Graphene oxidation: thickness-dependent etching and strong chemical doping

Patterned graphene shows substantial potential for applications in future molecular-scale integrated electronics. Environmental effects are a critical issue in a single-layer material where every atom is on the surface. Especially intriguing is the variety of rich chemical interactions shown by molecular oxygen with aromatic molecules. We find that O 2 etching kinetics vary strongly with the number of graphene layers in the sample. Three-layer-thick samples show etching similar to bulk natural graphite. Single-layer graphene reacts faster and shows random etch pits in contrast to natural graphite where nucleation occurs at point defects. In addition, basal plane oxygen species strongly hole dope graphene, with a Fermi level shift of approximately 0.5 eV. These oxygen species desorb partially in an Ar gas flow, or under irradiation by far UV light, and readsorb again in an O 2 atmosphere at room temperature. This strongly doped graphene is very different from "graphene oxide" made by mineral acid attack.     

Effects of Pre‐reducing Sb‐Doped SnO2 Electrodes in Viologen‐Anchored TiO2 Nanostructure‐Based Electrochromic Devices

In this paper, we investigate the effects of pre‐reducing Sb‐doped SnO₂ (ATO) electrodes in viologen‐anchored TiO₂ (VTO) nanostructure–based electrochromic devices. We find that by pre‐reducing an ATO electrode, the operating voltage of a VTO nanostructure–based electrochromic device can be lowered; consequently, such a device can be operated more stably with less hysteresis. Further, we find that a pre‐reduction of the ATO electrode does not affect the coloration efficiency of such a device. The aforementioned effects of a pre‐reduction are attributed to the fact that a pre‐reduced ATO electrode is more compatible with a VTO nanostructure–based electrochromic device than a non‐pre‐reduced ATO electrode, because of the initial oxidized state of the other electrode of the device, that is, a VTO nanostructure–based electrode. The oxidation state of a pre‐reduced ATO electrode plays a very important role in the operation of a VTO nanostructure–based electrochromic device because it strongly influences charge movement during electrochromic switching.     

Radicals masquerading as electrophiles: dual orbital effects in nitrogen-philic acyl radical cyclization and related addition reactions

Free-radical chemistry has come a long way in a relatively short period of time. The synthetic practitioner takes for granted the wealth of mechanistic and rate constant data now available and can apply free-radical techniques to the synthesis of many different classes of target molecule with confidence. Despite this, there are still mechanistic anomalies that need to be addressed. This Account highlights recent work involving nucleophilic radicals with low-lying unoccupied orbitals, such as acyl, oxyacyl, silyl, stannyl, and germyl radicals. Through interesting singly occupied molecular orbital (SOMO)-pi* and highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) interactions during these reactions, the radicals involved are able to mask as electrophiles, providing high levels of regiocontrol and efficient methods for the synthesis of important heterocycles.     

On the derivation of graphically inspired feasibility constraints for distillation network synthesis

We propose the integration of simplified graphically inspired feasibility constraints into optimization-based models for distillation network synthesis. The approach facilitates the use of surrogate, potentially data-based, distillation column models while considering feasibility in a computationally efficient manner. The proposed approach can aid the formulation of efficient approaches for preliminary distillation network synthesis.     

Ratio of aerosol and gases of radioactive chlorine and particle size distribution of aerosol formed by high-energy proton irradiation

To estimate internal doses due to the inhalation of radionuclides produced by the nuclear spallation of the air nuclei in high-energy proton accelerator facilities, the physicochemical properties of radionuclides are very important. Thus, the ratio of aerosol and gases of 38Cl and 39Cl formed by irradiating argon gas-added air with a 48 MeV proton beam has been measured. Radionuclides of 38Cl and 39Cl exist as aerosol, acid gas and non-acid gas. The percentages of activity of 38Cl and 39Cl aerosols are about 80%. The number size distributions of non-radioactive aerosol were characterised by two peaks with diameters of 10-20 nm and larger than 20 nm. As a result predicted by a simple surface model, it was found that the activity size distribution of 38Cl aerosols can be regarded as that having a single peak at 120 nm.     

Effect of pre-existing oxide film on the electrochemical fabrication of nanoporous alumina film

Different thickness of barrier-type oxide film was intentionally grown on the Al metal surface and the effect of barrier film on the formation of nanoporous aluminum oxide film during anodization was investigated to control the nanopore structure. Analysis of potential transients during anodization indicated that anodic oxide film is initially overlaid on the barrier film but the anodic film is more facile to dissolve than barrier film. As the thickness of barrier film increases, both nanopore diameter and density decrease but the pore length is irrespective of barrier-film thickness.     

