Showing papers in "ECS Journal of Solid State Science and Technology in 2022"

Optical Characteristics of Thermally Evaporated Thin a-(Cu2ZnGe)50-xSe50+x Films

Abstract: The optical characteristics of a-(Cu2ZnGe)50-xSe50+x, CZGSe, (0≤x≤20 at.wt.%) films were studied. The amorphous nature of the films was affirmed via X-ray diffractograms. Energy-dispersive X-ray spectroscopy confirmed matching between selected compositional element percentages and those measured for all films. Many optical properties and parameters of CZGSe films were studied using UV-Vis-INR spectroscopic transmission and reflection measurements. The envelope methods have been successfully applied on the measured transmission spectra according to the Swanepoel technique, along with reflection spectra in accordance with the Minkov method. Obtained results based on the Swanepoel analysis are in excellent agreement with those inferred from the Minkov method. A clear blueshift of the absorption edge was observed from 854 to 720 nm, in accordance with the increasing optical bandgap energy values from 1.456 to 1.722 eV, as Se-content increases from 50 to 70 at.wt.%. The electronic transitions of (Cu2ZnGe)50-xSe50+x films arose from allowed indirect transitions. The observed energy gap increase was interpreted according to the Mott and Davies model. The absorption coefficient values have been estimated and are found to be larger than10-4cm-1. All discussed parameters strongly depend on the Se-concentration. The bonding strength between the elements of samples strongly affects the optical properties.

Effect of Hybrid Reinforcements on the Mechanical Properties of Copper Nanocomposites

Abstract: Copper (Cu) composites hybridized with nano-sized reinforcing material are gathering attraction in such fields as automobile, aerospace, and power transmission due to their higher strength. Unlike conventional reinforcing materials, extraordinary mechanical properties and high electrical and thermal conductivity make nanomaterials highly useful reinforcement materials to improve the properties of pristine metals. Over the last two decades, several studies have been conducted to determine the effect of distinctive 2D nanomaterials, such as silicon carbide, aluminium oxide, copper nanotube, and graphene as reinforcement on properties of metal matrices. This study comprehensively reviews the effect of hybrid reinforcements on the mechanical properties of Cu composites having graphene as one of the reinforcements. Also, the contribution of these reinforced nanomaterials composition and their dispersion in the pure Cu matrices have also been explained in detail. In comparison with Cu composites fabricated with a single 2D reinforcement material, composites incorporating hybrid nano reinforcement, exhibit better mechanical behaviour. Additionally, the improvement in mechanical strength would enhance their capability to withstand altering thermal and surrounding environmental conditions.

Engineering Electrical and Thermal Attributes of Two-Dimensional Graphene Reinforced Copper/Aluminium Metal Matrix Composites for Smart Electronics

Abstract: Rising demand for reliable thermally and electrically conductive and stable, light weight, and mechanically enduring materials in architecting smart electronics has accelerated the research in engineering metal-matrix composites (MMCs). Among these, copper (Cu) and aluminium (Al) based MMCs are popular owing to high electrical conductivity, but large heat dissipation in compact electronic gadgets is still challenging. The reinforcement of Cu/Al with graphene caters to the problem of heat dissipation, strengthens mechanical endurance, and optimizes electronic and thermal conductivities as per device architecture and application. Here we systematically review the state-of-the-art Cu/Al MMCs using graphene reinforcement with enhanced electrical, thermal, and mechanical attributes for smart electronics manufacturing and discuss the fundamentals for optimising the electrical and thermal charge transport in Cu/Al MMCs through graphene reinforcement. In addition, we discuss challenges, alternate solutions, and advanced prospects of graphene reinforced Cu/Al MMCs for smart electronics manufacturing.

Review—Negative Thermal Quenching of Mn4+ Luminescence in Fluoride Phosphors: Effects of the 4 A 2g →4 T 2g Excitation Transitions and Normal Thermal Quenching

Abstract: Thermal stability of phosphor materials is of crucial importance and scientific interest. It is well known that various Mn4+-activated phosphors, especially Mn4+-activated fluoride and oxyfluoride phosphors, show an anomalous thermal quenching behavior, i.e., an increase in the integrated photoluminescence intensity I PL with increasing temperature T, known as the negative thermal quenching (TQ) behavior. The negative TQ has been understood to be due to the electric dipole (parity) forbidden transitions of 2 E g →4 A 2g gained by coupling with the odd-parity lattice vibrations, ν 3, ν 4, and ν 6. This article discusses the effects of the 4 A 2g →4 T 2g excitation transitions on a negative TQ phenomenon. Our previous study suggested that the 4 A 2g →4 T 2g excitation transitions in Mn4+-activated fluoride phosphors are strongly connected with the certain mode phonons, namely the gerade-mode ν 2 phonons, with an energy of ∼65 meV. Here, our analysis model considers this effect and is found to show good agreement with the experimental data. Discussion is also given of the temperature dependences of decay time τ(T) and quantum efficiency η(T) in comparison with I PL(T), demonstrating a strong correlation among such important phosphor properties except for an occurrence of negative TQ only in I PL(T).

