Taku Suzuki

Microfabrication of silicon using self-assembled monolayer resist and metastable helium beam

We herein report on the microfabrication of a Si(111) surface with a negative/positive contrast by atom lithography using a neutral metastable helium atom beam (He-MAB) and a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS). The OTS SAM bonded directly to the silicon surface as a resist and was exposed to He-MAB through a stencil mask to yield a latent image in it. Using chemical etching to develop and transfer the latent image directly onto the underlying silicon substrate, a square silicon micromesa and a microwell matrix with a nanoscale edge resolutions of approximately 100 nm on the Si(111) surface were fabricated. The negative/positive patterning mechanism was discussed in terms of the damage of the SAM resist under the irradiation of He-MAB and the possible effects of contamination.

Spin Polarization Measurement of Metastable He 23S1 Atoms in He Discharge

A method of measuring the polarization of metastable He 23S1 atoms (He*) in a He discharge is improved. He* density in each magnetic substate, i.e., mJ=+1, 0, -1, is estimated by measuring the attenuation of circularly and linearly polarized 1083 nm laser beams that are both tuned to the transition of He* 23S1 to 23P0 (the D0 line).

Current enhancement of a He+ ion beam by optical pumping

We observed that the current of a He+ ion beam generated from an RF ion source was enhanced by optical pumping (OP) using 1083 nm resonance radiation. The ion current enhancement became more remarkable with higher pressure and higher OP radiation density. The ion beam current with an OP irradiation of 0.5 W cm−2 at 65 Pa was 1.25 times larger than that without OP. We interpreted this OP effect on the ion current in terms of Penning ionization (PI) of He (23S) by He (23P). From the pressure dependence of the OP effect, we analysed the ratio of the rate constant of PI (RPI) to that of the total ionization process (RTotal). We verified the validity of this analysis for RPI/RTotal from the relationship of spin polarization between He (23S) atoms and He+ ions.

Electron emission from Na/Fe(100) surfaces by deexcitation of spin-polarized helium metastable atoms

A pulsed helium metastable atom beam was generated by the pulsed nozzle-skimmer discharge and a high degree of spin polarization of the helium beam was obtained using the optical pumping method. Spin polarization of the outermost surface electron was detected for clean and sodium covered Fe(100) films deposited on MgO(100) by measuring the secondary electrons ejected by the irradiation of the spin-polarized helium metastable atom beam. Secondary electrons correspond to the Fermi level for a clean iron surface and those corresponding to the Na 3s level for the sodium-covered surface show a positive asymmetry, which indicates the negative polarization of electrons at these levels. The negative polarization of the Na 3s electrons rapidly decreases with the thickness increasing of the Na layer up to 0.5 ML but remains almost constant at a higher coverage (3ML).