Shigeyuki Hosoki

Surface modification of MoS2 using an STM

Abstract Scanning tunneling microscopy is used to modify the surface structure of molybdenum disulfide (MoS 2 ). A natural MoS 2 crystal often has stable point defects. This study shows that surface sulfur atoms are excised by field evaporation and these artificial defects can be used to form characters at room temperature.

Tunneling acoustic microscope

A new type of microscope, which is based upon both a scanning tunneling microscope (STM) and a technique for detecting acoustic waves, is described. An acoustic wave generated in a STM’s sample, by vibration of its tip, is detected by a piezoelectric transducer coupled to the sample. The amplitude of the acoustic wave corresponds to the strength of the force interaction between the tip and the sample, and is sensitive to tip‐sample spacing. We have been successful in keeping the spacing constant by using a new feedback loop that holds this amplitude constant without tunneling. This method enhances the features of the STM without reducing its functions and enables simultaneous use of both force interactions and tunneling current to investigate the properties of samples. Topographies taken by the new feedback system and tunneling current images are shown.

Observation of pn junctions on implanted silicon using a scanning tunneling microscope

Si pn junctions fabricated by photoresist masked As+ implantation were observed using current imaging tunneling spectroscopy (CITS) in a scanning tunneling microscope (STM). Using the CITS, a specific bias was chosen to define n‐type or p‐type areas according to whether or not current flowed. The pn junctions could be easily identified from the current image at this bias and in the STM topographic image. It also proved possible to find processing faults related to implantation. The STM images also identified the structure (corrugations) near the junctions, associated with volume expansion caused by implantation and annealing.

Fabrication of nanostructures using scanning probe microscopes

We present nanostructure fabrication techniques using field evaporation and local heating in scanning probe microscopes, especially the scanning tunneling microscope (STM), atomic force microscope (AFM), and the scanning near‐field optical microscope (SNOM). The detachment of sulfur atoms from the surface of cleaved MoS2 and atomic scale fabrication were demonstrated with a field evaporation in STM. Field evaporation in AFM forms nanometer‐sized gold dots on a SiO2/Si substrate. Local heating with SNOM changes a phase of the GeSbTe recording film from amorphous to crystalline, and forms high reflectivity domains 60 nm in diameter. Moreover, we discuss these applications to a semiconductor process and data storage.

Stability of carbon field emission current

The stability of field emission (FE) current is evaluated for glassy carbon FE tips. Experimental findings are as follows: (1) Instability is proportional to the product of FE current level and the pressure under operation. (2) Instability is large for CO ambient and small for H2 ambient. (3) Instability consists mainly of steps and spikes instead of 1ƒ type. (4) Instability is reduced by heating the lip during operation. As a result, it is concluded that instability is due to dislodgement of adsorbed molecules on the tip surface by impinging ions formed near the tip by FE electron beam bombardment.

Au‐induced reconstructions of the Si(111) surface

Au‐adsorbed structures (∼1 ML) on the Si(111) surface are studied using a scanning tunneling microscope. In the initial stage of deposition, locally Au atoms are adsorbed onto the Si(111) surface with a 5×5 periodicity. At lower coverage, images showing a 5×2 periodicity are recorded, in which there are a dark line and two atomic rows running in the [101] direction in a five times period. In each atomic row, atoms are arranged in a two times period along the row. At higher coverage, images showing a (3)1/2×(3)1/2 structure are also recorded. In these images, in addition to the (3)1/2 ×(3)1/2 periodicity, there is an undulation which is explained as a phase shift of the (3)1/2 ×(3)1/2 structure.

Initial stage of Au adsorption onto a Si(111) surface studied by scanning tunneling microscopy

The initial stage of Au adsorption onto a Si(111) surface (<0.2 ML) is studied by scanning tunneling microscopy (STM). Au is deposited at room temperature, and then the sample is annealed at 700 °C. At the very early stage of Au adsorption, a Au‐adsorbed 5× structure is found not to break a 7×7 structure. By increasing the amount of adsorbed Au, the Si substrate itself shows a 5× structure. Rows of the Au‐adsorbed 5× structure are observed to have grown from the lower side of steps.

Scanning tunneling microscope with reliable coarse positioners

An inchworm system with a new type of clamping mechanism has been made for a coarse positioner in a scanning tunneling microscope. The clamping mechanism operates by means of springs and piezoelectric actuators. This system can move a probe tip transversely and longitudinally in the horizontal plane, and the sample vertically, in steps, with a range of 8 mm in each direction.

Development of boron liquid–metal–ion source

A boron liquid–metal–ion source is described that uses a combination of a glassy carbon or carbide emitter and a Ni–B base alloy as its source material. The B+ ion emission current is 25%–35% of the total emission current, and the energy spread for B+ ions is 12 eV at a total current of 30 μA. A source lifetime of more than 250 h was achieved with a total current of 30–50 μA. This source mounted on a mass‐separated focusing column has led to B+ submicron beams with maximum energies of 20 keV for preliminary experiments on maskless implantation.

Field emission characteristics of carbon tips

Field emission (FE) of glassy carbon tips is investigated. Experimental FE characteristics are as follows: (1) The decrease in FE current after flashing is very small or not recognized. (2) The FE current (about 1 micro A) is more stable than that of a tungsten tip for the same conditions as time increases. Current instabilities appear as step-wise fluctuations. (3) Instability dependences of FE current on ambient gases are in decreasing order, CO, H2O,O2 and H2. Dependence on CO is particularly remarkable. (4) FE angle is confined to 14–15 of that of a conventional tungsten tip, and depends only on geometrical tip shape.