Focused-ion-beam Chemical Vapor Deposition Research Articles

Shape Memory Alloy-Based Microscale Bending Actuator Fabricated by a Focused Ion Beam Chemical Vapor Deposition (FIB-CVD) Gap-Filling Process

Focused ion beam chemical vapor deposition (FIB-CVD) processes can be used to fabricate nano-/microstructures by enabling highly localized material deposition. Due to these advantages, the FIB-CVD process has been utilized extensively as a method for material analysis and device fabrication in the fields of nano-/microscale electronics, sensors, drivers, bio, and optics. In this study, we fabricated shape memory alloy (SMA) carbon composites using an FIB-CVD process and performed a micro-tensile test to evaluate the mechanical properties of the fabricated composites. According to the results of the tensile test, the fabricated composite structure had higher stiffness values and lower maximum tensile strength values than general SMA materials. Based on our experimental results, we fabricated an SMA microscale bending actuator by localized carbon block deposition and evaluated the bending characteristics of the microactuator.

Fabrication of Micro Structures by Ultrashort Voltage Pulse Electrical Discharge Machining

The machining of small holes and array holes has been a difficult problem in machining field. Tiny hole is widely used in mechanical field, for instance, fuel injection nozzles, spinneret holes for synthetic fibers and wire drawing dies. This paper investigated the application of EDM (electrical discharge machining) to the fabrication of micro structures. There are obvious limitations in the process of micro-electrical discharge machining, such as electrode wear, unstable discharge condition and low machining efficiency. The effects of EDM parameters were investigated, such as voltage, pulse frequency, and frequency of ultrasonic vibration applied to electrode. Micro holes were machined with Pt electrode made by focused-ion-beam chemical vapor deposition (FIB-CVD) and Cu electrode made by wire-electrode cutting. The comparison experiments between EDM and ECM (electrochemical machining) indicated that the processing of ECM has serious stray current corrosion and poor machining precision. Moreover, the workpiece vibration was firstly proposed to be utilized in the micro-electrical discharge machining. It can be concluded that maximum machine could be obtained under the amplitude ratio of 76%, which was an appropriate parameter.

Fabrication of Micro/Nanoelectrode Using Focused-ion-Beam Chemical Vapor Deposition, and its Application to Micro-ECDM

Micro electro-chemical discharge machining (micro-ECDM) is a key technology in the precision manufacturing. The electrode, which is the key element for achieving a high-precision ECDM, attracts the interests of many researchers. However, regarding the fabrication techniques of the electrode, the achievable precisions are still resting on micrometer scale, the processes are not simple, or electrodes with high complex three-dimensional (3D) shapes are difficult to be obtained. Basing on such a background, in this work, focused-ion-beam chemical vapor deposition (FIB-CVD) which is an effective tool in fabricating 3D micro/nanostructure for achieving various micro/nanoelectromechanical devices (MEMS/NEMS), was first time introduced to fabricate micro/nanoelectrode and furthermore ECDM processes using FIB-CVD-fabricated electrodes could be attempted. Differing to the conventional metallic electrodes, micro/nanoelectrodes in the material of amorphous platinum (Pt) were obtained. Three electrodes with the same diameter 10μm and height 28μm were fabricated on the polished tip surfaces of stainless needles, and consequently applied to micro-ECDM with varied low open voltages 10, 12.5 and 15V. Microholes were fabricated on the 304 austenitic stainless steel. The hole diameter and the unilateral discharge gap were found to be almost linearly increasing with the increase of open voltage. In case of using the open voltage 10V, the unilateral discharge gap was found to be 6.6μm. Moreover, fabrications of pillar, horn, corner, array types of 3D nanoelectrodes were demonstrated. These results indicate the potentialities of 3D micro-ECDM using complex 3D micro/nanoelectrode, and a deeper study into the science of ECDM/EDM phenomenon at submicron scale.

