Arseny Kalinin1 Stanislav Leesment1 Vyacheslav Polyakov1

1, NT-MDT Spectrum Instruments, Moscow, , Russian Federation

We present our recent development of a new group of atomic force microscopy (AFM) modes for non-destructive piezoelectric and thermoelectric studies simultaneously with topography and quantitative nanomechanical measurements. These modes – HybriD Piezoresponse Force Microscopy (HD PFM) and HybriD Scanning Thermoelectric Microscopy (HD SThEM) are extensions of recently introduced HybriD mode (HD mode) – scanning technique based on fast force-distance curves measurements with real-time processing of tip response [1]. In HD AFM mode, the sample or the tip is driven into a vertical oscillation and in every cycle the tip goes from non-contact to contact regime so wealth of useful information can be detected, also mapped during lateral scanning: topography, tip-sample adhesion force and quantitative value of E modulus. Additional signals can be also applied and recorded in operator-defined “time window”. For example current through conductive tip and sample can be measured during tip-surface contact for conductivity mapping of soft and loose samples together with above mentioned properties [2].
HD PFM and HD SThEM modes are also based on “time window” approach. In HD PFM mode an AC voltage is applied on the conductive coating of the tip when tip comes in contact with the sample while fast force spectroscopy. AC voltage causes mechanical oscillations of the piezoelectric (ferroelectric) sample and corresponding vertical and lateral motion of the AFM tip is recorded and processed to get amplitude and phase characterizing local piezoelectric coefficient and local polarization direction respectively. Since AFM tip retracts from the surface in each scanning point, the lateral tip-sample interaction force is noticeably reduced in comparison to conventional contact PFM technique. This opens-up the ability of piezoresponse studies of soft, loose and fragile objects like biological samples, nanoparticles etc. Additionally a thermal drift of the cantilever (for example caused by the samples temperature exchange) can be automatically compensated allowing in situ PFM measurements under variable temperature.
HD SThEM mode working principle is based on direct measurement of generated voltage when conductive tip and sample under different temperatures contact each other (Seebeck’s effect) while fast force spectroscopy measurement. This allows non-destructive mapping of Seebeck coefficient with tip radius-limited spatial resolution.
We demonstrate HD PFM and HD SThEM modes in its application to different types of nanostructures: diphenylalanine peptide nanotubes, collagen type-I matrix, tin-bismuth alloy and triglycine sulfate crystal while second-order phase translation.
[1] S. Magonov et al, Scanning probe based apparatus and methods for low-force profiling of sample surfaces in non-resonant oscillatory mode, US9110092B1, 2015.
[2] J. Montenegro et al, Coupling of carbon and peptide nanotubes, J. Am. Chem. Soc. 136 (2014) 2484–2491.