Vertical manipulation

The controlled manipulation of single atoms and molecules demands a higher stability and lower thermal drift of the STM than that required for surface imaging. Most experiments up to now have been performed at low temperatures since instrumental effects like piezo creep, hysteresis and thermal drift are then negligible. Due to the above-mentioned requirements a much lower precision was achieved in the experiments at room temperature than at low temperature. Nevertheless vertical manipulation can be done with atomic precision at room temperature as well. 

Other rigid molecules with a lower symmetry offer more possibilities for the manipulation with STM. The manipulation of the polar molecule phosphangulene adsorbed on a Ag(lll) surface was investigated in detail at low temperature. By lateral manipulation and vertical manipulation the... 

An STM manipulation mechanism related to the adsorption and desorption processes of single atoms and molecules is known as vertical manipulation (Fig. 10). This process involves transfer of single atoms or molecules between the tip and substrate and vice versa (Fig. 10(a)). An atomic switch realized by the repeated transfer of a Xe atom between the STM tip and a Ni(110) substrate is the first example of vertical manipulation [22]. The atom/molecule transfer process can be realized by using an electric field between the tip and sample, or by multiple excitations with inelastic tunneling electrons, or by making mechanical contact between the tip and atom/molecule. This transfer mechanism can be modeled by using a double potential well as shown in Fig. 10(b). At an imaging distance, approximately 6 A between tip and surface, the atom/molecule has two possible... 

The use of catalysts in chemistry increases reaction speed and lowers reaction temperatures. Metal catalysts are commonly used in many technologies — the detailed knowledge of catalyzed reaction steps can be used to improve efficiency or find new reaction pathways. Bond formation is the reverse process of bond breaking and constitutes an important basic step in a metal catalyzed reaction. In the simplest case, the transfer of an atom/molecule between the sample and the tip in the vertical manipulation procedure involves both bond breaking and bond formation processes. In this case, the substrate-atom/molecule bond is broken and a new bond between the atom/molecule and the tip-apex atom is formed or vice-versa [45]. Such a bond formation was demonstrated by Lee and Ho [46]. They deposited two CO molecules over an adsorbed Fe atom on a Cu(100) surface using the vertical manipulation procedure. Because an adsorbed Fe atom on this surface can accommodate two CO molecules, an Fe(CO)2 iron carbonyl was produced. 

The manipulation mode refers to operations of relocating or removing atoms on a surface. Figure 5.3 illustrates relocating an adatom (an atom attached to the surface) by vertical and lateral manipulation. In vertical manipulation, an adatom is transferred from the surface to the probe tip, and then is deposited at another location. The attachment and detachment of the atom to and from the tip is controlled by voltage pulses. In lateral manipulation, an adatom remains adsorbed on the surface and is moved laterally by the tip when there is a weak bond between the adatom and the tip. This technique has been used for serious as well as fanciful work. For example, a scientist at the IBM Corporation made an IBM symbol with a few atoms using the manipulation mode in an STM. 

Figure 5.3 Manipulation mode in the STM (a) vertical manipulation, where an adatom forms a strong bond with the tip and is detached from the surface, then it is transported by the tip and redeposited on the surface and (b) lateral manipulation where the tip forms a weak bond with an adatom and moves it along the line of manipulation. (Reproduced with kind permission of Springer Science and Business Media from E. Meyer, J.H. Hug, and R. Bennewitz, Scanning Probe Microscopy the Lab on a Tip, Springer-Verlag, Berlin. 2004 Springer-Verlag GmbH.)...

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. 

Oyabu, N., Custance, 6., Yi, 1., Sugawara, Y., and Morita, S. (2003) Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy. Phys. Rev. Lett., 90, 176102. 

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