Scanning-Probe-Based Techniques

Scanning-probe-based lithographic techniques have been successfully used for patterning and delivering material on nanometer scales in many different applications. These versatile techniques have also been applied to patterning and grafting CP nanostmctures. In this section, we will review important studies and progresses in this area. 

In the following, we introduce a few representative examples in which scanning tips are used to pattern, deliver, or grow nanoscale CP features. Based on the functionality of the probe, the approaches in this category include electrochemical polymerization, dip-pen, and nanomechanical scratching. 

The most common approach based on a scanning-probe technique is the electrochemical polymerization of the corresponding monomer. In such an approach CP patterns are electrochemically grown by applying an electrical potential between the scanning probe and the substrate in the present of monomer solution. There are two slightly different types of setup within this approach. 

With a different setup, a scanning probe can also be used in dip-pen lithography for the preparation of CP nanofeatures. In this case, the probe delivers a soluble CP ink onto a substrate following a programmed route to create CPNWs with the desired pattern and shape. 

Su et al. reported a slightly different method in which a monomer ink was transported from the AFM tip to the substrate while polymerizing chemically with an acid promoter to form CPNWs [30]. Another modification of such a dip-pen nanolithography method is called thermal dip-pen nanolithography , where a tip 

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Scanning tunneling microscopy (STM) and ATM are commonly used scanning probe-based microscopy techniques that were developed in the 1980s [33], STM usually has a probe made of tungsten (W) or praseodymium (Pr)/ iridium (Ir) alloy with only one atom at the end of the probe tip. A voltage difference is applied between the tip and the surface of the sample under high vacuum. The electrons can... 

Additional suggested resources for the reader include introductory articles on scanning probe techniques for materials properties measurement [82,83J. A comprehensive manual describing various surface preparation techniques, experimental procedures and instrumentation is also a good resource [84J, although the more recent modulation based techniques are not covered. Key textbooks include Johnson s on contact mechanics [51J and Israelachvili s on surface forces [18J, as well as a treatment of JKR/DMT issues by Maugis [85J. 

The concept of resolution in AFM is different from radiation-based microscopies because AFM imaging is a three-dimensional imaging technique. There is an important distinction between images resolved by wave optics and those resolved by scanning probe techniques. The former is limited by diffraction, whereas the latter is limited primarily by apical probe geometry and sample geometry. Usually the width of a DNA molecule is loosely used as a measure of resolution, because it has a known diameter of 2.0 nm in its B form. 

For direct patterning on the nanometer scale, scanning probe microscopy (SPM) based techniques such as dip-pen-nanolithography (DPN), [112-114] nanograftingf, nanoshaving or scanning tunneling microscopy (STM) based techniques such as electron induced diffusion or evaporation have recently been developed (Fig. 9.14) [115, 116]. The SPM based methods, allows the deposition of as-sembhes into restricted areas with 15 nm linewidths and 5 nm spatial resolution. Current capabihties and future applications of DPN are discussed in Ref. [117]. 

Among the many microscopy-based techniques for the study of biomolecular interactions on surfaces, scanning probe microscopies, and especially the atomic force microscopies (AFM), are the most used because of their molecular and sub-molecular level resolution and in situ imaging capability. Apart from the high resolution mapping of siuface nanotopographies, AFM can be used for the quantification and visualisation of the distribution of chemistry, hydrophobicity and local mechanical properties on surfaces, and for the fabrication of nanostructmes on surfaces. 

Combined scanning probe techniques 932 Compartmentalized surfaces 921 Competitive immunoassay el80 Composite electrodes 145 material 916 Concanavalin A 313, 317 Conducting polymer 44, 73 based ISE 74 Conductivity e62 Conductometric transducers 241 Conjugate 650 polymer 74... 

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