FYRIRLESTRAMARAÞON HR 2011 | RU LECTURE MARATHON 2011

Ágúst ValfellsScience and Engineering

SIZE MATTERS –ELECTRON BEAMS AT THE MICROSCALE

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solid state integrated circuit

vacuum electronics

high power microwaves

Solid state

Vacuum electronics

1 10 100Frequency[GHz]

101

102

103

104

105

CW

pow

er [W

]vacuum tubes

tubes are expensive to make

must maintain vacuum conditionsintegrated circuits are inexpensive

solid state electronics put limit on frequency and efficiency

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vacuum microelectronics

Cre

dit:

Zettl

Res

earc

h G

roup

, Law

renc

e B

erke

ley

Nat

iona

l Lab

orat

ory

and

Uni

vers

ity o

f C

alifo

rnia

at B

erke

ley

nanotube radio

Cre

dit P

aul S

cher

rer I

nstit

ute

field emission array

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possible advantages of vacuum microelectronics

high efficiency due to limited interaction with bulk structure

tolerance of high temperature and radiation

short path length decreases vacuum requirements

small length scales indicate possible high frequency f ~ 1 / L

rapid switching via field emission

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electron beams – emissionThermionic emission.

kT

weATJ

2

Photoemission.

wikipedia

Field emission

ECeECJ

221

Field emission is due to tunneling of electrons through the potential barrier. It is the dominant emission mechanism at high field strength.

Local enhancment of the electric field can lead to higher emission density.

Accurate assesment of surface field is difficult –much fudging.

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surface irregularities

Cre

dit J

ooni

l Seo

g

electric field is enhanced at protrusions

surface uniformity decreases at shorter length scales

variations in composition are also important

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electron beams - dynamics

electrons in vacuum region interact with surrounding structure

electrons interact with each other - nonlinearity

THz bunching due to space-charge limited emission. An intriguing possibility for generating radiation.

- +

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issues of interest at the vacuum scale

emission physics: i-v characteristics; energy and angular distribution of electrons from surface; accurate modeling –needs and limitations.

beam dynamics: emittance and brightness; long range and short range Coulomb interaction; transit time, frequency response.

electron backscattering and secondary electron emission.

quantum effects.

irregularity of surfaces; shot noise; cavity Q; surface roughness and skin depth

DissipatedEnergy StoredEnergy

Q

10-2 100 102 1040

1

2

3

4

Potential [V]

de B

rogl

ie w

avel

engt

h [n

m]

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computational vacuum microelectronics at RU

Microscale works to our advantage – full fidelity modeling EDLNe

2

100

1 nm 10 nm 50 nm