Partial cardiopulmonary bypass through left thoracotomy for coarctation repair in children.

BACKGROUND: A left thoracotomy approach is anatomically appropriate for childhood aortic coarctation; however, the pediatric femoral arteriovenous diameters are too small for cardiopulmonary bypass cannulation. We aimed to determine the safety of a partial cardiopulmonary bypass through the main pulmonary artery and the descending aorta in pediatric aortic coarctation repair. METHODS: We retrospectively reviewed 10 patients who underwent coarctation repair under partial main pulmonary artery-to-descending aorta cardiopulmonary bypass with a left thoracotomy as the CPB group. During the same period, 16 cases of simple coarctation of the aorta repair, with end-to-end anastomosis through a left thoracotomy without partial CPB assistance, were included as the non-CPB group to evaluate the impact of partial CPB. RESULTS: The median age and weight at surgery of the CPB group were 3.1 years (range, 9 days to 17.9 years) and 14.0 (range, 2.8-40.7) kg, respectively. Indications for the partial cardiopulmonary bypass with overlap were as follows: age > 1 year (n = 7), mild aortic coarctation (n = 3), and predicted ischemic time > 30 min (n = 5). Coarctation repair using autologous tissue was performed in seven cases and graft replacement in three. The mean partial cardiopulmonary bypass time, descending aortic clamp time, and cardiopulmonary bypass flow rate were 73 ± 37 min, 57 ± 27 min, and 1.6 ± 0.2 L/min/m2, respectively. Urine output during descending aortic clamping was observed in most cases in the CPB group (mean: 9.1 ± 7.9 mL/kg/h), and the total intraoperative urine output was 3.2 ± 2.7 mL/kg/h and 1.2 ± 1.5 mL/kg/h in the CPB and non-CPB group, respectively (p = 0.020). The median ventilation time was 1 day (range, 0-15), and the intensive care unit stay duration was 4 days (range, 1-16) with no surgical deaths. No major complications, including paraplegia or recurrent coarctation, occurred postoperatively during a median observation period of 8.1 (range, 3.4-17.5) years in the CPB group. In contrast, reoperation with recurrent coarctation was observed in 2 cases in the non-CPB group (p = 0.37). CONCLUSIONS: Partial cardiopulmonary bypass through the main pulmonary artery and descending aorta via a left thoracotomy is a safe and useful option for aortic coarctation repair in children.

Regulated Single-Axis Rotations of a Carbonaceous Guest in a van†der Waals Complex with an Entropy Cost.

In a tight host-guest complex assembled solely by nondirectional van der Waals forces, unique motions of the guest, such as solid-state inertial rotations, emerge. The regulation of dynamic motions is an important element to be explored for novel functions of such complexes, which may be seemingly difficult to achieve because of the nondirectionality of the assembling forces. A regulated, single-axis rotation was made possible by choosing an appropriate shape of the guest in the tubular host. Specifically, an ellipsoidal guest was made to stand along a cylinder axis of the host, which consequently resulted in single-axis rotations of the guest in the solid. The rotational frequency was considerably high for solid-state rotations but was suppressed to 10 GHz, which was 1/20 of the isotropic rotation of a spherical guest. In-depth kinetic analyses quantitatively revealed that the entropy cost was a determining factor that regulated the dynamics.

Monolayer MoS2 growth at the Au-SiO2 interface.

Atomically thin transition-metal dichalcogenides (TMDs) are attracting great interest for future electronic applications. Even though much effort has been devoted to preparing large-area, high-quality TMDs over the past few years, the samples are usually grown on substrate surfaces. Here, we demonstrate the direct growth of a MoS2 monolayer at the interface between a Au film and a SiO2 substrate. MoS2 grains were nucleated below Au films deposited on SiO2via interface diffusion and then grown into a continuous MoS2 film. By programming the Au pattern deposited, controlled growth of MoS2 with the desired size and geometry was achieved over preferred locations, facilitating its integration into functional field-effect transistors. Our findings elucidate the fabrication of a two-dimensional semiconductor at the interface of bulk three-dimensional solids, providing a novel means for establishing a clean interface junction. It also offers a promising alternative to the site-selective synthesis of TMDs, which is expected to aid the fabrication of TMD-based nanodevices.