Design and Investigation of a Novel Gate-All-Around Vertical Tunnel FET with Improved DC and Analog/RF Parameters

Abstract: A novel structure of GAA vertical TFET (GAA-VTFET) is proposed and investigated with the help of 3D TCAD simulator. It is found that GAA-VTFET offers much improvement in various DC parameters like ION, IOFF, SSAVG, and turn-on voltage (VT) compared to a conventional GAA-TFET. As the tunneling direction of charge carriers is in parallel to the gate electric field, channel thickness in GAA-VTFET is rigorously reduced and thus improves the tunneling rate at the source/channel interface during ON-state. Further, IOFF is significantly reduced due to deployment of a dielectric layer beneath the channel/drain interface. The impact of variation in geometric dimensions is also analyzed to obtain optimum performance of the GAA-VTFET. ION/IOFF is observed to be in order of ∼1013 while SSAVG of 56 mV/decade is achieved. Analog/RF parameters are also analyzed and it is noticed that an improved cut-off frequency of 593 GHz is achieved due to improvement in parasitic capacitances and transconductance. Next, benchmarking reveals that GAA-VTFET offers better ION/IOFF, VT, and SSAVG as compared with the similar devices. Finally, based on transient analysis of inverter circuit, GAA-VTFET is found to be more suitable for digital applications as it offers less rise-time along with full-voltage swing.

Investigation of Crosstalk Issues for MWCNT Bundled TSVs in Ternary Logic

Abstract: The investigation of crosstalk issues for coupled through silicon vias (TSVs) in ternary logic is presented in this study. The crosstalk issues are analyzed for coupled TSVs utilizing multi-walled carbon nanotube (MWCNT) as conductive filler, and polymer liners such as polyimide, polypropylene carbonate, and benzocyclobutene (BCB) as insulating materials. For the coupled TSVs, the electrical equivalent circuit model is used to investigate the crosstalk which is driven by the ternary inverter. Based on the Hewlett simulation program with integrated circuit emphasis simulations, the effects of crosstalk such as functional and dynamic crosstalk for proposed TSVs are compared with single-walled CNT (SWCNT) TSVs. Furthermore, the other performance parameters such as power dissipation, power delay product (PDP), and energy delay product are investigated. The crosstalk effects of the proposed model are also examined for various TSV heights. It is noticed that the BCB based coupled MWCNT TSVs provide a significant improvement in crosstalk at reduced TSV height. It is also noticed that the proposed TSVs improved the overall performance up to 30.21% compared to the SWCNT based TSVs. Hence, the MWCNT based TSVs with BCB liner are most suitable for ternary logic integrated circuits over the conventional TSVs.

A Charge-Based Analytical Model for Gate All Around Junction-Less Field Effect Transistor Including Interface Traps

Abstract: This article proposes an analytical charge-based model that incorporates interface trapping. The model's applicability to all operating zones includes various interface trap charges with varying doping concentrations. Using the analytical model, the impact of interface traps on different electrical parameters, such as channel potential, surface potential, electric field, and drain current, is examined. The transconductance and cut-off frequency models are also developed from the drain current model. To validate our model, the analytical model results were compared with TCAD device simulation results and available experimental data from the literature. The Fermi level location of interface traps greatly influences surface potential in the bandgap, leading to subthreshold deterioration and flat band shifting in Junction-Less Field Effect Transistor (GAAJLFET) with SiO2 as a gate insulator, which leads to performance degradation of different device parameters. To decrease the impact of the interface trap on the device's characteristics without impairing the performance, a suitable device with SiO2 and high-k gate-stack as an insulator is designed and compared with GAAJLFET with SiO2 as a gate insulator. A GAAJLFET with SiO2 as an insulating material has very different device parameters than a GAAJLFET with SiO2 and high-k gate-stack as a gate insulating material.

