Elsevier

Thin Solid Films

Volume 516, Issue 12, 30 April 2008, Pages 3741-3746
Thin Solid Films

Preparation and characterization of atomically flat and ordered silica films on a Pd(100) surface

https://doi.org/10.1016/j.tsf.2007.06.070Get rights and content

Abstract

Ultrathin silica films with different thicknesses have been grown on a Pd(100) surface by depositing silicon in the presence of O2. The film composition and electronic properties were characterized by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), and high-resolution electron energy loss spectroscopy (HREELS). Scanning tunneling microscopy was applied to investigate the film morphology and lattice structure. The results show that the obtained films are atomically flat and highly ordered in a long range. UPS and HREELS measurements indicate that the silica film has the same electronic and vibrational properties as bulk silica. A 2.8 nm thick film exhibits low defects in the film and high thermal stability up to 800 K, as evidenced by ion scattering spectroscopy and XPS.

Introduction

Silicon dioxide (SiO2) is extensively used as a catalyst support. For surface scientists it is highly desirable to develop model catalysts consisting of metal clusters or nanoparticles supported on the surfaces of SiO2. However, the insulating properties of bulk silica cause many experimental difficulties, such as surface charging, sample mounting, sample heating and cooling.

In order to circumvent these difficulties and to explore micro-processes on a silica surface (such as nanoparticle growth, surface chemical reaction, and thus induced structure change, etc. [1], [2], [3], [4], [5], [6]) using surface analysis techniques, several methods have been recently developed to synthesize ultrathin SiO2 films, among which two methods are frequently used. One is to directly expose single crystal silicon surfaces to oxygen, as in the case of Si(111)-7 × 7 [1], [2], [3] and Si(100) [4], [5]; the other is to deposit silicon in an oxygen atmosphere or to oxidize a silicon layer on a metal substrate, such as Mo(110) [6], [7], [8], Mo(100) [9], Mo(112) [10], [11], [12], [13], [14], and Ni(111) [15]. Numerous studies have been performed on the preparation and characterization of thin SiO2 films; while a few works are on the growth of ordered SiO2 films. Freund's group and Goodman's group have prepared monolayer crystalline silica films on Mo(112) surfaces. The typical recipe for the growth of SiO2 on Mo(112) consisted of repeated cycles of depositing one-half monolayer of silicon onto a Mo(112) surface at room temperature (RT) followed by oxidation at 800 K. The resulting SiO2 films were subsequently annealed in four steps, which took 15 min each in an O2 background of 1 × 10−3 Pa with the temperature ranging from 1100 to 1250 K [12], [13]. Kundu and Murata reported growth of a 4.0 nm thick crystalline SiO2 film on a Ni(111) surface [15]. Si was deposited on a clean Ni(111) surface at RT with 3 nm thickness followed by oxidation in the presence of atomic hydrogen for 1 h at a substrate temperature of 620 K. Finally the sample was annealed at 1100 K in an ambient O2 atmosphere of 2.6 × 10−5 Pa for 10 min.

In this paper, we report a system for easily growing atomically flat and well-ordered silica films. In our growing system, Pd(100) was chosen as a substrate, and silica films were grown by depositing silicon onto Pd(100) in the presence of O2. The morphologies, electronic properties, and thermal stabilities of films have been investigated by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), high-resolution electron energy loss spectroscopy (HREELS), and ion scattering spectroscopy (ISS).

Section snippets

Experimental details

The experiments were carried out in an Omicron multiprobe surface analysis system with a base pressure of below 3.0 ×10−8 Pa. The system consists of three ultrahigh vacuum chambers: preparation, spectroscopic and microscopic chambers. The preparation chamber is equipped with a silicon evaporator and an ion-sputtering gun for sample cleaning. The spectroscopic chamber is installed with XPS, UPS, ISS, and HREELS (LK-ELS5000). The microscopic chamber is equipped with STM (Omicron

Results and discussion

The thickness of silica films was controlled by the deposition time of Si in O2. A simple inelastic attenuation model was applied to estimate the film thickness, d, using the relation ofd=rt=λcosαln(I/I0).t is the deposition time of Si in O2, r is the growth rate, I0 and I are the XPS intensity of Pd 3d core level from bare Pd(100) and Pd(100) after deposition of SiO2, α (63°) is the take-off angle with respect to the surface normal, λ is the electron inelastic mean free path. In our work, λ

Conclusions

We demonstrated a method of preparation of ultrathin silica films on a Pd(100) surface by depositing silicon in the 1 × 10−3 Pa oxygen pressure at 500 K. SiO2 films with different thicknesses (0.4–6.5 nm) have been prepared. The 2.8 nm silica film shows smooth morphology, stoichiometry, and well-ordered structure in a long range. The lattice structure of the SiO2 film is closely related with the Pd substrate structure, with a lattice constant of 3.6 ± 0.2 Å, similar to 2 times of the Pd(100)

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (No. 90206036 and No. 20573107). We acknowledge Dr. Zhen Song, Prof. Qinlin Guo, and Dr. Xiulian Pan with pleasure for helpful discussions and critically reading the manuscript.

