fyrirlestramaraÞon hr 2011 | ru lecture marathon 2011 Ágúst valfells science and engineering size...
TRANSCRIPT
FYRIRLESTRAMARAÞON HR 2011 | RU LECTURE MARATHON 2011
Ágúst Valfells
Science and Engineering
SIZE MATTERS –ELECTRON BEAMS AT THE MICROSCALE
www.hr.is
solid state integrated circuit
vacuum electronics
high power microwaves
Solid state
Vacuum electronics
1 10 100
Frequency[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
www.hr.is
vacuum microelectronics
Cre
dit:
Zet
tl R
esea
rch
Gro
up, L
awre
nce
Ber
kele
y N
atio
nal L
abor
ator
y an
d U
nive
rsity
of
Cal
iforn
ia a
t Ber
kele
y
nanotube radio
Cre
dit P
aul S
cher
rer
Inst
itute
field emission array
www.hr.is
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
www.hr.is
electron beams – emissionThermionic emission.
kT
w
eATJ
2
Photoemission.
wikipedia
Field emission
EC
eECJ22
1
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.
www.hr.is
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
www.hr.is
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.
- +
www.hr.is
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
104
0
1
2
3
4
Potential [V]
de B
rogl
ie w
avel
engt
h [n
m]
www.hr.is
computational vacuum microelectronics at RU
Microscale works to our advantage – full fidelity modeling ED
LNe
2
100
1 nm 10 nm 50 nm