The necessity for new sources for greener and cleaner energy production to replace the existing ones has been increasingly growing in recent years. Of those new sources, the hydrogen evolution reaction has a large potential. In this work, for the first time, MoSe /Mo core-shell 3D-hierarchical nanostructures are created, which are derived from the Mo 3D-hierarchical nanostructures through a low-temperature plasma-assisted selenization process with controlled shapes grown by a glancing angle deposition system.

The formation of PtSe -layered films is reported in a large area by the direct plasma-assisted selenization of Pt films at a low temperature, where temperatures, as low as 100 °C at the applied plasma power of 400 W can be achieved. As the thickness of the Pt film exceeds 5 nm, the PtSe -layered film (five monolayers) exhibits a metallic behavior. A clear p-type semiconducting behavior of the PtSe -layered film (≈trilayers) is observed with the average field effective mobility of 0.7 cm V s from back-gated transistor measurements as the thickness of the Pt film reaches below 2.5 nm. A full PtSe field effect transistor is demonstrated where the thinner PtSe , exhibiting a semiconducting behavior, is used as the channel material, and the thicker PtSe , exhibiting a metallic behavior, is used as an electrode, yielding an ohmic contact. Furthermore, photodetectors using a few PtSe -layered films as an adsorption layer synthesized at the low temperature on a flexible substrate exhibit a wide range of absorption and photoresponse with the highest photocurrent of 9 µA under the laser wavelength of 408 nm. In addition, the device can maintain a high photoresponse under a large bending stress and 1000 bending cycles.

Integration of strain engineering of two-dimensional (2D) materials in order to enhance device performance is still a challenge. Here, we successfully demonstrated the thermally strained band gap engineering of transition-metal dichalcogenide bilayers by different thermal expansion coefficients between 2D materials and patterned sapphire structures, where MoS bilayers were chosen as the demonstrated materials. In particular, a blue shift in the band gap of the MoS bilayers can be tunable, displaying an extraordinary capability to drive electrons toward the electrode under the smaller driven bias, and the results were confirmed by simulation. A model to explain the thermal strain in the MoS bilayers during the synthesis was proposed, which enables us to precisely predict the band gap-shifted behaviors on patterned sapphire structures with different angles. Furthermore, photodetectors with enhancement of 286% and 897% based on the strained MoS on cone- and pyramid-patterned sapphire substrates were demonstrated, respectively.

In this report, we propose to enhance the hole injection efficiency by adjusting the barrier height of the p-type electron blocking layer (p-EBL) for ∼273 nm deep ultraviolet light-emitting diodes (DUV LEDs). The barrier height for the p-EBL is modified by employing a p-Al 0.60 Ga 0.40 N/ Al 0.50 Ga 0.50 N/p-Al 0.60 Ga 0.40 N structure, in which the very thin Al 0.50 Ga 0.50 N layer is able to achieve a high local hole concentration, which is very effective in reducing the effective barrier height of the p-EBL for holes. More importantly, besides the thermionic emission, such a p-EBL structure can also favor a strong intraband tunneling process for holes. As a result, we can obtain a more efficient hole injection into the quantum wells, leading to a remarkably improved optical power for the DUV LED with the proposed p-EBL architecture.

Utilization of light to boost the performance of gas sensors allows us to operate sensor devices at room temperature.