Conventional three-port laparoscopic appendectomy versus transumbilical and suprapubic single-incision laparoscopic appendectomy using only conventional laparoscopic instruments.

PURPOSE: Single-incision laparoscopic appendectomy (SILA) is usually performed using single-port instruments, which may restrict its development and application. This study explored the performance of transumbilical SILA (TSILA) and suprapubic SILA (SSILA) using only conventional laparoscopic instruments and compared them with conventional three-hole/port laparoscopic appendectomy (CLA). METHODS: This retrospective study included 174 patients who underwent CLA, TSILA, or SSILA for acute appendicitis at our hospital between June 2019 and July 2021. Demographic data and clinical outcomes were compared among the three groups. RESULTS: Compared with CLA, TSILA was associated with significant reductions in postoperative pain, length of hospital stay, and hospital cost, while SSILA was associated with significant reductions in length of hospital stay and hospital cost (all P < 0.05). Significantly more patients in the two SILA groups were cosmetically satisfied than those in the CLA group (all P < 0.05). However, compared with CLA, SSILA required a significantly longer operative time (65.3 ± 24.1 vs 56.5 ± 20.9, P = 0.039). Besides, compared with TSILA, SSILA showed significantly higher postoperative pain score (2 ± 2 vs 3 ± 2, P = 0.006). Mild incisional or intraabdominal infections were noticed in 2 (3.0%) patients in the CLA group, 3 (5.1%) in the TSILA group, and 3 (6.3%) in the SSILA group (P = 0.69). CONCLUSION: SILA performed with only conventional laparoscopic instruments was associated with reduced hospital stay and cost and higher cosmetic satisfaction in comparison to CLA. However, it is technically demanding and may increase operative time.

Electrically driven transport of photoinduced hot carriers in carbon nanotube fibers.

Hot carriers play a significant role in applications of photovoltaics, photodetection, and photocatalysis. However, effective methods for observing the ultrafast dynamic processes of hot carriers are concentrated on the time domain, on which it is difficult and complex to operate. We propose a novel, to the best of our knowledge, and creative strategy to convert the time-domain dynamic process into a spatially thermal redistribution in suspended carbon nanotube fibers. The large average free path of photoinduced hot holes ensures a prominent offset of temperature distribution. The experimental results confirm the theory about electrically driven transport of hot holes, which has rarely been reported.

Facile fabrication of eutectic gallium-indium alloy nanostructure and application in photodetection.

Eutectic gallium-indium (EGaIn) alloy is a kind of liquid metal and has attracted much attention due to good properties. In order to satisfy the trend of miniaturization and realize more practical applications, the exploration for preparation method and properties of EGaIn at nanoscale are very important. Here, facile vacuum thermal evaporation method is developed to fabricate EGaIn nanostructures. The EGaIn nanoparticle and nanofilm with naturally formed 5 nm thick oxide layers are well prepared. The oxide film formed on the EGaIn surface is an important factor, making the properties of the nanostructure different from the properties of the bulk. Compared with ignorance of oxide layer in bulk materials, the proportion of oxide layer increases evidently in nanostructures, which produce obvious influence on the electric and optical properties. The rectifying characteristic and optoelectronic performance are experimentally observed. The EGaIn nanostructures can generate evident photocurrent responses with good responsivities (∼1 mA W-1) and response speed (∼1 s) under irradiation of 206 nm, 405 nm, 532 nm, 635 nm, 808 nm, 1064 nm and 10.6 µm lasers. These properties are completely different from the metallic properties of EGaIn bulk material.

Generation of Ultrafine Droplets in Femtoliter Scale from a Large Needle with Diameter of 200 Microns.

Ultrafine droplets play important roles in many fields. Here, we prepare ultrafine droplets with volumes in femtoliter scale by applying an electrostatic field between a needle and substrate. The diameter of liquid is reduced significantly to about 1/50 that of the needle tip. By using some solvents consisting of small molecules, ultrafine droplets eject from the needle tip. The volume of the ultrafine droplets depend on the strength of the electrostatic field and properties of the liquid. Ultrafine droplets containing perovskite quantum dots are also ejected on the substrate by using this jetting method. The ultrafine droplets have great potentials in carrying tiny amount of quantum dots and even molecules for various applications.

In Situ Observation of Crystallization of Methylammonium Lead Iodide Perovskite from Microdroplets.

