Thin Geometry Research Articles

Dendrite orientation transition in Al[sbnd]Ge alloys

We report on a dendrite orientation transition (DOT) discovered in the AlGe system by conducting isothermal solidification experiments in thin samples under slow cooling conditions. The DOT was revealed using a combination of in situ X-radiography imaging and post-mortem electron backscatter diffraction. In Al-20 wt% Ge the primary arms grow along 〈100〉, whereas in Al-46 wt% Ge the primary arms grow along 〈110〉. At an intermediate composition of Al-29 wt% Ge, we observe both directions growing simultaneously. Phase-field simulations in which the solid-liquid interfacial energy anisotropy was systematically varied to correspond with the composition changes reproduced the experimentally observed microstructures. The remarkable agreement between the experimental observations and the simulations provides strong evidence that the DOT in this alloy system is caused by modification of surface energy anisotropy with increasing Ge content. Furthermore, we show that the confinement due to the thin sample geometry influences the selection of the primary growth directions, so that different growth morphologies develop depending on the orientation of the crystal in the sample.

High-Performance Black Phosphorus Field-Effect Transistors with Long-Term Air Stability.

Two-dimensional layered materials (2DLMs) are of considerable interest for high-performance electronic devices for their unique electronic properties and atomically thin geometry. However, the atomically thin geometry makes their electronic properties highly susceptible to the environment changes. In particular, some 2DLMs (e.g., black phosphorus (BP) and SnSe2) are unstable and could rapidly degrade over time when exposed to ambient conditions. Therefore, the development of proper passivation schemes that can preserve the intrinsic properties and enhance their lifetime represents a key challenge for these atomically thin electronic materials. Herein we introduce a simple, nondisruptive, and scalable van der Waals passivation approach by using organic thin films to simultaneously improve the performance and air stability of BP field-effect transistors (FETs). We show that dioctylbenzothienobenzothiophene (C8-BTBT) thin films can be readily deposited on BP via van der Waals epitaxy approach to protect BP against oxidation in ambient conditions over 20 d. Importantly, the noncovalent van der Waals interface between C8-BTBT and BP effectively preserves the intrinsic properties of BP, allowing us to demonstrate high-performance BP FETs with a record-high current density of 920 μA/um, hole drift velocity over 1 × 107 cm/s, and on/off ratio of 1 × 104 to ∼1 × 107 at room temperature. This approach is generally applicable to other unstable two-dimensional materials, defining a unique pathway to modulate their electronic properties and realize high-performance devices through hybrid heterojunctions.

Applying Machine Learnt Explicit Algebraic Stress and Scalar Flux Models to a Fundamental Trailing Edge Slot

Machine learning was applied to large-eddy simulation (LES) data to develop nonlinear turbulence stress and heat flux closures with increased prediction accuracy for trailing-edge cooling slot cases. The LES data were generated for a thick and a thin trailing-edge slot and shown to agree well with experimental data, thus providing suitable training data for model development. A gene expression programming (GEP) based algorithm was used to symbolically regress novel nonlinear explicit algebraic stress models and heat-flux closures based on either the gradient diffusion or the generalized gradient diffusion approaches. Steady Reynolds-averaged Navier–Stokes (RANS) calculations were then conducted with the new explicit algebraic stress models. The best overall agreement with LES data was found when selecting the near wall region, where high levels of anisotropy exist, as training region, and using the mean squared error of the anisotropy tensor as cost function. For the thin lip geometry, the adiabatic wall effectiveness was predicted in good agreement with the LES and experimental data when combining the GEP-trained model with the standard eddy-diffusivity model. Crucially, the same model combination also produced significant improvement in the predictive accuracy of adiabatic wall effectiveness for different blowing ratios (BRs), despite not having seen those in the training process. For the thick lip case, the match with reference values deteriorated due to the presence of large-scale, relative to slot height, vortex shedding. A GEP-trained scalar flux model, in conjunction with a trained RANS model, was found to significantly improve the prediction of the adiabatic wall effectiveness.

