Film Active Layer Research Articles

Antifouling polymeric nanocomposite membrane based on interfacial polymerization of polyamide enhanced with green TiO2nanoparticles for water desalination

In the present investigation, the preparation and characterization of polyamide/TiO2as thin film nanocomposites (TFN) for brackish water desalination was investigated. TiO2nanoparticles (NPs) were synthesized by a green method using thyme plant extract as a reducing and capping agent. The TiO2NPs was successfully prepared in pure crystalline anatase phase with 15 nm size, and −33.1 mV zeta potential. The antimicrobial tests confirmed the antimicrobial activity of TiO2against gram-positive and gram-negative bacteria. In addition, TiO2NPs showed a good photocatalytic activity in degradation of methylene blue dye. TFN based on interfacial polymerization was enhanced by embedding 5% of the greenly synthesized TiO2NPs within the polyamide thin film active layer. The incorporation of TiO2NPs was confirmed by SEM, atomic force microscope (AFM), surface wettability, and FTIR. Membranes performance was investigated based on flux, salt rejection and fouling resistance. The antifouling was examined using bovine serum albumin (BSA) as protein fouling by dead-end cell filtration system at 2 bar. The results showed the TFN increased in water flux by 40.9% and a slight decrease in NaCl rejection (6.3%) was observed, with enhancement in antifouling properties. The flux recovery rate of the modified TFN membranes after fouling with BSA solution was enhanced by 21.5% (from 61.7% for TFC to 83.2% for TFN). Also, they demonstrated remarkable anti-biofouling behavior against both bacterial strains.

GaAs thin-film solar cells photocurrent enhancement based on a new checkered grating back-reflector architecture

In this paper, a new back-reflector architecture has been investigated that can achieve a high short-circuit current density. For this, an ultra-thin film active layer of 150 nm GaAs is used, and the back-reflector structure is made of the checkered grating of Ag metal and photovoltaic material, i.e., GaAs. Hence, to decrease the initial reflection of the front surface of the cell and increase the optical path length, an anti-reflector layer is used. This checkered grating back-reflector structure by the scattering effect can reflect the unused photons into the photovoltaic layer, and these photons can travel a longer path in the photovoltaic layer, so have more chance to absorb. For proving of better performance of this structure, the simulation results are compared with a solar cell with flat BRS and the bare solar cell, that these two structures have the same volume of the photovoltaic layer as the main structure. The results of simulations show that the designed structure can achieve a short-circuit current density of 36.51 mA/cm2 and 28.04 mA/cm2, and conversion efficiency of 33.14% and 25.24%, respectively with and without the presence of anti-reflector coating.

Highly integrated fiber-shaped thermoelectric generators with radially heterogeneous interlayers

The construction of high-density thermoelectric (TE) pairs on small TE devices to improve the utilization of thermal energy has garnered extensive attention. The fabrication of high-density TE pairs in fiber-shaped TE devices with curved surfaces remains challenging. Herein, we report a flexible scrolled TE module with interlayers of radial heterojunction that possesses high-density p-n junctions, accomplished by rolling a patterned carbon nanotube film (active material layer) and a cellulose acetate nanofiber membrane (insulation). This module achieves high integration of ~3.32 mm3 per TE pair and a high output voltage density of ~65.4 mV/cm2 at a temperature difference of 41 K when the length of the scrolled module is 2 cm. Furthermore, a fiber-shaped TE device is designed by interconnecting the scrolled modules. The design of p-n junctions in the axial and radial directions of the fiber-shaped device is realized, and an open-circuit voltage (Voc) density of 0.176 mV/(cm·K) is achieved. In addition, the fiber-shaped TE device can be woven with commercial yarns to construct TE fabric for harvesting the thermal energy of the human body through alternating scrolled modules. This indicates its potential application for the harvesting of wearable energy.

