Abstract A sustainable world is only possible when we are ready to deliver a net zero carbon emission energy sector. In this regard, we must not only consider more renewable energy resources but also find alternate paths for making some popular molecules like NH 3 and urea for a lesser carbon footprint. This perspective article summarizes the recent progress of the photocatalytic synthesis of NH 3 , urea, and some amino acids using novel nanomaterials where we have focused on various approaches to catalyst design like metal oxides, metal sulfides, metal‐free catalysts, and biomimicking catalysts for ambient condition N 2 activation. Later we discussed general reaction pathways, a detailed mechanistic overview, and future material layout for a sustainable approach towards N 2 activation.
The results of moisture-absorption tests on 68L plastic-leaded chip-carriers (PLCC) are presented. Environmental variables include both temperature (30, 40, 50, 60 and 85 degrees C) and relative humidity (24, 40, 60 and 85%). Control samples of pure molding compound were tested to determine the effect of leads on the PLCC samples. Comparison was made between absorbed moisture measurements and predictions based on the one-dimensional Fickian diffusion solution. Nonlinear regression analysis indicates that Fickian diffusion behavior represents the actual moisture absorption for relative humidities below 85%. At 85% RH, however, the deviation becomes significant after 500 hr. On the basis of the agreement at moderate values of relative humidity and time, analytical models were developed that show the effect of temperature and relative humidity on moisture mass gain and diffusion coefficient. A stress and deformation analysis was performed to predict the envelope in parameter space separating cracked and uncracked packages. The model used depends on the presence of saturated water between the die paddle and the molding compound. Doming of the plastic underneath the paddle is attributed to flashing of all the trapped liquid water to steam.< >
I–III–VI2 semiconductor nanocrystals have been applied to a host of energy conversion devices with great success. Large scale implementation of device concepts based on these materials has, however, been somewhat stymied by the strong role of defects in determining the optoelectronic characteristics of these materials. Here we present a perspective view of the role of electronic structure and defects on the physical properties, particularly the spectroscopy, of this family of materials. Applications of these materials are further discussed in this context.
Abstract Since the early decades, through-tubing wireline (WL) interventions have been a necessary routine of the oil and gas industry. The practice of well intervention has benefited from the evolution of WL tools on its imposed quest to keep up with the trend of increasing complexity in wellbore and completion development. Deployment of WL tools through tubing, from early and simple devices (e.g., gauge cutters, lead impression blocks, tubing plugs) to state-of-the-art logging and well intervention prototypes, experienced a significant leap forward with the application of electric line (e-line) tractors in the mid-1990s. Since then, many oil companies have implemented the use of tractors to make a great variety of rigless well interventions feasible, both technically and economically. Over these lines, WL perforating of long, highly deviated wells through tubing, especially those with relevant ID restrictions, indubitably requires challenging, ingenious, and risked-assessed selection of the most convenient perforating and deployment systems. Working in remote locations, where availability of specialized tools and qualified personnel on short notice are often limited, adds an extra burden to the everyday complexity of operations. This paper describes the unconventional, but successful, use of a WL tractor to (1) investigate a tubing-conveyed perforating (TCP) completion failure and (2) save the highly deviated "S-shaped" well from a costly offshore rig workover by perforating with a strip gun deployed more than 14,000 ft from surface. The well is located in Angola at a water depth of 1,206 ft.
This article describes the optical properties of nanostructures composed of silver particles embedded into a gold matrix. In previous studies these materials were shown to exhibit temperature dependent transitions to a highly conductive and strongly diamagnetic state. Here we describe the anomalous optical properties of these nanostructures. Most notably, these materials fail to obey Mie theory and exhibit an unconventional resonance with a maximum at about 4 eV, while the usual gold and silver localized surface plasmon resonances are suppressed. This effect implies a significant deviation from the bulk dielectric functions of gold and silver. We further resolved this resonance into its absorbance and scattering sub-parts. It is observed that the resonance is largely comprised of scattering, with negligible losses even at ultraviolet frequencies.
