ZnO has intrinsic semiconductor conductivity because of an unintentional doping mechanism resulting from the growth process that is mainly attributable to oxygen vacancies (VO) positioned in the bandgap. ZnO has multiple electronic states that depend on the number of vacancies and the charge state of each vacancy. In addition to the individual electron states, the vacancies have different vibrational states. We developed a high-temperature precursor vapor mask technique using Al2O3 to pattern the atomic layer deposition of ZnO and Al:ZnO layers on ZnO-based substrates. This technique was used to create a memristor device based on Al:ZnO thin films having metallic and semiconducting and insulating transport properties ZnO. We demonstrated that adding combination of Al2O3 and TiO2 barrier layers improved the resistive switching behavior. The change in the resistance between the high- and low-resistivity states of the memristor with a combination of Al2O3 and TiO2 was approximately 157%. The devices were exposed to laser light from three different laser diodes. The 450 nm laser diode noticeably affected the combined Al2O3 and TiO2 barrier, creating a high-resistivity state with a 2.9% shift under illumination. The high-resistivity state shift under laser illumination indicates defect shifts and the thermodynamic transition of ZnO defects.

The ability to control the growth of materials with nanosized precision as well as a complex hollow morphology provides rationale for the study of systems comprising both characteristics. This study explores the design of TiO hollow nanotube shells deposited by atomic layer deposition (ALD) on vertically aligned SnO nanorods grown using the vapor-liquid-solid technique. The sacrificial template approach in combination with highly conformal coating advantages of ALD resulted in a highly reproducible method to create a large surface area covered by TiO-protected SnO nanorods, which are about 60-100 nm in diameter and approximately 1 μm in length. ZnO was used as a sacrificial layer to create a 30 nm gap between SnO nanorods and 10 nm of TiO shells. Chemical etching of the sacrificial layer was used to create the desired hollow nanocomposite. A coin half-cell battery has been assembled using the TiO-protected SnO nanorods as an anode electrode and lithium foil as a counter electrode and tested for lithium storage during 70 cycles of charge/discharge in a range of 0.5-2.5 V. The TiO hollow shell functioned as a good and robust enhancer for both absolute capacity and current rate capabilities of vertically aligned SnO nanorods; an improvement in cyclic stability was also observed. This advanced self-standing hollow configuration provides several unique advantages for energy storage device applications including enhanced lithiation for superior energy storage performance.

Tin Oxide (SnO 2 ) nanorods have been successfully grown on a p-type Si substrate by a low-temperature vapor-liquid-solid (VLS) technique. Tin chloride and zinc chloride powders were used as starting materials. Surface morphologies and structural properties of the SnO 2 nanorods were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The SEM images shows distinct hierarchical growth of SnO 2 as well as the mixture with ZnO microstructures. The structural studies demonstrated rutile crystal structure SnO 2 nanorods with square-shaped facets of 40-60 nm in cross section size and 2 μm in length approximately and ZnO microrods of 10 μm diameter and 50 μm length. The fabrication of a gas sensor for acetone and ethanol vapors is also reported and its properties are discussed.

Utilizing ultraviolet photochemical reduction of gold(III) chloride trihydrate (HAuCl4), a new kind of synthesis of a highly dense gold nanoparticle film on a p-type silicon wafer was conducted. Through scanning electron microscopy and atomic force microscopy, the gold nanoparticle film was confirmed to be 90 nm thick, with an average gold nanoparticle size of 125 nm in diameter. To explore applications in surface enhanced Raman spectroscopy (SERS), a protein model of streptavidin and pegylated biotin functionalized to the surface of gold nanoparticle films was employed. Observations indicate that there was a proximity induced excitation of localized surface plasmons due to the densely packed gold nanoparticle film. Excitation of the localized surface plasmons leading to hot spots of SERS activity on the gold nanoparticle film allowing it to act as an eco-friendly and highly sensitive SERS substrate for biomedical diagnostic applications.

The formation of self-assembled monolayers (SAM) of noble metals for optical sensing applications faces serious challenges when trying to achieve simplicity, cost efficacy, specificity, and versatility. Utilizing stable, SAM-forming alkanethiols, such as glutathione (GSH), enable for simple assembly and specific detection of proteins, trace metals, oxidants, etc., thus providing a sensing platform that not only can detect low levels of reactive oxygen species (ROS) for early determination of neurodegenerative diseases, but can also assess trace metals in freshwaters and marine waters, for example. Providing a universal device for detecting varieties of target materials would adapt, simplify, and reduce costs that come from current detection methods. Our research on improving these detection methods is demonstrated using the frequency-controlled self-assembly of a GSH-functionalized gold nanoparticle (Au NP) film as a platform for highly specific and sensitive sensing. We have previously demonstrated the use of an eco-friendly and highly sensitive surface enhanced Raman spectroscopy (SERS) substrate for biomedical diagnostic applications using an ultraviolet photochemical reaction of gold (III) chloride trihydrate (HAuCl4) to create a densely packed Au NP film that exhibits localized surface plasmon resonances [1]. By the firm anchoring of a thiol group to the Au NP surface, GSH assembles the Au NPs for SERS into a densely packed, dendritic structure. At a pH of ~1 in solution, GSH forms a y-shape [2], allowing its carboxyl and amino groups to create a hydrophilic interface and, therefore, be fully available for bonding to various functional molecules. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet-visible spectroscopy (UV-vis) were used to confirm the presence of GSH and enhancement capabilities of the SERS substrate. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) confirmed the Au NP film to be 90nm thick, with an average Au NP size of 125nm in diameter [1], and visually confirmed the dendritic assembly of the GSH-functionalized Au NPs. For application purposes, this study will evaluate the trace metal Pb2+ in water. The contamination of lead, and heavy metals in general, have a damaging impact on the health of both humans and our planet. The chelation of the GSH ligands with Pb2+ enables highly specific detection of Pb2+ in water. This method provides a simple, versatile SERS substrate with a dendritic assembly that creates intriguing optical properties and broadens the capability for potential applications. [1] G. Rutherford et al., ECS J. Solid State Sci. Tech. 4, S3071 (2015). [2] M. Bieri and T. Burgi, Langmuir 2005, 21, 1354-1362. Figure 1