Simulation and control of aggregate surface morphology in a two-stage thin film deposition process for improved light trapping

a b s t r a c t This work focuses on the development of a model predictive control algorithm to simultaneously regulate the aggregate surface slope and roughness of a thin film growth process to optimize thin film light reflectance and transmittance. Specifically, a two-stage thin film deposition process, which involves two microscopic processes: an adsorption process and a migration process, is modeled based on a one-dimensional solid-on-solid square lattice. The first stage of this process utilizes a uniform deposition rate profile to control the thickness of the thin film and the second stage of the process utilizes a spatially distributed deposition rate profile to control the surface morphology of the thin film. Kinetic Monte Carlo (kMC) methods are used to simulate this two-stage thin film deposition process. To characterize the surface morphology and to evaluate the light trapping efficiency of the thin film, aggregate surface roughness and slope corresponding to length scale of visible light are introduced as the root-mean squares of the aggregate surface height profile and aggregate surface slope profile. An Edwards-Wilkinson (EW)-type equation with appropriately computed parameters is used to describe the dynamics of the surface height profile and predict the evolution of the aggregate root-mean-square (RMS) roughness and aggregate RMS slope. A model predictive control algorithm is then developed on the basis of the EW equation model to regulate the aggregate RMS slope and the aggregate RMS roughness at desired levels. Closed-loop simulation results demonstrate the effectiveness of the proposed model predictive control algorithm in successfully regulating the aggregate RMS slope and the aggregate RMS roughness at desired levels that optimize thin film light reflectance and transmittance

Solid State Circuits Technologies

The evolution of solid-state circuit technology has a long history within a relatively short period of time. This technology has lead to the modern information society that connects us and tools, a large market, and many types of products and applications. The solid-state circuit technology continuously evolves via breakthroughs and improvements every year. This book is devoted to review and present novel approaches for some of the main issues involved in this exciting and vigorous technology. The book is composed of 22 chapters, written by authors coming from 30 different institutions located in 12 different countries throughout the Americas, Asia and Europe. Thus, reflecting the wide international contribution to the book. The broad range of subjects presented in the book offers a general overview of the main issues in modern solid-state circuit technology. Furthermore, the book offers an in depth analysis on specific subjects for specialists. We believe the book is of great scientific and educational value for many readers. I am profoundly indebted to the support provided by all of those involved in the work. First and foremost I would like to acknowledge and thank the authors who worked hard and generously agreed to share their results and knowledge. Second I would like to express my gratitude to the Intech team that invited me to edit the book and give me their full support and a fruitful experience while working together to combine this book

Probing multivalent particle–surface interactions using a quartz crystal resonator

The rise in market-approved cellular therapies demands for advancements in process analytical technology (PAT) capable of fulfilling the requirements of this new industry. Unlike conventional biopharmaceuticals, cell-based therapies (CBT) are complex “live” products, with a high degree of inherent biological variability. This exacerbates the need for in-process monitoring and control of critical product attributes, in order to guarantee safety, efficacious and continuous supply of this CBT. There are therefore mutual industrial and regulatory motivations for high throughput, non-invasive and non-destructive sensors, amenable to integration in an enclosed automated cell culture system. While a plethora of analytical methods is available for direct characterization of cellular parameters, only a few satisfy the requirements for online quality monitoring of industrial-scale bioprocesses. [Continues.

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Hydrogenated amorphous silicon:impact of process conditions on material properties and solar cell efficiency

Thin-film silicon solar cells are one possible answer to the increasing energy demand of today. Hydrogenated amorphous silicon (a-Si:H) plays a crucial role therein - as absorber layers, but also as doped layers to build p-i -n junctions. This thesis is devoted to a-Si:H, with the main focus on thin-film silicon solar cells, but also with applications for opto-electronic devices, detectors, and other types of solar cells such as heterojunction solar cells. We discuss models of a-Si:H and develop further the representation of defects by amphoteric states. Using a simple model, we show - in agreement with layer-by-layer simulations and experimental results - that trapped electrons tend to dominate the electric field deformation in the initial state, whereas positively charged defects dominate in the degraded state. Experimentally, we define the deposition parameter space accessible by plasma-enhanced chemical vapor deposition (PECVD) and explore that space by varying the deposition temperature, pressure, excitation frequency, power, and H2/SiH4 ratio for intrinsic absorber layers. This leads to a catalog of a-Si:H absorber layers with tunable properties and we incorporate these materials into solar cells. For every pressure, we find an optimum hydrogen dilution where the light-induced degradation of solar cells is minimal and comparable for all pressures. Using narrow-bandgap absorbers, we demonstrate short-circuit current densities of Jsc=18.2 mA/cm2 with a 300-nm-thick absorber layer and extract more than 20 mA/cm2 from a cell with a 1000-nm-thick absorber layer. Using wide-bandgap absorbers, we achieve open-circuit voltages (Voc) of 1.04 V and Voc-fill factor products of 739mV. For such materials, we find an increased Voc dependence on substrate roughness. This is investigated by transmission electron microscopy and is attributed to porous a-Si:H material grown above peaks on the textured substrates. Depositing absorber layers in a triode reactor, we achieve efficiencies of 10.0% after light soaking. Further, we describe observations of a reversible, light-induced Voc increase of solar cells with thin p-type layers, and decrease with thick p-type layers, with a magnified effect on rough substrates. Based on layer measurements and simulations, we attribute the Voc increase to the degradation of the p-layer and the Voc decrease to the degradation of the absorber layer