Interfacial polymerization of thin film selective membrane layers: Effect of polyketone substrates

Thin film composite (TFC) membranes are the most widely used technology in reverse osmosis (RO)-based desalination processes, due to their desirable separation performance derived from the combined structure of the porous support and thin film active layer. Typically, TFC membranes are fabricated via an interfacial polymerization (IP) technique, where the porous substrate plays an indispensable role in forming the thin film layer. In this study, a porous polyketone membrane with a fibrous structure and intrinsically moderate hydrophilicity prepared using non-solvent induced phase separation (NIPS) was employed as the substrate to explore its suitability for fabricating high-performance TFC membranes. Investigations on structure control and chemistry regulation via the NIPS process and in-situ post-treatment revealed that porous polyketone substrates display different morphologies and chemistries, significantly altering the thin layer formation during IP. The resulting TFC membranes exhibited up to 14-fold permeance difference, which was attributed to the variance of “ridge-and-valley” structures in different thin film layers formed on different polyketone substrates. It was found that a polyketone membrane with an appropriate surface roughness could generate favorable “ridge-and-valley” structures in the thin film layer to enhance the surface area, realizing high water permeance as well as high salt rejection in reverse osmotic desalination of NaCl solution.

Fabrication, optimization, and performance of a novel double-skinned Al2O3.TiO2 ceramic nanocomposite membrane for forward osmosis application

Abstract In this study, a thin film nanocomposite ceramic membrane with an Al2O3 substrate and TiO2 as the thin film active layer was fabricated via dip coating technique and optimized for application in FO purification of groundwater. The effect of parameters including sol aging, calcination temperature, and dip time was investigated. Based on the results, the least water flux was obtained during 6 h after sol preparation. Furthermore, boosting the synthesis temperature and dip time led to flux reduction. According to the optimization results, 6.75 h sol aging, 17.00 s dip time and a 319 °C calcination temperature, led to the maximal water flux of 168 L/m2 h bar and 48% salt rejection. In addition, by covering the substrate with 10 layers of TiO2, water flux was reduced to 10.82 L/m2 h bar. FO process using MgCl2 solution (2 M) as draw and DI water as feed solutions, resulted in an initial water flux of 17.04 L.m−2 h−1 (LMH). Replacing DI water with a 0.01 M NaCl solution as feed, the initial water flux was decreased to 15.5 LMH. Also, using groundwater as the feed solution with an EC of 1407, 14.1 LMH initial water flux was obtained.

Communication—High Fidelity All-Carbon Based Carbon Nanotube Thin Film Transistors

This work reports transfer curve characterization, capacitance-voltage measurement, bias stress test, bending and stretching tests of the high fidelity flexible and stretchable thin-film transistors constructed on unsorted single-walled carbon nanotubes drain-source-gate electrodes, sorted semiconducting single-walled carbon nanotubes thin film active layer, and nonpolar styrene−ethylene−butadiene−styrene (SEBS) hydrogenated elastomer dielectric and substrate. The air-stable, hysteresis-less, negligible threshold shift under bias stress test, stable performance during bending, and slightly current density changes under stretching strains of these all-carbon based thin-film transistors qualify for basic elements applicable in industrial flexible and stretchable electronics.

Effect of Various Shapes of Silver Nanoparticles on the Performance of Plasmonic Solar Cells Active Layer

In this work, the enhancement of optical absorption in organic thin film active layer was investigated theoretically. The optical absorption results reveal that the introduction of periodic silver (Ag) nanoparticles (NPs) into the thin film active layer influences the absorption spectra. In this study, copper phthalocyanine (CuPc) as one of the organic solar cell materials has been used. Finite Different Time Domain technique has been used to demonstrate the role of the three different shapes of the silver nanoparticles (SNPs). It has been found that the NPs can result in broadband optical absorption enhancement in the wavelength range (350-550) nm due to the surface plasmonic resonance (SPR) phenomena. Moreover, the investigation has been performed the effect of the few shapes of (Cylinder with radius (R) 20 nm and height (H) 60 nm, radius (R) 30 nm for Sphere NPs, and Ellipse NPs with radius R1, R2 of 20 and 30 nm respectively) on the absorption in the organic thin films.

