Top-Contact Self-Aligned Printing for High-Performance Carbon Nanotube Thin-Film Transistors with Sub-Micron Channel Length

Semiconducting single-wall carbon nanotubes are ideal semiconductors for printed thin-film transistors due to their excellent electrical performance and intrinsic printability with solution-based deposition. However, limited by resolution and registration accuracy of current printing techniques, previously reported fully printed nanotube transistors had rather long channel lengths (>20 μm) and consequently low current-drive capabilities (<0.2 μA/μm). Here we report fully inkjet printed nanotube transistors with dramatically enhanced on-state current density of ∼4.5 μA/μm by downscaling the devices to a sub-micron channel length with top-contact self-aligned printing and employing high-capacitance ion gel as the gate dielectric. Also, the printed transistors exhibited a high on/off ratio of ∼10⁵, low-voltage operation, and good mobility of ∼15.03 cm² V^–1s^–1. These advantageous features of our printed transistors are very promising for future high-definition printed displays and sensing systems, low-power consumer electronics, and large-scale integration of printed electronics

Screw-Dislocation-Driven Growth of Two-Dimensional Few-Layer and Pyramid-like WSe₂ by Sulfur-Assisted Chemical Vapor Deposition

Two-dimensional (2D) layered tungsten diselenides (WSe₂) material has recently drawn a lot of attention due to its unique optoelectronic properties and ambipolar transport behavior. However, direct chemical vapor deposition (CVD) synthesis of 2D WSe₂ is not as straightforward as other 2D materials due to the low reactivity between reactants in WSe₂ synthesis. In addition, the growth mechanism of WSe₂ in such CVD process remains unclear. Here we report the observation of a screw-dislocation-driven (SDD) spiral growth of 2D WSe₂ flakes and pyramid-like structures using a sulfur-assisted CVD method. Few-layer and pyramid-like WSe₂ flakes instead of monolayer were synthesized by introducing a small amount of sulfur as a reducer to help the selenization of WO₃, which is the precursor of tungsten. Clear observations of steps, helical fringes, and herringbone contours under atomic force microscope characterization reveal the existence of screw dislocations in the as-grown WSe₂. The generation and propagation mechanisms of screw dislocations during the growth of WSe₂ were discussed. Back-gated field-effect transistors were made on these 2D WSe₂ materials, which show on/off current ratios of 10⁶ and mobility up to 44 cm²/(V·s)

Room-Temperature Pressure Synthesis of Layered Black Phosphorus–Graphene Composite for Sodium-Ion Battery Anodes

Sodium-ion batteries offer an attractive option for grid-level energy storage due to the high natural abundance of sodium and low material cost of sodium compounds. Phosphorus (P) is a promising anode material for sodium-ion batteries, with a theoretical capacity of 2596 mAh/g. The red phosphorus (RP) form has worse electronic conductivity and lower initial Coulombic efficiency than black phosphorus (BP), but high material cost and limited production capacity have slowed the development of BP anodes. To address these challenges, we have developed a simple and scalable method to synthesize layered BP/graphene composite (BP/rGO) by pressurization at room temperature. A carbon-black-free and binder-free BP/rGO anode prepared with this method achieved specific charge capacities of 1460.1, 1401.2, 1377.6, 1339.7, 1277.8, 1123.78, and 720.8 mAh/g in a rate capability test at charge and discharge current densities of 0.1, 0.5, 1, 5, 10, 20, and 40 A/g, respectively. In a cycling performance test, after 500 deep cycles, the capacity of BP/rGO anodes stabilized at 1250 and 640 mAh/g at 1 and 40 A/g, respectively, which marks a significant performance improvement for sodium-ion battery anodes

Tin-Coated Viral Nanoforests as Sodium-Ion Battery Anodes

Designed as a high-capacity alloy host for Na-ion chemistry, a forest of Sn nanorods with a unique core–shell structure was synthesized on viral scaffolds, which were genetically engineered to ensure a nearly vertical alignment upon self-assembly onto a metal substrate. The interdigital spaces thus formed between individual rods effectively accommodated the volume expansion and contraction of the alloy upon sodiation/desodiation, while additional carbon-coating engineered over these nanorods further suppressed Sn aggregation during extended electrochemical cycling. Due to the unique nanohierarchy of multiple functional layers, the resultant 3D nanoforest of C/Sn/Ni/TMV1cys, binder-free composite electrode already and evenly assembled on a stainless steel current collector, exhibited supreme capacity utilization and cycling stability toward Na-ion storage and release. An initial capacity of 722 mA·h (g Sn)⁻¹ along with 405 mA·h (g Sn)⁻¹ retained after 150 deep cycles demonstrates the longest-cycling nano-Sn anode material for Na-ion batteries reported in the literature to date and marks a significant performance improvement for neat Sn material as alloy host for Na-ion chemistry

