Threshold Fluence Measurement for Laser Liftoff of InP Thin Films by Selective Absorption

We explore conditions for achieving laser liftoff in epitaxially grown heterojunctions, in which single crystal thin films can be separated from their growth substrates using a selectively absorbing buried intermediate layer. Because this highly non‐linear process is subject to a variety of process instabilities, it is essential to accurately characterize the parameters resulting in liftoff. Here, we present an InP/InGaAs/InP heterojunction as a model system for such characterization. We show separation of InP thin films from single crystal InP growth substrates, wherein a ≈10 ns, Nd:YAG laser pulse selectively heats a coherently strained, buried InGaAs layer. We develop a technique to measure liftoff threshold fluences within an inhomogeneous laser spatial profile, and apply this technique to determine threshold fluences of the order 0.5 J cm^?2 for our specimens. We find that the fluence at the InGaAs layer is limited by non‐linear absorption and InP surface damage at high powers, and measure the energy transmission in an InP substrate from 0 to 8 J cm^?2. Characterization of the ejected thin films shows crack‐free, single crystal InP. Finally, we present evidence that the hot InGaAs initiates a liquid phase front that travels into the InP substrate during liftoff.

     

Bulk mass flow in a vibratory finisher: mechanisms and effect of process parameters

Vibratory finishing is a widely-used manufacturing process in which a vibrating container filled with granular media becomes fluidized. The resulting bulk flow entrains workpieces and exposes their surfaces to the impacts resulting from the small-scale media vibrations. The bulk flow is responsible for entrainment and mixing, while the media vibration does work on the surfaces. The selection of machine vibration parameters is commonly based on experience due to the difficulty in predicting the fluidized bed behavior. In this work, a discrete element method was used to investigate how the bulk flow in an actual tub finisher filled with steel balls depends on the tub motion parameters through a parametric study. The underlying mechanisms that create and drive the bulk flow were identified by examining the relationships between the bulk flow rates and the wall forces. Finally, the connection between the wall motion and the wall forces was investigated. The tub frequency was the most effective control parameter and there was an optimal phase difference between the horizontal and vertical vibrations to maximize bulk flow. The relationship between the media packing at the walls and the tangential forces between the walls and the media explained the formation and speed of the bulk flow. Lastly, it was shown that the tangential wall forces, unlike the normal forces, cannot be obtained from the known wall motion alone since they also depend on the media velocities relative to the walls.     

Influence of process parameters on average particle speeds in a vibratory finisher

Vibratory finishing (VF) employs vibrationally-fluidized granular media to finish the surfaces of workpieces that are entrained in the flowing media. Its application has been based mostly on experience and trial-and-error due to the complexity of the granular material behavior. The present study used discrete element modeling (DEM) to investigate how the movement of a commercial two-dimensional tub finisher influenced the average particle speed of the media in a bed of smooth, steel, spherical particles, and thus the work that would be done on an entrained workpiece. The parameters governing the tub wall motion (frequency, in-plane amplitudes, and phases of vibration) and the coefficient of friction between the media and the wall were systematically varied in 71 three-dimensional DEM simulations. The average particle speed was affected mostly by the vertical amplitude of tub motion rather than by the frequency, and was mostly independent of other parameters of motion and of the wall friction. A strong relationship was found between the average particle speed and the work done by the wall per cycle of vibration. The normal force on the wall was also found to correlate strongly with the normal component of the wall velocity. Together, these relationships offer the potential to enable the analytical prediction of the average particle speed based on the motion parameters of the tub alone. The paper provides a set of practical guidelines for the control of the average particle speed in VF that are explained by the forces between the media and walls of the tub finisher.     

Bending impact on the performance of a flexible Li4Ti5O12-based all-solid-state thin-film battery

The growing demand of flexible electronic devices is increasing the requirements of their power sources. The effect of bending in thin-film batteries is still not well understood. Here, we successfully developed a high active area flexible all-solid-state battery as a model system that consists of thin-film layers of Li₄Ti₅O₁₂, LiPON, and Lithium deposited on a novel flexible ceramic substrate. A systematic study on the bending state and performance of the battery is presented. The battery withstands bending radii of at least 14 mm achieving 70% of the theoretical capacity. Here, we reveal that convex bending has a positive effect on battery capacity showing an average increase of 5.5%, whereas concave bending decreases the capacity by 4% in contrast with recent studies. We show that the change in capacity upon bending may well be associated to the Li-ion diffusion kinetic change through the electrode when different external forces are applied. Finally, an encapsulation scheme is presented allowing sufficient bending of the device and operation for at least 500 cycles in air. The results are meant to improve the understanding of the phenomena present in thin-film batteries while undergoing bending rather than showing improvements in battery performance and lifetime.     

