In-plane Alignment Research Articles

Modeling of planar germanium hole qubits in electric and magnetic fields

Hole-based spin qubits in strained planar germanium quantum wells have received considerable attention due to their favorable properties and remarkable experimental progress. The sizeable spin-orbit interaction in this structure allows for efficient qubit operations with electric fields. However, it also couples the qubit to electrical noise. In this work, we perform simulations of a heterostructure hosting these hole spin qubits. We solve the effective mass equations for a realistic heterostructure, provide a set of analytical basis wavefunctions, and compute the effective g-factor of the heavy-hole ground state. Our investigations reveal a strong impact of highly excited light-hole states located outside the quantum well on the g-factor. We find that sweet spots, points of operations that are least susceptible to charge noise, for out-of-plane magnetic fields are shifted to impractically large electric fields. However, for magnetic fields close to in-plane alignment, partial sweet spots at low electric fields are recovered. Furthermore, sweet spots with respect to multiple fluctuating charge traps can be found under certain circumstances for different magnetic field alignments. This work will be helpful in understanding and improving the coherence of germanium hole spin qubits.

Effects of three-dimensional femur and tibia postures on the parameters of standing long-leg radiographs for osteoarthritic knees in elderly female subjects

BackgroundLong-leg frontal radiographs of the lower extremities are used to assess knee osteoarthritis. Given the three-dimensional (3D) nature of alignment changes in osteoarthritis, postural alterations in the femur and tibia extend beyond the coronal plane (in-plane) to include the transverse and sagittal planes (out-of-plane). This study investigates the impact of these out-of-plane factors on in-plane knee alignment parameters observed in frontal radiographs. MethodsA total of 97 osteoarthritic knees in women were examined. Using a 3D-to-two-dimensional (2D) image matching technique, we evaluated the 3D postures of the femur and tibia in the standing position as viewed from frontal radiographs in the world coordinate system. Statistical analyses were conducted to explore associations between these 3D postures and 2D alignment parameters obtained from frontal radiographs under identical conditions. FindingsThe femur exhibited a medial inclination of 2.7°, a posterior inclination of 3.9°, and an internal rotation of 4.2°, whereas the tibia showed a lateral inclination of 6.4°, an anterior inclination of 6.7°, and an internal rotation of 6.7°. Both coronal and rotational postures of femur and tibia influenced the hip-knee-ankle angle, mechanical axis percentage, and medial proximal tibial angle. However, only coronal factors of tibia impacted tibial joint line obliquity relative to the floor. InterpretationAttention should be paid to the potential impact of the out-of-plane postures of the femur and tibia on parameters assessed in plain frontal radiographs of the lower extremities.

Enhancing Thermal Conductivity in Polymer Composites through Molding-Assisted Orientation of Boron Nitride.

Incrementing thermal conductivity in polymer composites through the incorporation of inorganic thermally conductive fillers is typically constrained by the requirement of high filler content. This necessity often complicates processing and adversely affects mechanical properties. This study presents the fabrication of a polystyrene (PS)/boron nitride (BN) composite exhibiting elevated thermal conductivity with a modest 10 wt% BN content, achieved through optimized compression molding. Adjustments to molding parameters, including molding-cycle numbers, temperature, and pressure, were explored. The molding process, conducted above the glass transition temperature of PS, facilitated orientational alignment of BN within the PS matrix predominantly in the in-plane direction. This orientation, achieved at low filler loading, resulted in a threefold enhancement of thermal conductivity following a single molding time. Furthermore, the in-plane alignment of BN within the PS matrix was found to intensify with increased molding time and pressure, markedly boosting the in-plane thermal conductivity of the PS/BN molded composites. Within the range of molding parameters examined, the highest thermal conductivity (1.6 W/m·K) was observed in PS/BN composites subjected to five molding cycles at 140 °C and 10 MPa, without compromising mechanical properties. This study suggests that compression molding, which allows low filler content and straightforward operation, offers a viable approach for the mass production of polymer composites with superior thermal conductivity.

