Cycling Endurance Research Articles

The Electroencephalogram (EEG) Study for Estimating Endurance Sports Performance Base on Eigenvalues Extraction Method

Objectives. Brain–behavior connections are a new means to evaluate sports performance. This electroencephalogram (EEG) study aims to estimate endurance exercise performance by investigating eigenvalue trends and comparing their sensitivity and linearity. Methods. Twenty-three cross-country skiers completed endurance cycling tasks. Twenty-four-channel full-brain EEG signals were recorded in the motor phase and recovery phase continuously. Eighteen EEG eigenvalues calculation methods were collected, commonly used in previous research. Time-frequency, band power, and nonlinear analyses were used to calculate the EEG eigenvalues. Their regression coefficients and correlation coefficients were calculated and compared, with the linear regression method. Results. The time-frequency eigenvalues shift slightly throughout the test. The power eigenvalues changed significantly before and after motor and recovery, but the linearity was not satisfactory. The sensitivity and linearity of the nonlinear eigenvalues were stronger than the other eigenvalues. Of all eigenvalues, Shannon entropy showed completely non-overlapping distribution intervals in the regression coefficients of the two phases, which were −0.1474 ± 0.0806 s−1 in the motor phase and 0.2560 ± 0.1365 s−1 in the recovery phase. Shannon entropy amplitude decreased more in the F region of the brain than in the other regions. Additionally, the higher the level of sport, the slower the decline in Shannon entropy of the athlete. Conclusions. The Shannon entropy method provided more accurate estimations for endurance exercise performance compared to other eigenvalues.

Assessing Energy Availability and Glucose Dynamics in Adolescent Cyclists: Implications for Nutritional Interventions During the Competitive Season

Background: The risk of developing a state of low energy availability (LEA) (<30 kcals/kg free-fat mass) in endurance athletes is known and recommendations for nutrition are available. However, information on male adolescent cyclists and the influence of hot temperatures is limited. Objectives: The aim of this study was to investigate the impact on energy availability of two 4-day nutritional intervention strategies: (1) supplementary carbohydrate (CHO) intake during exercise and (2) designing and implementing individual nutritional interventions. Methods: Each intervention was preceded by a 4-day basal assessment. Eight competitive male junior road cyclists (aged 16–17 years) were investigated using a 4-day diet and activity records, alongside bioelectric impedance analysis. Their real-time power output, interstitial glucose, and temperature were recorded via sensors and a bike computer. Their energy intake (EI) was estimated from daily, self-reported food diaries. Results: Overall, 100% and 71% of the cyclists were in a state of LEA during the baseline assessment of the supplementary CHO and nutritional interventions, respectively. LEA prevalence, not modified by supplementary CHO intake alone (from 100% to 87%, ns), was markedly reduced by the individual nutritional intervention (from 71% to 14%, p < 0.05). When considering all the data as a whole, LEA was positively influenced by the training load (OR 1.06; 95% Cl 1.03 to 1.09) and free-fat mass (OR 1.46; 1.04 to 2.04) and was negatively affected by EI (OR 0.994; 0.991 to 0.997). A hot environment (air temperature) failed to influence the LEA or glucose dynamics. Conclusions: the nutritional intervention, but not the supplementary CHO intake, markedly reduced the prevalence of LEA in adolescents, who often fail to match their energy expenditure with their energy intake during the competitive season. Nutritional education is essential for adolescent endurance cycling teams.

