Electronic Characterization of a Charge-Transfer Complex Monolayer on Graphene.

Organic charge-transfer complexes (CTCs) formed by strong electron acceptor and strong electron donor molecules are known to exhibit exotic effects such as superconductivity and charge density waves. We present a low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) study of a two-dimensional (2D) monolayer CTC of tetrathiafulvalene (TTF) and fluorinated tetracyanoquinodimethane (F4TCNQ), self-assembled on the surface of oxygen-intercalated epitaxial graphene on Ir(111) (G/O/Ir(111)). We confirm the formation of the charge-transfer complex by dI/dV spectroscopy and direct imaging of the singly occupied molecular orbitals. High-resolution spectroscopy reveals a gap at zero bias, suggesting the formation of a correlated ground state at low temperatures. These results point to the possibility to realize and study correlated ground states in charge-transfer complex monolayers on weakly interacting surfaces.

Two-Dimensional Band Structure in Honeycomb Metal-Organic Frameworks.

Two-dimensional (2D) metal-organic frameworks (MOFs) have been recently proposed as a flexible material platform for realizing exotic quantum phases including topological and anomalous quantum Hall insulators. Experimentally, direct synthesis of 2D MOFs has been essentially confined to metal substrates, where the strong interaction with the substrate masks the intrinsic electronic properties of the MOF. In addition to electronic decoupling from the underlying metal support, synthesis on weakly interacting substrates (e.g., graphene) would enable direct realization of heterostructures of 2D MOFs with inorganic 2D materials. Here, we demonstrate synthesis of 2D honeycomb MOFs on epitaxial graphene substrate. Using low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM) complemented by density-functional theory (DFT) calculations, we show the formation of a 2D band structure in the MOF decoupled from the substrate. These results open the experimental path toward MOF-based designer electronic materials with complex, engineered electronic structures.

Charge-Transfer-Driven Nonplanar Adsorption of F4TCNQ Molecules on Epitaxial Graphene.

π-conjugated organic molecules tend to adsorb in a planar configuration on graphene irrespective of their charge state. In contrast, here we demonstrate charging-induced strong structural relaxation of tetrafluorotetracyanoquinodimethane (F4TCNQ) on epitaxial graphene on Ir(111) (G/Ir(111)). The work function modulation over the graphene moiré unit cell causes site-selective charging of F4TCNQ. Upon charging, the molecule anchors to the face-centered cubic sites of the G/Ir(111) moiré through one or two cyano groups. The reaction is reversible and can be triggered on a single molecule by moving it between different adsorption sites. We introduce a model taking into account the trade-off between tilt-induced charging and reduced van der Waals interactions, which provides a general framework for understanding charging-induced structural relaxation on weakly interacting substrates. In addition, we argue that the partial sp3 rehybridization of the underlying graphene and the possible bonding mechanism between the cyano groups and the graphene substrate are also relevant for the complete understanding of the experiments. These results provide insight into molecular charging on graphene, and they are directly relevant for potential device applications where the use of molecules has been suggested for doping and band structure engineering.

Molecular assembly on two-dimensional materials.

Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging from flexible electronics and OLEDs to novel electronic devices and spintronics.

Laparoscopic ablative and reconstructive surgeries in genitourinary tuberculosis.

BACKGROUND AND OBJECTIVES: Laparoscopy is the present standard of care for urologic diseases. Laparoscopy in renal tuberculosis (genitourinary tuberculosis) is difficult because of inflammation and fibrosis associated with the disease. We present the outcome of our experience of laparoscopy in genitourinary tuberculosis, both ablative and reconstructive. METHODS: The detailed data of patients with genitourinary tuberculosis who underwent laparoscopic surgeries between January 2011 and September 2012 were reviewed. Indications, type of surgery, duration, blood loss, intraoperative problems, postoperative outcomes, and follow-up details were noted. RESULTS: Overall, 7 laparoscopic procedures were performed: 5 nephrectomies, 1 ureteric reimplantation with psoas hitch, and 1 combined nephrectomy and laparoscopy-assisted Mainz II pouch reconstruction. The mean operative time was 192 minutes for nephrectomy, 210 minutes for ureteric reimplantation, and 480 minutes for nephrectomy with Mainz II pouch reconstruction. There were no conversions to open surgery. The mean amount of blood loss was 70 mL for the nephrectomies, 100 mL for ureteric reimplantation, and 200 mL for nephrectomy with Mainz II pouch reconstruction. In 5 of 6 patients who underwent nephrectomy, there was severe perinephric and peripelvic fibrosis posing difficulty in dissection. However, the renal vessels could be controlled individually. The mean postoperative hospital stay was 3 days for the nephrectomies, 5 days for the ureteric reimplantation, and 10 days for the nephrectomy with Mainz II pouch reconstruction. In all cases the recovery was uneventful. CONCLUSIONS: Laparoscopy, though technically more demanding, is a feasible and safe option for ablative and complex reconstructive procedures in genitourinary tuberculosis. It offers the benefits of minimally invasive surgery. The difficulty with this procedure is mostly because of peripelvic and perinephric fibrosis, whereas the lower ureter and bladder are relatively easier to dissect.

Laparoscopic pyeloplasty for ureteropelvic junction obstruction in crossed fused ectopic pelvic kidney.

Crossed fused renal ectopia is a rare anomaly and may be associated with pelvic ureteric junction obstruction (PUJO). The L-shaped fusion variety is even rarer. We report such a case with a crossed fused ectopic pelvic kidney (L-type) with PUJO and its successful laparoscopic management. Through this report we emphasize the importance of adequate preoperative imaging and intraoperative details to avoid mishaps.

