[Abstract and figures of

K. Mase, T. Tachibana, E. Kobayashi, M. Mori, H. Yagi, K. K. Okudaira, N. Ueno, I. Arakawa  

J. Vac. Soc. Jpn. 48 (2005) 286-289 (in Japanese).

Uploaded with the permission of Vacuum Society of Japan.]

Measurements of Ion Kinetic Energy Distribution Using a Miniature Cylindrical Mirror Analyzer (CMA) –Application for H⁺ Desorption Induced by Core-Level Excitations of Condensed Water

Kazuhiko MASE^{*1, *2}, Takayuki TACHIBANA^*3, Eiichi KOBAYASHI^{*1, *4}, Masanobu MORI^*5, Hideki YAGI^*5, Koji K. OKUDAIRA^{*5, *6}, Nobuo UENO^{*5, *6}, Ichiro ARAKAWA^*3

^*1(Institute of Materials Structure Science, KEK, 1-1 Oho, Tsukuba 305-0801, Japan)

^*2(PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan)

^*3(Graduate School of Science and Technology, Gakushuin University, 1-5-1 Mejiro, Toshima-ku 152-8588, Japan)

^*4(Inoue Foundation for Science, 15-15 Nanpeidaicho, Shibuya-ku 150-0036, Japan)

^*5(Graduate School of Science and Technology, Chiba University, 1-33 Yayoi-cyo, Inage-ku 263-8522, Japan)

^*6(Faculty of Engineering, Chiba University, 1-33 Yayoi-cyo, Inage-ku 263-8522, Japan)

We have developed a miniature cylindrical mirror analyzer (CMA) for ion kinetic energy measurements.  The CMA consists of a shield for electric field, inner and outer cylinders, a pinhole, and microchannel plates.  We have applied it for the measurements of kinetic energy distribution of H⁺ desorbed by O 1s transitions of condensed H₂O.

Figure 1  Diagram of Auger stimulated ion desorption.  When a surface is irradiated by soft X-rays ion desorption is induced by a following three-step process, i.e., 1) formation of a core-hole ((core)^-1) state by a core-electron emission (~ 0.1 fs), 2) formation of a valence-orbital-two-hole (VO^-2) state by an Auger transition (1 ~ 10 fs), 3) ion desorption along repulsive potential energy surface (PES) of the VO^-2 states (10 ~ 100 fs). The origins of the repulsiveness are Coulomb repulsion of the two holes and the electron missing from the bonding orbitals. So, the degree of repulsiveness of the PES is different for different VO^-2 states. The ion kinetic energy (EK_ion) reflects the degree of repulsiveness of the PES of the VO^-2 states. When the PES is more repulsive, the corresponding EK_ion is larger.

Figure 2  Cross section of the miniature cylindrical mirror analyzer (CMA) for ion kinetic energy measurements.  The CMA consists of a shield for electric field, an inner cylindrical electrode with two meshes, an outer cylindrical electrode, and microchannel plates (MCP).  The trajectories of ions from a pointed source with a kinetic energy of 4.2 eV for polar angles of 29°〜41° with 2° step are shown based on the simulation with the SIMION 3D version 7.0.  The voltages of the sample and the inner cylindrical electrode are 0 V while that of the outer cylindrical electrode is +2.5 V. The voltage of the entrance of the MCP is –2000 V.

Figure 3  Photographs of the miniature CMA for ion kinetic measurements.  (a) The diagonal front view, (b) the side view, (c) the diagonal back view and (d) the front view.

Figure 4　 Kinetic energy distributions of ions desorbed from condensed H₂O measured using the miniature CMA at hν = 529.9, 530.9, 532.9, 535.9, 538.9, 539.9, 549.9, and 606.9 eV.  hν = 532.9 eV corresponds to　the 4a₁ ← O 1s resonant transition.  The ordinate corresponds to EN(E)) where N(E) is the ion number with a kinetic energy of E, because the distribution is measured by a CMA.  The energy resolution (E/ΔE) is 6.

Figure 5  Kinetic-energy-selected ion yield spectra for condensed H₂O measured using the miniature CMA. hν = 532.9 eV corresponds to　the 4a₁ ← O 1s resonant transition.