Tailoring breakdown strength and energy-storage performance of silicon-integrated lead-free epitaxial BZT thin films through multi-element B-site substitutions

Developing high-temperature dielectric thin films with high-performance energy-storage properties for harsh environment applications has received increased attention. Herein, a multi-element co-doping strategy is proposed to enhance the breakdown strength and energy storage properties of lead-free BaTiO3-based thin films, which were deposited on silicon substrates using pulsed laser deposition. Due to the difference in ionic radii and valence states between the multi-dopants and host Ti-cations, the local lattice distortion and local charged defects are induced, which results in the reduction in the size of polar nanoregions (PNRs) and weakened coupling interactions between these PNRs, thus achieving stronger breakdown strength (EBD). Accordingly, owing to an enhanced EBD of 7.8 MV/cm and a delayed polarization saturation, a superior recoverable energy-storage density (Ur) of 140.8 J/cm3 along with an excellent energy efficiency (η) of 93.2 % were achieved at room temperature in the multi-element doped Ba(Zr0.2Ti0.2Mn0.2Nb0.2Sm0.2)O3 (BZTMNS) thin film. Moreover, the BZTMNS thin film also exhibits an excellent Ur of 102.6 J/cm3, a good η of 86.4 %, and a high EBD of 6.6 MV/cm at an operating temperature of 200 °C. Additionally, a small fluctuation of Ur (-6.1 %) and η (-11.7 %) values can also be observed in BZTMNS thin film in high cycling endurance, up to 1010 cycles, even when operated at an elevated temperature of 200 °C. These findings in the BZTMNS thin film demonstrate a feasible way to design high-temperature capacitors for modern electronic devices for hybrid vehicles and underground oil/gas explorations.

Biocompatible Acellular Dermal Matrix-Based Neuromorphic Device with Ultralow Voltage, Ion Channel Emulation, and Synaptic Forgetting Visualization Computation.

Neuromorphic bioelectronics aim to integrate electronics with biological systems yet encounter challenges in biocompatibility, operating voltages, power consumption, and stability. This study presents biocompatible neuromorphic devices fabricated from acellular dermal matrix (ADM) derived from porcine dermis using low-temperature supercritical CO2 extraction. The ADM preserves the natural scaffold structure of collagen and minimizes immunogenicity by eliminating cells, fats, and noncollagenous impurities, ensuring excellent biocompatibility. The ADM-based devices emulate biological ion channels with biphasic membrane current modulation, exhibiting temperature dependency and pH sensitivity. It operates at an ultralow voltage of 1 mV and demonstrates reliable synaptic modulation exceeding 4 × 104 endurance cycles. The activation voltage can be theoretically as low as 59 μV, comparable to brainwave signals with a power of merely 7 aJ/event. Furthermore, a brain-like forgetting visualization algorithm is developed, leveraging the synaptic forgetting plasticity of ADM-based devices to achieve complex computing tasks in a highly energy-efficient manner. Neuromorphic devices based on ADM not only hold potential in implantable biointerfaces due to their exceptional biocompatibility, ultralow voltage, and power but also provide a feasible way for energy-efficient computing paradigms through a synergistic hardware-software approach.

Improving the Nonvolatile Memory Characteristics of Sol–Gel-Processed Y2O3 RRAM Devices Using Mono-Ethanolamine Additives

In this study, Y2O3-based resistive random-access memory (RRAM) devices with a mono-ethanolamine (MEA) stabilizer fabricated using the sol–gel process on indium tin oxide/glass substrates were investigated. The effects of MEA content on the structural, optical, chemical, and electrical characteristics were determined. As the MEA content increased, film thickness and crystallite size decreased. In particular, the increase in MEA content slightly decreased the oxygen vacancy concentration. The decreased film thickness decreased the physical distance for conductive filament formation, generating a strong electric field. However, owing to the lowest oxygen vacancy concentration, a large electrical field is required. To ensure data reliability, the endurance cycles across several devices were measured and presented statistically. Additionally, endurance performance improved with the increase in MEA content. Reduced oxygen vacancy concentration can successfully suppress the excess formation of the Ag conductive filament. This simplifies the transition from the high- to the low-resistance state and vice versa, thereby improving the endurance cycles of the RRAM devices.

