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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 C1 E 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 EnergyStored 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