Horizontally Aligned Research Articles

Lithium-Induced Reorientation of Few-Layer MoS2 Films.

Molybdenum disulfide (MoS2) few-layer films have gained considerable attention for their possible applications in electronics and optics and also as a promising material for energy conversion and storage. Intercalating alkali metals, such as lithium, offers the opportunity to engineer the electronic properties of MoS2. However, the influence of lithium on the growth of MoS2 layers has not been fully explored. Here, we have studied how lithium affects the structural and optical properties of the MoS2 few-layer films prepared using a new method based on one-zone sulfurization with Li2S as a source of lithium. This method enables incorporation of Li into octahedral and tetrahedral sites of the already prepared MoS2 films or during MoS2 formation. Our results discover an important effect of lithium promoting the epitaxial growth and horizontal alignment of the films. Moreover, we have observed a vertical-to-horizontal reorientation in vertically aligned MoS2 films upon lithiation. The measurements show long-term stability and preserved chemical composition of the horizontally aligned Li-doped MoS2.

Effects of head-elevated position on tracheal intubation using a McGrath MAC videolaryngoscope in patients with a simulated difficult airway: a prospective randomized crossover study

BackgroundThe head-elevated laryngoscopy position has been described to be optimal for intubation, particularly in obese patients and those with anticipated difficult airways. Horizontal alignment of the external auditory meatus and sternal notch (AM-S) can be used as endpoints for optimal positioning. Thus, we aligned the head-elevated position with the AM-S in the horizontal plane and evaluated its effect on laryngeal visualization and ease of intubation using a McGrath MAC videolaryngoscope in patients with a simulated difficult airway.MethodsSixty-four patients were included in this prospective, crossover, randomized controlled trial. A cervical collar was used to restrict neck movement and mouth opening. The head-elevated position was achieved by raising the back section of the operation room table and ensuring that the end point was horizontally aligned with the AM-S (table-ramp method). The laryngeal view was randomly assessed in both head-flat and head-elevated positions based on the percentage of glottic opening (POGO) score and modified Cormack–Lehane (MCL) grade. External laryngeal manipulation was not permitted when laryngeal visualization was scored. The trachea was intubated only once (in the second position). The ease of intubation was assessed based on the need for optimization maneuvers, intubation difficulty scale (IDS) scores and time to intubation.ResultsThe mean table-ramp angle required to achieve the horizontal alignment of AM-S was 17.5 ± 4.1°. The mean POGO score improved significantly in the head-elevated position (59.4 ± 23.8%) when compared with the head-flat position (37.5 ± 24%) (P < 0.0001). MCL grade 1 or 2a was achieved in 56 (85.9%) and 28 (43.7%) of patients in the head-elevated and head-flat positions, respectively (P < 0.0001). Optimization maneuvers for intubation were required in 7 (21.9%) and 17 (53.1%) patients in the head-elevated and head-flat positions, respectively (P < 0.0001). The IDS scores and time to intubation did not differ significantly between the two positions.ConclusionIn the head-elevated position, aligning the AM-S in the horizontal plane consistently improved laryngeal visualization without worsening the view when the McGrath MAC videolaryngoscope was used in patients with simulated difficult airways. It also improved the ease of intubation, which reduced the need for optimization maneuvers.Trial registrationThis trial was registered with www.clinicaltrials.gov, NCT04716218, on 20/01/2021.

3D Printed MXene Aerogels with Truly 3D Macrostructure and Highly Engineered Microstructure for Enhanced Electrical and Electrochemical Performance.

