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1. Mechanically rollable photodetectors enabled by centimetre-scale 2D MoS 2 layer/TOCN composites

   https://doi.org/10.1039/D0NA01053G  

   Yoo, Changhyeon ; Ko, Tae-Jun ; Han, Sang Sub ; Shawkat, Mashiyat Sumaiya ; Oh, Kyu Hwan ; Kim, Bo Kyoung ; Chung, Hee-Suk ; Jung, Yeonwoong ( June 2021 , Nanoscale Advances)

   null (Ed.)

   Two-dimensional (2D) molybdenum disulfide (MoS 2 ) layers are suitable for visible-to-near infrared photodetection owing to their tunable optical bandgaps. Also, their superior mechanical deformability enabled by an extremely small thickness and van der Waals (vdW) assembly allows them to be structured into unconventional physical forms, unattainable with any other materials. Herein, we demonstrate a new type of 2D MoS 2 layer-based rollable photodetector that can be mechanically reconfigured while maintaining excellent geometry-invariant photo-responsiveness. Large-area (>a few cm 2 ) 2D MoS 2 layers grown by chemical vapor deposition (CVD) were integrated on transparent and flexible substrates composed of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs) by a direct solution casting method. These composite materials in three-dimensionally rollable forms exhibited a large set of intriguing photo-responsiveness, well preserving intrinsic opto-electrical characteristics of the integrated 2D MoS 2 layers; i.e. , light intensity-dependent photocurrents insensitive to illumination angles as well as highly tunable photocurrents varying with the rolling number of 2D MoS 2 layers, which were impossible to achieve with conventional photodetectors. This study provides a new design principle for converting 2D materials to three-dimensional (3D) objects of tailored functionalities and structures, significantly broadening their potential and versatility in futuristic devices. 

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2. Humidity‐Driven High‐Performance Electrothermal Actuation of Vertically Stacked 2D PtTe 2 Layers/Cellulose Nanofibers

   https://doi.org/10.1002/aisy.202200269  

   Yoo, Changhyeon ; Han, Sang Sub ; Okogbue, Emmanuel ; Bae, Tae-Sung ; Jang, Jae Hyuck ; Cao, Justin ; Chung, Hee-Suk ; Jung, Yeonwoong ( January 2023 , Advanced Intelligent Systems)

   A new type of soft actuators based on a vertical stack of nanoporous 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐oxidized cellulose nanofibers (TOCNs) and atomically thin 2D platinum ditelluride (PtTe₂) layers is reported. The actuation of TOCNs is driven by the interfacing 2D PtTe₂layers whose electrothermal proficiency precisely controls their hydration/dehydration states sensitive to mechanical deformation. These vertically stacked TOCN/2D PtTe₂actuators present excellent actuation characteristics such as high linearity of bending curvature versus applied voltage and well‐preserved reversibility during cyclic operations. Most notably, they exhibit an extremely large weight‐lifting ratio, i.e., ≈1000 times the mass of the TOCN layers, confirming superior mechanical robustness. Furthermore, complicated actuations such as twisting in a 3D manner are demonstrated by judiciously controlling the surface wettability of TOCN layers. This study unveils opportunities for CNFs and 2D materials for actuator applications, as well as suggests new design strategies broadly applicable to soft robotics and biomimetic devices.

    

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3. Facile synthesis of hierarchical MoS 2 –carbon microspheres as a robust anode for lithium ion batteries

   https://doi.org/10.1039/C6TA03310E  

   Chen, Gen ; Wang, Shengping ; Yi, Ran ; Tan, Longfei ; Li, Hongbo ; Zhou, Meng ; Yan, Litao ; Jiang, Yingbing ; Tan, Shuai ; Wang, Donghai ; et al ( January 2016 , Journal of Materials Chemistry A)

