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Graphene electrode diagnostic with IR imaging of Joule heat emission
摘要： Conductive graphene electrode of large area is required for some applications like for example photovoltaics or touch screens. Such large area graphene membrane needs specific test methods to assess defects which may obstacle its performance. In this work the infrared imaging of Joule heated graphene was proposed to estimate its uniformity and mechanical continuity. Thermal signatures of the typical mechanical defects like scratches and local resistivity inhomogeneity were identified. Distribution of the heat emission around such defects were simulated using finite elements method and then experimentally verified by recording of thermal landscape around the corresponding real graphene defects. Proposed method gives micrometric resolution and ability to inspection of large area electrodes depending on applied optics. Presented results give suggestions how graphene imperfections generate observed hot points related to graphene layer defects.
关键词： Finite elements,Joule heat,Defect,Graphene,Infrared
更新于2025-09-23 15:23:52
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Temperature Measurement of Electromagnetic Launcher Rails Based on FBG
摘要： Rails worked under a harsh environment in the electromagnetic launching. Measurement of temperature at or close to the rail-and-armature interface of an electromagnetic launch (EML) is capability that would provide a significant insight into the EML performance. This interface is difficult to access and requires any sensor to tolerate sliding contacts, high electrical currents, and extreme temperatures. As a result, the existing temperature sensor technology has not been successful in providing data at that location. The development of the fiber Bragg grating (FBG) may provide a potential solution for this requirement. By designing and building a temperature measurement system based on FBG, we can collect dynamic temperature data of the rail during the launch. This paper establishes a model of transient thermal field of EML, calculates the variation of rail temperature under the effect of the Joule heat, and compares with the measurement result. After adding the model in the case of the protection package of FBG temperature sensor, the simulation data agrees well with the test data, and the sensors do not been destroyed even disturbed. All of the above prove that this method is feasible, and the sensors can be used in the following tests.
关键词： fiber Bragg grating (FBG),thermal field,Joule heat,temperature measurement,Electromagnetic launch (EML),rails
更新于2025-09-23 15:22:29
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Mechanism of non-saturated field electron emission from gated p-type Si tips
摘要： Gated p-type Si tip arrays with the same gate area (AG) but various tip numbers (Ntip) were investigated to clarify the mechanism of non-saturated electron emission. It was found that the Ntip/AG ratio determines the current increasing rate (dI/dVG) of the non-saturated emission. A surface depletion/inversion dominated electron supply model that considered the local Joule heat effect was proposed to interpret the variation of the increasing rate of the non-saturated current. Less emitter in an array would lead to a higher average current on each tip, and thereby much local Joule heat to induce a stronger non-saturated emission. This work clarifies the mechanism of non-saturated emission from gated p-type emitters, and shows that the current increasing rate can be modified by changing the Ntip/AG ratio. The findings are crucial for designing reliable and controllable Si-based electron sources.
关键词： electron supply,vacuum electronic devices,p-type field electron emitter,Joule heat
更新于2025-09-23 15:21:21
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Suppressing Efficiency Roll-Off at High Current Densities for Ultra-Bright Green Perovskite Light-Emitting Diodes
摘要： Perovskite light-emitting diodes (PeLEDs) have undergone rapid development in the last several years with external quantum efficiencies (EQE) reaching over 21%. However, most PeLEDs still suffer from severe efficiency roll-off (droop) at high injection current densities, thus limiting their achievable brightness and presenting a challenge to their use in laser diode applications. In this work, we show that the roll-off characteristics of PeLEDs are affected by a combination of charge injection imbalance, nonradiative Auger recombination, and Joule heating. To realize ultrabright and efficient PeLEDs, several strategies have been applied. First, we designed an energy ladder to balance the electron and hole transport. Second, we optimized perovskite materials to possess reduced Auger recombination rates and improved carrier mobility. Third, we replaced glass substrates with sapphire substrates to better dissipate joule heat. Finally, by applying a current-focusing architecture, we achieved PeLEDs with a record luminance of 7.6 Mcd/m2. The devices can be operated at very high current densities (J) up to ~ 1 kA/cm2. Our work suggests a broad application prospect of perovskite materials for high-brightness LEDs and ultimately a potential for solution-processed electrically pumped laser diodes.
关键词： Joule heat,efficiency roll-off,Auger recombination,charge injection balance,high injection current density,ultrahigh brightness,perovskite light emitting diodes
更新于2025-09-23 15:19:57
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Facile Fabrication of Highly Conductive, Ultra-Smooth and Flexible Silver Nanowire Electrode for Organic Optoelectronic Devices
摘要： So far, one of the fundamental limitations of silver nanowires is the high contact resistance among their junctions. Moreover, a rough surface due to its random arrangement is inevitable to electrical short when the nanowire-based electronics is driving. To improve the contact resistance, we suggest the particle-shape nanocrystals are intentionally reduced at the junctions by a localized Joule-heat reduction approach from the silver ions. Via localized reductions, the reduced nanoparticles effectively weld the junction’s areas resulting in a 19% decrease in sheet resistance to 9.9 ?sq-1. Besides, the nanowires are embedded into a polyamide film with a gentle hot pressing. Consequently, the roughness was considerably dropped so that it was successful to demonstrate OLEDs (organic light-emitting diodes) with nanowires, which was beneficial to be laminated with OLEDs under the low temperature. The experimental results show the Ag NW embedding films reach 10.9?sq-1 of the sheet resistance at 92% transmittance and the roughness was only 1.92nm.
关键词： embedding,transferring,joule-heat reduction,smooth surface,silver nanowire,transparent conductive electrode
更新于2025-09-19 17:13:59