Field emission from nonaligned zinc oxide nanowires

Zinc oxide (ZnO) nanowires with an average diameter of 15 nm were grown using a vapor phase transport process. Field emission was achieved from these nanowires in spite of their random orientation. The electric field for the extraction of a 10 μA/cm² current density was measured to range from 4.4 to 5.0 V/μm, and that for a 1 mA/cm² current density from 7.6 to 8.7 V/μm, depending on whether the sample was submitted to a heat treatment. The results exhibit the potential application of ZnO nanowires as field emitters in future flat panel displays.     

Field emission from oriented tin oxide rods

Tin oxide (SnO₂) films were grown on silicon substrates by a wet chemical route. It was found from scanning electron microscopy investigations that oriented SnO₂ rods normal to the substrates were obtained. Field emission studies were carried out in diode configuration in an all metal ultra high vacuum chamber at a base pressure ∼ 1.33 × 10^− 8 mbar. The ‘onset’ field required to draw 0.1 μA/cm² current density from the emitter cathode was found to be ∼ 3.4 V/μm for SnO₂ rods. The field emission current and applied field follows the Folwer-Nordheim relationship in low field regime. The observed results indicate that the field emission characteristics of chemically grown SnO₂ structures are comparable to the vapor grown nanostructures.     

Fabrication of carbon nanoflakes by RF sputtering for field emission applications

In this paper, an ultra thin sheet-like carbon nanostructure, carbon nanoflake (CNF), has been effectively fabricated by RF sputtering on Si substrate without any catalyst or special substrate pre-treatment. The CNFs were chosen to be the field emission emitters because of their very sharp and thin edges which are potentially good electron field emission sites. The effect of deposition parameters such as substrate temperature, gas flow ratio and RF power on the field emission properties is discussed in detail. The sheet-like structures with thickness of about 10 nm or less stand on edge on the substrate and have a defective graphite structure. The field emission properties of the sample deposited at the optimum deposition conditions are turn-on field of 5.5 V/μm and current density of 1.4 mA/cm² at 11 V/μm. Considering the inexpensive manufacturing cost, lower synthesis temperature and ease of large-area preparation, the CNFs with low turn-on field deposited by RF sputtering might have a potential application in field emission devices.     

A rapid and efficient method to prepare aligned SnO2 nanorod arrays for field-emission application

Aligned tin dioxide (SnO₂) nanorods have been synthesized by high-frequency inductive heating. Nanorods were grown on silicon substrates vertically in less than 3 min, using SnO₂ and graphite as the source powder. Scanning electron microscopy and transmission electron microscopy showed nanorod with diameters from 25 to 50 nm. The turn-on field needed to produce a current density of 10 μA/cm² is found to be 1.6 V/μm. This type of SnO₂ nanorods can be applied as field emitters in displays as well as vacuum electric devices.     

Fabrication of carbon nanoneedle and carbon nanowall mixture film with two-step growth method

A novel nano-carbon electron emitter film has been developed on a stainless steel substrate by a direct current plasma chemical vapor deposition system. Samples grown at temperatures of 900 °C and 1100 °C showed different surface morphologies. It is found that a two-step growth process established by combining these two temperature growths together is suitable for deposition of a high density emitter array film. The as-grown nano-carbon film indicates a carbon nanoneedle and carbon nanowall mixture film, where the needle array density is about 3 × 10⁷/cm². The I-V characteristic shows an emission current density of 228 mA/cm² at 2.5 V/μm, and the field emission current is stable, making it possibly suitable for developing field emission devices.     

UNCD electron emitters using Si nanostructure as a template

The electron field emission (EFE) properties of silicon nanostructures (SiNSs) coated with ultra-nanocrystalline diamond (UNCD) were characterized. The SiNS, comprising cauliflower-like grainy structure and nanorods, was generated by reaction of a Si substrate with an Au film at 1000 °C, and used as templates to grow UNCD. The UNCD films were deposited by microwave plasma-enhanced chemical vapour deposition (MPECVD) using methane and argon as reaction gases. The UNCD films can be grown on the SiNS with or without ultrasonication pretreatment with diamond particles. The EFE properties of the SiNS were improved by adding an UNCD film. The turn-on field (E₀) decreased from 17.6 V/μm for the SiNS to 15.2 V/μm for the UNCD/SiNS, and the emission current density increased from 0.095 to 3.8 mA/cm² at an electric field of 40 V/μm. Ultrasonication pretreatments of SiNS with diamond particles varied the structure and EFE properties of the UNCD/SiNS. It is shown that the ultrasonication pretreatment degraded the field emission properties of the UNCD/SiNS in this study.     

