STM lithography

J. R. Tucker and T.-C. Shen, Prospects for atomically ordered device structures based on STM lithography, Solid State Electronics 42, 1071 (1998). 

Lithography AFM Oxidation Lithography STM Lithography AFM Lithography-Scratching AFM Lithography-Dynamic Plowing... 

Gold beads were used, for example, by Crooks and coworkers [108, 109] to perform STM lithography on SAMs. The 0.25-mm diameter gold wire was first cleaned in Piranha solution, and then melted in a H2/O2 flame under nitrogen and annealed in a cooler region of the flame. This procedure yielded spheres 0.6-1 mm in diameter, which exhibited (111) facets, typically elliptical in shape with a long axis of ca. 100 xm, consisting... 

In contrast to electron-beam lithography, the mechanism of STM lithography is generally an inelastic electron tunneling process, with energy quanta of an electron volt. STM can also be used for single-atom or single-molecule manipulations for the fabrication of individual nanostructures. 

In January 2012 Weber et al reported that they had succeeded in fabricating and characterising a wire formed from heavily-doped silicon which was a single atomic layer high , only four atoms wide, and exhibited a resistivity of 0.3 mQ cm. The wire was fabricated, contacted, and embedded in a silicon substrate using a combination of STM lithography of H Si(100),... 

One of the more interesting new areas of surface science involves manipulation of adsorbates with the tip of an STM. This allows for the fonuation of artificial structures on a surface at the atomic level. In fact, STM tips are being investigated for possible use m lithography as part of the production of very small features on microcomputer chips [74]. 

Langer et al. [10] measured also electrical resistance of individual MWCNTs at very low temperatures and in the presence of a transverse magnetic field. As for the case of the microbundle, the CNTs were synthesised using the standard carbon arc-discharge technique. Electrical gold contacts have been attached to the CNTs via local electron beam lithography with an STM. The measured individual MWCNT had a diameter of about 20 nm and a total length of the order of 1 im. 

In the traditional lithography approach, researchers continued to consider the idea that modem STM (scanning tunnel Microscopy) could be the proper tool for the formation of two-junction systems when working with very small particles. This consideration had related the studies of single-electron phenomena to the concept of quantum dots (Glazman and Shechter 1989). 

Lithography With the STM Nonelectrochemical Methods. The prospect of atomic density information storage has spurred applications of the STM as a surface modification tool. In this application, the anisotropic current density distribution generated by an STM tip is exploited to "write" on a substrate surface. Features with critical dimensions < 5 nm have been written in UHV, in air, and under liquids. 

Although the mechanism by which modification of surfaces in UHV occurs is not clear for all cases, local heating effects appear to have effected the observed modification of glassy materials such as Pd81Si19 (81) and Rl Zr- j (82). The fluence of electrons from an STM tip has been used to accomplish nanometer scale electron beam lithography of CaF2 coated substrates (83). A somewhat different... 

Lithography With the STM Electrochemical Techniques. The nonuniform current density distribution generated by an STM tip has also been exploited for electrochemical surface modification schemes. These applications are treated in this paper as distinct from true in situ STM imaging because the electrochemical modification of a substrate does not a priori necessitate subsequent imaging with the STM. To date, all electrochemical modification experiments in which the tip has served as the counter electrode, the STM has been operated in a two-electrode mode, with the substrate surface acting as the working electrode. The tip-sample bias is typically adjusted to drive electrochemical reactions at both the sample surface and the STM tip. Because it has as yet been impossible to maintain feedback control of the z-piezo (tip-substrate distance) in the presence of significant faradaic current (vide infra), all electrochemical STM modification experiments to date have been performed in the absence of such feedback control. 

Since the applied field is a key factor for the anodic oxidation process the radius of curvature of the tip is also important. Most AFM tips available commercially have a tip radius of curvature of >10 nm. This limits the minimum resolution that one can obtain in an AFM-based lithography. Since well defined and controlled micromachining lithography is used to make these tips on the AFM cantilevers, they are of reproducible size, shape and aspect ratio. This is a big advantage when it comes to doing reproducible lithography of a given resolution. A sharper tip can be obtained in STM but it is difficult to produce a tip of reproducible radius of curvature and aspect ratio. 

Beyond imaging many more applications of SPM exist [1, 16, 17]. Each SPM realization has a spectroscopy mode where, for example, one parameter is determined as a function of another (e.g. current as a function of voltage) [18, 19]. Objects of nanometer size, can be moved (manipulated) with the scanning probe tips through the forces acting between the tip (or the electric field of the tip) and the objects [20-22]. Additionally on-site on-time [23], and even "real-time [24] observation of the processes on surfaces, e.g. adsorbate diffusion, is possible. On top of this, nano-lithography can be performed both with STM and AFM [25, 26]. 

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