Continuous Heteroepitaxy of Two-Dimensional Heterostructures Based on Layered Chalcogenides.

The in-plane connection and layer-by-layer stacking of atomically thin layered materials are expected to allow the fabrication of two-dimensional (2D) heterostructures with exotic physical properties and future engineering applications. However, it is currently necessary to develop a continuous growth process that allows the assembly of a wide variety of atomic layers without interface degradation, contamination, and/or alloying. Herein, we report the continuous heteroepitaxial growth of 2D multiheterostructures and nanoribbons based on layered transition metal dichalcogenide (TMDC) monolayers, employing metal organic liquid precursors with high supply controllability. This versatile process can avoid air exposure during growth process and enables the formation of in-plane heterostructures with ultraclean atomically sharp and zigzag-edge straight junctions without defects or alloy formation around the interface. For the samples grown directly on graphite, we have investigated the local electronic density of states of atomically sharp heterointerface by scanning tunneling microscopy and spectroscopy, together with first-principles calculations. These results demonstrate an approach to realizing diverse nanostructures such as atomic layer-based quantum wires and superlattices and suggest advanced applications in the fields of electronics and optoelectronics.

Restoring the intrinsic optical properties of CVD-grown MoS2 monolayers and their heterostructures.

This study investigated the intrinsic optical properties of MoS2 monolayers and MoS2/WS2 van der Waals (vdW) heterostructures, grown using chemical vapor deposition. To understand the effect of the growth substrate, samples grown on a SiO2/Si surface were transferred and suspended onto a porous substrate. This transfer resulted in a blue shift of the excitonic photoluminescence (PL) peak generated by MoS2 monolayers, together with an intensity increase. The blue shift and the intensity increase are attributed to the release of lattice strain and the elimination of substrate-induced non-radiative relaxation, respectively. This suspension technique also allowed the observation of PL resulting from interlayer excitons in the MoS2/WS2 vdW heterostructures. These results indicate that the suppression of lattice strain and non-radiative relaxation is essential for the formation of interlayer excitons, which in turn is crucial for understanding the intrinsic physical properties of vdW heterostructures.

Ratchet-free solid-state inertial rotation of a guest ball in a tight tubular host.

Dynamics of molecules in the solid state holds promise for connecting molecular behaviors with properties of bulk materials. Solid-state dynamics of [60]fullerene (C60) is controlled by intimate intermolecular contacts and results in restricted motions of a ratchet phase at low temperatures. Manipulation of the solid-state dynamics of fullerene molecules is thus an interesting yet challenging problem. Here we show that a tubular host for C60 liberates the solid-state dynamics of the guest from the motional restrictions. Although the intermolecular contacts between the host and C60 were present to enable a tight association with a large energy gain of -14 kcal mol-1, the dynamic rotations of C60 were simultaneously enabled by a small energy barrier of +2 kcal mol-1 for the reorientation. The solid-state rotational motions reached a non-Brownian, inertial regime with an extremely rapid rotational frequency of 213 GHz at 335 K.

Rotational dynamics and dynamical transition of water inside hydrophobic pores of carbon nanotubes.

Water in a nanoconfined geometry has attracted great interest from the viewpoint of not only basic science but also nanofluidic applications. Here, the rotational dynamics of water inside single-walled carbon nanotubes (SWCNTs) with mean diameters larger than ca. 1.4 nm were investigated systematically using 2H nuclear magnetic resonance spectroscopy with high-purity SWCNTs and molecular dynamics calculations. The results were compared with those for hydrophilic pores. It was found that faster water dynamics could be achieved by increasing the hydrophobicity of the pore walls and decreasing the pore diameters. These results suggest a strategy that paves the way for emerging high-performance filtration/separation devices. Upon cooling below 220 K, it was found that water undergoes a transition from fast to slow dynamics states. These results strongly suggest that the observed transition is linked to a liquid-liquid crossover or transition proposed in a two-liquid states scenario for bulk water.