Layer-by-layer assembly of graphene oxide nanoplatelets embedded desalination membranes with improved chlorine resistance

Membranes with polyamide thin film active layer are used in reverse osmosis-based water desalination applications. Incorporation of graphene oxide nanoplatelets (GONPs) in the polyamide layer can alter the surface characteristics, permeability, selectivity, and can enhance the chlorine resistance of these membranes. In this study, a layer-by-layer (LbL) synthesis technique has been developed for embedding GONPs in the polyamide layer. Polyamide layers with GONPs were synthesized in various sequences, such as alternating layers of GONPs and polyamide, and GONPs on top of the polyamide layer. Incorporation of GONPs resulted in an increase of surface hydrophilicity as captured by the change of the water contact angle. Water flux and salt rejection properties of synthesized membranes have been investigated by using a dead-end cell. The salt rejection ability of membranes increased slightly with the incorporation of GONPs, while the water flux found to be similar to that observed for the pristine membranes without GONPs. Upon exposure to chlorine, GONPs embedded membranes retained salt rejection performance better than the pristine membranes. Our approach provides an alternative framework to incorporate nanoparticles in thin film membranes in a precise manner and to investigate the effect of such nanoparticles on the membrane performances.

A new high performance MSM hybrid plasmonic photodetector based on nanogratings and dual mode horn shape waveguide

A new metal–semiconductor–metal photodetector (MSM-PD) based on a hybrid plasmonic and extra ordinary transmission (EOT) phenomenon is proposed. In the designed structure, we demonstrate that light transmission is improved by means of a new shape of surface nanograting and by optimizing the physical parameters of the metal. In this work the optical transfer parameters are strongly interrelated and all the parameters are optimized and the light transmission is enhanced by 55 times compared to the reference structure. Furthermore, the output port of the subwavelength slit in the presented MSM-PD has a dual horn shape and improves absorption light in the active layer of the structure. Also, by filling this port with the same type of material as that of the active layer, the absorption becomes greater than before. Moreover, the confinement region of the light in the active layer is reduced by using the hybrid plasmonic effect and therefore, the probability of the photon absorption is 101 times greater than that of the reference structure. Thus, the transmission and absorption enhancement improves the quantum efficiency and the electrical response of the presented MSM-PD. A high performance new photodetector is identified as an ultra-fast MSM-PD and because of its thin film active layer can be used as a low-noise one.

Investigation of top gate GaN thin-film transistor fabricated by DC magnetron sputtering

Top-gate thin-film transistors (TFTs) with an n-type GaN thin film active channel layer have been fabricated and characterized. At a substrate temperature of 550 °C, rather than room temperature, the GaN thin films deposited by the reactive direct current magnetron sputtering technique have an average grain size of 25 nm. Without high temperature postannealing process, the proposed GaN TFTs exhibit good electrical performance with a field effect mobility of 2.5 cm2/V s, a threshold voltage of 4.5 V, an on/off current ratio of 1.5 × 105, and a subthreshold swing of 0.7 V/decade. The proposed GaN thin film is promising for TFT active channel application in active-matrix display.

Modeling kV X-ray-Induced Coloration in Radiochromic Films

Commercially available radiochromic films are primarily designed for clinical X-ray dosimetry. These films change color upon exposures to radiation as a result of solid-state polymerization (SSP). Built on a previous model developed for SSP upon exposures to ultraviolet (UV) radiation, a new model was developed in the present work for X-ray-induced coloration in Gafchromic EBT3 films. Monte Carlo simulations using the Monte Carlo N-Particle (MCNP) code were employed to model the transport and interaction of photons and the generated secondary electrons within the film active layer. The films were exposed to continuous-energy photon beams. The dose DE in the external radiation detector (i.e., ionization chamber) was determined and the realistic dose DA in the film active layer was then obtained using the calibration coefficient R (=DA/DE). The finite element method (FEM) was used to solve the classical steady-state Helmholtz equation using the multifrontal massively parallel sparse direct solver (MUMPS). An extensive grid independence test was carried out and the numerical stability of the present model was ensured. The reflected light intensity from the film surface was used to theoretically obtain the net reflective optical density of the film exposed to X-ray. Good agreement was obtained between the experimental and theoretical results of the net reflective optical density of the film. For X-ray doses >~600 cGy, due to the already formed densely cross-linked structure in the active layer of the EBT3 film so further bond formation was less likely, the reflected light intensity from the film surface increased at a relatively lower rate when compared to those for dose values <~600 cGy.

