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We present a direct observation of carbon-atom tunneling in the flipping reaction of formaldehyde between its two mirror-reflected states on a Cu(110) surface using low-temperature scanning tunneling microscopy (STM). The flipping reaction was monitored in real time, and the reaction rate was found to be temperature independent below 10 K. This indicates that this reaction is governed by quantum mechanical tunneling, albeit involving a substantial motion of the carbon atom (∼1 Å). In addition, deuteration of the formaldehyde molecule resulted in a significant kinetic isotope effect (RCH2O/RCD2O ≈ 10). The adsorption structure, reaction pathway, and tunneling probability were examined by density functional theory calculations, which corroborate the experimental observations.

Hydration layers play a key role in many technical and biological systems, but our understanding of these structures remains very limited. Here, we investigate the molecular processes driving hydration of a chiral metal-organic surface, bitartrate on Cu(110), which consists of hydrogen-bonded bitartrate rows separated by exposed Cu. Initially water decorates the metal channels, hydrogen bonding to the exposed O ligands that bind bitartrate to Cu, but does not wet the bitartrate rows. At higher temperature, water inserts into the structure, breaks the existing intermolecular hydrogen bonds, and changes the adsorption site and footprint. Calculations show this process is driven by the creation of stable adsorption sites between the carboxylate ligands, to allow hydration of O-Cu ligands within the interior of the structure. This work suggests that hydration of polar metal-adsorbate ligands will be a dominant factor in many systems during surface hydration or self-assembly from solution.

Heterogeneous ice nucleation is a key process in many environmental and technical fields and is of particular importance in modeling atmospheric behavior and the Earth’s climate. Despite an improved understanding of how water binds at solid surfaces, no clear picture has emerged to describe how 3D ice grows from the first water layer, nor what makes a particular surface efficient at nucleating bulk ice. This study reports how water at a corrugated, hydrophilic/hydrophobic surface restructures from a complex 2D network, optimized to match the solid surface, to grow into a continuous ice film. Unlike the water networks formed on plane surfaces, the corrugated Cu(511) surface stabilizes a buckled hexagonal wetting layer containing both hydrogen acceptor and donor sites. First layer water is able to relax into an “icelike” arrangement as further water is deposited, creating an array of donor and acceptor sites with the correct spacing and corrugation to stabilize second layer ice and allow continued commensurate multilayer ice growth. Comparison to previous studies of flat surfaces indicates nanoscale corrugation strongly favors ice nucleation, implying surface corrugation will be an important aspect of the surface morphology on other natural or engineered surfaces.

Dissociation of molecular oxygen is an important elementary process in heterogeneous catalysis. Here, we report on a real-space observation of oxygen photolysis on the Ag(110) surface at 78 K by far- and near-field excitation in the ultraviolet–near-infrared range using a low-temperature scanning tunneling microscope (STM) combined with wavelength-tunable laser excitation. The photolysis of isolated oxygen molecules on the surface occurs even by visible light with the cross section of ∼10−19 cm2. Time-dependent density functional theory calculations reveal optical absorption of the hybridized O2–Ag(110) complex in the visible and the near-infrared range which is associated with the oxygen photolysis. We suggest that the photolysis mechanism involves a direct charge transfer process. We also demonstrate that the photolysis can be largely enhanced in plasmonic STM junctions, and the cross section is estimated to be ∼10−17 cm-2in the visible and the near-infrared range, which appears to be an interesting feature of plasmon-induced reactions from the perspective of photochemical conversion with the aid of solar energy.

Highly corrugated, stepped surfaces present regular 1D arrays of binding sites, creating a complex, heterogeneous environment to water. Rather than decorating the hydrophilic step sites to form 1D chains, water on stepped Cu(511) forms an extended 2D network that binds strongly to the steps but bridges across the intervening hydrophobic Cu(100) terraces. The hydrogen-bonded network contains pentamer, hexamer, and octomer water rings that leave a third of the stable Cu step sites unoccupied in order to bind water H down close to the step dipole and complete three hydrogen bonds per molecule.

After growth of graphene by chemical vapour deposition on copper foil, Cu(4 1 0) facets were distinguished from Cu(1 0 0) facets using the low energy electron diffraction technique. Evolution of the diffraction patterns was studied after oxidation of the Cu substrate and subsequent annealing in ultrahigh vacuum. An ordered Cu(4 1 0)–O phase was then identified. The distinction between Cu(4 1 0) and Cu(4 1 0)–O is relevant in determination of the coupling between graphene and the substrate.

