Use of atomic force microscopy AFM

AFM has been used in real time to image reacting surfaces in contact with a liquid phase [35]. A study ofthe self-passivating reactionbetween p-chloranil and an aromatic amine included monitoring the surface topography of the p-chloranil in contact with the amine in aqueous solution at 25-second intervals, Fig. 5.27. Under the conditions employed, passivation by the reaction product was shown to be complete in 5 minutes a concomitant hydroxide induced dissolution could also be monitored [7]. 

---

The so-called dip-pen nanolithography is one of these promising novel techniques. It has been developed by Ch. Mirkin etal. and is based on the use of Atomic Force Microscopy (AFM) tips to deposit functionalized molecules on appropriate surfaces. The molecules are first deposited in solid state on the tip. The transport to the surface happens by means of the water meniscus between the tip and the surface that is present in air of usual humidity. Gold surfaces are preferably used to deposit thiol molecules forming strong Au-S bonds. The places were thiol molecules are deposited simply depend on the software moving the AFM tip on the surface. Figure 13 explains in a simplified manner the process. 

The use of atomic force microscopy (AFM) and flow injection QCM in tandem provided important information about the surface coverage and orientation on gold of a thiolated DNA probe, as reported by Zhou and co-workers [58]. The effect of using a different alkanethiol to reorient the... 

First, it is the experimental and theoretical (including computer modeling) investigation of adsorption layers formed on solid surfaces by natural and synthetic polymers, especially by poly electrolytes. Such studies, and in particular those involving the use of Atomic Force Microscopy (AFM, see Chapter VII), provide important information regarding the optimal conditions for the use of polymers for flocculation or stabilization of disperse systems (Chapter VII), and establish the theoretical basis for understanding the mechanism behind the action of structural-mechanical barrier. 

Elemental and molecular surface chemistry plays an important role in the acceptance of an implant material [2-12]. In the study of the elemental and chemical composition of polymeric surfaces, XPS, secondary ion mass spectrometry (SIMS), and surface energy evaluations have emerged as the dominant methods for surface analysis. This is due to the ability of XPS to provide qualitative and quantitative elemental and chemical information (10-100 A), which is complemented by the molecular information obtained from SIMS over the outermost 5-25 A. Surface wettability measurements provide a rapid and quantitative measurement of the inherent surface wettability of a solid sample. When these measurements are accompanied by a Zisman plot, the polarity and critical surface tension (7. ) of the solid surface may be determined. The critical surface tension is a measure of the surface free energy (yj of solid materials. The surface morphology of the lenses studied here was investigated through the use of atomic force microscopy (AFM). The sensitivity of the technique allows submicrometer (to Angstroms) sized features to be examined. 

Differences in the surface conductivity with surface termination of diamond can be applied to the nanolithographic modification of diamond surfaces by use of atomic force microscopy (AFM) techniques [50-52]. Modification can be carried out by applying an electrical bias to the sample surface via a conductive cantilever tip, e.g., Au coated Si (Fig. 8.8). Surface modification using such an AFM technique is relatively general, and has been achieved for semiconductor materials such as Si [53], GaAs [54] and metals such as Ti [55]. Recently, Tachiki et al. and Kondo et al. have applied this technique to single-crystal homoepitaxial diamond thin films, undoped and boron-doped, respectively. In this section, we discuss the properties of diamond surfaces modified via AFM techniques and possible applications. 

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,... 

So far, few authors [7,8] have reported X-ray reflectivity data for nitrides. This technique offers a very precise method of measuring the thickness of layers thinner than about 2000 A and their roughness. With a growing number of nitride samples of a very small roughness, reflectivity will soon become a commonly used characterisation technique. However, one should be aware that the level of surface roughness obtained from reflectivity often does not coincide with the data of atomic force microscopy (AFM) or even optical microscopy. This is because each technique has a different length scale and studies using complementary methods are necessary to obtain a real model of the surface. 

Until fairly recently, the theories described in Secs. II and III for particle-surface interactions could not be verified by direct measurement, although plate-plate interactions could be studied by using the surface forces apparatus (SFA) [61,62]. However, in the past decade two techniques have been developed that specifically allow one to examine particles near surfaces, those being total internal reflection microscopy (TIRM) and an adapted version of atomic force microscopy (AFM). These two methods are, in a sense, complementary. In TIRM, one measures the position of a force-and torque-free, colloidal particle approximately 7-15 fim in dimension as it interacts with a nearby surface. In the AFM method, a small (3.5-10 jam) sphere is attached to the cantilever tip of an atomic force microscope, and when the tip is placed near a surface, the force measured is exactly the particle-surface interaction force. Hence, in TIRM one measures the position of a force-free particle, while in AFM one measures the force on a particle held at a fixed position. 

The work described in this chapter is especially concerned with three of the most widely used pressure driven membrane processes microfiltration, ultrafiltration and nanofiltration. These are usually classified in terms of the size of materials which they separate, with ranges typically given as 10.0-0.1 xm for microfiltration, 0.1 p.m-5 nm for ultrafiltration, and 1 nm for nanofiltration. The membranes used have pore sizes in these ranges. Such pores are best visualised by means of atomic force microscopy (AFM) [3]. Figure 14.1 shows an example of a single pore in each of these three types of membrane. An industrial membrane process may use several hundred square meters of membrane area containing billions of such pores. 

The goal of this chapter is to provide an overview of the measurement of colloidal forces at liquid/Iiquid interfaces, using predominately atomic force microscopy (AFM)-First, some of the types and origins of the relevant colloidal forces are introduced. This is followed by a general description of the operation of AFM at rigid interfaces. The next sections focus on forces at liquid/Iiquid interfaces, beginning with a discussion of other measuring techniques employed at liquid/Iiquid interfaces, followed by a summary of... 

In the example shown in Figure 4.23, a direct write lithographic technique, dip pen lithography [158, 159], which relies on a cantilever used for atomic force microscopy (AFM) to write on a substrate to create patterns of Au nanocrystals on mica substrates. Thus, nanocrystals of metals and semiconductors can be patterned into rectangles of varying aspect ratios. 

IR has been used in addition to many other techniques to anaiyze poiymer and copoiymer compositions, either by itseif or in addition to other techniques. Recentiy, the characterization by spatiai differentiation of submicrometer domains in poly(hydroxyalkanoate) copolymer by the combination of atomic force microscopy (AFM) and IR spectroscopy was reported [9, 10]. This new capability resulting from the combination of two single instruments enables the spectroscopic characterization of microdomainforming polymers at levels not previously possible. 

Recently, extensive work has been on going in the area of atomic force microscopy (AFM) where tests such as nanoindentation are being used to... 

---