Atomic force microscopy scanning modes

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... 

A number of methods are available for the characterization and examination of SAMs as well as for the observation of the reactions with the immobilized biomolecules. Only some of these methods are mentioned briefly here. These include surface plasmon resonance (SPR) [46], quartz crystal microbalance (QCM) [47,48], ellipsometry [12,49], contact angle measurement [50], infrared spectroscopy (FT-IR) [51,52], Raman spectroscopy [53], scanning tunneling microscopy (STM) [54], atomic force microscopy (AFM) [55,56], sum frequency spectroscopy. X-ray photoelectron spectroscopy (XPS) [57, 58], surface acoustic wave and acoustic plate mode devices, confocal imaging and optical microscopy, low-angle X-ray reflectometry, electrochemical methods [59] and Raster electron microscopy [60]. 

Although the resolution of atomic force microscopy (AFM) is basically inferior to that of STM, the technique has the advantage that insulating materials can also be used as substrates. In AFM the forces acting between the tip and the sample surface are detected. The probe tip mounted on a flexible cantilever scans over the sample. AFM can be operated in contact mode, exploiting repulsive forces, as well as in non-contact mode, exploiting attractive forces. In the contact mode the probe tip is in direct contact with the sample surface (Fig. 7.8). Either the tip is passed over the sample surface at constant height (CHM,... 

Sulchek, T., G.G.Yaralioglu, C.F. Quate, and S.C. Minne. 2002. Characterization and optimization of scan speed for tapping-mode atomic force microscopy. Rev. Sci. Instrum. 73 2928-2936. 

The topology of the microstructure was investigated by atomic force microscopy (DualScope/DME, Herlev, Denmark) in non-contacting mode. The scan speed of the cantilever was set to 50 xm/s at a constant force of0.16nN. 

Ceo = Fullerene SWNTs = Single-walled carbon nanotubes MWNTs = Multiwalled carbon nanotubes DWNTs = Double-walled carbon nanotubes CNTs = carbon nanotubes TEM = Transmission electron microscopy HRTEM = High-resolution transmission electron microscopy SEM = Scanning electron microscopy AFM = Atomic force microscopy Ch = Chiral vector CVD = Chemical vapor deposition HiPco process = High-pressure disproportionation of CO RBM = Radical breathing vibration modes DOS = Electronic density of states. 

As a final remark, a brief comment should be made on the capabilities of other scanning prohe microscopy techniques, particularly atomic force microscopy (AFM), for the visualization of pores in carbon materials. Fig. 6 shows an image of the studied ACFs obtained by tapping mode AFM. It is evident from Fig. 6 that the pore structure of the ACFs is not resolved and the surface appears extremely smooth. Such deficient performance of the AFM is mainly attributed to the relatively large curvature radius of the tips used (5-10 nm, among the shaipest available). This limits the width of the trenches that can be probed with reasonable accuracy and, in this case, prevents the detection of the micro- and mesopores of the ACF sample. 

In the longer term, picoindentation instruments are likely to be widely used to extend the technique to a still smaller scale, with the help of techniques developed for atomic force microscopy. Already, plastic deformation at depths of a few atomic layers, as well as the effect of surface forces, have been quantified by means of depth-load measurements, using a point force microscope, i.e. an AFM operated in static (non-scanning) mode (Burnham Colton, 1989). 

Atomic force microscopy (AFM) allows the topography of a sample to be scanned by using a very small tip made from silicon nitride. The tip is attached to a cantilever that is characterised by its spring constant, resonance frequency, and a quality factor. The sample rests on a piezoceramic tube which can be moved horizontally x,y motion) and vertically (z motion). Displacement of the cantilever is measured by the position of a laser beam reflected from the mirrored surface on the top side of the cantilever, whereby the reflected laser beam is detected by a photodetector. AFM can be operated in either contact or a noncontact mode. In contact mode the tip travels in close contact with the surface, whereas in noncontact mode the tip hovers 5-10 nm above the surface. 

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