Reusability of Photocatalytic CoFe2O4@ZnO Core–Shell Nanoparticles for Dye Degradation

Abstract: The reusability of CoFe2O4@ZnO core–shell nanoparticles (NPs) for the photocatalytic degradation of methylene blue (MB) under UV radiation was successfully investigated. CoFe2O4@ZnO NPs with various CoFe2O4-to-ZnO concentration ratios were synthesized as magnetic photocatalysts. The X-ray diffraction spectra showed that the NPs had a cubic spinel ferrite phase structure and a hexagonal wurtzite phase of ZnO. Fourier-transform infrared spectra showed the presence of Moct-O, Mtet-O, and Zn-O at 593, 347-389, and 410-429 cm-1, respectively. The CoFe2O4@ZnO NPs had a saturation magnetization of approximately 30 emu/g and a coercivity of approximately 280 Oe. The absorbance spectra showed that the absorbance peak of the CoFe2O4@ZnO NPs broadened and shifted to the right (higher wavelength) with increasing ZnO concentration. The CoFe2O4@ZnO NPs with higher ZnO concentrations exhibited higher photocatalytic activities and degradation rates. The enhancement of MB degradation can be attributed to the formation of an internal structure between CoFe2O4 and ZnO. The degradation rate of CoFe2O4@ZnO decreased slightly after each successive recycle. The results indicated that the recycled CoFe2O4@ZnO NPs could be reused three times for photocatalytic degradation. As there is no significant decrease in the photocatalytic degradation after four successive recycles, the CoFe2O4@ZnO NPs are suitable for application in dye degradation.

Design Insights into Thermal Performance of Vertically Stacked JL-NSFET with High-k Gate Dielectric for Sub 5-nm Technology Node

Abstract: This paper demonstrates the impact of temperature variation on vertically stacked junctionless nanosheet field effect transistor (JL-NSFET) concerning analog/RF performances using different gate lengths (Lg) along with high-k gate dielectrics. A comprehensive analysis of analog/RF performances like transconductance (gm), gate capacitance (Cgg), gate to drain capacitance (Cgd), output conductance (gds), intrinsic gain (Av), maximum oscillation frequency (fMAX), gain frequency product (GFP), and cutoff frequency (fT) is carried out for the temperature range 77-400 K. Note that with the decrease in temperature from 400 to 77 K, there is an improvement in AV, GFP, fT, and fMAX by ~7.43%, ~78.4%, ~78.38%, ~50.9%, respectively. It is also found AV gets degraded with the downscaling of Lg from 16 to 8 nm. However, the same resulted in the improvement of RF performance. From detailed analysis, it is further observed that the usage of high-k gate dielectrics (k=22) in JL-NSFET devices is not suitable due to the depreciation of analog/RF FOMs. Moreover, it is also noted that the improvement in analog/RF performance (ΔFoM = FoM(T=400) – FoM(T=100)) resulted from lowering the temperature can further be improved by downscaling of Lg and by using low-k gate dielectric.

Increasing the Gas Response of Ozone Sensors Based on Solution-Processed InGaZnO by Tuning the Size of the Nanostructure

Abstract: This study uses acetylacetone (acac) as an additive to control the size of the nanostructure of solution-processed a-IGZO for ozone (O3) gas sensor applications. It is found that by adding acac, the gas response, response time, and recovery time of an IGZO gas sensor are highly improved. Under the optimal condition (4 wt%), the IGZO sensor shows a gas response of 19 and a response/recovery time of 80/120 s, against 5 ppm O3. Adding acac significantly increases the number of oxygen vacancies within an a-IGZO film so more electrons are available for reaction with the gas. The increased number of oxygen vacancies means that more dangling bonds are created, which activates the gas adsorption process. Moreover, the IGZO gas sensor has an excellent long-term stability showing negligible variation in gas response over 2 months. This method allows easy fabrication of a high-performance gas sensor that uses solution-processed a-IGZO as a sensing layer.

Review—Next Generation 2D Material Molybdenum Disulfide (MoS2): Properties, Applications and Challenges

Abstract: The advancement of new 2D-TMDC material semiconductors remains a prominent research area as the number of scientific applications grows. One of those materials, "molybdenum disulfide," has been newly investigated as a graphene and Si material alternative. Single-layer molybdenum disulfide (SLMoS2) is used as substitute for graphene & other semiconductor appliances with a high capability of practices in nano-electronic, energy-storing, photocatalysts, optical sensors, biosensors, and electrochemical biosensors. It is also being used in a widespread variety of energy-related applications, including batteries, solar cells, microwaves, and Terahertz. Furthermore, future use as a material in nano-scale fields, having additional opportunities in spintronics and magneto-resistance. Many research papers have been published on the evolution and application of MoS2 materials but here we give a complete in-depth comprehensive examination and analysis of the evolution of various 2D materials, starting with their state of requirement, formation, properties, applications, and future challenges along with the various comparison simulation results.

