Defects and Calcium Diffusion in Wollastonite

Wollastonite (CaSiO3) is an important mineral that is widely used in ceramics and polymer industries. Defect energetics, diffusion of Ca ions and a solution of dopants are studied using atomistic-scale simulation based on the classical pair potentials. The energetically favourable defect process is calculated to be the Ca-Si anti-site defect cluster in which both Ca and Si swap their atomic positions simultaneously. It is calculated that the Ca ion migrates in the ab plane with an activation energy of 1.59 eV, inferring its slow diffusion. Favourable isovalent dopants on the Ca and Si sites are Sr2+ and Ge4+, respectively. Subvalent doping by Al on the Si site is a favourable process to incorporate additional Ca in the form of interstitials in CaSiO3. This engineering strategy would increase the capacity of this material

A new microfluidic pressure-controlled Field Effect Transistor (pFET) in digital fluidic switch operation mode

Lab-on-Chip is currently considered the technology with the potential to revolutionize future biochemical analysis providing miniaturized, low-reagent volume microchips as an alternative to traditional benchtop analysis. Automated control of droplet flow is currently a key objective in microfluidics research, aiming for droplet logic microfluidic circuits. To this end, microfluidic research has been following the electronics paradigm, with several digital fluidic components being demonstrated towards the realization of digital fluidic circuits for automated liquid control and delivery. In this work, we introduce a new concept of microfluidic pressure controlled field-effect transistors (pFETs), towards droplet logic operations. Using a fluidic with porous and hydrophobic walls, the inherently pinned plug depins by pressure application through the porous wall (backpressure), thus enabling the actuation and the downward transportation of the plug due the action of gravity. This concept resembles the logic operation of a metal–oxide–semiconductor field-effect transistor (MOSFET). The pFET operating parameters are thus defined in a manner analogous to MOSFET digital switches and their dependence on the channel width is studied also for the first time. The successful operation of pFET devices for droplet logic operation is verified in continuous ON/OFF cycles, achieving OFF-ON and ON-OFF switching times under 1 s (0.864 s and 0.841 s respectively) and therefore promising rapid liquid switching times, comparable to electronic circuit ones

Impact of oxygen on gallium doped germanium

Germanium (Ge) has advantageous materials properties and is considered as a mainstream material for nanoelectronic applications. Understanding dopant–defect interactions is important to form well-defined doped regions for devices. Gallium (Ga) is a key p-type dopant in Ge. In the present density functional theory study, we concentrate on the structures and electronic structures of Ga doped Ge in the presence of Ge vacancies and oxygen. We provide information on the defect structures and charge transfer between the doped Ga atom and the nearest neighbor Ge atom. The calculations show that the presence of Ga on the Ge site facilitates the formation of nearest neighbor Ge vacancies at 0.75 eV. The formation of interstitial oxygen is endoergic with the formation of −2 charge in both bulk Ge and Ga substituted Ge although the substitution of Ga has slightly less impact on the oxygen interstitial formation

Effect of halogen doping on the electronic,electrical, and optical properties of anatase TiO2

Titanium dioxide (TiO2) is one of the most used oxides in renewable energy applications, such as hydrogen production, photovoltaics, and light-emitting diodes. To further improve the efficiency of the devices, doping strategies are used to modify their fundamental properties. Here, we used density functional theory (DFT) simulations to explore the effect of all the halogen dopants on the structural, electronic, and optical properties of TiO2. We investigated both the interstitial and the oxygen substitutional positions, and for the optimized structures, we used hybrid DFT calculations to predict the electronic and optical properties. In all cases, we found that halogen dopants reduce the bandgap of the pristine TiO2 while gap states also arise. The halogen dopants constitute a single acceptor when they occupy interstitial sites, while when they are inserted in oxygen sites, they act as donors. This can be established by the states that form above the valence band. It is proposed that these states contribute to the significant changes in the optical and electronic properties of TiO2 and can be beneficial to the photovoltaic and photocatalytic applications of TiO2. Importantly, the iodine doping of TiO2 significantly reduces the bandgap of TiO2 while increasing its dielectric constant, making it suitable for light-harvesting applications

Impact of boron and indium doping on the structural, electronic and optical properties of SnO₂

Tin dioxide (SnO2), due to its non-toxicity, high stability and electron transport capability represents one of the most utilized metal oxides for many optoelectronic devices such as photocatalytic devices, photovoltaics (PVs) and light-emitting diodes (LEDs). Nevertheless, its wide bandgap reduces its charge carrier mobility and its photocatalytic activity. Doping with various elements is an efficient and low-cost way to decrease SnO2 band gap and maximize the potential for photocatalytic applications. Here, we apply density functional theory (DFT) calculations to examine the effect of p-type doping of SnO2 with boron (B) and indium (In) on its electronic and optical properties. DFT calculations predict the creation of available energy states near the conduction band, when the dopant (B or In) is in interstitial position. In the case of substitutional doping, a significant decrease of the band gap is calculated. We also investigate the effect of doping on the surface sites of SnO2. We find that B incorporation in the (110) does not alter the gap while In causes a considerable decrease. The present work highlights the significance of B and In doping in SnO2 both for solar cells and photocatalytic applications

Intrinsic Defects and H Doping in WO3.

WO3 is widely used as industrial catalyst. Intrinsic and/or extrinsic defects can tune the electronic properties and extend applications to gas sensors and optoelectonics. However, H doping is a challenge to WO3, the relevant mechanisms being hardly understood. In this context, we investigate intrinsic defects and H doping by density functional theory and experiments. Formation energies are calculated to determine the lowest energy defect states. O vacancies turn out to be stable in O-poor environment, in agreement with X-ray photoelectron spectroscopy, and O-H bond formation of H interstitial defects is predicted and confirmed by Fourier transform infrared spectroscopy

Atomic structure and electronic properties of hydrogenated X (=C, Si, Ge, and Sn) doped TiO2:A theoretical perspective

Titanium dioxide (TiO2) and especially its polymorph, anatase, are widely used transition-metal oxides for renewable energy applications such as photocatalytic and photovoltaic devices due to their chemical stability and their electrochemical and photocatalytic properties. However, the wide energy bandgap of anatase limits its photocatalytic ability and electron transport properties. Doping with appropriate elements is an established way to control and tune the optical and electronic properties of anatase such as conductivity, transparency, and bandgap. Metal doping can improve anatase’s properties as an electron transport layer, whereas non-metal (anion) doping is widely used to improve its photocatalytic activity. Herein, we investigate the effect of carbon group dopants in conjunction with hydrogenation of TiO2 by applying density functional theory. We find that hydrogenation has a positive impact on the structural and electronic properties of TiO2, thus making it an appropriate candidate for energy harvesting devices