B. Pittenger, C. Li, S. Hu, P. De Wolf
Bruker,
United States
Keywords: AFM, TUNA, sMIM, PFM, PeakForce QNM, peak force tapping
Summary:
Tapping mode and peak force tapping are intermittent contact AFM modes that provide high-resolution maps of topography and properties by analyzing the bending of a cantilever during oscillation near a sample surface. Since the cantilever is not touching the sample for a significant portion of the oscillation cycle, lateral forces remain small, preventing tip and sample wear. If the oscillation occurs well below the cantilever resonance, the frequency response of the probe is roughly constant and it is possible to directly pick out the details of the tip-sample interaction without deconvoluting the cantilever transfer function. PeakForce QNM uses this method to provide nanoscale maps of mechanical properties such as modulus, dissipation, and adhesion. The relatively low frequency of oscillation in peak force tapping also facilitates secondary measurements that can then be localized to a point of time (or Z position) in the oscillation cycle as well as a position in the XY plane. For example, current can be measured only while the tip is in contact with the surface or during a fraction of this contact time (typically centered around the point in time where the peak force is reached) [1]. The same "gated" measurement concept has been applied to contact resonance AFM [2], scanning non-linear dielectric microscopy [3], and kelvin probe force microscopy [4] among others. In addition to providing unique new property maps and protecting the tip and sample from damage, these methods benefit from co-located, simultaneous mapping of mechanical properties. In this talk, we examine the opportunities offered by gated peak force tapping measurements with examples in polymeric materials, semiconductors and 2D heterostructures. The expansion of this approach to other electrical, mechanical & chemical property measurements is reviewed, focusing on properties which are typically collected using contact mode. These operating modes include scanning microwave microscopy (SMIM), scanning capacitance microscopy (SCM), scanning thermal microscopy (SThM), piezoresponse force microscopy (PFM), resonance enhanced AFM-IR, and torsional resonance dynamic friction (TR-DFM also known as torsional force microscopy). We investigate practical aspects of system configuration such as the impact of the position and duration of the ‘gating’ as well as the oscillation frequency on signal-to-noise ratio and signal integrity. [1] S. Desbief, N. Hergué, O. Douhéret, M. Surin, P. Dubois, Y. Geerts, R. Lazzaroni, and P. Leclère, Nanoscale investigation of the electrical properties in semiconductor polymer-carbon nanotube hybrid materials, Nanoscale 4, 2705 (2012). doi: 10.1039/c2nr11888b [2] G. Stan and R. S. Gates, Intermittent contact resonance atomic force microscopy, Nanotechnology 25, 245702 (2014). doi: 10.1088/0957-4484/25/24/245702 [3] K. Yamasue and Y. Cho, Optimization of signal intensity in intermittent contact scanning nonlinear dielectric microscopy, Microelectronics Reliability 100–101, 113345 (2019). doi: 10.1016/j.microrel.2019.06.037 [4] D. S. Jakob, H. Wang, and X. G. Xu, Pulsed Force Kelvin Probe Force Microscopy, ACS Nano acsnano.0c00767 (2020). doi: 10.1021/acsnano.0c00767