This study presents in situ detection of Zn2+ using a novel two-step square-wave anodic stripping voltammetry (SWASV)-based needle-type microsensor for citrus plant applications. A double-barrel bismuth/platinum (Bi/Pt) microelectrode was fabricated with a solid metal tip (~110 µm), which was durable enough to penetrate the thick skin of the citrus leaves and sensitive enough to detect ppb changes in Zn2+ concentration using SWASV. The microelectrode tip size was also determined to reduce mass transport limitation and improve limit of detection. Overall, the developed Bi/Pt microelectrode successfully measured Zn2+ concentrations within the vascular bundle of citrus plants.

This work focuses on the syntheses of Zn-enriched PtZn nanoparticle electrocatalysts by solution combustion for ethanol oxidation reaction (EOR). Analytical techniques of x-ray diffraction, transmission electron microscopy (TEM), scanning electron microscopy, TEM/scanning TEM-energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy are used for the characterization of electrocatalysts. Cyclic voltammetry and chronoamperometry are applied for the electrocatalysis of C2H5OH and stability test in an alkaline medium, respectively. Electrochemical data show that PtZn/C has improved electrocatalytic activity by ~2.3 times compared with commercial Pt/C, in addition to having earlier onset potential and better stability for EOR. The variation of fuel amount in the synthesis has affected crystallite sizes, electronic, and electrochemical properties in electrocatalysts.

We report fabrication of 200 mm silicon (Si)-wafer mold structure for polydimethylsiloxane (PDMS) microfluidic devices to demonstrate a real-time fluorescence imaging of single DNA molecules. Conventional photolithography with deep reactive ion etching process allows us to build a “mesa”-type Si mold with a nanoscallop sidewall geometry aiding PDMS residue-free process. By optimizing fluorescence microscopy with the fabricated PDMS chamber, we obtain a protocol to visualize the motions of single DNA molecules. This integrative PDMS-based single-molecule imaging system can, in principle, be used as a platform to study biochemical reactions occurring in proteins, nucleotides, and vesicles.

A new phase of carbon named Q-carbon is found to be over 40% harder than diamond. This phase is formed by nanosecond laser melting of amorphous carbon and rapid quenching from the super-undercooled state. Closely packed atoms in molten metallic carbon are quenched into Q-carbon with 80–85% sp3 and the rest sp2. The number density of atoms in Q-carbon can vary from 40% to 60% higher than diamond cubic lattice, as the tetrahedra packing efficiency increases from 70% to 80%. Using this semiempirical approach, the corresponding increase in Q-carbon hardness is estimated to vary from 48% to 70% compared to diamond.

The present work demonstrates controllable directive radiation of a dipolar emitter coupled to a substrate-supported dielectric nanowire antenna. Nanoactuators, transparent-conducting oxides, and graphene are integrated into the substrate, respectively, to establish tunable antenna platforms in visible, near-infrared (IR), and far-IR frequency regimes. We exploit the substrate-induced interference effects and tunability mechanisms in each antenna system to achieve directive radiation with real-time steering capability. The design and modeling are rigorously carried out using an efficient and accurate semi-analytical framework based on transition matrix formulation. Each configuration is optimized to achieve maximal steering range while attaining a proper gain. Owing to subwavelength footprint, enhanced directionality, real-time tunability, and fairly simple geometry, the proposed platforms are ideal candidates for nanoantenna synthesis.

Germanium is a small-gap semiconductor that efficiently absorbs visible light, resulting in photoexcited electrons predicted to be sufficiently energetic to reduce H2O for H2 gas evolution. In order to protect the surface from corrosion and prevent surface charge recombination in contact with aqueous pH 7 electrolyte, we grew epitaxial SrTiO3 layers of different thicknesses on p-Ge (001) surfaces. Four-nanometer SrTiO3 allows photogenerated electrons to reach the surface and evolve H2 gas, while 13 nm SrTiO3 blocks these electrons. Ambient pressure x-ray photoelectron spectroscopy indicates that the surface readily dissociates H2O to form OH species, which may impact surface band bending.

