Field emission sensing for non-contact probe recording

Alexander J. le Fèbre

Research output: ThesisPhD Thesis - Research UT, graduation UT

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Abstract

The objective of this thesis is to investigate whether field emission can be used as an integrated method to control probe-medium distance for non-contact probe recording. Such a system is expected to offer a promising route towards extremely high-density recording, with bits of several nanometer or even atomic size. To reach these densities, individual control over the position of the probes is essential, to be able to operate the probes in non-contact as is for instance done in scanning tunneling microscopy (STM). Field emission can be used for displacement sensing and high-resolution positioning, since the emission current is proportional to the electrode gap.
In this thesis, a new model based on finite element calculations was developed to calculate the sensitivity of the field emission current for small tip-sample distances. For experimental demonstration, an ultra-high vacuum (UHV) scanning probe microscope was assembled, improved and tested. The field emission characteristics were measured for two types of probes: one custom made with a fixed tip on a substrate base and the other a commercially available atomic force microscopy (AFM) probe with the tip on a cantilever. The model was verified by measuring their I-V characteristics, for distances varying from 12.5 – 950 nm. By operating the probes in constant current mode and varying the applied voltage, the position can be raised up to ~ 100 nm. The non-linearity in the measured voltage-displacement curves agrees with our model. The sensitivity depends on the emitter tip radius and on the variation in field enhancement. Bias-dependent imaging can be used to scan on conducting patterned samples for increasing tip-sample distance. At larger distances the lateral resolution reduces, but higher scan rates can be used. At 50 V the resolution is ~ 20 nm, which is sufficient for probe recording applications. For practical applications, the current stability and emitter lifetime should be further improved in order to increase the accuracy and reproducibility of positioning also in poor vacuum conditions.
Original languageEnglish
QualificationDoctor of Philosophy
Awarding Institution
  • University of Twente
Supervisors/Advisors
  • Lodder, J.C., Supervisor
  • Abelmann, Leon, Co-Supervisor
Thesis sponsors
Award date28 Mar 2008
Place of PublicationZutphen
Publisher
Print ISBNs978-90-8570-300-6
DOIs
Publication statusPublished - 28 Mar 2008

Keywords

  • TST-uSPAM: micro Scanning Probe Array Memory
  • TST-SMI: Formerly in EWI-SMI

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