住友 弘二

The surface composition of Ge/Si(001)2 x 1 surfaces after atomic hydrogen (H) irradiation was investigated using IR reflection spectroscopy in UHV. It was confirmed that an extremely high dose of H at room temperature causes an etching reaction of the surface Ge layer. However, when H is irradiated at a temperature higher than 150 degrees C, the etching reaction does not occur; instead, Ge segregated at the surface is observed to move into a subsurface and Si tends to exist on the topmost surface as a hydride in mixed Ge-Si and pure Si-Si dimers. This is in remarkable contrast to the Ge/Si(001) surface in the absence of hydrogen, where Ge is segregated at the surface and forms Ge-Ge pure dimers. The phenomenon of 'reverse segregation' by H irradiation may be understood by the thermochemical consideration that Si-H bonds are much more stable than Ge-H bonds. The result of the first-principles total energy calculations in which the presence of hydrogen changes the stable composition at the surface from Ge to Si is also consistent with the phenomenon. (C) 1999 Elsevier Science B.V. All rights reserved.

The dimer composition on the Ge-segregated surface of a MBE-grown Si-layer/Ge/Si(001) structure was investigated using surface infrared (IR) spectroscopy on Si substrates with a buried metal layer (BML). The Ge-segregated surface was modified by atomic hydrogen in order to visualize dimer composition by IR spectroscopy. When the Si growth-layer is relatively thin (similar to 10 ML), almost all Ge atoms are segregated at the surface and form Ge-Ge pure dimers and a small amount of Ge-Si mixed dimers. As the growth-layer thickness increases, the portion of pure Ge-Ge dimers decreases, and finally, the surface is covered with mixed Ge-Si and pure Si-Si dimers at the thickness of 64 hit. This result indicates that mixed dimer formation should be considered as an important factor in the Ce segregation mechanism and Ge incorporation profiles. (C) 1999 Elsevier Science B.V. All rights reserved.

In this paper, we describe the results of a study of the interaction of oxygen with a SiGe epilayer which is already reacted with cobalt atoms. The epilayer was grown on Si(100) substrate using solid source molecular beam epitaxy. Techniques of ultra-violet and X-ray photoelectron spectroscopy and medium energy ion scattering are employed for the study. In a recent paper, we reported that the reaction of Co with epitaxially grown SiGe alloy leads to the selective formation of CoSi2 on the surface. On exposing such a Co reacted surface to oxygen at 285 degrees C, the surface Co-Si bonds break and Si-O bonds are formed. Further, the cobalt atoms thus released move inward and bond with Si atoms in the subsurface regions. These results indicate that it is possible to incorporate metallic and insulator features into SiGe alloy, which is an important device material, through in situ processes. (C) 1999 Elsevier Science B.V. All rights reserved.

The interaction of Co with a thin layer of SiGe (similar to 80:20), epitaxially grown on Si(100) surface, is investigated by combined use of ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) and medium energy ion scattering spectroscopy (MEIS). Deposition of Co onto the alloy surface at room temperature forms a mixture of CoxSiy and CoxGey phases on the surface. Upon annealing at 300 degrees C, Co diffuses inward and Co-Ge bonds are broken. This leads to the formation of CoSi2 layers. MEIS blocking profile data indicate that the cobalt silicide layer formed is strain free, and therefore suggest that CoSi2 can be a potential candidate for achieving metallic interconnections in SiGe based devices. (C) 1999 Elsevier Science B.V. All rights reserved.

In this account, we have described nanofabrication techniques on Si surfaces according to a strategy developed in our laboratory: that is, integration of atomically controlled nanostructures on a wafer scale. The approach consists of three steps: (1) control of surface structures such as atomic steps and phase boundaries of reconstructed domains to form a template of nanofabrication, (2) control of self-organization processes to fabricate semiconductor nanostructures, and (3) control of chemical reactions to form semiconductor/insulator/conductor nanostructures which are required for device applications. To understand the mechanisms of nanofabrication presented here, basic research on surface physics and chemistry is required. At the same time, we have to consider how this approach will bring about a break-through in semiconductor technology. The current MOS devices will undoubtedly continue to be the leading device in information processing systems. However, information processing is increasingly expanding its application in social issues. This implies that binary logic as the basis of MOS technology will not always be the best architecture. To handle information in human life, different processing systems, and consequently a novel device concept, will be required. We believe that our approach is one of the candidates for working toward realizing future Si technology.