Interfacial structure within thin films of decane isomers adsorbed on a metal substrate

Canonical-ensemble Monte Carlo simulations were used to examine the solid–liquid interfacial structure within neat and multicomponent solutions of decane isomers at 350 K. As seen both experimentally and computationally for many fluids, layering within the liquid film near the solid substrate was exhibited in all fluids examined here. The amount of branching within a molecule, though, limited the range of density oscillations, particularly for multicomponent fluids. Analysis of molecular orientation within the first layer showed a strong preference in most cases for molecules to adopt orientations that enhance the energy of adsorption. To this end, preferential absorption was observed in all fluid mixtures with n-decane present. For both n-decane and 2,2-dimethyloctane, whether neat or in solution, the preference for orientations that maximise interactions between the alkane backbone of the molecule and the substrate led to additional in-plane alignment between adjacent adsorbed molecules. In contrast, for 4-propylheptane little in-plane alignment or orientation preference was observed at the interface.

Formation of one-dimensionally self-aligned Si-QDs and their local electron discharging properties

Self-aligned Si-quantum-dots (Si-QDs) with an areal density as high as ∼1011 cm−2 have been fabricated on ultrathin SiO2 by using a ∼4.5 nm thick poly-Si on insulator (SOI) substrate, and controlling low-pressure CVD using monosilane (SiH4), and followed by thermal oxidation. By controlling the thermal oxidation processes of Si-QDs and the poly-Si layer, we have successfully demonstrated the vertical alignment of Si-QDs, where the Si-QDs are also used as a shadow mask of the underlying poly-Si layer. We also demonstrated in-plane alignment of the one-dimensionally self-aligned Si-QDs on line-patterned SiO2. In addition, from surface potential measurements by using atomic force microscopy/Kelvin probe force microscopy, we confirmed that the initial surface potential change caused by valence electron extraction from the dots to the tip was stably maintained until ∼120 min, implying the quantum confinement effect at discrete energy levels of the upper and lower-QDs.

Applications of the Peach-Koehler force in liquid crystals

ABSTRACT In solids, external stress induces the Peach-Koehler force, which drives dislocations to move. Similarly, in liquid crystals, an external angular stress creates an analogous force, which drives disclinations to move. In this work, we develop a method to calculate the relevant angular stress either analytically or numerically, and hence to determine the force on a disclination. We demonstrate this method by applying the Peach-Koehler force theory to four problems: (a) Single disclination in a liquid crystal cell between two uniform in-plane alignments perpendicular to each other. (b) Array of disclinations in a liquid crystal cell with patterned substrates. (c) Pair of disclinations in a long capillary tube with homeotropic anchoring. (d) Radial hedgehog or disclination loop inside a sphere with homeotropic anchoring, and its response to an applied magnetic field. In all of these problems, the Peach-Koehler force theory predicts the equilibrium defect structure, and the predictions are consistent with the results of minimising the total free energy.

Langmuir–Blodgett assisted alignment of 2D nanosheets in polymer nanocomposites for high-temperature dielectric energy storage applications

The Langmuir–Blodgett deposition technique enables a precise in-plane alignment and a densely packed arrangement of CNO nanosheets within the PEI matrix, resulting in a significant enhancement of energy storage performance at 150 °C.

Bilayer-structured carbon nanotube/ethylene–vinyl acetate flexible strain sensors with enhanced sensing performance prepared by biaxial stretching

