High-Performance p-Type Quasi-Ohmic of WSe2 Transistors Using Vanadium-Doped WSe2 as Intermediate Layer Contact.

Two-dimensional (2D) transition-metal dichalcogenides (TMDCs), such as tungsten diselenide (WSe2), hold immense potential for applications in electronic and optoelectronic devices. However, a significant Schottky barrier height (SBH) at the metal-semiconductor (MS) interface reduces the electronic device performance. Here, we present a unique 2D/2D contact method for minimizing contact resistance and reducing the SBH. This approach utilizes vanadium-doped WSe2 (V-WSe2) as the drain and source contacts. The fabricated transistor exhibited a stable operation with p-type quasi-ohmic contact and a high on/off current ratio surpassing 108 at room temperature, reaching 1011 at 10 K. The device achieved an on-current of 68.87 µA, a high mobility of 103.80 cm2 V-1 s-1, a low contact resistance of 0.92 kΩ, and remarkably low SBH values of 1.51 meV for holes at VGS = -120 V with fixed VDS = 1 V. Furthermore, a Schottky photodiode has been fabricated, utilizing V-WSe2 and Cr as the asymmetric contact platform, showing a responsivity of 116 mA W1-. The findings of this study suggest a simple and efficient method for improving the performance of TMDC-based transistors.

Ultrafast Negative Capacitance Transition for 2D Ferroelectric MoS2/Graphene Transistor.

Negative capacitance gives rise to subthreshold swing (SS) below the fundamental limit by efficient modulation of surface potential in transistors. While negative-capacitance transition is reported in polycrystalline Pb(Zr0.2Ti0.8)O3 (PZT) and HfZrO2 (HZO) thin-films in few microseconds timescale, low SS is not persistent over a wide range of drain current when used instead of conventional dielectrics. In this work, the clear nano-second negative transition states in 2D single-crystal CuInP2S6 (CIPS) flakes have been demonstrated by an alternative fast-transient measurement technique. Further, integrating this ultrafast NC transition with the localized density of states of Dirac contacts and controlled charge transfer in the CIPS/channel (MoS2/graphene) a state-of-the-art device architecture, negative capacitance Dirac source drain field effect transistor (FET) is introduced. This yields an ultralow SS of 4.8 mV dec-1 with an average sub-10 SS across five decades with on-off ratio exceeding 107, by simultaneous improvement of transport and body factors in monolayer MoS2-based FET, outperforming all previous reports. This approach could pave the way to achieve ultralow-SS FETs for future high-speed and low-power electronics.

Plasma-Induced Phase Transformation of SnS2 to SnS.

Layered van der Waals materials have recently attracted attention owing to their exceptional electrical and optical properties in thin layer form. One way to extend their utility is to form a heterostructure which combines various properties of layered materials to reveal intriguing behavior. Conventional heterostructure synthesis methods are difficult to develop and the heterostructure formed can be limited to a small area. Here, we investigate the phase transformation of SnS2 to SnS by removing sulfur atoms at the top surface using Ar plasma. By varying the plasma power and exposure time, we observed that SnS is subsequently formed on top of the mogul-like structure of SnS2. Since SnS is a p-type semiconductor and SnS2 is an n-type semiconductor, we naturally formed a vertical p-n junction. By using graphene at the top and bottom as transparent electrodes, a vertical p-n diode device is constructed. The device demonstrates good rectifying behavior and large photocurrent generation under white light. This method can be applied to large-area heterostructure synthesis using plasma via phase transformation of various metal dichalcogenides to metal monochalcogenides.

Highly selective colorimetric detection and preconcentration of Bi(III) ions by dithizone complexes anchored onto mesoporous TiO2.

We successfully developed a single-step detection and removal unit for Bi(III) ions based on dithizone (DZ) anchored on mesoporous TiO2 with rapid colorometric response and high selectivity for the first time. [(DZ)3-Bi] complex is easily separated and collected by mesoporous TiO2 as adsorbent and preconcentrator without any color change of the produced complex onto the surface of mesoporous TiO2 (TiO2-[(DZ)3-Bi]) at different Bi(III) concentrations. This is because highly potent mesoporous TiO2 architecture provides proficient channeling or movement of Bi(III) ions for efficient binding of metal ion, and the simultaneous excellent adsorbing nature of mesoporous TiO2 provides an extra plane for the removal of metal ions.

Synthesis of mesoporous ceria/titania thin films for self-cleaning applications.

CeO2/TiO2 thin films with a three-dimensional (3D) cubic structure were synthesized. Firstly, mesostructured 3D TiO2 films with high surface area and thermally stable have been prepared. Secondly, CeO2 was deposited on 3D mesoporous TiO2 film by two pathways: (i) cerium nitrate sol in presence of poly(ethylene glycol) was deposited on the prepared mesoporous TiO2 films by spin-coating to obtain 1, 3, and 5 layers CeO2/TiO2 and (ii) the second pathway, for thick CeO2, the prepared mesoporous TiO2 films were suspended into the high concentration of cerium nitrate in presence of poly(ethylene glycol) for 24h with magnetic stirring. FE-SEM images of the mesoporous CeO2/TiO2 films were crack-free and indicated a random worm-like network of the mesopores. The XRD patterns show for all prepared samples only TiO2 anatase phase. At five layers CeO2/TiO2, a weak and diffuse diffraction peak arises, corresponding to (111) plane of cubic CeO2. Methylene blue degradation was conducted to characterize the photocatalytic activity of films and compared with that of commercially available Pilkington Activ™ glass by the determination of their photonic efficiencies. Photonic efficiency of mesoporous TiO2~3.39% is higher than Pilkington Activ™ glass~10 times, probably due to the much larger surface area of the mesoporous films and its high crystallinity. Five layers CeO2/TiO2 films showed two times higher photoactivity for MB oxidation than mesoporous TiO2 film, and its photonic efficiency was found to be ~20 times higher than Pilkington Activ™ glass. Five layers CeO2/TiO2 was fixed after being used repetitively for five times.