Assembling 2D materials such as MXenes into functional 3D aerogels using 3D printing technologies gains attention due to simplicity of fabrication, customized geometry and physical properties, and improved performance. Also, the establishment of straightforward electrode fabrication methods with the aim to hinder the restack and/or aggregation of electrode materials, which limits the performance of the electrode, is of great significant. In this study, unidirectional freeze casting and inkjet-based 3D printing are combined to fabricate macroscopic porous aerogels with vertically aligned Ti3 C2 Tx sheets. The fabrication method is developed to easily control the aerogel microstructure and alignment of the MXene sheets. The aerogels show excellent electromechanical performance so that they can withstand almost 50% compression before recovering to the original shape and maintain their electrical conductivities during continuous compression cycles. To enhance the electrochemical performance, an inkjet-printed MXene current collector layer is added with horizontally aligned MXene sheets. This combines the superior electrical conductivity of the current collector layer with the improved ionic diffusion provided by the porous electrode. The cells fabricated with horizontal MXene sheets alignment as current collector with subsequent vertical MXene sheets alignment layers show the best electrochemical performance with thickness-independent capacitive behavior.

Deep Blue Fluorescent Material with an Extremely High Ratio of Horizontal Orientation to Enhance Light Outcoupling Efficiency (44%) and External Quantum Efficiency in Doped and Non-Doped Organic Light-Emitting Diodes

A novel bis-4Ph-substituted 9,10-dipehnylanthracene deep blue [1931 CIE (0.15, 0.08)] fluorescent compound, AnB4Ph, has been synthesized and characterized for organic light-emitting diode (OLED) applications. Our experimental study of AnB4Ph excludes the possibility of triplet-triplet annihilation, hybridized local and charge transfer, or thermally activated delayed fluorescent characteristics of the material. Since the solid-state photoluminescence quantum yield of AnB4Ph was determined to be 48%, assuming a 100% for the charge recombination efficiency, the light outcoupling efficiency (ηout) of an AnB4Ph non-doped OLED achieving an external quantum efficiency (EQE) of 5.3% is at least 44%, which is more than twofold higher than 20% for conventional OLEDs. Both grazing incidence wide-angle X-ray scattering (GIWAXS) and angle-dependent photoluminescence (ADPL) measurements reveal AnB4Ph having a high value of order parameter (SGIWAXS) of 0.61 for a ππ stacking along the normal direction and an orientation order parameter (SADPL) for a horizontal emitting dipole moment of -0.50 or Θ (horizontal-dipole ratios) of 100%, respectively. Otherwise, a refractive index (n) measurement provides a n = 1.80 for AnB4Ph thin films. Based on ηout = 1.2 × n-2, the calculated ηout is 37%, which is also in accordance with the results of GIWAXS and ADPL. We have also fabricated the classical fluorescent DPAVBi-doped AnB4Ph OLEDs, which display a true blue [1931 CIE (0.15 and 0.16)] electroluminescence with a high efficiency (EQE = 6.9%), surpassing the conventional ∼5% EQE. Based on an ηout of 42% for DPAVBi-doped AnB4Ph OLEDs, our studies suggest that the extremely horizontally aligned AnB4Ph host material exerts the same horizontal alignment on the DPAVBi dopant molecules.

Correlation Between the Crystalline Phase of Molybdenum Oxide and Horizontal Alignment in Thin MoS2 Films

The crystallographic alignment of an ultrathin MoS2 film strongly influences its properties and is, therefore, substantial for various applications. Developing methods for controlled growth is of primary importance for reproducible film fabrication. Among them, sulfurization of predeposited molybdenum or molybdenum oxide films is a method capable of growing large-area MoS2 layers with reasonable control over the layer alignment. However, the question of which growth parameters define the layer alignment still remains unresolved. We prepared 10 nm thick films of Mo and Mo oxides with different degrees of crystallinity and sulfurized them all under the same conditions. We demonstrate that the presence of the crystalline phase of MoO2 or MoO3 in the parent films promotes the growth of the horizontally aligned (HA) MoS2. This observation provides a simple criterion for controlling the layer alignment and for the growth of horizontal MoS2 layers of thicknesses at which only the vertical layers have hitherto been assumed to grow.

