Electroluminescent (EL) devices operating at alternating current (AC) electricity have been of great interest due to not only their unique light emitting mechanism of carrier generation and recombination but also their great potential for applications in displays, sensors, and lighting. Despite great success of AC–EL devices, most device properties are far from real implementation. In particular, the current state-of-the art brightness of the solution-processed AC–EL devices is a few hundred candela per square meter (cd m–2) and most of the works have been devoted to red and white emission. In this manuscript, we report extremely bright full color polymer AC–EL devices with brightness of approximately 2300, 6000, and 5000 cd m–2 for blue (B), green (G), and red (R) emission, respectively. The high brightness of blue emission was attributed to individually networked multiwalled carbon nanotubes (MWNTs) for the facile carrier injection as well as self-assembled block copolymer micelles for suppression of interchain nonradiative energy quenching. In addition, effective FRET from a solution-blended thin film of B-G and B-G-R fluorescent polymers led to very bright green and red EL under AC voltage, respectively. The solution-processed AC–EL device also worked properly with vacuum-free Ag paste on a mechanically flexible polymer substrate. Finally, we successfully demonstrated the long-term operation reliability of our AC–EL device for over 15 h.

The scientific community has witnessed tremendous expansion of research on layered (i.e. two-dimensional, 2D) materials, with increasing recent focus on applications to photonics. Layered materials are particularly exciting for manipulating light in the confined geometry of photonic integrated circuits, where key material properties include strong and controllable lightmatter interaction, and limited optical loss. Layered materials feature tunable optical properties, phases that are promising for electro-optics, and a panoply of polymorphs that suggest a rich design space for highly-nonperturbative photonic integrated devices based on phase-change functionality. All of these features are manifest in materials with band gap above the photonics-relevant nearinfrared (NIR) spectral band (~ 0.5 -1 eV), meaning that they can be harnessed in refractive (i.e. non-absorptive) applications.

A thorough understanding of native oxides is essential for designing semiconductor devices. Here, we report a study of the rate and mechanisms of spontaneous oxidation of bulk single crystals of ZrS x Se 2−x alloys and MoS 2 . ZrS x Se 2−x alloys oxidize rapidly, and the oxidation rate increases with Se content. Oxidation of basal surfaces is initiated by favorable O 2 adsorption and proceeds by a mechanism of Zr−O bond switching, that collapses the van der Waals gaps, and is facilitated by progressive redox transitions of the chalcogen. The rate-limiting process is the formation and out-diffusion of SO 2 . In contrast, MoS 2 basal surfaces are stable due to unfavorable oxygen adsorption. Our results provide insight and quantitative guidance for designing and processing semiconductor devices based on ZrS x Se 2−x and MoS 2 and identify the atomistic-scale mechanisms of bonding and phase transformations in layered materials with competing anions.

While transition metal dichalcogenide (TMD) thin films are most commonly synthesized by vapor transport using solid metal oxide precursors, directly converting metal thin films to TMDs may be more scalable and controllable, e.g., to enable large-area coating by vacuum deposition. The thermodynamics are favorable for MoS2 formation from Mo in sulfur-rich environments, but sulfurization tends to be slow and the product is highly dependent on the chemical pathway taken. Here, the authors report on the role of trace oxygen gas (O2) for the sulfurization of Mo films. They study the formation of MoS2 from Mo films in H2S vapor, between 350 and 500 °C and with varying levels of O2. They find that the presence of trace levels of O2 accelerates the crystallization of MoS2 and affects the layer orientation, without changing the kinetics of mass transport or the final film composition. O2 acts as a catalyst to promote the crystallization of MoS2 at lower temperatures than otherwise possible. These results provide new insights into the growth of MoS2 by sulfurization and suggest that introducing an appropriate catalyst during chalcogenide phase formation could enable new processes for making homogeneous, large-area MoS2 films at low processing temperature on a variety of substrates.

Transition metal dichalcogenides have shown great potential for next-generation electronic and optoelectronic devices. However, native oxidation remains a major issue in achieving their long-term stability, especially for Zr-containing materials such as ZrS2. Here, we develop a first principles-informed reactive forcefield for Zr/O/S to study oxidation dynamics of ZrS2. Simulation results reveal anisotropic oxidation rates between (210) and (001) surfaces. The oxidation rate is highly dependent on the initial adsorption of oxygen molecules on the surface. Simulation results also provide reaction mechanism for native oxide formation with atomistic details. Graphic Abstract