Conductive polymer composites (CPCs) consisting of polymer materials and conductive nanofillers have excellent flexibility, ease of processing, as well as excellent mechanical and electrical properties, resulting in an enormous application potential in flexible strain sensors and other fields. In this paper, a flexible strain sensor consisting of an ethylene–vinyl acetate (EVA) copolymer/carbon nanotube (CNT) CPC with a bilayer structure was prepared by biaxial stretching. The results indicated that the conductivity of the composites gradually decreased as the stretching ratio (SR) increased, due to the major destruction to the conductive network caused by biaxial stretching. Biaxial deformation facilitates the dispersion and in-plane alignment of CNTs, thereby enhancing the property of the sensor. Compared with the unstretched CNT/EVA-EVA-1.0 bilayer-structured sensor [gauge factor (GF) = 89.4, monitoring range 0.5–50%], the CNT/EVA-EVA-1.5 bilayer-structured sensor (SR = 1.5) after biaxially stretched exhibited higher sensitivity (GF = 349698.2) and a wider strain monitoring range (0.5–120%). In addition, compared with monolayer CNT/EVA sensors, the bilayer-structured sensors exhibited higher stability, highlighting their good application prospects in health monitoring in the field of artificial intelligence.

Epitaxial relationship of NiO on (02) β-Ga2O3

We investigated the epitaxial relationship of an electron-beam-evaporated NiO film on a custom-ordered (02) β-Ga2O3 substrate with a surface orientation rotated by 13.8° around [010] axis relative to the commonly-used (001) substrate. X-Ray diffraction and transmission electron microscopy measurements confirmed that the film was monocrystalline with out-of-plane and in-plane alignments of (110)NiO||(02)β-Ga2O3 and NiO||[010]β-Ga2O3, respectively, indicating that the film grew on the substrate while maintaining the orientation of the cubic-close-packed (ccp) oxygen sublattice across the interface. The use of the low-index (110) epitaxial plane within the ccp lattice may be preferred for pn-heterojunctions over the higher-index (331) plane on the (001) β-Ga2O3 substrate.

Full polarization reversal at room temperature in unsubstituted AlN

Room temperature ferroelectricity in unsubstituted AlN films is studied to examine the role of cation substitution into wurtzite materials. AlN and (Al0.7Sc0.3)N films deposited on (111) 0.5 wt. % Nb-doped SrTiO3 have a (0001)-orientation with different in-plane lattice alignments with respect to those of the substrate, depending on the composition and the deposition temperature. The AlN films deposited at 450 °C showed complete ferroelectric switching above 140 °C but local polarization switching at room temperature because a dielectric breakdown occurred before complete switching, while full polarization reversal was observed at all measurement temperatures for (Al0.7Sc0.3)N. Low-temperature deposition, such as at 250 °C, significantly enhanced the dielectric breakdown field and also increased leakage current. As a result, sufficient polarization switching at room temperature was observed in the AlN film deposited at 250 °C. Positive-up/negative-down pulse measurements showed remanent polarization of 150 μC/cm2 and a coercive field of 8.3 MV/cm, in agreement with the theoretical value and temperature dependence observed for the AlN film deposited at 450 °C. The observed coercive field value lies on the line composed of the previously reported data in Sc concentration dependence. This tendency implies that the reduction in the coercive field is primarily attributable to the alteration of crystal lattice anisotropy caused by Sc.

Large-Area MoS2 Films Grown on Sapphire and GaN Substrates by Pulsed Laser Deposition.

In this paper, we present the preparation of few-layer MoS2 films on single-crystal sapphire, as well as on heteroepitaxial GaN templates on sapphire substrates, using the pulsed laser deposition (PLD) technique. Detailed structural and chemical characterization of the films were performed using Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction measurements, and high-resolution transmission electron microscopy. According to X-ray diffraction studies, the films exhibit epitaxial growth, indicating a good in-plane alignment. Furthermore, the films demonstrate uniform thickness on large areas, as confirmed by Raman spectroscopy. The lateral electrical current transport of the MoS2 grown on sapphire was investigated by temperature (T)-dependent sheet resistance and Hall effect measurements, showing a high n-type doping of the semiconducting films (ns from ~1 × 1013 to ~3.4 × 1013 cm-2 from T = 300 K to 500 K), with a donor ionization energy of Ei = 93 ± 8 meV and a mobility decreasing with T. Finally, the vertical current injection across the MoS2/GaN heterojunction was investigated by means of conductive atomic force microscopy, showing the rectifying behavior of the I-V characteristics with a Schottky barrier height of ϕB ≈ 0.36 eV. The obtained results pave the way for the scalable application of PLD-grown MoS2 on GaN in electronics/optoelectronics.

