Advanced atomic force microscopy techniques V

• Philipp Rahe,
• Ilko Bald,
• Nadine Hauptmann,
• Regina Hoffmann-Vogel,
• Harry Mönig and
• Michael Reichling

Beilstein J. Nanotechnol. 2025, 16, 54–56, doi:10.3762/bjnano.16.6

• . Grévin et al. further push the boundaries of the detection by implementing an open-loop variant of KPFM which accesses the spectrum of a time-periodic surface potential [5]. By exploiting a double heterodyne frequency mixing effect, they can selectively transfer each harmonic component to the second

Dual-heterodyne Kelvin probe force microscopy

• Benjamin Grévin,
• Fatima Husainy,
• Dmitry Aldakov and
• Cyril Aumaître

Beilstein J. Nanotechnol. 2023, 14, 1068–1084, doi:10.3762/bjnano.14.88

• Benjamin Grevin Fatima Husainy Dmitry Aldakov Cyril Aumaitre Univ. Grenoble Alpes, CNRS, CEA, IRIG-SyMMES, 38000 Grenoble, France 10.3762/bjnano.14.88 Abstract We present a new open-loop implementation of Kelvin probe force microscopy (KPFM) that provides access to the Fourier spectrum of the

• ability to detect weak SPV signals and perform time-resolved measurements. Before ending this section, two final remarks should be made. DHe-KPFM is an "open loop" variant of KPFM. It does not rely on the application of an "active" compensation bias to probe the electrostatic potential of the sample. It

Comparing the performance of single and multifrequency Kelvin probe force microscopy techniques in air and water

• Jason I. Kilpatrick,
• Emrullah Kargin and
• Brian J. Rodriguez

Beilstein J. Nanotechnol. 2022, 13, 922–943, doi:10.3762/bjnano.13.82

• that are most suitable for operation in liquid environments where bias application can lead to unwanted electrochemical reactions. We conclude that open-loop multifrequency KPFM modes operated with the first harmonic of the electrostatic response on the first eigenmode offer the best performance in

• liquid environments whilst needing the smallest AC bias for operation. Keywords: AFM; atomic force microscopy; closed loop; Kelvin probe force microscope; KPFM; open loop; performance; signal-to-noise ratio; Introduction Atomic force microscopy (AFM) is an enabling technique for the nanoscale mapping

• capable of atomic-scale spatial resolution and nanosecond time resolution under specific conditions. KPFM-based techniques can largely be classified as either “open loop” (OL) or “closed loop” (CL). CL techniques employ a feedback loop to apply a bias to compensate for the electrostatic force (or force

Open-loop amplitude-modulation Kelvin probe force microscopy operated in single-pass PeakForce tapping mode

• Gheorghe Stan and
• Pradeep Namboodiri

Beilstein J. Nanotechnol. 2021, 12, 1115–1126, doi:10.3762/bjnano.12.83

• Gheorghe Stan Pradeep Namboodiri Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA 10.3762/bjnano.12.83 Abstract The open-loop

• probe force microscopy; open loop; surface potential; Introduction Over many years, an abundance of developments and applications has made Kelvin probe force microscopy (KPFM) [1] one of the most versatile nanoscale surface electronic characterization techniques. With its main measurement in terms of

• observed and recorded in OL KPFM measurements and a posteriori analysis can be more inclusive and customized to a given measurement setup. Open-loop AM-KPFM measurements and data analysis in one-pass PFT mode Various OL KPFM methods have been introduced as viable alternatives to the existing CL KPFM

Design of V-shaped cantilevers for enhanced multifrequency AFM measurements

• Mehrnoosh Damircheli and
• Babak Eslami

Beilstein J. Nanotechnol. 2020, 11, 1525–1541, doi:10.3762/bjnano.11.135

• -pass measurement [1]. In bimodal AFM, the first eigenmode is excited at or near the resonance frequency (reserved for topography measurements) while the second eigenmode is in open-loop capturing material composition via phase shift of the second eigenmode. Due to its unique capabilities

Measurement of electrostatic tip–sample interactions by time-domain Kelvin probe force microscopy

• Christian Ritz,
• Tino Wagner and
• Andreas Stemmer

Beilstein J. Nanotechnol. 2020, 11, 911–921, doi:10.3762/bjnano.11.76

• properties of tip and sample, e.g., the dielectric properties of a sample or the quantum capacitance [14]. Furthermore, this signal can be used to adjust the sensitivity of the KFM feedback loop [15]. Open-loop KFM techniques exploit the relationship of the contributions at ωm and 2ωm. Namely, Ulcpd can be

