Download Slide 1

SIZE MATTERS –ELECTRON BEAMS AT THE MICROSCALE
Ágúst Valfells
Science and Engineering
FYRIRLESTRAMARAÞON HR 2011 | RU LECTURE MARATHON 2011
vacuum electronics
vacuum tubes solid state integrated circuit
high power microwaves
CW power [W]
tubes are expensive to make
105
Vacuum electronics
must maintain
conditions
104 vacuum
integrated
circuits
are inexpensive
103
solid2 state electronics put limit on frequency and efficiency
10
Solid state
101
Frequency[GHz]
1
10
100
www.hr.is
nanotube radio
Credit Paul Scherrer Institute
Credit: Zettl Research Group, Lawrence
Berkeley National Laboratory and University of
California at Berkeley
vacuum microelectronics
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 – emission
Thermionic emission.
J  AT e
2
  w 
kT
Photoemission.
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.
wikipedia
Field emission
J  C1E e
2
C2
E
Accurate assesment of surface field is difficult –much fudging.
www.hr.is
surface irregularities
Credit Joonil Seog
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.
electron backscattering and secondary
electron emission.
quantum effects.
irregularity of surfaces; shot noise;
cavity Q; surface roughness and skin
depth
Energy Stored
Energy Dissipated
4
de Broglie wavelength [nm]
beam dynamics: emittance and
brightness; long range and short range
Coulomb interaction; transit time,
frequency response.
Q
3
2
1
0 -2
10
0
10
10
Potential [V]
2
4
10
www.hr.is
computational vacuum microelectronics at RU
Microscale works to our advantage – full fidelity modeling
1 nm
10 nm
L2
N e  100 E
D
50 nm
www.hr.is