Review—Temperature Dependence of Luminescence Intensity and Decay Time in Cr 3+ -Activated Oxide and Fluoride Phosphors

Abstract: Studying temperature dependence of light emission intensities in luminescent materials is not only of scientific interest but also technological importance. It is well known that Mn4+-activated “fluoride” phosphors sometimes show an anomalous thermal quenching (TQ) behavior. This behavior is an increase in the integrated photoluminescence (PL) intensity I PL with increasing temperature T, called negative TQ, and is understood to be due to the electric dipole (parity) forbidden transitions of 2 E g →4 A 2g gained by coupling with the odd-parity lattice vibrations, ν 3, ν 4, and ν 6. The present article discusses the temperature dependence of the integrated PL intensity for the Cr3+-activated “oxide” and “fluoride” phosphors with an emphasis on negative TQ phenomenon. The effects of the 4 A 2g →4 T 2g excitation transitions in conjunction with those of the normal (positive) TQ are considered for developing a new analysis model of I PL(T) data. Our new analysis model shows a good agreement with the experimental I PL(T) data. Discussion is also given on the temperature dependence of luminescence decay time τ(T), demonstrating a strong correlation between I PL(T) and τ(T) except for negative TQ occurring only in I PL(T).

Efficient and Highly Reliable Spintronic Non-volatile Quaternary Memory Based on Carbon Nanotube FETs and Multi-TMR MTJs

Abstract: Due to the limitations of traditional binary circuits, such as high power consumption and large area and interconnections density, multi-valued logic (MVL) was offered as a solution. Quaternary logic is a form of MVL that is highly compatible with binary systems. This paper proposes a low-cost and highly reliable non-volatile quaternary memory benefiting from the adjustable threshold voltage property of gate-all-around carbon nanotube field-effect transistors (GAA-CNTFET) and non-volatile nature of magnetic tunnel junctions (MTJ). The proposed quaternary memory occupies less area and consumes lower power. The simulation results show that the proposed design offers up to 53%, 41%, and 69% lower average power, static power, and write power. Moreover, it offers up to 47% and 34% lower read power delay product (PDP) and write PDP, respectively. The proposed latch also occupies up to 23% lower area than the state-of-the-art non-volatile quaternary memories.

A Dual-Drain Vertical Tunnel FET with Improved Device Performance: Proposal, Optimization, and Investigation

Abstract: In this manuscript, a dual-drain Vertical Tunnel FET structure is proposed and investigated for the first time. The simulation outcomes clearly manifest that reduction in channel thickness, which has inadequate impact on the tunneling region, significantly improves numerous DC parameters of the proposed device including subthreshold swing, on-state current and current-switching ratio by enhancing the band-to-band tunneling of the charge carriers at source/channel interface caused by enlarged electric field. In order to make the proposed device suitable for low power applications, dielectric material is incorporated in between two drain/channel interfaces to reduce the subthreshold leakage current. A detailed investigation is carried out to determine the influence of varying device footprints on various electrical parameters and accordingly, the optimized device performance is achieved. TCAD-based simulation results reveal that a considerably low subthreshold swing of 18 mV decade−1 along with a high current-switching ratio of 1.6 × 10 13 can be achieved with optimum geometric dimension of design parameters i.e., gate-oxide, source and channel. Further, the performance of the proposed device is compared with various existing TFET structures and found to be superior in terms of current switching ratio, average subthreshold swing and turn-on voltage. The probable fabrication process flow is also discussed for the proposed device and based on the proper benchmarking, it is revealed that improvement in the parameters like low-output voltage, peak overshoot and rise time defining the switching characteristics of an inverter makes the proposed device more suitable for digital circuit-based applications.

