Low-temperature Process Research Articles

Area-selective atomic layer deposition (AS-ALD) of low temperature (300 °C) cobalt thin film using octadecyltrichlorosilane (ODTS) self-assembled monolayers (SAMs)

As the semiconductor industry advances, manufacturing technologies encounter challenges in achieving precise alignment and thickness control with smaller and more intricate 3D structures. Addressing this, Area-selective atomic layer deposition (AS-ALD) emerges as a promising “bottom-up” approach, offering an alternative to current nano-patterning techniques. To achieve AS-ALD, self-assembled monolayers (SAMs) are employed as inhibitor agents. In this study, we employed plasma-enhanced atomic layer deposition (PEALD) to promote self-limiting surface reactions and enable low-temperature processing, thereby facilitating the implementation of high purity cobalt (Co) film through AS-ALD using octadecyltrichlorosilane (ODTS) SAM as an inhibitor. The selective deposition is achieved by employing SAMs as an inhibitor, belonging to the deactivation process, a common method for realizing a bottom-up approach. SAMs can form a thin organic film on a solid surface, allowing for surface modifications to become hydrophobic or hydrophilic. Through the selective deposition of Co in the PEALD low-temperature process (300 °C), we successfully addressed the degradation issue of ODTS SAM and verified the successful achievement of a high-purity selectively deposited 13.4 nm Co film. Our findings highlight the potential of selective Co deposition for realizing complex 3D structures and narrow interconnection layers.

Effect of phosphoric acid on leaching of monazite during low-temperature sulfuric acid cyclic leaching process

To completely recover valuable elements and reduce the amount of waste, the impact of phosphoric acid on the decomposition of rare earth, fluorine and phosphorus during cyclic leaching was studied based on the characteristics of low-temperature sulfuric acid decomposition. When a single monazite was leached using 75 wt% H2SO4 solution with phosphoric acid, the size and number of monazite particles in the washing slag gradually decrease with the increase in phosphoric acid content in the leaching solution. The monazite phase can hardly be found in the slag when the phosphoric acid content reaches 70 g/L, which indicates that phosphoric acid is favorable for monazite decomposition. The mixed rare earth concentrate was leached by 75 wt% H2SO4 containing 70 g/L phosphoric acid, the mineral compositions of the washing slag are only gypsum and unwashed rare earth sulfuric acid. After cyclic leaching of 75 wt% H2SO4, the mineral compositions of the primary leaching washing slag are mainly undecomposed monazite, rare earth sulfate and calcium sulfate. However, monazite is not found in the mineral phase of the second and third leaching washing slag. The leaching rates of rare earth and phosphorus gradually increase with the increase in cyclic leaching times. In addition, the phosphoric acid content in the leaching solution increases with the increase in the number of cyclic leaching time. However, the rising trend decreases when the phosphoric acid content reaches 50 g/L by adsorption and crystallization of phosphoric acid. A small amount of water can be used to clean the leaching residue before washing to recover the more soluble phosphorus acid according to the difference of dissolution between phosphoric acid and rare earth sulfuric acid.

Kapok fiber composites minimizing secondary waste and disposal costs for large-scale radioactive liquid treatment

Conventional liquid treatments for large-scale, low-level radioactive wastewater, such as ion exchange and waste solidification, face challenges due to the large amounts of secondary waste and high disposal costs. A new large-scale decontamination method is proposed that uses kapok fiber composites for rapid radionuclide adsorption and high volume reduction to minimize secondary waste. The composite consists of natural zeolite and kapok holocellulose, which has high water-soaking ability and low-temperature pyrolysis. The kapok composites, fabricated using a commercial wet-laid nonwoven manufacturing process, absorbs 99% of low-level radioactive cesium in 20 min, reducing the volume by 98% and the weight by 47% at 300 °C. The low-temperature pyrolysis process below 300 °C prevents cesium desorption and gasification by avoiding zeolite destruction. The mass-producible kapok composites can be used for adsorbing various radionuclides in large-scale wastewater by attaching specific adsorbents for target isotopes to the composites.

