Force modulation mode

There are several other operation modes, such as the intermittent contact mode, (Fig. 6c) where the cantilever oscillates and the tip records the repulsive contact with the surface at the lowest point of the oscillation, and the force modulation mode (Fig. 6d) where the tip does not leave the surface at all during the oscillation cycle. 

The so-called Force Modulation Mode (FMM) was introduced in 1991 as a modification of contact-mode SFM [123] and has since found a wide range of applications in heterogeneous polymer systems [124-129]. The FMM imaging is performed by z-modulating the probe (or sample) at a low frequency of about 5 to 20 kHz and an amplitude greater than 10 nm. The frequency is sig-... 

Characterization of the copolymers containing 10 - 30 wt% of silicone macromonomers was done by GPC, DSC, SEM, TEM, surface analysis (SIMS, XPS, contact angle), and especially atomic force microscopy (both Tapping Mode and force modulation mode). 

Fig. 6. Tapping Mode (left) versus force modulation mode (right) picture with the corresponding height and elasticity modulus profiles of a solution-cast 20wt% silicone thin copolymer film.

The identification of phases in polymer blends can be accomplished in force modulation mode (FMM) AFM. Using FMM AFM the relative moduli (a convolution of storage and loss moduli) are mapped on the specimen surface. The rms amplitude of the FMM cantilever, driven in an oscillatory fashion, reflects directly the modulus of underlying polymer specimen. In the blend discussed below three phases can be differentiated. 

Force Modulation Mode Contact Electric Force Microscopy (EFM) Young s Modulus Microscopy (YMM) Scanning near-field acoustic Force-distance measurements... 

Sasaki, S., Monimoto, M., Haga, H., Kawabata, K., Ito, E., Ushiki, T., Abe, K., and Sambongi, T., Elastic properties of living fibroblasts as imaged using force modulation mode in atomic force microscopy. Arch. Histol. Cytol. 61, 57-63 (1998). 

Differences in, for instance, modulus can give rise to excellent materials contrast in force modulation mode AFM or intermittent contact mode AFM phase imaging [144-146]. However, since this imaging contrast is not directly related to exposed functional groups and rather depends only on mechanical properties (including different indentation depths or energy dissipation), these and related approaches will not be considered here as chemically sensitive imaging [2,147]. 

First attempts to record the micro/nanomechanical surface properties with atomic force microscopy/scanning probe microscopy (AFM/SPM) probing were conducted by using the classical Sneddon s approach [1-3]. Further development lead to the micromapping of the surface mechanical properties with a force modulation mode [4-8]. Several studies were focused on the development of dc force-displacement probing of the micromechanical properties [9-15]. In this communication, we report on studies of the micromechanical properties of composite films of polystyrene/polybutadiene (PS/PB) and grafted PS layers and prove the feasibility of... 

FIGURE 3 Different AFM imaging modes. (A) Contact or normal force mode. (B) Lateral or friction force mode. (C) Intermittent contact mode, also known as noncontact or tapping mode. (D) Force modulation mode. 

The other proach based on AFM that is commonly used to study the interface region is force modulation mode. Mai et al, probed the interface in glass fiber-epoxy composites, using force modulation, and concluded that the interface was 1-3 am thick and either ductile or brittle, depending on whether the fiber was sized or unsized, respectively. Munz et al, also used force modulation to characterize the stiffiiess in a carbon fiber/qioxy composite. Investigations of the cross-sections perpendicular to the axis of the carbon fiber were used to determine the thickness of the interface that was estimated to be between 20-80 nm. 

Recently, dynamic mode SFM has been used for genltle and more controlled surface modification [464,465]. Depending on the substrate type, the loading force was varied with ca. 500 nN amplitude at a frequency of 0.1-10 kHz. Force modulation SFM was employed to write on polycarbonate surfaces with letters ca. 50 nm high (Fig. 50b) as the tip was in light contact with the surface and a modulation frequency was relatively low to ensure plastic deformation of the polymer [464]. 

General Experimental Protocols. As noted above, thermal mechanical analysis may be conducted in three separate modes standard, temperature-modulated, and force-modulated. Sample preparation requires dimensional stability, typically including either placement of the sample into a receptacle (useful for powders) or pressing into pellets or tablets. 

Force modulation imaging is the dynamic contact mode that identifies and maps differences in surface stiffness or elasticity. These techniques use a variety of surface properties to differentiate among materials where topographical differences are small or not measurable. 

Intermittent contact mode phase imaging is, similar to force modulation and pulsed, force mode, sensitive to differences in materials properties. In Fig. 3.67 (a), the stiffness difference between glass and a polymer-based matrix gives rise to excellent image contrast. In addition, the different components of the polymer blend can be recognized (compare schematic in Fig. 3.67 (b)). 

Forced Pulse-Width Modulation Mode (FPWM)... 

SFM-Based Stiffness Mapping in Force Modulation Microscopy (FMM) Mode... 

In the contact mode, there are static modes (de-modes), and dynamic modes (ac-modes). In the former, a cantilever-type spring bends in response to the force which acts on the probing tip until a static equilibrium is established [1]. In the dynamic mode, the lever oscillates close to its resonance frequency. A distance-dependence force shifts the resonance curve. Another technique is to modulate the position of the sample at a frequency below the cantilever resonance but above the feedback-response frequency and send the response signal to a lock-in amplifier to measure the signal s amplitude and phase [4]. The lock-in output is connected to the auxiliary data acquisition channels to form an image - this approach is popularly known as force modulation (FM-mode). FM-mode imaging or force cmve is an AFM technique that identifies and maps differences in surface stiffness or elasticity. 

Figure 8 Height mode topographical (A) and force modulation (B) images of colloidal hydrogel nanoparticles immobilized on a silica substrate. Scan domain is 12 pm x 12 pm. Note that in the topographical image darker areas represent lower regions, whereas in the force modulation image the darker areas represent greater surface stiffness.

Amplitude, modulation mode or dynamic force mode... 

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