Diamond stands out in its ability to host hundreds of color centers, the most studied of which may be the nitrogen-vacancy and NE8 centers. The NE8 center, in particular, can generate single photons at an energy of 1.56 eV, but synthesis efforts are low yield and lack precise control of the defect structure and resulting optical properties. Complementing a bottom-up synthesis effort, we develop a rapid-screening computational approach for screening potential color centers in nanodiamond, focusing here on the nickel–nitrogen complexes. Formation and optical absorption energies are characterized with respect to defect stoichiometry and structure.

A longitudinal field component parallel to the wave vector is generally considered in nonlocal optical response. Longitudinal volume plasmons accompanied by inhomogeneous internal field optically break symmetry for isotropic metal nanoparticles. Here, natural circular dichroism in the interband transitions of TiN nanocubes, Au nanospheres, and Cu nanospheres in solution is presented. A field gradient or volume plasmons exert an electric force and consequently Lorentz force on bound valence-band electrons inside the nanoparticles. It is generalized that interband transitions in nanoparticles intrinsically produce a positive rotational strength and optical right-handedness. Electromechanical chiralty is introduced to explain the optical activity of achiral nanoparticles.

This work presents an in-depth study of how the choice of boundary conditions can impact upon the calculated photovoltage and photocurrent in photoelectrochemical (PEC) devices. Utilizing a floating boundary condition for the electrostatic potential and pseudo-Schottky boundary conditions for the interfacial electron/hole currents, we show simultaneous calculation of photovoltage and photocurrent. We also explore the significance of capturing the photovoltage, with proper boundary conditions, to accurately replicate practical photocurrent along with the realistic band alignments. Finally, our results decouple the interfacial hole transfer from the recombination at the interface/space-charged region and suggest possible methods to engineer the mesoscopic transfer process at PEC electrodes.

End-stage renal disease (ESRD) is a life-threatening illness that presents significant healthcare challenges. About 90% of ESRD patients receive hemodialysis treatment, but the currently available hemodialysis systems are bulky and prone to complications. We report the design of a microfluidic hemodialysis device composed of two polydimethylsiloxane (PDMS) chambers separated by a cellulose ester (CE) membrane. The polyethylene glycol-passivated PDMS and CE surfaces reduced platelet adhesion by 74% and 86%, respectively. Moreover, the device exhibited a higher urea clearance rate per unit area than a healthy kidney. The reported design sets the foundation for a next-generation biomimetic portable hemodialysis device.

The electrochemical catalytic effects of the NiO islands and layer on n-type GaN were investigated. The NiO islands covered some parts of the GaN surface and were seen to improve photoanodic current and prevent photoanodic corrosion. However, the NiO layer was found to worsen the photoanodic current. Hole transportation is thought to occur from the GaN valence band edge to the NiO valence band edge in their surface plane direction due to the band alignment. In addition, the electron capture for water oxidation is expected to be the valence band edge of the NiO instead of the intermediate state.

Geometrical features are known to be very important in neuronal growth and the formation of neuronal networks. We present an experimental and theoretical investigation of axonal growth and dynamics for neurons cultured on patterned polydimethylsiloxane surfaces. We utilize fluorescence microscopy to image the axonal dynamics and show that these substrates impart a strong directional bias to neuronal growth. We model axonal dynamics using a general stochastic model and use this framework to extract key dynamical parameters. These results provide novel insight into how geometrical cues influence neuronal growth and represent important advances toward bioengineering neuronal growth platforms.

Biologic neural networks are immersed in common electrolyte environment, and homeoplasticity or global factors of this environment are forcing specific normalization functions that regulate the overall network behavior. In this work, a common electrolyte is used to gate a grid of organic electrochemical devices. The electrolyte functions as a global parameter that controls collectively the device grid. Statistical analysis of the grid and the subsequent definition of global metrics reveal that the grid behaves similarly to a single device. This global control modulates the gain of the device grid, a phenomenon analog to multiplicative scaling in biologic networks. This work demonstrates the potential use of electrolytes as homeostatic media in neuromorphic device architectures.

