Modeling viscoelasticity through spring–dashpot models in intermittent-contact atomic force microscopy

• Enrique A. López-Guerra and
• Santiago D. Solares

Beilstein J. Nanotechnol. 2014, 5, 2149–2163, doi:10.3762/bjnano.5.224

• contact mechanics to incorporate the contact area and sample deformation [7]. The dissipative part of this model, originally introduced by García and coworkers [34] has the following form: where η is the viscosity, R is the tip radius and δ is the sample deformation (tip–sample indentation). In this model

• that at low frequencies the dissipation loop is larger and also the tip position reaches lower values corresponding to a greater tip–sample indentation. As the tip reaches lower values, the minimum of the FD curve when the tip leaves the sample (the left-most minimum in the FD curves, corresponding to

Optical properties and electrical transport of thin films of terbium(III) bis(phthalocyanine) on cobalt

• Peter Robaschik,
• Pablo F. Siles,
• Daniel Bülz,
• Peter Richter,
• Manuel Monecke,
• Michael Fronk,
• Svetlana Klyatskaya,
• Daniel Grimm,
• Oliver G. Schmidt,
• Mario Ruben,
• Dietrich R. T. Zahn and
• Georgeta Salvan

Beilstein J. Nanotechnol. 2014, 5, 2070–2078, doi:10.3762/bjnano.5.215

• TbPc2 films. In order to obtain the current density from the cs-AFM measurements, we follow a similar approach as presented by Reid et al. [26], where the contact area between probe and sample is determined assuming a tip indentation of 1 nm for the same kind of Pt-coated hemispherical probes used in

Dissipation signals due to lateral tip oscillations in FM-AFM

• Michael Klocke and
• Dietrich E. Wolf

Beilstein J. Nanotechnol. 2014, 5, 2048–2057, doi:10.3762/bjnano.5.213

• , the effects that take place are far more complex than having just a single hysteresis loop. Depending on the indentation depth of the tip (or the minimum distance between tip and sample), multiple adhesion hysteresis loops might occur [10]. It can also happen that in some of the cycles, there is no

Mechanical properties of sol–gel derived SiO₂ nanotubes

• Boris Polyakov,
• Mikk Antsov,
• Sergei Vlassov,
• Leonid M Dorogin,
• Mikk Vahtrus,
• Roberts Zabels,
• Sven Lange and
• Rünno Lõhmus

Beilstein J. Nanotechnol. 2014, 5, 1808–1814, doi:10.3762/bjnano.5.191

• ). The problem of indentation of thick-walled elastic NTs was addressed and discussed. To the best of our knowledge, no in situ SEM bending tests, as well as AFM nanoindentation experiments were performed on sol–gel silica NTs previously. Experimental Ag/SiO2 core–shell NWs were synthesized by coating Ag

• indentation is limited to the thin-shell or membrane case [27]. Therefore, for the case of thick shells studied in this work, we employed finite element method (FEM, COMSOL Multiphysics) models instead, where all geometric parameters can be taken into account. The Solid Mechanics module was used, where the

• Poisson ratio ν1 = 0.22; and the shell: Young modulus E2 is to be found and Poisson ν2 = 0.17 [28]. For a reference we have also applied the thin-shell and Hertz models. The thin-shell approach allows one to neglect the indentation of the surface and the tip geometry by taking into account only the

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

• for constant-indentation imaging of the sample with increasing higher mode amplitude (if such a method can be developed) the level of dissipation decreases monotonically, which is as expected, since the SLS has only one characteristic relaxation time (governed by the damper) and the sample deformation

• higher eigenmodes in successive experiments, under constant indentation. The analysis could be repeated at different levels of indentation to give a complete picture of the depth-dependent behavior of the sample. Second, the further development of spectroscopy methods that provide the tip–sample force

Hydrophobic interaction governs unspecific adhesion of staphylococci: a single cell force spectroscopy study

