Formation of Nanometer-Scale Grooves in Silicon with a Scanning Tunneling Microscope

Self-Organized Nanostructures Generated on Metal Surfaces under Electron Irradiation

Irradiation of high-energy electrons can produce surface vacancies on the exit surface of thin foils by the sputtering of atoms. Although the sputtering randomly occurs in the area irradiated with an intense electron beam of several hundred nanometers in diameter, characteristic topographic features can appear under irradiation. This paper reviews a novel phenomenon on a self-organization of nanogrooves and nanoholes generated on the exit surface of thin metal foils irradiated with high doses of 360–1250 keV electrons. The phenomenon was discovered firstly for gold irradiated at temperatures about 100 K, which shows the formation of grooves and holes with widths between 1 and 2 nm. Irradiation along [001] produces grooves extending along [100] and [010], irradiation along [011] gives grooves along [100], whereas no clear grooves have been observed for [111] irradiations. By contrast, nanoholes, which may reach depths exceeding 20 nm, develop mainly along the beam direction. The formation of the nanostructures depends on the irradiation temperatures, exhibiting an existence of a critical temperature at about 240 K, above which the width significantly increases, and the density decreases. Nanostructures formed for silver, copper, nickel, and iron were also investigated. The self-organized process was discussed in terms of irradiation-induced effects.

The fabrication and characterization of PbTiO3 nanomesas realized on nanostructured SrRuO3/SrTiO3 templates

We report the fabrication of PbTiO(3) nanomesas down to 30 nm lateral size and 4 nm high on nanostructured SrRuO(3)/SrTiO(3) templates by off-axis radio frequency magnetron sputtering. The templates were prepared using a top-down lithography approach based on scanning tunneling microscopy. The growth rate of the PbTiO(3) nanomesas was found to decrease with increasing growth temperature as well as with shrinking template size. Piezoresponse force microscopy measurements for the PbTiO(3) nanomesas showed a strong increase in response with decreasing lateral size. A decrease of the coercive voltage was also observed for the same lateral size range. This laterally size-dependent behavior is attributed to reduction of in-plane strain, when shrinking the nanomesa lateral dimensions.

Fabrication and investigation of nanostructures on transition metal dichalcogenide surfaces using a scanning tunneling microscope

Nanometer-scale holes have been fabricated on the surfaces of the semiconducting transition metal dichalcogenides (TMDCs) molybdenum ditelluride (MoTe2) and molybdenum disulfide (MoS2) by applying voltage pulses from the tip of a scanning tunneling microscope (STM) operating in ultrahigh vacuum (UHV). It was found that the tip geometry (tip shape and sharpness) influences the formation and structure of the atomic-scale nanostructures. Threshold voltage ranges for the surface modification of MoTe2 (3.0 +/- 0.3 V) and MoS2 (3.4 +/- 0.3 V) were determined. Negative sample voltage pulses applied to a p-type MoTe2 surface produced much larger and deeper nanometer-scale holes when compared with those produced by positive voltage pulses. The existence of threshold voltages and the pulse polarity dependence of nanostructure fabrication suggests that an electric field evaporation mechanism is applicable. Support for this mechanism was obtained by nanostructuring metallic TMDC NbSe2, where both the produced features and the threshold voltages (3.0 +/- 0.3 V) were similar for both positive and negative voltage pulses.

Tip-state control of rates and branching ratios in atomic manipulation

We report the atomic manipulation properties of two distinct, stable, and reproducible states of a scanning tunneling microscope tip applied to chlorobenzene/Si(111)-(7x7). We show that the tip state influences the rates of (current-driven) molecular desorption and C-Cl dissociation as well as the branching ratio between these processes, but does not change the mediating electronic channel or the required number of electrons. These manipulation properties combined with the imaging properties of the two tip-states suggest the major difference between tip-states is their coupling efficiency to the pi-states of the chlorobenzene molecule.

Building Pb nanomesas with atomic-layer precision

We demonstrate a novel scheme for manipulating metallic nanostructures involving a macroscopic number of atoms, yet with precise control in their local structures. The scheme entails a two-step process: (a) a triggering step using a scanning tunneling microscope, followed by (b) self-driven and self-limiting mass-transfer process. By using this scheme, we construct Pb nanomesas on Si(111) substrates whose thickness can be controlled with atomic-layer precision. The kinetic barrier for the mass transfer and the underlying mechanism behind this novel manipulation are determined.

Mechanical vertical manipulation of selected single atoms by soft nanoindentation using near contact atomic force microscopy

A near contact atomic force microscope operated at low-temperature is used for vertical manipulation of selected single atoms from the Si(111)-(7 x 7) surface. The strong repulsive short-range chemical force interaction between the closest atoms of both tip apex and surface during a soft nanoindentation leads to the removal of a selected silicon atom from its equilibrium position at the surface without additional perturbation of the (7 x 7) unit cell. Deposition of a single atom on a created vacancy at the surface is achieved as well. These manipulation processes are purely mechanical, since neither bias voltage nor voltage pulse is applied between probe and sample. Differences in the mechanical response of the two nonequivalent adatoms of the Si(111)-(7 x 7) with the load applied is also detected.

Prospects for single-molecule information-processing devices for the next paradigm

Present information technologies use semiconductor devices and magnetic/optical disks; however, they are all foreseen to face fundamental limitations within a decade. Therefore, superceding devices are required for the next paradigm of high-performance information technologies. The paper first describes architectures suitable for single-molecule information processing, in which it is claimed that the performance of information processing is higher if speed and element number product is larger in almost all known architectures. Thus, single-molecule information-processing devices should be the most appropriate approach for the next paradigm. Then, prospects for single-molecule devices suitable for future information-processing technologies are described. Four possible milestones for realizing the Peta/Exa-floating operations per second (FLOPS) personal molecular supercomputer are proposed. Current status and necessary technologies of the first milestone are described, and necessary technologies for the next three milestones are also discussed.

Fabrication of Atomic-Scale Structures on Si(001) Surfaces

The scanning tunneling microscope has been used to define regular crystalline structures at room temperature by removing atoms from the silicon (001) surface. A single atomic layer can be removed to define features one atom deep and create trenches with ordered floors. Segments of individual dimer rows can be removed to create structures with atomically straight edges and with lateral features as small as one dimer wide. Conditions under which such removal is possible are defined, and a mechanism is proposed.