Field emission properties of electrodeposited cobalt nanowire arrays grown in anodic aluminum oxide

The excellent vertically aligned cobalt nanowire arrays were electrodeposited into anodic aluminum oxide (AAO) templates. Each nanowire has the same length with 20 μm and the diameter with 60 nm. The field emission characteristics of the nanowires were firstly studied based on current-voltage measurements and the Fowler-Nordheim equation. The electron field emission measurements on the samples showed a turn-on field (1 mA/cm²) of 1.66 V/μm, a field enhancement factor of β = 3054 and a current density of 600 mA/cm² at a relatively low voltage of 4.3 V/μm. The nanowire arrays could be an ideal alternative to carbon nanotubes and ZnO nanowires for the fabrication of flat panel displays.     

Electron field emission properties of carbon nanoflakes prepared by RF sputtering

Carbon nanoflakes (CNFs) with corrugated geometry were synthesized using RF sputtering process with Ar/CH₄ gas mixture. Transmission electron microscopic examination reveals that the introduction of H₂ in sputtering chamber leads to the preferential etching of amorphous carbons, while maintaining integrity for the nano-crystalline phases. The proportion of nano-sized crystalline clusters is thus increased, which improved the electron field emission (EFE) properties of the materials, viz. with turn-on field of E ₀ = 6.22 V/μm and FEE current density of J _e = 90.1 μA/cm² at 11.0 V/μm. The cathodes made of screen printing of CNFs-Ag paste exhibit even better EFE properties than the as-deposited CNFs. The EFE of the CNFs cathodes can be turned on at E ₀ = 5.71 V/μm, achieving J ₀ = 340.1 μA/cm² at 11.0 V/μm applied field. These results showed that the CNFs are inheritantly more robust in device fabrication process than the other carbon materials and thus possess better potential for electron field emitter applications.     

Fabrication and dielectric property of ferroelectric PLZT films grown on metal foils

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on platinized silicon and LaNiO₃-buffered nickel substrates by chemical solution deposition using a sol-gel process based on acetic acid chemistry. The following measurements were obtained under zero-bias field: relative permittivity of ≈960 and dielectric loss of ≈0.04 on the PLZT film grown on Pt/Si substrates, and relative permittivity of ≈820 and dielectric loss of ≈0.06 on the PLZT film grown on LNO-buffered Ni substrates. In addition, a relative permittivity of 125 and dielectric loss of 0.02 were measured at room temperature under a high bias field of 1 × 10⁶ V/cm on PLZT deposited on LNO-buffered nickel substrate. Furthermore, a steady-state leakage current density of ≈8.1 × 10⁻⁹ A/cm² and mean breakdown field strength of 1.7 × 10⁶ V/cm were measured at room temperature. Finally, remanent polarization (P_r) of ≈2.0 × 10⁻⁵ C/cm², coercive electric field (E_c) of ≈3.4 × 10⁴ V/cm, and energy density of ≈45 J/cm³ were determined from room-temperature hysteresis loop measurements on PLZT/LNO/Ni film-on-foil capacitors with 250-μm-diameter platinum top electrodes.     

Photoluminescence and field-emission characteristics of ZnO nanowires synthesized by two-step method

ZnO nanowires with excellent photoluminescence (PL) and field-emission properties were synthesized by a two-step method, and the ZnO nanowires grew along (0 0 2) direction. PL measurements showed that the ZnO nanowires have stronger ultraviolet emission properties at 376 nm and there is 3 nm blue shift after the nanowires were immersed in thiourea (TU) solution compared with those of without immersion. The immersed-ZnO nanowires show a turn-on field of 2.3 V/μm at a current density of 0.1 μA/cm and emission current density up to 1 mA/cm² at an applied field of 6.8 V/μm, which demonstrate that the immersed-ZnO nanowires posses efficient field-emission properties in contrast with those not immersed. The ZnO nanowires may be ideal candidates for making luminescent devices and field-emission displays.     

