Highly uniform wafer-scale synthesis of α-MoO3 by plasma enhanced chemical vapor deposition.

Molybdenum oxide (MoO3) has gained immense attention because of its high electron mobility, wide band gap, and excellent optical and catalytic properties. However, the synthesis of uniform and large-area MoO3 is challenging. Here, we report the synthesis of wafer-scale α-MoO3 by plasma oxidation of Mo deposited on Si/SiO2. Mo was oxidized by O2 plasma in a plasma enhanced chemical vapor deposition (PECVD) system at 150 °C. It was found that the synthesized α-MoO3 had a highly uniform crystalline structure. For the as-synthesized α-MoO3 sensor, we observed a current change when the relative humidity was increased from 11% to 95%. The sensor was exposed to different humidity levels with fast recovery time of about 8 s. Hence this feasibility study shows that MoO3 synthesized at low temperature can be utilized for gas sensing applications by adopting flexible device technology.

Chemical Amination via Cycloaddition of Graphene for Use in a Glucose Sensor.

Graphene was chemically aminated via cycloaddition. Aziridine-ring linkages were formed by covalently modifying the C-C double bonds in graphene. The aminated graphene presents an enhanced hydrophilicity, the contact angle with water decreases from 80.5 degrees to 58.5 degrees. And the conductivity of aminated graphene exhibits exponential decay as the reaction time increase. If the reaction time is 90 min, the resistance of aminated graphene was increased from -32 Ω to -2744 Ω. Because the amino group has good biocompatibility, the aminated graphene is designed for use as an enzyme sensor platform, such as glucose sensor based on glucose oxidase. The aminated graphene exhibited a good detection response for glucose. The increase in device current is about 12% in 1.2 mg/mL glucose solution.

Controlled MoS2 layer etching using CF4 plasma.

A few-layered molybdenum disulfide (MoS2) thin film grown by plasma enhanced chemical vapor deposition was etched using a CF4 inductively coupled plasma, and the possibility of controlling the MoS2 layer thickness to a monolayer of MoS2 over a large area substrate was investigated. In addition, damage and contamination of the remaining MoS2 layer surface after etching and a possible method for film recovery was also investigated. The results from Raman spectroscopy and atomic force microscopy showed that one monolayer of MoS2 was etched by exposure to a CF4 plasma for 20 s after an initial incubation time of 20 s, i.e., the number of MoS2 layers could be controlled by exposure to the CF4 plasma for a certain processing time. However, XPS data showed that exposure to CF4 plasma induced a certain amount of damage and contamination by fluorine of the remaining MoS2 surface. After exposure to a H2S plasma for more than 10 min, the damage and fluorine contamination of the etched MoS2 surface could be effectively removed.

Synthesis of multiphase MoS2 heterostructures using temperature-controlled plasma-sulfurization for photodetector applications.

Two-dimensional (2D) materials exhibit outstanding performance in photodetectors because of their excellent optical and electronic properties. Specifically, 2D-MoS2, a transition metal dichalcogenide, is a prominent candidate for flexible and portable photodetectors based on its inherent phase-dependent tunable optical band gap properties. This research focused on creating high-performance photodetectors by carefully arranging out-of-plane 2D heterostructures. The process involved stacking different phases of MoS2 (1T and 2H) using controlled temperature during plasma-enhanced chemical vapor deposition. Among the various phase combinations, the best photocurrent response was obtained for the 1T/2H-MoS2 heterostructure, which exhibited an approximately two-fold higher photocurrent than the 2H/1T-MoS2 heterostructure and 2H/2H-MoS2 monostructure. The 1T/2H-MoS2 heterostructure exhibited a higher photoresponse than the monostructured MoS2 of the same thickness (1T/1T- and 2H/2H-MoS2, respectively). The effect of the stacking sequences of different phases was examined, and their photoperformances were investigated. This study demonstrates that phase engineering in 2D-MoS2 van der Waals heterostructures has significant potential for developing high-performance photodetectors.

