Low energy Si+, SiCH5+, or C+ beam injections to silicon substrates during chemical vapor deposition with dimethylsilane.

We found that the atomic-concentration-ratio of carbon to silicon (C/Si ratio) in silicon carbide (SiC) films formed by thermal chemical vapor deposition (CVD) was much greater than 1 when the source gas for CVD was dimethylsilane (DMS). Thus, we tried to change carbon-inclusion levels in the film by injecting some ion beams into a depositing SiC film during the CVD process with DMS. Three ion beams, i.e., Si+, SiCH5+, or C+ ions were injected to depositing SiC films. The energy of Si+, SiCH5+, and C+ ions was 110 eV. The temperature of the substrate was 800 °C. X-ray diffraction of the deposited films showed that 3C-SiC was included in all three samples. X-ray photoelectron spectroscopy (XPS) showed that the C/Si ratio of the obtained SiC film increased significantly following the Si+ or C+ ion beam irradiations. The XPS measurements also showed that the C/Si ratio of the SiC film obtained by injecting SiCH5+ beam during thermal CVD with DMS was lower than that of the SiC film formed by thermal CVD with DMS alone.

Synergistic Effect of Allium-like Ni9 S8 & Cu7 S4 Electrodeposited on Nickel Foam for Enhanced Water Splitting Activity.

This study explores a water-splitting activity using a biphasic electrodeposited electrode on nickel foam (NF). The *Ni9 S8 /Cu7 S4 /NF electrode with citric acid reduction exhibits superior OER (oxygen evolution reaction) and HER (hydrogen evolution reaction) performance with reduced overpotential and a steeper Tafel slope. The *Ni9 S8 /Cu7 S4 /NF electrode displays the ultra-low overpotential value of 212 mV for OER and 109 mV for HER at the current density of 10 mA cm-2 . The Tafel slope of 25.4 mV dec-1 for OER and 108 mV dec-1 for HER was found from that electrode. The maximum electrochemical surface area (ECSA), lowest series resistance and lowest charge transfer resistance are found in citric acid reduced electrode, showing increased electrical conductivity and quick charge transfer kinetics. Remarkably, the *Ni9 S8 /Cu7 S4 /NF electrode demonstrated excellent stability for 80 hours in pure water splitting and 20 hours in seawater splitting. The synergistic effect of using bimetallic (Cu&Ni) sulfide and enhanced electrical conductivity of the electrode are caused by reduction of metal sulfide into metallic species resulting in improved water splitting performance.

Magnetization reversal of [Co/Pd] perpendicular magnetic thin film dot on (Bi,La)(Fe,Co)O3multiferroic thin film by applying electric field.

A multilayer structure with a high-quality (Bi,La)(Fe,Co)O3multiferroic thin film/[Co/Pd] perpendicular magnetic thin film dots was fabricated for demonstrating magnetization reversal of [Co/Pd] dots under an applied electric field. Although the magnetization direction of the multiferroic thin film was reversed under the electric field, the magnetic properties of the multiferroic thin films were generally low. If the multiferroic thin film in this structure can control the magnetization direction of the highly functional magnetic thin film under an electric field, high-performance magnetic devices with low power consumption are easily obtained. The magnetic domain structure of the [Co/Pd] dots fabricated on the (Bi,La)(Fe,Co)O3thin film was analyzed by magnetic force microscopy (MFM). The structure was de-magnetized before the local electric-field application and magnetized after applying the field, showing reduced magnetic contrast of the dot. The line profile of the MFM image revealed a downward magnetic moment of 75%, which reversed to upward under the local electric field. Magnetic interaction between the (Bi,La)(Fe,Co)O3and [Co/Pd] layers was also observed in magnetization hysteresis measurements. These results indicate that the magnetization direction of the [Co/Pd] dots was transferred through the magnetization reversal of the (Bi,La)(Fe,Co)O3layer under a local electric field. That is, the magnetization of [Co/Pd] dots were reversed by applying a local electric field to the multilayer structure. This demonstration can potentially realize high-performance magnetic devices such as large capacity memory with low power consumption.

Low-energy Ar+ ion-beam-induced chemical vapor deposition of silicon dioxide films using tetraethyl orthosilicate.