Wafer-scale control of nanofabrication on Si using selforganization processes are described. Unit cells of surface reconstruction, atomic steps, and domain boundaries of the reconstruction can be used as templates to control arrangement of self-organized nanostructures. We demonstrate that atomic-step network can be organized by controlling the step motion during surface atom evaporation, employing etched patterns formed by lithographic technique. Step/domainboundary network can be modified by using step-flow growth. Ge quantum dot network is self-formed on the surface with well organized templates. Strain distribution on the substrate surface is important for the size and shape control of Ge quantum dots. Chemical reaction control plays an important role in fabricating semiconductor-insulator-conductor nanostructures. In Si/Ge nanostructure, reaction selectivities between Si and Ge can be utilized to form oxide and silicide layers at the Si/Ge interfaces.

We have measured keV secondary electrons induced by 56 MeV O8+ under channeling and nonchanneling incidence conditions for Si and Ge crystals covered with noncrystalline Al, Si, Ag, and Au layers less than 350 A thick. The analysis indicates that the enhanced electron yield due to the thin overlayer in the channeling case results dominantly from the effective increase in the number of high-energy recoiled electrons that are incident on the underlying crystal region. In the nonchanneling case, backscattering of the recoiled electrons from the overlaid atoms is of essential importance to account for the observed yield. © 1998 Elsevier Science B.V.

We have determined the structure and positions of Ge and Sb dimer atoms on a Si(001)-2 × 1 surface using medium-energy ion scattering (MEIS), and demonstrated that the surface structure can be determined with a much higher accuracy by modifying the layer structure of the substrate. When a heavy atom layer (in this case Ge layer) is embedded with atomic scale layer precision, the blocking processes of scattered ions from the embedded layer are restricted and dips in the blocking profiles can be uniquely assigned to the scattering-blocking pairs. In addition, the effect of thermal vibration becomes small because a suitable distance between scattering and blocking atoms can be selected. Therefore, we can observe sharp blocking dips in the profile of embedded Ge signals, and they can be assigned to the dimer structures on the reconstructed surface. Based on the proposed method, the bond length and the tilt angle of asymmetric Ge-Ge dimers are determined to be 2.4 ± 0.1 Å and 13.5 ± 2.0°. The bond length of symmetric Sb-Sb dimers is determined to be 2.84 ± 0.1 Å. © 1998 Elsevier Science B.V. All rights reserved.

We investigated the growth of twinned epitaxial Si layers on a Si(111)√3 × √3-B surface. In the initial growth stages, untwinned bilayer-high (BL-high) and twinned 2-BL-high islands are nucleated, and the ratio of the number of Si atoms included in the twinned 2-BL-high islands to the number of the total deposited Si atoms increases as the surface B concentration increases. Preferred nucleation of Si islands occurs at domain boundaries of the √3 × √3 reconstruction. Moreover, BL-high islands rather than 2-BL-high islands nucleate there. Coalescence of 2-BL-high islands causes the domain boundary density on the first two bilayers to be much larger than that on the substrate. Therefore, after completion of the first twinned two bilayers, BL-high islands are formed predominantly. BL-high islands follow the stacking sequences of the twinned two bilayers. Thus, grown layers are totally twinned. We also investigated the thermal stability of twinned epitaxial layers. The temperature at which twinned epitaxial layers are transformed into untwinned layers strongly depends on the thickness. © 1998 Elsevier Science B.V. All rights reserved.

Reflection high-energy electron diffraction (RHEED) and medium-energy ion scattering (MEIS) were used to investigate the disordering of a Si(111) surface at high temperatures. RHEED intensities exhibit a steplike decrease around 1470 K during heating. There is a steplike increase in the surface-peak area measured using MEIS around this temperature. These results are consistent with the formation of a thin layer of positionally disordered atoms at the transition. © 1998 The American Physical Society.

We investigate the growth process of twinned epitaxial Si layers on Si(111)√3×√3-B and their thermal stability. In the initial growth stages, twinned two-bilayer-high (2-BL-high) and untwinned BL-high islands are formed, and at higher surface B concentration, there are more twinned 2BL islands than untwinned BL islands. Domain boundaries of the √3×√3 reconstruction act as preferential island nucleation sites, especially for untwinned BL islands. Therefore, to grow epitaxial layers twinned with the already-grown twinned layers, post-growth anneal is essential to increase the surface B concentration and to reduce the domain boundary density. On the other hand, the temperature at which twinned layers are transformed into untwinned layers strongly depends on the thickness. We demonstrate the possibility of growing superlattices of layers that have twinned and untwinned orientations with the substrate (polytypes) by precisely controlling the growth and post-growth anneal parameters. © 1998 American Vacuum Society.