Electrochemical fabrication of SrTiO3 nanowires with nanoporous alumina template

Strontium titanate nanowires were electrochemically synthesized with nanoporous alumina template. Both chemical and electrical variables such as electrolyte pH, temperature, and current waveform were modulated to investigate the synthesis process of SrTiO3 nanowires. Superimposed cathodic pulse and diffusion time accelerated the growth of SrTiO3 nanowires, which suggested that the concentration of H+ and Sr2+ ion inside alumina template had a strong influence on the formation of SrTiO3 nanowires. Morphology and crystallinity of SrTiO3 nanowires were investigated with scanning electron microscope, X-ray diffractometer and energy dispersive X-ray spectroscopy.     

Low temperature synthesis of colloidal CdSe quantum dots

In this study, the CdSe nanocrystals were prepared in phenyl ether and octyl amine to investigate the variations of their size, bandgap energy, and photoluminescence with growth time and temperature. The sizes of the CdSe nanocrystals were measured using High Resolution Transmission Electron Microscopy (HRTEM), and found to be nearly monodisperse for relatively low growth temperature, 130 degrees C. Their optic properties were characterized by photoluminescence measurements, which showed that the colors of the nanocrystals could be controlled. The bandgap energies of the nanocrystals were calculated theoretically and found to be in accord with quantum confinement theory. This synthetic method requires only a cheap solvent and offers good reproducibility at a lower price.     

Numerical optimization study to install air curtain in a subway tunnel by using design of experiment

Subways are a major mode of public transportation in metropolitan cities. A proper ventilation system is required to maintain indoor air quality in subway tunnels. Platform screen doors improve the platform environment but degrade air quality in subway tunnels. Trains transport fine particles from the tunnel into the platform. An air curtain installation in the subway tunnel permits traffic and reduces the transfer of bacteria and fine particles. The existing tunnel of Seoul subway was investigated by using computational fluid dynamics and design of experiment method for optimum air curtain installations. The flow field of the subway tunnel was computed by using ANSYS CFX software. Minitab software was used to generate the design process and to analyze the computational results. The computational domain of the existing tunnel included two natural ventilation shafts, one mechanical shaft, and the twin tracks. The height, width, and length of each track were 6, 4, and 400 m, respectively. The air curtain installation area was located between the natural and the mechanical ventilation shafts of Rrack 1. The design variables for the optimization study were the width, velocity, and installation location of the air curtain. The object function for optimization was mass flow rate at the natural ventilation shaft. The length of the air curtain was fixed at 4 m. The predicted mass flow rates were analyzed with the design variables by using the response surface method (RSM). The optimum values of the design variables, i.e., velocity, width, and installation location were 25 m/s, 0.2 m, and 5.8195 m, respectively. The maximum mass flow rate with the optimum design values was 114.4447 kg/s. The optimum values of the design variables were validated by computing the tunnel with the optimum values from RSM. The mass flow rate in the natural ventilation shaft 1 was 114.2 kg/s, as predicted. The optimization study can be helpful to set the optimum design conditions for the subway ventilation system.     

An analytical expression for end milling forces and tool deflection using Fourier series

In this research, a novel and generalized analytical expression of cutting force and tool deflection in end milling is presented as a function of tool rotational angle and other cutting parameters. The discontinuous cutting force function caused by periodic tool entry and exit is changed to an integrable continuous function using Fourier series expansion. Tool deflection is also formulated explicitly by the direct integration of the distributed loads along the helical cutting edges. Cutting conditions, tool geometry, runout components, and the stiffness of tool clamping part are considered in estimating the cutting force and tool deflection. Cumbersome computational procedures needed to check whether segmented cutting edges are engaged in cutting or not are eliminated by this proposed method. The presented analytical approach has advantages in flexibility, prediction time, and accuracy as compared with other numerical techniques. In addition, the effects of cutting conditions and run-outs, such as eccentricity and tilting on the cutting force and tool deflection, can be analyzed quantitatively in the time domain or frequency domain. The validity and effectiveness of the suggested method are verified through a series of cutting tests. The model presented in this research can be used in real-time machining error estimation and cutting condition selection for error minimization since the form accuracy is easily estimated from the acquired tool deflection curve.