We investigate the possibility of functionalizing Au tips by N2O molecules deposited on a Au(111) surface and their further use for imaging with submolecular resolution. First, we characterize the adsorption of the N2O species on Au(111) by means of atomic force microscopy with CO-functionalized tips and density functional theory (DFT) simulations. Subsequently we devise a method of attaching a single N2O to a metal tip apex and benchmark its high-resolution imaging and spectroscopic capabilities using FePc molecules. Our results demonstrate the feasibility of high-resolution imaging. However, we find an inherent asymmetry of the N2O probe-particle adsorption on the tip apex, in contrast to a CO tip reference. These findings are consistent with DFT calculations of the N2O- and CO tip apexes.
- Keywords
- Au(111), atomic force microscopy, carbon monoxide, functionalization, high resolution, nitrous oxide, submolecular resolution,
- Publication type
- Journal Article MeSH
Functionalization of a scanning microscopy probe with a single nickelocene allows reproducible spin-sensitive measurements of magnetic systems on surfaces. The triplet ground state of the nickelocene tip gives rise to a characteristic inelastic electron spin-flip excitation, which can change upon interaction with spin systems on the surface. These changes, together with theoretical simulations, enable us to determine the local spin moment on the surface. In this paper, we discuss the experimental and theoretical aspects of nickelocene-tip measurements. We rationalize the interactions between the nickelocene spin and the magnetic centers using a spin Heisenberg and dipole model, complemented by cotunneling theory, and compare the simulated dI/dV with selected experimental results. We developed a Python script to simulate this magnetic interaction, which is available on GitHub.
- Keywords
- STM, cotunelling theory, spin Hamiltonian, tip functionalization,
- Publication type
- Journal Article MeSH
A single atomic manipulation on the delta-doped B:Si(111)-(√3x√3)R30° surface using a low temperature dynamic atomic force microscopy based on the Kolibri sensor is investigated. Through a controlled vertical displacement of the probe, a single Si adatom in order to open a vacancy is removed. It is shown that this process is completely reversible, by accurately placing a Si atom back into the vacancy site. In addition, density functional theory simulations are carried out to understand the underlying mechanism of the atomic manipulation in detail. This process also rearranges the atoms at the tip apex, which can be effectively sharpened in this way. Such sharper tips allow for a deeper look into the Si adatom vacancy site. Namely, high-resolution images of the vacancy showing subsurface Si dangling bond triplets, which surround the substitutional B dopant atom in the first bilayer, are achieved.
- Keywords
- AFM, STM, functionalization, manipulation, semiconducting surfaces,
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
INTRODUCTION: Stroke is one of the most feared complications during catheter ablation of atrial fibrillation (AF). While symptomatic thromboembolic events are rare, magnetic resonance imaging (MRI) may identify asymptomatic (ie, silent) cerebral lesions (SCLs) following pulmonary vein isolation (PVI) procedures. METHODS AND RESULTS: The REDUCE-TE Pilot was a prospective multicenter, single-arm observational study investigating the incidence of SCL in patients with symptomatic paroxysmal AF undergoing PVI with a novel gold-tip, externally irrigated ablation catheter. After ablation, cerebral diffusion-weighted MRI and a postablation follow-up were performed at 1 to 3 days after the ablation procedure. A neurocognitive test was done before and after ablation. The primary study endpoint was the occurrence of one or more new SCLs. Secondary study endpoints included neurocognitive status, procedural success rate, and periprocedural complications including symptomatic thromboembolic events. A total of 104 patients were enrolled (69% male, mean age: 61.5 ± 9.7 years, mean CHA2 DS 2 -VASc score: 1.7 ± 1.2). Postprocedural MRI examination was performed in 97 patients, and in nine of them (9.3%; 95% CI: 4.3-16.9%) a total of 11 SCLs were detected. Univariate analyses did not reveal any significant predictor for new SCLs. Nonsignificant trends were observed for low activated clotting time during ablation and for international normalized ratio value outside the range of 2 to 3 at ablation. There was no evidence of significant deterioration of neurocognitive function after PVI. In four patients, a pericardial tamponade was noted but all patients fully recovered during follow-up. CONCLUSIONS: Ablation of AF using a novel gold-tip, externally irrigated ablation catheter, resulted in SCLs in approximately one out of 10 patients without a measurable effect on neurocognitive function.
