Shigekazu Nagai

Investigation of stability and charge state of Ne and Ar gas field ion source by time-of-flight mass spectrometry

Charge state distribution of the working gases of the Ar and Ne gas field ion source (GFIS) were investigated by the time-of-flight mass spectrometry using a newly designed experimental system. GIFS emitters having few atoms on the top of the (111) surface of tungsten were formed by a remolding and field evaporation sequence with electrochemically etched oriented tip. At a probe current of about 1 pA, the ratio of standard deviation of fluctuation and average ion current <2.5% was recorded from a single atom terminated emitter of the Ar GFIS. Mass analysis by the time-of-flight spectrometer showed that there were only singly charged ions both of the Ne and Ar GFIS. Furthermore, no impurity gas ion was detected in the mass spectrum.

Spin polarization of field-emitted electrons from half-metallic Co2MnSi thin films grown on a W(001) facet.

We measured spin polarization of electrons field-emitted from half-metallic Co(2)MnSi thin film grown on a W(001) facet via chromium buffer layer using Mott scattering. For spontaneously magnetized samples, values of polarization at room temperature were observed in a range from 10% to 46% and the polarization direction was 110 orientation of substrate tungsten, which agreed with an easy axis of magnetization of bulky Co(2)MnSi. An enhancement of polarization was observed as a consequence of applying a magnetic field of 350G perpendicular to the emitter axis after the annealing at 800K. This result is considered to be caused by improvement in crystallinity of the evaporated film due to annealing.

Atomic structure and spin polarization at the apex of tips used in spin-polarized scanning tunneling microscopy

To analyze spin-polarized scanning tunneling microscopy (STM) studies quantitatively, we evaluated the atomic structure and spin polarization at the apex of Cr/W and Fe/W tips using field ion microscopy (FIM) and field-emitted electron polarimetry, respectively. The patchwork-patterned H2-FIM images of the Cr/W tip indicated partially developed Cr planes, and the spin polarization at the surface was 10 ? 3% at room temperature. H2-FIM images of the Fe/W tip indicate the crystalline order of Fe layers on the W tip, and its spin polarization was 41 ? 2%. These first results allow us to quantify the spin polarization in spin-dependent STM measurements.

Measurement of z-direction component of electron spins field-emitted from a single-crystal magnetite whisker.

A 90° sector type spin rotator was developed for measurement of the z-direction component of a spin polarization, which is parallel to the emitter axis. The rotator enables us to measure all components of electron spins field-emitted from a single crystalline magnetite. In-plane component of spin polarization dominated of field-emitted electrons from single crystalline magnetite whisker, thus it is suggested that the magnetization of the magnetite whisker results from the anisotropy of crystalline structure rather than its shape.

Fabrication of a Spin-Polarized Electron Source with a Single Magnetite Whisker

-oriented single crystal magnetite whiskers 30 to 200 nm in diameter were synthesized on a stainless steel plate by means of the combustion flame thermal oxidation process. Microscopic analyses have revealed that the whiskers have some defects such as stacking faults and dislocations and also that manganese is the dominant impurity. A spin-polarized electron source with a single magnetite whisker was fabricated by using a micro-sampling instrument in a focused ion beam (FIB) system. The spin polarization of this sample was measured by using a Mott electron polarimeter and was found to be 15% at room temperature.

Verwey transition in field-emitted electrons from single ⟨110⟩-oriented magnetite whisker

The authors investigated the Verwey transition in field-emitted electrons from a ⟨110⟩-oriented magnetite whisker by means of temperature and emission-current-controlled spin-polarization measurements. Under a condition of total emission current of 1.5 nA, which is relatively high within the measured range, the spin polarization began to increase around 100 K due to the Verwey transition. At the low-temperature region, the spin polarization was sensitive to the emission current and the energy. Therefore, it is suggested that t2g band of Fe3O4 at the surface becomes narrower and possesses lower energy than that in an ideal bulky condition.

Spin polarization of electrons field-emitted from Cr thin film deposited on W tips

In this study, we measured spin polarization of electrons field-emitted from a topological antiferromagnetic Cr(001) surface, which is expected to generate a high and stable spin-polarized electron beam. When the Cr thin film deposited on a W<;001> tip was thicker than 20 nm, the spin polarization of the field-emitted electrons reached 50%. Furthermore, the magnitude and direction of the spin polarization were stable for 90 min. These results indicate that topological antiferromagnetic material is more effective than common ferromagnets as the cathode material of spin-polarized field emitters to achieve high and stable spin polarization.

Stability measurement of neon ion beam current emitted from supertip gas field ion source

So far, focused ion beam (FIB) has been contributed to the development of nanotechnology. However, liquid metal ion source (LMIS) equipped on commercial FIB systems has a serious problem which is the pollution of sample surfaces due to irradiated ion species. To develop the pollution-free and high-brightness ion source, we have focused on noble-gas field ion source (GFIS) and have developed the practical use of Ne- or Ar-GFIS. In this study, we report the stability of Ne ion current emitted from a supertip prepared by a modified field-induced oxygen etching.

Investigation of charge state of field-ionized noble gases by time-of-flight mass spectrometry

Charge state distributions of Ar and Ne Gas Field Ion Source (GFIS) were investigated by time-of-flight mass spectrometry using a newly designed experimental system. GIFS emitter having few atoms on the top of a (111) surface of tungsten were formed by remolding and field evaporation sequence with electrochemically etched <;111>; oriented tip. At the probe current of about lpA, the ratio of standard deviation of fluctuation and average ion current <; 2.5% was recorded from a single atom terminated emitter Ar-GFIS. Mass analysis by time-of-flight spectrometer showed that there were only singly charged ions both of Ne- and Ar-GFIS. Furthermore, no impurity gas was detected in the mass spectrum. These findings look promising for the development of both Ne and Ar GFIS systems.

Fabrication of spin-polarized electron emitter with single ⟨110⟩-oriented magnetite whisker

Magnetite (Fe3O4) is oxidative resistant and has a half metallic property and is expected to have spintronic applications. In this work, ⟨110⟩-oriented single crystal magnetite whiskers, 30–300 nm in diameter, were synthesized on a stainless steel plate by means of the combustion flame thermal oxidation process. An electron source with this single magnetite whisker was fabricated by using a microsampling instrument in a focused ion beam system. The spin polarization of the electron source was found to be 15% at room temperature by using a Mott electron polarimeter.