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<i>In-Situ</i> Measurement and Control of the Fermi Level in Colloidal Nanocrystal Thin Films during Their Fabrication
摘要： In engineering a high-performance semiconductor device, understanding of the Fermi level position is critical. Here, we demonstrate that open-circuit potential (OCP) measurements can be used to quantify the Fermi level in nanocrystal thin films in-situ during their solution-based fabrication. We use this method to study the influence of (1) a metal contact and (2) nanocrystal surface termination on the Fermi level of the nanocrystal film, and find that oxidization or reduction of the nanocrystals as well as surface terminations with dipoles can be used to tune the Fermi level over large energy ranges. Finally, to emphasize the compatibility of the technique with device fabrication, we show that we can use blends of ligands to design the Fermi level landscape in a nanocrystal film. Our work highlights that OCP measurements can be used to gain insights into existing device operation and direct further optimization of optoelectronic devices.
关键词： Fermi level,nanocrystals,quantum dots,electronic structure,In-situ measurement
更新于2025-09-04 15:30:14
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Electronic structure of the polymer-cathode interface of an organic electroluminescent device investigated using operando hard x-ray photoelectron spectroscopy
摘要： The electronic structure of a polymer-cathode interface of an operating organic light-emitting diode (OLED) was directly investigated using hard X-ray photoelectron spectroscopy (HAXPES). The potential distribution pro?le of the light-emitting copolymer layer as a function of the depth under the Al/Ba cathode layer in the OLED depended on the bias voltage. We found that band bending occurred in the copolymer of 9,9-dioctyl?uorene (50%) and N-(4-(2-butyl)-phenyl)diphenylamine (F8-PFB) layer near the cathode at 0 V bias, while a linear potential distribution formed in the F8-PFB when a bias voltage was applied to the OLED. Direct observation of the built-in potential and that band bending formed in the F8-PFB layer in the operating OLED suggested that charges moved in the F8-PFB layer before electron injection from the cathode.
关键词： polymer-cathode interface,band bending,organic light-emitting diode,electronic structure,hard X-ray photoelectron spectroscopy
更新于2025-09-04 15:30:14
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摘要： The spin-orbit coupling (SOC) interactions, electron-correlation effects, and Hund coupling cooperate and compete with each other, leading to novel properties, quantum phase, and nontrivial topological electronic behavior in iridium oxides. Because of the well-separated IrO6 octahedra approaching cubic crystal-field limit, the hexagonal iridates Sr3MIrO6 (M = Sr, Na, and Li) serve as canonical model systems to investigate the underlying physical properties that arise from the novel jeff state. Based on density-functional theory calculations complemented by Green’s function methods, we systematically explore the critical role of SOC on the electronic structure and magnetic properties of Sr3MIrO6. The crystal-field splitting combined with correlation effects are insufficient to account for the insulating nature, but the SOC interaction is the intrinsic source to trigger the insulating ground states in these hexagonal iridates. The decreasing geometry connectivity of IrO6 octahedra gives rise to the increase of effective electronic correlations and SOC interactions, tuning the hexagonal iridates from low-spin jeff = 1/2 states with large local magnetic moments for the Ir4+ (5d 5) ions in Sr4IrO6 to nonmagnetic singlet Jeff = 0 states without magnetic moments for the Ir5+ (5d 4) ions in Sr3NaIrO6 and Sr3LiIrO6. The theoretical calculated results are in good agreement with available experimental data, and explain the magnetic properties of Sr3MIrO6 well.
关键词： electronic structure,insulating state,magnetic properties,iridates,spin-orbit coupling
更新于2025-09-04 15:30:14
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[IEEE 2018 15th International Multi-Conference on Systems, Signals & Devices (SSD) - Yassmine Hammamet, Tunisia (2018.3.19-2018.3.22)] 2018 15th International Multi-Conference on Systems, Signals & Devices (SSD) - The New Candidate Materials for Infrared Optical Devices
摘要： In this study, We propose the cubic AlxB1-xBi ternary alloy as a promising infrared material. We used the full potential-linearized augmented plane wave (FP-LAPW) method within the Density Functional Theory (DFT) to predict the structural and electronic properties of the AlxB1-xBi ternary alloys. The structural properties such as the equilibrium lattice parameter, bulk modulus, and its pressure derivative are investigated with the effect of the concentration variation of Al atom, x (x=0, 0.25, 0.50, 0.75 and 1). We found that the equilibrium lattice parameter of AlxB1-xBi ternary alloys increases when increasing the doping concentration of the Al atom, while its bulk modulus decreases. The energy band gap of the AlxB1-xBi ternary alloys decreases with the increase in the Al doping concentration. The AlxB1-xBi alloys for 0.50 and 0.75 present a semi-metallic character the other concentrations and are compositions. Our results show the direct nature of the energy band gap of the ternary AlxB1-xBi alloy for all composition of Al substitution. To our knowledge, this is the first theoretical study of this ternary alloy that needs eventual experimental data for confirmations.
关键词： Optical properties,TB-MBJ,FP-LAPW,Electronic structure,GGA,DFT,Infrared Radiation,III-III-V ternary Alloy
更新于2025-09-04 15:30:14
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Model Calculation of the Piezoelectric Coefficient of Hexagonal 2D Materials
摘要： A quantum-mechanical microscopic model of the piezoelectric e?ect in 2D materials is developed. The piezoelectric coe?cient requires the calculation of an internal atomic displacement and an e?ective piezoelectric charge. The internal displacement is obtained from minimizing the strain energy given by a Keating-like model, while the e?ective charge takes into account the atomic displacements and also a redistribution of the electronic charge; a bond-orbital model is used to compute the latter. The ?nal theory only requires atomic energies and the elasticity constants of the materials as input parameters. The piezoelectric coe?cients of a number of II-VI, III-V and IV-IV materials that could stably form in the planar hexagonal structure are computed; results for the IV-IV materials are obtained for the ?rst time.
关键词： piezoelectric coefficient,electronic structure,2D materials,bond-orbital model
更新于2025-09-04 15:30:14
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Density-functional-theory calculations of structural and electronic properties of vacancies in monolayer hexagonal boron nitride (h-BN)
摘要： We have carried out the density functional theory calculations of vacancies in monolayer h-BN. We model five configurations, two configurations of monovacancies (VB and VN) and three configurations (VBB, VNN, and VBN) of divacancies. In the case of monovacancies, we find that VB and VN form a C3V symmetry. In the divacancy case, we find that VNN produces a heart-like configuration having two pentagons and leaving two dangling bonds, while VBB leaves four dangling bonds. As for VBN, it produces two pentagons and has no dangling bond. The calculated formation energies of VB; VN; VBB; VNN, and VBN are 11.65 eV, 12.05 eV, 17.59 eV, 22.32 eV, and 16.89 eV, respectively. These energies show that VB is more stable than VN, while VBB is more stable than VNN. We conclude that the N-rich h-BN sheet is energetically more favorable to be formed rather than the B-rich one. However, the most stable configuration of the divacancies belongs to VBN compensating from the absence of the dangling bond, which obeys the dangling-bond-counting-model. Furthermore, we calculate band structures of the most stable mono- and divacancies. We find that monovacancy somewhat changes the electronic structure, shown by localized states near the Fermi level, while the divacancy produces two new states above the Fermi level.
关键词： B-N vacancies,Electronic structure,Formation energy
更新于2025-09-04 15:30:14