Cold Field Emission Research Articles

Electron emission performance analysis and application of carbon nanotube cold cathode prepared by cold pressing process

In this work, a carbon nanotube (CNT) cold cathode electron emitter fabricated by the cold pressing process was developed and studied. The electron emission performance was investigated and the application of pulse x-ray emission and imaging was explored by this cold cathode. The results indicated that the electron emission performance was excellent with electric intensities of turn-on and threshold of 0.47 and 1.17 V/μm@1 mA/cm2, respectively, and the field enhancement factor reached 17 514. The application research results showed that the pulse x-ray waveform has a great corresponding well with the grid voltage, and the imaging of a screw was clear, whose thread and pitch could be seen clearly. This article proposed a cold pressing process prepared for the CNT cold cathode, providing a new technical approach for the development of field emission cold cathode preparation processes.

Near infrared laser precisely controlled ultrafast superhydrophilicity-to-hydrophobicity transition of copper sulfide nanosphere coating on cellulose fiber fabric.

Inspired by lotus leaf, biomimetic hydrophobic cellulose fiber-based textiles were usually fabricated by the lower surface energy materials. However, it is rare to witness a hydrophobic surface obtained by near infrared laser (NIR) irradiation a superhydrophilic nanomaterial, which remains a huge challenge. Herein, the CuS nanospheres was in-situ anchored on the surface of gallic acid self-polymer treated cotton fabric. Luckily, the excellent hydrophobicity of CuS nanospheres coating (contact angles of 142.7 ± 2.8°) was for the first time demonstrated after a NIR laser irradiation with 1.5 W/cm2 for 8-10 s. Notably, the novel hydrophobicity exhibits a significant advance compared with traditional hydrophobicity prepared by lower surface energy materials. Then, the laser-mediated hydrophobic mechanism was demonstrated by the cold-field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and thermal imager. Moreover, the dynamic contact angle revealed the uniform hydrophobicity. Furthermore, the hydrophobic nanospheres coating possessed good photothermal effect and UV resistance. Overall, this work renders a novel, feasible, and efficient strategy to rapidly obtain the hydrophobic surface by NIR laser-induced the superhydrophilic CuS nanospheres coating.

Direct method for microscale manipulation at liquid-liquid interfaces in ionic liquid media with real-time electron microscopy observation

A deep understanding of the processes in soft matter systems with liquid-liquid phase boundaries is of particular importance for materials science, chemistry and life sciences. A vast variety of physicochemical techniques have been proposed for the study of interfacial properties of liquid systems. Among them, electron microscopy methods occupy an important place due to the possibility of direct observation of the sample areas of interest with high spatial resolution; however, the harsh conditions of the electron microscope chamber impose significant restrictions on the possibilities of observing and manipulating unprotected liquids and related soft systems. To overcome these difficulties, in this work, we developed a methodology for direct probing of liquid-liquid interfaces with simultaneous control of the process using electron microscopy. Practically relevant liquid mixtures based on vacuum-compatible ionic liquid (IL) with water additives were probed with micrometer accuracy in real time inside an electron microscope chamber, which made it possible to reveal the role of specific ions aggregation and electrostatic phenomena in the stabilization of liquid microdomains. To test the versatility of the proposed approach, the morphology of a typical IL/water mixture was examined using a series of electron microscopes of various configurations, and it was shown that the best level of contrast between two chemically related liquid phases can be obtained in the case of a cold field emission electron source in combination with an in-lens secondary electron detector, regardless of the specific instrument manufacturer.

Experimental Verification of Inter Relation between Fowler–Nordheim and Millikan–Lauritsen Plot in Chemically Synthesized Zinc Oxide System

