Topological walls separating domains of continuous polarization, magnetization, and strain in ferroic materials hold promise of novel electronic properties, that are intrinsically localized on the ...nanoscale and that can be patterned on demand without change of material volume or elemental composition. We have revealed that ferroelectric domain walls in multiferroic BiFeO3 are inherently dynamic electronic conductors, closely mimicking memristive behavior and contrary to the usual assumption of rigid conductivity. Applied electric field can cause a localized transition between insulating and conducting domain walls, tune domain wall conductance by over an order of magnitude, and create a quasicontinuous spectrum of metastable conductance states. Our measurements identified that subtle and microscopically reversible distortion of the polarization structure at the domain wall is at the origin of the dynamic conductivity. The latter is therefore likely to be a universal property of topological defects in ferroelectric semiconductors.
In this work, with Ag alloying, we attempted to improve the microstructure and device performance of low-temperature grown Cu(In,Ga)Se2 (CIGS) solar cells. Ag precursors with various thicknesses are ...deposited onto Mo prior to the CIGS growth step, and absorber films are formed via a single-step co-evaporation at a substrate temperature of 350°C. The addition of Ag in low-temperature grown CIGS films induces significant recrystallization and Na incorporation. Through adjustment of the Ag content of the Ag-alloyed CIGS films, an improved device performance is obtained compared with a CIGS solar cell without Ag alloying.
Controlled Ag alloying of low-temperature grown CuInGaSe2 solar cells provides improved device performance compared to devices without Ag alloying
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•Ag was incorporated in low-temperature grown CIGS films using Ag precursor layers.•Ag alloyed CIGS (ACIGS) films exhibit significant recrystallization and Na incorporation.•The extent of Ag alloying affects the device performance.•Controlled Ag alloying provides better device performance compared to devices without Ag alloying.
▸ HA coatings synthesized by pulsed laser deposition. ▸ Comparative study of commercial vs. animal origin materials. ▸ HA coatings of animal origin were rougher and more adherent to substrates. ▸ ...Animal origin films can be considered as promising candidates for implant coatings.
We report on the synthesis of novel ovine and bovine derived hydroxyapatite thin films on titanium substrates by pulsed laser deposition for a new generation of implants. The calcination treatment applied to produce the hydroxyapatite powders from ovine/bovine bones was intended to induce crystallization and to prohibit the transmission of diseases.
The deposited films were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. Pull-off adherence and profilometry measurements were also carried out.
X-ray diffraction ascertained the polycrystalline hydroxyapatite nature of the powders and films. Fourier transform infrared spectroscopy evidenced the vibrational bands characteristic to a hydroxyapatite material slightly carbonated. The micrographs of the films showed a uniform distribution of spheroidal particulates with a mean diameter of ∼2μm. Pull-off measurements demonstrated excellent bonding strength values between the hydroxyapatite films and the titanium substrates.
Because of their physical–chemical properties and low cost fabrication from renewable resources, we think that these new coating materials could be considered as a prospective competitor to synthetic hydroxyapatite used for implantology applications.
Interfacially synthesized polyamide (PA) thin-film composite (TFC) membranes, as the state-of-the-art polymeric membranes for nanofiltration (NF), are prone to fouling in processing wastewaters and ...industrial fluids due to the inherent surface physicochemical properties of polyamide active layer. Here, we report the facile and effective modification of PA-TFC nanofiltration membranes for improved water permeability and antifouling property by surface grafting. Ttriethanolamine (TEOA) molecules were bonded onto the surface of PA-TFC NF membrane through esterification reaction between the hydroxyl groups of TEOA and the residual acyl chloride groups on the nascent PA-TFC membrane by pouring the TEOA aqueous solution on membrane surface. The covalent attachment of TEOA molecules was shown to tailor the surface chemistry of the composite membrane without altering the morphology of active layer. The PA-TFC membrane became more hydrophilic after modification and thus more permeable to water and antifouling against hydrophobic foulants, while maintaining its molecular weight cut-off. The results of tertiary treatment of industrial effluent also demonstrated that the modification performed in our study could effectively improve the water permeability and antifouling property of the PA-TFC NF membrane in processing wastewater.
•Triethanolamine (TEOA) was grafted onto the surface of TFC polyamide NF membrane.•The grafting of TEOA led to a more hydrophilic and less negatively charged surface.•The presence of TEOA did not affect the thickness and compactness of the active layer.•TEOA-modified membrane showed improved water permeability and antifouling property.•Modification enhanced membrane performance in tertiary treatment of industrial effluent.
Block copolymers (BCPs) must necessarily have high interaction parameters (χ), a fundamental measure of block incompatibility, to self-assemble into sub-10-nanometer features. Unfortunately, a high χ ...often results from blocks that have disparate interfacial energies, which makes the formation of useful thin-film domain orientations challenging. To mitigate interfacial forces, polymers composed of maleic anhydride and two other components have been designed as top coats that can be spin-coated from basic aqueous solution in the ring-opened, acid salt form. When baked, the anhydride reforms and switches polarity to create a neutral layer enabling BCP feature alignment not possible by thermal annealing alone. Top coats were applied to the lamella-forming block copolymers poly(styrene-block-trimethyilylstyrene-block-styrene) and poly(trimethylsilylstyrene-block-lactide), which were thermally annealed to produce perpendicular features with linewidths of 15 and 9 nanometers, respectively.