Factories of the Future

Engineering; Industrial engineering; Production engineerin

Micro-Scale Complex Flows Enables Robust DNA Replication, Enhanced Transport and Tunable Fluid-Particle Interactions

The ability of convective flows in micro-scale confinement to direct chemical processes along accelerated kinetic pathways has been recognized for some time. However, practical applications have been slow to emerge because optimal results are often counterintuitively achieved in flows that appear to possess undesirably high disorder. Here we investigate the nature of these thermal instability driven Rayleigh-Bénard convective flows by altering the Rayleigh number and geometry of the cylindrical enclosure and thus identifying the chaotic flow regime. We then assess the ability of these flows to replicate DNA through polymerase chain reaction (PCR) across a broad ensemble of geometric states. The resulting parametric map reveals an unexpectedly wide chaotic regime where reaction rates remain constant over 2 orders of magnitude of the Rayleigh number, enabling robust convective PCR. With the new optimal design rules, we engineer a rugged, ultra-portable (300 g), inexpensive (<$20) bioanalysis platform for rapid nucleic acid-based diagnostics. The isothermal convective isothermal PCR format enables low power operation (5 V USB source). Time-resolved fluorescence detection and quantification is achieved using a smart-phone camera and integrated image analysis app. These advancements make it possible to provide gold standard nucleic acid-based diagnostics to remote field sites using consumer class quad-copter drones. The surprising interplay between reactions and micro-scale convective flows led us to consider adaptations beyond PCR. Specifically, we demonstrate that such flows, naturally established over a broad range of hydrothermally relevant pore sizes, function as highly efficient conveyors to continually shuttle molecular precursors from the bulk fluid to targeted locations on the solid boundaries, enabling greatly accelerated chemical synthesis. Insights from this study has the potential to provide a breakthrough in our understanding of the fundamental biochemical processes underlying the origin of life. The phenomenon of particle resuspension plays a vital role in numerous fields and thus an accurate description and formulation of van der Waals (vdW) interactions between the particle and substrate is of utmost importance. An approach based on Lifshitz continuum theory has been developed to calculate the principal many body interactions between arbitrary geometries at all separation distances to a high degree of accuracy. The new formulation can now provide realistic interactions for various particle-substrate systems which can then be coupled with computational fluid dynamics (CFD) models to improve the predictive capabilities of particle resuspension dynamics. Finally, We analyze trajectories of micro sized particles subject to all relevant hydrodynamic forces and torques by coupling discrete element modeling with CFD. The results provide us with important design rules to construct membraneless microfluidic filtration channels where pressure driven transverse flows and curvature induced dean flows can be simultaneously harnessed to assist size based particle separation with high throughput

Performance and Safety Enhancement Strategies in Vehicle Dynamics and Ground Contact

Recent trends in vehicle engineering are testament to the great efforts that scientists and industries have made to seek solutions to enhance both the performance and safety of vehicular systems. This Special Issue aims to contribute to the study of modern vehicle dynamics, attracting recent experimental and in-simulation advances that are the basis for current technological growth and future mobility. The area involves research, studies, and projects derived from vehicle dynamics that aim to enhance vehicle performance in terms of handling, comfort, and adherence, and to examine safety optimization in the emerging contexts of smart, connected, and autonomous driving.This Special Issue focuses on new findings in the following topics:(1) Experimental and modelling activities that aim to investigate interaction phenomena from the macroscale, analyzing vehicle data, to the microscale, accounting for local contact mechanics; (2) Control strategies focused on vehicle performance enhancement, in terms of handling/grip, comfort and safety for passengers, motorsports, and future mobility scenarios; (3) Innovative technologies to improve the safety and performance of the vehicle and its subsystems; (4) Identification of vehicle and tire/wheel model parameters and status with innovative methodologies and algorithms; (5) Implementation of real-time software, logics, and models in onboard architectures and driving simulators; (6) Studies and analyses oriented toward the correlation among the factors affecting vehicle performance and safety; (7) Application use cases in road and off-road vehicles, e-bikes, motorcycles, buses, trucks, etc