Rheological characterization and macroscopic modeling and simulation of the molding process of a PA6 Glass Mat Thermoplastic (GMT)

This study targets the characterization and modeling of GMT press molding. The targeted material is TEPEX® flowcore, a long glass fiber mat reinforced polyamide (PA6/GF) manufactured by Lanxess. Press molding of flowcore comprises the sequential stages of material forming and material flow, including challenges like local wrinkling and incomplete mold filling, respectively. Therefore, a sequential modeling approach using a Lagrangian and an Eulerian discretization is pursued. Rheological characterization using rheometer setups and in-mold viscosity measurements reveals a significant anisotropy of viscosity resulting from the predominantly in-plane fiber alignment. Anisotropy of viscosity is successfully modeled and parameterized, enabling a unified material modeling for material forming and material flow. Good predictions are observed for both wrinkling and flow. In summary, molding simulation results reveal that the isotropic modeling of viscosity is sufficient for flow simulation, whereas considering the anisotropic viscosity is essential for the accurate prediction of material forming.

Tunable three-dimensional architecture of nematic disclination lines

Disclination lines play a key role in many physical processes, from the fracture of materials to the formation of the early universe. Achieving versatile control over disclinations is key to developing novel electro-optical devices, programmable origami, directed colloidal assembly, and controlling active matter. Here, we introduce a theoretical framework to tailor three-dimensional disclination architecture in nematic liquid crystals experimentally. We produce quantitative predictions for the connectivity and shape of disclination lines found in nematics confined between two thinly spaced glass substrates with strong patterned planar anchoring. By drawing an analogy between nematic liquid crystals and magnetostatics, we find that i) disclination lines connect defects with the same topological charge on opposite surfaces and ii) disclination lines are attracted to regions of the highest twist. Using polarized light to pattern the in-plane alignment of liquid crystal molecules, we test these predictions experimentally and identify critical parameters that tune the disclination lines' curvature. We verify our predictions with computer simulations and find nondimensional parameters enabling us to match experiments and simulations at different length scales. Our work provides a powerful method to understand and practically control defect lines in nematic liquid crystals.

Laser powder bed fusion of 316L stainless steel with 2 wt.% nanosized SiO2 additives: Powder processing and consolidation

Gas atomized 316L stainless steel powder was processed with 2 wt.% of nanosized SiO2 in a planetary ball milling (BM) system to produce feedstock material for laser powder bed fusion (L-PBF). X-ray diffraction (XRD) of powders revealed the development of micro-strains over increasing milling durations and the strain-induced ferrite formation. BM was limited in duration to preserve the austenitic phase and morphological characteristics analyzed by electron microscopy. In turn, 316L-2wt.% SiO2 feedstock powder was consolidated by L-PBF with varied process parameters and scanning strategies, that demonstrated a maximum density of 7.84 g/cm3 and relatively stable microhardness values close to 220 HV. A distinct (110) preferred orientation was observed in XRD pole figures of austenite for deeper melt pools over the building direction, whereas in-plane alignment reflected variations in scanning strategy. Furthermore, electron backscatter diffraction revealed columnar grains accompanied by the suspected depletion of SiO2, while electrochemical behavior displayed consistent characteristics.

Effect of in-plane alignment on selective area grown homo-epitaxial nanowires

In-plane selective area growth (SAG) of III–V nanowires (NWs) has emerged as a scalable materials platform for quantum electronics and photonics applications. Most applications impose strict requirements on the material characteristics which makes optimization of the crystal quality vital. Alignment of in-plane SAG NWs with respect to the substrate symmetry is of importance due to the large substrate-NW interface as well as to obtain nanostructures with well-defined facets. Understanding the role of mis-orientation is thus important for designing devices and interpretation of electrical performance of devices. Here we study the effect of mis-orientation on morphology of selectively grown NWs oriented along the [1 1̅ 1̅] direction on GaAs(2 1 1)B. Atomic force microscopy is performed to extract facet roughness as a measure of structural quality. Further, we evaluate the dependence of material incorporation in NWs on the orientation and present the facet evolution in between two high symmetry in-plane orientations. By investigating the length dependence of NW morphology, we find that the morphology of ≈1 μm long nominally aligned NWs remains unaffected by the unintentional misalignment associated with the processing and alignment of the sample under study. Finally, we show that using Sb as a surfactant during growth improves root-mean-square facet roughness for large misalignment but does not lower it for nominally aligned NWs.