CoFeS2@CoS2 Nanocubes Entangled with CNT for Efficient Bifunctional Performance for Oxygen Evolution and Oxygen Reduction Reactions.

Exploring bifunctional electrocatalysts to lower the activation energy barriers for sluggish electrochemical reactions for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great importance in achieving lower energy consumption and higher conversion efficiency for future energy conversion and storage system. Despite the excellent performance of precious metal-based electrocatalysts for OER and ORR, their high cost and scarcity hamper their large-scale industrial application. As alternatives to precious metal-based electrocatalysts, the development of earth-abundant and efficient catalysts with excellent electrocatalytic performance in both the OER and the ORR is urgently required. Herein, we report a core-shell CoFeS2@CoS2 heterostructure entangled with carbon nanotubes as an efficient bifunctional electrocatalyst for both the OER and the ORR. The CoFeS2@CoS2 nanocubes entangled with carbon nanotubes show superior electrochemical performance for both the OER and the ORR: a potential of 1.5 V (vs. RHE) at a current density of 10 mA cm-2 for the OER in alkaline medium and an onset potential of 0.976 V for the ORR. This work suggests a processing methodology for the development of the core-shell heterostructures with enhanced bifunctional performance for both the OER and the ORR.

Synthetic control of the surface area in nickel cobalt oxide for glucose detection via additive-assisted wet chemical method.

We investigated the effect of specific surface area on the electrochemical properties of NiCo2O4 (NCO) for glucose detection. NCO nanomaterials with controlled specific surface areas were prepared by additive-assisted hydrothermal synthesis, and self-assembled nanostructures with urchin-, pine-needle-, tremella-, and flower-like morphologies were obtained. The novelty of this method is the systematic control of chemical reaction routes assisted by the addition of different additives during synthesis, which results in the spontaneous formation of various morphologies without any difference in the crystal structure and chemical states of the constituent elements. Such morphological control of NCO nanomaterials leads to considerable changes in the electrochemical performance for glucose detection. Combined with materials characterization, the relationship between the specific surface area and the electrochemical performance is discussed for glucose detection. This work can provide scientific insights for tailoring the surface area of nanostructures, which determines their functionality for potential applications in glucose biosensors.

Synthesis of NiCo2O4 Nanostructures and Their Electrochemial Properties for Glucose Detection.

In this work, we prepared spinel-type NiCo2O4 (NCO) nanopowders as a low-cost and sensitive electrochemical sensor for nonenzymatic glucose detection. A facile and simple chemical bath method to synthesize the NCO nanopowders is demonstrated. The effect of pH and annealing temperature on the formation mechanism of NCO nanoparticles was systematically investigated. Our studies show that different pHs of the precursor solution during synthesis result in different intermediate phases and relating chemical reactions for the formation of NCO nanoparticles. Different morphologies of the NCO depending on pHs are also discussed based on the mechanism of growth. Electrochemical performance of the prepared NCO was characterized towards glucose, which reveals that sensitivity and selectivity of the NCO are significantly related with the final microstructure combined with constituent species with multiple oxidation states in the spinel structure.

Growth of Plasma-Treated Corn Seeds under Realistic Conditions.

In this study, the effect of the plasma treatment on corn seeds is investigated. Corn seeds were treated uniformly without burning or blackening by three kinds of plasma apparatus: RF plasma in vacuum, microwave-driven atmospheric-pressure plasma, DBD atmospheric-pressure plasma, and two other treatments: vacuum exposure only, and using plasma-activated water in the seed coating process, to investigate growth rate changes under realistic conditions. Each treatment was performed on a total of 1512 corn seeds. Seeds from each experimental condition were treated with the recommended rate of Poncho/VOTiVO with Acceleron, a commercial biological seed treatment that helps to protect the seeds from fungus, insects, and nematodes after planting. The 1512 seeds were divided evenly into three replications with 84 seeds planted for each replication at six unique locations across central Illinois. The results for germination, growth, and product yield over the 2017 growing season is presented. Overall no statistically significant difference in the yield of corn harvested was found between the control and any of the five treatments. This is likely due to the already near-100% germination rate of the corn hybrid used in the study and the use of the Poncho/VOTiVO protective coating on every sample.

