Molecular self-alignment on pre-structured Sm/Si(111) interfaces at room temperature (original) (raw)
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Dimer pinning and the assignment of semiconductor–adsorbate surface structures
The Journal of Chemical Physics, 2011
It has been observed in scanning tunneling microscopy (STM) that the adsorption of molecules on the (001) surface of a Group IV semiconductor can lead to an asymmetric ordering of the dimers immediately adjacent to the adsorbate. This so-called pinning may occur along the dimer row on only one, or both sides of the adsorbate. Here we present a straightforward methodology for predicting such pinning and illustrate this approach for several different adsorbate structures on the Si surface. This approach extends earlier work by including the effects of coupling across the adsorbate as well as the nearest-neighbor interactions between the chemisorbed dimer and its adjacent dimers. The results are shown to be in excellent agreement with the room temperature experimental STM data. The examples also show how this approach can serve as a powerful tool for discriminating between alternative possible adsorbate structures on a dimerized semiconductor (001) surface, especially in cases of molecular adsorption where the STM measurements provide insufficient details of the underlying atomic structure.
Surface Science, 2014
Low coverages of 4,4"-diamino-p-terphenyl (DAT) molecules deposited on a Si(001)-(2×1) surface in ultrahigh vacuum at room temperature were observed by scanning tunneling microscopy (STM). The linear framework of DAT, consisting of a central benzene ring, two phenyl rings (terphenyl) and two amino groups at both ends, mostly lay down laterally on the surface. The majority of DATs were tilted at about 17° with respect to the direction of a Si dimer row on the surface, though a variety of DAT configuration with different angles was found by STM. The histograms of the tilted angles showed that the most frequent angle was 17°. The apparent height of DAT tilted at 17° looked hollow at the center and lower than that of other configurations of DAT in STM images. This indicates that the DAT tends to take a double arched shape at the tilted angle of 17° in a stable conformation with butterfly-like bonding through the central benzene ring to a Si dimer as well as the two amino groups bonded to respective Si atoms on the dimer row.
The Journal of Physical Chemistry B, 2006
Scanning tunneling microscopy (STM) and computational modeling have been used to study the structure of ethyl-terminated Si(111) surfaces. The ethyl-terminated surface was prepared by treating the H-terminated Si(111) surface with PCl 5 to form a Cl-terminated Si(111) surface with subsequent exposure to C 2 H 5 MgCl in tetrahydrofuran to produce an alkylated Si(111) surface. The STM data at 77 K revealed local, close-packed, and relatively ordered regions with a nearest-neighbor spacing of 0.38 nm as well as disordered regions. The average spot density corresponded to ≈85% of the density of Si atop sites on an unreconstructed Si surface. Molecular dynamics simulations of a Si(111) surface randomly populated with ethyl groups to a total coverage of ≈80% confirmed that the ethyl-terminated Si(111) surface, in theory, can assume reasonable packing arrangements to accommodate such a high surface coverage, which could be produced by an exoergic surface functionalization route such as the two-step chlorination/alkylation process. Hence, it is possible to consistently interpret the STM data within a model suggested by recent X-ray photoelectron spectroscopic data and infrared absorption data, which indicate that the two-step halogenation/alkylation method can provide a relatively high coverage of ethyl groups on Si(111) surfaces.
Physical Review B, 1998
Using scanning tunneling microscopy ͑STM͒, the process of the Si(111)3ϫ1-Na phase formation induced by Na adsorption on the Si(111)7ϫ7 samples with a terrace width of 3000-6000 Å has been studied. The STM monitoring of the successive stages of the 7ϫ7 to 3ϫ1 transformation enables us to elucidate its main regularities. The redistribution of Si atoms in a top Si͑111͒ layer has been found to play a critical role in the Si(111)3ϫ1-Na growth mode. As a result of the Si redistribution, initially flat Si(111)7ϫ7 terrace converts into the two-level system of the 3ϫ1-Na islands on the 3ϫ1-Na terrace. From the quantitative consideration of the Si mass transport balance, the top Si atom density of the Si(111)3ϫ1-Na phase has been determined to be 4/3 monolayer. ͓S0163-1829͑98͒02535-1͔
Nanotechnology, 2008
Individual adsorption and two-dimensional assembling of 5,10,15,20-tetrakis-(4-bromophenyl)-porphyrin-Co (TBrPP-Co) molecules on a Si(111)-√ 3 × √ 3 Ag reconstructed surface have been studied using low-temperature scanning tunnelling microscopy (STM). All the isolated molecules are observed in a planar shape with slight distortion. The isolated molecules can be controllably rotated with an STM tip to the orientation along the trigonal lattice ([112] direction) of the substrate. With an increased coverage (0.07 ML) and appropriate annealing, the molecules assemble to form three types of ordered phase. The long-range ordered structures, however, disappear at higher coverage (0.75 ML).