Simulated and experimental analysis of electrodeposited β' Brass composition with DLA morphology

Electrodeposition of two ions like Copper and Zinc in the alloy of β' Brass is done in thin gap 2D geometry. The growth follows a Diffusion Limited Aggregation (DLA) like morphology. It is observed that the ratio of the two ions deposited remains almost constant with the distances from cathode. This ratio also depends on the composition of the cathodes. This has been shown experimentally and using a unique two-ion simulation model developed by us. The compositional analysis by EDX of the electrodeposited layers at different separations of 0.5 cm, 1.0 cm and 1.5 cm from the negative electrode shows a uniform ratio of 2.3087 for the two ions of copper and zinc. A two-ion simulation model made by us with different masses for the ions and for the same composition of cathode shows a uniform ratio of 2.3133 for the two ions systems and therefore, support the experimental observation to a high degree of accuracy. The results obtained have been explained theoretically.

Mg ii Line Properties in Lobe-dominated Quasars

Abstract We investigate the relationships between Mg ii λ2798 emission line properties, as well as between these properties and inclination angle and Fe ii strength, in a lobe-dominated quasar sample. We find no correlation between Mg ii line width and inclination, unlike previous studies of the general quasar population. This suggests that the Mg ii emission region in these objects is not of a thin disk geometry; however, the average equivalent width (EW) of the line negates a spherical alternative. A positive correlation between Mg ii EW and inclination cannot be ruled out, meaning there is no strong evidence that Mg ii emission is anisotropic. Since thin disk emission would be highly directional, the geometric implications of these two findings are compatible. The lack of line width correlation with inclination may also indicate that Mg ii is useful for estimating black hole masses in lobe-dominated quasar samples, since it is unbiased by orientation. Some quasars in our sample have almost edge-on viewing angles and therefore cannot have a smooth toroidal obscurer co-planar with the accretion disk. Alternatives may be a distorted dusty disk or a clumpy obscurer. This could result from the sample selection bias toward high inclination objects, rather than intrinsic differences between lobe-dominated and typical quasars. Five objects have visible [O iii], allowing EW calculation and revealing it to be higher than in typical quasars. Since these objects are of high inclination, this finding supports the positive correlation between [O iii] EW and inclination found in a previous study.

Synthesis of ultrathin two-dimensional nanosheets and van der Waals heterostructures from non-layered \u03b3-CuI

Two-dimensional (2D) nanosheets have attracted considerable recent interest for their atomically thin geometry and unique thickness-dependent electronic properties. The 2D nanosheets studied to date are generally limited to intrinsically layered materials, in which the covalently bonded atomic layers are held together by weak van der Waals forces and can be readily exfoliated to single or few-atom thick nanosheets. To prepare 2D nanosheets from non-layered materials can greatly expand the scope of 2D materials, but is much less straightforward. Here, we report the successful synthesis of ultrathin nanosheets from non-layered γ-CuI on SiO2/Si substrate using a facile physical vapor deposition process. The resulting γ-CuI nanosheets display a triangular and hexagonal geometry with the lateral dimension up to 5 μm and thickness down to 1 nm. Raman spectroscopy, X-ray diffraction, and transmission electron microscopy studies demonstrate the resulting nanosheets retain single-crystalline γ-CuI phase. Additionally, we further show the γ-CuI nanosheets can be readily grown on other 2D materials (e.g., 2D-WSe2, 2D-WS2) to form van der Waals heterostructures (vdWHs). Optical microscopy images and Raman intensity mappings confirm the formation of γ-CuI/WS2 and γ-CuI/WSe2 vertical heterostructures. The electrical transport studies show that γ-CuI nanosheets exhibit a low resistivity of ~0.3 Ω cm and γ-CuI/WS2 vertical heterostructures display a p-n diode behavior with distinct current rectification. The synthesis of γ-CuI nanosheets and heterostructures open a pathway to ultrathin nanosheets and van der Waals heterostructures from non-layered materials and could open up exciting opportunities in electronics and optoelectronics.

