Developing convenient and accurate SARS-CoV-2 antigen test and serology test is crucial in curbing the global COVID-19 pandemic. In this work, we report an improved indium oxide (In₂O₃) nanoribbon field-effect transistor (FET) biosensor platform detecting both SARS-CoV-2 antigen and antibody. Our FET biosensors, which were fabricated using a scalable and cost-efficient lithography-free process utilizing shadow masks, consist of an In₂O₃ channel and a newly developed stable enzyme reporter. During the biosensing process, the phosphatase enzymatic reaction generated pH change of the solution, which was then detected and converted to electrical signal by our In₂O₃ FETs. The biosensors applied phosphatase as enzyme reporter, which has a much better stability than the widely used urease in FET based biosensors. As proof-of-principle studies, we demonstrate the detection of SARS-CoV-2 spike protein in both phosphate-buffered saline (PBS) buffer and universal transport medium (UTM) (limit of detection [LoD]: 100 fg/mL). Following the SARS-CoV-2 antigen tests, we developed and characterized additional sensors aimed at SARS-CoV-2 IgG antibodies, which is important to trace past infection and vaccination. Our spike protein IgG antibody tests exhibit excellent detection limits in both PBS and human whole blood ((LoD): 1 pg/mL). Our biosensors display similar detection performance in different mediums, demonstrating that our biosensor approach is not limited by Debye screening from salts and can selectively detect biomarkers in physiological fluids. The newly selected enzyme for our platform performs much better performance and longer shelf life which will lead our biosensor platform to be capable for real clinical diagnosis usage.

Carbon nanotubes (CNTs) are ideal candidates for beyond-silicon nano-electronics because of their high mobility and low-cost processing. Recently, assembled massively aligned CNTs have emerged as an important platform for semiconductor electronics. However, realizing sophisticated complementary nano-electronics has been challenging due to the p-type nature of carbon nanotubes in air. Fabrication of n-type behavior field effect transistors (FETs) based on assembled aligned CNT arrays is needed for advanced CNT electronics. Here in this paper, we report a scalable process to make n-type behavior FETs based on assembled aligned CNT arrays. Air-stable and high-performance n-type behavior CNT FETs are achieved with high yield by combining the atomic layer deposition dielectric and metal contact engineering. We also systematically studied the contribution of metal contacts and atomic layer deposition passivation in determining the transistor polarity. Based on these experimental results, we report the successful demonstration of complementary metal-oxide-semiconductor inverters with good performance, which paves the way for realizing the promising future of carbon nanotube nano-electronics.

Orientation-controlled growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) may enable many new electronic and optical applications. However, previous studies reporting aligned growth of WSe₂ usually yielded very small domain sizes. Herein, we introduced gold vapor into the chemical vapor deposition (CVD) process as a catalyst to assist the growth of WSe₂ and successfully achieved highly aligned monolayer WSe₂ triangular flakes grown on c-plane sapphire with large domain sizes (130 μm) and fast growth rate (4.3 μm·s^-1). When the aligned WSe₂ domains merged together, a continuous monolayer WSe₂ was formed with good uniformity. After transferring to Si/SiO₂ substrates, field effect transistors were fabricated on the continuous monolayer WSe₂, and an average mobility of 12 cm²·V^-1·s^-1 was achieved, demonstrating the good quality of the material. This report paves the way to study the effect of catalytic metal vapor in the CVD process of TMDCs and contributes a novel approach to realize the growth of aligned TMDC flakes.

Quasi-two-dimensional (2D) β-Ga₂O₃ is a rediscovered metal-oxide semiconductor with an ultra-wide bandgap of 4.6–4.9 eV. It has been reported to be a promising material for next-generation power and radio frequency electronics. Field effect transistors (FETs) that can switch at high voltage are key components in power and radio frequency devices, and reliable Ohmic contacts are essential for high FET performance. However, obtaining low contact resistance on β-Ga₂O₃ FETs is difficult since reactions between β-Ga₂O₃ and metal contacts are not fully understood. Herein, we experimentally demonstrate the importance of reactions at the metal/β-Ga₂O₃ interface and the corresponding effects of these reactions on FET performance. When Ti is employed as the metal contact, annealing of β-Ga₂O₃ FETs in argon can effectively transform Schottky contacts into Ohmic contacts and permit a large drain current density of ~ 3.1 mA/μm. The contact resistance (R_contact) between the Ti electrodes and β-Ga₂O₃ decreased from ~ 430 to ~ 0.387 Ω·mm after annealing. X-ray photoelectron spectroscopy (XPS) confirmed the formation of oxygen vacancies at the Ti/β-Ga₂O₃ interface after annealing, which is believed to cause the improved FET performance. The results of this study pave the way for greater application of β-Ga₂O₃ in electronics.

Red phosphorus (RP) has attracted considerable attention as the anode for high-performance Na-ion batteries, owing to its low cost and high theoretical specific capacity of ~ 2, 600 mAh/g. In this study, a facile single-step flash-heat treatment was developed to achieve the reduction of graphene oxide (GO) and the simultaneous deposition of RP onto the reduced graphene oxide (rGO) sheets. The resulting RP/rGO composite was shown to be a promising candidate for overcoming the issues associated with the poor electronic conductivity and large volume variation of RP during cycling. The RP/rGO flexible film anode delivered an average capacity of 1, 625 mAh/g during 200 cycles at a charge/discharge current density of 1 A/g. Average charge capacities of 1, 786, 1, 597, 1, 324, and 679 mAh/g at 1, 2, 4, and 6 A/g current densities were obtained in the rate capability tests. Moreover, owing to the RP component, the RP/rGO film presented superior flame retardancy compared to an rGO film. This work thus introduces a highly accessible synthesis method to prepare flexible and safe RP anodes with superior electrochemical performance toward Na-ion storage.

