Enhanced sensitivity and contrast with bimodal atomic force microscopy with small and ultra-small amplitudes in ambient conditions

Abstract

Here, we introduce bimodal atomic force microscopy operated with sub-nm and ultra-small, i.e., sub-angstrom, first and second mode amplitudes in ambient conditions. We show how the tip can be made to oscillate in the proximity of the surface and in perpetual contact with the adsorbed water layers while the second mode amplitude and phase provide enhanced contrast and sensitivity.\ud Nonlinear and nonmonotonic behavior of the experimental observables is discussed theoretically with a view to high resolution, enhanced contrast, and minimally invasive mapping. Fractions of meV of energy dissipation are shown to provide contrast above the noise level.Peer ReviewedPostprint (published version

Amplitude dependence of image quality in atomically-resolved bimodal atomic force microscopy

“…[11][12][13] It was shown that the small oscillation of the second flexural mode could be used to increase sensitivity to material properties. [14][15][16][17] Several groups have applied this technique to biological samples, including antibodies 13 and proteins. 11 Schwenk and coworkers used bimodal AFM to increase the contrast stemming from magnetic interaction with a ferromagnetic tip.…”

“…12 More recently, Santos and coworkers have started to consider the advantages of small oscillations in both flexural modes. 15,21 In order to optimize the bimodal measurements for atomic resolution in both modes, data should be acquired with small amplitudes in both the first and second flexural modes. 15 This requires the use of a much stiffer sensor.…”

“…15,21 In order to optimize the bimodal measurements for atomic resolution in both modes, data should be acquired with small amplitudes in both the first and second flexural modes. 15 This requires the use of a much stiffer sensor. In this Letter, we present data acquired with a qPlus sensor.…”

Optimization of phase contrast in bimodal amplitude modulation AFM

“…It has several configurations depending on the feedback schemes [16][17][18][19][20][21][22][23][24]. In the first bimodal AFM configuration (bimodal AM) [15,16], the feedback acts on the amplitude of the first mode by keeping it at a fixed value during imaging while the second mode operates in an open loop.…”

Phase contrast and operation regimes in multifrequency atomic force microscopy

“…The single frequency virial that controls the phase shift might undergo transitions in sign while the average force (modal virial) remains positive (negative). Multifrequency atomic force microscopy (AFM) is an emerging 1,2 branch of AFM where two or more frequencies 3,4 are externally excited in order to map material composition, [5][6][7] enhance resolution 8 and sensitivity, [9][10][11] and quantify material properties [12][13][14] with gentle forces. The theory that controls the response of the cantilever while simultaneously exciting several frequencies and modes however is still emerging 12,15,16 and might result complex.…”