Scanning Probe Microscopy
- Contact Researcher: Franck ROSE, Dr.
- Hosted LIMMS Japanese Laboratory: Kawakatsu Lab --- thematiques
- Application of MEMS-AFM for Sensing and Lithography
- Nano Cantilevers
- Single Atom and Molecule Mass Sensing
- Stiction and Surface Loss
- Scanning Probe Microscopies in UHV: STM, NC-AFM, SEM, TEM
- Surface Science of Semiconductors
- Single Atom & Molecule Manipulations
- In-air and in-liquid AFM Imaging of Biological Samples
- Mesoscopic and 2D Behavior of Electrons in Graphite
- Context :
The Kawakatsu Laboratory for Applied Scientific Instruments has a state of the art expertise in nano-cantilever fabrication and in development and design of scanning probe microscopies such as NC-AFM, STM, FE-SEM, and TEM. Recenntly, our group expended its know-how and interest in Surface Science in order to address several issues at the frontier of Surface Science and MEMS. For example, problems such as single atom mass sensing, stiction, and surface loss are now under investigation in several works in progress related to cantilevers.
- Objectives :
The project reported here deals with the complex interplay between reconstructions, electronic band structure, nature of the atoms, and chemical reactivity on a surface. Since now, there is no study by one and the same group, and one and the same method of all reconstructions for even one group-IV semiconductor. Therefore, precise understanding of surface stabilization with 21, 77, and c(28) reconstructions of diamond, silicon, or germanium has not been investigated yet. So far, results concerning only the origin, formation, and geometrical structure of the Si(111)-c(28) has been reported.
- Methods :
The coexisting metastable reconstructions of the Si(111) surface have been investigated by NC-AFM1,2. For the first time, true at omic resolution (Fig.1) has been achieved in the NC-AFM imaging of the 77, c(28), 22, c(24), and √3√3 coexisting reconstructions of the same quenched surface sample. The electronic band structure of the Si(111)-c(28) surface is experimentally reported here for the first time (Fig.2) by mean of scanning tunneling spectroscopy (STS)3. The surface is found to be semiconducting with adatom and restatom bands lying inside the 0.8 eV energy band gap. The local density of states as well as the surface reactivity toward residual hydrogen atoms adsorption are compared for the c(28), 77 and 21 reconstructions coexisting on the same (111) quenched surface. The adsorption of molecular oxygen on the c(28) reconstruction of quenched Si(111) surfaces has been studied at the atomic scale using scanning tunneling microscopy (STM) at room temperature (RT)4. It has been found that clean well reconstructed c(28) adatoms do not react with O2 molecules (Fig.3) but that a limited oxidation can start where adatom sites arranged in √3√3 reconstructed structures are present. For low O2 exposures, bright and dark oxygen induced sites appear on the Si(111)-77, while Si(111)-c(28) does not oxidized at all. At high O2 exposures, large oxidation areas have spread on the 77 reconstruction, preferentially on the faulted halves of the unit cell, and smaller oxidation areas induced by topological defects have grown all around clean un-reacted c(28) regions. We have also shown2 that similarly to Ge(111)-c(28) the restatoms of the Si(111)-c(28) surface are the sites for individual hydrogen adsorption, inducing a local reverse charge transfer from the reconstruction. A systematic comparison between the local electronic density of states (LDOS) and chemical reactivity (toward H and O2) of the Si(111)-77, Si(111)-c(28), and Si(111)-21 reconstructions coexisting on the same quenched sample surface, have been carried out using non contact atomic force microscopy (NC-AFM) and scanning tunneling microscopy (STM) We finally draw the conclusions that in the case of group IV semiconductors, first, the nature of the atoms and the distance between them change radically the surface band structure for the same reconstruction; second, the reconstruction seems to be the most influent parameter when comparing the chemical reactivity of surfaces of different atomic nature.
- References :
- F.Rose, T.Ishii, S.Kawai, and H.Kawakatsu, "Non-Contact Atomic Force Microscopy and Scanning Tunneling Microscopy of Coexisting Reconstructions on Si(111)", e-Journal of Surface Science and Nanotechnology, 3, 258 (2005).
- F.Rose, S.Kawai,and H.Kawakatsu, "Low reactivity of molecular oxygen with Si(111)-c(28)", Surface Science, 600, 106 (2006)