• found from their ratio which otherwise only depends on the parameters of the applied modulation, Uac and Udc. When applying KFM as an open-loop technique, optimization of filter parameters is possible, leading to an improved controller performance [16]. For correct height measurements, it is necessary

• performed on Δftopo, where all electrostatic forces are compensated, including the static contribution . So far, recovering and fitting the Kelvin parabola is known as an open-loop technique, the so-called Kelvin probe force spectroscopy [22][23][24][25]. A real-time closed-loop technique has not been

Implementation of data-cube pump–probe KPFM on organic solar cells

• Benjamin Grévin,
• Olivier Bardagot and
• Renaud Demadrille

Beilstein J. Nanotechnol. 2020, 11, 323–337, doi:10.3762/bjnano.11.24

• ). Great care was taken to stabilize the setup before spectroscopic acquisition in open-loop configuration in order to minimize the impact of the z-drift on the KPFM potential. The residual z-drift less was smaller than 0.4 nm over a time lapse of 40 s, see Figure S1 in Supporting Information File 1

• the KPFM operation. Conclusion We have introduced an alternative approach to pp-KPFM based on the acquisition of spectroscopic curves of the KPFM compensation potential as a function of the pump–probe delay using an open-loop configuration. This configuration simplifies the operation of pp-KPFM, since

A review of demodulation techniques for multifrequency atomic force microscopy

• David M. Harcombe,
• Michael G. Ruppert and
• Andrew J. Fleming

Beilstein J. Nanotechnol. 2020, 11, 76–91, doi:10.3762/bjnano.11.8

• techniques are not discussed in this article. Synchronous demodulation techniques employ a reference oscillator and can be categorized as either open-loop or closed-loop, depending on whether they use feedback to estimate parameters. Open-loop demodulators include the lock-in amplifier and coherent

• in this section. Two distinct categories of synchronous demodulators can be seen; those that employ low-pass filtering of mixing products in open-loop configurations and those that use closed-loop model-based feedback to regulate the error. As shown in a previous work [28], the closed-loop methods

• complexity compared to the Kalman filter, floating point precision was also used to implement these methods. The open-loop methods include the lock-in amplifier and coherent demodulator, which are able to achieve Fs = 120 MHz for three modeled frequencies. In contrast to the closed-loop methods, the open

Direct AFM-based nanoscale mapping and tomography of open-circuit voltages for photovoltaics

• Katherine Atamanuk,
• Justin Luria and
• Bryan D. Huey

Beilstein J. Nanotechnol. 2018, 9, 1802–1808, doi:10.3762/bjnano.9.171

• directly with the AFM probe simultaneous to the repeated property mapping. Specific settings include a load of ca. 1 µN, a line rate of 0.5 Hz, and a low-deflection feedback gain producing near “open loop” scanning and hence an essentially planar surface milling [8]. Approximately 15 nm in depth are

Imaging of viscoelastic soft matter with small indentation using higher eigenmodes in single-eigenmode amplitude-modulation atomic force microscopy

• Miead Nikfarjam,
• Enrique A. López-Guerra,
• Santiago D. Solares and
• Babak Eslami

Beilstein J. Nanotechnol. 2018, 9, 1116–1122, doi:10.3762/bjnano.9.103

• [4], the first eigenmode of the cantilever is excited using the AM-AFM method and used for measuring topography, while a higher eigenmode (generally the second eigenmode) is simultaneously excited in “open loop” (with constant drive amplitude and frequency) to map the surface properties of the

High-stress study of bioinspired multifunctional PEDOT:PSS/nanoclay nanocomposites using AFM, SEM and numerical simulation

• Alfredo J. Diaz,
• Hanaul Noh,
• Tobias Meier and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2017, 8, 2069–2082, doi:10.3762/bjnano.8.207

• while the scanning conductive tip served as a movable nanoelectrode in continuous contact with the sample (Figure 6a). Bimodal AFM was used in the so-called amplitude modulated-open loop (AM-OL) scheme (shown in Figure 6b). In this scheme, the cantilever is excited at two eigenfrequencies simultaneously

A review of demodulation techniques for amplitude-modulation atomic force microscopy

• Michael G. Ruppert,
• David M. Harcombe,
• Michael R. P. Ragazzon,
• S. O. Reza Moheimani and
• Andrew J. Fleming

