Cavity Light-Emitting Diode for Durable, High-Brightness and High-Efficiency Lighting Applications: First Budget Period Technical Report

A COLED device consists of a top electrode (anode) and a bottom electrode (cathode) separated by a thin dielectric layer. In this metal/dielectric stack, numerous small wells, or cavities, are etched through the top electrode and the dielectric layer. These cavities are subsequently filled with LEP molecules. When a voltage is applied between the top and bottom electrodes, holes (from the top electrode) and electrons (from the bottom electrode) are injected into the polymer. Light emission is generated upon recombination of holes and electrons within the polymer along the perimeters of cavities. Figure 1 compares the structures of the COLED and the traditional OLED. The existing COLED fabrication process flow is illustrated in Figure 2. A COLED can potentially be 5 times more efficient and can operate at as much as 100 times higher current density with much longer lifetime than an OLED. To fully realize these potential advantages, the COLED technology must overcome the following technical barriers, which were the technical focused points for Years 1 and 2 (Phase I) of this project: (1) Construct optimum thickness dielectric layer: In the traditional OLED structure, the optimal thickness of the LEP film is approximately 80-100 nm. In a COLED device, the effective LEP thickness roughly equals the thickness of the dielectric layer. Therefore, the optimal dielectric thickness for a COLED should also be roughly equal to 80-100 nm. Generally speaking, it is technically challenging to produce a defect-free dielectric layer at this thickness with high uniformity, especially over a large area. (2) Develop low-work-function cathode: A desired cathode should have a low work function that matches the lowest unoccupied molecular orbital (LUMO) level of the LEP molecules. This is usually achieved by using a low-work-function metal such as calcium, barium, lithium, or magnesium as the cathode. However, these metals are very vulnerable to oxygen and water. Since the cathode of the COLED will be exposed to air and processing chemicals during the COLED fabrication process, these low-work-function metals cannot be used directly in the COLED structure. Thus, new materials with low work function and better chemical stability are needed for the COLED cathode. (3) Increase active device area: Since photons are only generated from perimeters of the cavities, the actual active area in a COLED device is smaller than the device surface area. The cavity diameter and cavity spacing of the COLED devices previously produced at SRI by conventional photolithography processing are typically in the range of 3 to 7 {mu}m with an estimated active area of 2-3%. To achieve the same brightness of a traditional OLED at the same applied voltage, the active device area of a COLED should be at least 20% (1/5) of the device surface area, provided the COLED has 5 times higher EQE. This requires reducing the cavity diameter and cavity spacing to the sub-micrometer region, which can be achieved by electron-beam lithography or nanoimprint lithography. (4) Improve metal/polymer interfaces: The polymer/metal interfaces are critical issues to improve and optimize since they directly affect the effectiveness and balance of hole and electron injection, and consequently the device performance. Conventional approaches for improving a metal/polymer interface include deposition of a special interfacial material on the selected electrode surface or applying a proper surface treatment prior to deposition of the LEP. Since these approaches are generally nonselective to the cathode and anode, they cannot be directly adopted for COLED devices. Generally, the interface integration in current OLED technology still needs a better chemical approach. Hence, advanced methodology developed for the COLED technology as promoted in this project may be also suitable for other OLED devices

A review of studies on mass-movements on the Moon

The study of the lunar surface is a significant field in exploring the Moon. As a non-negligible geological process shaping the lunar surface, however, the mass movements on the Moon have not been deeply studied regarding all available datasets. In this paper, we report the results of the literature review and quantitative analysis of 965 articles retrieved from the Scopus, WoS, and Astrophysics Data System databases using keyword search terms between the years 1872 and 2022. The main findings show that the lunar mass movements are a lasting but recent prosperous research topic (since 2009). The top three influential journals in this area are Icarus, JGR, and P&SS. Robinson, Lucchitta, and Carr are the most three productive authors. California Institute of Technology, Arizona State University, and Johns Hopkins University are active institutions leading the lunar mass movements research, and the related institutions are mainly located in the United States, Russia, and China. Articles are primarily published in journals specializing in the fields of astronomy and physics. The index analysis of citation indicates the growth of the academic impact of articles about the lunar mass movements. This article summarizes the datasets, methods, and relevant parameters of lunar mass movements to facilitate future research, as well as discussing the limitations and trends in the field. In addition, four unsolved issues are proposed, including: 1) the lack of a comprehensive global database that records all types of landslides incidents; 2) the need for definite classification indicators to quantify the classification criteria for lunar mass movements; 3) the absence of a mathematical model to explain the triggering mechanism of mass movements on the Moon; and 4) the lack of quantitative indexes to evaluate the modification effect of mass movements on the lunar surface morphology. With the support of big data, the combination of artificial intelligence and traditional GIS methods is expected to become the main approach for addressing these issues such a bibliometric analysis can inspire future researchers by exploring the overall characteristics of the published literature on lunar mass movements

Association Between Family Atmosphere and Internet Addiction Among Adolescents: The Mediating Role of Self-Esteem and Negative Emotions

Objectives: Family atmosphere is a significant predictor of internet addiction in adolescents. Based on the vulnerability model of emotion and the compensatory internet use theory, this study examined whether self-esteem and negative emotions (anxiety, depression) mediated the relationship between family atmosphere and internet addiction in parallel and sequence.Methods: A total of 3,065 Chinese middle school and high school students (1,524 females, mean age = 13.63 years, SD = 4.24) participated. They provided self-reported data on demographic variables, family atmosphere, self-esteem, anxiety, depression, and internet addiction through the Scale of Systemic Family Dynamic, Self-Esteem Scale, Self-Rating Anxiety Scale, Self-Rating Depression Scale, and Internet Addiction Test, respectively. We employed Hayes PROCESS macro for the SPSS program to scrutinize the suggested mediation model.Results: It revealed that self-esteem, anxiety, and depression mediated the relationship between family atmosphere and internet addiction in parallel and sequence. The pathway of family atmosphere-self-esteem-internet addiction played a more important role than others.Conclusion: The present study confirmed the mediating role of self-esteem and negative emotions between family atmosphere and internet addiction, providing intervention studies with important targeting factors