Impact of bias stress and endurance switching on electrical characteristics of polycrystalline ZnO-TFTs with Al2O3 gate dielectric

Abstract This study experimentally investigates electrical characteristics and degradation phenomena in polycrystalline zinc oxide thin-film transistors (ZnO-TFTs). ZnO-TFTs with Al2O3 gate dielectric, Al-doped ZnO (AZO) source–drain contacts, and AZO gate electrode are fabricated using remote plasma-enhanced atomic layer deposition at a maximum process temperature of 190 °C. We employ positive bias stress (PBS), negative bias stress (NBS), and endurance cycling measurements to evaluate the ZnO-TFT performance and examine carrier dynamics at the channel-dielectric interface and at grain boundaries in the polycrystalline channel. DC transfer measurements yield a threshold voltage of −5.95 V, a field-effect mobility of 53.5 cm2/(V∙s), a subthreshold swing of 136 mV dec−1, and an on-/off-current ratio above 109. PBS and NBS measurements, analysed using stretched-exponential fitting, reveal the dynamics of carrier trapping and de-trapping between the channel layer and the gate insulator. Carrier de-trapping time is 88 s under NBS at −15 V, compared to 1856 s trapping time under PBS at +15 V. Endurance tests across 109 cycles assess switching characteristics and temporal changes in ZnO-TFTs, focusing on threshold voltage and field-effect mobility. The threshold voltage shift observed during endurance cycling is similar to that of NBS due to the contrast in carrier trapping/de-trapping time. A measured mobility hysteresis of 19% between the forward and reverse measurement directions suggests grain boundary effects mediated by the applied gate bias. These findings underscore the electrical resilience of polycrystalline ZnO-TFTs and the aptitude for 3D heterogeneous integration applications.

Training for Elite Team-Pursuit Track Cyclists-Part I: A Profile of General Training Characteristics.

To profile the training characteristics of an elite team pursuit cycling squad and assess variations in training intensity and load accumulation across the 36-week period prior to a world-record performance at the 2018 Commonwealth Games. Training data of 5 male track endurance cyclists (mean [SD]; age 21.9 [3.52]y; 4.4 [0.16]W·kg-1 at anaerobic threshold; 6.2 [0.28]W·kg-1 maximal oxygen uptake 68.7 [2.99]mL kg·min-1) were analyzed with weekly total training volume and heart rate, power output, and torque intensity distributions calculated with reference to their 3:49.804min:s.ms performance requirements for a 4-km team pursuit. Athletes completed 543 (37)h-1 of training across 436 (16) sessions. On-bike activities accounted for 69.9% of all training sessions, with participants cycling 11,246 (1139)km-1 in the training period of interest, whereas 12.7% of sessions involved gym/strength training. A pyramidal intensity distribution was evident with over 65% and 70% of training, respectively, performed at low-intensity zone heart rate and power output, whereas 5.3% and 7.7% of training was performed above anaerobic threshold. The athletes accumulated 4.4% of total training volume at, or above, their world-record team pursuit lead position torque (55N·m). These data provide updated and novel insight to the power and torque demands and load accumulation contributing to world-record team pursuit performance. Although the observed pyramidal intensity distribution is common in endurance sports, the lack of shift toward a polarized intensity distribution during taper and competition peaking differs from previous research.

Training for Elite Team-Pursuit Track Cyclists-Part II: A Comparison of Preparation Phases in Consecutive World-Record-Breaking Seasons.

To compare the training characteristics of an elite team pursuit cycling squad in the 3-month preparation phases prior to 2 successive world-record (WR) performances. Training data of 5 male track endurance cyclists (mean [SD]; age 23.4 [3.46]y; body mass 80.2 [2.74]kg; 4.5 [0.17]W·kg-1 at LT2; maximal aerobic power6.2 [0.27]W·kg-1; maximal oxygen uptake 65.9 [2.89]mL·kg-1·min-1) were analyzed with weekly total training volume by training type and heart rate, power output, and torque intensity distributions calculated with reference to the respective WRs' performance requirements. Athletes completed 805 (82.81) and 725 (68.40)min·wk-1 of training, respectively, in each season. In the second season, there was a 32% increase in total track volume, although track sessions were shorter (ie,greater frequency) in the second season. A pyramidal intensity distribution was consistent across both seasons, with 81% of training, on average, performed below LT1 power output each week, whereas 6% of training was performed above LT2. Athletes accumulated greater volume above WR team pursuit lead power (2.4% vs 0.9%) and torque (6.2% vs 3.2%) in 2019. In one athlete, mean single-leg-press peak rate of force development was 71% and 46% higher at mid- and late-phases, respectively, during the preparation period. These findings provide novel insights into the common and contrasting methods contributing to successive WR team pursuit performances. Greater accumulation of volume above race-specific power and torque (eg,team pursuit lead), as well as improved neuromuscular force-generating capacities, may be worthy of investigation for implementation in training programs.