Assessment of two immersed boundary methods for flow over thin plates and sharp edges

The extension of two different immersed boundary methods is proposed and applied to the numerical computation of uniform flow over blunt and sharp bodies: a directional version of the multi-direct forcing method and a semi-implicit version of the local ghost cell method; the first is an indirect and the second a direct method. These methods are investigated by applying them to incompressible laminar flows. The salient features of the methods are described with special emphasis on the ability to compute flows past thin plates and sharp edges. The transport equations are discretized by using the finite difference method in a Cartesian grid. The immersed boundary is represented by a finite number of Lagrangian points distributed over the solid–fluid interface. In order to test the accuracy of these approaches, three different benchmark cases are assessed. The directional version of the multi-direct forcing method is in good accordance with the flow past blunt bodies. However, it shows some numerical inconsistency when dealing with sharp and thin geometries due to the discontinuity present in the velocity and pressure fields. On the other hand, the semi-implicit version of the local ghost cell method presents good agreement with analytical, numerical and experimental data of all simulated cases.

Insights into the Kinetics of Redox Mediation for Li-O2 Batteries: A Dems and RRDE Study

Due to its theoretical high specific energy Li-O2 systems have generated much interest within the electrochemical community [1]. Understanding the fundamentals of this system is import to improve it. Therefore, much effort has been put into characterizing the products and the mechanism of the underlying electrolyte systems and electrodes (also by ourselves [2-5]). Recently in the electrolyte, soluble redox mediators were proposed as additives to improve the sluggish kinetics of the oxygen reduction reaction (ORR) as well as the oxygen evolution reaction (OER)[6, 7]. Although the impact of this redox mediators is impressive, very little is known about the underlying mechanism. Therefore, we focused in this study our research in the mechanism of redox mediation of the ORR. We applied rotating ring disc technique (RRDE) as well as the differential electrochemical mass spectrometry (DEMS) to get insights into the kinetics of the mediated ORR and into the amount of consumed electrons per oxygen. The DEMS experiments were performed in a thin layer geometry without convective transport within the cell. In addition, the DEMS setup is highly sensitive to the gases formed during ORR and OER. At higher electrode potentials, the amount of evolved CO2 is reduced by adding a redox mediator to the electrolyte. We also observed that the amount of consumed oxygen is increased compared to the supporting electrolyte without redox mediator. In order to investigate the impact of the cationic charge density on the mechanism of the mediated ORR we also performed measurements in K+-, Mg2+-, Ca2+- containing electrolytes solutions. In our analysis of the data, we could calculate the share of current going into the mediation of the ORR. This analysis showed that for the investigated cations the amount of consumed electrons per oxygen molecule is 2 e-/O2. We found out, that the reaction speed of ORR could be influenced by changing the cation of the supporting electrolyte. The RRDE study revealed the generation of Li2O2 within the electrolyte volume through an analysis of the rotational dependency within the experiments. [1] K. M. Abraham and Z. Jiang, J. Electrochem. Soc., 143, 1 (1996). [2] P. Reinsberg, A. Weiss, P. P. Bawol and H. Baltruschat, J. Phys. Chem. C, 121, 7677 (2017). [3] C. J. Bondue, P. P. Bawol, A. A. Abd-El-Latif, P. Reinsberg and H. Baltruschat, J. Phys. Chem. C, 121, 8864 (2017). [4] C. Bondue, P. Reinsberg, A. A. Abd-El-Latif and H. Baltruschat, Phys. Chem. Chem. Phys., 17, 25593 (2015). [5] H. M. A. Amin, C. Molls, P. P. Bawol and H. Baltruschat, Electrochim. Acta (2017). [6] B. D. McCloskey and D. Addison, ACS Catalysis (2017). [7] X. Gao, Y. Chen, L. Johnson and P. G. Bruce, Nat. Mater., 15, 882 (2016).

Review of nano piezoelectric devices in biomedicine applications

The piezoelectric devices, based on micro–nano electromechanical systems, are well known nowadays due to their small features, ability for integration with the integrated circuit in a single platform, robust, and easily fabricated in bulk. The enhanced performance of piezoelectric systems, which is soft, flexible, and stretchable made them have unique opportunities to be used in bio-integrated applications as nanodevices for energy harvesting, sensing, actuation, and cell stimulation. The selection of optimized configurations depends on thin geometries, neutral mechanical plane construction, and controlled buckling, while inorganic piezoelectric materials are preferred for interfaces with human bodies. The key considerations in designs, the analytical derivations for voltage and displacement, and the effect of the voltmeter resistance on the voltage measurements are presented. Devices for energy harvesting from natural motions of internal organs, sensors, and actuators for medical applications are reviewed. The PMN-PT energy harvester that produced current of 0.22 mA is higher than the rest of the discussed harvesters. Thus, it is more suitable to be used as a sufficient source of energy in biomedical applications. The use of piezoelectric nanowires and ribbons proved successful, and the dual features of device (sensor and actuator) seem advantageous.

