Amplitude or frequency modulation-detection in Kelvin probe force microscopy

Glatzel, Thilo; Sadewasser, Sascha; Lux‐Steiner, Martha Ch.

doi:10.1016/s0169-4332(02)01484-8

Cited by 213 publications

(194 citation statements)

References 18 publications

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“…This is a consequence of the contributions of the cantilever and the tip shank to the KPFM signal in the AM mode, which are stronger on insulating samples. The same conclusion has previously been reached in comparisons of AM-and FM-KPFM measurements of long-range LCPD variations; such variations are caused by interactions of the biased probe with CPD inhomogeneities and surface charges on scales of several nanometers and above on conducting samples partly covered with ultrathin overlayers of different materials 13,31 . However, the strong mode-dependent influence of distant contributions to dC/ds on the atomicscale LCPD contrast has, to our knowledge, not been recognized because previous work on this topic assumed that only the tip apex mattered at sub-nanometer separations.…”

Section: Discussionsupporting

confidence: 78%

“…This effect is less pronounced in FMthan in AM-KPFM. 13,27,31,32 Several researchers developed models and computational schemes based on classical electrostatics which treated the tip and the sample (sometimes also the cantilever) as macroscopic bodies in order to interpret the resolution of KPFM images of inhomogeneous surfaces on lateral scales of several nanometers and above. [33][34][35][36][37][38][39][40] On the other hand, only few authors considered atomistic nano-scale tip-sample systems, either neglecting 16,41 or including the macroscopic contributions via simple approximations.…”

Section: 23mentioning

confidence: 99%

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Multiscale approach for simulations of Kelvin probe force microscopy with atomic resolution

et al. 2012

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The distance dependence and atomic-scale contrast recently observed in nominal contact potential difference (CPD) signals simultaneously recorded by KPFM using non-contact atomic force microscopy (NCAFM) on defect-free surfaces of insulating, as well as semiconducting samples, have stimulated theoretical attempts to explain such effects. Especially in the case of insulators, it is not quite clear how the applied bias voltage affects electrostatic forces acting on the atomic scale. We attack this problem in two steps. First, the electrostatics of the macroscopic tip-cantilever-sample system is treated by a finite-difference method on an adjustable nonuniform mesh. Then the resulting electric field under the tip apex is inserted into a series of atomistic wavelet-based density functional theory (DFT) calculations. Results are shown for a realistic neutral but reactive silicon nano-scale tip interacting with a NaCl(001) sample. Bias-dependent forces and resulting atomic displacements are computed to within an unprecedented accuracy.Theoretical expressions for amplitude modulation (AM) and frequency modulation (FM) KPFM signals and for the corresponding local contact potential differences (LCPD) are obtained by combining the macroscopic and atomistic contributions to the electrostatic force component generated at the voltage modulation frequency, and evaluated for several tip oscillation amplitudes A up to 10 nm. For A = 0.1Å, the computed LCPD contrast is proportional to the slope of the atomistic force versus bias in the AM mode and to its derivative with respect to the tip-sample separation in the FM mode. Being essentially constant over a few Volts, this slope is the basic quantity which determines variations of the atomic-scale LCPD contrast. Already above A = 1Å, the LCPD contrasts in both modes exhibit almost the same spatial dependence as the slope. In the AM mode, this contrast is approximately proportional to A −1/2 , but remains much weaker than the contrast in the FM mode, which drops somewhat faster as A is increased. These trends are a consequence of the macroscopic contributions to the KPFM signal, which are stronger in the AM-mode and especially important if the sample is an insulator even at sub-nanometer separations where atomic-scale contrast appears.

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Section: Discussionsupporting

confidence: 78%

Section: 23mentioning

confidence: 99%

Multiscale approach for simulations of Kelvin probe force microscopy with atomic resolution

et al. 2012

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“…This indicates that δV cpd is proportional to k/Q. In typical AM-KPFM measurements [17] where the second flexural mode oscillation is used for detecting electrostatic force, the improvement of δV cpd by the enhanced Q factor is partially cancelled by the substantially higher dynamic spring constant of the second mode with k 2nd ≈ 40k [22]. D-KPFM enables to fully take advantage of the resonance enhancement while retaining the advantages of the single-pass FM-AFM.…”

Section: Resultsmentioning

confidence: 99%

Kelvin Probe Force Microscopy by Dissipative Electrostatic Force Modulation

et al. 2015

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We report a new experimental technique for Kelvin probe force microscopy (KPFM) using the dissipation signal of frequency modulation atomic force microscopy for bias voltage feedback. It features a simple implementation and faster scanning as it requires no low frequency modulation. The dissipation is caused by the oscillating electrostatic force that is coherent with the tip oscillation, which is induced by a sinusoidally oscillating voltage applied between the tip and sample. We analyzed the effect of the phase of the oscillating force on the frequency shift and dissipation and found that the relative phase of 90 • that causes only the dissipation is the most appropriate for KPFM measurements. The present technique requires a significantly smaller ac voltage amplitude by virtue of enhanced force detection due to the resonance enhancement and the use of fundamental flexural mode oscillation for electrostatic force detection. This feature will be of great importance in the electrical characterizations of technically relevant materials whose electrical properties are influenced by the externally applied electric field as is the case in semiconductor electronic devices.

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“…A feedback loop minimizes the oscillations by applying a DC voltage (V DC ) to the probe to negate the contact potential difference (CPD) between the probe and the surface (defined here as V 0 = V tip − V surf ace ). This method has been used to measure SP for two decades [23], but suffers from low spatial resolution relative to FM-KPFM [24,25]. A recent variant, HAM-KPFM [26] increases the spatial resolution by removing cantileverinduced capacitive artifacts [27], and is implemented on our AFM (Cypher, Asylum Research) with an external frequency multiplier (Minicircuits ZAD-8+) and a homemade bandpass filter/amplifier (see Figure 1).…”

Section: Kelvin Probe Force Microscopymentioning

confidence: 99%

The effect of patch potentials in Casimir force measurements determined by heterodyne Kelvin probe force microscopy

Garrett

Somers

Munday

2015

J. Phys.: Condens. Matter

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Abstract.Measurements of the Casimir force require the elimination of electrostatic interactions between the surfaces. However, due to electrostatic patch potentials, the voltage required to minimize the total force may not be sufficient to completely nullify the electrostatic interaction. Thus, these surface potential variations cause an additional force, which can obscure the Casimir force signal. In this paper, we inspect the spatially varying surface potential (SP) of e-beamed, sputtered, sputtered and annealed, and template stripped gold surfaces with Heterodyne Amplitude Modulated Kelvin Probe Force Microscopy (HAM-KPFM). It is demonstrated that HAM-KPFM improves the spatial resolution of surface potential measurements compared to Amplitude Modulated Kelvin Probe Force Microscopy (AM-KPFM). We find that patch potentials vary depending on sample preparation, and that the calculated pressure can be similar to the pressure difference between Casimir force calculations employing the plasma and Drude models.

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Amplitude or frequency modulation-detection in Kelvin probe force microscopy

Cited by 213 publications

References 18 publications

Multiscale approach for simulations of Kelvin probe force microscopy with atomic resolution

Multiscale approach for simulations of Kelvin probe force microscopy with atomic resolution

Kelvin Probe Force Microscopy by Dissipative Electrostatic Force Modulation

The effect of patch potentials in Casimir force measurements determined by heterodyne Kelvin probe force microscopy

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