We investigated the change in the metal–molecule interaction in a 1,4-benzenedithiol (BDT) single-molecule junction using a combination of surface-enhanced Raman scattering spectra and ...current–voltage curves. During the stretching process, the conductance of the junction systematically decreased, accompanied by an increase in the vibrational energy of the CC stretching mode. By analyzing the current–voltage curves and Raman spectra, we found that the interaction between the π orbital of BDT and the electronic states of Au was diminished by the orientation change of BDT during the stretching process. A comparison with a 4,4′-bipyridine single-molecule junction revealed that the reduction of coupling of the Au–S contacts was smaller than that of Au–pyridine contacts. Therefore, the electronic states originating from the contact geometry are responsible for the tolerance to the stretching of thiol-terminated molecular junctions.
We have investigated the effect of the bias voltage on the 1,4-benzenethiol (BDT) single-molecule junction using the surface-enhanced Raman scattering (SERS). By measuring the bias voltage dependence ...of SERS for the identical sample, we can clearly observe the blue shift of the vibrational mode at 355 cm–1 by the application of the bias voltage. This measurement is possible by using a highly stable nanogap electrode which is fabricated with lithographic techniques. Meanwhile, the energy of other vibrational modes does not change with the bias voltage. The change in the bond strength can be explained by the charge transfer induced by the application of the bias voltage on the single-molecule junction. The theoretical calculation result reveals that the effect of bias voltage is a result of the rearrangement of the π system. The 355 cm–1 mode is an out-of-plane mode of the aromatic ring. In the BDT single-molecule junction, the π system is delocalized on the sulfur atom. This delocalization is suppressed by the application of the bias voltage, and thus, the aromatic ring is more “benzene-like” and the out-of-plain vibration shifts to higher energy.
We have studied the stretch dependence of the electronic structure and vibrational energy for the 4,4′-bipyridine (BPY) single molecule junction, which was fabricated by the mechanically controllable ...break junction (MCBJ) using the highly stable nano MCBJ electrodes. The electronic structure and vibrational energy of the single molecule junction were studied by the current-voltage (
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V
) curve and surface enhanced Raman scattering (SERS), respectively. The simultaneous SERS and
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V
curve measurements revealed the lowest unoccupied molecular orbital (LUMO) and vibrational energy of the C-C stretching mode decreased with an increase in the metal-molecule distance. The molecular orbital energy shift and vibrational energy shift can be explained by the change in the degree of the hybridization of molecular and metal orbitals.
Change in the molecular orbital energy and vibrational energy of the bipyridine single molecule junction as a function of stretch distance.
The electronic and magnetic properties of chemically modified graphene armchair edges are studied using a combination of tight-binding calculations, first-principles modelling, and low temperature ...scanning tunneling microscopy (STM) experiments. The atomically resolved STM images of the hydrogen etched graphitic edges suggest the presence of localized states at the Fermi level for certain armchair edges. We demonstrate theoretically that the topological zero-energy edge mode may emerge at armchair boundaries with asymmetrical chemical termination of the two outermost atoms in the unit cell. We particularly focus our attention on armchair edges terminated by various combinations of the hydrogen (H, H
) and methylene (CH
) groups. The inclusion of the spin component in our calculations reveals the appearance of π-electron-based magnetism at the armchair edges under consideration.
The atomic switches have attracted wide attention owing to their applications in nonvolatile electric devices. The atomic switch is operated by the formation and dissipation of a metallic filament ...inside a metal sulfide film, which is controlled by a solid electrochemical reaction. Although the metallic filament is considered to consist of metal atoms, the chemical species of the metallic filament are difficult to be identified due to challenges in observing the metallic filament inside the solid. In this study, we report the investigation on the metallic filament in the atomic switch with metal sulfide based on point-contact spectroscopy (PCS). By cooling the atomic switch, the switch voltage increased to 1 V, which allowed for the PCS measurement. The PCS revealed that the metallic filament was composed of Ag atoms in the case of the Pt/Ag2S/Ag atomic switch. We applied this technique to the Pt/Cu2S/Ag and Pt/Ag2S/Cu atomic switches to uncover the formation process of the metallic filament. In both atomic switches, the chemical species of the metallic filament were Ag. The metal atoms were supplied from both the metal electrode and the sulfide layer.