It is of great importance to investigate the crystallization of organometallic perovskite from solution for enhancing performance of perovskite solar cells. Here, this study develops a facile method for in situ observation of crystallization and growth of the methylammonium lead iodide (MAPbI3 ) perovskite from microdroplets ejected by an alternating viscous and inertial force jetting method. It is found that there are two crystallization modes when MAPbI3 grows from the CH3 NH3 I (MAI)/PbI2 /N,N-dimethylformamide (DMF) solution: needle precursors and granular perovskites. Generally, needle Lewis adduct of MAPbI3 ·DMF tends to nucleate and grow from the solution due to low solubility of PbI2 . The growth of MAPbI3 ·DMF depends on both the concentration of MAI and temperature. It tends to form large perovskite domains on substrates at high temperature. The MAPbI3 ·DMF coverts to nanocrystalline perovskite due to lattice shrinkage when DMF molecules escape from the Lewis adduct. Granular perovskite can also directly nucleate from the solution at high concentration of MAI due to compositional segregation.

Terahertz photodetector based on double-walled carbon nanotube macrobundle-metal contacts.

We report on the characterization of a terahertz (THz) photodetector with an extremely simple structure consisting of only a macroscopic bundle of double-walled carbon nanotubes (DWCNTs) suspended between two metal electrodes. Polarization-sensitive, broadband, and significant photoresponse occurring at the DWCNT-metal contacts under THz illumination are observed with room-temperature photocurrent and photovoltage responsivities up to ∼16 mA/W and ∼0.2 V/W at 2.52 THz, respectively. Scanning photocurrent measurements provide evidence that the photothermoelectric mechanism dominates the detector response. The simple geometry and compact nature of our device make it suitable for integration and show promising applications for THz detection.

All carbon coaxial supercapacitors based on hollow carbon nanotube sleeve structure.

All carbon coaxial supercapacitors based on hollow carbon nanotube (CNT) sleeve structure are assembled and tested. The key advantage of the structure is that the inner core electrode is variable from CNT sleeve sponges, to CNT fibers, reduced graphene oxide fibers, and graphene woven fabrics. By changing core electrodes from sleeve sponges to CNT fibers, the electrochemical performance has been significantly enhanced. The capacitance based on sleeve sponge + CNT fiber double the capacitances of double-sleeve sponge supercapacitors thanks to reduction of the series and internal resistances. Besides, the coaxial sleeve structure possesses many other features, including high rate capacitance, long cycle life, and good flexibility.

Photocurrent response of carbon nanotube-metal heterojunctions in the terahertz range.

We investigate the optoelectronic properties of a carbon nanotube (CNT)-metal heterostructure in the terahertz range. On the basis of terahertz time-domain spectroscopy characterization of a double-walled CNT (DWNT) film, we present and analyze the photocurrent measurement for a DWNT-nickel heterojunction illuminated by continuous-wave terahertz radiation. A significant current across the junction directly induced by terahertz excitation is observed and a negative photoconductivity behavior is found to occur in the device. The photocurrent shows a linear response to the bias voltage and the illumination power within the examined range. These phenomena support the feasibility of using CNT-metal heterojunctions as novel terahertz detectors.

Fabrication and oil adsorption of carbon nanotube/polyvinylpyrrolidone surface composite.

It needs to assemble the industrial CNT powders into macroscopic porous surface composite to utilize the surface properties of CNTs, as well as to prevent them entering into environments. We demonstrate a method to fabricate the surface composites from CNTs and polyvinylpyrrolidone (PVP) by electrospinning, where CNTs distribute firmly and mainly on the surface PVP nanofibers. The CNTs/PVP surface composites have high pore volume of 10 cc/g and remarkable CNTs load of 98%. Thus the surface composites show high oil adsorption capacity of 0.9~1.1 g/cm3. It can absorb more oil than commercial sponges due to the surface composite swells after absorbing oil. It shows attractive potential application of the CNT/PVP surface composite in oil spill cleanup.

Colloidal antireflection coating improves graphene-silicon solar cells.

Carbon nanotube-Si and graphene-Si solar cells have attracted much interest recently owing to their potential in simplifying manufacturing process and lowering cost compared to Si cells. Until now, the power conversion efficiency of graphene-Si cells remains under 10% and well below that of the nanotube-Si counterpart. Here, we involved a colloidal antireflection coating onto a monolayer graphene-Si solar cell and enhanced the cell efficiency to 14.5% under standard illumination (air mass 1.5, 100 mW/cm(2)) with a stable antireflection effect over long time. The antireflection treatment was realized by a simple spin-coating process, which significantly increased the short-circuit current density and the incident photon-to-electron conversion efficiency to about 90% across the visible range. Our results demonstrate a great promise in developing high-efficiency graphene-Si solar cells in parallel to the more extensively studied carbon nanotube-Si structures.

