In situ scanning electron microscopy of hydrogen embrittlement by near atmospheric-pressure hydrogen microplasma jet.

Elucidation of microstructures responsible for hydrogen embrittlement is hoped for research and development of high-strength low-alloy steel. For this purpose, a novel in situ scanning electron microscopy method of hydrogen embrittlement was developed by using a near atmospheric-pressure hydrogen microplasma jet excited by pulsed glow discharge. By the developed method, propagations of hydrogen embrittlement cracks in typical martensitic steel, Japanese Industrial Standards SCM435 steel, were successfully observed at frame rates at least up to 10.2 Hz with the same image quality as in high vacuum. The hydrogen microplasma jet neither elevated the specimen temperature nor damaged the specimen surface. Strain evolution prior to the crack propagations was also successfully observed in conjunction with the digital image correlation technique. It was found that a small electron scattering cross section of the hydrogen molecule, a large density of hydrogen ions in the near atmospheric-pressure microplasma jet, and stabilization of the glow discharge by the electron beam of the scanning electron microscope play a crucial role in the realization of the in situ observations.

Formation of Thermally Stable, High-Areal-Density, and Small-Diameter Catalyst Nanoparticles via Intermittent Sputtering Deposition for the High-Density Growth of Carbon Nanotubes.

We report the formation of thermally stable catalyst nanoparticles via intermittent sputtering deposition to prevent the agglomeration of the nanoparticles during thermal chemical vapor deposition (CVD) and for the high-density growth of carbon nanotubes (CNTs). The preparation of high-areal-density and small-diameter catalyst nanoparticles on substrates for the high-density growth of CNTs is still a challenging issue because surface diffusion and Ostwald ripening of the nanoparticles induce agglomeration, which results in the low-density growth of large-diameter CNTs during high-temperature thermal CVD. Enhancing the adhesion of nanoparticles or suppressing their diffusion on the substrate to retain a small particle diameter is desirable for the preparation of thermally stable, high-areal-density, and small-diameter catalyst nanoparticles. The intermittent sputtering method was employed to deposit Ni and Fe metal nanoparticles on a substrate for the synthesis of high-areal-density CNTs for Fe nanoparticle catalyst films. The metal particles deposited via intermittent sputtering with an interval time of over 30 s maintained their areal densities and diameters during the thermal CVD process in a vacuum for CNT synthesis. An interval of over 30 s was expected to oxidize the metal particles, which resulted in thermal stability during the CVD process. The intermittent sputtering method is thus a candidate process for the preparation of thermally stable catalyst films for the growth of a high density of long CNTs, which can be combined with the present CNT production process.

Fabrication of Self-Assembling Carbon Nanotube Forest Fishnet Metamaterials.

The investigation of the preparation of polystyrene (PS) nanosphere monolayers for the fabrication of carbon nanotube (CNT) forest fishnet metamaterial structures is studied in this paper, as a cheap alternative for top-down patterning methods. The precise control of dry etching conditions resulted in a highly controlled diameter of PS nanobeads, which were then used as a shadow mask for CNT fishnet preparation. The change of the size of the holes from 370 nm to 665 nm resulted in a gradual change of the CNT morphology from multi-walled to single-walled CNTs. The ultraviolet-visible (UV-Vis) reflectance spectra showed that the variation of the hole diameter resulted in the nonlinear light absorption in CNT fishnets that caused the change of the resonance frequency. The change of the fishnet wire width (inductance) and the hole size (capacitance) resulted in the blueshift of the broadband resonance frequency peak. The presented work has a significant potential to allow for the large-scale fabrication of CNT-based fishnet metamaterial structures for applications in energy harvesting, energy storage, solar cells, or optoelectronic devices, such as neuromorphic networks.

Shape-dependent infrared reflectance properties of CNT forest metamaterial arrays.

In this work, shape-dependent mid-infrared properties of novel split ring resonator (SRR) metamaterials composed of single-walled carbon nanotube (CNT) forest are investigated. The introduction of the gap and dip shape to the closed ring geometry reduced the total reflectance by 15%, due to the generation of circular currents and LC resonances in SRRs. The increase of the SRR height reduced the total IR reflectance by 25%. Unique one-dimensional anisotropic electric and photonic properties of CNTs, combined with an artificial refractive index induced in SRR circuits, will stimulate the development of new optoelectronics applications.

Novel high-frequency energy-efficient pulsed-dc generator for capacitively coupled plasma discharge.

