Vibron-assisted spin excitation in a magnetically anisotropic molecule

The electrical control and readout of molecular spin states are key for high-density storage. Expectations are that electrically-driven spin and vibrational excitations in a molecule should give rise to new conductance features in the presence of magnetic anisotropy, offering alternative routes to study and, ultimately, manipulate molecular magnetism. Here, we use inelastic electron tunneling spectroscopy to promote and detect the excited spin states of a prototypical molecule with magnetic anisotropy. We demonstrate the existence of a vibron-assisted spin excitation that can exceed in energy and in amplitude a simple excitation among spin states. This excitation, which can be quenched by structural changes in the magnetic molecule, is explained using first-principles calculations that include dynamical electronic correlations.

Ferromagnetic coupling of mononuclear Fe centers in a self-assembled metal-organic network on Au(111)

The magnetic state and magnetic coupling of individual atoms in nanoscale structures relies on a delicate balance between different interactions with the atomic-scale surroundings. Using scanning tunneling microscopy, we resolve the self-assembled formation of highly ordered bilayer structures of Fe atoms and organic linker molecules (T4PT) when deposited on a Au(111) surface. The Fe atoms are encaged in a three-dimensional coordination motif by three T4PT molecules in the surface plane and an additional T4PT unit on top. Within this crystal field, the Fe atoms retain a magnetic ground state with easy-axis anisotropy, as evidenced by x-ray absorption spectroscopy and x-ray magnetic circular dichroism. The magnetization curves reveal the existence of ferromagnetic coupling between the Fe centers.

Reversible change of the spin state in a manganese phthalocyanine by coordination of CO molecule

We show that the magnetic state of individual manganese phthalocyanine (MnPc) molecules on a Bi(110) surface is modified when the Mn2+ center coordinates to CO molecules adsorbed on top. Using scanning tunneling spectroscopy we identified this change in magnetic properties from the broadening of a Kondo-related zero-bias anomaly when the CO-MnPc complex is formed. The original magnetic state can be recovered by selective desorption of individual CO molecules. First principles calculations show that the CO molecule reduces the spin of the adsorbed MnPc from S=1 to S=1/2 and strongly modifies the respective screening channels, driving a transition from an underscreened Kondo state to a state of mixed valence.

Reversible electron-induced cis-trans isomerization mediated by intermolecular interactions

Reversible isomerization processes are rarely found when organic molecular switches are adsorbed on metal surfaces. One obstacle is the large energy difference of the isomeric forms, since usually the most planar conformer has the largest adsorption energy. In the example of an imine derivative, we show a strategy for also stabilizing the non-planar isomer by intermolecular bonding to its neighbors. Tunneling electrons from the tip of a scanning tunneling microscope can then be used to induce reversible switching between the trans and cis-like state. Supported by model force-field calculations, we illustrate that the most probable cause of the enhanced stability of the three-dimensional cis state at specific adsorption sites is the electrostatic interaction with N sites of the neighboring molecule.

Enhanced charge transfer in a monolayer of the organic charge transfer complex TTF-TNAP on Au(111)

Electronic doping is a key concept for tuning the properties of organic materials. In bulk structures, the charge transfer between donor and acceptor is mainly given by the respective ionization potential and electron affinity. In contrast, monolayers of charge transfer complexes in contact with a metal are affected by an intriguing interplay of hybridization and screening at the metallic interface, determining the resulting charge state. Using scanning tunneling microscopy and spectroscopy, we characterize the electronic properties of the organic acceptor molecule 11,11,12,12-tetracyanonaptho-2,6-quinodimethane (TNAP) adsorbed on a Au(111) surface. The ordered islands remain in a weakly physisorbed state with no charge transfer interaction with the substrate. When the electron donor tetrathiafulvalene (TTF) is added, ordered arrays of alternating TNAP and TTF rows are assembled. In these structures, we find the lowest unoccupied molecular orbital (LUMO) of the free TNAP molecule shifted well below the Fermi level of the substrate. The TNAP is thus charged with more than one electron.

Gating the charge state of single molecules by local electric fields

The electron-acceptor molecule TCNQ is found in either of two distinct integer charge states when embedded into a monolayer of a charge transfer complex on a gold surface. Scanning tunneling spectroscopy measurements identify these states through the presence or absence of a zero-bias Kondo resonance. Increasing the (tip-induced) electric field allows us to reversibly induce the oxidation or reduction of TCNQ species from their anionic or neutral ground state, respectively. We show that the different ground states arise from slight variations in the underlying surface potential, pictured here as the gate of a three-terminal device.

