William Paul Gillin

Low contamination trapped in nanomaterials is important for the performance, efficiency, and stability of advanced optoelectronic devices. Although vacuum conditions are standard for low-temperature fabrication of such devices, water contamination remains challenging to fully eliminate. Our study demonstrates that even under a pressure of –8 mbar, water molecules trapped in nanoscale thin films can exist at concentrations comparable to the functional materials. We employ the transient optical properties of perfluorinated organic erbium compounds to probe trapped water, offering an effective detection within 8 Å spatial resolution, which none of the available probing methods can ever achieve. These findings suggest that maintaining ultrahigh vacuum conditions below 10^–8 mbar is essential to minimize trapped water contamination in nanoscale thin films. Improved control of these contamination levels could contribute to enhanced stability and performance in nanoscale optoelectronic devices.

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. However, to realize this technological transformation, it is necessary to establish a scalable, robust, and cost-effective device fabrication process. Here we report the direct growth of high-quality monolayer graphene on sapphire wafers in a mass-producible, contamination-free, and transfer-free manner, using a commercially available metal-organic chemical vapor deposition (MOCVD) system. By taking advantage of this approach, graphene-electrode based memristors are developed, and all the processes used in the device fabrication incorporating graphene electrodes can be performed at wafer scale. The graphene electrode-based memristor demonstrates promising characteristics in terms of endurance, retention, and ON/OFF ratio. This work presents a possible and viable route to achieving robust graphene-based memristors in a commercially and technologically sustainable manner, paving the way for the realization of more powerful and compact integrated graphene electronics in the future.

Indium tin oxide (ITO) is widely used for transparent electrode applications due to its high electrical conductivity and relatively straightforward deposition technology. However, there are long standing concerns for its use due to the limited availability of indium in the Earth's crust. Graphene is considered as a promising material for replacing ITO but for this to become possible, a low‐cost and scalable fabrication method that produces graphene with comparable performance to ITO is required. By taking advantage of high‐quality monolayer graphene directly deposited on a transparent substrate using a commercially available metal–organic chemical vapor deposition (MOCVD) system, graphene‐based organic light‐emitting diodes (OLEDs) without the use of metal catalysts or a graphene transfer process are developed. The as‐grown graphene is patterned using photolithography and its conductivity is enhanced by doping with nitric acid prior to deposition of the OLED stack. The electrical and optical performances of the as‐fabricated graphene‐based OLEDs are identical to the control devices with conventional ITO anodes. All the processes used in the fabrication of graphene‐based OLEDs can be performed at wafer scale. This paper demonstrates the potential for graphene to replace ITO as anodes in OLED devices in a technologically and commercially effective manner.

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. A significant limitation in applying thin-film technology is represented by the difficulty of synthesizing compact layers with easily scalable methods. Here, the engineering of a two-step synthesis in an air of methylammonium bismuth iodide compact thin films is reported. The critical steps of the process have been highlighted so that the procedure can be adapted to different substrates and application areas.

Intense organic neodymium (Nd³⁺) emission is obtained with near-infrared (NIR) emission equivalent in intensity to that of an organic semiconductor emitting material. The advantage of Nd³⁺ 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 Nd³⁺ ions, and the organic perfluorinated system provides the ion excitations with a quantum efficiency of ∼40%. The material system is applicable to thin films that are compatible with integrated optics applications.

Vibrational modes of chemical bonds in organic erbium (Er³⁺) materials play an important role in determining the efficiency of the 1.5 μm Er³⁺ emission. This work studies the energy coupling of the Er³⁺ intra-4f transitions and vibrational modes. The results demonstrate that the coupling introduces enormous nonradiative internal relaxation, which condenses the excited erbium population on to the ⁴I_13/2 state. This suggests that vibrational modes can be advantageous for optimizing the branching ratio for the 1.5 μm transition in organic erbium materials. Through control of the quenching effect on to the ⁴I_13/2 state and a reliable determination of intrinsic radiative rates, it is found that the pump power for population inversion can be reduced by an order of magnitude at high erbium concentrations compared to conventional inorganic erbium materials.

Correction for ‘Enhanced 1.54 μm luminescence of a perfluorinated erbium complex sensitized by perfluorinated Pt(II) and Zn(II) phthalocyanines with 980 nm emission’ by Hongfei Li et al., J. Mater. Chem. C, 2021, DOI: 10.1039/d0tc05301e.

Metallophthalocyanines with ∼980 nm emission show sensitization effects on an erbium complex. A long lifetime of 1.05 ms, a PLQY of 13%, Er³⁺ 1.5 μm emission enhancement of 81 times are obtained in the perfluorinated organic erbium co-doped system.

In this study, both memcapacitive and memristive characteristics in the composite material based on the rhenium disulfide (ReS₂) rich in rhenium (VI) oxide (ReO₃) surface overlayer (ReO₃@ReS₂) and in the indium tin oxide (ITO)/ReO₃@ReS₂/aluminum (Al) device configuration is presented. Comprehensive experimental analysis of the ReO₃@ReS₂ 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 ReO₃@ReS₂ based on the experimental data. The ITO/ReO₃@ReS₂/Al charge carrier conduction was found to rely on the mixed electronic–ionic processes, involving electrochemical metallization and lattice oxygen atoms migration in response to the externally modulated electric field strength. The chemical potential generated by the electronic–ionic ITO/ReO₃@ReS₂/Al resistive memory cell non-equlibrium processes leads to the occurrence of the nanobattery effect. This finding supports the possibility of a nonvolatile memory cell with a new operation principle based on the potential read function.

Organic prolonged luminescent materials have attracted attention with various candidates reported providing both UV and visible emission for applications in bio-imaging, light storage, security, etc. However, there is a lack of prolonged near-infrared (NIR) emitting materials, which are highly desirable for many of the proposed applications. NIR-emitting organic lanthanide(III) molecules have suitable wavelengths, but all of them are unsuitable for persistent luminescence due to weak sensitization and the restricted intrinsic ion radiative lifetimes. Herein, this paper demonstrates efficiently sensitized organic Yb(III) compounds with prolonged emission lifetimes up to ∼0.3 s at 1 μm, far exceeding the intrinsic Yb³⁺ emission lifetime of ∼1 ms. The dynamic equilibrium is studied to demonstrate that this prolonged emission is caused by energy transfer from long-lived organic triplet excitons. Experiment and simulation results suggest a new route to develop bright and ultralong-lived 1 μm emitting materials that could be coupled with other existing organic persistent luminescence materials to shift their emission in to the infrared.