Structure Transformation of Bended Diamond-Like Carbon Free-Space Nanowiring by Ga Focused-Ion-Beam Irradiation

We observed Ga focused-ion-beam (FIB) irradiation effect onto diamond-like carbon (DLC) free-space nanowiring (FSW) fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD). A bended FIB-CVD FSW completely strained after Ga-FIB irradiation with raster scanning. This is probably caused by generation of compression stresses onto the surface of FSW, because the surface state of the nanowire changed with Ga-FIB irradiation. Transmission electron microscope (TEM) study indicates that Ga of FSW core part disappeared after Ga-FIB irradiation and a near-edge X-ray absorption fine structure (NEXAFS) analysis revealed C-Ga bond formation onto the surface. This is attributed to a movement of Ga from the core region to the surface, and/or an adsorption of Ga onto the surface by Ga-FIB scanned irradiation. The transformation of FSW is not only fascinating as physical phenomenon, but also effective for fabricating various 3-dimensional nanodevices equipped with nanowires utilized as electric wiring.

Humidity sensing characteristics of focused ion beam-induced suspended single tungsten nanowire

We demonstrated humidity sensing characteristics based on a suspended single tungsten nanowire. The nanowire is synthesized on batch-processed microelectrodes by focused ion beam-chemical vapor deposition (FIB-CVD) using tungsten hexacarbonyl [W(CO)6] as the precursor gas. Two different humidity sensing mechanisms, electrothermal sensing and chemical sensing, were demonstrated using as-deposited and annealed nanowires. When the relative humidity level was increased from 30% to 80%, the DC resistance of the as-deposited nanowire immediately showed 5.68% decrease by electrothermal sensing mechanism. Since the as-deposited nanowire is amorphous structure, no chemical sensing response was observed for the as-deposited nanowire case. On the contrary, the tungsten nanowire annealed at 700°C showed a 13.2% increase in its DC resistance by the chemical sensing mechanism when the relative humidity level was increased from 40% to 80%, revealing enhanced sensor responsiveness and improved linearity than the electrothermal sensing using as-deposited nanowire.

Growth of ultra-long free-space-nanowire by the real-time feedback control of the scanning speed on focused-ion-beam chemical vapor deposition

Free-space-nanowiring using focused-ion-beam chemical vapor deposition (FIB-CVD) has been demonstrated to enable the fabrication of various innovative three-dimensional (3D) nanodevices with overhanging structures. However, due to the change in growth characteristics, it is difficult to fabricate a free-space-nanostructure larger than several micrometers while keeping a uniform angle. Normally, the free-space-nanowire deviates downward from the starting angle after becoming approximately 2 μm long. In this study, the authors proposed a technology to fabricate ultralong horizontal free-space-nanowire by using the growth angle dependency of specimen current and carrying out feedback control of the scanning speed on Ga+ FIB. The feedback control system monitors the specimen current and controls the scanning speed of FIB in real-time while judging the value of specimen current. Ultralong horizontal free-space-nanowire with a length more than 30 μm and a length to thickness ratio as high as 300 was achieved. The results verified that real-time feedback control on FIB-CVD is a promising technology for the fabrication of large scale free-space-nanostructure and that a larger variety of 3D nanodevices can be achieved by applying this technology to the computer pattern generator.

Synthesis and Bidirectional Frequency Tuning of Cantilever-Shape Nano Resonators Using a Focused Ion Beam

The synthesis of cantilever-shape nano resonators and their resonant frequency tunings in both upward and downward directions have been demonstrated using FIB-CVD (focused ion beam-chemical vapor deposition). The in situ experimental observations of mechanical resonances as well as cutting and adding of resonator materials have been accomplished inside the FIB vacuum chamber. Extending the length of the cantilever-shape resonator by 500 nm scale using either the same material or alternating different materials effectively reduced resonant frequency. On the other hand, direct cutting and gradual trimming of the end point of nano resonator increases its resonant frequency. This simple yet versatile synthesis and frequency tuning scheme could be applicable to both constructing micro/nano scale resonators and tuning nanostructures with reduced efforts and enhanced efficiency.