Nearly 40% outcoupling efficiency in OLEDs with all-metal electrodes

Due to its high transparency and low sheet resistance, indium tin oxide (ITO) has been the material of choice for transparent anodes in organic light-emitting diodes (OLEDs). Indium tin oxide, however, is a source of outcoupling loss due to waveguiding and reduced mechanical stability on flexible/stretchable substrates due to its brittle nature. We demonstrate that highly efficient ITO-free OLEDs can be achieved using high quality silver electrodes and horizontally aligned dipole emitters to avoid plasmonic losses. Using an ultrathin Ag/MPTMS anode and a partially aligned phosphorescent emitter, we demonstrate OLEDs with 30% EQE, luminous efficiency exceeding 130 lm/W, and low leakage current. In addition, we demonstrate OLEDs with an optimized structure showing a 36.1% outcoupling efficiency. Theoretical calculations show that our approach can yield up to 48.4% outcoupling efficiency for perfect horizontal alignment, which exceeds the maximum achievable with ITO. The combination of a silver anode and a horizontal phosphorescent emitter is promising for the future design of ultra-efficient flexible OLEDs.

Effect of morphology on the electrophoretic deposition of hydroxyapatite nanoparticles

Electrophoretic deposition (EPD) was performed from alcoholic suspensions of spherical (SHA) and fiber (FHA) hydroxyapatite nanoparticles. FHA particles were horizontally aligned in deposits prepared at lower voltages since they can find enough space and time to rotate upon reaching the deposit and sit horizontally on it. While, they are more randomly oriented at higher voltages since more FHA particles aligned parallel to electric field reach to the substrate and also particles cannot find enough time and space for rotation. FHA particles are highly interlocked together in FHA deposits reinforcing them and also the drying shrinkages are lower for them resulting in their less cracking. The cracks are parallel to each other in FHA coating deposited from methanolic suspension at 5 V due to the more horizontal and parallel alignment of FHA particles in it. The crack-free SHA coating decreased the corrosion rate of substrate more efficiently due to its less porosity.

Label-free electronic detection of interleukin-6 using horizontally aligned carbon nanotubes

A facile, sensitive, and label-free assay for detection of interleukin-6 (IL-6) using liquid-gated field-effect transistor (FET) sensors based on horizontally aligned single-walled carbon nanotubes (SWCNT) is proposed. This approach relies on the drain current (Id) responses of the transistor upon interactions of IL-6 with its corresponding antibody (IL-6R) immobilized on SWCNT. The proposed immunosensor exhibits superior sensitivity (limit-of-detection=1.37pg/mL) in virtue of the reduced tube-to-tube contact resistance, good selectivity (no responses to bovine serum albumin and cysteine were observed and detection of target molecules in serum was achieved) as a result of the highly specific interaction between IL-6 and IL-6R, and excellent stability (no significant degradation in the electronic performance after storage under ambient conditions for up to 3months) in virtue of the strong adhesion of CNT to the quartz substrate and good horizontal alignment of these tubes. Therefore, the proposed immunosensor is a promising platform for early diagnosis of various diseases (including some cancers) that can be indicated by the circulating level of IL-6.

Configurations for single-scale cylinder pairs in natural convection

A thermal-fluid system consisting of an isothermal heated cylinder pair cooled naturally in air is examined. The single-scale cylinder pairs are horizontally orientated and investigated in both horizontal and vertical alignment to determine if optimal configurations exist which maximize heat dissipation at the local cylinder and global array levels. Numerical and experimental approaches are used to assess cylinder interactions in the laminar flow regime 104 ≤ RaD ≤ 105. Experimental measurements and numerical predictions confirm the scaling relationships determined using scale analyses and intersection of asymptotes methods. The optimal horizontally aligned configuration was found when the separation distance resulted in merging of the thermal boundary layers of adjacent cylinders, hence confirming the constructal approach for this geometry and flow regime. Similar separation distance result from combined objectives of maximizing local cylinder and overall array heat transfer performance. In contrast, vertically aligned pairs have multiple constructal configurations and depend on the significance of internal local convective resistances. Upper cylinder Nusselt number is enhanced over a single cylinder when the combined effects of lower cylinder plume velocity and temperature impose a beneficial buoyancy-assisted flow. Through defining the plume characteristics and applying a mixed convection analogy, a prediction of the local and global thermal performances is presented.

