Mechanism of Cu transport along clean Si surfaces

Cu diffusion along clean Si(111), (110) and (100) surfaces are investigated by Auger electron spectroscopy and low energy electron diffraction. The effective diffusion coefficients of copper are measured in the temperature range from 500 to 650°C. It is shown that the Cu transport along silicon surface occurs by the diffusion of Cu atoms through Si bulk and the segregation of Cu atoms to the surface during the diffusion process. It is found that the segregation coefficients of Cu to silicon surface during the diffusion process depend on surface orientation.     

Ge diffusion on Si surfaces

Ge diffusion on Si(100), (111), and (110) surfaces has been studied by Auger electron spectroscopy and low energy electron diffraction in the temperature range from 600 to 800 °C. Surface diffusion coefficients versus temperature have been measured.     

Diffusion of silver over atomically clean silicon surfaces

The diffusion of silver the (111), (100), and (110) silicon surfaces is studied by Auger electron spectroscopy and low-energy electron diffraction. The mechanisms of diffusion over the (111) and (110) surfaces are revealed, and the temperature dependences of diffusion coefficients are measured. An anisotropy of silver diffusion over the (110) surface is detected.     

Jump to contact and neck formation between Pb surfaces and a STM tip

We present a study of the interaction of a W STM tip and the (110) and (111) surfaces of Pb. Atomic resolution has been obtained at room temperature on Pb(110) and up to 330 K on Pb(111). At higher temperatures the surfaces can jump to mechanical contact with the STM tip, resulting in the formation of a connecting neck of Pb between tip and surface. As the tip is retracted, the neck elongates and finally breaks. The dependence of the maximum neck size on the temperature and the tip retraction speed indicates that surface diffusion is responsible for the neck build-up. When the surface is partially oxidized the maximum neck size is reduced. We derive a scaling relation between the maximum neck size, the retraction speed and the surface diffusion coefficient. With this relation and the temperature dependence of the maximum neck size we obtain activation energies for the neck build-up of 1.3 and 0.9 eV respectively for necks on Pb(110) and Pb(111). When a neck breaks, either a crater or a hillock is left on the surface.     

Visualization of submonolayers and surface topography by biassed secondary electron imaging: Application to Ag layers on Si and W surfaces

An ultra high vacuum-scanning electron microscope (UHV-SEM), equipped with micro-Auger electron spectroscopy, RHEED, and a deposition source has been used to study submpnolayers of Ag on Si(111), Si(100) and W(110) surfaces. A new SEM technique has been developed to visualize these submonolayers directly by applying a high negative bias (?500 V) to the sample. The dependence of the visibility on bias voltage, layer thickness and angle of incidence of the electron beam has been studied. The sensitivity was found to be better than 0.1 ML in the case of Ag on Si surfaces. Some applications to surface diffusion have been made and preliminary results for Ag on Si(111) are noted. Contrast at the 1 ML level can be > 10% in certain cases. The understanding of this contrast in terms of work function and ionization energy (band-bending) changes is discussed.     

Diffusion of tin over clean silicon surfaces

Diffusion of tin over the (111), (100), and (110) silicon surfaces has been studied by Auger electron spectroscopy and low-energy electron diffraction. The diffusion mechanisms have been established, and the temperature dependences of the diffusion coefficients have been obtained.     

Pb液滴在Ni基底润湿铺展行为的分子动力学模拟

采用分子动力学方法研究了Pb液滴在Ni(100)晶面、(110)晶面和(111)晶面的铺展润湿行为. 结果表明: Pb液滴在Ni(100)及(111)基底上的润湿铺展现象呈各向同性, 而在Ni(110)基底上的润湿铺展现象呈明显的各向异性, 且这种各向异性源于Ni(110)晶面点阵结构上Pb原子沿不同晶向的扩散机制及速度的明显差异; Pb液滴在Ni(111)晶面上铺展时, 未发生表面合金化, 液滴铺展动力学描述近似满足 R² ∝ t, 而液滴在(100)晶面和(110)晶面上铺展时表面产生合金化现象, 铺展动力学关系近似满足 R⁴ ∝ t, 且液滴在(100)晶面上的铺展速度高于(110)晶面上的铺展速度. 关键词： 分子动力学 润湿各向异性 铺展膜 扩散机制     

