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KatamariDamacy
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What is the minimum speed at which electrons can be emitted? Why is it I never heard of really slow moving electrons, like 10 meters per second slow?
davenn said:now when you said emitted can you be a little more specific please
KatamariDamacy said:I still don't see what's the limit to emitting slower electrons than that
or why we couldn't slow them down afterwards to even crawling speed like 1 meter per 10 seconds.
voko said:There is no such limit.
What makes you think that we cannot?
Here's an easy way of getting an electron to stand still (or move at any speed that I please):KatamariDamacy said:I also find it hard to imagine slow electrons, for some reason. If photons can't go any slower than the speed of light, then let's just say I wouldn't be surprised there are some bottom limits to electron speed as well.
Maybe even for the same reason, whatever reason that is, and so I wonder. Do you know why photons can't go any slower than the speed of light?
Drakkith said:Photons move at the velocity c because they are massless.
Electrons are not, though, and can go any speed below c, including zero.
Nugatory said:Take an electron source that emits electrons at some very high speed. Mount it in a car (or a plane, or a spaceship) pointing backwards. Drive the car forward at the same speed that the electrons are emitted backwards... And there you are.
vanhees71 said:...to construct an electron accelerator you are fine with the classical concepts
This comes pretty close to particles nearly at rest. An example are ultracold neutrons:
vanhees71 said:This comes pretty close to particles nearly at rest. An example are ultracold neutrons:
http://en.wikipedia.org/wiki/Ultracold_neutrons
vanhees71 said:Yes, the fact that neutrons are neutral and pretty much heavier than electrons in fact helps to achieve those low speeds for free neutrons as compared to free electrons. As I said, deceleration is almost as chalenging as acceleration.
KatamariDamacy said:What about emission? As I gathered we can get faster or slower electrons in cathode ray tube by supplying more or less voltage to "electron gun" apparatus. Is there anything then preventing us to supply some low voltage corresponding to electron speed of, say 10 m/s? And if that is so easy, then why I can't find anything about it on the whole internet?
Drakkith said:Electron guns typically rely on a method called "thermionic emission" to get enough electrons to be useful. This requires heating up a filament so that electrons near the surface get enough energy to escape the metal. The energy each electron receives just from the temperature of the filament accelerates them to a much higher velocity than 10 m/s.
Even the electron guns that don't use thermionic emission still impart enough energy into each escaped electron to accelerate them well above 10 m/s.
KatamariDamacy said:I approve. That way, or whatever other way, but has anyone actually done it?
Drakkith said:The transfer of energy to each electron is not smooth and continuous. Random vibrations and collisions produce a wide range of electron velocities. Sometimes an electron gets barely enough energy to exceed the work function of the material and escape, while another electron could get smacked so hard that it blazes out of the material at several times the average velocity.
An applied voltage can then accelerate the electron once it leaves the material to whatever velocity you desire. (Or reduce the work function on the material, allowing electrons to escape easier)
Nugatory said:yes. many many many times. Ever seen electronic equipment operate in a car?
KatamariDamacy said:So I guess that is another separate apparatus with its own functionality. Electron gun emits electrons, and than that piece of equipment has the job of accelerating them? What is that part called in CRTs, and do you think it would be possible for it to decelerate electrons, to somehow run "backwards" in reverse operation?
nsaspook said:We use several 'decel' sections in a typical advanced technology ion implanter to reduce the energy (it's much easer to form and control beam uniformity at higher energy) of the beam before it hits the wafer during wafer fabrication. At low energy levels for us (<500eV) beam stability becomes a problem (because of drift and space charge effects) if it needs to travel far so normally it's only decelerated to the final energy just before the beam hits the target.
A deceleration stage for electrons should be similar but without the mass selection stages.
http://www.google.com/patents/US6998625
http://patentimages.storage.googleapis.com/US6998625B1/US06998625-20060214-D00002.png
KatamariDamacy said:Interesting. I suppose the purpose of deceleration is to avoid damage. Can you express in meters per seconds how much are electrons slowed down, from what speed to what speed?
nsaspook said:We aren't using electrons as this application is used to dope wafers with the typical impurity ions to form substrates or junctions for circuits and normally control on total dose at a selected energy instead of ion carrier velocity but the depth of dose and damage to the wafer layer can be calculated from the KE/velocity of the ion type.
https://inst.eecs.berkeley.edu/~ee143/sp10/solutions/hw7.ee143.s10.soln.pdf
Nugatory said:yes. many many many times. Ever seen electronic equipment operate in a car?
KatamariDamacy said:I'm afraid I don't see what are you pointing at.
Slow moving electrons refer to electrons that have a lower velocity compared to other particles. They can be found in various materials and environments, including metals, semiconductors, and plasmas.
Regular electrons have a higher velocity and are more energetic compared to slow moving electrons. They are also able to move freely and conduct electricity, while slow moving electrons are often bound to atoms or molecules and do not contribute significantly to electrical conductivity.
The movement of electrons is influenced by various factors, such as temperature, electric and magnetic fields, and interactions with other particles. In some materials, electrons may also be slowed down due to collisions with atoms or impurities.
Yes, slow moving electrons have various important applications in fields such as electronics, materials science, and energy generation. For example, they play a crucial role in controlling the electrical conductivity of semiconductors and determining the properties of materials.
No, scientists have been studying slow moving electrons for many decades. However, with advancements in technology and research techniques, our understanding of their behavior and properties continues to improve and expand.