Biaxial atomically resolved force microscopy based on a qPlus sensor operated simultaneously in the first flexural and length extensional modes

Abstract

Frequency-modulation atomic force microscopy (AFM) with a qPlus sensor allows one to atomically resolve surfaces in a variety of environments ranging from low-temperature in ultra-high vacuum to ambient and liquid conditions. Typically, the tip is driven to oscillate vertically, giving a measure of the vertical force component. However, for many systems, the lateral force component provides valuable information about the sample. Measuring lateral and vertical force components simultaneously by oscillating vertically and laterally has so far only been demonstrated with relatively soft silicon cantilevers and optical detection. Here, we show that the qPlus sensor can be used in a biaxial mode with electrical detection by making use of the first flexural mode and the length extensional mode. We describe the necessary electrode configuration as well as the electrical detection circuit and compare the length extensional mode to the needle sensor. Finally, we show atomic resolution in ambient conditions of a mica surface and in ultra-high vacuum of a silicon surface. In addition to this, we show how any qPlus AFM setup can be modified to work as a biaxial sensor, allowing two independent force components to be recorded.

Simultaneous Deconvolution of In‐Plane and Out‐of‐Plane Forces of HOPG at the Atomic Scale under Ambient Conditions by Multifrequency Atomic Force Microscopy

“…However, although the combination of in‐plane and out‐of‐plane oscillation modes is feasible, the implementation is not straightforward because qPlus sensors require some nonstandard AFM equipment. [ 15–17 ] Another option for achieving ultrasmall oscillation amplitudes is to exploit higher flexural cantilever eigenmodes because they are stiffer than the fundamental eigenmode. Atomic resolution has been shown successfully on different substrates in air when higher eigenmodes were used for the amplitude or frequency‐shift feedback.…”

Measuring sliding friction at the atomic scale

“…We have recently demonstrated that both LFM and AFM are possible with a qPlus sensor by using the length-extension and first flexural modes at room temperature. 37) Yamada et al have also proposed implementing simultaneous LFM measurements with a longer tip that will oscillate laterally at the second flexural mode. 38) LFM is an exciting technique that is relatively straightforward to implement in any existing qPlus-based system.…”

A cantilever-based, ultrahigh-vacuum, low-temperature scanning probe instrument for multidimensional scanning force microscopy

“…Line 4: Tuning fork sensor [13] operated in its flexural mode for comparison with lines 1-3. Line 5: For bi-axial force gradient measurements with a tuning fork [65], its length extension mode was used to map the vertical force gradient. Line 6: The cantilever with the properties given in line 3 now compared to the sensitivity of the tuning fork length extension mode given in line 5.…”