Pattern transition from dense branching morphology to fractal for copper and β′ brass electrodeposition in thin gap geometry

Copper and β′ brass are electrodeposited in thin gap geometry and a clear transition from dense branching to fractal like pattern is observed with the variation of electric potential and concentration. The transition electric potential is 6V – 5V for copper and 25V for β′ brass. The explanation of the pattern transition is done first using the Laplacian growth as in the Di-electric Breakdown Model (DBM) and then on the basis of ion dynamics in terms of viscosity, ionic mobility, drift and thermal velocity. The fractal growth is more likely at higher electric potential as the electric field dominates and more likely to be dense branched at lower electric field when thermal motion dominates. This work inspires for further studies on modification of our model for the two ions electrodeposition and their compositional variation with different deposition parameters.

THE GEOMETRY OF BLUEPRINTS PART II: TITS–WEYL MODELS OF ALGEBRAIC GROUPS

This paper is dedicated to a problem raised by Jacquet Tits in 1956: the Weyl group of a Chevalley group should find an interpretation as a group over what is nowadays called$\mathbb{F}_{1}$,the field with one element. Based on Part I of The geometry of blueprints, we introduce the class ofTits morphismsbetween blue schemes. The resultingTits category$\text{Sch}_{{\mathcal{T}}}$comes together with a base extension to (semiring) schemes and the so-calledWeyl extensionto sets. We prove for${\mathcal{G}}$in a wide class of Chevalley groups—which includes the special and general linear groups, symplectic and special orthogonal groups, and all types of adjoint groups—that a linear representation of${\mathcal{G}}$defines a model$G$in$\text{Sch}_{{\mathcal{T}}}$whose Weyl extension is the Weyl group$W$of${\mathcal{G}}$. We call such modelsTits–Weyl models. The potential of Tits–Weyl models lies in(a)their intrinsic definition that is given by a linear representation;(b)the (yet to be formulated) unified approach towards thick and thin geometries; and(c)the extension of a Chevalley group to a functor on blueprints, which makes it, in particular, possible to consider Chevalley groups over semirings. This opens applications to idempotent analysis and tropical geometry.

Geochemical, petrographical, and petrophysical evaluations of a heterogeneous, stratiform dolomite from a Barremian oil field, offshore Abu Dhabi (United Arab Emirates)

A stratiform dolomite is developed in the Barremian carbonates of offshore Abu Dhabi, United Arab Emirates. Although the average thickness is only 1.1 m (3.6 ft), it is an important drilling target characterized by heterogeneous porosity–permeability values in the studied oil field. We discuss the origin and development of the dolomite based on geochemical, petrographical, and petrophysical evaluations using 81 cores recovered from the field. The δ13C values of the dolomites are relatively high (>5‰), and 87Sr/86Sr mostly fall in the range of Barremian seawater. The thin stratiform geometry and the geochemical signatures of the dolomite suggest early dolomitization just below the seafloor that was driven by the diffusion of Mg2+ from the seawater on top of a shallow platform. Lateral changes in the degree of dolomitization seem to be controlled by the permeability of the precursors. Dolomitization progressed further in packstone precursors (higher permeability) than in wackestone precursors (lower permeability), which led to greater permeability improvement in the packstone by replacement of fine matrix with larger dolomite crystals. Subsequently, late burial dolomite cementation occurred during oil migration, which preferentially affected the higher-permeability early dolomite, and areally, it progressed more in the flank of the field because of the delayed oil charge there. Dolomite-to-dolomite recrystallization became dominant after the oil emplacement. The recrystallization has been continuing under current burial temperatures (>100°C [>212°F]), fully resetting δ18O values and modifying the Fe and Mn concentrations of the dolomites, but has not significantly affected their petrography and petrophysics in the oil leg.