Cavity Light-Emitting Diode for Durable, High-Brightness and High-Efficiency Lighting Applications: First Budget Period Technical Report

A COLED device consists of a top electrode (anode) and a bottom electrode (cathode) separated by a thin dielectric layer. In this metal/dielectric stack, numerous small wells, or cavities, are etched through the top electrode and the dielectric layer. These cavities are subsequently filled with LEP molecules. When a voltage is applied between the top and bottom electrodes, holes (from the top electrode) and electrons (from the bottom electrode) are injected into the polymer. Light emission is generated upon recombination of holes and electrons within the polymer along the perimeters of cavities. Figure 1 compares the structures of the COLED and the traditional OLED. The existing COLED fabrication process flow is illustrated in Figure 2. A COLED can potentially be 5 times more efficient and can operate at as much as 100 times higher current density with much longer lifetime than an OLED. To fully realize these potential advantages, the COLED technology must overcome the following technical barriers, which were the technical focused points for Years 1 and 2 (Phase I) of this project: (1) Construct optimum thickness dielectric layer: In the traditional OLED structure, the optimal thickness of the LEP film is approximately 80-100 nm. In a COLED device, the effective LEP thickness roughly equals the thickness of the dielectric layer. Therefore, the optimal dielectric thickness for a COLED should also be roughly equal to 80-100 nm. Generally speaking, it is technically challenging to produce a defect-free dielectric layer at this thickness with high uniformity, especially over a large area. (2) Develop low-work-function cathode: A desired cathode should have a low work function that matches the lowest unoccupied molecular orbital (LUMO) level of the LEP molecules. This is usually achieved by using a low-work-function metal such as calcium, barium, lithium, or magnesium as the cathode. However, these metals are very vulnerable to oxygen and water. Since the cathode of the COLED will be exposed to air and processing chemicals during the COLED fabrication process, these low-work-function metals cannot be used directly in the COLED structure. Thus, new materials with low work function and better chemical stability are needed for the COLED cathode. (3) Increase active device area: Since photons are only generated from perimeters of the cavities, the actual active area in a COLED device is smaller than the device surface area. The cavity diameter and cavity spacing of the COLED devices previously produced at SRI by conventional photolithography processing are typically in the range of 3 to 7 {mu}m with an estimated active area of 2-3%. To achieve the same brightness of a traditional OLED at the same applied voltage, the active device area of a COLED should be at least 20% (1/5) of the device surface area, provided the COLED has 5 times higher EQE. This requires reducing the cavity diameter and cavity spacing to the sub-micrometer region, which can be achieved by electron-beam lithography or nanoimprint lithography. (4) Improve metal/polymer interfaces: The polymer/metal interfaces are critical issues to improve and optimize since they directly affect the effectiveness and balance of hole and electron injection, and consequently the device performance. Conventional approaches for improving a metal/polymer interface include deposition of a special interfacial material on the selected electrode surface or applying a proper surface treatment prior to deposition of the LEP. Since these approaches are generally nonselective to the cathode and anode, they cannot be directly adopted for COLED devices. Generally, the interface integration in current OLED technology still needs a better chemical approach. Hence, advanced methodology developed for the COLED technology as promoted in this project may be also suitable for other OLED devices

Computational Fluid Dynamics Simulation of Turbulent Waverider Flowfield with Sideslip

To better understand the waverider hypersonic flowfield with sideslip, the flowfield computational fluid dynamics simulation for a selected waverider at 5-deg angle of sideslip off-design condition is conducted. The off-design flow field is more complicated than the nominal design, inasmuch as there is very strong shock-wave/boundary-layer interaction at the windward waverider tip, and a detached shock at the leeward tip, whether the flow conditions are inviscid or viscous. For these different simulations, the pressure coefficient distribution basically has the same values except near the tip, but the shock attachment point on the lower surface and force coefficient value are different. The shock-wave/boundary-layer interaction and shock attachment pattern at the windward tip strongly affect the waverider pressure and local skin-friction coefficient distribution in that region. The simulated pressure coefficient distribution is in good agreement with available experimental results

Cone-Derived Waverider Flowfield Simulation Including Turbulence and Off-Design Conditions

Using the numerical scheme of Roe\u27s flux-difference splitting, the Baldwin-Lomax algebraic turbulent model,and the time-averaged thin-layer Navier-Stokes equation, the flowfields for a selected Rasmussen\u27s waveriderforebody are investigated. Specific cases include turbulent flow on-design condition (M^ = 4, a = 0), turbulent flowoff-design condition (Moo = 4, a = 5 deg), and laminar (and Euler) flow off-design condition (M^ = 5, a = 0). Forcomparison purposes, some results previously reported by the authors are presented. The off-design flowfields aremore complicated than the on-design ones. For the M^ = 5 waverider, there is very strong stock-wave/boundary-layer interaction. For the a = 5 deg waverider, there is a detached shock, resulting in a small separation bubble anda vortex on the upper surface. The shock-wave/boundary-layer interaction and shock attachment pattern stronglyaffect the waverider pressure and local skin-friction coefficient distributions