Manipulation of local optical properties and structures in molybdenum-disulfide monolayers using electric field-assisted near-field techniques.

Remarkable optical properties, such as quantum light emission and large optical nonlinearity, have been observed in peculiar local sites of transition metal dichalcogenide monolayers, and the ability to tune such properties is of great importance for their optoelectronic applications. For that purpose, it is crucial to elucidate and tune their local optical properties simultaneously. Here, we develop an electric field-assisted near-field technique. Using this technique we can clarify and tune the local optical properties simultaneously with a spatial resolution of approximately 100 nm due to the electric field from the cantilever. The photoluminescence at local sites in molybdenum-disulfide (MoS2) monolayers is reversibly modulated, and the inhomogeneity of the charge neutral points and quantum yields is suggested. We successfully etch MoS2 crystals and fabricate nanoribbons using near-field techniques in combination with an electric field. This study creates a way to tune the local optical properties and to freely design the structural shapes of atomic monolayers using near-field optics.

Modulation of electrical potential and conductivity in an atomic-layer semiconductor heterojunction.

Semiconductor heterojunction interfaces have been an important topic, both in modern solid state physics and in electronics and optoelectronics applications. Recently, the heterojunctions of atomically-thin transition metal dichalcogenides (TMDCs) are expected to realize one-dimensional (1D) electronic systems at their heterointerfaces due to their tunable electronic properties. Herein, we report unique conductivity enhancement and electrical potential modulation of heterojunction interfaces based on TMDC bilayers consisted of MoS2 and WS2. Scanning tunneling microscopy/spectroscopy analyses showed the formation of 1D confining potential (potential barrier) in the valence (conduction) band, as well as bandgap narrowing around the heterointerface. The modulation of electronic properties were also probed as the increase of current in conducting atomic force microscopy. Notably, the observed band bending can be explained by the presence of 1D fixed charges around the heterointerface. The present findings indicate that the atomic layer heterojunctions provide a novel approach to realizing tunable 1D electrical potential for embedded quantum wires and ultrashort barriers of electrical transport.

Selective Formation of Zigzag Edges in Graphene Cracks.

We report the thermally induced unconventional cracking of graphene to generate zigzag edges. This crystallography-selective cracking was observed for as-grown graphene films immediately following the cooling process subsequent to chemical vapor deposition (CVD) on Cu foil. Results from Raman spectroscopy show that the crack-derived edges have smoother zigzag edges than the chemically formed grain edges of CVD graphene. Using these cracks as nanogaps, we were also able to demonstrate the carrier tuning of graphene through the electric field effect. Statistical analysis of visual observations indicated that the crack formation results from uniaxial tension imparted by the Cu substrates together with the stress concentration at notches in the polycrystalline graphene films. On the basis of simulation results using a simplified thermal shrinkage model, we propose that the cooling-induced tension is derived from the transient lattice expansion of narrow Cu grains imparted by the thermal shrinkage of adjacent Cu grains.

Growth and Optical Properties of High-Quality Monolayer WS2 on Graphite.

Atomic-layer transition metal dichalcogenides (TMDCs) have attracted appreciable interest due to their tunable band gap, spin-valley physics, and potential device applications. However, the quality of TMDC samples available still poses serious problems, such as inhomogeneous lattice strain, charge doping, and structural defects. Here, we report on the growth of high-quality, monolayer WS2 onto exfoliated graphite by high-temperature chemical vapor deposition (CVD). Monolayer-grown WS2 single crystals present a uniform, single excitonic photoluminescence peak with a Lorentzian profile and a very small full-width at half-maximum of 21 meV at room temperature and 8 meV at 79 K. Furthermore, in these samples, no additional peaks are observed for charged and/or bound excitons, even at low temperature. These optical responses are completely different from the results of previously reported TMDCs obtained by mechanical exfoliation and CVD. Our findings indicate that the combination of high-temperature CVD with a cleaved graphite surface is an ideal condition for the growth of high-quality TMDCs, and such samples will be essential for revealing intrinsic physical properties and for future applications.

