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A comparative ab initio study of the structural, mechanical, electronic and optical behaviors of ZnO:Ni thin films with nanometer scale
摘要： The electronic and optical properties of undoped and Ni–doped ZnO thin films with nanometer scale have been studied in the wurtzite phase, by first–principle approach. Density functional theory has been employed to calculate the fundamental properties of the films using full–potential linearized augmented plane–wave method. Ni doping was found to reduce the bandgap value of the material. Additionally, DOS effective mass of the electrons was evaluated. It was revealed that the effective mass of the electrons at the bottom of conduction band increased with Ni doping. Decrease of reflectance for thin films with nanometer scale in the UV–vis region was observed. The substitution by Ni decreased the intensity of the peaks, and a red shift was observed in the absorption peak. Moreover, the static dielectric constant, and static refractive index decreased with Ni content. Energy loss function of the modeled compounds was also evaluated. All calculated parameters were compared with the available experimental and other theoretical results.
关键词： DFT,band structure,structural properties,electronic behaviors,optical properties,ZnO:Ni thin film
更新于2025-09-23 15:23:52
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Effect of donor acceptor substitution position on the electrical responsive properties of azulene system: a computational study
摘要： Effect of donor–acceptor substitution position on the electrical responsive properties like polarisability, first hyper polarisability of donor–acceptor substituted azulene derivatives have been investigated using HF and Density functional theory with various hybrid functional and basis. It is observed that among the DFT methods, CAM-B3LYP hybrid functional with correlation consistent polarised triple-zeta, cc-pVTZ basis show less overestimated value of polarisability and first hyperpolarisability compare to other hybrid functional and it is again advantageous than HF with similar basis in term of its price and performance ratio. An apparent violation of minimum polarisability principle among the studied azulene derivatives are observed and it has been explain due to non-constancy of the potential functions upon substitution of donor (NMe2) and acceptor (NO2) groups at different position of azulene ring. Computed βav values are in accordance with the extent of charge transfer character of the azulene with a few exceptions. Position of donor and acceptor group at the five- and seven-member ring also play a big role in determining the electrical responsive parameter has been discussed. It is also observed that 2 and 6 carbon atom of azulene are highly sensitive towards donor acceptor substitution.
关键词： chemical hardness,electronic spatial extent (<R2>),Polarisability,optical gap,first hyper-polarisability
更新于2025-09-23 15:23:52
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Multimodal hard x-ray imaging with resolution approaching 10 nm for studies in material science
摘要： We report multimodal scanning hard x-ray imaging with spatial resolution approaching 10 nm and its application to contemporary studies in the field of material science. The high spatial resolution is achieved by focusing hard x-rays with two crossed multilayer Laue lenses and raster-scanning a sample with respect to the nanofocusing optics. Various techniques are used to characterize and verify the achieved focus size and imaging resolution. The multimodal imaging is realized by utilizing simultaneously absorption-, phase-, and fluorescence-contrast mechanisms. The combination of high spatial resolution and multimodal imaging enables a comprehensive study of a sample on a very fine length scale. In this work, the unique multimodal imaging capability was used to investigate a mixed ionic-electronic conducting ceramic-based membrane material employed in solid oxide fuel cells and membrane separations (compound of Ce0.8Gd0.2O2?x and CoFe2O4) which revealed the existence of an emergent material phase and quantified the chemical complexity at the nanoscale.
