Image-potential-induced surface state at Si(100)

We have identified a surface state on Si(100) (2×1) at a binding energy of 0.69±0.05 eV with respect to the vacuum level. Band-structure calculations within the GW method reveal that almost 80% of the probability density of the resonance is located in front of the surface. We therefore assign the surface resonance to an image-potential state. It has a lifetime of about 10 fs and contributes significantly to two-photon photoemission from Si(100). PACS 73.20.At; 79.60.Bm; 79.60.Dp; 79.60.Ht     

Structural phase transitions of the Si(100) surface

A Monte Carlo study of the structural phase transitions on the Si(100) surface for both the “(2×1)” and “c(2×2)” reconstruction families is carried out using the asymmetric dimer model. A second order phase transition is observed at about 250 K from a p(2×2) (layered antiferromagnetic) to a disordered (paramagnetic) state in the “2×1” family. A similar transition is observed about 800 K from a c(2×2) (ferromagnetic) to a disordered state in the “c(2×2)” family. These results are in agreement with real-space renormalization group results. The variation of the specific heat, susceptability and the absolute value of the order parameter as a function of temperature is obtained in the range 200 to 300 K for the “2×1” family and 750 to 850 K for the “c(2×2)” family. Also, the order parameter correlation function is computed for ten different temperatures in the above ranges.     

Spontaneous N incorporation onto a Si(100) surface

Initial nitridation of the Si(100) surface is investigated using photoemission, ion-scattering and ab initio calculations. After dissociation of NO or NH3, nitrogen atoms are found to spontaneously form a stable, highly coordinated N[triple bond]Si(3) species even at room temperature. The majority of the N species is incorporated into the subsurface Si layers occupying an interstitial site, whose atomic structure and unique bonding mechanism is clarified through ab initio calculations. This unusual adsorption behavior elucidates the atomistic mechanism of initial silicon nitride formation on the surface and has important implication on the N-rich layer formation at the SiO(x)N(y)/Si interface.     

Twisting of dimers on the Si(100) surface

We investigate the twisting of asymmetric dimers on the Si(100) surface, as predicted by the LEED results of Yang, Jona and Marcus. Minimisation of the MINDO/3 cluster energy yields no twisting for clusters containing a single dimer or a pair of parallel dimers. The long range electrostatic interaction of the dipoles associated with the charge transfer in the asymmetric dimer does indeed produce a twisting torque, but it is too small to account for the elastic distortion required by the LEED model.     

DC-electric-field-modified second-harmonic generation at the Si(100) surface

1 resonances for clean and H covered surfaces shift as a function of the dc field in agreement with experiment. This suggests the presence of built-in electric fields whose strength depends on the H coverage, and which are strongly localized in the subsurface region. Received: 20 September 1998     

Interaction of cobalt atoms with an oxidized Si(100)2 × 1 surface

The initial stages of oxidation of a Si(100)2 × 1 surface and the interaction of cobalt atoms with it were studied by core-level photoelectron spectroscopy. The study was carried out with cobalt coverages of up to 8 ML. Computer modeling of the spectra of photoexcited electrons revealed Co atom penetration under the silicon oxide layer, an effect observed even at room temperature. This process was shown to give rise to the disappearance of silicon interface phases at the oxide-layer-silicon boundary and to the formation of a more complex phase involving atoms of Co, O, and Si. After completion of the process, a Co-Si solid solution forms at the interface.     

Two-state double-continuum Fano resonance at the Si(100) surface

Fano resonances are well-known manifestations of the interference between a direct and an indirect ionization process. Here we report on a more complicated interference pattern observed in two-photon photoemission at the Si(100) surface. This two-dimensional Fano profile involves two discrete surface resonances which couple as initial and intermediate states to the silicon valence and conduction band, respectively. Tuning the photon energy across the surface resonance reveals asymmetric line profiles with pronounced destructive interference in the two-photon photoelectron intensities of both initial and intermediate states. The interference pattern is explained by an analytic extension of Fano's model to describe the coupling of two discrete states with two continua. This coupling strongly modifies the photoabsorption and is of general importance for light conversion in nanostructures and light-harvesting devices.     