High-Performance WSe₂ Field-Effect Transistors <i>via</i> Controlled Formation of In-Plane Heterojunctions

Monolayer WSe₂ is a two-dimensional (2D) semiconductor with a direct band gap, and it has been recently explored as a promising material for electronics and optoelectronics. Low field-effect mobility is the main constraint preventing WSe₂ from becoming one of the competing channel materials for field-effect transistors (FETs). Recent results have demonstrated that chemical treatments can modify the electrical properties of transition metal dichalcogenides (TMDCs), including MoS₂ and WSe₂. Here, we report that controlled heating in air significantly improves device performance of WSe₂ FETs in terms of on-state currents and field-effect mobilities. Specifically, after being heated at optimized conditions, chemical vapor deposition grown monolayer WSe₂ FETs showed an average FET mobility of 31 cm²·V^–1·s^–1 and on/off current ratios up to 5 × 10⁸. For few-layer WSe₂ FETs, after the same treatment applied, we achieved a high mobility up to 92 cm²·V^–1·s^–1. These values are significantly higher than FETs fabricated using as-grown WSe₂ flakes without heating treatment, demonstrating the effectiveness of air heating on the performance improvements of WSe₂ FETs. The underlying chemical processes involved during air heating and the formation of in-plane heterojunctions of WSe₂ and WO_3–<i>x</i>, which is believed to be the reason for the improved FET performance, were studied by spectroscopy and transmission electron microscopy. We further demonstrated that, by combining the air heating method developed in this work with supporting 2D materials on the BN substrate, we achieved a noteworthy field-effect mobility of 83 cm²·V^–1·s^–1 for monolayer WSe₂ FETs. This work is a step toward controlled modification of the properties of WSe₂ and potentially other TMDCs and may greatly improve device performance for future applications of 2D materials in electronics and optoelectronics

Hoop-Strong Nanotubes for Battery Electrodes

The engineering of hollow nanostructures is a promising approach to addressing instabilities in silicon-based electrodes for lithium-ion batteries. Previous studies showed that a SiO_<i>x</i> coating on silicon nanotubes (SiNTs) could function as a constraining layer and enhance capacity retention in electrodes with low mass loading, but we show here that similarly produced electrodes having negligible SiO_<i>x</i> coating and significantly higher mass loading show relatively low capacity retention, fading quickly within the early cycles. We find that the SiNT performance can still be enhanced, even in electrodes with high mass loading, by the use of Ni functional coatings on the outer surface, leading to greatly enhanced capacity retention in a manner that could scale better to industrially relevant battery capacities. <i>In situ</i> transmission electron microscopy studies reveal that the Ni coatings suppress the Si wall from expanding outward, instead carrying the large hoop stress and forcing the Si to expand inward toward the hollow inner core. Evidence shows that these controlled volume changes in Ni-coated SiNTs, accompanied by the electrochemically inert nature of Ni coatings, unlike SiO_<i>x</i>, may enhance the stability of the electrolyte at the outer surface against forming a thick solid electrolyte interphase (SEI) layer. These results provide useful guidelines for designing nanostructured silicon electrodes for viable lithium-ion battery applications

Hoop-Strong Nanotubes for Battery Electrodes

The engineering of hollow nanostructures is a promising approach to addressing instabilities in silicon-based electrodes for lithium-ion batteries. Previous studies showed that a SiO_<i>x</i> coating on silicon nanotubes (SiNTs) could function as a constraining layer and enhance capacity retention in electrodes with low mass loading, but we show here that similarly produced electrodes having negligible SiO_<i>x</i> coating and significantly higher mass loading show relatively low capacity retention, fading quickly within the early cycles. We find that the SiNT performance can still be enhanced, even in electrodes with high mass loading, by the use of Ni functional coatings on the outer surface, leading to greatly enhanced capacity retention in a manner that could scale better to industrially relevant battery capacities. <i>In situ</i> transmission electron microscopy studies reveal that the Ni coatings suppress the Si wall from expanding outward, instead carrying the large hoop stress and forcing the Si to expand inward toward the hollow inner core. Evidence shows that these controlled volume changes in Ni-coated SiNTs, accompanied by the electrochemically inert nature of Ni coatings, unlike SiO_<i>x</i>, may enhance the stability of the electrolyte at the outer surface against forming a thick solid electrolyte interphase (SEI) layer. These results provide useful guidelines for designing nanostructured silicon electrodes for viable lithium-ion battery applications

