Chih-Chung Su

Fabrication of High Sensitivity Carbon Microcoil Pressure Sensors

This work demonstrates a highly sensitive pressure sensor that was fabricated using carbon microcoils (CMCs) and polydimethylsiloxane (PDMS). CMCs were grown by chemical vapor deposition using various ratios of Fe-Sn catalytic solution. The pressure sensor has a sandwiched structure, in which the as-grown CMCs were inserted between two PDMS layers. The pressure sensor exhibits piezo-resistivity changes in response to mechanical loading using a load cell system. The yields of the growth of CMCs at a catalyst proportion of Fe:Sn = 95:5 reach 95%. Experimental results show that the sensor achieves a high sensitivity of 0.93%/kPa from the CMC yield of 95%. The sensitivity of the pressure sensor increases with increasing yield of CMCs. The demonstrated pressure sensor shows the advantage of high sensitivity and is suitable for mass production.

Piezoelectric Sensor to Measure Soft and Hard Stiffness with High Sensitivity for Ultrasonic Transducers

During dental sinus lift surgery, it is important to monitor the thickness of the remaining maxilla to avoid perforating the sinus membrane. Therefore, a sensor should be integrated into ultrasonic dental tools to prevent undesirable damage. This paper presents a piezoelectric (PZT) sensor installed in an ultrasonic transducer to measure the stiffness of high and low materials. Four design types using three PZT ring materials and a split PZT for actuator and sensor ring materials were studied. Three sensor locations were also examined. The voltage signals of the sensor and the displacement of the actuator were analyzed to distinguish the low and high stiffness. Using sensor type T1 made of the PZT-1 material and the front location A1 provided a high sensitivity of 2.47 Vm/kN. The experimental results demonstrated that our design can measure soft and hard stiffness.

Fabrication of Aligned Carbon Nanocoil Thermal Sensor With a High Temperature Coefficient of Electrical Resistance at 25–100 °C

This paper presents a novel thermal sensor using carbon nanocoils (CNCs) as sensing elements with a high-temperature coefficient of electrical resistance (TCR) at 25-100 °C. CNCs have been synthesized at 700 °C using Fe-Sn catalytic solution by chemical vapor deposition from acetylene. The as-grown CNC has a coil diameter of 200-1500 nm, a pitch of 100-1000 nm, and a fiber diameter of 80-550 nm. The CNC thermal sensor was fabricated in four types in this paper: bulk CNCs, a single CNC, multiple CNCs, and bundled CNCs. The thermal sensors of CNCs were measured in a furnace to evaluate the TCR of the thermal sensor at 25-100 °C. It was found that the TCR of thermal sensors of CNCs was distributed from -0.12%/°C to -1.12%/°C, depending on different sensing elements. The stabilizing contact resistance between CNCs and electrodes was improved by annealing. The high TCR values of thermal sensors of CNCs suggest the Schottky contact with the interface of CNCs and electrode after annealing.

Improving the Compressive Strength of Carbon Nanotube Turfs by Adding Iron Nanowires to the Nanotube Core

The cores of carbon nanotubes (CNTs) are partially filled by Fe nanowires during synthesis by chemical vapor deposition from an acetylene-ferrocene mixture. A Fe-filled CNT turf is produced with a height exceeding 100 μm and a Fe-filling ratio of 33%-48%. The diameters of the Fe nanowires inside the CNTs range from 10 to 20 nm. With the Fe-filling of the CNT core rising to 48.1%, the compressive modulus of the turf increases from 4.9 to 71.8 MPa and the hardness from 0.534 to 2.044 MPa.

Synthesize uniform carbon nanocoils by anodic aluminum oxide

In this study, we utilized porous anodic aluminum oxide (AAO) template to assist synthesizing carbon nanocoils with high uniformity. By confining the space of growth, we have successfully obtained carbon nanocoils with superior uniformity. Synthesizing carbon nanocoils with catalytic thermal chemical vapor deposition assisted by removable anodic aluminum oxide template. We obtained uniform carbon nanocoils which has coil diameter between 100 ~ 500 nm, pitch between 100 ~ 500 nm, and fiber diameter between 60 ~ 260 nm, both were decreased more than 50 percent compared with which growth without the template. The approach of synthesizing CNCs with superior uniformity is able to be extensively integrated into electronic devices for further applications