Change in the nature of the Ni diffusion mechanism on the Si(111) surface with adsorption of Co atoms

The diffusion of Ni on a Si (111) surface is investigated by LEED and Auger electron spectroscopy. It is found that, in contrast to the process on the initially clean Si (111)−7×7 surface, on Si (111) surfaces with submonolayer Co coverages the nature of the Ni transport mechanism changes at a temperature of about 750 °C, and the Ni surface diffusion coefficients increase sharply below this temperature. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 9, 611–614 (10 November 1997)     

Vibrational EELS studies of CO chemisorption on clean and carbided (111), (100) and (110) nickel surfaces

Room temperature adsorption of CO on bare and carbided (111), (100) and (110) nickel surfaces has been studied by vibrational electron energy loss spectroscopy (EELS) and thermal desorption. On the clean (100) and (110) surfaces two configurations of CO adsorbed species, namely “terminal” and bridge bonded CO, are observed simultaneously. On Ni(111), only two-fold sites are involved. The presence of superficial carbon lowers markedly the bond strength of CO on Ni(111)C and Ni(110)C surfaces, while no adsorption has been detected on the Ni(100)C surface. Moreover, on the carbided Ni(110)C surface, the adsorption mode for adsorbed CO is changed with respect to the clean surface; only “terminal” CO is then observed.     

Probing the temperature dependence of the dysprosium-silicon interface

Summary Photoemission electron spectroscopic measurements were done on the Dy-Si interfaces prepared by Dy deposition onto cleaved Si(111) surface with the use of synchrotron radiation as a light source. Results show that an interfacial reaction takes place even at room temperature. Temperature dependence studies for Dy deposited on Si(111) demonstrate the importance of overlayer thickness and substrate temperature during deposition.     

Single atom self-diffusion on nickel surfaces

Results of a field ion microscope study of single atom self-diffusion on Ni(311), (331), (110), (111) and (100) planes are presented, including detailed information on the self-diffusion parameters on (311), (331), and (110) surfaces, and activation energies for diffusion on the (111), and (100) surfaces. Evidence is presented for the existence of two types of adsorption site and surface site geometry for single nickel atoms on the (111) surface. The presence of adsorbed hydrogen on the (110), (311), and (331) surfaces is shown to lower the onset temperature for self-diffusion on these planes.     

不同衬底上Pb(Zr0.52Ti0.48)O3择优取向铁电薄膜的制备和研究

通过MOD法在Si(100)和Pt(111)/Ti/SiO₂/Si基片上制备出LaNiO₃ ( LNO)薄膜.再通过修 正的Sol-gel法，在Pt(111)/Ti/SiO₂/Si,LNO/Si(100)和LNO/Pt/Ti/SiO_{2< /sub>/Si三种衬底上 制备出具有择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜. 经XRD分析表明，L NO薄膜具有(100)择优取向的类钙钛矿结构；PZT薄膜均具有钙钛矿结构，且在Pt(111)/Ti/S iO2/Si衬底上的薄膜以(110)择优取向，在LNO/Pt/Ti/SiO2/Si和LN O/Si(100)衬底上的 薄膜以(100)择优取向.经场发射SEM分析和介电、铁电性能测试表明，在LNO/Si和LNO/Pt/Ti /SiO2/Si衬底上的PZT薄膜的平均粒径、介电常数以及剩余极化强度均比以Pt/T i/SiO2/Si为衬底的薄膜大. 关键词： 3}薄膜')" href="#">LaNiO₃薄膜 PZT铁电薄膜 择优取向 剩余极化强度     

Growth of metallic nanowires on anisotropic Si substrates: Pb on vicinal Si(0 0 1), Si(7 5 5), Si(5 3 3), and Si(1 1 0)