Local polarization redistribution in ZnmIn2S3+m for the enhancing synergetic piezo-photocatalytic overall water splitting

Piezo-photocatalytic water (deuterium oxide) decomposition is a promising strategy for realizing renewable energy, but the manipulation of the polar center remains a big challenge. This study uses a simple low-temperature hydrothermal process to successfully manufacture ZnmIn2Sm+3 (m = 1–3) (ZnIn2S4, Zn2In2S5 and Zn3In2S6). Incorporating both experimental and theoretical analyses, the structural contraction and local polarization of the Zn-S bond in Zn2In2S5 enhance the piezoelectric response and surface charge accumulation, which facilitate charge transfer and reduce the activation energy of water. Remarkably, Zn2In2S5 exhibits excellent piezoelectric photocatalytic total water splitting performance (H2/O2: 4284.72/1967.00 μmol g-1h−1), which is 1.77 times that of photocatalytic performance. Moreover, a significant enhancement in D2O splitting performance can be obtained for the optimized Zn2In2S5. Our work offers valuable insights into the disclosure of local polarization in catalysts for enhancing piezo-photocatalytic overall water splitting.

Nanocavity-Mediated Purcell Enhancement of Er in TiO2 Thin Films Grown via Atomic Layer Deposition.

The use of trivalent erbium (Er3+), typically embedded as an atomic defect in the solid-state, has widespread adoption as a dopant in telecommunication devices and shows promise as a spin-based quantum memory for quantum communication. In particular, its natural telecom C-band optical transition and spin-photon interface make it an ideal candidate for integration into existing optical fiber networks without the need for quantum frequency conversion. However, successful scaling requires a host material with few intrinsic nuclear spins, compatibility with semiconductor foundry processes, and straightforward integration with silicon photonics. Here, we present Er-doped titanium dioxide (TiO2) thin film growth on silicon substrates using a foundry-scalable atomic layer deposition process with a wide range of doping controls over the Er concentration. Even though the as-grown films are amorphous after oxygen annealing, they exhibit relatively large crystalline grains, and the embedded Er ions exhibit the characteristic optical emission spectrum from anatase TiO2. Critically, this growth and annealing process maintains the low surface roughness required for nanophotonic integration. Finally, we interface Er ensembles with high quality factor Si nanophotonic cavities via evanescent coupling and demonstrate a large Purcell enhancement (≈300) of their optical lifetime. Our findings demonstrate a low-temperature, nondestructive, and substrate-independent process for integrating Er-doped materials with silicon photonics. At high doping densities this platform can enable integrated photonic components such as on-chip amplifiers and lasers, while dilute concentrations can realize single ion quantum memories.

Towards greener water remediation: Ca-impregnated pyro-hydrochar of spent mushroom substrate for enhanced adsorption of acridine red and methylene blue

Sustainable solutions for environmental remediation are of great interest due to the escalated release of toxic substances into the ecosystem. Here, Ca-impregnated pyro-hydrocarbon (Ca-SMS) was synthesized from spent mushroom substrate (SMS) via hydrothermal carbonization at a relatively low process temperature, followed by subsequent physicochemical activation. Ca-SMS underwent characterization using various analytical techniques, and its efficacy in removing acridine red (AR) and methylene blue (MB) was assessed through batch experiments. The results suggested that Ca-SMS is an effective adsorbent for AR and MB, visiting a removal capacity of 33.82 and 81.98 mg g−1 at 35 °C, respectively. The kinetic investigation uncovered that the dye removal process mostly agreed with the pseudo-second-order (PSO), while the Langmuir and Freundlich models were the most suitable to describe the removal of dyes. Thermodynamic analyses showed that the remediation process is spontaneous and endothermic. Adsorption mechanisms among dyes and Ca-SMS were multiple: physical adsorption, surface complexation, electrostatic, and π-π interaction. The feasibility of the proposed method for real sample treatment was demonstrated. These findings indicate that Ca-SMS is an effective alternative sorbent for the remediation of textile wastewater and is a viable solution for waste reduction in the rising mushroom cultivation sector.

Novel Study on Cryogenic Distillation Process and Application by Using CHEMCAD Simulation.

