Low-field Electron Emission Research Articles

On the possible nature of deep centers in Ga2O3

The electric field dependence of emission rate of the deep traps with level near Ec−0.6 eV, so-called E1 traps, was studied by means of deep level transient spectroscopy measurements over a wide range of applied voltages. The traps were initially introduced by 900 °C ampoule annealing in molecular hydrogen. The results indicate the activation energy of the centers and the ratio of high-field to low-field electron emission rates at a fixed temperature scale as the square root of electric field, suggesting that the centers behave as deep donors. The possible microscopic nature of the centers in view of recent theoretical calculations is discussed. The most likely candidates for the E1 centers are SiGa1–H or SnGa2–H complexes.

Low-Field Electron Emission Capability of Thin Films on Flat Silicon Substrates: Experiments with Mo and General Model for Refractory Metals and Carbon.

Herein, we describe a study of the phenomenon of field-induced electron emission from thin films deposited on flat Si substrates. Films of Mo with an effective thickness of 6–10 nm showed room-temperature low-field emissivity; a 100 nA current was extracted at macroscopic field magnitudes as low as 1.4–3.7 V/μm. This result was achieved after formation treatment of the samples by combined action of elevated temperatures (100–600 °C) and the electric field. Morphology of the films was assessed by AFM, SEM, and STM/STS methods before and after the emission tests. The images showed that forming treatment and emission experiments resulted in the appearance of numerous defects at the initially continuous and smooth films; in some regions, the Mo layer was found to consist of separate nanosized islets. Film structure reconstruction (dewetting) was apparently induced by emission-related factors, such as local heating and/or ion irradiation. These results were compared with our previous data obtained in experiments with carbon islet films of similar average thickness deposited onto identical substrates. On this basis, we suggest a novel model of emission mechanism that might be common for thin films of carbon and refractory metals. The model combines elements of the well-known patch field, multiple barriers, and thermoelectric models of low-macroscopic-field electron emission from electrically nanostructured heterogeneous materials.

Field Emission Characteristics of Double Walled TiO2 Nanotubes

Double walled TiO2 nanotubes have been synthesized by two probe anodization method on highly pure Titanium (Ti) substrate. FESEM and XRD analyses revealed the morphological and structural properties of the as-synthesized double walled TiO2 nanotubes. Investigation of their field emission characteristics in a planar diode configuration at a base pressure of 1 x 10-8 mbar has been done. The turn-on field defined for the emission current density of 10 µA/cm2 is found to be 2.1 V/µm. As the field is increased further to 2.95 V/µm maximum, a current density of 890 µA/cm2 is achieved. Current-time (I-t) measurement at a preset value of 1 µA emission current for the duration of 3 h demonstrates a robust emission current stability. The observed low turn-on field and stable electron emission makes the double walled TiO2 nanotubes a suitable emitter for various electronics devices applications.

Low-field electron emission from carbon cluster films: combined thermoelectric/hot-electron model of the phenomenon

Thin carbon films consisting of separate nanometer-scale sp2 carbon islands with smooth vacuum boundary deposited on Si wafers were found to be capable of low-field electron emission – starting from macroscopic field magnitudes as low as ∼1 V/µm. For such films, we suggest a novel model of emission facilitation by thermoelectric field associated with heat generation concentrated in nanosized areas. Quantitative estimates performed on the basis of this hypothesis for typical experimental conditions gave estimates for local thermoelectric field magnitude and lateral non-uniformity of surface potential as high as ∼100 V/μm and a few Volts, respectively. Thus, the suggested model explains the low-field emission capability of smooth-surface nanocarbon films observed in many previous experiments.