• Nicolas Thewes,
• Peter Loskill,
• Philipp Jung,
• Henrik Peisker,
• Markus Bischoff,
• Mathias Herrmann and
• Karin Jacobs

Beilstein J. Nanotechnol. 2014, 5, 1501–1512, doi:10.3762/bjnano.5.163

• , yet, due to adhesive forces, a deep global minimum is recorded. Further retraction provokes a loss of contact (“jump-off contact”). In the repulsive regime (F > 0), a force of 150 pN is not enough to deform the bacterium: With a force trigger of 150 nN, only an indentation of ca. 10 nm is reached (cf

Surface topography and contact mechanics of dry and wet human skin

• Alexander E. Kovalev,
• Kirstin Dening,
• Bo N. J. Persson and
• Stanislav N. Gorb

Beilstein J. Nanotechnol. 2014, 5, 1341–1348, doi:10.3762/bjnano.5.147

• corneum are very soft. This has been demonstrated in indentation experiments on the inner forearm by using a macroscopic indentor (a ball with a diameter of about 1 cm). The measurements are explained well by using the Hertzian contact theory. The effective elastic modulus was found to be 10–40 kPa [3

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

• experiments on Nafion® proton exchange membranes and numerical simulations illustrating the trade-offs between the optimization of compositional contrast and the modulation of tip indentation depth in bimodal atomic force microscopy (AFM). We focus on the original bimodal AFM method, which uses amplitude

• modulate tip indentation depth, in addition to providing sample topography and material property contrast, although there are important competing effects between the optimization of sensitivity and the control of indentation depth, both of which strongly influence the contrast quality. Furthermore, we

• ; 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

Dry friction of microstructured polymer surfaces inspired by snake skin

• Martina J. Baum,
• Lars Heepe,
• Elena Fadeeva and
• Stanislav N. Gorb

Beilstein J. Nanotechnol. 2014, 5, 1091–1103, doi:10.3762/bjnano.5.122

• and flat surface under an applied normal force F was characterised by the indentation depth d and indentation radius a (Figure 4). The contact radius a can be described by [37]: The relationship between applied force and geometrical deformation can be described by the following formula [37]: where The

• calculated contact area between the tribo-pair on smooth and flat surfaces was 40 µm2 corresponding to a contact radius of 3.5 µm and an indentation depth of 25 nm. The actual contact areas in case of the microstructured surfaces were indeed smaller. The following calculations are dealing with the geometric

• the exact geometry of PGMS topography is listed in Table 3. The measured details are described in Figure 2. The indentation depth h of the glass sphere was calculated according to the following formula modified after Sondhauß et al. [38]. With the indentation radius a and the periodicity of the

Insect attachment on crystalline bioinspired wax surfaces formed by alkanes of varying chain lengths

• Elena Gorb,
• Sandro Böhm,
• Nadine Jacky,
• Louis-Philippe Maier,
• Kirstin Dening,
• Sasha Pechook,
• Boaz Pokroy and
• Stanislav Gorb

Beilstein J. Nanotechnol. 2014, 5, 1031–1041, doi:10.3762/bjnano.5.116

• : first on hydrophilic smooth glass (glass 1), then on one of the wax surfaces, and once more on glass (glass 2). Each insect individual was tested on all wax surfaces. We used 20 male beetles and carried out 240 traction tests in total. Pull-off forces were measured in indentation experiments with the

Scale effects of nanomechanical properties and deformation behavior of Au nanoparticle and thin film using depth sensing nanoindentation

• Dave Maharaj and
• Bharat Bhushan

Beilstein J. Nanotechnol. 2014, 5, 822–836, doi:10.3762/bjnano.5.94

• nano-objects that are continually being developed and incorporated into a wide variety of macro- to nanoscale systems [3]. With the depth-sensing nanoindenter, indentation studies with a sharp three-sided pyramidal Berkovich tip and compression studies with a flat punch have been performed. The sharp