Ag deposition-based multicolor electrochromic (EC) device we reported can switch various optical states among transparent, black, silver, cyan, magenta, and yellow by only using electrochemical deposition of Ag. However, the EC device had poor color retention property under open-circuit state because of dissolution of deposited Ag metal by Cu2+ ions, which is essential because it acts as redox material at counter electrode. Here, we introduced an anion exchange membrane to separate Cu2+ from the Ag deposit. The improved device achieved longer retention time of colored state. It is effective to maintain the coloring state without electric power for practical application.

In this work, we present a solvothermal method to prepare bismuth (Bi)-doped CuGaS2 chalcopyrite nanocrystals ink and apply it to an all-solution-processed approach for the preparation of films with a thickness of approximately 730 nm and with enhanced optical properties and lower band gap energy than the undoped semiconductor films. The low-cost deposition method is comprised by spray deposition of the chalcogenide nanocrystals ink onto the molybdenum substrates, producing microcrystalline films with grains larger than 400 nm originated from coalescence of Bi-doped nanocrystals. Bi-doped CuGaS2 microcrystalline films are a good candidate to be applied as an absorber layer in thin-film solar cells.

The emerging planar subwavelength microlens has attracted wide attention recently. There exists a trade-off in the selection of phase shifter materials for the lens designed with linearly polarized incidence. In this work, we have discovered that it is possible to utilize tapered nanostructure to increase the transmission of phase shifters built with high refractive index materials. A typical grating microlens is demonstrated to examine the effectiveness of taper-enhancement effect—the focus efficiency is increased from 9% to 28% with the properly designed tapered sidewall. Our work will provide a novel method to enhance performance using high refractive index materials in the emerging microlens field.

We report on the low-temperature electrical characterization of bilayer MoS2 treated with increasing dose of oxygen:argon (1:3) plasma. We characterize the effective Schottky barrier heights as a function of plasma exposure time and observe a significant barrier lowering, with no accompanying p-type conduction in the negative bias region. Furthermore, we observe a crossover in the temperature-dependent conduction regimes below 181 K due to the plasma exposure. The Efros–Shklovskii (ES) hopping regime is seen to transform upon plasma exposure to a mixed ES/thermally-activated regime at high temperatures, and to a strongly short-range Arrhenius regime at low temperatures. We attribute the observed crossovers to a critical defect density created by the surface reaction with the plasma.

To evaluate whether the photocatalysis efficiency of titanium oxide (TiO2) increases under the shading of carbon aerogel (CA), super black CA/TiO2 composite sheets were directly fabricated by physical mixing of CA, TiO2 powder, and binder. It was found that the photocatalysis efficiency of composite sheets were higher than that of pure TiO2 sheet. We attribute this phenomenon to the hot electrons coupling between CA and TiO2. Besides the direct light absorption of TiO2, the hot electrons generating and indirect energy transfer from CA to TiO2 may enhance the photocatalysis efficiency of TiO2.

We have studied the effect of hydrostatic pressure on the confined exciton in a spherical core–shell quantum dot. Using a simple variational approach under the framework of effective mass approximation, we have computed the excitonic binding energy as a function of the shell thickness under the applied hydrostatic pressure. Our results show that the ground state binding energy of exciton depends greatly on the shell thickness, which tends to the two-dimensional limit of 4RX, when the ratio a/b tends to unity. The numerical calculations also suggest that the applied hydrostatic pressure favors the attraction between electrons and holes so the excitonic binding energy increases when pressure increases.

We provide insights pertaining the dependence of undercooling in the formation of graphite, nanodiamonds, and Q-carbon nanocomposites by nanosecond laser melting of diamond-like carbon (DLC). The DLC films are melted rapidly in a super-undercooled state and subsequently quenched to room temperature. Substrates exhibiting different thermal properties—silicon and sapphire, are used to demonstrate that substrates with lower thermal conductivity trap heat flow, inducing larger undercooling, both experimentally and theoretically via finite element simulations. The increased undercooling facilitates the formation of Q-carbon. The Q-carbon is used as nucleation seeds for diamond growth via laser remelting and hot-filament chemical vapor deposition.