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Chitosan/ZnO (CS/ZnO) nanocomposite materials have recently attracted intensive research interest because of their combined ZnO bactericidal activity and good biological compatibility of CS. In this study, ZnO NPs were synthesized via a green process using orange peel extract as a reducing agent. The CS/ZnO nanocomposites were chemically synthesized with different CS/ZnO weight ratios. The microstructure, morphology, and thermal stability of the nanocomposite materials greatly depended on the weight ratio of CS/ZnO. The nanocomposite materials exhibited strong antimicrobial activity towards both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) in the absence of UV light at all of the investigated CS/ZnO ratios. Due to the different characteristics of bacteria types, the activity inhibition towards E. coli was nearly constant in all samples, while that towards S. aureus slightly decreased with the increment of chitosan content. The results of this study suggest that the nanocomposites have potential applications in controlling the spread of infection by various bacteria.

Introduction: Zinc oxide (ZnO) is well-known as a promising thermoelectric material owing to its safety, inexpensiveness, and thermal stability. This research provides an overview of thermoelectric potentials, including structure, electrical conductivity, Seebeck coefficient, and power factor of pure ZnO semiconductor synthesized in bulk and thin-film forms. Methods: The ZnO bulk was synthesized by solid-state reaction at high temperature, while the thin film was prepared by d.c. magnetron sputtering technique. The temperature-dependent thermoelectric properties of all the samples were measured by the Seebeck LSR-3 system. The crystallographic and surface morphological information of the samples were obtained by using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM), respectively. Results: The XRD results confirm that both the bulk and thin-film have polycrystalline structure and characteristics of hexagonal-wurtzite ZnO. Through the FESEM observation, the bulk is well densified under high-temperature condition, while the thin-film achieve good orientation and close-packed grains. At 573 K, the obtained thermoelectric properties (electrical conductivity, Seebeck coefficient, and power factor) are respectively 352.4 S/cm, -89.5 µV/K and 282.5 µW/mK2 for the ZnO bulk; and 289 S/cm, -113.8 µV/K and 374.3 µW/mK2 for the ZnO film. Conclusion: The comparative study shows the good thermoelectric potential of ZnO material in both forms of bulk and thin film. Among them, the thin film has better results, especially in the Seebeck coefficient and power factor than one.

In this work, several X-ray and nuclear analysis techniques were used to examine ZnO materials co-doped with In and Ga, or IGZO materials. X-ray diffraction analysis, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy revealed multi-scale defects in the materials. A nanoscale secondary Ga2Zn9O12 spinel phase, mesoscale grain boundaries, and atomic-scale lattice defects were detected. The lattice defects included oxygen vacancies, zinc vacancies, and complex defects. Positron annihilation spectroscopy and Doppler broadening spectroscopy provided evidence of interactions between charge carriers and defects sites, which explained the low thermal conductivities of the IGZO materials (κtotal ≈ 3.9 W/mK) at 773 K. This combination of X-ray and nuclear analytical techniques can be viewed as a novel approach for investigating the thermoelectric properties of materials with complex crystal structures that contain atomic-scale voids, nanoscale secondary phases, and mesoscale grain boundaries.

In this study, a thin film of methylammonium lead iodide (MAPbI3) was employed as the switching layer in the metal/MAPbI3/FTO devices. Two metals, Ag and Cr, were used as active and inert top electrodes to govern the hysteresis effect of memory devices, respectively. While the Cr/MAPbI3/FTO device displayed an analog resistive switching (RS) behavior and a comparatively low ON/OFF ratio of 10, the Ag/MAPbI3/FTO structure displayed digital bipolar RS and a high ON/OFF ratio of 102. The density functional theory simulations suggest that these various behaviors may be caused by variations in the mutual interaction between the iodine vacancy defect and the metal contact properties. The SET process involved switching both devices from a high-resistance state to a low-resistance one using the space charge-limited current mechanism. In the RESET process, the Ag-electrode device is allocated the Poole–Frenkel emission mechanism, and the Cr-electrode device is followed the Fowler–Nordheim tunneling mechanism. The formation and dissociation of iodine vacancy filaments via the dielectric layer were identified as the RS mechanism in both devices. The findings show that organic–inorganic hybrid perovskite has a strong potential for data storage.