AbstractCold cathode emission or cold field emission (CFE) is a purely quantum mechanical phenomenon and a phenomenon of wonder. The exact science behind the observed current (I)–voltage (V) is yet to be pin pointed. For instance, a good cold emitter is very reasonably supposed to have low work function and good conductivity whereas a carbon allotropes like diamonds have just the reverse in both the cases, i.e., it is insulating in nature having very wide band gap as well as high work function yet it is considered to be an efficient field emitter. Since early of 20th century, till its middle a number of groups have suggested different equations or relations that can adequately describe the experimental CFE I–V characteristics adequately. Although they all fundamentally follow an exponential law, but so far, the relation suggests by Fowler and Nordheim (F–N) is the most accepted one. However, there is another relationship suggested by Millikan and Lauritsen (M–L) which is in spite of being reasonable not so common now a day to use. This work revisits different popular approaches for analyzing cold emission data. With this aim, the experimental CFE data obtained for chemically synthesized zinc oxide nanorods are chosen. The proper phase formation of ZnO is confirmed by XRD study whereas FESEM shows the rod like morphology. EDX confirms the proper stoichiometric ratio for the sample. After detail analysis it is confirmed that the theoretically proposed relation between F–N and M–L experimentally holds good as well and thus it would not be wrong to analyze the CFE data by simple M–L theory.

Comprehensive analysis of charge carriers dynamics through the honeycomb structure of graphite thin films and polymer graphite with applications in cold field emission and scanning tunneling microscopy

Polymer graphite electron sources have performed satisfactorily as field emission emitters and scanning tunneling microscopy probes in the past few years. However, the emission process was characterized by limited total emission currents. This paper introduces the elemental, vibrational, electronic structure, and optical analysis of polymer graphite and glass-graphite composite field emission cathodes to study these limitations. Moreover, the field emission characteristics are studied including the changes in the potential energy barrier of the used materials and structures. Among the studied structures, the cathodes prepared from graphite thin films deposited on a micropointed glass substrate (film-GMF) showed superior performance as random field emission arrays. This includes obtaining much higher emission current values ≈ 20 times) and lower threshold voltages ≈ 1/2) compared to the results obtained from polymer graphite samples. The enhancement factor in such emitters is believed to be the three-dimensional honeycomb structure of graphite. Moreover, the study includes applying graphite coatings to tungsten nano-field emission cathodes and scanning tunneling microscopy probes, which improves the performance of such cathodes/probes in both microscopic techniques.

Research on high-strength and rapid-hardening magnesium phosphate as a novel bonding material for limestone artifacts

Due to natural erosion and human interference, limestone artifacts often suffer from cracks and gradual detachment. There is a critical need for new bonding materials that possess excellent aging resistance and high compatibility with the artifact substrates. This study investigates the effects of varying proportions of citric acid (CA) and borax (B) as composite retarders on the fundamental properties of magnesium phosphate cement (MPC). Through the application of X-ray diffraction techniques and cold field emission scanning electron microscopy, this research elucidates the mechanisms by which the retarders affect MPC. It was found that a 5 % addition of CA and B significantly reduces the hydration temperature during the early stages of MPC setting, enhances the unconfined compressive strength (reaching 44.3 MPa at 28 days), and allows for controllable setting times (17 minutes). Additionally, the presence of CA was found to delay crystal growth, resulting in an increased quantity of the amorphous phase and higher density of MPC. The optimal MPC formulation was selected as a bonding and repair material for limestone artifacts. For comparative analysis, traditional glutinous rice lime mortar (GL) and commercially available epoxy resin (EP) were tested under wet-dry cycling and UV aging conditions. Results indicated that EP materials demonstrated significant aesthetic incompatibilities and progressive cracking and detachment as aging tests progressed. GL materials exhibited significantly lower bonding strength compared to EP and MPC. In contrast, MPC displayed excellent aging resistance, moderate bonding strength, and a Shore hardness value closely matching that of the limestone substrates. Therefore, high-strength, rapid-hardening MPC represents a valuable and forward-looking solution for the conservation of limestone artifacts.

Precise measurement of spatial coherence and axial brightness based on the Wigner function reconstruction in transmission electron microscopes with field emission guns and a thermionic emission gun.

The spatial coherence and the axial brightness of a cold field emission gun, a Schottky field emission gun and a $\mathrm{LaB}_6$ thermionic gun are precisely measured. By analyzing the Airy pattern from a selected area aperture, various parameters including the spatial coherence length are determined. Using the determined coherence length, the axial brightness of the field emission guns is estimated using the equation which we previously derived based on the discussion of the Wigner function of an electron beam. We also make some extensions in the method to be applicable to the measurements of the thermionic gun, which has anisotropic intensity distribution in most case unlike the field emission guns. Not conventional average brightness but the axial brightness measured for the three kinds of emitters are compared accurately and precisely without influenced by the measurement conditions.