Epitaxial tin selenide thin film thermoelectrics

To enable the realization of miniaturized thermoelectric energy generation (TEG) devices for autonomous wireless sensors, high-quality thin film architectures are required. Although tin selenide (SnSe) has been identified as a promising thermoelectric material exhibiting ZT values up to 2.6 at 923 K for single crystals, most thin film studies evaluated polycrystalline or textured SnSe samples. Here, we have explored for the first time the impact of epitaxial alignment of the orthorhombic SnSe crystal structure on an orthorhombic DyScO3 substrate, in strong contrast to the few previous studies on cubic substrates. The achieved (100)-oriented single crystalline SnSe thin films exhibit the formation of two SnSe domain types. The in-plane electrical conductivity along the (b,c)-plane shows an abrupt increase above 400 K instead of the typical steady increase. The in-plane Seebeck coefficients exhibit very similar values as single crystals, leading to a maximum power factor of about 6.0 μW·K−2·cm−1. For these SnSe thin films, exhibiting two domain variants with in-plane alignment of the (b,c)-plane, a typical low thermal conductivity is expected, demonstrating the effectiveness of epitaxial alignment to enhance thermoelectric performance and to enable the realization of miniaturized thermoelectric energy generation (TEG) devices for autonomous wireless sensors.

Scalable anisotropic cooling aerogels by additive freeze-casting

Cooling in buildings is vital to human well-being but inevitability consumes significant energy, adding pressure on achieving carbon neutrality. Thermally superinsulating aerogels are promising to isolate the heat for more energy-efficient cooling. However, most aerogels tend to absorb the sunlight for unwanted solar heat gain, and it is challenging to scale up the aerogel fabrication while maintaining consistent properties. Herein, we develop a thermally insulating, solar-reflective anisotropic cooling aerogel panel containing in-plane aligned pores with engineered pore walls using boron nitride nanosheets by an additive freeze-casting technique. The additive freeze-casting offers highly controllable and cumulative freezing dynamics for fabricating decimeter-scale aerogel panels with consistent in-plane pore alignments. The unique anisotropic thermo-optical properties of the nanosheets combined with in-plane pore channels enable the anisotropic cooling aerogel to deliver an ultralow out-of-plane thermal conductivity of 16.9 mW m−1 K−1 and a high solar reflectance of 97%. The excellent dual functionalities allow the anisotropic cooling aerogel to minimize both parasitic and solar heat gains when used as cooling panels under direct sunlight, achieving an up to 7 °C lower interior temperature than commercial silica aerogels. This work offers a new paradigm for the bottom-up fabrication of scalable anisotropic aerogels towards practical energy-efficient cooling applications.

Template and Temperature-Controlled Polymorph Formation in Squaraine Thin Films.