The purpose of this study was to examine the cryogenic separation process used in air separation plants with the CHEMCAD simulation program. A preliminary analysis was carried out with the literature about the operation of the process. In light of the technical information, the simulation of the cryogenic separation process was utilized with the program. While no changes were analyzed in the basic parts of the process, the filtration of the air and separation from moisture and carbon dioxide were not included in the simulation. The simulation showed the three basic components of air, nitrogen, oxygen, and argon obtained as a product of the desired purity rather than a one-to-one demonstration of the applications in the industry. In addition, the low-temperature separation process of an air separation unit was studied to obtain high-purity products (99.49-99.99%) achieving the expected separation efficiency. As a result, the production of all three substances in desired purity was achieved successfully.

An investigation of novel biodegradable flexible copolyester derived from bio-based isosorbide: Synthesis and characterization of poly(butylene-co-isosorbide sebacate)

A series of fully bio-based poly(butylene-co-isosorbide sebacate) (PBISe) copolyesters are synthesized from sebacic acid (Se), 1,4-butanediol (BDO), and isosorbide (IS) via a two-step melt polycondensation method. The synthesized PBISe copolyesters are characterized using various techniques, including 1H NMR spectroscopy; GPC; FT-IR spectroscopy; HR-XRD; DSC; TGA; transparency, tensile, and tear strength testing; and rheological property analysis. The Mw and Mn values of the PBISe copolyesters are 126,000–148,000 and 50,000–63,500, respectively. The introduction of the rigid, bulky, and asymmetric IS unit disrupts the regularity and mobility of the polymer chain, resulting in a nearly linear reduction of the melting temperature, enthalpy, and crystallinity, from 66 to 42 °C, 81 to 37 J/g, and 41.4 to 19.0%, respectively, with an increase in the IS content from 0 to 30 mol% relative to the total diol concentration. The reduction of crystallinity without the formation of new crystal planes with the poly(butylene sebacate (PBSe) copolyester containing 30 mol% IS resulted in improved transparency (73.8% transmittance at 600 nm). Additionally, the PBISe copolyesters exhibit Tonset and Tmax in excess of 405 °C and 425 °C, respectively, as well as shear-thinning and viscous melt-flow behaviors, making them suitable for melt processing. The tensile strength and elongation at break of the hot-pressed films of the IS-added PBISe copolyesters with ≤16% content are 31.6–36.3 MPa and 639.2–809.9%, respectively. The developed PBISe copolyesters have great potential as bio-based, biodegradable, and flexible materials for packaging and coating applications with low processing temperatures.

Approach to Low Contact Resistance Formation on Buried Interface in Oxide Thin-Film Transistors: Utilization of Palladium-Mediated Hydrogen Pathway.

Amorphous oxide semiconductors (AOSs) with low off-currents and processing temperatures offer promising alternative materials for next-generation high-density memory devices. The complex vertical stacking process of memory devices significantly increases the probability of encountering internal contact issues. Conventional surface treatment methods developed for planar devices necessitate efficient approaches to eliminate contact issues at deep internal interfaces in the nanoscale complex structures of AOS devices. In this work, we report the pioneering use of palladium thin film as a high-efficiency active hydrogen transfer pathway from the outside to the internal contact interface via low-temperature postannealing in the H2 atmosphere, and the formation of highly conductive metallic interlayer effectively solves the contact issues at the deeply buried interfaces in devices. The application of this method reduced the contact resistance of Pd electrodes/amorphous indium-gallium-zinc oxide (a-IGZO) thin-film by 2 orders of magnitude, and thereby the mobility of thin-film transistor was increased from 3.2 cm2 V-1 s-1 to nearly 20 cm2 V-1 s-1, preserving an excellent bias stress stability. This technology has wide applicability for the solution of contact resistance issues in oxide semiconductor devices with complex architectures.

