Mitsunori Kurahashi

A metastable helium atom source directly pulsed by a nozzle-skimmer discharge

The discharge excited atom beam source we designed uses a trigger electrode between a nozzle and skimmer to generate a metastable helium atom beam that is directly discharge pulsed. A pulsed discharge current up to 200 mA maintained between the needle cathode behind the nozzle and the skimmer anode produced an intense pulsed metastable helium atom beam equivalent to a continuous total flux of with mechanical chopping.

Electronic structure of pentacene adsorbates on Au(111) surfaces

The electronic structure of pentacene deposited on a Au(111) substrate in the initial stage of growth was investigated using metastable deexcitation spectroscopy. The occupation of the pentacene π* 4b1u orbital, which corresponds to the lowest unoccupied molecular orbital of the gas phase species, was found at the Fermi level. The donation and backdonation-type interactions between the pentacene adsorbate and the Au surface are discussed.

Extremely surface-sensitive hysteresis loop measurement with a spin-polarized metastable helium atom beam

The sample current induced by the deexcitation of He* atoms on a ferromagnetic surface was found to depend on the He* spin direction. This spin dependence was used for measuring the hysteresis loop of an Fe film on Cu(100). The hysteresis loop is extremely surface specific because the spin dependence is due to the electron emission via the He* deexcitation that occurs on the vacuum side of the topmost surface layer. The hysteresis loop for a 2.2ML Fe film on Cu(100) has been found to agree well with that measured with the surface magneto-optic Kerr effect.

Surface magnetization measurement with a spin-polarized metastable He beam under high magnetic fields of 0–5T

An apparatus for measuring the surface magnetization with a spin-polarized metastable helium atom (He(*)) beam under external magnetic fields of 0-5 T was developed. The He(*) beam, spin polarized by a sextupole magnet, was directed to the sample placed in the bore of 5 T superconducting magnet. A zero-field spin flipper was used for switching the polarity of beam polarization. A Stern-Gerlach analysis indicated the beam polarization of nearly 100% and the spin flipping efficiency of >90%. A surface magnetization curve was successfully measured from 0 to 5 T for an FeCu(100) surface.

Production of a single spin-rotational state [(J,M)=(2,2)] selected molecular oxygen (Σ3g−) beam by a hexapole magnet

A state-selected O(2)((3)Sigma(g)(-)) molecular beam, in which nearly 100% of the molecules are in the spin-rotational state of (J,M) = (2,2), has been produced by combining a supersonic seeded O(2) beam with a hexapole magnet. The (2,-2) beam has also been obtained by the state inversion of the (2,2) beam through the nonadiabatic passage in a reversing longitudinal magnetic field along the beam axis. The intensities of the other (2,M) states, which appear when applying additional transverse magnetic fields to the reversing field region, were well reproduced by the Majoranas formula for J = 2. The (2,+/-2) beam, for which we can determine the spin and rotational angular momenta of O(2) almost independently, is the most promising probe for studying the spin effects as well as the steric effects in O(2) molecular scattering.

A metastable-atom deexcitation spectroscopy (MDS) study of water adsorption on Cu(100): a new feature at around the Fermi level

Abstract We have investigated the water adsorption on Cu(100) using metastable-atom deexcitation spectroscopy (MDS). A new feature was found that indicates the presence of the partially filled electronic states at around the Fermi level. The feature has been assigned to the antibonding states that result from the combination of the water lone pair orbitals (1b1, 3a1) and electronic states of the metal substrate.

Observation of a high negative spin polarization at the Fe/MgO(100) surface oxidized at room temperature

Spin polarization of an Fe/MgO(100) surface oxidized at room temperature has been analyzed with a spin-polarized metastable helium beam, which is an extremely surface sensitive spin probe, under high magnetic fields (0–50 kOe). The spin polarization of the Fe surface, although it initially decays with oxygen exposure, increases at >20 L (1 L=10−6 Torr sec) and becomes comparable to that observed for a clean Fe surface at >100 L. The polarization is negative and especially high at around the Fermi level. This may be understood if we assume the formation of Fe3O4.

Characterization of nanoscale patterns prepared by metastable helium atom beam and butanethiol self-assembled monolayers

Abstract By using a helium metastable atom beam and butanethiol (BT) self-assembled monolayers (SAM), the metastable atom lithography to the gold film on muscovite mica having a flat surface was carried out. Large-area intact and clean patterns with a nanoscale width of the edge, approximately 50–70 nm, were obtained. Meanwhile, we found that the shorter chain molecules like the BT can be used as resist and may result in sharper edge of patterns, but the roughness of gold patterns with the BT SAM is larger than that with the Octanethiol (OT) SAM and similar to that with the Dodecanethiol (DDT) SAM. This observation can be interpreted by the presence of the liquid phase in the short-chain homologues. All information indicated that the BT SAMs on atomically flat surfaces could be used as a resist for exposure to metastable atom beams.

Observation of H+ desorption stimulated by the impact of metastable helium atoms

Abstract H + desorption induced by the impact of metastable helium atoms (He ∗ ) with a thermal kinetic energy has been observed. The measurements were carried out for an alkali metal (K, Na)-covered Ni(110) surface using a time-of-flight technique and a pulsed-discharge-type He ∗ source. It is concluded that the H + desorption by He ∗ is induced by a hole created on the valence levels via the Auger deexcitation of He ∗ .

Magnetization hysteresis loop measurement with a spin-polarized metastable He* beam and an electromagnet of 1.8 kOe

An experimental apparatus for measuring the magnetization hysteresis loop with a spin-polarized metastable helium (He*) beam, which is an extremely surface-sensitive spin probe, and an electromagnet of 1.8 kOe was developed. The He* beam, spin polarized by optical pumping, was directed to the sample through a hole drilled in the Fe pole pieces of the electromagnet. The sample current difference when reversing the He* spin polarization was measured with a lock-in technique. The hysteresis loop of an Fe∕Cu(100) surface measured at 90 K is presented.