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Design Principles for Trap-Free CsPbX <sub/>3</sub> Nanocrystals: Enumerating and Eliminating Surface Halide Vacancies with Softer Lewis Bases
摘要： We introduce a general surface passivation mechanism for cesium lead halide perovskite materials (CsPbX3, X = Cl, Br, I) that is supported by a combined experimental and theoretical study of the nanocrystal surface chemistry. A variety of spectroscopic methods are employed together with ab initio calculations to identify surface halide vacancies as the predominant source of charge trapping. The number of surface traps per nanocrystal is quantified by 1H NMR spectroscopy, and that number is consistent with a simple trapping model in which surface halide vacancies create deleterious under-coordinated lead atoms. These halide vacancies exhibit trapping behavior that differs between CsPbCl3, CsPbBr3, and CsPbI3. Ab initio calculations suggest that introduction of anionic X-type ligands can produce trap-free band gaps by altering the energetics of lead-based defect levels. General rules for selecting effective passivating ligand pairs are introduced by considering established principles of coordination chemistry. Introducing softer, anionic, X-type Lewis bases that target under-coordinated lead atoms results in absolute quantum yields approaching unity and monoexponential luminescence decay kinetics, thereby indicating full trap passivation. This work provides a systematic framework for preparing highly luminescent CsPbX3 nanocrystals with variable compositions and dimensionalities, thereby improving fundamental understanding of these materials and informing future synthetic and post-synthetic efforts towards trap-free CsPbX3 nanocrystals.
关键词： charge trapping,nanocrystals,surface passivation,ab initio calculations,halide vacancies,CsPbX3,ligand exchange,quantum yield
更新于2025-09-10 09:29:36
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Total Ionization Dose Effects on Charge Storage Capability of Al <sub/>2</sub> O <sub/>3</sub> /HfO <sub/>2</sub> /Al <sub/>2</sub> O <sub/>3</sub> -Based Charge Trapping Memory Cell
摘要： Because of the discrete charge storage mechanism, charge trapping memory (CTM) technique is a good candidate for aerospace and military missions. The total ionization dose (TID) effects on CTM cells with Al2O3/HfO2/Al2O3 (AHA) high-?? gate stack structure under in-situ 10 keV x-rays are studied. The ??–?? characteristics at different radiation doses demonstrate that charge stored in the device continues to be leaked away during the irradiation, thereby inducing the shift of flatband voltage (??fb). The dc memory window shows insignificant changes, suggesting the existence of good P/E ability. Furthermore, the physical mechanisms of TID induced radiation damages in AHA-based CTM are analyzed.
关键词： Total Ionization Dose Effects,Flatband Voltage,Charge Trapping Memory,Al2O3/HfO2/Al2O3,X-rays
更新于2025-09-09 09:28:46
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centers in amorphous
摘要： We investigate the charge-trapping behavior in nitrogen-deficient amorphous silicon nitride (a-Si3N4?x) using first-principles calculations. The amorphous ensembles with one nitrogen atom missing are generated through melt-quench procedures. The nitrogen deficiency mainly produces one Si—Si bond and one K center (Si dangling bond). The energy level of defect states indicates that the K centers act as possible trap sites. The transition levels of K centers are estimated, and it is found that the Hubbard U energy ranges from ?1.14 to 1.11 eV. Even though most K centers show positive U, the charge states of most centers in the ensemble are either positive or negative under the charge-neutrality condition, resulting in 'seemingly negative-U' behavior. This is consistent with the diamagnetic signal in experiments. The charge-injection energy of K centers is evaluated on the basis of the Franck-Condon approximation, and the average trap depths for electrons (1.33 eV below the conduction edge) and holes (1.54 eV above the valence edge) are in good agreement with experimental data.
关键词： K centers,Franck-Condon approximation,first-principles calculations,Hubbard U energy,amorphous silicon nitride,charge-trapping behavior
更新于2025-09-04 15:30:14
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Multiple Resistive Switching Behaviours of CH3NH3PbI3 Perovskite film with Different Metal Electrodes
摘要： The utilization of defects in organic-inorganic hybrid perovskite materials such as CH3NH3PbI3 is beneficial for memory applications. In this work, a simple CH3NH3PbI3 memory device with various commonly used electrodes such as aluminium (Al), silver (Ag), and gold (Au) yielded different switching behaviours. Using Al in ITO/CH3NH3PbI3/Al device reveals Resistive Random Access Memory (ReRAM) behaviour with a SET voltage of 4.5 V and can be RESET by applying a negative sweep voltage above 1.3 V due to the formation of iodide vacancy filament. Interestingly, by using Ag and Au cathodes to replace Al, yielded Write-Once-Read-Many (WORM) resistive switching characteristics. The conversion process from OFF to ON occur at around 4.7 V and 4.0 V for Ag and Au, respectively. The “shorting effect” remains even though a reverse voltage was applied indicating data retention. These fabricated devices could contribute to further understanding of selecting the right electrodes and open up new possibility of studies in the direction of resistive switching memory applications.
关键词： organic-inorganic perovskite,resistive switching,filamentary conduction,charge trapping
更新于2025-09-04 15:30:14