Chitosan has attracted significant attention in the past decade because of its potential applications in water engineering, the food and nutrition technology, the textile and paper industries, and drug delivery. Recently, a particularly interesting application of chitosan has been proposed in transparent flexible electronic devices, including memristors and transistors. In this work, the resistive switching (RS) effect of chitosan thin films in a capacitor-like structure with Ag and Al as alternative top electrodes was studied. Both the devices showed a bistable RS effect under an external electric field with a high endurance of 102. The electrical conduction and RS mechanisms of chitosan-based devices were investigated. The trap-controlled space charge–limited current was responsible for electrical transport at the low-resistance state of both devices, while direct tunneling and Schottky emission at the high-resistance state were related to Ag/chitosan/fluorine-doped tin oxide (FTO) and Al/chitosan/FTO, respectively. The RS mechanism of the Ag/chitosan/FTO device was attributed to the formation and dissociation of Ag filaments through the dielectric layer, whereas the change in the barrier height at the Al and chitosan interface under an external electric field could control the RS mechanism of the Al/chitosan/FTO device.

We investigated the coupling phenomenon between plasmonic resonance and waveguide modes through theoretical and experimental parametric analyses on the bimetallic waveguide-coupled long-range surface plasmon resonance (Bi-WCLRSPR) structure. The calculation results indicated that the multi-plasmonic coupling gives rise to the enhanced depth-to-width ratio of the reflection dip compared to that of LRSPR excited using a single set of Ag and Teflon. The optimized thickness of Ag(40 nm)/Teflon(700 nm)/Ag(5 nm)/Au(5 nm) was obtained and generated the highest plasmon intensity enhancement, which was 2.38 folds in comparison to the conventional bimetallic surface plasmon resonance (SPR) configuration (Ag/Au). 17β-Estradiol was used in the fluorescence enhancement experiment by the reflection geometry-based system, wherein the excitation light source was on the side of a WC-LRSPR chip opposite to that of the light detection unit. The phenomenon of surface plasmon-couple emission (SPCE) depends on the number of 17β-estradiol molecule promoters from female sex steroid hormones, which demonstrated a limit of detection (LOD) of 2 pg mL−1 and 1.47-fold fluorescence improvement as compared to the non-coated material on the surface of pristine glass. This enhanced WC-LRSPR can readily find application in fluorescence escalation needed in cases where a weak fluorescence signal is predicted, such as the small volume of liquid containing fluorescent dyes in biological diagnosis.

Resistive random access memory (RRAM) is emerging as a new class of nonvolatile memory that offers promising electronic properties and simple metal-insulator-metal (MIM) structures for sandwich layers, such as organics, inorganics, and hybrid materials. Hybrid structures have attracted much interest recently because of their advantageous properties. The combination of chitosan (CS) and graphene oxide (GO) acts as switching layers in the Al/CS-GO/FTO RRAM structure it is studied with bipolar switching behavior at approximately 102 ON/OFF ratios during 100 cycles. This hybrid interaction is identified by shifts in the D, G, and 2D bands using Raman spectroscopy. The conduction mechanism is proposed to be a space-charge-limited conduction (SCLC) mechanism and trap-assisted tunneling conduction mechanism in the ON and OFF states, respectively. The trapped and detrapped electrons move through the trap sites with external electric fields, and this movement is responsible for the switching mechanism of the CS-GO nanocomposite memory device.

In this paper, thermoelectric performance of the ZnO thin films were investigated via doping (Gallium - Ga and Indium - In) and post-thermal treatment. Various kinds of defects, such as zinc (Zn) vacancies, Ga substitute for Zn, zinc interstitials, oxygen vacancies, oxygen interstitials, oxygen antisite, were induced in the ZnO thin films by doping with Ga, In and post-thermal treatment. Annealed thin films have better thermoelectric performance than unannealed thin films. The figure of merit ZT values at 300 °C were 0.114 and 0.186 for the single Ga-doped ZnO (GZO@500) and dually In, Ga doped ZnO (IGZO@500) thin films annealed at 500 °C, respectively. Higher concentration of zinc interstitial led the GZO@500 thin film to have larger power factor and larger total thermal conductivity, resulting in lower ZT than the IGZO@500 thin film. To the best of our knowledge, the ZT value of 0.186 at 300 °C obtained from our IGZO@500 thin films is the highest ever reported for n-type ZnO based thin films.

