Kotone Akiyama

Development of a metal–tip cantilever for noncontact atomic force microscopy

We report on a focused-ion-beam fabrication of a metal–tip cantilever for noncontact atomic force microscopy (AFM) and demonstrate its superior performance by observing atomically resolved AFM images of the Si(111)7×7 surface. Characterization of the tip apex by transmission electron microscope revealed that the tip radius is less than 5nm. Detrimental changes in the resonance frequency and the Q factor of the cantilever due to the attachment of the metal tip are small and do not affect the performance of the AFM imaging. Since the fabrication technique is applicable to any materials, various functional probes can be developed with this method.

Atomically-resolved imaging by frequency-modulation atomic force microscopy using a quartz length-extension resonator

Using a 1MHz length-extension type of quartz resonator as a force sensor for frequency-modulation atomic force microscopy (AFM), atomically resolved images of the Si(111)-(7×7) surface was obtained. Fabrications of a tip attached at the front end of the resonator by focused ion beam, and removal of the native oxide layer on the tip by in-situ field ion microscopy are found effective for achieving the highly-resolved AFM imaging.

Element specific imaging by scanning tunneling microscopy combined with synchrotron radiation light

Microscopic surface images showing a distribution of a designated element was obtained by scanning tunneling microscopy combined with synchrotron radiation light. A tip current induced by photoirradiation is found to increase when the photon energy is just above the absorption edge of a sample element. From the photoinduced current measured during the tip scanning over the surface, element specific images were obtained. An estimated spatial resolution of the chemical imaging is less than 20nm, better than that achieved by photoemission electron microscopy.

Atomically resolved imaging by low-temperature frequency-modulation atomic force microscopy using a quartz length-extension resonator.

Low-temperature ultrahigh vacuum frequency-modulation atomic force microscopy (AFM) was performed using a 1 MHz length-extension type of quartz resonator as a force sensor. Taking advantage of the high stiffness of the resonator, the AFM was operated with an oscillation amplitude smaller than 100 pm, which is favorable for high spatial resolution, without snapping an AFM tip onto a sample surface. Atomically resolved imaging of the adatom structure on the Si(111)-(7x7) surface was successfully obtained.

Fabrication of a glass-coated metal tip for synchrotron-radiation-light-irradiated scanning tunneling microscopy

A method to fabricate a glass-coated tungsten tip and the performance of the tip in scanning tunneling microscopy (STM) under irradiation of the synchrotron radiation light are reported. A tungsten tip was first coated with glass, and then the glass layer on the tip apex was removed by a focused ion beam. The bare area of the tip apex is less than 5μm in length. Using the tip, atomically resolved STM images were obtained in ultrahigh vacuum conditions without significant contaminations. STM studies under the irradiation revealed that the coating is effective in blocking photoinduced electrons impinging on the sidewall of the tip and in extracting photoelectron current emitted from a small area below the tip apex.

Calculation of Noise Intensity in the Frequency Demodulation for Atomic Force Microscopy

Noise intensity in the resonance frequency shift (Δf) signal of the cantilever oscillation, which is an indirect measure of force in non-contact atomic force microscopy, was calculated and compared with those measured experimentally. It is found that the output noise amplitude is proportional to the ratio of noise to the oscillation amplitude measured at the input of the frequency demodulator. Our analysis indicates that improving the sensitivity to cantilever deflection can reduce the noise in the Δf signal.