The Influence of Differently Shaped Gold Nanoparticles Functionalized with NIPAM-Based Hydrogels on the Release of Cytochrome C.

Here, we report the synthesis and functionalization of five different shapes of Au nanoparticles (NPs), namely nanorods, tetrahexahedral, bipyramids, nanomakura, and spheres with PEG and poly (N-isopropylacrylamide)-acrylic acid (pNIPAm-AAc) hydrogels. The anisotropic NPs are synthesized using seed-mediated growth in the presence of silver. The NPs have been characterized using Dynamic Light Scattering (DLS), zeta potential measurements, UV-Visible spectrophotometry (UV-Vis), and Scanning Transmission Electron Microscopy (S(T)EM). Cyt C was loaded into the PEG-hydrogel-coated AuNPs using a modified breathing-in method. Loading efficiencies (up to 80%), dependent on particle geometry, concentration, and hydrogel content, were obtained. Release experiments conducted at high temperature (40 °C) and acidic pH (3) showed higher release for larger sizes of PEG-hydrogel-coated AuNPs, with temporal transition from spherical to thin film release geometry. AuNP shape, size, number density, and hydrogel content are found to influence the loading as well as release kinetics of Cyt C from these systems.

MoS2 nanosheet photodetectors with ultrafast response

Two-dimensional layered materials, such as molybdenum disulfide, are emerging as an exciting material system for future electronics due to their unique electronic properties and atomically thin geometry. In this work, MoS2-based FETs are fabricated using mechanical cleavage and standard photolithographic and metal evaporation techniques, and the detector exhibits a good ohmic contact. We show that the multilayer molybdenum disulfide photodetector has a fast photoresponse as short as 42 μs. The fast photodetector response is due to the decrease in the trap states in MoS2 flakes compared to monolayer MoS2, making its photoresponse time close to its intrinsic response. The large photocurrent with the responsivity and external quantum efficiency of 59 A/W and 13 800% for the wavelength of 532 nm was also measured. The fast response time, high responsivity, and the ease of fabrication of these devices make them important components for future optoelectronic devices.

Ultrathin Colloidal Quantum Dot Films for Optical Amplification: The Role of Modal Confinement and Heat Dissipation.

We demonstrate optical pumping lasers based on colloidal quantum dots, with a very thin geometry consisting of a ≈20 nm thick film. Obstacles in ultrasmall laser devices come from the limitation of gain materials and the size of cavities for lasing modes, which requires a minimum thickness of the gain media (typically greater than 50-100 nm). Here we introduce dielectric waveguide structures with a high refractive index, in order to reduce the thickness of quantum dot gain media as well as their threshold energy (≈39 % compared to the original gain medium). Finite-difference time-domain simulations show that the modal confinement factor of thinner quantum dot films can be improved by the presence of an adjacent waveguide layer. We also discuss the possible role of dielectric waveguide layers for efficient heat dissipation during optical pumping. Integrating an extremely thin colloidal quantum dot gain medium into optical waveguides is a promising platform for downscaling on-chip photonic integrated devices, as well as investigating extreme interactions between light and matter such as surface plasmon-photon coupling.

Reduced-Dose Imageless Needle and Patient Tracking in Interventional CT Procedures.

This paper describes a new method for imageless needle and patient tracking in interventional CT procedures based on fractional CT scanning. Our method accurately locates a needle with a spherical marker attached to it at a known distance from the tip with respect to the patient in the CT scanner coordinate frame with online sparse scan sampling and without reconstructing the CT image. The key principle of our method is to detect the needle and attached spherical marker in projection (sinogram) space based on the strongly attenuated X-ray signal due to the metallic composition of the needle and the needle's thin cylindrical geometry, and based on the marker's spherical geometry. A transformation from projection space to physical space uniquely determines the location and orientation of the needle and the needle tip position. Our method works directly in projection space and simultaneously performs patient registration and needle localization for every fractional CT scanning acquisition using the same sparse set of views. We performed registration and needle tip localization in five abdomen phantom scans using a rigid needle, and obtained a voxel-size tip localization error. Our experimental results indicate a voxel-sized deviation of the localization from a comparable method in 3-D image space, with the benefit of allowing X-ray dose reduction via fractional scanning at each localization. This benefit enables more frequent tip localizations during needle insertion for a similar total dose, or a reduced total dose for the same frequency of tip localization.

