STUDIES ON THE PRODUCTION OF SPIN-POLALIZED HELIUM IONS BY UTILIZING THE FIELD IONIZATION PROCESS

2002 Fiscal Year Final Research Report Summary

• Project/Area Number: 13650030
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 表面界面物性
• Research Institution: OSAKA CITY UNIVERSITY
• Principal Investigator: KOBAYASHI Ataru OSAKA CITY UNIVERSITY, APPLIED PHYSICS, ASSISTANT PROFESSOR, 大学院・工学研究科, 講師 (30271373)
• Project Period (FY): 2001 – 2002
• Keywords: SPIN-POLARIZED ION / HELIUM ION / FIELD IONIZATION / KINETIC ENERGY / SURFACE STATE DENSITY / FIELD IONIZATION SPECTROSCOPY

Research Abstract

The aim of this research project is to present a novel method of producing spin-polarized helium ion, He^+(1^2s), by utilizing the field ionization process on ferromagnetic surfaces such as Fe, Co and Ni. To demonstrate its feasibility, we newly constructed an apparatus based on an atom-probe field ion microscope (AP-FIM) combined with an ion energy analyzer called Wien filter. Produced helium ion is velocity selected with the analyzer and the number of ions with a specific velocity is pulse counted by microchannel plate (MCP). Measured kinetic energy distribution spectrum of produced helium ions represents useful information regarding the unoccupied state densities of sample surface.
With a newly constructed apparatus, field-ionized ions from a specific site on a sample surface are selectively admitted to a velocity filter called Wien-filter via a probe-hole located at the center of MCP for FIM imaging. The energy resolution for traveling ions is set at 0.2 eV. We could therefore measu re a kinetic energy distribution spectrum of field ions with good accuracy, which solely reflects the tunneling probability of spin-selected electron from a helium atom into the unoccupied states of the sample surface. In the previous term of project (1999-2000), we have attained to the primary goal of simply measuring the field-ion signals of AT produced on tungsten surface by direct pulse counting method with MCP located downstream of the Wien-filter. For more improved measurement system, a new data acquisition and display system for kinetic energy distribution measurement is equipped in the current project term (2001-2002). To measure the reliable kinetic energy of field-ion, the tip potential should be maintained slightly above ground potential, while positive high voltage is applied to the counter-electrode located just in front of the tip apex with a distance of 3mm forming effectively critical field strength for field ionization on the tip surface. The distinct design requirement of the counter-electrode as well as the critical dimensions between the tip and the electrode should be optimized for well resolved FIM images. The optimization is now underway with a help of numerical calculation of field distributions as well as the ion trajectories by Simion electrostatic modeling package.