Experimental Characterisation of BGBC OTFT for Indoor CO<sub>2</sub> Gas Sensing

Global warming is a concern nowadays due to excessive release of harmful gasses to the environment, leading to greenhouse effect phenomena worldwide. Based on the data provided by global pollution agencies, the release of greenhouse gasses to the atmosphere is the main cause of pollution and the increase in atmospheric temperature due to warming. Greenhouse gasses (GHGs) contents released to the environment is worrying, with carbon dioxide (CO2) is reported at the highest concentration compared to other gasses. There are many studies conducted to develop and evaluate the performance of harmful gas sensors incorporating inorganic and organic semiconductive materials. Organic semiconductors (OSCs) are environmentally friendly materials, relatively cheaper technology, and comprised of a wide range of materials with good carrier mobility. Therefore, in this work, Organic Thin Film Transistor (OTFT) is developed for gas sensor application. As global warming is becoming more serious, this solution is instead a sustainable solution to the environment, as organic molecules which are held together via Van der Waals bond are easily processed via low-temperature deposition and solution processing as compared to more complicated processes involved in conventional inorganic counterpart. In addition, the developed sensor is generally robust due to the ability to withstand high humidity conditions and can be fabricated on flexible substrates. In this work, suitable materials are identified in basic OTFT construction, which are the electrodes, dielectric and substrate. The scope is mainly focusing on the development of bottom gate OTFT construction, incorporating p-type active material which are Trisisopropylsilylethynyl Pentacene (TIPS Pentacene), Aluminium (Al) as drain and source electrodes, PEDOT: PSS as gate electrode and Polyvinyl alcohol (PVA) as gate dielectric. The materials in bottom gate bottom contact (BGBC) configuration, fabricated via screen printing technique is experimentally tested towards CO2 detection. CO2 is initially detected at 1618 ppm with contact resistance of 15 kΩ, and at 10 ml/minute flow rate, the developed configuration is demonstrated able to achieve sensitivity of 2.069 Ω/ppm. In conclusion, the studied BGBC OTFT has demonstrated suitability and applicability in CO2 gas sensing for sustainable environmental condition monitoring, that could lead to safer environment for the living things on earth. With the proposed dimensions, in the future it is possible to proceed with this work to be fabricated by using more advanced techniques such as photolithography and many others.

Numerical investigations and design optimization of cryogenic plate-fin heat exchanger in Electric Arc Furnace using radiative heat transfer model

The most crucial element affecting cryogenic systems’ energy efficiency is heat exchangers. In this article, a model for cryogenic plate-fin heat exchanger (PFHE) under thermal-hydraulic performance with various blends is proposed. To reduce five objective functions total heat transfer rate, total weight, total mass flow rate, number of entropy generating units, and whole annual cost the study carried out the PFHE’s optimal design. This study innovatively focuses on optimizing PFHE design for cryogenic conditions using Opposition Learning with the Beetle Swarm algorithm. The proposed geometry addresses non-uniform temperature distribution, emphasizing thermal-hydraulic properties in various blends. Additionally, a second-order semi-discretization radiative heat transfer approach enhances boiler simulation accuracy. A multi-objective optimization of Opposition Learning with Beetle Swarm (MO-OBBS) optimization approach was suggested in the article for the design of PFHE. Despite the significant potential for renewable energy the low-temperature waste heat treatment process is rarely examined from a sustainability perspective. Consequently, the study proposed a second-order semi-discretization radiative heat transfer method to simulate a furnace using a water heat recovery process. The cooling panel’s numerical analysis was conducted using computed temperature fields. The performance of the various algorithms is compared using the Freidman rank-sum test to determine the statistical significance of the findings obtained. In logarithmic coordinates, the proposed method’s faster convergence is compared to GQB-PSO, SLTLBO, Jaya, CKKO, and OLE-SCA algorithms. The proposed method exhibits a maximum average increase of 115.39% for PFHE design. When the numerical simulation results are compared to measurements of output water temperature, the accuracy is highly improved.

Ge1−xSnx layers with x∼0.25 on InP(001) substrate grown by low-temperature molecular beam epitaxy reaching 70 °C and in-situ Sb doping

Ge1−xSnx with x∼25%, group-IV alloy semiconductor, is highly attracted to mid-infrared (MIR) photodetector applications because of its narrow bandgap with ∼0.25 eV, the compatibility to the Si integrated circuit platform, and lattice matching of Ge0.75Sn0.25 to InP substrate. Although the heteroepitaxial growth of Ge0.75Sn0.25 on InP has been reported, the basic physical properties of Ge0.75Sn0.25 have not yet been clarified. In this study, we discuss three topics: (1) understanding the crystalline growth features of Ge0.75Sn0.25 on InP, (2) revealing the thermal stability of Ge0.75Sn0.25, and (3) developing a carrier-control technique. First, we found that a low-temperature molecular beam epitaxy could achieve a Ge0.75Sn0.25 layer with superior crystallinity without dislocations. However, low Sn-content Ge1−xSnx regions are locally formed during the Ge0.75Sn0.25 heteroepitaxy; the origins of the low Sn-content Ge1−xSnx regions were discussed by transmission electron microscopy analysis. In addition, we found that lowering the growth temperature from 100 °C to 70 °C also effectively reduces the area of the low Sn-content Ge1−xSnx regions. Next, we found that Ge0.75Sn0.25 layers grown at 70 °C sustain thermal stability up to 200 °C without causing crystalline degradations. Finally, we demonstrated the in-situ Sb doping to Ge0.75Sn0.25. We found that the undoped and in-situ Sb-doped Ge0.75Sn0.25 layers exhibited p-type and n-type conduction, respectively, with carrier concentrations of order 1019 cm−3 by Hall effect measurement. This study suggests the MIR photodetector application is practically possible using low-temperature processes with process temperatures lower than 200 °C.