In the present work, we develop a scalable and inexpensive design for lithium-sulfur (Li-S) batteries by capping a flexible gel polymer/carbon nanofiber (CNF)composite membrane onto a free-standing and binder-free CNF + Li₂S₆ cathode, thus achieving a three-dimensional (3D) structural design. The CNF network is used as the current collector and S holder to overcome the insulating nature and volume expansion of S, while the composite membrane comprises a gel polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and CNF additive is used as an interlayer to trap polysulfides and recycle the remaining S species, leading to a high specific capacity and long cycle life. This 3D structure enables excellent cyclability for 500 cycles at 0.5 ℃ with a small capacity decay of 0.092% per cycle. Furthermore, an outstanding cycle stability was also achieved at even higher current densities (1.0 to 2.0 ℃), indicating its good potential for practical applications of Li-S batteries.

Li metal is considered one of the most promising candidates for the anode material in high-energy-density Li-ion batteries. However, the dendritic growth of Li metal during the plating/stripping process can severely reduce Coulombic efficiency and cause safety problems, which is a key issue limiting the application of Li metal anodes. Herein, we present a novel strategy for dendrite-free deposition of Li by modifying the Cu current collector with a three-dimensional carbon nanofiber (CNF) network. Owing to the large surface area and high conductivity of the CNF network, Li metal is inserted into and deposited onto the CNF directly, and no dendritic Li metal is observed, leaving a flat Li metal surface. With Li metal as the counter electrode for Li deposition, an average Coulombic efficiency of 99.9% was achieved for more than 300 cycles, at large current densities of 1.0 and 2.0 mA·cm^-2, and with a high Li loading of 1 mAh·cm^-2. The scalability of the preparation method and the impressive results achieved here demonstrate the potential for the application of our design to the future development of dendrite-free Li metal anodes.

In this paper, we report polyfluorene-separated ultra-high purity semiconducting carbon nanotube radio frequency transistors with a self-aligned T-shape gate structure. Because of the ultra-high semiconducting tube purity and self-aligned T-shape gate structure, these transistors showed an excellent direct current and radio frequency performance. In regard to the direct current characteristics, these transistors showed a transconductance up to 40 μS/μm and an excellent current saturation behavior with an output resistance greater than 200 kΩ·μm. In terms of the radio frequency characteristics, an extrinsic maximum oscillation frequency (f_max) of 19 GHz was achieved, which is a record among all kinds of carbon nanotube transistors, and an extrinsic current gain cut-off frequency (f_T) of 22 GHz was achieved, which is the highest among transistors based on carbon nanotube networks. Our results take the radio frequency performance of carbon nanotube transistors to a new level and can further accelerate the application of carbon nanotubes for future radio frequency electronics.

Carbon nanotubes (CNTs) have emerged as an important material for printed macroelectronics. However, achieving printed complementary macroelectronics solely based on CNTs is difficult because it is still challenging to make reliable n-type CNT transistors. In this study, we report threshold voltage (V_th) tuning and printing of complementary transistors and inverters composed of thin films of CNTs and indium zinc oxide (IZO) as p-type and n-type transistors, respectively. We have optimized the V_th of p-type transistors by comparing Ti/Au and Ti/Pd as source/drain electrodes, and observed that CNT transistors with Ti/Au electrodes exhibited enhancement mode operation (V_th < 0). In addition, the optimized In: Zn ratio offers good n-type transistors with high on-state current (I_on) and enhancement mode operation (V_th > 0). For example, an In: Zn ratio of 2:1 yielded an enhancement mode n-type transistor with V_th ~ 1 V and I_on of 5.2 μA. Furthermore, by printing a CNT thin film and an IZO thin film on the same substrate, we have fabricated a complementary inverter with an output swing of 99.6% of the supply voltage and a voltage gain of 16.9. This work shows the promise of the hybrid integration of p-type CNT and n-type IZO for complementary transistors and circuits.

Due to their excellent electrical properties and compatibility with room-temperature deposition/printing processing, high-purity single-walled semiconducting carbon nanotubes hold great potential for macroelectronic applications such as in thin-film transistors and display back-panel electronics. However, the relative advantages and disadvantages of various nanotubes for macroelectronics remains an open issue, despite the great significance. Here in this paper, we report a comparative and systematic study of three kinds of mainstream carbon nanotubes (arc-discharge, HiPCO, CoMoCAT) separated using low-cost gel-based column chromatography for thin-film transistor applications, and high performance transistors-which satisfy the requirements for transistors used in active matrix organic light-emitting diode displays-have been achieved. We observe a trade-off between transistor mobility and on/off ratio depending on the nanotube diameter. While arc-discharge nanotubes with larger diameters lead to high device mobility, HiPCO and CoMoCAT nanotubes with smaller diameters can provide high on/off ratios (> 10⁶) for transistors with comparable dimensions. Furthermore, we have also compared gel-based separated nanotubes with nanotubes separated using the density gradient ultracentrifuge (DGU) method, and find that gel-separated nanotubes can offer purity and thin-film transistor performance as good as DGU-separated nanotubes. Our approach can serve as the critical foundation for future carbon nanotube-based thin-film macroelectronics.