Study of nanocarbon thin-film field-electron emitters by Raman spectroscopy

Raman spectroscopy was used to study the features of the electron-phonon interaction in thin carbon films that are capable of low-field emission of electrons. It was found that in the Raman spectra of samples with this ability the characteristic peaks of carbon were almost completely suppressed, and also a wide photoluminescence band could be present. At the same time, the Raman spectra of non-emitting samples had the form typical of graphite-like carbon spectrum. This observation is in accordance with the two-barrier model of low-field electron emission from thin films of considered type, corresponding to which their emissive capability is maintained by the presence of hot electrons. Thus, in thin films consisting of numerous isolated carbon islands (nanoclusters) the extraction of electrons into the vacuum is facilitated by prolonged hot electron lifetime. Such prolongation, in turn, can be associated with the suppression of electron-phonon interactions by the spatial confinement effect. Consequently, it should result in the decrease of prominent bands in Raman spectra which are originated by electron-phonon interactions, while the photoluminescence intensity may, on the contrary, rise. Particularly such deformations of the Raman spectra were observed in the present study.

Characterization of thin carbon films capable of low-field electron emission

Previous experiments have demonstrated that carbon nanoisland films (or disordered quantum-dot arrays) deposited on silicon wafers may possess the property of low-field electron emission. This paper presents our new work on comparative characterization of emitting and nonemitting thin carbon films. The experimental results acquired by Auger spectroscopy, electron energy loss spectroscopy, Anderson's technique for workfunction measurement, and secondary-emission techniques confirmed that the emitting films are discontinuous and consist of carbon in sp2-hybridization state, while their workfunction is relatively high (>4 eV). These experimental data clearly contradict the commonly accepted Fowler–Nordheim theory of field emission and suggest that the observed emission phenomenon has a different nature. A novel model is proposed as a development of the well-known hot-electron emission mechanism supplemented with nanoscale-related features of thermoelectric phenomena.

Multifunctional π-conjugated poly (3-methylthiophene) nanotubes for optoelectronic and field emissive devices

Multifunctional properties of nanomaterials becomes a hot topic in nano research for the development of multifunctional devices, because modern devices need multifunctional platform for the high efficient plural performance on a single device. Here, we introduce a multifunctional π-conjugated poly (3-methylthiophene) (P3MT) nanotube (NT), showing controllable optical and electrical properties through the control of doping level. P3MT NTs were electrochemically synthesized in the low temperature (−40 °C) on the nanoporous template. The change of doping level by post cyclic voltammetry (CV) treatment on the P3MT lead the variance of polaron/bipolaron band, resulting into the drastic change of ultraviolet-visible absorption and photoluminescence properties. While P3MT NTs before CV treatment show an ohmic behavior in the current-voltage characteristics, those after CV treatment show high photocurrent. From the field emission experiment, the P3MT NTs before CV treatment have a relatively low turn-on electric field and stable electron emission property compared to the P3MT NTs after CV treatment. This shows that the π-conjugated polymers should be shed new light on their multifunctionality for the potential application to the multifunctional platform of opto-electronic nanodevices.

Peculiarities of field electron emission from submicron protrusions on a rough InSb surface

Mechanisms of field-electron emission (FEE) from submicron protrusions on a rough InSb surface have been studied. It is established that the FEE current is satisfactorily described by the Morgulis-Stratton theory. Interpretation of the obtained dependencies suggests that they correspond to low-field electron emission. Analysis of the experimental tunneling spectra shows that peaks of the coefficient of I–V curve non-linearity can be considered as features of the energy spectrum of a quantum-dimensional object.

Influence of Silver Incorporation on the Structural and Electrical Properties of Diamond-Like Carbon Thin Films

A simple approach is proposed for obtaining low threshold field electron emission from large area diamond-like carbon (DLC) thin films by sandwiching either Ag dots or a thin Ag layer between DLC and nitrogen-containing DLC films. The introduction of silver and nitrogen is found to reduce the threshold field for emission to under 6 V/μm representing a near 46% reduction when compared with unmodified films. The reduction in the threshold field is correlated with the morphology, microstructure, interface, and bonding environment of the films. We find modifications to the structure of the DLC films through promotion of metal-induced sp2 bonding and the introduction of surface asperities, which significantly reduce the value of the threshold field. This can lead to the next-generation, large-area simple and inexpensive field emission devices.