Significantly enhanced photoresponse in carbon nanotube film/TiO2 nanotube array heterojunctions by pre-electroforming.

Traditional TiO2 based photodetectors (PDs) suffer from high dark resistance, which increases loss of photoexcited charge carriers. Here, we report a new and simple way to improve the performance of PDs based on double-walled carbon nanotube (DWCNT)/TiO2 nanotube heterojunctions. Highly ordered TiO2 nanotube arrays were fabricated using a two-step anodic oxidation method, and coated with a DWCNT film, which functioned as a semitransparent electrode and a photoactive layer. Via pre-electroforming, the device was switched from a high resistance state (HRS) to a low resistance state (LRS). At an applied bias of 1 V, the dark resistance was reduced from 926 to 0.67 kΩ, as a result of the formation of oxygen vacancy related conducting filaments. The photoresponse (ΔI = Ip - Id, where Ip and Id represents photocurrent and dark current, respectively) of the PD in LRS reached 816.76 µA W(-1) under 532 nm laser illumination and 802.89 µA W(-1) under 1064 nm laser irradiation, which is 965 and 3980 times higher, respectively, than those obtained from the HRS device under the same conditions. This strategy for enhancing the photoresponse of TiO2 based PDs may have applications in further improving the power conversion efficiency of dye-sensitized solar cells.

Suppression of the coffee-ring effect by self-assembling graphene oxide and monolayer titania.

The in situ self-assembly of two types of typical two-dimensional (2D) nanomaterials (i.e., graphene oxide (GO) and monolayer titania (TO)) is realized using a simple drop-casting method. Within the as-prepared hybrid films, the GO and TO nanosheets arrange alternately into a lamellar structure. Notably, the hybridization of GO and TO suppresses the formation of coffee-rings when drop-cast, which is attributed to the strong interactions between the GO and TO nanosheets. Finally, the mechanism for the in situ hybridization of these two types of nanosheets into heterogeneous lamellar films and the suppression of the coffee-ring effect are discussed. These results demonstrate the potential applications of drop-cast hybrid films for high-quality membrane deposition from liquid phases.

Flexible all solid-state supercapacitors based on chemical vapor deposition derived graphene fibers.

Flexible all-solid-state supercapacitors based on graphene fibers are demonstrated in this study. Surface-deposited oxide nanoparticles are used as pseudo-capacitor electrodes to achieve high capacitance. This supercapacitor electrode has an areal capacitance of 42 mF cm(-2), which is comparable to the capacitance for fiber-based supercapacitors reported to date. During the bending and cycling of the fiber-based supercapacitor, the stability could be maintained without sacrificing the electrochemical performance, which provides a novel and simple way to develop flexible, lightweight and efficient graphene-based devices.

The Influence of Heat Treatment Temperature on Tensile Properties of Metal-Bonded Diamond Composites Fabricated via Selective Laser Melting.

Selective Laser Melting (SLM) is an effective technology for fabricating new types of porous metal-bonded diamond tools with complex geometries. However, due to the high cooling rate and internal stresses during SLM fabrication, defects such as high porosities and interface gaps still need to be resolved before it can be considered for use in other applications. The influence of heat treatment temperature on internal characterization, interface microstructures, and tensile properties of AlSi7Mg-bonded diamond composites fabricated by SLM were investigated in this work. From experimental results, the porosities of HT-200, HT-350, and HT-500 specimens were 12.19%, 11.37%, and 11.14%, respectively, showing a slightly lower percentage than that of the No-HT specimen (13.34%). Here, HT represents "Heat Treatment". For No-HT specimens, an obvious un-bonding area can be seen in the interface between AlSi7Mg and diamond, whereas a relative closer interface can be observed for HT-500 specimens. After heat treatment, the elastic modulus of specimens showed a relative stable value (16.77 ± 2.79~18.23 ± 1.72 GPa), while the value of yield strength decreased from 97.24 ± 4.48 to 44.94 ± 7.06 MPa and the value of elongation increased from 1.98 ± 0.05 to 6.62 ± 0.51%. This difference can be attributed mainly to the disappearance of the solid-solution hardening effect due to the increase of Si content after heat treatment.