Physical Review B, 2003
The adsorption and diffusion of single Pb atoms on Si(111)-(7ϫ7) surfaces have been studied by scanning tunneling microscopy ͑STM͒ and first-principles density functional calculations. STM experiments at temperatures from 100 to 130 K have revealed three regions of preferential adsorption, inside each half-unit cell, as well as real time diffusion events between them. The stable adsorption sites have been determined by firstprinciples calculations and by comparing simulated and measured STM images. The activation barriers for the motion inside the half-unit cells have been calculated and measured experimentally. A very good agreement between calculations and experiments has been found.
Langmuir, 2013
The self-polymerization of 4-chloromethylphenyltrichlorosilane (CMPS) was studied within spatially confined nanoholes on Si(111) using atomic force microscopy (AFM). Surface platforms of nanoholes were fabricated within a film of octadecyltrichlorosilane using immersion particle lithography. A heating step was developed to temporarily solder the silica mesospheres to the surface, to enable sustained immersion of mesoparticle masks in solvent solutions for the particle lithography protocol. Substrates with a film of mesospheres were heated briefly to anneal the particles to the surface, followed by a rinsing step with sonication to remove the silica beads to generate nanopores within an octadecyltrichlorosilane (OTS) film. Nanopatterned surface templates were immersed in CMPS solutions and removed at different time points to monitor the successive growth of nanostructures over time. Analysis of AFM images after progressive exposure of the nanoholes to solutions of CMPS provided quantitative information and details of the surface self-assembly reaction. Pillar nanostructures of CMPS with different heights and diameters were produced exclusively within the exposed areas of the substrates. Throughout the reaction, the surrounding matrix of OTS-passivated substrate did not evidence growth of CMPS; the surface assembly of CMPS was strictly confined within the nanopores. The diameter of the CMPS nanostructures grew to match the initial sizes of the confined areas of Si(111) but did not spread out beyond the edges of the OTS nanocontainers. However, the vertical growth of columns was affected by the initial size of the sites of uncovered substrate, evidencing a direct correspondence; larger sites produced taller structures, and correspondingly the growth of shorter structures was observed within smaller nanoholes. The heights of CMPS nanostructures indicate that multilayers were formed, with taller columns generated after longer immersion times. These experiments offer intriguing possibilities for using particle lithography as a general approach for nanoscale studies of molecular self-assembly.
Atom-resolved surface chemistry studied by scanning tunneling microscopy and spectroscopy
Physical review, 1989
We have used scanning tunneling microscopy and spectroscopy to study the reaction of Si(111)-(7X 7) with NH3. We have found that by use of topographs obtained at different energies, as well as atom-resolved spectra, reacted and unreacted surface sites can be imaged selectively. Thus we have been able to probe the spatial distribution of the surface reaction on an atom-by-atom basis. We find that there are significant differences in reactivity between the various dangling-bond sites on the Si(111)-(7X 7) surface. Specifically, rest-atom sites are more reactive than adatom sites and, moreover, center-adatom sites are more reactive than corner-adatom sites. We ascribe the reduced reactivity at adatom sites to the delocalized nature of their dangling-bond state. We suggest that a bonding interaction between adatoms and the Si atoms directly below them is responsible for this behaviora suggestion supported by electronic-structure calculations. Thus, while reaction at a rest-atom site can be considered a dangling-bond saturation process, reaction at an adatom site involves the formation of a hypervalent (fivefold-coordinated) adatom. We tentatively ascribe the reactivity differences between center and corner adatoms to differences in the strain they induce upon reaction on the dimer bonds. Atom-resolved spectroscopy allows us to probe interactions and charge transfer between surface sites, and for the first time, we can directly observe how chemisorption affects the substrate electronic structure at neighboring unreacted sites.
Surface Science, 2009
Adsorption of 1,1-dichloroethene (1,1-DCE) at the Si(1 1 1)-7 Â 7 surface has been investigated using scanning tunneling microscopy. 1,1-DCE dissociates upon adsorption by breaking one or both CACl bonds. The appearance of reacted adatoms in the 7 Â 7 reconstruction is found to vary for both positive and negative sample bias voltages in the range of 0.8 V to 2.5 V. Dissociated Cl atoms bond to adatom sites and appear bright for bias voltages higher than ±1.4 V. The other dissociated species appear dark for bias voltages below ±1.85 V with a preference of 2:1 for bonding to center relative to corner adatom sites. The faulted half unit cell is preferred. It is demonstrated that rest atoms are active in the dissociation of two-thirds of the 1,1-DCE molecules.