To date, hybrid polyvinyl alcohol (PVA) and TiO2 nanocomposites have been widely studied for numerous practical applications including enhanced visible-light photocatalytic activities, shield coatings against UV light, electrolyte membranes for fuel cells, hybrid fibers and proton conduction layers in biological systems. However, the properties of interaction between PVA and the TiO2 surface, particularly the band offset of organic–inorganic constituents, are still unclear and under debate. In this work, we studied the resistive switching characteristics and mechanism of hybrid PVA and TiO2 nanotube (TNT) nanocomposites. By embedding TNTs into the PVA matrix, the resistive switching performance of devices is significantly enhanced, with an excellent retention of 104 seconds and large resistance ratio >104. Density functional theory (DFT) calculations confirmed that strong bonds were formed between the O atoms in PVA's OH groups and the five-coordinated Ti atoms on the surface of TiO2, corresponding to the significant decrease of vibrational intensity of the OH-group in the FTIR spectra. In addition, band offsets of the TiO2/PVA interface illustrated the very low minimum conduction band energy level of TiO2 compared to that of crystalline PVA, implying that TNTs act as trap centers for electrons in the insulating layer. Consequently, the current transport and switching mechanisms of the devices were suggested using the models of trap controlled space-charge-limited conduction and the charge carrier trapping–de-trapping process at the centers of TNTs in the PVA polymer matrix, respectively.

Mg-doped CuCrO2 material has emerged as a p-type semiconductor, especially, in the field of thermoelectric materials because of its lowest resistivity in delafossite material family. In this work, CuCr0.95Mg0.05O2 bulk materials were prepared in a series of sintering temperatures including 1000, 1200, and 1400°C using solid-state reaction method. From XRD results, all samples exhibit the significant existence of delafossite phase CuCrO2, and a small portion belongs to the spinel phase MgCr2O4. An interesting finding in this study is that the Vickers hardness is mainly governed by the crystallite size of (110) plane. Besides, the change in the crystallite size of (110) plane also indirectly affects the carrier concentration of the compounds with increasing sintering temperature. The highest power factor (PF) was reached for the sample prepared at the sintering temperature 1400°C with the value of 193 μW/mK2 along with the Seebeck coefficient value of 600 μV/K measured at 400°C.

In this study, the memory device of iron oxide (IO) nanoparticles (NPs) embedded in polyvinyl alcohol (PVA) demonstrates the bipolar resistive switching characteristics under an external electric field. The phase and magnetic properties of iron oxide nanoparticles change corresponding to its resistive states. At the high resistance state (HRS) of device, iron oxide nanoparticles are primarily in Fe

Metal-organic framework (MOF) materials have recently attracted much attention for use in resistive random-access memory due to the advantages of having high insulative properties, well-defined structures, a large specific surface area, and an adjustable pore size. In this study, the memory device based on zirconium (IV)-carboxylate MOF (UiO-66) nanoparticles exhibits the low operation voltage (V

In this work, role of phase composition and interstitial oxygen on the thermoelectric properties of CuCr0.85Mg0.15O2 materials prepared at different sintering temperatures (1273–1673 K) for short time (3 h) are reported. Interestingly, the samples sintered at 1273 K and 1673 K had the same Seebeck coefficient, despite the 1273 K sample having significantly lower conductivity, which are discussed via phase composition and interstitial oxygen induced during the CuCrO2 phase formation and its related defect (VCu, VCr, …). Besides, high conductivity of the 1673 K sample originated from the low percentage of CuO phase and the appearance of Cu2O phase. Since the 1273 K and 1673 K sintered samples have almost the same percentage of delafossite and spinel phases so the 1673 K sample still remain its high Seebeck coefficient. We suggest some reaction chemical equations for elucidating the roles of interstitial oxygen on the phase composition and thermoelectric properties CuCr0.85Mg0.15O2 delafossite material.

The characteristics of nano-fillers in a polymer matrix have a significant influence on the microstructural, thermo-mechanical, optical, and conductivity properties of organic-inorganic nanocomposites. In this study, we investigated the influence of inorganic component – ZnO nanoparticles (NPs) on the characteristics and properties of PVA-ZnO nanocomposites which have been applied as an insulation layer in a resistive switching (RS) device. Three nanocomposites originating from three different types of ZnO NPs exhibit different RS characteristics: Abnormal volatile RS is observed with the ∼20-nm-sized spherical-like NPs (Z1) and 15–20-nm-sized mixed shaped NPs (Z2), whereas normal nonvolatile bipolar RS is observed with the 50–150-nm-sized hexagonal rod-like NPs (Z3). The concentration and size of the intrinsic defects of the ZnO NPs as well as the thickness of the PVA-ZnO interface are responsible for the different charge transport paths, operating voltage ranges, and ON/OFF switching ratios of the memory devices. Simultaneously, the distinct sizes and morphologies of the ZnO NPs can affect the nanoholes among the PVA chains and induce various fractional free volumes in the nanocomposites. It may modify the conductivity of the nanocomposite layer or the resistance ratio of the memory devices. Understanding the influence of ZnO NPs size, morphology, and defects on the characteristics of RS of PVA-ZnO nanocomposites can help in the selection and management of functional applications, especially in the data storage field.