Tuning of the thermoelectric properties of one-dimensional material networks by electric double layer techniques using ionic liquids.

We report across-bandgap p-type and n-type control over the Seebeck coefficients of semiconducting single-wall carbon nanotube networks through an electric double layer transistor setup using an ionic liquid as the electrolyte. All-around gating characteristics by electric double layer formation upon the surface of the nanotubes enabled the tuning of the Seebeck coefficient of the nanotube networks by the shift in gate voltage, which opened the path to Fermi-level-controlled three-dimensional thermoelectric devices composed of one-dimensional nanomaterials.

Single chirality extraction of single-wall carbon nanotubes for the encapsulation of organic molecules.

The hollow inner spaces of single-wall carbon nanotubes (SWCNTs) can confine various types of molecules. Many remarkable phenomena have been observed inside SWCNTs while encapsulating organic molecules (peapods). However, a mixed electronic structure state of the surrounding SWCNTs has impeded a detailed understanding of the physical/chemical properties of peapods and their device applications. We present a single-chirality purification method for SWCNTs that can encapsulate organic molecules. A single-chiral state of (11,10) SWCNTs with a diameter of 1.44 nm, which is large enough for molecular encapsulation, was obtained after a two-step purification method: metal-semiconductor sorting and cesium-chloride sorting. The encapsulation of C(60) to the (11,10) SWCNTs was also succeeded, promising a route toward single-chirality peapod devices.

Confined water inside single-walled carbon nanotubes: global phase diagram and effect of finite length.

Studies on confined water are important not only from the viewpoint of scientific interest but also for the development of new nanoscale devices. In this work, we aimed to clarify the properties of confined water in the cylindrical pores of single-walled carbon nanotubes (SWCNTs) that had diameters in the range of 1.46 to 2.40 nm. A combination of x-ray diffraction (XRD), nuclear magnetic resonance, and electrical resistance measurements revealed that water inside SWCNTs with diameters between 1.68 and 2.40 nm undergoes a wet-dry type transition with the lowering of temperature; below the transition temperature T(wd), water was ejected from the SWCNTs. T(wd) increased with increasing SWCNT diameter D. For the SWCNTs with D = 1.68, 2.00, 2.18, and 2.40 nm, T(wd) obtained by the XRD measurements were 218, 225, 236, and 237 K, respectively. We performed a systematic study on finite length SWCNT systems using classical molecular dynamics calculations to clarify the effect of open ends of the SWCNTs and water content on the water structure. It was found that ice structures that were formed at low temperatures were strongly affected by the bore diameter, a = D - σ(OC), where σ(OC) is gap distance between the SWCNT and oxygen atom in water, and the number of water molecules in the system. In small pores (a < 1.02 nm), tubule ices or the so-called ice nanotubes (ice NTs) were formed irrespective of the water content. On the other hand, in larger pores (a > 1.10 nm) with small water content, filled water clusters were formed leaving some empty space in the SWCNT pore, which grew to fill the pore with increasing water content. For pores with sizes in between these two regimes (1.02 < a < 1.10 nm), tubule ice also appeared with small water content and grew with increasing water content. However, once the tubule ice filled the entire SWCNT pore, further increase in the water content resulted in encapsulation of the additional water molecules inside the tubule ice. Corresponding XRD measurements on SWCNTs with a mean diameter of 1.46 nm strongly suggested the presence of such a filled structure.

Transport mechanisms in metallic and semiconducting single-wall carbon nanotube networks.

A fundamental understanding of the conduction mechanisms in single-wall carbon nanotube (SWCNT) networks is crucial for their use in thin-film transistors and conducting films. However, the uncontrollable mixture state of metallic and semiconducting SWCNTs has always been an obstacle in this regard. In the present study, we revealed that the conduction mechanisms in nanotube networks formed by high-purity metallic and semiconducting SWCNTs are completely different. Quantum transport was observed in macroscopic networks of pure metallic SWCNTs. However, for semiconducting SWCNT networks, Coulomb-gap-type conduction was observed, due to Coulomb interactions between localized electrons. Crossovers among a weakly localized state and strongly localized states with and without Coulomb interactions were observed for transport electrons by varying the relative content of metallic and semiconducting SWCNTs. It was found that hopping barriers, which always exist in normal SWCNT networks and are serious obstacles to achieving high conductivity, were not present in pure metallic SWCNT networks.

