Goede vooruitzichten voor spintronica in silicium Spintronica is een nieuw concept voor de opslag en verwerking van digitale informatie. Spintronica maakt gebruik van de spin van elektronen om digitale gegevens te representeren en is dus niet, zoals in de huidige technologie, gebaseerd op de elektrische lading van elektronen. Met behulp van elektronische, op spintronica gebaseerde componenten wordt het mogelijk nieuwe energiezuinige systemen te ontwikkelen waarin de niet-vluchtige opslag van data en snelle dataverwerking gecombineerd wordt. Het gebruik van silicium, het meest gangbare materiaal in elektronica, is hiervoor cruciaal. In zijn proefschrift beschrijft Sandeep Sharma onderzoek naar de belangrijkste bouwstenen van silicium spintronica, namelijk de creatie, detectie en manipulatie van spins in silicium bij kamertemperatuur. Het proefschrift begint met de beschrijving van experimenten waarmee met succes wordt aangetoond dat het inderdaad mogelijk is spinpolarisatie in silicium te induceren, detecteren en manipuleren, met behulp van het Hanle effect, en dit alles bij kamertemperatuur. Dat was nog niet eerder gedaan. Ferromagnetische tunnelcontacten op het silicium bleken hiervoor uitermate geschikt. Er werden tunnelcontacten met verschillende materialen onderzocht, waarbij de spinsignalen bestudeerd zijn als functie van de aangelegde spanning, stroomdichtheid, temperatuur en de dikte van de tunnelbarriere. Controle-experimenten lieten duidelijk zien dat de spinsignalen daadwerkelijk het resultaat zijn van spingepolariseerd transport en het ontstaan van een spinpolarisatie in het silicium. De anisotropie van het tunnelproces in ferromagnetische contacten op silicium is ook in detail onderzocht. De resultaten vormen een belangrijke doorbraak in de ontwikkeling en het begrip van silicium spintronica.
In this study we focused on the effect of Fe2O3 on structural properties of ZnO–V2O5 based varistor. ZnO ceramics doped with 3 mol% of V2O5 as a varistor-forming oxide and 0 to 0.5 mol% Fe2O3 were prepared by conventional powder processing route using high energy ball mill and sintered at 900°C for 4 h. It was observed that the grain growth behavior in ZnO-V2O5 system was strongly influenced by the presence of Fe2O3. Moreover, due to doping of V2O5 lower temperatures about 900°C could be used for sintering. The microstructure of the samples consists of ZnO grains as a main phase and Zn3(VO4)2 as a secondary phase. Structural properties of samples have been investigated by using lattice parameter calculated from rietveld refinements. Absence of any impure element or phase is confirmed by XRD and EDX data. XRD data reveals that low content of iron oxide did not contribute in phase formation but only change the lattice parameters and increased the grain size of sample.
Here, we report the room-temperature dual discrimination of N,N-dimethylformamide (DMF) and aniline using a 1T′/2H mixed phase tungsten diselenide (WSe2) chemiresistive gas sensor. Mixed phase WSe2 microspheres were synthesized in a thermally controlled environment via a facile solvothermal method. Structural analysis using various characterization techniques confirmed the spherical flower-like morphology and presence of mixed phases. Further, a slight increase in the 1T′/2H ratio of WSe2 showed a significant conductivity change, as confirmed using electrochemical impedance spectroscopy and two-terminal current voltage measurements. The sensing properties were investigated under varying relative humidity (40–90%) for two different devices made from WSe2 synthesized at 200 and 220 °C, respectively. The sensing device created with WSe2 synthesized at 200 °C exhibited response and recovery times of 157 and 68 s, respectively, for DMF (4 ppm). This device revealed a response of 2.77% toward 32 ppm DMF and a theoretically calculated limit of detection (LOD) of ∼114 ppb. The sensor created with WSe2 synthesized at 220 °C displayed response and recovery times of 78 and 89 s, respectively, for aniline (3 ppm) under ambient conditions. This device exhibited a significant drop in response (0.04%) toward DMF in comparison to aniline and displayed a response of (1.07%) at room temperature with a calculated LOD of ∼250 ppb. The sensors showed higher resilience toward increased humidity levels. The absolutely clean, stable, and reproducible responses (2.35% and 1.61%) toward DMF and (0.9% and 0.66%) aniline vapors under relative humidities of 40% and 90%, respectively, confirm the durable behavior of the devices. The gas sensing mechanism was explained using appropriate energy level diagrams, as well as adequate surface reactions, which were then validated using the gas chromatography–mass spectroscopy (GC-MS) approach. The present work emphasizes a straightforward and facile approach to develop 1T′/2H mixed phase WSe2 for the dual detection of DMF and aniline under ambient conditions.
