Lateral Manipulation of Single Adsorbates and Substrate Atoms With the Scanning Tunneling Microscope

Abstract

The stability and precision of modern scanning-tunneling-microscope (STM) systems allow positioning of the tip on a subnanometer scale. This advancement has stimulated diverse efforts on surface modifications in the nanometer and even atomic range, as recently reviewed by Avouris. The lateral movement of individual adatoms and molecules in a controlled manner on solid surfaces and the construction of structures on a nanoscale were first demonstrated by Eigler and collaborators at 4 K. The reason for operating the STM at low temperatures (apart from increased stability and sensitivity of the STM setup itself) is the necessity to freeze the motion of single adsorbates, which are very often mobile at ambient temperatures. By selecting strongly bonded adsorbate/substrate combinations and large molecules, it was possible to extend the lateral manipulation technique even to room temperature. In the case of large molecules, not only their translational motion but also internal flexure of the molecule during the positioning process must be considered. In general, different physical and chemical interaction mechanisms between tip and sample can be exploited for atomic-scale manipulation. We will concentrate in the following on lateral manipulation where solely the forces that act on the adsorbate because of the proximity of the tip are used. This means that long-range van der Waals and short-range chemical forces can be used to move atoms or molecules along the surface. No bias voltage or tunneling current is necessary. Apart from this technique, additional advances using the effects caused by the electric field generated by the bias voltage between tip and sample and by the current flowing through the gap region can be used for atomic or molecular modification.

Nanosphere Lithography: Size-Tunable Silver Nanoparticle and Surface Cluster Arrays

“…Toward this goal, two basic strategies have been employed: (i) serial nanolithography based on scanning probe microscopy and (ii) parallel nanolithography based on phenomena with naturally occurring nanometer-scale periodicities. Scanning probe lithography based on AFM, − scanning tunneling microscopy (STM), − and scanning near-field optical microscopy (NSOM) , has been implemented, which is capable of manipulating individual atoms, molecules, and nanocrystals. Although scanning probe methodologies have demonstrated individual object control and excellent spatial resolution, the throughput of these methods is limited by their inherent serial processing speeds …”

A Scanning Tunneling Microscopy Study of Electrostatic and Proximity Effects in Tip-Assisted Migration and Desorption of a DNA Base Molecule on SrTiO3

“…These forces can be adjusted by varying the separation between the tip and the adsorbate, to achieve precise pulling, sliding, and pushing processes. 32 In this case, z′ = 5.5 Å (corresponding to tunneling resistance R = 2 GΩ), which is too great for the lateral pushing mechanism. In fact, the pushing mechanism has only been feasible for structurally high molecules such as Cu-TBP porphyrin, 1 C 60 , 2 and DNA oligomer, 3 whose structural height is more than approximately 8 Å.…”

“…The atomic force comprises three different forces: long-range van der Waals attractive force, short-range chemical forces and repulsive force (physical contact). These forces can be adjusted by varying the separation between the tip and the adsorbate, to achieve precise pulling, sliding, and pushing processes . In this case, z ‘ ≅ 5.5 Å (corresponding to tunneling resistance R ≅ 2 GΩ), which is too great for the lateral pushing mechanism.…”

Unconventional Methods for Fabricating and Patterning Nanostructures

“…The demonstrated ability of the scanning probe microscope (for example, STM, AFM, NSOM, and SECM) to image and modify surfaces with atomic resolution suggests opportunities for their use in generating nanostructures and nanodevices. , Atomic force microscopy has been the most widely used technique; typical approaches include the use of an AFM tip to scratch nanostructure in soft materials, , to expose thin films of resist, , to induce and/or enhance oxidation of H-terminated Si(100), to change the headgroups or packing density of organic monolayers catalytically, and to “write” 30-nm patterns of alkanethiols on gold . STM tips have been used to alter the structure or order of organic monolayers, to oxidize hydrogen-terminated silicon, , to induce phase transition in a solid material, and to manipulate atoms or molecules. , Other uses of scanning probes include an NSOM tip to expose photoresist films ,, and an SECM tip to deposit metals . Figure shows AFM images of a nanostructure that has been machined in a thin film of MoO 3 . , The AFM tip was also used to manipulate and transfer this carved nanostructure.…”

“…151 STM tips have been used to alter the structure or order of organic monolayers, 152 to oxidize hydrogen-terminated silicon, 78,153 to induce phase transition in a solid material, 154 and to manipulate atoms or molecules. 155,156 Other uses of scanning probes include an NSOM tip to expose photoresist films 15,157,158 and an SECM tip to deposit metals. 80 Figure 2 shows AFM images of a nanostructure that has been machined in a thin film of MoO 3 .…”