Effects Of Endurance Cycling Training With Electrical Muscle Stimulation Of Lower Limb On The Endothelial Function

Effects Of Endurance Cycling Training With Electrical Muscle Stimulation Of Lower Limb On The Endothelial Function

Ferroelectricity of Hf0.5Zr0.5O2 thin films grown by atomic layer deposition on epitaxial TiN bottom electrodes

In this study, the effects of the epitaxial TiN bottom electrode on the crystallinity and ferroelectricity of Hf0.5Zr0.5O2 (HZO) thin films were investigated. HZO thin films were deposited using atomic layer deposition on epitaxial TiN(100) on MgO(100), epitaxial TiN(111) on Al2O3(0001), and polycrystalline TiN on Si(100) for comparison. The HZO thin films on epitaxial TiN(100) exhibited the largest remanent polarization of ∼26 μC/cm2, with the largest orthorhombic phase fraction. Conversely, the HZO thin film on polycrystalline TiN showed the smallest remanent polarization ∼19 μC/cm2, with the smallest orthorhombic phase fraction. High-resolution transmission electron microscopy analysis confirmed the dominance of the orthorhombic phase in the HZO thin film on epitaxial TiN(100). Reliability tests showed that the HZO thin films on epitaxial TiN (100) exhibited superior retention with a smaller wake-up effect compared to those of the HZO thin films on polycrystalline TiN but they displayed inferior cycling endurance characteristics.

Reconfiguring Zn2+ Solvation Network and Interfacial Chemistry of Zn Metal Anode with Molecular Engineered Crown Ether Additive

AbstractThe practical deployment of rechargeable aqueous zinc‐ion batteries (RAZBs) in the scaled power system suffers from unregulated Zn dendrite growth as well as parasitic reactions at the zinc foil/aqueous electrolyte interface, leading to insufficient zinc utilization and severe electrode corrosion. Herein, a novel crown ether additive is developed, with tailored molecular engineering, to stepwise regulate the Zn2+ solvation network and interfacial chemistry of Zn metal anode. The designed crown ether (C5SeCN), featuring zincophilic cyano group and hydrophobic selenium, efficiently reconstructs the solvation sheath of Zn ions at the 0.3 wt.% dose amount. Additionally, the ozone plasma treatment tethers the O2‐ groups onto the thin‐layer zinc foil, which thus binds Se atoms of the C5SeCN to the Zn anode. The Zn||Zn symmetric cells exhibit a lifespan of over 4500 h at 1 mA cm−2 and high current density endurance of up to 10 mA cm−2. Moreover, the 2 mAh cm−2 Zn||V2O5 full cell model, at the low N/P ratio of 2.8 with a lean electrolyte (E/C ratio = 10 µL mAh−1), enables robust cycling endurance at 2 A g⁻¹ for 300 cycles. This study unravels the interfacial design rationales for maximizing zinc utilization and highlights the commercial potential of crown ether additives for RAZBs development.