Significant changes in the Raman spectrum of single-layer graphene grown on a copper film were observed after the spontaneous oxidation of the underlying substrate that occurred under ambient conditions. The frequencies of the graphene G and 2D Raman modes were found to undergo red shifts, while the intensities of the two bands change by more than an order of magnitude. To understand the origin of these effects, we further characterized the samples by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and atomic force microscopy (AFM). The oxidation of the substrate produced an appreciable corrugation in the substrate without disrupting the crystalline order of the graphene overlayer and/or changing the carrier doping level. We explain the red shifts of the Raman frequencies in terms of tensile strain induced by corrugation of the graphene layer. The changes in Raman intensity with oxidation arise from the influence of the thin cuprous oxide film on the efficiency of light coupling with the graphene layer in the Raman scattering process.

Ag nanowire with the receiving and transmitting Ag bow tie antenna pairs at its incident and emission ends was patterned on the SiO(2) substrate to realize an enhanced surface plasmon emission with a factor of 45 compared to the single Ag nanowire without antenna pairs. The receiving and transmitting bow tie antenna pairs enhanced the plasmon coupling and emission efficiencies of the Ag nanowire. And the maximum plasmon emission sensitively depended on the length of Ag nanowire, the arm length of bow tie antennas, and the incident angle of optical excitation. This enhanced plasmon emission was confirmed by finite-difference time-domain simulations and explored with analytical calculations using the impedance matching theory at optical frequency.

The surface plasmon polariton (SPP) coupling and enhancement in silver nanowire–nanoantenna structure is proposed and simulated by using finite difference time domain method. The results demonstrate that three-arm antenna can effectively enhance the coupling efficiency at the incident end and the SPP field intensity at the emission end. The enhancement factor, which is defined as the ratio of the SPP field intensity at the emission end with and without the three-arm antenna, for the various antenna arm lengths and incident wavelengths under different incident angles are calculated. The suggested structure can be served as an enhanced plasmonic waveguide for the nanophotonic and plasmonic circuits in the future.

Agriculture in Taiwan is input-intensive. Chemical fertilizers are heavily used, and most arable land contains less than 2% of soil organic matter (SOM). To improve soil quality, to make agriculture sustainable, and to avoid over-production of rice, paddy rice–upland rotation and application of organic substances have been widely promoted. A change in the system often begins to alter the SOM content which takes from several up to even a hundred years to stabilize into a new SOM level. The purpose of this study was to find methods of determining long-term changes in SOM based on short-term data and to evaluate the effects of different kinds of organic materials in paddy–upland rotation. Organic matter was supplied as green manure, compost, and peat at similar intensity. SOM data were collected from the 1st to the 13th year for the calibration and validation of the model that was intentionally assembled for less mechanisms yet research purpose achievable. The ratio of the quantity of organic matter applied to that retained in soil was the lowest when organic C was supplied by growing green manure and the highest, or 3.7 times the control plot, when it was supplied in the form of compost. The minimum period for which data of SOM was required to calibrate the model varied with the form of organic matter: 5 years for green manure, 6 years for compost or peat, and 7 years for the control. The minimum years of data required for reliable calibration were significantly related to the return amounts of crop residues (R2 = 0.807). In each application strategy, SOM contents in the 12th and 13th years were validated well with those predicted by the calibrated model. Relative sensitivity analysis showed that soil temperature and water are the two major factors that affected SOM content; while the humus-like portion of organic matter determined the potential to accumulate SOM. Long-term simulations suggested that it might take at least 20 years for SOM in these fields to be stabilized.

Although regionalization policies have been proven as good strategies for municipal solid waste (MSW) management in previous studies, the optimal allocation of the waste stream is significantly affected by several influential factors, thus further investigation of the impacts of these factors on regional MSW management strategies is necessary. This study demonstrated the impacts of waste-to-electricity transformation coefficient (WETC) of incinerators and the fluctuation of unit tipping fees on the regional MSW flow/allocation of the Taipei metropolitan area from practical and economic perspectives. Real-world data and linear programming were used to obtain the least-cost alternatives under different scenarios. Analytical results indicated some treatment facilities had geographic superiority and their priorities changed when actual WETCs of incinerators were considered. Treatment facilities located at weighted centers were identified. The allocation of MSW among incinerators and landfills is affected by fluctuation of unit tipping fees within a certain range. Treatment facilities sensitive to the changes in unit tipping fees were also identified. Regression equations were also established that can estimate the cost items of MSW management scenarios with different unit tipping fees. The results of this study are very useful for daily basis regulation of MSW administration.

Municipal solid waste (MSW) management is a major concern for highly urbanized societies. Among proposed MSW management systems, regionalization programs generally have received considerable attention. This study analyzes real-world operational data to assess different MSW management policies, especially regionalization strategies, and their impact on MSW management systems in the Taipei metropolitan area. Linear programming is also used to identify the minimum costs sustained by each policy. The linear programming results show that regionalization programs are more economical and also improve incinerator operation efficiency. Sensitivity analysis indicates that the minimum treatment requirement of incinerators is a very sensitive influence on the MSW flows distributed through the entire region. The MSW of several "sensitive" administrative districts will be allocated to different treatment facilities according to different management strategies. A list of preferential sequences of MSW treatment and disposal facilities can also be identified by the model presented in this study. The results of this study may provide a useful tool for aiding decision-making related to real-world MSW management problems.