• ][17] made of various materials including Al, Au, Ag, Cu, GaAs, GaP, Si, Ti, ZnSe and Ni, scale effects on hardness with respect to the depth of penetration or indentation size effect (ISE) and decreasing film thickness have been reported. Pharr and Oliver [9] and Bhushan et al. [11], for example

• , found that a decreasing indentation depth resulted in higher hardness of Ag and Si surfaces, respectively. In both cases the hardness of the nano-objects was higher than that of the bulk material. Other studies revealed the relationship between film thickness and hardness. Cao et al. [15] and Dietiker

The softening of human bladder cancer cells happens at an early stage of the malignancy process

• Jorge R. Ramos,
• Joanna Pabijan,
• Ricardo Garcia and
• Malgorzata Lekka

Beilstein J. Nanotechnol. 2014, 5, 447–457, doi:10.3762/bjnano.5.52

• [27]. First, the force curves were converted into force-versus-indentation curves and those curve were fitted to Equation 1 (see section Experimental: Force spectroscopy on living cells). Because the Young’s modulus of the tip is about 160 GPa (seven orders of magnitude larger than that of the cells

• the stiff and compliant surface gives the indentation (Equation 2, see section Experimental: Force spectroscopy on living cells). Figure 4B shows the force-versus-indentation curve derived from Figure 4A and the fit obtained with the Sneddon’s model assuming a conical AFM tip with half-angle of 20

• (indentation). For that reason, any conclusion derived from the data has to be verified for all the indentation depths studied here. On the other hand, the relative error in the determination of the contact point will decrease for larger indentations. The results obtained for all recorded cell lines yielded

Uncertainties in forces extracted from non-contact atomic force microscopy measurements by fitting of long-range background forces

• Adam Sweetman and
• Andrew Stannard

Beilstein J. Nanotechnol. 2014, 5, 386–393, doi:10.3762/bjnano.5.45

• , and, based on previous measurements of similar sensors [5][15], assume an effective stiffness of k ≈ 2000 N/m. The sensors were first prepared on a clean silicon surface by standard STM techniques (pulsing and indentation) until good STM and NC-AFM resolution was achieved. Typically we used

• indentation of the tip into the surface will require the tip structure checks to be repeated. This is likely to be even more important in the case of experiments using qPlus-type setups, where STM tip treatment methods are often used to prepare tips in situ on the surface. In these cases, significant transfer

Influence of the adsorption geometry of PTCDA on Ag(111) on the tip–molecule forces in non-contact atomic force microscopy

• Gernot Langewisch,
• Jens Falter,
• André Schirmeisen and
• Harald Fuchs

Beilstein J. Nanotechnol. 2014, 5, 98–104, doi:10.3762/bjnano.5.9

• oscillation was held constant at A = 0.40 nm. To avoid crosstalk between tunneling current and deflection signal, no voltage was applied to the tip during NC-AFM operation. The tip was prepared by voltage pulses and soft indentation into the Ag sample most likely resulting in a Ag-terminated apex. However, it

Structural development and energy dissipation in simulated silicon apices

• Samuel Paul Jarvis,
• Lev Kantorovich and
• Philip Moriarty

Beilstein J. Nanotechnol. 2013, 4, 941–948, doi:10.3762/bjnano.4.106

• structural evolution of the tip apex within a low temperature NC-AFM experiment, we simulated a repeated tip–surface indentation until the tip structure converged to a stable termination and the characteristic hysteretic behaviour was no longer observed. Our calculations suggest that varying just a single

• dominant role in many experimental dissipation observations. Enhancing tip stability via surface indentation Examination of the tip geometries in our simulations suggest that the increase in F(z) hysteresis is driven by significant structural rearrangements. Our calculations suggest that the D2 tip

• are not reduced sufficiently upon interaction with the surface. Therefore, in some instances, the presence of a tip-hysteresis may act as an identifier for a potentially unstable tip configurations. Tip indentation is a commonly applied technique to improve the quality of tips in NC-AFM, and in turn