Modification of Iron with Degradable Silver Phases Processed via Laser Beam Melting for Implants with Adapted Degradation Rate

In medical technology, implants are used to improve the quality of patients’ lives. The development of materials with adapted properties can further increase the benefit of implants. If implants are only needed temporarily, biodegradable materials are beneficial. In this context, iron-based materials are promising due to their biocompatibility and mechanical properties, but the degradation rate needs to be accelerated. Apart from alloying, the creation of noble phases to cause anodic dissolution of the iron-based matrix is promising. Due to its high electrochemical potential, immiscibility with iron, biocompatibility, and antibacterial properties, silver is suited for the creation of such phases. A suitable technology for processing immiscible material combinations is powder-bed-based procedure like laser beam melting. This procedure offers short exposure times to high temperatures and therefore a limited time for diffusion of alloying elements. As the silver phases remain after the dissolution of the iron matrix, a modification is needed to ensure their degradability. Following this strategy, pure iron with 5 wt% of a degradable silver–calcium–lanthanum alloy is processed via laser beam melting. Investigation of the microstructure yields achievement of the intended microstructure and long-term degradation tests indicates an impact on the degradation, but no increased degradation rate.     

Using Selective Electron Beam Melting to Enhance the High-Temperature Strength and Creep Resistance of NiAl–28Cr–6Mo In Situ Composites

By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF-EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate-like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF-EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material.     

Novel Aerosol-Based Approach toward Mesoporous Silica Nanoparticles

This study introduces a novel gas-phase method for the synthesis of mesoporous silica nanoparticles (MSNs). The method is a two-step templating approach by first forming silicon-coated carbon structures in a hybrid microwave-plasma/hot-wall reactor followed by an annealing step to produce mesoporous silica with distinct nanostructure and porosity. Two different (sacrificial) carbonaceous templates have been prepared (plasma reactor) and coated (hot-wall reactor), 2D few-layer graphene (FLG) flakes and soot-like fractal aggregates. Results show that the wall thickness of the porous silica structures can be adjusted by changing the concentration of the silicon precursor (monosilane). High monosilane concentrations, however, result in solid silica particles after annealing. Using soot-like particle templates permitted to control of the shell thickness of the hollow porous particles, while the FLG template results in ultrathin silica sheets after heat treatment. The pore volume and specific surface area increase up to 263 m² g⁻¹ and 0.6 cm³ g⁻¹, respectively, by the formation of hollow porous particles. An adsorption study on carbamazepine reveals up to ≈86% removal. The gas-phase aerosol-based template method presented here offers scalability and versatility, and it is capable of producing MSNs with a controlled structure and porosity by modifying the carbonaceous templates.     

Measurement and analysis of low-acceleration and long-duration longitudinal events using delivery van

This study investigates longitudinal acceleration events during freight transportation characterized as low-acceleration and long-duration using delivery van type vehicles. In the past several decades, there has been an increase in shipments requiring only single or small pallet load quantities and mixed palletized unit loads comprised of different goods. These loads are often transported in delivery vans without load securing devices, increasing the risk of product loss and damage due to load failures resulting from unit loads shifting. A field data acquisition system was used to observe and record the random acceleration events from five vehicles for 5 days, explicitly targeting the vehicles' braking and acceleration manoeuvres. The study aimed to understand the physical phenomenon and provide new information that can be used during preshipment tests to prevent damage to goods and ensure unit load integrity is maintained throughout the supply chain. The events were statistically analysed to understand their probability of occurrence, severity level, and quantify critical parameters such as event rise and hold times. For the braking manoeuvre, the statistical mean of average deceleration was 0.25 g with a corresponding rise and hold duration of 0.83 and 1.27 s, respectively. During the vehicle's acceleration manoeuvre, the statistical mean of average acceleration was 0.29 g with a rise and hold time of 1.29 and 1.39 s, respectively. Utilizing the field data, composite profiles were developed, and these profiles were compared to the currently available test procedures and previous results of other studies.     

Observation of Anomalously Low Momentum Transfer in the Low Energy Scattering of Large 4He Droplets From 4He and 3He Atoms

The momentum transferred to large superfluid ⁴ He droplets in low energy ( 4–10 K) scattering from ⁴ He and ³ He atoms was determined from time of flight measurements after the droplets have passed through a low temperature (T = 1.7–4.2 K) scattering box filled with the gas of either He isotope. The results are compared with ³ He droplets scattered from either ⁴ He or ³ He gas for which all of the incident momentum is transferred, as expected for classical capture of the scattering gas atoms. In the case of the ⁴ He droplets a smaller momentum transfer is found amounting to 65% for ⁴ He atoms and 45% for ³ He atoms but only at the lowest collision energies. These results are consistent with transmission of some of the atoms through the droplets.     

Combining make to order and make to stock

In inventory control and production planning one is tempted to use one of two strategies: produce all demand to stock or produce all demand to order. The disadvantages are well-known. In the make everything to order case (MTO) the response times may become quite long if the load is high, in the make everything to stock case (MTS) one gets an enormous inventory if the number of different products is large.In this paper we study two simple models which combine MTO and MTS, and investigate the effect of combining MTO and MTS on the production lead times.