Contact mode atomic force microscopy

SAMs of allgrlphosphonic acids (butylphosphonic acid, octylphosphonic acid, undecylphosphonic acid and octadecylphosphonic acid) on native niekel oxide allow substrates to be functionalized easily. Monolayer formation has been investigated by diffuse reflectance Fourier transform infrared spectroscopy, non-contact mode atomic force microscopy, contact angle measurements and matrix-assisted laser desorption ionization mass spectrometry. Cyclic voltammetry and electrochemical impedance spectroscopy studies showed that the monolayer increased surface resistance to oxidation. 

Contact dermatitis, from nickel, 17 119 Contact dryers, coatings, 7 29 Contact drying, 9 105-107 Contact icing, of food, 21 561 Contacting, differential, 10 760-762 Contact mechanics, 1 515-517 Contact mode atomic force microscopy, 3 320-325 17 63 Contact nucleation, 8 105 Contactors ozone, 17 801-802 selection of, 10 767-768... 

The technique of atomic force microscopy (AFM) has permitted the direct observation of single polysilane molecules. Poly[//-decyl-(high molecular weight (4/w = 5,330,000 and Mn = 4,110,000), PSS, helicity, and rigid rod-like structure due to the aliphatic chiral side chains, was deposited from a very dilute (10-10 Si-unit) dm-3] toluene solution onto a (hydrophobic) atomically flat (atomic layer steps only present) sapphire (1012) surface. After drying the surface for a few minutes in a vacuum, AFM images were taken at room temperature in air in the non-contact mode.204,253 An example is shown in Figure 22, in which the polymer chain is evident as a yellow trace. 

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]. 

The force microscope, in general, has several modes of operation. In the repulsive-force or contact mode, the force is of the order of 1-10 eV/A, or 10 -10 newton, and individual atoms can be imaged. In the attractive-force or noncontact mode, the van der Waals force, the exchange force, the electrostatic force, or magnetic force is detected. The latter does not provide atomic resolution, but important information about the surface is obtained. Those modes comprise different fields in force microscopy, such as electric force microscopy and magnetic force microscopy (Sarid, 1991). Owing to the limited space, we will concentrate on atomic force microscopy, which is STM s next of kin. 

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,... 

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. 

Figure 1. Morphological analysis of dog pancreatic rough ER microsomes. (A) Electron micrograph of dog pancreatic rough microsomes. Arrows indicate ribosomes at the surface of ER microsomal membranes. (B) Contact mode Atomic Force Microscopy micrograph of purified ER microsomes fused on mica. Scale bars are 1 jxm.

Le Grimellec C, Lesniewska E, Giocondi MC, Finot E, Vie V, Goudonnet JP. Imaging of the surface of living cells by low-force contact-mode atomic force microscopy. Biophys. J. 1998 75 695-703. 

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). 

Figure 5.13 The dynamic non-contact mode. The frequency shift of the cantilever oscillation is used to operate the feedback loop. (Reproduced with permission from P.C. Braga and D. Ricci (eds), Atomic Force Microscopy, Humana Press. 2004 Humana Press.)...

Figure 6.10 Ambient contact mode atomic force microscopy images of an AgFON structure. The structure was made by depositing 200nm of Ag over 542 nm diameter polystyrene spheres, (a) The array of spheres and (b) image of one Ag-coated...

The atomic structure of the carbon deposited was studied by TEM using a JEM-IOOC electron microscope in the micro-diffraction mode. The structure of the carbyne crystals is analyzed by atomic force microscopy (AFM). The images are obtained by contact mode. The film thickness was determined from SEM observations of the film cross sections. 

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. 

The image and cross-section of the indentation were investigated by atomic force microscopy (AFM) "Nanoscop-111 A" in a mode of periodic contact with silicon probes with nominal radius of an edge with 10 nm. 

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