Review—Chemical Structures and Stability of Carbon-doped Graphene Nanomaterials and the Growth Temperature of Carbon Nanomaterials Grown by Chemical Vapor Deposition for Electrochemical Catalysis Reactions

Abstract: Carbon nanotubes (CNTs) have been studied extensively utilizing the catalytic chemical vapor deposition (CCVD) process for several decades. CCVD is seen to have a better degree of control and scalability. CNTs have proved to be useful in single-molecule transistors, scanning electron microscope (SEM) tips, gas and electrochemical storage, electron field emitting flat panel displays, and sensors. This review summarizes various stabilizing agents such as cobalt ferrite and molybdenum disulphide that can increase the electrochemical activity of the carbon doped-graphene nanomaterials as graphene doped with carbon shows a great improvement in the properties in various aspects. We also looked into the electrochemical applications where CNTs are used as a prerequisite. Carbon nanotubes are seen in biosensors, energy storage, conductive plastics, and power fuel cells. Carbon nanomaterials’ influence on symmetrical and asymmetrical supercapacitors, carbon nanomaterials to power dye-synthesized solar cells, and the importance of CVD in the synthesis of carbon nanomaterials were also investigated.

Review—Temperature Dependence of Transition-Metal and Rare-Earth Ion Luminescence (Mn4+, Cr3+, Mn2+, Eu2+, Eu3+, Tb3+, etc.) I: Fundamental Principles

Abstract: Thermal stability of the phosphor materials is of crucial importance and scientific interest. Various Mn4+-activated fluoride, oxide, and oxyfluoride phosphors show an anomalous thermal quenching (TQ) behavior, i.e., no decrease or an increase in the integrated photoluminescence intensity I PL with increasing temperature T, known as zero or negative TQ. The purpose of this article is to discuss such anomalous behaviors of thermal stability of the phosphors doped with various kinds of activator ions from an aspect of solid-state physics. Mn4+ (3d 3)-activated fluoride phosphor is a good example to understand the fundamentals of such foreign ion-activated phosphors. The luminescence transitions of 2 Eg →4 A 2g in 3d 3-configuration ions are both parity and spin-forbidden transitions and, therefore, one can expect no strong light emission. Herein, Mn4+ luminescence is discussed from an aspect of parity integral. This approach helps better understanding of the peculiar luminescence properties observed in the various 3d 3 ion-activated phosphors. The luminescence properties of the HK3SnF8:Mn4+ and Cs2WO2F4:Mn4+ phosphors are examined in detail as a verification of our proposed model. This model will also be successfully applied to other kinds of activator ions like Cr3+, Mn2+, Eu2+, Eu3+, and Tb3+ in a separate article (II).

Preparation and Characterization of Radio Frequency Sputtered Delafossite Copper Gallium Oxide (CuGaO2) Thin Films

Abstract: In this research, CuGaO2 thin films were prepared on quartz substrates by a radio frequency magnetron sputtering technique at 400℃ followed by subsequent annealing in N2 ambience. The effects of annealing temperature on structural, morphological, optical, and electrical properties of CuGaO2 thin films is reported. X-ray Diffraction (XRD) analysis confirmed the presence of single phase CuGaO2 in the film annealed at 900℃. Near stoichiometric composition ratio of Cu:Ga (1:1.08) was identified in the film annealed at 900℃. Field emission scanning electron microscopy showed an increase in the grain size with increase in annealing temperature. A UV-Vis spectrophotometer was used to perform optical studies in the 200-800nm wavelength region on all films. The optical bandgap was calculated from the transmission studies and was found to be in the range of 2.77 to 3.43 eV. The films annealed at temperatures 800℃ and above were found to be p-type. The lowest resistivity value of 230 Ω-cm was achieved for the film annealed at 900℃.

Review—Hybrid Bonding-Based Interconnects: A Status on the Last Robustness and Reliability Achievements

Abstract: This paper reviews the most significant qualification and reliability achievements obtained, over the last 6 years, by the scientific community for hybrid bonding-based interconnects (HB) also called Cu-Cu or Cu/SiO2 bonding. First, the definition of words qualification, robustness and reliability are given to avoid misunderstanding about the published results. Second, the five potential threats (moisture ingress, thermomechanical stresses,electromigration, Cu diffusion, dielectric breakdown) are presented. Finally, the publications of six industrials or research and technology organizations are summarized and discussed. Most of the published data are related to qualification results (pass or fail). Few studies published in-depth studies, mainly on electromigration (Black’s parameters extraction and failure analysis) and copper diffusion (electrical and analytical characterizations). To conclude, once the manufacturing issues (surface preparation, alignment…) have been solved, this technology is robust and reliable at pitches > 1 μm as it reacts, roughly, like a conventional back-end of line (BEoL) interconnect.