Competition of superconducting phenomena and Kondo screening at the nanoscale

Magnetic and superconducting interactions couple electrons together to form complex states of matter. We show that, at the atomic scale, both types of interactions can coexist and compete to influence the ground state of a localized magnetic moment. Local spectroscopy at 4.5 kelvin shows that the spin-1 system formed by manganese-phthalocyanine (MnPc) adsorbed on Pb(111) can lie in two different magnetic ground states. These are determined by the balance between Kondo screening and superconducting pair-breaking interactions. Both ground states alternate at nanometer length scales to form a Moiré-like superstructure. The quantum phase transition connecting the two (singlet and doublet) ground states is thus tuned by small changes in the molecule-lead interaction.

Site-Dependent Coordination Bonding in Self-Assembled Metal-Organic Networks

The combination of organic linkers with metal atoms on top of inorganic substrates offers promising perspectives for functional electronic and magnetic nanoscale devices. Typically, coordination bonds between electron-rich end groups and transition-metal atoms lead to the self-assembly of metal-organic nanostructures, whose shape and electronic and magnetic properties crucially depend on the type of ligand. Here, we report on the site-selective bonding properties of Co atoms to the dichotomic dicyanoazobenzene molecule with its carbonitrile and diazo N-based moieties as possible ligands. Using low-temperature scanning tunneling microscopy (STM) and spectroscopy measurements, we resolve the formation of self-assembled metal-organic motifs. Cobalt atoms exhibit a clear spectroscopic fingerprint dependent on the different coordination site, which is further used to map their position, otherwise not clearly visible in the topographic STM images. Density functional theory corroborates the observed bonding patterns and evidences their coordinative nature.

Nondegenerate metallic States on Bi(114): a one-dimensional topological metal

The (114) surface of the semimetal Bi is found to support a quasi-one-dimensional, metallic surface state. As required by symmetry, the state is degenerate along the Gamma-Y line of the surface Brillouin zone with a highest binding energy of approximately 150 meV. In the Gamma-X direction the degeneracy is lifted by the strong spin-orbit splitting in Bi, as directly shown by spin-resolved photoemission. This results in a Fermi contour consisting of two closely separated, parallel lines of opposite spin direction. It is argued that similar states on related insulators would give rise to a one-dimensional quantum spin Hall effect.

Vibrational Kondo effect in pure organic charge-transfer assemblies

A Kondo resonance has been observed using a scanning tunneling microscope on a single molecular layer of a purely organic charge-transfer salt grown on a metal surface. Analysis of the Kondo anomaly reveals that the electron acceptor of the film possesses a spin-1/2 ground state due to the localization of an unpaired electron in the conjugated lowest unoccupied molecular orbital. Because of the pi character of this molecular state the unpaired electron is strongly coupled to molecular vibrations, leading to the split of the Kondo resonance in vibrational sidebands.

Formation of dispersive hybrid bands at an organic-metal interface

An electronic band with quasi-one-dimensional dispersion is found at the interface between a monolayer of a charge-transfer complex (TTF-TCNQ) and a Au(111) surface. Combined local spectroscopy and numerical calculations show that the band results from a complex mixing of metal and molecular states. The molecular layer folds the underlying metal states and mixes with them selectively, through the TTF component, giving rise to anisotropic hybrid bands. Our results suggest that, by tuning the components of such molecular layers, the dimensionality and dispersion of organic-metal interface states can be engineered.

Resonant electron heating and molecular phonon cooling in single C60 junctions

We study heating and heat dissipation of a single C(60) molecule in the junction of a scanning tunneling microscope by measuring the electron current required to thermally decompose the fullerene cage. The power for decomposition varies with electron energy and reflects the molecular resonance structure. When the scanning tunneling microscope tip contacts the fullerene the molecule can sustain much larger currents. Transport simulations explain these effects by molecular heating due to resonant electron-phonon coupling and molecular cooling by vibrational decay into the tip upon contact formation.

Reducing the molecule-substrate coupling in C60-based nanostructures by molecular interactions

Codeposition of C60 and the three-dimensional molecular hydrocarbon 1,3,5,7-tetraphenyladamantane (TPA) on Au(111) leads to the spontaneous formation of molecular nanostructures in which each fullerene is locked into a specific orientation by three surrounding TPA. Scanning tunneling spectroscopy shows that the electronic coupling of C60 with the surface is significantly reduced in these nanostructures, enhancing the free-molecule properties. As evidenced by density functional theory simulations, the nanostructures are stabilized by 18 local electrostatic forces between C60 and TPA, resulting in a lifting of the C60 cage from the surface.