Intermixing of Ge(0.15 ML, 1 ML)/Si(001) grown at 400 degrees C was studied by a new method of surface energy loss spectroscopy of medium energy ion scattering. We measured the inelastic energy losses of scattered ions from Ge for 100.0 keV H+ incidence as a function of exit angle. In the previous work for 50 and 100 keV H+ backscattered from the Si(001) 2 x 1-Sb surface [Phys. Rev. B in press], we showed that the surface stopping cross-section was expressed by extending the bulk stopping region from the top atomic plane toward the vacuum side by d, which was given by 2d rho=sigma (sigma is the areal density of top surface and rho is the bulk atomic density) as the first approximation. The above approximation uas applied to analysis of the Ge:/Si(001) interface. The present analysis revealed that the deposited Ge atoms were distributed over the first to third atom layers with a ratio of 4:3:1 or 4:2:2 for both 0.15 ML and 1 ML coverage. This result is consistent with that reported by Sasaki et al. [Appl. Surf. Sci. 82-83 (1994) 387] using Auger electron and X-ray photoelectron diffraction. (C) 1997 Elsevier Science B.V.

Interaction of Co with a Ge covered Si(111) surface is studied employing ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS), medium energy ion scattering spectroscopy (MEIS), cross sectional transmission electron microscopy (XTEM), low energy electron diffraction (LEED), reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM). 2 ML of Co is deposited on a Si(111) surface, which is covered with similar to 3 ML of Ge, both at room temperature. On annealing the sample at 460 degrees C, Co diffuses through the Ge layer and reacts with the Si atoms underneath. This results in the formation of a buried CoSi2 layer. XTEM pictures as well as the blocking dip pattern in MEIS suggest that the CoSi2 formed at the interface between Si and Ge, is a B-type epitaxial. The Co layer undergoes agglomeration and forms Ge/CoSi2/Si dot structures and Ge/Si terraces. A mixture of 1 x 1 and 5 x 5 patterns originating, respectively, from Ge/CoSi2/Si and Ge/Si regions are observed in RHEED and LEED. The results open up a novel way of fabrication of buried epitaxial metallic layers and semiconductor/metal nanostructures.

The incorporation of metallic layers into the bulk of semiconductors is gaining tremendous attention for device applications. This is mainly achieved by ion beam synthesis. In the ultrathin film regime, however, this technique is not practical due to the damage incurred. Here we report a technique by which fabrication of buried epitaxial CoSi2 is achieved by making use of the selective diffusion behavior of Co. Co atoms diffuse through a Ge overlayer on a Si(lll) substrate and are terminated by reaction with the Si atoms underneath. Ion scattering as well as high resolution microscopy results confirm that the CoSi2 layer thus formed is in epitaxial form. This method would help in providing functionality to nanostructure based devices. (C) 1997 American Institute of Physics.

We propose a novel technique based on preferential oxidation of Si in the Si/Ge system. Oxygen ions were implanted at 30 keV into Si/Ge multilayers while the substrate temperature was kept below 100 degrees C. Significant oxygen concentration was then observed at the Si/Ge interfaces and at a thin Si layer embedded into the Ge layer. When the samples were then annealed above 400 degrees C, the bonding state of the Si oxide approached that of SiO2. During this process, Ge atoms were expelled from the oxide layers. Transmission electron microscopy confirmed that silicon dioxide layers were formed. This new technique can be used to form semiconductor/insulator multilayered structures from Si/Ge multilayers.

Surface stopping powers were measured for 50- and 100-keV (Formula presented) ions passing through the Si(001)2×1-Sb surface. The energy losses as a function of the exit angle are fit successfully by a simple relationship involving the time spent near the surface. The fitting parameter is in agreement with the value expected from the bulk Sb stopping cross section and the areal Sb density. This result suggests continuity of the stopping power from the bulk to the surface. It provides a useful method for determining the distance between the plane of deposited atoms and of a substrate surface and for measuring the composition of the topmost atomic layer. The estimated energy loss by surface-plasmon excitation is negligibly small in the present system. The energy straggling as a function of exit angle was also measured for 50- and 100-keV (Formula presented) incidence and the results are compared here with the bulk straggling values. © 1997 The American Physical Society.