Ammonium iodide-incorporated SnO2 obtains perovskite solar cells with over 24% efficiency

Tin dioxide (SnO2) as the most promising electron transport layer (ETL) has been widely used in high-efficiency perovskite solar cells (PSCs) due to its excellent optical/electronic properties, chemical stability, and low-temperature processing. However, the surface of SnO2 ETL contains defect sites, which result in energy losses in PSCs. In order to passivate the defects of SnO2 surface and together tune the electronic properties of SnO2 ETL for getting high-performance PSCs, we herein incorporate the low-cost material ammonium iodide (NH4I) into the SnO2. After the NH4I doping, the optimized photovoltaic power conversation efficiency is significantly enhanced (the highest efficiency can reach 24.4%), the hysteresis of device is largely suppressed to a negligible level, and the stability of device is also obviously improved. The origin of these enhancements is further disclosed by the positive effects of NH4I doping on both ETL and perovskite film: the surface morphology of ETL is effectively flatten, the energy level of ETL is suitably adjusted, the electron mobility of ETL and the perovskite grain size are clearly increased, the surface defects of ETL and the trap states in the perovskite film are greatly reduced, and the PbI2 residue in the perovskite layer is obviously diminished. The study here of incorporating cheap inorganic small molecule in the ETL provides an ingenious way to enhance the performance of the planar PSCs.

Efficacy of mosquito repellent finishes on polyester fabrics using four essential oils against the vector of the West Nile virus, Culex pipiens (Diptera: Culicidae)

One of the most common ways to prevent mosquito bites is to use treated textiles, which can be used to repel mosquitoes in the form of nets, clothing, uniforms, and other items. Four eco-friendly essential oils: lemongrass (Cymbopogon citratus), eucalyptus (Eucalyptus camaldulensis), clove (Dianthus caryophyllus), and marjoram (Origanum vulgare), were evaluated and used to finish polyester fabrics (PE) to give them a pleasant odor and antibacterial properties, as well as mosquito repellent as medical textiles. A low-temperature drying process and thermal stabilization technique were used to bond the polyester to the fragrance-containing compounds. The effect of essential oil finishes on polyester textile properties has been studied using various techniques such as mechanical measurements, contact angle, ultraviolet tests, infrared spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, GC-MS analysis, etc. Scanning electron microscopy showed the physical adsorption of oil on PE surfaces and the penetration of oil droplets between PE fibers. The ability of polyester textiles treated with essential oils of lemongrass, eucalyptus, clove, and marjoram to kill Staphylococcus aureus, Escherichia coli, Candida albicans, and Aspergillus niger was also tested. Polyester fabrics treated with clove showed the strongest antibacterial effect, surpassing that of eucalyptus oil. 12 essential oils were screened to determine their superiority in repelling mosquitoes at a concentration of 1% through the CDC bottle and WHO cone tests. Cymbopogon citratus (LT50 = 60.03 min) oil was the most effective against Cx. pipiens, followed by Eucalyptus camaldulensis (LT50 = 61.65 min) and Dianthus caryophyllus (LT50 = 64.73 min) with CDC tests. It was found that finishing PE with clove and eucalyptus oils provided 76 and 68% protection from Culex pipiens mosquitoes, even after 6 cycles of washing. This approach is innovative because it meets the goal of having antibacterial, mosquito-repellent, and pleasant-smelling fabrics as requirements for economically viable medical textiles. There is an urgent need to engineer textiles, with or without insecticides, to effectively repel mosquitoes. Our data showed the efficiency of polyester fabric treated with clove and eucalyptus oils in repelling mosquitoes after 6 washings.

