Now showing 1 - 3 of 3
  • Publication
    Frequency modulation atomic force microscopy in ambient environments utilizing robust feedback tuning
    (American Institute of Physics, 2009-02-02) ; ; ;
    Frequency modulation atomic force microscopy (FM-AFM) is rapidly evolving as the technique of choice in the pursuit of high resolution imaging of biological samples in ambient environments. The enhanced stability afforded by this dynamic AFM mode combined with quantitative analysis enables the study of complex biological systems, at the nanoscale, in their native physiological environment. The operational bandwidth and accuracy of constant amplitude FM-AFM in low Q environments is heavily dependent on the cantilever dynamics and the performance of the demodulation and feedback loops employed to oscillate the cantilever at its resonant frequency with a constant amplitude. Often researchers use ad hoc feedback gains or instrument default values that can result in an inability to quantify experimental data. Poor choice of gains or exceeding the operational bandwidth can result in imaging artifacts and damage to the tip and/or sample. To alleviate this situation we present here a methodology to determine feedback gains for the amplitude and frequency loops that are specific to the cantilever and its environment, which can serve as a reasonable "first guess", thus making quantitative FM-AFM in low Q environments more accessible to the nonexpert. This technique is successfully demonstrated for the low Q systems of air (Q∼40) and water (Q∼1). In addition, we present FM-AFM images of MC3T3-E1 preosteoblast cells acquired using the gains calculated by this methodology demonstrating the effectiveness of this technique.
    Scopus© Citations 28  627
  • Publication
    Dual harmonic Kelvin probe force microscopy for surface potential measurements of ferroelectrics
    In this work, we implemented dual harmonic Kelvin probe force microscopy (DH-KPFM) for surface potential mapping of ferroelectric thin films, namely bismuth ferrite (BFO) and strontium barium niobate (SBN). We applied DH and conventional KPFM to charge-patterned BFO and found agreement between recorded relative surface potential values between domains, demonstrating that DH-KPFM can be used for quantitative mapping of relative surface potentials. We used piezoresponse force microscopy (PFM) to determine whether polarization switching had occurred. From the PFM data, we found that BFO was poled successfully, and that the measured surface potential was consistent with the sign of the bound polarization charge. For SBN, a thin surface layer was evident in the topography after the application of DC bias, suggesting an electrochemical reaction had taken place between the tip and the sample. We used DH-KPFM to simultaneously map the surface potential and changes in the dielectric properties resulting from this surface layer. The results presented herein demonstrate that DH-KPFM can be used for electric characterization of voltagesensitive materials, and we anticipate that DH-KFPM will become a useful tool for non-intrusive electrical characterization of materials.
    Scopus© Citations 15  623
  • Publication
    High viscosity environments: an unexpected route to obtain true atomic resolution with atomic force microscopy
    Atomic force microscopy (AFM) is widely used in liquid environments, where true atomic resolution at the solid–liquid interface can now be routinely achieved. It is generally expected that AFM operation in more viscous environments results in an increased noise contribution from the thermal motion of the cantilever, thereby reducing the signal-to-noise ratio (SNR). Thus, viscous fluids such as ionic and organic liquids have been generally avoided for high-resolution AFM studies despite their relevance to, e.g. energy applications. Here, we investigate the thermal noise limitations of dynamic AFM operation in both low and high viscosity environments theoretically, deriving expressions for the amplitude, phase and frequency noise resulting from the thermal motion of the cantilever, thereby defining the performance limits of amplitude modulation, phase modulation and frequency modulation AFM. We show that the assumption of a reduced SNR in viscous environments is not inherent to the technique and demonstrate that SNR values comparable to ultra-high vacuum systems can be obtained in high viscosity environments under certain conditions. Finally, we have obtained true atomic resolution images of highly ordered pyrolytic graphite and mica surfaces, thus revealing the potential of high-resolution imaging in high viscosity environments.
    Scopus© Citations 7  415