Fabrication of carbon nanocoils based tactile sensor

This study investigated the high sensitivity tactile sensors which were fabricated using carbon nanocoil mats (CNCs) and PDMS (polydimethyl siloxane). Tactile sensor is the sandwiched structure that the CNCs were inserted between two PDMS layers. The sensing principle is based on the piezoresistivity effect of the CNCs. We first synthesized the CNCs using the chemical vapor deposition technique using two components of the catalyst. The yield of CNCs growth reaches 95 % at the mass ratio of the catalyst Fe:Sn at 95:5. To investigate the effect of the composition ratio of carbon nanocoils and carbon fibers, the tactile sensors with different ratio of the CNC composition were fabricated for experimental comparison. It is found that the ratio of carbon fibers and carbon nanocoils in the sensor dramatically affected the sensing characterization. Finally, the tactile pressure can achieve the sensitivity of 0.99 %/KPa.

Compressive Strength Enhancement of Vertically Aligned Carbon Nanotube Forests by Constraint of Graphene Sheets

We fabricated a 3D sandwich hybrid material composed of graphene and vertically aligned carbon nanotube forests (VACNTs) using chemical vapor deposition. The graphene was first synthesized on Cu foil. Then it was transferred to a substrate which had a pre-deposited catalyst Fe film and a buffer film of Al2O3 for the growth of VACNTs. The VACNTs were grown underneath the graphene and lifted up the graphene. The graphene, with its edges anchored on the Al2O3, provided a constrained boundary condition for the VACNTs and hence affected the growth height and mechanical strength of the VACNTs. We prepared three groups of samples: VACNTs without graphene, VACNTs with graphene transferred once (1-Gr/VACNTs), and VACNTs with graphene transferred twice (2-Gr/VACNTs). A nano-indentation system was used to measure the reduced compressive modulus (Er) and hardness (H). The Er and H of Gr/VACNTs increased with the number of transfers of the anchored graphene. The 2-Gr/VACNTs had the largest Er and H, 23.8 MPa and 912 KPa, which are 6.6 times and 5.2 times those of VACNTs without the anchored graphene, respectively. In this work, we have demonstrated a simple method to increase the mechanical properties and suppress the height of VACNTs with the anchored graphene and number of transfers.

Thermoelectric property of vertically aligned carbon nanotube carpets

This work is to consider the thermoelectric effect based on the vertically aligned carbon nanotube carpets (VACNTs) and vertically aligned iron-filled CNTs (Fe-filled VacNts) have been grown using a chemical vapor deposition (CVD) method. The results show the Seebeck coefficient can be improved by controlling the layer number of Fe-filled VACNTs. It found the Seebeck coefficient of the single layer Fe-filled VACNTs is approximately -65 μV/K at 120 °C, which is two times higher than that of non Fe-filled VACNTs. Briefly, this work presented a simple method for producing thermoelectric materials with well Seebeck coefficient performance.

Synthesis of uniform carbon micro-coils by using hybrid catalyst of Fe thin film and SnO 2 powder

Carbon micro-coils (CMCs) with high yield have been synthesized by chemical vapor deposition (CVD) using hybrid catalyst. The hybrid catalysts consist of two forms, i.e. thin film catalyst and powered catalyst, which was selected. It was found that the prepared catalyst by the combination of Fe thin film and SnO2 power exhibits the highest uniformity, which significantly results in uniform carbon micro-coils. The optimum condition for thickness of Fe thin film is 300 nm, and the size of SnO2 powders is approximate 100 nm. The fiber diameter of the as-grown CMCs is determined by the size of the SnO2 particles after treatment with Fe film by CVD. CMCs with controlled diameters have an average coil diameter of 3.36 µm, a fiber diameter of 385 nm, and a pitch of 1.82 µm. A 90% of yield of CMCs is achieved.

Growth of Carbon Nanocoils Using Chemical Vapor Deposition

We present the synthesis of carbon nanocoils using the chemical vapor deposition technique with metal catalysts on silicon substrates. The optimum synthesis conditions and coil geometry are summarized. The coils have distribution of the outside diameter of 300 nm to 1200 nm, wire diameter of 150 nm to 400 nm and the pitch of the coil of 150 nm to 1200 nm. Applications of the developed carbon nanocoils can be electro-mechanical sensing and the electro-magnetic insulation.