Electron field emission from the carbon-doped TiO2 nanotube arrays

The field-emission characteristics of the carbon-doped TiO₂ nanotube arrays (TNAs), which can be obtained by a heat treatment of the as-fabricated TNAs under a continuous argon and acetylene flux, were investigated. The morphology, crystalline structure, and composition of the as-grown specimens were characterized by the use of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. It was found that the samples' turn-on electric field is reduced from 21.9 to 5.0 V/μm and the field-emission current density rapidly reaches about 9.0 mA/cm² at 11.8 V/μm after carbon doping. The dramatically improved field-emission characteristics would be mainly attributed to the reduced work function and the enhanced conductivity due to the carbon doping into TNAs.     

Efficient field emission properties of ZnO (core)/graphite (shell) nanowires

In this work the field emission studies of a new type of field emitter, zinc oxide (ZnO) core/graphitic (g-C) shell nanowires are presented. The nanowires are synthesized by chemical vapor deposition of zinc acetate at 1300 °C Scanning and transmission electron microscopy characterization confirm high aspect ratio and novel core–shell morphology of the nanowires. Raman spectrum of the nanowires mat represents the characteristic Raman modes from g-C shell as well as from the ZnO core. A low turn on field of 2.75 V/μm and a high current density of 1.0 mA/cm² at 4.5 V/μm for ZnO/g-C nanowires ensure the superior field emission behavior compared to the bare ZnO nanowires.     

Improved dielectric properties of lead lanthanum zirconate titanate thin films on copper substrates

Thin films of lead lanthanum zirconate titanate (PLZT) were directly deposited on copper substrates by chemical solution deposition and crystallized at temperatures of ~ 650 °C under low oxygen partial pressure (pO₂) to create film-on-foil capacitor sheets. The dielectric properties of the capacitors formed have much improved dielectric properties compared to those reported previously. The key to the enhanced properties is a reduction in the time that the film is exposed to lower pO₂ by employing a direct insertion strategy to crystallize the films together with the solution chemistry employed. Films exhibited well-saturated hysteresis loops with remanent polarization of ~ 20 μC/cm², dielectric constant of > 1100, and dielectric loss of < 0.07. Energy densities of ~ 32 J/cm³ were obtained at a field of ~ 1.9 MV/cm on a ~ 1 μm thick film with 250 μm Pt electrodes.     

Field emission properties of metallic element-containing glassy carbon films

Field emission properties of metallic element-containing glassy carbon (GC) films were investigated. The metallic element-containing GC films were prepared by carbonization process (i.e., heat treatment in an inert atmosphere) of synthesized polyimide including a metallic compound. In the alkaline (lithium(Li) or cesium(Cs)) or alkali-earth (calcium(Ca), strontium(Sr), or barium(Ba)) metallic element-containing GC films, threshold electric field, E_th, decreased and emission current density, J, increased. In particular, as for the Ba-containing GC film, E_th was decreased to 1.5 V/μm compared with E_th of 3.5 V/μm for the pure GC film without the metallic element addition, and the J reached more than 0.8 mA/cm² at an electric field of 3.0 V/μm. Analysis based on the Fowler-Nordheim model suggests that the amplification of the local-field-conversion factor β and/or the lowering of the effective-surface-potential barrier ? are due to the metallic elements contained in the GC films. Moreover, structural and compositional analyses showed that compositional modification of the GC film by the metallic elements plays an important role in allowing easy field emission.     

Electron emission properties of CNT arrays grown with micro-molding in capillary (MIMIC) assisted process

We have selectively fabricated carbon nanotubes (CNTs) emitter arrays with a micro mold in capillary (MIMIC) assisted process. The electron emitter growth site was fabricated by resist patterning using the MIMIC process. The pattern was uniformly transferred to the substrate and well aligned CNTs were grown. The emitter produces a turn-on field of 2.7 V/μm with a field emission current of 10 μA/cm². The electron emission current can be controlled by emitter pattern width and pitch variation.     