Beilstein J. Nanotechnol. 2017, 8, 1407–1426, doi:10.3762/bjnano.8.142

• implementations, or a sinusoid, most commonly used for digital implementations as is the case in this paper. Within the class of demodulators using mixing, further classification can be made based on how the 2fc component from the mixing process is filtered out. While the open-loop methods rely on either general

Role of solvents in the electronic transport properties of single-molecule junctions

• Katharina Luka-Guth,
• Sebastian Hambsch,
• Andreas Bloch,
• Philipp Ehrenreich,
• Bernd Michael Briechle,
• Filip Kilibarda,
• Torsten Sendler,
• Dmytro Sysoiev,
• Thomas Huhn,
• Artur Erbe and
• Elke Scheer

Beilstein J. Nanotechnol. 2016, 7, 1055–1067, doi:10.3762/bjnano.7.99

• . The open-loop effects develop non-uniformly with time when continuously stretching a sample and may disappear abruptly when having closed the contact again. For all solvents except for IPA it was also possible to record I–Vs without current offset at zero voltage. The open-loop curves were discarded

• abundance of open-loop effects; 2. the percentage of I–Vs being well described by the SLM; 3. the similarity of best-fit parameters with the SLM or SM with those of typical functional molecules; 4. the probability of step-formation in the stretching curves. For a given solvent, all these values should be

• junctions analysed in detail here. This estimation suggests that the high-conductance junctions formed in IPA and Tol/THF might reveal contributions of direct conductance through the solvent, while pure EtOH may still be considered as tunnel barrier. EtOH and IPA show the open-loop effect most prominently

Kelvin probe force microscopy for local characterisation of active nanoelectronic devices

• Tino Wagner,
• Hannes Beyer,
• Patrick Reissner,
• Philipp Mensch,
• Heike Riel,
• Bernd Gotsmann and
• Andreas Stemmer

Beilstein J. Nanotechnol. 2015, 6, 2193–2206, doi:10.3762/bjnano.6.225

• major methods to find the local contact potential difference at every point during the scan. Open-loop KFM exploits the fact that the 2ωm amplitudes do depend on C'' but not on Udc − Ulcpd. As demonstrated in Figure 4, the ratio of the ωm and 2ωm sidebands is independent of changes in C'' and only

• open-loop method. A PLL can reduce these effects, but then its transfer function needs to be considered as well [27], and the bandwidth must be larger than 2ωm. In closed-loop KFM, the local contact potential difference is found by nullifying the in-phase components of the ωm sidebands (Equation 13

• dynamic AFM modes. Precise knowledge of their frequency dependence in low and high Q environments is not only neccessary for accurate open-loop KFM techniques, but also offers a direct approach to noise performance and optimisation of frequency modulated KFM [19]. For example, ωm should ideally be chosen

Closed-loop conductance scanning tunneling spectroscopy: demonstrating the equivalence to the open-loop alternative

• Chris Hellenthal,
• Kai Sotthewes,
• Martin H. Siekman,
• E. Stefan Kooij and
• Harold J. W. Zandvliet

Beilstein J. Nanotechnol. 2015, 6, 1116–1124, doi:10.3762/bjnano.6.113

• using closed-loop z(V) conductance scanning tunneling spectroscopy (STS) measurements for the determination of the effective tunneling barrier by comparing them to more conventional open-loop I(z) measurements. Through the development of a numerical model, the individual contributions to the effective

• making a spatial map of the LDOS, standing wave patterns and local electron distributions can be visualized, enabling further understanding of the exact local quantum behavior of features on the surface [3][4]. LDOS information is typically extracted through open-loop I(V) measurements, although recent

• equation as follows: Substituting Equation 5 then gives Working through all the partial derivatives (see Supporting Information File 1 for a full derivation) eventually yields with This resulting equation can be used to determine the work function and image charge constant ζ from a standard, open-loop I(z

Optimization of phase contrast in bimodal amplitude modulation AFM

• Mehrnoosh Damircheli,
• Amir F. Payam and
• Ricardo Garcia

Beilstein J. Nanotechnol. 2015, 6, 1072–1081, doi:10.3762/bjnano.6.108

• on the feedback schemes [16][17][18][19][20][21][22][23][24]. In the first bimodal AFM configuration (bimodal AM) [15][16], the feedback acts on the amplitude of the first mode by keeping it at a fixed value during imaging while the second mode operates in an open loop. The ability of bimodal AM to

• dForce simulator [49]. Phase contrast in the attractive regime (no dissipation): A02 > A01 (inverted bimodal excitation) In the first bimodal AM experiments the first mode carried the feedback controls while the second has an open loop (no feedback). This configuration introduced a significant asymmetry