High Aspect Ratio Thin Rib Shape Processing of Carbon Material for Electrical Discharge Machining Molds

Aluminum alloy die casting products are used for automotive LED lamp installation parts. The high aspect ratio shape used for large-volume heat problems needs thin rib parts. In the present study, we obtained basic data for the development of long axis type end mill tools for electrical discharge machining carbon material processing. At the same time, to evaluate the prototype development work, a special tool that enables high aspect ratio thin rib geometry processing was used. Longitudinal direction traverse cutting was done with a small diameter ball end mill tool in the carbon material for electrical discharge machining mold. The transfer accuracy and pick feed shape in the finished surface, the cutting resistance force, and the cutting edge shapes were examined to clarify the relationship between the cutting conditions set. Prototype development of the small-diameter end mill tool with a high rigidity, long axis was done using FEM numerical analysis method. The results showed that the small-diameter ball end mill tool with a tapered length axis in the prototype development had transfer accuracy of the cutting edge shape, and it was possible to reduce the finished surface roughness. Factors such as differences in tool shape are considered to greatly affect the tool rigidity.

Precursor of the Laughlin state of hard-core bosons on a two-leg ladder

We study hard core bosons on a two leg ladder lattice under the orbital effect of a uniform magnetic field. At densities which are incommensurate with flux, the ground state is a Meissner state, or a vortex state, depending on the strength of the flux. When the density is commensurate with the flux, analytical arguments predict the existence of a ground state of central charge $c = 1$, which displays signatures compatible with the expected Laughlin state at $\nu=1/2$. This differs from the coupled wire construction of the Laughlin state in that there exists a nonzero backscattering term in the edge Hamiltonian. We construct a phase diagram versus density and flux in order to delimit the region where this precursor to the Laughlin state is the ground state, by using a combination of bosonization and numerics based on the density matrix renormalization group (DMRG) and exact diagonalization. We obtain the phase diagram from local observables and central charge. We use bipartite charge fluctuations to deduce the Luttinger parameter for the edge Luttinger liquid corresponding to the Laughlin state. The properties studied with local observables are confirmed by the long distance behavior of correlation functions. Our findings are consistent with a calculation of the many body ground state transverse conductivity in a thin torus geometry for parameters corresponding to the Laughlin state. The model considered is simple enough such that the precursor to the Laughlin state could be realized in current ultracold atom, Josephson junction array, and quantum circuit experiments.

Graphene-Based Three-Dimensional Capacitive Touch Sensor for Wearable Electronics.

The development of input device technology in a conformal and stretchable format is important for the advancement of various wearable electronics. Herein, we report a capacitive touch sensor with good sensing capabilities in both contact and noncontact modes, enabled by the use of graphene and a thin device geometry. This device can be integrated with highly deformable areas of the human body, such as the forearms and palms. This touch sensor detects multiple touch signals in acute recordings and recognizes the distance and shape of the approaching objects before direct contact is made. This technology offers a convenient and immersive human-machine interface and additional potential utility as a multifunctional sensor for emerging wearable electronics and robotics.

The A-B transition in superfluid helium-3 under confinement in a thin slab geometry

The influence of confinement on the phases of superfluid helium-3 is studied using the torsional pendulum method. We focus on the transition between the A and B phases, where the A phase is stabilized by confinement and a spatially modulated stripe phase is predicted at the A–B phase boundary. Here we discuss results from superfluid helium-3 contained in a single 1.08-μm-thick nanofluidic cavity incorporated into a high-precision torsion pendulum, and map the phase diagram between 0.1 and 5.6 bar. We observe only small supercooling of the A phase, in comparison to bulk or when confined in aerogel, with evidence for a non-monotonic pressure dependence. This suggests that an intrinsic B-phase nucleation mechanism operates under confinement. Both the phase diagram and the relative superfluid fraction of the A and B phases, show that strong coupling is present at all pressures, with implications for the stability of the stripe phase.