This study was conducted to determine whether the simultaneous injections of Ar+ ions and tetraethyl orthosilicate (TEOS) to a substrate are able to fabricate a film on the substrate. The Ar+ ion energy was 100 eV. After the injections, we found a film deposited on the substrate. Following the analyses of the film with X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, it was found that the deposited film was silicon dioxide (SiO2). We conclude that the low-energy Ar+ ion-beam-induced deposition method using TEOS is useful for the growth of SiO2 films.

Low-energy Ar+ and N+ ion beam induced chemical vapor deposition using hexamethyldisilazane for the formation of nitrogen containing SiC and carbon containing SiN films.

We proposed an experimental methodology for producing films on substrates with an ion beam induced chemical vapor deposition (IBICVD) method using hexamethyldisilazane (HMDS) as a source material. In this study, both HMDS and ion beam were simultaneously injected onto a Si substrate. We selected Ar+ and N+ as the ion beam. The energy of the ion beam was 101 eV. Temperature of the Si substrate was set at 540 °C. After the experiments, films were found to be deposited on the substrates. The films were then analyzed by Fourier transform infrared (FTIR) spectroscopy, stylus profilometer, X-ray diffraction, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS). The FTIR and XPS results showed that silicon carbide films containing small amount of nitrogen were formed when Ar+ ions were injected in conjunction with HMDS. On the other hand, in the cases of N+ ion beam irradiation, silicon nitride films involving small amount of carbon were formed. It was noted that no film deposition was observed when HMDS alone was supplied to the substrates without any ion beam injections.

Identification of fragment ions produced by the decomposition of tetramethyltin and the production of low-energy Sn+ ion beam.

Tetramethyltin was decomposed in an ion source and the fragment ions produced were identified using a low-energy mass-selected ion beam machine. Dominant fragment ions were found to be H+, CH2+, and Sn+. Subsequently, fragment ions were mass-selected. The mass spectrum of the selected ions indicated that only a single peak appeared at the mass number of 120 u, being suggestive of the presence of 120Sn+ ions. The ion energy was set at the range of 20-100 eV. The Sn+ ion beam was irradiated to a Si substrate, and a film was then found deposited on the substrate after the ion beam irradiation. An X-ray diffraction measurement showed that the film obtained was metallic Sn. Then, the Sn+ ion beam was irradiated to a quartz crystal microbalance substrate. We found that most of the irradiated Sn+ ions were adhered to the substrate, at the ion energy levels of 25 and 58 eV, producing the Sn film, whereas a 107 eV Sn+ beam caused a significant proportion of Sn atoms in the film to detach from the substrate, probably due to sputtering.

Magnetic properties of (Bi1-xLax)(Fe,Co)O3 films fabricated by a pulsed DC reactive sputtering and demonstration of magnetization reversal by electric field.

(Bi1-xLax)(Fe,Co)O3 multiferroic magnetic film were fabricated using pulsed DC (direct current) sputtering technique and demonstrated magnetization reversal by applied electric field. The fabricated (Bi0.41La0.59)(Fe0.75Co0.25)O3 films exhibited hysteresis curves of both ferromagnetic and ferroelectric behavior. The saturated magnetization (Ms) of the multiferroic film was about 70 emu/cm3. The squareness (S) (= remanent magnetization (Mr)/Ms) and coercivity (Hc) of perpendicular to film plane are 0.64 and 4.2 kOe which are larger compared with films in parallel to film plane of 0.5 and 2.5 kOe. The electric and magnetic domain structures of the (Bi0.41La0.59)(Fe0.75Co0.25)O3 film analyzed by electric force microscopy (EFM) and magnetic force microscopy (MFM) were clearly induced with submicron scale by applying a local electric field. This magnetization reversal indicates the future realization of high performance magnetic device with low power consumption.

Magnetic domain structure imaging near sample surface with alternating magnetic force microscopy by using AC magnetic field modulated superparamagnetic tip.

For magnetic domain imaging, with a very high spatial resolution magnetic force microscope, the tip-sample distance should be as small as possible. However, magnetic imaging near the sample surface is very difficult with conventional magnetic force microscopy (MFM) because the interactive forces between the tip and sample include van der Waals and electrostatic forces along with a magnetic force. In this study, we proposed alternating MFM which only extracts a magnetic force near the sample surface without any topographic and electrical crosstalk. In the present method, the magnetization of an FeCo-GdO x superparamagnetic tip is modulated by an external AC magnetic field in order to measure the magnetic domain structure without any perturbation from the other forces near the sample surface. Moreover, it is demonstrated that the proposed method can also measure the strength and identify the polarities of the second derivative of the perpendicular stray field from a thin film permanent magnet with a DC demagnetized state and remanent state.