The organic carbon in highly variable dye wastewater could be decomposed by microorganisms. The carbon turnover had some similarity to the transformation of soil organic matter, in that both systems had complicated carbons in the initial, intermediate and final phases, with microorganisms activating the decomposition. These processes could be simulated using a dynamic model that includes a system of differential equations representing six state variables, namely the liable decomposable fraction (LDF), the resistant decomposable fraction (RDF), active biomass (BAC), inactive biomass (BIA), decomposable (DOM) and non-decomposable organic materials (NDM). The relationship between these variables and traditional wastewater properties, e.g. chemical oxygen demand (COD) and biological oxygen demand (BOD), was defined in the context of experimental data acquisition and model evaluation. The model was calibrated by simulating several conditions, such as increasing the organic loading and hydraulic retention time (HRT), varying the C/N ratio of the organic substances in the dye wastewater and changing the treatment temperature. With the data from these experiments, a set of parameters related to the transformation rate and proportion was identified to represent the results from each experiment. This fitting allowed the model to be useful in carrying out more simulations for characterizing the efficiency of different treatment strategies. The results showed that in order to meet discharge COD regulations

We report preparation of large area quasi-one-dimensional (1D) monolayer graphene superlattices on a prototypical high-index surface Cu(410)-O and characterization by Raman spectroscopy, Auger electron spectroscopy, low-energy electron diffraction, scanning tunneling microscopy, and scanning tunneling spectroscopy. The periodically stepped substrate gives a 1D modulation to graphene, forming a superlattice of the same superperiodicity. Consequently, the moir\'e pattern is also quasi-1D, with a different periodicity. Scanning tunneling spectroscopy measurements revealed new Dirac points formed at the superlattice Brillouin zone boundary as predicted by theories.

Ordered configurations of hydrogen adatoms on graphene have long been proposed, calculated, and searched for. Here, we report direct observation of several ordered configurations of H adatoms on graphene by scanning tunneling microscopy. On the top side of the graphene plane, H atoms in the configurations appear to stick to carbon atoms in the same sublattice. Scanning tunneling spectroscopy measurements revealed a substantial gap in the local density of states in H-contained regions as well as in-gap states below the conduction band due to the incompleteness of H ordering. These findings can be well explained by density functional theory calculations based on double-sided H configurations. In addition, factors that may influence H ordering are discussed.

Selective growth of either monolayer or bilayer graphene is of great importance. We developed a method to readily tune large area graphene growth from complete monolayer to complete bilayer. In an ambient pressure chemical vapor deposition process, we used the sample temperature at which to start the H2 flow as the control parameter and realized the change from monolayer to bilayer growth of graphene on Cu foil. When the H2 starting temperature was above 700°C, continuous monolayer graphene films were obtained. When the H2 starting temperature was below 350°C, continuous bilayer films were obtained. Detailed characterization of the samples treated under various conditions revealed that heating without the H2 flow caused Cu oxidation. The more the Cu substrate oxidized, the less graphene bilayer could form.

The antenna-mediated coupling of light into Ag nanowire is investigated both in experiments and simulations. The coupling efficiency is strongly depended on the architecture of the metallic particles related to the Ag nanowire. Different incident angles of excitation laser are also tested for the maximum coupling effiecieny. The results demonstrate three-arm triangle antenna group fabricated at the incident end can effectively enhance the surface plasmon polariton (SPP) coupling and propagation. The SPP resonance and the Fabry-Perot cavity theory are used to explain the plasmon enhancement and propagation phenomena. The suggested structure can be served as an enhanced plasmonic waveguide for the nanophotonic and plasmonic circuits in the future.

Planar plasmonic focusing of surface plasmon polaritons (SPPs) by an in-plane nanostructure consisting of Ag-column arrays and an in-plane Fresnel zone plate (FZP) with a Cu grating underneath for energy compensation was demonstrated. The CdS-based hybrid plasmonic waveguide generated in the Ag-column arrays was characterized with a scanning near-field optical microscope. By using the FZP focusing structure, the SPP modes were separated from the CdS photoluminescence background and focused at the FZP focus area, and in this way, were used as the source for the SPP waveguide. Finite-difference time-domain simulations correspond with the experimental observations, suggesting that this is indeed an effective approach to control SPP coupling within the dielectric nanoribbon waveguide.

Few-layer graphene grown on Ni thin films has been studied by scanning tunneling microscopy. In most areas on the surfaces, moire patterns resulted from rotational stacking faults were observed. At a bias lower than 200 mV, only one sublattice shows up in regions without moire patterns while both sublattices are seen in regions with moire pattens. This phenomenon can be used to identify AB stacked regions. The scattering characteristics at various types of step edges are different from those of monolayer graphene edges, either armchair or zigzag.