- Keywords
- ablation, atrial fibrillation, cognitive function, gold-tip catheter, irrigated catheter, pulmonary vein isolation, silent cerebral embolism,
- MeSH
- Action Potentials MeSH
- Asymptomatic Diseases MeSH
- Time Factors MeSH
- Equipment Design MeSH
- Diffusion Magnetic Resonance Imaging MeSH
- Atrial Fibrillation complications diagnosis physiopathology surgery MeSH
- Incidence MeSH
- Intracranial Embolism diagnostic imaging epidemiology MeSH
- Catheter Ablation adverse effects instrumentation MeSH
- Cognition * MeSH
- Therapeutic Irrigation adverse effects instrumentation MeSH
- Middle Aged MeSH
- Humans MeSH
- Pilot Projects MeSH
- Postoperative Cognitive Complications diagnosis epidemiology psychology MeSH
- Aged MeSH
- Heart Rate MeSH
- Cardiac Catheters * MeSH
- Mental Status and Dementia Tests MeSH
- Pulmonary Veins physiopathology surgery MeSH
- Treatment Outcome MeSH
- Gold * MeSH
- Check Tag
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Aged MeSH
- Female MeSH
- Publication type
- Journal Article MeSH
- Multicenter Study MeSH
- Observational Study MeSH
- Research Support, Non-U.S. Gov't MeSH
- Geographicals
- Germany epidemiology MeSH
- Names of Substances
- Gold * MeSH
We study the conductance of N-heterocyclic carbene-based (NHC) molecules on gold by means of first-principles calculations based on density-functional theory and non-equilibrium Green's functions. We consider several tip structures and find a strong dependence of the position of the NHC molecular levels with the atomistic structure of the tip. The position of the lowest unoccupied molecular orbital (LUMO) can change by almost 0.8 eV with tip shape. Through an analysis of the net charge transfer, electron redistribution and work function for each tip structure, we rationalize the LUMO shifts in terms of the sum of the work function and the maximum electrostatic potential arising from charge rearrangement. These differences in the LUMO position, effectively gating the molecular levels, result in large conductance variations. These findings open the way to modulating the conductance of NHC-based molecular circuits through the controlled design of the tip atomistic structure.
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
The scanning tunneling microscope (STM) provides access to atomic-scale properties of a conductive sample. While single-molecule tip functionalization has become a standard procedure, fluorescent molecular probes remained absent from the available tool set. Here, the plasmonic tip of an STM is functionalized with a single fluorescent molecule and is scanned on a plasmonic substrate. The tunneling current flowing through the tip-molecule-substrate junction generates a narrow-line emission of light corresponding to the fluorescence of the negatively charged molecule suspended at the apex of the tip, i.e., the emission of the excited molecular anion. The fluorescence of this molecular probe is recorded for tip-substrate nanocavities featuring different plasmonic resonances, for different tip-substrate distances and applied bias voltages, and on different substrates. We demonstrate that the width of the emission peak can be used as a probe of the exciton-plasmon coupling strength and that the energy of the emitted photons is governed by the molecule interactions with its environment. Additionally, we theoretically elucidate why the direct contact of the suspended molecule with the metallic tip does not totally quench the radiative emission of the molecule.
- Publication type
- Journal Article MeSH
Interaction of molecular oxygen with semiconducting oxide surfaces plays a key role in many technologies. The topic is difficult to approach both by experiment and in theory, mainly due to multiple stable charge states, adsorption configurations, and reaction channels of adsorbed oxygen species. Here we use a combination of noncontact atomic force microscopy (AFM) and density functional theory (DFT) to resolve [Formula: see text] adsorption on the rutile [Formula: see text](110) surface, which presents a longstanding challenge in the surface chemistry of metal oxides. We show that chemically inert AFM tips terminated by an oxygen adatom provide excellent resolution of both the adsorbed species and the oxygen sublattice of the substrate. Adsorbed [Formula: see text] molecules can accept either one or two electron polarons from the surface, forming superoxo or peroxo species. The peroxo state is energetically preferred under any conditions relevant for applications. The possibility of nonintrusive imaging allows us to explain behavior related to electron/hole injection from the tip, interaction with UV light, and the effect of thermal annealing.
