Effect of lateral tip motion on multifrequency atomic force microscopy

Abstract

In atomic force microscopy (AFM), the angle relative to the vertical ($\theta_{i}$) that the tip apex of a cantilever moves is determined by the tilt of the probe holder and the geometries of the cantilever and actuated eigenmode $i$. Even though the effects of $\theta_{i}$ on static and single-frequency AFM are known (increased effective spring constant, sensitivity to sample anisotropy, etc), the higher eigenmodes used in multifrequency force microscopy lead to additional effects that have not been fully explored. Here we use Kelvin probe force microscopy (KPFM) to investigate how $\theta_{i}$ affects not only the signal amplitude and phase, but can also lead to behaviors such as destabilization of the KPFM voltage feedback loop. We find that longer cantilevers and modified sample orientations improve voltage feedback loop stability, even though variations to scanning parameters such as cantilever shake amplitude and lift height do not.Comment: 5 pages of text, 5 figures. Revision replaces discussion of bimodal AFM with more discussion of experimental result

Exclusive Magnetic Excitation Enabled by Structured Light Illumination in a Nanoscale Mie Resonator

“…In contrast to optical microscopy that sees specimens from far-field probing of the scattered field, the PiFM feels specimens directly from the near-field interaction force between a subwavelength probe-tip and the sample surface. ,− PiFM possesses the merits that are desired for our purpose. Most importantly, force detection enables the measurement of photoinduced electric or magnetic forces which can be related to the corresponding electric or magnetic material properties. ,,,, Furthermore, the photoinduced force exerted on the probe-tip is always local on a subwavelength scale and independent of background scattering photons, in contrast to far-field microscopy. ,− Therefore, PiFM has a high intrinsic resolution, limited only by the size of the tip, and low background noise. , Finally, the force is a vector quantity with both amplitude and direction, which provides more information than the detected power in far-field light scattering measurements. − The instrument used here employs a gold-coated tip, as the probe of the photoinduced electric force in a modified atomic force microscopy (AFM) system. ,,,, The PiFM detects the photoinduced electric force that indicates the local electric field intensity distribution of light near a nanoscale sample, with superior signal-to-noise ratio (SNR) and stability compared to light scattering based techniques such as near-field scanning optical microscopy (NSOM). ,, …”

Multiscale Functional Imaging of Interfaces through Atomic Force Microscopy Using Harmonic Mixing

“…Because the HM technique relies on modifying a signal’s d -dependence to control the spatial resolution, we first test its ability to effectively tailor this d -dependence. We apply an ac voltage to the probe and use the F 2ω force to drive oscillations at ω D because it is insensitive to potential changes that would otherwise affect the magnitude of the generated signal . Signal versus separation curves are plotted in Figure for n = 0–3.…”

“…Because the AFM already detects the cantilever’s displacement, the amplitude of the separation oscillation can be directly monitored and controlled. In addition, the direction of modulation can be controlled through the choice of actuated eigenmodes, which can be used to map in-plane forces. ,, As the separation changes, the total tip–sample force is itself modulated at ω M . Mixing the force modulation at ω M with motion at ω T generates a force at ω D .…”

“…We apply an ac voltage to the probe and use the F 2ω force to drive oscillations at ω D because it is insensitive to potential changes that would otherwise affect the magnitude of the generated signal. 53 Signal versus separation curves are plotted in Figure 2 for n = 0−3. The signals' d-dependence is found to roughly follow the predicted power laws, with n = 0 and 1 showing excess signal at large separations because of stray capacitance from the cantilever that is not included in the model (discussed below) and n = 2 and 3 showing excess signal at short separations.…”

Enhancing multiple harmonics in tapping mode atomic force microscopy by added mass with finite size

“…[1][2][3][4] The intermittent contact between the tip and the sample surface substantially reduces the lateral force, and explains its ability to image soft materials, such as DNA, cells or polymers. [5][6] The decay length of the interaction force is, however, less than the cantilever oscillation amplitude, leading to highly nonlinear characteristics in the dynamics. [7][8] The nonlinearity could introduce higher harmonic components in the cantilever's motion, which are integer multiple of the excitation frequency.…”