Peak forces and lateral resolution in amplitude modulation force microscopy in liquid

• Horacio V. Guzman and
• Ricardo Garcia

Beilstein J. Nanotechnol. 2013, 4, 852–859, doi:10.3762/bjnano.4.96

• the Hertzian mechanics. The average model follows the trend of the Tatara model for the peak forces when varying the set-point amplitude for soft samples. For soft materials, the indentation of the tip could be higher than Asp. Thus the tip and the sample are in permanent contact during the whole

• displacements are part of the contact force computed with this model. where The subindexes “t” and “s” stand, respectively, for tip and sample. In the above equations, δ is the indentation depth, ν is the Poisson coefficient (νt = 0.3 and νs = 0.4) and E the Young modulus with Et = 170 GPa. Each contact

• forces derived from the Hertz model for relatively soft materials. Sample deformation in terms of Es, A0, and Rt The deformation (indentation) exerted by the tip can be considered as an indicator of the degree of invasiveness of the technique. The dependence of the indentation on the Young modulus for

Dynamic nanoindentation by instrumented nanoindentation and force microscopy: a comparative review

• Sidney R. Cohen and
• Estelle Kalfon-Cohen

Beilstein J. Nanotechnol. 2013, 4, 815–833, doi:10.3762/bjnano.4.93

• ]. This approach uses relations that were derived by Sneddon [8] in order to extract the indentation modulus from the slope of the unloading curve according to Equation 1 [23][24] where S is stiffness, given by the slope dF/dh of the unloading curve, and A the contact area between the indenter and the

• sample. Er is the reduced modulus which accounts for both sample and indenter Poisson ratio and modulus – υs, Es and υi, Ei respectively: Several depth sensing indentation methods were developed to evaluate A [23][24][25], which allow for evaluation of hardness and modulus without imaging the indentation

• , meet the basic requirements. For instance, in heterogeneous materials, sub-micron sized domains can be treated by this analysis when using an indenter with nanometric radius and small indentation depths. Thin, soft films on hard substrates also are well-described by this equation when the indentation

Nanoglasses: a new kind of noncrystalline materials

• Herbert Gleiter

Beilstein J. Nanotechnol. 2013, 4, 517–533, doi:10.3762/bjnano.4.61

• al. [37]. These results are in line with observations on pre-induced shear bands produced by indentation [37] or cold rolling [54] where structural disorder was found to be retained even after annealing. The effect of the chemical composition of the glassy regions on the plastic deformation of

Digging gold: keV He⁺ ion interaction with Au

• Vasilisa Veligura,
• Gregor Hlawacek,
• Robin P. Berkelaar,
• Raoul van Gastel,
• Harold J. W. Zandvliet and
• Bene Poelsema

Beilstein J. Nanotechnol. 2013, 4, 453–460, doi:10.3762/bjnano.4.53

• respect to the nonirradiated surface. This is the result of sputtering of a few gold layers. The signature of this sputtering-related indentation remains discernible in all subsequent images. After doubling the dose to 1.2 × 1017 cm−2, helium implantation has a noticeable effect: the surface of the

Growth behaviour and mechanical properties of PLL/HA multilayer films studied by AFM

• Cagri Üzüm,
• Johannes Hellwig,
• Narayanan Madaboosi,
• Dmitry Volodkin and
• Regine von Klitzing

Beilstein J. Nanotechnol. 2012, 3, 778–788, doi:10.3762/bjnano.3.87

• Institute of Colloids and Interfaces, Am Mühlenberg 1, 14476 Potsdam-Golm, Germany 10.3762/bjnano.3.87 Abstract Scanning- and colloidal-probe atomic force microscopy were used to study the mechanical properties of poly(L-lysine)/hyaluronan (PLL/HA)n films as a function of indentation velocity and the