Abstract CuAlS 2 /ZnS Quantum dots (QDs) are known to directly convert aqueous solutions of bicarbonate ions to oxygen and organic molecules such as formate with a remarkable efficiency even under sunlight. In cases, fairly complicated organic reaction products such as acetate and methanol have been observed when reactions are allowed to continue for longer periods of time. Here, we investigate the electron dynamics that occurs within CuAlS 2 /ZnS QDs and show that it is essentially dominated by ultrafast electron transfer (560 fs for 0.4 excitons per dot) to the surface. The electron dwell time in the conduction band increases exponentially (for example 872 fs for 1.4 excitons per dot) with the excitation fluence. This is reverse of the auger limited response of conventional QDs and is hypothesized to exhibit strong charge separation that lies at the root of the remarkable photocatalytic activity. We further investigate this system through multi‐pump experiments. We find that the system response to prior excitation changes over the period of nanoseconds, consistent with the charge reorganization in the system, well after the initial electron transfer. The results of these experiments are summarized in terms of a coulomb‐well interpretation.
We describe the electronic structure and spectroscopic properties of CuAlₓFe₁–ₓS₂ nanocrystals and their core/shell structures. The as-synthesized CuAlₓFe₁–ₓS₂ core exhibits a tetragonal chalcopyrite structure. The core material exhibits tunable band gap that spans the entire visible to near-infrared spectrum, from 3.48 to 0.53 eV. This tunability is achieved by varying the mole fraction of aluminum and iron from 1:0 to 0:1. The band gap variation with composition deviates from Vegard’s law and corresponds to a bowing coefficient of 1.59 eV. Our observations are interpreted using density functional theoretical calculations. In particular, we find that the significant bowing is well accounted for through significant localization of the Fe electronic states. Most significantly, CuAlₓFe₁–ₓS₂ shows photoluminescence upon making a shell of zinc sulfide, which is tunable from 400 to 1400 nm (3.1 to 0.89 eV). CuAlₓFe₁–ₓS₂/ZnS are until date the only visible-infrared tunable nanocrystal fluorophore composed entirely of earth abundant elements with atomic numbers 30 and lower.
Abstract In this study, a low‐melting organic‐inorganic crystalline ionic liquid compound, N ‐butyl pyridinium tetrachlorido ferrate (III) is described. The material can easily be synthesized using a one‐pot approach in an ionic liquid medium. Single‐crystal X‐ray diffraction confirms that the basic inorganic block is [FeCl 4 ] − , which is counterbalanced by an N ‐butyl pyridinium cation. The compound exhibits a melting point of 37.6 °C by differential scanning calorimetry, which is among the lowest values for a pyridinium‐based metal‐containing ionic liquid. The material shows promising electrochemical behavior at room temperature in both aqueous and nonaqueous solvents, and at elevated temperatures in its pure liquid state. Given its appreciable solubility in both water and acetonitrile, the compound can act as a redox‐active species in a supporting electrolyte for redox flow battery applications. These classes of low‐melting ionic solids with long‐range order and interesting electrochemical applications are potential candidates for a range of green energy storage and harvesting systems.
The collapse of carriers into polarons strongly impacts properties such as charge transport, separation and recombination that are of fundamental relevance to opto-electronic devices such as photovoltaics. Here we observe the real-time process of the collapse of a wavefunction using ultrafast spectroscopy. We develop a method to extract changes in spontaneous lifetimes of an emitter over the course of its emission lifetime. This method enables us to detect the wavefunction collapse of photogenerated holes in quantum dots (QDs) . In particular, we observe that the spontaneous emission lifetime of these QDs is ~46 ns immediately after excitonic cooling but changes drastically to ~294 ns over the first 15 ps. The evolution in emission lifetimes and the corresponding variation in emission energetics imply changes in the hole wavefunction even after usual excitonic cooling is complete, and is consistent in its migration into a phonon coupled state located within the semiconductor band gap.
General visible light-mediated aerobic oxidation of boronic acids is unveiled using CdSe nanocrystal quantum dots (QDs) as the photoredox catalyst. This protocol requires mild reaction conditions and low catalyst loading (down to 10 ppm), and tolerates various functional groups. The resulting phenols and aliphatic alcohols are produced in good to high yield with turnover numbers as high as >62000. The reaction mechanism is probed using ultrafast transient absorption and luminescence spectroscopy. The existence of a rapid 350 ps initial electron transfer followed by a hole transfer is demonstrated.
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