Horizontally suspended carbon nanotube bundles patterned on silicon trench sidewalls

The strong interaction between horizontally aligned carbon nanotubes (CNTs) and the growth substrate has long been impeding the application of CNTs in micro/nano electronics, the shape and dimension of densely packed CNT bundles are also highly desirable in interconnects and sensor applications. In this paper, we report a method to grow horizontally suspended carbon nanotube (HSCNT) bundles patterned on selected silicon trench sidewalls. Semiconductor microfabrication technologies were employed to prepare the growth substrate, and the key process is to pattern an iron (Fe) catalyst layer onto selected silicon trench sidewalls via a shadow mask placed on top of silicon trenches by the tilted electron beam evaporation technique. The CNT growth process was conducted in a conventional thermal chemical vapour deposition (TCVD) furnace. The resultant CNTs are densely packed in bundles with very good horizontal alignment, their interactions with the silicon trench bottom are negligible since they are horizontally suspended from desired trench sidewalls. On the other hand, the dimension and shape of these HSCNT bundles were determined by the CNT growth duration, the deposition direction of the Fe catalyst relative to the substrate, and the open windows in the shadow mask. These results will facilitate the application of CNTs in micro/nano electronics.

Helical graphite

One-handed helical graphite films with a structure controlled by that of the original iodine-doped helical polyacetylene (H-PA) films were prepared using the recently developed morphology-retaining carbonization method. The fibrillar structure of the H-PA film remains unchanged even after carbonization at 800 °C. The weight loss of the film due to carbonization was very small; only 10–29% of the weight of the film before doping was lost. Furthermore, the graphite film prepared by subsequent heating at 2600 °C retained the same structure as that of the precursor films. The screw direction, degree of twist, and vertical or horizontal alignment of the helical graphite film were well controlled by changing the sense and pitch of the helix, and the orientation of the chiral nematic liquid crystal (N*-LC) used as an asymmetric LC reaction field. The important potential of these graphite films is exemplified in their electrical properties. The horizontally aligned helical graphite film exhibits an increase in electrical conductivity compared to the nonaligned one. The aligned helical graphite film also shows an electrical anisotropy in which conductivity parallel to the helical axis of the fibril bundle is higher than that perpendicular to the axis. [TANSO 2013 (No. 258) 201–9.]

Step-edge induced ordered growth: targeting to assemble super long horizontal nanowire alignment in large-scale

Nowadays, the development of nano-synthesis has turned to controllable design for specific demands in micro-nano device application, to be integrated into functional units more conveniently with low-cost and efficiency principles. In this case, an appropriate approach for directly obtaining horizontally aligned nanowires in a large scale would be of great significance in future micro-nano device integration. Here, on the HOPG surface, we managed to achieve this. The approach is versatile to various kinds of materials. Horizontally aligned nanowires of Al-C based materials, such as Al4C3 and Al4O4C, were achieved. All of the nanowires exhibit a high degree ordered alignments and possess super aspect ratios with uniform widths of about 100 nm and lengths on the millimeter level. We believe the assembly mechanism lies in a step-edge induced ordered growth process, through which quaternary Al-Si-O-C nanoball alignment could also be obtained. It is expected that this method could be beneficial to adjust many useful materials for micro device integration in the future.

Temperature and Chemical Bonding‐Directed Self‐Assembly of Cobalt Phosphide Nanowires in Reaction Solutions into Vertical and Horizontal Alignments

The preparation of vertically or horizontally aligned self-assemblies of CoP nanowires is demonstrated for the first time by aging them in the reaction solution for a sufficient time at 20 or 0 °C. This strategy opens up a way for exploring the controlled self-assembly of various highly anisotropic nanostructures into long-range ordered structures with collective properties.

CVD‐Grown Horizontally Aligned Single‐Walled Carbon Nanotubes: Synthesis Routes and Growth Mechanisms

Single-walled carbon nanotubes (SWCNTs) have attractive electrical and physical properties, which make them very promising for use in various applications. For some applications however, in particular those involving electronics, SWCNTs need to be synthesized with a high degree of control with respect to yield, length, alignment, diameter, and chirality. With this in mind, a great deal of effort is being directed to the precision control of vertically and horizontally aligned nanotubes. In this review the focus is on the latter, horizontally aligned tubes grown by chemical vapor deposition (CVD). The reader is provided with an in-depth review of the established vapor deposition orientation techniques. Detailed discussions on the characterization routes, growth parameters, and growth mechanisms are also provided.

