Faculty of Engineering and Natural Sciences
NEAR FIELD EMISSION SCANNING ELECTRON MICROSCOPY
T. L. Kirk*, U. Ramsperger, and D. Pescia
Laboratorium für Festkörperphysik, Eidgenössische Technische Hochschule Zürich (ETH), CH-8093 Zürich, Switzerland
*presenting author: email@example.com
In conventional scanning electron microscopy (SEM) the lateral resolution is limited by the electron beam diameter impinging on the specimen surface and interaction volume of the electron collisions. This limit is also critical for the subsequent analysis of the resultant electrons, e.g. spin polarization (SEMPA), electron energy loss spectroscopy (EELS), and auger electron spectroscopy (AES). The close proximity between the probe and sample surface of a scanning tunneling microscope (STM) operating in field emission (FE) mode provides a means of overcoming this limit.
We present a simple “near field emission scanning electron microscope” (NFESEM) capable of imaging conducting surfaces with high spatial resolution; whereby electrons are excited from the sample surface after undergoing interactions with a low-voltage (< 60V) beam of electrons field-emitted from a Tungsten tip positioned tens of nanometers above the sample surface. Topographic images, determined from the intensity variations of secondary and backscattered electrons, yield a vertical resolution on an atomic scale and a lateral resolution of less than two nanometers. We report on the first topographic electron intensity images of terraces and mono-atomic steps on a single crystal substrate, not yet attained with a remote electron gun in conventional SEM. The topographic contrast of the extracted electrons and the FE current are indistinguishable, in agreement with theoretical models of optimal spatial resolution. Moreover we have studied the current-voltage characteristics of FE from curved surfaces, which are used to estimate the nominal emission radii. Complimentary STM imaging, directly following NFESEM measurements, is feasible and can easily be performed. We assert that additional analysis of the secondary electrons will also exhibit a comparable resolution.
November 20, 2008, 13:40, FENS L047