Low-energy electron diffraction analysis of the Si(111)7×7 structure

Tong, S. Y.; Huang, Huan; Wei, C. M.; Packard, William E.; Men, F. K.; Glander, G. S.; Webb, M. B.

doi:10.1116/1.575179

Cited by 217 publications

(35 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Robinson et al [60], the LEED study by Tong et al [61], and the STM study by Hamers et al [62] confirmed and refined this model, which is now widely accepted.…”

Section: The Si(111)7×7 Surface: Spatial and Electronic Structuresupporting

confidence: 53%

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

McGuire¹

2004

View full text Add to dashboard Cite

The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces.The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7×7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 fs pulse tunable around 800 nm. The measured spectral holes yield homogeneous dephasing times of a few tens of femtoseconds. Fits with a Lorentzian spectral hole centered at zero probe detuning show a linear dependence of the hole width on pump fluence, which suggests that charge carrier-carrier scattering dominates the dephasing dynamics at the measured excitation densities. Extrapolation of the deduced homogeneous dephasing times to zero excitation density yields an intrinsic dephasing time of ∼ 70 fs. The presence of a secondary spectral hole indicates that scattering of the surface electrons with surface optical phonons at 570 cm −1 occurs within the first 200 fs after excitation.The broad bandwidth of femtosecond IR pulses is used to perform IR-visible sumfrequency vibrational spectroscopy. By implementing a Fourier-transform technique, we demonstrate the ability to obtain sub-laser-bandwidth spectral resolution. FT-SFG yields a greater signal when implemented with a stretched visible pulse than with a femtosecond visible pulse. However, when compared with multichannel spectroscopy using a femtosecond IR pulse but a narrowband visible pulse, Fourier-transform SFG is found to have an inferior signal-to-noise ratio. A mathematical analysis of the signal-to-noise ratio illustrates the constraints on the Fourier-transform approach.

show abstract

“…Robinson et al [60], the LEED study by Tong et al [61], and the STM study by Hamers et al [62] confirmed and refined this model, which is now widely accepted.…”

Section: The Si(111)7×7 Surface: Spatial and Electronic Structuresupporting

confidence: 53%

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

McGuire¹

2004

View full text Add to dashboard Cite

show abstract

“…4b). These molecular adsorption processes are plausible because the typical Cl-to-Cl separations along the C@C bond (3.1 Å ) and diagonally across the molecule (4.4 Å ) for PCE and TCE are physically compatible with the adatom-to-rest-atom separation (4.6 Å ) and adatom-adatom separation across the dimer row (6.7 Å ) on the 7 · 7 surface [28]. Furthermore, dechlorination of PCE and TCE is found to be the major pathway at RT on Si(1 1 1)7 · 7 ( Fig.…”

Section: Discussionmentioning

confidence: 92%

“…This preference could also be understood in terms of the polarity of the adsorbate and the relative electronegativity of the substrate Si atoms. However, the follow-up chlorine elimination as observed on Cu(1 0 0) [26] would not be feasible on Si(1 1 1)7 · 7 at RT because the Si-Si bond distances between Si atoms with dangling bonds are not physically compatible for further Cl abstraction from the non-ipso C. In particular, the distances between two adatoms (6.65-7.68 Å ) and between an adatom and a rest-atom (4.56 Å ) on the 7 · 7 surface [27,28] are considerably greater than the molecular dimension of TCE with C@C and C-Cl bond lengths of 1.34 Å and 1.73 Å respectively [29]. Although breakage of the back-bond (between an adatom and a pedestal atom with a typical separation of 2.36 Å [28,29]) has been proposed earlier as a viable mechanism for the adsorption of electronegative adsorbates [30,31], such a process would be more likely at elevated temperatures.…”

Section: Resultsmentioning

confidence: 98%

Room-temperature chemisorption and thermal evolution of perchloroethylene and trichloroethylene on Si(111)7×7: Formation of chlorinated vinylene and vinylidene and acetylide adspecies, and thermal etching reactions