Size engineering of metal nanoparticles to diameter-specified growth of single-walled carbon nanotubes with horizontal alignment on quartz

The electronic, physical and optical properties of single-walled carbon nanotubes (SWNTs) are governed by their diameter and chirality, and thus much research has been focused on controlling the diameter and chirality of SWNTs. To date, control of the catalyst particle size has been thought to be one of the most promising approaches to control the diameter or chirality of SWNTs owing to the correlation between catalyst particle size and tube diameter. In this study, we demonstrate the size engineering of catalytic nanoparticles for the controlled growth of diameter-specified and horizontally aligned SWNTs on quartz substrates. Uniformly sized iron nanoparticles derived from ferritin molecules were used as a catalyst, and their size was intentionally decreased via thermal heat treatment at 900 °C under atmospheric Ar ambient. ST-cut quartz wafers were used as growth substrates in order to elucidate the effect of the size of the nanoparticles on the tube diameter and the effect of catalyst size on the degree of parallel alignment on the quartz substrates. SWNTs grown by chemical vapor deposition using methane as feedstock exhibited a high degree of horizontal alignment when the particle density was low enough to produce individual SWNTs without bundling. Annealing for 60 min at 900 °C produced a reduction of nanoparticle diameter from 2.6 to 1.8 nm and a decrease in the mean tube diameter from 1.2 to 0.8 nm, respectively. Raman spectroscopy results corroborated the observation that prolonged heat treatment of nanoparticles yields thinner tubes with narrower size distributions. The results of this work suggest that straightforward thermal annealing can be a facile way to obtain uniform-sized SWNTs as well as catalytic nanoparticles.

Radar Scattering from Ice Aggregates Using the Horizontally Aligned Oblate Spheroid Approximation

AbstractThe assumed relationship between ice particle mass and size is profoundly important in radar retrievals of ice clouds, but, for millimeter-wave radars, shape and preferred orientation are important as well. In this paper the authors first examine the consequences of the fact that the widely used “Brown and Francis” mass–size relationship has often been applied to maximum particle dimension observed by aircraftDmaxrather than to the mean of the particle dimensions in two orthogonal directionsDmean, which was originally used by Brown and Francis. Analysis of particle images reveals thatDmax≃ 1.25Dmean, and therefore, for clouds for which this mass–size relationship holds, the consequences are overestimates of ice water content by around 53% and of Rayleigh-scattering radar reflectivity factor by 3.7 dB. Simultaneous radar and aircraft measurements demonstrate that much better agreement in reflectivity factor is provided by using this mass–size relationship withDmean. The authors then examine the importance of particle shape and fall orientation for millimeter-wave radars. Simultaneous radar measurements and aircraft calculations of differential reflectivity and dual-wavelength ratio are presented to demonstrate that ice particles may usually be treated as horizontally aligned oblate spheroids with an axial ratio of 0.6, consistent with them being aggregates. An accurate formula is presented for the backscatter cross section apparent to a vertically pointing millimeter-wave radar on the basis of a modified version of Rayleigh–Gans theory. It is then shown that the consequence of treating ice particles as Mie-scattering spheres is to substantially underestimate millimeter-wave reflectivity factor when millimeter-sized particles are present, which can lead to retrieved ice water content being overestimated by a factor of 4.