Effect of atomic layer deposition process parameters on TiN electrode for Hf0.5Zr0.5O2 ferroelectric capacitor

Abstract Hf0.5Zr0.5O2 (HZO), as a novel and outstanding ferroelectric material, exhibits an extremely high sensitivity, rendering it quite susceptible to electrode effect. Titanium nitride (TiN) is a commonly employed as electrode material in the complementary metal-oxide-semiconductor (CMOS) process. Adjusting the process parameters of preparing TiN film can alter matching degree with HZO, so as to find the optimal parameters of TiN process to improve ferroelectric property of HZO. In this study, the impact of key process parameters in atomic layer deposition (ALD) TiN, including cycle number, TiCl4 and NH3 pluse time, process temperature (Tp) on film thickness, crystalline phases of TiN, square resistivity (Rs), surface average roughness (Ra) and the root-mean-square roughness (Rq) of TiN film are comprehensively investigated. Through optimization, ~10nm ALD TiN film can achieve excellent uniformity of 0.43%, low Rs of 286.9Ω/sq, improved Ra and Rq of 1.82Å and 2.28Å. The results show that the maximum 2 times remnant polarization (2Pr) of the HZO ferroelectric capacitor with optimized TiN electrodes can reach 36.34µC/cm2, and the switching cycle endurance exceeds 1E7.

Study of resistive properties and neural response of ZrO2/TiO2 heterojunction nanowire array (NWA) RRAM

Nowadays, the researcher has an eye on enhancing the performance of resistive random-access memory (RRAM) and exploring new demands and applications, particularly in the field of artificial intelligence and neural computing. It is crucially important for accurately replicating the observed plasticity within synapses to achieve superior RRAM performance in low-dimensional nanomaterials. In this work, we focus on addressing certainly unsatisfactory electrical properties of RRAM based on titanium oxide nanowire array (TiO2 NWA), for example, short retention time (∼103 s). Theoretically and experimentally, a novel and solution-based RRAM structure, namely ZrO2/TiO2(NWA), has been conducted. With the help of the ZrO2 insertion layer, the RRAM device shows impressive resistive switching characteristics, including 200 current–voltage(I-V) sweeps without degradation, increased cycling endurance (>105 cycles), and a long retention time (∼9 × 104 s). These findings hold significant implications for digital computing systems. Moreover, the successful implementation of the proposed device enables the emulation of fundamental synaptic biological features such as non-linear transmission properties, learning experiences behavior, short-term potentiation (STP) and long-term potentiation (LTP). This research provides evidence of the immense potential of the Ag/ZrO2/TiO2(NWA)/FTO RRAM device in bipolar non-volatile memory (NVM) and biomimetic neuromorphic systems.

Enhancing Zn2+/H+ Joint Charge Storage in MnO2: Concurrently Tailoring Mn's Local Electron Density and O's p-Band Center.

Enhancing proton storage in the zinc-ion battery cathode material of MnO2 holds promise in promoting its electrochemical performance by mitigating the intense Coulombic interaction between divalent zinc ions and the host structure. However, challenges persist in addressing the structural instability caused by Jahn-Teller effects and accurately modulating H+ intercalation in MnO2. Herein, the doping of high-electronegativity Sb with fully occupied d-orbital in MnO2 is reported. The Sb doping strategy engenders the formation of Mn-O-Sb path in the structure with a strong dipole polarization field, which facilitates the delocalization of eg orbital electron in Mn and thus mitigates the Jahn-Teller effects. Simultaneously, adjusting the level of Sb doping in MnO2 leads to modulation of the p-band center of O, optimizing its interaction with hydrogen and thereby enhancing proton storage. Consequently, MnO2 doped with 6% Sb exhibits commendable performance in both rate capability and cycling endurance, delivering 113 mAh g-1 at 2 A g-1 after 2000 cycles. This investigation underscores the crucial role of electronic structural engineering in elevating the electrochemical performance of cathode materials for zinc-ion batteries.