Leung

2005

Surface Science

View full text Add to dashboard Cite

“…The positions of the surface atoms in the Si (111)-(7 × 7) reconstruction have been studied experimentally by lowenergy electron diffraction (LEED) [10] as well as theoretically [11]. The 12 adatoms and 6 restatoms within one unit cell belong to 4 and 2 different symmetry types respectively.…”

mentioning

confidence: 99%

Imaging silicon by atomic force microscopy with crystallographically oriented tips

et al. 2001

View full text Add to dashboard Cite

Abstract. The images obtained by atomic force microscopy (AFM) originate from a convolution of atomic tip and sample states. Since the vertical resolution of AFM is approaching the picometer level, the atomic and subatomic structure of the tip is becoming increasingly important. Here, we demonstrate the preparation of crystallographically oriented AFM tips by breaking a silicon wafer along its preferential cleavage planes. Assuming bulk termination, the front atom of this tip should expose a single dangling bond. Images derived with this tip are consistent with this speculated tip geometry and show unprecedented vertical distinction of the six different surface atom sites of the Si(111)-(7 × 7) structure. 07.79.Lh; 34.20.Cf; 68.37.E Recently, sub-atomic resolution on the surface of silicon (111)-(7 × 7) with frequency-modulation atomic force microscopy (FM-AFM) [1] has been demonstrated. The subatomic structure of the adatom images was attributed to a tip with a very special symmetry: a tip with a front atom exposing two unsaturated bonds. The experimental observation at subatomic resolution outlines the importance of both the chemical nature and the geometric orientation of the front atom with respect to its nearest neighbors in the tip. While the preparation of the silicon sample to obtain the 7 × 7 reconstruction is straightforward, the preparation of the tip is more challenging. Here, we report on the construction of a deliberately shaped tip with predetermined crystallographic orientation. PACS:Most force sensors for AFM are microfabricated, and the crystallographic orientation of the tip is determined by the manufacturing process of the whole cantilever. Typically, the tips of micromachined cantilevers point in the 100 direction of the crystallographic orientation between tip and sample is given by the tilt angle of the cantilever. To assure that the micromachined tip is closer to the flat sample than any other parts of the cantilever and mounting devices, tilt angles between 10 • and 25 • typically have to be applied. The angle between the orientations of tip and sample cannot be freely chosen. This constraint does not apply to force sensors based on a tuning fork ("qPlus" sensor, see Fig. 1 in [3]), since it is possible to attach large tips on these sensors with a deliberate crystallographic orientation.The natural cleavage planes of silicon are (111) planes, since the free surface energy is minimal for this orientation. Each Si-Si bond has a bonding energy of approximately 2.3 eV, and the density of unsaturated bonds (dangling bonds) is 7.8 nm −2 for the (111) orientation and 13.6 nm −2 for the (100) orientation. Therefore, silicon exhibits a very strong preference to form (111) limited planes as boundaries of mesoscopic structures. This is nicely evident in the work of Baumgärtner et al., where silicon has been deposited by molecular beam epitaxy onto a Si (100) wafer through a square shaped 350 nm × 350 nm aperture. The resulting structure was a pyramid with (111) plane boundaries, rather than a pi...

show abstract

Low-energy electron diffraction analysis of the Si(111)7×7 structure

Cited by 217 publications

References 0 publications

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

Femtosecond nonlinear spectroscopy at surfaces: Second-harmonic probing of hole burning at the Si(111)7x7 surface and fourier-transform sum-frequency vibrational spectroscopy

Room-temperature chemisorption and thermal evolution of perchloroethylene and trichloroethylene on Si(111)7×7: Formation of chlorinated vinylene and vinylidene and acetylide adspecies, and thermal etching reactions

Imaging silicon by atomic force microscopy with crystallographically oriented tips

Contact Info

Product

Resources

About