Objective Refluxing perforators contribute to venous ulceration. We sought to describe patient characteristics and procedural factors that (1) impact rates of incompetent perforator vein (IPV) ...thrombosis with ultrasound-guided sclerotherapy (UGS) and (2) impact the healing of venous ulcers (CEAP 6) without axial reflux. Methods A retrospective review of UGS of IPV injections from January 2010 to November 2012 identified 73 treated venous ulcers in 62 patients. Patients had no other superficial or axial reflux and were treated with standard wound care and compression. Ultrasound imaging was used to screen for refluxing perforators near ulcer(s). These were injected with sodium tetradecyl sulfate or polidocanol foam and assessed for thrombosis at 2 weeks. Demographic data, comorbidities, treatment details, and outcomes were analyzed. Univariate and multivariable modeling was performed to determine covariates predicting IPV thrombosis and ulcer healing. Results There were 62 patients (55% male; average age, 57.1 years) with active ulcers for an average of 28 months with compression therapy before perforator treatment, and 36% had a history of deep venous thrombosis and 30% had deep venous reflux. At a mean follow-up of 30.2 months, ulcers healed in 32 patients (52%) and did not heal in 30 patients (48%). Ulcers were treated with 189 injections, with an average thrombosis rate of 54%. Of 73 ulcers, 43 ulcers (59%) healed, and 30 (41%) did not heal. The IPV thrombosis rate was 69% in patients whose ulcers healed vs 38% in patients whose ulcers did not heal ( P < .001). Multivariate models demonstrated male gender ( P = .03) and warfarin use ( P = .01) negatively predicted thrombosis of IPVs. A multivariate model for ulcer healing found complete IPV thrombosis was a positive predictor ( P = .02), whereas a large initial ulcer area was a negative predictor ( P = .08). Increased age was associated with fewer ulcer recurrences ( P = .05). Predictors of increased ulcer recurrences were hypertension ( P = .04) and increased follow-up time ( P = .02). Calf vein thrombosis occurred after 3% (six of 189) of injections. Conclusions Thrombosis of IPVs with UGS increases venous ulcer healing in a difficult patient population. Complete closure of all IPVs in an ulcerated limb was the only predictor of ulcer healing. Men and patients taking warfarin have decreased rates of IPV thrombosis with UGS.
Objective The objective of this study was to review the current anatomic indications for and early results of aortouni-iliac (AUI) devices for endovascular aneurysm repair. Methods A total of 128 ...patients receiving an Endurant (Medtronic Inc, Minneapolis, Minn) AUI device in the U.S. Investigational Device Exemption trial (44 patients) or the Endurant Stent Graft Natural Selection Global Postmarket Registry (84 patients) were reviewed. Preoperative computed tomography imaging of patients in the Investigational Device Exemption trial and case report forms of Registry patients were used to determine anatomic indications. Baseline characteristics and early results were compared with those of 1305 patients receiving a bifurcated (BIF) device in sister studies. Results The indication for the AUI device was unclear from case report forms in two Registry cases. The remaining 126 patients had a unilateral iliac occlusion in 30 (23%), a severely narrowed aortic segment in 58 (45%), severe iliac occlusive disease in 28 (22%), severe iliac tortuosity in 29 (23%), or complex iliac aneurysms in 19 (15%). Two patients had a previous aortobifemoral graft; 38 patients (30%) had multiple indications. The AUI cohort included more women than the BIF group did (19% vs 10%; P < .01) and had more severe comorbidities. Successful deployment was achieved in all AUI cases. The 30-day mortality was 2% (BIF cohort, 1%; P = .21). More AUI patients underwent repair under general anesthesia (81% vs 64%; P < .01), and procedures were longer (110.9 ± 54.9 minutes vs 99.2 ± 44.3 minutes; P = .02). Except for longer intensive care unit stays (19.6 ± 80.0 hours vs 9.0 ± 34.8 hours; P = .01) and higher myocardial infarction rates (4% vs 1%; P < .01), outcomes of the AUI cohort were similar to those of the BIF cohort. There were no migrations, ruptures, fractures, or open conversions at up to 1-year follow-up. Conclusions The AUI configuration extends endovascular aneurysm repair feasibility to several hostile anatomic conditions. Despite increased comorbidities in the recipient patient population and associated higher rates of postoperative myocardial infarction and respiratory complications, early outcomes with the new generation of AUI devices are acceptable and comparable to those after treatment with BIF configurations.