Experimental investigation of GafChromic® EBT3 intrinsic energy dependence with kilovoltage x rays, 137 Cs, and 60 Co.

To determine experimentally the intrinsic energy response, kbq , of EBT3 GafChromic® radiochromic film with kilovoltage x rays, 137 Cs, and 60 Co in therapeutic and diagnostic dose ranges through direct measurement with an accompanying mathematical approach to describe the physical processes involved. The EBT3 film was irradiated with known doses using 60 Co, 137 Cs, and 13 NIST-matched kilovoltage x-ray beams. Seven dose levels, ranging from 57 to 7002mGy, were chosen for this work. Monte Carlo methods were used to convert air-kerma rates to dose rates to the film active layer for each energy. A total of 738 film dosimeters, each measuring (1.2×1.2) cm2 , were cut from three film sheets out of the same lot of the latest version of EBT3 film, to allow for multiple dosimeters to be irradiated by each target dose and beam quality as well as unirradiated dosimeters to be used as controls. Net change in optical density in excess of the unirradiated controls was measured using the UWMRRC Laser Densitometry System (LDS). The dosimeter intrinsic energy response, kbq , for each dose level was determined relative to 60 Co, as the ratio of dosimeter response to each beam quality relative to the absorbed dose to the film active volume at the same dose level. A simplified, single-hit mathematical model was used to derive a single-free-parameter, β, which is a proportionality constant that is dependent on beam quality and describes the microdosimetric interactions within the active layer of film. The response of β for each beam quality relative to 60 Co was also determined. kbq was determined for a wide range of doses and energies. The results show a unique variation of kbq as a function of energy, and agree well with results from other investigations. There was no measurable dose dependence for kbq within the 500-7002mGy range outside of the expanded measurement uncertainty of 3.65% (k=2). For doses less than 500mGy, the signal-to-noise ratio was too low to determine kbq accurately. The single-free-parameter, β, fit calculations derived from the single-hit model show a correlation with kbq that suggests that β, at least in part, characterizes the microdosimetric interactions that determine kbq . For the beam qualities investigated, a single energy-dependent kbq correction can be used for doses between 500 and 7002mGy. Using the single-hit model with the single-free-parameter fit to solve for β shows promise in the determination of the intrinsic energy response of film, with β being the mathematical analog of the measured kbq .

Multiple parallel channels for improved resistance to repeated bending and unbending of amorphous indium–gallium–zinc oxide thin film transistors

A simple approach has been taken to improve the resistance to the repeated bending and unbending of amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs). Splitting a conventional thin film active layer of a-IGZO into numerous parallel quasi-one-dimensional sub-channels at micrometer scale, separated by relatively compliant gap regions, allowed improved flexibility of the overall device structure as well as lower strain in the active region. Such scheme resulted in somewhat degraded initial device performance due to the exposure of side walls of the quasi-one-dimensional sub-channels and possible damages there introduced during the photolithography process. However, inherent flexibility of the device structure as proposed herein worked favorably for at least 50 times longer device lifetime under repeated bending and unbending with the bending radius of 3mm as compared to the reference device having a typical thin film active layer. It is therefore proposed that the device structure as adopted in this study can be a potential candidate for flexible thin film transistors.

Fabrication, characterization and electroluminescence studies of SrS: Ce3+ ACTFEL device

The SrS: Ce3+ thin film active phosphor layer of different thickness based alternating current thin-film electroluminescent (ACTFEL) devices are fabricated by electron beam evaporation deposition (EBED) method. The morphology and chemical composition of the deposited films are investigated by field emission scanning electron microscopy (FESEM). The optical transmittance in visible range for the optimum film and optical band gap of SrS: Ce3+ film is described on the basis of Ce3+ doping concentration.