Dopant-pair structures segregated on a hydrogen-terminated Si(100) surface

Novel atomic structures on a H-terminated Si(100)-(2x1)-H surface were found using scanning tunneling microscopy (STM). The structures are distinguishable only from Si dimers in empty-state STM images. They were observed on arsenic- and phosphorus-doped substrates, but not on boron-doped substrates. Surface density of these structures was found to be proportional to the dopant density in the substrate. First-principles calculations clarify that they are consisting of dopant pairs that are segregated from the bulk material. Hydrogen atoms attached to the dopant pair are found to flip between two positions on the surface due to a quantum effect.     

Influence of sublayer atoms on Si(100) surface reconstructions

Influence of sublayer atoms on Si(100) surface reconstruction has been examined with density functional theory and molecular dynamic simulation. We found that the displacements of sublayer atoms under the buckled dimer affect the motions of their neighboring atoms and thus play an important role in determining the surface reconstructions. The present results reveal the relationship between the surface dimer reconstruction and the motion of the sublayer atoms and provide an account for experimental observations of Si(100) surface reconstructions at very low temperatures.     

Thermal desorption of surface phosphorus on Si(100) surfaces

Thermal desorption of phosphorus on Si(100) surfaces has been investigated by varying the phosphorus coverage from zero to one monolayer (ML). The reaction path of phosphorus desorption is complicated and strongly dependent upon the phosphorus coverage. In the thermal desorption spectra, there are three apparent desorption peaks at 750, 850 and 1000°C. The entire phosphorus atoms on the surface desorb as P₂ through recombinative reactions irrespective of the desorption temperature and the coverage. In the lower coverages below 0.2 ML, the thermal desorption spectra are characterized by a single peak at 900°C which is considered to be the desorption from Si---P heterodimers. At higher coverages exceeding 0.2 ML, it is considered that three desorption schemes from P---P, Si---P dimers and defects coexist in the reaction stage.     

Imaging and manipulation of the Si(100) surface by small-amplitude NC-AFM at zero and very low applied bias

We use a noncontact atomic force microscope in the qPlus configuration to investigate the structure and influence of defects on the Si(100) surface. By applying millivolt biases, simultaneous tunnel current data is acquired, providing information about the electronic properties of the surface at biases often inaccessible during conventional STM imaging, and highlighting the difference between the contrast observed in NC-AFM and tunnel current images. We also show how NC-AFM (in the absence of tunnel current) can be used to manipulate both the clean c(4 × 2) surface and dopant-related defects.     

The Si (100) surface: Symmetric or asymmetric dimers?

We present new results obtained with medium energy ion beam crystallography on the clean Si (100)?(2 × 1) surface. This study, meant to discriminate between symmetric and asymmetric dimer models for the reconstruction, shows that symmetric dimers are not consistent with our results. We conclude that the Si (100)?(2 × 1) surface is reconstructed in asymmetric dimers, accompanied by extensive subsurface distortions.     

Biological functionalization of the amine-terminated Si(100) surface by glycine

A peptide reaction of glycine on an amine-terminated Si(100) surface was investigated using C 1s, N 1s, O 1s, and Si 2p core-level spectroscopy, where the amine-terminated Si(100) surface was prepared using NH₃. In-situ thermal treatments at a mild temperature of 50 °C after the adsorption of glycine on a room-temperature amine-terminated Si(100) surface induced the peptide reaction between the carboxyl group of glycine and the amine group of the surface. This suggests that the amine-terminated Si(100) surface can be an excellent template for constructing a junction between a biomaterial and a Si surface using a dry process.     

Control of the degree of surface graphitization on 3C-SiC(100)/Si(100)

The current method of growing graphene by thermal decomposition of 3C-SiC(100) on silicon substrates is technologically attractive. Here, we investigate the evolution of the surface graphitization as a function of the synthesis temperature. We establish that the carbon enrichment of the surface is characterized by a clear modulation of the surface potential and structuration. The structural properties analysis of the graphene layers by low energy electron diffraction and micro-Raman spectroscopy demonstrate a graphitization of the surface.