Long-range repulsive interaction between molecules on a metal surface induced by charge transfer

The adsorption of a molecular electron donor on Au(111) is characterized by the spontaneous formation of a superlattice of monomers spaced several nanometers apart. The coverage-dependent molecular pair distributions obtained from scanning tunneling microscopy data reveal an intermolecular long-range repulsive potential, which decreases as the inverse of the molecular separation. Density functional theory calculations show a charge accumulation in the molecules due to electron donation into the metal. Our results suggest that electrostatic repulsion between molecules persists on the surface of a metal.

Spontaneous Formation of Triptycene Supramolecules on Surfaces

In the limit of weak molecular interaction with an inorganic surface, noncovalent interactions between molecules dominate the nucleation and thin-film growth. Here, we report on the formation of three-dimensional triptycene clusters with a particularly stable structure. Once formed at the early stage of molecular adsorption, the clusters are stable for all temperatures until desorption. Furthermore, the clusters diffuse and nucleate as individual entities, therefore constituting building blocks for the later thin-film formation. High resolution scanning tunneling microscopy images indicate that the cluster is stabilized by C-H-pi interactions. The formation of such molecular structures at a surface is possible because the three-dimensional structure of the triptycene molecule leads to a very weak and mobile adsorption state. These results show that it is possible to investigate complex pathways in the formation of three-dimensional supramolecules at surfaces using a scanning tunneling microscope.

Bulk electronic structure of metals resolved with scanning tunneling microscopy

We demonstrate that bulk band structure can have a strong influence in scanning tunneling microscopy measurements by resolving electronic interference patterns associated with scattering phenomena of bulk states at a metal surface and reconstructing the bulk band topology. Our data reveal that bulk information can be detected because states at the edge of the surface-projected bulk band have a predominant role on the scattering patterns. With the aid of density functional calculations, we associate this effect with an intrinsic increase in the projected density of states of edge states. This enhancement is characteristic of the three-dimensional bulk band curvature, a phenomenon analog to a van Hove singularity.

[Laparoscopic surgery in urology]

At the present time minimally invasive surgery is present in all the standards of quality of a surgical service. Laparoscopic surgery, the basis of this minimally invasive surgery, is revolutionizing the teaching and handling of many surgical pathologies. In the urological sphere, although with a delay of 5 years with respect to neighbouring countries, laparoscopy has become established as a prevalent technique in many processes of the urinary-genital apparatus. At present it is the chosen technique for the surgical treatment of the suprarenal, and it is rapidly becoming established in different pathologies such as renal tumours, prostate tumours, staging in neoplastic diseases of the testicles, benign surgical pathology and in reconstructive surgery. Since 1995, the Urology Service at the Hospital de Navarra has been a pioneer in the employment of this type of technique, and, since 1998, it has been a pioneer of so-called advanced laparoscopic surgery, in which it is a national reference point in some of the procedures, such as laparoscopic adrenalectomy. At present, all of the laparoscopic procedures are incorporated in the service, with a learning curve that has been surpassed. All of this has made it possible to improve patient care, to obtain a reduction in postoperative pain and in length of hospital stay, and a rapid return to labour activity with oncological results that can be equivalent on those of open surgery.

Role of spin in quasiparticle interference

Quasiparticle interference patterns measured by scanning tunneling microscopy can be used to study the local electronic structure of metal surfaces and high-temperature superconductors. Here, we show that even in nonmagnetic systems the spin of the quasiparticles can have a profound effect on the interference patterns. On Bi(110), where the surface state bands are not spin degenerate, the patterns are not related to the dispersion of the electronic states in a simple way. In fact, the features which are expected for the spin-independent situation are absent and the observed interference patterns can be interpreted only by taking spin-conserving scattering events into account.

Mesoscopic chiral reshaping of the Ag(110) surface induced by the organic molecule PVBA

We report scanning tunneling microscopy observations on the restructuring of a Ag(110) surface induced by the molecule 4-[trans-2-(pyrid-4-yl-vinyl)]benzoic acid (PVBA). Our data reveal that the surface undergoes a mesoscopic step faceting following exposure to submonolayer coverages and thermal activation. A sawtooth arrangement evolves implying long-range mass transport of substrate atoms and forming a regular arrangement of kink sites. Its formation is associated with the molecules' functional headgroups forming carboxylates with [100] Ag microfacets at step edges, and eventually operating to reshape the surface morphology. Interestingly, the resulting microfacets act as chiral templates for the growth of supramolecular PVBA structures. Theoretical modeling based on ab initio results indicates that chiral recognition processes discriminating between the two enantiomers of adsorbed PVBA molecules occur in this process.

