Resolution nanolithography

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]. 

Controlled delivery of collections of molecules onto a substrate with nanometre resolution can be achieved with the tip of an AFM. This positive printing mode technique is called dip-pen nanolithography (DPN) and its working principle is illustrated in Fig. 3.27. DPN uses an AFM tip as a nanopencil, a substrate as the paper and molecules with a chemical affinity for the substrate as the ink. Capillary transport of molecules from the AFM tip to the solid substrate is used in DPN to directly write patterns consisting of a relatively small collection of molecules in submicrometre dimensions. The hrst example introducing the technique was the transfer of octadecanethiol onto gold surfaces (Piner et al, 1999). 

The kinetics data of the geminate ion recombination in irradiated liquid hydrocarbons obtained by the subpicosecond pulse radiolysis was analyzed by Monte Carlo simulation based on the diffusion in an electric field [77,81,82], The simulation data were convoluted by the response function and fitted to the experimental data. By transforming the time-dependent behavior of cation radicals to the distribution function of cation radical-electron distance, the time-dependent distribution was obtained. Subsequently, the relationship between the space resolution and the space distribution of ionic species was discussed. The space distribution of reactive intermediates produced by radiation is very important for advanced science and technology using ionizing radiation such as nanolithography and nanotechnology [77,82]. 

The application of scanning probe lithography (SPL) has been widespread owing to its ability to modify substrates with very high resolution and ultimate pattern flexibility.96 Dip-pen nanolithography (DPN),97 high contact force AFM,98 and constructive nanolithography99 are some of the most commonly employed techniques, all of which aim to control the position and directed assembly of molecules and nanoparticles. 

Dip-pen nanolithography is a high resolution patterning technique that enables the creation of patterns from the sub lOOnm to many micrometers length scale.76 This technique uses an ink-coated AFM (atomic force microscopy) tip as a nanopen. The ink molecules are transported from the tip to a substrate, normally by capillary forces when the tip is in contact with the surface of the substrate.77 The driving force for such transport is chemisorption of the ink to the underlying substrate due to a chemical78 or electrochemical force.79... 

Films prepared by the LB method have found application in nonlinear optics, but they have also found applications in nanolithography. The miniaturization of ICs reqmres high resolution, and electron beams have been used, as explained in Section... 

Dip-Pen Nanolithography, Fig. 2 Example of high-resolution pattern of mercaptohexadecanoic acid on atomically flat gold surface formed using DPN (Courtesy Mirkin group, Northwestern University)... 

The dip-pen nanolithography technique allows directly printing a wide variety of biomaterials including DNA, phospholipids, and proteins with a resolution below 50 nm (94-96). 

Figure 12 Principle of dip-pen nanolithography , whereby SAM-forming molecules are transported to a specific position with nanometer resolution, by means of an AFM tip. The molecules are transported within the water meniscus at the tip-substrate interface. From Reference 54 with kind permission.

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