Long‐Range Ordered Crystals of 3D InorganicOrganic Heterojunctions via Colloidal Lithography

Colloidal lithography (CL) has evolved as an alternative to conventional photo‐ and electron‐beam lithography to pattern surfaces with nanometer range resolution. As CL offers substrate‐independent precise positioning and patterning of nanomaterials as long‐range ordered crystals, this has seen new opportunities in optoelectronics. Herein, the scope of CL is expanded to fabricate for the first time, 3D organicinorganic heterojunction photocatalysts with well‐controlled spacing and coverage density. To achieve this, monodisperse polystyrene (PS) beads of different sizes are used as colloidal masks on a ZnO substrate. Electron beam assisted silver deposition onto these PS masks, and subsequent removal of PS lead to the formation of patterns of silver nanostars on the ZnO thin film. The solidvapor reaction of silver nanostars with a metal‐coordinating charge‐transfer complex of 7,7,8,8‐tetracyanoquinodimethane (TCNQ) allows spontaneous conversion of Ag nanostars to the large aspect ratio nanowires of metalorganic AgTCNQ semiconductors. This strategy, combining the strengths of CL with high electron affinity of TCNQ molecules allows facile fabrication of long‐range patterns of the heterojunctions of organic (AgTCNQ) and inorganic (ZnO) semiconductors. These surface‐supported 3D heterojunctions act as outstanding photocatalysts through their ability to efficiently separate the electronhole pairs and thus increasing the electronhole life times

Co3O4 needles on Au honeycomb as a non-invasive electrochemical biosensor for glucose in saliva

While glucose monitoring technology is widely available, the continued prevalence of diabetes around the world coupled with its debilitating effects continues to grow. The significant limitations which exist in the current technology, instils the need for materials capable of non-invasive glucose detection. In this study a unique non-enzymatic electrochemical glucose sensor was developed, utilising a gold honeycomb-like framework upon which sharp Co3O4 needles are anchored. This composite nanomaterial demonstrates excellent sensing performance in glucose concentrations ranging between 20 μM and 4 mM, exceeding the range required for non-invasive glucose sensing. In conjunction with this high sensitivity (2.014 mA mM−1·cm−2), the material possesses excellent selectivity towards glucose for commonly interfering physiological species such as uric acid and ascorbic acid. Glucose detection in synthetic saliva was then performed showing excellent capability in the low concentration range (20 μM1 mM) for non-invasive sensing performance. Further tests showed good selectivity of the sensor in physiological contaminants commonly found in saliva such as cortisol and dopamine. This development provides excellent scope to create next-generation non-invasive diabetes monitoring platforms, with excellent performance when detecting low glucose concentrations in complex solutions such as saliva

Multi-directional electrodeposited gold nanospikes for antibacterial surface applications

The incorporation of high-aspect-ratio nanostructures across surfaces has been widely reported to impart antibacterial characteristics to a substratum. This occurs because the presence of such nanostructures can induce the mechanical rupture of attaching bacteria, causing cell death. As such, the development of high-efficacy antibacterial nano-architectures fabricated on a variety of biologically relevant materials is critical to the wider acceptance of this technology. In this study, we report the antibacterial behavior of a series of substrata containing multi-directional electrodeposited gold (Au) nanospikes, as both a function of deposition time and precursor concentration. Firstly, the bactericidal efficacy of substrata containing Au nanospikes was assessed as a function of deposition time to elucidate the nanopattern that exhibited the greatest degree of biocidal activity. Here, it was established that multi-directional nanospikes with an average height of ∼302 nm ± 57 nm (formed after a deposition time of 540 s) exhibited the greatest level of biocidal activity, with ∼88% ± 8% of the bacterial cells being inactivated. The deposition time was then kept constant, while the concentration of the HAuCl4 and Pb(CH3COO)2 precursor materials (used for the formation of the Au nanospikes) was varied, resulting in differing nanospike architectures. Altering the Pb(CH3COO)2 precursor concentration produced multi-directional nanostructures with a wider distribution of heights, which increased the average antibacterial efficacy against both Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus bacteria. Importantly, the in situ electrochemical fabrication method used in this work is robust and straightforward, and is able to produce highly reproducible antibacterial surfaces. The results of this research will assist in the wider utilization of mechano-responsive nano-architectures for antimicrobial surface technologies

Donor-induced performance tuning of amorphous SrTiO3 memristive nanodevices: Multistate resistive switching and mechanical tunability

Metal-oxide valence-change memristive devices are the key contenders for the development of multilevel nonvolatile analog memories and neuromorphic computing architectures. Reliable low energy performance and tunability of nonlinear resistive switching dynamics are essential to streamline the high-density circuit level integration of these devices. Here, manipulation of room temperature-synthesized defect chemistry is employed to enhance and tune the switching characteristics of high-performance amorphous SrTiO3 (a-STO) memristors. Substitutional donor (Nb) doping with low concentrations in the a-STO oxide structure allows extensive improvements in energy requirements, stability, and controllability of the memristive performance, as well as field-dependent multistate resistive switching. Evidence is presented that room temperature donor doping results in a modified insulator oxide where dislocation sites act as charge carrier modulators for low energy and multilevel operation. Finally, the performance of donor-doped a-STO-based memristive nanodevices is showcased, with the possibility of mechanical modulation of the nonlinear memristive characteristics of these devices demonstrated. These results highlight the potential of donor-doped a-STO nanodevices for high-density integration as analog memories and multifunctional alternative logic elements

Zinc Titanate Nanoarrays with Superior Optoelectrochemical Properties for Chemical Sensing

In this report, the gas sensing performance of zinc titanate (ZnTiO3) nanoarrays (NAs) synthesized by coating hydrothermally formed zinc oxide (ZnO) NAs with TiO2 using low-temperature chemical vapor deposition is presented. By controlling the annealing temperature, diffusion of ZnO into TiO2 forms a mixed oxide of ZnTiO3 NAs. The uniformity and the electrical properties of ZnTiO3 NAs made them ideal for light-activated acetone gas sensing applications for which such materials are not well studied. The acetone sensing performance of the ZnTiO3 NAs is tested by biasing the sensor with voltages from 0.1 to 9 V dc in an amperometric mode. An increase in the applied bias was found to increase the sensitivity of the device toward acetone under photoinduced and nonphotoinduced (dark) conditions. When illuminated with 365 nm UV light, the sensitivity was observed to increase by 3.4 times toward 12.5 ppm acetone at 350 °C with an applied bias of 9 V, as compared to dark conditions. The sensor was also observed to have significantly reduced the adsorption time, desorption time, and limit of detection (LoD) when excited by the light source. For example, LoD of the sensor in the dark and under UV light at 350 °C with a 9 V bias is found to be 80 and 10 ppb, respectively. The described approach also enabled acetone sensing at an operating temperature down to 45 °C with a repeatability of >99% and a LoD of 90 ppb when operated under light, thus indicating that the ZnTiO3 NAs are a promising material for low concentration acetone gas sensing applications