Superconductivity in Tungsten-Carbide Nanowires Deposited from the Mixtures of W(CO)6 and C14H10

Tungsten-carbide (W-C) nanowires have been deposited by focused-ion-beam chemical vapor deposition (FIB-CVD). Mixtures of C14H10 and W(CO)6 are used as precursors. For certain precursor ratios, our nanowires become superconducting with a Tc as high as 5.8 K. Also, freestanding W-C nano pillars were grown by FIB-CVD. The growth rate of the deposition from the mixture is at most 4.25 times higher than W(CO)6 is used as the precursor. This growth rate greatly facilitates the fabrication of three-dimensional superconducting structures.

Three-Dimensional Nanostructure Fabrication by Controlling Downward Growth on Focused-Ion-Beam Chemical Vapor Deposition

Focused-ion-beam chemical vapor deposition (FIB-CVD) is a key technology to achieve the arbitrary three-dimensional (3D) nano- and microstructure fabrication. However, most of 3D nanostructure fabrications have focused on upward or lateral growth whereas few of them focused on downward growth. The downward growth characteristics of air nanowires were investigated in order to achieve the fabrication of more arbitrary 3D nanostructures. As a result, it was not able to fabricate a 1 µm long downward growth nanowire with an angle lower than -10°. Also, we found that a nanowire with an angle lower than -18° cannot be fabricated. Furthermore, we demonstrated the fabrication of 3D nanostructure including downward growth by changing the scan speeds of Ga+ FIB during fabrication. With controlling the downward growth, the fabrication of more various 3D nanostructures can be achieved.

Thermal Durability of Diamond Like Carbon Films Containing Tungsten Fabricated by Focused-Ion-Beam Chemical Vapor Deposition

Diamond like carbon film containing tungsten (W-DLC) was fabricated by focused-ion-beam chemical-vapor deposition (FIB-CVD), and its thermal durability was investigated using near the carbon K-edge X-ray absorption fine structure (C-K NEXAFS) spectroscopy and a combination of Rutherford backscattering and elastic recoil detection analysis, in comparison with those of commercial DLC and W-DLC films. The concentration of W in the films did not decrease when the annealing temperature was increased, while the concentration of H did. The sp2/(sp2+sp3) ratio of carbon atoms in the films increased with annealing temperature. The W-DLC film fabricated by FIB-CVD unchanged after annealing for 32 h at 873 K in vacuum. Its thermal durability was comparable to that of commercially available films.

Three-Dimensional Nanostructure Fabrication by Controlling Downward Growth on Focused-Ion-Beam Chemical Vapor Deposition

Focused-ion-beam chemical vapor deposition (FIB-CVD) is a key technology to achieve the arbitrary three-dimensional (3D) nano- and microstructure fabrication. However, most of 3D nanostructure fabrications have focused on upward or lateral growth whereas few of them focused on downward growth. The downward growth characteristics of air nanowires were investigated in order to achieve the fabrication of more arbitrary 3D nanostructures. As a result, it was not able to fabricate a 1 µm long downward growth nanowire with an angle lower than -10°. Also, we found that a nanowire with an angle lower than -18° cannot be fabricated. Furthermore, we demonstrated the fabrication of 3D nanostructure including downward growth by changing the scan speeds of Ga+ FIB during fabrication. With controlling the downward growth, the fabrication of more various 3D nanostructures can be achieved.