Selectivity in vibrationally mediated single-molecule chemistry

The selective excitation of molecular vibrations provides a means to directly influence the speed and outcome of chemical reactions. Such mode-selective chemistry has traditionally used laser pulses to prepare reactants in specific vibrational states to enhance reactivity or modify the distribution of product species. Inelastic tunnelling electrons may also excite molecular vibrations and have been used to that effect on adsorbed molecules, to cleave individual chemical bonds and induce molecular motion or dissociation. Here we demonstrate that inelastic tunnelling electrons can be tuned to induce selectively either the translation or desorption of individual ammonia molecules on a Cu(100) surface. We are able to select a particular reaction pathway by adjusting the electronic tunnelling current and energy during the reaction induction such that we activate either the stretching vibration of ammonia or the inversion of its pyramidal structure. Our results illustrate the ability of the scanning tunnelling microscope to probe single-molecule events in the limit of very low yield and very low power irradiation, which should allow the investigation of reaction pathways not readily amenable to study by more conventional approaches.

Spinal implants of olfactory ensheathing cells promote axon regeneration and bladder activity after bilateral lumbosacral dorsal rhizotomy in the adult rat

PURPOSE

We performed spinal implantation of olfactory ensheathing cells to demonstrate dorsal root afferent regeneration as well as bladder activity restoration after lumbosacral L6 to S2 rhizotomy.

MATERIALS AND METHODS

Spinal segments receiving bladder innervation, usually L6, S1 and S2, were identified by bipolar stimulation of the ventral roots. Bilateral section of the identified dorsal roots L6 to S2 was performed in 18 male Wistar rats. Immediately after rhizotomy olfactory ensheathing cells or vehicle was unilaterally injected in the vicinity of the sacral parasympathetic nucleus in 9 rats each using a glass micropipette and air pulse system. The severed roots were reattached to the cord with fibrin glue and the animals recovered under antibiotic prophylaxis.

RESULTS

Anatomical regeneration of bladder wall primary afferents was demonstrated by the presence of labeled wheat germ agglutinin-horseradish peroxidase fibers in the dorsal horn and sacral parasympathetic nucleus in 8 of 9 cases of olfactory ensheathing cell implantation but not in the 9 controls injected with vehicle. One week after surgery all rats had an atonic bladder on cystometrography. At 6 weeks 8 of the 9 olfactory ensheathing cell implanted rats had recovered bladder activity. No recovery was observed in controls, in which vehicle was injected instead of olfactory ensheathing cells.

CONCLUSIONS

Regenerated primary afferent fibers from the bladder project to the sacral parasympathetic nucleus, where they presumably form synapses mediating the recovery of bladder activity. Thus, olfactory ensheathing cell implants in the adult rat promote sensory axon regeneration, target reinnervation and bladder activity restoration.

Adsorbate-substrate vibrational modes of benzene on Ag(110) resolved with scanning tunneling spectroscopy

Using a low temperature scanning tunneling microscope, we have detected low energy adsorbate-substrate (external or frustrated) vibrational modes of benzene molecules adsorbed on a Ag(110) surface. We demonstrate that such vibrations represent a fingerprint of the molecules' chemical state and environment; two different vibrational spectra are measured on molecules populating two different adsorption states. We also find that the distortion of the adsorption geometry of the molecules may give rise to the excitation of additional (initially hidden) modes. Important differences in the spatial distribution of the inelastic signal are also observed for these external modes.

[Effects of selective vegetative denervation on the urinary bladder of the adult rat]

The present work is a study of the plastic capacity of the peripheral nervous system subjected to different aggressions in the case of 28 rats of the Wistar breed. They were divided into four groups: 1) sympathetic deafness (n=9); 2) parasympathetic deafness (n=9); 3) evaluation of regeneration (n=9); 4) control group (n=5). An image analyser was used to study the acetylcholinesterase (AChE) and Tyrosine Hydroxylase (TH) positive ganglionic neurones of the pelvic ganglion (GP) as well as the dorsal ganglions (GRD) compared with the control group. With group 3 a study was also made of the possible plasticity of the transacted axons using a wheat germ agglutinin conjugated-horseradish peroxidase (WGA-HRP) neurotracer. The statistical study was carried out by means of the analysis of variance (ANOVA), Fisher test and Scheffe method, with a p<0.05 taken as significant. The results show the predominant role of the pelvic nerve in the modulation of the plastic changes produced at the ganglionic level, with a lesser influence of the hypogastric nerve. Further studies are needed in order to define the specific role of each of these in the act of miction.

