of Er(3+)-doped Y2O3: a time-resolved spectroscopy analysis.

In this paper, a series of Er(3+)-doped Y2O3 samples are systematically investigated, focusing on the effect of the doping concentration on the emission lifetime and spectrum under both 488 nm and 980 nm excitations. Decay times of the (4)S3/2 and (4)F9/2 emitting states under 488 nm and 980 nm excitations are found to be different and concentration dependent. We explain these variations in terms of the changes in the up-conversion routes caused by the predominance of energy exchanges that involve the lowest lying excited states.

Visible-Range Sensitization of Er(3+)-Based Infrared Emission from Perfluorinated 2-Acylphenoxide Complexes.

Five new fully fluorinated acylphenoxide ligands, which are aromatic analogues of β-diketonates, provide visible photosensitization of the Er(3+4)I13/2 → (4)I15/2 emission at ∼1540 nm (of interest for telecommunications) via the "antenna effect", as observed in Cs[ErL4] compounds. Depending on the chemical functionalization, the excitation wavelength can be tuned in the 400-650 nm range. Decay times for the solids are in the range of 7-16 μs, proving that the complexes can be of interest for a number of optoelectronic and photonic applications.

Organo-erbium systems for optical amplification at telecommunications wavelengths.

Modern telecommunications rely on the transmission and manipulation of optical signals. Optical amplification plays a vital part in this technology, as all components in a real telecommunications system produce some loss. The two main issues with present amplifiers, which rely on erbium ions in a glass matrix, are the difficulty in integration onto a single substrate and the need of high pump power densities to produce gain.

Importance of spin-orbit interaction for the electron spin relaxation in organic semiconductors.

Despite the great interest organic spintronics has recently attracted, there is only a partial understanding of the fundamental physics behind electron spin relaxation in organic semiconductors. Mechanisms based on hyperfine interaction have been demonstrated, but the role of the spin-orbit interaction remains elusive. Here, we report muon spin spectroscopy and time-resolved photoluminescence measurements on two series of molecular semiconductors in which the strength of the spin-orbit interaction has been systematically modified with a targeted chemical substitution of different atoms at a particular molecular site.

Efficient sensitized emission in Yb(III) pentachlorotropolonate complexes.

New Yb(III) complexes based on the pentachlorotropolonate (pctrop) ligand show enhanced infrared emission when excited in the orange organic chromophore. Yb(pctrop)(3)(DMF-d(7))(2) presents the highest reported quantum yield for a nonfluorinated infrared-emitting organolanthanide complex.

Luminescent zinc(II) complexes of fluorinated benzothiazol-2-yl substituted phenoxide and enolate ligands.

Zn(II) complexes of the following new, fluorine-containing, benzothiazole-derived ligands have been synthesized and characterized crystallographically: 2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (3), 4,5,6,7-tetrafluoro-2-(3,3,3-trifluoro-2-oxopropyl)benzothiazole (4), 4,5,6,7-tetrafluoro-2-(2-hydroxyphenyl)benzothiazole (12), 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)-4,5,6,7-tetrafluorobenzothiazole (13), and 2-(3,4,5,6-tetrafluoro-2-hydroxyphenyl)benzothiazole (16); the Cu(II) complex of ligand 4 is also reported. These are analogs of the important photo- and electroluminescent material [Zn(BTZ)(2)](2), where H-BTZ = 2-(2-hydroxyphenyl)benzothiazole. DFT calculations indicate that HOMO and LUMO energy levels in these materials are substantially lowered by fluorination.

A single-device universal logic gate based on a magnetically enhanced memristor.

Memristors are one of the most promising candidates for future information and communications technology (ICT) architectures. Two experimental proofs of concept are presented based on the intermixing of spintronic and memristive effects into a single device, a magnetically enhanced memristor (MEM). By exploiting the interaction between the memristance and the giant magnetoresistance (GMR), a universal implication (IMP) logic gate based on a single MEM device is realized.

Ambipolar charge transport in "traditional" organic hole transport layers.

Organic semiconductors are often labeled as electron or hole transport materials due to the primary role they perform in devices. However, despite these labels we have shown using time-of-flight that two of the traditional "hole transport materials" TPD and NPB are actually excellent electron transporters the electron transport properties of which are comparable to those for holes.

Efficient white light emission by upconversion in Yb(3+)-, Er(3+)- and Tm(3+)-doped Y2BaZnO5.

We report efficient white upconversion luminescence in Yb(3+)-, Er(3+)- and Tm(3+)-doped monophasic and biphasic Y(2)BaZnO(5) phosphors under 977 nm near-infrared excitation and at low excitation power densities (down to ∼25 mW mm(-2)).

Engineering spin propagation across a hybrid organic/inorganic interface using a polar layer.

Spintronics has shown a remarkable and rapid development, for example from the initial discovery of giant magnetoresistance in spin valves to their ubiquity in hard-disk read heads in a relatively short time. However, the ability to fully harness electron spin as another degree of freedom in semiconductor devices has been slower to take off. One future avenue that may expand the spintronic technology base is to take advantage of the flexibility intrinsic to organic semiconductors (OSCs), where it is possible to engineer and control their electronic properties and tailor them to obtain new device concepts.