An experimental investigation on the damage mechanisms of red glutenite in the Mount Wuyi cultural and natural heritage site subject to acid rain and wet-dry cycles: a macro-to-micro approach

The safety of rock landscapes in Mount Wuyi is significantly impacted by acid rain and wet-dry cycles. In this paper, the decay characteristics of the physical–mechanical properties of red glutenite were investigated under acidic wet-dry cycles. A systematic approach, including cold field emission scanning electron microscopy (CFE-SEM), image processing techniques, and X-ray diffraction (XRD), was proposed to investigate the damage mechanism of red glutenite under acidic wet-dry cycles. The results indicate that with increasing solution acidity and wet-dry cycles, dry density (DD), longitudinal wave velocity (LWV), uniaxial compressive strength (UCS), and elastic modulus (EM) of red glutenite significantly decrease. Under different acidic conditions, DD, LWV, and UCS exhibit exponential decay with wet-dry cycles, while EM exhibits linear decay. A regression fitting was employed to establish a prediction model for UCS, which exhibited a better capability in predicting the correlation between UCS, pH, and the number of wet-dry cycles. Microscopic comprehensive analysis reveals that the interaction between rock dissolution and desiccation is the primary factor leading to changes in the microstructure and mineral composition of red glutenite, culminating in the decay of its physical–mechanical properties. This study holds significant guidance implications for the preservation of cultural and natural heritage in Mount Wuyi.

Inverse Modeling of Heterogeneous Structures in Electron Probe Microanalysis.

Electron probe microanalysis (EPMA) is a powerful tool for chemical characterization of materials on a microscopic scale. However, EPMA has the drawback that its information volume has a spatial extent of some 100 nm to a few µm. With the introduction of new electron sources, i.e., Schottky Thermal Field and Cold Field Emitter, where the electron beam is focused down to a few nm, measurements can be nowadays performed on the sub-micrometer scale. The goal of the work is to reveal the chemical composition of structures smaller than the excitation volume. New strategies are presented where the acquisition is performed at different positions on the sample and as a scan across a fine structure by using one or more single beam energies. Besides the well-known Monte-Carlo simulation, a deterministic model is also used. The deterministic model is based on moment equations of the Boltzmann equation. Inverse modeling is presented for several case studies. Due to the highly complex nonlinearity of the inverse model, an ill-posed and well-posed problem is shown as well. Finally, the method is extended to reconstruct 2D structures, i.e., rectangular shaped particles, with heterogeneous composition on lateral and depth scale.

Comprehensive Analysis of E478 Single-Component Epoxy Resin and Tungsten-E478 Interface for Metallic-Polymer Composite Electron Source Applications.

This study provides comprehensive elemental, optical, and energy gap characteristics of the E478 single-component epoxy resin. This type of epoxy resin has imperative applications in medium voltage insulation and cold field emission of electrons. X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and hydrogen nuclear magnetic resonance (1H-NMR) were used to study the elemental and structural analyses, ultraviolet photoelectron spectroscopy (UPS) was used to obtain the local work function and the ionization potential energies, and ultraviolet/visible light spectroscopy (UV/VIS) was used to report the optical and energy gap characteristics of the epoxy resin being studied. Moreover, the UPS and UV/VIS analyses were merged to obtain the electron affinity of the E478 epoxy resin and to study the epoxy's energy band diagram and the tungsten-epoxy interface band structure. The results showed that the E478 epoxy resin is considered an n-type semiconductor of energy gap ∼3.94 eV, local work function ∼3.42 eV, ionization potential ∼6.10 eV, electron affinity ∼2.16 eV, and tungsten-epoxy Schottky contact barrier height ∼2.50 eV.