• between the roles of the excited modes. This raises the question about the equivalence of the excited modes 1 and 2 for bimodal AM operation. To answer this question we have simulated a situation where the feedback operates in the second mode while the first mode has an open loop (inverted bimodal

A scanning probe microscope for magnetoresistive cantilevers utilizing a nested scanner design for large-area scans

• Tobias Meier,
• Alexander Förste,
• Ali Tavassolizadeh,
• Karsten Rott,
• Dirk Meyners,
• Roland Gröger,
• Günter Reiss,
• Eckhard Quandt,
• Thomas Schimmel and
• Hendrik Hölscher

Beilstein J. Nanotechnol. 2015, 6, 451–461, doi:10.3762/bjnano.6.46

• pass towards the camera. The AFM is operated through a commercial AFM controller (Asylum Research). The controller can directly drive open-loop piezo scanners, because of its integrated high-voltage amplifier, as well as closed-loop scanners with an attached high voltage amplifier and closed-loop

• while holding the large-area scanner at a fixed position. The high resolution open-loop scanner is thereby mounted on a large-area scan stage. The high resolution scanner was realized by using a stack of shear actors for x–y scanning and a stack piezo actor with a travel of 5 μm and a resonance

• frequency of 14 kHz while carrying the open-loop scanner. For closed-loop operation of the AFM, this piezo is equipped with a strain gauge sensor which is read out by the AFM controller. Results and Discussion Characterization of the microscope For successful switching from the large scanner to the nested

Kelvin probe force microscopy in liquid using electrochemical force microscopy

• Liam Collins,
• Stephen Jesse,
• Jason I. Kilpatrick,
• Alexander Tselev,
• M. Baris Okatan,
• Sergei V. Kalinin and
• Brian J. Rodriguez

Beilstein J. Nanotechnol. 2015, 6, 201–214, doi:10.3762/bjnano.6.19

• dynamics and electrochemical processes [39][40][41][42][43]. One approach to avoid diffuse charge dynamics has been to implement KPFM in non-polar solutions [39]. Open loop-KPFM approaches, offering a promising approach for measuring electrostatic properties in ionically-active liquids, have also been

• previously reported [40][41][42][43]. In general, open loop-KPFM does not require the application of a DC bias via a feedback loop and can be performed by utilizing either (i) both AC voltage and DC bias (referred to here as open loop bias spectroscopy, OLBS) [44], or (ii) AC voltage alone (referred to here

Probing viscoelastic surfaces with bimodal tapping-mode atomic force microscopy: Underlying physics and observables for a standard linear solid model

• Santiago D. Solares

Beilstein J. Nanotechnol. 2014, 5, 1649–1663, doi:10.3762/bjnano.5.176

• paper this mode of operation is referred to as AM-OL since the first mode is driven by using amplitude-modulation and the second mode is driven in ‘open loop’). Since the settings of the higher eigenmode are not controlled by the AM-AFM loop, its excitation amplitude (and in principle also the drive

• ][35][36] methods. Within multi-frequency AFM, Lozano et al. analyzed the behavior of Vts and Pts for the original bimodal AFM method, which uses an open loop drive to excite the higher eigenmode [32][37]. Naitoh and coworkers reported bimodal experiments by using FM-AFM to drive both eigenmodes, in

• order to simultaneously acquire the topography and quantify the elasticity of a Ge(001) surface with high resolution [17]. Li and coworkers used a bimodal method in which the first eigenmode was driven by using the phase modulation scheme and the higher mode was driven in open loop, which allowed them

Multi-frequency tapping-mode atomic force microscopy beyond three eigenmodes in ambient air

• Santiago D. Solares,
• Sangmin An and
• Christian J. Long

Beilstein J. Nanotechnol. 2014, 5, 1637–1648, doi:10.3762/bjnano.5.175

• future research opportunities. Keywords: amplitude-modulation; bimodal; frequency-modulation; multi-frequency atomic force microscopy; multimodal; open loop; trimodal; Introduction Multi-frequency atomic force microscopy (AFM) refers to a family of techniques in which the microcantilever probe is

• higher modes are excited by using constant drive frequency and amplitude without any feedback (i.e., in ‘open loop’ [2][3]). In such cases, as long as the oscillation is not chaotic, the user will generally be able to obtain an image, but imaging stability does not guarantee that the results are