Preparation of Copper Doped Conducting Polymers and Their Supercapacitor Applications

Abstract: In this work, copper doped polyaniline and polypyrrole based materials were synthesized by in-situ chemical synthesis method using of copper salt as oxidant for the first time in the literature. Prepared materials were characterized by using of microscopic, spectroscopic, and thermal methods. Doping of polyaniline and polypyrrole in the form of Cu(II) ions and Cu-N were confirmed by the analyses of X-ray photoelectron spectroscopy. The interaction mechanisms of copper and polyaniline and polypyrrole were discussed in the given work. Morphology of the copper doped conducting polymers were characterized by using of scanning electron microscopy. Particle size distribution of the prepared powders were in micron scale from 60 to 478 µm. Then, prepared copper doped conducting polymers were used as electrode materials of asymmetric type supercapacitors in 1.0 M sulfuric acid and 1.0 M sodium sulfate. The highest areal capacitance was determined as 185 mF.cm−2 at 5 mV.s−1 in copper doped polypyrrole prepared 0.4 M pyrrole, 0.5 M CuCl2 and 0.2 M HCl including medium. Here, copper doping of the conducting polymers increased capacitive properties of these materials.

Perspective—The Elusive Quantum Anomalous Hall Effect in MnBi2Te4: Materials

Abstract: Observation of the quantum anomalous Hall effect (QAHE) in MnBi2Te4 fakes is one of the most exciting results in the study of the intrinsic magnetic topological insulator MnBi2Te4 and related compounds. This fascinating result is yet to be reproduced two years after its first report. The quality of starting MnBi2Te4 crystals is believed to be a key factor. An interesting and important question to address is what is the correct quality to enable the QAHE. Here, we present possible approaches to tuning the magnetic and topological properties of MnBi2Te4 using lattice imperfections, strain, stacking sequence, and interactions between the substrate and flakes/films.

Multifunctional CeO2 Nanomaterials: Wet Chemical Synthesis, Characterization, and NIR Pigmentation Applications

Abstract: Herein, we report the methods adopted for the syntheses of nano-scale CeO2 materials by wet chemical routes (solution combustion, hydrothermal, and precipitation by NH4OH and mixture of NH4HCO3 and NH4OH) and their experimental results supported by differential thermal analysis, X-ray diffraction, field-emission scanning electron microscopy energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, and near-infrared characterization techniques. The nano-scale CeO2 materials were obtained through wet chemical and simple calcination methods in a single-step process. The thermal profile of precursor salt ((NH4)2Ce(NO3)6) reveals ~72% of weight loss in the temperature ranges from 30 to 800°C, whereas the different as-obtained CeO2 materials showed ~3-13% of weight loss indicating the formation of cubic nanostructured CeO2 materials, as evidenced from XRD patterns. All of the pure materials obtained in a single step crystallized in cubic nanostructured CeO2 phase with the average crystalline sizes in the range of 3–28 nm. The morphology of the combustion obtained CeO2 materials exhibits spherical-shaped fine particles with moderate agglomeration. The as-obtained CeO2 materials can be used in the solar reflective and color pigment applications as it shows remarkably high NIR reflectance in the NIR region, 750–2500 nm compared to other binary oxides.

Review—Temperature Dependence of Luminescence Intensity and Decay Time in Mn4+-Activated Oxide Phosphors

Abstract: Thermal stability of the phosphor materials is of crucial importance and scientific interest. Mn4+-activated “fluoride” phosphors are known to sometimes show an anomalous thermal quenching (TQ) behavior. This behavior is an increase in the integrated photoluminescence (PL) intensity I PL with increasing temperature T, called negative TQ, and is understood to be due to the electric dipole (parity) forbidden transitions of 2 E g →4 A 2g gained by coupling with the odd-parity lattice vibrations, ν 3, ν 4, and ν 6. The same behavior can also occur in Mn4+-activated “oxide” phosphors. The present article discusses the temperature dependence of the integrated PL intensity I PL(T) for the Mn4+-activated oxide phosphors focusing on the negative TQ phenomenon. The effects of the 4 A 2g →4 T 2g excitation transitions in conjunction with those of the normal (i.e., positive) TQ are considered for developing new analysis model of I PL vs T data. Our proposed analysis model shows a good agreement with the experimental data. Discussion is also given on the temperature dependence of decay time τ(T) and quantum efficiency η(T), in comparison with I PL(T), demonstrating a strong correlation among such important phosphor properties except for an occurrence of negative TQ only in I PL(T).

