The brightest beam in science: New directions in electron microscopy and interferometry

Abstract

An ultrasharp electron field-emission source, with emission region on the order of atomic size (i.e., fraction of a nanometer), produces a bright, strongly self-focused, highly coherent electron beam—indeed the brightest particle beam currently known to science. Employed in the configuration of a point-production microscope, this ‘‘nanotip’’ source facilitates low-energy electron imaging of fragile structures at atomic-scale resolution. When slightly out of focus, the microscope serves as perhaps the world’s simplest electron interferometer providing Fresnel diffraction patterns from which important information like effective source size, source brightness, and beam degeneracy can be determined. One remarkable feature of point sources is the perfect (i.e., aberration-free), lensless imaging of periodic structures at a denumerable set of focal planes with complete suppression of nonperiodic detail. The high degeneracy and coherent emission of an electron pointlike source can be exploited in new types of quantum interferometry involving correlated electrons.

Resolving power of lens‐less low energy electron point source microscopy

“…The energy dispersion will reduce the resolution in images obtained because the electron wave packet has a finite lifetime T c = h /Δ E . This is a consequence of the uncertainty principle and gives rise to an associated length called the longitudinal coherence length L c of the wave packet, given by: where v is the mean speed of the emitted electrons (Silverman et al , 1995). This is a function of the kinetic energy of electrons that have tunnelled through the potential barrier E initial , which for tungsten tips is assumed to be 0.15–0.25 eV (Qian et al , 1993).…”

Computer Simulation of Quantum Phenomena in Nanoscale Devices

“…3,4 These properties make such electron sources very attractive for applications to electron microscopy, holography and interferometry. 5 For the materials used to fabricate the tips, e.g., tungsten, iron, gold,..., X F ~ 10 A.…”

Characterization of nanowires with the low energy electron point source (LEEPS) microscope

“…Since then, several groups explored its experimental and theoretical foundations. Experimental imaging has been performed with carbon fibers [7,8], carbon nanotubes [9][10][11][12], and thin metal wires [13]. Holographic imaging of single polymer fibers [14] and of unstained individual DNA molecules [15,16] was also reported.…”