The circuit design, assembly, and operating tests of a high-frequency and high-voltage (HV) pulsed dc generator (PDG) for capacitively coupled plasma (CCP) discharge inside a vacuum chamber are reported. For capacitive loads, it is challenging to obtain sharp rectangular pulses with fast rising and falling edges, requiring intense current for quick charging and discharging. The requirement of intense current generally limits the pulse operation frequency. In this study, we present a new type of PDG consisting of a pair of half-resonant converters and a constant current-controller circuit connected with HV solid-state power switches that can deliver almost rectangular high voltage pulses with fast rising and falling edges for CCP discharge. A prototype of the PDG is assembled to modulate from a high-voltage direct current (HVdc) input into a pulsed HVdc output, while following an input pulse signal and a set current level. The pulse rise time and fall time are less than 500 ns and 800 ns, respectively, and the minimum pulse width is 1 µs. The maximum voltage for a negative pulse is 1000 V, and the maximum repetition frequency is 500 kHz. During the pulse on time, the plasma discharge current is controlled steadily at the set value. The half-resonant converters in the PDG perform recovery of the remaining energy from the capacitive load at every termination of pulse discharge. The PDG performed with a high energy efficiency of 85% from the HVdc input to the pulsed dc output at a repetition rate of 1 kHz and with stable plasma operation in various discharge conditions. The results suggest that the developed PDG can be considered to be more efficient for plasma processing by CCP.

A new approach to surface activation of porous nanomaterials using non-thermal helium atmospheric pressure plasma jet treatment.

Non-thermal helium atmospheric pressure plasma jet treatment is applied to the surface activation of porous TiO2 nanoparticle assemblies. Treatment conditions such as the working distance of the plasma discharge, helium gas flow rate, and treatment time are optimized for effective removal of contaminants from the assembly surface. Laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF MS) is applied to detect trace amounts of contaminants on assembly surfaces. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations confirm that the nanoparticle assemblies retain their original perfect spherical structures as well as their ultra-fine convex-concave nano-surfaces even after the plasma jet treatment. N2 adsorption/desorption and X-ray diffraction (XRD) measurements show no significant changes in their BET specific surface areas and crystal structures, respectively. The plasma jet-treated TiO2 nanoparticle assemblies show a 3.8 fold improvement in their reaction rate constants for methylene blue degradation and a 2 fold enhancement of their photocurrents under UV irradiation when compared with untreated TiO2.

Plasma cell treatment device Plasma-on-Chip: Monitoring plasma-generated reactive species in microwells.

We have developed a plasma cell treatment device called Plasma-on-Chip that enables the real-time monitoring of a single cell culture during plasma treatment. The device consists of three parts: 1) microwells for cell culture, 2) a microplasma device for generating reactive oxygen and nitrogen species (RONS) for use in cell treatment, and 3) through-holes (microchannels) that connect each microwell with the microplasma region for RONS delivery. Here, we analysed the delivery of the RONS to the liquid culture medium stored in the microwells. We developed a simple experimental set-up using a microdevice and applied in situ ultraviolet absorption spectroscopy with high sensitivity for detecting RONS in liquid. The plasma-generated RONS were delivered into the liquid culture medium via the through-holes fabricated into the microdevice. The RONS concentrations were on the order of 10-100 µM depending on the size of the through-holes. In contrast, we found that the amount of dissolved oxygen was almost constant. To investigate the process of RONS generation, we numerically analysed the gas flow in the through-holes. We suggest that the circulating gas flow in the through-holes promotes the interaction between the plasma (ionised gas) and the liquid, resulting in enhanced RONS concentrations.

FIB Secondary Etching Method for Fabrication of Fine CNT Forest Metamaterials.

Anisotropic materials, like carbon nanotubes (CNTs), are the perfect substitutes to overcome the limitations of conventional metamaterials; however, the successful fabrication of CNT forest metamaterial structures is still very challenging. In this study, a new method utilizing a focused ion beam (FIB) with additional secondary etching is presented, which can obtain uniform and fine patterning of CNT forest nanostructures for metamaterials and ranging in sizes from hundreds of nanometers to several micrometers. The influence of the FIB processing parameters on the morphology of the catalyst surface and the growth of the CNT forest was investigated, including the removal of redeposited material, decreasing the average surface roughness (from 0.45 to 0.15 nm), and a decrease in the thickness of the Fe catalyst. The results showed that the combination of FIB patterning and secondary etching enabled the growth of highly aligned, high-density CNT forest metamaterials. The improvement in the quality of single-walled CNTs (SWNTs), defined by the very high G/D peak ratio intensity of 10.47, demonstrated successful fine patterning of CNT forest for the first time. With a FIB patterning depth of 10 nm and a secondary etching of 0.5 nm, a minimum size of 150 nm of CNT forest metamaterials was achieved. The development of the FIB secondary etching method enabled for the first time, the fabrication of SWNT forest metamaterials for the optical and infrared regime, for future applications, e.g., in superlenses, antennas, or thermal metamaterials.

