The 1st CBRM Seminar

We developed a UHV low-temperature cantilever-based scanning force microscope (SFM) system relying on a fiber-optical interferometer optical deflection sensor and a tip-sample gap stability of better than 1pm [1]. Because of the fiber-optical deflection sensor, microfabricated cantilevers best matched to the measurement tasks can be used. Examples are cantilevers with stiffnesses much below 1N/m and quality factors up to 500’000 for most sensitive measurements of longer-ranged forces, e.g. of magnetic origin [2,3,4]. Cantilever force sensors can also be operated on multiple oscillation modes, like on a flexural modes and on side-bands of those, for KPFM or advanced distance control for MFM [5], on multiple flexural resonances of the cantilever to simultaneously map long-ranged electrical and magnetic forces together with short-ranged tip-sample interactions (for example for atomic resolution imaging), or can be simultaneously driven on flexural and torsional resonances. The latter provides the possibility to map vertical and lateral forces simultaneously for example to manipulate molecules on surfaces. After a short introduction into the technology of this new instrument, and a review on the advantages of cantilever-based SFM, various recent examples, ranging from mapping magnetic stray fields with highest sensitivity, to mapping mono- and double-layer NiBr2 islands on Au(111) with atomic resolution or atomic step resolution combined with KPFM and MFM, as well as a study of surface diffusion and manipulation of trimethyl and triethylbenzene molecules on Cu(111) will be discussed.


Figure 1: a) to f) MFM data of on F/Fi/F multilayers with different thicknesses tFe = 0.18 – 0.35 nm acquired with frequency-modulated tip-sample distance control revealing different densitities of tubular/incomplete, i.e. two types of skyrmions. F = [Ir(1)/Fe(tFe)/Co(0.6)/Pt(1)]5 and Fi = [(TbGd)(0.2)/Co(0.4)]×6/TbGd(0.2). f) NiBr2 islands on Au(111) showing NiBr2, NiBr2-x, and Br-mesh phases. g) atomic resolution image of NiBr2. h), i), and j) topography, Kelvin signal, and MFM data acquired simultaneously using multifrequency techniques.

[1] H. Liu et al., Beilstein J Nanotech 13, 1120 (2022).2
[2] Y. Feng et al., J Magn Magn Mater 551, 169073 (2022).
[3] A. O. Mandru et al., Nature Communications 11, 6365 (2020).
[4] Y. Feng et al., Phys Rev Appl 18, 024016 (2022).
[5] X. Zhao et al., New Journal of Physics 20, 013018 (2018).