X-ray image resolution of carbon nanotube emitters grown with resist-assisted patterning process

We obtained X-ray images using carbon nanotube arrays. The electron emitter was fabricated using the resist-assisted patterning (RAP) process. The X-ray image was obtained with a current of 300 μA at an anode bias of 30 kVp. The emitter had a pattern width of 5 μm and a pitch of 40 μm producing a turn-on field of 1.5 V/μm with a field emission current of 10 μA/cm². The resulting X-ray image clearly shows micrometer scale lines on an integrated circuit chip bonded in a printed circuit board.     

Amorphous structure and electrical performance of low-temperature annealed amorphous indium zinc oxide transparent thin film transistors

The effect of low-temperature (200 °C) annealing on the threshold voltage, carrier density, and interface defect density of amorphous indium zinc oxide (a-IZO) thin film transistors (TFTs) is reported. Transmission electron microscopy and x-ray diffraction analysis show that the amorphous structure is retained after 1 h at 200 °C. The TFTs fabricated from as-deposited IZO operate in the depletion mode with on-off ratio of > 10⁶, sub-threshold slope (S) of ~ 1.5 V/decade, field effect mobility (μ_FE) of 18 ± 1.6 cm²/Vs, and threshold voltage (V_Th) of − 3 ± 0.7 V. Low-temperature annealing at 200 °C in air improves the on-current, decreases the sub-threshold slope (1.56 vs. 1.18 V/decade), and increases the field effect mobility (μ_FE) from 18.2 to 23.3 cm²/Vs but also results in a V_Th shift of − 15 ± 1.1 V. The carrier density in the channel of the as-deposited (4.3 × 10¹⁶ /cm³) and annealed at 200 °C (8.1 × 10¹⁷ /cm³) devices were estimated from test-TFT structures using the transmission line measurement methods to find channel resistivity at zero gate voltage and the TFT structures to estimate carrier mobility.     

Properties of amorphous Si thin film anodes prepared by pulsed laser deposition

Amorphous Si (a-Si) thin film anodes were prepared by pulsed laser deposition (PLD) at room temperature. Structures and properties of the thin films were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements. Galvanostatic charge/discharge tests of half cells using lithium counter electrode were conducted at a constant current density of 100 μA/cm² in different voltage windows. Cyclic voltammetry (CV) was obtained between 0 and 1.5 V at various scan rates from 0.1 to 2 mV/s. The apparent diffusion coefficient (D_Li) calculated from the CV measurements was about ∼10⁻¹³ cm²/s. The Si thin film anode was also successfully coupled with LiCoO₂ thin film cathode. The a-Si/LiCoO₂ full cell showed stable cycle performance between 1 and 4 V.     

Enhancing electron field emission of carbon nanoflakes by hydrogen post-annealing process

In this study, the carbon nanoflakes (CNFs) fabricated by sputtering were chosen as the field emission emitters because of their very sharp and thin edges which are potentially good electron field emission sites. The as-deposited CNFs were annealed in the furnace under hydrogen atmosphere. The results showed that the optimum field emission properties with smaller turn-on field and larger current density were obtained at annealing temperature of 600 °C for 10 min. The hydrogen thermal annealing has chemical etching on the surface of the CNFs and produces appropriate emission site density to increase the emission current density. The turn-on field was reduced from 6.7 to 5.8 V/μm and electric current density was increased from 22 to 187 μA/cm² under 8 V/μm after hydrogen thermal annealing.     

The fabrication and properties of field emission display based on ZnO tetrapod-liked nanostructure

ZnO tetrapod-liked nanostructure with fine crystalline structure and high purity was synthesized via CVD method. Each branch of the nanotetrapod was 50-200 nm in diameter and the nanotetrapod structure exhibited a high aspect ratio. Cathode emission materials with this nanostructure were employed to fabricate field emission display with 72 × 72 pixel array. The as-obtained device showed an ideal field emission property with a threshold electric field of 4.1 V/μm and an emission current density of 1 mA/cm² when the electric field reached 11.5 V/μm. The field enhancement factor of the nanotetrapods was calculated to be 1852. Using proper circuit drive, dynamic Chinese characters can be successfully displayed in the device.