Atomic force microscopy nanofabrication

Several striking examples demonstrating the atomically precise control exercised by the STM have been reported. A "quantum corral" of Fe atoms has been fabricated by placing 48 atoms in a circle on a flat Cu(lll) surface at 4K (Fig. 4) (94). Both STM (under ultrahigh vacuum) and atomic force microscopy (AFM, under ambient conditions) have been employed to fabricate nanoscale magnetic mounds of Fe, Co, Ni, and CoCr on metal and insulator substrates (95). The AFM has also been used to deposit organic material, such as octadecanethiol onto the surface of mica (96). New appHcations of this type of nanofabrication ate being reported at an ever-faster rate (97—99). 

A hollow needle-hke capillary is not essential for electrospinning — a droplet on a sohd electrode behaves similarly. Ultrafine droplets picked up by an atomic force microscopy (AFM) tip, nanofabricated microfluidic channels (Kameoka and Craighead 2003), or by a dip-pen type tip (Sun et al. 2006) have been electrospun successfiiUy. 

Recently developed nanofabrication techniques include dip-pen nanolithography (DPN), which uses functionalized atomic force microscopy (AFM) tips to deposit biomolecules on surfaces with pattern features as small as 10 nm [68]. Used for the creation of protein nanoarrays and virus arrays, this technique can create patterns with multiple components [68,69]. Enzymes have also been selectively deposited for biochemical modification of self-assembled monolayers [70]. While nanofabrication techniques are effective for patterning two-dimensional surfaces, these methods are quite limited in terms of processing time and are not suitable for three-dimensional scaffolds. 

Although nanochemical control was proposed decades ago, it was only recently that many of the tools necessary for studying the nanoworld were developed. These include the scanning tunneling microscope (STM), atomic force microscope (AFM), high resolution scanning and transmission electron microscopies, x rays, ion and electron beam probes, and new methods for nanofabrication and Uthography. 

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