Decoupling of the copper core in a single copperphthalocyanine molecule.

Here, we show how a copper atom in a copperphthalocyanine (CuPc) molecule can be decoupled from its environment. This is realized by trapping the CuPc molecule between two adjacent nanowires that are 1.6 nm apart. Using low-temperature scanning tunnelling microscopy and spectroscopy, the structural and electronic properties of CuPc in the stable "molecular bridge" configuration have been studied. Constant current and differential conductivity maps are recorded to reveal the spatial variation of the electronic structure of the cores and the lobes of CuPc molecules. The core of CuPc molecule is dim at low voltages, but suddenly becomes bright at a voltage of 5 V. Time-resolved scanning tunnelling microscopy measurements show that some of the CuPc lobes are very stable, while other lobes are very dynamic.

Molecular dynamics and energy landscape of decanethiolates in self-assembled monolayers on Au(111) studied by scanning tunneling microscopy.

The energetics and dynamics of the various phases of decanethiolate self-assembled monolayers on Au(111) surfaces were studied with scanning tunneling microscopy. We have observed five different phases of the decanethiolate monolayer on Au(111): four ordered phases (ß, δ, χ*, and φ) and one disordered phase (ε). We have determined the boundary free energies between the disordered and order phases by analyzing the thermally induced meandering of the domain boundaries. On the basis of these results, we are able to accurately predict the two-dimensional phase diagram of the decanethiolate/Au(111) system. The order-disorder phase transition of the χ* phase occurs at 295 K, followed by the order-disorder phase transition of the ß phase at 325 K. Above temperatures of 325 K, only the densely packed φ and disordered ε phases remain. Our findings are in good agreement with the phase diagram of the decanethiolate/Au(111) system that was put forward by Poirier et al. [Langmuir 2001, 17 (4), 1176-1183].

Dynamics of decanethiol self-assembled monolayers on Au(111) studied by time-resolved scanning tunneling microscopy.

We investigated the dynamics of decanethiol self-assembled monolayers on Au(111) surfaces using time-resolved scanning tunneling microscopy at room temperature. The expected ordered phases (ß, δ, χ*, and φ) and a disordered phase (ε) were observed. Current-time traces with the feedback loop disabled were recorded at different locations on the surface. The sulfur end group of the decanethiolate molecule exhibits a stochastic two-level switching process when the molecule is adsorbed in a (local) ß phase registry. This two-level process is attributed to the diffusion of the Au-thiolate complex between two adjacent adsorption sites. The irregular current jumps in the current-time traces recorded on the tails of decanethiolate molecules in the ordered ß, δ, and χ* phases are ascribed to wagging of the alkyl tails. Finally, the disordered phase is characterized by even larger current jumps, which indicates that the tail of the decanethiolate flips up occasionally and makes contact with the tip. Our experiments reveal that the massive dynamics of the self-assembled monolayer is due to diffusion of decanethiol-Au complexes, rather than the diffusion of decanethiolate molecules.

Randomized clinical trial comparing effectiveness of intracorpus spongiosum block versus topical anesthesia for performing visual internal urethrotomy for urethral stricture disease.

OBJECTIVE: To compare the efficacy and safety of intracorpus spongiosum block (ICSB) over topical anesthesia for performing visual internal urethrotomy (VIU) in a randomized clinical trial. METHODS: VIU for urethral stricture can be performed under various types of anesthesia, including topical anesthesia. Although recent studies have shown that ICSB and general anesthesia have comparable efficacy for performing VIU, no studies have compared ICSB with topical anesthesia. Forty consenting patients with single, short, passable anterior urethral stricture were randomized into two groups. Group 1 patients received topical 2% lignocaine jelly and group 2 patients received 1% lignocaine ICSB for undergoing VIU. Pain perception during and after the procedure was assessed by visual analog scale (VAS). The changes in vital parameters during the procedure and procedure-related complications were recorded. Statistical analysis was done using the Mann-Whitney test or t test. RESULTS: The mean±standard deviation VAS scores intraoperatively (2.85±1.34) and at 1-hour postoperatively (1.17±0.96) were significantly lower (P<01) in group 2 patients than the corresponding scores in group 1 (4.9±1.9 and 2.35±1.34 respectively). The intraoperative rise in pulse rate and in blood pressure were significantly greater (P<.05) in group 1 patients (13±5.1/min and 11.3±6.44 mm Hg) than in group 2 (8.05±5.54/min and 6.35±5.86 mm Hg). CONCLUSION: ICSB is safe and more effective than topical anesthesia for providing pain relief during VIU. This should become the local anesthesia technique of choice for performing VIU.

Electron-induced dynamics of heptathioether ß-cyclodextrin molecules.

Variable-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) measurements are performed on heptathioether ß-cyclodextrin (ß-CD) self-assembled monolayers (SAMs) on Au. The ß-CD molecules exhibit very rich dynamical behavior, which is not apparent in ensemble-averaged studies. The dynamics are reflected in the tunneling current-time traces, which are recorded with the STM feedback loop disabled. The dynamics are temperature independent, but increase with increasing tunneling current and sample bias, thus indicating that the conformational changes of the ß-CD molecules are induced by electrons that tunnel inelastically. Even for sample biases as low as 10 mV, well-defined levels are observed in the tunneling current-time traces. These jumps are attributed to the excitations of the molecular vibration of the macrocyclic ß-CD molecule. The results are of great importance for a proper understanding of transport measurements in SAMs.