Ultra low field electron emission of graphene exfoliated from carbon cloth

Graphene emitters with high enhancement factor and ultra low emission field were exfoliated from carbon fibers in carbon cloth. This method made the graphene sheets to stay on the carbon fiber and were used, in situ, as emitters. Due to their high multistage enhancement factor and intrinsic good contact, electron emission from these graphene sheets required ultra low emission field. The threshold-field corresponding to emission current density of 1 mA/cm2 was about 0.7 V/μm. This high enhancement factor was attributed to the effects of the high aspect ratio of graphene sheets and the geometry of carbon cloth.

The determination of key factors for low-field electron emission from carbon nanostructures

A new statistical method for determining the key factors of the process of field electron emission (FEE) from nanostructures based on a comparison of the microscopic measurements of the work function of electrons with the results of a macroscopic characterization of the FEE is presented. Using the example of nanocrystalline carbon films, the possibilities of this statistical method for a quantitative estimation of the influence of the local field enhancement and the work function reduction on the FEE threshold decrease are demonstrated.

Low threshold field electron emission from solvothermally synthesized WO2.72 nanowires

Field emission studies of WO2.72 nanowires synthesized by a solvothermal method have been performed in the planar diode configuration under ultra high vacuum conditions. Fowler–Nordheim plots obtained from the current-voltage characteristics follow the quantum mechanical tunneling process and a current density of ∼8.3×106 μA/cm2 can be drawn at an applied electric field of 2 V/μm. The field enhancement factor is 33025, while the turn-on field is only 1.4 V/μm. The emission current-time plot recorded at the pre-set value of emission current of 1 μA over a period of more than 3 h exhibits an initial increase and a subsequent stabilization of the emission current. The results reveal that the WO2.72 nanowire emitters synthesized by the solvothermal method are promising cathode materials for practical applications.

Size-dependent ultraviolet luminescence and low-field electron emission of TiO2 nanodots formed by phase-separation-induced self-assembly

We present a study of phase-separation-induced self-assembled TiO2 nanodots. The Marangoni effect is utilized in the preparation of this TiO2 nanostructure. Unique and strong ultraviolet (UV) luminescence is observed from the TiO2 nanodots at room temperature. As the nanodot size reduces from 93 to 48 nm, the bandgap energy shifts from 3.43 to 3.76 eV and the luminescence peak energy increases from 3.38 to 3.58 eV. High electron emission at low electric field is also obtained from TiO2 nanodots. The turn-on field and threshold field for emission current densities of 1 µA cm−2 and 1 mA cm−2 are as low as 0.7 and 3.7 V µm−1, the lowest values ever reported for TiO2 materials.

Catalyst-Free Growth of Well Vertically Aligned GaN Needlelike Nanowire Array with Low-Field Electron Emission Properties

An array of high-density, vertically aligned GaN nanowires is fabricated through thermal evaporation of GaN powder with the assistance of HCl gas. All GaN nanowires with needlelike tips are well-aligned with the axis direction perpendicular to the substrate without the use of catalysts. A possible growth mechanism of the vertical GaN nanowires array is proposed. Furthermore, field emission measurement shows that the obtained GaN nanowires array has a lower turn-on field of 2.1 V/μm, and the current density is about 1 mA/cm(2) at a bias field of 4.5 V/μm, which means such GaN nanowires are good candidates for large area and uniform flat display applications.

Low-field electron emission from pinaster-like MoO2 nanoarrays as two-stage emitters

Low-field electron emission is obtained from the pinaster-like MoO2 nanoarrays. The turn-on field of the pinasterlike MoO2 nanoarrays is found to be as low as 2.39 V/μm with the current density of 10μA/cm2. The enhancement factor is extracted to be 3590 from the Fowler–Nordheim plot. These excellent emission properties are attributed to the special structure of the pinaster-like MoO2 nanoarrays and confirmed by the calculation in the frame of the two-stage model. Our results show that the pinaster-like MoO2 nanoarrays are promising candidate in realizing field emission displays.