Hierarchically Controlled Helical Graphite Films Prepared from Iodine-Doped Helical Polyacetylene Films Using Morphology-Retaining Carbonization

One-handed helical graphite films with a hierarchically controlled morphology were prepared from iodine-doped helical polyacetylene (H-PA) films using the recently developed morphology-retaining carbonization method. Results from scanning electron microscopy indicate that the hierarchical helical morphology of the H-PA film remains unchanged even after carbonization at 800 °C. The weight loss of the film due to carbonization was very small; only 10-29% of the weight of the film before doping was lost. Furthermore, the graphite film prepared by subsequent heating at 2600 °C retained the same morphology as that of the original H-PA film and that of the helical carbon film prepared at 800 °C. The screwed direction, twisted degree, and vertical or horizontal alignment of the helical graphite film were well controlled by changing the helical sense, helical pitch, and orientation state of the chiral nematic liquid crystal (N*-LC) used as an asymmetric LC reaction field. X-ray diffraction and Raman scattering measurements showed that graphitic crystallization proceeds in the carbon film during heat treatment at 2600 °C. Transmission electron microscopy measurements indicate that ultrasonication of the helical graphite film in ethanol for several hours gives rise to a single helical graphite fibril. The profound potentiality of the present graphite films is exemplified in their electrical properties. The horizontally aligned helical graphite film exhibits an enhancement in electrical conductivity and an evolution of electrical anisotropy in which conductivity parallel to the helical axis of the fibril bundle is higher than that perpendicular to the axis.

Ultrahigh-Vacuum-Assisted Control of Metal Nanoparticles for Horizontally Aligned Single-Walled Carbon Nanotubes with Extraordinary Uniform Diameters

Uniform diameter, horizontally aligned single-walled carbon nanotubes (SWNTs) are grown on sapphire substrate through the control of Fe nanoparticle size by annealing in ultrahigh vacuum (UHV). We find that thermal annealing in UHV reduces the Fe nanoparticle size and significantly narrows their size distribution. These size-controlled Fe nanoparticles enable the catalytic growth of uniform-diameter SWNTs while maintaining their horizontal alignment. Systematic analyses of Raman radial breathing modes with three laser wavelengths indicate that ∼76% of the horizontally aligned SWNTs have diameters in the range of 1.3–1.4 nm under optimized annealing conditions. Longer UHV annealing induces the increase in the Fe nanoparticle size, giving large-diameter SWNTs. Precise correlation between the metal nanoparticle size and SWNT diameter is demonstrated. Effects of UHV annealing on the nanoparticle size are discussed in terms of evaporation, subsurface diffusion, and surface precipitation of catalyst metals.

Growth of horizontally aligned dense carbon nanotubes from trench sidewalls

Horizontally aligned, dense carbon nanotubes (HADCNTs) in the form of CNTcantilevers/bridges were grown from selected trench sidewalls in silicon substrate bychemical vapor deposition (CVD). The as-grown CNT cantilevers/bridges are packedwith multiwalled carbon nanotubes (MWCNTs) with a linear density of about10 CNTs µm − 1. The excellent horizontal alignment of these CNTs is mainly ascribed to the van der Waalsinteractions within the dense CNT bundles. What is more, the Raman intensity ratioIG/ID shows a gradual increase from the CNT roots to tips, indicating a defect gradient alongCNTs generated during their growth. These results will inspire further efforts to explorethe fundamentals and applications of HADCNTs.

Formation and mechanical characterisation of SU8 composite films reinforced with horizontally aligned and high volume fraction CNTs

Carbon nanotube (CNT) reinforced composites have been identified as promising structural materials for the mechanical components of microelectromechanical systems (MEMS), potentially leading to advanced performance. High alignment and volume fraction of CNTs in the composites are the prerequisites to achieve such desirable mechanical characteristics. In particular, horizontal CNT alignment in composite films is necessary to enable high longitudinal moduli of the composites which is crucial for the performance of microactuators. A practical process has been developed to transfer CNT arrays from vertical to horizontal alignment which is followed by in situ wetting, realign and pressurized consolidation processes, which lead to a high CNT volume fraction in the range of 46–63%. As a result, SU8 epoxy composite films reinforced with horizontally aligned CNTs and a high volume faction of CNTs have been achieved with outstanding mechanical characteristics. The transverse modulus of the composite films has been characterised through nanoindentation and the longitudinal elastic modulus has been investigated. An experimental transverse modulus of 9.6 GPa and an inferred longitudinal modulus in the range of 460–630 GPa have been achieved, which demonstrate effective CNT reinforcement in the SU8 matrix.