Properties of Metallic Nanowires: From Conductance Quantization to Localization

Material structures of reduced dimensions exhibit electrical and mechanical properties different from those in the bulk. Measurements of room-temperature electronic transport in pulled metallic nanowires are presented, demonstrating that the conductance characteristics depend on the length, lateral dimensions, state and degree of disorder, and elongation mechanism of the wire. Conductance during the elongation of short wires (length l approximately 50 angstroms) exhibits periodic quantization steps with characteristic dips, correlating with the order-disorder states of layers of atoms in the wire predicted by molecular dynamics simulations. The resistance R of wires as long as l approximately 400 angstroms exhibits localization characteristics with In R(l) approximately l(2).

Urinary bladder innervation in male rat: termination of primary afferents in the spinal cord as determined by transganglionic transport of WGA-HRP

The distribution of afferents innervating the urinary bladder in the spinal cord of male rats has been studied with the axonal tracer horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) injected into various portions of one side of the urinary bladder (dome, body, base, or neck) and other pelvic organs (prostate and rectum). Labeled neurons were found in dorsal root ganglia of the lumbosacral cord (L1-S3, peak in S1-S2). The strongest and most extensive transganglionic labeling of primary afferents resulted after injections in the body of the bladder. Primary afferents were observed bilaterally in Lissauer's tract and laminae I-II at the apex of the dorsal horn, from L6 to S3. The projection extended laterally up to the sacral parasympathetic nucleus and medially up to the gray matter dorsal to the central canal, where they formed a plexus of fibers and terminals. Deposits in the dome and base of the bladder labeled more heavily the medial projection, while the least intense projection was seen after injections in the bladder neck. Our results indicate a common pattern of termination of primary afferents from the bladder, although some topographical differences exist.

Pudendal nerve topography in the rat spinal cord projections studied with the axonal tracer wheat germ agglutinin conjugated-horseradish peroxidase

The spinal cord termination of the sensory fibers of the rat pudendal nerve has been determined by using the transganglionic transport of horseradish peroxidase conjugated to wheat germ agglutinin. The gross anatomical examination of the pudendal plexus indicated the existence of dorsal and ventral branches in the sensory division of the pudendal nerve. Either branch or both were sectioned and exposed to a 1% solution of the enzyme. After an average survival period of 48 hours, the resulting reaction product was studied both at the level of the dorsal root ganglia and the spinal cord. Labeled dorsal root ganglion cells were observed between L1 and S4 (peak in S1 and L6). Evidence of transganglionic transport of the tracer was observed from L5 to S2. The ventral branch projected medially in the superficial dorsal horn, while the dorsal branch projected laterally. Our findings are consistent with a segregation of sensibilities for the ventral and dorsal branches that convey urogenital (ventral branch) and anal (dorsal branch) cutaneous sensations at the level of termination of primary afferents.

[Congenital bladder diverticulum as a cause of acute urinary retention]

A case of acute urinary retention secondary to a giant bladder diverticulum in a 23-year-old patient is described. Its etiopathogenesis is briefly discussed, highlighting its congenital origin which, in our view, must be based on the histological examination of the specimen.

[Bladder bilharziasis. Presentation of a clinical case]

We present a case of vesical Bilharziosis in a young black man. We briefly discuss the pathogeny, the diagnosis, based fundamentally on the microscopic study of urine and cystoscopy, as well as the treatment with Praziquantel as the preferential medication in Schistosomiasis due to S. haematobium.

The pelvic innervation in the rat: different spinal origin and projections in Sprague-Dawley and Wistar rats

WGA-HRP was applied to the pelvic and pudendal nerves of Sprague-Dawley and Wistar rats to compare the segmental levels of the resulting labeling. L6 and S1 were the segments at which the sacral parasympathetic nucleus and the denser primary afferents occurred in Sprague-Dawley rats. The levels found in Wistar rats were S1 and S2, thus indicating a disparity between both strains of rats in the spinal level of the sacral parasympathetic nucleus and the primary afferents.