Coupled Monte Carlo density functional theory calculations of cold and laser-assisted electron field emission from graphene-coated copper cathode

Field emission is an important process with a variety of applications. Quantitative predictions of such electron emission need to include details of the internal potentials that shape the electronic wavefunctions (and hence the tunneling probability), predictive analysis of the work function barrier (ΦB), and knowledge of the electron distribution at the surface that constitutes the supply function. Here, these various factors were all collectively considered based on a combined Monte Carlo-density functional theory approach. Results were obtained for both the field-dependent cold electron emission current density as well as photoemission from a short laser pulse. The method also allows for calculations of field-dependent emittance. The technique is general and could be extended to include plasmon–polariton modes, different thicknesses of coatings, and role of surface adsorbates and defects.

Field-Emission Energy Distribution of Carbon Nanotube Film and Single Tube under High Current.

A narrow energy distribution is a prominent characteristic of field-emission cold cathodes. When applied in a vacuum electronic device, the cold cathode is fabricated over a large area and works under a high current and current density. It is interesting to see the energy distribution of the field emitter under such a working situation. In this work, the energy distribution spectra of a single carbon nanotube (CNT) and a CNT film were investigated across a range of currents, spanning from low to high. A consistent result indicated that, at low current emission, the CNT film (area: 0.585 mm2) exhibited a narrow electron energy distribution as small as 0.5 eV, similar to that of a single CNT, while the energy distribution broadened with increased current and voltage, accompanied by a peak position shift. The influencing factors related to the electric field, Joule heating, Coulomb interaction, and emission site over a large area were discussed to elucidate the underlying mechanism. The results provide guidance for the electron source application of nano-materials in cold cathode devices.

Modification of bacterial cellulose using silk fibroin β-sheet crystals induced by ultrasonication

Silk fibroin (SF) has been continuously explored as a biomaterial due to its biocompatibility, tunability, and self-healing properties. In this work, we present a novel approach to the modification of bacterial cellulose (BC) with SF β-sheet dominant structures induced via ultrasonication. Secondary structure analysis through infrared spectroscopy, thioflavin T assay, and circular dichroism spectropolarimetry revealed a conversion of silk I to silk II structures within the protein mixture. Cold field emission scanning electron microscope images revealed the tightly packed fibers coated with the protein. Thermogravimetric curves demonstrated higher resistance to temperature degradation supplemented by broader and flatter DSC curves attributed to the highly bonded and dense composite. Successful conversion of amide I to amide II and amide III allowed for the more stable β-crystals to contribute to a more thermodynamically stable double-network hydrogel. The conversion of silk I to silk II structures offers a viable and highly biocompatible material that is both thermodynamically and biochemically stable for various potential biomedical applications.

Investigation of silicon-on-insulator back-gate nano vacuum channel transistor array

Recent advances in nanofabrication have made it possible to combine planar solid-state devices with vacuum electronics to create planar nano vacuum channel transistors that offer the advantages of cold-field emission and ballistic transmission. However, the current research is mainly limited to the study of a single field emission transistor, which has problems such as low current and poor gate control capability. To solve the above problems, a multitip field emission array is used in this work, and gate modulation is performed by a back-gate structure to fabricate and process a back-gate nano vacuum transistor array. First, we conducted simulation modeling of the back-gate nano vacuum transistor, investigated the impact of its structural parameters on its performance, and obtained the optimal simulation results. Then, structural parameters of the back-gate nano vacuum channel transistor array (BG-NVCTA) are selected based on the simulation results and fabricated by electron beam lithography on the silicon wafer. The experimental results, agreed well with the simulation results, show that the BG-NVCTA device has excellent gate control characteristics and a high current density. Its anode current is greater than 5 μA, and the transconductance is 1.05 μS when the anode voltage is 5 V.