Controllable growth of triangular hexagonal boron nitride domains on copper foils by an improved low-pressure chemical vapor deposition method.

We demonstrate an improved low-pressure chemical vapor deposition method to fabricate hexagonal boron nitride (h-BN) domains of a few layers (one-four layers) from ammonia borane by adding a small quartz tube to stabilize the gas flow over the copper substrate and reducing the growing rate of h-BN. The h-BN grows freely and spontaneously to form triangular domains on the Cu (100) plane. The triangular domains are prone to be parallel to each other on the copper substrate. The h-BN domains grow by extending in the normal direction of the triangle and form a large thin film by joining together. Both the size and coverage rate on Cu foils are well controlled by tuning the amount of ammonia borane.

Topology evolution of graphene in chemical vapor deposition, a combined theoretical/experimental approach toward shape control of graphene domains.

Morphology control of thin film relies on understanding multiple ongoing processes during deposition and growth. To reveal the shape evolution of graphene domains on copper surfaces in chemical vapor deposition (CVD), a combinative study is performed on the CVD growth of graphene on copper surfaces. To identify the factors that influence the adsorption and diffusion of carbon atoms and further determine the domain shape, simulations based on kinetic Monte Carlo techniques are carried out. The results reveal the dependence of the graphene domain shapes on the crystalline orientation of the underlying copper substrate surfaces.

Sharp burnout failure observed in high current-carrying double-walled carbon nanotube fibers.

We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 µm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 10(5) S m(-1) and over 1 × 10(5) A cm(-2) in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers.

Preparation of highly oxidized nitrogen-doped carbon nanotubes.

A method for the preparation of highly oxidized nitrogen-doped carbon nanotubes (N-CNTs) from KMnO(4) + H(2)SO(4) solution is described. The atomic ratio of C/O in oxidized N-CNTs is as low as 1.2. The x-ray photoelectron spectroscopy results show that about 75% of the carbon atoms are oxidized and bound to oxygen-containing functional groups. The oxidation reaction mainly occurs at the outer sidewalls, which destroys the graphene stack to an sp(3)-rich structure and helps to preserve the tubular structure of the inner N-CNTs. The oxidized N-CNTs show an energy gap of ~2.1 eV.

Wire-supported CdSe nanowire array photoelectrochemical solar cells.

Previous fiber-shaped solar cells are based on polymeric materials or dye-sensitized wide band-gap oxides. Here, we show that efficient fiber solar cells can be made from semiconducting nanostructures (e.g. CdSe) with smaller band-gap as the light absorption material. We directly grow a vertical array of CdSe nanowires uniformly around a core metal wire and make the device by covering the top of nanowires with a carbon nanotube (CNT) film as the porous transparent electrode. The CdSe-CNT fiber solar cells show power conversion efficiencies of 1-2% under AM 1.5 illumination after the nanowires are infiltrated with redox electrolyte. We do not use a secondary metal wire (e.g. Pt) as in conventional fiber-shaped devices, instead, the end part of the CNT film is condensed into a conductive yarn to serve as the secondary electrode. In addition, our CdSe nanowire-based photoelectrochemical fiber solar cells maintain good flexibility and stable performance upon rotation and bending to large angles.

Strong and reversible modulation of carbon nanotube-silicon heterojunction solar cells by an interfacial oxide layer.

Deposition of nanostructures such as carbon nanotubes on Si wafers to make heterojunction structures is a promising route toward high efficiency solar cells with reduced cost. Here, we show a significant enhancement in the cell characteristics and power conversion efficiency by growing a silicon oxide layer at the interface between the nanotube film and Si substrate. The cell efficiency increases steadily from 0.5% without interfacial oxide to 8.8% with an optimal oxide thickness of about 1 nm. This systematic study reveals that formation of an oxide layer switches charge transport from thermionic emission to a mixture of thermionic emission and tunneling and improves overall diode properties, which are critical factors for tailoring the cell behavior. By controlled formation and removal of interfacial oxide, we demonstrate oscillation of the cell parameters between two extreme states, where the cell efficiency can be reversibly altered by a factor of 500. Our results suggest that the oxide layer plays an important role in Si-based photovoltaics, and it might be utilized to tune the cell performance in various nanostructure-Si heterojunction structures.