• number of polymer deposition steps n. The film thickness was determined by two independent AFM-based methods: scratch-and-scan and newly developed full-indentation. The advantages and disadvantages of both methods are highlighted, and error minimization techniques in elasticity measurements are addressed

• measurements show that PLL/HA films have a viscoelastic behaviour, regardless of their thickness. If indentation is performed several times at the same lateral position on the film, a viscous/plastic deformation takes place. Keywords: atomic force microscopy; polyelectrolyte multilayers; stress relaxation

Friction and durability of virgin and damaged skin with and without skin cream treatment using atomic force microscopy

• Bharat Bhushan,
• Si Chen and
• Shirong Ge

Beilstein J. Nanotechnol. 2012, 3, 731–746, doi:10.3762/bjnano.3.83

• , the maximum indentation displacement was controlled to be 1000 nm [6]. The method for the hardness (H) and the elastic modulus (E) determination was based on established methods [37][38]. Briefly, H was calculated from where Pmax is the maximum imposed load, and A is the projected contact area. The

The memory effect of nanoscale memristors investigated by conducting scanning probe microscopy methods

• César Moreno,
• Carmen Munuera,
• Xavier Obradors and
• Carmen Ocal

Beilstein J. Nanotechnol. 2012, 3, 722–730, doi:10.3762/bjnano.3.82

• modify (writing/erasing) or to characterize (reading) the electrical properties of the sample under study. Current images were acquired in a noninvasive manner (no sample indentation) by using the contact operation mode at the lowest possible applied load while still obtaining stable signals. The

Mapping mechanical properties of organic thin films by force-modulation microscopy in aqueous media

• Jianming Zhang,
• Zehra Parlak,
• Carleen M. Bowers,
• Terrence Oas and
• Stefan Zauscher

Beilstein J. Nanotechnol. 2012, 3, 464–474, doi:10.3762/bjnano.3.53

• apparent stiffness of the EG3 layer (see Supporting Information File 1 for details) [65]. The apparent Young’s modulus of the thiols on the surface is around 30 GPa, consistent with moduli of short alkanethiol chains obtained by using SEM and nano-indentation [66][67]. The approach to deconvolute these

• four regimes: (A) free oscillation, (B) partial contact, (C) soft contact, and (D) hard contact. To highlight the differences in cantilever bending and the level of indentation in the four regimes, the schematic is not drawn to scale. FMM images of SpA-N B-domain protein patterns on a gold surface

Mechanical characterization of carbon nanomembranes from self-assembled monolayers

• Xianghui Zhang,
• André Beyer and
• Armin Gölzhäuser

Beilstein J. Nanotechnol. 2011, 2, 826–833, doi:10.3762/bjnano.2.92

• resolution in the range of hundreds of nanometers. Atomic force microscopy (AFM) has also been used for indentation studies on soft [14] as well as stiff [15] membranes. In addition, it was recently reported that the curvature of a bulged membrane was determined by AFM, while its deflection was measured with

• a pressure–deflection curve. This force corresponds to an indentation depth δ0, which appears as a step height in topographic AFM images of nonpressurized membranes. The indentation depth δ of pressurized membranes was evaluated in order to correct the measured deflection, as described previously

• [10]. In this system, the tension of the CNM is assumed to be the main contribution balancing the AFM tip force. The force contributed by the bending stiffness and the adhesion between the tip and the membrane was neglected. For a pressurized membrane, the indentation depth δ decreases with increasing

The effect of surface anisotropy in the slippery zone of Nepenthes alata pitchers on beetle attachment

• Elena V. Gorb and
• Stanislav N. Gorb

Beilstein J. Nanotechnol. 2011, 2, 302–310, doi:10.3762/bjnano.2.35

• surfaces than on their replicas may be explained by the different mechanical and physicochemical properties of both substrates. We surmise that the softer and more compliant material of the plant tissue promotes insect interlocking due to easier indentation of claw tips into a softer substrate. This effect