Preparation of a Low Cost Carbon Nanotubes Field Electron Emission Thin Film and its Initial Application Research

A large area perfect aligned carbon nanotubes (CNTs) thin film was grown directly on a stainless steel substrates by a low cost bias-assisted hot-filament chemical-vapor deposition (BA HF-CVD) technology. The CNT’s / stainless steel field emission array (FEA) cathode (CNT’s/FEA) has been fabricated. The field electron emission behavior of the CNT’s/FEA cathode was characterized in a vacuum condition, a high electron emission of about 10mA/cm2 at a low electric field of 4V/μm implies the promising the application as a cathode of the flat panel display device, so further assembled this cathode in a kind of vacuum device, and the possibility of the operation from a flat panel character (Pictures) display tube FCT has been tested initially.

Enhanced electron emission from diamond film deposited on pre-seeded Si substrate with nanosized diamond power

Diamond film was synthesized by microwave plasma chemical vapor deposition (MWPCVD) method. The deposition process of diamond film on 4-in. pre-seeded mirror polished silicon wafer was divided into four steps: (a) seeding nano-diamond powder on Si surface; (b) annealing for increasing the adsorbed strength between diamond powder and substrate; (c) diamond film growth; (d) bombarding with H + ion for decreasing film stress and obtaining planar field emission from diamond film with large area. Scanning electron microscopy (SEM), Raman spectroscopy and stress measurement system were used to characterize the structure and property of diamond film. The electron emission from large area diamond film on seeded substrate was described and compared with that from diamond film deposited on Si substrate scratched by diamond powder. The results suggested that low-field electron emission and high emission current could be obtained from diamond film deposited on seeded substrate due to the reduction of interface energy barrier for electron tunneling. A threshold field of 3.0 V/μm and emission current density of 1 mA/cm 2 at 30 V/μm were achieved.

Low macroscopic field electron emission from surface of plasma sprayed and laser engraved TiO 2, Al 2O 3+13TiO 2 and Al 2O 3+40TiO 2 coatings

The paper deals with investigation of electron field emission from plasma sprayed and laser engraved TiO 2 and Al 2O 3–TiO 2 coatings of two compositions (13 and 40 wt.% of TiO 2). The coatings were plasma sprayed onto aluminum rolls coated initially with Ni20Cr alloy. Their technology included also grinding and polishing prior to CO 2 laser treatment. The treatment was similar to that applied for anilox rolls manufacturing and allowed a production of three different patterns with the lines densities of 60, 100 and 200 cm −1 and depths of approximately 80, 50 and 10 μm correspondingly. The patterns were engraved under angle of 60° that results in a honeycomb geometry of cells. Measurements of emission current under macroscopic electric field up to 150 V/μm for all the samples were carried out. The SEM observations of engraved coating morphology were made in order to find the electron emission spots and XRD analysis allowed to identify the crystal phases present in the coatings. A tentative explanation of a field emission mechanism basing onto Fowler–Nordheim (FN) model is also presented.

Low-field electron emission from nano-carbons

To explain low-field electron emission from some certain carbon nanostructured materials and related phenomena we propose an empirical model based on the assumption of heterogeneity of the carbon cathode surface. An essential feature of the model is well ordered structure of the two types of carbon: graphite type material (with sp 2 bonding), which is capped with clusters having diamond type (with sp 3 bonding) electronic properties. The theoretical analysis of corresponding energy band configuration with two potential barriers on the cathode surface shows a possibility of low-voltage cold electron emission. Its originate is in resonance tunneling via local electron state in quantum well between these two barriers on the surface of the carbon emitter.

Fundamental Aspects and Applications of Low Field Electron Emission from Nanocarbons

Low field electron emission from nanocarbon materials obtained by chemical vapour deposition (CVD) was studied to evaluate both the emission mechanism and material's applicability for cold cathodes. Statistical behaviour of nanocarbon cathodes shows narrow distribution of emission sites parameters and their significant contradiction to the usual Fowler - Nordheim theory. An energy band diagram of emission sites including two potential barriers was proposed on the basis of experimental comparative analysis of the field emission characteristics, structural and other properties of the CVD nanocarbon films. This two barrier model explains low field emission and other phenomena related to nanocarbon materials. Experimental verification of nanocarbon cathodes was demonstrated in prototypes of cathodoluminescent lamps.