Graphene-based gas sensors have attracted significant attention due to advantages like high surface-to-volume ratio, excellent electrical conductivity, and good mechanical properties. Although great progress has been made in recent years toward improving the sensing performance of these sensors, still lack of selectivity and costly fabrication of graphene impose challenges toward the commercial application of these sensors. On the other hand, metal oxide nanowires (NWs) are well-established sensing materials for the detection of various oxidizing and reducing gases with excellent sensing properties and ease of manufacture. In this chapter, we shall discuss the application of metal oxide NWs and graphene-based hybrid structures toward the detection of various toxic gases at room temperature.
Layered two-dimensional transition metal dichalcogenides, due to their semiconducting nature and large surface-to-volume ratio, have created their own niche in the field of gas sensing. Their large recovery time and accompanied incomplete recovery result in inferior sensing properties. Here, we report a composite-based strategy to overcome these issues. In this study, we report a facile double-step synthesis of a MoS2/SnO2 composite and its successful use as a superior room-temperature ammonia sensor. Contrary to the pristine nanosheet-based sensors, the devices made using the composite display superior gas sensing characteristics with faster response. Specifically, at room temperature (30° C), the composite-based sensor exhibited excellent sensitivity (10%) at an ammonia concentration down to 0.4 ppm along with the response and recovery times of 2 and 10 s, respectively. Moreover, the device also exhibited long-term durability, reproducibility, and selectivity toward ammonia against hydrogen sulfide, methanol, ethanol, benzene, acetone, and formaldehyde. Sensor devices made on quartz and alumina substrates with different roughnesses have yielded almost an identical response, except for slight variations in response and recovery transients. Further, to shed light on the underlying adsorption energetics and selectivity, density functional theory simulations were employed. The improved response and enhanced selectivity of the composite were explicitly discussed in terms of adsorption energy. Lowdin charge analysis was performed to understand the charge transfer mechanism between NH3, H2S, CH3OH, HCHO, and the underlying MoS2/SnO2 composite surface. The long-term durability of the sensor was evident from the stable response curves even after 2 months. These results indicate that hydrothermally synthesized MoS2/SnO2 composite-based gas sensors can be used as a promising sensing material for monitoring ammonia gas in real fields.
As a typical volatile organic compound (VOC), N,N-dimethylformamide (DMF) is a popular solvent and tracer for environmental air quality monitoring. Highly selective detection with low electrical noise, quick response/recovery times, and superior sensitivity at room temperature against VOCs, especially at the parts per billion (ppb) level, continues to be a significant challenge in gas-sensing applications. To address the issue, herein we demonstrate an MoSe2/multiwalled carbon nanotube composite based chemiresitor sensor for the detection of DMF. MoSe2 with a layered sheetlike structure supports MWCNTs to enhance the specific surface area, thereby increasing the sensitivity (down to 0.1 ppm for DMF) and selectivity and improving the response over a wider range of relative humidities (30–80%). The composite-based sensor shows good sensitivity (12.3% for 5 ppm of DMF), better selectivity, and faster response (65 s) and recovery (90 s) times in comparison to the MoSe2 sensor (192, 392 s), respectively, and a consistent response over 35 days. Density functional theory simulations were employed to understand the adsorption process and sensing mechanism. An analysis revealed a negative adsorption energy of −716 meV, implying that the adsorption process is spontaneous and exothermic. Further, charge transfer (0.013 e) using the Bader scheme confirms the process to be physisorption in nature. The results were further supported using an electrochemical impedance spectroscopy analysis. These results indicate the great potential of the composite for selective and stable sensing of DMF over a wider range of relative humidities. The present work suggests that a composite of MoSe2 with MWCNTs could be useful to design DMF sensors with improved sensitivity and selectivity under various environmental conditions.
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