Focused electron beam induced deposition of high resolution magnetic scanning probe tips

Apexes of commercial pyramidal silicon scanning microscopy tips were magnetically functionalized by means of local focused electron beam induced deposition. High aspect ratio supertips and local tip coatings with varying apex diameters can be produced by varying exposure time, beam current, and scan mode. The carbonyl precursor Co2(CO)8 was used as source of magnetic metal. Tip performance was tested with magnetic force microscopy (tapping / lift-retrace mode) and magnetically actuated cantilever atomic force microscopy. The deposit contains 34±2 at.% Co, dispersed as 2-5 nm metal nanocrystals in a carbonaceous matrix. Specific surface reactions and Boudouard reactions are proposed to explain the resulting deposit composition measured by Auger spectroscopy. The electrical resistivity is 10 higher than bulk Co resistivity. INTRODUCTION In view of future’s magnetic data storage single-grain addressing at ultrahigh densities becomes a challenge. Self-assembly of regular 4 nm iron-platinum dot patterns (4 Tbit/cm) was recently achieved [1]. To be able to characterize such grains there is need for magnetic force microscopy (MFM) of very high resolution. Furthermore, some designs of ultrahigh-density magnetic readout systems rely on magnetic force tips to perform the actual data access. Today’s commercially produced magnetic tips are fabricated by physical or chemical vapor deposition of a magnetic thin film onto Si or Si3N4 tips on cantilevers for scanning probe microscopy systems having relatively large apex diameters of about 80-100 nm. Furthermore, oxidation protective coatings of several nm-thickness on top of magnetic films are often applied. Focused Electron Beam (FEB) induced deposition is a local chemical vapor deposition technique, which can produce high aspect ratio tips and other more complex 3D nanostructures [2]. The first single-step production of magnetic FEB tips was carried out in our group [3]. In this paper we report on further characterization of these magnetic deposits and their use in wet cell magnetically actuated cantilever setups for atomic force microscopy of biological samples. EXPERIMENTAL DETAILS Our FEB-system is based on a Cambridge S100 Scanning Electron Microscope (SEM) with tungsten thermionic emitter. With an oil-free turbomolecular pump backed by a membrane pump a chamber background pressure of 1x10mbar is achieved. The volatile precursor Mat. Res. Soc. Symp. Proc. Vol. 706 © 2002 Materials Research Society