Atom-tracking

Swaitzentruber, B.S. 1996. Direct measurement of surface diffusion using atom-tracking scanning tunneling microscopy. Phys. Rev. Lett. 76 459-462. 

Basic nanostructures encompass such simple and useful items as wires (a thin line of conducting atoms surrounded by an equally thin shell of insulating atoms), rods (which can be used in a variety of applications, from information storage and sensors to miniature diodes, cathodes and other integral components for electronics) and dots (small but exceedingly useful markers that can be used as atomic tracking devices). Other materials that will no doubt become extremely useful for self-assembly include nanocatalysts, which speed up chemical reactions. 

Add extra columns as required for atoms tracked by oxidation state. Copy and paste cells in delta column and delta row as appropriate. All cell formulas are copied with complete fidelity. Check that numerator in cell formula for HI refers to sum of delta row column. 

STM studies of the ground state c(4x2) reconstruction revealed a surprising dynamics even at a very low temperature of 5 K [25]. Everyone would have guessed that a Si surface with its strong covalent bonds would be immobile at low temperatures and any motion of the atoms would be frozen-in. Atom tracking experiments revealed that the thermal motion of Si adatoms may be observed stiU at room temperature [26], while epitaxial growth of Si requires temperatures well above 300 °C [27]. 

The force microscope is also well suited for atomic and molecular manipulation as it allows the measurement and control of forces involved in the manipulation process. In fact, the force needed to move a Co atom or a CO molecule across a Cu(lll) surface has been quantified in a combined NC-AFM/STM experiment [238]. This experiment and other NC-AFM manipulation experiments have initially been performed at cryogenic temperatures in analogy to procedures known from STM manipulation. However, sophisticated experimental methods of atom tracking and feed-forward techniques also allow imaging, manipulation, and spectroscopy with atomic precision at room temperature [239-242]. Controlled vertical manipulation has been demonstrated by displacement of individual silicon atoms on a Si(lll)7x7 surface by soft nanoindentation [243] and lateral manipulation for adsorbates on a Ge(lll)-c(2x8) surface [244]. The concept of lateral manipulation has further been developed to create atomic structures on semiconductor surfaces at room temperature by using sophisticated manipulation protocols [245, 246]. Room-temperature, atomic-scale manipulation has also been achieved on insulating surfaces [247, 248] however, the processes involved are more complicated and the degree of control is lower in this case. 

Further development in this field will be governed by questions related to the yet unsolved fundamental and technical issues as well as the quest for more user-fnendly implementations of the techniques. Although the STM and NC-AFM technologies already allow operation at most advanced levels, still most technical implementations operate at technical rather than physical hmits. This specifically applies to the NC-AFM where improvements in the detection optics and electronics, frequency demodulation, control software, and electronics still have to be made [275]. An equally important technical issue is the further development and widespread implementation of advanced atom tracking and feed-forward... 

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