The spontaneous formation of mesoscopic Pb-wires, on 4° off-cut Si(0 0 1) vicinal surface, Si(7 5 5), Si(5 3 3), and Si(1 1 0) substrates was studied by low-energy electron microscopy. Before the deposition of Pb the substrates were modified by predeposition of a submonolayer amount of Au followed by annealing. The Au-induced reconstruction creates quasi-one-dimensional facets and superstructures. Their width ranged from several hundred nm in the case of the vicinal Si(0 0 1) down to atomic scale size, for the Si(1 1 0) surface. The best-developed arrays of parallel aligned mesoscopic wires were obtained during the deposition of Pb on substrates cooled slightly below room temperature. Wires with length to width ratio reaching 130 were produced on the Si(7 5 5) and the Si(5 3 3) substrates. The width of these nanowires was uniform over the whole substrate and was about 60 nm. The driving forces for the formation of the mesoscopic wires are the anisotropic strain due to the large misfit between the Pb and the Si lattice and one-dimensional diffusion of Pb.     

Effect of adsorbed Sn on Ge diffusivity on Si(111) surface

The effect of adsorbed Sn as a surfactant on Ge diffusion on a Si(111) surface has been studied by Low Energy Electron Diffraction and Auger Electron Spectroscopy. The experimental dependence of Ge diffusion coefficients on the Si(111) surface versus temperature in the presence of adsorbed Sn atoms has been measured in the range from 300 to 650°C. It has been shown that at a Sn coverage of about 1 monolayer the mobility of Ge atoms increases by several orders of magnitude.      

Comparative AES and RHEED study of the formation of Pd silicide on clean and oxide covered Si(100) and (111) surfaces

The formation and epitaxial orientation of Pd silicide on clean and native oxide covered Si(100) and (111) surfaces was studied by Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Pd was vapor deposited in UHV on to the substrates up to thicknesses of about 6 nm. On clean Si substrates, ultra-thin Pd deposits reacted to form Pd₂Si already at room temperature, as detected by a characteristic splitting of the Si LVV Auger peak. However, a polycrystalline structure with very small crystallite sizes was indicated by diffuse ring patterns in RHEED. When the initial thickness of the Pd deposit exceeded about 3 nm, the diffraction ring pattern of unreacted metal developed. During annealing of room temperature deposits of Pd, the (100) and (111) substrates behaved differently. Larger crystallites formed on Si(100), but the films remained polycrystalline, though textured. On Si(111), virtually perfect epitaxial re-orientation of the silicide was found. When the substrates were initially covered with native oxide of about 2 nm thickness, silicide formation started at about 200°C, resulting in polycrystalline, but strongly textured Pd₂Si. Upon further annealing at temperatures up to 600°C, an additional phase of epitaxially oriented Pd₂Si developed on Si(111), similar to that on clean Si(100). In all experiments, extended annealing at temperatures above 250°C caused segregation of Si to the surface. This was accompanied by the development of an additional peak in the Auger electron spectra at about 313 eV, which we assign to a plasmon loss of δE = 17 eV in the Si overlayer, being excited by Pd Auger electrons of energy 330 eV.     

A study of a coadsorbate surface diffusion (Pb on C/W)

The influence of a coadsorbed submonolayer (carbon) on the diffusion of adatoms (lead) along a crystal surface (tungsten) is studied in a preliminary manner by a field electron microscope technique. Experiments show that the surface diffusion of lead is strongly affected by the coadsorption of carbon: (1) The diffusion of Pb which is easy around (110) and (111) and difficult around (100) on clean tungsten becomes easier around (100) than around (110) and (111). (2) The diffusion anisotropy on the stepped surface around (100) is changed by carbon adsorption. (3) C adatoms enhance the diffusion of Pb especially around (100). (4) The mean carbon coverage required to observe these effects is only a few hundredths of a monolayer. The dependence of the surface diffusion on such small impurity coverages is discussed.     

Hydrogen adsorption and surface structures of silicon

The adsorption of atomic hydrogen on silicon (111)2 × 1 cleaved, (111) 7 × 7, and (100) 2 × 1 surfaces has been studied by using electron energy loss spectrscopy (ELS) and Photoemission spectroscopy (UPS). On all surfaces the hydrogen removes the “dangling bond” surface state and a new peak in the density of states at lower energies corresponding to the SiH bond is found. The LEED pattern of the equilibrium surfaces (111) 7 × 7 and (100) 2 × 1 is not altered by hydrogen adsorption, while on the cleaved (111) 2 × 1 surface the fractional order spots are extinguished. The Haneman surface-buckling model therefore provides an explanation for the surface reconstruction of the cleaved (111) 2 × 1 surfaces. For the equilibrium surfaces, (111) 7 × 7 and the (100) 2 × 1, the data are consistent with the Lander-Phillips model.     

