Near Field Emission Scanning Electron Microscopy

Low beam energies have been implemented in a simplified SEM technique; where the electron source, remote in standard SEMs, is brought within tens of nanometers to the object. This method, known as the "near field emission scanning electron microscopy" (NFESEM), is capable of imaging conducting surfaces with nanometer resolution using beam energies less than 60 eV. The terminology "near" refers to the locality of the field-emitted electron source; which is to distinguish itself from the "remote" field emission gun sources used in standard SEMs. The main aim of this instrument is the realization of some kind of surface topography image due to the exposure of a primary beam of electrons, as it is rastered along the sample surface. This will be achieved by two distinct (although related) experiments: measuring the field emission (FE) current while scanning and detecting the secondary electrons (SE)s generated when the electron beam impinges on the surface. Here, the FE properties, in accordance with the tip-sample separation, will be emphasized, since the variations in SE yield are directly proportional to the impinging primary electron beam. We observe a direct correlation between the image contrast and the FE current, where the image is enhanced with increasing FE current. Moreover, simple electrostatic measurements can be used to define the performance of the device.