Conductive AFM Topography of Intrinsic Conductivity Variations in Silica Based Dielectrics for Memory Applications

As flash memory approaches its scaling limit, resistive RAM (ReRAM) devices are showing promise in providing the next generation of electronic memories. This comes about as a result of their simple structure, small size and low operating voltages, enabling denser device packing and lower power consumption. Many materials have shown desirable properties as thin film active layers in ReRAM architectures, yet silicon based memories allow for facile integration into existing CMOS infrastructures, making them a particularly suitable class of devices for development. We have looked specifically at devices containing amorphous silicon suboxide or hydrogen silsesquioxane (HSQ) active layers sandwiched between a number of different electrode materials, including titanium nitride and platinum. Here, we present recent characterisation results in which we have probed the three-dimensional structure of conducting filaments in our silicon memories. These filaments govern the switching mechanism that gives dielectric materials their memory function and are thought to be composed of oxygen vacancies, generated as the device is subjected to an electric field. Such features are difficult to image with conventional topographical and cross-sectioning techniques, owing to their low contrast against the background of pristine material. Our results demonstrate the importance of conductive atomic force microscopy for three-dimensional analyses and show that the filament formation is closely linked to the pristine structure of the dielectric. Growth pathways conform to the intrinsic inhomogeneities of the films, a feature that is thought to produce defect clustering and thus promote the generation of oxygen vacancies under electrical stress. We have also been able to demonstrate, for the first time in an intrinsic switching material, that multiple growths compete to bridge the active layer while only a single pathway is finally successful.

Optimum absorbed dose versus energy response of Gafchromic EBT2 and EBT3 films exposed to 20–160 kV x-rays and 60Co gamma

High-accuracy in the absorbed-dose and small energy-dependence are important features of a dosimeter to be considered ideal for medical applications. This work investigated the relation between the optimum absorbed-dose in terms of combined standard-uncertainty and energy-response of EBT2 and EBT3 films exposed to five x-ray beams and 60Co. A systematic analysis was performed to control the fitting procedure in order to find the parameter-values that best describe the experimental data. Six EBT2 and three EBT3 film pieces per absorbed-dose were exposed to 0.05–100 Gy and 0.1–15 Gy, respectively. HP Scanjet-7650 and Epson Expression-11000XL document scanners were used to read the EBT2 and EBT3 films, respectively both in transmission mode, 48-bit at 300 dpi spatial-resolution. Images were analysed using ImageJ-software. The results indicate that, independent of the photon-energy beam, taking or not into account the uncertainty of the experimental data during the fitting process has a notable impact on the fit parameters for describing the measurements as well as on the uncertainty in the absorbed dose that can be measured with both films. Furthermore, the degree of energy dependence of both films depends on the absorbed-dose and the minimum absorbed-dose that can be measured with them is an intrinsic characteristic of each film model and depends on the photon energy as well as the colour channel. Lower the photon-energy, smaller the combined standard uncertainty, possibly associated to higher ionisation-density pattern of secondary-electrons released locally within the film active layer by low photon-energy comparing to high-energy. Thus, based on the results of this work, we suggest the inclusion of the uncertainty on the experimental data in the fitting procedure of the film calibration curve and an optimum absorbed-dose of 10 Gy for EBT3 in green-channel and 3 Gy for EBT2 in red-channel when use in modern radiotherapy techniques.

Characterization of a Gafchromic film for the two-dimensional profile measurement of low-energy heavy-ion beams

The feasibility of the transverse intensity distribution measurement of low-energy (keV/u range) heavy-ion beams using radiochromic films is experimentally explored. We employ a Gafchromic radiochromic film, HD-V2, whose active layer is not laminated by a surface-protection layer. The coloration response of films irradiated with several ion beams is characterized in terms of optical density (OD) by reading the films with a general-purpose scanner. To explore the energy dependence of the film response widely, the kinetic energy of the beams is varied from 1.5keV/u to 27MeV/u. We have found that the coloration of HD-V2 films is induced by irradiation with low-energy ion beams of the order of 10keV/u. The range of the beams is considerably shorter than the thickness of the film's active layer. The dependence of OD response on ion species is also discussed. We demonstrate that the Gafchromic film used here is useful for measuring the intensity distribution of such low-energy ion beams.

Measurement of gold nanofilm dose enhancement using unlaminated radiochromic film.