OS2-2-4 集束イオンビーム化学気相成長法による空中水平長尺ナノ構造形成(OS2 三次元の微細形状創成技術(2))

Focused-ion-beam chemical vapor deposition (FIB-CVD) is a key technology to achieve the arbitrary three-dimensional (3D) nano- and microstructure fabrication. It has been demonstrated of free-space-nanowiring, which enables the fabrication of various innovative devices with overhanging structures. However, due to the inhomogeneous distribution of source gas density, and the accumulation of heat and electric charge on nanostructure, it is difficult to fabricate ultra-long free-space-nanowire with a constant growth angle. Usually, the free-space-nanowire deviates downward from the starting angle after growing several micrometers long. And also, it was noted that the intensity of substrate current and secondary electrons (SEs) depends on the growth angle of nanowire. This growth angle dependency is useful to monitor the growth shape during fabrication. In this study, we developed a technology to fabricate ultra-long free-space-nanowire with a length more than 10 μm by real-time monitoring the substrate current and feedback controlling the scanning speeds of FIB during the fabrication.

Selective graphene growth from DLC thin film patterned by focused-ion-beam chemical vapor deposition

The authors were able to grow a few-layer graphene film on a SiO2 substrate directly and selectively by using focused-ion-beam chemical vapor deposition (FIB-CVD) and a Ga evaporation process. FIB-CVD can control the thickness of the diamondlike carbon (DLC) film and potentially control the number of graphene layers, and Ga evaporation causes the direct transformation of patterned DLC into graphene. DLC was graphitized by annealing with a Ga film at 1000 °C and 1100 °C. Increasing the thickness of the Ga film resulted in a graphitized pattern that had a strong Raman 2D band. The formation of graphene above and around a dimple on the SiO2 layer indicates that Ga dissolved the DLC and graphene precipitated not between the liquid Ga and the SiO2 substrate but, rather, on the small droplets of Ga. This behavior is different than that reported in previous studies of graphitization at the interface between a carbon layer and liquid Ga.

Annealing Effect of W Incorporated Diamond-Like Carbon Fabricated by Ga Focused Ion Beam Chemical Vapor Deposition

The effects of thermal annealing of W incorporated diamond-like carbon (W-DLC) films fabricated with focused ion beam chemical vapor deposition (FIB-CVD) were investigated using X-ray absorption fine structure near the carbon K-edge (C-K NEXAFS) and the combination of Rutherford backscattering (RBS) and elastic recoil detection analysis (ERDA). W-DLC films were annealed for 32 h at temperatures, Ta, between 673 and 1073 K. Comparing the Ta dependences of Ga and H contents obtained from RBS-ERDA and the sp2/(sp2 + sp3) ratios from C-K NEXAFS, it was found that even a trace amount of W incorporation into DLC films fabricated by Ga+ FIB-CVD may cause a significant sp3 →sp2 structural change.

Nanoimprint replication of nonplanar nanostructure fabricated by focused-ion-beam chemical vapor deposition

Nanoimprint lithography (NIL) is a very useful technique for replicating planar nanostructures at low cost with high throughput, but an expansion from planar to nonplanar will probably be required to enhance the functional capabilities of nanodevices. On the other hand, focused-ion-beam chemical vapor deposition (FIB-CVD) is a promising technology for fabricating nonplanar nanostructures. In this study, the authors demonstrated a new nonplanar replication method using a combination of FIB-CVD and NIL to achieve nonplanar replication with submicrometer feature sizes. Furthermore, they replicated nonplanar nanostructures by using step and repeat NIL.

1-1 集束イオンビーム化学気相成長法における成長高さ補正に関する研究(OS2-1 三次元の微細形状創成技術)

Focused-ion-beam chemical vapor deposition (FIB-CVD) is a key technology to fabricate the three-dimensional (3-D) nano- and microstructures. However, FIB-CVD has a problem on the faithfulness of the 3-D structure growth. Therefore, vertical growth characteristics of a quadrangular prism as an evaluation model were evaluated in this study. As a result, the growth height of a quadrangular prism structure depended on the number of the irradiation point, and the correction method of a growth error was also examined to achieve the arbitrary 3-D structures. And, we found that the vertical growth rates follow the sigmoid function and the vertical growth error can be corrected by controlling the irradiation time of Ga^+ FIB.