The structure of the GaAs(001)-2 × 4 reconstructed surface is studied using medium-energy ion scattering (MEIS). The MEIS profiles clearly show splitting blocking dips, which originate in the surface reconstruction. We have quantitatively determined the atomic displacement from these blocking dips. The topmost As atoms forming the symmetric dimers are displaced laterally 0.55 ± 0.05 Å, and the bond length of the As dimer is 2.89 ± 0.1 Å. The Ga atoms of the second atomic layer, which bond with the As dimer atoms, are also displaced laterally and the displacement is 0.44 ± 0.05 Å. These surface atoms also move vertically and the surface layers shrink.

Thermal effects in a high vacuum on horizontal Bridgman grown GaAs(001) surface prepared by deoxygenated and de-ionized water treatment were investigated by x-ray photoelectron spectroscopy, low-energy electron diffraction, ultraviolet photoelectron spectroscopy, and photoluminescence (PL) measurement. The ultraviolet photoelectron spectra show that, below 450 degrees C, the surface Fermi level lies at almost 0.85-1.0 and 0.68-0.8 eV above the valence-band maximum, respectively, for lightly and highly Si-doped GaAs surfaces. Above 480 degrees C, the surface Fermi levels of both the surfaces gradually come close to 0.45-0.54 eV above the valence-band maximum even though the surface keeps the 2X4 structure. PL measurements suggest that the surface Fermi level position is strongly affected by arsenic and gallium vacancies created near the surface during thermal processing. (C) 1996 American Institute of Physics.

We report the occurrence of a diffusion mediated chemical reaction in the layered structure Co/Ge/Si(100) to form Ge/CoSi2/Si(100). This is possible due to the lower onset temperature of inward diffusion of Co in Ge(100) (∼150°C) compared to that in Si(100) (∼300°C). Deposition of ∼2 monolayer (ML) of Co at room temperature, onto a Ge covered (∼3 ML) Si(100) surface, mainly forms CoxGey species on the surface. However, annealing the sample at 400°C, Co diffuses through the Ge layer and reacts with Si and forms buried cobalt silicide of the structure Ge/CoSi2/Si(100). X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), medium energy ion scattering (MEIS) are employed for the study. The results open up a possibility to fabricate metal/semiconductor heterostructures in a novel way. © 1996 American Institute of Physics.

The preparation and characterization of an atomically flat and well-ordered surface on the Si(001) substrate with a buried metal layer (BML) are reported. The BML substrate was formed by implantation of Co+ ion and subsequent annealing. After molecular beam epitaxy growth of the Si overlayer on the cleaned BML sample in ultrahigh vacuum, clear 2×1 patterned and ordered steps with regular terrace width were observed by reflection high energy electron diffraction and atomic force microscopy. No contamination, including Co, was observed in the spectra of Auger electron spectroscopy and x-ray photoelectron spectroscopy. Ultraviolet photoelectron spectra showed a distinct surface peak that originated from surface dangling bonds and is characteristic of a clean and ordered surface. The surface atomic structure, including stress and damage caused by ion implantation, was characterized by medium energy ion scattering (MEIS). Very low χmin (1.7% with 300 keV H+) and a dip pattern in blocking profile in the MEIS spectra indicate that surface crystal quality is comparable to that of a homoepitaxially grown Si layer on normal Si substrate without BML. These results show that the BML substrate obtained by the procedure is quite useful for the structural investigation of surface species on Si by infrared (IR) reflection spectroscopy. Typical examples of IR spectra qualifying the BML substrate for surface studies are also presented. © 1996 American Vacuum Society.

Stopping powers and energy straggling for 50-300 keV H+ beams in amorphous Si and Ge films were measured with a toroidal electrostatic analyzer. The samples prepared are Sb(1ML)/Si(001) and amorphous Si (a-Si)/Sb(1ML)/Si(001) and a-Ge/Si(111) formed by molecular beam epitaxy and with an electron beam evaporator. Atomic force and cross sectional transmission electron microscopes revealed the formation of uniform and amorphous thin films with sharp interfaces. Ion scattering measurements were performed in situ first for Sb(1ML)/Si(001) and subsequently for a-Si films deposited on Sb(1ML)/Si(001) under an ultrahigh vacuum condition. The Sb peak shift and the broadening of the Sb energy spectrum give the stopping power and energy straggling, respectively. For a-Ge films, we extracted the stopping power and straggling values from the energy width and the slopes at the front and rear edges of the Ge spectrum, respectively. The present results are compared with the theoretical predictions and other experimental data.