Although a great deal of research has been conducted on the electrical properties of organic devices, numerous crucial problems still remain. Of these, the study of charge mobility in organic ...semiconductor systems has been one of the most important subjects that has remained a puzzle for many years. It is essential to quantitatively understand conduction charge-molecular vibration coupling as well as the intermolecular interaction to discuss mobility. This article describes recent successes with direct measurements of valence hole–vibration coupling in ultrathin films of organic semiconductors with ultraviolet photoelectron spectroscopy (UPS), which can be used to experimentally study charge mobility based on energy and momentum conservation rules. The method may thus be categorized as a first-principles study of charge mobility. The detection of hole–vibration coupling of the highest occupied molecular orbital (HOMO) state in a thin film by UPS is essential to comprehending hole-hopping transport and polaron-related transport in organic semiconductors. We also need to experimentally determine energy-band dispersion or energy-level splitting in a molecular multilayer to obtain information on intermolecular interactions. Since the information on these is concealed behind the finite bandwidth of the HOMO in UPS spectra, we need to obtain high-resolution UPS measurements on organic thin films. Only careful measurements can attain the high-resolution spectra and provide these key parameters in hole-transport dynamics. A key method in achieving such high-resolution UPS measurements is also described.
Controlling the crystallization dynamics is one key in optimizing the performance of perovskite solar cells (PSCs). The present study provides a simple approach using a low temperature ...stable-transition-film (STF) to prepare highly-dense and pinhole-free CsPbIBr2 thin film with high crystalline quality, as well as a new structural design (FTO/NiOx/CsPbIBr2/MoOx/Au) of all-inorganic perovskite solar cells toward long-term thermal stability. For the first time, we demonstrate that MoOx can independently serve as an outstanding cathode buffer layer on an inorganic perovskite layer. The lower work-function MoOx with ultra-thin thickness (4nm) leads to decreases of the Schottky barrier, the contact resistance and the interface trap-state density. This increases the power conversion efficiency (PCE) of all-inorganic planar PSCs from 1.3% to 5.52%. Inspiringly, the FTO/NiOx/CsPbIBr2/MoOx/Au all-inorganic PSCs were demonstrated to possess excellent long-term thermal stability at high temperatures up to 160°C.
A simple approach using a low temperature stable-transition-film (STF) to prepare highly-dense and pinhole-free CsPbIBr2 thin film with high bromine content, and a new structural design (FTO/NiOx/CsPbIBr2/MoOx/Au) of MoOx independently buffered all-inorganic perovskite solar cells (PSCs) toward long-term thermal stability. Display omitted
•We demonstrated a low-temperature stable-transition-film to prepare uniform CsPbIBr2 thin film.•An ultra-thin MoOx thin film with low work function was realized by post annealing process in nitrogen atmosphere.•MoOx independently served as the cathode buffer layer in all-inorganic perovskite solar cells (FTO/NiOx/CsPbIBr2/MoOx/Au).•The all-inorganic perovskite solar cells were demonstrated to own long-term stability at high temperatures up to 160°C.
Total-ionizing-dose (TID) effects are evaluated in back-gated IGZO thin-film transistors irradiated under different gate biases. Negative-bias irradiation leads to worst-case degradation of TID ...response in these devices, primarily as a result of enhanced charge trapping in the SiO 2 overlayer. The relatively small peak transconductance decrease after irradiation illustrates that IGZO transistors are much less sensitive to interface-trap buildup and other instabilities due to hydrogen release and transport than amorphous Si thin film transistors examined previously. The TID response of devices with different gate sizes is also investigated. No significant geometry dependence is observed, which is promising for future scaling down of the technology.
Lead scandium tantalate, Pb(Sc,Ta)O
, is an excellent electrocaloric material showing large temperature variations, good efficiency, and a broad operating temperature window. In form of multilayer ...ceramic capacitors integrated into a cooling device, the device can generate a temperature difference larger than 13 K. Here, we investigate Pb(Sc,Ta)O
in form of thin films prepared using the sol-gel chemical solution deposition method. We report the detailed fabrication process of high-quality films on various substrates such as c-sapphire and fused silica. The main originality of this research is the use of interdigitated top electrodes, enabling the application of very large electric fields in PST. We provide structural and electrical characterisation, as well as electrocaloric temperature variation, using the Maxwell relation approach. Films do not show a B-site ordering. The temperature variation from 7.2 to 15.7 K was measured on the Pb(Sc,Ta)O
film on a c-sapphire substrate under the electric field of 1330 kV/cm between 14.5 °C and 50 °C. This temperature variation is the highest reported so far in Pb(Sc,Ta)O
thin films. Moreover, stress seems to have an effect on the maximum permittivity temperature and thus electrocaloric temperature variation with temperature in Pb(Sc,Ta)O
films. Tensile stress induced by fused silica shifts the "transition" of Pb(Sc,Ta)O
to lower temperatures. This study shows the possibility for electrocaloric temperature variation tuning with stress conditions.
