Chemical bond imaging using torsional and flexural higher eigenmodes of qPlus sensors

Abstract

Non-contact atomic force microscopy (AFM) with CO-functionalized tips allows visualizing the chemical structure of individual adsorbed molecules. Particularly high image contrast is observed by exciting a torsional eigenmode of the AFM sensor.

Experimental validation of contact resonance AFM using long massive tips

“…In recent years, scientists have used AFM sensors equipped with nano-needles [3][4][5][6][7][8][9][10] and quartz tuning fork sensors [11][12][13][14][15][16] to probe biological samples in their natural physiological liquid environment, while the sensor's body remains out of the liquid and is therefore not affected by hydrodynamic forces (Trolling Mode). The colloidal probe is another form of large, massive-tip sensor, widely used by the AFM community [17][18][19][20][21][22][23][24] to probe samples that might be damaged from an ultra-sharp tip.…”

Fundamental and higher eigenmodes of qPlus sensors with a long probe for vertical-lateral bimodal atomic force microscopy

“…The effective spring constant of the qPlus sensor with a long probe was already analyzed by FEM 28,30,31 . Some methods to calibrate the amplitude of the higher mode of the qPlus sensor with a long probe were proposed, such as scanning electron microscopy 28,30 and laser Doppler vibrometry 31,32 . Furthermore, analysis of piezoelectric sensitivity, which is the ratio of the output voltage signals to the tip oscillation am- plitude, is crucial because it determines the deflection noise density, which dominates the minimum detectable force gradient in AFM 33 .…”

“…There is another way to oscillate the probe apex laterally, which uses the higher eigenmodes of the QTF sensor with a long probe. 20,[28][29][30][31][32] Higuchi et al analyzed the eigenmodes of the QTF sensor with an angled-attached long probe by the nite element method (FEM). 28 They revealed the lateral tip oscillation in the second mode and demonstrated topographic imaging with the sensor.…”

“…28,30,31 Some methods to calibrate the amplitude of the higher mode of the qPlus sensor with a long probe were proposed, such as scanning electron microscopy 28,30 and laser Doppler vibrometry. 31,32 Furthermore, the analysis of piezoelectric sensitivity, which is the ratio of the output voltage signals to the tip oscillation amplitude, is crucial because it determines the deection noise density, which dominates the minimum detectable force gradient in AFM. 33 Although several research groups have analyzed the piezoelectric current, 30 to the best of our knowledge, there have been no studies analyzing piezoelectric sensitivity.…”