Seiji Akita

Orientation and purification of carbon nanotubes using ac electrophoresis

Orientation and purification of carbon nanotubes have been demonstrated using ac electrophoresis in isopropyl alcohol. Nanotubes move towards the electrodes for all frequencies of applied electric field from 10 Hz to 10 MHz. However, carbon particles contained as impurites become harder to move with increasing frequency. The degree of orientation of nanotubes is higher when the frequency is higher and nanotubes are longer.

Carbon-nanotube tips for scanning probe microscopy: Preparation by a controlled process and observation of deoxyribonucleic acid

We report a controlled process to make carbon-nanotube tips for scanning probe microscopes. The process consists of three steps: (1) purification and alignment of carbon nanotubes using electrophoresis, (2) transfer of a single aligned nanotube onto a conventional Si tip under the view of a scanning electron microscope, and (3) attachment of the nanotube on the Si tip by carbon deposition. Nanotube tips fabricated using this procedure exhibit strong adhesion and are mechanically robust. Finally, the performance of these tips is demonstrated by imaging the fine structure of twinned deoxyribonucleic acid with tapping-mode atomic force microscopy in air.

Nanotweezers consisting of carbon nanotubes operating in an atomic force microscope

We have developed nanotweezers consisting of carbon nanotubes that will operate in an atomic force microscope. The two nanotubes were attached on the metal electrodes patterned on a conventional Si tip and their fixations were made by carbon deposition. These processes were made under the view of a scanning electron microscope. The application of a dc voltage to the two nanotube arms induces their movement to approach each other. The numerical simulation by taking into account the balance between the electrostatic attraction and the bending moment of the nanotubes well explains the motion of the nanotube arms.

Orientation of Carbon Nanotubes Using Electrophoresis

Electric field orientation of carbon nanotubes has been demonstrated using electrophoresis in isopropyl alcohol. The carbon nanotubes move towards the cathode during this process. The nanotubes align along the electric field due to the anisotropy of their electrophoresis velocity. The mobility has been estimated to be higher than ~5×10-5 cm2 V-1 s-1. The results suggest that it is possible to purify and handle carbon nanotubes using electrophoresis.

Fully Printed, Highly Sensitive Multifunctional Artificial Electronic Whisker Arrays Integrated with Strain and Temperature Sensors

Mammalian-mimicking functional electrical devices have tremendous potential in robotics, wearable and health monitoring systems, and human interfaces. The keys to achieve these devices are (1) highly sensitive sensors, (2) economically fabricated macroscale devices on flexible substrates, and (3) multifunctions beyond mammalian functions. Although highly sensitive artificial electronic devices have been reported, none have been fabricated using cost-effective macroscale printing methods and demonstrate multifunctionalities of artificial electronics. Herein we report fully printed high-sensitivity multifunctional artificial electronic whiskers (e-whisker) integrated with strain and temperature sensors using printable nanocomposite inks. Importantly, changing the composition ratio tunes the sensitivity of strain. Additionally, the printed temperature sensor array can be incorporated with the strain sensor array beyond mammalian whisker functionalities. The sensitivity for the strain sensor is impressively high (∼59%/Pa), which is the best sensitivity reported to date (>7× improvement). As the proof-of-concept for a truly printable multifunctional artificial e-whisker array, two- and three-dimensional space and temperature distribution mapping are demonstrated. This fully printable flexible sensor array should be applicable to a wide range of low-cost macroscale electrical applications.

Fully Printed Flexible Fingerprint-like Three-Axis Tactile and Slip Force and Temperature Sensors for Artificial Skin

A three-axis tactile force sensor that determines the touch and slip/friction force may advance artificial skin and robotic applications by fully imitating human skin. The ability to detect slip/friction and tactile forces simultaneously allows unknown objects to be held in robotic applications. However, the functionalities of flexible devices have been limited to a tactile force in one direction due to difficulties fabricating devices on flexible substrates. Here we demonstrate a fully printed fingerprint-like three-axis tactile force and temperature sensor for artificial skin applications. To achieve economic macroscale devices, these sensors are fabricated and integrated using only printing methods. Strain engineering enables the strain distribution to be detected upon applying a slip/friction force. By reading the strain difference at four integrated force sensors for a pixel, both the tactile and slip/friction forces can be analyzed simultaneously. As a proof of concept, the high sensitivity and selectivity for both force and temperature are demonstrated using a 3×3 array artificial skin that senses tactile, slip/friction, and temperature. Multifunctional sensing components for a flexible device are important advances for both practical applications and basic research in flexible electronics.

Carbon nanotube oscillators toward zeptogram detection

We demonstrate an application of a nanotube cantilever for zeptogram-level mass detection. This letter presents a quantitative method to measure the oscillation amplitude of a nanotube cantilever using a focused electron beam of a scanning electron microscope. The quality factor of ∼1000 for the nanotube cantilever is revealed and the resolution of the resonant frequency is achieved to be ∼10Hz, which corresponds to a mass range of less than 100zg at room temperature.

Toward Flexible and Wearable Human‐Interactive Health‐Monitoring Devices

This Progress Report introduces flexible wearable health-monitoring devices that interact with a person by detecting from and stimulating the body. Interactive health-monitoring devices should be highly flexible and attach to the body without awareness like a bandage. This type of wearable health-monitoring device will realize a new class of electronics, which will be applicable not only to health monitoring, but also to other electrical devices. However, to realize wearable health-monitoring devices, many obstacles must be overcome to economically form the active electrical components on a flexible substrate using macroscale fabrication processes. In particular, health-monitoring sensors and curing functions need to be integrated. Here recent developments and advancements toward flexible health-monitoring devices are presented, including conceptual designs of human-interactive devices.

Carbon Nanotube Resonator in Liquid

To achieve mass measurement of biological molecules in viscous fluids using carbon nanotube resonators, we investigated the vibration of nanotube cantilevers in water using the optical detection technique. In vacuum, we often found a few resonance modes of nanotube vibrations. However, the nanotube lost its fundamental oscillation once immersed in water, suggesting a great viscous resistance to the nanotube vibration in water. The resonant frequency of the nanotube in water decreased with lowering the water temperature, corresponding to the natural phenomenon by which liquid viscosity tends to increase at lower temperatures.

Extraction of inner layer from multiwall carbon nanotubes for scanning probe microscope tip

Carbon nanotube tips and tweezers, for scanning probe microscopes (SPM) open out the possibility of processing and manipulating in the nanometer-scale region. The tip radius of the nanotube is crucial to taking a high resolution image in the SPM measurement, but it is difficult to control the tip shape. In this study, we have discovered a process to prepare a capped thin nanotube tip by extracting an inner nanotube from multiwall nanotubes. We demonstrate the extraction of the inner layer of multiwall nanotubes for providing a capped sharp probe for SPM using electrical breakdown and the SEM manipulation.