Influence of Processing Conditions on Mechanical and Structural Properties of DLC Produced by FIB-CVD Method

ABSTRACTInfluence of processing condition on mechanical and structural properties of diamond-like carbon (DLC) by focused ion-beam chemical vapor deposition (FIB-CVD) method was investigated. The DLC specimens were produced under conditions of varying supplied amount of material gas and probe current of FIB. Volume determination results of DLC structures indicated that a deposition rate was increased with both the amount of gas and the probe current. To evaluation of mechanical property, indentation hardness was measured by a nano-indentation tester. From evaluation of mechanical property, it was found that the indentation hardness was sensitive to the processing condition, showing in the range of 8-13 GPa. The hardness of DLC structures was seemed to be lower when etching process higher contributed for formation process. Crystallographic structure of DLC remained amorphous even though the mechanical properties varied widely. Results of hydrogen concentration measurement indicated that increase of hydrogen concentration might lead to decrease of hardness.

Piezoresistive effect in the three-dimensional diamondlike carbon nanostructure fabricated by focused-ion-beam chemical vapor deposition

In this study, the electrical material characteristics of a three-dimensional (3D) diamondlike carbon (DLC) structure fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) were evaluated to realize functional 3D nano- and micromechanical devices based on the piezoresistive material. However, the DLC cantilever structure fabricated by FIB-CVD did not exhibit piezoresistive properties due to the incorporated gallium (Ga), which was implanted by Ga+ FIB irradiation. Therefore, a method for the modification of material characteristics was examined to introduce piezoresistive properties in the 3D DLC structure fabricated by FIB-CVD. Long-time annealing (12 h or more) at a low temperature (300 °C) was found to be an effective method to realize a 3D DLC structure with piezoresistive properties. Long-time annealing at low temperatures caused Ga elimination from the DLC without any change in the sp2/(sp2+sp3) ratio. The values of the gauge factor were in the range of 2–34. 3D nano- and microstructures with piezoresistive properties could be realized by FIB-CVD and annealing treatment.

Non-Core–Shell Nanostructure Deposition on Focused-Ion-Beam Chemical Vapor Deposition

Nano- and microstructures fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) have a core–shell structure caused by the scattering profiles of Ga ions and secondary electrons (SEs). This structural characteristic makes it difficult to design functions of nano-electromechanical devices. Therefore, non-core–shell structure deposition by the control of SE emission was examined to facilitate the function design of nanoelectromechanical devices. Non-core–shell structure deposition was achieved by applying voltage during carbon nanostructure growth. We also evaluated the growth characteristics of non-core–shell structure deposition. We found that the growth rate of a nanostructure did not change when voltage was applied. Furthermore, we evaluated the mechanical material characteristics (density and Young's modulus) of a non-core–shell structure by measuring of the resonant frequency shift of a Si cantilever using the electron beam method. We found that the non-core–shell structure had a high density (6.5 g/cm3) and a high Young's modulus (800 GPa). These results indicate that the technique for non-core–shell structure deposition is useful in achieving nanoelectromechanical devices.

Mechanical Characteristics of Nanosprings Fabricated by Focused-Ion-Beam Chemical Vapor Deposition Using Ferrocene Source Gas

The mechanical characteristics of iron-containing nanosprings (Fe-containing nanosprings) fabricated by focused-ion-beam chemical vapor deposition (FIB-CVD) using a ferrocene (C10H10Fe) source gas were investigated. The shear and Young's moduli were 34 and 92 GPa, respectively. We also evaluated the annealing effect of Fe-containing nanosprings and observed a droplet containing Fe and Ga on the nanospring after annealing at 600 °C. The spring constant rapidly decreased after annealing at 600 °C. By scanning electron microscopy energy–dispersive X-ray spectroscopy (SEM–EDX) and transmission electron microscopy energy–dispersive X-ray spectroscopy (TEM–EDX) line analysis, it was confirmed that the decrease in the spring constant was due to Ga removal.