The interrelation between microstructure of chromium oxide films (CrOx) and formation of silver (Ag) filament in Ag/CrOx/Pt devices has been investigated at various annealing temperatures. It is revealed that Cr2O3 phase is dominant at high annealing temperatures and different microstructures of the CrOx films exhibit different resistance switching characteristics. As-deposited CrOx films with amorphous structure show highly reliable and reproducible resistance switching due to an easy formation of thin Ag filaments. 300°C-annealed CrOx films with denser structure exhibit a fluctuating switching characteristics, relating to negative differential resistance (NDR) effect, in the first several tens of switching cycles, followed by a stable switching characteristics. On the contrary, the resistance switching is not observed in 500°C-annealed CrOx films due to presence of voids or pinholes created at high annealing temperature. The roles of NDR effect and voids/pinholes on resistance switching characteristics of CrOx thin films are also discussed.

We investigated the effect of single and multidopants on the thermoelectrical properties of host ZnO films. Incorporation of the single dopant Ga in the ZnO films improved the conductivity and mobility but lowered the Seebeck coefficient. Dual Ga- and In-doped ZnO thin films show slightly decreased electrical conductivity but improved Seebeck coefficient. The variation of thermoelectric properties is discussed in terms of film crystallinity, which is subject to the dopants' radius. Small amounts of In dopants with a large radius may introduce localized regions in the host film, affecting the thermoelectric properties. Consequently, a 1.5 times increase in power factor, three times reduction in thermal conductivity, and 5-fold enhancement in the figure of merit ZT have been achieved at 110 °C. The results also indicate that the balanced control of both electron and lattice thermal conductivities through dopant selection are necessary to attain low total thermal conductivity.

In this study, we have fabricated resistive switching memory device based on TiO2 thin films on ITO/PET commercial substrate. The study on the transmittance spectra showed that with the 100 nm-TiO2/ITO/PET device, the transmission is more than 80 % in the visible region and approximately of 85 % at wavelength of 550 nm. Ag/TiO2/ITO devices exhibit excellent stable bipolar resistive switching characteristics under electrical field bias of -2 V -> 2 V range on the flat state and even after reproductive physical stresses of 500 cycles. Our study on TiO2 based memristors suggests that resistive switching memories are suitable for flexible transparent application in the future.

In this study, we have investigated influences of the thickness on the structure, surface morphology and resistive switching characteristics of CrOx thin films prepared by using DC reactive sputtering technique. The Raman and FTIR analysis revealed that multiphases including Cr2O3, CrO2, Cr8O21... phases coexist in the microstructure of CrOx film. It is noticed that the amount of stoichiometric Cr2O3 phase increased significantly as well as the surface morphology were more visible with less voids and more densed particles with larger thickness films. The Ag/CrOx/FTO devices exhibited bipolar resistive switching behavior and high reliability. The resistive switching ratio has decreased slightly with the thickness increments and was best achieved at CrOx – 100 nm devices.

The interactions between organic and inorganic components of nanocomposites plays a key role in their microstructure and optoelectrical properties. The comprehensive understanding of these interactions can promote various potential applications of materials, especially in the field of electronic memory devices. In this study, we investigate the interactions of polyvinyl alcohol (PVA) and oxygen vacancy-rich ZnO nanoparticles (NPs) and resistive switching effect of PVA:ZnO nanocomposite. The density functional theory calculation indicates that the PVA chemisorption and the oxygen vacancies of ZnO play a key role in strongly reducing the work function of ZnO NPs of which conduction band can act as a bottom of potential well for trapping electrons in the PVA:ZnO nanocomposite. The oxygen vacancies also increase the stability of the potential well by enhancing chemical bonding between PVA and ZnO. Moreover, we show that at a specific content of ZnO NPs in the PVA matrix, the Ag/PVA:ZnO/FTO memory device has the best resistive switching behavior (operating voltage

