Interfacial bonding geometry and electronic structures of In(2)O on InAs and In(0.53)Ga(0.47)As(001)-(4×2) have been investigated by scanning tunneling microscopy/scanning tunneling spectroscopy (STM/STS). STM images show that the In(2)O forms an ordered monolayer on both InAs and InGaAs surfaces. In(2)O deposition on the InAs(001)-(4×2) surface does not displace any surface atoms during both room temperature deposition and postdeposition annealing. Oxygen atoms from In(2)O molecules bond with trough In/Ga atoms on the surface to form a new layer of O-In/Ga bonds, which restore many of the strained trough In/Ga atoms into more bulklike tetrahedral sp(3) bonding environments. STS reveals that for both p-type and n-type clean In(0.53)Ga(0.47)As(001)-(4×2) surfaces, the Fermi level resides near the valence band maximum (VBM); however, after In(2)O deposition and postdeposition annealings, the Fermi level position is close to the VBM for p-type samples and close to the conduction band minimum for n-type samples. This result indicates that In(2)O bonding eliminates surface states within the bandgap and forms an unpinned interface when bonding with In(0.53)Ga(0.47)As/InP(001)-(4×2). Density function theory is used to confirm the experimental finding.
We present a study of graphene/substrate interactions on UHV-grown graphene
islands with minimal surface contamination using \emph{in situ} low-temperature
scanning tunneling microscopy (STM). We compare the physical and electronic
structure of the sample surface with atomic spatial resolution on graphene
islands versus regions of bare Cu(111) substrate. We find that the Rydberg-like
series of image potential states is shifted toward lower energy over the
graphene islands relative to Cu(111), indicating a decrease in the local work
function, and the resonances have a much smaller linewidth, indicating reduced
coupling to the bulk. In addition, we show the dispersion of the occupied
Cu(111) Shockley surface state is influenced by the graphene layer, and both
the band edge and effective mass are shifted relative to bare Cu(111).Comment: 12 pages, 3 figure
The interaction of tartaric acid (C4H6O6), including both (R,R) and (S,S) enantiomers, with Ag(111) has been
studied using low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy
(STM). As evidenced by both diffraction and microscopy, this molecule binds very weakly to the Ag lattice,
and the interadsorbate forces strongly dictate the formation of ordered monolayers that are globally chiral. In
addition to a discussion of the role that hydrogen bonding plays in the formation of monolayer domains,
comparisons of this system to the growth of tartaric acid on other metallic surfaces will be made.
The influence of intermolecular interactions involving molecular chiral centers on two-dimensional organization in the limit of a weak adsorbate-surface interaction has been studied with low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT). A model system composed of a chiral organic molecule, tartaric acid, and an inert metallic surface, Ag(111), was employed. Dual component films formed from the serial deposition of (S,S)-and (R,R)-tartaric acid enantiomers onto this surface exhibit homochiral domain formation as revealed by molecularly resolved STM images. In contrast, a unique tartaric acid enantiomeric heteropair is experimentally and computationally verified as the basis unit of films formed via the deposition of both enantiomers simultaneously from a racemic (1:1) mixture. The molecular adsorption geometry relative to the Ag(111) lattice in both enantiomerically pure and racemic domains is determined primarily by the interaction of chiral centers between nearest neighbors.
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