Using medium-energy ion scattering, we have studied interface structures between Si and Ge thin layers in GenSim strained-layer superlattices (SLSs) grown by molecular beam epitaxy. In this systems, the horizontal strain caused by lattice mismatch, further causes vertical atomic displacement. The embedded Ge layers are compressed horizontally and expanded vertically compared with the ideal cubic crystal. Since the interfaces of Si layers grown onto Ge layers in SLS are not so abrupt at the atomic scale because of the Ge segregation effect, Ge atoms at the interfaces are displaced not only vertically but also laterally. We observed a peculiar blocking dip, which is explained by an interfacial structure characterized as alternate Si and Ge arrangement forming a 2 × n periodicity.

We report the occurrence of a diffusion mediated chemical reaction in the layered structure Co/Ge/Si(100) to form Ge/CoSi2/Si(100). This is possible due to the lower onset temperature of inward diffusion of Co in Ge(100) (∼150°C) compared to that in Si(100) (∼300°C). Deposition of ∼2 monolayer (ML) of Co at room temperature, onto a Ge covered (∼3 ML) Si(100) surface, mainly forms CoxGey species on the surface. However, annealing the sample at 400°C, Co diffuses through the Ge layer and reacts with Si and forms buried cobalt silicide of the structure Ge/CoSi2/Si(100). X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), medium energy ion scattering (MEIS) are employed for the study. The results open up a possibility to fabricate metal/semiconductor heterostructures in a novel way. © 1996 American Institute of Physics.

The formation of three-dimensional Ge islands in solid phase epitaxy is studied by medium-energy ion scattering and atomic force microscopy. When a six-monolayer Ge film on a Si(111) substrate is annealed below 580 °C, many small islands of various heights below 100 angstrom form on the two-dimensional layer strained by lattice mismatch. After annealing at higher temperatures such as 770 °C, the islands agglomerate to form large islands higher than 100 angstrom with definite facets. These three-dimensional islands do not relax completely from the lattice mismatch strain they are compressed horizontally and expanded vertically compared with the ideal Ge bulk crystal. The vertical lattice length is 2.3% longer than the in-plane length.

The interface structure between a Ge thin film and Si(111) substrate during solid-phase epitaxy of Ge is studied by medium-energy ion scattering. Intermixing within the bilayer between the two-dimensional Ge layer with the critical thickness of 4 monolayers (ML) and the Si substrate occurs at 550 °C and above. The intermixing advances into deeper layers with annealing at higher temperatures, and Si atoms from the substrate migrate to the uppermost surface above 770 °C. When Ge is deposited, in excess of the critical thickness, three-dimensional islands form on the two-dimensional layer with a thickness of 4 ML before intermixing between Ge and Si layers begins. Atomic displacement is observed in both the Ge film and the substrate near the interface. The substrate is compressed vertically about 1.2%. However, the strain caused by the lattice mismatch between Ge and Si is relaxed by intermixing, so atomic displacement is partially restored. © 1995, American Vacuum Society. All rights reserved.

An ultrathin SiGe layer prepared by growing Ge epitaxially on Si(001) was oxidized and investigated using X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS). Growth at a substrate temperature 550° C leads to the formation of a mixed SiGe layer on Si(001). Oxidation of this sample at 250° C forms predominantly SiO2 and a small amount of GeO. MEIS shows evidence for the diffusion of Ge inwards by 2–3 Å and of Si towards the surface resulting in the pile up of Ge at the SiO2/SiGe interface. On annealing the oxidized surface at 360° C, oxygen leaves the Ge sites and form SiO2 thereby reducing GeO to elemental Ge. The concentration of oxygen remains the same through out this reaction. © 1994 The Japan Society of Applied Physics.

On a clean Si(111)-7X7 surface, Ge grows in the Stranski-Krastanov mode. At 300-450 degrees C, relaxed islands begin to form when. the Ge growth is 6 monolayers (ML) thick. When Ge is grown on a Pb/Si(111)-root 3X root 3 surface, Pb segregates on the surface and agglomerates into two-dimensional islands. And the critical thickness for the formation of relaxed island becomes 4 ML. This change in critical thickness is explained by Pb reducing the surface energy or by an improved crystallinity of Ge layers (due to a simplified substrate surface reconstruction), or by both.