• , and that the work reported here represents by no means an exhaustive study. High-damping environments may offer even greater complexities [31] and our amplitude-modulation/open-loop results are not directly applicable to vacuum environments [24][32]. Methods Experimental The tetramodal experiments

Trade-offs in sensitivity and sampling depth in bimodal atomic force microscopy and comparison to the trimodal case

• Babak Eslami,
• Daniel Ebeling and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2014, 5, 1144–1151, doi:10.3762/bjnano.5.125

• modulation to acquire the topography through the first cantilever eigenmode, and drives a higher eigenmode in open-loop to perform compositional mapping. This method is attractive due to its relative simplicity, robustness and commercial availability. We show that this technique offers the capability to

• ; multifrequency atomic force microscopy; indentation depth modulation; Nafion; open loop; proton exchange membranes; trimodal; Introduction Since its invention in the early 1980s [1], atomic force microscopy (AFM) has become one of the most widely used characterization tools in nanotechnology and a wide range of

• eigenmode of the cantilever is driven using the amplitude modulation scheme (AM-AFM [14]) while a higher eigenmode is simultaneously driven at or near its resonance frequency with constant amplitude and frequency (i.e., in “open loop”) in order to track its phase with respect to the excitation signal. Since

Challenges and complexities of multifrequency atomic force microscopy in liquid environments

• Santiago D. Solares

Beilstein J. Nanotechnol. 2014, 5, 298–307, doi:10.3762/bjnano.5.33

• discussion are mostly applicable to the cases where higher eigenmodes are driven in open loop and frequency modulation within bimodal schemes, but some concepts are also applicable to other types of multifrequency operations and to single-eigenmode amplitude and frequency modulation methods. Keywords

• these methods was proposed by García and coworkers in 2004 to carry out simultaneous non-contact amplitude-modulation imaging and open-loop (phase contrast) compositional mapping of surfaces in air by exciting and controlling the first two eigenmodes of the cantilever [2]. This approach has since been

• extended to intermittent contact characterization using open loop and frequency modulation [3][4], imaging in liquid and vacuum environments [5][6][7][8], and to trimodal operation [9][10][11]. There also exist a number of other multifrequency and multiharmonic AFM techniques which have been developed for

Unlocking higher harmonics in atomic force microscopy with gentle interactions

• Sergio Santos,
• Victor Barcons,
• Josep Font and
• Albert Verdaguer

Beilstein J. Nanotechnol. 2014, 5, 268–277, doi:10.3762/bjnano.5.29

• , and by driving with sufficiently small (sub-nanometer) second mode amplitudes, the first mode amplitude [24] or frequency [17] can be employed to track the sample in amplitude or frequency modulation (AM and FM), respectively. The second mode can then be left as an open loop for high sensitivity

Noise performance of frequency modulation Kelvin force microscopy

• Heinrich Diesinger,
• Dominique Deresmes and
• Thierry Mélin

Beilstein J. Nanotechnol. 2014, 5, 1–18, doi:10.3762/bjnano.5.1

• knowledge has not yet been applied to noise propagation in scanning probe microscopy. The PLL output noise PSD is now obtained using the noise gain formalism: Regarding the PLL forward gain APLL, Equation 7, it is noteworthy that the open loop gain of the phase as function of frequency excursion has the

• bias is applied. The objective is to cancel the CPD by applying a Kelvin voltage to the tip such that CPD − VK = 0. Open loop forward gain The CPD, the Kelvin voltage, VK, and the AC voltage, Vmod, cause an electrostatic field gradient that alters the resonance frequency: The assumption of a constant

• crossing matters, but not the height of the plateau of the |1/FK| function. In the P–I representation, the IK component would need to be set to a specific value while the PK could be varied in a wide range. With the known open loop forward gain and output noise PSD (Δf)n of the PLL, it is possible to

Bimodal atomic force microscopy driving the higher eigenmode in frequency-modulation mode: Implementation, advantages, disadvantages and comparison to the open-loop case

• Daniel Ebeling and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2013, 4, 198–207, doi:10.3762/bjnano.4.20

• the amplitude-modulation (AM) scheme while the second eigenmode was driven with a much smaller amplitude in open loop (OL, that is, only the first mode amplitude signal was used to control the tip–sample distance feedback loop. The second eigenmode drive signal had a constant amplitude and frequency

• , namely AM-OL, AM-FM (CE), and AM-FM (CA), which differ in the type of control scheme used to drive the higher eigenmode (open loop, constant-excitation frequency-modulation, and constant-amplitude frequency-modulation, respectively). The corresponding higher eigenmode channels exhibit clear differences