   Molybdenum disulfide (MoS 2 ) may be a promising alternative for lithium ion batteries (LIBs) because it offers a unique layered crystal structure with a large and tunable distance between layers. This enables the anticipated excellent rate and cycling stability because they can promote the reversible lithium ion intercalation and de-intercalation without huge volume change which consequently prevents the pulverization of active materials during repeated charge and discharge processes. Herein, we prepared hierarchical MoS 2 –carbon (MoS 2 –C) microspheres via a continuous and scalable ultrasonic nebulization assisted route. The structure, composition, and electrochemical properties are investigated in detail. The MoS 2 –C microspheres consist of few-layer MoS 2 nanosheets bridged by carbon, which separates the exfoliated MoS 2 layers and prevents their aggregation and restacking, thus leading to improved kinetic, enhanced conductivity and structural integrity. The novel architecture offers additional merits such as overall large size and high packing density, which promotes their practical applications. The MoS 2 –C microspheres have been demonstrated with excellent electrochemical performances in terms of low resistance, high capacity even at large current density, stable cycling performance, etc. The electrodes exhibited 800 mA h g −1 at 1000 mA g −1 over 170 cycles. At a higher current density of 3200 mA g −1 , a capacity of 730 mA h g −1 can be also maintained. The MoS 2 –C microspheres are practically applicable not only because of the continuous and large scale synthesis via the current strategy, but also the possess a robust and integrated architecture which ensures the excellent electrochemical properties. 

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4. Thickness-dependent phase transition kinetics in lithium-intercalated MoS 2

   https://doi.org/10.1088/2053-1583/ac4e9b  

   Pondick, Joshua V ; Yazdani, Sajad ; Kumar, Aakash ; Hynek, David J ; Hart, James L ; Wang, Mengjing ; Qiu, Diana Y ; Cha, Judy J ( February 2022 , 2D Materials)

   Abstract The phase transitions of two-dimensional (2D) materials are key to the operation of many devices with applications including energy storage and low power electronics. Nanoscale confinement in the form of reduced thickness can modulate the phase transitions of 2D materials both in their thermodynamics and kinetics. Here, using in situ Raman spectroscopy we demonstrate that reducing the thickness of MoS 2 below five layers slows the kinetics of the phase transition from 2H- to 1T′-MoS 2 induced by the electrochemical intercalation of lithium. We observe that the growth rate of 1T′ domains is suppressed in thin MoS 2 supported by SiO 2 , and attribute this growth suppression to increased interfacial effects as the thickness is reduced below 5 nm. The suppressed kinetics can be reversed by placing MoS 2 on a 2D hexagonal boron nitride ( h BN) support, which readily facilitates the release of strain induced by the phase transition. Additionally, we show that the irreversible conversion of intercalated 1T′-MoS 2 into Li 2 S and Mo is also thickness-dependent and the stability of 1T′-MoS 2 is significantly increased below five layers, requiring a much higher applied electrochemical potential to break down 1T′-MoS 2 into Li 2 S and Mo nanoclusters. 

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5. All‐Printed Ultrahigh‐Responsivity MoS 2 Nanosheet Photodetectors Enabled by Megasonic Exfoliation

   https://doi.org/10.1002/adma.202203772  

   Kuo, Lidia ; Sangwan, Vinod K. ; Rangnekar, Sonal V. ; Chu, Ting‐Ching ; Lam, David ; Zhu, Zhehao ; Richter, Lee J. ; Li, Ruipeng ; Szydłowska, Beata M. ; Downing, Julia R. ; et al ( July 2022 , Advanced Materials)

   Printed 2D materials, derived from solution‐processed inks, offer scalable and cost‐effective routes to mechanically flexible optoelectronics. With micrometer‐scale control and broad processing latitude, aerosol‐jet printing (AJP) is of particular interest for all‐printed circuits and systems. Here, AJP is utilized to achieve ultrahigh‐responsivity photodetectors consisting of well‐aligned, percolating networks of semiconducting MoS₂nanosheets and graphene electrodes on flexible polyimide substrates. Ultrathin (≈1.2 nm thick) and high‐aspect‐ratio (≈1 μm lateral size) MoS₂nanosheets are obtained by electrochemical intercalation followed by megasonic atomization during AJP, which not only aerosolizes the inks but also further exfoliates the nanosheets. The incorporation of the high‐boiling‐point solvent terpineol into the MoS₂ink is critical for achieving a highly aligned and flat thin‐film morphology following AJP as confirmed by grazing‐incidence wide‐angle X‐ray scattering and atomic force microscopy. Following AJP, curing is achieved with photonic annealing, which yields quasi‐ohmic contacts and photoactive channels with responsivities exceeding 10³ A W⁻¹that outperform previously reported all‐printed visible‐light photodetectors by over three orders of magnitude. Megasonic exfoliation coupled with properly designed AJP ink formulations enables the superlative optoelectronic properties of ultrathin MoS₂nanosheets to be preserved and exploited for the scalable additive manufacturing of mechanically flexible optoelectronics.

    

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