Cleaning of tungsten tips for subsequent use as cold field emitters or STM probes

AbstractThis study investigates the crucial process of cleaning cold field emission electron emitters and scanning tunnel microscopy (STM) probes, particularly focusing on tungsten tips. The cleanliness of these tips is essential for maintaining optimal cathode properties, preventing impurities that can significantly affect the emission process. Various cleaning methods, including macroetching, ammonia cleaning, and hydrofluoric acid (HF) cleaning were explored and compared by scanning electron microscopy. The macroetching method, involving a mixture of hydrochloric acid, nitric acid, and hydrogen fluoride, proved to be too reactive, causing significant material removal and altering the tip’s structure. Ammonia cleaning did not significantly improve or harm the samples. However, oxide islands appeared in some areas, suggesting the potential formation of ammonium tungsten oxide. HF cleaning, specifically at 20% and 50% concentrations, demonstrated effectiveness in removing tungsten oxides without damaging the tip. Pre-cleaning with water and ethanol proved beneficial for subsequent HF refinement. Results suggest that HF is the most suitable method for oxide removal but a rinse with water is essential for removing residual sodium hydroxide. To maintain optimal properties, it is crucial to apply a less reactive layer quickly or transfer the tips to a water/ethanol bath to prevent oxidation.

A Modified Tape Pretreatment Process for Enhanced Field Emission Cold Cathode

A Modified Tape Pretreatment Process for Enhanced Field Emission Cold Cathode

Development and characterization of a laser-driven cold-field emission source

Development and characterization of a laser-driven cold-field emission source

Structural Inhomogeneities and Nonlinear Phenomena in Charge Transfer under Cold Field Emission in Individual Closed Carbon Nanotubes

The structure and phenomena arising from charge transfer in cold field emission mode in a single closed carbon nanotube (CNT) under cold field emission conditions are studied. Inhomogeneities of the structure of CNT in the form of two types of superlattices are found by studying microphotographs obtained by AFM, SEM, and TEM. The features of charge transfer in a quasi-one-dimensional carbon nanotube emitter with a small gap between the anode and cathode are studied under conditions of low-voltage field emission. It is established that the I-V characteristics reveal voltage thresholds and resonant peaks, which are associated with the opening of conduction channels in the region of van Hove singularities. In the region of peaks in the I-V characteristics, the emission current exceeds the one calculated using the Fowler–Nordheim (F-N) function by one to three orders of magnitude. The I-V characteristic is not that the curve straightens in F-N coordinates. It is found that the peaks in the I-V characteristics have distinct regions of negative differential conductivity.

Gun energy filter for a low energy electron microscope

In a Low Energy Electron Microscope (LEEM) the sample is illuminated with an electron beam with typical electron landing energies from 0–100 eV. The energy spread of the electron beam is determined by the characteristics of the electron source. For the two most commonly used electron sources, LaB6 and cold field emission W, typical energy spreads ΔE are 0.75 and 0.25 eV at full width half maximum, respectively. Here we present a design for a LEEM gun energy filter, that reduces ΔE to ∼100 meV. Such a filter has been incorporated in the IBM/SPECS AC-LEEM system at IBM. Experimental results are presented and found to be in excellent agreement with expectations.

Differences in mass concentration and elemental composition of leaf surface particulate matter: Plant species and particle size ranges

Leaf surface particulate matter (PM) is an optimal material for the environmental monitoring of urban green spaces Currently, most studies have looked at leaf surface PM, using only its mass concentration to investigate the dust retention capacity and mechanisms of different plant leaves. The elemental composition of leaf surface PM has been neglected as a reflection of the environment and its sources. Therefore, in this study, ten common plant species were selected from the Olympic Forest Park, an urban green space in Beijing, and the characteristics of leaf surface PM were analysed in depth in terms of mass concentration and elemental composition. The leaf surface PM mass concentration was first obtained by vacuum filtration (VF) method, and then the leaf surface PM attached to the filter membrane obtained from the previous step was used as experimental material to study its elemental composition using cold field emission scanning electron microscopy combined with energy dispersive X-ray spectroscopy (FESEM-EDS). The results show that (1) In terms of mass concentration, were Hemerocallis fulva, Poa pratensis, Acorus calamus, Typha orientalis, and Phragmites communis had better dust retention capacity; (2) The five most important elements deposited on the leaf surface of plants in Beijing were C, O, Mg, Al, and Si, with a total of 26 elements detected; (3) The particulate matter retained on the leaf surface of plants in Beijing was classified as Geogenic particles (57.70%) > Anthropogenic particles (22.30%) > Biogenic particles (20.00%). The results at this stage are expected to promote the in-depth understanding of plant leaf remediation of PM.