Cold Field Emitter Current Stability via Periodic Heating Pulses
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Solution Overview
Problem
Cold field emitters experience instability and emission current decline due to adsorption and desorption of residual gas molecules, leading to fluctuations and potential emitter tip destruction, despite their high brightness and low energy spread advantages.
Innovation Solution
A method involving frequent cleaning processes with heating pulses to maintain the emitter surface in a clean condition, keeping the emission current above the stable mean value by applying heating pulses before the emission current declines to a lower stable mean, and adjusting the electric extraction field strength to compensate for fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cold field emitter is operated under constant extraction field and vacuum conditions, then the emission current initially remains high, but it continuously declines due to adsorption of residual gas molecules on the emitter tip surface
Solution Approach 1:
The patent applies periodic heating pulses (flashing) to the emitter tip at predetermined time intervals during operation. This periodic thermal action removes adsorbed gas molecules from the emitter surface, restoring the emission current to high levels and preventing continuous decline, thereby resolving the contradiction between maintaining stable emission and preserving high productivity
Solution Approach 2:
The patent performs cleaning by heating pulses before the emission current fully declines to low stable levels. By proactively removing contaminants at predetermined intervals, the system prevents the emission current from dropping, maintaining both stability and high current levels throughout operation
2Reliability
If the vacuum pressure is reduced to improve emission stability, then adsorption of gas molecules decreases, but the system complexity and cost increase
Solution Approach 1:
The patent enables the emitter tip to clean itself through periodic heating pulses that thermally desorb adsorbed gas molecules. This self-cleaning mechanism eliminates the need for excessively complex vacuum systems, maintaining emission stability through an active cleaning process rather than relying solely on ultra-high vacuum conditions
Solution Approach 2:
The patent temporarily changes the temperature parameter of the emitter tip by applying heating pulses. This thermal parameter change facilitates desorption of gas molecules without requiring permanent ultra-high vacuum conditions, thereby reducing overall system complexity while maintaining emission stability
3Reliability
If heating pulses are applied frequently to maintain high emission current, then the emitter surface remains clean, but energy consumption increases
Solution Approach 1:
The patent employs periodic heating pulses at predetermined time intervals rather than continuous heating. This periodic thermal action maintains emitter cleanliness and emission stability while minimizing energy consumption by applying heat only when necessary to remove adsorbed molecules, resolving the contradiction between reliability and energy efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly increases and maintains the emission current at a high level over a long period, reducing fluctuations and extending the emitter's operational stability and lifespan.
Implementation Method 1
performing a cleaning process by applying at least one heating pulse to the charged particle beam source for heating the emitter surface to a temperature TC
Implementation Method 2
the emission current declines continuously due to increasing adsorption of residual gas molecules on the surface of the emitter tip. At the same time, gas molecules adhering to the emitter surface begin to desorb from the emitter surface
Implementation Method 3
When applying a voltage to the cold field emitter, a very strong electric field is formed at the emitter tip due to the tip's small curvature. The strong electric field enables the electrons to pass the potential barrier between the metal and the vacuum
Implementation Method 4
cold field emitters are not heated so that electrons are only emitted due to the presence of the strong electric field
Data Source
AI summary
A method for operating a charged particle beam emitting device and, in particular, an electron beam emitting device including a cold field emitter is provided. The method includes the steps of placing the cold field emitter in a vacuum of a given pressure, the emitter exhibiting a high initial emission current I0 and a lower stable mean emission current IS under a given electric extraction field; applying the given electric extraction field to the emitter for emitting electrons from the emitter surface; performing a cleaning process by applying at least one heating pulse to the cold field emitter for heating the emitter surface, whereby the cleaning process is performed before the emission current of the cold field emitter has declined to the lower stable mean emission value IS; and repeating the cleaning process to keep the emission current of the emitter continuously above the substantially stable emission value IS.