DC Microplasma Jet for Local a:C-H Deposition Operated in SEM Chamber.

A DC micro plasma jet for local micro deposition of a:C-H film in the ambient vacuum of scanning electron microscope (SEM) chamber is proposed. Acetylene (C2H2) gas was locally fed into the chamber through an orifice shaped gas nozzle (OGN) at 6.6 sccm in flow rate by applying 80 kPa-inlet pressure with an additional direct pumping system equipped on the SEM chamber. As a cathode, a cut of n-type silicon (Si) wafer was placed right in front of the OGN at 200 µm gap distance. By applying a positive DC voltage to the OGN, C2H2 plasma was generated locally between the electrodes. During discharge, the voltage increased and the current decreased due to deposition of insulating film on the Si wafer with resulting in automatic termination of discharge at the constant source voltage. A symmetric mountain-shaped a:C-H film of 5 µm height was deposited at the center by operation for 15 s. Films were deposited with variation of gas flow rate, gap distance, voltage and current, and deposition time. The films were directly observed by SEM and analyzed by surface profiler and by Raman spectroscopy.

Carbon Nanotube (CNT) Honeycomb Cell Area-Dependent Optical Reflectance.

The relationship between the physical structure of carbon nanotube (CNT) honeycomb structures and their total, diffuse, and specular reflectance is investigated for the first time. It is found that CNT honeycomb structures with average cell areas of smaller than 30 µm² show a higher total reflectance. Particularly, a thinner, highly packed CNT (buckypaper) film, along with a larger wall height and higher ratio of wall height to cell area, markedly increase the total reflectance for cell areas smaller than 30 µm², which means that a higher total area of buckypapers in CNT walls and bottom areas increases the total reflectance, including the diffuse reflectance. It is also found that the total reflection of non-absorbed light in CNT honeycomb structures consists primarily of diffuse reflectance.

[Evaluation of the effects of microwave tissue coagulation, radiofrequency ablation or ultrasonically-activated scalpel on renal tissue as a minimally invasive therapy].

PURPOSE: The objective of this study was to optimize least invasive techniques, like microwave tissue coagulation (MCT), radiofrequency ablation (RFA) or ultrasonically-activated scalpel (USS) for the electric and thermal conduction in kidney. MATERIALS AND METHODS: Needle electrode of MCT, RFA or USS were inserted into pig's kidney, under general anesthesia. We examined if the interruption of renal artery or cooling of renal parenchyma by irrigation in the renal pelvis had an effect on the tissue temperature distribution and area of tissue degeneration. The tissue parenchyma temperatures were measured at regular intervals of area (each 2.5-5.0 mm) from needle electrode or hook probe and of time (each 10 sec) using by needle temperature sensor, and pathological investigations on the tissue degeneration of the renal parenchyma were done. RESULTS: By MCT, interruption of renal artery had no effect on the distribution of tissue temperature and the area of tissue degeneration. Cooling of renal parenchyma by irrigation in the renal pelvis did not affect the area of tissue degeneration but the tissue temperature was elevated significantly. By RFA, particular interest, interruption of renal artery and cooling of renal parenchyma enhanced to increase both the tissue temperature and the area of tissue degeneration. By USS, interruption of renal artery enhanced to increase both the tissue temperature and the area of tissue degeneration. Cooling of renal parenchyma by irrigation in the renal pelvis had no effect on the distribution of temperature and the area of tissue degeneration. We also examined weather cooling of renal parenchyma by several irrigation solutions which have different electric conductivity (EC) such as normal saline solution (EC: 15,800 microS/cm), tap water (EC: 133 microS/cm) and glucose solution (EC: 8.6 microS/cm) in the renal pelvis using ureteral catheter would effect on the distribution of temperature and the area of tissue degeneration. In MCT and USS, these solutions did not have any effect, but in RFA the degree of tissue temperature elevation by normal saline, tap water and glucose solution were high, intermediate and low, respectively. CONCLUSION: As RFA and USS tend to be affected by the surrounding environment, electric and thermal conductivity should be applied with caution, while using these techniques.