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Alignment of liquid crystals using Langmuir?Blodgett films of unsymmetrical bent-core liquid crystals
摘要： The properties of the thin films of liquid crystal (LC) molecules can be governed easily by external fields. The anisotropic structure of the LC molecules has a large impact on the electrical and optical properties of the film. The Langmuir monolayer (LM) of LC molecules at the air–water interface is known to exhibit a variety of surface phases which can be transferred onto a solid substrate using the Langmuir?Blodgett (LB) technique. Here, we have studied the LM and LB films of asymmetrically substituted bent-core LC molecules. The morphology of LB film of the molecules is found to be a controlling parameter for aligning bulk LC in the nematic phase. It was found that the LB films of the bent-core molecules possessing defects favour the planar orientation of nematic LC, whereas the LB films with fewer defects show homeotropic alignment. The defect in LB films may introduce splay or bend distortions in the nematic near the alignment layer which can govern the planar alignment of the bulk LC. The uniform layer of LB film facilitates the molecules of nematic to anchor vertically due to a strong van der Waals interaction between the aliphatic chains leading to a homeotropic alignment.
关键词： field emission scanning electron microscope,atomic force microscope,Langmuir?Blodgett film,liquid crystals,Brewster angle microscopy,Langmuir monolayer
更新于2025-11-21 11:01:37
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Effect of Electron Irradiation on the Transport and Field Emission Properties of Few-Layer MoS <sub/>2</sub> Field-Effect Transistors
摘要： Electrical characterization of few-layer MoS2 based field effect transistors with Ti/Au electrodes is performed in the vacuum chamber of a scanning electron microscope in order to study the effects of electron beam irradiation on the transport properties of the device. A negative threshold voltage shift and a carrier mobility enhancement is observed and explained in terms of positive charges trapped in the SiO2 gate oxide, during the irradiation. The transistor channel current is increased up to three order of magnitudes after the exposure to an irradiation dose of 100e-/nm2. Finally, a complete field emission characterization of the MoS2 flake, achieving emission stability for several hours and a minimum turn-on field of ≈ 20 V/μm with a field enhancement factor of about 500 at anode-cathode distance of ~1.5 μm, demonstrates the suitability of few-layer MoS2 as two-dimensional emitting surface for cold-cathode applications.
关键词： electron beam irradiation,2D materials,field emission,molybdenum disulfide,field effect transistors
更新于2025-09-23 15:23:52
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Alkali-metal-adsorbed g-GaN monolayer: ultralow work functions and optical properties
摘要： The electronic and optical properties of alkali-metal-adsorbed graphene-like gallium nitride (g-GaN) have been investigated using density functional theory. The results denote that alkali-metal-adsorbed g-GaN systems are stable compounds, with the most stable adsorption site being the center of the hexagonal ring. In addition, because of charge transfer from the alkali-metal atom to the host, the g-GaN layer shows clear n-type doping behavior. The adsorption of alkali metal atoms on g-GaN occurs via chemisorption. More importantly, the work function of g-GaN is substantially reduced following the adsorption of alkali-metal atoms. Specifically, the Cs-adsorbed g-GaN system shows an ultralow work function of 0.84 eV, which has great potential application in field-emission devices. In addition, the alkali-metal adsorption can lead to an increase in the static dielectric constant and extend the absorption spectrum of g-GaN.
关键词： Density functional theory,Optical properties,Field emission device,Adsorption,Work function,G-GaN
更新于2025-09-23 15:23:52
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Hierarchical MoS2-Based Onion-Flower-like Nanostructures with and without Seedpods via Hydrothermal Route Exhibiting Low Turn-on Field Emission
摘要： Herein, we report facile hydrothermal synthesis of hierarchical MoS2 -based nanomorphs (displaying onion-flower-like features) with the primary focus on field-emitter applications. The synthesized nanostructures were characterized physicochemically to understand their basic structural and morphological features. Interesting nanoscale morphological evolution of onion-flower-like MoS2—from plain nanoflowers to those containing seedpods—is observed with the change in hydrothermal reaction time from 9 h to 21 h. Peculiarly, MoS2 nanomorphs with only onion-flower-like morphology displayed lower turn-on field value of 3.7 V/μm as compared to 4.2 V/μm for the nanoflowers containing seedpod-like particles. This might be attributed to the possibility of an easy electron conduction path available for the petals in plain nanoflowers, which may be impeded by the seedpod-like particles in the latter case.
关键词： Molybdenum disulfide,hierarchical nanostructures,field emission,hydrothermal
更新于2025-09-23 15:23:52
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Luminescence enhancement of spherical Sr3La(PO4)3:Eu3+ red nanophosphor with core–shell configuration and added sensitizer for low-voltage field-emission lamp
摘要： Spherical red Sr3La(PO4)3:Bi3+,Eu3+ (SLPO:Bi3+,Eu3+) nanophosphors were synthesized by coprecipitation and thermal annealing for a low-voltage field-emission lamp (FEL). The luminescence intensity of the phosphor was improved using a coreeshell configuration with SiO2 as the core with a diameter of 360 nm and 5e15-nm-thick phosphor as the shell. A 4.4-fold enhancement in the external quantum efficiency (EQE) was obtained. A bright red cathodoluminescence was observed from a 0.25-cm2 FEL at 400 V. The excitation energy efficiently cascade-transferred through the Bi3+ sensitizer to the Eu3+ activator. A coreeshell SLPO:Bi3+,Eu3+ nanophosphor with a maximum EQE of 25.4% and high color purity of 99.7% was obtained when 5-mol% Bi3+ was doped. The energy transfer mechanism and model of the phosphor are proposed.
