Daisuke Saya

Towards atomic force microscopy up to 100 MHz

An atomic force microscope for nanocantilevers measuring from a few 100 nm to a few μm in length was implemented. The natural frequencies of the nanocantilevers lie in the range of 1 MHz to 1 GHz, and optical detection schemes adapted to their size and frequency range was selected. A helium neon laser with a beat frequency of 890 MHz was used as the laser source. The beat was shifted to 1090 MHz by an acousto-optical-modulator, and used as the carrier for heterodyne laser Doppler measurement. This enabled velocity measurement up to around 100 MHz. The probe beam of the Doppler interferometer was guided to the nanocantilever by a single mode polarization-maintaining optical fiber terminated by a collimating lens, a quarter wave plate, and a focusing lens. Reflected light was collected by the same optics and mixed with the reference beam. Self-excitation of the nanocantilever at its lowest natural frequency was implemented for an amplitude of 1 nmp-p at 36 MHz. The Q factor of the cantilever was 8000. Noise...

Millions of cantilevers for atomic force microscopy

Millions of single-crystal silicon cantilevers were fabricated by anisotropic etching of silicon by KOH. They could be tailored to measure from 500 nm to 100 μm in length and from 30 to 100 nm in thickness. Since the tips and the cantilevers were formed by a combination of crystal-line facets, they had very high uniformity, well-defined shape, and size. The density of the cantilevers was over 1 mil cantilevers per square centimeter. Typical mechanical characteristics of cantilevers measuring a few microns in length were spring constant a few N/m, natural frequency around 10 MHz, Q factor 5 in air, and 104 in vacuum. The natural frequency of cantilevers within the same row differed by 0.01%. Displacement measurement of the cantilever from the back surface of the silicon substrate by an infrared Fizeau interferometer had a visibility of 0.1.

Development of a Versatile Atomic Force Microscope within a Scanning Electron Microscope

We have developed a new versatile scanning electron microscope (SEM)-atomic force microscope (AFM) system capable of simultaneous SEM and AFM operation. The system consists of a SEM and a detachable AFM module that can be taken outside of the SEM chamber. By keeping the height of AFM module to less than 36 mm, and the AFM tip 5 mm below the highest point of the AFM module, clear SEM image and variable viewing angle are achieved. The AFM utilizes the conventional optical lever method. The sample stage of the AFM module is equipped with remote controlled piezoelectric actuators enabling three degree-of-freedom positioning with sub-nanometer resolution and millimeter range. The optical lever path can also be modified by remote control after the module is placed within the SEM. The SEM-AFM system can also be used as a tool for micro scale processing and manipulation by replacing the cantilever with a designated probe.

A Microcantilever-Based Picoliter Droplet Dispenser With Integrated Force Sensors and Electroassisted Deposition Means

This paper introduces a picoliter droplet dispenser relying on an array of silicon microcantilevers. The microcantilevers bear fluidic channels, and liquid transfer is achieved by a direct contact of the cantilever tip and the surface. A high degree of control over the location and geometry of the fabricated patterns is ensured by incorporating force sensors and electroassisted deposition means, i.e., electrowetting actuation and electrospotting, to the devices. The cantilever array, a PC-controlled stage, and an electronic circuit dedicated to the piezoresistance measurements form a closed-loop system that enables the automatic displacement of the array and the control of the deposition parameters. By using an external loading chip, different liquids are loaded onto the cantilevers, enabling the parallel deposition of several entities in a single spotting run. This paper details the design of the cantilevers assisted by finite-element modeling, the fabrication of the cantilever array, and the closed-loop operation. Moreover, proof-of-concept experiments are presented to demonstrate the versatility of our deposition system in terms of deposited materials and spot sizes. The control of the spotting process, the versatility of the printed materials, and the added electroassisted features prove that this tool has a real potential for research work and industrial applications.

Detection of gold colloid adsorption at a solid/liquid interface using micromachined piezoelectric resonators

Microfabricated piezoelectric resonators have been used in a liquid environment for real time detection of gold colloid adsorption at a solid/liquid interface. Negatively charged gold colloids in suspension in a buffer solution adsorb on the surface of the piezoelectric microresonator passivated with a silicon dioxide layer that has been functionalized with an amino-silane self-assembled monolayer. The mass loading induced by adsorption on the surface of the piezoelectric resonator leads to a change in resonant frequency. Measured frequency shift as a function of time incubation in a colloidal suspension was observed and correlated with the mass of adsorbed gold colloids.

