Itsuo Katayama

A TOF-ISS/ERDA apparatus for solid surface analysis

Abstract A time-of-flight (TOF) system has been constructed to perform surface-structure analysis by impact collision ion scattering spectroscopy with primary noble-gas ions and scattered-neutral detection. The structure of thin Ag films (1–5 ML thickness) deposited onto a clean Si(111) substrate has been studied.

Surface science lettersAdsorption of H on Si(111) −3 × 3 − Ag: evidence for Ag(111) agglomerates formation

In this low-energy ion scattering study we find that the reaction of H with Si(111) − √3 × √3 − Ag results in an extensive surface modification. Saturated adsorption of H of about 1.5 ML coverage below 100 ° C transforms an uniform Ag monolayer in the √3 × √3 lattice into very small crystallites of Ag(111) grown epitaxially on the Si(111) substrate. The thickness of the Ag(111) crystallites is found to be three atomic layers. When only H is thermally desorbed by moderate heating above 400 ° C, the crystallite disappears and the original √3 × √3 − Ag is recovered.

Atomic‐hydrogen‐induced Ag cluster formation on Si(111)‐√3×√3–Ag surface observed by scanning tunneling microscopy

The scanning tunneling microscope has been used to study structural transformation of the Si(111)‐√3×√3(R30°)–Ag surface caused by atomic hydrogen adsorption. Atomically resolved scanning tunneling microscope images reveal a structure model for exchange adsorption of hydrogen and silver atoms. It has been shown that the proposed model can well explain various experimental results reported so far on this system.

Charge-changing contribution to energy loss of 32 MeV 3He+ in the charge state non-equilibrium region☆

Abstract Energy losses of 32 MeV 3 He ions by carbon foils were measured in the charge state non-equilibrium region. The mean energy losses exhibited an abrupt change as a functiion of the foil thickness around 40–50 μg/cm 2 . This behavior is quantitatively explained by considering the contribution from charge-changing collisions.

Low energy ion scattering study of hydrogen-induced reordering of Pb monolayer films on Si(111) surfaces

Abstract The structural change of a Pb monolayer film caused by atomic hydrogen adsorption has been studied by using low-energy ion-scattering spectroscopy. Time-of-flight impact collision ion scattering spectroscopy and LEED are used in ultrahigh vacuum. It has been found that atomic hydrogen adsorption onto a Si(111)-√3 × √3-Pb surface at room temperature transforms a uniform Pb monolayer in the √3 × √3 lattice into very small clusters of Pb(111) grown epitaxially on the Si(111) substrate.

Structural study of Ag overlayers deposited on a Si(111) substrate by impact-collision ion-scattering-spectroscopy with time-of-flight detection

Abstract Using the technique of time-of-flight mode impact-collision ion-scattering-spectroscopy, we have studied the structure of two kinds of Ag thin films deposited onto Si(111)7×7 substrates. We have shown that (1) the RT deposited Ag thin film of 10 ML thickness consists of type-A and type-B domains of Ag(111), with type-B being rotated 180° about the surface normal, (2) the experimental ICISS angle scans for the Si(111)√3×√3R30°-Ag surface cannot be explained by the embedded-Ag model proposed so far, (3) the Ag honeycomb structure residing on top of Si is unlikely for the √3 × √3-Ag surface, and (4) both the Ag-trimer and the HCT model, residing on top of Si are more likely, though a clear preference between these two models has not been obtained as yet.

Reconstruction and growth of Ag on hydrogen-terminated Si(111) surfaces

Abstract Initial stage of Ag film formation on hydrogen-terminated Si(111) surfaces at room temperature (RT) and high temperatures has been investigated by scanning tunneling microscopy. Ag atoms formed clusters on the hydrogen-terminated Si(111) at all temperatures, though the size and number were different in each case. When Ag was deposited at RT, relatively large and uniform Ag clusters were formed on the surface, compared with Ag deposition on a clean Si(111)-7×7 surface. On increasing the deposition temperature to 200 and 300°C, the size of Ag clusters became larger and the number of Ag clusters became less. When the surface where Ag was deposited on the hydrogen-terminated Si(111) at RT was annealed at 350°C, shallow and deep areas of 3 − Ag structure appeared, due to hydrogen desorption. We demonstrate the usefulness of hydrogen termination for Ag deposition on the Si surface to fabricate flat and uniform thin films.

Growth processes of Si(111)-√3×√3-Ag studied by scanning tunneling microscope

Domain growth processes of Si(111)√3×√3-R30 o -Ag surfaces and their dependence upon deposition conditions have been investigated by means of scanning tunneling microscope. When Ag is deposited at room temperature, small islands are formed on the terraces. After annealing at 350 o C, these small islands change into √3-Ag domains on the terraces without diffusion of Ag atoms to the step edges. On the other hand, when Ag is deposited on a hot substrate of about 350 o C, the √3-Ag domains nucleate at the step edges and few √3-Ag domains are observed on the terraces. Moreover, two kinds of √3-Ag domains are found in either case: one domain is geometrically higher than the other domain

Scanning tunneling microscopy observation of hydrogen-induced Ag cluster formation on the Si(111) surfaces

Using a scanning tunneling microscopy (STM) we have studied the nucleation and growth process of Ag clusters induced by the atomic hydrogen adsorption on the Si(111) √3×√3(R30°)‐Ag (simply √3‐Ag) surface. Size distributions of the clusters have been investigated as a function of the exposure of atomic hydrogen, and it is strongly suggested that the surface migration of Ag atoms over the hydrogen‐reacted regions is largely suppressed compared with that on the √3‐Ag surface. The size of Ag clusters is less than 150 A and their average height is estimated to be 3.1 atomic layers, consistent with previous ion scattering results. We have proposed the model of nucleation and growth process of hydrogen‐induced Ag clustering in which the broadened H/√3‐Ag regions suppress the migration of expelled Ag atoms and lead to the formation of many small clusters.

TOF-ICISS study of surface damage formed by Ar ion bombardment on Si(100)

Abstract The surface damage formed on a clean Si(100)-2 × 1 surface by low-energy Ar ion bombardment has been studied in situ using the impact collision ion scattering spectroscopy (ICISS) method and the time-of-flight (TOF) technique. The Ar ion energy was 1 keV and the ion doses were in the range of 10 14 -10 15 ions/cm 2 . Channeling and focusing effects were observed very clearly on a clean and well-ordered surface. With the increase of the Ar ion dose, such channeling and focusing effects gradually disappear. The annealing process of the surface damage was also investigated.