Superconductivity in alkali-metal-doped picene.

Efforts to identify and develop new superconducting materials continue apace, motivated by both fundamental science and the prospects for application. For example, several new superconducting material systems have been developed in the recent past, including calcium-intercalated graphite compounds, boron-doped diamond and-most prominently-iron arsenides such as LaO(1-x)F(x)FeAs (ref. 3). In the case of organic superconductors, however, no new material system with a high superconducting transition temperature (T(c)) has been discovered in the past decade. Here we report that intercalating an alkali metal into picene, a wide-bandgap semiconducting solid hydrocarbon, produces metallic behaviour and superconductivity. Solid potassium-intercalated picene (K(x)picene) shows T(c) values of 7 K and 18 K, depending on the metal content. The drop of magnetization in K(x)picene solids at the transition temperature is sharp (<2 K), similar to the behaviour of Ca-intercalated graphite. The T(c) of 18 K is comparable to that of K-intercalated C(60) (ref. 4). This discovery of superconductivity in K(x)picene shows that organic hydrocarbons are promising candidates for improved T(c) values.

Dielectric properties of water inside single-walled carbon nanotubes.

In this paper, we report novel ferroelectric properties of a new form of ice inside single-walled carbon nanotubes (SWCNTs). These are called "ice nanotubes" (ice NTs) and they consist of polygonal water rings stacked one-dimensionally along the SWCNT axis. We performed molecular dynamics (MD) calculations for the ice NTs under an external electric field and in a temperature range between 100 and 350 K. It is revealed that ice NTs show stepwise polarization with a significant hysteresis loop as a function of the external field strength. In particular, pentagonal and heptagonal ice NTs are found to be the world's smallest ferroelectrics with spontaneous polarization of around 1 microC/cm(2). The n-gonal ice NT, where n = 5, 6, or 7, has (n + 1)-polarized structures with different polarizations. These findings suggest potential applications of SWCNTs encapsulating dielectric materials for the fabrication of the smallest ferroelectric devices. Experimental evidence for the presence of ice NTs inside SWCNTs is also discussed in great detail.

Photosensitive function of encapsulated dye in carbon nanotubes.

Single-wall carbon nanotubes (SWCNTs) exhibit resonant absorption localized in specific spectral regions. To expand the light spectrum that can be utilized by SWCNTs, we have encapsulated squarylium dye into SWCNTs and clarified its microscopic structure and photosensitizing function. X-ray diffraction and polarization-resolved optical absorption measurements revealed that the encapsulated dye molecules are located at an off center position inside the tubes and aligned to the nanotube axis. Efficient energy transfer from the encapsulated dye to SWCNTs was clearly observed in the photoluminescence spectra. Enhancement of transient absorption saturation in the S1 state of the semiconducting SWCNTs was detected after the photoexcitation of the encapsulated dye, which indicates that ultrafast (<190 fs) energy transfer occurred from the dye to the SWCNTs.

Water-filled single-wall carbon nanotubes as molecular nanovalves.

It is known that at low temperature, water inside single-wall carbon nanotubes (water-SWNTs) undergoes a structural transition to form tube-like solid structures. The resulting ice NTs are hollow cylinders with diameters comparable to those of typical gas molecules. Hence, the gas-adsorption properties of ice- and water-SWNTs are of interest. Here, we carry out the first systematic investigation into the stability of water-SWNTs in various gas atmospheres below 0.1 MPa by means of electrical resistance, X-ray diffraction, NMR measurements and molecular dynamics calculations. It is found that the resistivity of water-SWNTs exhibits a significant increase in gas atmospheres below a critical temperature Tc, at which a particular type of atmospheric gas molecule enters the SWNTs in an on-off fashion. On the basis of this phenomenon, it is proposed that water-SWNTs can be used to fabricate a new type of molecular nanovalve.