Controlling the polymorph formation in organic semiconductor thin films by the choice of processing parameters is a key factor for targeted device performance. Small molecular semiconductors such as the prototypical anilino squaraine compound with branched butyl chains as terminal functionalization (SQIB) allow both solution and vapor phase deposition methods. SQIB has been considered for various photovoltaic applications mainly as amorphous isotropic thin films due to its broad absorption within the visible to deep-red spectral range. The two known crystalline polymorphs adopting a monoclinic and orthorhombic crystal phase show characteristic Frenkel excitonic spectral signatures of overall H-type and J-type aggregates, respectively, with additional pronounced Davydov splitting. This gives a recognizable polarized optical response of crystalline thin films suitable for identification of the polymorphs. Both phases emerge with a strongly preferred out-of-plane and rather random in-plane orientation in spin-casted thin films depending on subsequent thermal annealing. By contrast, upon vapor deposition on dielectric and conductive substrates, such as silicon dioxide, potassium chloride, graphene, and gold, the polymorph expression depends basically on the choice of growth substrate. The same pronounced out-of-plane orientation is adopted in all crystalline cases, but with a surface templated in-plane alignment in case of crystalline substrates. Strikingly, the amorphous isotropic thin films obtained by vapor deposition cannot be crystallized by thermal postannealing, which is a key feature for the spin-casted thin films, here monitored by polarized in situ microscopy. Combining X-ray diffraction, atomic force microscopy, ellipsometry, and polarized spectro-microscopy, we identify the processing-dependent evolution of the crystal phases, correlating morphology and molecular orientations within the textured SQIB films.

The Use of a New Device-Assisted Needle Guidance versus Conventional Approach to Perform Ultrasound Guided Brachial Plexus Blockade: A Randomized Controlled Study.

PurposeUltrasound guidance during nerve blockade poses the challenge of maintaining in-plane alignment of the needle tip. The needle guidance device maintains needle alignment and assists with in-plane needle visualization. The purpose of this study is to evaluate the utility of this device by comparing procedure performance during brachial plexus blockade with the conventional approach.MethodsAfter the Institutional Review Board approval and obtaining informed consent, 70 patients receiving either interscalene or supraclavicular nerve blocks were randomly assigned into 2 groups, a conventional approach versus utilizing the needle guidance device. An independent observer recorded: total procedure time; needle insertion time; number of unplanned redirections; and number of reinsertions. Additionally, physician satisfaction and ease of needle visualization were assessed.ResultsData from seventy patients were analyzed. The median [25th percentile-75th percentile] time to complete the block by the device assisted needle guidance group was 3 (2–3.75) minutes and 4 (3–6) minutes in the conventional approach group (p < 0.001). Additionally, subgroup analyses were performed in the supraclavicular block and interscalene block. Supraclavicular blockade, needle insertion time (median [25th percentile-75th percentile] in seconds) (106 [92–162] vs 197 [140–278]), total procedure time (3 [2–3] vs 4.5 [4–6] in minutes) and unplanned needle redirections (2 [1–5] vs 5.5 [3–9]) were significantly lower in needle guidance group (p < 0.001). With interscalene blockade, needle insertion time (86 [76–146] vs 126 [94–295]) and unplanned needle redirections (2 [1–3] vs 4 [2–8.5]) were significantly lower with needle guidance (p < 0.001), but total procedure time was similar. All the physicians reported that they would use the needle guidance again, and 90% would prefer it for in-plane blocks.ConclusionPerforming regional blocks using the needle guidance device reduces needle insertion time and unplanned needle redirections in brachial plexus blockade. Moreover, physician satisfaction also improved compared to the use of the conventional technique.

Plasma assisted micro poling of glassy surfaces: a new tool to achieve liquid crystal multi-domain alignments [Invited

We propose an innovative approach to program the alignment of liquid crystal (LC) assemblies allowing for the formation of multi-domain alignments whose orientation axis and sizes are controlled at the micrometer scale by an electrically patterned glass surface. The glass surface preparation is based on a thermo-electrical imprinting process to induce localized space charge implantations in the glass matrix just below its anode surface. To demonstrate this new approach, a commercial soda-lime glass slide has been polarized using as anode a simple micrometric nickel grid. Characterizing the polarized glass surface by second harmonic generation polarized microscopy; we show an accurate control of both location and spatial components of frozen static fields embedded in the glass as a function of the electrode patterns. The polarized glassy surface is then used in the conception of a LC cell in which homeotropic or planar alignments can be controlled following the electrical pattern induced on the glass surface. This study also points out the importance of plasma discharges spatially controlled along the electrode pattern during the process in order to promote the in-plane electrical polarization effects, which are essential for the programming of the in-plane LC alignment on the polarized glass surface.