Study on separation of CO2 condensation from natural gas based on cellular automaton method

ABSTRACT The CO2-containing natural gas is increasing, and there is an urgent need for green treatment of natural gas containing CO2 to realize the utilization of natural gas. Conventional natural gas decarbonization methods have drawbacks such as non-environmental friendliness, and the low-temperature condensation separation of carbon dioxide (snowing-separation) method as a green method of carbon capture is proposed in this paper. Aiming at the characteristics of CO2 condensation in the snowing-separation process, the growth process of CO2 crystals is obtained by simulation using the CA (Cellular Automata) method and finds that the effect of supersaturation on the growth of CO2 crystals is exponential. The snowing-separation process at .5 MPa is analyzed, and it is found that the condensation range is 158.51 K–173.86 K, the upper limit of CO2 mole fraction in natural gas is 10.1%, and the minimum separation time is 8.65 × 10−8s. Analyzing the influencing factors of CO2 separation efficiency, combining the simulation results with the experimental results, the maximum relative error is 13.93%, which can better predict the snowing-separation technology of CO2 in natural gas, and then promote the development of efficient low-temperature carbon capture process.

Anion Hybridization for Enhanced Broadband Optical Response in Bi‐Doped Photonic Glass and Fiber

AbstractGiven the ever‐increasing demand for transmission capacity in optical fiber communication systems, there is a growing focus on developing active fibers and devices with an optical response across a wider spectrum. Bismuth (Bi)‐doped photonic glasses have attracted significant interest for their exceptional ultra‐broadband optical response, particularly within telecommunication bands. However, developing advanced Bi‐activated materials with robust optical response, high compatibility with commercial transmission systems, and low processing temperature remains a huge challenge. Herein, an anion hybridization strategy is proposed to overcome the aforementioned limitations. The anion hybridization significantly enhances the broadband optical response (≈10 times) of the Bi center following the introduction of fluorine ions, and reduces the transition temperature of the photonic glass (≈200 °C). Moreover, the near‐infrared optical response bandwidth experiences significant broadening, a result attributed to the larger inhomogeneous broadening. Furthermore, successful fabrication of the anion‐hybridized Bi‐activated glass fiber is achieved, demonstrating excellent compatibility with commercial transmission fibers. Additionally, the fabricated fiber exhibits an amplified spontaneous emission and on‐off gain across a broad waveband, further validating its efficacy. These results indicate that anion hybridization offers an effective strategy to optimize the optical and thermal properties of photonic materials to develop novel advanced photonic devices.

Comprehensive evaluation of low-temperature oxidation characteristics of low-rank bituminous coal and oil shale

The coexistence of coal and oil shale mining conditions exacerbates the complexity of coal spontaneous combustion (CSC) prevention, so conducting in-depth research on the spontaneous combustion characteristics of coal, oil shale, and their mixed samples is necessary. A programmed heating system simulated the low-temperature oxidation process of bituminous coal and oil shale under different air volumes. It was found that CO concentration, C2H4 concentration, and Graham's fire coefficient (R1, R2) can be used as indicator gases to predict the CSC process. Compared with oil shale and mixed samples, bituminous coal has a higher CO production rate, oxygen consumption rate, heat release intensity, and lower apparent activation energy during the slow oxidation stage. Meanwhile, bituminous coal also has lower peak values of minimum float coal thickness, lower limit oxygen concentration, and maximal air leakage intensity, which means that bituminous coal in the goaf is more prone to oxidation. However, the abundant free hydrogen bonds in oil shale can stabilize the hydrogen-deficient functional groups of bituminous coal, which weakens the oxidation ability of the mixed sample during the accelerated oxidation stage. In addition, the increased air volume fraction increases the oxygen adsorption efficiency of the mixed sample throughout the low-temperature oxidation process, which means that the M70 sample has a higher CSC risk. The results have enriched the research on the spontaneous combustion characteristics of coal, oil shale, and mixed samples, which may strengthen the management and control of CSC in coal and oil shale co-mining mines.