Evaluation of Structural and Optical Properties of Nanocrystalline Cubic Y2O3 Phase Materials via Combustion Method Using Different Fuels

Abstract: We have carried out combustion synthesis of nanocrystalline Y2O3 materials using hexamine, polyethylene glycol(200) (PEG(200)), and ethylene glycol (EG) as fuels. In addition, the impact of mechanical stirring of commercial Y2O3 powder with various dilutions of PEG(200) with distilled water as a solvent was also examined. The as-prepared combustion product of the hexamine is significantly different from other fuels (PEG(200) and EG). The annealed combustion products crystallize in the pure cubic Y2O3 phase. The combustion product of PEG(200) reveals a maximum weight loss of ~46% at 800°C in the TG curve. The UV-Vis-NIR features of different samples show quite interesting results. The Eg values obtained from the Tauc plots are found in the range of 5.48 to 5.71 eV for the different samples. The observed strong FTIR band at 560 ~ 415 cm−1is owing to the vibrational Y-O bond in the present series samples. The Raman spectra show the highest intensity peak at wavenumber 374 cm−1is owing to the Fg vibrational mode of the Y2O3phase. Agglomerated nature of nanoparticles is seen in the Y2O3 phase samples obtained from EG and hexamine as fuels.

Ambipolarity Suppression of a Double Gate Tunnel FET using High-k Drain Dielectric Pocket

Abstract: We investigated the impact of placing a high-k dielectric pocket (DP) region in the drain of a double gate silicon TFET. The sheer existence of the high-k DP significantly reduces the ambipolarity due to the higher effective tunneling width at the channel/drain interface. The electrical performance investigation has been carried out by positioning the DP asymmetrically (Top or Bottom) and symmetrically on both sides of the drain. The Asymmetric DPTop configuration with an optimized thickness of 8 nm and length of 25 nm offers the lowest ambipolar current (Iamb) of 4.30×10-16 A/µm at gate voltage = -1.5 V, which is ~ 7-decades lower compared to the conventional DGTFET. This reduced Iamb further provides the highest Ion/Iamb current ratio of 4.63×1011 without degrading the average subthreshold swing (SS) of 26 mV/decade. The small-signal parameter study and RF performance analysis of the device structure have also been carried out. The proposed TFET configuration has potential for devices to be used in ultra-low-power integrated circuits and SRAM digital circuits owing to its suppressed ambipolarity and ease in the fabrication process.

Synergetic Effect of CeO2 Doping on Structural and Tribological Behavior of Fe-Al2O3 Metal Matrix Nanocomposites

Abstract: Cerium oxide (CeO2) doped iron (Fe) - alumina (Al2O3) metal matrix nanocomposites were studied. Doped with 0.5 and 1.0 percent CeO2, the nanocomposites in this system were made in the lab. Powder milling, die pressing, and sintering at 1100°C for one hour in an atmosphere-controlled furnace were used to develop the specimens. Microstructural inspection of a worn-out surface on the prepared specimens was performed in addition to the phase determination and microstructural assessment that were performed on the fabricated specimens. Fe, Al2O3, CeO2, and FeAl2O4 phases were all seen in the X-ray diffraction data. There were nano dispersion of FeAl2O4 and CeO2 particles in the dense phase microstructure of the produced samples. Increasing the amount of cerium oxide in the material resulted in an increase in both density and hardness. The specimen's wear rate was shown to decrease with an increase in cerium oxide content %. The present developed material will be useful for heavy duty applications like railway wagon wheels.

Plasma-Induced Modifications on High Density Polyethylene and Polyethylene Terephthalate

Abstract: This work presents a comprehensive study of high-density polyethylene (HDPE) and polyethylene terephthalate (PET) surface properties after exposure to 1.5, 3, 4.5, and 6 min oxygen (O2) plasma. The polymer surface structure was analyzed by Raman spectroscopy, which revealed surface restructuring modifications. The contact angle of HDPE and PET decreased gradually, and the work of adhesion was improved with O2 plasma. The water contact angle was reduced from 61.6o to 36.3° for HDPE and from 72.4o to 37.5° for PET by increasing plasma time from 1.5 to 6 min. The surface free energy is enhanced from 27.8 to 69.0 mJ/m2 for HDPE and from 29.8 to 67.2 mJ/m2 for PET, when the plasma time increased from 0 to 6 min. The polar groups significantly reduced the hydrophobicity of the irradiated films, and consequently the surface wettability was improved. The results show observed improvement in surface properties of HDPE and PET polymeric films to be use in different applications such as printings, coatings, and optoelectronics

Strain-Driven Optical, Electronic, and Mechanical Properties of Inorganic Halide Perovskite CsGeBr3