A sensitive electrochemical sensor for in vitro detection of parathyroid hormone based on a MoS2-graphene composite.

This paper reports a biosensor based on a MoS2-graphene (MG) composite that can measure the parathyroid hormone (PTH) concentration in serum samples from patients. The interaction between PTH and MG was analysed via an electrochemical sensing technique. The MG was functionalized using l-cysteine. Following this, PTH could be covalently immobilized on the MG sensing electrode. The properties of MG were evaluated using scanning electron microscopy, high-resolution transmission electron microscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectrometry. Following optimization of immobilized materials-such as MG, PTH, and alkaline phosphatase (ALP)-the performance of the MG sensor was investigated via cyclic voltammetry, to assess its linearity, repeatability, and reproducibility. Electrochemical impedance spectroscopy was performed on graphene oxide (GO) and MG-modified electrodes to confirm the capture of a monoclonal antibody (MAb) targeting PTH. Furthermore, the ALP-PTH-MG sensor exhibits a linear response towards PTH from artificial serum over a range of 1-50 pg mL-1. Moreover, patient sera (n = 30) were evaluated using the ALP-PTH-MG sensor and compared using standard equipment (Roche E 170). The P-value is less than 0.01 when evaluated with a t-test using Welch's correction. This implies that the fabricated sensor can be deployed for medical diagnosis.

Low-Temperature Synthesis of Large-Scale Molybdenum Disulfide Thin Films Directly on a Plastic Substrate Using Plasma-Enhanced Chemical Vapor Deposition.

By plasma-enhanced chemical vapor deposition, a molybdenum disulfide (MoS2 ) thin film is synthesized directly on a wafer-scale plastic substrate at below 300 °C. The carrier mobility of the films is 3.74 cm(2) V(-1) s(-1) . Also, humidity is successfully detected with MoS2 -based sensors fabricated on the flexible substrate, which reveals its potential for flexible sensing devices.

Nanoetching process on silicon solar cell wafers during mass production for surface texture improvement.

Major challenge in nanotechnology is to improve the solar cells efficiency. This can be achieved by controlling the silicon solar cell wafer surface structure. Herein, we report a KOH wet etching process along with an ultrasonic cleaning process to improve the surface texture of silicon solar cell wafers. We evaluated the KOH temperature, concentration, and ultra-sonication time. It was observed that the surface texture of the silicon solar wafer changed from a pyramid shape to a rectangular shape under edge cutting as the concentration of the KOH solution was increased. We controlled the etching time to avoid pattern damage and any further increase of the reflectance. The present study will be helpful for the mass processing of silicon solar cell wafers with improved reflectance.

The label free DNA sensor using a silicon nanowire array.

Biosensors based on silicon nanowire (Si-NW) promise highly sensitive dynamic label free electrical detection of various biological molecules. Here we report Si-NW array electronic devices that function as sensitive and selective detectors of as synthesized 2D DNA lattices with biotins. The Si-NW array was fabricated using top-down approach consists of 250 nanowires of 20 µm in length, equally spaced with an interval of 3.2 µm. Measurements of photoresistivity of the Si-NW array device with streptavidin (SA) attached on biotinylated DNA lattices at different concentration were observed and analyzed.. The conductivity in the DNA lattices with protein SA shows significant change in the photoresistivity of Si-NW array device. This Si-NW based DNA sensor would be one of very efficient devices for direct, label free DNA detection and could provide a pathway to immunological assays, DNA forensics and toxin detection in modern biotechnology.