Fabrication and piezoelectric analysis based on nanogrid architecture composed of ZnO ultrathin nanosheets grown on fiber paper substrates for wearable energy harvesting

In this work, three-dimensional (3D) nanogrid architecture composed of two-dimensional (2D) ZnO ultrathin nanosheets (ZUNSs) is grown on fiber paper substrates by a two-step low-temperature hydrothermal process, and a flexible piezoelectric nanogenerator (PENG) is also developed based on the as-grown ZUNS-paper. Piezoelectric signals were also measured under compressive forces that can harvest energy up to 30 nA and 120 mV. In order to exploit the piezoelectric properties of the unique ZnO nanostructure, a series of simulation experiments based on ZUNSs were conducted systematically through the finite element method (FEM, COMSOL). The size-dependent simulation analysis (including thickness, length, and height) under two different force modes manifests that the ZUNSs possess tremendous merits for optimizing the output performance of piezoelectric nanogenerators, especially in the case of lateral bending. Besides, the anisotropic electricity generation has been investigated and analyzed within the ZUNSs via applying force with various orientations. Our results may provide guidance for the design and performance optimization of wearable self-powered micro/nanoelectric devices.

Run-indexed time-varying Bayesian optimization with positional encoding for auto-tuning of controllers: Application to a plasma-assisted deposition process with run-to-run drifts

Bayesian optimization (BO) has emerged as a useful paradigm for automatic calibration (aka auto-tuning) of advanced optimization- and learning-based controllers whose closed-loop performance depends on the choice of several tuning parameters in highly nonlinear and nonconvex ways. However, BO approaches to controller auto-tuning commonly rely on the assumption that system dynamics remain constant, which does not hold for systems with time-varying dynamics, for example, due to gradual aging or persistent environmental drifts. This challenge can be further compounded when gradual and persistent system drifts occur over a series of process runs. Existing time-varying BO (TVBO) approaches with spatio-temporal kernels fall short of effectively handling an integer run index, which is imperative for capturing run-to-run changes in the system behavior. To this end, this paper presents a run-indexed TVBO (RI-TVBO) approach that can systematically account for run-to-run process drifts as the system is queried over sequential process runs. The proposed approach relies on adapting the non-stationary Wiener process kernel to accommodate an integer run index, instead of time. This is done via positional encoding that incorporates the integer run index and, thus, enables describing run-to-run variations in system dynamics. The positional embedding vector associated with each run index is then mapped onto a scalar value to leverage the relationships between different process runs within the probabilistic surrogate model of the objective function in RI-TVBO. The performance of RI-TVBO is evaluated for auto-tuning of an offset-free model predictive controller for a low-temperature plasma-assisted process for thin film deposition. Simulation results demonstrate the superior performance of RI-TVBO over standard BO and TVBO under different scenarios of run-to-run process drifts encountered in plasma-assisted deposition processes in semiconductor manufacturing.

Studies on catalyst assisted low-temperature curing of benzoxazines

The present study addresses an increasing interest in achieving low-temperature curing of benzoxazines by utilizing chemical substances with acid moieties of varying functionalities as curing catalysts. Specifically, cardanol-furfurylamine (1), card-bisphenol-furfurylamine (2), bisphenol-A-aniline (3) and bisphenol-F-aniline (4) based benzoxazines were chosen for curing studies. The selected catalysts were systematically applied into benzoxazines and its curing behavior was studied with minimum amount of 5 wt%. Catalysts, including those with carboxyl and N,N-dimethyl functionalities, were evaluated based on their performance, with a focus on their substituent effect on curing behavior. The results contribute to the identification of catalysts with optimal potential for achieving the efficient low-temperature curing of benzoxazines with an objective of utilizing them for wide area of applications. Among the catalysts studied, gallic acid was found to be the better catalyst and reduces the curing temperature to 130 °C. The conversion graph for both bisphenol-A-aniline benzoxazine (3) in the absence of catalysts and bisphenol-A-aniline benzoxazine in the presence of catalysts (3 s) have been studied by DSC analysis. The activation energy (Ea) has been calculated using Kissinger-Ozawa method through DSC analysis. Data resulted from different catalysts used for curing of benzoxazines, it was inferred that the pKa values of the catalysts also play a crucial role in the polymerization of benzoxazines. Further, the study aims to meet the growing demand for efficient and economically viable low-temperature curing processes for benzoxazines.