关键词： Nanophosphor,Sensitizer,Field emission lamp,Coreeshell
更新于2025-09-23 15:23:52
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Exact Evaluation of K. Jensen's General Thermal-Field-Photoemission Integral
摘要： Jensen has developed a general expression for the current density JGT F emitted from a surface by thermal or field emission, or by a combination of these processes; he has also shown how the same expression may be analytically extended to compute the current density due to photoemission. JGT F is expressed as a single integral, which Jensen evaluates analytically in certain limits and numerically outside those limits. In this paper, we show how the integral may be expressed generally as convergent series that are easily evaluated numerically for all values of the physical parameters. No real or apparent singularities, like those that appear in the function Z defined by Jensen occur in the series obtained here.
关键词： photoemission,field emission,thermal emission,Electron emission
更新于2025-09-23 15:22:29
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Cathodoluminescent lamp for general lighting using carbon fiber field emission cathode
摘要： The prototype of cathodoluminescent bulb for general lighting with field emission cathode on the basis of carbon fiber is manufactured. The bulb comprises a high-voltage built-in AC-DC converter of the electric line voltage and a standard E27 cap. A high frequency converter is used to obtain high voltage. The anode voltage relative to the modulator is up to +20 kV; the cathode voltage is up to –4 kV; the current value is of the order of 1 mA. The voltage converter is located in the bulb cap and around the neck of the glass envelope.
关键词： cathode-ray-tube phosphor,carbon fiber,light sources,field emission cathodes,cathodoluminescence
更新于2025-09-23 15:22:29
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Optical Band Gap, Local Work Function and Field Emission Properties of MBE Grown β-MoO3 Nanoribbons
摘要： Monoclinic molybdenum trioxide (β-MoO3) nanostructures (shaped like nanoribbons: NRs) were grown on Si(100), Si(5512) and fluorine-doped tin oxide (FTO) by molecular beam epitaxy (MBE) technique under ultra-high vacuum (UHV) conditions. The dependence of substrate conditions and the effective thickness of MoO3 films on the morphology of nanostructures and their structural aspects were reported. The electron microscopy measurements show that the length and the aspect ratio of nanostructures increased by, 260% without any significant change in the width for a change in effective thickness from 5 nm to 30 nm. NRs are grown along <011> for all the effective thickness of MoO3 films. Similarly, when we increased the film thickness from 5 nm to 30 nm, the optical band gap decreased from 3.38± 0.01eV to 3.17± 0.01eV and the local work function increased from 5.397 ± 0.025 eV to 5.757 ± 0.030 eV. Field emission turn-on field decreased from 3.58 V/μm for 10-μA/cm2 to 2.5 V/μm and field enhancement factor increased from 1.1×104 to 5.9×104 for effective thickness variation of 5 nm to 30 nm β-MoO3 structures. The β-MoO3 nanostructures found to be much better than the α-MoO3 nanostructures due to low work function, low turn on field and high field enhancement factor, and are expected to be useful applications.
关键词： β-MoO3 nanostructures,Field emission and Kelvin probe force microscopy (KPFM),Optical band gap,Molecular beam epitaxy (MBE),Electron microscopy
更新于2025-09-23 15:22:29
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Enhanced electron field emission from nanocrystalline orthorhombic boron nitride films
摘要： Nanocrystalline orthorhombic boron nitride (oBN) thin films with an island-in-honeycomb morphology were prepared on graphite substrate by radio frequency (r.f.) magnetron sputtering. The Field emission (FE) measurement results indicated that the FE properties are significantly enhanced in oBN films compared to high quality cBN films, the turn-on electric field of oBN films is decreased from 17.0 V/μm to 6 V/μm, and the highest emission current density is increased from 2.8 × 10?? to 3 × 10?? A/cm2. The enhanced FE properties of the oBN films can be attributed to significant reduction in effective potential barrier caused by both protruded island-in-honeycomb morphology and honeycomb-like interconnected internal structure.
关键词： Semiconductors,Thin films,Electron field emission,Boron nitride,Physical vapour deposition
更新于2025-09-23 15:22:29
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A comparison of the morphological and electrical properties of sol-gel dip coating and atomic layer deposition of ZnO on 3D nanospring mats
摘要： We report on the morphological and electrical properties, with (light) and without (dark) UV illumination, of conformal coatings of ZnO on silica nanosprings deposited by sol-gel and atomic layer deposition (ALD) for the first time. Field Emission Scanning Electron Microscopy (FESEM) imaging showed that both methods produce conformal coatings of ZnO on the nanosprings. The surface of the sol-gel coatings exhibited cracks at higher numbers of dipping/sintering cycles, while the morphology of ALD ZnO films were always smooth and devoid of cracks. The effective photoconductivity of the sol-gel ZnO coated nanospring mats increased nonlinearly with increasing coating thickness. The corresponding dark effective conductivity of the sol-gel ZnO coated nanospring mats also increased within the same thickness range. Alternatively, the effective photoconductivity of the ALD ZnO coated nanospring mats increased linearly with increasing coating thickness. The corresponding dark effective conductivity also increased within the same thickness range. The superior effective conductivity and photoconductivity of the ALD ZnO coated nanospring mats is attributed to the uniformity of the coating and the absence of cracks, which are observed for the thicker sol-gel ZnO coatings.
关键词： atomic layer deposition (ALD),semiconductors,sol-gel,nanosprings,field emission scanning electron microscopy,conductivity,ZnO
更新于2025-09-23 15:22:29