The thermoelectric performance of CuCr1-xMgxO2 materials in terms of multi-scale defects induced at various Mg dopant concentrations (x = 0–0.3) was thoroughly studied in this paper. At 748 K and for x = 0.05, 0.15, and 0.30, we report the following power factors and thermal conductivities: 175, 213, and 2.3 μW/m K2 and 7.85, 5.60, and 3.82 W/m K, respectively. In the low doping regime (x

We investigate the structure, optical properties, and thermoelectric power in terms of residual stresses induced in the undoped ZnO and X-doped ZnO (X = Al, Ga) films. The results show that the different native seed layers self-grown during the initial growth cause compressive stress for ZnO and Ga-doped ZnO films and tensile stress for Al-doped ZnO films. The band-gap of the investigated films follows the Burstein–Moss (BM) effect. It is noted that the ZnO film with the lowest compressive stress has a better PF value below 275 °C. The GZO film is more stable at higher temperatures; therefore, it has a better PF value above 275 °C. The residual stress induced in the investigated films is demonstrated through the formation of a self-grown seed layer under the bombardment of high-energy sputtered Ga, Al, Zn, and O species onto the substrate and during film growth.

In this study, the memory device of iron oxide (IO) nanoparticles (NPs) embedded in polyvinyl alcohol (PVA) demonstrates the bipolar resistive switching characteristics under an external electric field. The phase and magnetic properties of iron oxide nanoparticles change corresponding to its resistive states. At the high resistance state (HRS) of device, iron oxide nanoparticles are primarily in Fe2O3 phase and the ferromagnetism behavior is observed. In contrast, the iron oxide nanoparticles clustered by the bridging oxygen vacancies lead to mainly Fe3O4 phase and no hysteresis magnetic curve is observed at the low resistance state (LRS) of device. The results reveal that oxygen vacancies/ions in nanoparticles notably influence the resistance and magnetic behavior of nanocomposite thin films. Our study indicated that the magnetic NPs is high potential of multi-dimensional storage fields.

We have investigated the switching behavior of as-deposited CrO x and post-annealed CrO y films by use of a variety of electrodes (top electrode Ag, Ti; bottom electrode Pt, fluorine tin oxide (FTO)). Resistance switching is highly dependent on electrode material and post-annealing treatment. Among Pt devices, I–V hysteresis was observed for the Ag/CrO x /Pt device only; no resistance switching was observed for Ag/CrO y /Pt, Ti/CrO x /Pt, and Ti/CrO y /Pt devices. Among FTO devices, I–V hysteresis was observed for the Ag/CrO x /FTO device whereas I–V hysteresis with the opposite switching direction was observed for Ag/CrO y /FTO, Ti/CrO x /FTO, and Ti/CrO y /FTO devices. The direction of switching depends not only on electrode material but also on post-annealing treatment, which affects the density of grain boundaries. Thus, the density of grain boundaries determines the type of charge carrier involved in the switching process. For as-deposited CrO x films with a high density of grain boundaries Ag filament paths mediated by electrochemical redox reaction were observed, irrespective of bottom electrode material (Pt or FTO). Post-annealed CrO y films with a low density of grain boundaries suppressed electrochemical redox reaction in the Ag/CrO y /Pt device but promoted short-range movement of O2− ions through the bottom interface, resulting in resistance switching in the Ag/CrO y /FTO device. Electrochemical redox reaction-controlled resistance switching occurred solely in oxides with a high density of grain boundaries or dislocations.

Audit quality is considered as an essential factor affecting the reliability of financial information. The aim of this study is to assess the effects of audit firm characteristics, including audit reputation, audit fees and audit firm size, on audit quality. A sample of 192 companies listed on Hanoi and Ho Chi Minh Stock Exchange for the period of 2006-2014 was selected. Multiple regression was used to analyze the data. The findings show that Big 4 auditors in Vietnam provide high audit quality than non-Big 4 auditors. Interestingly, in Vietnam context, except for the audit firms in the Big 4 group, the findings suggest that smaller audit firms provide better audit quality. Additionally, the results reveal that the more audit fees the auditors receive, the lower audit quality they provide. The critical role of audit quality has attracted significantly scholarly attention, however, prior studies have mainly focused on firms in developed countries. Little is known about audit quality in an emerging economy context such as Vietnam. This study adds to the limited number of studies on audit quality of listed companies in emerging economies.