- Keywords
- O2, TiO2, nc-AFM, oxides, tip functionalization,
- Publication type
- Journal Article MeSH
PURPOSE OF THE STUDY: This study investigated the relationship between the position of the tip of the coracoid process (CP) relative to the glenoid with subscapularis (Ssc) tears. We hypothesized that the coracoid tip is more inferior, lateral and posterior in patients with Ssc tear. MATERIAL AND METHODS: This research enrolled 34 isolated Ssc tears and 44 controls. We introduced the axial central glenoid-coracoid angle (acGCA) and sagittal central glenoid-coracoid angle (scGCA) to evaluate the position of the tip of the CP relative to the glenoid center on MRI images. In both groups, acGCA, scGCA on MRI and critical shoulder angle (CSA), glenoid inclination (GI) on true anterior-posterior shoulder radiography were evaluated. RESULTS: When both groups were compared in terms of acGCA, the acGCA values of the Ssc tear group were significantly higher than the control group (p<0.001). The best cut-off value of acGCA for Ssc tears was 28.3°. acGCA values higher than 28.3° showed 93.3% sensitivity and 93.1% specificity for Ssc tears (likelihood ratio:13.53, AUC: 0.979, 95% CI of AUC: 0.950- 0.999). In terms of acGCA, the power analysis between Ssc tears group and control group was 99.9% between Ssc tears and the control group (effect size d=2.63). When both groups were compared in terms of scGCA, the scGCA values of the Ssc tear group were significantly higher than the control group (p<0.001). The best cut-off value of scGCA for Ssc tears was 41.4°. Scores of scGCA greater than 41.8° showed 80% sensitivity and 89.7% specificity for Ssc tears (likelihood ratio: 7.73, AUC: 0.899 95% CI of AUC: 0.837-0.958). In terms of scGCA, the power analysis between Ssc tear and control group was 99.8% (effect size d=1.23). When both groups were compared in terms of CSA and GI; CSA and GI values in the Ssc tear group were significantly higher (p<0.001 and p<0.012, respectively). CONCLUSIONS: AcGCA values higher than 28.3° indicate that the coracoid tip is located more laterally and posteriorly; scGCA values higher than 41.8° indicate that the coracoid tip is located more inferiorly and these two new indexes are showing that more laterally, posteriorly and inferiorly coracoid tip is related to subscapularis tears. KEY WORDS: coracoid process, subscapularis tear, coracoid morphology, scapula morphology.
- MeSH
- Adult MeSH
- Middle Aged MeSH
- Humans MeSH
- Magnetic Resonance Imaging * methods MeSH
- Rotator Cuff Injuries * diagnostic imaging MeSH
- Coracoid Process * injuries diagnostic imaging MeSH
- Shoulder Joint diagnostic imaging MeSH
- Sensitivity and Specificity MeSH
- Case-Control Studies MeSH
- Check Tag
- Adult MeSH
- Middle Aged MeSH
- Humans MeSH
- Male MeSH
- Female MeSH
- Publication type
- Journal Article MeSH
We investigate electroluminescence of single molecular emitters on NaCl on Ag(111) and Au(111) with submolecular resolution in a low-temperature scanning probe microscope with tunneling current, atomic force, and light detection capabilities. The role of the tip state is studied in the photon maps of a prototypical emitter, zinc phthalocyanine (ZnPc), using metal and CO-metal tips. CO-functionalization is found to have an impact on the resolution and contrast of the photon maps due to the localized overlap of the p-orbitals on the tip with the molecular orbitals of the emitter. The possibility of using the same CO-functionalized tip for tip-enhanced photon detection and high resolution atomic force is demonstrated. We study the electroluminescence of ZnPc, induced by charge carrier injection at sufficiently high bias voltages. We propose that the distinct level alignment of the ZnPc frontier orbitals with the Au(111) and Ag(111) Fermi levels governs the primary excitation mechanisms as the injection of electrons and holes from the tip into the molecule, respectively. These findings put forward the importance of the tip status in the photon maps and contribute to a better understanding of the photophysics of organic molecules on surfaces.
The distal end of the eukaryotic flagellum/cilium is important for axonemal growth and signaling and has distinct biomechanical properties. Specific flagellum tip structures exist, yet their composition, dynamics, and functions are largely unknown. We used biochemical approaches to identify seven constituents of the flagella connector at the tip of an assembling trypanosome flagellum and three constituents of the axonemal capping structure at the tips of both assembling and mature flagella. Both tip structures contain evolutionarily conserved as well as kinetoplastid-specific proteins, and component assembly into the structures occurs very early during flagellum extension. Localization and functional studies reveal that the flagella connector membrane junction is attached to the tips of extending microtubules of the assembling flagellum by a kinesin-15 family member. On the opposite side, a kinetoplastid-specific kinesin facilitates attachment of the junction to the microtubules in the mature flagellum. Functional studies also suggest roles of several other components and the definition of subdomains in the tip structures.
- Keywords
- axonemal capping structure, flagella connector, flagellar distal end, structure immunoprecipitation, trypanosome,
- MeSH
- Axoneme chemistry metabolism MeSH
- Flagella chemistry metabolism MeSH
- Kinesins chemistry metabolism MeSH
- Protozoan Proteins chemistry metabolism MeSH
- Trypanosoma brucei brucei chemistry metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Names of Substances
- Kinesins MeSH
- Protozoan Proteins MeSH