关键词： mixed ionic-electronic conducting membrane,x-ray nanoscale imaging,multimodal imaging,high spatial resolution
更新于2025-09-23 15:23:52
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Electronic structure, mechanical and optical properties of ternary semiconductors Si <sub/>1-x</sub> Ge <sub/>x</sub> C (X?=?0, 0.25, 0.50, 0.75, 1)
摘要： The electronic structure of silicon carbide with increasing germanium content have been examined using first principles calculations based on density functional theory. The structural stability is analysed between two different phases, namely, cubic zinc blende and hexagonal phases. The zinc blende structure is found to be the stable one for all the Si1-xGexC semiconducting carbides at normal pressure. Effect of substitution of Ge for Si in SiC on electronic and mechanical properties is studied. It is observed that cubic SiC is a semiconductor with the band gap value 1.243 eV. The band gap value of SiC is increased due to the substitution of Ge and the band gap values of Si 0.75 Ge 0.25 C, Si 0.50 Ge 0.50 C, Si 0.25 Ge 0.75 C and GeC are 1.322 eV, 1.413 eV, 1.574 eV and 1.657 eV respectively. As the pressure is increased, it is found that the energy gap gets decreased for Si1-x GexC (X = 0, 0.25, 0.50, 0.75, 1). The elastic constants satisfy the Born – Huang elastic stability criteria. The bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio are also calculated and compared with the other available results.
关键词： mechanical properties,electronic structure,optical properties,First principles study
更新于2025-09-23 15:23:52
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Electronic properties of hybrid organic/inorganic semiconductor pn-junctions
摘要： Hybrid inorganic/organic semiconductor heterojunctions are candidates to expand the scope of purely organic or inorganic junctions in electronic and optoelectronic devices. Comprehensive understanding of bulk and interface doping on the junction’s electronic properties is therefore desirable. In this work, we elucidate the energy level alignment and its mechanisms at a prototypical hybrid pn-junction comprising ZnO (n-type) and p-doped N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (α-NPD) as semiconductors, using photoelectron spectroscopy. The level alignment can be quantitatively described by the interplay of contact-induced band and energy level bending in the inorganic and organic component away from the interface, and an interface dipole due to the push-back effect. By adjusting the dopant concentration in α-NPD, the position of the frontier energy levels of ZnO can be varied by over 0.5 eV and that of α-NPD by over 1 eV. The tunability of this pn-junction’s energy levels evidences the substantial potential of the hybrid approach for enhancing device functionality.
关键词： semiconductors,electronic properties,photoelectron spectroscopy,interfaces
更新于2025-09-23 15:23:52
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Impurity induced cross luminescence in KMgCl3 : An ab-initio study
摘要： Density functional theory calculations have been carried out to calculate the electronic structure and optical properties of host and Cs doped KMgCl3. All the calculations were performed by using the Tran and Blaha modified Becke-Johnson potential (TB-mBJ) in order to accurately predict the band gap and the optical spectra. The investigated compound is found to be an insulator with direct band gap of 4.7, 6.9 eV using Generalized Gradient Approximation (GGA), and TB-mBJ functionals respectively. The calculated refractive index shows the optical isotropy of this compound in the low energy region, though the structure is anisotropic. From our theoretical calculations we predict KMgCl3 doped with Cs to be a better cross luminescence material compared to host compound, where additional Cs states are present below the valence band of the compound. Detailed discussion is presented in the manuscript.
关键词： Scintillators,Cross luminescence,Optical properties,Electronic structure
更新于2025-09-23 15:23:52
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Tuneable thermal expansion of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate
摘要： The linear coefficient of thermal expansion for a mixture of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS) is calculated using density functional theory and the Debye-Grüneisen model. The linear coefficient of thermal expansion is a key factor in thermal management (thermal conductivity, thermal stress and thermal fatigue) of microelectronic and energy devices, being common applications of the conjugated polymeric PEDOT:PSS system. The obtained value of 53×10-6 K-1 at room temperature can be rationalised based on the electronic structure analysis. The PEDOT and PSS units are bonded by a dipole-dipole interaction between S in PEDOT and H in PSS. A C-C bond in a benzene ring (PSS) or thiophene (PEDOT) is up to 13 times stronger than the S-H bond. By adjusting the population of the S-H bonds by deprotonating PSS, the linear coefficient of thermal expansion can be enhanced by 57%. This allows for tuning the thermal properties of PEDOT:PSS in cutting-edge devices.