<i>In Situ</i> Formed Lithium Sulfide/Microporous Carbon Cathodes for Lithium-Ion Batteries

Highly stable sulfur/microporous carbon (S/MC) composites are prepared by vacuum infusion of sulfur vapor into microporous carbon at 600 °C, and lithium sulfide/microporous carbon (Li₂S/MC) cathodes are fabricated <i>via</i> a novel and facile <i>in situ</i> lithiation strategy, <i>i</i>.<i>e</i>., spraying commercial stabilized lithium metal powder (SLMP) onto a prepared S/MC film cathode prior to the routine compressing process in cell assembly. The <i>in situ</i> formed Li₂S/MC film cathode shows high Coulombic efficiency and long cycling stability in a conventional commercial Li-ion battery electrolyte (1.0 M LiPF₆ + EC/DEC (1:1 v/v)). The reversible capacities of Li₂S/MC cathodes remain about 650 mAh/g even after 900 charge/discharge cycles, and the Coulombic efficiency is close to 100% at a current density of 0.1C, which demonstrates the best electrochemical performance of Li₂S/MC cathodes reported to date. Furthermore, this Li₂S/MC film cathode fabricated <i>via</i> our <i>in situ</i> lithiation strategy can be coupled with a Li-free anode, such as graphite, carbon/tin alloys, or Si nanowires to form a rechargeable Li-ion cell. As the Li₂S/MC cathode is paired with a commercial graphite anode, the full cell of Li₂S/MC-graphite (Li₂S-G) shows a stable capacity of around 600 mAh/g in 150 cycles. The Li₂S/MC cathodes prepared by high-temperate sulfur infusion and SLMP prelithiation before cell assembly are ready to fit into current Li-ion batteries manufacturing processes and will pave the way to commercialize low-cost Li₂S-G Li-ion batteries

Electrospun Sb/C Fibers for a Stable and Fast Sodium-Ion Battery Anode

Sodium-ion batteries (SIBs) are considered a top alternative to lithium-ion batteries (LIBs) for large-scale renewable energy storage units due to their low cost and the abundance of sodium-bearing precursors in the earth’s mineral deposits. However, the development of anode materials for SIBs to date has been mainly limited to carbonaceous materials with minimal research devoted to high capacity alloy-based materials. In this study, an antimony (Sb)/carbon (C) electrode with ∼30 nm Sb nanoparticles (NPs) uniformly encapsulated in interconnecting one-dimensional (1D) 400 nm carbon fibers (denoted as SbNP@C) was fabricated using a simple and scalable electrospinning method. This binder-free, current collector-free SbNP@C electrode demonstrated high capacity and stable long-term cycling performance at various current densities. The SbNP@C electrode showed an initial total capacity of 422 mAh/g_electrode and retained 350 mAh/g_electrode after 300 deep charge–discharge cycles under 100 mA/g_Sb. Moreover, because of the efficient 1D sodium-ion transport pathway and the highly conductive network of SbNP@C, the electrode preserved high overall capacities even when cycled at high currents, extending its usability to high power applications

Highly Sensitive and Wearable In₂O₃ Nanoribbon Transistor Biosensors with Integrated On-Chip Gate for Glucose Monitoring in Body Fluids

Nanoribbon- and nanowire-based field-effect transistor (FET) biosensors have stimulated a lot of interest. However, most FET biosensors were achieved by using bulky Ag/AgCl electrodes or metal wire gates, which have prevented the biosensors from becoming truly wearable. Here, we demonstrate highly sensitive and conformal In₂O₃ nanoribbon FET biosensors with a fully integrated on-chip gold side gate, which have been laminated onto various surfaces, such as artificial arms and watches, and have enabled glucose detection in various body fluids, such as sweat and saliva. The shadow-mask-fabricated devices show good electrical performance with gate voltage applied using a gold side gate electrode and through an aqueous electrolyte. The resulting transistors show mobilities of ∼22 cm² V^–1 s^–1 in 0.1× phosphate-buffered saline, a high on–off ratio (10⁵), and good mechanical robustness. With the electrodes functionalized with glucose oxidase, chitosan, and single-walled carbon nanotubes, the glucose sensors show a very wide detection range spanning at least 5 orders of magnitude and a detection limit down to 10 nM. Therefore, our high-performance In₂O₃ nanoribbon sensing platform has great potential to work as indispensable components for wearable healthcare electronics