Methods for measuring the local emission characteristics of CNT based multi-tip emitters

The work is aimed at obtaining microscopic emission characteristics of individual emission sites of a multi-tip field cathode or large-area emitter (LAFE) based on processing the current-voltage characteristics and emission glow patterns. Processing was carried out on a hardware-software complex for the study of field emission characteristics in real time. The calculation of the microscopic characteristics of the local emission sites — the field enhancement factor and emission area — was carried out by several different algorithms. A comparison of the results showed that the algorithms gave close values of the characteristics, which increases the reliability of the estimates made.

Field electron emission from a nanostructured tungsten surface

In this paper, the electron emission from a nanostructured tungsten surface was investigated. A method for measuring an extremely low current (10−12 – 10−14 A) has been tested. It made possible to reduce the effect of the electric field on the sample surface and to minimize the probability of spontaneous breakdowns. For a detailed study of tungsten fuzz, a point tungsten anode (diameter 90 μm) was used. Field enhancement factor (β = 2000 – 3000) and effective emission area were calculated using the Fowler–Nordheim plots. The pre-breakdown current rise was studied. The emission current waveforms suggest the formation of several emission structures before the breakdown.

Unveiling the Nottingham Inversion Instability during the thermo-field emission from refractory metal micro-protrusions

The electron emission by micro-protrusions has been studied for over a century, but the complete explanation of the unstable behaviors and their origin remains an open issue. These systems often evolve towards vacuum breakdown, which makes experimental studies of instabilities very difficult. Modeling studies are therefore necessary. In our model, refractory metals have shown the most striking results for discontinuities or jumps recorded on the electron emitted current under high applied voltages. Herein, we provide evidence on the mechanisms responsible for the initiation of a thermal instability during the field emission from refractory metal micro-protrusions. A jump in the emission current at steady state is found beyond a threshold electric field, and it is correlated to a similar jump in temperature. These jumps are related to a transient runaway of the resistive heating that occurs after the Nottingham flux inversion. That causes the hottest region to move beneath the apex, and generates an emerging heat reflux towards the emitting surface. Two additional conditions are required to initiate the runaway. The emitter geometry must ensure a large emission area and the thermal conductivity must be high enough at high temperatures so that the heat reflux can significantly compete with the heat diffusion towards the thermostat. The whole phenomenon, that we propose to call the Nottingham Inversion Instability, can explain unexpected thermal failures and breakdowns observed with field emitters.

Large Area Emission in p-Type Polymer-Based Light-Emitting Field-Effect Transistors by Incorporating Charge Injection Interlayers

Organic light-emitting field-effect transistors (LEFETs) provide the possibility of simplifying the display pixilation design as they integrate the drive-transistor and the light emission in a single architecture. However, in p-type LEFETs, simultaneously achieving higher external quantum efficiency (EQE) at higher brightness, larger and stable emission area, and high switching speed are the limiting factors for to realise their applications. Herein, we present a p-type polymer heterostructure-based LEFET architecture with electron and hole injection interlayers to improve the charge injection into the light-emitting layer, which leads to better recombination. This device structure provides access to hole mobility of ~2.1 cm2 V−1 s−1 and EQE of 1.6% at a luminance of 2600 cd m−2. Most importantly, we observed a large area emission under the entire drain electrode, which was spatially stable (emission area is not dependent on the gate voltage and current density). These results show an important advancement in polymer-based LEFET technology toward realizing new digital display applications.

Inkjet Printing of an Electron Injection Layer: New Role of Cesium Carbonate Interlayer in Polymer OLEDs

Among solution-processable techniques, inkjet printing is a potential method for manufacturing low-cost and high-resolution polymer organic light-emitting diodes (PLEDs) for displays/solid-state lighting applications. Herein, we demonstrate use of the inkjet printed cesium carbonate (Cs2CO3) film as an electron injection interlayer. We have elaborated the Cs2CO3 ink using an alcohol-based solvent for the industrial-grade printhead. The printed Cs2CO3 layer morphology was investigated by means of an optical microscope and an atomic force microscope. The PLEDs based on emissive polymer (Super Yellow) with printed Cs2CO3 interlayer show a remarkable current efficiency and luminance compared to the PLEDs made without the Cs2CO3 layer. Such results suggest that the Cs2CO3 is a promising material for the formulation of the electron injecting inkjet inks. The possibility of inkjet printing of an efficient electron injecting layer enables in situ patterning of PLEDs’ emission area. Such a simple and flexible technique can be applied for a wide range of applications such as signage, pictograms, advertising, smart packaging, etc.

High-efficiency Wavelength Tunable Monolayer LED with Hybrid Continuous-pulsed Injection

High-efficiency and wavelength-tunable light emitting diode (LED) devices will play an important role in future advanced optoelectronic systems. Traditional semiconductor LED devices typically have a fixed emission wavelength that is determined by the energy of the emission states. Here, we developed a novel high-efficiency and wavelength-tunable monolayer WS2 LED device, which operates in the hybrid mode of continuous-pulsed injection. This hybrid injection enables highly enhanced emission efficiency (> 20 times) and the effective size of emission area (> 5 times) at room temperature. The emission wavelength of WS2 monolayer LED device can be tuned over more than 40 nm by driving AC voltages, from exciton emission to trion emission, and further to defect emissions. The quantum efficiency of defect electroluminescence (EL) emission is measured to be more than 24.5 times larger than that from free exciton and trion EL emissions. The separate carrier injection in our LED also demonstrate advantage in allowing to visualize and distinguish defect species in real space. Those defects are assigned to be negatively charged defects. Our results open a new route to develop high-performance and wavelength-tunable LED devices for future advanced optoelectronic applications.