The authors have previously demonstrated that VenaSeal (Medtronic, Inc, Minneapolis, Minn) adhesive, compared with radiofrequency ablation (RFA, ClosureFast; Medtronic, Inc), in treatment of ...refluxing saphenous veins in CEAP 6 limbs, results in shorter healing times of venous ulcers. The authors hypothesize that the longer treated length possible with VenaSeal's nonthermal modality may affect the number of critical refluxing perforators contributing to the nonhealing wound. This follow-up study compares the need for follow-up treatment of perforator veins after saphenous vein treatment with either radiofrequency ablation (ClosureFast RFA) or adhesive closure (VenaSeal).
A multi-institutional retrospective review of CEAP 6 patients who had closure of their saphenous veins from 2015 to 2020 was conducted. Patients who underwent follow-up treatment of perforator veins were grouped according to their method of initial management of their saphenous veins. The primary end point was incidence of a perforator procedure after ClosureFast or VenaSeal ablation. Secondary end points included sclerotherapy to facilitate wound healing. Bivariate analysis used the χ2 test, Fisher exact test, t-test, and Wilcoxon rank sum test. A P value of <.05 defined statistical significance.
There were 119 CEAP 6 patients with saphenous closure: 51 limbs treated with VenaSeal and 68 with RFA. Median follow-up was 105 days (interquartile range: 44, 208). All limbs achieved wound healing during the study period. Mean time to wound healing post index procedure was shorter for VenaSeal than RFA (72 vs 293.8 days, P > .0009), as was median time (43 vs 104 days, P = .001). More limbs treated with RFA had previous known deep vein thrombosis (29% vs 10%, P = .009), deep venous insufficiency (82% vs 51%, P = .0003), and perforator reflux (57% vs 29%, P = .002). Limbs with identified follow-up perforator reflux treated with RFA had a higher prevalence of initially treated saphenous veins with RFA compared with those treated with VenaSeal (49% vs 27%, P = .003). There was no difference between the methods of vein closure and use of concurrent sclerotherapy.
ClosureFast and VenaSeal are both effective and safe modalities of saphenous ablation, but VenaSeal treatment was associated with less perforator RFA intervention.
A single-molecule junction, where a single molecule is connected to metal electrodes, has been investigated for potential device applications. π molecules have various functions, and thus, they are ...ideal molecules as active components of electronic devices. A single-molecule junction study can also reveal the intrinsic properties of a molecule without the effect of intermolecular interaction. Meanwhile, the molecule in the single-molecule junction can exhibit unconventional physical and chemical properties which are not observed in other phases (
e.g.
gases and bulk crystals), when a molecule strongly interacts with metal. Under the strong metal-molecule interaction, the single-molecule junction can be regarded as a new material including metal electrodes, and a double interface material. A single-molecule junction is, thus, a fascinating research target for a wide range of areas from application to fundamental science.
An investigation on a single-molecule junction reveals the intrinsic properties of a π molecule without the effect of intermolecular interaction and also uncovers its unique properties.
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