Magnetic resonance force microscopy using ferromagnetic resonance of a magnetic tip excited by microwave transmission via a coaxial resonator.

The present work proposes magnetic resonance force microscopy (MRFM) based on ferromagnetic resonance (FMR) modulation of a magnetic tip using microwave transmission via a coaxial resonator instead of using conventional microwave irradiation by an external antenna. In this MRFM, the coaxial resonator is electrically connected to the magnetic cantilever tip, which enables simple implementation of FMR excitation of a magnetic tip in conventional magnetic force microscopy. The FMR frequency of the tip can be easily extracted from the reflection spectrum of a transmission line connected to the magnetic tip. The excitation of tip FMR is confirmed from the microwave frequency dependence of the mechanical response of the tip oscillation. This MRFM is effective for extracting the magnetic interaction force near a sample surface without perturbation of its magnetic state. Nanometer-scale imaging of magnetic domain structures on a demagnetized thin-film permanent magnet is successfully demonstrated.

Quantitatively probing the magnetic behavior of individual nanoparticles by an AC field-modulated magnetic force microscopy.

Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometer scale spatial resolution remains an outstanding challenge. Current approaches, for example, Hall micromagnetometer and nitrogen-vacancy magnetometer, are limited by highly complex experimental apparatus and a dedicated sample preparation process. Here we present a new AC field-modulated magnetic force microscopy (MFM) and report the local and quantitative measurements of the magnetic information of individual magnetic nanoparticles (MNPs), which is one of the most iconic objects of nanomagnetism. This technique provides simultaneously a direct visualization of the magnetization process of the individual MNPs, with spatial resolution and magnetic sensitivity of about 4.8 nm and 1.85 × 10(-20) A m(2), respectively, enabling us to separately estimate the distributions of the dipolar fields and the local switching fields of individual MNPs. Moreover, we demonstrate that quantitative magnetization moment of individual MNPs can be routinely obtained using MFM signals. Therefore, it underscores the power of the AC field-modulated MFM for biological and biomedical applications of MNPs and opens up the possibility for directly and quantitatively probing the weak magnetic stray fields from nanoscale magnetic systems with superior spatial resolution.

Magnetic force microscopy using tip magnetization modulated by ferromagnetic resonance.

In magnetic force microscopy (MFM), the tip-sample distance should be reduced to analyze the microscopic magnetic domain structure with high spatial resolution. However, achieving a small tip-sample distance has been difficult because of superimposition of interaction forces such as van der Waals and electrostatic forces induced by the sample surface. In this study, we propose a new method of MFM using ferromagnetic resonance (FMR) to extract only the magnetic field near the sample surface. In this method, the magnetization of a magnetic cantilever is modulated by FMR to separate the magnetic field and topographic structure. We demonstrate the modulation of the magnetization of the cantilever and the identification of the polarities of a perpendicular magnetic medium.

Quantitative analysis of the magnetic domain structure in polycrystalline La(0.7)Sr(0.3)MnO3 thin films by magnetic force microscopy.

The nanoscale magnetic domain structure of the polycrystalline La(0.7)Sr(0.3)MnO(3) granular thin films was imaged with a developed magnetic force microscopy technique by simultaneously detecting both the perpendicular and in-plane components of magnetic field gradients during the same scan of the tip oscillation. The characteristics of both the perpendicular and in-plane magnetic field gradient at the grain edges or the nonmagnetic grain boundary phase for LSMO films were demonstrated and can be used to evaluate the magnetic domain structure and magnetic isolation between neighboring grains. A two dimensional signal transformation algorithm to reconstruct the in-plane magnetization distribution of the polycrystalline LSMO thin films from the measured raw MFM images with the aid of the deconvolution technique was presented. The comparison between the experimental and simulated MFM images indicates that the magnetic grains or clusters are in the single domain (SD) or multi-domain (MD) state with the magnetic moments parallel or anti-parallel to the effective magnetic field of each grain, possibly due to the need for minimizing the total energy. The quantitative interpretation of the magnetic domain structure indicates that the large magnetoresistance in the studied LSMO films is mainly due to tunnel effect and scattering of conducted electrons at the nonmagnetic grain boundary phase related to the different configurations of magnetic domain states between neighboring grains.