Abstract: Of late, inorganic perovskite material, especially the lead-free CsGeBr3, has gained considerable interest in the green photovoltaic industry due to its outstanding optoelectronic, thermal, and elastic properties. In this work, we systematically investigated the strain-driven optical, electronic, and mechanical properties of CsGeBr3 through the first-principles density functional theory. The unstrained planar CsGeBr3 compound demonstrates a direct bandgap of 0.92 eV at its R-point. However, by incorporating external biaxial tensile (compressive) strain the bandgap lowering (increasing) can be tuned to this perovskite. Moreover, due to the increase of tensile (compressive) strain, a red-shift (blue-shift) behavior of the absorption-coefficient and dielectric function is found in the photon energy spectrum. Strain-induced mechanical properties also reveal that CsGeBr3 perovskites are mechanically stable and highly ductile material and can be made suitable for photovoltaic applications. The strain-dependent optoelectronic and mechanical behaviors of CsGeBr3 explored here would be beneficial for its future applications in optoelectronics and photovoltaic cells design.

Perspective—Temperature Dependencies and Charge Transport Mechanisms in Molecular Tunneling Junctions Induced by Redox-Reactions

Abstract: We discuss complex charge transport behaviors induced by redox-reactions in molecular tunneling junctions by gauging the development of charge transport theories which allow for more unified approaches between temperature-dependent and temperature-independent transport. A context is drawn for current experimental works which previously demonstrated behaviors that could not have been explained by traditional Marcus and Landauer theories. The work discusses not only the reported temperature-independent long-range tunneling and their corresponding theoretical explanations but also correlates the influence of structural and thermodynamic factors that influence such peculiar temperature dependencies in molecular junctions.

The Impact of Variation in Diameter and Dielectric Materials of the CNT Field-Effect Transistor

Abstract: In today’s semiconductor industry, transistor size has been continuously scaled down due to the competition between developers to provide a better performance device. Based on Moore’s Law, the use of metal oxide semiconductor field-effect transistor (MOSFET) technology might end due to its dimensional limitation, which affects its performance. Carbon nanotube field-effect transistor (CNTFET) has become a good candidate to replace MOSFET technology due to its carbon nanotube properties (CNT). In the CNTFET design parameters, the changes in the diameter of CNT and the dielectric materials of the oxide layer significantly affect the transistor’s performance. The results show that by increasing the diameter of CNT and having a higher dielectric constant material, the on-current (Ion) and the transconductance, gm of the CNTFET will significantly increase. This effect will produce a device with a higher current ratio (Ion/Ioff) and provide a better device performance. The study also included the effect of this design parameter on the channel’s average electron velocity. From this study, it can be deduced that the diameter of CNT and the dielectric material of the oxide layer greatly affect the transistor’s performance.

Temperature Dependence of Transition-Metal and Rare-Earth Ion Luminescence (Mn4+, Cr3+, Mn2+, Eu2+, Eu3+, Tb3+, etc.) II: Experimental Data Analyses

Abstract: An analysis method presented in a seprate article can be applicable not only to Mn4+ ion, but also to other kinds of ions like Mn4+, Cr3+, Mn2+, Eu2+, Eu3+, and Tb3+. Herein, the characteristic luminescence behaviors of such ion-activated phosphors are summarized from various spectroscopic points of view. The phosphors discussed in this article are classified into five groups: (i) transition-metal 3d 3-activated phosphors of types F-Mn, O-Mn (Mn4+), and O-Cr-A (Cr3+), (ii) transition-metal 3d 3-activated phosphors of types F-Cr and O-Cr-B (Cr3+), (iii) transition-metal 3d 5-activated phosphors (Mn2+), (iv) divalent rare-earth ion-activated phosphors (Eu2+), and (v) trivalent rare-earth ion-activated phosphors (Eu3+, Tb3+). Particularly, the effects of the crystal field on the electronic energy-level scheme of these ions are demonstrated in graphical form, presenting their typical excitation absorption and luminescence spectra. The phosphor materials actually examined here are: (i) Rb2GeF6:Mn4+ and K2SiF6:Mn4+, (ii) RbIn(WO4)2:Cr3+, (iii) Zn4B6O13:Mn2+, (iv) SrSi2O2N2:Eu2+, and (v) CaTiO3:Eu3+ and Ca3Ga2Ge3O12:Tb3+. The experimental photoluminescence intensity (I PL) vs T data for these phosphors is analyzed using our proposed model. An electron trap model has recently been proposed as an alternative model to explain negative or zero thermal quenching phenomenon. Detailed discussion is also given on the reliability of this electron-trap model.