Quasi-equilibrium growth of inch-scale single-crystal monolayer α-In2Se3 on fluor-phlogopite

Epitaxial growth of two-dimensional (2D) materials with uniform orientation has been previously realized by introducing a small binding energy difference between the two locally most stable orientations. However, this small energy difference can be easily disturbed by uncontrollable dynamics during the growth process, limiting its practical applications. Herein, we propose a quasi-equilibrium growth (QEG) strategy to synthesize inch-scale monolayer α-In2Se3 single crystals, a semiconductor with ferroelectric properties, on fluor-phlogopite substrates. The QEG facilitates the discrimination of small differences in binding energy between the two locally most stable orientations, realizing robust single-orientation epitaxy within a broad growth window. Thus, single-crystal α-In2Se3 film can be epitaxially grown on fluor-phlogopite, the cleavage surface atomic layer of which has the same 3-fold rotational symmetry with α-In2Se3. The resulting crystalline quality enables high electron mobility up to 117.2 cm2 V−1 s−1 in α-In2Se3 ferroelectric field-effect transistors, exhibiting reliable nonvolatile memory performance with long retention time and robust cycling endurance. In brief, the developed QEG method provides a route for preparing larger-area single-crystal 2D materials and a promising opportunity for applications of 2D ferroelectric devices and nanoelectronics.

Exploring the ergogenic potential of carbohydrate-caffeine combined mouth rinse on exercise and cognitive performance: a systematic review.

Carbohydrate (CHO) and caffeine (CAF) mouth rinsing have been independently reported to benefit sport performance. The proposed mechanisms by which mouth rinsing CHO exerts an influence are reported to be different from those for mouth rinsing CAF. However, the potential ergogenic effects of combining CHO and CAF in a single mouth rinse solution, are unclear. This study aimed to review the available evidence of CHO-CAF combined mouth rinse on exercise and cognitive performance in human participants. A systematic literature search was conducted using five databases until April 2024, following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) recommendations. Among the nine randomized crossover studies included, only one study showed significant improvements in lower-body muscular endurance with CHO-CAF mouth rinse (effect size (ES): 0.48; p<0.05), while two studies reported non-statistically significant improvements in repeated sprint performance compared to other mouth rinse and placebo conditions (ES: 0.20-0.81; p=0.07-0.18). However, for other performance measures, including repeated jumps, upper-body strength and endurance, endurance cycling, and intermittent recovery run, most evidence (five studies) did not demonstrate significant ergogenic effects. Notably, of the two studies that examined cognitive performance, both reported significant improvements with CHO-CAF mouth rinse compared with the placebo condition (ES: 0.45-3.45; p<0.05). Overall, a synergistic influence of CHO-CAF mouth rinse on physical exercise performance is not evident, but preliminary evidence suggests potential benefits on cognitive performance. Future studies are required to address various methodological issues identified in this review, while practitioners and athletes should exercise caution when considering this novel nutritional strategy.

The Responsiveness of Exercise Tests in COPD: A Randomized Controlled Trial

BackgroundChronic obstructive pulmonary disease (COPD) is characterised by reduced exercise tolerance and improving physical performance is an important therapeutic goal. A variety of exercise tests are commonly used to assess exercise tolerance, including laboratory and field-based tests. The responsiveness of these tests to common COPD interventions is yet to be compared, but may inform test selection in clinical and research settings. Research QuestionWhat exercise test possesses the greatest sensitivity to change pre- to post-intervention in patients with COPD? Study Design and Methods154 patients with symptomatic COPD were recruited and randomised (2:1:1) to six weeks of long-acting muscarinic antagonist (LAMA), pulmonary rehabilitation (PR), or usual care (UC). Pre- and post-intervention, participants performed a ramp-incremental and constant work rate cycle ergometer exercise test (ICET and CWRCT), incremental and endurance shuttle walk test (ISWT and ESWT), six-minute walk test (6MWT), and a four metre gait speed test (4MGS). Results103 participants (67 ± 8 y; 75 [73%] males; FEV1: 50.6 ± 16.8 % predicted) completed the study. Significant improvements in the ICET, CWRCT, ISWT, ESWT, and 6MWT were observed following PR (p<0.05), with the greatest improvements seen in the constant work rate protocols (% change: CWRCT: 42%; ESWT: 41%). InterpretationThe ESWT and CWRCT appeared to be the most responsive exercise test protocols to LAMA and PR. The magnitude of change was much greater after a programme of rehabilitation compared to bronchodilator therapy.