A leed-aes study of thin Pd films on Si(111) and (100) substrates

A system Pd (deposit)-Si (substrate) has been studied by LEED and AES. Pd₂Si formed on Si(111) became epitaxial after a short time of annealing at a temperature between 300 and 700°C, while the Pd₂Si formed on Si(100) did not, in both cases the surfaces of the Pd₂Si being covered with a very thin Si layer. A sequence of superstructures (3√3 × 3√3), (1 × 1), and (2√3 × 2√3) was observed successively in Pd/Si(111) as the annealing temperature was increased. A (√3 × √3) structure was obtained by sputtering the 3√3 surface slightly. It was found that the √3 structure corresponds to Pd²Si(0001)-(1 × 1) grown epitaxially on Si(111), and that the 3√3 structure comes from the thin Si layer accumulated over the silicide surface, while the 2√3 and 1 structures arise from a submonolayer of Pd adsorbed on Si(111). Superstructures observed on a Pd/Si(100) system are also studied.     

Lead growth on Si(111) surfaces reconstructed by indium

We study the Pb growth on both √3 × √3-In and 4 × 1-In reconstructed Si(111) surfaces at room and low temperature (160 K). The study takes place with complementary techniques, to investigate the role of the substrate reconstruction and temperature in determining the growth mode of Pb. Specifically, we focus on the correlation between the growth morphology and the electronic structure of the Pb films. The information is obtained by using Auger electron spectroscopy, low energy electron diffraction, soft x-ray photoelectron spectroscopy, scanning tunneling microscopy and spot profile analysis-low energy electron diffraction. The results show that, at low temperature and coverage ≤12 ML on the Si(111)√3 × √3-In surface, Pb does not alter the initial semiconducting character of the substrate and three-dimensional Pb islands with poor crystallinity are grown on a wetting layer. On the other hand, for the same coverage range, Pb growth on the Si(111)4 × 1-In surface results in metallic Pb(111) crystalline islands after the completion of a double incomplete wetting layer. In addition, the bond arrangement of the adatoms is studied, confirming that In adatoms interact more strongly with the silicon substrate than the Pb ones. This promotes a stronger Pb-Pb interaction and enhances metallization. The onset of the metallization is correlated with the amount of pre-deposited In on the Si(111) surface. The decoupling of the Pb film from the 4 × 1-In interface can also explain the unusual thermal stability of the uniform height islands observed on this interface. The formation of these Pb islands is driven by quantum size effects. Finally, the different results of Pb growth on the two reconstructed surfaces confirm the importance of the interface, and also that the growth morphology, as well as the electronic structure of the Pb film can be tuned with the initial substrate reconstruction.     

The three-dimensional equilibrium crystal shape of Pb: Recent results of theory and experiment

The three-dimensional equilibrium crystal shape (ECS) is constructed from a set of 35 orientation-dependent surface energies of fcc Pb which are calculated by density functional theory in the local-density approximation and distributed over the [110] and [001] zones of the stereographic triangle. Surface relaxation has a pronounced influence on the equilibrium shape. The (111), (100), (110), (211), (221), (411), (665), (15,1,1), (410) and (320) facets are present after relaxation of all considered surfaces, while only the low-index facets (111), (100) and (110) exist for the unrelaxed ECS. The result for the relaxed Pb crystal state is in support of the experimental ECS of Pb at 320–350 K. On the other hand, approximating the surface energies of vicinal surfaces by assuming a linear relationship between the Pb(111) first-principles surface energy and the number of broken bonds of surface atoms leads to a trivial ECS that shows only (111) and (100) facets, with a sixfold symmetric (111) facet instead of the correct threefold symmetry. It is concluded that the broken bond rule in this simple linear form is not a suitable approximation for obtaining the proper three-dimensional ECS and correct step formation energies. PACS 05.70.Np; 61.50.Jr; 68.35.Md; 71.15.Mb