Bombarding high-Z material with x-ray radiation releases Auger electrons and Coster-Kronig electrons, along with deeper penetrating fluorescent x-rays and photoelectrons. The Auger and Coster-Kronig electron penetration distance is on the order of nanometers to micrometers in water or tissue, creating a large dose enhancement accompanied by a RBE greater than 1 at the cellular level. The authors' aim is to measure the gold nanofilm dose enhancement factor (DEF) at the cellular level with unlaminated radiochromic film via primary 50 kVp tungsten x-ray spectrum interaction, similar to an electronic brachytherapy spectrum. Unlaminated Gafchromic(®) EBT2 film and Monte Carlo modeling were combined to derive DEF models. Gold film of thickness 23.1 ± 4.3 nm and surface roughness of 1.2 ± 0.2 nm was placed in contact with unlaminated radiochromic film in a downstream orientation and exposed to a 50 kVp tungsten bremsstrahlung, mean energy 19.2 keV. Film response correction factors were derived by Monte Carlo modeling of electron energy deposition in the film's active layer, and by measuring film energy dependence from 4.5 keV to 50 kVp. The measured DEF within a 13.6 μm thick water layer was 0.29 with a mean dose of 94 ± 9.4 cGy from Au emissions and 324 ± 32.4 cGy from the 50 kVp primary beam. Monte Carlo derived correction factors allowed determination of Au contributed dose in shallower depths at 0.25 μm intervals. Maximum DEF of 18.31 was found in the first 0.25 μm water depth. Dose enhancement from Au nanofilm can be measured at the cellular level using unlaminated radiochromic film. Complementing the measured dose value with Monte Carlo calculations allows estimation of dose enhancement at depth increments within the cellular range.

Nonvolatile Memory Device Using Mobile Protons via Insertion Hydrogen Neutral Beam Treatment Process between SiO2 Deposition Processes at Room Temperature

We demonstrated the nonvolatile memory functionality of nano-crystalline silicon (nc-Si) field effect transistors (FETs) using mobile protons that are generated by very short time (within 2 minutes) hydrogen neutral beam (H-NB) treatment at room temperature (25 °C). Some researches try to hydrogen insertion process via long time (40 minutes) high-pressure hydrogen annealing (HPHA) at high temperature (400 °C) that also need several steps such as poly silicon deposition, HPHA process, and poly silicon etching process. However our hydrogen insertion process does not need any other additional process but only H-NB process during normal thin film transistor fabrication. Also the whole memory fabrication process kept under 50 °C (except SiO2deposition process; 300 °C). These nc-Si devices exhibited reproducible hysteresis, reversible switching, and nonvolatile memory behaviors in comparison with those of the conventional FET devices. We think that the memory characteristics are attributed to the movement of protons between the Si(gate)/SiO2(gate insulator) interface and the SiO2/nc-Si thin film (active layer) interface by the applied gate electric field. Our study will further provide a useful route of creating memory functionality and incorporating proton-based storage elements onto a modified CMOS platform for FET memory devices using nanomaterials, and probability of next generation flexible memorable electronics.

Panchromatic small molecules for UV-Vis-NIR photodetectors with high detectivity

Two donor–acceptor–donor (D–A–D) type low-bandgap small molecules, M1 and M2, with bis(2-thienyl)-N-alkylpyrrole (TPT) as the donor and thieno[3,4-b]thiadiazole (TT) as the acceptor were designed and synthesized. The absorption, transmission, electrochemical, thermal and film properties were studied. The compounds showed panchromatic absorption in the spectral range of 300–1000 nm. Moreover, they also exhibited semi-transparent property in the visible region (400–700 nm). Small molecule photodetectors (SMPDs) based on M1 and M2 were fabricated and studied. For the SMPD with BCP as the hole blocking layer (HBL), a detectivity of 5.0 × 1011 Jones at 800 nm at −0.1 V was obtained, which is among the highest detectivities reported for NIR SMPDs. With a sufficiently thin silver electrode, visibly transparent PDs with an average transmittance of 45% in the visible region were obtained for the first time. The transparent PDs exhibited fairly constant and high detectivity between 1011 and 1012 Jones over a broad spectral range of 300–900 nm. In addition, side chains of the compounds exhibited a great influence on the device performance, which could be assigned to their film absorption coefficient, molecular packing and active layer morphology.