Production of polarized atomic hydrogen beam and its application to spin-selected Si surface reaction

用六极磁铁可以获得自旋极化的氢原子束。其基本原理是，具有磁偶极矩的氢原子在不均匀磁场中受力。如果原子处于上自旋状态，它们将受到朝向非均匀六极磁场中心的力，而处于下自旋状态的原子将受到朝向相反方向的力。因此，只有上自旋态的粒子在通过六极磁场后可以优先聚焦。我们用电子轰击的钨管产生了氢原子束。用四极质谱计检测极化氢原子。然而，在磁场从零到5000千克的范围内，我们没有得到任何聚焦偏振光束的积极证据。这一结果应该与具有三重态的超音速氧分子在2-3kGauss的磁场中真正聚焦的情况进行比较。在超音速氧束的情况下，光束沿六极磁铁的轴线准直良好，而来自加热的W管的氢原子束必须散焦。因此，我们认为自旋极化氢束聚焦失败的原因是六极磁铁入口处的束流发散较大。我们正在利用射频等离子体的超音速膨胀来改进原子氢源。我们用未极化的氢束测量了氢原子在Ge(100)表面上诱导的吸氢。这是表面自旋选择反应的初步实验。在H束照射下，发现HD和D2分子解吸了D/Ge(100)表面。揭示了氢诱导半导体表面吸附和脱附的机理。

Spin polarized atomic hydrogen beam can be obtained with a hexapole magnet. The basic principle is that hydrogen atoms with a magnetic dipole moment receive a force in an inhomogeneous magnetic field. If the atoms have an up-spin state they will receive a force towards the center of the inhomogeneous hexapole magnetic field, while the atoms with a down-spin state will receive a force towards the opposite direction. Thus, the only up-spin state particles can be preferentially focussed after passing a hexapole magnetic field. We produced atomic hydrogen beams from an electron-bombarded W tube. A quadrupole mass spectrometer was used to detect polarized hydrogen atoms. However, we could not get any positive evidence of a focussed polaized beam for the range of magnetic field from a zero to 5000kG. This result should be compared with the case that the supersonic oxygen molecules with a triplet state could be really focussed at the magnetic field of 2-3kGauss. In case of the supersonic oxygen beam the beam is well collimated along the axis of the hexapole maget, while the hydrogen atomic beam from the heated W tube must be defocussed. Therefore, we consider that the failure in focussing the spin polaized hydrogen beam is due to the big divergence of the beam at the entrance of the hexapole magnet. We are now improving the atomic hydrogen source by employing a super sonic expansion of RF plasma.We measured hydrogen atom-induced deuterium abstraction on the Ge(100) surfaces with the unpolarized H beam. This was the preliminary experiment for the spin selected reaction on surfaces. Upon the H beam exposure, HD as well D2 molecules were found to desorb the D/Ge(100) surfaces. We revealed the mechanism of H-induced abstraction and desorption on the semiconductor surfaces.