中エネルギーイオン散乱法(MEIS)では,結晶成長もしくは種々のプロセスにより形成された表面層,あるいは埋もれた界面の急峻性,原子の変位,組成に関する知見をほぼ非破壊で得ることができる。MEISによる測定とシミュレーションとの比較解析により,化学処理にて形成した自然酸化膜下のSi(111)結晶では2-bilayer程度の原子が酸化膜側に持ち上がった構造をもつことがわかった。熱酸化膜/Siでは自然酸化膜/Siに比べて結晶のSi原子の変位は小さい。自然酸化膜/Siに見られる結晶Siの変位は500℃のJ処理により解消する。MBE成長をしたGe/Si(111)における界面近傍のGe原子は膜厚方向に0.1～0.2Åの歪みをもつ。室温で形成したGe/Si(111)に熱処理を施すと,500℃以上の温度でGeとSi原子の相互拡散が生じ混合層が形成される。熱処理に伴って相互拡散開始前後の温度(～550℃)までは膜厚方向の歪みが存在しているのに対し,より高温では混合層の形成とともに歪みが緩和されることが示された。

A thin layer of Ge grown on Si(001) surface is oxidized in situ and investigated using XPS, AES, RHEED, and MEIS. The samples used are, Ge layer formed by deposition at room temperature and SiGe mixed layer formed by deposition at 550°C. Oxidation at 250°C of the RT grown layer leads to the formation of GeO and on heating the surface to 360°C, oxygen bonds with Si forming SiO2, thereby reducing GeO to elemental Ge. In the epitaxially grown layer (grown at 550°C), after oxidation, SiO2 and a small amount of GeO are formed. Similar reaction takes place on this surface also, forming SiO2 as the final product on the surface. In the RT grown layer, after oxidation, MEIS shows evidence for the diffusion of Si through the Ge layer towards the surface.

The structural change of Si(111)-√3 × √3-Ag surfaces caused by atomic hydrogen adsorption has been studied using low-energy ion scattering spectroscopy. Computer simulations of ion scattering spectra have been carried out for various kinds of the morphology of the Ag deposit. Comparison of the simulation results with the observed change of the spectra reveals that the Ag monolayer with the √3 × √3-Ag structure is transformed into small Ag(111) clusters epitaxially grown on Si(111) by hydrogen adsorption at room temperature. © 1992.

Using time-of-flight (TOF) type low-energy impact-collision ion scattering spectroscopy (ICISS) and elastic recoil detection analysis (ERDA), we have investigated (1) the effect of the saturation of surface dangling bonds of Si(100) surfaces with atomic hydrogen upon Ag thin film growth, and (2) the effect of hydrogen adsorption onto Ag thin films (∼ 1 ML coverage) on the clean surfaces. We find that (1) epitaxial growth of Ag films is promoted by the hydrogen atoms residing at the film/substrate interface and (2) adsorption of hydrogen onto Ag monolayer deposited on Si(100) surfaces transforms the Ag monolayer into very small crystallites of Ag(100) grown epitaxially on the Si(100) substrate. © 1992.

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 transform 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. © 1991.

Hydrogen adsorbed Si(100)-2 × 1 surfaces have been studied by low-energy recoil-ion spectroscopy (LE-RIS). It was found that the adsorption processes could be easily monitored by observing the hydrogen positive-recoils associated with the Ne+ion beam having the energy between 500 and 2000 eV. A detection sensitivity of the surface hydrogen was estimated to be 0.03 monolayer (ML) based on the results of elastic recoil detection analysis (ERDA). For a Si(100)-2 × 1 : H monohydride surface, hydrogen recoil ion intensity profiles showed periodic structures as a function of azimuthal angle, reflecting a surface atomic arrangement. From these periodic structures and computer simulations, a possible hydrogen adsorption site model was proposed. © 1991.

The surface damage formed on a clean Si(100)-2 x 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/cm2. 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.

We have investigated the effect of the saturation of surface dangling bonds of Si(111) surfaces with atomic hydrogen upon Ag thin-film growth. By using time-of-flight-type low-energy ion scattering-recoil analysis techniques, we find that the growth mode of Ag thin films is drastically changed by the hydrogen termination of Si(111)-7×7 surfaces and that the epitaxial growth of A-type Ag(111) films is promoted by the hydrogen atoms residing at the film/substrate interface. © 1991 The American Physical Society.

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. © 1989.

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. © 1988.