Fabrication of a silicon based nanometric oscillator with a tip form mass for scanning force microcopy operating in the GHz range

The detectable force resolution of a mechanical oscillator used in scanning force microscopy can be improved by increasing its natural frequency fo and quality factor Q, and by decreasing the spring constant k and the temperature of operation T. For an oscillator having a structure that can be modeled as a concentrated mass-spring model, decreasing the mass of the oscillator is desirable since high fo can then be obtained without increasing the spring constant k. We have developed a novel fabrication technique for fabricating a nanometric oscillator by selective etching of silicon on insulator (SOI) wafers. The oscillator has the form of a tip supported by an elastic neck, and the tip serves as the mass. The tip and the neck length measure approximately 100 nm when fabricated using a separation by implanted oxygen wafer, and are around 1000 nm when fabricated using a bonded SOI wafer. The tips were made of silicon and the necks were made of silicon dioxide. The oscillator could be tailored to have its nat...

Fabrication of Silicon-Based Filiform-Necked Nanometric Oscillators

For the purpose of improving the resolution of force and mass detection of a noncontact-mode atomic force microscope (AFM), we are developing a mechanical oscillator of nanometric size which consists of a head mass supported by an elastic neck. A silicon-on-insulator (SOI) wafer with the laminated structure top Si layer/buried SiO2 layer/base Si is used in the fabrication of the nanometric oscillators. By selective etching of Si and SiO2, nanometric oscillators are successfully obtained. The top Si layer is etched to form a tetrahedral Si dot, which is the mass of the oscillator, and the buried SiO2 layer is etched to form the elastic neck resting on the base Si. The size of the tetrahedral Si dot is determined by the thickness of the top Si layer without depending on the precision of the lithography technique. We found that the cross-sectional shape of the SiO2 neck is a right-angled triangle and that the neck is situated at the center of the tetrahedral Si dot. According to calculations, the oscillators we obtained have spring constants around 1 N/m and a resonance frequency from 3 MHz to 300 MHz according to their dimensions.

A Silicon Based Nanometric Oscillator for Scanning Force Microcopy Operating in the 100 MHz Range

The detectable force resolution of a mechanical oscillator used in scanning force microscopy can be improved by increasing its natural frequency fo, quality factor Q, and by decreasing the spring constant k and the temperature of operation T. For an oscillator having a structure that can be modeled as a concentrated mass-spring model, decreasing the mass of the oscillator is desirable, since high fo can then be obtained without increasing the spring constant k. We have developed a novel fabrication technique for a head-neck shaped nanometric oscillator by selective etching of a laminated silicon substrate known as SIMOX. The oscillator head or mass measures 60 nm or 170 nm in thickness and 100 nm to 500 nm in diameter, depending on the size of the mask. The neck, which serves as an elastic support for the mass, measures 100 nm in length. The oscillator could be tailored to have its natural frequency in the range of 0.01 GHz to 0.5 GHz, and a spring constant between 10-1 N/m and 102 N/m.

Measurement of mechanical properties of three-dimensional nanometric objects by an atomic force microscope incorporated in a scanning electron microscope

An atomic force microscope that mounts on a sample stage of a scanning force microscope (SEMAFM) was developed. It was implemented for measurement of static mechanical properties of three-dimensional nanometric objects. The sample stage of the AFM was equipped with piezoelectric actuators enabling raster scanning as well as three degrees of freedom positioning with sub nm resolution and mm movable range. This enabled centering the AFM tip to the field of view of the SEM. Measurement of the spring constant and rupture force of three-dimensional nanometric structures was made possible. The SEMAFM also functioned as a conventional AFM.

Feasibility Studies on a Nanometric Oscillator Fabricated by Surface Diffusion for Use as a Force Detector in Scanning Force Microscopy.

A metal ball supported by a nanometric filiform neck, made by surface diffusion in vacuum, has the potential to be used as an oscillating force detector in scanning force microscopy. Although in most cases, the oscillator is extremely fragile and does not survive the transport from one vacuum chamber to the other, there still remains the possibility that it can be used if fabricated and utilized in situ. With the aim of characterizing the oscillator without breaking the vacuum, we have made a scanning tunneling/force microscope (STM, SFM) with a heating filament for fabrication of the oscillator in a scanning electron microscope (SEM). The formation of the oscillator was observed with the SEM, and then, the tip of the STM/SFM was used for the application of force to verify its feasibility as an oscillator.