关键词： electronic structure,thermal properties,density functional theory,conjugated polymers
更新于2025-09-23 15:23:52
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Testbeam results of irradiated ams H18 HV-CMOS pixel sensor prototypes
摘要： HV-CMOS pixel sensors are a promising option for the tracker upgrade of the ATLAS experiment at the LHC, as well as for other future tracking applications in which large areas are to be instrumented with radiation-tolerant silicon pixel sensors. We present results of testbeam characterisations of the 4th generation of Capacitively Coupled Pixel Detectors (CCPDv4) produced with the ams H18 HV-CMOS process that have been irradiated with different particles (reactor neutrons and 18 MeV protons) to fluences between 1 × 10^14 and 5 × 10^15 1-MeV- neq/cm^2. The sensors were glued to ATLAS FE-I4 pixel readout chips and measured at the CERN SPS H8 beamline using the FE-I4 beam telescope. Results for all fluences are very encouraging with all hit efficiencies being better than 97% for bias voltages of 85 V. The sample irradiated to a fluence of 1 × 10^15 neq/cm^2 — a relevant value for a large volume of the upgraded tracker — exhibited 99.7% average hit efficiency. The results give strong evidence for the radiation tolerance of HV-CMOS sensors and their suitability as sensors for the experimental HL-LHC upgrades and future large-area silicon-based tracking detectors in high-radiation environments.
关键词： Particle tracking detectors (Solid-state detectors),Solid state detectors,Radiation-hard detectors,Electronic detector readout concepts (solid-state)
更新于2025-09-23 15:23:52
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Transport properties of doped zigzag graphene nanoribbons
摘要： Numerous studies on materials have driven the development of modern nanoelectronic devices. And research also shown that the integrated circuits have entered the era of the nanoelectronic scales from the scale of microelectronics. But the limitations of copper as a traditional connection, such as the resistivity increases a lot, further causing a lot of heat in the interconnect, have been highlighted. Therefore, we need new materials as the substitution of copper. The metallic properties exhibited by the zigzag graphene nanoribbons (ZGNRs) can be controlled by the edge states, doping and different widths of the nanoribbons. In this paper, we applied simulation to dope copper atom chains on ZGNRs. We found an energetic phenomenon that after doping the nanoribbons conductivity have increased significantly than the original. In addition, the transmission channels are mainly concentrated near the doping position, and the width used for transmission is greatly reduced after doping. It is expected to be used as an inter-connect application in nano-integrated circuits in the future.
关键词： Density functional theory,Interconnect,Electronic transport property,Non-equilibrium Green's function,Zigzag graphene nanoribbons,Doping
更新于2025-09-23 15:23:52
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[IEEE 2018 International IEEE Conference and workshop in óbuda on Electrical and Power Engineering (CANDO-EPE) - Budapest, Hungary (2018.11.20-2018.11.21)] 2018 International IEEE Conference and Workshop in óbuda on Electrical and Power Engineering (CANDO-EPE) - Plasma ignition and current control considerations for magnetron sputtering power supplies
摘要： Physical vapor deposition processes require different types of special power supplies for the ignition and sustaining of the plasma inside the sputtering chamber. The paper identifies some requirements for the design of a pulsed DC converter. Experiments have been carried out to identify the current-voltage characteristics of the vacuum chamber with the supply of different gases, and gas mixtures in the usable pressure domain. The vacuum chamber was supplied with voltage and current impulse trains with various parameters in order to acquire relevant data regarding the gas breakdown in pulsed power mode. A power electronic converter topology and control routine has been proposed, which is suitable for plasma ignition and discharge current control. The proof of concept has been demonstrated with the help of the magnetron sputtering chamber supplied by a test circuit.
关键词： current control,power electronic converter,plasma ignition,magnetron sputtering
更新于2025-09-23 15:23:52