References (33)

  • J.B. Zhou et al.

    Surf. Sci.

    (1997)
  • J.T. Mayer et al.

    Surf. Sci.

    (1992)
  • H. Ikeda et al.

    Thin Solid Films

    (1999)
  • Y. Nakagawa et al.

    Appl. Surf. Sci.

    (1998)
  • X. Xu et al.

    Surf. Sci.

    (1993)
  • J.W. He et al.

    Surf. Sci.

    (1992)
  • T. Schroeder et al.

    Solid State Electron.

    (2001)
  • R.G. Musket et al.

    Appl. Surf. Sci.

    (1982)
  • M.H. Schaffner et al.

    Surf. Sci.

    (1998)
  • B. Schleich et al.

    Surf. Sci.

    (1987)
  • A. Di Pomponio et al.

    Solid State Commun.

    (1995)
  • J.A. Schaefer et al.

    Surf. Sci.

    (1985)
  • L. Giordano et al.

    Surf. Sci.

    (2005)
  • B.K. Min et al.

    Catal. Today

    (2003)
  • J. Wang et al.

    Surf. Sci.

    (2002)
  • X.P. Xu et al.

    Science

    (1992)
  • Cited by (35)

    • Interface-doping modulated structural and electronic properties of two-dimensional silica supported on metal substrate

      2020, Applied Surface Science
      Citation Excerpt :

      In recent years, ultrathin silica films with high crystallinity have been successfully synthesized on many metal substrates, such as Mo(1 1 2) [24–27], Ni(1 1 1) [28], Pd(1 0 0) [29], Pt(1 1 1) [30] and Ru(0 0 0 1) [31]. Unlike a monolayer of corner-sharing [SiO4] tetrahedra chemically bonded to Mo (1 1 2) surface by one corner oxygen atom, 2D silica film on Pd(1 1 1), Pt(1 1 1) and Ru(0 0 0 1) exhibits a network of bilayer corner-sharing [SiO4] tetrahedra with hexagonal rings that is weakly bound to the metal surface [21,29–32]. Due to the weak interaction, it is possible to intercalate small gas molecules such as CO and D2, as well as metal atom (such as Pd) to the interface [33,34], which provides an interesting system to explore the effects of confined space at the interface on the reaction of oxygen and hydrogen atoms for water formation [35].

    • Gas-surface interactions on two-dimensional crystals

      2019, Surface Science Reports
      Citation Excerpt :

      Shortly before publication of this review another UHV TDS study about benzene on graphene appeared, see Ref. [146]. Silicatene consists of a monoatomic layer of silica, 2D SiO2 [126,127,132,133,329]. Gas-surface interactions on silicatene have not been studied in much detail.

    • Benzene adsorption on two-dimensional silica films – Benzene on silicatene

      2017, Chemical Physics Letters
      Citation Excerpt :

      An interesting example of a 2D crystal is silicatene which consists of a monoatomic layer of silica, SiO2. The silicatene films were originally grown on Mo(1 1 2) supports [3–5], but more recently also other supports such as Pd(1 0 0) and Ni(1 1 1) were used [6,7]. Besides fundamental interests, applications of silicatene may include microelectronics and sensors, but also model catalysis studies since doped silicatene may be considered as a 2D version of zeolite-like materials [8,9].

    • Water adsorption on two-dimensional silica films

      2016, Applied Surface Science
      Citation Excerpt :

      However, only recently UHV preparation procedures were published, initially by Freund, et al., and Goodman, et al. (see e.g. refs.[4,5]), allowing for the fabrication of epitaxial atomically thin crystalline 2D silica films (“inorganic graphene”, silicatene[6]). In the meanwhile a few more groups described preparation procedures of silicatene on different substrates.[7,8] Mo(112) was initially used to grow silicatene; even a 2D analog of zeolites was made by Al doping.[9,10]

    View all citing articles on Scopus
    View full text