α-CsPbI3 Quantum Dots ReRAM with High Air Stability Working by Valance Change Filamentary Mechanism.

The current memory system is facing obstacles to improvement, and ReRAM is considered a powerful alternative. All-inorganic α-CsPbI3 perovskite-based ReRAM working by electrochemical mechanism is reported, but the electrochemically active electrode raised difficulty in long-term stable operation, and bulk α-CsPbI3 device can not show resistive switching behavior with an inert metal top electrode. Herein, by making the α-CsPbI3 into QDs and applying it to the device with inert Au as the top electrode, the devices working by valence change mechanism are successfully fabricated. The large surface-to-volume ratio made an abundant amount of iodine vacancies and facile migration of vacancies allowed the device to work by valence change mechanism. The devices show reliable electrical characteristics, 800 cycles endurance and retention for over 4 × 104 s, and air stability for 1 month. This work demonstrates that applying the QDs can improve the stability and enable a new type of working mechanism in ReRAM.

Understanding the Reversible Transition of Unipolar and Bipolar Resistive Switching Characteristics in Solution-Derived Nanocrystalline Au-Co3O4 Thin-Film Memristors.

Nanocrystalline Au-Co3O4 thin films were fabricated through a facile solution-processing method, and voltage-polarity-dependent resistive switching (RS) characteristics including variability of Set/Reset voltages, stability of cycling endurance, and carriers transport mechanism were studied in the Pt/Au-Co3O4/Pt memory devices. The switching voltages of the Set and Reset processes in the bipolar RS memristors exhibited lower variability as compared to the unipolar resistance switching devices. Moreover, the switching performance of cycle-to-cycle endurance in bipolar mode had a smaller fluctuation than those of unipolar switching behavior. Based on the current-voltage curve fitting analysis, it was found that Ohmic-conduction behaviors dominated the carriers transport of low-resistance state regardless of unipolar or bipolar switching behaviors. The carrier transport of high resistance state was governed following Poole-Frenkel emission and Schottky emission mechanisms in the unipolar and bipolar switching modes, respectively. The physical switching mechanism of Pt/Au-Co3O4/Pt memory devices was proposed using the model by means of growth and disruption of conducting filaments, involved in memory effects of thermochemical mechanism and valence change mechanism in the unipolar and bipolar RS, respectively. The proposed model following the finite element method revealed the roles of electrical field distribution and temperature gradient to further clarify the RS mechanism. Our results open a door for understanding and optimizing oxide-based thin-film resistance switching memory devices.

Effect of dimensional confinement on the memristive properties of the perovskite-inspired novel CuxAgBiI4+x halide compound

Low dimensional halide perovskite materials have shown significant performance enhancement in memristor devices. In search of highly stable and robust perovskites, several perovskite-inspired structures are proposed. This present study demonstrates the fabrication of novel lead-free all-inorganic CuxAgBiI4+x (x = 1 or 2) as the active material sandwiched between gold and indium doped tin oxide electrodes. Initial studies revealed that the memristor devices consisting of two-dimensional Cu2AgBiI6 have higher current on/off ratio as compared to the three-dimensional CuAgBiI5. This is ascribed to the elevated Schottky barrier at the Au/Cu2AgBiI6 interface as suggested by ultraviolet photoelectron spectroscopy, which resulted low current in the high resistance state (HRS) of the device. Kelvin probe force microscopy shows that the charge accumulation property is similar in both the materials although the CuAgBiI5 possesses less vacancies. However, the high switching window of the Cu2AgBiI6-based device succeeded in retaining the stable on/off ratio in the cycling endurance. Artificial synaptic characterizations have been carried out in the Cu2AgBiI6 based device due to low HRS current. The device could mimic paired-pulsed facilitation, transition from short-term to long-term potentiation and thus establishes the fact that low dimensional perovskite-type materials possess great potential for memristor application.