Search results for "scanning tunneling microscope"
showing 10 items of 127 documents
Defects, Disorder, and Strong Electron Correlations in Orbital Degenerate, Doped Mott Insulators.
2015
We elucidate the effects of defect disorder and $e$-$e$ interaction on the spectral density of the defect states emerging in the Mott-Hubbard gap of doped transition-metal oxides, such as Y$_{1-x}$Ca$_{x}$VO$_{3}$. A soft gap of kinetic origin develops in the defect band and survives defect disorder for $e$-$e$ interaction strengths comparable to the defect potential and hopping integral values above a doping dependent threshold, otherwise only a pseudogap persists. These two regimes naturally emerge in the statistical distribution of gaps among different defect realizations, which turns out to be of Weibull type. Its shape parameter $k$ determines the exponent of the power-law dependence o…
First Specifications of a PSTM Working In the Infrared
1993
One of the most promising extension of the photon scanning tunneling microscope (PSTM) is its use as a locally resolved spectroscopic tool. The infrared (IR) spectral window offers a wide variety of interesting applications since many materials have a well-defined signature in this range. We have undertaken the experimental modifications that are necessary to operate the existing PSTM’s in the IR domain. In this work, we present preliminary data obtained with two IR light sources: an extended source (Globar type) and the free electron IR laser source (CLIO) available at LURE (Orsay). In both cases, the evanescent field has been detected with a fluoride glass optical fiber and the characteri…
Chiral charge order in the superconductor 2H-TaS(2)
2011
Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM
Strong Bonding of Single C60 Molecules to (1 × 2)-Pt(110): an STM/DFT Investigation.
2007
International audience; The interaction of single C60 molecules with the (1 × 2)-Pt(110) surface has been studied by scanning tunneling microscopy and density functional theory (DFT) calculations on slab models. Molecules are observed to be frozen at room temperature and are found to be almost exclusively in the same configuration. Extensive DFT calculations show that this configuration is the global energy minimum, suggesting that adsorbed molecules have enough rototranslational freedom to escape from the numerous local minima. The adsorption energy (3.81 eV) is the strongest ever found for C60, and it is roughly proportional to the number of the Pt and C atoms at contact distance. Analysi…
Mo(CO)6 dissociation on Cu(111) stimulated by a Scanning Tunneling Microscope
2013
Abstract The surface of Cu(111) was exposed to molybdenum hexacarbonyl Mo(CO)6 with monolayer coverage at temperature 160 K and studied by a Scanning Tunneling Microscope. The monolayer structure has a hexagonal arrangement and forms a (√7 × √7) R19 superlattice on the copper (111) plane. Upon repeated scanning the monolayer is transformed into a (1 × 2) superstructure with 3-fold oriented domains. The domains of (1 × 2) superstructure can change orientation under scanning according to 3-fold surface symmetry. From analysis of the domain mobility, it follows that CO groups of carbonyl fragments are organized in the (1 × 2) superstructure conditioning the domain reorientation. The observed s…
Numerical simulations of photon scanning tunneling microscopy: role of a probe tip geometry in image formation
2005
Abstract Numerical simulations of two-dimensional probe–object system emulating a photon scanning tunnelling microscope are presented. R -matrix propagation algorithm incorporated into the differential method was used to achieve an extended capability to rigorously model a realistic system consisting of both a probe and a sample. Influence of the probe tip parameters on image formation in scanning near-field microscopy has been investigated. Coupling of the near-field to a single-mode probe and formation of a guided fundamental mode in a probe were investigated for various probe widths and lengths. The influence of the probe taper shape and apex size on near-field images was studied for sin…
Analysis of image formation with a photon scanning tunneling microscope
1996
International audience; The photon scanning tunneling microscope (PSTM) is based on the frustration of a total internal reflected beam by the end of an optical fiber. Until now it has been used to obtain topographic information, generally for smooth samples. We report theoretical as well as experimental results on the observation of a step on a quartz substrate with the PSTM. These results demonstrate the effects on image formation of the distance between the fiber tip and the sample surface, the orientation of the incident beam with respect to the step, the polarization, and the coherence of the light. Good agreement exists between numerical simulations and experiments. We show that a pert…
L-Tryptophan on Cu(111): engineering a molecular labyrinth driven by indole groups
2015
The present article investigates the adsorption and molecular orientation of L-Tryptophan, which is both an essential amino acid important for protein synthesis and of particular interest for the development of chiral molecular electronics and biocompatible processes and devices, on Cu(111) using scanning tunneling microscopy and spectroscopy at 55 K and at room temperature. The arrangement of chemisorbed L-Tryptophan on the copper surface varies with both temperature and surface coverage. At low coverage, small clusters form on the surface irrespective of temperature, while at high coverage an ordered chain structure emerges at room temperature, and a tightly packed structure forms a molec…
Role of Deprotonation and Cu Adatom Migration in Determining the Reaction Pathways of Oxalic Acid Adsorption on Cu(111)
2011
Scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and first principles theoretical calculations have been used to gain insight into the fundamental processes involved in the adsorption and self-assembly of oxalic acid on Cu(111). The experimental data demonstrate that several reaction pathways are involved in the chemisorption of oxalic acid on Cu(111), one of which leads to deprotonation of the acid into oxalate molecules that form ordered structures on the surface. Theoretical calculations indicate that the adsorption of oxalate molecules is not stable on the surface unless copper adatoms are taken into consideration. Coordination with copper adatoms prevents ox…
Atomic-scale magnetic domain walls in quasi-one-dimensional Fe nanostripes.
2001
Fe nanostripes on W(110) are investigated by Kerr magnetometry and spin-polarized scanning tunneling microscopy (SP-STM). An Arrhenius law is observed for the temperature dependent magnetic susceptibility indicating a one-dimensional magnetic behavior. The activation energy for creating antiparallel spin blocks indicates extremely narrow domain walls with a width on a length scale of the lattice constant. This is confirmed by imaging the domain wall by SP-STM. This information allows the quantification of the exchange stiffness and the anisotropy constant.